Thursday, November 27, 2008

Useful products from crude oil- igcse

Useful products from crude oil

HydrocarbonsHydrocarbons are compounds which contain only the elements carbon and hydrogen. Crude oil is a mixture of different sized hydrocarbon molecules. These hydrocarbons are basically fuels such as petrol.Task C4.11 Pick out the hydrocarbons in the following list CH4, CH3OH, C6H6, C2H6, H2O, C8H18, C4H8, C2H3N, C5H12, C6H14.

Fractional distillation of crude oilThe fractional distillation of crude oil is the process which gives us the different substances (fractions) made from crude oil. The crude oil is pumped in to the fractional column from the bottom. The heat is applied at the bottom of the fractionating column. The different fractions are obtained in different positions in the column.

Top 70oC, small molecules, light colour, runny, easy to light

Lubricating oil
Fuel oil
BitumenBottom 360oC,

large molecules, dark colour, viscous, hard to light

Draw diagrams to show the relative sizes of molecules of gas, diesel and bitumen.

The size of molecules and boiling pointAs the size of a hydrocarbon molecule increases the boiling point increases. If it has a low boiling point it is very volatile (forms a vapour easily). If it has a high boiling point it is not volatile.

size of hydrocarbon molecule (carbon atoms)

Boiling point/oC

4-12 carbon




15-19 carbon


Over 50 carbon

Over 340

Uses of fractions from crude oil




Bottled gas for gas cookers, boilers, camping gas


Cars, electricity generators


Jet fuel

Diesel oil

Trucks, and some cars



Fuel oil

Boilers in ships or buildings


Covering road surfaces

Butane gas for camping

Complete and incomplete combustionComplete combustionHappens with plenty of oxygen. All of the carbon and hydrogen in a hydrocarbon turns to carbon dioxide and water.

Hydrocarbon + oxygen carbon dioxide + water

e.g. CH4 + 2O2 --> CO2 + 2H2O

carbon dioxide

Not poisonous but build up in atmosphere. carbon dioxide molecules trap energy from the sun. This leads to global warming.

harmless product
Sulphur Dioxide

Produced by sulphur impurities in burning fossil fuels. Can be dangerous if inhaled. Also it can dissolve into clouds to form acid rain. When this precipitates it is harmful to the environment by killing fish in lakes, damaging forests and can corrode buildings and metals structures.
Nitrogen Dioxide

This is formed in car engines when oxygen and nitrogen combine. This is an acid gas and turns into nitric acid when it dissolves. Acid rain results.

Complete the following equations for complete combustion of hydrocarbonsethene + oxygen ---> C2H4 + 3O2 --->ethyne + oxygen --->2C2H2 + 5O2 ---> propane +oxygen --->C3H8 +5O2 --->Incomplete combustionHappens if there is not enough oxygen.

The hydrocarbon turns into soot (carbon) and poisonous carbon monoxide as well as carbon dioxide.

Hydrocarbon + oxygen ---> carbon monoxide + water 2CH4 + 3O2 ---> 2CO + 4H2O

Formed by incomplete combustion as soot. It is bad for the lungs and disfigures buildings.
Carbon Monoxide

This is produced by traffic and some gas fires. When inhaled by people it replaces oxygen in the haemoglobin, however, it does not give it up, this eventually leads to suffocation.

Complete the following equations for incomplete combustion of hydrocarbonsethyne +oxygen --->

Match these combustion products to their formulae: carbon, water, C, sulfur dioxide, CO2, nitrogen dioxide, NO2, carbon dioxide, SO2, carbon monoxide, H2O, CO.

Chemical tests for carbon dioxide and waterIf carbon dioxide is bubbled through limewater it turns milky. We can test for the presence of water using anhydrous copper sulphate which is white. The copper sulphate turns blue when water is added to it. Cobalt chloride can also be used. This turns from blue to pink when water is added.Task C4.16 Show the above information in a suitable table.

CrackingCracking is the splitting up of long chain hydrocarbons in to smaller chains. Cracking is a form of thermal decomposition. A lot of longer molecules produced from fractional distillation are cracked into smaller ones because there's more demand for products like petrol and Kerosine than for diesel oil. The products include compounds with double bonds such as ethene. For example kerosine could be broken down to octane and ethene.

C-C-C-C-C-C-C-C-C-C- ----cracking-----> C=C + C=C-C + C-C=C + C-Cbig molecules small moleculealkanes mostly alkenessingle bonds double bondssaturated unsaturatedonly good for fuels can be made into polymers

Industrial conditions for crackingIndustrial conditions for cracking vaporised hydrocarbons are to use a powdered catalyst at about 400ºC to 700ºC. The catalyst could be Aluminium oxide.

The products of crackingCracking turns big molecules into small molecules which are mostly alkenes. Some alkanes are also made.

Saturated and unsaturated hydrocarbonsAlkanes are saturated hydrocarbons. They have single C-C bonds only.Alkenes are unsaturated hydrocarbons. They have double C=C bonds.Saturated hydrocarbons are so called because their C atoms have no spare bonds left to join with any more hydrogen atoms. They contain C-C single bonds and each C atom is joined to 4 other atoms. Unsaturated hydrocarbons are so called because they have some spare bonds which could be used to add on some more hydrogen atoms.

Natural gasNatural gas is mostly made up of an alkane called methane CH4.

The formulae and structures of alkanesMethane CH4 H H-C-H H
Ethane C2H6 H H H-C-C-H H H
Propane C3H8 H H H H-C-C-C-H H H H
Butane C4H10 H H H H H-C-C-C-C-H H H H H

Formulae and Structures of alkenes
Ethene C2H4 H H C=C H H
Propene C3H6 H H H H-C-C=C-H H C4.24 Testing alkanes and alkenes with bromine water

Making polymers from small moleculesPolymers like polythene, polypropene and polystyrene are large molecules, which can be formed by combinations of many smaller molecules called monomers.

Addition polymerslots of monomers add together ---> 1 addition polymerEach has C=C bonds only single bondsunsaturated saturatedlots of ethene molecule ---> 1 polyethene moleculeH H H H H H H H H H H H H H C=C + C=C + C=C + .... ---> -(C- C- C- C-C- C- C- C)-n H H H H H H H H H H H H H H

Draw structures and equations as above for the formation of polypropene and polychloroethene.

Uses and properties of polymers
Plastic bags, bottles, buckets and bowls
Softens when warm so easily formed and moulded
Crates, rope, carpets, car bumpers, fishing nets
tough and strong
poly(chloroethene)polyvinyl chloridePVC
gutter, drain pipes, window frames, covering for electrical wiring.
electrical and heat insulator, tough, not easliy decomposed by sunlight

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