4.2.2 Neutralisation of Acids and Salt Production

When acids react with alkalis (such as soluble metal hydroxides), bases (such as insoluble metal hydroxides and metal oxides), or metal carbonates, neutralisation occurs. This process results in the production of salts, water, and in the case of metal carbonates, carbon dioxide.

The specific salt formed in a reaction between an acid and a base, alkali, or carbonate depends on two factors:

• The type of acid used: Different acids will produce salts with specific anions. For example, hydrochloric acid (HCl) produces chlorides, nitric acid (HNO₃) produces nitrates, and sulfuric acid (H₂SO₄) produces sulfates.
• The positive ions present in the base, alkali, or carbonate: The specific cation from the base, alkali, or carbonate will combine with the anion from the acid to form the salt.

Predicting Products of a Neutralisation Reaction

Predicting the products of a neutralisation reaction given the reactants involves understanding the concept of ionic bonding and the formation of salts. By examining the reactants in a neutralisation reaction, you should be able to determine the combination of ions that will form the resulting salt.

For example, when an acid reacts with an alkali, such as hydrochloric acid (HCl) reacting with sodium hydroxide (NaOH), the hydrogen ions (H⁺) from the acid combine with the hydroxide ions (OH^-) from the alkali to form water (H₂O). The remaining ions, sodium (Na⁺) and chloride (Cl^-), combine to form the salt sodium chloride (NaCl).

Deducing the Formulae of Salts

By combining the correct ratio of positive and negative ions, you can determine the formula of the salt produced.

For example, when sulfuric acid (H₂SO₄) reacts with calcium hydroxide (Ca(OH)₂), the hydrogen ions (H⁺) from the acid combine with the hydroxide ions (OH^-) from the base to form water (H₂O). The remaining ions, calcium (Ca²⁺) and sulfate (SO₄^2-), combine to form the salt calcium sulfate (CaSO₄).