texts: Natural orbital population analysis in Gaussian

texts:
Within (restricted) density functional theory and Hartree-Fock, respectively the Kohn-Sham orbitals and spin orbitals are the natural orbitals, with occupation numbers either 2 or 0.

As I understood, this also applies to spin-unrestricted calculations, is this correct?

Now, when doing UDFT or UHF with Gaussian and specifying pop=NaturalOrbitals, the natural orbitals are different from the KS/canonical orbitals and some occupations numbers are also different from 2 and 0. Unfortunately Gaussian manual provides no reference to how the natural orbitals analysis is done exactly and the literature is fairly confusing (spin-projection vs non-spin projection etc.).

Could anybody give me an overview or reference regarding what Gaussian exactly does when this pop=NaturalOrbitals keyword is turned on?


texts: Can TBE electrophoresis buffer be stored in a PETE container?

texts: I'm doing a science project on agarose gel electrophoresis and would like to know if it is safe to store Tris/Borate/EDTA buffer solution inside a PETE container since I will be making about 10L of the buffer solution and do not have access to a spigoted carboy or any such container.


texts: How to apply the Henderson–Hasselbalch equation when adding KOH to an acidic acid buffer?

texts: Will the Henderson–Hasselbalch equation be able to calculate the pH when you have an acidic solution and you add a basic solution? Will that be possible or can you only use it for adding an acid to an acidic buffer to calculate the pH, or only a base to a basic buffer? If it can, how is the pH calculated, if you add 0.025 mol of solid KOH to 1 L of an acidic acid buffer solution of pH 3.97.


texts: Petroleum Benzine or Normal-Hexane for removing a silicone based adhesive?

texts:
I’m trying to remove the glass panel wich is glued to the polarizer of an LCD display (an Apple iMac display with broken glass but working LCD wich I would like to repurpose).

It seems to be fixed with a soft, non-curing, silicone-based adhesive . But the process of removing it is terribly tedious and I was wondering if there was a solvent that might help me.

LG, the manufacturer states in the display's data sheet that touches from bare hands, grease, some cosmetics, acetone, alcohol and toluene will harm the polarizer‘s surface.

Some people claim that they removed the glass successfully using baby oil but given that info from the data sheet I'm not sure if the oil may be harmful to the polarizer.

LG recommends to use petroleum benzine or normal-hexane for cleaning the polarizer surface.

Now, my question is if one of these two might be a helpful substance for the task of dissolving/weakening the silicon adhesive and removing the glass?

Thank you!


texts: Wikipedia has a thorough article on the benzodiazepines. Of course, it is written primarly  from the pharmacological point of view; but there is also the "Chemistry" section, which includes the IUPAC name. The parent hydride for the compound class is named 1H-benzo[e][1,4]diazepine. I do not understand why it is benzo[e][1,4]diazepine and not benzo[f][1,4]diazepine: shouldn't the bond alphabetic designation sequence go around the original diazepine ring, starting with the 1,2-bond (a), then continuing to 2,3 (b), 3,4 (c), 4,5 (d), 5,6 (e) and, finally, 6,7 (f), to which side the benzene ring is attached? Could please someone clarify the matter to me?


texts: Why are 1,3-diols protected with aldehydes but 1,2-diols are protected with ketones?

texts: 1,3 diols are usually reacted with benzaldehyde when protection of the OH groups is desirable, but acetone is used when the relation between the hydroxyl groups is 1,2. Why is it so?


texts: Measuring Cu2O Thickness in Oxidized Copper Sheet

texts:
I have Cu2O fabricated using thermal oxidation of Cu sheets in air at  high temperatures. The thickness of Cu2O is expected to be at least 100 microns. There is still plenty of unoxidized Cu metal inside the Cu2O, so cleaving it to perform cross-sectional SEM is not trival. It is also too thick for spectroscopic ellipsometry and XRR.

What are some other methods of measuring the thickness of this Cu2O thermal oxide layer?


texts: Why, in an applied magnetic field, is electron with spin parallel to the magnetic field higher?

texts: My lecturer today said that when an applied magnetic field, $B_0$, is applied, the electron with spin parallel to $B_0$ is higher in energy than the electron with spin antiparallel to $B_0$. Similarly, in protons, it is the opposite; parallel spin is lower in energy and antiparallel spin is higher in energy. Why is that?


texts: What is the role of hydration enthalpy in oxidation?

texts:
My textbook says that the greater oxidising behavior of fluorine than chlorine can be attributed to the high hydration enthalpy of $\ce{F-}$ ions and the low dissociation enthalpy of $\ce{F-F}$ bond.
While the second reason makes perfect sense to me, I can't reason why hydration enthalpy comes into play. I know that these elements act as oxidising agents in aqueous media, but I still can't understand why we need to consider hydration enthalpies.


texts:
My textbook defines $\mathrm{t_{2g}}$ orbitals as

  $\mathrm{t_{2g}}$ stands for a set of three orbitals which are asymmetric with respect to $C_2$ axes, perpendicular to the highest $C_n$ axes, but which is symmetric in sign through the centre of inversion.

I know that “$\mathrm{t}$” is a randomly chosen letter as suggested by M. Farooq, “$\mathrm{g}$” comes from gerade (MOT), that's what  the last line says. Though “$2$” in subscript must have come from $C_2$, but I didn't get the meaning of

  …which are asymmetric with respect to $C_2$ axes, perpendicular to the highest $C_n$ axes.

Please explain what does this line conveys.


texts:
The groups go from 1 to 18 in the periodic table. When looking at the transition metals in the periodic table, You see roman numerals labelled with 'B,' in the order of III, IV, V, VI, VII, VIII, VIII, VIII, I, II.
Why does III - VIII come before I and II? And why does VIII get repeated three times?

Also, what is the difference in the groups labelled A and B, besides the fact that the B groups are the transition metals?


texts: Why does mercury not form amalgam with iron?

texts:
I am learning about solutions and while giving an example of a liquid (solute) and a solid (solvent), my teacher told us that mercury forms an amalgam with all the metals except iron.

I want to know why this is so?


texts: Conditions for Complete hydrolysis of salt

texts:
My text book says that the cations (or anions) which are stronger than hydronium ion(or OH-) and their conjugate base (or acid) being very much weaker than water show complete hydrolysis.
 While the cations(or anions) which are weaker than hydronium (or OH-)and their conjugate base(or acid) being stronger than water but weaker than hydroxide(or H3O+) exhibit hydrolysis to Limited extent.

I don't quite understand why is this so?


texts:
I understand the concept of an equilibrium buffer solution, however I am a bit hung on how creating it doesn't shift the weak acid equilibrium.

$$\ce{CH3COOH + H2O <=> CH3COO- + H3O+}$$
$$ K_\mathrm{eq} = 1.8 \times 10^{-5}$$

If I add in equimolar amounts of $\ce{CH3COO-}$ (from a salt) to the acid, why wouldn't that just push equilibrium to the left, creating a lot more of the acetic acid, as the $ K_\mathrm{eq}$ is very low, thus shouldn't the concentration of acetate ions be always very low (I can understand that it will increase, but wouldn't it be a minor increase as most of added $\ce{CH3COO-}$ react to form acetic acid)? How would it be possible to have almost the same amount of them?


texts: In the p-orbitals, there are 3 dumbbell-shaped lobes, each of which can contain 2 electrons. In the diagrams of the d- and f-orbitals, there are two or more lobes (or orbital shapes) or each value of m.  In all of these cases, which lobes/shapes do the electrons occupy for any given element?


texts:
For a solution of $\ce{HA-}$, I have seen the following approximations for the $\mathrm{pH}:$

$$\mathrm{pH} = \frac{1}{2}(\mathrm{p}K_\mathrm{a1} + \mathrm{p}K_\mathrm{a2})\tag{1}$$

$$\mathrm{pH} = \sqrt{\frac{K_1K_2[\ce{HA-}] + K_1K_\mathrm{w}}{K_1 + [\ce{HA-}]}}\tag{2}$$

How do they differ? Is the second approximation always more accurate than the first? I know that the second is derived from the mass and charge balance equations and the first is the same as the second, with several assumptions.


texts: Does this produce the anti-Markovnikov product because of the ROOR?

texts: I know that the anti-Markovnikov product is produced when there is a free radical present. Does the ROOR separate into two free radicals and that changes the reaction? But ROOR doesn't end up in the product at all right? Why? Is my thinking correct?


texts: Risks from overheated phenolphthalein in green/orange silica gel drying

texts:
Recently I tried to dry out some indicating silica gel. When I googled, I found advice on line saying that it should be heated to 150 C and that such was a standard procedure, so I popped it into the toaster oven set it to 300 F which is just over 150 C and it started to make a smell and turn black. I stopped of course, cooled it down, and aired out my kitchen. Futher research indicates that the temperature I used is applicable to blue indicating or non-incdicating gel, but the newer Orange/Green gels contains an organic indicator which turns out to be phenolphthalein, rather than Cobalt Chloride and as such should not be heated above 120 C. Basically I followed outdated advice for the older type of product, a classic internet fail.
So now the question is, what have I done? What did I breath? I was cautious, watched the process stopped it early and don't have any outward symptoms, but now I'm curious how dangerous this was.
I've done a lot of searching and found nothing beyond "Toxic oxides of carbon, acrid and irritating fumes" in MSDS sheets regarding what happens when phenolphthalein combusts let alone what might happen as it degrades inside a silca gel bead. MSDS for the beads are just as vague. The lack of info is slightly alarming considering the ease with which a mistake such as mine could be made. Does anyone know what happens when heating breaks down phenolphthalein? There was a smell so something's definitely been produced other than water vapor, and the blackening of the beads might indicate that some carbon probably was left behind.
I understand that a variety of chemicals might be released, but I wonder if anyone is aware of a characterization of the types and relative quantities, or if there are any specific concerns.


texts:
My teacher tried to teach this concept to us in 5 minutes. I'm lost but I've made an effort to understand it all (but I need clarification.)

If we have a compound such as LiOH, what element would be needed to neutralize it? As in, I understand that this element has to be a base but, there are SO MANY bases. Can you maybe teach how to do these using the LiOH example and another example using HCl (aq). Any examples, really. I just need to understand that.

Secondly, we haven't learned solubility tables yet, I can identify an acid (H ...) and bases (... OH) but what if there's a compound like MgCl2, what do I do now? Do I use a table to look up the states or the pH? Is there another approach?

I learned that Alkali Metal + O2 = Oxides but I can't really apply that here, can I?

Literally any help will be appreciated, I'm not cramming rather just don't understand the concept.


texts: origin of use of differential equations for modeling chemical reactions?

texts:
what are some of the original examples of uses of differential equations for modeling and analyzing chemical reactions, particularly those relevant to biochemistry, involving proteins and enzymes? Michaelis and Menten's work in 1910s is one example.

What are the earlier examples or antecedents to this work? (references to good historical accounts of this modeling endeavor would also be helpful).


texts:
Is this mechanism will be similar to ozonolysis ?

My try :

My Question is will B be the answer ? And what does Me2S do ?


texts:
It's stated in my textbook that at the freezing point, the vapour pressure of the solid phase equals the vapour pressure of the liquid phase. In a mixture, since the vapour pressure of the solution is lower than the vapour pressure of pure solvent, the temperature has to be lowered in order for the vapour pressures to equalize and hence freezing to take place.

According to what I understand after reading my textbook, when a solution freezes, it's the solvent which converts into solid and leaves behind liquid phase consisting of both the solvent and solute. Thus, how can the pure solid solvent and liquid phase mixture have the same vapour pressure at the same temperature, since the vapour pressure of pure solvent at any temperature is greater than the vapour pressure of mixture?


texts: What barriers prevent plastic from becoming a fiber optic, data transmission medium?

texts:
This is a question that has bothered me for a while.  In the past many years, no company has been able to develop a material that can transmit light nearly as well as fiber optic glass, or at least not as cheaply.

After doing a bit of research, I found that although there is fiber optic plastic, the quality is considerably poor when compared to the standard glass medium.  I would assume that developing a highly-transparent, high-quality plastic that is cheap to manufacture would be considered the holy grail of data communication (not to mention, quite profitable.)

Why is it that in the many, many years that fiber optic data transmission has been around, no one has been able to develop such a form of plastic?  In fact, I've never even heard of such research making headlines on the more common tech news sites.


texts: Why Gold and Silver react minimally with atmosphere?

texts: Gold and Silver atoms interact with one another to form reasonably strong metallic bonds, but surprisingly they have almost no chemical interaction with atmosphere. How can we explain it based on the atomic structure of Gold and Silver. What is so unique about its chemical structure that is not present in other transition metals that makes them noble (non-reactive)?


texts: Why doesn't N2O give a positive brown ring test?

texts:
A common nitrate test, known as the brown ring test can be
performed by adding iron(II) sulfate to a solution of a nitrate, then
slowly adding concentrated sulfuric acid such that the acid forms a
layer below the aqueous solution. A brown ring will form at the
junction of the two layers, indicating the presence of the nitrate ion.

I know for sure that certain oxides of nitrogen, such as $\ce{NO}$ and $\ce{NO2}$ test positively in the brown ring test for nitrates, but I had never found a reliable source stating the same for the other oxides of nitrogen.
But one of the questions in a class test I took was:

Which one of the following does not give the Brown Ring test?

$\ce{N2O}$
$\ce{NO}$
$\ce{N2O3}$
$\ce{N2O5}$

The answer was given as $\ce{N2O}$ and I am unable to identify the logic behind the answer. Could it be because the nitrogen compound is reduced in the process of forming the brown complex with iron, while $\ce{N2O}$ already has too small an oxidation state to be reduced to $\ce{NO+}$?


texts: Is it possible to disable the splash screen of ChemDraw? I can't find a corresponding setting in the preferences dialog. Is there maybe a hidden setting / some configuration file that can be modified?


texts: Changing the order of the reaction with change in concentration

texts:
The reaction

$$\ce{2 A + B + C -> D + 2 E}$$

is found to follow the rate law as

$$r = k[\ce{A}][\ce{B}]^2[\ce{C}]^0$$

If the concentration of $\ce{A}$, $\ce{B}$ and $\ce{C}$ increases two times then the rate of reaction becomes eight times higher:

$$r' = k\cdot 2[\ce{A}]\left(2[\ce{B}]\right)^2\left(2[\ce{C}]\right)^0 = 8k[\ce{A}][\ce{B}]^2$$

Note: there is no change in the order of reaction. I want to change the order of this reaction by changing the concentration of reactants. Can I do this?

Because if we double the concentration of $\ce{A}$, $\ce{B}$ or $\ce{C}$, it does not change the order. But if we increase  the concentration of $\ce{A}$ by 4 times, then we can change order by

$$\left(4[\ce{A}]\right)^2 = \left(2[\ce{A}]\right)^{2+2} = \left(2[\ce{A}]\right)^4$$


texts: Number of mercury atoms in a drop of mercury

texts:
Question:

  A) Calculate the mass of a mercury atom in kg.
  B) How many atoms of mercury does a drop of mercury contain, knowing that the volume of a drop of mercury is $\pu{0.05mL}$ and that the density of mercury is $13.6 \times 10^3 \mathrm{kg/m^3}$

I know that $\mathrm{1 mL = 1 cm^3}=1.0\times10^{-6} \mathrm{m^3}$

And the mass of a drop of mercury is $\mathrm{m=v}\times \mathrm{density}
= 5.0\times10^{-18} \times 13.6\times{10^3}
=6.8\times10^{-14}$

What I want to know is how to proceed to find how many atoms mercury are present in its one drop? Do I simply divide the mass of a drop of mercury by the mass of a mercury atom, or do I use the Avogadro's number?  I don't want a straight-off answer, I only wish to know how to calculate it.


texts: Are molecules chiral if a rotation leads back to the same compound?

texts:
I understand that if you rotate a molecule and it has the same configuration as its enantiomer, then it is indeed the same compound as the enantiomer (meso), and hence is achiral (despite having chirality centers).

If compound is rotated and the resulting Fisher projection has exactly the same configuration after its rotation, what does that mean in terms of chirality? (I'm not talking about enantiomers here,) It will have a different enantiomer (and hence not be meso), and will be polarizable, but the compound itself has exactly the same perspective if you rotate it. Does this hold any signifance chemically or stereochemically, or is it meaningless?

Take for example D-idaric acid (2S,3R,4R,5S)-2,3,4,5-tetrahydroxyhexanedioic acid).

In the below example of Idaric acid, the enantiomer appears to be a different compound. When the compound is rotated 180 degrees, it looks exactly the same.

In the below example of galactaric acid, when the compound is rotated 180 degrees, it is a different image. This is despite it being meso.

Obviously, being meso has a lot of chemical significance (no polarization of light). But does a compound possessing the property of being rotated 180 degrees, and having the same image (in Fischer form) present any chemical significance compared to a compound that doesn't do this?


texts: Concentration of Amino acid calculation?

texts:
I found the $\mathrm{pH}$ of alanine solution, and I need its concentration, I'm given the formula below:
$$\mathrm{pH}=\frac 12 (\mathrm{p}K_\mathrm{a}- \log c)$$
My try:
I have calculated $\mathrm{pH}$, to find $c$ I need $\mathrm{p}K_\mathrm{a}$. Can someone explain that formula, what is $\mathrm{p}K_\mathrm{a}$?
I know that this amino acid has $\mathrm{p}K_\mathrm{a1}$ and $\mathrm{p}K_\mathrm{a2}$, which do I use?


texts: Ideal gas equation derivation proportionality

texts:
While deriving the Ideal gas Equation using Boyle's, Charles', and Avogadro Laws,
how are each of the laws, which have different proportionality constants and different quantities as constant combined?
(eg: Boyle's  law which assumes the temperature and moles of gas to be constant, but in Charles' law temperature changes. How is it possible?)


texts: How to convert soluble colorless [HgI₄]²⁻ back to insoluble red HgI₂?

texts:
When a solution contains $\ce{Hg^2+}$ and $\ce{I-}$, depend on the concentration ratio of $\ce{Hg^2+}$ and $\ce{I-}$, the following reactions can happen:

$$\ce{Hg^2+ + 2 I- ⟶ \underset{insoluble red color solid}{HgI2}}$$

If there is excess $\ce{I-}$, then this red solid will continue to react with excess $\ce{I-}$ to form an colorless soluble complex:

$$\ce{HgI2 + I- ⟶ [HgI3]^-}$$

$$\ce{[HgI3]^- +  I- ⟶ [HgI4]^2-}$$

Is there a way to revert $\ce{[HgI4]^2-}$ back to $\ce{HgI2}$?


texts: Why do these two calculations give me different answers for the same acid-base titration?

texts:
In class, I performed an weak acid-strong base titration using commercial white vinegar and sodium hydroxide with the aim of finding the concentration of of ethanoic acid in the vinegar, and I used stoichiometric calculations as well as the $\mathrm{p}K_\mathrm{a}$ equation to find the concentration from the data I collected. However, these two methods are giving me different answers and I have no idea if I did something wrong in my calculations, or used the wrong method outright.

As a bit of background info, the label on the vinegar says it has a $\ce{CH3COOH}$ concentration of $5\%$, which according to my calculations (I measured the density of the vinegar to figure this out) is around $0.9\mathrm{~mol~dm^{-3}}$.

Here's the data from the titration:

Volume of $\ce{CH3COOH}$: $3.1\mathrm{~cm^3}$ (diluted with water to the $50\mathrm{~cm^3}$ mark for experimental purposes)

Concentration of $\ce{NaOH}$: $0.1 \mathrm{~M}$

Volume of $\ce{NaOH}$ added: $33.1\mathrm{~cm^3}$

Initial $\mathrm{pH}$ of $\ce{CH3COOH}$: $3.0$

Half-equivalence $\mathrm{pH}$: $4.6$

So, using the stoichiometric method, we have the formula

$$M_\mathrm{acid} V_\mathrm{acid} = M_\mathrm{base} V_\mathrm{base}$$

so,

$$M_\mathrm{acid}(0.0031) = (0.1)(0.0331)$$

$$M_\mathrm{acid} = \frac{(0.1)(0.0331)}{0.0031} = 1.067 \mathrm{~mol~dm^{-3}}$$

This answer is fairly close to the literature value, so I'm assuming it's accurate. (The percentage concentration works out to be about $6.1\%$.)

On the other hand, the $\mathrm{p}K_\mathrm{a}$ equation is $K_\mathrm{a} = \frac{[\ce{A-}][\ce{H+}]}{[\ce{HA}]}$

Since $\mathrm{p}K_\mathrm{a} = \mathrm{pH}$ at the half-equivalence point, the $K_\mathrm{a}$ is $10^{-4.6} = 2.5 \times 10^{-5}$; similarly the initial $\mathrm{pH}$ is $3$, so the initial $[\ce{H+}]$ is $10^{-3}$.

So,

$$2.5 \times 10^{-5} = \frac{(10^{-3})^2}{[\ce{HA}]-0.001}$$

Entering this into a calculator returns the value $[\ce{HA}] = 0.041 \mathrm{~mol~dm^{-3}}$.

So, why is the second answer so much smaller than the first? Have I used one of the equations incorrectly or made an error in calculation? Does one of the methods not work for the acid-base titration in question (and why would that be?)

I sincerely apologize for the messy formatting; I literally had to learn LaTeX from scratch just to post this question. Thank you so much in advance.


texts: Carbocation Rearrangement - Till which neighbouring carbon is it possible?

texts:
In the above reaction, clearly the OH will be protonated followed H2O leaving, seeing that it's a good leaving group.

Now there can be two possibilities either a alkene is formed as is, or the carbocation rearranges and ends up opening the ring, thus increasing the final stability of molecule, followed by alkene formation. (5 carbon ring is more stable)

But as per some texts, the Carbocation only rearranges until the neighbouring carbon and then alkene is formed without ring opening. Is that correct, if yes, why?


texts: Possible to find expression for the energy of mixing with the Helmholtz free Energy?

texts: I am aware that the energy of mixing can be found using the thermodynamic identity for the Gibbs free Energy and plugging in the expression for the entropy of mixing which finds;-∆G_Mixing≈-TNk (xlnx+(1-x)ln(1-x)) with particles of type A: N_A= (1-x)N and type B: N_B= xN. I was wondering if, when the temperature, number of particles and volume (one type of the particles being in a much greater presence) is held constant, the Helmholtz free energy could be used to find the energy of mixing?


texts: Are there any full worked examples of DFT calculations?

texts:
I just started learning DFT and now I am totally confused.

Assuming I want to use B3LYP:
\begin{align}
v_s\left(\textbf{r}\right) &= v_\text{ext}\left(\textbf{r}\right) + \int d^3r\frac{n\left( \textbf{r}\right) }{\left|\textbf{r} - \textbf{r}^\prime\right|} + v_{\text{XC}}\left[ n \right]\left(\textbf{r}\right)\\
v_{\text{XC}}\left( r \right) &= \frac{\delta E_\text{XC}}{\delta n \left(\textbf{r}\right) }\\
\end{align}

I know that we use B3LYP for approximation of $v_{\text{XC}}$ - but I have no idea about how - and then we use some basis sets to run an SCF calculation to minimize the energy.
I downloaded a bunch of articles and bought some books and read them, but all of them give very detailed discussion about all the basics (e.g. what a functional is, or Kohn and Sham theorem, etc.), but no one talks about how to use them.

I am looking for a reading material or video that explains all the calculation, step by step, for example, some material that shows all the calculations for a CO molecule, from the beginning to the end of the SCF calculation.


texts: Using IR to detect / quantify a molecule at low concentrations

texts:
I want to detect / quantify a specific terpenoid molecule from a microbiological growth medium. The molecule will however be present at very low levels approx. 10-100 mg/L.

Is it viable to use the IR spectrum to detect this molecule at such low levels? If not quantitatively at least in a qualitative sense? The idea is to have some sort of method that is amenable to reasonably high throughput screening.

A GC / GCMS which is the typical assay method is too time consuming for screening a lot of samples.

The IR spectrum is shown below. Can I just monitor a specific wavelength with max absorbance, (say) 3000 cm-1? That way I won't have to scan the whole wavelength range.

Any other ideas?


texts: Why can alcohol undergo elimination just by sulphuric acid?

texts:
In both $\mathrm{E1}$ and $\mathrm{E2}$ reactions with alcohol, loss of a leaving group and proton transfer are required. And proton transfer requires a base to get that hydrogen in alcohol.
I know that $\ce{H_2SO_4}$ can make a bad $\ce{ROH}$ group into a good leaving group ($\ce{ROH_2^+}$) by protonation, but how can it (strong acid) serve as a base for proton transfer to happen (in this 1 step process)?
What I think:

$\ce{H_2SO_4}$ is a dehydrating agent, so it can 'suck out' the $\ce{OH}$ together with heat, like dehydration with sugar into pure carbon (from my high school textbook)? However, is this mechanism even called $\mathrm{E1/E2}$?


texts: Mechanism of pseudo buffer pH maintenance

texts: Some solutions, like concentrated HCl, act as buffers even though they lack the buffering component. What is the cause for such a behaviour?


texts:
Which name is the Preferred IUPAC Name of the above molecule? 3-methyl-4-oxobutanenitrile or 3-formylbutanenitrile?

I feel the second one is the PIN, since it's shorter than the first one. But, I haven't been able to navigate the IUPAC Blue Book, regarding such cases.


texts: Does heat loosen "corrosive bonds" in iron compounds... permanently?

texts: One [obvious] way to remove a seized nut is to heat it [thus enlarge it]... more than the bolt. But that's not the only way to use heat in this application. Apparently you can also let the stuff cool down and the nut will still be significantly easier to remove than before applying theat. Why does this happen? The description of this latter video says something about heat "separating the corrosive bonds". Is there real science behind this claim?


texts:
How can you elegantly describe that a polymorphic substance changes its structure?

  It polymorphs
  It morphs
  It undergoes polymorphic transition
  It experiences a morphic change

Or what would be even better terms?


texts: I thought that Organic Naming was based on alphabetical for alkyl branches, so I thought it was ethyldimethylamine, however google results show me Dimethylethylamine. So which one is right? And is this an IUPAC rule?


texts: How to derive the relation between gibbs energy and equilibrium constant?

texts:
I want to understand the derivation between gibbs energy and equillibrium constant $$\Delta G=\Delta G^o+RT\ln Q?$$
I have seen a similar post on CSE  Derivation of relationship between equilibrium constant and Gibbs free energy change   which seems to be incomplete and still confusing so I am again asking this question.

The derivation that was written in the post was as follows:

  Using the fundamental equations for the state function (and its natural variables):_
  $$dG=-SdT+VdP$$
  $$V=(\dfrac {\partial G}{\partial P})_T$$
  $$\bar G(T,P_2)=\bar G(T,P_1)+\int_{P_1}^{P_2}\bar V dp$$
  Here $\bar x$ represents molar $x$, i.e. $x$ per mole
  $$\bar V=\frac {RT}{P}$$
  $$\bar G(T,P_2)=\bar G(T,P_1)+RT \ln\frac {P_2}{P_1}$$
  Defining standard state as $P=1\text{bar}$ and $\bar G=\mu$
  $$\mu(T,P)=\mu^o (T)+RT\ln \frac{P}{P_o}$$
  consider the general gaseous reaction $aA+bB\rightarrow cC+dD$
  $$\Delta G=(c\mu_C+d\mu_D-a\mu_A-b\mu_B)$$
  for "unit progress" in reaction. Using $\mu_i=\mu^o_i+RT\ln \frac{P_i}{1bar}$
  $$\Delta G=(c\mu^o_C+d\mu^o_D-a\mu^o_A-b\mu^o_B)+RT\ln \frac{P_C^cP_D^d}{P_A^aP_B^b}$$
  $$\Delta G=\Delta G^o+RT\ln Q$$

I know the relation between Gibbs free energy,Enthalpy,Entropy and Temperature as $$G = H - TS$$
how is the relation $dG=-SdT+VdP$ derived from the above formula?
Why do we take a path where Entropy and volume are constant  in the equation $dG=-SdT+VdP$ as in a chemical reaction both volume and entropy can change?


texts:
The NMR technicians where I work have recently started replacing the standard 2D NMR experiments (COSY, HSQC) with NUS variants (25% sampling). For the uninitiated, the rationale behind the technique is summarised by Claridge (who does a better job of explaining than I would):

  The classical sampling of 2D (and more generally multi-dimensional) NMR experiments requires the uniform sampling of data in the indirect dimension(s) that allows for the processing of the data by the discrete Fourier transform. This means a sequential, stepwise increment of the t1 period of a 2D data set is made to the limit t1 which dictates the resolution in this dimension. The number of such t1 increments employed ultimately defines the total duration of the experiment. The method of non-uniform sampling (NUS) seeks to reduce the number of data points collected in the indirect dimension(s) and so reduces the total experiment time.

  Claridge, T.D.W. High-Resolution NMR Techniques
  in Organic Chemistry, 2016

My experience of these experiments has been overwhelmingly positive so far: shorter experiment times and greater resolution, even when acquiring spectra of small quantities (0.1 - 0.5 mg) of large molecules (ca. 1000 Da).

The challenge is knowing what to do when the spectrum doesn't come out looking quite right. With 'traditional' experiments, running more scans often fixes a multitude of sins (up to a point), but with random point sampling I can't see this holding up so well.

The processing of data is also causing some confusion - TopSpin and MNova give (often very) different results, despite both having NUS processing capability. This processing issue leads me to suspect that many of the issues I'm having with spectra from NUS pulse sequences are actually due to the processing (which isn't terribly well covered in the TopSpin manual).

My question, therefore, is what considerations should be taken into account with NUS spectra: are there instances where its better to take the hit and run a long HSQC? What do I need to be careful of when processing data to ensure spectra come out looking okay?


texts:
I have recently bought a carbon monoxide spot detector which is not working the way I intended for it. A carbon monoxide spot detector is an analog carbon-monoxide detecting patch that changes color when it comes in contact with carbon monoxide. The problem is that it changes back to it's original color whenever the carbon monoxide leaves the room.

I'd wish for it to stay the same color it changed to after it came into contact with carbon monoxide. What should the reaction look like to fix this problem? I have copy/pasted a scholarly paper from Google to better explain what's happening inside of the patch:

  Principle of the $\ce{CO}$ – Detector: The palladium (II) chloride inside is reduced into metallic palladium when exposed to $\ce{CO}$. While the $\ce{CO}$ – level in air is rising, higher amount of palladium is formed. A color change of the solution from pale yellowish orange to orange or grey is followed.
  $$\ce{CO + PdCl2.2H2O → CO2 + Pd + 2HCl + H2}$$
  Afterwards, when exposing to $\ce{CO}$ – free air, copper (II) chloride oxidizes palladium back into palladium (II) chloride. In addition, copper (II) chloride is reduced to copper (I) chloride.
  $$\ce{Pd + 2CuCl2.2H2O → PdCl2.2H2O + Cu2Cl2}$$
  Then, the regeneration of copper (II) chloride occurs.
  $$\ce{Cu2Cl2 + 2HCl + H2O + 1/2 O2 → 2CuCl2.2H2O}$$
  Thus, the solution resumes to its initial state. (the oxygen comes from the surrounding air)


texts: What would be a stable way to hold lithium hydride powder?

texts:
I currently have 100 grams of lithium hydride powder that needs to be held in a solid form. Initially, I was considering using cement, however, the moisture require converts the lithium hydride to lithium hydroxide. What would another moisture-free agent be that I could use for this task?

If it helps, the lithium hydride and the solidifying agent are to be used for neutron moderation.


texts: Why is platinum an excellent catalyst in comparison with similar metals?

texts: What is special about platinum structure which actively participate in catalytic reactions while similar metals with similar atomic structures cannot.


texts: Why is degree of dissociation used to estimate strength of an acid?

texts:
Problem

Which of the following will give strength of acid?
A) pH
B) Normality
C) Degree of dissociation
D) Dissociation constant

Answer

 C, D

Question
If pH is not considered as a metric to assess the strength of an acid because it depends on dilution (even strong acids can have high pH), then why is degree of dissociation a reliable metric for the same? Doesn't degree to dissociation depend on dilution as well?


texts: Angular momentum - Question on Zare's use of the Vector Model to Estimate Probability

texts:
My question regards a specific example, although I get the feeling that the answer is simpler than I imagine. In Zare's Angular Momentum: Understanding Spatial Aspects in Chemistry and Physics pgs 53-54, He discusses the vector model for coupled and uncoupled representations for the addition of two angular momenta.

I've scanned and included the picture I am going to refer to for clarity:

The image above is a modified representation of the uncoupled representation, although it appears very similar to the coupled diagram, the difference is that j1 has been arbitrarily fixed, and j2 is precessing in the dashed circle, around an axis parallel to z.

Zare expands the dot product of $\mathbf{j_1}$ and $\mathbf{j_2}$
(Eq 2.34):

$\mathbf{j_1 . j_2} = |\mathbf{j_1}||\mathbf{j_2}| cos(\gamma)$

$=|\mathbf{j_1}||\mathbf{j_2}| [ cos(\theta_1) cos(\theta_2)+  sin(\theta_1) sin(\theta_2) cos(\theta_1) cos(\phi_1 -\phi_2)]$

So far, so good, no problem. Then he instructs:

"Let us differentiate Eq (2.34) with respect to time to obtain the rate of change of the length of $\mathbf{j}$. From the law of cosines

$|\mathbf{j}|^2 = |\mathbf{j_1}|^2 + |\mathbf{j_2}|^2 - 2 |\mathbf{j_1}| |\mathbf{j_2}| cos(\gamma)$

$=|\mathbf{j_1}|^2 + |\mathbf{j_2}|^2 - 2 \mathbf{j_1} . \mathbf{j_2}$

So that

$\frac d{dt} (\mathbf{j_1} . \mathbf{j_2}) = -\frac 12 \frac d{dt} [ |\mathbf{j}|^2 + |\mathbf{j_1}|^2 - |\mathbf{j_2}|^2 ]$"

And THIS next step is where I get lost:

He IMMEDIATELY equates that expression with the following:

$$ = -|\mathbf{j}| \frac {d|\mathbf{j}|}{dt} $$

So that there's no confusion, what I do not understand is the statement:

$$\frac d{dt} (\mathbf{j_1} . \mathbf{j_2}) = -\frac 12 \frac d{dt} [ |\mathbf{j}|^2 + |\mathbf{j_1}|^2 - |\mathbf{j_2}|^2 ] = -|\mathbf{j}| \frac {d|\mathbf{j}|}{dt}$$

Now, if I explicitly expand all components of the vector norms: $\mathbf{j_1}$,$\mathbf{j_2}$,and $\mathbf{j}$, and try to solve for what's inside the brackets on the LHS, I just regenerate the expression:

$|\mathbf{j}|^2 =|\mathbf{j_1}|^2 + |\mathbf{j_2}|^2 - 2 \mathbf{j_1} . \mathbf{j_2}$, which is of no use in aiding me as far as I can see.

Furthermore, it is explicitly stated that the only time-dependent component of this system is the dihedral angle $\phi_1 - \phi_2$, and in any expansion of the vector $|\mathbf{j}|$ into its components, a time derivative would render the any other independent parts mute.

I am thoroughly confused. I have consulted the following textbooks and not found any sign of this exact derivation:

Cohen-Tannoudji (volumes I and II), Feynman's lectures on Physics Vol III, Shankar, Atkin's physical chemistry, Engel and Reid's physical chemistry, Gaziorowicz, and Eisberg and Resnick.

What I suspect is that I'm simply lacking in some fundamental piece of calculus or arithmetic. Whether there's some simple trick of Vector Calculus that I haven't employed to give me the identity placed here? I would love a direct answer, but will also accept a nudge in the right direction. Right now it just feels like I'm leafing through books without a compass.

Best,

and THANKS!


texts: Why is aqueous solution of lauyl glucoside alkaline?

texts: What is the reaction of dissociation of lauryl glucoside? It's aqueous solution pH is much higher than 7, it's definately alkaline. Why is that? It's nonionic surfactant and as far as I know it only creates hydrogen bonds with water (the hydrophilic part of the molecule, oxygen atom). Lauryl glucoside is the combination of glucose and dodecanol. Glucose itself when diluted in water is neither acidic nor alkaline. Why is glucoside then alkaline?


texts: Compounds that adopt the zincblende structure

texts:
Zinc sulfide, copper iodide and copper bromide all adopt the zincblende structure. My lecture notes suggest that this structure is adopted preferentially over the wurtzite structure if the bonding is more covalent (why is this?); thus, it’s adopted where there is a polarizing cation and a polarizable anion.

However, surely a polarizing cation should be small and highly charged (i.e. not ions like $\ce{Cu+}$ surely? It has a low charge and large-ish radius). What makes this polarizing? I’ve also heard this about $\ce{Ag+}$.


texts: What is the equation and conditions for the synthesis of phenols? Would it work if we added $\ce{NaOH}$ to benzene and then refluxed?


texts: Why is in the reaction of cyclic unsaturated aldehydes with hydrazine and hydrogen peroxide the aldehyde preserved?

texts:
Question
  What is the product of this reaction?

  The answer given:

At first, I thought this was a typical Wolff-Kishner reduction, but then I saw the reagents didn't match up (no $\ce{OH-}$).

How is this getting formed? Shouldn't the $\ce{CHO}$ group be reduced? What am I missing here?


texts: Are the canonical orbitals of Hartree-Fock also the natural orbitals?

texts: My question stems from the comments on my answer to After a unitary transformation, is Koopmans' theorem still valid?. There was some confusion relating to differing terminology referring to different, mostly unrelated density matrices. As of now, I'm uncertain as to what density matrix one diagonalizes to obtain the natural orbitals. Is it the density matrix that appears in the HF calculation or some different density matrix?


texts: How can I separate sodium ions from brine or molten NaCl?

texts: Is possible to separate sodium ions from an aqueous solution of NaCl? If so, how do I go about it?


texts: Making a reasonable slab of alpha quartz

texts:
I want to perform a molecular dynamics simulation with alpha-quartz as my mineral surface. I want to study adsorption of water on alpha-quartz. The most dominant error that I came up with is the problem with my initial physical configuration. In other words error is: System is too far from equilibrium. I think the major problem is related to chemical structure of alpha-quartz slab.

I used the experimental data for unit cell of alpha quartz and then replicate it for making a slab of it. My question is: Is this structure stressed in some way? My cell is periodic in 3 directions and some of oxygen atoms are not in the right place! Can it be the problem?

How to replicate unit cell of alpha quartz for obtaining a reasonable structure? Where can I find a right data for unit cell of alpha quartz?


texts:
I learned that all strong acids have a 100% degree of ionization and that there are no degrees of strength in acids; however, I also read that fluoroantimonic acid is 20 quintillion times stronger than 100% sulfuric acid !!

Can you please explain the chemistry behind this?


texts:
Is there a way to get lead cheaply from local sources? I can buy ingots off eBay and there is a non-ferrous metal supplier I know who sells it for $12 for 5 pounds, but the shipping is nuts.

I considered salvaging lead from a battery, but apparently that is not viable cause the battery is contaminated with a lot of lead oxides, lead carbonates and antimony.

I also considered fishing weights, but I am concerned about alloyed contaminants and also it is getting difficult to find lead fishing weights, especially large ones.

I am interested mostly in "technical grade" just for weighting stuff down (like apparatus stands), but also having a small amount available that is reagent quality.


texts:
If I asked you to draw me an amide, we'd likely end up with something in the form of:

The exact definition of this is given fairly clearly in the IUPAC gold book.

  Derivatives of oxoacids [...] in which an acidic hydroxy group has been replaced by an amino or substituted amino group. Chalcogen replacement analogues are called thio-, seleno- and telluro-amides. Compounds having one, two or three acyl groups on a given nitrogen are generically included and may be designated as primary, secondary and tertiary amides, respectively
  Source: IUPAC Gold Book, 1995 recommendations

There is however another class of compounds which we call 'amides', for instance LDA (lithium diisopropylamide). Again, the IUPAC gold book has this covered.

  The term applies also to metal derivatives of ammonia and amines, in which a cation replaces a hydrogen atom on nitrogen.

I fully accept this, my question is, why we decided to re-use the word 'amide' to describe these compounds. Is the reason historical (i.e. before we knew better), or is there a logical basis for the grouping of the two classes of compounds.


texts: Molar conductivities of aqueous electrolytes at 1 M

texts:
In the following table from the CRC Handbook, molar conductivities of aqueous electrolytes are given for concentrations from infinite dilution to 0.1 M.  However, I am looking for values at 1 M, and I'm having a hard time finding that information.  (The following table probably stops at 0.1 M because the Debye-Huckel-Onsager equation is only accurate for very dilute solutions.)
This is a soft question, I admit, but can anyone suggest resources for finding tables of molar conductivities of aqueous electrolytes (i.e., typical ones like $KCl$, $KOH$, $H_2SO_4$) at 1 M?


texts: What is the mechanism that creates a potential between Zn and Cu when they are connected with a wire?

texts: When people explain a galvanic reaction, they usually stop the explanation in the dogma that one is more reactive/electronegative/nobler then the other. But that doesn't really explain the mechanism. I mean, why there would be a electrostatic force between elements with different reactivity?  What mechanism creates a potential there? Why electrons get repelled from $\ce{Zn}$ and get attracted to $\ce{Cu}$?


texts: Does higher electron density mean better transport?

texts: In a nano device, do areas with higher electron density necessarily contribute more the to the overall transport compared to areas with lower electron density?


texts: Number of optically active compounds among the products of ozonolysis

texts:
The number of optically active compound(s) obtained upon complete ozonolysis of
  the following optically active compound is

In the question, I broke all the double bonds and added a $\ce{-CHO}$ group according to the question (ozonolysis).
Checking for the optically active compounds I found two of them:

But the solution has given only one compound! Can you please help me with this?


texts:
The reaction of alcohols $\ce{ ROH }$ with $\ce{ PCl5 }$ and $\ce{ PCl3 }$ yields an alkyl halide $\ce{RCl}.$ With $\ce{ PCl5 }$, the reaction is quite simple leading to the formation of $\ce{ RCl }$ and $\ce{ POCl3 }.$

But with $\ce{ PCl3 }$  a problem arises. Since $\ce{ PCl3 }$ has both a lone pair and vacant $\ce{3d}$ orbitals it can act both as a Lewis base and a Lewis acid.

In the first figure, $\ce{ PCl3 }$ accepts a lone pair showing its acidic character and expelling $\ce{Cl-}$ out. Now this is where I am getting confused. On one hand we have  a Lewis base $\ce{ PCl3 }$ and on the other we have the "expelled" $\ce{Cl-}$? Now in this case why does $\ce{PCl3}$ take away the proton and not $\ce{Cl-}$?

And in the next step, why does  $\ce{Cl-}$ attacks the carbon not the  $\ce{H+}$?


texts: Calculating Standard Gibbs Energy of Dissolution

texts:
The solubility of mercury (I) iodide is $\mathrm{5.5\ fmol/L}$ in water at $25\ \mathrm{^\circ C}$. What is the standard Gibbs energy of dissolution of the salt?
  The reaction is
  $$\ce{Hg2I2(s) -> Hg2^2+(aq) + 2I- (aq)}$$

Here is what I think I need in order to solve the question:

$$\Delta G=-RT\ln(K)$$ where $K$ will be the solubility constant. When the question says “solubility of mercury (I) iodide is $\mathrm{5.5\ fmol/L}$” I don’t exactly understand what this means.
The units make it seem like a concentration to me.


texts: How many Ga atoms are connected to one As atom in solid gallium arsenide?

texts:
In Boylestad and Nashelsky's Electronic Devices and Circuit Theory, the structure of GaAs is shown as follows:

Arsenic is shown making five covalent bonds to neighbouring gallium atoms.

However, I recently also saw an alternative depiction in Razeghi's Fundamentals of Solid State Engineering:

Here, arsenic is shown making four covalent bonds to neighbouring gallium.

Which source is correct? Please give appropriate references or experimental proof.


texts:
Why is it that the chlorination of 1-chloro-3-nitrobenzene (18) gives 1,4-dichloro-2-nitrobenzene (19) as the major product, 1,2-dichloro-3-nitrobenzene (20) as a minor product and 1,2-dichloro-4-nitrobenzene (21) is not formed at all?

I know $\ce{-NO2}$ is a deactivating, meta-directing group and hence it decreases the electron density at positions 2, 4, 6 while position 5 is unaffected. On the other hand, $\ce{-Cl}$ is a deactivating, o-p directing group and hence it directs the incoming group to positions 2,4 or 6. Taking into account the fact that $\ce{-NO2}$ is a more powerful deactivating group than $\ce{-Cl}$, the incoming $\ce{Cl+}$ should be attached at position 5 as it has more electron-density than 6,2 or 4 position. But the product with $\ce{Cl}$ at position 5 is not formed. Why so? I am unable to rationalise this.

Source: page 583 of "March's Advanced Organic Chemistry, 7th ed." under the heading "Orientation in benzene rings with more than one substituent".


texts:
I am trying to cast bismuth, which melts at 271.4 °C. Silicone rubber seemed like a good material to use for a mold, given its flexibility and the ease with which it can be cast itself, as well as its high (~300 °C from some sources) heat tolerance.

I have had the opportunity to test casting bismuth in this way once so far (will have the opportunity to try again this weekend) using a mixture of acetoxy silicone and cornstarch as the mold, for ease of molding and quicker curing.

While the mold itself seemed to stand up well to the heating, aside from discoloration, there was a large amount of bubbling as the bismuth cooled, resulting in deformation of the final structure.

My best guess as to the cause of the bubbling is that the silicone had not finished curing, and trapped, evaporating water and acetic acid were the source of the bubbles. Is this likely to be correct, and if so, is there a way to avoid this in future casts, such as possibly by letting the silicone cure longer? Alternately, are there different formulations/materials that may perform better, without being significantly harder to make?


texts:
I'm trying to synthesize of silver particles by using glucose as reducing agent, PVP as dispersant, and NaOH as pH control. Before adding silver nitrate solution, I've produced a solution which is combination of glucose, PVP and NaOH in distilled water.
In the polymer solution, I see that the color changes, from colorless to dark orange/brown solution. Is there any reaction that occurs in the polymer solution which contains glucose, PVP, and NaOH due to the changes of color?
I know from researching that the solution is expected to turn yellow when glucose and sodium hydroxide are mixed, which I observe, but I do not understand why the solution changes to darkish orange to brown when PVP is added?


texts: How do I know what the end products of the reaction of glucose and fructose?

texts:
I am unsure about why the end products of the reaction are what they are.
Let's say I was combining glucose and fructose in a dehydration synthesis reaction to create sucrose. The equation is:

$$\ce{C_6H_{12}O_6 + C_{6}H_{12}O_{6} \rightarrow C_{12}H_{22}O_{11} + H_{2}O}$$

How do I know it is not:

$$\ce{C_6H_{12}O_6 + C_{6}H_{12}O_{6} \rightarrow C_{12}H_{24}O_{12}}$$


texts: As an end of high school treat, my class is trying to convince our chemistry teacher to make an explosion as a demonstration. What sort of reactions are beautifully explosive but safe enough to do in a school lab environment, when performed by a teacher who knows what they're doing?


texts: What would happen if the reaction of reduction of carboxylic acids by LiAlH4 is carried out in alcohol?

texts:
Which is the intermediate compound in the reduction of carboxylic acids by $\ce{LiAlH4}$ and what would happen if the reduction of carboxylic acids is carried out in alcohol?

From my knowledge I know that a geminal diol is formed and then elimination takes place to form $\ce{R-CH=O}$. If this is reacted with alcohol instead of $\ce{LiAlH4}$ again what are the expected products?


texts: Arrow pushing: why does the O become positive when its lone pair becomes a double bond?

texts:
In the following image:

The oxygen's top pair of electrons forms a double bond.

But in a covalent bonds, aren't the electrons shared? So won't the oxygen still have these $2$ electrons (that it turned into a double bond) in its outer shell? Leaving its charge as $0$?

So why would its charge change?

I think what is confusing me is what the negative and positive signs mean and how this relates to it's formal charge and its octet.

I know the left structure's oxygen has a formal charge of $0$, and the right hand structure's oxygen has a formal charge of $+1$.

So are plus and minus signs showing formal charge, and not the number of valence electrons?

If so, does the plus sign have nothing to do with the number of valence electrons?


texts: Why do we use Ḡ ("G bar") as a notation for partial molar free energy?

texts:
For partial molar entropy there is a bar that is positioned above the $G$ with a subscript I that is sometimes added to the $G~(\bar{G}).$ The bar I read sometimes denote the "partial nature of the $G$".

However, is it not rhetorical. I am looking for the explanation as to what is so partial about this quantity with regard to it's occurrence in the equation.


texts: What is the value of the gas constant derived from the kinetic model of gases?

texts:
I used this resource (http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1151&context=physicskatz) to derive the ideal gas law from the kinetic model of gases:

$$PV=n(2/3)N_oT$$
with T being equal to $(1/2)mv_{average}^2$.

And now I'm super confused. Does this mean that the universal gas constant R is simply equal to (2/3)*avogadro's number?


texts: Why does copper jewelry & wire smell bad - even when I'm not wearing it?

texts: I make jewelry by weaving a frame from copper wire for a gemstone, then making copper coils or spirals, etc for further decoration. Even 'on the roll', the copper wire smells bad - and the smell increases as I work with the wire.  The smell also clings to my hands, and I have to wash it off.  I read about the chemistry that is created when copper touches skin. But the problem is, copper jewelry that has been hanging, without being worn, has begun to smell even worse - to the point that I can't even consider hanging it around my neck. Can you give me a reason for this odor (not a chemical reaction after touching my skin), and hopefully a remedy for it? I would hate to imagine what other sensitive customers would think after having one of my jewelry pieces for a few months.  Thanks for helping.


texts: Anion-exchanged compound - smaller 1H NMR integrations

texts:
I anion exchanged one of my compounds (Br- to PF6-) and the NMR integrations changed as shown on the two NMRs below. The aliphatic region peaks integrate to smaller values in the second one. Are there any known cases where PF6- somehow influences the relaxation time?

The other possibility is that this product decomposed to a similar compound, which would slightly throw off the integrations...


texts:
I am interested in the effects of plant environments on their biochemistry in relation to their effects on the environment and animals(us).

Could sodium fluoride or aluminum  accumulation in soils contribute to increased amounts of palmitic acid in food?

Thus increasing the inflammatory effects of certain foods?


texts:
When we are determining if a given compound is aromatic using Hückel's rule, we count the number of delocalized $\pi$ electrons.

In tropone for example, if I wanted to count the number of delocalized $\pi$ electrons, should I count the $\pi$ electrons of the $\ce{C=O}$ bond?

Or is the aromaticity of tropone because we can draw a more stable aromatic resonating structure in which the $\ce{C}$ acquires a positive charge and the $\ce{O}$ a negative charge?


texts: What does the formula (CH2O)106(NH3)16H3PO4 represent?

texts:
The molecular formula $\ce{(CH2O)106(NH3)16H3PO4}$  appears in the wikipedia entry for "anoxic bodies of water". A quick search suggests that it represents the product of photosynthesis, or the generic starting point for breakdown of organic matter in the nitrogen cycle, in particular the process of denitrification of "organic matter". On page 271 of Ref. (1) it is suggested  that it represents the structure of "marine plankton". This formula seems relatively widespread in use. Exactly what "organic matter" is this supposed to represent?  What is its origin (who first proposed and perpetuated its use)?

References

Derek E. G. Briggs (Ed.), Peter R. Crowther (Ed.). Palaeobiology II (1st Ed.). Wiley-Blackwell (March 5, 2001).


texts: Are glycans, such as glucose, considered alicyclic compounds?

texts: That's my question. If true, it would make my job a lot easier. I will appreciate any feedback on the matter.


texts: Other than heating, is there any evidence that normal RF radiation (say, microwave range) can affect chemical reactions?

texts: There's been a lot written (and debunked) about alleged biological effects from RF radiation, even when it's too low powered to cause heating effects or ionization. Is there any chemical reason to believe it's possible for an effect to exist?


texts: Why sp3 hybridisation in NH3 but bonding with pure p orbitals in case of other hydrides of group 15

texts:
According to my book, the following line was given relating to the bond angle in Group 15 elements

  The bond angle in PH3, AsH3 and SbH3 is close to 92° which suggests that the orbitals used for bonding are close to pure p-orbitals.

I wanted to ask if there is any reason for having sp3 hybridised orbitals for N, but not so for other elements of that group in their hydrides. Or is it completely based on experimental observations?


texts: Hair is fibrous... Is there a good reason, why we don't recycle our own hair (and clothing, what have you) into paper-products? (rather than cutting down trees)?


texts: How to determine the most stable carbanion?

texts:
Which of the following carbanions is the most stable?

I think the answer is either a or c, as in d there are no chances for the carbanion to have its charge become less. In b I think there is a + inductive effect due to methyl group which gives it more negative charge.
The ones left are a and c.  Nitrogen is an electronegative element so it might lessen the charge on the carbanion, but in both a and c the carbanion is same distance from it. I am unable to reason out it from here.


texts: Colorimetric test to measure dissolved oxygen in salt water

texts:
Are there any simple colorimetric tests for measuring the dissolved oxygen in salt water, which do not involve titration like in Winkler method ?  i.e. Are there any chemical reagents, which when added to a salt water sample, would cause a change in the colour of the solution , giving us the measure of DO ?

Regards.


texts: Thermodynamics adding salt to water changes the temperature

texts:
$5\:\mathrm{g}$ of an unknown salt are dissolved in $325\:\mathrm{g}$ of water. Both the water and the salt are initially the same temperature. The water's temperature falls by $11.4\:\mathrm{^\circ{}C}$. Explain how it is possible for the salt and water to change temperature even though both substances are initially at the same temperature.

My approach:

We know that $$q = mc \Delta T$$

Since $q, m,$ and $\Delta T$ aren't changed by this action, this process must result in the raising of water's specific heat. Is this correct?


texts: How to derive the conductivity titration curve which accounts for salt formation

texts:
I derived an equation that gave me the volume of base required to get a certain $\mathrm{pH}$:

In a titration between a weak acid $\ce{HA}$ and weak base $\ce{B}$ (adding base into acid solution) the following equations apply:

$$
\begin{align}
\ce{HA &<=> H+ + A- & K_{a}&=\frac{[H+][A-]}{[HA]}}\\
\ce{B + H2O & <=> HB+ + OH- & K_{b}&=\frac{[HB+][OH-]}{[B]}}\\
\ce{H2O & <=> H+ + OH- &K_{w}&=[H+][OH-]=10^{-14}} \\
\ce{Deg[A-] &= \frac{K_{a}}{K_{a} +[H+]} &Deg[HB+]&=\frac{K_{b}}{K_{b} + [OH-]}}
\end{align}
$$

These can be substituted into a charge balance and solved for $V_{b}$ (volume of base added):

$$
\begin{align}
\ce{[A-] + [OH-] &= [H+] + [HB+]}\\
\ce{\frac{K_{a}}{K_{a} + [H+]}\times\frac{C_{a}V_{a}}{V_{a} +V_{b}} + \frac{K_{w}}{[H+]} &=[H+] + \frac{K_{b}}{K_{b} + \frac{K_{w}}{[H+]}}\times\frac{C_{a}V_{a}}{V_{a} +V_{b}}}\\
\cdots&\cdots\\
\ce{V_{b} &=\frac{\left([H+] - \frac{K_{w}}{[H+]}-\frac{C_{a}K_{a}}{K_{a} + [H+]}\right)\times V_{a}}{\frac{K_{w}}{[H+]} -[H+] - \frac{K_{b}C_{b}}{K_{b} + \frac{K_{w}}{[H+]}}}}
\end{align}
$$

I used this to generate a pH curve and conductivity curve for the titration using the concentration of the various chemical species in solution:

For calculating the conductivity of the solution:

$$
\kappa_{\rm{soln}}=\lambda_{\ce{A-}}\times\left[\ce{A-}\right] + \lambda_{\ce{HB+}}\times\left[\ce{HB+}\right]+\lambda_{\ce{H+}}\times\left[\ce{H+}\right] + \lambda_{\ce{OH-}}\times\left[\ce{OH-}\right]
$$

Where $\lambda\chi$ is the conductivity constant for chemical species $\chi$

I was told (by a person we shall call $X$) that this model is incorrect as the weak acid/weak base titration does not have a sharp gradient change at the equivalence point but is rather sloped/gently curved due to the following equilibrium:

$$
\ce{HBA <=> HB+ + A-}\tag{$K_{\rm{sp}}=[\ce{HB+}][\ce{A-}]$}
$$

Is there a more mathematical explanation and is it possible to incorporate this equilibrium expression into the titration curve.

Please note that I know that a strong acid/base-weak base/acid conductivity curve does not have a well defined equivalence point (being rather curved), and upon asking $X$, she said that the weak acid/weak base conductivity curve was also curved at equivalence and not as distinctly sharp as my model predicts


texts: Could alloys be electroplated onto a substrate?

texts:
For example, if I want to electroplate stainless steel onto copper, could that work?
I understand that different ions would need different voltages, but would those lower voltage ions merely make the lower voltage ion be deposited faster, or completely prevent the higher voltage ion from depositing at all?


texts: Getting the molality of a solution given molarity and density

texts:
If a solution of $\ce{HNO3}$ has a molarity of 16 and a density of
  $1.42\ \rm{g/mL}$, what is the molality of the solution?

Well, a molarity of 16 means that there are 16 moles of solute for every liter of solution.

Based on density, if we have 1000 milliliters, we have 1420 grams of solution.

To calculate the molality I need:

$$\frac{16}{\text{kilograms of solvent}}$$

Since we have 16 moles, and the molar mass of $\ce{HNO3}$ is 63, we know that we have 1008 grams of solute, meaning there are 412 grams of solvent.

So I calculate the molality to be 0.038.

This answer is wrong because it is not among the options. What did I do wrong?


texts: Electronegativity of Potassium (Pauling)

texts: Just a little question, I was taught that the electronegativity of potassium[K] is 1, but I recently discovered most internet resources say 0.82. Some even say both. What is the actual electronegativity of potassium, 0.82 or 1?


texts: Colour due to F-centre is same as that produced in a flame test, why?

texts:
I have noticed that the colours that the F-centres impart in Alkali metal halides are the same that the corresponding alkali metals impart to their flames.

$\ce{NaCl}$ when heated in an atmosphere of $\ce{Na}$ becomes yellow.

$\ce{LiCl} \rightarrow$ pink

$\ce{KCl} \rightarrow$ violet/lilac

Why ?


texts: Why do BF3 and NH3 react when B has an expanded octet in the adduct?

texts:
I know that some elements like sulfur are able to have an expanded octet due to vacant $\mathrm{d}$ orbitals. However, boron and nitrogen do not have any such vacant place so how is it that $\ce{NH3}$ with its extra electron pair is able to share it with $\ce{BF3}$ and form a compound?

This is an example of a Lewis acid-base reaction that I read in my textbook.


texts: Is fluorinated steel corrosion resistant from normal oxidation?

texts: I've recently learned of a compound named Chlorine trifluoride a powerful fluorinating agent. The common way to store it seems to be in regular steel drums where it flash oxidizes the inside of the drum to make a metallic fluoride. This layer of metallic fluoride keeps the substance from reacting any further with the steel drum and passivates the steel from further oxidation by fluorine. My question is if steel that has been fluorinated comes in contact with water and oxygen(or even worse a hydrogen peroxide water mix) is the metallic flouride layer fully passivated or is it pourous like the magnetite layer used in gun bluing? Would this result in any better corrosion resistance than chrome plating, aluminizing, bluing or galvanizing? I can't seem to find any studies on the mechanical properties of the fluorine passivated layer of steel and I am curious if anyone has any experience with working with either flouring gas and steel or even chlorine trifuoride itself.


texts: A compound that absorbs all visible light

texts: Is there a compound that absorbs all visible light?


texts:
DNA is deoxyribonucleic acid because it has phosphate groups in every one of it's nucleotides.

However, in aqueous solutions protons will ionize, leaving phosphates alone as negative groups, i.e., lewis bases.

In this case, which is seen in all of our cells, is DNA structure actually the conjugate base of the theoretically described crystal form of DNA?


texts: Can someone explain what is water plasticization? I tried to look for the definition but could not find one that explains it.


texts:
The question is:

If $2.0 \cdot 10^{-4}$ moles of dye in $\pu{50 mL}$ of solution is consumed in 188 seconds, what is the average rate of consumption of dye in $\pu{mol L-1 s-1}$?

I am not sure if I have done this correctly. I use the rate of reaction formula which is $\text{Rate} = -\frac{\mathrm{d[A]}}{\mathrm dt}$ There is a negative sign because the dye is being consumed and it is disappearing.
Given:

[dye] = $2.0 \cdot 10^{-4}$ moles in $\pu{50 mL}$

volume of solution = $\pu{50 mL}$ = $\pu{0.05 L}$

$t = \pu{188 s}$

Since we have $2.0 \cdot 10^{-4}$ moles of dye per $\pu{50 mL}$ of solution, that means in $\pu{1 L}$ of solution, we get $2*(2.0 \cdot 10^{-4})$ moles of dye = $4.0 \cdot 10^{-4}$ moles
\begin{align}
\text{Rate of consumption/disappearance} &= \frac{-4.0 \cdot 10^{-4} \, \pu{mol}}{\pu{188 s}} \\
 &= -2.1 \cdot 10^{-6} \pu{mol L-1 s-1}
\end{align}
Is my answer correct? Please point out my mistakes if I did it incorrectly.


texts: Is there any chemical that can catalyze "reverse combustion?"

texts: I am trying to build a machine that converts carbon dioxide and water into gasoline (i.e. octane). Because the energy needs are so large, is there any catalyst chemical that can cause "reverse combustion" at room temperature?


texts: I am evaluating a paper Gan et. al. 2013 (https://doi.org/10.1016/j.chroma.2012.11.081) Table S4 (see image below) and I am focusing on evaluating the percent recovery for using different solid-phase extraction (SPE) cartridges. Investigators were measuring different artificial sweetener concentrations in water samples. This table suggests that their sucralose (SUC) % recovery was 106% when they used 1 mM TRIS buffer and eluted with methanol and they used a Waters Oasis WAX SPE cartridge. I am assuming n = 3 means they did a sucralose measurement 3 times. My ultimate question is, how can something have recovery greater than 100% after SPE? Does the precision and error inflate this recovery value to be over 100?


texts: Flow cup viscometer vs rotational viscometer: limitations and use cases for each

texts: What are the limitations of an inexpensive flow cup viscometer (or any other manual test viscometer) when compared to an expensive digital rotational viscometer?


texts: To calculate total vapour pressure of a solution

texts:
Question:
1 mole each of A and B were mixed to obtain an ideal solution of which one mole went to the vapour phase at equilibrium.
If $P°_\mathrm{A} = \pu{100 torr}$ and $P°_\mathrm{B} = \pu{900 torr}$, then $P_\mathrm{S}$ would be?

For the above question, I first calculated vapour pressure of A and B which came out to be $\pu{50 torr}$ and $\pu{450 torr}$ respectively (using $P°_\mathrm{A} × X_\mathrm{A}$ where $X_\mathrm{A}$ is mole fraction of A) and then I calculated vapour pressure for A and B in vapour phase which came out to be $0.1$ and $0.9$ respectively, so the amount remaining in the liquid phase will be $\pu{0.9 mole}$ for A and $\pu{0.1 mole}$ for B, according to which the $P_\mathrm{S}$ should be $\pu{180 torr}$, but the answer provided is $\pu{300 torr}$, am I missing something? (also see the image below for better understanding of my approach).
Any help is appreciated! Thanks in advance!


texts:
(i) What happens when you put $\ce{Ag_{10}}$ and $\ce{Ag_5}$ clusters into an aqueous solution of pH = $13$
(ii) What happens when you put $\ce{Ag_{10}}$ and $\ce{Ag_5}$ clusters into an aqueous solution of pH = $5$

In the previous questions they have asked to calculate the solubility product of $\ce{AgCl}$ and the standard potentials of $\ce{Ag_5}$ and $\ce{Ag_{10}}$ which I calculated them to be $1.4 \times 10^{-10}$,$\ -0.5184\ \mathrm{V}$,$0.0816\ \mathrm{V}$ respectively. The question  has given no other data.
I have no idea how these 3 values that I have calculate has anything to do with the solubility of $\ce{Ag_5}$ and $\ce{Ag_{10}}$ let alone how I am suppose to relate it to pH.
Could anyone point me into the right direction. Any help is much appreciated.
Thanks.


texts:
So for a school chemistry assignment I was given 5 water samples and a bunch of different reagents to help me find out what was in the solutions. I'm  stuck on two.

The first one had a pH of 7 and only reacted with silver nitrate and formed a white precipitate. the second had a pH of 14 and turned brown when silver nitrate was added to it. Does anyone know of any chemicals that would do this?


texts:
Noon Chai (as described in this question) from Kashmir is prepared by adding common salt and sodium bicarbonate to green tea and cooking it for quite some time (~ 30 minutes).

Noon Chai is also associated with gastric cancer; the mechanism is assumed to be endogenous nitrosation of caffeidine by which then carcinogenic nitrosamines (dinitrosocaffeidine) are produced.

The question is: how does Noon Chai get its high amount of caffeidine in the first place?

Somehow the caffeine

is converted to caffeidine

by the special way to prepare the tea.

What is the reaction that happens there?


texts: Purification of primary amines using Schiff base immobilization

texts:
I want to purify all primary amines containing compounds in a complex mixture (cell-extracted metabolites). I'm unaware of any published methods to do so. So I am thinking of making my own using a reversible Schiff base immobilization.
My input is a 1 mL metabolite extract that contains hundreds of compounds with a total molarity of ~1 mM. Of this ~50% contain a primary amine. Glyoxal agarose typically has 40–50 μmol aldehydes per mL, so capacity is not an issue.
Impurities that I want to get rid of are, among others, organic acids like malate, pyruvate and succinate, sugars like glucose and glucose-phosphate, lipids and all non-volatile salts.
The idea is to use Schiff base chemistry:
$$\ce{R^1CHO + R^2NH2 <=>[$k_1$][$k_2$] R^1CH=NR^2 + H2O}$$
An immobilized aldehyde is used to capture all compounds containing primary amines. A Schiff base is generally stabilized under high pH and destabilized at low pH. It can be further stabilized by dehydration to shift the equilibrium towards the Schiff base side. Therefore, I would add my input at pH = 10 in 95% MeOH, wash under dehydrated conditions e.g. using 100% MeOH, and elude at pH = 2 using 0.1 M aqueous formic acid. Alternatively, adding glycine in the elution buffer to compete off remaining amines.
For immobilized aldehydes I'm thinking about using aldehyde activated beads e.g. glyoxal agarose beads:

My questions are:

Are there alternative ways to purify primary amines from a complex mixture which I'm unaware of?

Did anyone publish a paper that used Schiff base chemistry to purify primary amines?

What would be your odds that this could work? Is it worth pursuing?

Any ideas for improvements? Eluate has to be run on mass-spectrometer, so my requirements are:
a. no non-volatile salts;
b. no solvents with MW above 150 Da.


texts: Why should the redox reaction happen between the copper ions and iron atoms?

texts:
I know that when $\ce{Cu^{2+}}$ ions react to $\ce{Fe}$ atoms, it becomes $\ce{Cu}$ + $\ce{Fe^{2+}}$. My question is, why?
Copper atoms normally have 29 electrons. This means that in the K-shell there are 2 electrons, in $L = 8$ electrons, in $M = 18$ electrons and in $N = 1$ electron. (Yes I know that there is a system with s and other letters, but I haven't been taught in that way at my school). Therefore $\ce{Cu^{2+}}$ should have 27 electrons, which means that the shells are assigned like this: $K = 2, L = 8, M = 17$.
So when the $\ce{Cu^{2+}}$ ions react with $\ce{Fe}$, why does it want to become $\ce{Cu}$? Because $\ce{Cu}$ doesn't have a complete electron shell at the end. Why doesn't it want to become $\ce{Cu+}$, because then it would have a complete shell at the end ($K=2, L=8, M=18$).
I know that when you take away electrons from copper, it does it in a special way. I'm 15 years old and not english so I'm really not an expert or anything, I'm just wondering why $\ce{Cu^{2+}}$ would want to become $\ce{Cu}$ when it meets iron ($\ce{Fe}$).


texts: Does melanostatin peptide whiten the skin in a similar manner as to how melanotan darkens it?

texts:
I was reading about peptides and came across an interesting peptide that bodybuilders use to darken their skin.

How can peptides change the genetic makeup of someone's skin and darken it?

I also found another peptide called melanostatin that inhibits alpha-MSH. So my question is, can it whiten the skin?

Because bodybuilders aren't very much interested in whitening their skin, there were no trials and experiences with that peptide.

So does melanostatin work similarly to how Melanotan darkens the skin?

Disclaimer: I do not intend on using this peptide on animal experiment, nor humans for that matter. My question is purely theoretical and for educational purposes.


texts: I'm studying organic chemistry, and I noticed that there are fluoro-, chloro-, bromo-, and iodoalkanes. However, there are none for Astatine. Could someone shed some light on this, and what it would be called?


texts: What is the oxidation state of Mn in HMn(CO)5?

texts:
What is the oxidation state of $\ce{Mn}$ in $\ce{HMn(CO)5}$? If $\ce{H}$ has an oxidation state of $+1$, then $\ce{Mn}$ should have oxidation state of $-1$, which I'm not sure is possible.

On the other hand, if $\ce{H}$ has an oxidation state of $-1$, then $\ce{Mn}$ has an oxidation state of $+1$. However, Wikipedia says:

  The pKa of $\ce{HMn(CO)5}$ in water is $7.1$.

This means that the $\ce{Mn(CO)5}^-$ complex exists, implying a $-1$ oxidation state for $\ce{Mn}$. Again, I am not sure that a metal can adopt a negative oxidation state.


texts: Why can't the molecularity be determined from the rate law?

texts: Basically can someone explain why the molecularity cannot be determined from the rate law?


texts: How do computational chemistry programs determine the irreducible representation of a molecular orbital?

texts: I was coding a simple RHF code to test my understanding of computational chemistry when I stumbled upon this question. How exactly do computer programs like Gaussian, GAMESS-US etc. know which irreducible representation to assign to the molecular orbitals generated?


texts: How are van der Waals parameters determined experimentally?

texts:
If the ideal gas law $PV=nRT$ is not enough, as a second approximation the van der Waals equation

$$\left(P+a\frac{n^2}{V}\right)\left(V-nb\right)=nRT$$

is applied. The constants $a$ and $b$ are van der Waals constants which take into account some of the attraction and repulsion  that the ideal gas law does not.

Solving for $P$,

$$P=\frac{nRT}{V-nb}-a\frac{n^2}{V^2}$$

and plugging it into the definition formula of compression factor $Z$ yields
$$Z=\frac{V_{m,real}}{(RT)/P}=\frac{V_{real}}{(nRT)/P}=\frac{V_{real}}{V-nb}-a\frac{nV_{real}}{RTV^2}.$$

This result, supposedly, helps in the measuring of constants $a$ and $b$. But how is it really done? What are the more rigorous definitions of the constants?


texts: What is the difference between an Aryl Halide and a Vinyl Halide?

texts: Are aryl halides a type of vinyl halide? From my knowledge, when a Halogen atom is directly bonded to a doubly bonded carbon atom it is a Vinyl halide. When we look at halogen atom directly bonded to a benzene ring we see a similar thing. So are these terms never correlated? Also is Phenylic Halide a term which exists?


texts: Enol content of acetylacetone and ethyl acetoacetate

texts: Why is the enol content of acetylacetone higher than that of acetoacetic ester? Hydrogen bonding stabilisation is present in enol form of both of them. I cannot figure out which factor makes one predominate over another.


texts: What are known examples of drugs that racemize/stereoconvert in vivo, and how are they converted?

texts: It is known that although only the (S)-enantiomer of the infamous sedative thalidomide possesses teratogenic properties, it is not very useful to administer the pure (R)-enantiomer since it is racemized within the body. Are there other known examples of drugs that are stereoconverted in vivo? How does the body perform the conversion?


texts: Amorphous to crystalline: Opposite trend?

texts: Well my book says that on heating- amorphous solids crystalline at some temperature. As far as I know , amorphous solids have a very disordered structure compared to crystalline solids and on further heating the level of disorder should increase. So why do they become more ordered or crystalline at high temperatures or am I missing something fundamental in here?


texts: How to calculate the concentration of the diluted solution given a source concentration in ppm?

texts:
A student adds $37.4~\mathrm{ml}$ of a $50.0~\mathrm{ppm}$ solution to a $100~\mathrm{ml}$ volumetric flask and dilutes to the mark. What is the concentration of the diluted solution?

  $13.7~\mathrm{ppm}$
  $7.5~\mathrm{ppm}$
  $37.4~\mathrm{ppm}$
  $23.6~\mathrm{ppm}$

I used $$M_1V_1 = M_2V_2$$ which worked for all the others and I assumed would work for this considering I had all of the variables except for the 2nd concentration, but those calculations gave me $18.7~\mathrm{ppm}$, which is not an answer choice.


texts: Why do SN1 reactions prefer tertiary carbons?

texts:
I can understand that $\mathrm{S_N2}$ reactions prefer primary carbons, because of the steric hindrance that would be an obstacle.

But what is the exact reason that $\mathrm{S_N1}$ reactions prefer tertiary carbons ?


texts:
The reaction of sodium with water is quite infamous.

$\ce{2Na + 2H_2O \rightarrow 2NaOH + H_2}$

But exactly why does $\ce{Na}$ displace $\ce H$ in $\ce{H_2O}$?


texts: Why don't sponges foam up an hour later?

texts:
When I add dish soap to a sponge it is able to foam up. But if I leave the sponge alone for an hour, it doesn't foam up, not even if it is wetted.

Why? The sponge should still contain dish soap an hour later.


texts: Methods to prepare lactic acid from acetaldehyde

texts:
I got one method [here](using acetaldehyde and carbon monoxide)1.

But is there any alternative method (using specific catalyst)?


texts: For this compound, I think the ethyl group should be in the parent chain and the numbering should start from the right-most carbon. Hence, the compound should be named 2-methylhept-1-ene-1,3,4,5-tetracarbonitrile, instead of the name given above. Am I wrong somewhere?


texts: Under what circumstances that Liquid-Liquid extraction would be good to use?

texts:
Under what circumstances that LLE would be useful ?
Are the 2 top reasons -
1. Difference between the boiling points of the components are very low or similar.
2. For Temperature sensitive compounds as there is no heating which may cause thermal decomposition.

are there any other reasons ?


texts:
According to IUPAC goldbook:

  A tele-substituion is a substitution reaction in which the entering
  group takes up a position more than one atom away from the atom to
  which the leaving group was attached:

And that's the only example given. What is the mechanism of this reaction?


texts: why is methane gas solubility in water higher than carbon monoxide solubility in water?

texts:
The above graph depicts solubility in water at various temps.
If we are dissolving in polar water, why is methane more soluble than a polar molecule like carbon monoxide?


texts: Which compound will have the most stable enol form?

texts:
Which compound will have the most stable enol form, Phloroglucinol or 4-Pyridone?

My Thoughts:

Both in their enol form are aromatic. I am not sure how do I compare their stabilities. The answer given is 4-Pyridone though.

Any help would be appreciated.


texts: Black substances covering Aluminum Electrode

texts:
I have use two aluminum pieces as electrodes to electrolys salt (NaCl) water. After the experiment, I found that wherever electricity flows, the electrode will be covered in some blackish substances. One electrode has more dark substances than the other

Are they Al2O3? Or are they some other substances? Why is one electrode having more and the other having less?


texts:
A restorer of antique barometers reported in a blog post that he has had a barometer on his wall that has shown no "visible" loss of mercury in 15 years.

I was kind of curious about this, wondering how long it would be before a barometer would evaporate completely. How can I compute the rate of evaporation from the vapor pressure?

For the barometer reading to become inaccurate, the well would have to evaporate completely until the 0 point was reached (at highest pressure), then it would start becoming inaccurate.


texts: Do core electrons have molecular orbitals?

texts: Valence electrons are associated with molecular orbitals and hybridizations. Do core electrons have molecular/hybridized orbitals, or the original atomic orbitals?


texts: Why is the standard atomic weight of chlorine not a whole number?

texts: Why is the standard atomic weight of chlorine, 35.5, not a whole number? Like for example, it could be exactly 35 or exactly 36. Please show the solution of formulae on how u reach to 35.5) with some English words so I can write the answer in my homework assignment and please make it small. Thanks


texts: What is the equation for solving the concentration of the unknown from a Single-point Standard Addition Calibration for Potentiometry?

texts:
I know how to use the standard addition equation for a single-point analysis from an equation I got from the Analytical Chemistry book "Quantitative Chemical Analysis" 9ed by D. Harris.

However, solving for a potentiometry problem, the equation doesn't seem to be effective anymore. I keep on getting negative value for the initial concentration of the unknown sample.

The problem goes like this:

The Na+ concentration of a solution was determined by measurement with a sodium ion-selective electrode. The electrode system developed a potential of -0.2462 V when immersed in 10.0 mL of the solution of unknown concentration. After addition of 1.00 mL of 2.00 x 10-2 M NaCl, the potential changed to -0.1994 V. Calculate the Na+ concentration of the original solution.

Is there a specific equation I can use so I can correctly solve for the concentration of the unknwon solution?


texts:
In my textbook, it’s given that the trend of the basicity of the elements of group 15 is $$\ce{NH3 > PH3 > AsH3 > SbH3 \ge BiH3}$$
Also, it’s said that the reducing character decreases down the group. (Which is the ability to lose $\ce{e-}$)
It’s also give (on a different page) that $\ce{H3PO3}$ and $\ce{H3PO4}$ are di- and tri-basic respectively.

Phosphoric acid (presumably, a Brønsted-Lowry base) has a basicity of 3. This would imply that basicity is a property of acids. However, Ammonia (which is a Lewis base) has the highest basicity. Further, quickly Google search of the definition of basicity states: “Basicity is the number of hydrogen atoms replaceable by a base in a particular acid.”

My question is, how does Ammonia (a Lewis base) have a basicity (i.e. acid character)... shouldn’t it be a weak base? Or is my understanding of the definition of basicity wrong?


texts:
I know , Average Atomic Mass of an element is - the sum of the Masses of its isotopes,each multiplied by its Relative Abundance percentage (in decimal notation).

But what confusing me is, what is the concept of Average Atomic Mass. In other words,why we want to take average atomic mass of every element on the periodic table,why not Atomic mass ? Why we need it and when to use it?


texts:
What is the net ionic equation of sodium hydroxide when it dissolves in water?

For the net ionic equation I got
$$\ce{NaOH(s) + H2O(l) -> NaH+(aq) + OH- (aq) + H2O(l)}$$
but it was wrong.
Then I tried:
$$\ce{NaOH(aq) -> Na+(aq) + OH- (aq)}$$
and it was wrong as well.
Can someone please explain?


texts: Are there any crystals that are theoretically possible, but haven't yet been made?

texts:
Are there any crystals (that exist at standard temperature and pressure) that are theoretically possible, but haven't yet been made?

For example, the predicted requirements for temperature, pressure, materials, etc. for crystallisation to occur are too difficult to achieve.


texts: large wavelength range and list of x/y numerical data points of elements

texts:
I'm trying to get a set of FTIR or (FTIR like range) x/y numerical data points for a couple of elements,  namely Silver, Platinum, Palladium, Gold and Sodium.  I've looked on line and found images only of the FTIR but I need the numerical x/y data points with the largest wavelength range.  I tried NIST but they just show the NMR data.  Is there a site where I can get just these or can someone send these/post these for me?  And is it possible to get an FTIR of Sodium just by itself or does it need to be combined with another element.

Thanks

Please note I know metals (due to covalent bonds) don't work well with FTIR but I'm trying to get / see if it's possible to get a large wavelength range analysis of the items above like in FTIR.  Sorry for using the FTIR term I don't know the proper term to use at the moment.


texts:
I have a question about dissimilar metals/galvanic corrosion.
I am designing a printed circuit board (PCB), which should be mounted on bare aluminium. For cost reasons, the aluminium part cannot be treated.
The PCB itself contains copper traces

Until now, I have used HAL plating (Hot Air Leveling) on the copper traces, which is a 1 to 5 um tin plating.
This tin plating should be sufficient to form a barrier between the copper and the aluminium.

The manufacturers are moving to ENIG plating (Electroless Nickel Immersion Gold), which consists of a 3 to 6 um nickel layer on the copper with a 0.1 to 0.2 um gold flash on top.

Gold and Aluminium do not behave too well together, but I heard that since the gold is a very thin layer, one can assume it is not there, and therefore in the galvanic series, only the nickel to aluminium voltage will exist.

It is hard for me to find literature/references to this subject, especially in combination with very thin layers. This may just be because it is not my field of expertise. I myself am an electronics design engineer

Could someone enlighten me about this subject?

PS: I was wondering whether to put this in Chemistry or in Physics. In neither I could find related questions.


texts: What is antisymmetric exchange? What is J-strain? Where does it come from?

texts:
I'm reading a paper1 by Sanakis, et al. that characterises the magnetic coupling in the $\ce{Fe3S4}$ clusters present in bacterial ferredoxin II and beef heart aconitase as arising through something called 'antisymmetric exchange'. This looks like it may be a result of the apparent magnetic frustration of the system (three high-spin $\ce{Fe^{3+}}$ ions, all in essentially identical environments, all antiferromagnetically coupled with respect to their neighbours). The paper says that the clusters have a S=1/2 ground state, which is incompatible with a broken-symmetry model.

The wikipedia article on antisymmetric exchange (all four sentences of it) is not particularly edifying. I'm hoping an expert can explain what antisymmetric exchange is and what causes it as I've not heard of it be before. The paper also notes that the exchange situation in the cluster gives rise to three slightly different $J_{ij}$ values (again, despite the symmetry of the ions) and terms this 'J-strain'. This makes me doubt that, for instance, 'antisymmetric' is being used as a synonym for 'antiferromagnetic'.

[Edit]

Here's an example of the general connectivity of this kind of $\ce{Fe3S4}$ cluster (based on D. Gigas FdII (PDB entry 1F2G)). The cluster comprises a hemicubane. $\ce{S_{Cys}}$ denotes a cysteinyl sulfur.

(1) Sanakis, Y.; Macedo, A.L.; Moura, I.; Moura, J.J.G.; Papaefthymiou, V.; Münck, E.; Evidence for Antisymmetric Exchange in Cuboidal $\ce{[3Fe-4S]^+}$ Clusters; J. Am. Chem. Soc.; 2000, 122, pp. 11855-11863


texts: Gaussian: Relaxed scan with modredundant optimization and dummy atoms

texts:
I would like to perform a relaxed scan in Gaussian09 on my molecule using the modredundant optimization. Because I want to scan over two bond lengths simultaneously, I defined some dummy atoms which are close to the real atoms whose bond lenghts should be scanned. However, this approach does not work, because I can't properly index the dummy atoms. The Gaussian09 documentation says (emphasis mine):

  [Type] N1 [N2 [N3 [N4]]] S nsteps stepsize [[min] max]]

  N1, N2, N3 and N4 are atom numbers or wildcards (discussed below). Atom numbering begins at 1, and any dummy atoms are not counted.

How can I then perform a scan referencing a dummy atom? I don't want to do the scan using the z-matrix optimization because it does not converge.

Here is my input file:

%nprocshared=16
%mem=5gb
%chk=4MeAminoButanal
#P HF/6-31G(d) opt=(modredundant) scrf=(pcm) nosymm

4MeAminoButanal dummy scan

0 1
 C     0.000000     0.000000     0.000000
 N     0.000000     0.000000     1.451901
 C     1.325038     0.000000     2.055476
 C     1.991320     1.377897     2.032970
 C     1.229182     2.449098     2.809397
 C     1.309917     2.335179     4.306919
 X    -0.248373    -0.404008     1.611583
 X    -1.041414    -0.131882     1.066579
 H     1.218960    -0.323776     3.083767
 H     1.990264    -0.714465     1.564774
 H     2.993872     1.281489     2.436811
 H     2.106328     1.711600     1.006802
 H     1.602469     3.443240     2.566292
 H     0.178120     2.455789     2.536445
 H     0.708887     3.065770     4.854632
 H    -1.016528    -0.113770    -0.358506
 H     0.375985     0.943036    -0.379032
 H     0.606031    -0.798850    -0.431982
 X     1.641992     1.939406     4.607116
 X     1.311963     2.318294     5.471711
 O     1.974063     1.543637     4.907309
 H    -0.496745    -0.808017     1.771266

B 7 19 S 60 -0.05
B 22 7 F
B 2 7 F
B 6 19 F
B 21 19 F

When I run it, Gaussian09 obviously complains with

  The following ModRedundant input section has been read:
   Invalid atom number.
   B 7 19 S 60 -0.05


texts:
Outside of bonds between metal atoms=metallic bonds, non-metals=covalent bonds (molecules), it is difficult for me to determine what kind of bond it is.
I know that in the rule metals and non-metals form ionic bonds and that the ionic part of such bonds increases with increasing electronegativity difference and that Fajans' rules states that large cations with small positive charge and small anions characteristically form ionic bonds. But to me all these measures seem very fuzzy. I can say that SnCl2 is more ionic than SnCl4 because of the smaller positive charge of Sn (when considered as a cation) in SnCl2 (Sn2+) compared to SnCl4 (Sn4+). But how do I know that SnCl4 is a molecule?
Are there clear rules for determining the type of bond? How to proceed if criteria of the Fajans' rule contradict each other and at what point is it no longer an ionic bond with covalent character but a covalent bond (for metal-non-metal bonds like SnCl4, would SnO be a molecule or salt?)?


texts: I am trying to find the solubility of benzoic acid in different solvents to prepare a liquid-liquid extraction

texts:
I need to prepare a liquid-liquid extraction using the partition coefficient (K) of benzoic acid in different solvents and water:

K ~ solubility of benzoic acid in solvent/solubility of benzoic acid in water

Several solvents are offered to me (e.g. ethyl acetate, chloroform,...), and I am trying to find the solubility of benzoic acid in each of those solvents. The problem is that I can't find all of them (e.g. benzoic acid in ethyl acetate). I can't seem to find a database of such solubilities. I would greatly appreciate if someone could please re-direct me to such database. Conversely, can solubility be predicted efficiently?

Thank you very much for your time!!


texts: Calculating the ionic polarizability from the Clausius-Mossoti relation

texts:
The concentration of atoms in a crystal is $N_d = \pu{2.24e28 m-3}$, and the relative dielectric constant is $\varepsilon_{r} = 5.62$. The crystal has a refractive index of $n = 1.5$. Using the Clausius-Mossoti relation,

$$
\frac{\varepsilon_{r} - 1}{\varepsilon_{r} + 2} = \frac{N\alpha}{3\varepsilon_{0}},
$$

I got that

$$
\alpha_\mathrm{i} = \pu{8.26e-40 F m2}.
$$

However, the correct answer is

$$
\alpha_\mathrm{i} = \pu{3.7e-40 F m2}.
$$

Was the refractive index useless info here, or have I missed something?


texts: What is the vapor pressure of a liquid if it is not in a sealed container(i.e., a river or lake)? Is it just the atmospheric pressure?

texts:
From what I understand, the boiling point of a liquid is when its surrounding pressure is equal to its vapor pressure. The vapor pressure is the pressure of the gas form of the liquid in a container when the rate of condensation equals the rate of evaporation. If this is the case, what is the vapor pressure of a liquid that is not placed in a container(i.e., a river or lake)? Is it the same as the pressure of the atmosphere? If so, then how does this affect its boiling point?

(Please correct me if what I know is not true).


texts: Beer's law: UV-Vis absorbance values exceeding 2

texts:
In classical analytical chemistry, absorbance values in Beer's law can theoretically range from 0 to infinity.

As general rule of thumb neither high, nor very low absorbance are used for constructing calibration curves. The reason for avoiding high absorbance is that when absorbance is 2, only 1% light reaches the detector and with 3, only 0.1% light reaches the detector. Analytical chemists were taught to avoid absorbance > 1.5.  Low absorbance values are avoided because it hard to distinguish the light beam with and without the cuvet in place. The question then arises how much is the real absorbance and how much is contributed by noise.

Nowadays (= within the last decade), I am seeing UV-Vis spectrophotometers have absorbance ranges from 0 to 3, and some have even more. One day a PhD student showed an absorbance > 5 for a spectra, apparently without even thinking twice on the meaning of absorbance. Similarly, researchers showed an absorbance spectrum with the maximum at absorbance of 3.

My question is this a fundamental flaw in Beer's law that high absorbance values are erroneous or it is limitation in detector technology and the intensity of light sources? Please ignore the chemical reasons for deviations in Beer's law.

Imagine, if we had very high intensity light source, such as xenon arc lamp, instead of a typical deuterium or a tungsten lamp, would we get less error in the absorbance measurements of concentrated solutions? Absorbance is a ratio technique, but the number of photons reaching the detector will be high, even with conc. solutions, with intense light sources.

Can any spectroscopist shed some light on this issue (no pun intended) whether high intensity sources would beneficial in UV-Vis spectrophotometry of concentrated solutions?


texts: Nitration of tri-substituted benzene with Acetic acid and HNO3

texts:
So I looked it up on the internet and it says that this is to be a nitration reaction. But how is the $\ce{NO2+}$ formed? I simply cant seem to be able to do the first step of the mechanism, that is the generation of the electrophile.

I thought that as $\ce{HNO3}$ would be the stronger acid, it would lose $\ce{H+}$ that would get added to the acetic acid and it would lose water to form a the electrophile that gets added to the ring. But apparently this is not the case. Why? Could someone show the mechanism?


texts: Discrepancy in MO diagrams for Period 2 homonuclear diatomics

texts:
I've recently noticed that different sources on the internet and in books have different ideas of whcih atomic orbital influences which molecular orbital. In the diagram, where the lines connect the AO to the MO to show their influence, I noticed that in some of the MO diagrams, the $\mathrm{2p}$ orbital does not connect to the $\sigma_1$ orbital (the lowest in energy) and the $\mathrm{2s}$ orbital does not connect to the $\sigma_4$ orbital (the highest in energy). On the other hand, I also see the case where the opposite is true and they DO connect (this is the case for my own chemistry lecturer's notes).

I asked her if she could explain this difference, and she said that the $\sigma_1$ should have some $\mathrm{p}$ character and that the $\sigma_4$ should have some $\mathrm{s}$ character, so they do connect. She didn't however say that the other way was wrong. As a result I'm not sure whether the other way is wrong, or whether it's just like a difference in notation.

I hope someone can help clarify for me. I've attached two photos of the different cases.

Thank you.

$\hspace{15 mm}$

(source)

versus

$\hspace{30 mm}$


texts: Determining the order of basicity of acetate, phenoxide, hydroperoxide, and hydroxide ions

texts:
Arrange the following ions in order of basicity:
  (1) $\ce{CH3COO-}$ (acetate)
  (2) $\ce{PhO-}$ (phenoxide)
  (3) $\ce{HOO-}$ (hydroperoxide)
  (4) $\ce{HO-}$ (hydroxide)

The first thing I see is that all of them have the same donor atom, i.e. oxygen.

In both $\ce{CH3COO-}$ and $\ce{PhO-}$, the charge is stabilized by resonance. So, they are least basic, $\ce{PhO-}$ being the less basic among the two as you can see that in case of $\ce{PhO-}$, the number of resonance structures are more than $\ce{CH3COO-}$.

Next, comparing $\ce{HO-}$ and $\ce{HOO-}$ I find that the negative charge on $\ce{O-}$in $\ce{HOO-}$ maybe slightly more stable as the charge may be shared by the other oxygen, whereas $\ce{HO-}$ has no such option.

So I get the basicity order as 4 > 3 > 1 > 2. But the answer is 3 > 4 > 2 > 1. Where am I wrong?


texts:
I don't understand why the keto form is present more at equilibrium. Yes I know that for phenols or instances where the enol form can have H-bonding the enol form is preferred, but generally I have seen the equilibrium arrow be bigger in the direction of the keto form.
Is this because the CO bond is more stable than the CC bond formed in the enol form?


texts: Effect of optical isomerism on colour of transition metal complexes

texts: I know that different stereoisomers of a given transition metal complex (cis- and trans- forms) have different colours. But do different optical isomers (non-superimposable mirror images) have different colours, or do both optical isomers have the same colour?