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Question
CBSEENCH12005751

A solution containing 8 g of a substance in 100 g of diethyl ether boils at 36.860C, whereas pure ether boils at 35.600C. Determine the molecular mass of the solute. (For ether Kb= 2.02 K kg mol–1) .

Solution
Answer;

We have given that

Tb = (36.86-35.60) = 1.26 KMB = ?,    WB = 8g,  WA = 100 gkb = 2.202 K kg mol-1


kb = Tb×MBWAWb×1000


Therefore
         2.02 = 1.26×MB×1008×1000

or         MB = 2.02×8×10001.26×100=128.25.