Zinc Zn

B. Amalgamated, Zinc [Mercury alloy (Hg, Zn)]. Zinc powder (206 g., 3.15 moles) is placed in a 1-1. beaker, covered with 250 ml. of aqueous 10% hydrochloric acid, and stirred for 2 minutes. The acid is then decanted and replaced by distilled water, the mixture is stirred, and the supernatant is decanted. Washing is continued in this way until the water is neutral to litmus. A warm solution of 40 g. (0.15 mole) of mercuric chloride [Mercury chloride (HgCl2)] in 250 ml. of distilled water is then poured onto the zinc, and the mixture is stirred gently for 10 minutes. After filtration, the powder is washed with 250 ml. of distilled water, five 250-ml. portions of 95% ethanol, and five 250-ml. portions of anhydrous ether. Drying under vacuum gives 196 g. of zinc amalgam. 

Many other metal displacement reactions can be visualized, but not all of them occur. Some metals are oxidized readily, but others are highly resistant to oxidation. Likewise, some metal cations are highly susceptible to reduction, but others resist reduction. Zinc displaces copper ions from aqueous solutions, but copper will not replace zinc ions, because Cu is easier to reduce than Zn . Zinc will not displace ions, because... 

Two structures are homeotypic if they are similar, but fail to fulfill the aforementioned conditions for isotypism because of different symmetry, because corresponding atomic positions are occupied by several different kinds of atoms (substitution derivatives) or because the geometric conditions differ (different axes ratios, angles, or atomic coordinates). An example of substitution derivatives is C (diamond)-ZnS (zinc blende)-Cu3SbS4 (famatinite). The most appropriate method to work out the relations between homeotypic structures takes advantage of their symmetry relations (cf. Chapter 18). 

Atoms of an element in symmetry-equivalent positions are substituted by several kinds of atoms. For example CC (diamond) -t ZnS (zinc blende). 

H = hydrogen N = nitrogen No = sodium P = phosphorus K = potassium Cr = chromium Co = cobalt Zn = zinc Mo = molybdenum... 

A common critical limit for Zn deficiency in soils has been 0.5 mg/kg DTPA-extractable Zn for different crops (maize, wheat, and rice) (Sillanpaa, 1982). DTPA-extractable Zn concentration of 0.5-1.0 mg/kg has been marginal for sensitive crops (Sillanpaa, 1982). Brown isohumic calcareous soils of New South Wales in Australia with 35-60 mg/kg of total Zn showed Zn deficiency due to the low bioavailability of Zn. Zinc deficiency has been reported to occur in wheat on solidized solonetz and solodic soils and other calcareous soils of South Australia. Zinc application at the rate of 0.6-28 kg/ha to cereals, pastures, and maize of Australia has been reported (Reuter, 1975). Zn deficiency occurs in Turkey, India, Iraq, Mexico, and Pakistan (Table 7.8). Zinc deficiency is frequently observed in rice on calcareous paddy soils. 

Furthermore, crystals whose structures are not centrosymmetric have different hardnesses on opposite sides of a given crystal even though the Miller indices of the surface planes are the same. For example, the hardness of the (0001) plane of ZnS (zinc blende structure) is not the same as that of the (000-1) plane. 

VT—ventricular tachycardia W bancrojti—Wucherena bancrojti Zn—zinc... 

The data described above demonstrate a substantial fractionation of isotopes for both Cu and Zn. Zinc isotopic variability is particularly noticeable in the marine environment the 8 Zn... 

VT—ventricular tachycardia W. bancrofti—Wuchereria bancrofti Zn—zinc... 

Using Figures 1.30, 1.31, and 1.37 together with models if necessary, draw unit cell projections for (a) CsCl, (b) NaCl, and (c) ZnS (zinc blende). 

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