Sodium carbonate is an important alkaline inorganic compound widely used in industries and households. It is an ionic compound and the disodium salt of carbonic acid. Compared to strong bases like sodium hydroxide, it is less corrosive and safer to handle. In aqueous solution, it behaves as a basic substance, making it useful in cleaning and manufacturing processes.
Chemical Formula and Composition
1. Chemical Formula: The chemical formula of Sodium carbonate is Na₂CO₃.
2. Composition: It consists of 2 Na⁺ ions and a CO₃²⁻ ion, forming a stable ionic compound. Na₂CO₃ consists of three types of atoms:
- Sodium (Na): 2 atoms
- Carbon (C): 1 atom
- Oxygen (O): 3 atoms
Molecular Structure
The carbonate ion (CO₃²⁻) has a trigonal planar geometry with resonance:
- Carbon is bonded to three oxygen atoms
- The negative charge is delocalized over the oxygen atoms
- Two Na⁺ ions balance the overall charge, making the compound neutral
Preparation of Sodium Carbonate
1. From Baking Soda (Thermal Decomposition)
Sodium carbonate is prepared by heating sodium hydrogen carbonate.
2\text{NaHCO}_3 \xrightarrow{\Delta} \text{Na}_2\text{CO}_3 + H_2O + CO_2
2. By Solvay Process (Industrial Method)
\text{NaCl} + NH_3 + H_2O + CO_2 \rightarrow \text{NaHCO}_3 + NH_4Cl On heating:
2\text{NaHCO}_3 \rightarrow \text{Na}_2\text{CO}_3 + H_2O + CO_2
Physical Properties
- White, crystalline, odorless solid.
- Exists commonly as decahydrate (Na₂CO₃·10H₂O).
- Good solubility in water.
- Molar mass: 105.99 g/mol.
- High melting point (851°C).
- Shows efflorescence (loses water of crystallization on exposure to air).
Chemical Properties
- Stable compound; melts without decomposition.
- Hydrolyses in water to give a basic solution.
- Reacts with acids to release CO₂ gas.
\mathrm{Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2 \uparrow} - Reacts with CO₂ and water to form sodium bicarbonate
\mathrm{Na_2CO_3 + H_2O + CO_2 \rightarrow 2NaHCO_3} - Forms precipitates with Ca²⁺ and Mg²⁺ ions, thus softening hard water.
- Alkaline in nature (pH ≈ 11).
Sodium Carbonate vs Sodium Bicarbonate
| Property | Sodium Carbonate | Sodium Bicarbonate |
|---|---|---|
| Formula | Na₂CO₃ | NaHCO₃ |
| Nature | Strongly alkaline | Weakly alkaline |
| pH | ~11–12 | ~8.2 |
| Decomposition | At high temperature | At low temperature |
| Reaction with acids | Vigorous | Slow |
| Uses | Glass, soaps, detergents | Baking, antacid |
Uses
- Manufacture of soaps, detergents, and paper.
- Softening of hard water by removing Ca²⁺ and Mg²⁺.
- Used in food industry as stabilizer and anticaking agent.
- Used in making borax, glass, and rayon.