Chapter 15 week 7

Chapter 15 week 7 - Chapter 15 Lecture Notes Chemistry of...

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Chapter 15 Lecture Notes Chemistry of the N-Ne main group family of elements
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Cl Ar Br Kr I Xe At Rn Oxides of the nonmetals N, P, S, Se, Cl, Br, and I all dissolve in water to give acids whose strength depends on their oxidation state.
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Group V elements exhibit complex chemistry as oxidation states from +5 to -3 are known for N, P, and As. More metallic Sb and Bi tend to be in 3+ and 5+ oxidation states. Sb a low conductivity metalloid.
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N ≡N Nitrogen Only nitrogen and phosphorus exist in molecular forms as elements Note: periodic trend is multiple bonds only common for first row elements, thus CO 2 vs. SiO 2 and N 2 vs P 4 or O 2 vs. S 8 .
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Liquid N 2 at 77K Red P, white P 4 and black polymeric allotropes known overhead of phosphorus allotropes As Sb Bi
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Plants consist primarily of carbohydrates made from oxygen and carbon dioxide in the air and water from rain by photosynthesis. Proteins contain C, H, O, and N. The nitrogen must be obtained from soluble nitrate or ammonium in soil. Ultimately, nitrogen is obtained by nitrogen fixing bacteria (eqn below) or by nitrates produced from bird excrement or urea from mammals. N 2 + 8H + + 8e + 16 ATP 2NH 3 + H 2 + 16ADP + 16 PO 4 3- Anerobic rhizomes containing nitrogen fixing bacteria, which use the enzyme nitrogenase to catalyze the reaction.
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Nitrogen Fertilizers Humans help agricultural productivity by applying N, P, K nutrients in the form of inorganic fertilizers. For nitrogen it begins with the Haber-Bosch process: N 2(g) + 3 H 2(g) 2 NH 3(g) (iron catalyst at 200 atm and 400C) Since the reaction is exothermic (-92 kJ/mol) it is better to carry out this reaction at room temperature as nature does. The ammonia is used directly and as NH 4 NO 3 (also a high explosive), (NH 4 ) 2 SO 4 , (NH 4 ) 2 (HPO 4 ), and urea (NH 2 CONH 2 ) all made by combining ammonia with other inexpensive large volume chemicals.
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Ostwald Process for Nitric Acid Synthesis Not surprisingly, the other key starting point for nitrogen chemistry involves a compound at the opposite extreme of nitrogen’s oxidation states. It is prepared by catalytic oxidation of ammonia with oxygen. Before 1902 Chilean saltpeter deposits (NaNO 3 ) were the main nitrate source for fertilizers and explosives. 1000 C/Pt-Rh 4 NH 3(g) + 5 O 2(g) 4 NO (g) + 6H 2 O (g) Followed by further reaction with oxygen to NO 2 . 2 NO (g) + O 2(g) 2 NO 2(g) The final step is disproportionation in water to generate nitric acid and NO, which is recycled. 3 NO 2(g) + H 2 O (l) 2 HNO 3(l) + 2NO (g)
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For environmental significance and role in photochemical smog see: http://chem-faculty.ucsd.edu/trogler/CurrentNitroWeb/Intro/intro.html
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Forms as a blue liquid when NO (colorless) and NO 2 (brown) are condensed. Since both are free radicals, no surprise they form a weak N-N bond in the condensed phase.
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Phosphorus Chemistry Key facts: Phosphate and its anhydrides are the most important compounds. It starts with fluoroapatite mineral. Ca
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This note was uploaded on 06/12/2008 for the course CHEM 6C taught by Professor Hoeger during the Spring '08 term at UCSD.

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Chapter 15 week 7 - Chapter 15 Lecture Notes Chemistry of...

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