Neutralisation of Acids and Salt Production (AQA GCSE Chemistry)

• When an acid reacts with a base, a neutralisation reaction occurs
• Bases have pH values above 7
• Many bases are insoluble in water but the ones that do dissolve in water are called alkalis
• They thus form an alkaline solution
• Examples of alkalis are soluble metal hydroxides such as NaOH and Ca(OH)₂
• 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 salts and nitric acid produces nitrates

Reactions of Acids with Metal Oxides and Metal Hydroxides

• Metal oxides and metal hydroxides act as bases
• When they react with acid, a neutralisation reaction occurs
• In all acid-base neutralisation reactions, salt and water are produced

• 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

• 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

• Acids will react with metal carbonates to form the corresponding metal salt, carbon dioxide and water
• These reactions are easily distinguishable from acid – metal oxide/hydroxide reactions due to the presence of effervescence caused by the carbon dioxide gas

• 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

Salts

• A salt is a compound that is formed when the hydrogen ion in an acid is replaced by a metal ion 
• For example if we replace the hydrogen ion in HCl with a potassium ion, then the salt potassium chloride is formed, KCl
• Salts are an important branch of chemistry due to the varied and important uses of this class of compounds
  • These uses include fertilisers, batteries, cleaning products, healthcare products and fungicides

Naming 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
• The name of the salt can be determined by looking at the reactants
• For example hydrochloric acid always produces salts that end in chloride and contain the chloride ion, Cl^–
• Other examples:
  • Sodium hydroxide reacts with hydrochloric acid to produce sodium chloride
  • Zinc oxide reacts with sulfuric acid to produce zinc sulfate
    
    
• A list of the common ions and their formulae is shown below:

Naming Salts Table

• Salts have no overall charge since the sum of the charges on the ions is equal to zero
• From the table of the common ions it is clear the charges on each the Group I elements is always 1+, Group II is 2+, Group VI is 2- and Group VII is 1-
• If you know the ions present in a salt you can identify the formula from balancing the charges