Percent Composition of an Oreo Cookie

Whenever possible, I try to begin a topic with something my students are familar with. For the introduction of Percent Composition in my general chemistry course, I brought in bags of Oreo cookies. Seeing the bags upon entering class was a great attention getter. If you are looking for ways to add more inquiry to your chemistry course, this a an example of how can experiment with giving up a little control. Try it and see how it goes.

I wrote the following directions on the board:

Obtain an Oreo. The cookie is made up of WAFER and CREAMY FILLING. Using a balance, a plastic knife and a napkin (to keep the cookie from directly touching the balance), calculate the percent of the cookie that is made up of each part. You have 10 minutes to complete and be ready to explain the process and your answer.

I created a data table and asked my students to record the percent of creamy filling in the cookie they chose.

Students were keen to explain how they solved the problem. Then I showed them samples of sodium chloride, sugar and water. I asked them to calculate the percent composition of each element in the samples. I had to walk some through the first calculation, but the students easily jumped on board.

I then gave them another assignment.

Obtain a small slice of fruit. (I provided small pieces of cut up fruit like kiwi, grapes, banana, apple, …) You may use a balance and an aluminum weigh boat. (You could use cupcake liner papers also.) Find the percent of water in the piece of fruit. You will have to leave the sample in the drying oven overnight at 200°F.

Students came in the next day and easily calculated the percent of water in their fruit. I gave them a few notes on hydrates and how we name them. Then, I gave them one more assignment: Obtain 1.5 to 2.5 grams of hydrate. (I provide copper II sulfate and at least one more hydrate that I have in my chemical storage.) Find the percent of water present in the sample. You may use any items present on the lab counters. You can provide crucibles and Bunsen burners or a drying oven and any other equipment that you would routinely use in the conventional Percent Composition of a Hydrate Lab most of us are familiar with. Most students successfully found the relationship between finding percent composition with Oreos and fruit and finding percent composition of a hydrate. I helped them see the ratio between the number of moles of the anhydrous compound and the water from the hydrate. I then gave them sample lab data for other hydrates, so that they could find how many moles of water were attached to each of the hydrates referred to.

My students respond well to this type of activity. They are motivated and engaged. I never lectured over this topic. If you have trouble giving up control of your classroom to try inquiry activities, experiment with this activity. I hope you will find that it isn’t too scary. Let me know how it goes and/or share a similar activity/idea.

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