I begin the lesson by telling students that they will be testing a mystery food (marshmallows) in today's lab and deciding whether or not the food is a healthy food. I inform the students that they will need to test the food for the presence of starch, glucose, fat, and protein. Because my students will have to perform four different tests on one food, I review the test procedures that the students learned in the preceding labs throughout the Food Chemistry unit.
To test for starch, students will need to use iodine. The students will be able to identify a positive test result if the food sample turns a purple-black color. To test for glucose, the students will need to use a glucose test strip and read the results using a color comparison chart. To test for fat, students will need to rub the food sample on a paper bag. To test for protein, the students will place a test strip coated with the food in developer solution (equal parts rubbing alcohol and vinegar.
Next, I distribute a copy of the food chemistry experiment outline to each student. I display my copy on the document camera and review each step in the experiment. First, I ask students to create a descriptive title for their experiment. Next, I ask students to make a hypothesis about whether or not this food is healthy based on their own personal experience. I ask students to work with their science groups to write out the procedures they will follow as they conduct their experiment and the materials that their group will need.
I provide all the materials for the lab in a materials center so that students can gather supplies and work at their own pace. I am students to record their results as they work.
A video of my students engaged in the mystery food lab can be found here.
After each group has conducted all four tests on the marshmallow, I ask them to collaborate as they draft a conclusion about the food they tested. I ask each group to determine whether they think the food is healthy or unhealthy and to use evidence from their tests to support their opinion.