When of an unknown, non-volatile, and non-electrolyte solute is completely dissolved in of pure wate — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

The relative lowering of vapour pressure (RLVP) is given by $\frac{\Delta P}{P^0} = \frac{n}{n+N} \approx \frac{n}{N}$ (for dilute solutions). Here, $RLVP = 0.1$. Moles of solvent (water) $N = \frac{108}{18} = 6\text{ moles}$. Moles of solute $n = \frac{12}{M}$. Applying the approximation: $\frac{12/M}{6} = 0.1 \implies \frac{2}{M} = 0.1 \implies M = 20\text{ g mol}^{-1}$.