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JEE Mains · Chemistry · STD 12 -1. Solution and colligative properties

Considering acetic acid dissociates in water, its dissociation constant is \(6.25 \times 10^{-5}\). If \(5 \mathrm{~mL}\) of acetic acid is dissolved in \(1\) litre water, the solution will freeze at \(-\mathrm{x} \times 10^{-2}{ }^{\circ} \mathrm{C}\), provided pure water freezes at \(0^{\circ} \mathrm{C}\). \(\mathrm{x}=\) _______ (Nearest integer) Given : \(\left(\mathrm{K}_{\mathrm{r}}\right)_{\text {water }}=1.86 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}\). density of acetic acid is \(1.2 \mathrm{~g} \mathrm{~mol}^{-1}\) molar mass of water \(=18 \mathrm{~g} \mathrm{~mol}^{-1}\). molar mass of acetic acid \(=60 \mathrm{~g} \mathrm{~mol}^{-1}\). density of water \(=1 \mathrm{~g} \mathrm{~cm}^{-3}\) Acetic acid dissociates as \(\mathrm{CH}_3 \mathrm{COOH} \rightleftharpoons \mathrm{CH}_3 \mathrm{COO}^{\oplus}+\mathrm{H}^{\oplus}\)

  1. A \(19\)
  2. B \(20\)
  3. C \(25\)
  4. D \(30\)
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Answer & Solution

Correct Answer

(A) \(19\)

Step-by-step Solution

Detailed explanation

\(\text { Mass of } \mathrm{CH}_3 \mathrm{COOH}=\mathrm{V} \times \mathrm{d}\) \(=5 \mathrm{ml} \times 1.2 \mathrm{~g} / \mathrm{ml}\) \(=6 \mathrm{gm}\) \(\mathrm{n}_{\mathrm{CH}_3 \mathrm{COOH}}=\frac{6}{60}=0.1 \mathrm{~mol}\)…
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