Electrolysis of Copper (II) Sulphate?

NetherCraft 0

When Copper (II) Sulphate is electrolysed with carbon electrodes a colourless gas is given off at the anode and the solution goes from blue to colourless.

Explain these observations.

Also please do explain why when the electrolysis is carried out using copper electrodes the solution remains blue.

What is the name of the clear solution when electrolsis is carried out with carbon electrodes.

3 Answers

  • The above is essentially correct except that there are no O2- ions in water. The source of the oxygen is effectively the OH- ion.

    So at the cathode (where reduction takes place):

    Cu2+(aq) + 2e –> Cu(s)

    At the anode (where oxidation takes place):

    4(OH-) –> O2(g) + 2H2O + 4e

    (…though I suppose you should double the top equation to make the number of electrons lost/gained at each electrode the same)

    With copper electrodes (which is the way copper is purified to make high-quality “electrolytic” copper: a small pure copper cathode is used in conjunction with the piece of impure copper as the anode. The impurities collect below the anode as the delightfully named “anode sludge” and are a significant source of silver and gold!)

    At the Cathode:

    Cu2+(aq) + 2e –> Cu(s)

    At the Anode:

    Cu(s) –> Cu2+(aq) + 2e

  • Electrolysis Of Copper

  • Oxidation occurs at the anode. Therefore the gas must be oxygen gas, as O2- is oxidized to O2. Copper ions are therefore reduced to copper metal at the cathode (where reduction takes place), which would account for the loss of blue color, which of course, is due to hydrated copper (II) ions.

    If the carbon electrodes are replaced by copper metal then just as quickly as copper is being reduced it one electrode it is being oxidized at the other and the number of copper ions in solution stays constant.

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