Emf measurement

The electromotive force (EMF) mediated in CaO-CaCl2 melt was measured between two different oxygen partial pressures, Fo2(I) and Fo2(H)- If only oxygen ions have the potential to carry the electric charge, the 

Molten Salts Chemistry and Technology, First Edition. Edited by Marcelle Gaune-Escard and Geir Martin Flaarberg. 2014 John Wiley Sons, Ltd. Published 2014 by John Wiley Sons, Ltd. 

When two solid substances, metal (M) and its lowest oxide (MO), can coexist thermodynamically in equilibrium, the equilibrium oxygen partial pressure, Fq2(M-MO), is automatically fixed only as a function of temperature, based on the thermochemical phase rule. Here five kinds of M-MO equilibrium are tested to 

CaO-CaCl2 melt at 1073-1173 K, but there still exist the other factors as well as 0 transfer. 

This shows that the oxygen ion can carry the charge, but that it does not deny the other possible charge carriers such as calcium ion. For the local electro-neutrality in the melt, the counter motion of calcium seems interesting. A further study based on the thermochemical activity of calcium will be conducted. 

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Of all the techniques, it is those of Group 1 that are likely to give the most realistic data, simply because they measure transport of charged species only. They are not the easiest experimental techniques to perform on polymeric systems and this probably explains why so few studies have been undertaken. The experimental difficulties associated with the Tubandt-Hittorf method are in maintaining nonadherent thin-film compartments. One way is to use crosslinked films [79], while an alternative has been to use a redesigned Hittorf cell [80]. Although very succesful experimentally, the latter has analytical problems. Likewise, emf measurements can be performed with relative ease [81, 82] it is the necessary determination of activity coefficients that is difficult. 

E6.12 The HC1 pressure in equilibrium with a 1.20 molal solution is 5.15 x 10 8 MPa and the mean ionic activity coefficient is known from emf measurements to be 0.842 at T = 298.15 K. Calculate the mean ionic activity coefficients of HC1 in the following solutions from the given HC1 pressures... 

The vapor pressures (fugacities) shown in Figure 6.14 were reported by J. J. Fritz and C. R. Fuget, Vapor Pressure of Aqueous Hydrogen Chloride Solutions", Chem. Eng. Data Ser., 1, 10-12 (1956). The vapor pressures are too small to measure directly. The values reported were calculated from the results of emf measurements made on an electrochemical cell. In Chapter 9, we will describe this and other cells in detail. 

In this expression, E° is the standard emf of the cell, the emf measured when all the species taking part are in their standard states. In practice, this condition means that all gases are at 1 bar, all participating solutes are at 1 molT-1, and all liquids and solids are pure. For example, to measure the standard emf of the Daniell cell, we use 1 M CuS04(aq) and a pure copper electrode in one electrode compartment and 1 M ZnS04(aq) and a pure zinc electrode in the other. 

The value of Kip is the same as that listed in Table 11.4. Many of the solubility products listed in tables were determined from emf measurements and calculations like this one. 

A silver concentration cell is constructed with the electrolyte at both electrodes being initially 0.10 M AgNO(aq) at 25°C. The electrolyte at one electrode is diluted by a factor of 10 five times and the emf measured each time, (a) Plot the emf of this cell on a graph as a function of In AgT ln)K,e. 

Rabideau , using emf measurements to obtain rate data, has since reinvestigated the disproportionation reaction of Pu(V), using solutions containing very small amounts of Pu(IV) and Pu(III). He was able to conclude from the dependence of the rate coefficient (fcj) on the first power of [H ] that the steps and equilibrium present were... 

However, in this case the EMF measured will be distorted by another effect [i.e., the variation of electrostatic potential within a given conductor, which is caused by a temperature gradient in the conductor (the Thomson effect, 1856)]. Potential gradients will arise even at zero current, in both the electrolyte (between points and Aj)... 

FIG. 6 Dependence of the square root of the SHG intensity ( I(2a>)) for membrane 2 without KTpCIPB (a) with KTpCIPB (b) on K+ ion concentrations in the adjacent aqueous solution containing KCl (O) and KSCN ( ), respectively. Inset The corresponding observed EMF to KCl and KSCN. The concentrations of ionophore 2 and KTpCIPB were 3.0 X 10 M and 1.0 x 10 M, respectively for both SHG and EMF measurements. The data points present averages for three sets of measurements. Error bars show standard deviations. (From Ref. 15.)... 

If the unknown cell in the Cu-Zn cell is connected to the circuit, the emf measured is the combined potentials of two single electrode potentials for the two metals (zinc and copper) making up the cell, and it is impossible to state from the value of the emf measured what proportion is due either to the zinc, or to the copper. 

The pH dependence described above indicates that a pH meter is merely a pre-calibrated voltmeter, which converts the emf measured into a solution pH, according to the following relationship ... 

The above three sources of error all result from the fact we assume that the emf measured in a potentiometric experiment comprises only two terms, i.e. one... 

In this cell, two amalgams with different mole fractions of lead act as electrodes in a common electrolyte solution containing a lead salt. The activities of lead in these amalgams can be calculated from emf measurements with this cell. 

The electromotive force (emf) of liquid membrane electrodes depends on the activity of the ions in solution and their performance is similar in principle to that of the glass electrode. To characterize the behavior of liquid membrane electrodes, the linearity of the emf measurements vs. concentration of a certain ion in solution is checked. Additional performance data are the Nernstian slope of the linear range and the pH range over which the potential of the electrode is constant. 

Bostrom D. and Rosen E. (1988). Determination of activity-composition in (Ni,Mg)2Si04 solid solution at 1200-1600 K by solid state emf measurements. Acta Chim. Scand., A42 149-155. 

EMF-measurements are, therefore, a method for directly assessing the relative stability of the complexes of the valinomycin group antibiotics in water and water-like solvents (cf. Fig. 11 and Ref. (87)). The selectivity constants of the liquid membranes are in this case independent of the ion-selective behavior of the membrane solvents used. 

EMF-measurements may also be used to estimate relative complex formation constants in membrane solvents. To this end, the selectivity constant Ryot of the pure membrane solvent must be measured, in addition to Kyot, the selectivity constant for the membrane plus ligand. Using Table 6 and Eq. (9) one finally obtains ... 

That this is reasonable is demonstrated by EMF-measurements using antibiotics of the nigericin group in liquid membranes (90) at the same time, it must be realized that the information provided by these measurements is, by necessity, only qualitative. 

This shows that the parameter derived from EMF-measurements, Kyot, used to describe the monovalent-divalent ion selectivity, depends not only on the ligand and the membrane solvent but is also a function of the activities in the outside solution (26)1). Therefore, any numerical values pertaining to a so-called selectivity constant are meaningful only as long as the exact composition of the outside solution is cited. 

The usefulness of this ligand in the construction of Ca2+-sensors has been confirmed. The selectivity behavior of a liquid membrane, which consists of a filter paper impregnated with a 20% solution of the ligand in p-nitroethylbenzene (117), was determined by means of EMF-measure-ments conducted on the cell ... 

There are also other methods for measuring hydrogen ion concentration, for instance, Sorensen s (psH) unit or the activity coefficient unit (paH), based on emf measurements Refs l) L. Michaelis, Die Wasserstoffionen-Konzentration, translated from the 2nd German edition (1922) by W.A. Perlzweig and published by Williams Wilkins, Baltimore (1926) 2)... 

The standard potential of the Na+/Na couple can be obtained from these emf values. However, it can also be obtained by calculation from thermodynamic data [2] and the result agrees well with the result by emf measurement. 

In potentiometry, we measure the emf of a cell consisting of an indicator electrode and a reference electrode. For emf measurements, we generally use a pH/ mV meter of high input impedance. The potential of the reference electrode must be stable and reproducible. If there is a liquid junction between the indicator electrode and the reference electrode, we should take the liquid junction potential into account. 

Delay et al (Ref 12) detd IR absorption spectra in the range 3 to l9u and from the intensities of the bands concluded that the sym form was more abundant in the azides of Ag, Cu, Hg Na but the reverse was true for the azides of Pb Tl. Gray Wad ding ton (Ref 18) stated th at TlNj crysts are isomor-phous with those of Na Rb azides. The elec conductivity of TIN, is 5.9 x 10 s mho at 275° (Ref 18). Brouty (Ref 10) detd the mean activity coefficient of TIN, by EMF+ measurements and calcd ionic radii of Ti Nj. Conductivity measurements by Brouty (Ref 11) did not agree with Onsager s theory deviations were found at very high dilutions. An electro-chem cell used by Suzuki (Ref 16) gave a Ap1 29S° value of 59.17 kcal/mol for... 

Both AGt(x)e and AGt(x)e mix refer to a neutral solute species or a neutral combination of ions X. These quantities may be determined thermodynamically from emf measurements on suitable cells or from solubility studies in the mixed or pure solvents. The splitting of these quantities into separate contributions from the ions has been the subject of much speculation (8). We may regard Equations 16 and 17 as valid if the species X bears a charge, provided the ionic contributions are added to obtain the values for a neutral combination of ions. 

Thermodynamic Study of Hydrobromic Acid in Water-1,2-Dimethoxyethane (Monoglyme) from EMF Measurements... 

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