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The Effects of Carbon Dioxide on the Environment

The Effects of Carbon Dioxide on the Environment. Vanderbilt Student Volunteers for Science Presentation Spring 2012. Safety. The students should not handle the dry ice You will be placing it in their cups for them. I. Introduction. Discuss CO 2 in the atmosphere

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The Effects of Carbon Dioxide on the Environment

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  1. The Effects of Carbon Dioxide on the Environment Vanderbilt Student Volunteers for Science Presentation Spring 2012

  2. Safety • The students should not handle the dry ice • You will be placing it in their cups for them

  3. I. Introduction • Discuss CO2 in the atmosphere • Explain the difference between acidified rainwater and acid rain • Acidified = naturally dissolved CO2 (pH ~5.6-7) • Acid Rain = sulfuric acid, nitric acid, and others causing a very low pH (<< 5.6)

  4. II. Demonstration • Discuss acids, bases, and indicators • Pour 3 cups 1/3 full each of: “rain water,” drinking water, and “ocean water.” • Note: the “rain water” and “ocean water” are synthetically prepared and have abnormal pHs so students can observe the color change • One cup is basic, one neutral, and one acidic • Hand out color charts • Add some bromothymol blue to each cup to show colors to students

  5. IIIA. Experiment • Pass out plates, cups w/ 1/3 ocean water • Students describe liquid, THEN add indicator • Go around and add 1 piece of dry ice to the cups • Students observe color change Source: serc.carleton.edu Basic Acidic Neutral

  6. IIIB and IV. Explanation • CO2 + H2O → H2CO3 • Bubbling CO2 in water makes carbonic acid • Why does ocean water start basic? • Dissolved minerals make it basic • Why does the color change? • The indicator shows the water becoming acidic due to the formation of carbonic acid • Discuss consequences of acidifying oceans

  7. V. Effects of CO2 on Land • Discuss what might happen with acidic rain • Tell students some CO2 dissolves naturally in rain water • Slightly acidic • This affects exposed rocks • Rain trickles through soils • IMPORTANT: water gets most of its CO2 from soils where CO2 partial pressure is 10-100 times that of the atmosphere. This is important for cave systems. • Water is now more acidic and can dissolve calcite, the mineral in limestone

  8. VI. Experiment – Limewater • Pass out cups with 2/3 limewater • Drop 1 piece of dry ice in students cups • Have them observe the reactions • Cloudy in ~10 seconds, clear again in ~3 minutes

  9. VI. (Cont.) Explanation • CO2 dissolves after subliming • CO2 reacts with Ca(OH)2 to form calcium carbonate (CaCO3) • Insoluble suspension, solution becomes cloudy • Excess CO2 mixes with CaCO3 to form calcium bicarbonate (Ca(HCO3)2) which is soluble • Solution becomes clear since the solid is no longer suspended in solution

  10. VI. (Cont.) Cave Formation • Reference the cave diagram while explaining: • Rainwater falls, dissolves CO2 in soils • Water percolates through limestone • Reacts with calcite (CaCO3) to dissolve it. • Leaves behind small cavities which grow over time • Water moves elsewhere in the system • CO2 slowly exolves (leaves solution) converting Ca(HCO3)2 → CaCO3 which is left as a solid • Cave formations such as stalactites/stalagmites

  11. How do caves form? (flow chart)

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