Question

A hcl solution is 35.0% (by mass) hcl in water. Determine the molality in hcl if the solution has a density of 1.15 g/mol

Answer 1

consider 1 Kg of solution

mass of solution = 1 Kg = 1000 g

So,

mass of HCl = 35.0 % of 1000 g = 350 g

Molar mass of HCl,

MM = 1*MM(H) + 1*MM(Cl)

= 1*1.008 + 1*35.45

= 36.458 g/mol

mass(HCl)= 350 g

number of mol of HCl,

n = mass/molar mass

=(350.0 g)/(36.458 g/mol)

= 9.60 mol

mass os solvent = mass of solution - mass of HCl

= 1000 g - 350 g

= 650 g

= 0.650 Kg

molality = number of mol of HCl / mass of solvent in Kg

= 9.60 mol / 0.650 Kg

= 14.8 molal

Answer: 14.8 molal