Question

How is the method of extraction of metals, high up in the reactivity series different from that for metals in the middle? Why cannot the same process be applied to them? Name and explain the process of extraction of sodium.

Answer 1

The difference in the extraction process:

• Metals high up in reactivity series generally occur in the form of their oxides which are stable and can't be extracted by reducing the oxides with carbon.
• The metals placed in higher reactivity series can replace the lower metals and from their oxides.
• The middle of the reactivity series occurs in the form of carbonates and sulfides which are first converted into oxides by various processes and then into metals
• The same method cannot be used because of the difference in their reactivity due to which they occur in different forms as ores.
• The method which is used for the extraction of highly reactive metals is the electrolytic reduction and the extraction of moderately reactive metals is calcination or roasting followed by reduction.

Extraction of Sodium($\mathrm{Na}$):

• Sodium($\mathrm{Na}$) is extracted by electrolytic reduction of molten sodium chloride($\mathrm{NaCl}$).
• It is a process by which electrical energy is used to produce a chemical change.
• The electrolysis cell consists of two metallic rods known as electrodes that are connected to a battery and dipped into molten electrolyte or electrolyte solution.
• The electrode connected to the positive side of the battery is called the anode.
• The electrode connected to the negative side of the battery is called the cathode.
• On passing electricity through molten Sodium chloride($\mathrm{NaCl}$), decomposition occurs and Sodium metal($\mathrm{Na}$) and Chlorine gas($\mathrm{Cl}$) are formed.
• The positively charged Sodium ions move toward the cathode and negatively charged Chlorine ions move towards the anode.
• When the Chlorine ions reach the anode, they are discharged through electron removal(oxidation), liberating neutral atoms or molecules at the electrode.
• Sodium ions are neutralized through electron addition(reduction) when they reach the cathode.
• There is a potential difference between the electrode and the electrolyte known as the potential of the electrode.
• ${\mathrm{Na}}^{+}$ ions being cations, therefore they are attracted to the cathode and get deposited there.

Cathode: ${\mathrm{Na}}^{+}+{\mathrm{e}}^{-}\to \mathrm{Na}$

• ${\mathrm{Cl}}^{-}$ ions being anions, therefore they are attracted to the anode and get deposited there.

Anode: $2{\mathrm{Cl}}^{-}\to {\mathrm{Cl}}_2+2{\mathrm{e}}^{-}$