At `25^(@)C` , the vapour pressure of pure water is 23.76mm of Hg and that of an aqueous dilute solution of urea is 22.98 mm of Hg . Calculate the molality of the solution .

Answer

1.83 m

Explanation

`(23.76-22.98)/(23.56) = x_(B)`
or `" " x_(B) = 0.0033`
Now for the dilute solution ,
`x_(B) = (n_(B))/(n_(A))" "….(i)`
Molality m ` =(n_(B))/(w_(A)) xx 1000" "….(ii)`
Dividing eq.(ii) by eq.(i) .
`(m)/(x_(B)) = (1000)/(w_(A)) xx n_(A) = (1000)/(w_(A)) xx (w_(A))/(18)`
` m = x_(B) xx (1000)/(18) = (0.033 xx 1000)/(18)`
` = 1.83m`