This is the fifth and final regular Investigation of the LabLearner CELL Properties of Compounds. In it, students will examine the combination and reaction of compounds.

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A. Begin the lesson by reviewing with the class what they have investigated thus far in this CELL.

1. Ask students: What properties have you investigated in Investigations One through Four? Students have investigated the qualitative properties of color and state of matter, as well as the quantitative properties of mass, volume, solubility, and pH.

2. Remind students that throughout Investigations One through Four, they have worked to answer two main questions:

a. Do compounds made of similar elements have similar properties?

b. Do compounds made of different elements have different properties?

3. Ask students: How have you answered these questions based on your lab experiences? Student answers may vary. Students should recall that compounds made of similar elements do not always have similar properties. They may vary in mass, volume, solubility, and pH. Similarly, compounds made of different elements do not always have different properties. They may share similar properties.

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B. Explain to students that Investigation Five will guide them in exploring an additional property of compounds, chemical reactivity.

1. Encourage students to realize that compounds combine in unique ways. Sometimes when compounds combine, a chemical change occurs.

2. Ask students: What is a chemical change? Student answers may vary. A chemical change is a change in which a new substance or substances are produced.

a. Students may recall from other experiences with chemical reactions that when a chemical change occurs between substances (the reactants), a new substance or substances are produced. These are called the products of the chemical reaction.

b. If needed, encourage students to find and read the definition of chemical change in the Scientist’s Glossary.

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3. Explain to students that sometimes when chemicals combine, a chemical change takes place.  Guide students in performing the following role-play to increase their understanding of chemical change.

a. Choose four student volunteers.  Two students will together represent Compound A-B, and two students will represent Compound C-D.  One student in each pair will represent one atom in the compound. For example, one student in the first pair will represent atom A and one student will represent atom B. Provide each student with a letter sign representing his or her role in a compound pair. Use masking tape to attach each student’s sign to the front of his or her shirt.

b. Direct each pair of students to hold hands, link arms, or stand close together and walk from opposite ends of the classroom so that A and C are opposite one another, and B and D are opposite one another.  This represents the two compounds being put into a beaker or other container.

c. When the student pairs meet, have them shake hands with one another. Student A should shake hands with student C, while student B should shake hands with student D.

d. Explain to students that they should keep contact after ending the handshake by holding hands, linking arms, or standing close together. This represents the reaction process.

e. Direct the new pairs to turn and walk back to opposite ends of the room. This represents the formation of new chemicals.

4. Tell students that the role play illustrated what occurs during a chemical change. Compound A-B combined with Compound C-D to create two new compounds: Compound A-C and Compound B-D.

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5. Explain to students that sometimes when chemicals combine, a chemical change does not occur.  Guide students in performing the role play in the following manner to illustrate the lack of a chemical change.

a. Instruct students to return to their original positions from the beginning of the role play. Student A and student B should pair up again and stand at one end of the classroom. Student C and student D should stand on the opposite side of the classroom. Each pair of students holds hands, link arms, or stand close together and walk from opposite ends of the classroom so that A and C are opposite one another, and B and D are opposite one another. This again represents the two compounds being put into a beaker or other container.

b. When the student pairs meet, students should wave to one another. The compounds do not react to create new compounds.

c. Direct the student pairs to turn and walk back to opposite ends of the room.

6. Tell students that the role play illustrated what occurs when two chemicals do not undergo a chemical change. The original chemicals remain and no new compounds are formed.

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C. As a class, begin to discuss how a chemical change is determined.

1. Ask students: How do you know when a chemical change has occurred? Student answers may vary. Some students may recall from other experiences that there are 10 common signs of a chemical change. Other students may have different backgrounds.

2. Instruct students to refer to Problem 1 in their Student Data Record. Tell students that scientists use a list of ten common signs when deciding if a chemical change has occurred. Ask student volunteers to read aloud from the list:

a. A change in volume.

b. A change in temperature.

c. An unexpected change in color.

d. A change in electrical conductivity.

e. A precipitate forms (a chemical falls out of solution as a solid or a liquid).

f. A gas is produced.

g. A change in pH.

h. A change in a chemical or physical properties occurs.

i. A change in odor.

j. A change in melting or boiling point.

3. Encourage students to realize that scientists use these signs as a reference in determining whether or not a chemical change occurs.  Observing a large or distinct change or sign indicates that a chemical change likely occurred. Observing a smaller or less distinct change or sign may not indicate with certainty that a chemical change occurred. Scientists may use a less obvious sign to indicate that more testing should be done to determine whether or not a chemical change has occurred.

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D. Tell students they will create six different combinations of substances in the lab. As students conduct their experiment, ask them to consider the following question:

• Do compounds made of the same elements react the same way with other substances?