The questions below refer to the following system: Co(H2O)62+ + 4 Cl–------> CoCl42– + 6H2O?
The questions below refer to the following system:
Co(H2O)62+ + 4 Cl–------> CoCl42– + 6H2O
(pink) (blue)
Cobalt chloride is added to pure water. The Co2+ ions hydrate. The hydrated form then reacts with the Cl– ions to set up the equilibrium shown here:
Which statement below describes the change that the system will undergo if silver nitrate is added?
A. It should become more blue.
B. Nothing will change.
C. It should become more pink.
D. Water will be produced.
E. The silver ion will react with the CoCl42–.
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The reaction is in fact an equilibrium and all 1st Row TM cmplxs change within seconds when the equilibrium is altered, except cmplxs of Cr(III) and Co(III):
[Co(H2O)6]^2+ + 4Cl- ⇄ [CoCl4]^2- + 6H2O
pale pink deep blue
Now when you add Ag^+ you will immediately ppt AgCl:
Ag^+ Cl- → AgCl(s)↓
By Le Chatelier's principle if Cl- is removed the equilibrium will shift to the left and the solution will turn pink, so the answer is C. E is a little ambiguous because the net result is that the Ag^+ HAS reacted with [CoCl4]^2- but I have gone with C, even the solution is blue to begin with so it is not really become MORE pink.
This my expert opinion. (I have done this rxn numerous times in my lectures.)