Question

Answer the following question:
Carbon cannot reduce the oxides of sodium, magnesium, and aluminum to their respective metals. Why? Where are these metals placed in the reactivity series? How are these metals obtained from their ores? Take an example to explain the process of extraction along with chemical equations.

Answer 1

Oxides of sodium, magnesium and aluminium are very strong oxides as these metal are very reactive metals, but carbon is not a strong reducing agent and hence cannot reduce the reactive metal oxides to metals.

In the reactivity series, sodium, magnesium and aluminium are placed in the upper portion which means these metals are very reactive in nature and carbon is less reactive.
K > Na > Ca > Mg > Al > C > Zn > Fe

Oxides of reactive metals are directly put for electrolytic reduction process to obtain the pure metal.
For the oxide of a reactive metal like aluminium oxide, as the metal is already in its oxide state so, it is directly put for the electrolytic reduction process. In this process, graphite electrodes are used as anode and cathode in the electrolytic chamber. The pure aluminium is attracted to the cathode, which is a lining of graphite. The oxygen is attracted to the anode, and bubbles through the solution. 
Cathode reaction: at cathode reduction of aluminium takes place and thus aluminium is discharged at the cathode.

\[\ce{Al^3+ + 3e- -> Al}\]

Anode reaction: at anode oxidation takes place and oxygen gas is evolved.

\[\ce{2O^2- -> O2 + 4e-}\]