Question

A hydrochloric acid solution contains 36 percent HCl by mass. Calculate its molality

Answer 1

The Molarity M of a solute in a solution is defined as:

M=moles of solution / kilograms of solvent

Mass %= (mass solute/mass solution)x100%

Assume 100g of solution

Find moles of solute

Mass solute = (mass %/100%)mass solution

=(36%/100)100g=36 gHCL

36 gHCL 1 mol HCL/36.458 gHCL= 0.987molHCL

36% HCL by mass 100 g solution
36g HCL 0.987Mol HCL

Molarity=moles solute/kg solvent

Find kg solvent
Mass solution = mass solute + mass solvent
Mass solvent = mass solution - mass solute
= 100 g-36=64 g solvent

64 g solvent = 1 kg solvent/1000 g solvent = 0,064 kg solute

Molarity= molHCL/0.064 kg solvent

=0.987/0.064
=15.42 mHCL