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Topic: pH Indicators and Solvent Based Systems  (Read 6376 times)

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Offline gluedudeguru

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pH Indicators and Solvent Based Systems
« on: December 07, 2009, 10:39:14 AM »
I have a very hydrophobic solvent solution and its current pH is around 7.  I have been trying to use phnthln as an idicator (which the system accepts seeing as though it is 95% ethanol).  The problem comes when trying to pH adjust the solution with 50/50 NaOH.  This being dissolved in water does not play nice with the already solvent/hydrophobic system.  The closest i have gotten is to just use a cowell mixer and just beat the crap out of the solution while adding the indicator and then slowly the NaOH, the solution is very thick (2000 cPs ish) so the globules of indicator and NaOH are suspended in soln, but eventually fall out (and even sometimes turn a yellow).  i need the color to be dispersed throught the product for an extended period of time, months.  Any help or guidance would be greatly appreciated.

  • Any way to make the solvent system change pH without using water based NaOH (some other pH modifier), or to disguise the base as a water hating
  • Also, why does the pH/NaOH turn yellow of all colors after settling and reacting with air?

Offline Borek

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Re: pH Indicators and Solvent Based Systems
« Reply #1 on: December 07, 2009, 11:08:38 AM »
I have a very hydrophobic solvent solution and its current pH is around 7.

How do you measure the pH? How much water is in the solution?
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Offline gluedudeguru

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Re: pH Indicators and Solvent Based Systems
« Reply #2 on: December 08, 2009, 07:45:21 AM »
There is no water in the system (assuming the company we get our solvents from).  The pH was tested via pH meter as well as the aforemention phenolphthalein, titration with 50% NaOH.  The NaOH will float in globules in solution, clear at first, but turning pink after the base addition.  I know that solvents dont necessarily work the same way as aquesous solutions, but is there a way to get these solvents to uptake a more basic soln, or a mediary between the aqueous and the non-aquesous, a soap of sorts?

Offline Borek

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Re: pH Indicators and Solvent Based Systems
« Reply #3 on: December 08, 2009, 09:47:01 AM »
Whatever your pH meter shows, it lies - it is not designed to work in other solvents then water. Besides, pH scale is defined for water systems, so trying to apply it to system that doesn't contain water doesn't make much sense. Even if activity of H+ is 10-7 (that is, straight and blind application of pH) it doesn't necesarilly mean solution is neutral, that happens only for water at (more or less) room temperature.
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Offline gluedudeguru

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Re: pH Indicators and Solvent Based Systems
« Reply #4 on: January 06, 2010, 07:41:18 AM »
I do agree that solvents void of any water do not have a traditional pH, it still has an effect with the indicator in the mixture when adding the NaOH.  The pH of the solution is not important, the color change is what i am looking for.  I want the wet and viscous mixture to be colored when wet, but clear when dry.  (base when wet, pink, CO2 in air makes mixture acidic, clear)

And why does phenolphthalein go yellow well after it goes pink?  It only happens to half the trials.

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