A school student was asked to explain rusting and how aluminium protects iron, and to label electrodes in an electrolysis experiment.

Here are the answers to your questions:

6. The setup of these three test tubes was used to investigate rusting of iron. Study it and answer the questions that follow:

   • i) Give a reason why rusting did not occur in test tube C. (1mk) Test tube C contains boiled water, which has had dissolved oxygen removed, and anhydrous calcium chloride, which absorbs any remaining moisture. Rusting requires both oxygen and water, so its absence prevents rusting.

   • ii) Aluminium is used to protect iron sheets from rusting. Explain two ways in which aluminium protects iron from rusting. (2mks)

     • 1. Barrier protection: Aluminium forms a tough, impervious layer of aluminium oxide on its surface, which prevents oxygen and water from reaching the iron.
     • 2. Sacrificial protection: Aluminium is more reactive than iron. If the aluminium coating is scratched, the aluminium will corrode preferentially (act as a sacrificial anode) instead of the iron.

7. The diagram below shows an experiment for investigating electrical conduction in lead (II) iodide. Study it and answer the questions that follow:

   • a) On the diagram:

     • i) Label the anode and the cathode. (2mks) (The labels are already correctly marked on the diagram in the image: the electrode connected to the positive terminal of the power source is the anode, and the electrode connected to the negative terminal is the cathode.)

     • ii) Show the direction of movement of electrons. (1mk) (The direction of electron movement in the external circuit is from the negative terminal of the power source to the cathode, and from the anode to the positive terminal of the power source.)