DM.4

Question 1

What do redox reactions involve?

Answer 1

Electron transfer.

Question 2

What is an equation called when spectator ions are removed from the overall equation of the reaction?

Answer 2

It is now an ionic equation.

Question 3

What happens in terms of electrons in the oxidation half equation?

Answer 3

Electrons are produced.

Question 4

What happens in terms of electrons in the reduction half equation?

Answer 4

Electrons are accepted/used up.

Question 5

When is something an oxidising agent?

Answer 5

When it accepts electrons to aid the oxidation of another substance. It is reduced itself.

Question 6

When is something a reducing agent?

Answer 6

When it produces electrons to aid the reduction of another substance. It is oxidised itself.

Question 7

What are two parts of an electrochemical cell, where one is accepting electrons and one is producing electrons, individually known as?

Answer 7

Half cells.

Question 8

Are individual half equations reversible?

Answer 8

Yes, electrons can be lost or gained, it just depends on what they’re reacting with?

Question 9

When two half cells are combined, what is it called?

Answer 9

A full electrochemical cell.

Question 10

What does the voltage measure?

Answer 10

The potential difference between the negative and positive terminals.

Question 11

What is E cell the value of?

Answer 11

The potential difference of the cell when no current flows.

Question 12

What happens to the voltage when a higher current is drawn?

Answer 12

The voltage would decrease.

Question 13

What type of voltmeter is used when measuring E cell?

Answer 13

A high-resistance voltmeter. This will record the maximum potential difference between the electrodes of the half cells.

Question 14

How does a half cell have its own potential difference? Using zinc as an example.

Answer 14

Zinc atoms in the solid zinc strip release electrons and form Zn2+ ions. This makes the zinc strip negatively charged relative to the solution of Zn2+ ions. Zn2+ ions in the solution accept electrons and reform Zn atoms. This sets up a dynamic equilibrium, and the position of the equilibrium determines the size of the potential difference.

Question 15

What is the general equilibrium equation for a metal half cell?

Answer 15

M2+(aq) + 2e- —-> M(s)

Question 16

What does the electrode potential of a half cell represent?

Answer 16

Its tendency to be reduced or oxidised.

Question 17

What does a more positive electrode potential mean about the half cell?

Answer 17

It has a greater tendency to be reduced. It is a better oxidising agent.

Question 18

What does a more negative electrode potentail mean about the half cell?

Answer 18

It has a greater tendency to be oxidised. It is a better reducing agent.

Question 19

When two half cells are connected to a make full cell, which terminal is the one with the more positive electrode potential?

Answer 19

Positive terminal, as this half cell has a higher tendency reduced and electrons are gained.

Question 20

When two half cells are connected to make a full cell, which terminal is the one with the more negative electrode potential?

Answer 20

Negative terminal, as this half cell has a higher tendency to be oxidised and electrons are lost.

Question 21

What is used to complete the circuit when the half cells are set up in separate beakers?

Answer 21

A salt bridge between beakers and a metal wire connecting electrode to a voltmeter (high-resistance).

Question 22

What is a salt bridge made of?

Answer 22

It is a strip of filter paper soaked in a saturated potassium nitrate(V) solution.

Question 23

How does the salt bridge complete the circuit?

Answer 23

By the movement of ions, not electrons. The potassium ions and nitrate ions carry the current to allow electrical contact. A salt bridge is sometimes also known as an ion bridge.

Question 24

What half-cell is used as a reference half-cell that all other half cells are measured against?

Answer 24

The standard hydrogen half cell. Also known as the standard hydrogen electrode.

Question 25

What is the standard conditions for the hydrogen half cell?

Answer 25

Concentration of hydrogen [H+(aq)] = 1 moldm-3

Pressure of hydrogen gas 10^5 Pa( 1 atm) and temperature of 298K (which is rtp)

Question 26

What is the half equation of the standard hydrogen half cell?

Answer 26

2H+(aq) + 2e- —> H2(g)

Question 27

What factors will vary the electrode potential of a half cell?

Answer 27

Temperature, concentration/pressure.

Question 28

What are the standard conditions for measuring the standard electrode potential of a half cell?

Answer 28

1 moldm-3 solution.

298K and 10^5 Pa (1 atm) (rtp).

Question 29

What voltage is chosen to define the standard hydrogen half cell’s potential?

Answer 29

0V.

Question 30

What symbol represents the standard electrode potential of a half cell?

Answer 30

E⦵

Question 31

What is the definition of the standard electrode potential of a half cell, E⦵?

Answer 31

The potential difference between the half cell and a standard hydrogen half cell.

Question 32

What electrode can be used when the half cell does not contain metal?

Answer 32

An inert metal electrode like platinum.

Question 33

What is the equation to work out the E cell (the potential difference of the cell as a whole)?

Answer 33

E cell = E⦵reduced - E⦵oxidised

Question 34

What can you use electrode potentials for?

Answer 34

To make predictions about the feasibility of redox reactions.

Question 35

When is a redox reaction feasible?

Answer 35

When the E cell value is positive.

Question 36

If the redox reaction is predicted to be feasible, but nothing seems to happen, what might be the reason for this?

Answer 36

The rate of the redox reaction cannot be predicted, therefore although it may be feasible, the rate may be so slow that it essential doesn’t happen at all.

Question 37

If the reaction is feasible but the rate is too slow, what could this mean about the reaction?

Answer 37

It must have a very high activation enthalpy. Adding a catalyst could increase the rate.

Question 38

How can you make a redox reaction that is not feasible under standard condition happen?

Answer 38

Change the conditions.