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Q106 (NDA-II/2025) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Applied everyday chemistry Answer Verified

Which one of the following salts is responsible for temporary hardness of water ?

Result
Your answer: —  Â·  Correct: C
Explanation

Water hardness is classified into temporary and permanent types based on the dissolved mineral salts. Temporary hardness, also known as carbonate hardness, is primarily caused by the presence of dissolved bicarbonates (hydrogen carbonates) of calcium and magnesium [1]. These salts are considered 'temporary' because they can be removed by simply boiling the water. Heating causes the soluble bicarbonates to decompose into insoluble carbonates, carbon dioxide, and water, which then precipitate as scale. Specifically, magnesium bicarbonate (Mg(HCO3)2) and calcium bicarbonate are the key agents responsible for this phenomenon. In contrast, permanent hardness is caused by the sulphates and chlorides of calcium and magnesium, such as calcium sulphate or magnesium chloride, which cannot be removed by boiling and require chemical treatment or ion exchange for removal.

Sources

  1. [1] https://www.sciencedirect.com/topics/engineering/carbonate-hardness
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SIMILAR QUESTIONS

NDA-I · 2017 · Q7 Relevance score: 7.15

Temporary hardness in water is due to which one of the following of Calcium and Magnesium ?

CAPF · 2012 · Q45 Relevance score: 6.61

Which one among the following salts causes hardness to the water?

NDA-I · 2011 · Q35 Relevance score: 5.84

Which of the statements given below is/ are correct ? Permanent hardness of water is due to the presence of soluble : 1. chloride of calcium. 2. bicarbonate of calcium. 3. sulphate of magnesium. 4. bicarbonate of magnesium. Select the correct answer using the code given below :

NDA-I · 2015 · Q45 Relevance score: 5.35

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CDS-I · 2018 · Q30 Relevance score: 4.99

Which of the following substances cause temporary hardness in water? 1. Mg(HC03)2 2. Ca(HC03)2 3. CaCl2 4. MgS04 Select the correct answer using the code given below.