The reactivity series and displacement reactions
Chemistry · GCSE · The School
The reactivity series ranks metals by how easily they react
Potassium, sodium and calcium sit at the top: they react vigorously, even with cold water. Copper, silver and gold sit at the bottom: they barely react at all, which is why gold jewellery does not tarnish. Between them, metals like zinc and iron react with acids but not with cold water. The order is found by testing metals against water, dilute acid, and each other.
A more reactive metal displaces a less reactive one
Add iron powder to copper sulfate solution and the iron dissolves while copper metal appears — iron is more reactive than copper, so it displaces copper from the compound. Add copper to iron sulfate solution and nothing happens: copper cannot displace a metal above it in the series. The direction only ever goes one way.
A worked prediction
Magnesium is added to zinc sulfate solution. Is magnesium more reactive than zinc? Checking the series: magnesium sits above zinc. So magnesium displaces zinc: Mg + ZnSO₄ → MgSO₄ + Zn. The solid zinc that appears and the magnesium that dissolves are both evidence the prediction was right.
Extraction method depends on reactivity
Metals below carbon in the series, like iron, are extracted by heating their ore with carbon — carbon is reactive enough to displace them. Metals above carbon, like aluminium, cannot be extracted this way; they need electrolysis instead, which is far more expensive in energy. Metals at the very bottom, like gold, are found already as the pure metal and need no extraction at all.
Reading the evidence, not just the result
A displacement reaction in class is usually seen two ways: a colour change in the solution, and a change in the appearance of the solid. Copper sulfate is blue; once the copper is displaced out, the remaining iron sulfate solution turns pale green. Naming BOTH observations, not just "a reaction happened", is what a full-mark answer does.
Carbon is a special case in the series
Carbon is not a metal, but it is placed IN the reactivity series anyway, because it is used to decide extraction methods. A metal below carbon can be displaced from its oxide by carbon; a metal above it cannot. That single placement is the reason iron is cheap to extract and aluminium is not — remembering carbon’s position answers most extraction questions on its own.