Science 30 Unit B Chemistry and the Environment

Transcription

1 Science 30 Unit B Chemistry and the Environment Outcome 2: Students will analyze the sources of organic compounds and their effects on the environment. Specific Outcome 2.3: Identify organic compounds commonly considered to be environmental pollutants; i.e., hydrocarbons, organic waste, CFC s, polychlorinated biphenyls (PCBs), dioxins and furans. Specific Outcome 2.4: List sources of, and analyze the hazards posed by, halogenated hydrocarbons and benzene derivatives. Specific Outcome 2.5: Identify and explain how human activities and natural events contribute to the production of photochemical smog, the depletion of the ozone layer and increased concentration of organic compounds in the environment. Specific Outcome 2.6: Explain the mechanism and significance of biomagnification. Textbook reference pages: p in Science 30 ORGANIC CHEMISTRY AND THE ENVIRONMENT BENZENE AND ITS CONSEQUENCES - Naturally occur in petroleum and coal (gasoline and diesel is a mixture of hydrocarbons, including aromatics). - Evidence indicates that benzene is a carcinogen - this has led to a decrease in the amount of aromatics now present in gasoline - Also evidence that exposure effects the body's production of red blood cells Gasoline and Oil Spills - Some aromatics are soluble in water...this leads to concerns about these compounds leaching into the water system when there is a petroleum spill - When there is a spill on the ground, it must be cleaned up through the process of remediation (breakdown of hydrocarbons) o Linear hydrocarbons can be broken down quickly by soil bacteria o Cyclic hydrocarbons are much more stable and take much longer to break down (they are termed persistent organic compounds, or POCs). Benzene in Food? - Incomplete combustion of oils in food can produce polycyclic aromatic hydrocarbons (PAHs). (Think charred steak...) 1

2 - PAHs are also found in the particulate emissions from combustion of hydrocarbons - There is evidence that PAHs may interact with DNA and cause mutations. - Many benzene-containing molecules are considered to be PERSISTENT ORGANIC POLLUTANTS (POPs)POPs undergo BIOLOGICAL MAGNIFICATION - their concentration increases as they move up the food chain CHLOROFLUOROCARBONS AND ITS CONSEQUENCES - One important group of halogenated hydrocarbons is known as CHLOROFLUOROCARBONS (CFC) - Invented by chemists in 1920 s to replace toxic compounds used in refrigerators and air conditioning systems. They were praised for being non-toxic, very stable and nonreactive. - In the early 1970s scientists discovered that the ozone layer was becoming depleted and CFCs are linked to depletion. - There is a natural concentration of OZONE in the stratosphere - This ozone layer reflects harmful ultraviolet away from the earth 2

3 How is Ozone (O3) Created? - O2 in the stratosphere is exposed to UV radiation, initiating the development of O3. Reactions between O3 and CFC s - UV radiation releases a Cl atom from CFC o Free Cl atom decomposes ozone Cl(g) + O3(g) ClO(g) + O2(g) - There is also the natural decomposition of ozone occurring o O3(g) + UV O2(g) + O(g) - Free O atom reacts with ClO, regenerating the free chlorine atom, allowing the cycle to continue o O(g) + ClO(g) Cl(g) + O2(g) OZONE DEPLETION LEADS TO INCREASED UV RADIATION - UV radiation is know as IONIZING RADIATION because it can disrupt chemical bonds. - Cancer is caused by damage done to the DNA by UV rays. ENVIROMENTAL POLLUTANTS - Many synthetic products contain halogenated Hydrocarbons like: plastics, fire retardants, paints, solvents, cleaning supplies, pesticides, and herbicides. 3

4 - DDT and toxaphene have a tendency not to break down in food chains and exhibit biomagnification. - Dioxins and furans are halogenated hydrocarbons that are by-product of the chlorinebleaching process for wood pulp and incineration of plastics. - Many chemicals, including pesticides, dioxins and furans have travelled thousands of kilometres from their source to be detected in the food chains in the Arctic. - PCB concentrations have been found to be several times higher than normal in the breast milk of some populations of Canadian Inuit women. - Prevailing winds can cause persistent organic pollutants to become more concentrated at the poles. BIOMAGNIFICATION - The inability for an organism to use or eliminate a substance leads to biomagnification. There are many different substance that can build up in organisms, such as pesticides, lead, and mercury. - The organism that suffers from biomagnification is the one highest up in the food chain. - Each level of the food chain requires more energy from the level below so the chemicals get more concentrated as you move up the food chain. - The higher up the food chain the organism is, the greater the concentration of the chemical. - This build-up of chemical can be toxic for the organism. 4

5 Assignment: You are going to use your textbook from pages to answer the following questions regarding ozone depletion and CFC s. A) CFCs and Ozone a. Define the following terms: i. Stratosphere the portion of the atmosphere between 10 km and 50 km above Earth s surface. ii. Ozone layer the portion of the stratosphere, where the highest concentrations of ozone occur. iii. Free radical chemical species that have an unpaired electron in their valence shell. iv. Antioxidant a substance that prevents the oxidation of another substance; generally reacts with free radicals. B) There are reactions between ozone and CFCs. Use diagrams, words and chemical reactions (see pages 253 and 254) C) The reaction described above is cyclical in nature. Explain why. The free oxygen created when UV radiation breaks down ozone join with chlorine monoxide to free a chlorine. This free chlorine reacts with ozone to form oxygen and chlorine monoxide providing more ClO to combine with free oxygen creating a cycle. 5

6 D) Monitoring ozone how do we determine the thickness of the ozone layer (page 257) The thickness of the ozone layer is determined by data collected by satellites and devices attached to weather balloons. They measure the reflected UV radiation and the temperature of the atmosphere which determines the ozone thickness. E) International agreements What is being done to prevent the use of CFC s in order to save our ozone layer? (Page 258) The Montreal Protocol, an international treaty signed in 1987, is an agreement between countries to commit to phase out the production and use of ozonedepleting substances. Practice Problems: Page 257, #10, 11 6