Acid Rain and Buffered Solutions Chapter Notes

Rainwater Rainwater is naturally acidic—one source of its acidity is from carbon dioxide There are about 810 billion tons of CO 2 in the atmosphere from natural resources, like volcanoes and decaying organic matter, and human activities Water in the atmosphere reacts with carbon dioxide to form carbonic acid CO 2 + H 2 O  H 2 CO 3 Carbonic acid lowers the pH of water—CO 2 in the atmosphere makes rain water have a pH of about 5.6

Acid Rain Acid rain is the term used for rain that has a pH lower than 5 Created when airborne pollutants, such as sulfur dioxide, are absorbed by atmospheric moisture Sulfur dioxide is converted to sulfur trioxide, which reacts with water to form sulfuric acid 2 SO 2 (sulfur dioxide) + O 2  2 SO 3 (sulfur trioxide) SO 3 + H 2 O  H 2 SO 4 (sulfuric acid) Sulfuric acid is much stronger than carbonic acid Rain with carbonic acid can erode land Rain with sulfuric acid can erode metal, paint, and other exposed surfaces

Environmental Impact of Acid Rain Impacts depend on the geology In the Midwestern U.S., the ground contains large amount of calcium carbonate (limestone), which is a basic compound and will neutralize the acid rain before damage is done In northeastern U.S. and other regions, the effects of acid rain are greater because the ground does not contain a lot of limestone A solution to the damaging effects of acid rain is called liming—the pH of lakes and rivers is increased by adding calcium carbonate Long-term solution is to prevent sulfur dioxide from entering the atmosphere

Indicators Indicators are substances that change color in the presence of whatever they are testing for (there are many different indicators that can check for many different substances) Indicators change color because of Le Chatelier’s Principles

Acid/Base Indicators Acid/base indicators will change color when there is a change in pH The universal indicator solution (phenolphthalein, bromothymol blue, and methyl red dissolved in ethanol and water) will change colors at each integral pH value (1, 2, 3, … 14)

Other pH indicators Litmus and phenolphthalein are indicators

Buffer Solution A buffer solution is any solution that resists large changes in pH They work by containing two components: one component neutralizes any added base and the other component neutralizes any added acid Effective buffer solutions are made by mixing a weak acid with a salt of the weak acid Example: mixing acetic acid, C 2 H 4 O 2, with sodium acetate, NaC 2 H 4 O 2

Connections to our Lives Our blood is a buffered solution—the pH needs to stay between 7.35 and 7.45 If the pH of our blood goes above or below this range, it can kill us A blood pH above 7.45 is called alkalosis A blood pH below 7.35 is called acidosis

Homework Using the litmus paper provided, check to see if two different items found in your home are acidic or basic Staple/tape the litmus paper to a separate sheet of paper Label what the items are and if they are acidic or basic Use common sense—do not test anything dangerous! Also, page 354, #20-24, 26, 29