Cell potential determination

Exercise 6,7. By (a) using the rule just stated above, and (b) by calculating the standard cell potential, determine whether, under standard conditions, Fe (aq) will oxidize Cl"(aq) to Cl2(g) to a significant extent. 

A problem that has fascinated surface chemists is whether, through suitable measurements, one can determine absolute half-cell potentials. If some one standard half-cell potential can be determined on an absolute basis, then all others are known through the table of standard potentials. Thus, if we know E for... 

In potentiometry, the concentration of analyte in the cathodic half-cell is generally unknown, and the measured cell potential is used to determine its concentration. Thus, if the potential for the cell in Figure 11.5 is measured at -1-1.50 V, and the concentration of Zn + remains at 0.0167 M, then the concentration of Ag+ is determined by making appropriate substitutions to equation 11.3... 

Plot of cell potential versus the log of the analyte s concentration In the presence of a fixed concentration of Interferent, showing the determination of the selectivity coefficient. 

The potentiometric determination of an analyte s concentration is one of the most common quantitative analytical techniques. Perhaps the most frequently employed, routine quantitative measurement is the potentiometric determination of a solution s pH, a technique considered in more detail in the following discussion. Other areas in which potentiometric applications are important include clinical chemistry, environmental chemistry, and potentiometric titrations. Before considering these applications, however, we must first examine more closely the relationship between cell potential and the analyte s concentration, as well as methods for standardizing potentiometric measurements. 

The concentration of Ca + in a water sample was determined by the method of external standards. The ionic strength of the samples and standards was maintained at a nearly constant level by making each solution 0.5 M in KNO3. The measured cell potentials for the external standards are shown in the following table. 

Determining the cell potential requites knowledge of the thermodynamic and transport properties of the system. The analysis of the thermodynamics of electrochemical systems is analogous to that of neutral systems. Eor ionic species, however, the electrochemical potential replaces the chemical potential (1). 

Predicting the cell potential requires knowledge of thermodynamic properties and transport processes ia the cell. Conversely, the measurement of cell potentials can be used to determine both thermodynamic and transport properties (4). 

The above considerations show that the equilibrium e.m.f. of a reversible cell is determined solely by the interfacial potentials at the two electrodes constituting the cell, providing the liquid junction can be eliminated or made negligible, and under these circumstances the interfacial potentials will be related to the chemical potentials of the species involved in the equilibrium. In the case of an irreversible cell, e.g. 

Chemists have determined a large number of these half-cell potentials. The magnitude of the voltage is a quantitative measure of the tendency of that half-reaction to release electrons in comparison to the H2-2H+ half-reaction. If the sign is positive, the half-reaction has greater tendency to release electrons than does the H2-2H+ half-... 

Such changes in the pH are sensed by the inner glass electrode. The overall cell potential is thus determined by the carbon dioxide concentration in the sample ... 

The difference in electrical potential between two electrodes is the cell potential, designated E and measured in volts (V). The magnitude of E increases as the amount of charge imbalance between the two electrodes increases. For any galvanic cell, the value of E and the direction of electron flow can be determined experimentally by inserting a voltmeter in the external circuit. 

The zinc-copper galvanic cell is under standard conditions when the concentration of each ion is 1.00 M, as shown in Figure 19-13. The cell potential under these conditions can be determined by connecting the electrodes to a voltmeter. The measured potential is 1.10 V, with the Zn electrode at the higher (more negative) potential, so Zn gives up electrons and E eii = 1.10 V ... 

Tabulated standard reduction potentials allow us to determine the potential of any cell under standard conditions. This net standard cell potential is obtained by subtracting the more negative standard reduction potential from the more positive standard reduction potential, giving a positive overall potential. 

C19-0020. Use standard reduction potentials to determine the net reaction and standard cell potential for cells of two compartments, each containing a 1.00 M solution of the indicated cation in contact with an... 

This is a quantitative problem, so we follow the standard strategy. The problem asks about an actual potential under nonstandard conditions. Before we determine the potential, we must visualize the electrochemical cell and determine the balanced chemical reaction. The half-reactions are given in the problem. To obtain the balanced equation, reverse the direction of the reduction half-reaction with the... 

As the Nemst equation describes, cell potentials are linked quantitatively to concentrations. One practical consequence of this relationship is that potential measurements can be used to determine concentrations of ions in... 

The standard cell potential for the hydrogen-oxygen reaction is then determined by the free energy of formation of water (gas) by... 

An interesting idea has been to prepare the photosensitive electrode on site having the liquid play the dual role of a medium for anodic film growth on a metal electrode and a potential-determining redox electrolyte in the electrochemical solar cell. Such integration of the preparation process with PEC realization was demonstrated initially by Miller and Heller [86], who showed that photosensitive sulfide layers could be grown on bismuth and cadmium electrodes in solutions of sodium polysulfide and then used in situ as photoanodes driving the... 

One is by now familiar with the equation that expresses the reversible potential of an electrode as a function of the activities of participants in the electrode reaction. If the activities of resultants (or products) of the electrode reaction are standardized and taken arbitrarily to be unity, this equation or expression takes the form of one in which the electrode potential is a function of the activity of one type of ion only. It should clearly be possible to construct two similar electrodes to take up reversible potentials corresponding to different activities of this one type of ion, and emf of the cell formed by the combination of such a pair of electrodes should, therefore, take up a potential determined by both the activities concerned. Cells of this type, in which the reversible emf is a function of the different activities of one participant in the electrode reaction, are termed concentration cells. 

In voltammetry (abbreviation of voltamperometry), a current-potential curve of a suitably chosen electrochemical cell is determined, from which qualitative and/or quantitative analytical data can be obtained. 

Concentration cells are a useful example demonstrating the difference between galvanic cells with and without transfer. These cells consist of chemically identical electrodes, each in a solution with a different activity of potential-determining ions, and are discussed on page 171. 

A First we write down the two half-equations, obtain the half-cell potential for each, and then calculate c0ell. From that value, we determine AG°... 

B We determine the value for the hypothetical reaction s cell potential. 

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