Effects of pH on EcosystemsEffects of pH on Ecosystems

Acids and BasesAcids 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

Acids and BasesAcids 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

Acids and Bases Are Measured By pHAcids 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

pH Shows the Concentration of HpH Shows the Concentration of H++ Ions 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

Pure water is neutral – the number of H+ ions equals number of OH- ions

Now the solution is acidic – the number of H+ ions is greater than the number of OH- ions

Now, let’s add a strong acid, such as HCl:HCl

H+ Cl-

pH Shows the Concentration of HpH Shows the Concentration of H++ Ions 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

Pure water is neutral – the number of H+ ions equals number of OH- ions

Now the solution is basic – the number of H+ ions is less than the number of OH- ions

Now, let’s add a strong base, such as NaOH:NaOH

Na+ OH-

pH Shows the Concentration of HpH Shows the Concentration of H++ Ions 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

Practice Calculating pHPractice 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

Acid RainAcid 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

Acid Rain FormationAcid 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

Acid Rain FormationAcid 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

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

Nitrogen deposition 1989 - 1991 Nitrogen deposition 1995 - 1998

Nitrogen DepositionNitrogen Deposition

ION CONCENTRATION ION CONCENTRATION MEASUREMENTS IN RAINMEASUREMENTS IN RAIN

Affected AreasAffected 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

Sensitive SoilSensitive 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

Surface water sensitivity to Acid DepositionSurface water sensitivity to Acid Deposition

Acid Rain Kills FishAcid 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

Acid Rain Kills FishAcid 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

SourcesSources• 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