Crude Oil, Hydrocarbons & Alkanes

Crude oil

• Crude oil is a finite resource found in rocks. It is the remains of ancient biomass, mainly plankton, buried in mud and compressed over millions of years
• It is a mixture of a very large number of compounds, most of them hydrocarbons: molecules made of hydrogen and carbon atoms only
• Because it is a mixture it can be separated by a physical process, fractional distillation

Alkanes

• Most of the hydrocarbons in crude oil are alkanes
• Alkanes are a homologous series: a family of compounds with the same general formula and similar chemical properties, each member differing by $\text{CH}_2$
• General formula: $\text{C}_n\text{H}_{2n+2}$
• Alkanes are saturated: every carbon–carbon bond is a single bond, so each carbon has four single bonds in total

• To recognise an alkane from its formula, check that the hydrogens are $2n + 2$: $\text{C}_8\text{H}_{18}$ is an alkane, $\text{C}_8\text{H}_{16}$ is not