How does a metal's reactivity decide how it is extracted from its ore?
Extracting metals: the reactivity series, oxidation and reduction in terms of oxygen and electrons, extraction by reduction with carbon, extraction by electrolysis, and alternative biological methods.
A focused answer to Edexcel GCSE Chemistry topic 4, covering the reactivity series, oxidation and reduction defined by oxygen and by electron transfer, why a metal's position decides its extraction method, reduction with carbon for less reactive metals, electrolysis for reactive metals, and biological extraction methods.
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What this dot point is asking
Edexcel wants you to use the reactivity series, define oxidation and reduction in terms of both oxygen and electrons, explain why a metal's reactivity decides its extraction method, describe extraction by reduction with carbon for less reactive metals and by electrolysis for reactive metals, and outline biological methods such as phytomining and bioleaching. This links the reactivity series to industrial chemistry.
The reactivity series
Carbon and hydrogen, although non-metals, are placed in the series for comparison. A metal's position decides how it reacts with water and acids and, importantly, how it is extracted.
Oxidation and reduction
The two definitions you must know:
- In terms of oxygen: oxidation is the gain of oxygen, reduction is the loss of oxygen. So extracting a metal from its oxide is a reduction.
- In terms of electrons: oxidation is loss of electrons, reduction is gain of electrons (remember OIL RIG).
A reaction in which one species is oxidised and another reduced is a redox reaction. Metal extraction is always a reduction of the metal from its compound.
Why reactivity decides the extraction method
Most metals are found combined in ores, usually as oxides. To extract the metal you must remove the oxygen, that is reduce the metal compound. How you do this depends on the metal's reactivity:
Extraction by reduction with carbon
For metals below carbon, the metal oxide is heated with carbon (often as coke). The carbon is more reactive, so it takes the oxygen and is itself oxidised to carbon dioxide, while the metal oxide is reduced to the metal. For iron in the blast furnace:
The iron oxide is reduced (loses oxygen) and the carbon is oxidised (gains oxygen).
Extraction by electrolysis
For metals above carbon, electrolysis of the molten compound is used. The compound is melted so the ions can move, and a current decomposes it: metal forms at the cathode and a non-metal at the anode. Aluminium is extracted by electrolysing molten aluminium oxide (dissolved in cryolite to lower the melting point). Electrolysis is expensive because of the large amount of electrical energy needed to melt the compound and drive the reaction, which is why reactive metals cost more.
Biological methods
Low-grade ores can be treated using living organisms, which avoids digging up and processing large amounts of rock:
- Phytomining: plants absorb metal compounds from the soil; the plants are burned and the metal is extracted from the ash.
- Bioleaching: bacteria produce solutions (leachates) containing metal compounds from low-grade ore, from which the metal is obtained.
Try this
Q1. Define oxidation in terms of electrons. [1 mark]
- Cue. The loss of electrons.
Q2. State the method used to extract zinc from zinc oxide and explain why. [2 marks]
- Cue. Reduction with carbon, because zinc is less reactive than carbon, so carbon can remove the oxygen.
Q3. Explain why aluminium is more expensive to extract than iron. [2 marks]
- Cue. Aluminium is extracted by electrolysis, which needs a large amount of electrical energy, while iron is reduced more cheaply with carbon.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20194 marksIron is extracted by heating iron(III) oxide with carbon: . Explain why this reaction is a reduction of iron(III) oxide and why carbon can be used to extract iron but not aluminium.Show worked answer →
A 4-mark redox and extraction-choice question.
The iron(III) oxide loses oxygen to form iron, and loss of oxygen is reduction, so the oxide is reduced (1 mark for loss of oxygen, 1 mark for reduction). Carbon can reduce iron oxide because carbon is more reactive than iron, so it can take the oxygen from it (1 mark). Aluminium is more reactive than carbon, so carbon cannot remove the oxygen from aluminium oxide, and aluminium must be extracted by electrolysis instead (1 mark).
Markers reward defining reduction as loss of oxygen and linking the choice of method to the metal's position relative to carbon.
Edexcel 20213 marksDefine oxidation and reduction in terms of electrons, and state which process occurs at the cathode during the extraction of a reactive metal by electrolysis.Show worked answer →
A 3-mark redox-definition question.
Oxidation is the loss of electrons and reduction is the gain of electrons (1 mark for both definitions). At the cathode, the positive metal ions gain electrons to form metal atoms (1 mark), so reduction occurs at the cathode (1 mark).
Markers reward the electron definitions (OIL RIG) and identifying the cathode reaction as reduction.
Related dot points
- Reactions of metals: reactions with oxygen, water and dilute acids, using these to place metals in a reactivity series, displacement reactions, and recycling and life cycle considerations.
A focused answer to Edexcel GCSE Chemistry topic 4, covering how metals react with oxygen, water and dilute acids, using the observations to order metals in a reactivity series, displacement reactions of more reactive metals, writing ionic equations for displacement, and why metals are recycled.
- Reversible reactions and equilibria: reversible reactions and the use of the reversible arrow, the energy change in each direction, dynamic equilibrium in a closed system, and the idea that the conditions affect the position of equilibrium.
A focused answer to Edexcel GCSE Chemistry topic 4, covering reversible reactions and the reversible arrow, why the forward and backward reactions have opposite energy changes, what dynamic equilibrium means in a closed system, and the qualitative effect of changing conditions on the position of equilibrium.
- Electrolysis: electrolysis of molten ionic compounds and aqueous solutions, predicting the products at the electrodes, writing half-equations, and the electrolysis of copper sulfate core practical.
A focused answer to Edexcel GCSE Chemistry topic 3, covering what electrolysis is, the electrolysis of molten ionic compounds, the rules for predicting products at the cathode and anode in aqueous solutions, writing half-equations, oxidation and reduction at the electrodes, and the copper sulfate electrolysis core practical.
- Reactions of acids: the general reactions of acids with metals, metal oxides, metal hydroxides and metal carbonates, the salts produced, and the tests for hydrogen and carbon dioxide.
A focused answer to Edexcel GCSE Chemistry topic 3, covering the general reactions of acids with metals, metal oxides, metal hydroxides and metal carbonates, the salts each acid produces, writing balanced and ionic equations, and the chemical tests for hydrogen and carbon dioxide.
- Transition metals, alloys and corrosion: the properties of transition metals compared with Group 1, the structure and uses of alloys, the conditions needed for rusting, and methods of preventing corrosion.
A focused answer to Edexcel GCSE Chemistry topic 5 (separate chemistry), covering the typical properties of transition metals compared with Group 1 metals, why alloys are harder than pure metals, common alloys and their uses, the conditions required for iron to rust, and methods of preventing corrosion including barriers and sacrificial protection.
Sources & how we know this
- Pearson Edexcel GCSE (9-1) Chemistry (1CH0) specification — Pearson Edexcel (2016)