Alejandro L. answered 09/22/16
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The reason it doesn't work as well when adding NaCl is because its solubility in ethanol is not high to begin with.
If you calculate how much HCl you had to add in terms of stoichiometric equivalents in relation to CoCl2(aq) you would realize that the amount of NaCl needed in solution would never be reached and so, you would only slightly shift the equilibrium to the right.
I hope that clarified your question.