IB Chemistry/Environmental Chemistry
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[edit] E1 Air Pollution
[edit] E.1.1 Describe the main sources of carbon monoxide (CO), oxides of nitrogen and sulfur, particulates and volatile organic compounds in the atmosphere.
see chart below
[edit] E.1.2 Evaluate the current methods for the reduction of air pollution.
[edit] E2 Acid Deposition
[edit] E.2.1 State what is meant by the term acid deposition and outline its origins.
Acid deposition: 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.
Natural acid rain: CO2
- NO + H2O --> HNO3
- SO3 + H2O --> H2SO4
- CO2 + H2O --> H2CO3
- NO2 + H2O --> HNO3
- SO2 + H2O --> H2SO3
[edit] E.2.2 Discuss the environmental effects of acid deposition and possible methods to counteract them.
Effects:
• leeches important nutrients from soil such as Ca+2, Mg+2, 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
Methods to counteract:
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
Reduce the amount of fuel burned—alternative energy methods, mass transportation
Alkaline scrubbers: CaCO3 and CaO
Adding CaO or CaOH to lakes neutralizes acidity, increases amount of calcium ions, and precipitates Al from the solution
[edit] E3 Greenhouse Effect
[edit] E.3.1 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.
[edit] E.3.2 List the main greenhouse gases and their sources, and discuss their relative effects.
[edit] E.3.3 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.
[edit] E4 Ozone Depletion
[edit] E.4.1 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
[edit] A.4.2 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.
CF2Cl2 + UV --> Cl◦ + CF2Cl◦ Initiation
Cl◦ + O3 --> ClO◦ + O2
ClO◦ + O◦ --> O2 + Cl◦ or
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
O3 + O◦ --> O2 (net effect)
NO2 + UV --> NO + O◦
O3 + O◦ --> 2O2
[edit] E.4.3 Discuss the alternatives to CFCs in terms of properties.
HCFC Chlorotrifluoromethane 1,1,1,2 tetrafluoroethane 2-methylpropane These molecules maintain the necessary polar structure of CFCs, but without the detrimental chlorine.
[edit] E5 Dissolved oxygen in water
[edit] E.5.1 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.
[edit] E.5.2 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-, PO4-3, SO4-2, 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. Anaerobic decomposition produces H2S, NH3, and PH3, all of which have foul odors. They break down C, N, H, S, and P to form CH4, NH3, H2O, H2S, and PH3.
[edit] E.5.3 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 maste 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:
[edit] E.5.4 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.
[edit] E6 Water Treatment
[edit] E.6.1 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 PCB – Polychlorinated biphenyl: used in transformers and capacitors. Persists in the environment and can accumulate in the liver, also carcinogenic Nitrates—toxic at high levels, especially to babies because they have less stomach acid than adults, can cause blue baby syndrome Heavy metals – Cd, Hg, Pb
[edit] E.6.2 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
• Bar screens remove large objects and debris from the surface of the water and remove floating solids.
• Grit chambers are used to settle out sand, grit, and small objects from the water; these particles are then sent to landfills.
• Sedimentation tanks: Alum (Ca(OH)2 and Al2(SO4)3) precipitates out and carry with them solid suspended particles (flocculate)
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.
• Water-containing decomposed suspended particles are passed through the sedimentation tanks where the activated sludge is collected.
• Some of the sludge is recycled, and some is sent to landfills.
• 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 electrodialysis.
Tertiary Treatment: the removal of remaining organics, nutrients and toxic heavy metal ions
• Heavy metal ions and phosphates are removed by precipitation
• Aluminum sulfate and phosphates are removed by precipitation
• Aluminum sulfate and calcium oxide can be used to remove phosphates
o Al+3 + PO4-3 --> AlPO4(s)
o 3Ca+2 + 2PO4-3 --> Ca(PO4)2(s)
• Heavy metals will precipitate in the presence of hydroxide
o Cr+3 + 3OH- --> Cr(OH)3
• Nitrates are difficult to remove by precipitation because they’re very soluble.
o Anaerobic denitrifying bacteria can reduce nitrates into nitrogen.
o Another method is to pass them into algae ponds where algae uses nitrate as a nutrient
o Anaerobic reactions convert:
- C-->CH4
- SO4-2 --> H2S
- Nitrate --> NH3
- PO4-3 --> PH3
• Methods:
o carbon bed to remove remaining organics
o ion exchange removes remaining soluble ions:
sea water is passed through columns containing natural materials with silicate-type structures (zeolites) or synthetic ion exchange resins.
Hard water contains Ca+2, Mg+2, Fe+2, CO3-2 and SO4+2
These ions are exchanged for H+ and OH-, thus producing pure water
o reverse osmosis removes all impurities
o electrolysis
[edit] E.6.3 Evaluate the process to obtain fresh water from sea water using multi-stage distillation and reverse osmosis.
Distillation: the process that allows the sepatation of a volatile liquid (ex. water) from a non-volatile material (ex. Salt)
Osmosis: the movement of a solvent (water) through a semi-permeable membrane from a low solute concentration to a high solute concentration
Reverse osmosis: a high pressure (6-7 atmospheres) is added to the solution side of a semi-permeable membranemade of cellulose ethanoate, thus forcing water out of the salt solution to the purified water side
[edit] E7 Soil
[edit] E.7.1 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:
a) acidification b) salinization c) contamination d) desertification e) erosion
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.
[edit] E.7.2 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.
Benefits: helps soil to retain moisture, and dark color helps to retain heat and warm the soil during the spring. Also, biologically, humus provides a source of nutrients (such as N, P, and S) to the soil. Chemically, it 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.
[edit] E.7.3 List common organic soil pollutants and their sources
Petroleum hydrocarbons, Agrichemicals, VOC’s (volatile organic compounds), SVOC’s (semi-volatile organic compounds), PCB’s (polychlorinated biphenyls), Polyaromatic hydrocarbons.
[edit] E8 Waste
[edit] E.8.1 Outline and compare various methods for waste disposal.
Method of disposal| Advantages (+)| Disadvantages (-) Landfill| (+)Cheap, large amount of land reused after fill| (-)Leech into soil and ground water, time to settle, maintenance for methane|
Open Dumping| (+)Really really cheap, convenient| (-)Unsightly, disease, odor, ground water pollution|
Ocean Dumping| (+)Cheap, convenient| (-)Toxic in oceans, dangerous to fish, pollutes the sea
Incineration| (+)Source of energy, takes up little space, reduces volume, stable residue| (-)Pollution|
Recycling| (+)Reusing, creating a sustainable environment| (-)Expensive, still some air pollution
[edit] E.8.2 Describe the recycling of metal, glass, plastic and paper products, and outline its benefits.
Items are being reused which conserves the natural resources. Recycle metal, glass, plastic and paper. Aluminum and glass can be re-melted to be reused. Plastic can be dissolved and reformed to create new products. Paper can also be dissolved and used to make new paper, or used as insulation.
[edit] A.8.3 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)
[edit] A.8.4 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 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.
[edit] E9 Ozone Depletion [HL only from now on]
[edit] E.9.1 Explain the dependence of O2 and O2 dissociation on the wavelength of light.
O2 λ = 242 nm O2 +Uv --> 2O◦ short λ, more energy, 2 bond order, more difficult to break
O3 λ= 330 nm O3 --> O2 + O◦ long λ, less energy, 1.5 bond order, easier to break
[edit] E.9.2 Describe the mechanism in the catalysis of O3 depletions by CFCs and NOx
See A.4.2
[edit] E.9.3 Outline the reasons for greater ozone depletion in the polar regions.
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 chemicals produced by man. In the winter (Jun-Sept), NO2 and CH4 are trapped with ClO and Cl2 on the surface of ice. A catalytic reaction on the surface of the ice converts the ClO into Cl2 and HClO forming a “chlorine reservoir.” This temporarily lessens the amount of chlorine released into the atmosphere. When the ice melts in the spring, the chlorine contained in the ice crystals surges into the atmosphere, thus causing the hole in the ozone layer to temporarily expand.
[edit] E10 Smog
[edit] E.10.1 State the source of primary pollutants and the conditions necessary for the formation of photochemical smog.
Smog is a poisonous combination of smoke, fog, air and other chemicals. Photochemical smog occurs in cities where exhaust from internal combustion engines concentrates in the atmosphere. Oxides of nitrogen and hydrocarbon give the air a characteristic yellow/brown color. In the sunlight, these chemicals are converted into secondary pollutants. Smog tends to form in large cities and is favored by a lack of wind. It also occurs more often in bowl-shaped cities because the higher ground surrounding these cities prevents the movement of air. Smogs typically occur where there is a temperature inversion. Normally, the temperature decreases with altitude. Warm air typically rises, takes the pollutants with it, and is then replaced by cleaner cooler air. However, typically in areas which are notorious for smog, the atmospheric conditions cause a layer of still warm air to layer a blanket of cooler air. The trapped pollutants cannot rise, and if the condition persists, the amount of pollutants in the warm air near the ground can rise to dangerous levels.
[edit] E.10.2 Outline the formation of secondary pollutants in photochemical smog.
Photochemical smog is a chemical soup containing hundreds of different chemicals formed in the atmosphere as a result of free radical reactions caused by UV light.
In the early morning hours, a buildup of hydrocarbons (VOCs) and NOx from car exhaust occurs. As the sun comes out, the NO2 absorbs sunlight and forms free radicals.
N2 + O2 --> NO2 (Primary Pollutant)
NO2 + UV --> NO + O◦
These radicals react with O2 to form ozone and water or to form hydroxyl radicals.
O◦ + O2 --> O3 (Secondary Pollutant)
O◦ + H2O --> 2OH◦
Secondary photochemical oxidants react with a variety of molecules and hydrocarbons to form peroxides, aldehydes and ketones.
OH◦ + NO2 --> HNO3
OH◦ + RH --> R◦ + H2O
R◦ + O2 --> ROO◦ (Peroxide Radical)
Chain termination can occur when peroxide radicals react with NO2 to form Peroxyacetylnitrates (PANs) which are irritants to the eyes and skin.
O◦ + HC --> HCO3◦
O3 + HC --> HCO3◦ (Reactive organic peroxides)
HCO3◦ + NO2 --> PANs
[edit] E11 Acid Deposition
[edit] E.11.1 Describe the mechanism of acid deposition caused by the oxides of nitrogen and oxides of sulfur.
NOx and SOx are converted into acid via free radical reactions:
H2O + O3 --> 2HO◦ + O2 or H2O + O3 --> 2HO◦ + O2
The hydroxyl radicals then react directly with SOx and NOx in the presence of water to form acids.
HO◦ + NO2 --> HNO3
HO◦ + NO --> HNO2
HO◦ + SO2 --> HOSO2◦
then HOSO2◦ + O2 --> HO2◦ + SO3
then SO3 + H2O --> H2SO4
[edit] E.11.2 Explain the role of ammonia in acid deposition.
Ammonia gas can to a small extent neutralize the effect of acid rain in the atmosphere by the formation of (NH4)2SO4 and NH4NO3:
NH4+ + 2O2 --> H3O+ +NH3
NH4+ is a strong conjugate acid, so when ammonium salts sink into the ground, the NH4 enters the soil where acidification and nitration can occur.
[edit] E12 Water and Soil
[edit] E.12.1 Solve problems relating to the removal of heavy-metal ions, the phosphates and nitrates from water by chemical precipitation.
Some of the salt in the soil dissolves, however most remains in solid form, thus creating equilibrium. Remember these 5 steps:
1. write a balanced equation
2. find the equilibrium equation (Ksp = [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 Ksp if appropriate.)
[edit] E.12.2 State what is meant by the term cation-exchange capacity (CEC) and outline its importance.
Both SOM and clay have negatively charged particles which will bond to cations such as Ca+2, Mg+2, Na+, K+, Al+3. 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.
[edit] E.12.3 Discuss the effects of soil pH on cation-exchange capacity and availability of nutrients.
If soil is more acidic, there is a higher percentage of acidic cations found in the soil. Soil pH is important because acid cations such as aluminum ions are harmful to the plants. Although soil has some buffering capacity, it is sometimes necessary to add lime to the soil to raise the pH and increase the concentration of basic cations held by the clay and the SOM.
When soil is analyzed, the total concentration of basic cations is compared to the total concentration of acidic cations. Cations such as Al+3 are harmful to plants. Soil pH is important because above pH=5, Al+3 will precipitate out of solution. If there is acid in the rain which lowers the pH of the soil, the Al+3 will no longer precipitate out of the solution. This cation is toxic to plants, so in essence, acid rain would be killing the plants.
[edit] E.12.4 Describe the chemical functions of soil organic matter (SOM).
In addition to the nutrient cations required by the plants and organic matter, SOM can also bind to organic and inorganic compounds in the soil which helps to reduce the negative environmental effects of contaminants such as pesticides, heavy metal ions and other pollutants. SOM contributes to CEC, enhances the ability of soil to buffer changes in pH, and forms stable complexes with cations. SOM also reduces the effect of pesticide, heavy metals, and other pollutants.
