Sciencemadness Discussion Board

Liquid Iodine

YT2095 - 10-7-2006 at 08:17

Today I saw Liquid Iodine as standard room pressure (and almost Temp).

this particular demo I discovered by Pure accident and couldn`t beleive my eyes!

all you`ll need is a simple test tube capable of taking boiling heat, some elemental Iodine crystals (prills in my case), and Potassium Carbonate anhydrous, and some deionised water (although Ordinary tap water should work I think).

put 3 ml of water in the test tube and add 3 Large crystals or prills of Iodine (roughly 100mg) and then heat it gently, not enough to make it sublime out the water , but enough to dissolve some of it.
then add a good 1.5 g of the anydrous K carbonate.
it will get Very warm you`ll also lose the reddy/brown color in the water.
the iodine will be sunk under this K Carb, but it will melt!

stir it until the iodine comes to the top of the K Carb layer, you`ll see it as a Black liquid that acts much like Mercury does, it`ll make many tiny balls when shocked that will all join back up again when rolled around.
this liquid will cool, and even at hand heat the iodine will still be liquid!

I can`t explain this either, it just happens, i suspect that it MAYBE local heating around the iodine itself as it reacts, and that no Vapor can be evolved because as soon as it does the Basic AQ layer absorbs and reacts with it.
but for a good 10 to 15 mins you will have Liquid Iodine to look at and Own :)

Enjoy :D

unionised - 10-7-2006 at 09:21

Iodine melts at 113C and the liquid would be pretty dense so it would sink to the bottom of most aqueous solutions. With that much K2CO3 in the water its boiling point will be markedly increased. Similarly, with lots of oportunities for impurities disolving in the I2 its melting point will be depressed; so it's not so suprising that you see the iodine as a liquid under an aqueous layer.

YT2095 - 10-7-2006 at 09:53

well, It`s certainly surprising to Me considering that I was taught I2 Sublimes and that it`s only ever a Solid or gas, and never a liquid unless under special conditions of Pressure etc...

although there is One thing that confuses me, I use K Carbonate, where does the CO2 go???

the only answer I can think of is that it only loses One K from the K2 and that gets replaced by Hydrogen, making potassium Bicarbonate.

other than that, I have no idea where it could go, there was certainly no visible gas evolved.

[Edited on 10-7-2006 by YT2095]

The_Davster - 10-7-2006 at 14:09

I did this a while back to make K-iodate. The literature I read on this before doing it stated carbon dioxide will come off as a gas. I did not notice any gas either, but it may be like the reaction of formic acid and sulfuric acid, giving off a gas without causing bubbling. My iodine liquified when doing this as well, I had assumed it was because of the iodine vapours not being able to excape and being under a bit of pressure. I had intended to see what happened by placing iodine in plain water and heating, but I never got around to it because I was out of Iodine.
EDIT: I know I took a picture I'll try to find it.

[Edited on 10-7-2006 by rogue chemist]

Jdurg - 11-7-2006 at 18:36

You don't even need the layer of water to generate liquid iodine. You just need a test tube with a somewhat narrow diameter and a moderate amount of solid I2. Put your I2 in the bottom of the tube and heat it up. The iodine will start to sublime, but the high density of the I2 vapor will cause it to create some localized high pressure. As a result, the remaining solid I2 will liquify instead of subliming. You'll see the very dark, purple/black liquid with an intensely purple covered vapor hanging above it. If you coold off the tube, the I2 will solidify again and will leave a trace of its once liquid state.

The I2 in my element collection was solidified in that manner. I had it sealed in a glass ampoule, and when doing the sealing process the I2 at the bottom liquified. It shocked me too since I once though you needed high pressures to see liquid I2. Instead, you just need high localized pressures to see it, and if you have enough I2 you'll have enough pressure.