Neutralisation of Acids and Salt Production (AQA GCSE Chemistry)

Acid-base reactions

• When an acid reacts with a base, a neutralisation reaction occurs

• A base is a chemical that neutralises acids

• Examples of bases include:

  • Metal oxides, e.g. copper(II) oxide, Cu₂O

  • Metal hydroxides, e.g. sodium hydroxide, NaOH

  • Metal carbonates, e.g. calcium carbonate, CaCO₃ 

• Bases have pH values above 7

• Many bases are insoluble in water

• Some bases dissolve in water and are called alkalis because they form an alkaline solution

  • Examples of alkalis are soluble metal hydroxides such as sodium hydroxide, NaOH (aq), and calcium hydroxide, Ca(OH)₂ (aq)

Neutralisation reactions

• In all acid-base neutralisation reactions, salt and water are produced:

acid + base ⟶ salt + water

• If the base is a metal carbonate, carbon dioxide is also produced:

acid + base ⟶ salt + water + carbon dioxide

• The identity of the salt produced depends on the acid used and the positive ions in the base

  • Hydrochloric acid produces chlorides

  • Sulfuric acid produces sulfate

  • Nitric acid produces nitrates

Table salt / sodium chloride

Sodium chloride is commonly known as table salt and can be formed from a neutralisation reaction

Photo by Chemical Safety Facts

Reactions of acids with metal oxides

• Metal oxides also act as bases by reacting with acids in a neutralisation reaction to produce the corresponding metal salt and water

• The following are some specific examples of reactions between acids and metal oxides:

2HCl + CuO ⟶ CuCl₂ + H₂O

H₂SO₄ + Na₂O⟶ Na₂SO₄ + H₂O

2HNO₃ + MgO ⟶ Mg(NO₃)₂ + H₂O

Reactions of acids with metal hydroxides

• Metal hydroxides also act as bases by reacting with acids in a neutralisation reaction to produce the corresponding metal salt and water

• The following are some specific examples of reactions between acids and metal hydroxides:

2HCl + 2LiOH ⟶ 2LiCl + H₂O

H₂SO₄ + 2NaOH ⟶ Na₂SO₄ + 2H₂O

HNO₃ + KOH ⟶ KNO₃ + H₂O

Reactions of acids with metal carbonates

• Metal carbonates act as bases by reacting with acids in a neutralisation reaction to form the corresponding metal salt, carbon dioxide and water

• These reactions are easily distinguishable from acid – metal oxide/hydroxide reactions due to the effervescence caused by the release of carbon dioxide gas

  • We can test for the presence of carbon dioxide gas by bubbling it through limewater

  • If the limewater turns milky or cloudy carbon dioxide is present

• The following are some specific examples of reactions between acids and metal carbonates:

2HCl + Na₂CO₃ ⟶ 2NaCl + H₂O + CO₂

H₂SO₄ + CaCO₃⟶ CaSO₄ + H₂O + CO₂

2HNO₃ + MgCO₃ → Mg(NO₃)₂ + H₂O + CO₂

Predicting the salts

• The name of a salt has two parts

  • The first part comes from the metal, metal oxide or metal carbonate used in the reaction

  • The second part comes from the acid

• Hydrochloric acid always produces salts that end in chloride and contain the chloride ion, Cl^–

• Sulfuric acid always produces salts that end in chloride and contain the sulfate ion, SO₄^2–

• Nitric acid always produces salts that end in chloride and contain the nitrate ion, NO₃^–

Naming salts examples

• Salts have no overall charge since the sum of the charges on the ions is equal to zero

• If you know the ions present in a salt you can identify the formula from balancing the charges

Naming salts using ions table