Solutions

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 \(\left( {K_f^{water}} \right) = 1.86\) K kg mol\(^{-1}\)

Freezing point depression constant of ethanol \(\left( {K_f^{ethanol}} \right) = 2.0\) K kg mol\(^{-1}\)

Boiling point elevation constant of water \(\left( {K_b^{water}} \right) = 0.52\) K kg mol\(^{-1}\)

Boiling point elevation constant of ethanol \(\left( {K_b^{ethanol}} \right) = 1.2\) 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 water = 40 mm Hg

Molecular weight of water = 18 g mol\(^{-1}\)

Molecular weight of ethanol = 46 g mol\(^{-1}\)

In answering 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 :