A solution containing 30 gms of non-volatile solute in exactly 90 gm water has a vapour pressure of 21.85 mm Hg at `25^(@)`C. Further 18 gms of water is then added to the solution. The resulting solution has a vapour pressure of 22.15 mm Hg at `25^(@)`C. Calculate the molecular weight of the soluteA. 74.2B. 75.6C. 67.83D. 78.7

A solution containing 30 gms of non-volatile solute in exactly 90 gm w

1.	A solution containing 30 gms of non-volatile solute in exactly 90 gm water has a vapour pressure of 21.85 mm Hg at `25^(@)`C. Further 18 gms of water is then added to the solution. The resulting solution has a vapour pressure of 22.15 mm Hg at `25^(@)`C. Calculate the molecular weight of the soluteA. 74.2B. 75.6C. 67.83D. 78.7
Answer» Correct Answer - C We have, `(p^(@)-21.85)/(21.85)=(30xx18)/(90xx m)`, for 1 case …….(i) Wt. of solvent `= 90+18=108 gm` `(p^(@)-22.15)/(22.15)=(30xx18)/(108xx m)`, for II case …..(ii) By eq. (1) `p^(@)m-21.85m=21.85xx6=131.1` By eq. (2) `p^(@)m-22.15m =22.15xx5=110.75` `0.30m=20.35` `m=(20.35)/(0.30)=67.83`

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