Water treatment (hardness): Permanent hardness of water can be removed by adding which chemical? Target the sulfate/chloride salts of Ca/Mg (non-carbonate hardness). Choose the correct reagent.
General Knowledge
General Science
Difficulty: Easy
Choose an option
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AWashing soda (sodium carbonate, Na2CO3)
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BLime [calcium hydroxide, Ca(OH)2]
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CBaking soda (sodium bicarbonate, NaHCO3)
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DPotassium permanganate (KMnO4)
Answer
Correct Answer: Washing soda (sodium carbonate, Na2CO3)
Explanation
What is being asked?The reagent that removes permanent hardness (Ca/Mg chlorides/sulfates) by precipitation.
Given data
- Permanent hardness ≠ carbonate hardness
Concept/ApproachNa2CO3 reacts with Ca2+/Mg2+ to form insoluble carbonates (CaCO3, MgCO3), thus softening the water. Lime mainly addresses temporary hardness by precipitating carbonates from bicarbonates.
Final AnswerWashing soda (sodium carbonate, Na2CO3)