Standard potential of silver

Tab. 4.3 Standard potentials of. silver cryptates-silver electrodes (AgL+/Ag) [4] 1) ...

The procedure may be illustrated with reference to the determination of the standard potential of silver, of which the only convenient salt for experimental purposes is the nitrate. Since the most reliable reference electrodes contain solutions of halides, it is necessary to interpose a bridge solution between them the result is... 

The value of A is known to be 0.509 for water at 25 , and that of C is found empirically another term, Dy , with an empirical value of D, may be added if necessary, and the true dissociation constant K can then be calculated from the experimental data. In this manner, it was found that K is 0.531 at 25 , and hence from equations (12) and (13), making use of the fact that the standard potential of silver is — 0.799, it follows that at 25 ... 

Another important use of standard potentials is for the determination of sdubility products, for these are essentially equilibrium constants ( 39j). If M Al, is a sparingly solvble salt, a knowledge of the standard potentials of the electrodes M, M, A, (s), A - and M, M + permits the solubility product to be evaluated. A simple example is provided by silver chloride Ifor which the standard (oxidation) potential of the Ag, AgCl( ), Cl electrode is known to be — 0.2224 volt at 25 C. The activity of the chloride ion in the standard electrode is unity, and hence the silver ion activity must be equal to the solubility product of silver chloride. The value of Oa may be derived from equation (45.13), utilizing the standard potential of silver thus Eu i — 0.22 volt, E for silver is — 0.799, and z is 1, so that at 25 C,... 

In computing a standard potential of silver from, for instance, a potential measurement, E, on a cell of the type... 

The Standard Potential of Silver, The standard potential of silver has been measured by Lewis 20 and by Noyes and Brann 21 who used the cell... 

This relation enables us to measure the activity of the unknown solution without needing to know the value of the standard potential of silver. ... 

K. H. Khoo, J. Chem. Soc., 2932 (1971). The standard potentials of silver-silver halide electrodes and ion solvation in dimethylsulfoxide-water mixtures at 25°C. 

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). 

As may be seen from the diagram, silver in highly alkaline solution corrodes only within a narrow region of potential, provided complexants are absent. It is widely employed to handle aqueous solutions of sodium or potassium hydroxides at all concentrations it is also unaffected by fused alkalis, but is rapidly attacked by fused peroxides, which are powerful oxidising agents and result in the formation of the AgO ion Table 6.6 gives the standard electrode potentials of silver systems. 

Figure 4 shows what is known to date about the standard potential of the silver microelectrode as a function of the agglomeration number n f For n = 1, i.e. the redox system... 

F. 4. Standard potential of the silver microelectrode as a function of the agglomeration number n... 

Figure 4 illustrates that our present knowledge about the dependence of the standard potential of very small silver microelectrodes on the agglomeration number is rather fragmentary. Even less is known about this dependence for other metals. The experiments of Fig. 5 prove that the rate of an electrochemical reaction in which a small microelectrode is involved, may strongly depend on the size of the microelectrode. 

It can be seen from this equation that the solubility product of silver chloride can be calculated from the known standard potentials of the silver... 

The silver chloride electrode is preferable for precise measurements. The standard potentials of some electrodes of the second kind are listed in Table 3.4. Various electrode constructions are shown in Fig. 3.8. 

This theory has been successfully verified experimentally. Buck and Shepard [51] demonstrated that electrodes of the all-solid-state type have a response that is identical to that of similar electrodes of the second kind for response to halide ions and to a silver electrode for response to silver ions, depending on the degree of saturation with silver. This is achieved by soldering a silver contact to the membrane. If however the internal contact material is more noble than silver (platinum, graphite, mercury), the electrode with response to silver ions may attain a potential between the standard potential of a silver electrode g /Ag and the value... 

The standard potential of these ISEs, analogous to halide ISEs, depends on the activities of silver and sulphur in the membrane. When metallic silver is used as a contact soldered directly onto the membrane, the silver activity in the membrane equals one and the Ag2 S ISE has properties identical with a silver electrode of the first kind or with a silver sulphide electrode of the second kind, depending on the solution with which it is in contact [203], The membrane that is in contact with electrolyte on both sides behaves similarly [106],... 

If the graphite contact in cell (6.2.1) is replaced by a silver contact, quantity 6 corresponds to saturation of silver sulphide with silver and the silver activity in Ag2 S equals unity. Then juQ = ju and E=0. The standard potential of the Ag2 S ISE is identical with the standard potential of the silver electrode, O.ISE AgVAg = + 0.799 V versus SCE. On the other hand, when Ag2 S is in equilibrium with elementary sulphur (for example, when Ag2 S is prepared in an oxidizing medium [417]) then... 

One more example demonstrates how to use standard reduction potentials to determine the standard potential of a cell. Let s say you wanted to construct a cell using silver and zinc. This cell resembles the Daniell cell of the previous example except that a silver electrode is substituted for the copper electrode and a silver nitrate solution is used in place of copper sulfate. From Table 14.2, it is determined that when silver and copper interact silver is reduced and copper oxidized. The two relevant reactions are... 

Table 4.3 shows the standard potentials of the Ag+/Ag and AgL+/Ag electrodes in various aprotic solvents, where L stands for cryptands [4]. The standard potential of the Ag+/Ag electrode varies with solvent by more than 500 mV. However, the standard potentials of the AgL+/Ag electrodes are not much influenced by solvent, the variations being 80 mV at most. For silver cryptates, AgL+, the relation logy, (Agl., R-> S) logyt(L, R-> S) holds, as described in Section 2.4. From this and p=1 in Eq. (4.7), the relation °(R) °(S) can be expected. 

Colloid silver was chosen as label for the assay because its standard potential is more negative than the standard potential of gold. Thus, the potential window is more convenient for signal registration than in Ref. [30]. 

Both the ions of Ag+ and Cif are easily complexed by ammonia (amine) and the corresponding complexes are very stable [204]. In the system of silver-ammonia complex ions the oxidation-reduction standard electrode potential of silver is expressed by... 

Standard emf Values for the Cell H2/HCl/AgCl, Ag in Various Aqueous Solutions of Organic Solvents at Various Temperatures Temperature Dependence of the Standard Potential of the Silver Chloride Electrode Standard Electrode Potentials of Electrodes of the First Kind Standard Electrode Potentials of Electrodes of the Second Kind Polarographic Half-Wave Potentials (E1/2) of Inorganic Cations Polarographic E1/2 Ranges (in V vs. SCE) for the Reduction of Benzene Derivatives Vapor Pressure of Mercury... 

Bates, R.G. and Bower, V.E., Standard potential of the silver silver-chloride electrode from 0-degrees C to 95-degrees C and the thermodynamic properties of dilute hydrochloric acid solutions, J. Res. Natl. Bur. Stand., 53, 283, 1954. 

Temperature Dependence of the Standard Potential of the Silver Chloride Electrode... 

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... 

In order to get a clearer picture of conditions existing on deposition of metals, let us discuss some examples. The deposition potential of silver from a normal solution of its salt almost equals the standard reduction potential tca = + 0.8 V, and the potential of hydrogen evolved from a neutral solution Ttn, equals 0.059 log 10-7 = —0.41 V. Both potentials are so wide apart that not even the polarization occurring at higher current densities can considerably affect the relative position of both curves. For this reason, silver will be deposited from the solution prior to hydrogen until practically all Ag+ ions will be... 

The standard potential of the silver azide electrode, i.e., Ag AgN3(s) N3", is -0.2919 V at 25°C. If the solubility of silver chloride is 1.314xl0 5 molal, calculate that of silver azide at 25°C. (Complete dissociation may be assumed for the dissolved material in the saturated solution in each case.)... 

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