The freezing point of the solution M is — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

Since $X_{\text{ethanol}} = 0.9$, ethanol is the solvent and water is the non-volatile solute ($X_{\text{water}} = 0.1$). Molality of water $m = X_{\text{water}} / (X_{\text{ethanol}} \times M_{\text{ethanol}}) \times 1000 = 0.1 / (0.9 \times 46) \times 1000 = 100 / 41.4 = 2.415 \text{ m}$. Depression $\Delta T_f = K_f^{\text{ethanol}} \times m = 2.0 \times 2.415 = 4.83 \text{ K}$. Freezing point = $155.7 - 4.83 = 150.87 \text{ K} \approx 150.9 \text{ K}$. Therefore, correct answer is D.