Question

The cation exchange ability of ........... is exploited to remove the dissolved salts in the form of sulphates and chlorides.

• A. Activated Silica
• B. Chlorine
• C. Zeolites
• D. Sodium Hexametaphosphate

Hint:

Zeolites are often called "Permutits" in industrial water softening. Remember: Zeolites = Ion Exchange = Softening.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks for the material used in water treatment or food processing that utilizes cation exchange to remove dissolved salts like sulphates and chlorides. This is a common process in water softening and purification.
Key Formula or Approach:
The approach involves understanding ion exchange mechanisms. Cation exchangers replace undesirable cations in water (like $Ca^{2+}$ or $Mg^{2+}$) with more desirable ones (like $Na^+$ or $H^+$), often using aluminosilicate minerals or synthetic resins.

Step 2: Detailed Explanation:

• Zeolites: Zeolites are naturally occurring or synthetic microporous, aluminosilicate minerals. They possess a crystalline structure that forms a framework of cavities and channels.

• Ion Exchange Mechanism: The framework of zeolites is negatively charged, which is balanced by cations (usually sodium or potassium) held loosely within the pores. When water containing dissolved salts (cations like calcium or magnesium associated with sulphates/chlorides) passes through, these ions are swapped with the sodium ions.

• Softening Process: In the context of removing dissolved hardness salts, zeolites act as "molecular sieves" and ion exchangers. While the question mentions removing salts "in the form of" sulphates and chlorides, it technically refers to removing the cationic part of these salts that contribute to hardness or salinity.

• Comparison with other options:
• Activated Silica: Primarily used as a coagulant aid in water treatment to assist in the sedimentation of flocs.
• Chlorine: A powerful oxidizing agent used mainly for disinfection to kill pathogens.
• Sodium Hexametaphosphate (SHMP): A sequestrant used to prevent scale formation by complexing metal ions, but it does not work by cation exchange.

Step 3: Final Answer: Zeolites are the correct choice as they are specifically known for their ion-exchange capacity used to treat water by removing dissolved mineral cations.