The vapour pressure of a `5%` aqueous solution of a non-volatile organic substance at `373 K`. Is `745 mm`. Calculate the molecular mass of the solute.

Answer

`48 g mol^(-1)`

Explanation

`(p_(A)^(@) - p_(A))/(p_(A)^(@)) = (w_(B) xx M_(A))/(w_(A) xx M_(B))`
` w_(B) = 5.0g , w_(A) = 100-5.0 = 95 g`
`p_(A)^(@) = 760 mm , p_(A) = 745 ` mm
`(760 - 754)/(760) = (5.0 xx 18)/(95 xx M_(B))`
Solving
`M_(B) = 48 gmol^(-1)`