Ch 16: Dilutions

Figure 16.10 The student is preparing 100 mL of 0.40M MgSO4 from a stock solution of 2.0M MgSO4. She measures 20 mL of the stock solution with a 20-mL pipet. She transfers the 20 mL to a 100-mL volumetric flask. She carefully adds water to the mark to make 100 mL of solution. Inferring How many significant figures does the new molarity have?
Moles of solute before dilution = moles of solute after dilution
Recall the definition of molarity.

Rearranging the equation gives an expression for moles of solute.
Moles of solute = molarity (M) × liters of solution (V)
The total number of moles of solute remains unchanged upon dilution, so you can write this equation.
Moles of solute = M1 × V1 = M2 × V2
M1 and V1 are the molarity and volume of the initial solution, and M2 and V2 are the molarity and volume of the diluted solution. Volumes can be in liters or milliliters, as long as the same units are used for both V1 and V2.