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In the title I am refering to silver spoons, which, when used to consume milk products (like yogurt), get a weird taste. It could be described as umami/meaty, a little bit like onions. I came to the conclusion that it must be the silver, because this taste is never observed when using steel spoons.
My guess was: the... |
You're right: the silver is reacting with sulphur compounds in the food to form a tarnish of silver sulphide. This is most commonly observed, in my experience, using silver teaspoons with boiled eggs, which are [pretty rich in sulphur](http://healthyeatingclub.com/info/books-phds/books/foodfacts/html/data/data5g.html).... |
I think your problem with this reaction lies in the easily confused term *syn* and *cis*. Both appear to mean that two functional groups are oriented in the same direction. On a cyclic molecule, *syn* and *cis* are the same. However, *cis* is a stereochemical descriptor and *syn* is a conformational descriptor. Simplif... |
I know that at extremely low temperatures (mK and lower), [Helium can form diatomic molecules](http://isites.harvard.edu/fs/docs/icb.topic105883.files/deBroglie_wavelength/He2_Molecular_Diffraction.pdf). Do the other noble gasses also form molecules at extremely low temperatures? |
Do noble gasses besides Helium form diatomic molecules at low temperatures? |
I know that at extremely low temperatures (in mK and lower), [Helium can form diatomic molecules](http://isites.harvard.edu/fs/docs/icb.topic105883.files/deBroglie_wavelength/He2_Molecular_Diffraction.pdf). Do the other noble gases also form molecules at extremely low temperatures? |
Do noble gases besides Helium form diatomic molecules at low temperatures? |
I'm currently studying VCE BioChemistry, and we're studying the separation of DNA strings of different lengths via Gel Electrophoresis.
(This involves having 'clumps' of DNA at one end of a gel medium and applying an electric current, pushing the DNA strands across the gel. Different sized strands move at differen... |
Gel electrophoresis - What causes the DNA fragments to stop? |
I keep hoping someone will jump in and answer this question to save me from thinking about it. Odds and ends from researching this question that might help someone else answer it.
- Clusters of water and ammomia, such as $\ce{NH3(H2O)20}$ as well as various other ratios, are [known][1] and have been [investiga... |
I'm currently studying VCE BioChemistry, and we're studying the separation of DNA strings of different lengths via Gel Electrophoresis.
(This involves having 'clumps' of DNA at one end of a gel medium and applying an electric current, pushing the DNA strands across the gel. Different sized strands move at differen... |
I wish I could answer your question outright, but this is outside my area of expertise. The best I can give you is a place to start. I expect any recent book on proteomics would cover this topic. For example [Introduction to Proteomics: Principles and Applications (Methods of Biochemical Analysis)](http://www.amazon.co... |
I know that at extremely low temperatures (mK and lower), [Helium can form diatomic molecules](http://isites.harvard.edu/fs/docs/icb.topic105883.files/deBroglie_wavelength/He2_Molecular_Diffraction.pdf). Do the other noble gasses also form molecules at extremely low temperatures? |
Do noble gasses besides Helium form diatomic molecules at low temperatures? |
This difference between living and non-living polymerizations is small in words but large in effects. In principle cationic and anionic polymerizations can be living. In practice, it is not as easy as it looks on paper. See below.
A living polymerization is any chain (or addition) polymerization that is prevented fr... |
This afternoon I was having some trouble with an HSQC (Heteronuclear Single Quantum Coherence Spectroscopy) spectrum I was trying to aquire, and the spectroscopist recommended I try an HMQC (Heteronuclear Multiple Quantum Coherence) spectrum, as they are more robust. I did so, and got a very nice spectrum in about half... |
What is the diffrence between an HMQC and HMSQ experiment? |
This afternoon, I was having some trouble with an HSQC (Heteronuclear Single Quantum Coherence Spectroscopy) spectrum I was trying to aquire, and the spectroscopist recommended I try an HMQC (Heteronuclear Multiple Quantum Coherence) spectrum, as they are more robust. I did so, and got a very nice spectrum in about hal... |
What is the difference between an HMQC and HSQC experiment? |
This afternoon, I was having some trouble with an HSQC (Heteronuclear Single Quantum Coherence Spectroscopy) spectrum I was trying to aquire, and the spectroscopist recommended I try an HMQC (Heteronuclear Multiple Quantum Coherence) spectrum, as they are more robust. I did so, and got a very nice spectrum in about hal... |
What is the timescale of disulfide bond formation in a given protein? What influences it? Finally, how does one actually measure it?
From what I understand, the reduction and oxidation of bonds happens on the order of 10<sup>-8</sup>s. However, it appears that the timescale of disulfide bond formation in macromolecu... |
What is the timescale of disulfide bond formation? |
While reading [this paper][1] (suggested by @Janice [here][2]), I came across the following line:
> Surface reconstruction is known to be extremely important for Si, the material of 20th century electronics. However, surface reconstruction has been much less studied for graphite. One of the reasons might be graphit... |
**2012-05-25: Massive update: New answers, new notations, new graphics**
Your first question was:
_"... can an atom have more than 8 valence electrons?"_
Yes, but the optimum number of valence electrons remains 8. The only exceptions to that rule are hydrogen and helium, for which the optimum number of valence... |
In my textbook, for calculating the percentage dissociation of HOCL for the given equation:
$$\ce{HF + H2O <-> H3O+ + F-}$$
The solution is:
Initial Concentrations
$$[\ce{HOCL}] = 0.08M, \: \ce{[H3O+]} = 0, \:\ce{[F- ]}= 0$$
Equilibrium concentrations
$$[\ce{HOCL}] = 0.08M - x, \: \ce{[H3O+]} = x, \:\ce{[F- ]... |
FX thank you for your answer, helped me find exactly what i was looking for.
The stone or mineral is called Ulexite
found a site that sells it when searching for calcite.
http://www.google.com/search?hl=en&safe=off&q=Ulexite&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&biw=1920&bih=995&um=1&ie=UTF-8&tbm=isch&source=og&sa=... |
Using Fx's answer as a starting point, I found the mineral--it's called [Ulexite][1]
http://www.google.com/search?hl=en&safe=off&q=Ulexite&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&biw=1920&bih=995&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&ei=NIbBT--WKceJiALKtYT-Dg
[1]: http://en.wikipedia.org/wiki/Ulexite |
Is there a formal definition or algorithm that can take a list of reactions and tell me whether it contains a set of species that can produce itself autocatalytically?
It is clear that the following reaction is autocatalytic:
$$\ce{
A + B \to 2 B
}$$
B appears on both sides of the equation, so it's a catalysis ... |
In this molecule, which is 3,5-dimethyl-4-carboxypyrazolate (unless I got it wrong):
![enter image description here][1]
I do not think there is free rotation around the bond indicated in red, because one can write a resonnance structure with significant reasonable weight where a double bond would be located betwe... |
Magnetite, $\ce{Fe3O4}$ is able to capture $\ce{As(III)}$ and $\ce{As(V)}$ from drinking water through the following mechanisms.
---
![enter image description here][1]
Bidentate-binuclear complex
---
![enter image description here][2]
Monodentate-binuclear complex (both from [here](http://arsenic.tamu.edu... |
Inspired by [this question][1], I'm wondering why arsenous acid is frequently denoted $\ce{H3AsO3}$, as opposed to $\ce{As(OH)3}$, which would appear to more accurately reflect its connectivity?
[1]: http://chemistry.stackexchange.com/questions/472/what-are-the-mechanisms-for-capture-of-ceasiii-and-ceasv-by-magn... |
Why is arsenous acid denoted $\ce{H3AsO3}$? |
<sup>All quoted stuff copied from [IUPAC Red Book][1], IR-4 unless otherwise specified</sup>
It's not only $\ce{H3AsO3}$ . What about $\ce{H3BO3,H3PO4,H2SO4,HClO4}$? Or indeed, any other oxyacid?
Basically, **we have multiple ways of writing inline formulae of covalent compounds**. One is the boring way(**molecul... |
**2012-05-25: Massive update: New answers, new notations, new graphics**
Your first question was:
_"... can an atom have more than 8 valence electrons?"_
Yes, but the optimum number of valence electrons remains 8. The only exceptions to that rule are hydrogen and helium, for which the optimum number of valence... |
Inspired by [this question][1], I'm wondering why arsenous acid is frequently denoted $\ce{H3AsO3}$, as opposed to $\ce{As(OH)3}$, which would appear to more accurately reflect its connectivity?
**[edit]**
I feel like such a doofus, forgetting about $\ce{H2SO4}$, $\ce{H3PO4}$, etc. Great discussion, people!
... |
<sup>All quoted stuff copied from [IUPAC Red Book][1], IR-4 unless otherwise specified</sup>
It's not only $\ce{H3AsO3}$ . What about $\ce{H3BO3,H3PO4,H2SO4,HClO4}$? Or indeed, any other oxyacid?
Basically, **we have multiple ways of writing inline formulae of covalent compounds**. One is the boring way (**molecu... |
I am currently reading the CRC Handbook of Phosphorus-31 Nuclear Magnetic Resonance Data by John C. Tebby (CRC Press, 1991) and on several figures (ex. pages 9 to 14) there is a caption that reads along these lines
> $^{31}$P NMR chemical shifts of three coordinate ($\lambda3 \ \sigma 3$) phosphorus compounds. (Tabl... |
What does this notation mean? |
What organic solvents are suitable to use with potassium permanganate? |
I am currently reading the CRC Handbook of Phosphorus-31 Nuclear Magnetic Resonance Data by John C. Tebby (CRC Press, 1991) and on several figures (ex. pages 9 to 14) there is a caption that reads along these lines
> $^{31}$P NMR chemical shifts of three coordinate ($\lambda3 \ \sigma 3$) phosphorus compounds. (Tabl... |
I am currently reading the CRC Handbook of Phosphorus-31 Nuclear Magnetic Resonance Data by John C. Tebby (CRC Press, 1991) and on several figures (ex. pages 9 to 14) there is a caption that reads along these lines
> $^{31}$P NMR chemical shifts of three coordinate (λ3 σ3) phosphorus compounds. (Tables B to E.)
W... |
Azane all by itself has an inversion barrier of about 6 kcal/mol, which is pretty low compared with phosphine's approximately 30 kcal/mol barrier. Pyramidal nitrogen inversion requires going through a planar transition state. A classical model is used easily to model the thermal rate and we could say $$k \propto e^{-E_... |
Azane all by itself has an inversion barrier of about 6 kcal/mol, which is pretty low compared with phosphine's approximately 30 kcal/mol barrier. Pyramidal nitrogen inversion requires going through a planar transition state. A classical model is used easily to model the thermal rate and we could say $$k \propto e^{-E_... |
Azane all by itself has an inversion barrier of about 6 kcal/mol, which is low compared to phosphine's approximately 30 kcal/mol barrier. Pyramidal nitrogen inversion requires a planar transition state. One can use a classical theory to model the thermal rate and we could write $$k \propto e^{-E_a/RT} $$ and using mod... |
[Oobleck][1] is basically a mixture of cornstarch and water. It has the interesting property of going hard when pressure is applied. For example, it feels like a liquid when you swirl your fingers through it, but it becomes hard for a second if you punch it.
The common explanation for this is that the starch-water ... |
How does oobleck work? |
[Copper sulphate][1], in its hydrated form, is crystalline, whereas the anhydrous form is amorphous.
[Gypsum][2] has a similar story-- on heating the crystalline dihydrate we get an amorphous hemihydrate. (Gypsum in fact has two different crystalline forms of the dihydrate, and has an anhydrous form as well).
I'v... |
How do copper sulphate and the like change crystal structure on adding water of hydration? |
Well, I have seen many comical acts where people balance a spoon (or a fork) on different parts of the face like on the tip of the nose, forehead etc.
The do this by blowing moist air (see below) and immediately putting it on the face
![enter image description here][1]
So i wanted to know is what is ... |
I suspect the answer is an issue of process rather than of fundamentals.
That is, if you could find a non-aqueous medium that readily dissolves the anhydrous form of some salt, my very strong suspicion is that you could grow excellent clear crystals of it that would look almost nothing like the hydrous crystalline f... |
I suspect the answer is an issue of process rather than of fundamentals.
That is, if you could find a non-aqueous medium that readily dissolves the anhydrous form of some salt, my very strong suspicion is that you could grow excellent clear crystals of it that would look almost nothing like the hydrous crystalline f... |
[Manishearth, I'm not sure I'm even answering the right question below. After reading your question more carefully, I think you were more interested in how water molecules help crystals form, rather than whether or not the anhydrous forms can form crystals also (versus being strictly amorphous). So, oops. Maybe some on... |
I am confused about the justification for the corrections to the ideal gas law in the Van der Waals equation: $$pV=\frac{nRT}{V-nb}-a(\frac{n}{V})^2$$
I understand that the equation attempts to correct for attractive and repulsive forces between molecules, and that at high volumes the corrections are negligible, at ... |
What is a rigorous definition of gas volume, and how is the Van der Waals equation derived? |
I am confused about the justification for the corrections to the ideal gas law in the Van der Waals equation: $$pV=\frac{nRT}{V-nb}-a(\frac{n}{V})^2$$
I understand that the equation attempts to correct for attractive and repulsive forces between molecules, and that at high volumes the corrections are negligible, at ... |
In my textbook, for calculating the percentage dissociation of HOCL for the given equation:
$$\ce{HF + H2O <-> H3O+ + F-}$$
The solution is:
Initial Concentrations
$$[\ce{HF}] = 0.08M, \: \ce{[H3O+]} = 0, \:\ce{[F- ]}= 0$$
Equilibrium concentrations
$$[\ce{HF}] = 0.08M - x, \: \ce{[H3O+]} = x, \:\ce{[F- ]}= x... |
2D spectrum take up a large amount of hard disk space. At my last lab it was standard practice to delete the imaginary portions of the spectrum with `xfb n` (We used TopSpin) and if needed later, to regenerate it from the Real part of the data with a Hilbert transform (Related, the TopSpin Commands and References, ~pg ... |
I am confused about the justification for the corrections to the ideal gas law in the Van der Waals equation: $$pV=\frac{nRT}{V-nb}-a(\frac{n}{V})^2$$
I understand that the equation attempts to correct for attractive and repulsive forces between molecules, and that at high volumes the corrections are negligible, at ... |
I am confused about the justification for the corrections to the ideal gas law in the Van der Waals equation: $$p=\frac{nRT}{V-nb}-a(\frac{n}{V})^2$$
I understand that the equation attempts to correct for attractive and repulsive forces between molecules, and that at high volumes the corrections are negligible, at i... |
Most of the existing software I know (like VMD or Pymol) say that they can be used to create PDF files with 3D representations of molecules: actual 3D models, which you can rotate inside the Adobe Acrobat viewer. However, they all require the use of “Adobe Acrobat Pro 9 Extended” for its 3D capture feature. From what [... |
What open-source software can produce 3D PDF representation of molecules? |
It's a common cooking advice: if you want a somewhat softer caramel, [add some lemon juice to the sugar](http://allrecipes.com/howto/sugar-cooking/):
> To help prevent the caramel from crystallizing, you can add an acid to the sugar before you begin: add about half a tablespoon of lemon juice to each cup of sugar an... |
How does adding lemon juice to sugar make better caramel? |
In my textbook, for calculating the percentage dissociation of HOCL for the given equation:
$$\ce{HF + H2O <-> H3O+ + F-}$$
The solution is:
Initial Concentrations
$$[\ce{HF}] = 0.08M, \: \ce{[H3O+]} = 0, \:\ce{[F- ]}= 0$$
Equilibrium concentrations
$$[\ce{HF}] = 0.08M - x, \: \ce{[H3O+]} = x, \:\ce{[F- ]}= x... |
Disclaimer
---
1. This is *not* for the faint-hearted.
2. If you are not interested in using [LaTeX][1], stop reading now, as this uses the `media15` or `movie9` packages to embed U3D in a pdfLaTeX generated PDF. This answer assumes basic familiarity with LaTeX. I have tested this with pdfLaTeX and it should wor... |
Especially when drinking water after the fact, mint can give a sharp cold sensation inside one's mouth. What process causes the sensation to occur? |
Why does menthol (e.g. peppermint) feel cool to the tongue? |
Here is my interpretation when asked to:
> By drawing arrows in the appropriate boxes, complete the outer electron structures for Cu and Cu<sup>2+</sup>
![My electron box plot][1]
I had no problem in drawing out the electron structure, but am a little confused by the orientation of my arrows. I understand tha... |
Is the order of orientation of electron box diagrams meaningful or arbitrary? |
This is my first time taking a 13c NMR spectrum and while I'm aware the signal to noise ratio is much lower compared to 1H NMR, I didn't realize it was quite this bad. I took a spectrum and I only see the CDCl3 triplet. What concentration range is generally appropriate given say 256 scans (10 minutes on our machines?),... |
**Raise hell with the grader.** There's no reason whatsoever for this answer to be rejected. A [Google book search](http://www.google.com/search?q=electron+box+diagram&btnG=Search+Books&tbm=bks&tbo=1) can substantiate your argument, and the first example from a textbook is actually in your order:
 can substantiate your argument, and the first example from a textbook is actually in your order:
![enter im... |
Macromolecular NMR spectra are difficult to compute because macromolecular electronic structures are computationally expensive to solve with accuracy. Obtaining precise chemical shifts and splitting requires accurate treatment of electron density and geometry, especially for simulation of NOESY, which I understand is i... |
In the [borax bead test][1], we take a crystal of borax and then heat it.
> A small loop is made in the end of a platinum or nichrome wire (as used in the flame test) and heated in a Bunsen flame until red hot. It is then dipped into powdered borax, and the adhering solid is held in the hottest part of the flame whe... |
When we heat a borax crystal, why does it first expand and then contract? |
Some NMR experiments can be halted partway through the acquisition and still give perfectly valid results: The traditional 1H experiment for example. Others, like a Saturation Transfer Difference Spectrum will have errors in the magnitude of the peaks in it if it is halted, due to the fact it uses groups of pulses and ... |
Can a NOESY NMR experiment be halted partway through and give meaninful results? |
Why is it so difficult to create mock NMR spectra of macromolecules? |
I want to know what's the most stable furan resonance structures. I know that structure number 1 is the most stable. But which one comes after?
http://i.imgur.com/LtvCR.png |
The most stable Furan resonance structures? |
I know that [anthocyanins][1] are a class of compounds responsible for the purple colors found in flower petals.
> Anthocyanins (also anthocyans; from Greek: ἀνθός (anthos) = flower + κυανός (kyanos) = blue) are water-soluble vacuolar pigments that may appear red, purple, or blue depending on the pH. (same referenc... |
Chemical compounds responsible for the colors in flowers? |
I want to know which are the most stable furan resonance structures. I know that structure number 1 is the most stable, but which one comes after?
![http://i.imgur.com/LtvCR.png][1]
[1]: https://i.stack.imgur.com/ulVgN.png |
The most stable furan resonance structures? |
I know that [anthocyanins][1] are a class of compounds responsible for the purple colors found in flower petals.
> Anthocyanins (also anthocyans; from Greek: ἀνθός (anthos) = flower + κυανός (kyanos) = blue) are water-soluble vacuolar pigments that may appear red, purple, or blue depending on the pH. (same referenc... |
When purchasing chemicals from Sigma, Fisher, or wherever, there are often *-grade*'s attached to their description like *reagent-grade*, *technical-grade*, *analytical-grade*, or more niche-sounding *biotech-grade*, *HPLC-grade*, *DNA grade* (DNase free perhaps?)
Is there some sort of standard for what these actual... |
What do the different grades of chemicals mean? |
I am trying to build a system of two connected chambers, one of which is also connected to a cuvette, so I can perform a spectrometry experiment with different concentrations of KNO3 solution. In its simplest form, the cuvette and the first chamber would hold solution at the same concentration, while the second chamber... |
How to calculate the equilibration time of two connected chambers of salt solution, initially at different concentrations? |
I am trying to build a system of two connected chambers, one of which is also connected to a cuvette, so I can perform a spectrometry experiment with different concentrations of KNO3 solution. In its simplest form, the cuvette and the first chamber would hold solution at the same concentration, while the second chamber... |
> Cross- posted to http://chemistry.stackexchange.com/questions/578/choice-of-semiconductor-doping-elements
In a typical semiconducting material, we start with
Silicon (Group IV) and introduce atoms of Groups V or III depending on whether we are constructing an n- or p-type semiconductor respectively.
Why is... |
In a typical semiconducting material, we start with
Silicon (Group IV) and introduce atoms of Groups V or III depending on whether we are constructing an n- or p-type semiconductor respectively.
Why is it optimal to choose doping atoms one Group away? Why not introduce atoms from Groups VI or II, for instance? |
In one variation of the Iodine Clock Demonstration, you add two colorless solutions together and apparently nothing happens. After about 30 seconds to a minute, you get an "instantaneous" change to a dark blue color.
Solution A is 0.006M $\ce{KIO3}$ and is stable over at least a year or two.
Solution B is made w... |
Why is a sodium metabisulfite-starch-HCl solution unstable? |
I know that [anthocyanins][1] are a class of compounds responsible for the purple colors found in flower petals.
> Anthocyanins (also anthocyans; from Greek: ἀνθός (anthos) = flower + κυανός (kyanos) = blue) are water-soluble vacuolar pigments that may appear red, purple, or blue depending on the pH. (same referenc... |
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