Effects of pH on Ecosystems

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

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

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

pH Shows the Concentration of H + 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+H+ Cl -

pH Shows the Concentration of H + 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 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 , or pH is the negative log of [H + ] –As pH gets lower, the [H + ] number gets higher

Practice Calculating pH Determine the pH of a M solution of HNO 3 pH = -log[H + ] = -log(0.0034) = 2.47 Determine the pH of a 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 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 (SO 2 ) and nitrogen oxides (NOx) resulting from fossil fuel combustion

Acid Rain Formation Sulfur dioxide and nitrogen oxides are released when fossil fuels are burned (such as coal) SO 2 and NO x molecules react in sunlight to create sulfuric acid and nitric acid

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

Major Power Plants Sources of NO x Emissions and Acid rain

Nitrogen deposition Nitrogen deposition Nitrogen Deposition

ION CONCENTRATION MEASUREMENTS IN RAIN

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

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

Surface water sensitivity to Acid Deposition

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

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

Sources ppt