Summary

In this lab, students will investigate an endothermic chemical reaction by combining baking soda, hand soap and citric acid. The students will be tasked with differentiating between chemical and physical changes during this experiment.

Grade Level

Elementary School

Objectives

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

• Differentiate between physical and chemical change
• Identify indicators of chemical change during a chemical reaction
• Define an endothermic reaction and identify when such a change has occurred

Chemistry Topics

This lab supports students’ understanding of

• Reactions
• Chemical change
• Physical change
• Indicators of chemical change
• Endothermic
• Conducting investigations

Time

Teacher Preparation: 20 minutes
Lesson: 45 minutes

Materials

Needed for each group of students

• goggles
• stir sticks
• large plastic cup, or bowl
• measuring cups (¼ cup and ¾ cup)
• measuring spoons (1 tbsp)
• paper towels
• deep sensory tub (or other deep container to contain mixture)
• ¼ cup clear hand soap
• ¾ cup warm water
• 2 tbsp. baking soda
• 2 tbsp. Citric Acid (and a little extra keep the reaction going)
• food coloring

Example demo materials (needed to create a mixture)

• Sand
• Water
• Plastic Beads
• Rocks

Safety

• Always wear safety goggles when handling chemicals in the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
• Students should wash their hands thoroughly before leaving the lab.
  

Teacher Notes

• In simplest terms, a chemical change (or chemical reaction) occurs when two or more substances are mixed together and transform into a third substance. Not all substances react chemically when mixed together, sometimes they simply remain a mixture of those substances.
• This lab is intended for use in PreK–4th grade classrooms.
• I suggest that you premeasure the materials and have all items already laid out for students.
• Citric acid can be found in the canning section of your grocery store
• Before the lesson, collect several items that can be used for a teacher demo of mixtures (see suggestions in materials list above).
• Tell the students that they are going to watch what happens when different materials are mixed together.
• Begin by mixing water and sand together.
• Ask – When water and sand are mixed together, do they change into something else? (Some students might say that a change has occurred because the mixture looks different from its original ingredients.)
• Ask – Can this mixture be separated back into its original parts? (yes) How? (The water could be filtered out of the sand.)
• Now ask students to predict what will happen if the following substances were mixed together: plastic beads and vegetable oil; air and water (blow air through a straw into a cup of water); rocks and packing peanuts. Demonstrate each example as you go. (The materials do not change when mixed together; individual components can be easily separated from the mixture.)
• Tell students that sometimes when two (or more) materials are mixed together, a change occurs and another substance is created. This is called a chemical reaction. Some observations that indicate a chemical reaction has occurred include: gas may form, heat or cold may be produced and colors may change. When the temperature of the mixture decreases during a chemical reaction, it is classified as an endothermic reaction. If the temperature increased during the reaction it would be called an exothermic reaction.
• This can be a messy lab if students are not properly supervised. Volunteer adult support is recommended.

• Food coloring can be removed from lab, but if used, it should be added by an adult.
• Differentiation: for higher grade levels, the lab could be expanded into creating the mixture under pressure (erupting bottles or film canister rockets) with added lessons in acids and bases.
• Based on the grade level of students, use the student section as a handout/worksheet, or lead the class together through the questions, procedure, data collection and conclusion.
• See photos below for example results: