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Solutions question

2016 · Shift 2 · Q3
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Solutions question

2016 · Shift 2 · Q3

JEE AdvancedChemistrySolutionsMultiple correct+4 / −2
Mixture (s) showing positive deviation from Raoult’s law at 35oC is (are)
  1. A
    carbon tetrachloride + methanol
  2. B
    carbon disulphide + acetone
  3. C
    benzene + toluene
  4. D
    phenol + aniline
View written solutionFree

Correct answer: A, B

  1. Concept used: Deviation from Raoult’s law

For a liquid mixture:

  • Positive deviation occurs when unlike intermolecular forces AAA–BBB are weaker than like forces AAA–AAA and BBB–BBB.

  • Then the components escape more easily to vapour phase, so vapour pressure is higher than predicted by Raoult’s law.

  • Negative deviation occurs when AAA–BBB interactions are stronger than the pure-component interactions.


  1. 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–CCl4\mathrm{CCl_4}CCl4​ interactions.

Therefore, unlike interactions are weaker.

⇒Positive deviation\Rightarrow \text{Positive deviation}⇒Positive deviation

So, A is correct.


Option B: carbon disulphide + acetone

  • Carbon disulphide CS2\mathrm{CS_2}CS2​ is non-polar (or very weakly interacting).
  • Acetone is polar and has dipole–dipole interactions among its molecules.
  • On mixing, the acetone–CS2\mathrm{CS_2}CS2​ interactions are weaker than acetone–acetone interactions.

Hence the escaping tendency increases.

⇒Positive deviation\Rightarrow \text{Positive deviation}⇒Positive deviation

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.

⇒No significant deviation from Raoult’s law\Rightarrow \text{No significant deviation from Raoult’s law}⇒No significant deviation from Raoult’s law

So, C is not correct.


Option D: phenol + aniline

  • Phenol and aniline can form strong intermolecular hydrogen bonding:
    • phenol provides O−H\mathrm{O-H}O−H
    • aniline has lone pair on nitrogen
  • Thus unlike interactions are stronger than the like interactions.

⇒Negative deviation\Rightarrow \text{Negative deviation}⇒Negative deviation

So, D is not correct.


  1. Final answer

The mixtures showing positive deviation from Raoult’s law are:

A, B\boxed{\text{A, B}}A, B​


  1. Comparison with stored correct answer

Stored correct answer: A, B

My derived answer: A, B

They match.

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