[ROSETTA]

Hi there, on addition of 50 % methanol to a phosphate buffer solution, the pH increases, because the dielectric constant is lowered, suppressing the ionisation of the ionic species.
Conversely on addition of 50% methanol to a glycine buffer, the pH decreases.
My question is, if you have a buffer of ammonium acetate, is the ionisation of both species affected by the addition of methanol, and therefore, the pH is altered as a balance between the two
Hope someone can clarify
Rosie

[Arkcon]

Addition of solvents other than water to a aqueous solution shifts the pH closer to neutral.  This effect is not due to a shift in dielectric constant, but instead due to a different dissociation constant for [H]⁺.  Now, starting with that, what is your question again?

[ROSETTA]

Hi, on addition of methanol to ammonium acetate buffers will the pH increase or decrease?
Considering that for ammonium buffers the pH decreases, and for acetic acid buffers increases
The hypothesis of the dielectric constant was postulated by Tindall and Perry JCA 988 (2003) 309-312 based on the work of de Ligny et al
Hope you can help
Thanks Rosie

[Arkcon]

Hi, on addition of methanol to ammonium acetate buffers will the pH increase or decrease?
Considering that for ammonium buffers the pH decreases, and for acetic acid buffers increases

The pH of the final buffer shifts closer to neutral.  How much closer, is different for each ionic species.  Determine experimentally.

The hypothesis of the dielectric constant was postulated by Tindall and Perry JCA 988 (2003) 309-312 based on the work of de Ligny et al

I do not have access to peer-reviewed periodicals.    My statement, regarding the disassociation constant of [H]⁺ is based on the classical definition of pH=pKa log₁₀([H]⁺).  The activity of [H]⁺ will be different for methanol, acetonitrile, and others, generally lower, than for water.

[ROSETTA]

Hi there Arkon, thank you for taking the time to reply, I will indeed determine experimentally
Many thanks
Rosie

[ARGOS++]

Dear Rosetta;

I’m interested how you will determine it experimentally, because electrodes “don’t work”, or at least not properly in/with organic solvents. Also Calibration in Solvents is nearly impossible too!

I ask, because I think I have an Idea how it can practically/experimentally be done anyway.

Good Luck!
                    ARGOS⁺⁺