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Environmental Chemistry

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Deisy Rosales

on 27 March 2015

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Transcript of Environmental Chemistry

Ozone Depletion E.4.1
Environmental
Chemistry

GreenHouse Effect E.3.1
GreenHouse Effect
gases in atmosphere allow passage of incoming short wave radiation but absorb some reflected infrared radiation and re-radiate it back to Earth
temperature of earth is regulated through a balance from energy received from sun and energy from earth to space
Incoming radiation
short ultraviolet wave and visible
some is absorbed in atmosphere and reflected back to space
Radiated back from earth to space
longer infrared radiation
Air Pollution;E1
Sources
Carbon Monoxide
Antrhopogenic
incomplete combustion of fosil fuels and forest fires :2C(s) + O2 (g)->2CO (g)
Natural
Atomospheric oxidation of methane gas (CH4)
2CH4(g)+302(g)->2CO2(g) +4H20(l)
Nitrogen Oxides

Antrhopogenic
Motor Vechiles (high temp.): N2+O2-> 2NO(g)
Natural
bacteria action in soil from lightning storms: N2(g)+O2(g)-> 2NO(g)
Reaction with hydrocarbons to form acid rain
Air Pollution E.1.2
Sulfur Oxides
Anthropogenic
Burning Fossil Fuels: Coal has sulfur :S(s) +O2(g)->SO2(g)
Smelting Plants: oxidize sulfide ores to metal oxidize
Sulfuric Acid Plants
2H2O(l)+2SO2 (g)+O2(g)->2H2SO4(aq)
Natural
Volcanoes,rotting vegetables
produced as second pollutant by oxidation of Hydrogen Sulfide:
2H2S(g)+3O2(g)->2SO2(g)+2H20(l)
Particulates
Natural
Dust from mechanical break-up of solid matter
pollen,bacterial/fungal spunes
Anthropogenic
Coal at power stations:incomplete combustion of hydrocarbons
Arsenic from insecticides
Asbestos
Volatile Organic Compounds
Natural
CH4 from bacterial decombustions of organic matter in water,trees, plants: produce hydrocarbons
Anthropogenic
unburned petroleum, solvents
Air Pollution E.1.2
METHODS FOR REDUCTION
Carbon Monoxide and Nitrogen oxides
Catalytic Converter and use of lean burn engines
Sulfur Dioxide
Sulfur Dioxide Emissions; remove the sulfur before or after combustion
Particulates
removal of such through gravitational settling, rain and snow
prevent entering the atmosphere: filtration, centrifugal filtration
Volatile
Oxidation catalytic converter or thermal exhaust
reactors:hydrocarbons oxidized to carbon dioxide and water
Acid Deposition E.2.1
Refers to the process where acidic particles, gases and precipitation leave the atmosphere
Dry deposition: acidic gases and particles
caused by the sulfur and nitrogen oxides
wet disposition: Acid rain, fog, snow
Acid Rain: acidic gases dissolved in water
sulfur dioxide dissolves in water to form Sulfurous Acid : H2O(l)+SO2(g)->H2SO3 (aq)
Sulfuric Acid
Formed when Sulfur Dioxide is oxidized to sulfur trioxide and dissolved in water
H2O(l)+SO3(g)->H2SO4(aq)
Nitrogen Dioxide:
dissolves in water to form a mixture of nitrous and nitric acid
H2O(l)+2NO2(g)->HNO2(aq)+HNO3(aq)
Acid Deposition E.2.2
Environmental Effects
washes out critical nutrients in soil; magnesium,calcium, and potassium but releases Al+3 ions from rocks into soil but are dangerous
reduces ability of plants to photosynthesize
results in stunted growth and leaf loss
Al+3 ions are trapped in rock
damage roots in trees and prevent water and nutrients to be taken into trees
GreenHouse Effect E.3.3
Influence of increasing greenhouse gases in atmosphere
average world temperature has increased
estimated: Carbon dioxide levels will double in 100 years
agriculture and bio distribution changes with climate change
rising sea levels
melting of polar ice caps and glaciers
Formation
Strong covalent bond in O2 is broken by high energy UV radiation to form 2 oxygen atoms:With UV light:
O2(g)->2O+(g)
oxygen atoms are reactive free radicals and react with other oxygen molecule to create the Ozone
O+(g)+O2(g) -> O3(g)
Depletion
bonds in ozone are weaker than the double bond in oxgen
ultraviolet light of lower energy is needed to break bonds:with UV light
O3(g)->O+(g)+O2(g)
Oxygen atoms react with other ozone molecule to make two oxygen molecules
O3(g)+O+(g)->2O2(g)
Ozone Depletion E.4.2
Pollutants and their sources
Nitrogen Oxides
Nitrogen monoxide
Jet aircraft inject nitrogen oxides into ozone layer
Chlorofluorcarbons (CFCs)
found in aerosols, refrigerants,solvents, foaming agents and plastics
remain in troposphere but eventually diffuse into stratosphere and produce reactive chlorine atoms
CCl2F2(g)->CClF2*(g)+Cl(g)
Ozone Depletion E.4.3
Alternatives for CFCs
similar properties include low reactivity, not produce free radicals when exposed to UV light
Hydrocarbons
propane 2-methylpropane in refrigerant coolants
H atom instead of Cl atom allow for easier decomposition and C-H bond is stronger
Flucarbons : strong C-F bond allows them to atable to ultraviolet radiation=can't catalyze ozone depletion
Hydrochloroflucarbons(HCFCs)
less destructive than CFCs, do contain C-Cl bonds but get detroyed in lower atomsphere before ozone layer
Hydrofluorocarbons(HFCs)
the BEST alternative
Dissolved Oxygen in water E.5.1
Biological Oxygen Demand(BOD)
measure of the dissolved oxygen (ppm)required to decompose organic matter
measured over a time period of 5 days
Fast flowing rivers can recover its purity because water get oxygenated thru mechanical action of flow
waters with little flow,re oxygenation is slow
the greater quantity of degradable organic waste,higher BOD
Pure water=BOD of <1ppm
polluted water=BOD >5ppm
Dissolved Oxygen in water E.5.2
Aerobic and Anaerobic Decomposition
Aerobic
organic material decay with sufficient oxygen ; oxides are produced
decay products
CO2
H20
NO3-
Anaerobic
involves organisms which do not require oxygen, products in reduced form
foul smelling and toxic
CH4-marsh gas
PH3-phospine
H2S-'rotten egg' gas
Dissolved Oxygen in water
E.5.3
Eutrophilication
excessive addition of nutrients to the water, such as nitrates and phosphates
BOD of water increases
Nitrate ion promotes plant growth through protein synthesis ; also promotes growth of algae
happens in slow moving areas of water
found in fertilizers & detergents

1.plants and algae die aerobically
-increase of nutrients and oxygen levels fall
2. form carbon dioxide and water
3.Anaerobic bacteria take over and produce gases: ammonia & Hydrogen Sulfide
-create unpleasant smells and poison water
4. will cause other deaths and process continues, until everything die
More species will die resulting in more anaerobic decay and the lake becomes devoid of life
Dissolved Oxygen in water E.5.4
Thermal Pollution in water
Source
From industries
addition of heat to water systems
water is removed from rivers in power stations, and returned with temperature increase
concentration of oxygen decreases with rising temperature
Effects
metabolic rate of organisms increase w/ temperature
oxygen concentration is insufficient for survival of fish
biochemical processes may cause organisms to die
spawning, fertilization, and hatching of eggs are sensitive to temperature change - disrupt life cycles
Water Treatment E.6.1
Primary Pollutants
Heavy metals
exist as ions: mercury,lead,nickel,copper,zinc,etc.
Zinc=mining,batteries,paints
mercury=used as fungicide in seed dressings
Lead=paints,leaded gas,car batteries
others=industrial processes
Pesticides
insecticides
DDT,herbicides,etc
Dioxin
waste materials that contain organochlorine compounds are not at required high temperatures
extremely toxic, accumulates in fat and liver cells
cause malformations in fetuses
Polychlrinated biphenyls, PCBs
chemically stable and have high electrical resistance
used in transformers&capacitors
persist in environment and accumulate in fatty tissue
impair learning ability in children
Nitrates
Enter water thru.:
intensive animal farming
artificial fertilizers
acid rain
accumulate because the are soluble
Water Treatment E.6.2
Primary
waste water is passed screens and grids and filter out large insoluble solid objects & floating objects from surface
water passed into sedimentation tank to settle
resulting sludge is removed
flocs are formed by the addition of aluminum sulfate and calcium hydroxide in water and form a precipitate of aluminum hydroxide
Secondary
involves bacterial activity and requires aeration
large blowers are used to bubble-air thru waste water
allow aerobic bacteria to mix with sewage; to oxidize and break down organic matter
process is called activated sludge process
water with decomposed particles passes through a sedimentation tank: large quantities of sludge is collected
part is recycled,other is disposed
Removes about 90% of organic oxygen-demanding wastes and particles
Tertiary
involves specialized chemical, biological, or physical processes
remove remaining organic/inorganic materials: toxic metal ions & nitrate/phosphate ions
Heavy metal ions (lead,mercury,etc) easily removed by precipitation as sulfide salts
then removed by filtration
Water Treatment E.6.3
Obtaining Fresh water
Distillation
sea water is heated
passed into an evacuated chamber and then boils: leaving dissolved compounds in the solutions
steam passed through condensed
cooled by pipes containing more sea water
Sea water is then heated and distilled
Reverse Osmosis
Osmosis: movement of water passing from a dilute to a concentrated solution through a semi-permeable membrane
Semi-permeable membrane allows only the solvent to pass through
Can be reversed:
pressure of 70atm (osmotic pressure) is applied to the more concentrated salt-solution
water passes through the semi-permeable membrane
leaves dissolved salts behind
Soil E.7.1
Soil Degradation: quality of soil is affected and crop production is lowered
Salinization
caused by constant/excess irrigation
water used for irrigation has dissolved salts
when the water evaporates;leaves salts behind
salts will accumulate in the fertile topsoil
effects that lead to dead crops
salts build up to toxic levels
Or die of dehydration because roots are incapable of consuming water from dirty soil
Nutrient Depletion
crops are harvested
nutrients and minerals that were absorbed from soil are REMOVED
farming is now intensive
nutrients can be replenished with the use of artificial fertilizers
Soil Pollution
industrial discharge and improper dumping of toxic waste material cause long term soil pollution
organic soil pollution; from illegal dumping of engine oil , has short term effects
pesticides and fertilizers can disrupt the food chain: destroy species
reduces soil's biodiversity and ruins it
pollutants can run into surface waters and pollute groundwater
Soil E.7.2
Relevance of the soil organic matter in preventing soil degradation
SOM represents organic constituents of the soil
plant and animal tissues: partial decomposition and soil biomass
decomposition of plants produce high molecular mass organic molecules
polysaccharides and proteins
More simple substances
such as amino acids and sugars
Resulting mixture of such is known as humus
Biological Functions
Provides a source of energy (humus)
a source of the essential nutrient elements phosphorus, nitrogen, and sulfur
sustains healthy growth
Physical Functions
helps soil retain moisture
increases soil's capacity to withstand drought conditions
encourages formation of good soil structure
absorbs heat; helps warm the cold soil during spring
Soil E.7.3
Common organic soil pollutants
Hydrocarbons and volatile organic compounds
transportation, solvents, and industrial processes
Agrichemicals
pesticides, herbicide, and fungicides
Polyaromatic hydrocarbons
incomplete combustion of coal,oil,gas, and garbage
PCBs
coolant and insulator in electrical equipment
Organotin Compounds
bactericides and fungicides used in paper, wood, textile
Waste E.8.1
Methods of waste disposal
*Landfill
efficient method to deal with large amounts
may require maintenance as methane is released
Open dumping and Ocean Dumping
Both convenient and inexpensive
contribute to pollution
Incineration and Recycling
Incineration: can be used as a source of energy
Recycling: provides sustainable environment
Both:
expensive
can cause pollutants
Waste E.8.2
RECYCLING
Metals
sorted then melted. Re-used directly or added to purification stage of metals formed from their ores
important for metals that require a lot of energy to produce direct from ore
Paper
sorted into grades,washed to remove inks,made into new paper
used for cardboard and newspapers
Glass
separated by color because of diff. chemical compositions, crushed and melted, then molded into new products
reduces energy costs and needs for limestone
can be recycled many times
Plastics
heated in the absence of air split up in their monomers( pyrolysis), gasification and thermal cracking then repolymerized.
causes less pollutants
use less energy producing new plastics from crude oil
Waste E.8.3
Radioactive Wastes
Low Level
activity level is low half-lives of radioactive isotopes are short
rubber gloves, paper towels, and protective clothing with radioactive exposure
High Level
high activity with long half-lives, waste remains active for a long time
come from spent fuel rods
reprocessing of spent nuclear fuel
Waste E.8.4
Low level waste
discharged straight to the sea and becomes diluted
stored in vast tanks of cooled water (ponds) and loses activity, because decay produces heat
Before discharged into sea: its filtered an ion exchange resin tat removes strontium and caesium ( responsible for radioactivity)
can also keep waste in steel containers inside concrete-lined vaults
High Level Waste
liquid waste is dried in a furnace and then fed into a melting pot together w/ glass making material
molten material put in stainless steel tubes where it solidifies, and kept cool
burying waste in deep remote places(disused mines or in granite rock)
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