In permutit process, what is the role of the addition of the concentrated solution of the solid compound obtained due to the reaction between NaOH with HCl? Explain.

Explanation

In permutit process, sodium permutit that is `Na_(2)Al_(2)Si_(2)O_(8).xH_(2)O` is used. When hard water is treated with sodium permutit, `Ca^(+2) and Mg^(+2)` ions are exchanged with the `Na^(+)` ions present in the permutit. After long use, most of the sodium ions present in permutit are replaced with calcium and magnesium ions, and hence, it becomes ineffective. Sodium hydroxide reacts with HCl to form NaCl. Concentrated NaCl solution is added to regenerate the permutit.