The addition of aqueous ammonia to the cathode compartment of the cell described below reduces the cell potential. Likewise, the addition of aqueous ammonia to the anode compartment increases the cell potential.
Zn(s)/Zn^2+(aq)//Cu^2+/Cu(s)
Assume that [Cu^2+(aq)]0=[Zn^2+(aq)]0=0.10M and that both Cu^2+ and Zn^2+ form very stable complexes with ammonia (overall formation constants 10>10^10), each with a coordination number of 4.
A. Show how to estimate the ratio of the overall formation constant for [Zn(NH3)4]^2+ to the overall formation constant for [Cu(NH3)4]^2+ if the cell potential is observed to be 0.96 V after adding equal amounts (assume a large excess) of 6 M NH3 to each compartment (assume that T=298K).
B. Which of the two transition metal complexes is more thermodynamically stable? How much more stable is it than the other complex?