Pretreated bright palladium electrode in potentiometric redox titrations Titration of Cr(2)O(7)(2-) and Ce(4+) with Fe(2+)

The behaviour of the bright palladium electrode toward the redox systems Cr(2)O(7)(2-)/Fe(2+) and Ce(4+)/Fe(2+) (in potentiometric titration) has been investigated as a function of pretreatment of the electrode. Anodization of the electrode at potentials higher than 800 mV increases DeltaE at the equivalence point by 300-400 mV for the dichromate titration. The sharp change in potential is due to the reaction between PdO(2) and Fe(2+). The equivalence point corresponds to the beginning of the potential drop, rather than the inflexion point, especially for dilute solutions. If the electrode is ignited before use the surface oxide PdO is oxidized to PdO(2) by Cr(V), the potential increases during the titration and DeltaE is 200 mV bigger than when an untreated electrode is used. In the titration of Ce(4+) with Fe(2+) the DeltaE is largest with untreated electrodes, and if the anodized electrode is used, the titration curves clearly show the reaction between PdO(2) and Fe(2+).     

Study of the thermal decomposition of solids in a fluidized bed, III

The influence of the air humidity upon the thermal decomposition of diammonium hydrogen phosphate was studied in a fluidized bed, under isothermal conditions. It was found that the increase of the decomposition rate is influenced directly by the partial pressure of the water vapour in the air, and indirectly by the working temperature. The moisture effect is explained by the salt hydrolysis in the water condensed on the grain surface. The energy of activation of the thermal decomposition decreases when the air humidity increases.

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Zusammenfassung Der Einfluß der Luftfeuchtigkeit auf die thermische Zersetzung des Diammoniumhydrogenphosphats wurde in fluidisiertem Bett unter isothermen Verhältnissen studiert. Die Zunahme der Zersetzungsgeschwindigkeit war direkt proportional dem partialen Wasserdampfdruck in der Luft und indirekt proportional der Arbeitstemperatur. Diese Wirkung wird durch Salzhydrolyse in dem kondensierten Wasser an der Kernoberfläche erklärt. Die Aktivierungsenergie der thermischen Zersetzung nimmt mit zunehmendem Feuchtigkeitsgehalt ab.

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Résumé On a étudié l'influence de l'humidité atmosphérique sur la décomposition thermique de (NH₄)₂HPO₄ en lit fluidisé, en conditions isothermes. La pression partielle de la vapeur d'eau dans l'air intervient directement sur l'augmentation de la vitesse de décomposition et exerce une action indirecte sur la température de travail. On a expliqué l'effet de l'humidité par l'hydrolyse du sel dans l'eau condensée à la surface des grains. La valeur de l'énergie d'activation de la décomposition thermique diminue quand l'humidité atmosphérique augmente.

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Utilization of an Hg(2+)-sensitive membrane-electrode in the complexometric determination of Bi(3+), Fe(3+) and Cr(3+)

The paper reports the results obtained in the complexometric determination of Bi(3+), Fe(3+) and Cr(3+) by using an Hg(2+)-sensitive membrane-electrode for the end-point indication. The determination of Bi(3+) and Fe(3+) is performed after addition of mercuric complexonate from which these cations release Hg(2+) by means of which the electrode senses the equivalence point. In the case of Cr(3+) an excess of complexone is added and the surplus is titrated with a standard solution of Hg(2+) in the presence of the Hg(2+)-sensitive membrane-electrode.     

Niederschlagsbildung-III Kristallwachstum und einfluss der fremdionenkonzentration in der bariumsulfatfällung

The influence of foreign ions on the particle size of barium sulphate precipitates has been investigated by sedimentation experiments, establishing that NaCl, NaNO(3), KBr, KNO(3), and other salts at high concentrations powerfully hinder the growth of the crystals even at high supersaturation. The linear growth rate has been measured as a function of BaSO(4) concentration, foreign ion concentration and [BaCl(2)]/[K(2)SO(4)] ratio. Because the growth is already diffusion controlled at a fivefold supersaturation, the BaSO(4) precipitates will not undergo Ostwald ripening. A suitable apparatus has been devised for the investigations.     

Study of the thermal decomposition of solids in a fluidized bed,II

In order to eliminate the errors of the TG method with a static layer, and to determine the influence of the heating rate, the composition of the carrier gas and the particle size of the solids, a method of thermal gas evolution from a fluidized bed (FTGE) with continuous and linear increase of temperature was worked out and the thermal decomposition of diammonium hydrogen phosphate was followed. This method gives reproducible results and makes possible the determination of the apparent activation energies and kinetic parameters.

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Zusammenfassung Um die Fehler der TG Methode unter fixierten Verhältnissen zu eliminieren, den Einfluß der Temperaturerhöhung, der Zusammensetzung des Trägergases und des Ausmaßes der Festkörper zu klären, wurde eine thermogasanalytische Methode im fluidisierten Bett (FTGE) mit kontinuierlichem und linearem Temperaturanstieg entwickelt und die thermische Zersetzung des Diammonium-biphosphates verfolgt. Man erhielt mit dieser Methode reproduzierbare Ergebnisse. Sie ist zur Bestimmung der scheinbaren Aktivierungsenergien und kinetischer Parameter geeignet.

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Résumé Dans le but d'éliminer les erreurs des procédés thermogravimétriques avec couches fixes, et de mettre en évidence l'influence de la vitesse d'échauffement de la composition du gaz porteur et de la dimension des solides, on a développé une méthode d'analyse des gaz dégagés, avec lit fluidifié et élévation de la température continue et linéaire. On a suivi ainsi la décomposition thermique de (NH₄)₂HPO₄. Cette méthode donne des résultats reproductibles et rend possible la détermination des énergies d'activation apparentes et des paramètres cinétiques.

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Some parts presented at the IIIrd Analytical Conference, Budapest, 1970     

Conductometric titration with indicating resistance-III Mechanism of the PVC + Alassion CS (Cationite R-H) + dioctyl phthalate (plasticizer) membrane as indicating resistance

The problem of conductometric acid-base titration in a highly-conducting medium (5M sodium chloride) has been solved by introducing a PVC + Alassion CS + dioctyl phthalate membrane between the two electrodes. The equivalence point is marked by a sudden decrease in conductivity. The membrane (obtained by plasticization at 175 degrees ) functions through the phthalic acid dissolved in the PVC membrane, this acid being formed by decomposition of the dioctyl phthalate by the sulphonic acid groups of the cation-exchanger. In this process the sulphonic acid groups are esterified, but hydrolyse on being treated for 2-3 hr with NaOH, and then increase the conductivity in the membrane.     

In Process Citation

A first attempt to apply inorganic membranes made from parchment paper impregnated with alkaline earth precipitates, as indicating electrodes for potentiometric acid-base titrations in nonaqueous media, is presented. Mixtures of acids can be titrated and the course of the titration is a function of the nature of the solvent and the titrant.     

Characterization of ceramic ion-selective membrane-electrodes-I The Ag(2)S electrode

The behaviour of a new type of electrode, made from ceramic Ag(2)S, has been investigated. The electrode response is Nernstian for Ag(+) over the range 10(-6)-2M and for Hg(2+) in the concentration range 10(-6)-10(-2)M, both at constant ionic strength (0.1M). The electrode is Ag(+)-selective, with maximum interference from Hg(2+). It can be used for acid-base potentiometric titration and for potentiometric Ag(+) and Hg(2+) precipitation titrations.     

Conductometric titration with indicating resistance--IV: the use of membranes with some organic and inorganic acids as active components, for HCl titration in a highly conducting medium

Membranes consisting of a methyl polymethacrylate or collodion support containing sparingly soluble inorganic or organic acids can be used for end-point detection in acid-base titrations in high-conductivity media. The collodion + Na(3)[As(Mo(3)O(10))(4)].nH(2)O + Na-Alassion CS membrane is a very good conductometric sensor if given preliminary treatment to form molybdic acid. The conductivity jump with this membrane starts at pH approximately 7 and permits titration of strong acid down to 10(-4)M concentration in highly conducting medium. Similar membranes containing some organic acids such as benzoic, o-chlorobenzoic, and o-phthalic also behave as conductometric sensors, giving a conductivity change at a ph which depends on the dissociation constant of the organic acid used and on the way it interacts with the support and the conducting medium used.