Acidity and Protolytic Equilibria

Orthophosphoric acid is a medium-strength proton donor. On a large scale in a dilute aqueous solution, only the first proton is dissociated [3-5]  

At a comjxrsition of 7 wf% P2O5 (10 wl% H JPO4), a degree of dissociation of about 16% is reached. In contrast, diphosphoric acid is a strong proton donor. It exceeds orthophosphoric acid by one order of magnitude when comparing the equihbrium constants Ka (see Table 12.1)  

In concentrated aqueous solutions, above 61.6 wl% P2O5 (85 wt% H3P04),theratio between water and phosphoric add molecules is 1. In such highly concentrated solutions autoprotolysis also takes place [8]  

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