JEE Main 2019 Chemistry question
Molecules of benzoic acid (CHCOOH) dimerise in benzene. 'w' g of the acid dissolved in 30 g of benzene shows a depression in freezing point equal to 2 K. If the percentage association of the acid to form dimer in the solution is 80, then w is: (Given that = 5 K kg mol, Molar mass of benzoic acid = 122 g mol)
Answer: (D)
Solution
i = 1 − 0.8 + 0.4 = 0.6; 2 = 0.6 × 5 × (w/122)/0.030 ⇒ w ≈ 2.4 g.