An aqueous solution of a non-volatile, non-electrolyte solute (molecular mass = 150) boils at 373.26 K. The composition of solution, in terms of mass per cent of solute, is ( of water = 0.52)

Question

An aqueous solution of a non-volatile, non-electrolyte solute (molecular mass = 150) boils at 373.26 K. The composition of solution, in terms of mass per cent of solute, is ($K_b$ of water = 0.52)

Prashant Kotian · Accepted Answer

Correct answer: C. Pure water boils at 100°C (373.15 K). Thus, ΔT_b = 373.26 - 373.15 = 0.11 K (or using standard pure boiling point as exactly 373 K in some questions, ΔT_b = 0.26 K). Let's use ΔT_b = 0.26 K to match options: ΔT_b = * m => 0.26 = 0.52 * m => m = 0.5 molal. A 0.5 molal solution contains 0.5 moles of solute in 1000 g of water. Mass of solute = 0.5 * 150 = 75 g. Mass of solution = mass of solute + mass of water = 75 + 1000 = 1075 g. Mass per cent of solute = (75 / 1075) * 100 = 6.98%.

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