Topic 8 - Chemical Analysis

• Pure substances have a specific melting/boiling point
• Pure substances are substances made of only one type of particle
• Formulations are mixtures of a certain quantity of substances to fulfil a specific purpose
• Examples of formulations:

  • Paint
  • Make Up
  • Cleaning Supplies
  • Cake
  • Fuels
  • Fertilisers
• Chromatography: The separation of a mixture to identify its consistent substances e.g pigment in ink
• The mobile phase is the solvent e.g water
• The stationary phase is the chromatography paper
• The mobile phase is moved up the stationary phases due to capillary action
• Chromatography relies on a substance's solubility for how far it moves up the paper
• Starting line is in pencil so it doesn't move up with the solvent and mess up the results
• Retention factor= distance substance (ink) moved/ distance mobile phase (water) moved
• Compare calculated Rf value with known Rf values to identify them
• Hydrogen:

  Lit splint creates a squeaky pop
• Oxygen:

  Relight a glowing splint
• Carbon Dioxide:

  Bubble through limewater and it turns cloudy
• Chlorine:

  Bleaches blue litmus paper
• Can't do the chlorine test in lab as chlorine is toxic
• Lithium:

  Crimson flame
• Sodium:

  Yellow flame
• Potassium:

  Lilac flame
• Calcium:

  Orange/Red flame
• Copper:

  Green flame
• Metal ions in solution:

  Add sodium hydroxide to make a metal hydroxide (coloured precipitate)
• Aluminium/calcium/magnesium:

  White precipitate
• Aluminium hydroxide will disappear with added sodium hydroxide
• Copper (II):

  Blue precipitate
• Iron (II):

  Green precipitate
• Iron (III):

  Brown precipitate
• Chloride ions = white
• Bromide ions = cream
• Iodide ions = yellow
• Test for halide ions:

  • Add a few drops of nitric acid to the solution (purifies it)
  • Add silver nitrate
• Test for sulfate ions:

  • Add a few drops of hydrochloric acid (to purify it)
  • Add barium chloride
• Sulfate ions form a white precipitate
• Sophisticated instruments can analyse substances effectively
• Advantages of sophisticated instruments:

  • Accurate
  • Fast
  • Sensitive (can pick up minuscule traces in very small substances)
• Disadvantage of sophisticated instruments:

  • Expensive
• Flame Emission Spectroscopy=

  analysing the wavelengths of light emitted from a flame - used to identify ions effectively