Marge's Systematic Observation


Objectives: After completing the lesson, students will be able to:

  carry out a simplified version of a systematic observation, in which they make a prediction, carry out an investigation to test that prediction, and offer an explanation of the results of their investigation

  explain phase changes using a molecular model of matter


Key Question: "What happens when you put dry ice into a soap solution?"



            The first section of this lesson introduces students to the concept of a systematic observation. They begin with an initial inquiry question: "What happens when you put dry ice into a soap solution?"Through class discussion, students are asked to predict what they guess will be the answer to the initial question. The meaning of a variable is introduced as part of this discussion. Once an outline of the procedure is given, students acquire materials and carry out the observation, making sure to take notes and drawings of what they observe. This section concludes with a discussion of what each group observed, and possible explanations.

            The second section of this lesson introduces the vocabulary of the three states, or phases, of matter: solid, liquid, and gas. Students discuss the phase changes that occur when energy (heat) is added to matter: melting and evaporation. The phase changes associated with the removal of energy are discussed next: condensation and freezing. The unique process of sublimation that dry ice undergoes is then defined and explained. The lesson concludes with a review of the particulate model of matter, and the kinetic molecular theory, to explain phase changes, using the petri dish models of solids, liquids, and gases first introduced in Lesson 5 (Matter and Energy).


Time Required: 45-60 minutes (1 class session).



for the class

  dry ice, broken into  pieces about 1 1/2" in diameter

  insulated container suitable for storing dry ice

  dishwashing soap

  one overhead transparency of each of the following (from the Dry Ice  GEMS guide): "Phase Change Diagram A" (p. 72); and, "Phase Change Diagram B" (p. 73)

  three petri dish models from Lesson 5 (Matter and Energy)


for each group

  2-3 plastic spoons

  2-3 clear plastic cups

  1 tray

  newspapers to cover work surface



for each student

  1 copy of "Marge's Systematic Observation" handout (p. 71)

Procedure: see pp. 64-70 in the Dry Ice  GEMS guide.




  class discussion of systematic observation results and explanations

  "Marge's Systematic Observation" student handout


Homework: Read the student handout, "What Is the Scientific Method?"


OUSD Science Content Standards (State of  California Science Content Standards):   1-a; 1-b; 1-e; 1-f (7-a; 7-b; 7-d; 7-e).



Barber, Jacqueline, Kevin Beals, and Lincoln Bergman. Dry Ice Investigations: Teacher's Guide. Berkeley, CA.: Lawrence Hall of Science, University of California, Berkeley, 1999, pp. 63-73.


Notes: It is important to emphasize to students that scientists design and carry out observations and experiments in order to test various explanations for questions they have. Systematic observations and experiments are part of a process of asking, testing, and answering questions. This process leads to new questions, tests, and explanations in a never ending process.


Key Vocabulary:

condensation: when a gas turns into a liquid.


evaporation: when a liquid turns into a gas.


freezing: when a liquid turns into a solid.


kinetic molecular theory: when heat is added to an object, the molecules that make up the object move faster and farther apart.


melting: when a solid turns into a liquid.


phases: the three states in which matter occurs: solid, liquid, and gas, or vapor.


phase change: when matter turns from one state into another.


sublimation: when a solid turns into a gas without first becoming a liquid.


systematic observation: In a systematic observation, you make a plan, decide on the conditions, follow the plan, and then carefully observe and record what happens over time.


variable: A variable is something which can vary each time you do something.