We use aluminum foil every day, but it can be quite reactive under the right circumstances. This gif shows aluminum reacting with bromine, a halogen. Aluminum foil sticks out of the test tube and falls in as the reaction progresses. Susan Vickers used this reaction when she was a Ph.D. candidate at the University of British Columbia to demonstrate halogen reactivity for first-year students. To make the reaction start faster, Vickers removed the aluminum oxide layer on the foil’s surface by very gently scratching it with sandpaper. The sparks you see here are melted bits of aluminum foil; the orange vapor is bromine, and the gray smoke is aluminum bromide.
Credit: Susan Vickers
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This article was updated on June 8, 2018, to correct Susan Vickers's affiliation and to indicate that the gray smoke resulting from the reaction is aluminum bromide, not aluminum.