2.7 EXERCISE 2 – Extraction of aluminium, titanium and tungsten

1) Explain why aluminium is not extracted by reaction of its oxide with carbonAluminium is more reactive than carbon and so cannot be displaced by it.

2.Explain why aluminium oxide is dissolved in molten cryolite.

The melting point of pure aluminium oxide is very highdissolving it allows the electrolysis to be carried out at a lower temperature

3 .Write half-equations for the reactions at each electrode, and write an overall equation for the reaction.

Anode : 2O2- O2 + 4e-Cathode : Al3+ + 3e- AlOverall equation : 4Al3+ + 6O2- 3O2 + 4Al

4.State what each electrode is made of.Both electrodes are made of graphite.

5.Explain why the anodes need to be regularly replaced.The graphite reacts with oxygen at the anode.

6. Explain why the elctrolysis of aluminium oxide is expensive. a large amount of energy is required

to supply electricity for the electrolysisand to melt the cryolite

7. Explain why aluminium is recycled although aluminium oxide is in plentiful supply. ( 3 marks )

Expensive electrolysis or lots of electricity needed to extract Al (from Al2O3) (1)

Recycling Al from scrap means only heat needed or requires less energy (1)

Pollution by either no need to dispose of Al scrap (e.g. by landfill)

or less extraction of Al2O3, less holes

or less red mud waste

or A1 or fluoride or cryolite toxicity/health risk (1)

Aluminium oxide is a non-renewable source.

Do not allow cheaper or less expensive 3

8. State two essential conditions used for the electrolytic extraction of aluminium from aluminium oxide.

Molten ( 1 mark ) cryolite , Na3AlF6 (1 mark )

9. Name two impurities contained in bauxite ( aluminium oxide )i) Silicon (IV) oxideii) Iron (III) oxide

9. Explain why titanium dioxide cannot be reduced by electrolysis.Titanium dioxide is not ionic / is a covalent compound - does not contain mobile / free-moving ions.

10. Explain why titanium dioxide cannot be reduced by reaction with carbon (give an equation).

it forms titanium carbide and not pure titanium

11. Explain how titanium dioxide is converted into its chloride (give an equation).

12. Describe two ways in which titanium tetrachloride is reduced to titanium (give two equations).

13. Explain why an atmosphere of argon is required in the reduction process.

14. Explain why this process is so expensive.

15. Write an equation to show how titanium is extracted from its oxide and give the main hazard associated with this process.

16. Give the three main problems normally associated with recycling.