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Topic: Borax dissociation constant  (Read 1691 times)

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Offline agBr

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Borax dissociation constant
« on: September 09, 2018, 03:21:42 AM »
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!

Offline billnotgatez

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Re: Borax dissociation constant
« Reply #1 on: September 09, 2018, 02:07:07 PM »
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?

Offline Borek

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Re: Borax dissociation constant
« Reply #2 on: September 11, 2018, 06:36:58 AM »
This is tricky, as there is no single dissociation reaction, rather a complex set of equilibria.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info, PZWT_s1

Offline agBr

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Re: Borax dissociation constant
« Reply #3 on: September 11, 2018, 03:40:30 PM »
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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