DrP - 28-9-2005 at 04:49
I have some Urea Phosphate. All the safety data says it is compleatly harmless. When I dissolve it in water the pH drops to about 0.5!!
1) Is this phosphoric acid, Uric acid or something else>
2) How is this harmless if it produces a strong acid - wouldn't it disolve in the moisture on the skin and then burn?
Cheers!
chemoleo - 28-9-2005 at 05:17
You have to specify a bit more:
Is it triurea phosphate, diurea phosphate or monourea phosphate?
I suspect it's the last one.
In that case, the low pH is easily explained - there are still two acid OH present, which both can form salts.
It might well burn a little, yes. But then, in principle it is similar i.e. to ammonium dihydrogen phosphate, which is also a stable yet acidic salt,
and not terribly dangerous.
DrP - 28-9-2005 at 06:11
Thanks, MSDS just says Urea Phosphate - phosphoric acid, urea salt.
Der.. I guess this answers my question - it will be phosphoric acid! ?
chemoleo - 28-9-2005 at 07:56
Yes it is, but it is the mono-basic version. So still acidic.
Tell me, is urea phosphate your flame retardant that produces acidic conditions on the fabric? If so, you could have really written this in the same
thread, no?
Anyway - if this is the case, then I very much suspect that the acidity is in part responsible for the flame retardation, and I don't see an easy
solution to it.
Did you try to add some more urea to make it i.e. dibasic?
unionised - 1-10-2005 at 06:01
Even with a monobasic acid like perchloric the salt will form an acidic solution in water.
Urea is a weak base and the corresponding ion CON2H5+ is a fairly strong acid.
DrP - 3-10-2005 at 06:55
Added more Urea (2, 3 and 4 times amount of phosphate) - brings pH up a fraction but not by much. Thanks.
Nicodem - 3-10-2005 at 07:30
You can't raise the pH by adding more urea. Urea in water solution can barely get protonated.
The pKa of the protonated urea is 0.18 which means it is a relatively strong acid. For comparison H3O+ has a pKa of -1.7. Hence as you see, urea
can't really be called a base in the clasic sense. It can only form salts with strong mineral acids and urea phosphate can only be one urea per
one H3PO4 and in water it is prevalently dissociated in unprotonated urea and H3PO4 and its dissociation ions (pKa1 of diluted H3PO4 is 0.9, hence
protonated urea is a stronger acid than H3PO4).
[Edited on 3-10-2005 by Nicodem]
DrP - 7-11-2005 at 08:15
I found some sodium citrate and disolved it in water - it gives a pH of around 8. This seems to bring the pH up of the Urea Phos solution up quite a
bit without leaving any salty deposits. Hopefully the mixture will still do the same job it was supposed to in the first place (ongoing tests).
I was expecting the Na Citrate to be an acidic solution because of the citrate, but I guess the Na gives NaOH??
neutrino - 7-11-2005 at 14:42
Actually, the citrate ion is responsible for the pH.
HOH + Citrate<sup>-</sup> <--> Citric acid + OH<sup>-</sup>
This equilibrium is shifted a little to the right because citric acid is a weak acid (and thus a stable molecule).