dis is 4 da edexcel ppl doing extension unit aka triple science

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  • Created on: 24-03-12 16:54
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Chemical detection
Chemical analysis
Forensic science- investigating substance that were involved in crime
Substances present in food- allergic reactions to certain food.
Checking purity of water- potentially dangerous substances
Qualitry control process- at the right purity- copper wire needs high purity, if not pure, cant condict
Qualitative analysis
Tells you what is present
Doing tests to work out the identity of a mystery substance
E.g. your substance is an ionic compound- find positive ion by test and negative ion by diff test
Quantitative analysis
Tells you how much is present
Test for positive ions
Flame test
Metal Symbol ion Colour
Sodium Na+ Orange/ yellow
Potassium K+ Lilac
Calcium Ca2+ Brick-red
Copper Cu2+ Blue- green
Precipitate test
Add few drops of sodium hydroxide- if you get an insoluble hydroxide- you know the colour
Metal Colour of precipitate Ionic reaction
Calcium, Ca2+ White Ca2+ (aq) + 2OH- (aq) Ca(OH)2(s)
Copper(II), Cu2+ Blue Cu2+(aq) + 2OH- (aq) Cu(OH)2(s)
Iron(II), Fe2+ Sludgy green Fe2+(aq) + 2OH- (aq) Fe(OH)2(s)
Iron(III), Fe3+ Reddish brown Fe3+(aq) + 3OH- (aq) Fe(OH)3(s)
Aluminium, Al3+ White at first, redissolves in Al3+(aq) + 3OH- (aq) Al(OH)3(s)
excess NaOH form a colourless then Al(OH)3(s) OH- Al(OH)4-(aq)
Ammonium, NH4+ No precipitate- heating gives of
ammonia, which has a distinctive
Test for Negative ions
Hydrochloric acid can help detect carbonate and sulphites
We are now going to test for Sulphates with Hydrochloric acid and Barium Chloride
Sulphate ions produce a white precipitate
To test for Sulphate ions add dilute HCL followed by Barium Chloride
If the solutions turns white then it means the original compounds was a sulphate

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Tests for Halides (Cl-, Br-, I- ) with Nitric Acid and Silver Nitrate
So basically you start off with one of them halides and add dilute nitric acid and then Silver nitrate
If you start with Cl- you get a WHITE precipitate of SILVER CHLORIDE
If you start with Br- you get a CREAM precipitate of SILVER BROMIDE
If you start with I- you get a YELLOW precipitate of SILVER IODIDE
N of moles= Mass in grams (of element or compound)/ Mr (of element or…read more

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