| Determination of Ksp Values Using the Nernst Equation |
| If Keq can be determined then it is reasonable
to assume
that other equilibrium constants can be determined by using half-cell
reaction.
By measuring the voltage of an appropriate cell we can calculate the Eo
value.
|
| The electrochmeical call for determining the Ksp for AgCl
is below.
|
 |
| In this cell, the anode consists of a piece of metallic
silver immersed
in a 1 M Cl-1 ion solution with excess AgCl(s).
The cathode is a standard Ag(s) | Ag+1 half
cell. The schematic is:
Ag | AgCl(s) | Cl-1 (1 M) || Ag+1 (1 M)
|
Ag(s)
|
| The anode half cell potential at SATP is -0.22 V for the
reaction:
|
| The standard state cathode potential for silver is +0.80
V.
|
| Therefore -0.22 V + 0.80 V= 0.58 V is the overall reaction
potential
for
|
| At equilibrium Ecell = 0
|
| Therefore 0 = 0.58 V - 0.059/1 log
(1 /
[Ag+1][Cl-1])
-0.58 V = 0.059 log [Ag+1][Cl-1] -0.58 V = 0.059 log Ksp log Ksp = -9.8 Ksp = 10-9.8 = 1.6 X 10-10 |