Lakhmir Singh Solutions Class 10 Chemistry Solutions for Exercise in Chapter 2 - Chapter 2 Acids, Bases and Salts

Question 191 Exercise

(a) Describe how washing soda is produced starting from sodium chloride (common salt). Write equations of all the reactions involved.

(b) State whether an aqueous solution of washing soda is acidic or alkaline. Give reason for your answer.

(c) What is meant by saying that washing soda has detergent properties?

(d) Mention two important uses of washing soda (or sodium carbonate).


Washing soda is produced from sodium chloride in the following process:

Step 1: A cold and concentrated solution of sodium chloride called brine is reacted with ammonia and carbon dioxide to obtain sodium hydrogen carbonate.

NaCl + NH3 + H2O + CO2 → NaHHCO3 + NH4Cl

Step 2: Sodium hydrogen carbonate formed is separated by filtration dried and heated. It further decomposes to sodium carbonate.

2NaHCO3 → Na2CO3 +  CO2 + H2O

Anhydrous sodium carbonate is called soda ash.

Step 3: Soda ash is then dissolved in water and recrystallized to get washing soda crystals containing 10 molecules of water of crystallization.

Na2CO3 + 10H2O → Na2CO3.10H2O

(b) An aqueous solution of washing soda is alkaline because it turns red litmus to blue.

(c) Washing soda has a cleansing property thus it removes dirt and grease from dirty clothes. These add to the detergent properties of washing soda.

(d) Washing soda can be used for:

Used as a cleansing agent.

Used to remove the permanent hardness of the water.

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