Solutions Question 55

Question: A 0.2 molal aqueous solution of a weak acid (HX) is 20% ionised. The freezing point of this solution is (Given $ K_{f}={{1.86}^{o}}C/m $ for water) [IIT 1995]

Options:

A) $ -{{0.31}^{o}}C $

B) $ -{{0.45}^{o}}C $

C) $ -{{0.53}^{o}}C $

D) $ -{{0.90}^{o}}C $

Show Answer

Answer:

Correct Answer: B

Solution:

$ \Delta T_{f}=molality\times K_{f}\times (1+\alpha ) $

$ \alpha =0.2 $ , Molality = 0.2, $ K_{f}=1.86 $

$ \Delta T_{f}=0.2\times 1.2\times 1.86={{0.4464}^{o}} $ Freezing point = $ -{{0.45}^{o}}C $ .



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