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1145climber

Cheap NaOH (from NaHCO3)

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1145climber    10

I was wondering if the following set of reactions would be a cheap way to obtain sodium hydroxide or sodium hydroxide solution... If it would work, then I could use my nearly endless supply of cheap sodium bicarbonate (baking soda) to make NaOH, which is a little harder/more expensive to obtain

 

2NaHCO3 → Na2CO3 + H2O + CO2 (at 200° C)

Na2CO3 → Na2O + CO2

Na2O + H2O → 2 NaOH

 

Would this work? Why or why not? I'm only in honors chem, so I don't fully understand what's required to make a reaction happen or not, but this seems plausible... and in addition, I found mention of it on wikipedia at the below links:

http://en.wikipedia.org/wiki/Sodium_bicarbonate#Thermal_decomposition

http://en.wikipedia.org/wiki/Sodium_oxide

 

Any comments?

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woelen    18

The first step of NaHCO3 being converted to Na2CO3, CO2 and H2O is easy. the second step is amazingly difficult and not of any practical use. In order to decompose Na2CO3 to Na2O and CO2 you'll need temperatures of 1000 C or even more, not something you easily achieve at home. Even with a propane torch, directly blowing on the Na2CO3 at full blast you will not even come near the required temperature.

 

No, this is not a decent way to make NaOH.

 

One way to make NaOH could be to use CaO or Ca(OH)2 with Na2CO3. When both are dissolved, then CaCO3 precipitates and NaOH remains in solution. This method was known a long time ago already. Making CaO can be done by strongly heating CaCO3 (plain chalk). CaCO3 decomposes more easily than Na2CO3, although that still requires quite some heat.

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soultech    10

I thought calcium sulphate, was plain chalk Ca2SO4 I think your refering to Lime. Perhap you could use by products from steelworks Blast furnaces to make caustic soda that way.

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YT2095    591
I thought calcium sulphate, was plain chalk Ca2SO4 I think your refering to Lime. Perhap you could use by products from steelworks Blast furnaces to make caustic soda that way.

 

no one mentioned Calcium sulphate other than you?

and also, there no `2` is CaSO4 calcium sulphate.

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1145climber    10
The first step of NaHCO3 being converted to Na2CO3, CO2 and H2O is easy. the second step is amazingly difficult and not of any practical use. In order to decompose Na2CO3 to Na2O and CO2 you'll need temperatures of 1000 C or even more, not something you easily achieve at home. Even with a propane torch, directly blowing on the Na2CO3 at full blast you will not even come near the required temperature.

 

No, this is not a decent way to make NaOH.

 

One way to make NaOH could be to use CaO or Ca(OH)2 with Na2CO3. When both are dissolved, then CaCO3 precipitates and NaOH remains in solution. This method was known a long time ago already. Making CaO can be done by strongly heating CaCO3 (plain chalk). CaCO3 decomposes more easily than Na2CO3, although that still requires quite some heat.

 

 

sweet, thanks so much...

 

out of curiosity, at what temperature does the complex decomposition of CaCO3 occur?

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1145climber    10

so there's not really a practical way of decomposing large batches of CaCO3 into CaO, is there? my oven doesn't go up to 825°C...

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John Cuthber    3237

Lime kilns have been practical since at least Roman times. Not easy to set up in the kitchen.

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woelen    18

You could use charcoal, with a blast furnace. Inside this, you take a metal can (e.g. from food), with the chalk inside. After a few hours at glowing hot fire, it will have decomposed, but it indeed is a cumbersome thing to do at home.

 

The problem is that many industrial large scale processes cannot easily be scaled down to a home situation.

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BlackPaw    10

Explain a bit the process by which Ca(OH)2 is created from dissolving CaO in water.

 

1. I dissolved CaO in H2O - and i got a solution which i think it is Ca(OH)2 (a milky substance)

 

2. Then i heated NaHCO3 up to 200 C. (and i think i got Na2CO3 + H2O + CO2)

 

3. The i mixed the Ca(OH)2 with the Na2CO3 and i got nothing.

 

By the way how would you know if heated enough the NaHCO3 to get Na2CO3 (how does it looks like)?

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Kelaniz    10

I started doing this myself after getting sick of price increases on NaOH. Not to mention dealing with paranoid shippers charging outrageously high hazmat fees.

 

Anyway, when NaHCO3 gets to the proper temperature, it'll literally bubble (especially if you stir it). It looks like air bubbling up through wet sand at the beach. When it stops bubbling, it's done. Na2CO3 looks a little more grayish than NaHCO3, and is a little bit more free-flowing.

 

As for the Ca(OH)2, you can still easily that at any grocery store. I buy MrsWAGES pickling lime from the canning section. It's a big, green, 16oz HDPE canister an costs around $4 where I live. There are a few brands that have additives, but the one above is 100% food-grade hydrated lime. I see it everywhere. Guess that means nobody's figured out how to make an illegal substance with it yet. :/

 

Kel

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ochoco    10

Not concerned about making caustic, but am concerned about decomposition of Na2CO3 to CO2(g) and Na2O(s) in a high temperature operation in our plant. I understand that decomposition can begin at 400 C. Fusion occurs at 854 C, with a corresponding increase in decomp pressure (CO2 gas). What I'm interested in is: What are the decomposition pressures within the range of 400 C to 880 C, before fusion occurs?

 

thanks.

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ajkoer    1

Hi, came across an old (over a century) process by Lowig described as an easy contact like reaction method in which to prepare NaOH.

 

Heat an excess of Fe2O3 and Na2CO3 to red heat. Dissolve the mass in warm water to recover NaOH. The author noted that the Fe2O3 was regenerated.

 

My attempt at the chemistry: Red Heat

Na2CO3 + Fe2O3 + O2 = Fe3O4 + FeCO3 + Na2O

 

Note, the high temperature converts some of the Fe2O3 to Fe3O4 and, in addition, the FeCO3 decomposes and regenerates the iron oxide:

4 FeCO3 + O2 = 2 Fe2O3 + 4 CO2

 

And finally:

Na2O + H20 = 2 NaOH

 

Caution, the reaction may be thermite like in nature (hence "easy"?).

 

Reference is The principles of chemistry – Dmitry Ivanovich Mendeleyev, page 520. a free online Google Book. Link:

http://books.google....r&output=reader

Edited by ajkoer

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zoteman94    0

Can't you do electrolysis of it with carbon (or anything inert) as an electrode?

So... Sodium goes to cathode and reacts with water to make NaOH and H2 (be careful of not igniting it if you're using a lot of current, do it outside or with fume-hood), and at anode if I'm not wrong HCO3 reacts with water to make H2CO3+OH, H2CO3 decomposes to H2O and CO2 and OH radicals react to make water and oxygen.

So it would be an easy way, the part I'm not totally sure is if HCO3 radical reacts with water to do the above reaction or does something different (like reacting with more HCO3 to make H2C2O6, and that's a peroxide and is probably unstable, or if it makes H2 and CO2) Anyway you get some NaOH...

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John Cuthber    3237

couldnt you just by it?

Yes, I could, but I'm saving my money for a grammar and spelling checker.

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skwiff    4

Yes, I could, but I'm saving my money for a grammar and spelling checker.

 

 

its about £1.85-2 in wilkinsons not really expensive, in fact you would spend more trying to make it!

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ajkoer    1

Per Wikipedia (link below), the following reaction occurs at only 500C and may provide a more accessible way for some to make CaO from CaCO3 for use in the preparation of NaOH:

 

4 H2 + CaCO3 --> CH4 + CaO + 2 H2O

 

That is, heat Calcium carbonate to 500C in an atmosphere of hydrogen.

 

Note, in the same Wikipedia article, the cited temperature decomposition of CaCO3 is 1,500C!!!

 

Caco3 --> CO2 + CaO

 

One reason given on the web for the wide range in temperature ranges for the decomposition of CaCO3 is that there is a significant difference between the "onset" temperature and the "practical" temperature where a significant yield can be obtained.

 

http://en.wikipedia.org/wiki/Abiogenic_petroleum_origin

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ajkoer    1

Per Wikipedia (link below), the following reaction occurs at only 500C and may provide a more accessible way for some to make CaO from CaCO3 for use in the preparation of NaOH:

 

4 H2 + CaCO3 --> CH4 + CaO + 2 H2O

 

That is, heat Calcium carbonate to 500C in an atmosphere of hydrogen.

 

Note, in the same Wikipedia article, the cited temperature decomposition of CaCO3 is 1,500C!!!

 

Caco3 --> CO2 + CaO

 

One reason given on the web for the wide range in temperature ranges for the decomposition of CaCO3 is that there is a significant difference between the "onset" temperature and the "practical" temperature where a significant yield can be obtained.

 

http://en.wikipedia....etroleum_origin

 

An interesting idea is to replace CaCO3 with Na2CO3, and the reaction directly producing Na2O:

 

4 H2 + Na2CO3 --> CH4 + Na2O + 2 H2O

 

The reaction temperature is also possibly in the range of 500C as well.

 

As a word of caution, the auto-ignition temperature for H2 is varyingly reported as between 500C to 585C (other values 536C, 560C and 565.5C) with a heated glass vessel yielding the lower value, jet streams and heated wire somewhat higher. Also, the lower flammability level for H2 is unusually low at 4% (so 4 parts of H2 in 96 parts of air may auto-ignite at around 500C depending on the nature of the heat source) and the upper flammability limit is 75. The bottom line, the proximity of the reaction temperature to H2 auto-ignition threshold and the wide range in H2 flammability limits are dangers to be addressed in attempting this experiment.

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skwiff    4

do electrolysis of metal and NaCl, the sample will not be the most pure, but you can recrystalize it.

 

ionic equation (using copper as the metal)

2Na+ + 2Cl- + Cu2+ + 2H+ + 2OH --> CuCl + NaOH + H2

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pippo    12

Wow- so much work/expense just to make sodium hydroxide. Amazing. Its the bleach of the chemical industry.

 

(also, CaSO4- another name is plaster of paris, I believe...)

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