Electrolysis

Question 1

Electrolysis

Answer 1

Splitting of ions from their ionic compounds into their pure elements as atoms with no charge
Using electricity

Question 2

What must we use in electrolysis?

Answer 2

A liquid ionic compound as molten or dissolved in water
Because only then can they conduct electricity and transfer electrons

Question 3

Electrolytes

Answer 3

Liquid ionic compound which can conduct electricity

Question 4

Cathode

Answer 4

Negative electrode covered in electrons from the power pack

Question 5

Anode

Answer 5

Positive electrode with no electrons from the power pack

Question 6

What happens in electrolysis of a molten solution?

Answer 6

Positive metal ions are attracted to the cathode and gain electrons to form metal atoms (reduced)
Negative non metal ions are attracted to the anode and lose electrons to form non metal atoms (oxidised)

Question 7

Why do we use electrolysis for extraction?

Answer 7

If it’s more reactive than carbon so cannot be displaced from its oxide compound
Including aluminium

Question 8

Where is aluminium extracted from?

Answer 8

Aluminium oxide using electrolysis

Question 9

Aluminium oxide

Answer 9

Aluminium ions Al³⁺
Oxide ions O²⁻

Question 10

How do we turn aluminium oxide into a liquid?

Answer 10

Mix with cryolite to lower its melting point so it can become liquid easier

Question 11

Why do we use cryolite with aluminium oxide?

Answer 11

Because by lowering its melting point we use less energy to melt it therefore save money

Question 12

What are electrodes made of in molten electrolysis and why?

Answer 12

Graphite
Because it’s made of a giant carbon structure
Can conduct electricity as it has delocalised electrons
High melting point

Question 13

What happens at the cathode in electrolysis of aluminium oxide?

Answer 13

Al³⁺ + 3e- ——> Al
Reduced = gains electrons

Question 14

What happens at the Anode of electrolysis in aluminium oxide?

Answer 14

2O²⁻ ——> O₂ + 4e-
Oxidation

Question 15

Why must the anode be replaced regularly

Answer 15

Because oxygen molecules produced at anode react with carbon on surface of electrode to form CO2 = slowly wearing away the electrode

Question 16

Why is electrolysis expensive?

Answer 16

High energy costs:
Lots required to melt the compound
Lots required to produce the electric current

Question 17

What other ions are present in the electrolysis of aqueos solutions?

Answer 17

H+ ions
OH- ions
These are what water molecules ionise into

Question 18

In an electrolysis of aqueous solution what forms at the cathode?

Answer 18

If the metal is less reactive than hydrogen = metal discharged
If metal is more reactive than hydrogen = hydrogen discharged

Question 19

In electrolysis of aqueous solution what forms at the anode?

Answer 19

If the ionic compound contains a halogen the halide ion is discharged
If not oxygen is discharged
(Water is too but water already in the solution)

Question 20

What material do we use for the electrodes in aqueous electrolysis?

Answer 20

Platinum as its inert and unreactive
So it doesn’t react with stuff easily

Question 21

Electrolysis of aqueous solution anode half equation if a halogen ion isn’t present

Answer 21

4OH- ——> O₂ + 2H₂O + 4e-
Oxidation

Question 22

If a halogen isn’t present in electrolysis of aqueous solution why don’t we say water is discharged?

Answer 22

Because water is already in the solution
We just point out oxygen

Question 23

Electrolysis of aqueous solution if the metal is more reactive than hydrogen half equation

Answer 23

2H+ + 2e- ——> H₂
Reduction