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Offline bezoar

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Dry Ice
« on: 18/01/2004 13:32:21 »
I got some dry ice at work (Botox is shipped on dry ice) and brought it home to the grandson to teach about heat and cold, and the states of matter.  In the course of our play, I put acetone in a plastic cup with the dry ice, then put a flower into it so he could fracture the frozen flower.  Anyway, the cup was a semi-opaque, slightly hazy plastic cup, and it got a bluish tint while the ice and acetone were in it.  After it came to room temperature, it reverted back to its normal color, but now, every time we put something cold in the cup, it turns blue again.  How come?

Bezoar


 

Offline chris

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Re: Dry Ice
« Reply #1 on: 18/01/2004 21:29:51 »
Out of interest, why did you put acetone in there anyway ?

As to the fantastic observation, a total mystery to me !

Someone with more knowledge of polymers, acetone and low temperatures will have to help out.

Best

Chris

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Offline Quantumcat

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Re: Dry Ice
« Reply #2 on: 19/01/2004 08:54:48 »
Dry ice is the stuff that people put above ^ponds and things to smoke, right? I saw a decorative water thing with smoke coming out, I assumed it was dry ice but my host mother asked the shop person what it was and she said it was just water vapour. Can that be right? The bowl wasn't at all hot. There was a little box with a red light attached to a power thing that seemed to be making the smoke.

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Offline Ylide

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Re: Dry Ice
« Reply #3 on: 20/01/2004 00:50:08 »
QC, that fountain probably just had an atomizer in it.  You can make fog from water just by making superfine particles of it.  

I'm not 100% sure why the cup turned blue, but I suspect it has to do with the way it refracts light as a crystalline structure.  The coldness of the dry ice/acetone mixture would contract the cup.  If you contract a clear or semi-opaque solid, you change the way it refracrs light through its structure.  It sounds like the structure was changed just enough so that it reflected some blue light but not other wavelengths.  But, I could just be talking out my arse, so you never know....that's just my slightly-educated guess.


On a side note, if you're ever in a chemistry lab and want to do something amusing, take a 2L beaker and fill it halfway with water, some harsh basic handsoap (the solid gritty stuff thats in most labs), and some phenolphhtalein.  Now, drop in a sizable piece of dry ice.  It gradually changes color from pink to clear (a cookie to whoever can tell me why), and the foam makes a cool looking brain-like structure that oozes out the top.  



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Offline tweener

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Re: Dry Ice
« Reply #4 on: 20/01/2004 03:45:06 »
I don't know anything about it, but I'm surprised the acetone didn't disolve the plastic cup and give you a real mess.

Chris, again I don't know, but I'm thinking the acetone was to have a liquid that would be as cold as the dry ice but not solidify.  That would allow submersing a flower and freezing it, which sounds like the point of the exercise.  Am I right B?


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Offline chris

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Re: Dry Ice
« Reply #5 on: 20/01/2004 12:24:24 »
Well done John, that sounds too logical not to be true !

I too was surprised that the acetone didn't eat its way out of the cup, but I wonder whether it partially did and in some way changed the structure or composition of the plastic - so that it nows behaves in a strange way towards light at different temperatures.

Anyone have any experience of how this might happen ?

Chris

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Offline chris

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Re: Dry Ice
« Reply #6 on: 20/01/2004 12:26:57 »
Oh, by the way Cannabinoid. The soap is alkaline (saponified fat using a base like NaOH). The dry ice yields carbon dixoide which dissolves. Being an acid anhydride, as the dry ice vapourises some of the CO2 yielded dissolves in the water and lowers the pH. The phenophthalein decolourises as the pH switches from >7 to <7. I think.

Chris

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Offline bezoar

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Re: Dry Ice
« Reply #7 on: 20/01/2004 14:03:25 »
Yep, I put the acentone and dry ice together to freeze the flower, and when we took it out, it broke like fine glass.  The grandson is four, and I think it's never too early to get them started on science.  It was just a general discussion on the states of matter, because the smoke from the dry ice also provides a good visualization of a gas, which is hard for children to imagine if they can't see it.  By the way, I did the experiment outside in case the plastic didn't hold the solution.  I was more afraid that the plastic would become brittle and crack, but it didn't and now we have a cup that turns blue only with iced drinks.  It's a good gimmick for kids cups, huh?

By the way, cannabanoid, where can I find phenolphhtalein, and is that the correct spelling or a typo?  That would be a fun thing to do next.

The cup was not that clear brittle plastic that cracks if you squeeze it too tightly.  It was the more malleable, slightly cloudy, semi-opaque plastic cup.  It is still soft, so it hasn't changed the flexibility of the substance.

Bezoar
« Last Edit: 20/01/2004 14:08:28 by bezoar »
 

Offline Ylide

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Re: Dry Ice
« Reply #8 on: 20/01/2004 15:25:33 »
You transposed the t and h, but thats prolly just a typo.  Youve spelled it correctly.  (phenolphthalein)  I don't think it's commonly available, but I also don' think it's a controlled substance as it's not particularly toxic or used in drug manufacture.  You could probably get it from a chemical supply store...check your local yellow pages.  It's not very expensive, they sell it in either as crystals or in an alcohol solution.  (i'd buy the solution)

If you have trouble finding it, you can use the colored fluid from red cabbage.  Puree it and strain, and collect the red juice that comes off...it contains anthrocynin dye, which is a natural acid/base indicator.  It will be greenish at higher pH and turn purple at neutral pH and red at acidic pH.  This might actually even be more fun, as it's an true color change rather than just a color disappearance.  

The laxative ExLax contains phenolphthalein, so you can always buy some of the tablets and grind one into the water.  It doesn't take much to work as an indicator.  



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Offline Quantumcat

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Re: Dry Ice
« Reply #9 on: 20/01/2004 15:28:24 »
Well I don't really understand anything.

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Offline bezoar

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Re: Dry Ice
« Reply #10 on: 21/01/2004 11:19:04 »
Think I'll try the ExLax and red cabbage.  It's much easier to come by.

Bezoar
 

Offline Ylide

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Re: Dry Ice
« Reply #11 on: 22/01/2004 07:48:55 »
At least you'll be regular.  :P

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Offline bezoar

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Re: Dry Ice
« Reply #12 on: 22/01/2004 21:55:12 »
Ha ha ha ha.  I walked right into that one.
 

Offline Donnah

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Re: Dry Ice
« Reply #13 on: 22/01/2004 22:52:55 »
You sure you weren't running?:D
 

Offline Steve Vai

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Re: Dry Ice
« Reply #14 on: 02/09/2005 12:57:23 »
Hey,

my first post, been looking around a bit, ive heard dry ice mentioned before, so i wondered - what actually is it? and how do you make it?


thanks

alex

"Turkeys killed my family" - Chip, 02/09/2005, 12:49
 

Offline Simmer

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Re: Dry Ice
« Reply #15 on: 02/09/2005 19:56:27 »
It's frozen carbon dioxide (~-80 C IIRC).  

I don't know how they make it industrially but you can make it by rapid expansion of pressurised carbon dioxide gas (eg fire extinguisher).  You can buy kit to make blocks of it this way but I would think that it would be cheaper to buy the stuff from a supplier.
 

Offline Steve Vai

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Re: Dry Ice
« Reply #16 on: 03/09/2005 18:22:09 »
so in theory, bursting a can of pressurised CO2 would create dry ice?

"Turkeys killed my family" - Chip, 02/09/2005, 12:49
 

Offline rosy

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Re: Dry Ice
« Reply #17 on: 03/09/2005 21:53:22 »
Someone was asking further up the thread why put dry ice in acetone... the reason is that as dry ice is solid it makes rubbish thermal contact. Acetone is a liquid at -80C so the dry ice just makes the acetone really cold, a bit like putting water ice in your drink.
 

Offline Simmer

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Re: Dry Ice
« Reply #18 on: 03/09/2005 23:36:25 »
quote:
Originally posted by Steve Vai

so in theory, bursting a can of pressurised CO2 would create dry ice?


I suppose so, in theory, but I doubt if you would see much in practice.  With a CO2 extinguisher you start to see flecks of it forming in the nozzle when the extinguisher has been running for a while, i.e. where you have a cold surface and a high concentration of cold gas.  That wouldn't be the case if you just burst a cylinder.

I think you would get better results by discharging it rapidly onto a well insulated, low thermal mass surface, preferably somewhat confined (like an open-ended tube) to keep the concentration of CO2 high without impeding its expansion too much.  

Watch out though as everything, including the gas cylinder, will get very cold and you can give yourself a serious "burn" if it comes into contact with bare skin.  Also bear in mind ventilation, a high concentration of CO2 can make breathing tricky! :)
 

Offline Steve Vai

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Re: Dry Ice
« Reply #19 on: 04/09/2005 00:36:57 »
thanks, i guess a CO2 extinguisher could be fun for experimenting with then, try to create dry ice....then do stuff with it, i havent thought that far ahead

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Offline Simmer

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Re: Dry Ice
« Reply #20 on: 04/09/2005 01:05:07 »
Good luck with that :)

PS Watch out for water ice forming on surfaces in contact with air, the pure dry ice will be on the surfaces protected by the blanket of CO2
 

Offline simeonie

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Re: Dry Ice
« Reply #21 on: 05/09/2005 09:39:08 »
How do i get my hands on some dry ice. Not literally though because it can hurt

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Offline David Sparkman

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Re: Dry Ice
« Reply #22 on: 05/09/2005 15:59:13 »
Many years ago I could buy it from normal ice companies. I would start there and ask them the question.

David
 

Offline Steve Vai

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Re: Dry Ice
« Reply #23 on: 06/09/2005 18:56:52 »
today in chemistry, we were reacting calcium carbonate with hydrochloric acid. As this reaction produces lots of Carbon dioxide, we decided to hold our finger over the bung and let the pressure build up. when we eventually took off the bung, i felt the glass at the top get colder, and we noticed a small amount of the visible CO2 that comes wiht dry ice.

would it be possible to create dry ice in this way, but by trapping the expanding CO2 in a container, possibly a very cold container to help it solidify?

"Turkeys killed my family" - Chip, 02/09/2005, 12:49
 

Offline DrN

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Re: Dry Ice
« Reply #24 on: 06/09/2005 22:27:24 »
which is colder - dry ice or liquid nitrogen? I'm guessing liquid nitrogen, as when you put dry ice in it, it doesn't melt. or maybe it does, and i just can't see it through the smoke.

thats pretty cool about the cup turning blue when you put cold stuff in it. is that how they manufacture those cups that do the same thing? havn't seen them advertised in a while, so I hope they were safe!

when i use acetone as a fixative in plastic dishes, the plastic goes white and rough, almost like its been sandpapered, so it must do something nasty to it!

 

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Re: Dry Ice
« Reply #24 on: 06/09/2005 22:27:24 »

 

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