If this solution is under standard conditions, then it will be possible to explain the products of this electrolysis (, , ) with reference to the standard reduction potentials.
Explanation:
Assume that this solution is under standard conditions, including:
A concentration of
, A pressure of
, andA temperature of
.
This solution (in water) would include the following species:
ions,
ions, and
molecules.
(The carbon electrode is relatively inert and typically won't take part in the chemical reaction.)
Consider the electrolysis of this solution as the sum of the reduction half-reaction and the oxidation half-reaction. Look up the standard reduction potential for half-reactions involving these species:
. Standard reduction potential: .
. Standard reduction potential: .
. Standard reduction potential: .
. Standard reduction potential: .
. Standard reduction potential: .
(Species found in this solution are shown in bold typeface.)
Reduction Half-reaction
Note, that in the first four reactions, species from this solution are all on the same side as . In other words, in those four reactions, these species would gain electrons and are reduced. These reactions are thus plausible reduction half-reactions. The standard electrode potential of each half reaction will be the same as the standard reduction potential. Because reduction takes place at the cathode, these potentials are denoted as .
. .
. .
. .
. .
The only reduction half-reaction that will take place will be the one with the most positive (least negative) electrode potential. Among these four plausible half-reaction, that reaction would be the reduction of to (elemental copper,) , with an electrode potential of . That explains why metallic copper will deposit on the cathode.
Oxidation Half-reaction
On the other hand, the reaction seems to be the only one that involves species from this solution on the opposite side of . The actual reaction would take place in the other direction:
.
The corresponding electrode potential will be the opposite of the standard reduction potential. Because this reaction corresponds to oxidation, it will happen at the anode.
.
That explains why will be produced at the anode.
Overall Reaction
Multiply coefficients in the reduction half-reaction by two and combine the two half-reactions. Make sure that electrons are eliminated from both sides of this equation:
.
would be the spectator ion. Add that to the reaction to obtain the chemical equation of this electrolysis:
.