Question

A Ag/Fe voltaic cell has an E⁰ of ___(a)____ V. If you change the concentration of the solution in each cell to 0.01 M, the EMF is ___(b)____V. This change is because the standard potential, E⁰ is defined at ___(c)____ K,  ___(d)____atm, and ___(e)____ M, so differing from those standard conditions will change the observed EMF of the cell.

Answer 1

Oxidation half reaction :

Fe (s) ------------> Fe^2+ (aq) + 2 e^- E0Fe2+/Fe = - 0.447 V

Reduction half reaction:

Ag^+ (aq) + e^- --------> Ag (s) ; E0Ag+/Ag = + 0.800 V

Overall cell reaction:

Fe (s) + 2 Ag^+ (aq) ----------> Fe^2+ (aq) + 2 Ag (s)

E0cell = E0Ag+/Ag - E0Fe2+/Fe = 0.800 - ( - 0.447 ) = + 1.247 V

[Ag^+] = 0.01 M

[Fe^2+] = 0.01 M

n = 2 electrons

Applying Nernst equation for cell reaction,

Ecell = E0cell - ( 0.0592 / n ) x Log[Fe^2+] / [Ag^+]^2

Ecell = + 1.247 - ( 0.0592 / 2 ) x Log( 0.01 / 0.01^2 )

Ecell = 1.188 V

Standard conditions,

T = 298 K

P = 1 atm

[Ag^+] = 1.00 M

Therefore,

a. 1.247 V

b. 1.188 V

c. 298 K

d. 1.00 atm

e. 1.00 M