Metals: IGCSE Chemistry Exam Guide

Metals questions on 0620 revolve around one idea: the reactivity series. Every question about extraction, displacement, reactions with water or acid, and rusting prevention traces back to how reactive the metal is. Learn the series and its consequences, and the topic becomes a set of predictable patterns. The full topic is covered under metals.

The reactivity series and what it predicts

The series, from most to least reactive: K, Na, Ca, Mg, Al, (C), Zn, Fe, (H), Cu, Ag, Au.

Carbon and hydrogen sit in the series as reference points, not as metals. Their positions decide two things:

1. Extraction method. Metals above carbon: electrolysis. Metals below carbon: reduction with carbon.
2. Reaction with dilute acid. Metals above hydrogen react with dilute acid to produce hydrogen. Metals below hydrogen (copper, silver, gold) do not react with dilute acid.

Question type 1: extraction of metals

The exam asks you to explain why aluminium is extracted by electrolysis while iron is extracted by carbon reduction.

The answer structure that scores:

• Aluminium is more reactive than carbon, so carbon cannot reduce aluminium oxide. Electrolysis of molten aluminium oxide is needed, using a large amount of electrical energy (1-2 marks).
• Iron is less reactive than carbon, so iron oxide can be reduced by heating with carbon (or coke) in a blast furnace (1-2 marks).

The extended response version asks about the economics: electrolysis is expensive because of the energy cost, which is why aluminium costs more than iron despite being more abundant in the Earth’s crust.

Aluminium extraction detail

The exam expects specific details for aluminium extraction:

• Aluminium oxide is dissolved in molten cryolite to lower the melting point (saves energy).
• The electrolyte is molten aluminium oxide in cryolite.
• Aluminium forms at the cathode (reduction: Al3+ + 3e- -> Al).
• Oxygen forms at the anode (oxidation: 2O2- -> O2 + 4e-).
• The carbon anodes burn away in the oxygen produced and must be replaced regularly.

The connection to electrolysis technique is covered in electrolysis exam technique.

Question type 2: displacement reactions

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

Zn + CuSO4 -> ZnSO4 + Cu

Zinc is more reactive than copper, so zinc displaces copper from copper sulfate solution. The observation: the zinc dissolves (or decreases in mass), the blue colour fades, and a brown/red-brown deposit of copper appears.

What the examiner wants in your answer:

• Name the more reactive metal and state that it displaces the less reactive one (1 mark).
• Write the balanced equation (1-2 marks).
• Describe the observations with colours and states (1-2 marks).

Common error: writing observations without colours. “A deposit forms” does not score where “a red-brown deposit of copper forms” does.

Question type 3: reactions with water and acid

The exam tests a grid: metals vs water, metals vs dilute acid.

Metal	Water	Dilute HCl
Potassium	Vigorous reaction, lilac flame, KOH + H2	Too dangerous to test
Sodium	Vigorous fizzing, melts, NaOH + H2	Too dangerous to test
Calcium	Steady fizzing, Ca(OH)2 + H2	Reacts, CaCl2 + H2
Magnesium	Very slow with cold water; reacts with steam	Vigorous fizzing, MgCl2 + H2
Zinc	No reaction with water	Slow reaction, ZnCl2 + H2
Iron	No reaction with water (rusts slowly)	Very slow reaction, FeCl2 + H2
Copper	No reaction	No reaction

The MCQ uses this grid directly. Paper 4 asks you to predict reactions and write equations for specific metal-acid or metal-water combinations.

Question type 4: rusting and corrosion prevention

Rusting requires both water and oxygen. The exam tests this with the controlled experiment using three test tubes, then asks about prevention methods:

• Painting, oiling, greasing, plastic coating: barrier methods that keep water and oxygen away from the iron surface.
• Galvanising: coating with zinc. Even if the coating is scratched, zinc is more reactive than iron and corrodes preferentially (sacrificial protection).
• Sacrificial protection: attaching blocks of a more reactive metal (zinc or magnesium) to the iron structure. The more reactive metal corrodes instead of the iron.

The explain mark for sacrificial protection requires stating that the more reactive metal loses electrons / is oxidised in preference to the iron.

Question type 5: alloys

An alloy is a mixture of a metal with one or more other elements. The exam expects you to explain why alloys are harder than pure metals:

“In a pure metal, the atoms are arranged in regular layers that can slide over each other. In an alloy, atoms of different sizes disrupt the regular arrangement, preventing the layers from sliding, making the alloy harder.”

Named alloys the syllabus expects: steel (iron + carbon), brass (copper + zinc), bronze (copper + tin).

Worked exam question

Q (Paper 4): A student places iron nails into four different solutions: copper sulfate, magnesium sulfate, zinc sulfate and silver nitrate. In which solutions will a reaction occur? Explain your answer. (4 marks)

Model answer: A reaction occurs in copper sulfate solution and silver nitrate solution (1). Iron is more reactive than copper and more reactive than silver, so iron displaces them from their compounds (1). No reaction occurs in magnesium sulfate or zinc sulfate because magnesium and zinc are both more reactive than iron (1), so iron cannot displace them (1).

The marks are awarded for identifying the correct solutions, then explaining using the reactivity series. The most common error is claiming iron reacts with zinc sulfate because students confuse the order of zinc and iron in the series.

If the reactivity series and its applications are consistently costing marks, a trial lesson can pinpoint whether the issue is the order itself or applying it to unfamiliar contexts.