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.

63 questions with no upvoted or accepted answers
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11
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158 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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601 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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154 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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375 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,...
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59 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 ...
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1k views

Why is hexacyanoferrate(II) colored and at the same time diamagnetic?

I am wondering why $\ce{[Fe(CN)6]^4-}$ is colored and at the same time diamagnetic. For a transition metal to be diamagnetic all the electrons should be paired up in the d orbitals and at the same ...
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65 views

Why does my drierite turn bright bright blue, instead of pink?

Drierite a brand name of a commonly-used, calcium sulfate-based dessicant in many chemistry labs. The lab I work in has a dessicator box we use to store hygroscopic materials. It isn't a a true dry ...
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2k 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-...
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448 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? ...
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213 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 ...
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3k 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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191 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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118 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 $\pu{5E-3 M}$. ...
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240 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 ...
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439 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 ...
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101 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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475 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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49 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 ...
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1k 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 ...
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179 views

Colour of VO3^-?

To aquire the yellow colour of vanadium ion, it must be present in a 5+ oxdiation state. This can be acheived (according to my textbook) by adding dilute sulfuric acid to $\ce{NH4VO3}$, then followed ...
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76 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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46 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 ...
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672 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 ...
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154 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, ...
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389 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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414 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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61 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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257 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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157 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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112 views

Why are polynuclear carbonyl complexes coloured?

We know that polynuclear carbonyls are colored and their intensity increases with increase in metal ions. But why does the color arise? I am aware that this is due to some transition between ...
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47 views

Why are Buckminsterfullerene (C60) solutions pink/purple?

A solution of Buckminsterfullerene $\ce{(C60)}$ is shown below: According to the April 8th Wikipedia page on Buckminsterfullerene $\ce{(C60)}$: Solutions of pure C60 have a deep purple color which ...
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77 views

Effect of optical isomerism on colour of transition metal complexes

I know that different stereoisomers of a given transition metal complex (cis- and trans- forms) have different colours. But do different optical isomers (non-superimposable mirror images) have ...
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49 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
46 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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56 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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180 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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132 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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147 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 ...
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0answers
36 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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58 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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64 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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275 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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659 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. Which ...
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121 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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356 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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57 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
605 views

Chemical reaction for the flow color change from blue to red and again to blue

I am trying to demonstrate color change in the liquid as it passes through a channel to demonstrate blood getting purified after passing through certain organs of the body. I want the initial color of ...
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0answers
859 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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108 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 ...