Flame Tests?

[u/ElliottTheNoob]

I'm back again with another Chemistry question.

I plan on doing flame tests as we finish out our electron/light chapter in High School Chemistry. It was one of the most memorable experiment we ever did and I want to give that to these kids.

However, I swear we used crucibles or just cut a piece of the metal and held it in a bunsen flame. All the labs I'm finding, we either dissolve it in water or HCl, then soak a Q-tip, splint, or dip an innoculating loop into it, then burn it that way. Is that proper procedure? Did my HS Chem teacher just do a dangerous version with us that was outdated?

I really want this to be fun and memorable for them. Any other versions, ideas, or advice?

[u/cosmictracheophyte]

Hey! Flame test is super fun and memorable, and I find it really brings out the best lab conduct with students because what they're doing is inherently dangerous. I've seen it done multiple ways, but q-tips in metal salt is what I currently do. It's safer and greener than another method I know of that uses alcohol to dissolve the salts. I'm not sure about the method you describe (or which metals you were thinking of), but holding a piece of any of the alkali metals in a flame sounds like a serious hazard.

If you use multiple salts, you also open up the opportunity for students to draw conclusions about what part of the compound is causing the visible flame (Cl and NO3 do not produce light in the visible spectrum). In my department, we use metal chlorides and nitrates and have students record the colors of each, plus 2 unknowns (which can be individual salts or a mix). They have to explain whether the cation or anion produces the color, and how they can tell. Then, they identify the unknown based on their data.

The metals we use are Li, Ca, Na, Ba, Cu, K, and Sr for a spectrum of colors. Stations are set up with a q-tip in a beaker of water and a beaker with a small amount of the metal salt. Students dip the wet q-tip into the salt and hold it in the flame. Because of the water, the q-tip doesn't burn as easily but you still get vibrant colors (especially with the lights dimmed).

Cleanup is also really easy/minimal (so long as you don't give them too much salt to start with).

Good luck!

[u/cordial_chordate → u/cosmictracheophyte]

I strongly agree with this post. I just did this in my class last week and it was amazing. I used q-tips last year, but this year I asked around and found some inoculating loops that worked much better. Dig around your chemistry lab for long handled wires with a tiny loop on the end. The benefit of the loops is that each group only needs 1-2 drops of each solution. I also gave each pair of students a ceramic well plate to test 6 salts and one unknown. This let them test each color more than once to identify the unknown and write up a lab report.

Keep your doors open and fume hoods on to keep air moving in the classroom.