Question

What is the standard reduction potential of the Y¹⁺/Y redox couple if the cell potential of the following cell at 25 ^oC is 0.98 V?

Zn / Zn²⁺ (0.34 M) // Y¹⁺ (1.1 M) / Y

E^o =

What is the cathode pH in Co/Co²⁺(1.00 M)//H¹⁺(x M), H₂(1.0 atm)/Pt if E = 0.06 V? Give the pH to 0.01.

pH=

Answer 1

Ans 1- using the nernst equation

E = Eo - (RT/nF) x ln ([Zn2+] / [Y+])

E = 0.98V
R = 8.314
T = 25 + 273.15 =298.15 K
n = 2
F = 96500
[Zn2+] = 0.34 M
[Y+] = 1.1 M

0.98 = Eo - (8.314*298.15/2*96500) * ln (0.34/1.1)

0.98 = Eo + 0.0151

Eo = 0.98 - 0.0151 = 0.9649 V

Ans 2-

The related standard reduction potentials are:
2H+(aq) + 2e- ==> H2(g), E° = 0.00V
Co(2+)(aq) + 2e- ==> Co(s), E° = -0.277 V
So the overall reaction is:
Co(s) + 2H+(aq) ==> Co(2+)(aq) + H2(g), E° = 0.277 V.

Using Nernst equation:
E = E° + (0.0591/n)*log([H+]^2/{[Co(2+)]*P(H2)})

0.06 = 0.277+(0.0591/2)*log([H+]^2)

log([H+]) = (0.06-0.277)/0.0591 = -3.67

pH = -log([H+]) = 3.67