1. Acid rain is caused by the emission of sulfur dioxide and other pollutants. Sulfur dioxide is released through the burning of coal and oil in power plants, refineries, steam generators, factories, and homes.
  2. Acid rain lowers the pH levels of water and soil to levels that are intolerable to animals and plants.For precipitation to be acidic, the pH value must be less than that of normal rainfall (usually a pH value of 5.0 - 5.6).
  3. The pH scale is used to measure whether a substance is acidic or basic. Pure water has a pH of 7, which is neutral. Substances having a pH of 1 (such as battery acid) are extremely acidic, while substances having a pH of 13 (such as lye) are extremely basic or alkaline. The pH scale is logarithmic: a tenfold difference exists between each value.


  • litmus paper with a color range from 3.0 to 6.0
  • corresponding pH color chart
  • foreceps
  • collection vials for rainwater
  • fresh rainwater
  • containers to hold other liquids
  • other liquids to measure pH (ie: lemonade. tap water, milk, vinegar, soft drink)
  • student journal
  • optional: computers with data base, spreadsheet, or word processors




  1. To measure the pH, set a pH strip into each liquid for approximately 2 seconds. Be sure to use the forceps to handle the litmus paper as body oil may affect the readings.
  2. Remove the strip with forceps and compare the strip's color to the pH color chart and find the corresponding numeric value that matches.
  3. Record the pH data and the liquids tested in journals or on a spreadsheet.
  4. Collect rainwater in vials.
  5. Measure the pH. Acid rain usually has a pH between 4 and 4.6. Normal rain water ranges from 5.0 to 5.6. 6. Record the results and continue to monitor the pH over a period of time. Does the pH change and if so, what might be the cause?


  • A significant contributor to acid rain is sulfur dioxide, (SO2 ), from the combustion of fossil fuels. This compound, when mixed with water vapor, forms sulfuric acid (H2SO4). Other significant contributors are nitrous oxide (NO2) and peroxy-acetyl nitrate (PAN).

Assessment Ideas

  • Check the accuracy of pH measurements and consistency in readings within class groups.
  • Students can create histograms to graphically compare readings.
  • Discuss acid rain and its effect on biological systems.


  • English/Language Arts: Have students keep a journal.
  • Mathematics: Graph the result of the experiment and the data.


  • acid rain: precipitation in which the pH of the water is less than that of pure rain water as a result of pollution in the air.
  • pH scale: the level of acidity of a substance. pH is expressed as a value between 1 and 14 (1 being the most acidic and 14 the least acidic or alkaline). A substance with a pH of 7 is considered normal


  • "Winds of Change" educational CD-ROM, Copyright Caltech and NASA/Jet Propulsion Laboratory