1. Some of the gases present in our atmosphere dissolve in rain water and cause it to become acidic. Here we will examine some of these.

2. Carbon dioxide has been present in Earth’s atmosphere for billions of years, long before humans were around. Thanks to Ewa Urban for sharing this image on Pixabay

3. Because CO2 is present in the air, it comes in contact with water droplets in clouds. When CO2 dissolves in water, it reacts with the water

4. To produce hydronium ions

5. And hydrogen carbonate ions.

6. H 3 O + formed by dissolved CO 2 has always been present H 3 O + formed by dissolved CO 2 has always been present and has always caused rainwater to be slightly acidic

7. and has always caused rainwater to be slightly acidic H 3 O + formed by dissolved CO 2 has always been present and has always caused rainwater to be slightly acidic

8. The presence of dissolved CO2 in natural rainwater, unaffected by human activity (click) produces enough hydronium to bring the pH as low as 5.6. 01234567891011121314 pH

9. CO 2(g) + 2H 2 O (l)  H 3 O + (aq) + HCO 3 – (aq) Because natural rainwater has a pH as low as 5.6 01234567891011121314 pH pH = 5.6 Natural Rainwater

10. Rain with any pH 5.6 or above is NOT called acid rain, 01234567891011121314 pH pH = 5.6 NOT called acid rain

11. even though a pH of 5.6 to 7 is acidic. 01234567891011121314 pH NOT called acid rain acidic

12. Rain with a pH below 5.6 (click) IS called acid rain because is it more acidic than rain naturally is. 01234567891011121314 pH pH = 5.6 called acid rain

13. Generally rainwater with a pH below 5.6 is caused by gases from human activities. Some gases produced by naturally occurring phenomena such as volcanoes or lightning can also cause acid rain in localized areas. 01234567891011121314 pH Caused by gases from human activities, volcanoes, and lightning called acid rain

14. It’s important to remember that rainwater with any pH 5.6 or above, is not technically called acid rain, while rainwater with any pH below 5.6 IS called acid rain. 01234567891011121314 pH Called acid rain pH = 5.6 NOT called acid rain

15. You may recall that Nonmetal Oxides are oxides of elements on the right side of the staircase on the periodic table. Nonmetals Metals Nonmetal Oxides form Acidic Solutions

16. Remember, nonmetal oxides react with water to form acidic solutions. Nonmetals Metals Nonmetal Oxides form Acidic Solutions

17. Nonmetal oxides produced by human activities are the major sources of acid rain.

18. The nonmetal oxides produced by human activities that contribute most to acid rain include Nonmetal Oxides Produced by Human Activities

19. Nitrogen monoxide, or NO gas NO (g), Nonmetal Oxides Produced by Human Activities

20. Nitrogen dioxide, or NO2 gas NO (g), NO 2(g), Nonmetal Oxides Produced by Human Activities

21. Which is sometimes referred to as N2O4 gas NO (g), NO 2(g), Nonmetal Oxides Produced by Human Activities Also referred to as N 2 O 4(g)

22. Sulphur dioxide or SO2 gas NO (g), NO 2(g), SO 2(g), Nonmetal Oxides Produced by Human Activities

23. And sulphur trioxide, or SO3, which is present in the air as liquid droplets. NO (g), NO 2(g), SO 2(g), and SO 3( l ) Nonmetal Oxides Produced by Human Activities

24. Nitrogen oxides NO (g) and NO 2(g) are present in exhaust gases of internal combustion engines that run on gasoline or diesel fuel. Nitrogen oxides NO (g) and NO 2(g) are present in exhaust gases of gasoline and diesel engines

25. So the main source of nitrogen oxides, sometimes collectively referred to as NO X, is automobile exhaust. The main source of nitrogen oxides (sometimes referred to as NO x ) is automobile exhaust Thanks to Pat McKane for sharing this image on Pixabay

26. Air is about 78% nitrogen Air is about: 78% nitrogen (N 2(g) ) 21% oxygen (O 2(g) )

27. And about 21% oxygen. Air forms part of the mixture injected into the cylinders of an internal combustion engine. Air is about: 78% nitrogen (N 2(g) ) 21% oxygen (O 2(g) )

28. Inside the cylinders of this type of engine, the temperature can reach as high as 1900 degrees Celsius. At this high temperature, (click) nitrogen can react with oxygen,

29. To produce nitrogen monoxide gas

30. They can also react (click) to produce nitrogen dioxide gas, NO2.

31. Some of the The NO produced (click) also reacts with oxygen

32. To produce NO2 gas

33. this NO2 will be present in the exhaust of vehicles using these engines, and some of it will reach the atmosphere

34. where it will react with water droplets

35. to produce nitrous acid, HNO2…

36. And nitric acid HNO3.

37. Because it is a weak acid, HNO2

38. Undergoes partial ionization in rainwater

39. To produce hydronium ions

40. And nitrite ions, NO2 minus

41. The strong acid HNO3, or nitric acid

42. Will completely ionize in rainwater

43. To produce hydronium ions

44. And nitrate ions NO3 minus

45. The presence of hydronium ions formed from both acids, causes the rain (click) to be acidic, or acid rain. acid rain

46. You may want to pause the video, take a screen shot of this page and print it. It is good to be familiar with these equations. acid rain

47. Two other harmful substances that are produced by (click) human activities are sulphur dioxide, released from coal burning power plants and smelters

48. And sulphur trioxide, which forms when sulphur dioxide reacts with air.

49. Let’s see how these two substances are formed. Thanks to Emilian Robert Vicol for sharing this image on Pixabay.

50. Fossil fuels, such as coal usually contain small amounts of sulphur. When they re burned, the sulphur in them burns too. Burning Fuels Containing Sulphur Roasting Ores in Smelters Fossil fuels contain small amounts of sulphur

51. When sulphur Burning Fuels Containing Sulphur Roasting Ores in Smelters

52. burns in air, Burning Fuels Containing Sulphur Roasting Ores in Smelters

53. It produces sulphur dioxide gas or SO2. But SO2 can also come from other sources… Burning Fuels Containing Sulphur Roasting Ores in Smelters

54. Metals occur in nature in ores, which are compounds of the metals with nonmetals. A metal combined with the nonmetal sulphur is called a sulphide ore. Burning Fuels Containing Sulphur Roasting Ores in Smelters

55. Two examples of sulphide ores are zinc sulphide and iron(IV) sulphide. Burning Fuels Containing Sulphur Roasting Ores in Smelters

56. Sulphur is removed from ores in a process called roasting, where the ores are heated in a high oxygen environment. This is one of the processes that occur in refining or smelting metals. Burning Fuels Containing Sulphur Roasting Ores in Smelters

57. The equation that describes the roasting of the ore zinc sulphide is 2ZnS plus 3 O2 … Burning Fuels Containing Sulphur Roasting Ores in Smelters

58. Gives 2ZnO or zinc oxide Burning Fuels Containing Sulphur Roasting Ores in Smelters

59. Plus 2SO2 Burning Fuels Containing Sulphur Roasting Ores in Smelters

60. Similarly, a common iron ore, Iron(IV) sulphide, or iron pyrite, is heated in oxygen Burning Fuels Containing Sulphur Roasting Ores in Smelters

61. To produce iron(III) oxide, or Fe2O3, Burning Fuels Containing Sulphur Roasting Ores in Smelters

62. And SO2. Burning Fuels Containing Sulphur Roasting Ores in Smelters

63. Some of this SO2, in the air Burning Fuels Containing Sulphur Roasting Ores in Smelters

64. Will react with oxygen in the air… Burning Fuels Containing Sulphur Roasting Ores in Smelters

65. To produce sulphur trioxide, SO3. This reaction often takes place on the surfaces of dust particles in the air. Burning Fuels Containing Sulphur Roasting Ores in Smelters

66. SO2, being a nonmetal oxide, Burning Fuels Containing Sulphur Roasting Ores in Smelters

67. Will react with water droplets in the air Burning Fuels Containing Sulphur Roasting Ores in Smelters

68. To produce H2SO3, Burning Fuels Containing Sulphur Roasting Ores in Smelters

69. Or sulphurous acid. Sulphurous acid is classified as a weak acid. Burning Fuels Containing Sulphur Roasting Ores in Smelters

70. SO3 present in the mixture is also a nonmetal oxide, Burning Fuels Containing Sulphur Roasting Ores in Smelters

71. So it will react with water Burning Fuels Containing Sulphur Roasting Ores in Smelters

72. Producing H2SO4, Burning Fuels Containing Sulphur Roasting Ores in Smelters

73. Or sulphuric acid. Sulphuric acid is classified as a strong acid. Burning Fuels Containing Sulphur Roasting Ores in Smelters

74. Because H2SO3 is a weak acid, Burning Fuels Containing Sulphur Roasting Ores in Smelters

75. It undergoes partial ionization in water Burning Fuels Containing Sulphur Roasting Ores in Smelters

76. To produce hydronium ions Burning Fuels Containing Sulphur Roasting Ores in Smelters

77. And hydrogen sulphite ions Burning Fuels Containing Sulphur Roasting Ores in Smelters

78. And because H2SO4 is a strong acid Burning Fuels Containing Sulphur Roasting Ores in Smelters

79. It ionizes completely in water Burning Fuels Containing Sulphur Roasting Ores in Smelters

80. To produce hydronium ions Burning Fuels Containing Sulphur Roasting Ores in Smelters

81. And hydrogen sulphate ions Burning Fuels Containing Sulphur Roasting Ores in Smelters

82. The presence of hydronium ions in the water results in the (click) formation of acid rain acid rain Burning Fuels Containing Sulphur Roasting Ores in Smelters

83. You may want to pause the video, take a screen shot of this page and print it. It is good to be familiar with these equations. acid rain Burning Fuels Containing Sulphur Roasting Ores in Smelters

84. Humans are not the only source of acid rain. It can also be caused by natural phenomena.

85. Volcanoes can release large amounts of SO2 into the atmosphere. Mt St Helens volcano eruption Image Number: AC80-0513-29 Date: 1980 - NASA photograph

86. And the extreme localized heating caused by lightning can cause nitrogen and oxygen in the air to react

87. And form nitrogen monoxide, which using the sequence of reactions we discussed, can cause acid rain. Thanks to sethink for sharing this image on Pixabay

88. The reason people are concerned about acid rain is it has some serious effects.

89. We’ll outline some of the effects of acid rain here: Acid rain Acid rain:  causes soil and rock to release Al 3+ ions, which are toxic to many fish species and can affect the health of trees and crops  washes away many nutrients that are important for the growth of trees and crops  damages stone buildings and statues by dissolving limestone (CaCO 3 ) in the rocks  dissolves substances that can contaminate water supplies

90. causes soil and rock to release Al 3+ ions. Aluminum ions are toxic to many fish species and can seriously affect the health of trees and crops Acid rain:  causes soil and rock to release Al 3+ ions, which are toxic to many fish species and can affect the health of trees and crops  washes away many nutrients that are important for the growth of trees and crops  damages stone buildings and statues by dissolving limestone (CaCO 3 ) in the rocks  dissolves substances that can contaminate water supplies

91. Acid rain can also dissolve and wash away many of the good nutrients that are needed by trees and crops. When trees are weakened by acid rain they are more susceptible to disease Acid rain:  causes soil and rock to release Al 3+ ions, which are toxic to many fish species and can affect the health of trees and crops  washes away many nutrients that are important for the growth of trees and crops  damages stone buildings and statues by dissolving limestone (CaCO 3 ) in the rocks  dissolves substances that can contaminate water supplies

92. Acid rain dissolves certain rocks such as limestone or marble, which are made up of calcium carbonate. Many buildings and statues have been damaged by years of exposure to acid rain. Acid rain:  causes soil and rock to release Al 3+ ions, which are toxic to many fish species and can affect the health of trees and crops  washes away many nutrients that are important for the growth of trees and crops  damages stone buildings and statues by dissolving limestone (CaCO 3 ) in the rocks  dissolves substances that can contaminate water supplies

93. Acid rain can also dissolve toxic metals present in rocks and soils. The resulting ions of these metals can then enter water supplies and contaminate them. Acid rain:  causes soil and rock to release Al 3+ ions, which are toxic to many fish species and can affect the health of trees and crops  washes away many nutrients that are important for the growth of trees and crops  damages stone buildings and statues by dissolving limestone (CaCO 3 ) in the rocks  dissolves substances that can contaminate water supplies

94. Acid rain is not as big a problem as it once was in many places. This is due to increased awareness of the problem and pressure on governments to react. Measures to Minimize Acid rain:  Since the 1970’s governments have imposed strict regulations on air quality. This includes emissions from thermal power plants, vehicles, and industrial processes.  New vehicles are all equipped with multiple devices to control emissions. These include sophisticated catalytic converters to break down exhaust gases. In addition, an increasing number of hybrid vehicles are being sold. These have lower emissions than other vehicles.  Alternate forms of energy are being employed in many countries. These include wind-powered, tidal powered, and geothermal generating plants.  SO 2 from smelting is reclaimed and used to produce sulphuric acid instead of being released to the environment.

95. Beginning in 1970’s, many governments have imposed strict regulations concerning air quality. This includes emissions from thermal power plants, vehicles, and industrial processes Measures to Minimize Acid rain:  Since the 1970’s governments have imposed strict regulations on air quality. This includes emissions from thermal power plants, vehicles, and industrial processes.  New vehicles are all equipped with multiple devices to control emissions. These include sophisticated catalytic converters to break down exhaust gases. In addition, an increasing number of hybrid vehicles are being sold. These have lower emissions than other vehicles.  Alternate forms of energy are being employed in many countries. These include wind-powered, tidal powered, and geothermal generating plants.  SO 2 from smelting is reclaimed and used to produce sulphuric acid instead of being released to the environment.

96. You’re probably aware that new vehicles are all equipped with numerous devices to control emissions. One of the most important are catalytic converters, which greatly minimize the release of harmful exhaust products. Measures to Minimize Acid rain:  Since the 1970’s governments have imposed strict regulations on air quality. This includes emissions from thermal power plants, vehicles, and industrial processes.  New vehicles are all equipped with multiple devices to control emissions. These include sophisticated catalytic converters to break down exhaust gases. In addition, an increasing number of hybrid vehicles are being sold. These have lower emissions than other vehicles.  Alternate forms of energy are being employed in many countries. These include wind-powered, tidal powered, and geothermal generating plants.  SO 2 from smelting is reclaimed and used to produce sulphuric acid instead of being released to the environment.

97. You may also have noticed that there is are more and more hybrid vehicles of the roads. These have lower emissions than other vehicles. There are also some vehicles that run on fuel cells, which have zero emissions of harmful gases. Measures to Minimize Acid rain:  Since the 1970’s governments have imposed strict regulations on air quality. This includes emissions from thermal power plants, vehicles, and industrial processes.  New vehicles are all equipped with multiple devices to control emissions. These include sophisticated catalytic converters to break down exhaust gases. In addition, an increasing number of hybrid vehicles are being sold. These have lower emissions than other vehicles.  Alternate forms of energy are being employed in many countries. These include wind-powered, tidal powered, and geothermal generating plants.  SO 2 from smelting is reclaimed and used to produce sulphuric acid instead of being released to the environment.

98. In many places in the world, thermal coal-burning power plants are being phased out and alternate sources of energy, such as wind, tidal power, and geothermal energy are being used instead. Measures to Minimize Acid rain:  Since the 1970’s governments have imposed strict regulations on air quality. This includes emissions from thermal power plants, vehicles, and industrial processes.  New vehicles are all equipped with multiple devices to control emissions. These include sophisticated catalytic converters to break down exhaust gases. In addition, an increasing number of hybrid vehicles are being sold. These have lower emissions than other vehicles.  Alternate forms of energy are being employed in many countries. These include wind-powered, tidal powered, and geothermal generating plants.  SO 2 from smelting is reclaimed and used to produce sulphuric acid instead of being released to the environment.

99. We had mentioned that SO2 is a product of smelting sulphide ores of metals. In many places, this SO2 is reclaimed and used to produce sulphuric acid on an industrial scale, with very little of it reaching the environment. Measures to Minimize Acid rain:  Since the 1970’s governments have imposed strict regulations on air quality. This includes emissions from thermal power plants, vehicles, and industrial processes.  New vehicles are all equipped with multiple devices to control emissions. These include sophisticated catalytic converters to break down exhaust gases. In addition, an increasing number of hybrid vehicles are being sold. These have lower emissions than other vehicles.  Alternate forms of energy are being employed in many countries. These include wind-powered, tidal powered, and geothermal generating plants.  SO 2 from smelting is reclaimed and used to produce sulphuric acid instead of being released to the environment.