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24 Metals and Metallurgy Review Questions 24.1 The source of vanadium in some crude oil is the very animals from which the oil was formed. It appears that some extinct animals used vanadium for oxygen transport. 24.3 Even though over 2% of the Earth's mass is nickel, most of this is in the Earth's core, and because the core is so far from the surface, it is not accessible. 24.5 The mineral is the phase that contains the desired element(s), and the gangue is the undesired material. These are generally separated by physical methods. 24.7 Sodium cyanide has traditionally been used to leach gold by forming a soluble gold complex (Au(CN)₂⁻). The problem with this process is that cyanide is very toxic and the process has often resulted in the contamination of streams and rivers. New alternatives using thiosulfate ions (S₂O₃⁻) are being investigated to replace sodium cyanide. 24.9 The body-centered cubic unit cell consists of a cube with one atom at each corner and one atom in the center of the cube. In the body-centered unit cell, the atoms do not touch along each edge of the cube; rather, they touch along the diagonal line that runs from one corner through the middle of the cube to the opposite corner. The body-centered unit cell contains two atoms per unit cell because the center atom is not shared with any other neighboring cells. The coordination number of the body-centered cubic unit cell is 8, and the packing efficiency is 68%. The face-centered cubic unit cell is character- ized by a cube with one atom at each corner and one atom in the center of each cube face. In the face- centered unit cell (like the body-centered unit cell), the atoms do not touch along each edge of the cube. Instead, the atoms touch along the face diagonal. The face-centered unit cell contains four atoms per unit cell because the center atoms on each of the six faces are shared between two unit cells. So there are X 6 = 3 face-centered atoms plus X 8 = 1 corner atoms, for a total of four atoms per unit cell. The coordination number of the face-centered cubic unit cell is 12, and its packing efficiency is 74%. In the face-centered structure, any one atom strongly interacts with more atoms than in either the simple cubic unit cell or the body-centered cubic unit cell. 24.11 Copper was one of the first metals used because it could be found in nature in its elemental form. 24.13 Bronze is an alloy of copper and tin. Brass is an alloy of copper and zinc. Problems by Topic The General Properties and Natural Distribution of Metals 24.15 Metals are opaque, are good conductors of heat and electricity, and are ductile and malleable, meaning that they can be drawn into wires and flattened into sheets. 24.17 Aluminum, iron, calcium, magnesium, sodium, and potassium are over 1% of the Earth's crust, as shown in Figure 23.2. 509 Copyright © 2017 Pearson Education, Inc.