An acid is a substance that dissociates in water to give Hydrogen ions (H+) as the only positively charged ions.

An acid is any substance that contains a hydrogen ion which is partly or wholly replaced by a metal or a non-metallic radical with the formation of a salt.

An acid can also be defined as a proton donor; this is according to J. N. Bronsted from Denmark and J. M. Lawry from England.

Properties of acids

Acids react with metals to liberate;

  • A salt
  • Hydrogen gas

Magnesium + hydrochloric acid                                              magnesium chloride + hydrogen gas

+                                                                                            +

Magnesium + ethanoic acid                                                magnesium ethanoate + Hydrogen gas

+    2                                                                     ( +

Magnesium + sulphuric VI acid                                           magnesium sulphate +hydrogen gas

+    SO4                                                                              MgSO4    + H2

Magnesium + ethanedioic acid                                              magnesium oxalate +   hydrogen gas

Mg             +   H2C2O4                                                                             MgC2O4   + H2

The Hydrogen gas is formed when hydrogen ions present in the solution are displaced by the Mg.

The salt formed depends on the metal and acid. For example, when zinc metal reacts with hydrochloric acid, zinc chloride is formed.

Zinc metal +    hydrochloric acid                                      zinc chloride + Hydrogen gas

In this reaction, zinc combines with the chloride ion from hydrochloric acid to form zinc chloride

When copper metal reacts with nitric acid, copper nitrate is formed.

Copper metal   + nitric acid                                             copper nitrate +    Hydrogen gas

In this reaction copper combines with the nitrate ion from nitric acid to form copper nitrate.


  1. Acids react with carbonates to form a salt and carbon IV Oxide(CO2)

When a metal carbonate is placed in an acid, there is effervescence, evidence that a gas is produced. This gas is carbon dioxide (CO2).


When a metal carbonate is placed in an acid, effervescence occurs. In this reaction, three products are formed:

  • A salt
  • Water
  • Carbon dioxide (CO2)

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