Solid silver electrode

Iodjn6 Solid Silver electrode Ag-ionic electrode conductor... 

The diffusion coefficient of oxygen in solid silver was measured with a rod of silver initially containing oxygen at a conceim ation cq placed end-on in contact with a calcia-zirconia electrolyte and an Fe/FeO electrode. A constant potential was applied across dre resulting cell... 

Other useful solid-state electrodes are based on silver compounds (particularly silver sulfide). Silver sulfide is an ionic conductor, in which silver ions are the mobile ions. Mixed pellets containing Ag2S-AgX (where X = Cl, Br, I, SCN) have been successfiilly used for the determination of one of these particular anions. The behavior of these electrodes is determined primarily by the solubility products involved. The relative solubility products of various ions with Ag+ thus dictate the selectivity (i.e., kt] = KSp(Agf)/KSP(Aw)). Consequently, the iodide electrode (membrane of Ag2S/AgI) displays high selectivity over Br- and Cl-. In contrast, die chloride electrode suffers from severe interference from Br- and I-. Similarly, mixtures of silver sulfide with CdS, CuS, or PbS provide membranes that are responsive to Cd2+, Cu2+, or Pb2+, respectively. A limitation of these mixed-salt electrodes is tiiat the solubility of die second salt must be much larger than that of silver sulfide. A silver sulfide membrane by itself responds to either S2- or Ag+ ions, down to die 10-8M level. 

In this cell, the following independent phases must be considered platinum, silver, gaseous hydrogen, solid silver chloride electrolyte, and an aqueous solution of hydrogen chloride. In order to be able to determine the EMF of the cell, the leads must be made of the same material and thus, to simplify matters, a platinum lead must be connected to the silver electrode. It will be seen in the conclusion to this section that the electromotive force of a cell does not depend on the material from which the leads are made, so that the whole derivation could be carried out with different, e.g. copper, leads. In addition to Cl- and H30+ ions (further written as H+), the solution also contains Ag+ ions in a small concentration corresponding to a saturated solution of silver chloride in hydrochloric acid. Thus, the following scheme of the phases can be written (the parentheses enclose the species present in the given phase) ... 

Figure 2.51 Plots of azide surface concentration, T, against electrode potential, , for the silver electrode in 0.01 M NaN3/0.49M NaC104. The solid curve is as determined by differential-capacitance potential measurements, and the dashed curve from the integrated infrared intensities of the positive-going bands in Figure 2.50. Copyright 1986 American Chemical Society.

Metals which form sparingly soluble salts will also respond to changes in the activity of the relevant anion provided the solution is saturated with the salt, e.g. for silver in contact with a saturated solution of silver chloride and containing solid silver chloride the electrode reaction is AgCl + e = Ag + Cl, and the electrode potential is given by ... 

Figure 4.11 A solid-state electrode showing a first-order response. An electrode designed to measure the activity of silver ions uses a crystalline membrane of silver sulphide. An equilibrium between the mobile silver ions of the membrane and the silver ions in the solutions results in the development of a potential difference across the membrane.

Figure 4.12 A solid-state electrode showing a second-order response. The electrode shown in Figure 4.11 can be modified by the incorporation of silver chloride into the membrane to enable the activity of chloride ions in a sample to be measured. A surface reaction between the test chloride ions and the membrane silver ions alters the activity of the latter, resulting in a change in the potential difference across the membrane.

Figure 4.13 A solid-state electrode showing a third-order response. An alternative modification to the electrode described in Figure 4.11 will permit the measurement of cadmium ions in solution. The membrane is composed of a mixture of silver and cadmium sulphides. The surface reaction between the cadmium ions in the test solution and the sulphide ions in the membrane will affect the equilibrium between the sulphide ions and the silver ions in the membrane.

The silver-silver chloride electrode (Ag AgCl) is easily and cheaply made. Two silver electrodes are cleaned (see Section 9.1.1 above) and immersed in aqueous KCl solution (a concentration of 0.1 mol dm is convenient). Next, a potential of about 2 V is applied across them for c. 10 min, causing a thin outer film of silver chloride to develop on the positive electrode. Solid AgCl is formed by a two-step reaction, involving first the electro-formation of silver ion ... 

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... 

Equation (6.3.4) is valid for all-solid-state electrodes only when the membrane has a silver contact. The cell [203]... 

Silver-Silver Chloride Electrode. This reference electrode consists of a pure silver wire in a solution of KCl saturated with solid silver chloride. The electrode reaction is... 

We see from the example that a silver electrode is also a halide electrode, if solid silver halide is present,6 If the solution contains AgCl(.v), we substitute [Ag+] = Jfsp/[C1 ] into Equation 15-1 to find an expression relating the cell voltage to [Cl ... 

One exception is a solid-state electrode based on silver chloride with a membrane covered by acetyl cellulose, which is occasionally used in some setups (OCD, prev. Kodak). 

Other useful solid-state electrodes are based on silver compounds (particularly silver sulfide). Silver sulfide is an ionic conductor, in which silver ions are the mobile ions. Mixed pellets containing Ag2S-AgX (where X = Cl, Br,... 

Much has been written about solid metal electrodes, which have now largely displaced liquid mercury. Those most often used as redox ( inert ) electrodes for studying electron transfer kinetics and mechanism, and determining thermodynamic parameters are platinum, gold, and silver. However, it should be remembered that their inertness is relative at certain values of applied potential bonds are formed between the metal and oxygen or hydrogen in aqueous and some non-aqueous solutions. Platinum also exhibits catalytic properties. 

The - electrochemical window of polished solid silver amalgam electrode (p-AgSAE) as for an electrode which does not contain liquid mercury is exceptionally broad. This fact allows the application of p-MeSAE for determination of species at rather negative potentials. An important advantage is that the electrodes from solid amalgams of different metals can be prepared in a relatively simple way, and that in their applications specific interactions between these metals and the studied compounds can be utilized. 

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