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Author Topic: Borax dissociation constant  (Read 1043 times)

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agBr

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Borax dissociation constant
« on: September 08, 2018, 09:21:42 PM »

Hello everyone.
I've been trying to find the dissociation constant of borax and sodium metaborate, unsuccessfuly.
I think that if a conjugate K is known, then we can know the K (by just replacing ka by kb or viceversa), but I don't know the conjugates neither.

Maybe I can dissolve some different quantities in pure water, then use kb=[B+][OH-]/[BOH]
For example, for an unkown pkB 3.67, if I measured:
molar    pH
0.0001  9.87
0.001   10.56
0.01    11.13
0.1     11.65
Then I could see the expected logarithmic relation to concentration, and estimate kb.

I was looking for a published data, as my pH meter is not high quality, and I'm not very experienced.
It seems strange to me though, as borax is such a common chemical, very much used.

Any recommendation?
Thanks!
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billnotgatez

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Re: Borax dissociation constant
« Reply #1 on: September 09, 2018, 08:07:07 AM »

Did you see this

Using Ksp for the Dissolution of Borax in Water to Determine: ∆G°, ∆H° and ∆S°

https://www.scribd.com/doc/227420851/Using-Ksp-for-the-Dissolution-of-Borax-in-Water-to-Determine-G-H-and-S

Are you doing this at home or in school?
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Borek

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Re: Borax dissociation constant
« Reply #2 on: September 11, 2018, 12:36:58 AM »

This is tricky, as there is no single dissociation reaction, rather a complex set of equilibria.
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agBr

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Re: Borax dissociation constant
« Reply #3 on: September 11, 2018, 09:40:30 AM »

billnotgatez, at home; no special equipment.

Borek, that might explain why I couldn't find a simple answer.

I was looking for it, to be able to predict (approx) the pH of a solution as a first guess, then fine tune it experimentally.
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