Life of weak (~1%) Potassium Ferricyanide solution?

[Steve Goldstein]

I believe the dry chemical in brown bottles keeps about forever with proper storage, but what about solutions? I'd like to keep some on hand to save mixing every time, but as I can't get into the darkroom frequently I'm concerned if it's likely to go bad over time. While it's not that expensive, I don't want to waste it.

Thanks.

 

[Gerald C Koch]

Not a problem IF the solution is protected from light and kept in a brown glass bottle.

 

[jochen]

Hello Steve,
i'd recommend not to store the solution for more than about a week. Always make only the amount you need in a forseeable time. The hexacyanoferrate(II) is light-sensitive and can be oxidized to iron (III) compounds, so a brown bottle is the least you can do.

 

[Steve Goldstein]

I do have appropriate small brown glass bottles for storage. Mainly I want to avoid the need to weigh out very tiny quantities like 0.25gm, which requires resolution better than my small electronic scale can provide.

How about a stronger ferri solution, like maybe 10%? Is there any storage advantage to that, again in a brown bottle? I have some small syringe bodies so measuring out 1-2 ml is not difficult.

 

[Steve Goldstein]

Problem solved. I didn't realize how cheap a scale with 0.01g could be. $10 including shipping on you-know-where.

 

[David Lyga]

Is 'you know where' Amazon or EBay? - David Lyga

 

[Steve Goldstein]

eBay in this case, I looked there first.

 

[Rudeofus]

I'd recommend not to store the solution for more than about a week. Always make only the amount you need in a forseeable time. The hexacyanoferrate(II) is light-sensitive and can be oxidized to iron (III) compounds, so a brown bottle is the least you can do.

Please note that Ferricyanide is the Fe-III complex (K3Fe(CN)6), so it won't be oxidized by O2.

 

[Doremus Scudder]

I don't know about a weak solution, but I have a PET bottle of ferricyanide/bromide bleach that I use for bleach-redevelopment that is well over two years old and still works fine. It's about 2% if I remember correctly.

Best,

Doremus


www.DoremusScudder.com

 

[RalphLambrecht]

from experience, i'd guess >1 year.

 

[Kirk Keyes]

Ferricyanide solution at 1000 ug/ml as CN only lasts about a week before it starts to form a precipitate. But that's only important when testing for CN...
For use as bleach, it's good for much longer. I'd say over a year, easy. But store in the dark, like in a cupboard.