The flame test lab absolutely made me a chemistry major. When we first did the flame test lab in my high school chemistry class I instantly fell in love with chemistry. My chemistry teacher Mrs. P was very easily able to persuade me to take AP Chemistry after the flame test lab.
And know what the lab did for me, I knew that I needed to do this lab as often as I could. So in my first year of teaching where I didn’t have a chemistry lab, I bought colored birthday candles. There was clearly some metal ions in the wick or wax that changed the color of the flame. I’d do that as a demo and play a flame test youtube video. (Plus we’d use the candles to sing happy birthday throughout the year.) When I was finally in a school that had a full chemistry lab, I knew I “made it.”
Flame Test Background:
When atoms get enough heat or electrical energy, the electrons can overcome their attraction to the nucleus and jump to higher energy levels. They eventually fall back down due to their attraction. When that happens, the electrons release energy in the form of colored light. This gives us the results of the flame test. To do a flame test, you heat the sample in the flame of a Bunsen burner. It changes the color of the flame!
You could also do it with spectral tubes. In that case, instead of heat, you’d add electrical energy to gases in tubes. The spectral tubes, I find, are WAY better for measuring spectral lines. If that’s your thing.
Set Up:
To do a flame test, you’ll need (at least) 1 molar metal chloride or metal nitrate solutions. You’ll also need wooden splints (coffee stirrers), a Bunsen burner of course, test tubes for your solutions, a test tube rack, and a water beaker for used splints. I like to use sodium, potassium, lithium, calcium, strontium, copper and barium chlorides. It’s best to give the splints at least a few hours to soak before using them. I like this because the longer they soak, the harder it is for the flame to dry them out and just burn the splint.
I have done the salts scooped on the wire, but I don’t love them. They have a larger safety concern than the wooden splints, as many of the salts will melt in the flame. And for that reason they make a bigger mess of the Bunsen burner. They can drip into the burner and be difficult to get out. I have found that the salts on the thin metal wire gives a more dramatic flame color though. I think it’s best to save the salts for teacher demos and the soaked splints for students to use themselves.
My tips for the flame test lab:
You could do this in stations. It’s definitely the easiest in terms of set up and chemical distribution. Also, you’ll likely use less materials doing it in stations. Honestly, I prefer to give my students the whole set of samples though. I prepare the samples for them and send lab groups off with the test tube rack with some soaked splints. I find that it works best in terms of their excitement and engagement in the flame test lab activity.
Assign an unknown or two to get the students to use the data they’ve collected to do some real investigating. I specifically include two flame tests that look near identical calcium and sodium. First off, it’s really great to see that there are only so many results to the flame test. Then my students realize that it may be a quick way, but not a definitive way to identify metal ions. This because I want to help them write their conclusion paragraphs. I will often have one of these metal ions be one of the unknowns I assign. I love intentionally adding error to their labs to try to get them to catch it!
Make sure you tell your students to bring their phones to class. Although, I’m sure that won’t be a problem. Usually at the end of the class, I’ll have the students come circle around the teacher demo counter so they can snap all the pictures they want. Snapping pictures during the lab isn’t always safe, so I promise them some time at the end! Plus that means I get to do the flame test too!
Feeling Nervous?
If you’re feeling nervous or uneasy about your students using the Bunsen burner, check out this post. It’s all about my Bunsen burner training and how I make sure both me and my students feel good about using the burners. You can even grab a free sample of the full Bunsen burner training here.
