Chemistry - Chemicals From Alkenes

These cards are for AQA GCSE and have five sub - sub topics which are:

1.Cracking     2. Polymers     3. New Uses for Polymers     4. Disposing of Polymers     5. Ethanol Production

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Cracking

Crude oil is a mixture that is separated into fractions. Some of these fractions have a higher demand than others and the demad is solved by cracking whre larger molecules are broken down into smaller ones.

Crude Oil is a mixture made up mostly of hydrocarbons most of which are alkanes. Shorter fractions of alkanes are easier to ingnite and burn with a cleaner flame, this makes them more useful and have a higher demand.

In cracking the hydrocarbons must be heated to condense and are passed over a catylist. This is a thermal decompostion reaction to break the molecules down and much energy is needed to break the covalent bonds.Cracking produces shorter alkanes and alkenes, which means there are more useful hydrocarbons, the alkenes then can be made into plastics.

Alkanes are saturated meaning that they only have single bonds and alkenes are unsaturated meaning they contain one or more double bonds. A test to separate alkanes from alkenes is to add the to broine water and if the liquid turn from orange to colourless it is an alkene if it stays the same it is an alkane.

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Polymers

Polymers are large molecules and were brought together through polymerisation. Polymerisation is when the double bond in an alkene monomer is broken and joined together to another alkene monomer with its double bond split.

So when ethen is polymerised it becomes polyethene, polyethen can be used for plastic bag and is flexible.

Polypropene, a.k.a polypropylene, is also flexible and used for crisp packets, crates, ropes and carpets.          Polychloroethene, a.k.a PVC, is tough and hard and used for window frames, gutters and pipes.          Polytetraflouroethene, a.k.a teflon / PTFE is tough and slippery and used for frying pan coatings and stain-proof carpets.          Perspex is tough, hard and clear and used for shatter proof glass.          Polyethanol, a.k.a PVA, dissolves in water and is used for hospital laundry bags.

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New Uses For Polymers

Smart materials are materials that will change shape or size depending on the change of conditions, temperature, pH.

Shape Memory Polymers, an example of smart materials, change shape with the temperature, however, when high enough it will go back to its original shape. Some polymers will also change colour as the temperature changes.

Hydrogels will turn into gels when they absorb lts of water, nappies, compost. Waterproof coating for fabribs will not allow water in but will allow water vapour out.

Dental monomers are chemicals including a monomer plus chemicals to start polymerisation. The mixture is placed in the cacity and when a blue light is shone, polymerisation occour to produce a polymer in the tooth.

Packaging materials have effects like package that will change colour if the food inside is off preventing food poisoning and there are packages that are biodegradable.

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Disposing of Polymers

One way of disposing of polymers is landfill ehich is cheap and easy. However, most polymers are not biodegradable meaning they cannot be broken down by micro-organisms so will not decompose or rot if dropped as litter. This causes disruption of natural habitats and destroys veiw points.

Incineration can be used and is where polymers are burned. This gets rid of a lot of waste and can be used to generate electricity however, it produces CO2 which contributes to global warming. If there is incomplete combustion, CO, hydrogen chloride and hydrogen cyanide is produced which is a poisonous gas.

Most polymers can be recycled which avoids landfill and incineration.Polyers can be chopped up into pellets that are melted and moulded into a new product. Polymers must be seperated into their different types which is time consuming and expensive.

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Ethanol Produtcion - Making of Ethanol

Ethanol is used can be used for medicines and detergants but can also be used for fuels and alchohol.

Ehtanol can be made through fermentation and over 90% is made through fermentation, this is from lots of crops containing carbohydrates such as sugar cane.

Ethanol can also be made through the hydration of ethene. This is where ethene is made from crude oil and the crude oil is hydrated which forms ethene.

Fermentation is made at 30 - 40 degrees and with ethene the temperature has to be at 300. This uses a lot of energy. Also, fermentation uses renewable sources, crops, while ethen is non - renewable and is a cheaper process.

However, fermentation is a slow process and is not a continuous process. Fermentation also produces impure ethanol as there is also some water.

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Comments

:) PurpleJaguar (: - Team GR

Really helpful notes thanks :)

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