Question

A `0.5`molal aqueous solution of a weak acid (HX) is 20 per cent ionized.The lowering in freezing point of this solution is
`(K_(f)=1.86 "K/m for water")`
A. `1.12K`
B. `-0.56K`
C. `0.56K`
D. `-1.12K`

Answer 1

Correct Answer - A
`DeltaT=iK_(f)m`
we know,`alpha=(i-1)/(n-1)`(disssociation)
`alpha=(i-1)/(2-1)i=alpha+1`
so `DeltaT_(f)=(alpha+1)K_(f)m`
Given`alpha=0.2, "molarity" =0.5,K_(f)=1.86`
`:.DeltaT=0.5xx1.2xx1.86=1.116K`