What is the reactivity series and how is it built?

The reactivity series is a list of metals in order of how readily they react, from the most reactive (such as potassium, sodium and calcium) down to the least reactive (such as copper, silver and gold). It is built by comparing how vigorously metals react with oxygen, with water or steam and with dilute acid: a more reactive metal reacts faster and more vigorously. The series predicts behaviour, including which metals displace others from their compounds and which method is needed to extract a metal from its ore.

How does the reactivity series predict a displacement reaction?

A more reactive metal will displace a less reactive metal from a solution of its salt or from its oxide, because the more reactive metal holds on to electrons less strongly and pushes the less reactive metal out of the compound. For example, iron added to copper(II) sulfate solution displaces copper, because iron is more reactive than copper; the blue solution fades and a brown deposit of copper forms. A less reactive metal cannot displace a more reactive one.

Why does the method of extracting a metal depend on its reactivity?

A metal is found combined in its ore, and the harder it holds on to the other element, the more energy is needed to free it. Very reactive metals above carbon in the series (such as aluminium) must be extracted by electrolysis. Metals below carbon (such as iron, zinc and lead) can be reduced by heating with carbon, as in the blast furnace. The least reactive metals (such as gold) are found uncombined as the native element and need no chemical extraction.

What conditions are needed for iron to rust, and how is rusting prevented?

Rusting needs both oxygen and water; either alone will not cause iron to rust. Rusting is the slow oxidation of iron to hydrated iron(III) oxide. It is prevented by keeping out oxygen and water with a barrier such as paint, oil, grease or a layer of a less reactive metal, by galvanising (coating with zinc), or by sacrificial protection, in which a more reactive metal such as zinc or magnesium is attached and corrodes in place of the iron.

How is Metals and the Reactivity Series assessed in O-Level Chemistry 6092?

It is examined across all three papers. Paper 1 (multiple choice, 40 marks, 30 percent) tests the order of the series, displacement and extraction methods. Paper 2 (structured and free response, 80 marks, 50 percent) rewards predicting and explaining displacement, describing the blast furnace with equations and explaining rust prevention including sacrificial protection. Paper 3 (practical, 40 marks, 20 percent) can involve comparing the reactions of metals or investigating the conditions needed for rusting.

SingaporeChemistry

Metals and the Reactivity Series (Singapore O-Level Chemistry 6092): ordering metals by reactivity, predicting displacement, matching extraction method to reactivity, the blast furnace, and the rusting and protection of iron

A Singapore O-Level Chemistry (SEAB 6092) overview of Metals and the Reactivity Series. Ordering metals by their reactions with oxygen, water and acid, predicting displacement, matching the extraction method to reactivity including the blast furnace, and the conditions for rusting and how to prevent it, with links to every dot point.

Generated by Claude Opus 4.86 min readSEAB-6092Updated 2026-06-13

Reviewed by: AI editorial process; not yet individually human-reviewed

Jump to a section

What this topic is really about
Building and using the reactivity series
Extracting metals from their ores
Rusting and the protection of iron
How this topic is examined
Check your knowledge

What this topic is really about

Metals and the Reactivity Series is one idea applied three ways. The single idea is an order of metals from most to least reactive, built from how they behave with oxygen, water and acid. Once you have that order, you can predict displacement reactions, decide how each metal must be extracted from its ore, and explain why iron rusts and how to stop it. The unifying thread is that reactivity is about how readily a metal loses electrons to form positive ions. This guide ties the three dot points together and links to each one.

The complete set of dot-point pages for this topic, each with worked examples and questions, lives at /sg-o-level/chemistry/syllabus/metals-and-reactivity.

Building and using the reactivity series

The reactivity series orders metals by comparing their reactions with oxygen, water or steam and dilute acid. The order, from most to least reactive, runs roughly potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, copper, silver, gold, with carbon and hydrogen placed in for reference. A more reactive metal displaces a less reactive one from its salt solution or oxide.

Extracting metals from their ores

Extraction of metals connects reactivity to method. Metals above carbon are extracted by electrolysis (aluminium from molten aluminium oxide); metals below carbon are reduced by heating with carbon; the least reactive metals occur native. The set-piece example is iron in the blast furnace, where carbon and carbon monoxide reduce iron(III) oxide.

Reduction of iron oxide in the blast furnace

step Make the reducing agent

Coke (carbon) burns in the hot air blast to form carbon dioxide, which then reacts with more hot coke to form carbon monoxide:

\text{C}(s) + \text{O}_2(g) \rightarrow \text{CO}_2(g)

\text{CO}_2(g) + \text{C}(s) \rightarrow 2\text{CO}(g)

step Reduce the iron oxide

The carbon monoxide reduces iron(III) oxide to molten iron:

\text{Fe}_2\text{O}_3(s) + 3\text{CO}(g) \rightarrow 2\text{Fe}(l) + 3\text{CO}_2(g)

step Remove the impurities

Limestone decomposes to calcium oxide, which reacts with sand (silicon dioxide) impurity to form molten slag (calcium silicate) that floats on the iron and is run off.

Rusting and the protection of iron

Iron, steel and corrosion covers the conditions for rusting (both oxygen and water are needed) and the ways to prevent it: barrier methods such as painting and oiling, galvanising with zinc, and sacrificial protection, where a more reactive metal corrodes in place of the iron. The same page links the properties of steel and other alloys to their uses.

How this topic is examined

Predict and explain displacement. State that the more reactive metal displaces the less reactive one, and back it with the order of the series and an observation.
Match extraction to position. Use carbon's position to decide electrolysis versus reduction by carbon, and quote the blast furnace equations.
Name both conditions for rusting. Markers want both oxygen and water, and a named prevention method explained, especially sacrificial protection.

Check your knowledge

A mix of recall, reasoning and explanation questions covering Metals and the Reactivity Series. Attempt them under timed conditions, then check against the solutions.

State the three types of reaction used to place metals in order of reactivity. (3 marks)
Predict and explain what happens when a piece of zinc is added to copper(II) sulfate solution. (3 marks)
Explain why aluminium is extracted by electrolysis but iron is extracted using carbon. (2 marks)
State the two conditions needed for iron to rust. (2 marks)
Explain how sacrificial protection prevents an iron object from rusting. (3 marks)

Solutions

Q1: Their reactions with oxygen, with water (or steam), and with dilute acid. A more reactive metal reacts more vigorously in each case.
Q2: Zinc is more reactive than copper, so zinc displaces copper from the solution. The blue colour of the copper(II) sulfate fades and a reddish-brown deposit of copper forms on the zinc, while the zinc gradually dissolves to form colourless zinc sulfate.
Q3: Aluminium is above carbon in the reactivity series, so it is too reactive to be reduced by carbon and must be extracted by electrolysis. Iron is below carbon, so it can be reduced by heating its oxide with carbon (carbon monoxide) in the blast furnace.
Q4: Oxygen (air) and water. Both must be present for iron to rust.
Q5: A more reactive metal such as zinc or magnesium is attached to (or coated onto) the iron. Because it is more reactive, it loses electrons and corrodes in preference to the iron, so it is oxidised instead of the iron. The iron is protected for as long as the sacrificial metal remains.

Sources & how we know this

Singapore-Cambridge GCE O-Level Chemistry (Syllabus 6092) — Singapore Examinations and Assessment Board (2026)
Cambridge Assessment International Education, working with SEAB on the Singapore-Cambridge GCE O-Level — Cambridge Assessment International Education (2026)