1.

At 25^(@)C , the vapour pressure of pure water is23.76mm of Hgand thatof an aqueousdilutesolutionof urea is 22.98 mm of Hg . Calculate themolalityof the solution .

Answer»


SOLUTION :`(23.76-22.98)/(23.56) = x_(B)`
or `"" x_(B) = 0.0033`
Now for thedilutesolution ,
`x_(B) = (n_(B))/(n_(A))""….(i)`
Molalitym ` =(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`


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