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The Aqueous Chemistry of the Elements$
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George K. Schweitzer and Lester L. Pesterfield

Print publication date: 2010

Print ISBN-13: 9780195393354

Published to Oxford Scholarship Online: November 2020

DOI: 10.1093/oso/9780195393354.001.0001

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The Ti Group and the 5B, 6B, 7B and 8B Heavy Elements

The Ti Group and the 5B, 6B, 7B and 8B Heavy Elements

(p.288) 13 The Ti Group and the 5B, 6B, 7B and 8B Heavy Elements
The Aqueous Chemistry of the Elements

George K. Schweitzer

Lester L. Pesterfield

Oxford University Press

The elements to be treated in this chapter may be considered to be of three types. All of them show one species which dominates the water domain in the E–pH diagram. The dominant species in the E–pH diagrams and the elements which display it are as follows: (1) an insoluble oxide: Ti, Zr, Hf (Group 4B) and Nb, Ta (Group 5B), (2) a high-oxidation-state anion: Mo, W (Group 6B) and Tc, Re (Group 7B), (3) a noble metal: Ru, Rh, Pd, Os, Ir, Pt (Group 8B). These five elements all show highly stable inert oxides which occupy the majority of the water domain in their E–pH diagrams. This can be seen in Figures 13.1 through 13.5. The three 4B oxides (TiO2, ZrO2, HfO2) are insoluble in HOH, dilute acids, dilute bases, and concentrated bases, but are soluble in strong concentrated acids to give TiO+2, ZrO+2, and HfO+2. The two 5B oxides (Nb2O5, Ta2O5) are insoluble in HOH, dilute acids, and dilute bases, but Nb2O5 dissolves in concentrated bases whereas Ta2O5 does not. All the elements in their highest oxidation state are hard cations and therefore will be particularly attracted to the hard atoms F and O. a. E–pH diagram. The E–pH diagram in Figure 13.1 shows Ti in oxidation states of 0, II, III, and IV. In the legend of the diagram, equations for the lines between the species are presented. Table 13.1 displays ions and compounds of Ti. The metal appears to be very active, but a thin refractory oxide coating renders it inactive to all but extreme treatment. Ions and compounds in oxidation states of II and III are unstable with regard to atmospheric O2 and also with regard to HOH except for Ti+3 in strongly acidic solution. b. Discovery, occurrence, and extraction. Ti, named after the Titans, the mythological first sons of the earth, was discovered by Gregor in 1791 in the mineral menachanite, a variety of ilmenite. The major sources of Ti are the minerals rutile TiO2 and ilmenite FeTiO3. They are treated with Cl2 and C at elevated temperatures to generate gaseous TiCl4 which condenses to a colorless liquid at 136°C.

Keywords:   High Oxidation State Anion Group (see molybdenum, rhenium, technetium, tungsten), Insoluble Oxide Group (see hafnium, niobium, tantalum, titanium, zirconium) characteristics, Noble Metal Group (see iridium, osmium, palladium, platinum, rhodium, ruthenium)

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