 The concepts acids and bases were loosely defined as substances that change some properties of water.  One of the criteria that was often used was taste.  Substances were classified  salty-tasting  sour-tasting  sweet-tasting  bitter-tasting 2

þ Produce H + (as H 3 O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) þ Taste sour þ Corrode metals þ Good Electrolytes þ React with bases to form a salt and water þ pH is less than 7 3

 Generally produce OH - ions in water  Taste bitter, chalky  Are electrolytes  Feel soapy, slippery  React with acids to form salts and water  pH greater than 7 4

 Acid solutions contain higher amounts of H+ ions than pure water and have a pH below 7.  Base solutions have more OH- ions than pure water and have a pH higher than 7

 A water molecule can react to form ions (charged particles).  H 2 O can break up into H+ (hydrogen ion) and OH- (hydroxide)  Acid - Substances in water that increase the concentration of hydrogen ions (H + ).  Base - Substances in water that increase concentration of hydroxide ions (OH - )  In pure water, the number of H+ and OH- ions are equal so the solution is neutral.

 The pH scale ranges from 0 to 14.  Pure water has a pH of 7. Tap water, mineral water, pond water, are not neutral, why?  The lower the pH, the more acidic the substance.  The higher the pH, the more basic the substance.

 Precipitation that has a pH of less than that of natural rainwater (which is about 5.6 due to dissolved carbon dioxide). H CO 2 = H 2 C0 3  It is formed when sulfur dioxides (S0 x ) and nitrogen oxides (NO x ), as gases or fine particles in the atmosphere, combine with water vapor and precipitate as sulfuric acid or nitric acid in rain, snow, or fog.

 Natural Sources  Emissions from volcanoes and from biological processes that occur on the land, in wetlands, and in the oceans contribute acid-producing gases to the atmosphere

 The principal cause of acid rain is from human sources (known as “anthropogenic sources”)  Industrial factories, power-generating plants and vehicles  Sulfur dioxide and oxides of nitrogen are released during the fuel burning process (i.e. combustion) MSN Encarta

 Wet Refers to acid rain, fog, sleet, cloud vapor and snow.  Dry Refers to acidic gases and particles.

 When water vapor condenses, or as the rain falls, the condensation nuclei dissolve in the water to form sulfuric acid (H 2 SO 4 ) and nitric acid (H 2 NO 3 ).  While the air in cleaned of the pollutants in this way, it also causes precipitation to become acidic, forming acid rain

 CO 2 + H 2 OH 2 CO 3 (carbonic acid)  SO 2 + H 2 O + O 2 H 2 SO 4  (Sulfuric Acid)  SO 2 + H 2 O H 2 SO 3  (sulfurous acid)  NO 2 + H 2 OHNO 2 (nitrous acid) + HNO 3 (nitric acid)

Acidic Precipitation Fossil fuels Power plants Industrial emissions Auto emissions Primary Pollutants SO 2 NO 2 Secondary Pollutants H 2 SO 4 HNO 2 sulfuric acidnitric acid soils leaching of minerals vegetation direct toxicity indirect health effects water sediments leaching aluminum acidic precipitation

Wind Transformation to sulfuric acid (H 2 SO 4 ) and nitric acid (HNO 3 ) Nitric oxide (NO) Acid fog Ocean Sulfur dioxide (SO 2 ) and NO Windborne ammonia gas and particles of cultivated soil partially neutralize acids and form dry sulfate and nitrate salts Dry acid deposition (sulfur dioxide gas and particles of sulfate and nitrate salts) Farm Lakes in deep soil high in limestone are buffered Lakes in shallow soil low in limestone become acidic Wet acid deposition (droplets of H 2 SO 4 and HNO 3 dissolved in rain and snow) AcidicPrecipitation

Fig , p. 428 pH Levels in the United States

Acid rain does not usually kill trees directly. Instead, it is more likely to weaken trees – Damaging their leaves – Limiting the nutrients available to them – Exposing them to toxic substances slowly released from the soil.

Effects on Wildlife Generally, the young of most species are more sensitive to environmental conditions than adults. Generally, the young of most species are more sensitive to environmental conditions than adults. At pH 5, most fish eggs cannot hatch. At pH 5, most fish eggs cannot hatch. At lower pH levels, some adult fish die. At lower pH levels, some adult fish die. Some acid lakes have no fish. Some acid lakes have no fish.

Germany Mongolia

Effects of Acid Rain Great Smoky Mountains, NC

MSN Encarta rns_pH2_30d.gif

 Accelerates weathering in metal and stone structures  Eg. Parthenon in Athens, Greece; Taj Mahal in Agra, India Encarta

 Affects human health  Respiratory problems, asthma, dry coughs, headaches and throat irritations  Leaching of toxins from the soil by acid rain can be absorbed by plants and animals. When consumed, these toxins affect humans severely.  Brain damage, kidney problems, and Alzheimer's disease has been linked to people eating "toxic" animals/plants.

Congress found: Most people now live in urban areas Growth results in air pollution Air pollution endangers living things It decided: Prevention and control at the source was appropriate Such efforts are the responsibility of states and local authorities Federal funds and leadership are essential for the development of effective programs

 Originally signed 1963  States controlled standards  1970 – Uniform Standards by Federal Govt.  Criteria Pollutants  Primary – Human health risk  Secondary – Protect materials, crops, climate, visibility, personal comfort

 Reduce amount of sulfur dioxide and oxides of nitrogen released into the atmosphere  Use less energy (hence less fuel burnt)  Use cleaner fuels  Remove oxides of sulfur and oxides of nitrogen before releasing  Flue gas desulphurization  Catalytic Converters

 Use cleaner fuels  Coal that contains less sulfur  "Washing" the coal to reduce sulfur content  Natural Gas

 Use other sources of electricity (i.e. nuclear power, hydro-electricity, wind energy, geothermal energy, and solar energy)  Issue of cost

 Liming  Powdered limestone/limewater added to water and soil to neutralize acid  Used extensively in Norway and Sweden  Expensive, short-term remedy

 Suppose you worked in the government. A company wants to set up a factory in your country. It would bring jobs, but it would also bring about pollution, which would lead to acid rain. Would you allow it? Justify your answer.

Acidic particles and vapors are deposited via two processes - wet and dry deposition. Wet deposition is acid rain, the process by which acids with a pH normally below 5.6 are removed from the atmosphere in rain, snow, sleet or hail. Dry deposition takes place when particles such as fly ash, sulfates, nitrates, and gases (such as SO 2 and NO), are deposited on, or absorbed onto, surfaces. The gases can then be converted into acids when they contact water. [[ continued: ]]