Don’t get me wrong, I love the iodine clock reaction. I mean, who doesn’t. It’s a classic equilibrium lab activity for your students to be utterly fascinated by. But unfortunately, those chemical heavy labs aren’t always an option in some high school chemistry classrooms. Let me introduce you to my favorite “chemical free” equilibrium lab activity that you can use in your high school chemistry class.
Materials Needed
You will need only a few simple things: two graduated cylinders, some water, two straws with different widths and food coloring if you wish. Now, we all know that water is a chemical, but it doesn’t count in your science budget, and usually is readily available in schools. Well, at least, I’d hope so!
Background or Inquiry?
I personally choose to use this lab activity after my students have an understanding of chemical equilibrium. I find it to be the best use of the time in my classroom. (Also I hate teaching the Kinetics & Equilibrium units so the faster we can get through it, the better.) The questions in the lab worksheet that I provide more so lend itself to having this lab cement the very abstract nature of chemical equilibrium – not teach it by inquiry. This also helps students to understand graphing equilibrium reactions, which I choose to use as the main focus of this lab activity.
ALTHOUGH this would make an excellent demo for you at the start of your Kinetics & Equilibrium unit that you can then have students revisit in the lab activity! Sign up here for a free list of Kinetics & Equilibrium phenomena to use in your classroom.
Lab Process
Students start with some volume of water in only 1 graduated cylinder. Those are the reactants. In pairs, students take their straws and drop them to the bottom of their assigned cylinders, press a finger on to the top and swap whatever volume of liquid they pick up. The two different straws represent the forward and reverse reactions. Students should pick up their samples at the same time. This helps them to see that the forward and reverse reactions occur at the same time.
Eventually the volumes will come to a constant volume even though with straws of different width, they are picking up a different amount of water than the other student/reaction. I really love to see them graph the process. That’s where it really clicks for them.
If you choose to use the food coloring, you can use one color for reactants and one for products. The colors will blend over time, which can help students to see the reaction is constantly exchanging reactants and products. Until the color remains constant (because there has been thorough mixing). Plus, who doesn’t need a little added color in their lives?
Final Thoughts
Even though this is a VERY simple lab, students get a good grasp of equilibrium. Reaction rates are equal – the forward and reverse reactions occur at the same time. The concentration of the reactants and products is constant, which is represented the volume of water they pick up once they reach equilibrium.
You can find this lab in my TPT store. Included is the student lab activity, a teacher answer key, and a teacher set up guide. There’s also Google Sheet calculator so you can check on student results.
