RAIN
Published on Nov 25, 2015
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PRESENTATION OUTLINE
Sun heats water - steam - goes up to sky - form clouds - more steam - heavier grey clouds - too heavy - breaks apart - rain falls
Photo by Luke Peterson Photography
pure water : pH 7.0
natural unpolluted rainwater: pH 5.6 (acidic)
- natural presence of CO2, NO and SO2
CO2 + H2O → H2CO3
H2CO3 →H+ + HCO3-
ability of H2CO3 to deliver H+ → an acid → lowering the pH of a solution.
Nitric oxide (NO),
formed during lightning storms.
By reaction of nitrogen and oxygen
N2 + O2 (&lightning)→2NO
NO + 1/2O2 → NO2
3NO2+H2O→2HNO3+NO
dissociates in water - hydrogen ions and nitrate ions - lowering the pH of the solution.
Human industrial activity produces additional acid-forming compounds - greater quantities than the natural sources of acidity.
pH of rainwater can be 3.0 or lower (approximately 1000x > acidic than normal rainwater).
Rainwater too acidic, cause problems (killing freshwater fish and damaging crops, eroding buildings and monuments).
Photo by db™
What causes such a dramatic increase in the acidity of rain relative to pure water?
concentrations of nitric oxide and sulfur dioxide in polluted air
Humans - combustion processes - increase concentrations of acid-producing oxides
CO2 is present - higher concentration than NO and SO2 - CO2 does not form acid - same extent
large increase - concentration of NO and SO2 - affects the pH of rainwater
About 1/4 of acidity of rain is accounted for by nitric acid (HNO3).
high-temperature air combustion produces large amounts of NO gas (forms nitric acid).
A process that occurs naturally at levels tolerable by the environment can harm the environment when human activity causes the process to occur to a much greater extent.
What about the other 75% of the acidity of rain?
sulfuric acid (H2SO4) in rainwater.
produced naturally in small quantities from biological decay and volcanic activity
produced almost entirely by human activity,
fossil fuels are burned, the sulfur contained reacts with oxygen from air to form sulfur dioxide.
SO2 + O2 →SO3 + H2O → H2SO4
Photo by eutrophication&hypoxia
Sulfuric acid - strong acid - dissociates in water - H+ ion and HSO4- ion .
H2SO4 → HSO4- + H+
H2SO4- → SO2-4 + H+
presence of H2SO4 - concentration of H+ ions - increase - pH of the rainwater drops to harmful levels.
Environmental effect
Photo by angela7dreams
Acidic lakes - fish cannot live.
Degradation of soil minerals - metal ions washed away in the run off :
1) Release of toxic ions (e.g. Al3+) into the water supply.
2) Loss of important minerals (e.g. Ca2+) , killing trees and damaging crops.
Atmospheric pollutants - easily moved by wind currents - acid-rain effects - felt far - pollutants are generated
Erosion of highly durable materials, buildings and outdoor monuments made of marble and limestone
Photo by VinothChandar
How does this happen?
CaCO3 + H2SO4 → Ca2+ + SO2-4 + H2O + CO2
AIM
Photo by VinothChandar
Determine the acidity of rain at different locations.
RESULTS
Photo by Camil Tulcan
Most pH 5 - 5.5
Two lowest readings : pH 4 and 4.4
The neutral reading which sounds impossible was from Bukit kempas
pH 5 - 5.5 : still consider as natural rain water (gases found in atmosphere)
pH 4 and 4.4 : rain water is slightly acidic
pH 7 (neutral) : use of alkaline (detergent, factories producing domestic chemical products that wash to water and eventually evaporates to air)
CONCLUSION
Photo by John-Morgan
The lower the rain’s pH, the more acidic it is.
LIMITATIONS
Photo by deeplifequotes
