Sciencemadness Discussion Board

Dissolving Manganese Dioxide in Sulfuric Acid?

nikotyna1939 - 14-3-2024 at 00:44

At what temprerature will Manganese Dioxide starting to dissolve in Sulfuric Acid to produce Manganese Sulfate?
Does Manganese Dioxide reacts with Sulfuric Acid at room temprerature?

RU_KLO - 14-3-2024 at 03:53

I think not, because MnO2 is insoluble.
But boiling concentrated H2SO4 (VERY VERY DANGEROUS) could dissolve MnSO4.

like I said in another of your posts, the route is to transform MnO2 to Mn2O3 by blowtorch heat and then leach it with H2SO4. ( I use 30% conc. ie battery acid concentration)

Check the permanganate post.

Sulaiman - 14-3-2024 at 05:43

In Wikipedia, manganese dioxide, reactions

Hot concentrated sulfuric acid reduces MnO2 to manganese(II) sulfate:

2 MnO2 + 2 H2SO4 → 2 MnSO4 + O2 + 2 H2O
......................................
So the evolution of oxygen should drive the reaction,

and, at a guess, if hot enough (boiling) the water would also be boiled off, increasing yield that may otherwise be decreased by atmospheric oxygen?
(as above - boiling conc. sulphuric acid is hazardous - it can 'bump' VIOLENTLY, so take extra care)

PS when the solution cools I would expect anhydrous manganese sulphate to precipitate out,
probably VERY hygroscopic.
Another guess ;)

[Edited on 14-3-2024 by Sulaiman]

DraconicAcid - 14-3-2024 at 06:13

Add a reducing agent such as hydrogen peroxide (in dilute, not concentrated acid) if you want the reaction to go at reasonable temperatures.

chornedsnorkack - 15-3-2024 at 05:23

Remember that "concentrated sulphuric acid" actually spans a vast range of Hammett acidity values.
Quoting some numbers from a table by Ryabova et al. 1966:


So, not only the behaviour of 30% and 96% acid are different, but both are quite different from what happens at 70% or 100,00%.


[Edited on 15-3-2024 by chornedsnorkack]

Sulaiman - 15-3-2024 at 05:56

In a textbook/lab/home/classroom context
unless otherwise specified
"concentrated sulphuric acid"
means near azeotropic.
Anything else would need a concentration specification.
(molarity, w/w%, 'chamber' etc.)

[Edited on 15-3-2024 by Sulaiman]

fx-991ex - 15-3-2024 at 07:14

Am sorry to drift this off topic a little, but why the dioxide not react with sulfuric acid to make Mn(SO4)2?, i expect oxidizer to react with acid usually.

[Edited on 15-3-2024 by fx-991ex]

solo - 15-3-2024 at 08:29

Quote: Originally posted by chornedsnorkack  
Remember that "concentrated sulphuric acid" actually spans a vast range of Hammett acidity values.
Quoting some numbers from a table by Ryabova et al. 1966:


  • 3% +0,31
  • 5% -0,02
  • 18% -0,97
  • 20% -1,10
  • 30% -1,82
  • 32% -1,96
  • 35% -2,19
  • 45% -2,95
  • 47% -3,13
  • 55% -3,91
  • 57% -4,15
  • 62% -4,82
  • 65% -5,18
  • 70% -5,92
  • 72% -6,23
  • 75% -6,72
  • 77% -7,05
  • 82% -7,84
  • 85% -8,29
  • 87% -8,60
  • 90% -9,03
  • 96% -9,88
  • 98% -10,27
  • 99% -10,57
  • 99,6% -10,92
  • 99,7% -11,01
  • 99,95% -11,64
  • 100.00% -11,94

So, not only the behaviour of 30% and 96% acid are different, but both are quite different from what happens at 70% or 100,00%.


[Edited on 15-3-2024 by chornedsnorkack]



...is that the density of each concentration of the acid?

DraconicAcid - 15-3-2024 at 09:28

Quote: Originally posted by solo  
Quote: Originally posted by chornedsnorkack  
Remember that "concentrated sulphuric acid" actually spans a vast range of Hammett acidity values.
Quoting some numbers from a table by Ryabova et al. 1966:


  • 3% +0,31
  • 5% -0,02
  • 18% -0,97
  • 20% -1,10
  • 30% -1,82
  • 32% -1,96
  • 35% -2,19
  • 45% -2,95
  • 47% -3,13
  • 55% -3,91
  • 57% -4,15
  • 62% -4,82
  • 65% -5,18
  • 70% -5,92
  • 72% -6,23
  • 75% -6,72
  • 77% -7,05
  • 82% -7,84
  • 85% -8,29
  • 87% -8,60
  • 90% -9,03
  • 96% -9,88
  • 98% -10,27
  • 99% -10,57
  • 99,6% -10,92
  • 99,7% -11,01
  • 99,95% -11,64
  • 100.00% -11,94

So, not only the behaviour of 30% and 96% acid are different, but both are quite different from what happens at 70% or 100,00%.


[Edited on 15-3-2024 by chornedsnorkack]



...is that the density of each concentration of the acid?


The Hammett acidity function is essentially an extension of the pH scale into non-aqueous solvents.

bnull - 15-3-2024 at 09:34

Quote: Originally posted by fx-991ex  
Am sorry to drift this off topic a little, but why the dioxide not react with sulfuric acid to make Mn(SO4)2?, i expect oxidizer to react with acid usually.

Did you mean oxide? Mn4+ is not much stable. Its only compounds that I know are our subject (MnO2) and MnF4, which is unstable and reacts with anything (air, water, solvents). Manganese likes to be 2+, that's why we need a reducing agent.

@solo: Those are the values in the Hammett acidity scale. It's like pH, for concentrated solutions. At low concentrations, the pH and Hammett values are very close. (Nevermind.)

[Edited on 15-3-2024 by bnull]

RU_KLO - 17-3-2024 at 02:37

Quote: Originally posted by fx-991ex  
Am sorry to drift this off topic a little, but why the dioxide not react with sulfuric acid to make Mn(SO4)2?, i expect oxidizer to react with acid usually.

[Edited on 15-3-2024 by fx-991ex]


It could react, but you need boiling concentrated, or maybe digestion ( long time medium temperature acid)

I think its because solubility of MnO2 is insoluble.


" Manganese (IV) dioxide (MnO2) is a strong oxidizer and is insoluble in water, nitric acid, or cold sulfuric acid, and it may slowly dissolve in aqueous HCl to give off Cl 2 gas."

Methods for converting manganese dioxide into water-soluble manganese salts
goggle patent. EP2930163A1


maldi-tof - 12-5-2024 at 12:26

Add the oxide to some water, slowly add sulphuric acid and hydrogen peroxide until you obtain a pink solution. Filter and then concentrate. You'll get MnSO4 1-Hydrate.

It is better to separate the crystals from mother liquors after a few hours at room temperature.