wymanthescienceman
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Registered: 18-3-2008
Location: Minnesota, USA
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Detection of Ammnium ion in Ca(NO3)2 Solution
Hi all, I have a question I hope can be answered here.
I've tried synthesizing Ca(NO3)2 from NH4NO3, via addition of Ca(OH)2 to a solution of NH4NO3. When the hydroxide is added, a strong ammonia smell is
immediately noticed so I have reason to believe it is working the way it should. I let it react until no more ammonia was noticed, filtered off the
bit of excess hydroxide, and evaporated the solution to get a crystalline product.
My question is: How would I be able to tell whether or not all of the NH4NO3 reacted? Since I used a slight excess of Ca(OH)2 and no more ammonia was
being released, I assumed it all has but I can't be sure. Would there be a way of detecting any leftover ammonium ion left in the product? I can't go
the usual NaOH route to see if ammonia is released, as Ca(OH)2 immediately precipitates from a solution of the product. I've tried searching but
everything says to use NaOH to detect ammonium... 
Any help on how I can be relatively sure there is no more ammonium left in my product would be appreciated. It's just a quality thing so it's not a
huge deal, I just wanna know... 
Running is not a plan, running is what you do when a plan fails.
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not_important
International Hazard
Posts: 3873
Registered: 21-7-2006
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Use NaOH to release ammonia ... seriously, you do the test on a few ml of the solution, not on the bulk of it. Use enough NaOH to react with all the
nitrate in the few ml and heat it.
But you really don't need to do that. Start out adding an excess (by calculation) of Ca(OH)2, stir for awhile, then while stirring slowly bring the
solution to a boil for a few minutes. This will drive off the free NH3, and with excess Ca(OH)2 there won't be any ammonium salts.
That the boiling solution and carbonate it - bubble CO2 thru it - to convert excess Ca(OH)2 to CaCO3, doing this hot prevents overcarbonation from
making the somewhat soluble bicarbonate. Stop the CO2, continue to boil briefly, filter while hot.
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