The following is the edited text of a winning essay.
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A Winning Essay


Our invisible friend - CO2

by Leighton Sickler, Regiopolis-Notre-Dame, 130 Russell Street, Kingston ON K7K 2E9


Carbon dioxide was first identified in the 1750s by Joseph Black, a Scottish chemist and physician.

Carbon dioxide is a colouriess, odourless gas. It occurs in the atmospheres of many planets, including that of the earth. On the earth, all green plants must absorb carbon dioxide from the atmosphere to live and grow.

Green plants convert carbon dioxide and water into food and oxygen. Plants and animals, in turn, "burn" the food by combining it with oxygen to release energy for growth and other life activities. This process, called respiration, is the reverse of photosynthesis. Oxygen is used up and carbon dioxide and water are used to produce more food and oxygen. The cycle of photosynthesis and respiration maintains the earth's natural balance of carbon dioxide and oxygen.

Carbon dioxide is essential in the role of internal respiration. Internal respiration refers to the process by which oxygen'is transported to body tissues and carbon dioxide is carried away from them. This carbon dioxide is also a chief guardian of the pH of the blood, which is essential for survival. This buffer system - called the carbonate buffer - is made up of bicarbonate ion and dissolved carbon dioxide plus carbonic acid. The carbonic acid can neutralize hydroxide ions which, if added, would increase the pH of the blood and cause alkalosis. The bicarbonate ion can neutralize hydrogen ions which, if added, would cause a decrease in the pH of the blood and lead to acidosis. Both changes in pH are life threatening.

The carbon dioxide in the earth's atmosphere helps regulate the planet's temperature. When sunlight reaches the earth, some of it is converted into heat. The carbon dioxide absorbs some of the heat and so helps keep it near the earth's surface. If all the heat from the sunlight escaped into outer space, the earth would become very cold. The amount of carbon dioxide in the atmosphere has been increasing since about 1890, chiefly as a result of the burning of fuels that contain carbon. This increase has caused a slight rise in the earth's average temperature.

Carbon dioxide has important uses in the home and in industry. For example, carbon dioxide released by baking powder or yeast makes cake batter rise. Carbon dioxide in soft drinks, beer, and sparkling wines gives the beverages their fizz. Some fire extinguishers use carbon dioxide because it does not bum and because pure carbon dioxide is denser than air. Carbon dioxide's heaviness enables it to blanket a fire and prevent oxygen from getting to the fire thus starving the burning material of the oxygen it needs to continue burning.

Dry ice is solid carbon dioxide. Carbon dioxide becomes a solid at -78.5 0C. The name dry ice refers to the fact that the substance changes from a solid to a gas without first becoming a liquid. Because of this property, dry ice is widely used in industry to refrigerate food, medicine, and other materials that would be damaged by the melting of ordinary ice.

Carbon dioxide is one of the most important compounds on earth. Its importance to industry and the survival of all life are well documented. Without it, all human life would cease to exist. We all owe a debt of gratitude to our little friend CO2.

That is why I believe the Chemistry Hall of Fame at York should adopt carbon dioxide into its halls, and give it the credit it well deserves.

Bibliography
1. Brady, James and Holum, John, Fundamentals of Chemistry, New York, John Wiley & Sons, 1988.
2. World Book Encyclopedia, 1992 edition, see "Carbon dioxide".
3. Science and Invention, 1983 edition, see "Carbon dioxide".
4. McGraw-Hill Encyclopedia of Science and Technology, 1987 edition, see "Carbon dioxide".


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