A) Identify the cell shown above.

Here are the answers to the questions regarding the extraction of aluminum:

a) Identify the cell shown above.
The cell shown is a $\boxed{\text{Hall-Héroult cell}}$ or an $\boxed{\text{electrolytic cell for aluminium extraction}}$.

b) Write the formula of the chief ore from which aluminium is extracted.
The chief ore is bauxite, which is primarily aluminium oxide.
Formula: $\boxed{\text{Al}_2\text{O}_3}$

c) Name the impurities which are removed at the purification stage.
The main impurities removed are $\boxed{\text{iron(III) oxide (Fe}_2\text{O}_3\text{) and silicon dioxide (SiO}_2\text{)}}$.

d) Label on the diagram, the anode, the cathode and region containing the electrolyte.

• Anode: The carbon blocks suspended into the molten mixture.
• Cathode: The graphite lining of the steel tank.
• Electrolyte: The molten mixture of aluminium oxide and cryolite. (Please refer to the diagram provided in the question for the exact labeling points. The carbon blocks are the anodes, the outer lining is the cathode, and the molten substance between them is the electrolyte.)

e) The melting point of aluminium oxide is 2054°C but the electrolysis is carried out at a temperature between 800°C-900°C.

(i) Why is the electrolysis is not carried out at 2054°C?
Carrying out the electrolysis at 2054°C would be $\boxed{\text{too expensive due to the extremely high energy costs}}$ required to maintain such a high temperature.

(ii) What is done to lower the temperature?
$\boxed{\text{Cryolite (Na}_3\text{AlF}_6\text{) is added to the aluminium oxide}}$. Cryolite acts as a solvent, lowering the melting point of the mixture to around 800-900°C.

(iii) The aluminium produced is tapped out as liquid. What does this suggest about its boiling point?
This suggests that the $\boxed{\text{boiling point of aluminium is higher than the operating temperature (800-900°C)}}$.

f) In the extraction of aluminium from its ore by use of electrolysis, explain the following observations:

(i) The graphite anode is replaced from time to time.
At the anode, oxygen gas is produced from the electrolysis of aluminium oxide. This hot oxygen reacts with the carbon (graphite) anode to form carbon dioxide gas, causing the anode to be $\boxed{\text{gradually consumed and eroded}}$.

$$\text{C(s)} + \text{O}_2\text{(g)} \rightarrow \text{CO}_2\text{(g)}$$

(ii) The steel tank which can also serve as an electrode is also lined with graphite cathode.
Graphite is used as the cathode lining because it is a $\boxed{\text{good electrical conductor}}$ and is $\boxed{\text{inert (unreactive) to the molten aluminium and the electrolyte}}$.

g) Explain why aluminium is heated before it is electrolyzed.
It is the $\boxed{\text{aluminium oxide (alumina) that is heated to melt it}}$ (or dissolve it in molten cryolite). Aluminium oxide must be in a molten state for its ions ($\text{Al}^{3+}$ and $\text{O}^{2-}$) to be mobile and conduct electricity, allowing electrolysis to occur.