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

• Incomplete combustion of hydrocarbons can result in the formation of carbon monoxide

• Impurities in the fuel can cause the release of1. Oxides of Sulfur (sour gas) SOx

2. Oxides of Nitrogen NOx

3. Metals and Metal Oxides4. Particulate Matter

1.2 Chemistry of Acids and Bases

• 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

• Acids are aqueous solutions that have the following empirical properties

1. Electrolytic2. Corrosive3. Turns blue litmus red4. Reacts with active metals to produce hydrogen gas5. Neutralized by bases6. Taste sour

1.2 Chemistry of Acids and Bases

• Bases are aqueous solutions that have the following empirical properties:

1. Electrolytic2. Corrosive3. Turns re litmus blue4. Feels slippery5. Neutralized by acids6. Taste bitter

1.2 Chemistry of Acids and Bases

• 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

• 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

• 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

• Acid deposition can affect ecosystems around the globe due to:1. Wind patterns (jet stream)2. Lake acidification (relatively low buffering capacity)3. Soil acidification (variable buffering capacity)4. Nutrient and metal leaching (biogeochemical cycles)5. Biomagnification6. Abiotic effects, biotic effects and declining biodiversity

1.4 Quantifying Acid Deposition

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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

• 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:

• Broad spectrum: low target specificity and will affect many species• Target Specific: affect one or only a few species

2.3 Understanding Exposure

• Pesticides include• 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

• 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

• Limiting exposure involves:1. Bioremediation2. Biological controls for pests3. Biodegradeable products4. Monitoring5. Education (workforce and the general public)