How are metals ordered by reactivity, and how does this decide how a metal is extracted?
The reactivity series, displacement reactions, and how the method of extracting a metal depends on its reactivity.
A focused answer to the WJEC GCSE Science Double Award Unit 5 topic on metals, covering the reactivity series, displacement reactions, and how the method of extracting a metal depends on its position in the reactivity series.
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What this dot point is asking
WJEC Double Award Unit 5 wants you to describe the reactivity series, displacement reactions, and how the method of extracting a metal depends on its reactivity.
The reactivity series
A common order (most to least reactive): potassium, sodium, calcium, magnesium, aluminium, (carbon), zinc, iron, (hydrogen), copper, silver, gold. The more reactive a metal, the more easily it loses electrons to form positive ions, and the more vigorously it reacts.
Displacement reactions
This happens because the more reactive metal "takes the place" of the less reactive one in the compound. Displacement reactions are used to confirm the order of the reactivity series.
How reactivity decides extraction
Carbon can only displace metals less reactive than itself, which is why the position of carbon in the series is the key dividing line.
Why electrolysis is more expensive
Extracting a metal by electrolysis uses a lot of electricity, which is expensive, so it costs more than reduction with carbon. This is why aluminium, which must be extracted by electrolysis, is more expensive to produce than iron, which can be reduced with cheap carbon. The link between a metal's reactivity, its extraction method and its cost is a common exam point: the more reactive the metal, the harder and more expensive it is to extract.
Reactions with water and acid
The reactivity series can also be seen in how metals react with water and acid. The most reactive metals (potassium, sodium, calcium) react with cold water, giving hydrogen and a hydroxide; less reactive metals (magnesium, zinc, iron) react with acid to give hydrogen and a salt, more vigorously the more reactive they are; and unreactive metals (copper, silver, gold) do not react with water or acid. The vigour of these reactions is direct evidence for the order of the series, and a common way exam questions ask you to place metals in order.
Oxidation and reduction
Extracting a metal from its ore is an example of reduction, while a metal reacting with oxygen is oxidation. Oxidation is the gain of oxygen (for example a metal rusting or burning), and reduction is the loss of oxygen (for example iron oxide being reduced to iron in the blast furnace). Metals high in the reactivity series are easily oxidised, which is why they are found as compounds and are hard to extract, while unreactive metals resist oxidation. Knowing the meanings of oxidation and reduction in terms of oxygen helps explain extraction and corrosion.
Try this
Q1. Will magnesium displace copper from copper sulfate? [1 mark]
- Cue. Yes, because magnesium is more reactive than copper.
Q2. How is iron extracted from its ore? [1 mark]
- Cue. By reduction with carbon (in the blast furnace).
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style4 marksExplain why iron is extracted by reduction with carbon, but aluminium must be extracted by electrolysis.Show worked answer →
A Unit 5 explain question worth 4 marks. Reward: iron is less reactive than carbon, so carbon can displace (reduce) it from its ore in a blast furnace (2); aluminium is more reactive than carbon, so carbon cannot displace it (1); aluminium must therefore be extracted by electrolysis, which uses electricity to separate the very reactive metal from its compound (1). Markers credit the comparison with carbon for each metal and the link to the extraction method. A common error is to say aluminium is cheaper to extract (electrolysis is expensive).
WJEC style3 marksZinc is added to copper sulfate solution. Describe and explain what happens.Show worked answer →
A Unit 5 displacement question. Reward: zinc is more reactive than copper, so zinc displaces the copper from the solution (1); copper is deposited (a brown coating forms) and the blue colour fades as zinc sulfate forms (1); the word equation is zinc + copper sulfate to zinc sulfate + copper (1). Markers credit the more reactive metal displacing the less reactive one, the observation, and the equation. A common error is to say copper displaces zinc.
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