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A solution `M` is prepared by mixing ethanol and water. The mole fraction of ethanol in the mixture is `0.9` Given: Freezing point depression constant of water `(K_(f)^(water)=1.86 K kg mol^(-1))` Freezing point depression constant to ethanol `(K_(f)^(ethanol))=2.0 K kg mol^(-1))` Boiling point elevation constant of water `(K_(b)^(water))=0.52 K kg mol^(-1))` Boiling point elevation constant of ethanol `(K_(b)^(ethanol))=1.2 K kg mol^(-1))` Standard freezing point of water = `273 K ` Standard freezing point of ethanol = `155.7 K ` Standard boiling point of water = `373 K ` Standard boiling point of ethanol = `351.5 K ` Vapour pressure of pure water =`32.8 mm Hg` Vapour pressure of pure ethanol =`40 mm Hg` Molecular weight of water =`18 g mol^(-1)` Molecular weight of ethanol =`46 g mol^(-1)` In anwering the following questions consider the solutions to be ideal dilute solutions and solutes to be non-volatile and non-dissociative. Water is added to the solution `M` such that the mole fraction of water in the solution becomes `0.9`. The boiling point of this solution isA. `380.4 K`B. `376.2 K`C. `375.5 K`D. `354.7 K` |
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Answer» Correct Answer - B `chi_(H2O)=0.9 (solvent)`,`chi_C_(2)H_(5)OH=0.1 (solute)` Molality of `C_(2)H_(5)OH (m_(C_(2)H_(5)OH))=(chi_(2) xx 1000)/(chi_1 xx Mw_(1))` `(0.1 xx 1000)/(0.9 xx 18)` `DeltaT_(b)=K_(b) xx m` `=0.52 xx (0.1 xx 1000)/(0.9 xx 18) =3.2 K` Boiling point =`373 + 3.2 =376.2 K` |
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