Question

A solution containing 2.5 × 10-3 kg of a solute dissolved in 75 × 10-3 kg of water boils at 373.535 K. The molar mass of the solute is _____ g mol-1. [nearest integer] (Given : Kb(H2O) = 0.52 K kg mol-1 and boiling point of water = 373.15 K)

Answer 1

The correct answer is 45
Wsolute = 2.5 × 10–3 kg
Wsolvent = 75 × 10–3 kg
ΔTb = 373.535 – 373.15= 0.385 K
Kb(H2O) = 0.52 K kg mol–1
$△T_b=\frac{K_b×10^3×W_{solute}}{M_{solute}×W_{solvent}}$
$M_{solute}=\frac{0.52×10^3×2.5×10^{−3}}{75×10^{−3}×0.385}$
= 45.02 ≈ 45