Examkin

Question

Difficulty: MediumPurification and Treatment of Water for Supply

In a municipal water treatment system, the effluent water following alum coagulation and filtration is found to be slightly acidic and retains a persistent earthy odor. Which pair of chemical substances should be added to neutralize the acidity and eliminate the odor, respectively?

  1. Slaked lime and activated carbonAnswer
  2. B
    Calcium tetraoxosulfate(VI) and chlorine gas
  3. C
    Washing soda and potash alum
  4. D
    Concentrated tetraoxosulfate(VI) acid and bleaching powder

Answer

Slaked lime (Ca(OH)2\text{Ca(OH)}_2) or soda ash is added to neutralize acidity (raising pH), while activated carbon (charcoal) is used to remove unpleasant odors and tastes via adsorption.
Slaked lime (Ca(OH)2\text{Ca(OH)}_2) acts as a base to neutralize hydrogen ions, correcting acidity, while activated carbon effectively adsorbs volatile organic compounds that cause unpleasant tastes and odors in water.

Step-by-Step Solution

1
Identify the cause of acidity and the substance required to raise pH.
Coagulation with alum leaves acidic residues due to hydrolysis. An alkali such as slaked lime, Ca(OH)2\text{Ca(OH)}_2, neutralizes acidity.
Acids are neutralized by adding basic compounds to adjust the water pH to a safe drinking level.
2
Identify the process and agent required for odor removal.
Activated carbon (charcoal) possesses a high surface area that adsorbs dissolved organic volatile impurities responsible for odor.
Physical adsorption on activated carbon removes taste and odor without introducing additional chemical pollutants.

Key Concept

Chemical roles in water purification: pH adjustment using slaked lime/soda ash and taste/odor removal using activated carbon.
Estimated Time:1m 0s
Rate this question

Topics

Purification and Treatment of Water for Supply

More questions from this topic