Mercury potential diagram

Fig. 3. Evans-diagram for the cementation of Cu2+ and Pb2 with zinc amalgam of different zinc content. If the zinc concentration in the mercury employed for this special extraction technique is low, the anodic zinc-dissolution current density may be diffusion controlled and below the limiting cathodic current density for the copper reduction. The resulting mixed potential will lie near the halfwave potential for the reaction Cu2+ + 2e j Cu°(Hg) and only Cu2 ions are cemented into the mercury.

Of the Group 12 elements, zinc, cadmium and mercury, only Hg has a water-stable -I-1 state, and all three elements have + 2 states that are water-stable. Their reduction potentials are summarized in the Latimer diagram ... 

The diagram can be made clear if one restricts it at first to a presentation of the reaction on one metal (e.g., mercury) and one electrode potential. Then the figure would look like Fig. 9.9. 

A single example of the application of electrode potentials to chemistry in am-monia will suffice. The Latimer diagram for mercury in acidic solution is... 

Diagram (6) shows similar, but opposite, phenomena with the capillary active cations, tetramethyl and tetraethyl ammonium. The phenomena are reversed the rising part of the curve is not affected the falling part, and the maximum, are depressed and the maximum is shifted to more positive potentials. This is because the adsorption tends to form a double layer in the water, with the positive ions nearer the surface than the negative, and this positive adsorption potential aids in attracting electrons to the mercury surface and neutralizing it, so that the maximum is reached with the application of smaller negative potentials E. 

The importance of many-body interactions for accurate prediction of phase diagrams of rare gases has been demonstrated.87 A study on liquid mercury that uses an ab initio pair potential and a semiempirical many-body correction to produce an effective three-body potential that was able to predict the liquid-vapour phase diagram well,110 suggests that the main deficiency of the classical pair potential is the neglect of many-body effects. 

The mercury level in natural gas streams can be quite varied and the problems caused by high levels quite catastrophic. As such, online measurement can be essential in spotting potential problems allowing a measured response to increased Hg levels, potentially saving millions of dollars. A schematic block diagram of the online system is shown in Fig. 3. 

Phase Transition Temperatures How to calculate the phase transition temperatures now appears obvious If a substance like lead is solid at room temperature, this is because its chemical potential has its lowest value in the solid state. The potential of liquid lead has to exceed that of solid lead otherwise, at room temperature, it would be liquid like mercury. We will now visualize this in a diagram (Fig. 5.3). 

Fig. 3 Schematic diagram of the model for a lipid monolayer deposited on mercury. The dashed curve represents the profile of the average potential against the distance from the mercury surface. The diffuse-layer thickness has been compressed with respect to the monolayer thickness, for ease of representation [34].

Fig. 5.9 - Potential of the outer Helmholtz plane 02 a function of the rational potential for the mercury-aqueous NaF electrode. Concentrations of NaF are indicated on the diagram in moldm" . Reproduced with permission from R. Parsons, Advances in Electrochem. and Electrochem. Eng., 1 (1961), 1.

Ultimately, AfG° values must be based on experimental results in many cases, these experimental results are themselves obtained from ° values. Early in the twentieth century, G. N. Lewis conceived of an experimental approach for obtaining standard potentials of the alkali metals. This approach involved using a solvent with which the alkali metals do not react. Ethylamine was the solvent chosen. In the following cell diagram, Na(amalg, 0.206%) represents a solution of 0.206% Na in liquid mercury. 

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