How reactive are different metals, and how does this affect how they are extracted?
The reactivity series; reactions of metals with water and acids; displacement reactions; oxidation and reduction in terms of oxygen and electrons; and extraction of metals by reduction with carbon.
A focused answer to AQA GCSE Chemistry 4.4.1, covering the reactivity series, metal reactions with water and acids, displacement reactions, oxidation and reduction, and how metals are extracted by reduction with carbon depending on their reactivity.
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What this dot point is asking
AQA wants you to use the reactivity series to predict and explain metal reactions with water and acids, describe displacement reactions, define oxidation and reduction in terms of oxygen and electrons, and explain how a metal's reactivity decides whether it is extracted by reduction with carbon or by electrolysis. The reactivity series is the organising idea that links all of these together.
The reactivity series
A metal high in the series loses electrons easily, so it is very reactive; a metal low down (such as gold) barely reacts at all, which is why gold is found native (uncombined) in nature.
Reactions with water and acids
- With water: very reactive metals (potassium, sodium, calcium) react with cold water to form a metal hydroxide and hydrogen. Potassium reacts most vigorously, even igniting the hydrogen.
- With acids: metals above hydrogen react with dilute acids to form a salt and hydrogen. The more reactive the metal, the faster the reaction (more bubbles, faster fizzing). Metals below hydrogen, such as copper, do not react with dilute acids.
Displacement reactions
Displacement reactions can be used to place an unknown metal in the reactivity series by testing which metal salts it can displace.
Oxidation and reduction
In a displacement reaction the more reactive metal is oxidised (loses electrons to form ions) and the metal ion is reduced (gains electrons to form the metal). These reactions where electrons are transferred are called redox reactions.
Extraction of metals
How a metal is extracted depends on its position in the reactivity series:
- Metals less reactive than carbon (such as iron, copper, zinc) are extracted by reduction with carbon, because carbon removes the oxygen from the metal oxide.
- Metals more reactive than carbon (such as aluminium) must be extracted by electrolysis, because carbon cannot remove their oxygen.
Try this
Q1. State the products when a metal reacts with a dilute acid. [1 mark]
- Cue. A salt and hydrogen.
Q2. Explain why aluminium is extracted by electrolysis rather than reduction with carbon. [2 marks]
- Cue. Aluminium is more reactive than carbon, so carbon cannot remove its oxygen.
Q3. In the reaction , state which species is oxidised and explain why. [2 marks]
- Cue. Magnesium is oxidised because it loses electrons to form ions.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20194 marksIron is added to copper(II) sulfate solution and a reaction occurs. Name the products, write the ionic half-equations for the species oxidised and reduced, and explain which species is oxidised.Show worked answer →
A 4-mark Higher question on displacement and redox.
Products (1 mark): iron sulfate and copper (the more reactive iron displaces the less reactive copper). Half-equations (2 marks): iron is oxidised, ; copper ions are reduced, . Explanation (1 mark): iron is oxidised because it loses electrons (OIL RIG), forming positive ions, while the copper ions gain those electrons and are reduced.
Markers reward correctly identifying loss of electrons as oxidation and balanced half-equations.
AQA 20214 marksExplain, using the reactivity series, why iron is extracted from its ore by reduction with carbon but aluminium is extracted by electrolysis. Define reduction in terms of oxygen, and state which substance is reduced in the extraction of iron.Show worked answer →
A 4-mark question on extraction method and redox definition.
Iron (1 mark): iron is less reactive than carbon, so carbon can remove the oxygen from iron oxide by reduction. Aluminium (1 mark): aluminium is more reactive than carbon, so carbon cannot remove its oxygen; electrolysis is needed instead. Reduction (1 mark): the loss of oxygen. Substance reduced (1 mark): the iron oxide is reduced, because it loses its oxygen to the carbon.
Markers want the reactivity comparison against carbon as the deciding factor.
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Sources & how we know this
- AQA GCSE Chemistry (8462) specification — AQA (2016)