Sciencemadness Discussion Board

Is P2O5 dangerous

smithdotyu - 4-3-2015 at 05:16

Hi all;
I have buy 500g P2O5 to make H3PO4, I think the P2O5 will react with hot water to make H3PO4。
my country china is wet this day，so I think the P2O5 will react with H2O in the air，and before I do this experiment，I prepare a glass 、a gloves。。。and what i will need？

Bert - 4-3-2015 at 05:31

Yes, it can be dangerous. The reaction will get very hot, so hot that some of the water will probably boil off. Be prepared for acid to spatter out of the reaction vessel!

I would NOT use hot water, adding more heat for this reaction isn't needed.

If the dry P2O5 touches organic material, it may dehydrate it and get so hot that it starts a fire. Be careful and wear protective clothes/eye protection/gloves for both chemical and thermal burns, work on an acid and heat resistant surface.

[Edited on 4-3-2015 by Bert]

Metacelsus - 4-3-2015 at 06:11

Why are you making phosphoric acid from your P2O5? At least where I live, phosphoric acid is much easier to get.

Anyway, make sure you add the P2O5 to the water, and not the other way around. Bert is right; use cold water.

smithdotyu - 4-3-2015 at 06:36

Quote: Originally posted by Bert  
Yes, it can be dangerous. The reaction will get very hot, so hot that some of the water will probably boil off. Be prepared for acid to spatter out of the reaction vessel!

I would NOT use hot water, adding more heat for this reaction isn't needed.

If the dry P2O5 touches organic material, it may dehydrate it and get so hot that it starts a fire. Be careful and wear protective clothes/eye protection/gloves for both chemical and thermal burns, work on an acid and heat resistant surface.

[Edited on 4-3-2015 by Bert]


Thank you for your advice, this is very useful for me, in our country schoolbook said P2O5 react with cold water and make HPO3，so I use Hot water。。。this react looks like more violent than CaO with water

smithdotyu - 4-3-2015 at 06:40

Quote: Originally posted by Cheddite Cheese  
Why are you making phosphoric acid from your P2O5? At least where I live, phosphoric acid is much easier to get.

Anyway, make sure you add the P2O5 to the water, and not the other way around. Bert is right; use cold water.


Because I only can use experiment to buy chemical reagents，www.1688.com,you know,likes ebay in your country,think the H3PO4 is liquid and more hard to transport

smithdotyu - 4-3-2015 at 06:43

Quote: Originally posted by smithdotyu  
Quote: Originally posted by Cheddite Cheese  
Why are you making phosphoric acid from your P2O5? At least where I live, phosphoric acid is much easier to get.

Anyway, make sure you add the P2O5 to the water, and not the other way around. Bert is right; use cold water.


Because I only can use experiment to buy chemical reagents，www.1688.com,you know,likes ebay in your country,think the H3PO4 is liquid and more hard to transport


sorry for my poor English ，It is express not experiment

Bert - 4-3-2015 at 07:00

In USA, P2O5 is hard for an amateur to buy, but phosphoric acid is fairly easy to get. So USA amateurs think it strange to "waste valuable P2O5 making cheap phosphoric acid".

unionised - 4-3-2015 at 12:13

P2O5 reacts violently with warm water.
You are mainly warm water.

deltaH - 4-3-2015 at 13:04

Quote: Originally posted by smithdotyu  
Hi all;
I have buy 500g P2O5 to make H3PO4, I think the P2O5 will react with hot water to make H3PO4。
my country china is wet this day，so I think the P2O5 will react with H2O in the air，and before I do this experiment，I prepare a glass 、a gloves。。。and what i will need？


Why is the reaction with humidity a bad thing if you want to prepare phosphoric acid? Sounds like a great way to hydrate it safely. If it was me, I'd weigh out a portion of P2O5 and its container, mark it clearly as corrosive and dangerous and keep it out of reach of people and animals, then leave it open to hydrate from air until it forms a viscous goop, then weigh again and add enough water to ultimately form a 85% solution of phosphoric acid, then stir and boil to complete the hydration of the polyphosphoric acids, finally, recheck mass and make-up for lost water. Seems like a great exercise in water balancing :)

[Edited on 4-3-2015 by deltaH]

smithdotyu - 5-3-2015 at 03:58

Quote: Originally posted by deltaH  
Quote: Originally posted by smithdotyu  
Hi all;
I have buy 500g P2O5 to make H3PO4, I think the P2O5 will react with hot water to make H3PO4。
my country china is wet this day，so I think the P2O5 will react with H2O in the air，and before I do this experiment，I prepare a glass 、a gloves。。。and what i will need？


Why is the reaction with humidity a bad thing if you want to prepare phosphoric acid? Sounds like a great way to hydrate it safely. If it was me, I'd weigh out a portion of P2O5 and its container, mark it clearly as corrosive and dangerous and keep it out of reach of people and animals, then leave it open to hydrate from air until it forms a viscous goop, then weigh again and add enough water to ultimately form a 85% solution of phosphoric acid, then stir and boil to complete the hydration of the polyphosphoric acids, finally, recheck mass and make-up for lost water. Seems like a great exercise in water balancing :)

[Edited on 4-3-2015 by deltaH]


It may come into being HPO3 not H3PO4，the HPO3 is poisonous

smithdotyu - 5-3-2015 at 04:04

Quote: Originally posted by Bert  
In USA, P2O5 is hard for an amateur to buy, but phosphoric acid is fairly easy to get. So USA amateurs think it strange to "waste valuable P2O5 making cheap phosphoric acid".


I finished this experiment，I post it in our chinese website，here is，http://bbs.kechuang.org/read/70369,i don‘t record the monment when P2O5 react with water because this experiment must be careful

[Edited on 5-3-2015 by smithdotyu]

deltaH - 5-3-2015 at 05:46

Quote: Originally posted by smithdotyu  


It may come into being HPO3 not H3PO4，the HPO3 is poisonous


Metaphosphoric acid is not poisonous, but it is corrosive being the product of a partial hydration (see attached MSDS).

Attachment: metaphosphoric acid MSDS.pdf (37kB)
This file has been downloaded 1626 times

It is also hygroscopic so it would hydrate further if left open to air. Eventually, mixing with excess water and boiling will finish it off.

[Edited on 5-3-2015 by deltaH]

smithdotyu - 6-3-2015 at 05:18

Quote: Originally posted by deltaH  
Quote: Originally posted by smithdotyu  


It may come into being HPO3 not H3PO4，the HPO3 is poisonous


Metaphosphoric acid is not poisonous, but it is corrosive being the product of a partial hydration (see attached MSDS).



It is also hygroscopic so it would hydrate further if left open to air. Eventually, mixing with excess water and boiling will finish it off.

[Edited on 5-3-2015 by deltaH]


thank you, It's look's like chinese wiki about HPO3 is wrong

deltaH - 6-3-2015 at 05:43

Well, I suppose it depends how you look at it, if you eat it, it probably will kill you ;)

But that's because it's gonna burn the #$%^ out of you. It's only halfway in hydration between P2O5 and H3PO4 so probably a strong desiccant.

Anyhow, your final boiling step handles any outstanding hydration that is still needed.

maleic - 9-3-2015 at 23:27

It seems you already know how dangerous it is. Carefully to use it.

chornedsnorkack - 10-3-2015 at 08:27

Is the reaction of P2O5 with ice exothermic? And is it spontaneous?

vmelkon - 11-3-2015 at 09:28

HPO3? Metaphosphoric acid is (HPO3)x. I guess it is a polymeric coumpound. Free HPO3, the equivalent of HNO3 doesn't exist.