Zat amfoter adalah zat yang dapat bertindak sebagai asam dan basa.
\(\ce{H2PO4-}\) sebagai asam
\(\ce{$\underset {\text{Asam}} {\ce{H2PO4-}}$ + $\underset{\text{Basa}}{\ce{OH-}}$ <=> $\underset {\text{Basa konjugasi}} {\ce{HPO4^{2-}}}$ + $\underset{\text{Asam konjugasi}}{\ce{H2O}}$}\)
\(\ce{H2PO4-}\) sebagai basa
\(\ce{$\underset {\text{Basa}} {\ce{H2PO4-}}$ + $\underset{\text{Asam}}{\ce{HBr}}$ <=> $\underset {\text{Asam konjugasi}} {\ce{H3PO4}}$ + $\underset{\text{Basa konjugasi}}{\ce{Br-}}$}\)
\(\ce{H2O}\) sebagai asam dan basa
\(\ce{$\underset {\text{Asam}} {\ce{H2O}}$ + $\underset {\text{Basa}} {\ce{H2O}}$ <=> $\underset {\text{Basa konjugasi}} {\ce{OH-}}$ + $\underset {\text{Asam konjugasi}} {\ce{H3O+}}$}\)
\(\ce{NH3}\) sebagai asam dan basa
\(\ce{$\underset {\text{Asam}} {\ce{NH3}}$ + $\underset {\text{Basa}} {\ce{NH3}}$ <=> $\underset {\text{Basa konjugasi}} {\ce{NH4+}}$ + $\underset {\text{Asam konjugasi}} {\ce{NH2-}}$}\)