Reference
Half-Cells
A reference half-cell is used to
determine the relative reduction
potential of other half-cells
A reference half-cell has Eo = 0.00 V
The standard hydrogen half-cell is a
commonly used reference half-cell.
2 H+(aq) + 2 e−
H2(g)
Eo = 0.00 V
If a half-cell contains an oxidizing
agent stronger than H+(aq), it will
have a Eo > 0.00 V
If a half-cell contains an oxidizing
agent weaker than H+(aq), it will
have a Eo < 0.00 V
If a different reference half-cell had
been selected, the individual Eo
would all be different but the relative
difference between them would
remain constant.
Reduction
Half-Reactions
Cu2+(aq) + 2e-
Cu(s)
2 H+(aq) + 2e-
H2(g)
Zn2+(aq) + 2e-
Zn(s)
Reference Half Cell
Hydrogen
Copper
Zinc
How would the Eo values in the table
be affected if the reference half-cell
was switched to become:
a) the nickel half-cell?
b) the iron(III) half-cell?
Create a table of reduction half-reactions, in
which the indium half-cell is the reference.
Cathode
Half-Cell
Anode
Half-Cell
Cell
Potential (V)
Ni(s) | Ni2+(aq)
Zr(s) | Zr4+(aq)
0.384
In(s) | In3+(aq)
Ni(s) | Ni2+ (aq)
0.091
Ni(s) | Ni2+ (aq)
Nb(s) | Nb3+(aq)
0.300
Pd(s) | Pd2+(aq)
Nb(s) | Nb3+ (aq)
0.505
W(s) | W6+(aq)
Ni(s) | Ni2+ (aq)
0.264