topic c8- chemical analysis

• pure substance

  • a substance containing only one element or compound
  • melt or boil at a specific temperature
• impurities in the sample will

  • lower melting point
  • increase melting range
  • increase boiling point
  • increase boiling range
• formulations

  • useful mixtures with a precise purpose made by a 'formula'
  • each component in a formulation is present in a measured quantity and contributes to the properties of the formulation so that it meets it's required function
• examples of formulations

  • metal alloys
  • medicines
  • fertilisers
  • paints
  • food
  • cosmetics
  • fuels
  • cloning products
• paper chromatography

  • analytical method used to separate the substances in a mixture
• paper chromatography- mobile phase

  • the molecules can move
  • always a liquid or a gas
  • solvent
• paper chromatography- stationary phase

  • the molecules can't move
  • can be a solid or a thick liquid
  • chromatography paper
• paper chromatography- the amount of time the molecules spend in each phase depends on

  • how soluble they are in the solvent
  • how attracted they are to the paper
• paper chromatography

  molecules with a higher solubility will spend more time in the mobile phase
• paper chromatography- how to calculate Rf (ratio)

  distance travelled by substance (B)/ distance travelled by solvent (A)
• test for gases- hydrogen

  • hold a lit splint at the open end of the test tube
  • hear a "squeaky pop"
• test for gases- oxygen

  • put a glowing splint inside the test tube
  • the O2 will relight the splint
• test for gases- chlorine

  bleaches damp litmus paper white
• test for gases- carbon dioxide

  • makes lime water turn cloudy
  • when shaken or bubbled through it
• gas tests

  • hydrogen- "squeaky pop", lit splint
  • oxygen- relight glowing splint
  • chlorine- bleaches damp litmus paper white
  • carbon dioxide- lime water turns cloudy