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.
General Knowledge
General Science
Difficulty: Easy
Choose an option
Answer
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.
Final Answer Washing soda (Na2CO3)