The vapour pressure of water at T (K) is 20 mm Hg. The following solution are prepared at T (K) :
I. 6g of urea (mol. Wt = 60) is dissolved in 178.2g of water
II. 0.01 mole glucose is dissolved in 179.82 g of water
III. 53g of `Na_(2)CO_(3)` (mo. wt. 106) is dissolved in 179.1g of water
Identify the correct order in which the vapour pressures of solutions increases :

Options

A. III,I,II
B. II,III,I
C. I,II,III
D. I,III,II

Answer

A

Explanation

I. `x_(B)=(n_(B))/(n_(A)+n_(B))=(6//60)/(178.2//18)+(6)/(60)=0.01`
`(Deltap)/(p_(0))=x_(B)=0.01`
II. `x_(B)=(n_(B))/(n_(A)+n_(B))=(0.01)/((179.82)/(18)+0.01)=0.001`
`(Deltap)/(p_(0))=0.001`
III. `x_(B)=(n_(B))/(n_(A)+n_(B))=(5.3//106)/((179.1)/(18)+(5.3)/(106))`
`(Deltap)/(p_(0))=ix_(B)`
`=3xx0.005=0.015`
`:.` Vapour pressures of solutions will increase in the following sequence :
`(III) lt (I) lt (II)`.]