Crude Oil and Fuels

- crude oil is a mixture of many different compounds

- most of the compounds in crude oil are hydrocarbons- they contain only hydrogen and carbon atoms

- alkanes are saturated hydrocarbons, they contain as many hydrogen atoms as possible in their molecules

- the general formula of an alkane is:

    Cn = H2n+2

- crude oil is separated into fractions using fractional distillation

- the properties of each fraction depend on the size of the hydrocarbon molecules in it

- lighter fractions make better fuels as they ignite more easily and burn well, with cleaner (less smokey) flames

- when hydrocarbon fuels are burned in plenty of ai, the carbon and hydrogen in the fuel are completely oxidised, they produce carbon dioxide and water

- can test the gases formed in complete combustion of a hydrocarbon:

    the carbon dioxide turns limewater cloudy, water turns blue cobalt, chloride paper pink

- incomplete combustion of a hydrocarbon produces carbon monoixde (a toxic gas) as one of its products

- large hydrocarbon molecules can be broken up into smaller molecules by passing the vapours over a hot catalyst, or by mixing them with a steam and heating them to a very high temperature

- cracking produces saturated hydrocarbons used as fuels, and unsaturated hydrocarbons (alkenes)

- alkenes (and other unsaturated compounds containing carbon-carbon double bonds) react with orange bromine water, turning it colourless