Zinc
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purifying NaNO3
I am preparing about 500-600 grams of NaNO3 from NH4NO3 and NaHCO3. When the process is done I wil probably have 90-95 percent NaNO3. What would be
the easiest and best way to purify NaNO3 to at least 98%?
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Xenoid
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| Quote: | Originally posted by Zinc
What would be the easiest and best way to purify NaNO3 to at least 98%? |
Recrystallisation, what else!
Solubility of NaNO3 is about 170g/100g water at 100 oC. and only about 75g/100g water at 0 oC. Just concentrate the solution and harvest the crystals
after cooling in the fridge. Repeat two or three times. The final solution will contain all the impurities.
Regards, Xenoid
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Zinc
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Approximately how much sodium nitrate would I loose?
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Xenoid
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Well, simple maths;
In theory;
If you started with a saturated solution of say 170g at 100 oC, after the first crystallisation you would have 170g - 75g = 95g of crystals or 56%, if
you reconcentrate the solution ( containing 75g) by boiling until it is again saturated and recrystallising again you wil get another 42g of crystals
(56%). If you do this a third time you will get another 18.5g of crystals. Thus 95 + 42 + 18.5 = 155.5g crystals, this is 155.5/170 = .91 or 91%
recovery.
If your initial impurity levels are low you could even do this a fourth time, for a higher recovery, but the rule of diminishing returns starts to set
in and it is hardly worth trying to recover a few grams. In addition you would be defeating the purpose of the exercise, which is to concentrate the
impurities in the remaining solution!
Edit: I suppose I should mention that all the above is only one purification step, I would imagine it would get you to 98% at least. To get to really
high levels of purity you would repeat the crystallisation(s) with the previously recovered crystals. Each time a substance is recrystallised it will
become purer, the contaminants remain in the solution as they never reach saturation level, being only present in low concentrations.
Regards, Xenoid
[Edited on 15-10-2007 by Xenoid]
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chloric1
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If you have a slight excess of baking soda, some could drop out during the initial concentration step. But, since you would be heating above 50C you
will get carbonate or sesquicarbonate. In any case if solid drops out while boiling just discard it as your nitrate will be coming out at cold
temperatures. The properties of sodium nitrate remind me so much of sodium chlorate its scary.
Fellow molecular manipulator
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woelen
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You could do the 3-step purification, as xenoid described, two times, giving a yield of appr. 80%.
With this kind of things, I also always keep the remaining material, of course in a separate container. This raw and impure stuff can be used for
crude pyrotechnics experiments, or just for fun (in my case, impressing my kids with nice flashes and flames). The raw material is perfectly suitable
for that purpose  .
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