How many grams of CaCl_2 are needed to make 259.7 g of a solution that is 34.5%

Question

How many grams of CaCl_2 are needed to make 259.7 g of a solution that is 34.5% (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? What is the volume percent % (v/v) of an alcohol solution made by dissolving 121 mL of isopropyl alcohol in 737 mL of water? (Assume that volumes are additive.) 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 650 mL of a 32.0% (w/v) sucrose solution?

Explanation / Answer

Ans. a. 34.5 % m/m (= mass/ mass) solution means 34.5 gram solute (here, CaCl2) in total 100 gram solution.

Given, total amass of the solution = 259.7 gram

Amount (mass) of CaCl2 = 34.5 % of 259.7 gram = 89.5965 gram

Mass of water = total mass of solution – mass of CaCl2

= 259.7 gram - 89.5965 gram = 170.1035 gram

Ans. b. total volume of the solution = volume of solute + volume of water (solvent)

                                                            = 121 mL + 737 mL = 858 mL

% (V/V) concentration of alcohol = (volume of alcohol / total volume of solution) x 100

                                                = (121 mL / 858 mL) x 100

                                                = 14.10 %

Ans. c. Given, total volume of the solution = 655 mL

32.0 % (weight / volume) means 32.0 gram solute in 100 mL of solution.

So, 32% = 32 gram solute / 100 mL solution

amount (mass) of sucrose required = (32 gram/ 100 mL) x 655 mL

                                                            = 209.60 gram

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