The molality of a solution made by dissolving 2.5 g of ethanoic acid (CH3COOH) in 75 g of benzene is :

CUET · CHEMISTRY · PYQ PAPER 2025

The molality of a solution made by dissolving 2.5 g of ethanoic acid (CH₃COOH) in 75 g of benzene is :

A 0.432 mol kg^-1
B 0.556 mol kg^-1
C 0.332 mol kg^-1
D 0.752 mol kg^-1

Verified Solution

Answer & Solution

Correct Answer

(B) 0.556 mol kg^-1

Step-by-step Solution

Detailed explanation

\( M(\text{CH}_3\text{COOH}) = 2(12.01) + 4(1.008) + 2(16.00) = 60.052 \text{ g/mol} \) \( n(\text{CH}_3\text{COOH}) = \frac{2.5 \text{ g}}{60.052 \text{ g/mol}} = 0.04163 \text{ mol} \)…

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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Choose the correct answer from the options given below:

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