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 Calculate the fraction of phenol that has dimerised. (Kf for benzene = 5.12 K kg mol-1)

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 Calculate the fraction of phenol that has dimerised. (Kf for benzene = 5.12 K kg mol-1) (A) 28.5 % (B) 32.6 % (C) 73.3 % (D) 82 %

Tardigrade Admin · Accepted Answer

Observed mol. mass =(1000× Kf× w/W×Δ Tf) =(1000×5.12×20×10-3/1×0.69)=148.4 Normal mol. mass of phenol = 94 i=( textNormal mol. mass/ textObserved mol. mass)=(94/148.4)=0.633 Since, phenol is dimerized ∴ n=2 Also, i=1+[(1/n)-1]α=1+[(1/2)-1]α=1-(α/2) ⇒ 0.633=1-(α/2) ⇒ (α/2)=0.367 ⇒ α=0.733 α=0.733×100=73.3 %

Q. Phenol associates in benzene to a certain extent to form a dimer. A solution containing $20 \times 1 0^{- 3} k g$ of phenol in $1.0 k g$ of benzene has its freezing point depressed by $0.69 K$ Calculate the fraction of phenol that has dimerised. $(K_{f}$ for benzene $= 5.12 K k g m o l^{- 1})$

$28.5%$

$32.6%$

$73.3%$

$82%$

Q. Phenol associates in benzene to a certain extent to form a dimer. A solution containing 20×10−3kg of phenol in 1.0kg of benzene has its freezing point depressed by 0.69K Calculate the fraction of phenol that has dimerised. (Kf​ for benzene =5.12Kkgmol−1)

28.5%

32.6%

73.3%

82%

Q. Phenol associates in benzene to a certain extent to form a dimer. A solution containing $20 \times 1 0^{- 3} k g$ of phenol in $1.0 k g$ of benzene has its freezing point depressed by $0.69 K$ Calculate the fraction of phenol that has dimerised. $(K_{f}$ for benzene $= 5.12 K k g m o l^{- 1})$

$28.5%$

$32.6%$

$73.3%$

$82%$