Sciencemadness Discussion Board

Looking for a chemical that can be sprayed a color but then turn clear when dry?

ThomasJPeriodical - 4-1-2016 at 13:52

Hello,

My name is Thomas, and am very curious about chemicals. I'm doing some at home experiments with my young children and trying to see if any non-harmful chemicals can be sprayed from a plastic dispenser (air tight) and turn a color once hitting the air (oxygen), but then turn Clear when the chemical has become dry. Does anyone have any insight on this? Or any other ideas or suggestions?

My chemical knowledge is pretty minimal - but I thought I'd try reaching out to everyone on here!

Thank you,
Thomas

mayko - 4-1-2016 at 14:40

For a substance that sprays on colored and dries to colorless (as in your title), the first thing that comes to mind is a solution of ammonia and phenolphthalein. This is pink, but loses its color as the ammonia evaporates.

The body of your message suggests there might be further constraints (that the liquid be colorless beforehand, that it become colored in reponse to oxygen specifically) which would complicate things. Are these constraints essential? (maybe tell us more about your end goal)

BromicAcid - 4-1-2016 at 15:38

Check out the blue bottle experiment. Traditionally performed in a flask, the mixture is initially blue but on standing turns colorless, the blue color can be restored by shaking. The colorless solution when sprayed should become blue but it will unfortunately stay blue.

careysub - 4-1-2016 at 15:49

Back in the 1960s, when I was a child, there was a "fake blood" product that was red in the bottle, but when squirted on something would decolorize in seconds.

Now you have me wondering what was in it - a little Googling does not turn up a likely reaction right away.

[Now that I think about it sounds like it could be the phenolphthalein/ammonia system in the first post. that did not occur to me at first since I think of phenolthalein as being purplish and not red.

I wonder it anyone would make an phenolphthalein/ammonia for kids to squirt at each other any more. ]

There are also other redox indicator dyes (like methylene blue), some of which are colorless in its oxidized form. The Wikipedia page on redox indicators:
https://en.wikipedia.org/wiki/Redox_indicator
does not list one that is red when reduced, but colorless when oxidized. Viologen though is blue when reduced, and colorless when oxidized (but is listed as being "toxic").

https://en.wikipedia.org/wiki/Viologen

Getting something that changes from colorless to a color and back to colorless would be a bit more of a trick.

[Edited on 5-1-2016 by careysub]

[Edited on 5-1-2016 by careysub]

mayko - 4-1-2016 at 16:06

Quote: Originally posted by careysub  
Back in the 1960s, when I was a child, there was a "fake blood" product that was red in the bottle, but when squirted on something would decolorize in seconds. Wonder if they could sell that now.

Now you have me wondering what was in it - a little Googling does not turn up a likely reaction right away.



I've never seen fake blood, but disappearing ink appears to still be available:
http://www.thingsyouneverknew.com/product/disappearing+ink+p...
(It's also a plot driver in Who Framed Roger Rabbit?)

I'm not sure what is in that particular product, but most of the google hits for disappering ink recipe involve thymolphthalein or phenolphthalein.

btw, a related chem demo is to paint a piece of paper with different, colorless indicators, and then 'develop' it by spraying with a dilute sodium hydroxide or ammonia solution.

Be careful not to inhale the aerosolsized liquids!

[Edited on 5-1-2016 by mayko]

careysub - 4-1-2016 at 16:23

A particularly notable color changing reaction is the theatrical stigmata reaction: thiocyanate plus iron(III) ions, both colorless, produces a convincing looking blood when mixed.

A typical set-up would be to paint one surface with ammonium or potassium thiocyanate, and then bring a rubber dagger painted with an iron(III) salt (chloride perhaps) in contact, producing a bright red streak.

What makes this reaction especially interesting from a scientific point of view is that the colored iron thiocyanate complex that produces the blood color is very similar to what produces the blood color of actual blood: 4 nitrogens bonded to an Fe(II) ion.

Etaoin Shrdlu - 4-1-2016 at 16:24

On a tangent, you may find yourself interested in cyanotypes. https://en.m.wikipedia.org/wiki/Cyanotype

Very cool, very easy to do at home.

Looking for a chemical that can be sprayed a color but then turn clear when dry?

ThomasJPeriodical - 4-1-2016 at 19:38

Quote: Originally posted by mayko  
For a substance that sprays on colored and dries to colorless (as in your title), the first thing that comes to mind is a solution of ammonia and phenolphthalein. This is pink, but loses its color as the ammonia evaporates.

The body of your message suggests there might be further constraints (that the liquid be colorless beforehand, that it become colored in reponse to oxygen specifically) which would complicate things. Are these constraints essential? (maybe tell us more about your end goal)


Thank you Mayko and everyone else for all for the fast responses. Would you be able to mix alcohol with this or would that contaminate the ammonia and phenolphthalein and ruin he color and the experiment?

careysub - 5-1-2016 at 06:48

Quote: Originally posted by ThomasJPeriodical  

Thank you Mayko and everyone else for all for the fast responses. Would you be able to mix alcohol with this or would that contaminate the ammonia and phenolphthalein and ruin he color and the experiment?


Alcohol is no problem. Phenolphthalein is commonly dissolved in ethanol or some other alcohol as the preferred method of preparation of lab use.