Summary

In this demonstration, students will observe a chemical reaction, and see how the product can be used to extinguish a fire.

Grade Level

Elementary, Middle or High

NGSS 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.
• 5-PS1-4: Conduct an investigation to determine whether the mixing of two or more substances results in new substances.

Objectives

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

• Differentiate between reactants and products in a chemical reaction.
• Recognize that carbon dioxide is denser than air.
• List the components necessary to sustain a combustion reaction.
• Understand the connection between their observations and the purpose of a fire extinguisher.

Chemistry Topics

This demonstration supports students’ understanding of

• Chemical Reactions
• Chemical Change
• Gases
• Density

Time

Teacher Preparation: 5-10 minutes

Lesson: 15 minutes

Materials

• Large beaker (1000 ml) or mixing bowl with spout/pour (clear glass or plastic is suggested)
• Large beaker (600ml-1000ml) or large glass Pyrex mixing bowl (needs to be transparent)
• 8-10 small candles/tea lights
• Matches or lighter
• Baking Soda (30g-50g, or approximately 3-5 teaspoons)
• Vinegar (300-500ml)

Safety

• Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
• Always use caution around open flames. Keep flames away from flammable substances.
• Always be aware of an open flame. Do not reach over it, tie back hair, and secure loose clothing.
• Open flames can cause burns. Liquid wax is hot and can burn the skin.
• An operational fire extinguisher should be in the classroom.

Teacher Notes

• Consider connecting this demonstration to an example of a fire extinguisher. Students might research the chemicals in a fire extinguisher and find out how and why it is effective. Scientific American has an informative resource.

• In this demonstration it is fine to use kitchen materials, such as bowls, but is much better if they are clear so that students can clearly see what is happening.
• It is strongly suggested to practice this demonstration prior to completing it in your classroom.

• Procedure

1. Place 8-10 candles in a large beaker (600 ml- 1000ml) or a glass Pyrex bowl.
2. Light all of the candles using matches or a lighter.

3. In a separate large beaker (1000ml) or large bowl with a spout/pour, measure approximately 22.5 grams or 4 teaspoons of baking soda.
4. Add 1 cup of vinegar (~235ml) to the baking soda.
5. Students should observe a reaction in the bowl between the baking soda and vinegar:

HC₂H₃O₂(aq) + NaHCO₃(aq) ⇾ NaC₂H₃O₂(aq) + H₂O(l) + CO₂(g)

Acetic Acid + Sodium Bicarbonate Sodium Acetate + carbon dioxide
(Vinegar) (baking soda) (dissolved in water)

Note: Let the reaction between the baking soda and vinegar occur for approximately 1 minute. Wait for the gas production and bubbling to be complete (the solution should be very quiet!) During this time the carbon dioxide gas product will build up above the solution.

6. Pick up the large beaker or bowl, containing the products of the reaction, and pour the gas into the container with the burning candles. Do not allow any of the solution to leave the container; only pour the invisible carbon dioxide gas!

7. Students will observe the gas extinguishing the burning flames (see video!)

• Teaching Points
  • Discuss the reactants and products of the reaction.
  • Discuss indicators or chemical change (question students: Did they notice any of the following: Temperature change? Heat produced? Formation of gas? Odor? Color Change? Formation of a precipitate?
  • Carbon dioxide gas is one of the products of this chemical reaction. Carbon dioxide is an invisible gas that is denser than air. Since it is so dense, it won’t float away after it is produced in the reaction, it will remain in the bowl. The fire was extinguished by pouring the carbon dioxide gas over the burning candles. Again, since it is denser than air, it will move towards the bottom of the container holding the candles, and extinguish the flames!