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The fluorides and chlorides of many metallic elements

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Unformatted text preview: oncentrated sulfuric acid in the presence of MnO2 . 2NaCl(aq) + 2H2 SO4 (aq) + MnO2 (s) → C l 2 (g) + Na2 SO4 (aq) + MnSO4 (aq) + 2H2 O(l) Oxoacids of the Halogens. Most of the halides (halogens with an oxidation number of –1 as in chloride) can be classified into two categories: ionic and covalent. The fluorides and chlorides of many metallic elements, especially those belonging to the Group 1A and 2A metals, are ionic compounds. The halides of nonmetals are covalent compounds. Because fluorine is the most electronegative element and because of its unusually weak F—F bond, fluorine has a chemistry somewhat different from the rest of the halogens. Five differences are pointed out in Section 21.6 of the text. • • • • • Fluorine is the most reactive of all of the halogens. Hydrogen fluoride exhibits hydrogen bonding. None of the other hydrogen halides do. Hydrofluoric acid is a weak acid. All other HX acids are strong. Fluorine reacts with cold NaOH solution. Silver fluoride is soluble. All other silver halides are insoluble. The halogens form a series of oxoacids with the following general formulas: HOX hypohalous acid Back Forward HXO2 halous acid Main Menu TOC HXO3 halic acid HXO4 perhalic acid Study Guide TOC Textbook Website MHHE Website 4 26 / Nonmetallic Elements and Their Compounds Table 21.5 in the text lists the oxoacids of the halogens. Hypochlorous, hypobromous, and hypoiodous acids can be prepared by the reaction of the elemental halogen with water. X2 + H2 O HX + hydrohalic acid HOX hypohalous acid The smaller the radius of the halogen atom, the farther the equilibrium lies to the right. Mixtures of these halogen acids react with bases to produce hypohalite salts (NaOX) HX + HOX + 2NaOH → NaX + NaOX + 2H2 O When the elemental form of a halogen, X2 , is dissolved in a base the net reaction is X2 + 2NaOH → NaX + NaOX + H2 O This is another example of a type of redox reaction called disproportionation reaction. In this type of reaction the same element (the halogen) is both oxidized and reduced. One halogen atom in X—X is the reducing agent and the other is the oxidizing agent. Interhalogens are compounds formed when molecules of two different halogens react. The interhalogen molecules consist of an atom of the larger halogen bound to an odd number of atoms of the smaller halogen. They have the following formulas: XX', XX'3 , XX' 5 , and XX'7 , where X and X' are different halogens and X is the larger atom of the two. Uses of the Halogens. The halogens and their compounds find many uses in industry, the home, and in the field of health. Fluorine is used in fluoride toothpaste, in uranium isotope separation as UF6 , and in the manufacture of Teflon for electrical insulators, plastics, and cooking utensils. Chlorine is widely used as a bleaching agent and as a disinfectant for water purification. Household bleach is 5.25 percent NaOCl by mass. The major end uses of chlorine are in manufacturing polymers such as polyvinyl chloride, in chemical solvents, in the pulp and...
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