3.11 - Reactions of acids

Naming the salt

In these reactions, the salt contains the metal ion from the metal or metal compound and the negative ion from the acid. An aqueous acid is dissolved in water.

For example, zinc oxide and nitric acid produce zinc nitrate: zinc supplies the first part of the name and nitric acid supplies the nitrate part. Naming the salt does not yet tell you the other products; those depend on the other reactant's family.

Metals release hydrogen

A suitable reactive metal with dilute hydrochloric acid or dilute sulfuric acid gives a salt and hydrogen:

acid + metal → salt + hydrogen

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)

Hydrogen ions from the acid gain electrons from the metal and form hydrogen molecules. The metal forms positive ions in the salt. You may observe the metal getting smaller and bubbles of gas.

The conditions matter. Metals below hydrogen in the reactivity series, such as copper, do not displace hydrogen from these dilute acids. Nitric acid and concentrated sulfuric acid need different reaction rules; do not automatically apply the hydrogen pattern to them.

Oxides and hydroxides form water

Basic metal oxides and hydroxides react with acids to form salt and water:

acid + metal oxide → salt + water

acid + metal hydroxide → salt + water

CuO(s) + H₂SO₄(aq) → CuSO₄(aq) + H₂O(l)

NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)

Here the oxide or hydroxide reacts with hydrogen ions to make water; no hydrogen gas is produced. An insoluble oxide such as copper(II) oxide can disappear as it reacts, while the soluble salt remains in solution. A soluble hydroxide is an alkali, but insoluble hydroxides can also react with acids.