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Unformatted text preview: Back Forward Main Menu TOC Study Guide TOC Textbook Website MHHE Website 4 22 / Nonmetallic Elements and Their Compounds
8. What are the oxidation numbers of nitrogen in nitrate ion and nitrite ion?
9. Write three equations that show the steps in the production of nitric acid from ammonia.
10. Compare the stability of white and red phosphorus. OXYGEN AND SULFUR
3. Describe the allotropic forms of oxygen and sulfur.
Distinguish between oxides, peroxides, and superoxides.
List some of the compounds of oxygen and sulfur and describe their chemical properties. Allotropic Forms of Oxygen. Oxygen is the most abundant element in Earth's crust, making up about
46% by mass. As the free element oxygen exists in two allotropic forms, diatomic oxygen (O2 ) and ozone (O3 ).
Diatomic oxygen makes up 21 percent of Earth's atmosphere by volume. Industrially, oxygen is obtained by
liquefaction of air followed by fractional distillation. In the laboratory, oxygen is obtained by heating potassium
chlorate in the presence of MnO2 catalyst.
3 KClO3 (s) → KCl(s) + 2 O2 (g)
Ozone is a less stable form of oxygen. It is produced by the action of an electrical discharge or ultraviolet
(UV) light on diatomic oxygen.
O2 (g) + UV light → O(g) + O(g)
O(g) + O2 (g) → O3 (g)
Ozone's presence in the atmosphere prevents the sun's UV light from reaching Earth's surface. Ozone
absorbs the light in the following reaction:
O3 (g) + UV light → O2 (g) + O(g)
Both ozone and diatomic oxygen are strong oxidizing agents.
O2 (g) + 4H + + 4e – → 2H2 O(l)
O3 (g) + 2H + + 2e – → O2 (g) + H 2 O(l) E° = 1.23 V
E° = 2.02 V Ozone is used mainly to purify drinking water, to deodorize air and sewage gases, and to bleach waxes, oils,
and textiles. About 65 percent of all the diatomic oxygen produced in the United States is used in the basic
oxygen process for making steel. Pure oxygen gas is blown over the surface of molten iron to lower the carbon
content by burning it to CO2 . At the same time silicon and phosphorus impurities are oxidized and later
removed as slag. Hydrogen Peroxide. Besides forming water, oxygen forms another important binary compound with
hydrogen: hydrogen peroxide (H2 O2 ). Hydrogen peroxide is never used as a pure substance because of its
tendency to explode. Back Forward Main Menu TOC Study Guide TOC Textbook Website MHHE Website Nonmetallic Elements and Their Compounds / 4 23
2– Metal peroxides contain the peroxide ion, O2 . These ions are strong Brønsted bases. All the metal
peroxides hydrolyze in acidic solutions to form hydrogen peroxide. Hydrogen peroxide can be prepared in the
laboratory from barium hydroxide octahydrate and sulfuric acid.
BaO2 ·8H2 O(s) + 2H 2 SO4 (aq) → BaSO4 (aq) + H2 O2 (aq) + 8H2 O(l)
In aqueous solutions, H 2 O2 can act both as an oxidizing agent and a reducing agent. For example, H2 O2
oxidizes iron(II) ion to iron(III) ion.
H2 O2 (aq) + 2Fe2+ (aq) + 2H+(aq) → 2Fe 3+ (aq) + 2H2 O(l)
It reduces silver oxide to metallic silver:
H2 O2 (aq) + Ag2 O(s) → 2Ag(s) + H 2 O(l) + O 2...
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