Chemical analysis

• Pure substances melt and boil at specific temperatures but mixtures will show a range of temperatures for melting and boiling
• What is a formulation?

  A mixture that has been designed as a useful product
• What is chromatography?

  A technique used to separate mixtures and give information to help identify substances
• Chromatography involves a stationary phase (paper) and the mobile phase (water moving up the paper)
• Rf value = Distance moved by substance/distance moved by solvent
• How does chromatography work?

  As the solvent moves through the paper the different substances have different solubility and it will therefore travel up the paper to different distances
• Hydrogen - (magnesium powder and hydrochloric acid)

  Lighted splint

  Squeaky pop
• Oxygen

  Re-ignite glowing splint
• Carbon Dioxide - (carbonate + acid)

  Bubble through limewater

  Turns cloudy
• Chlorine

  Damp litmus paper turns white (bleaches)
• Instrumental methods

  Quick, accurate and sensitive

  Detect very small amounts

  Very expensive
• Lithium in the flame test

  Crimson
• Sodium in flame test

  Yellow
• Potassium in the flame test

  Lilac
• Calcium in the flame test

  Brick red
• Barium/Copper in the flame test

  Green
• Aluminium reaction with sodium hydroxide

  White precipitate which dissolves in excess
• Calcium reaction with sodium hydroxide

  White precipitate
• Magnesium reaction with sodium hydroxide

  White precipitate
• Copper || reaction with sodium hydroxide

  Blue precipitate
• Iron || reaction with sodium hydroxide

  Green precipitate
• Iron ||| reaction with sodium hydroxide

  Brown precipitate
• Carbonate ion (calcium carbonate with dilute hydrochloric acid)

  Bubble gas into limewater which turns cloudy
• Silver chloride (silver nitrate and nitric acid)

  White precipitate
• Silver bromide (Silver nitrate and nitric acid)

  Cream precipitate
• Silver iodide (Silver nitrate and nitric acid)

  Yellow precipitate
• Sulphate ions (barium chloride and a few drops of hydrochloric acid)

  White precipiate
• Flame emission spectroscopy

  Colours are produced by electrons moving out of their electron shells and emmiting wave radiation when they return
• Each element emits light at a characteristic wavelength so the line spectrum is individual for each element