C6 Electrolysis
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What is electrolysis
The decomposition of an ionic substance by passing electric current through it. The ionic substance is called the electrolyte
What is the electrolyte
The ionic substance that has a current passed through it during electrolysis
What state must the electrolyte be in for the current to be passed through it
The electrolyte must be in a molten or aqueous form because ionic substances only conduct electricity when in molten or aqueous state because the ions are free to move around and conduct
What is the negative electrode called and what are the ions called that are drawn to it
Called the cathode and it attracts cations ( pussitive )
What is the postive electrode called and what are the ions called that are drawn to it
Called the anode and anions are attracted ( negative )
What happens when a current is put through the ionic compound
When a current is put through a molten or aqueous ionic compound, the ions move towards the electrodes and discharge Anions move to the anode and lose electrons. This is oxidation Cations move to the cathode and gain electrons. This is reduction
What happens at the cathode
The cathode ‘ gives out electrons ‘ and cations come here to be reduced and have a neutral charge
What happens at the anode
The anode ‘ has a lack of electrons ‘ and anions come there to lose electrons and get oxidised to have a neutral charge
Give half equations of what will happen at the electrodes for the electrolysis of lead bromide PbBr2
Anode: 2Br^- - 2e^- = Br2 Cathode Pb^2+ + 2e^- = Pb
Why is alumium oxide mixed with cyolite before it is electrolised
Cryolite acts as a catalyst to reduce the melting point of aluminium oxide so less energy is needed to melt ( saves money )
What is bauxite
It is the ore that alumium oxide is from
In the electrolysis of alumium what is deposited at each of the electrodes
Cathode: alumium Anode: oxygen
What is different about the set up of the process to electrolyse aluminium
There are two positive electrodes and the lining of the cell is the negative electrode
Why do the carbon anodes need to be replaced often during the electrolysis of aluminium
Carbon dioxide is released due to the carbon anodes reacting with oxygen. This means that they will gradually burn away and shrink which will stop the process
What are the 3 useful products found after the electrolysis of brine and what is brine
Brine is concentrated sodium chloride solution Products include: hydrogen gas, chlorine gas, sodium hydroxide solution
What the test for chlorine at the electrodes
If it bleaches damp litmus paper
What can water ionise into
It can ionise into H+ ions and OH- ions in a reversible reaction
What are the rules for the products at the negative electrode when electrolysing auqeous solutions
If the metal is more reactive than hydrogen ( on the reactivity series ), hydrogen gas will be discharged at the cathode because it is easier for hydrogen to gain an electron ( the reactive metal has more electronic shielding ). If the metal is less reactive than hydrogen ( on the reactivity series ) then the metal will get deposited at the cathode
What are the rules for the products at the positive electrode when electrolysing auqeous solutions
If there is a halide ( ion from halogens ) then that will get discharged because halogens are the most reactive and best at gaining electrons, otherwise oxygen will get discharged (the halogen are the most reactive non metals ).