Question

Will the elevation in boiling point be the same if 0.1 mol of sodium chloride or 0.1 mol of sugar is dissolved in 1L of water?

Answer 1

Boiling point elevation is a phenomenon in which boiling point of a solvent or a liquid becomes higher after adding another compound to it. This means that the final solution now possesses a higher boiling point in comparison to a pure solvent.

Complete step by step answer:
The boiling point elevation can be estimated by applying Raoult's law and Clausius–Clapeyron relation assuming that the solute is non-volatile. The equation to calculate boiling point elevation can be stated as follows:
$\Delta {T_b} = {K_b}.{b_{solute}}.i$
Here, $\Delta {T_b}$is the boiling point elevation (i.e. ${T_{b(solution)}}$ – ${T_{b(pure solvent)}}$), ${K_b}$is ebullioscopic constant, $b_{solute}$ is molality of solute, and i is the Van’t Hoff factor.
The boiling point elevation is actually a colligative property i.e. it depends upon the existence of dissolved particles as well as their number. In the present scenario, sugar (non-electrolyte) does not dissociate into ions in aqueous solution. On the other hand, NaCl (electrolyte) completely dissociates into ions yielding sodium as well as chloride ions. This is explained more clearly by the following equations:
$Sugar \to Sugar(aq) \\\ {\text{ (1) (1) }} \\\ i = \dfrac{1}{1} = 1 \\\ \Delta {T_b} = {K_b} \times 0.1 \times 1 = 0.1{K_b} \\\$
$NaCl \to N{a^ + } + C{l^ - } \\\ {\text{ (1) (1) (1)}} \\\ i = \dfrac{{1 + 1}}{1} = 2 \\\ \Delta {T_b} = {K_b} \times 0.1 \times 2 = 0.2{K_b} \\\$
Hence, elevation in boiling point in both the cases is not the same. Elevation in boiling point in case of dissolving 0.1 mol of sodium chloride in 1 L of water will be higher as compared to that of 0.1 mol of sugar.

Note:
The elevation in boiling point is employed to measure the dissociation degree and the molar mass of solute. This measurement is also known as ebullioscopy (meaning in greek is boiling-viewing). Elevation in boiling point can be correlated with freezing point depression. Depression in freezing point is the lowering in freezing point of a solvent owing to the solute’s addition. Elevation in boiling point of a solvent is inversely proportional to its freezing point.