What weight of the non -volatile solute, urea needs to be dissolved in 100g of water, in order to decrease the vapour pressure of water by 25%? What will be the molality of the solution?

Answer

53.46 mm Hg

Explanation

`w_(A) = 90 g , w_(B) = 10 g`
`(p_(A)^(@) - p_(A))/(p_(A)^(@)) = (w_(B) xx M_(A))/(w_(A) xx M_(B))`
`(55.3-p_(A))/(55.3) = (10 xx 18)/(90 xx 60) = 0.0333`
` 55.3 -p_(A) = 1.84`
`therefore " " p_(A) = 53.46 mm Hg`