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7.19: Acid Rain

Difficulty Level: Basic Created by: CK-12
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What would the artists think?

Notre Dame Cathedral in Paris opened in 1345. Construction took almost 200 years. For about 500 years the cathedral was pristine. Yet this gargoyle has pits in it. The pits are caused by acid rain. Acid rain forms from pollutants from fossil fuel burning.

Acid Rain

Acid rain is rain that has a pH less than 5 (see Figure below). Acidity is measured on the pH scale. Lower numbers are more acidic and higher numbers are less acidic (also called more alkaline). An acid has a pH of less than 7. The pH of normal rain is 5.6. It’s slightly acidic because carbon dioxide in the air dissolves in rain. This forms carbonic acid, a weak acid.

This pH scale includes both normal and acid rain. At what pH do fish have problems reproducing?

How Acid Rain Forms

Acid rain forms when nitrogen and sulfur oxides in air dissolve in rain (see Figure below). This forms nitric and sulfuric acids. Both are strong acids. Acid rain with a pH as low as 4.0 is now common in many areas. Acid fog may be even more acidic than acid rain. Fog with a pH as low as 1.7 has been recorded. That’s the same pH as toilet bowl cleaner!

Nitrogen and sulfur oxides combine with rain to form acid rain.

Effects of Acid Rain

Figure below shows some of the damage done by acid rain. Acid rain ends up in soil and bodies of water. This can make them very acidic. The acid strips soil of its nutrients. These changes can kill trees, fish, and other living things. Acid rain also dissolves limestone and marble. This can damage buildings, monuments, and statues.

Acid rain has killed trees in this forest in the Czech Republic.


  • acid: A substance with a pH of less than 7.0.
  • acid rain: Rain that has a pH of less than 5.0.
  • alkaline: Also called basic. Substances that have a pH of greater than 7.0.
  • pH scale: A scale that measures the acidity of a solution. A pH of 7 is neutral. Smaller numbers are more acidic and larger numbers are more alkaline.


  • Nitrogen and sulfur compounds emitted high into the atmosphere create acids. These acids may fall as acid rain.
  • Acidity is measured on a pH scale. Rain that is 5.0 or less on that scale is considered acid rain.
  • Acid rain weakens plants and animals and damages cultural treasures.


Use this resource to answer the questions that follow.

Coal Combustion and Acid Rain at http://www.youtube.com/watch?feature=player_embedded&v=HE6Y0iEuXMQ (2:04)

  1. What causes acid rain?
  2. What two gases react with water to make acid rain?
  3. What damage can acid rain cause?
  4. How can we reduce acid rain?
  5. What are scrubbers?
  6. What is slurry?
  7. How effective are scrubbers?


  1. Where does much of the acid rain fall? Where does acid rain do the most damage?
  2. What damage does acid rain do to organisms? What damage does it do to cultural structures?
  3. Describe the pH scale. What can you say about a liquid with a pH of 2.5? What about a liquid with a pH of 10.5?

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Substance with a pH of less than 7.0.

acid rain

Rain that has a pH of less than 5.0.


Also called basic; substances that have a pH of greater than 7.0.

pH scale

Scale that measures the acidity of a solution; a pH of 7 is neutral; smaller numbers are more acidic, and larger numbers are more alkaline.

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Date Created:
Jan 04, 2013
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Aug 29, 2016
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