Heat-Trapping Gases Lab

Transcription

1 Heat-Trapping Gases Lab Before performing the lab, show this video to the students. Objective: The main goal of this activity is instrumentally demonstrate the heattrapping power of some gases found in Earth s atmosphere. Time needed : 55 minute period Materials needed for a class of 30 students: Bottle of white vinegar Box of baking soda ml beakers Methane gas (lab gas) 40 - large lab thermometers 50 - large latex balloons (more than needed to account for breakage) 40 - large Solo cups (clear) 10 - light sockets with plug Watt incandescent bulbs Large sponge cut into meter sticks Scissors pieces Data collection sheets Clock with second hand X-acto knife Procedure: Each lab group will use the following diagram as a guide to setup their lab. Instructor: 1. Divide the students into groups of three. 2. Gather ml beakers and to each, add about 1½ teaspoons of baking soda and 90 ml of vinegar. Allow these reactions to proceed without disturbing them.

2 Students: 3. Gather materials for your group. (4 cups, 4 balloons, 4 lab thermometers, a 3cm square section of sponge, a flat-bottom light socket with an incandescent bulb, meter stick, and a pair of scissors) 4. Cut the balloons to make 4 cup covers then secure each one of these covers to the top of a Solo cup. Make a small hole in the top of each balloon with the end of an X-acto knife for a thermometer to be inserted inside the cup. The balloon should make a tight seal around the thermometer. 5. Make labels to lay on the table by each cup representing the gas it contains (methane, carbon dioxide, water vapor, and atmospheric air). 6. Insert a lab thermometer in the top of one of the balloon covers that is secured to a cup and place it beside the label marked atmospheric air. 7. Soak then lightly squeeze out water from the 3 cm square of sponge. (It should still be quite damp.) Place in the bottom of cup 2, the balloon cover replaced and a thermometer placed inside as was done for the atmospheric air cup. (Make sure the thermometer s bulb is not touching the sponge.) This cup should be placed beside the water vapor label. 8. Bring cup 3 to the instructor to be filled with methane. Since the density of methane is less than atmospheric air, the cup should be inverted to hold the gas and the balloon cover/thermometer assembly placed on while in this position. Place this cup beside the methane label. 9. Take cup 4 to the table containing the beakers of CO2 that have been generated while the other setup was taking place. This final Solo cup can now be filled by carefully pouring the gas contents of one of the 500 ml beakers containing CO2 into their cup and carefully sealing the top with the balloon/thermometer assembly. If the beakers or cup are jostled, some of the CO2 will be lost to the floor move slowly around this table. This final cup should be placed beside the label marked carbon dioxide. 10. Arrange the cups of gases so that each is 20 cm from the center of the light source. The temperatures will be read for 12 minutes and the cups will need to be left in place for this entire time so students place them so that the thermometers can be read without adjusting the cup positions. If any of the balloons seem to be leaking their gas contents, seal the opening with masking tape. Secure each cup to the lab table with masking tape. 11. Before the bulb is powered, enter the initial temperature for each gas in the Time = 0 min row of the data table. One student can be responsible for recording temperatures and signaling each minute that passes. The other members can each be responsible for reading the temperatures of two different bottles of gas. 12. Power up the bulb and record gas temperatures for each of the gases at one minute intervals until twelve minutes have passed. Assessment: Make your own copy of the temperatures recorded for each time to use as a reference for the homework assignment. Generate a graph of time vs. temperature for each of the four gases. Each gas should be represented by a different color line on the same graph for easy comparison. This can be done with Excel or by hand on graph paper.

3

4 A sample of expected results:

5 Analysis Questions 1) Describe the general trend in temperature over time that was observed in each cup. For example, does each gas show a rapid rise and then level off, or did it reach a peak temperature above which it rose no further? 2) Compare and contrast the temperature change of each gas tested. Which one showed the lowest temperature rise? Which one showed the greatest temperature rise? 3) What was the apparent effect on temperature when adding CO2, CH4, or H2O to the cups? 4) This activity is an investigation into thermal properties of several gases found in the atmosphere but it is not meant to be a model for what is occurring in the atmosphere. In what way is Earth s atmosphere different than what is found in the cups? How does Earth s atmosphere differ in composition and what processes are occurring in the atmosphere that are not occurring in the cups? The phenomenon that this activity explores is typically called the greenhouse effect. Do you think this is a good term to use? Why or why not? Adapted from