Chemistry(2)

Most metals in everyday use are mixtures of metals called ALLOYS.

Cast iron

Iron oxide is reduced to iron in a BLAST FURNACE. Iron straight from the blast furnace is about 96% pure. The impurities it contains make the iron BRITTLE and this limits its uses.

Blast furnace iton is used as CAST IRON.

Cast iron is strong in compression.

Crude oil is a mixture of a very large number of compounds, most of which are hydrocarbons.

Alkanes

A HYDROCARBON is a compound made up of hydrogen atoms and carbon atoms only. Most of the hydrocarbon molecules in crude oil are ALKANES.

Alkanes have the general formula CnH2n+2. For example, the chemical formula for butane (which contains four carbon atoms) is C4H10.

A compound consists of two or more elements chemically combined together. Take care not to write that hydrocarbons are mixtures of hydrogen and carbon.

An alkane molecule can be represented by its chemical formula or by its DISPLAYED STRUCTURE.

Mixtures

The substances in a mixture are not chemically combined together. These substances can be:

• two or more elements
• two or more compounds
• elements and compounds

Mixing does not change the chemical properties of each substance in a mixture.

Distillation

DISTILLATION is one of the several physical methods that can be used to seperate the substances in a mixture. It is used to seperate a mixture of liquids that have dissolved into each other. The mixture is heated until one of the liquids evaporates. Its vapours are then cooled and condensed to form a seperated liquid.

Complete combustion

The combustion of hydrocarbon fuels releases energy to the surroundings. The hydrogen and carbon in the fuel reacts with oxygen and is OXIDISED. If there is plenty of oxygen, COMPLETE COMBUSTION occurs. The hydrogen atoms in the fuel are oxidised to produce water vapour:

Partial combustion

If there is not enough oxygen, INCOMPLETE COMBUSTION (partial combustion) occurs. The hydrogen in the fuel is still oxidised to water vapour, but the carbon is not fully oxidised.