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ACID RAIN. ACID RAIN. CaCO 3 ( s ) + H +  CO 2 ( g ) + H 2 O + Ca 2+.

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CaCO3(s) + H+ CO2(g) + H2O + Ca2+

Scientists know that acidic water dissolves the nutrients and helpful minerals in the soil and then washes them away before trees and other plants can use them to grow. At the same time, acid rain causes the release of substances that are toxic to trees and plants, such as aluminum, into the soil. Scientists believe that this combination of loss of soil nutrients and increase of toxic aluminum may be one way that acid rain harms trees. Such substances also wash away in the runoff and are carried into streams, rivers, and lakes. More of these substances are released from the soil when the rainfall is more acidic.


Svante Arrhenius(1859-1927)

Swedish chemist who explained the electrical conductivity of ionic solutions by presuming that compounds dissociated into oppositely charged ions whose motions constituted a current.

This conclusion was supported by observing that the freezing point depression of ionic solids were integer multiples larger than their concentrations would indicate according to Raoult's Law.


Svante Arrhenius(1859-1927)

He described his theory in his 1884 thesis, which passed the defense with the lowest passing grade.

However, it won him the Nobel Prize in chemistry in 1903.

He also discovered the Arrhenius Rate Law, which describes the rate at which chemical reactions occur.



Acids donate H+ ions

to other ions or molecules,

which act as a base.

  • In an operational sense:

  • an acidis any substance that increases the concentration of the H+ ion when it dissolves in water.

  • a base is any substance that increases the concentration of the OH- ion when it dissolves in water.





Gas – solution eaquilibrium KH

Henry’s Law

CO2 dissolves in water:CO2(g) + H2O <==> H2CO3 (aq)

KH = 3.4 x 10-2at a CO2 pressure of 3 x 10-4 atmospheres,

what is the concentration of the carbonic acid in the water?

H2CO3 <==> H+ + HCO3— Ka = 4.68 x 10-7

What is [H+]? - What is pH?







Programs that monitor acid rain analyze hydrogen content to determine pH. They also measure atmospheric concentrations of nitric acid, nitrate, sulfur dioxide, sulfate and ammonium. In the United States, the National Atmospheric Deposition Program (NADP) supervises wet deposition while the Clean Air Status and Trends Network (CASTNET) observes dry deposition.

Monitoring acid deposition helps determine critical loads, or the amount of pollutants an ecosystem can support before damage. Accurate critical loads help set effective targets for SO2 and NOx reductions.

Most sulfur dioxide comes from power plants that use coal as their fuel.  These plants emit 100 million tons of sulfur dioxide, 70% of that in the world.

Automobiles produce about half of the world's nitrogen oxide.

Though human causes are primarily responsible for acid rain, natural causes exist as well.  Fires, volcanic eruptions, bacterial decomposition, and lightening also greatly increase the amount of nitrogen oxide on the planet.  However, even the gigantic explosion of Mt. St. Helens released only about what one coal power plant emits in a year.

The problem of acid rain is rapidly spreading.  Because it is mainly caused by industrial processes, automobiles, and power plants, those countries that are developed have the most severe acid rain problems.   However, as the undeveloped nations begin to industrialize, acid rain will increase greatly.

The toxic ions released due to acid rain form the greatest threat to humans. Mobilized copper has been implicated in outbreaks of diarrhea in young children and it is thought that water supplies contaminated with aluminium causes Alzheimers disease.

crustaceans, insects, and some plankton species begin to disappear.

  • major changes in the makeup of the plankton community occur.

  • less desirable species of mosses and plankton may begin to invade.

  • the progressive loss of some fish populations is likely, with the more highly valued species being generally the least tolerant of acidity.

  • the water is largely devoid of fish.

  • the bottom is covered with undecayed material.

  • the nearshore areas may be dominated by mosses.

  • terrestrial animals, dependent on aquatic ecosystems, are affected. Waterfowl, for example, depend on aquatic organisms for nourishment and nutrients. As these food sources are reduced or eliminated, the quality of habitat declines and the reproductive success of birds is affected.

negotiating treaties

Scrubbers remove 80-95 percent of the sulfur oxides. Certain types do not remove nitrogen oxides. They are costly to retrofit to existing power plants. They increase the electric generating costs by 10-15 %.

Scrubbers are like "liquid" filters for the gases resulting from combustion. The exhaust gases are forced through a spray of water containing lime (calcium hydroxide). The sulfur dioxide gas reacts with the lime to produce a solid of calcium sulfate.

There are then problems in getting rid of the liquid sludge that is produced.


Coal Company Views:

Many coal companies in the Midwest may go broke and cause high unemployment rates among coal miners if power companies switch to low sulfur coat from the West.

The cost of this massive reduction in sulfur oxides could be as high as $21 billion

The Edison Institute expects 10-15 percent electricity rate increases in several states. At ten particularly hard-hit utilities the rate increases may exceed 20%.

EPA Views:

The EPA calls the estimates made by electric power companies as excessive. The EPA estimates that the total cost of implementing the 1990 Clean Air act would be less than $4 billion a year. This translates to an increase of 1-1.5 % in consumer electric bills.

solution to the problem of acid rain at Harvard

Convention on Long-Range Transboundary Air Pollution

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