How do we rank metals by reactivity, and how does this decide how they are extracted?
The reactivity series of metals, the reactions of metals with water and acid, displacement reactions, oxidation and reduction in terms of oxygen and electrons, and how reactivity determines the method of extracting a metal from its ore.
A focused CCEA GCSE Double Award Science (Chemistry Unit C2) answer on metals, covering the reactivity series, reactions with water and acid, displacement reactions, oxidation and reduction in terms of oxygen and electrons, and how reactivity decides the method of extraction.
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What this dot point is asking
CCEA Double Award wants the reactivity series, how metals react with water and acid, displacement reactions, oxidation and reduction defined two ways, and how reactivity decides the extraction method. The link between a metal's reactivity and how it is extracted is the central, high-mark idea.
The reactivity series
The series is built from how vigorously metals react. The most reactive metals react with cold water; less reactive ones react only with acid; and the least reactive (such as gold) hardly react at all.
Reactions with water and acid
The most reactive metals (potassium, sodium, calcium) react with water to give a metal hydroxide and hydrogen. Many metals react with dilute acid to give a salt and hydrogen: the more reactive the metal, the faster the fizzing. Very unreactive metals like copper and gold do not react with dilute acid at all, which is why they survive in the environment.
Displacement reactions
The word equation is magnesium + copper sulfate gives magnesium sulfate + copper. The blue solution fades and brown copper appears. Displacement is a quick way to compare the reactivity of two metals.
Oxidation and reduction (redox)
In a displacement reaction, the more reactive metal is oxidised (loses electrons to form ions) and the metal ions in solution are reduced (gain electrons to form the metal). Reactions where one substance is oxidised and another reduced are called redox reactions.
Extracting metals
How a metal is extracted depends on its reactivity compared with carbon:
- A metal less reactive than carbon (such as iron) is extracted by reduction with carbon. In the blast furnace, carbon (as coke) reduces iron oxide to iron.
- A metal more reactive than carbon (such as aluminium) cannot be displaced by carbon, so it is extracted by electrolysis.
- Very unreactive metals (such as gold) are found native (as the metal itself) and need no extraction.
Examples in context
Example 1. Why iron rusts but gold does not. Iron is reactive enough to react with oxygen and water to form rust, but gold is so unreactive it stays shiny for thousands of years. Their positions in the reactivity series explain why ancient gold jewellery survives while iron objects corrode.
Example 2. The thermite reaction. Aluminium displaces iron from iron oxide in a very exothermic reaction used to weld railway tracks. Aluminium is more reactive than iron, so it is oxidised while the iron oxide is reduced - a dramatic redox displacement.
Try this
Q1. What is oxidation in terms of electrons? [1 mark]
- Cue. The loss of electrons.
Q2. Why is aluminium extracted by electrolysis and not with carbon? [1 mark]
- Cue. Aluminium is more reactive than carbon, so carbon cannot displace it.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA-style4 marksExplain why iron is extracted by reduction with carbon but aluminium is extracted by electrolysis.Show worked answer →
Link reactivity to the method for four marks.
Iron is less reactive than carbon, so carbon can displace iron from its oxide by reduction in the blast furnace.
Aluminium is more reactive than carbon, so carbon cannot displace it.
A more reactive metal must be extracted by electrolysis, which uses electrical energy to separate the ions.
So the extraction method depends on the metal's position relative to carbon in the reactivity series. Markers reward carbon reducing less reactive metals and electrolysis for those more reactive than carbon.
CCEA-style3 marksMagnesium displaces copper from copper sulfate solution. Explain this reaction in terms of reactivity and write the word equation.Show worked answer →
Identify the displacement and explain it for three marks.
Magnesium is more reactive than copper, so it displaces copper from the solution.
The word equation is magnesium + copper sulfate gives magnesium sulfate + copper.
The blue solution fades and a brown coating of copper forms. Markers reward the displacement, the reason and the correct equation.
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Sources & how we know this
- CCEA GCSE Science Double Award specification — CCEA (2017)