The flame test lab, where you place different chemicals in a flame and produce different colored flames is always a fun lab and one I’ve done many times before. But this time I used another lab, Chapter 4- the Flame Test Lab, from Ian Guch’s 24 Lessons that Rocked the World. The kit I had purchased years ago from the Home Science tools website comes with the chemicals and a simple spectroscope that will let you estimate the wavelength of the light. This kit only has you soak the sticks and then stick them in the chemicals so that a bit of it ends up on the stick, which you then put in the flame. Ian Guch’s lab has the teacher make up 0.5 Molar solutions of each salt with distilled water. Then the sticks were soaking in the solutions and the flames were much better than we had achieved in previous flame tests. I also added some cupric chloride, as a 6th chemical, that I bought separately because it produces a beautiful green flame. The little butane burners worked really nicely for this lab since they don’t produce much of a flame.
I used 50 ml centrifuge tubes to mix the chemicals in and we used wooden skewers (cut in half) instead of toothpicks. I mainly used the wooden skewers because the centrifuge tubes were tall and I wanted the students to be able to pull out the skewers with tongs easily. It also kept them from having to get too close to the flame. A couple of the chemicals we used are hazardous so the students used tongs to grab the skewers. You do NOT use gloves because the gloves could melt on to your hand if you got too close to the flame. We did make sure long hair was tied back and aprons and goggles were worn.
The lab entailed looking at 6 known, labeled chemicals and determining the color of the flame. Some of the students used the spectroscope to also record the wavelength of light since some of the colors were pretty close. Then they had to identify 6 unknown chemicals by looking at their flame test results. Some of them like the cupric chloride were easy to identify (the solution itself is blue) but there were a couple of chemicals that gave orange flames and two that gave red flames.
You can see in the photo above that I had the centrifuge tubes in glass beakers or jars to keep them from falling over. The beakers were themselves contained in a plastic container. The tubes had to be open at the same time so the skewers could be soaking in the chemicals and I was afraid they would fall over and that would be in the end of the lab. This set up worked really well and we had no spills. I had two skewers in each tube and since only one person was doing a flame test at a time, it was relatively easy to make sure they put the skewer back in the right tube.
At the end of the class the groups which correctly identified all 6 chemicals were the same groups that used the spectroscope to estimate the wavelength, so if you have a spectroscope available, its worth doing. You can make your own spectroscope, there are a lot of DIY instructions available on the internet. We used this one a year or two ago, papercraft spectrometry starter kit, but I never had much luck with the computer part of it. It just seemed to take forever to upload the files.
Before we started the lab we discussed why the chemicals give off light (excited electrons dropping down to the ground state) and why different elements give off different colors (elements have different numbers of electrons in different levels so the energy/color given off is different). We also talked about why this is useful, identifying unknown chemicals/impurities in water or learning about the elements in stars.
I suggested students watch these videos before class:
Crash Course Chemistry #5, the Electron
Wave-Particle Duality and the Photoelectric Effect by Professor Dave Explains
Quantum Numbers, Atomic Orbitals, and Electron Configurations by Professor dave Explains.