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

Question

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, 191.9, 90, 45, 20

MARKS App · Accepted Answer

(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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