3.1.11.2 Commercial applications of electrochemical cells Quiz: AQA Chemistry, Unit 1

The 20 questions

1. In a lithium cell, what is the negative electrode reaction?

   • Li+ + CoO2 + e- -> Li+[CoO2]-
   • CoO2 -> Co + O2
   • Li+ + e- -> Li
   • Li -> Li+ + e-

2. In a lithium cell, what is the positive electrode reaction?

   • Li -> Li+ + e-
   • Li+ + CoO2 + e- -> Li+[CoO2]-
   • Li+[CoO2]- -> Li+ + CoO2 + e-
   • 2Li+ + 2e- -> 2Li

3. What is the overall reaction in a lithium cell from the two electrode reactions?

   • Li -> Li+ + CoO2
   • Li + CoO2 -> Li+[CoO2]-
   • Li+ + CoO2 -> Li+[CoO2]-
   • Li + 2CoO2 -> Li+[CoO2]-

4. Which statement describes a fuel cell?

   • A cell that generates an electric current and does not need to be electrically recharged, because its fuel is supplied continuously
   • A cell that stores electricity in a solid form and releases it as heat, so that it can be recharged from a mains supply
   • A cell that must be recharged with electricity after every use, because its electrodes are consumed by the reaction each time
   • A cell that uses a catalyst to produce hydrogen from water without any electrical output at all, and so cannot power a device

5. In an alkaline hydrogen-oxygen fuel cell, what is the electrode reaction at the negative electrode?

   • O2 + 2H2O + 4e- -> 4OH-
   • H2 + 2OH- -> 2H2O + 2e-
   • H2 + 2e- -> 2H-
   • 2H2O + 2e- -> H2 + 2OH-

6. In an alkaline hydrogen-oxygen fuel cell, what is the electrode reaction at the positive electrode?

   • O2 + 2H2O + 4e- -> 4OH-
   • H2 + 2OH- -> 2H2O + 2e-
   • 4OH- -> O2 + 2H2O + 4e-
   • O2 + 4H+ + 4e- -> 2H2O only in acid, so the alkaline form is O2 -> 2O2-

7. What is the overall reaction of the alkaline hydrogen-oxygen fuel cell?

   • 2H2 + 2O2 -> 2H2O2
   • H2 + O2 -> H2O2
   • H2 + O2 -> 2OH-
   • 2H2 + O2 -> 2H2O

8. Which product is the only one formed in the overall reaction of a hydrogen-oxygen fuel cell?

   • Water
   • Hydrogen peroxide
   • Carbon dioxide
   • Hydrogen chloride

9. What does it mean for a cell to be non-rechargeable, or irreversible?

   • The cell reaction produces no electrons, so no current is ever produced by the cell during its normal use at all
   • The cell reaction can be reversed at any time with no energy input at all, so the cell can be recharged by simply waiting
   • The cell reaction uses gases that are continuously pumped through the cell, so it cannot store any chemical energy at all
   • The cell reaction cannot be reversed by applying an external current, so the cell cannot be recharged

10. Which description fits a rechargeable cell?

    • The electrode reactions are not reversible, so the cell becomes useless after one use and must be thrown away at once
    • The electrode reactions can be reversed by applying an external potential, restoring the original reactants
    • The electrode reactions are fed continuously with fuel from an external tank, so the cell never needs any recharging at all
    • The electrode reactions produce only gases that escape into the air, so the cell cannot be used a second time at all

11. Using data given for an alkaline hydrogen-oxygen fuel cell, E(O2/OH-) = +0.40 V and E(H2O/H2, alkaline) = -0.83 V, what is the EMF of the cell?

    • +1.23 V
    • +0.83 V
    • -1.23 V
    • +0.43 V

12. A fuel cell is described as having a benefit to society. Which statement is the most accurate?

    • It produces no electricity at all, but stores heat in a solid form for later use in heating buildings in winter
    • It produces electricity with carbon dioxide as the only product, which can be captured and sold as a cleaning agent later
    • It produces electricity only when it is exposed to strong sunlight, so it is always silent and produces no waste at all
    • It produces electricity with water as the only product at the point of use, which avoids direct carbon dioxide emissions in the cell

13. Which is a risk to society associated with some electrochemical cells?

    • Electrochemical cells require mains electricity to operate at all, which makes them a hazard in a home setting
    • Toxic metals, such as cobalt in lithium cells, can enter the environment if cells are not disposed of safely
    • Electrochemical cells make the air around them more acidic by releasing hydrogen ions into the room air
    • Electrochemical cells release large amounts of carbon dioxide as their only waste, which is the main risk from them

14. In a lithium cell, what is the oxidation state change of lithium at the negative electrode?

    • From +2 to +1
    • From 0 to -1
    • From +1 to 0
    • From 0 to +1

15. Why does a fuel cell need an electrolyte that allows ions to move between the electrodes?

    • To complete the electrical circuit inside the cell, so that the charge balances as electrons flow through the external circuit
    • To act as the fuel, which is consumed in the reaction to produce electricity and must be replaced regularly during use
    • To carry the electrons directly from the negative electrode to the positive one through the solution without the wire
    • To supply the oxygen that is needed for the positive electrode reaction, which is otherwise unable to take place in the cell at all

16. Which statement explains how the electrode reactions of a cell generate an electric current?

    • Electrons released at the negative electrode flow through the external circuit to the positive electrode, where they are used in reduction
    • Electrons are released at the positive electrode and flow to the negative electrode through the electrolyte only
    • The current comes from the salt bridge, which stores electrons until the reaction is complete
    • The current comes from heat released in the electrolyte, which drives electrons along the wire

17. Why is a hydrogen fuel cell described as clean at the point of use, while a whole hydrogen energy system still raises questions?

    • The cell produces carbon monoxide, which is clean at the point of use but dangerous to breathe, and hydrogen cannot be stored at all
    • The cell needs no fuel at all, so the energy system is always net-zero with no further issues to consider in any case
    • The cell produces only hydrogen gas, which is toxic and must be captured in sealed tanks at all times during operation
    • The only product in the cell is water, but making, storing and transporting hydrogen can require substantial energy and raise safety issues

18. In an alkaline hydrogen-oxygen fuel cell, which electrode is the negative electrode, where hydrogen is oxidised?

    • The external wire, which is the only site where oxidation takes place
    • The electrolyte, which carries the electrons back to the hydrogen electrode
    • The hydrogen electrode, where H2 reacts with hydroxide ions to form water
    • The oxygen electrode, where O2 is reduced to hydroxide ions

19. Why is a rechargeable cell more sustainable for consumers than a non-rechargeable cell?

    • It can be used many times, which reduces the number of cells that must be thrown away
    • It runs without any electrode reactions, so it cannot release any metal into the environment
    • It needs no electrolyte, so there is no chemical waste at all
    • It produces a larger EMF than any non-rechargeable cell, so it never needs replacing

20. Why does oxygen gain electrons at the positive electrode of a hydrogen-oxygen fuel cell?

    • It forms a salt bridge that carries electrons between the electrodes
    • It releases electrons into the external circuit, which is oxidised to water
    • It is the fuel, which is consumed and releases electrons into the electrolyte
    • It receives electrons from the external circuit, which is reduced to hydroxide ions with water

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