JEE AdvancedChemistrySolutionsMultiple correct+4 / −2
Mixture (s) showing positive deviation from Raoult’s law at 35oC is (are)
- Acarbon tetrachloride + methanol
- Bcarbon disulphide + acetone
- Cbenzene + toluene
- Dphenol + aniline
View written solutionFree
Correct answer: A, B
- Concept used: Deviation from Raoult’s law
For a liquid mixture:
-
Positive deviation occurs when unlike intermolecular forces – are weaker than like forces – and –.
-
Then the components escape more easily to vapour phase, so vapour pressure is higher than predicted by Raoult’s law.
-
Negative deviation occurs when – interactions are stronger than the pure-component interactions.
- Check each option
Option A: carbon tetrachloride + methanol
- Methanol has strong hydrogen bonding among its own molecules.
- Carbon tetrachloride is non-polar and cannot form hydrogen bonds with methanol.
- On mixing, strong methanol–methanol interactions are disrupted and replaced partly by weaker methanol– interactions.
Therefore, unlike interactions are weaker.
So, A is correct.
Option B: carbon disulphide + acetone
- Carbon disulphide is non-polar (or very weakly interacting).
- Acetone is polar and has dipole–dipole interactions among its molecules.
- On mixing, the acetone– interactions are weaker than acetone–acetone interactions.
Hence the escaping tendency increases.
So, B is correct.
Option C: benzene + toluene
- Benzene and toluene are both non-polar aromatic liquids.
- Their intermolecular interactions are very similar.
- Such mixtures are nearly ideal.
So, C is not correct.
Option D: phenol + aniline
- Phenol and aniline can form strong intermolecular hydrogen bonding:
- phenol provides
- aniline has lone pair on nitrogen
- Thus unlike interactions are stronger than the like interactions.
So, D is not correct.
- Final answer
The mixtures showing positive deviation from Raoult’s law are:
- Comparison with stored correct answer
Stored correct answer: A, B
My derived answer: A, B
They match.
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