Electrochemistry

Question 1

What is electrolysis?

Answer 1

The process of breaking down an ionic compound using electricity.

Question 2

What is an inert electrode?

Answer 2

An electrode that does not react during electrolysis, usually made of graphite or platinum.

Question 3

What is the anode in electrolysis?

Answer 3

The positive electrode where oxidation occurs.

Question 4

What is the cathode in electrolysis?

Answer 4

The negative electrode where reduction occurs.

Question 5

What is an electrolyte?

Answer 5

A molten or dissolved ionic compound that conducts electricity by the movement of ions.

Question 6

How does conduction occur in an electrolyte?

Answer 6

Ions move through the liquid and carry electric charge.

Question 7

What type of ions move to the cathode?

Answer 7

Positive ions (cations) are attracted to the negative cathode.

Question 8

What type of ions move to the anode?

Answer 8

Negative ions (anions) are attracted to the positive anode.

Question 9

What are the products of electrolysis of molten lithium chloride?

Answer 9

Lithium at the cathode and chlorine at the anode.

Question 10

What are the observations at the electrodes during electrolysis of lithium chloride?

Answer 10

Silver metal appears at the cathode and bubbles of pale green gas at the anode.

Question 11

What are the products of electrolysis of molten lead(II) bromide?

Answer 11

Lead at the cathode and bromine at the anode.

Question 12

What are the observations during electrolysis of molten lead(II) bromide?

Answer 12

Grey metal forms at cathode; orange gas (bromine) at anode.

Question 13

Write the half-equation for lithium at the cathode.

Answer 13

Li⁺ + e⁻ → Li

Question 14

Write the half-equation for chloride at the anode.

Answer 14

2Cl⁻ → Cl₂ + 2e⁻

Question 15

Write the half-equation for lead at the cathode.

Answer 15

Pb²⁺ + 2e⁻ → Pb

Question 16

Write the half-equation for bromide at the anode.

Answer 16

2Br⁻ → Br₂ + 2e⁻

Question 17

What happens at the cathode during electrolysis of any molten salt?

Answer 17

Positive metal ions gain electrons (reduction) to form metal atoms.

Question 18

What happens at the anode during electrolysis of any molten halide?

Answer 18

Negative halide ions lose electrons (oxidation) to form halogen gases.

Question 19

What is the main ore of aluminium?

Answer 19

Bauxite.

Question 20

From what is alumina extracted?

Answer 20

Alumina is purified from bauxite ore.

Question 21

Why is alumina dissolved in molten cryolite in electrolysis?

Answer 21

To lower its melting point and reduce energy costs.

Question 22

What are the electrodes made of in aluminium extraction?

Answer 22

Graphite.

Question 23

Why do the carbon anodes need to be replaced regularly in aluminium extraction?

Answer 23

They react with oxygen to form carbon dioxide and wear away.

Question 24

What are the half-equations for aluminium extraction?

Answer 24

Cathode: Al³⁺ + 3e⁻ → Al; Anode: 2O²⁻ → O₂ + 4e⁻

Question 25

What is the overall reaction in aluminium extraction?

Answer 25

2Al₂O₃ → 4Al + 3O₂

Question 26

Why is recycling aluminium important?

Answer 26

It saves energy and reduces waste.

Question 27

How much energy does recycling aluminium use compared to extraction?

Answer 27

Only a small fraction of the energy required to extract aluminium from bauxite.

Question 28

What are the benefits of recycling aluminium?

Answer 28

Conserves resources, reduces environmental damage, and saves energy.

Question 29

Why is electrolysis expensive?

Answer 29

Because it requires a large amount of electrical energy to melt compounds and drive the reaction.

Question 30

How do molten ionic compounds conduct electricity?

Answer 30

Ions are free to move and carry charge.

Question 31

Why can solid ionic compounds not be electrolysed?

Answer 31

Ions are fixed in place and cannot move.

Question 32

Why is graphite used as an electrode?

Answer 32

It is inert, conducts electricity well, and does not react with the electrolyte (in most cases).

Question 33

What gas is produced at the anode during aluminium extraction?

Answer 33

Oxygen.

Question 34

What metal is produced at the cathode during aluminium extraction?

Answer 34

Aluminium.

Question 35

Why must the anodes in aluminium extraction be made of carbon?

Answer 35

They conduct electricity and react with oxygen to form carbon dioxide.

Question 36

Why is aluminium expensive to extract?

Answer 36

Because of the high energy needed for electrolysis and to keep the electrolyte molten.

Question 37

What happens to oxygen ions at the anode in aluminium extraction?

Answer 37

They lose electrons to form oxygen gas (oxidation).

Question 38

Is aluminium extraction reduction or oxidation?

Answer 38

It involves reduction of aluminium ions at the cathode.