Washing Soda (Uses) MCQs Quiz | Class 10

Overview of Washing Soda

Washing soda is a chemical compound with the formula Na₂CO₃·10H₂O (Sodium Carbonate Decahydrate). It is obtained by the recrystallisation of sodium carbonate in water. Since sodium carbonate is a salt of a strong base (NaOH) and a weak acid (H₂CO₃), its aqueous solution is basic in nature.

Key Uses and Applications

• Cleaning Agent: It is widely used for domestic purposes as a cleaning agent for clothes and laundry.
• Water Softening: It is used for removing the permanent hardness of water. It reacts with soluble calcium and magnesium chlorides or sulphates in hard water to form insoluble carbonates.
• Industrial Uses: It is a key raw material in the glass, soap, and paper industries.
• Borax Manufacture: It is used in the manufacture of sodium compounds such as borax.

Chemical Properties Table

Quick Revision Points

• Sodium carbonate is prepared by the Solvay process.
• The ’10H₂O’ signifies ten molecules of water of crystallisation attached to one formula unit of the salt. It makes the crystal wet to touch? No, it remains dry but gives the crystal structure.
• When exposed to air, it loses 9 water molecules (efflorescence) to form a monohydrate.

Extra Practice Questions

1. What happens when washing soda is heated strongly? (Answer: It loses all water molecules to become anhydrous sodium carbonate.)
2. Why is washing soda basic? (Answer: Hydrolysis produces strong base NaOH and weak acid Carbonic acid.)
3. Write the reaction for removing permanent hardness. (Answer: CaCl₂ + Na₂CO₃ → CaCO₃ + 2NaCl)
4. Is washing soda corrosive? (Answer: It is a mild alkali and less corrosive than caustic soda.)
5. Difference between baking soda and washing soda? (Answer: Baking soda is NaHCO₃; Washing soda is Na₂CO₃·10H₂O.)