Question

What is the molality (m) of a 36.45% (by weight) solution of HCl in water?

A. 0.0157 m

B. 0.0274 m

C. 1.00 m

D. 15.74 m

E. 63.55 m

Please explain!

Answer 1

molality = (mass of solute/ molar mass of solute) x (1 / mass of solvent in Kg)

Let us assume , mass of solution = 100 g

Given that mass % of HCl = 36.45 %

Hence,

mass of HCl (solute) = 36.45 g

mass of solvent (water)= 100 -36.45 g = 63.55 g = 0.06355 kg

molar mass of HCl = 36.5 g/mol

Hence,

molality = (mass of HCl/ molar mass of HCl) x (1 / mass of water in Kg)

=  (36.45 g/36.5 g/mol ) x (1 / 0.06355 kg)

= 15.74 m

Therefore,

molality of given solution = 15.74 m