« Return to AACT homepage

AACT Member-Only Content

You have to be an AACT member to access this content, but good news: anyone can join!

Need Help?

Alien Invasion? Mark as Favorite (1 Favorite)

LESSON PLAN in Observations, Chemical Change, Inferences, Physical Change, Identifying an Unknown, Solute & Solvent, Kitchen Chemistry. Last updated May 03, 2023.


In this lesson, students will explore both physical and chemical changes as they try to help the Department of Homeland Security analyze and identify materials found in a mysterious capsule. Students will examine and observe an unknown object (a frozen water balloon) as it changes (melts). They then mix combinations of everyday substances to observe chemical changes.

Grade Level

Elementary school


By the end of this lesson students should be able to:

  • Describe the difference between a physical change and a chemical change.
  • Identify examples of physical changes and chemical changes.

Chemistry Topics

This lesson supports students’ understanding of the following topics in chemistry:

  • States of matter
  • Physical change
  • Chemical change
  • Solutions
  • Observations
  • Inferences


Teacher Preparation: 15 minutes for each part of the lesson

Lesson: 2 or 3 classes, 45 minutes each


For each group:

Part A

  • A balloon full of water, frozen
  • Bowl
  • Hand lens
  • Ruler
  • Thermometer
  • Science journal
  • Safety goggles
  • Scale or balance

Part B

  • Water
  • Vinegar
  • Seltzer tablets
  • Salt
  • Sugar
  • Baking soda
  • Food coloring
  • Thermometer
  • Test tubes, vials, or mixing containers
  • Measuring spoons
  • Stirring rods or spoons
  • Safety goggles
  • Science journal


  • Students should wear goggles throughout the activity.
  • Remind students that although they are mixing unknown substances in this activity, they should never on their own mix substances that are unknown.
  • Clean up should be done carefully so that materials are not mixed together.
  • Remind students not to put anything in their mouths.

Vocabulary Terms

  • Chemical change
  • Inference
  • Observation
  • State change
  • Physical change


chemical change, physical change, state change, solvent, solute

Teacher Notes

  • This activity can be done with students who already have some background with physical vs. chemical changes, or it can be modified to be an introduction to the topic.
  • To engage students quickly in the scenario, you may wish to be dramatic. For example, students from another class could rush in to bring the news or the principal could cut into the class on the intercom to give students their instructions. You may wish to create a capsule for students to find the materials in.
  • It is important not to tell students what any of the materials or substances are (for example, don’t refer to the frozen water balloon as a frozen water balloon).

Teacher preparation

Prepare the “alien” capsule for students to explore or for you to present.

  • Freeze water in balloons (have enough for one balloon per group)
  • Fill vials or small containers, each with one of the following: sugar, salt, baking soda, vinegar, water, over-the-counter antacid tablets (sodium bicarbonate), and any other safe substances from the kitchen. Label each vial of the same substance with the same symbol, letter, or number so students can identify which substance is which. There should be enough so that each group gets one vial of each substance.



Begin by explaining to students that an object thought to be a space capsule has been found in the schoolyard. It contained a refrigerated compartment with large, round objects in it and several smaller unrefrigerated compartments with different vials of fluids. The Department of Homeland Security (DHS) wants to know what the contents are so they can figure out where the capsule came from and what it means. DHS has asked your class to help analyze the materials. They are looking for younger students that can think creatively and help to resolve the issue.

As a class, you need to answer the following questions:

Objects in the refrigerated compartment

  • What are the physical properties of the object in the refrigerated compartment?
  • What are the objects? What are they made of?
  • Are the objects in the refrigerated compartment changing? If so, are they undergoing physical changes or chemical changes?

Substances in the vials

  • What are the physical and chemical properties of the substances in the vials?
  • What happens when the substances in the vials are mixed with other substances?
  • If there is a change, is the change physical or chemical?

Challenge the class to come up with ways to answer the questions. Explain that DHS will require explanations for all of the answers. They will need to know what observations were made and what analyses were conducted, so it is important to take careful notes in the science journals.

Part A: Alien Frozen Material (Physical change investigation)


  1. Put the frozen balloon in a bowl in the middle of each group of students and instruct them to examine it, describe it, and infer what it is. Explain to students that they MUST NOT destroy the object in any way. They should record their observations (something directly observable) and inferences (understanding that is not directly observed but is based on direct observations) so that they can compare with the other groups. As they are working, challenge students to think critically about their observations and inferences:
  • What is this made of? What is on the outside? What is on the inside?
  • What can you actually observe with your eyes, hands, ears, and nose?
  • What are you inferring: what do you think you know based on your observations?
  • Can you be 100% sure?
  • What could you do to be 100% sure?

Download the Teacher Guide to view the rest of this lesson.