abcd
Electrolysis


USES AND APPLICATIONS OF ELECTROLYSIS

1.Extraction of reactive metals (Potassium to Aluminium) high in Electrochemical series


Extraction of Aluminium from Bauxite


Electrolysis is used to extract Aluminium from the aluminium ore, Bauxite . Firstly, Bauxite has to be purified to obtain pure Aluminium Oxide(Al2O3),
then cryolite (Na3AlF6) is added to it to lower the melting point of Aluminium oxide from 2050.C to 900.C. After melting it, it is put into a carbon-lined steel tank which acts as a cathode. On the surface of the molten Al2O3 and cryolite, graphite electrodes are used as anodes.

external image Coord11.4_extraction%20of%20aluminium_v2.gif

Al3+ will be attracted to the carbon-lined steel tank and form as liquid aluminium. Every mole of Al3+ receives 3 moles of electrons to form 1 mole of Aluminium.

Cathode equation : Al3+ (l) + 3e- --> Al(l)

The molten aluminium deposited at the bottom of the tank, is then periodically removed and cast into ingots.

O2- ions are attracted to the graphite electrodes. 2 moles of O2- loses 4 moles of electrons to form 1 more of oxygen gas.

Anode equation: 2O2- (l) --> O2 (g) + 4e-

Overall: 2Al2O3 --> 4Al (l) + 3O2(g)

The graphite also needs to be replaced at certain intervals due to the reaction with oxygen liberated at the anode at high temperatures.

C(s) + O2 --> CO2 (g)



2. Electroplating


Electroplating a metal with another metal to prevent corrosion has been made possible by the use of electrolysis.

Eg. Silver plating.

To prevent the underlying metal from corrosion and to improve the appearance of the metal, a metal object such as a spoon or knife can be electroplated with silver with the use of electrolysis
external image 250px-Electroplating-of-spoon.PNG
Cathode will be the object that is to be plated whereas the Anode is the metal which is to be plated with. The Electrolyte should also be a solution of a compound of the anode.

In this case we have Silver Nitrate as our electrolyte , the spoon as our cathode, and a silver metal as our anode.

The ions present in this electrolyte are : Ag+ , NO3-, H+, OH-

Cathode equation : Ag+(aq) + e- --> Ag (s)
Anode equation : Ag(s) --> Ag+(aq) + e-

Silver ions are more preferentially discharged because of their lower position in the electrochemical series as compared to hydrogen ions.

Eventually, the spoon will be electroplated and covered with a layer of silver.



3. Purification of metals : Electro-refining



Metals such as copper, which are going to be used for making copper wires which need the copper to be as pure as possible, can be purified through the use of electrolysis. Impure copper drawn into wires will cause the wires to have a higher resistance and lower electric conductivity.

The impure copper which contains various impurities will be used as the anode.
The cathode will be a thin sheet of pure copper and the electrolyte, aqueous copper(II) sulfate.


Cathode Equation: Cu2+(aq) + 2e- --> Cu(s)
Anode Equation: Cu(s) --> Cu2+ (aq) + 2e-

The less reactive impurities from the impure copper anode will sink to the bottom and is called Anode sludge. while the more reactive metals such as Zinc lose their electrons and remain in the electrolyte.