What is a substance that can behave as an acid or a base?

2 Answers
Dec 7, 2016




These substances are called amphiprotic. Water, amino acids, hydrogen carbonate ions, and hydrogen sulfate ions are common examples.

Hope this helps :)

Dec 23, 2016


Technically, a substance that can behave as an acid or a base is amphoteric.


A substance is amphoteric (from Greek amphoteros = "each of two") if it can act as an acid or a base.

For example, aluminum hydroxide is amphoteric because it can act as a base and neutralize strong acids.

#underbrace("Al(OH)"_3)_color(red)("base") + underbrace("3HCl")_color(red)("acid") → "AlCl"_3 + "3H"_2"O"#

It can also act as an acid and neutralize strong bases:

#underbrace("Al(OH)"_3)_color(red)("acid") + underbrace("3NaOH")_color(red)("base") → "Na"_3"AlO"_3 + "3H"_2"O"#

A substance is amphiprotic (Greek "both" + "proton") if it is able both to donate and accept a proton (i.e. to act as a Brønsted-Lowry acid or base).

One example of an amphiprotic compound is the hydrogen sulfate ion, #"HSO"_4^"-"#.

It can act as an acid by donating a proton:

#underbrace("HSO"_4^"-")_color(red)("proton donor") + underbrace("H"_2"O")_color(red)("proton acceptor") ⇌ "SO"_4^"2-" + "H"_3"O"^"+"#

It can also act as a base by accepting a proton:

#underbrace("HSO"_4^"-")_color(red)("proton acceptor") + underbrace("H"_3"O"^"+")_color(red)("proton donor") → "H"_2"SO"_4 + "H"_2"O"#

NOTE: All amphiprotic substances are also amphoteric, but not all amphoteric substances are amphiprotic.

Nevertheless, many chemists ignore the distinction and use the term "amphoteric" for all cases.