teacherinfo

Teacher Information for "Learning About Burning"

(This page is for teacher use. Notes for students can be found here. )

General Notes

This series of activities is designed to allow students to discover the similarity between combustion and respiration, two important reactions in the carbon cycle. At the end of the activity students should be able to

write an equation for both combustion and respiration
state similarities and differences between combustion and respiration
understand the roles of combustion and respiration in the carbon cycle.

National Science Education Standards

This activity satisfies the following content standards:

5-8 Standards

content standard A (doing and understanding scientific inquiry)
content standard B (transfer of energy)
content standard C (structure and function in living systems)

9-12 Standards

content standard A (doing and understanding scientific inquiry)
content standard B (chemical reactions)
content standard C (interdependence of organisms, matter, energy, and organization in living systems)

Link to National Science Education Standards

Part 1 - Burning a Candle

In this activity, students burn a birthday candle and investigate the gases evolved from the burning reaction. By collecting a bit of the gases in an inverted cold beaker, students should notice two things. First, water vapor condenses on the glass, proving that water vapor is a product of burning. Second, when enough gas product is accumulated the flame is extinguished, proving that carbon dioxide (a known flame extinguisher) is also produced.

Even if students are familiar with carbon dioxide's role in flame extinguishing, the activity with the inverted funnel allows them to see another effect of carbon dioxide. A few drops of bromothymol blue placed inside an inverted funnel will turn greenish when held above a burning candle. This method allows enough carbon dioxide to accumulate to cause a reaction with the indicator, but it allows enough oxygen to reach the candle to continue the burning reaction.

Students may notice soot as another product of the burning reaction. Soot is residual carbon deposited when some carbon from the wax fails to combine with oxygen.

Students may not realize that heat is a product of combustion. If it is appropriate for your course, the concept of a burning candle could be used to spark a discussion about the nature of catalysts and activation energy.

Part 2 - Humans Are a Lot Like Candles

In this simple activity, students will discover two things. First, our skin excretes water continuously; this can be noticed when the water is trapped in a plastic bag. Second, carbon dioxide is excreted as we exhale; this can be noted by exhaling gently into some bromothymol blue. (Keep the volume of bromothymol blue small!) Thus, both combustion and respiration can be summarized by the following equation:

carbon source

oxygen

----->

carbon dioxide

water

heat

After completing these two parts, students should be able to compare and contrast combustion and respiration.

Part 3 - An Inquiry - Who Else Makes Carbon Dioxide?

Since inquiry learning involves students designing their own procedures and investigations, this section is purposefully short on instructions. Several ideas are suggested for student investigations into carbon dioxide production.

Investigations which focus on respiration are probably a lot safer than those which involve combustion. One possible inquiry might develop as follows:

Which organisms produce carbon dioxide the fastest?

Students can obtain a variety of simple organisms like aquatic plants, protists, yeast, etc. By placing sample of each in a solution with a small amount of dilute bromothymol blue, students can monitor the indicator for color changes. Changes with yeast can be detected in one class period. Alernately, students could set up a tube of each organism with a hose designed to bubble any evolved gas into a recipient tube with bromothymol blue (see diagram at left). Such a set-up can be left overnight and observed the next day.

An initial investigation would show that yeast are quick producers of carbon dioxide. Students might then want to determine if feeding the yeast a carbon source alters the rate of their carbon dioxide production. For example, students could set up an experiment in which samples of yeast are fed sugar, saccharin, or nothing (see picture). Since the uptake of the carbon source is expected to take some time, production of carbon dioxide should probably be monitored more slowly through the tubing method shown in the picture.

A true inquiry will take students in many different directions, thus finding materials and equipment will be the most difficult aspects of leading students through an inquiry. If students design their inquiry activities in class, the teacher can examine their list of materials and gather the necessary resources. Besides the equipment mentioned in parts 1 and 2, it might be useful to anticipate the following needs for the inquiry:

aquatic plants
yeast
pond water
significant amounts of carbon dioxide indicator
thermometers
heat sources

Part 4 - Tying It All Together

After the completion of an inquiry, it is often difficult to assess students as a whole since students have each learned different things. After having completed the Carbon Cycle Inquiry Game, and after competing this entire lesson, however, students should be able to answer the nine questions about the carbon cycle presented in this section.

Here are some suggested assessment activities:

Students demonstrate successful navigation through the nine-question quiz in part four.
Students draw their own representation of the carbon cycle focusing on the concepts they learned from all parts of this activity.
Students write a portion of an autobigraphy of a carbon atom.
Students play the Carbon Cycle game and see how many points they can earn.

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