Apply limiting reagent calculations with Jet Boat Races
- Brennan Koch
- Mar 8, 2024
- 4 min read
Updated: Feb 14
While the applications of limiting reagent calculations might feel obvious to you and I, they aren’t to the students. Often, the students just want to memorize the method in order to get the answer in order to get you off their back. But the concept of limiting reagent is what drives chemistry! It has so many applications to industry and the real world. I have redesigned my Jet Boar Race lab, and the results were great! The result was a ton of fun and the kids started to see the real applications of their calculations. Here’s how I did it.
Jet Boat Design
I used the good old baking soda and vinegar reaction to produce carbon dioxide. I had these old dropper bottles in the lab that I used to make a “boat”. I pulled the dropper tip out of the bottle and then poked a small hole with a dissecting probe on the “shoulder” of the bottle under the cap. On the opposite side of the bottle I drew a large arrow. The arrow showed the kids which side to put up as well as which way the boat travels.
Students would measure a certain volume of vinegar into the bottle and then a certain amount of baking soda into the lid. If they slowly put the lid on while holding the bottle at an angle, the reaction wouldn’t start until they shook the boat. Once they shake it, the carbon dioxide forms and starts shooting the gas and extra vinegar out the hole propelling it down the water trough.
I made a water trough from a piece of metal drip edge cut to 1.8 m long. I hot glued some plastic ends on the drip edge making a trough. I drew a goal area (two lines about .25m apart) with marker that were 1.2 m from the start. The challenge in the lab was for the kids to manipulate the limiting reagents to make the boat stop in the goal zone. Here is a video of what that looks like.
The Good
I loved the engagement that I got from the kids. I also loved the number of stoichiometric calculations that they made, but with a purpose. You can only do so many practice problems in class before they are just practice problems. But this time we were solving a problem and being competitive.
The students could see quantifiably, how limiting reagent effected a process in real time. Put less baking soda in, the boat doesn’t go far. I know that seems silly, but honestly many of our students have never actually visualized the impact of limiting reagent. One group today was using vinegar as the limiting reagent. They put in half the amount of vinegar as the trial before. It went half the distance. With a tone of sassiness, she said, "See Mr. Koch, I knew that was going to happen. I cut it in half." That is exactly what I want them thinking!
The Bad
Vinegar isn’t pure acetic acid. In order to do a limiting reagent problem with my first-year chem students, I had to make conversion factor that isn’t standard. I calculated that in 1 mL of vinegar there is 0.00083 mol of acetic acid. This felt a little artificial and the kids were slow to embrace the unorthodox conversion factor. After reiterating and showing how to use it, kids were able to get on board. But it was definitely slower that I wanted.
The Best
Last year, when I first tried this lab, the kids never got to the challenge portion. This year, I got several groups to the challenge. They have to use a new reactant, sodium carbonate. They balance the new reaction and see a new mole ration for acetic acid.
The students then take the liters of carbon dioxide that they discovered it takes to get to the finish line. They do two stoichiometric calculations to see how much vinegar and how much sodium carbonate it would take to get to the goal.
The grand finale is that they only get one shot to hit the goal. They use their perfectly calculated quantities and try it. Today, every single group that made it to the challenge hit the goal perfectly. Ever single one. It was like the lightbulb turned on. They could predict outcomes of new reactions without ever seeing it. It felt like magic! I even had groups stay in for lunch so they could try their hands at the stoichiometric magic. That is a win for sure.
Will I Use it Again?
Absolutely. The kids were manipulating reactions in order to change outcomes. And then doing the math to prove it. That is a huge win toward kids understanding the purpose of limiting reagents. You can download the writeup in its current form here. Please change it and make it better (and then send me a copy!).
I figure if chemistry teachers aren’t trying new and exciting things, then nobody is. Take a risk. Try something new. Write your own lab. Will you fail sometimes? Sure. But other times you will be off to the races! (See what I did there? Jet boat races… sheesh).
Check out this email that I just received from a customer talking about Up & Atom.
"We played with our Up & Atom cards for the first time, and wow! It was slow at first, but the conversations and collaboration was amazing to be a part of... At the beginning of the period were groans and statements like, "I don't want to do moles again!" which moved to, "Oh, I get it now!" and, "Can we play this again tomorrow?" So, thank you!!" -Erica C.
Want to join in a new way of engaging students? Try Stoich Decks curriculum-centric games today!
Is there a particular reason you switch to Sodium Carbonate as opposed to finishing the lab with the Sodium Bicarbonate you used for the trials? Or is it to add that extra layer of another balanced equation, different molar ratio, molar mass, etc?
What size dropper bottle do you use?
Do you have sample student data? Also are they using the 22.4 L/1 mole conversion for volume of CO2 or are they using PV=nRT. Thanks so much for this idea!