Solutions Question 45

Question: A solution containing 30 gms of non-volatile solute in exactly 90 gm water has a vapour pressure of 21.85 mm Hg at 25oC . Further 18 gms of water is then added to the solution. The resulting solution has a vapour pressure of 22.15 mm Hg at 25oC . Calculate the molecular weight of the solute [UPSEAT 2001]

Options:

A) 74.2

B) 75.6

C) 67.83

D) 78.7

Show Answer

Answer:

Correct Answer: C

Solution:

We have, p021.8521.85=30×1890×m , for I case …..(i) wt. of solvent =90+18=108gm

p022.1522.15=30×18108×m , for II case …..(ii) By eq. (1) pm021.85m=21.85×6=131.1 By eq. (2) pm022.15m=22.15×5=110.75 0.30m = 20.35 m=20.350.30=67.83



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