QUESTION 1

a. Which key term best matches with the following statements or definitions

(i) The temperature at which a substance changes from the liquid to the gas phase

(ii) A pure substance that cannot be broken down into simpler substances

(iii) A process that can be used to separate an insoluble solid from a liquid

(iv) Weak induced dipole-induced dipole forces of attraction between molecules

(v) The tendency of atoms to attract electrons to themselves in a chemical bond

(vi) The number of protons present in an atom of an element

(vii) The process whereby a gas turns into a liquid

(viii) The number of atoms present in one mole of an element

(ix) The process whereby a chemical reaction is driven by the use of an electric current

(x) Atoms of the same element having the same atomic number but different mass numbers

b. Give a full description of the basic structure of an atom

QUESTION 2

a. Aluminium metal does not exist as the elemental metal in nature. It exists as compounds found in ores. Bauxite is the most common ore of aluminium

After bauxite is mined it is heated under high temperature and pressure in aqueous sodium hydroxide. This forms a mixture of red mud (impurity) and water-soluble gibbsite. The red mud is removed from the mixture and the remaining gibbsite is cooled until solid particles form. These particles are then separated from the liquid and heated to form molten aluminium oxide ( ). The final step is the breaking apart of the by electricity to obtain liquid aluminium metal and oxygen gas. Al₂O₃. Al₂O₃

(i) Name and briefly describe two techniques by which the red mud impurity can be removed from the gibbsite/mud mixture.

(ii) Give the name of the process by which solid gibbsite is obtained from the water soluble gibbsite

(iii) Write a balanced equation for the electrolysis of aluminium oxide

(iv) How would you test for the gas liberated during the electrolysis step? What would you observe?

(v) Is it easier to separate the red mud from the aqueous solution of gibbsite than it is to separate the oxygen and aluminium from the molten aluminium oxide? Justify your answer

b. Aluminium is often preferred to iron for use because it is said to be ‘corrosion-free'. Explain how aluminium resists to corrosion

c. Which property of aluminium makes it suitable for the manufacture of aircrafts?

d. Give one reason why aluminium is commonly recycled?