Question

14. Temporary hardness of water is caused due to:
(A) Presence of magnesium in water.
(B) Presence of calcium bicarbonate in water.
(C) Both (A) and (B)
(D) Either (A) or (B)
(E) None of these ​

Answer 1

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Hardness of water is of two types :

1. Temporary hardness : This is due to presence of hydrogen carbonates of magnesium and calcium. It can be removed by

• Boiling or by clark's method in which lime is added to hard water which precipitates out calcium carbonate and magnesium hydroxide$.$

2. Permanent hardness : This is due to the presence of chlorides and sulphates of magnesium and calcium. It can be removed by

• Treatment with washing soda
• Calgon
• Ion-exchange or zeolite/permutit process
• Synthetic resins method

Hence (D) is the correct answer!

Answer 2

Explanation:

→ temporary hardness is caused by Mg+² or by Ca+²

( in form of their bicarbonates , not by the element )

→ it can be removed by boiling or by adding Ca(OH)2

i.e CLARK METHOD

→ permanent hardness is caused by chloride and sulphate

of Mg and Ca

→ it can be removed by using washing soda , by using CALGON