Summary

In this demonstration the teacher will complete two chemical reactions inside of separate balloons that each produces a gas. Students will observe and record data as the teacher attempts to ignite each balloon. This demonstration will help students better understand how to predict products, as well as familiarize them with double replacement and combustion reactions.

Grade Level

High School

NGSS Alignment

This demonstration will help prepare your students to meet the performance expectations in the following standards:

• MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
• HS-PS1-4: Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy.
• Scientific and Engineering Practices:
  • Analyzing and Interpreting Data
  • Engaging in Argument from Evidence

Objectives

By the end of this demonstration, students should be able to

• Use the given reactants in a double replacement reaction to predict the possible products.
• Use data from observations to make evidence-based conclusions.
• Predict the products of a combustion reaction.
• Identify a reversible and a nonreversible reaction.

Chemistry Topics

This demonstration supports students’ understanding of

• Chemical Reactions
• Classifying Reactions
• Predicting Products
• Balancing Equations
• Stoichiometry
• Combustion Reactions
• Reversible Reactions
• Nonreversible Reactions

Time

Teacher Preparation: 20-30 minutes

Lesson: Demonstration takes ⁓ 10 minutes; follow-up discussion 20-30 minutes

Materials

• 8 grams Calcium carbide
• 20 mL Water
• 150mL Vinegar
• 10 grams Baking soda
• 3-5L capacity Latex balloons
• Funnel
• Wooden splints
• Lighter
• Meter/wooden stick
• Safety shield

Safety

• Always wear safety goggles when handling chemicals in the lab.
• When lighting the match and wooden splint, be cautious with the flame.
• An operational fire extinguisher should be in the classroom.
• A safety shield should be used during this demonstration.
• Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.

Teacher Notes

• In this demonstration you will create two chemical reactions, one in each balloon. Each chemical reaction will produce a gas, which will be contained in the balloon. You will then attempt to burn each of the gases in the balloons. One balloon will contain the reaction between baking soda and vinegar, which produces carbon dioxide gas (when it is produced it will cause the balloon to expand). In the other balloon, calcium carbide and water react together to produce acetylene gas.
• You can view a video of me performing this demonstration on YouTube.
• Prior to the demonstration students should be asked several questions to explore their prior knowledge about the products of chemical reactions. Also, encourage students to predict what may happen to the balloons when a lit splint is drawn close. When students observe the reactions they will discover the properties of carbon dioxide and acetylene based on their observations, and the concept of reversible or non-reversible reactions.
• Students should be able to describe carbon dioxide as a product of a combustion reaction, which is a non-reversible reaction. They also should be able to offer an explanation about why one balloon puts out fires and the other is combustible.
• It’s encouraged that this demonstration is conducted outside. Try to pick a day/area with no wind.
• This demonstration should be practiced and successfully performed by the teacher prior to demonstrating in front of students.
• The acetylene balloon should not be ignited inside. The black smoke is very thick. Review the Material Safety Data Sheet for Acetylene, as the gas is dangerous.
• When preparing the materials, be sure to add the solids to the balloons before the liquids.

Procedure:

1. Start with the baking soda, adding the 10 grams of baking soda to the balloon with a metal scoop.
2. Twist the balloon just above the baking soda in order to prevent the baking soda and vinegar from reacting right away. Then add the 150mL of vinegar with a funnel (if it is available it works better if you use a slightly more concentrated acetic acid).
3. Tie off the balloon as the reaction begins so that the gas doesn’t escape.
4. Plan to fill the acetylene balloon right before you will use it. The reaction is hot and may melt through the balloon.
5. Add 8 grams of calcium carbide with the metal scoop to the balloon.
6. Add 20 mL of water with the funnel. The recipe includes excess water to help cool the reaction.
7. Place the balloons on a nonflammable ground, outdoors, and use a safety shield as a barricade between the balloons and students.
8. The wooden splint should be attached to the end of the meter stick. Ignite the end of the splint and first draw it close to the baking soda and vinegar balloon. As it burns a hole in the balloon the carbon dioxide gas released will extinguish the flame.
9. Finally, ignite the end of the splint and first draw it close to the balloon containing calcium carbide and water. As it burns a hole in the balloon the acetylene gas released will ignite.
10. It is important to discuss the outcomes with your students during the demonstration.

• Possible ways that the demonstration may not produce expected results:
  • Be sure to have a large flame on the acetylene balloon, or it might not ignite well.
  • The faster the balloon is ignited, the better the reaction.
• An answer key has been provided as a separate document for download.
• Another great lab, Classifying Reaction Types, could be used to help teach this topic.