AQA GCSE Chemistry

Revision Notes

10.3.2 Alloys as Useful Materials

Composition of Alloys

  • Alloys are mixtures of metals where the metals are not chemically combined
  • They can also be made from metals mixed with non-metals such as carbon or phosphorus
  • Alloys often have properties that can be very different from the metals they contain, for example they can have more strength, hardness or resistance to corrosion or extreme temperatures
  • Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms
  • This makes it more difficult for the layers to slide over each other, so they are usually much harder and stronger than the pure metal

Structure of alloy, IGCSE & GCSE Chemistry revision notes

The regular arrangement of a metal lattice structure is distorted in alloys

Exam Tip

Alloys are mixtures of substances, they are not chemically combined and an alloy is not a compound.

Properties & Uses

  • Many of the metals that are in everyday use around us are alloys
  • Some common examples are discussed below

Copper Alloys

  • Bronze is an alloy made of copper and tin. It is harder than copper and is used to make ornaments and medals
  • Brass is a common example of an alloy which contains 70% copper and 30% zinc. It is decorative and corrosion resistant and is used for low friction ornamental purposes such as plumbing and carpentry fittings

Brass, IGCSE & GCSE Chemistry revision notes

Brass is used extensively in modern kitchen and bathroom fittings

Aluminium Alloys

  • Aluminium is mixed with copper, manganese and silicon for aircraft body production as aluminium alloys tend to be stronger and lighter than pure aluminium
  • Aluminium and magnesium (5%) make an interesting alloy called magnalium which is also used extensively in automobile and aircraft construction
  • As well as being lighter and stronger, it is also more corrosion resistant than aluminium
  • Magnalium with 50% magnesium is used in the production of fireworks as it is more stable than pure magnesium but still burns brightly

Gold Alloys

  • Gold alloys are used to make jewellery
  • Gold metal is relatively soft and malleable so other metals such as copper, zinc and silver are added to provide strength and toughness
  • Carats are used to express the purity of gold jewellery.
  • Pure gold with nothing else added is said to be 24 carat
  • A 12 carat piece of gold jewellery therefore contains 50% gold
  • For example a 12 carat necklace that weighs 50g contains 50% gold, so 25 grams

Steel Alloys

  • Iron from a blast furnace is an alloy of 96% iron, with carbon, phosphorus, silicon and sulfur impurities
  • It is called cast iron and is too brittle for many uses, so most of it is converted into steel by removing some of the impurities
  • Not all of the carbon is removed as steel contains some carbon, the percentage of which depends on the use of the steel
  • Alloys of steel are made from adding other metals to steel such as chromium, manganese or nickel
  • By carefully controlling the amounts added, the particular type of alloy required can be produced
  • Steel alloys are used in construction, transport, manufacturing and other industries

Exam Tip

The composition of alloys can be carefully controlled to ensure the finished alloys have desired characteristics for particular uses.

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.

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