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Chemistry > 3.1.11 - Electrochemistry > Flashcards

3.1.11 - Electrochemistry Flashcards

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1
Q

What is the salt bridge made up of in an electrochemical cell?

A

Filter paper soaked in KNO3.

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2
Q

How do you remember what side of the electrochemical cell is negative/positive, oxidation/reduction?

A

LEFT, OXIDATION, NEGATIVE.

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3
Q

In a half cell, if there is no metal, what is the electrode made of?

A

Platinum.

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4
Q

Define ‘standard electrode potential’.

A

The potential of a redox system to lose or gain electrons compared to the standard hydrogen electrode.

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5
Q

Recall standard conditions.

A

All solutions have concentration 1 moldm-3, all gases have pressure 100kPa, temperature 298K, platinum electrode if no metal.

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6
Q

How are reactions written in the electrochemical series?

A

As reductions.

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7
Q

An oxidising agent will oxidise anything that is _____ it in the electrochemical series.

A

Above.

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8
Q

What are the advantages of non-chargeable batteries?

A

Cheaper to buy, work for longer, can be recycled, don’t contain toxic Pb/Cd so less dangerous in landfill.

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9
Q

What are the advantages of rechargeable batteries?

A

Can be reused so cheaper long term, can be recycled, less need to be produced.

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10
Q

What are the negatives of a platinum electrode?

A

Expensive.

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11
Q

How is an electrochemical cell created?

A

By joining 2 different half cells together.

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12
Q

Define Voltmeter.

A

A device used to measure the potential difference between 2 half cells called EMF or an Ecell.

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13
Q

Where do electrons flow in an electrochemical cell?

A

From a more reactive metal to a less reactive one.

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14
Q

What happens to the half cell that undergoes oxidation?

A

Giving electrons, which causes the half cell to become thinner as more electrons are used.

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15
Q

Formula to calculate Electrode motive force (EMF).

A

EMF = ERHS - ELHS.

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16
Q

Why is platinum used as a catalyst?

A

Unreactive, metal - conducts electricity.

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17
Q

What is indicated when an Electrode potential is negative?

A

The species has undergone oxidation.

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18
Q

Explain the process of fuel cells.

A
  1. Hydrogen is fed into the alkaline-hydrogen oxygen fuel cell, forming water and 4 electrons. 2. Electrons travel through the platinum electrode where platinum is chemically inert and a good conductor of electricity. 3. Used to power something e.g. a car. 4. O2 is fed, reacting with 2 lots of water and 4 electrons, forming 4 OH- ions used to react with H2. 5. Negative electrode (cathode) where electrons flow to the negative electrode which is made from platinum. 6. Electrolyte is made from KOH solution carrying OH- ions from cathode to anode. 7. Electrons flow to anode. 8. Water is emitted. 9. OH- ions carried towards electrolyte.
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19
Q

What is the Electrolyte made of in a fuel cell?

A

Electrolyte is made from KOH solution carrying OH- ions from cathode to anode.

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20
Q

Advantages of using a rechargeable cell.

A

Less waste, cheaper in the long run, lower environmental impact.

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21
Q

Define electrochemical series.

A

List of electrode potentials in numerical order.

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22
Q

State the purpose of the salt bridge.

A

The ions in the ionic substance in the salt bridge move through the salt bridge to maintain charge balance / complete the circuit.

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23
Q

What does the Standard Hydrogen electrode consist of?

A

Electrode consisting of hydrogen gas in contact with H+ ions on a platinum surface. The standard conditions for this half cell apply to all other half cells to ensure they can be compared.

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24
Q

Is the SHE an oxidation or reduction?

A

By convention, it must be at a negative electrode.

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25
Q

Define standard electrode potential.

A

The electrode potential of a standard electrode with the ion concentration of 1.00 mol dm-3 at 298 K connected to a Standard Hydrogen Electrode and a high-resistance voltmeter and a salt bridge.

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26
Q

What is the strongest reducing agent?

A

The most negative.

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27
Q

Why can non-rechargeable cells not be recharged?

A

Reaction is not reversible.

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28
Q

Why does zinc in a non-rechargeable cell leak?

A

As zinc is used up to form Zn2+.

29
Q

What does a fuel cell do?

A

A fuel cell is an electric current that converts chemical energy of a REDOX reaction into electrical energy.

30
Q

Advantages and Disadvantages of using a hydrogen fuel cell.

A

Advantages: Only waste product is water. Disadvantages: Hydrogen produced by electrolysis of water and the burning of fossil fuels is needed to produce electricity, producing CO2.

31
Q

Advantages of an Ethanol fuel cell.

A

Higher hydrogen density, made in large quantities, easier to store than hydrogen gas, methanol made from CO2.

32
Q

How does an ethanol fuel cell reduce CO2 emissions?

A

Made from CO2; so reduces the amount of CO2 in the atmosphere.

33
Q

Explain the purpose of a salt bridge.

A

The ions in the ionic substance in the salt bridge move through the salt bridge to maintain charge balance / complete the circuit.

34
Q

Define the term reducing agent.

A

Electron donor.

35
Q

Suggest the function of the porous separator.

A

Allows ions to flow through.

36
Q

What is the alkaline-hydrogen oxygen fuel cell used for?

A

To power vehicles.

37
Q

What do you replace the high resistant voltmeter with?

A

Something like a bulb - allows the current to flow.

38
Q

What is an electrochemical cell?

A

An electrochemical cell consists of two half-cells, each containing a metal electrode and a solution of a salt containing the metal.

39
Q

What is the purpose of a salt bridge in an electrochemical cell?

A

A salt bridge completes the electrical circuit between the two half-cells by allowing ions to move between them, thus maintaining electrical neutrality.

40
Q

Why does a voltage form in electrochemical cells?

A

A voltage forms because there is a difference in the tendency of the metals in the two half-cells to oxidise.

41
Q

Why is a high resistance voltmeter used in measuring the cell potential?

A

A high resistance voltmeter is necessary to prevent current from flowing through it.

42
Q

What happens in the reactions at the electrodes when current is allowed to flow?

A

When current flows, oxidation occurs at the anode and reduction occurs at the cathode.

43
Q

How are electrochemical cells represented diagrammatically?

A

Electrochemical cells are represented by cell diagrams such as ‘Zn(s) | Zn2+ (aq) || Cu2+ (aq) | Cu(s)’.

44
Q

When is a platinum electrode used in cell diagrams?

A

A platinum electrode is used when the system does not include a solid conducting surface.

45
Q

How are electrode potentials measured?

A

Electrode potentials are measured relative to a standard hydrogen electrode (SHE).

46
Q

Describe the standard hydrogen electrode.

A

The standard hydrogen electrode (SHE) consists of a platinum wire coated with platinum black, in contact with 1M HCl and hydrogen gas at 100 kPa.

47
Q

What are standard electrode potentials and how are they expressed?

A

Standard electrode potentials are measured under standard conditions and indicate the voltage of a half-cell relative to the SHE.

48
Q

How does Le Chatelier’s principle apply to changes in Ecell?

A

Le Chatelier’s principle indicates that any change in conditions will shift the equilibrium to oppose the change.

49
Q

What does a more positive Ecell indicate about a cell reaction?

A

A more positive Ecell indicates that the cell reaction is more likely to proceed.

50
Q

What happens to Ecell when current is allowed to flow in a cell?

A

When current flows, it allows the cell reactions to proceed, leading to the consumption of reactants.

51
Q

How does changing reactant and product concentrations affect Ecell?

A

Increasing the concentration of reactants or decreasing the concentration of products will increase Ecell.

52
Q

How does an increase in temperature affect Ecell for exothermic reactions?

A

For exothermic reactions, increasing the temperature decreases Ecell.

53
Q

Explain how rechargeable cells like lead-acid batteries function with respect to Ecell.

A

In rechargeable cells, the forward reaction decreases Ecell by converting chemical energy into electrical energy.

54
Q

Compare the reversibility of non-rechargeable and rechargeable electrochemical cells.

A

Non-rechargeable cells undergo irreversible reactions, while rechargeable cells allow the reactions to reverse.

55
Q

How does altering the concentrations of Fe2+ and Zn2+ affect the Ecell in a zinc-iron cell?

A

Increasing the concentration of Fe2+ and decreasing the concentration of Zn2+ will increase Ecell.

56
Q

What is the electrochemical series?

A

The electrochemical series is a list of elements and compounds arranged by their standard electrode potentials.

57
Q

What are the standard conditions for measuring electrode potentials?

A

Standard conditions include a temperature of 298 K, a concentration of 1 mol dm³ for solutions, and a pressure of 100 kPa for gases.

58
Q

How can you identify the weakest reducing agent from a series of electrode potentials?

A

The weakest reducing agent is the one with the most positive potential.

59
Q

Explain why a redox reaction between two species occurs based on their electrode potentials.

A

A redox reaction occurs when one species can act as an oxidising agent and accept electrons from the other species.

60
Q

How do you calculate the cell EMF from electrode potentials?

A

Calculate the cell EMF by taking the difference between the reduction potential of the cathode and the oxidation potential of the anode.

61
Q

Why might the EMF of a commercial cell differ from calculated values?

A

Differences can arise due to non-standard conditions.

62
Q

What is the function of a salt bridge in an electrochemical cell?

A

The salt bridge maintains electrical neutrality within the internal circuit of the cell.

63
Q

Explain what a metal has a tendency to do when it is dipped into a solution of its ions.

A

Form positive ions and go into solution.

64
Q

What is a half-cell or electrode?

A

A metal dipping into a solution of its ions.

65
Q

State the three types of electrodes.

A
  1. Metal electrode: metal surrounded by a solution of its ions.
66
Q

State the three types of electrodes.

A
  1. Metal electrode: metal surrounded by its ions in solution.
  2. Gas electrode: gas and a solution of its ions. (Pt (s) | H2 (g) | H+ (aq))
  3. Redox electrode: 2 different ions of the same element, where 2 types of ions are present.
67
Q

State the 3 factors that impact the cell potential.

A
  1. Temperature
  2. Pressure
  3. Concentration
68
Q

Explain the benefits and risks of using rechargeable cells.

A

+:
- Less waste
- Cheaper in long run
- Low environmental impact
-:
- Some waste issues at end of life.

Chemistry (18 decks)

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