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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1answer
65 views

Why are porphyrins colored when porphyrinogens are colorless?

In heme synthesis, porphyrinogens are colorless but upon their oxidation (from removing 6 hydrogen atoms), they become colored porphyrins. Why does the change in color occur? Is red the only color it ...
0
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0answers
21 views

What determines the color of a object? [duplicate]

Why is gold yellow for example? Which property of the atom determines the color?
9
votes
3answers
89 views

Is there a gas with metallic luster?

We know that both solids and liquids can exhibit metallic luster. I wonder whether there is a gas that when filling a transparent envelope (such as a glass tube) would make it appear with metallic ...
3
votes
1answer
186 views

Yellow Color of NaCl

My book says - "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 NaCl." My question is, how does an ...
9
votes
1answer
93 views

What color is solid methane?

Is it blueish, perfect white or some other color? I am interested because some celestial bodies are said to be covered with methane ice.
0
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0answers
12 views

Absorbance of dpph test for antioxidant activity

What is the range absorbance for essential oil sample in dpph test (antioxidant activity)? My absorbance was 1.322. And the inhibition concentration was 21.121. My control absorbance was 1.676. Is ...
2
votes
1answer
38 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 ...
7
votes
1answer
51 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 ...
6
votes
1answer
66 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 $\pm\mathrm{30~nm}$.
13
votes
1answer
328 views

What causes the iridescent colour in laboratory grown bismuth?

Artificially grown bismuth crystals are arguably magnificent, as seen in the image below: Image source: Minerals.net The website states that: They have hopper-like growths in pseudocubic ...
7
votes
1answer
337 views

What turns clear liquid soap blue?

Liquid soap that sits in metal pump handles turns blue after a week or so, as in this photo comparing the soap in its initial clear state and then after pumping from the dispenser. The pumps are ...
3
votes
1answer
84 views

Why are compounds of V5+ and Cr6+ colored?

As far as my knowledge goes, transition metal complex ions show a color due to a transfer of electrons between the levels of split $d$-orbitals. In the case of $\ce{V^{5+}}$ and $\ce{Cr^{6+}}$ ...
5
votes
1answer
26 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 ...
2
votes
0answers
42 views

why HgO & CdS compounds are 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 ...
3
votes
2answers
81 views

Why do s-block elements impart color to a flame?

Flame tests are a common way of identifying trace amounts of alkali metals (and to a lesser extent alkaline earth metals) in mixtures. Certain salts of $\ce{Ba, Sr}$ are also used in fireworks for ...
12
votes
1answer
724 views

Why does copper precipitate out as a pink solid?

When copper is precipitated out of a solution e.g from CuI, why does it appear pink instead of copper-coloured? Are there other situations where copper appears pink in solid form?
3
votes
1answer
72 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 ...
2
votes
1answer
35 views

50-90'C color changing chemical to use as warning marker for hot electronics?

I am testing electronics with many potentially unstable contacts, and I wish to monitor if they rise above 50 to 90 degrees Celsius, i.e. using carbon paper that would darken progressively from 50 to ...
1
vote
0answers
47 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 ...
3
votes
1answer
47 views

Why do complex ions not emit light from de-excitations of electrons?

I understand that complex ions are coloured due to d-orbital splitting which results in electrons being able to absorb wavelengths of visible light and become excited to the higher energy state ...
5
votes
3answers
371 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 ...
4
votes
1answer
159 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 ...
6
votes
0answers
62 views

Paint Changes Color on Stucco. Chemical Reaction is Occurring, but What is Reacting?

PROBLEM: When I apply paint to my home’s exterior stucco(currently white), the paint changes color. The grays change to purple. The whites change to yellow. Greenish-beige becomes orange. I have ...
11
votes
2answers
131 views

Why is there a difference in the colours of K₂Cr₂O₇ and K₂CrO₄?

In both the compounds the oxidation state of Chromium is +6 so why is there a difference in the colours of their aqueous solutions. $\ce{K2Cr2O7}$ is red-yellow and $\ce{K2CrO4}$ is bright yellow I ...
2
votes
1answer
48 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
2
votes
1answer
37 views

Coloration of substances because of F-Centers

In case of metal deficient defects in the crystal lattice of a metal, the positive voids are filled by electrons. How does this result in the coloration of a substance? Does this condition arise ...
0
votes
1answer
29 views

Color of Phenomelanin?

Do we know what is the wavelength of the color of Phenomelanin? If not, can we use the color of Phenomelanin-rich areas, like the lips, to discern the color of Phenomelanin?
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0answers
18 views

Reason behind ZnO color [duplicate]

Why is zinc oxide yellow when hot and white when cold? Is it yellow because of the flame used to make it hot?
2
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0answers
47 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?
6
votes
1answer
79 views

How hydrate isomerism results difference in colours?

The standard example is $\ce{CrCl3.6H2O}$, which can have three distinctly different crystalline compounds now known as $\ce{[Cr(H2O)6]Cl3}$ (violet), $\ce{[CrCl(H2O)5]Cl .H2O}$ (blue-green), and ...
1
vote
1answer
67 views

Iodine color change in different complexes

Why does the color of iodine differ when it forms a charge transfer complex with benzene (pi donor) - pink and ethanol (electron pair donor) - brown? Does the HOMO-LUMO energy differ, if so how?
1
vote
0answers
28 views

why colour of CuSO4 and CuCl3 is different? [duplicate]

These two are simple ionic compounds , not complexes [if I do not consider water of hydration] then how can I rationalise the difference in colour?
10
votes
2answers
546 views

Would it be possible to create a (non-toxic) alcoholic drink that, when zapped with laser, changes color?

Would it be possible to create a (non-toxic) alcoholic drink that, when zapped with a 0.5mW laser pointer, changes color? This would be mainly for the visual effects (bartender show) so it should not ...
2
votes
1answer
63 views

Mixing Different Solutions with Different Wavelengths to Get Different Colors?

I recently was told that the reason you can mix colors (blue and yellow make green because wavelengths 605nm + 450nm = green) was based on wavelength (which seems very obvious when you think about it ...
19
votes
2answers
2k views

Why is snow white?

I know that this is a rather ambiguous question; but my question is, whenever we take water and freeze it in the freezer, it still tends to stay clear. Since snow is just frozen water, why is it ...
3
votes
1answer
122 views

Why did the solution turn green?

I mixed L Arginine with l Citrulline in Hibiscus and green tea water which was red in color. Once the red liquid hit the mix of powdered Aminoacids the solution changed green. Can someone tell me why? ...
2
votes
1answer
60 views

Thermochromic pigment that changes at around 50 °C / 120 °F?

I wish to find a pigment that can indicate when a battery contact is getting too hot, and all the thermochromic pigments from hobby stores change color below body temperature, at 31 °C is the highest ...
5
votes
1answer
496 views

Acetone and Sodium Hydroxide

I have put in a beaker acetone and sodium hydroxide solution (approximately 1M $\ce{NaOH}$) and didn't see any colour change for 1 day (actually, it was transparent, no colour). After almost 2 days, ...
1
vote
1answer
43 views

How pigments actually function as colorants?

Pigments are insoluble colorants that have no affinity to the substrate. So how can they function as colorants if they "can't stick"? Are pigments always applied together with a "binder"?
1
vote
0answers
23 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. ...
9
votes
3answers
370 views

Are there yellow metals besides gold and copper?

Are there yellow metals besides gold and copper? Are there metals with color different than yellow and grey?
2
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1answer
45 views

Alcohol spectrophotometry

A couple of weeks ago we did a lab where we had a bunch of standard solutions of alcohol, dichromate, and sulfuric acid. We also had one unknown concentration. We heated them so they would all react, ...
4
votes
1answer
179 views

Is it possible to make broad spectrum light absorbing paint?

Is there such a paint / pigment that absorbs most wavelengths of light (beyond the visible light range) that can be used for solar heat generating applications? If not, would it be possible to make ...
6
votes
1answer
56 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 ...
1
vote
1answer
77 views

How does UV affect skin colors in dark-skinned people?

Skin color is one of the things one would rather not ask anything about! Only in humans, it can vary from very dark brown to pale pink. In darker-skinned people, the color is mainly due to melanin, ...
3
votes
3answers
208 views

How to make permanent ink that appears after some time?

I'd like to ask, how to make permanent ink, that will be invisible when used, but after like 30 minutes it will appear (preferably dark color)? Thanks.
8
votes
1answer
1k views

Does bleach turn a substance white or colorless?

From what I understand, bleach works to weaken the ability of a substance to absorb light. Thus this seems to be "whitening" i.e. reflecting all light. In contrast, colorlessness (according to ...
4
votes
1answer
97 views

why does a glass tube show white bands after being heated with a torch?

When I use a torch to split a glass tube, there's always a hazy white band which appears. Does anyone know what the cause of this is? (FYI, it was a hydrogen-oxygen torch. The glass is fused quartz ...
4
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1answer
115 views

Ultraviolet acid base indicator

Is there a chemical(s) that provides good discrimination between absorbance curves for different pHs in the UV light spectrum (100-400nm?)
-4
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1answer
104 views

How to change color of urine safely? [closed]

I am trying to find a SAFE way to change the colour of my urine, from what I have read online, Methylene Blue is relatively safe, and will change urine to blue or green. Is it safe? Can I put this in ...