Cappy
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Sodium carbonate?
Could I make sodium carbonate from carbonic acid (seltzer water) and sodium bicarbonate, or would all of the carbon be removed as carbon dioxide
(leaving me with NaOH)?
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madscientist
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That won't work. However, you can convert sodium bicarbonate into sodium carbonate by heating over flame:
2NaHCO<sub>3</sub> ----> Na<sub>2</sub>CO<sub>3</sub> + H<sub>2</sub>O + CO<sub>2</sub>
I've found that about 30g of sodium bicarbonate less than half an hour of heating on a propane burner to quantitatively convert it into sodium
carbonate.
[Edited on 12-4-2003 by madscientist]
I weep at the sight of flaming acetic anhydride.
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Polverone
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less than 30 minutes?
WAY less than 30 minutes should do just fine! Keep stirring it. When it stops frothing, it's done. This should take just a few minutes for such a
small batch.
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Cappy
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Will this work?
Na2CO3 + H20 --> 2NaOH + CO2 with simple mixing? This is the basis of Pool pH up, right?
Also, are there any visible signs that all the sodium bicarbonate has been converted to sodium carbonate?
[Edited on 4/12/2003 by Cappy]
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Darkfire
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"...When it stops frothing, it's done..."
CTR
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madscientist
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The reaction requires fairly high temperatures, isn't exactly furiously rapid, and there is no frothing involved because of the aforementioned.
I weep at the sight of flaming acetic anhydride.
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Polverone
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No, there is frothing
Did you finish that last post?
I don't know what sort of ill, sickly, propane burner you are using, but when I heat NaHCO3 over mine the mass froths, bubbles, and churns almost
like boiling water, as the fine particles are fluidized by the escaping CO2/H2O vapor. And as long as you stir it to bring fresh portions in contact
with the hot metal (so the bulk of the mass isn't insulated by powder further down) the conversion is over in less than 5 minutes, at least on a
small scale.
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rikkitikkitavi
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bicarbonate decomposes at about 150-200 C, the main reason why you use it in bread , e t c. The name "baking soda" rings a bell?
cappy, the reaction you describe doesnt work.
But if you heat Na2CO3 to about 1000 C
Na2CO3 => Na2O + CO2
and then
Na2O + H2O => 2 NaOH (extremely exothermic)
You might not end up with exactly Na2O, some Na2O2 may formed but all NaOx reacts with water producing sodium hydroxide. Also beware that molten Na2O
is extremely corrosive towards steel, porcelain e t c. You need a basic refractory (like CaO ) to prevent it from simply burn right trhough your
vessel
/rickard
[Edited on 12-4-2003 by rikkitikkitavi]
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Organikum
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Got no frothing. 
after spanking my propane burner for his lousy performance - Polverone will you disclose me and the others what type/brand of burner you use?
Spanking didn´t improve the performance a bit  so to aquire another burner is
considered by me now.
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Polverone
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I don't know the exact name/model. It was acquired at a university sale some years ago. It's a large lab burner, designed to hook up to a
natural gas line, that has been slightly modified to hook up to a propane tank. It's about 2.5 cm in diameter at the top, 2 cm around in the main
body, with a crisscrossing metal grid at the burner top to give a lot of small, hot cones of flame. It makes a pleasant sort of roaring noise when
it's lit. Depending on the pressure of the gas source it's hooked to, it can generate a flame up to about 80 cm high. Of course it's
not very practical/efficient to run it that way. Like other lab burners, it can have the air/gas mixture adjusted by opening/closing a gap near the
bottom of the burner.
I also have around here some sort of torch that was designed to run on natural gas and compressed air. That would be even better! Unfortunately, I
don't have an air compressor handy and I would need to modify this one to connect to a propane tank also.
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Cappy
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| Quote: | Originally posted by Darkfire
"...When it stops frothing, it's done..."
CTR |
Unfortunately, I don't have Polverone's hell hose. I placed the sodium bicarbonate on aluminum foil in an empty pot. I don't know what
temperatures I could get from my electric stove top, but I didn't want to waste lighter to try this. Next time I might try broiling it in the
oven, but I don't have a bunsen burner, yet.
So anyways, you could only barely see water vapor leaving the sodium carbonate. I left it on high for a half hour, but I don't think much changed
to sodium carbonate.
On second thought, maybe I won't broil it in the oven. I just noticed that H2 is given off, not H20!
[Edited on 4/12/2003 by Cappy]
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Marvin
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Do your supermarkets not sell washing soda?
Thats Na2CO3 with about 10 molecules of water. Very easy to dehydrate and almost dirt cheap.
I have the funny feeling Na2O will be mostly gas phase at its formation. Na2O2 shouldnt exist at such a high temperature.
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Polverone
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Marvin:
Check your U2U messages.
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madscientist
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Cappy, H<sub>2</sub> isn't generated by heating sodium bicarbonate, it was a typo.  I edited my above post in order to fix that.
I weep at the sight of flaming acetic anhydride.
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madscientist
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Merck on Na<sub>2</sub>O: "Melts at a dull red heat and begins to dec >400degrees into sodium peroxide and metal."
I weep at the sight of flaming acetic anhydride.
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Marvin
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Hmm, now thats interesting, by which I mean very irritating.
CRC indicates Na2O is stable and sublimes at 1275C, it also indicates that the peroxide Na2O2 melts with decomposition at 460, and boils with
decomposition at 657.
The MSDS at oxford says it sublimes at 1275C, though this was probably lifted from CRC.
Greenwood an Earnshaw however only states that generally for all alkali monoxides, 'The compounds are fairly stable towards heat, and thermal
decomposition is not extensive below 500C. About peroxides, 'In the absense of oxygen or oxidisable substances, the peroxides (except for
lithium) are stable towards thermal decomposition up to quite high temperatures eg Na2O2, around 675C, Cs2O2 590C. Lithium peroxide decomposes to the
monoxide at 195C." K and higher produce superoxides with oxygen, which is mainly why thats there I think.
Webelements for Na2O gives a melting point of 1132, and a boiling point of 'decomposes at 1950'.
The NIST webbook avoids the issue alltogether by not giving melting points.
Mellor says mainly about this subject that pure Na2O cant be made by burning sodium in air, that the product is contaminated by higher oxides and
sodium. Molten sodium peroxide attacks platinum, but can be melted in gold silver or nickel crucibles and can be made by the action of oxygen on
sodium monoxide at 300C.
J.D. Lee, doesnt say a lot at all, but that sodium peroxide can be converted to superoxide with 300 atmosphers of oxygen at 450C.
Sharpe simply says that the peroxide of sodium is the major product when sodium is heated in excess air.
Cotton and wilkinson is laughably short in its alkali metal section and mainly concerned with complexes.
That about exhausts my information on the subject. Its not conclusive but the Merk info seems to be the furthest fetched from everything else by
quite a long way in terms of very high temperatures. Maybe the disproprotionation is only very limited, and the peroxide is destroyed on use of much
higher temperatures.
Ive read somewhere that reduction of sodium carbonate is easier with powdered carbon, forming sodium oxide and carbon monoxide, if the sodium oxide
decomposed during these conditions it would be a good way to make sodium metal, virtually all the references on sodium peroxide say how reactive an
oxidising agent it is, frequently explosive, since people at the time were using sodium chloride and iron, I think this doesnt work for the metal as
youd expect if Na2O decomposed to the metal and peroxide. Might be easier to obtain solid Na2O though.
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rstar
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To make Na2CO3.
Simply add NaHCO3 to hot (near 85C, but not boiling) water.
Add slowly the NaHCO3 and it will decompose to Na2CO3, H2O and bubbles of CO2. You can see that the bicarbonate is decomposing or not by checking the
production of CO2 bubbles.
Boil off all the water and you will be left with solid whit Na2CO3
"A tidy laboratory means a lazy chemist "
- Jöns Jacob Berzelius
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ScienceSquirrel
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Just put it in a pyrex dish and bake it in the oven at 300 C, the powder seems to boil as the carbon dioxide and water vapour pour off.
If you use food or pharmacopia grade sodium bicarbonate then I reckon your product is a lot better than 99+% pure.
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blogfast25
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Quote: Originally posted by Polverone  | | I don't know the exact name/model. It was acquired at a university sale some years ago. It's a large lab burner, designed to hook up to a natural gas
line, that has been slightly modified to hook up to a propane tank. It's about 2.5 cm in diameter at the top, 2 cm around in the main body, with a
crisscrossing metal grid at the burner top to give a lot of small, hot cones of flame. It makes a pleasant sort of roaring noise when it's lit.
Depending on the pressure of the gas source it's hooked to, it can generate a flame up to about 80 cm high. |
That's a Meker burner: much more heat flux than a single Bunsen. That would make it froth alright.
I've never seen it froth either but it's true that it doesn't take long to quantitatively decompose at food techn. temperatures, 150 to 200 C... Nice
way of making some clean, anh. Na2CO3 if your bicarbonate is clean: food grades often contain rice powder anti caking agent and tend to brown on
heating.
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ScienceSquirrel
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I do it using a beaker and a heating mantle.
Add the weighed sodium carbonate to the beaker, heat until it stops frothing, cool and weigh again. Yield is always about 99 to 98% of theory.
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White Yeti
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I tried making it in a regular fire. I took tons of fallen tree limbs (from hurricane Irene) and built a fire. I left mine for 45mins and it wasn't
enough. I was working with large quantities ~270g and my yield was about 80%. I wish I had the opportunity to mix it...
"Ja, Kalzium, das ist alles!" -Otto Loewi
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Endimion17
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That's mainly dirty potassium carbonate you've got. Few recrystalizations might do the trick.
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White Yeti
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I wasn't collecting wood ashes, if that was what my post led you to believe. I thought that since most of the thread dealt with the decomposition of
sodium bicarbonate, I wouldn't have to specify which chemical I was decomposing.
Apologies.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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ldanielrosa
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@White Yeti, are you doing this for the experiment or for the product? A standard cooking oven gets plenty hot to convert bicarb into sodium
carbonate.
I use a glass pan with loose fitting lid to keep oven debris out, and ramp up the temperature from warm to full broil over about 4 hours. The yield
is near ideal. This is actually one step from NaK tartrate synthesis.
If you just need an excuse to light a bonfire I understand.
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White Yeti
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| Quote: Originally posted by ldanielrosa | @White Yeti, are you doing this for the experiment or for the product? A standard cooking oven gets plenty hot to convert bicarb into sodium
carbonate.
I use a glass pan with loose fitting lid to keep oven debris out, and ramp up the temperature from warm to full broil over about 4 hours. The yield
is near ideal. This is actually one step from NaK tartrate synthesis.
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I've tried to make some sodium carbonate via an electric cook top (that gets up to about 400C), but I've failed quite a few times, I'm not quite sure
why. My yields were awful, so I decided to work with larger quantities and higher temperatures. I just so happen to have lots of wood and a nice
rocket stove that can heat steel up to a faint red glow (~800C).
I didn't use my oven because its energy consumption is phenomenal. I'd rather just use a fire because it's just more convenient believe it or not.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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