Redox Reactions (Oxford AQA IGCSE Chemistry): Revision Note
Exam code: 9202
Redox Reactions
When oxidation and reduction are happening at the same time this is known as a redox reaction
For example
zinc + copper sulphate → zinc sulphate + copper
Zn + CuSO4 → ZnSO4 + Cu
The ions present (with state symbols) in the equation are:
Zn (s) + Cu2+ (aq) + SO42- (aq) →Zn2+ (aq) + SO42- (aq) + Cu (s)
The spectator ions (those that do not change) are SO42-(aq) and are removed
Zn(s) + Cu2+(aq) → Zn2+(aq) + Cu(s)
We can split the reaction into two half equations
Zn (s) → Zn2+ (aq) + 2e-
Cu2+ (aq) + 2e- → Cu (s)
Zinc has been oxidised as it has lost electrons
Copper ions have been reduced as they have gained electrons
Worked Example
When iron reacts with bromine to form iron(II) bromide, a redox reaction reaction occurs:
Fe + Br2 → FeBr2
What has been reduced in the reaction?
Answer:
Step 1 - Write half equations to work out what has gained/lost electrons
Fe → Fe2+ + 2e-
Br2 + 2e- → 2Br-
Fe loses electrons; Br2 gains electrons
Step 2 - Deduce what has been oxidised/reduced (remember OIL RIG)
Fe has been oxidised as it has lost electrons
Br2 has been reduced as it has gained electrons
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