MHT CET · Chemistry · Solutions

What is the molar mass of solute when 2.3 gram non-volatile solute dissolved in 46 gram benzene at \(30^{\circ} \mathrm{C}\) ?
(Relative lowering of vapour pressure is 0.06 and molar mass of benzene is 78 gram mol\(^{-1}\) )

A 65 gram mol\({ }^{-1}\)
B \(80 \mathrm{gram} \mathrm{mol}^{-1}\)
C 72 gram mol\({ }^{-1}\)
D \(48 \mathrm{gram} \mathrm{mol}^{-1}\)

Verified Solution

Answer & Solution

Correct Answer

(A) 65 gram mol\({ }^{-1}\)

Step-by-step Solution

Detailed explanation

\(\begin{aligned} & \frac{\Delta \mathrm{P}}{\mathrm{P}_{\mathrm{A}}^0}=\frac{\mathrm{n}_{\mathrm{B}}}{\mathrm{n}_{\mathrm{A}}}=\frac{\mathrm{W}_{\mathrm{B}}}{\mathrm{M}_{\mathrm{B}}} \times \frac{\mathrm{M}_{\mathrm{A}}}{\mathrm{W}_{\mathrm{A}}} \\ & 0.06=\frac{2.3}{\mathrm{M}_{\mathrm{B}}} \times \frac{78}{46}\end{aligned}\)
\(M_B=65\)

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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What is the molar mass of solute when 2.3 gram non-volatile solute dissolved in 46 gram benzene at \(30^{\circ} \mathrm{C}\) ?(Relative lowering of vapour pressure is 0.06 and molar mass of benzene is 78 gram mol\(^{-1}\) )

Step-by-step Solution

What is the molar mass of solute when 2.3 gram non-volatile solute dissolved in 46 gram benzene at \(30^{\circ} \mathrm{C}\) ?
(Relative lowering of vapour pressure is 0.06 and molar mass of benzene is 78 gram mol\(^{-1}\) )