Silver-potential

The titration course can be illustrated (see Fig. 2.20) by a pAg curve whose values are obtained from the silver potential EAg = E g + RT/Fln aAg+ or at 25° C EAg = EAg - 0.05916 pAg. As AgN03 as a salt is fully dissociated into ions, the initial point of the curve is determined by the original concentration the later part of the curve up to the titration end-point can be obtained in the same way because the Ag+ concentration undergoes a simple reduction as a consequence of the withdrawal of Ag+ into the AgCl precipitate. At the... 

Figure 4.1.3 shows a more concrete scheme of a typical controlled double-jet (CDJ) system, in which the flow rate of the AgN03 solution is previously programed, while the flow rate of the KBr solution is precisely controlled to keep the excess concentration of Br ions constant in response to the silver potential monitored with a silver electrode (7). 

The standard potentials for (Zn2+ Zn) and (Ag+ Ag) are —0.763 V and 0.799 V from Table 19-1. The standard potential of the cell is the difference between these two numbers, 0.779 V —(—0.763) = 1.542 V. The silver potential is higher, and this means that the silver ion is the oxidizing agent. The zinc couple provides the reducing agent and is the negative electrode. The equation for the cell is... 

Early in Section 1.2.2 it was shown that if the potential of a developing agent is more negative than the silver ion potential, then development or silver ion reduction is thermodynamically possible. The difference between the equilibrium silver potential and the developer or redox buffer potential Ejev is ... 

However, if the silver ion concentration is kept low in another way, the silver potential is low and less powerful oxidants can be used for bleaching. The silver ion concentration can be reduced by precipitation with halide ions (Eq. (87)). 

It can be seen that at low pH the oxidation is most likely to occur but the potential of persulfate is always in the passivation region. It was observed by Lumieres and Seyewetz [139] that reduction of the image density with persulfate had a notable induction period and the reaction appeared to be autocatalytic. It was suggested that silver ions themselves catalyze the reaction. It is possible that the buildup of silver ions lowered the silver potential sufficiently for corrosion to occur alternatively the production of silver(III) compounds might be responsible for the acceleration. 

Since the Agl2" complex appears to be stable in relation to the precipitation of Agl in acetone while no such behavior is noticeable in water, a study of this behavior in mixtures of the two solvents was made and is shown in Fig. 3. As the water content of the solvent increases, precipitation occurs earlier and in 50 water is immediate. The lowered stability of the complex is shown in the disappearance of the inflection at the 2 1 iodide-silver ratio. The decrease in potential range is also reflected in the lowering of the excess-silver potential curve as the water content of the solvent increases. This... 

There are two procedures for doing this. The first makes use of a metal probe coated with an emitter such as polonium or Am (around 1 mCi) and placed above the surface. The resulting air ionization makes the gap between the probe and the liquid sufficiently conducting that the potential difference can be measured by means of a high-impedance dc voltmeter that serves as a null indicator in a standard potentiometer circuit. A submerged reference electrode may be a silver-silver chloride electrode. One generally compares the potential of the film-covered surface with that of the film-free one [83, 84]. 

The f potential of silver iodide can be varied over the range 75 mV, by varying the Ag or 1 concentration again demonstrating that varying the concentration of potential-determining ions can reverse the sign of the f potential. 

In these equations the electrostatic potential i might be thought to be the potential at the actual electrodes, the platinum on the left and the silver on the right. However, electrons are not the hypothetical test particles of physics, and the electrostatic potential difference at a junction between two metals is nnmeasurable. Wliat is measurable is the difference in the electrochemical potential p of the electron, which at equilibrium must be the same in any two wires that are in electrical contact. One assumes that the electrochemical potential can be written as the combination of two tenns, a chemical potential minus the electrical potential (- / because of the negative charge on the electron). Wlien two copper wires are connected to the two electrodes, the... 

As a furtlier example for tire meaning of ex situ investigations of emersed electrodes witli surface analytical teclmiques, results obtained for tire double layer on poly crystalline silver in alkaline solutions are presented in figure C2.10.3. This system is of scientific interest, since tliin silver oxide overlayers (tliickness up to about 5 nm) are fonned for sufficiently anodic potentials, which implies tliat tire adsorjDtion of anions, cations and water can be studied on tire clean metal as well as on an oxide covered surface [55, 56]. For tire latter situation, a changed... 

Bromine has a lower electron affinity and electrode potential than chlorine but is still a very reactive element. It combines violently with alkali metals and reacts spontaneously with phosphorus, arsenic and antimony. When heated it reacts with many other elements, including gold, but it does not attack platinum, and silver forms a protective film of silver bromide. Because of the strong oxidising properties, bromine, like fluorine and chlorine, tends to form compounds with the electropositive element in a high oxidation state. 

From the theory of the electrochemical cell, the potential in volts of a silver-silver chloride-hydrogen cell is related to the molarity m of HCI by the equation... 

The two estimates for the first or a parameter of the parabolic fit are the intercepts on the voltage axis of Eig. 3-1, so both procedures arrive at a standard potential of the silver-silver chloride half-cell of 0.2225 V. The accepted modem value is 0.2223 V (Barrow, 1996). 

Electrodes of the Second Kind An electrode of the first kind involving an M"+/M redox couple will respond to the concentration of another species if that species is in equilibrium with M"+. For example, the potential of a silver electrode in a solution of Ag+ is given by... 

When the potential of an electrode of the first kind responds to the potential of another ion that is in equilibrium with M"+, it is called an electrode of the second kind. Two common electrodes of the second kind are the calomel and silver/silver chloride reference electrodes. Electrodes of the second kind also can be based on complexation reactions. Eor example, an electrode for EDTA is constructed by coupling a Hg +/Hg electrode of the first kind to EDTA by taking advantage of its formation of a stable complex with Hg +. 

If a mixture of an insoluble silver salt and Ag2S is used to make the membrane, then the membrane potential also responds to the concentration of the anion of the added silver salt. Thus, pellets made from a mixture of Ag2S and AgCl can serve as a Ck ion-selective electrode, with a cell potential of... 

A 0.3619-g sample of tetrachloropicolinic acid, C6HNO2CI4, is dissolved in distilled water, transferred to a 1000-mL volumetric flask, and diluted to volume. An exhaustive controlled-potential electrolysis of a 10.00-mL portion of this solution at a spongy silver cathode requires 5.374 C of charge. What is the value of n for this reduction reaction ... 

The silver fluorocomplexes, ie, silver hexafluoroantimonate [26042-64-8], AgSbF silver hexafluorophosphate [26042-63-7], AgPF silver tetrafluoroborate [14104-20-2], AgBF and other salts such as silver trifluoromethane sulfonate [2923-28-6], CF SO Ag, and silver trifluoroacetate [2966-50-9], CF COOAg, play an important role in the synthesis of organic compounds and have gained potential industrial importance. 

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