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• Metals mostly occur as compounds in rocks and minerals and must be extracted before they can be used.
• The method used to extract the pure metal depends on its position in the reactivity series.

Metals are very important materials in our everyday lives. There is a high demand for metals to be used in many kinds of industries.

Metals are found in rocks in the Earth’s crust which must be processed to get the pure metal. This is called extraction and can involve several different steps, including chemical reactions.

Unreactive metals

The most unreactive metals, silver and gold, are found as elements in the rocks. They are not chemically bonded to other elements in compounds.

For example, gold (element symbol Au) is an unreactive metal and is found as an element in rocks.

Metals in compounds

Most of the metals found in rocks are combined with other elements in compounds. These compounds are called minerals.

For example, iron (element symbol Fe) is mostly found as the minerals magnetite Fe₃O₄ and hematite Fe₂O₃. Both are compounds of iron chemically bonded to oxygen.

Copper is more reactive than gold and so is found in rocks as a compound. This image of a green rock contains malachite, a compound of copper, carbon and oxygen.

Did you know?

Minerals can have really complicated formulas.

For example, the rare red mineral eudialyte has a simplified formula of ����₁₅�䲹₆F��₃M��₃Z����Ⱦ�₂₅��₈₄��₈C��₂.

That is nine different elements and over 100 atoms in each formula unit.

Different methods are used to extract a metal depending on its position in the reactivity series.

The diagram shows a simple reactivity series, including carbon and hydrogen. Carbon and hydrogen are often included in a reactivity series as they allow us to predict particular chemical reactions.

The reactivity series can be split up to show how metals are extracted into three groups:

1. Metals which are found in the pure crust.

2. Reduction of metal oxides using carbon.

3. Extraction using electrolysis.

Metals with very low reactivity can be found as elements in rocks, such as silver and gold.

The metal is visible running through the rock. They do not need to be treated using a chemical reaction for the pure metal to be obtained.

To extract the metal from the rock, the rock is crushed and the metal is then melted out

Zinc, iron and copper are all found as compounds within rocks. They are generally found bonded to oxygen as compounds called metal oxides.

These metals are extracted using carbon in a displacement reaction. This is because carbon is cheap and readily available.

The reactants are the metal oxide compound and carbon. The products are the pure metal and either carbon monoxide or carbon dioxide.

For example:

metal oxide + carbon → metal + carbon oxide

Carbon is more reactive than zinc, iron and copper. This means the carbon takes the oxygen away and displaces the metal. This leaves the metal as a pure element.

The carbon makes an oxide - either carbon monoxide (CO) or carbon dioxide (CO₂).

This is a specific type of displacement reaction. The more reactive element (carbon) is displacing the less reactive element (in this case a metal) from its compound.

A chemical reaction where oxygen is removed from a compound is called a reduction. This method is called reduction with carbon.

These reactions can be described using either word or symbolchemical equations.

For example, the word equation for the reduction of zinc oxide with carbon is:

zinc oxide + carbon → zinc + carbon monoxide

The symbol equation for the reduction of zinc oxide with carbon is:

ZnO + C → Zn + CO

When metals are above carbon in the reactivity series, they cannot be extracted using reduction with carbon. Carbon is not reactive enough to take the oxygen away from the metal.

These metals are extracted using a process called electrolysis. In electrolysis, an electric current is passed through the compound to split up the metal and the oxygen. In industry, this is carried out on a large scale, but a small scale experiment can be carried out using a power pack to provide the electricity.

For example, an electric current can be passed through aluminium oxide (the compound) to split up the metal (aluminium) and the oxygen.

Making predictions

Not all metals in the periodic table are shown in a simple reactivity series. We can use information about their place in an expanded reactivity series to predict the method of extraction.

For example, platinum is a less reactive metal than gold. Gold is found as an element, so we can predict that platinum will also be found as an element and won’t need a chemical reaction to extract it.

Use the simple reactivity series to make predictions for the following questions.