The electrochemical equivalent of pure silver - a value of the Faraday

Abstract

Oxygen-free high-pu rity samples were used in a precise deter mina tion of the electrochemi cal equival ent of silver . A comprehensive mass spec trometric analysis for impurities was performed . Our value agrees well wi th prior meas urements of the same qua ntity at th e Na ti onal Bureau of Sta ndards (NBS) by Craig and coworke rs_ We find the elec troc hemi cal equivalent of pure silver to be 1.1179648 mg C-')8S' Attached to this figur e is an unce rtainty whose random co mponent (standa rd deviation of th e mean of 8 deter minati ons) is 9.5 X 10-7 mg Co, (0.85 ppm). Th e roo t-sum-squ are of systema tic uncertainties of known origin is 1.07 X 10-6 mg Co, (0.96 ppm). The above value for the elec trochemical equival ent of silver'leads us to cal culate th e Faraday to be: F = 96486.33 (24) AN B s . s . mol-' (2.5 ppm).

Atomic weights of the elements. Review 2000 (IUPAC Technical Report)

“…In an attempt to resolve the discrepancy, a new experimental determination was performed on the mass equivalence of the unit quantity of electricity involved in the electrochemical deposition or dissolution of Ag (E Ag ). Using the IUPAC value for the atomic weight of Ag, 107.8682 (10), and the equation F = M(Ag) / E Ag , a new value of F = 96 486.33 C mol -1 was obtained [101]. The relative uncertainty of 2.5 × 10 -6 in this value represented an approximate threefold improvement over the previous best determination of F. More importantly, it was consistent with the earlier electrochemically based determinations.…”

The 1986 adjustment of the fundamental physical constants

“…The 1960 NBS experiments were repeated in a series of measurements extending over a nine-year period (1975 -1984). The electrochemical equivalent of Ag was measured by Bower and Davis (1980) while the isotopic analysis and the determination of the molar mass of the sample of Ag used in the electrolysis is due to Powell, Murphy, and Gramlich (1982). More recently, motivated by the present adjustment of the constants, additional measurements of the impurity content of the Ag used in the experiment were carried out (Taylor, 1985).…”

On the dimensionality of the Avogadro constant and the definition of the mole

“…The latest IAC result has u r = 3 × 10 -8 [35], still more than an order of magnitude greater than u r (α 2 ). The best practical determination of F is by silver coulometry, and gives a relative uncertainty of 1.3 × 10 -6 [21,58,59], almost three orders of magnitude higher than u r (α 2 ). 10 The current value of R comes from direct measurements of the speed of sound in argon, and has u r = 1.7 × 10 -6 [21,58,60,61]: although there are ongoing efforts to measure k directly [62,63], rather than to determine it by k = R/N A (23) these have yet to reach the necessary precision even to supersede the value obtained from equation (22) [64,65].…”