Chemical Forums
Specialty Chemistry Forums => Citizen Chemist => Topic started by: ryanv777 on February 24, 2013, 06:39:55 PM
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I have a question, but first a little bit of back story. The other day, i was considering the odd properties of water, primarily the unusual relative densities of it's various phases, (IE. water is denser than ice). I was thinking about this, when I had an idea. What would happen if i froze a layer of water beneath a layer of some other immiscible liquid that's denser than ice, but less dense as water. Would individual ice crystals freeze and float to the surface? So a few hours of research, gave me Castor oil, as a candidate for my first experiment. After browsing through a few stores, I found a 4oz bottle in CVS for six bucks. Well that was easy. Unfortunately, when I attempted to preform the experiment, I discovered that Castor oil was far too viscous to allow ice to easily float to the surface through it. So I am now continuing my search for two liquids that will work with this experiment, but i seam to have exhausted any possible liquids that would be easily attained. So before I even begin trying to find out where I would get astoundingly, cyclohexane, or any other chemical with an unusual name, I decided to ask on this forum if anybody knows what, if anything, will happen. Any help would REALLY be appreciated. Of course, I understand that by using two liquids, neither of which water, the process will be reversed and the less dense liquid on top will freeze and sink to the bottom. Thanks in advance! :D
As a sidenote, my only chemistry background is one year of high school chem that I took last year, so on the extremely likely event that nothing i have just said has any scientific basis, my apologies, I'm new to this :)
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Here's what you can do: go to a public library, and look for the CRC, its a reference book of chemistry. It will have a table of all organic liquids, and you can compare the densities to water and ice, and know what to try. As a guess, by the time water is cold enough to freeze, the orgainic phase will be too viscous to let the ice float.
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Thanks for the help, unfortunately I believe that I have already found the tables from that book online. That's where I found Castor oil. That, and a few other oils were the only listed substances with densities between .92 g/ml and 1g/ml that wouldn't mix with water. However, after the first failed experiment, I've found this http://chemistry.kenyon.edu/getzler/Research%20files/miscibility_elutropicity.pdf (http://chemistry.kenyon.edu/getzler/Research%20files/miscibility_elutropicity.pdf) chart. I checked the densities, freezing points, etc., for many of the substances, but they mostly seem somewhat obscure. Finding anything about their viscosity turned up a blank, for example. However, I'm assuming they will not be nearly as bad as the oil. The two chemicals I mentioned before, Acetonitrile and Cyclohexane, seem to be possiblities. They won't mix, and have very close densities. Cyclohexane is slightly less dense, but has a higher freezing temp (6.6 °C), and in it's solid form it should become denser than the Acetonitrile below it. However, i can't find much information on the properties of these two chemicals, and have yet to even search for somewhere to acquire them. :(
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Acetonitrile is miscible with water. That's the only thing that I know off the top of my head. But go ahead and try some hexanes. You can find mixed hexanes at some hardware stores.
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Thanks. They may be mixable with water, but those two chemicals can't be mixed with each other. Sorry, i wasn't very clear with that. If i'm not able to find a good substance to use with water, i would just use two other chemicals together, and those two were one idea. ;D
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My bet is that the outcome of the experiment will depend on the way it is performed, and on several hard to predict factors that will depend on the other liquid used.
When water freezes ice is created on the surface, but whether it will be able to float up depends on whether the other liquid is able to get between the ice and the water - and whether it can or not, depends on the wetting of the ice. If the interactions between water and ice is stronger than the interaction between ice and the other liquid, at least initially the ice would be kept on the water surface. Later it can float up - but if it will cover whole water surface (touching vessel walls), there will be no way for the other liquid to get under the ice for purely mechanical reasons, so the ice will stay where it is.
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Liquids get viscous close to their Freezing Points I assume. Hence I'd try to find the other liquid such that it has a very low Freezing Point.
How about 1-Hexanol (-45C) or Xylene (-40 C) or Acetic Anhydride.
As to how you can get your hands on these I do not know.
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Another idea is why not try silicone oils?
http://www.powerchemical.net/library/Silicone_Oil.pdf
They have low freezing points, yet seem entirely water immiscible and low viscosity.
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Simethicone?
- Water Insoluble
- Freezes at -50 C
- non toxic
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Acetic Anhydride
With water?
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Acetic Anhydride
With water?
Brain fart. :P
Right you are: won't work.
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Like Borek: said, we know that the solution is immiscible with water, so why would ice leave the water, associate with the solvent, and float away? Its just not likely. Unless ... there's very little water, so as soon as it freezes, all the liquid water is gone, and floats away. Now that could be fun ... if there's no liquid water, just the small amount of water dissolved in the "immiscible" solvent, you might get a suspension of ice crystals. Or maybe even one large one crystallizing free from the solvent.
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Like Borek: said, we know that the solution is immiscible with water, so why would ice leave the water, associate with the solvent, and float away?
Why not? The density induced force ought to be stronger than the molecular forces that cause phase separation (I think). At least for larger ice crystals.
I agree with Borek in the sense that viscosity and other mechanical considerations might prevail and sometimes prevent the separation.
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I'm thinking like dissolves like. What we're working with is a polar solid -- ice, suspended in a polar solvent -- water (yeah, that does sound weird, but if we're at equilibrium, both exist) and checking its interaction with a non-polar solvent. Maybe gravity can pull this into three phases -- ice over solvent over water. But is it really that easy to get three phases? Can you pull an light suspended insoluble powder, out of a water suspension, using a solvent? If that's ever done, then it could be applicable here.
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I'm thinking like dissolves like. What we're working with is a polar solid -- ice, suspended in a polar solvent -- water (yeah, that does sound weird, but if we're at equilibrium, both exist) and checking its interaction with a non-polar solvent. Maybe gravity can pull this into three phases -- ice over solvent over water. But is it really that easy to get three phases? Can you pull an light suspended insoluble powder, out of a water suspension, using a solvent? If that's ever done, then it could be applicable here.
All good questions. I don't know but it's an interesting experiment..
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Wow, a lot of really helpful feedback. Just something to keep in mind is that if I decide to use substance A and B, then the denser substance(unless were using water for substance B), A, must:
1. Not mix with B
2. Have a density between that of liquid B, and solid B
3. Have a freezing point significantly lower than B
4. Have a low viscosity
I don't believe that silicone oil or simethicone fulfill the second requirement if it were used with water. Can anyone see any problem using Acetonitrile and Cyclohexane together? (No water would be used in this case)
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OK, here's another easier one -- you can suspend carbon powder in water, it is less dense than water, and will often float on top. It isn't soluble in any organic solvent, either. So if you shake all three up, will the carbon powder partition itself anywhere? I just don't see that happening. Unless a state of affairs is more energetically stable, like dissolves in one or the other, why would it move? Again, gravity is the answer, but is it enough? This is a pretty fun question to think about.
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Indeed, it is interesting.