Chemistry: Out There

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  • Chemistry: out there
    • redox reactions
      • if electrons are transferred it is a redox reaction
      • displacement is a redox reaction  the reactive displaces the less
      • metal ion reduces
      • metal atom oxidised
    • rusting of iron
      • iron + oxygen +water = hydrated iron oxide
      • iron is oxidized oxygen is reduced
      • prevention against rusting
      • combine with non rusting metals
      • paints the metal
      • oiling on moving parts
      • tin plating
      • sacrificial methods used where other metals lose electrons instead
    • electrolysis
      • copper sulfate can be electrolysed to form copper and oxygen
      • cathode negative
      • anode positive
      • an ionic solid cant be electrolysed because the ions cannot move
      • more electrons forms more substance
      • more charge = more product
      • Q=it
      • Q - charge
      • i - current
      • t - time in seconds
    • fuel cells
      • hydrogen and oxygen give out energy when they react
      • the reaction between H and O2 is exothermic
      • main one - hydrogen-oxygen fuel cell
      • hydrogen into anode
      • oxygen into cathode
      • cathode makes OH- ions
      • anode makes water and electrons through oxidation
      • reduction at cathode oxidation at anode
      • REDOX reaction
      • reaction produces energy and water
      • advantages:efficient, direct energy transfer, little energy loss, no pollution
      • disadvantages: may need energy from fossil fuels, may contain poisonous catalysts
    • CFC's and ozone layer
      • chlorofluorocarbons - CCl2F2
      • non toxic, non flammable and unreactive
      • used in fridges and air conditioning
      • the chlorine could break down the ozone
      • reducing the amount of ozone means more UV rays
      • more UV can cause skin cancer
      • many countries banned CFC's completely
      • if a covalent bond is broken evenly, each atom gets a shared electron called a free radical
      • free radicals are very reactive
      • it is the chlorine free radicals which damage the ozone
      • CFC's stay in the atmosphere for a very long time
      • use alkanes and HFC's instead
    • hardness of water
      • forms limescale
      • formed by calcium and magnesium ions
      • carbon dioxide + water +calcium carbonate -> calcium hydrogencarbonate
      • temporary hardness - hydrogencarbonate ion
      • permanent hardness - dissolved calcium sulphate
      • removed by boiling
      • adding sodium carbonate
      • both removed by ion exchange resin
      • test for hard water
      • add 100cm3 water to conical flask
      • add 1cm3 soap to water
      • repeat until good lather
      • record soap needed
    • alcohols
      • general formula - CnH2n+1OH
      • methanol, ethanol, propanol, butanol, pentanol
      • fermentation produces ethanol
      • oxygen converts ethanol into ethanoic acid
      • fractional distillation produces pure ethanol
      • ethene reacts with steam to make ethanol
      • advantages of fermentation: renewable fuel
      • disadvantages of fermentation: slow, not pure, low atom economy
      • advantages of hydration: quick, very pure, high atom economy, 95% yeild
      • disadvantages of hydration: expensive, non renewable
    • fats and oils
      • are esters: reacted acid and alcohol
      • made from glycerol and fatty acids
      • oils do not mix in water
      • milk is an oil in water emulsion
      • butter is a water in oil emulsion
      • vegetable oils can make biodeisel
      • fats and oils make soap
    • using plant oils
      • unsaturated oils contain double bonds
      • bromine turns colourless in an unsaturated oil
      • vegetable oils are hardened by hydrogenation
      • partially hydrogenated oil forms a spreadable margarine
      • saturated fats and oils increase cholesterol levels
    • detergents
      • hydrophilic - loves water
      • hydrophobic - hates water
      • detergents form strong bonds with water and oils to lift the stain
      • dry cleaning covers grease in solvent, then both are removed
      • biological detergents work best at low temperatures due to enzymes

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