Reduction of phosphoric acid to phosphorous acid has a potential of -0.267V source
This means it should be easily reduced by metals like iron or zinc. Would this be reasonable to do?12AX7 - 30-4-2007 at 17:34
For some reason, those tetrahedral acids are rather hard to break down.
Sulfate and perchlorate (Eo = 1.20V to ClO3-) are other examples. Has anyone ever had one of these ions get cathodically reduced in solution to any
significant amount?
Thermodynamically I can accept that sulfate is better (read: lower energy) than sulfite, but the electric potential is supposed to be reversible by
definition.
Timguy - 30-4-2007 at 18:04
I know sulfate does it fairly well. I was touching some sodium bisulfate with a galvinized nail and an odor of H2S came out.vulture - 1-5-2007 at 02:44
Quote:
Has anyone ever had one of these ions get cathodically reduced in solution to any significant amount?
The problem is that you're always having either H+ or OH- in solution which are skewing the potentials and getting reduced/oxidized themselves.
roll over?
roamingnome - 1-5-2007 at 09:07
i was looking into this prep the other day, but couldnt really find anything so far.
but the following link suggests that nitrous acid is formed from nitric acid with argon in it and applied ultrasound.
i dont know how practical it all is, and if it cold work for phosphoric acid as well...
also nitrous oxide would be a bit precious to just bubble around...guy - 1-5-2007 at 11:29
I can get molten ammonium dihydrogen phosphate. So maybe that can reduce it easier.woelen - 1-5-2007 at 13:24
I once made an attempt, but it failed.
I did an experiment with phoshoric acid (10% or so), to which a small amount of zinc was added. The zinc dissolves (actually quite slowly). I left
this standing for a day, such that all zinc has dissolved. After this, I added a tiny amount of potassium dichromate (definitely, zinc was in large
excess, relative to the amount of potassium dichromate). If any phosphite were formed, then the dichromate should be reduced to green chromium (III).
But this did not happen. Even after several minutes, the liquid still was purely orange/yellow, not the faintest hint of green.
So, I think that reducing phosphoric acid with zinc is not easy at all. The only thing which is reduced are the H(+) ions, and hydrogen is produced.
Maybe it works with sodium/mercury amalgam, but I unfortunately cannot test that.
I can confirm that with sulfate indeed some of this is reduced by zinc. A smell of sulfide can be observed, but I think only a very small fraction is
reduced, the rest simply is reduction of H(+).Dr. Beaker - 1-5-2007 at 14:33
E0 of a reaction only tells you something about its thermodynamics, but nothing on the kinetics, or in other words - reduction by Zn is possible - but
very slow.
