Electromotive series of metals

Fig. 7. Electromotive series of metals. Franklin (F15). Copyright Engineering and Mining Journal, April, 1958, McGraw-Hill Inc.

Economic lot size, 350 Effective interest, 218-222, 224, 241 Efficiency, packing, 702-706 plate, 661-667 pump, 517-518, 520 Ejectors, cost of, 528 Electrical installation, cost of, 174, 807 Electricity, cost of, 815 Electromotive series of metals, 433 Emissivity of surfaces, 582-585 Energy balance, mechanical, 479-480 for reactor design, 715-716 total, 479-480... 

TABLE 3.4. Position of Thngsten in the Electromotive Series of Metals in Different Molten Salts... 

Standard [reduction] potentials for hundreds of electrodes have been determined (mostly in the period 1925-45, during which time they were referred to as oxidation potentials ) and are usually tabulated in order of increasing tendency to accept electrons. This ordering is also known as the electromotive series of the elements. As can be seen in the abbreviated version in Table 1, sodium is the most active of the metallic elements in the sense that its oxidation product Na+ shows the smallest tendency (as indicated by the highly negative voltage) to undergo reduction. 

Electromotive Series of the Metals, (a) Place a few pieces of zinc in 5 cc. of 0.2 A solution of copper sulphate, shake the mixture frequently, and after about 15 minutes withdraw 1 cc. of the solution and test it for copper and for zinc ions, applying the information obtained from the preceding experiments. If any copper ions are still present let the remainder of the mixture stand for 15 minutes more with frequent shaking, and repeat the test. Continue until you have reached a conclusion as to whether copper ions can be completely displaced from solution by zinc. 

Electromotive Series. Review Experiment 19, page 92, and make what further experiments of a similar nature are necessary to determine the relative position in the electromotive series of the heavy metals considered in this chapter. 

The first step in this new stain protocol employs copper acetate, a metal salt that is both a good fixative ( ) and a silver stain enhancer. The mechanism of copper s stain enhancement, in this and other silver stains, may be similar to its action in the biuret reaction (15.), in which a characteristic color shift, from violet to pink, is achieved by titrating peptides in the presence of copper ions. Copper complexes formed with the N-peptide atoms of the peptide bonds are primarily responsible for this reaction. There are also some number of secondary sites which may interact with copper. Any elemental copper formed may displace positive silver ions from solution as copper has a greater tendency to donate electrons than silver, indicated by its position in the electromotive series of the elements. Following the treatment with copper acetate, the membrane is sequentially soaked in a solution containing chloride and citrate ions and then in a solution containing silver nitrate. The membrane is then irradiated with light while it is in the silver nitrate... 

A long memoir by Volta in two parts summarises his lecture to the Institut, repeats the above statements, and reports that by measuring the electrometer deflections with different pairs of metals he found that the forces which drive the electric fluid (alia forza. .. quelle spinge il fluido elettrico) from the first metal to the second are silver/copper i, copper/iron 2, iron/tin 3, lead/tin i, lead/zinc 5. Then the force for silver/zinc in immediate contact is 12 ( = i+ 2 + 3 + i+5), copper/tin 5 ( = 3 + 2), iron/zinc 9 (= 5 +1 + 3), etc. Thus the force or impulsion with which two metals act on the electric fluid is equal to the sum of the forces of the series of metals which stand between them, and... the electric force is the same as that which arises when the two extreme metals are in direct contact. Metals of any kind interposed between the two extreme metals have no effect on the force of the latter. This is the first statement of what Maxwell called Volta s law of contact electricity . Volta showed that it did not hold if humid conductors were in the circuit. E.g. HgO/Zn = I, hence if the law held HgO/Ag should be 13, but it was only i ( 25). The humid conductor reduces the electromotive force between the metals so that it is not balanced at the metallic junction, and a continuous current is kept up ( 7). In a summary of his publications Volta repeats his view that the current arises from the contact of two different conductors, above all metallic , and that the chemical action in the pile is not concerned with the production of electricity. 

Standard Electromotive Force Potentials Galvanic Series of Metals Galvanic Series of Metals in Sea Water Corrosion... 

Flengas, S.N., and Ingraham, T.R. (1959). Electromotive force series of metals in fused salts and activities of metal chlorides in 1 1 molar KCl-NaCl soXvXxons, J.Electrochem.Soc. 106, 84-91. Tumidajski, P.J., and Flengas S.N. (1991). Potential measurements of reactive metal chloride in alkali halide solution. W.CYiiormwm, J.Electrochem.Soc. 138, 1659-1665. 

A wide variety of data is available to characterize the nature of the reaction between engineering materials and their chemical environments (Shackelford, Alexander, and Park, 1994). Perhaps no such data are more fundamental and practical than the electromotive force series of metals shown in Table 2.29. The voltage associated with various half-cell reactions in standard aqueous environments are arranged in order, with... 

According to the electromotive series of the elements there are innumerable pairs which will yield electrochemical energy accumulators. For instance, take a metal and a metallic oxide and immerse them in a liquid electrolyte. These are the main parts of a cell as Figure 15.1 demonstrates. 

Each metal or metal area will develop an electrode with a measurable electrical potential. This potential can be referenced to that of a standard hydrogen electrode, which by convention is set at zero. Thus, all metals have either a higher or lower potential compared to hydrogen, and a comparative list of metals can be produced indicating their relative nobility. This list is the galvanic or electrochemical series and measured as an electromotive force (EMF). 

Other organometallic compounds that are hydrolyzed by water are those of sodium, potassium, lithium, zinc, and so on, the ones high in the electromotive series. Enantioselective protonation of lithium enolates and cyclopropyllithium compounds have been reported. When the metal is less active, stronger acids are required. For example, R2Zn compounds react explosively with water, R2Cd slowly, and R2Hg not at all, though the latter can be cleaved with concentrated HCl. How-... 

Many organometallic compounds are best prepared by this reaction, which involves replacement of a metal in an organometallic compound by another metal. The compound RM can be successfully prepared only when M is above M in the electromotive series, unless some other way is found to shift the equilibrium. That is, RM is usually an unreactive compound and M is a metal more active than M. Most often, RM is R2Hg, since mercury alkyls are easy to prepare and mercury is far down in the electromotive series." Alkyls of Li, Na, K, Be, Mg, Al, Ga, Zn, Cd, Te, Sn, and so on have been prepared this way. An important advantage of this method over 12-36 is that it ensures that the organometallic compound will be prepared free of any possible halide. This method can be used for the isolation of solid sodium and potassium alkyls." If the metals lie too close together in the series, it may not be... 

When a metal is immersed into the solution of salt of another metal farther to the right in the electromotive series, the first metal dissolves (is oxidized) while the second metal is deposited (its ions are reduced). Thus, the first metal displaces the second from its solution. 

Nowadays, tables of standard electrode potentials are used instead of the electromotive series. They include electrode reactions not only of metals but also of other substances [Table 3.1 for detailed tables, see the books of Lewis and Rendall (1923) and Bard et al. (1985)]. 

The process of precipitation of a metal from an aqueous solution of its salt by another metal is the well-known cementation process, so named because the precipitated metal is usually cemented on the metal introduced into the system. The process prediction stems from consideration of electrode potentials of metals. The metal positioned with greater (oxidation) potential in the electromotive series will pass into solution and remove a metal positioned with a less positive potential. The larger the spread of the positions of the two metals in the series, the greater is the possibility or feasibility of cementing out one by the other. 

Considerable practical importance attaches to the fact that the data in Table 6.11 refer to electrode potentials which are thermodynamically reversible. There are electrode processes which are highly irreversible so that the order of ionic displacement indicated by the electromotive series becomes distorted. One condition under which this situation arises is when the dissolving metal passes into the solution as a complex anion, which dissociates to a very small extent and maintains a very low concentration of metallic cations in the solution. This mechanism explains why copper metal dissolves in potassium cyanide solution with the evolution of hydrogen. The copper in the solution is present almost entirely as cuprocyanide anions [Cu(CN)4]3, the dissociation of which by the process... 

Metal Corrosion.—When a metal above hydrogen in the electromotive series is placed in a solution of an electrolyte there is a tendency for the metal to ionize i.e., to split into ions and electrons for instance, with iron, the following reaction tends to take place... 

The Electrodeposition of Metals.—If hydrogen were evolved at a cathode at its reversible potential under all conditions no metal higher in the electromotive series than hydrogen could be deposited electro-lytically from an aqueous solution. Due to hydrogen overvoltage, however, it is possible to obtain deposits of these metals as high in the... 

Al possesses a great affinity for oxygen and when finely divided (powdered, flaked, etc) it bums in the air. It burns also when made in the form of a thin ribbon similar to that of Mg. When Al powder is mixed and heated with an oxide of a metal below it in the electromotive series, displacement takes place, for instance in Thermite (qv) ... 

---