Sciencemadness Discussion Board

Testing the purity of a nitrate salt

Turner - 17-6-2014 at 14:24

Hello,

I have been using the cold packs from Walgreens as AN (dissolve in water. filter off binder which is a very minimal amount, then precipitate)

but I am starting to suspect they are not pure AN, maybe a Urea/AN mix. All synthesis requiring AN have only turned up around 60% yields for me.

I suppose I could test by adding a noted amount of this material to sulfuric acid to create nitric acid and then add a stoichiometric amount of copper,

using the equation: 4HNO3 + Cu ---> Cu(NO3)2 + 2NO2 +2H2O

and see if all copper reacts as it would if it was pure AN, but isn't it hard to predict how much nitrate reacts with the copper and how much is produced as NO2/NO and very much is a function of temperature?




Has anyone found that it is in fact pure AN, or isn't?

[Edited on 17-6-2014 by Turner]

FireLion3 - 17-6-2014 at 14:39

Is there a reason you just don't buy it pure? Both Ammonium and Potassium Nitrate can be bought relatively pure in the USA. A quick google search reveals dozens of searches. Reagent quantities online, or 55lb bags for around $100, or cheaper. Both of these can be bought both online and over the counter at a hardware, gardening, and sometimes organic stores.


There is a store about 40 minutes from me that I believe sells 25 lb bags (may be 55lb) of potassium nitrate (could be ammonium) for under $80. I asked the clerk once and they told me they are relatively pure so that people can formulate their own fertilizers. They literally had stacks of them. Last time I was there they had roughly 50 bags. The stuff is definitely not facing any sort of shortage in the US.

Turner - 17-6-2014 at 15:03

Haven't found any NH4NO3 OTC as fertilizer where I live aside from the AN in cold packs.
I can buy pure KNO3, although expensive.


Burner - 17-6-2014 at 15:16

Easy enough to make Ammonium Nitrate...

Calcium Nitrate and Ammonium Sulfate are available at most well-stocked garden supply stores. Mix them together and the calcium sulfate drops right out. If done in hot water at higher concentration, after filtering out the precipitate, the ammonium nitrate crystalizes out beautifully. :D

[Edited on 17-6-2014 by Burner]

Rogeryermaw - 17-6-2014 at 15:16

order certi-cool cold compress. google it. i get them for less than $1 each. good purity and no complaints with my uses of it as a reagent.

Artemus Gordon - 17-6-2014 at 19:05

Turner, did you find Walgreens cold packs that listed the ingedients? I have looked at the ones at Walgreens in northern California and i have never found ingredients listed, so I assumed they don't use AN at all. I can get AN packs at my Lucky supermarket, but I always wondered whether the Walgreens ones use urea or even something else.

Rogeryermaw, i'm glad the CertiCool packs work well for you, but their MSDS doesn't inspire confidence. It lists "Ammonium Nitrate (HN4NO3)"!
LOL



[Edited on 18-6-2014 by Artemus Gordon]

Turner - 17-6-2014 at 20:04

There definitely is AN in those cold packs I know for fact but I don't know if they add urea to make these explosively inert, urea is equally effective as an instant cold pack

Motherload - 25-6-2014 at 20:11

I would say if you just add conc H2SO4 to it ... It will make HNO3 along with the presence of H2SO4 .... Any urea present would nitrate to Nitro Urea (not efficiently).
It would give you a white Precipate upon dilution

AJKOER - 2-7-2014 at 18:14

Per Wikipedia (http://en.m.wikipedia.org/wiki/Instant_cold_pack ), to quote:

"An instant cold pack is a device that consists of two bags; one containing water, inside a bag containing ammonium nitrate, calcium ammonium nitrate or urea. "

Actually, I am not finding the description above on the contents clear. Is it either pure ammonium nitrate or calcium ammonium nitrate or urea? Or, is it NH4NO3 plus either calcium ammonium nitrate or urea? Or is it urea plus either NH4NO3 or calcium ammonium nitrate?

[Edited on 3-7-2014 by AJKOER]

Motherload - 2-7-2014 at 20:24

Is the MSDS not available for the specific brand you have ?

violet sin - 2-7-2014 at 20:41

http://www.cvs.com/shop/product-detail/CVS-Instant-Cold-Pain...
under ingredients tab: "ammonium nitrate, water"

http://answers.walmart.com/answers/1336/product/23598500/que...
second question at bottom of page: "Is the chemical that makes them get cold urea or ammonium nitrate?" ... " The Equate Instant Cold Compress Pads uses Calcium Ammonium Nitrate and Water."

a couple I found quite easily

Texium - 2-7-2014 at 20:47

Quote: Originally posted by FireLion3  

There is a store about 40 minutes from me that I believe sells 25 lb bags (may be 55lb) of potassium nitrate (could be ammonium) for under $80. I asked the clerk once and they told me they are relatively pure so that people can formulate their own fertilizers. They literally had stacks of them. Last time I was there they had roughly 50 bags. The stuff is definitely not facing any sort of shortage in the US.

Mind sharing the name of that store? I've never seen anything like that anywhere I go. All the fertilizers Ive found are in mixes, like 13-13-13, etc.
Or is it just some local thing that wouldn't be in most places?

[Edited on 7-3-2014 by zts16]

Ascaridole - 7-7-2014 at 13:28

To test the purity of a nitrate salt (potassium or sodium) reflux a solution of the salt with Devarda alloy (see wikipedia) and capture the ammonia in a boric acid solution and titrate remaining boric acid to determine ammonia produce and from that amount of nitrate.

For ammonium nitrate you can simply add excess of base and trap the formed ammonia in a boric acid solution and titrate remaining boric acid to determine ammonia liberated from your solution. To capture the ammonia form both methods use a kjedalh setup.

If you suspect urea you can heat a solution of your salt with some methyl red and see if it goes basic.On the same not you could just reflux a solution of your salt and see if any ammonia is produced from the thermal decomposition of urea by capturing the gases produced in a kjedahl like setup.

Your idea of titrating against copper is as you noted flawed with the fact that as the copper reacts with the nitric acid the formation of NO/NO2 is unknown. Also direct titration of nitric acid is difficult as most indicators are destroyed by the nitric acid. A back titration is necessary, even then it can be a bit fussy depending on concentration.

Even if you were to buy "pure" commercial material I would still perform an analysis if purity is of concern.