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Standard IX

Chemistry

Fractional Distillation

Which of the ...

Question

Which of the following solution pairs can be separated by fractional distillation?

C_{2} H_{5} O H

-water (Boiling point of ethanol = 351.45 K; boiling point of water = 373.2 K)

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Water-

H C l

(Boiling point of water = 373.2 K; boiling point of hydrochloric acid = 188.1 K)

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Benzene-toluene (Boiling point of benzene= 353.2 K; boiling point of toluene = 383.8 K)

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All of these

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Solution

The correct option is C $C_{2} H_{5} O H$ -water (Boiling point of ethanol = 351.45 K; boiling point of water = 373.2 K)
Fractional distillation is used for separating liquids that have difference in boiling points less than 25 K. Only for the liquid pairs in the first option, the boiling points differ by less than 25 K.

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Q. Assertion :Benzene (boiling point

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Properties such as boiling point, freezing point and vapour pressure of a pure solvent change when solute molecules are added to get homogeneous solution. These are called colligative properties. Applications of colligative properties are very useful in day-to - day life.
One of its examples is the use of ethylene glycol and water mixture as anti-freezing liquid in the radiator of automobiles.
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
$(K_{f}^{w a t e r}) = 1.86 K k g m o l^{- 1}$
Freezing point depression constant of ethanol
$(K_{b}^{w a t e r}) = 2.0 K k g m o l^{- 1}$
Boiling point elevation constant of water
$(K_{b}^{w a t e r}) = 0.52 K k g m o l^{- 1}$
Boiling point elevation constant of ethanol
$(K_{b}^{e t h a n o l}) = 1.2 K k g m o l^{- 1}$
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 = 351.5K
Vapour pressure of pure water = 32.8 mm Hg
Vapour pressure of pure ethanol = 40 mm Hg
Molecular weight of water $= 18 g m o l^{- 1}$
Molecular weight of ethanol $= 46 g m o l^{- 1}$
In answering 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 is -

Q. The boiling point elevation constant

(K_{b})

of water is

0.52 {K kg mol}^{- 1}

. The boiling point of

0.1 m a q .

solution of urea is:

What method will you use to separate ethanol from a mixture of ethanol (boiling point 78°C) and water (boiling point 100°C)?

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