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Topic: What is the equilibrium when HCl is added to an aq solution of cobalt chloride?  (Read 3593 times)

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Offline Bob Sacamano

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What is the equilibrium when HCl is added to an aq solution of cobalt chloride?
« on: September 17, 2010, 01:37:24 PM »
A pink to blue color change is observed when HCl is added to an aq solution of cobalt chloride. A shift back to pink is observed when the solution is diluted.

What is the equilibrium equation?
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Offline Borek

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Re: What is the equilibrium when HCl is added to an aq solution of cobalt chloride?
« Reply #1 on: September 18, 2010, 03:23:35 AM »
You have to try by yourself first.
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Offline Bob Sacamano

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Re: What is the equilibrium when HCl is added to an aq solution of cobalt chloride?
« Reply #2 on: September 18, 2010, 01:15:37 PM »
At first I thought:

[Co(H2O)6]2+ + 4Cl- ⇔ [CoCl4]2- + 6H2O

Then I thought:

[Co(H2O)6]2+ + 2Cl- ⇔ [CoCl2(H2O)2] + 4H2O
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Offline Borek

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Re: What is the equilibrium when HCl is added to an aq solution of cobalt chloride?
« Reply #3 on: September 18, 2010, 02:20:33 PM »
I would say both answers are to some extent correct. I don't have data on this particular system at hand, but the equilibrium is often multistep, with water molecules being replaced by other ligands one by one.

I wonder if there really is a change of the molecule geometry as you suggest.
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