Carbon in the Reactivity Series

Is carbon in the reactivity series, and where does it sit?

Yes. Carbon is included in the reactivity series as a reference point even though it is not a metal. The reactivity series with carbon included places it below aluminium but above zinc and iron: potassium, sodium, lithium, calcium, magnesium, aluminium, carbon, zinc, iron, tin, lead, hydrogen, copper, silver and gold. The exact list taught may include a few additional metals, but carbon's relative position is what lets you make predictions.

Metals near the top react more readily and form positive ions more easily. Potassium and sodium react vigorously with water, while copper, silver and gold are much less reactive. A metal higher in the series can displace a lower metal from one of its compounds because the higher metal has a greater tendency to form ions.

Why is carbon included in the reactivity series?

Carbon is included because its position predicts whether carbon reduction can extract a metal from its ore. Many metal ores contain metal oxides. If the metal is below carbon in the reactivity series, carbon can remove oxygen from the metal oxide when the mixture is heated. This method can be used for metals such as zinc and iron; for example, carbon can reduce iron oxide because iron is less reactive than carbon.

Metals above carbon hold on to oxygen too strongly for carbon reduction. Aluminium, magnesium, calcium and the alkali metals are therefore extracted using electrolysis of molten compounds. Electrolysis requires substantial electrical energy, which helps explain why extracting very reactive metals is more expensive.

How to answer reactivity-series questions

First locate both elements in the series. For a displacement question, the free metal must be higher than the metal in the compound for a reaction to occur. For an extraction question, compare the metal with carbon. For reactions with acid, compare the metal with hydrogen: metals above hydrogen usually displace hydrogen from dilute acids, while copper, silver and gold do not. Always state the comparison as part of the explanation rather than giving only the predicted result.

Three reactivity questions with explained answers

• Why can carbon reduce iron oxide but not aluminium oxide? Iron is below carbon, so carbon can remove oxygen from iron oxide. Aluminium is above carbon and forms an oxide too stable for carbon reduction.
• What happens when zinc and silver are separately placed in a copper salt solution? Zinc is above copper, so zinc displaces copper. Silver is below copper, so silver does not displace copper and no displacement reaction occurs.
• Why is magnesium extracted by electrolysis rather than reduction with carbon? Magnesium is above carbon, so carbon cannot remove oxygen from magnesium oxide; electrolysis is needed to break down a molten magnesium compound.