Pretty cool YouTube vid

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SirStev0

Lifer
Nov 13, 2003
10,449
6
81
pretty cool stuff... still it is just the same concept as rock candy... heating the water, you can dissolve more solute into the water than it should be able to hold...
Once cool, any major shock will cause it to go solid...


EDIT: missed an vowel.
 
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SirStev0

Lifer
Nov 13, 2003
10,449
6
81
Originally posted by: Gerbil333
Originally posted by: E equals MC2
what triggers it to freeze? warmth? friction?
Click to expand...

It's not freezing, it's around 50C. Don't remember why...
Click to expand...

Technically it is still freezing but it isn't the water... it is the sodium acetate coming out of solution and forming a crystal structure.
 
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SirStev0

Lifer
Nov 13, 2003
10,449
6
81
if you look carefully at his finger when he touches it ... he looks to have a grain of solute on his finger... It is called seeding the solution... it probably helped the solution turn so pretty... if anyone actually tries this I would suggest doing that as well...

He insinuates it when he talks about making sure that undissolved grains are in the solution... otherwise once cooled the solution would never stay liquid and you would come back to a solid...

 
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Paperdoc

Platinum Member
Aug 17, 2006
2,520
383
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Originally posted by: E equals MC2
what triggers it to freeze? warmth? friction?
Click to expand...

The experiment creates what is called a Supersaturated Solution. Recall that the procedure was to heat water to boiling, add as much Sodium Acetate as it takes to make sure that a little bit of it does not dissolve, and then pour off the clear solution. This means the solution is "saturated" - it has the maximum amount of Sodium Acetate dissolved that it can take. Now, that "maximum amount" is greater for a hot solution than for a cold one. So when the solution is placed in the fridge and cooled to room temperature, it now has 'way too much Sodium Acetate in it. Theoretically, you can't make that solution! Well, as shown here, you can make it, but it is VERY unstable - it wants to get rid of all the excess Sodium Acetate crystals. It is called "Supersaturated". Any small disturbance will trigger the formation of one tiny crystal, and then much more of it will crystallize on that one until the solution returns down to the Saturated state (at room temperature). In this case, so much material crystallizes that the resulting mass is completely solid and just a bit damp.

For some solids being dissolved in a liquid, it takes energy input in the form of heat to break up the crystals and allow them to dissolve. This is called Heat of Solution, and the dissolving process is called "Endothermic" if it needs heat to promote it, as this system of Sodium Acetate in water does; in these cases the solution would get cold if you don't provide outside heat. Now, imagine what happens when you reverse the process - you take a solution and cause it to "un-dissolve", or crystallize out the solid. Then heat is RELEASED and the mixture becomes warm.
 
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uclaLabrat

Diamond Member
Aug 2, 2007
5,632
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Yup, paperdoc's on the money. It's just a recrystallization. It's used in the lab to purify solids, it's the same thing as making rock candy.

It's not actually ice, it's just solid sodium acetate.
 
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