electrode potentias.

Question 1

pt What is a half cell?

Answer 1

= one half of an eletrochemical cell
= metal dipped into its ions
= platinum electrode with 2 aqeous ions
= electrocgemical cell is joining 2 half cells

Question 1

What do we use for the electrode with 2 aqeous ions?

Answer 1

= inert but electrically conductive electrode
=platinum
=

Question 2

What is an electrochemical cell made from?

Answer 2

= 2half cells- one is undergoing reduction the other oxidation
= wire
= voltmeter
= salt bridge

Question 3

What is the movement of electrons?

Answer 3

= electrons move from a more reavtive metal to a less reactive

Question 4

WHat happens with the oxidation side?

Answer 4

= the metal ion is produced, the electrode becomes thinner as more ion is produced to make electrions
= oxidation is the loss of electrons

Question 5

What happens in the reduction side?

Answer 5

= the metal ion gains electrons to form the metal

Question 6

What is the salt bridge?

Answer 6

= KNO3
= filter paper dipped in solution, ions flow through to balance the charge in the ionic substance
= complete the circuit

Question 7

What is electrode potential:?

Answer 7

= measured in volts
= tells us how easily the half cells gives up electrons, oxidised
= the half cells have reversible reactions
= the forwqards reaction is the reduced form

Question 8

What is the cathode and what is the anode?

Answer 8

= the more negative is the andode- this is oxidised, and on the , the more positibe is the cathode, this is reduced and on the rhs

Question 9

In the electrochemical series what happens as we go up?

Answer 9

= stronger reducing agent as we go up, with descending values
= agents on left are more easilt reduced, so are a better oxidising agent
=

Question 10

In the electrochemical series what happens if we go down?

Answer 10

= stronger reducing agent as we go down, if the values are descending
= agents on the right are moe reasily oxidised,

Question 11

How do we calculate the standard cell potential?

Answer 11

RHS-LHS
= rhs is the agent getting reduced, and lhs is the agent getting oxidised
rhs-lhs

Question 12

What are cell notations?

Answer 12

= draw set up of cell
= standard way of presenting cells
= negative goes on left (anode) and cathode goes on rigt positive
= reduced form l oxidised form l oxidised l reduced
= double lines show the salt bridge

Question 13

What happens if you two have aqeous ions?

Answer 13

= write bith oxidisisng states, wigh comma, and platinum when using 2 non metals

Question 14

How do we predict feasability?

Answer 14

= identify the cathode and anode- whether which one is oxidised and reduced
= oxidised equation is reversed
= combind the equations
= calculate the ecell, all feasible reactions this will be positive

Question 15

What are batteries?

Answer 15

= electrochemical cells, that come in 2 main forms, rechargable and nonrechargable

Question 16

what are non rechargable batteris + key points?

Answer 16

= tend to be cheaper
= reversible, last longer and cheaper in long term
e.g lithium ion batteries
= metals can be reused

Question 17

What is the electrolyte?

Answer 17

= part of the batery that acts as a conductive pathway for ions, to move from one electrode to the other

Question 18

How do rechargable batteries work?

Answer 18

= plugging them into supply a current
= current forces electrons, to flow in opposite direction
= reverse the discharge equation to show battery recharging

Question 19

What are fuel cells?

Answer 19

= electricity is generated, by a continious external supply of chemicals rather than ready store in batteries
= a fuel cell uses energy, from the reaction of a fuel with oxygen to create a voltage

Question 20

For the lithium nattery what are the details?

Answer 20

= Li + CoO2 => Li+[CoO2]-
= Li | Li+ ||Li+, CoO2 |Pt
= reagants in the cell are absorbed, onto powdered graphite, that acts as a support medium
= allows ions to react in the absence of a solvent, such a water
= water would not be a good solvent, react with metal

Question 21

What is the overall equation for a hydrogen fuel cell?

Answer 21

= 2H2 + O2 => 2H2O

Question 22

Why will fuel cells maintain a constant voltage?

Answer 22

= over time maintain a constant voltage
= contionously fed with fresh H2 and O2 so maintaining a constant concentration, of reactants
= differs from ordinary cells, where voltaged drops as reactant concentration drops

Question 23

What conditions do we use for this?

Answer 23

= rate is too slow originally
= high temperature are used, to increase rate of reaction, a higher pressure is used to counteract the fact that e cell falls

Question 24

What are the advantages of fuel cells?

Answer 24

= less pollution = less co2 = greater effieincy

Question 25

What are the limitation of hydrogen fuel cells?

Answer 25

= expensive- Hydrogen is readily available by the electrolysis of water, but this is expensive = storing and transporting hydrogen, = limited lifetime0 require replacements, and hih production costs = use of toxic chemicals in production = hydrogen is explosibe

Question 26

What is the standard hydrogen electrode?

Answer 26

= potentials of all cells are measured by comparing their potential to this = all reactions must be in standard conditions and states

Question 27

What is the hydrogen electrode equalibrian>?

Answer 27

= H2 => 2H+ + 2e- = pt| H2| H+ =

Question 28

What conditions are needed?

Answer 28

= hydrogen gas at 100kpa = solution conaining hydrogen ions 1 mol dm^-3 or hcl = 298k = platinum electrode =

Question 29

What are secondary standards?

Answer 29

= often a different standard is used =

Question 30

WHat will colbalt change to?

Answer 30

= +4 to +3

Question 31

What are the equations for lithium ion cell, reduction?

Answer 31

Li+ + CoO2 +e- => Li+[CoO2]-

Question 32

What is the equation for the lithium ion cell, oxidation?

Answer 32

= Li+ + e- => Li

Question 33

What is the advantage of ethanol fuel cells?

Answer 33

= ethanol can be made from renewable sources-carbon nuetral = raw materials to produce ethanol, by fermination are abundant = less explosive compared to hydrogen,

Question 34

What is an electrochemical series?

Answer 34

= list of electrode potentials in numerical order

Question 35

Why may emf values be different?

Answer 35

= may not be in standard conditions

Question 36

why may a cell leak?

Answer 36

= has reacted, may be oxidised

Question 37

What are the advantages of ethanol fuel cells?

Answer 37

= ethanol can be made from renewable sources, (glucose fermentation), carbon nuetral = ethanol is less explosive, easier to store than hydrogen =

Question 38

What happens at tge oxygen electrode?

Answer 38

4e- + 4H+ + O2 => 2H2O

Question 39

What happens at the ethanol electrode?

Answer 39

= C2H4OH + 3H2o => 2CO2 + 12H+ + 12e-

Question 40

What is the overall equation?

Answer 40

= c2H5OH + 3O2 => 2Co2 + 3H2o

Question 41

What happens to oxygen equation?

Answer 41

= o2 + 4H+ + 4e- => 2H2O

Question 42

why is ethanol carbon nuetral?

Answer 42

= when ethanol is in fermentation, produces co2 and this is used in photosynthesis.

Question 43

For an alkaline hydrogen fuel cell what is the equation for notion?

Answer 43

= Pt|H2(g)|OH– (aq),H2O(l)||O2(g)|H2O(l),OH– (aq)|Pt

Question 44

What is an disadvntage of a fuel cell?

Answer 44

= fossil fuels are used, this contributes to co2 emissions,

Question 45

What is an advantage?

Answer 45

= more efficient than combustion engines = more energ is turned into kinetic energy, o bsution engines wasdte a lot more as thermal energy