Chemistry GCSE (C1) Polymers and Plant oils

The smaller hyrdocarbon fractions obtained from crude oil are the most useful so are in heavy demand, particulary gasoline (petrol). It is possible to break down the long chain hydrocarbons into smaller, more useful resources by a process called catalytic cracking.

Firstly the large molecules are vaporised by being heated. Then they are passed over a hot catalyst, this splits the molecule in a reaction known as thermal decomposition. As well as producing a smaller, more useful alkane other products including alkenes are made.

For example: Decane - Octane + Ethene

Alkenes (made from cracking) are unsaturated hydrocarbons- they have a double bond between two of their carbon atoms.

Their general formula is: CnH2n

To test to see if a compound/mixture is saturated (an alkane) or unstaurated (an alkene) bromine water is added to them. If the bromine water turns colourless then the mixture is an unsaturated alkene. If the bromine water doesn't change colour it is an alkane. The alkane doesn't affect the bromine water's colour becasue it is already saturated.

Alkenes are not very good fuels because they burn with a smoky/dirty flame however...

Alkenes are useful for making polymers and polymers are useful because they are all plastics.

This bit is a little bit confusing but...Polymers are made from lots of small reactive alkenes. These small molecules are called monomers so a polymer is made from lots of monomers.

A plastic bag is made from polythene: hundreds of ethene monomers join together when they are heated, under pressure, in the presence of a catalyst. The double bond in each ethene monomer breaks and they join together forming a long chain polymer. This is known as polymerisation.

Nowadays there are many different polymers. Often they have been designed with a special property so they are suitable for specific jobs....

Hydro-gels are very useful polymers. they are long chain molecules which grab onto water molecules. This means they are super absorbent.

Hydrogels can be used for many things:

1) In nappies

2) In water conservation

3) Solving other environmental issues

Vegetable oils are made by plants using the glucose made during photosynthesis. The seeds are harvested and crushed and then pressed to remove the oil from them. Once the oil has been removed it can be purified and used to make important foods. Fats are important part of a balanced diet because they store energy.

Cooking: The boiling point of a liquid depends on the forces between its molecules. The stronger the forces the more energy is needed to separate the molecules by overcoming the forces, so the higher the boiling point. Cooking food in vegetable oil is different from cooking food in water because oil has a lot higher boiling point. Cooking in oil means the food is cooked quicker. However food cooked in oil is unhealthier because it absorbs some of the oil whilst cooking.

Hardening: Most vegetable oils are liquid at room temp. They are unsaturated so they have double bonds. To produce a solid at room temp from vegetable oils they need to be hydrogenated. This involves reacting the oil with HYDROGEN in a NICKEL CATALYST at 60 DEGREES C.

Oil and water are immiscible- this means that oil doesn't dissolve in water but two layers form.

When people want them to mix they add an emulsifier to the mixture. The emulsifier compounds have one hydrophobic end which buries into the oil and another hydrophilic end, which has a negative charge, is left in the water. Negatives repel so the oil molecules repel away from each other, keeping the solution mixed.