Calomel saturated

Example 13 The following data were recorded for the potential E of an electrode, measured against the saturated calomel electrode, as a function of concentration C (moles liter ). 

Table 8.31 Half-Wave Potentials (vs. Saturated Calomel Electrode) of Organic...

The saturated calomel electrode (SCE), which is constructed using an aqueous solution saturated with KCl, has a potential at 25 °C of -hO.2444 V. A typical SCE is shown in Eigure 11.8 and consists of an inner tube, packed with a paste of Hg, HgiCli, and saturated KCl, situated within a second tube filled with a saturated solution of KCl. A small hole connects the two tubes, and an asbestos fiber serves as a salt bridge to the solution in which the SCE is immersed. The stopper in the outer tube may be removed when additional saturated KCl is needed. The shorthand notation for this cell is... 

As with the saturated calomel electrode, the potential of the Ag/AgCl electrode is determined by the concentration of Cb used in its preparation. 

If the copper electrode is the indicator electrode in a potentiometric electrochemical cell that also includes a saturated calomel reference electrode... 

The following data were collected for the analysis of fluoride in tap water and in toothpaste, (a) For the analysis of tap water, three 25.0-mL samples were each mixed with 25.0 mL of TISAB, and the potential was measured with an F ISE relative to a saturated calomel electrode. Five 1.00-mL additions of a standard solution of 100.0-ppm F were added to each, measuring the potential following each addition. 

The titanium oxide film consists of mtile or anatase (31) and is typically 250-A thick. It is insoluble, repairable, and nonporous in many chemical media and provides excellent corrosion resistance. The oxide is fully stable in aqueous environments over a range of pH, from highly oxidizing to mildly reducing. However, when this oxide film is broken, the corrosion rate is very rapid. Usually the presence of a small amount of water is sufficient to repair the damaged oxide film. In a seawater solution, this film is maintained in the passive region from ca 0.2 to 10 V versus the saturated calomel electrode (32,33). 

Steady-state potential, negative to saturated calomel half-ceU. 

The polarographic half-wave reduction potential of 4-nitroisothiazole is -0.45 V (pH 7, vs. saturated calomel electrode). This potential is related to the electron affinity of the molecule and it provides a measure of the energy of the LUMO. Pulse radiolysis and ESR studies have been carried out on the radical anions arising from one-electron reduction of 4-nitroisothiazole and other nitro-heterocycles (76MI41704). 

The electroreductive cyclization of the furanone 118 (R = -(CH2)4CH=CH— COOMe Scheme 36) using a mercury pool cathode, a platinum anode, a saturated calomel reference electrode, and a degassed solution of dry CH3CN containing -Bu4NBr as the electrolyte, gave the spirocyclic lactones 119 and 120 in a ratio 1.0 1.1 (Scheme 37)(91T383). 

These values are roughly constant across a range of electrolyte environments except where noted but the variations between alloys, heat treatment conditions, etc. creates a range for each metal. For some metals such as iron and steel the range is low ( 100 mV), but for lead, nickel, stainless steels a range is given. The corrosion potential is reported with respect to the saturated calomel reference electrode. 

Stainless steel pipes (buried in the ground) and the interiors of stainless steel heat exchangers have been successfully cathodically protected, but CP is rarely used for materials other than steel. The protection potential usually adopted for steel is —850 mV to the saturated calomel reference electrode. This varies with temperature and the presence of other aggressive species in the environment. 

In general, however, for titanium immersed in acid solutions, potentials above zero on the saturated calomel scale are conducive to the formation of protective oxide, while at certain negative potentials hydride films, which also confer some protection, can be formed. Between the potential at which a continuous hydride film is formed and that at which protective oxide films appear, soluble titanium ions are produced and rapid corrosion ensues. 

Various types of reference electrodes have been considered in Section 20.3, and the potentials of these electrodes and their variation with the activity of the electrolyte are listed in Table 21.7, Chapter 21. It is appropriate, however to point out here that the saturated calomel electrode (S.C.E.), the silver-silver chloride electrode and the copper-copper sulphate electrode are the most widely used in corrosion testing and monitoring. 

The mechanism of the action of metallic copper was investigated by Streicher who determined the potential of a Type 314 stainless steel, the redox potential of the solution (as indicated by a platinised-Pt electrode) and the potential of the copper. The actual measurements were made with a saturated calomel electrode, but the results reported below are with reference to S.H.E. In the absence of copper the corrosion potential of the stainless steel was 0-58 V, whereas the potential of the Pt electrode was... 

A basic circuit is shown schematically in Fig. 19.36(a). The specimen C., or working electrode W.E. is the metal under study, the auxiliary electrode A.E. is usually platinum and R.E. is the reference electrode, for instance a saturated calomel electrode. The desired potential difference between the specimen and the reference electrode is set with the backing circuit B. Any... 

Potentiometric titration using a bright platinum-saturated calomel electrode system this can be used when the reaction involves two different oxidation states of a given metal. 

In the common method of electro-gravimetric analysis, a potential slightly in excess of the decomposition potential of the electrolyte under investigation is applied, and the electrolysis allowed to proceed without further attention, except perhaps occasionally to increase the applied potential to keep the current at approximately the same value. This procedure, termed constant-current electrolysis, is (as explained in Section 12.4) of limited value for the separation of mixtures of metallic ions. The separation of the components of a mixture where the decomposition potentials are not widely separated may be effected by the application of controlled cathode potential electrolysis. An auxiliary standard electrode (which may be a saturated calomel electrode with the tip of the salt bridge very close to the cathode or working electrode) is inserted in the... 

If a controlled-potential determination is to be carried out, additional equipment will be required, namely an electronic voltmeter, a potentiostat and a reference electrode. The latter is most commonly a saturated calomel electrode, the construction of which is described in Chapter 14. 

Apparatus. The source of current is a potentiostat which is used in conjunction with a reference electrode (commonly a saturated calomel electrode) to control the potential of the working electrode. The circuit will be essentially that shown in Fig. 12.2(a) but with the addition of the integrator or of a coulometer. 

The evolution of nitrogen aids in removing dissolved air. A salt bridge (4 mm tube) attached to the saturated calomel electrode is filled with 3 per cent agar gel saturated with potassium chloride and its tip is placed within 1 mm of the mercury cathode when the mercury is not being stirred this ensures that the tip trails in the mercury surface when the latter is stirred. It is essential that the mercury-solution interface (not merely the solution) be vigorously stirred, and for this purpose the propeller blades of the glass stirrer are partially immersed in the mercury. 

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