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Q55 (CAPF/2019) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Applied everyday chemistry Answer Verified

Which one of the following is used for water softening?

Result
Your answer: —  Â·  Correct: C
Explanation

Water softening involves the removal of calcium and magnesium ions that cause hardness. Sodium hexametaphosphate, represented by the formula Na6P6O18 (commercially known as Calgon), is a widely used sequestering agent for this purpose [1]. It functions by reacting with calcium and magnesium ions to form soluble complex salts, thereby preventing them from precipitating with soap [1]. While sodium carbonate (washing soda) is also used to remove permanent hardness [1], Na6P6O18 is specifically valued in industrial and domestic water treatment for its ability to keep these ions in solution. In contrast, Mg(HCO3)2 is a cause of temporary hardness rather than a softening agent, and the other phosphate variants listed (Na3PO4 and Na2HPO4) are typically used as boiler water conditioners or pH buffers rather than primary sequestering softeners in this specific context.

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > Uses of washing soda > p. 32
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SIMILAR QUESTIONS

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