C4b-Chemical Changes: Electrolysis

Question 1

What is electrolysis?

Answer 1

The breakdown of ionic compounds using electricity

Question 2

What are electrolytes?

Answer 2

Ionic compounds (salts) that are either in the molten state or dissolved in water

Question 2

How is electrolysis set up?

Answer 2

1) First you add the electrolyte solution to a beaker
2) Next you put a lid on top of the beaker
3) Next you place the electrodes in
4) Next you connect a power pack
5) Next you observe the negative electrode
6) Next you observe the positive electrode
7) Finally you place litmus paper next to the positive electrode and observe

Question 3

What is the negative electrode called?

Answer 3

The cathode

Question 4

What is the positive electrode called?

Answer 4

The anode

Question 5

Finish the sentence:

During electrolysis, positively charged ions (…………..) move to the (…………..) and negatively charged ions (…………..) move to the (…………..)

Answer 5

• Cations
• Cathode
• Anions
• Anode

Question 6

What type of ions are metals?

Answer 6

Positive

Question 7

What type of ions are non metals?

Answer 7

Negative

Question 8

What happens when the ions reach the electrodes?

Answer 8

They lose their charge and become elements

Question 9

What would the electrolysis of Lead Bromide produce and where?

Answer 9

• Lead-Negative electrode-cathode
• Bromine-Positive electrode-anode

Question 10

What is it called when ions lose and gain electrons?

Answer 10

• Lose electrons-oxidation
• Gain electrons-reduction

Question 11

What would the half equation be at the cathode when electrolysing lead bromide?

Answer 11

Pb²⁺ + 2e⁻ –> Pb

Question 12

What would the half equation be at the anode when electrolysing lead bromide?

Answer 12

2Br⁻ –> Br₂ +2e⁻

Question 13

What ions does water contain?

Answer 13

Hydrogen and Hydroxide ions-H⁺ and OH⁻

Question 14

Where in electrolysis are the H⁺ ions attracted to?

Answer 14

The cathode

Question 15

Where in electrolysis are the OH⁻ ions attracted to?

Answer 15

The anode

Question 16

What determines what is formed at each electrode?

Answer 16

The less reactive element will usually be formed

Question 17

What is the half equation of H⁺ ions at the cathode?

Answer 17

2H⁺ + 2e⁻ –> H₂

Question 18

What is the half equation of OH⁻ ions at the anode?

Answer 18

4OH⁻ –> 2H₂O + O₂ + 4e⁻

Question 19

When would Hydroxide ions not be formed at the anode?

Answer 19

If there is a reasonably high concentration of a halogen ion

Question 20

What is aluminium ore called?

Answer 20

Bauxite

Question 21

What must happen to aluminium oxide after it has been purified?

Answer 21

It needs to be melted-enabling the ions to move to the electrodes

Question 22

What is cryolyte?

Answer 22

A type of aluminium ore as well as a catalyst-it reduces the temperature needed for the aluminium to become molten from 2050°C to 850°C

Question 23

What is the reaction for electrolyis for aluminium?

Answer 23

2Al₂O₃ –> 4Al + 3O₂

Question 24

What are the half equations of aluminium oxide for electrolysis?

Answer 24

Cathode-AL³⁺ +3e⁻ –> Al
Anode-2O²⁻ –> O² +4e⁻

Question 25

Why does the carbon anodes need to be replaced regularly?

Answer 25

They gradually burn away as the oxygen reacts with the hot carbon anodes, forming carbon dioxide

Question 26

How is the electrolysis of brine carried out?

Answer 26

sodium chloride solution –> Hydrogen gas, Chlorine gas, Sodium hydroxide solution

Question 27

What is the half equation at the anode for the electrolysis of brine?

Answer 27

2Cl⁻ –> Cl₂ + 2e⁻