Electrode concentration cell

Concentration cells may be classified into two main groups (i) electrode-concentration cells and (ii) electrolyte-concentration cells. Of the two, those belonging to the second category are by far the most important. 

To describe a specific example of electrode-concentration cells, it is possible to consider two zinc amalgams at different concentrations, dipped into a solution containing zinc ions ... 

As has been pointed out, another interesting type of electrode-concentration cell is that comprising two hydrogen electrodes working at different pressures and remaining immersed in a solution of hydrochloric acid. The cell may be represented as ... 

To form an electrode concentration cell the electrode material must have a variable concentration. Amalgam and gaseous electrodes frill into this classification. An example of electrode concentration cells is the one in which two amalgam electrodes of different concentrations dip into a solution containing the solute metal ions. 

An electrode concentration cell can be constructed using two electrodes which consist of a gas at different partial pressures. The following is an example of the hydrogen electrode concentration cell ... 

Ridley, M.K. et al., Poteirtiometric studies of the rutile-water interface Hydrogen-electrode concentration-cell versus glass-electrode titrations. Colloids Surf. A, 204, 295, 2002. 

D7.7 Electrode combinations that produce identical cell compartments with differing concentrations only (electrolyte concentration cells) have a cell potential dependence upon the liquid junction potential and the concentration difference. If the cell has identical compartments with either gaseous or amalgam electrodes (electrode concentration cell), the cell potential will depend upon the gas pressure differences or the amalgam concentration differences but will not have a liquid junction potential. Other electrode combinations produce cells for which the cell potential depends upon the half-reaction reduction potentials. 

Mesmer and Baes (P6) studied the dissociation equilibria potentiometrically over a wide temperature range. Using a hydrogen-electrode concentration cell measurements were made to SOO C. The equilibria were expressed as neutralization reactions ... 

Therefore the setup where the dissolution reaction is followed by potentiometric measurements of the pertinent H -concentration within the galvanic cell (glass electrode solution salt bridge reference electrode) is an optimal system for solubility measurements. This method is called potentiometric method of solubility measiuements ( Potentio in Table 1.1). An example of such measurements could be tiiat of solubility of metal oxides at temperatures up to 300°C performed in ORNL using simultaneously sampling method and the hydrogen-electrode concentration cell (HECC). The details of such measurements and experimental setup can be found in Chapter 3 in this Book. 

It is highly desirable to establish a set of pH buffer solutions which can be used at temperatures above 100 °C. Thus far, little has been done to develop the necessary sets of the high-temperature buffer systems as primary standards. Only a 0.05 mol-kg potassium hydrogen phthalate solution has been adopted by lUPAC as an appropriate primary buffer system to be used at temperatures up to about 225 °C. However, the acid dissociation constants of many organic and inorganic buffers have been measured with the hydrogen-electrode concentration cell (see discussion below) and these results are currently available for developing the secondary pH standards to 250 °C. 

Hydrogen-Electrode Concentration Cell for Solubility Measurements... 

The simplest type of galvanic cell has a single electrolyte common to both electrodes (as in Fig. 5.3). In some cases it is necessary to immerse the electrodes in different electrolytes, as in the DanieU cell (Fig. 5.7), in which the redox couple at one electrode is Cu VCu and at the other is Zn VZn. In an electrolyte concentration cell, which would be constructed Hke the cell in Fig. 5.4, the electrode compartments are of identical composition except for the concentrations of the electrolytes. In an electrode concentration cell the electrodes themselves have different concentrations, either because they are gas electrodes operating at different pressures or because they are amalgams (solutions in mercury) with different concentrations. 

If one specifies the activities of the solids as described in Section 3.4 (ordinarily very close to unity) then a measurement of the cell emf yields the mean molal activity coefficient of ZnCl2 in solution, (b) Electrode concentration cell Here a mirror image cell is set up in which the electrodes differ solely in the concentration of surroundings. As an illustration consider the cell... 

Cathode The electrode of a galvanic cell where positive current flows from the solution to the electrode. Concentration cell A galvanic cell in which the emf is due to the difference in the concentration of reactive constituents of the electrolyte. 

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