Electrolysis

Question 1

What is electrolysis?

Answer 1

The separation of a compound using electricity

Question 2

Define oxidation and reduction.

Answer 2

Oxidation- Loss of electrons
Reduction- Gain of electrons

Question 3

What are the electrodes?

Answer 3

Anode- Positively charged
Cathode- Negatively charged
They are the solid conductors in electrolysis.

Question 4

What needs to be done to Lead Bromide before electrolysis is conducted on it?

Answer 4

It needs to be melted (its insoluble) so the ions are free to move

Question 5

Which electrode would metals be attracted to?

Answer 5

Cathode (Negative electrode)

Question 6

Describe the products of the electrolysis of Lead Bromide.

Answer 6

Anode- Bromine atoms discharge (lose electron) pair up and create a gas
Cathode- Lead ions discharge (gain electrons) and lead falls to bottom.

Question 7

Give the half equations for the electrolysis of Lead Bromide

Answer 7

Pb²* + 2e —> Pb (reduced)
2Br- —> Br²+ 2e (oxidized)

Question 8

How do we extract metals from metal oxides?

Answer 8

Electrolysis: Reduce the metal (gain electrons)

Question 9

Metal oxide + Carbon —> ?

Answer 9

Pure metal + Carbon dioxide (reduction)

Question 10

For metals less reactive than carbon, how does electrolysis take place?

Answer 10

Carbon = more reactive so displaces the metal to form Pure metal + Carbon dioxide

Question 11

State the order of the reactivity series?

Answer 11

Potassium
Sodium
Calcium
Magnesium
Aluminum
Carbon
Zinc
Iron
Tin
Lead
Hydrogen
Copper
Silver
Gold

Question 12

How are metal oxides extracted?

Answer 12

Need to be melted using cryolite (lowers MP) e.g Aluminum Oxide to allow ions to move freely. Extracted using Carbon because metal less reactive.

Question 13

Describe the products of the electrolysis of Aluminum oxide.

Answer 13

Anode- Oxygen (2O²-) loses 4 electrons, lost as gas
Cathode- Aluminium (2Al²*) gains 4 electrons and is collected as pure molten metal.

Question 14

Give the half equations of the electrolysis of Aluminum Oxide.

Answer 14

Al^3* + 3e ==> Al (reduction)
2O^2- ==> O² + 4e (oxidation)

Question 15

When is electrolysis done with aqueous solutions?

Answer 15

When the compound we are separating is soluble e.g Copper sulfate and Sodium Chloride

Question 16

Describe the products of electrolysis of Copper sulphate.

Answer 16

Cathode- Copper is discharged as its less reactive than hydrogen.
Anode- Hydroxide is discharged, oxygen and water are the products.

Question 17

Describe the products of the electrolysis of Sodium Chloride.

Answer 17

Anode- Chloride=> halide is discharged and chlorine gas is released.
Cathode- Hydrogen=> released since less reactive than Sodium.

Question 18

What are ‘electrolytes’?

Answer 18

Liquid containing ionic compounds

Question 19

What must be done to ionic compounds before electrolysis?

Answer 19

Melted/aqueous so ions are free to move e.g Lead Bromide melted as insoluble

Question 20

What is bauxite?

Answer 20

Ore which contains metal oxides.

Question 21

What does H²O disassociate into?

Answer 21

OH- ions and H+ ions

Question 22

In aqueous solutions, what will be produced at the anode?

Answer 22

If halide present, then halogen gas produced
If no halide, then OH- ions discharge, producing oxygen gas and water.

Question 23

In aqueous solutions, what will be produced at the cathode?

Answer 23

If metal more reactive, hydrogen gas released.
If metal less reactive, metal produced.

Question 24

Give the method for electrolysis in aqueous solutions.

Answer 24

-Set up apparatus + add electrolyte solution
-Add 2 graphite rods+ connect to 12V battery
-Check if metal’s been deposited
-Test for gas