12 votes

What is the reason for the blue color of an ammoniated electron?

To expand on Thawn's answer to #1 a bit: In quantum systems, a particle is bound to discrete states when it is constrained by a sufficiently deep potential well; otherwise its energy is continuous$^\...
  • 16.9k
12 votes

What is the reason for the blue color of an ammoniated electron?

Both of your questions could benefit from more background, so please forgive me if I understood something wrong. However, I'll try to answer as best I can: The excess electron in liquid ammonia is ...
  • 544
8 votes

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 ...
  • 1,562
7 votes

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 ...
  • 27.6k
7 votes

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 ...
  • 11.6k
7 votes
Accepted

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 ...
6 votes

Relative strength of desiccants

At hydrous equilibrium will the "stronger" desiccant contain virtually all of the water? Or is the equilibrium distribution of water a function of the desiccants' relative "hygroscopy," rates of ...
  • 20.4k
6 votes
Accepted

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 ...
  • 625
6 votes

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 ...
  • 33.7k
6 votes

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 ...
  • 33.7k
6 votes

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 ...
  • 32.6k
6 votes

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 ...
4 votes
Accepted

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 ...
  • 3,534
4 votes
Accepted

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 ...
  • 39.1k
4 votes
Accepted

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 $\ce{N}$...
4 votes
Accepted

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 ...
4 votes
Accepted

Relative strength of desiccants

Yes, it is meaningful, but often ignored for practical reasons. In the lab, e.g. in a desiccator, you would just use a large excess of the desiccant of choice which would always work. It’s often more ...
  • 64.8k
4 votes
Accepted

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 ...
  • 27.6k
4 votes

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 ...
  • 32.6k
3 votes
Accepted

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 ...
  • 27.6k
3 votes
Accepted

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: ...
  • 12k
3 votes

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 ...
3 votes

What is the cause of hygroscopy?

Ions are hygroscopic because they form very stable, low energy hydrates, which are thermodynamically favorable over water vapor. I.E. salt attracts water vapor because the hydrated salt is lower ...
3 votes

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 ...
  • 35.7k
3 votes

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 ...
  • 42.5k
3 votes

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 ...
  • 33.7k
3 votes
Accepted

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 ...
  • 33.7k
2 votes

What is the cause of hygroscopy?

Some salts have high tendency to be hydrated, like Li salts. The reason is that their hydration energy is very high, meaning that when they are hydrated, lot of energy is released. Since lower energy ...

Only top scored, non community-wiki answers of a minimum length are eligible