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-   -   synthesis of ammonium magnesium phosphate x 6 H2O (http://chemistryhelpforum.com/showthread.php?t=146462)

Oldschool Oct 29th 2017 10:49 AM

synthesis of ammonium magnesium phosphate x 6 H2O
 
Any help appreciated, it's been 37 yrs. since I was in univ. chemistry class.

Trying to flesh out the stochiometric/molar quantities (grams) of magnesium oxide to be combined with monoammoniumphosphate (MAP, a common fertilizer) to create ammonium magnesium phosphate x 6 H2O ?

I'm guessing I can simply heat it the combination in distilled H2O on a magnetic stirrer overnight, then try cooling it to separate by crystals , but I have read that AMP is sparingly soluble in water, so maybe just push pH slightly above 7, cool in fridge, decant and harvest the "sludge" or crystals ?

This substance is a common problem in sewage treatment plants where it precipitates on pipes, as well as kidney stones in humans and dogs.

Oldschool Oct 29th 2017 10:58 AM

reaction should yield simple water, beside mag. ammon. phosphate
 
Forgot to add:

MAP (NH4H2PO4) is an acidic dihydrogen compound, MO is an alkaline oxide.

Combining the two should yield H2O.

Oldschool Nov 6th 2017 06:03 AM

Answered my own question - - easier than expected
 
Well, MgO is typically dead burnt magnesium oxide at very highrefractory temps.

I stored the MgO free samples in outdoors in humidity for 10 years, so it's likely absorbed moisture and even Co2 converting it to magnesium carbonate, precise stochiometry isn't much use here.

Fact is MgO and the carbonate are not very soluble in water, whereas MAP is quite soluble.

So, just combine an excess amount of Mg carb. based on it molar stochiometry with the MAP in hot stirred solution (assuming I now have carbonate), allow to react overnight, then decant liquid, through fine filter paper, boil off water to obtain crystals of ammonium magnesium phosphate.

Throw out sludge residue that does not react.

Bingo !


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