Lessons

A Series of Lessons

Here is a set of lessons that could be used to expose students to rates of reactions.

Day One

Introduction to rates of reactions.
Definitions of rates, reactions, etc.
Show demonstration on rates of reactions (starch-iodine reaction: add iodine to two solutions: starch and hot water, and starch and cold water. Have students observe differences in the time it takes for the solution to turn purple/blue).

FOCUS LESSON

Day Two

Lecture/discussion on kinetics and significance of rates in industry.
Set up experiment involving rust using the steel wool. Place students in groups of two.

Day Three

Take a look at the results from steel wool experiment.
Group discussions of what happened.
Bring students back together and discuss elements necessary for rusting: water, iron, and air.

Day Four

Discuss rate laws and activation energy.
Handout on rate laws
- Include graph of typical energy diagram
- Include examples where products energy is higher than reactants

Day Five

Discuss orders of reactions, half-life
Handout on carbon dating

Day Six

Alka-Seltzer activity.

At the end, have a race for students to fill up a balloon with the most amount of gas. Allow students three Alka-Seltzer tablets, one balloon, one bottle, and thirty seconds. The reactions must be stopped after thirty seconds, and the group with the largest balloon wins.

Discuss the strategies each group employed, and continue discussion on day seven.

Day Seven

Reference Alka-Seltzer activity and the requirements for reaction: surface area, temperature, pressure, etc.

Day Eight

Introduce concept of catalysis using sugar cube demonstration.
Define catalyst, enzyme
Discuss biological implications of enzymes
Discuss food chemistry applications of hydrogenation

Day Nine

Laboratory on autocatalysis.
Discussion of results and theories about why things happened as they did.

Day Ten

Review of rates, rate laws, orders of reactions, half-life, factors influencing rates, catalysts, and enzymes.

Focus Lesson: Steel Wool

Rationale:

This is a lesson that might encourage student participation. Here the students are working with objects that they have see or handled before. Not only will this topic tie in with the web of ideas, but it will also introduce the concept of rates through a familiar means. Most students have seen a piece of steel wool at least once in their lives. Stressing that the exact same thing that happens to steel wool is happening to your car as you speak is important. This gives the students some connections to familiar phenomena.

Materials:

30 pieces of steel wool (if you do the extensions part of the lesson)
Some tape or putty
30 pie pans
30 glass beakers or tubes (preferably long tubes)

Locating the activity in conceptual space
Students will gain an understanding of the relationships existing between pressure and equilibrium. Also, students will be able to explore side issues related to this topic, as discussed in extensions.

Conducting the activity

Begin with lecture/discussion of kinetics and industrial importance (20 min)
Hand out instructions for steel wool experiment (procedure from steel wool phenomena page).
Split students up into groups of two.
Outline the experiment - discuss students' ideas on what might happen in the tube.
Have students begin setting up experiment
Students must record initial observations and predictions as to what will occur.

Extentions
Students will be given the opportunity to analyze the oxygen content in the air. As described in the steel wool phenomena page, it might be beneficial to find out if the exact same amount of water rises into the beaker, regardless of the amount of water in the pan initially. To try this, have the students set up the same experiment once again. This time, vary the amount of water in the pans. Be sure to mark off where the water level started, and when the experiment is over, mark off where the water levels rose to. Be sure to use the exact same sized tubes. Or, you can mark off the water line from where the original experiment ended. Then, using the same glass tube, repeat the experiment with a higher water level and see if the water rises to the exact same point.

Expectations
Students will be expected to complete the lab and the associated lab report by the next day (by day four). I would hope that students would take the following from this lesson:

1. The rusting of iron depends on a combination of water and oxygen.

2. Reactions may involve changes in pressure.

3. Air contains a fixed percentage of oxygen.

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