when a solution of Iron (II)ammonium sulfate was mixed with K4FE(CN)6, the precipitate was initially white but turned blue upon exposure to air. what happen to the Iron(II)ionwhen the precipitate turned blue
Fe in the K4Fe(CN)6 is +2 oxidation state; probably it was oxidized to +3 by oxygen in the air.
When the precipitate formed by mixing a solution of Iron (II) ammonium sulfate with K4Fe(CN)6 turned blue upon exposure to air, it indicates the oxidation of Iron (II) ions to Iron (III) ions. This reaction is known as the auto-oxidation of ferrous ion.
The process is explained as follows:
1. Initially, when the solution is prepared, the Iron (II) ions present in the Iron (II) ammonium sulfate complex are in the +2 oxidation state. This is indicated by the white precipitate that forms.
2. When the precipitate is exposed to air, it reacts with oxygen present in the atmospheric air. Oxygen can oxidize the Iron (II) ions to Iron (III) ions according to the following reaction:
2 Fe2+ + O2 → 2 Fe3+
3. The formation of Iron (III) ions leads to a blue color observed in the solution. This blue color is due to the formation of a complex called Prussian blue, which is an intense blue pigment produced by the reaction of Fe3+ ions with the cyanide ions from K4Fe(CN)6.
To confirm the presence of Iron (III) ions, you could conduct a confirmatory test. This can be done by adding a few drops of potassium thiocyanate (KSCN) solution to the blue solution. If Iron (III) ions are present, the solution will turn reddish due to the formation of a complex between the Iron (III) ions and thiocyanate ions.