Rates of Reaction: Lessons
Rationale
Materials
Locating the activity in the conceptual
space
Conducting the activities
Extensions
Expectations
Rationale
This set of lessons is intended to expose the students to the
concept of rates. It is important to introduce this topic because
all biological and physical processes are governed by their rates.
If a student ever wondered why his/her grandmother's antique silverware
is tarnishing over time, this unit on rates of reaction can explain
this. If a student ever wondered how someone is lactose intolerate,
this unit on rates of reaction can explain this. It is important
for students to realize that chemistry is a dynamic subject. Things
are constantly changing all around us, some very quickly, and
others, very slowly.
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Materials:
Day One: Starch-Iodine
- Teacher only - starch, iodine, water (hot and cold)
Day Two: Steel Wool and Rust
- 30 pieces of steel wool
- Some tape or putty
- 30 pie pans
- 30 glass beakers
Day Four: Discussion on Rate Laws
- Handout on rate laws and activation energy
Day Five: Discussion of Half-life, Orders
- Handout on carbon-14 dating
Day Six: Alka-Seltzer
- 100 tablets of Alka-Seltzer or generic
- 10 narrow neck bottles (glass or plastic)
- 10-20 glass beakers
- 10 stirring rods
- 10 helium balloons
- 10 stop watches
- Hot plate to heat water
- Ice to make ice water
Day Eight: Catalysis
- Three sugar cubes
- Ash from either burnt paper, wood, or cigarette
- Tongs
- Matches
Day Nine: Autocatalysis
- 70 grams potassium chlorate
- 200 grams sodium sulfite
- 1 gram bromophenol blue indicator
- 100 mL 3 M sulfuric acid
- water
- 15 100 mL graduated cylinder
- 30 beakers
- Safety goggles
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Locating the activity in conceptual
space:
These activities are meant to expose students to the importance
of rates of reactions. The first demonstration is meant to show
students that not everything happens at the same time. Using hot
and cold water, the rates of the same reaction may differ signficantly.
For the steel wool experiment, students
will learn that the necessary components for rusting are water
(in either liquid or vapor form), air (and more importantly oxygen),
and iron. Teacher will leave a piece of steel wool overnight in
water to show that water alone is not enough to start the rusting.
The handout on rate laws and activation energy will give graphs and
example reactions where energy must be added for the reaction to proceed.
Students may draw upon energy as background
knowledge.
The carbon-14 dating sheet will give a brief history and process
description of carbon-14 dating. This deals with half-life and order of
reactions
The Alka-Seltzer lab activity really drives
home the ideas of concentration, surface area, temperature, and their effects on rates of reactions. Students should have a good
idea of the interconnectedness of these factors, as well as the idea that
many factors may influence the rate at which the reactions proceed.
The sugar cube demonstration is one of my favorites. Students are
able to see that sugar will not ignite on its own. It must have something
else there to help the reaction proceed. An understanding of catalysis should be gained from this
demonstration.
The autocatalysis takes the sugar cube demonstration to a new level.
Students will be able to perform their own catalysis experiment, and watch
as their yellow-blue interface slowly travels down the flask. Clearly,
the areas of time, catalysis, and
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Conducting the activities
Click here to view the series of lessons
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Extensions
- Have students create their own study of reaction rates. Allow
them to design their own experiments on the subject and use any
materials from the class that they need.
- Explore a software program by Logal Software entitled "Chemistry
Gateways: Reaction Rates and Chemical Kinetics." This program
will expose students to the molecular side of reactions.
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Expectations
Students will be given homework on the rate laws and orders of
reactions. There will be lab reports for both the Alka-Seltzer
lab and the autocatalysis lab. I expect students to participate
in the group discussions, and be involved in the class and the
labs.
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