Subtopic: Concentration and drying of liquid foods – evaporators, tray, drum and spray dryers
Question Statement:
20% sucrose solution is boiled and frozen separately. Latent heat of vapourization at 100°C = 2257 kJ kg⁻¹, latent heat of crystallization at 0°C = 334 kJ kg⁻¹. The ratio of freezing point depression to boiling point elevation is
Options:
(A) 6.3
(B) 4.2
(C) 3.6
(D) 2.4
Official Answer Key:
C
Step-by-Step Solution & Explanation
Colligative property relations: ΔT_b = R·T_b²·x/L_v (per unit solute mole fraction) and ΔT_f = R·T_f²·x/L_f, with the same solute concentration x cancelling in the ratio. ΔT_f/ΔT_b = (T_f²/L_f)/(T_b²/L_v) = [(273.15)²/334]/[(373.15)²/2257] = 223.4/61.7 = 3.62 ≈ 3.6.
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