DM - Electrode potentials

Question 1

What are electrode potentials measured against?

Answer 1

Standard hydrogen electrodes.

Question 2

What is the standard electrode potential of a half-cell?

Answer 2

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

Question 3

What are standard conditions?

Answer 3

1) Any solutions must have a concentration of 1.00 mol dm^-3.
2) Temperature must be 298K (25 degrees).
3) Pressure must be 100kPa.

Question 4

Which side is the hydrogen electrode always shown on?

Answer 4

The left.

Question 5

What is the value of the standard hydrogen electrode half-cell?

Answer 5

0.00V

Question 6

What does the reading of 0.00V on the standard hydrogen electrode half-cell mean?

Answer 6

The voltage reading (whether it is positive or negative) will be equal to the standard electrode potential of the other half-cell (as the standard hydrogen electrode is 0.00V)

Question 7

Whether the voltage reading is positive or negative depends on what?

Answer 7

Depends on which way the electrons flow.

Question 8

What can you use standard electrode potentials to do?

Answer 8

Calculate the cell potential of an electrochemical cell.

Question 9

Will the cell potential always be a positive or negative voltage?

Answer 9

Positive voltage

Question 10

Why will the cell potential always be a positive voltage?

Answer 10

Because the more negative standard electrode potential value is being subtracted from the more positive standard electrode potential value.

Question 11

What sort of standard electrode potential do reactive metals have?

Answer 11

Large negative electrode potentials.

Question 12

Why do more reactive metals have more negative standard electrode potentials?

Answer 12

Because the more reactive a metal is, the more it wants to lose electrons to form a positive ion.

Question 13

What sort of standard electrode potential do reactive non-metals have?

Answer 13

More positive electrode potentials.

Question 14

Why do more reactive non-metals have more positive standard electrode potentials?

Answer 14

The more reactive a non-metal is, the more it wants to gain electrons to form a negative ion.

Question 15

What is an electrochemical series?

Answer 15

A list of redox equilibria.

Question 16

What does the electrochemical series show?

Answer 16

What is reactive and what isn’t.

Question 17

How is the electrochemical series arranged?

Answer 17

In order of electrode potential. The redox equations with the most negative standard electrode potentials are at the top, and those with the most positive electrode potentials are at the bottom.

Question 18

What does a more positive electrode potential mean?

Answer 18

1) The left-hand substances are more easily reduced.

2) The right-hand substances are more stable.

Question 19

What does a more negative electrode potential mean?

Answer 19

1) The right-hand substances are more easily oxidised.

2) The left-hand substances are more stable.

Question 20

What can you use electrode potentials to predict?

Answer 20

Whether a reaction will happen

Question 21

How do you figure out if a metal will react with the aqueous ions of another metal using electrode potential values? (method)

Answer 21

1) Write the two half equations down as reduction reactions.

2) Look at the standard electrode potentials.
- The half-equation with the more negative electrode potential will move to the left.
- The half-equation with the more positive electrode potential will move to the right.

3) Combine the two half equations.
- If the direction of this redox reaction matches the reaction described in the question, it is feasible.
- If the correct ions are reacting together it is also feasible.

Question 22

What does a prediction using standard electrodes only state?

Answer 22

Only states if a reaction is possible under standard conditions.

Question 23

When could the prediction using standard electrode potentials be wrong?

Answer 23

If the reaction kinetics are not favourable.

If the conditions are not standard.

Question 24

Why could the prediction using standard electrode potentials be wrong if the reaction kinetics are not favourable?

Answer 24

• The rate of reaction may be so slow that the reaction might not appear to happen.
• If a reaction has a high activation energy, this may stop it happening.

Question 25

Why could the prediction using standard electrode potentials be wrong if the conditions are not standard?

Answer 25

Changing the concentration (or temperature) of the solution can cause the electrode potential to change.

• The shifting of the equilibrium may either reduce the ease of electron loss so an electrode becomes less negative and the whole cell potential decrease, or, it may increase the ease of electron gain so an electrode becomes more positive and the whole cell potential will be higher.