Crazy_Chemist - 9-3-2022 at 22:09
When you put hydrochloric acid on potassium permanganate, chlorine gas is evolved. But why does not the same reaction occur, but with fluorine gas
being developed instead if you put hydrofluoric acid on potassium permanganate?
The reaction between hydrochloric acid and potassium permanganate:
2 KMnO4 (s) + 16 HCl (aq) → 2 MnCl2 (aq) + 2 KCl (aq) + 5 Cl2 (g) + 8 H2O (l)
It's just like I read, that the reaction does not develop fluorine gas, I have not tried and do not dare to do so.
woelen - 10-3-2022 at 00:00
Getting fluorine out of fluorides, such as HF, requires a very strong oxidizer. The permanganate ion simply is not a sufficiently strong oxidizer.
Oxidizers can be ordered in strength (at a certain pH and within a certain coordinating environment). This concept is explained quite well in the
following wiki: https://en.wikipedia.org/wiki/Standard_electrode_potential_(data_page)
As you can see, fluorine is at the bottom end of the table and only oxidizers, which are below the entries for fluorine could (in theory) release
fluorine from fluoride.
The table only tells whether a reaction is thermodynamically feasible or not. In practice there may be other limitations. E.g. perchlorate is quite a
strong oxidizer, but in practice, in aqueous solution, it hardly reacts, due to kinetic reasons. So, having the right order in the table is a
requirement for a reaction being possible, but it is not a guarantee that the reaction will occur in practice.
One way to make a really strong oxidizer is using electrolysis. The voltage, applied to the cell, actually is the maximum redox potential which can be
bridged. E.g. with 4 volts across a cell, one could make fluorine, such as in a cell with KF, dissolved in HF. Of course, the anode material must then
be such, that it (at least kinetically) withstands the fluorine, formed at it.
chornedsnorkack - 10-3-2022 at 06:26
And a key factor is that fluorine is much stronger oxidizer than oxygen. Thus, when oxidized substances might evolve oxygen or fluorine, they
consistently evolve oxygen not fluorine.