electrode potential and electochemical cells

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 own ions or a platinum electrode dipped with 2 aqueous ions

Question 2

why is a platinum electrode used in half cells?

Answer 2

it is inert (chemical inert) and electricallly conductive

Question 3

what are electrochemical cells made off?

Answer 3

2 half cells, voltmeter,salt bridge (filter paper dipped in KNO3), wire

Question 4

what type of reaction happens at an electrochemical

Answer 4

their is a redox reaction

one side is doing a reduction one side is doing oxdation

Question 5

how doe electrons move in an electrochemical cell?

Answer 5

electrons move from the more reactive metal to the less reactive metal

Question 6

what happens to the electrodes as the electrons move?

Answer 6

the electrode that is being oxidised becomes thinner

the electrode that is being reduced becomes thicker

Question 7

What is the electrode potential (E^0)?

Answer 7

It tells us how easily an electrode loses its electrons (oxidised)

Question 8

how does electrode potential oxidation/reduction?

Answer 8

the most negative electrode potential undergoes oxidation

the most positive electrode potential undergoes reduction

Question 9

what is the standard hydrogen electrode?

Answer 9

reference to measure standard electron potential

it is equal to 0.00V

Question 10

what are the standard conditions for electrode potentials?

Answer 10

100kpa
298k
ions conc at 1 mol/dm3

Question 11

What is the difference to get one mole of H+ ions from HCL vs h2so4?

Answer 11

One mole of HCL produces one mole H+ ions

However only 0.5 moles of H2SO4 is needed to make one mole of H+ ions

Question 12

what is a reducing agent?

Answer 12

is the element /compound that donates electrons to the element/compound being reduced

Question 13

what is oxidising agent?

Answer 13

is the element/compound accepting an electron from the element/compound being oxidised

Question 14

what is the best oxidising agent in the electrochemical cell?

Answer 14

the best oxidising agent is the most positive electrode potential
it is only the molecules on the left hand side
Cl2 + 2e–>2cl-
Cl2 is oxidising agent
2cl- has been reduced

Question 15

what is the best reducing agent?

Answer 15

the best reducing agent is the most negative electode potential
it is the molecule on the right hand side?
Mg-> mg2+ + 2e
mg2+ is being oxidised
Mg2is the reducing agent

Question 16

how cab standard cell potential be calculated?

Answer 16

E0cell=E0 reduced -E0 oxidised

Question 17

what is the notation for electrochemical cells?

Answer 17

most negative half cell potential salt bridge more positice half cell potential
reduced form I oxidised form II oxidised form I reduced form

I=change in state
, = no change in state

Question 18

what do you have to do with the oxidised half cell?

Answer 18

flip the equation
e.gMg +2e–>2Mg -
is written as
Mg-> Mg2+ + 2e

Question 19

how can you predict feasibilty of electrochemical cell reactions

Answer 19

take the reduction reaction Cl2 + 2e-> 2cl-
take the oxidation reaction and flip it Mg-> Mg2+ + 2e
combine the reactions Cl2 + Mg ->2cl- + Mg2+
plug in electrode potential into E cell = Ereduced - Eoxidised
if the answer is positive the reaction is feasible under standard conditions

Question 20

what is an electrolyte ?

Answer 20

part of the battery that is conductive and allows ions to move from one electrode to the other

Question 21

describe the lithium ion cell that mobile phones use?

Answer 21

Electrode A- Lithium cobalt oxide LiCoO2
Electrode B-graphite
electrolyte - Lithium salt dissolved in an organic solvent

Question 22

how do batteries discharge

Answer 22

find half equation for reduction Li+ + CoO2 + e ->LiCoO2
flip half equation for oxidation Li -> Li+ + e
combine reactions Li + CoO2 -> LiCoO2
work out the e- cell (it should be positive)

Question 23

how do batteries recharge?

Answer 23

plugging them into a current.
this forces electrons to flow the opposite way
This reverses the original discharge reaction

Question 24

describe how fuel cells work?

Answer 24

1)hydrogen is fed in and reacts with OH- ions in solution (2H2+4OH->4H2O + 4e)
2)Electrons flow through platinum electrode
3)The flow of electrons to the component power something
4)Oxygen is fed on the other side and reacts with the 4e and water to make OH-
(O2 +2H2O + 4e -> 4OH-)
5)Electrons flow to the negative electrode (platinum)
6)the electrolyte (KOH) carries the OH- from the cathode to the anode
7) from the anode they travel around back to the cathode
8)The H2O from step 1 is emitted
9) OH- ions produced are carride towards anode via electrolyte
Ion exchange membranes only allow OH- ions through not O or H

Question 25

in a fuel cell what are the 2 half reactions and full reaction?`

Answer 25

H2 + 2OH- -> 2H2O + 2e- 2H2O + O2 +4e->4OH- 2H2 + O2 ->2H2O

Question 26

advantages of fuel cells?

Answer 26

emits H2O not CO2 like fossil fuels more efficient produced more kinetic energy combustion engines wastes a lot of thermal energy Do not need to be recharged like batteries just a supply of H and O

Question 27

disadvantages of fuel cells?

Answer 27

Hydrogen is flamable so must be stored and transported correctly storage and transportaton of hydrogen is expensive (pressurrised containers) Energy is required in Making pure H and O which usually requires fossil fuels

Question 28

explain the function of salt bridge?

Answer 28

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

Question 29

The aluminium used as the electrode is rubbed with sandpaper prior to use. Suggest the reason for this.

Answer 29

to remove the oxide layer

Question 30

A simple salt bridge can be prepared by dipping a piece of filter paper into potassium carbonate solution. Explain why such a salt bridge would not be suitable for use in this cell.

Answer 30

The carbonate ion can react with acid

Question 31

define standard electrode potential

Answer 31

The emf measured when a metal / metal ion electrode is coupled to a hydrogen electrode under standard conditions is known as the standard electrode potential of that metal / metal ion combination.

Question 32

what is the setup for standard electrode which is measured against hydrogen

Answer 32

Pt|H2|H+||x|x

Question 33

Suggest why the recharging of a lithium cell may lead to release of carbon dioxide into the atmosphere.

Answer 33

The electricity when recharging may come from power stations where fossil fuels are burnt

Question 34

how is current generated in fuel cell?

Answer 34

hydrogen produces electrons | oxygen uses electrons

Question 35

what is the positive and negative electrode?

Answer 35

positive electrode is where the reduction occurs (posiitive e value) cathode negative electrode where the oxidation occurs (negative e value) anode

Question 36

Use data from the table to explain why Au+ ions are not normally found in aqueous solution.

Answer 36

as the e value for Au+ is higher than h2o. H2o will get oxidised

Question 37

in cells what it is the role of electrolyte ?

Answer 37

only allow ions to pass through

Question 38

Suggest why ethanol can be considered to be a carbon-neutral fuel

Answer 38

the Co2 released through its combustion is equal to the co2 a plants takes up in photosynthesis to make it

Question 39

why Fe2+/Fe3+ solutions standard electrode potential measured with platinum electrode?

Answer 39

Fe cannot exist as a pure metal for long as it quickly gets oxidised by oxygen in the air. Platinum is a better aternative as it is inert and less reactive

Question 40

Advantage of fuel cell in internal combustion engine

Answer 40

A fuel cell converts more of the available energy from combustion of hydrogen into kinetic energy of the car / an internal combustion engine wastes more (heat) energy