Group 6 Cations

Cations
Group 6 consists of copper 2+ blue cation, mercury 2+ colourless cation, cobalt 2+ pink cation and nickel 2+ green cation.

Common reagent
The common reagent of this group is aqueous ammonia solution NH4OH. When ammonia solution is added, cations of this group form precipitates of various colors.

When excess ammonia solution is added, these precipitates will dissolve into colorful solutions.

Determination
Copper 2+
We can use a flame test and see the blue-green flame.
Also we can use the reaction with potassium ferrocyanide K4[Fe(CN)6]. This reaction yields to the formation of brown-red precipitate Cu2[Fe(CN)6].

Mercury 2+
We can use the reaction with potassium iodide KI. The brown-red precipitate of mercury iodide HgI2 is formed.
Hg2+ + KI = HgI2↓ + K+

Cobalt 2+
We can use the reaction ammonium thiocyanate NH4SCN. The solution turns to blue. For this reaction we should use an organic compound for extraction.

Nickel 2+
We can use the reaction with Dimethylglyoxime. The crimson precipitate is formed.

Application
Compounds of Group 6 cations found a use in medicine and pharmacy. For example, mercury oxide is a part of some medicinal creams, mercury chloride and copper sulfate are used in antiseptics.