The dissociation constants of H2S and HS–1 are respectively 10–7 and 10–13. The PH of the aqueous solution containing 0.2 mole of H2S dissolved in 1 lit water is

In case of weak diprotic acid, the H+ ions are mainly contributed in the first dissociation step.Neglecting x in front of C0 and y infront of xPH = 4 - log 1.414 ~ 4.