Magnesium
Magnesium is a reactive, light metal. Like sodium, it does not occur in nature as the free metal.
In sea water it is present as magnesium chloride. Left open to the air it tarnishes, so no shine can be seen — but rub it with a piece of sandpaper and the lustre appears.
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Physical properties
- Denser than water — density 1740 kg m−3.
- A good conductor of heat and electricity.
Compare it with sodium
Sodium floats on water; magnesium sinks. Both are called light metals, but only one of them is less dense than water.
Chemical properties
- Heated in air, magnesium burns with a brilliant white flame, forming white magnesium oxide.
- It shows no reaction with cold water, but it does react with hot water, forming magnesium hydroxide and hydrogen gas.
- Heated in steam, it forms magnesium oxide and hydrogen gas.
- It reacts rapidly with dilute acids to form the corresponding magnesium salt and hydrogen gas.
Uses
- Mixed with aluminium it forms the alloy magnalium — a strong, light, corrosion-resistant metal used in making aircraft and vehicle parts.
- Producing medicines — milk of magnesia.
- Used as a sacrificial metal to prevent corrosion.