5.1C Recall that most metals are transition metals and that their typical properties include: high melting point, high density, the formation of coloured compounds, catalytic activity of the metals and their compounds as exemplified by iron
- High melting point due to electrostatic forces of attraction between positively charged metal ions and ‘sea’ of electrons
- High density
- They have ions with many different charges
- Form coloured compounds
- Are useful as catalysts.
- Shown by iron and its use in the Haber process as a catalyst
5.2C Recall that the oxidation of metals results in corrosion
- Corrosion = destruction of materials by chemical reactions with substances in the environment
- e.g. rusting
- Both air and water are necessary for iron to rust – i.e. oxidation – gain of oxygen results in corrosion
- e.g. rusting
5.3C Explain how rusting of iron can be prevented by: exclusion of oxygen, exclusion of water, and sacrificial protection
- Can be prevented by applying a coating that acts as a barrier, such as greasing, painting or electroplating – i.e. exclusion of oxygen and water
- Aluminium has an oxide coating that protects the metal from further corrosion – exclusion of oxygen and water
- Some coatings are reactive and contain a more reactive metal to provide sacrificial protection
- e.g. zinc is used to galvanise iron
5.4C Explain how electroplating can be used to improve the appearance and/or the resistance to corrosion of metal objects
- Electroplating acts as a barrier in order to exclude oxygen and water
- Also improves appearance as you can electroplate a metal with an unreactive metal such as gold that is beautiful and will not corrode
5.5C Explain, using models, why converting pure metals into alloys often increases the strength of the product
- Iron from the blast surface contains about 96% iron. The impurities make it brittle so it has limited uses
- Blast furnace iron is used as cast iron because of its strength in compression
- Most iron is converted into steels.
- Steels are alloys since they used mixtures of carbon and iron
- Some steels contain other metals. Alloys can be designed to specific uses.
- Low-carbon steels are easily shaped, high carbon steels are hard, and stainless steels are resistant to corrosion.
- Most metals in everyday uses are alloys. Pure copper, gold, iron and aluminium are all too soft for everyday uses and so are mixed with small amounts of similar metals to make them harder for everyday use.
- Gold in jewellery is usually an alloy with silver, copper and zinc
Example of an alloy – two different metals
5.6C Explain why iron is alloyed with other metals to produce alloy steels
5.7C Explain how the uses of metals are related to their properties (and vice versa), including aluminium, copper and gold and their alloys including magnalium and brass