Electrochemistry

Question 1

Define electrolysis.

Answer 1

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

Question 2

What is the anode?

Answer 2

the positive electrode

Question 3

What is the cathode?

Answer 3

the negative electron

Question 4

What is the electrolyte?

Answer 4

the molten or aqueous substance that undergoes electrolysis

Question 5

What process occurs at the anode?

Answer 5

oxidation

Question 6

What process occurs at the cathode?

Answer 6

reduction

Question 7

Why are metal objects electroplated?

Answer 7

to improve their appearance and resistance to corrosion

Question 8

What process makes metal objects more resistant to corrosion and with improved appearance?

Answer 8

electroplating

Question 9

What does a hydrogen–oxygen fuel cell do?

Answer 9

uses hydrogen and oxygen to produce electricity with water as the only chemical product

Question 10

Electrolysis of MOLTEN LEAD(II) BROMIDE: product at the anode

Answer 10

bromine

Question 11

Electrolysis of MOLTEN LEAD(II) BROMIDE: product at the cathode

Answer 11

lead

Question 12

Electrolysis of MOLTEN LEAD(II) BROMIDE: observations

Answer 12

cathode: silvery solid
anode: brown gas

Question 13

Electrolysis of concentrated aqueous NaCl: product at the anode

Answer 13

chlorine

Question 14

Electrolysis of concentrated aqueous NaCl: product at the cathode

Answer 14

hydrogen

Question 15

Electrolysis of concentrated aqueous NaCl: observations

Answer 15

cathode: colourless gas, lit splint squeaky pop

anode: pale yellow-green gas (turns UI red and bleaches red litmus)

Question 16

Electrolysis of dilute sulfuric acid: product at the anode

Answer 16

oxygen

Question 17

Electrolysis of dilute sulfuric acid: product at the cathode

Answer 17

hydrogen

Question 18

Electrolysis of dilute sulfuric acid: observations

Answer 18

anode: colourless gas, relights glowing splint
cathode: colourless gas, lit splint squeaky pop

Question 19

What forms at the cathode in the electrolysis of aqueous electrolytes?

Answer 19

cation below hydrogen in reactivity series- metal forms

cation above hydrogen- hydrogen gas forms, metal ion stays in solution

Question 20

What forms at the anode in the electrolysis of aqueous electrolytes?

Answer 20

• halide ions (like Cl– , Br– or I–) present - the element will form (chlorine etc)
• other anions (eg sulfate, nitrate) - oxygen will form
• from the dissociation of OH– ions as nitrate/sulfate ions are more reactive than OH- ions

Question 21

What forms at the anode in the electrolysis of molten electrolytes?

Answer 21

non-metal

Question 22

What forms at the cathode in the electrolysis of molten electrolytes?

Answer 22

metal

Question 23

What forms in the anode?

Answer 23

non-metals (other than hydrogen)

Question 24

What forms in the cathode?

Answer 24

metals, or hydrogen

Question 25

Advantages of hydrogen fuel cell

Answer 25

high energy density, high fuel efficiency, minimal pollution

Question 26

Disadvantages of hydrogen fuel cells

Answer 26

hydrogen has to be produced (often involving burning fossil fuels), stored as a compressed gas so difficult to transport, highly flammable

Question 27

a hydrogen–oxygen fuel cell uses

Answer 27

hydrogen and oxygen to produce electricity with water as the only chemical product

Question 28

Describe how metals are electroplated.

Answer 28

metal ions migrate via a solution from a positive electrode to a negative one

Question 29

why are metal objects electroplated

Answer 29

improve their appearance and resistance to corrosion.

Question 30

Describe the extraction of aluminium from purified bauxite / aluminium oxide

Answer 30

- Bauxite is first purified to produce aluminium oxide, Al2O3 - Aluminium oxide is then dissolved in molten cryolite - This is because aluminium oxide has a melting point of over 2000°C which would use a lot of energy and be very expensive - The resulting mixture has a lower melting point without interfering with the reaction - The mixture is placed in an electrolysis cell, made from steel, lined with graphite - The graphite lining acts as the negative electrode, with several large graphite blocks as the positive electrodes

Question 31

aluminium cathode

Answer 31

Al3+ + 3e- → Al

Question 32

aluminium anode

Answer 32

2O2- → O2 + 4e-

Question 33

aluminium overall

Answer 33

2Al2O3 → 4Al + 3O2

Question 34

Explain why the carbon anode has to be replaced regularly.

Answer 34

carbon reacts with oxygen and forms carbon dioxide

Question 35

aqueous copper (II) sulphate products in graphite

Answer 35

cathode: copper anode: oxygen

Question 36

aqueous copper (II) sulphate products in copper

Answer 36

cathode: copper anode: copper

Question 37

reduction of hydrogen

Answer 37

2H+(aq) + 2e– → H2(g)

Question 38

hydroxide equation

Answer 38

4OH–(aq)→2H2O(l)+O2(g)+4e–