C6 Electrolysis

Question 1

What is electrolysis

Answer 1

The decomposition of an ionic substance by passing electric current through it. The ionic substance is called the electrolyte

Question 2

What is the electrolyte

Answer 2

The ionic substance that has a current passed through it during electrolysis

Question 3

What state must the electrolyte be in for the current to be passed through it

Answer 3

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

Question 4

What is the negative electrode called and what are the ions called that are drawn to it

Answer 4

Called the cathode and it attracts cations ( pussitive )

Question 5

What is the postive electrode called and what are the ions called that are drawn to it

Answer 5

Called the anode and anions are attracted ( negative )

Question 6

What happens when a current is put through the ionic compound

Answer 6

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

Question 7

What happens at the cathode

Answer 7

The cathode ‘ gives out electrons ‘ and cations come here to be reduced and have a neutral charge

Question 8

What happens at the anode

Answer 8

The anode ‘ has a lack of electrons ‘ and anions come there to lose electrons and get oxidised to have a neutral charge

Question 9

Give half equations of what will happen at the electrodes for the electrolysis of lead bromide PbBr2

Answer 9

Anode: 2Br^- - 2e^- = Br2

Cathode Pb^2+ + 2e^- = Pb

Question 10

Why is alumium oxide mixed with cyolite before it is electrolised

Answer 10

Cryolite acts as a catalyst to reduce the melting point of aluminium oxide so less energy is needed to melt ( saves money )

Question 11

What is bauxite

Answer 11

It is the ore that alumium oxide is from

Question 12

In the electrolysis of alumium what is deposited at each of the electrodes

Answer 12

Cathode: alumium
Anode: oxygen

Question 13

What is different about the set up of the process to electrolyse aluminium

Answer 13

There are two positive electrodes and the lining of the cell is the negative electrode

Question 14

Why do the carbon anodes need to be replaced often during the electrolysis of aluminium

Answer 14

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

Question 15

What are the 3 useful products found after the electrolysis of brine and what is brine

Answer 15

Brine is concentrated sodium chloride solution

Products include: hydrogen gas, chlorine gas, sodium hydroxide solution

Question 16

What the test for chlorine at the electrodes

Answer 16

If it bleaches damp litmus paper

Question 17

What can water ionise into

Answer 17

It can ionise into H+ ions and OH- ions in a reversible reaction

Question 18

What are the rules for the products at the negative electrode when electrolysing auqeous solutions

Answer 18

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

Question 19

What are the rules for the products at the positive electrode when electrolysing auqeous solutions

Answer 19

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 ).