Zinc, metal

Sillimanite, see Aluminum silicon oxide (1/1) Smithsonite, see Zinc carbonate Soda ash, see Sodium carbonate Spelter, see Zinc metal Sphalerite, see Zinc sulflde Spherocobaltite, see Cobalt(II) carbonate Spinel, see Magnesium aluminate(2—)... 

K4[Fe(CN)], 3H3O 422.41 Dissolve the high-purity commercial salt in distilled water containing 0.2 g/L of Na2C03. Kept in an amber container and away from direct sunlight, solutions are stable for a month or more. Standardize against zinc metal. 

Fig. 6. Roast-Leach electrowinning process for the production of zinc metal from a sulfide concentrate.

Zinc and Zinc Alloys. Zinc metal is highly reactive in acid solutions such as sulfuric, hydrochloric, and nitric dissolving rapidly at acid concentrations normally used to pickle steel and aluminum. Dilute (1—4%) solutions of these acids can be used with caution to remove zinc oxides. 

Sulfamic acid at concentrations of 2—6%, in conjunction with the proper proprietary inhibitor, can be effective in removing zinc oxides and corrosion by-products without attacking the zinc metal. 

Production processes are given in Table 12. Electrolytic processes are dominant because of lower cost and fewer environmental problems. Production of slab zinc in Tennessee commenced in 1978 when Jersey Miniere Zinc Company began operation of its new 90,000 t/yr electrolytic smelter at Clarksville. Today, Tennessee is the leading producer of slab zinc. Although the U.S. demand for zinc metal in the past 16 years has increased by 47%, smelting capacity has declined by almost 50%. Plants closed because they were obsolete and could not meet environmental standards or obtain sufficient concentrate. Consequendy, slab zinc has replaced concentrates as the principal import form. This situation is expected to prevail up to the year 2000 (69-71). 

Further dechlorination may occur with the formation of substituted diphenyhnethanes. If enough aluminum metal is present, the Friedel-Crafts reactions involved may generate considerable heat and smoke and substantial amounts of hydrogen chloride, which reacts with more aluminum metal, rapidly forming AlCl. The addition of an epoxide inhibits the initiation of this reaction by consuming HCl. Alkali, alkaline-earth, magnesium, and zinc metals also present a potential reactivity hazard with chlorinated solvents such as methylene chloride. 

The American Zinc Association is a trade organization comprising primary and secondary producers of zinc metal, zinc oxide and zinc dust marketed in the United States. 

The carbon-fluonne bond is normally resistant to cleavage by zinc metal so that the carbon-chlonne bond in chlorodifluoromethyl ketones is selecnvely reduced The... 

Table 4. Preparation of Fluorinated Vinylzinc Reagents from (F)-Vinyl Halides and Zinc Metal [110]...

The classical Reformatsky reaction consists of the treatment of an a-halo ester 1 with zinc metal and subsequent reaction with an aldehyde or ketone 3. Nowadays the name is used generally for reactions that involve insertion of a metal into a carbon-halogen bond and subsequent reaction with an electrophile. Formally the Reformatsky reaction is similar to the Grignard reaction. 

By reaction of an a-halo ester 1 with zinc metal in an inert solvent such as diethyl ether, tetrahydrofuran or dioxane, an organozinc compound 2 is formed (a Grignard reagent-like species). Some of these organozinc compounds are quite stable even a structure elucidation by x-ray analysis is possible in certain cases ... 

A voltaic cell produces electrical energy through spontaneous redox chemical reactions. When zinc metal is placed in a solution of copper sulfate, an electron transfer takes place between the zinc metal and copper ions. The driving force for the reaction is the greater attraction of the copper ions for electrons ... 

During the operation of the cell (or during the direct interaction of zinc metal and cupric ions in a beaker) the zinc is oxidised to Zn and corrodes, and the Daniell cell has been widely used to illustrate the electrochemical mechanism of corrosion. This analogy between the Daniell cell and a corrosion cell is perhaps unfortunate, since it tends to create the impression that corrosion occurs only when two dissimilar metals are placed in contact and that the electrodes are always physically separable. Furthermore, although reduction of Cu (aq.) does occur in certain corrosion reactions it is of less importance than reduction of HjO ions or dissolved oxygen. 

Delpeuc h, Y., Zinc Metallizing of Lock Gates and Barriers, Zinc, Cadmium et AUiages (37) (1964) (reprint in French)... 

Zinc-Rich Primer an anticorrosive primer for iron and steel incorporating zinc dust in a concentration sufficient to give electrical conductivity in the dried films, thus enabling the zinc metal to corrode preferentially to the substrate, i.e. to give cathodic protection. 

Figures 19.62 and 19.63 were taken at the time of investigation into a failure of 1001 of steel which should have been coated with a nearly maintenance-free system. Zinc metal spray and four coats of paint were specified but, for reasons of economy, special measures for inspection were not taken. Within months of erection areas were flaking off where millscale had not been removed (Fig. 19.62) and other areas were blistering. Figure...

Fig. 19.62 Result of millscale not being removed from steelwork before zinc metal spraying...

Low -molecular-weight ozonides are explosive and are theretore not isolated. Instead, the ozonide is immediately treated with a reducing agent such as zinc metal in acetic acid to convert it to carbonyl compounds. The net result of the ozonolysis/reduction sequence is that the C=C bond is cleaved and oxygen becomes doubly bonded to each of the original alkene carbons. If an alkene with a letrasubstituted double bond is ozonized, two ketone fragments result if an alkene with a trisubstituted double bond is ozonized, one ketone and one aldehyde result and so on. 

Alkenes are reduced by addition of H2 in the presence of a catalyst such as platinum or palladium to yield alkanes, a process called catalytic hydrogenation. Alkenes are also oxidized by reaction with a peroxyacid to give epoxides, which can be converted into lTans-l,2-diols by acid-catalyzed epoxide hydrolysis. The corresponding cis-l,2-diols can be made directly from alkenes by hydroxylation with 0s04. Alkenes can also be cleaved to produce carbonyl compounds by reaction with ozone, followed by reduction with zinc metal. 

Thus for the equilibrium attained when zinc metal reacts with acid,... 

Oxidation takes place at the anode, where a species such as zinc metal produces electrons anode Zn(s)--- Zn2+(og) + 2e ... 

Another spontaneous redox reaction that can serve as a source of electrical energy is that between zinc metal and Co3+ ions ... 

Zinc metal dissolves in a solution of gaseous chlorine in water as follows ... 

Zn+i(aq) + H2(g) + 20r(aq) Recognizing that zinc metal must release electrons to form Zn+1(aq), explain how these reactions demonstrate that gaseous hydrogen does not behave like a halogen. 

Liberation of Hydrogen Gas. The aqueous solutions of each compound produce hydrogen gas, H2, if zinc metal is added. 

What is the common factor that makes these different substances behave in the same ways In water they all form conducting solutions we conclude that they all form ions in water. Each substance contains hydrogen and each reacts with zinc metal to produce hydrogen gas. Perhaps all of these aqueous solutions contain the same ion and this ion accounts for the formation of Hfg). It is reasonable to propose that the common ion is H+(aq). We postulate a substance has the properties of an add if it can release hydrogen ions. 

Listing the Zn-Zn+2 half-reaction first tells us that it releases electrons more readily than does the Cu-Cu+2 half-reaction. But if this is true, then the Zn-Zn+2 half-reaction must also release electrons more readily than does the Ag-Ag+ half-reaction. Our list leads us to expect that zinc metal will release electrons to silver ion, reacting to produce zinc ion and silver metal. 

We should test this proposal We dip a piece of zinc metal in a solution of silver nitrate. The result confirms our expectation zinc metal dissolves and bright crystals of metallic silver appear. 

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