The freezing point of a 0.05 molal solution of a non- electrolyte in water is — Solutions and Colligative Properties Chemistry Question

💡 Solution & Explanation

I need to find the freezing point of a 0.05 molal non-electrolyte solution in water. **Step 1: Identify the colligative property** Freezing point depression is a colligative property given by: $$\Delta T_f = K_f \times m \times i$$ where: - $K_f$ = cryoscopic constant for water = 1.86 K·kg/mol - $m$ = molality = 0.05 mol/kg - $i$ = van't Hoff factor = 1 (non-electrolyte doesn't dissociate) **Step 2: Calculate freezing point depression** $$\Delta T_f = 1.86 \times 0.05 \times 1 = 0.093 \text{ K} \approx 0.09°C$$ **Step 3: Find the new freezing point** The normal freezing point of water is 0°C. The solution freezes at a lower temperature: $$T_f = 0°C - 0.09°C = -0.09°C$$ Or more precisely: $T_f \approx -0.093°C \approx -0.1°C$ **Answer:** The freezing point is approximately **−0.09°C or −0.1°C** (Option C, assuming this matches your answer choices showing values in this range). This makes sense because the solute particles disrupt the crystalline structure of ice, requiring lower temperature to achieve the same vapor pressure equilibrium between solid and liquid phases.