Question

Commercially available $HCl$ contains $38\%$ $HCl$ by mass. Calculate molality of the solution.

Answer 1

$38\%HCl$ by mass means $38g$ of $HCl$ in $100g$ of solution.

As we know that,

molality $=\frac{\text{No. of moles of solute}}{{\text{Wt. of solvent}}_{\left(\text{in Kg}\right)}}$

Therefore,

Weight of solvent $=100-38=62g$

Molecular weight of $HCl=36.5g$

No. of moles of $HCl=\frac{38}{36.5}=1.041\text{mol}$

$\therefore$ molality $=\frac{1.041}{62}\times 1000=16.79$

Hence the molality of solution is $16.79$.