Le Chatelier's Principle

Question

Please explain what happens when NaNO3 is added to a saturated CuCl₂ aq solution. The CuCl2 solution is blue and then turned a very dark green black when the NaNO₃ was added. I understand there is not a common ion effect but was wondering if the Na+ ions capture some to the Cl- ions to lower the Cl- concentration. This would then shift the equilibrium to towards the left/ reactants ( Cu⁺² aq + Cl^-1 aq -->/<--- CuCl₄²⁺ aq). I guess I was expecting more of a dark blue color change.

Answer 1

The reaction is trying to proceed toward the product side assuming when you state the CuCl2 solution, you mean there is not any NaNO3. If you add the NaNO3 to the solution, this would cause the the following reaction to occur:

CuCl2(aq) + 2NaNO3(aq) <=> Cu(NO3)2(aq) + 2NaCl(aq)

As you can see, this is a simple displacement reaction where the ions are exchanged. If you want me to further explain this, please let me know.