Electrode potentials snd electrochemical cells 3.1.11

Question 1

what is a half cell

Answer 1

One half of an electrochemical cell . they can be constructed of a metal dipped in its ions , or a platinum electrode with 2 aqueous ions

Question 2

what is an inert but electrically conductive electrode commonly used

Answer 2

platinum

Question 3

how is an electrochemical cell created

Answer 3

by joining 2 different half cells together

Question 4

what are electro cells made up of

Answer 4

2 half cells joined by a wire voltmeter and a salt bridge

Question 5

what does a voltmeter do

Answer 5

•Measures voltage between two half cells . Known as the emf
• electrons flow from a more reactive metal to a less reactive one

Question 6

what is a salt bridge made out of

Answer 6

filter paper with potassium nitrate solution

Question 7

what does a salt bridge do

Answer 7

The ions in the ionic substance in the salt bridge move through the salt bridge .
To complete the circuit

Question 8

what does the electrode potential value measure

Answer 8

tells us how easily the half cell gives up electrons ( oxidised )

Question 9

how can you tell which half cell is being reduced or oxidised

Answer 9

Look at the their electrode potential value from the data book

Question 10

what if the electrode potential value is negative

Answer 10

it undergoes oxidation

Question 11

what if the electrode potential value is positive

Answer 11

undergoes reduction

Question 12

what is the standard hydrogen electrode

Answer 12

Is used to as a reference to measure standard electrode potentials

Question 13

what’s the electrode potential value for the standard hydrogen electrode

Answer 13

0.00V

Question 14

what are the general conditions and set ip for the standard hydrogen electrode

Answer 14

• H2(g) in at 298K and 100KPa
• 1 moldm-^3 of Cu2+ ions ( solution)
• 1 moldm-3 of H+ ions (solution)
• Platinum electrode

Question 15

what is the electrochemical series

Answer 15

A list of electrode potentials in numerical order

Question 16

What order can the electrochemical series be in

Answer 16

either ascending or descending order

Question 17

what are oxidising agents

Answer 17

increasing tendency to gain electrons

Question 18

which half cell reactions would be stronger oxidising agents

Answer 18

The ones with a more positive electrode potential

Question 19

if the electrochemical series was in descending order which parts of the half cell reactions would be an oxidising agent or a reducing agent

Answer 19

-agents on the left hand side of the equation are more easily reduce so they are more powerful oxidising agents
- agents in the right hand side of the equation are more easily oxidised so they are more powerful reducing agents

Question 20

what is a reducing agent

Answer 20

They have an increasing tendency to lose electrons

Question 21

what is the equation to work out the cell potential

Answer 21

E cell = E reduced ( most positive) - E oxidised ( most negative )

Question 22

what are cell notations

Answer 22

Used to simplify how we draw the set up of cell . They are the standard way of representing cells in chemistry

Question 23

what’s the general way of writing cell notation

Answer 23

Reduced form | oxidised form | | oxidised form | reduced form
( the most negative half cell potential goes to the left of the double line )

Question 24

what does the solid line in a cell notation represent

Answer 24

Show a physical change in state e.g solid to gas

Question 25

what do double solid lines show in a cell notation

Answer 25

a salt bridge

Question 26

what if there are 2 aqueous ions in a half cell how would you represent that in a cell notation

Answer 26

Separate ions with a comma

Question 27

what can standard electrode potentials be used for

Answer 27

to predict if a stated reaction is likely to proceed under standard conditions

Question 28

what do we do with an oxidation equation

Answer 28

have to reverse it

Question 29

what are the steps to predict feasibility in reactions

Answer 29

1) identify which is being oxidised
2) take the oxidised equation and reverse it. Write two equations next to each other
3) combine the 2 equations to obtain a feasible reaction
4) compare this equation to the reaction stated in the question
5) confirm this by calculated the E cell . All feasible reactions will have a positive E cell value

Question 30

how can you tell if a reaction is feasible

Answer 30

work out E cell.
All feasible reactions will have a positive E cell value

Question 31

what are batteries

Answer 31

electrochemical cells that come in 2 main forms . rechargeable and non- rechargeable

Question 32

what are some features of non rechargeable batteries

Answer 32

• tend to be cheaper than rechargeable batteries.
however rechargeable batteries are reversible and can last longer so cheaper in the long term

Question 33

what are lithium ion batteries

Answer 33

an example of a rechargeable battery.

Question 34

what are lithium ion batteries commonly used in

Answer 34

wireless power tools
tablets
mobile phones
electric cars

Question 35

what are the components of a mobile phone that use a lithium ion cell

Answer 35

Electrode A - lithium cobalt oxide (LiCoO2)
Electrode B - graphite (C)
Electrolyte - Lithium salt dissolved in an organic solvent

Question 36

how do rechargeable batteries work

Answer 36

Plugging them in to supply a current
This current forces electrons to flow in the opposite way
all we do is reverse the overall discharge equation to show a battery recharging it

Question 37

what is a fuel cell

Answer 37

electricity generated by a continuous external supply of chemicals rather than a “ready store” like in batteries

Question 38

what’s an example of a fuel cell

Answer 38

an alkaline hydrogen - oxygen fuel cell

Question 39

what are the stages that happens in an alkaline hydrogen-oxygen fuel cell

Answer 39

1) Hydrogen feed
Hydrogen is fed here. It reacts with OH- ions in solution. The reaction :
2H2(g) + 4OH-(aq) => 4H2O(l) + 4e-
2) Flow of electrons
Electrons produced in reaction 1 travel through a platinum electrode. Platinum is a good conductor of electricity but inert.
3) Component
The flow of electrons is used to power something
4) Oxygen Feed
Oxygen is fed in here. It reacts with water and the 4 electrons made from step 1 to make OH- ions.
The reaction : O2(g) + 2H2O (l) + 4e- => 4OH- (aq)
5) Negative electrode (cathode)
Electrons flow to the negative electrode which is made from platinum
6) Electrolyte
The electrolyte is made from KOH solution . It carries the OH- ions from the cathode to the anode
7) Positive electrode (anode)
Electrons flow from the positive electrode which is made from platinum
8) Water emitted
The product of the reaction in step 1 is released into the surroundings
9) Movement of OH- ions
OH- ions produced from reaction 4 are carried towards the anode via the electrolyte

Question 40

what are Ion exchange membranes in an alkaline hydrogen-oxygen fuel cell

Answer 40

These lines on the platinum electrodes and these allow OH- pins to pass through but NOT hydrogen and oxygen gas

Question 41

what are the reactions taken place in an alkaline hydrogen - oxygen fuel cell

Answer 41

Half equations :
2H2 (g) + 4OH- (aq) => 4H2O(l) + 4e-
O2 (g) + 2H2O(l) + 4e- => 4OH-(aq)

Overall equation :
2H2(g) + O2(g) => 2H2O

Question 42

What are advantages of fuel cells

Answer 42

• more efficient
• more energy is converted into kinetic energy
• fuel cells don’t need to be recharged ~ you just need a ready supply of oxygen and hydrogen
• the only waste product is water and no co2 emitted directly from the cell unlike a combustion engine

Question 43

what are some disadvantages of fuel cells

Answer 43

• hydrogen is highly flammable and must be stored and transported correctly
• It is expensive to transport and store hydrogen. Storage of hydrogen is in pressurised containers
• energy is required to make the hydrogen and oxygen in the first place.
Fossil fuels are generally used to pass water through an electrolysis process. the use of fossil fuels contributes to CO2 emissions

Question 44

EQ : An Emf Value for a commercial lithium-iodine cell is 2.80V
Suggest why this value is different from the value calculated in part (b) (1)

Answer 44

Non - standard conditions

Question 45

Equation for the reaction that occurs at the positive lithium cobalt oxide electrode

Answer 45

Li^+ + CoO2 + e^- => LiCoO2