Tuesday, March 31, 2009
Quiz Make up 2 or bonus
all questions and answers must be hand written in your notebook
1. What is a quantum number? (use your text or the internet)
2. what is an orbital?
3. What is the aufbau principle?
4. What is the Pauli Exclusion principle
5. What is Hund's Rule
1. What is a quantum number? (use your text or the internet)
2. what is an orbital?
3. What is the aufbau principle?
4. What is the Pauli Exclusion principle
5. What is Hund's Rule
Monday, March 30, 2009
Bonus to the First Ten People Week of 3/29/2009
Answer the question in your notebook:
1. The difference between anionic and nonionic surfactant, and its application to detergent
2. Can glycerin remove both water-based and oil-based stains? Are these characteristics of glycerin related to its chemical structure?
3. The volume was decreased when a substance was dissolved in water. Why? e.g. I put pellet type sodium hydroxide in a measuring flask, and put distilled water in the flask, then I shook it very well. After that, I realized that the volume was decreased (the top of the solution was below the line of the measuring flask).
4. Where is the extra electron located in the hydroxide ion?
5. When I dip a piece of copper plate and a piece of silver plate in a lemon, a simple chemical cell is formed. Copper slowly dissolves in the lemon to form copper (II) ions. Which ions receive the electrons? My colleague says that it is the hydrogen ion in the lemon juice that receives the electrons
given out by copper, but copper is lower than hydrogen in activity series.
1. The difference between anionic and nonionic surfactant, and its application to detergent
2. Can glycerin remove both water-based and oil-based stains? Are these characteristics of glycerin related to its chemical structure?
3. The volume was decreased when a substance was dissolved in water. Why? e.g. I put pellet type sodium hydroxide in a measuring flask, and put distilled water in the flask, then I shook it very well. After that, I realized that the volume was decreased (the top of the solution was below the line of the measuring flask).
4. Where is the extra electron located in the hydroxide ion?
5. When I dip a piece of copper plate and a piece of silver plate in a lemon, a simple chemical cell is formed. Copper slowly dissolves in the lemon to form copper (II) ions. Which ions receive the electrons? My colleague says that it is the hydrogen ion in the lemon juice that receives the electrons
given out by copper, but copper is lower than hydrogen in activity series.
Saturday, March 28, 2009
debate motions for EUTU April 18-21
5th EU-Thailand National Intervarsity Debate Championship Motions
Thailand
This house believes that Thailand should have a general re-election.
This house would grant Thaksin amnesty.
This house would make students take mandatory HIV / AIDS test.
Environment
This house would hold MNC accountable for environmental damages done by their subsidaries.
This house believes that forests should be controlled by local community.
This house would use market mechanisms to fight global warming.
Asia / Middle East
This house would cancel regional war games.
This house believes that Israel's attack on Gaza was justified.
This house would create a Tamil State.
European Union
This house would have an EU standing army.
This house believes that EU enlargement should not be used as political tools.
This house believes that the Lisbon Treaty is undemocratic.
Economics
This house would make measures fighting global warming the condition for receiving stimulus money
This house would lower trade barriers to countries that comply with human rights standards.
This house would make a Thailand-EU FTA.
Thailand
This house believes that Thailand should have a general re-election.
This house would grant Thaksin amnesty.
This house would make students take mandatory HIV / AIDS test.
Environment
This house would hold MNC accountable for environmental damages done by their subsidaries.
This house believes that forests should be controlled by local community.
This house would use market mechanisms to fight global warming.
Asia / Middle East
This house would cancel regional war games.
This house believes that Israel's attack on Gaza was justified.
This house would create a Tamil State.
European Union
This house would have an EU standing army.
This house believes that EU enlargement should not be used as political tools.
This house believes that the Lisbon Treaty is undemocratic.
Economics
This house would make measures fighting global warming the condition for receiving stimulus money
This house would lower trade barriers to countries that comply with human rights standards.
This house would make a Thailand-EU FTA.
Wednesday, March 25, 2009
Make Up Quiz Summer 1: Ep 4
Answer for me in your notebook--handwritten:
1. What is the scientific method?
2. who made the standard units?
3. what are the careers possible if you are a chemist--name three. Drug dealer doesn't count.
4. Who is Mendeleev? Rutherford? in regard to chemistry
1. What is the scientific method?
2. who made the standard units?
3. what are the careers possible if you are a chemist--name three. Drug dealer doesn't count.
4. Who is Mendeleev? Rutherford? in regard to chemistry
Monday, March 23, 2009
Reading Chapter Three: 3.4
Connecting to Your World Have you ever wondered why some objects float in water, while others sink? If you think that these lily pads float because they are lightweight, you are only partially correct. The ratio of the mass of an object to its volume can be used to determine whether an object floats or sinks in water. For pure water at 4°C, this ratio is 1.000 g/cm3. If an object has a mass-to-volume ratio less than 1.000 g/cm3, it will float in water. If an object has a mass-to-volume ratio greater than this value, it will sink in water.
Key Concepts
*
What determines the density of a substance?
*
How does a change in temperature affect density?
Vocabulary
*
density
Reading Strategy
Identifying Main Idea As you read, write the main idea of the text that follows each heading.
Determining Density
Perhaps someone has tricked you with this question: “Which is heavier, a pound of lead or a pound of feathers?” Most people would not give the question much thought and would incorrectly answer “lead.” Of course, a pound of lead has the same mass as a pound of feathers. What concept, instead of mass, are people really thinking of when they answer this question?
View HTML
Simulation 1 Rank materials according to their densities.
Most people are incorrectly applying a perfectly correct idea: namely, that if a piece of lead and a feather of the same volume are weighed, the lead would have a greater mass than the feather. It would take a much larger volume of feathers to equal the mass of a given volume of lead.
The important relationship in this case is between the object’s mass and its volume. This relationship is called density. Density is the ratio of the mass of an object to its volume.
A 10.0-cm3 piece of lead, for example, has a mass of 114 g. What, then, is the density of lead? You can calculate it by substituting the mass and volume into the equation above.
Note that when mass is measured in grams, and volume in cubic centimeters, density has units of grams per cubic centimeter (g/cm3).
Figure 3.13 compares the density of three substances. Why does each10-g sample have a different volume? The volumes vary because the substances have different densities. Density is an intensive property that depends only on the composition of a substance, not on the size of the sample. With a mixture, density can vary because the composition of a mixture can vary.
PDF
Figure 3.13
What do you think will happen if corn oil is poured into a glass containing corn syrup? Using Table 3.6, you can see that the density of corn oil is less than the density of corn syrup. For that reason, the oil floats on top of the syrup, as shown in Figure 3.14.
Figure 3.14 Because of differences in density, corn oil floats on top of corn syrup.
You have probably seen a helium-filled balloon rapidly rise to the ceiling when it is released. Whether a gas-filled balloon will sink or rise when released depends on how the density of the gas compares with the density of air. Helium is less dense than air, so a helium-filled balloon rises. The densities of various gases are listed in Table 3.6.
Determining Density
Perhaps someone has tricked you with this question: “Which is heavier, a pound of lead or a pound of feathers?” Most people would not give the question much thought and would incorrectly answer “lead.” Of course, a pound of lead has the same mass as a pound of feathers. What concept, instead of mass, are people really thinking of when they answer this question?
View HTML
Simulation 1 Rank materials according to their densities.
Most people are incorrectly applying a perfectly correct idea: namely, that if a piece of lead and a feather of the same volume are weighed, the lead would have a greater mass than the feather. It would take a much larger volume of feathers to equal the mass of a given volume of lead.
The important relationship in this case is between the object’s mass and its volume. This relationship is called density. Density is the ratio of the mass of an object to its volume.
A 10.0-cm3 piece of lead, for example, has a mass of 114 g. What, then, is the density of lead? You can calculate it by substituting the mass and volume into the equation above.
Note that when mass is measured in grams, and volume in cubic centimeters, density has units of grams per cubic centimeter (g/cm3).
Figure 3.13 compares the density of three substances. Why does each10-g sample have a different volume? The volumes vary because the substances have different densities. Density is an intensive property that depends only on the composition of a substance, not on the size of the sample. With a mixture, density can vary because the composition of a mixture can vary.
PDF
Figure 3.13
What do you think will happen if corn oil is poured into a glass containing corn syrup? Using Table 3.6, you can see that the density of corn oil is less than the density of corn syrup. For that reason, the oil floats on top of the syrup, as shown in Figure 3.14.
Figure 3.14 Because of differences in density, corn oil floats on top of corn syrup.
You have probably seen a helium-filled balloon rapidly rise to the ceiling when it is released. Whether a gas-filled balloon will sink or rise when released depends on how the density of the gas compares with the density of air. Helium is less dense than air, so a helium-filled balloon rises. The densities of various gases are listed in Table 3.6.
Key Concepts
3.1 Measurements and Their Uncertainty
*
Measurements are fundamental to the experimental sciences.Hint
*
To evaluate accuracy, the measured value must be compared to the correct value. To evaluate precision, you must compare the values of repeated measurements.Hint
*
Calculated answers often depend on the number of significant figures in the values used in the calculation.Hint
*
In general, a calculated answer cannot be more precise than the least precise measurement from which it was calculated.Hint
3.2 The International System of Units
*
Five commonly used SI base units are the meter, kilogram, kelvin, second, and mole.Hint
*
Common metric units of length: cm, m, km. Common metric units of volume: μL, mL, L, cm3. Common metric units of mass: mg, g, kg. Common units of temperature: °C and K. Common units of energy: J and cal.Hint
3.3 Conversion Problems
*
Multiplying by a conversion factor does not change the actual size of a measurement.Hint
*
Dimensional analysis provides an alternative approach to problem solving.Hint
*
Conversion problems are easily solved using dimensional analysis.Hint
3.4 Density
*
Density is an intensive property that depends only on the composition of a substance.Hint
*
The density of a substance generally decreases as its temperature increases.Hint
Vocabulary
PDF
Vocabulary Review
*
absolute zero
*
accepted value
*
accuracy
*
calorie (cal)
*
Celsius scale
*
conversion factor
*
density
*
dimensional analysis
*
energy
*
error
*
experimental value
*
gram (g)
*
International System of Units (SI)
*
joule (J)
*
Kelvin scale
*
kilogram (kg)
*
liter (L)
*
measurement
*
meter (m)
*
percent error
*
precision
*
scientific notation
*
significant figures
*
temperature
*
weight
Key Equations
*
Error = experimental value − accepted value Hint
*
Hint
*
K = °C + 273and °C = K − 273Hint
*
1 J = 0.2390 cal and 1 cal = 4.184 JHint
*
Hint
Key Concepts
*
What determines the density of a substance?
*
How does a change in temperature affect density?
Vocabulary
*
density
Reading Strategy
Identifying Main Idea As you read, write the main idea of the text that follows each heading.
Determining Density
Perhaps someone has tricked you with this question: “Which is heavier, a pound of lead or a pound of feathers?” Most people would not give the question much thought and would incorrectly answer “lead.” Of course, a pound of lead has the same mass as a pound of feathers. What concept, instead of mass, are people really thinking of when they answer this question?
View HTML
Simulation 1 Rank materials according to their densities.
Most people are incorrectly applying a perfectly correct idea: namely, that if a piece of lead and a feather of the same volume are weighed, the lead would have a greater mass than the feather. It would take a much larger volume of feathers to equal the mass of a given volume of lead.
The important relationship in this case is between the object’s mass and its volume. This relationship is called density. Density is the ratio of the mass of an object to its volume.
A 10.0-cm3 piece of lead, for example, has a mass of 114 g. What, then, is the density of lead? You can calculate it by substituting the mass and volume into the equation above.
Note that when mass is measured in grams, and volume in cubic centimeters, density has units of grams per cubic centimeter (g/cm3).
Figure 3.13 compares the density of three substances. Why does each10-g sample have a different volume? The volumes vary because the substances have different densities. Density is an intensive property that depends only on the composition of a substance, not on the size of the sample. With a mixture, density can vary because the composition of a mixture can vary.
Figure 3.13
What do you think will happen if corn oil is poured into a glass containing corn syrup? Using Table 3.6, you can see that the density of corn oil is less than the density of corn syrup. For that reason, the oil floats on top of the syrup, as shown in Figure 3.14.
Figure 3.14 Because of differences in density, corn oil floats on top of corn syrup.
You have probably seen a helium-filled balloon rapidly rise to the ceiling when it is released. Whether a gas-filled balloon will sink or rise when released depends on how the density of the gas compares with the density of air. Helium is less dense than air, so a helium-filled balloon rises. The densities of various gases are listed in Table 3.6.
Determining Density
Perhaps someone has tricked you with this question: “Which is heavier, a pound of lead or a pound of feathers?” Most people would not give the question much thought and would incorrectly answer “lead.” Of course, a pound of lead has the same mass as a pound of feathers. What concept, instead of mass, are people really thinking of when they answer this question?
View HTML
Simulation 1 Rank materials according to their densities.
Most people are incorrectly applying a perfectly correct idea: namely, that if a piece of lead and a feather of the same volume are weighed, the lead would have a greater mass than the feather. It would take a much larger volume of feathers to equal the mass of a given volume of lead.
The important relationship in this case is between the object’s mass and its volume. This relationship is called density. Density is the ratio of the mass of an object to its volume.
A 10.0-cm3 piece of lead, for example, has a mass of 114 g. What, then, is the density of lead? You can calculate it by substituting the mass and volume into the equation above.
Note that when mass is measured in grams, and volume in cubic centimeters, density has units of grams per cubic centimeter (g/cm3).
Figure 3.13 compares the density of three substances. Why does each10-g sample have a different volume? The volumes vary because the substances have different densities. Density is an intensive property that depends only on the composition of a substance, not on the size of the sample. With a mixture, density can vary because the composition of a mixture can vary.
Figure 3.13
What do you think will happen if corn oil is poured into a glass containing corn syrup? Using Table 3.6, you can see that the density of corn oil is less than the density of corn syrup. For that reason, the oil floats on top of the syrup, as shown in Figure 3.14.
Figure 3.14 Because of differences in density, corn oil floats on top of corn syrup.
You have probably seen a helium-filled balloon rapidly rise to the ceiling when it is released. Whether a gas-filled balloon will sink or rise when released depends on how the density of the gas compares with the density of air. Helium is less dense than air, so a helium-filled balloon rises. The densities of various gases are listed in Table 3.6.
Key Concepts
3.1 Measurements and Their Uncertainty
*
Measurements are fundamental to the experimental sciences.Hint
*
To evaluate accuracy, the measured value must be compared to the correct value. To evaluate precision, you must compare the values of repeated measurements.Hint
*
Calculated answers often depend on the number of significant figures in the values used in the calculation.Hint
*
In general, a calculated answer cannot be more precise than the least precise measurement from which it was calculated.Hint
3.2 The International System of Units
*
Five commonly used SI base units are the meter, kilogram, kelvin, second, and mole.Hint
*
Common metric units of length: cm, m, km. Common metric units of volume: μL, mL, L, cm3. Common metric units of mass: mg, g, kg. Common units of temperature: °C and K. Common units of energy: J and cal.Hint
3.3 Conversion Problems
*
Multiplying by a conversion factor does not change the actual size of a measurement.Hint
*
Dimensional analysis provides an alternative approach to problem solving.Hint
*
Conversion problems are easily solved using dimensional analysis.Hint
3.4 Density
*
Density is an intensive property that depends only on the composition of a substance.Hint
*
The density of a substance generally decreases as its temperature increases.Hint
Vocabulary
Vocabulary Review
*
absolute zero
*
accepted value
*
accuracy
*
calorie (cal)
*
Celsius scale
*
conversion factor
*
density
*
dimensional analysis
*
energy
*
error
*
experimental value
*
gram (g)
*
International System of Units (SI)
*
joule (J)
*
Kelvin scale
*
kilogram (kg)
*
liter (L)
*
measurement
*
meter (m)
*
percent error
*
precision
*
scientific notation
*
significant figures
*
temperature
*
weight
Key Equations
*
Error = experimental value − accepted value Hint
*
Hint
*
K = °C + 273and °C = K − 273Hint
*
1 J = 0.2390 cal and 1 cal = 4.184 JHint
*
Hint
Reading Chapter Three: 3.3
Connecting to Your World Perhaps you have traveled abroad or are planning to do so. If so, you know—or will soon discover—that different countries have different currencies. As a tourist, exchanging money is essential to the enjoyment of your trip. After all, you must pay for your meals, hotel, transportation, gift purchases, and tickets to exhibits and events. Because each country’scurrency compares differently with the U.S. dollar, knowing how to convert currency units correctly is very important. Conversion problems are readily solved by a problem-solving approach called dimensional analysis.
Key Concepts
*
What happens when a measurement is multiplied by a conversion factor?
*
Why is dimensional analysis useful?
*
What types of problems are easily solved by using dimensional analysis?
Vocabulary
*
conversion factor
*
dimensional analysis
Reading Strategy
Monitoring Your Understanding Preview the Key Concepts, the section heads, and boldfaced terms. List three things you expect to learn. After reading, state what you learned about each item listed.
Conversion Factors
If you think about any number of everyday situations, you will realize that a quantity can usually be expressed in several different ways. For example, consider the monetary amount $1.
1 dollar = 4 quarters = 10 dimes = 20 nickels = 100 pennies
These are all expressions, or measurements, of the same amount of money. The same thing is true of scientific quantities. For example, consider a distance that measures exactly 1 meter.
1 meter = 10 decimeters = 100 centimeters = 1000 millimeters
These are different ways to express the same length.
Whenever two measurements are equivalent, a ratio of the two measurements will equal 1, or unity. For example, you can divide both sides of the equation 1 m = 100 cm by 1 m or by 100 cm.
View HTML
Animation 3 Learn how to select the proper conversion factor and how to use it.
A conversion factor is a ratio of equivalent measurements. The ratios 100 cm/1 m and 1 m/100 cm are examples of conversion factors. In a conversion factor, the measurement in the numerator (on the top) is equivalent to the measurement in the denominator (on the bottom). The conversion factors above are read “one hundred centimeters per meter” and “one meter per hundred centimeters.” Figure 3.11 illustrates another way to look at the relationships in a conversion factor. Notice that the smaller number is part of the measurement with the larger unit. That is, a meter is physically larger than a centimeter. The larger number is part of the measurement with the smaller unit.
PDF
Figure 3.11
Conversion factors are useful in solving problems in which a given measurement must be expressed in some other unit of measure.When a measurement is multiplied by a conversion factor, the numerical value is generally changed, but the actual size of the quantity measured remains the same. For example, even though the numbers in the measurements 1 g and 10 dg (decigrams) differ, both measurements represent the same mass. In addition, conversion factors within a system of measurement are defined quantities or exact quantities. Therefore, they have an unlimited number of significant figures, and do not affect the rounding of a calculated answer.
Here are some additional examples of pairs of conversion factors written from equivalent measurements. The relationship between grams and kilograms is 1000 g = 1 kg. The conversion factors are:
The scale of the micrograph in Figure 3.12 is in nanometers. Using the relationship 109 nm = 1 m, you can write the following conversion factors.
Figure 3.12 In this computer image of atoms, distance is marked off in nanometers (nm). Inferring What conversion factor would you use to convert nanometers to meters?
Common volumetric units used in chemistry include the liter and the microliter. The relationship 1 L = 106 μL yields the following conversion factors
Based on what you know about metric prefixes, you should be able to easily write conversion factors that relate equivalent metric quantities.
Dimensional Analysis
No single method is best for solving every type of problem. Several good approaches are available, and generally one of the best is dimensional analysis. Dimensional analysis is a way to analyze and solve problems using the units, or dimensions, of the measurements. The best way to explain this problem-solving technique is to use it to solve an everyday situation.
PDF
3.5 Using Dimensional Analysis
PDF
View HTML
Problem-Solving 3.29 Solve Problem 29 with the help of an interactive guided tutorial.
There is usually more than one way to solve a problem. When you first read Sample Problem 3.5, you may have thought about different and equally correct ways to approach and solve the problem. Some problems are easily worked with simple algebra.Dimensional analysis provides you with an alternative approach to problem solving. In either case, you should choose the problem-solving method that works best.
Converting Between Units
In chemistry, as in many other subjects, you often need to express a measurement in a unit different from the one given or measured initially. Problems in which a measurement with one unit is converted to an equivalent measurement with another unit are easily solved using dimensional analysis.
Suppose that a laboratory experiment requires 7.5 dg of magnesium metal, and 100 students will do the experiment. How many grams of magnesium should your teacher have on hand? Multiplying 100 students by 7.5 dg/student gives you 750 dg. But then you must convert dg to grams. Sample Problem 3.7 shows you how to do the conversion.
PDF
3.7 Converting Between Metric Units
View HTML
Problem-Solving 3.33 Solve Problem 33 with the help of an interactive guided tutorial.
Multistep Problems
Many complex tasks in your everyday life are best handled by breaking them down into manageable parts. For example, if you were cleaning a car, you might first vacuum the inside, then wash the exterior, then dry the exterior, and finally put on a fresh coat of wax. Similarly, many complex word problems are more easily solved by breaking the solution down into steps.
When converting between units, it is often necessary to use more than one conversion factor. Sample Problem 3.8 illustrates the use of multiple conversion factors.
Reading Checkpoint
PDF
3.8 Converting Between Metric Units
Chemath
Scientific Notation
A It is often convenient to express very large or very small numbers in scientific notation. The distance between the sun and Earth is 150,000,000 km, which can be written as 1.5 × 108 km. The diameter of a gold atom is 0.000 000 000 274 m, or 2.74 × 10−10 m. When multiplying numbers written in scientific notation, add the exponents. When dividing numbers written in scientific notation, subtract the exponent in the denominator from the exponent in the numerator.
PDF
View HTML
Problem-Solving 3.35 Solve Problem 35 with the help of an interactive guided tutorial.
Converting Complex Units
Many common measurements are expressed as a ratio of two units. For example, the results of international car races often give average lap speeds in kilometers per hour. You measure the densities of solids and liquids in grams per cubic centimeter. You measure the gas mileage in a car in miles per gallon of gasoline. If you use dimensional analysis, converting these complex units is just as easy as converting single units. It will just take multiple steps to arrive at an answer.
Key Concepts
*
What happens when a measurement is multiplied by a conversion factor?
*
Why is dimensional analysis useful?
*
What types of problems are easily solved by using dimensional analysis?
Vocabulary
*
conversion factor
*
dimensional analysis
Reading Strategy
Monitoring Your Understanding Preview the Key Concepts, the section heads, and boldfaced terms. List three things you expect to learn. After reading, state what you learned about each item listed.
Conversion Factors
If you think about any number of everyday situations, you will realize that a quantity can usually be expressed in several different ways. For example, consider the monetary amount $1.
1 dollar = 4 quarters = 10 dimes = 20 nickels = 100 pennies
These are all expressions, or measurements, of the same amount of money. The same thing is true of scientific quantities. For example, consider a distance that measures exactly 1 meter.
1 meter = 10 decimeters = 100 centimeters = 1000 millimeters
These are different ways to express the same length.
Whenever two measurements are equivalent, a ratio of the two measurements will equal 1, or unity. For example, you can divide both sides of the equation 1 m = 100 cm by 1 m or by 100 cm.
View HTML
Animation 3 Learn how to select the proper conversion factor and how to use it.
A conversion factor is a ratio of equivalent measurements. The ratios 100 cm/1 m and 1 m/100 cm are examples of conversion factors. In a conversion factor, the measurement in the numerator (on the top) is equivalent to the measurement in the denominator (on the bottom). The conversion factors above are read “one hundred centimeters per meter” and “one meter per hundred centimeters.” Figure 3.11 illustrates another way to look at the relationships in a conversion factor. Notice that the smaller number is part of the measurement with the larger unit. That is, a meter is physically larger than a centimeter. The larger number is part of the measurement with the smaller unit.
Figure 3.11
Conversion factors are useful in solving problems in which a given measurement must be expressed in some other unit of measure.When a measurement is multiplied by a conversion factor, the numerical value is generally changed, but the actual size of the quantity measured remains the same. For example, even though the numbers in the measurements 1 g and 10 dg (decigrams) differ, both measurements represent the same mass. In addition, conversion factors within a system of measurement are defined quantities or exact quantities. Therefore, they have an unlimited number of significant figures, and do not affect the rounding of a calculated answer.
Here are some additional examples of pairs of conversion factors written from equivalent measurements. The relationship between grams and kilograms is 1000 g = 1 kg. The conversion factors are:
The scale of the micrograph in Figure 3.12 is in nanometers. Using the relationship 109 nm = 1 m, you can write the following conversion factors.
Figure 3.12 In this computer image of atoms, distance is marked off in nanometers (nm). Inferring What conversion factor would you use to convert nanometers to meters?
Common volumetric units used in chemistry include the liter and the microliter. The relationship 1 L = 106 μL yields the following conversion factors
Based on what you know about metric prefixes, you should be able to easily write conversion factors that relate equivalent metric quantities.
Dimensional Analysis
No single method is best for solving every type of problem. Several good approaches are available, and generally one of the best is dimensional analysis. Dimensional analysis is a way to analyze and solve problems using the units, or dimensions, of the measurements. The best way to explain this problem-solving technique is to use it to solve an everyday situation.
3.5 Using Dimensional Analysis
View HTML
Problem-Solving 3.29 Solve Problem 29 with the help of an interactive guided tutorial.
There is usually more than one way to solve a problem. When you first read Sample Problem 3.5, you may have thought about different and equally correct ways to approach and solve the problem. Some problems are easily worked with simple algebra.Dimensional analysis provides you with an alternative approach to problem solving. In either case, you should choose the problem-solving method that works best.
Converting Between Units
In chemistry, as in many other subjects, you often need to express a measurement in a unit different from the one given or measured initially. Problems in which a measurement with one unit is converted to an equivalent measurement with another unit are easily solved using dimensional analysis.
Suppose that a laboratory experiment requires 7.5 dg of magnesium metal, and 100 students will do the experiment. How many grams of magnesium should your teacher have on hand? Multiplying 100 students by 7.5 dg/student gives you 750 dg. But then you must convert dg to grams. Sample Problem 3.7 shows you how to do the conversion.
3.7 Converting Between Metric Units
View HTML
Problem-Solving 3.33 Solve Problem 33 with the help of an interactive guided tutorial.
Multistep Problems
Many complex tasks in your everyday life are best handled by breaking them down into manageable parts. For example, if you were cleaning a car, you might first vacuum the inside, then wash the exterior, then dry the exterior, and finally put on a fresh coat of wax. Similarly, many complex word problems are more easily solved by breaking the solution down into steps.
When converting between units, it is often necessary to use more than one conversion factor. Sample Problem 3.8 illustrates the use of multiple conversion factors.
Reading Checkpoint
3.8 Converting Between Metric Units
Chemath
Scientific Notation
A It is often convenient to express very large or very small numbers in scientific notation. The distance between the sun and Earth is 150,000,000 km, which can be written as 1.5 × 108 km. The diameter of a gold atom is 0.000 000 000 274 m, or 2.74 × 10−10 m. When multiplying numbers written in scientific notation, add the exponents. When dividing numbers written in scientific notation, subtract the exponent in the denominator from the exponent in the numerator.
View HTML
Problem-Solving 3.35 Solve Problem 35 with the help of an interactive guided tutorial.
Converting Complex Units
Many common measurements are expressed as a ratio of two units. For example, the results of international car races often give average lap speeds in kilometers per hour. You measure the densities of solids and liquids in grams per cubic centimeter. You measure the gas mileage in a car in miles per gallon of gasoline. If you use dimensional analysis, converting these complex units is just as easy as converting single units. It will just take multiple steps to arrive at an answer.
Reading Chapter Three: 3.2
Connecting to Your World “Are we there yet?” You may have asked this question during a long road trip with family or friends. To find out how much farther you have to go, you can read the roadside signs that list destinations and their distances. In the signs shown here, however, the distances are listed as numbers with no units attached. Is Carrieton 44 kilometers or 44 miles away? Without the units, you can’t be sure. When you make a measurement, you must assign the correct units to the numerical value. Without the units, it is impossible to communicate the measurement clearly to others.
Key Concepts
*
Which five SI base units do chemists commonly use?
*
What metric units are commonly used to measure length, volume, mass, temperature, and energy?
Vocabulary
*
International System of Units (SI)
*
meter (m)
*
liter (L)
*
kilogram (kg)
*
gram (g)
*
weight
*
temperature
*
Celsius scale
*
Kelvin scale
*
absolute zero
*
energy
*
joule (J)
*
calorie (cal)
Reading Strategy
Summarizing As you read about SI units, summarize the main ideas in the text that follows the red and blue headings.
Connecting to Your World “Are we there yet?” You may have asked this question during a long road trip with family or friends. To find out how much farther you have to go, you can read the roadside signs that list destinations and their distances. In the signs shown here, however, the distances are listed as numbers with no units attached. Is Carrieton 44 kilometers or 44 miles away? Without the units, you can’t be sure. When you make a measurement, you must assign the correct units to the numerical value. Without the units, it is impossible to communicate the measurement clearly to others.
Key Concepts
*
Which five SI base units do chemists commonly use?
*
What metric units are commonly used to measure length, volume, mass, temperature, and energy?
Vocabulary
*
International System of Units (SI)
*
meter (m)
*
liter (L)
*
kilogram (kg)
*
gram (g)
*
weight
*
temperature
*
Celsius scale
*
Kelvin scale
*
absolute zero
*
energy
*
joule (J)
*
calorie (cal)
Reading Strategy
Summarizing As you read about SI units, summarize the main ideas in the text that follows the red and blue headings.
Units and Quantities
As you already know, you don’t measure length in kilograms or mass in centimeters. Different quantities require different units. Before you make a measurement, you must be familiar with the units corresponding to the quantity that you are trying to measure.
Units of Length
Size is an important property of matter. In SI, the basic unit of length, or linear measure, is the meter (m). All measurements of length can be expressed in meters. (The length of a page in this book is about one-fourth of a meter.) For very large and very small lengths, however, it may be more convenient to use a unit of length that has a prefix. Table 3.2 lists the prefixes in common use. For example, the prefix milli- means 1/1000 (one-thousandth), so a millimeter (mm) is 1/1000 of a meter, or 0.001 m. A hyphen (-) measures about 1 mm.
PDF
Table 3.2: Commonly Used Metric Prefixes
For large distances, it is usually most appropriate to express measurements in kilometers (km). The prefix kilo- means 1000, so 1 km equals 1000 m. A standard marathon distance race of about 42,000 m is more conveniently expressed as 42 km (42 × 1000 m). Common metric units of length include the centimeter, meter, and kilometer. Table 3.3 summarizes the relationships among metric units of length.
PDF
Table 3.3: Metric Units of Length
PDF
Length of 5 city blocks ≈ 1 km
Units of Volume
The space occupied by any sample of matter is called its volume. You calculate the volume of any cubic or rectangular solid by multiplying its length by its width by its height. The unit for volume is thus derived from units of length. The SI unit of volume is the amount of space occupied by a cube that is 1 m along each edge. This volume is a cubic meter (m3). An automatic dishwasher has a volume of about 1 m3.
A more convenient unit of volume for everyday use is the liter, anon-SI unit. A liter (L) is the volume of a cube that is 10 centimeters (10 cm) along each edge (10 cm × 10 cm × 10 cm = 1000 cm3 = 1 L). A decimeter (dm) is equal to 10 cm, so 1 L is also equal to 1 cubic decimeter (dm3). A smaller non-SI unit of volume is the milliliter (mL); 1 mL is 1/1000 of a liter. Thus there are 1000 mL in 1 L. Because 1 L is defined as 1000 cm3, 1 mL and 1 cm3 are the same volume. The units milliliter and cubic centimeter are thus used interchangeably. Common metric units of volume include the liter, milliliter, cubic centimeter, and microliter. Table 3.4 summarizes the relationships among these units of volume.
Figure 3.6 These photographs above give you some idea of the relative sizes of some different units of volume. a The volume of 20 drops of liquid from a medicine dropper is approximately 1 mL. b A sugar cube is 1 cm on each edge and has a volume of 1 cm3. Note that 1 mL is the same as 1 cm3. c A gallon of milk has about twice the volume of a 2-L bottle of soda. Calculating How many cubic centimeters are in 2 liters?
PDF
Table 3.4: Metric Units of Volume
There're many devices for measuring liquid volumes, including graduated cylinders, pipets, burets, volumetric flasks, and syringes. Note that the volume of any solid, liquid, or gas will change with temperature (although the change is much more dramatic for gases). Consequently, accurate -volume-measuring devices are calibrated at a given temperature—usually 20 degrees Celsius (20°C), which is about normal room temperature.
Reading Checkpoint
Units of Mass
The mass of an object is measured in comparison to a standard mass of 1 kilogram (kg), which is the basic SI unit of mass. A kilogram was originally defined as the mass of 1 L of liquid water at 4°C. A cube of water at 4°C measuring 10 cm on each edge would have a volume of 1 L and a mass of 1000 grams (g), or 1 kg. A gram (g) is 1/1000 of a kilogram; the mass of 1 cm3 of water at 4°C is 1 g. Common metric units of mass include the kilogram, gram, milligram, and microgram. The relationships among units of mass are shown in Table 3.5.
PDF
Table 3.5: Metric Units of Mass
You can use a platform balance to measure the mass of an object. The object is placed on one side of the balance, and standard masses are added to the other side until the balance beam is level. The unknown mass is equal to the sum of the standard masses. Laboratory balances range from very sensitive instruments with a maximum capacity of only a few milligrams to devices for measuring quantities in kilograms. An analytical balance is used to measure objects of less than 100 g and can determine mass to the nearest 0.0001 g (0.1 mg).
The astronaut shown on the surface of the moon in Figure 3.7 weighs one sixth of what he weighs on Earth. The reason for this difference is that the force of gravity on Earth is about six times what it is on the moon. Weight is a force that measures the pull on a given mass by gravity. Weight, a measure of force, is different from mass, which is a measure of the quantity of matter. Although the weight of an object can change with its location, its mass remains constant regardless of its location. Objects can thus become weightless, but they can never become massless.
Figure 3.7 An astronaut’s weight on the moon is one sixth as much as it is on Earth. Earth exerts six times the force of gravity as the moon. Inferring How does the astronaut’s mass on the moon compare to his mass on Earth?
Reading Checkpoint
Units of Temperature
When you hold a glass of hot water, the glass feels hot because heat transfers from the glass to your hand. When you hold an ice cube, it feels cold because heat transfers from your hand to the ice cube. Temperature is a measure of how hot or cold an object is. An object’s temperature determines the direction of heat transfer. When two objects at different temperatures are in contact, heat moves from the object at the higher temperature to the object at the lower temperature.
Almost all substances expand with an increase in temperature and contract as the temperature decreases. (A very important exception is water.) These properties are the basis for the common liquid-in-glass thermometer. The liquid in the thermometer expands and contracts more than the volume of the glass, producing changes in the column height of liquid. Figure 3.8 shows a few different types of thermometers.
Figure 3.8 Thermometers are used to measure temperature. a A liquid-in-glass thermometer contains alcohol or mineral spirits. b A dial thermometer contains a coiled bimetallic strip. c A Galileo thermometer contains several glass bulbs that are calibrated to sink or float depending on the temperature. The Galileo thermometer shown uses the Fahrenheit scale, which sets the freezing point of water at 32°F and the boiling point of water at 212°F.
Several temperature scales with different units have been devised. Scientists commonly use two equivalent units of temperature, the degree Celsius and the kelvin. The Celsius scale of the metric system is named after the Swedish astronomer Anders Celsius (1701–1744). It uses two readily determined temperatures as reference temperature values: the freezing point and the boiling point of water. The Celsius scale sets the freezing point of water at 0°C and the boiling point of water at 100°C. The distance between these two fixed points is divided into 100 equal intervals, or degrees Celsius (°C).
Another temperature scale used in the physical sciences is the Kelvin, or absolute, scale. This scale is named for Lord Kelvin (1824–1907), a Scottish physicist and mathematician. On the Kelvin scale, the freezing point of water is 273.15 kelvins (K), and the boiling point is 373.15 K. Notice that with the Kelvin scale, the degree sign is not used. Figure 3.9 on the next page compares the Celsius and Kelvin scales. A change of one degree on the Celsius scale is equivalent to one kelvin on the Kelvin scale. The zero point on the Kelvinscale, 0 K, or absolute zero, is equal to −273.15°C. For problems in this text, you can round −273.15°C to −273°C. Because one degree on the Celsius scale is equivalent to one kelvin on the Kelvin scale, converting from one temperature to another is easy. You simply add or subtract 273, as shown in the following equations.
PDF
Figure 3.9
K = °C + 273
°C = K − 273
Go Online
For: Links on Temperature Scales
Visit: www.SciLinks.org
Web Code: cdn-1032
PDF
3.4 Converting Between Temperature Scales
PDF
View HTML
Problem-Solving 3.17 Solve Problem 17 with the help of an interactive guided tutorial.
Units of Energy
Figure 3.10 shows a house equipped with solar panels. The solar panels convert the radiant energy from the sun into electrical energy that can be used to heat water and power appliances. Energy is the capacity to do work or to produce heat.
Figure 3.10 Photoelectric panels convert solar energy into electricity.
Like any other quantity, energy can be measured.The joule and the calorie are common units of energy. The joule (J) is the SI unit of energy. It is named after the English physicist James Prescott Joule (1818–1889). One calorie (cal) is the quantity of heat that raises the temperature of 1 g of pure water by 1°C. Conversions between joules and calories can be carried out using the following relationships.
1J = 0.2390 cal 1 cal = 4.184 J
Key Concepts
*
Which five SI base units do chemists commonly use?
*
What metric units are commonly used to measure length, volume, mass, temperature, and energy?
Vocabulary
*
International System of Units (SI)
*
meter (m)
*
liter (L)
*
kilogram (kg)
*
gram (g)
*
weight
*
temperature
*
Celsius scale
*
Kelvin scale
*
absolute zero
*
energy
*
joule (J)
*
calorie (cal)
Reading Strategy
Summarizing As you read about SI units, summarize the main ideas in the text that follows the red and blue headings.
Connecting to Your World “Are we there yet?” You may have asked this question during a long road trip with family or friends. To find out how much farther you have to go, you can read the roadside signs that list destinations and their distances. In the signs shown here, however, the distances are listed as numbers with no units attached. Is Carrieton 44 kilometers or 44 miles away? Without the units, you can’t be sure. When you make a measurement, you must assign the correct units to the numerical value. Without the units, it is impossible to communicate the measurement clearly to others.
Key Concepts
*
Which five SI base units do chemists commonly use?
*
What metric units are commonly used to measure length, volume, mass, temperature, and energy?
Vocabulary
*
International System of Units (SI)
*
meter (m)
*
liter (L)
*
kilogram (kg)
*
gram (g)
*
weight
*
temperature
*
Celsius scale
*
Kelvin scale
*
absolute zero
*
energy
*
joule (J)
*
calorie (cal)
Reading Strategy
Summarizing As you read about SI units, summarize the main ideas in the text that follows the red and blue headings.
Units and Quantities
As you already know, you don’t measure length in kilograms or mass in centimeters. Different quantities require different units. Before you make a measurement, you must be familiar with the units corresponding to the quantity that you are trying to measure.
Units of Length
Size is an important property of matter. In SI, the basic unit of length, or linear measure, is the meter (m). All measurements of length can be expressed in meters. (The length of a page in this book is about one-fourth of a meter.) For very large and very small lengths, however, it may be more convenient to use a unit of length that has a prefix. Table 3.2 lists the prefixes in common use. For example, the prefix milli- means 1/1000 (one-thousandth), so a millimeter (mm) is 1/1000 of a meter, or 0.001 m. A hyphen (-) measures about 1 mm.
Table 3.2: Commonly Used Metric Prefixes
For large distances, it is usually most appropriate to express measurements in kilometers (km). The prefix kilo- means 1000, so 1 km equals 1000 m. A standard marathon distance race of about 42,000 m is more conveniently expressed as 42 km (42 × 1000 m). Common metric units of length include the centimeter, meter, and kilometer. Table 3.3 summarizes the relationships among metric units of length.
Table 3.3: Metric Units of Length
Length of 5 city blocks ≈ 1 km
Units of Volume
The space occupied by any sample of matter is called its volume. You calculate the volume of any cubic or rectangular solid by multiplying its length by its width by its height. The unit for volume is thus derived from units of length. The SI unit of volume is the amount of space occupied by a cube that is 1 m along each edge. This volume is a cubic meter (m3). An automatic dishwasher has a volume of about 1 m3.
A more convenient unit of volume for everyday use is the liter, anon-SI unit. A liter (L) is the volume of a cube that is 10 centimeters (10 cm) along each edge (10 cm × 10 cm × 10 cm = 1000 cm3 = 1 L). A decimeter (dm) is equal to 10 cm, so 1 L is also equal to 1 cubic decimeter (dm3). A smaller non-SI unit of volume is the milliliter (mL); 1 mL is 1/1000 of a liter. Thus there are 1000 mL in 1 L. Because 1 L is defined as 1000 cm3, 1 mL and 1 cm3 are the same volume. The units milliliter and cubic centimeter are thus used interchangeably. Common metric units of volume include the liter, milliliter, cubic centimeter, and microliter. Table 3.4 summarizes the relationships among these units of volume.
Figure 3.6 These photographs above give you some idea of the relative sizes of some different units of volume. a The volume of 20 drops of liquid from a medicine dropper is approximately 1 mL. b A sugar cube is 1 cm on each edge and has a volume of 1 cm3. Note that 1 mL is the same as 1 cm3. c A gallon of milk has about twice the volume of a 2-L bottle of soda. Calculating How many cubic centimeters are in 2 liters?
Table 3.4: Metric Units of Volume
There're many devices for measuring liquid volumes, including graduated cylinders, pipets, burets, volumetric flasks, and syringes. Note that the volume of any solid, liquid, or gas will change with temperature (although the change is much more dramatic for gases). Consequently, accurate -volume-measuring devices are calibrated at a given temperature—usually 20 degrees Celsius (20°C), which is about normal room temperature.
Reading Checkpoint
Units of Mass
The mass of an object is measured in comparison to a standard mass of 1 kilogram (kg), which is the basic SI unit of mass. A kilogram was originally defined as the mass of 1 L of liquid water at 4°C. A cube of water at 4°C measuring 10 cm on each edge would have a volume of 1 L and a mass of 1000 grams (g), or 1 kg. A gram (g) is 1/1000 of a kilogram; the mass of 1 cm3 of water at 4°C is 1 g. Common metric units of mass include the kilogram, gram, milligram, and microgram. The relationships among units of mass are shown in Table 3.5.
Table 3.5: Metric Units of Mass
You can use a platform balance to measure the mass of an object. The object is placed on one side of the balance, and standard masses are added to the other side until the balance beam is level. The unknown mass is equal to the sum of the standard masses. Laboratory balances range from very sensitive instruments with a maximum capacity of only a few milligrams to devices for measuring quantities in kilograms. An analytical balance is used to measure objects of less than 100 g and can determine mass to the nearest 0.0001 g (0.1 mg).
The astronaut shown on the surface of the moon in Figure 3.7 weighs one sixth of what he weighs on Earth. The reason for this difference is that the force of gravity on Earth is about six times what it is on the moon. Weight is a force that measures the pull on a given mass by gravity. Weight, a measure of force, is different from mass, which is a measure of the quantity of matter. Although the weight of an object can change with its location, its mass remains constant regardless of its location. Objects can thus become weightless, but they can never become massless.
Figure 3.7 An astronaut’s weight on the moon is one sixth as much as it is on Earth. Earth exerts six times the force of gravity as the moon. Inferring How does the astronaut’s mass on the moon compare to his mass on Earth?
Reading Checkpoint
Units of Temperature
When you hold a glass of hot water, the glass feels hot because heat transfers from the glass to your hand. When you hold an ice cube, it feels cold because heat transfers from your hand to the ice cube. Temperature is a measure of how hot or cold an object is. An object’s temperature determines the direction of heat transfer. When two objects at different temperatures are in contact, heat moves from the object at the higher temperature to the object at the lower temperature.
Almost all substances expand with an increase in temperature and contract as the temperature decreases. (A very important exception is water.) These properties are the basis for the common liquid-in-glass thermometer. The liquid in the thermometer expands and contracts more than the volume of the glass, producing changes in the column height of liquid. Figure 3.8 shows a few different types of thermometers.
Figure 3.8 Thermometers are used to measure temperature. a A liquid-in-glass thermometer contains alcohol or mineral spirits. b A dial thermometer contains a coiled bimetallic strip. c A Galileo thermometer contains several glass bulbs that are calibrated to sink or float depending on the temperature. The Galileo thermometer shown uses the Fahrenheit scale, which sets the freezing point of water at 32°F and the boiling point of water at 212°F.
Several temperature scales with different units have been devised. Scientists commonly use two equivalent units of temperature, the degree Celsius and the kelvin. The Celsius scale of the metric system is named after the Swedish astronomer Anders Celsius (1701–1744). It uses two readily determined temperatures as reference temperature values: the freezing point and the boiling point of water. The Celsius scale sets the freezing point of water at 0°C and the boiling point of water at 100°C. The distance between these two fixed points is divided into 100 equal intervals, or degrees Celsius (°C).
Another temperature scale used in the physical sciences is the Kelvin, or absolute, scale. This scale is named for Lord Kelvin (1824–1907), a Scottish physicist and mathematician. On the Kelvin scale, the freezing point of water is 273.15 kelvins (K), and the boiling point is 373.15 K. Notice that with the Kelvin scale, the degree sign is not used. Figure 3.9 on the next page compares the Celsius and Kelvin scales. A change of one degree on the Celsius scale is equivalent to one kelvin on the Kelvin scale. The zero point on the Kelvinscale, 0 K, or absolute zero, is equal to −273.15°C. For problems in this text, you can round −273.15°C to −273°C. Because one degree on the Celsius scale is equivalent to one kelvin on the Kelvin scale, converting from one temperature to another is easy. You simply add or subtract 273, as shown in the following equations.
Figure 3.9
K = °C + 273
°C = K − 273
Go Online
For: Links on Temperature Scales
Visit: www.SciLinks.org
Web Code: cdn-1032
3.4 Converting Between Temperature Scales
View HTML
Problem-Solving 3.17 Solve Problem 17 with the help of an interactive guided tutorial.
Units of Energy
Figure 3.10 shows a house equipped with solar panels. The solar panels convert the radiant energy from the sun into electrical energy that can be used to heat water and power appliances. Energy is the capacity to do work or to produce heat.
Figure 3.10 Photoelectric panels convert solar energy into electricity.
Like any other quantity, energy can be measured.The joule and the calorie are common units of energy. The joule (J) is the SI unit of energy. It is named after the English physicist James Prescott Joule (1818–1889). One calorie (cal) is the quantity of heat that raises the temperature of 1 g of pure water by 1°C. Conversions between joules and calories can be carried out using the following relationships.
1J = 0.2390 cal 1 cal = 4.184 J
Reading Chapter Three: 3.1
Connecting to Your World On January 4, 2004, the Mars Exploration Rover Spirit landed on Mars. Equipped with five scientific instruments and a rock abrasion tool (shown at left), Spirit was sent to examine the Martian surface around Gusev Crater, a wide basin that may have once held a lake. Each day of its mission, Spirit recorded measurements for analysis. This data helped scientists learn about the geology and climate on Mars. All measurements have some uncertainty. In the chemistry laboratory, you must strive for accuracy and precision in your measurements.
Key Concepts
*
How do measurements relate to science?
*
How do you evaluate accuracy and precision?
*
Why must measurements be reported to the correct number of significant figures?
*
How does the precision of a calculated answer compare to the precision of the measurements used to obtain it?
Vocabulary
*
measurement
*
scientific notation
*
accuracy
*
precision
*
accepted value
*
experimental value
*
error
*
percent error
*
significant figures
Reading Strategy
Building Vocabulary As you read, write a definition of each key term in your own words.
Using and Expressing Measurements
Your height (67 inches), your weight (134 pounds), and the speed you drive on the highway (65 miles/hour) are some familiar examples of measurements. A measurement is a quantity that has both a number and a unit. Everyone makes and uses measurements. For instance, you decide how to dress in the morning based on the temperature outside. If you were baking cookies, you would measure the volumes of the ingredients as indicated in the recipe.
Such everyday situations are similar to those faced by scientists. Measurements are fundamental to the experimental sciences. For that reason, it isimportant to be able to make measurements and to decide whether a measurement is correct. The units typically used in the sciences are those of the International System of Measurements(SI).
In chemistry, you will often encounter very large or very small numbers. A single gram of hydrogen, for example, contains approximately 602,000,000,000,000,000,000,000 hydrogenatoms. The mass of an atom of gold is 0.000 000 000 000 000 000 000 327 gram. Writing and using such large and small numbers is very cumbersome. You can work more easily with these numbers by writing them in scientific, or exponential, notation.
In scientific notation, a given number is written as the product of two numbers: a coefficient and 10 raised to a power. For example, the number 602,000,000,000,000,000,000,000written in scientific notation is 6.02 × 1023. The coefficient in this number is 6.02. In scientific notation, the coefficient is always a number equal to or greater than one and less than ten. The power of 10, or exponent, in this example is 23. Figure 3.1 illustrate show to express the number of stars in a galaxy by using scientific notation. For more practice on writing numbers in scientific notation, refer to page R56 of Appendix C.
Accuracy, Precision, and Error
Your success in the chemistry lab and in many of your daily activities depends on your ability to make reliable measurements. Ideally, measurements should be both correct and reproducible.
Accuracy and Precision
Correctness and reproducibility relate to the concepts of accuracy and precision, two words that mean the same thing to many people. In chemistry, however, their meanings are quite different. Accuracy is a measure of how close a measurement comes to the actual or true value of whatever is measured. Precision is a measure of how close a series of measurements are to one another.To evaluate the accuracy of a measurement, the measured value must be compared to the correct value. To evaluate the precision of a measurement, you must compare the values of two or more repeated measurements.
Darts on a dartboard illustrate accuracy and precision in measurement. Let the bull’s-eye of the dartboard represent the true, or correct, value of what you are measuring. The closeness of a dart to the bull’s-eye corresponds to the degree of accuracy. The closer it comes to the bull’s-eye,the more accurately the dart was thrown. The closeness of several darts to one another corresponds to the degree of precision. The closer together the darts are, the greater the precision and the reproducibility.
Look at Figure 3.2 as you consider the following outcomes.
1.
All of the darts land close to the bull’s-eye and to one another. Closeness to the bull’s-eye means that the degree of accuracy is great. Each dart in the bull’s-eye corresponds to an accurate measurement of a value. Closeness of the darts to one another indicates high precision.
2.
All of the darts land close to one another but far from the bull’s-eye. The precision is high because of the closeness of grouping and thus the high level of reproducibility. The results are inaccurate, however, because of the distance of the darts from the bull’s-eye.
3.
The darts land far from one another and from the bull’s-eye.The results are both inaccurate and imprecise.
Figure 3.2 The distribution of darts illustrates the difference between accuracy and precision. a Good accuracy and good precision: The darts are close to the bull’s-eye and to one another. b Poor accuracy and good precision: The darts are far from the bull’s-eye but close to one another. c Poor accuracy and poor precision: The darts are far from the bull’s-eye and from one another.
Reading Checkpoint
Determining Error
Note that an individual measurement may be accurate or inaccurate. Suppose you use a thermometer to measure the boiling point of pure water at standard pressure. The thermometer reads 99.1°C. You probably know that the true or accepted value of the boiling point of pure water under these conditions is actually 100.0°C. There is a difference between the accepted value, which is the correct value based on reliable references, and the experimental value, the value measured in the lab. The difference between the experimental value and the accepted value is called the error.
Error = experimental value − accepted value
Error can be positive or negative depending on whether the experimental value is greater than or less than the accepted value.
For the boiling-point measurement, the error is 99.1°C − 100.0°C,or − 0.9° C. The magnitude of the error shows the amount by which the experimental value differs from the accepted value. Often, it is useful to calculate the relative error, or percent error. The percent error is the absolute value of the error divided by the accepted value, multiplied by 100%.
Word Origins
Percent comes from the Latin words per, meaning “by” or “through,” and centum, meaning “100.” What do you think the phrase per annum means?
Using the absolute value of the error means that the percent error will always be a positive value. For the boiling-point measurement, the percent error is calculated as follows.
= 0.009 × 100%
= 0.9%
Just because a measuring device works doesn’t necessarily mean that it is accurate. As Figure 3.3 shows, a weighing scale that does not read zero when nothing is on it is bound to yield error. In order to weigh yourself accurately, you must first make sure that the scale is zeroed.
Figure 3.3 The scale below has not been properly zeroed so the reading obtained for the person's weight is inaccurate. There is a difference between the person's correct weight and the measured value. Calculating What is the percent error of a measured value of 114 lb if the person's actual weight is 107 lb?
Previous page
Significant Figures in Measurements
Supermarkets often provide scales like the one in Figure 3.4. Customers use these scales to measure the weight of produce that is priced per pound. If you use a scale that is calibrated in 0.1-lb intervals, you can easily read the scale to the nearest tenth of a pound. With such a scale, however, you can also estimate the weight to the nearest hundredth of a pound by noting the position of the pointer between calibration marks.
Figure 3.4 The precision of a weighing scale depends on how finely it is calibrated.
Suppose you estimate a weight that lies between 2.4 lb and 2.5 lb to be 2.46 lb. The number in this estimated measurement has three digits. The first two digits in the measurement (2 and 4) are known with certainty. But the rightmost digit (6) has been estimated and involves some uncertainty. These three reported digits all convey useful information, however, and are called significant figures. The significant figures in a measurement include all of the digits that are known, plus a last digit that is estimated. Measurements must always be reported to the correct number of significant figures because calculated answers often depend on the number of significant figures in the values used in the calculation.
Significant Figures in Calculations
Suppose you use a calculator to find the area of a floor that measures 7.7 meters by 5.4 meters. The calculator would give an answer of 41.58 square meters. The calculated area is expressed to four significant figures. However, each of the measurements used in the calculation is expressed to only two significant figures. So the answer must also be reported to two significant figures (42 m2). In general, a calculated answer cannot be more precise than the least precise measurement from which it was calculated. The calculated value must be rounded to make it consistent with the measurements from which it was calculated.
Rounding
To round a number, you must first decide how many significant figures the answer should have. This decision depends on the given measurements and on the mathematical process used to arrive at the answer. Once you know the number of significant figures your answer should have, round to that many digits, counting from the left. If the digit immediately to the right of the last significant digit is less than 5, it is simply dropped and the value of the last significant digit stays the same. If the digit in question is 5 or greater, the value of the digit in the last significant place is increased by 1.
Reading Checkpoint
PDF
3.1 Rounding Measurements
PDF
View HTML
Problem-Solving 3.3 Solve Problem 3 with the help of an interactive guided tutorial.
Addition and Subtraction
The answer to an addition or subtraction calculation should be rounded to the same number of decimal places (not digits) as the measurement with the least number of decimal places. Work through Sample Problem 3.2 below which provides an example of rounding in an addition calculation.
PDF
3.2 Significant Figures in Addition
PDF
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Problem Solving 3.6 Solve Problem 6 with the help of an interactive guided tutorial.
Multiplication and Division
In calculations involving multiplication and division, you need to round the answer to the same number of significant figures as the measurement with the least number of significant figures. The position of the decimal point has nothing to do with the rounding process when multiplying and dividing measurements. The position of the decimal point is important only in rounding the answers of addition or subtraction problems.
Key Concepts
*
How do measurements relate to science?
*
How do you evaluate accuracy and precision?
*
Why must measurements be reported to the correct number of significant figures?
*
How does the precision of a calculated answer compare to the precision of the measurements used to obtain it?
Vocabulary
*
measurement
*
scientific notation
*
accuracy
*
precision
*
accepted value
*
experimental value
*
error
*
percent error
*
significant figures
Reading Strategy
Building Vocabulary As you read, write a definition of each key term in your own words.
Using and Expressing Measurements
Your height (67 inches), your weight (134 pounds), and the speed you drive on the highway (65 miles/hour) are some familiar examples of measurements. A measurement is a quantity that has both a number and a unit. Everyone makes and uses measurements. For instance, you decide how to dress in the morning based on the temperature outside. If you were baking cookies, you would measure the volumes of the ingredients as indicated in the recipe.
Such everyday situations are similar to those faced by scientists. Measurements are fundamental to the experimental sciences. For that reason, it isimportant to be able to make measurements and to decide whether a measurement is correct. The units typically used in the sciences are those of the International System of Measurements(SI).
In chemistry, you will often encounter very large or very small numbers. A single gram of hydrogen, for example, contains approximately 602,000,000,000,000,000,000,000 hydrogenatoms. The mass of an atom of gold is 0.000 000 000 000 000 000 000 327 gram. Writing and using such large and small numbers is very cumbersome. You can work more easily with these numbers by writing them in scientific, or exponential, notation.
In scientific notation, a given number is written as the product of two numbers: a coefficient and 10 raised to a power. For example, the number 602,000,000,000,000,000,000,000written in scientific notation is 6.02 × 1023. The coefficient in this number is 6.02. In scientific notation, the coefficient is always a number equal to or greater than one and less than ten. The power of 10, or exponent, in this example is 23. Figure 3.1 illustrate show to express the number of stars in a galaxy by using scientific notation. For more practice on writing numbers in scientific notation, refer to page R56 of Appendix C.
Accuracy, Precision, and Error
Your success in the chemistry lab and in many of your daily activities depends on your ability to make reliable measurements. Ideally, measurements should be both correct and reproducible.
Accuracy and Precision
Correctness and reproducibility relate to the concepts of accuracy and precision, two words that mean the same thing to many people. In chemistry, however, their meanings are quite different. Accuracy is a measure of how close a measurement comes to the actual or true value of whatever is measured. Precision is a measure of how close a series of measurements are to one another.To evaluate the accuracy of a measurement, the measured value must be compared to the correct value. To evaluate the precision of a measurement, you must compare the values of two or more repeated measurements.
Darts on a dartboard illustrate accuracy and precision in measurement. Let the bull’s-eye of the dartboard represent the true, or correct, value of what you are measuring. The closeness of a dart to the bull’s-eye corresponds to the degree of accuracy. The closer it comes to the bull’s-eye,the more accurately the dart was thrown. The closeness of several darts to one another corresponds to the degree of precision. The closer together the darts are, the greater the precision and the reproducibility.
Look at Figure 3.2 as you consider the following outcomes.
1.
All of the darts land close to the bull’s-eye and to one another. Closeness to the bull’s-eye means that the degree of accuracy is great. Each dart in the bull’s-eye corresponds to an accurate measurement of a value. Closeness of the darts to one another indicates high precision.
2.
All of the darts land close to one another but far from the bull’s-eye. The precision is high because of the closeness of grouping and thus the high level of reproducibility. The results are inaccurate, however, because of the distance of the darts from the bull’s-eye.
3.
The darts land far from one another and from the bull’s-eye.The results are both inaccurate and imprecise.
Figure 3.2 The distribution of darts illustrates the difference between accuracy and precision. a Good accuracy and good precision: The darts are close to the bull’s-eye and to one another. b Poor accuracy and good precision: The darts are far from the bull’s-eye but close to one another. c Poor accuracy and poor precision: The darts are far from the bull’s-eye and from one another.
Reading Checkpoint
Determining Error
Note that an individual measurement may be accurate or inaccurate. Suppose you use a thermometer to measure the boiling point of pure water at standard pressure. The thermometer reads 99.1°C. You probably know that the true or accepted value of the boiling point of pure water under these conditions is actually 100.0°C. There is a difference between the accepted value, which is the correct value based on reliable references, and the experimental value, the value measured in the lab. The difference between the experimental value and the accepted value is called the error.
Error = experimental value − accepted value
Error can be positive or negative depending on whether the experimental value is greater than or less than the accepted value.
For the boiling-point measurement, the error is 99.1°C − 100.0°C,or − 0.9° C. The magnitude of the error shows the amount by which the experimental value differs from the accepted value. Often, it is useful to calculate the relative error, or percent error. The percent error is the absolute value of the error divided by the accepted value, multiplied by 100%.
Word Origins
Percent comes from the Latin words per, meaning “by” or “through,” and centum, meaning “100.” What do you think the phrase per annum means?
Using the absolute value of the error means that the percent error will always be a positive value. For the boiling-point measurement, the percent error is calculated as follows.
= 0.009 × 100%
= 0.9%
Just because a measuring device works doesn’t necessarily mean that it is accurate. As Figure 3.3 shows, a weighing scale that does not read zero when nothing is on it is bound to yield error. In order to weigh yourself accurately, you must first make sure that the scale is zeroed.
Figure 3.3 The scale below has not been properly zeroed so the reading obtained for the person's weight is inaccurate. There is a difference between the person's correct weight and the measured value. Calculating What is the percent error of a measured value of 114 lb if the person's actual weight is 107 lb?
Previous page
Significant Figures in Measurements
Supermarkets often provide scales like the one in Figure 3.4. Customers use these scales to measure the weight of produce that is priced per pound. If you use a scale that is calibrated in 0.1-lb intervals, you can easily read the scale to the nearest tenth of a pound. With such a scale, however, you can also estimate the weight to the nearest hundredth of a pound by noting the position of the pointer between calibration marks.
Figure 3.4 The precision of a weighing scale depends on how finely it is calibrated.
Suppose you estimate a weight that lies between 2.4 lb and 2.5 lb to be 2.46 lb. The number in this estimated measurement has three digits. The first two digits in the measurement (2 and 4) are known with certainty. But the rightmost digit (6) has been estimated and involves some uncertainty. These three reported digits all convey useful information, however, and are called significant figures. The significant figures in a measurement include all of the digits that are known, plus a last digit that is estimated. Measurements must always be reported to the correct number of significant figures because calculated answers often depend on the number of significant figures in the values used in the calculation.
Significant Figures in Calculations
Suppose you use a calculator to find the area of a floor that measures 7.7 meters by 5.4 meters. The calculator would give an answer of 41.58 square meters. The calculated area is expressed to four significant figures. However, each of the measurements used in the calculation is expressed to only two significant figures. So the answer must also be reported to two significant figures (42 m2). In general, a calculated answer cannot be more precise than the least precise measurement from which it was calculated. The calculated value must be rounded to make it consistent with the measurements from which it was calculated.
Rounding
To round a number, you must first decide how many significant figures the answer should have. This decision depends on the given measurements and on the mathematical process used to arrive at the answer. Once you know the number of significant figures your answer should have, round to that many digits, counting from the left. If the digit immediately to the right of the last significant digit is less than 5, it is simply dropped and the value of the last significant digit stays the same. If the digit in question is 5 or greater, the value of the digit in the last significant place is increased by 1.
Reading Checkpoint
3.1 Rounding Measurements
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Problem-Solving 3.3 Solve Problem 3 with the help of an interactive guided tutorial.
Addition and Subtraction
The answer to an addition or subtraction calculation should be rounded to the same number of decimal places (not digits) as the measurement with the least number of decimal places. Work through Sample Problem 3.2 below which provides an example of rounding in an addition calculation.
3.2 Significant Figures in Addition
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Problem Solving 3.6 Solve Problem 6 with the help of an interactive guided tutorial.
Multiplication and Division
In calculations involving multiplication and division, you need to round the answer to the same number of significant figures as the measurement with the least number of significant figures. The position of the decimal point has nothing to do with the rounding process when multiplying and dividing measurements. The position of the decimal point is important only in rounding the answers of addition or subtraction problems.
Reading Chapter Two: 2.4
Connecting to Your World Iron is an element with many desirable properties. It is abundant, easy to shape when heated, and relatively strong, especially when mixed with carbon in steel. Iron has one main disadvantage. Over time, objects made of iron will rust if they are left exposed to air. The brittle layer of rust that forms on the surface of the object flakes off, exposing more iron to the air. In this section, you will learn to recognize chemical changes and to distinguish them from physical changes.
Key Concepts
*
What always happens during a chemical change?
*
What are four possible clues that a chemical change has taken place?
*
How are the mass of the reactants and the mass of the products of a chemical reaction related?
Vocabulary
*
chemical property
*
chemical reaction
*
reactant
*
product
*
precipitate
*
law of conservation of mass
Reading Strategy
Predicting Before you read, predict what will happen to the mass of a sample of matter that burns. After you read, check the accuracy of your prediction and correct any misconceptions.
Chemical Changes
The compound formed when iron rusts is iron oxide (Fe2O3). Words such as burn, rot, rust, decompose, ferment, explode, and corrode usually signify a chemical change. The ability of a substance to undergo a specific chemical change is called a chemical property. Iron is able to combine with oxygen to form rust. So the ability to rust is a chemical property of iron. Chemical properties can be used to identify a substance. But chemical properties can be observed only when a substance undergoes a chemical change.
Figure 2.13 compares a physical change and a chemical change that can occur in a mixture of iron and sulfur. When a magnet is used to separate iron from sulfur, the change is a physical change. The substances present before the change are the same substances present after the change, although they are no longer physically blended. Recall that during a physical change, the composition of matter never changes. During a chemical change, the composition of matter always changes. When the mixture of iron and sulfur is heated, a chemical change occurs. The sulfur and iron react and form iron sulfide (FeS).
Figure 2.13 A mixture of iron filings and sulfur can be changed. (a) A magnet separates the iron from the sulfur. (b) Heat combines iron and sulfur in a compound. Classifying Which change is a chemical change? Explain.
A chemical change is also called a chemical reaction. One or more substances change into one or more new substances during a chemical reaction. A substance present at the start of the reaction is a reactant. A substance produced in the reaction is a product. In the reaction of iron and sulfur, iron and sulfur are reactants and iron sulfide is a product.
Recognizing Chemical Changes
How can you tell whether a chemical change has taken place? There are four clues that can serve as a guide. Possible clues to chemical change include a transfer of energy, a change in color, the production of a gas, or the formation of a precipitate.
Go Online
For: Links on Chemical and Physical Changes
Visit: www.SciLinks.org
Web Code: cdn-1024
Every chemical change involves a transfer of energy. For example, energy stored in natural gas is used to cook food. When the methane in natural gas combines with oxygen in the air, energy is given off in the form of heat and light. Some of this energy is transferred to and absorbed by food that is cooking over a lit gas burner. The energy causes chemical changes to take place in the food. The food may brown as it cooks, which is another clue that chemical changes are occurring.
You can observe two other clues to chemical change while cleaning a bathtub. The ring of soap scum that can form in a bathtub is an example of a precipitate. A precipitate is a solid that forms and settles out of a liquid mixture. Some bathroom cleaners that you can use to remove soap scum start to bubble when you spray them on the scum. The bubbles are a product of a chemical change that is taking place in the cleaner.
If you observe a clue to chemical change, you cannot be certain that a chemical change has taken place. The clue may be the result of a physical change. For example, energy is always transferred when matter changes from one state to another. Bubbles form when you boil water or open a carbonated drink. The only way to be sure that a chemical change has occurred is to test the composition of a sample before and after the change. Figure 2.14 shows examples of practical situations in which different clues to chemical change are visible.
Conservation of Mass
When wood burns, substances in the wood combine with oxygen from the air. As the wood burns, a sizable amount of matter is reduced to a small pile of ashes. The reaction seems to involve a reduction in the amount of matter. But appearances can be deceiving. During any chemical reaction, the mass of the products is always equal to the mass of the reactants. Two of the products of burning wood—carbon dioxide gas and water vapor—are released into the air. When the mass of these gases is considered, the amount of matter is unchanged. Careful measurements show that the total mass of the reactants (wood and the oxygen consumed) equals the total mass of the products (carbon dioxide, water vapor, and ash).
Mass also holds constant during physical changes. For example, when 10 grams of ice melt, 10 grams of liquid water are produced. Similar observations have been recorded for all chemical and physical changes studied. The scientific law that reflects these observations is the law of conservation of mass. The law of conservation of mass states that in any physical change or chemical reaction, mass is conserved. Mass is neither created nor destroyed. The conservation of mass is more easily observed when a change occurs in a closed container, as in Figure 2.15.
Key Concepts
2.1 Properties of Matter
*
Properties used to describe matter can be classified as extensive or intensive.Hint
*
Every sample of a given substance has identical intensive properties because every sample has the same composition.Hint
*
Three states of matter are solid, liquid, and gas.Hint
*
Physical changes can be classified as reversible or irreversible.Hint
2.2 Mixtures
*
Mixtures can be classified as heterogeneous mixtures or as homogeneous mixtures, based on the distribution of their components.Hint
*
Differences in physical properties can be used to separate mixtures.Hint
2.3 Elements and Compounds
*
Compounds can be broken down into simpler substances by chemical means, but elements cannot.Hint
*
If the composition of a material is fixed, the material is a substance. If the composition may vary, the material is a mixture.Hint
*
Chemists use chemical symbols to represent elements, and chemical formulas to represent compounds.Hint
2.4 Chemical Reactions
*
During a chemical change, the composition of matter always changes.Hint
*
Four possible clues to chemical change include a transfer of energy, a change in color, the production of a gas, or the formation of a precipitate.Hint
*
During any chemical reaction, the mass of the products is always equal to the mass of the reactants.Hint
Vocabulary
PDF
Vocabulary Review
*
chemical change
*
chemical property
*
chemical reaction
*
chemical symbol
*
compound
*
distillation
*
element
*
extensive property
*
filtration
*
gas
*
heterogeneous mixture
*
homogeneous mixture
*
intensive property
*
law of conservation of mass
*
liquid
*
mass
*
mixture
*
phase
*
physical change
*
physical property
*
precipitate
*
product
*
reactant
*
solid
*
solution
*
substance
*
vapor
*
volume
Key Concepts
*
What always happens during a chemical change?
*
What are four possible clues that a chemical change has taken place?
*
How are the mass of the reactants and the mass of the products of a chemical reaction related?
Vocabulary
*
chemical property
*
chemical reaction
*
reactant
*
product
*
precipitate
*
law of conservation of mass
Reading Strategy
Predicting Before you read, predict what will happen to the mass of a sample of matter that burns. After you read, check the accuracy of your prediction and correct any misconceptions.
Chemical Changes
The compound formed when iron rusts is iron oxide (Fe2O3). Words such as burn, rot, rust, decompose, ferment, explode, and corrode usually signify a chemical change. The ability of a substance to undergo a specific chemical change is called a chemical property. Iron is able to combine with oxygen to form rust. So the ability to rust is a chemical property of iron. Chemical properties can be used to identify a substance. But chemical properties can be observed only when a substance undergoes a chemical change.
Figure 2.13 compares a physical change and a chemical change that can occur in a mixture of iron and sulfur. When a magnet is used to separate iron from sulfur, the change is a physical change. The substances present before the change are the same substances present after the change, although they are no longer physically blended. Recall that during a physical change, the composition of matter never changes. During a chemical change, the composition of matter always changes. When the mixture of iron and sulfur is heated, a chemical change occurs. The sulfur and iron react and form iron sulfide (FeS).
Figure 2.13 A mixture of iron filings and sulfur can be changed. (a) A magnet separates the iron from the sulfur. (b) Heat combines iron and sulfur in a compound. Classifying Which change is a chemical change? Explain.
A chemical change is also called a chemical reaction. One or more substances change into one or more new substances during a chemical reaction. A substance present at the start of the reaction is a reactant. A substance produced in the reaction is a product. In the reaction of iron and sulfur, iron and sulfur are reactants and iron sulfide is a product.
Recognizing Chemical Changes
How can you tell whether a chemical change has taken place? There are four clues that can serve as a guide. Possible clues to chemical change include a transfer of energy, a change in color, the production of a gas, or the formation of a precipitate.
Go Online
For: Links on Chemical and Physical Changes
Visit: www.SciLinks.org
Web Code: cdn-1024
Every chemical change involves a transfer of energy. For example, energy stored in natural gas is used to cook food. When the methane in natural gas combines with oxygen in the air, energy is given off in the form of heat and light. Some of this energy is transferred to and absorbed by food that is cooking over a lit gas burner. The energy causes chemical changes to take place in the food. The food may brown as it cooks, which is another clue that chemical changes are occurring.
You can observe two other clues to chemical change while cleaning a bathtub. The ring of soap scum that can form in a bathtub is an example of a precipitate. A precipitate is a solid that forms and settles out of a liquid mixture. Some bathroom cleaners that you can use to remove soap scum start to bubble when you spray them on the scum. The bubbles are a product of a chemical change that is taking place in the cleaner.
If you observe a clue to chemical change, you cannot be certain that a chemical change has taken place. The clue may be the result of a physical change. For example, energy is always transferred when matter changes from one state to another. Bubbles form when you boil water or open a carbonated drink. The only way to be sure that a chemical change has occurred is to test the composition of a sample before and after the change. Figure 2.14 shows examples of practical situations in which different clues to chemical change are visible.
Conservation of Mass
When wood burns, substances in the wood combine with oxygen from the air. As the wood burns, a sizable amount of matter is reduced to a small pile of ashes. The reaction seems to involve a reduction in the amount of matter. But appearances can be deceiving. During any chemical reaction, the mass of the products is always equal to the mass of the reactants. Two of the products of burning wood—carbon dioxide gas and water vapor—are released into the air. When the mass of these gases is considered, the amount of matter is unchanged. Careful measurements show that the total mass of the reactants (wood and the oxygen consumed) equals the total mass of the products (carbon dioxide, water vapor, and ash).
Mass also holds constant during physical changes. For example, when 10 grams of ice melt, 10 grams of liquid water are produced. Similar observations have been recorded for all chemical and physical changes studied. The scientific law that reflects these observations is the law of conservation of mass. The law of conservation of mass states that in any physical change or chemical reaction, mass is conserved. Mass is neither created nor destroyed. The conservation of mass is more easily observed when a change occurs in a closed container, as in Figure 2.15.
Key Concepts
2.1 Properties of Matter
*
Properties used to describe matter can be classified as extensive or intensive.Hint
*
Every sample of a given substance has identical intensive properties because every sample has the same composition.Hint
*
Three states of matter are solid, liquid, and gas.Hint
*
Physical changes can be classified as reversible or irreversible.Hint
2.2 Mixtures
*
Mixtures can be classified as heterogeneous mixtures or as homogeneous mixtures, based on the distribution of their components.Hint
*
Differences in physical properties can be used to separate mixtures.Hint
2.3 Elements and Compounds
*
Compounds can be broken down into simpler substances by chemical means, but elements cannot.Hint
*
If the composition of a material is fixed, the material is a substance. If the composition may vary, the material is a mixture.Hint
*
Chemists use chemical symbols to represent elements, and chemical formulas to represent compounds.Hint
2.4 Chemical Reactions
*
During a chemical change, the composition of matter always changes.Hint
*
Four possible clues to chemical change include a transfer of energy, a change in color, the production of a gas, or the formation of a precipitate.Hint
*
During any chemical reaction, the mass of the products is always equal to the mass of the reactants.Hint
Vocabulary
Vocabulary Review
*
chemical change
*
chemical property
*
chemical reaction
*
chemical symbol
*
compound
*
distillation
*
element
*
extensive property
*
filtration
*
gas
*
heterogeneous mixture
*
homogeneous mixture
*
intensive property
*
law of conservation of mass
*
liquid
*
mass
*
mixture
*
phase
*
physical change
*
physical property
*
precipitate
*
product
*
reactant
*
solid
*
solution
*
substance
*
vapor
*
volume
Reading Chapter Two: 2.3
Connecting to Your World Take two pounds of sugar, two cups of boiling water, and one-quarter teaspoon of cream of tartar. You have the ingredients to make spun sugar. Add food coloring and you have the sticky, sweet concoction sold at baseball games and amusement parks as cotton candy. Sugar is a substance that contains three other substances—carbon, hydrogen, and oxygen. In this section, you will learn how substances are classified as elements or compounds.
Key Concepts
*
How are elements and compounds different?
*
How can substances and mixtures be distinguished?
*
What do chemists use to represent elements and compounds?
Vocabulary
*
element
*
compound
*
chemical change
*
chemical symbol
Reading Strategy
Relating Text And Visuals As you read, look at Figure 2.10. Explain how this illustration helps you understand the relationship between different kinds of matter.
Distinguishing Elements and Compounds
Substances can be classified as elements or compounds. An element is the simplest form of matter that has a unique set of properties. Oxygen and hydrogen are two of the more than 100 known elements. A compound is a substance that contains two or more elements chemically combined in a fixed proportion. For example, carbon, oxygen, and hydrogen are chemically combined in the compound sucrose, the sugar in spun sugar. (Sometimes sucrose is referred to as table sugar to distinguish it from other sugar compounds.) In every sample of sucrose there are twice as many hydrogen particles as oxygen particles. The proportion of hydrogen particles to oxygen particles in sucrose is fixed. There is a key difference between elements and compounds. Compounds can be broken down into simpler substances by chemical means, but elements cannot.
Word Origins
Compound comes from a Latin word componere, meaning “to put together.” Elements are put together, or chemically combined, in compounds. What items are put together in a compound sentence?
Breaking Down Compounds
Physical methods that are used to separate mixtures cannot be used to break a compound into simpler substances. Boil liquid water and you get water vapor, not the oxygen and hydrogen that water contains. Dissolve a sugar cube in water and you still have sucrose, not oxygen, carbon, and hydrogen. This result does not mean that sucrose or water cannot be broken down into simpler substances. But the methods must involve a chemical change. A chemical change is a change that produces matter with a different composition than the original matter. Heating is one of the processes used to break down compounds into simpler substances. The layer of sugar in Figure 2.9 is heated in a skillet until it breaks down into solid carbon and water vapor. Can the substances that are produced also be broken down?
Figure 2.9 When table sugar is heated, it goes through a series of chemical changes. The final products of these changes are solid carbon and water vapor.
There is no chemical process that will break down carbon into simpler substances because carbon is an element. Heating will not cause water to break down, but electricity will. When an electric current passes through water, oxygen gas and hydrogen gas are produced. The following diagram summarizes the overall process.
PDF
Chemical change
Properties of Compounds
In general, the properties of compounds are quite different from those of their component elements. Sugar is a sweet-tasting, white solid, but carbon is a black, tasteless solid. Hydrogen is a gas that burns in the presence of oxygen—a colorless gas that supports burning. The product of this chemical change is water, a liquid that can stop materials from burning. Figure 2.10 shows samples of table salt (sodium chloride), sodium, and chlorine. When the elements sodium and chlorine combine chemically to form sodium chloride, there is a change in composition and a change in properties. Sodium is a soft, gray metal. Chlorine is a pale yellow-green poisonous gas. Sodium chloride is a white solid.
Distinguishing Substances and Mixtures
Deciding whether a sample of matter is a substance or a mixture based solely on appearance can be difficult. After all, homogeneous mixtures and substances will both appear to contain only one kind of matter. Sometimes you can decide by considering whether there is more than one version of the material in question. For example, you can buy whole milk, low-fat milk, no-fat milk, light cream, and heavy cream. From this information, you can conclude that milk and cream are mixtures. You might infer that these mixtures differ in the amount of fat they contain. Most gas stations offer at least two blends of gasoline. The blends have different octane ratings and different costs per gallon, with premium blends costing more than regular blends. So gasoline must be a mixture.
You can use their general characteristics to distinguish substances from mixtures. If the composition of a material is fixed, the material is a substance. If the composition of a material may vary, the material is a mixture. Figure 2.11 summarizes the general characteristics of elements, compounds, and mixtures.
Symbols and Formulas
The common names water and table salt do not provide information about the chemical composition of these substances. Also, words are not ideal for showing what happens to the composition of matter during a chemical change. Chemists use chemical symbols to represent elements, and chemical formulas to represent compounds.
Using symbols to represent different kinds of matter is not a new idea. Figure 2.12 shows some symbols that were used in earlier centuries. The symbols used today for elements are based on a system developed by a Swedish chemist, Jöns Jacob Berzelius (1779–1848). He based his symbols on the Latin names of elements. Each element is represented by a one or two letter chemical symbol. The first letter of a chemical symbol is always capitalized. When a second letter is used, it is lowercase.
Figure 2.12 The symbols used to represent elements have changed over time. Alchemists and the English chemist John Dalton (1766–1844) both used drawings to represent chemical elements. Today, elements are represented by one or two letter symbols.
If the English name and the Latin name of an element are similar, the symbol will appear to have been derived from the English name. Examples include Ca for calcium, N for nitrogen, and S for sulfur. Table 2.2 shows examples of elements where the symbols do not match the English names.
PDF
Table 2.2 Symbols and Latin Names for Some Elements
Go Online
For: Links on Element Names
Visit: www.SciLinks.org
Web Code: cdn-1023
Chemical symbols provide a shorthand way to write the chemical formulas of compounds. The symbols for hydrogen, oxygen, and carbon are H, O, and C. The formula for water is H2O. The formula for sucrose, or table sugar, is C12H22O11. Subscripts in chemical formulas are used to indicate the relative proportions of the elements in the compound. For example, the subscript 2 in H2O indicates that there are always two parts of hydrogen for each part of oxygen in water. Because a compound has a fixed composition, the formula for a compound is always the same.
Key Concepts
*
How are elements and compounds different?
*
How can substances and mixtures be distinguished?
*
What do chemists use to represent elements and compounds?
Vocabulary
*
element
*
compound
*
chemical change
*
chemical symbol
Reading Strategy
Relating Text And Visuals As you read, look at Figure 2.10. Explain how this illustration helps you understand the relationship between different kinds of matter.
Distinguishing Elements and Compounds
Substances can be classified as elements or compounds. An element is the simplest form of matter that has a unique set of properties. Oxygen and hydrogen are two of the more than 100 known elements. A compound is a substance that contains two or more elements chemically combined in a fixed proportion. For example, carbon, oxygen, and hydrogen are chemically combined in the compound sucrose, the sugar in spun sugar. (Sometimes sucrose is referred to as table sugar to distinguish it from other sugar compounds.) In every sample of sucrose there are twice as many hydrogen particles as oxygen particles. The proportion of hydrogen particles to oxygen particles in sucrose is fixed. There is a key difference between elements and compounds. Compounds can be broken down into simpler substances by chemical means, but elements cannot.
Word Origins
Compound comes from a Latin word componere, meaning “to put together.” Elements are put together, or chemically combined, in compounds. What items are put together in a compound sentence?
Breaking Down Compounds
Physical methods that are used to separate mixtures cannot be used to break a compound into simpler substances. Boil liquid water and you get water vapor, not the oxygen and hydrogen that water contains. Dissolve a sugar cube in water and you still have sucrose, not oxygen, carbon, and hydrogen. This result does not mean that sucrose or water cannot be broken down into simpler substances. But the methods must involve a chemical change. A chemical change is a change that produces matter with a different composition than the original matter. Heating is one of the processes used to break down compounds into simpler substances. The layer of sugar in Figure 2.9 is heated in a skillet until it breaks down into solid carbon and water vapor. Can the substances that are produced also be broken down?
Figure 2.9 When table sugar is heated, it goes through a series of chemical changes. The final products of these changes are solid carbon and water vapor.
There is no chemical process that will break down carbon into simpler substances because carbon is an element. Heating will not cause water to break down, but electricity will. When an electric current passes through water, oxygen gas and hydrogen gas are produced. The following diagram summarizes the overall process.
Chemical change
Properties of Compounds
In general, the properties of compounds are quite different from those of their component elements. Sugar is a sweet-tasting, white solid, but carbon is a black, tasteless solid. Hydrogen is a gas that burns in the presence of oxygen—a colorless gas that supports burning. The product of this chemical change is water, a liquid that can stop materials from burning. Figure 2.10 shows samples of table salt (sodium chloride), sodium, and chlorine. When the elements sodium and chlorine combine chemically to form sodium chloride, there is a change in composition and a change in properties. Sodium is a soft, gray metal. Chlorine is a pale yellow-green poisonous gas. Sodium chloride is a white solid.
Distinguishing Substances and Mixtures
Deciding whether a sample of matter is a substance or a mixture based solely on appearance can be difficult. After all, homogeneous mixtures and substances will both appear to contain only one kind of matter. Sometimes you can decide by considering whether there is more than one version of the material in question. For example, you can buy whole milk, low-fat milk, no-fat milk, light cream, and heavy cream. From this information, you can conclude that milk and cream are mixtures. You might infer that these mixtures differ in the amount of fat they contain. Most gas stations offer at least two blends of gasoline. The blends have different octane ratings and different costs per gallon, with premium blends costing more than regular blends. So gasoline must be a mixture.
You can use their general characteristics to distinguish substances from mixtures. If the composition of a material is fixed, the material is a substance. If the composition of a material may vary, the material is a mixture. Figure 2.11 summarizes the general characteristics of elements, compounds, and mixtures.
Symbols and Formulas
The common names water and table salt do not provide information about the chemical composition of these substances. Also, words are not ideal for showing what happens to the composition of matter during a chemical change. Chemists use chemical symbols to represent elements, and chemical formulas to represent compounds.
Using symbols to represent different kinds of matter is not a new idea. Figure 2.12 shows some symbols that were used in earlier centuries. The symbols used today for elements are based on a system developed by a Swedish chemist, Jöns Jacob Berzelius (1779–1848). He based his symbols on the Latin names of elements. Each element is represented by a one or two letter chemical symbol. The first letter of a chemical symbol is always capitalized. When a second letter is used, it is lowercase.
Figure 2.12 The symbols used to represent elements have changed over time. Alchemists and the English chemist John Dalton (1766–1844) both used drawings to represent chemical elements. Today, elements are represented by one or two letter symbols.
If the English name and the Latin name of an element are similar, the symbol will appear to have been derived from the English name. Examples include Ca for calcium, N for nitrogen, and S for sulfur. Table 2.2 shows examples of elements where the symbols do not match the English names.
Table 2.2 Symbols and Latin Names for Some Elements
Go Online
For: Links on Element Names
Visit: www.SciLinks.org
Web Code: cdn-1023
Chemical symbols provide a shorthand way to write the chemical formulas of compounds. The symbols for hydrogen, oxygen, and carbon are H, O, and C. The formula for water is H2O. The formula for sucrose, or table sugar, is C12H22O11. Subscripts in chemical formulas are used to indicate the relative proportions of the elements in the compound. For example, the subscript 2 in H2O indicates that there are always two parts of hydrogen for each part of oxygen in water. Because a compound has a fixed composition, the formula for a compound is always the same.
Sunday, March 22, 2009
Reading Chapter Two: 2.2
Connecting to Your World In 1848, gold was discovered in California. This discovery led to a massive migration, or rush, of people to California. Panning is one way to separate gold from a mixture of gold and materials such as sand or gravel. A pan containing the mixture is placed underwater and shaken vigorously from left to right. This motion causes heavier materials, such as gold, to move to the bottom of the pan and lighter materials, such as sand, to move to the top where they can be swept away. In this section, you will learn how to classify and separate mixtures.
Key Concepts
*
How can mixtures be classified?
*
How can mixtures be separated?
Vocabulary
*
mixture
*
heterogeneous mixture
*
homogeneous mixture
*
solution
*
phase
*
filtration
*
distillation
Reading Strategy
Building Vocabulary After you read this section, explain the difference between homogeneous and heterogeneous mixtures.
Classifying Mixtures
A salad bar, like the one in Figure 2.5, provides a range of items, such as cucumbers and hot peppers. Customers choose which items to use in their salads and how much of each item to use. So each salad has a different composition. A mixture is a physical blend of two or more components.
Figure 2.5 You can choose the amount of each item you select from a salad bar. So your salad is unlikely to have the same composition as other salads containing the same items.
Most samples of matter are mixtures. Some mixtures are easier to recognize than others. You can easily recognize chicken noodle soup as a mixture of chicken, noodles, and broth. Recognizing air as a mixture of gases is more difficult. But the fact that air can be drier or more humid shows that the amount of one component of air—water vapor—can vary. Chicken noodle soup and air represent two different types of mixtures. Based on the distribution of their components, mixtures can be classified as heterogeneous mixtures or as homogeneous mixtures.
Heterogeneous Mixtures
In chicken noodle soup, the ingredients are not evenly distributed throughout the mixture. There is likely to be more chicken in one spoonful than in another spoonful. A mixture in which the composition is not uniform throughout is a heterogeneous mixture.
Homogeneous Mixtures
The substances in the olive oil and vinegar in Figure 2.6 are evenly distributed throughout these mixtures. So olive oil doesn’t look like a mixture. The same is true for vinegar. Vinegar is a mixture of water and acetic acid, which dissolves in the water. Olive oil and vinegar are homogeneous mixtures. A homogeneous mixture is a mixture in which the composition is uniform throughout. Another name for a homogeneous mixture is a solution. Many solutions are liquids. But some are gases, like air, and some are solids, like stainless steel, which is a mixture of iron, chromium, and nickel.
The term phase is used to describe any part of a sample with uniform composition and properties. By definition, a homogeneous mixture consists of a single phase. A heterogeneous mixture consists of two or more phases. When oil and vinegar are mixed, they form layers, or phases, as shown in Figure 2.6. The oil phase floats on the water phase.
Separating Mixtures
If you have a salad containing an ingredient you don’t like, you can use a fork to remove the pieces of the unwanted ingredient. Many mixtures are not as easy to separate. To separate a mixture of olive oil and vinegar, for example, you could decant, or pour off, the oil layer. Or you might cool the mixture until the oil turned solid. The first method takes advantage of the fact that oil floats on water. The second method takes advantage of a difference in the temperatures at which the olive oil and vinegar freeze. Differences in physical properties can be used to separate mixtures.
Filtration
The colander in Figure 2.7 can separate cooked pasta from the cooking water. The water passes through the holes in the colander, but the pasta does not. The holes, or pores, in a coffee filter are smaller than the holes in a colander to retain coffee grains. But the holes are not small enough to retain the particles in water. The process that separates a solid from the liquid in a heterogeneous mixture is called filtration.
Figure 2.7 A colander is used to separate pasta from the water in which it was cooked. This process is a type of filtration.
Distillation
Tap water is a homogeneous mixture of water and substances that dissolved in the water. One way to separate water from the other components in tap water is through a process called distillation. During a distillation, a liquid is boiled to produce a vapor that is then condensed into a liquid. Figure 2.8 shows an apparatus that can be used to perform a small-scale distillation.
PDF
Figure 2.8
As water in the distillation flask is heated, water vapor forms, rises in the flask, and passes into a glass tube in the condenser. The tube is surrounded by cold water, which cools the vapor to a temperature at which it turns back into a liquid. The liquid water is collected in a second flask. The solid substances that were dissolved in the water remain in the distillation flask because their boiling points are much higher than the boiling point of water.
Key Concepts
*
How can mixtures be classified?
*
How can mixtures be separated?
Vocabulary
*
mixture
*
heterogeneous mixture
*
homogeneous mixture
*
solution
*
phase
*
filtration
*
distillation
Reading Strategy
Building Vocabulary After you read this section, explain the difference between homogeneous and heterogeneous mixtures.
Classifying Mixtures
A salad bar, like the one in Figure 2.5, provides a range of items, such as cucumbers and hot peppers. Customers choose which items to use in their salads and how much of each item to use. So each salad has a different composition. A mixture is a physical blend of two or more components.
Figure 2.5 You can choose the amount of each item you select from a salad bar. So your salad is unlikely to have the same composition as other salads containing the same items.
Most samples of matter are mixtures. Some mixtures are easier to recognize than others. You can easily recognize chicken noodle soup as a mixture of chicken, noodles, and broth. Recognizing air as a mixture of gases is more difficult. But the fact that air can be drier or more humid shows that the amount of one component of air—water vapor—can vary. Chicken noodle soup and air represent two different types of mixtures. Based on the distribution of their components, mixtures can be classified as heterogeneous mixtures or as homogeneous mixtures.
Heterogeneous Mixtures
In chicken noodle soup, the ingredients are not evenly distributed throughout the mixture. There is likely to be more chicken in one spoonful than in another spoonful. A mixture in which the composition is not uniform throughout is a heterogeneous mixture.
Homogeneous Mixtures
The substances in the olive oil and vinegar in Figure 2.6 are evenly distributed throughout these mixtures. So olive oil doesn’t look like a mixture. The same is true for vinegar. Vinegar is a mixture of water and acetic acid, which dissolves in the water. Olive oil and vinegar are homogeneous mixtures. A homogeneous mixture is a mixture in which the composition is uniform throughout. Another name for a homogeneous mixture is a solution. Many solutions are liquids. But some are gases, like air, and some are solids, like stainless steel, which is a mixture of iron, chromium, and nickel.
The term phase is used to describe any part of a sample with uniform composition and properties. By definition, a homogeneous mixture consists of a single phase. A heterogeneous mixture consists of two or more phases. When oil and vinegar are mixed, they form layers, or phases, as shown in Figure 2.6. The oil phase floats on the water phase.
Separating Mixtures
If you have a salad containing an ingredient you don’t like, you can use a fork to remove the pieces of the unwanted ingredient. Many mixtures are not as easy to separate. To separate a mixture of olive oil and vinegar, for example, you could decant, or pour off, the oil layer. Or you might cool the mixture until the oil turned solid. The first method takes advantage of the fact that oil floats on water. The second method takes advantage of a difference in the temperatures at which the olive oil and vinegar freeze. Differences in physical properties can be used to separate mixtures.
Filtration
The colander in Figure 2.7 can separate cooked pasta from the cooking water. The water passes through the holes in the colander, but the pasta does not. The holes, or pores, in a coffee filter are smaller than the holes in a colander to retain coffee grains. But the holes are not small enough to retain the particles in water. The process that separates a solid from the liquid in a heterogeneous mixture is called filtration.
Figure 2.7 A colander is used to separate pasta from the water in which it was cooked. This process is a type of filtration.
Distillation
Tap water is a homogeneous mixture of water and substances that dissolved in the water. One way to separate water from the other components in tap water is through a process called distillation. During a distillation, a liquid is boiled to produce a vapor that is then condensed into a liquid. Figure 2.8 shows an apparatus that can be used to perform a small-scale distillation.
Figure 2.8
As water in the distillation flask is heated, water vapor forms, rises in the flask, and passes into a glass tube in the condenser. The tube is surrounded by cold water, which cools the vapor to a temperature at which it turns back into a liquid. The liquid water is collected in a second flask. The solid substances that were dissolved in the water remain in the distillation flask because their boiling points are much higher than the boiling point of water.
Reading Chapter Two: 2.1
Connecting to Your World The more than 1200 species of bamboo belong to a family of grasses that includes wheat and corn. In tropical regions, bamboo plants grow rapidly to great heights. The tender shoots of some bamboo plants are a favorite food of pandas. People use the woody stems of mature plants to make furniture, fishing rods, and flooring. Because bamboo is inexpensive and abundant, disposable chopsticks are usually made from bamboo. Bamboo has properties that make it a good choice for use in chopsticks. It has no noticeable odor or taste. It is hard, yet easy to split, and it is heat resistant. In this section, you will learn how properties can be used to classify and identify matter.
Key Concepts
*
How can properties used to describe matter be classified?
*
Why do all samples of a substance have the same intensive properties?
*
What are three states of matter?
*
How can physical changes be classified?
Vocabulary
*
mass
*
volume
*
extensive property
*
intensive property
*
substance
*
physical property
*
solid
*
liquid
*
gas
*
vapor
*
physical change
Reading Strategy
Using Prior Knowledge Before you read, write a definition for the term liquid. After you read this section, compare and contrast the definition of liquid in the text with your original definition.
Describing Matter
Understanding matter begins with observation and what you observe when you look at a particular sample of matter is its properties. Is a solid shiny or dull? Does a liquid flow quickly or slowly? Is a gas odorless or does it have a smell? Properties used to describe matter can be classified as extensive or intensive.
Extensive Properties
Recall that matter is anything that has mass and takes up space. The mass of an object is a measure of the amount of matter the object contains. The mass of a bowling ball with finger holes is five or six times greater than the mass of the bowling ball shown in Figure 2.1, which is used to play a game called candlepins. There is also a difference in the volume of the balls. The volume of an object is a measure of the space occupied by the object. Mass and volume are examples of extensive properties. An extensive property is a property that depends on the amount of matter in a sample.
Figure 2.1 This bowling ball and candlepin are used in a game played mainly in New England.
Intensive Properties
There are properties to consider when selecting a bowling ball other than mass. Beginning bowlers want a bowling ball that is likely to maintain a straight path. They use bowling balls with a hard surface made from polyester. Experienced bowlers want a bowling ball they can curve, or hook, toward the pins. Often, they use a polyurethane ball, which has a softer surface. Hardness is an example of an intensive property. An intensive property is a property that depends on the type of matter in a sample, not the amount of matter.
Describing Matter
Understanding matter begins with observation and what you observe when you look at a particular sample of matter is its properties. Is a solid shiny or dull? Does a liquid flow quickly or slowly? Is a gas odorless or does it have a smell? Properties used to describe matter can be classified as extensive or intensive.
Extensive Properties
Recall that matter is anything that has mass and takes up space. The mass of an object is a measure of the amount of matter the object contains. The mass of a bowling ball with finger holes is five or six times greater than the mass of the bowling ball shown in Figure 2.1, which is used to play a game called candlepins. There is also a difference in the volume of the balls. The volume of an object is a measure of the space occupied by the object. Mass and volume are examples of extensive properties. An extensive property is a property that depends on the amount of matter in a sample.
Figure 2.1 This bowling ball and candlepin are used in a game played mainly in New England.
Intensive Properties
There are properties to consider when selecting a bowling ball other than mass. Beginning bowlers want a bowling ball that is likely to maintain a straight path. They use bowling balls with a hard surface made from polyester. Experienced bowlers want a bowling ball they can curve, or hook, toward the pins. Often, they use a polyurethane ball, which has a softer surface. Hardness is an example of an intensive property. An intensive property is a property that depends on the type of matter in a sample, not the amount of matter.
Identifying Substances
Each object in Figure 2.2 has a different chemical makeup, or composition. The sculpture of a falcon is mainly gold. The kettles are mainly copper. Matter that has a uniform and definite composition is called a substance. Gold and copper are examples of substances, which are also referred to as pure substances. Every sample of a given substance has identical intensive properties because very sample has the same composition.
Figure 2.2 This gold falcon standard from Egypt is about 3000 years old. The copper kettles are about 150 years old. Analyzing Data Which of the properties listed in Table 2.1 could not be used to distinguish copper from gold?
Gold and copper have some properties in common, but there are differences besides their distinctive colors. Pure copper can scratch the surface of pure gold because copper is harder than gold. Copper is better than gold as a conductor of heat or electric current. Both gold and copper are malleable, which means they can be hammered into sheets without breaking. But gold is more malleable than copper. Hardness, color, conductivity, and malleability are examples of physical properties. A physical property is a quality or condition of a substance that can be observed or measured without changing the substance’s composition.
Go Online
For: Links on Physical Properties of Matter
Visit: www.SciLinks.org
Web Code: cdn-1021
Table 2.1 lists physical properties for some substances. The states of the substances are given at room temperature. (Although scientists use room temperature to refer to a range of temperatures, in this book it will be used to refer to a specific temperature, 20°C.) Physical properties can help chemists identify substances. For example, a colorless substance that was found to boil at 100°C and melt at 0°C would likely be water. A colorless substance that boiled at 78°C and melted at −117°C would most certainly not be water. Based on Table 2.1, it would likely be ethanol.
States of Matter
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Depending on the circumstances, you use three different words to refer to water— water, ice, and steam. Water, which is a common substance, exists in three different physical states. So can most other substances. Three states of matter are solid, liquid, and gas. Certain characteristics that can distinguish these three states of matter are summarized in Figure 2.3.
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Figure 2.3
Solids
A solid is a form of matter that has a definite shape and volume. The shape of a solid doesn’t depend on the shape of its container. The particles in a solid are packed tightly together, often in an orderly arrangement, as shown in Figure 2.3a. As a result, solids are almost incompressible; that is, it is difficult to squeeze a solid into a smaller volume. In addition, solids expand only slightly when heated.
Liquids
Look at Figure 2.3b. The particles in a liquid are in close contact with one another, but the arrangement of particles in a liquid is not rigid or orderly. Because the particles in a liquid are free to flow from one location to another, a liquid takes the shape of the container in which it is placed. However, the volume of the liquid doesn’t change as its shape changes. The volume of a liquid is fixed or constant. Thus, a liquid is a form of matter that has an indefinite shape, flows, yet has a fixed volume. Liquids are almost incompressible, but they tend to expand slightly when heated.
Gases
Like a liquid, a gas takes the shape of its container. But unlike a liquid, a gas can expand to fill any volume. A gas is a form of matter that takes both the shape and volume of its container. Look back at Figure 2.3c. As shown in the model, the particles in a gas are usually much farther apart than the particles in a liquid. Because of the space between particles, gases are easily compressed into a smaller volume.
The words vapor and gas are sometimes used interchangeably. But there is a difference. The term gas is used for substances, like oxygen, that exist in the gaseous state at room temperature. (Gaseous is the adjective form of gas.) Vapor describes the gaseous state of a substance that is generally a liquid or solid at room temperature, as in water vapor.
Physical Changes
The melting point of gallium metal is 30°C. Figure 2.4 shows how heat from a person’s hand can melt a sample of gallium. The shape of the sample changes during melting as the liquid begins to flow, but the composition of the sample does not change. Melting is an example of a physical change. During a physical change, some properties of a material change, but the composition of the material does not change.
Figure 2.4 The silvery substance in the photograph is gallium, which has a melting point of 30°C. Inferring What can you infer about the temperature of the hand holding the gallium?
Words such as boil, freeze, melt, and condense are used to describe physical changes. So are words such as break, split, grind, cut, and crush. However, there is a difference between these two sets of words. Each set describes a different type of physical change. Physical changes can be classified as reversible or irreversible. Melting is an example of a reversible physical change. If a sample of liquid gallium is cooled below its melting point, the liquid will become a solid. All physical changes that involve a change from one state to another are reversible. Cutting hair, filing nails, and cracking an egg are examples of irreversible physical changes.
Key Concepts
*
How can properties used to describe matter be classified?
*
Why do all samples of a substance have the same intensive properties?
*
What are three states of matter?
*
How can physical changes be classified?
Vocabulary
*
mass
*
volume
*
extensive property
*
intensive property
*
substance
*
physical property
*
solid
*
liquid
*
gas
*
vapor
*
physical change
Reading Strategy
Using Prior Knowledge Before you read, write a definition for the term liquid. After you read this section, compare and contrast the definition of liquid in the text with your original definition.
Describing Matter
Understanding matter begins with observation and what you observe when you look at a particular sample of matter is its properties. Is a solid shiny or dull? Does a liquid flow quickly or slowly? Is a gas odorless or does it have a smell? Properties used to describe matter can be classified as extensive or intensive.
Extensive Properties
Recall that matter is anything that has mass and takes up space. The mass of an object is a measure of the amount of matter the object contains. The mass of a bowling ball with finger holes is five or six times greater than the mass of the bowling ball shown in Figure 2.1, which is used to play a game called candlepins. There is also a difference in the volume of the balls. The volume of an object is a measure of the space occupied by the object. Mass and volume are examples of extensive properties. An extensive property is a property that depends on the amount of matter in a sample.
Figure 2.1 This bowling ball and candlepin are used in a game played mainly in New England.
Intensive Properties
There are properties to consider when selecting a bowling ball other than mass. Beginning bowlers want a bowling ball that is likely to maintain a straight path. They use bowling balls with a hard surface made from polyester. Experienced bowlers want a bowling ball they can curve, or hook, toward the pins. Often, they use a polyurethane ball, which has a softer surface. Hardness is an example of an intensive property. An intensive property is a property that depends on the type of matter in a sample, not the amount of matter.
Describing Matter
Understanding matter begins with observation and what you observe when you look at a particular sample of matter is its properties. Is a solid shiny or dull? Does a liquid flow quickly or slowly? Is a gas odorless or does it have a smell? Properties used to describe matter can be classified as extensive or intensive.
Extensive Properties
Recall that matter is anything that has mass and takes up space. The mass of an object is a measure of the amount of matter the object contains. The mass of a bowling ball with finger holes is five or six times greater than the mass of the bowling ball shown in Figure 2.1, which is used to play a game called candlepins. There is also a difference in the volume of the balls. The volume of an object is a measure of the space occupied by the object. Mass and volume are examples of extensive properties. An extensive property is a property that depends on the amount of matter in a sample.
Figure 2.1 This bowling ball and candlepin are used in a game played mainly in New England.
Intensive Properties
There are properties to consider when selecting a bowling ball other than mass. Beginning bowlers want a bowling ball that is likely to maintain a straight path. They use bowling balls with a hard surface made from polyester. Experienced bowlers want a bowling ball they can curve, or hook, toward the pins. Often, they use a polyurethane ball, which has a softer surface. Hardness is an example of an intensive property. An intensive property is a property that depends on the type of matter in a sample, not the amount of matter.
Identifying Substances
Each object in Figure 2.2 has a different chemical makeup, or composition. The sculpture of a falcon is mainly gold. The kettles are mainly copper. Matter that has a uniform and definite composition is called a substance. Gold and copper are examples of substances, which are also referred to as pure substances. Every sample of a given substance has identical intensive properties because very sample has the same composition.
Figure 2.2 This gold falcon standard from Egypt is about 3000 years old. The copper kettles are about 150 years old. Analyzing Data Which of the properties listed in Table 2.1 could not be used to distinguish copper from gold?
Gold and copper have some properties in common, but there are differences besides their distinctive colors. Pure copper can scratch the surface of pure gold because copper is harder than gold. Copper is better than gold as a conductor of heat or electric current. Both gold and copper are malleable, which means they can be hammered into sheets without breaking. But gold is more malleable than copper. Hardness, color, conductivity, and malleability are examples of physical properties. A physical property is a quality or condition of a substance that can be observed or measured without changing the substance’s composition.
Go Online
For: Links on Physical Properties of Matter
Visit: www.SciLinks.org
Web Code: cdn-1021
Table 2.1 lists physical properties for some substances. The states of the substances are given at room temperature. (Although scientists use room temperature to refer to a range of temperatures, in this book it will be used to refer to a specific temperature, 20°C.) Physical properties can help chemists identify substances. For example, a colorless substance that was found to boil at 100°C and melt at 0°C would likely be water. A colorless substance that boiled at 78°C and melted at −117°C would most certainly not be water. Based on Table 2.1, it would likely be ethanol.
States of Matter
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Depending on the circumstances, you use three different words to refer to water— water, ice, and steam. Water, which is a common substance, exists in three different physical states. So can most other substances. Three states of matter are solid, liquid, and gas. Certain characteristics that can distinguish these three states of matter are summarized in Figure 2.3.
Figure 2.3
Solids
A solid is a form of matter that has a definite shape and volume. The shape of a solid doesn’t depend on the shape of its container. The particles in a solid are packed tightly together, often in an orderly arrangement, as shown in Figure 2.3a. As a result, solids are almost incompressible; that is, it is difficult to squeeze a solid into a smaller volume. In addition, solids expand only slightly when heated.
Liquids
Look at Figure 2.3b. The particles in a liquid are in close contact with one another, but the arrangement of particles in a liquid is not rigid or orderly. Because the particles in a liquid are free to flow from one location to another, a liquid takes the shape of the container in which it is placed. However, the volume of the liquid doesn’t change as its shape changes. The volume of a liquid is fixed or constant. Thus, a liquid is a form of matter that has an indefinite shape, flows, yet has a fixed volume. Liquids are almost incompressible, but they tend to expand slightly when heated.
Gases
Like a liquid, a gas takes the shape of its container. But unlike a liquid, a gas can expand to fill any volume. A gas is a form of matter that takes both the shape and volume of its container. Look back at Figure 2.3c. As shown in the model, the particles in a gas are usually much farther apart than the particles in a liquid. Because of the space between particles, gases are easily compressed into a smaller volume.
The words vapor and gas are sometimes used interchangeably. But there is a difference. The term gas is used for substances, like oxygen, that exist in the gaseous state at room temperature. (Gaseous is the adjective form of gas.) Vapor describes the gaseous state of a substance that is generally a liquid or solid at room temperature, as in water vapor.
Physical Changes
The melting point of gallium metal is 30°C. Figure 2.4 shows how heat from a person’s hand can melt a sample of gallium. The shape of the sample changes during melting as the liquid begins to flow, but the composition of the sample does not change. Melting is an example of a physical change. During a physical change, some properties of a material change, but the composition of the material does not change.
Figure 2.4 The silvery substance in the photograph is gallium, which has a melting point of 30°C. Inferring What can you infer about the temperature of the hand holding the gallium?
Words such as boil, freeze, melt, and condense are used to describe physical changes. So are words such as break, split, grind, cut, and crush. However, there is a difference between these two sets of words. Each set describes a different type of physical change. Physical changes can be classified as reversible or irreversible. Melting is an example of a reversible physical change. If a sample of liquid gallium is cooled below its melting point, the liquid will become a solid. All physical changes that involve a change from one state to another are reversible. Cutting hair, filing nails, and cracking an egg are examples of irreversible physical changes.
Reading Chapter One: 1.4
Connecting to Your World Shape-sorter toys fascinate young children. Typically, the children try placing a shape in different holes until they find the right one. They may try to place an incorrect shape in the same hole over and over again. An older child has enough experience to place the correct shape in each hole on the first try. The trial-and-error approach used by young children is one method of problem solving, but it is usually not the best one. In this section, you will learn effective ways to solve problems in chemistry.
Key Concepts
*
What is a general approach to solving a problem?
*
What are the three steps for solving numeric problems?
*
What are the two steps for solving conceptual problems?
Reading Strategy
Identifying Main Idea Details Under the heading Solving Numeric Problems, there are three main ideas presented as subheads. As you read, list two details that support each main idea.
Skills Used in Solving Problems
Problem solving is a skill you use all the time. You are in a supermarket. Do you buy a name brand or the store brand of peanut butter? Do you buy the 1-liter bottle or the 2-liter bottle of a carbonated beverage? Do you choose the express line if there are five customers ahead of you or the non-express line with a single shopper who has lots of items?
When you solve a problem you may have a data table, a graph, or another type of visual to refer to. The shopper in Figure 1.23 is reading the label on a can while trying to decide whether to buy the item. She may need to avoid certain ingredients because of a food allergy. Or she may want to know the amount of Calories per serving.
Figure 1.23 A shopper must make many decisions. Some of those decisions are based on data, like the information on a food label.
The skills you use to solve a word problem in chemistry are not that different from those you use while shopping or cooking or planning a party. Effective problem solving always involves developing a plan and then implementing that plan.
Solving Numeric Problems
Because measurement is such an important part of chemistry, most word problems in chemistry require some math. The techniques used in this book to solve numeric problems are conveniently organized into a three-step, problem-solving approach. This approach has been shown to be very helpful and effective. So we recommend that you follow this approach when working on numeric problems in this textbook. The steps for solving a numeric word problem are analyze, calculate, and evaluate. Figure 1.24 summarizes the three-step process and Sample Problem 1.1 shows how the steps work in a problem.
Figure 1.24 This flowchart summarizes the steps for solving a numeric problem. Predicting In which step do you make a plan for getting from what is known to what is unknown?
Analyze
To solve a word problem, you must first determine where you are starting from (identify what is known) and where you are going (identify the unknown). What is known may be a measurement. Or it may be an equation that shows a relationship between measurements. If you expect the answer (the unknown) to be a number, you need to determine what units the answer should have before you do any calculations.
After you identify the known and the unknown, you need to make a plan for getting from the known to the unknown. Planning is at the heart of successful problem solving. As part of planning, you might draw a diagram that helps you visualize a relationship between the known and the unknown. You might need to use a table or graph to identify data or to identify a relationship between a known quantity and the unknown. You may need to select an equation that you can use to calculate the unknown.
Calculate
If you make an effective plan, doing the calculations is usually the easiest part of the process. For some problems, you will have to convert a measurement from one unit to another. Or you may need to rearrange an equation before you can solve for an unknown. However, you will be taught these math skills as needed. There will also be reminders throughout the textbook to use the Math Handbook in Appendix C.
Evaluate
After you calculate an answer, you should evaluate it. Is the answer reasonable? Does it make sense? If not, reread the word problem. Did you copy the data correctly? Did you choose the right equations? It helps to round off the numbers and make an estimate of the answer. If the answer is much larger or much smaller than your estimate, check your calculations.
Check that your answer has the correct unit and the correct number of significant figures. You may need to use scientific notation in your answer. You will study significant figures and scientific notation in Chapter 3.
1.1 Chemistry
*
Because living and nonliving things are made of matter, chemistry affects all aspects of life and most natural events.Hint
*
Chemistry can be divided into five traditional areas of study: organic chemistry, inorganic chemistry, biochemistry, analytical chemistry, and physical chemistry.Hint
*
Pure research can lead directly to an application, but an application can exist before research is done to explain how it works.Hint
*
Chemistry can be useful in explaining the natural world, preparing people for career opportunities, and producing informed citizens.Hint
1.2 Chemistry Far and Wide
*
Chemists design materials to fit specific needs. Chemists play an essential role in finding ways to conserve energy, produce energy, and store energy.Hint
*
Chemists supply the medicines, materials, and technology that doctors use to treat patients. Chemists help to develop more productive crops and safer, more effective ways to protect crops.Hint
*
Chemists help to identify pollutants and prevent pollution.Hint
*
To study the universe, chemists gather data from afar and analyze matter that is brought back to Earth.Hint
1.3 Thinking Like a Scientist
*
Alchemists developed tools and techniques for working with chemicals.Hint
*
Lavoisier helped to transform chemistry from a science of observation to the science of measurement that it is today.Hint
*
Steps in the scientific method include making observations, testing hypotheses, and developing theories.Hint
*
When scientists collaborate and communicate, they increase the likelihood of a successful outcome.Hint
1.4 Problem Solving in Chemistry
*
Effective problem solving always involves developing a plan and then implementing the plan.Hint
*
The steps for solving a numeric word problem are analyze, calculate, and evaluate. The steps for solving a conceptual problem are analyze and solve.Hint
PDF
Vocabulary Review
Vocabulary
*
analytical chemistry
*
applied chemistry
*
biochemistry
*
biotechnology
*
chemistry
*
experiment
*
hypothesis
*
inorganic chemistry
*
macroscopic
*
matter
*
microscopic
*
manipulated variable
*
observation
*
organic chemistry
*
physical chemistry
*
pollutant
*
pure chemistry
*
responding variable
*
scientific law
*
scientific method
*
technology
*
theory
Key Concepts
*
What is a general approach to solving a problem?
*
What are the three steps for solving numeric problems?
*
What are the two steps for solving conceptual problems?
Reading Strategy
Identifying Main Idea Details Under the heading Solving Numeric Problems, there are three main ideas presented as subheads. As you read, list two details that support each main idea.
Skills Used in Solving Problems
Problem solving is a skill you use all the time. You are in a supermarket. Do you buy a name brand or the store brand of peanut butter? Do you buy the 1-liter bottle or the 2-liter bottle of a carbonated beverage? Do you choose the express line if there are five customers ahead of you or the non-express line with a single shopper who has lots of items?
When you solve a problem you may have a data table, a graph, or another type of visual to refer to. The shopper in Figure 1.23 is reading the label on a can while trying to decide whether to buy the item. She may need to avoid certain ingredients because of a food allergy. Or she may want to know the amount of Calories per serving.
Figure 1.23 A shopper must make many decisions. Some of those decisions are based on data, like the information on a food label.
The skills you use to solve a word problem in chemistry are not that different from those you use while shopping or cooking or planning a party. Effective problem solving always involves developing a plan and then implementing that plan.
Solving Numeric Problems
Because measurement is such an important part of chemistry, most word problems in chemistry require some math. The techniques used in this book to solve numeric problems are conveniently organized into a three-step, problem-solving approach. This approach has been shown to be very helpful and effective. So we recommend that you follow this approach when working on numeric problems in this textbook. The steps for solving a numeric word problem are analyze, calculate, and evaluate. Figure 1.24 summarizes the three-step process and Sample Problem 1.1 shows how the steps work in a problem.
Figure 1.24 This flowchart summarizes the steps for solving a numeric problem. Predicting In which step do you make a plan for getting from what is known to what is unknown?
Analyze
To solve a word problem, you must first determine where you are starting from (identify what is known) and where you are going (identify the unknown). What is known may be a measurement. Or it may be an equation that shows a relationship between measurements. If you expect the answer (the unknown) to be a number, you need to determine what units the answer should have before you do any calculations.
After you identify the known and the unknown, you need to make a plan for getting from the known to the unknown. Planning is at the heart of successful problem solving. As part of planning, you might draw a diagram that helps you visualize a relationship between the known and the unknown. You might need to use a table or graph to identify data or to identify a relationship between a known quantity and the unknown. You may need to select an equation that you can use to calculate the unknown.
Calculate
If you make an effective plan, doing the calculations is usually the easiest part of the process. For some problems, you will have to convert a measurement from one unit to another. Or you may need to rearrange an equation before you can solve for an unknown. However, you will be taught these math skills as needed. There will also be reminders throughout the textbook to use the Math Handbook in Appendix C.
Evaluate
After you calculate an answer, you should evaluate it. Is the answer reasonable? Does it make sense? If not, reread the word problem. Did you copy the data correctly? Did you choose the right equations? It helps to round off the numbers and make an estimate of the answer. If the answer is much larger or much smaller than your estimate, check your calculations.
Check that your answer has the correct unit and the correct number of significant figures. You may need to use scientific notation in your answer. You will study significant figures and scientific notation in Chapter 3.
1.1 Chemistry
*
Because living and nonliving things are made of matter, chemistry affects all aspects of life and most natural events.Hint
*
Chemistry can be divided into five traditional areas of study: organic chemistry, inorganic chemistry, biochemistry, analytical chemistry, and physical chemistry.Hint
*
Pure research can lead directly to an application, but an application can exist before research is done to explain how it works.Hint
*
Chemistry can be useful in explaining the natural world, preparing people for career opportunities, and producing informed citizens.Hint
1.2 Chemistry Far and Wide
*
Chemists design materials to fit specific needs. Chemists play an essential role in finding ways to conserve energy, produce energy, and store energy.Hint
*
Chemists supply the medicines, materials, and technology that doctors use to treat patients. Chemists help to develop more productive crops and safer, more effective ways to protect crops.Hint
*
Chemists help to identify pollutants and prevent pollution.Hint
*
To study the universe, chemists gather data from afar and analyze matter that is brought back to Earth.Hint
1.3 Thinking Like a Scientist
*
Alchemists developed tools and techniques for working with chemicals.Hint
*
Lavoisier helped to transform chemistry from a science of observation to the science of measurement that it is today.Hint
*
Steps in the scientific method include making observations, testing hypotheses, and developing theories.Hint
*
When scientists collaborate and communicate, they increase the likelihood of a successful outcome.Hint
1.4 Problem Solving in Chemistry
*
Effective problem solving always involves developing a plan and then implementing the plan.Hint
*
The steps for solving a numeric word problem are analyze, calculate, and evaluate. The steps for solving a conceptual problem are analyze and solve.Hint
Vocabulary Review
Vocabulary
*
analytical chemistry
*
applied chemistry
*
biochemistry
*
biotechnology
*
chemistry
*
experiment
*
hypothesis
*
inorganic chemistry
*
macroscopic
*
matter
*
microscopic
*
manipulated variable
*
observation
*
organic chemistry
*
physical chemistry
*
pollutant
*
pure chemistry
*
responding variable
*
scientific law
*
scientific method
*
technology
*
theory
Reading Chapter One: 1.3
Connecting to Your World In 1928, Alexander Fleming, a Scottish scientist, noticed that a bacteria he was studying did not grow in the presence of a yellow-green mold. Other scientists had made the same observation, but Fleming was the first to recognize its importance. He assumed that the mold had released a chemical that prevented the growth of the bacteria. That chemical was penicillin, which can kill a wide range of harmful bacteria. In 1945, Fleming shared a Nobel Prize for Medicine with Howard Florey and Ernst Chain, who led the team that isolated penicillin. In this section you will study the methods scientists use to solve problems.
Key Concepts
*
How did alchemy lay the groundwork for chemistry?
*
How did Lavoisier help to transform chemistry?
*
What are the steps in the scientific method?
*
What role do collaboration and communication play in science?
Vocabulary
*
scientific method
*
observation
*
hypothesis
*
experiment
*
manipulated variable
*
responding variable
*
theory
*
scientific law
Alchemy
The word chemistry comes from alchemy. Long before there were chemists, alchemists were studying matter. Alchemy arose independently in many regions of the world. It was practiced in China and India as early as 400 B.C. In the eighth century, Arabs brought alchemy to Spain, from where it spread quickly to other parts of Europe.
Alchemy had a practical side and a mystical side. Practical alchemy focused on developing techniques for working with metals, glass, and dyes. Mystical alchemy focused on concepts like perfection. Because gold was seen as the perfect metal, alchemists were searching for a way to change other metals, such as lead, into gold. Although alchemists did not succeed in this quest, the work they did spurred the development of chemistry.
Figure 1.15 A bowl-shaped mortar and a club-shaped pestle are used to grind or crush materials such as herbs, spices, and paint pigments. The mortar and pestle in the photograph is made of porcelain, which is a hard material.
Alchemists developed the tools and techniques for working with chemicals. Alchemists developed processes for separating mixtures and purifying chemicals. They designed equipment that is still used today, including beakers, flasks, tongs, funnels, and the mortar and pestle in Figure 1.15. What they did not do was provide a logical set of explanations for the changes in matter that they observed. That task was left for chemists to accomplish.
An Experimental Approach to Science
By the 1500s in Europe, there was a shift from alchemy to science. Science flourished in Britain in the 1600s, partly because King Charles II was a supporter of the sciences. With his permission, some scientists formed the Royal Society of London for the Promotion of Natural Knowledge. The scientists met to discuss scientific topics and conduct experiments. The society’s aim was to encourage scientists to base their conclusions about the natural world on experimental evidence, not on philosophical debates.
Figure 1.16 This portrait of Antoine Lavoisier and his wife Marie Anne was painted by Jacques Louis David in 1788. The painting includes some equipment that Lavoisier used in his experiments.
In France, Antoine-Laurent Lavoisier did work in the late 1700s that would revolutionize the science of chemistry. Lavoisier helped to transform chemistry from a science of observation to the science of measurement that it is today. To make careful measurements, Lavoisier designed a balance that could measure mass to the nearest 0.0005 gram.
Figure 1.17 This reconstruction of Lavoisier’s laboratory is in a museum in Paris, France. Interpreting Photographs What objects do you recognize that are similar to objects that you use in the laboratory?
One of the many things Lavoisier accomplished was to settle a long-standing debate about how materials burn. The accepted explanation was that materials burn because they contain phlogiston, which is released into the air as a material burns. To support this explanation, scientists had to ignore the evidence that metals can gain mass as they burn. By the time Lavoisier did his experiments, he knew that there were two main gases in air—oxygen and nitrogen. Lavoisier was able to show that oxygen is required for a material to burn. Lavoisier’s wife Marie Anne, shown in Figure 1.16, helped with his scientific work. She made drawings of his experiments and translated scientific papers from English. Figure 1.17 shows a reconstruction of Lavoisier’s laboratory in a museum in Paris, France.
At the time of the French Revolution, Lavoisier was a member of the despised royal taxation commission. He took the position to finance his scientific work. Although he was dedicated to improving the lives of the common people, his association with taxation made him a target of the revolution. In 1794 he was arrested, tried, and beheaded.
An Experimental Approach to Science
By the 1500s in Europe, there was a shift from alchemy to science. Science flourished in Britain in the 1600s, partly because King Charles II was a supporter of the sciences. With his permission, some scientists formed the Royal Society of London for the Promotion of Natural Knowledge. The scientists met to discuss scientific topics and conduct experiments. The society’s aim was to encourage scientists to base their conclusions about the natural world on experimental evidence, not on philosophical debates.
Figure 1.16 This portrait of Antoine Lavoisier and his wife Marie Anne was painted by Jacques Louis David in 1788. The painting includes some equipment that Lavoisier used in his experiments.
In France, Antoine-Laurent Lavoisier did work in the late 1700s that would revolutionize the science of chemistry. Lavoisier helped to transform chemistry from a science of observation to the science of measurement that it is today. To make careful measurements, Lavoisier designed a balance that could measure mass to the nearest 0.0005 gram.
Figure 1.17 This reconstruction of Lavoisier’s laboratory is in a museum in Paris, France. Interpreting Photographs What objects do you recognize that are similar to objects that you use in the laboratory?
One of the many things Lavoisier accomplished was to settle a long-standing debate about how materials burn. The accepted explanation was that materials burn because they contain phlogiston, which is released into the air as a material burns. To support this explanation, scientists had to ignore the evidence that metals can gain mass as they burn. By the time Lavoisier did his experiments, he knew that there were two main gases in air—oxygen and nitrogen. Lavoisier was able to show that oxygen is required for a material to burn. Lavoisier’s wife Marie Anne, shown in Figure 1.16, helped with his scientific work. She made drawings of his experiments and translated scientific papers from English. Figure 1.17 shows a reconstruction of Lavoisier’s laboratory in a museum in Paris, France.
At the time of the French Revolution, Lavoisier was a member of the despised royal taxation commission. He took the position to finance his scientific work. Although he was dedicated to improving the lives of the common people, his association with taxation made him a target of the revolution. In 1794 he was arrested, tried, and beheaded.
Developing Theories
Once a hypothesis meets the test of repeated experimentation, it may be raised to a higher level of ideas. It may become a theory. A theory is a well-tested explanation for a broad set of observations. In chemistry, one theory addresses the fundamental structure of matter. This theory is very useful because it helps you form mental pictures of objects that you cannot see. Other theories allow you to predict the behavior of matter.
When scientists say that a theory can never be proved, they are not saying that a theory is unreliable. They are simply leaving open the possibility that a theory may need to be changed at some point in the future to explain new observations or experimental results.
Scientific Laws
Figure 1.19 shows how scientific experiments can lead to laws as well as theories. A scientific law is a concise statement that summarizes the results of many observations and experiments. In Chapter 14, you will study laws that describe how gases behave. One law describes the relationship between the volume of a gas in a container and its temperature. If all other variables are kept constant, the volume of the gas increases as the temperature increases. The law doesn’t try to explain the relationship it describes. That explanation requires a theory.
Collaboration and Communication
No matter how talented the players on a team, one player cannot ensure victory for the team. Individuals must collaborate, or work together, for the good of the team. Think about the volleyball players in Figure 1.20. In volleyball, the person who spikes the ball depends on the person who sets the ball. Unless the ball is set properly, the spiker will have limited success. Many sports recognize the importance of collaboration by keeping track of assists. During a volleyball game, the players also communicate with one another so it is clear who is going to do which task. Strategies that are successful in sports can work in other fields, such as science. When scientists collaborate and communicate, they increase the likelihood of a successful outcome.
Figure 1.20 For a volleyball team to win, the players must collaborate, or work together.
Collaboration
Scientists choose to collaborate for different reasons. For example, some research problems are so complex that no one person could have all the knowledge, skills, and resources to solve the problem. It is often necessary to bring together individuals from different disciplines. Each scientist will typically bring different knowledge and, perhaps, a different approach to bear on a problem. Just talking with a scientist from another discipline may provide insights that are helpful.
There may be a practical reason for collaboration. For example, an industry may give a university funding for pure research in an area of interest to the industry. Scientists at the university get the equipment and the time required to do research. In exchange, the scientists provide ideas and expertise. The industry may profit from its investment by marketing applications based on the research.
Collaboration isn’t always a smooth process. Conflicts can arise about use of resources, amount of work, who is to receive credit, and when and what to publish. Like the students in Figure 1.21, you will likely work on a team in the laboratory. If so, you may face some challenges. But you can also experience the benefits of a successful collaboration.
Figure 1.21 Working in a group can be challenging, but it can also be rewarding. Applying Concepts What steps in the scientific method are these students using?
Communication
The way that scientists communicate with each other and with the public has changed over the centuries. In earlier centuries, scientists exchanged ideas through letters. They also formed societies to discuss the latest work of their members. When societies began to publish journals, scientists could use the journals to keep up with new discoveries.
Today, many scientists, like those in Figure 1.22, work as a team. They can communicate face to face. They also can exchange ideas with other scientists by e-mail, by phone, and at international conferences. Scientists still publish their results in scientific journals, which are the most reliable source of information about new discoveries. Articles are published only after being reviewed by experts in the author’s field. Reviewers may find errors in experimental design or challenge the author’s conclusions. This review process is good for science because work that is not well founded is usually not published.
Figure 1.22 Communication between scientists can occur face to face. These chemists are using the model projected on the screen to discuss the merits of a new medicine.
The Internet is a major source of information. One advantage of the Internet is that anyone can get access to its information. One disadvantage is that anyone can post information on the Internet without first having that information reviewed. To judge the reliability of information you find on the Internet, you have to consider the source. This same advice applies to articles in news-papers and magazines or the news you receive from television. If a media outlet has a reporter who specializes in science, chances are better that a report will be accurate.
Key Concepts
*
How did alchemy lay the groundwork for chemistry?
*
How did Lavoisier help to transform chemistry?
*
What are the steps in the scientific method?
*
What role do collaboration and communication play in science?
Vocabulary
*
scientific method
*
observation
*
hypothesis
*
experiment
*
manipulated variable
*
responding variable
*
theory
*
scientific law
Alchemy
The word chemistry comes from alchemy. Long before there were chemists, alchemists were studying matter. Alchemy arose independently in many regions of the world. It was practiced in China and India as early as 400 B.C. In the eighth century, Arabs brought alchemy to Spain, from where it spread quickly to other parts of Europe.
Alchemy had a practical side and a mystical side. Practical alchemy focused on developing techniques for working with metals, glass, and dyes. Mystical alchemy focused on concepts like perfection. Because gold was seen as the perfect metal, alchemists were searching for a way to change other metals, such as lead, into gold. Although alchemists did not succeed in this quest, the work they did spurred the development of chemistry.
Figure 1.15 A bowl-shaped mortar and a club-shaped pestle are used to grind or crush materials such as herbs, spices, and paint pigments. The mortar and pestle in the photograph is made of porcelain, which is a hard material.
Alchemists developed the tools and techniques for working with chemicals. Alchemists developed processes for separating mixtures and purifying chemicals. They designed equipment that is still used today, including beakers, flasks, tongs, funnels, and the mortar and pestle in Figure 1.15. What they did not do was provide a logical set of explanations for the changes in matter that they observed. That task was left for chemists to accomplish.
An Experimental Approach to Science
By the 1500s in Europe, there was a shift from alchemy to science. Science flourished in Britain in the 1600s, partly because King Charles II was a supporter of the sciences. With his permission, some scientists formed the Royal Society of London for the Promotion of Natural Knowledge. The scientists met to discuss scientific topics and conduct experiments. The society’s aim was to encourage scientists to base their conclusions about the natural world on experimental evidence, not on philosophical debates.
Figure 1.16 This portrait of Antoine Lavoisier and his wife Marie Anne was painted by Jacques Louis David in 1788. The painting includes some equipment that Lavoisier used in his experiments.
In France, Antoine-Laurent Lavoisier did work in the late 1700s that would revolutionize the science of chemistry. Lavoisier helped to transform chemistry from a science of observation to the science of measurement that it is today. To make careful measurements, Lavoisier designed a balance that could measure mass to the nearest 0.0005 gram.
Figure 1.17 This reconstruction of Lavoisier’s laboratory is in a museum in Paris, France. Interpreting Photographs What objects do you recognize that are similar to objects that you use in the laboratory?
One of the many things Lavoisier accomplished was to settle a long-standing debate about how materials burn. The accepted explanation was that materials burn because they contain phlogiston, which is released into the air as a material burns. To support this explanation, scientists had to ignore the evidence that metals can gain mass as they burn. By the time Lavoisier did his experiments, he knew that there were two main gases in air—oxygen and nitrogen. Lavoisier was able to show that oxygen is required for a material to burn. Lavoisier’s wife Marie Anne, shown in Figure 1.16, helped with his scientific work. She made drawings of his experiments and translated scientific papers from English. Figure 1.17 shows a reconstruction of Lavoisier’s laboratory in a museum in Paris, France.
At the time of the French Revolution, Lavoisier was a member of the despised royal taxation commission. He took the position to finance his scientific work. Although he was dedicated to improving the lives of the common people, his association with taxation made him a target of the revolution. In 1794 he was arrested, tried, and beheaded.
An Experimental Approach to Science
By the 1500s in Europe, there was a shift from alchemy to science. Science flourished in Britain in the 1600s, partly because King Charles II was a supporter of the sciences. With his permission, some scientists formed the Royal Society of London for the Promotion of Natural Knowledge. The scientists met to discuss scientific topics and conduct experiments. The society’s aim was to encourage scientists to base their conclusions about the natural world on experimental evidence, not on philosophical debates.
Figure 1.16 This portrait of Antoine Lavoisier and his wife Marie Anne was painted by Jacques Louis David in 1788. The painting includes some equipment that Lavoisier used in his experiments.
In France, Antoine-Laurent Lavoisier did work in the late 1700s that would revolutionize the science of chemistry. Lavoisier helped to transform chemistry from a science of observation to the science of measurement that it is today. To make careful measurements, Lavoisier designed a balance that could measure mass to the nearest 0.0005 gram.
Figure 1.17 This reconstruction of Lavoisier’s laboratory is in a museum in Paris, France. Interpreting Photographs What objects do you recognize that are similar to objects that you use in the laboratory?
One of the many things Lavoisier accomplished was to settle a long-standing debate about how materials burn. The accepted explanation was that materials burn because they contain phlogiston, which is released into the air as a material burns. To support this explanation, scientists had to ignore the evidence that metals can gain mass as they burn. By the time Lavoisier did his experiments, he knew that there were two main gases in air—oxygen and nitrogen. Lavoisier was able to show that oxygen is required for a material to burn. Lavoisier’s wife Marie Anne, shown in Figure 1.16, helped with his scientific work. She made drawings of his experiments and translated scientific papers from English. Figure 1.17 shows a reconstruction of Lavoisier’s laboratory in a museum in Paris, France.
At the time of the French Revolution, Lavoisier was a member of the despised royal taxation commission. He took the position to finance his scientific work. Although he was dedicated to improving the lives of the common people, his association with taxation made him a target of the revolution. In 1794 he was arrested, tried, and beheaded.
Developing Theories
Once a hypothesis meets the test of repeated experimentation, it may be raised to a higher level of ideas. It may become a theory. A theory is a well-tested explanation for a broad set of observations. In chemistry, one theory addresses the fundamental structure of matter. This theory is very useful because it helps you form mental pictures of objects that you cannot see. Other theories allow you to predict the behavior of matter.
When scientists say that a theory can never be proved, they are not saying that a theory is unreliable. They are simply leaving open the possibility that a theory may need to be changed at some point in the future to explain new observations or experimental results.
Scientific Laws
Figure 1.19 shows how scientific experiments can lead to laws as well as theories. A scientific law is a concise statement that summarizes the results of many observations and experiments. In Chapter 14, you will study laws that describe how gases behave. One law describes the relationship between the volume of a gas in a container and its temperature. If all other variables are kept constant, the volume of the gas increases as the temperature increases. The law doesn’t try to explain the relationship it describes. That explanation requires a theory.
Collaboration and Communication
No matter how talented the players on a team, one player cannot ensure victory for the team. Individuals must collaborate, or work together, for the good of the team. Think about the volleyball players in Figure 1.20. In volleyball, the person who spikes the ball depends on the person who sets the ball. Unless the ball is set properly, the spiker will have limited success. Many sports recognize the importance of collaboration by keeping track of assists. During a volleyball game, the players also communicate with one another so it is clear who is going to do which task. Strategies that are successful in sports can work in other fields, such as science. When scientists collaborate and communicate, they increase the likelihood of a successful outcome.
Figure 1.20 For a volleyball team to win, the players must collaborate, or work together.
Collaboration
Scientists choose to collaborate for different reasons. For example, some research problems are so complex that no one person could have all the knowledge, skills, and resources to solve the problem. It is often necessary to bring together individuals from different disciplines. Each scientist will typically bring different knowledge and, perhaps, a different approach to bear on a problem. Just talking with a scientist from another discipline may provide insights that are helpful.
There may be a practical reason for collaboration. For example, an industry may give a university funding for pure research in an area of interest to the industry. Scientists at the university get the equipment and the time required to do research. In exchange, the scientists provide ideas and expertise. The industry may profit from its investment by marketing applications based on the research.
Collaboration isn’t always a smooth process. Conflicts can arise about use of resources, amount of work, who is to receive credit, and when and what to publish. Like the students in Figure 1.21, you will likely work on a team in the laboratory. If so, you may face some challenges. But you can also experience the benefits of a successful collaboration.
Figure 1.21 Working in a group can be challenging, but it can also be rewarding. Applying Concepts What steps in the scientific method are these students using?
Communication
The way that scientists communicate with each other and with the public has changed over the centuries. In earlier centuries, scientists exchanged ideas through letters. They also formed societies to discuss the latest work of their members. When societies began to publish journals, scientists could use the journals to keep up with new discoveries.
Today, many scientists, like those in Figure 1.22, work as a team. They can communicate face to face. They also can exchange ideas with other scientists by e-mail, by phone, and at international conferences. Scientists still publish their results in scientific journals, which are the most reliable source of information about new discoveries. Articles are published only after being reviewed by experts in the author’s field. Reviewers may find errors in experimental design or challenge the author’s conclusions. This review process is good for science because work that is not well founded is usually not published.
Figure 1.22 Communication between scientists can occur face to face. These chemists are using the model projected on the screen to discuss the merits of a new medicine.
The Internet is a major source of information. One advantage of the Internet is that anyone can get access to its information. One disadvantage is that anyone can post information on the Internet without first having that information reviewed. To judge the reliability of information you find on the Internet, you have to consider the source. This same advice applies to articles in news-papers and magazines or the news you receive from television. If a media outlet has a reporter who specializes in science, chances are better that a report will be accurate.
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About Me
- Gary Hi10spro Sakuma
- I have played for 25 years and coached for the last 17 years--certified United States Professional Tennis Association Professional One--worked for Punahou Schools-voted the #1 Sports School in the United States, as a Program Supervisor, in charge of coaching the High Performance Players as well as coordinating programs for K-12 and Tennis Pro Education.