Neutralisation Reactions (SQA National 5 Chemistry): Revision Note

Neutralisation reactions & equations

Reacting acids & bases

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

  • These reactions are exothermic

• Bases have pH values above 7

• Many bases are insoluble in water

• But, the ones that do dissolve in water are called alkalis

  • So, they form an alkaline solution

• Examples of alkalis are soluble metal hydroxides such as:

  • Sodium hydroxide, NaOH

  • Calcium hydroxide, 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 + carbonate ⟶ 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 sulfates 

  • Nitric acid produces nitrates

Table salt or sodium chloride

Photo by Chemical Safety Facts (opens in a new tab)

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

• All acid-base neutralisation reactions produce:

  • The corresponding salt 

  • Water

Reactions of acids with metal oxides

• The general reaction of an acid with a metal oxide is:

acid + metal oxide ⟶ salt + water

• Here are some specific examples of acid and metal oxide reactions:

2HCl + CuO ⟶ CuCl₂ + H₂O

H₂SO₄ + Na₂O⟶ Na₂SO₄ + H₂O

2HNO₃ + MgO ⟶ Mg(NO₃)₂ + H₂O

Reactions of acids with metal hydroxides

• The general reaction of an acid with a metal hydroxide is:

acid + metal hydroxide ⟶ salt + water

• Here are some specific examples of acid and metal hydroxide reactions:

HCl + LiOH ⟶ LiCl + 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 salt

  • Carbon dioxide 

  • Water

• These reactions are easily distinguishable from the reactions of acids with metal oxides or hydroxides

• The reaction of an acid with a metal carbonate shows effervescence (fizzing) caused by 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 general reaction of an acid with a metal carbonate is:

acid + metal carbonate ⟶ metal salt + carbon dioxide + water

• Here are some specific examples acid and metal carbonate reactions:

2HCl + Na₂CO₃ ⟶ 2NaCl + H₂O + CO₂

H₂SO₄ + CaCO₃⟶ CaSO₄ + H₂O + CO₂

2HNO₃ + MgCO₃ → Mg(NO₃)₂ + H₂O + CO₂

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

• Hydrochloric acid always produces salts that end in chloride

  • These contain the chloride ion, Cl^–

• Sulfuric acid always produces salts that end in sulfate

  • These contain the sulfate ion, SO₄^2–

• Nitric acid always produces salts that end in nitrate

  • These contain the nitrate ion, NO₃^–

Naming salts examples