7. Controlling Chemical Reactions

Objective:  Factors that Affect the Rate of a Chemical Reaction

Big Idea Application:
During chemical processes matter can change forms.

The overarching essential questions being considered:
What happens during a chemical reaction?

The essential questions being considered:
How can you tell if a chemical reaction has occurred, when two chemicals are mixed?

Approach/ Strategy being applied:

• Engagement, Exploration, Explanation, Elaboration, Evaluation- 5E Instructional Model
• Evaluation Tool from the Poison Project Article (Crawford, 1998).
• Structured Inquiry
• Guided Inquiry in the Conclusions Section of the Lab

Standards Addressed:
5a: Students know reactant atoms and molecules interact to form products with different chemical properties.
5c: Students know chemical reactions usually liberate heat or absorb heat.

Materials:

• Controlling Reactions Student Sheet: Can you speed up or slow down a reaction? (attached below)
• 3 Test tubes, Spatula
• Goggles
• Iodine
• Three ½ tablets of Vitamin C
• Clock/ Stop Watch
• Water
• Heat source

Anticipatory Set (Hook):

1. Provide the students with a cracker.  
2. Ask them to observe the cracker.
3. Have them chew the cracker, but not swallow it.
4. Ask the students:

• What is happening to the cracker?
• Why?
• What factors in your mouth contribute to these changes?

Lesson Plan:
Review terminology- activation energy

Lab: Can you speed up or slow down a reaction?

1. Put on your safety goggles.
2. Obtain a test tube rack with three test tubes.
3. Fill one test tube with 125ml warm water, one with 125ml cold water and one with 125ml room temperature water. 
4. Place a scrap of paper under each test tube and label it with the water's temperature to help you remember which test tube is which.
5. Carefully add three drops of iodine solution to each test tube and stir. 
6. What color is the water?_____________________ (They should all be the same.)
7. Crush up one of the ½ tablets of vitamin C.
8. What do you think will happen to each of the test tubes when the vitamin C is added? _____________________________________________
9. Get your clock or stop watch ready. Pour the vitamin C into your warm water test tube. 
10. Time how long it takes for the test tube to change color.
11. Record your observations on the data table.
12. Repeat steps 8-10 using the other 2 test tubes.

Assessment:
Complete Analysis and Conclusion Questions
                                                                                         
Contribution to student understanding:
This lesson asks the students to describe, explain, and predict the outcomes of the experiment.  Using this type of questioning will increase their "scientific literacy" and foster their understanding of the "nature of science," which states that all scientific knowledge is based, at least partially, on and/ or derived from observation of the natural world.