Thu March 27, 2014 By: Sanskrati Gawande

describe the solvays method of for preparation of washing soda.what is the use of washing soda?

Expert Reply
Thu March 27, 2014

The Solvay process is used for the manufacture sodium carbonate Na2CO3 (washing soda). In this process, brine (NaCl), NH3 and CO2 are the raw materials.

The steps involved in this process are:

1. Purification of saturated brine

2. Reaction of saturated brine with gaseous ammonia

3. The ammoniated brine is carbonated with CO2 to form NaHCO3

4. NaHCO3 is insoluble in brine solution. so it can be filtered out.

5. On heating, NaHCO3 decomposes to Na2CO3

6. CaCO3 is also used to provide CO2



1. CO2 reacts with ammonia to form ammonium carbonate.

2NH3 + CO2 + H2O → (NH4)2CO3


2. Ammonium carbonate further reacts with CO2 to form ammonium bicarbonate.

(NH4)2CO3 + CO2 + H2O → 2NH4HCO3 (aq.)


3. Ammonium bicarbonate then react with NaCl to form sodium bicarbonate.

NH4HCO3 + NaCl → NaHCO3 + NH4Cl

Due to exothermic nature of above reactions, solubility of NaHCO3 increases. To counter this effect, the solution is cooled, precipitate of NaHCO3 are separated by vacuum filtration and washed to remove ammonium salts.


4. Dry sodium bicarbonate is then heated to give anhydrous sodium carbonate. Carbon dioxide is then again recirculated.

2NaHCO3 →  Na2CO3 + CO2 + H2O


Properties and Uses of Sodium Carbonate

Sodium carbonate, Na2CO3, dissolves in water to form an alkaline solution.

Used as a base, sodium carbonate is cheaper and safer than sodium hydroxide.

Uses of Sodium Carbonate


Process Notes

Glass Making

A mixture of Na2CO3, CaCO3 and SiO2(silicon dioxide sand) is used for window or bottle glass.

Water Softening Agent

CO32- from dissolved Na2CO3 can precipitate Mg2+ and Ca2+ ions from hard water as the insoluble carbonates, preventing them from forming a precipitate with soap resulting in scum.
For this reason, sodium carbonate is also known as washing soda.

Paper Making

Na2CO3 is used to produce the NaHSO3necessary for the sulfite method of separating lignin from cellulose.

Baking Soda Production

Baking soda (or sodium hydrogen carbonate or sodium bicarbonate), NaHCO3, is used in food preparation and in fire extinguishers.

Sodium Hydroxide Production for Soaps and Detergents

Na2CO3 is reacted with a Ca(OH)2, slaked lime, suspension.

Wool Processing

Na2CO3 removes grease from wool and neutralises acidic solutions.

Power Generation

Na2CO3 is used to remove SO2(g) from flue gases in power stations.


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