Sciencemadness Discussion Board

Iodine turning into unknown liquid

mirgp - 20-11-2016 at 11:24

I was doing a little experimention on how iodine stains different surfaces and materials and noticed that when I put iodine granules on steel they seem to "melt" and turn into a black almost metallic looking liquid (the process takes about 10 mintes to start) I ended up cleaning it away and later decided to redo to experiment but have it go on for a longer time. This time I decided to use the bottom of an aluminium can as the surface. I put down about 8-9 granules on the can and let it sit for a while.

After about an hour or so the iodine had began "melting" and there were some clear red dropplets around the melting iodine.

The next day all the iodine had "melted" and there was alot of that red liquid stuff around it.

The day after that both the dropplets around the iodine and the iodine itself (if I can even call it that by this point) had turned into a clear liquid.

I tried looking up information on what this liquid could be but I couldnt fine anything about it. If anyone might know what this liquid might be please let me know.

[Edited on 20-11-2016 by mirgp]

ave369 - 20-11-2016 at 14:02

I can tell most definitely what the liquid on aluminium was: aluminium iodide hexahydrate. It is hygroscopic, takes moisture from air and liquesces, turning into a clear liquid. The red stuff, I think, was the unstable monoiodide, anhydrous iodide or some other intermediate compound.

What the metallic liquid on iron was, I don't know. Might be iron (II) iodide, but I know exactly squat about this compound.

[Edited on 20-11-2016 by ave369]

mirgp - 21-11-2016 at 00:33

Quote: Originally posted by ave369  
I can tell most definitely what the liquid on aluminium was: aluminium iodide hexahydrate. It is hygroscopic, takes moisture from air and liquesces, turning into a clear liquid. The red stuff, I think, was the unstable monoiodide, anhydrous iodide or some other intermediate compound.

What the metallic liquid on iron was, I don't know. Might be iron (II) iodide, but I know exactly squat about this compound.

[Edited on 20-11-2016 by ave369]
Do you think heating the liquid will remove the water without destroying the aluminium iodide?

Tsjerk - 21-11-2016 at 01:12

No, aluminium halides cannot be dehydrated to the halide. They will decompose into aluminium oxide/hydroxides or a mix of both and HI.

ave369 - 21-11-2016 at 01:48

Quote: Originally posted by mirgp  
Do you think heating the liquid will remove the water without destroying the aluminium iodide?


You can't get anhydrous iodide this way. To make it, you have to react aluminium and iodine again, but this time without access to air. But you can make crystalline aluminium iodide hexahydrate by heating the liquid solution or putting it into a desiccator. Note: if you want to heat it, add some azeotropic HI into the solution to stabilize it and prevent hydrolysis. This is standard procedure when crystallizing salts of very weak bases and volatile acids: add the acid in excess. HI will decompose on heating and foul your yield with iodine, but at least you'll have a yield.



[Edited on 21-11-2016 by ave369]