Question

What is the molarity of an aqueous solution of hydrochloric acid given that it is 36% by weight hcl and the density of the solution is 1.2 g ml-1 ?

Answer 1

Assume you have 1000 mL = 1 L of solution.

Mass of solution = 1000 mL solution x (1.2 g solution/1 mL solution)

= 1200 g solution

Mass of HCl = 1200 g solution x (36 g HCl/100 g solution) = 432 g HCl

MM of HCl = (1.008 + 35.45) g/mol = 36.458 g/mol

Moles of HCl = 432 g HCl x (1 mol HCl/36.458 g HCl) = 11.8 mol HCl

Molarity = (moles of solute)/(litres of solution) = (11.8 mol)/(1 L) = 12 mol/L