Most compounds behave either just as acids or just as bases no matter what other
chemical species are in solution. However, a handful of molecules/ions can act
as either acids or bases. They elect to either donate or accept H+(aq) in response
to whatever else is in solution; these are called amphoteric molecules/ions. One
example of an amphoteric ion is the bicarbonate ion, HCO 3 −(aq).
In acidic solutions, the following reaction occurs:
HCO 3 −(aq) + H+(aq) → H 2 CO 3 (aq)While in basic solutions, the following reaction takes place:
HCO 3 −(aq) + OH−(aq) → CO 3 2−(aq) + H 2 O(l)Strong Acids and Bases
Acids and bases that dissociate completely and stay dissociated are referred to as
strong acids and bases. The term strong is NOT used as a common adjective in
acid-base chemistry; it has a very specific meaning. It means completely
dissociating. For example, HCl is a strong acid, and NaOH is a strong base.
HCl(aq) → H+(aq) + Cl−(aq)NaOH(aq) → Na+(aq) + OH−(aq)In the case of strong acids and bases, dissociation is considered 100 percent and
irreversible, so a one-way reaction arrow is used in reactions of strong acids and
bases. (Keep this in mind when you’re asked to calculate the pH of strong acid-
base solutions; it makes the math simpler.)
For the test, you MUST memorize the following list of strong acids and bases:
Strong Acids
HCl hydrochloric acid
HBr hydrobromic acid
HI hydroiodic acid
HNO 3 nitric acid