Liquid color change brown to clear

[opwierde]

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

 

[aspearin1]

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

Aaron A. Spearin
ASQ CSSBB

http://www.Engineering6ss.com

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

 

[opwierde]

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

 

[bimr]

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

 

[moltenmetal]

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.