The electrochemical cell shown below is a concentration cell.M|M2+ (sa...
The electrochemical cell shown below is a concentration cell.M|M2+ (sa...
Given information:
- Electrochemical cell is a concentration cell.
- Half-cell reactions: M+ + e- → M (saturated solution of a sparingly soluble salt, MX2)
M2+ + 2e- → M (0.001 mol dm-3)
- EMF of the cell at 298K = 0.059 V
- 2.303RT/F = 0.059 V (at 298K)
To find: Solubility product (Ksp) of MX2 at 298K
Solution:
The given cell is a concentration cell, which means that the two half-cells have the same electrode but different concentrations of M2+ ions. The concentration of M2+ ions at the two electrodes can be related to the solubility product of MX2 using the Nernst equation:
Ecell = E°cell - (RT/nF) ln Q
where Ecell is the cell potential, E°cell is the standard cell potential, R is the gas constant, T is the temperature, n is the number of electrons transferred in the cell reaction, F is the Faraday constant, and Q is the reaction quotient.
For the given cell, the half-cell reactions and their standard reduction potentials are:
M+ + e- → M (saturated solution of a sparingly soluble salt, MX2) E°1 = ?
M2+ + 2e- → M E°2 = E°°M2+/M - E°°M
The standard potential of the M2+/M half-reaction can be calculated using the Nernst equation:
E°°M2+/M = (RT/nF) ln(Ksp)
where Ksp is the solubility product of MX2.
Substituting the given values into the Nernst equation for the cell:
0.059 V = E°1 - (RT/nF) ln(Q)
where Q = [M2+] / [M+] (the concentration of M+ ions is assumed to be constant and equal to the saturation concentration)
Taking the antilog of both sides:
Q = [M2+] / [M+] = e^(nF(E°1 - 0.059 V) / RT)
Substituting the standard potential of the M2+/M half-reaction and rearranging:
Ksp = [M2+]^2 [M+]^-1 = e^(2nF(E°1 - 0.059 V) / RT)
Using the value of 2.303RT/F = 0.059 V at 298K and n = 2 (since two electrons are transferred in the cell reaction):
Ksp = e^(4.605(E°1 - 0.059) / 0.059) = e^(78.0508E°1 - 78.0508)
Taking the antilog of both sides:
Ksp = 10^(78.0508E°1 - 78.0508)
To find the value of E°1, we can use the standard potentials of the half-reactions for M and M2+ ions:
E°1 = E°°M - E°°M2+/M = E°°M - (RT/2F) ln([M2+]/[M])
Substituting the given values:
E°1 = -0.059 - (