Mercury surface, equation state

For the familiar dropping mercury electrode, the electrical potential 1J1 at the metal surface relative to the bulk region of the electrolyte is controlled by an external potential source - a constant voltage source. In this case, can be set to any value (within reasonable physical limits) as the mercury/electrolyte interface does not allow charge transfer or chemical reactions to occur (at least to a good approximation for the case of NaF). Therefore, we can say that the equation of state of the mercury surface is... 

This is the Ilkovic equation, which was developed by solving the diffusion equations directly very early in the history of polarography. It shows that the diffusion current varies with (Obviously the maximum current will depend on r/, where is the duration of drop life.) It also shows that the current depends on the rate of flow of mercury. However, the quantity m is not very easily determined, although it can be measured if needed. The parameter that can be measured easily is the height of the surface of the mercury in the reservoir (Fig. 12) above the tip of the capillary, h, Poiseuille s equation states that m is proportional to h and that is inversely proportional to h. Thus // is proportional to h. Thus, in order to determine whether a current measured with the d.m.e. is diffusion controlled, all that is necessary is to check whether I is proportional to both and The current actually measured and reported in polarography is not the instantaneous one but an average current... 

This equation states that the pressure required to force a fluid to penetrate into a pore is proportional to the surface tension and inversely proportional to the pore radius. Techniques used to determine membrane pore size or pore size distribution include bubble point, mercury porosimetry, gas-liquid displacement, and liquid-liquid displacement (Table 15.3a-d) [171-173],... 

In view of the difficulty in deciding whether or not the initial tension is that of pure mercury, attempts to deduce the equation of state from measurements of the lowering of surface tension at various vapour pressures are open to doubt. Most workers have abandoned the attempt to do this with ordinary gases.7 Oliphant8 and Bosworth9 have, however, measured directly the amounts of carbon dioxide, sulphur dioxide, water vapour, and hydrogen adsorbed on a stream of freshly formed mercury drops. These were found to adsorb the maximum, final amount of gas in a fraction of a second and this was liberated,... 

Some forms of polarographically active substances are adsorbed at the mercury dropping electrode. In such instances two waves may be observed on polarographic curves, one of which corresponds to the reduction (or oxidation) of the free form and the other of the substance in the adsorbed state. The adsorption current increases with the increasing concentration of the electroactive species, but only to a certain value, which is a function of the surface of the electrode. No further increase of current is observed with further increases of concentration, and we suppose that the surface of the electrode under such conditions is covered by a layer of the adsorbed substance. The adsorption current (fo) is given by the equation< >... 

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