Oxides and Oxoacids

Phosphoric acids and phosphates, (a) phosphoric acid, H3PO4 (b) two phosphoric acid molecules split out a molecule of water to form pyrophosphoric acid, H4P2O7 (c) pyrophosphate (cf) tricyclophosphate  

Phosphorus add and phosphites, (o) Phosphorus add, H3PO3. (b) Two phosphorus add molecules split out a molecule of water to form (c) pyrophosphorus acid, H4P2O5. Again, note the presence of formal P=0 dw-pw bonds in these phosphites. 

Equation (16.8) is the basis of the excellent desiccant properties of P40io which is widely employed in glove bags and boxes to ensure that the inert atmospheres in these spaces are free of trace amounts of water. 

When antimony and bismuth are burned in air, only the +3 oxides result. The amphoteric Sb40g is structurally similar to the phosphorus(III) oxide and with some difficulty can be oxidized to a polymeric +5 oxide. The more ionic Bi203 is very difficult to oxidize and is distinctly basic in character. Bismuth hydroxide, Bi(OH)3, a true base, can be precipitated out of various bismuth(III) solutions with the addition of hydroxide ions. 

The chemistry of the oxides and their corresponding oxoacids (or in the case of bismuth, the corresponding hydroxide) demonstrates that both (1) the stability of the +5 oxidation state and (2) the acidity of the oxides steadily decrease down the group. 

Within the sulfur sub-group, there are two main types of oxides, the dioxides X 02 (X = S, Se, Te, Po) and the trioxides X Os (X = S, Se, Te). In addition, sulfur also forms disulfur monoxide, S2O. Transient XO species are known in the gaseous phase for S, Se, and Te. Polonium forms a black monoxide PoO. 

Sulfur dioxide is a colorless gas with a suffocating smell, which at 10 °C and normal pressure is condensed to a colorless liquid. It is made on a vast industrial 

The higher acids, selenic (H2Se04) and telluric (H2Te04), containing the chalco-gen in the +VI oxidation state, are also known these correspond to the sulfuric acid. 

Selenic acid, H2Se04, is a strong acid (/fai 2) and the solubility of its salts parallels that of the corresponding sulfates. It is formed by the oxidation of selenous acid or elemental selenium with strong oxidizing agents in the presence of water. Telluric acid, H2Te04, or tellurates are obtained by oxidation of tellurides, 

Let us add here that despite the general similarities of selenium and sulfur in their chemical properties, the chemistry of selenium differs from that of sulfur in two important aspects their oxoanions are not similarly reduced, and their hydrides have different acid strengths. For example, Se(-HlV) tends to undergo reduction to Se(-II), whereas S(-hIV) tends to undergo oxidation. This difference is evidenced by the ability of selenous acid to oxidize sulftirous acid  

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This section deals with the binary compounds that nitrogen forms with metals, and then describes the extensive chemistry of the hydrides, halides, pseudohalides, oxides and oxoacids of the element. The chemistry of P-N compounds is deferred until Chapter 12 (p. 531) and S-N... 

The amphoteric nature of AS2O3 and the trends in properties of several of the oxides and oxoacids... 

Nitrogen forms oxides in each of its integer oxidation states front +1 to +5 the properties of the oxides and oxoacids are related to the oxidation number of nitrogen in the compound. 

Sulfur forms several oxides that in atmospheric chemistry are referred to collectively as SOx (read sox ). The most important oxides and oxoacids of sulfur are the dioxide and trioxide and the corresponding sulfurous and sulfuric acids. Sulfur burns in air to form sulfur dioxide, S02 (11), a colorless, choking, poisonous gas (recall Fig. C.1). About 7 X 1010 kg of sulfur dioxide is produced annually from the decomposition of vegetation and from volcanic emissions. In addition, approximately 1 X 1011 kg of naturally occurring hydrogen sulfide is oxidized each year to the dioxide by atmospheric oxygen ... 

The xenon fluorides are used to prepare the xenon oxides and oxoacids and, in a series of disproportionations, to bring the oxidation number of xenon up to +8. First, xenon tetrafluoride is hydrolyzed to xenon trioxide, Xe03 in a disproportionation reaction ... 

Oxides and Oxoacids of Phosphorus When phosphorus burns in air or oxygen, it yields tetraphosphorus hexoxide (P4Og, mp 24°C) or tetraphosphorus decoxide (P4Oio, mp 420°C), depending on the amount of oxygen present ... 

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