Chemical Analysis

Chemical Analysis

Purity and Formulations

Paper Chromatography

• Chromatography is a method used to separate substances within a mixture. Chromatography always consists of two phases:
• Mobile phase - where the molecules can move (liquid or gas)
• Stationary phase - where molecules can't move (solid or thick liquid)
• During a chromatography experiment the substances move between the mobile and stationary phases. An equilibrium is formed between these phases
• The mobile phase moves through the stationary phase and anything dissolved within the mobile phase also moves with it.
• The speed of movement depends upon the distribution between the two phases (whether it spends longer in the mobile phase or the stationary phase)
• The chemicals that are in the mobile phase for longer will move further
• 
• Caption: A chromatography experiment

Required Practical: Testing Gases

• Chlorine - bleaches damp litmus paper (turns it white)
• Oxygen - a glowing splint will relight in a test tube of oxygen
• Carbon Dioxide - bubbling carbon dioxide through lime-water (calcium hydroxide) causes a white precipitate to form (it goes cloudy)
• Hydrogen - a lit splint in a test tube of hydrogen will result in a squeaky "pop" (the hydrogen burns quickly with oxygen to form water)

Testing for Carbonates

• 
• Caption: Testing for carbonates
• Acid + Carbonate -> Salt + Water + Carbon Dioxide
• If you react a carbonate with dilute acid then carbon dioxide will be released. You can then test for carbon dioxide using limewater

Testing for Sulfates

• 
• Caption: Testing for sulfates
• Dilute Hydrochloric acid and barium chloride solution is needed
• Add a few drops of the Hydrochloric acid
• Then add a few drops of barium chloride solution
• If sulfate ions are present then a white precipitate of barium sulfate will form

Testing for Halides

• 
• Caption: Testing for halides
• Dilute nitric acid will be needed with silver nitrate solution
• Add a few drops of nitric acid
• Then add a few drops of silver nitrate solution
• Chloride - white precipitate
• Bromide - cream precipitate
• Iodide - yellow precipitate

Required Practical: Flame Tests

• lithium compounds result in a crimson flame
• sodium compounds result in a yellow flame
• potassium compounds result in a lilac flame
• calcium compounds result in an orange-red flame
• copper compounds result in a green flame.
• 
• Caption: Flame tests

Testing for Metals

• Some metal hydroxides have a characteristic colour. Adding a few drops of sodium hydroxide will cause the formation of an insoluble hydroxide precipitate.
• Calcium - Ca2+ - White ppt
• Copper (II) - Cu2+ - Blue ppt
• Iron (II) - Fe2+ - green ppt
• Iron (III) - Fe3+ - brown ppt
• Aluminium - Al3+ - white ppt (redissolves in excess)
• Magnesium - Mg2+ - white ppt

Flame Emission Spectroscopy

• 
• Caption: An example of line spectra