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Question: Answered & Verified by Expert
Ratio of  Δ T b K b  of 10 g AB2 and 14 g A2B per 100 g of solvent in their respective, solution (AB2 and A2B both are non-electroytes) is 1 mol/kg in both cases. Hence, atomic wt. of A and B are respectively :
ChemistrySolutionsJEE Main
Options:
  • A 100, 40
  • B 60, 20
  • C 20, 60
  • D None of these
Solution:
2051 Upvotes Verified Answer
The correct answer is: 60, 20
Δ T b = K b w solute W solvent × 1 M solute × 1 0 0 0

1 = 1 0 0 0 × 1 0 1 0 0 × M AB 2 M AB 2 = 1 0 0

Similarly  M A 2 B = 1 4 0

               1 0 0 = M A + 2 · M B

and         1 4 0 = 2 · M A + M B ;

               M A = 6 0 and M B = 2 0

Alternative solution

Δ T b K b = 1 = 1 0 M A + 2 M B 0.1

M A + 2 M B = 1 0 0    ........ (1)

Δ T b K b = 1 = 1 4 2M A + M B 0.1

2 M A + M B = 1 4 0    ........ (2)

M A = 60, M B = 2 0

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