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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: victoriayepez on November 28, 2015, 05:02:22 PM

Title: PH levels in Non-Aqueous Solution
Post by: victoriayepez on November 28, 2015, 05:02:22 PM
Does PH matter in a dry crystalline solution? When do you take into account PH? How do you determine a good buffer system for a solid mixture?

Thanks
Victoria

Title: Re: PH levels in Non-Aqueous Solution
Post by: Arkcon on November 28, 2015, 05:17:56 PM
Basically, pH isn't defined except as a dilute aqueous solution.  So there's really no useful answer we can give to any of your questions.
Title: Re: PH levels in Non-Aqueous Solution
Post by: electronpusher96 on November 29, 2015, 07:36:53 PM
Does PH matter in a dry crystalline solution? When do you take into account PH? How do you determine a good buffer system for a solid mixture?

Thanks
Victoria

1)pH is important in many non-aquaous solutions, but defined differently due to different/no dissociation.  I've always been a bit unclear on it; they don't give you a good understanding of it in general chem/analytical chem.   

http://www.iupac.org/publications/analytical_compendium/Cha03sec5.pdf


2) Most solids don't normally have a "pH" in the sense that there's a variable H+ concentration, but they can change a solution's pH after dissolution.  To determine a solid's effect on pH, determine what ions are produced by dissolution and review their pKa values.

Please correct me if I'm wrong, I know this is very generalized and I'm not an expert.
Title: Re: PH levels in Non-Aqueous Solution
Post by: victoriayepez on November 29, 2015, 08:53:42 PM
Thanks so much. Very Helpful puts me one the right track.
Title: Re: PH levels in Non-Aqueous Solution
Post by: Borek on November 30, 2015, 02:18:45 AM
pH is important in many non-aquaous solutions, but defined differently due to different/no dissociation.  I've always been a bit unclear on it; they don't give you a good understanding of it in general chem/analytical chem.

Just like Arckon said - pH is defined for aqueous (and not too concentrated solutions). That means - between other things - that we know how to measure pH of diluted water solutions, but the same technique, if applied to concentrated solutions/non-aqueous solutions is not guaranteed to give reliable results. In other words - if we were both to measure pH of a 0.1 M acetic acid solutions using different electrodes and different ORP meters we will get the same result, but if we were to measure pH of 0.1 M acetic acid in ethanol (using the same devices and electrodes), we would probably get different results, and neither could be called a "correct one". At the same time "acidity" is an important parameter for almost every mixture in which chemical processes take place. There is no such thing as a "universal pH scale", one that would work in every mixture, but we often extend water pH scale to other solutions in a handwavy manner, assuming it will give at least qualitatively correct result. In most cases it does, but there is always a risk it will fail.