Chemistry Solutions

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I came to teaching with 10 years of experience and safety training in the chemical industry. Even so, my students and I experienced a few incidents in my classrooms over the years. Thankfully, because I was prepared and my students followed safety rules, we never experienced a major injury. But I do have stories … and lessons learned during my 20-plus years of teaching.

From Industry to the Classroom: Bringing Safety Culture with Me

Before becoming a teacher, I was a chemical engineer for 10 years working in Research and Development. My projects ranged from lab-scale to full-scale chemical plants, using a wide variety of equipment and hazardous chemicals. My company prided itself on its safety culture, and employees—including me—had extensive training not only before new projects, but also during weekly and monthly safety meetings. I had steel-toed shoes, prescription safety glasses with side shields, a hard hat, and a serious awareness of chemicals and their effects.

When I started teaching high school chemistry, I brought with me that ingrained safety culture and very healthy respect for chemicals and equipment. I had even stopped wearing contacts due to the constant potential for chemical exposure; I wore closed-toed shoes exclusively; and I always highlighted safety concerns and proper PPE to my students before every lab.

Despite that, things happened. No student was ever seriously injured, but we did have some heart-stopping moments. In retrospect, some were funny, some were frightening, and all were learning experiences.

Figure 1. Always use rubber bottle carriers to transport breakable bottles. Photo from author.

As a student teacher, I was assigned a fantastic mentor-teacher who absolutely loved doing labs and demonstrations. He taught me all my favorite demos, along with my most corny chemistry puns. He adored shocking his students (and me!) with demos that looked dangerous but were actually quite safe and taught a strong lesson.

One day, he was discussing the hazards of concentrated hydrochloric acid before lab began. He showed students the stockroom 2.5-L bottle of 12M HCl and then pointed out its protective coating, which reduced harmful consequences if the bottle accidentally broke. He then said, “Whoops!” and dropped the entire, full bottle of 12M HCl on the floor.

Because it was coated, the bottle didn’t shatter, but it was broken beyond recovery, and acid was clearly leaking onto the floor. I couldn’t hide my horrified expression. He looked at me and laughed, asking, “Do you think I would actually drop a bottle of acid? It’s just water!”

Phew!

Although I never did that demo with students, when I became responsible for the science department at a new high school, I ordered rubber bottle carriers (Figure 1) to ensure that bottles of HCl, or anything else, could never accidentally slip and fall during transport.

Figure 2. Pure calcium metal, although beautiful, must always be handled with care. Photo from Wikipedia.

One of the first labs I assisted with during my student teaching year was comparing metals to nonmetals based on physical and chemical properties. Using small pieces of elements such as silicon, aluminum, calcium, magnesium, and sulfur, students tested their brittleness, conductivity, and reactivity. To prepare, I had broken up larger pieces of calcium from our stockroom into smaller pieces using a hammer in the fume hood.

Afterwards, I used a very wet paper towel to wipe up the small calcium particles and dust covering the fume hood. Ouch!! Of course I knew that calcium reacts with water exothermically—I had done that demo! And that’s when I realized that while we teachers always consider safety concerns for students, sometimes we’re blinded to our own safety. I didn’t burn myself that day but learned a valuable lesson all the same. Always think about the hazards of prep work and cleanup for yourself as well as for your students!

My First Few Years: Even Prepared Teachers Have Accidents

In my first teaching assignment, I was in a very old school building (think no air-conditioning!), and my chemistry students sat in long rows of lab tables rather than at individual desks. Each table had a sink and gas jets plus seating for two students.

One day, a bored young man who had been playing with his sink’s faucet managed to snap off the entire faucet from the base—resulting in an immediate, huge geyser of water that shot up to the ceiling! There were shrieks and gasps, and students raced to save papers and books as they got out of the water’s way. The room’s ceiling tiles—never meant to withstand that type of treatment—disintegrated and fell onto everything.

I was paralyzed for a brief moment before realizing I had no idea how to shut off the water. I ordered a student to run for my department chairperson while I helped others move their belongings. The department chair arrived a few minutes later, took a look at the devastation, and quickly dove under the fountain of water to the bottom of the lab table, where he turned off the valve.

Every time I’ve moved between schools or even just classrooms, I thought about this incident. As teachers, we show students the locations of standard safety equipment—fire extinguisher, eyewash, safety shower—but teachers should also know where the shutoff switches are for gas, electricity, and— yes—water. Possibly more importantly, we must know how to operate them as well. If I’d had that knowledge, I could have avoided the huge mess that nearly decimated my classroom. That day, I also learned to implement a rule to not touch the sinks except during lab!

That same year—still my first—I was preparing to demonstrate the beautiful colors that different chloride salts would burn when dissolved in ethanol. Well aware of this demo’s hazards, I knew not to add ethanol to a burning sample.

I borrowed thick-walled glass petri dishes from a biology teacher and practiced the demo before class. When my first period students came in, we turned off the lights before I lit the prepared petri dishes, much to the appreciation of my audience.

But after only moments, the dishes started to break one by one, spreading the burning, colored ethanol all over my demo table! Though horrified, I realized it was safer to let the flames burn out on their own, because the amount of ethanol was limited, and the demonstration table was fireproof.

My students thought this was all part of the demo and yelled and cheered while I, mortified, tried to figure out why my careful plan had imploded. Turned out that the petri dishes were plain glass, not Pyrex, and couldn’t withstand heat despite their thick walls. I had actually weakened the dishes when—ironically doing the right thing—I’d practiced the demo before class! Lesson learned—always check that equipment is appropriate for the task.

*Editor’s note: AACT and the ACS Committee on Chemical Safety recommend that the “Rainbow” demonstration on open benches involving the use of flammable solvents such as methanol be discontinued immediately due to extreme risk of flash fires and flame jetting. Find the safer Flame Test in the AACT classroom resource library.

Flash-forward to a year later. My students were doing a Brass Penny Lab, in which a penny is heated with zinc pieces in a sodium hydroxide bath, and then the zinc-coated penny is heated in a Bunsen burner flame to form a beautiful, shiny brass alloy. I had seen the lab, practiced it, and considered the safety concerns.

The lab was a success, and afterward I poured everyone’s waste products into a beaker, rinsed it with water, and threw the remaining solid zinc pieces into the trashcan. It wasn’t long before a student noticed smoke coming from the trash can! That same sharp-eyed student reacted quickly and used our classroom fire extinguisher to put out the small flames that were rapidly consuming the trash.

Evidently, even though the zinc had been rinsed, it hadn’t been rinsed for long enough. Residual NaOH on the zinc had reacted and the paper towels in the trash can acted as fuel for the resulting heat. This safety incident was frustrating because the lab instructions did not actually include waste disposal. I had done what I presumed was right, but my process was clearly inadequate.

After that incident, I prioritized including clear instructions about waste disposal on every lab, even if I had to research proper waste procedures myself. The next time we did the Brass Penny Lab, I used powdered zinc rather than mossy zinc, to reduce the possibility of sodium hydroxide finding little spaces to hide on the surface of the zinc pieces. As a further precaution, I also rinsed the waste multiple times, and then let it sit for several days before disposal.

The Danger of Feeling Like You've Got This

Over the years, I gained confidence in the classroom. My curriculum was full of demos and hands-on labs. I moved to a new state, helped start a new high school, and provided annual safety training for district science teachers. But about eight years into my teaching groove, I had the most potentially catastrophic safety incident of my career.

My students were doing a Conservation of Mass Lab, which I’d learned while student teaching and had conducted every year since. For the experiment, students added vinegar to a 1-L glass bottle, weighed it, and then added a small pre-weighed test tube containing baking soda. The bottle was capped and weighed, and the contents were mixed, allowing a reaction to occur. Then the bottle was weighed again before students carefully opened the lid to hear a satisfying psssst of escaping CO₂ gas.

On this particular day, a student was about to open his bottle when we heard a loud BOOM and saw it explode in his hand. Pieces of glass went flying, and the lid landed clear across the room, near where I stood. I quickly ran over to make sure everyone was okay and saw one girl with a small cut on her arm and the student who’d been holding the bottle very shaken. Thankfully no one had been seriously hurt because everyone had been wearing their safety goggles. More amazingly, the student across the lab table reported that a flying piece of glass had bounced off her goggle lens.

Figure 4. New and improved setup for the Conservation of Mass Lab. Photo from author.

We all stopped what we were doing and looked for pieces of glass, which had landed all over the room. I immediately told my chemistry colleagues not to perform the lab using glass bottles. In our team debrief, we could not determine why the bottle had failed so spectacularly. Our equipment was relatively new, we had done this lab in years prior, the bottle had been checked for cracks, and the amount of gas generated should have been small enough to be safely contained. This was simply an accident—one that had miraculously caused no major injuries because safety procedures had been followed.

In the end, our team of chemistry teachers decided to modify the lab to use plastic soda bottles, which could be replaced annually. We decreased reactant quantities to reduce the amount of gas produced and added directions for students to point their bottle at the wall when opening it.

At the beginning of each school year, I share this story with my students as part of our safety overview and highlighted the critical need to wear goggles anytime our class uses heat, glassware, or chemicals of any kind. I emphasize that even if they follow directions, accidents can (and do!) happen, and injuries can often be prevented by following safety protocols.

Lessons From My Struggles, So You Can Skip Them

Even with my background in a safety culture, most of my lab incidents happened early in my teaching career—which shouldn't surprise anyone! The mix of 20 to 30 high school students, chemicals, and glassware with only one adult in the room can make for a sometimes volatile situation.

During my career, the more experience I obtained, the better I could predict mistakes that students might make—and the consequences. My first steps to improve safety in the classroom included modifying lab procedures and instructions to avoid common errors—and emphasizing specific safety issues before every lab.

That said, teachers shouldn't need close calls to build safer labs. As science teachers, we carry an awesome responsibility for our students' safety and our own. A culture of safety and responsibility in the lab, modeled by the teacher, has to begin on Day 1 and continue at the same high level every day. Learning from mistakes is valuable, but in a chemistry lab, avoiding them is better, especially when the consequences can be severe.