What are the conjugate acid and base of #H_2PO_4#?

1 Answer
anor277
Aug 25, 2016

Simply add or substract a proton from #H_3PO_4#.

Explanation:

Phosphoric acid is the parent acid, i.e. #H_3PO_4#.

Remove a proton from this, we get, #H_2PO_4^-# as the conjugate base. Or rather phosphoric acid donates a proton to water to give #H_3O^+# and #H_2PO_4^-#.

And remove a proton from #H_2PO_4^-# to get #HPO_4^(2-)# as the conjugate base.

In water that's about as far as you go. But when we speak of conjugate acidity/basicity all we are doing is exchanging protons, #H^+# with the solvent. Mass and charge are conserved, as they must be.

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