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The Unique Purple of Chemistry – Young Scientists Journal
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The Unique Purple of Chemistry

· Other, Photo Competition
Author

Theme: Energy
Award: Highly Commended
Photographer: Gwen Lam
Oxidation of finely dispersed aluminium with iodine can be initiated using drops of water. The reaction is strongly exothermis, producing a lot of heat energy. The excess iodine vaporises, forming a deep violet vapour. The reaction is : 2Al(s) +3I2(s) –> Al2I6(s)
Anhydrous aluminium halides, such as aluminium iodide produced here, react vigorously with water, sometimes violently if freshly prepared and still hot, releasing fumes of corresponding hydrogen halide.
At the very high temperatures generated in this exothermic reaction, the aluminium can also start to burn, reaction with the oxygen in the air to produce solid white aluminium oxide: 4Al(s) +3O2(g) –>2Al2O3(s)
I find this reaction inspiring as it illustrates nicely that the energy generated in exothermic reactions comes from within the chemicals reacting. Nothing was hot to start with, but after the water is added a large amount of heat energy is released. I also find the clouds of iodine vapour fascinating- the intense purple colour isn’t like any other kind of smoke or vapour and is rather unique. The heat generated in the reaction makes the solid mass glow quite brightly, but from within the mass not on the surface so the orange- white light leaks out through cracks in the solid crust.
I have used Photoscape to strengthen the contrast of the photo, making the purple vapour and the light stand out from the photo.

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