Chemical Analysis

• Pure substance


  Just one thing in it, either an element or one compound
• Mixture


  Lots of different elements and compounds, not chemically bonded together
• Compound


  Chemically bonded together
• Pure substance


  • Melts at its melting point
• Mixture


  • Melts over a range of melting points
• Melting point test


  1. Put crystals in thin tube

  2. Put tube in melting point apparatus

  3. Slowly heat and observe through window

  4. See if melts at one temperature or over a range
• Chromatography

  1. Separate out compounds

  2. Make sure paper end is just in water

  3. Draw start line in pencil, not pen

  4. Put lid on to stop solvent evaporating

  5. Calculate Rf value (distance moved by spot / distance moved by solvent)
• Types of gases

  • Hydrogen
  • Oxygen
  • Carbon dioxide
  • Chlorine
• Hydrogen gas test

  Squeaky pop
• Oxygen gas test


  Relights a glowing splint
• Carbon dioxide test

  Turns limewater cloudy
• Flame test colours

  • Lithium - crimson
  • Sodium - yellow
  • Caesium - lilac
  • Calcium - red
  • Barium - green
  • Copper - blue-green
• Testing for positive ions

  1. Look at ionic equations

  2. Look at precipitates formed with sodium hydroxide:

  Aluminium - white ppt that dissolves

  Calcium - white ppt that doesn't dissolve

  Magnesium - white ppt

  Copper - light blue ppt

  Iron(II) - grey-green ppt

  Iron(III) - orange ppt
• Testing for halide ions

  Add silver nitrate:

  Chloride - white ppt

  Bromide - cream ppt

  Iodide - yellow ppt
• Testing for carbonate ions

  Add hydrochloric acid, collect gas in limewater - if cloudy, contains carbon dioxide
• Instrumental methods can be faster, more accurate and unbiased compared to testing in class