chemical analysis

• A formulation is a mixture that has been designed as a useful product
• The components of a formulation will all have a specific purpose and their quantities will be carefully measured and controlled
• Rf value


  Distance travelled by sample / distance travelled by solvent
• Pure substances melt and boil at specific temperatures
• Mixtures melt and boil over a range of temperatures
• Chromatography


  A very powerful method of separating many types of mixtures
• Forms of chromatography


  • Paper chromatography
  • Thin layer chromatography (TLC)
  • Column chromatography
  • Gas chromatography
• Chromatography


  • There is a stationary phase (the part that does not move)
  • There is a mobile phase (the part that moves)
• Paper chromatography


  1. Draw starting line in pencil

  2. Place small spots of each sample on starting line

  3. Leave paper vertically in solvent

  4. Solvent soaks up paper for a few minutes

  5. Mark solvent level when near top

  6. Leave paper to dry
• Substances in a mixture separate


  They have different attractions to the stationary phase and mobile phase
• Substance more strongly attracted to solvent


  Moves a long way with solvent
• Substance more strongly attracted to paper


  Moves a short distance
• Hydrogen Gas Test


  Hold a lit splint in the gas once it has been collected into a container
• Oxygen Gas Test


  Hold a glowing splint in the gas once it has been collected into a container
• Carbon Dioxide Gas Test

  Collect the gas into a container, then bubble the gas through limewater (a solution of calcium hydroxide)
• Chlorine Gas Test


  Collect the gas into a container, then hold some damp litmus paper in the gas
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  The gas burns with a 'squeaky pop' sound if it is hydrogen
• 
  

  The splint will relight if the gas is oxygen
• The limewater will turn cloudy if the gas is Carbon Dioxide
• The litmus paper will be 'bleached white' if the gas is chlorine