Question

The binary liquid mixture that has positive deviation from Raoult's law is

• A. Chloroform-Acetone
• B. Chloroethane-Bromoethane
• C. Phenol-Aniline
• D. Benzene-Toluene
• E. Ethanol-Acetone

Hint:

Positive deviation = Weaker A-B bonds; Negative deviation = Stronger A-B bonds.

Answer 1

Answer: (E)

Step 1: Understanding the Concept:
This question is about deviations from Raoult's law for non-ideal solutions. We need to identify a pair of liquids that, when mixed, exhibit positive deviation.
Step 2: Key Formula or Approach:
- Raoult's Law: Describes an ideal solution where the intermolecular forces between unlike molecules (A-B) are the same as the forces between like molecules (A-A and B-B). - Positive Deviation: Occurs when the intermolecular forces between unlike molecules (A-B) are weaker than the average forces between like molecules (A-A and B-B). This makes it easier for molecules to escape into the vapor phase, leading to a higher than expected vapor pressure. This happens when mixing breaks existing strong interactions like hydrogen bonds. - Negative Deviation: Occurs when the intermolecular forces between unlike molecules (A-B) are stronger than the forces between like molecules. This makes it harder for molecules to escape, leading to a lower than expected vapor pressure. This often happens when the two components form hydrogen bonds with each other. Step 3: Detailed Explanation:
Let's analyze the intermolecular forces in each pair: - (A) Chloroform (CHCl\(_3\)) - Acetone (CH\(_3\)COCH\(_3\)): Chloroform's hydrogen can form a hydrogen bond with the oxygen of acetone's carbonyl group. This creates strong A-B interactions. This pair shows negative deviation. - (B) Chloroethane - Bromoethane: Both are similar haloalkanes with similar dipole-dipole forces. This mixture behaves nearly ideally. - (C) Phenol - Aniline: The hydrogen of phenol's -OH group can form a strong hydrogen bond with the lone pair on the nitrogen of aniline. This creates strong A-B interactions. This pair shows negative deviation. - (D) Benzene - Toluene: Both are non-polar aromatic hydrocarbons with similar London dispersion forces. This mixture behaves nearly ideally. - (E) Ethanol (C\(_2\)H\(_5\)OH) - Acetone (CH\(_3\)COCH\(_3\)): Ethanol molecules are strongly associated with each other through hydrogen bonding. Acetone molecules have dipole-dipole interactions. When acetone is added to ethanol, the acetone molecules get in between the ethanol molecules, breaking some of the strong hydrogen bonds of ethanol. The new interactions between ethanol and acetone are weaker than the original ethanol-ethanol hydrogen bonds. This makes the molecules escape more easily. This pair shows positive deviation. Step 4: Final Answer:
The mixture of Ethanol-Acetone shows positive deviation from Raoult's law.