texts: Covalent bonds other then 2-center, 2-electron bonds

texts:
I've heard of single bonds, double bonds, triple bonds, and quadruple bonds between two atoms, but in each of those bonds the two atoms contribute the same number of electrons from each of their valence shells.

My question is, why can't the atoms contribute an uneven number of electrons? For example, why can't there be a situation where a carbon atom contributes two valence electrons while a nitrogen atom only contributes one?

Surely the sigma bonds arising from the overlap of two valence orbitals allow one valence orbital to have two valence electrons while the other only has one. (I don't know about pi-bonds, and I don't know if it is possible for a carbon atom and a nitrogen atom to give two and one valence electrons, respectively, but maybe there is another pair of atoms that would allow this).


texts:
Sephadex is useful for the separation and purification of many natural products.
 Is it also useful for the separation and purification of artificial chemicals (in organic synthesis ) or not and why ?


texts: Chemical safety information: Where to look to find out how poisonous poisons are?

texts:
Could someone point me toward a primer on how to read the toxicity warnings on standard chemical data sheets? Or alternatively, where one should look for more precise information than is contained on such sheets? Specifically, when I see that "Poison" skull and crossbones, I don't know how to tell when it means "Don't drink a quart of it" as versus "If it splashes on your finger, chop it off immediately."
I looked at a data sheet for rosmarinic acid, a component of rosemary, and the Caymen Chemical data sheet it said it was acutely toxic if ingested. So I looked at a data sheet for curcumin, which I have been taking three grams a day of for ten years, and the ThermoFisher data sheet said to seek medical attention immediately if you get any on your skin. That is clearly not right, or I would be dead. Which makes me wonder, in general, where to look for safe levels of exposure, and specifically, how to tell toxic rosemarinic acid (which has been reported to increase the average lifespan of c. elegans by 63 percent*) is to humans.

Biogerontology 12(4): 329–347. doi:10.1007/s10522-011-9334-7.  Biofactors 45(5): 774–787. doi: 10.1002/biof.1536.


texts: Why isn't the orbital angular momentum also considered while calculating the magnetic moments 3d transition elements?

texts:
My textbook (Chapter: The d- and f- Block Elements) makes an interesting assertion, however, without any reason to back it up.

Paramagnetism arises from the presence of unpaired electons, each such electron having a magnetic moment associated with its spin angular momentum and orbital angular momentum. For the compounds of the first series of transition metals, the contribution of the orbital angular momentum is effectively quenched and hence is of no significance. For these, the magnetic moment is determined by the number of unpaired electrons and is calculated by using the ‘spin-only’ formula, i.e.,
$$\mu = \sqrt{n (n + 2)}$$
where $n$ is the number of unpaired electrons and $\mu$ is the magnetic moment in units of Bohr magneton (BM). A single unpaired electron has a magnetic moment of $1.73$ Bohr magnetons (BM).

Now from what I've learnt from my physics classes last week, the magnetic moment of an electron is calculated using the formula:

$$\frac{m}{L} = \frac{e}{2 m_e}$$
Magnetic moment of revolving electron,
$$m = \frac{e}{2 m_e}L$$
In vector form,
$$\vec{m} = - \frac{e}{2m_e}\vec{L}$$

Where $m$ is the mass of the electron, $e$ is the magnitude of charge associated with the electron and $L$ is the angular momentum of the electron.
Now as I understand it, the angular momentum of an electron in an atom is the resultant of the electron's spin angular momentum and its orbital angular momentum.
But (as you can clearly see) my textbook exhibits an unexplained enthusiasm for only the spin angular momentum. It dismisses the contribution of the orbital angular momentum, as inconsequential, when determining the magnetic moments of electrons in the 3d elements.
As for the 'reason' provided by my textbook:

For the compounds of the first series of transition metals, the contribution of the orbital angular momentum is effectively quenched and is hence of no significance.

Well, I fail to see how that even counts as a 'reason'. I did ask my teacher about this, but she expressed her reluctance to go into the details; she's of the opinion that my particular query is “not worth clarifying” since it has no significance from the examination point of view (“Just give them what's in the textbook Aaron, nothing more and certainly not anything less”).
Subsequent internet searches have not yield any satisfying explanation (Perhaps I didn't use the right keywords while searching?).
So I'll just break up my question, point-wise, and list them below:

Is the orbital angular really of no significance when calculating the magnetic dipole moment for 3d elements? If it is significant, is there any 'educational' purpose behind that omission in my textbook, or is it just a mistake?

(As stated in the book) What causes the 'quenching'? How is this 'quenching' effect caused?

Do the transition elements of the other periods also have "insignificant" orbital angular momentum contributions? Is it for the same reason as the 3d transition elements.


texts:
Suppose the pressure is 1 atm and we put water (at 25 °C) in an open container. After some time the water will disappear as the water evaporates. We know that water at 25 °C and 1 atm has a vapour pressure. And this vapour pressure is obviously less than the atmospheric pressure or external pressure as no boiling is occurring at this pressure, temperature. If they were equal, boiling would occur which is clearly not happening.
So, if the vapour pressure is less than the atmospheric pressure, then how are are liquid molecules converting into gaseous molecules? I mean the atmospheric pressure above the liquid is exerting a greater force on the liquid and it's vapour pressure is less than the atmospheric pressure.
Then how are the liquid molecules overcoming the atmospheric pressure and changing into gaseous molecules if their vapour pressure is less than the atmospheric pressure? They can only change into gaseous molecules when they can overcome the atmospheric pressure which can occur when their vapour pressure equals atmospheric pressure.


texts: Which ligand names have to be parenthesized while naming the Mononuclear Coordination entities

texts:
While studying about the Nomenclature of Coordination Compounds I came to know that

While writing formulae of Mononuclear Coordination entities polyatomic ligands are enclosed in parenthesis and also their abbreviations.

But while naming the entities should I follow the same rule?
Like for $\ce{[Ni(H2O)2(en)2]SO4}$ should it be named as

Di(aqua)bis(ethylene-1,2-diamine)nickel(II) suphate

Or

Diaquabis(ethylene-1,2-diamine)nickel(II) sulphate

I Mean is there any rule that says you only need to close certain species of ligands like specifically bidentate (such as en) and polydented ligands (such as EDTA) and can keep the others as they are?
Thanks.


texts: how is the esterification of amino acid carried on in this reaction

texts: i was asked to synthesis this compound from this amino acid, i first alkylated the alpha carbon using enolate alkylating method then i esterficated the amino acid but i'm doubtful that my steps are right, do i need to protect the amino group in the esterification step? or even before ?


texts: Why does thiocyanate bind to Fe³⁺ with the S side instead of the N side?

texts:
According to hard and soft acids and bases (HSAB) theory, "soft" Lewis bases bind to "soft" Lewis acids, and "hard" Lewis bases bind to "hard" Lewis acids.

$\ce{Fe^3+}$ is a hard Lewis acid. In $\ce{SCN-}$, either the $\ce{N}$ or the $\ce{S}$ side of the molecule can bind with $\ce{Fe^3+}$. Of the two, $\ce{N}$ is the harder Lewis base. But $\ce{[Fe(SCN)6]^3-}$ has a $\ce{Fe-S}$ bond and not a $\ce{Fe-N}$ bond. Why is this so?


texts: Does "soluble in alcohol" imply ethanol?

texts:
Sources like Wikipedia and SolubilityOfThings say that copper (II) acetate is soluble in alcohol.

Does that mean any alcohol, or does "alcohol" in this context mean ethanol?


texts: How to identify the concentration of nitric acid?

texts:
I have quite a small quantity of concentrated nitric acid I had acquired about two years ago. This was given to me by a friend in a couple of Pyrex volumetric flasks with stopper and some in a borosilicate reagent bottles. The acid does have a whiskey brown color now.
Is there any simple method or visual cue to identify what concentration the nitric acid could be with a simple test? I want to see if the acid is 70% nitric acid. If it's the higher concentration of 90%, then I want to dilute it to 70%. I have attached a picture of one of the bottles for reference to see the color below.


texts: Theoretical comparison of dipole moments of N,N-dimethyl-4-nitroaniline and N,N,2,3,5,6-hexamethyl-4-nitroaniline

texts:
These two compounds are given in my workbook, and I am supposed to compare their net dipole:

The solution given in the workbook is that:

Molecule A (N,N-dimethyl-4-nitroaniline) has a "net shifting of electrons" in the downward direction - due to $+M$ effect of $\ce{NMe2}$ and $-M$ effect of $\ce{-NO2}$;
Molecule B (N,N,2,3,5,6-hexamethyl-4-nitroaniline) - due to steric hindrance - does not undergo resonance to an appreciable extent, hence, there is negligible "net shifting of electrons" in any direction. The lone pair of $\ce{NMe2}$ almost remains in its place.

Hence, molecule A has a higher dipole than molecule B. I am content with this explanation.

However, my question is:

  Is this explanation actually correct, or is it just a theoretical mask to explain an experimental observation (i.e. they just made up a random theory on their own to explain an observation)?

Are such types of explanations common, universally accepted, etc?


texts: How to deterime the number of equivalents of Grignard reagent used for this reaction?

texts: I know that the amount of substance of Grignard reagent used is 5 moles. But the answer given is 2. Is this anything to do with 'equivalents'?


texts: Why does the COO- ion is pulled at during critical Micelle concentration?

texts: During the Micelle formation of a soap (made of sodium), when soap comes in contact with water, it dissociate into Na+ ions and RCOO-  ions(where R is an hydrocarbon chain). Then in the RCOO- ions, R is  hydrophobic and COO is hydrophylic. So at critical Micelle concentration, what happens to this RCOO- ion?


texts: Do electrons hybridize only during bonding?

texts: Do electron orbitals hybridize on their own in an solitary atom or do they only do this only when bonding is a posibility? If hybridization does occur in atoms without bonds, then is it random? Do the electrons mix and match as they tumble around in space?


texts: For my chemistry IA, I am planning to determine the reaction rate and activation energy of the acid catalyzed hydrolysis of ethyl acetate. Where can I find literature values for these, so i can compare my results and evaluate my erros?


texts: At what acid concentration does potassium metabisulfite react?

texts:
I'm in the process of developing a well preserved food-stuff containing potassium metabisulfite and a number of acids (acetic, ascorbic, malic, tartaric, citric, lactic). Wine-making literature suggests that K-meta is added for its antibacterial and antioxidative properties.

However, other literature claims that K-meta reacts with acids. In what concentration does this acid reaction occur? How violent is the reaction, and are any very harmful (if ingested) substances formed?

A simple test shows that the pH of my food-stuff is lower than 4.0, but greater than 3.0 before the addition of K-meta.


texts: How are phase transition diagrams calculated?

texts: How are diagrams such as above plotted? Since empirical studies are slightly off from the 'ideal', what is the source for the phase plots?


texts: What is the fire point of sucrose with an average particle diameter of 60 micrometres? I can't seem to find any documentation on this, online.


texts: I am not expert in chemistry. I need to find a way to identify a $\ce{KNO3}$ and $\ce{KH2PO4}$ powder at home. I suspect the seller gave me the wrong powder. What is a simple way to test between these compounds at home?


texts: Why does potential energy relate to exothermic reactions in this way?

texts: I am not understanding how potential energy (which is the energy that results from position or configuration) relate to exothermic reactions. We say that exothermic reactions give off heat and so lose energy but I don't see how I can use this definition of potential energy to say that potential energy is lost from the system of an exothermic reaction. It might be my definition for potential energy that is wrong, I don't know.


texts: Whats the difference between reversible process in thermodynamics and reversible chemical reactions?

texts: We know that in thermodynamics, reversible process never occur since entropy should be conserved. However, in chemistry we do have a lot of reversed chemical reactions that forms reactants from products, previously formed by a direct reaction. So, what is the misunderstanding here?


texts: Drawing the condensed structure of ethylcyclobutane

texts:
The IUPAC name for this is ethylcyclobutane. I know that the formula is $\ce{C6H12}$.

I have no problems drawing the skeletal structure, but I have a little difficulty drawing the condensed structure. I know this is basic, but I just started learning how to name them.

I tried it below. For $\ce{CHCH2CH3}$, am I right to write it in a straight chain?


texts: Stereochemistry of eliminations similar to E2' elimination

texts:
In the E2 reaction, the proton and the leaving group are anti-periplanar typically, so as to attain best overlap of the C-H bonding orbital and C-LG anti-bonding orbital.

In a similar reaction, with a hydrogen alpha to a C=C and a leaving group alpha the other side, we have a syn-elimination, which can be explained by a tau-bond model. Eg:

Eliminates to give:

Demonstrating that the groups eliminate from the same side in a so called E2' reaction.

My question is what happens to the required stereo-chemistry as a we increased the number of alkenes units in between - does the stereo-chemistry flip-flop, or do we get a fixed stereo-chemistry requirement. Or is the stereochemistry requirment, as I would theorise, relaxed as we increased the number of alkenes?


texts: I do not understand why you could not fill a bowl full of adenosine triphosphate (ATP) and eat it. Is there a way to make ATP other than inside a cell and apply it to your body by injection, ingestion, topical absorption, inhalation, or another method?


texts:
What is the difference between crystal radius and ionic radius? For $\ce{NaCl}$ for example the ions combine to a crystal, and I would have guessed they are equal. But I then found an example of data, where they are not.

I am aware that ionic radius is the radius of an atom's ion. Quite simple. So what is crystal radius?


texts: Rate of hydrolysis of silicon tetrahalides

texts:
Concise Inorganic Chemistry for JEE(Main and Advanced) by JD Lee(Third Edition) writes

  If we compare the rate of hydrolysis for $\ce{SiX4}$(where X= F,Cl,Br,I), it is in the same order as that of their Lewis acid strength order,i.e.
  $\ce{SiF4}$ > $\ce{SiCl4}$ > $\ce{SiBr4}$ > $\ce{SiI4}$
  .This is because the effect of π back bonding is less dominant over the negative inductive effect.

My question is, why is the π back bonding neglected here even though 3dπ-2pπ back bonding is strong enough to be evoked in many other cases? Also, Wikipedia lists the bond strengths of $\ce{Si-X}$ as $\ce{Si-F}$ > $\ce{Si-Cl}$ > $\ce{Si-Br}$ > $\ce{Si-I}$ , and I feel that the rate of hydrolysis should be inversely proportional to this order as it will become increasingly difficult to break the silicon-halide bond when bond strength increases,and consequently difficult to hydrolyse the molecule


texts: What is the "curse of dimensionality" in molecular dynamics?

texts:
The 'curse of dimensionality' or the 'bottleneck problem' in molecular dynamics is explained in page 5 and 6 of Ab Initio Molecular Dynamics: Basic Theory and Advanced Methods by Dominic Marx and Jurg Hutter .

They proved that Car-Parrinello MD outperforms classical MD with a computational advantage growing as $\sim 10^N$ with system size, which I am unable to understand, especially the last paragraph of page 5.

To be more specific, I am copying the relevant contents:

  In the case of using classical mechanics to describe the dynamics - which is the focus of the present book - the limiting step for large systems is the first one, why should this be so? There are $3N-6$ internal degrees of freedom that span the global potential energy surface of an unconstrained $N$-body system.  Using, for simplicity, 10 discretization points per coordinate implies that of the order of $10^{3N-6}$ electronic structure calculations are needed in order to map such a global potential energy surface. Thus, the computational workload for the first step in the approach outlined above grows roughly like ∼$10^N$ with increasing system size ∼$N$. This is what might be called the curse of dimensionality or dimensionality bottleneck of calculations that rely on global
  potential energy surfaces.

What is needed in ab initio molecular dynamics instead? I am confused about the parts placed in bold:

  Suppose that a useful trajectory consists of about $10^M$ molecular dynamics steps, i.e. $10^M$ electronic structure calculations are needed to generate one trajectory. Furthermore, it is assumed that $10^n$ independent trajectories are necessary in order to average over different initial conditions so that $10^{M+n}$ ab initio molecular dynamics steps are required in total. Finally, it is assumed that each single-point electronic structure calculation needed to devise the global potential energy surface and one ab initio molecular dynamics time step require roughly the same amount of cpu time. Based on this truly simplistic order of magnitude estimate, the advantage of ab initio molecular dynamics vs.  calculations relying on the computation of a global potential energy surface amounts to about $10^{3N-6-M-n}$. The crucial point is that for a given statistical accuracy (that is for $M$ and $n$ fixed and independent of $N$) and for a given electronic structure method, the computational advantage of ``on-the-fly” approaches grows like ∼$10^N$ with system size. Thus, Car–Parrinello methods always outperform the traditional three-step approaches if the system is sufficiently large and complex. Conversely, computing global potential energy surfaces beforehand and running many classical trajectories afterwards without much additional cost always pays off for a given system size $N$ like ∼$10^{M+n}$ if the system is small enough so that a global potential energy surface can be computed and parameterized.

How do the bolded points prove that fact that "computational advantage of 'on-the-fly' approaches grows like ∼$10^N$ with system size" over classical MD?


texts: How does cross-linking between polymer chains increase the melting point of the polymer?

texts:
https://i.stack.imgur.com/uUcQr.jpg

Suppose we have this polymer chain. Now, we cross link some chains ( not all ) , so some chains get linked, and others remain as they are. What we now have is a 'mixture' of polymer chains which are linked, and those which aren't. My question is how does this increase the melting point? I've read that intermolecular forces between chains is replaced by the covalent bonds of cross-linking, which are much stronger, and thus melting requires much more energy. But melting doesn't involve the breaking of covalent bonds unless the structure we have is 'one giant molecule', like Diamond, in which there are no 'intermolecular forces' because it's just one molecule.

In our case, we most certainly will have more than one molecule, and so the melting point should depend on the intermolecular forces between the chains. As these forces are largely unchanged, the melting point should be unaffected. When we heat this molecule, the weakest of the forces ( intermolecular ) should be broken first, and thus the melting point should remain unchanged.

I've been confused about this for about a week now, and I'm surprised google cannot find a similar question.


texts: A charged particle like an ion, does its repulsive or attractive effect on other particles change with temperature? Are electrostatic effects temperature dependent?


texts: Can anyone explain, why there are coefficients 2 in the equation for rate of change [A]?

texts:
The reaction mechanism for the decomposition of $\ce{A2}$ is thought to be:
\begin{align}
\ce{A2 &<=>[$k_1$][$k_1'$] A + A} & &\text{ (fast)} \\[0.2cm]
\ce{A + B &<=>[$k_2$] P} & &\text{ (slow)}
\end{align}
The rate of formation of intermediate $\ce{A}$ is given by:
\begin{align}
\frac{\mathrm{d}[\ce{A}]}{\mathrm{d}t} = \color{red}{2} k_1[\ce{A2}] - \color{red}{2}k_1'[\ce{A}]^2 - k_2[\ce{A}][\ce{B}] \approx 0
\end{align}

In the equation above, why is the coefficient of $2$ present for both the forward and reverse reactions (highlighted in red)?


texts: Are there any Nitrate salts that are generally insoluble in water at room temperature? Textbooks are generally vague about this. They say that all nitrate salts are mostly soluble in water, or that there are "few exceptions". I understand that insoluble doesn't mean 0% of solute dissolves, and I also understand that when something is soluble, that doesn't mean it is 100% soluble under normal conditions. I just want to know if any nitrate salts exist that are relatively insoluble in water at room temperature. Also, when I say "exist", I mean it occurs naturally and is relatively stable.


texts: What is the effect of basis set on charge transfer?

texts:
I am calculating the energy and charge transfer of a globally neutral system, composed by two opposely charged monomers (EMIM-BF4), coming closer to each other, with DFT (B3LYP) and MP2.

As a thumb rule, the larger the basis set, the better the energy result should be (given BSSE is taken in account). Is this also valid for charge transfer? What is the role of polarizability? Is there a theoretical argument to trust the results from one basis set against another one, besides the size of the basis set?

I am comparing Pople's STO (minimal bs), Pople's N-311G(p,d) (triple split bs),
Dunning-type Correlation Consistent basis (CCQ or cc-pVQZ) and APCseg-1 ( Augmented Polarization Consistent bs) and I get different results for each case when distance reaches 3 Angstrom (check the attachment).

Which one should I trust?

Thank you


texts:
I got some chromium(III) oxide ($\ce{Cr2O3}$) sold as pigment, called "Chrome Green". I've been having a hard time trying to react it with $\ce{HCl}$ to make $\ce{CrCl3}$. I thought it was just hard to break the $\ce{Cr-O}$ bond.

Now I'm just afraid that the pigment that I bought was actually cut with something else, like a silicate-type of pigment. How do I test for chrome(III) oxide, if I can't get it to become a salt in the first place?


texts: small negative frequencies in DF T optimizations with organic molecules containing CF3 groups

texts:
When optimizing by DFT medium-sized organic molecules containing aromatic CF3 groups (for example, adducts involving takemoto's catalyst), the frequency calculation on optimized structures have always small negative frequencies involving CF3 groups (small rotations), no matter which program (gaussian or orca), which functional (b3lyp, m06-2x, pbeh-3c or b97-3c), which grid (ultrafine, grid6), which base (double or triple-zeta, with or without diffuse or polarization terms) or convergence criteria.
The only solution is to manually rotate the groups a bit and launch another optimization (with smaller step) and another frequency calculation, over and over (sometimes I finally find a true minimum after 3 or 4 optimization/frequency cycles, sometimes after 7 or 8).
This procedure is quite time-consuming, considering the number of frequency calculations involved.
Anyone has ever faced a similar problem? Are there any tips or tricks able to solve (or mitigate) this problem?
thanks


texts: What is the molecular interpretation of Raoult's law?

texts:
I was reading about Raoult's law which states:

It states that the partial vapour pressure of each component of an ideal mixture of liquids is equal to the vapour pressure of the pure component multiplied by its mole fraction in the mixture.

Regarding the molecular origin of this law, Peter Atkins in his book writes:

The molecular origin of Raoult's law is the effect of the solute on the entropy of the solution. In the pure solvent, the molecules have a certain disorder & a corresponding entropy; the vapour pressure then represents the tendency of the system & its surroundings to reach a higher entropy.
[...] Because the entropy of the solution is higher than the pure solvent, the solution has a lower tendency to acquire an even high entropy by the solvent vaporising. In other words, the vapour pressure of the solvent in the solution is lower than that of the pure solvent.

I've not understood his explanation especially the bold lines above.
$\bullet$ Firstly, how could vapour pressure represent the tendency of the system & its surroundings to reach a higher entropy?
$\bullet$ Why does the solution has a lower tendency to acquire an even high entropy by the solvent vaporising ? After-all every system has greater tendency to acquire high entropy, isn't it? Is not this statement contradictory to the Second law by saying lower tendency to acquire high entropy?
Could anyone please explain that to me?


texts:
I'm rather unfamiliar with chemistry but I want to electroplate steel with copper.

From Wikipedia:

  The cations associate with the anions in the solution. These cations are reduced at the cathode to deposit in the metallic, zero valence state. For example, in an acid solution, copper is oxidized at the anode to $\ce{Cu^2+}$ by losing two electrons. The $\ce{Cu^2+}$ associates with the anion $\ce{SO4^{2−}}$ in the solution to form copper sulfate. At the cathode, the $\ce{Cu^2+}$ is reduced to metallic copper by gaining two electrons. The result is the effective transfer of copper from the anode source to a plate covering the cathode.

I have also found a YouTube video where a guy uses $\ce{HCl}$ instead of $\ce{H2SO4}$.

What are the requirements for the reaction to work? Does it have to be an acid solution? Can I use vinegar?


texts:
I live in a high humidity location and every winter, mold forms on one of my walls due to water sticking on it during the cold times. This also ruins the paint.

I found out that certain materials absorb water from the air, so I decided to make my own dehumidifier based on sea salt. The problem is alleviated slightly, but not fully - the salt becomes moist, but I think after a certain point it just can't absorb any more humidity.

So I was wondering how much salt I would need to bring the humidity in my room to a normal level.

I looked for things like "hygroscopic materials water absorption levels" on Google, but I did not have much luck.

What I am looking for is a formula like:

X kg of sea salt will absorb Y kg of water at Z% humidity

I have no background in chemistry, unfortunately, so I am not even sure if I am searching for this formula using the right terms.


texts: In the above we need to find the configuration of the two double bonds whether (E) or (Z) according to me the one with the cyanides should be (E) and the other (E) however my book say that the correct answers are (E,Z) (in the same order as above) . Please explain how ?


texts:
I'm currently preparing my exam and while I did never think about this question during the course, it begins to confuse me right now...

Why is it the structure of $\ce {ClO_{2}-}$ like $\ce {O-Cl-O}$ and not like $\ce {O-O-Cl}$?

I know how to place the covalent bonds and the electrons, but I don't know how to figure out the basic structure of the molecule. Is there a relatively simple rule to solve (and understand) such relatively simple molecules?


texts: NiO and ZnO electrical conductivity with oxygen pressure

texts:
NiO is a Mott-Hubbard insulator and increasing oxygen concentration leads to anion excess and oxidation of Nickel so electron hopping is more favourable so electron repulsion is reduced and it becomes metallic. This makes sense to me but I think it can also be explained as a p-type semiconductor since you're essentially adding Ni(III). So you'd expect to get a band structure with a very narrow empty band above a filled band. However, I don't see how these ideas match up?

ZnO has ten d electrons so isn't a Mott Hubbard insulator so can only be a n-type semiconductor since it won't be oxidised. This leaves a narrow filled band below and empty band right? But what is the empty band? The s band? Is my reasoning okay?


texts:
Raw Tahini seems to me like a non-Newtonian substance. When I mix it fast, it gets tougher. When I mix it slowly, it gets softer.
Is there any truth to that?


texts: Are the entropy values calculated with average heat capacities

texts: I asked myself whether the entropy values in an ordinary table in thermochemistry are calculated with exact specific heat capacities for each little temperature change or if they are averaged the capacities and assumed to be constant.


texts: Why Does Activation Energy not change with Temperature change

texts:
As The Graph Shows; $E_a$ (Activation Energy) = Energy Of transition State(Threshold Energy) $-$ Energy of Reactants.
So let This be the graph at Temperature $T_1$, Now say We Increase The Temperature to say $T_2$ and so the energy of reactants must increase (as kinetic energy of molecules increases). So at $T_2$, reactants would start with more energy. So Shouldn't the Activation Energy decrease as now less energy is needed to reach Transition State.
Or I can say that since $E_a$ (Activation Energy) = Energy Of transition State(Threshold Energy) $-$ Energy of Reactants, So as Energy of Reactants has changed so should Activation Energy.
I already saw answers on a similar question but couldn't figure out what's wrong with my approach.


texts: I am told that in a chemical equation the metal comes first and then the non metal. for example MgO, ZnSO4,etc. But when both the elements are non metals or metals, the one with the lower atomic number would come first. for example:- H2O,CO2,HF,etc. But why is it that hydroxide is OH- and not HO-? Also why is methane CH4 and not H4C?


texts: Is there a stable and non-toxic hydro-nitrogen-oxygen compound that's liquid in room temperature?

texts:
Is there a stable (i.e. does not turn into other substance when stored in a bottle exposed to the elements  or explode/combust spontaneously or under mechanical impact) compound that contains just $\mathrm{N}$, $\mathrm{H}$ and $\mathrm{O}$ but no $\mathrm{C}$ and is (a) either liquid or can exist as a high concentration ($80\%+$) water solution at the range of $-50\,{}^\circ\mathrm{C}\sim+70\,{}^\circ\mathrm{C}$ and (b) preferably non-toxic (c) combustible, but this seems to be usually implicit from its composition?

(Aside from $\mathrm{N}\mathrm{H}_3$, $\mathrm{N}_2\mathrm{H}_4$, $\mathrm{H}\mathrm{N}\mathrm{O}_3$, or $\mathrm{N}\mathrm{H}_4\mathrm{N}\mathrm{O}_3$ that is.)


texts: Nomenclature: equivalent atoms by single locant

texts:
Sometimes the IUPAC name is too verbose despite the structure's high symmetry. If we could use only the first locant of the ("topologically symmetrically") equivalent set of locants, and designate all of them by some symbol (e.g. xallsym, which is too long, and Greek letter sigma has some meanings already, so I will use Greek letter stigma), then we could have

1,3,5-trinitrohexahydro-s-triazine vs
1ς-trinitrohexahydro-s-triazine or
Nς-trinitrohexahydro-s-triazine

naphthalene-1,4,5,8-tetrol vs
naphthalene-1ς-tetrol

naphthalene-1,2,4,5,8-pentol vs
naphthalene-1ς,2-pentol

naphthalene-1,2,3,6,7-pentol vs
naphthalene-1,2ς-pentol

1,5(1,2,3),2,4,6,8,9(1,4),3,7(1,2)-nonabenzenabicyclo[3.3.1]nonaphane vs
1ς(1,2,3),2ς(1,4),3ς(1,2)-nonabenzenabicyclo[3.3.1]nonaphane

1,2,3,4,5,6-hexachlorobenzene or
hexachlorobenzene vs
1ς-hexachlorobenzene (the name is not convenient in this case)

1,2,3,4,5,6-hexachlorocyclohexane vs
1ς-hexachlorocyclohexane

1,1,2,2,3,3,4,4,5,5,6,6-dodecachlorocyclohexane or
perchlorocyclohexane vs
1ς,ς-dodecachlorocyclohexane
(not convenient in this case, but mentioned the special feature, listing two identical sets. Imagine 1ς means 1,2,3,4,5,6; 1ς,ς would mean 1,2,3,4,5,6,1,2,3,4,5,6)

Wrong usage can lead to contadictions/confusion, e.g. 1ς-trichlorobenzene would be illegal, because benzene carbon 1 is equivalent with all other carbons, total 6. But it is distantly similar problem like for with name like 1,2,3-hexachlorobenzene.

Is anyone aware of such feature in any chemical nomenclature?


texts:
I'm newish to RDKit and couldn't find an answer to this online.  The following is a minimal representation of how I drew a molecule

from rdkit import Chem
from rdkit.Chem import Draw as Draw
from rdkit.Chem.rdMolDescriptors import CalcMolFormula

# .. read mol_a from file... then
print(repr(mol_a))
<rdkit.Chem.rdchem.Mol object at 0x7fd5c5494dc0>

print(CalcMolFormula(mol_a))
C4H11N

Draw.MolToImageFile(mol_a, 'pic.png')

Here is what I get:

What are those red boxes?

I'm running Ubuntu 16.04, Python 3.7.3

I had three semesters of college chemistry about a decade ago.

Thanks!


texts:
Wikipedia has this plot of the absorption spectrum of liquid water:

The vertical axis seems weird to me. The Beer-Lambert Law says $T=10^{Ax}$ where $T$ is the fraction of light transmitted, $A$ is the absorption coefficient, and $x$ is the optical distance through the material. If we take the values listed on the vertical axis to be $A$ as I've described it here, the transmittance ranges from 80% transmittance though a 1 nm (!) thick sample at 80 nm wavelength ($10^{-10^8*10^{-9}}$) to 80% transmittance through a 10 m thick sample at 500 nm wavelength ($10^{-10^{-2}*10}$).

Alternatively phrased, the absorption coefficient at 2 um is 10^4. Therefore the transmittance would be $10^{-10^4*0.01}$ through a 1 cm sample. That would be one in $10^{-100}$ photons transmitted through the sample. Given that IR spectroscopy is possible, that sure doesn't seem right to me.

Does the transmission of light through water really vary by 10 orders of magnitude or am I misreading this?


texts: Can fully-hydrogenated oils be mixed with unsaturated oils for use in food (margarines, etc)?

texts:
Would it be feasible to mix fully hydrogenated oils with unsaturated oils (eg. soybean oil) to create an edible fat with the consistency of margarine?

If so, what is the motivation for interesterified oils? If not, then what is the constraint that prevents this? Do the fats not form a solution?

I'm trying to understand how palm oil came to replace partially hydrogenated oils in margarines in response to trans-fat bans, and what possible alternatives might be.


texts:
The fourth principle of Molecular Orbitals state that:

Molecular orbitals are best formed when composed of Atomic orbitals of like energies.

I'm not sure about how I should interpret this; which is the correct?

It means that the molecular orbitals that I need to consider are the ones formed by the same orbitals on each atom (like a pair of $2p$, two $3s$, etc).
It means that I need to evaluate the actual energy on each orbital using: $$E = \frac{-13.6 z^2}{n^2}$$ And then compare the energies of every orbital, to match each orbital on Atom 1 to the closest one on Atom 2? Meaning that I could possibly have a $2s$ pairing with a $3p$, depending on both atoms? (Note that the formula gives different results for each Atomic Orbital depending on the atom's $z$).

I known that every possible orbital combination exists, but I'm asking about the ones that are more relevant and thus need to be considered.


texts: Decarboxylation / Elimination type reaction

texts:
I'm quite familiar with E1/E2 reactions and usually use those ideas to explain elimination reactions, however I came across a reaction which was a bit different (in the sense it isn't E1/E2) but still an elimination.

Looking at this reaction I ruled out an E2 type elimination because there's no axial hydrogen which is trans to the bromine group, so something else must have happened here. I drew out the lowest energy chair conformation ('locked' in that conformer because of the t-butyl group) that would react to help me understand what happened and this is what I came up with (excuse the poor chair drawings):

I know hydride is a very strong base and the first step would be deprotonation of the carboxylic acid group (Due to it being the most acidic proton). However after this, mechanistically I wasn't so sure what would happen and how it would happen. My thinking was the oxygen which is now quite charged would push the electron density in towards the carbonyl carbon, and hence the bond would break (between the carbonyl carbon and the cyclohexane carbon). That would form a double bond, and $\ce{CO2}$ and bromide would leave. Is this realistically a correct explanation for what is observed? Also what kind of reaction is this? I haven't come across it before during the usual E1/E2 reactions. Are there any other examples of similar elimination reactions?


texts: What is the mechanism of photosynthesis?

texts: I just want to know what particle in plants can change $\ce{H2O}$ into $\ce{O2}$ and what $\ce{CO2}$ does in this conversion system. What if we just use $\ce{H2O}$ and light to convert it into $\ce{O2}$?  If light is what we need to convert $\ce{CO2}$ into glucose and $\ce{H2O}$ into oxygen, why can't scientists make a machine to do that?


texts: Standard Solutions for UV-Spectrophotometry

texts: Can one use a mixture of compounds when making a standard solution for UV-Spectrophotometry. For instance, one is attempting to find the casein concentration of milk using UV-spec and they have milk protein which has casein protein in, but not pure casein protein. Would it be feasible to make the standard solutions using the milk protein, knowing how much casein is in it, even if there are other proteins in there or if it is not pure casein?


texts:
I searched for the strongest oxidising agent and I found different results: $\ce{ClF3}$, $\ce{HArF}$, $\ce{F2}$ were among them.

Many said $\ce{ClF3}$ is the most powerful as it oxidises everything, even asbestos, sand, concrete, and can set easily fire to anything which can't be stopped; it can only be stored in Teflon.

And $\ce{HArF}$ could be a very powerful oxidant due to high instability as a compound of argon with fluorine, but was it even used as such?

What compound is actually used as oxidising agent and was proven to be stronger then others, by, for example, standard reduction potential?


texts: Inorganic IUPAC for Compounds with bridged ligands?

texts:
Can we use  bis(tetraammine) instead of octaammine is the 2nd example ?

As in the 1st example they used  bis(pentaammine)  and also in the 3 one the used bis(carbonylcyclopentadienyliron)


texts: How do we turn PTFE powder into a paste we can dilute in a solvent

texts:
We want to create a binder we can use in our filter elements that is PTFE based, so we need to somehow create a paste, we can thin down with a solvent that will still hold the PTFE in suspension, long enough to dip our virgin glass microfibre elements in and get an even distribution through the element structure.
So far we have tried a DMP and DIBK mix to make a paste, and then diluted in MEK but we cannot get the PTFE to remain in suspension long enough.


texts:
To be specific, what I mean is: is the following situation possible? At given temperature T, there are two substances, X and Y, such that pure X is a solid, pure Y is a liquid, and X and Y mix to form a single phase in all proportions.

The closest I could find was this phase diagram for silver and gold (two very similar metals, I suppose):
http://www.crct.polymtl.ca/fact/phase_diagram.php?file=Ag-Au.jpg&dir=SGTE

But it looks like there is still a narrow region in which there are two phases.


texts: How to define the reduced mass for estimating Kinetic Isotope Effects

texts:
I am trying to think about radical reactions using zero-point energies (from the harmonic oscillator model). I have read that substitution of a bond with isotopes can alter the rate of a reaction.

For example, consider the reaction:

$\ce{CH4 + Br2 -> CH3Br + HBr }$

Suppose the 3 non reacted hydrogens are instead deuterated. The new reaction will be:

$\ce{CD3H + Br2 -> CD3Br + HBr}$

Now, based on the harmonic oscillator model, the zero point energy of the C-H bond in $\ce{CH4}$ can be calculated from $E_0=\frac{1}{2}h\frac{1}{2\pi}\sqrt{\frac{k}{\mu}}$ where $k$=the force constant for the bond and $\mu$ is the reduced mass.

I read that "isotopic substitution does not change the potential energy surface of molecules" so the value of $k$ is unaffected by isotopic substitution. Thus in a kinetic isotope effect analysis based on zero-point energies, we need only consider the change in reduced mass.

Now my question is about the specifics of handling the listed reaction above. For calculating the reduced mass of the C-H bond, would you use the mass of the whole molecule (1) or just the mass of the carbon atom that the hydrogen is bonded to (2)?

In case the wording is confusing, in the example reaction the difference between the reduced masses would be:

$\mu=\frac{m_1 m_2}{m_1+m_2}$

(1) $\mu=\frac{15\cdot2}{15+2}=1.76$

This version of the calculation takes $m_1$ as the mass of the rest of the molecule ($\ce{CD3}$) beyond the C-H bond.

(2) $\mu=\frac{12\cdot2}{12+2}=1.714$

This version takes $m_1$ as the mass of only the carbon atom in the bond.

Which would be the correct way to carry out the calculation?

I kept the rest of the molecule simple in the calculation, but if the rest of the molecule had a much larger molar mass (say 200), then the reduced mass would become closer to 2, so I feel like the difference between the two methods could significantly affect the results of calculations on more complex molecules.


texts: How does a 5th hydrogen bind to carbon atom in CH5[+]?

texts:
Can we bind a fifth hydrogen to a carbon atom if carbon is not in excited state?

We have a big discussion in class and cannot clearly answer the question. If carbon atom excites an electron from $2\text{s}$ orbital to $2\mathrm{p^3}$ orbital, it can covalently bind four hydrogens each with one electron. In this case the $\ce{CH5^+}$ couldn't be created.

But what if carbon atom stays in its ground state so that there will be $2$ electrons in its s-orbital and $2$ electrons in its p-orbital? We discuss that then four hydrogens (each with one electron) could bind to carbon covalently, filling its p-orbitals, and the fifth hydrogen nucleus (without any electron) would bind to carbon s-orbital via coordinate bond.

Is it possible that two hydrogen atoms (each with one electron) would fill one vacant (plain) orbital of other element, e.g. carbon, and thus bind to it?


texts:
I am working on my scholarship exam practice assuming high school chemistry knowledge and struggling at how I can rationalize this question.

  Which of acid aqueous solution 1) to 4) is non-volatile one?
  1) $\ce{CH3COOH}$
  2) $\ce{H2SO4}$
  3) $\ce{HCl}$
  4) $\ce{HF}$

The answer key provided is 2) $\ce{H2SO4}$ but I wonder, in the exam condition, how should I solve this rationally? What thought should I have on this to determine the volatility of the compound? Please help.li


texts: The atomic number of Na is 11 (2, 8, 1). Na loses an electron to achieve octet stability but why can't it just accept an electron to complete duplet stability?


texts: Valence Bond Theory tells us that each of the “sp3” (in reality, 44% s character) oxygen line pairs in water can act as electron donors, but observing the MO diagram for water tells us that the 2 non-bonding orbitals are of vastly different energies. (One of the “lone pairs” has bonding character too.) As such, how does water even form 2 electron-donating hydrogen bonds?


texts:
If we put a diatomic molecule under pressure the interatomic distance will be decreased and according to this graph the potential energy of the bonding molecular orbital will be increased.

What will happen to the energy of the antibonding molecular orbitals?


texts: I read that the primary amine product of Gabriel Synthesis is a racemic mixture. However, when analyzing the reaction the stereochemical step(s) are all $S_N2$. Thus, I figured if you are careful you can track the stereochemistry of the (or both) $S_N2$ reaction(s). Can anyone clarify this for me?


texts: Will the volume occupied by a mixture of nitrogen and water be same as the volume occupied by them individually?

texts:
I am currently studying gaseous state and I encountered the following problem.

  A container with a volume 3 liter holds $\ce{N2(g)}$ and $\ce{H2O(l)}$ at $\pu{29 ^\circ C}$. The pressure is found to be $\pu{1 atm}$. The water is then split into hydrogen and oxygen by electrolysis according to the reaction
  $$\ce{H2O (l) -> H2 (g) + 1/2 O2 (g)}$$ After the reaction is complete, the pressure is $\pu{1.86 atm}$. What mass of water was present in the container? The aqueous tension of water at $\pu{29 ^\circ C}$ is $\pu{0.04 atm}$.

This is one of the steps of the solution given along with the question (edited to show the units):

  Amount of substance of nitrogen:
  $$n(\ce{N2}) = \frac{\pu{0.96 atm} \cdot \pu{3 L}}{\pu{0.0821 atm L mol-1 K-1}\cdot \pu{302 K}} = \pu{0.116 mol}$$
  Amount of substance of water:
  $$n(\ce{H2O}) = \frac{\pu{0.04 atm} \cdot \pu{3 L}}{\pu{0.0821 atm L mol-1 K-1}\cdot \pu{302 K}} = \pu{0.00484 mol}$$

The thing I don't understand here is that how can the volume of nitrogen and water be taken as $\pu{3 l}$? Both of them would occupy some volume not the whole volume will not be occupied by one of them.


texts: Is the elimination reaction between 1 1 dibromo cyclopropane and phenyl lithium feasible in alkaline medium (and some heat)

texts:
I found this question in one of my question papers for the JEE ,
My sir gave me an explanation that due to resonance between lone pairs of the bromide and π bond formed.

This reasoning doesn't seem to be satisfying because of the cyclopropyl ring strain which is not lost even at the end of reaction.
Please give an alternate pathway of the above product is not correct.


texts: Do absorbances of different compounds at one wavelength sum up?

texts:
Question on my practice exam. The answers to the questions were not released, otherwise I could work backwards to figure out how to solve it. As it stands, though, I can only guess the method to solve this question.

The extinction coefficients of the 4 natural nucleoside-5'monophosphates @ 260nm
(Cavaluzzi,MJ,Nucleic Acids Res., 2004, 32,e13).

*pdA = 1.506 E4 L/mol/cm
*pdG = 1.218 E4 --
*pdC = 7.10 E3 --
*pdT = 8.56 E3 --

Find the Extinction Coefficient of a single stranded, 5'-phosphorylated Dickerson Dodecamer sequence d(pCGCGAATTCGC)

If I saw this question on a test, my first instinct would be to add up the values for pdC+pdG+pdC etc...(following the sequence of letters). Or maybe average them all.

We did learn the Beer-Lambert Law used in absorption spectrum, where e was extinction coeffecient: $$A=E(extinction)*b*c$$  but I can see no way to use this equation, since i'm only given a wavelength and a whole bunch of coefficients.

Does anyone know how to solve this? Is there an equation I'm missing?

Thanks in advance.


texts: Does resorcinol give positive iodoform test?

texts:
It's given in my book that other than the usual compounds that answer iodoform test, resorcinol (benzene-1,3-diol) also gives positive iodoform test.

Is this because of tautomerization which gives a diketone with an active methylene group? But why should a ring lose its aromaticity by doing so?


texts: Why only one peak is observed in NMR spectrum of H2?

texts:
Assuming a downward magnetic field is applied and the nuclear spin of two equivalent protons in $\ce{H2}$ are all in ground state $\downarrow\downarrow$ initially. Would the required energy of one of the protons excited to spin up state $\uparrow\downarrow$ be different from the energy of proton excited form state $\uparrow\downarrow$ to state $\uparrow\uparrow$ ?

And if it's true why only one peak is observed in NMR spectrum?


texts:
Given that $K=18$ for the equilibrium below, calculate the total pressure in a sealed vessel initially containing only $\ce{NH4I(s)}$, that reaches equilibrium.
$$\ce{NH4I(s) \leftrightharpoons NH3(g) + HI(g)}$$
a) $4.2\mathrm{~atm}$
b) $8.5~\mathrm{atm}$
c) $2.1~\mathrm{atm}$
d) $\mathrm{18~atm}$
e) $\mathrm{6.3~atm}$

Using $K = \ce{[NH3][HI]} = 18$, I found $\ce{[NH3]=[HI]=}~\frac{4.24mol}{L}$, and therefore $8.48~\mathrm{mol}$ of gas is produced, but I don't know how to find the equilibrium pressure without temperature and volume.


texts: Suggestions for 200-600 nm range transmitting polymers/materials

texts:
I am a student of physics who is doing research related to Cherenkov measurements. For that purpose, I need suggestions for some materials that have the following properties:

$80\%$ transparency in the range of $200$-$600$ $\mathrm{nm}$
Low scintillation light produced from electrons
Relatively lower density
A high refractive index

Some materials in this regard that I have tested are PMMA, TPX, NAS, LURAN, TOPAX, and Plexiglass. I want to test more materials to see if something does better; what polymers or other materials might I try to achieve these properties?


texts: Is it possible to perform ROMP2 numerical optimizations in Gaussian09?

texts:
I wish to perform an restricted open-shell MP2 (ROMP2) geometry optimization.

Gaussian09 currently only provides energies at ROMP2 level of theory.

It should be possible to perform an optimization by displacement of the structure followed by single-point-energy evaluations at the displaced geometries to obtain a gradient. In other quantum-chemical software packages this (slower) numerical optimization technique is readily available. I cannot seem to get it to work in the case of ROMP2 in Gaussian09. I have already tried the usual options, such as #p opt roMP2/cc-pVDZ scf=tight and so on. All of my approaches failed and yielded the following error:

 NEF-NEF-NEF-NEF-NEF-NEF-NEF-NEF-NEF-NEF-NEF-NEF-NEF-NEF-NEF-NEF-NEF-NEF-
 NUMERICAL EIGENVECTOR FOLLOWING MINIMUM SEARCH
 INITIALIZATION PASS

 ************************************************
 ** ERROR IN INITNF. NUMBER OF VARIABLES (  0) **
 **   INCORRECT (SHOULD BE BETWEEN 1 AND 50)   **
 ************************************************

I am aware of this website: http://www.somewhereville.com/?p=1571
and I have tried the solution outlined therein, but it has failed in the same manner as well.

Any help or pointers towards other software that is capable of ROMP2 optimizations would be appreciated.


texts: Get the molar mass of an unknown liquid in a dissolution

texts:
A dissolution has $10$g of some unknown liquid and also $90$g of
  water. The freezing point of this dissolution is $-3.33^\text{o}$C.
  What is the molar mass of the unknown liquid in g/mol?

Alright. First of all, the formula to calculate the freezing point of a dissolution is

$$T_f - \Delta_f$$

Where

$$\Delta_f = \text{m} \cdot K_f$$

In our case, it would be

$$-3.33 = 0 - (\text{m}\cdot 1.86)$$

The molality m is

$$\frac{\text{moles of unknown liquid}}{\text{kg of water}} = \frac{\text{moles of unknown liquid}}{0.09}$$

We have to solve the equation:

$$-3.33=-\frac{\text{moles of unknown liquid}}{0.09}\cdot 1.86$$

Which yields

$$0.16 = \text{moles of unknown liquid}$$

However, I need the molar mass of this unknown liquid. How do I get it?


texts: Are there any molecules with the same spectrum?

texts: Are there any two distinct types of atom or molecule that have identical emission or absorption spectra?


texts: Why is the sum of two inexact differentials exact?

texts:
From the first law of thermodynamics, $\mathrm{d}U = đQ + đW$, where $\mathrm{d}$ represents an exact differential and $đ$ an inexact differential. Exact differentials correspond to state functions and are path-independent.
How is it possible, and what does it imply, when we say that the sum of two inexact differentials is an exact differential? Is the sum of two path-dependent functions always a path-independent function? Also, what is the difference between a partial derivative and an inexact derivative / differential, apart from mathematical implications?


texts: How To find which organic compound gives effervescence when reacts with $\ce{NaHCO3}$? Specially in case of phenols, which one reacts and which does not? According to my professor, all acids stronger than $\ce{H2CO3}$ evolve $\ce{CO2}$ when treated with $\ce{NaHCO3}$. But I do not understand how to find which acid is stronger than $\ce{H2CO3}$, further how to find same for $\ce{Na}$ and $\ce{NaOH}$  especially when the pKa values are not given in question.


texts: Why second ionisation energy greater than the first?

texts: Why is the second ionisation energy for atoms with more than 1 electron in the outermost sublevel greater than that of the first, if you are removing an electron from the same sublevel ? Why is there a greater attraction for an electron in the same sublevel?


texts: Does trans 1,3-dichlorocyclobutane have zero dipole moment?

texts:
Does this compound have zero dipole moment?

I think it has a non-zero dipole moment. If I assume the ring to be planar, then the dipole moments of each $\ce{C-Cl}$ bond cancel out. (One is upward and the other is downward.)

But if I take the actual puckered structure of cyclobutane, one $\ce{C-Cl}$ bond is axial and the other is equatorial and hence they won't cancel out and the compound has a non-zero dipole moment.

But the answer given in my book says the compound has zero dipole moment.


texts: Do you break the metallic bond when you break a metal into two pieces?

texts: As we all know, metallic ions are surrounded by a sea of electrons. If we continually bend or stretch a metal, say, iron, it will break. Does that mean we break the metallic bond in subatomic level?


texts:
I came across a question that asked for a method to convert propene to glycerol. I used the method in the pic, but I'm worried about two steps-

Step-2, This reaction is just made up by myself! I'm using a 'bulky' base to favour elimination. Is this reaction feasible? Will it occur without giving any byproducts?

Step-3, Can I use MCPBA to convert an alkene containing an alcohol group to its corresponding epoxide? I'm worried that MCPBA can protonate the alcohol to generate the carbocation (moreover, the allylic carbocation makes it even more probable!) and that will lead to byproducts.

That's all.

Any help will be appreciated.


texts: I have a range of sodium hydroxide solutions with different concentrations. (from 1.0 mol dm^-3 to 0.5 mol dm^-3). The max volume of each is 100ml. How can you easily dispose of these? Can I pour them down the sink?


texts: How to decide what pathway a reaction will follow, elimination, addition to a carbonyl or nucleophilic substitution?

texts:
There is a substrate such as this,

and it is treated with alcoholic KOH.

I know that a hydrogen in $\alpha$-position to the carbonyl group will be abstracted, leaving a carbanion. My query lies in deciding what pathway will the substrate follow from hereon. I see three options: An E1cB elimination of the bromide, aldol condensation by nucleophilic addition to the carbonyl group and SN2 with the 1 degree bromide.
Which pathway will be favored and why?

I'd be glad if someone could specify the conditions for one pathway being predominantly favored over another (even if I haven't provided information regarding that, like temperature, solvent, etc) or some empirical data on one pathway being faster or slower. Any degree of help will be appreciated, thank you.

Edit: The answer in the book where this question is from says that nucleophilic addition should predominate (providing neither justification nor data), which contradicts my guess that elimination would dominate because of it being an internal mechanism.


texts: Does it matter which end of a chain one sets to be 1 when drawing the structure of organic compounds?

texts:
For example, if I were to draw the structure of 1,2,4-trimethylcyclohexane, then would one or both of these be wrong?

Or are both right? I'm wondering if it matters where I start to count from 1 in these cases, if there is some convention to it or if it doesn't matter much.


texts: Understanding elementary rate laws from a probability stand point

texts:
I am learning about chemical kinetics and dynamics and as I understand for a general chemical reaction
$$\ce{aA + bB -> cC + dD} $$ whose reaction rate, r, can be described by an elementary rate law can be written as follows: $$r= k[\ce{A]^a[\ce{B}]^b} $$

What I do not seem to conceptually understand is if you look at a chemical reaction from a collision theory standpoint, would it not be true that as one reactant that is in a higher stoichiometric ratio relative to the other, the probabilty that the reactants collide (assuming any collision gives a reaction) would be inversely proportional to the stoichiometry of the reactant. For example in the following:
$$\ce {A + 2B -> C} $$

You basically need 2 mols of B for every mol of A for a successful reaction to produce C, so if the probability that A successfully collides with a mol of B is $\propto$ to $1/z$, then the probability that A successfully collides with TWO mols of B  $\propto 1/z^2$ which is lower, so why does a reaction rate, which is $\propto$ to the probability of a collision, with an elementary rate law $\propto$ to a concentration raised to an exponent?


texts: Deciding higher priority order between a triple bond and tertiary carbon

texts: I want to know which of the groups will be given higher priority $\ce{-C#CH}$ or $\ce{-C(CH3)3}$ and why. I tried resolving the triple bond to single bonds such that they are phantom atoms. But that gave me a structure in which there are no atoms after the first point of difference. How is this (see image) wrong and if this is correct then isn't it a contradiction? After first point of difference, there are two difference one is nothing v/s $\ce H$ and other is $\ce C$ vs $\ce H$ and both situation seem to contradict in giving their respective group higher priority order.


texts: Is my analysis of quantum numbers describing the ground state of At correct?

texts:
Which series of quantum numbers describes the highest (energy) occupied orbital in a ground state of At atom?

a) n = 6, l = 0
b) n = 6, l = 2
c) n = 5, l = 2
d) n = 4, l = 3
e) n = 6, l = 1

According to my teacher, the answer is e.

My analysis:

The electron configuration of At atom:

$$\begin{aligned}1s^22s^22p^63s^23p^6\ce{3d^10}4s^24p^64\ce{d^10}5s^25p^64\ce{f^14}\ce{5d^10}6s^26p^5
\end{aligned}$$

Knowing for levels 0,1,2,3 correspond to s,p,d,f respectively we can say that:

a) $$\begin{aligned}6s^2\end{aligned}$$
b) $$\begin{aligned}Nothing \end{aligned}$$
c) $$\begin{aligned}\ce{5d^10}\end{aligned}$$
d) $$\begin{aligned}\ce{4f^14}\end{aligned}$$
e) $$\begin{aligned}\ce{6p^5}\end{aligned}$$

What I thought here first is that d is the answer since 4f14 has the largest number of electrons, and thus will occupy the highest energy around.

Then I saw on another question that the orbitals are filled so that the ones of lowest energy are filled first.

$$1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p < 5s < 4d < 5p < 6s < 4f < 5d < 6p < 7s ...$$

In this case, e is the answer since 6p5 has the highest energy regardless of the number of electrons it is holding?


texts: Fitting of interatomic potentials to a training set

texts:
I have read several times in the literature the following:

"The fittings were accomplished using a combination of the singular value decomposition method for linear parameters and the Simplex method for nonlinear parameters."

What I understand from it is that the non-linear parameters are optimized iteratively and for each choice new optimized linear parameters have to be computed. In other words, the full optimization of all parameters therefore entails a linear optimization nested in a non-linear one.

I'm planing to implement this on my own code, although How can I justify this procedure?, is there any reference or book that you could recommend me for reading??

Lets take, for instance, the Buckingham potential

$\Phi _{{12}}(r)=A\exp \left(-Br\right)-{\frac  {C}{r^{6}}}$


texts: Can activated charcoal retain adsorbtion properties even when submerged in liquids?

texts:
This is following a question on Skeptics Stackexchange, where apparently medical science claims that activated charcoal can adsorb poison when ingested.
One of the members posted a related question on this forum asking about burnt toast having properties of activated charcoal.

Although the question on the toast isn't answered properly, at least could anyone here validate if activated charcoal can actually retain its adsorptive properties even when it is soaked in human saliva, digestive juices and tea and/or water?


texts: Why do we compare acidic strength of oxides of nitrogen even though they don't have hydrogen?


texts: How can I obtain oxygen gas from plagioclase

texts:
I would like to know if there is a possibility to decompose plagioclase to obtain oxygen gas to be used in a combustion reaction?

I know that oxygen represents $47\%$ of the weight of 1 mole of plagioclase (albite $\ce{NaAlSi3O8}$ – anorthite $\ce{CaAl2Si2O8}$), which equals to $\pu{130 g}$ out of $\pu{277 g}$, so it will be very nice if I could decompose plagioclase and obtain oxygen gas, but I don't know if that is possible or not?


texts: Which will be oxidised between water and Copper?

texts: I have always read that the one having higher  discharge potential undergoes the reaction( oxidation or reduction). But In this example why is there also oxidation of water?


texts: I have a solution of copper(II) sulfate, and I would love to precipitate the copper metal. From looking at the standard reduction potential table, it appears that I can do this by bubbling hydrogen gas through the solution. However, the potential is not very large, so I am unsure of how well this approach would work. I was also wondering if sodium metabisulfite could be used for this purpose. I know I can precipitate copper carbonate with sodium carbonate and reduce with carbon, but this will take more time, and probably result in a large loss of product. I would also like to avoid precipitating the metal with another metal, because I am demonstrating how metals can be isolated so it would be silly to use a metal that is even harder to reduce.


texts: How many atoms of carbon are needed to produce 0.45 mol aluminium?

texts:
How many atoms of carbon are needed to produce $\pu{0.45 mol} ~\ce{Al}$?
  $$\ce{3C + 2Al2O3 -> 4Al + 3CO2}$$

I am not sure where to start, whether or not I convert moles straight to atoms or convert moles to grams of $\ce{Al}$, then to moles of $\ce{C}$ and then to atoms? I tried the latter of my suggestions and ended up with $\pu{9.8E24}$, but  I don't know if this is correct.


texts: The structure of sodium cuprous thiosulphate

texts:
While studying about copper sulphate, I came across a reaction involving sodium thiosulphate (Hypo) and copper sulphate.

Although I don't know the utility of this reaction, I felt that it was important to understand the structure of $\ce{Na4[Cu6(S2O3)5]}$, which is formed as a the major product of the overall reaction.

The full set of reactions is given as follows:

$$
\begin{align}
\ce{CuSO4 + Na2S2O3 &-> CuS2O3 + Na2SO4}\\
\ce{2CuS2O3 + Na2S2O3 &-> Cu2S2O3 + Na2S4O6}\\
\ce{3CuS2O3 + 2Na2S2O3 &-> Na4[Cu6(S2O3)5]}
\end{align}
$$

  What is the structure (3D, not Lewis structure) of $\ce{Na4[Cu6(S2O3)5]}$ (or the ion $\ce{[Cu6(S2O3)5]^{-4}}$)?

Reference: Allen JEE-Mains+Advanced Chemistry, Unit 10, Chapter: Transition Elements:


texts: Relationship between vapour pressure and saturated vapour pressure

texts: I need clarity on saturated vapour pressure in a closed system at equilibrium. How does saturated vapour pressure relate to vapour pressure?


texts: What is the most acidic neutral hydrocarbon?

texts:
This is a question I've been thinking about quite frequently. I had seen that this hydrocarbon has a low $\mathrm pK_\mathrm a$ with reference to the highlighted H-atom

Loss of the central gives aromatic character to the three 5-membered rings in the compound, contributing to its acidity.

Are there any other neutral hydrocarbons which are stronger acids? How do their $\mathrm pK_\mathrm a$'s stack up against, say another organic acid such as acetic acid?

EDIT: As pointed out in the comments, $\ce{CH_5^+}$ (methanium) is a superacid, but is not a neutral hydrocarbon.


texts: Transfer of odor molecules from oil to water

texts:
I brew beer, I'm not a chemist.  I want to add natural peanut aroma to a beer.  The most common way this is being done by brewers is the addition of peanut powder, which is essentially the product left over after pressing most of the oil out of roasted peanuts.  This product is preferable in brewing to whole peanuts because the introduction of significant amounts of oil into beer will affect desirable characteristics like the "head retention".

I don't like the idea of using this powder for various reasons. First, odor molecules like to be in oil, so pressing out the oil means pressing out a lot of the aroma.  Second, by adding all that powder to the beer, the beer ends up with far too much body and the powder absorbs some of the beer which lowers the yield.

If you've ever tasted roasted peanut oil, you'd notice that it is intensely flavorful of roasted peanuts.  What I'd like to do is extract odor molecules from the peanut oil and ultimately get them dissolved into a water based solution (a.k.a. beer).  This is where I was looking for help/ideas.

I've mixed aromatic fats with ethanol/water solutions (like everclear) and I've found there to be a reasonable transfer of aroma into the ethanol/water. I don't see this working in this case though.  The amount of odor molecules transferred to the solution would be insufficient when used to flavor beer.  The alcohol content of the beer would end up too high by the time enough of the solution was added to get the desired aroma intensity.


texts: Jahn Teller Effect for d4 low spin configurations

texts: Why does Z-in take place in $d^{4}$ low spin configuration whereas in Z-out one can get all the 4 electrons in $d_{xz}, d_{yz}$ which would lead to lower energy


texts: Is it accurate to describe these radiation measurement units in terms of where-it's-measured and relationship-to-time?

texts:
I'm reading about measuring radiation and trying to come up with a more intuitive retelling for an audience familiar with math but not necessarily chemistry or any physical science. Is any or all of the following inaccurate or oversimplified?

Radioactivity (Ci, Bq) - Radiation from the material's point of view. Measured as a rate of disintegration.

Exposure (R, C/kg) - Radiation from the air's point of view. Measured as a sum of radiation that's passed through.

Absorbed dose (rad, Gy) - Radiation from the absorbing target's point of view. Measured as a sum of energy deposited.

Dose equivalent (rem, Sv) - Radiation also in terms of sum energy-absorption, but adjusted for a medical point of view.

As you can tell, the 2 pieces I want to highlight are (1) where-it's-measured and (2) time dimensionality (rate versus summable quantity).
My objective question is, where have I got it wrong? What has potential to cause confusion?
But of course, interested in complete reformulations.


texts: How exactly does the reaction between alkyl halides and silver nitrite occur?

texts:
$$\ce{R-X + AgNO_2 -> RNO_2}$$
Now depending on the $\ce{R}$ and solvent the reaction can occur via $\mathrm{S_N1}$ or $\mathrm{S_N2}$.
When the reaction proceeds via $\mathrm{S_N1}$ the product formed is $\ce{R-O-N=O}$ whereas for $\mathrm{S_N2}$ it is $\ce{R-NO_2}$.
Why is this so? According to me as the $\ce{Ag-O}$ bond is covalent the lone pairs on nitrogen must attack in both the cases forming the product $\ce{R-NO_2}$.


texts: Reasoning for redox reactions to be classified as such

texts:
Could anyone help me out solving this question regarding redox reactions? I am fairly new to this topic.

Which of the following is a redox reaction?
(1) $\ce{NaCl + KNO3 -> NaNO3 + KCl}$
(2) $\ce{CaCO3 -> CaO + CO2}$
(3) $\ce{Mg(OH)2 + 2NH4Cl -> MgCl2 + 2NH4OH}$
(4) $\ce{Zn + 2AgCN -> 2Ag + Zn(CN)2}$

I know that the answer here is option (4) but could someone help me understand why this is so? I see a change in oxidation in the other three equations but it is not redox.


texts: How can collission theory of chemical reaction and Law of mass action be connected?

texts:
From Wikipedia,

  Collision theory is a theory ... that qualitatively explains how chemical reactions occur and why reaction rates differ for different reactions. The collision theory states that when suitable particles of the reactant hit each other, only a certain percentage of the collisions cause any noticeable or significant chemical change; these successful changes are called successful collisions. The successful collisions must have enough energy, also known as activation energy, at the moment of impact to break the preexisting bonds and form all new bonds.

From Britannnica,

  Law of mass action, law stating that the rate of any chemical reaction is proportional to the product of the masses of the reacting substances, with each mass raised to a power equal to the coefficient that occurs in the chemical equation.

How can both explain and imply each other?

My theory: Due to more availability of reacting species (due to more amount), rate of reaction of increases. But it does not explain the reason of exponentiation of stoichiometric coefficients.


texts:
What is the $\ce{OH}$ functional group in alcohol (ethanol)? My teacher told me it isn't the same as the $\ce{OH-}$ ion or hydroxide.
But it does donate one electron to the respective carbon chain and it's very tempting to say it's hydroxide as it fits perfectly into the role. What exactly is it?


texts: Analytically combining Dynamic Equilibria that have a two way affect?

texts:
Lets say I want to model a water system as the following set of equilibria:

$\ce{H2O <=> OH- + H3O+}$ | $\ce{A=[OH^{-}][H3O+]}$

$\ce{CO2 + H2O <=> H2CO3}$ | $\ce{B=\frac{[H2CO3]}{[CO2]}}$

$\ce{H2CO3 + H2O <=> HCO3- + H3O+}$ |  $\ce{C=\frac{[HCO3-][H3O+]}{[H2CO3]}}$

$\ce{HCO3 + H2O <=> CO3^{2-} + H3O+}$ |  $\ce{D=\frac{[CO3^{2-}][H3O+]}{[HCO3-]}}$

The whole system starts off as just $\ce{H2O}$ and $\ce{CO2}$ from the atmosphere. Now consider that calcium carbonate ($\ce{CaCO3}$) from limestone is going to react with carbonic acid in the water ($\ce{H2CO3}$) to cause the dissolution of calcium ions, increasing the water hardness (We will ignore the small affect of calcium carbonate dissolving on its own very slowly). Thus the following equilibrium also exists:

$\ce{CaCO3 + H2CO3 <=> Ca^{2+} + 2HCO3-}$ |  $\ce{E=\frac{[Ca^{2+}][HCO3-]^2}{[H2CO3]}}$

Using basic math, I can find the relationship between hydronium and calcium concentration:

$\ce{\frac{(E[H3O+]^2)}{(C^2 B[CO2] )}=[Ca^{2+}]}$

This can be linked to pH:

$\ce{\frac{E}{(C^2 B[CO2 ](10^{2pH}) )}=[Ca^{2+}]}$

My question is, can I change this to take into consideration the change in pH over time caused by the change in Carbonic Acid etc. without a computer?


texts: Electronegativity Considerations in Assigning Oxidation States

texts:
I have never seen anything other than a set of rules like these when textbooks present how to assign oxidation numbers. Such as these:

However, if we keep in mind that oxidation numbers are simply imaginary numbers which suppose all bonding to be ionic - i.e. not electron sharing - and if we keep in mind simply relative electronegativity, we can easily work out the oxidation state of any element in any compound.

For example, take water. Bonding order: $\ce{H-O-H}$. Oxygen has two lone pairs. Oxygen is more electronegative than hydrogen. So we suppose that oxygen takes both electrons in both bonding pairs. Oxygen has 8 electrons. Its valence is 6. 6-8 is -2; oxygen has two more electrons assigned to it than what it has in its valence, so naturally its oxidation state is negative 2. No rules needed.

Now hydrogen peroxide. $\ce{H-O-O-H}$. Here we have an oxygen-oxygen bond so in this case, neither element wins the electronegativity battle. Electrons are split between the oxygen and the oxygen. However, since the oxygens are much more electronegative than the hydrogens, we assign both electrons in both the $\ce{O-H}$ bonding pairs to oxygen. Oxygen has 7 electrons assigned to it; oxygen has a valence of 6; oxidation state: -1. No need to memorize exceptions as stated in the table above.

We could go on. However, I am curious:

1) Has anyone been taught to assign oxidation states this way?
2) If not, what do you think of this method?


texts: Would the hydrocarbon gas dissolve in gelled oil based drilling mud (OBM)

texts:
I am an oil well integrity engineer.  Need help in understanding gas solubility in oil-based drilling mud (OBM) when the mud is gelled.  Normally, oil based mud is an emulsion, where continuous phase is some type of oil (~70%), and remaining is dispersed water/brine droplets, various additives to get to desired drilling mud properties.  Gas is highly soluble in OBM, mostly due to base oil is it's main component.  However, drilling mud is thixotropic and becomes like a gel when static.  Don't know exact mechanism, but something like molecules connect to create long chain polymers, thus forming gel (?).

I am trying to understand, if gas is diffused into the mud after it has become like gel, would the gas dissolve in the same way as it would in thin mud (before it's gelled).  Considering, how non-polar molecules dissolve in non-polar solvents, I tend to think that not as much gas would dissolve, but I might be wrong.  Please, help me.


texts: Brillouin zones of a compound after structural relaxation

texts:
My background in solid-state chemistry isn't much, so I apologize in advance if there arises the need to raise a basic fact while answering my question. I've been learning mostly from the web, with my main text resource  'Band Theory of Solids: An Introduction from the point of view of symmetry.' by Simon L. Altmann.

From what I understand, Brillouin zones are areas (or volumes in 3-D) in reciprocal space where you use to describe the energy levels with respect to the k-vectors. Thus typically in band structure plots the k-vectors range from the origin Γ along some straight path which contains points like Δ, K etc.

So far the common examples I've seen for a Brillouin zone are for 'pure' elements (Si, Cu etc.) where you have the atoms in a crystal formation, which you obtain direct lattice pattern, and then the reciprocal space, and finally the Brillouin zone polyhedron.

What I'm really curious about is, if I have a material that I know the Brillouin zone (like a graphite sheet), and this material reacts with another molecule (like a dopant), how would the Brillouin zone change? A scenario would be performing structural relaxation of a carbon nanotube with some dopants, and the nanotube deforms slightly (with the dopants moving to an equilibrium configuration). In this case even if I know the Brillouin zone of a pure (undoped) carbon nanotube, with the deformation, how should I determine which are the k-vector points then?


texts: Drinking water out of a 24 year old Ether Bottle

texts:
I have an empty aluminum Ether bottle (Shipping name diethyl Ether) that I'd like to use as a large drinking bottle as this is thick aluminum. Is it dangerous? Here is some of the info on the bottle.

  Chemical Composition: (C-2 H-5)2-O f.w.74.12.

  Name:  Ether Purified (For Fat Extraction)

  Other: Mallinckrodt (Brand?)
   5.51 lb

  0884

  Diethyl Ether 60-29-7

  Ethyl Alcohol 64-17-5


texts: Bridgehead carbocation: Violation of Bredt's Rule

texts:
This is the solution of a university's problem set (nucleophilic substitutions)
It says that the given compound undergoes SN1 type substitution.

What confuses me is that even though iodide is a good leaving group, bridgehead carbocations (sp² bridgeheads) are extremely unstable. According to me, this reaction shouldn't occur.

Could anyone explain what's going on here? If the explanation is just thermodynamic (hopefully not), could some data be provided? Thanks!


texts:
The Sudan IV is a molecule used to detect lipids in a substance, especially the triglycerides. The Sudan IV molecule formula is  $\ce{C24H20N4O}$ and a triglyceride molecule could have this molecule formula $\ce{C55H98O6}$.

When the two solutions are mixed, there is a color change. What causes this? I assume that it is because a new compound is produced and this compound is red colored.

Is it possible to find the chemical equation of the reaction between Sudan IV and triglyceride?


texts: Why doesn't the solute settle out of a solution, such as brine or sugar water?

texts:
If I have a solution of salt or sugar dissolved in water, the solute will never settle out or "fall to the bottom", no matter low long I wait. Why is that?

Since salt and sugar (in their pure, solid forms) are denser than water, I would intuitively expect that gravity would eventually pull all the salt and sugar to the bottom. Why doesn't this happen?

Now, I'm guessing that salt and sugar solutions have lower energy than mixtures of solid salt or solid sugar with water. So that may explain why salt and sugar don't spontaneously settle out; reactions tend to proceed from a high-energy state to a lower-energy state, not vice versa. (In "explain like I'm 5" terminology, maybe sugar sticks to water better than sugar sticks to sugar.) Is that accurate?

I've heard that the favorability of a reaction is determined by such things as energy, entropy and enthalpy, but I don't know the details. I'm guessing the answer has something to do with those.

This question is inspired by this question over at the Earth Science site: Why does the salt in the oceans not sink to the bottom?

(I'm surprised that I wasn't able to find a previous question about why solutions don't settle. All I found was a question about why colloids don't settle, which is also an interesting question, but it's not the same thing.)


texts: How to calculate the amount of water produced by the incomplete combustion of propane?

texts:
I was wondering if someone could walk me through how to do the following two questions?

  The complete combustion of pentane has a enthalpy change of $-3509~\mathrm{mol^{-1}}$. Write an equation for the complete combustion of pentane. Write a possible equation for the imcomplete combustion of pentane.

For this question, would the following equation suffice:
$$\ce{ C5H12 (g) + 8O2(g) -> 5CO2 (g) + 6H2O (g)  }$$

For an incomplete reaction, the products will be water, carbon/and or carbon monoxide due to insufficient oxygen, so would this equation be correct:
$$\ce{C5H12 (g) + 11/2 O2 (g) -> 5CO (g) + 6H2O (g)}$$

  $17~\mathrm{L}$ of Propane are incompletely combusted in $34~\mathrm{L}$ of oxygen at $25~^\circ\mathrm{C}$ and $100~\mathrm{kPa}$ into only water and carbon. Write a balanced chemical question to represent this including state symbols. What is the mass of the water produced? What observable change would indicate that a chemical change occurred?

Would an equation like this work: $$\ce{C3H8 (g) + 7O2 (g) -> 3CO2 (g) + 4H2O (g)}$$

The ratio for the above equation will be 1:7:3:4.

I am given the volume of the propane to be $17~\mathrm{L}$ and the volume of the oxygen to be $34~\mathrm{L}$. Since the question is a molar calculation, I think I have to convert the $~\mathrm{L}$ into the SI units of grams. This means $17~\mathrm{L} \Rightarrow 17000~\mathrm{g}$ and $34~\mathrm{L} \Rightarrow 34000~\mathrm{g}$.

The I have to calculate the number of moles for propane and oxygen (I think).

$$
\text{number of moles} = \frac{\text{mass}}{\text{molar mass}}\\
\text{number of moles of propane} = \frac{17000}{44.1} = 385.4~\mathrm{\frac{mol}{gram}}\\
\text{number of moles of oxygen} = \frac{34000}{16} = 2125~\mathrm{\frac{mol}{gram}}$$

Finally I have to find the mass of the resulting water, which is the part I am stuck at. I know I have to find the number of moles times the molar mass of water to find the total mass of the water, but I am just somewhat stumped as to how to find the number of moles of water given what I have worked out above.

For chemical changes, I think that bubbles of gas may appear, a temperature change will occur since this is a combustion reaction, and maybe a change of mass/volume?


texts: Why does AlCl3 dimerise to Al2Cl6 at low temperatures?

texts: I know that it has something to do with HOMOs and LUMOs (I can't what the HOMO/LUMO for AlCl3 is, though).


texts: Calculating concentration of H+ Ions using Ka Value

texts:
I have this homework question that I am a bit stuck on for an answer. If anyone could help that would be great.

Question:

  For a $\pu{0.2M}$ $\ce{HNO2}$ solution ($\pu{K_a= 4.5 \times 10^{-4}}$) calculate the concentration of the $\ce{H+}$ and $\ce{NO2-}$ ions, $\ce{HNO2}$ molecules and the $\ce{pH}$ of the solution.

If anyone could give any hints or answers that would be great.


texts: Pauli-forbidden term symbols for atomic carbon

texts:
Carbon has a $\mathrm{p^2}$ configuration, and within the Russell-Saunders coupling scheme, we have

$$\begin{align}
s_1 = s_2 &= \frac{1}{2} & S &= 1,0 \\
l_1 = l_2 &= 1 & L &= 2,1,0 \\
\end{align}$$

which gives rise to $^3D$, $^1D$, $^3P$, $^1P$, $^3S$, and $^1S$ terms. Out of these six, only $^1D$, $^3P$, and $^1S$ are allowed by the Pauli principle.

It's not hard to show that the $^3D$ term is forbidden, since this term has to contain one state with $m_{l1} = m_{l2} = 1$, which would correspond to a spatial wavefunction that is symmetric with respect to interchange of the two electrons. Pairing this with a triplet spin wavefunction, which is also symmetric, would lead to an overall symmetric wavefunction, which is not allowed.

But that's all the textbooks say - they don't describe why the $^1P$ term is forbidden, for example. I know how to construct a table of microstates, and I know I can use the direct product table of the full rotation group to find that $P \times P = S + [P] + D$, and I know that both of these methods show that the allowed term symbols are only $^1D$, $^3P$, and $^1S$.

Essentially, I am looking for a more intuitive explanation of why the $^1P$ and $^3S$ states are forbidden that preferably links back to the requirement that the wavefunction be antisymmetric - if that is possible.

Alternatively, an explanation of why $P \times P = S + [P] + D$ would also work. I know that from the Clebsch-Gordan series we get $S$, $P$, and $D$ terms, but not why the $P$ state should be antisymmetric. I do know the general idea of how to obtain the vector coupling coefficients (by repeated application of raising/lowering operators), and these do show that the $P$ state is antisymmetric, but I'd like a more interpretative answer than just "that's how the maths works out".


texts: Partial reactions in redox formation of rust

texts:
In the iron oxidation that results in rust, the first step is to steal 2 electrons from $\ce{Fe}$. The main thief is said to be the oxygen dissolved in water, witch uses the stolen electrons to form $\ce{OH-}$ according to the reaction $\ce{O2 + 2H2O + 4e-  ->  4OH-}$.

What is really going on in this reaction? I cannot believe that this 3 reactants bump together at the same time and magically  $\ce{4 OH-}$ comes out of the collision. I imagine that there must be some steps between the reactants and $\ce{4OH-}$. Is it that, first, $\ce{O2}$ steals the two electrons from the $\ce{Fe}$ lattice becoming $\ce{2O-}$ and then, later, each $\ce{O-}$ takes an $\ce{H}$ from $\ce{H2O}$ to form $\ce{2OH-}$? That does not seem right to me, because this means that what is happening is:

$$\ce{O2 +  4e-  -> 2O-}$$

$$\ce{2O- + 2H2O  -> 4OH-}$$

But the reaction "$\ce{O2 +  4e-  -> 2O-}$"  implies that $\ce{2O-}$ is more stable than $\ce{O2}$. Is that right?


texts: why can't I get my absorbance values to come out right on my oxybenzone uv-vis assay test?

texts:
I am attempting to assay a raw material sample, oxybenzone, against oxybenzone, USP using UV-vis. The requirement for acceptance is NLT 99% mg C14H12O3/mg raw material sample. The method instructs a standard preparation of 10ug/mL in CH3OH, and then a sample preparation by 100 mg sample oxybenzone in 100 mL, pipette one mL into another 100 mL flask, dilute to volume with CH3OH. I used these same steps to prepare my standard solution as well. Scan and use A value to calculate mg C14H12O3 in the sample using 10(C)(At/As) with At being A of the sample and As being A of the standard, C being concentration of the standard solution in ug/mL

assuming I know my sample should pass, my results make no sense.

As=.8341
At=.6304
C= 10

I used methanol as the blank per the method.

I am sure I must have made a mistake somewhere, but I am stuck. The only thing I can think of is if I made a mistake preparing the standard solution and it was too concentrated perhaps A would go up, but I don't think I did. I weighed 100 mg oxybenzone USP standard, diluted to volume, removed 1 mL, diluted to 100 mL again, same as I did for the sample solution prep.


texts: How much heat (in J) is required to produce 2.0L of N2(g) at 77.36 K and 1.0 atm?

texts:
The only thing that is given is:

The enthalpy of vaporization for $N_2(l)$ is 5.56 kJ/mol.

There aren't any examples similar to this problem in the textbook. I only know how to get energy using:

$q=mcΔT$ and $w=PΔV$

No clue what to do with the enthalpy of vaporization value.

UPDATE: Solved it by first getting number of moles ($n$) via $PV=nRT$ then multiplying moles by 5.56 kJ/mol. Moles cancel out, leaving only kJ, 1.75kJ to be precise.


texts:
My book gives the following reaction:
$$\ce{SiCl4 + H2O -> HCl + Si(OH)4}$$
Since equilibrium favours the formation of weaker acids. How is this reaction able to proceed if a strong acid like HCl is being formed? Am I missing some point here? Or is my interpretation or equilibrium in this case is faulty?


texts: What is the mechanism for the reaction of acetyl chloride and aniline?

texts:
I want to devise the synthesis of 1,2-dinitrobenzene without producing a large amount of 1,3 or 1,4 products.

In my synthesis I have a step in which I obtain aniline. I would like to know the mechanism for protecting the amine using $\ce{CH3COCl}$ and triethylamine so I can keep it from reacting in the next step of my synthesis. I'm not really "fluent" with amine chemistry, and I have no good idea at the moment.

If you cannot make picture of mechanism, please explain it with words. I must understand!


texts:
I've been stuck with this for some time. I just don't see it. As the reactant is Pd(0), I think oxidative addition will happen to the bromine. Then I would say an insertion reaction happens. However this would form a 7-membered ring which isn't as stable as a 5-or 6-membered ring and isn't even in the final product.

Then I tried complexating it with the double bond next to the ether. However I don't see what use the Pd could have from there. Maybe deprotonate the alpha-carbon which would give a hapto-3 complexation? But what next, I wouldn't know. Any help would be appreciated!


texts: Looking for an isomerization reaction that involves a color change for classroom demonstration purposes

texts:
I am in the process of designing a chemical kinetics course for undergraduates. I would like to demonstrate isomerization equilibria, and therefore am looking for a reaction A <-> B fulfilling the following criteria:

At least one of the reactants has a color;
The equilibrium is reached in a few minutes so that the color change is easy to follow (not too fast or slow);
The reaction is safe and could be demonstrated in a beaker on the table;
The reaction is reversible and e.g. by gentle heating the equilibrium could be shifted easily.

Titration of some weak acids/bases with suitable indicators might also be good, but of course these are not isomerisations and are a bit more complex than a simple A <-> B reaction.

Any creative ideas are welcome. Thanks!


texts: Why don't particles of a colloid settle?

texts:
Why don't particles of a colloid settle but those of a suspension do?
- Is it because they are really small and so remain in constant motion which overcomes the force of gravity and prevents them from settling?
- Is it because they are charged and so they repel each other and stay suspended in the solution as they try to go away from each other?


texts: Why homolytic fission of polar molecules is possible at higher temperature?

texts: While studying alkanes I came across the nitration of alkanes using Nitric acid at very high temperature, which apparently follows "free radical" mechanisms, by formation of OH°  °NO2 free radical ! How "homolytic" cleavage of N-OH (a polar bond)  is possible at any temperature instead of heterolytic cleavage i.e formation of ions  ?


texts:
I have an older stainless steel saucepan with what I've always called a Bakelite handle.  The pan fell, the handle broke.  If possible, I'd like to glue it.  The break is near where the handle attaches to the pan.  So, the repair would ideally bond Bakelite-to-metal stud as well as Bakelite to itself.  (pic below.  NB: the color is off: it's actually 'light black', there is no blue.)

If it matters, the pan doesn't ever go in the oven, but is used to pour boiling water.

If anyone knows what glue to use, I'd appreciate hearing.  If I should just forget about it, knowing that would help too.


texts: Heat capacity of calorimeter is negative?

texts:
I was doing a science lab and the first part had us combine 100mL of room temperature water with 100mL of hot water, then record the final temperature. Here's the data I got:

It asked us to find the heat capacity of the calorimeter, which is deduced using the following equation:

So after plugging in my data, I get that the heat capacity of the calorimeter is negative.

From what I understand this doesn't make sense since that would mean putting in more energy would lower the temperature. Did I do something wrong in my experiment or is this possible? The calorimeter was made out of styrofoam.


texts: Naming an Ion with respect to its oxidation state

texts: When identifying compounds, where certain elements are in various oxidation states we write the oxidation state in Roman numbers after it. Does the same go for ions? What would the correct way of writing Cu$^{2+}$ in words be?


texts: I have been trying to understand the reaction mechanism for ozonolysis but I am not able to understand what happens after the intermediate trioxolane is formed. I have searched online but didn't really get any intuitive understanding. Can you provide an explanation of how the reaction proceeds after trioxolane is formed?


texts: ligand pi system irreducible representation for trigonal bipyramidal transition metal complex

texts:
I am considering a D$_{3h}$ trigonal bipyramidal transition metal complex MX$_5$.  I have found that the irreducible representation for the ligand s and $\sigma$ systems is 2A$_1'$+A$_2''$+E$'$.  I have
\begin{array}{|c|c|c|c|c|c|}
\hline
&E& 2C_3 & 3C_2 & \sigma_h & 2S_3&3\sigma_v\\ \hline
 \Gamma_s&5& 2& 1&3&0&3\\ \hline
 \Gamma_\sigma&5& 2& 1&3&0&3\\ \hline
 \Gamma_{\pi+\pi'}&10&0&-2&0&0&0\\ \hline
\end{array}
However, I think that my $\Gamma_{\pi+\pi'}$ is incorrect since I get fractional values for coefficients for the irreducible representations when I try to reduce it to irreducible representations.  But from sketching the trigonal pyramidal complex, I cannot see how my $\chi(R)$ are wrong for the pi system representation, $\Gamma_{\pi+\pi'}$.  Any help would be appreciated.


texts: Effect of clemmensen reagent on 4-oxo-4-phenylbutanoic acid

texts: When I first solved the question, I had reduced the ketonic group. Then as the medium is acidic the -OH in carboxylic acid, will get protonated and there will be formation of stable carbocation and it will attach to the benzene ring. I hope you get it. But in the answer, the carboxylic acid retained and only ketonic group is reduced. Please help.


texts: Potential wells and symmetry in absorption spectroscopy

texts:
In a course I am following, we are analyzing the potential wells in molecular absorption spectroscopy.

For molecules with more than one normal mode, we can study the potential wells involved in transitions for each mode and apply the Franck-Condon principle to determine the intensity of each possible electronic and vibrational transition. In these transitions, some of them will not change the geometry of the molecular equilibrium geometry, others will. This leads to think about how the transition change the point group symmetry of that molecule.

Here comes my question: my teacher said that

  modes that are non totally symmetric wont maintain the symmetry of the molecule and therefore the potential wells associated with the electronic ground state and excited state will be one just above the other, with the same equilibrium position and just an increase in energy, while totally symmetric modes won't have this property.

I can't understand why this is true, if there are approximations underlying it and also I can't find any reference for it.

This has been used, later, to distinguish between totally symmetric and non totally symmetric modes in the expression of the transition dipole moment, because for wells not one above the other (totally symmetric) we need to calculate a superposition integral between the two vibrational states, while for totally symmetric modes we know it can be written as a Kronecker delta.


texts: Why do disproportionation reactions take place?

texts:
I want to know what are the conditions when disproportionation reaction is feasible. Is it just because of stability factors or it has other dimensions to it. As an example:
$$\ce{3HNO2 ->  HNO3 + 2NO + H2O}$$

Nitrous acid disproportionates to nitric acid and nitrogen monoxide. Here stability of +5 in nitric acid is understandable but how +2 in the monoxide is stable if the disproportionation takes place to gain stability.

Am I ignoring some other factors like pH or hydration enthalpy. I would be very thankful if someone gives me some general ideas on these reactions.


texts: Non-bonding molecular orbital in triatomic hydrogen

texts:
I am slightly confused about how non-bonding MOs form, for example in H3+  ion as shown below.

Why does the central atom not contribute an orbital?

The source mentions symmetry, but I can only see that the central orbital has a positive or negative phase, so it will inevitably cancel somewhat on one side and add with the wavefunction on the other side. This orbital will have a distinct appearance.

Could someone explain why there is no contribution, despite us adding s orbitals whose symmetry always allows them to be added (and even if we had p orbitals, surely the p orbital which can contribute will contribute?)


texts: Why is the addition of a singlet carbene to an alkene stereospecific?

texts: Why is the addition of a singlet carbene to an alkene stereospecific, but not when a triplet carbene is added?


texts: What's the explanation for the chelate effect?

texts: I got that multidentate ligands form more stable coordination complexes than monodentate ligands, but why?


texts: Removing Epoxy Glue from a ceramic piezostack

texts: I am going to stick a strain gauge to the side of an expanding piezocrystal using a basic 2 part epoxy glue. I am eventually also going to be sticking other things to it. Does anyone know a safe way to remove the glue without damaging the piezostack? The manual says specifically not to use acetone.


texts: Constructing a partition function for a gas-solid equilibrium in canonical ensemeble

texts:
For a closed system at fixed N,V,T there is a solid in equilibrium with its vapor. I'm told that I can minimize the helmholtz free energy to find that the equilibrium condition is given by

$N_g = \frac{q_g}{q_s} $ Where $N_g$ is the Number of particles in the gas phase, and $q_s$ and $q_g$ are the partition functions for the solid and gas phase respectively.

I'm also given that $Q_s = q_s^{N_s}$.

I've attempted to solve $ \frac{\partial A}{\partial N_g} = 0$ to show this.

Since N,V,T are fixed I know it's a canonical ensemble and that $A = -kTln(Q)$.

What I'm unsure on is how to find the partition function Q.

In the Atkins and DePaula textbook there's a brief example of factorizing the molecular partition function to isolate the different contributions from vibration, rotation, etc. I'm unsure if this applies here. The textbook starts from finding the total energy of the system from a sum of its parts. I don't intuit that a solid-gas equilibrium should follow the same logic but nevertheless I tried continuing assuming this would work so then

$Q = Q_sQ_g$

I first tried with the gas particles distinguishable (so I wouldn't have to deal with a factorial in the derivative) and found

$Q_g = q_g^{N_g},  Q_s = q_s^{N-N_g}, Q = q_g^{N_g}q_s^{N-N_g}$ (since the total number of particles N is constant, $N = N_g + N_s$)

which gives

$\frac{\partial A}{\partial N_g} = 0 = -kT(ln(\frac{q_g}{q_s})) => \frac{q_g}{q_s} = 1 $

I then tried with an indistinguishable partition function for the gas phase

$Q_g = \frac{q_g^{N_g}}{N_g!}$

I'm less familiar with this math so I relied on wolfram alpha for the derivative which gives

$\frac{\partial A}{\partial N_g} = 0 = \frac{\Gamma(N_g+1)\psi^{(0)}(N_g+1)}{N_g!} - ln(\frac{q_g}{q_s})$

Before I go any further, is this how I should construct the partition function? Is there a text online that someone could point me to?