Emf Of Cell Research Articles

The Liquid Junction Potential in Potentiometric Titrations. IX. The Calculation of Potentials Across Liquid Junctions of the Type, AY|AY+BY z(B)+HY+ A y L, for Emf Cells where Strong or Weak Complexes are Formed, Respectively, at [Y−] = C mol⋅L−1, Constant and −log 10[H+]≤ 7

In the present part, potential functions are derived for the calculation of the total potential anomalies, Δ EB and Δ EH, for Emf cells where strong or weak complexes are formed, respectively. A weak or strong electrolyte is considered to be used as complexing agent (AyL), respectively, at the experimental condition, [Y−] = C mol⋅L−1, constant. The cells have indicator electrodes reversible to Bz(B)+ (cell B) and H+ ions (cell H), respectively.

Thermodynamic properties of scandium-copper compounds

We have determined the Gibbs energy, the enthalpy, and the entropy of formation for the compounds ScCu4, ScCu2, and ScCu by measuring the emf of galvanic cells in the temperature range 845–980 K. We compared the experimental results obtained with known literature data.

A Concept of Chemical Potential Pumping Effect of Nonstoichiometric Oxides and the NOx Sensing Mechanism of the Perovskite-Type La0.5Sr0.5FeO3

A concept of chemical potential pumping effect was introduced to describe the NOx sensing mechanism of oxide catalysts with high electronic conductivity and large carrier density. When NOx gas in a gas-stream decomposed on the surface of the catalyst oxides continuously, the high oxygen potential released by the decomposition of NOx stationarily covered the whole surface of the oxide. Then, the bulk oxide was equilibrated with the steady-state high oxygen potential of the surface, which was much larger than that determined by the oxygen pressure of the surrounding gas-phase. This effect was confirmed by the conductivity enhancement of La2CuO4 and La0.5Sr0.5FeO3 with NO2 as well as nonstoichiometry variation of La0.5Sr0.5CoO3 and EMF of galvanic cell with La0.6Sr0.4CoO3−d. It was shown that the chemical potential pumping effect appears essentially on dense materials while the effect is hardly observed on porous material with large surface relative. On La0.5Sr0.5FeO3 as well as on La2CuO4, NO2 was found to decompose into NO and O2, while NO was almost inactive on these oxides.

Activity Measurements of Solid Ni–In Alloys by EMF Method with Zirconia Solid Electrolyte

The EMF of galvanic cells with stabilized zirconia solid electrolyte was measured to determine the activity of indium in solid Ni–In alloys in the temperature range of 970–1170 K and composition range of 5–55 mol% In. Activity of indium increases sharply in the ζ phase and Ni13In9 phase. The activity values are compared with literature data.

Physico-chemical studies on mixed oppositely charged surfactants: Their uses in the preparation of surfactant ion selective membrane and monolayer behavior at the air water interface

Surfactant ion selective membranes, prepared using different sets of catanionic species, have been found superior to the membranes prepared earlier in terms of sensitivity and durability. The aggregates (or coacervates) of cetyltrimethylammonium (CTA +) ion with dodecylsulfate (DS −), dodecylbenzenesulfonate (DBS −), dioctylsulfosuccinate (AOT −), deoxycholate (DC −), and taurochenodeoxycholate (TCDC −) ions in 1:1 molar ratio were used as the carrier complexes in the membrane for estimating anionic surfactants whereas carrier complexes of DBS − with CTA +, tetradecyltrimethylammonium (TTA +) and dodecyltrimethylammonium (DTA +) cations (1:1 molar ratio) were employed for estimating the cationic surfactants. Electrochemical behavior of membrane electrodes was, although, not always Nernstian, the cell emf versus log[surfactant] plots were linear with sharp breaks corresponding to the critical micelle concentration (CMC). Film behavior of complex aggregates (coacervates) was studied at the air–water interface by surface pressure ( π)–area ( A) measurements. Limiting area per molecule, maximum attainable surface pressure, film compressibility, etc., were evaluated from the experimental data. Formation of probe-excluded regions of compressed monolayers, doped with a fluorescent probe (NBD-PC) was observed by epifluorescence microscopy.

Activity coefficients and thermodynamic parameters for RbCl/CsCl + amide (acetamide, propanamide, and n-butanamide) + water system at 298.15 K

Electromotive force (emf) of the chemical cell without liquid-junction K-ISE | RbCl/CsCl ( m E) | ISE-Cl and K-ISE | RbCl/CsCl ( m E), amide ( m N) | ISE-Cl, have been measured at 298.15 K, where m E = (0.005 to 0.5) mol kg − 1 and m N= (0.05 to 3.0) mol kg − 1 . The activity coefficients of RbCl/CsCl in amide (acetamide, propanamide, and n-butanamide) + water mixture can be obtained from these electromotive force data and in the mean time the Gibbs free energy interaction parameters of RbCl/CsCl + amide pair in water, g EN, as well as the salt constant, k S, can be evaluated. The results show that both g EN > 0, k S > 0 at 298.15 K, and all the activity coefficients of electrolyte in amide + water mixture increase with increasing the m N, but it is a little complicated for the dependence of activity coefficients on m E. These thermodynamic parameters were discussed in terms of a model of the structural interaction and electrostatic interaction and the dependence of them on the number of carbon atoms in amide as well as the radius of metal ions were interpreted by the group additivity principle.

Mixed conductivity, thermal expansion, and oxygen permeability of Ce(Pr,Zr)O 2 − δ

The use of Pr x Ce 1 − x O 2 − δ fluorites in electrochemical devices is hindered by several fundamental problems, one of which is the high thermal expansion coefficients (TECs), which have been shown to vary in the range (10–40) × 10 − 6 K − 1 between the temperatures 0 and 1000 °C. Thermogravimetric study shows that such a fluctuation of TECs, and non-linear lattice expansion on heating, are related to oxygen losses and can be controlled, to a substantial extent, by compositional selection. The influence of composition upon resultant mixed conductivity and oxygen permeability values is analysed for the compositions Zr 0.1Ce 0.9 − x Pr x O 2 − δ and Ce 1 − x Pr x O 2 − δ ( x = 0.2–0.3). Zr substitution leads to a decrease in total conductivity and an increase in average grain size. Oxygen permeability in these materials is controlled by both ambipolar bulk conductivity and oxygen surface exchange rates. Typical values of specific oxygen permeability are approximately 3 × 10 − 8 mol/s cm at 1000 °C and compare well with other phases that are promising as oxide catalyst supports and precursors, such as La(Fe,Ni)O 3 − δ perovskites. A decrease in both ionic and electronic conductivities is observed with decreasing p(O 2) by measurements of oxygen concentration cell emf combined with impedance spectroscopy. Ion transference numbers show a positive temperature dependence, with typical values t o = 0.8 at 950 °C under oxidizing conditions.

Experimental study on gallium activity in the liquid Ga–In–Tl alloys by EMF method with zirconia solid electrolyte

EMF of galvanic cells with zirconia solid electrolytes was measured to determine the activity of gallium in liquid Ga–In–Tl alloys in the temperature range of 950–1300 K along three pseudo-binary lines of (In y Tl 1 − y )–Ga where y = 0.25, 0.50 and 0.75. A mixture of Ga and Ga 2O 3 was used as a reference electrode. The activity curves of Ga show positive deviations from ideality in the whole composition range. Isoactivity curves at 1073 K in the ternary Ga–In–Tl alloys were derived by combining the activity data of Ga–In and Ga–Tl alloys. Excess free energy of mixing Δ G Ex(=Δ G − Δ G ideal) at 1073 K was derived by Darken's equation using the binary data of In–Tl and ternary data in this study. The values in this study are smaller than those calculated from the general model calculation proposed by Chou.

Hydrogen isotope sensor using high temperature proton conductors

EMF of the hydrogen isotope cell has been applied to the sensing of hydrogen isotopes. In this paper, the atomic hydrogen isotope composition and the total pressure of the hydrogen isotopes were determined simultaneously by use of two electrochemical cells with different kind of proton-conducting electrolytes. Among the several proton conductors, CaZr 0.9In 0.1O 3− α and SrCe 0.95Yb 0.05O 3− α were chosen for the sensor. The difference in EMFs of the two proton conductor cells was independent of the total pressure of hydrogen isotopes and, thus, served to determine the atomic hydrogen isotope compositions in gases.

Electrode dynamic study of exhaust gas oxygen sensors

We investigate the electrode dynamics of exhaust gas oxygen sensors in order to identify the rate-determining step. The rate-determining step is the two-dimensional surface diffusion mechanism, at the exhaust gas platinum electrode. The diffusion species is the adsorbed oxygen atom. This conclusion results from the study of the transfer function of the electrode dynamic of the exhaust gas platinum electrode. This transfer function is obtained by measuring the ratio of the transfer functions of a wide range air to fuel ratio sensor operated at electromotive force ( emf) mode and pump-mode. This is made possible by utilizing the fact that in pump-mode, the electrode dynamic effect is annulled by a negative proportional feedback loop, which pumps oxygen in and out to keep the emf cells at constant regardless how the exhaust gas changes.

An Optoelectronic Switch of Voltage Polarity at a Nanovolt Level

A theoretical model of the contact metal topography of a photoconductive cell and a thermal model of an optoelectronic switch of the voltage polarity are considered. Expressions for photo and thermal emf of photoconductive cells with arbitrary contact metal topographies and distributions of the illumination and temperature at the cell surface are obtained. The regularities of minimization of parasitic emf of photoconductive cells are revealed. An optoelectronic switch of the voltage polarity with low levels of temperature (<2 nV/°C) and temporal (3–4 nV/h) drifts of the intrinsic emf, resistances in the ON and OFF states of ∼100 and 1012 Ω, respectively, an insulation resistance of 1011 Ω a switching time of 0.5 ms, and a transfer capacitance of 0.1 pF is developed.

Applications of oxidic high-temperature proton conductors

A classification of the possible applications is given first. For certain cases, the emf of a concentration cell is the dominant quantity as in some sensors. For other cases, the protonic current is of interest. In some applications the chemical reactions at the cathode and anode are of importance, while in further areas only the fact of relevance is that protons are transported to the cathode. The domain of sensors of hydrogen, steam and hydrogen containing organics is covered. The first commercial application of oxidic high-temperature proton conductors, the quantitative detection of hydrogen in molten metals, belongs to that group. In the fuel cell area, prototypical high-temperature fuel cells based on proton motion are discussed. Important here is the distinction between thick, medium thickness and thin film electrolytes. As in the case of 8YSZ, high current densities can only be obtained with the latter. Proton conductors also allow the pumping of hydrogen and steam. Novel vacuum leaks for the introduction of hydrogen into vacua are presented as a case in point. A combination of proton and oxygen ion conductors permits the in situ generation of steam, whereas the reverse, steam electrolysis, allows the production of high purity hydrogen.

Thermodynamic Properties of SrRuO3(s).

Abstract The enthalpy increment measurements and the standard molar Gibb’s energy of formation of SrRuO3(s) were measured using a high-temperature Calvet micro-calorimeter and a galvanic cell, respectively. The enthalpy increments can be represented by the polynomial expression: H0(T)−H0(298.15 K) (J mol−1)=−43517.2+120.8T (K)+0.898×10−2T2 (K)+19.97×105/T (K) [SrRuO3(s), 310.4≤T (K)≤798.8]. The heat capacity C0p,m(T), the first differential of H0(T)−H0(298.15 K) with respect to temperature is given by: C0p,m (SrRuO3, s, T) (J mol−1 K−1)=120.8+1.796×10−2T (K)−19.97×105/T2 (K). The standard Gibbs energy of formation of SrRuO3(s) has been determined by a galvanic cell using CaF2(s) as the solid electrolyte. The fluoride cell is represented by: (−)Pt/O2(g), {CaO(s)+CaF2(s)}//CaF2//{SrF2(s)+RuO2(s)+SrRuO3(s)}, O2(g)/Pt(+). The electromotive force (emf) of the above cell was measured as a function of temperature in the range from 894.4 to 1098 K. The standard Gibb’s energy of formation of SrRuO3(s) from elements in their standard state obtained by the fluoride cell can be given by: ΔfG0[SrRuO3(s)]/kJ mol−1(±2)=−941.0+0.2586·(T/K) (894.4

고등학교 화학 교과서에 기술된 볼타 전지의 오개념을 줄이기 위한 실험 장치 개발

볼타 전지에 대한 학생들의 오개념과 고등학교 화학 2 교과서에서 기술된 내용을 연구, 분석하였다. 볼타 전지에 대해 많은 학생들이 오개념을 가지고 있으며 몇몇 화학교과서의 경우 내용이 잘못 기술되어 있다는 것을 본 연구에서 밝혔다. 대부분의 교과서에는 볼타 전지의 초기 측정 전압이 왜 1.1V와 유사하며 시간이 지남에 따라 감소하는지에 대한 명확한 설명이 없다. 표준상태에서 볼타 전지의 기전력은 0.76V 이지만 어떤 교과서에는 다니엘 전지처럼 1.1V로 기술되어 있다. 대부분의 학생들은 볼타 전지를 배우거나 실험을 한 후에도 여전히 오개념을 가지고 있으며 이것은 적어도 다음 두 가지 요인에서 기인된다고 여겨진다. 첫째, 볼타 전지의 초기 측정 전위값이 다니엘 전지의 전위와 매우 유사하기 때문에 학생들이 혼동하여 오개념을 가진다. 둘째, 대부분 교과서의 볼타 전지 실험은 표준 상태가 아닌 조건에서 수행되도록 기술되어 있으므로 학생들이 실험을 하더라도 표준 상태 기전력값을 얻을 수 없기 때문에 여전히 오개념을 가지게 된다. 따라서 우리는 학생들의 오개념을 줄일 수 있는 개선된 볼타 전지의 실험 모형을 제안하였다. Misconceptions of students for a Voltaic cell were studied and their contents described in the high school chemistry II textbooks were analyzed. This study shows that students have many misconceptions and a few of chemistry textbooks contain some false description in a Voltaic cell. In the most textbooks, the reasons why the measured cell voltage of a Voltaic cell is near 1.1 V at the initial stage and then it decreases with time are not explained clearly. The emf of a Voltaic cell at a standard state is 0.76 V but in some textbooks it is described as 1.1 V of a Daniel cell. Even after learning the Voltaic cell or performing the experiment of textbooks, most students still have some misconceptions. These may be due to at least two following facts: the first is that the measured cell voltage of a Voltaic cell at the initial stage is very similar to that of a Daniel cell. The second is that the most experiment of a Voltaic cell is not performed under the condition of a standard state. Therefore, we have suggested a model of the modified experimental setup of a Voltaic cell that could reduce misconceptions of students.

System Dy—Fe—O: Thermodynamic Properties of Ternary Oxides Using Calvet Calorimetry and Solid‐State Electrochemical Cell

AbstractFor Abstract see ChemInform Abstract in Full Text.

Thermodynamic properties of SrRuO 3(s)

The enthalpy increment measurements and the standard molar Gibb’s energy of formation of SrRuO 3(s) were measured using a high-temperature Calvet micro-calorimeter and a galvanic cell, respectively. The enthalpy increments can be represented by the polynomial expression: H 0( T)− H 0(298.15 K) (J mol −1)=−43517.2+120.8 T (K)+0.898×10 −2 T 2 (K)+19.97×10 5/ T (K) [SrRuO 3(s), 310.4≤ T (K)≤798.8]. The heat capacity C 0 p,m( T), the first differential of H 0( T)− H 0(298.15 K) with respect to temperature is given by: C 0 p,m (SrRuO 3, s, T) (J mol −1 K −1)=120.8+1.796×10 −2 T (K)−19.97×10 5/ T 2 (K). The standard Gibbs energy of formation of SrRuO 3(s) has been determined by a galvanic cell using CaF 2(s) as the solid electrolyte. The fluoride cell is represented by: (−)Pt/O 2(g), {CaO(s)+CaF 2(s)}//CaF 2//{SrF 2(s)+RuO 2(s)+SrRuO 3(s)}, O 2(g)/Pt(+). The electromotive force (emf) of the above cell was measured as a function of temperature in the range from 894.4 to 1098 K. The standard Gibb’s energy of formation of SrRuO 3(s) from elements in their standard state obtained by the fluoride cell can be given by: Δ f G 0[SrRuO 3(s)]/kJ mol −1(±2)=−941.0+0.2586·( T/K) (894.4< T/K<1098). The slope and intercept of the above equation gives the entropy and enthalpy of formation of the compound at the average experimental temperature T av=996.2 K. The heat capacity of SrRuO 3(s) determined by Calvet calorimeter and the data obtained from fluoride cell were used to calculate the standard enthalpy and entropy of formation of the compound at 298.15 K. The second law method gives Δ f H 0[SrRuO 3(s), 298.15 K] and Δ f S 0[SrRuO 3(s), 298.15 K] of the compound from elements in their standard state to be −955.0 kJ mol −1 and 111.04 J K −1 mol −1, respectively.

Studying Phase and Structure Conversions in Silver Iodide and Copper Bromide by Measuring EMF of an Electrochemical Cell

The large difference in the temperature dependences of EMF of cells C|Cu|CuBr|C and C|Ag|AgI|C, obtained when heating and cooling, is probably due to the retention in the samples of a “high-temperature” phase with a disordered cationic sublattice. Some features of the dependences are associated with silver iodide and copper bromide changing their modifications; others, presumably with the cationic-sublattice disordering and with the compounds" conversion into a high-conductivity phase.

Thermodynamic properties of alanylpeptide buffer systems and their potential as standards in biological applications

The second dissociation constants pK2of the NH3+charge center of the alanylpeptides, alanylglutamine (Ala–Gln), alanylleucine (Ala–Leu), alanylglycine (Ala–Gly), and DL-alanyl–DL-methionine (DL-Ala–DL-Met) were determined at ten temperatures in the range, 5–50°C. These pK2values were calculated from the emf of cells containing buffer solutions of these dipeptides. A cell of the type described by Harned and Ehlers,(1)utilizing hydrogen and silver–silver bromide electrodes was used. The thermodynamic quantities, ΔHo, ΔSo, and ΔCpowere derived from the temperature coefficients of the dissociation constants. The pK2values at 25°C, 8.2105 ( Ala–Gln), 8.2668 ( Ala–Leu), 8.2940 ( Ala–Gly), and 8.3054 ( DL-Ala–DL-Met). These values show that different substituent groups on the α-carbon atom (which include polar and nonpolar groups), have a small effect on the dissociation of the NH3+charge center. These compounds were also found to be suitable as buffers in the pH range(7–9). The thermodynamics of the solute–solvent interaction is interpreted in terms of the mixture model.(2)

Electrochemical sensors for sulfur- and lead-containing gases: Effect of nonstoichiometry of measuring electrodes

In accordance with the fact that the region of homogeneity of lead sulfide is two-sided, i.e. it includes compositions with both sulfur excess and lead excess relative to the stoichiometric composition, it is shown that a sensor with a Pb1 ± δS measuring electrode (ME) may be used for analyzing both sulfur- and lead-containing media. The general principle of operation of electrochemical sensor Me, Pb/PbCl2–CaCl2/Pb1 ± δS, is based on measuring EMF of an electrochemical circuit with a lead-conducting electrolyte at a specified sulfur vapor pressure above the reference electrode. At a fixed temperature, the cell's EMF is uniquely defined by the sulfur content on ME. The studies are done in the temperature interval 285 to 300°C where characteristics of the solid electrolyte used are optimum; its upper boundary is limited by mp of the lead reference electrode (327°С). The interval of determinable concentrations of sulfur- and lead-containing gases is 10–1 to 10–9 vol %. If analysis is performed in a dynamic mode (in a carrier gas flow), the limiting stage is the adsorption of gas molecules on the ME surface and the sensor sensitivity increases after modifying the surface by various techniques and also due to the ME composition altering only in a surface layer. The sensor's working characteristics are affected mostly by the degree of deviation of the ME material from stoichiometry.

Thermodynamic properties of U0.718Ce0.282O2±x

An experimental study of the structure and thermodynamic properties of a sample of U0.718Ce0.282O2±x , which is an analogue of uranium–plutonium oxide, is performed to study the effect of adding cerium oxide on the properties of oxide fuel. The experimental specimens were obtained by powder metallurgy. x-Ray diffraction analysis of sintered tablets showed the formation of an equilibrium one-phase solid substitution solution based on UO2 with substoichiometric composition. The potentiometric method of the emf of a solid-electrolyte galvanic cell in the range 850–1050°C and solid-phase coulometric titration with working temperature 1000°C were used to study the dependence of the oxygen potential of uranium-cerium oxide on the oxygen/metal ratio and the temperature. The concentration dependences of the enthalpy and the entropy of dissolution of oxygen in uranium-cerium oxide are calculated and constructed and it is determined that these dependences vary strongly at near-stoichiometric composition. The results can be used to analyze the properties of uranium–plutonium oxide fuel.