- #1
Enigman
- 647
- 311
Why is the cation exchange always carried out before anion exchange in softening of hard water by ion exchange resins?
Plz. Help:(
Plz. Help:(
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Discussion Overview
The discussion centers on the process of softening hard water using ion exchange resins, specifically the sequence of cation and anion exchange. Participants explore the chemical compounds formed during these processes and their implications on the physical properties of the resulting solutions.
Discussion Character
- Technical explanation
- Debate/contested
- Conceptual clarification
Main Points Raised
- One participant questions why cation exchange is performed before anion exchange in water softening.
- Another participant inquires about the compounds formed during the two exchange processes and their physical properties.
- A participant suggests that hydronium ions are produced during cation exchange and hydroxyl ions during anion exchange, linking this to pH changes in the resulting solutions.
- Concerns are raised about the reactivity of cation exchange resins, with speculation about the potential attack on the resin by hydroxyl ions.
- One participant asserts that solubility of the products is not relevant, stating that the products are completely ionizable and do not form precipitates unless interacting with the resin.
- A later reply mentions that reversing the sequence of exchanges could lead to degradation of the cation exchange resin due to alkali formation, while the usual sequence allows acids to pass through harmlessly.
Areas of Agreement / Disagreement
Participants express differing views on the relevance of solubility and the effects of reversing the order of ion exchange. There is no consensus on the implications of these processes or the mechanisms involved.
Contextual Notes
Some assumptions about the reactivity of the resins and the specific mechanisms of degradation remain unresolved, as do the details of the physical properties of the compounds formed.
- #2
DrDu
Science Advisor
- 6,423
- 1,004
What compounds are predominantly formed in the two alternative exchange processes?
What are their physical properties?
What are their physical properties?
- #3
Enigman
- 647
- 311
DrDu said:
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.
- #4
DrDu
Science Advisor
- 6,423
- 1,004
How soluble are the products?
- #5
Enigman
- 647
- 311
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...
- #6
DrDu
Science Advisor
- 6,423
- 1,004
Well, if you don't take a hint, you have to find a solution on your own.
- #7
Enigman
- 647
- 311
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...
) 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...