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I found a package containing some Iodine I bought a while ago. It was contained in a plastic jar placed inside an Aluminium coated plastic pocket. The pocket had strange green worm like trails over its surface. In the most advanced place, it actually seems to have removed the Aluminium and left the plastic transparent with a green / yellow tinge. I wonder what reaction was occurring here?

Aluminium and Iodine should produce Aluminium Iodide which is white. Why it appears green from the outside of the pocket is not clear. Perhaps it is the hydrate form which is yellow so with the plastic colour somehow appears green?

Why this pattern advanced in strange worm like patterns is also not clear to me.

As an aside, I assume this was the Iodine I purchased, it is present as a solid spheres which appears through the brown plastic bottle as shiny black/brown. When it was shipped I assumed it would be safe to leave as it is. It has never been exposed to high temperatures or sunlight. Apparently I need to research a better storage system than that provided to me as the wax seal they appear to have tried to apply round the neck of the jar has not worked to contained the Iodine.

Bag previously containing bottle of iodine plus bottle of iodine in sink

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    $\begingroup$ Please leave a comment if you're going to downvote... otherwise I have no idea how to improve the question... or what to avoid in the future apart from: Avoid StackExchange, which would be sad! $\endgroup$
    – AJP
    Commented Aug 10, 2020 at 21:08
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    $\begingroup$ welcome to Chemistry Stack-Exchange ! $\endgroup$
    – user96208
    Commented Aug 11, 2020 at 5:33
  • $\begingroup$ I think the worm like patterns are to attributed to the packaging case textures as seen on the image $\endgroup$
    – user96208
    Commented Aug 11, 2020 at 5:44
  • $\begingroup$ Is the appearance of the iodine within the glass container ok? With a small-scale reaction / analysis you already know and may reference to, does this iodine still (re)act as anticipated? If so, you could continue with the earlier anticipated task and deploy the iodine as intended. $\endgroup$
    – Buttonwood
    Commented Aug 11, 2020 at 10:45
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    $\begingroup$ Hahaha XD @pipiedipie :) I've caught up now! :) $\endgroup$
    – AJP
    Commented Aug 18, 2020 at 13:55

2 Answers 2

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Just speculating, but Aluminum is commonly employed in products as an alloy. For example, per a source, to quote:

Aluminium alloys (or aluminum alloys; see spelling differences) are alloys in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin and zinc.

As such, here my guess is a small presence of copper ions to account for the green hue (other Cu related green compounds include, for example, Verdigris). Also relatedly, my experience with ammonia complexes of Cu, for example, indicates an ability of the metal complex to display strong coloration at even very low concentrations.

As to exactly what inorganic/organic iodine related compound/complex, may possibly be present speculatively with copper, I will leave to others.

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No. Aluminium salts, even basic ones, are transparent (unless anion is colored, and iodine isn't colored)

Of common metals, blue-green hues are typical for copper. The exact compound, however, is very debatable. it's definitely not a simple copper iodide, as it is very pale yellow-brown, so it is something resulted from subsequent reaction with air.

Another source of greenish hues is iron, but those are typically unstable long-term in air unless the compound is in a big chunk. Glasses often have greenish hue due to presence of iron and are stable, because iron there cannot easily be oxidized. On the other hand, greenish solutions of Iron (II) are readily oxidize by air with formation of brownish hues.

Finally, green hue are characteristic to chromium (III). But I don't see how such an alloy could be used here.

My bet is on copper.

Note, the coloring you observed might be cause even by very small amount of coloring ions.

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