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

BaSO4(s)Ba2+(aq)+SO42-(aq)Ksp for BaSO4=[Ba2+][SO42-]=s×s=s2But s=8×10-4 mol dm-3Ksp=(8×10-4)2=64×10-8
In this presence of 0.01 MH2SO4, the expression for Ksp will be
Ksp=[Ba2+][SO42-]Ksp=(s)(s+0.01)       (0.01 M SO42- ions from 0.01 M H2SO4)64×10-8=s·(s+0.01)s2+0.01s-64×10-8=0s=-0.01±(0.01)2+(4×64×10-8)2=-0.01±10-4+(256×10-8)2=-0.01±10-4(1+256×10-4)2=-0.01±10-21+0.02562=10-2(-1±1.012719)2=5×10-3(-1+1.012719)=6.4×10-5 mol dm-3