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Testing for ions flow chart
Testing for ions flow chart
Identify ions flow chart.pdfTesting for Cations
Testing for Cations
Testing for Sodium ions, Na+ (aq)
Testing for Sodium ions, Na+ (aq)
Testing for Iron (II) ions, Fe2+ (aq)
Testing for Iron (II) ions, Fe2+ (aq)
Add 2 drops of sodium hydroxide, NaOH, to a sample of the solution.
A green precipitate of iron (II) hydroxide, Fe(OH)2(s) forms.
Fe2+ (aq) + 2OH- (aq) 🡪 Fe(OH)2(s)
It is not Na+ as that does not form a precipitate with NaOH. It is not the other cations because they do not form green precipitates. Only Fe2+ forms a green precipitate with NaOH.
Testing for Iron (III) ions, Fe3+ (aq)
Testing for Iron (III) ions, Fe3+ (aq)
Add 2 drops of sodium hydroxide, NaOH, to a sample of the solution.
An orange precipitate of iron (III) hydroxide, Fe(OH)3(s) forms.
Fe3+ (aq) + 3OH- (aq) 🡪 Fe(OH)3(s)
It is not Na+ as that does not form a precipitate with NaOH. It is not the other cations because they do not form orange precipitates. Only Fe3+ forms an orange precipitate with NaOH.
To confirm the presence of iron (III) ions to a new sample add 2 drops KSCN (potassium thiocyanate) solution.
A deep red/blood red solution forms which is a complex ion. The equation for the complex ion formation is:
Fe3+(aq) + SCN-(aq) 🡪 [FeSCN]2+ (aq)
It must be Fe3+ , as Fe3+ is the only cation that forms a blood red/deep red solution when KSCN (potassium thiocyanate) is added.
Testing for Copper (II) ions, Cu2+ (aq)
Testing for Copper (II) ions, Cu2+ (aq)
Add 2 drops of sodium hydroxide, NaOH, to a sample of the solution.
An blue gelatinous precipitate of copper (II) hydroxide, Cu(OH)2(s) forms.
Cu2+ (aq) + 2OH- (aq) 🡪 Cu(OH)2(s)
It is not Na+ as that does not form a precipitate with NaOH. It is not the other cations because they do not form blue precipitates. Only Cu2+ forms a blue precipitate with NaOH.
To confirm the presence of copper (II) ions to a new sample add 2 drops of ammonia, NH3, solution, and then excess ammonia solution
A blue gelatinous precipitate of copper (II) hydroxide, Cu(OH)2(s) forms.
Cu2+ (aq) + 2OH- (aq) 🡪 Cu(OH)2(s)
When you add the excess ammonia solution, the blue gelatinous precipitate dissolves and a deep blue complex ion forms.
Cu(OH)2(s) + 4NH3(aq)🡪 [Cu(NH3)4]2+(aq) +2OH- (aq)
Only Cu2+ forms a blue precipitate which disappears in excess NH3 solution to form a deep blue solution.
Testing for Silver ions, Ag+ (aq)
Testing for Silver ions, Ag+ (aq)
Add 2 drops of sodium hydroxide, NaOH, to a sample of the solution.
A brown precipitate of silver oxide, Ag2O, forms.
2Ag+ (aq) + 2OH- (aq) 🡪 Ag2O(s) + H2O(l)
It is not Na+ as it does not form a precipitate with NaOH. It is not Al3+, Mg2+, Ba2+, Pb2+, or Zn2+ as they form white precipitates with NaOH. It is not Fe2+ or Cu2+ as they form green and blue precipitates respectively. It could be Fe3+ because the precipitate could be orange/brown or it could be Ag+ as it forms a brown precipitate.
To a new sample add 2 drops (then excess) NH3 solution.
A brown precipitate of silver oxide, Ag2O, forms when two drops of NH3 solution is added.
2Ag+ (aq) + 2OH- (aq) 🡪 Ag2O(s) + H2O(l)
The brown precipitate of silver oxide, Ag2O, disappears when excess NH3 solution is added. This colourless solution is a complex ion given by the equation below:
Ag2O(s)+H2O(l)+4NH3(aq)🡪2[Ag(NH3)2]+(aq)+2OH(aq)
This confirms the presence of silver ions.
The ion must be Ag+ as it is the only ion out of Ag+ or Fe3+ that forms a brown precipitate with NH3 solution that then disappears to form a colourless solution in excess NH3.
Testing for Barium ions, Ba2+ (aq)
Testing for Barium ions, Ba2+ (aq)
Add 2 drops of sodium hydroxide, NaOH, to a sample of the solution.
A white precipitate of barium hydroxide, Ba(OH)2, forms.
Ba2+ (aq) + 2OH- (aq) 🡪 Ba(OH)2 (s)
The ion could be Al3+, Mg2+, Ba2+, Pb2+, or Zn2+ as they form white precipitates with NaOH. It is not the other ions as they do not form white precipitates with NaOH.
Add excess NaOH to the white precipitate. The precipitate remains.
The ion could be Mg2+ or Ba2+ as the precipitate remained in excess NaOH. It is not Al3+, Pb2+, or Zn2+ as the precipitate did not disappear in excess NaOH.
To a new sample of the solution add dilute sulfuric acid, H2SO4.
A white precipitate of barium sulfate, BaSO4 forms.
Ba2+ (aq) + SO42- (aq) 🡪 BaSO4 (s)
The sample must be Ba2+ as a white precipitate formed with dilute H2SO4. Mg2+ does not form a white precipitate with dilute H2SO4.
Testing for Magnesium ions, Mg2+ (aq)
Testing for Magnesium ions, Mg2+ (aq)
Add 2 drops of sodium hydroxide, NaOH, to a sample of the solution.
A white precipitate of magnesium hydroxide, Mg(OH)2, forms.
Mg2+ (aq) + 2OH- (aq) 🡪 Mg(OH)2 (s)
The ion is not Na+ as that does not form a precipitate with NaOH. It is not Fe2+, Fe3+, Cu2+, or Ag+ as they do not form white precipitates with NaOH. It could be Mg2+, Zn2+, Pb2+, Ba2+, or Al3+ .
Add excess NaOH to the white precipitate. The white precipitate remains.
It could be Mg2+ or Ba2+ as the precipitate remained. It is not Zn2+, Pb2+, or Al3+ as the precipitate did not disappear.
To a new sample add H2SO4.
No precipitate forms
The ion must be Mg2+ as no precipitate formed with H2SO4. It is not Ba2+ as a white precipitate would have formed with H2SO4.
Testing for ions videos
Testing for ions videos
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