CUET · CHEMISTRY · PYQ PAPER 2025

Calculate the molality of KI if the density of 20% (mass/mass) aqueous solution of KI is 1.202 g mL^-1.
(Molar mass of KI is 166 g mol^-1)

A 1.5 mol kg^-1
B 1.2 mol kg^-1
C 15 mol kg^-1
D 0.12 mol kg^-1

Verified Solution

Answer & Solution

Correct Answer

(A) 1.5 mol kg^-1

Step-by-step Solution

Detailed explanation

Mass of KI \( = 20 \text{ g} \) Mass of solvent \( = 100 \text{ g} - 20 \text{ g} = 80 \text{ g} = 0.080 \text{ kg} \) Moles of KI \( = \frac{20 \text{ g}}{166 \text{ g mol}^{-1}} \approx 0.1205 \text{ mol} \) Molality…

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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Calculate the molality of KI if the density of 20% (mass/mass) aqueous solution of KI is 1.202 g mL-1.(Molar mass of KI is 166 g mol-1)

Step-by-step Solution

Calculate the molality of KI if the density of 20% (mass/mass) aqueous solution of KI is 1.202 g mL^-1.
(Molar mass of KI is 166 g mol^-1)