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CUET · CHEMISTRY · PYQ PAPER 2023

0.5 molal aqueous solution of a weak acid (HX) is 20% ionised.
If \(\text{K}_\text{f}\) for water is 1.86 \(\text{K kg mol}^{-1}\) the lowering in freezing point of solution will be:

  1. A \(0.56\text{K}\)
  2. B \(1.12\text{K}\)
  3. C \(-0.56\text{K}\)
  4. D \(-1.12\text{K}\)
Verified Solution

Answer & Solution

Correct Answer

(B) \(1.12\text{K}\)

Step-by-step Solution

Detailed explanation

\(i = 1 + (n-1)\alpha\) \(i = 1 + (2-1) \times 0.20 = 1.20\) \(\Delta T_f = i \cdot K_f \cdot m\) \(\Delta T_f = 1.20 \times 1.86 \text{ K kg mol}^{-1} \times 0.5 \text{ mol kg}^{-1} = 1.116 \text{ K}\) \(\Delta T_f \approx 1.12 \text{ K}\)
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