Physical versus Chemical: How do you know?

We are in the first two weeks of chemistry and everything is about "How science is done?": the maths, measurements, observations, evidence, data recording, you know the stuff.  One of the labs was a nine-station physical versus chemical lab. When they were finished with the experiments I had the students go back to tables that did not include their lab partners and consult with others on their conclusions. They shared observations and were directed to argue with each other on whether a particular station was a chemical change or physical change. I felt this piece of the work was important for students to understand that their analysis and conclusion must be defendable with evidence. We also used this time to talk about when scientists disagree. Last year I incorporated POGIL into my lessons. This year I am adding ideas about teaching and learning through argumentation; argumentation is really evidence-based reasoning in relation to scientific and social issues.

A couple of side notes:

• A variety of waste disposal methods are asked for, depending on the station, which was good practice for the students. 
• Nine stations may be too many for some classes. I found it perfect for many, but one too many for some.

After the lab, the class shared results as a whole and came up with definitions for physical change, evidence of physical change, chemical change, and evidence of chemical change.  These definitions were added to the students' interactive notebooks in the form of the following foldable. 

Finally, for the assessment, students were asked to write a well-developed conclusion (at least 4 sentences) about what was learned and what types of observations (evidences) can be used to tell whether a physical or chemical change has occurred.

For those that are interested, the entire lab assignment follows.

Physical vs. Chemical Change Lab

Background Information

How can you describe a pile of gold scientifically? You talk about its physical and chemical properties.  Physical properties are characteristics that can be observed or measured without changing the makeup of the substance. Examples of physical properties are each phase of matter, color, density, weight, volume, texture, taste and smell. Chemical properties are characteristics that identify the chemical makeup; examples are elements from the periodic table.

What happens if I want to melt my pile of gold to make coins? This would result in a physical change.  These physical and chemical properties can change. Physical change defines when a substance has changed its “look”, but not its chemical substance. Examples of physical changes are melting, freezing, cutting, boiling or mending. A chemical change forms new substances; material goes through a chemical reaction. Examples of chemical reactions are rusting, creation of gases or bubbles, burning wood, cooking.

Pre-Lab:

Write a description of the differences between physical and chemical reactions. What are properties and changes? What are examples of physical properties, physical changes, chemical properties and chemical changes?

Procedure

Set up a data table in your journal that allows for identification of the station, recording of observations, and whether it was a physical or chemical change. 

Example data table:

Station # and name	Observations	Physical or chemical change?

Station 1

·         Add a small scoopful of sodium chloride into a half-full 100 mL beaker of water. Stir the contents of the beaker for approximately one minute.

·         Record your observations.

·         Pour the solution down the sink and rinse out the beaker when you are finished.

Station 2

·         Pick up a small piece of magnesium ribbon with the crucible tongs and heat it over the Bunsen burner until you observe a change.

Station 3

·         Pick up a small piece of zinc with crucible tongs and heat it over the Bunsen burner until you observe a change.

·         When you have finished, place the residue into the beaker of water provided.

Station 4

·         Fill a test tube halfway with silver nitrate solution.

·         Quickly squirt an entire pipette full of sodium chloride solution into the test tube.

·         Record observations.

·         When you are finished at this station, pour the contents of the test tube into the waste jar provided, fill the test tube with water (for rinsing) and pour that water into the waste jar.

Station 5

·         Pour 25 mL of acetone into the glass dish.

·         Place a piece of Styrofoam in the acetone.

·         After making observations, remove the Styrofoam with a glass stirring rod. Pour the acetone into the used acetone beaker provided.

Station 6

·         Cut a SMALL fresh slice from the potato.

·         Use a dropper to put 3-4 drops of iodine solution on the potato slice. Record observations.

·         After your observations are complete, throw away the used slice of potato into the trash can.

Station 7

·         Strike a match and watch it as it burns. Blow the match out before it burns your fingers.

·         Dispose in the used matches can.

Station 8

·         Pour about 1 cm of hydrochloric acid into a test tube.

·         Place a small chip of marble in the same test tube.  Make sure the acid covers the chip.

·         Record observations.

·         When you are finished making observations, pour the test tube contents into the waste HCl beaker provided and rinse out the test tube.

Station 9

·         Take full dropper of the acetic acid (vinegar) solution and squirt its contents into a 50 ml beaker.

·         Using the ammonia dropper bottle, add ammonia drop-wise into the 50 ml beaker.

·         When your observations are completed, pour the contents down the drain and clean the beaker with water.

Data Analysis

Answer the following questions in your journal:

1. List all of the chemical changes you observed.

2. List all of the physical changes you observed.

3. What were some of the observations that indicated a physical change had occurred?

4. What were some of the observations that indicated a chemical reaction had occurred?

Conclusion

Write a well-developed conclusion (at least 4 sentences) about what was learned and what types of observations (evidences) can be used to tell whether a physical or chemical change has occurred.