Neutralizing The Threat of Acid Rain

Transcription

1 Neutralizing The Threat of Acid Rain Practice Questions: 1, 4, 7a, 11, 17, 26, 31, 33, 35, 39 What is an acid? Sour taste; found in vinegar, citrus fruits, and candies. Changes litmus from blue to red. Reacts with carbonates; dissolves egg shells and limestone. HF, HCl, H 2 SO 4, HNO 3 are common acids. An Acid is Any substance that generates hydrogen ions, H +, in aqueous (H 2 O) solution HCl (g) H + (aq) + Cl - (aq) H + + H 2 O H 3 O + (solvated protons give hydroniumions). HCl + H 2 O H 3 O + +Cl - (aq) What is a base? Bitter taste; not used in food. Slippery to touch; soapy feel. Changes litmus from red to blue Strong base can cause severe damage to eyes, skin, & clothing. Aqueous solutions of ammonia (NH 3 ) and sodium hydroxide (NaOH). A base is Any substance that produces hydroxide ions (OH - ) in aqueous solution. NaOH(s) Na + (aq) + OH - (aq) Ca(OH) 2 (s) Ca 2+ (aq) + 2 OH - (aq) NH 3 + H 2 O NH 4+ (aq) + OH - (aq) Neutralization Acid + Base Salt + H 2 O HCl (aq) + NaOH (aq) NaCl (aq) + H 2 O Net reaction: H + + OH - H 2 O In a neutralization reaction, the H + from the acid combine with the OH - from the base to form water. 1

2 Acidic or Basic or Neutral? [H + ] [OH - ] = 1 x ; [ ] = Molarity In an acidic solution; [H + ]> [OH - ]or [H + ]>10 7 M In a basic solution; [H + ]< [OH - ] or [H + ]<10 7 M ph Scale for Acidity or Basicity Neutral solution; H + = OH - = 10 7 M Numerical scale between 0 and 14 As the ph value increases, acidity decreases. Acid Rain National Acid Precipitation Assessment Program (1980) created by Congress. Clean Air Act Phase I (1995) reduction of acid rain precursors by power plants. Acid deposition via rain, snow, fog & mist is a regional issue (note: precipitatin= rain + snow). Pollutant transport from Midwest (Ohio River valley) to Northeast and Southeast; from Germany, Poland, U. K. to Sweden & Norway.. ph data collected weekly at >225 sites since 1970; more sites located in Northeast U. S. Fig. 6.8 Figure 6.3 page 237 Importance of CO 2 in Affecting ph Atmospheric CO 2 is about 370 ppm. CO 2 (g) + H 2 O(l) H 2 CO 3 H + (aq) + HCO 3- (aq) CO 2 is the source of slight acidity in normal rainfall (i.e. ph of 5.6). HCO 3- in blood provides a ph buffer that keeps the blood ph at ~7.2. CO 2 is used in beverage industry for producing soda drinks with ph at ~

3 Extra Acidity Sulfur oxides, SO x and nitrogen oxides, NO x (acid anhydrides). Acid rain occurs in regions with the most SO x and NO x emissions. SO x is emitted from coal-fired power plants, steel mills, and other coal-burning industries (e.g. Allegheny County, PA). NO x is found in urban areas with high population densities and heavy automobile traffic (e.g. Los Angeles, Houston). The world s largest smelter converts nickel sulfide to nickel with the emission of SO 2 ; the smokestack of 1250 feet is the tallest in the world. SO 2 (g) + H 2 O(l) H 2 SO 3 (aq) 2 H + (aq) + SO 3 2- (aq) SO 3 (g) + H 2 O(l) H 2 SO 4 (aq) 2 H + (aq) + SO 4 2- (aq) The production of SO 3 is slow but is catalyzed by fly ash; 20-25% of H 2 SO 4 is produced by SO 2 + OH. Figure 6.6 page 242 3

4 Fig Fig Figure 6.7 page 244 Table 6.1 page 245 Figures 6.8 and 6.9 on page 246: corrosion of limestone statues due to acid rain. Fig Page 248 CaCO 3 (s) + 2 H + (aq) Ca 2+ (aq) + CO 2 (g) + H 2 O (l) 4

5 Fig. p.266 Acid Neutralizing Capacity (ANC) Midwest lakes have limestone (CaCO 3 ) to neutralize acids; but Northeastern lakes are surrounded by granite with little ANC. Granite releases Al 3+ in acidic water to form mucus in fish gills or worsen the acidity by: Al 3+ (aq) + H 2 O(l) H + (aq)+ [Al(OH)] 2+ (aq) Adirondack lakes and mid-appalachian streams have reached N saturation and are susceptible to episodic and chronic acidification. Curing acidic lakes by adding Ca(OH) 2 (Figure 6.10 p. 249); neutralize SO 2 by basic fly ash. Page 251 Healthy lakes ph = 6.5 ph < 6 = trouble ph < 4 = dead lake Unhealthy Forests Big problem in Europe; fir and spruce trees at high altitudes; loss of leaves and needles; weakened trees killed by drought, cold, wind, and insects. North American Sugar Maple Decline Project -10 states & 4 provinces in New England states and eastern Canada; decline of red spruce in Appalachian Acid precipitation is a contributing factor besides pest and ozone; tree ring & surface water acidity studies. Ozone and nitrogen oxides attack the waxy coating on leaves, allowing H+ to deplete nutrients; soil acidification mobilizes metals that attack tree roots by preventing nutrient uptake and leaches out key nutrients. Page 252 What can be done? Limit SO x emissions from industries; restriction of grandfather clause; emission credit trading. Clean Coal Technology; low NO x burner, reburning, coal switching (anthracite), coal washing with water, and scrubbing acidic gases with powdered limestone. 2 SO 2 + O 2 + CaCO 3 CaSO CO 2 Public transportation and electric cars 5