Obtaining & Using Metals Notes

Edexcel GCSE Chemistry: Revision notes

Key facts

  • A more reactive metal displaces a less reactive one from its compound.
  • Extraction of metals from ores is reduction (loss of oxygen).
  • Metals less reactive than carbon are extracted by heating with carbon; more reactive ones need electrolysis.
  • Unreactive metals such as gold are found uncombined.
  • Recycling saves energy and raw materials; a life-cycle assessment covers the whole life of a product.

Most reactive

  • Potassium
  • Sodium
  • Calcium
  • Magnesium
  • Aluminium

Middle

  • (Carbon)
  • Zinc
  • Iron
  • (Hydrogen)

Least reactive

  • Copper
  • Silver
  • Gold

The reactivity series

A more reactive metal loses electrons more readily and displaces less reactive metals from their compounds.

Relative reactivity is deduced from reactions with water, acids and salt solutions. A more reactive metal forms cations more readily. (Higher tier) Displacement reactions are redox reactions: the more reactive metal is oxidised and the less reactive metal's ions are reduced.

  1. 1

    Add magnesium to copper sulfate

    Magnesium is more reactive than copper.

  2. 2

    Mg atoms lose electrons

    Magnesium is oxidised to Mg²⁺ ions.

  3. 3

    Cu²⁺ ions gain electrons

    Copper ions are reduced to copper atoms.

  4. 4

    Copper is displaced

    Brown copper forms and the blue colour fades.

Magnesium displaces copper from copper sulfate solution

Most reactive

  • Potassium
  • Sodium
  • Calcium
  • Magnesium
  • Aluminium

Middle

  • (Carbon)
  • Zinc
  • Iron
  • (Hydrogen)

Least reactive

  • Copper
  • Silver
  • Gold

Worked example

Magnesium is added to copper sulfate solution. What happens?

Will zinc displace magnesium from magnesium sulfate solution?

Extracting metals from ores

Extraction is reduction, and the method depends on the metal's reactivity and the cost.

Most metals come from ores, usually metal oxides. Oxidation is gain of oxygen and reduction is loss of oxygen, so extraction is reduction. Very unreactive metals such as gold are found uncombined.

  1. 1

    Mine the ore

    Usually a metal oxide.

  2. 2

    Compare the metal with carbon

    Is it more or less reactive than carbon?

  3. 3

    Less reactive: heat with carbon

    Carbon removes the oxygen (reduction), as with iron.

  4. 4

    More reactive: electrolysis

    Molten compound electrolysed, as with aluminium (expensive).

Choosing an extraction method

More reactive than carbon

Example:
Aluminium
Extraction method:
Electrolysis (expensive)

Less reactive than carbon

Example:
Iron
Extraction method:
Heating with carbon

Very unreactive

Example:
Gold
Extraction method:
Found uncombined

Why is aluminium extracted by electrolysis rather than by heating with carbon?

Biological extraction (Higher tier)

Bioleaching and phytoextraction use living things to extract metals, even from low-grade ores.

These methods are useful as ore quality declines. They are generally slower than traditional extraction but can have a lower environmental impact.

  1. 1

    Grow plants

    on soil containing metal compounds

  2. 2

    Roots absorb

    the metal compounds

  3. 3

    Burn the plants

    to leave ash

  4. 4

    Extract the metal

    from the ash

Phytoextraction

Bioleaching

  • Bacteria break down the ore
  • Metal ions go into a leachate solution
  • Extract by electrolysis or displacement

Phytoextraction

  • Plants absorb metal compounds
  • Plants are burned
  • Metal extracted from the ash

Give one advantage of bioleaching over traditional extraction.

Recycling and life-cycle assessment

Recycling saves energy and raw materials, and a life-cycle assessment compares environmental impact.

A metal's resistance to oxidation (corrosion) is linked to its place in the reactivity series: less reactive metals stay shinier longer. A life-cycle assessment (LCA) considers the environmental effect of a product across its whole life and can compare products or processes.

  1. 1

    Raw materials

    obtaining them

  2. 2

    Manufacture

    making the product

  3. 3

    Use

    using the product

  4. 4

    Disposal

    disposing of the product

Stages of a life-cycle assessment

Recycling metals

  • Saves energy
  • Reduces mining
  • Reduces landfill
  • Lowers production costs

Corrosion

  • Less reactive metals resist oxidation
  • More reactive metals corrode readily

Name the four stages considered in a life-cycle assessment.

Try an exam question

Explain why iron can be extracted by heating with carbon but aluminium cannot.

[3 marks]

That's the notes covered.

Carry on to the next subtopic.