Question

In a solution of copper(II) chloride, the following equilibrium exists:
CuCl42-(aq) (dark green) + 4H2O(l) <--> Cu(H2O)42+(aq)(blue) +4 Cl-(aq)

Predict the shift in the equilibrium and draw a graph of concentration versus time for relevant reactants to communicate the shift after the following stresses are applied to the system:
(a) HCL acid is added
(b) Silver nitrate is added.

Answer 1

It is impossible to draw diagrams on the board to show you how this works and words sometimes fail to communicate properly; however, remember Le Chatelier's Principle. A reaction at equilibrium will try to UNDO what we do to it (although Le Chatelier's statement was much more esoteric). Therefore, it we add HCl (we are adding Cl^-), the reaction will shift so as to undo what we did. Since we added Cl^-, the reaction will shirt to try to get rid of Cl^-; ie., use it up. If it shift to the right, more Cl^- is formed so it won't do that. Shifting to the left uses Cl^- and that is what it will do.
Add AgNO3 and you know Ag^+ will react with Cl^- to produce insoluble AgCl
Ag^+(aq) + Cl^-(aq) ==> AgCl(s)

So we are removing Cl^- from the reaction to form solid AgCl. The reaction will shift so as to undo what we did. Since Cl^- is being removed, the reaction will shift to produce more Cl^- which means it will shift to the right.