Question

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

Answer 1

• The process of removing Ca²⁺ ions from hard water through the help of zeolite is called permutit process.
• The formula of Permutit is Hydrated sodium aluminium silicate (${\mathrm{Na}}_2{\mathrm{Al}}_2{\mathrm{Si}}_2{\mathrm{O}}_8.{\mathrm{xH}}_2\mathrm{O}$)
• When hard water is treated with sodium permutit then (Calcium) Ca²⁺and (Magnesium) Mg²⁺ ions are exchanged with sodium (Na⁺)ions which are present in sodium permutit.

Role of addition of the concentrated solution of solid compound Sodium chloride (NaCl)

• After long use most of the sodium ions present in permutit are replaced by calcium and magnesium ions and hence it becomes ineffective.
• When sodium hydroxide(NaOH) reacts with HCl (hydrochloric acid) it forms sodium chloride (NaCl) and water.

$\underset{\mathrm{Sodium}\mathrm{hydroxide}}{\mathrm{NaOH}}+\hspace{0.17em}\underset{\mathrm{hydrochloric}\mathrm{acid}}{\mathrm{HCl}}\to \underset{\mathrm{Sodium}\mathrm{chloride}}{\mathrm{NaCl}}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}}$

• So, concentrated NaCl solution is added to regenerate the permutit.

Hence, after the reaction between NaOH and HCl, NaCl and water are obtained which helps to regenerate the permutit.