The freezing point depression constant for water is `1. 86^(@)K gm mol ^(-1).` If `5g Na _(2) SO_(4)` is dissolved in 45 g water, the depression in freezing point is `3.64 ^(@)C.` The van't Hoff factor for `Na _(2) SO _(4)` is ……

Options

A. `2.50`
B. `2.63`
C. `3.64`
D. `5.50`

Answer

A

Explanation

`K _(f) = 1. 86 , W_(2) = 5g, Delta T _(f ) =3.64, M _(2) = 142, W_(1) = 45 g`
`Delta T_(f) = I xx K _(f)`
`i = (Delta T _(f) xxM _(2) xx W_(1))/( K _(f) xx W _(2) xx 1000)`
`= (3.64 xx 142 xx 45)/(1. 86 xx 5 xx 1000)`
`i = 2.5`