Sodium Carbonate - Na₂CO₃

What is Sodium Carbonate?

Sodium carbonate is an inorganic chemical compound. Sodium carbonate is what is commonly known as Soda ash. Soda ash is extracted from trona. Trona is a double salt containing sodium carbonate and sodium hydrogen carbonate formed as a result of the series of evaporation processes taking place at lakes.

Sodium carbonate often called washing soda or soda ash is the most important of all basic heavy chemicals. Its great advantage over sodium hydroxide is that it is no-corrosive and is, therefore, safer to handle.

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Sodium Carbonate Formula

Sodium carbonate is a diazonium salt of carbonic acid with the chemical formula Na₂CO₃. It is also known as Soda crystals, soda ash, washing soda. This inorganic compound is water-soluble and when dissolved in water, it forms carbonic acid and sodium hydroxide. In its pure form, it is a white powder and odourless. It is a strong base and acts as an antacid.

Sodium carbonate can be produced by four processes – “Solvay process, Labnac process, Dual-process, Electrolytic process”. Since it is a weak acid it is slightly soluble in ethanol and insoluble in alcohol. One of the important uses of Na₂CO₃ is as a water softener. pH is about 11.

Synthesis of Sodium Carbonate – Na₂CO₃

Sodium carbonate is now exclusively manufactured by the Solvay process. In this process carbon dioxide and ammonia are passed into a cold saturated solution of sodium chloride. In the reactions which occur sodium hydrogen carbonate is formed which is only very slightly soluble in the presence of sodium ions, is almost completely precipitated. It is removed by filtration and ignited to produce sodium carbonate.

The ingredients of this process are readily available and inexpensive. These are salt brine (NaCl), ammonia (NH₃) and limestone (CaCO₃). In this process, CaCl₂ is an important by-product obtained.

The reactions can be represented by the following equation.

2NH₃ + H₂O + CO₂ → (NH₄)₂CO₃
(NH₄)₂CO₃ + H₂O + CO₂ → 2NH₄HCO₃

Addition of common salt to the solution containing NH₄⁺ and HCO₃^– results in the precipitation of NaHCO₃ which is the least soluble. It is then filtered off.

NH₄HCO₃ + NaCl → NH₄Cl + NaHCO₃

Sodium bicarbonate is then heated to give Na₂CO₃.

2NaHCO₃ → Na₂CO₃ + CO₂ + H₂O

The CO₂ gas evolved can be reused again.

Anhydrous sodium carbonate is dissolved in water and recrystallizes to get washing soda crystals containing 10 molecules of water of crystallization.

Properties of Sodium Carbonate – Na₂CO₃

Chemical Properties of Sodium Carbonate – Na₂CO₃

1. Anhydrous sodium carbonate is stable towards heat. It melts without decomposition at 852^oC.

2. Aqueous solutions of sodium carbonate are mildly alkaline due to hydrolysis which releases OH^–(aq) ions.

Na₂CO₃(s) + 2H₂O(l) → H₂CO₃(aq) + 2Na⁺(aq) + 2OH^–(aq)

3. Aqueous solutions of sodium carbonate absorb carbon dioxide from the air forming sodium hydrogen carbonate.

Na₂CO₃(aq) + H₂O + CO₂(g) → 2NaHCO₃(aq)

4. Sodium carbonate reacts with acids like weak vegetable acids, such as lime juice liberating carbon dioxide.

Na₂CO₃(aq) + 2H⁺(aq) → 2Na⁺(aq) + H₂O(l) + CO₂(g)
Na₂CO₃(aq) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g)

Sodium Carbonate Structure – Na₂CO₃

The structure of sodium carbonate molecules is illustrated below. It can be noted that each molecule of sodium carbonate contains 2 sodium atoms, 3 oxygen atoms and one carbon atom. Each sodium cation holds a charge of +1 whereas the polyatomic carbonate anion holds a net charge of magnitude -2. Sodium carbonate is, therefore, a neutrally charged molecule.

Uses of Sodium Carbonate (Na₂CO₃)

The uses of sodium carbonate are listed below.

• It is used in the manufacture of detergents, soaps, and paper.
• Also used in the manufacture of water glass (sodium silicate), borax, sodium phosphate, and many other sodium compounds.
• It is used as a wetting agent in the brick industry
• It is used as an abrasive and foaming agent in toothpaste
• It is used as a pH modifier
• It is used as a water softener –  Hard water which consists of magnesium and calcium ions are precipitated by carbonate.
• As a laboratory reagent to standardize acids and as an analytical reagent.

Also, Read: Preparation of Standard Solution of Sodium Carbonate

Learn more about the chemical behaviour and importance of Na₂CO₃ with the expert faculties at BYJU’S.