IIT-JEE 2008 · Paper 1, Chemistry question 68

Paragraph for Question Nos. 67 to 69

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 $(K_f^{water})=1.86$ K kg mol⁻¹
• Freezing point depression constant of 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 answering the following questions, consider the solutions to be ideal dilute solutions and solutes to be non-volatile and non-dissociative.