CBSE Class 10 Science 2020 · Paper 31/1/1 · Question 16(b)
How is washing soda prepared from sodium carbonate? Give its chemical equation. State the type of this salt. Name the type of hardness of water which can be removed by it?
Answer
Recrystallising sodium carbonate from water gives washing soda; it is a basic salt and removes permanent hardness of water.
Washing soda is prepared by recrystallisation of sodium carbonate: sodium carbonate is dissolved in water and crystallised, and each formula unit takes up ten molecules of water of crystallisation.
It is a basic salt (the salt of the strong base sodium hydroxide and the weak acid carbonic acid).
It removes the permanent hardness of water.
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