Q.
The boiling point of benzene is 3 53.23 K. When 1.80 g of a non-volatile solute was dissolved in 90 g of benzene, the boiling point is raised to 354.11 K. Calculate the molar mass of the solute. (Kb for benzene is 2.53 K kg mol-1)
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a
58 g mol-1
b
49 g mol-1
c
85 g mol-1
d
94 g mol-1
answer is A.
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Detailed Solution
The elevation ΔTb in boiling point =354.11K−353.23K=0.88K ΔTb=Kf×w2×103M2×w1 and M2=Kf×w2×103ΔTb×w1∴ M2=2.53Kkgmol−1×1.8g×1000gkg−10.88K×90g ≈58gmol−1Therefore, molar mass of the solute, M2 = 58 g mol-1
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