Tests for ions

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  • Created on: 10-01-12 19:16
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C3 Testing for ions
Flame tests for positive ions
Lithium (Li+)- crimson red flame
Sodium (Na+)- yellow/ orange flame
Potassium (K+)- lilac flame
Calcium (Ca2+)- brick-red flame
Barium (Ba2+)- yellow/ green flame
When sodium hydroxide (NaOH) is added, the colour of the precipitate can tell you
which metal is in the compound
Calcium (Ca2+)- forms a white precipitate
Copper(II) (Cu2+)- forms a blue precipitate
Iron(II) (Fe2+)- forms a `sludgy' green precipitate
Iron(III) (Fe3+)- forms a reddish brown precipitate
Aluminium (Al3+)- white precipitate at first but with excess NaOH it dissolves to
form a colourless solution
Testing for ammonium ions
Damp red litmus paper turns blue, also it smells.
Testing for carbonates- check for carbon dioxide
Bubble the gas through limewater. If the limewater turns milky then the gas
contains CO2.
Testing for halides:
To test for halides add dilute nitric acid and then add silver nitrate.
Chloride= white precipitate of silver chloride
Bromide= cream precipitate of silver bromide
Iodide= yellow precipitate of silver iodide
Test for sulphate ions:
Add dilute hydrochloric acid and then add barium chloride.
If a white precipitate is formed then the original compound was a sulphate.
Testing for nitrates:
Add some aluminium powder, then add a few drops of sodium hydroxide solution
and heat. If the original substance was a nitrate it would be reduced to ammonia.
You then test for ammonia by seeing if damp red litmus paper turns blue.

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