How to Study Metals and Reactivity for IGCSE Chemistry

The metals topic in 0620 is built on one central idea: the reactivity series. Everything else — extraction methods, displacement reactions, rusting, alloys — follows from where a metal sits in the series. Students who memorise the reactivity series and understand what it predicts find this topic straightforward. Students who skip the series and try to learn each reaction individually drown in disconnected facts.

The reactivity series: the backbone of the topic

Learn the series in order, including carbon and hydrogen:

K > Na > Ca > Mg > Al > (C) > Zn > Fe > (H) > Cu > Ag > Au

Carbon and hydrogen are not metals, but their positions matter:

• Metals above carbon are extracted by electrolysis
• Metals between carbon and hydrogen are extracted by reduction with carbon
• Metals below hydrogen do not react with dilute acids
• Metals below hydrogen are found native (uncombined) in the earth

Memory technique: Use a mnemonic sentence. Any sentence that works for you is fine. Test yourself using active recall — write the series from memory every day for a week, then weekly after that.

Reactions of metals: use the series to predict

With water

• K, Na, Ca: react with cold water to produce a metal hydroxide and hydrogen. Vigour increases up the series.
• Mg: reacts very slowly with cold water but reacts with steam to produce magnesium oxide and hydrogen.
• Zn, Fe: react with steam only, producing the metal oxide and hydrogen.
• Cu, Ag, Au: no reaction with water or steam.

With dilute acid

• Metals above hydrogen react with dilute hydrochloric acid or dilute sulfuric acid to produce a salt and hydrogen.
• Metals below hydrogen (Cu, Ag, Au) do not react with dilute acids.
• Reactivity order is visible in the vigour: Mg reacts vigorously, Zn reacts steadily, Fe reacts slowly, Cu does not react.

Displacement reactions

A more reactive metal displaces a less reactive metal from its salt solution:

• Zn + CuSO4 → ZnSO4 + Cu (zinc is above copper, so zinc displaces copper)
• Cu + ZnSO4 → no reaction (copper is below zinc)

The observation matters for exam marks: in the zinc + copper sulfate example, the blue solution decolourises (Cu2+ ions removed) and a red-brown deposit of copper appears on the zinc.

Metal extraction: two methods, one rule

Electrolysis (metals above carbon)

Aluminium is the main example. It is extracted from molten aluminium oxide (bauxite dissolved in cryolite to lower the melting point) by electrolysis:

• Cathode: Al3+ + 3e- → Al (aluminium deposited)
• Anode: 2O2- → O2 + 4e- (oxygen produced, which reacts with the carbon anode, requiring regular replacement)

Link to electrochemistry — the electrolysis principles are identical.

Carbon reduction (metals between carbon and hydrogen)

Iron is the main example. It is extracted in a blast furnace:

• Coke (carbon) burns to produce carbon monoxide: 2C + O2 → 2CO
• Carbon monoxide reduces iron oxide: Fe2O3 + 3CO → 2Fe + 3CO2
• Limestone removes acidic impurities as slag: CaCO3 → CaO + CO2, then CaO + SiO2 → CaSiO3

The blast furnace diagram is a favourite exam question. Practise drawing and labelling it from memory: the charge (iron ore, coke, limestone) goes in at the top, hot air blasts in near the bottom, molten iron collects at the base, and slag floats on top.

Rusting

Rusting requires both water and oxygen (air). This is demonstrated by the classic experiment with three test tubes of iron nails: one in dry air (no rust), one in boiled water sealed with oil (no rust), one in normal aerated water (rust). Iron is the only metal that “rusts” specifically; other metals corrode.

Prevention methods:

• Painting, oiling, greasing, plastic coating: barrier methods that exclude water and air
• Galvanising: coating with zinc. Zinc is more reactive than iron, so even if the coating is scratched, zinc corrodes preferentially (sacrificial protection)
• Sacrificial protection: attaching a more reactive metal (zinc or magnesium blocks on ships’ hulls)
• Electroplating: coating with a less reactive but attractive metal (chromium, tin)

For exam purposes, know the difference between barrier protection (just blocks water/air) and sacrificial protection (the more reactive metal corrodes instead of the iron).

Alloys

An alloy is a mixture of a metal with one or more other elements, usually metals. The atoms of different sizes disrupt the regular lattice structure, preventing layers from sliding over each other, making the alloy harder than the pure metal.

Key alloys for 0620:

• Steel: iron + carbon (and sometimes other metals). Harder and stronger than pure iron.
• Brass: copper + zinc.
• Bronze: copper + tin.
• Stainless steel: iron + chromium + nickel. Resists rusting.

The exam typically asks why alloys are harder than pure metals. The answer centres on the different-sized atoms disrupting the regular arrangement of layers.

Study approach

Phase 1: The reactivity series (3 days)

Memorise the series. Use flashcards and daily recall tests. This is pure memory work.

Phase 2: Reactions of metals (4 days)

Study each type of reaction (with water, with acid, displacement) using the series to predict products. Write balanced equations for each. The key is pattern recognition: you do not need to memorise each individual reaction if you can predict it from the series.

Phase 3: Extraction (3 days)

Learn the electrolysis-or-carbon-reduction rule. Study the blast furnace diagram and the aluminium extraction cell in detail. Draw both from memory.

Phase 4: Rusting and alloys (2 days)

Learn the rusting conditions experiment. Card the prevention methods with the principle behind each. Learn the alloy hardness explanation.

Phase 5: Past papers (ongoing)

Work through metals exam guide questions. Metals questions often combine with other topics: displacement links to electrochemistry, extraction links to stoichiometry, and rusting links to oxidation.

Common errors

• Placing carbon and hydrogen in the wrong position in the reactivity series
• Confusing the products of metal + water (hydroxide + hydrogen) with metal + acid (salt + hydrogen)
• Writing that zinc is extracted by electrolysis (zinc is below carbon, so it is extracted by carbon reduction)
• Forgetting that galvanising works by sacrificial protection, not just as a barrier
• Describing alloys as “compounds” instead of “mixtures”