Question

Starting with sodium chloride how would you proceed to prepare (i) sodium metal, (ii) sodium hydroxide, (iii) sodium peroxide, (iv) sodium carbonate?

Answer 1

Hint: >Sodium chloride is also called brine. Sodium metal can be prepared from sodium chloride by using Downs process.
>Sodium hydroxide can be prepared from the electrolysis of sodium chloride.
>The sodium metal obtained from Downs process is heated with an excess amount of oxygen to prepare sodium peroxide.
>Sodium carbonate can be prepared by using the Solvay process.

Complete step by step answer:
(i) Preparation of sodium metal from sodium chloride by Downs process.
>In this process a mixture of 40% NaCl and 60% Calcium chloride at 873 K using graphite as anode and iron rod as a cathode. In this process sodium metal is going to collect at anode and chlorine is liberated as a gas at the cathode.
>The chemical reactions of preparation of sodium are as follows.
\[\begin{align}
  & NaCl\to N{{a}^{+}}+C{{l}^{-}}\text{(electrolysis)} \\
 & N{{a}^{+}}+{{e}^{-}}\to Na(\text{at anode)} \\
 & 2C{{l}^{-}}\to C{{l}_{2}}+2{{e}^{-}}\text{(at cathode)} \\
\end{align}\]

(ii) Preparation of Sodium Hydroxide (NaOH) from sodium chloride
>Sodium Hydroxide can be prepared by the electrolysis of an aqueous solution of sodium chloride by using Castner-Kellner cell. In this method mercury acts as cathode and carbon as anode. The sodium metal deposited at cathode reacts with mercury and forms sodium amalgam.
>And chlorine is liberated at the anode as a gas.
>The chemical reactions of preparation of sodium hydroxide are as follows.
\[\begin{align}
  & N{{a}^{+}}+{{e}^{-}}\to Na-\text{amalgam}(\text{at anode)} \\
 & 2C{{l}^{-}}\to C{{l}_{2}}+2{{e}^{-}}\text{(at cathode)} \\
\end{align}\]
The formed sodium amalgam reacts with water and forms sodium hydroxide, mercury and hydrogen gas.
\[2Na-\text{amalgam+2}{{\text{H}}_{\text{2}}}\text{O}\to \text{2NaOH+2Hg+}{{\text{H}}_{\text{2}}}\]

(iii) Sodium peroxide (\[N{{a}_{2}}{{O}_{2}}\]) can be prepared by the heating sodium metal (which is obtained by Downs process) with the excess amount of air.
>The preparation of sodium peroxide from sodium metal is a two-step process.
>In the first step sodium metal (Na) reacts with oxygen (\[{{O}_{2}}\]) and forms sodium oxide (\[N{{a}_{2}}O\]). In the second step the formed sodium oxide (\[N{{a}_{2}}O\]) reacts with more amount of oxygen and forms sodium peroxide (\[N{{a}_{2}}{{O}_{2}}\]).
>The chemical reactions of preparation of sodium peroxide are as follows.
\[\begin{align}
  & 4Na+{{O}_{2}}\to 2N{{a}_{2}}O \\
 & 2N{{a}_{2}}O+{{O}_{2}}\to N{{a}_{2}}{{O}_{2}} \\
\end{align}\]

(iv) Sodium carbonate can be prepared from sodium chloride by using the Solvay process.
>In this process carbon dioxide (\[C{{O}_{2}}\]) is going to pass through a concentrated solution of brine (NaCl) saturated with ammonia (\[N{{H}_{3}}\]). In this process sodium bicarbonate (\[NaHC{{O}_{3}}\]) is obtained as an initial product. Later on subsequent heating of sodium bicarbonate gives sodium carbonate (\[N{{a}_{2}}C{{O}_{3}}\]) as a final product.
>The chemical reactions of preparation of sodium carbonate are as follows.
\[\begin{align}
  & NaCl+N{{H}_{3}}+C{{O}_{2}}+{{H}_{2}}O\to NaHC{{O}_{3}}+N{{H}_{4}}Cl \\
 & 2NaHC{{O}_{3}}\to N{{a}_{2}}C{{O}_{3}}+C{{O}_{2}}+{{H}_{2}}O \\
\end{align}\]

Note:>Sodium metal is highly reactive in nature, it rapidly reacts with water and ice and forms sodium hydroxide.
>Sodium hydroxide is used in the manufacturing, oil refining, and in water treatment.
>Sodium peroxide is used to bleach wood pulp for the preparation of the paper.
>Sodium carbonate is commonly called as washing soda and it is used in cleaning products.