Practice Problem 11
Use the following standard-state cell potentials to calculate the complex formation equilibrium constant for the Zn(NH3)42+ complex ion.
|Zn(NH3)42+ + 2 e- Zn + 4 NH3||Eored = -1.04 V|
|Zn2+ + 2 e- Zn||Eored = -0.7628 V|
By reversing the first half-reaction and adding it to the second, we can obtain an overall equation that corresponds to the complex formation equilibrium.
|Eoox = 1.04 V|
|+ Zn2+ +
||Eored = -0.7628 V|
|Zn2+ + 4 NH3 Zn(NH3)42+||Eo = 0.28 V|
When this reaction comes to equilibrium, the cell potential is zero and the reaction quotient is equal to the complex formation equilibrium constant for the Zn(NH3)42+ complex ion.
We now solve this equation for the natural logarithm of the equilibrium constant and calculate the value of Kf for this reaction.