Synthesis of Coordination Compounds and the Role of Charcoal

[John Ker]

Homework Statement

I performed a lab that has the main objective of reacting a cobalt(II) chloride solution through a series of steps to achieve the following two compounds:
Compound A - Purple - [Co(NH3)5Cl]Cl2
Compound B - Orange - [Co(NH3)6]Cl3
The only difference when performing the reaction was the addition of charcoal during the beginning, (that acts as a catalyst), the question that is brought forward is
Why does the addition of charcoal lead to the Orange results of [Co(NH3)6]Cl3 and what role does it play?

Homework Equations

The Attempt at a Solution

I'm really struggling to see how it affects how the solution will react? I understand it will accelerate it, but why does that lead to a completely different compound. Could it be the fact of it being Carbon have anything to do with it? Any lead would be great,
Thanks

 

[trurle]

Textbook says charcoal catalyze connection of ammonia to cobalt, and transformation of Co²⁺ to Co³⁺, therefore favouring hexammine complex formation kinetically.
I tend to doubt it is only role though - same textbook recommend to add 2 mol of carbon per 1 mol of cobalt chloride, which is unusually large amount for a catalyst.

May be, more important effect is carbon having a slight affinity for chloride ions, therefore it may work simply by lowering concentration of dissolved chloride ions, which make formation of all-ammonia inner ligands more likely. In this case you actually need to add a lot of carbon, as recommended. It would be interesting to add unrelated chloride and see if carbon catalyst is still effective.