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: Understanding the Concept:
Deviations from Raoult's law occur when the intermolecular forces between components in a mixture (A-B) are different from the forces in the pure components (A-A or B-B).
Step 2: Detailed Explanation:
1. Type of Deviation: A mixture of ethanol and acetone shows positive deviation from Raoult's law.
2. Reason: Pure ethanol has strong intermolecular hydrogen bonding. When acetone is added, its molecules get in between the ethanol molecules and break some of the hydrogen bonds. Consequently, the A-B (ethanol-acetone) interactions are weaker than the A-A (ethanol-ethanol) interactions.
3. Effect on Boiling Point: Since the interactions are weaker, the vapor pressure of the solution increases. Solutions with higher vapor pressure have lower boiling points. Thus, the boiling point of the solution decreases.
Step 3: Final Answer:
It shows positive deviation because A-B interactions are weaker than A-A. The boiling point decreases.