Iodine Solution

[Satu11]

Hi,
I have been trying to make iodine solution.I have tried disloving iodine in conc KI, but still it does not disolve fully.Could anybody give tips on how to make iodine solution and how residual iodine could disolve.Thanx.

[Xenon]

I use 5% w/v I in 10% w/v KI for iodine stain (takes a long time to dissolve - overnight with magnetic stirrer)
Prepare 10% v/v of this solution for Lugol's (starch indicator)

[Satu11]

Thanx I will try....

[RosalieM]

Do a search on here for iodine and you will come up with other recipes. The iodine won't fully dissolve - just filter it off.

[Satu11]

Thanx Rosalie ...I figured that out...

[Ian]

Now this is not so much a reply as a personal observation and another question, but as it is related, please forgive me for being a little off topic.

I generally make up my I/KI solution by throwing a scoop of KI and a good shake of I into a beaker of water and leaving it overnight untill I get a good dark black/purple solution. ....BUT after about 6 months, it begins to fade to clear.

During a clean up at the end of last year, I found a 2.5L bottle of iodine solution that must have been made up by the previous labbie who left 4 years ago. It was as good as new!! Can anybody tell me what I do wrong and what she apparently did right?

Ian

[smiley]

I dunno. I always leave some Iodine in the bottom of the stock bottle anyway. I also chuck in the little bits of Iodine that get used in the Soluble/Insoluble experiments. Works for me.

[Voice]

I do use the recipe as stated in resource books but one of the things I do is grind the iodine down into a powder before weighing the required amount.
After that it goes into the KI solution (maybe 3/4 of the amount) and put on the stirrer for overnight dissolving. In the morning I pour off the solution and if any iodine is left in the beaker, I then use the last of the KI solution to dissolve that on the stirrer. It usually all works out.
One of the reasons your hidden Iodine solution is good is probably because it has been hidden away from the light!
Maree

[RosalieM]

Ian, do you keep yours in clear or amber bottles? It needs to be stored in amber as the light does something to it. I can't remember what, exactly, but perhaps that is why?

[Ian]

Ian, do you keep yours in clear or amber bottles? It needs to be stored in amber as the light does something to it. I can't remember what, exactly, but perhaps that is why?

Yeah. All my dropper bottles are amber, and the Chem store light is a special pinkish one that is supposed to be less damaging to chemicals than ordinary white light. Most of the time it is pitch black in the Chem store. (I prefer it that way!)

My memory has a similar problem to my iodine solution. It just fades away after a few months. I wonder if there is a connection?

Ian

[Jen1]

I have had the same problem with my dropper bottles fading to clear after a month or so. They are amber bottles but with a dropper and red rubber teat on the end. My stock solution (of the same concentration) is kept in the chem store in an amber bottle and this stays yellow for ever. I have tried keeping the dropper bottles in the chem store thinking the light must still be getting to them in my prep room, but they still fade to clear.
I cant work it out, any ideas out there??

[Labbie]

Their are different recipes, Alcoholic Iodine, Aqueous Iodine, Lugol Iodine, Stronger of the two. And then Grams iodine. Each has a different recipe.

Alcoholic: add a few flakes to Methylated spirit
Aqueous: Add 1g Iodine & 5g Pot iodide to 20ml water dilute to 1 litre
Lugol: 4g Iodine 6g Pot Iodide to 100ml make to up 1 litre
Grams: 1g Iodine 2g Pot Iodide to 300ml walter make up to 1 Litre

I always make up the Lugol one it is strong, but lasts for years and years. Do give it 24 hours to fully dissolve.

[RosalieM]

Perhaps it has something to do with the droppers themselves then... Have you tried storing them with ordinary lids on instead of the droppers? maybe it has something to do with the air getting through the rubber... I don't actually know, I'm just thinking of possible variables...

[jenny walter]

The quickest way to make iodine solution is to grind iodine and potassium iodide together in a mortar and pestle together with a little water. You will find that the iodine will dissolve up really fast when it's with such a concentrated form of potassium iodide. Now all you do is decant carefully into volumetric flask with plenty of washes make to mark and bravo!! It is all done in a matter of minutes. Enjoy!!!
Jenny

[Jen1]

Hi Rosalie,
I have tried your suggestion of removing the droppers and capping the dropper bottles.
Now to leave them for a few weeks and see what happens!

[RosalieM]

I also read just this morning that it keeps better in the fridge, so maybe the stock bottle in the store room is cooler than the dropper bottles in the prep room? Could be another variable to consider. A larger bottle would take much longer than a smaller one (due to surface area/volume ratio etc) to heat up... Please let me know if the caps make a difference! Maybe you could put half your capped droppers in the fridge and half where they usually live and see if there is a difference between those ones as well?

[lada]

The main reason iodine solution fades is sunlight.
Does not matter if you have dropper bottles. If you keep solution away from light(in cupboards) will last much longer.
I have mine in amber droppers and will last a term on the shelf, away from direct light, but will last longer in the cupboard. Teacher did food testing on Mon THIS week and left bottles in lab on window sill and came to me this morning, because test did not work. Window faces north and it was enough sunlight to discolour Iodine solution completely even in amber bottles.
Lada

[Rowyrow]

I made some up at the end of last year in december but i didn't have any amber dropper bottles just clear( plastic) stul bottles so i tried to light proof them by glueing black plastic from a printer cartridge bag around them. I keep the bottles in an ice cream container and then keep that in my chem store wrapped in the remainder of the black plastic bag from the printer. It's not something I recommend . I just had a look at the solution and although it does work for the starch test it is looking rather pale and the bottles are a little worse for wear. I guess it's a lesson, and something to add to my list of tings to buy. amber glass dropper bottles.