Commercial grade HCl solutions are typically 39.0% (by mass)HCl in water.Determine the molality of the HCl,if the solution has a density of 1.20 g/mL.
A) 39.0 m
B) 17.5 m
C) 6.39 m
D) 10.7 m
E) 9.44 m

Question

Quizplus · Accepted Answer

The molality (m) of a solution is defined as the number of moles of solute per kilogram of solvent. Given a 39.0% (by mass) HCl solution, for every 100 g of solution, there are 39.0 g of HCl. The molar mass of HCl is approximately 36.46 g/mol, so the number of moles of HCl in 100 g of solution is 39.0 g / 36.46 g/mol = 1.07 mol. The mass of water (solvent) in 100 g of solution is 100 g - 39.0 g = 61.0 g, which is 0.061 kg. Therefore, the molality of the solution is 1.07 mol / 0.061 kg = 17.5 m.

Commercial Grade HCl Solutions Are Typically 39