Sodium carbonate, commonly called washing soda or soda ash, is an important industrial chemical. It is a white, crystalline solid that is soluble in water and has strong alkaline properties. Its decahydrate form is written as Na₂CO₃·10H₂O.

In the laboratory, sodium carbonate can be prepared by reacting carbon dioxide gas with sodium hydroxide solution.

Chemical Equation:

$$ 2NaOH + CO_2 \rightarrow Na_2CO_3 + H_2O $$

Procedure: Pass a slow stream of carbon dioxide gas into a cold, concentrated solution of sodium hydroxide until the solution becomes saturated. Crystals of sodium carbonate can then be obtained by evaporation.

The Solvay Process is the main industrial method for producing sodium carbonate. It involves the use of inexpensive raw materials such as sodium chloride (NaCl), limestone (CaCO₃), and ammonia (NH₃).

Steps involved:

1. Formation of Ammonium Bicarbonate:
   $$ \small{NH_3 + CO_2 + H_2O \rightarrow NH_4HCO_3 }$$
2. Precipitation of Sodium Hydrogen Carbonate:
   $$ \tiny{NH_4HCO_3 + NaCl \rightarrow NaHCO_3 \downarrow + NH_4Cl} $$
3. Conversion to Sodium Carbonate:
   The sodium hydrogen carbonate is filtered, dried, and heated to form sodium carbonate: $$\small{2NaHCO_3 \xrightarrow .Na_2CO_3 + CO_2 + H_2O }$$
4. Recovery of Ammonia:
   The ammonia is recovered by treating ammonium chloride with calcium hydroxide (from limestone): $$ \tiny{2NH_4Cl + Ca(OH)_2 \rightarrow 2NH_3 + CaCl_2 + 2H_2O} $$

Note: The Solvay process is economical because the ammonia used is continuously recovered and reused.

• White crystalline solid.
• Soluble in water, forming a strongly alkaline solution.
• Efflorescent — loses water of crystallization on exposure to air.
• Melting point: about 851°C.
• Forms decahydrate (Na₂CO₃·10H₂O), known as washing soda.

• 1. Reaction with acids: Produces carbon dioxide gas, salt, and water.

  $$ \tiny{Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2 }$$

• 2. Reaction with water: Forms an alkaline solution due to hydrolysis.

  $$\tiny{ Na_2CO_3 + H_2O \rightarrow 2NaOH + CO_2 }$$

• 3. Reaction with ammonium salts: Produces ammonia gas.

  $$\tiny{ Na_2CO_3 + 2NH_4Cl \rightarrow 2NaCl + 2NH_3 + H_2O + CO_2} $$

• 4. Reaction with lime (Ca(OH)₂): Used to prepare sodium hydroxide.

  $$ \tiny{Na_2CO_3 + Ca(OH)_2 \rightarrow 2NaOH + CaCO_3 \downarrow }$$

1. Add dilute hydrochloric acid (HCl) to a small sample of sodium carbonate.
2. Effervescence occurs — a gas is evolved.
3. Pass the gas through limewater.
4. Limewater turns milky, showing that the gas is CO₂.

Chemical reactions:
$$ \small{Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2} $$
$$ \small{Ca(OH)_2 + CO_2 \rightarrow CaCO_3 \downarrow + H_2O} $$

• Used in the manufacture of glass, soap, and detergents.
• Used to soften hard water.
• Used in the paper, textile, and chemical industries.
• Used in laboratories as a standard alkali for acid-base titrations.
• Used in the production of sodium hydroxide by reaction with lime.