topic 2 : states of matters and mixtures

• desalination is extracting potable water from the sea water- requires lots of energy and is expensive
• how to get fresh water: first filter it through a wire mesh, then pass it through a bed of sand, this is called sedimentation and then sterilise it either with UV light or chlorine, this is called chlorination
• changes of state are considered physical changes because they don't create new chemicals and can easily be reversed
• sewage treatment: first screening-removes anything large, then sewage sits in a settlement tank-undergoes sedimentation, this breaks down all organic matter
• heavier bits sink down to form the sludge and lighter bits float to form the effluent
• the effluent is kept in aerobic conditions and the sludge is kept in anaerobic
• deposition is gas to solid and sublimation is solid to gas
• a pure substance boils at 100 degrees as all the bonds are the same and require the same amount of energy to break
• a pure substance is a substance that is made up of one element or compound, not mixed with any other substance
• a mixture consists of 2 or more elements or compounds that are not chemically combined together
• getting fresh water by distillation:

  1. filter
  2. boil
  3. water vapour cooled and condensed