chemistry

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  • FOOD ADITIVES
  • SMELLS
  • MAKING CRUDE OIL USEFUL
  • MAKING POLYMERS
  • USING CARBON FUELS
  • ENERGY
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COOKING

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· Some foods must be cooked: it kills harmful microbes with high temps, improves the taste/texture, makes it easier to digest

· The final product is different because of chemical reactions

· Irreversible change, requiring energy, meat and eggs are high in protein, when an egg is heated, protein molecules change shape – denaturing,

· Potatoes are carbohydrates containing cellulose which forms cell walls around starch, so uncooked potatoes are difficult to digest, cooking breaks down the walls and releases the starch which becomes a gel by absorbing water

· Baking powder is a raising agent (contains sodium hydrogencarbonate), this decomposes when baked to produce CO2 which rises making ‘bubbles’

· Limewater (calcium hydroxide) can be used to test CO2 as it turns cloudy

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FOOD ADITIVES

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· Additives have to be approved of safety, all approved additives have E-numbers

· Emulsifiers: oil + water don’t mix, adding an emulsifier makes an emulsion (+shaking), emulsifier molecules have a hydrophilic head which has an ionic charge and an hydrophobic tail, the heads repel each other due to their charge

· Active or intelligent packaging is used to preserve foods, keeping out oxygen and water helps stop bacteria growing, there are 2 ways of controlling free rad. no.’s

· 1:Oxygen scavengers: chemicals are placed in packaging that remove oxygen and so prevent any oxygen reacting with it creating harmful free radicals

· 2:Antioxidants in the packaging combine with free radicals in the food before they breakdown the food/packaging

· Some film packaging lets oxygen in but ethene (which causes fruit to ripen) out

· Cans can heat/cool their contents when opened and widgets in beer cans froth it

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SMELLS

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  • Perfumes can be made from esters which are made by blending together natural oils or made synthetically, esters are also used as flavouring agents and solvents
  • Mixtures of esters are very concentrated and are diluted by adding solvents
  • Perfumes are mainly used in everyday products like polishers and air refreshers
  • Organic acid + alcohol ® ester + water, (ethanoic acid + ethanol ® ethyl ethanoate)
  • Perfumes: need to evaporate - volatile, be non-toxic, non-irritant, insoluble in water
  • High volatility – weak attraction, high energy
  • Esters can be used as solvents (solution = solvent + solute [that do not separate]), they dissolve many substances which don’t dissolve by water e.g. NVR
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MAKING CRUDE OIL USEFUL

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  • Crude oil formed when small sea creatures and plants died and buried, formed in high temps. and pressures and in absence of air
  • Oil can be forced through cracks and low b.p. hydrocarbons evaporate forming pitch
  • Fractions (of similar b.p.): bitumen, fuel oil, heating oil, paraffin, diesel, petrol , LPG
  • Covalent bonds between H and C are strong, longer chains = higher b.p.
  • Cracking: alkane --> smaller alkane + alkene
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MAKING POLYMERS

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  • Polymers are long chain molecules – a single unit is a monomer e.g. Poly(ethene) is lots of ethene monomers in a chain
  • Alkanes = CnH2n+2, single covalent bonds only – so they are saturated
  • Alkenes = CnH2n, at least one C=C covalent bond – so they are unsaturated
  • Bromine water goes from yellow to clear if unsaturated
  • Addition polymerisation is joining monomers by a series of addition reactions

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USING CARBON FUELS

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  • Fuels react with oxygen to make energy, there are many with different properties
  • Complete combustion = methane + oxygen --> carbon dioxide + water
  • Incomplete = methane + oxygen --> carbon monoxide + carbon (soot) + water
  • Complete is better: less soot, more heat, CO (poisonous is not produced
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ENERGY

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  • Exothermic/endothermic – give out/take in energy, bond forming is exothermic, bond breaking is endothermic. Combustion is exothermic in O2
  • Calorimeter(metal can which measures the heat)
  • Energy = mass(kg) x s.h.c.(4.2 for water) x temp. change(°C)
  • Energy per gram(J/g) = energy supplied(J) / mass of fuel burned(g)
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