NEET · Chemistry · STD 12 -1. Solution and colligative properties

Which of the following statements about the composition of the vapour over an ideal \(1: 1\) molar mixture of benzene and toluene is correct ? Assume that the temperature is constant at \(25\,^o C\). (Given, vapour pressure data at \(25\,^oC\), benzene \(= 12.8\, kPa,\) toluene \(= 3.85 \,kPa)\)

A The vapour will contain equal amounts of benzene and toluene.
B Not enough information is given to make a prediction.
C The vapour will contain a higher percentage of benzene.
D The vapour will contain a higher percentage of toluene.

Verified Solution

Answer & Solution

Correct Answer

(C) The vapour will contain a higher percentage of benzene.

Step-by-step Solution

Detailed explanation

\(\mathrm{V} . \mathrm{P}\) of \(\mathrm{C}_{6} \mathrm{H}_{6}>\mathrm{V} . \mathrm{P}\) of \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{3}\) \(\because \mathrm{YA}=\frac{\mathrm{P}^{o} \mathrm{A} \mathrm{X} \mathrm{A}}{\mathrm{P}}, \mathrm{YB}=\frac{\mathrm{P}^{o} \mathrm{BXB}}{\mathrm{P}}\)

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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