Answers

Unit 9: Link and Think

1. According to the U.S. Geological Service, the term acid rain describes rain or snow that has a pH lower than what is natural for a given area. The normal rain can have a pH as low as 5.6. While the EPA defines acid rain as any rain more acidic than this, the USGS defines acid rain as having a pH of 5.0 or less.
   
   
2. Rain reacts with carbon dioxide, a naturally abundant gas, to form carbonic acid, a weak acid. (Carbonic acid is also found in carbonated beverages.) Rain can also react with chlorine gas to form hydrochloric acid. This reaction is not a major contributor to rain's natural acidity because chlorine gas normally exists in very low concentrations in our atmosphere.
   
   
3. Sulfur dioxide and nitrogen oxides react with water, oxygen, and oxidants to form mild solutions of sulfuric acid and nitric acid. These gases are emitted by the burning of fossil fuels by electric power plants and automobiles.
   
   
4. Ohio, Pennsylvania, and Indiana.
   
   
5. Midwestern states, like Nebraska and Indiana, have soils that are able to resist changes in pH.
   
   
6. According to the graph, frogs can survive in water of with pH as low as 4.0. However, the page also says that mayflies cannot tolerate water with a pH of less than 5.5. If the animals below the frog on the food chain die at pH 4.5 or below, you are not likely to find frogs in the pond.