Nernst equation chloride

Thus under standard conditions chloride ions are not oxidised to chlorine by dichromate(Vr) ions. However, it is necessary to emphasise that changes in the concentration of the dichromate(VI) and chloride ions alters their redox potentials as indicated by the Nernst equation. Hence, when concentrated hydrochloric acid is added to solid potassium dichromate and the mixture warmed, chlorine is liberated. 

Another problem is that the Nernst equation is a function of activities, not concentrations. As a result, cell potentials may show significant matrix effects. This problem is compounded when the analyte participates in additional equilibria. For example, the standard-state potential for the Fe "/Fe " redox couple is +0.767 V in 1 M 1TC104, H-0.70 V in 1 M ITCl, and -H0.53 in 10 M ITCl. The shift toward more negative potentials with an increasing concentration of ITCl is due to chloride s ability to form stronger complexes with Fe " than with Fe ". This problem can be minimized by replacing the standard-state potential with a matrix-dependent formal potential. Most tables of standard-state potentials also include a list of selected formal potentials (see Appendix 3D). 

When paint films are immersed in water or solutions of electrolytes they acquire a charge. The existence of this charge is based on the following evidence. In a junction between two solutions of potassium chloride, 0 -1 N and 0 01 N, there will be no diffusion potential, because the transport numbers of both the and the Cl" ions are almost 0-5. If the solutions are separated by a membrane equally permeable to both ions, there will still be no diffusion potential, but if the membrane is more permeable to one ion than to the other a diffusion potential will arise it can be calculated from the Nernst equation that when the membrane is permeable to only one ion, the potential will have the value of 56 mV. 

The construction of these electrodes is exactly similar to that already described for the pH responsive glass electrode. They must of course be used in conjunction with a reference electrode and for this purpose a silver-silver chloride electrode is usually preferred. A double junction reference electrode is often used. The electrode response to the activity of the appropriate cation is given by the usual Nernst equation ... 

Equilibrium potentials calculated at 37°C from the Nernst equation. Calculated assuming a —90 mV resting potential for the muscle membrane and assuming that chloride ions are at equilibrium at rest. 

The cell consists of an indicator and a reference electrode, the latter usually being the calomel or silver-silver chloride type. The potential of the indicator electrode is related to the activities of one or more of the components of the solution and it therefore determines the overall cell potential. Ideally, its response to changes of activity should be rapid, reversible and governed by the Nernst equation. There are two types of indicator electrode which possess the desired characteristics - metallic and membrane. 

The purpose of the silver-silver chloride combination is to prevent the potential that develops from changing due to possible changes in the interior of the electrode. The potential that develops is a membrane potential. Since the glass membrane at the tip is thin, a potential develops due to the fact that the chemical composition inside is different from the chemical composition outside. Specifically, it is the difference in the concentration of the hydrogen ions on opposite sides of the membrane that causes the potential—the membrane potential—to develop. There is no half-cell reaction involved. The Nernst equation is... 

Using the Nernst equation, tell how the silver-silver chloride electrode works as a reference electrode. 

The Nernst equation defining the potential of the silver-silver chloride electrode is Equation (14.9). Since the [CF] in such an electrode is a constant, the potential also must be a constant (the requirement of a reference electrode) because [CF] is the only variable on which the potential depends. 

The concentrations of ions in equilibrium with a sparingly soluble salt are sufficiently low that the Nernst equation can be used with little error. Rather than measuring the concentration of the relevant ions directly, the more common procedure is to set up a cell in which one of the electrodes involves the insoluble salt, and whose net cell reaction is just the dissolution of the salt. For example, to determine the Ksp for silver chloride, we could use the cell... 

Avith unit activity of both chloride and hypochloride ions (aLl == a(1(>- = 1) folloAvs from the Nernst, equation ... 

The Tafel expressions for both the anodic and the cathodic reaction can be directly incorporated into a mixed potential model. In modeling terms, a Tafel relationship can be defined in terms of the Tafel slope (b), the equilibrium potential for the specific half-reaction ( e), and the exchange current density (70), where the latter can be easily expressed as a rate constant, k. An attempt to illustrate this is shown in Fig. 10 using the corrosion of Cu in neutral aerated chloride solutions as an example. The equilibrium potential is calculated from the Nernst equation e.g., for the 02 reduction reaction,... 

Similarly, from the Tables 1.17 and 1.18 we can see, for example, that permanganate ions (in acid medium) can oxidize chloride, bromide, iodide, iron(II), and hexacyanoferrate(II) ions, also that iron(III) ions may oxidize arsenite or iodide ions but never chromium(III) or chloride ions etc. It must be emphasized that the standard potentials are to be used only as a rough guide the direction of a reaction will depend on the actual values of oxidation-reduction potentials. These, if the concentrations of the species are known, can be calculated easily by means of the Nernst equation. 

The chloride ion concentration at any point on the titration curve can be calculated from equation 20-5, which can be derived from the Nernst equation. 

Most pH determinations are made by electrometric methods, the pH of the unkown solution (X) being calculated from that of a known standard (S) and the emf ( x and s) of a cell composed of a hydrogen ion-responsive electrode (for example, a glass electrode or a hydrogen gas electrode) coupled with a reference electrode (calomel, silver-silver chloride). This cell is filled successively with the standard solution S and with the unknown solution X. A liquid junction potential j exists where these solutions make contact with the concentrated KCl solution of the reference electrode. From the Nernst equation for the cell reactions and assuming an ideal hydrogen ion response ... 

Hence, the activity/concentration of chloride ions near the surface of the electrode would decrease, which would make the potential of the reference electrode more positive than its true equilibrium value based on the actual activity of chloride ion in the reference half-cell since the Nernst equation for this half-cell is ... 

A cell is constructed at 25°C as follows. One half-cell consists of a chlorine/chloride, CI2/CE, electrode with the partial pressure of CI2 = 0.100 atm and [Cl ] = 0.100 M. The other halfcell involves the Mn04 /Mn + couple in acidic solution with [Mn04 ] = 0.100 M, [Mn +] = 0.100 M, and [H ] = 0.100 M. Apply the Nernst equation to the overall cell reaction to determine the cell potential for this cell. 

Diffusion potentials for the primary biological ions (potassium, sodium, and chloride) represent the primary source of the resting membrane potential. The diffusion potential for a given ionic species can be calculated from the modified Nernst equation developed by Hodgkin and Huxley. The equation is ordinarily written as... 

To calculate an E(W) one uses the Nernst equation assuming pH 7 and 1 x 10 chloride ion since it is a common constituent in natural waters and [CH2CI2] = [CHCI3] = 1. 

A metal electrode of the second kind consists of a metal coated with one of its sparingly soluble salts (or immersed in a saturated solution of its sparingly soluble salt). This electrode responds to the anion of the salt. For example, a silver wire coated with AgCl will respond to changes in chloride activity because the silver ion activity is controlled by the solubility of AgCl. The electrode reaction is AgCl(s) -I- e Ag(s) -I- Cl , with a potential = 0.222 V. The Nernst equation expression for the electrode potential at 25°C is = 0.222 - 0.05916 log[Cr]. 

This results in the following Nernst equation, so that the electrode potential is proportional to the logarithm of the activity of the chloride in the electrolyte solution ... 

The characteristics of an ideal reference electrode are that it should have a fixed potential over time and temperature, long-term stability, and the ability to return to the initial potential after exposure to small currents (i.e., it should be reversible), and it should follow the Nernst equation. Two common reference electrodes that come close to behaving ideally are the saturated calomel electrode (SCE) and the silver/silver chloride electrode. 

Chloride activity measurements are done in the same manner as the potassium measurements, except that the Nernst equation was used instead of the Nicolski equation to describe the potential difference due to the difference of chloride activities between the inside and outside of the cell. We know that there are no interfering ions in the solution on the outside. We assume that there are no interfering anions inside the cell. This assumption is necessary because we simply do not have any information about what ions are present and what their activities are. 

---