GCSE Chemistry revision

Reactions of acids with metals

Reactions of acids

AQA 4.4.2.1 Includes HT-only content

Your specification

AQA student objectives

Learning pathway

ALL 🎯

MOST 🎯🎯

SOME 🎯🎯🎯

Revision summary

Read on screen, then print for Cornell-style active revision.

The term 'redox' is short for reduction-oxidation, reflecting that both processes occur together.
Because electrons cannot simply disappear, if one substance loses electrons, another must gain them at the same time.

Redox reactions are reactions in which both oxidation and reduction take place simultaneously, since if one substance loses electrons, another must gain them.
The term 'redox' is simply short for reduction-oxidation.
When magnesium reacts with dilute acid (H⁺ ions), magnesium atoms are oxidised (lose electrons) whilst hydrogen ions are reduced (gain electrons) to form hydrogen gas.

2. What are Redox Reactions? AQA

Redox reactions are reactions in which both oxidation and reduction take place simultaneously, since if one substance loses electrons, another must gain them.
The term 'redox' is simply short for reduction-oxidation.
When magnesium reacts with dilute acid (H⁺ ions), magnesium atoms are oxidised (lose electrons) whilst hydrogen ions are reduced (gain electrons) to form hydrogen gas.

Displacement reactions involve a more reactive metal displacing a less reactive metal from its salt solution.
The reactivity series is used to predict which metal will displace another (e.g. calcium is more reactive than iron).
When calcium is added to iron sulfate solution, calcium displaces iron, forming calcium sulfate whilst iron precipitates out as a solid.

3. Displacement Reactions AQA

Displacement reactions involve a more reactive metal displacing a less reactive metal from its salt solution.
The reactivity series is used to predict which metal will displace another (e.g. calcium is more reactive than iron).
When calcium is added to iron sulfate solution, calcium displaces iron, forming calcium sulfate whilst iron precipitates out as a solid.

Ionic equations show only the particles that actually change or take part in the reaction.
Spectator ions are ions that remain unchanged throughout the reaction (e.g. sulfate ions, SO₄^2-, in the calcium and iron sulfate reaction) and are removed from the equation.
Removing spectator ions from the full equation leaves the net ionic equation, which more clearly shows what is actually happening chemically.

4. Ionic Equations AQA

Ionic equations show only the particles that actually change or take part in the reaction.
Spectator ions are ions that remain unchanged throughout the reaction (e.g. sulfate ions, SO₄^2-, in the calcium and iron sulfate reaction) and are removed from the equation.
Removing spectator ions from the full equation leaves the net ionic equation, which more clearly shows what is actually happening chemically.

Half equations show the gain or loss of electrons for each individual element involved in a redox reaction separately.
For the oxidation half equation of calcium: Ca → Ca²⁺ + 2e⁻ (electrons are placed on the right as they are lost).
For the reduction half equation of iron: Fe²⁺ + 2e⁻ → Fe (electrons are placed on the left as they are gained).
Always check that the overall charge balances on both sides of a half equation to verify it is correct.

5. Writing Half Equations AQA

Half equations show the gain or loss of electrons for each individual element involved in a redox reaction separately.
For the oxidation half equation of calcium: Ca → Ca²⁺ + 2e⁻ (electrons are placed on the right as they are lost).
For the reduction half equation of iron: Fe²⁺ + 2e⁻ → Fe (electrons are placed on the left as they are gained).
Always check that the overall charge balances on both sides of a half equation to verify it is correct.

In the iron half equation, the left side has a 2+ charge and two 1− charges from the electrons, giving a total charge of zero, which matches the neutral iron atom on the right.
If the charges on each side of a half equation do not balance, the electrons have likely been placed on the wrong side.
Balancing charges is the key check to confirm a half equation has been written correctly.

6. Checking Half Equations for Balance AQA

In the iron half equation, the left side has a 2+ charge and two 1− charges from the electrons, giving a total charge of zero, which matches the neutral iron atom on the right.
If the charges on each side of a half equation do not balance, the electrons have likely been placed on the wrong side.
Balancing charges is the key check to confirm a half equation has been written correctly.