Consider the following statements:
1. The temporary hardness in water is due to the presence of bicarbonates of calcium.
2. The permanent hardness in water is due to the presence of soluble chlorides and sulphates of calcium and magnesium.
3. The permanent hardness in water is removed by adding Na2CO3 to water.
Which of the statements given above are correct?
A.1 and 2 only
B.2 and 3 only
C.1 and 3 only
D.1, 2 and 3✓ Correct
Explanation
All three statements are correct. Temporary hardness arises from dissolved bicarbonates of calcium and magnesium [Ca(HCO3)2 and Mg(HCO3)2], removable by boiling. Permanent hardness is caused by dissolved chlorides and sulphates of calcium and magnesium, which cannot be removed by boiling. Permanent hardness can be removed by adding washing soda (Na2CO3), which precipitates Ca²⁺ and Mg²⁺ as insoluble carbonates. Therefore all three statements 1, 2 and 3 are correct.
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