Environmental Chemistry - SL & HL

E.1 - Air Pollution - questions

E.1.1 - What does it mean that a source of pollution is anthropogenic ?

E.1.2 - What are particulates ?

E.1.3 - What are VOCs ?

E.1.4 - What are aerosols ?

E.1.5 - What is anaerobic decomposition ?

E.1.6 - Describe the main sources of carbon monoxide, oxides of nitrogen, oxides of sulfur, particulates and volatile organic compounds in the atmosphere.

E.1.7 - List all the current methods for the reduction of air pollution !

E.1.8 - Explain the methods for the reduction of Carbon Monoxide !

E.1.9 - Explain the methods for the reduction of Nitrogen Oxides !

E.1.10 - Explain the methods for the reduction of Sulfur Oxides !

E.1.11 - Explain the methods for the reduction of Particulates !

E.1.12 - Explain the methods for the reduction of Volatile Organic Compounds !

E.10 - Smog - questions

E.10.1 - What is a free radical ?

E.10.2 - What are the two main types of smog ?

E.10.3 - What are the primary pollutants in the two main types of smog ?

E.10.4 - State the source of these primary pollutants !

E.10.5 - What are the conditions necessary for the formation of photochemical smog ?

E.10.6 - How are the secondary pollutants in photochemical smog formed.

E.10.7 - Explain  

E.10.8 - How can a thermal inversion be created ?

E.10.9 - What are the bad effects of photochemical smog ?

E.2 & E.11 - Acid Deposition - questions

E.2.1 - All rain is naturally acidic. Why ?

E.2.2 - What is the definition of acid rain ?

E.2.3 - State what is meant by the term acid deposition.

E.2.4 - What causes acid deposition ?

E.2.5 - Discuss the effects of acid deposition as well as possible methods to counteract them.

E.11.1 - Describe the mechanism of acid deposition caused by the oxides of nitrogen and oxides of sulfur.

E.11.2 - Explain the role of ammonia in acid deposition.

E.3 - Greenhouse Effect - questions

E.3.1 - Describe the greenhouse effect.

E.3.2 - Why are some gases greenhouse gases and some are not ?

E.3.3 - List the main greenhouse gases and their sources and discuss their relative effects.

E.3.4 - Discuss the influence and effects of increasing amounts of greenhouse gases in the atmosphere.

E.4 & E.9 - Ozone Depletion - questions

E.4.0 - Describe the regions of the atmosphere and where the ozone layer is.

E.9.1 - Explain the dependence of O₂ and O₃ dissociation on the wavelength of light.

E.4.1 - Describe the formation and depletion of ozone in the stratosphere by natural process.

E.4.2 - List the ozone-depleting pollutants and their sources.

E.9.2 - Describe the mechanism in the catalysis of O₃ depletion by CFCs and NO_x.

E.4.3 - Discuss the alternatives to CFCs in terms of their properties.

E.9.3 - Outline the reasons for greater ozone depletion in polar regions.

E.5 - Dissolved Oxygen In Water - questions

E.5.1 - What is ppm ?

E.5.2 - Discuss dissolved oxygen levels in water !

E.5.3 - Explain what BOD is !

E.5.4 - How can one measure BOD ?

E.5.5 - What is the difference between Aerobic and Anaerobic decomposition ?

E.5.6 - Distinguish between aerobic and anaerobic decomposition of organic material in water.

E.5.7 - What does eutrophication mean ?

E.5.8 - Describe the process of eutrophication and its effects.

E.5.9 - Describe the source and effects of thermal pollution in water.

E.6 - Water Treatment - questions

E.6.1 - List the primary pollutants found in waste water and identify their sources.

E.6.2 - Outline primary, secondary and tertiary stages of waste water treatment, and state the substance that is removed during each stage.

E.6.3 - Discuss the methods for tertiary sewage treatment !

E.6.4 - Evaluate the process to obtain fresh water from sea water using multi-stage distillation and reverse osmosis.

E.6.5 - Discuss advantages and disadvantages of different anti-bacterial treatments.

E.7 - Soil - questions

E.7.1 - What does soil consist of ?

E.7.2 - What is SOM ?

E.7.3 - What is humus ?

E.7.4 - Discuss different types of soil degradation !

E.7.5 - How does SOMs prevent soil degradation and discuss the functions of SOMs !

E.7.6 - What are advantages and disadvantages of tillage ?

E.7.7 - List common organic soil pollutants and their sources.

E.12 - Water and Soil - questions

E.12.1 - What is the solubility product constant ?

E.12.2 - What does the value of the K_sp indicate ?

E.12.3 - What factors does K_sp depend on ?

E.12.4 - How can one remove heavy metals in water ?

E.12.5 - How does the addition of more hydrogen sulfide change the concentration of heavy metal ions in a saturated solution ?

E.12.6 - How do you solve problems relating to the removal of heavy-metal ions by chemical precipitation ?

E.12.7 - What is Silica ?

E.12.8 - Why does clay attract positive ions to its surface ?

E.12.9 - Describe cation-exchange in the soil !

E.12.10 - State what is meant by the term cation-exchange capacity (CEC) and outline its importance.

E.12.11 - Discuss the effects of soil pH on cation-exchange capacity and availability of nutrients. What pH does different cations need ?

E.8 - Waste - questions

E.8.1 - Outline and compare various methods for waste disposal.

E.8.2 - Describe the recycling of metal, glass, plastic and paper products, and outline its benefits.

E.8.3 - Describe the characteristics and sources of different types of radioactive waste.

E.8.4 - Compare the storage and disposal methods for different types of radioactive waste.

E.1 - Air pollution

SOURCES

Carbon Monoxide:
Anthropogenic sources which include incomplete combustion of fossil fuels and forest fires, where there is a limited supply of oxygen:


In internal combustions engines in cars it is incomplete combustion of octane:


Nitrogen Oxides:
There are many known nitrogen oxides which can be formed from natural or anthropogenic sources (NO, NO₂, N₂O). Anthropogenic sources of nitrogen oxides in the atmosphere are motor vehicles, industrial burning of fossil fuels, coal and oil fired power stations:



The biggest source is motor vehicles that can produce NO at high temperature:


Sulfur Oxides:
There are two oxides: Sulfur Dioxide (SO₂) and Sulfur Trioxide (SO₃).
The natural sources of Sulfur Dioxide include volcanoes and rotting vegetables. It can also be produced as a secondary pollutant by the oxidation of hydrogen sulfide.

The main human source of sulfur oxide pollution comes from the burning of sulfur-containing fuels:


and from smelting plants which oxidize sulfide ores to metal oxides:

METHODS FOR REDUCTION OF AIR POLLUTION

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Carbon Monoxide:

1. Thermal Exhaust reactor: The heat of the exhaust gases is used to make carbon monoxide react with more air so that it is converted to carbon dioxide: 2CO + O₂ → 2CO₂

2. Catalytic converters: Hot exhaust gases are passed over a platinum-based catalyst which converts carbon monoxide to carbon dioxide: 2CO + O₂ → 2CO₂

3. Lean burn engines: If more air is added to the combustion process in an engine then carbon dioxide is produced instead of carbon monoxide. However, this decreases the power of the engine. Compare incomplete combustion of octane when CO is produced with complete combustion of octane when CO₂ is produced:

Nitrogen Oxides:

1. Recirculation of exhaust gases: By sending the exhaust gases back into the engine one can LOWER its operating temperature and this reduces the amount of nitrogen oxide that is produced.

2. Catalytic converters: Hot exhaust gases are passed over a platinum-based catalyst which not only converts carbon monoxide to carbon dioxide but which also converts nitrogen monoxide into nitrogen gas: 2CO + 2NO → 2CO₂ + N₂

3. Lean burn engines: If more air is added to the combustion process in an engine then there is less CO and nitrogen oxides being produced.

Sulfur Oxides:

1. Removal of sulfur from fossil fuels: The sulphur in coal can be removed by crushing it and washing with water. The heavy metal sulfides then sinks to the bottom.

2. Alkaline scrubbing: Exhaust gases containing SO₂ are mixed with an alkaline such as calcium oxide (CaO) and solid CaSO₃ and CaSO₄ waste is produced.


3. Fluidized bed combustion: Here the coal (instead of the exhaust gases) is mixed with powdered calcium oxide (CaO) before burning it and SO₂ is removed while solid CaSO₃ and CaSO₄ waste is produced.

Particulates:

1. Gravity settling chambers: Dirty air is sent to a chamber where particulates fall to the bottom thanks to gravity.


2. Cyclone separators: The exhaust gases are spun rapidly so that the particulates are thrown outwards were they are collected.

3. Electrostatic precipitators: The dirty air is passed through a high voltage electric field that makes the particulates negatively charged. The air is then sent pass positively charged plates where the particulates gets stuck.

4. Wet scrubbers: Wet scrubbers remove dust particles by capturing them in water droplets. The water droplets with the particulates are then removed.

Volatile Organic Compounds:

1. Catalytic converters: Hot exhaust gases are passed over a platinum-based catalyst which oxidizes the hydrocarbons to carbon dioxide and water.

Photochemical smog and "pea soup smog".

PRIMARY POLLUTANTS:

Photochemical smog: Nitrogen monoxide (NO) that is created when nitrogen and oxygen are combined at high temperature (N₂ + O₂ → 2NO) and VOCs from unburnt petroleum such as RH and RCH₃.

"Pea soup" smog: Sulfur dioxide (SO₂) and carbon particulates (C).

Photochemical smog: Traffic exhaust fumes

"Pea soup" smog: Burning of coal to heat houses (does not happen much anymore).

CONDITIONS REQUIRED:

1. Thermal inversion: Normally air temperature goes down with increasing altitude and since warm air filled with pollution has a lower density it goes up and disappears in the atmosphere. In some cases a thermal inversion can occur over a city. Warm air is then trapped in a layer and acts as a lid that traps the pollutants.

2. Dry sunshine: Sunlight is needed for nitrogen dioxide to participate in photochemical reactions that produces free radicals.

SECONDARY POLLUTANTS:

Remember that the primary pollutant is nitrogen monoxide (NO) and VOCs such as RH and RCH₃

PRODUCTION OF NITROGEN DIOXIDE
The brown colour of photochemical smog is due to the presence of nitrogen dioxide. This secondary pollutant is formed by the direct oxidation of nitrogen monoxide by oxygen:
2NO + O₂ → 2NO₂

THE PHOTOCHEMICAL REACTION
The photochemical reaction begins with the absorption of light by the secondary pollutant nitrogen dioxide, (which builds up during rush hour traffic as the primary pollutant nitrogen monoxide is oxidized) which breaks it up so that a free oxygen radical is formed:
NO₂ --(UV light)--> NO + O-radical

PRODUCTION OF OZONE
The reactive oxygen atom then reacts with molecular oxygen to produce ozone.
So the O-radical from the production of nitrogen dioxide reacts with dioxygen to create ozone:
O₂ + O-radical → O₃
The Ozone and Oxygen causes Oxidation.

A thermal inversion occurs naturally in the stratosphere. Ozone absorbs high energy UV radiation which leads to an increase in the kinetic energy of the gas particles and thus the temperature of the gas molecules.

Effects of smog:

1. Health effects (eyes and lungs).

2. Corrosion of metals and stonework.

3. Reduced visibility.

4. Effects on plants due to toxic pollutants.

All rain is acidic because carbon dioxide in air reacts with water so that carbonic acid is produced:
CO₂ + H₂O → H₂CO₃

Acid rain has a pH < 5.6 .

Acid deposition refers to the process by which acidic particles, gases and precipitation leave the atmosphere. It is a more general term than acid rain and extends to pollution in the absence of water. It is divide up into:

Wet deposition: acid rain, snow and fog.

Dry deposition: acid gases and particles.

Acid deposition is caused by sulfur dioxide from power plants and nitrogen oxide from cars.

SULFUR DIOXIDE

Sulfur dioxide can be oxidized to sulfuric acid in the presence of sunlight and aerosols that acts as catalysts:


NITROGEN DIOXIDE

Nitrogen dioxide dissolves in water to form a mixture of nitrous acid and nitric acid:

Acid deposition has many effects on materials, plant life, water and human health.

EFFECTS ON MATERIALS
The building materials marble and limestone are both forms of calcium carbonate and when sulfur dioxide from dry deposition and sulfuric acid from acid rain react to form calcium sulfate. Calcium sulfate is more soluble than calcium carbonate, so it washes out of the limestone. It also has a greater molar volume than calcium carbonate so its formation causes expansion and stress in the stonework. Acid rain also corrodes metals.

EFFECTS ON PLANT LIFE
Acid rain damages plant life as it washes out important nutrients such as Mg+ as well as Ca⁺ and K⁺ ions from the soil and releases the dangerous Al³⁺ ions from rocks into the soil. Without these essential nutrients, plants starve to death.

EFFECTS ON WATER
Acidic rain causes a number of lakes to become fishless or "dead". Fishes such as trout and perch cannot survive at pH values below 5. We call rivers dead when their pH is at 4.0 due to dangerous Al³⁺ ions "trapped" in the rocks are dissolve under acidic conditions.
The nitric acid present in acid rain poses a particular problem as the nitrates present can lead to eutrophication.

EFFECTS ON HUMAN HEALTH
Breathing air which contains acid gases irritates the respiratory tract from mucous membranes in the nose and throat to the lung tissue. This increases the risk of respiratory illnesses such as asthma, bronchitis and emphysema. It can also cause irritation to the eyes.

Control Strategies

NITRIC ACID IS FORMED FROM NITROGEN DIOXIDE

Ammonia is present in the atmosphere from both natural and synthetic sources. It is produced naturally by animal livestock and by the action of certain bacteria and also from artificial fertilizers. The weak base ammonia reacts with the strong acids present in acid to produce ammonium sulfate and ammonium nitrate.

1. The solar radiation that hits the earth has visible and ultraviolet wavelengths.

2. This solar radiation is:
a) reflected back into space
b) absorbed by gases in the atmosphere
c) warming the earth's surface.

3. When the earth's surface is heated up it radiates infrared radiation with longer wavelength.

4. This infrared radiation is:
a) radiating heat into space
b) warming up some gases in the atmosphere (the greenhouse gases).

5. When the greenhouse gases are heated up they also radiate infrared radiation.

6. This infrared radiation is:
a) radiating heat into space
b) radiating heat back to the earth's surface.

7. The process of the greenhouse gases preventing a part of the infrared radiation from the earth's surface to go out into space is called the greenhouse effect.

Greenhouse gases allow the passage of incoming solar short-wave radiation but absorb the longer-wavelength radiation from the earth.

In order for them to do this they have to have covalent bonds with the same vibration frequency as the frequency of the infrared radiation.

Water - H₂O

Increasing greenhouse gases could increase the earth’s natural greenhouse effect and lead to global warming. In the last 50 years the amount of CO₂ has increased and the average temperature has increased. If this continuous it could have the following effects:

1. The sea-level rise because of thermal expansion (warm water has a larger volume than cold water).
2. The sea-level rise because of melting of the polar ice caps and glaciers.
3. Changes in crop yield due to warmer climate.
4. The deserts will become larger.
5. Fish living in cold waters will lose its habitat.
6. Some animal and plant species may become extinct (lower biodiversity).
7. More extreme weather with more cyclones and flooding.

The energy of a light photon is given by E = hf = hc/λ so a small wavelength (λ) means high energy.

O₂ has a bond order of 2 (a double bond), therefore it is more difficult to break. This means that it will require more energy to do so, so a shorter wavelength (<242 nm).

O₂ + UV (<242 nm) → 2O*

O₃, due to its resonant structure, has a bond order of 1.5, meaning it is less difficult to break than the double bond in O₂. This means that it will require less energy to do so, meaning a longer wavelength (<330 nm).

O₃ + UV (<330 nm) → O₂ + O*

The ozone layer occurs in the stratosphere between 12km and 50 km from the surface of the Earth. Stratospheric ozone is in dynamic equilibrium with oxygen and is continually being formed and decomposed. When this happens dangerous ultraviolet light is being absorbed and the stratosphere is warmed up. Both are essential for life on earth.

Formation:
O₂ + UV → 2O*
O₂ + O* → O₃

Depletion:
O₃ + UV → O₂ + O*
O₃ + O* → 2O₂

The Chapman cycle:

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CFCs - Chlorofluorocarbons: These were previously used as in aerosols, refrigerants, foaming agents, plastics and cleaning solvents. Unfortunately, these molecules can destroy the ozone layer by producing free Cl-radicals that acts as catalysts in a process where ozone is turned into oxygen gas. Because they are catalysts the Cl-radicals themselves are not destroyed in the process and one Cl* can destroy many O₃.

NO_x - Nitrogen oxides: These are produced by cars and jet aircrafts. NOx* radicals can also react catalytically with O₃.

FREON - CCl₂F₂

0. Chloro Fluoro Carbons - CFCs: Non-flammable. Non-toxic. Used in aerosols and as refrigerants in refrigerators and air conditioners. The Cl-atom destroys the ozone layer.

1. Hydro Carbons: Flammable. Toxic. Used in refrigerators. The Cl-atom has been replaced by a H-atom and the hydrocarbons do not destroy the ozone layer.

2. Fluoro Carbons: Non-flammable. Non-toxic. The strong C-F bond makes them stable to ultraviolet light. Do not destroy the ozone layer.

3. Hydro Fluoro Carbons - HFCs: Non-flammable. Low toxicity. No Cl-atoms. Do not destroy the ozone layer.

4. Hydro Chloro Fluoro Carbons - HCFCs: Non-flammable. Moderate toxicity. They contain Cl-atoms but most molecules are destroyed in the lower atmosphere before reaching the ozone layer. Destroy the ozone-layer 30 times less than CFCs.

A hole in the ozone layer is found above Antarctica. Depletion is seasonal with the largest holes occurring during the early spring (October/November). This decrease is due to chemicals produced by man.

In the winter (Jun-Sept), clouds of ice particles are formed in the stratosphere. The ice particles contains molecules that contains Cl. For example HCl. A catalytic reaction on the surface of the ice produces Cl₂ which forms a “chlorine reservoir.”

When the sun comes out at the end of winter in October the sunlight makes the chlorine molecules photo-dissociate:
Cl₂ → Cl* + Cl*

These Cl atoms destroys the ozone layer in the usual way and creates the ozone hole.

ppm stands for Parts Per Million. In case of pollutants in water this means the number of grams of pollutants in 1000 kg of water or in one m³ of water.

The level of dissolved oxygen in water is one of the most important indicators of water quality. The maximum amount of oxygen one can have in water is 9 ppm at 20 ^oC. Fish needs 3 ppm to survive.

BOD = Biological Oxygen Demand. It is a measure of the dissolved oxygen (in parts per million) required to decompose all organic waste and ammonia in water biologically over a 5 day period at 20C. The wastes demand oxygen to be decomposed. It measures the level of organic pollution in water. Fish cannot survive when the BOD is greater than the oxygen content.

One measure the dissolved oxygen in a water sample (I) and let it stay in a dark place for 5 days and then measure the dissolved oxygen level again (F). The BOD is then calculated as:

BOD = I-F where I = initial oxygen level in ppm, F = final oxygen level in ppm.

If one saturates the sample with oxygen to start with one knows that I = 9 ppm.

Aerobic decomposition means decomposition with oxygen and Anaerobic decomposition means decomposition without oxygen.

Aerobic Decomposition: If there’s sufficient oxygen present in the water, organic matter is broken down by microbes aerobically. The organic compounds are oxidized.

Anaerobic Decomposition: If there’s an insufficient amount of oxygen present in the water, organic matter is decomposed by microbes that don’t require oxygen. The organic compounds are reduced.

CARBON:
Aerobic decay product: CO₂
Anaerobic decay product: CH₄

NITROGEN:
Aerobic decay product: NO₃^-
Anaerobic decay product: NH₃

SULFUR:
Aerobic decay product: SO₄^2-
Anaerobic decay product: H₂S

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 dissolved oxygen 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.

The Eutrophication Process:
Nutrients increase → Plant growth increases → BOD increases → Dissolved oxygen decreases → Stagnant of body of water

If water is heated by for example electric power stations, the solubility of oxygen in the water decreases so the amount of dissolved oxygen goes down.. At the same time, fish are cold-blooded, so as the temperature of the water increases, their metabolism increases and they need more oxygen. So fish and other organisms may die if water is heated.

Dioxins:
Chemical structure:  
Source: Dioxin is formed by burning chlorine-based chemical compounds with hydrocarbons. This happens for example when rubbish with PVC plastic is burned.

Health hazard: Extremely toxic. Cancer and damage to liver, heart and memory.

Environmental hazard: ?

Pesticides:
Chemical structure of DDT:  
Source: Pesticides include insecticides, herbicides, fungicides and are spread by farmers.

Health hazard: Neurological, birth defects, fetal death, and neurodevelopmental disorder.

Environmental hazard: DDT is very stable and build up in animals at the top of the food chain. It is disastrous for birds.

Polychlorobiphenyls (PCBs):
Chemical structure of PCB:  
Source: used in transformers and capacitors.

Health hazard: Accumulate in fatty tissue. Carcinogenic. Impair learning in children.

Environmental hazard: PCBs are very stable compounds and do not decompose readily so they build up in the environment.

Nitrates:

Chemical structure:   NO₃^-

Source: from fertilisers or acid rain.

Health hazard: They are toxic at high levels, especially to babies because they have less stomach acid than adults, can cause blue baby syndrome.

Environmental hazard: ?

Heavy metals:

Primary Treatment: the removal of large solids

Tertiary Treatment

In distillation, sea water is pumped into a reservoir, at which point it is heated. It is then passed into an evacuated chamber where it boils. The salt is left as a salty brine, which is then pumped out while the steam goes to a condenser which is cooled by pipes with sea water. This cooling water is heated by this and can then be used in the distillation.


Another method used is the reverse osmosis system. Osmosis is the movement of water from a dilute to a concentrated solution through a semi-permeable membrane which allows the solvent but not the solutes to pass through it. In the reverse osmosis system, water is pumped through the semi-permeable membrane at very high pressure. So this is the opposite of a normal osmosis system (in which water would flow from low concentration to high concentration). If the high pressure is applied to salt water, the water passes through the membrane and leaves the salt behind.

Typically soil has a layer of dead plant and animal matter on top of it. Under the dead plants is the humus layer. The topsoil layer (horizon) contains most of the living material + organic matter from decomposition of dead organisms. The subsoil layers contain inorganic material from the parent rock.

The term soil organic matter (SOM) refers to all the organic matter in soil including living matter (active roots, living organisms) and non-living components (root exudates, decomposing plant and animal material, humus and charcoal).

Humus refers to any organic matter that has reached a point of stability, where it will break down no further and might, if conditions do not change, remain as it is for centuries, if not millennia. So it is the end-product of decomposition. Humus should be differentiated from decomposing organic matter in that the latter is rough-looking material, with the original plant remains still visible, whereas fully humified organic matter is uniform in appearance (a dark, spongy, jelly-like substance) and amorphous in structure, and may remain such for millennia or more.

One should distinguish between:

1. Decomposing organic matter.

2. Humus which is what is left after the decomposition has finished.

3. SOM which is all Soil Organic Matter = Living organic matter + Dead and decomposing organic matter + Humus.

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 farming, desertification, erosion and pollution.

There are different forms of soil degradation: acidification, salinization, nutrient depletion, chemical contamination (pollution) and erosion.

Salinization

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.

Biological functions

TILLAGE

ADVANTAGES: The objectives of tilling the soil include seedbed preparation, water and soil conservation and weed control. This increases food production.

DISADVANTAGES: Tillage reduces SOMs which is a form of soil degradation. Therefore one has to add manure or sewage sludge to increase the SOM levels.

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Here is a list of common soil pollutants and their major sources:

Agrichemicals: from pesticides, herbicides and fungicides.

Polyaromatic hydrocarbons: from incomplete combustion of coal, oil, gas, wood and garbage.

Polychlorinated biphenyls (PCBs): from transformers and generators (they are used as a coolant).

Organotin compounds (organic chemicals that contains tin): from bactericides and fungicides (used in paper, wood, textile and anti-fouling paint).

Hydrocarbons and other VOCs: from transport, solvents and industrial processes.

Assume that you have a salt (MS) in a water solution so that it contains metal ions (M²⁺ = Hg²⁺ or Pb²⁺ or Zn²⁺) and non-metal ions such as sulfide ions (S^2-).

At some point there will be equilibrium between the salt in solid form and the ions in the solution:
MS(s) ↔ M²⁺(aq) + S^2-(aq)

The solubility product constant is then defined as K_sp = [M²⁺] [S^2-]

A small K_sp means that the salt has a low solubility.

K_sp depends only on the temperature.

Assume you have heavy metal ions (Hg²⁺ or Pb²⁺ or Zn²⁺) in waste water and you want to remove them.

If you add hydrogensulfide (H₂S) to the solution you will create a metal salt (HgS):
Hg²⁺(aq) + H₂S(aq) → HgS(s) + 2H⁺(aq)

Not all the Hg will turn into salt. Instead one will reach an equilibrium with
HgS(s) ↔ Hg²⁺(aq) + S^2-(aq)

The more S^2- one puts in the more one will push the equilibrium to the left and the more salt is produced.

MS(s) ↔ M²⁺(aq) + S^2-(aq)

K_sp = [M²⁺] [S^2-]

[M²⁺] = K_sp / [S^2-]

This means that if one increases the concentration of S^2- the concentration of metal ions M²⁺ has to go down.

Salt in the water dissolves, however if some remains in solid form, it will eventually be in equilibrium. Remember these 5 steps:

1.Write a balanced equation
2.Find the equilibrium equation (K_sp = [ion conc.][ion conc.])
3.Identify the direction of the change in equilibrium
4.ICE it! Initial, Change, Equilibrium
5.Plug the E line into the equilibrium equation and solve for x, then follow through to find what the question is asking for (i.e. plug back into 2x if concentration, or find _sp if appropriate.)

Silica is another name for Silicon dioxide SO₂.

One Silicon atom does NOT double bond with two oxygen atoms as one would expect. Instead each Silicon atoms bonds with 4 Oxygen atoms creating huge crystals. This is called a giant covalent structure. It continues on and on in three dimensions. It is not a giant single molecule, because the number of atoms joined up in a Silica crystal is completely variable - depending on the size of the crystal.



Another example of a giant covalent structure is the diamond where each Carbon atom is bonded to four other Carbon atoms:

Clay consists of giant covalent Silica structures. However, a large part of the Silicon atoms in the structure are replaced by Al³⁺ ions. This creates a surplus of electrons which attracts positive ions (Na⁺, K⁺, Ca²⁺, Mg²⁺) to its surface.

There are two parts of the soil that can exchange cations (positive ions) with other cations that are in the water of the soil:

CLAY: The cations that are on the surface of the clay are not held tightly and so they can be exchanged. Example:
K⁺(clay) + H⁺(aq) ↔ H⁺(clay) + K⁺(aq)

HUMUS: In humus (SOMs) there is weak organic acids and their salts which makes cation exchange possible. Example:
RCOONa(humus) + H⁺(aq) ↔ RCOOH(humus) + Na⁺(aq)

As plants take up nutrients from the soil, cation exchange take place and the nutrient cations are replaced by hydrogen ions:

Cation-exchange capacity (CEC): Both SOM and clay have negatively charged particles which will bond to cations such as Ca⁺², Mg⁺², Na⁺, K⁺, Al⁺³ and the amount of positively charged cations that soil can hold is called the cation-exchange capacity (CEC). A larger CEC indicates a larger capacity to hold cations. These cations are exchanged with cations such as hydrogen on the root hairs of a plant to provide it with nutrients. CEC is defined as the number of moles of singly charged positive ions that can be held in 1 kg of soil.

Importance: A large CEC value means the soil can absorb many cations and make them available to plants so a high CEC value means more nutrients for the plants.

The growth of plants depends on the amount of nutrients which in turn depends on the pH. The pH of soil varies between 3 to 9 but a pH between 6 and 6.5 (slightly acidic) gives the best availability of most nutrients.

The exception is Al and Fe cations that are highly acidic and only available at low pH ( < 5.5 ).

Method of disposal | Advantages (+) | Disadvantages (-)

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-moulded --> re-used.
Glass: sorted (colour) --> washed --> crushed --> re-moulded --> re-used.
Plastics: sorted --> degraded to monomers (through pyrolysis, hdrogenation, gasification and thermal cracking) --> repolymerised --> 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.

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)

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 glass-making 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.

Particulates are solid particles of carbon or dust, or liquid droplets of mist or fog suspended or carried in the air. They are large enough to be seen. As many particulates are polar, they attracted into water droplets and form aerosols.

An aerosol is a gaseous suspension of very small particles of a liquid.

Volatile Organic Compounds (or VOC's) are organic chemicals that have a high vapor pressure at room-temperature conditions. Their high vapor pressure results from a low boiling point, which causes large numbers of molecules to evaporate or sublimate from the liquid or solid form of the compound and enter the surrounding air.

Free Radicals are atoms, molecules or ions with unpaired electrons on an open shell configuration. The unpaired electron cause radicals to be highly chemically reactive.

Eutrophication refers to the excessive addition of nutrients. The word derives from Greek for "well nourished".

Anaerobic decomposition is the decomposition of organic matter in the absence of oxygen.

Anthropogenic sources are those caused by humans. As opposed to natural sources.