Q. 1.00 g of a non-electrolyte solute (molar mass 250 g mol⁻¹) was dissolved in 51.2 g of benzene. If the freezing point depression constant, Kf of benzene is 5.12 K kg mol⁻¹, the freezing point of benzene will be lowered by :

A) 0.4 K
B) 0.8 K
C) 0.12 K
D) 0.24 K
Explanation

[Solution from source] Molality m = (1.00/250)/(51.2/1000) = 0.004/0.0512 = 0.078 mol kg⁻¹. ΔTf = Kf × m = 5.12 × 0.078 = 0.40 K. Forgetting to convert grams of benzene to kilograms changes the answer by a factor of 1000. Answer (1).

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

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