Question

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

Answer 1

Before answering this question, we should know A molecule or ion which reacts with both acid as an acid and as a base are amphoteric substances. The derivation of the word amphoteric comes from the Greek word Amphi i.e both.

Complete answer:
Amphiprotic molecules are those which can donate or accept a (${{H}^{+}}$) proton. An example of an amphiprotic is a Hydrogen sulfate ion.
It acts as an acid by giving up proton:
$HSO_{4}^{-}+{{H}_{2}}O\to S{{O}_{2}}^{2-}+{{H}_{3}}{{O}^{+}}$
It accepts a proton and acts as a base:
$HS{{O}_{4}}^{-}+{{H}_{3}}{{O}^{+}}\to {{H}_{2}}S{{O}_{4}}+{{H}_{2}}O$
Amphoteric oxides are the oxides that react with both acids and bases as well to form salts and water. Zinc, tin, lead, aluminum, and beryllium are some metals that produce amphoteric oxides or hydroxides. The oxidation state of oxides decides the amphoterism. One example of amphoteric oxides is $A{{l}_{2}}{{O}_{3}}$. Other examples are Lead(II) oxide, zinc(II) oxide, etc.
Let’s see one more example-
$Al{{(OH)}_{3}}$: Aluminium hydroxide is an Amphoteric
It acts as a base and neutralizes strong acids
$Al{{(OH)}_{3}}$+ 3HCl$\to AlC{{l}_{3}}+3{{H}_{2}}O$
It acts as an acid and neutralizes strong bases
$Al{{(OH)}_{3}}$+ 3NaOH$\to N{{a}_{3}}Al{{O}_{3}}+3{{H}_{2}}O$
They are one of the amphoteric species. Amino acids, proteins, and water are examples, It involves amine and carboxylic acids groups. Water is a self ionizable compound.
Not all amphoteric substances are amphiprotic but all amphiprotic substances are amphoteric.
Amphoteric is a substance that can behave as an acid and base.

Note:
The amphoteric molecules that have both acidic and basic groups are ampholytes. It exists as zwitterions in a specific range of pH. The isoelectronic point of a molecule is the pH in which the average charge is zero. A stable pH gradient is established for use by ampholytes.