How is the reactivity series built from the reactions of metals, and how does it predict displacement?
Place metals in order of reactivity using their reactions with oxygen, water and acids, and use the reactivity series to predict displacement reactions of metals from their compounds
A focused answer to the O-Level Chemistry outcome on the reactivity series. Ordering metals from their reactions with oxygen, water and acid, and using the series to predict metal displacement reactions.
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What this dot point is asking
SEAB wants you to place metals in a reactivity series using their reactions with oxygen, water and dilute acid, and then use that order to predict displacement reactions, where a more reactive metal displaces a less reactive one from a compound. The reactivity series is the organising idea for the whole metals topic, linking forward to extraction and corrosion.
The answer
The reactivity series
The reactivity series lists metals in order of how readily they react, most reactive at the top. A common O-Level order is:
potassium, sodium, calcium, magnesium, aluminium, zinc, iron, lead, (hydrogen), copper, silver, gold.
The more reactive a metal, the more strongly it tends to lose electrons and form positive ions. Hydrogen is included as a reference point even though it is not a metal.
Reactions used to build the series
The order comes from comparing how vigorously metals react:
- With oxygen: reactive metals burn brightly to form oxides; unreactive metals (copper, gold) react slowly or not at all. The brighter and faster the reaction, the more reactive the metal.
- With water: the most reactive metals (potassium, sodium, calcium) react with cold water to give a hydroxide and hydrogen. Less reactive metals (magnesium, zinc, iron) react only with steam to give an oxide and hydrogen. Copper and below do not react.
- With dilute acid: metals above hydrogen react with dilute acid to give a salt and hydrogen, more reactive metals fizzing faster; metals below hydrogen (copper, silver, gold) do not react with dilute acid.
The pattern of "reacts with cold water", then "reacts with steam or acid", then "reacts with neither" places any metal in the series.
Displacement reactions
The series predicts displacement: a more reactive metal displaces a less reactive metal from a solution of its compound (or from its oxide). For example, iron is more reactive than copper, so iron displaces copper from copper(II) sulfate:
The more reactive metal gives up electrons more readily, taking the place of the less reactive metal, which is deposited as the free metal. The colour change of the solution and the new solid deposited are the visible evidence.
Why the series matters
A metal's place in the series predicts not just displacement but also how it is extracted (next dot point) and how easily it corrodes. The single ordering therefore explains a wide range of metal behaviour, which is why it is worth memorising.
Examples in context
Example 1. The thermite reaction. Aluminium, being more reactive than iron, displaces iron from iron(III) oxide in the thermite reaction, releasing so much heat that molten iron is produced. This dramatic displacement is used to weld railway tracks, showing the reactivity series at work in industry.
Example 2. Why copper pipes are safe but iron rusts. Copper sits low in the reactivity series, so it does not react with water or weak acids and is used for water pipes. Iron, higher in the series, reacts with water and air and rusts, which is why the position of a metal predicts its everyday durability.
Try this
Q1. State what is meant by a displacement reaction of metals. [1 mark]
- Cue. A reaction in which a more reactive metal takes the place of a less reactive metal in its compound.
Q2. A metal reacts with cold water to give hydrogen. State what this shows about its position in the reactivity series. [1 mark]
- Cue. It is a very reactive metal, near the top of the series (such as potassium, sodium or calcium).
Q3. Predict whether iron will displace zinc from zinc sulfate solution, with a reason. [2 marks]
- Cue. No; zinc is more reactive than iron, so iron (the less reactive metal) cannot displace zinc from its compound.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original5 marksThree metals X, Y and Z are tested. X reacts vigorously with cold water; Y does not react with water but reacts with dilute acid; Z does not react with water or with dilute acid. (a) Place the three metals in order of reactivity, most reactive first. (b) Suggest an identity for each from: copper, magnesium, potassium.Show worked answer →
(a) Order, most reactive first: X, then Y, then Z. X reacts with cold water (very reactive); Y reacts only with acid (moderately reactive); Z reacts with neither (least reactive).
(b) X reacts with cold water, so X is potassium. Y reacts with acid but not water, so Y is magnesium. Z reacts with neither, so Z is copper.
Markers reward the order from the strength of reaction (water then acid then neither), and matching each metal to the correct identity based on its behaviour.
Original4 marksA strip of zinc is placed in copper(II) sulfate solution. (a) State what is observed. (b) Explain the observation using the reactivity series. (c) Write a word equation for the reaction.Show worked answer →
(a) The blue colour of the solution fades, and a pink-brown (red-brown) solid (copper) is deposited on the zinc, which slowly dissolves.
(b) Zinc is more reactive than copper, so zinc displaces copper from copper(II) sulfate solution. The more reactive metal takes the place of the less reactive one in the compound.
(c) Zinc + copper(II) sulfate zinc sulfate + copper.
Markers reward the fading blue colour and copper deposited, the explanation that the more reactive zinc displaces the less reactive copper, and a correct word equation.
Related dot points
- Relate the method of extracting a metal to its position in the reactivity series, describe the extraction of iron in the blast furnace, and explain reduction by carbon and by electrolysis
A focused answer to the O-Level Chemistry outcome on metal extraction. Why reactivity decides the extraction method, the reduction of iron oxide by carbon in the blast furnace, and why very reactive metals need electrolysis.
- Describe the conditions needed for iron to rust, explain methods of rust prevention including sacrificial protection, and relate the properties of steel and alloys to their uses
A focused answer to the O-Level Chemistry outcome on rusting and steel. The conditions needed for iron to rust, methods of prevention including barriers and sacrificial protection, and how steel and other alloys are matched to their uses.
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A focused answer to the O-Level Chemistry outcome on redox. Oxidation and reduction defined by oxygen and by electron transfer, identifying oxidising and reducing agents, and the colour-change tests that detect them.