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.
"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.
From: Meg Osterby <megosterby**At_Symbol_Here**GMAIL.COM>
To: DCHAS-L <DCHAS-L**At_Symbol_Here**PRINCETON.EDU>
Sent: Thu, Jun 27, 2019 5:39 am
Subject: Re: [DCHAS-L] [EXT] Rainbow Flame Demo Alternatives
While teaching at Western, I moved away from the solutions with Pt wire loop, because the loop needs to be cleaned between solutions in order to avoid cross contamination and un-interpretable results. The wires are generally cleaned by swishing several times in an acid solution, typically 1M or 3M HCl. However, this use seemed to make my students become cavalier using acids and even splash it and not do anything to clean it up. Also, the acid solution becomes progressively more contaminated, and therefore cross contaminates the solutions with each other, giving meaningless results. I didn't like making the students lose respect for acids, and I didn't like that the results were hard to see and interpret. My students did 6 known solutions and then 3 unknown ones (three of the same salts) and they had a lot of trouble with the identifications with the wire loop in solutions method.
I saw the wood-stick cotton swab method in the Flinn Catalog (although more recently they espouse soaking wood splints in aqueous solutions of the salts. The cotton swabs are wet with distilled water (they keep a beaker on the bench with tap water half filling it) by holding the tip over the beaker and using their distilled water wash bottle to wet it and the beaker to catch the excess water. Then, they placed a microspoon of the solid for that test into one of the shallow wells of a spot plate, roll the wet swab tip in the solid, then put that tip in the hottest part of the flame. The colors were bright and unequivocal, and the students never failed to identify their three unknowns. When the stick catches on fire, they place the flaming swab into the beaker of water.
I liked this method better than the wood splint method, because the salt stays on the swab, and since the salts don't burn, having it just as visible on the swab provided an easy way to demonstrate that. (The metals in the salt get excited, moving an electron to a higher level, from which it falls emitting light.) Since the salt doesn't burn or disappear, the students can SEE that burning it isn't what causes the color. The salts don't change on the swab, and the students can see they don't.
So even if the wire loop method with solutions of the salts is easy, the dampened cotton swab rolled in the salts gives better results. And it doesn't require students using acid, in a way that familiarity leads to disrespect or contempt. And that leads to the potential of future accidents.
"It's better to be careful 100 times than to be killed once." Mark Twain
Just thinking outside the box here: it might be possible to not use flames at all and instead direct a light source through a synthetic gemstone or a piece of stained glass and make the same observations with a spectroscope. Both stained glass and synthetic gems are doped with certain elements like chromium and strontium to produce colors. The down side is that you may not be able to get all the elements that are usually flame tested. The up side is that your synthetic ruby is probably not going to set anyone on fire.
While the starting cost might be an issue for some teachers, you can get a synthetic ruby (doped with chromium) for less than the list price of a bottle of chromium trioxide, and it has an interesting spectrum. You could probably just glue the pieces on a light table with black paint or paper to block out the light so that it only shines through the crystal.
I haven't actually tried the stained glass, so I don't know how that would work. I'd be glad to know if anyone else thinks this might be feasible.
From: ACS Division of Chemical Health and Safety [mailto:DCHAS-L**At_Symbol_Here**PRINCETON.EDU] On Behalf Of Samuella Beth Sigmann
Sent: Tuesday, June 25, 2019 11:50 AM
Subject: Re: [DCHAS-L] [EXT] Re: [DCHAS-L] Letter to the National PTAregarding the rainbow flame demo
Yes. We currently do this as an experiment with aqueous solutions and get very nice colors with the chloride salts of K, Ba, Sr, Na, Li, Cu, Ca. They can even observe and measure the spectral lines with spectroscopes.
On 6/25/2019 11:09 AM, Monona Rossol wrote:
100 years ago when I was in qualitative analysis, we did it our damn selves in the lab. We made saturated solutions and used a platinum wire loop to get enough liquid in the loop to see an nice clear colored flame. Do they still do that?
The KCl flame was very hard to see. I have done this demo with (wood stick) cotton swabs, wet with distilled water and the tip rolled in the solid. The color is bright and long lasting and the purple/pink in the flame is easy to see. It=E2=80™s the only way I know of to do KCl and get such a good color.
W831 County Road K
Stoddard, WI 54658
"It's better to be careful 100 times than to be killed once." Mark Twain
I have been following the discussion regarding the rainbow flame demo. My colleague Kim Duncan and I have collaborate to put together the following site related to the safer flame tests.
If you have any suggestions how to improve this page, please let me know. Please feel free to use this page in your communications with teachers.
I have done this as a microscale lab. I make the solutions before hand and never have the alcohol still in the lab. I use small candles and cotton swabs. It has worked safely but I can see where it can go wrong. I am going to try the method mentioned using long cotton swabs soaked in distilled water and dipped in the salts. If it gives the same results, I will switch to the new method and share with my colleagues. We have been told not to use methanol and I have only used it for this lab. I think the AP Chemistry teacher used it last year. I will be that teacher this next year and will look to see if methanol can be completely removed.
I agree with Peter.
What we do is soak cotton swabs (The long Q-tip type ones) in
distilled water for about an hour. Dip the end in the various salts
and get the same result when burning. Others use wooden stirrers /
popsicle type sticks and do the same and get the same result.
Perhaps we should be assisting those in the classroom with viable
alternatives for this and other activities.
On 6/22/19, pzavon**At_Symbol_Here**rochester.rr.com <pzavon**At_Symbol_Here**rochester.rr.com> wrote:
> One thing I notice about this letter and many other comments about
> this demonstration directed to educators is the frequent absence of
> guidance on how to perform it more safely, or on alternative, less
> hazardous, demonstrations that would illustrate the same principles.
> In my experience, it is usually more effective to provide alternatives
> than to simply say "don't do that."
> Decades ago, my then boss at Princeton University used to say to
> faculty members something along the lines of "I am not telling you
> that you can't to that; I am telling you that you can't do it in the
> way you have been accustomed to doing it."
> Peter Zavon, CIHPenfield, NY(on location in Cincinnati, OH)
> -----------------------------------------From: "davivid"
> To: DCHAS-L**At_Symbol_Here**PRINCETON.EDU
> Sent: Friday June 21 2019 6:36:30PM
> Subject: [DCHAS-L] Letter to the National PTA regarding the rainbow
> flame demo
> Here is a letter I just emailed to the National PTA. Let's hope this
> helps get some progress on the issue.
> Dave Lane
> Clavis Technology Development
> -------- Forwarded Message --------
> Subject: Dangerous classroom demonstration
> Date: Fri, 21 Jun 2019 15:31:09 -0700
> From: davivid
> To: info**At_Symbol_Here**pta.org
> Dear PTA Gatekeeper
> I write to call your attention to a common classroom demonstration
> injures students in several incidents every year. I hope that the PTA
> can help end this practice by informing parents and schools of the
> The demonstration is typically called the "Rainbow Flame" or similar.
> involves solutions of various metal salts dissolved in alcohol that
> set on fire. The different metal salts give various colored flames,
> hence "rainbow flame". If alcohol is poured near flame or other
> source the alcohol can suddenly erupt from the bottle in a phenomenon
> called "flame jetting". The jet of flaming alcohol can severely burn
> anyone in the path of the flames even as far as ten feet away.
> Here are some links describing flame jetting.
> Dangerous =E2=80=98Flame Jetting' Phenomenon Kills Hundreds Every Year
> Here are links to some recent instances of flame jetting that have
> injured students
>  https://www.youtube.com/watch?v=kkBFG1mTSBk
> /> A Safer
> For more information about the DCHAS-L e-mail list, contact the Divisional
> membership chair at membership**At_Symbol_Here**dchas.org
> Follow us on Twitter **At_Symbol_Here**acsdchas
Eric W. Goff
For more information about the DCHAS-L e-mail list, contact the Divisional membership chair at membership**At_Symbol_Here**dchas.org
Follow us on Twitter **At_Symbol_Here**acsdchas
We, the willing, led by the unknowing, are doing the impossible for the ungrateful. We have done so much, for so long, with so little, we are now qualified to do everything with nothing. Teresa Arnold paraphrased from Konstantin Josef Jire=C4=8Dek (1854 - 1918)
Samuella B. Sigmann, MS, NRCC-CHO
Senior Lecturer/Safety Committee Chair/Director of Stockroom
Appalachian State University