Multiple choice general knowledge

Permanent hardness of water can be removed by adding

  1. potassium permanganate

  2. chlorine

  3. bleaching powder

  4. washing soda

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Permanent hardness of water is caused by dissolved chlorides and sulfates of calcium and magnesium, which cannot be removed by boiling. Washing soda (sodium carbonate decahydrate, Na2CO3·10H2O) removes permanent hardness through a chemical reaction: sodium carbonate reacts with calcium and magnesium salts to form insoluble carbonates that precipitate out, softening the water. Potassium permanganate, chlorine, and bleaching powder are disinfectants/oxidizers, not water softeners.