madfromscience
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Phosphoric acid preparation
Please help me!
As i am only starting my chemist career and i need some help!
I need ortophosphoric acid 88,8% (density 1.75).
i have P2O5 and ortophosphoric acid 85%.
1) How much water i have to use to make 88.8% acid from P2O5. It's good idea to make such acid by this way?
2) Maybe it's possible to add P2O5 to ortophosphoric acid to increase concentration?
[Edited on 27-4-2012 by madfromscience]
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Magpie
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Oh the injustice! I can't buy or make P2O5 for love nor money. And yet you in Latvia are willing to add water to it on purpose!
please see:
http://www.sciencemadness.org/talk/viewthread.php?tid=19150#...
The single most important condition for a successful synthesis is good mixing - Nicodem
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Hexavalent
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I can second what Magpie says.
If you tell us what reaction you are doing, it may be possible and worthwhile just to use a calculated excess of the 85% stuff and conserve your
supply of the pentoxide.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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madfromscience
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This formula i know:
P4O10 + 6 H2O = 4 H3PO4
But i found in internet that this is only theoretically.
When you will really do this reaction, you will get not only H3PO4.
So maybe somebody already tried to perform this reaction?
And have any advices.
As i want to get high concentration, best quality H3PO4.
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Hexavalent
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Please read others' comments before posting again.
What reaction are you performing? You may be able to substitute an equivalent amount of the 85% acid, and save the more valuable, sought-after
phosphorus pentoxide.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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madfromscience
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Sorry for late post.
I will use this phosphoric acid for acid catalysed hydrolyses.
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weiming1998
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85% is definitely well enough for acid-catalyzed hydrolysis reactions, which generally use a slightly more dilute acid. No need to waste perfectly
good P2O5, which is extremely useful for other reactions.
What hydrolysis reaction is it? Because acid-catalyzed hydrolysis reactions generally either use H2SO4 or HCl. Why use H3PO4?
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woelen
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You can concentrate H3PO4 by heating it. Your 85% acid can be concentrated to 90% by simply heating and boiling off some water. Getting it more
concentrated may be hard though.
Adding P4O10 to the acid in my eyes is a waste, as mentioned already before. But there is another reason why you might not want to do this. If you do
this, then you don't get H3PO4 alone, but also H4P2O7 (pyrophosphoric acid) or maybe even (HPO3)n, metaphosphoric acid. These acids in the long run
react with water to form H3PO4, but these reactions are slow, very slow (days or even weeks). Your liquid will become a sticky very viscous mass.
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madfromscience
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I will try to substitute an equivalent amount of the 85% phosphoric acid as it's the easiest way for me
I tried to use H2SO4. In small flask everything was good, but when i tried to use bigger flask i got a lot of charring and yield decreased. Maybe you
have ideas how to avoid this?
[Edited on 8-5-2012 by madfromscience]
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