RogueRose
International Hazard
Posts: 1594
Registered: 16-6-2014
Member Is Offline
|
|
Sodium acetate trihydrate - What is proper temp for "hot ice" to remove excess water from vinegar?
I've made anhydous sodium acetate before but this time I'm interested in using it as a hot pack. I used vinegar and baking soda for the reaction and
then boiled it down. I noticed that when I got about 2/3 boiled away the temp rose above the boiling point of water and there still should have been
a lot of water left in the solution. When I noticed, the temp was about 228F. The tri-hydrate melts at 136F and boils/decomposes at 252F to the
anhydrous state. The thing is that there still should have been a fair amount of water left to be boiled off to get a pure trihydrate but the temp
was already higher than the BP of water.
I poured some into a SS bowl and placed it in ice water bath and after about 2-3 mins I tapped it with a knife and it started crystallizing but there
was a fair amount of liquid in the bowl as well.
The heating packs I have used the acetate always turned pretty hard after 2-3 minutes, meaning it wasn't slushy or have other liquids.
My question is what is going on with the boiling point and why is the water boiling at 212? If I want pure trihydrate should activate the crystals
and then filter with the crystals being the pure product - and then try boiling down the liquid that was filtered and see if it will eventually
concentrate enough to make crystals as well - then repeat?
I did add about an extra .5-.75% vinegar to make sure all the bi-carb had converted and AA has a BP around 244 (which is the highest point I finally
got to)
Finally, I've looked all over and haven't found many ideas on how to activate the nucleation when it is being used as a sealed heating pack. The
commercial ones have a little "snap disc" but I don't think those are publicly available. I heard someone recommend a spring (methodology not
explained) which got me to thinking about those metal spring paper clips (they make REALLY small ones now) but IDK if that would work. Have any of
you worked with something like this or heard of something? I thought putting something like this paperclip inside and then squeezing it and allowing
it to snap shut may be a potential solution. Interested to hear what others thinks as to whether this would work or better optinos.
|
|
|
Texium
Administrator
Posts: 4583
Registered: 11-1-2014
Location: Salt Lake City
Member Is Online
Mood: PhD candidate!
|
|
Read up on boiling point elevation and melting point depression. Salts dissolved in water will cause the water to boil at a higher temperature as well
as freeze at a lower temperature.
|
|
|
Texium
|
Thread Moved
10-2-2017 at 12:40 |
RogueRose
International Hazard
Posts: 1594
Registered: 16-6-2014
Member Is Offline
|
|
After looking at more videos on how others make this stuff, none of them state a temp that should be reached to remove the water - some say to go by
color.
Well I ran the process to 242 when I noticed a crystal layer forming on the surface. I poured this into a jar to cool and something unexpected
happened. In the videos the crystals form a white opaque substance when nucleation is activated. In my case, the liquid cooled slowly and slowly
solidified to a moderately clear form with the top layer much less transparent like crushed foggy tempered glass. As I chipped away at the top layers
these "crystals" came out and there was what resembled ice "slush" underneath with a small amount of liquid remaining. As I chipped away with an ice
pick this liquid crystallized and everything looked like the foggy crushed tempered glass though I didn't notice any heat generation in this process.
I found that it was EXTREMELY difficult to chip away at these crystals - it was like plastic ice - the toughness of plastic but hardness of ice.
I finally ended up heating the remaining acetate in the microwave which turned some of it into semi-liquid and could scrape it out with less effort
(though still significant). When it cooled it took on the same appearance.
I'm now wondering what the heating packs contain as I don't think they are 100% sodium acetate as the color and texture are nothing the same. I think
there might be water or maybe alcohol mixed with the acetate so I will try a few combinations to see what works the best for this application. I
still need to figure out what device I can use to initiate the nucleation and wonder if the spring paperclip would work.
|
|
|
JJay
International Hazard
Posts: 3440
Registered: 15-10-2015
Member Is Offline
|
|
According to Doug of Doug's lab, 150 C is a good temperature for dehydrating sodium acetate: https://www.youtube.com/watch?v=tilSHVPiVCQ
It's much easier to simply buy food grade sodium acetate dihydrate and dehydrate it than it is to make it at home in large quantities, but it's also
pretty easy to make at home if you want to try it. Anhydrous sodium acetate likes to stick to glass, so it's a good idea to stir occasionally when
preparing it. Make sure have plenty of empty space in the container you use to dehydrate it (and be careful of course) because partially dehydrated
sodium acetate tends to form mini volcanoes of hot-ice lava that you don't want to clean out of the oven, you certainly don't want a mini-eruption
spewing onto your skin when you stir it.
While food grade sodium acetate is nontoxic, in order to avoid home chemistry hazards such as poisoning, smells, damage to the oven, getting grounded,
divorce etc., it is generally advised to refrain from doing chemistry experiments in your kitchen oven. You can get a small toaster oven quite
inexpensively at Walmart, thrift stores etc., and it can be hosed out more easily than your typical kitchen oven. They also make ovens for lab use.
[Edited on 12-2-2017 by JJay]
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
