kazaa81
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Purity test for grocery Ca(NO3)2
I came around 5kg bags of Ca(NO3)2 in pottery, but I'm not sure of it's purity. It's a white powder, but the stange thing is that on the bag aren't
wrote N contents and/or purity.
Just a big "Calcium Nitrate".
It seems strange that it's 95+% pure or something like that, of course for pottery things 45% is enough...otherwise too much N will come to grass etc.
Can anyone suggest me a test about purity? Even because I couldn't imagine how to purify, if I don't know what is and in what conc.
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skippy
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If it says 95% pure, it probably is at least that pure. Does it all dissolve? Anything that doesn't dissolve definately isn't calcium nitrate and
that would be one easy thing to isolate
It was made by reacting nitric acid with calcium carbonate, and whatever soluble impurities are present are probably those that were in the
neutralized limestone (calcium carbonate). Maybe some magnesium? How pure do you actually need it to be? 95% is probably fine for many uses.
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kazaa81
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Yes, 95% is very good purity for me....however, maybe you don't caught the problem....the bag is without writings, except a big "Calcium Nitrate" on
the front, but that's all...no tables, purity etc.
[Edited on 9-5-2006 by kazaa81]
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guy
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Dissolve a sample and try precipitating it. Mass the precipitate and see how it compares with the stoichiometry.
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kazaa81
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Precipitate? maybe dissolve in water and then crystallize
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guy
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I mean dissolve, then treat with carbonate or something. Make sure to wash the precipitate to make it as pure as possible.
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skippy
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I'm not so sure now if it is made from limestone. It can be made (evidently) from phosphate rock. They suck out the calcium (along with any
impurities, I'm sure) from the phosphate rock. This also facilitates making phosphate fertilizers
Is there no manufacturer or packager contact on the bag? If so maybe you could phone? Lord knows that would be easier than trying to analyze it
yourself.
I think that Sweden makes a lot of nitrate fertilizers and maybe you could learn something from this angle. http://www.idswater.com/water/europe/Yara_international_asc/...
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kazaa81
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| Quote: | Originally posted by skippy
It was made by reacting nitric acid with calcium carbonate, and whatever soluble impurities are present are probably those that were in the
neutralized limestone (calcium carbonate). Maybe some magnesium? How pure do you actually need it to be? 95% is probably fine for many uses.
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Impurities? I don't think that a fertilizer supplier would make a ton of 99% Ca(NO3)2 and sell you 99% in 5kg bags at pottery...I think that it would
dilute the ton and make at least 2 tons of 50% Ca(NO3)2 and sell it. So impurities are not only by the process, but also added.
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DrP
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What would they add - CaCO3? Dolomite? If for pottery then something more heat resistant for firing like a cheap mullite or something?
I rekon the same as skippy anyway - ring the manufacturer (or supplier) - they should know the purity.
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Ramiel
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You could precipitate the Calcium as an insoluble salt… I’d be worried about error here, how much of the salt is still in solution? Gravimetric
analysis is very finicky in the first place (requiring accurate scales and expensive filtering – sintered glass filters and vacuum filtration is
ideal). At large scale, sulphuric gravimetric would work okay – since I guess magnesium would be the largest contaminant.
I could recommend a titration, and I know it sounds tedious at first for the home experimenter, but if you really want to find out the purity [and
IMHO, titrations are <i>always</i> quicker and easier than gravimetric!].
As for nitrate… total kjeldahl nitrogen if you are sure it’s all nitrate, or a metal oxidation titration to determine nitrate?
Caveat Orator
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unionised
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"You could precipitate the Calcium as an insoluble salt… I’d be worried about error here, how much of the salt is still in solution?"
Er, pretty much none, otherwise it doesn't really count as an insoluble salt.
While it's interesting to speculate on the purity and on the nature of the possible contaminants, who cares?
If it's cheap, buy some and try to use it. If it works then it's pure enough. If not, then I guess you might need to recrystalise it or some such. If
the use involves heating it with nitric acid you might want to do it on a very small scale first.
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