kt5000
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Making sodium acetate, odd yellow liquid and black liquid
I have been tinkering a bit seeing what kind of substances I can make with household chemicals. Sodium acetate seemed like a good place to start.. I
mixed sodium bicarbonate and vinegar (4% acetic acid) until all the sodium bicarbonate dissolved. I put it in a boiling flask and raised it to about
125C.
I ended up with a white crystalline substance which I expected and two liquids I did not.. A yellow liquid formed and floated to the top when
stirred. The white crystals would not dissolve in that yellow liquid, so I assume the yellow stuff contained no water.
The second liquid formed at the bottom of the boiling flask where the heat was higher. The white crystals actually seemed to melt into this liquid.
I guess the yellow liquid may be impurities (sulfur something?). The black liquid has me really confused. Looking at wikipedia, anhydrous sodium
bicarbonate melts at 324C. I really don't think it got that hot. Would liquid sodium acetate be black?
Any insight is greatly appreciated 
[Edited on 28-3-2013 by kt5000]
I added the photo below showing the yellow stuff on the white crystals (left) and the silvery stuff that was the black liquid (right).
[Edited on 28-3-2013 by kt5000]
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IanCaio
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I'm not sure about the yellow liquid, but I believe this black liquid may be a result of some decomposition of sugars in the vinegar.
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kt5000
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Wishing I took a photo before cleaning it all up. Worth noting that the mysterious black liquid turned into a silvery solid substance, rather
quickly, when heat was removed.
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Hockeydemon
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Mind you I'm just speculating.. However I believe you just decomposed the trihydrate. You would not have any sulfur in the mixture this isn't
possible. You can't add sulfur (S) to a molecule without sulfur being present CH3COOH + NaHCO3 → CH3COONa + H2O + CO2 doesn't contain (S). I'm
not sure you can get the solution to be anhydrous using baking soda & household vinegar, but I really have no basis for this assertion other than
I couldn't find any easy way via google to make anhydrous sodium acetate.
Did you boil the solution until no liquid remained? Or did you boil the solution until a crystal film developed on the surface, and then remove it
from heat allowing it to dry on it's own?
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Endimion17
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You're working with vinegar. What did you expect to happen, a stoichiometric, neat reaction?
That's a bunch of organic gunk inside that gets worse with increasing concentration of acetate. It's a bunch of condensation reactions impossible to
write all down.
You might succeed in removing most of it by boiling the aqueous solution with fresh activated charcoal, and then filtering and
recrystalizing.
If you want to make a chemical compound, don't use things like vinegar. There's 80% acetic acid available, which is reasonably pure. Vinegar is for
food and household cleaning... and for kids making experiments with making CO2 in elementary school.
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Imakethings
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One thing that nobody seems to have asked yet, what kind of vinegar did you use?
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Hockeydemon
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He said 4% acetic acid.. Unless you're referring to brand isn't this to be assumed as household vinegar?
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Imakethings
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Quote: Originally posted by kt5000  | | I have been tinkering a bit seeing what kind of substances I can make with household chemicals. Sodium acetate seemed like a good place to start.. I
mixed sodium bicarbonate and vinegar (4% acetic acid) until all the sodium bicarbonate dissolved. I put it in a
boiling flask and raised it to about 125C. |
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Hockeydemon
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You quoting him just puzzled me until I stopped being an idiot and realized you're referring to the plethora of different vinegar types ha. I'd still
assume white vinegar though.. I would only think to specify the vinegar type if it was something other than white vinegar, but this could just be
ignorant on my part.
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kt5000
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White distilled vinegar.. Yeah.
As for the trihydrate --> anhydrous transition, the wikipedia page below says that the trihydrate decomposes at 122C. I assumed that meant it
would split into anhydrous and H2O molecules. Might it have decomposed to something else?
http://en.wikipedia.org/wiki/Sodium_acetate
Thanks for all the feedback
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kt5000
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The yellow stuff boils at the top of the sodium acetate crystals and doesn't seem to dissolve them. Might I just dump off the yellow liquid at that
point, cool the flask, add some distilled water to dissolve the crystals, and repeat that process to remove any other impurities? Seems possible..
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Hockeydemon
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I would think that the act of turning something anhydrous would be described as dehydration.
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kt5000
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I think I found my answer.. From a Sodium Acetate MSDS sheet: "It emits toxic oxides of carbon and acetic acid when heated to decomposition."
(oops!)
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Hockeydemon
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There are plenty of video's on YouTube with examples of how to make Sodium Acetate.. Nerd Rage's is the most popular that I'm aware of.
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kt5000
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I was looking at some Youtube videos last night, looking for answers. Those seemed to state that you stop heating immediately when sodium acetate
crystals begin forming on the surface.
That would be an aqueous solution of sodium acetate trihydrate, right? I was hoping to go farther and get sodium acetate (anhydrous or trihydrate) in
the solid state.
If I stopped at the aqueous solution, as in the videos, the color of the solution was a dark yellow-brown at that point, suggesting lots of impurity.
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kt5000
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| Quote: Originally posted by Hockeydemon | Mind you I'm just speculating.. However I believe you just decomposed the trihydrate. You would not have any sulfur in the mixture this isn't
possible. You can't add sulfur (S) to a molecule without sulfur being present CH3COOH + NaHCO3 → CH3COONa + H2O + CO2 doesn't contain (S). I'm
not sure you can get the solution to be anhydrous using baking soda & household vinegar, but I really have no basis for this assertion other than
I couldn't find any easy way via google to make anhydrous sodium acetate.
Did you boil the solution until no liquid remained? Or did you boil the solution until a crystal film developed on the surface, and then remove it
from heat allowing it to dry on it's own? |
I attempted to boil it until no liquid remained. I think you're right about the decomposition.
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macckone
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You might try fractional distillation of the vinegar first.
That will give a cleaner product.
Otherwise fractional crystallization of the the product is your best bet.
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kt5000
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Might the trihydrate have decomposed like this?
CH3COONa*3H20 ==> CH3COOH + NaOH + 2H2O
I don't see how that decomposition could yield both acetic acid AND carbon oxides like the MSDS sheet suggested. There's not enough (C) to create
both.
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Dr.Bob
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The MSDS is describing what can happen in a fire type decomposition. Almost every MSDS says that decomp. can provide oxides of carbon, since most
fires exit CO2 and CO. That part of the MSDS is not useful for laboratory work, most often.
You would first want to heat the solution until it is concentrated enough to be saturated with sodium acetate. Then allow it to cool, perhaps pouring
the solution into a fresh beaker if if there is crude on the bottom, or spooning out anything floating on top. One the solution cools, the crystals
formed from water will be the hydrate. Once the crystals are collected and air dried as well as possible, then you might be able to dry them, but
harsh heating will just likely decompose the acetate as shown above. If you heat a solution to dryness, you rarely get clean product, as the
crystallization from a solution helps to purify the material. Plus, the temperature can then go well above 100C which is also not ideal.
So usually people crystallize something to purify it, THEN try to dry it. Trying to do both in one step is often a recipe for failure. Not all
salts can be dried of their water easily. And many reactions don't need anhydrous salts in order to work, so trying to dry all salts can be a waste
if not needed.
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kt5000
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| Quote: Originally posted by Dr.Bob |
So usually people crystallize something to purify it, THEN try to dry it. Trying to do both in one step is often a recipe for failure. Not all
salts can be dried of their water easily. And many reactions don't need anhydrous salts in order to work, so trying to dry all salts can be a waste
if not needed. |
That makes a lot of sense.. I assumed that doing both steps at once would be the simplest approach. This is mostly an exercise to learn about making
salts and what can be done with them, so good fun
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S.C. Wack
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I think they're all mostly sodium acetate. Recrystallize, adjust pH as necessary to what isn't crystallized. It does not become anhydrous at 122C.
125C is nowhere near enough to harm acetate by itself, unless a strong heat source raised the inner surface temp enough. Distilled vinegar should be,
because it isn't. Presto the acetate magically boils down clean.
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kt5000
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Damn vinegar.. I redid the heating, poured off the yellow/brown liquid, and the stuff smells and looks like molasses! Must have been dissolved
sugars from the vinegar..
Might fractionally distilling the vinegar separate the acetic acid from the water/sugar mix? I see acetic acid's boiling point as 118C, so distilling
seems like it would remove the water and leave a acetic acid & sugar mix behind.
I'm spending the $25 for a liter of 99% acetic acid next time
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