3.1.11 Electrode potentials and electrochemical cells

Question 1

How do you write cell notation?

Answer 1

R|O||O|R

Question 2

What is the function of a salt bridge?

Answer 2

Allows ions to move across the salt bridge and completes the circuit

Question 3

Give the characteristics of solution used in the salt bridge, what are some common examples?

Answer 3

• Inert, should not react with either electrolyte
• Any reaction that did occur would change the cell EMF
• KCl, AgNO3 and NaCl

Question 4

When preparing a metal electrode like aluminium, why should you clean the piece of metal using sandpaper?

Answer 4

Removes the oxide layer (impurity)

Question 5

When is the Pt (s) electrode required?

Answer 5

When there is no solid metal electrode present

Question 6

At what electrode does reduction occur.

Answer 6

• RHS
• Cathode (+ve)

Question 7

At what electrode does oxidation occur.

Answer 7

• LHS
• Anode (-ve)

Question 8

What are the standard conditions in an electrochemical cell?

Answer 8

• 1 moldm-3
• 298 K
• 100 kPa

Question 9

What is the SHE and what is its role in calculating standard elctrode potentials?

Answer 9

Standard hydrogen electrode
- All other electrodes are compared to this standard value (0.00V)
- Measured relative to SHE

Question 10

How do you calculate the standard electrode potential of a cell?

Answer 10

EΦcell = EΦ(RHS) - EΦ(LHS)

Question 11

When is a reaction feasible and not deasible in terms of the EΦcell value?

Answer 11

When EΦcell < 0 : not feasible

When EΦcell > 0 : feasible

Question 12

When a half-cell has a more positive EΦcell is it oxidised or reduced in the reaction?

Answer 12

Reduced
- This is the positive cathode
- Electrons flow from negative to positive cathode

Question 13

Give examples of:
a) rechargeable cell
b) non-rechargeable cell
c) fuel

Answer 13

a) Lead-acid batteries, lithium cells
b) Zinc-carbon cells
c) Hydrogen-oxygen fuel cells

Question 14

Give an equation for the reaction that occurs at the positive lithium cobalt oxide electrode.

Answer 14

Li+ + CoO2 + e– → LiCoO2-

Question 15

Why can you not recharge a zinc-carbon cell (or any non-rechargeable cell)?

Answer 15

The reaction is impossible to reverse

Question 16

How do you recharge a cell and why do you not need to recharge a fuel cell?

Answer 16

• Current is applied which forces the elcetrons in the opposite direction
• Reactents of a fuel cell are supplied continuosly

Question 17

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

Answer 17

• Prevents pollution of the environment y toxic compounds found in the cells
• Compounds can leach into environment when placed in landfills

Question 18

How may the recharging of a cell lead to the release of CO2 into the atmosphere?

Answer 18

Requires energy which may have come from the burning of fossil fuels in power stations

Question 19

Why might a rechargeable cell be connected to a solar cell sed to power road signs?

Answer 19

• Solar cell does not work all the time, only when it is light out
• Rechargeable cell can store electrical energy and work when the solar cell is not

Question 20

What are the half cell reactions in a hydrogen-oxygen fuel cell?

Answer 20

H2 + 2OH- → 2H2O + 2e-
O2 + 2H20 + 4e- → 4OH-

Question 21

Suggest the main advantage of using hydrogen in a fuel cell rather than in an internal combustion engine of a car.

Answer 21

In the fuel cell, a greater proportion of energy available from the hydrogen-oxygen reaction is converted into useful energy

Question 22

Highlight the postives and negatives of non-rechargeable cells?

Answer 22

Positives:

Negatives: can’t recharge, lots of waste

Question 23

Highlight the postives and negatives of rechargeable cells?

Answer 23

Positives: recharge, less waste

Negatives: requires energy to recharge that can come from fossil fuels (carbon dioxide)

Question 24

Highlight the postives and negatives of fuel cells?

Answer 24

Positives: only water produced, less damage to environemnt, no harmful nitrogen oxides produced

Negatives: relies on crude oil (non-renewables), hydrogen gas is highly flammable