The degree of dissociation of `Ca(NO_(3))_(2)` in a dilute solution containing 14g of the salt per 200g of water at `100^(@)C` is 70%. If the vapour pressure of water is 760 mm, calculate the vapour pressure of solution.

Explanation

`Deltap_(theo)=` Lowering in vapour pressure when there is no dissociation
`= p_(0)xx(wM)/(Wm) ("given",p_(0)=760mm, w=14g,W=200g,M=18,m=164)`
`= (760xx14xx18)/(200xx164)=5.84` mm
Degree of dissociation `= (70)/(100)=0.7`
`Ca(NO_(3))_(2)hArrCa^(2+)+underset((n=3))(2NO_(3)^(-))`
`(Deltap_(obs))/(Deltap_(theo))=("No. of particles after dissociation")/("No. of particles when there is no dissociation")`
`=(1+(n-1)alpha)/(1)=(1+(3-1)xx0.7)/(1)=2.4`
So, `Deltap_(obs)=2.4xxDeltap_(theo)=2.4xx5.84`
`= 14.02 mm`
`p_(0)-p_(s)=Delta p_(obs)=14.02`
`p_(s)=p_(0)-14.02=760-14.02=745.98` mm.