Summary

In this demonstration, the teacher will perform two chemical reactions, one will be between acetic acid (vinegar) and sodium bicarbonate (baking soda) and the other will be between Alka-Seltzer and water. Both reactions will produce gas and will be conducted in a Ziploc® bag, causing it to inflate. Students will observe the reactions and analyze the results in order to understand indicators of chemical change. Students will also determine that these are both endothermic reactions based on their observations.

Grade Level

Elementary school

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.
• MS-PS1-6: Undertake a design project to construct, test, and modify a device that either releases or absorbs thermal energy by chemical processes.
• 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

• Define chemical reaction.
• Identify indicators of chemical change.
• Identify a reaction as endothermic or exothermic based on lab observations.

Chemistry Topics

This demonstration supports students’ understanding of

• Chemical reactions
• Indicators of Chemical change
• Observations
• Endothermic and Exothermic reactions

Time

Teacher Preparation: 15 minutes
Lesson: 30 minutes

Materials

• 1 tsp baking soda (sodium bicarbonate, NaHCO₃)
• ¼ cup (60ml) of store bought vinegar
• (5% by mass acetic acid solution, HC₂H₃O₂)
• 2 Alka-Seltzer tablets
• ¼ cup (60ml) of water
• 2 Ziploc® sandwich bags
• 1 tsp measuring spoon
• ¼ cup measuring cup
• 2 small rubber bands

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
• Students should wash their hands thoroughly before leaving the lab.
• Sodium Bicarbonate (Baking Soda) SDS
• Vinegar SDS

Teacher Notes

• This is a great demonstration to show student prior to completing the Rocket Challenge Lab or the Alka-Seltzer Rockets Lab.
• The reaction of sodium bicarbonate (baking soda) and acetic acid (vinegar) produces carbon dioxide gas, water and sodium acetate (soluble in water). The carbon dioxide gas can originally be seen as bubbles in the solution, but will quickly be released from the solution. The amount of carbon dioxide gas produced will inflate the Ziploc® bag.
• Chemical Equation: NaHCO₃ + HC₂H₃O₂ → NaC₂H₃O₂ + H₂O + CO₂
• An Alka-Seltzer tablet contains aspirin, citric acid and sodium bicarbonate. When it is mixed with water, it also will produce carbon dioxide gas, and can originally be seen as bubbles in the solution, but will quickly be released from the solution. The amount of carbon dioxide gas produced will inflate the Ziploc® bag.
• Teachers should engage students in a discussion about each of the reactions observed in this demonstration and focus on:
  • Indicators of a Chemical Reaction (gas produced, heat absorbed and temperature will drop)
  • Amount of reactants used
  • Amount of products formed

Procedure

1. Label 2 bags with a sharpie as: 1 & 2.
2. Measure 1 tsp of baking soda into the Ziploc® bag #1, place it in the corner of the bag, and tie it off with a rubber band, as shown.
3. Place two Alka-Seltzer tablets in the corner of bag #2 and tie it off with a rubber band.
4. Measure ¼ cup or 60ml of vinegar and add the vinegar to the other corner of Ziploc® bag 1. Remove excess air from bag and securely zip it shut. You may want to have a student assist with this step.
5. Measure ¼ cup or 60ml of water and add the water to the other corner of Ziploc® bag 2. Remove excess air from bag and securely zip it shut. You may want to have a student assist with this step.
6. Remove the rubber band and allow the vinegar and baking soda to mix in bag 1.
7. Remove the rubber band and allow the water and Alka-Seltzer tablet to mix in bag 2.
8. Shake the bag to mix the baking soda and vinegar. When bubbling stops make observations about the contents and temperature of the bag.
9. Shake the bag, and break the Alka-Seltzer tablet to mix contents of bag 2. When bubbling stops make observations about the contents and temperature of the bag (the mixtures should both be cool to the touch).
10. Do not open or empty bags until you have made observations and comparisons of all of them.