Question

name the salt of sodium which is used to remove permanent hardness of water give its molecular formula

Answer 1

It is known that temperary Hardness can be removed thermal treatment. It is due to the presence of Calcium, Megnesium, carbonate and bicarbonate ions. Same way Permanent hardness is due to the presence of Calcium, Megnesium, Sulphate and Chloride ions.

Answer 2

Salt of sodium which is used to remove permanent hardness of water is sodium carbonate. Its Molecular formula is $\bold{Na_2CO_3}$

Explanation:

• The water possess hardness or it is said to have hardness  elements like  chlorides, nitrates and sulfates of calcium and magnesium are present.

• The elements does not forms precipitate on boiling.

• The harness can be removed by Permutit process  where the water is treated with soda water

• During this process the carbonate ions from soda water( $Na_2CO_3$) react with the calcium and magnesium ions in the water and gives out a precipitate of calcium carbonate or magnesium carbonate.

• Removing the   calcium carbonate or magnesium carbonate precipitates removes the hardness of the water

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