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 $ .
