• The acids and bases come in conjugate pairs.
• The acids donate $H^{+}$ and the bases accept them.
• They only differ by one proton!

Amphiprotic

The substance can act as both an acid and a base. Water as a base: $\text{ce}H2O+HCl->H3O++Cl-$ Water as an acid: $\text{ce}H2O+NH3->NH4++OH-$

Amphoteric

The substance can react with both acids and bases: $\text{ce}ZnO+2HCl->ZnCl2+H2O$ Or: $\text{ce}ZnO+2NaOH+H2O->Na2(Zn(OH)4)$ But remember, Zinc is not donating any protons, so it is not amphiprotic.

Alkalis

Alkalis form $O{H}^{-}$ when put into water.