What is the molality of a 10.0% (by mass)aqueous solution of hydrochloric acid?
A)160 m
B)1.45 m
C)3.05 m
D)2.20 m
E)The density of the solution is needed to solve the problem.

Question

Quizplus · Accepted Answer

Molality is defined as the number of moles of solute per kilogram of solvent.

Step 1: Convert the percentage by mass of hydrochloric acid to grams per 100 grams of solution.

10.0% by mass means that there are 10.0 grams of HCl for every 100 grams of solution.

Step 2: Calculate the molar mass of HCl.

HCl has a molar mass of 36.46 g/mol.

Step 3: Calculate the number of moles of HCl in 100 g of solution.

10.0 g / 36.46 g/mol = 0.2745 mol

Step 4: Calculate the mass of water in the solution.

The solution is 100 g, and 10.0 g of that is HCl. Therefore, there are 90.0 g of water in the solution.

Step 5: Convert the mass of water to kilograms.

90.0 g ÷ 1000 g/kg = 0.0900 kg

Step 6: Calculate the molality.

molality = moles of solute / mass of solvent in kilograms

molality = 0.2745 mol / 0.0900 kg = 3.05 m

Therefore, the molality of the solution is 3.05 m. The answer is (C).

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