Chemistry - Liquid Solution Question with Solution | TestHub

The elevation in boiling point is given by the formula:

$\Delta T_b=K_b\times m$

where $m$ is the molality of the solution. Rearranging for molality:

$m=\frac{\Delta T_b}{K_b}$

Substituting the given values $\Delta T_b=0.3\text{ K}$ and $K_b=1.8{\text{ K kg mol}}^{-1}$:

$m=\frac{0.3}{1.8}=\frac{1}{6}{\text{ mol kg}}^{-1}$

Molality is also defined as the number of moles of solute ($n$) divided by the mass of the solvent in kg ($W$).

$m=\frac{n}{W}$

Rearranging to find the number of moles:

$n=m\times W$

Given the mass of the solvent $W=0.3\text{ kg}$:

$n=\frac{1}{6}\times 0.3=0.050\text{ mol}$

Answer: $0.050$