When HCl is added to a cobalt/cobalt chloride solution, it turns from pink to blue-violet, why?

Question

Where does LeChatelier's principle say the shift happens? Would it be towards the right because: [Co(h2o6)2+ + 4Cl- <=> [CoCl4]2- + 6H2O. And since Cocl4 is blue, the solution turning that color would mean its shifting right, then?

Answer 1

Hello Lily. You have made some great deductions, which lead you to the correct answer.

I would like to solidify the idea for you, so that the idea is more ground in understanding the science and the tool, LeChateller's principle.

Starting the chemical equation you have written out, if we convert the equation back into an uneven chemical equation (dropping charge and molar equivalents):

[Co(H₂O)₆] + HCl <==> [CoCl₄]^2- + H₂O

we can now see a place for HCl (this is also where the Cl^- originated from). Now if Cl^- and HCl are approximately equivalent, and HCl is increased in solution, what will happen to the equilibrium, ideally?

As you concluded Lily, it will shift to the products (or to the right) side.