Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: Teri on July 06, 2005, 07:33:02 AM
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I need to add some ammonium phosphate to my ICP multi-element standard solutions (for use in a DCP), but I'm not sure how long I need to dry the ammonium phosphate in a desiccator before weighing (ammonium phosphate is hygroscopic). Is there a general rule for how long you should dry a hygroscopic chemical? Thanks for your *delete me*
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The efficiency of drying is very poor in a desiccator. The drying occurs when you place the chemical in an oven with heat or vacuum. The general rule for water is 1 h at 105 C if the chemical can tolerate those conditions. Otherwise, some lower temperature with a vacuum can be used. The desiccator is usually just a dry storage chamber that you store the chemical in until you are ready to use it.
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Agreed.
You'll have to look up the melting/decomposition point of your chemical, and judge where to go from there.
And, as a side note, make sure you know which 'ammonium phosphate' you're using...there's monobasic (NH4H2PO4), dibasic ((NH4)2HPO4), and tribasic (the REAL one, (NH4)3PO4)...and each has its own property
Each can be called "Ammonium Phosphate"...even though TECHNICALLY only the tribasic one is...some chemists are lazy :P
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Thanks for the information! I put the monobasic ammonium phosphate in the drying oven this afternoon. Although it might be overkill, I went for the overnight approach since the MSDS said the chemical should be fine at 105C.
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Dessicating monoammonium phosphate by heating is not a good idea since some loss of ammonia is possible, and you can obtain a vitrous product that is the mixture of your chemical with phosphoric acid