# What chemical would can change color back and forth in water?

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Hello,

What kind of chemical would be able to be put in water, in a see-thru tube, and as it passes a certain point, through some force whether magnetic or heat or something, it changes color. I mean it has to be visible color change.

The water is in a loop and needs to be able to change back and forth in color.. it doesn't necessarily need to be color.. maybe turns really murky or really dark or something.

Nothing can be added to the tube to change it after the assembly.. this colour change needs to be done by something outside of the tube.

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Hmmm... Just an idea, but it Might be worth looking into Liquid Crystal technology and modifying the design a little so the principals still apply.

eitherway, I expect youll need some form of polarisation filters in place rather than rely on a Chemical reaction.

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I was thinking you can achieve a similar effect with liquid crystals, but it's a bit more complicated than what you seem to be wanting (you need polarisers)... But you can change the director (and the polarisation conversion) just by applying an electric field.

Also an issue with flowing liquid crystals is that changes their director profile, and this is not well understood (one of my friends works on this)... So it'd be guess work, with trial and error....

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Is this for a demonstration of some sort? If so, what if you used some temperature sensitive ink as a coating on the tube? As the warm water passes, it will heat the tube, causing the ink to change color.

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A reversible photochemical change could do the trick (something akin to the reaction of retinal in the eye). I don't know any such compounds off the top of my head, but they do exist.

There's also the option of setting up a chemical oscillator, but this changes colour with a certain frequency rather than responding to a stimulus.

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Concentrated aqueous solutions of Cobalt chloride or Copper chloride will change color upon heating. Lower temperatures favor more water ligands around the metal ion, while higher termperatures favor chloride ligands. Cold CoCl2 solutions are pink, but become blue upon heating. CuCl2 solutions are blue when cold and become increasingly green when heated. This is a large temperature swing though and perhaps unsuitable for what you want.

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to add to the above, you can set the point at which the color changes with Cobalt Chloride by altering the solvent its dissolved in, in Ethanol the color change requires below freezing temps

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How about a Briggs-Rauscher reaction? It would require no input besides the three chemicals, and changes colors repeatedly by itself.

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Thanks. \Concentrated aqueous solutions of Cobalt chloride\ seems to be my best bet! Thanks for the help, ill look into it and get back to ya'll with more Q's.

Edited by Jesse.J
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• 2 weeks later...

By any chance, are you thinking of a BZ reaction? oscillates in color back and forth...

http://en.wikipedia.org/wiki/Belousov-Zhabotinsky_reaction

It's really quite remarkable, colors oscillate for quite a while

Merged post follows:

Consecutive posts merged

actually in that video, they only oscillate once, but just type bz reaction you should get quite a bit.

i believe they all have something to do with bromine and different colored cations

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