1.

30 g of urea (M = 60 g "mol"^(-1)) is dissolved in 846 g of water. Calculate the vapour pressureof water for this solution if vapour pressure of pure water at 298 K is 23.8 mm Hg.

Answer»

Solution :The solution MAY be taken as dilute solution.
Applying the RELATIONSHIP :
`(p_1^0 - p_1)/(p_1^0) = (w_2 XX M_1)/(M_2 xx w_1)`
` 1 - (p_1)/(p_1^0) = (w_2 xx M_1)/(M_2 xx w_1)`
Substituting the values of the above EQUATION, we have
` 1- (p_1)/(23.8) = (30 xx 18)/(60 xx 846)`
` 1 - (p_1)/(23.8) = 0.0106 `
`(p_1)/(23.8) = 1- 0.0106`
`(p_1)/(23.8) = 0.9894" or" p_1 = 0.9894 xx 23.8`
`p_1 = 23.55 mg Hg `


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