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The freezing point of a 3% aqueous solution of 'A' is equal to the freezing point of 9% aqueous solution 'B'. If the molecular weight of 'A' is 60, then the molecular weight of 'B' will be

Options

  1. A191.9
  2. B90
  3. C45
  4. D20

Correct answer

A. 191.9

Step-by-step solution

(T f ) A   =   (T f ) B ⇒ (ΔT f ) A = (ΔT f ) B ⇒ i × K f × m A = i × K f × m B ⇒ m A = m B ⇒ w A M A × 1000 w solvent (g) = w B M B × 1000 w solvent (g) ⇒ 3 60 × 1000 97 = 9 M B × 1000 91 ⇒ M B = 9 × 60 × 97 3 × 91 ∴ M B = 191.9 g/mol

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