Electrode Potentials

Question 1

Which metal is more reactive, copper or zinc?

Answer 1

zinc

Question 2

What is the reactivity series?

Answer 2

K, Na, Li, Ca, Mg, Al, Zn, Fe, Cu, Ag, Au

Question 3

What would happen in the reaction between copper sulphate (III) and zinc

Answer 3

Zn metal would disappear
Cu metal would ppt out of solution
Blue colour of Cu2+ would disappear and colourless solution would form

Question 4

Would there be a reaction between zinc (II) sulphate and copper?

Answer 4

No, this reaction would not take place. Zn2+ is not reactive enough (a powerful enough oxidising reagent) to remove the electrons from Cu metal.

Question 5

what is a cell?

Answer 5

An electrochemical cell, or voltaic cell, allows the transfer of electrons to be
‘captured’ in an electrical circu

Question 6

Why do electrons flow from left to right in a cell built from the reaction of copper (II) sulphate and zinc

Answer 6

zinc electrode is more negative than the copper and so electrons flow from
left to right on this diagram.

Question 7

What are the types of half cell?

Answer 7

Metal Electrode & Metal Ions
Platinum Electrode & Metal Ions
Platinum Electrode, Ions in acid solution
Platinum Electrode & Gas System

Question 8

When labelling the gas on a pt electrode and gas system, what must I include?

Answer 8

gas pressure

Question 9

What is an example of metal electrode and metal ions?

Answer 9

Fe2+ + 2 e− → Fe

Question 10

What is an example of pt electrode and metal ions?

Answer 10

Fe3+ + e− → Fe2+

Question 11

What is an example of pt electrode, ions in acidic solution?

Answer 11

MnO4− + 8 H+ + 2 e− → Mn2+ + 4 H2O

Question 12

What is an example of Platinum Electrode & Gas System?

Answer 12

Cl2 + 2e− → 2Cl−

Question 13

What does a half cell represent?

Answer 13

represents the half-equation in a redox reaction

Question 14

what does a full cell represent?

Answer 14

A cell, the combination of
two half-cells, represent the full redox reaction.

Question 15

What is ONE ROPE?

Answer 15

-oxidation positive electrode
-reduction on negative electrode

Question 16

What does the standard hydrogen electrode do?

Answer 16

standard allows measurement of the oxidising or reducing ability of each
different system

Question 17

What is happening at the standard hydrogen electrode?

Answer 17

As the hydrogen gas flows over the porous platinum, an equilibrium is
set up between hydrogen molecules and hydrogen ions in solution.
Platinum provides a surface for this reaction to happen

Question 18

What are the standard conditions for the standard hydrogen electrode?

Answer 18

-The position of any equilibrium can be changed by changing conditions. That means that the conditions must be standardised so that you can make fair comparisons.
• The gas pressure is 100 kPa
• The temperature is 298 K (25°C).
• All ions concentrations are taken as being 1 mol dm−3

Question 19

when are pt electrodes used?

Answer 19

when you cannot make an electrode (an electrically conducting solid) out of one of the species involved in the half equation

Question 20

What is the salt bridge includes to do?

Answer 20

– to complete the electrical circuit, without introducing any more metal into the system.

Question 21

what does a salt bridge look like?

Answer 21

It is a glass tube filled with an electrolyte like potassium nitrate solution (usually more of a paste).

Question 22

why are the ends of a salt bridge stoppers by bits of cotton wool?

Answer 22

stops too much mixing of the contents of the salt bridge with the contents
of the two beakers.

Question 23

how is the electrolyte in a salt bridge chosen?

Answer 23

The electrolyte in the salt bridge is chosen so that it does not react with
the contents of either beaker. This allows a beaker to remain neutral.

Question 24

What is standard electrode potential?

Answer 24

The voltage measured when the named electrode is connected to the standard hydrogen electrode, at 298 K under 100 kPa with solutions of 1.00 moldm−3.

Question 25

What do cells and half cells respond to?

Answer 25

are at equilibria and respond to le Chatelier’s principle- Decreasing the concentration of a species on the left-hand side of the reduction half-equation will make the electrode potential less positive

Question 26

What must I know?

Answer 26

• For metals and their ions, the metal is the electrode • For non-metals that are gases, we use the half-cell for gases with a platinum electrode • For ions of the same element we use a mixture of the ions (sometimes in acidic conditions) in the same beaker, at standard concentrations, with a platinum electrode.

Question 27

What does a more the positive value mean?

Answer 27

the more likely that reaction is to go from left to right,

Question 28

What does the more negative the value mean?

Answer 28

more likely it is to go from right to left. a

Question 29

where is the strongest oxidising agent found?

Answer 29

on the LHS of the most +ve SEP half equation.

Question 30

where is the strongest oxidising agent found?

Answer 30

The strongest reducing agent is found on the RHS of the most -ve SEP half equation

Question 31

What way will the equilibrium with the more negative E value move?

Answer 31

to the left

Question 32

What way will the equilibrium with the more positive E value move?

Answer 32

right

Question 33

how can we work out the cell reaction and cell potential?

Answer 33

by: • more positive - less positive • adding the two standard electrode potentials • work out the overall reaction by combining the two half equations.

Question 34

what role doesn’t apply when working out if a reaction is feasible?

Answer 34

more positive take less negative

Question 35

If a reaction is found to be feasible, why does it not necessarily mean that the reaction takes place?

Answer 35

-some reactions have a very large activation energy and therefore there will be a very slow rate of reaction. –the calculations above are based on data obtained under standard conditions. If, for example, the concentration of a reactant is not 1 moldm−3, then the half-cell potential will be different. Also, some reactions do not take place in aqueous solutions and may need a solvent that is not water.

Question 36

(check notes) x 2

Question 37

How do you know which is the strongest reducing agent?

Answer 37

• Eθ for forward reaction is least positive • Reverse reaction (oxidation) more likely to occur

Question 38

why does is cobalt (III) more stable in ammonia than in water?

Answer 38

• Ammonia is a stronger ligand than water • Ammonia is a stronger base • Ammonia can donate its lone pair more easily.

Question 39

how do you measure a standard cell potential?

Answer 39

-Prepare two standard half cells. Think about the contents of each half cell – reacting ions should have concentrations of 1 moldm−3, gases pressures of 100 kPa, temperature should be 298K. Do you need a platinum electrode? -Connect the electrodes of the half cells to a voltmeter using wires. -Prepare a salt bridge by soaking a piece of filter paper in aqueous KNO3. -Connect the two solutions of the half cells with a salt bridge. -Record the standard cell potential from the voltmeter.

Question 40

when does the overall equation of an electrochemicals occur?

Answer 40

when the cell is discharging

Question 41

What are single use cells sometimes called?

Answer 41

primary cells

Question 42

what are cells that can be recharged sometimes called?

Answer 42

Secondary cells

Question 43

what happens when a rechargeable battery is charging?

Answer 43

voltage is applied to reverse any chemical change that has taken place whilst the battery was discharging. This is called charging or recharging

Question 44

what is the definition of a fuel cell?

Answer 44

A fuel cell uses the energy generated from the reaction between a fuel and oxygen to create a voltage.

Question 45

(check notes)