At what Hammett acidity values do nitric and permanganic acids have isoelectric points?
If they do.
For permanganic acid, it should be relatively easy to determine because permanganic composition is strongly absorbing in visible light.
Nitric acid can react as follows:
NO3-+H+=HNO3
HNO3+2H+=NO2++H3O+
Permanganic acid can react:
MnO4-+H+=HMnO4
But I have seen two contradicting paths for next step:
HMnO4+2H2SO4=MnO3HSO4+H3O++HSO4-
and then arguably
MnO3HSO4=MnO3++HSO4-
So what is the evidence for this? It seems to me that it should be fairly obvious!
There have been studies at some length about electric conductivity of concentrated sulphuric acid and oleum. Revealing blunt maxima around 90%
sulphuric acid and 12% oleum, and a sharp minimum near 100 %.
Near but not exactly; detailed studies showed that the exact conductivity minimum of H2SO4 and D2SO4 is on
different side of 100 %!
Now, it is well known that in concentrated H2SO4, excess permanganate precipitates as liquid (and explosive)
Mn2O7. A more modest concentration of permanganate, however, stays dissolved - forming a green solution in concentrated
H2SO4.
However, in less concentrated H2SO4, permanganate solution is pink/purple.
So is there an isoelectric point somewhere? When you produce dilute solutions of permanganate in various concentrations of concentrated sulphuric
acid/oleum, the pink includes MnO4- anion, which should migrate to anode on electrophoresis. But what is the green species? Is
it MnO3HSO4, as an undissociated molecular species, in which case there should be no isoelectric point because at all
concentrations most manganese is stationary as neutral HMnO4 and MnO3HSO4 and therefore the only motion is with the
few MnO4- towards anode? Or does the green species actually form dissociated MnO3+ cations which migrate
to cathode and at some Hammett H0 (sulphuric acid/oleum concentration) give an actual isoelectric point? The contrast between the green manganese
solution and colourless oleum should help tracking the migration!bnull - 12-5-2024 at 11:20
