Acid rain

    [S]Natural, unpolluted rainwater actually has a PH of about 5.6.And rain with pH below 5.6 is described as acid rain.

  [T]Is all rain acidic?

   [S]Yes, both ‘clean’ and acid rain are

    [T] What are the causes of acidity of rain?

   [S]The acidity of rainwater comes from the natural presence of three substances (CO2, NOx, and SO2) found in the atmosphere. Carbon dioxide (CO2) is present in the greatest concentration and therefore contributes the most to the natural acidity of rainwater.

[T]Where does carbon dioxide come from?

[S]Carbon dioxide, produced in the decomposition of organic material, is the primary source of acidity in unpolluted rainwater.

[T]What are other natural sources of acidic gas?

[S]Very little amount of nitric oxide and sulfur dioxide are released to the atmosphere in the electric discharge    process and the eruption of volcano 

     [T] Yes, what you have said is correct Human industrial activity produces

additional acid-forming compounds           in far greater quantities than the          natural sources of acidity. And the concentrations of nitrogen oxides and sulfur dioxide in polluted air are the main cause of acid rain.

[T] What are the human sources of acidic gas (SO2)?

[S]Half the sulfur dioxide (SO2) in the atmosphere comes from the combustion of fossil fuels (e.g. coal, natural gas, oil). The gas then forms sulfuric acid.

[T]what are the human sources of acidic Gas (NOx)?

[S]High-temperature air combustion, such as occurs in car engines and power plants, produces large amounts of NOx gas. These gas then forms nitric acid.

[T]who can write down the equations of these reaction?

[S]Sulfur dioxide, like the oxides of carbon, reacts with water to form sulfuric acid.

SO2(g) + O2(g) =SO3(g)

SO3(g) + H2O(l) = H2SO4(aq)

In air, NO is oxidized to nitrogen dioxide (NO2), which in turn reacts with water to give nitric acid (HNO3).

2NO(g) + O2(g) =2NO2(g)

4NO2(g) + O2(g) + 2H2O(l) = 4HNO3(aq)

[[][Acid rain has caused great damages to the natural environment and human[buildings. Building stone may be

limestone or marble, both calcium      carbonate. These materials are attacked by acid rain to form soluble substances or solids, which run off the surface.

[T] Then what can we do to deal with it?

[S] Nitrogen oxides and sulfur dioxide are the culprits in the formation of acid rain. Thus, reducing the amount of these gases releasing to the atmosphere will be the general rule to cure acid rain.

[T] Then what can we do?

[S] 1.Saving energy and subsequently producing less acidic gas is the guideline here.

   2.Turn off lights, computers, and other electronic devices when you're not using them.

3.Use public transportation (公共交通), or better yet, walk or bicycle whenever possible.

 [T] Who can give us a summary for today’ lesson? Acid rain has

[][[] The PH of acid rain is below 5.6.

2.The concentration of nitrogen oxides and sulfur dioxide in polluted air is the main cause of acid rain.

3.Acid rain has resulted in the death of fish in the lake, the death of trees, and the corrosions of many buildings.

4.Reducing the emission of acidic gas, SO2 and NOx, is the general rule.