Galvanic cells standard electrode potential

The potentials of the metals in their 1 mol U salt solution are all related to the standard or normal hydrogen electrode (NHE). For the measurement, the hydrogen half-cell is combined with another half-cell to form a galvanic cell. The measured voltage is called the normal potential or standard electrode potential, E° of the metal. If the metals are ranked according to their normal potentials, the resulting order is called the electrochemi-... 

Chemistry Video Consortium, Practical Laboratory Chemistry, Educational Media Film and Video Ltd, Harrow, Essex, UK - Electrochemical techniques (using galvanic cells, using conductometric cells, determining standard electrode potentials, determining solubility products, thermodynamic characteristics of cells, conductometric titrations and using an automatic titrator). 

Referring to a list of standard electrode potentials, such as in Table 8.3, one speaks of an electrochemical series, and the metals lower down in the se-ries(with positive electrode potentials) are called noble metals. Any combination of half-reactions in an electrochemical cell, which gives a nonzero E value, can be used as a galvanic cell (i.e., a battery). If the reaction is driven by an applied external potential, we speak of an electrolytic cell. Reduction takes place at the cathode and oxidation at the anode. The reduction reactions in Table 8.3 are ordered with increasing potential or pe values. The oxidant in reactions with latter pe (or E°) can oxidize a reductant at a lower pe (or ) and vice versa for example, combining half-reactions we obtain an overall redox reaction ... 

The standard electrode potential is sometimes called the standard reduction potential because it is listed by the reduction half-reactions. However, a voltmeter allows no current in the cell during the measurement. Therefore, the conditions are neither galvanic nor electrolytic—the cell is at equilibrium. As a result, the half-reactions listed in the table are shown as reversible. If the reaction occurs in the opposite direction, as an oxidation half-reaction, E° will have the opposite sign. 

We can use standard electrode potentials and the Nernst equation to calculate the potential obtainable from a galvanic cell or the potential required to operate an electrolytic cell. The calculated potentials (sometimes called thermodynamic potentials) are theoretical in the sense that they refer to cells in which there is no current. As we show in Chapter 22, additional factors must be taken into account if a current is involved. 

Standard Electrode Potentials from Galvanic Cells without Liquid Junctions... 

This condition is met in a method called internal electrolysis (or spontaneous electrogravimetric analysis), first described by Ullgren in 1868, in which electrolysis occurs by spontaneous discharge of a galvanic cell. To illustrate the principle, consider two half-cells, comprising a zinc rod in a zinc sulfate solution and a copper rod in a copper sulfate solution. At open circuit, 25 °C, the reversible cell potential is related to the two standard electrode potentials (E°) ... 

In order to determine the standard electrode potential for a metal, the galvanic cell is designed so that a half-cell is formed by a piece of metal immersed in a solution that contains 1.00 M of ions of that metal, and one half-cell with potential convention defined to be exactly zero volts. This electrode is called the standard hydrogen electrode (SHE) and it consists of a platinum electrode over which Hj gas at 1-atm of pressure is bubbled, immersed in a solution that contains 1.00 M of hydronium ion at 25°C. 

By devising various galvanic cells and measuring their electromotive forces, tables of values of standard electrode potentials can be constructed. A table that lists the value of electrode potential for any half-cell in which all concentrations are IM and all gases are at 1-atm pressure is a Table of Standard Reduction Potential (Table 3.2). By convention, the tabulated values are standard reduction potentials relative to the potential of the standard hydrogen electrode, which is defined as exactly zero volts. The analysis of the data from Table 3.2 highlights some important aspects. 

CHAPTER 14 GALVANIC CELLS 14.6 Standard Electrode potentials... 

Equation 14.6.3 is a general relation applicable to any galvanic cell. It should be apparent that we can use the relation to calculate the standard electrode potential of an electrode from the standard electrode potential of a different electrode and the standard cell potential of a cell that contains both electrodes. Neither electrode has to be a hydrogen electrode, which is difficult to work with experimentally. 

A problem with compiling a list of standard potentials is that we know only the overall emf of the cell, not the contribution of a single electrode. A voltmeter placed between the two electrodes of a galvanic cell measures the difference of their potentials, not the individual values. To provide numerical values for individual standard potentials, we arbitrarily set the standard potential of one particular electrode, the hydrogen electrode, equal to zero at all temperatures ... 

A student was given a standard Fe(s) Fe2+(aq) half-cell and another half-cell containing an unknown metal M immersed in 1.00 M MNO,(aq). When these two half-cells were connected at 25°C, the complete cell functioned as a galvanic cell with E = +1.24 V. The reaction was allowed to continue overnight and the two electrodes were weighed. The iron electrode was found to be lighter and the unknown metal electrode was heavier. What is the standard potential of the unknown MT/M couple ... 

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 ... 

A galvanic cell can be constmcted from a zinc electrode immersed in a solution of zinc sulfate and an iron electrode immersed in a solution of iron(II) sulfate. What is the standard potential of this cell, and what is its spontaneous direction under standard conditions ... 

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