Which of the following substances cause temporary hardness in water?

1. Mg(HCO₃)₂
2. Ca(HCO₃)₂
3. CaCl₂
4. MgSO₄

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3 and 4

2 and 3

1 and 4

1 and 2

Answer is Right!

Answer is Wrong!

This question was previously asked in

UPSC CDS-1 – 2018

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Temporary hardness in water is caused by the presence of dissolved bicarbonates of calcium (Ca(HCO3)2) and magnesium (Mg(HCO3)2). These compounds decompose when water is boiled, forming insoluble calcium carbonate and magnesium carbonate, which precipitate out, thereby removing the hardness.
From the given list:
1. Mg(HCO3)2 – Magnesium bicarbonate (causes temporary hardness)
2. Ca(HCO3)2 – Calcium bicarbonate (causes temporary hardness)
3. CaCl2 – Calcium chloride (causes permanent hardness)
4. MgSO4 – Magnesium sulfate (causes permanent hardness)
Therefore, substances 1 and 2 cause temporary hardness.

Temporary hardness is primarily caused by dissolved calcium and magnesium bicarbonates.

Permanent hardness is caused by dissolved sulfates and chlorides of calcium and magnesium. It cannot be removed by simple boiling but requires other methods like ion exchange or chemical precipitation using agents like washing soda.

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