Solve this multiple-choice question and choose the correct option.

Given data Permanently hard water contains Ca2+/Mg2+ (as chlorides/sulfates). Concept/Approach Adding sodium carbonate (washing soda) precipitates CaCO3/MgCO3, removing hardness ions from solution. Step-by-step • CaCl2 + Na2CO3 → CaCO3↓ + 2 NaCl • MgSO4 + Na2CO3 → MgCO3↓ + Na2SO4 Common pitfalls Chlorine/bleaching powder disinfect; KMnO4 is an oxidant, not a hardness remover. Final Answer Washing soda (Na2CO3)

Home » General Knowledge » General Science

Water treatment (hardness): Removing permanent hardness of water by chemical addition. Select the compound that effectively removes Ca<sup>2+</sup>/Mg<sup>2+</sup> hardness by precipitation. Choose the correct reagent.

Difficulty: Easy

Washing soda (Na₂CO₃)
Chlorine
Potassium permanganate
Bleaching powder

Correct Answer: Washing soda (Na₂CO₃)

Explanation:

Given data

Permanently hard water contains Ca²⁺/Mg²⁺ (as chlorides/sulfates).

Concept/Approach Adding sodium carbonate (washing soda) precipitates CaCO₃/MgCO₃, removing hardness ions from solution.

Step-by-step • CaCl₂ + Na₂CO₃ → CaCO₃↓ + 2 NaCl • MgSO₄ + Na₂CO₃ → MgCO₃↓ + Na₂SO₄

Common pitfalls Chlorine/bleaching powder disinfect; KMnO₄ is an oxidant, not a hardness remover.

Water treatment (hardness): Removing permanent hardness of water by chemical addition. Select the compound that effectively removes Ca<sup>2+</sup>/Mg<sup>2+</sup> hardness by precipitation. Choose the correct reagent.

More Questions from General Science

Discussion & Comments