1.

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 boilingpoint of water = 373 K Standard boilingpoint 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. The freezing point of the solution M is

Answer»

`268.7 K`
`268.5 K`
`234.2 K`
`150.9 K`

Solution :Solution M is MIXTURE of ethanol and water, Mole fraction of ethanol is 0.9 (Solvent is `C_(2)H_(5)OH`) Mole fraction water is 0.1(`H_(2)O` is solute)
Molality of `H_(2)O=(n_(2)xx1000)/(n_(1)M_(1))`
`=(0.1xx1000)/(0.9xx46)=2.415` m
`DeltaT_(f)=K_(f)m=2xx2.2415=4.83`
FREEZING POINT of solution
`= 155.7 - 4.83 = 150.87 K`
Total vapour pressure, `p=p_(A)^(@)xx A`.


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