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#1
I was restandardising perchloric acid the other day and used crystal violet indicator; the method specified to an 'emerald green' endpoint. Now there was some confusion and conflicting ideas in the lab about what 'emerald green' was exactly. Is it that bluey turquoise or that bright apple-green? (I used the titre from the bright one, it was the logical choice after I did the calc's.)

Anyway my real reason for this post is this - does anyone know of a standard system whereby indicator colour changes are specifically linked to structure and the colour more specifically named? And some way of telling whether to go to the first or second change when a method does not say?

If there is nothing like this, then I will make my own
Last edited by mind_meld at Mar 13, 2015,
#3
mate just get a colour chart
It's over simplified, So what!

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#6
Um the chromophore of an organic molecule will absorb light of a certain wavelength. You can do UV/vis spectroscopy of coloured solutions to discover the absorbance or transmittance of the solution. Each colour has a wavelength of light associated with it in nanometers which corresponds to its position on the electromagnetic spectra. That's really how you standardise the colours. For example the wavelength of red light is around 650 nm.

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#8
But yeah the chromophores are typically in organic structures, made up of structures of benzene rings. The different groups surrounding the rings will change the electronic properties of the rings and the energy transitions of the electrons within the ring. Different transitions due to the energy gaps show will cause different

Changing the groups surrounding the chromophores (adding carbon chains, alkene groups, alcohol groups, basically different functionalities) will basically change the electronic properties of the chromophore leading to different energy gaps leading to different wavelengths of lights being absorbed/emitted.

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#9
the colour itself is associated with the molecule, the degree or colour change and intensity is related to the concentration of the molecule in the solvent. you can use the beer-lambert equations to determine the concentrations of the solutes
#10
funny E = cl

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#11
Quote by RedDeath9
the colour itself is associated with the molecule, the degree or colour change and intensity is related to the concentration of the molecule in the solvent. you can use the beer-lambert equations to determine the concentrations of the solutes


alternatively, use the beer-mouth process to determine how little you care
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#12
Quote by EndTheRapture51
But yeah the chromophores are typically in organic structures, made up of structures of benzene rings. The different groups surrounding the rings will change the electronic properties of the rings and the energy transitions of the electrons within the ring. Different transitions due to the energy gaps show will cause different

Changing the groups surrounding the chromophores (adding carbon chains, alkene groups, alcohol groups, basically different functionalities) will basically change the electronic properties of the chromophore leading to different energy gaps leading to different wavelengths of lights being absorbed/emitted.

i don't know what any of this means but it sounds cool
#13
Quote by mind_meld
I was restandardising perchloric acid the other day and used crystal violet indicator; the method specified to an 'emerald green' endpoint. Now there was some confusion and conflicting ideas in the lab about what 'emerald green' was exactly. Is it that bluey turquoise or that bright apple-green? (I used the titre from the bright one, it was the logical choice after I did the calc's.)

Emerald green is the more-saturated, brighter colour.

End points are usually when the colour first stays despite mixing. Like, when you're getting close you'll see the drop change colour and then immediately change back to the original colour. When it doesn't change back then you're at the end point.

Anyway my real reason for this post is this - does anyone know of a standard system whereby indicator colour changes are specifically linked to structure and the colour more specifically named?

Basically any organic indicator.
And some way of telling whether to go to the first or second change when a method does not say?

If there is nothing like this, then I will make my own

I don't fully understand what you're asking here. The first and second changes should occur at very different pHs and your indicator should specify.
#14
Quote by So-Cal
i don't know what any of this means but it sounds cool

Rocks is rocks and they got their own molecular makeup that can make colors and shit, but you can change that by pouring shit on the rocks. so you can't always rely on the name of the rock to match the color you're thinking of.
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#17
OK I understand how colour itself works, and chromophores, that's pretty basic (pardon the pun).

What I'm talking about it the subjectivity of it. So phenolphthalein is easy, it's either pink or clear. But crystal violet will go through several colours, and stay that colour unless more acid/base is added.

What I'm looking for is something that says ok the first colour means this, second means this... does this clarify things?? Like matching the colours on a pH indicator strip to the standard on the box or container or whatever.
#18
Quote by Victory2134
Rocks is rocks and they got their own molecular makeup that can make colors and shit, but you can change that by pouring shit on the rocks. so you can't always rely on the name of the rock to match the color you're thinking of.

cool
#19
Originally posted by metal4eva_22
End points are usually when the colour first stays despite mixing. Like, when you're getting close you'll see the drop change colour and then immediately change back to the original colour. When it doesn't change back then you're at the end point.


This has more or less always been my experience.

If you want to get serious about it, you could always use a spectrophotometer, but that seems unnecessary to me. >.>
Last edited by mmistermeh at Mar 13, 2015,
#20
I thought about running it on UV/Vis but it kind of doesn't matter, I just want to know at which point to stop. I've done several assays where the reaction is at equivalence at different points. The only reason I knew the bright green was the right one was because the concentration was lower as opposed to the deeper green titre .05mL previous.
#21
if it is asking for emerald green then they are asking for a green where you can no longer see any purple in it, it is pure green.

so yeah, add a few drops at a time until it stops changing color basically.

also dont ph strips usually come with a color chart? if you are really confused you could use that
Last edited by Dirge Humani at Mar 13, 2015,
#22
Thanks to everyone so far...

It's become apparent that the kind of thing I'm looking for doesn't exist so I guess there's a gap in the market now...

Now would be the right time to crack a pun about a pHd
#24
Quote by mind_meld
I thought about running it on UV/Vis but it kind of doesn't matter, I just want to know at which point to stop. I've done several assays where the reaction is at equivalence at different points. The only reason I knew the bright green was the right one was because the concentration was lower as opposed to the deeper green titre .05mL previous.


Just stop the reaction when the wavelength of light of the product is at a strong absorbance at a certain point. Same as when you'd take aliquots of a reaction and run them under IR spectroscopy and stop when all of your OH peaks had been converted into something else or similar.

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#25
I think I will actually do this, create some standard reference literature. I work in a pharmaceutical/manufacturing lab so I do something different every day, I might perform a test only once a year or use a reagent every two years so it's not like I can simply use experience. Also BP and USP can be vague at times.
#26
Quote by EndTheRapture51
Um the chromophore of an organic molecule will absorb light of a certain wavelength. You can do UV/vis spectroscopy of coloured solutions to discover the absorbance or transmittance of the solution. Each colour has a wavelength of light associated with it in nanometers which corresponds to its position on the electromagnetic spectra. That's really how you standardise the colours. For example the wavelength of red light is around 650 nm.


sounds like you just copied this out of your organic chem book.
#27
Quote by chev311e
sounds like you just copied this out of your organic chem book.


I am an organic chem textbook

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#28
I did not get any puns. I feel so stupid.
Maybe I am stupid since I went into a thread for scientists, while I myself am not a scientist
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#29
Quote by BjarnedeGraaf
I did not get any puns. I feel so stupid.

Maybe I am stupid since I went into a thread for scientists, while I myself am not a scientist


#30
I doubt this would help for your purposes but I did make a reference chart with uv vis when I was using dyes in organic waste purification experiments. I'd have 60 test tubes to compare at any given time and it just got annoying and messy since other people kept moving my equipment around so having this thing on hand was quite useful - I knew exactly which dilution to start with for the next stage or whatever instead of testing everything all over again.

Plus everyone in my lab started arguing over whether one of my test tubes was orange or yellow and where gold is and apparently they were still talking about it after I was done with my research so I'm glad I didn't have to rely on just the colors alone lol.
cat
#31
wait wait wait, I'm a computer scientist in a way.


Still did not get the puns though
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My beginner rig:

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Line 6 Spider IV (Don't judge me, I was young and stupid)
Stagg SW203N
Yamaha APX500
#32
I'm not a scientist, but this stuff is interesting. Please talk more about spectrophotometry and pH values and stuff, because I have to read about a lot of that stuff at work.
#34
pH is so dull so is UV/vis

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#36
Column chromotagraphy made me want to die. Either way I prefer using FTIR to follow reactions progress and NMR to confirm identity of products. UV/vis is useful I suppose but just a bit boring, there's so much more information you can extract from an IR spectra.

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#37
One of the first things they taught us was that if you aren't sure what an indicator looks like at the titration endpoint, just take a strong acid or base and put a drop of the indicator into it. Or write down the volume at what you think might be the equivalence point and add a few drops or the reagent to make sure.

Structure changes linked to color and samples of the specific colours of the indicator are almost always found on Wikipedia, unless you're using some obscure ass shit that your grandma found in the back of her cupboard.

But more importantly, how did you manage to find an entire lab of chemists that didn't know what emerald green looks like? Potassium manganate anyone?

I think Periodic Videos made a vid about it recently. I'll post a link to it here.

https://www.youtube.com/watch?v=uTVtBuY9Q-0


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Last edited by JamSessionFreak at Mar 15, 2015,
#38
I also hate indicators.

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#39
I do IRs all the time, so I get sick of them pretty quick, especially solids bleugh.
I use UV/Vis for colour value, dye content, ID (mostly just on alcohols) assays, etc. Never used NMR cos I don't work in research

I love GC-MS though
#40
How could you get sick of solid IRs it's so easy what's annoying is when you have to make a nujol mull up and get it to dissolve.

NMR is proper chemistry. MS is also pretty good if you'r just confirming based on other evidence, it's simple and a donkey can read the results but NMR analysis is significantly more tricky.

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