Monona,
I think you got the wrong impression. I didn't stop teaching acid safety completely. But that lab, where they are seeing the spectral colors, the colors are what the important part of the lesson is. I made the decision to switch the lab to one without acid, because trying to teach the chemistry of the spectral colors and the precautions one should use when working with acids, was too much info to get across and have them remember in a single 2 hour lab period.
I taught about handling acids safely in a different lab. They did an experiment where they "pretended to be analytical chemists" and identified the anion and cation in a while crystalline solid. There was a limited list of cations it could be and an even more limited list of anions it could be, and they were to run chemical tests to determine which cation and which anion were in their salt. The experiment was semi-micro, and no more than 1 mL of any substance was used, and often much less.
The test for chloride ion with silver nitrate could give a false positive with carbonate, since silver carbonate is insoluble too. So, to differentiate between the two precipitates (or to confirm chloride) by adding several drops of 6 M nitric acid to the tube and agitate the tube. If the precipitate dissolves, the test is negative for chloride. If it doesn't, it's positive. A similar result can happen for the test for sulfate with barium. Barium carbonate could precipitate instead of barium sulfate and be a false positive, so acid is again added.
I would spend several minutes in the pre-lab for this experiment teaching them to handle the acid safely, to be aware of and properly clean up any spills, even of one drop. I stressed the PPE needed, and our lab rule was any acid over 1M required nitrile gloves (which my budget bought). So I also taught glove etiquette that day as well. I also explained that we were not measuring anything precisely in the experiment because it was a qualitative experiment, so that any acid added to a test tube was likely still there when cleaning up, so gloves were required for clean up too. The gloves we used were blue, and if they begin to go green, it's a sign they are compromised, and I taught them to look for the color change and how to properly change to fresh gloves, and safely dispose of the contaminated, compromised gloves.
So I did teach about handling of acids, just not in the flame test experiment, where it just became too much information, and would be ignored, and I worried that would make the students use less than needed care when handling acids in the future. There were 15 weeks in our semester, so 15 lab periods, each only 2 hours long (the State of Wisconsin doesn't believe that technical college labs need to be any longer than 2 hours, go figure). The first was all safety, then 13 weeks of experiments where I worked at teaching them safe chemical handling, and always explained the why of any safely rule, and later in the semester, had them tell me why. The last week of the semester I did not have a lab, since that was finals week, and was too much for the students to cope with.
But you are partly right. I did have to think about planning around that stupidest student or the one who thought s/he knew more than me. I told stories about my own mistakes and accidents, showed them the holes I'd burned in my lab coat or shoes with drops of acid, etc. because most of them told me they thought I was so smart that I wouldn't make mistakes. So I taught about when accidents happen, (we're too tired and not paying enough attention), about realizing that chem lab is different that their regular life, so you can't react to an accident the same way, or risk making it worse, etc. But, since I did know better, and did still have accidents, incidents and near misses, I felt the students needed to know that, and that not knowing how I was keeping them safe, would mean that at some future time, they'd make a mistake due to ignorance of my precautions for their safety. So, I taught them what I did and why to keep them safe.. I wanted that stupidest student (or more correctly the most ignorant, since most weren't really stupid), to know that I wouldn=E2=80™t do many of the demos I saw on YouTube, and that they were inherently dangerous. I was trying to instill in them a healthy respect or fear for chemicals that they knew nothing about. They told me in evaluations that I did succeed in those aims.
Meg Osterby
megosterby**At_Symbol_Here**gmail.com
"It's better to be careful 100 times than to be killed once." Mark Twain
Meg, Isn't it interesting how you have to defeat the proclivities of students to develop a lack of respect for the properties of their materials such as acids by keeping them from exposure to them. It seems explaining the hazards to them doesn't work.
It's the difference between the child who can understand the verbal warning about your tongue sticking to a metal flag pole in winter, and one who just seems to have to find out for themselves. But today, we reorganize the whole lesson to protect the kid who will put his tongue on the pole. And perhaps that's the reason we see so many bad decisions by adults who have never experienced the consequences of not listening to their teachers.
And yes, the wire loop took some doing. For example, It didn't work for me the first time. Instead, I learned that a wire that LOOKS clean may still not BE clean. And you had to be rather dexterous and patient to get the bead to form on the wire -- a skill under-developed in the generation that thinks with their thumbs.
But from what you describe, the stupidity of the student and the teacher's liability for that stupidest student is the driving factor in your design of lessons.
1. All of your reasoning for the choice of materials, why they work better, and why provide more lessons is absolutely brilliant.
2. The reason you have to think and plan this way is what is disturbing.
