The freezing point depression constant for water is `1. 86^(@)C m^(-1). `If 5 g of `Na2 SO_(4)` is dissolved in `45 g H_(2)O, `the freezing point is changed by `–3.82^(@)C.` Calculate the Van't Hoff factor for `Na2SO_(4).`

Options

A. `2 05`
B. `2. 63`
C. `3. 11`
D. `0. 381`

Answer

B

Explanation

We know that , `Delta T _(f) = i xx K _(f) xx ( W _(B) xx 1000)/( m _(B) xx W _(A))`
Given : `Delta T _(f) = 3. 82 , K _(f) = 1 . 86`
`W _(B) = 5, m _(B) = 142, w _(A)= 45`
`i = ( Delta Txx m _(B) xx W _(A))/( K _(f) xx W _(B) xx 1000) = ( 3. 82 xx 142 xx 45)/( 1. 86 xx 5 xx 1000) = 2. 63`