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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
Pt electrode

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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
What is an oxidising agent
A species which gains electrons
26
What is a reducing agent
A species which looses electrons
27
What is reduction
The gain of electrons
28
What is oxidation
The loss of electrons
29
In an electrochemical series, which species is the strongest oxidising agent
The most POSITIVE species on the LEFT hand side OAPL (Opal - this acronym is a gem)
30
In an electrochemical series, which species is the strongest reducing agent
The most NEGATIVE species on the RIGHT hand side RANR
31
What is the equation for E°cell
E°cell = R - L E° of what is going right (reduction) minus E° of what is going left (oxidation)
32
In cell notation, which half cell goes left of the salt bridge
The more negative one (Positive Right)(PR)
33
Which species goes closest to the salt bridge in cell notation
Species with the highest oxidation state
34
How do we separate species in cell notation of different states
Solid line
35
How do we separate species in cell notation of same states
Comma
36
When and where do we write Pt in cell notation
If there is no solid metal, we use Pt and put it at the very end furthest from the salt bridge
37
What does a positive E°cell mean in terms of feasibility
Reaction is feasible
38
What does a negative E°cell mean in terms of feasibility
Reaction not feasible (requires energy)
39
What are the 2 main forms of batteries
Rechargeable Non rechargeable
40
What are the components of a lithium ion battery
Electrode A - Lithium cobalt oxide (LiCoO2) Electrode B - Graphite (C) Electrolyte - Lithium salt dissolved in an organic solvent
41
What is the purpose of the electrolyte in a battery
Acts as a conductive pathway for ions to move from one electrode to another
42
How do we identify which electrode is the negative electrode in a battery
Must establish which electrode is undergoing electrons
43
Which electrode is the anode
The side of the half cell undergoing oxidation
44
Which electrode is the cathode
The side of the half cell undergoing reduction
45
What is the equation for the reaction occurring at the anode in a lithium ion battery
Li → Li+ + e–
46
What is the equation for the reaction occurring at the cathode in a lithium ion battery
Li+ + CoO2 + e– → Li+ [CoO2]–
47
What is the overall equation of discharge of a lithium ion battery
(Combining two half equation) Li + CoO2 <---> Li+[CoO2]-
48
What is the equation of recharge of a battery
The opposite of discharge equation
49
Describe the feasibility of discharge of a lithium ion battery
Feasible since E°cell is positive
50
Why are lithium ion battery good at powering electronics
Significant potential difference Need a lot of power for phones laptops etc
51
What is the main difference between a fuel cell and a battery
Electricity is generated by a continuous external supply of chemicals rather than a ready store like in batteries
52
What is the middle part of a hydrogen oxygen fuel cell
The electrolyte
53
What is the electrolyte in a hydrogen oxygen fuel cell
KOH solution
54
What is the purpose of the electrolyte in a hydrogen oxygen fuel cell
Carries OH- ions from the cathode to the anode
55
Which way do electrons flow in a hydrogen oxygen fuel cell
From the anode to the cathode
56
What is the only product in a hydrogen oxygen fuel cell
Water
57
What are platinum electrodes lined with in a hydrogen oxygen fuel cell
Ion exchange membrane
58
What is the purpose of the ion exchange membrane on the platinum electrode in a hydrogen oxygen fuel cell
Allow OH- ions to pass through but not hydrogen and oxygen gas
59
What is the equation for the reaction at the anode in a hydrogen oxygen fuel cell in basic conditions
H2(g) + 2OH-(aq) --> 2H2O(l) + 2e-
60
What is the equation for the reaction at the cathode in a hydrogen oxygen fuel cell in basic conditions
02(g) + 2H2O(l) + 4e- ----> 4OH-(aq)
61
What is the overall reaction occurring in a hydrogen oxygen fuel cell
2H2(g) + O2(g) ---> 2H2O(g)
62
What are 4 advantages of fuel cells
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)
63
Give 3 disadvantages of fuel cells
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)
64
What type of reaction occurs at the anode
Oxidation (No problem, negative oxidation)
65
What type of reaction occurs at the cathode
Reduction (No Problem, Positive reduction)
66
How does a salt bridge provide an electrical connection between two half cells
Ions can move freely through it
67
What is the equation for the reaction at the cathode in a hydrogen oxygen fuel cell in acidic conditions
1/2O2 + 2H+ + 2e- —> H2O
68
What is the equation for the reaction at the anode in a hydrogen oxygen fuel cell in acidic conditions
H2 —> 2H+ +2e-
69
Sketch a hydrogen oxygen fuel cell stating what occurs at each stage
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.
70
What is the equation of the reaction occurring at the anode when measuring electrode potentials using the SHE
H2 ---> 2H+ + 2e-

Chemistry (Physical) (13 decks)

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