Electrolysis

Question 1

Define Electrolytes

Answer 1

ionic compounds in a molten state or dissolved in water

Question 2

What must the substance be to do electrolysis

Answer 2

ionic and liquid.
solids ions cannot move enough
covalent cannot as they share electrons

Question 3

What are the negatively charged anions attracted to

Answer 3

Attracted to the positive anode

Question 4

What are the positively charged cations attracted to

Answer 4

Attracted to the negative cathode

Question 5

What is a pneumonic to remember electrode charges

Answer 5

PANIC

Positive Anode Negative Is Cathode

Question 6

What is a pneumonic to remember where reduction takes place

Answer 6

REDCAT

Reduction At Cathode

Question 7

Where are metals and non metals always formed in electrolysis

Answer 7

Metal is always formed at cathode and non-metal at anode

Question 8

What happens in the electrolysis of molten Lead Bromine

Answer 8

Lead formed at cathode, Bromine gas formed at anode

Question 9

What happens in the electrolysis of water

Answer 9

When water is slightly acidified it causes dissociation creating H+ and OH- ions which attract to electrodes

Hydrogen and oxygen gas formed

Question 10

What ions does an electrolyte dissolved in water contain

Answer 10

H+ ions, OH- ions and the two ions from ionic compound

Question 11

What happens at the anode with electrolysis in solution

Answer 11

All ions ending with -ate are not discharged but oxygen from water instead

If Halides are present then halides are discharged instead

Question 12

What are some examples of halides

Answer 12

Diatomic molecules; Chlorine, Bromine, Iodine

Question 13

What happens at cathode with electrolysis in solution

Answer 13

Metals more reactive than hydrogen are not discharged, metals less reactive than hydrogen are discharged

Question 14

What is the equation for production of oxygen from water

Answer 14

4OH- - 4e- –> O2 + 2H2O

Question 15

What happens if the anode is carbon and oxygen is produced

Answer 15

Anodes have to be replaced frequently as CO2 is produced e.g. production of aluminium oxide

Question 16

What is a half equation

Answer 16

represent the reaction that happens at an electrode during electrolysis. It shows what happens when ions gain or lose electrons

Question 17

What are the rules of a half equation

Answer 17

• electrons are shown as e-
• the numbers of atoms of each element must be the same on both sides
• the total charge on each side must be the same (usually zero)

Question 18

What is the solution left behind for electrolysis of copper using graphite electrodes

Answer 18

Dilute sulphuric acid

Question 19

What is the solution left behind for purification of copper using copper electrodes

Answer 19

Copper sulphate

Question 20

What are the anode and cathode made of in purification of copper

Answer 20

Anode is impure copper and cathode is pure copper

Question 21

How is sludge formed during purification of copper

Answer 21

From the impurities of the impure copper anode

Question 22

What happens to the anode and cathode in purification of copper

Answer 22

During electrolysis, the anode loses mass as copper dissolves, and the cathode gains mass as copper is deposited.

Question 23

What are the half equations for purification of copper

Answer 23

Cathode: Cu2+ + 2e- –> Cu

Anode : Cu –> Cu2+ + 2e-

Question 24

What is electroplating

Answer 24

Coating objects with a thin layer of metal using electrolysis

Question 25

What should be the negative cathode when electroplating

Answer 25

Negative cathode is the object to be electroplated

Question 26

What should be the positive anode when electroplating

Answer 26

Positive anode should be the metal that you want to coat the object with

Question 27

What should be the electrolyte when electroplating

Answer 27

solution of the coating metal

Question 28

How do you electroplate a spoon with silver

Answer 28

a metal spoon, is connected to the negative terminal of the power supply. A piece of silver is connected to the positive terminal. The electrolyte is silver nitrate solution.

Question 29

what is used to lower the melting point of aluminium oxide

Answer 29

aluminium oxide dissolved in cryolite

Question 30

What are the electrodes made in purification of aluminium oxide

Answer 30

graphite

Question 31

What happens at anode and cathode during electrolysis of aluminium oxide

Answer 31

Aluminium reduced at cathode then topped off | Oxygen produced at anode to make oxygen gas

Question 32

Why do positive electrodes need to be replaced frequently

Answer 32

As oxygen is being produced at anode so it reacts with graphite electrodes so CO2 produced

Question 33

Important factors when choosing aluminium extraction points

Answer 33

- in close proximity to a power station, in order to provide the large supply of electricity - near the coast to allow for materials import - near roads and railway lines to allow for product transport - near a town or city for workers to live by - away from built-up areas, so that the noise and pollution of the site do not affect the local population