Sciencemadness Discussion Board

Potassium Permanganate Standard

chloric1 - 28-8-2024 at 04:59

I am curious to know what concentration of an acidified permanganate standard solution you find most satisfactory in wet chemistry? I want to make my own for testing nitrites, oxalates and other things that discolor permanganate in acid solution. But I don’t want it so strong that it will crystallize if I let it get cooler than 20 Celsius inadvertently.

bnull - 28-8-2024 at 05:30

Quote:
But I don’t want it so strong that it will crystallize if I let it get cooler than 20 Celsius inadvertently.

Solubility of KMnO4 is 50 g/L at 20 °C; you don't need that much permanganate for titration. A 0.1 N solution (~5 g in 1.5 L of water) should be good enough.

chloric1 - 28-8-2024 at 07:19

Thanks! I get me some amber Boston round bottles with the cone seal and a 500 ml volumetric flask. Just verified solubility of potassium permanganate has a solubility of 2.83 grams per 100 ml water at 0 degrees Celsius. I knew this solution could be fairly dilute since it is its own indicator.

Sulaiman - 28-8-2024 at 18:51

I think that you should make your solution when needed,
rather than store any, due to decomposition.

greenlight - 28-8-2024 at 21:44

Just used permanganate solution (standardised with potassium oxalate) to titrate an iron oxalate complex samplw to find the concentrations of Fe²+ and C2O4 in solution solution acidified with sulfuric acid..
The potassium permanganate was calculated at 0.0205M and worked fine.

j_sum1 - 29-8-2024 at 14:18

Quote: Originally posted by Sulaiman  
I think that you should make your solution when needed,
rather than store any, due to decomposition.

I second this.

Even at low concentration and stored in glass, over a period of time a manganese oxide coating builds up on the surface of the container.

bnull - 29-8-2024 at 15:22

Hamilton & Simpsons' Quantitative Chemical Analysis (https://archive.org/details/quantitativechem00hami/page/210/...) has instructions on how to prepare and standardize a potassium permanganate solution for titration.

Another thing: the solution absorbs organics from the air. Living beings, especially humans, exhale organic compounds.

Strangely enough, I was able to keep about 0.5 mL of a solution of KMnO4 in acetone (don't do that!) for some days without decompositon. Then it all went brown and stuck to the glass.

EF2000 - 29-8-2024 at 22:51

When you use standard permanganate solution that was stored, you need to filter it through some inorganic filter, like glass wool.

Bedlasky - 3-9-2024 at 19:03

As others said, concentrations around 0,1 mol/l are suitable. I wouldn't be that harsh regarding storage. Like yeah, it will slowly decompose to MnO2, but that decomposition is pretty slow. I never encounter any problems with storage on a few months periods. You can occasionaly filter it through glass wool or glass filter (but if you don't swirl MnO2 during pouting in to a beaker, you will be fine even without it). You will have slight decrease in concentration over time, so it would be optimal to standardize it once per month. Store it in brown glass bottle in dark.

I covered some basics of volumetric analysis here. There is also list of suitable standards for various compounds.

https://www.sciencemadness.org/whisper/viewthread.php?tid=16...

Btw let your permanganate stand for a few days and filter it before standardization. First few days it will react with organics in the water. Also how many samples and how often do you use it? And what's your burette volume?

[Edited on 4-9-2024 by Bedlasky]

chloric1 - 4-9-2024 at 02:44

Quote: Originally posted by Bedlasky  
As others said, concentrations around 0,1 mol/l are suitable. I wouldn't be that harsh regarding storage. Like yeah, it will slowly decompose to MnO2, but that decomposition is pretty slow. I never encounter any problems with storage on a few months periods. You can occasionaly filter it through glass wool or glass filter (but if you don't swirl MnO2 during pouting in to a beaker, you will be fine even without it). You will have slight decrease in concentration over time, so it would be optimal to standardize it once per month. Store it in brown glass bottle in dark.

I covered some basics of volumetric analysis here. There is also list of suitable standards for various compounds.

https://www.sciencemadness.org/whisper/viewthread.php?tid=16...

Btw let your permanganate stand for a few days and filter it before standardization. First few days it will react with organics in the water. Also how many samples and how often do you use it? And what's your burette volume?

[Edited on 4-9-2024 by Bedlasky]


I have not procured a burette or potassium permanganate yet for that matter. I just wanted the info you guys gave me. I plan to have all these things when I get into nitrites. Also, I find oxalates and oxalato complexes intriguing. Not sure if I may need to titrate Mohrs salt with permanganate or not.

Bedlasky - 4-9-2024 at 05:39

You can titrate Mohr's salt with permanganate.