10
votes
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Why not use all the colours in colorimetry?
Why not send in white light (with all the wavelengths at once)?
This is certainly and routinely done today. The main thing is how much price are we willing to pay? In a rigorous sense, colorimetry ...
- 42.6k
9
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Visible Light Spectrophotometer Recommendations
Good spectrometers in "new, unopened" condition are out of your budget. Their prices start at about 2000 USD. This also includes the spectrometers specifically made for education—like the ones from ...
- 1,005
8
votes
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Notation for excited states
As has already been mentioned in comments, those letters and numbers for each state correspond to their symmetry, specifically the symmetry of the (purely electronic) wavefunction. For more ...
- 7,540
8
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Visible Light Spectrophotometer Recommendations
Disclaimer: I'm not affiliated with any company
However,
Ocean Optics cuvette spectrophotometers are a good choice
This model is used in some undergraduate labs and is good because the cuvette ...
- 824
7
votes
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What is an exocyclic double bond?
Surely you are aware that the calculation of this sort is but a very rough estimate, yet still I feel the urge to stress that once more. Having said that, let's look at the double bond in the first ...
- 31.6k
7
votes
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De-excitation of a molecule
After radiation is absorbed and the electron is at an excited state in the molecule there are several pathways for de-excitation to occur (see fig.). The pathway of choice depends on its rate, ie how ...
- 1,623
7
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Why not use all the colours in colorimetry?
The previous answers by @Buck Thorn and @M. Farooq are very good, but not quite complete. The main advantages of FT UV-Vis spectroscopy would be 1) accuracy of wavelength (or wavenumber) determination ...
- 5,080
7
votes
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Reason for usage of Metal chlorides and Platinum or Nichrome wires in flame test
Metal chlorides are usually much easier volatilized than oxides or sulfates. They melt or sublime at temperatures much lower than 800°C. So they are volatilized in any flame like Bunsen burners.
...
- 30k
7
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Why is 295 nm a good wavelength to check absorbance when testing for aspirin?
I think this was basically an educational experiment. Your analytical method assumes that the hydrolysis was complete (this is the key requirement of a successful calibration curve). Your experiment ...
- 42.6k
7
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 ...
- 42.6k
6
votes
Accepted
pKa of phenols using UV-Vis spectroscopy
To quote the key points of an easy to read publication by Salgado and Vargas-Hernández (doi 10.4236/ajac.2014.517135, open access):
All starts with the dissociation equilibrium between the acid $\ce{...
- 31.3k
6
votes
Why is the graph of fluorescence vs. wavelength continuous?
There are two main reasons for what you're describing.
The first is the fundamental properties of the molecules involved, as mentioned in the comments. Even for isolated molecules, the transition is ...
- 10.4k
6
votes
Accepted
Why diethyl ether does not absorb in UV region?
We can measure the UV-Vis spectra for π → π* or n → π* electronic transitions (other transitions are forbidden according to selection rule) [1, pp. 577–578]. But in diethyl ether, being a saturated ...
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5
votes
Why not use all the colours in colorimetry?
An explanation is provided in this abstract (1):
Fourier transform spectrometry in the UV-Vis region (FT/UV-Vis),
because it is source shot-noise limited, has a signal-to-noise ratio
(S/N) ...
- 22.9k
5
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Why does benzene have 3 π–π* transitions in the UV range, but ethene, butadiene, and hexatriene each have only 1?
It seems that here we only need to consider the lowest energy transitions, i.e. HOMO–LUMO transitions. The difference between benzene and the linear polyenes is that both the HOMO and LUMO of benzene ...
- 71.9k
5
votes
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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 ...
- 31.4k
5
votes
How to Combine an Emission spectrum into a colour?
It is not simple -- for example, to many people, red + blue spectral lines appear purple/violet, i.e., shorter wavelength than pure blue! Though you could assign a color name to a pure spectral line, ...
- 35.3k
4
votes
Evidence for a chemical reaction
Most light doesn't result from chemical reactions
While there are many chemical reactions that can emit light and many related reactions where the emission is related to chemistry (for example the ...
- 37.8k
4
votes
Accepted
Beer's law with a polychromatic light source
There are several ways to answer the question, so here are my three. The first answer involves using a simple integer wavelengths approximation, i.e., noticing that Figs. 1 and 2 have 1 nm point ...
- 5,080
4
votes
Does broader peak mean stronger absorber in UV/VIS?
The classical concept of oscillator strength $f$ is useful here, but it should be used only in a qualitative way. This is defined as $f=a\int\epsilon_\nu d\nu$ where $a$ is set of units with value $4....
- 31.4k
4
votes
laser diode problem
I just did the experiment suggested by @porphyin. I used a 405 nm laser diode built into a toy "Space Gun" and the orange long pass filter shown in the figure below:
The results are in the next dark ...
- 5,080
4
votes
How can I prove ascorbic acid degradation with Uv-vis spectroscopy?
Some of the experimental details are missing, but if you recall
$$\mathrm{Abs} = \varepsilon \cdot c \cdot d$$
about the absorption depending on the molar extinction coefficient $\varepsilon$, the ...
- 31.3k
4
votes
Accepted
How can I compare the UV/Vis absorption difference after metal ion chelating of crown ether-containing polymer?
About the salt: Instead of $\ce{CsCO3}$ I would try $\ce{CsCl}$ for which sciencemadness reports a solubility in ethanol of $\pu{0.76 g/100 mL}$ (at $\pu{25 ^\circ{}C}$). Perhaps this little already ...
- 31.3k
4
votes
Accepted
UV-Vis spectrum of 1,3-butadiene
In the context of the free-electron molecular orbital (FEMO) model, it is easy to understand what's going on: The trans conformation can be modeled as a 1D box, which has an inversion center. ...
4
votes
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UV-vis spectra - maximum absorption
If you have a noisy UV-VIS spectrum, one cannot pick the highest value in the spectrum because each point is "contaminated" with noise. I am assuming you are not measuring very large ...
- 42.6k
4
votes
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Why don't similar locations of spectral lines produce similar "colors"?
This is more an illustrated comment, than an answer. The question is incompletely addressed; though it links to a source to retrieve the illustration, it does not provide the text (i.e., the very ...
- 31.3k
3
votes
Why is UV-Vis Spectroscopy not like IR Spectroscopy
I'm collecting ideas from the excellent comments and adding some of my own:
The typical UV/Vis spectrum has a narrow range
On the low energy side, it ends where the visible spectrum ends, at about ...
- 42.3k
3
votes
Molar absorption coefficient for potassium hydrogen phthalate
I would imagine that you could just use one of the spectrophotometers you have available to determine the molar absorptivity constant experimentally. After all, the molar absortivity constant is ...
- 366
3
votes
Accepted
What interesting things can be seen in spectra between 400-700nm?
Absorbance spectrum of colored solutions may be boring for a "sight seeing" student, as you call yourself. Emission spectrum is far more interesting for visual learners. Anything luminous, which you ...
- 42.6k
3
votes
What is an exocyclic double bond?
The double bond B is exocyclic to ring 2 as it is attached to an atom which is shared between ring 1 and ring 2 while the double bond A is not connected to any ring 2 atoms and is within just one ring,...
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