Concept:Permutit softens water by exchanging its sodium ions for calcium and magnesium ions; regeneration reverses this exchange using a concentrated sodium salt solution.
Explanation:After softening, the permutit is enriched with calcium and magnesium ions, so it is no longer effective.
It is regenerated by passing a strong brine solution, which is concentrated sodium chloride (
NaClaq), through the spent permutit.
The high concentration of sodium ions in brine displaces the calcium or magnesium ions from the permutit.
The reaction is represented by:
CaR2(s)+2NaClaq→CaCl2(aq)+2NaR(s)In this way, the permutit is converted back to its sodium form and becomes ready for another softening cycle.
Therefore, the strong solution used for regenerating permutit is sodium chloride.
Answer:D.
NaCl