Preliminary evaluation of the impact of the take-home challenges shows that students reporting themselves as receiving a B or C grade in the course find the challenges very useful in helping them gain a conceptual understanding of the phenomena addressed. Students earning an A grade report little or no impact on their learning.

Prepared as one-page handouts, each take-home challenge begins with a scene-setting introduction followed by pertinent background information, a list of materials to be collected, and any appropriate safety precautions. The exploration component of the activity integrates leading questions with the procedural instructions to help guide the students through the discovery process and challenge them to stretch their understanding of the chemistry. After completing a take-home challenge activity, students submit written reports containing responses to the questions posed, observations of data collected, and their responses to the challenge.

The accompanying sample take-home challenge activity is provided as a novel adaptation of the belch phenomenon that challenges students to experiment in order to explain the factors that account for the observed behavior. Persons interested in field testing the take-home challenges with their classes should contact the authors.

Belch Bottle

Introductory Remarks

Materials

• 2 plastic soft-drink bottles of the same size
• one of the following sets of materials:

  potato; barrel of a Bic pen; tape (cellophane, electrical, or masking); 8-in. piece of wire, or

  2 1-hole #3 stoppers; barrel of a Bic pen; tape (cellophane, electrical, or masking)

• water
• shallow tray or sink
• (optional) food color
• (optional) narrow-necked bottle made of glass (or other rigid material)

Getting Ready

1. Cut one of the soft-drink bottles a few inches above the bottom to make a tall funnel as shown in Figure 1. Fill the second, uncut bottle half-full with water.
2. If there is a hole in the side of the pen barrel, wrap tape around it.
3. If 1-hole stoppers are available, slide one onto each end of the pen barrel and use this assembly to connect the cut funnel and the half-filled, uncut bottle. Alternatively, push the barrel all the way through a potato, leaving an approximately equal amount of pen barrel sticking out each side of the potato. If potato becomes lodged inside the pen barrel (that would restrict air or water flow), use a wire to push it out. Slide one end of the pen barrel into the mouth of the funnel all the way to the potato and gently screw the potato onto the thread of the funnel. Gently screw the other end of the potato onto the threads of the neck of the half-filled, uncut bottle. (See Fig. 2.) Your goal is to create an airtight seal between the funnel and the uncut soft-drink bottle.

Procedure

1. Place the apparatus in a shallow tray or sink. Fill the funnel 3/4 full with water. (Colored water is easier to see.) Give the bottle a slight squeeze. Watch for several minutes. What do you observe? Explain your observations.
2. Disconnect the bottle from the connector. Pour water out of the bottle until it is again only half full. Reconnect the connector to the bottle and fill the funnel full of water. Do not squeeze the bottle to start the "belch." How long does it take to begin on its own? Explain any differences in time from that observed in Step 1.
3. What is the importance of having water in both the funnel and bottle? Why is it important that all seals be airtight?
4. Try to make a "belch bottle" using a bottle made of glass (or other rigid material) instead of the uncut soft-drink bottle. Why or why not were you able to get it to belch? Draw or describe your setup and results.
5. Answer the challenge!