Electrode Potentials And Electrochmical Cells

Question 1

Identify weakest oxidising agent and why

Answer 1

Fe2+ ions
Smalles/most negative E

Question 2

Answer 2

Question 3

Answer 3

(e)
A fuel cell converts more of the available energy from combustion of hydrogen into kinetic energy of the car / an internal combustion engine wastes more (heat) energy

Question 4

Answer 4

Reaction cannot be reversed

Question 5

Answer 5

Question 6

Explain why a fuel cell does not need to be recharged.

Answer 6

Reactants continuously supples

Question 7

To provide energy for a vehicle, hydrogen can be used either in a fuel cell or in an internal combustion engine.
Suggest the main advantage of using hydrogen in a fuel cell rather than in an internal combustion engine.

Answer 7

In the fuel cell, a greater proportion of the energy available from the hydrogen-oxygen reaction is converted into useful energy
Allow less energy wasted / more efficient

Question 8

Answer 8

Question 9

Solar cells generate an electric current from sunlight. These cells are often used to provide electrical energy for illuminated road signs.
Explain why rechargeable cells are connected to these solar cells.

Suggest one reason why many waste disposal centres contain a separate section for cells and batteries

Answer 9

(a) Solar cells do not supply electrical energy all the time

Rechargeable cells can store electrical energy for use when the solar cells are not working
(b)
Prevent pollution of the environment by toxic or dangerous substances / recycling of valuable components

Question 10

Answer 10

Question 11

Suggest why the recharging of a lithium cell may lead to release of carbon dioxide into the atmosphere.

Answer 11

Electricity for recharging the cell may come from power stations burning (fossil) fuel

Question 12

Describe standard hydrogen electrode

Answer 12

Question 13

Answer 13

Question 14

Suggest the function of the carbon rod in the cell.

Answer 14

Allows electrons to flow / makes electrical contact / conductor

Question 15

State one environmental advantage of this rechargeable cell compared with the non-rechargeable cell

Answer 15

Metal / metal compounds are re-used / supplies are not depleted / It (the cell) can be re-used

Question 16

Answer 16

Question 17

Suggest why ethanol can be considered to be a carbon-neutral fuel.

Answer 17

(iv)
CO2 released by combustion / fermentation / fuel cell / reaction with water
(atmospheric) CO2 taken up in photosynthesis

Question 18

Answer 18

Question 19

Answer 19

Very dilute/lots of water added

Question 20

Answer 20

KCL
Do not react with either electrode
Ions can move

Question 21

Answer 21

Question 22

(c)
Suggest one reason why the redox reaction between chlorine and water does not normally occur in the absence of light.

Answer 22

Activation energy is high / light/UV provides the activation energy / light breaks chlorine molecule / CI-CI bond

Question 23

one reason why the cell cannot be electrically recharged.

Answer 23

Reaction not reversible

Question 24

Answer 24

Question 25

Answer 25

Question 26

Describe a standard hydrogen electrode.

Answer 26

Question 27

Answer 27

Question 28

Write the conventional representation for an alkaline hydrogen-oxygen fuel cell.

Answer 28

Question 29

Suggest why the e.m.f. of a hydrogen oxygen fuel cell, operating in acidic conditions, is exactly the same as that of an alkaline fuel cell.

Answer 29

Overall reaction is the same

Question 30

Hydrogen-oxygen fuel cells are sometimes regarded as a source of energy that is carbon neutral. Give one reason why this may not be true.

Answer 30

Hydrogen may need to be made using an energy source that is not ‘carbon neutral’

Question 31

Answer 31

Question 32

Answer 32

Question 33

Answer 33

Question 34

Give one reason why the e.m.f. of this cell changes when the electrodes are connected and a current flows.

Answer 34

The concentration of the ions change or are no longer standard or the e.m.f is determined when no current flows

Question 35

Answer 35

D

Question 36

What is the function of a platinum electrode

Answer 36

To allow transfer of electrons / provide a reaction surface (1)

Question 37

Answer 37