Effects of pH on Ecosystems

1. Effects of pH on Ecosystems

2. Acids and Bases • Acids release a hydrogen ion into water (aqueous) solution • Acids neutralize bases in a neutralization reaction • An acid and a base combine to make a salt and water • Acids corrode active metals   • Acids taste sour • Stomach acid is hydrochloric acid • Acetic acid is the acid ingredient in vinegar • Citrus fruits such as lemons, grapefruit, oranges, and limes have citric acid in the juice • Sour milk, sour cream, yogurt, and cottage cheese have lactic acid from the fermentation of the sugar lactose

3. Acids and Bases • Bases release a hydroxide ion into water solution • Bases neutralize acids in a neutralization reaction • Acid plus base makes water plus a salt • Bases denature protein • Bases are slippery to the touch • Strong bases are very dangerous because a great amount of the material of humans is made of protein • Bases taste bitter • There are very few food materials that are alkaline, but those that are taste bitter

4. Acids and Bases Are Measured By pH • Acids have a low pH (less than 7) • Bases have a high pH (greater than 7, up to 14) • Neutral solutions have a pH of approximately 7

5. pH Shows the Concentration of H+ Ions Pure water is neutral – the number of H+ ions equals number of OH- ions • [H+] is the concentration of hydrogen ions in a solution • Lots of hydrogen ions = a strong acid • Very few hydrogen ions = a strong base Now, let’s add a strong acid, such as HCl: HCl H+ Cl- Now the solution is acidic – the number of H+ ions is greater than the number of OH- ions

6. pH Shows the Concentration of H+ Ions Pure water is neutral – the number of H+ ions equals number of OH- ions • [H+] is the concentration of hydrogen ions in a solution • Lots of hydrogen ions = a strong acid • Very few hydrogen ions = a strong base Now, let’s add a strong base, such as NaOH: NaOH Na+ OH- Now the solution is basic – the number of H+ ions is less than the number of OH- ions

7. pH Shows the Concentration of H+ Ions • [H+] is the concentration of hydrogen ions in a solution • Lots of hydrogen ions = a strong acid • Gastric juice has an H+ concentration of 1 x 10-1, or .1 • Very few hydrogen ions = a strong base • Ammonia has an H+ concentration of 1 x 10-12, or .000000000001 • pH is the negative log of [H+] • As pH gets lower, the [H+] number gets higher

8. Practice Calculating pH • Determine the pH of a 0.0034 M solution of HNO3 pH = -log[H+] = -log(0.0034) = 2.47 • Determine the pH of a 0.001 M solution of HCl pH = -log[H+] = -log(0.001) = 3 • Determine the pH of a 0.09 M solution of HBr pH = -log[H+] = -log(0.09) = 1.05

9. Acid Rain • Deposited material from the atmosphere containing higher than normal amounts of nitric and sulfuric acids • Acid rain formation results from both natural sources and man- made sources • Natural: Volcanoes and decaying vegetation • Man-made: Emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) resulting from fossil fuel combustion

10. Acid Rain Formation • Sulfur dioxide and nitrogen oxides are released when fossil fuels are burned (such as coal) • SO2 and NOx molecules react in sunlight to create sulfuric acid and nitric acid

11. Acid Rain Formation • Some of these particles fall down to the ground as dry deposition • Other particles mix with water in the clouds, and the resulting rain has a high acidity due to release of H+ ions

12. Major Power Plants Sources of NOx Emissions and Acid rain

13. Nitrogen Deposition Nitrogen deposition 1989 - 1991 Nitrogen deposition 1995 - 1998

15. ION CONCENTRATION MEASUREMENTS IN RAIN

16. Affected Areas Acid rain is a problem in Eastern Canada and the Northeastern USA Large smelters in western Ontario and steel processing plants in Indiana, Ohio use coal as a source of fuel Acid rain from power plants in the Midwest harms the forests of upstate New York and New England The sulfur dioxide is carried eastward by the jet stream

17. Sensitive Soil • If a body of water is surrounded by limestone, that can act as a buffer to the acid • In many areas water and soil systems lack natural alkalinity like limestone and cannot neutralize acid

18. Surface water sensitivity to Acid Deposition

19. Acid Rain Kills Fish • Acid rain runoff through soil mobilizes metals • Acid reacts with metals such as aluminum • Normally aluminum is immobile • below pH 5 - mobile aluminum • Water with mobile aluminum runs off into lakes and streams • Fish breath in the water, and aluminum clogs gills causing suffocation

20. Acid Rain Kills Fish • Fish eggs often will not hatch water with a pH of 5 or less • Young fish are more sensitive to water acidity than adult fish

21. Sources • http://www.chemtutor.com/acid.htm • http://water.me.vccs.edu/courses/env211/lesson7.htm • http://lincoln.pps.k12.or.us/lscheffler/AcidRain.ppt • http://academic.engr.arizona.edu/HWR/Brooks/NATS101sec48/lectures/4-22-2003.ppt • http://www.nicholas.duke.edu/downloads/psk9/teaching/env279/topic9.ppt • http://www.epa.gov/airtrends/aqtrnd95/no2.html • http://www.epa.gov/acidrain/index.html • http://misterguch.brinkster.net/WKS001_017_424346.pdf • http://misterguch.brinkster.net/PRA027.pdf