Rainbow Challenge Lab

The primary goal of this activity is to have students apply the principles learned about liquids in class. Students will need to determine the density differences of the different "pops" in order to successfully layer them in the test tube. This will require quantitative measurement of mass and volume to calculate density. The students will also use trail and error methods to compare the selected pops and determine which 6 pops will work the best.

This activity is best suited for high school Chemistry students in grades 11-12. I have used this with students working in groups of 2-4. The activity is meant to be an inquiry-based lab, but I have also used it as an alternative assessment. The activity may be completed with standard lab equipment, such as graduates, electronic balances, etc. The students will need to identify the procedures that they will follow to complete the activity. These may be submitted prior to beginning the activity if the instructor chooses. I have usually used this activity when discussing liquids and their properties, but it could be also be incorporated into a unit on the properties of matter to illustrate the effect of density differences.

I adapted this activity from an assessment developed by Mr. Ken Beck of Solon High School in Solon, IA. I have used it primarily as an inquiry lab.

I introduce the lab by explaining the overall goal of the lab to the students and identifying the "pops" that they will have available. I try to have a wide range of selections, both regular and diet. Last year we also incorporated some energy drinks, such as Red Bull, Rock Star, etc. I explain the goal, give them the time-line (usually two 50 minute class periods is enough), briefly go over the equipment available, and then I let them begin. When the students start the activity, I will only assist them in obtaining and using equipment and answering questions pertaining to methods, but I do not help them discover the properties of the liquids. At the end of the time period designated, I have them stopper their test tube and hand them in for evaluation.

I use a rubric to qualitatively assess their tubes based on the following characteristics: Separation of the liquids, color scheme selected, distance (thickness) of each layer, and time. The separation and thickness are the most important because of the precision involved in doing these well.

The most important tip is that a wide range of "pops" should be provided for the students to select from. The greater the number of choices the students have, the more experimentation and analysis they will do. The one safety guideline that has to be watched for is consumption of the "pop." The students will need to be reminded that the "pop" is a experimental variable, not a treat, so they are not allowed to consume any. Otherwise, as long as the students are careful in determining the characteristics of each selected sample, they should be able to produce a good test tube of layered solutions.

By assessing the separation between the six solutions, the instructor can determine if the students understand the relationship between the solutions of different densities. Measuring the precision used in preparing the layers can also assess the precision of the students' lab methods.

9-12.I.B.1,2, and 4 - Scientific Inquiry
9-12.II.A.7 - Structure of Matter