(N/A) The elevation in boiling point is defined as the increase in the boiling point of a solution when $1 \ mol$ of a non-volatile solute is dissolved in $1 \ kg$ of solvent.
The boiling point of a solution is always higher than that of the pure solvent. This elevation depends on the number of solute particles rather than their nature.
Let $T_{b}^{0}$ be the boiling point of the pure solvent and $T_{b}$ be the boiling point of the solution. The increase in boiling point is given by $\Delta T_{b} = T_{b} - T_{b}^{0}$.
For dilute solutions,the elevation of boiling point $(\Delta T_{b})$ is directly proportional to the molal concentration $(m)$ of the solute:
$\Delta T_{b} \propto m$
$\Delta T_{b} = K_{b} \times m$
Where $K_{b}$ is the Boiling Point Elevation Constant or Ebullioscopic Constant. Its unit is $K \ kg \ mol^{-1}$.
If $w_{2}$ grams of solute with molar mass $M_{2}$ are dissolved in $w_{1}$ grams of solvent,the molality $(m)$ is:
$m = \frac{w_{2} \times 1000}{M_{2} \times w_{1}}$
Substituting $m$ into the equation for $\Delta T_{b}$:
$\Delta T_{b} = \frac{K_{b} \times 1000 \times w_{2}}{M_{2} \times w_{1}}$
Rearranging to find the molar mass of the solute:
$M_{2} = \frac{1000 \times w_{2} \times K_{b}}{\Delta T_{b} \times w_{1}}$