The reactivity series

The reactivity series is a list of metals in order of how vigorously they react, from potassium at the top to gold at the bottom. For GCSE you need to know the order, describe how the metals react with water and dilute acids, and use the series to predict displacement reactions and how each metal is extracted. Carbon and hydrogen are usually included as reference points.

The reactivity series in order

AQA's GCSE specification names eight metals you must be able to order from their reactions with water and dilute acids: potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper. It adds that the non-metals hydrogen and carbon are often included. Aluminium, silver and gold appear in other parts of the course, so it helps to know where they fit too.

Reactivity series mnemonic

A mnemonic is a sentence whose first letters match the list. A popular one for the 13 elements above is:

Please Send Lions, Cats, Monkeys And Cute Zebras Into Hot Countries, Signed Gordon.

That gives Potassium, Sodium, Lithium, Calcium, Magnesium, Aluminium, Carbon, Zinc, Iron, Hydrogen, Copper, Silver, Gold. If you prefer another, try Peter Smith Likes Cooking Many Amazing Cakes, Zesty Iced Honey Cakes, Sweet Gingerbread. Or make up your own: one you invent yourself is usually easier to remember.

Why some metals are more reactive

When metals react, their atoms lose electrons to form positive ions. AQA puts it this way: the reactivity of a metal is related to its tendency to form positive ions. Potassium loses its one outer electron very easily, so it reacts violently. Copper holds on to its electrons much more strongly, so it barely reacts at all. The more easily a metal forms positive ions, the higher it is in the series.

Reactions with water and dilute acids

This is how you place metals in order in the lab. The reactions are at room temperature: with cold water, not steam.

The general equations are worth learning:

• metal + water → metal hydroxide + hydrogen, for example 2Na + 2H₂O → 2NaOH + H₂
• metal + acid → salt + hydrogen, for example Mg + 2HCl → MgCl₂ + H₂

The gas is hydrogen in both cases: bring a burning splint near it and it ignites with a squeaky pop. Metals below hydrogen in the series, such as copper, don't react with dilute acids, because they can't displace hydrogen from the acid.

Displacement reactions

A more reactive metal can displace a less reactive metal from a compound. Put a more reactive metal into a solution of a less reactive metal's salt, and the two swap places. If the metal added is less reactive, nothing happens.

Example 1: magnesium and zinc sulfate

Magnesium is above zinc, so it displaces it: magnesium + zinc sulfate → magnesium sulfate + zinc. In symbols, Mg + ZnSO₄ → MgSO₄ + Zn. You would see a grey coating of zinc form on the magnesium.

Example 2: copper and iron(II) sulfate

Copper is below iron, so it can't displace it. No reaction. Always check the positions before writing products.

Example 3: ionic and half equations (Higher)

In a displacement reaction the sulfate ions don't change, so they are spectator ions. Leaving them out gives the ionic equation for example 1:

Mg + Zn²⁺ → Mg²⁺ + Zn

• Mg → Mg²⁺ + 2e⁻: magnesium loses electrons, so it is oxidised.
• Zn²⁺ + 2e⁻ → Zn: zinc ions gain electrons, so they are reduced.

Remember OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons). Displacement reactions are redox reactions.

Working out an order from results

AQA asks you to deduce an order of reactivity from experimental results. A student puts three metals, P, Q and R, into solutions of each other's nitrates and records which ones react.

1. Q displaces both P and R, so Q is the most reactive.
2. P displaces R but not Q, so P is in the middle.
3. R displaces nothing, so R is the least reactive.
4. Order: Q, then P, then R.

The more reactions a metal causes, the higher it goes.

Using the series to extract metals

Where a metal sits in the series decides how it is got out of its ore:

For example, iron is extracted from iron(III) oxide by heating with carbon: 2Fe₂O₃ + 3C → 4Fe + 3CO₂. The iron oxide loses oxygen, so it is reduced, and the carbon gains oxygen, so it is oxidised. Carbon can't do this for aluminium, because aluminium is more reactive than carbon. The electrolysis guide explains how those metals are extracted instead.

Common mistakes

• Mixing up the Cs. The order is calcium, magnesium, aluminium, carbon, zinc: carbon comes after aluminium, not after calcium.
• Predicting a reaction that can't happen. A metal only displaces metals below it.
• Writing hydrogen for metal and water reactions only. Metals that react with dilute acids give hydrogen too.
• Forgetting aluminium's oxide layer. Aluminium is high in the series but can look unreactive, because a thin layer of aluminium oxide protects its surface.
• Getting oxidised and reduced the wrong way round. The metal atoms that lose electrons are oxidised.

To practise reactivity and redox questions with other topics, try today's GCSE Chemistry Higher or GCSE Combined Science Higher short timed paper.

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