pH of 0.08 mol dm-3 HOCl solution is 2.85. Calculate its ionisation constant.

pH of HOCl=2.85
But -pH=log [H+]
 -2.85=log [H+]
3¯.15=log [H+]
[H+]=1.413×10-3
For weak monobasic acid [H+]=Ka×C
 Ka=[H+]2C=(1.413×10-3)20.08
=24.957×10-6=2.4957×10-5