Electrochemistry

Question

Calculate the emf of the following voltaic cells;

(a) Pt/Fe2+(0.1M),Fe3+(0.2M)//Ag+(1M)/Ag

(b)Zn/Zn3+(10^-3M)//Ag+(10^-3M)/Ag

(c)Al/Al3+(0.1M)//Sn2+(0.37M)/Sn

Answer 1

(a) Pt/Fe²⁺(0.1M),Fe³⁺(0.2M)//Ag+(1M)/Ag

From a table of standard reduction potentials, I find the following:

Fe3+ + e- ==> Fe2+ Eº = 0.77 V (anode)

Ag+ + e- ==> Ag Eº = 0.80 (cathode)

Overall:

Ag⁺ + Fe²⁺ ==> Ag + Fe³⁺ Eº = 0.80 - 0.77 = 0.03 V

Use Nernst equation to solve for Ecell under these non-standard conditions:

Ecell = Eº -RT / nF ln Q and assuming the temperature is 298K, this reduces to ...

Ecell = Eº - 0.0592 / n log Q

n = 1

Q = [Fe³⁺] / [Ag⁺] = 0.2 / 1 = 0.2

Ecell = 0.03 - 0.0592(-0.699)

Ecell = 0.03 + 0.04

Ecell = 0.07 V

Do the others in the same fashion.

(b) Ag (cathode), Zn (anode)

(c) Sn (cathode), Al (anode)

If you have difficulties doing (b) and (c), repost with those as separate questions.