In a 0.2 molal aqueous solution of a weal acid, HX, the degree of dissociation is 0.3 . Taking `K_(f)` for water as 1.85, the freezing point of the solution will be nearest to

Options

A. `-0.360^(@)C`
B. `-0.206^(@)C`
C. `+0.480^(@)C`
D. `-0.480^(@)C`

Answer

D

Explanation

The weak acid ionizes as
`{:(,HX,hArr,H^(+),+,X^(-)),("Initial",1,,0,,0),("After dissociation",1-0.3,,0.3,,0.3):}`
Total moles `=1-0.3+0.3+0.3=1.3`
`i=(1.3)/(1)=1.3`
`DeltaT_(f)=iK_(f)xxm=1.3xx1.85xx0.2=0.481`
`T_(f)=0-0.481= -0.481^(@)C`.