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We did a basic flame test, and I understand that different salts produce different spectra because of atoms present in the salts.

When I was doing the test, I noticed that when I dipped the nichrome wire into the solution of $\ce{SrCl2}$ and placed it on the tip of the flame, I got the expected red color. However, what would happen is I would get the red color, and then it would disappear, going back to the typical bluish flame, the nichrome would glow orange hot, and the red colored flame would return.

Essentially, the red color appears, disappears, and then reappears. I thought that it might be "wicking" the strontium chloride from another part of the dipstick, but I was careful to only submerge a small part in the solution.

What's happening here?

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Good, careful observation! Here's my assumption of what happened:

  1. The $\ce{SrCl2}$ solution on the wire boiled violently, releasing a large amount of the salt into the flame.

  2. Some remaining anhydrous $\ce{SrCl2}$ stuck to the nichrome after all water boiled off, and melted when the wire reached ~$\pu{874^\circ C}$, coating the loop with a thin layer of the salt.

  3. Additional heating, after melting the salt, went into raising its temperature until it approached the boiling point, ~$\pu{1250 ^\circ C}$. Nichrome can withstand ~$\pu{1400 ^\circ C}$ before melting, but you don't even need to reach the b.p of $\ce{SrCl2}$ to have a bit evaporate and color the flame. Ergo, the flame turned red again.

By the way, this implies you could melt $\ce{SrCl2}$ in a ceramic crucible, insert two nichrome wires connected to a battery, and electrolyze the molten salt to see a bit of strontium (which will catch fire as soon as it rises to the surface, with its characteristic flame color). Do this only under a teacher's supervision.

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