[Dolphinsiu]

I need to an experiment as follows:

Measure the conductivity and pH in the following cases:

1. Passing treated tape water through after cationic ion-exchanger(resin column) and then anionic ion-exchanger.
2. Passing treated tape water through after anionic ion-exchanger and then cationic ion-exchanger.
3.Passing treated tape water through after mixed ion-exchanger.

Are the conductivity and pH of the water samples treated by different methods the same? If not, suggest reason(s) for the difference(s).
My answer is no (not the same), but I don't know the reasons. Does any website contain similiar information? Thank you!

[Borek]

Is your answer result of an experiment, or just a wild guess?

[Dolphinsiu]

Just a wild guess! If yes, we needn't to suggest reasons!

So I think there is 99.9% probability confident interval to say that the answer is no!

But I cannot suggest any reasons! Would you give me some hints??

[Borek]

What ion exchanger does?

[Dolphinsiu]

Cationic exchanger is to remove all cations with the replacement of hydrogen ions
whereas anionic exchanger is to remove all anions with the replacement of hydroxide ions.
Mixed exchangers is to remove both ions with the replacement of water.
But is the above information really an answers for reasons?Is it enough?

[Borek]

IMHO that's all information you need. I don't think it is a trick question - or at least I am not aware of any way this question could be tricky.

[Dolphinsiu]

Thank you for your hint and opinion!But why the conductivity decreases in both cases:

1. when passing through cationic ion-exchanger
2. when passing through anionic ion-exchanger
3. when passing through mixed ion-exchanger

Is it related to electrochemical series? (or to see which one is preferentially discharged ??)

1. When compared to K+, Ca2+, H+ is preferentially discharged. High conductivity is resulted.
2. When compared to Cl-, Br-, OH- is preferentially discharged. High conductivity is resulted.
(Am I wrong?)

3. When compared to ionic cpd like KCl, H2O is covalent. Low conductivity is resulted

[Borek]

Sorry, but I have no idea what you mean. You refer to 'both' but you list three cases. You ask why conductivity decrases, but you list cases when it increases. I can't follow.

Electrochemical series has nothing to do with the case. Differences in specific condutivity and neutralization should be enough to explain all effects you observe/expect.

[Dolphinsiu]

Do u mean case 3 is okay? but case 1 and 2 need to use 'neutralization' to explain their difference in conductivity. But how?

Actually conductivity dependa on what factors?

For case one, I have seen some website, only saying that as metallic ions (like Ca2+, Na+, Mg2+ ) decreases then conductivity decreases. Is this explaination too simple?

[Borek]

Conductivity is a sum of individual conductivities (as long as we are not talking concentrated solutions). H⁺ and OH^- have higher specific conductivity than any other ion.

If you replace cations with equivalent concentration of H⁺ what would you expect?

If you reaplace anions with equivalent concentration of OH^- what would you expect?

Finally, what happens when you have both H⁺ and OH^- in the solution?

[Dolphinsiu]

When H+ is replaced, what the solution left is all H+ ions and anionic ions. As H+ has higher specific conductivity, conductivity increases.

When H+ is replaced, what the solution left is all OH- ions and cationic ions. As OH- has higher specific conductivity, conductivity increases.

When both H+/OH- in the solution, as H+ and OH- have higher specific conductivity than any other ion, conductivity increases.

Then all these three expectations are against the experimental results, does the measuring instrument have something wrong?

[ARGOS++]

Dear Dolphinsiu,

You may have forgotten to put “something” in your calculation, that’s
telling you How Much H⁺ and How Much OH^-  CAN EXIST AT the SAME Time in
the whole amount of Water.
Somebody call it a constant wit name: “…….”.
But, of WHAT NATURE will the Product be?

May it be a Hint to you?
Good Luck!
                    ARGOS⁺⁺

[Borek]

Just a wild guess!

Then all these three expectations are against the experimental results, does the measuring instrument have something wrong?

How can they be against experimental results, if what you have is just a wild guess?

[Dolphinsiu]

For case 1, saturated H+ in treated water will make conductivity decreases although H+ has higher specific conductivity than other cations. It seems I can get your meaning.

Do saturated H2O molecules do the same thing?

[ARGOS++]

Dear Dolphinsiu,

Have you thought about, That ONLY a very small Amount of “ionised water” can exist in water? 
Otherwise you would nearly NOT be able to measure any pH.
And of what nature is “recombined” (not "saturated"!??!) water?

Good Luck!
                    ARGOS⁺⁺