Sciencemadness Discussion Board

Sodium BiCarb to Carbonate conversion via Solvay process

RogueRose - 15-2-2016 at 17:07

From reviewing the Solvay process it says that sodium bicarbonate can be heated to decompose to sodium carbonate at fairly low temps (in comparison to other calcination processes).

I have tried this in an oven as the highest temp stated for the calcination is 240C (464F). I am unsure that this was successful even after 5+ hours at 500F in an electric oven. The powder seems of similar consistency as the bicarb after the process.

If bicarb were placed in a steel container/bowl and placed over an open fire where it was guaranteed to reach > 800F, would this harm the end product of carbonate at all? I would suspect that heating the bicarb to this temp would guarantee the conversion to carbonate but I want to make sure there is no problem with heating to a temp of this degree.

When a process like this is undertaken, is there any way to determine when all the bicarb has decomposed to carbonate, or methods to make this process better?

What would be a good way to test the product to verify that it is carbonate and not bicarb?

Etaoin Shrdlu - 15-2-2016 at 17:34

Titrate.

It should be, though.

Detonationology - 15-2-2016 at 17:55

Thermal decomp. of bicarb goes as follows:

2 NaOCOOH --> NaOCOONa + CO2 + H2O

However, carbonate can experience thermal decomp. as follows:

NaOCOONa --> Na2O + CO2

As long as it does not experience excessive heating, the major product should be carbonate.

blogfast25 - 15-2-2016 at 19:15

Quote: Originally posted by Detonationology  

NaOCOONa --> Na2O + CO2

As long as it does not experience excessive heating, the major product should be carbonate.


Trust me, you need seriously high temperatures to decompose Na2CO3.

"Bicar" is used as baking powder because it loses 1 mol CO2/mol bicarbonate fairly quickly at as little as 180 - 200 C.

Oscilllator - 15-2-2016 at 20:03

Guys it's called baking powder for a reason. It decomposes when you put it in baked goods to make them delicious and fluffy :)
RogueRose if you want to check if your NaHCO3 has completely decomposed, simply weigh it before and after, measure the difference and compare it to theory. Detonationology has posted the reaction equation, so that should be easy.

UC235 - 15-2-2016 at 21:53

Quote: Originally posted by Oscilllator  
Guys it's called baking powder for a reason. It decomposes when you put it in baked goods to make them delicious and fluffy :)
RogueRose if you want to check if your NaHCO3 has completely decomposed, simply weigh it before and after, measure the difference and compare it to theory. Detonationology has posted the reaction equation, so that should be easy.


Actually, it's baking soda. It's intended to be used in recipes that contain an acid already like lemon juice, vinegar, or buttermilk. Baking powder is pre-mixed with an acid that forms a storage stable mixture. Typical acids are calcium dihydrogen phosphate, sodium alum, potassium bitartrate, or disodium pyrophosphate.

Compare baker's ammonia which is ammonium carbonate. It decomposes to gasses by itself, and at temperatures low enough to occur in a baked good (which containing water will not get much above 100C).

If you have a cheap pot you can decompose the bicarb on the stovetop, but prepare for a mess. The bottom of the pot will probably also be discolored from the heat. Rapidly evolving water vapor and CO2 fluidize the powder which appears to boil (this also kicks up irritating dust that goes everywhere). The end product is a very fine, loose, and dry powder.

[Edited on 16-2-2016 by UC235]

Herr Haber - 15-2-2016 at 22:09

Make a saturated solution of bicarb. Leave some at the bottom if you need visual proof.
Heat it on your heating plate.
Not googling it to verify, but CO2 bubbles appear around 60c° so far below the boiling point of water.

As the reaction proceeds, the bicarb will dissolve into the carbonate / water solution. and bubbling will stop (unless you go to 100c° !)

Just not sure what the températures are needed as a solid, but as mentioned above, bicarb is used as baking powder and I doubt the ovens are set for températures much higher than 160-200 c°

NedsHead - 15-2-2016 at 23:05

plenty of soap makers do this process on a hotplate or in an oven, I would probably choose to do it on a hotplate so you can see when you have reached the endpoint, here's a video on it https://www.youtube.com/watch?v=HFKP3VvCU_0

AJKOER - 17-2-2016 at 17:46

I just thought of a radical way of turning a solution of NaHCO3 into a mix of Na2CO4 and Na2CO3 with, depending on the duration of the processing, left over NaHCO3.

Just treat the aqueous (and not concentrated) NaHCO3 with N2O (a source generator of hydroxyl radicals) and sunlight allowing any formed CO2 to escape. My take on the radical chemistry:

N2O + hv ---) N2 + .O-

.O- + H2O = .OH + OH-

HCO3- + OH- --) H2O + CO3 (2-)

HCO3- + .OH --) H2O + .CO3- (see, for example, https://books.google.com/books?id=cH3k6988upsC&pg=PA28&a... )

.CO3- + .CO3- --) CO2 + CO4 (2-) (see eq 14.23 on page 277 at https://books.google.com/books?id=efTs8ZqCbYAC&pg=PA277&... )

In words, the N2O in sunlight forms a hydroxyl radical and a hydroxyl anion. The latter can react with the amphoteric bicarbonate anion to produce a carbonate ion. Also, the bicarbonate anion can be converted by a hydroxyl radical into the carbonate radical anion. The latter can disproportionate into CO2 and CO4 (2-) ion.

So, no heating involved, just some laughing gas and sunlight.

[Edit] Note, in place of N2O, one could employ H2O2, however, a possible formation of peroxymonocarbonate ion (HCO4-), see, for example, discussion at http://pubs.acs.org/doi/abs/10.1021/ja9927467?src=recsys&... .

[Edited on 18-2-2016 by AJKOER]

ave369 - 18-2-2016 at 00:10

Use an universal indicator paper strip and check the pH. Bicarbonate of soda is very mildly basic, it turns the paper green. Carbonate is quite basic, it turns the paper deep blue.