# What is the conjugate base of HPO4^2-?

The conjugate base of a species is simply the acid less a ${H}^{+}$ species.
So what is the creature we get when we take ${H}^{+}$ from biphosphate ion, $H P {O}_{4}^{2 -}$. When you do this operation, remember you must conserve both MASS and CHARGE.