Explain why on addition of 1 mol of glucose to 1 litre of water, the boiling point of water increases. (Comptt. Delhi 2017)

The boiling point of water increases upon the addition of 1 mol of glucose due to a phenomenon known as boiling point elevation. Here's a step-by-step explanation:

1. Boiling Point Elevation: This is a colligative property of a solution, which means it depends on the number of solute particles in the solution, not on the nature of the solute. When a non-volatile solute (like glucose) is added to a solvent (like water), it increases the boiling point of the solvent.

2. Dissolution of Glucose: When glucose is added to water, it dissociates into its individual molecules. This increases the number of particles in the solution.

3. Vapor Pressure Lowering: The addition of glucose molecules to the water decreases its vapor pressure. This is because the glucose molecules at the surface of the solution hinder the escape of water molecules into the gas phase.

4. Increased Boiling Point: Boiling occurs when the vapor pressure of a liquid equals the atmospheric pressure. Since the vapor pressure of the water has been lowered by the addition of glucose, it now needs to be heated to a higher temperature to reach the point where its vapor pressure equals the atmospheric pressure. This is why the boiling point increases.

5. Molar Concentration: In this case, 1 mol of glucose is added to 1 litre of water. This means the molar concentration of the solution is 1 mol/L. The higher the molar concentration of the solute, the greater the boiling point elevation.

So, the addition of 1 mol of glucose to 1 litre of water increases the boiling point of water due to the colligative property of boiling point elevation.