Oxidation number acid character

The acidic character of siUca is shown by its reaction with a large number of basic oxides to form siUcates. The phase relations of numerous oxide systems involving siUca have been summarized (23). Reactions of siUca at elevated temperatures with alkaU and alkaline-earth carbonates result in the displacement of the more volatile acid, CO2, and the formation of the corresponding siUcates. Similar reactions occur with a number of nitrates and sulfates. Sihca at high temperature in the presence of sulfides gives thiosiUcates or siUcon disulfide, SiS2. 

The pattern of oxidation states correlates with the pattern of acid-base behavior of d-metal oxides. Although most d-metal oxides are basic, the oxides of a given element show a shift toward acidic character with increasing oxidation number, just as the oxoacids do (recall Section 10.10). The family of chromium oxides is a good... 

Chlorine is one of the strongest oxidants whether it is in the elementary form or as oxidised anions, with oxidation states of +l (hypochlorites) to +VII (perchlorates). The chloride ion with an oxidation state of -I is very stable (octet electronic structure) only hydrochloric acid is dangerously reactive, linked to its strongly acidic character. This explains the nature of the dangerous reactions which have already been described and have caused a large number of accidents. The accidental aspect is aggravated by the fact that the derivatives mentioned in this paragraph are much used. 

The effect of chemisorption temperature on the ammonia uptake capacity of 6.5 wt% V20c/Ti02 is shown in Fig. 1. Ammonia chemisorption capacities increase with temperature upto 150°C and then decrease with further Increase up to 400°C. It is worth noting that there is considerable NH uptake even at 400°C. These results are in accordance with the reported literature. A number of studies have been reported on the acidic character of supported transition-metal oxides (22,34-38). Ammonia on V20g can be either adsorbed in the form of NH species on Bronsted acid sites or coordlnatively bonded to vanadium ions on Lewis acid sites (39,40). The latter species were observed up to 250°C,... 

The acid-base properties and the ionic-covalent character of an element s oxide depend on both the element s position in the periodic table and its oxidation number. As Figure 14.6 shows, both the acidic character and the covalent character of an oxide increase across the periodic table from the active metals on the left to the electronegative nonmetals on the right. In the third row, for example, Na20... 

Both the acidic character and the covalent character of different oxides of the same element increase with increasing oxidation number of the element. Thus, sulfur(VI) oxide (S03) is more acidic than sulfur(IV) oxide (S02). Reaction of S03 with water gives a strong acid (sulfuric acid, H2SC>4), whereas reaction of S02 with water yields a weak acid (sulfurous acid, H2S03). The oxides of chromium exhibit the same trend. Chromium(VI) oxide (Cr03) is acidic, chromium(III) oxide (Cr203) is amphoteric, and chromium(II) oxide (CrO) is basic. 

As can be seen from the above, there is a big difference between presented data evolving not only from the applied method but also on the method of the sample preparation. The investigations of the alkali-acid character of the surface hydroxyl groups showed that some of them reveal acid and other alkaline properties depending on the reagent character, also on the different number of surface groups of oxide. 

The oxides of the Group 15 elements clearly exemplify two important trends that are manifest to some extent in all main groups of the Periodic Table (1) the stability of the higher oxidation state decreases with increasing atomic number, and (2) in a given oxidation state the metallic character of the elements, therefore the basicity of the oxides, increases with increasing atomic number. Thus Pm and Asra oxides are acidic, Sb111 oxide is amphoteric, and Bim oxide is strictly basic. 

Oxidation number Predominating ion or oxide Acidic or basic character of hydroxide... 

Transition metal enolate complexes have been prepared with most or all transition metals, and the enolate ligands have been shown to adopt a variety of bonding modes. Bofli early and late transition metal enolate complexes are intermediates in a number of important catalytic processes. Early transition metal enolates are important intermediates in asymmetric aldol reactions that exploit the Lewis acidic character of early metals. Late transition metal enolates are intermediates in aldol and Michael addition processes, -Saegusa oxidations,Heck-type processes, catalytic asymmetric conjugate additions, - and cross coupling of enolate nucleophiles. - ... 

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