From explosive potassium to lazy copper — the reactivity series, displacement reactions, metal extraction, and the electron-level chemistry behind it all.
🦙 tropical chemistry • reactivity island • metals in paradise 🦙
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Metal Oxides (4.1.1)
🌺 Metals Reacting with Oxygen
When metals react with oxygen, they produce metal oxides.
The carbon is oxidised (gains oxygen) and the metal oxide is reduced (loses oxygen).
This works for zinc, iron, and copper but NOT for metals above carbon in the reactivity series (K, Na, Li, Ca, Mg).
🍹 Exam Tip — Spot Oxidation & Reduction
In any reaction, ask: what gained oxygen? (oxidised) and what lost oxygen? (reduced). For example, in iron oxide + carbon → iron + CO₂: the iron oxide is reduced (lost oxygen), and the carbon is oxidised (gained oxygen).
🦙 Metals Above Carbon
Metals more reactive than carbon (K, Na, Li, Ca, Mg) cannot be extracted by reduction with carbon.
These metals are extracted using electrolysis — which is more expensive and energy-intensive.
This is why aluminium (above carbon) is more expensive to produce than iron (below carbon).
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Oxidation & Reduction — Electrons (4.1.4)
🦜 OIL RIG — The Electron Definition
OIL — Oxidation Is Loss (of electrons)
RIG — Reduction Is Gain (of electrons)
When a metal reacts, it loses electrons to form positive ions — so it is oxidised.
The other substance gains electrons — so it is reduced.
🌺 Ionic Equations for Displacement
Consider: Mg + CuSO₄ → MgSO₄ + Cu
Magnesium atoms lose electrons: Mg → Mg²⁺ + 2e⁻ (oxidation — loss of electrons)
Copper ions gain electrons: Cu²⁺ + 2e⁻ → Cu (reduction — gain of electrons)
The magnesium is oxidised (it loses electrons and forms Mg²⁺ ions).
The copper ions are reduced (they gain electrons and become copper atoms).
🍹 How to Identify Oxidised & Reduced Species
Look at what loses electrons → that species is oxidised.
Look at what gains electrons → that species is reduced.
In displacement reactions, the more reactive metal is always oxidised and the less reactive metal ion is always reduced.
🚨 Common Exam Mistake
Students often say "copper sulfate is reduced." Be specific! It is the copper ions (Cu²⁺) that are reduced, not the whole compound. Always name the exact species being oxidised or reduced.
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Question 01 [2 marks]
When magnesium is burned in air, it reacts with oxygen to form magnesium oxide. Explain why this is an oxidation reaction.
🦜 Answer
This is an oxidation reaction because the magnesium gains oxygen (1 mark). Oxidation is defined as the gain of oxygen (1 mark).
Question 02 [2 marks]
Place these metals in order of reactivity from most reactive to least reactive: Iron, Potassium, Copper, Magnesium.
🦜 Answer
Potassium, Magnesium, Iron, Copper (2 marks — all four correct. Lose 1 mark for each pair in the wrong order).
Question 03 [3 marks]
Describe the difference in how potassium and magnesium react with cold water.
🦜 Answer
Potassium reacts very vigorously with cold water (1 mark), fizzing and producing a lilac flame (1 mark). Magnesium reacts very slowly with cold water (1 mark), though it does react vigorously with steam.
Question 04 [2 marks]
Zinc is added to copper sulfate solution. A reaction occurs. Explain why, and write a word equation for this reaction.
🦜 Answer
Zinc is more reactive than copper, so it can displace copper from the solution (1 mark). Zinc + copper sulfate → zinc sulfate + copper (1 mark).
Question 05 [2 marks]
Explain why gold is found in the Earth as the metal itself, but iron is found as an ore.
🦜 Answer
Gold is very unreactive, so it does not combine with other elements and exists as the pure metal (1 mark). Iron is more reactive and reacts with other elements (e.g. oxygen), so it is found as a compound in an ore and must be extracted (1 mark).
Question 06 [3 marks]
Iron oxide is reduced using carbon in a blast furnace. Write a word equation for this reaction. Identify what is oxidised and what is reduced.
🦜 Answer
Iron oxide + carbon → iron + carbon dioxide (1 mark). The iron oxide is reduced because it loses oxygen (1 mark). The carbon is oxidised because it gains oxygen (1 mark).
Question 07 [2 marks]
Explain why aluminium cannot be extracted from its ore by heating with carbon, but iron can.
🦜 Answer
Aluminium is more reactive than carbon in the reactivity series, so carbon cannot reduce aluminium oxide (1 mark). Iron is less reactive than carbon, so carbon can reduce iron oxide by removing its oxygen (1 mark).
Question 08 [2 marks]
What does OIL RIG stand for? Explain what it means in terms of electrons.
🦜 Answer
OIL = Oxidation Is Loss (of electrons) (1 mark). RIG = Reduction Is Gain (of electrons) (1 mark). When a substance is oxidised it loses electrons; when it is reduced it gains electrons.
Question 09 [3 marks]
In the reaction Mg + CuSO₄ → MgSO₄ + Cu, write the ionic half-equations and identify which species is oxidised and which is reduced.
🦜 Answer
Mg → Mg²⁺ + 2e⁻ — magnesium is oxidised (loses electrons) (1 mark). Cu²⁺ + 2e⁻ → Cu — copper ions are reduced (gain electrons) (1 mark). Magnesium displaces copper because it is more reactive / has a greater tendency to form positive ions (1 mark).
Question 10 [3 marks]
A student adds a piece of iron to zinc sulfate solution. No reaction occurs. The student then adds a piece of magnesium to zinc sulfate solution and observes a reaction. Explain these observations using the reactivity series.
🦜 Answer
Iron is less reactive than zinc, so it cannot displace zinc from the solution — no reaction occurs (1 mark). Magnesium is more reactive than zinc, so it can displace zinc from the solution (1 mark). A more reactive metal will always displace a less reactive metal from a solution of its salt (1 mark).