Aerosol Activity: Exploding Volcano

Grade Level: 5-8

National Science Content Standards

Description of Activity

This activity is a simulation of an explosive volcanic eruption. The film canister represents the volcano, and the alka seltzer is the gas pressure. The experiment can be modified to show that an eruption will not occur if there is not enough gas pressure generated (small piece of alka seltzer) or if gas is allowed to escape gradually through holes punched in lid of film canister.

Caution: Beware of flying lids.

Materials

1. Plastic film canisters with lids (black cylinders with gray lids are best) typically free from photo processing services
2. Water
3. Graduated cylinders (small)
4. Alka seltzer (regular strength) tablets, cut into halves and quarters
5. Lots of paper towels for clean up

** Optional:

• Powder (Baby powder, talc)
• Fine sand

Procedures

1. Put about 20 ml of water into canister (No need to be exact.)

2. Add quarter tablet of alka seltzer and quickly put on cap.

3. Observe what happens for about 2 minutes.

4. Repeat using half of an alka seltzer tablet. (Watch out!)

5. Repeat using half of a tablet and lid with perforations that allow gas to escape.

• With the sand on the top of the canister cap. Repeat with the powder.

Results and Discussion

1. What happens? The lid on canister containing a quarter tablet will balloon upwards as the pressure increases, then deflate as it decreases, or it may possibly pop off gently. The lid on the canister containing a half of a tablet will bulge and then blow off surprisingly violently, rising several feet in the air or traveling laterally 5 or 6 feet. The perforated lids will not blow off.

2. Why? There is not enough gas generated by one quarter of a tablet of alka seltzer to build sufficient pressure to blow the lid off. However, the gas generated by a half of an alka seltzer tablet is plenty to blow the lid part way across the room, as long as the lid is put on quickly and firmly so that no gas escapes. Students can use the ballooning of the lid prior to its blowing off to predict when the lid will blow off. This is analogous to volcanologists predicting when an eruption will occur based on the measurable bulging of a volcano. If the gas is allowed to escape gradually through holes in the lid, the gas pressure from the dissolving alka seltzer will not build up to the point where it exceeds the confining pressure of the lid, and the lid will not blow off.

3. If the powder and sand are used what were the results?

Source:

Molly F. Miller and Thomas C. Moyer; Geology Department; Vanderbilt University
http://www.beloit.edu/sepm/Earth_Works/Modeling_a_Volcano.html