HgDinis25 - 16-3-2014 at 08:02
Hi everyone. So yesterday I made some Sodium Nitrite by the usual metal reduction. I placed 100g of Pb in a stainless steel cup and heated to melting
and then added 35g NaNO3 (small stoychiometric excess of lead). I let it on heating for one hour. Once I removed it from heating there was a
significant amount of PbO (orange slug).
Anyway, I started wondering about the decomposition temperature of NaNO2, and the mechanics of this reaction. I based my procedure on the normal Lead
reduction, like this one:
http://www.sciencemadness.org/talk/files.php?pid=293897&...
http://www.sciencemadness.org/talk/files.php?pid=293897&...
http://www.sciencemadness.org/talk/files.php?pid=293897&...
(Posted by AndersHoveland, in http://www.sciencemadness.org/talk/viewthread.php?tid=16941#...)
All the procedures I've consulted call for High temperatues. However, wiki states the decomposition temp. of NaNO2 at 271ºC (http://en.wikipedia.org/wiki/Sodium_nitrite#cite_note-5)
Isn't this a contradiction? I mean, the reduction with molten lead will overpass that temperature easily. Wouldn't the NaNO2 formed, decompose?
This paper (page 21) also states NaNO2 decomposition temp. at about 330ºC:
http://www.nist.gov/data/PDFfiles/jpcrd11.pdf
Any ideas about this? I know that NaNO2 production has been discused way too many times here, but I couldn't find a anything related to this
contradiction.
macckone - 16-3-2014 at 08:15
This is probably one of those situations where decomposition begins at a certain temperature but proceeds slowly until a much higher temperature.
Lead melts at 327C, so 300C is not that much lower than the lead melts. You may get a mix of sodium oxide and sodium nitrite by this method. I would
dissolve a little bit in water and see what the PH is. Keeping in mind that exposing sodium oxide to air will result in sodium carbonate VERY
quickly.
Zyklon-A - 16-3-2014 at 09:01
http://www.sciencemadness.org/talk/viewthread.php?tid=29163#...
AJKOER - 17-3-2014 at 10:24
For those who feel more comfortable working with aqueous Pb, you may wish to try this path suggested in an old journal, "Journal of the Society of
Chemical Industry", Volume 27, based on commercial processes with some very insightful commentary on actual processes (see pages 484 to 485, link
provided below in a prior SM thread). For example, an interesting mention of an aqueous method. To quote:
"The heating of a concentrated solution of lead nitrate with finely divided lead leads to the formation of insoluble basic lead nitrite, which
furnishes sodium nitrite by double decomposition with sodium carbonate. This reaction is, however, only of theoretical interest. "
For a source of the "finely divided lead" try the thermal decomposition of Lead oxalate, said to proceed as follows:
3 PbC2O4 --Heat--> 2 PbO + Pb + 4 CO2 + 2 CO
You maybe able to improve yield of Lead powder by heating the Lead oxalate in a vertical tube reducing O2 exposure and venting the exit gas CO over
hot PbO.
Also, for those who believe heating KNO3 is a good path to KNO2:
"Thermal decomposition.—The alkali nitrates when heated above their fusion point evolve oxygen and furnish nitrites, but this reaction is, of no
practical importance owing to the simultaneous occurrence of a further decomposition to oxide. "
See discussion and references at http://www.sciencemadness.org/talk/viewthread.php?tid=29163#...
HgDinis25 - 17-3-2014 at 12:07
I've looked into this a little bit further and I believe macckone is right. Another run at this (not enough time for a good hield, just to test the
pH) yelded a quite alkaline soluton. Although Sodium Nitrite is a little bit alkaline, the solution was to alkaline, probably because of the
conversion of Sodium Oxide to Sodium Hydroxide. Whatsoever, the lead reduction is still a good method to produce Nitrite, the product will siply be
contaminated. A few sources call for the use of Methanol as the extractor solvent, probably to minimize Nitrite oxidation and other impurities going
into solution. Other sources also state the purification using sodium sulfate to remove any soluble lead salts that may have formed (in tiny
quantities).