guy - 21-4-2004 at 21:06
Can this reaction produce NaOH?
Na2CO3 + Ca(OH)2 -> NaOH + CaCO3
I tried it and it produced insoluble CaCO3 but I don't know if there is NaOH.
t_Pyro - 21-4-2004 at 23:13
If you got a ppt of CaCO<sub>3</sub>, then there has to be some NaOH. However, it won't be too pure.
I am a fish - 22-4-2004 at 00:22
Up until the 1940's, this reaction was used industrially to convert sodium carbonate into sodium hydroxide. After the CaCO3 was filtered out, it
was heated, to produce CaO, which was then hydrated to produce the next batch of Ca(OH)2.
It is possible (given pure reagents) to produce pure NaOH. However you would need measure out the reagents precisely in order to prevent an excess of
one from contaminating the product. Given that both are hygroscopic, this wouldn't be easy.
vulture - 22-4-2004 at 07:52
Ca(OH)2 isn't exactly hygroscopic, but it absorbs CO2 from the air.
This can be used in your advantage:
Use an excess of Ca(OH)2 to ensure complete conversion of the Na2CO3.
After the reaction finished, bubble air through your solution for some time, which converts the Ca(OH)2 to insoluble CaCO3.
I am a fish - 22-4-2004 at 08:56
Yes, but the following will also happen:
2NaOH + CO2 --> Na2CO3 + H2O
Bubbling CO2 through the mixture will simply get you back to where you started.
[Edited on 22-4-2004 by I am a fish]
Marvin - 22-4-2004 at 10:04
To get a reasonable conversion, the usual method is to add the slaked lime slurry (calcium hydroxide isnt that soluable either) in large excess to the
carbonate solution, and boil out of contact with the air for some time. The sodium hydroxide is then strained and concentrated, sodium carbonate
being crystalised first.
Potassium carbonate gives up its CO2 even less readily, and several boilings with fresh portions of slaked lime are usually required.
[Edited on 22-4-2004 by Marvin]
rikkitikkitavi - 22-4-2004 at 10:41
I would say:
use an excess of Ca(OH)2 , mixed with Na2CO3. CaCO3 preciptates and drives the reaction almost to full conversion
Then solubility of Ca(OH)2 in f e x 1 M NaOH is of course very low, we are talking mmoles per liter . So the NaOH solution will be pure when filtered
(which might be difficult, since the CaCO3 probably preciptates as very fine particles.
/rickard