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Author Topic: Negative pH, is it possible.  (Read 8159 times)

paul.fr

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Negative pH, is it possible.
« on: 15/08/2007 16:24:30 »
Last weeks kitchen science reminded me to ask this question, i then forgot but eventually remembered.

Is negative pH possible?


 

Offline eric l

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Negative pH, is it possible.
« Reply #1 on: 15/08/2007 16:58:10 »
One question is :  how will you measure it, and how will you make the calibrations.  If your pH meter is calibrated for working exactly and precisely at values between 4 and 10 (standard lab situation) it will not work perfectly even at pH 1.
pH 1 is what you would expect from 0.1 M HCl, and that is a concentration every chemistry student has had to prepare early in his career as a titrant solution.  At this concentration, you can expect the HCl to be completely hydrolyzed into H+ and Cl-, which would be a H+concentration of 10-1.  Still - according to my experience - your pH meter will read something like 1.6 or 1.8.
Concentrated HCl has a concentration about 12 M.  If this could be completely hydrolyzed (which is not the case) the pH would be about -1.05.  With concentrated H2SO4 the H+concentration would be about 36 M, resulting in a pH about -1.56.  But again, this can not be completely hydrolyzed, simply by the lack of water.
In order to have an idea of the degree of hydrolysis at thigh concentrations, conductivity measurements are often preferred above the use of pH meters.
« Last Edit: 15/08/2007 16:59:53 by eric l »
 

Offline lightarrow

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Negative pH, is it possible.
« Reply #2 on: 15/08/2007 20:31:42 »
Last weeks kitchen science reminded me to ask this question, i then forgot but eventually remembered.

Is negative pH possible?

http://en.wikipedia.org/wiki/Super_acidic

Quote
The strongest superacid system, the so-called fluoroantimonic acid, is a combination of hydrogen fluoride and SbF5. In this system, HF releases its proton (H+) concomitant with the binding of F− by the antimony pentafluoride. The resulting anion (SbF6) is both a weak nucleophile and a weak base. The proton effectively becomes "naked", which accounts for the system's extreme acidity. Fluoroantimonic acid is 1019 times stronger than 100% sulfuric acid, and can produce solutions with a pH down to 25.
 

another_someone

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Negative pH, is it possible.
« Reply #3 on: 15/08/2007 23:57:35 »
With such a potent ability to create naked protons, it is interesting to ask if such superacids could be used as the basis for very high energy density electrical batteries?
 

Offline lightarrow

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Negative pH, is it possible.
« Reply #4 on: 16/08/2007 07:59:12 »
With such a potent ability to create naked protons, it is interesting to ask if such superacids could be used as the basis for very high energy density electrical batteries?
Why? How does those batteries work?
 

another_someone

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Negative pH, is it possible.
« Reply #5 on: 16/08/2007 12:48:23 »
With such a potent ability to create naked protons, it is interesting to ask if such superacids could be used as the basis for very high energy density electrical batteries?
Why? How does those batteries work?

I was thinking of using a metal plate with a teflon coating with nono scale holes that allow the protons through but not the larger anions.  This would form the cathode of the battery, but I have not worked out what to do about the anode.
 

Offline daveshorts

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Negative pH, is it possible.
« Reply #6 on: 16/08/2007 14:39:52 »
the H+ ions in acids are not naked protons, they are actually in the form of H3O+ ions which are a lot more stable.

All batteries are based around a chemical reaction that releases energy. I think this is normally the difficult bit to make light, which is why they are using lithium - a light reactive metal, these days.
 

Offline lightarrow

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Negative pH, is it possible.
« Reply #7 on: 16/08/2007 18:56:38 »
the H+ ions in acids are not naked protons, they are actually in the form of H3O+ ions which are a lot more stable.
Yes, this is true in the presence of water molecules, but in those super acids there aren't.
 

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Negative pH, is it possible.
« Reply #7 on: 16/08/2007 18:56:38 »

 

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