chloric1
International Hazard
Posts: 1135
Registered: 8-10-2003
Location: GroupVII of the periodic table
Member Is Offline
Mood: Stoichiometrically Balanced
|
|
Potassium Permanganate Standard
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.
Fellow molecular manipulator
|
|
|
bnull
Hazard to Others
Posts: 386
Registered: 15-1-2024
Location: South of the border, wherever the border is.
Member Is Offline
Mood: Dazed and confused.
|
|
| 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.
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
|
|
|
chloric1
International Hazard
Posts: 1135
Registered: 8-10-2003
Location: GroupVII of the periodic table
Member Is Offline
Mood: Stoichiometrically Balanced
|
|
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.
Fellow molecular manipulator
|
|
|
Sulaiman
International Hazard
Posts: 3677
Registered: 8-2-2015
Location: 3rd rock from the sun
Member Is Offline
|
|
I think that you should make your solution when needed,
rather than store any, due to decomposition.
CAUTION : Hobby Chemist, not Professional or even Amateur
|
|
|
greenlight
National Hazard
Posts: 734
Registered: 3-11-2014
Member Is Offline
Mood: Energetic
|
|
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.
Be good, otherwise be good at it 
|
|
|
j_sum1
Administrator
Posts: 6306
Registered: 4-10-2014
Location: At home
Member Is Offline
Mood: Most of the ducks are in a row
|
|
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
Hazard to Others
Posts: 386
Registered: 15-1-2024
Location: South of the border, wherever the border is.
Member Is Offline
Mood: Dazed and confused.
|
|
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.
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
|
|
|
EF2000
Hazard to Others
Posts: 153
Registered: 10-5-2023
Location: The Steppes
Member Is Offline
Mood: Taste testing the Tonka fuel
|
|
When you use standard permanganate solution that was stored, you need to filter it through some inorganic filter, like glass wool.
Wroom wroom
"The practice of pouring yourself alcohol from a rocket fuel tank is to be strongly condemned encouraged"
-R-1 User's Guide
|
|
|
Bedlasky
International Hazard
Posts: 1233
Registered: 15-4-2019
Location: Period 5, group 6
Member Is Offline
Mood: Volatile
|
|
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
International Hazard
Posts: 1135
Registered: 8-10-2003
Location: GroupVII of the periodic table
Member Is Offline
Mood: Stoichiometrically Balanced
|
|
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.
Fellow molecular manipulator
|
|
|
Bedlasky
International Hazard
Posts: 1233
Registered: 15-4-2019
Location: Period 5, group 6
Member Is Offline
Mood: Volatile
|
|
You can titrate Mohr's salt with permanganate.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
