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Author: Subject: Preparation of ionic nitrites
RU_KLO
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[*] posted on 27-5-2024 at 06:46


Im trying to make NaNO2 for first time.

I choose NO2+NO bubbling in NaOH.

So I made a 4M NaOH solution (100 ml), in which a mix of NO2 - NO gas was bubbled.
NO2-NO gas was made from copper + 7M (aprox) HNO3 dripping (100ml). The dripping was adjusted, as so the inner color of the reaction flask. Mild - almost transparent - red brown color was tried. (i.e. one drop every 1-2 seconds).

All this was in a negative pressure setup (a cheap 12V water/air pump was used).

It took a while - maybe 2 hours and copper needed to be replenished.

After this, ph was meassured, it was highly alkaline (NaOH excess).
(on a test, after adding some acid to a sample, till acidic, there were some red fumes from this solution. So probably some NaNO2 was in solution)
Next HNO3 was added to neutralize the NaOH. Ph was taken to 6-7.

Next a solution of Na2SO3 (unknown molarity) was added.
The idea was to transform the NaNO3 (from the neutralization) to NaNO2.
(some sulfur was in the Na2SO3 and some sulfur was precipitated - or I think it was

At the end was left with 250 ml which was boilled down till 50-40ml which crashed "a lot" of salt. (check picture)

Now, I need to somehow purify and get NaNO2.
Whats in the "soup":
1) 2 NaOH + NO2 + NO → 2 NaNO2 + H2O
2) NaOH + HNO3 = NaNO3 + H2O
3) Na2SO3 + NaNO3 = NaNO2 + Na2SO4 (maybe?) is this correct? (or maybe some sulfur is made?

what are my best route?

1) add more Na2SO3 to convert any NaNO3 left. (will an excess of Na2SO3 hurt?

regarding purification by recristallization, what the best route, because Im not having good results - maybe bad procedure.

NaNO2
Solubility in water
71.4 g/100 mL (0 °C)
84.8 g/100 mL (25 °C)
160 g/100 mL (100 °C)

Na2SO4
Solubility in water
Heptahydrate:
19.5 g/100 ml (0 °C)
44 g/100 ml (20 °C)

Na2SO3
Solubility in water
27.0 g/100 mL water (20 °C).

If I add little water, heat to dissolve everything, and let it crash out, will get the same result.

So how is it done?
a) add boiling water instead of cold till everything dissolves?
b) add cold water till everything is dissolves, remove X% of it (lets say 30%) take it to freezer or ice (0ºC) filter. then remove the last portion till some cristals are seen?
c) filter what you got, dry, weight and from there, add enough ice cold water to dissolve the NaNO2 but not to the Na2SO4
Example: 10grs (dry mixed salt) was obtained,
(solubility per ml NaNO2 = 0.71gr (0ºC); Na2SO4 (0.195gr (0ºC))
So for NaNO2 is 14 ml of water. and for Na2SO4 is 51.28ml.
So if I add 14ml of H2O 0ºC, NaNO2 will be dissolved and excess of Na2SO4 will not.

Or maybe is simplier o more complicated than this (because of common ion effect)

Any help or step by step procedure for purifying is well received.

As side note, a small sample of this salt was tested with HCl and a lot of red fumes were watched.

and as bonus: If you have Sulfite and nitrate, you could directly made nitrite.... Is this correct?

thanks





nitirte.jpg - 437kB




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[*] posted on 27-5-2024 at 08:11


I dont think mixing Na2SO3 and NaNO3 in sln will reduce to SO4 and NO2. This usually is done in a crucible under high temp(300C) using CaSO3 instead of the Na salt.(for ease of purification)
When you add acid it do make red fumes but that do not mean its NaNO2.

The Na2SO3 react with acid to liberate SO2 gas which probably react with NaNO3 to release NO2 while making Na2SO4.

I did something similar last year, mixing NaNO3 and CaSO3 gave red fumes upon addition of Acid. but after removing by filtration the CaSO3(No CaSO4 as expected), it was only unreacted NaNO3, no red fume upon addition of acid.

What you want to do is, react your Na2SO3 With CaCl2, filter and keep he solid CaSO3. then react this CaSO3 with your NaNO3 under high temperature(300C for 15 minute).
Then you can filter out the CaSO4 and evaporate water to keep the NaNO2.

Also the CaSO3 crystalize as hydrates so more is needed if its not dehydrated and having a slight excess dont hurt things. Most people seem to overlook this part giving bad yield because they dont use enough CaSO3.

[Edited on 27-5-2024 by fx-991ex]

[Edited on 27-5-2024 by fx-991ex]
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[*] posted on 28-5-2024 at 07:27


After "bad" news from fx... and that is possible that I do not have any nitrite, performed the following test.
diferent reagents (used in the procedure) where added to a potassium permangante solution to see if they reduce it.

the nitrite? (prepared solution) and the sodium sulfite reduced it, the rest did not. (check picture)

So as fx said, probably I got no nitrite and the excess sulfite is doing the reduction.

So I will try to take a sample of the nitrite? and add some BaCl2 to precipitate BaSO3 (solubility 0.0011 g/100 mL) This will remove the sulfite and left with nitrite "only" in the solution and check if this new solution reduce the KMnO4.

(note: already tried BaCl2 + Na2SO3 and a fine white precipitate precipitates)


test nitrite.jpg - 233kB




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[*] posted on 2-6-2024 at 14:04


Last experiment was failure.

So i tried the Pb - Nitrate procedure. It seems it worked.

Tested the supernatant, few drops on potassium permanganate in H2SO4, it cleared, so there must be some nitrites.

Currently the Nitrite is drying. Im following Nurd rage permanganate standarization (with Sodium oxalate), so I can follow (previuos in this post) titration of the nitrite/nitrate, so to know how good it was.

attached some pictures.

The sodium nitrite I got is white, not yellow as stated in this post from others.

The PbO I got is creamy white , but pictures show it is yellow...

Are this colors I got correct?

Lead was from UPS batteries, maybe some contaminats are there.




NITRITE.jpg - 135kBPBO.jpg - 123kB




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[*] posted on 3-6-2024 at 13:33


PbO is usually black, red, brown or yellow depending on the oxidation state.
That looks like white lead.... googling 2PbCO3·Pb(OH)2wiki
, heating a sample over a flame it should cause a color change, or react it with an acid to evolve CO2.
Heat it to about 650c and it should turn black if its PbO. Just remember its toxic and will contaminate all your gear




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