Zinc chemical properties

Selective Reduction. In aqueous solution, europium(III) [22541 -18-0] reduction to europium(II) [16910-54-6] is carried out by treatment with amalgams or zinc, or by continuous electrolytic reduction. Photochemical reduction has also been proposed. When reduced to the divalent state, europium exhibits chemical properties similar to the alkaline-earth elements and can be selectively precipitated as a sulfate, for example. This process is highly selective and allows production of high purity europium fromlow europium content solutions (see Calcium compounds Strontiumand strontium compounds). 

The most significant chemical property of zinc is its high reduction potential. Zinc, which is above iron in the electromotive series, displaces iron ions from solution and prevents dissolution of the iron. For this reason, zinc is used extensively in coating steel, eg, by galvanizing and in zinc dust paints, and as a sacrificial anode in protecting pipelines, ship hulls, etc. 

Properties of zinc salts of inorganic and organic salts are Hsted in Table 1 with other commercially important zinc chemicals. In the dithiocarbamates, 2-mercaptobenzothiazole, and formaldehyde sulfoxylate, zinc is covalendy bound to sulfur. In compounds such as the oxide, borate, and sihcate, the covalent bonds with oxygen are very stable. Zinc—carbon bonds occur in diorganozinc compounds, eg, diethjizinc [557-20-0]. Such compounds were much used in organic synthesis prior to the development of the more convenient Grignard route (see Grignard reactions). 

The side chains of the 20 different amino acids listed in Panel 1.1 (pp. 6-7) have very different chemical properties and are utilized for a wide variety of biological functions. However, their chemical versatility is not unlimited, and for some functions metal atoms are more suitable and more efficient. Electron-transfer reactions are an important example. Fortunately the side chains of histidine, cysteine, aspartic acid, and glutamic acid are excellent metal ligands, and a fairly large number of proteins have recruited metal atoms as intrinsic parts of their structures among the frequently used metals are iron, zinc, magnesium, and calcium. Several metallo proteins are discussed in detail in later chapters and it suffices here to mention briefly a few examples of iron and zinc proteins. 

Whereas the utility of these methods has been amply documented, they are limited in the structures they can provide because of their dependence on the diazoacetate functionality and its unique chemical properties. Transfer of a simple, unsubstituted methylene would allow access to a more general subset of chiral cyclopropanes. However, attempts to utilize simple diazo compounds, such as diazomethane, have never approached the high selectivities observed with the related diazoacetates (Scheme 3.2) [4]. Traditional strategies involving rhodium [3a,c], copper [ 3b, 5] and palladium have yet to provide a solution to this synthetic problem. The most promising results to date involve the use of zinc carbenoids albeit with selectivities less than those obtained using the diazoacetates. 

This example of aluminium illustrates the importance of the protective him, and hlms that are hard, dense and adherent will provide better protection than those that are loosely adherent or that are brittle and therefore crack and spall when the metal is subjected to stress. The ability of the metal to reform a protective him is highly important and metals like titanium and tantalum that are readily passivated are more resistant to erosion-corrosion than copper, brass, lead and some of the stainless steels. There is some evidence that the hardness of a metal is a signihcant factor in resistance to erosion-corrosion, but since alloying to increase hardness will also affect the chemical properties of the alloy it is difficult to separate these two factors. Thus althou copper is highly susceptible to impingement attack its resistance increases with increase in zinc content, with a corresponding increase in hardness. However, the increase in resistance to attack is due to the formation of a more protective him rather than to an increase in hardness. 

Chemistry is concerned with the properties of matter, its distinguishing characteristics. A physical property of a substance is a characteristic that we can observe or measure without changing the identity of the substance. For example, a physical property of a sample of water is its mass another is its temperature. Physical properties include characteristics such as melting point (the temperature at which a solid turns into a liquid), hardness, color, state of matter (solid, liquid, or gas), and density. A chemical property refers to the ability of a substance to change into another substance. For example, a chemical property of the gas hydrogen is that it reacts with (burns in) oxygen to produce water a chemical property of the metal zinc is that it reacts with acids to produce hydrogen gas. The rest of the book is concerned primarily with chemical properties here we shall review some important physical properties. 

Mendeleev also predicted the existence of elements that had not yet been discovered. His arrangement of the then-known elements left some obvious holes in the periodic table. For instance, between zinc (combines with 2 Cl) and arsenic (combines with 5 Cl) were holes for one element that would combine with three chlorine atoms and another that would combine with four. Mendeleev assigned these holes to two new elements. He predicted that one element would have a molar mass of 68 g/mol and chemical properties like those of aluminum, while the other would have a molar mass of 72 g /mol and chemical properties similar to silicon. These elements, gallium (Z = 31, M M = 69.7 g/mol) and germanium (Z = 32, M M — 72.6 g/mol), were discovered within 15 years. Chemists soon verified that gallium resembles aluminum in its chemishy, while germanium resembles silicon, just as Mendeleev had predicted. 

The chemical properties of copper, lead, lead-zinc, and zinc slags are essentially as ferrous silicates, whereas nickel slags are primarily calcium/magnesium silicates. Table 4.13 lists typical chemical compositions of these slags. 

Although zinc is formally a 4-block element, some of its chemical properties are similar to those of the alkaline earth metals, especially those of magnesium. This is mainly due to zinc s exclusive exhibition of the +2 oxidation state in all its compounds and its appreciable electropositive character. With a standard potential of —0.763 V, zinc is considerably more electropositive than copper and cadmium. 

Zinc is a bluish-white metal which dissolves readily in strong acids. In nature it occurs as a sulfide, oxide, or carbonate. In solution, it is divalent and can form hydrated Zn2+ cations in acids, and zincated anions — probably Zn(OH)42 — in strong bases (USEPA 1980, 1987). Zinc dust and powder are sold commercially under a variety of trade names Asarco, Blue powder, Cl 77949, Cl pigment metal 6, Emanay zinc dust, granular zinc, JASAD Merrillite, LI 5, and PASCO (USPHS 1989). Selected physical and chemical properties of zinc, zinc chloride, and zinc sulfate are listed in Table 9.2. 

One key experimental observation regarding the ZP films is that the films found on the tops of asperities are stiffer and exhibit chemical spectra indicative of longer phosphate chain lengths than films found in the valleys between asperities. These observations that differences in the conditions at the two distinct locations alter the elastic and chemical properties of the films. One of the key differences between the tops of asperities and the valleys is the pressure experienced by the zinc phosphates. Since the highest pressures, and greatest potential for wear, are achieved at the tops of the asperities, determining the response of ZPs to these pressures may aid in developing a clear picture of how the anti-wear films work. 

CHEMICAL PROPERTIES OF ZINC COMPOUNDS Oxidation state + 2... 

One final comment on the Fe/E O system is needed if Fig. 15.3 were extended beyond pH 14, we would have to include the stability fields of Fe(OH)4 (aq) and Fe(OH)3 (aq).12 In other words, iron, like aluminum, chromium, zinc, and many other metals, exhibits amphoteric behavior (i.e., has both acidic and base like properties), but only if a sufficiently wide range of pH is considered. Amphoteric behavior, like many other chemical properties, is not so much something that a given element does or does not exhibit, but rather is a trait that different elements display to different extents. 

Chemical Properties. Zinc oxide is amphoteric it reacts with organic and inorganic acids, and also dissolves in alkalis and ammonia solution to form zincates. It combines readily with acidic gases (e.g., C02, S02, and H2S). It reacts at high temperatures with other oxides to form compounds such as zinc ferrites. 

Jhe distribution of beryllium, boron, titanium, vanadium, chromium, cobalt, nickel, copper, zinc, gallium, germanium, tin, molybdenum, yttrium, and lanthanum in the principal coal-producing beds of the Interior Province has been studied by the U. S. Geological Survey. Data, methods of sampling, and analyses are discussed by Zubovic and others (II, 12). This chapter discusses the occurrence of 13 of these elements with respect to geological and geochemical environments of coal deposition and chemical properties of the elements. Zinc and tin are not included in this study because they were detected in only a few samples. 

In the chemistry of the fuel cycle and reactor operations, one must deal with the chemical properties of the actinide elements, particularly uranium and plutonium and those of the fission products. In this section, we focus on the fission products and then chemistry. In Figures 16.2 and 16.3, we show the chemical composition and associated fission product activities in irradiated fuel. The fission products include the elements from zinc to dysprosium, with all periodic table groups being represented. 

Common chemical properties The alkali metals are so chemically reactive that they are never found free in nature. Sodium and potassium react explosively with water to produce hydrogen gas. The alkaline earth metals are not quite as reactive as the alkali metals. The alkali metals react with water but not explosively. The transition metals are generally the least reactive of all the metals. However, when they combine with other elements, they form a large variety of colored compounds. Chromium oxide is green, titanium oxide and zinc oxide are white, manganese oxide is purple, and iron oxide is ochre. 

Trivalent chromium compounds, except for acetate, nitrate, and chromium(III) chloride-hexahydrate salts, are generally insoluble in water. Some hexavalent compounds, such as chromium trioxide (or chromic acid) and the ammonium and alkali metal (e.g., sodium, potassium) salts of chromic acid are readily soluble in water. The alkaline metal (e.g., calcium, strontium) salts of chromic acid are less soluble in water. The zinc and lead salts of chromic acid are practically insoluble in cold water. Chromium(VI) compounds are reduced to chromium(III) in the presence of oxidizable organic matter. However, in natural waters where there is a low concentration of reducing materials, chromium(VI) compounds are more stable (EPA 1984a). For more information on the physical and chemical properties of chromium, see Chapter 3. 

---