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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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8
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2answers
6k views

Why do alkyl bromides and iodides develop colour when exposed to light?

My book says alkyl halides are colourless when pure. However, bromides and iodides develop colour when exposed to light. Why do they develop colour when exposed to light? It is important to note that ...
8
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1answer
1k views

Very slow chemical clock reaction

I'd like to preface this with a declaration of my understanding that this is not necessarily possible. I was wondering if anyone knew of a chemical clock reaction where the period before the first ...
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2answers
1k views

Colour due to F-centre is same as that produced in a flame test, why?

I have noticed that the colours that the F-centres impart in Alkali metal halides are the same that the corresponding alkali metals impart to their flames. $\ce{NaCl}$ when heated in an atmosphere of ...
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0answers
782 views

What is the chemistry behind black colour of platinum black? [duplicate]

Platinum is a silvery white metal and is highly unreactive then why it's powdered form "platinum black" is platinum metal but is black in colour. why would a metal such as platinum become black as a ...
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3answers
12k views

What is the origin of the colour of azo dyes?

Is it the same reason as to why transition metal complexes have colour?
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2answers
3k views

Why lithium gives flame coloration?

Theoretically speaking, beryllium and magnesium does not give flame test because their atoms are comparatively smaller and the valance electrons are strongly attached to the nucleus. Therefore their ...
7
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3answers
7k views

How to determine bond length and angle in a conjugated pi-system (polymethine)?

I have a polymethine molecule with let's say 9 $\ce{C}$ atoms. $\ce{H-CH=CH-CH=CH-CH=CH-CH=CH-CH3}$ How can I calculate the length of the whole molecule? I need this number to compute the ...
7
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1answer
3k views

Why are compounds of V5+ and Cr6+ colored? [duplicate]

As far as my knowledge goes, transition metal complex ions show a color due to a transfer of electrons between the levels of split $\mathrm d$-orbitals. In the case of $\ce{V^5+}$ and $\ce{Cr^6+}$ ...
7
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2answers
2k views

Why is the photon energy of lithium flame coloring lower than that of cesium?

Why does $\ce{Li}$ give a red flame color which has lower photon energy compared to $\ce{Cs}$ which gives a violet flame color according to $E=h\nu$? This is my attempt: Since lithium has smaller ...
7
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1answer
88 views

Is there a known chemical that makes it possible to control the opacity of a large surface?

I have this idea of creating a large domed ceiling/roof for a building that can be made clear to see the actual sky, or made fully opaque/dark grey/black to project an artificial sky onto. I know ...
7
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1answer
1k views

Why does sunlight cause plastics to become a faded blue color?

Due to the UV absorption, I knew that the plastics can be easily affected, especially PP. But is it normal that the change is always into faded blue from white color? and Why? Because I made an ...
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1answer
1k 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
2k views

Why color of alkali metal peroxides, superoxides and ozonides deepens down the group?

This is basically a continuation of the question-"Why is potassium monoxide (K2O) coloured?" I knew that color of alkali metal oxides deepens down the group: Lithium oxide ($\ce{Li2O}$) is the ...
7
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1answer
1k views

Why does iodine have different colors in different media?

It is violet in trichloromethane, but brown in water. why? In the Shriver Atkins book, they tried to explain this using Molecular Orbital Theory which was not clear to me
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116 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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430 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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1answer
3k views

Why is tetrathiocyanatocobaltate(II) blue?

Why is $\ce{Co(SCN)_{4}^{2-}}$ blue? I simply can't predict the colors of such inorganic salts. I have learned that $\ce {Co^{2+}}$ salts are pink in color. Also, if the ligand is a strong field ...
6
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2answers
4k views

Yellow color of NaCl

My book says: $\ce{NaCl}$ shows metal excess defect, which results into the formation of an F-center in the crystal. This F-center is responsible for the yellow color of $\ce{NaCl}$. How does an F-...
6
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2answers
401 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. ...
6
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2answers
851 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 ...
6
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1answer
2k views

Color of Anhydrous Transition Metal Salt

Why are some anhydrous transition metal salts colored? Here are some examples I found. Anhydrous cobalt(II) chloride ($\ce{CoCl2}$), with sky-blue color. Anhydrous chromium(III) chloride ($\ce{CrCl3}...
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1answer
2k views

Can I synthesize iron acetate like this?

The oxidation state of the iron doesn't matter too much; I am just trying to make an attractive red-brown ink. Here are some instructions I prescribed to a friend. Here's an approximately decent ...
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2answers
1k views

What chemical compounds were used in CRT phosphors?

In the old days computer monitors and televisions were built from cathode ray tubes (CRTs) where the image was generated by an electron beam hitting phosphors which emitted light approximating the ...
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1answer
307 views

Colour of polytetrafluorethylene

Why are teflon coated dishes black or dark grey in colour when teflon as such is white (and the underlying aluminum is not black either)?
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1answer
1k views

Increasing Covalent character increases Colour intensity

I observed some trends as follows:- $\ce{PbCl2}$ white and $\ce{PbI2}$ yellow $\ce{SnCl2}$ white, $\ce{SnCl4}$ red and $\ce{SnI4}$ black $\ce{AgCl}$ white, $\ce{AgI}$, $\ce{AgBr}$ and $\ce{Ag2CO3}$ ...
6
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1answer
654 views

How can I make a black precipitate without a sulfide?

I'm supposed to make a black precipitate using only the following chemicals: copper sulfate(II), lead nitrate, acetic acid, barium chloride, sodium hydroxide, copper(II) carbonate, methanol, potassium ...
6
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1answer
92 views

What are the physical properties affected in ZnO when there is a sulfur impurity?

I have a question. I work at a brass metal foundry where one of our waste products is $\ce{ZnO}$, which we sell. Because we have been making new alloys which contain sulfur, our $\ce{ZnO}$ has a very ...
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4answers
312 views

Can you color a flame and what would the effects be?

I read this question (Flame temperature for cooking food) and came up with the following questions: Could companies color their flames so that products would heat quicker? How would they do this? ...
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3answers
5k views

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 $...
5
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1answer
234 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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1answer
1k views

why are simple organic molecules usually white?

I have heard that it is because they absorb electronically in the ultraviolet range, if this is true, why is it true. What is it about the nature of organic molecules that make them absorb in the ...
5
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1answer
343 views

Colour of colloids

Why colours of colloidal solutions are different when viewed along different directions? For example Milk appears blue when viewed by reflected light and red when viewed by transmitted light Is it ...
5
votes
1answer
812 views

Why is potassium monoxide (K2O) coloured?

Potassium monoxide is rarely formed and is a pale yellow solid. I don't understand how is this compound coloured because in oxide anion electron cannot excite in the next orbital due to huge energy ...
5
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1answer
222 views

Wavelengths of the visible spectrum

Why is data about wavelengths of different colors and the visible spectrum in general so different in different sources? On Wikipedia, the numbers differ by up to $\pm\mathrm{30~nm}$.
5
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3answers
4k views

Colour intensity of transition metal complexes

Even though they are both $\mathrm{d^7}$ complexes, the colour of $\ce{[Co(H2O)6]^2+}$ is pale whereas that of $\ce{[CoCl4]^2-}$ is more intense. Does the octahedral or tetrahedral geometry matter in ...
5
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1answer
585 views

What gives brown butter its color?

Brown butter is butter that has been heated until the water content has boiled off and the remaining liquid has turned brown. It is often called for in cooking and baking, for example in recipes for ...
5
votes
1answer
250 views

IR fluorescent material for outdoor use

I am experimenting with IR video cameras. They have a broad sensitivity peak at 940 nm. There is a filter blocking 750 nm and shorter in front of the sensor. I am looking for an IR fluorescent ...
5
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0answers
48 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
214 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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2answers
3k 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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1answer
659 views

What gives milk its characteristic white color?

The other day, my kid brother asked me this: What pigment gives milk a white color? Now, I found that particular question quite interesting since, as a student of Biology, I already had a rough ...
4
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1answer
2k views

Is chromium the shiniest metal?

I have seen many pictures of chromium, and it's pretty lustrous as I must say. Here are some examples. Is it the most lustrous metal known? Edit: By lustre, I mean suppose if we have a mirror ...
4
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2answers
677 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 ...
4
votes
1answer
137 views

What chemical properties that allow for colour exist in the dark?

Of course if there's no light around, there's no colour that you can see. On the other hand, the wall must have some property that makes it be blue. That property is still there in the dark. — ...
4
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1answer
2k views

What makes many water soluble fertilizers blue?

I've noticed that water soluble fertilizers tend to be blue. What chemicals or chemical reactions cause this color here? Is this necessary or for aesthetic purposes? I haven't seen this in organic ...
4
votes
1answer
111 views

Identify this solution

The solution is emerald green in colour. When added with water, it gives a pale blue solution When reacted with $\ce{BaCl2}$, it gives a sky blue solution and a white precipitate. When reacted with $...
4
votes
1answer
946 views

Why are HgO and CdS compounds colourful?

We know that the electron configuration in $3d$ orbitals of $\ce{Zn^2+}$, in $4d$ orbitals of $\ce{Cd^2+}$ and in $5d$ orbitals of $\ce{Hg^2+}$ ions are completely same. Then why the compounds of $\...
4
votes
1answer
186 views

Peroxide bleaching for bast fibres?

Is peroxide bleaching ($\ce{H2O2}$) suitable for treating bast fibres? I read that to be successful, it needs to be combined with chlorine bleaching. Because of the end usage, I don't want to use this ...
4
votes
2answers
27k views

Difference between white sugar, brown sugar and red sugar

I always get confusing why the appearance of normal sugar (the white one), brown sugar and red sugar are different although they are sugar. Is it because they each have different molecular formulae or ...
4
votes
1answer
801 views

The walls of a plastic vial with Mercury inside are darkening. What is causing this?

I have a sample of Mercury in a plastic vial, The vial is a BD Vacutainer (genuine), made of polyethylene terephthalate. It is used for blood samples, and the one I used was new. When the vial was ...