Chemical reactions are the most exciting part of chemistry class. Over the past five years I have developed an experience-based chemical reactions unit that features instructional videos coupled with a small group laboratory experience, whole-class demonstrations, and an interactive “demo test” as a final assessment. By the end of the unit, my students have either conducted or observed over 20 chemical reactions! My students leave class each day energized by what they have experienced in the lab. Through this fun lab-based unit, my students begin to recognize the similarities of each reaction type and build a repertoire of chemistry knowledge.
The heart of the unit is the lab called “Classifying Chemical Reactions, Analyzing and Predicting Products”, which is found in Flinn ChemTopic Labs Volume 6, Chemical Reactions. I have adapted this excellent lab into eight stations that include the following reaction types: synthesis, decomposition, single displacement, double displacement, combustion of a hydrocarbon and neutralization.
Each station includes an instructional video1 on the reaction type as well as materials required to conduct the associated chemical reaction.2 The students work with their lab partner to write a complete chemical equation for each reaction they do. By having the reactions coupled with the videos, students can work at their own pace, and they can review the reactions they have learned for homework. The extra class time that I gain from using the videos is devoted to more in-depth learning in the lab. I have effectively transformed this excellent experiment from a confirmation lab into a learning event.
After the students have completed the experiment, I use a series of demonstrations3 to review the six reaction types and practice predicting the products of a chemical reaction. The students observe the reaction demos and then work in groups to write the chemical reactions on white boards. For this part of the unit, I like to use demonstrations that the students can’t easily set up on their own; for example, thermite, “death of a gummy bear” and the singing flame tube demonstrations.
The final piece of the unit is an interactive “demo test” for the assessment. Students observe reactions4 which I conduct as demonstrations and write the chemical equations based on their observations. The demos I use for the test are quick and easy reactions that are similar to the ones they experienced in the lab. The students love this unit because of the wide range of reactions that they conduct and observe. This exciting lab-based exploration brings chemistry to life for my students.
Since the examples below are common in the chemistry classroom, the detailed instructions and descriptions are not listed here but are posted under “Geyer” on the ChemEd 2013 website presenters-and-handouts. Here you will find: instructions for each lab station, a handout listing questions for each video and the demo test.
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Notes
- Videos: Colby Tucker and I have made up the following one to two minute videos — freely available online — describing each type of reaction along with an example(s).
- Lab stations: The following reactions are to be completed at each station:
- Hydrochloric acid and magnesium metal; copper(II) sulfate and zinc metal (single displacement)
- Heating ammonium carbonate with a Bunsen burner (decomposition)
- Copper(II) sulfate and sodium phosphate (double displacement)
- Calcium carbonate and hydrochloric acid; hydrochloric acid and sodium hydroxide (neutralization)
- Burning magnesium (synthesis)
- Burning ethyl alcohol (combustion)
- Demonstrations: I typically present my favorite collection of demonstrations: Gummy Bear Reaction, Whoosh Bottle, Singing Flame Tube, Milk of Magnesia demo and Thermite Reaction. For the double displacement I usually mix iron(III) chloride solution and sodium phosphate solution.Like all demonstrations, these take time, safety knowledge and practice to perform. Be sure to use safety goggles and follow proper safety precautions for all of these demos.
- Test: On the demo test, students must indicate: the type of reaction, the evidence of chemical change and the balanced chemical equation.
Demos performed for test were as follows:- Reaction of aluminum foil in copper(II) chloride.
- Combination of sodium chloride and silver nitrate solutions.
- Combustion of steel wool.
- Decomposition of hydrogen peroxide in the presence of a catalyst.
- Reaction of solid sodium carbonate with hydrochloric acid.
- Burning of an US dollar bill. The bill is first dunked in a mixture of rubbing alcohol and water. This allows the alcohol to burn, leaving an intact, but wet, dollar bill.
- Reaction of magnesium metal with hydrochloric acid. The gas product is trapped in a balloon. Bonus question: What reaction took place when the balloon was ignited?
The students perform an ethanol combustion reaction. The students hold a test tube of cold water over the reaction to try to see condensation from the water vapor product.
Two stations have single displacement reactions. One has students add zinc metal to a copper(II) sulfate solution. The copper precipitate that is formed is a beautiful rust color. At the other station they add zinc metal to hydrochloric acid to produce hydrogen gas. They love to “pop” the hydrogen in the test tube.
Two stations are dedicated to neutralization reactions: one with a classic acid and base reaction and another with a reaction of an acid with a carbonate. Students add 1 M hydrochloric acid to a small sample of calcium carbonate.
The second activity is creating a beautiful pink color by adding phenolphthalein to NaOH. The students then add HCl to the test tube until the color disappears.
The synthesis reaction is a classic chemistry experience that all high school students will remember. A small piece of magnesium ribbon reacts with oxygen from the air by heating it with a Bunsen burner. The students often forget to include oxygen as a reactant in this chemical equation.
The decomposition reaction starts with a small sample of solid ammonium carbonate. The students heat the solid in a test tube until it is all gone. The three products of the reaction are gases!
The double displacement reaction is the quickest reaction to perform, but the most challenging reaction to write into an equation. The students add a small portion of 0.5 M copper(II) sulfate solution to an equal volume of 0.5 M sodium phosphate solution. The milky bluish-white copper(II) phosphate precipitate that forms is a surprise to the students.
