For non-ideal solutions exhibiting positive deviation :

A. The vapour pressure is lower than that predicted by Raoult's law.

B. The vapour pressure is higher than that predicted by Raoult's law.

C. The interaction at the molecular level are weaker than in the pure state.

D. The interaction at the molecular level are stronger than in the pure state. 

E. Mixture of chloroform and acetone is a suitable example.

Choose the correct answers from the options given below:

B, C only

The correct answer is option 4. B, C only.

Let us look at each of the given statements carefully:

A. The vapour pressure is lower than that predicted by Raoult's law: This is incorrect. Non-ideal solutions exhibiting positive deviation have a higher vapour pressure than predicted by Raoult's law, not lower.

B. The vapour pressure is higher than that predicted by Raoult's law: This is correct. Positive deviation means the intermolecular interactions between the solute and solvent molecules are weaker than those between the pure solvent and solute molecules, making it easier for them to escape into the gas phase and leading to a higher vapour pressure.

C. The interaction at the molecular level are weaker than in the pure state: This is correct. As mentioned in B, weaker intermolecular interactions between solute and solvent molecules are characteristic of positive deviation.

D. The interaction at the molecular level are stronger than in the pure state: This is incorrect. This describes solutions exhibiting negative deviation, not positive deviation.

E. mixture of chloroform and acetone is a suitable example: This is correct. Chloroform and acetone are a classic example of a non-ideal solution exhibiting positive deviation due to their weak intermolecular interactions.

Therefore, the correct answer is option 4. B, C only.

Additional Information:

Understanding Positive Deviation in Non-Ideal Solutions

Non-ideal solutions occur when the interactions between the solute and solvent molecules differ from the interactions within the pure components. In the case of positive deviation, these interactions are weaker when the molecules are mixed than when they are separate. This leads to several distinct behaviours compared to ideal solutions that follow Raoult's law.

Explanation of Key Points:

1. Higher Vapour Pressure:

• In Raoult's law, the total vapour pressure of an ideal solution is directly proportional to the mole fraction of each component and their individual vapour pressures in the pure state.
• For non-ideal solutions with positive deviation, the intermolecular forces between unlike molecules (solute and solvent) are weaker than those between like molecules (pure solvent and pure solute). This weakens the overall attractive forces holding the solution together, making it easier for molecules to escape the liquid phase and enter the gas phase.
• Consequently, the actual vapour pressure of the solution becomes higher than expected from Raoult's law calculation. This phenomenon is observed because more molecules are leaving the liquid phase than expected based on the ideal interactions.

2. Weaker Intermolecular Interactions:

The positive deviation arises from weaker intermolecular interactions between solute and solvent molecules compared to their pure states. These interactions can be:

• Dipole-dipole interactions: If the solute and solvent have different polarities, they may weakly attract or even repel each other, leading to less energy holding them together in the solution.
• Hydrogen bonding: If the solute and solvent can form hydrogen bonds with each other, but there are fewer potential partners compared to the pure states, the overall hydrogen bonding network weakens, resulting in positive deviation.
• Dispersion forces: In some cases, the size and shape of the molecules prevent them from packing efficiently in the mixed state, leading to weaker dispersion forces and positive deviation.

3. Examples:

• Chloroform and acetone: This is a classic example due to the weak dipole-dipole interactions between the molecules.
• Ethanol and water: Hydrogen bonding between ethanol and water is weaker than the extensive hydrogen bonding within pure water, leading to positive deviation.
• Benzene and carbon disulphide: The large size and different shapes of these molecules prevent tight packing and hinder dispersion forces, causing positive deviation.

Additional Notes:

• Not all non-ideal solutions exhibit positive deviation. Negative deviation occurs when the solute and solvent have stronger interactions than in their pure states, leading to a lower vapour pressure.
• The extent of positive deviation depends on the strength of the solute-solvent interactions and the individual properties of the components.