Acid-base equilibria
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i'm really confused about the dissociation of dibasic acids, and consequently what effect does it have on the equilibrium using Le Chatelier?
Ulex writes
When a dibasic acid such as sulphuric acid dissociates, the first proton is easily removed by water. The second proton, however, has to leave a negative ion, HSO4-, and is consequently lost only with difficulty. Sulphuric acid is thus a strong acid as far as its first ionisation is concerned but quite a weak one in its second ionisation.
If you remove hydrogen ions by reaction with, say, hydroxide ions, according to Le Chatelier, more HSO4- dissociates to take the replace of those hydrogen ions which react. This goes on until there is none left. In other words, the sulphuric acid reacts completely with excess sodium hydroxide to give sodium sulphate, but will react with half as much sodium hydroxide to give sodium hydrogensulphate, NaHSO4.
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updated: 27 January 2006
