Reagent
|
Cation
|
Effect
|
|
Potassium hexacyanoferrate(II) solution
K4Fe(CN)6(aq)
(Potassium ferrocyanide) |
Cu2+ |
Red brown ppt. soluble in dil. NH3(aq)
2Cu2+(aq) + [Fe(CN)6]4-(aq)
®
Cu2 Fe(CN)6(s)
Cu2 Fe(CN)6(s) + 8NH3(aq)
®
2[Cu(NH3)4]2+(aq) + [Fe(CN)6]4-(aq) |
|
Fe2+ |
Pale blue ppt. turning dark on exposure to
air or oxidising agent.
Fe2+(aq) + [Fe(CN)6]4-(aq) + 2K+(aq)
®
K2Fe[Fe(CN)6](s)
K2Fe[Fe(CN)6](s)
®
KFe[Fe(CN)6](s) + K+(aq) + e-
Turnbull’s blue |
|
Fe3+ |
Dark blue ppt. (Prussian blue) soluble in conc. HCl(aq) to give blue
solution.
Fe3+(aq) + [Fe(CN)6]4-(aq) + K+(aq)
®
KFe[Fe(CN)6](s)
KFe[Fe(CN)6](s) + 4Cl-(aq)
®
FeCl4-(aq) + K+(aq) + [Fe(CN)6]4-(aq) |
|
Zn2+ |
Yellowish white ppt. insoluble in dilute NH3(aq) ,
insoluble in acids.
2Zn2+(aq) + [Fe(CN)6]4-(aq)
®
Zn2Fe(CN)6(s) |
|
Ni2+ |
Greenish ppt., soluble in dilute NH3(aq)
2Ni2+(aq) + [Fe(CN)6]4-(aq)
®
Ni2Fe(CN)6(s)
Ni2Fe(CN)6(s) + 8NH3(aq)
®
2[Ni(NH3)4]2+(aq) + [Fe(CN)6]4-(aq) |
|
Potassium hexacyanoferrate(III) solution
K3Fe(CN)6(aq)
(Potassium ferricyanide) |
Fe2+ |
Dark blue ppt. (Turnbull’s blue) soluble in conc. HCl(aq) to give blue
solution.
Fe2+(aq) + [Fe(CN)6]3-(aq) + K+(aq)
®
KFe[Fe(CN)6](s) |
|
Fe3+ |
Brown or green colouration, no ppt.
Fe3+(aq) + [Fe(CN)6]3-(aq)
®
Fe[Fe(CN)6](aq) |
|
Ni2+ |
Greenish yellow ppt., soluble in dil. NH3, insoluble in
acids.
3Ni2+(aq) + 2[Fe(CN)6]4-(aq)
®
Ni3[Fe(CN)6]2(s) |
|
Zn2+ |
Yellow ppt., soluble in acids, soluble NH3(aq)
3Zn2+(aq) + 2[Fe(CN)6]3-(aq)
®
Zn3[Fe(CN)6]2(s)
Zn3[Fe(CN)6(s)]2 + 12NH3(aq)
®
3[Zn(NH3)4]2+(aq) + 2[Fe(CN)6]4-(aq |
|
Mn2+ |
Brown ppt. Insoluble in acids and NH3(aq). Decomposed by
hot dil. HCl.
3Mn2+(aq) + 2[Fe(CN)6]4-(aq)
®
Mn3[Fe(CN)6]2(s) |
|
Butanedionedioxime solution
(Dimethylyglyoxime)
(DMGH2(aq)), (CH3.C:NOH)2 |
Ni2+ |
Bright red ppt. when oxidising agents are absent.
Ni2+(aq) + 2DMGH-(aq)
®
Ni(DMGH)2(s) |
|
Fe2+ |
Light red solution formed.
Perhaps: Fe2+(aq) + DMGH-(aq)
®
[FeDMGH]+(aq) |
|
Fe3 |
Wine red solution formed.
Perhaps: Fe3+(aq) + DMGH-(aq)
®
[FeDMGH]2+(aq) |
|
Ammonium thiocyanate or potassium thiocyanate
solution, NH4SCN(aq) or KSCN |
Fe3+ |
Deep red solution formed.
Fe3+(aq) + SCN-(aq)
®
[FeSCN]2+(aq) |
|
Fe2+ |
No reaction. |
|
Co2+ |
Deep blue solution formed.
Co2+(aq) + 4SCN!(aq)
®
[Co(SCN)4]2!(aq) |