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Solutions question

2007 · Q85
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Solutions question

2007 · Q85

NEETChemistrySolutionsMCQ+4 / −1
0.5 molal aqueous solution of a weak acid (HX) is 20% ionised. If Kf for water is 1.86 K kg mol−-−1, the lowering in freezing point of the solution is
  1. A
    0.56 K
  2. B
    1.12 K
  3. C
    −-− 0.56 K
  4. D
    −-− 1.12 K
View written solutionFree

Correct answer: B

HX⇌H++X-
Initially100
At equilibrium1 - $\alpha $$\alpha $$\alpha $


Total moles = 1 – $\alpha $ + $\alpha $ + $\alpha $ = 1 + $\alpha $

$ \therefore $ i = $${{1 + \alpha } \over 1}$$

Given, $\alpha $ = 20% = 0.2

$ \therefore $ i = 1 + $\alpha $ = 1 + 0.2 = 1.2

$\Delta $Tf = ikf m = 1.2 × 1.86 × 0.5 = 1.12 K
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