Supersaturated Sodium Acetate | Tales from the Prep Room

A beautiful transformation and a curious conundrum. Watch as Andy turns liquid into solid in a matter of seconds, experimenting with a supersaturated solution of sodium acetate.
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It just takes one small nudge to spark the transformation of a seemingly stable liquid into a solid. The liquid - a supersaturated solution of sodium acetate - consists of water with more dissolved sodium acetate salt than can be stably sustained. When Andy drops in a salt crystal, he provides the kick needed to start the transformation into the more thermodynamically favourable solid state.
At least, that’s what’s meant to happen. Just like science in a lab, science in the Prep Room doesn’t always go to plan first time. It’s a process of trial and error, explaining the unexpected, and exploring the phenomena at work. Curiously, when he goes to start the process, Andy finds that the crystallisation has half-completed - something which should, in theory, be impossible, because once one crystal forms it should kick-start the full process throughout the liquid.
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[@TheRoyalInstitution]

NEW FILM: Andy Marmery transforms a supersaturated solution of sodium acetate from liquid to solid in just a few seconds in the latest instalment of Tales from the Prep Room.

[@dg-hughes]

I like how there is a nice even bow or wave of it flowing across the dish it's not all jagged or blotchy it's smooth and orderly (like the very last one you see).

[@hendrikhendrikson2941]

I can see a sodium acetate bucket challenge coming! **bloop**

[@WabuhWabuh]

it is friction based reaction. stimulated by electrons rubbing into each other. Friction gives it enough energy to start a reaction just like lighting gas on fire. You dont need the crystal dropping to induce the reaction...just vibration.

[@Carsandbikes193]

The thing that gets me the most is that when he initialized the recrystallization process it caused the solid to appear cracked.

[@TheSciGuys]

I loved the video!! I wonder if the liquid was too warm to cause a full crystallization of the sodium acetate. When we did this experiment in one of our videos with at home ingredients we had to cool the solution in the fridge or an ice bath for a while before it would crystallize properly.

[@kosherlaw8095]

Get a life

[@locouk]

Hmmm, schrödinger's sodium acetate. It's neither in one state of the other unless you look at it. (Or it fails)

[@nootnoot5833]

But looking at it wouldn't do anything to it, an element colliding with it would actually change something.

[@rammerstheman]

For certain crystals the driving force for growth can vary depending on the crystal direction. It's interesting to observe that all of your crystals in the semi-crystalised sample are needle like. If you have a piece of contaminant that can provide a seeding point for one of this directions, but there is not enough of a driving force for any of the other directions (perhaps you cooled the sample quickly), you can imagine needle like crystals could form around this point, which is fairly similar to what you see in the dish.

[@bashkillszombies]

It isn't because of the small quantity being used, pocket hand warmers contain about that much and work 100% as expected (as a motorcyclist those suckers have saved my life several dozen times by keeping my core temp up enough to make it home in the cold and wet), so the quantity isn't the issue.

[@robbiekavanagh2802]

My theory is that there's a different layout/structure that the molecules can crystallise into given the right time and/or temperature, so it doesn't trigger a chain reaction of the typical crystalline structures all snapping into place.

[@johnium]

If you put powerful enough lamps directly aimed at the solution it may have been heating it up enough to prevent crystallization from occurring quickly. (that would be my guess)

[@JonathanSanderson]

Possibly, but from what I can tell from the video (my memory is useless in such circumstances...) I had a small LED lamp close to the sample, and a tungsten lamp rather a long way back. I doubt the latter would have much of a heating effect, to be honest. Interesting thought, though. Not the first time that a reliable demo failed completely as soon as it was placed in front of a camera!

[@ErgoCogita]

Stab in the dark: Surface tension might be creating either a barrier and/or a scaffolding for a crystal shape that cannot propagate down into the rest of the dish.

[@Ben123466789]

This is more plausible than people saying it was too warm or the lights were heating it up as if they didn't watch it crystallise normally a few seconds later

[@andresebastianmoreno]

The solutions in the Petri dishes are not sealed, like your typical sodium acetate handwarners or heat packs. They are also probably not prepared consistently and protected completely from environmental contamination. Likely, the acetate in the semi-solid dish was either not prepared correctly, or has become contaminated with some substance partially inhibiting crystallization. Since the release of the stored heat in the supersaturaturated solution brings it to 130°F (1.3 times the temperature of a healthy cow), the more complete release of heat may finish the process by driving off an excess volatile like water, or may simply impart sufficient kinetic and heat energy to complete the reaction in a contaminated medium.

[@PaulK390S90V]

if you put a the crystals in a few different spots around the edge I bet it would look pretty sweet. or add some color to it

[@brianbrane]

Polar alignment will allow the crystals to form. The mixed state solution would be unaligned due to temperature and brownian motion. You could try wating a very long time at a steady temperature to see if they eventually aligned, but this might take a few million years.

[@Rubikorigami]

It's nice that this experiment is not that purity-sensitive, and that Sodium Acetate is easy to sythesize. I actually managed to perform that quite easily! Also, can't wait for antibubbles.

[@piranha031091]

As to why crystals started to appear in the petri dish without seeding the whole solution (2:50), my guess would be that maybe some sodium acetate started crystallizing in a different hydratation state (perhaps it somehow started nucleating as a dihydrate or monohydrate), or maybe even as a different allotrope, therefore having a different crystal structure and not providing proper nucleation sites for the "normal" trihydrate. I guess the only way of knowing would have been keeping some of those crystals and performing an XRD analysis.

[@ThomasHaberkorn]

what is the microstructure of the supersaturated state (was 'makes' it supersaturated)?

[@TheRealReTox]

Would love to see that captured by a high speed uHD camera.

[@edgeeffect]

I love the music during the crystallization... can anyone tell me who/what it is?

[@cuteagrawal]

edgeeffect no

[@laurenceperkins7468]

I don't know the physics, but the large crystals like that form when it's just a tiny bit too concentrated, but not by so much that it just falls out of solution immediately. In my experience they're only stable if they're absolutely not disturbed while cooling. Possibly it's a different crystal structure. If you have a way to put it under a sufficiently powerful microscope that might give some hints.

[@DarkParadeHF]

My guess is the liquid separates leaving enough salt on top to create the small crystals that we see

[@prakharabhiraj]

I loved the video, it’d have been utterly pleasing to watch if you could kick off crystallisation from the centre of the disk

[@SodiumInteresting]

It's just bicarb and vinegar try it yourself

[@user-ln9bk7mo3l]

It seems the concentration of the Sodium Acetate is not as high or as "pure" as it ought to be.

[@ajuntey83]

Hi sir how can i make half saturated aqueous sodium acetate

[@jeniferlay9322]

hello what is the liquid solution, and what did you drop in the liquid solution? does it affect the temperature? for research purposes

[@Noob___Noob]

my guess is there might be two forms of crystal structures.

[@downey6666]

long shot, but could it have been seeded by dust particles? (irregular enough, to mimic the shape of sodium acetate crystals); producing Crystallites, with defective boundaries

[@AnonEyeMouse]

The black background material, plus camera lighting, plus breath... all may be messing with your temperature.

[@LiLi-or2gm]

Great video! Zit was distracting, though. 9.5/10.

[@morlanius]

The area immediately (micron scale) around the crystals had a lower in concentration than the overall solution due to the formation of those crystals.

[@TheNaz01]

+Morlanius but doesn't that mean that the concentration gradient would reach equilibrium just quickly and therefore continue to crystalize?

[@morlanius]

TheNaz The depletion layer around it insulates the rest of the solution from the reaction.

[@Namchild]

How KZbin conversations should be.

[@yukevin560]

it might require crystallization sites to kick off the transformation

[@xelionizer]

I wonder if radiation could initiate crystalization? If so: what energies are we talking about?

[@idontthinkso9537]

crystals on bottom outside, not bottom inside

[@TheNanning]

To me and i'm a total no no at Physics and Chemisty it looks like the cristals form on the triggering crystal just like they are copying the crystal surface and go on throughout the hole petridish. So the surface of the triggering crystal would be a nice thing to investigate , in what way does this influence the outcome of the crystals made.And maybe explaining some of the unconventional outcome. (But maybe thats done already in the past by someone.) Anyway a lovely video!

[@carloscordeiro8592]

is it safe to eat or to put food on top of it? whats the temperature of the frozen final solution?

[@Ben123466789]

Firstly no as it is not sodium chloride which is normal salt you put on food. As for the second question, it is not freezing it is crystallising. The crystallisation makes it get fairly hot from the temperature it was previously at making it ideal for hand warmers. I'd say it reaches about 35-45 degrees Celsius. It gets hotter not colder.

[@carloscordeiro8592]

Ben Sweeney Thanks for your answer mate. You see, I'm a cook and I've been watching videos about this supersaturated liquid and I came up with the idea of using it as a dish wear. Imagine getting to the table a plate with a liquid in with you tap it and it crystallizes then you can actually sear a thin piece of meat or something, and as I thought sodium chloride would have the same effect as salting, so it would be even more amazing. But I guess theres not a chance that could happen with this solution and it wouldn't be safe for eating, even though you're not eating the solution it self, but the food on top of it. Do you have any idea with a similar compound that would work? Thanks for you time anyway. You have been really helpful.

[@supersmashsam]

Actually, sodium acetate is not very toxic. If you compare the LD50 (median lethal dose) of sodium chloride aka table salt (3000 mg/kg) with the value for sodium acetate (3530 mg/kg), you'll notice that sodium acetate is actually a bit less toxic than regular salt. However, as with table salt, I wouldn’t recommend eating a spoonful of sodium acetate, since that would probably cause side effects. I have to admit that LD50 doesn't say everything, but it is usually a good reference for immediate toxicity. The reason behind such a low toxicity is that the acetate part is ubiquitous in nature. It is used in many biochemical processes happening in pretty much every living being. Sodium acetate is actually used in the food industry in the form of sodium diacetate, a mixture of sodium acetate and acetic acid (the acid in vinegar) as a seasoning for salt and vinegar chips. As for an application in molecular gastronomy or whatever you want to call it, I don’t consider myself knowledgeable enough to give you a good idea. However I do think that a nice idea you got there! I wonder if anyone else has tough of cooking with sodium acetate. I think the main drawback is that sodium acetate would be considered as a «chemical» and therefore as «nasty».

[@Ben123466789]

supersmashsam While you can eat it the main problem is it won't taste like normal salt. It will taste very bitter, much like vinegar (Oh and it smells like vinegar too). It is sometimes listed as irritant on safety labels though. Carlos Cordeiro If you want to try it you can find a guide online telling you how to make it out of baking soda and distilled vinegar or you can buy it from an online lab to ensure you get a pure sample. When you make it at home it is slightly brown. The last problem is (if you think it tastes okay) be aware that as the crystals are so small if you put a layer on a plate it will crumble and break very, very easily. (Especially so if you are cutting along the lines of the direction it crystallised, it will just separate. Also you only want a minimal amount on the food because as supersmashsam said it has a similar toxicity as salt. Just use it as you would use salt. You sound like a very creative chef, and the only way you'll be able to find this out for sure is test it yourself, first taste and then your use. Good luck with your experiments. If you're in North America here is somewhere you can order it from www.sciencecompany.com/Sodium-Acetate-Trihydrate-500g-P16276.aspx

[@nickoolay]

if done ideally, 58 celsium

[@effyoo6081]

All of the salt loads were dropped at the edge. Do it again and drop a load in the middle of the liquid. I wanted to see a star crystal.

[@LisaTansey]

Seems like there might be some sociological parallel. It's not optimal for any one person to change state even if there is a good reason do so, but as soon as there enough adventurers - the small committed group, they can start a movement. Prions.

[@andresebastianmoreno]

The solutions in the Petri dishes are not sealed, like your typical sodium acetate handwarners or heat packs. They are also probably not prepared consistently and protected completely from environmental contamination. Likely, the acetate in the semi-solid dish was either not prepared correctly, or has become contaminated with some substance partially inhibiting crystallization. Since the release of the stored heat in the supersaturaturated solution brings it to 130°F (1.3 times the temperature of a healthy cow), the more complete release of heat may finish the process by driving off an excess volatile like water, or may simply impart sufficient kinetic and heat energy to complete the reaction in a contaminated medium.

[@andresebastianmoreno]

Or, like he said. The water is evaporating out of the dishes.

[@douglassoranno473]

Reminds me of Michael Feldman's "What do you know?" Under the category Things you should have learned in school. "What's a petri dish? The answer correctly given but due to the caveat "although the questions have been thoroughly researched, the answers have not. "A dish Laura fixed for Rob." Sorry about that.

[@andresebastianmoreno]

Yeah, except the consensus is that the character's last name was spelled Petrie. But she was enough of a babe, you could have actually referred to Mary Tyler Moore as "that Petrie dish." The crowd goes wild....

[@e.j.w1748]

I would guess there was a bit of contamination or the solution was not homogeneous

[@vinceanthony7046]

the first crystals were bubbles.

[@MarinusMakesStuff]

Would've been great if filmed on a non-white surface :) Haha, oh!!! Spoke too fast, I only saw the beginning part and was already criticizing!

[@PatriotsPulse]

not gonna lie the sound effects are kinda weird

[@nikolatasevski8015]

1

[@thomasarnett9986]

1:35 His shirt changes. Just want to point it out. Edit: 3:24 His shirt changes back! See for yourself!

[@JonathanSanderson]

Absolutely true - good spot! One of the reasons this film has been sitting on my drive for [mumble mumble] months [mumbleyearsmumble] is that I really struggled to make it work. In the end, accepting that Andy was clearly changing shirt on different days was, I thought, the least bad option. I hope it's not too distracting!

[@edgeeffect]

+Jonathan Sanderson I love the music during the crystallization... can you tell me who/what it is?

[@JonathanSanderson]

+edgeeffect According to the film credits, it's David Aubrun, Electro-Insect.

[@edgeeffect]

Yeah... oops... comment first, read later :( ;) Now I've got to navigate all those awful torrent-indexing sites to work out how to download it.

[@JonathanSanderson]

Hah! Yeah, it used to be up on Jamendo or something, but seems to have disappeared. Sorry.