Softening of water by ion exchange resins

[Enigman]

Why is the cation exchange always carried out before anion exchange in softening of hard water by ion exchange resins?

Plz. Help:(

 

[DrDu]

What compounds are predominantly formed in the two alternative exchange processes?
What are their physical properties?

 

[Enigman]

What compounds are predominantly formed in the two alternative exchange processes?
What are their physical properties?

Ummm... Hydronium ions in cathode exchange and hydroxyl ion in anode exchange...products after cathode exchange are acidic if carried out first (H2SO4,HCl...etc.) if anion exchange is carried out first products will be basic (Ca(OH)2, Mg(OH)2...etc.)
So it has some thing to do with pH.
Are cation exchange resins reactive?
Cation exchange resins are styrene-divinyl benzene copolymers maybe the benzene ring is attacked by hydroxyl ions? Could you please confirm the solution?or
Thanks in advance.

 

[DrDu]

How soluble are the products?

 

[Enigman]

Don't think solubility has anything to do with it, the products are completely ionizable (all are bases, when anion exchange is carried out first.), so no ppt. should be formed. Unless if it is with the resin itself...

 

[DrDu]

Well, if you don't take a hint, you have to find a solution on your own.

 

[Enigman]

I did, a book I issued from the library confirms my theory that when the sequence is reversed the alkali formed in anion exchange will attack the cation exchange resin (the mechanism isn't mentioned ) and thus degrade it. While in the usual sequence the acid formed in cation exchange passes harmlessly through anion exchange resin.
Thanks for your help.
P.S. I still didn't get what you were trying to point me towards...