A solution is prepared by dissolving 10 g of non-volatile solute in 200 g of water. It has a vapour pressure of 31.84 mm Hg at 308 K. Calculate the molar mass of the solute. [ Vapour pressure of pure water at 308 K = 32 mm Hg]

Explanation

Apply the relation
`(p_1^0 - p_1)/(p_1^0) = (w_2 xx M_1)/(M_2 xx w_1)`

Substituting the values in the above relation, we have
`(32-31.84)/(32) = (10 xx 18)/(M_2 xx 200)`
`(0.16)/(32) = (180)/(200M_2)`
`M_2 = (180 xx 32)/(0.16 xx 200) = 180`