Download Chemistry and the Environment

Chemistry and the Environment
Chapter 1: Acid Deposition
Chapter 2: The Chemical Legacy of Human Activity
Acid Deposition
1.1 Products of Combustion Reaction
1.2 Chemistry of Acids and Bases
1.3 Impact of Acid Deposition on Ecosystems
1.4 Quantifying Acid Deposition and Monitoring its Effects
1.5 Learning From Acid Deposition
1.1 Products of Combustion Reactions
• A combustion reaction is a chemical reaction that
takes place in the presence of oxygen and results in
the release of energy
• Combustion reactions involve a fuel (often a
hydrocarbon) and emissions
• Combustion reactions must be balanced
1.1 Products of Combustion Reactions
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Incomplete combustion of hydrocarbons can result in the
formation of carbon monoxide
Impurities in the fuel can cause the release of
Oxides of Sulfur (sour gas) SOx
Oxides of Nitrogen NOx
Metals and Metal Oxides
Particulate Matter
1.2 Chemistry of Acids and Bases
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Solutions are homogeneous mixtures with a solute and a solvent
Aqueous solutions have water as the solvent
Solutes can be ionic or molecular
Ionic solutes dissociate in water
Ionic solutes are electrolytic
Molecular solutes dissolve in water if they are polar
The concentration of a solution is the amount of solute in a volume
of solution (usually expressed in mol/L)
1.2 Chemistry of Acids and Bases
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Acids are aqueous solutions that have the following empirical
properties
Electrolytic
Corrosive
Turns blue litmus red
Reacts with active metals to produce hydrogen gas
Neutralized by bases
Taste sour
1.2 Chemistry of Acids and Bases
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Bases are aqueous solutions that have the following empirical
properties:
Electrolytic
Corrosive
Turns re litmus blue
Feels slippery
Neutralized by acids
Taste bitter
1.2 Chemistry of Acids and Bases
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Theoretical properties of acids
Arrhenius: acids are molecular solutes that ionize to form
H+(aq)
Modified Arrhenius: acids react with water to form
hydronium ions H3O+(aq)
Bronsted-Lowry: acids are molecular solutes that donate
protons (H+) to another substance in a chemical
reaction…examples
1.2 Chemistry of Acids and Bases
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Theoretical properties of bases
Arrhenius: bases are solutes that ionize to form OH-(aq)
Modified Arrhenius: bases react with water to form OH(aq)
Bronsted-Lowry: bases are molecular solutes that accept
protons (H+) from another substance in a chemical
reaction…examples
1.2 Chemistry of Acids and Bases
• Acid deposition is the result of emissions reacting
with water to make acidic solutions
• Anthropogenic emissions are due to human activity
• Acid rain is any form of precipitation containing
excess of dissolved acids such that the pH is less than
5.6
1.2 Chemistry of Acids and Bases
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pH is a common way to represent the concentration of H3O+(aq) in
a solution
pH = -log[H3O+]
One pH unit is equivalent to a tenfold change in the
concentration of H3O+(aq)
An indicator is a chemical whose colour changes at different pH
levels
The pH of a solution can be estimated using multiple indicators
1.3 Impact of Acid Deposition on Ecosystems
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Acid deposition can affect ecosystems around the globe due to:
Wind patterns (jet stream)
Lake acidification (relatively low buffering capacity)
Soil acidification (variable buffering capacity)
Nutrient and metal leaching (biogeochemical cycles)
Biomagnification
Abiotic effects, biotic effects and declining biodiversity
1.4 Quantifying Acid Deposition
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Qualitative analysis: recording observable properties of a system
Quantitative analysis: measuring using a numerical value
Titration is a method of measuring the concentration of a
solution
In a titration, the titrant is added to the sample until a chemical
reaction is complete
The volume and concentration of one substance is used to
determine the concentration of the other
1.4 Quantifying Acid Deposition
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A titration curve is a graph to represent a titration
A titration curve can determine the buffering capacity of a
solution
A strong acid reacts completely with water to form hydronium
ions
A weak acid reacts incompletely with water to form hydronium
ions
Two acids of the same concentration can have different pH levels
1.5 Learning From Acid Deposition
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The effects of acid deposition on ecosystems can be
minimized by:
1. Reducing emissions: cleaner fuels, scrubbing SOX from coal
fired plants, catalytic converters removing NOX from vehicle
exhaust, and reducing combustion
2. Recovering from acid deposition: liming acidified lakes and soil
• Reducing NOX can help reduce photochemical smog and the
effects of VOC’s
The Chemical Legacy of Human Activity
2.1 Organic Compounds
2.2 Alcohols, Carboxylic Acids and Esters
2.3 Understanding Exposure
2.1 Organic Compounds
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Organic Chemistry: the study of compounds composed of
carbon
Hydrocarbons: organic compounds made of only carbon and
hydrogen atoms
Saturated Hydrocarbons: hydrocarbons that have single
bonds between carbon atoms (alkanes)
Unsaturated Hydrocarbons: hydrocarbons that have one or
more double bonds between carbon atoms (alkenes)
2.1 Organic Compounds
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Hydrocarbons are named based on the number of carbon
atoms they possess and whether the chain saturated or not
Rules for naming alkanes
Rules for naming alkenes
Aromatic hydrocarbons have a benzene ring in the molecular
structure
Benzene demonstrates a unique chemical bonding arrangement
called resonance
2.1 Organic Compounds
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Benzene is very stable and is carcinogenic
Benzene remediation is necessary to remove benzene
contamination from soil
PAH’s are polycyclic aromatic hydrocarbons and are common
carcinogens
Halogenated hydrocarbons have one or more halogen added
to an alkane, alkene or aromatic hydrocarbon
Rules for naming halogenated hydrocarbons (p251)
2.1 Organic Compounds
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Chlorofluorocarbons (CFC’s) are linked to ozone depletion
Other halogenated hydrocarbons are linked to health and
environmental problems
2.2 Alcohols, Carboxylic Acids and Esters
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Alcohols are hydrocarbons with one or more hydroxyl
functional groups
Alcohols are used for cleaning solvents, disinfectants, fuels,
production of pharmaceuticals, dessicants
Rules for naming alcohols (p264)
Carboxylic acids are hydrocarbons with a carboxyl functional
group
2.2 Alcohols, Carboxylic Acids and Esters
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Carboxylic acids are weak acids that include ethanoic acid
(vinegar), lactic acid and PABA
Rules for naming carboxylic acids (same as alcohols but use
the suffix “oic acid”
Esters are formed by reacting a carboxylic acid with an alcohol
Esters make up common flavours, odours and fats
Rules for naming esters (p272)
Many plastics are polymers of esters (polyesters)
2.3 Understanding Exposure
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Volatile organic compounds (VOC’s) are chemicals that
evaporate or sublimate easily during off-gassing and affect
indoor air quality
Off- gassing affects both human and environmental health
Using low VOC products can reduce these problems
Persistent organic pollutants (POP’s) include pesticides:
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Broad spectrum: low target specificity and will affect many species
Target Specific: affect one or only a few species
2.3 Understanding Exposure
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Pesticides include
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Insecticides
Herbicides
Fungicides
Others
• The toxicity of a chemical can be determined by LD50 or LC50
testing (Note: low LD50 means high toxicity)
• The use of pesticides is subject to drift, the grasshopper effect
(p286) and persistence
2.3 Understanding Exposure
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Water quality is affected by fertilizers and organic matter
Fertilizers contain nutrients that encourage the growth of algae
Algal blooms can result in the build up of organic matter and
eutrophication of a body of water
Low dissolved oxygen concentrations can lead to winterkill of
Alberta lakes
Biochemical oxygen demand is a measure of the rate at which
dissolved oxygen becomes depleted in a water sample
2.3 Understanding Exposure
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Limiting exposure involves:
Bioremediation
Biological controls for pests
Biodegradeable products
Monitoring
Education (workforce and the general public)