chemistry topic 2

• Chromatography steps

  
  

  1. Draw a pencil line on the paper

  2. Put a spot of the mixture on the pencil line

  3. Fill a beaker with solvent and allow it to touch the bottom of the paper below the pencil line

  4. Solvent will move up the paper, dissolving chemicals in the mixture and carrying them up the paper

  5. Chemicals separate out forming spots along the paper

  6. Remove the paper before the solvent reaches the top and draw the solvent front
• Rf value


  Distance moved by spot / distance moved by solvent
• If substances have the same Rf values, they are probably the same compound
• Pure substance


  A single substance with nothing else mixed into it
• Pure mixture

  Two or more physically joined pure substances
• Pure substances

  • Have a fixed melting point and boiling point
• Impure substances

  • Have a range of melting/boiling points
• Measuring melting point

  1. Use melting point apparatus

  2. Heat a small sample of solid

  3. Measure the temperature at which it melts
• Potable water


  Drinkable water
• Types of water

  • Ground water
  • Surface water
  • Waste water
• Water purification

  1. Filtration

  2. Sedimentation

  3. Chlorination
• Distillation can make water potable but is expensive and energy intensive
• Deionised water should be used for water analysis to avoid false results
• Combining separation techniques

  Can be used to analyse the composition of an ink (e.g. simple distillation and chromatography)
• Ink is a mixture of different dyes dissolved in a solvent
• Analysing ink composition

  1. Simple distillation to evaporate off the solvent

  2. Paper chromatography to separate out the different dyes
• The boiling point of the solvent can be used to identify it
• Rf values of the dye spots can be compared to reference values to identify the dyes
• chromatography

  separation of mixtures of soluble solids substances

  by running a solvent across the paper which causes the substances to move at diff rates
• mobile phase

  when the solvent allows the substances molecules to move up the page
• stationary phase

  the acc paper, when the molecules cant move