The vapour pressure of a solution of a non-volatile electrolyte B in a solvent A is 95% of the vapour pressure of the solvent at the same temperature. If the molecular weight of the solvent is 0.3 tim

Question

The vapour pressure of a solution of a non-volatile electrolyte B in a solvent A is 95% of the vapour pressure of the solvent at the same temperature. If the molecular weight of the solvent is 0.3 times the molecular weight of solute, the weight ratio of the solvent and solute are

TestHub · Accepted Answer

Raoult's Law: P A ​ = X A ​ P A 0 ​ . Given P A ​ = 0.95 P A 0 ​ , so X A ​ = 0.95 . Thus, X B ​ = 1 − X A ​ = 0.05 . X B ​ = n A ​ + n B ​ n B ​ ​ = 0.05 . n B ​ n A ​ ​ = X B ​ 1 − X B ​ ​ = 0.05 0.95 ​ = 19 . We are given M A ​ = 0.3 M B ​ . Weight ratio w B ​ w A ​ ​ = n B ​ M B ​ n A ​ M A ​ ​ = n B ​ n A ​ ​ × M B ​ M A ​ ​ = 19 × 0.3 = 5.7 .

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