The vapour pressure of acetone at `20^(@)C` is 185 torr. When `1.2 g` of non-volatile substance was dissolved in `100g` of acetone at `20^(@)C` its vapour pressure was 183 torr. The moalr mass `(g mol^(-1))` of the substance is:

Options

A. 488
B. 32
C. 64
D. 128

Answer

C

Explanation

For dilute solutions,
`(Deltap)/(p_(0))=(w_(B)xxm_(A))/(m_(B)xxw_(A))`
`(185-183)/(185)=(1.2xx58)/(m_(B)xx100)`
`m_(B)=64.38`
`~~ 64 g mol^(-1)`]