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A solution of non-volite solute in water...

A solution of non-volite solute in water freezes at `-0.80^(@)C`.The vapour pressure of pure water at `298 K` is `23.51 mm Hg`.and `K_(f)` for water is `1.86 `degree per molal. Calculate the vapour pressure of this solution at `298 K`.

Text Solution

Verified by Experts

Depression in freezing point, `DeltaT_(f)=0-(0.30)=0.30`
Now,`DeltaT_(f)=K_(f)xxm`
or ` :.m=0.80/1.86=0.430`
According to Raoult's law,
`(P^(@)-P)/(P^(@))=(chi_(B))=(n_(B))/(n_(A)+n_(B))`,
`(P^(@)-P)/(P^(@))=(n_(B))/(n_(A))` (for dilut e solution)
Here,`n_(B)=0.430`,`n_(A)=1000/18`,`(P^(@))=23.51`
`(23.51-P)/(23.51)=0.43xx18/1000 =0.00774`
`P=23.51-(23.51xx0.00774)=23.32 mm Hg`
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