1. Useful Products from Organic Sources
KS4
Useful Products from Organic Sources
ORGANIC CHEMISTRY

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

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
Big molecules
Medium molecules

6. Fractional Distillation
cool
hot
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.

7. Fractional Distillation
cool
hot
Copy the column and arrange the fractions in the right order next to the arrows.
Fuel gas
Petroleum
Fraction
Boiling Range
(oC)
Kerosine
Diesel
220 – 275
Petrol
Bitumen
>350
Fuel gas
Below 40
Lubricating oil
Kerosine
Diesel
Lub. Oil
Bitumen

8. 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
(oC)

10. Fraction Boiling Range (oC) Number of carbons 1-5 5-10 9-14 13-17
Here are the boiling ranges of some fractions obtained from distillation of petroleum.
Using the previous graph, estimate the size range of the molecules present in each fraction.
Fraction
Boiling Range
(oC)
Number of carbons
Fuel gas
Below 40
Petrol
Kerosine
Diesel
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. Substance Flash Point Kerosine <23 Petrol 85 - 150 Fuel Oil 23 - 61
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.
Substance
Flash Point
Kerosine
<23
Petrol
Fuel Oil

13. 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.

14. 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).
Bigger molecules
Higher viscosity
“Treacly”
Smaller molecules
Lower viscosity
“Runny”

15. 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.
Increasing size of molecules 

16. The composition of fractions?
We already know that each petroleum fraction consist of hydrocarbon molecules falling within a particular size range.
The proportions of the different hydrocarbons present in oil can vary greatly across the world.
It is therefore not surprising that the exact nature of the fractions collected will vary both in amount and detailed composition.
Nonetheless most crude oil will give rise to some quantity of each type of fraction.

17. Uses of each fraction Fuel gas Petrol / gasoline Naphtha Paraffin /
Burned in the refinery to fuel the distillation process, sold as LPG, purified and sold as bottled camping gas
Fuel gas
Petrol
/ gasoline
Fuel for cars and motorcycles, also used to make chemicals.
Naphtha
Used to make chemicals.
Paraffin /
Kerosine
Fuel for greenhouse heaters and jet engines, manufacture of chemicals.
Diesel fuel
Fuel for lorries, trains.
Fuel and
lubricating
oil
Fuel for the heating systems of large buildings, fuel for ships, lubricating oil.
Bitumen
Roofing, and road surfaces.

18. Burning hydrocarbons
The apparatus below is used to test the products of combustion of a hydrocarbon.
Suction
pump
ice-
water
Lime water
Candle wax is the
hydrocarbon here
Liquid collected
can be tested with
anhydrous cobalt chloride
paper (bluepink).
any hydrocarbon + oxygen  water + carbon dioxide

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

20. 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.
Oil is separated into alkanes and alkenes.

21. 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, diesel, kerosine, bitumen.
Fuel gas, petrol, kerosine, diesel, bitumen.

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