SC2

• Pure - a substance that is made up of only one element or compound
• Impure substances will have multiple melting points whereas pure substances only have one
• Simple Distillation:

  1. Pour mixture into distillation flask
  2. Connect bottom of condenser to a cold tap using rubber tubing and run water to keep it cool
  3. Slowly heat distillation flask so the substance with the lowest boiling point will evaporate first
  4. Evaporated substance will condense and travel down into a beaker
  5. Pure substances are collected
• Fractional Distillation:

  1. Put a mixture in a flask and attach a fractionating column
  2. Slowly heat the flask so the substances evaporate at different times
  3. Substance at lowest boiling point will go to the top first and collect pure substance before raising temperature again
• Filtration:

  • separate a solid from a liquid
  • filter paper in a funnel
• Crystallisation:

  • heat evaporating dish with solution to make it concentrated
  • cool it for large crystals to form (soluble solid)
• Paper Chromatography:

  • Mobile - where molecules can move (solvent)
  • Stationary - where molecules can't move (filter paper)
  • Solvent front - distance the solvent has moved up the filter paper
  • mark start line with pencil as it's insoluble
  • point of origin is where unknown substances start
  • Rf value - distance travelled by solute divided by distance travelled by solvent
• Analysing Mixtures Practical:

  1. Use simple distillation to separate the ink solvent
  2. The thermometer will show the boiling point of the solvent which can help predict what the substance is (e.g. 100'C is water)
  3. Paper chromatography will separate the different dyes
  4. Compare the Rf values
• Surface Water - lakes, rivers and reservoirs

  Ground Water - water trapped inside rocks called aquifers

  Waste Water - water contaminated by human processes
• Purifying Water:

  1. Filtration - a wire mesh removes any large substances like twigs then gravel and sand remove other solids
  2. Sedimentation - iron/aluminium sulfate is added so fine particles clump together and sink
  3. Chlorination - chlorine gas kills any harmful bacteria and other microbes so the water is potable

  Potable water can also be made when sea water is distilled
• Analysing Water - water must be deionised so that the ions usually present do not interfere with experiments (invalid test)