Question

(a) How many grams of CaCl2 are needed to make 250.9 g of a solution that is 30.5% (m/m) calcium chloride in water? Note that mass is not technically the same thing as weight, but (m/m) has the same meaning as (w/w).

-How many grams of water are needed to make this solution?

(b) What is the volume percent % (v/v) of an alcohol solution made by dissolving 117 mL of isopropyl alcohol in 747 mL of water? (Assume that volumes are additive.)

(c) The mass of solute per 100 mL of solution is abbreviated as % (m/v). (The abbreviation % (w/v) is also common.) How many grams of sucrose are needed to make 735 mL of a 34.0% (w/v) sucrose solution?

Answer 1

mass of solution = 250.9 g

CaCl2 weight % = (solute weight / solution weight ) x 100

    30.5 = (solute weight / 250.9 ) x 100

solute weight = 76.5 g

CaCl2 weight = 76.5 g

mass of water = mass of solution - mass of solute

                        = 250.9 - 76.5

                        = 174.4 g

mass of water = 174.4 g

b)

volume percent % (v/v) = (volume of isopropyl alcohol / total volume of solution ) x 100

                                      = [117 / (117 + 747)] x 100

                                      = 13.54%

volume percent % (v/v) = 13.54%

c)

(w/v) % = (mass of sucrose / volume of solution ) x 100

34 = (mass of sucrose / 735 ) x 100

mass of sucrose = 249.9 g