Electrolysis of Aqueous Salt Solutions |
Key Concepts
- Dissloving a salt in water enables it to conduct electricity.
- The species present in the electrolyte are:
water (as the solvent)
cations (from the salt)
anions (from the salt)
- The use of inert electrodes, electrodes made of a material that will not take part in the reactions, means the only species present that can take part in the electrolytic cell reactions are the anions and cations of which the salt is composed and water.
- At the anode, either water is oxidised or the anions of the salt are oxidized.
As a first approximation it is likely that if
(i) water is a stronger reductant than the anions, water will be oxidized at the anode.
(ii) the anion is a stronger reductant than water, anions will be oxidized at the anode.
- At the cathode, either water is reduced or the cations of the salt are reduced.
As a first approximation it is likely that if
(i) water is a stronger oxidant than the cations, water will be reduced at the cathode.
(ii) the cation is a stronger oxidant than water, cations will be reduced at the cathode.
- Electrolysis is a non-spontaneous reaction: Eo for the electrolytic cell is negative*.
- Applied emf must be greater than the emf for the cell, ie greater than -Eo.
- Mass of substance produced electrolytically is proportional to the quantity of electricity flowing.
Examples of the Electrolysis of Aqueous Salt Solutions
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| *This discussion assumes that all species are present in their standard states so that the electrode potentials are standard electrode potentials. |
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