Question

Phenol associates in benzene to a certain extent to form a dimer. A solution containing 20 × 10^-3 kg of phenol in 1.0 kg of benzene has its freezing point depressed by 0.69 K The fraction of phenol that has dimerised is ______. (K_f for benzene = 5.12 K kg mol^-1)

विकल्प

• 0.568

• 0.001

• 0.733

• 0896

Answer 1

Phenol associates in benzene to a certain extent to form a dimer. A solution containing 20 × 10^-3 kg of phenol in 1.0 kg of benzene has its freezing point depressed by 0.69 K The fraction of phenol that has dimerised is 0.733.

Explanation:

Observed Molecular mass

`= (1000 xx k_f xx w)/(w xx Delta "T")`

`= (1000 xx 5.12 xx 20 xx 10^-3)/(1 xx 0.69)`

= 148.4

Normal Molecular mass of phenol = 94

`therefore ("Normal Molecular mass")/("Observed Molecular mass")`

`= 94/148.4 = 0.633`

`= 1 + [1/"n" - 1] alpha = 0.633`

`= 1 + [1/2 - 1] alpha = 0.633`

`=> 1 - alpha/2 = 0.633`

α = 0.733