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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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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