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Their structures are shown in figure 219 in the text

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Unformatted text preview: It is used as an anesthetic in dental and minor surgery. Phosphorus. There are several allotropic forms of phosphorus. The most important ones are white and red phosphorus. Their structures are shown in Figure 21.9 in the text. White phosphorus consists of discrete P4 molecules. The white solid melts at 44°C and is insoluble in water. It is usually stored under water to prevent contact with air. White phosphorus is extremely reactive and bursts into flame when exposed to air. P 4 (s) + 5O 2 (g) → P 4 O10 (s) When white phosphorus is heated to 300°C in the absence of air it is slowly converted to red phosphorus. Red phosphorus has a polymeric structure. It is much more stable than white phosphorus. It melts at 600°C and is stable toward oxygen at room temperature. Red phosphorus must be heated to about 400°C before it will ignite in air. Back Forward Main Menu TOC Study Guide TOC Textbook Website MHHE Website Nonmetallic Elements and Their Compounds / 4 21 Oxides of Phosphorus. The two important oxides of phosphorus are tetraphosphorus hexaoxide (P4 O6 ) and tetraphosphorus decaoxide (P4 O10 ) (Figure 21.10 in the text). Both oxides are acidic. P 4 O6 (s) + 6H 2 O(l) → 4H3 PO3 (aq) P 4 O10 (s) + 6H 2 O(l) → 4H3 PO4 (aq) Phosphoric Acid. Industrially, phosphoric acid is prepared by the reaction of sulfuric acid with calcium phosphate: Ca3 (PO4 )2 (s) + 3H 2 SO4 (aq) → 2H3 PO4 (aq) + 3CaSO4 (aq) Phosphoric acid is not a particularly strong acid, as indicated by its first ionization constant. H3 PO4 – H+ + H2 PO4 K a1 = 7.5 × 10 –3 Large quantities of phosphoric acid are produced commercially every year. Its main uses are in the production of phosphate fertilizers, cattle feed additives, and water softeners (builders) in household detergents. _______________________________________________________________________________ EXAMPLE 21.3 Oxidation Numbers of Nitrogen List the known oxidation numbers of nitrogen and write the formula of a compound or ion that exemplifies each oxidation number. •Method of Solution ____________________________________________________________ Oxidation Number Compound Formula ____________________________________________________________ – + 5 (maximum) nitrate ion NO3 +4 nitrogen dioxide NO2 – +3 nitrite ion NO2 +2 nitric oxide NO +1 nitrous oxide N2 O 0 nitrogen gas N2 (not a compound) –1 chloramine NH2 Cl –2 hydrazine N2 H4 –3 ammonia and nitride NH3 and N3– ______________________________________________________________ _______________________________________________________________________________ EXAMPLE 21.4 Allotropic Forms Starting with white phosphorus, write equations for the steps needed to prepare phosphoric acid. •Method of Solution First, burn the white phosphorus in excess oxygen to make tetraphosphorus decaoxide. P 4 (s) + 5O 2 (g) → P 4 O10 (s) The oxide is an acidic oxide and is converted to phosphoric acid in water. P 4 O10 (s) + 6H 2 O(l) → 4H3 PO4 (aq) _______________________________________________________________________________...
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