The pH Scale

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Rain with a pH below 5.6 is “acid rain“

CO2 in the air forms carbonic acid

CO2 + H2O H2CO3

Adds to H+ of rain

H2CO3 H+ (aq) + HCO3-(aq)

Formation of acid rain:

1. Emission of sulfur and nitrogen oxides from the burning of fuels expecially coal with high S content, power stations, oil refineries, vehicles as well as bacterial decomposition, and lighting hitting N2

SO2 26 million tons in 1980

NO and NO2 22 million tons in 1980

Mt. St Helens (1980) 400,000 tons SO2

2. Reactions in the atmosphere form SO3

2SO2 + O2  2 SO3

3. Reactions with atmosphere water form acids

SO3 + H2O  H2SO4 sulfuric acid

NO + H2O  HNO2 nitrous acid

HNO2 + H2O  HNO3 nitric acid

4. Effects of Acid Rain

Decline in fish populations in rivers and lasts due to toxic effect of Al leached from soil by acid rain

Extensive fish kills in spring from runoff due to accumulation of large amounts of acid on the snow

Dissolves minerals Mg, Ca, and K from the soil and waxy coatings that protect leaves from bacteria

Corrodes metals, textiles, paper and leather

Slide 31

Sources of Acid Rain

LecturePLUS Timberlake

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Power stations

Oil refineries

Coal with high S content

Car and truck emissions

Bacterial decomposition, and lighting hitting N2

Slide 32

LecturePLUS Timberlake

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SO2 26 million tons in 1980

NO and NO2 22 million tons in 1980

Mt. St Helens (1980) 400,000 tons SO2

Reactions with oxygen in air form SO3

2SO2 + O2 2 SO3

Reactions with water in air form acids

SO3 + H2O H2SO4 sulfuric acid

NO + H2O HNO2 nitrous acid

HNO2 + H2O HNO3 nitric acid

Slide 33

Effects of Acid Rain

LecturePLUS Timberlake

33

Leaches Al from soil, which kills fish

Fish kills in spring from runoff due to accumulation of large amounts of acid in snow

Dissolves waxy coatings that protect leaves from bacteria

Corrodes metals, textiles, paper and leather