18 g of a compound is dissolved in 10 kg of water so that the resulting solution freezes at ` - 8^(@) C`. If `K_(f)` for water = 1 . 86 K/m . Calculate the molecular mass of the compound

Answer

4 . 2u

Explanation

`W_(B) = 18 g, W_(A) = 1 kg `
`Delta T_(f) = [0 - (- 8)]^(@) C = 8^(@) C = 8 K`
`K_(f) = 1 . 86 K//m = 1 . 86 K kg mol^(-1)`
`M_(B) = ?`
`Delta T_(f) = K_(f) xx (W_(B))/( M_(B)) xx (1)/(W_(A) (kg))`
`M_(B) = (K_(f) xx W_(B))/(Delta T_(f) xx W_(A) (kg))`
`= (1 . 86 K kg mol^(-1) xx 18 g)/( 8 K xx 1 kg)`
`= 4 . 2 g mol^(-1) = 4 .2 u`