jamit
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phosphoric acid synthesis
Has anyone actually made any reasonably pure phosphoric acid using a phosphate salt like trisodium phosphate and sulfuric acid?
I check some search on "phosphoric acid" and the results seem inconclusive. There are topics on orthophosphoric acid and heating it to make
metaphosphoric acid, etc. 
Any help would be appreciated.
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Magpie
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http://www.sciencemadness.org/talk/viewthread.php?tid=2923&a...
The single most important condition for a successful synthesis is good mixing - Nicodem
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jamit
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Thanks Magpie!!
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jamit
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I'm still a little unclear even after reading the thread Magpie suggested. Can someone clarify?
After mixing trisodium phosphate with rooto sulfuric acid, you get sodium sulfate (Na2SO4) in solution (at room temp) and phosphoric acid (H3PO4).
Many note that sodium sulfate should be filtered but it hasn't ppted. Should i put it in the refrigerator and cool it and force out the ppt
(4.7g/100ml at 0C)?
Then should i take the filtrate solution of H3PO4 and distilled it? Some say that I should vacuum evaporate? What is vacuum evaporation?
Can someone help me on this? thanks in advance.
[Edited on 19-7-2011 by jamit]
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Magpie
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Quote: Originally posted by jamit  | I'm still a little unclear even after reading the thread Magpie suggested. Can someone clarify?
After mixing trisodium phosphate with rooto sulfuric acid, you get sodium sulfate (Na2SO4) in solution (at room temp) and phosphoric acid (H3PO4).
Many note that sodium sulfate should be filtered but it hasn't ppted. Should i put it in the refrigerator and cool it and force out the ppt
(4.7g/100ml at 0C)? |
What I used was Ca3(PO4)2 as indicated in my post, not Na3(PO4). This gives CaSO4 when sulfuric acid is added. This is insoluble and can be filtered
out.
| Quote: Originally posted by jamit |
Then should i take the filtrate solution of H3PO4 and distilled it? Some say that I should vacuum evaporate? What is vacuum evaporation?
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Yes, use vacuum evaporation (distillation). This is potentially dangerous due to flying glass from an implosion if your glassware is not vacuum
capable or is defective. You should already be proficient in distillations before trying a vacuum distillation. Get a good organic lab text and read
up on vacuum distillation beforehand.
If you don't want to make H3PO4 maybe you can get it at a brewing supplies store. My local supplier was selling it by the gallon the last time I
noticed.
The single most important condition for a successful synthesis is good mixing - Nicodem
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jamit
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thanks Magpie!
I noticed that in your comment on the thread, that your filtered product was cloudy. How did you get rid of that cloudiness? Was it caused by
calcium sulfate? And did your final product after vacuum evaporation produce a clear concentrated solution of phosphoric acid?
thanks in advance!
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Magpie
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The acid I show is the concentrated pot product. IIRC I didn't do anything more to it. So I don't know what the fine material is that caused the
cloudiness. I have very little use for this acid so never worried about it anymore. If I wanted to clarify it now I would try my newly acquired
glass frit filter funnel.
When I make a reagent I always have an end use in mind. If the contaminant won't affect the end use or intended purpose I don't worry about it. It's
the same philosophy as why buy chemically pure when technical is good enough?
Edit: Product is in the pot, a concentrate.
[Edited on 20-7-2011 by Magpie]
The single most important condition for a successful synthesis is good mixing - Nicodem
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Bitburger
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Pure phosphoric acid is a pale pink coloured, waxy solid. It is very
hygroscopic. I obtained it once when I used dilute HCl as solvent for the reaction between calcium phosphate and sulphuric acid. After leaving the
solid CaSO4.xH2O behind, the 5%HCl solution was evaporated at only 20°C but with a air humidity of 0% since it was freezing outside and when the
surrounding air warms up it takes up the water vapour really easy...
So, no need for an expensive and hard to catch vacuum oilpump
Good to be wrong
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