Question

Calculate the molarity of a 10.0% (by mass) aqueous solution of hydrochloric acid. The density of this solution is 1.01 g/mL. a. 0.277 M b. 2.77 M c. 3.04 M d. 4.33 M e. The density of the solution is needed to solve the problem

Answer 1

[HCl] = 2.77 M (option b)

Step-by-step explanation:

A 10% by mass is an information that means, 10 g of solute are contained in 100 g of solution.

Density is mass / volume and it always corresponds to solution.

So solution mass is 100 g. Let's find out solution volume with density

Solution mass / Solution volume = Solution density

100 g / Solution volume = 1.01 g/mL

100 g / 1.01 g/mL = 99 mL

In conclusion our 10 g of HCl are contained in 99 mL of solution

Molarity is mol of solute in 1L of solution

Let's convert the mass to moles (mass / molar mass)

10 g / 36.45 g/mol = 0.274 moles

Let's convert the mL in L

99 mL = 0.099L

Molarity is mol/L → 0.274 mol / 0.099L = 2.77M