An ordinary ziploc bag can unlock a world of interest in chemistry and in the reactions within and around us. In this project, safe materials are mixed to change colors and produce bubbles, heat, gas, and odor. Explore endothermic and exothermic chemical reactions and help students develop skills in observation, experimentation, and inference. These activities are targeted for students in grade 3, 4, and 5, although they may also be used for higher grade levels.
The purpose is to generate student interest in chemistry. Students will observe, experiment, and learn to draw inferences.
These quantities are suitable for a group of 30 students to perform each activity 2-3 times:
- 5-6 plastic ziploc-style bags per lab group
- 5-6 clear plastic vials or test tubes (may be used instead of baggies)
- 1 gallon bromothymol blue indicator
- 10-ml graduated cylinders, one per lab group
- teaspoons, 1-2 per lab group
- 3 pounds calcium chloride (CaCl2, from chemical supply house or from store selling this type of 'road salt' or 'laundry aid')
- 1-1/2 pounds sodium bicarbonate (NaHCO3, baking soda)
Explain to the students that they will be performing chemical reactions, making observations about the results of these reactions, and then designing their own experiments to explain their observations and test hypotheses that they develop. It may be helpful to review the steps of the scientific method.
- First, direct the students to spend 5-10 minutes exploring the lab materials using all of their senses except taste. Have them write down their observations regarding the way the chemicals look and smell and feel, etc.
- Have the students explore what happens when the chemicals are mixed in baggies or test tubes. Demonstrate how to level a teaspoon and measure using a graduated cylinder so that students can record how much of a substance is used. For example, a student could mix a teaspoon of sodium bicarbonate with 10 ml of bromothymol blue solution. What happens? How does this compare with the results of mixing a teaspoon of calcium chloride with 10 ml of indicator? What if a teaspoon of each solid and the indicator are mixed? Students should record what they mixed, including quantities, the time involved to see a reaction (warn them that everything will happen very fast!), the color, temperature, odor, or bubbles involved... anything they can record. There should be observations such as:
- Gets hot
- Gets cold
- Turns yellow
- Turns green
- Turns blue
- Produces gas
- Show students how these observations can be written down to describe rudimentary chemical reactions. For example, calcium chloride + bromothymol blue indicator --> heat. Have the students write out reactions for their mixtures.
- Next, students can design experiments to test hypotheses they develop. What do they expect to happen when quantities are changed? What would happen if two components are mixed before a third is added? Ask them to use their imagination.
- Discuss what happened and go over the meanings of the results.