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AQA A-Level Chemistry > Electrochemistry > Flashcards

Electrochemistry Flashcards

1
Q

What is an electrode and how does it work?

4

A
  • Metal dipped in solution of its metal ions
  • equilibrium is set up
  • metal has a tendency to form positive ions and go into solution
  • metal ions have tendency to gain electrons and form metal
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2
Q

What does it mean if the electrode potential equilibrium is left?
Is the electrode potential positive or negative?
Redox?
4

A
  • Metal has a negative charge
  • build up of electrons on metal
  • so negative electrode potential
  • anode is oxidised
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3
Q

What does it mean if the electrode potential equilibrium is right?
Is the electrode potential positive or negative?
Redox?
4

A
  • metal has a positive charge
  • electrons used up to form metal
  • so has positive electrode potential
  • cathode is reduced
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4
Q

What are the standard conditions for half cells?
Conc
Temp
Pressure

A

1.0 moldm-3 of ions involved in the half equation

298K

100kPa (only affects half-cells with gases

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5
Q

What is an electode?

two words

A

Half cell

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6
Q

What is a metal electrode?

1

A

-Metal surrounded by a solution of its ions

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7
Q

What is a gas electrode?

2

A
  • gas with a solution of its ions

- inert metal (which is the actual electrode) for flow of electrons

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8
Q

What is a redox electrode?

2

A
  • two different ions of the same element

- two types present with inert metal electrode

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9
Q

What is the purpose of the salt bridge?

2

A
  • allow ions in ionic solution to flow through

- maintains charge balance/completes circuit

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10
Q

How does salt bridge maintain equilibrium of positive ions?

1

A

there is a build up of positive charge at the anode due to the loss of electrons so negative salt bridge ions are attracted to it which maintains flow of ions

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11
Q

How does salt bridge maintain equilibrium of negative ions?

1

A

ions are being removed at the cathode as they are attracted to electrons so form solid metal, positive salt bridge ions are attracted so maintains flow of ions

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12
Q

Which electrode is traditionally more positive?

Left or right?

A

Right, cathode

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13
Q

How do you measure the electrode potential of a half cell?

3

A
  • Connect with a half-cell of known potential
  • measure potential difference using a high resistance voltmeter
  • this is so potential can be measured under zero-current conditions as no current can be drawn from the cell
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14
Q

What is the SHE?
use?
What is looks like?
3

A

Standard hydrogen electrode

used as primary standard so all potentials are compared to it so it has 0 volts

Pt(s) | H2(g) | H+(aq)

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15
Q

Why are standard conditions needed?

1

A

Position of the redox equilibrium will change with conditions
(remember equilibria)

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16
Q

What is the set up of an electrochemical cell?

3/4

A
  • Two half cells
  • the two metals joined with a wire (e- flow)
  • two solutions joined with salt bridge (flow of ions)
  • voltmeter to measure potential difference (emf)
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17
Q

Which electrode is oxidised and which is reduced?

anode vs cathode

A 
Anode = oxidised
Cathode = reduced
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18
Q

What is emf?
2
including equation

A

Electromotive force

E* Cell = E* right - E* left

(E* = electrode potential under standard conditions)

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19
Q

What is the conventional representation of cells?

1

A

R | O || O | R

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20
Q

What are the | lines and why are they important?

3

A
  • the are phase boundaries
  • use them whenever there is a change in state
  • if none then use comma
21
Q

What does || represent?

A

Salt bridge

22
Q

What does ROOR stand for?

2

A

Reduced, oxidised, oxidised, reduced

-species with highest oxidation state near salt bridge

23
Q

Which electrode is the standard electrode?

right or left?

A

Left

24
Q

Why are standards other than the SHE used sometimes?
What is a secondary standard?
3

A
  • SHE is difficult to use as it involves and gas and is flammable so other standards are used
  • they are calibrated against the SHE and are known as
  • secondary standards
25
Q

What happens at the anode?
Redox
3

A
  • The metal loses electrons so is oxidised to its metal ions
  • these electrons make the electrode negative
  • these electrons travel through the wire to the other electrode, adding to ions to produce metal ions
26
Q

What happens at the cathode?

redox

A
  • The metal ions gain electrons and so are reduced to metal atoms
  • as electrons are used up this makes the electrode positive
27
Q

What is the electrochemical series?

2

A

List of half cell potentials in order of decreasing/increasing potential

compared against SHE

28
Q

What does it mean if an electrode is negative in the electrochemical series?

A

It is worse than Hydrogen at gaining electrons / less reductive / more oxidative

29
Q

What does it mean if an electrode is positive in the electrochemical series?

A

It is better than Hydrogen at gaining electrons / more reductive / less oxidative

30
Q

What are the half equations in the electrochemical series written as? Why
2

A

Reduction half equations

measure of how easily it reduces

31
Q

What are three types of commercial cells?

A
  • Non-rechargeable
  • rechargeable
  • fuel cells
32
Q

What happens in non-rechargeable cells?

2

A
  • The chemicals are used up over time and the emf drops

- once one or more of the chemicals have been used up the cell is flat and emf is 0 volts

33
Q

What happens in rechargeable cells?

2

A
  • the reactions are reversible

- they are reversed by applying an external current and regenerating the chemicals

34
Q

What happens in fuel cells?

2

A
  • have a continuous supply of the chemicals so don’t run out of chemicals and don’t need recharging
  • do need constant supply of chemicals
35
Q

What is an example of a rechargeable cell? what is it used for?

A

Lithium ion

phones, tablets, cameras, laptops etc

36
Q

What is the equation at the positive electrode of a lithium ion cell?
This is also what happens during discharge

A

Li+ + CoO2 + e– → Li+[CoO2]–

37
Q

What is the equation at the negative electrode of a lithium ion cell?
This is also what happens during re-charge

A

Li → Li+ + e–

38
Q

What is an example of a fuel cell?

A

Alkaline Hydrogen Fuel Cell

39
Q

What happens at the anode and cathode of an alkaline hydrogen fuel cell?

A 
Anode = H2 in
cathode = O2 in and H2O out
40
Q

How/where do the ions travel in an alkaline hydrogen fuel cell?
2

A

H+ ions move between electrodes through the electrolyte

electrons move between electrodes through a wire

41
Q

What reaction happens at the anode of an alkaline hydrogen fuel cell? equation

A

H2 + 2OH- –> @H2O + 2e-

42
Q

What reaction happens at the cathode of an alkaline hydrogen fuel cell? equation

A

O2 + 2H2O + 4e- —> 4OH-

43
Q

What is the overall equation for an alkaline hydrogen fuel cell?

A

2H2 + O2 –> 2H2O

44
Q

What the benefits of using non-rechargeable cells?

1

A

Cheap

45
Q

What the risks of using non-rechargeable cells?
1
plus explanation

A

Waste issues

-they leak and corrode and chemicals sink into the soil contaminating ground water

46
Q

What the benefits of using rechargeable cells?

3

A

less waste
cheaper in the long run
lower environmental impact

47
Q

What the risks of using rechargeable cells?
1
plus explanation

A

some waste issues at end of useful life

-they leak and corrode and chemicals sink into the soil contaminating ground water

48
Q

What the benefits of using hydrogen fuel cells?

3

A

only waste product is water
do not need recharging
very efficient- less energy wasted and it converts more of the available energy from hydrogen into kinetic energy than other cells

49
Q

What the risks of using hydrogen fuel cells?

4

A

need constant supply of fuels
hydrogen is flammable and explosive
hydrogen usually made using fossil fuels
high cost of fuel cells

AQA A-Level Chemistry (12 decks)

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