Instructables


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   Procedures for purifying chemicals are being invented and re-invented all the time. Purification depends very much on the chemicals that are considered the “contamination”, and their properties compare to the chemical you are trying to purify. The mixture that you are trying to purify will dictate how easy the purification process will be. There are no– "one fit all solutions", and indeed, some chemicals are so hard to purify that the finished purified product will fetch amazing prices.

   Recrystallization is a physical method targeting the purification of compounds. This procedure involves dissolving a compound in a hot solvent to form the saturated solution followed by cooling down the solution. The dissolved compound would crystallize from the solution due to the difference in solubility at high and low temperatures. This method is especially effective for potassium nitrate (KNO3) since its solubility in 158g of water is 247g at 100 degrees C, and only 13.3g at 0 degrees C.

 

Supplies:

Stump remover that contains Saltpeter (KNO3)

Water (H2O)

Paint stick or spoon

Pot or pan

Jar

Funnel (optional)

Hot plate

Safety glasses

 
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Step 1: Measurements

   First, weigh out 247g of stump remover and set it to the side. Now measure 175ml of H2O (which is about 158g in weight). You can multiply these numbers if you would like.

Step 2: Dissolving the Salt

   Pour the water into a pot or pan and bring the water to a boil on a hot plate. When the H2O starts to boil, lower the hot plate’s temperature and empty the stump remover into the pot.

   After that, stir the mixture with a spoon or paint stick, preferably with a paint stick, until the stump remover has completely dissolved.

   Continue to heat and not boil the solution as you stir it for a few minutes. Add a little more water to the solution if you notice that plenty of the H2O has evaporated. The amount of water is not critical however; you do not want too much or too little water in your solution.

kymyst12 months ago
I think you are wasting your time with this procedure. According to the label, the stump remover is 40 % potassium nitrate and 60 % something else. All you are doing with this procedure is dissolving and recrystallising the water soluble salts, and what you finished with is probably STILL only 40 % potassium nitrate. I tend to concur with corradini that someone who knows as little chemistry as yourself should not be messing about with pyrotechnics, nor giving advice to others about making these products. Do you know what happens if you steel ball mill magnesium and potassium nitrate together ? DON'T try it !!!!
BytePilot4 years ago
Something ain't right... Water is pretty close to 1g/ml so 100g of water should be 100ml not 175ml...
YoungPyro19 (author)  BytePilot4 years ago
Okay you just about right. I measured and weighed the H2O again and it turned out that 175ml weighs 158g.
Even that's a bit of a worry. At 20 degrees C (approx room temperature) the density of water is 998.2 kg/m^3 that means it should be 0.998g/ml. That would put 175ml of water at 174.6g If your scales are showing 158g they may not be as accurate as needed for this task. But hey, if you always use the same scales and the same measurements, you should get the same resuts.
YoungPyro19 (author)  BytePilot4 years ago
I don’t know much about water density, but I suppose you’re right. Also, when I measured the H2O for a second time I used a more accurate scale.
Dude. 'I don't know much about water density' -- SERIOUSLY? Let me clue you in - as others have sort of tried here:

1 ML OF WATER WEIGHS 1 GRAM.

And to get all complete, here: a cubic centimeter of water is a milliliter. which weighs a gram. Kind of why the metric system is all nice and neat. (And, to Mr. '998.2' kg/m^3' -- sometimes being 'super-accurate' isn't 'super-helpful'. A gram is a cc is a ml is just fine, here.;-)

Back to you, YoungPyro19: if you started out with solubility of 247 g in 158g of water -- but don't even know that 158g of water is NOT 175ml -- I'd bet a kidney you cut-and-pasted your recipe. Which is fine for peach pie -- BUT I DON"T THINK YOU OUGHTA BE POSTING CHEMISTRY PROCEDURES.

Ummm...especially seeing as how - guessing from 'YoungPyro19'? And the fact that we're dealing w/ nitrates here? I SO don't want to be negative, per Instructables 'be nice' policy, but, dude, it's not Sherlock to suppose that (a) your advice is intended for people who want things that go kapow or boom, and (b) you don't even have a CLUE about -- jeezus -- about pretty much THE most fundamental measurement concept in chemistry.

Y'know, when you're making things that go boom or kapow (again, your handle is 'YoungPyro19', so I'm not stretching it much to assume that), things like 'oops!' (or, to quote you directly: 'I don't know much about water density', and thus being off by, oh, tens of percents) -- cost people fingers and hands and eyes.
minerug3 years ago
Can this work for getting potassium nitrate out of garden fertilizer?
YoungPyro19 (author)  minerug3 years ago
This procedure is just for purifying KNO3 from stump remover.

I think this is what you’re looking for==> http://www.youtube.com/watch?v=g4FpKqG93rY

The process is similar. Study the video and improvise.
I've been needing this!
YoungPyro19 (author)  masterochicken4 years ago
Ok, well I hope it will be very helpful to you.
Smoke bomb time!
YoungPyro19 (author)  masterochicken4 years ago
Ohh YEAH! =)
jtobako4 years ago
How would 175ml H2O be less than 175g?
YoungPyro19 (author)  jtobako4 years ago
Weight is not the same as volume. Volume is how much three-dimensional space a substance (solid, liquid, gas, or plasma) occupies. Weight is a measure of the heaviness of an object.
Right. And water has a density of 1g/ml. Strange how the French chose it that way : )
D6U44 years ago
or you could go on ebay and just buy kno3
YoungPyro19 (author)  D6U44 years ago
Yes, but shipping cost can kill. This process is not hard at all.