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Topic: Conductivity of 2 M KCL  (Read 683 times)

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Offline dalav24

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Conductivity of 2 M KCL
« on: January 26, 2024, 10:35:59 AM »
hi,

I thought it would be an easy task to find an answer, but after hours of searching I couldn't find more information that what CRC handbook can offer (reliable information). Conductivity of KCL in 15% mass percent solution at 20C is 208 mS/cm, but I think KCL is not yet saturated at that point. Anyone could help me on this?

A

Offline Borek

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Re: Conductivity of 2 M KCL
« Reply #1 on: January 26, 2024, 11:54:38 AM »
I am not sure what you are asking, what saturation has to do with the question?

2M solution is about 13.7%, for most practical applications just assuming linear dependence between conductivity at 15% and 13.7% is enough to get a reasonably accurate estimate.
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Offline dalav24

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Re: Conductivity of 2 M KCL
« Reply #2 on: January 26, 2024, 12:25:52 PM »
hi,

I am asking what is the conductivity of 2 M KCL solution? CRC handbook ends at 15%, but I think 20% of KCL is still possible. And 25%, but probably not much higher than that...
I don't mind finding an answer in mass percent or mole weight. I am trying to find a conductivity value that is higher than 1M or 15% (those ones I know).

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Offline Borek

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Re: Conductivity of 2 M KCL
« Reply #3 on: January 26, 2024, 02:25:03 PM »
As I already wrote: 2M solution is 13.7%, you don't need tables going up to 20%.

15% KCl solution is 2.2M.
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Offline dalav24

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Re: Conductivity of 2 M KCL
« Reply #4 on: January 26, 2024, 03:17:39 PM »
And the question is still about conductivity. The unit of the questions is S.
Conductivity of 15% KCL at 20C is 208 mS/cm. How about 2 M, 3 M, 20% or 25%?


Offline dalav24

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Re: Conductivity of 2 M KCL
« Reply #6 on: January 26, 2024, 04:20:33 PM »
Thanks Hunter, but I found those already. They do not have an answer. The best source I have found so far is the CRC handbook. Unfortunately it only covers conductivity up to 15% (of KCL solution).

A

Offline Borek

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Re: Conductivity of 2 M KCL
« Reply #7 on: January 26, 2024, 05:58:04 PM »
And the question is still about conductivity. The unit of the questions is S.
Conductivity of 15% KCL at 20C is 208 mS/cm. How about 2 M, 3 M, 20% or 25%?

As I wrote, you can easily extrapolate - 13.7/15*208 mS/cm will give reasonably accurate estimate for 2M solution, as these concentrations are close. In typical applications you rarely know exact concentrations, and you rarely know the geometry of the cell precisely enough to bother with a small error in the conductivity.

This approach won't work for highly different concentrations (so for example I would not suggest to use this approach for 0.1 M solution).
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Offline dalav24

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Re: Conductivity of 2 M KCL
« Reply #8 on: January 27, 2024, 03:27:04 AM »
Thank you Borek for your effort, but unfortunately that is not accurate enough. I am currently using polynomial equation to get conductivity of higher concentrated KCL solutions, but I am looking for an exact answer.

This is pretty close between 5% and 25%:
-6,8672*POWER("mass-percent",2) + 83,01*"mass-percent" + 0,1971

This is 3rd polynomial, which is a bit closer
= -0,3741*POWER("mass-percent",3) - 3,5001*POWER("mass-percent",2) + 74,181*"mass-percent" + 6,4824

Errors are 0.56% and -0.09% respectively based on math. But I am looking for an answer based on fact.

"13.7/15*208" is too far off.

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Offline dalav24

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Re: Conductivity of 2 M KCL
« Reply #9 on: January 27, 2024, 03:45:52 AM »
And before I get a reply started by "As I wrote..." I must clarify that polynomial equations are based on known conductivity values between 5% and 15%. How accurate the equation is between 20% and 25% I do not know - hence the question. I do know how much they deviates based on math, but unfortunately chemistry does not follow equations exactly what comes to conductivity (and not limited to that).

So, if anyone has actual knowledge of how to make KCL solution between 250-300 mS/cm, I am appreciated to know the answer.

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Offline Borek

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Re: Conductivity of 2 M KCL
« Reply #10 on: January 27, 2024, 04:20:40 AM »
I am completely lost.

You originally asked about 2 M. Now I fell like this number doesn't actually matter much, what you are really looking for is a conductivity of solutions above 15%, right?



Note: sounds like you are assuming 208 mS and 15% are exact numbers ("a fact"). They are not. They were measured with unknown accuracy (perhaps defined in the original source, whatever it was, CRC is just a compilation of data). Every number you will find in tables will be just some approximate result of measurement. What makes things worse if you will find different sources of measurements they will differ in numbers listed. Been there, wasted way too much time hoping to find the "real truth" in density tables. Futile exercise. Since then I never hesitate to estimate data between points, they are about as close to the real thing as one will ever get.
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Offline dalav24

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Re: Conductivity of 2 M KCL
« Reply #11 on: January 27, 2024, 07:09:57 AM »
"what you are really looking for is a conductivity of solutions above 15%, right?"
"Since then I never hesitate to estimate data between points"

Yes, you got this right. The number does not actually matter as long as it is higher than what I already have to fine-tune my formula more accurate. I asked using an exact mole weight to clarify what I am asking rather than "give me a conductivity value of high density KCL solution". Then you would reply that I need to be more specific what I ask. Actually.... I don't think it is not possible to ask this the right Borek way since you obviously try to find everything that is wrong in my question.

And I am fully aware that numbers vary between sources. I have done quite a lot researching myself too.

A

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