Chem Topic 8

• How can we tell something is a pure substance?

  It has a very specific melting/boiling point.
• What are formulations?

  Mixtures of certain quantities of substances designed to fulfil a specific purpose

  E.g.

  • Paints, fuels, alloys & fertilisers
• What is chromatography?

  The separating of a mixture to identify its constituent substances e.g. pigments in ink, drugs in urine sample
• What is the mobile phase?

  The solvent which moves up the stationary phase (chromatography/filter paper) due to capillary action
• What must we do in chromatography?

  • Make sure line is drawn in pencil just above water to prevent it from ruining the experiment
• What is the retention factor?

  Values that can be compared against that of known substances to identify them

  Rf value = distance substance moved/distance mobile phase moved
• How do we test for gases?

  Hydrogen: Lit splint produces squeaky pop

  Oxygen: Will relight glowing splint

  Carbon Dioxide: Causes limewater to turn cloudy when bubbled through it

  Chlorine: Bleaches blue litmus paper
• What are the flame tests for metals ions?

  Lithium - Crimson

  Sodium - Yellow

  Potassium - Lilac

  Calcium - Orange red

  Copper - Green
• What is the test for metal ions in a solution?

  Add sodium hydroxide to make metal hydroxide (coloured precipitate)

  Aluminium/calcium/magnesium:

  White precipitate (dissolves/disappears with excess NaOH)

  Copper (II) ions:

  Blue precipitate

  Iron (II) ions

  Green precipitate

  Iron (III) ions

  Brown precipitate
• Testing for carbonates, halides & sulphates?

  Carbonates react with acid to produce carbon dioxide

  Halide ions will produce a precipitate when mixed with silver nitrate & nitric acid:

  Chloride ions - white precipitate

  Bromide ions - cream precipitate

  Iodide ions - Yellow precipitate

  Sulphate ions produce a white precipitate when mixed with barium chloride & hydrochloric acid
• What are instrumental methods?


  Sophisticated instruments can analyse substances effectively. They're accurate, sensitive and rapid. Flame emission spectroscopy is an example