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Questions tagged [color]

Questions where color (wavelengths associated with the visible region of the electromagnetic spectrum of about 400-800nm), or a color change is discussed.

60 questions with no upvoted or accepted answers
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10
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131 views

Color of methoxy substituted phenyl rings when heated in the presence of acid

Anyone who's familiar with organic synthesis will probably have came across the DMB and PMB protecting groups. When TLC-ing compounds containing these protecting groups using common stains like ...
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109 views

Green colour resulting from the formation of pi complex

Peter Sykes mentions in Guidebook to Mechanism in Organic Chemistry (6th ed.) on p.132 that there would significant differences in physical properties of the resultant mixture when we: React ...
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404 views

Finding the wavelength of maximum absorption of Tartrazine using Fieser-Kuhn

How would you use Fieser-Kuhn rules to calculate the wavelength of maximum absorption for tartrazine? Fieser-Kuhn rules states that: $\lambda_{max}=114+5M+n(48-1.7n)-16.5\ R_{endo} - 10\ R_{exo}$ ...
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46 views

Why does my rainwater turn yellow if I increase the pH to 7?

My rainwater is colourless when collected, but if I add a small amount of sodium hydroxide to increase the pH to about 7, after a few days it goes yellow. The colour change happens more quickly if I ...
5
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0answers
200 views

What substances are typically used to produce cyan, magenta, and yellow ink?

Early in grade-school you learn blue, red, and yellow are the primary colors that can be used to produce any other color. If you're curious enough, you later learn the primary colors are actually cyan,...
5
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2answers
2k views

Why is anhydrous CuSO4 White while hydrated CuSO4 is Blue? (even though both have one unpaired electron)

We all know that $\ce{CuSO4.5H2O}$ is blue and it turns to $\ce{CuSO4}$ on heating which is white. I also learnt about coordination complexes and d-d transitions and how transition metal compounds are ...
4
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252 views

Mechanism of DPD (N,N-diethyl-p-phenylenediamine) reaction with free chlorine

NOTE: As I've been finding new informations about the question, I've been editing the question to keep it up to date. If some comment doesn't make sense just check the Edit History. DPD (N,N-diethyl-...
4
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2answers
557 views

Considering the d-d transition how, does tetracyanidonickelate(II) ion exist as a colored complex?

As I refer on google, the resources indicated that, the d block elements which have unpaired electrons as in their ions, when they are making complexes with ligands, they can absorb different ...
4
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174 views

Why does the electrolyte used in Lechlanché cell turn blue?

In my school there are jars which are turned into Lechlanché cells. Basically the cell has aqueous ammonium chloride solution as the electrolyte which is obviously transparent in the beginning. The ...
4
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2k views

Why is the geometry of [Ni(CN)4)]2- square planar? Why is it colorless?

Why is the geometry of $\ce{[Ni(CN)4)]^{2-}}$ square planar given that it has a coordination number of 4? Shouldn't its geometry be tetrahedral as it would minimise the bond angle and hence repulsion?...
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170 views

Can pure elements have different colors?

This question was inspired by this: Are there colorful metals besides gold and copper? I was wondering how the color of a pure element could be changed. I know that it is possible for color to change ...
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60 views

Dilute FeCl3 colour is darker at 5e-4M than at 5e-3M. Why?

I did two different dilutions of $\ce{FeCl3}$ (within a $\pu{1h}$ timespan) from $\pu{0.05 M}$, and the one with $\pu{5E-4 M}$ concentration looked a darker orange than the one with $\pu{5E-3 M}$. ...
3
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1answer
4k views

Explaining the colour change in the potassium permanganate titration of iron(II) ions

In the redox titration: $$\ce{MnO4- + 8 H+ + 5 Fe^2+ -> Mn^2+ + 4 H2O + 5 Fe^3+}$$ the colour change which occurs is purple to colourless, because of the decreased concentration of permanganate ...
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232 views

Why is nitrogen dioxide brown?

Nitrogen dioxide (NO2) is a reddish brown molecule, while its dimer nitrogen tetroxide (N2O4) is colorless. Can you give a reasonably detailed explanation for this from electronic structure theory? ...
3
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170 views

Explaining color differences using bond conjugation

I'd like to ask about how the color differences between the dyes methyl violet and malachite green can be explained. Looking at the conjugated bonds of each, methyl violet seems to be more conjugated ...
3
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328 views

How do counter-ions influence the color of coordination compounds?

I've been asking myself for a while now how counter-ions sometimes change the colors of coordination compounds. Like when I use d-metals as counter-ions to precipitate Cyanoferrates. I looked at ...
3
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86 views

Colour change on exposure to singlet oxygen?

Is there a dye that is particularly well suited to radical colour change on interaction with singlet oxygen, preferably non-toxic? Based on this answer: https://chemistry.stackexchange.com/a/27633/...
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355 views

How does a photochemical reaction of lignin with oxygen (yellowing of paper) produce chromophores?

Edit: This question is about chromophore production in lignin as found in low cost or short-term use paper such as newsprint. A different, excellent answer describes oxidation yellowing of the ...
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45 views

Trouble understanding Bradford Assay

From what I understand, the Bradford reagent contains Coomassie Brilliant Blue in an acidic solution so both of the (sulfonic acid groups? I'm not sure if this is the correct name- I can't seem to ...
3
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0answers
672 views

How does the “methylamine test for sugars” work exactly?

There is a test that enables distinction of sugars between mono- and oligosachharides. It consists letting methylamine react with an aqueous solution of the sugar under alkalic conditions and ...
2
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0answers
44 views

What is the right color of calcium copper titanate?

I'm browsing Alibaba for calcium copper titanium oxide $\ce{CaCu3Ti4O12}$ (CCTO) and I find it variety of colors: pure brown, pale brown, reddish brown or grayish dark brown. Wikipedia does not tell ...
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31 views

Reduction of triphenylmethane dyes in ink

Right now I'm trying to explain why the ink from an ink pen turns colourless in water. I know that the pH is responsible as it breaks apart the conjugated system of double bonds. I'm just not sure on ...
2
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0answers
227 views

Why does LDA solution gradually turn dark brown?

LDA (lithium diisopropylamide) solution in THF/hexane gradually turns red-brown liquid. Especially commercially available one is extremely dark red-brown. What makes it brown? I've searched online ...
2
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0answers
32 views

Benzophenone Ketyl color origin

I was recently preparing the benzophenone ketyl radical by reacting it with sodium in toluene. Although this compound is really well known and it seems somewhat obvious and accepted in literature that ...
2
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0answers
63 views

Color Visible in Large Quantities of Ethanol

I am currently writing a sci-fi novel and have come upon a rather ponderous question that I have thus been incapable of discerning an answer for. If a planet were to have oceans composed not of water, ...
2
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0answers
307 views

Why is silver chromate red?

Copper(II) ions are blue and chromate(VI) ions are yellow therefore copper(II) chromate(VI) would turn out to be green because it's a mixture of blue and yellow. In the same way, silver ions are ...
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84 views

Do filter-specific dyes exist? Equivalently, do dye-specific filters exist?

Apologies if this isn't chemistry enough for chemistry.se. I'm happy to go elsewhere if there are suggestions. Blue + Red = Purple is arbitrary here. If any different colors might make this more ...
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0answers
318 views

Difference in color between the chromate and permanganate ions

As the title states, I'm wondering why the $\ce{[CrO4]^2-}$ and $\ce{[MnO4]-}$ ions display different colors in solution. Both of the metal ions have a $\mathrm{d}^0$ electron configuration, have the ...
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0answers
59 views

Looking for an isomerization reaction that involves a color change for classroom demonstration purposes

I am in the process of designing a chemical kinetics course for undergraduates. I would like to demonstrate isomerization equilibria, and therefore am looking for a reaction A <-> B fulfilling the ...
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0answers
106 views

Why most excreta are brown?

This might sound funny but my friend asked me why most - if not every - faeces are of a brown or brownish color? Why not grey or slightly bluish or green for example? Is there any simple scientific ...
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0answers
253 views

Why does egg yolk turn white when washed with water?

I recently noticed that whenever I washed the egg yolk stuck on some utensils the water becomes milky white. It has to be the egg yolk that turns white and give off the white color to water right?
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0answers
154 views

What reaction took place?

Okay, so I was fiddling about in the chemistry lab, and I added: Sodium Nitroprusside (soln) $\ce{Na_2[Fe(CN)_5NO]}$ with Potassium Ferrocyanide (soln) $\ce{K_4[Fe(CN)_6]}$. $\ce{Na_2[Fe(CN)_5NO]}$ ...
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0answers
25 views

Mixing ink with alcohol, MEG and water

First of all, I'm not a chemist and my knowledge in chemistry is not that extensive. However, I would like ask the following question: are there any chemical reasons that would explain that mixing a ...
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0answers
33 views

Comparing the emission spectrum of ethanol and mixture of alcohols

Sorry if this question has a simple answer, but I've been unable to find it elsewhere. Using a diffraction grating, burning ethanol (99.9%) will produce a rainbow of colours. However, when burning ...
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0answers
34 views

When can colourimetry be used to determine the rate of reaction?

Can colourimetry be used if a coloured reactant react to give a coloured product? For example, in the reaction of reacting dichromate ions with oxalate ions in acidic environment, where dichormate ...
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0answers
85 views

Why does blood turn reddish brown?

Why does blood take on such a colour after a couple of hours? Is this the iron in my blood being oxidised to iron (III) oxide or is this something else? I have checked this article, and no I do not ...
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0answers
100 views

White compound, insoluble in water, turns pink and then white again on adding water

Which white, ionic compound(s) that is insoluble in water turns pink when you add only a little of water but white again when you add more water? I know that the cation is one of the following: $$\...
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0answers
96 views

How to rationalize the colour change of the thermochromic bis(diethyl-ammonium) tetrachloridocuprate(II) complex

The colour of the compound changes from deep green/green-blue to yellow upon raising the temperature. I'm trying to rationalise this by using the d-orbital splitting, but I've got myself in a logic ...
1
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0answers
33 views

How to safely change the color of a fire tornado?

So I've been watching a lot of fire tornado videos and I came across one that had a reasonable and safe setup (around the 3:23 mark): Fire Tornado DIY Is there a way to change the color of the fire ...
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0answers
56 views

Krazy Glue Color Change

A type of Krazy Glue changes from purple to clear when it dries. What is the chemistry behind the color change? Is it due to a particular compound only found in this particular Glue? A description of ...
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0answers
57 views

Coordination Chemistry: Predict colors (simple model, old)

I remember many years ago, when I prepared for a talk on coordination chemistry I found a PDF with a theory about how to predict the colors of simple coordination compounds. I remember the name of the ...
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0answers
143 views

Problem in Colour in Cerium (IV)Sulphate due to charge transfer

My text says that $\ce{Ce(SO4)2}$ is coloured due to charge transfer spectra. It also gives other examples such as $\ce{KMnO_4}$ and $\ce{K_2Cr_2O_7}$, to which I agree but when I read the conditions ...
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0answers
430 views

Ultramarine blue colour absorbing agent

Ultramarine blue ($\ce{Na2Al2SiO8 + Na2S}$, a sulfide-silicate complex containing sodium and aluminium) is insoluble when mixed in water and gives a blue color appearance to the water solution. ...
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0answers
104 views

Are there art supplies that create a new color by mixing through a chemical reaction?

When two elements or compounds react together, they form new compounds, which more often than not assume new colors. If the two elements or compounds don't react, they form uniform or non-uniform ...
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0answers
340 views

What gives variations in the color of cadmium sulfide paint pigment?

Oil paint manufacturers sometimes make several "shades" of a color, all of which list the exact same chemical ingredient. For example, look at Gamblin's artist grade oils, in the yellow colors, ...
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0answers
52 views

Origin of different colour for thio analogue of indigo from blue to red

Why the thio analogue of indigo is red? What is the reason behind change of colour from indigo to red just by change of N to S. What I get is that there will be electronegativity, lone pair ...
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0answers
746 views

Predict flame test color?

If you know the composition of any sample of compound, is it possible to predict it's flame test color? For eg, if you can given Sodium Chloride, then without actually doing the flame test, can you ...
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0answers
59 views

How to choose a colorant for a given substrate?

I know there are volumes of International Colour Index (homepage, wiki, paper), but I can't really extract from there for example what red colorants are compatible with both silk and polyester, etc. ...
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19 views

What solvents can solve aromatic urethane resins?

Do you have any information about chemical resistance of hexa-functional aromatic urethane acrylate? I want to know what solvents can solve aromatic urethane resins.
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48 views

Does something like a fluorescent foil or a fluorescent film exist?

During my experiments I want the emitted laser beams to come back with a different wavelength than the original wavelength using a fluorescent foil or fluorescent film. The laser I'm currently using ...