Question

What type of deviation from Raoult’s law is shown by mixture of ethanol and acetone? Give reason. What will happen to the boiling point of the solution on mixing ethanol and acetone?

Hint:

Positive Deviation \(\rightarrow\) Higher Vapor Pressure \(\rightarrow\) Lower Boiling Point (Minimum boiling azeotrope).
Negative Deviation \(\rightarrow\) Lower Vapor Pressure \(\rightarrow\) Higher Boiling Point (Maximum boiling azeotrope).

Answer 1

Step 1: Conceptual Overview:
Deviations from Raoult's law occur when the intermolecular forces between the components in a mixture (A-B) differ from the forces between the pure components (A-A or B-B). These deviations affect the properties of the mixture, such as vapor pressure and boiling point.
Step 2: Detailed Explanation:
1. Type of Deviation: A mixture of ethanol and acetone exhibits positive deviation from Raoult's law.
2. Reason: Pure ethanol molecules experience strong intermolecular hydrogen bonding. When acetone is added to the mixture, its molecules fit between the ethanol molecules and disrupt some of the hydrogen bonds. As a result, the interactions between the ethanol and acetone molecules (A-B) are weaker than the ethanol-ethanol (A-A) interactions.
3. Effect on Boiling Point: The weakening of intermolecular forces leads to an increase in the vapor pressure of the solution. Since vapor pressure is directly related to the boiling point, an increase in vapor pressure results in a decrease in the boiling point of the solution.
Step 3: Final Conclusion:
The solution shows positive deviation because the A-B interactions (ethanol-acetone) are weaker than the A-A interactions (ethanol-ethanol), and this results in a decrease in the boiling point.