The melting point of a diamond is extremely high

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Unformatted text preview: re 11.28 in the text). Therefore, a diamond is a single giant molecule. The melting point of a diamond is extremely high, 3550°C. Graphite is the "lead" in lead pencils. On heating carbon and silicon at 1500°C a compound called silicon carbide or carborundum (SiC) is formed. Silicon carbide is almost as hard as diamond and has the diamond structure. Its melting point is about 2700°C. The hardness of diamond and carborundum are put to important uses. Synthetic diamonds are not of gem quality, but are used as abrasives in cutting concrete and many other hard substances. Carborundum is used for cutting, grinding, and polishing metals and glasses. Carbon forms two important classes of compounds called carbides and cyanides. CaC2 and Be2 C contain 2– carbon in the form of C 2 and C4– ions, respectively. The carbide ion contains a triple bond, –C C – . These ions are strong Brønsted bases and react with water as follows. 2– C 2 (aq) + 2H2 O(l) → 2OH– (aq) + C2 H2 (g) C 4– (aq) + 4H2 O(l) → 4OH– (aq) + CH4 (g) Cyanides contain the cyanide anion, C well-known cyanide compounds. N– . Hydrogen cyanide, sodium cyanide, and potassium cyanide are Oxides of Carbon. Carbon forms two important oxides, CO and CO2 . Carbon monoxide is a colorless, odorless, and poisonous gas. It is formed by incomplete combustion of carbon compounds. Carbon monoxide burns readily in air. Back Forward Main Menu TOC Study Guide TOC Textbook Website MHHE Website Nonmetallic Elements and Their Compounds / 4 19 Carbon dioxide is a colorless and odorless gas. It 's concentration in air is 350 ppm. At this concentration, it is not toxic. In enclosed low-lying places such as abandoned mines, CO2 concentrations can build up to suffocating levels. Carbon dioxide is formed by the complete combustion of carbon-containing compounds and fuels. If oxygen is restricted from reaching the combustion zone, carbon monoxide is formed instead. Since CO2 cannot be oxidized further, it finds use in fire extinguishers. Dry ice (solid carbon dioxide) is used as a refrigerant. EXERCISES 5. 6. 7. Diamond is the highest melting substance. Why is the melting point of diamond so high? Write formulas for the cyanide ion and two kinds of carbide ions. Which oxide of carbon is flammable? NITROGEN AND PHOSPHORUS STUDY OBJECTIVES 1. 2. Describe the chemical properties and uses of nitrogen and some of its compounds. Describe the allotropic forms of phosphorus, and list the main phosphorus compounds. N. Molecular nitrogen is obtained from air, of which nitrogen makes up 78 percent by volume. When air under a pressure of 30 atm is cooled to –190°C, it liquefies. Fractional distillation of liquid air yields pure N 2 . Nitrogen is used in the laboratory to create atmospheres devoid of oxygen. This is desirable when working with chemicals that are attacked and degraded by oxygen, or that burn spontaneously in it. Liquid N2 is used as a coolant, providing a temperature of –196°C. Nitrogen (N2 ). The elemental form of nitrogen is extremely stable owing to its triple bond, N Nitrides (...
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