Molal depression constant for a solvent is $4.0 \mathrm{~K} \mathrm{Kg} \mathrm{mol}^{-1}$. The depression in the freezing point of the solvent for $0.03 \mathrm{~mol} \mathrm{~kg}^{-1}$ solution of $\mathrm{K}_{2} \mathrm{SO}_{4}$ is: (Assume complete dissociation of the electrolyte)

JEE Main · 2019 · 09 Apr 2019 · Shift 2 · Solutions

Molal depression constant for a solvent is

4.0 K Kg mol^{- 1}

. The depression in the freezing point of the solvent for

0.03 mol kg^{- 1}

solution of

K_{2} SO_{4}

is: (Assume complete dissociation of the electrolyte)

(A)0.12 K
(B)0.36 K✓ Correct
(C)0.18 K
(D)0.24 K

Answer: (B)

Solution

Potassium sulphate dissociates completely into three ions, two

K X^{+}

and one

SO X_{4} X^{2 -}

, so its van't Hoff factor is

i = 3

. The freezing-point depression is then

Δ T_{f} = i K_{f} m = 3 \times 4.0 \times 0.03 = 0.36

JEE Main · 2019 · 09 Apr 2019 · Shift 2 · Single correct option

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