Obtaining & Using MetalsEdexcel GCSE Chemistry: Revision notes

The relative reactivity of metals can be deduced from their reactions with water, acids and salt solutions. A more reactive metal will displace a less reactive metal from a compound (a displacement reaction).

The reactivity series (most to least reactive) covered is: potassium, sodium, calcium, magnesium, aluminium, (carbon), zinc, iron, (hydrogen), copper, silver, gold.

These reactions show the relative tendency of metal atoms to form cations (positive ions) — the more reactive the metal, the more readily it loses electrons to form positive ions.

(Higher tier) Displacement reactions are redox reactions: the more reactive metal loses electrons (is oxidised) to form ions, while ions of the less reactive metal gain electrons (are reduced) to form the metal.

Most metals are extracted from ores found in the Earth's crust. Very unreactive metals (e.g. gold) are found in the crust as the uncombined element, because they do not readily react to form compounds.

Oxidation is the gain of oxygen; reduction is the loss of oxygen. The extraction of metals from their ores involves reduction, since metal ores are usually metal oxides (or compounds convertible to oxides) that must lose oxygen to form the pure metal.

The method used to extract a metal depends on its position in the reactivity series and the cost of the extraction process:

• Metals less reactive than carbon (e.g. iron) can be extracted by heating with carbon, since carbon displaces them by reduction
• Metals more reactive than carbon (e.g. aluminium) cannot be extracted this way and must be extracted using electrolysis, which requires large amounts of electrical energy and is more expensive

Some metals can be extracted using biological methods, which are useful as ore quality declines:

• Bacterial extraction (bioleaching): bacteria break down ore, releasing metal ions into a leachate solution, from which the metal can be extracted (e.g. by electrolysis or displacement)
• Phytoextraction: plants absorb metal compounds from the soil through their roots; the plants are then burned, and the metal is extracted from the ash

These methods are generally slower than traditional extraction but can be used on low-grade ores and can have a lower environmental impact.

A metal's resistance to oxidation (corrosion) is related to its position in the reactivity series: less reactive metals resist oxidation better and stay shinier for longer, while more reactive metals corrode more readily.

Recycling metals has advantages: it saves energy (recycling usually needs less energy than extracting new metal from ore), reduces the need for mining (preserving raw materials and the environment), reduces waste sent to landfill, and can be economically beneficial by lowering production costs.

A life-cycle assessment (LCA) considers the environmental effect of a product across its whole life:

1. Obtaining raw materials
2. Manufacturing the product
3. Using the product
4. Disposing of the product

LCA data can be used to compare products or processes and evaluate which has less overall environmental impact.