Reactions Of Acids (AQA GCSE Combined Science: Synergy: Physical Sciences): Revision Note

Reactions of acids with metals

• Only metals above hydrogen in the reactivity series will react with dilute acids

  • Therefore copper can not react with acids

• The more reactive the metal then the more vigorous the reaction will be

• Metals that are placed high on the reactivity series such as potassium and sodium are very dangerous and react explosively with acids

• When acids react with metals they form a salt and hydrogen gas:

• The general equation is:

metal + acid ⟶ salt + hydrogen

• Some examples of metal-acid reactions and their equations are given below:

Test for Hydrogen Gas

• The test for hydrogen consists of holding a burning splint at the open end of a test tube of gas

• If the gas is hydrogen it burns with a loud “squeaky pop”

Carbonate & Acid 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, CuO

  • 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

Reactions of acids with metal carbonates

• Metal carbonates act as bases

  • They react with acids in a neutralisation reaction to form the corresponding metal salt, carbon dioxide and water

• 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

• These reactions are easy to distinguish by the effervescence (fizzing) caused by the release of carbon dioxide gas

Testing for carbon dioxide gas

• The test for carbon dioxide involves bubbling the gas through an aqueous solution of limewater (calcium hydroxide)

• If the gas is carbon dioxide, the limewater turns cloudy white