Download - Testing for Ions -Summary
Testing for Ions
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Summary
There is a variety of simple chemical tests we can use to find out what ions are present in a solution.
We can test for common anions (negative ions) as shown in the table below.
Anion Test
chlorideDissolve in dilute nitric acid, then a white precipitate forms with silver nitrate solution.
(The precipitate dissolves in dilute ammonia solution.)
bromideDissolve in dilute nitric acid, then a cream precipitate forms with silver nitrate solution.(The precipitate is insoluble in dilute ammonia solution, but will dissolve in concentrated
ammonia solution)
iodideDissolve in dilute nitric acid, then a pale yellow precipitate forms with silver nitratesolution. (The precipitate is insoluble in dilute and concentrated ammonia solution)
sulfateDissolve in dilute nitric acid, then a white precipitate forms with barium chloride
solution.
nitrateAdd sodium hydroxide solution and warm with powdered aluminium, then test the gas
given off (ammonia) with damp red litmus paper, which turns blue.
carbonateAdd dilute acid, then pass the carbon dioxide gas through limewater, which turns milky
(cloudy).
We can test for positive ions by adding sodium hydroxide solution and noting the colour of the
precipitate, as shown in the table below.
Cation Result of adding sodium hydroxide solution
copper(II) pale blue precipitate
iron(II) dirty green precipitate
iron(III) rusty brown precipitate
aluminium white precipitate which dissolves in excess sodium hydroxide
magnesium white precipitate
calcium white precipitate
Ammonium ions give off ammonia gas when we heat them with sodium hydroxide solution.
Some metal ions also give out coloured light when we heat them in a Bunsen flame. Their characteristic
colours are shown in the table below.
Cation Colour of flame test
lithium red (scarlet)
sodium bright yellow
potassium lilac
barium apple green
calcium brick red
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