Instructional Activities

One to two 50-min periods, or one 90 min period

The purpose of these preliminary experiments is for students to become familiar with carbon dioxide (CO₂).  In particular, these experiments aim to provide context for the role of carbon dioxide in global climate change and ocean acidification.  Therefore, students should come away with an understanding of the natural and anthropogenic sources of CO₂ as well as the interaction between carbon dioxide and water.  These experiments are designed for small groups to rotate through different stations in a round robin set-up.

INTRODUCTION and ADVANCED PREP:  

Carbon dioxide is a naturally occurring gas in the earth's atmosphere important to many biological processes.  In the natural carbon dioxide cycle, the production and fixation processes for CO₂ are in equilibrium. Prior to human interference, atmospheric CO₂ levels maintained a fairly stable level of about 280 ppm (parts per million).  However, since the Industrial Revolution, human activity has produced more CO₂ than natural fixation processes are able to remove from the atmosphere.  Thus, human activity has caused a net increase in CO₂ levels.  Since the 1800's the atmospheric carbon dioxide level has increased to about 400 ppm.  The rate of this change is greater than ever before observed in history, as measured through methods such as ice core samples¹.  Throughout these lessons, we will discuss the effect of this increase, focusing specifically on the earth's oceans.

There are two recommended options for Lesson 2.

• A)  Allow students to design their own inquiry investigation exploring properties of CO₂.  Give them a list of materials such as yeast, sugar, water, baking soda, vinegar, soda, dry ice, bromthymol blue (BTB), universal indicator, etc. to use and then guide them through developing their question and experimental plan.

• B)  Lead students through a lab rotation that considers the following questions:
  1. Where does CO₂ come from naturally?
  2. Which human activities, starting during the Industrial Revolution, produce large amounts of CO₂?
  3. What happens to water when CO₂ levels in the air surrounding the water increase?

For either of these options, we recommend a couple of quick demonstrations to engage and remind students of what they know and what they have questions on. These two demonstrations should help students with two important concepts going into these lessons.

1. CO₂, while a seemingly harmless substance, has a dramatic effect on pH.
2. CO₂ sinks and falls readily to the ground and if in the atmosphere above the ocean, will fall into the ocean.

• Visual pH scale - use the steps below to demonstrate the effect CO₂ has on water.  Or use this demonstration designed by Flinn Scientific.

1. Take 7, 400 mL beakers.  Fill with water.
2. Add universal indicator to each to achieve a nice green color in each beaker.
3. The middle beaker will stay neutral. With your gloves and protective eye wear on, add 1 or 2 drops of 0.1 M HCl to the beaker to the left of center, 3-4 drops into the next beaker to the left, 5-6 drops HCl into the last beaker.  You should have a sequence of colors from stronger acid to neutral.
4. Using the same approach as in step 3, beginning with the beaker to the right of center, add drops of 0.1 M NaOH to create a series of basic solutions.  The most basic (far right) beaker should be purple.  This should complete your visual pH scale.
5. Take a large flask (2L if possible) and fill 3/4 full with water.  Add indicator.  Add NaOH until it reaches purple.  Drop some chunks of dry ice (CO₂) into the flask.  Remember to use appropriate safety techniques when handling dry ice.  Hold the flask above the visual pH beakers and watch the CO₂turn the flask from purple to dark orange demonstrating the dramatic pH change.  Typically you can get dry ice from your local grocery store or fish market.  If you do not have dry ice, you could use some other source of CO₂ (such as that produced from baking soda and vinegar).

• Balloon drop:  Take a small flask and drop a small pellet of dry ice into it (~3g) (again use appropriate dry ice safety techniques).  Cover the flask with a balloon.  Let the balloon fill, then tie it off.  Meanwhile, fill another balloon with air to the same volume as the CO₂ balloon.  Hold them high and let them both drop.  See the CO₂ balloon reach the floor first.  Ask students to consider why one balloon would fall faster than the other.

STUDENT EXPERIMENTATION

1. Chemical Reactions Lab
2. Combustion Lab
3. Cellular Respiration Lab
4. Detecting Carbon Dioxide Lab

For large classes, these labs can be set up in duplicate so that you have 8 stations set up in your lab.  If you have space, specifically having multiple "Detecting CO₂" stations will prevent any bottleneck.  All needed materials are listed in the above 4 documents for this lab activity.  In addition, here is a compiled list of materials for your convenience.

Common Misconceptions - Students may think that a small change in pH is a small change overall.  See below for a list of possible pH activities to help avoid this misconception.  Also, a quick review on logarithms may be required to fully comprehend how an increase in CO₂ emissions impacts pH.  It is important for students to see that a change from pH 8.2 to 8.1 is a BIG deal.  Here are some resources that we have found to be helpful for students completing this module:

• How We Use Logarithms - An excerpt and figure from University of Manitoba in Canada that helps students understand the difference between Linear and Logarithmic scales.
• A list of various pH resources
• Adaptations from the PhET project at the University of Colorado
  • pH simulation student worksheet - PhET pH Intro
  • pH simulation student worksheet with more emphasis on math - PhET pH Intro too
  • pH simulation student worksheet - PhET Acids and Bases
  • pH simulation student worksheet with more emphasis on math - PhET Acids and Bases too
• Please note that there are a lot of chemistry concepts that we purposefully left out of this lesson.  For instance, Limewater and BTB, two indicators used in this lesson, have very interesting chemical properties.  Originally, when developing these lessons, we considered teaching students why and how Limewater and BTB change in the presence of CO2.  However, after field testing, we purposefully left this out in order to focus students' learning on experiential understanding of Carbon dioxide as a phenomenon that is making great change in ocean water. The chemistry behind the reactions of Limewater and BTB were too complex to cover as part of a general class and not needed to achieve the main goal.  If you are teaching this module as part of an Advanced Chemistry course, then you might want to have students work towards understanding the chemistry behind saturation curves, reversible indicators, precipitation reactions, etc.

WRITING SCIENTIFIC ARGUMENTS

This lesson offers a good opportunity for scientific writing.  Specifically, using a "Claim-Evidence-Reasoning" prompt leads to further scientific understanding as well as gains in thinking and writing skills. Claim-Evidence-Reasoning is the format for writing a scientific argument that is part of Common Core standards.  Here are two examples for incorporating this format into this lesson:  Have students make a claim about whether or not burning wax is a combustion reaction. Students should cite the evidence that supports their claim (for this example:  mostly the BTB change and/or Vernier CO₂ probes if you used them).  Students should reason through why a color change in BTB indicated the presence of carbon dioxide. You can also have them make a claim for what was required for respiration (i.e., sugar or no sugar), using the same structure. The above labs offer many good ways to introduce writing scientific arguments.  Feel free to adapt your prompts to fit the labs the students completed.