Sciencemadness Discussion Board

sodium nitrate from potassium nitrate

ahill - 24-10-2016 at 21:14

I need some sodium nitrate - the only nitrate I have is potassium nitrate.

The only route I can think of, is to make up some nitric acid from the KNO3 - (I've got sulphuric acid), and neutralise it with sodium bicarbonate. I figure that should give me a really good quality product - but making nitric acid is quite a bother - I really like to side step that if I could.

My google-foo is weak today - can anyone suggest a more direct or easier route ?

Sulaiman - 25-10-2016 at 00:47

I can't answer your question
but I am curious what reaction works with NaNO3 that soes not work with KNO3 ?

j_sum1 - 25-10-2016 at 01:25

Some photographic applications are specific to sodium or potassium salts and do not work if substituted. But I don't know specifics.
Similarly, medical applications would be intolerant of substitutions but I doubt ahill is into that.

You might be able to exploit solubility differences between some sodium and potassium salts and use that to drive a conversion. But separation is not going to be clean at all. I would anticipate that it would be more problematic than making nitric acid and I doubt this would open up a practical route.

(by way of example:
Na2Cr2O7 is abut 20 times as soluble in water as K2Cr2O7.
So, adding solutions of sodium dichromate and potassium nitrate at very high concentrations will precipitate some potassium dichromate and leave you with sodium nitrate in solution.
Sounds like an awful mess to me.)

symboom - 25-10-2016 at 01:33

By precipitation of potassium sulfate
Sodium nitrate and sulfate is much more souble than potassium sulfate

Or maybe using sodium hypochlorite disproportionate to sodium.chlorate and chloride than adding potassium nitrate to precipitate potassium chlorate

Sulaiman - 25-10-2016 at 02:14

O.K. ... I should have asked ahill
"what is the specific reaction that you wish to perform that can be performed with NaNO3 yet not with KNO3 ?"
as in most cases either can be used, obviously products will have K instead of Na but does that matter ?

ahill - 25-10-2016 at 05:02

Hey Sulaiman - you are probably right - I probably can use Potassium Nitrate. I am suddenly interested in cultivating blue green algae (to which end I've ordered a spirulina culture from the Americas) .. and the Internet seems to think the growing medium of choice is Zarrouk's, the guts of which is :-

NAHCO3 (Sodium bicarbonate) 16.8g
K2HPO4 (Dipotassium hydrogen phosphate) 0.5g
NaNO3 (Sodium nitrate) 2.5g
K2SO4 (Potassium Sulfate) 1.0g
MgSO4 . 7 H2O (Magnesium sulfate) 0.20g
CaCl2 (calcium chloride) 0.04g
FeSO4 . 7 H2O (Ferrous sulfate) 0.01g
EDTA (ethylene diamino tetracetic acid) 0.08

Aside from EDTA and sodium nitrate, I've got these in the cupboard.

..and as I've got almost no idea what I am doing - I thought I might, at least at very first, try following the instructions.

Dmishin - 25-10-2016 at 05:19

ahill, in solution it is only important what ions are present, it does not matter what solid compound they came from.

I am sure you can use KNO3. This substitution will increase concentration of K+ and decrease Na+, so you may adjust other compounds accordingly (for example, by substituting some K2SO4 with Na2SO4).

Sulaiman - 25-10-2016 at 05:31

Looks to me that the NaNO3 is just for the nitrate ion,
and there is plenty Na from the bicarbonate,
so I think that you can use 3g of your KNO3 instead of 2.5g NaNO3 to maintain NO3 ratio.

yobbo II - 25-10-2016 at 06:31

No need to make the Na nitrate as stated above. But if you insist you could obtain a cold solution of sodium perchorate, add to a concentrated solution of your potassium nitrate untill the white precipitate stops forming. Potassium perchlorate will be precipitating and you will be left with mainly a solution of sodium nitrate. Filter out the k pekchlorate.

Maroboduus - 25-10-2016 at 08:56

Substituting your potassium salts for sodium salts to compensate for the potassium nitrate will still leave you with a fair amount more potassium than you want.
I think you'd get closer to the formula above by precipitating potassium sulphate, as symboom suggested above

And then if you really want to be sure of what you've got take the resulting salt and dissolve in ethanol.

None of the impurities have much solubility in ethanol.

If you have a Soxhlet it would be easy to make up a whole bunch at once, or you could wrap it in filter paper and stick it in a condenser and just reflux ethanol through it to leach the NaNO3 out.

You might also be able to just make more of the impurities crystalize out of the solution you're left with after adding sodium sulphate to potassium nitrate by adding alcohol to it.

[Edited on 25-10-2016 by Maroboduus]

Sulaiman - 25-10-2016 at 10:33

Out of curiosity I had a look at the Wikipedia page for spirulina
the nutrient mix recommender there is

Baking soda- 16 g/L (61 g/US gal)
Potassium nitrate- 2 g/L (7.6 g/US gal)
Sea salt- 1 g/L (3.8 g/US gal)
Potassium phosphate- 0.1 g/L (0.38 g/US gal)
Iron sulphate- 0.0378 g/L (0.143 g/US gal)

since you would have to make enough NaNO3 for all trials, for consistency
assuming that NaNO3 is not easy to acquire and KNO3 is,
you may as well start with what you have / can obtain.

P.S the nutritional information sidebar of the Wikipedia page gives, per 100g dry matter;
Potassium 1363 mg
Sodium 1048 mg

so maybe even more potassium is better ?

[Edited on 25-10-2016 by Sulaiman]

Neuro- - 25-10-2016 at 13:42

Although it doesn't use potassium nitrate, mixing sodium carbonate and calcium nitrate fertilizer, filtering off the calcium carbonate, then evaporating and recrystallizing the sodium nitrate should do the job nicely and easily.

j_sum1 - 25-10-2016 at 14:26

Quote: Originally posted by Neuro-  
Although it doesn't use potassium nitrate, mixing sodium carbonate and calcium nitrate fertilizer, filtering off the calcium carbonate, then evaporating and recrystallizing the sodium nitrate should do the job nicely and easily.

I feel well, "duh". There was the easy solution.

Sniffity - 25-10-2016 at 18:38

Find a sodium salt with an appropriate counter ion with high solubility in water, but whose potassium salt with the same counter ion has low solubility. Then go for a double displacement reaction, which will precipitate the potassium salt and leave sodium nitrate in solution.

Filter, evaporate of the filtered solution to recover sodium nitrate, recrystallize if desired.

Mabus - 31-10-2016 at 11:46

What's wrong with mixing sodium hydroxide and ammonium nitrate? Both should be available in most places (caustic soda and instant cold packs if AN fertilizer is unavailable).