75.2 ~g of C ₆ H ₅ OH (phenol) is dissolved in a solvent of K_f=14 . If the depression in freezing point is 7 ~K , then find the % of phenol that dimerises.

Step-by-step solution

Phenol is dimerised as follows At t=0 2 C ₆ H ₅ OH ( C ₆ H ₅ OH )₂ At equilibrium (1- ) / 2 Total moles after dimerisation =1- + / 2=1- / 2 aligned Van't Hoff factor (i) & = Normal molecular wt. of phenol Abnormal molecular wt. of phenol = 94 m_ a b m_ a b & = 1000 K_f w T_f W aligned Given that aligned & K_f=14 & w=72.5 gm & W=1000 gm & m_ a b = 1000 14 72.5 7 1000 =145 & aligned i= 94 145 (i) = No. of particles after dimerisation No. of particles before dimerisation = 1- / 2 1 From eq. (i) and (ii) aligned 1- / 2