Chemical Analysis

Chemical Analysis

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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

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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

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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

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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

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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 flamesodium compounds result in a yellow flamepotassium compounds result in a lilac flamecalcium compounds result in an orange-red flamecopper compounds result in a green flame.

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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

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Caption: : An example of line spectra