# What are the "conjugate acids" of HO^-, HCO_3^(-), HPO_4^(2-), and CO_3^(2-) ions?

For the conjugate acid, simply add a ${H}^{+}$ unit to the starting material. Mass and charge are conserved, i.e:
$H P {O}_{4}^{2 -} + {H}^{+} \rightarrow {H}_{2} P {O}_{4}^{-}$