The depression in freezing points is 0.69 K when 2g phenol is dissolved in 100g benzene. If it is associated as dimeric then find its degree of association. The molal depression constant for solvent is 5.12 K kg `mol^(-1)` (C = 12, H = 1, O = 16g/mol)

Options

A. `0.633`
B. `0.743`
C. `0.367`
D. `0.734`

Answer

C

Explanation

`Delta T_(f)=0.69 K, w_(2)=2g, w_(1)=100 g`,
`M_(2)=94, n = 2, K_(f)=5.12`
`Delta T_(f)=(K_(f)xx 1000xx w_(2)xx i)/(M_(2)xx w_(1))`
`i=(0.69xx94xx100)/(1000xx2xx5.12)=0.633`
`alpha =(1-i)(n)/(n-1)=(1-0.633)xx2=0.733`