5.2.3 Redox and Electrode Potentials

Question 1

Standard electrode potential

Answer 1

Uses an inert platinum electrode
The emf of a half cell compared to the (standard) hydrogen electrode at a concentration of 1 mol dm-3 and at a pressure of 101 kPa AND a temperature of 298 K

Question 2

Negative electrode

Answer 2

Electrode with more reactive metal which loses electrons and is oxidised

Question 3

Positive elecrode

Answer 3

Electrode with less reactive metal which loses electrons and is oxidised

Question 4

Measuring a standard electrode potential

Answer 4

• Half-cell is connected toa standard hydrogen electrode
• The two electrodes are connected by a wire to allow a controlled flow of electrons
• The two solutions are connected with a salt bridge - allows ions to flow
• Typically contains a concentrated solution of an electrolyte that does not react with either solution

Question 5

More negative E* value

Answer 5

• Greater tendency to lose electrons + undergo oxidation
• less tendency to gain electrons + undergo reduction

Question 6

More positive E* value

Answer 6

-Greater tendency to gain electrons and undergo reduction
- Less tendency to lose electrons and undergo oxidation

Question 7

Calculation of a standard cell potential

Answer 7

Ecell = E(positive electrode) - E*(negative electrode)

Question 8

Limitations of predictions using E* values - Reaction rate

Answer 8

• Reactions with a large activation energy, resulting in very slow rate
• electrode potentials may indicate the thermodynamic feasibility of a reaction, but give no indication of rate of reaction

Question 9

Limitations of predictions using E* values - Concentration

Answer 9

Many reactions take place using conc or dilute solutions
- If conc is not 1moldm-3, the value of electrode potential will be different than the standard value
- any change to the electrode potential will affect the value of the overall cell potential