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QJEEM19Ch42f1: JEE Main 2019 Chemistry - Class 12 JEEM19Ch42f1 Solution: Molecules of benzoic acid (C 6 H 5 COOH) dimerise in benzene.…

Molecules of benzoic acid (C6H5COOH) dimerise in benzene. 'w' g of the acid dissolved in 30 g of benzene shows a depression in freezing point equal to 2K. If the percentage association of the acid to form dimmer in the solution is 80, then w is – (Its given that Kf = 5 K kg mol–1, Molar mass of benzoic acid = 122 g mol–1)

Multiple Choice Options

  • A 1.5 g
  • B 1.8 g
  • C 1.0 g
  • D 2.4 g

Step-by-Step Verified Solution

JEE Main 2019 (Online) 12th January Evening Slot Chemistry - Solutions Question 116 English Explanation
We know,

ΔTf = i Kf × wM×1000ws

i = 1 + α(1n−1)

Here Benzoic acid dimerise, so value of n = 2

∴  i = 1 + 0.8 (12−1)

= 1 − 0.4

= 0.6

∴  2 = 0.6 × 5 × w122×100030

⇒  w = 2.44 g

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