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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.

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Blue color in the blue persian salt

Blue persian salt has tiny blue framgents. So far I could found two explanations: It is sylvinite mineral inclusions As said in Wikipedia, "The intriguing blue colour occurs during the forming of ...
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Metal colored flame and safety

For Chrismtas I was a given a wonderful gas lighter, that produced a pink flame by heating small metal pads (when the pads are cold, the flame is blue, once they are red hot, the flame is colored). ...
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What explains the stark white colour of my iodometric titration analyte solution?

During my Advanced Higher (secondary school) investigation, I reacted pure copper with concentrated nitric acid to acquire a copper nitrate solution. This was neutralised with excess sodium carbonate ...
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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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Why does cooked liver turn green after a while?

I've noticed that cooked liver tends to turn green if not consumed shortly after cooking. The picture below shows cooked pork liver with green patches which developed after being chopped into pieces ...
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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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29 views

Will UVC light/ozone affects color on fabrics?

I'm planning to put a low power UVC light bulb into my wardrobe to kill bacteria and prevent bad smell on clothes but I'm wondering will it affect color on the clothes? I've done some research but ...
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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 ...
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1answer
866 views

Colour of platinum

Why does platinum have silvery shine whereas platinum black (finely powdered platinum) is black in colour although both have the same constitution of pure platinum? Due to similar composition, both ...
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1answer
59 views

Is a hue indistinguishable from its equivalent frequency of light?

A hue is the color characteristic of a pigment, a particular chemical molecule, when illuminated by sunlight. Of course such a molecule will not emit a single frequency of light, but will emit a ...
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1answer
31 views

Pigmentation of aromates [closed]

So, they try to color naftalene, nitrobenzeen and benzene. Only one of them colors. They can say with certainty that this is nitrobenzeen. Right/wrong and why? Sorry if my English isn't that great, ...
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What does “off-hue” constitute in the context of analyzing a sample using the Pt-Co color scale?

ASTM D1209, the method describing how to perform the Pt-Co color scale test for a sample, recommends reporting material that can't be matched to a particular standard as "off-hue". For color based ...
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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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27 views

What decrease the whiteness index of virgin PTFE powder?

I have a friend doing PTFE recycling where scrap PTFE were grind into powder form in a grinding machine where tab water is used for machine cooling. I had been told that high TDS (total dissolved ...
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1answer
285 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 ...
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1answer
314 views

Why does molten salt turn black?

Lately I have been seeing quite a few videos on YouTube about molten salt, specifically table salt (NaCl). One of the things that interests me about it is that regardless of what melting technique or ...
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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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3answers
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What exactly is formed when K2Cr2O7 is reduced?

I read on Wikipedia and in many books that when $\ce{K2Cr2O7}$ is reduced, it forms $\ce{Cr^3+}$ and a change is noticed from orange color to green. I want to know in what exact complex/salt/compound $...
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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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1answer
1k views

Explaining the colour change in the potassium permanganate titration of Fe2+ ions

In the redox titration: $$\ce{MnO4- + 8H+ + 5Fe^2+ -> Mn^2+ + 4H2O + 5Fe^3+}$$ the colour change which occurs is purple to colourless, because of the decreased concentration of permanganate ions. ...
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70 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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1answer
629 views

Is chromium (III) green or violet in solution? [duplicate]

Is chromium (III) green or violet in solution? In terms of oxidation reactions between chromate and $\ce{Cr}$ (III) it forms a green color in solution, but when I searched online in different sources ...
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1answer
100 views

Why does the gas from dry ice flow down?

I am reading Dan Broughton's answer in replying to the question "why does the gas from dry ice flow down" here. According to the answer, the fog is water's color and water is condensed and suspended ...
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1answer
446 views

Colored Flames Experiment

I am going to be doing a gender reveal for my sister's pregnancy. To do this, we wanted to light a huge fire pit and throw in a chemical to change the fire into the color (red/pink for girl, blue/...
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2answers
243 views

Producing sulphur dioxide for using in a reaction

I am doing an investigatory project on studying the coloured reactions of d-block and f-block elements. I have included two reactions that require sulphur dioxide as a part of my study. $$\ce{5SO2 ...
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2answers
751 views

Why is a [Cu(SCN)2] complex black?

I've been creating various Copper(II) complexes using different ligands and predicting their relative hues using Crystal Field Theory by using the spectrochemical series to predict the extent of d ...
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3answers
92 views

When an electron returns to it's ground state does it release the same wavelength of light that promoted it in the first place?

If this is true, I fail to understand why we see colour at all -- wouldn't any wavelengths absorbed by electron promotion be inconsequential to colour because there would an equal amount, and ...
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1answer
196 views

Material that changes color when changing phase from solid to liquid [closed]

I was asked and am wondering myself, what are materials that change color when molten? I could not find any examples online, but it really interests me. I would to get some examples which have one ...
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23 views

Chemistry d block [duplicate]

In, transition metals, they show coloured compounds Why do some of them do not show any colour. Why ti3+ shows colour as it does not have any electron in d orbital and what is zn2+ colorless
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286 views

Why do transition metals make colored compounds despite the remaining d orbitals being hybridized? [closed]

I know that transition metals make colored compounds when they forms a bond with a ligand, as the ligand increases the energy level of $\ce{d_{x^2-y^2}}$ and $\ce{d_{z^2}}$ orbital by repelling these ...
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1answer
53 views

Prevent/Slow down oxidation of organic material

I'm having the hobby to draw paintings with the tea I drink trough the day. Usually I pour a tablespoon of the hot tea away, wait until it dries and gets more concentrated, so the colour is more ...
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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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1answer
153 views

Why objects usually don't exibit fluorescence/phosphorescence?

We learn in school that the color we perceive is determined by the light that is reflected back at us. Not all wavelengths of light reflect back at our eyes, some wavelengths are absorbed. I'm ...
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515 views

In the blue bottle experiment, will it eventually be “used up” after repeated use?

The blue bottle experiment is a bottle half full of a colorless solution (dextrose, KOH, and methylene blue, in the version that I saw) and air that, when shaken, turns blue through the methylene blue ...
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0answers
135 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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169 views

Changing the color of bismuth crystals

Could someone please help me with a project? I can quite confidently grow bismuth crystals with the usual violet, purple, and blue colours (and in the very centre green), but how can I obtain just ...
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291 views

HOMO Odd, LUMO Even: Why does the affected orbital change depending on the carbon? How are carbons numbered?

While looking at how substituents affect the absorption spectra of molecules, I came across this: Substituents alter the emitted wavelengths of these molecules by affecting the electron densities. ...
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133 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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253 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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2answers
425 views

What causes the yellow colour in the Briggs-Rauscher oscillating reaction?

The color changes are due to different concentrations of supposedly $\ce{I2}$ (which causes the yellow/amber color), $\ce{I-}$ (colorless) and $\ce{I3-}$ (dark blue). Since iodine ($\ce{I2}$) is ...
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1answer
221 views

Lack of colour in Nitric Oxide

Usually compounds' colours are explained by the presence of unpaired electrons which is free to excite and de-excite giving the compound a charectistic colour. NO has atleast one unpaired electron but ...
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101 views

Anthracine blue composition

In 1873 a German chemist named Springmühl announced a derivative of alizarin which acted as a blue dye and he sold this dye for a high price. The dye was sometimes called "anthracine blue" and ...
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1answer
1k views

Which compound or compounds are responsible for color change in blue butterfly pea flower tea?

Blue Butterfly Pea flower tea is blue by default. Add citrus juice and it turns purple. What compound or compounds are responsible for this reaction to change in pH? Wikipedia doesn't say, nor can I ...
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1answer
574 views

Colour change of fluorescein in acidic and basic medium

I prepared fluorescein for my chemistry project in school and I realised that this molecule and its preparation steps are very closely related to that of phenolphthalein. I have studied briefly about ...
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1answer
465 views

Ethanol discolored yellow when stored with a rubber stopper. Forming fine white precipitate when added to water

I stored some Klean-Strip denatured alcohol in a test tube and capped it with a rubber stopper. I did this in preparation for a chemistry demonstration. When I opened my kit a few days later at the ...
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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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2answers
793 views

Chemistry behind lip balm coloring based on skin pH

I stumbled across an ad for a clear, colorless lip balm that purportedly tints your lips a shade of pink determined by your skin's pH. This balm stain applies on clear then reacts with your skin's ...
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121 views

Transition Metals that react with Vanillin and their Complexes [closed]

My question is simply whether anyone knows what are the transition metals that the phenol group of the vanillin molecule could react with, and thereby produce discolorations. This question is ...
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How do colour pigments chemically work? [closed]

How do color pigments colour the plastics? Is there any chemical reaction, molecular association, or physical reaction? What kind of bonding mechanism is there between pigment molecules and plastics? ...
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1answer
2k views

Bleach turned towel bright pink before fading to white

We have some relatively new white towels that were getting dirty, so we decided to clean them with bleach (standard Clorox). When we sprayed the diluted bleach on the towels they immediately turned ...