01/08/2014

1. 01/08/2014 Fractional Distillation in the Laboratory • L.O. • I can carry out the fractional distillation of crude oil safely in the laboratory. • I can recognise the trends in the properties of the fractions relating to their boiling points. 1:30 AM

2. cool hot Starter / Settler Activity Fuel gas In backs of books put the fractions in the right order starting at the top of the fractionating column. Petroleum Kerosene Diesel Lub. Oil Bitumen

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

4. Here are the boiling ranges of some fractions obtained from distillation of petroleum. Using the graph on the handout, complete the table by estimating the size range of the molecules present in each fraction. 1-5 5-10 9-14 13-17

5. 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. • 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.

6. The viscosity of molecules • When we pour a liquid the molecules have to pass each other. The easier they do this, the runnier the liquid is. • The molecules in fuel oil and bitumen may contain up to 400 carbon atoms in long chain structures. • These chains easily become entangled reducing the runniness of the liquid and so those made up of big molecules tend to be viscous (treacly) not runny.

7. Smaller molecules Lower viscosity “Runny” Bigger molecules Higher viscosity “Treacly” The viscosity of molecules • In contrast, small molecules are more spherical and tend not to get tangled. • They are therefore likely to have a low viscosity (be runny).

8. Fractional Distillation of Crude Oil in the Laboratory thermometer Method We heated the crude oil to various temperatures and collected the fractions. crude oil Fractions collected heat

9. Results colourless runny easy clean yellow thicker harder dirty

10. Here are the viscosities of 5 hydrocarbons. The higher the value the less runny the hydrocarbon is. Draw arrows joining the hydrocarbon with the appropriate value.

11. Industrial Distillation of Crude Oil L.O. • I know how crude oil is fractionally distilled industrially

12. Increasing size of molecules  The colour of molecules • Small hydrocarbon molecules are gases or transparent liquids. • As the molecules get larger the colour becomes increasingly yellow through to the brown/black colour of bitumen used on roads and roof repairs.

14. Which is a correct statement about crude oil? • Formed by the decay of dead sea creatures. • Consist of a mixture of very large molecules. • Is purified in an oil rig.

15. Which is a correct statement about fractional distillation? • Oil is separated into fractions with the same size molecule. • Oil is separated into fractions with the same density. • Oil is separated into fractions with similar size molecules.

16. Which is a correct order for these fractions working down from the top of the column? • Fuel gas, kerosine, petrol, diesel, bitumen. • Fuel gas, diesel, kerosine, petrol, bitumen. • Fuel gas, petrol, kerosine, diesel, bitumen.

17. Which of these is a true statement about the changes that occur as hydrocarbon molecules get larger? • Boiling point decreases. • Viscosity increases. • Flammability increases.