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This might sound a silly question but....here goes....

how long does acidified potassium permanganate last or should it be made up fresh each time ?
Its for Yr 11/12 Chemistry

Thanks in anticipation for your answer

Hi Smee,
I make it up fresh each time. I use the recipe : 100mLs 0.01M KMnO4 + 17mLs conc Sulfuric acid. I just checked some I prepared on Wed, and it's gone clear already.
Cheers, Ellice.

According to these websites it is up to year but I make mine fresh
http://www.romil.com/Shelf_Life_SLV.pdf
http://chemistry.slss.ie/resources/down ... lflife.pdf

Hi All,

It is better to make it fresh as oxidation with natural/artificial light will cause the Permanganate to be reduced to manganate (Brown) solution rendering the solution not fit for use.

Overnight storage can be performed by storing it in the fridge.

Cheers,

Robb.....

How do you make acidified potassium permanganate?

Make up the desired strength ie 0.01M and add a few squirts of concentrated acid. I actually can't remember whether I use HCl or H2SO4, maybe it doesn't matter.

Hi,

If you do a search for acidified potassium permanganate you will find quite a few previous discussions with various recipes.
Good luck.

Lorrae

Hi all,

I have done a search here and found a couple of recipes, but does anyone have a tried and true recipe for acidified potassium permanganate?
I need it for Friday, so should it be made up freshly on Friday morning?

TIA,
Helen

Yes fresh is best

My Chem teacher gets his students to acidify it themselves - 4mL 0.1M potassium permanganate (which I supply) and they add 2mL 1M sulfuric acid.
Too easy!

Thanks Merilyn and Labbie!

Hi. Just wanting to ask another question about this. What happens to the acidified potassium permanganate over time that necessitates making it up fresh? Does it just neutralise, so go back to unacidified, or does something else happen? Just wondering if I had some bottles of "acidified potassium permanganate" made up ages ago, can I just add some additional concentrated sulfuric acid to that freshly, or would that not work?

Also wondering, if this is not possible, what should I do with excess "acidified potassium permanganate" that is not able to be used anymore?

Thanks!

OK, have done a bit more research and I think it's the actual potassium permanganate that degrades over time. Does the acid accelerate this maybe? The non-acidified solution that we have is still nice and purple, but the dropper bottles labelled acidified are all clear with brown precipitate, so they're no good.

This from RiskAssess for KMnO4 >0.38M disposal - <60 mL/day may be diluted with 10 times the volume of water and poured down the drain. Larger volumes should be placed in a Manganese waste container.
Also from RiskAssess regarding the permanganate ion - Highly toxic to aquatic life, but reacts in sewer with organic
matter to form Mn(II) and MnO2.
For sulfuric acid <1.7M - <60 mL/day may be added slowly, with stirring, to 10 times the volume of water, then poured down the drain. Larger quantities should be placed in an Acid waste container.
So my advice is chuck it down the sink.
With regard to your original question of why this solution is made fresh - I have no idea. Hopefully someone will know and will post an answer.

Also check 'potassium permanganate disposal' in this forum.