Co2

[hermanntrude]

It does sublime, because "sublimation" is just the process of solid turning into vapor.

 

Fair enough. I was thinking about sublimation as being exclusively going from solid to gas without any appreciable melting, but that's the wrong definition

[John Cuthber]

It's interesting to see that the case of I2 is closed. In reallity, you can melt it in a test tube.It's nothing special. Since it's pretty volatile, you get a lot of vapour too, but if you pre heat the tube to a temperature between the melting and boiling points ( not too difficult) you readily get the liquid phase. I'm not wasting my time videoing this just because it will "stun" Jdurg.

[jdurg]

I've seen it in a test tube many times. I've never seen it on a wide open surface before like I've seen ice and every other solid that melts. (E.G. on the bottom of a carboard box, or a wooden plank). Again, show me a video of it melting without being confined. Put it in a test tube and the vapor will sit on top and create a higher pressure at the surface of the I2 making the liquification much easier because there is a greater localized pressure.

[John Cuthber]

"I've never seen it on a wide open surface before "

From the point of view of an iodine molecule, a test tube is a wide open surface.

 

"Put it in a test tube and the vapor will sit on top and create a higher pressure at the surface of the I2 making the liquification much easier because there is a greater localized pressure"

The test tube has roughly 70 miles of air above it exerting about 760 mmHg pressure.

From the data above, the vapour (in a sealed container) would only add about 130mm Hg to that. Since the tube is open the additional pressure is only the weight of the few inches of I2 vapour in the tube which is obviously tiny compared to the 70 miles of air.

[jdurg]

How about you get off your high horse and contribute something positive to this forum. I'd like to see some posts from you where you're not giving a holier-than-thou attitude and actually contribute something to this forum. You seem to get high off of nit-picking every single thing that someone posts here.

 

The point of a public forum is to help people, not sit there and make people not want to come back.

 

Seriously. Have you EVER posted something that was helpful and at the same time cordial? I think not.

[John Cuthber]

Cordial is something I can leave to others to judge.

This website is about science- ie knowledge. In order to be of any use it needs to be accurate, therefore I consider my post correcting your error to be helpful to the board in general. As you say, "The point of a public forum is to help people", we can't do that by posting stuff that's incorrect.

Perhaps you might like to explain why you chose to post something which was both off-topic and incorrect, before criticising what I posted.

[insane_alien]

John, while your post was correcting jdurg was technically correct you could do with getting off your high horse as if you had never made even the slightest error in your life. it makes you sound like a pompous ass.

[John Cuthber]

I've made plenty of errors. I just don't usually resort to ad hom attacks on those who point them out.

[jdurg]

Please prove my error. I said that in an open container (and by open I mean a flat surface, a cereal bowl, anything that doesn't have exposure to the atmosphere of a mere 1 cm) I2 will sublime. It will. You will NEVER have liquid iodine unless it is in a confined space where the high vapor pressure of gaseous I2 will allow it to liquify before it turns into a gas.

 

Again, by confined space I mean a space where the gaseous I2 is forced to remain in place. If we go by your nitpicking, then there is NOTHING that sublimes. NOTHING. And sublimation is hence an incorrect term.

 

I'm sorry if you thought my truthful, factual statement about you being a pompous ass was an ad hom attack.

[insane_alien]

Jdurg, while john is being a bit of a prat he is right, iodine has a liquid phase at standard pressure.

 

see the phase diagram here -> http://radio.weblogs.com/0101365/2004/06/04.html

 

but you are right that if left on an open surface that is not heated it will sublime because it is below the melting point.

[jdurg]

But even if heated it will sublime and not melt as the vapor moves away far too quickly. Again, if I were to see a video of a puddle of liquid I2 I will quickly change my views, but I have yet to see that happen.

[insane_alien]

i thought you knew how to read a phase diagram. it HAS A LIQUID PHASE BELOW 1 ATM.

 

i do not have any substantial amounts of iodine so cannot make a video of it and have had no luck finding one on the net. probably because it is an entirely unabnormal phenomenon.

 

wikipedia states this specifically under its sublimation article (http://en.wikipedia.org/wiki/Sublimation_(chemistry))

 

Iodine is another example of a substance that produces fumes on gentle heating. In contrast to CO2, though, it is possible to obtain liquid iodine at atmospheric pressure by controlling the temperature at just above the iodine's melting point.

[John Cuthber]

Jdurg, I don't think it falls to us to prove your error. You are the one making the claim that something unusual happens so it is your job to prove it.

However, the phase diagram give in IA's post could only have been produced by someone who did essentially the experiment you are talking about (at lots of different pressures). I accept it's not on video, but it is evidence.

[jdurg]

DID THEY DO IT IN A CONTAINER WHICH HOLDS ON TO THE VAPOR ABOVE THE SURFACE OF THE LIQUID IODINE?!!!!!!!!!

 

Good Christ, that is what I am trying to explain. Yes, Liquid I2 does exist. I've seen it, I've made it. I just have NEVER seen a substantial quantity of it liquify unless it was in a test tube or container with the lid on. I think there is a communication failure going on here.

[John Cuthber]

I just have NEVER seen a substantial quantity of it liquify unless it was in a test tube or container with the lid on. I think there is a communication failure going on here.

There's some sort of communication failure here.

A test tube is an open container.

A few inches of dilute iodine vapour aboue the liquid is going to make less difference to the pressure than going down the stairs to the next floor of the building.

How could it make any difference to the melting point?

Those phase diagrams ar about equilibrium conditions so the rate of loss of vapour doesn't enter into the debate. If you get I2 to about 150C at atmospheric pressure it will melt. It's very volatile under those conditions, but the liqid does exist.

[frank burns]

Dear jdurg,

 

 

If you can show me a video of I2 out in an open container melting, then I'll admit I'm wrong. I'll just be stunned if you can give me that proof.

If you have access to iodine crystals, do the following. Dip in a small stainless steel spatula. Hold the little heap of crystals over a Bunsen burner. You will get some sublimated into a red vapor at first, but after just a few seconds, lo and behold, the iodine will quickly melt all over the blade of your spatula and almost immediately begin to boil. If you take the spatula out before it all boils away you will have lots of time to see the iodine as a liquid, on an "open" surface, at room pressure. It will discolor your nice shiny stainless steel spatula (turn it black), but it is worth it, to feel that emotion of being "stunned". How often do you get that feeling?