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ChemistryInteger+4 / -1Question 85 of 90

JEE Main 2022 · 27 Jun · Shift 2, Chemistry question 85

A solution containing 2.5×10−32.5\times10^{-3} kg of a solute dissolved in 75×10−375\times10^{-3} kg of water boils at 373.535 K. The molar mass of the solute is ______ g mol−1^{-1}. [nearest integer] (Given : Kb(H2O)=0.52K_b(\mathrm{H_2O})=0.52 K kg mol−1^{-1} and boiling point of water = 373.15 K)

Answer and worked solution

Official answer: 45

Molality. 0.3850.52≈0.740\dfrac{0.385}{0.52}\approx0.740 mol kg−1^{-1}, so moles =0.740×0.075≈0.0555=0.740\times0.075\approx0.0555.

Molar mass. 2.50.0555≈45\dfrac{2.5}{0.0555}\approx45 g mol−1^{-1}.

Answer: 45

Topics:Colligative properties
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