Chemistry - C1.5 - Products from Oil - Revision Cards in GCSE Chemistry

C1.5.1 - Cracking Hydrocarbons

Cracking - breaking large hydrocarbon molecules down into smaller molecules, done in two ways: heating mixture of hydrocarbon vapours and steam to high temperatures or passing hydrocarbon vapours over a hot catalyst
During cracking thermal decomposition reactions produce mixture of smaller molecules - some are alkanes - saturated hydrocarbons - and are more useful as fuel as they're smaller
Alkenes - unsaturated hydrocabons - are also formed, they are unsaturated as they have fewer hydrogen atoms than alkanes with the same no of carbon atoms - they have double bonds -> more reactive than alkanes, react with bromine water - orange->colourless

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Plastics made from polymers - many small molecules (monomers) joined together, reaction to make a polymer called polymerisation - double bond breaks and joins to other carbon atoms making a long chain
Many ethene molecules join to form polyethene/polythene and propene molecules form polypropene
Many plastic bags, bottles, containers and toys are made from alkenes

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Polymers can be designed to make materials with special properties used for packaging, clothing and medical applications
Polymer materials have been developed to be used as fillings instead of mercury, light-sensitive polymers used in plasters so they can be removed easily (two layers, bottom one unsticks when exposed to light), hydrogels are polymers that trap water so used in dressings - let body heal in moist, sterile conditions
Shape-memory polymers - smart polymer, return to original shape when temperature or other conditions change - eg. stitching wounds - changes shape when heated to body temperature - tightens then can dissolve
Fibres in fabrics coated in polymers to be waterproof and breathable
Plastic drink bottles recycled to make polyester fibres for clothing or filling for pillows and duvets

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Most polymers aren't biodegradable - plastic waste isn't broken down when left in the environment, unless disposed of properly it gets everywhere - it's unsightly, harms wildlife, takes up landfill space
Biodegradable plastics are being used more and broken down by mircroorganisms which break down when coming in contact with soil
Non-biodegradable plastics - cornstarch added, microorgansims break down cornstarch so plastic breaks down to small pieces to be mixed with soil or compost
Biodegradavle plastics - sometimes made from plant material - eg. polymer made from cornstarch to make biodegradable food packaging
Some plastics can be recycled but many different types of plastic make sorting difficult

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C2H6O or C2H5OH - shows the OH group in the molecule = alcohol
Can be made by sugar plant fermentation using yeast - enzymes in the yeast produce C2H6O and CO2 from sugar
Can be made from hydration of ethene - reacted with steam at high temperatures with catalyst (ethene obtained from crude oil by cracking)
Fermentation - renewable, done at room temperature, only produces dilute aqueous solution of ethanol - must be separated by fractional distillation to produce pure ethanol
Produced from ethene - non-renewable (crude oil), runs continuously, produces pure ethanol, needs high temperatures

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