Chapter 9

Acid Rain

• Is Rain Water Hard or Soft?– SOFT, salts and minerals do not evaporate

• Is Rain Water Acidic or Basic?– ACIDIC, carbon dioxide is soluble in water

Rain

CO2 + H2O H2CO3

Carbonic Acid

• Carbonic Acid is a weak acid

• carbone dioxide is an anhydride

• [H+] = 2.5 x 10-6 M

• pH = 5.6

CO2 + H2O H2CO3

H2CO3 + H2O H3O+ + HCO3-

Acid Rain• What is Acid Rain?

– rain with lower than normal pH– pollutants from industrial process, automobiles

and energy generation lower the pH– combustion of fossil fuels

• Pollutants– SO2 and SO3 called sulfoxides (SOx)– NO and NO2 called nitroxides (NOx)– Small amount of HCl and volatile organics

Pollutants• Sulfur Dioxide

– by-products from the combustion of coal – coal can contain up to 3-5% Sulfur

S(s) + O2(g) SO2(g)

– sulfur dioxide is released into the air

– laws now regulate the release of SO2

Pollutants• Sulfur Dioxide

– the purification of sulfide ores– most common ores are of copper and iron

Cu2S(s) + 3 O2(g) 2 CuO(s) + 2 SO2(g)

2 CuO(s) + Cu2S(g) 6 Cu(s) + SO2(g)

– coal also has some of these metal ores

Pollutants• Sulfoxides

– sulfur dioxide combines with oxygen to form sulfur trioxide

2 SO2(g) + O2(g) 2 SO3(g)

– This is a more hazardous pollutant because it results in a stronger acid

Pollutants• Nitroxides

– Primary from the high temperatures from the combustion of fossil fuels

N2(g) + O2(g) 2 NO(g)

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

Acid Rain

• Pollutants react with water to form acids

SO2(g) + H2O(g) H2SO3(aq)

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

NO(g) + H2O(g) HNO2(aq)

NO2(g) + H2O(g) HNO3(aq)

Acid Rain

Damage by Acid Rain

• Lakes and streams

• Forest

• Buildings and statues

• Corrosion of Metals

Lakes and Streams• Aquatic Life prolific with pH 6.6-9.2

– pH 6.0 fish begin to die off– pH 5.5 most species are affected– pH 5.0 most aquatic life is dead– pH 4.0 “dead” lake, can not support life

• Some lake and streams are more resistant to change in pH called Acid Neutralization Capacity (ANC)

Lakes and Streams• Another problem is Leaching 침출

• Aluminum concentration increase 1000-fold with a pH change from 6.0 to 5.0

• Lead, mercury, cadmium are trace metal ions that increase with decrease in pH

• Harm fish and aquatic life, but also pollute water supplies

Forests• Acid Rain is a contributing factor for

destruction and death of trees

• Other factors include– increase in ground-level ozone (O3)

– increase in the use of nitrogen fertilizers– trace metals released by acid rain– natural causes

Urban Structure

• 탄산칼슘 , Calcium Carbonate, CaCO3

2 H+(aq) + CaCO3(s) Ca2+

(aq) + CO2(g) + H2O(l)

H2SO4(aq) + CaCO3(s) CaSO4(aq) + CO2(g) + H2O(l)

• Calcium Sulfate, CaSO4

– more soluble and can be washed away

Corrosion of Metals• Metals are also susceptible to acid rain

• Iron rusts when exposed to air and water

4 Fe(s) + 2 O2(g) + 8 H+(aq) 4 Fe2+

(aq) + H2O(l)

4 Fe2+(aq) + O2(g) + 4 H2O(aq) 2 Fe2O3(s) + 8 H+

(aq)

4 Fe(s) + 3 O2(g) 2 Fe2O3(s)

Solving the Problem• The problem is complicated but the solution

is even more complex.– politics, economics and environment

• Clean Air Act 1990

• Control Strategies– Reducing Emission– Cleaner Energy Sources

Control Strategies• Upgrade Catalytic Converter

– change NO back to N2 and O2

• Burn cleaner coal (less sulfur)

• Coal Cleaning

• “Scrubbing” - SO2 removal