At 100 ^ o C the vapour pressure of a solution of 6.5 g of a non-volatile solute in 100 g water is 732 mm. If K _ b = 0.52 , the boiling point of this solution will be:

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Correct answer: A. 101 ^ o C

At 100 ^ o C (boiling point) Vapour pressure of water P ^ o = P _ atm = 760mm ∴ P ^ o - P _ s P ^ o = X _ solute ⇒ (760 - 732)/(760) = n _ solute n _ solvent m = molarmassofsolute ⇒ (28)/(732) = (6.5 / m)/(100 / 18) ⇒ m = (6.5 × 18 × 732)/(28 × 100) 30.6 Now, ∆ T _ b = K _ b × molality = 0.52 × (6.5 / 30.6)/(0.1) = 1 . 1 ° C ∴ Boiling point of solution = 100 + 1 . 1 = 101 . 1 ^ o C ≃ 101 ° C

At 100 ^ o C the vapour pressure of a solution of 6.5 g of a...

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