Electrode Potentials and Cells: Electrode Potentials and Cells

Question 1

What are electrochemical cells used for?

Answer 1

• Used to measure electrode potentials by reference to the standard hydrogen electrode

Question 2

What happens when a rod of metal is dipped into a solution of its own ions?

Answer 2

• An equilibrium is set up between the solid metal and the aqueous metal ions

Question 3

What are electrode potentials?

Answer 3

• The potential difference of a cell consisting of a specific electrode as the cathode and the standard hydrogen electrode as the anode

Question 4

How do you draw electrochemical cells using conventional representation?

Answer 4

• Half-cell with more negative electrode potential goes on left
• Write out left-hand half-equation as oxidation reaction
• Write out right-hand half-equation as reduction reaction
• Write reactants and products of oxidation reaction then repeat with reduction reaction
• Draw single line between reagents in different phases or put a comma between any reagents in same phase
• Draw double line between half-cells to represent salt bridge

Question 5

What are the conditions for a standard electrode potential, EƟ?

Answer 5

• 298K
• 100 kPa
• 1.00 mol dm−3 solution of ions (0.50 mol dm-3 for diprotic acid)

Question 6

What does a standard hydrogen cell consist of?

Answer 6

• Hydrochloric acid (1 moldm-3)
• Hydrogen gas
• Platinum electrode

Question 7

What is the function and benefit of the platinum electrode?

Answer 7

• To allow transfer of electrons

- Inert

Question 8

How do you calculate cell potential or EMF, EƟcell?

Answer 8

• EƟcell = EƟ positive - EƟ negative

Question 9

What does a positive EƟ cell value tell us?

Answer 9

• Positive Ecell value means reaction will occur spontaneously
• The higher the Ecell value, the more attracted electrons are to that electrode (species reduced)
• The lower the Ecell value, the less attracted electrons are to that electrode (species oxidised)

Question 10

What does the Ecell value tell us about the reducing/oxidising abilities of a species?

Answer 10

• Oxidising agent

• The species with higher Ecell value, the more attracted electrons are to that electrode
• Species reduced so acts as oxidising agent

• Reducing agent

• The species with lower Ecell value, the less attracted electrons are to that electrode
• Species oxidised so acts as reducing agent

Question 11

How can you use Ecell values to predict the direction of simple redox reactions?

Answer 11

• Reducing agents

• In an electrochemical series, species on right are reducing agents
• They can only reduce species on left with higher Ecell values

• Oxidising agents

• Species on left are oxidising agents
• They can only oxidise species on right with lower Ecell values
• Use to figure out if species can be reduced or oxidised