Electrolysis

Question 1

In what state does an ionic compound need to be for electrolysis to take place?

Answer 1

The ionic compound needs to be molten or dissolved in water.

Question 2

Why does the ionic compound need to be molten or dissolved in water?

Answer 2

The electrostatic forces between the ions are broken.
So, the ions are free to move and conduct electricity.

Question 3

What are the liquids or solutions in electrolysis called?

Answer 3

The electrolyte.

Question 4

What is the negative electrode called?

Answer 4

The cathode.

Question 5

What is the positive electrode called?

Answer 5

The anode.

Question 6

What happens at the cathode?

Answer 6

Reduction - the positive metal ion gains electrons.

Question 7

What happens at the anode.

Answer 7

Oxidation- The negative non-metal ion loses electrons.

Question 8

What metals can be separated from their oxides through reduction with carbon?

Answer 8

Metals less reactive than carbon.

Question 9

What metals can be separated using electrolysis?

Answer 9

Metals more reactive than carbon.
Or, that react with carbon itself.

Question 10

What is the name of the ore containing aluminium oxide?

Answer 10

Bauxite.

Question 11

What is the name of the compound that is mixed with aluminium oxide?

Answer 11

Cryolite.

Question 12

Why is cryolite mixed with the aluminium oxide?

Answer 12

Cryolite lowers the melting point.
This reduces the amount of energy needed and saves money.

Question 13

What are the electrodes made out of, and why?

Answer 13

The electrodes are made of graphite ( carbon ).
Graphite is a very good conductor of electricity and has a high melting point.
So it can be used in high temperatures.

Question 14

During the electrolysis of aluminium oxide, what is the half equation at the cathode?

Answer 14

Al(3+) + 3 e- -> Al

Question 15

During the electrolysis of aluminium oxide, what is the half equation at the anode?

Answer 15

2 O2(2-) -> O2 + 4 e(-)

Question 16

Why must the anode be replaced regularly?

Answer 16

The oxygen molecules react with the carbon atoms in the graphite.
This produces carbon dioxide.
O2 + C -> CO2

Question 17

Why is electrolysis expensive?

Answer 17

Melting the compounds requires a lot of energy.
A lot of energy is required to produce an electric current.

Question 18

What is the half equation of the copper ion at the cathode?

Answer 18

Cu(2+) + 2e(-) -> Cu
This is a reduction reaction.

Question 19

What is the half equation of the hydroxide ion at the anode?

Answer 19

4 OH(-) -> O2 + 2 H2O + 4e(-)
This is an oxidation reaction.

Question 20

What is the rule for determining which ion will be oxidised at the anode?

Answer 20

It will always be the OH- ion, unless there is a halide present.

Question 21

What is the rule for determining which ion will be reduced at the cathode?

Answer 21

If the ion is more reactive than hydrogen, then hydrogen will be reduced. If the ion is less reactive than hydrogen, such as copper, then it will be reduced.