1. 1
   A student investigates simple cells for a science fair, dipping pairs of different metal electrodes into copper sulfate solution and connecting them with a wire and voltmeter. The metals tested are magnesium, zinc, iron and copper, and the reactivity order is magnesium > zinc > iron > copper.

   (a)

   Based on this reactivity order, which pair of electrodes would be expected to produce the highest voltage?

   [1 mark]

   • AMagnesium and copper
   • BZinc and copper
   • CIron and copper
   • DCopper and copper

   (b)

   What voltage would the student expect to measure if both electrodes in the cell were made of copper?

   [1 mark]

   • AA very high voltage
   • BA negative voltage
   • CApproximately zero volts
   • DA voltage that increases over time

   (c)

   Explain why the voltage produced by a simple cell depends on the difference in reactivity between the two electrode metals used.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A toy manufacturer compares non-rechargeable alkaline batteries with rechargeable nickel-metal-hydride batteries for use in a remote-control car, connecting several cells together to power the motor.

   (a)

   What is a battery, in terms of its components?

   [1 mark]

   • AA single electrode dipped in an electrolyte
   • BTwo or more cells connected together, usually in series
   • CAn electrolyte solution with no electrodes
   • DA single wire connecting two containers of electrolyte

   (b)

   What happens inside a non-rechargeable cell in the remote-control car once one of the reactants has been completely used up?

   [1 mark]

   • AThe cell recharges itself from the surrounding air
   • BThe chemical reaction automatically reverses
   • CThe voltage produced increases sharply
   • DThe chemical reaction stops and the cell can no longer supply useful current

   (c)

   Explain what happens inside the rechargeable nickel-metal-hydride battery when it is connected to an external electrical supply, and explain how this differs from what happens in the non-rechargeable battery.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A city transport authority trials hydrogen fuel cell buses alongside battery-electric buses. Each fuel cell bus is refuelled with hydrogen gas at a depot and draws oxygen from the surrounding air.

   (a)

   Describe how a hydrogen fuel cell produces electricity, referring to the reactants supplied to the cell and the overall chemical reaction taking place.

   [3 marks]

   (b)

   Evaluate the use of hydrogen fuel cells compared with rechargeable batteries for powering the buses, giving one advantage and one disadvantage of each.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An engineering student researching hydrogen fuel cell vehicles for a university project models the reactions occurring at each electrode inside an acidic hydrogen fuel cell, and compares fuel cells with other power sources for road vehicles.

   (a)

   Write balanced half equations for the reaction at the negative electrode (where hydrogen is oxidised) and the reaction at the positive electrode (where oxygen is reduced), and show how these combine to give the overall equation for the reaction of hydrogen with oxygen.

   [6 marks]

   (b)

   The student then evaluates hydrogen fuel cells against rechargeable batteries as a power source for road vehicles more generally. Discuss the environmental impact, refuelling or recharging time, and supporting infrastructure of each technology, and reach a justified conclusion about which is currently more practical for widespread use.

   [6 marks]

   Total for question 4: 12 marks

End of questions