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Feb. 07, 2011

Explosive Science

by Science Friday Education

Click to enlarge images
Firework explosions never fail to capture the attention of anyone watching or listening. Unfortunately, most explosions are very dangerous and should be done only by experts. However, there are some types of simple explosions that can be replicated and observed on a much smaller scale.
 
In this activity, students will use household materials to investigate and explore how the release of carbon dioxide gas from a chemical reaction can cause a small-scale explosion. Students then will experiment with variables to determine which factors launch a film canister the highest.
 
Grade Level: 6th – 8th grade
Subject Matter: Physical Science
National Standards: NS.5-8.1, NS.5-8.2
New Year’s or July Fourth: time for parties and chemistry. In this video, Bassam Shakhashiri, chemistry professor at the University of Wisconsin-Madison, explains some of the science of fireworks.
 
Activity Materials
Alka-Seltzer tablets, two for each student
Gallon-sized plastic bags that can be resealed, two for each student
Film canisters, one for each student. These can be ordered online; see links at bottom of lesson.
Water, enough to fill each film canister halfway
Safety glasses – one pair for each student
One or two yardsticks
 
Vocabulary
Explosion: the sudden loud release of energy caused by a rapidly expanding volume of gas
Air Pressure: the amount of force that air will exert on an object in or around it.
Chemical reaction or change: a change that leads to the transformation of one substance into a different substance.
Physical reaction or change: a change in which the physical properties (state, size, shape) of a substance alters, but the chemical make up remains the same.
 
What To Do
Recommendation: These experiments will cause spillage. If possible, use an outdoor space for these experiments; they can be messy. Otherwise, prepare your space for spills and clean ups.
 

1. Begin the lesson by having students watch the Science Friday Video, “Celebrating Explosive Chemistry.” Begin a discussion with the students on what they think the definition of an “explosion” is. What are some ways explosions are created? Where are some places they have seen explosions? Are all explosions the same?

2. Tell students that they will conduct a series of experiments to observe how explosions can be caused by a chemical reaction. Inform students that even though the experiments are simple and safe explosions, they still should follow safety procedures. Review the importance of following proper safety procedures, particularly the use of safety glasses at all times. Although the chemicals being used are non-toxic, students should not taste any of the solutions.

Experiment 1

1. Hand out to each student: a large plastic bag that can be resealed, an Alka-Seltzer tablet, a film canister half-filled with water, and a pair of safety glasses. Remind students to keep their safety glasses on throughout the experiment.

2. Have students place an Alka-Seltzer tablet in one corner of the bag. Then have students very carefully place the open film canister in the other corner of the bag without causing the water to spill. Students must prevent the contents from mixing.

3. Discuss with students what Alka-Seltzer is used for and what it is made of. Ask them to predict what they think will happen if the tablet mixes with the water.

4. Instruct students to squeeze as much air as possible out of the bag without tipping over the film canister. Then seal the bag as tightly as possible.

5. Have students tip over the film canister, causing the water to mix with the tablet inside the bag. What do they observe is happening? Were their predictions correct? Discuss with students the reaction among the ingredients inside the bag.

Experiment 2

1. Ask students what they think would happen if the same experiment were conducted in a container that was unable to expand. Lead a discussion on air pressure and the possible effects of gas pressure building up inside such a container.

2. Challenge student to use the same materials (water, film canister with lid and Alka-Seltzer tablet) to propel a film canister into the air like a rocket. Allow students to experiment with the materials to launch their film canister. Students should keep notes on their experimentation and record the results.

3. After 5-10 minutes of experimentation, demonstrate to students how to launch a film canister by placing an Alka-Seltzer tablet inside a film canister half filled with water, immediately capping the film canister, and placing it top side down on the ground while backing away.

4. Have students compare their results to the one demonstrated. Did any students have a similar or different type of launch?

5. Allow students to modify their experiment in order to yield the highest rocket launch. Use yardsticks to record the height level of each launch and discuss with students what factors yielded the highest rocket launch.

What's Happening?
Firework explosions are caused by the burning of flammable materials that create very large amounts of hot gas that expand very rapidly. However, not all explosions are caused by the burning of flammable materials. Explosions can also occur through a sudden release of energy caused by a chemical reaction.
 
Alka-Seltzer tablets are composed of sodium bicarbonate and citric acid. When dry, the two powders do not react with each other, even though they are physically together. However, when water is added, it triggers a reaction that produces a large volume of carbon dioxide gas. Pressure inside the canister or sealed plastic bag increases as it fills with carbon dioxide gas that builds up from the chemical reaction. Pressure is the amount of force a gas exerts on the things in and around it. The pressure inside the bag or canister causes the container to break, creating an explosion that releases the pressure. If the canister happens to be placed upside down on a hard surface, the expanding gas pushes down on the top and upwards on the container, launching it high into the air.
 
Topics for Science Class Discussion
• What are other ways that explosions are made other than through a chemical reaction?
• Are there explosions that are useful or beneficial to us?
• How were fireworks first invented?
 
Extended Activities and Links
Extend the first experiment by having students design their own experiments to determine how different factors affect the production of carbon dioxide gas. Variables to be altered could be:
a. Amount of water
b. Number of tablets
c. Condition of tablet (whole, halved, quartered, crushed, powdered, etc.)
 
Try another fun and safe explosion using Mentos candy and Coke:
http://www.stevespanglerscience.com/experiment/original-mentos-diet-coke-geyser
 
Explore more cool experiments using Alka-Seltzer tablets at:
http://www.alka-seltzer.com/as/student_experiment.html
 
Learn more about the history and science of fireworks:
http://www.pbs.org/wgbh/nova/fireworks/
 
Sources of film canisters
These are required because they have a lid that pops up. Although most people use digital cameras at present, film canisters are still available online for educational purposes. TeacherSource.com offers a pack of 24 for $9.99:
http://www.teachersource.com/Energy/EnergyConversion/RocketFilmCanisters.aspx
 

 

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