Tests for ions

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C7.10 Precipitation reactions and tests for ions
Compounds containing a metal or ammonium in the name are ionic. These compounds contain ions which can be worked out from the name. Eg. aluminium sulfate contains an aluminium Al³⁺ and sulfate ions SO₄^2-.

ion name	ion formula	example compound with ion
hydrogen	H⁺	any acid e.g. hydrochloric acid HCl
sodium	Na⁺	sodium bromide NaBr
potassium	K⁺	potassium iodide KI
aluminium	Al³⁺	aluminium sulfate Al₂(SO₄)₃
calcium	Ca²⁺	calcium sulfate CaSO₄
copper	Cu²⁺	copper sulfate CuSO₄
iron II	Fe²⁺	iron II sulfate FeSO₄
iron III	Fe³⁺	iron III sulfate Fe₂(SO₄)₃
ammonium	NH₄⁺	ammonium chloride NH₄Cl
carbonate	CO₃^2-	potassium carbonate K₂CO₃
sulfite	SO₃^2-	calcium sulfite CaSO₃
sulfate	SO₄^2-	magnesium sulfate MgSO₄
chloride	Cl^-	lead chloride PbCl₂
bromide	Br^-	silver bromide AgBr
iodide	I^-	sodium iodide NaI
hydroxide	OH^-	sodium hydroxide NaOH

If any of the above ions that can combine to make an insoluble compound are present in a mixture of ionic compounds in solution then they will do so. The result will be the formation of a precipitate. e.g. You can work out that iron II hydroxide is insoluble and that iron II sulfate and sodium hydroxide are soluble. When mixed that following ions are present; iron II, hydroxide, sulfate, and sodium. The result will be a precipitate of iron II hydroxide.
learning activity - name both of the ions in each of the compounds in the table above.
list the soluble and insoluble compounds in the table
name pairs of soluble compounds from the table and name the precipitate formed

C7.11 Tests for common ions

name of ion	test	result of positive test
hydrogen	add universal indicator	indicator turns red
hydrogen	add carbonate	effervescence carbon dioxide detected
hydrogen	add magnesium	effervescence hydrogen detected
sodium	flame test	yellow flame
potassium	flame test	lilac flame
calcium	flame test	brick red flame
copper	flame test	blue/green flame
aluminium	add drop aqueous sodium hydroxide add excess aqueous sodium hydroxide	white precipitate forms white precipitate redissolves
calcium	add drop aqueous sodium hydroxide add excess aqueous sodium hydroxide	fine white precipitate forms precipitate does not dissolve
copper	add drop aqueous sodium hydroxide	blue precipitate form
iron II	add drop aqueous sodium hydroxide	green precipitate forms
iron III	add drop aqueous sodium hydroxide	brown precipitate forms
ammonium	add 5cm3 of sodium hydroxide and warm	ammonia detected
carbonate	add a little dilute acid	effervescence carbon dioxide detected
sulfite	add a little dilute hydrochloric acid, warm	sulfur dioxide detected
sulfate	add dilute hydrochloric acid then a few drops of aqueous barium chloride	white precipitate formed
chloride	add dilute nitric acid then a few drops of silver nitrate	white precipitate forms
bromide	add dilute nitric acid then a few drops of silver nitrate	buff precipitate forms
iodide	add dilute nitric acid then a few drops of silver nitrate	yellow precipitate form
hydroxide	add universal indicator	indicator turns blue
hydroxide	add ammonium compound and warm	ammonia detected

What would you see with named compounds and named reagents?
Identify X if Y seen with reagent Z
How would you test compound X?

C7.12 explaining ion tests with equations
hydrogen ions
hydrochloric acid + magnesium ---> magnesium chloride + hydrogen
2HCl(aq) + Mg(s) ---> MgCl₂(aq) + H₂(aq)
2H⁺(aq) + Mg(s) ---> Mg²⁺(aq) + H₂(g)
nitric acid + sodium carbonate --> sodium nitrate + water + carbon dioxide
2HNO₃(aq) + Na₂CO₃(aq) ---> 2NaNO₃(aq) +H₂O(l) + CO₂(g)
2H⁺(aq) + CO₃^2-(aq) ---> H₂O(l) + CO₂(g)
Aluminium ions
aluminium sulfate + sodium hydroxide ---> aluminium hydroxide + sodium sulfate
Al₂(SO₄)₃(aq) + 6NaOH(aq) ---> 2Al(OH)₃(s) + 3Na₂SO₄(aq)
2Al³⁺(aq) + 6OH^----> 2Al(OH)₃(s)
aluminium hydroxide + sodium hydroxide ---> sodium aluminate
Al(OH)₃(s) + NaOH(aq) ---> NaAl(OH)₄(aq)
Al(OH)₃(s) + OH^-(aq) ---> Al(OH)₄^-(aq)
calcium ions
calcium nitrate + sodium hydroxide ---> calcium hydroxide + sodium nitrate
Ca(NO₃)₂(aq) + 2NaOH(aq) ---> Ca(OH)₂(s) + 2NaNO₃(aq)
Ca²⁺(aq) + 2OH^-(aq) ---> Ca(OH)₂(s)
copper ions
copper chloride + sodium hydroxide ---> copper hydroxide + sodium chloride
CuCl₂(aq) + NaOH(aq) ---> Cu(OH)₂(s) + NaCl(aq)
Cu²⁺(aq) + OH^-(aq) ---> Cu(OH)₂(s)
iron II ions
iron II chloride + sodium hydroxide ---> iron II hydroxide + sodium chloride
FeCl₂(aq) + NaOH(aq) ---> Fe(OH)₂(s) + NaCl(aq)
Fe²⁺(aq) + OH^-(aq) ---> Fe(OH)₂(s)
iron III ions
iron III sulfate + sodium hydroxide ---> iron III sulfate + sodium sulfate
Fe₂(SO₄)₃(aq) + 6NaOH(aq) ---> 2Fe(OH)₃(aq) + 3Na₂SO₄(aq)
Fe³⁺(aq) + 3OH^-(aq) ---> Fe(OH)₃(aq)
ammonium ions or hydroxide ions
ammonium chloride + sodium hydroxide ---> sodium chloride + water + ammonia
NH₄Cl(aq) + NaOH(aq) ---> NaCl(aq) + H₂O(l) + NH₃(g)
NH₄⁺(aq) + OH^-(aq) ---> H₂O(l) + NH₃(g)
carbonate ions
sodium carbonate + nitric acid --->sodium nitrate + water + carbon dioxide
Na₂CO₃(aq) + 2HNO₃(aq) ---> 2NaNO₃(aq) + H₂O(aq) + CO₂(aq)
CO₃^2-(aq) + 2H⁺(aq) --- > H₂O(aq) + CO₂(aq)
sulfite
sodium sulfite + hydrochloric acid ---> sodium chloride + water + sulfur dioxide
Na₂SO₃(aq) + 2HCl ---> 2NaCl(aq) + H₂O(aq) + SO₂(aq)
SO₃^2-(aq) + 2H⁺(aq) ---> H₂O(aq) + SO₂(aq)
sulfate
sodium sulfate + barium chloride ---> barium sulfate + sodium chloride
Na₂SO₄(aq) + BaCl₂(aq) ---> BaSO₄(s) + 2NaCl(aq)
SO₄^2-(aq) + Ba²⁺(aq) ---> BaSO₄(s)
chloride
sodium chloride + silver nitrate ---> silver chloride + sodium nitrate
NaCl(aq) + AgNO₃(aq) ---> AgCl(s) + NaNO₃(aq)
Cl^-(aq) + Ag⁺(aq) ---> AgCl(s)
bromide
sodium bromide + silver nitrate ---> silver bromide + sodium nitrate
NaBr(aq) + AgNO₃(aq) ---> AgBr(s) + NaNO₃(aq)
Br^-(aq) + Ag⁺(aq) ---> AgBr(s)
iodide
sodium iodide + silver nitrate ---> silver iodide + sodium nitrate
NaI(aq) + AgNO₃(aq) ---> AgI(s) + NaNO₃(aq)
I^-(aq) + Ag⁺(aq) ---> AgI(s)