Topic 5 - Electrolysis (Year 10)

Question 1

What is the name given to the negative electrode in elecotrolysis?

Answer 1

Cathode

Question 2

What is the name given to the positive electrode in elecotrolysis?

Answer 2

Anode

Question 3

What is an electrolyte?

Answer 3

Solution of ions that can conduct electricity

Question 4

What term can be used to remember which elctrode has which charge?

Answer 4

PANIC (Positive Anode Negative Is Cathode)

Question 5

Which Electrode would a Pb²⁺ ion move towards in the electrolysis of molton lead bromide?

Answer 5

Negative

Question 6

What type of electrodes are used in electrolysis?

Answer 6

Two inert, carbon electrodes

Question 7

Define electrolysis

Answer 7

The spliiting up of an ionic compound into it’s constituent elements usinng electricity

Question 8

What would be produced at the negative electrode in the electrolysis od NaCl?

Answer 8

Na (Sodium)

Question 9

What would be produced at the positive electrode in the electrolysis od NaCl?

Answer 9

Cl₂ (Chlorine)

Question 10

Describe how the electrolysis of a molten ionic substance is carried out in a lab

Answer 10

Two inert electrodes are cleaned using sand paper. The ionic compound is heated in a crucible over a bunsen burner. The electrodes are placed into the electrolyte and connected to a power source.

Question 11

Give the half equation for the reduction of K⁺ ions during the electrolysis of KCl

Answer 11

K⁺ + e^- → K

Question 12

Give the half equation for the oxidation of Cl^- ions during the electrolysis of KCl

Answer 12

2Cl^- → Cl₂ + 2e^-

Question 13

Give the name of the ions produced when water molecules are broken down

Answer 13

H⁺ and OH^- (Hydrogen ion and Hydroxide Ion)

Question 14

Can ionic substances be electrolysed when solid?

Answer 14

No

Question 15

Why can’t ionic substances be electrolysed when solid?

Answer 15

ions cannot move.

Question 16

What will be produced at the positive electrode in a solution containing both OH^- ions and Cl^- ions?

Answer 16

Chlorine (Cl₂)

Question 17

What will be produced at the positive electrode in a solution containing both OH^- ions and SO₄^2- ions?

Answer 17

Oxygen (O₂)

Question 18

Why in a solution where sodium chloride has been dissolved in water. In electrolysis sodium isn’t produced at the negative electrode?

Answer 18

Sodium is more reactive than hydrogen, therefore it stays in the solution and Hydrogen would be formed

Question 19

What is the half equation for the reduction of hydrogen ions?

Answer 19

2H⁺ + 2e^- → H₂

Question 20

What are the four different ions present in a copper sulfate solution?

Answer 20

Cu²⁺, H⁺, SO4^2-, OH^-

Question 21

What are the products formed at the anode and cathode in the electrolysis of sopper sulfate solution?

Answer 21

Oxygen is produced at the anode, Copper is produced at the cathode

Question 22

Explain how the electrolysis of copper sulfate can be used to purify copper

Answer 22

An impure sample of copper is used as the anode and a thin pure piece of copper is used as the cathode. The impure copper is oxidised and dissolved into the solution of ions. The copper ions in the solution are reduced at the cathode, forming a layer of pure copper of the electrode.

Question 23

What are the two half equations for the electrolysis of copper sulfate solution using copper electrodes?

Answer 23

Cu²⁺ + 2e^- → Cu and Cu → Cu²⁺ + 2e^-

Question 24

What ions would NaCl split into when molten?

Answer 24

Na⁺ + Cl^-

Question 25

What ions would CuSO₄ split into when molten?

Answer 25

Cu²⁺ + SO₄^2-

Question 26

Descirbe what you would expect to see when conducting the electrolysis of copper chloride solution using graphite (inert) electrodes.

Answer 26

The cathode will be coated with a brownish layer.

This shows copper is being produced

At the anode there will be bubbles.

This indicates that a gas is being produced

If you hold a damp blue litmus paper near this, it will turn red and then bleach white.

This indicates that the gas produced is chlorine

Question 27

Descirbe what you would expect to see when conducting the electrolysis of copper chloride solution using an impure copper anode and a pure copper cathode.

Answer 27

The anode will appear to be smaller (it will have lost mass)

The cathode will appear bigger (it has gained mass)

Under the anode, there will be a collection of impurities that have settled

This shows that the pure copper ions have migrated from the anode to the cathode

Question 28

What’s attracted to cathodes and what charge?

Answer 28

Cations (positive)

Question 29

What’s attracted to anodes and what charge

Answer 29

Anions (negative)

Question 30

What happens when the cations reach the cathode?

Answer 30

They are reduced (gain electrons) and discharged.

Question 31

When anions move to the anode, what do they do?

Answer 31

They are oxidised (lose electrons) and so are discharged

Question 32

What happens at the cathode in electrolysis of aqueous solutions?

Answer 32

If the metal is more reactive than hydrogen, hydrogen is produced. If the metal is less reactive than hydrogen, the metal is produced.

Question 33

What happens at the anode in electrolysis of aqueous solutions?

Answer 33

If a halide is present, the halide is produced. If there’s no halide present, oxygen is produced.

Question 34

In purification if copper what’s the cathode made out of?

Answer 34

Pure copper

Question 35

In purification of copper, what’s the anode made out of?

Answer 35

Impure copper

Question 36

In purification of copper, what’s the electrolyte?

Answer 36

In purification of copper, what’s the electrolyte ?

Question 37

In purification of copper, what is the colopur of copper sulphate?

Answer 37

Blue

Question 38

What’s the voltage directly proportionate to in purification of copper?

Answer 38

The mass of the cathode due to quicker donation and loss of electrons.

Question 39

What does the cathode do in purification of copper ?

Answer 39

It grows heavier due to reduction of copper ions leading to discharged atoms deposited on the cathode.

Question 40

What does the anode do during copper purification?

Answer 40

It grows lighter due to oxidisation of the impure copper molecules causing more copper to dissolve into the solution. The impurities are left as a slush at the bottom.