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ChemistryInteger+4 / -1Question 83 of 90

JEE Main 2022 · 29 Jun · Shift 1, Chemistry question 83

1.2 mL of acetic acid is dissolved in water to make 2.0 L of solution. The depression in freezing point observed for this strength of acid is 0.0198°C. The percentage of dissociation of the acid is ______. (Nearest integer)

[Given : Density of acetic acid is 1.02 g mL−1^{-1}; Molar mass of acetic acid is 60 g mol−1^{-1}; Kf(H2O)=1.85K_f(\mathrm{H_2O})=1.85 K kg mol−1^{-1}]

Answer and worked solution

Official answer: 5

Molality. 1.2×1.0260=0.0204\frac{1.2\times1.02}{60}=0.0204 mol in about 2 kg water: 0.0102 m; expected ΔTf=1.85×0.0102=0.01887\Delta T_f=1.85\times0.0102=0.01887.

van 't Hoff factor. i=0.01980.01887≈1.05i=\frac{0.0198}{0.01887}\approx1.05, so about 5% dissociated.

Answer: 5

Topics:van't Hoff factorColligative properties
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