The Effects of Carbon Dioxide on the Environment

Vanderbilt Student Volunteers for SciencePresentationSpring 2012

Safety

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

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)

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 changeSource:serc.carleton.edu

Basic Neutral Acidic

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

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

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

• 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

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

How do caves form? (flow chart)

Leaves behind tunnels

Caves Deposit formations

Form carbonic acid (H2CO3)

Seeps into bedrock Dissolves limestone

Rain falls and mixes with:

CO2 in atmosphere CO2 in soil