question_answer

0.5 molal aqueous solution of a weak acid (HX) is 20% ionised. If \[{{K}_{f}}\] for water is\[1.86K\text{ }kg\text{ }mo{{l}^{-1}}\], the

A) 0.56K                           

B) 1.12K

C) \[-0.56K\]          

D) \[-1.12K\]

Correct Answer: B

Solution :

[b] As \[\Delta {{T}_{f}}={{K}_{f}}.m\] For, Total no. of moles \[=1-0.20+0.20+0.20\] \[=1+0.20=1.2\] \[\therefore \text{ }\Delta {{T}_{f}}=1.2\times 1.86\times 0.5=1.1160\approx 1.12K\]