Hydrogen Balloon Demonstration (Melissa Dietz)

Principle(s) Investigated:

• Students will be able to identify an exothermic reaction.
• Students will be able to see differences in the rates of chemical reactions (using surface area, temperature, and concentration).
• Students will be able to understand fire and fire safety.

Standards:

8.5. Chemical reactions are processes in which atoms are rearranged into different combinations of molecules. As a basis for understanding this concept:

a. Students know reactant atoms and molecules interact to form products with different chemical properties.

b. Students know the idea of atoms explains the conservation of matter: In chemical reactions the number of atoms stays the same no matter how they are arranged, so their total mass stays the same.

c. Students know chemical reactions usually liberate heat or absorb heat.

Materials:

• 3 1000 mL Erlenmeyer flasks
• Aluminum foil
• Helium balloons (at least 2)
• 20 g of sodium hydroxide (NaOH)
• 1000 mL of H₂O
• 25 mL of hydrogen peroxide (H₂O₂)
• A pinch of manganese dioxide (MnO₂)
• 100 mL graduated cylinder
• Balance or scale
• Candle on long stick and matches
• Tub, ice, water (to make water bath)
• String and tape

Procedure:

1. Fill 2 Erlenmeyer flasks with 500 mL of H₂O. The water should be at room temperature or cooler. If the water is too hot, then the reaction will occur too quickly.
2. Have an ice water bath next to you for safety precautions. If the reaction occurs too quickly, immediately immerse flask in ice bath to cool down reaction as quickly as possible. Handle with care. Be aware that heat that is given off.
3. Add 10 g of NaOH to each flask of H₂O. Stir for 5 seconds.
4. For each Erlenmeyer flask, cut a 12 x 12 inch square of aluminum foil. Then, cut into smaller strips. Manipulate surface area of foil to allow students to see different rates of reactions.
5. Stir for 5 seconds and quickly place helium balloon over opening. Make sure it is securely attached to flask to prevent it from flying off. Caution: Do Not Breathe in Fumes!
6. Allow enough time for the reaction to occur. Look to see if the aluminum is still reacting with the NaOH and H₂O. At this time the balloon is filling with hydrogen gas.
7. Carefully twist balloon at neck and tie it shut. Add a string and tape the string to a table or place of interest.
8. Turn off lights for better effect.
9. Light candle and blow up balloon. Turn on lights when finished.
10. Add H₂O₂ and MnO₂ solution to the 3^rd Erlenmeyer flask.
11. Take the second balloon and carefully place opening on top of flask of H₂O₂ and MnO₂ solution.
12. Let it sit until the reaction has occurred.
13. Carefully twist balloon at neck and tie it shut. Add a string and tape the string to table or place of interest.
14. Turn off lights for better effect. Light candle and blow up balloon.

Student Prior Knowledge:

The students should know many different concepts before the demonstration. This demonstration allows students to utilize what they know and apply multiple concepts into one reaction; this works well as a review on chemical reactions. Prior to the demonstration, students should understand the concepts of density, exothermic/endothermic reactions, as well as different rates of reactions. This can be modified for your classroom. The multitude of concepts presented allows you to present the concept that you wish to teach.

Explanation:

Under normal conditions aluminum and water do not react because there is a protective layer of Al₂O₃ preventing the reaction from occurring.

2 Al + 6 H₂O --> 2 Al(OH)₃ + 3 H₂

Al(OH)₃ + NaOH --> Na⁺ + [Al(OH)₄]^-

Adding NaOH disrupts the aluminum oxide layer and the chemical reaction is activated.

Al₂O₃ + 2 NaOH + 3 H₂O --> 2 Na⁺ + 2 [Al(OH)₄]^-

If you touch the flask during the reaction you can feel the heat given off. Students will understand that this is an exothermic reaction because heat is being released, not absorbed. Do not breathe in fumes, the vapor is harmful because it contains NaOH. After letting the reaction happen for some time, the balloon fills with hydrogen gas.

Adding hydrogen peroxide with manganese dioxide in another flask, manganese dioxide acts as a catalyst for hydrogen peroxide to form oxygen and water. This is one way to add oxygen to the balloon and show the students how the reaction changes when oxygen is in direct contact with the hydrogen before the energy is added. The more MnO₂ is added, the faster the reaction will go.

2 H₂O_{2 (aq)} O_{2 (g)} + 2 H₂O_(l)

Questions & Answers:

1. What will happen to the reaction if the same amount of aluminum foil is added to the H₂O and NaOH solution, but the surface area of the aluminum is greater in one solution than the other?

A: The aluminum foil with the larger surface area will react faster than the aluminum foil with the smaller surface area because more particles of aluminum are exposed to the water and sodium hydroxide.

2. What effect will oxygen have on the chemicals in the balloon if it is added to the balloon prior to the explosion?

A: If the oxygen is mixed with the hydrogen in the balloon, the molecules will be next to each other and the reaction will occur more quickly.

3. What is a potential use for this reaction?

A: Hydrogen powered cars (mobility powered by hydrogen energy).

Applications to Everyday Life:

• On May 6, 1937, the Hindenburg disaster shocked the world. The Hindenburg was the first transatlantic passenger flight from Europe to America. The airship used hydrogen, which is extremely flammable, and the ship went up in flames just before landing. The rate of the airship being engulfed in flames occurred within seconds. A total of 97 people were on the airship, and luckily more than half survived the flight. The initial cause of what sparked the fire is still unknown.
• Exothermic reactions occur everyday. One example is burning fuel.
• It is hopeful that hydrogen will start powering automobiles within the next 20 years. This will have a huge eco-friendly impact on the environment.

Photographs:

Videos:

See attachments below.

References:

4.4.10 Reaction of Aluminum with Water and Sodium Hydroxide.

http://www2.uni-siegen.de/~pci/versuche/english/v44-10.html

Franek, J. (2000). Genie in a Bottle. The University of Minnesota

http://www.chem.umn.edu/services/lecturedemo/info/genie.htm

Petrovic, J. & Thomas, G. (2008). Reaction of Aluminum with Water to Produce

Hydrogen: A Study of Issues Related to the Use of Aluminum for On-Board

Vehicular Hydrogen Storage. http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/aluminium_water_hydrogen.pdf