CBSE Class 12 Chemistry 2026: question 24

Hints

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Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

1. For dimerisation $2{\mathrm{C}}_6{\mathrm{H}}_5\mathrm{COOH}\rightleftharpoons ({\mathrm{C}}_6{\mathrm{H}}_5\mathrm{COOH}{)}_2$ with $\alpha =0.88$:
   $i=1-\alpha +\frac{\alpha }{2}=1-\frac{\alpha }{2}=1-0.44=0.56$

   ½ mark

2. Molality: $m=\frac{0.61/122}{5/1000}=\frac{0.005\text{mol}}{0.005\text{kg}}=1\mathrm{mol}\mathrm{k}{\mathrm{g}}^{-1}$

   ½ mark

3. $\Delta T_b=i{K}_{b}m=0.56\times 2.3\times 1=1.288\text{K}$

   1 mark

4. Boiling point of the solution $=46.2+1.288=47.488{}^{\circ }\mathrm{C}\approx 47.49{}^{\circ }\mathrm{C}$

   1 mark

Answer: Boiling point ≈ 47.49 °C (ΔT_b = 1.288 K, i = 0.56)

Revise the chapter

• Chapter: Solutions (notes, formulas, where marks are lost and every past question)
• Topic: Elevation of Boiling Point and Depression of Freezing Point