Softening of water and deionization method, Chemistry

Q. What is softening of water? Describe deionization method of water softening with diagram.

Ans. Softening of water: The process of removing the hardness causing salts from water is called softening of water. Hard water is unsuitable for industries as well as for domestic purposes. Therefore, it is necessary to remove the hardness of water before using in various industries, boilers etc. The softening of hard water can be done by:

Removal of hardness causing salts of calcium and magnesium.

Conversion of these salts into soluble sodium salts.

Combination of the above methods. The hardness causing salts can be removed mainly by three methods.

(a) Lime-soda method

(b) Zeolite method and

(c) Ion-exchange methods.

Ion Exchange process (Determination or Deionization):

The substances capable of exchange of ions with the electrolyte solution are called ion exchangers. The process of ion exchange is the property of a ion exchangers to exchange an ion in its structure with ion in solution that is brought in contact with it. Since all the cations and anions are completely removed in this process, so it is known as "complete deionization". Ion exchange are organic cross, linked, insoluble, high molecular weight, polymers with a porous structure, and the "functional structure" attached to the chains are responsible for the ion-exchange properties. The ion exchange or ion-exchanger resins may be classified as:

Cations exchangers: Resins containing acidic functional groups like (-COOH, -SO3H etc.) are capable of exchanging their H+ ions with other cations which comes in their contact; and hence they are termed as cations exchangers e.g. styrene divine benzene copolymers which on sulphonation.

They can be represented as R-H+ where R- represents the insoluble polymer matrix. The exchange reactions are:

2R- - H+ + Mg+2 = R2Mg + 2H+

 2R- - H+ + Ca+2 = R2Ca + 2H+

 Amberlite IR-120; and Do vex -50 are commercially available cations exchange resins.

Anion exchangers: Resin containing basic functional group like ammonia or quaternary ammonium or quaternary phosphonium or hydroxides or hydrochloride are capable of exchanging their anions in water and therefore are known as anion exchangers e.g. styrene benzene or ammine formaldehyde copolymers. These after treatment with dilute 2NaOH solution, become capable to exchange their OH- anions with other anions present in water. They can be represented as R+ OH- where R+  

2R+ + OH- + SO4-2 = R2SO4 + 2OH-

R+OH- + Cl- = RCl + OH-

Process: The apparatus used for softening hard water by this method consists of two containers, one containing cations exchange resin and the other anions exchange resin over a bed of gravel. Hard water is first passed through the cations exchange resin. The cations present in hard water get exchanged with H+ ions of the resin. The water coming out of the first container thus contains free yyhjions in acidic in nature. It is now passed through the anion exchange resin. These resin exchangers the anions with OH- ions.

R+ - OH- + Cl- = RCl + OH-

The OH- ions thus formed combine with free H+ ions to form H2O molecules. all cations and anions that were present in hard water. It is known as deionised or demineralised water.  

Posted Date: 7/21/2012 9:12:50 AM | Location : United States







Related Discussions:- Softening of water and deionization method, Assignment Help, Ask Question on Softening of water and deionization method, Get Answer, Expert's Help, Softening of water and deionization method Discussions

Write discussion on Softening of water and deionization method
Your posts are moderated
Related Questions
does nitro compounds cause any harmful effect on living things?

diagrams of f orbitals


Simultaneous determination of exact position and momentum of an electron is: (1) Possible (2) Impossible (3) Sometimes possible sometimes impossible (4) None of the ab

For the energy levels in an atom, which one of the following statements is correct: (1) There are seven principal electron energy levels (2) The second principal energy leve

Q. Show the Multiple covalent bonds between electron pairs? Ans. Two atoms may share one electron pair, two electron pairs or three electron pairs. The bonds formed in th

Q. Determine mass of an electron? Ans. Three years later after J.J Thomson discovered the electron, the American scientist Robert Millikan used an oil drop experiment to accu

Write the chemical equation for the entire combustion of heptane, C 7 H 16 . The heat of combustion for heptane is 4817 kJ/mol. How much heat could be released if 250 kg of hept

Q. What is Oxidation Numbers? Ans. Chemists find it useful to describe the oxidation states of an element by means of oxidation numbers. The oxidation number of an element