INTERPRETATION OF pH MEASUREMENTS IN ALCOHOL—WATER SOLVENTS¹

Abstract

The operational pH numbers for solutions in alcohol-water solvents obtained from the e.m.f. of the cell with hydrogen (or glass) electrode, salt bridge, and calomel reference electrode, standardized with aqueous buffer standards, are subject to no simple interpretation. Because of the indeterminate potential at the junction solution X (alcohol-HaO) j KC1 bridge (aq.), they do not lie on a conventional scale of hydrogen ion activity referred either to the aqueous standard state ( ) or to the standard state in the alcoholic medium (pon*)• Values of £¡ + log m7ci (where E¡ is the liquid-junction potential expressed in pH units and "7ci is the primary medium effect of chloride ion) -were found to be as constant for different buffer solutions in alcoholic solvents of fixed composition as for the strictly aqueous medium. Inasmuch as m7ci at a given temperature is dependent only on solvent composition, the liquid-junction potential must therefore also be nearly constant for a given solvent medium. Correction terms E¡ -log myn = 5 have been calculated, and it is shown that pHclosely approximates pan* under optimum conditions of measurement. An operational scale of pH* (which is related to * in the same way that pH is related to pan) is described. Values of pan* were obtained for 12 solutions in methanol-water solvents (0 to 68.1 wt. % MeOH) and for 3 solutions in ethanol-water solvents (0 to 100% EtOH).chosen for measurement of the difference pH*(X) -pH*(S).

Polyphenol extraction from grape wastes: Solvent and pH effect

“…The values of δ were obtained from the literature, ranging from −2.9 to 0 [15,16]. The liquid extracts were analyzed for their total polyphenolic index (TPI) at different times during 8 h, for the determination of extraction kinetics.…”

A Novel Cholinergic Action of Alcohol and the Development of Tolerance to That Effect inCaenorhabditis elegans

“…At the concentration of ethanol we used, neither acidity nor viscosity are expected to be different from that in NGM media alone (Bates et al 1963;Khattab et al 2012). In the sealed petri plate, we might expect the presence of ethanol to alter vapor pressure.…”

Practical measurement of pH in amphiprotic and mixed solvents

“…It is the purpose ofthis report to recommend a procedure which, with further development, gives promise of permitting a useful interpretation, under optimum conditions, of practical pH numbers for many amphiprotic and mixed solvents. This approach, which has already been set forth elsewhere4, 6, has its roots in earlier proposals for the useful measurement of acidity in various media7-9.…”

“…Similarly, molal activity coefficients are designated either wYi or sYi, depending on the standard state used. The difference between the two acidity functions is always (6) where m YHCI is the "medium effect" for the transfer of hydrochloric acid from the aqueous standard state to the standard state in solvent s. It has been shown6 that measurements of pH, Pw(aHyCI), and mYHCh together with a Debye-Hückel correction for interionic effects (small for dilute buffer solutions) can Iead to the useful quantity 8 8::::: Ei-log mYH (…”