Key point (we assume that standard emf of the cell E°cell is known) For the given equilibrium, Cd2++4NH3⇌Cd(NH3)42+ At equilibrium, E°cell =0 Hence, we can calculate the equilibrium constant for reaction as follows: E°cell =
0.0591V
n
‌log‌KC Where, KC is unknown E°cell =0.21V 0.21V=