C2.7 Electrolysis

  • Created by: Fiona S
  • Created on: 10-05-15 11:16


Electrolysis is using electricity to separate molten or aqueous ionic compounds into their elements.

We use an electric current to breakdown a molten ionic substance. We call that substance that it is broken down into is called an electrolyte.

During electrolysis, the positively charged ions move towards the negative electrode. The negatively charged ions move towards the positive electrode.

At the negative electrode the positive metal ions gain electrons. This is called reduction

E.g. Na+ + e- --> Na

At the positive electrode the negative metal ions lose electrons. This is called oxidation

E.g. 2Cl- --> Cl2 + 2e-

The electrodes are often made of unreactive (or inert) substances. This is so the electrodes don't react with the electrolyte or the products made in electrolysis.

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Na+  Cl-  H+  OH-

Negative Electrode

Na+  H+
least reactive is reduced (H+)
2H+(aq) + 2e- --> H2(g)

Hydrogen Gas

Positive Electrode

Cl- OH-
group 7 or OH- oxidised
2Cl-(aq) --> Cl2(g) + 2e-


Na+ OH- --> NaOH

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Copper Sulphate

Cu2+  SO4(2-)  H+  OH-

Negative Electrode
Cu2+  H+
Cu2+ + 2e- --> Cu(s)

Positive Electrode
SO4(2-)  OH-
4OH- --> O2 + 2H2O +4e-

Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite. Aluminium forms at the negative electrode and oxygen at the positive electrode. The positive electrode is made of carbon, which reacts with the oxygen to produce carbon dioxide. Cryolite is used in this process to reduce some of the energy costs involved in extracting aluminium.

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Coat a nickel key in copper. Negative key to coat with positive Cu ions.

Cu(s) --> Cu2+(aq) + 2e-  oxidation

Cu2+(aq) + 2e- -> Cu(s) reduction

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