A) What missing condition is needed for the reaction? b) Write the chemical equation for the reaction. c) What gas is burnt at Y and why? 9. a) What do CFC's stand for? b) What is one effect of CFC's

8. a) The missing condition is heat. The reaction between hydrogen gas and iron oxide requires heating.

8. b) The chemical equation for the reaction taking place in the combustion tube (assuming iron(III) oxide) is:

$$Fe_2O_3(s) + 3H_2(g) \xrightarrow{\text{heat}} 2Fe(s) + 3H_2O(g)$$

8. c) The gas being burnt at point Y is excess hydrogen gas. It is burnt to prevent an explosion, as hydrogen is highly flammable and explosive when mixed with air.

9. a) CFC's stands for Chlorofluorocarbons.

9. b) One effect of the use of CFC's to the environment is the depletion of the ozone layer, which leads to increased ultraviolet (UV) radiation reaching the Earth's surface.

10. a) Considering the elements sodium, Aluminium, Silicon, and Sulphur, Sulphur will form an oxide that will give a pH of less than 7 while in solution. Sulphur oxides ($SO_2$, $SO_3$) are acidic.

10. b) Many cooking pans are made of aluminium though it is a reactive metal because aluminium forms a thin, tough, and unreactive layer of aluminium oxide ($Al_2O_3$) on its surface when exposed to air. This oxide layer protects the underlying aluminium from further corrosion and reaction with food.

10. c) It is not advisable to wash utensils made of aluminium with ash because ash contains alkaline substances. Aluminium oxide, which forms a protective layer on aluminium, is amphoteric and reacts with strong bases (like those in ash), causing the protective layer to dissolve and exposing the aluminium to corrosion.