Climate and Earth's Energy Balance

Materials:

Note the list of materials described below is for one lab team.

• 3-4 (depending on variables to be tested) - Clear plastic water bottles with hole drilled into cap. The bottles should all be the same type and size (approximately 1-liter). The bottles should be transparent plastic (remove any labels), black bases are acceptable. The bottles need to have tightly fitting screw-on tops. Seltzer water bottles are a good type of bottle. (Recommend: 1 bottle for every variable).
• 4 - Thermometers (analogue, digital, or digital recording; one for each bottle). Inexpensive digital probes, such as the ones pictured here, can be purchased online. Vernier and Pasco, as well as other companies, sell excellent probes for this type of investigation.
• A clock or watch showing minutes and seconds.
• 150 mL (2/3rd cup) of vinegar
• 250 mL (1 cup) of baking soda
• 3 - Sponge pieces of equal dimensions; saturated with water for one bottle, left dry for the other two. Kitchen sponges can be cut into 3 pieces to fit the bottles.
• Light Source:
  Indoors: Light source (clamp lamp or goose neck) and bulb (standard incandescent or directed spot; one setup for each bottle).
  
  
  Outdoors: Sheltered area with direct sunlight for duration of lab. A means for shading the bottles for the second half of the lab. A cardboard piece folded in half and placed tent-like over the bottles works well. Or you can plan to move the bottles into the classroom for the cooling phase.

Pre-lab preparations:

1. Assemble all materials and select a sheltered site (out of the wind) to work if working out-of-doors.
2. Pre-drill holes in the caps of the bottles. Make sure you have enough bottles and caps for the entire group.
3. Insert temperature probes and seal the holes with modeling clay, hot glue, or silicone sealant.
4. Cut sponge pieces to size (should cover half the of bottle bottom) and insert in bottles. Leave the lids off the bottles and let the sponge pieces dry for the dry air and CO₂ bottles.
5. Prepare the gases for the bottles before beginning the activity using the instructions below. Seal the bottles after preparing them.
6. Preview the lab methods with your lab team so that you are ready to go at the start of the class period.

Preparation of Bottles:

For the bottle with air: Be sure that air is dry use a warm hair dryer to heat the air, for a few minutes then just tighten the cap. Let the bottle cool before the lab.

For the bottle with saturated air: Pour small amount of water in the bottle to saturate the piece of saturated sponge in the bottom of the bottle. Make certain the sponge is wet but there is no extra water in the bottle. Seal the bottle.

For the bottle with carbon dioxide and for pouring the gas into the bottle: Carbon dioxide can be easily made with baking soda and vinegar. Vinegar (acetic acid) CH₃COOH, and baking soda (sodium bicarbonate) NaHCO₃ produces an acid-base reaction when they come in contact with one another. The fizzing and bubbling indicates that a gas (CO₂) is being produced.

1. Pour 30 ml (about 1 ounce) of vinegar into an extra plastic bottle or tall beaker.
2. Spoon in ½ tsp of baking soda. Allow the reaction to bubble and fizz without disturbing it.
3. When the fizzing is over, carefully pour the CO₂ into the bottle. [Adding more vinegar and baking soda will just make the reaction bubble excessively, and the CO₂ will tend to bubble over the beaker and you won't be able to get it into the bottle.] BE CERTAIN NOT TO POUR ANY LIQUID INTO THE BOTTLE!
4. Repeat this process two more times.
5. Put the cap with the probe on the bottle. Another way to produce CO₂ is to dissolve an effervescent tablet like Alka Seltzer in the bottle. If using this method, you will need to put an equal amount of water in the bottle with water.

Note: CO₂ gas is more dense than air. It will stay in the beaker, forcing out the air. Although you can't see it, you can pour CO₂ gas out of the beaker just like you would pour a liquid. By way of teacher demonstration, a match can be lit and placed down into the gas. The match will be extinguished showing that the oxygen in the air has now been forced out, replaced by the carbon dioxide. Students can also feel the CO₂ being poured out of the beaker because it's cold (similar to cold carbon dioxide gas coming out of a fire extinguisher). As the reaction with baking soda and vinegar is "endothermic," meaning that energy (as well as CO₂) leaves the products during the reaction cold, care should be taken not to introduce any of the liquid into the bottle as it will continue to keep the temperature of the liquid depressed.