Sciencemadness Discussion Board - Is there a liquid iodine form?

Is there a liquid iodine form?

craynerd - 21-12-2006 at 10:16

BAsically, i have made a sealed quarts crystal glass ampule containing 3 small iodine crystals (maybe 0.5g ish?). When i heat it gently with a match, i get purple vapour, but as i heat it for longer i am almost positive i get a liquid.

I`m confused, i didnt think iodine had a liquid form or is it due to the high pressure it will be under? I suppose there are a lot of crystals in there for such a small ampule (1cm3 ampule)

Help would be appreciated!

Chris

The_Davster - 21-12-2006 at 10:22

Under atmospheric pressure iodine will just sublimate, but anything higher and iodine will have a liquid state. Even heating a mix of iodine under water will cause liquid iodine to form. Or heating a small ammount of iodine in a capped vial.

Mr. Wizard - 21-12-2006 at 17:23

I have played with Iodine crystals in a Pyrex test tube that was sealed by melting the end. When heated there is a liquid material, with a violet cloud above it. The pressure in the tube is above atmospheric, no doubt.

The first step in doing this is to heat a small test tube and stretch the tube down to a narrow opening, which can then be quickly sealed. After the initial stretching the tube is allowed to cool. and Iodine crystals are pushed through the small neck and allowed to fall to the bottom of the tube. The neck is then quickly heated to seal the opening while the bottom of the tube is cooled with a wet rag, to lower the pressure inside while the sealing is taking place.

Waffles - 21-12-2006 at 17:54

Quote:

Originally posted by craynerd
BAsically, i have made a sealed quarts crystal glass ampule containing 3 small iodine crystals (maybe 0.5g ish?). When i heat it gently with a match, i get purple vapour, but as i heat it for longer i am almost positive i get a liquid.

I`m confused, i didnt think iodine had a liquid form or is it due to the high pressure it will be under? I suppose there are a lot of crystals in there for such a small ampule (1cm3 ampule)

First of all, there is a big difference between normal glass, 'lab' glass (usually pyrex), and quartz. I sincerely doubt your iodine is ampouled in quartz if you made it yourself (considering you probably don't have access to the flame temperature needed to work quartz, usually done with an oxyhydrogen flame).

But yes, your thinking is correct. Normally, when you heat iodine, it simply sublimes. But when the vapor pressure of the atmosphere (or the vaporized iodine sitting on top of it) is slightly more than standard, you will see liquid iodine. Cool stuff, no? Thin opaque purple liquid, like Br except in hue, which makes sense.

Every element HAS a liquid form, though not at every temperature (because of the critical temp)

Jdurg - 21-12-2006 at 19:11

Yes, liquid iodine is pretty neat to see. If you take a standard testtube and place about a centimeters worth of I2 nodules in the bottom and heat it up, you'll see the dense purple cloud right above the iodine, but the iodine itself will liquify as the vapor pressure above it is apparently enough to make the solid I2 go liquid. Really neat to see. I remember when I first noticed that happening I was kind of shocked because I thought iodine needed really high pressures to form a liquid. I was glad to be wrong.

not_important - 21-12-2006 at 23:27

By my CRC, the melting point of iodine is 113.9 C, at which temperature its vapour pressure is a tad under 100 mmHg. It will sublime without any melting so long as the vapour pressure of I2 is less than 100 mm, it doesn't take much containment to reach that level.

woelen - 22-12-2006 at 03:19

Quote:

Originally posted by iamthewaffler
Every element HAS a liquid form, though not at every temperature (because of the critical temp)

Is this really true? I think it is true for every element, except carbon and boron. Or is this true but we simply cannot make liquid forms of these elements? I've never read anything about pure liquid carbon.

Waffles - 22-12-2006 at 04:17

Quote:

Originally posted by woelen

Quote:

Originally posted by iamthewaffler
Every element HAS a liquid form, though not at every temperature (because of the critical temp)

I actually thought the same thing for awhile, but I was wrong. My friend who works at a particular government laboratory said that they used fair amounts of liquid carbon somewhat often, although I have no idea how it was stored. Also, what's REALLY interesting (also courtesy of him) is that at the tip of a carbon electrode, while there is an arc, FOUR phases of carbon are present at once. Apparently, the very tip is solid, liquid further back a little bit, vaporizing because of the heat, and ionizing to plasma because of the heat and charge. Some guys did a study of it, really cool stuff.
Boron- just sort of sucks at life. You can liquefy it, but it's probably not worth your while. I couldn't even find a decent phase diagram, but indeed every element CAN exist as all of the three (four, six seven whatever it is now) phases.

[Edited on 22-12-2006 by iamthewaffler]

The_Davster - 22-12-2006 at 13:56

Boron melts, I have done it with an arc melter. Unfortunatly a weird effect occurs and the outside melts first very slowly, and then the pellet of molten boron explodes with green light. Unfortunatly I had to melt it with magnesium, and by the time the boron had begun to melt/explode the magnesium had already boiled off.

I gave up the study of the phase diagram with boron/Nd/Mg after this. It was just so annoying to melt!

[Edited on 22-12-2006 by The_Davster]

Sauron - 23-12-2006 at 02:18

There are several liquid at STP interhalogen compounds of iodine, most commonly available of these being ICl and ICl3, but, of course, they are not what you meant.

unionised - 23-12-2006 at 02:45

What's the fuss about?
This data
"By my CRC, the melting point of iodine is 113.9 C, at which temperature its vapour pressure is a tad under 100 mmHg. It will sublime without any melting so long as the vapour pressure of I2 is less than 100 mm, it doesn't take much containment to reach that level. " looks about right (thanks not important).
At 115C iodine is a volatile liquid like ether at 25C.
Nothing special.