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Electrochemistry
Published in W. John Rankin, Chemical Thermodynamics, 2019
A salt bridge (a liquid form of ionic bridge) is commonly employed to minimise or stabilise the liquid junction potential at the interfaces of two miscible electrolyte solutions. A salt bridge is a bridge between the two solutions which consists typically of a saturated solution of potassium chloride or ammonium nitrate (contained in a gel) between the two solutions constituting the junction (see Figure 16.12). The cations and anions in these solutions have very similar diffusion rates, and because they are present in large concentration at the junction they carry almost all the current across the boundary without creating a junction potential. The ions in the salt bridge (such as K+) diffuse into the solution to replace Cu2+ ions and are themselves replaced in the salt bridge by diffusion of Zn2+ ions; they play no part in the cathode reaction. The cell in this case is represented as follows: Cu(s)|CuSO4(aq)||||ZnSO4(aq)|Zn(s)
Control of pH
Published in William S. Levine, Control System Applications, 2018
The liquid-junction potential represents any voltage developed by diffusion of ions across the junction between the solution being measured and that of the reference electrode. Potassium chloride is selected for the reference solution, because its ions have approximately the same ionic mobility, thereby minimizing the junction potential. For most solutions, Ej is less than 1 mV, and is not considered a major source of error.
pH Measurement
Published in Béla G. Lipták, Analytical Instrumentation, 2018
A. C. Blake, T. S. Light, D. L. Hoyle, T. J. Myron, G. K. Mcmillan
The pH measurement error in process applications is an order of magnitude larger than the normally stated electrode error, due to varying glass surface conditions, dissociation constants, streaming potentials, concentration gradients, and diffusion or liquid junction potentials of actual installations. Optimistic users and suppliers who provide one electrode per point in the process may believe they have achieved accuracies of 0.02 pH or better. Results of installations with three electrodes per point in the process show that the accuracy over a month is at best 0.25 pH and can only be obtained after frequent process calibration adjustments. In fact, if all three electrodes agree within a tenth of a pH for more than a few minutes in an industrial application, it indicates that the electrodes are probably coated, broken, or still have on protective caps.1
On the stability of shale: the role of zeta potential (ζ) and Debye Hückel length (κ−1) on shale swelling
Published in Petroleum Science and Technology, 2021
When ions move at different velocities across a membrane, a diffusion potential or liquid junction potentials is developed. The extent of the liquid junction potential depends on the ionic concentration (water activity) and respective transport numbers of cations and anions in the medium solution as follows (Lomba, Chenevert, and Sharma 2000):