The freezing point of a 1.00 m aqueous solution ofHF is found to be `-1.91 ^(@)C.` The freezing point constant of water, K1is `1 .86 K kg mol^(-1)` The percentage dissociation ofHF at this concentration is

Options

A. `30%`
B. `10%`
C. `5.2%`
D. `2.7%`

Answer

D

Explanation

`Delta T_(t)=K_(f) xx m xx i`
`I = (Delta T_(f))/(K _(f) xxm ) = (1.91)/(1.86xx1) =1.02`
For `HI hArr H ^(+) + I ^(-)`
`1- alpha + alpha + alpha =i= 1.027`
`1+ alpha =1.02`
`alpha = 0.02 or 2.7%`