At , the vapour pressure of 0.1 molal aqueous solution of urea is 0.03 mm less than that of water an — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

The lowering of vapour pressure ($\Delta P$) is directly proportional to the effective molality ($i \times m$) for very dilute solutions. Urea is a non-electrolyte ($i=1$), so $\Delta P_1 \propto 1 \times 0.1$. KCl dissociates, so $\Delta P_2 \propto i \times 0.1$. Taking the ratio: $\Delta P_2 / \Delta P_1 = i / 1 \implies 0.0594 / 0.03 = i \implies i = 1.98$. For KCl, $i = 1 + \alpha \implies 1.98 = 1 + \alpha \implies \alpha = 0.98$. The percentage dissociation is 98%. Therefore, correct answer is 0098.