Per - 12-4-2007 at 12:00
I have a solution 1:1 of NaNO2 and NaNO3, now I´m thniking how to separate these two saltes.
Recristalisation wouldn´t work because the solubilities of the saltes by 20°C are nearly the same ( about 800g/L).
Maybe the solubilities of the saltes are different by increasing the temperature but I don´t know how much NaNO2/NaNO3 are in boiling water soluble.
Or maybe it would e the best to oxidice the NaNO2 to NaNO3 to get at least one pure salt.
Have anybody any good ideas?
Magpie - 12-4-2007 at 15:04
Here some speculation. It's not for separation, but to obtain pure NaNO2:
To obtain pure NaNO2 you could use the classical reduction procedure for converting KNO3 to KNO2. This requires high heat and the melting of Pb. I
don't know why it wouldn't work for the Na salts as well as the K salts. There is a thread on this.
[Edited on by Magpie]
Eclectic - 12-4-2007 at 17:11
You can add KCl to crystalize out KNO3, then boil down and filter out NaCl, and recover NaNO2 by cooling.
woelen - 12-4-2007 at 22:29
If you want at least one pure salt, you could add H2O2 in excess to convert the NaNO2 to NaNO3. Boiling down will remove/break down any excess H2O2
and pure NaNO3 is left. But personally, I would prefer a 1 : 1 mix of NaNO2 and NaNO3 over pure NaNO3. Nitrite ion is so interesting.
Is there really a need for purifying the nitrite? With almost all experiments, which require nitrite in aqueous solution, the presence of the nitrate
does no harm. Anyway, I would not do the KCl-trick. It adds chloride to your mix and even if you could remove 90% of it, the end-product in my opinion
would be less interesting than 1 : 1 NaNO2/NaNO3. The presence of chloride in NaNO2, even a few percent is killing for MANY interesting experiment.
Chloride reacts with nitrite in acid to give nitrosylchloride, it also gives rise to complex formation with many metals, strongly affecting the
experimental outcome. On the other hand, nitrate ion is almost inert in aqueous chemistry, only in the most concentrated acids it will be a facile
oxidizer.
garage chemist - 12-4-2007 at 23:46
The best method of separating nitrate/nitrite mix is to make isopropyl nitrite from this via the known method (add slight excess of IPA in regard to
nitrite, cool in ice, add dilute H2SO4 with strong stirring, separate IPN layer).
The nitrate ion will not react in this synthesis (if you dont use HCl as the acid, otherwise there will be formation of chlorine and NOCl via the aqua
regia reaction). Remember to use a bit less than the stochiometric amount of H2SO4, alkyl nitrites really dont like acidic solutions when there is no
more nitrite.
Then hydrolyse the IPN by stirring with NaOH solution (use slight excess of IPN so that no NaOH will be left) and there you have a solution of pure
nitrite. You even get back the IPA if you distill it off.
Separation of NaNO3/NaNO2 can also be done by recrytallization from ethanol, as nitrite is three times more soluble than nitrate in it. But there will
be a lot of losses if a pure product is desired, and multiple recrystallizations would be necessary.
The method via IPN is simply the best procedure for this separation.
Per - 13-4-2007 at 06:30
Thanks,
the IPA method seems to be really interesting also IPN is a really useful chemical (protecting from HCN). So I´m going to provide me any IPA.
But when just a unpure NaNO2 is needed I would prefer the ethanol method to make the salt at least a bit more pure. Hope that it wouldn´t oxidise the
ethanol as it do with Ac2O when I distill the rest of the alcohol off.
Magpie, I tried the Pb method already with NaNO3 and it doesn´t work at all as you mentioned.
Eclectic - 13-4-2007 at 09:15
If what you need is pure NaNO2, then you should recrystallize it from clean water. NaCl will mostly be driven out of solution by saturated
NaNO2/NO3, KNO3 will crystallize upon cooling, KNO2 is extremely soluble and will remain in solution.
I was assuming what was needed was a method to recover NaNO2 from a NaNO3 melt reduction and not waste the left over nitrate.