Over the weekend, several of us attended a workshop to discuss chemical hazard assessment needs with high school teachers. As the example activity to assess the hazards of, we used the "Hollow Penny" activity described at
This protocol calls for 6M HCl to be used to digest the zinc interior of the penny. One of the teachers commented that they are uncomfortable with using HCl this concentrated with the teen age students she oversees, so she uses 3 M HCl and lets the penny digest over the weekend so there's enough time to do the job. Other teachers use the 6 M HCl in a lab setting (i.e. students do the hands on work), whereas others said that they did this only as a demo (i.e. the teacher was the only person who touched the acid until the hollow penny is decontaminated). Some teachers avoided this activity altogether. Interestingly, the SDS's we found on the web for HCl indicated that any concentration above 0.1 M has both the corrosive and irritant designations. The 0.1 M SDS I found showed only an irritant designation.
We are not second guessing anyone's professional judgement as to which option they chose. Previous discussion that day made it clear that factors such as 1) the facilities and equipment available, 2) the nature of the students involved in the class and 3) the availability of PPE all made a difference in what people decided to do. These factors vary widely from school to school.
There are three questions we'd like the list's thoughts on:
- Is there a significant hazard difference between 6 M and 3 M HCl in the high school lab setting?
- How would you determine this difference from GHS (or other) information available for these solutions?
- Does the choice of which approach (lab, demo, avoid the activity) impact the educational value of the class?
Thanks for any help with this.
Ralph Stuart, CIH, CCHO
Environmental Safety Manager
Keene State College
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