For example, the gases fraction contains hydrocarbons with one to four carbon atoms. These have boiling points below room temperature. They are very flammable and have a low viscosity because they are gases.
The hydrocarbons in different fractions differ in these properties. For example, the bitumen fraction contains hydrocarbons with more than 35 carbon atoms. These have boiling points well above room temperature. They are very difficult to ignite and have a high viscosity (they flow with difficulty).
The table shows four alkanes, their molecular formulae and their structures.
The general formula for the alkanes is CnH2n+2 (where n stands for the number of carbon atoms). As the number of carbon atoms increases:
Describe how you can tell from their molecular formulae that ethane, propane and butane are neighbouring compounds in the same homologous series.
Their molecular formulae differ by CH2 from one compound to the next. For example, ethane is C2H6 but propane is C3H8 (and the next one, butane, is C4H10).