One of my favorite activities is the Rainbow Lab. This is a great activity for practicing their measurement skills, ability to follow directions, precision, working as a group, following correct lab procedures, equipment use and identification, solutions, mixtures, physical changes, problem solving, etc… It’s chock-full of stuff.
What I also love about this lab is the importance of not fudging your data, and reporting what actually happened in the lab, not what you think should have happened, or covering up “mistakes”. If one of your lab partners spilled the yellow, you have to account for the loss of the yellow in your data, how it affected your measurements, etc. What do we do if someone breaks a test tube? What if I spilled something onto my clothes or skin? How can I avoid contamination of my colors when using only one graduated cylinder?
To set up this lab, I use a concentration of 5 drops of food coloring per 100 mL of water. Each group gets one set of test tubes, a beaker for waste water, a beaker of clean water, a pipette, 25 mL graduated cylinder, 3 flasks, and stoppers. The stoppers are important because if a group does not finish the experiment in one class and has to continue the next day, it prevents evaporation – which would alter their data.
Before I start a lab, we always meet as a group, usually around a table with one set-up. I explained the lab, and talked about what a solution is, and what the solutes and solvents were for this lab. We talked about how this was a homogeneous solution, the food coloring does not settle out over time.
I stress the importance of avoiding contamination, or the “Big C”. We don’t want colors mixing together and making muddy colors. I show them how to rinse out their graduated cylinder between measurements, and dumping the “dirty” water into the waste water beaker. I show them how to twist the graduated cylinder as they pour, this cleans the sides of any food coloring residue. I also reminded them about the meniscus when reading measurements.
When completed, the measurements for each test tube should read A-F: 10, 11, 10, 11, 10, 11 with a total of 63 mL. They also have to account for having more or less than 63 mL, where did the extra volume come from if they went over? Where did it go if they were short?
I don’t tell the kids how much they should have had until the next day, when we go over the analysis questions.
- Rainbow Lab- updated for the interactive notebook