Metals, electromotive series

Volta discovered that when he used different metals in his pile some combinations had a stronger effect than others. From that information he constructed an electromotive series. How would Volta have ordered the following metals, if he put the most strongly reducing metal first Fe, Ag, Au, Zn, Cu, Ni. Co, Al ... 

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) ... 

ACTIVITY SERIES- Also referred to as the electromotive series or the displacement series, this is an arrangement of the metals (other elements can be included) in the order of their tendency to react with water and acids, so that each metal displaces from solution those below itiu the series and is displaced by those above it. See Table 1. Since the electrode potential of a metal in equilibrium with a solution of its ions cannot be measured directly, the values in the activity series are, in each case, the difference between the electrode potential of the given metal tor element) in equilibrium with a solution of its ions, and that of hydrogen in equilibrium with a solution of its ions. Thus in the table, it will be noted that hydrogen lias a value of 0.000. In experimental procedure, the hydrogen electrode is used as the standard with which the electrode potentials of other substances are compared. The theory of displacement plays a major role in electrochemistry and corrosion engineering. See also Corrosion and Electrochemistry. 

In his original design Volta stacked couples of unlike metals one upon another in order to increase the intensity of the current. This arrangement became known as the "voltaic pile." He studied many metallic combinations and was able to arrange the metals in an "electromotive series" in which each nielal was positive when connected to the one below it in the series. Volta s pile was the precursor of modem batteries. 

Additional explanatory material is added throughout the book. Some of the material explains further and simplifies concepts under discussion, while other material adds new information. In Chapter 2 paint pigments and binders are discussed. New information on surprising origins of ancient paint pigments and binders is added. In Chapter 3 supports for paints are described, and information is added about supports used in 50 B.C. that are still used today. In Chapter 6, in which jewelry making and the study of metals and electrochemistry are combined, an electromotive series is added to enhance cell voltage calculations. 

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. 

Ionic Displacement. Electromotive Series. When a strip of zinc is placed in a solution of copper sulphate, it is noticed that a spongy deposit of copper metal soon appears on the surface of the zinc, and that the solution loses its blue color. Then if the solution is tested for the presence of copper and zinc ions by adding ammonium sulphide, it is found that this reagent gives a white precipitate. This test shows that copper ions are now absent and that zinc ions are present because we know ammonium sulphide will precipitate black copper sulphide from a solution of copper ions, and white zinc sulphide from a solution of zinc ions. Since ordinary pieces of metal are not charged, it is obvious that the reaction consists in a transfer of the positive charges of the copper ions to the zinc atoms, or, more strictly, of negative electrons from the zinc atoms to the copper ions ... 

The metals, including hydrogen, may be arranged in the order in which they tend to pass into the ionic condition, as, in this case, zinc does at the expense of copper. Such a series is known as the electromotive series, because the electromotive force of such reactions, if properly disposed in a cell, may be made to send a current through an external wire connector. (See Electromotive Series, Appendix, page 353.)... 

On the other hand, a characteristic of some of the most pronouncedly non-metallic elements, fluorine, chlorine, bromine, iodine, and sulphur, is that they can form simple negative ions. No non-metal ever forms simple positive ions. The non-metals may be arranged in a negative electromotive series. 

It must be remembered that an uncombined element is electrically neutral, but every element, with the exception of the rare gases, has a more or less strong tendency to assume an electrified condition, the strength of which tendency is indicated by the position of the element in the electromotive series. When a metal and a non-metal combine chemically with each other we can con-... 

From this experiment and the preceding one we should conclude that the non-metallic elements fall in the order F, Cl, Br, 0, I, S (fluorine being strongest) with respect to their activity in aqueous solutions containing free acid. This is approximately the order of the electromotive series for these non-metals. If the solution is made neutral the electromotive potential of oxygen is lowered so that the oxygen is no longer able to displace iodine. 

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. 

Compare the metals of this chapter among themselves with regard to their position in the electromotive series, also with the metals of the A families of Groups I and II, and with aluminum. 

Warm a piece of metallic antimony with hydrochloric acid. Where does antimony stand in the electromotive series ... 

Bismuth stands low in the electromotive series, and its salts are easily reduced to the metal which in the finely divided state is intensely black. 

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