Phenol associates in Benzene to a certain extent to form dimer. A solution containing 2.0 × 1 0 - 2 kg of…

Phenol associates in Benzene to a certain extent to form dimer. A solution containing  2.0 × 1 0 - 2  kg  of Phenol in 1.0 kg of benzene has its freezing point decreased by 0.69 K. The percentage degree of association of Phenol is K f for benzene =5.12 K  kg mol −1
  1. 73.4
  2. 50.1
  3. 42.3
  4. 25.1

Solution

Weight of Phenol w A =2.0× 10 −2  kg=20 g

Weight of Benzene w B =1.0 kg

Δ T i =0.69 K           K f =5 .12 K kg mol −1

Δ T f = i K f m

i= Δ T f K f m = 0.69 5.12× 20 94 = 0.69×94 5.12×20 ,  i=0.63

2 A ⇌ A 2 1 - x x / 2

Particle after association   i  = 1 - x + x / 2 = 1 - x / 2

i = 1 - x / 2

0.63 = 1- x 2 x ⇒ 0.734  i.e., 73.4 %
 

Asked in: JEE-TOPICTESTS-CHEMISTRY

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