1. 1
   A student sets up a simple chemical cell using a zinc rod and a copper rod, both dipped into a beaker of copper sulfate solution, connected by wires and a voltmeter to a small bulb. The bulb glows brightly at first, but after several hours it dims and eventually goes out, even though both metal rods are still present in the solution.

   (a)

   What is the main reason the cell stops producing a useful voltage?

   [1 mark]

   • AThe wires connecting the cell to the bulb corrode
   • BThe copper sulfate solution evaporates completely
   • COne of the reactants (the zinc metal) is gradually used up as the reaction proceeds
   • DThe voltmeter runs out of battery power

   (b)

   In this chemical cell, which process occurs at the zinc electrode as the cell produces its voltage?

   [1 mark]

   • AZinc ions gain electrons and form zinc atoms
   • BZinc atoms lose electrons and form zinc ions
   • CCopper atoms are deposited directly onto the zinc rod
   • DWater molecules are split into hydrogen and oxygen

   (c)

   Explain, in terms of the reaction taking place, why the voltage produced by this cell decreases over time and eventually reaches zero.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An engineer tests a hydrogen–oxygen fuel cell in which hydrogen gas and oxygen gas are continuously fed into separate sides of the cell to generate electricity, powering a small motor for as long as the gas supply lasts.

   (a)

   What is the only substance produced at the outlet of this fuel cell?

   [1 mark]

   • ASulfur dioxide
   • BCarbon dioxide
   • CWater
   • DHydrogen peroxide

   (b)

   The engineer notices that, unlike the earlier zinc–copper cell, this fuel cell keeps powering the motor at a steady voltage for as long as she runs the experiment. What is the main reason for this difference?

   [1 mark]

   • AThe fuel cell stores a very large reserve of electricity inside its casing
   • BThe fuel cell does not involve a chemical reaction, so nothing is consumed
   • CThe fuel cell generates electricity from heat rather than from a reaction between substances
   • DThe fuel cell is continuously supplied with fresh hydrogen and oxygen, so the reactants are not used up in the way a sealed chemical cell's reactants are

   (c)

   Explain why this fuel cell can continue producing a steady voltage for as long as the experiment runs, whereas the zinc–copper chemical cell described earlier gradually loses its voltage.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A delivery company is comparing hydrogen fuel cell vans with diesel vans for its local delivery fleet.

   (a)

   Give three strengths of using hydrogen fuel cells instead of diesel engines for these vans.

   [3 marks]

   (b)

   Give four weaknesses the delivery company should consider before switching its diesel vans to hydrogen fuel cell vans.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A city bus company is deciding whether to replace its ageing diesel bus fleet with hydrogen fuel cell buses.

   (a)

   Discuss the environmental benefits and environmental drawbacks of making this switch.

   [6 marks]

   (b)

   Beyond the environmental issues, discuss the practical and economic considerations the bus company should weigh up before switching its diesel fleet to hydrogen fuel cell buses.

   [6 marks]

   Total for question 4: 12 marks

End of questions