How are metals ranked by reactivity, and how does reactivity decide how a metal is extracted and how it corrodes?
The reactivity series, the reactions of metals with water and acid, displacement reactions, how reactivity decides extraction by carbon reduction or electrolysis, the extraction of iron in the blast furnace, and the rusting of iron and its prevention.
A focused CCEA GCSE Single Award Science answer on metals, covering the reactivity series, reactions with water and acid, displacement reactions, extraction by carbon reduction or electrolysis, the blast furnace, and the rusting of iron and how it is prevented.
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What this dot point is asking
CCEA wants you to know the reactivity series, describe how metals react with water and acid, explain displacement, explain how reactivity decides extraction by carbon reduction or electrolysis, describe the blast furnace, and explain the rusting of iron and how it is prevented.
The reactivity series
- With water: very reactive metals (potassium, sodium, calcium) react with cold water to give a hydroxide and hydrogen. Magnesium reacts slowly with water but readily with steam.
- With dilute acid: metals above hydrogen give a salt and hydrogen, fizzing more the higher they are. Copper and below do not react.
Displacement reactions
A metal cannot displace one above it in the series, so copper added to zinc sulfate gives no reaction.
Extraction of metals
In the blast furnace, iron oxide is reduced by carbon monoxide: , and molten iron runs to the bottom.
Rusting and its prevention
Prevention methods include painting, oiling or greasing, and galvanising (coating with zinc). Zinc is more reactive than iron, so it corrodes instead of the iron, giving sacrificial protection.
Examples in context
Example 1. Why gold is found as the metal but iron is not. Gold is so unreactive that it does not combine with oxygen, so it is found native, as nuggets, and needs no chemical extraction. Iron is more reactive, so it is always found as an ore (iron oxide) and must be reduced with carbon to get the metal. This links a metal's reactivity directly to how it occurs in nature.
Example 2. Galvanising a steel fence. Coating steel with zinc protects it twice over: the zinc layer keeps water and oxygen off the iron, and even if the layer is scratched, the zinc still corrodes in preference to the iron because it is more reactive. This sacrificial protection is why galvanised steel lasts so long outdoors, a favourite CCEA application.
Try this
Q1. Name the gas given off when a reactive metal reacts with dilute acid. [1 mark]
- Cue. Hydrogen.
Q2. State the two substances that must both be present for iron to rust. [1 mark]
- Cue. Water and oxygen.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA SAS 20194 marksExplain why iron is extracted by heating its oxide with carbon, but aluminium is extracted by electrolysis.Show worked answer →
Four marks for the reactivity comparison and both methods.
Carbon sits in the reactivity series between aluminium and iron.
Iron is less reactive than carbon, so carbon can remove the oxygen from iron oxide (reduction), which is cheaper.
Aluminium is more reactive than carbon, so carbon cannot remove its oxygen.
Aluminium is therefore extracted by electrolysis of its molten compound, which uses electrical energy to break the strong bonds. Markers reward the position of carbon, iron below carbon (reduction works) and aluminium above carbon (electrolysis needed).
CCEA SAS 20214 marksDescribe an experiment to show that iron rusts only when both water and oxygen are present, and state two ways of preventing rusting.Show worked answer →
Four marks for the experiment and two prevention methods.
Set up three test tubes with a nail: one with water and air, one with boiled water and oil on top to keep oxygen out, and one with dry air and a drying agent to keep water out.
Only the nail with both water and air rusts, showing both are needed.
Two prevention methods: paint or oil the iron to keep out water and oxygen; or galvanise it by coating with zinc (sacrificial protection).
Markers reward the controlled tubes removing water or oxygen, the result that both are needed, and two valid prevention methods.
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Sources & how we know this
- CCEA GCSE Science: Single Award specification — CCEA (2017)