Reactions of acids with metals

Acids take part in reactions in which salts are produced. In these reactions, the hydrogen ions in the acids are replaced by metal ions.

Reactions of acids with metals

When acids react with metals, the products are a salt and hydrogen. In general:

Acid + metal → salt + hydrogen

For example:

Hydrochloric acid + magnesium → magnesium chloride + hydrogen

2HCl(aq) + Mg(s) → MgCl2(aq) + H2(g)

Zinc and iron also react with hydrochloric acid.

Magnesium, zinc and iron also react with sulfuric acid. The products are a salt (in this case a sulfate) and hydrogen. For example:

sulfuric acid + iron → iron(II) sulfate + hydrogen

H2SO4(aq) + Fe(s) → FeSO4(aq) + H2(g)


Name the two products of the reaction of zinc with hydrochloric acid.

The products are zinc chloride and hydrogen.


Name the products of the reaction between zinc and sulfuric acid, and write an equation for the reaction.

The products are zinc sulfate and hydrogen.

H2SO4(aq) + Zn(s) → ZnSO4(aq) + H2(g)

Testing for hydrogen gas

Hydrogen gas is highly flammable. You can safely test for small quantities of hydrogen gas (eg collected in a test tube) by holding a burning splint near to the top of the test tube. The positive result is a squeaky pop sound as the hydrogen reacts with oxygen in the air in a small explosion.

Explaining the reactions of acids with metals - Higher

The reactions of acids with metals are redox reactions. For example, the ionic equation for the reaction of magnesium with hydrochloric acid is:

2H+(aq) + Mg(s) → Mg2+(aq) + H2(g)

This ionic equation can be split into two half equations:

  • Mg(s) → Mg2+(aq) + 2e- (oxidation)
  • 2H+(aq) + 2e- → H2(g) (reduction)

Notice that:

Reduction and oxidation happen at the same time, so the reactions are called redox reactions.


Use half equations to explain why the reaction of zinc with sulfuric acid is a redox reaction.

The two half equations are:

  • Zn(s) → Zn2+(aq) + 2e-
  • 2H+(aq) + 2e- → H2(g)

Zinc atoms lose electrons, so they are oxidised. Hydrogen ions gain electrons, so they are reduced. Since reduction and oxidation happen at the same time, the reaction is a redox reaction.