In the removal of water hardness, permutit is regenerated with a strong solution of

Analysis

The question asks for the chemical substance used to regenerate "permutit" (also known as zeolite) after it has been used to soften hard water.

Concept Explanation

Permutit (Zeolite) is a naturally occurring or synthetic hydrated sodium aluminosilicate (represented as $Na_2Ze$).

1. How it works: When hard water (containing $Ca^{2+}$ or $Mg^{2+}$ ions) passes through a bed of permutit, the sodium ions ($Na^+$) in the permutit are exchanged for the calcium or magnesium ions in the water. This removes the hardness: $Na_2Ze(s) + Ca^{2+}(aq) \rightarrow CaZe(s) + 2Na^+(aq)$
2. The Regeneration Process: Eventually, the permutit becomes "exhausted" (all the $Na^+$ ions are replaced by $Ca^{2+}$ or $Mg^{2+}$). To reuse it, we must displace the calcium and magnesium ions and replace them with sodium ions again. This is done by flushing the exhausted permutit with a concentrated solution of sodium chloride (brine). $CaZe(s) + 2NaCl(aq) \rightarrow Na_2Ze(s) + CaCl_2(aq)$

Step-by-Step Solution

• Step 1: Identify the exhausted material. The exhausted permutit is in the form of Calcium-zeolite ($CaZe$).
• Step 2: Identify the goal. We need to restore it to Sodium-zeolite ($Na_2Ze$).
• Step 3: Select the reagent. We need a source of concentrated sodium ions ($Na^+$) that will force the equilibrium to shift back to the sodium form. A concentrated solution of common salt (NaCl) is the standard industrial reagent for this ion-exchange regeneration.

Conclusion

Comparing this to your options: A. NaOH (Sodium hydroxide) - Not used for this purpose. B. $Na_3SO_4$ - Incorrect formula and not used for regeneration. C. $Na_3CO_3$ - Incorrect formula (Sodium carbonate is $Na_2CO_3$). D. NaCl (Sodium chloride) - This is the correct reagent used for regeneration.

Exam Tip: Remember that "Permutit" and "Zeolite" are often used interchangeably in JAMB questions. Always associate them with Ion-Exchange and Brine (NaCl) for regeneration. Don't get confused by the chemical formulas; just look for the sodium salt that provides the $Na^+$ ions needed to "recharge" the zeolite.