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Chemistry (Physical) > Electrode potentials and cells > Flashcards

Electrode potentials and cells Flashcards

1
Q

What 2 things can a half cell be constructed of

A

Metal dipped into its ions
Or
Platinum electrode with 2 aqueous ions

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2
Q

Why do we use a platinum electrode

A

Its inert but electrically conductive

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3
Q

What is an electrochemical cell made up of

A

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

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4
Q

What is a voltmeter used for

A

Used to measure the potential difference between 2 half cells

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5
Q

Which way do electrons flow in a cell

A

From a more reactive metal to a less reactive one

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6
Q

What is a common salt bridge

A

Filter paper dipped in KNO3(aq)

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7
Q

What is the purpose of the salt bridge

A

To maintain electrical neutrality/charge balance and allow ions to move between half cells

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8
Q

What must the salt bridge not touch and what must it make contact with

A

Must make contact with solution, but not the metal

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9
Q

What is E°

A

(standard) electrode potential

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10
Q

What is E° measured in

A

Volts

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11
Q

What does E° tell us

A

How easily a half cell gives up electrons (is oxidised)

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12
Q

What is the acronym to find out which half cell is undergoing oxidation/reduction from E° values

A

No Problem

Negative - Oxidation
Positive - Reduction

Most negative - oxidation
Most positive - reduction

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13
Q

Which way is reduction when given a conventional equation and E° values

A

Reduction - Right
RR

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14
Q

Which way is oxidation when given a conventional equation and E° values

A

Oxidation - Left

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15
Q

Which half cell equation do we flip when showing what occurs at each half cell

A

The half cell undergoing oxidation

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16
Q

How are E° values calculated

A

Measured against a reference half cell: The SHE

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17
Q

What are standard conditions

A

298K
100kPa
Concentration of ions at 1moldm-3

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18
Q

What is the SHE

A

Used as a reference to measure E°

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19
Q

What is the E° value of the SHE

A

0.00V

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20
Q

Which side is the SHE electrode always on

A

Left

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21
Q

What are the standard conditions of the SHE

A

H2(g) in at 298K, 100kPa
1moldm-3 of H+ ions

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22
Q

How many moldm-3 of HCl do we need for the SHE

A

1moldm-3

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23
Q

How many moldm-3 of H2SO4 do we need for the SHE

A

0.5moldm-3
(diprotic acids mean only need 0.5 since to H+ ions are produced)

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24
Q

What is the electrochemical series

A

A list of half cell reactions and their E°

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25
Q

What is an oxidising agent

A

A species which gains electrons

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26
Q

What is a reducing agent

A

A species which looses electrons

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27
Q

What is reduction

A

The gain of electrons

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28
Q

What is oxidation

A

The loss of electrons

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29
Q

In an electrochemical series, which species is the strongest oxidising agent

A

The most POSITIVE species on the LEFT hand side
OAPL (Opal - this acronym is a gem)

30
Q

In an electrochemical series, which species is the strongest reducing agent

A

The most NEGATIVE species on the RIGHT hand side
RANR

31
Q

What is the equation for E°cell

A

E°cell = R - L
E° of what is going right (reduction)
minus
E° of what is going left (oxidation)

32
Q

In cell notation, which half cell goes left of the salt bridge

A

The more negative one
(Positive Right)(PR)

33
Q

Which species goes closest to the salt bridge in cell notation

A

Species with the highest oxidation state

34
Q

How do we separate species in cell notation of different states

A

Solid line

35
Q

How do we separate species in cell notation of same states

36
Q

When and where do we write Pt in cell notation

A

If there is no solid metal, we use Pt and put it at the very end furthest from the salt bridge

37
Q

What does a positive E°cell mean in terms of feasibility

A

Reaction is feasible

38
Q

What does a negative E°cell mean in terms of feasibility

A

Reaction not feasible (requires energy)

39
Q

What are the 2 main forms of batteries

A

Rechargeable
Non rechargeable

40
Q

What are the components of a lithium ion battery

A

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

41
Q

What is the purpose of the electrolyte in a battery

A

Acts as a conductive pathway for ions to move from one electrode to another

42
Q

How do we identify which electrode is the negative electrode in a battery

A

Must establish which electrode is undergoing electrons

43
Q

Which electrode is the anode

A

The side of the half cell undergoing oxidation

44
Q

Which electrode is the cathode

A

The side of the half cell undergoing reduction

45
Q

What is the equation for the reaction occurring at the anode in a lithium ion battery

A

Li → Li+ + e–

46
Q

What is the equation for the reaction occurring at the cathode in a lithium ion battery

A

Li+ + CoO2 + e– → Li+ [CoO2]–

47
Q

What is the overall equation of discharge of a lithium ion battery

A

(Combining two half equation)
Li + CoO2 <—> Li+[CoO2]-

48
Q

What is the equation of recharge of a battery

A

The opposite of discharge equation

49
Q

Describe the feasibility of discharge of a lithium ion battery

A

Feasible since E°cell is positive

50
Q

Why are lithium ion battery good at powering electronics

A

Significant potential difference
Need a lot of power for phones laptops etc

51
Q

What is the main difference between a fuel cell and a battery

A

Electricity is generated by a continuous external supply of chemicals rather than a ready store like in batteries

52
Q

What is the equation for the reaction of hydrogen and OH- ions in a hydrogen oxygen fuel cell (reaction 1)

A

2H2(g) + 4OH-(aq) –> 4H2O(l) + 4e-

53
Q

What is the equation for the formation of OH- ions in a hydrogen oxygen fuel cell

A

02(g) + 2H2O(l) + 4e- —-> 4OH-(aq)

54
Q

What is the middle part of a hydrogen oxygen fuel cell

A

The electrolyte

55
Q

What is the electrolyte in a hydrogen oxygen fuel cell

A

KOH solution

56
Q

What is the purpose of the electrolyte in a hydrogen oxygen fuel cell

A

Carries OH- ions from the cathode to the anode

57
Q

Which way do electrons flow in a hydrogen oxygen fuel cell

A

From the anode to the cathode

58
Q

What is the only product in a hydrogen oxygen fuel cell

59
Q

What are platinum electrodes lined with in a hydrogen oxygen fuel cell

A

Ion exchange membrane

60
Q

What is the purpose of the ion exchange membrane on the platinum electrode in a hydrogen oxygen fuel cell

A

Allow OH- ions to pass through but not hydrogen and oxygen gas

61
Q

What is the equation for the reaction at the anode in a hydrogen oxygen fuel cell in basic conditions

A

H2(g) + 2OH-(aq) –> 2H2O(l) + 2e-

62
Q

What is the equation for the reaction at the cathode in a hydrogen oxygen fuel cell in basic conditions

A

02(g) + 2H2O(l) + 4e- —-> 4OH-(aq)

63
Q

What is the overall reaction occurring in a hydrogen oxygen fuel cell

A

2H2(g) + O2(g) —> 2H2O(g)

64
Q

What are 4 advantages of fuel cells

A

More efficient than internal combustion engines in machines (H powered cars)
More energy is converted into Ke (combustion engines waste a lot as thermal energy)
Unlike batteries, fuel cells don’t need to be recharged, just a ready supply of hydrogen and oxygen
The only waste product is water (no CO2 like combustion engines)

65
Q

Give 3 disadvantages of fuel cells

A

Hydrogen is highly flammable
Expensive to store and transport (stored in pressurised containers)
Energy required to make hydrogen and oxygen (fossil fuels generally used to pass water through an electrolysis process)

66
Q

What type of reaction occurs at the anode

A

Oxidation
(No problem, negative oxidation)

67
Q

What type of reaction occurs at the cathode

A

Reduction
(No Problem, Positive reduction)

68
Q

How does a salt bridge provide an electrical connection between two half cells

A

Ions can move freely through it

70
Q

What is the equation for the reaction at the cathode in a hydrogen oxygen fuel cell in acidic conditions

A

1/2O2 + 2H+ + 2e- —> H2O

71
Q

What is the equation for the reaction at the anode in a hydrogen oxygen fuel cell in acidic conditions

A

H2 —> 2H+ +2e-

72
Q

Sketch a hydrogen oxygen fuel cell stating what occurs at each stage

A
  1. Hydrogen feed:
    Hydrogen is fed in here. It reacts with OH- ions in solution in 9 (more on this later). The reaction that occurs is-
    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. E.g. a car
  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 that occurs is-
    02(g) + 2H2O(l) + 4e- → 40H- (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.

Chemistry (Physical) (12 decks)

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