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Liquid color change brown to clear

Liquid color change brown to clear

Liquid color change brown to clear

(OP)
To symbolically demonstrate the neutralization of a waste water stream I want to have a transparent vessel of water change from brown to clear after adding a clear liquid. I have found some indicators that will go from yellow to clear that I will use in a pinch (p-nitrophenol) but I would prefer brown. Any tips? Maybe with potassium iodide?

tia, Peter

RE: Liquid color change brown to clear

Perhaps tea?  May not turn completely clear, but it is a brown pH indicator.

Aaron A. Spearin
ASQ CSSBB
www.Engineering6ss.com

"The only constant in life is change." -Bruce Lee

RE: Liquid color change brown to clear

(OP)
Thanks for the tip. I didn't know tea reacts to pH.
The setup is working now with a diluted iodine solution. After I add sodium thiosulfate it reacts and the solution goes clear. Your suggestion is a bit less poisonous though.

Peter

RE: Liquid color change brown to clear

Maybe you can use an iron laden solution. The addition of HCL will dissolve the iron. Iron is reddish brown.

RE: Liquid color change brown to clear

Unfortunately "brown" isn't a pure colour:  you need orange and green, or perhaps red and green, to get that sort of "dirty" colour.  Maybe fluorescein (going from colourless to fluorescent green from pH 4 to pH 4.5) mixed with ethyl red (going from colourless at pH 4 to red at pH 5.8) would give you the brown colour at neutral pH you want.  Add acid and voila, colour goes away- but probably not leaving a totally clear and colourless solution.  Neither of them are particularly toxic.

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