Be a Detective! Is it a Physical or a Chemical Change?

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Updated on Feb 11, 2012

Grade Level: 7th - 8th; Type: Chemistry


To determine whether a physical or a chemical change has taken place?

Research Questions:

  • How are the following terms defined: matter, mass, solid, liquid, gas, plasma, volume,
  • properties, physical change, chemical change and reversibility?
  • What is Boyle’s Law?
  • What is Charles’ Law?
  • How does a physical change differ from a chemical change?
  • Why is it of value to differentiate between physical and chemical changes?

On the information level, this experiment serves to acquaint students with basic information as to how chemists differentiate between chemical and physical changes. Students learn to observe both the physical and chemical properties of elements and compounds as well as changes which result in new substances and compounds. This project is an excellent vehicle to provide basic concepts in chemistry such as the nature o matter, the states or phases of matter, the properties of matter, the theories as to how these changes occur and the resultant products of physical and chemical changes. In the process the students learn to take safety precautions and to work effectively in a lab situation. This science fair experiment also serves to acquaint students with the essential processes of sciencing such as the importance of the use of a control, of identifying dependent and independent variables, of data collection, of pictorial and or graphic presentation of data and of being able to make better judgments as to the validity and reliability of their findings. They take on the role of scientists and in the process they learn to act as one.


  • Baking soda
  • calcium chloride
  • phenol red solution
  • 1 large sized plastic ziplock bag
  • 1 vial with cover, 2 spoons
  • 1 beaker
  • 1 graduated cylinder or measuring cup
  • paper towels for clean up
  • safety glasses
  • gloves
  • lab apron.
  • These are readily available from Chem. Scientific. Somemay be borrowed from the school’s lab.

Experimental Procedure

  1. Gather all the materials you will need for this project. These include baking soda, calcium chloride, phenol red solution, one large sized plastic zip lock bag, one graduated cylinder or measuring cup, one vial with cover, one beaker, two spoons, paper towels for clean up, a camera to take photos of the experiment (if you wish) , safety glasses, gloves and lab apron.
  2. Put on your safety equipment. Do not handle any of these substances with your bare hands!
  3. Copy the Data Chart provided on the next page so that you can readily record your observations.
  4. Start with the chemicals your are to work with and note their properties in the chart. Include solid, liquid, gas, odor, texture, color. Do not taste any of them!!!!!
  5. Are your gloves on? Begin by placing one teaspoon of baking soda into the plastic bag. Now add one teaspoon of calcium chloride to the bag and mix them.
  6. Using your graduated cylinder or your measuring cup, pour out 10 mL of the phenol red solution and pour it into a vial. Now, very carefully place the vial upright into the bag with the powders.Now seal the bag.
  7. With care, make sure you are keeping the bag closed. Now, tilt the bag empting the phenol into the baking soda and the calcium chloride mixture. Hold the bag. Observe what happened. Record the changes. Any evidence of a physical or a chemical change? Now make certain to wash your gloved hands thoroughly!!!!
  8. Study the data you have just gathered. Stop and consider. Were there any physical changes made, any chemical changes made? What evidence would you present for each case?
  9. What happened that was unexpected? Was the unexpected of any possible value?
  10. Investigate further .Are there any chemical changes that produce the reverse results? Would that have any practical applications?
  11. Were you to investigate this change process in the future, what else might you doing? Any new directions?
  12. Write up your investigation. You may wish to include photos of the before and sifter stages of this experiment. Be sure to include your bibliography.

Chart of Observations

Chemicals Used Before Mixing: Properties After Mixing: Properties
Calcium chloride
Baking Powder (not soda)
Solution of Phenol Red

Terms/Concepts: Matter, solids, liquids, gases, plasma, mass, volume, atomic particles, Boyle’s Law, Charles’ Law, physical change, chemical change, reversible, hand warmers.


VanCleave, Janice, Chemistry For Every Kid, John Wiley & Sons Inc., New York, N.Y. 1989, pp91 -119

Hone, E , Joseph, A, Victor, Brandwein, P, A Sourcebook for Elementary Science, Harcourt, Brace & World, Inc. New York/Burlingame, 1962

Dr. Muriel Gerhard (Ed.D.) is a retired educator with fifty seven years of experience in all aspects of public education. She has been a teacher, principal, administrator, college professor, researcher, grants writer, change agent and science editor. She is the author of several books on education used as college texts. These include the best selling Effective Teaching Strategies with the Behavioral Outcomes Approach and The Behavioral Outcomes Handbook for Teachers and Administrators. Presently she is a consultant in science education and curriculum development, a marriage and family therapist, a newspaper columnist and an author. Her latest book, recently published, is a memoir of sixty vignettes entitled âNow That I`m Dead, I Decided to Write this Bookâ.

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