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KS3 Science · Year 8Chapter 8 · Reactions of metals
Year 8 · Chapter 8

Reactions of metals

By the end of this chapter you will be able to

  • Write word equations for metals reacting with oxygen, water and dilute acids
  • Put metals in order of reactivity, using their reactions
  • Explain a displacement reaction, and predict whether it happens
  • Use a bubble count to compare the reactivity of metals fairly
  • Write and balance simple symbol equations for these reactions

You should already know

  • Word equations and signs of reaction (Year 7 Chapter 9)
  • Elements, atoms and the periodic table (Year 8 Chapter 7)

Where this leads

  • Acids, alkalis and pH (Year 8 Chapter 9)

National Curriculum for England, Key Stage 3 science, Year 8. Content: 8C3 reactions of metals with oxygen, water and dilute acids; the reactivity series; displacement reactions; word and symbol equations for these reactions (basic).

Exercise P  Do you remember?

1
FWrite the word equation: magnesium + oxygen → magnesium oxide. What is the product? Write the name.
2
FWhat is the name of the symbol for copper? Write the symbol.
3
FWhat is 60 divided by 3? Write the number.
4
FWhat is the name of the gas that a metal releases when it reacts with a dilute acid? Write the word.
5
FWhich group of the periodic table are the alkali metals in? Write the number.
8.1

Metals and oxygen

Year 8
8C3: reactions of metals with oxygen to form metal oxides
Video lesson: Metals and oxygenComing soon
Story. Ruby sees magnesium ribbon burn with a bright white light in a demonstration. A white powder is left behind. “Where did the powder come from?” she asks. Her teacher says, “The magnesium reacted with oxygen from the air, to make a new substance, magnesium oxide.”

Metals react with oxygen to form metal oxides. The reaction is a chemical reaction, and a new substance is made. The rate of reaction varies: magnesium burns vigorously, iron reacts slowly over time to form rust, and copper reacts slowly to form a black oxide.

Magnesium reacting with oxygen is a teacher demonstration only. It is very bright and hot.

The word equation for magnesium burning is: magnesium + oxygen → magnesium oxide.

Key ideas

  • A metal reacts with oxygen to form a metal oxide.
  • The reaction is a chemical change, with a new substance made.
  • Metals differ in how fast they react with oxygen.
  • Burning metals are demonstrations for the teacher only.
Worked example 8.1.1
What is the product when magnesium reacts with oxygen? Write the name.

Method. Read the right side of the word equation.

  1. Read. The product written after the arrow is magnesium oxide.
    magnesium oxide
  2. Name it. So the product is magnesium oxide.
    magnesium oxide
  3. Write the answer.
    magnesium oxide

Check. Magnesium oxide is a white powder. ✓

Worked example 8.1.2
What is the name for the type of substance formed when a metal reacts with oxygen? Write the words.

Method. Recall the words.

  1. Recall. A compound of a metal and oxygen is a metal oxide.
    metal oxide
  2. Name it. So the substance is a metal oxide.
    metal oxide
  3. Write the answer.
    metal oxide

Check. Oxide means a compound with oxygen. ✓

Worked example 8.1.3
Which metal reacts slowly with oxygen and air to form rust? Write the word.

Method. Recall the example.

  1. Recall. Iron reacts slowly with oxygen and water to form rust.
    rust
  2. Name it. So the metal is iron.
    iron
  3. Write the answer.
    iron

Check. Rust is a form of iron oxide. ✓

Watch out

Watch out: the metal does not disappear; the new substance contains the metal and oxygen. The mass of the product is greater than the mass of the metal.

Exam tip

Exam tip. Name the product as a metal oxide, and check that oxygen is a reactant.

Try it (with your teacher, or a grown-up at home). Look at a labelled photograph of rust on an old metal gate, and name the metal and the product. Do not burn or heat any metal yourself; your teacher does any demonstration.

Exercise 8A  Metals and oxygen

1
FWhat type of substance is formed when a metal reacts with oxygen? Write the words.
2
FWhat is the reactant that a metal combines with to form an oxide? Write the word.
3
FWhat is the name of the product of magnesium and oxygen? Write the words.
4
FWhat is the name of the substance that makes rust? Write the words.
5
FWhich metal reacts most vigorously with oxygen in the list: magnesium or copper? Write the word.
6
FIs the reaction of a metal with oxygen a chemical change? Write yes or no.
7
FIs the metal oxide heavier than the metal before it reacted? Write yes or no.
8
FWrite the word equation: copper + oxygen → copper oxide. Write the product.
9
PSAli says that a metal reacts with oxygen in the air, and the metal disappears. Is Ali right? Write yes or no.
10
PSWorking scientifically: a pupil wants to compare how fast two metals react with oxygen. Name one variable to control. Accept any one: the mass of metal, or the temperature.
11
RExplain why magnesium reacts more vigorously with oxygen than copper does. Write one sentence.
12
RChallenge: explain why a metal oxide is not a mixture of the metal and oxygen. Write one sentence.
8.2

The reactivity series

Year 8
8C3: the reactivity series of metals, from their reactions with water and dilute acids
Video lesson: The reactivity seriesComing soon
Story. Omar has five metal samples and wants to know which is the most reactive. “How can I tell without guessing?” he asks. His teacher says, “Compare how each reacts with water and with dilute acid. Put them in order from the most to the least reactive.”

The reactivity series is a list of metals in order of how reactive they are. Potassium is the most reactive of those listed here, and copper the least. A more reactive metal reacts more vigorously, and reacts with water or acid at a lower temperature or more quickly.

Metals above copper in the series react with dilute acids to give off hydrogen. Potassium, sodium and calcium react with cold water. Metals such as magnesium react only with steam. Copper does not react with water or dilute acid.

Reactivity series (most reactive at the top)potassiumsodiumcalciummagnesiumzincironcoppermore reactiveless reactive
The reactivity series of the metals in this chapter, from most to least reactive.

The table gives the reactions of four metals with water and with dilute hydrochloric acid. Pupils never handle the acid; this is a teacher demonstration.

MetalWith waterWith dilute hydrochloric acid
magnesiumvery slow with cold water; reacts with steamreacts quickly, with bubbles
zincno reaction with cold waterreacts steadily, with bubbles
ironno reaction with cold waterreacts slowly, with bubbles
copperno reactionno reaction

Key ideas

  • The reactivity series ranks metals by how reactive they are.
  • Potassium is more reactive than sodium, which is more reactive than calcium.
  • Metals above copper react with dilute acid to give hydrogen.
  • Copper does not react with water or dilute acid.
Worked example 8.2.1
Which metal in the list is the least reactive? Write the name.

Method. Find the lowest position in the series.

  1. Look. Copper is at the bottom of the series shown.
    bottom
  2. Name it. So copper is the least reactive.
    copper
  3. Write the answer.
    copper

Check. Copper does not react with dilute acid. ✓

Worked example 8.2.2
Do any of the four metals in the table react with cold water? Write yes or no.

Method. Read the table.

  1. Read. Zinc and iron show no reaction with cold water; magnesium reacts only with steam.
    no reaction
  2. Decide. Copper shows no reaction with water either.
    no reaction
  3. Name it. So none of these four reacts with cold water; the answer is no.
    no
  4. Write the answer.
    no

Check. Only potassium, sodium and calcium react with cold water. ✓

Worked example 8.2.3
Which metal in the table reacts with dilute acid but not with cold water, and reacts more than iron? Write the word.

Method. Read the table for acid and water.

  1. Read. Zinc reacts steadily with acid and does not react with cold water.
    steadily
  2. Compare. Zinc reacts more than iron with dilute acid.
    more than iron
  3. Name it. So the metal is zinc.
    zinc
  4. Write the answer.
    zinc

Check. Zinc is above iron in the series. ✓

Watch out

Watch out: the reactivity series is about how fast a metal reacts, not how heavy it is or how useful it is.

Exam tip

Exam tip. Compare the reactions in the same conditions. Name the metals in order, most reactive first.

Try it (with your teacher, or a grown-up at home). Look at the reactivity series picture. Write the metals in order, most reactive first, and check that the order matches the table. Do not add any acid to any metal.

Exercise 8B  The reactivity series

1
FWhich metal is the most reactive of the seven shown? Write the name.
2
FWhich metal in the series is the least reactive? Write the name.
3
FIs sodium more reactive than calcium? Write yes or no.
4
FWhich gas is released when a metal above copper reacts with dilute acid? Write the word.
5
FWhich metal in the table reacts with steam but not with cold water? Write the word.
6
FDoes copper react with dilute hydrochloric acid? Write yes or no.
7
FWhich is more reactive: iron or zinc? Write the word.
8
FWrite the names of the metals in order, from most reactive to least reactive, for magnesium, zinc and copper. Write the three names.
9
PSAli says that potassium is less reactive than copper, because it is lighter. Is Ali right? Write yes or no.
10
PSWorking scientifically: a pupil sorts the metals by the bubbles from acid, not by the series. Name one way this sorting could be unfair. Accept any one: different sizes of metal, or different acid concentrations.
11
RExplain why copper is not used to displace hydrogen from acid. Write one sentence.
12
RChallenge: explain why potassium is kept away from water in a laboratory. Write one sentence.
8.3

Comparing metals with dilute acid

Year 8
8C3: comparing the reactivity of metals with dilute acid, by counting bubbles, in a fair test
Video lesson: Comparing metals with dilute acidComing soon
Story. Ruby’s class compares four metals in the same dilute acid, counting the bubbles for one minute each. “Which one is most reactive?” asks Ruby. “Count only the bubbles of gas, and keep every test the same,” says the teacher.”

In a fair test the metals are the same size and mass, the acid is the same concentration and volume, and the counting is done for the same time. The number of bubbles of hydrogen per minute shows the rate of reaction, and so the reactivity of each metal.

The table gives example class data. The graph shows the same data.

MetalBubbles of hydrogen per minute
magnesium60
zinc20
iron5
copper0
Bubbles of hydrogen per minute (example data)60magnesium20zinc5iron0copperMore bubbles means a faster reaction.
Bubbles of hydrogen per minute for magnesium, zinc, iron and copper.

Key ideas

  • More bubbles per minute means a faster reaction.
  • Keep the metal size, acid volume and concentration the same.
  • Count the bubbles for the same time for each metal.
  • Copper shows no bubbles, so it does not react with dilute acid.
Worked example 8.3.1
Using the table, which metal gives the most bubbles per minute? Write the name.

Method. Find the largest number of bubbles.

  1. Look. The largest value is 60 bubbles per minute, from magnesium.
    60
  2. Name it. So magnesium gives the most bubbles.
    magnesium
  3. Write the answer.
    magnesium

Check. Magnesium is most reactive in the series. ✓

Worked example 8.3.2
How many more bubbles per minute does magnesium give than zinc? Write the number.

Method. Subtract the zinc value from the magnesium value.

  1. Read. Magnesium gives 60 and zinc gives 20 bubbles per minute.
    60 and 20
  2. Calculate. The difference is 60 minus 20.
    60 - 20 = 40
  3. Write the answer.
    40

Check. 20 + 40 = 60. ✓

Worked example 8.3.3
How many times as many bubbles does magnesium give as zinc? Write the number.

Method. Divide the magnesium value by the zinc value.

  1. Read. Magnesium gives 60 and zinc gives 20 bubbles per minute.
    60 and 20
  2. Calculate. The ratio is 60 divided by 20.
    60 / 20 = 3
  3. Write the answer.
    3

Check. 20 x 3 = 60. ✓

Watch out

Watch out: a metal with no bubbles is not always unreactive in every condition; here it means no reaction with this acid, under these conditions.

Exam tip

Exam tip. Say which variable you control and why. Count bubbles over the same time each time.

Try it (with your teacher, or a grown-up at home). Ask your teacher to show a demonstration with dilute acid and two metal strips of the same size. Count the bubbles for one minute and write them down. Do not touch the acid; wash hands after the lesson.

Exercise 8C  Comparing metals with dilute acid

1
FWhat is a bubble of hydrogen a measure of in this test? Write the word: rate or mass.
2
FWhich metal gave no bubbles in the table? Write the name.
3
FUsing the table, how many bubbles per minute did iron give? Write the number.
4
FUsing the table, how many bubbles per minute did zinc give? Write the number.
5
FWhich metal gave the fewest bubbles that were not zero? Write the name.
6
FWhat is the difference in bubbles per minute between zinc and iron? Write the number.
7
FIs magnesium more reactive than zinc, from the table? Write yes or no.
8
PSWorking scientifically: name one variable to keep the same for every metal. Accept any one: the size of the metal, the acid volume, or the time counted.
9
PSRuby says that the bubbles counted in the first 20 seconds should be doubled to find the bubbles per minute. Is Ruby right? Write yes or no.
10
PSWorking scientifically: a pupil has counted 9 bubbles in 15 seconds. How many would this be per minute at the same rate? Write the number.
11
RExplain why a fair test uses the same mass of each metal. Write one sentence.
12
RChallenge: explain why magnesium gives more bubbles than zinc, using the reactivity series. Write one sentence.
8.4

Displacement reactions

Year 8
8C3: displacement reactions, where a more reactive metal takes the place of a less reactive metal in its compound
Video lesson: Displacement reactionsComing soon
Story. Sam drops a piece of zinc into a blue solution of copper sulfate, and it slowly becomes coated with a brown solid. “Has the zinc turned into copper?” he asks. His teacher says, “The zinc is more reactive, so it takes the place of the copper in the compound. The copper is pushed out as a solid.”

A displacement reaction happens when a more reactive metal takes the place of a less reactive metal in a compound. The more reactive metal forms a new compound, and the less reactive metal is set free as the element.

Zinc displaces copper from copper sulfate: zinc + copper sulfate → zinc sulfate + copper. Copper does not displace zinc, because copper is less reactive.

zinc + copper sulfatezinc sulfate + copperzinc is more reactive than copper, so it displaces copper
Zinc displaces copper from copper sulfate.

The table gives the word equations for some displacement and related reactions. Each one is a teacher demonstration.

ReactantsProductsNote
magnesium + oxygenmagnesium oxideteacher demonstration only
zinc + hydrochloric acidzinc chloride + hydrogenbubbles of hydrogen; teacher demonstration
magnesium + hydrochloric acidmagnesium chloride + hydrogenbubbles of hydrogen; teacher demonstration
zinc + copper sulfatezinc sulfate + coppera displacement reaction; teacher demonstration
magnesium + copper sulfatemagnesium sulfate + coppera displacement reaction; teacher demonstration

Key ideas

  • In a displacement, the more reactive metal takes the place of the less reactive one.
  • The less reactive metal is set free as the element.
  • A less reactive metal does not displace a more reactive one.
  • Use the reactivity series to predict whether a displacement happens.
Worked example 8.4.1
In the reaction zinc + copper sulfate, which metal is displaced? Write the name.

Method. Find the metal that is pushed out.

  1. Look. The zinc takes the place of copper in the compound.
    takes the place
  2. Name it. So copper is displaced.
    copper
  3. Write the answer.
    copper

Check. Copper is less reactive than zinc. ✓

Worked example 8.4.2
Will copper displace zinc from zinc sulfate? Write yes or no.

Method. Use the reactivity series.

  1. Check. Copper is less reactive than zinc, so it cannot take zinc’s place.
    less reactive
  2. Decide. So no displacement happens; the answer is no.
    no
  3. Write the answer.
    no

Check. Only a more reactive metal displaces a less reactive one. ✓

Worked example 8.4.3
Write the product that is set free as an element in the zinc and copper sulfate reaction. Write the name.

Method. Read the right side of the equation.

  1. Read. The products are zinc sulfate and copper.
    zinc sulfate and copper
  2. Name it. Copper is the element set free.
    copper
  3. Write the answer.
    copper

Check. Zinc sulfate is the new compound. ✓

Watch out

Watch out: in a displacement the metal that is set free is the less reactive one. Do not confuse it with the metal that is added.

Exam tip

Exam tip. Write the equation with the more reactive metal on the left, and the less reactive metal set free on the right.

Try it (with your teacher, or a grown-up at home). Look at the displacement picture. Say which metal is more reactive, which metal is displaced, and what the new compound is. Do not handle copper sulfate or zinc in the lab; use the picture.

Exercise 8D  Displacement reactions

1
FWhat is the name for a reaction where a more reactive metal takes the place of a less reactive metal in a compound? Write the words.
2
FIn the zinc and copper sulfate reaction, which metal is the more reactive? Write the name.
3
FWhat is the product that is set free as an element? Write the name, from the zinc and copper sulfate reaction.
4
FWhich compound is formed when zinc displaces copper? Write the name.
5
FWill magnesium displace copper from copper sulfate? Write yes or no.
6
FWill copper displace zinc from zinc sulfate? Write yes or no.
7
FIn the reaction magnesium + copper sulfate, what is the metal that is set free? Write the name.
8
FWrite the name of the compound formed from magnesium and copper sulfate. Write the name.
9
PSAli says copper displaces magnesium from magnesium sulfate. Is Ali right? Write yes or no.
10
PSWorking scientifically: a pupil predicts whether iron will displace zinc from zinc sulfate. Write yes or no.
11
RExplain why a displacement reaction tells us which metal is more reactive. Write one sentence.
12
RChallenge: explain why iron displaces copper from copper sulfate. Write one sentence.
8.5

Writing symbol equations

Year 8
8C3: write and balance simple symbol equations for the reactions in this chapter
Video lesson: Writing symbol equationsComing soon
Story. Sam writes the word equation for magnesium burning: magnesium + oxygen → magnesium oxide. “Now the symbol equation,” says his teacher. “Count the atoms on each side. They must be the same, so you may need a number in front of a formula.”

A symbol equation uses chemical symbols and formulas. It must be balanced: the number of atoms of each element is the same on both sides. A number in front of a formula multiplies every atom in it.

For magnesium burning: 2Mg + O2 → 2MgO. There are two magnesium atoms and two oxygen atoms on each side.

The table gives three balanced symbol equations used in this chapter.

Symbol equation (balanced)
2Mg + O2 -> 2MgO
Mg + 2HCl -> MgCl2 + H2
Zn + CuSO4 -> ZnSO4 + Cu

Key ideas

  • A symbol equation uses symbols and formulas.
  • It must be balanced: equal atoms of each element on both sides.
  • A number in front multiplies all the atoms in that formula.
  • Only change the numbers in front; never change a formula.
Worked example 8.5.1
In 2Mg + O2 → 2MgO, how many magnesium atoms are on the right? Write the number.

Method. Count the magnesium on the right.

  1. Read. The right side is 2MgO, so there are 2 magnesium atoms.
    2MgO
  2. Count. So there are 2 magnesium atoms on the right.
    2
  3. Write the answer.
    2

Check. Two magnesium atoms on each side. ✓

Worked example 8.5.2
In Mg + 2HCl → MgCl2 + H2, how many hydrogen atoms are on the left? Write the number.

Method. Multiply the number in front by the atoms in the formula.

  1. Read. The left side has 2HCl, so there is 1 hydrogen atom in each HCl.
    2HCl
  2. Calculate. 2 times 1 hydrogen atom makes 2 hydrogen atoms.
    2 x 1 = 2
  3. Write the answer.
    2

Check. H2 on the right gives 2 hydrogen atoms. ✓

Worked example 8.5.3
Write the symbol equation for magnesium reacting with oxygen, balanced. Write it in full.

Method. Balance the oxygen, then the magnesium.

  1. Oxygen. O2 gives two oxygen atoms; MgO has one each, so use 2MgO.
    2MgO
  2. Magnesium. Two magnesium atoms are then needed on the left: 2Mg.
    2Mg
  3. Write the answer.
    2Mg + O2 → 2MgO

Check. Both sides now have 2 Mg and 2 O. ✓

Watch out

Watch out: you must not change the formula of a substance to balance an equation. Only add a number in front.

Exam tip

Exam tip. Count each element on both sides. Check the balancing at the end.

Try it (with your teacher, or a grown-up at home). Write the balanced symbol equation for magnesium with hydrochloric acid in your notebook, using the table above. Check each element on both sides with a partner.

Exercise 8E  Writing symbol equations

1
FIn 2MgO, how many oxygen atoms are there? Write the number.
2
FIn 2Mg + O2, how many magnesium atoms are there on the left? Write the number.
3
FIn Zn + CuSO4 → ZnSO4 + Cu, how many sulfur atoms are there on each side? Write the number.
4
FIn Mg + 2HCl → MgCl2 + H2, how many chlorine atoms are on each side? Write the number.
5
FIn Mg + 2HCl → MgCl2 + H2, what is the number in front of HCl? Write the number.
6
FWrite the balanced symbol equation for zinc and copper sulfate, with no numbers changed in the formulas. Write the equation.
7
FIn the symbol equation Mg + O2 → MgO, which number needs changing to balance it? Write the number that must go in front of MgO.
8
PSAli writes Mg + O2 → MgO2 for magnesium oxide. Is this a correct formula? Write yes or no.
9
PSWorking scientifically: a student counts the atoms in 3Mg. How many magnesium atoms are there? Write the number.
10
RExplain why a symbol equation must be balanced. Write one sentence.
11
RChallenge: write the balanced symbol equation for magnesium with oxygen, using the symbols Mg, O2 and MgO. Write the equation.

Chapter summary

SkillMethod
Metal and oxygenMetal + oxygen gives a metal oxide; a chemical change.
Reactivity seriesPotassium, sodium, calcium, magnesium, zinc, iron, copper: most to least reactive.
Metal and acidMetal + dilute acid gives a salt and hydrogen; copper does not react.
DisplacementA more reactive metal takes the place of a less reactive one in its compound.
Symbol equationsBalanced: equal atoms on both sides; change only the numbers in front.

Can you…?

  • I can write word equations for metals reacting with oxygen, water and dilute acids
  • I can put metals in order of reactivity using their reactions
  • I can explain and predict a displacement reaction
  • I can compare metals fairly using a bubble count
  • I can write and balance simple symbol equations for these reactions

Key terms

reactivity series
a list of metals in order of how reactive they are
metal oxide
a compound of a metal with oxygen
displacement reaction
a more reactive metal takes the place of a less reactive one in a compound
symbol equation
an equation using chemical symbols and formulas, which must be balanced
balanced
having equal numbers of each type of atom on both sides
rate of reaction
how fast a reaction happens

Exercise 8Z  Check-up

1
What type of substance is formed when a metal reacts with oxygen? Write the words.
2
Which metal is the most reactive of the seven in the series? Write the name.
3
Which gas is released when a metal above copper reacts with dilute acid? Write the word.
4
Using the bubble table, how many bubbles per minute did magnesium give? Write the number.
5
Using the bubble table, how many more bubbles did zinc give than iron? Write the number.
6
In zinc + copper sulfate, which metal is set free? Write the name.
7
Will copper displace zinc from zinc sulfate? Write yes or no.
8
In 2MgO, how many oxygen atoms are there? Write the number.
9
Write the balanced symbol equation for magnesium with oxygen. Write the equation.
10
Explain why copper does not react with dilute acid. Write one sentence.

Total 15 marks. Allow about 15 minutes.

Exercise 8X  Practice test questions

1
FWhat is the name of the product of magnesium and oxygen? Write the name.[1 mark]
2
FPut these metals in order, most reactive first: copper, magnesium, zinc. Write the three names.[2 marks]
3
FWhich gas is released when zinc reacts with dilute hydrochloric acid? Write the word.[1 mark]
4
RExplain why magnesium is more reactive than zinc. Write one sentence.[2 marks]
5
FWill iron displace copper from copper sulfate? Write yes or no.[1 mark]
6
PSUsing the bubble table, what is the difference between magnesium and zinc? Write the number.[2 marks]
7
FWrite the symbol equation for magnesium reacting with oxygen, balanced. Write the equation.[2 marks]
8
FWhat is the name of a reaction in which a more reactive metal takes the place of a less reactive metal? Write the words.[1 mark]
9
RExplain why a fair test uses the same mass of each metal. Write one sentence.[2 marks]
10
FName the metal that does not react with dilute hydrochloric acid in the table. Write the name.[1 mark]
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