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A solution containing 30g of a nonvolati...

A solution containing `30g` of a nonvolatile solute in exactly `90g` water has a vapour pressure of `21.85 mm Hg` at `25^(@)C`. Further `18g` of water is then added to the solution. The resulting solution has vapour pressure of `22.18 mm Hg` at `25^(@)C`. calculate (a) molar mass of the solute, and (b) vapour pressure of water at `25^(@)C`.

Text Solution

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The correct Answer is:
(a) `61.21 g mol^(-1)`, (b) `23.99 mm Hg`
`(P^(@) -21.85)/(21.85) = (30xx 18)/(90 xxm)` for I case...I
Now weight of solvent `=90 +18 = 108 g`
`(P^(@) -22.15)/(22.15) = (30 xx 18)/(108 xx m)` for II case...II
`{:( :.,By eq.(i),P^(@)m-21.85m=21.85xx6 = 131.1),(,Byeq.(ii),P^(@)m-22.15m=22.15xx5 = 110.75),(,,ul" + - +"):}`
`:. 0.30 m = 20.35` ltBRgt `:. M = (20.35)/(0.30) =67.83`
`(P^(@) -21.85)/(21.85) = (30 xx18)/(90 xx 67.83)`
`:. P^(@) = 23.78 mm`
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