Henry H. Bauer

The electrochemical transfer-coefficient

Summary In discussions of the kinetics of electrode reactions, the central issue is the manner in which the rate constants depend on the electrode potential. It is often stated ex cathedra that this dependence is exponential and that constant fractions of the electrode potential appear in the exponential terms; these fractions are characterized by the “transfer coefficient, α” or “symmetry factor, β”. The impression is thereby given that we understand the physical nature of the “transfer” or “symmetry” that determines the magnitude of α or β. In fact, the terminology “transfer coefficient” was introduced in connection with a model for the electron transfer that is not accpted; and the interpretation of β as describing the symmetry of the energy barrier is inadequate since, by definition, β describes the change in the barrier as the potential changes, and not any property of the barrier at a particular potential. There is no adequate justification for an a priori introduction of the transfer coefficient as an implicitly potential-independent parameter.

Supporting-electrolyte effects in tensammetry

Summary The adsorption of n -amyl alcohol has been studied by tensammetry in the presence of various electrolytes. The apparent adsorbability of the alcohol increased with increasing concentration of sodium sulfate under certain circumstances. This apparent anomaly disappears when corrections are made for changes of the activity coefficient of the alcohol, resulting from salting out.

Specific adsorption of anions from tensammetric measurements

Abstract Measurement of desorption potentials of surfactants in a variety of electrolytes indicates that the relative specific adsorbabilities of the electrolyte ions can be rapidly determined by comparing the shifts of the desorption potentials. Differences seen at positively and negatively charged mercury could be due to variations in the orientation of water and/or surfactant molecules.

Phase-Selective Fundamental and Second Harmonic Tensammetry

Abstract Phase-selective fundamental and second-harmonic tensammetry show that the desorption of uncharged surfactants is strongly influenced by the supporting electrolyte in the region of the desorption peaks. Quantitative data, however, can be extracted only if assumptions are made about adsorption isotherms, and in particular about the potential-dependence of the surface coverage around the desorption peaks. A satisfactory model and theoretical treatment has to be developed. In the meantime, such studies can provide useful empirical data.

Desorption Potentials of Alkyl Alcohols and Specific Adsorption of Anions

Abstract : The potentials of desorption of various alkyl alcohols have been studied as a function of concentration of the alcohol and of the nature and concentration of various electrolytes. Specific adsorption of the electrolyte ions in reflected in shifts of the desorption peaks of the alcohols. At anodic potentials, the order of specific adsorption appears to be chloride, sulfate, perchlorate, fluoride, and at cathodic potentials (vs. S.C.E.), chloride, perchlorate, sulfate, and fluoride. Under some conditions, the order may be different, but the present results do not provide sufficiently strong evidence to reach firm conclusions about this. (Author)

USE OF A COMMERCIAL LOCK-IN AMPLIFIER IN PHASE-SELECTIVE SECOND-HARMONIC A.C. POLAROGRAPHY.

Abstract : Lock-in amplifiers are now quite commonly used in a. c. polarography. The same units can be used for the measurement of higher harmonics. Several possible ways of using one such unit for second-harmonic studies are discussed, and one technique recommended. (Author)

Determination of the double-layer capacity in the presence of a depolarizer

Summary A method is described by which the double-layer capacity can be measured at potentials where an a.c. polarographic wave (faradaic admittance) is present. No special assumptions are made about the nature of the faradaic admittance and the latter can therefore be measured and studied in cases where it is “anomalous”, e.g., in systems involving adsorbed depolarizers.

Electrolytic reduction of 3-carbethoxyquinoline

Abstract Two well-defined one-electron waves are observed on the polarograms for the reduction of 3-carbethoxyquinoline in 95% aqueous ethanol containing 1 M ammonium acetate. During macroscate electrolysis at a potential on the plateau of either wave, the ratio of the heights of the waves remains equal to one. Polarographic and voltammetric evidence is presented that the first wave represents a reversible one-electron reduction to a radical which rapidly dimerizes; and the second wave represents an irreversible one-electron reduction of the initially formed radical. The reduction mechanism suggested by the electrochemical evidence is verified by the isolation of dimeric products from controlled-potential electrolysis at the top of the first wave and the isolation of 1,4-dihydro-3-carbethoxyquinoline at the top of the second wave. The chemical characteristics of the dimeric products are discussed.

Measurement of solution streaming in polarographic maxima of the second kind

Summary A detailed procedure for the measurement of the speed of solution streaming in maxima of the second kind is described. The solution velocities increase to maximal values at the drop surface and different velocities are found in various regions around the drop. The effect of varying flow rate of mercury, concentration of supporting electrolyte and presence of a surfactant on these velocities is reported.

A precision audio-frequency voltage regulator

Abstract : A source of precisely known alternating voltages is described. The output remains constant to within 0.1% for variation of plus or minus 40% in the input voltage (frequencies between 30 Hz and 4 kHz). The principle of operation is based on negative feedback, using a light-emitting diode and photosensitive resistor to control the gain. The instrument will serve to increase the accuracy of studies of the behavior of electrochemical cells under applied alternating voltages. (Author)