Metal Displacement Reactions and Redox

Section 1 of 9Recap and link

Displacement

• Displacement A more reactive metal pushes a less reactive metal out of its salt solution.

Redox definition

• Redox definition Oxidation is loss of electrons and reduction is gain of electrons.

The link

• The link The metal atoms lose electrons to become ions while the ions of the other metal gain electrons to become atoms, so electrons are transferred.

Section 2 of 9Worked example: zinc and copper(II) sulfate

1

Write the full equation: Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s).

2

Write it as ions: Zn + Cu²⁺ + SO₄²⁻ → Zn²⁺ + SO₄²⁻ + Cu.

3

Cross out the sulfate ions, which are spectator ions and appear unchanged on both sides.

4

The net ionic equation is Zn + Cu²⁺ → Zn²⁺ + Cu.

5

Split into half equations: Zn → Zn²⁺ + 2e⁻ (oxidation) and Cu²⁺ + 2e⁻ → Cu (reduction).

Section 3 of 9Spotting oxidation and reduction

Species	What happens	Process
Zinc atoms	Lose 2 electrons to become Zn2+	Oxidation
Copper(II) ions	Gain 2 electrons to become Cu atoms	Reduction
Sulfate ions	No change	Spectators
Zinc overall	Acts as the reducing agent	Gives electrons
Copper(II) ions overall	Act as the oxidising agent	Accept electrons

Section 4 of 9Observations in this reaction

1Zinc added

• Zinc added A piece of zinc is placed in blue copper sulfate solution.

2Electron transfer

• Electron transfer Zinc atoms give electrons to copper ions in the solution.

3Copper forms

• Copper forms Brown copper metal coats the zinc.

4Solution fades

• Solution fades As blue Cu²⁺ ions are used up, the solution becomes colourless.

Section 5 of 9More displacement reactions as redox

Reaction	Net ionic equation	Species oxidised
Magnesium + copper(II) sulfate	Mg + Cu2+ → Mg2+ + Cu	Magnesium
Iron + copper(II) sulfate	Fe + Cu2+ → Fe2+ + Cu	Iron
Copper + silver nitrate	Cu + 2Ag+ → Cu2+ + 2Ag	Copper
Zinc + magnesium sulfate	No reaction, because zinc is less reactive than magnesium	None

Section 6 of 9Remembering redox

OIL RIG

• OIL RIG Oxidation Is Loss of electrons and Reduction Is Gain of electrons.

Reactivity series link

• Reactivity series link The more reactive metal is the one that loses electrons more easily, so it is oxidised and displaces the less reactive metal.

Balancing electrons

• Balancing electrons In the copper and silver nitrate reaction each copper atom loses 2 electrons but each silver ion gains only 1,
  • so two silver ions are needed for every copper atom.

Section 7 of 9Method: displacement of copper by a metal

1

Measure about 25 cm³ of copper(II) sulfate solution into a beaker and record its temperature and colour.

2

Add a small amount of the metal powder, such as zinc, and stir.

3

Observe the colour of the solution and the solid that forms, and record the highest temperature reached.

4

A temperature rise shows that the displacement reaction is exothermic.

5

Repeat with other metals to rank them in order of reactivity.

Section 8 of 9Key terms

Term	Meaning
Spectator ion	An ion present in the mixture that does not take part in the reaction.
Ionic equation	An equation showing only the particles that change during the reaction.
Oxidation	Loss of electrons.
Reduction	Gain of electrons.
Half equation	An equation showing electron loss or gain by one species only.

Section 9 of 9Exam technique

1

Leaving spectator ions in the net ionic equation.

2

Mixing up which species is oxidisedthe more reactive metal loses electrons, so it is oxidised.

3

Writing half equations where the electrons do not balance the charge; check that both sides have the same total charge.

4

Saying electrons are gained by the zinc; zinc loses them to the copper ions.