Redox Reactions

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CognitoRedox reactions and OIL RIG

Key facts & methods

Oxidation and reduction

OIL RIG: Oxidation Is Loss (of electrons). Reduction Is Gain (of electrons).
Oxidation and reduction always occur simultaneously (one substance is oxidised as another is reduced).
Oxidising agent: causes oxidation of another substance; it is itself reduced.
Reducing agent: causes reduction of another substance; it is itself oxidised.
In terms of oxygen: oxidation = gain of oxygen. Reduction = loss of oxygen.

Half equations

A half equation shows what happens to just one species (gains or loses electrons).
Reduction (at cathode): Cu2+ + 2e- → Cu. Electrons on the LEFT.
Oxidation (at anode): 2Cl- → Cl2 + 2e-. Electrons on the RIGHT.
Balance atoms first, then balance charge by adding electrons.
Full ionic equation = add two balanced half equations so electrons cancel.

Oxidation states and displacement reactions

Displacement reactions are redox reactions: more reactive metal displaces less reactive metal.
Fe + CuSO4 → FeSO4 + Cu. Iron displaces copper. Iron is oxidised (Fe → Fe2+). Copper is reduced (Cu2+ → Cu).
The reactivity series predicts which metals displace which.
Observations: blue copper sulfate solution decolourises; orange-pink copper deposits on iron.
Halogen displacement reactions are also redox: Cl2 + 2KBr → 2KCl + Br2.

Exam questions — 4 questions · 10 marks · AQA 8462 style

1 markOIL RIGAQA 8462 style

A zinc atom loses two electrons to form Zn2+. Which statement is correct?

A Zinc is reduced because it loses electrons

B Zinc is oxidised because it loses electrons

C Zinc is the reducing agent and is also reduced

D Zinc gains electrons so it is oxidised

3 marksHalf equationsAQA 8462 style

In the electrolysis of copper(II) sulfate solution with copper electrodes, write half equations for: (a) what happens at the cathode, and (b) what happens at the anode. (3 marks)

Hint: Cathode = reduction = electrons gained (left side). Anode = oxidation = electrons lost (right side). With Cu electrodes, Cu dissolves at anode and deposits at cathode.

+30 XP

1 markOxidising agentAQA 8462 style

In the reaction Mg + CuSO4 → MgSO4 + Cu, which species is the oxidising agent?

A Magnesium (Mg)

B Cu2+ ions

C Sulfate ions (SO42-)

D Magnesium sulfate (MgSO4)

3 marksDisplacement redoxAQA 8462 style

Iron filings are added to blue copper sulfate solution. Describe what you would observe and explain the observations in terms of electron transfer. (3 marks)

Hint: Observe: blue fades, copper deposits. Explain: iron loses electrons (oxidised) → iron ions form. Copper ions gain electrons (reduced) → copper metal.

+30 XP

Oxidation and reduction

Half equations

Oxidation states and displacement reactions

Module complete! 🎉