Mercury solution

Assume that an aqueous solute adsorbs at the mercury-water interface according to the Langmuir equation x/xm = bc/( + be), where Xm is the maximum possible amount and x/x = 0.5 at C = 0.3Af. Neglecting activity coefficient effects, estimate the value of the mercury-solution interfacial tension when C is Q.IM. The limiting molecular area of the solute is 20 A per molecule. The temperature is 25°C. 

A typical example of an ideal polarizable interface is the mercury-solution interface [1,2]. From an experimental point of view it is characterized by its electrocapillary curve describing the variation of the interfacial tension 7 with the potential drop across the interface, 0. Using the thermodynamic relation due to Lippmann, we get the charge of the wall a (-a is the charge on the solution side) from the derivative of the electrocapillary curve ... 

Fig. 20.4 Lippmann electrometer for studying the variation of the excess charge on mercury with variation in potential difference at the mercury solution interface...

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. 

The diffusion current Id depends upon several factors, such as temperature, the viscosity of the medium, the composition of the base electrolyte, the molecular or ionic state of the electro-active species, the dimensions of the capillary, and the pressure on the dropping mercury. The temperature coefficient is about 1.5-2 per cent °C 1 precise measurements of the diffusion current require temperature control to about 0.2 °C, which is generally achieved by immersing the cell in a water thermostat (preferably at 25 °C). A metal ion complex usually yields a different diffusion current from the simple (hydrated) metal ion. The drop time t depends largely upon the pressure on the dropping mercury and to a smaller extent upon the interfacial tension at the mercury-solution interface the latter is dependent upon the potential of the electrode. Fortunately t appears only as the sixth root in the Ilkovib equation, so that variation in this quantity will have a relatively small effect upon the diffusion current. The product m2/3 t1/6 is important because it permits results with different capillaries under otherwise identical conditions to be compared the ratio of the diffusion currents is simply the ratio of the m2/3 r1/6 values. 

Trasatti has calculated the potentials of several organic, solvents from Volta potentials and the partial surface potentials on the mercury solution phase boundaries at the potential of zero charge. ... 

Electrocapillary curves, i.e., the interfacial tension vs. the applied potential curves are well known for the mercury-solution interface and have been utilized also for interpreting the... 

Since this capacitance is supposed to be in series with that of the solution and since capacitances of mercury-solution interfaces are much larger than 2 F/cm2, this number is too low. The Thomas-Fermi theory as well as the neglect of interactions between metal electrons and the electrolyte are at fault. To reduce the metal s contribution to the inverse capacitance, a model must include6 penetration of the electron tail of the metal into the solvent region, where the dielectric constant is higher, as the models discussed below do. 

Subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS), has been used extensively to examine interactions of species at the electrode/electrolyte interface. In the present work, the method has been extended to probe interactions at the mercury solution interface. The diminished potential dependent frequency shifts of species adsorbed at mercury electrodes are compared with shifts observed for similar species adsorbed at d-band metals. 

Based on the discussion above, it seems evident that a detailed understanding of kinetic processes occurring at semiconductor electrodes requires the determination of the interfacial energetics. Electrostatic models are available that allow calculation of the spatial distributions of potential and charged species from interfacial capacitance vs. applied potential data (23.24). Like metal electrodes, these models can only be applied at ideal polarizable semiconductor-solution interfaces (25)- In accordance with the behavior of the mercury-solution interface, a set of criteria for ideal interfaces is f. The electrode surface is clean or can be readily renewed within the timescale of... 

Mercaptohexadecanol, adsorption, 979 Mercury in electrode kinetics, 1093, 1195 Mercury solution interface, ideal polarizable interface, 848 Metal capacity, 888 determination. 890 -water interactions, 896, 897... 

Fig. 6.65. (a) Representation of the Gouy-Chapman theory according to Eq. (6.130). (b) Plots of the differential capacity of the mercury/solution interface vs. electrode potential for various concentrations of A/,A/dimethylacetamide in 0.15 M Na2S04-water.(Reprinted with permission from W. R. Fawcett, G. Y. Champagne, S. Komo, and A. J. Motheo, J. Phys. Chem. 92 6368, Fig. 6, copyright 1988, American Chemical Society.)... 

Fig. 6.82. Surface potential of water at the mercury/solution interface as a function of charge density on the metal. (Reprinted from J. O M. Bockris and M. A. Habib, Electrochim. Acta 22 41, copyright 1977, Fig. 2, with permission from Elsevier Science.)...

Starting from the Lippmann equation, derive an expression for the variation of the radius of a mercury drop as a function of potential in a solution where there is no specific adsorption. Assume that the double layer at the mercury solution interface can be treated as a parallel-plate capacitor. (Contractor)... 

Consider a simple interfacial region at a mercury/solution interface. The electrolyte is 0.01 M NaF and the charge on the electrode is 10 iC negative to the pzc. The zeta potential is -10 mV on the same scale. What is the capacitance of the Helmholtz layer and that of the diffuse layer Galculate the capacitance of the interfaces. Take the thickness of the double layer as the distance between the center of the mercury atoms and that of hydrated K+in contact with the electrode through its water layer. (Bockris)... 

To 1 g shredded aluminum foil there was added a solution of 20 mg HgCI2 in 15 mL H20. After 15 min the amalgamated aluminum was drained free of the mercury solution, well washed with fresh H20, and shaken as dry as possible. There was then added, in sequence, a solution of... 

In this discussion the mercury-solution interface is assumed to be completely polarizable that is, there is no transfer of charge across the interface. Therefore each of the charged species (including electrons) occurs in only one of the phases. The requirement of complete polarizability means that the surface excess may be divided between that in the aqueous phase (W) and that in the mercury (Hg). In view of Equations (85) and (86), we write... 

Another interpretation of the electrocapillary curve is easily obtained from Equation (89). We wish to investigate the effect of changes in the concentration of the aqueous phase on the interfacial tension at constant applied potential. Several assumptions are made at this point to simplify the desired result. More comprehensive treatments of this subject may be consulted for additional details (e.g., Overbeek 1952). We assume that (a) the aqueous phase contains only 1 1 electrolyte, (b) the solution is sufficiently dilute to neglect activity coefficients, (c) the composition of the metallic phase (and therefore jt,Hg) is constant, (d) only the potential drop at the mercury-solution interface is affected by the composition of the solution, and (e) the Gibbs dividing surface can be located in such a way as to make the surface excess equal to zero for all uncharged components (T, = 0). With these assumptions, Equation (89) becomes... 

Beside this basic method of manufacturing mercury fulminate, which is widely practised, there are alternate processes. Angelico [11] recognized that mercury fulminate is formed by treating a mercury solution in an excess of nitric acid with a concentrated aqueous solution of malonic acid in the presence of a small amount of sodium nitrate. The reaction results in a considerable rise of temperature, C02 evolution and the precipitation of the fulminate (L. W. Jones [12]). 

The temperature of the mercury solution lies between 40 and 55 °C, that of the alcohol between 20 and 35 °C. A grey product is formed. In order to obtain a white... 

Mercury flows from the capillary in small drops. The size of these drops is determined by the interfacial tension at the mercury-solution interface. The internal pressure in the drop acting against Pt is, according to Kucera, given by the relation... 

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