Year 10 Science Unit 2 · Chemical Reactions Lesson 7 of 20 45 min

Displacement and Neutralisation Reactions

Not all metals are created equal. Some are so reactive they will eagerly push others out of compounds, while barely reactive metals sit untouched. Discover the metal reactivity series, witness dramatic displacement reactions, and revisit neutralisation as a powerful reaction type in its own right.

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Think First

Before You Begin

Imagine you drop a shiny new iron nail into a blue copper sulfate solution.

What do you think might happen to the colour of the solution?
What might happen to the surface of the iron nail?
Why do you think this might happen?

Write down your predictions before reading on:

Write your thinking in your book before reading on.

Learning Intentions

Know

The definition of a displacement reaction
The metal reactivity series at Stage 5 level
That neutralisation is a reaction type: acid + base → salt + water

Understand

Why a more reactive metal displaces a less reactive metal from its compound
How to use the reactivity series to predict displacement outcomes
The observations that indicate a displacement reaction has occurred

Can Do

Predict whether a displacement reaction will occur using the reactivity series
Describe the practical observations of displacement reactions
Classify neutralisation as a distinct reaction type

Key Terms

Displacement reaction A reaction where a more reactive element replaces a less reactive element in a compound.

Reactivity series A list of metals arranged in order of reactivity, from most reactive to least reactive.

Metal A class of elements that are typically shiny, malleable, ductile and good conductors of heat and electricity.

Salt An ionic compound formed when an acid reacts with a base (neutralisation).

Neutralisation A reaction between an acid and a base that produces a salt and water.

Precipitate A solid that forms from a solution during a chemical reaction.

Core Content

Displacement Reactions

The more reactive metal wins

Reaction Rates

In a displacement reaction, a more reactive element pushes out (displaces) a less reactive element from its compound. The general pattern is:

A + BC → AC + B

where A is more reactive than B. This means A takes B's place in the compound.

At Stage 5, we focus on metal displacement in solutions. For example, if you place a strip of magnesium (very reactive) into copper sulfate solution, the magnesium displaces the copper. The blue solution fades as colourless magnesium sulfate forms, and reddish-brown copper metal deposits on the magnesium strip.

Remember A more reactive metal will always displace a less reactive metal from its compound. The less reactive metal is left on its own.

The Metal Reactivity Series

Your prediction tool

The reactivity series is a list of metals arranged from most reactive to least reactive. At Stage 5, the key metals to know are:

Most reactive
magnesium > aluminium > zinc > iron > tin > lead > copper > silver > gold
Least reactive

Any metal can displace any metal below it in the series. Magnesium displaces copper, zinc and iron. Zinc displaces copper and silver. But copper cannot displace zinc or magnesium.

Examples of displacement

Reaction	Word equation	Observations
Mg in CuSO₄	magnesium + copper sulfate → magnesium sulfate + copper	Blue solution fades; reddish-brown solid forms
Zn in CuSO₄	zinc + copper sulfate → zinc sulfate + copper	Blue solution fades; reddish-brown solid forms
Fe in CuSO₄	iron + copper sulfate → iron sulfate + copper	Blue solution fades; reddish-brown solid forms
Cu in AgNO₃	copper + silver nitrate → copper nitrate + silver	Colourless solution turns blue; silver solid forms

Important If a metal is placed in a solution of a compound containing a metal lower in the reactivity series, displacement will occur. If the compound contains a metal higher in the series, no reaction occurs.

Neutralisation Revisited

Acid + base → salt + water

Neutralisation is a reaction type in its own right. When an acid reacts with a base, they neutralise each other to produce a salt and water. The general word equation is:

acid + base → salt + water

Examples include hydrochloric acid reacting with sodium hydroxide to form sodium chloride (table salt) and water, and sulfuric acid reacting with copper oxide to form copper sulfate and water.

Neutralisation reactions are usually exothermic — they release heat. You can feel the test tube warm up when an acid and base react. They also typically cause a pH change from acidic or alkaline toward neutral (pH 7).

Think about it Why is neutralisation not a displacement reaction? (Hint: think about what is reacting and what is produced. In neutralisation, two compounds swap parts — this is different from one element pushing another out.)

Common Misconceptions

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"Any metal can displace any other metal." No — only a more reactive metal can displace a less reactive one. Gold cannot displace zinc.

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"A displacement reaction is the same as a decomposition reaction." No — displacement involves one element replacing another in a compound. Decomposition is one compound breaking apart.

✗trong>"Neutralisation is not a real chemical reaction." Yes it is — new substances (salt and water) are formed, and the reaction is usually exothermic with observable temperature change.

Australian Context

Galvanising and the Mining Industry

Australia is one of the world's largest producers of iron ore and zinc. The reactivity series has direct industrial applications here. Galvanising is the process of coating iron or steel with a layer of zinc. Even if the zinc coating is scratched, the zinc (more reactive) will corrode preferentially, protecting the iron underneath. This is why galvanised steel is used for Australian fencing, roofing and outdoor structures.

In Australian mining, understanding the reactivity series helps engineers choose the best methods for extracting metals from their ores. More reactive metals like aluminium require electrolysis for extraction, while less reactive metals like copper can be extracted using simpler chemical methods.

✍ Copy Into Your Books

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Displacement Reactions

General: A + BC → AC + B
More reactive displaces less reactive
Look for colour changes and metal deposition

Reactivity Series (key metals)

Mg > Al > Zn > Fe > Sn > Pb > Cu > Ag > Au
Any metal displaces metals below it
Gold is least reactive; magnesium is very reactive

Neutralisation

acid + base → salt + water
Usually exothermic (releases heat)
pH moves toward 7 (neutral)

Activities

Activity 1

Predict the Outcome

Use the reactivity series to predict whether a displacement reaction will occur. Explain your reasoning.

1 A strip of zinc is placed in copper sulfate solution.

Answer in your book.

2 A strip of copper is placed in magnesium sulfate solution.

Answer in your book.

3 A strip of iron is placed in silver nitrate solution.

Answer in your book.

Activity 2

Describe the Evidence

For each displacement reaction that occurs, describe the observations you would expect.

1 Magnesium strip in copper sulfate solution.

Answer in your book.

2 Copper strip in silver nitrate solution.

Answer in your book.

3 Zinc strip in iron sulfate solution.

Answer in your book.

Multiple Choice

Test Your Understanding

UnderstandBand 3

1. What happens in a displacement reaction?

ATwo elements combine to form a compound

BA single compound breaks down into simpler substances

CA more reactive element replaces a less reactive element in a compound

DAn acid reacts with a base to form a salt and water

UnderstandBand 3

2. According to the reactivity series, which of these metals is the MOST reactive?

AGold

BCopper

CZinc

DMagnesium

ApplyBand 4

3. A magnesium strip is placed in copper sulfate solution. What would you observe?

ANo visible change occurs

BThe blue solution stays blue and a silver coating forms

CThe blue solution fades and a reddish-brown solid forms on the strip

DBubbles of gas are produced

ApplyBand 4

4. Which of the following would NOT result in a displacement reaction?

AZinc strip in iron sulfate solution

BCopper strip in silver nitrate solution

CMagnesium strip in zinc sulfate solution

DCopper strip in magnesium sulfate solution

AnalyseBand 5

5. Iron is coated with zinc (galvanising) to prevent rusting. Using the reactivity series, which is the best explanation for why zinc protects iron even when scratched?

AZinc is less reactive than iron, so it blocks oxygen

BZinc is more reactive than iron, so it corrodes preferentially

CZinc and iron have the same reactivity

DZinc is a catalyst that speeds up rusting of the iron

Short Answer

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Short Answer Questions

UnderstandBand 3

1. Explain what a displacement reaction is and how the reactivity series helps predict whether a displacement will occur. 4 MARKS

Answer in your book.

ApplyBand 4

2. A student places a zinc strip into copper sulfate solution. Describe the expected observations and explain the reaction using the reactivity series. 4 MARKS

Answer in your book with reasoning.

AnalyseBand 5

3. Explain why galvanising iron with zinc protects the iron from rusting, even if the zinc coating is scratched. Use the reactivity series in your answer. 4 MARKS

Answer in your book.

Revisit Your Thinking

Go back to your Think First answer. Has your understanding changed?

Were your predictions about the iron nail and copper sulfate correct?
Can you now explain what happens using the reactivity series?

Update your thinking in your book.

Answers

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MCQ 1

C — In a displacement reaction, a more reactive element replaces a less reactive element in a compound.

MCQ 2

D — Magnesium is the most reactive metal in the list provided. Gold is the least reactive.

MCQ 3

C — Magnesium is more reactive than copper, so it displaces copper from copper sulfate. The blue solution fades as colourless magnesium sulfate forms, and reddish-brown copper metal deposits on the magnesium strip.

MCQ 4

D — Copper is less reactive than magnesium, so copper cannot displace magnesium from magnesium sulfate solution. No reaction occurs.

MCQ 5

B — Zinc is more reactive than iron in the reactivity series. This means zinc will corrode (react with oxygen and water) preferentially, protecting the iron underneath. Even if scratched, the zinc continues to sacrifice itself.

Short Answer 1

Model answer: A displacement reaction is a reaction where a more reactive element replaces a less reactive element in a compound. The reactivity series helps predict displacement because it ranks metals from most reactive to least reactive. Any metal can displace any metal below it in the series. For example, zinc (above copper) can displace copper from copper sulfate, but copper (below zinc) cannot displace zinc from zinc sulfate.

Short Answer 2

Model answer: The expected observations are: the blue colour of the copper sulfate solution gradually fades as colourless zinc sulfate forms, and a reddish-brown solid (copper metal) deposits on the surface of the zinc strip. Using the reactivity series, zinc is more reactive than copper. This means zinc displaces copper from the copper sulfate solution. The word equation is: zinc + copper sulfate → zinc sulfate + copper.

Short Answer 3

Model answer: Galvanising protects iron because zinc is more reactive than iron in the reactivity series. When the iron is coated with zinc, the zinc reacts with oxygen and water in preference to the iron, preventing rust. Even if the zinc coating is scratched, the exposed zinc still protects the iron because zinc corrodes preferentially — it 'sacrifices' itself. This is called sacrificial protection and is widely used in Australian fencing, roofing and marine structures.

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Lesson Game

Displacement Blaster

Test your knowledge of displacement reactions and the reactivity series. Predict outcomes, identify observations and blast your way to a high score!

Mark lesson as complete

Tick when you have finished all activities and checked your answers.

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Unit 2 overview · Science subject page