Why is aluminium more expensive to extract than iron?

Aluminium is more expensive because it is above carbon in the reactivity series, so it cannot be extracted by reduction with carbon. Instead, it must be extracted by electrolysis of molten aluminium oxide, which requires a lot of electrical energy. In contrast, iron is below carbon and can be extracted in a blast furnace using coke, which is cheaper. The high energy cost of electrolysis makes aluminium extraction more expensive.

How do I remember the reactivity series?

A common mnemonic is 'Please Stop Calling Me A Zebra, I Like Cats, Silly Pandas' for K, Na, Ca, Mg, Al, Zn, Fe, Sn, Pb, Cu, Ag, Au. Alternatively, you can make up your own. Remember that carbon and hydrogen are often included between aluminium and zinc, and between lead and copper, respectively. Practice writing the series from memory until it becomes automatic.

What is the thermite reaction and why is it useful?

The thermite reaction is a displacement reaction between aluminium and iron(III) oxide: 2Al + Fe₂O₃ → Al₂O₃ + 2Fe. It is highly exothermic, producing molten iron. This is useful for welding railway tracks because the molten iron can fill gaps and solidify quickly. It also demonstrates that aluminium is more reactive than iron, as it displaces iron from its oxide.

Can you extract copper by heating copper oxide with carbon?

Yes, copper can be extracted by heating copper oxide with carbon because copper is below carbon in the reactivity series. The reaction is: 2CuO + C → 2Cu + CO₂. This is a reduction reaction where carbon removes oxygen from copper oxide. However, for low-grade ores, a different method called bioleaching or phytomining may be used, which is more environmentally friendly.

Why is cryolite used in aluminium extraction?

Cryolite (Na₃AlF₆) is added to aluminium oxide (Al₂O₃) to lower its melting point from over 2000°C to around 900°C. This saves a significant amount of energy because less heat is required to melt the mixture. It also increases the conductivity of the molten mixture, making the electrolysis process more efficient. Without cryolite, the cost of extracting aluminium would be much higher.

What is the difference between a native metal and an ore?

A native metal is a metal that occurs in its pure, uncombined form in the Earth's crust, such as gold, silver, and platinum. These metals are very unreactive and do not easily form compounds. An ore is a rock that contains a metal compound (usually an oxide or sulfide) from which the metal can be extracted economically. For example, iron is extracted from hematite (Fe₂O₃) ore, and aluminium from bauxite (Al₂O₃). Most metals are found as ores because they are reactive enough to form compounds.

Reactivity series and extraction of metals

WJEC

GCSE

This topic explores the reactivity series of metals, established through displacement reactions, and introduces redox processes defined by oxygen and electron transfer. It covers industrial extraction methods for iron and aluminium, the principles of electrolysis for molten and aqueous compounds, and the evaluation of alternative extraction techniques like phytoextraction.

Objectives

Exam Tips

Pitfalls

Key Terms

Mark Points

Topic Overview

The reactivity series is a list of metals arranged in order of their reactivity, from most reactive (potassium) to least reactive (gold). This topic is fundamental to understanding how metals behave in chemical reactions, particularly with oxygen, water, and acids. The series helps predict whether a metal will displace another from its compound, which is crucial for extracting metals from their ores. In the WJEC GCSE Chemistry course, you'll learn how the reactivity series links to extraction methods: highly reactive metals require electrolysis, while less reactive metals can be extracted by reduction with carbon. This knowledge is essential for understanding industrial processes like the blast furnace for iron extraction and the environmental impact of mining.

The extraction of metals is directly tied to their position in the reactivity series. Metals above carbon in the series (e.g., aluminium) must be extracted by electrolysis because they are too reactive to be reduced by carbon. Metals below carbon (e.g., iron, copper) can be extracted by reduction with carbon, which is cheaper and more energy-efficient. The most unreactive metals, like gold and platinum, occur native (as pure elements) and require no chemical extraction. Understanding this hierarchy allows you to explain why different methods are used and why recycling metals is important for conserving resources and reducing energy consumption.

This topic also connects to everyday applications, such as why iron rusts (reacts with oxygen) but gold does not, and why sacrificial protection (using a more reactive metal like zinc to protect iron) works. Mastery of the reactivity series and extraction methods is essential for tackling exam questions on displacement reactions, thermite reactions, and the environmental impacts of metal production. By the end of this topic, you should be able to predict the products of reactions, write balanced equations, and justify the choice of extraction method for a given metal.

Key Concepts

Core ideas you must understand for this topic

→The reactivity series: K, Na, Ca, Mg, Al, (C), Zn, Fe, Sn, Pb, (H), Cu, Ag, Au – memorise this order and know that carbon and hydrogen are included for comparison.
→Displacement reactions: A more reactive metal will displace a less reactive metal from its compound (e.g., Fe + CuSO₄ → FeSO₄ + Cu).
→Extraction methods: Metals above carbon (e.g., Al) need electrolysis; metals below carbon (e.g., Fe) can be reduced by carbon; native metals (e.g., Au) occur uncombined.
→Reduction and oxidation: In extraction, the metal oxide is reduced (gains electrons) to form the metal, while carbon is oxidised to CO₂.
→The blast furnace: Used to extract iron from iron ore (Fe₂O₃) using carbon (coke) and limestone; the overall reaction is Fe₂O₃ + 3CO → 2Fe + 3CO₂.

What You Need to Demonstrate

Key skills and knowledge for this topic

Correct identification of oxidation and reduction in terms of oxygen and electron transfer
Ability to deduce reactivity order from experimental displacement data
Explanation of the link between metal reactivity and extraction method (e.g., carbon reduction vs electrolysis)
Description of electrode processes in electrolysis using half equations
Identification of products at the cathode and anode for molten and aqueous electrolytes
Evaluation of environmental and economic impacts of metal extraction methods

Marking Points

Key points examiners look for in your answers

Correct identification of oxidation and reduction in terms of oxygen and electron transfer
Ability to deduce reactivity order from experimental displacement data
Explanation of the link between metal reactivity and extraction method (e.g., carbon reduction vs electrolysis)
Description of electrode processes in electrolysis using half equations
Identification of products at the cathode and anode for molten and aqueous electrolytes
Evaluation of environmental and economic impacts of metal extraction methods

Examiner Tips

Expert advice for maximising your marks

💡Always check if the electrolyte is molten or aqueous before predicting electrolysis products
💡Use the mnemonic OIL RIG (Oxidation Is Loss, Reduction Is Gain) to remember electron transfer
💡When describing the blast furnace, ensure you mention both the reduction of iron ore and the removal of impurities as slag
💡Be prepared to write half equations for reactions occurring at the electrodes
💡Always learn the reactivity series in order, including carbon and hydrogen. You will often need to use it to predict whether a reaction occurs. A common exam question asks you to place an unfamiliar metal in the series based on its reactions.
💡When writing equations for extraction, ensure you balance them and include state symbols. For example, in the blast furnace, carbon monoxide is the reducing agent: Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g).
💡For electrolysis of aluminium oxide, remember that cryolite is added to lower the melting point, saving energy. You may be asked why this is necessary or to explain the reactions at each electrode.

Common Mistakes

Pitfalls to avoid in your exam answers

Confusing oxidation and reduction definitions (OIL RIG)
Incorrectly predicting products in aqueous electrolysis by ignoring the presence of water/hydrogen ions
Failing to link the position of a metal in the reactivity series to its specific extraction method
Inaccurate use of state symbols in ionic equations
Misconception: All metals can be extracted by heating with carbon. Correction: Only metals less reactive than carbon (below carbon in the series) can be reduced by carbon. Metals like aluminium are too reactive and require electrolysis.
Misconception: The reactivity series is the same as the electrochemical series. Correction: While related, the reactivity series is based on reactions with oxygen, water, and acids, whereas the electrochemical series is based on electrode potentials. For GCSE, focus on the reactivity series as taught.
Misconception: Displacement reactions only happen in solutions. Correction: Displacement can also occur in solid-state reactions, such as the thermite reaction (Al + Fe₂O₃ → Al₂O₃ + Fe), which is used to weld railway tracks.

Frequently Asked Questions

Common questions students ask about this topic

Before You Start

Prior knowledge that will help with this topic

•Basic atomic structure and bonding (ions and ionic compounds) – understanding that metals form positive ions is key to displacement and electrolysis.
•Chemical equations and balancing – you'll need to write and balance equations for reactions like reduction of metal oxides.
•Oxidation and reduction (redox) – knowing that reduction is gain of electrons and oxidation is loss of electrons helps explain extraction processes.

Study Guide Available

Comprehensive revision notes & examples

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Likely Command Words

How questions on this topic are typically asked

Explain

Describe

Deduce

Investigate

Evaluate

Predict

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Practice questions tailored to this topic

Reactivity series and extraction of metals

Topic Overview

Key Concepts

What You Need to Demonstrate

Marking Points

Examiner Tips

Common Mistakes

Frequently Asked Questions

Before You Start

Study Guide Available

Likely Command Words

Ready to test yourself?

Related Topics in WJEC GCSE Chemistry

Bonding, structure and properties

Carbon compounds

Chemical formulae, equations and amount of substance

Chemistry of acids

Topic Synopsis

Key Concepts & Core Principles

Exam Tips & Revision Strategies

Common Misconceptions & Mistakes to Avoid

Examiner Marking Points

Reactivity series and extraction of metals

Topic Overview

Key Concepts

What You Need to Demonstrate

Marking Points

Examiner Tips

Common Mistakes

Frequently Asked Questions

Why is aluminium more expensive to extract than iron?

How do I remember the reactivity series?

What is the thermite reaction and why is it useful?

Can you extract copper by heating copper oxide with carbon?

Why is cryolite used in aluminium extraction?

What is the difference between a native metal and an ore?

Before You Start

Study Guide Available

Likely Command Words

Ready to test yourself?

Related Topics in WJEC GCSE Chemistry

Bonding, structure and properties

Carbon compounds

Chemical formulae, equations and amount of substance

Chemistry of acids