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Chem Science
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Help me identify this compound
I have this compound and dont know what it is. It a green powder that dissolves in water to give blue solution.
In acidic pH turns yellowIn (Reversible)
In basic pH turns colorless (Irreversible)
Here are some pictures. If you want i can do extra test and report back
  
[Edited on 21-8-2021 by Chem Science]
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unionised
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What happens if you heat it?
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Texium
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Any context on where you got it? Like, did it come from a lab, or did you find it in the trash?
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Jenks
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Bromophenol blue if yellow at pH 3 and blue at pH 4.6.
Bromocresol green is yellow at pH 4 and blue at pH 5.6.
Bromothymol blue is yellow at pH 6 and blue at pH 7.6.
Structures of all three are similar.
Source
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Texium
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Bromocresol green is a beige solid though, not green like pictured. I just used some yesterday.
Edit: I just found jars of the other two indicators at work, and bromophenol blue is a yellow/beige solid and bromthymol blue is a light pink solid.
Not that this unequivocally proves that what you have is not one of those three compounds, since the color of the solid may depend on hydration,
impurities, and whether or not it's in the salt form.
[Edited on 8-21-2021 by Texium]
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Tsjerk
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What I think is interesting is that the loss of color is irreversible. I have no idea what it could be however.
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unionised
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Quote: Originally posted by Tsjerk  | | What I think is interesting is that the loss of color is irreversible. I have no idea what it could be however. |
One thing it means is that the stuff probably isn't a normal pH indicator.
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Jenks
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The first picture looks like thymol blue on its wikipedia page. But thymol blue is red below pH 1.2, just as bromothymol blue turns magenta below pH 0.
So I think a couple tests that would help would be to see if the yellow color changes again to magenta or red on further acidification, and to find
the particular pH where the yellow changes to blue.
I didn't see anything on wikipedia about an indicator that is irreversibly decolorized when basic.
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Triflic Acid
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What base are you using?
Hope is not a reagent
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DraconicAcid
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He has bottles of hydrochloric acid and sodium hydroxide out, so those are probably what he used.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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NitratedKittens
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https://en.wikipedia.org/wiki/Malachite_green
This seems like a possibility. See if you can get the colour back from the alkaline solution by the use of an oxidising agent
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Chem Science
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Ok so answering the questions.
Texium: Yes it's from a lab, so it's a pure substance (I hope)
Tsjerk: Yea the loss of color is irreversible and also strike me.
unionised: Yeah i thought it was some sort of pH indicator but after seeing the base reaction made me think it may not be
Jenks: No the color at pH<1 is yellow 
NitrateKittens: Here are the results ..
  
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NitratedKittens
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Well that rules out formation of a leuco dye at high pH. Perhaps the color loss is due to hydrolysis.
Maybe the dye is an ester? If you have access to hydroxylamine and ferric chloride you could do the following test: https://www.youtube.com/watch?v=SymjxfSmN0E
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NitratedKittens
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Is the compound soluble in acetone just out of interest? If so does it display these same color changes under anhydrous conditions (HCl bubbling/use
of an amine)
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zed
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You have no idea?
Do a flame test. Try to rule out inorganic.
Organic? Do a melting point depression test, to approximate molecular wt..
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Texium
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I could have told you it isn’t malachite green to begin with. It’s truly green in solution, not blue like the picture here.
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Chem Science
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Here are some results:
Solubility
_Acetone: Soluble with purple colour
_Benzene: Insoluble
_Perchloroethylene: Insoluble
Beilstein Test NEGATIVE
Colurs in Acetone
Acetone Alone: Purple Colour
Acetone + Diethylamine = Colorless or slightly yellow
Acetone + Diethylamine + HCl = Blue colour to green
Hydrloxylamine Test
Unfortunately it seems like my hydroxylamine is no good because i ran the experiment with Iso-Amyl Acetate and it didn't work.
        
[Edited on 22-8-2021 by Chem Science]
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Chem Science
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I think it is Methylene Green. However i can't find much info about these compound.
If you have any info in these compound please share
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Jenks
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| Quote: Originally posted by Chem Science | I think it is Methylene Green. However i can't find much info about these compound.
If you have any info in these compound please share |
All I found was that methylene green powder is supposed to be black.
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Texium
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Well, if you want to take the boring but reliable route to identifying it, you could send me 10 milligrams in an envelope and I could run an NMR.
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Chem Science
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Ohh ... Well my powder is green.
But i did found that it does dissolve to give a blue solution, and these made me suspect it might be it.
| Quote: Originally posted by Texium | | Well, if you want to take the boring but reliable route to identifying it, you could send me 10 milligrams in an envelope and I could run an NMR.
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That's very nice, but im from Argentina, and i highly think it will be very difficult for me to send you a sample :'(
I'll see if i can pay an NMR and come back with it 
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Jenks
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I would be willing to cover shipping if you can take paypal or cash app.
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vano
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Hi. I also have green compound and I don't know what it's. It has very dark green colour and it is indicator. First photo: acidic, neutral, basic.
Basic solution is opaque. Also compound isn't very soluble in water.
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Texium
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| Quote: Originally posted by Chem Science |
That's very nice, but im from Argentina, and i highly think it will be very difficult for me to send you a sample :'(
I'll see if i can pay an NMR and come back with it |
Shipping shouldn’t be too bad if you can put it in a small envelope and send it by regular mail. Prices jump for actual packages.
From a quick Google search, I see postage of an envelope from Argentina to the US should be about $3-5 USD. Definitely would cost less than paying
someone to get an NMR for you, unless you know someone locally who can do it for free or cheap.
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Jenks
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| Quote: Originally posted by vano | | Hi. I also have green compound and I don't know what it's. It has very dark green colour and it is indicator. First photo: acidic, neutral, basic.
Basic solution is opaque. Also compound isn't very soluble in water. |
Can you use a second, known pH indicator (pH paper or pH meter) to determine at what pH the color of your unknown is changing? It would also help if
you could dilute the basified indicator to show what color it has become.
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