In this lesson we will answer the following questions:
- How does carbon dioxide affect water?
- How does carbon dioxide affect the atmosphere?
Read Chapter 6 in Simplified Procedures for Water Examination.
What is Carbon Dioxide?
Carbon dioxide forms the bubbles in bread and in
soft drinks. Dry ice is a solid form of carbon dioxide.
Carbon dioxide, or CO2, is a compound which is found as a gas at room temperature. As you can see in the picture above, carbon dioxide is responsible for the bubbles in soft drinks. Baking powder, baking soda, and yeast all release carbon dioxide, making breads rise. Dry ice is the solid form of carbon dioxide which is produced by cooling carbon dioxide to -109.3°F.
Carbon dioxide is also present as a natural part of our atmosphere, making up about 1% of the air. All animals, including humans, breathe out carbon dioxide as a result of respiration. Plants, on the other hand, "inhale" carbon dioxide and use the gas to produce sugars in a process called photosynthesis. In addition to the biological processes noted here, carbon dioxide is formed when organic compounds are burned.
As you should remember from Lesson 7, carbon dioxide can become dissolved in water. Some of the dissolved carbon dioxide typically remains in the form of a gas. However, a portion of the carbon dioxide reacts with water to form carbonic acid.
Carbonic acid is a weak acid which can have a variety of effects on water. If limestone is present in the surroundings, carbonic acid will help dissolve the calcium carbonate, buffering the water. However, in the absence of limestone, carbonic acid makes the water acidic and can lead to corrosion of pipes in the distribution system. Carbonic acid will also react with lime added to the water, reducing lime's softening capabilities.
Carbonic acid is known as a volatile acid because it can change back into carbon dioxide and water vapor when heat is applied. As a result, heating water which contains carbonic acid can raise the pH.
The climate of the earth is constantly changing. During the past billion years, the earth has passed through four ice ages, which are periods during which the earth's temperature drops. During ice ages, glaciers covered large parts of the earth's surface, as shown above. A drop in the average global temperature of as little as 5°F can be sufficient to trigger an ice age.
Ice ages typically last for 80,000 to 100,000 years, during which time there can be several short, warmer periods known as interglacials. Many scientists theorize that we are currently in an interglacial period, which began about 14,000 years ago. Interglacials are much shorter than the periods of temperate climate between ice ages, usually lasting only about 10,000 years. The temperate periods between ice ages typically last for millions of years.
Ice ages, interglacials, and temperate periods can be caused by a variety of factors including the wobble of earth's orbit, the arrangement of the continents, and the concentration of carbon dioxide and methane in the air. The most important of these causes of climate change may be the carbon dioxide content of the air.
Carbon dioxide, methane, nitrous oxide, and ozone are all known as greenhouse gases because they trap heat between the earth and the atmosphere. The larger the concentration of each of these gases in the atmosphere, the more heat is trapped and the warmer the earth becomes.
The diagram above illustrates the greenhouse effect, which is the manner in which the greenhouse gases warm the earth. The source of the earth's heat is light from the sun, which is able to pass directly through the atmosphere to the earth. Some of this sunlight is reflected back into space, but a large percentage of the sun's light is turned into infrared rays - or heat.
Some of the infrared radiation absorbed by the earth is re-emitted into the atmosphere. On a planet without an atmosphere, this heat would all be lost into space. However, on earth, a large percentage of the infrared rays are reflected by the greenhouse gases in the atmosphere. The reflected heat returns to the earth and increases its temperature.
The greenhouse effect has always been present on earth and has served to moderate earth's temperature. But in recent years, the burning of fossil fuels has greatly increased the carbon dioxide concentration in our atmosphere, which is causing the earth's temperature to become warmer than usual. As you can see from the graph below, the earth's temperature has warmed by about a degree in the past hundred years.
This accelerated change in the earth's temperature is known as global warming. Scientists expect global warming to result in widespread climate change, some symptoms of which we are already observing. The higher temperatures are beginning to melt the polar ice caps, with the additional water from these glaciers entering the oceans and causing a rise in ocean levels. Sea level has already risen by between four and eight inches in the last century, and scientists expect that the water will rise by two more feet over the next century.
Global warming is also expected to result in a hotter, drier climate. Deserts would increase in size and other habitats would change size or location, or would disappear altogether. Some species may become extinct as a result of global warming.
Humans may also have problems resulting from global warming. Not only will our coastal cities be flooded and uninhabitable, but the future weather is expected to include more extremes - heavy rainfall followed by extreme droughts and abnormally hot or cold seasons. These climate changes could make it difficult to grow enough food to eat.
Scientists are still debating the causes and effects of global warming. However, most scientists agree that reducing the emission of greenhouse gases will help improve the situation. The EPA has published a webpage giving information about what individuals can to to help slow global warming.
Carbon dioxide concentration in water is important because it can help dissolve limestone, can cause corrosion, and can use up lime in the water. In the air, carbon dioxide contributes to the greenhouse effect, with additional carbon dioxide from the burning of fossil fuels resulting in global warming.
"Carbon Dioxide." January 31, 2005. Wikipedia
"Climate Change." Encyclopedia of the Atmospheric Environment
"Global Warming - Climate." January 7, 2000. U.S. Environmental Protection Agency.
"Ice Age." February 1, 2005. Wikipedia
Complete the questions for Assignment 16. When you have gotten all the answers correct, print the page and either mail or fax it to the instructor. You may also take the quiz online and directly submit it into the database for a grade.
Read the Carbon Dioxide lab and do the assignment listed above, there are questions concerning the virtual lab included.
Answer the questions in the Quiz 16. When you have gotten all the answers correct, print the page and either mail or fax it to the instructor.