Acid rain, Chapter

Adds, and their chemical opposite, bases, are all around us. We eat them, smell them, and use them in a number of household products and pharmaceuticals. In this chapter, we will examine their properties and their uses. We will also reexamine, this time with more chemical insight, a topic from a previous chapter, acid rain. 

Reality Check That is 1.78 cubic meters. The roasting of sulfide ores is a major source of the gaseous pollutant S02, which contributes to acid rain (Chapter 14). 

Nitric oxide (NO) is a minor but villainous component of the atmosphere. It is involved in the formation of both smog (Chapter 11) and acid rain (Chapter 14). You may be surprised to learn that small amounts of NO are also produced in the human body, where it has a generally beneficial effect. In particular, it has the ability to dilate blood vessels, lowering blood pressure and reducing the likelihood of strokes or heart attacks. Beyond that, NO is effective in treating what television commercials refer to as erectile dysfunction it increases blood flow to the penis. 

As described in Chapter 5, sulfur dioxide, a by-product of burning fossil fuels, is the primary contributor to acid rain. Determine the Lewis stmcture of SO2. ... 

Hydrogen sulfide is released primarily as a gas and will spread in the air. However, in some instances, it may be released in the liquid waste of an industrial facility. When hydrogen sulfide is released as a gas, it may form sulfur dioxide and sulfuric acid in the atmosphere. Sulfur dioxide can be further broken down and is a major contributor to acid rain. Hydrogen sulfide is estimated to remain in the atmosphere for an average of 18 hours. You will find more about what happens to hydrogen sulfide when it enters the environment in Chapters 4 and 5. 

This is an extremely important reaction to which we wiU refer throughout this book. It is responsible for all NO, formation in the atmosphere (the brown color of the air over large cities) as well as nitric acid and acid rain. This reaction only occurs in high-temperature combustion processes and in lightning bolts, and it occurs in automobile engines by free-radical chain reaction steps, which will be the subject of Chapter 10. It is removed from the automobile exhaust in the automotive catalytic converter, which wiU be considered in Chapter 7. 

Acid rain arises from the oxidation of S02 and N02 in the troposphere to form sulfuric and nitric acids, as well as other species, which are subsequently deposited at the earth s surface, either in precipitation (wet deposition) or in dry form (dry deposition). The contribution of organic acids has also been recognized recently (see Chapter 8). These oxidation and deposition processes can occur over relatively short distances from the primary pollutant sources or at distances of a fOOO km or more. Thus both short-range and long-range transport must be considered. 

Because of the gaseous nature of many of the important primary and secondary pollutants, the emphasis in kinetic studies of atmospheric reactions historically has been on gas-phase systems. However, it is now clear that reactions that occur in the liquid phase and on the surfaces of solids and liquids play important roles in such problems as stratospheric ozone depletion (Chapters 12 and 13), acid rain, and fogs (Chapters 7 and 8) and in the growth and properties of aerosol particles (Chapter 9). We therefore briefly discuss reaction kinetics in solution in this section and heterogeneous kinetics in Section E. 

While nitric acid is one of the major contributors to acid deposition (more colloquially acid rain ), we treat its chemistry separately from that of sulfuric and organic acids discussed in the following chapter. The reason for treating it first is that the chemistry of... 

Dust (especially from industrial activities) and salt spray will also exacerbate atmospheric corrosion (Section 16.4). In enclosed industrial premises, atmospheric corrosion could be minimized by preventing noxious emissions, filtering the air to remove particulate matter, and scrubbing the air with water to remove SO2 and other objectionable gases, although the humidity should itself be kept as low as possible (e.g., steam leaks should not be tolerated). On the global scale, however, the cost to the public of atmospheric corrosion could be substantially reduced by sharply limiting SO2 and, to a lesser extent, NO. emissions from power plants, smelters, automobiles, and other industrial functions. This is an aspect of the acid rain threat (Chapter 8) that is usually overlooked. 

Equilibria govern diverse phenomena from the folding of proteins to the action of acid rain on minerals to the aqueous reactions used in analytical chemistry. This chapter introduces equilibria for the solubility of ionic compounds, complex formation, and acid-base reactions. Chemical equilibrium provides a foundation not only for chemical analysis, but also for other subjects such as biochemistry, geology, and oceanography. 

Elemental sulfur is obtained from underground deposits and recovered from natural gas and crude oil. Sulfur is removed from these fuels prior to burning in order to prevent pollution of the air with S02 and subsequent formation of acid rain (see the Interlude in Chapter 15). The sulfur compounds in gas and oil are first converted to H2S, one-third of which is then burned to give S02. Subsequent reaction of the S02 with the remaining H2S yields elemental sulfur ... 

This dissolves in water to produce nitric acid (this is a contributor to acid rain see Chapter 12 p. 198). Many non-metal oxides, such as nitrogen dioxide and carbon dioxide (see Chapter 13 p. 214), form acidic solutions. 

A further reaction occurs in which the sulfurous acid is oxidised to sulfuric acid. Solutions of these acids are the principal contributors to acid rain. For a further discussion of acid rain, see Chapter 12, p. 198. 

Most aluminum-containing compounds do not dissolve much in water unless the water is acidic. However, when acid rain falls, aluminum compounds in the soil may dissolve and enter lakes and streams. Since the affected bodies of water are often acidic themselves from the acid rain, the dissolved aluminum does not combine with other elements in the water and settle out as it would under normal (i.e., non-acidic) conditions. In this situation, abnormally high concentrations of aluminum may occur. For more information on aluminum in the environment, see Chapter 5. 

On several occasions during the past few years, you have studied the environmental issue of acid rain. Now that you have further developed your understanding of acids and bases in this chapter, reflect on your earlier understandings. 

N and ppm levels of various metals such as vanadium and nickel). These elements are harmful to the environment, as upon combustion they produce SOx and NOx gases (responsible for acid rain), and to the chemical industry, as these molecules can poison the catalysts needed for the subsequent cracking and reforming operations (see Box 2, and Chapter 1, Section 1.2.1). 

New and exciting chapter opening introductions, accompanied by applied photos, present a relevant example of one of the chapter topics. Examples include stalagmites and stalactites as an illustration of an equilibrium process (Chapter 9), the effects of acid rain (Chapter 16), and the oxidation/reduction properties of chlorophyll (Chapter 19). 

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