0.5 m aqueous solution of a weak acid (HX) is 20 % ionissed. If `K _(f)` for water is `1. 86 K kg mol ^(-1),` the following in freezing point of the solution is :

Options

A. `0. 56 k `
B. `1.12 K `
C. `- 0. 56 k`
D. `- 1. 12 K `

Answer

B

Explanation

`{:( HX " "hArr " "H ^(+) " "+ " "X ^(-)), ( 1 - alpha " "alpha " "alpha ) :}`
Total ` = 1 + alpha`
`therefore i =1 + alpha = 1 + 0.2 = 1.2`
`Delta T _(f) = i xx K _(f) xx m = 1. 2 xx 1. 86 xx 0. 5 = 1.116 K ~~ 1.12 K`