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C6: ELECTROLYSIS (Changes at the Electrodes (When electrolysis happens in…
C6: ELECTROLYSIS
Introduction to Electrolysis
Electrolysis breaks down a substance using electricity
Ionic compounds can only be electrolysed when they are molten or dissolved in water
This is because their ions become delocalised in those states so they can carry their charge to the electrodes
In electrolysis, positive ions move to the cathode (negative electrode) while negative ions move to the anode (positive electrode)
Changes at the Electrodes
In electrolysis, the ions move towards the oppositely charged electrodes
At the negative electrode (cathode), positive ions lose their electrons,so are reduced
At the positive electrode (anode), negative ions lose their extra electrons, so are oxidised
When electrolysis happens in the aqueous solution, the less reactive element (either hydrogen or the metal) is usually produced at the cathode
In this situation, you either get oxygen gas given off from hydroxide ions from water, or a halogen produced if the solution is of a halide at the anode
The Extraction of Aluminium
Aluminum oxide, from the ore bauxite, is electrolysed in the extraction of aluminum metal
The aluminum oxide is mixed with molten cryolite to lower its melting point, reducing the energy needed to extract the aluminum
Aluminum forms at the cathode and oxygen forms at the anode
The carbon anodes are replaced regularly as they gradually burn away as the oxygen reacts with the hot carbon anodes, forming carbon dioxide gas
Electrolysis of Aqueous Solutions
When you electrolyse sodium chloride solution,you get 3 products: chlorine and hydrogen gas at the electrodes and sodium hydroxide left in the solution
Hydrogen is produced at the cathode as H+ (aq) ions are discharged from solution in preference to Na+ (aq) ions
Chlorine is produced at the anode as Cl + (aq) ions are discharged from solution in preference to OH- (aq) solutions