| High-precision coulometric titrations of the weak acids, benzoic, furoic and adipic have been performed for the purpose of redetermining the value of the faraday. The titrations have been performed in water and in mixed solvents consisting of water plus water-miscible liquids.;A new, high-precision coulometric titration apparatus has been assembled in which the uncertainties of the measurements have been reduced to less than one part per million (p.p.m.). A bubble trap has been perfected which eliminates the loss of the electrolyte by entrapment in the gasses released by the working electrode. National Bureau of Standards (NBS) SRM 84d Potassium Hydrogen Phthalate has been titrated as a check on the operation of the titration apparatus.;The inflection-point in the titration curve of a strong acid obtained coulometrically with the glass electrode has been found to coincide with the equivalence-point.;Electromigration of hydroxide ions, hydrogen ions and hydrogen phthalate anions across the porous membranes separating the compartments of the coulometric titration cell has been investigated.;The purity of NBS 84d Potassium Hydrogen Phthalate has been determined by coulometric titration to be 99.9930 per cent, the relative standard deviation being 19 p.p.m.;The purity of NBS SRM 350 Benzoic Acid has been determined by coulometric titration in 30 per cent methanol-70 per cent water and found to be 99.9901 per cent, the relative standard deviation being 54 p.p.m. Titration in water has been found impossible because of low solubility of the acid.;Benzoic acid purified by sublimation has been titrated in various mixed solvents yielding for the purity: (a) in 30 per cent methanol, 100.0041 per cent; and (b) in 30 per cent 2-propanol, 100.0019 per cent. The sublimed acid has been fused under a vacuum and titrated yielding for the purity: (a) in 30 per cent acetone, 100.0010 per cent; and (b) in 50 per cent acetone, 100.0036 per cent. The relative standard deviation in these solvents has been high, 56 to 163 p.p.m.;Coulometric titrations of furoic acid purified by sublimation has yielded for the purity and relative standard deviation: (a) 99.9964 per cent, 19 p.p.m., in water; and (b) 99.9966 per cent, 60 p.p.m., in 30 per cent methanol. Coulometric titrations using mixed solvents have been found to have high standard deviations compared to water but the results in the mixed solvents have been identical with the results in water.;As judged by coulometric titration, the purity of adipic acid has not been improved by sublimation. |
