Question

0.5 molar aqueous solution of a weak acid (HX) is 20% ionised. If `K_(f)` for water is `1.86 K kg mol^(-1)`, the lowering in freezing point of the solution is
A. `-0.56K`
B. `-1.12K`
C. `0.56K`
D. `1.12K`

Answer 1

Correct Answer - D
`{:(,"HX",hArr,H^(+)+,X^(-)),("Initial","1 mole",,,),("After ionization",1-a,,a,a):}`
Total no. of moles at equilibrium `= 1+ alpha`
`:. i=1 +a = 1+ 0.20 = 1.20`
`Delta T_(f) = iK_(f)m`
`=1.20 xx 1.80 xx 0.5 = 1.20K`.