Electrolysis

Question 1

What is electrolysis?

Answer 1

breakdown of an ionic compound (when molten or in aqueous solution) by passage of electricity

Question 2

What is an electrolyte?

Answer 2

Aqueous solution of ionic substance or molten ionic salt

Question 3

Why does an electrolyte conduct electricity?

Answer 3

Conducts electricity due to the presence of mobile ions

Question 4

What are electrodes?

Answer 4

Rods which help current enter the electrolyte

Question 5

What are the products formed from the electrolysis of Molten lead(II) bromide?

Answer 5

At cathode: lead

At anode: bromine

Question 6

What are the products formed from the electrolysis of Concentrated hydrochloric acid?

Answer 6

At cathode: Hydrogen

At anode: chlorine

Question 7

What are the products formed from the electrolysis of Concentrated aqueous sodium chloride?

Answer 7

At cathode: hydrogen

At anode: chlorine

Question 8

What is formed at the cathode?

Answer 8

Metal/Hydrogen

Question 9

What is formed at the anode?

Answer 9

Non-metal/Oxygen (OH-)

Question 10

What is electroplating?

Answer 10

Coating one metallic object with another metal using electrolysis

Question 11

What are the materials needed for electroplating? (3)

Answer 11

Anode made of metal you want to electroplate object with
Ions of same metal as anode in solution
Object to be plated at cathode

Question 12

What are the uses of electroplating? (3)

Answer 12

Improving metal appearance
Galvanise
Prevent corrosion

Question 13

Why is aluminum used for electricity cables? (4)

Answer 13

Light
Non-corrosive
Good conductor
Cheaper than copper

Question 14

Why is copper used in electrical wiring? (2)

Answer 14

Good conductor

Ductile

Question 15

Why are plastics & ceramics used as insulators?

Answer 15

Don’t conduct electricity

Conduct heat poorly

Question 16

How is copper purified?

Answer 16

By using an impure copper anode and a pure copper cathode

Using inert electrodes

Question 17

What are the materials needed for the purification of copper with copper electrodes?

Answer 17

Anode: Impure copper
Cathode: Pure copper
Copper sulfate solution

Question 18

What happens during electrolysis using copper electrodes?

Answer 18

the metal atoms at the anode lose electrons to form positive ions

Question 19

What are the materials needed for the purification of copper with inert electrodes?

Answer 19

Inert anode: Graphite
Inert cathode: Graphite
Copper sulfate solution

Question 20

What happens during electrolysis using inert electrodes?

Answer 20

Negative ions in the electrolyte lose electrons to anode

Question 21

What happens at the anode?

Answer 21

Reduction of positive ions

Question 22

What happens at the cathode?

Answer 22

Oxidation of negative ions

Question 23

What is the main ore of aluminum?

Answer 23

Bauxite

Question 24

What are the electrodes used in the extracting aluminum made of?

Answer 24

Carbon

Question 25

What is the electrolyte in the cell?

Answer 25

molten aluminium oxide dissolved in molten cryolite

Question 26

Why is aluminum oxide dissolved in cryolite?

Answer 26

Decrease melting point, improve conductivity

Question 27

Describe the process of extracting aluminium

Answer 27

1) Bauxite treated w/ sodium hydroxide to form sodium aluminate and heated to form aluminum oxide
2) Aluminum oxide dissolved in cryolite
3) Electrolysis using carbon electrodes
4) At cathode aluminum ions gain electrons, reduced to aluminum
5) At anode, oxide ions are oxidised to oxygen
6) Oxygen reacts w/ carbon

Question 28

What are the products in extracting aluminum?

Answer 28

At cathode: aluminum

At anode: oxygen

Question 29

What is brine?

Answer 29

Concentrated aqueous solution of sodium chloride

Question 30

Identify the ions present in brine (4)

Answer 30

Na+ , Cl-, H+ and OH-

Question 31

Where is brine electrolyzed?

Answer 31

In a diaphragm cell

Question 32

What are the products electrolysis of brine? (3)

Answer 32

At cathode: Hydrogen
At anode: Chlorine
Sodium hydroxide forms in solution

Question 33

What are the uses of chlorine? (2)

Answer 33

• treating drinking water

- making bleach

Question 34

What are the uses of hydrogen? (2)

Answer 34

• making ammonia

- making margarine

Question 35

What is the use of sodium hydroxide?

Answer 35

soap

Question 36

Explain ionic movement in electrolysis

Answer 36

• In a molten ionic compound, ions able to move
• When current applied, cations move towards cathode - anions move towards anode
• Cations reach cathode and gains electrons (reduction)
• Anions reach anode and lose electrons (oxidation)

Question 37

Where does reduction occur?

Answer 37

Cathode

Question 38

What is copper refining?

Answer 38

When copper is purified by electrolysis

Question 39

In copper refining, what electrodes are used?

Answer 39

Anode: Impure copper
Cathode: Pure copper

Question 40

During electrolysis using inert electrodes, what happens to the negative ions in the electrolyte?

Answer 40

They lose their electrons to the anode

Question 41

In copper refining using inert electrodes, why does the eletrolyte lose its blue colour?

Answer 41

Copper ions in solution are turning into copper atoms at the cathode

Question 42

In copper refining using 2 copper electrodes, what happens to the anode?

Answer 42

As the anode is not inert, it loses electrons and copper ions go into solution - anode gets smaller

Question 43

In copper refining using 2 copper electrodes, why does the electrolyte remain the same deep blue colour?

Answer 43

Copper ions removed from solution at cathode are replaced in solution by copper ions formed at the anode - going in to solution

Question 44

What is the overall equation for the electrolysis of aluminium oxide using electrolysis?

Answer 44

2Al2O3 => 4Al + 3O2