2. Crude oil mixtureCrude oil is a mixture. It contains hundreds of different compounds. Some are small but most are large. only.Nearly all of these compounds contain carbon and hydrogen only. They are called hydrocarbons. only Hydrocarbons are molecules that contain carbon and hydrogen only.

3. The importance of oil These hydrocarbons are vital to our way of life. We use them as highly portable fuels for many forms of transport. We also use them as raw materials from which a huge range of useful everyday substances are made.

4. Although we can get useful substances from oil, crude oil itself has no uses. In order to make crude oil into useful substances we first have to separate the mixture into molecules of similar size. oil refineryThis is done in an oil refinery. Making oil useful

5. What is crude oil? Crude oil is a mixture of different sized hydrocarbons. The exact composition depends upon where the oil comes from but typically it contains a lot of big molecules. Small molecules Medium molecules Big molecules

6. Fractional Distillation fractional distillation.Crude oil is split into fractions containing similar sized molecules using fractional distillation. The oil is heated until it vaporises. It then passes up a tall tower that is hot at the bottom but cool at the top. As the vapour passes up this tower the molecules cool and condense back to liquid. coolcool hothot

7. Copy the column and arrange the fractions in the right order next to the arrows. FractionBoiling Range ( o C) Kerosine150 - 240 Diesel220 – 275 Petrol40 - 175 Bitumen>350 Fuel gasBelow 40 Lubricating oil250-350 coolcool hothot Fuel gas Petroleum Kerosine Diesel Lub. Oil Bitumen Fractional Distillation

9. The boiling points of molecules We have already said that, in general, the bigger the molecule the higher the boiling point. No. Carbon atoms   B.Pt ( o C)

10. Here are the boiling ranges of some fractions obtained from distillation of petroleum. 1. Using the previous graph, estimate the size range of the molecules present in each fraction. FractionBoiling Range ( o C) Number of carbons Fuel gasBelow 40 Petrol40 - 175 Kerosine150 - 240 Diesel220 - 275 1-5 5-10 9-14 13-17

11. The flammability of molecules When hydrocarbons burn they are reacting with oxygen in the air. In general, the smaller the molecule the better it will mix and then react with the air.

12. Flash points are (roughly) the temperature below which you cannot ignite the substance. Here is some flash points data for oil fractions. Link the molecule to the flash point. SubstanceFlash Point Kerosine<23 Petrol85 - 150 Fuel Oil23 - 61