Chemical analysis

• +ve ion test - Flame Test:

  • Clean a nichrome wire by dipping it in concentrated Hydrochloric acid and then heat strongly in a blue Bunsen Flame to vaporise impurities
  • Repeat this until the wire does not produce any colour in flame
  • Moisten the wire again in conc. HCl. and dip the moistened wire in a small amount of the solid salt.
  • Heat strongly in the flame and note any flame colour
• Flame Test Results

  Lithium, Li+: Crimson

  Sodium, Na+: Yellow

  Potassium, K+: Lilac

  Calcium, Ca2+: Brick Red

  Copper, Cu2+: Blue-green
• +ve ion test - Using Sodium hydroxide/ Ammonia solution

  When a metal ion solution is mixed with sodium hydroxide solution or ammonia solution, precipitates are produced. These can be used to identify the metal cation

  a precipitate is a solid formed when two solutions are mixed. In some cases, the precipitate will dissolve if an excess of NaOH / NH3 solution is added
• Using NaOH/NH3 solution: Method

  Make up a solution of the full samples as follows:

  • Place a spatula full of the solid in a beaker, add deionised water(25cm3) and stir with a glass rod to dissolve the salt
  • Pour a little of the solution into a test tube(2cm depth)
  • Add a few drops of NaOh(aq), then add an excess of NaOh(aq) and note any further observations(if any)
  • repeat the whole experiment using ammonia solution instead of sodium hydroxide solution
• Both sodium hydroxide and ammonia solution contain hydroxide ions. When the negative hydroxide ions react with the positive metal ions an insoluble precipitate forms. Metal hydroxides (except group 1 metal hydroxides) are insoluble