Question

In comparison to the zeolite process for the removal of permanent hardness, the synthetic resins method is:
A. More efficient as it can exchange only cations.
B. Less efficient as the resins cannot be regenerated.
C. More efficient as it can exchange both cations as well as anions.
D. Less efficient as it can exchange only anions.

Answer 1

Hint: Permanent hardness in water occurs due to the presence of the chlorides, nitrates and sulphates of calcium and magnesium. This makes water difficult for use. Therefore, water is generally softened by removal of these compounds.

Complete step by step answer:
Let us solve this question by understanding the zeolite process and the synthetic resins method for the removal of permanent hardness.
Zeolite process
It removes only the cations responsible for permanent hardness.
The reaction is as given below –
\[2NaZ+{{M}^{2+}}(aq)\to M{{Z}_{2}}(s)+2N{{a}^{+}}(aq)\] ;(M – Mg, Ca)
Synthetic resins method
It removes the cations, as well as the anions responsible for permanent hardness.
The reaction is as given below –
For cations
\[2RNa(s)+{{M}^{2+}}(aq)\to {{R}_{2}}M(s)+2N{{a}^{+}}(aq)\];(M – Mg, Ca)
For anions
\[RNH_{3}^{+}O{{H}^{-}}(s)+{{X}^{-}}(aq)\to RNH_{3}^{+}{{X}^{-}}(s)+O{{H}^{-}}(aq)\];(X – anions – Chloride, sulphate, etc.)
Since the zeolite process utilizes the mineral zeolite as the exchanging resin for only cation in hard water, and synthetic resins method utilizes many different resins for the ion exchange, hence, it is more efficient.
Therefore, the answer is – option (c) – The synthetic resins method is more efficient as it can exchange both cations as well as anions.

Note: Other methods for removing permanent hardness is cold lime-soda process or hot lime-soda process. In this method, calculated amounts of lime and soda are added so that the soluble calcium and magnesium salts in water are chemically converted into insoluble compounds.