Electrode potentials and electrochemical cells

Question 1

What is a half-cell?

Answer 1

it is one half of an electrochemical cell.

Question 2

How can a half cell be made?

Answer 2

They can be constructed of a metal dipped in it ions or a platinum electrode with 2 aqueous ions.

Question 3

What is a half cell?

Answer 3

One half of an electrochemical cell.

Question 4

How can a half cell be constructed?

Answer 4

They can be constructed of a metal dipped in its ions/ platinum electrode with 2 aqueous ions.

Question 5

What is used in a half cell which has 2 aqueous ions?

Answer 5

An inert but electrically conductive electrode. - Platinum is commonly used.

Question 6

How is an electrochemical cell created?

Answer 6

By joining 2 different half cells together joined by a wire, voltmeter and a salt bridge.

Question 7

What type of reaction is essentially occurring in an electrochemical cell?

Answer 7

A redox reaction

as one half cell undergoes reduction.

and the other half cell undergoes oxidation.

Question 8

What is the use of the voltmeter in an electrochemical cell?

Answer 8

To measure the voltage between 2 half cells.

This is called EMF or Ecell

Question 9

What is the direction that electrons flow?

Answer 9

from a more reactive metal to a less reactive one/

Question 10

How does the size of the electrode change according to what redox is occurring?

Answer 10

oxidation- thinner due to loss of electrons

reduction- thicker due to gain of electrons

Question 11

What is the purpose of a salt bridge?

Answer 11

To complete the circuit

Question 12

What is an electrode potential of a half cell?

Answer 12

Each half cell has an electrode potential value which is measured in volts. It tells us how easily the half cell gives up the electrons (oxidised)

Question 13

What form are the equations written in for electrochemical cells?

Answer 13

the reduced form , this means we always show e- behind arrow

Question 14

‘NO PRoblem’ eunomic

Answer 14

The most Negative half cell will undergo Oxidation

The most Positive half cell will undergo Reduction

Question 15

What do you do to an equation that is undergoing oxidation for the equations displayed in electrochemical series?

Answer 15

You would flip the equation. (e-) on the right hand side of arrow.

Question 16

What is a standard hydrogen electrode (SHE) used for and what is its own electrode potential ?

Answer 16

As a reference to measure standard electrode potentials.

Its electrode potential is 0.00V

Question 17

What are the standard conditions for the set up of a standard hydrogen electrode (SHE)?

Answer 17

• temperature at 298 K

-pressure at 100 KPa

• concentration of ions at
  1 moldm-3

Question 18

what is an electrochemical series?

Answer 18

The electrochemical series is a list of half cell reactions and their standard electrode potentials.

Question 19

What is likely to happen to agents on the left hand side of a half-cell reaction?

Answer 19

reduction AS THESE ARE CONSIDERED OXIDISING AGENTS.

Question 20

What is likely to happen to agents on the RIGHT hand side of a half-cell reaction?

Answer 20

oxidation AS THESE ARE CONSIDERED REDUCING AGENTS

Question 21

What would the strongest oxidising agent be ?

Answer 21

the most positive standard electrode potential

Question 22

What would the strongest reducing agent be

Answer 22

the most negative standard electrode potential

Question 23

How is standard cell potential calculated?

Answer 23

EØCELL= EØReduced- EØoxidised

Question 24

Why is a cell notation used?

Answer 24

They’re used to simplify how we draw the set up of a cell. They are the standard way of representing cells in chemistry.

Question 25

How is a cell notation set up?

Answer 25

Reduced form|oxidised form||Oxidised form |Reduced form

The most negative half cell goes to the left of the double line

solid lines show a physical state change

double lines show a salt bridge

If you have 2 aqueous ions you separate the 2 with a comma and not a line as they are in the same physical state.

Question 26

What do you add the notation if there is no solid on one side?

Answer 26

You add Pt (s) - platinum

Question 27

How can standard electrode potentials be used to predict if a stated reaction is likely to proceed under standard conditions?

Answer 27

1) identify what is being oxidised and flip this equation

2) combine both equations indicated by question to obtain ‘feasible’ reaction (cancel out electrons)

3) if change occurs in reaction it suggests reaction is feasible

• you can check your answer by using SCP equation - if reaction is + it means reaction is feasible

Question 28

What are the 2 main forms that electrochemical cells come in and the difference?

Answer 28

Rechargeable
- Reversible and can last longer so cheaper in the long termm.

Non-rechargeable
- cheaper to get initially

Question 29

What is the role of an electrolyte in parts of batteries?

Answer 29

The electrolyte is the part of a battery that acts as a conductive pathway for ions to move from one electrode to another.

Question 30

What are lithium ion batteries?

Answer 30

They are an example of rechargeable battery, commonly used in mobile phones, electric cars and wireless power tools.

Question 30

What electrode produces electrons?

Answer 30

The most negative electrode. (where oxidation is occurring)

Question 31

How do rechargeable batteries work?

Answer 31

They work by simply plugging them in to supply a current.

The current forces electrons to flow the opposite way.

All that is done is the reverse of overall discharge equation to show a batter recharging.

Question 32

What is the difference between fuel cells and batteries?

Answer 32

Fuel cells require a continuous supply of fuel.

Electricity in a fuel cell is generated by a continuous external supply of chemicals rather than a ‘ready store’ like in batteries.

Question 33

What are the steps for an alkaline hydrogen-oxygen fuel cell?

Answer 33

1) Hydrogen feed
Hydrogen is fed into fuel cell.
Hydrogen reacts with oxygen to produce water and electrons.
2H2(g) +40H- –>4h2o(l) + 4e-

2) Flow of electrons
Electrons produced in reaction 1 travel through platinum electrode. (Platinum is a good conductor of electricity but is inert)

3) Component
The flow of electrons are used to power something eg. car

4)Oxygen feed
Oxygen is fed in here and reacts with water and 4 e- made from step one to make 0h- ions.
O2+2h2o +4e- –>4OH-

5) Negative electrode (cathode)
electrons flow to the negative electrode which is made of platinum.

6) Electrolyte
Made of KOH solution which carries OH- ions from cathode to anode

7) positive electrode (anode)
electrons flow from the positive electrode made of platinum to cathode

8)Water emitted
the product from reaction in step 1 is released into surroundings

Question 34

Why is hydrogen fuel cell much cleaner than other fuels?

Answer 34

Only emits water as a by product

Question 35

What are the 2 main steps of fuelling cell reactions?

Answer 35

1) Hydrogen feed

hydrogen is fed here and reacts with OH- ions in solution.

2H2+ + 4OH- –> 4H20 + 4e-

2) Oxygen feed

oxygen is fed here as it reacts with water and 4e- to produce OH- using electrons from step 1.

O2 + 2H20 +4e- –> 4OH-

Question 36

Advantages of hydrogen fuel cell?

Answer 36

fuel cells are more efficient as more energy is converted into kinetic energy energy.

Fuel cells do not have to be recharged you just need a ready supply of oxygen and hydrogen.

Only waste product is water

Question 37

disadvantages of hydrogen fuel cell?

Answer 37

Hydrogen is highly flammable

So is expensive to store and transport correctly

energy is required to make the hydrogen and oxygen in the first place.