Chemistry C3 - Rocks and Salts

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  • Created by: ameliaG72
  • Created on: 14-05-14 21:02
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  • C3- Chemicals in our lives(rocks and salts)
    • Making of rocks
      • Earth is made up of 12 tectonic plates, convection currents make them move.
      • scientists use magnetic clues in rocks- magnetite- to track continent movements, this means that ancient continents that now make up Britain have moved so different rocks were formed in other climates
      • Processes that form rocks are: sedimentation, erosion, evaporation and mountain building
      • Sedimentation- and compression formed limestone when remains of dead sea animals fell to the bottom of warm seas near the equator
      • Erosion- of rocks from rivers formed sand which deposited in layers to form sandstone
      • Evaporation- formed rock salt when sea moved inland and then water evaporated. salty water formed when salts from rocks dissolved in the water flowing over them.
      • Mountain Building- pushed coal towards surface in the peak district, coal formed when tree ferns in swamps died, were compressed and heated.
    • Signs of how rocks were made
      • fossils tell us about animals at different times from the age of the rock they are in
      • comparing sand grains in deserts and rivers to sand grains in sandstone tells what sort of sand formed the sandstone
      • shapes of ripples in rocks give clues about whether sandstone was made from river bed sand or desert sand
      • tiny shell fragments in limestone tell us about the conditions when rocks formed
    • Salt Production
      • salt for food must be pure so comes from the sea, this can be done through evaporation of sea water which leaves only the salt
      • Countries with hot climates use evaporation methods as it saves energy
      • rock salt is mixture of salt and clay, used for de-icing so does not need to be pure. Mined from underground
      • salt for chemistry industry must also be very pure, which is obtained through solution mining.
      • Solution Mining is when water is injected into the carvern through the outer tube, the salt then dissolves in this and is pumped back up as the pressure is changed in the inside tube, the salt is then extracted above ground.
      • Solution mining can cause subsidence, now these are internally supported, filled in.
    • salts and food
      • Salt is used in food because: flavouring and preservatives
      • Eating too much salt can raise your blood pressure which increases risk of stroke or heart attack
      • Government does risk assessments on food chemicals and give advice to the public on this.
      • Manufacturers do not take out the salt, as costs too much to take it out and change recipes, need sales on flavour and costs too much if go out of date quickly

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