Pt (s) | Cu2+ (aq), H+ (aq)
Note that the spectator ions, oxide and chloride, have been left out of the
notation and that
the anode is written to the far left.
The salt bridge or porous disk is shown in the notation as a double line (
|| ). Therefore, a
cell that undergoes the oxidation of magnesium by Al3+ could
have the
following cell notation if the anode is magnesium and the cathode is aluminum:
Mg (s) | Mg2+ (aq) || Al3+ (aq) | Al (s)
Standard Reduction Potentials
One can measure the cell potential, Ecell, in volts, of any
galvanic cell
with the aid of a potentiometer. However, it is impossible to directly
measure the
potential of each individual half-cell. Chemists, however, have devised a
method to
measure the ability of a chemical species to reduce another by compiling
tables of
standard reduction potentials, Eo (the o
indicates that the
reaction is at standard state). Arbitrarily assigning a value of exactly
zero to the potential of
the standard hydrogen electrode allows us to measure the Eo
of any half-
reaction. That measurement is made by constructing a galvanic cell between
the SHE and
the unknown half-cell at standard state conditions. For example, when the
following cell is
constructed (see Heading for a review of the line notation), an
Eocell of 0.34 V is observed (note the setup of the
SHE as the
anode because Cu2+ has a greater reduction potential than
H+):
Pt (s) | H2 (g) | H+ (aq) || Cu2+ (aq) |
Cu (s)
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