5.0 Compounds of Sodium

  s Block Elements

1. Sodium oxide ($N{a_2}O$):

• Preparation: Obtained by burning sodium at ${1800^ \circ }C$ in a limited supply of air or oxygen and distilling off the excess of sodium in vaccum, or by heating sodium peroxide ($N{a_2}{O_2}$), nitrate ($NaNO_3$) with sodium. $$\begin{equation} \begin{aligned} 2Na + \frac{1}{2}{O_2} \to N{a_2}O \\ N{a_2}{O_2} + 2Na \to 2N{a_2}O \\ 2NaN{O_3} + 10Na \to 6N{a_2}O + {N_2} \\\end{aligned} \end{equation} $$

• Properties:

a. Sodium oxide is a colourless ionic solid.

b. Aqueous solution of sodium oxide is strongly basic. $$N{a_2}O + {H_2}O \to 2NaOH$$

c. Sodium oxide on reaction with liquid ammonia forms sodamide. $$N{a_2}{O_2} + N{H_3} \to NaN{H_2} + NaOH$$

2. Sodium peroxide ($N{a_2}{O_2}$):

• Preparation: Sodium when heated in excess of air (free from moisture and carbon dioxide) or when heated in excess of pure oxygen gives sodium peroxide. $$2Na + {O_2}\left( {excess} \right)\mathop \to \limits^{350} N{a_2}{O_2}$$

• Properties:

a. Sodium peroxide is a pale yellow diamagnetic compound.

b. It is a powerful oxidizing agent.

c. It dissolves in ice-cold dilute mineral acid yielding $H_2O_2$.

d. It combines with $CO$ and $CO_2$ to give carbonate.

3. Sodium Hydroxide (Caustic soda) ($NaOH$):

• Preparation:

a. Gossage Process: When sodium carbonate is treated with calcium hydroxide it give calcium carbonate along with sodium hydroxide. $$N{a_2}C{O_3} + Ca{\left( {OH} \right)_2} \to 2NaOH + CaC{O_3}$$

b. By electrolysis of $NaCl$ solution (brine).

c. Electrolysis of $NaCl$: Castner-Kellner Cell.

d. Electrolysis of Brine: Kellner-Solvay cell.

• Properties:
  

a. Forms sodium salt of oxyacid of non-metal. $$2B + 6NaOH \to 2N{a_3}B{O_3} + 3{H_2}$$

b. Hydroxides of amphoteric elements like Al, Zn, etc. are initially precipitated by $NaOH$ followed by re-dissolution due to complex formation. $$ZnS{O_4} + 2NaOH \to NaS{O_4} + Zn{\left( {OH} \right)_2}\left( {ppt.} \right)\mathop \to \limits^{NaOH} N{a_2}Zn{O_2}\left( {soluble} \right)$$

c. Forms sodium formate with $CO$ under pressure.

• Uses:

a. In the manufacture of sodium metal, soap, rayon, paper dyes, drugs etc.

b. As a reagent in the laboratory.

4. Washing soda or Soda ash ($N{a_2}C{O_3}.10{H_2}O$):

• Preparation: Solvay Ammonia Process $$\begin{equation} \begin{aligned} N{H_3} + {H_2}O + C{O_2} \to N{H_4}HC{O_3} \\ NaCl + N{H_4}HC{O_3} \to NaHC{O_3} + N{H_4}Cl \\ 2NaHC{O_3}\mathop \to \limits^\Delta N{a_2}C{O_3} + {H_2}O + C{O_2} \\\end{aligned} \end{equation} $$

• Properties:
  

a. Sodium carbonate is a white crystalline solid.

b. $N{a_2}C{O_3}.10{H_2}O$ is known as washing soda. $N{a_2}C{O_3}.{H_2}O$ is known as crystal carbonate. $N{a_2}C{O_3}$ is known as light ash/soda ash.

c. $N{a_2}C{O_3}$ is a thermally stable compound.

e. Sodium carbonate on reaction with $CO_2$ gives sodium bicarbonate. $$N{a_2}C{O_3} + {H_2}O + C{O_2} \to 2NaHC{O_3}$$

f. Sodium carbonate on reaction with sulphur dioxide gives sodium sulphite which on further reaction gives sodium thiosulphate. $$\begin{equation} \begin{aligned} N{a_2}C{O_3} + S{O_2}\mathop \to \limits^{{H_2}O} N{a_2}S{O_3} + C{O_2} \\ N{a_2}S{O_3} + S \to N{a_2}{S_2}{O_3} \\\end{aligned} \end{equation} $$

g. Sodium carbonate reacts with metal salts (except alkali metals) to give carbonates. $$CaC{l_2} + N{a_2}C{O_3} \to CaC{O_3} + 2NaCl$$

Uses:

a. In laundries and in softening of water as washing soda.

b. In manufacturing of glass, caustic soda.

c. In textile industry and petroleum refining.

5. Sodium bicarbonate ($NaHCO_3$):

• Preparation:

a. Solvay Process: $$NaCl + N{H_3} + C{O_2} + {H_2} \to NaHC{O_3} + N{H_4}Cl$$

b. When NaOH is treated with $CO_2$ in presence of $H_2O$ it gives sodium bicarbonate.

6. Sodium sulphate ($Na_2SO_4$):

• Preparation: Obtained by heating $NaCl$ with $NaHSO_4$. $$NaCl + NaHS{O_4} \to N{a_2}S{O_4}\left( {anhydrous} \right)({\text{salt cake}}) + HCl$$

• Uses: In paper industry, in detergents and in the manufacture of glass.