C14: Electrolysis
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Electrolyte
A liquid containing free moving ions that is broken down by electricity during the process of electrolysis.
Electrolysis
The breakdown of a substance containing ions by electricity.
The positive electrode
Anode
The negative electrode
Cathode
What sort of compounds are usually electrolysed?
Ionic compounds. Covalent compounds can only do it if they react in the water to form ions.
Equation at the anode
n- -> n + e-
Equation at the cathode
n+ + e- -> n
Will the more or less reactive element be formed at the cathode?
Less reactive
What is the ‘order of discharge’ at the anode?
Halide ion > Hydroxide > All other negatively charged ions.
What gas is often given off at the anode?
Oxygen
Name of aluminium ore
Bauxite
What substance is mixed with aluminium during electrolysis and why?
Molten cryolite It reduces the melting point
What happens at the cathode during the electrolysis of aluminium?
Al3+ ions are reduced to form Al atoms. This forms aluminium at the bottom of the tank and is then siphoned off.
What happens at the anodes during the electrolysis of aluminium?
O2- ions turn into oxygen atoms. These bond in pairs to form oxygen gas. The oxygen reacts with the carbon anodes, forming Carbon Dioxide. Due to the this the anodes must be replaced regularly.
What three products are formed in the electrolysis of brine and where?
> Chlorine gas- anode Hydrogen gas- cathode Sodium Hydroxide solution
How is brine electrolysed in industry?
Using a diaphragm cell, where the two electrodes are separated by a porous membrane.
Why is sodium hydroxide produced in the electrolysis of brine?
During the electrolysis of brine, Na+, Cl-, H+ and OH- are present. Chlorine and Hydrogen gas are emitted during the electrolysis process, which leaves only sodium and hydroxide.
2 uses of chlorine.
> When reacted with sodium hydroxide it can be used as bleach. Plastics such as PVC
Use for hydrogen
> Makes margarine when combined with veritable oils.
Use for sodium hydroxide
> Important alkali in industry Bleach Soap Paper
Electroplating
The process of depositing a thin layer of metal onto an object during electrolysis.
Why do we electroplate objects?
> To protect the metal beneath from corrosion. To make the object look more attractive. To increase the hardness or resistance to scratching. To save money.
In electroplating, what substances make up the anode and cathode?
> Cathode- Object to be electroplated > Anode - Metal to plate the Object.