Potentials neglecting liquid junction potential

The small potential difference produced at the contact between the two solutions (the so-called liquid-junction potential) is neglected. 

For an electrochemical cell consisting of a metal at the potential of zero charge in a solution of surface-inactive electrolyte and a reference electrode (let us assume that any liquid junction potential can be neglected), the electrode potential is given by (cf. Eq. (20)]... 

The membrane phase m is a solution of hydrophobic anion Ax (ion-exchanger ion) and cation Bx+ in an organic solvent that is immiscible with water. Solution 1 (the test aqueous solution) contains the salt of cation Bx+ with the hydrophilic anion A2. The Gibbs transfer energy of anions Ax and A2 is such that transport of these anions into the second phase is negligible. Solution 2 (the internal solution of the ion-selective electrode) contains the salt of cation B with anion A2 (or some other similar hydrophilic anion). The reference electrodes are identical and the liquid junction potentials A0L(1) and A0L(2) will be neglected. 

Henderson or Plank formalisms. Mobilities for several ions can be seen in Table 18a. 1. Liquid junction potentials can become more problematic with voltammetric or amperometric measurements. For example, the redox potentials of a given analyte measured in different solvent systems cannot be directly compared, since the liquid junction potential will be different for each solvent system. However, the junction potential Ej can be constant and reproducible. It can also be very small (about 2-3 mV) if the anion and cation of the salt bridge have similar mobilities. As a result, for most practical measurements the liquid junction potential can be neglected [9]. 

Ideal potentiometric measurements, especially in analytical chemistry, would require that the potential of the reference electrode be fixed and known, and that the composition of the studied solution affect only the potential of the indicator electrode. This would occur only if the liquid-junction potential could be completely neglected. In practice this situation can be attained only if the whole system contains an indifferent electrolyte in a much larger concentration than that of the other electrolytes, so that the concentration of a particular component in the analysed solution, which is not present in the reference electrode solution, has only a negligible effect on the liquid-junction potential Such a situation rarely occurs, so that it is necessary to know or at least fix the liquid junction potential... 

In this cell there are three significant interfacial potential differences (neglecting any small liquid junction potential difference) ... 

The further exact application of (22) to the experimental data really requires consideration of the effects of changes in composition on the liquid-liquid junction potential between phase j8 and the reference electrode. Neglecting any changes at this junction, however, so that dE is still equal to —d(A ), and assuming that the solution is ideal, so that = RTdlogcP and remem-... 

This result is at variance with the accepted values of the second dissociation constants of the acids. Reference [92GRE/FUG] selects log K° = - 1.80 for selenic and log,o K2 = -. 98 for sulphuric acid. The expected potential difference would therefore be about 1 to 2 mV from these data if the liquid junction potential ( ,) is ignored, and not a few tenths of a millivolt. The contradiction can probably be traced to the neglect of An estimate of Ej by the Henderson equation indicates that the first term in the above expression for E is largely cancelled by the second term. The same... 

The review finds it difficult to assess this paper as experimental conditions and primary data are lacking. There can be no doubt that the authors have used concentrations instead of activities in their calculations. The activity of water was set equal to 1 despite the high concentration of solutes and any liquid junction potentials have been neglected. It appears fortuitous that Nemstian slopes were observed. The large concen-... 

This value is calculated from the information in Figure 1.3.4. The experimental value would also include the effects of activity coefficients and the liquid junction potential, which are neglected here. See Chapter 2. 

E2.10. (a) Calculate the cell potential of a concentration cell constructed from a zinc electrode in 0.2 M ZnS04 and 0.6 M ZnS04 solution. Neglect the liquid junction potential. 

Initial e.m.f. studies were concerned with the evaluation of °(Va). Kolthoff and Reddy obtained the formal potential of this cell from measurements with the glass electrode. The formal potential, was established as —0.392 V at 25°C. Due to the neglect of the liquid junction potential and the fact that E — )/pH was not 0.059 V, but rather 0.070 V, it is difficult to relate this formal potential to (Va). According to these authors the Pt, Hg electrode in HCl-DMSO solutions reacts with the solvent and is therefore unreliable. MoreF made e.m.f. measurements on the cell... 

The values cited neglect the liquid-junction potential at the KCl boundary, which in the case of strong acids, for example, increases the absolute value an average of several millivolts. 

M CUSO4 and 0.5 M CUSO4, neglecting the liquid-junction potential, (h) Write the spontaneous reaction of the cell and indicate which electrode is anode. 

Find the potential difference of a Daniell cell if the activity of zinc ions is equal to 0.500 and the activity of copper ions is equal to 0.350. Neglect the liquid junction potential. 

The standard states for the half-cells are the same, so E° vanishes, as it does for any concentration cell. If we neglect the liquid junction potential, the Nernst equation for our concentration cell is... 

Assuming that AH is constant, find E° at 323.15 K for the Daniell cell. Neglect the liquid junction potential. 

If a solution of NaOH with a molality of 0.100 mol kg is placed in a cell with a standard hydrogen electrode and a normal calomel electrode at 298.15 K, find the cell voltage and the pH of the solution. Neglect the liquid junction potential. State any other assumptions. 

The potential of liquid junction in electrochemical cells including ionic melts as solvents are usually less than to 0.001 that gives possibility to neglect this experimental error in the estimation of the equilibrium constants. The known reference electrodes were metalhc (i.e., metal immersed in solution with the definite concentration of the corresponding cation) or gas oxygen electrodes iimnersed in solutions with definite oxide ion concentrations (concentration cells). 

Fig. 3.6 Energy diagram for the semiconductor-vacuum, semiconductor-liquid and liquid-vacuum interfaces 0 , work functions ex, ex surface dipole contributions (neglected at the semiconductor-liquid junction) eA

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