A 0.2 molal aqueous solution of weak acid (HX) is 20% ionised. The freezing point of this solution is (Given, `K_(f) = 1.86^(@) C m^(-1)` for water)

Options

A. `-0.45^(@)C`
B. `-0.90^(@)C`
C. `-0.31^(@)C`
D. `-0.53^(@)C`

Answer

A

Explanation

`Delta T_(f) =i xx "molality" xx K_(f)`
`= (1 + alpha) xx "molality" xx K_(f)`
Given alpha `= 0.2 xx K_(f) = 1.86`
`:. Delta T_(f)=(1 +0.2) xx 0.2 xx 1.86`
`=1.2 xx 0.2 xx 1.86 = 0.4464^(0)C`
f.pt. =`-0.45^(@)C`