Edexcel IGCSE Chemistry · Spec 2.16-2.20
The Reactivity Series, Metal Oxides and Redox Agents
Covers recall the required reactivity sequence, Predict metal and metal-oxide displacement and Identify oxidising and reducing agents.
Chemistry revision video
The Reactivity Series, Metal Oxides and Redox Agents
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Explained
The reactivity series, and what redox actually means
The order to learn is potassium, sodium, lithium, calcium, magnesium, aluminium, carbon, zinc, iron, hydrogen, copper, silver, gold. Carbon and hydrogen are in there deliberately, because their positions decide how a metal can be extracted and whether it reacts with acid.
What the order means
A metal higher in the series loses electrons more readily than one below it. That single statement explains displacement, extraction and corrosion, and it is the sentence to reach for whenever a question asks why.
Displacement
A more reactive metal displaces a less reactive one from its compound. Magnesium added to copper sulfate solution gives magnesium sulfate and copper, because magnesium loses electrons more readily than copper does.
The same holds for metal oxides. Carbon can reduce zinc oxide, iron oxide and copper oxide because carbon sits above all three. It cannot reduce aluminium oxide, which is why aluminium is extracted by electrolysis instead.
Oxidation and reduction happen together
Oxidation is loss of electrons, or gain of oxygen. Reduction is gain of electrons, or loss of oxygen. In any displacement both occur, which is what redox means.
In the magnesium and copper sulfate example, magnesium loses electrons so it is oxidised, and copper ions gain electrons so they are reduced.
Agents are the opposite of what they do
An oxidising agent oxidises something else, and is itself reduced. A reducing agent reduces something else, and is itself oxidised.
So in that reaction magnesium is the reducing agent, even though magnesium is the thing being oxidised. Work out what happens to each substance first, then name the agents last. Trying to do both at once is where the confusion starts.
What examiners say about this topic
Principal examiner reports for Edexcel International GCSE Chemistry are blunt. Candidates generally performed poorly on applied redox questions, and the reports note this has been true across several years. Applying the idea of an oxidising agent in context is described as one of the less familiar and more difficult terms.
They also record a specific habit that costs marks. Many responses stated that silver was unreactive, or at the bottom of the reactivity series, without making a direct comparison with copper. A reactivity question is a comparison, so name both substances and say which is more reactive than which.
One response is described as earning a mark for the observation but losing the next because it never linked the answer to redox. If the question mentions redox, oxidation or reduction, use those words in the answer.
Reactions with water and acid
Potassium, sodium, lithium and calcium react with cold water. Magnesium reacts very slowly with cold water but readily with steam. Metals below hydrogen, such as copper, silver and gold, do not react with dilute acid at all, because they cannot displace hydrogen from it.
That last point is the reason hydrogen appears in a list of metals, and it is worth being able to explain rather than just recite.
Spec 2.16-2.20
What you need to know
- Recall the required reactivity sequence
- Predict metal and metal-oxide displacement
- Identify oxidising and reducing agents
Active recall
Quick check
Answer each question before opening the answer.
Place zinc, aluminium and iron in decreasing reactivity
Aluminium, zinc, iron
What happens when magnesium is heated with copper oxide?
Magnesium oxide and copper form
What happens to an oxidising agent?
It gains electrons and is reduced
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