So I was inspired by that Nurd Rage video and decided to make some Iodine today (legal in Canada).
When I was trying to re-sublime it the remaining water was screwing everything up. So I poured some H2SO4 on it to remove all the water. I then melted
the I2 under the acid, then let it cool and poured most of it off.
When I tried to sublime it again something really weird happened!!! The iodine turned into a boiling liquid with a reflux ring. I had to crank the
heat up to get the vapor to move up to the RBF to collect the crystals. When I finished up I took the flask off and all the remaining iodine turned
into vapor quickly, followed by really dense white fumes.
So whats going on here, do Iodine and H2SO4 interact at high temperature? entropy51 - 1-11-2009 at 16:46
When I was trying to re-sublime it the remaining water was screwing everything up. So I poured some H2SO4 on it to remove all the water.
Where did the H2SO4 put the water that it removed? I'd really like to know how that works!
Quote:
decided to make some Iodine today (legal in Canada)
Theoretically, but it might be prudent to be sure that
there are no cold pills in the house, just in case.
[Edited on 2-11-2009 by entropy51]mr.crow - 1-11-2009 at 16:53
The H2SO4 absorbs the water rather violently, then carries it away when I pour it off. It also lets you melt the iodine into a solid mass.entropy51 - 1-11-2009 at 17:25
The H2SO4 absorbs the water rather violently, then carries it away when I pour it off.
I think "dissolves
in" would be a more precise term than "absorbs", don't you? Generally when one has an (almost) insoluble solid (I2) in a liquid (H2O) one separates
the two by a neat process known as "filtration" whereby the solid remains on the filter and the liquid passes through. If the amount of water is
small one could get really sophisticated and press the wet solid between pieces of filter paper, thus absorbing (!) the water on the paper. mr.crow - 1-11-2009 at 17:47
I guess dissolve is the correct word.
I did squeeze all the water out using filter paper, getting some nice crumbly gray lumps. The weight indicated a significant amount of water remained
and water definitely screwed up the sublimation. It is really hard to get the water out of the precipitated iodine.
Now thats all beside the point. Why the heck was the iodine boiling and making a reflux ring with the acid present? I have never heard of that before.entropy51 - 1-11-2009 at 18:12
Quote:
Why the heck was the iodine boiling and making a reflux ring with the acid present?
Because you heated it to
it's boiling point? (It does have one).
I believe I2 sublimes at low temperatures and boils at higher temperatures, but when I've sublimed I2 I've heated it gently so I've
never seen a reflux ring. Did you try to resublime those "nice crumbly gray lumps". I'm guessing that those would have sublimed if heated gently.
It sounds as if the water messed up your sublimation because you heated it so hot that the water vapor came off with the I2 vapor. I think gentle
heating is the ticket.
Maybe you try this again without "drying" it with H2SO4. I've never heard of drying a solid by adding H2SO4. Drying a solid over H2SO4 or other
dessicant in a dessicator is the usual procedure. Br2 can of course be dried with conc. H2SO4, but it forms a layer which can be drawn off in a sep
funnel, a very different situation than yours.
[Edited on 2-11-2009 by entropy51]S.C. Wack - 1-11-2009 at 18:42
Sounds like you made some HI somehow. Try the sublimation while the iodine is in the conc. acid instead.mr.crow - 1-11-2009 at 21:15
The idea to use the acid came from that German chemistry forum. Subliming the gray lumps caused water to condense on the flask too
So it boils at 184.3 degrees, I don't think I would have gone that far. It could also be a sulfuric acid hydrate boiling.
I had to really crank the temperature to get the vapor up to the flask. The air was only 10 degrees with a fan blowing on it.
Im also impatient, and it still took all day!
So anyways thats my strange observation. I got about 20g of pure Iodine so I am happy JohnWW - 2-11-2009 at 05:00
I think I have read somewhere of iodine being capable of forming, with the strongest acids and with some oxidation, salts of I+ and IO+.mr.crow - 3-11-2009 at 11:43
So I thought about it some more
The small amount of liquid on the hotplate (Corning PC420) could have reached the boiling point. It could have had a thin layer of acid on the top
preventing proper sublimation. Once the vapor reaches the flask it only takes a few minutes to get a nice crop of crystals.
I doubt its reacting with the acid, its the opposite of the sulfur-iodine cycle.
Nevertheless its was a beautiful sight to behold entropy51 - 3-11-2009 at 13:11
If we agree, we must both be wrong!woelen - 6-11-2009 at 01:17
Actually, the method of drying I2 with H2SO4 is a good one. You can use it to get pure iodine. I have done it as well and it works great.
I have made iodine from KI, dilute H2SO4 and slight excess of H2O2. I filtered on a fritte (sp?). Paper is not suitable, iodine stains the paper and
the paper becomes very brittle and dark brown, very messy. The wet crystal mass was added to H2SO4, swirled for a while and then heated, such that
liquid I2 is below the acid. Yes, this works if carefully heated. You get liquid I2 under acid.
Next, let it cool down and decant the acid from the iodine. You can add a new small amount of fresh conc. H2SO4 to remove the last traces of water.
Decant the acid from the solid I2 again.
Next, transfer the iodine (with adhering acid) to a clean small beaker and heat such that dense purple vapors appear. The vapors can best be condensed
on a cold watch glass (cold air blowing on the glass).
The fritte can easily be cleaned by rinsing it with a dilute acidified solution of sodium sulfite or sodium metabisulfite.
