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 Explain the difference between acidified rainwater and acid rain – Acidified = naturally dissolved CO 2 (pH ~5.6-7) – Acid Rain = sulfuric acid, nitric acid, and others causing a very low pH (<< 5.6)

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

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 Neutral Acidic

IIIB and IV. Explanation CO 2 + H 2 O → H 2 CO 3 – 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

V. Effects of CO 2 on Land Discuss what might happen with acidic rain Tell students some CO 2 dissolves naturally in rain water – Slightly acidic – This affects exposed rocks Rain trickles through soils – IMPORTANT: water gets most of its CO 2 from soils where CO 2 partial pressure is times that of the atmosphere. This is important for cave systems. Water is now more acidic and can dissolve calcite, the mineral in limestone

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

VI. (Cont.) Explanation CO 2 dissolves after subliming CO 2 reacts with Ca(OH) 2 to form calcium carbonate (CaCO 3 ) – Insoluble suspension, solution becomes cloudy Excess CO 2 mixes with CaCO 3 to form calcium bicarbonate (Ca(HCO 3 ) 2 ) which is soluble Solution becomes clear since the solid is no longer suspended in solution

VI. (Cont.) Cave Formation Reference the cave diagram while explaining: Rainwater falls, dissolves CO 2 in soils Water percolates through limestone Reacts with calcite (CaCO 3 ) to dissolve it. – Leaves behind small cavities which grow over time Water moves elsewhere in the system – CO 2 slowly exolves (leaves solution) converting Ca(HCO 3 ) 2 → CaCO 3 which is left as a solid – Cave formations such as stalactites/stalagmites

How do caves form? (flow chart) Leaves behind tunnels CavesDeposit formations Form carbonic acid (H2CO3) Seeps into bedrockDissolves limestone Rain falls and mixes with: CO2 in atmosphereCO2 in soil