Intermolecular Forces and FLIR Cameras

What are we doing to help kids achieve?

Intermolecular forces is a topic that consumes a considerable amount of time in the chemistry curriculum. This one topic can carry over into bonding, nomenclature, modeling, labs and other areas. Intermolecular forces are often a challenge for students. Students struggle to make the connection between the particulate world of hydrogen bonding, London dispersion forces and the macroscale world of evaporation of compounds. There are many moving parts. These parts include the general relationship that shows more intermolecular forces the more energy required to boil and evaporate materials. Evaporation requires energy. The longer it a materials takes to evaporate, the less change in temperature is recorded. This relationship translates back to more intermolecular forces between molecules. Students really struggle with this idea. This multi level relationship involves many moving parts and the idea of energy which in itself is a big concept. FLIR cameras may help students with this complex concept.

FLIR cameras are an affordable method of recording temperature change and viewing the change in the infra red. There have been mentions of this method in this space before (check out Ben Meacham's blog, Seeing Chemistry in a Different Light—FLIR Thermal Cameras in the Classroom). A few years ago Travis Cole Green through Bowling Green State University also worked on the use of FLIR cameras in the high school classroom (check out this introductory video). I decided to use this idea in my classroom. I was able to get a small grant for some FLIR cameras from our local ACS educator's group and our school PTA. I received the cameras last spring as schools shut down and just now have been able to adapt and create a hybrid lab for students.

The goal of the lab was to examine the evaporation and intermolecular forces of four compounds. This lab was traditionally accomplished with temperature probes. Students wrap a piece of filter paper around the temperature probe and soak the paper in one of the liquids. The chemical with the weakest intermolecular forces evaporates faster. Faster evaporation produces a large drop in temperature. Slower evaporation  produces a small drop in termperature over a longer period of time. This is my attempt to recreate and adapt this lab with FLIR cameras.

I wanted to do this with six lab groups. I did not have enough petri dishes so I tested a quick adaptation. I cut up a bunch of filter paper into one by two inch rectangles. Each rectangle was labeled with a corresponding liquid. The paper was soaked in the liquid, placed on a lab bench and filmed with a FLIR camera. The results were fairly good and as predicted. Next, I had to convince six students to download an app on their phones.  Only a few students were willing to try the app and the camera. However, once they did and started "playing" with the camera, everyone wanted to try it. The engagement increased dramatically. We spent one class period learning how to use the cameras and talking about intermolecular forces. Each group labeled their four papers. The next day, students came in and I had their four papers soaking in respective liquids. They started recording with the infrared cameras as soon as the respective samples were placed on their lab benches. They recorded the video with their voices as a commentary. Students had the ability to go back and watch a relatively short recording to collect more data. Again, engagement was extremely high. One potential problem was that there was always one group that struggled with the technology. I had a pre recorded sampling that I did and I was able to send them the link. See video 1 below.

Video 1: FLIR and Evaporating Solvents, Chad Husting's You Tube Channel (accessed March 15, 2021)

Next came the post lab. Students were highly engaged on multiple levels. Some students had questions about the connections between the "coldness" of these solvents and what happens when they sweat or get out of a shower in the morning. Others noticed that the alcohol samples smelled like the "Doctor's Office". This lead to a discussion about the use of alcohol as a solvent to clean our skin before shots. They also noticed that it felt "cold" when that happened. There were also many unexpected connections. One parent wanted to know if his son could bring the camera home for the weekend so they could check their windows around their house to see if they were "leaking energy". Another unexpected connection was the clean up. All of the papers were easily disposed of accept the one soaked in oil. It left an oil slick on the lab tables. Never wanting to miss a teachable moment, we experimented with a couple of different soaps and found that shaving cream was the best method of cleaning up the oil of the tables. It is probably due to the long carbon chained stearic acid that has a little bit of polarity. Again, intermolecular forces in action.

The next day, students turned in the lab. The lab contained a question in which students had to predict what would happen if pentane had been used in the experiment. It provided a great opportunity to review intermolecular forces, evaporation, temperature and the relationships between all three. See video 2 for a recording for pentane.

Video 2: FLIR and Evaporation of Pentane, Chad Husting's You Tube Channel (accessed March 15, 2021)

Overall, I was satisfied with this first attempt of using FLIR cameras as an educational tool. There was high student engagement. It was easy to provide virtual components. This is a technology that can be widely adapted for a number of situations. I will continue to use these and hopefully have more to report in the future.