Question

Is Acetic acid a strong acid or a weak acid?

Answer 1

Hint: Use the Arrhenius Acid-base theory to determine the strength of acetic acid. Write down the dissociation reaction of acetic acid and compare it with those of mineral acids to find out its relative strength in aqueous medium.

Complete answer:
According to the Arrhenius Acid-base theory, any chemical compound that releases hydrogen ions(or protons) in aqueous solutions is called an acid and the one that releases hydroxide ions in aqueous solution is called a base.
The strength of an Arrhenius acid is determined by the amount of hydrogen ions \[{H^ + }\] released and that of an Arrhenius base is determined by the amount of hydroxide ions \[O{H^ - }\] released by it. The higher the amount of \[{H^ + }\] ions released, lower will the pH and stronger will be the acid. The higher the amount of \[O{H^ - }\] ions released, higher will be the pH and stronger will be the base.
In order to be a strong acid and release sufficient amounts of \[{H^ + }\] ions in the solution, the acid must dissociate completely into its ions. Partial dissociation of an acid makes it a weak Arrhenius acid.
\[HA(aq) \to {H^ + } + {A^ - }{\text{ (strong acid)}}\]
\[HA(aq) \rightleftharpoons {H^ + } + {A^ - }{\text{ (weak acid)}}\]
The partial dissociation in case of weak acids leads to an equilibrium between the dissociated ions and the acid which limits the amount of \[{H^ + }\] being released.
According to this theory mineral acids like hydrochloric acid \[(HCl)\] and sulphuric acid \[({H_2}S{O_4})\] are strong acids that undergo complete dissociation in aqueous medium.
But Acetic acid is an organic acid that shows only partial dissociation and releases a very small amount of \[{H^ + }\] ions in the aqueous medium. The \[{H^ + }\] and (acetate) \[C{H_3}CO{O^ - }\] ions are always in equilibrium with the acid.
\[C{H_3}COOH(aq) \rightleftharpoons {H^ + } + C{H_3}CO{O^ - }{\text{ (partial dissociation)}}\]
Thus acetic acid is a weak Arrhenius acid.

Note:
The acidic strength of acetic acid is compared with mineral acids on the basis of Arrhenius theory and it is therefore a weak acid. On comparing acetic acid with other organic molecules, we find that acetic acid is one of the strongest organic acids known.