How do we rank metals by reactivity, and what are displacement reactions?
The reactivity series of metals, the reactions of metals with water and acid, and displacement reactions of metals with metal salt solutions.
A CCEA GCSE Chemistry answer on the reactivity series, covering how metals are ranked by their reactions with water and acid, the order of the common metals, and how a more reactive metal displaces a less reactive one from its salt solution.
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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 with acid, use those reactions to rank metals, and explain and write equations for displacement reactions.
The reactivity series
Hydrogen is included as a reference point: metals above hydrogen react with dilute acid to give hydrogen, while metals below it (copper, silver, gold) do not.
Reactions with water and acid
So watching how readily a metal reacts with water and acid lets you place it in the series, as in the worked questions.
Displacement reactions
For example, adding zinc to copper sulfate solution displaces copper: the zinc dissolves as , and copper metal is deposited as the blue solution fades. A metal cannot displace one above it in the series, so copper added to zinc sulfate gives no reaction.
Worked example
Examples in context
- Example 1. Galvanising and protection
- The reactivity series explains why a more reactive metal such as zinc is attached to iron to protect it: the zinc reacts in preference to the iron. This sacrificial protection is a direct application of the order of reactivity.
- Example 2. Extracting copper from solution
- Scrap iron is added to solutions containing copper ions to displace and recover the copper, because iron is more reactive. This thermit-free, low-cost recovery method relies entirely on displacement chemistry.
- Example 3. The thermit reaction
- Aluminium displaces iron from iron(III) oxide in the thermit reaction, releasing so much heat that the iron is produced molten and can weld railway tracks together on site. This dramatic use of displacement works because aluminium is more reactive than iron and so takes its oxygen.
Linking reactivity to electron loss
The order of the reactivity series is really an order of how readily each metal loses electrons to form positive ions. The most reactive metals, potassium and sodium, lose their outer electron extremely easily, which is why they react so violently with water. Less reactive metals such as copper hold their electrons more tightly, so they react slowly or not at all. Seeing the series this way connects it directly to redox: a displacement reaction happens because the more reactive metal gives up its electrons to the ions of the less reactive metal, and CCEA often asks you to explain a displacement in exactly these terms.
Try this
Q1. State what is produced when a metal above hydrogen reacts with dilute acid. [1 mark]
- Cue. A salt and hydrogen.
Q2. Explain why zinc displaces copper from copper sulfate. [2 marks]
- Cue. Zinc is more reactive than copper, so it takes copper's place, forming zinc ions and copper metal.
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 20194 marksDescribe how the reactions of calcium, magnesium and copper with water and dilute acid can be used to place them in order of reactivity.Show worked answer →
Markers want the observations linked to the order.
Calcium reacts steadily with cold water, giving off hydrogen and forming an alkaline solution, and reacts vigorously with acid. This shows it is the most reactive.
Magnesium reacts only very slowly with cold water but reacts quite vigorously with dilute acid, giving hydrogen. This places it below calcium.
Copper does not react with water or with dilute acid at all. This shows it is the least reactive.
So the order of reactivity is calcium > magnesium > copper, with the most reactive reacting most readily with water and acid.
Markers reward the observations (calcium reacts with cold water, magnesium with acid, copper not at all) and the resulting order.
CCEA 20213 marksIron is added to copper(II) sulfate solution. State what you would observe and write the ionic equation for the displacement reaction.Show worked answer →
The marks are for the observation and a balanced ionic equation.
Iron is more reactive than copper, so iron displaces copper from the solution. You would see a brown/pink coating of copper form on the iron, and the blue colour of the solution fades as copper ions are removed.
The ionic equation is:
Markers reward copper deposited on the iron and the blue solution fading, plus a correctly balanced ionic equation.
Related dot points
- Oxidation and reduction defined in terms of oxygen and of electrons (OIL RIG), identifying redox in displacement and other reactions, and writing half-equations.
A CCEA GCSE Chemistry answer on redox reactions, covering oxidation and reduction defined by the gain and loss of oxygen and of electrons (OIL RIG), how to identify oxidation and reduction in displacement and other reactions, and how to write half-equations.
- How the reactivity of a metal determines its extraction method, the extraction of iron by reduction with carbon in the blast furnace, and why reactive metals are extracted by electrolysis.
A CCEA GCSE Chemistry answer on the extraction of metals, covering how a metal's position in the reactivity series sets its extraction method, the reduction of iron oxide with carbon in the blast furnace, and why metals above carbon are extracted by electrolysis.
- The rusting of iron and the conditions needed, and methods of preventing corrosion including barrier methods, galvanising and sacrificial protection.
A CCEA GCSE Chemistry answer on corrosion, covering the rusting of iron, the conditions of water and oxygen needed, and the methods used to prevent corrosion including barrier methods, galvanising and sacrificial protection.
- Electrolysis of molten ionic compounds and of aqueous solutions including brine, predicting the products at each electrode, and writing electrode half-equations.
A CCEA GCSE Chemistry answer on electrolysis, covering how molten ionic compounds and aqueous solutions are split by an electric current, the rules for predicting the products at the cathode and anode including the electrolysis of brine, and writing electrode half-equations.
- The properties and trends of the Group 1 alkali metals, the Group 7 halogens and the Group 0 noble gases, including reactivity trends and displacement reactions of the halogens.
A CCEA GCSE Chemistry answer on group trends, covering the properties and reactivity of the Group 1 alkali metals, the Group 7 halogens with their displacement reactions, and the unreactive Group 0 noble gases, and explaining each trend in terms of electron arrangement.
Sources & how we know this
- CCEA GCSE Chemistry specification (1110) — CCEA (2017)