Edexcel GCSE Chemistry Topic 4 Extracting metals and equilibria: a complete overview

What Topic 4 actually demands

Extracting metals and equilibria links the reactivity series to industrial chemistry and introduces reversible reactions. Edexcel tests precise redox definitions, the reasoning that connects a metal's reactivity to its extraction method, displacement reactions with ionic equations, and a clear understanding of dynamic equilibrium.

This guide walks through the topic in specification order, then sets out the exam patterns Edexcel repeats. Each dot point has a matching page with practice questions; this overview ties them together.

The reactivity series and redox

The reactivity series ranks metals by how readily they lose electrons to form positive ions. Oxidation is the gain of oxygen or loss of electrons; reduction is the loss of oxygen or gain of electrons (OIL RIG). Metal extraction is always a reduction of the metal from its compound.

Reactions of metals and displacement

Metals react with oxygen to form oxides, with water or steam to form a hydroxide or oxide and hydrogen, and with dilute acids to form a salt and hydrogen, with the vigour reflecting reactivity. A more reactive metal displaces a less reactive metal from a solution of its compound, a redox reaction shown by an ionic equation such as $Zn + Cu^{2+} \rightarrow Zn^{2+} + Cu$.

Extracting metals

The method depends on the metal's position relative to carbon:

• More reactive than carbon (such as aluminium): extracted by electrolysis of the molten compound, which is energy-intensive and expensive.
• Less reactive than carbon (such as iron, zinc, copper): extracted by heating the oxide with carbon, which reduces it.
• Low-grade ores: extracted by phytomining (plants then ash) or bioleaching (bacteria).

Recycling metals conserves finite ore, saves energy and reduces waste.

Reversible reactions and dynamic equilibrium

A reversible reaction ($\rightleftharpoons$) can go both ways, and the forward and backward energy changes are equal and opposite. In a closed system it reaches dynamic equilibrium, where the forward and backward reactions continue at equal rates, so the amounts stay constant. Changing the conditions shifts the position of equilibrium.

How Topic 4 is examined

A typical Edexcel profile for this topic:

• Redox definitions. Oxidation and reduction in terms of oxygen and electrons.
• Extraction choice. Justifying carbon reduction versus electrolysis from reactivity.
• Displacement. Predicting reactions and writing ionic equations.
• Equilibrium. Explaining dynamic equilibrium and reversible energy changes.

Check your knowledge

A mix of recall and application questions covering Topic 4. Attempt them under timed conditions, then check against the solutions.

1. Define reduction in terms of oxygen and in terms of electrons. (2 marks)
2. Explain why aluminium is extracted by electrolysis rather than with carbon. (2 marks)
3. State the products when calcium reacts with cold water. (2 marks)
4. Write the ionic equation for zinc displacing copper from copper sulfate solution. (1 mark)
5. Name two biological methods of extracting metals from low-grade ores. (2 marks)
6. Give two reasons for recycling metals. (2 marks)
7. State what the reversible arrow means. (1 mark)
8. Explain what happens to the forward and backward reactions at dynamic equilibrium. (2 marks)