How acids react
Acids react in four characteristic ways.
With metals — hydrogen
A dilute acid reacts with a metal above hydrogen in the activity series, such as magnesium, to give a salt of the metal and hydrogen gas.
Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)
With carbonates — carbon dioxide
In the laboratory, carbon dioxide is made by adding dilute hydrochloric acid to calcium carbonate. Giving carbon dioxide with a carbonate or hydrogencarbonate is a characteristic property of an acid.
CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + H2O (l) + CO2 (g)
With bases — a salt and water
Acids react with bases to form a salt and water. Sulphuric acid and sodium hydroxide give sodium sulphate:
H2SO4 (aq) + 2NaOH (aq) → Na2SO4 (aq) + 2H2O (l)
With litmus
Acids turn blue litmus red. This is a simple test for an acid.