KOH "neutrilizes" iodine

[akcapr]

I noticed that a drop of KOH solution added to iodine solution (iodine tincture and iodine+ethanol) casues it to completelly lose color. I had a iodine stain in the bathroom, and when i added 1 drop of KOH to it it almost instantly disapered and became a perfectly clean countertop. does anyone kno the reaction or wats goin on here?

[H2SO4]

i dont know, but i know if you ad vitamin C (ascorbic acid) to iodine it looses color also. I guess oyu could use it to see how much vitamin c is in stuff.

[YT2095]

it makes potassium Iodide (a clear compound) try using NaOh instead, it has a similar effect, but will leave a precipitate of Sodium Iodide crystals, those are a bright yellow color

[jdurg]

Are you sure it's not producing hypoiodate ions akin to when you dissolve chlorine into a sodium or potassium hydroxide solution?

[YT2095]

possitive, at least it doesn`t with NaOH, you DO get the Sodium Iodide salt

[budullewraagh]

i dont agree, yt; iodine is a lot easier to oxidize than chlorine. i wouldnt be surpirised if you got iodite instead of hypoiodite. of course it depends on how hot the solution is, but i know you can get iodate if you do that in boiling solution.

[YT2095]

well I always keep those sort of chems in specialy marked box in the fridge anyway, so boiling didn`t feature anywhere, and the crystal shape and scintilation reactions worked just the same too (that`s why I made some!). so I`de have to say quite conclusively that NaI was the product

[jdurg]

NaI or KI was the product, but it wasn't the only one. You actually got a mixture of NaIO3 and NaI (Or KIO3 and KI) salts. However, 1/6th of that is the NaIO3/KIO3 while the rest is the simple diatomic salt. Also YT, if your sodium iodide is coming out as yellow crystals, then you have a SERIOUS contamination problem there as NaI is a completely colorless compound. It's very soluble so it would not ppt out of a solution. PbI is a nice yellow colored salt that ppts out of solution, however.

[YT2095]

Hmmm... the iodine ticture was a mix of several compounds (non were Lead however) and contamination of lead can be ruled out at those amounts.

 

seriosly try adding iodine tinc (phamacutical grade) to NaOH soln (Strong) titrametricaly then filter and wash the product, yellow cubic crystals,

that Scintilate too!

[jdurg]

Hmmm. I can tell you with 100% certainty that sodium iodide is not a yellow crystal, however. I also know that it is completely soluble. So I'll have to pick up some tincture this weekend and give it a try...........

[budullewraagh]

sodium iodide definitely has been known to be, on occasion, somewhat yellow. it's highly soluble and deliquescent

[jdurg]

sodium iodide definitely has been known to be, on occasion, somewhat yellow. it's highly soluble and deliquescent

 

Yes, but the fact that it's soluble means that it's not going to ppt out of solution into these bright yellow crystals that YT is describing. Any 'yellow' color would most likely be due to some free iodine that is trapped into the crystal structure, and if that's the case, then you certainly don't have pure NaI.

[budullewraagh]

which reminds me that the hydroiodic acid i have prepared has been yellow. except once when i produced the gas, which happened to be reddish. what do you suppose the red comes from?

[jdurg]

Well, the only red gases I know of are bromine or nitrogen dioxide. NO2 may arise if there were some nitrates/nitrites in the salt that you were generating the HI from, while Br would appear if there were some bromide ions that were oxidized. What you may also see, if you used H2SO4 to create the HI, is the triiodide ion forming since H2SO4 is such a strong oxidizer that it will oxidize the HI into elemental iodine. The mixture of the iodine and iodide ions results in the formation of the red triiodide ion. This is why when HI is made, it's best to do so using concentrated phosphoric acid since phosphoric acid is a very poor oxidizer and will not oxidize your HI.

[budullewraagh]

no, HI is definitely reddish.

my salt was pure, reagent grade KI. there may have been a few ppm Br, but certainly not enough to produce such a great amount of the red gas. i saw triiodide in the solution, but the H2SO4 dehydrated the products on contact AND reduced to form SO2 and H2S. i definitely saw HI gas though, which can easily be reddish-yellow

[YT2095]

Jdurg I agree with you the solubility, my data books say the same too (there`s no mention of color in there so it assumed to be colorless by default). but non the less that is the result, in fact Fafalone when he was here tried it also and it did the same (he wanted to make some HI). it must be a contaminant, but the HI obtained from it seemed to work quite well.

I think you`ll agree that it wouldn`t be very "Scientific" to present what SHOULD happen, in favour of what actualy DOES happen, I`ll not falsify results for the sake of convenience