Electrolysis (C4)

Question 1

What is an electrolyte

Answer 1

A liquid or solution that can conduct electricity

Question 2

What is an electrode

Answer 2

A solid that conducts electricity and is submerged in the electrolyte

Question 3

What is electrolysis

Answer 3

The process by which is a substance is split up by using electric current

Question 4

What happens to positive ions in electrolyte

Answer 4

They move towards the cathode (negative electrode) and gain electrons (they are reduced)

Question 5

What are cations

Answer 5

Positive ions

Question 6

What is a cathode

Answer 6

Negative electrode

Question 7

What are anions

Answer 7

Negative ions

Question 8

What is the anode

Answer 8

Positive electrode

Question 9

What is reduction

Answer 9

• gain of electrons
• loss of oxygen

Question 10

What is oxidation

Answer 10

• loss of electrons
• gain of oxygen

Question 11

Nitrate symbols

Answer 11

NO3-

Question 12

Sulfate symbols

Answer 12

SO4^2-

Question 13

Carbonate symbols

Answer 13

CO3^2-

Question 14

Ammonium ion symbols

Answer 14

NH4^+

Question 15

Silver ion symbols

Answer 15

Ag+

Question 16

Zinc ion symbols

Answer 16

Zn^2+

Question 17

Word equation for electrolysis of aluminium oxide

Answer 17

Aluminium oxide — aluminium + oxygen

Question 18

Symbol equation for electrolysis of aluminium oxide

Answer 18

2Al2O3 — 4Al + 3O2

Question 19

What happens at negative electrode of electrolysis of aluminium oxide

Answer 19

• aluminium is produced
• there is a reduction
• Al^3+ + 3e^- — Al

Question 20

What happens at positive electrode of electrolysis of aluminium oxide

Answer 20

• oxidation
• oxygen is produced at positive electrode
• 2O^2- — O2 + 4e^-

Question 21

What is cryolite

Answer 21

• aluminium based compound
• lower melting point than aluminium oxide

Question 22

What is bauxite

Answer 22

Contains aluminium oxide

Question 23

Extraction of metals from ores using electrolysis

Answer 23

1. Aluminium is extracted from the ore by electrolysis
2. Aluminium oxide has a very high melting temperature so its mixed with cryolite to lower the melting point
3. The molten mixture contains free ions - so it’ll conduct electricity
4. The positive aluminium ions are attracted to the negative electrode where they pick up three electrons and turn into neutral aluminium aluminium atoms. These then sink to the bottom of the electrolysis tank
5. The negative oxygen ions are attracted to the positive electrode where they each lose two electrons. Te neutral oxygen atoms will ten combine to form O2 molecules

Question 24

Why do anodes of electrolysis of aluminium oxide need to be replaced regularly

Answer 24

• they’re made of carbon
• the react with oxygen to produce carbon dioxide

Question 25

Half equation wen halide isn’t present in aqueous solution

Answer 25

4OH- — O2 + 2H2O + 4e-

Question 26

What happens at cathode (hydrogen or metal)

Answer 26

- if metal is more reactive than hydrogen, hydrogen is produced - if metal is less reactive than hydrogen, the metal is produced

Question 27

What happens at anode (oxygen or halide)

Answer 27

- if halide is present (group 7), then that is what s produced - if halide isn’t present, then oxygen is produced

Question 28

What is brine

Answer 28

Seawater or water with salt dissolved in it

Question 29

Reactivity series

Answer 29

Potassium Sodium Calcium Magnesium Aluminium CARBON Zinc iron tin lead HYDROGEN Copper Silver gold Platinum

Question 30

Difference between solution and molten

Answer 30

- molten is only the metal - solution is with water so there are H+ and OH- ions

Question 31

Why is electrolysis of aluminium oxide so expensive

Answer 31

Requires a lot of electricity