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Electrolysis with different substances

Example 2: Copper (II) chloride solution in water (where the electrodes are inert)

Copper chloride and water is the solution for electrolysis


If you are asked about the electrolysis of this solution in an exam you would not be expected to know the details of the shell arrangement for the element copper (because we only need the first 20 elements).

But the name 'copper (II)' is a massive clue and all you need to assume is that Cu(II) means Cu2+.

So starting with all the basic elements we get:

Copper, Chlorine, Hydrogen and Oxygen are the elements used in this experiment, the examination will not expect you to know the molecular structure of copper

 Copper chloride and water molecule structure

But dissolved in solution with each other, chemists would say we have:

Chemists would see copper chloride and water a different way in electrolysis

At the cathode

Rule one says copper will form at the cathode because copper is less reactive than hydrogen
 Rule 1 says copper forms at the cathode not hydrogen (as copper is less reactive than hydrogen).

So at the cathode electrons are given out (to the copper ions) and:

 Electrons of the chloride is stripped and given to the copper this time it coats the cathode

This time, the pure copper begins to coat the electrode.

The half equation is:

                                                    Cu2+ (aq)          +          ?          →        Cu (s)

So the electron balance is      Cu2+                         +          2e-         →        Cu (s)

Or                                                Cu2+                                              →        Cu      –      2e-

 Copper plates the cathode

At the anode

Electrons are stripped from the chlorine


Rule 2 says halogen (Cl) forms at the anode and not hydroxide (OH-). So at the anode, electrons are taken away from the chlorine.

The stripped chlorine becomes reactive


But as chlorine always goes around in pairs (as in a diatomic gas), two chlorine atoms now combine to form chlorine gas.

Chlorine needs to be paired to give a gas


The half equation is:

                                                   Cl- (aq)             +          ?          →        Cl2 (g)

To balance this                        2Cl- (aq)           +          ?          →        Cl2 (g) 

And the electron balance       2Cl- (aq)           -          2e-       →        Cl2 (g)

Or                                                2Cl-                                                         →        Cl2 + 2e-


The hydrogen and hydroxide ions left in the solution combine to form water.

The remaining solution is pure water

They combine to give H2O.

Water remains

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