C4.1 - Electrolysis

Question 1

What is electrolysis? [2]

Answer 1

the decomposition of an ionic compound, when molten or in aqueous solution, by the passage of an electric current

Question 2

What is electrolysis simply? [2]

Answer 2

breaking apart ionic compounds, using electricity

Question 3

What is an electrode? [3]

Answer 3

• a conductor
• often a metal or graphite rod
• allows electric current to go in or out of an electrolyte

Question 4

What is an electrolyte? [2]

Answer 4

• the molten or aqueous substance that undergoes electrolysis

Question 5

What is a cation? [3]

Answer 5

• when an atom loses electrons
• it becomes positively charged
• this is a cation

Question 6

What is an anion? [3]

Answer 6

• when an atom gains or takes in electrons
• it becomes negatively charged
• this is an anion

Question 7

What is a cathode? [1]

Answer 7

the negative electrode

Question 8

What do cathodes attract and why? [2]

Answer 8

• positively charged cations
• because opposite charges attract and since the cathode is negative, it’ll attract positive ions

Question 9

What is an anode? [1]

Answer 9

the positive electrode

Question 10

What do anodes attract and why? [2]

Answer 10

• negatively charged anions
• because opposite charges attract and so since the anode is positive, it’ll attract negative ions

Question 11

How do you remember which electrode attracts which ion? [2]

Answer 11

CAThode –> CATion
ANode –> ANion

Question 12

What is required during electrolysis? [1]

Answer 12

an electric current to flow through the circuit

Question 13

What carries the electric charge in an external circuit and where does this happen? [3]

Answer 13

• electrons carry this electric charge
• they carry it from the power supply to the cathode - making it negatively charged
• the anode becomes positively cahrged as it loses electrons

Question 14

What carries the electric charge in the electrolyte? [1]

Answer 14

the ions carry this electrical charge

Question 15

What can electrolytes either be? [2]

Answer 15

• a molten compound
• an aqueous solution

Question 16

What happens when ions touch the electrode? [2]

Answer 16

electrons are either lost or gained, to create neutral substances

Question 17

What happens to the neutral substances produced after ions touch the electrodes? [1]

Answer 17

they are released as products at the electrodes

Question 18

What happens at the anode? [1]

Answer 18

anions lose electrons

Question 19

What happens at the cathode? [1]

Answer 19

cations gain electrons

Question 20

What is oxidation? [1]

Answer 20

the loss of electrons

Question 21

What is reduction? [1]

Answer 21

the gain of electrons

Question 22

What are molten substances? [2]

Answer 22

substances in a liquid state, resulted from being heated above their melting points

Question 23

What are electrodes made of? [3]

Answer 23

• platinum
• carbon
• graphite

Question 24

What happens during the electrolysis of molten lead(II) bromide to the ions? [2]

Answer 24

• bromide ions (-) will be attracted to the anode (+)
• lead ions (+) will travel towards the cathode (-)

Question 25

What are observations seen in the electrolysis of molten lead(II) bromide? [2]

Answer 25

- at the anode, bromine gas is formed which is seen as brown gas bubbles - at the cathode, lead forms and can be seen as a grey metal (molten lead)

Question 26

What does aqueous mean? [1]

Answer 26

a substance mixed with water

Question 27

Where do the ions in the electrolyte come from? [3]

Answer 27

- the dissolved substance - and water - which contains hydrogen and hydroxide ions

Question 28

What is formed at the cathode? [2]

Answer 28

- metals - or hydrogen

Question 29

What is formed at the anode? [1]

Answer 29

- non-metals (except hydrogen)

Question 30

What is the rule for what is discharged at the cathode? [1]

Answer 30

jewellery metal otherwise hydrogen

Question 31

What are examples of jewellery metals? [4]

Answer 31

- copper - gold - silver - platinum

Question 32

What is the rule for what is discharged at the anode? [1]

Answer 32

halogen otherwise oxygen

Question 33

What is the KEY formula for reduction (Hydrogen formula)? [2]

Answer 33

2H⁺ + 2e⁻ --> H₂ (g)

Question 34

What is the KEY formula for oxidation (Hydroxide formula)? [2]

Answer 34

4OH⁻ --> O₂ + 2H₂O + 4e⁻

Question 35

What happens during the electrolysis of aqueous copper(II) sulphate using copper electrodes? [2]

Answer 35

- the concentration of Cu²⁺ ions in the electrolytes remains the same - since one electrode produces copper ions and the other removes them

Question 36

What is electroplating? [2]

Answer 36

a method used to put a thin layer of a metal onto a metal object, using electrolysis

Question 37

Why are metal objects electoplated? [2]

Answer 37

- to improve their appearance - to improve their resistance to corrosion

Question 38

What is the object that gets electroplated? [1]

Answer 38

the cathode

Question 39

What is the current flow in an electric circuit for electrolysis and why? [2]

Answer 39

- D.C. current - because A.C. current would make the direction of the current move many times, hence the electrons wouldn't be able to follow

Question 40

Why does the mass of a cathode increase after it has been electroplated? [2]

Answer 40

- because ions go and coat it - positive ions are attracted to the cathode and make it stronger

Question 41

What is needed for electroplating? Give an example as well. [2]

Answer 41

- the ions in the solutions of the thing your plating - e.g. if you're electroplating gold, you need gold solution