IB Chemistry/Environmental Chemistry
Air Pollution
Describe the main sources of carbon monoxide (CO), oxides of nitrogen and sulfur, particulates and volatile organic
compounds in the atmosphere.
Evaluate the current methods for the reduction of air pollution.
Acid Deposition
State what is meant by the term acid deposition and outline its origins.
Acid deposition is the process by which acidic particles, gases, and precipitation leave the atmosphere. Rain is
naturally acidic with a pH of about 5.6 due to dissolved CO2, but acid rain has a pH below 5.6 and is caused by
oxides of sulfur and nitrogen. These oxides react with rain water to form acids:
CO2 + H2O → H2CO3
NO + H2O → HNO3
NO2 + H2O → HNO3
SO2 + H2O → H2SO3
SO3 + H2O → H2SO4
Discuss the environmental effects of acid deposition and possible methods to counteract them.
Some effects of acid deposition include:

Leeches important nutrients from soil such as Ca2+, Mg2+, and K+ which can lead to reduction in chlorophyll and
therefore the ability to photosynthesize.

Can kill aquatic life in lakes and rivers, and nitrates can lead to eutrophication.

Erosion of stone which contains calcium carbonate (such as marble)

Irritation of the mucus membranes increases the risk of respiratory illness such as asthma, bronchitis and
emphysema
Acid deposition can be counteracted by lower the amount of sulfur and nitrogen oxides with:

Improved engine design

Catalytic converters

Removing sulfur before, during, and after use of sulfur-containing fuels
It can also include the reduction of the amount of fuel burned, alternative energy methods and the use of mass
transportation. Alkaline scrubbers, such as CaO, may also be used to remove the oxides.
Adding CaO or Ca(OH)2 to lakes may also neutralize acidity, increases amount of calcium ions, and precipitate
Al from the solution.
Greenhouse Effect
Describe the greenhouse effect.
Greenhouse gases allow the passage of incoming solar short-wave radiation but absorb the longer-wavelength
radiation from the earth. Some of the absorbed re-radiation is re-radiated back to earth.
List the main greenhouse gases and their sources, and discuss their relative effects.
Gas
Source
Heat trapping compared to
CO2
Contribution to global
warming
CH4




Anaerobic decay
Termites
Rice fields
Petroleum and natural gas production
30x
18%
H2O


Evaporation
Combustion of hydrocarbons
0.1x
>1%
CO2





Combustion of fossil fuels, biomass
Decay of plants and animals
Oxidation of soil
Forest fires
Internal combustion engines
1x
50%
N2O


Bacterial action
Fertilizers
150x
6%
O3

Secondary pollutant smog
2000x
12%
CFCs


Refrigerants
Propellants
2500-10000x
14%
Discuss the influence of increasing amounts of greenhouse gases on the atmosphere.
Increasing greenhouse gases could increase the earth’s natural greenhouse effect and lead to global warming.
The oceans may expand with an increase in temperature, and polar ice caps may melt. Also, changes in
temperature and precipitation, thus leading to changes in crop production may result from a possible global
warming.
Ozone Depletion
Describe the formation and depletion of ozone in the stratosphere by natural processes.
The ozone layer occurs in the stratosphere between 12kn and 50 km from the surface of the Earth. Stratospheric
ozone is in dynamic equilibrium with oxygen and is continually being formed and decomposed.
Formation:
O2 + UV → 2O◦
O2 + O◦ → O3
Depletion:
O3 + UV → O2 + O◦
O3 + O◦ → 2O2
List the ozone-depleting pollutants and their sources.
Chlorofluorocarbons were previously used as refrigerants, propellants, and cleaning solvents. Unfortunately,
these molecules can destroy the ozone layer.
Initiation:
CF2Cl2 + UV → Cl◦ + CF2Cl◦
Propagation:
Cl◦ + O3 → Cl◦ + O2
ClO◦ + O◦ → O2 + Cl◦
Termination:
ClO◦ + ClO◦ → 2Cl◦ + O2
In this way, the CFC is acting as a catalyst—destroying the existing O3 and preventing the formation of O3
without being consumed. NOx can also react catalytically with O3.
NO + O3 → NO2 + O2
NO2 + O◦ → NO + O2
Net effect: O3 + O◦ → 2O2
NO2 + UV → NO + O◦
O3 + O◦ → 2O2
Discuss the alternatives to CFCs in terms of properties.
Some options include HCFCs (Hydrochlorofluorocarbons), HFCs (Hydro fluorocarbons), and other nonchlorine containing hydrocarbons. Examples include: Chlorotrifluoromethane, 1,1,1,2-tetrafluoroethane, and 2methylpropane. By replacing some of the chlorine atoms with fluorine, which requires more energy in breaking
the bond, there is less radicalization taking place.
Dissolved oxygen in water
Outline biochemical oxygen demand (BOD) as a measure of oxygen-demanding wastes in water.
BOD is the measure of dissolved oxygen (in parts per million) required to decompose all organic waste and
ammonia in water biologically over a 5 day period at 20⁰C. The wastes demand oxygen to be decomposed.
Distinguish between aerobic and anaerobic decomposition of organic material in water.
If there’s sufficient oxygen present in the water, organic matter is broken down by microbes aerobically. This
oxidizes the C, N, P, S, and H to produce CO2, NO3- PO43-, SO42-, and H2O.
If there’s an insufficient amount of oxygen present in the water, organic matter is decomposed by microbes that
don’t require oxygen. They break down C, N, S, and P to form CH4, NH3, H2S, and PH3.
Element Anaerobic product Aerobic product
C
CO2
CH4
N
NO3-
NH3
P
PO43−
PH3
S
SO42−
H2S
Describe the process of eutrophication and its effects.
Nitrates from fertilizers and phosphates from detergents can accumulate in lakes and streams. These nutrients
can increase the growth of plants and algae. This impacts the BOD because if plant growth increases too fast
and the DO is not sufficient to decompose all organic material and waste by aerobic decomposition, anaerobic
decomposition will occur. More species will die as a result of the anaerobic decay. The lake will become
stagnant and devoid of life.
Eutrophication:
Describe the source and effects of thermal pollution in water.
If water is heated, the solubility of oxygen in the water decreases. At the same time, fish are cold-blooded, so as
the temperature of the water increases, their metabolism increases. This forms a dilemma since the DO
decreases as the BOD increases. This process helps to contribute to red tide.
Water Treatment
List the primary pollutants found in waste water and identify their sources.
Waste water contains floating, suspended, and colloidal organic matter, dissolved ions with a wide range of
microorganisms and bacteria as well as miscellaneous grit, trash, grease and other chemicals.
Pesticides: DDT, herbicides, paraquat, fungicides
Dioxins: formed when organochlorine compounds are not incinerated at high enough temperatures. Very toxic
and can accumulate in the liver
Polychlorobiphenyls (PCBs): used in transformers and capacitors. Persists in the environment and can
accumulate in the liver, also carcinogenic
Nitrates: from fertilizers or acid rain. they are toxic at high levels, especially to babies because they have less
stomach acid than adults, can cause blue baby syndrome
Heavy metals: Cadmium (Cd) (from rechargeable batteries), Mercury (Hg) (from batteries), Copper (Cu) (from
household plumbing), Lead (Pb).
Outline primary, secondary, and tertiary stages of waste water treatment, and state the substance that is removed
during each stage.
Primary Treatment: the removal of large solids
Primary treatment removes 60% of the solid material and a third of the BOD waste in the water. However,
afterwards the water will still not be safe to drink.
Primary treatment involves running water through the below mechanisms in order:
1. Bar screens: these remove large objects and debris from the surface of the water and remove floating solids.
2. Settling tanks: these are used to settle out sand, grit, and small objects from the water (as they sink to the
bottom); these particles are then sent to landfills.
3. Sedimentation tanks: Alum (Ca(OH)2 and Al2(SO4)3) precipitates out and carry with them solid suspended
particles (this process is called flocculation).
Secondary Treatment: the removal of organic materials using microbes



Activated sludge process:
o Air is bubbled into sewage which has been mixed with bacteria-laden sludge.
o Aerobic bacteria oxidize organic material in the sewage.
o Water-containing decomposed suspended particles are passed through the sedimentation tanks where
the activated sludge is collected.
o Some of the sludge is recycled, and some is sent to landfills.
o This removes 90% of organic oxygen-demanding waste, 50% of nitrogen, and 30% of phosphates
Effluent is then treated with chlorine or ozone to kill pathogenic bacteria before releasing the water to lakes or
rivers
Other methods include a carbon bed to remove the remaining organics, ion exchange which removes many
soluble ions, reverse osmosis and electro-dialysis.
Tertiary Treatment: the removal of remaining organics, nutrients and toxic heavy metal ions

Heavy metal ions and phosphates are removed by precipitation, for example, nickel:
Ni2+(aq) + OH−(aq) → Ni(OH)2 (s)

Aluminum sulfate and phosphates are removed by precipitation:
Al3+(aq) + PO3−4 (aq) → AlPO4 (s)
Al3+(aq) + SO2−4 (aq) → Al2(SO4)3 (s)

Aluminum sulfate and calcium oxide can be used to remove phosphates:
3CaO(aq) + 2PO3−4 (aq) + 3H2O → Ca3(PO4)2 (s) + 6OH−(aq)

Heavy metals will precipitate in the presence of hydroxide:
Cr3+(aq) + 3OH−(aq) → Cr(OH)3 (s)

Nitrates are more difficult to remove by precipitation because they’re quite soluble, however, there are some
ways to remove them:
o Anaerobic denitrifying bacteria can reduce nitrates into nitrogen
2NO2−3 (aq) → N2 (g) + 3O2 (g)

Another method is to pass them into algae ponds where algae uses nitrate as a nutrient
Other treatments
There are also a few other treatments, such as distillation. In distillation, sea water is pumped into a reservoir, at
which point it is heated. The pure water which evaporates condenses on the cool water being pumped in,
leaving a salty brine, which is then pumped out.
Another method used is the reverse osmosis system. In this type of system, there is a semi-permeable membrane
which the water is pumped through, thereby being the opposite of a normal osmosis system (in which water
would flow from low concentration to high concentration).
Soil
Discuss salinization, nutrient depletion and soil pollution as causes of soil degradation.
Soil is a complex mixture of inorganic and organic materials, including living organisms. Soil degradation
lowers crop production and is caused by a variety of human factors including; acidification, salinization,
contamination, desertification, erosion.
We are interested in the following factors:

Salinization: the result of continual irrigation of soil; In poorly drained soil, after the water evaporates, salt is left
behind, and plants die because they are unable to take water away from the salty soil.

Nutrient Depletion: plants remove nutrients and minerals from soil as they grow. If not properly managed by
crop rotation or fertilizing the soil, nutrients will become depleted.

Soil Depletion: caused by improper use of pesticides and over-fertilizing; chemicals can disrupt the food web,
reducing soil’s biodiversity, and ultimately ruining the soil.
Describe the relevance of the soil organic matter (SOM) in preventing soil degradation, and outline its
physical and biological functions.
SOM refers to the organic constituents in the soil. This includes plant and animal tissue, partial decomposition
products and soil biomass. Chemicals found in SOM from decomposition of plants are high molecular mass
organics such as Polysaccharides, proteins, sugars, and amino acids. The end product of decomposition is
humus. Humus is the organic decomposition layer which plants live on. It has a mixture of simple and more
complex organic chemicals from plants, animals, or microbial origin.
How SOM prevents soil degradation:




helps soil to retain moisture, and dark color helps to retain heat and warm the soil during the spring.
contains mineral nutrients that it exchanges with plants (at the roots).
it improves the soil structure
it reduces soil erosion.
Biological functions of SOM:

Humus provides a source of nutrients (such as N, P, and S) to the soil. Nitrogen provides proteins, Phosphorus
provides enzymes, and Sulfur provides amino acids.
Physical functions of SOM:

SOM can retain several times its mass of water (like a sponge). Therefore more SOM means more water, making
the soil more stable.
Chemically, SOM acts like clay with cation exchange capacity (CEC): it contains active sites that enable it to
bind to nutrient cations. Humus also has the ability to maintain a constant pH by acting as a buffer.
List common organic soil pollutants and their sources
Here is a list of common soil pollutants and their major sources:
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

Agrichemicals: from pesticides, herbicides and fungicides.
Poly-aromatic hydrocarbons: from incomplete combustion of coal, oil, gas, wood and garbage.
Polychlorinated biphenyls (PCBs): from transformers and generators (they are used as a coolant).
Organo-tin compounds: from bactericides and fungicides (used in paper, wood, textile and anti-fouling paint).
Hydrocarbons and other VOCS: from transport, solvents and industrial processes.
Waste
Outline and compare various methods for waste disposal.
Method of disposal | Advantages (+) | Disadvantages (-)
Landfill | (+) Cheap, leaves large amount of land reused after fill | (-) Leaches into soil and ground water; needs
time to settle, maintenance for methane
Open Dumping | (+) extremely cheap, convenient | (-) Unsightly; causes disease, odor, ground water pollution
Ocean Dumping | (+) Cheap, convenient | (-) Toxic in oceans, dangerous to fish, pollutes the sea
Incineration | (+) Provides source of energy, takes up little space, has stable residue | (-) Causes air pollution
Recycling | (+) Produces new raw materials, creates a sustainable environment | (-) Expensive, still causes some
air pollution
Describe the recycling of metal, glass, plastic and paper products, and outline its benefits.
There are 3 main benefits to recycling that apply to metal, glass, plastic and paper. These are:



Saving raw materials
Saving energy (as energy is required to produce new materials)
Saving space (in landfills)
In addition, glass and metals can be constantly recycled (over and over) without much degradation in the
material.
The processes of recycling for each of the materials are as follows:




Metals: sorted (by magnets or flotation) --> melted --> re-molded --> re-used.
Glass: sorted (color) --> washed --> crushed --> re-molded --> re-used.
Plastics: sorted --> degraded to monomers (through pyrolysis, hydrogenation, gasification and thermal cracking)
--> re-polymerized --> re-used.
Paper: mixed into water and chemicals (to form pulp) --> pulp is spun (removes staples/paper clips) --> washed
to remove ink --> dried and bleached white --> re-used.
Describe the characteristics and sources of different types of radioactive waste.
Low-level waste includes any gloves, paper towels or protective clothing that has been used in areas where
radioactive materials have been handled. The level of activity is low and the half lives are short. This waste
generally comes from hospitals due to cancer treatment, and includes any items that have come in contact with
the radioactive material.
High-level waste is generated by nuclear power plants and the military. It demonstrates a high level of activity
and generally isotopes have long half-lives. High-level waste also comes from fuel rods or the reprocessing of
spent fuel (power companies, military)
Compare the storage and disposal methods for different types of radioactive waste.
The nuclear decay process produces heat and energy. Low-level waste is stored in cooling ponds until the
activity has fallen to safe levels (generally a few years). The water is then passed through ion exchange resins
which remove isotopes responsible for activity. The water is then diluted and released into the sea.
High-level waste takes thousands of years to lose activity. Much of spent radioactive fuel is recovered for reuse.
If not, the waste, generally a liquid mixture of radioactive waste, is converted into a solid glass component
through a vitrification process: The waste is dried in a furnace and fed into a melting pot together with glassmaking material (sand). The molten material is then poured into a stainless steel container where it cools and
solidifies. These containers will remain radioactive for thousands of years. The containers are currently stored
in concrete vaults, but it is hoped that they will later be transferred to salt chambers one day to be stored for
thousands of years until the activity falls to safe levels.