H2SO4 is dibasic acid. It ionises in two stages and hence has two dissociation constants as given below:
(i) H2SO4(aq) + H2O(l) → H3O+(aq) + HSO–4(aq) ; Ka1 > 10
(ii) HSO–4(aq) + H2O(l) → H3O+(aq) + SO2-4(aq) ; Ka2 = 1.2 x 10-2
Ka1 is greater than Kay, i.e., tendancy to move towards the products is greater in (i) than in (ii). This is because the negatively charged HSO–4 ion has much less tendancy to donate a proton to H2O as compared to neutral H2SO4.
