Video: The pH of acid phosphate ions

The assumption by most students is that any ‘acid’ anion will be acidic. The dihydrogen phosphate ion is indeed acidic:

H2PO4-(aq) + H2O(l) ? H3O+(aq) + HPO42-(aq)

But the hydrogen phosphate ion is basic:

HPO42-(aq) + H2O(l) ? OH-(aq) + H2PO4-(aq)