Topic 14 - Redox 2

Question 1

What is standard electrode potential?

Answer 1

voltage measured under standard conditions when the half cell is connected to a standard hydrogen electrode

Question 2

What are the standard condition for standard electron potential?

Answer 2

temp 298K
pressure 100kPa
conc 1 moldm-3 of ion

Question 3

Why is it important to use standard conditions when measuring electrode potentials?

Answer 3

electrode potentials are affected by temp, pressure and conc so if they are kept the same, the value for the half cell’s electrode potential will be the same every time

Question 4

What does an electrochemical cell contain?

Answer 4

2 solutions
2 electrodes
salt bridge
(+high resistance voltmeter)

Question 5

What is the purpose of a salt bridge?

Answer 5

completes the circuit

• salt ions can flow through salt bridge
• charges of electrodes are balanced out

Question 6

What is the salt bridge (aka filter paper) soaked in?

Answer 6

potassium nitrate

KNO3

Question 7

What is used as a reference electrode?

Answer 7

standard hydrogen electrode

always on left

Question 8

What is used in the standard hydrogen electrode?

Answer 8

hydrogen gas passed over platinum wire

-eqm set up between H2 gas and H+ ions in acidic soln

Question 9

Why is a reference electrode necessary?

Answer 9

• allows all half cells to be compared to the same value
• hydrogen half cell has a value of 0V so the voltage reading will always be equivalent to the electrode potential of the other half cell

Question 10

E⦵ =

Answer 10

E⦵red - E⦵ox

Question 11

Is a positive electrode potential feasible or not feasible?

Answer 11

feasible

thermodynamically unstable

Question 12

Is a negative electrode potential feasible or not feasible?

Answer 12

not feasible

thermodynamically stable

Question 13

What is E⦵cell directly proportional to?

Answer 13

ΔStot

lnK

Question 14

Why could the predictions of a reaction’s feasibility (based on electrode potentials) be wrong?

Answer 14

• conditions aren’t standard (diff temp, conc, pressure) as eqm would be affected
• reaction is kinetically stable (high Ea)

Question 15

What reaction happens at the anode in an acidic hydrogen-oxygen fuel cell?

Answer 15

H2 → 2H+ + 2e-

Question 16

What reaction happens at the cathode in an acidic hydrogen-oxygen fuel cell?

Answer 16

2H+ + 1/2O2 + 2e- → H2O

Question 17

What reaction happens at the anode in an alkaline hydrogen-oxygen fuel cell?

Answer 17

H2 + OH- → 2H2O + 2e-

Question 18

What reaction happens at the cathode in an alkaline hydrogen-oxygen fuel cell?

Answer 18

1/2O2 + 2e- → OH-

Question 19

What is the overall reaction in a hydrogen-oxygen fuel cell?

Answer 19

H2 + 1/2 O2 → H2O

Question 20

What are the advantages of the hydrogen-oxygen fuel cell?

Answer 20

• renewable energy

- no direct carbon emissions or impurities

Question 21

What are the disadvantages of the hydrogen-oxygen fuel cell?

Answer 21

• hydrogen gas is very flammable
• (hydrogen) gas is hard to store
• requires energy (eg. from fossil fuels) to obtain hydrogen gas

Question 22

What are the advantages of a hydrogen-rich fuel with oxygen fuel cell?

Answer 22

• easier to store fuel like methanol (compared to gases)

- fuel can come from plant matter

Question 23

What are the disadvantages of a hydrogen-rich fuel with oxygen fuel cell?

Answer 23

• carbon dioxide produced
• not as efficient (as hydrogen-oxygen fuel cell)
• water vapour produced