30 g of urea (M=60g `mol^(-1)`) is dissolved in 846g of water. Calculate the vapour pressure of water for this solution if vapour pressure of pure water at 298 K is 23.8 mm Hg.
(b) Write two differences between ideal solutions and non-ideal solutions,

Answer

23.55 mm Hg

Explanation

`(p_(A)^(@) - p_(A))/(p_(A)^(@)) = (w_(B) xx M_(A))/(M_(B) xx w_(A))`
`p_(A)^(@) = 23.8 mm , w_(B) = 30 g, w_(A) = 846 g`
`M_(B) = 60 g mol^(-1) , M_(A) = 18 g mol^(-1)`
` (23.8- p_(A))/(23.8) = (30 xx 18)/(60 xx 846)`
` 23.8- p_(A) = (30xx 158 xx 23.8)/(60xx846) = 0.2532`
`p_(A) = 23.8 - 0.2532 = 23.8-0.2532 = 23.55` mm Hg