8
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If polyethylene glycol (PEG) is hygroscopic, how does it protect wood?
The reason why PEG is suitable for this purpose has many reasons including the wood chemistry and degradation of wood in water.
Degraded wood usually very characteristic chemical losses. The ...
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8
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Why is the IUPAC definition of adsorption so different from other definitions?
The IUPAC defintion isn't more limited than the ones you've read. Instead, it is more general.
Your confusion results from not being familiar with the term "condensed phase". You think a ...
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8
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Ozone from 10um IR?
Absorption in low energy thermal IR region does not break chemical bonds, but affects vibration of chemical bonds and rotation of molecules.
Energy of $\pu{10 \mu m}$ photons is about 40 times ...
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7
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Using table salt as a way to limit humidity in an unoccupied house
According to Transportation Information Service: Salt:
At up to 74% relative humidity and 20°C, salt does not absorb any appreciable quantities of water vapor. The critical water content of sodium ...
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7
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Absorption and emission at same wavelength?
Yes it is very common particularly in the more rigid type of molecule. The best example is chlorophyll and this overlap of absorption and emission leads to energy transfer in photosynthesis. The ...
- 30.8k
7
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The reason for selection of wavelengths in the spectrophotometry of Quinoline Yellow SS
The experiment in your link pg 31 is "Path Length Dependence of Absorbance Values". As you stated, quinoline absorption spectrum has a dip near 337 nm. The reason for choosing the wavelength ...
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7
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When pigments absorb light only around a single particular wavelength, why aren't they still white?
You are right that an individual transition from one state to another by absorption of a photon is connected to a very well defined energy. However, an absorption band in UV/VIS results from ...
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How to find the infrared absorption spectrum of O2 and N2?
There is a good reason for not being able to find the mid-IR absorption spectra of nitrogen and oxygen. Their vibrations are infrared inactive. Infrared absorption peaks are observed when there is a ...
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6
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When making a calibration curve, do we have to use the wavelength at maximum absorbance?
No it doesn’t. Measurements can in principle be made at any wavelength.
If there are two colored specimens in the same solution, it is actually better to measure at the wavelength where the ...
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6
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When pigments absorb light only around a single particular wavelength, why aren't they still white?
Color perception is a complex topic and one cannot make generalized statements.
If you are seriously investigating and want to have a deeper understanding, then get hold of a beautiful book called The ...
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6
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When pigments absorb light only around a single particular wavelength, why aren't they still white?
Some types of light absorbance show very narrow lines while others show broad peaks.
Atomic spectra have sharp lines when the atoms are in the gas phase. One example is the absorption of sunlight by ...
- 41.2k
6
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When pigments absorb light only around a single particular wavelength, why aren't they still white?
As others have brought up, indeed the absorption features of most compounds with electronic transitions in the visible light range are rather broad, and this breadth is important in generating a ...
5
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Why do some molecules show non-symmetric absorption and emission bands?
Mirror image spectra are only observed in solution and then only if the ground and excited state potential energies have almost exactly the same shape. Thus in rigid molecules such as anthracene a ...
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5
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Look for superabsorbent balls whose expansion is reversible
Yes. The ones I have are known commercially as Jelly Marbles or Orbeez. They're sold at gardening stores, home decor, and online. They're used as toys but also as gardening products that absorb excess ...
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How to determine chlorophyll content from spectrophotometry data (absorbance vs wavelength)?
How to determine chlorophyll content from spectrophotometry data (absorbance vs wavelength)?
You have to consider two pigments, chlorophyll A and chlorophyll B, along with other substances that ...
- 41.2k
4
votes
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Effective attenuation coefficient for polychromatic light
The intensity transmitted at wavelength $a$ where the extinction coefficient is $\epsilon_a$ is $I_a=I_{0a}\exp(-\epsilon_a L C)$ with path length $L$ and concentration $C$, and similarly for a ...
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4
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Lipinski's Rule of 5 Oxygen Rules
In Advanced Drug Delivery Reviews, 2001, 46, 3-26, (DOI) Lipinski and coworkers write:
Too many hydrogen bond acceptor groups also hinder permeability across a membrane bi-layer. The sum of $\ce{N}$...
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4
votes
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Is UV-Vis absorption polarization dependent ? Why?
With the experimental setup you describe, you would not observe any intentional polarization dependence, because the light passes only through a beam splitter, not a polarizer.
There can be ...
- 7,499
4
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Can physical absorption happen despite the formation of products?
When you consider the dissolution of a gas like $\ce{SO3}$ , $\ce{CO2}$, $\ce{SO2}$ etc. there are three equilibria existing at the same time:
$$\ce{SO2(g)\overset{H2O}{<=>}SO2(aq)\overset{H2O}{&...
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3
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When making a calibration curve, do we have to use the wavelength at maximum absorbance?
Yes, it does, and especially for calibration curves [1, p. 439, 455]:
For spectrophotometric analysis, we normally choose the wavelength of maximum absorbance for two reasons:
(1) The sensitivity of ...
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3
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Are there chemicals that absorb and release upon heating oxygen more efficiently than potassium oxide?
If you are looking for something that can be made using elemental oxygen as an oxidizer and reversibly release the excess oxygen below 1000 °C, sodium peroxide beats potassium peroxide by using ...
- 60k
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Why do some molecules show non-symmetric absorption and emission bands?
From the Jablonski diagram,
The mirror image is only true if you are talking about transitions from $S_0$ to $S_1$ (absorption) and $S_1$ to $S_0$. Also read about Kasha's rule.
Quinine is the ...
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3
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Hygroscopic Substances and Drying Agents
Read closer:
Most of the hygroscopic substances are drying agents
not
all drying agents are hygroscopic substances.
First Terminology:
Hygroscopic: Absorbs water from air
Drying agent: ...
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3
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What kind of drugs can be absorbed through skin?
The skin is able to prevent some things from passing in and out of a person but it is not a perfect barrier.
The lipophilic things like nicotine, hydrogen flouride, VX, hexane and iodine vapour can ...
- 5,194
3
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Vibronic coupling: How do I determine the new point group after vibration?
I don't believe it is strictly necessary to determine the subgroup induced by a vibration in order to determine if a vibronic transition is allowed. You can simply use the equation from your 2nd ...
- 11.8k
3
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The negative absorbance values in the baseline measurement
Negative absorbance in a double beam instrument has no physical meaning because absorbance, by definition, cannot be negative. It ranges from $0$ to $\infty$.
Instrumentally, all that means is that ...
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3
votes
Solubility of nitrogen dioxide in sodium hydroxide
A numerous studies have shown that the absorbtion of $\ce{NO2}$ in alkaline solutions is due to the reaction (For example, Ref.1):
$$\ce{2NO2 + 2OH- -> NO2- + NO3- + H2O} \tag1$$
Thus, as Poutnik ...
3
votes
Does ionization energy play a role in absorption spectrometry of non metals?
Your intuitive argument is not that far off. I am sure you are talking about atomic absorption spectrometry (AAS). Analyzing metals is routine but analyzing non-metals is indeed near impossible ...
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2
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Vibronic coupling: How do I determine the new point group after vibration?
I don't know if it's okay to give an additional question like that but I feared that editing the original post would lead to confusions in the continuity of the answers and it's probably not advisable ...
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