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:

Question

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:, 101 o C, 100 o C, 102 o C, 103 o C

MARKS App · Accepted Answer

At 100 o C (boiling point) Vapour pressure of water P o = P a t m = 760 mm ∴ P o - P s P o = X s o l u t e ⇒ 760 - 732 760 = n s o l u t e n s o l v e n t { m = m o l a r m a s s o f s o l u t e } ⇒ 28 732 = 6.5 / m 100 / 18 ⇒ m = 6.5 × 18 × 732 28 × 100 ≈ 30.6 Now, ∆ T b = K b × m o l a l i t y = 0.52 × 6.5 / 30.6 0.1 = 1 . 1 ° C ∴ Boiling point of solution = 100 + 1 . 1 = 101 . 1 o C ≃ 101 ° C

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