Calculate emf of the following cell at 25∘C:
Sn|Sn2+(0.001M)||H+(0.01M)|H2(g)(1bar)|Pt(s)E∘Sn2+|Sn=−0.14VE∘H+H2=0.00V
According to Nernst equation,
Ecell=E∘cell−0.0592nlog[P][R]E∘cell=E∘Oxi(anode)−E∘Oxi(cathode)
−E∘Sn|Sn2+−E∘H2|2H2+
= -0.14 - 0.0
= -0.14
Reactions :
Anode (oxidation) : Sn(s)→Sn2+(aq)+2e−
Cathode (reduction) : 2H+(aq)+2e−→H2(g)
Net reaction : Sn(s)+2H+(aq)→Sn2+(aq)+H2(g)
∴ n = 2 (number of electrons transferred)
[P]=[Sn+2] = 0.001 M
[R]=[H+] = 0.01 M
So, putting the above values in the formula,
Ecell=−0.14−0.05922log[0.001][0.01]2
Ecell=−0.1696V