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

______________________________________________

A. Begin the lesson by reviewing the experiments performed in each of the labs in the Property of Compounds CELL. Ask the following questions and involve students in the discussion to aid the review:

1. Ask students: What properties did you explore in Investigations One through Four? Students investigated mass, volume, pH, solubility, concentration, and saturation point.

2. Ask students: What new property did you explore in Investigation Five? Students investigated chemical reactivity.

3. Ask students: How did you investigate chemical reactivity? Students combined various compounds and observed the interaction between them to observe or draw conclusions about a compound’s reactivity.

4. Ask students: What chemical combinations did you explore? As students list the chemical combinations, instruct them to write them in the table in Problem 8.

Trial 1:  vinegar and baking soda

Trial 2:  rubbing alcohol and baking soda

Trial 3:  vinegar and salt

Trial 4:  potato and water

Trial 5:  potato and hydrogen peroxide

5. Ask students to think about the focus of this Investigation.

a. During this PostLab analysis, students will come to answer the following question: Do compounds made of the same elements react the same way?

b. Encourage students to realize that to answer this question, they must study the chemical formulas of each compound while examining the interactions between the compounds.

To prepare for this exploration, instruct students to write the chemical formula for each compound in the Table in Problem 8.  The Table is reproduced here and includes the chemical formulas for compounds used in this Lab.

______________________________________________

B. Ask students to reflect on combining vinegar and baking soda in Trial 1.

1. Ask students: Think about what occurred when you combined vinegar and baking soda. What did you observe? Students observed the formation of bubbles.

2. Ask students: Did you see any signs of a chemical change from your observations? Students first observed the production of bubbles, indicating the production of a gas.

3. Ask students: Based on your observations, do you think a chemical change occurred? Student answers may vary. Students will likely determine that a chemical change did occur, a conclusion supported by observing gas formation.

4. Instruct students to record in the Table in Problem 8 that a chemical change occurred in Trial 1. Students should put a “yes” in the last column of the Trial 1 row in the Table.

______________________________________________

C. Encourage students to think back to Trials 2 and 3, combining rubbing alcohol with a baking soda solution and vinegar with a salt solution.

1. Instruct students to first think about what occurred when combining rubbing alcohol and the baking soda solution.

a. Ask students: What did you observe? Students did not observe anything unexpected.

b. Ask students: Did you see any signs of a chemical change from your observations? Student answers may vary. The interaction between the chemicals did not produce any qualitative changes that were indicative of a chemical change.

2. Instruct students to think about what occurred when combining vinegar and the salt solution.

a. Ask students: What did you observe? Students did not observe anything unexpected.

b. Ask students: Did you see any signs of a chemical change from your observations? Student answers may vary. The interaction between the chemicals did not produce any qualitative changes that were indicative of a chemical change.

3. Ask students: Did a chemical change occur when combining rubbing alcohol with the baking soda or vinegar and the salt solution? Student answers may vary. There were no observable chemical changes.

4. Explain to students that scientists know that no chemical change occurs when combining rubbing alcohol and baking soda or vinegar and salt.

5. Instruct students to record that no chemical change occurred in Trials 2 or 3 by putting a “no” in the correct box of the table in Problem 8.

______________________________________________

D. Ask students to study the table in Problem 8 to help them draw conclusions about the chemical reactivity of vinegar, baking soda, rubbing alcohol, and salt.

1. Remind students that they combined baking soda with two compounds.

a. Ask students: Which two compounds did you add to baking soda? Students combined baking soda solution with vinegar and rubbing alcohol.

b. Ask students: How do the chemical formulas for vinegar and rubbing alcohol compare? Both compounds are made of carbon, hydrogen, and oxygen atoms.

c. Ask students to think about their conclusions concerning baking soda and vinegar as well as those concerning baking soda and rubbing alcohol. 

Ask students: Based on these observations, do compounds containing the same elements have the same chemical reactivity? Students should conclude that compounds made of the same elements do not necessarily have the same chemical reactivity.

______________________________________________

D. Ask students to study the table in Problem 8 to help them draw conclusions about the chemical reactivity of vinegar, baking soda, rubbing alcohol, and salt.

1. Remind students that they combined baking soda with two compounds.

a. Ask students: Which two compounds did you add to baking soda? Students combined baking soda solution with vinegar and rubbing alcohol.

b. Ask students: How do the chemical formulas for vinegar and rubbing alcohol compare? Both compounds are made of carbon, hydrogen, and oxygen atoms.

c. Ask students to think about their conclusions concerning baking soda and vinegar as well as those concerning baking soda and rubbing alcohol.

Ask students: Based on these observations, do compounds containing the same elements have the same chemical reactivity? Students should conclude that compounds made of the same elements do not necessarily have the same chemical reactivity.

______________________________________________

2. Remind students that they combined vinegar with two compounds.

a. Ask students: Which two compounds did you add to vinegar? Students combined vinegar with baking soda and salt.

b. Ask students: How do the chemical formulas for baking soda and salt compare? Although slightly dissimilar, both compounds contain sodium (Na).

c. Ask students to think about their conclusions concerning baking soda and vinegar as well as their conclusions concerning salt and vinegar. 

Ask students: Based on these observations, do compounds containing of the same elements have the same chemical reactivity? Students should conclude that compounds made of the same elements do not necessarily have the same chemical reactivity.

3. Instruct students to answer Problem 9 in the Student Data Record.

______________________________________________

E. Tell students that they will now analyze the data they gathered in Trials 4 and 5 to see if their experiments with the potato support the conclusion that was recorded in Problem 9.

1. For this activity, divide students into groups of three. Each group will work together to analyze their data from Trials 4 and 5.

2. Ask students to work together to answer Problems 10 through 13. Allow students sufficient time to answer these questions.

3. After students are finished, discuss the questions as a class.

a. Ask students: Did the potato in water act the same or different from the potato in hydrogen peroxide?  Explain your answer.  When the potato was placed in water, it sank to the bottom and remained inactive. This was in contrast to when the potato was placed in hydrogen peroxide. The potato in hydrogen peroxide produced gas, and bubbles formed.

b. Ask students: Do you think that a chemical change occurred in either Trial? Student answers may vary. Students should conclude that a chemical change may have occurred when placing the potato in hydrogen peroxide, indicated by the release of bubbles.

c. Tell students that a chemical change occurred when adding the potato to hydrogen peroxide but did not occur when adding the potato to water. Instruct students to complete the Table in Problem 8 by adding this information to the last column of the Table.

d. Ask students: Why do you think that there may have been a difference in the interaction between potato and water and potato and hydrogen peroxide? Student answers may vary. Students should conclude that the difference comes as a result of the unique chemical combination in the water and the hydrogen peroxide. Although they both contain hydrogen and oxygen, hydrogen peroxide contains an additional atom of oxygen per molecule of the compound. This change in the chemical composition causes a difference in chemical reactivity.

e. Ask students: Do the experiments involving the potato support your conclusion about the relationship between chemical makeup and chemical reactivity? Why or why not? Student answers may vary. Like Trials 1 through 3, the Trials involving the potato also show that compounds made of similar elements do not always have the same chemical reactivity. Although both contain only hydrogen and oxygen, hydrogen peroxide and water react differently to the potato.

______________________________________________

F. Close this CELL by leading the class to discuss their conclusions.

1. Instruct students to think about the experiments they performed in this CELL.

2. Ask students: Based on the experiments you conducted in Investigations One through Five, how would you answer the questions on this slide? Instruct students to answer this question in Problem 14 of their Student Data Record. Student answers may vary. Students should suggest that compounds made of the same elements may have different or similar properties, and compounds made of different elements may have similar or different properties. 

For example, vinegar and rubbing alcohol contain hydrogen, carbon, and oxygen. They are both clear liquids. However, they have different reactivity when combined with baking soda.

In addition, salt contains sodium and chlorine, while sugar contains carbon, hydrogen, and oxygen. They have different levels of solubility and different masses per volume. However, they are both white solids.

Therefore, through these explorations, students should conclude that its unique chemical formulas determine the properties of each compound. Although compounds may have shared some properties, each compound has its own unique set of properties. This set of properties distinguishes one compound from the next.