AQA GCSE C1b module
These are for the AQA GCSE specification, chemistry module 1b. Topics included are:
- Cracking Crude Oil
- Alkenes and Ethanol
- Using Alkenes to Make Polymers
- Plant Oils and Emulsions
- Extracting and Using Plant Oils
- Food Additives
- Plate Tectonics
- The Earth's Structure
- The Evolution of the Atmosphere
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- Created by: Hannah Buckley
- Created on: 29-05-11 11:05
Cracking Crude Oil
- cracking means splitting up long-chain hydrocarbons
- long-chain hydrocarbons form thick gloopy liquids (like tar)-not very useful
- longer molocules from fractional distillation are turned into smaller ones
- some of the products of cracking are useful as fuels (petrol, paraffin)
- also produces substances like ethene-needed for making plastics
- diesel-----cracking-----petrol, paraffin, ethene
- cracking=passing vapour over a hot catalyst
- cracking is a thermal decomposition reaction-breaking molecules by heating
- heat long-chain hydrocarbons to vaporise them
- vapour passed over powdered catalyst - temp. of about 400-700 degrees C
- catalyst used is aluminium oxide
- long-chain molecules split apart on the surface of the specks of catalyst
- vaporised kerosine-----catalyst-----octane+ethene
- most products of cracking are alkanes and alkenes
- long-chain hydrocarbon-----shorter alkane molecule+alkene
- kerosene(C10H22)-----octane(C8H18)+ethene(C2H4-double bond)
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Alkenes and Ethanol
- alkenes have a C=C double bond
- alkenes-hydrocarbons which have a double bond between 2 carbon atoms
- unsaturated-can make more bonds (double bond can open up)
- first 3 alkenes: ethene (C2H4), propene (C3H6) and butene (C4H8)
- alkene formula: CnH2n
- carbon atoms always make 4 bonds-sometimes a double bond formed
- ethene can be reacted with steam to produce ethanol
- needs temp. of 300 degrees C, pressure of 70 atmospheres
- catalyst is phosphoric acid
- cheap process-ethene is cheap and little wasted
- ethene is produced from crude oil: non-renewable resource-soon process will be very expensive
- ethanol can also be produced from renewable resources by fermentation
- sugar converted into ethanol using yeast
- lower temperature and simpler equipment, all raw materials are renewable
- ethanol produced this way can be used as a cheap fuel where petrol isn't as available
- produced this way-not very concentrated, needs distilling and purifying
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Using Alkenes to Make Polymers
- alkenes used to make polymers-polymerisation: joining together lots of small alkene molecules (monomers)-form large molecules-polymers: many ethene molecules can be joined up to make polyethene: many monomers---catalyst+pressure---polymer: n(ethene)---(polyethene)n
- different polymers have different physical properties: physical properties depend on what it's made from and temperature/pressure of polymerisation: high pressure+temperature= flexible and low density, whereas, low pressure and temperature with a catalyst=rigid and dense
- polyethenol forms slime when mixed with different concentrations of sodium tetraborate, more concentrated=more viscous and gungy
- different properties=good for different uses: light, stretchable polymers: used for plastic bags-elastic polymer fibres: used for stretchy spandex fibre (for tights)-new uses are always being developed: waterproof coatings, dental polymers and hydrogel wound dressings (keeps wounds moist)-memory foam: smart material: polymer that gets softer as it gets warmer
- polymers are cheap but don't rot (hard to get rid of)-aren't biodegradable-best to reuse them as much as possible-things made from polymers are usually cheaper but crude oil gets used up so prices will rise
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Plant Oils and Emulsions
- oil can be extracted from plants-used for food or fuel
- material crushed and pressed to extract oils
- oil separated from plant material by centrifuge (like spin drying) or by using solvents
- distillation refines oil, removes water, solvents and impurities
- vegetable oils produce a lot of energy and nutrients-contain essential fatty acids
- emulsions can be made from oil and water-suspend droplets of one liquid in another liquid-thicker than oil or water-more oil=thicker
- lots of uses in foods
- also used in moisturiser
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Extracting and Using Plant Oils
- vegetable oils can be used to produce fuels-because they produce a lot of energy-biodiesel
- biodiesel is a renewable fuel-comes from plant crops-releases less pollution than diesel-less sulfur dioxide and particulates-biodegradable and less toxic
- does release same amount of CO2 but it only releases carbon that has been recently taken in by the plants
- fossil fuels contain carbon from millions of years ago that was taken out of the atmosphere-increase in current CO2
- biodiesel is expensive and it's difficult to make enough-not enough space for crops-makes it expensive-people won't buy until it's cheaper
- doesn't require engine to change and can use same filling stations-unlike running on gas or electric
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Using Plant Oils
- unsaturated oils contain C=C double bonds
- oils and fats contain long-chain molecules with lots of carbon atoms-either saturated or unsaturated
- test for unsaturated with bromine or iodine-unsaturated=colourless
- monounsaturated fats contain 1 C=C bond
- polyunsaturated fats contain more than 1 C=C bond
- unsaturated oils can be hydrogenated-reacted with hydrogen, nickel catalyst, 60 degrees C-removes double bond
- hydrogenated oils have a higher melting point than unsaturated oils-more solid at room temperature
- margarine is made with partial hydrogenation-not all double bonds are turned into single bonds-results in unhealthy trans fats
- vegetable oils in food can affect health-tend to be unsaturated
- saturated fats are less healthy for you but trans fats change this-bad cholesterol increases
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Food Additives
- processed foods often contain additives-improve apperance, taste, texture and shelf life
- artificial colours can be detected by chromatography-different dyes wash through wet filter paper at different paces-more soluable=faster it travels
- food additives have benefits and drawbacks
- preservatives help food stay fresh, colourings and flavourings make food look and taste better, emulsifiers and stabilisers stop emulsions from separating, sweetners can replace sugars
- some food colours can make children hyperactive, some people are allergic to additives, some additives aren't suitable for vegetarians
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Plate Tectonics
- wegners theory of continental drift wasn't accepted for many years-jigsaw, similar rocks, had been one supercontinent "Pangaea"
- unconvincing explanation, used inaccurate data in calculations, other geologists didn't agree
- new evidence-theory was mostly correct
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The Earth's Structure
- earth has a crust (very thin-20km), mantle (solid but flows very slowly, radioactive decay occurs, produces convection currents, moves plates), inner core and outer core (iron and nickel)
- earth's surface is made up of techtonic plates-move a few cm a year-occasional sudden movements cause earthquakes-volcanoes can form at boundaries
- scientists can't predict earthquake and volcanic eruptions-impossible because they are very sudden-random
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The Evolution of the Atmosphere
- phase 1:volcanoes gave out gases-CO2, water vapour and nitrogen-mostly CO2, virtually no oxygen
- phase 2:green plants evolved and produced oxygen-early CO2 dissolved in oceans and was taken in by plants
- phase 3:ozone layer allows evolution of complex animals-build-up of oxygen allowed more complex organisms to evolve-created ozone layer which blocked harmful rays
- about 1% of the atomsphere is noble gases
- competing theories about atmospheric change
- atmosphere is still changing-CO2 has incresed by 25% since 1750, amount of ozone has decreased over last 50 years
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