How can we order metals by how reactive they are, and use that order to predict reactions?
State the reactivity series, compare the reactions of metals with water and acid, and use the series to predict displacement reactions
A focused answer to the N(A) Chemistry outcome on the reactivity series. The order of common metals, how their reactions with water and acid compare, and how to use the series to predict displacement reactions.
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What this dot point is asking
The syllabus wants you to know the reactivity series, the order of common metals from most to least reactive, to compare how metals react with water and acid, and to use the series to predict displacement reactions. The key idea is that a more reactive metal will push a less reactive metal out of its compound. This order explains how metals are extracted and why some corrode while others do not.
The answer
The reactivity series
The common metals, from most reactive to least reactive, are:
potassium, sodium, calcium, magnesium, aluminium, zinc, iron, (hydrogen), copper, silver, gold.
Hydrogen is included as a reference point even though it is not a metal. Metals above hydrogen react with dilute acids; metals below hydrogen do not.
Reaction with water
How a metal reacts with water shows its place near the top:
- Very reactive metals (potassium, sodium, calcium) react with cold water, giving hydrogen and an alkaline hydroxide.
- Moderately reactive metals (such as magnesium and zinc) react only slowly with cold water but react with steam.
- Unreactive metals (such as copper) do not react with water at all.
Reaction with dilute acid
How a metal reacts with acid also shows its reactivity:
- metals above hydrogen react with dilute acid to give a salt and hydrogen gas, more reactive metals fizzing faster,
- metals below hydrogen (copper, silver, gold) do not react with dilute acid.
Displacement reactions
A more reactive metal will displace a less reactive metal from a solution of its compound. The more reactive metal goes into solution, and the less reactive metal is pushed out as a solid. For example, iron displaces copper from copper(II) sulfate, so a brown copper coating forms and the blue colour fades.
Examples in context
Example 1. Choosing a metal for water pipes. Copper is used for water pipes partly because it is low in the reactivity series and does not react with water. A reactive metal such as sodium would be useless, as it would react with the water at once, showing how the series guides material choice.
Example 2. Sacrificial protection of ships. Blocks of a more reactive metal such as zinc are attached to steel ship hulls. Because zinc is more reactive than iron, it reacts in preference to the iron and protects it from rusting. This is a direct use of the reactivity order to prevent corrosion.
Try this
Q1. State which of these metals reacts with cold water: copper, sodium, iron. [1 mark]
- Cue. Sodium reacts with cold water; it is one of the most reactive metals, while copper and iron do not react with cold water.
Q2. Explain why zinc displaces copper from copper(II) sulfate solution but copper does not displace zinc from zinc sulfate solution. [2 marks]
- Cue. Zinc is more reactive than copper, so zinc displaces copper; copper is less reactive than zinc, so it cannot displace zinc.
Q3. A metal does not react with dilute hydrochloric acid. State what this tells you about its position in the reactivity series. [1 mark]
- Cue. The metal is below hydrogen in the series (unreactive), so it does not react with dilute acid to give hydrogen.
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.
Original4 marksA piece of iron is placed in blue copper(II) sulfate solution. (a) State what you would observe. (b) Explain the reaction using the reactivity series. (c) Write the word equation.Show worked answer →
(a) The blue colour of the solution fades, and a brown or pink coating of copper forms on the iron.
(b) Iron is more reactive than copper, so iron displaces copper from copper(II) sulfate. The iron goes into solution and the copper is pushed out as a solid.
(c) Iron + copper(II) sulfate iron(II) sulfate + copper.
What markers reward: the blue fading and copper coating the iron, iron being more reactive so it displaces copper, and the correct word equation.
Original4 marksThree metals X, Y and Z are tested. X reacts violently with cold water. Y reacts with dilute acid but not with cold water. Z does not react with dilute acid. (a) Place the metals in order of reactivity, most reactive first. (b) Suggest which metal could be Z.Show worked answer →
(a) X reacts with cold water (most reactive), Y reacts only with acid (middle), Z does not react with acid (least reactive). Order: X, then Y, then Z.
(b) Z does not react with dilute acid, so it is a very unreactive metal such as copper (silver or gold are also acceptable).
What markers reward: the order X, Y, Z based on the test results, and a sensible unreactive metal such as copper for Z.
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