The Reduction Potential of Pentavalent Vanadium to Vanadyl Ion in Hydrochloric Acid Solutions. Fluoresenzversuch AnOrganische Daempfe, Besonders Aceton. Studies of the Nature and Reactions of Oxidized Silver Compounds, Especially in Nitric Acid

Citation

Coryell, Charles Dubois (1935) The Reduction Potential of Pentavalent Vanadium to Vanadyl Ion in Hydrochloric Acid Solutions. Fluoresenzversuch AnOrganische Daempfe, Besonders Aceton. Studies of the Nature and Reactions of Oxidized Silver Compounds, Especially in Nitric Acid. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/A37S-KX50. https://resolver.caltech.edu/CaltechTHESIS:01312011-113455408

Abstract

I:
A series of measurements of the electromotive force of half-cells made up of solutions of V₂O₅ and VOCl₂ in excess HCl against calomel half cells in HCl of the same strength,for which there were negligible liquid junctions, is presented. The acid concentration was varied from 0.01012 to 2.146 M. The observed potentials were corrected for calomel cell and for other concentrations as per the following assumed reaction:
VO⁺⁺ + 2 H₂O == HVO₃ + 3 H⁺ E^-.
Values of E₀ so obtained decreased with decreasing acid concentration. This decrease was correlated with complex formation ( V(OH)⁺₄, etc.) noted in increased solubility of freshly precipitated HVO₃ in HCl as measured. The potential in molal HCl is -1.0216 Volts, corresponding to a free energy decrease of +23,572 cal. when 1/2 H₂ reduces a pentavalent atom of vanadium (irrespective of nature) in 1.00 M HC1. From the temperature coefficient of the cell, the heat content increase for the same reaction was found to be -29,350 cal.

II:
Experiments carried out in the Physico-chemical Institute of the Technische Hochschule München in searching for a discrete fluorescence spectrum of acetone vapor are given. A detailed description of the apparatus for studying flowing gases at various pressures is included, as well as a study of benzene fluorescence which was used to standardize technique and test the sensitivity of the methods. Long illuminations of acetone vapor at various pressures with powerful Al sparks gave no fluorescence, although the line 1862 Å was absorbed. A mercury arc produced in short time three continua in the visible, two of which were already known, but no line spectrum. Conditions were found with Tesla excitation in which output of light was good but little CO was formed in decomposition. Nine hours exposure yielded only the continua mentioned. Preliminary work was done on methyl iodide.

III:
The analytical chemistry of bivalent silver solutions is discussed, especially the exact TlNO₃ method and the rapid Cr(NO₃)₃ method. Conditions prevailing in anodic oxidation are outlined, as well as a convenient method for preparation of solution. The main work deals with the complicated kinetics of oxidation of water by argentic silver at 25° and at 0°. The rate of decomposition of the argentic silver solution may be represented at constant acid by the equation:
-d(Ag⁺⁺)/dt = k₂(Ag⁺⁺²/(Ag⁺) + k₄(Ag⁺⁺⁴/(Ag⁺)
where k₂ varies roughly inversely as the square of the hydrogen ion concentration and is not greatly decreased by increasing ionic strength while k_4 falls off very rapidly with increasing acid and ionic strength. The mechanism seems to involve tervalent silver. From existent data the free energies of formation at 0° C. of the following are calculated: Ag⁺⁺, Ag₂O₃, AgO, Ag₂O, O₃, H₂O and Ag⁺, and a number of equilibria involving them are predicted and discussed.

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