Vapour pressure of pure water at `27^@C` is 3000k Pa. By dissolving 5 g of a non volatile molecular solid in 100 g of water the vapour pressure is decreased to 2985 k Pa. What si the molecular weight of solute?

Explanation

According to Raoult.s law,
`(p^@ - p)/(p^@) = (wM)/(Wm) , (3000 - 2985)/(3000) = (5 xx 18)/(100 xx m). ` Moleculare weight of solute , `m = (5 xx 18 xx 30)/(100 xx 15) = 180`.