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Tests for Cations - Flame Test
A nickel-chrome wire is dipped into hydrochloric acid and then put in a blue
Metal Cation Flame Colour
Lithium Crimson-Red
Sodium Yellow-Orange
Potassium Lilac
Calcium Brick-Red
Barium Green…read more

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Tests for Cations - Metal Ions in Solution
A few drops of Sodium Hydroxide are added to 1cm³ of the solution. Then add
another 1cm³ of Sodium Hydroxide
All of these metals make insoluble hydroxides, so, when reacted with Sodium
Hydroxide, the metal hydroxides formed precipitate out
Mg2+ + 2OH- Mg(OH) 2
Cation in Solution Observation on addition of Observation on addition of
NaOH excess NaOH
Calcium White Precipitate Precipitate Remains
Magnesium White Precipitate Precipitate Remains
Aluminium White Precipitate Precipitate Redissolves
Copper II Blue Precipitate Precipitate Remains
Iron II Green Precipitate Precipitate Remains
Iron III Reddish Brown Precipitate Precipitate Remains…read more

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Tests for Cations - Ammonium Ions
1cm³ of Sodium Hydroxide is added to 1cm³ of the solution, and a small piece
of damp red litmus paper is folded over the test tube. If nothing happens,
solution can be wafted over a blue Bunsen flame
Ammonium ions react with hydroxide ions to make ammonia and water.
Ammonia isn't very soluble in water, so some escapes as vapour, turning the
red litmus paper blue as it is alkali
NH4 + OH- NH3 + H2O
Cation in Solution Observation
Ammonium Red litmus paper turns blue, as alkali gas
is given off…read more

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Tests for Cations - Metal Carbonate
The compound is heated strongly, and left to cool (thermal decomposition).
Any gas produced is bubbled through limewater
Copper and Zinc Carbonate both undergo thermal decomposition to form the
metal oxide (copper oxide or zinc oxide) and carbon dioxide
ZnCO3 ZnO + CO2
Metal Carbonate Observation of Limewater Observation of Solid
during Thermal during Thermal
Decomposition Decomposition
Copper Carbonate Went cloudy (as carbon dioxide Turns from green to black,
is given off) and stays black when
Zinc Carbonate Went cloudy (as carbon dioxide Turns from white to yellow,
is given off) and turns back to white
when cooled…read more

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Tests for Anions - Carbonate
1cm³ of dilute acid, e.g. dilute hydrochloric acid, is added to the solution
Carbonates react with acids to form carbon dioxide gas, a salt and water
Acid + Carbonate Carbon Dioxide + Salt + Water
Na2CO3 + 2HCl 2NaCl + CO2 + H2O
Anion in Solution Observation
Carbonate The solution fizzes (as it is carbon dioxide.
It can be bubbled through limewater to
check that it is carbon dioxide)…read more

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