Identifying substances

• Chromatography


  Used to separate mixtures of soluble substances
• Rf value


  Distance travelled by substance divided by distance travelled by solvent
• Chromatogram can tell if a substance is pure or a mixture
• Mixture


  Consists of two or more substances that are not chemically bonded together
• Pure substance


  Consists of only one element or compound
• Testing for a pure substance 


  Has a specific melting point
• Gas tests (oxygen)


  Glowing splint will relight
• Gas tests (Hydrogen)


  Lit splint will make a squeaky pop
• Gas tests (Chlorine)


  Damp litmus paper will be bleached/ clear
• Gas test (Carbon dioxide)


  Lime water will turn cloudy when the gas is bubbles through it
• Formulation 


  Mixture designed as a useful product (paint, cleaning products)
• Chromatography

  • Spots of ink placed on a pencil line 1cm from the bottom of the paper with a capillary tube
  • paper lowered into solvent
  • Allow solvent to move through the paper
  • Remove the paper before solvent reaches the top
  • Measure distance travelled by spot and solvent to calculate Rf value