texts: How to calculate the percentage yield for a reaction with excess reagent?

texts:
A chemist mixed $12~\mathrm{g}$ of phosphorus with $35.5\ \mathrm{g}$ of chlorine gas to synthesize phosphorus(III) chloride (phosphorus trichloride). The yield was $42.4~\mathrm{g}$ of $\ce{PCl3}$. The equation is
  $$\ce{2P + 3Cl2 -> 2PCl3}$$
  Calculate the percentage yield.

I think that the amount of phosphorus the chemist used is in excess. I figured that only 1/3 of the amount of phosphorus the chemist used reacted to produce phosphorus trichloride. But the question didn't mention anything about products in excess that is why I am not so sure of my answer, which is $92.51$.

First I found the amount of substance of phosphorus used which is $12/31$. Then I calculated the amount of substance of chlorine gas used (and it's $0.5$). But $12/31\ \mathrm{mol}$ of $\ce{P}$ needs $1.5 \times (12/31)\ \mathrm{mol}$ of chlorine gas, so $\ce{P}$ is in excess. The amount of substance of $\ce{P}$ that will react will be $$0.5/1.5 = 1/3$$ Now $1/3\ \mathrm{mol}$ of $\ce{P}$ produces $1/3\ \mathrm{mol}$ of $\ce{PCl3}$ and the molecular mass of $\ce{PCl3}$ is $137.5$ so the mass that is supposed to be produced is $137.5 \times 1/3$. Then I divided $42.4$ by $(137.5 \times 1/3)$ and multiplied by $100$.


texts: Which free radical is more stable, allyl free radical or benzyl free radical?

texts:
Can someone pls tell me which one is it? Benzyl free radical has 4 resonance structures compared to allyl free radical which has only 2. More the resonance structures should mean more stable the radical.

But in the book I am referring it is written that free radical stability depends on bond dissociation energy.

According to this Allyl free radical should be more stable but according to resonance structures Benzyl free radical should be stable. Which one is correct?


texts: Sigma electron movement in resonance forms

texts:
I have come across an example in my textbook, which shows resonance structures for the bromonium ion. However, I am confused as to why the sigma bond electrons "move" to get the tertiary carbocation and the secondary carbocation. Are sigma bond electrons not strictly localized and pi electrons delocalized?

My question is: When are we allowed to move the sigma electrons when writing resonance forms?


texts: Enthalpy is a sum of $U$ and $PV$, and I thought that for different isotopes, internal energy values may differ. Is it true? There are three stable isotopes of $\textrm{Mg}$, mass number 24, 25, and 26. If enthalpy is different, which one is a standard for enthalpy $0$? I read somewhere on the web that enthalpy of a covalent bond is affected by isotopes, but I'm confused when there are no covalent bonds.


texts: Computational Efficiency of Periodic Boundary Conditions

texts:
From what I understand, in a molecular dynamics simulation the number of molecules included is limited by the computational power available.

In order to simulate macroscopic properties, one needs to ensure that the particles experience forces as if they were in the bulk, so the system is replicated in all directions through the application of a periodic boundary condition.

How is the creation of this larger, periodic system any more computationally efficient than just simulating a non-periodic system of similar size?


texts:
Are there any common elemental (single-step) reactions with three reactants?

Everything I've found either says that they're very rare, or can be broken down into two bimolecular steps with combined reaction rates far greater than the termolecular step.

What reactions require an indivisible termolecular step?


texts: Computational methods to obtain relative energies of electronic configurations of atoms

texts:
When one learns the Aufbau principle to “predict” electronic configurations, and the $(n + \ell)$ ordering rule (or Madelung rule), one also learns of the exceptions to the rules… some of which (Cr, Cu, Mo, Ag, Au) can be half-explained by adding another “rule”, some of which (Nb, Ru, Rh, …) cannot. We have on this site our fair share of electronic-configuration questions dealing with these: Nb, Pt, Pd, Cu, Th, etc.

My question here is not about rules or theories to rationalize and understand these complicated electronic configurations, but rather about computational tools to predict them. What computational methods (and software) would one use to compute the different energies of several electronic configurations of an atom?

For example, take niobium. How would I answer, with computational quantum chemistry methods, the following question:

  what is the energy difference between the 5s1 4d4 and 5s2 4d3 electronic configurations of niobium?

And would that method also give some interpretation in terms of what these energy differences arise from?


texts: Balanced reactions at the anode and cathode

texts:
A current of 2.25 A is applied to  $\ce{NiCl2}$ solution

A. Write the balanced half reaction that takes place at the anode
B. Write the balanced half reaction that takes place at the cathode

Can someone check if my answers seem logical? I'm not quite sure if I did the problem correctly

Anode: $\ce{O2 + 4H+ + 4e- -> 2H2O}$

Cathode: $\ce{2Ni^{2+} + 4e- -> 4Ni}$


texts: Why are alcohols with longer chains less polar?

texts:
In my self-study, I recently came across the following question:

"Choose the solute of each pair that would be more soluble in hexane ($\ce{C6H14}$). Explain your answer.

(a) $\ce{CH3(CH2)10OH}$ or $\ce{CH3(CH2)2OH}$ ..."

Undecanol is more soluble in hexane because it is apparently less polar than propanol. Further Internet searches revealed that alcohols decrease in polarity as the chain length increases (assuming a basis in an alkane; don't know if this rule generalizes which I guess is a sub-question) but it is still not clear why. None of the sources I found explained this. The way I imagine things, the carbon-hydrogen bonds should add a bunch of zero vectors to the the O–H vector that both molecules share, giving the same polarity in both cases. But this is apparently wrong.

So why is undecanol less polar than propanol then? Does it have something to do with a more advanced bonding theory?


texts: What does the small, steep curve at the very beginning of a weak acid strong base titration curve come from?

texts:
I understand that a buffer solution is being made, but I don't understand why the titration curve is different from a strong acid strong base one (apart from the steeper pH change). I understand the half-equivalence point and the rest of the titration curve. If Le Châtelier's applies here, please explain with it, as it makes more intuitive sense for me rather than the Henderson-Hasselbalch equation.

I included this animation if it makes it easier to explain, thanks!

http://www.chembio.uoguelph.ca/educmat/chm19104/chemtoons/chemtoons9.htm


texts: Anodisation of aluminium in sulfuric acid - Electrolysis reactions

texts:
As an experiment for electrolysis and to show how a metal can be protected of corrosion, I am trying to anodize an aluminium plate, using sulfuric acid as electrolyte.

I know the aluminium plate is the cathode and, thus, connected to the positive terminal of the generator, while for the cathode I am using aluminium foil.

Supposing I have $H_{2}SO_{4}:80ml, 3M$. I have two questions:

$1.$ Knowing:
$$\epsilon^{o}_{Al^{3+}/Al} = -1.67V\\
  \epsilon^{o}_{O_{2}/H_{2}O} = 1.23V, pH = 0\\
  \epsilon^{o}_{2H^{+}/H_{2}} = 0V, pH = 0\\
  \epsilon^{o}_{2H_{2}O/H_{2}} = -0.83V, pH = 14$$
I want an explicit explanation using those potentials as to why the reaction at the cathode is $$2H^{+} + 2e^{-}\rightarrow H_{2}$$
and why the reactions at the anode are ( If i am not mistaken )
$$Al \rightarrow Al^{3+} + 3e^{-}\\
  2Al^{3+} + 3O^{2-}\rightarrow Al_{2}O_{3}\\
  2Al^{3+} + 3OH^{-} \rightarrow Al_{2}O_{3} + 3H^{+}$$
  Especially the second and third reactions confuse me

$2.$ Knowing:
$$\epsilon^{o}_{Cu^{2+}/Cu} = 0.34V\\
\epsilon^{o}_{Pb^{2+}/Pb} = -0.13V\\$$
Could I use a plomb or copper blade instead of the aluminium foil?


texts: Which species occupy the equatorial positions in VSEPR's trigonal bipyramidal and octahedral geometry

texts:
Which species (electronegative, double and triple bonded atoms, ions, lone pair etc.) occupy the equitorial position in the trigonal bipyramidal and octahedral geometry when we find the shape using VSEPR theory?

Which species are given more priority and why?


texts: Calculating empirical formula of vitamin C

texts:
Combustion of 0.2000 g of vitamin C gives 0.2998 g $\ce{CO2}$ and 0.819 g of water. What is the empirical formula of vitamin C?

My work:

I calculated moles of products and found the mole ratio but it's not coming to be a whole number.


texts: What is the phase of matter that has flexible volume, but constant shape?

texts:
In this YouTube video it argued that:

Solids have constant volume, and constant shape
Liquids have constant volume, but flexible shape
Gases have flexible volume, and flexible shape (in fact they don't have volume and shape at all)

So, this table came to my mind:

Do we have a phase of matter that fits in the red cell? In other words, do we have a phase of matter that keeps its shape, and only changes its volume? If so, what is the name of that phase?


texts: Lewis dot structure of beryllium fluoride

texts: I'm so confused because I'm trying to draw $\ce{BeF2}$ … and the way it's drawn (something like $\ce{F-Be-F}$) just doesn't make sense to me because Be can only hold 2 valence electrons. But this structure shows it having 4.


texts:
The SN1 is a two-step mechanism which begins with heterolysis of the C-X bond. What triggers this? Are there external causes that prompt the leaving group to simply leave?

This question is more conceptual than anything, but I can't seem to find answers anywhere.


texts: The reaction which forms a pair of diastereomers

texts:
The reactions among the following which results in the formation of a pair of diastereomers are:

I am aware of the fact that $\ce{HBr}$ gives anti addition product and $\ce{BH3}$ forms syn addition product. In part (a) since the back side is less sterically hindered ( due to presence of only $\ce{H}$ ) $\ce{BR-}$   preferentially attacks from the back side.Similar is the case with (b).c) proceeds with a free radical mechanism.d) however occurs via anti-markinicoff addition so that $\ce{OH}$ adds to the primary carbon.Since there are two possible ways in which the $\ce{OH}$ group may add( either from the back side or the front side)my idea is that it may result in a pair of diastereomers. However I am not quite sure about it. Thanks.


texts: Why is maximum buffer capacity for some diprotic buffers not when pH = pKa?

texts:
According to Rajkovic et al. [1]:

$$β = \frac{[\ce{H+}]}{K_\mathrm{w}} + 2.303\cdot\frac{[\ce{H+}]\cdot K_\mathrm{a}\cdot c}{[\ce{H+}] + K_\mathrm{a}}$$
where $K_\mathrm{a}$ is the dissociation constant of the acid; $c$ is the concentration of the acid in all forms; and $K_\mathrm{w}$ is the ionization constant of water $(1·10^{–14})$. It can be seen that the buffer capacity of the acid is greatest when $[\ce{H+}]$ equals $K_\mathrm{a}$ (or when the $\mathrm{pH}$ is equal to the $\mathrm{p}K_\mathrm{a}$ of the acid). This relationship can be used for mixtures of monoprotic acids and many diprotic acids (by considering them to be made up of two monoprotic acids). Unfortunately, this is not true for most of the diprotic acids found in wines because the second dissociation is not completely independent of the first.

Is it true that for some diprotic acids maximum buffer capacity is not reached when $\mathrm{pH} = \mathrm{p}K_\mathrm{a}$? If so, why is it true? Also, then when is buffer capacity maximum? Can it only be determined experimentally?
Or did I just misinterpret the article? Is it saying that this equation of buffer capacity is invalid for some diprotic acids instead of the fact that buffer capacity is max when $\mathrm{pH} = \mathrm{p}K_\mathrm{a}$?
References

Rajkovic, M.; Novakovic, I.; Petrovic, A. Determination of Titratable Acidity in White Wine. Journal of Agricultural Sciences, Belgrade 2007, 52 (2), 169–184. https://doi.org/10.2298/JAS0702169R.


texts: I know that the lower the pH the faster fermentation occurs. Why does this happen?


texts: Which one of the following is optically active?

texts: To be optically active the presence of chiral centres are very important but if there exists a plane centre or axis of symmetry then the molecules are optically inactive.  How to determine the optical activity when more than one ring are present?  Is it sufficient to check those two mentioned condition?


texts: Need for enthalpy of vaporization in calculating bond dissociation enthalpy

texts:
In our chemical bonding class we were given the following problem:

I am confused by how the question says that you need to consider the heat of vaporization/sublimation for HBr and HI.

Bond dissociation enthalpy is defined as "the energy needed to break one mole of the bond to give separated atoms - everything being in the gas state."

So if you can find the heat of formation of that molecule in the gas phase, why would you need anything else?
My attempt:

The above answer obtained is not the one provided by the professor so I assume I'm missing something here. The answer provided is-

364 kJ/mol


texts: Synthesizing monodisperse PbS quantum dots

texts:
For a research project, I am trying to synthesize lead (II) sulfide quantum dots using the method of Li et al..  I am injecting sulfur dissolved in 1-octadecene into a mixture of $\ce{PbO}$, oleic acid, oleylamine, and 1-octadecene at $210^{\circ}\ce{C}$, waiting 5 minutes, and quenching the reaction in an ice bath. The oleic acid : $\ce{PbO}$ molar ratio is 10 : 1 which, I think (roughly extrapolating from the data presented in the paper), should result in uniform sized quantum dots with absorption peak of about 900 nm. As described in the paper, the solution I'm working with turns black almost instantly, suggesting nanocrystal nucleation.

The problem is, when I characterize them with UV-Vis-NIR (after precipitation, centrifugation, and dispersion in hexane), instead of getting a clear absorption peak, I get a weird wavelength-vs-absorbance graph that shoots up abruptly at 300 nm and then gradually curves downward, with no indication of a peak anywhere near 900 nm. Why is this, and what are possible solutions?

I think it might have something to do with how I'm extrapolating the trend for oleic acid : $\ce{PbO}$ ratio, or perhaps how I'm precipitating/centrifuging/redissolving the QDs (though I'm not sure how this would affect the size or spectra). Or maybe some other factor I haven't thought of that affects the nucleation rate. Any ideas?


texts: Why can't light pass through a gold foil, but alpha particles can?

texts: Rutherfords experiment showed that most of the alpha particles passed through a thin gold foil undeflected. So why can't light pass through the foil, which is supposedly thinner than the heavy alpha particles?


texts: Is pentamine or pentylamine the correct name?

texts:
For $\ce{CH3CH2CH2CH2CH2NH2}$, is the correct name pentylamine or pentamine?

From http://antoine.frostburg.edu/chem/senese/101/organic/faq/yl-ending.shtml

  "The -yl ending means "a fragment of an alkane formed by removing a hydrogen".

How does the above definition apply to this problem?

Does it mean, if the N wasn't there it would be a carbon and 3 hydrogens would attach to the carbon; but with the nitrogen there there is only 2 hydrogens attached to a the nitrogen?

Thank you


texts: Why should I acidify twice in the procedure for qualitative analysis of chloride anions?

texts:
Separation of the Chloride ($\ce{Cl-}$); Confirmation of Chloride.

  Chloride ion forms an insoluble silver compound. Silver chloride is a white solid.
  $$\ce{Cl^-(aq) + Ag+(aq) -> AgCl(s)}$$
  Silver chloride dissolves in $\pu{6 M}$ ammonia, $\ce{NH3}$, forming the colorless ion $\ce{Ag(NH3)2+}$. If nitric acid, $\ce{HNO3}$, is added to a solution containing this ion, the ammonia in the complex reacts with hydrogen ions to form ammonium ions, and the silver recombines with the chloride ions that are still present in solution.
  \begin{align}
\ce{AgCl(s) + 2NH3(aq) &-> Ag(NH3)2+(aq) + Cl^-(aq)} \\
\ce{Ag(NH3)2+(aq) + Cl^-(aq) + 2H+(aq) &-> AgCl(s) + 2NH4+(aq)}
\end{align}

  a. Place 10 drops of the original test solution (or unknown solution) in a test tube. Test to see if the solution is acidic. If it is not, add $\pu{6 M}$ acetic acid, $\ce{CH3COOH}$, dropwise with stirring until the solution is acidic.

  b. Add 10 drops of $\pu{0.1 M}$ silver nitrate, $\ce{AgNO3}$. A precipitate of $\ce{AgCl}$ will form.

  c. Centrifuge and pour off the supernatant liquid.

  d. Wash the solid with $\pu{0.5 mL}$ distilled water, centrifuge and discard the wash water.

  e. Add $\pu{0.5 mL}$ $\pu{6 M}$ ammonia, $\ce{NH3}$, to the precipitate. Stir to dissolve any $\ce{AgCl}$.

  f. Centrifuge, and pour the supernatant liquid into another test tube to test for chloride ion.

  g. Add $\pu{1 mL}$ $\pu{6 M}$ nitric acid, $\ce{HNO3}$, to the solution containing the dissolved silver chloride. The solution will get hot and smoke from the reaction with the excess ammonia whether or not silver chloride is present.

  h. Test with litmus or pH paper to see if the solution is acidic. If it is not, add more $\ce{HNO3}$ until the solution is acidic. The appearance of the white precipitate of $\ce{AgCl}$ in the acidic solution confirms the presence of chloride.

From the procedure above, if you all could take a loot at step 1a. It makes no sense to me. I do not understand why adding $\ce{CH3COOH}$ has any effect on the solution whatsoever. What is the point of adding it when we later add $\ce{HNO3}$?


texts: Cationic vacancies created when non-stoichiometric iron oxide is doped with silicon(IV) ions

texts:
Problem

It is believed that non-stoichiometric compound $\ce{F_{0.93}O}$ forms by doping of $\ce{Fe^3+}$ ions in $\ce{FeO}$ crystal by replacement of $\ce{Fe^2+}$. Calculate the number of cationic vacancies if all of the $\ce{Fe^2+}$ ions are replaced by $\ce{Si^4+}$ ions in $\pu{0.1 mol}$ of $\ce{Fe_{0.93}O}$. Express your answer as a multiple of Avogadro's Number.

Answer stated by the book

 0.0465

My Solution
As the compound is electrically neutral I equated the net charges due to the cations and anions like this, assuming $x$ to be the fraction of $\ce{Fe^2+}$ in the compound.
$$[2x + 3(0.93-x)] - 2 = 0$$
This gave $x = 0.79$. Now, in $\pu{0.1 mol}$ of the compound there would be $\pu{0.079 mol}$ of $\ce{Fe^2+}$. As each silicon ion would replace two ions of $\ce{Fe^2+}$, one vacancy would be created for every replacement.
The number of replacements would be $\left(\frac{0.079}{2}\right)\times N_\mathrm{A} = 0.0395 N_\mathrm{A}$, and we would have as many vacancies. ($N_\mathrm{A}$ is Avogadro's Number)
Can anyone point out the error in my solution?


texts:
I would like to know which of the two is the stronger base, tri-(n-butyl)amine or tri-(tert-butyl)amine?

I feel that the one with tert-butyl would be stronger as the inductive effect of tert-butyl on the nitrogen atom is stronger, making the nitrogen atom more electron-rich and better able to act as a base. This is because the carbon atoms in tri-(tert-butyl)amine are closer to the nitrogen atom, with the furthest carbon just 2 carbons away. However, for the other amine, the furthest carbon is 4 carbons away. I am not sure if my reasoning is flawed. Could someone clarify?

I am also not sure if steric hindrance is an important consideration here, considering the bulkiness of the tert-butyl substituent compared to the n-butyl substituent.

Also, pardon me if I had written the names of the chemicals wrongly.


texts: Everytime I walk by the balloon stall, I know that they use helium to make the balloons float in the air. But my problem is why when I leave the balloon aside, the balloon sinks to the bottom. Is there anything happen to the  helium inside?


texts: Tight binding model for nanoparticles as finite systems

texts:
I'm still trying to calculate the band structure ab initio for some hypothetical nanoparticles. It seems that I can directly build a tight-binding model by forming Bloch functions, numerically calculate the dispersion relation, and then apply Brus equation to get band gaps for nanoparticles.

Another strategy I've tried is just to treat the nanoparticle as a large molecule and use MO calculation; however, the problem is that the matrix grows too large when working in three dimensions and using basis sets with multiple orbitals (consider a $20 × 20 × 20$ cubic lattice with $\mathrm{sp^3d}$ basis, that should be a whooping $20^3 · 5^2 = 200\ 000 × 200\ 000$ matrix).

I'm asking if there's some modified version of tight-binding model that specifically work for finite systems. I'm aware that tight-binding model can be used to study nanowires, but the wires themselves are assumed to be infinitely long in one direction so that's not quite what I want.

My chemistry professor suggested modifying the Bloch functions using wavefunctions that are solutions to the particle in a box model. However, I'm not sure how to do this properly, or what's the justification for this.


texts: Obtaining electron density from orbital information in the Molden format

texts:
I'm trying to obtain an electron density from orbital information written in the Molden format by the formula,
$$
\rho(\mathbf{r}) = \sum_{i}^{occ} |\phi_{i}(\mathbf{r})|^{2}.
$$
Is there any post-processing program to handle this job?
I believe that I can make a script on my own, because the Molden file seems to provide with coefficients of GTO, but want to check if there is already working examples.


texts: What is the concept behind the calculations for the dilution of solutions?

texts:
I'm interested in the concept behind this computation and was wondering if anyone could give me some pointers or hints.
I've prepared $0.28~\mathrm{L}$ solution of $0.8500~\mathrm{M}$ of $\ce{Al(NO3)3}$.
I need a $50~\mathrm{mL}$ solution of $0.450~\mathrm{M}$ of $\ce{Al(NO3)3}$ made from my original solution.

For my dimensional analysis what I need should be up front right?
$50~\mathrm{mL}$ of the solution first converted to liters for the bridge conversion to 0.450 moles.

Once I have the molarity of my $50~\mathrm{mL}$ set to $0.450~\mathrm{mol/L}$ I divide my molarity by the molarity of the original solution I am taking this out of in the first place which gives me 0.026 liters of solution

$0.026~\mathrm{L}$ of solution is then what I need out of my $0.28~\mathrm{L}$ $0.8500~\mathrm{M}$ solution in order to come up with my 50 milliliters of $0.450~\mathrm{M}$ of solution? (I feel that something is missing)

My computations (conceptually explained above in my best effort)

$50~\mathrm{mL} \cdot 1~\mathrm{L}/1000~\mathrm{mL} \cdot 0.450~\mathrm{M}/1~\mathrm{L} \cdot 1~\mathrm{L}/0.8500~\mathrm{M} = 0.026~\mathrm{L}$ of $0.8500~\mathrm{M}$ solution needed to prepare $50~\mathrm{mL}$ solution of $0.450~\mathrm{M}$.


texts: Chemistry: What's the difference between "binding energy" and "ionization energy"?

texts:
In respect to PhotoElectron Spectroscopy (PES), we are analyzing graphs with "binding energy (MegaJoules)" on the x-axis, and with "relative number of electrons" on the y-axis.

I have also seen the x-axis be labeled as "ionization energy." I am really familiar with what ionization energy is (it's the energy required to strip off the highest-energy electron from an atom), but I'm not really sure what binding energy  means. My chemistry instructor says that ionization energy and binding energy are different things, but we were not sure why; since 2 different PES graphs used ionization energy and binding energy interchangeably on the x-axis, are they the same? I've also noticed the trends in ionization and binding energy follow each other-- for instance, lower-energy orbitals (like 1s) have higher binding and ionization energies. Thus, what's the difference between these two terms?


texts:
Respective aromatic substitution: Why isn't the $\pi$ bond attacked by the catalyst $\ce{FeBr3}$?

$\ce{Fe}$ must have a strong partial positive charge and acts as an electron acceptor to form a $\ce{Fe-Br}$ complex, but why can't it accept the electrons from the $\pi$ bond?


texts:
For the question

  Why is $\ce{ICl5}$ unstable?

my textbook gave an answer of

  $\ce{ICl5}$ has too many highly electronegative chlorine atoms present on the central iodine.

But how does having electronegative atoms around a central atom make a molecule unstable? For example, $\ce{SF6}$ is very stable.


texts: Number of possible isomers (including optical/geometric ones) with C4H8O molecular formula

texts:
I found 32 isomers but I think I made a miscount.

Chain alcohols: 6, chain ethers: 5, and chain carbonyl compounds
(ketones/aldehydes): 3
Three-member ring alcohols: 7, three-member ethers: 6 (including ones
that have the ether-bond outside the ring)
Four-member ring compounds: 4, five-member compounds: 1

(Note: Enols are not counted because they're unstable)


texts: Why is benzene not called as a cyclo triene? Wikipedia says benzene is a IUPAC name, but isn't it a common name?


texts: Benzene ring position labeling (ortho vs para)

texts: Why is the ortho position on a benzene ring next to the primary carbon and not in the opposite position, as ortho means "straight", not "next to" as in para?


texts: Ratio of Total energy to Kinetic energy in hydrogen atom when the reference is changed

texts:
If in the hydrogen atom Potential Energy at $\infty$ is chosen to be $13.6$eV then the ratio of total energy and kinetic energy (with the sign) for $1$st Bohr Orbit is?

My Attempt
I just simply gave the answer given the relation that,
$$\text{T.E}:\text{K.E}:\text{P.E} = -1:1:-2$$

Because I think we don't consider the reference frame while speaking of this relation.

But the answer given is 0. Any help would be appreciated.


texts:
I'm a beginner in spectroscopy and I have troubles understanding papers describing values of spectroscopic constants. This paper, for example, describes constants $T_e, R_e, \omega_e, \omega_ex_e, B_e, \alpha_e, D_0$ and $D_e$.

I can see, that $R_e$ is an internuclear distance, but I have no idea, what are the remaining constants.

Could you provide some brief explanation? Preferably with picture of some potential energy curve(s), if possible, as I find it much easier to understand such concepts from schemes.


texts: Methods of splitting carbon dioxide into elements

texts:
Is it possible to split $\ce{CO2}$ into C and O? If so, what are some methods and their efficacies?

This question originated because I was wondering if it was possible, and if so, how, to convert ice from the ice caps on Mars (made up of frozen $\ce{H2O}$ and $\ce{CO2}$) into oxygen.


texts: Combustion of cyanamide in a bomb calorimeter at constant volume and at 25°C

texts:
In a bomb calorimeter, cyanamide was subjected to combustion at constant volume, and the heat evolved was found to be $\pu{742.7 KJ}$ at $\pu{25 ^\circ C}$. Find $q_p$.

This is a question in my textbook. Given in the question that the volume is constant so how are we going to find $q_p$? Since it's a bomb calorimeter so pressure isn't constant. Is the question wrong?


texts: What toxic gases are emitted during the combustion of potassium ferrocyanide?

texts: I have read that Hydrogen Cyanide is emitted if Potassium Ferricyanide is combusted, but would this be the same case for Potassium Ferrocyanide? I am preparing to perform some case hardening on steel using a compound that contains 30-50% Potassium Ferrocyanide, so I need to be sure what measures are needed for protection from the fume.


texts: Do alkali metals not form diatomic molecules?

texts:
I know hydrogen forms a diatomic molecule $\ce{H2}$, where the electronic configuration of hydrogen is $\ce{1s}$.

But why doesn't lithium also form a diatomic molecule? Its electronic structure is $\ce{1s^2 2s}$, so can't two lithium atoms come together, share their outer electron and form $\ce{Li2}$? Same with $\ce{Na}$, $\ce{K}$ etc.

Am I missing something obvious?


texts: Is there a Material that is High Heat Resistent and soluble?

texts:
What i‘m looking for is any sort of material that dissolves, while being able to resist temperatures of up to 1000°C.
And it doesn‘t have to resist during dissolution, only while it‘s solid.
And the solvent should not be corrosive, or at least only be corrosive for the soluble Material, but not for other (or most) materials (mainly metals).

Also it would be good if said material can be reused afterwards.
(Like you can reuse salt if you dissolved it in water and then dried it again.)
And the solvent should be environmentaly friendly.

Now, the first Part is basically what i‘m looking for and the Second is just some bonus, so it‘s good even if it‘s not consistent with the 2nd Part.

If anyone knows such a Material, it‘d be nice if you could tell me.

Thanks in advance


texts: What to do when there is an odd number of valence electrons left on the the central atom?

texts:
For example, I'm trying to write the formula for $\ce{NO}$, and $\ce{ClO2}$.
If you count the total number of electrons in these molecules, it's odd. This means that no matter how you arrange the electrons, some atom is not going to have a full octet, and some atom is going to have an unpaired electron somewhere - it's inevitable. So my advice is: don't worry about the central atom not having a full octet. Just try and get as many full octets as you can. Of course, don't ever stuff more than 8 valence electrons into a Period 2 element. That's a big no-no. Once you have a structure that you think is reasonable, just check Google for the structures.
The steps my teacher gave me always assume that the central atom has a full valence, or more than full, after the outer atoms have been bonded with it. I'm running into trouble here because my central atom in these cases does not have enough electrons!
I know I could Google what they look like, but it doesn't help me understand why.


texts: What should be the name of this compound containg both double and triple bond?

texts: Which is a more correct name, according to IUPAC nomenclature: pent-2-ene-4-yne, or pent-3-ene-1-yne?


texts: Filtration methods at removing ions present in water

texts:
I'm doing a lab where I have to first find out what ions are present in the water (easy part). The next part is to filter out those ions from the water. Here are some methods that are stated on the paper: Coffee filter, Your own design, Britta filter. I've done my research and just can't seem to find what ions coffee filters and Brita filters filter out.

My question is: What are some own designs that i can create to filter out some ions ($\ce{Ca^{2+}}$, $\ce{Pb^{2+}}$, $\ce{Ba^{2+}}$, $\ce{Zn^{2+}}$, $\ce{SO4^{2-}}$, $\ce{PO4^{3-}}$, $\ce{Cl-}$, and $\ce{OH-}$).
Or do those filters actually filter any of those ions?


texts: How is a side-group that contains a double bond named?

texts:
In my chemistry lecture, we are working on the naming and nomenclature of organic molecules. When we got to the naming of alkenes and alkynes, we were told that the functional group had to be in the main, name giving chain of carbons. This brought up the question: What if there are multiple functional groups arranged in such a fashion as for it to be impossible for them to all be on the main chain (see example below)? How would one go about naming such a molecule? I would much appreciate any clarification that can be provided. I have already checked the IUPAC rules, and unless I totally missed it, it isn't addressed.

Here is the Picture of the molecule in question:

$\hspace{45 mm}$

Thanks in advance for any light you can shed on this question.


texts: How to determine concentration of an unknown solution using Beer's Law?

texts: What if the concentration of an unknown is higher than the range of concentration used when you were doing an Absorption v. Concentration graph? How can you figure out the concentration of an unknown solution, basically, if it falls above the range? I have literally no idea how to go about doing it.


texts:
Ok, so I understand that solubility is a measure of how well a compound is solvated by the solvent. And dissociation is a measure of how much of a compound splits into its ionized forms.
Does HF have high solubility, but low dissociation (weak acid)? How can that be?

Is it because it forms strong hydrogen bonds in solution and thus forms stable solvation spheres (solubility), but its high electronegativity prevents H+ atoms from leaving its vicinity (dissociation)?


texts: Why doesn’t aniline undergo Friedel-Crafts alkylation?

texts:
Even though aniline is an activated benzene derivative, it still doesn’t undergo Friedel-Crafts alkylation. Why?

Can it undergo Friedel-Crafts acylation?


texts: Why do acetylene and chlorine react to yield carbon and HCl, but acetylene and bromine react less intensely?

texts:
In the famous "underwater fireworks" reaction we get

$$\ce{C2H2 + Cl2 -> 2C + 2HCl}$$

On the other hand, when we react acetylene with bromine, we get

$$\ce{CH#CH + Br2 -> CHBr=CHBr}$$
$$\ce{CHBr#CHBr + Br2 -> CHBr2-CHBr2}$$

Why don't we get carbon and HBr? Or do we get it?


texts: Why do chlorinated silanes have lower boiling points than their methane analogs?

texts:
The boiling points of the chlorinated silanes and methanes are given below:

$$\begin{array}{ccc}
\hline
\text{Species} & \text{Boiling point (X = Si) / }\mathrm{^\circ C} & \text{Boiling point (X = C) / }\mathrm{^\circ C} \\
\hline
\ce{XH3Cl} & -30.4 & -24.2 \\
\ce{XH2Cl2} & 8 & 39.6 \\
\ce{XHCl3} & 31.8 & 69.2 \\
\ce{XCl4} & 57.6 & 76.7 \\
\hline
\end{array}$$

The chlorosilanes are expected to have larger dipole moments and stronger dispersion forces.  Why do the silanes instead have lower boiling points than the methanes?


texts: Is Cracking of Every HydroCarbon Family possible? (Alkane ,Alkenes,Arenes)

texts:
I know Cracking is usually used to crack alkanes to get smaller hydrocarbons (as they are easier to ignite) and alkenes(as they have more industrial uses)...but can we crack arenes and alkenes as they are also included in hydrocarbons definition.
But I really doubt about cracking of benzene as lot of energy is required to destroy the delocalised ring. But given infinite energy that is surely possible.... but the product won't be stable... :/


texts: Can negative (abnormally) lattice enthalpies during the formation of ionic compounds exist?

texts:
Why do compounds form bonds? I've got three words for you: Less potential energy. I don't remember a case of positive lattice enthalpies $\ldots$ - My comment

This makes me wonder. I remember seeing $\Delta H_{\mathrm{lattice}}$ of "common" ionic compounds like $\mathrm{NaCl}$ and considered them fairly positivea:
\begin{array}{|c|c|} \hline
\mathbf{Ionic~compound} & \mathbf{\Delta H^\circ (kJ~mol^{-1})} \\\hline
\ce{LiF} & 1022^\mathrm{\,b} \\\hline
\ce{NaCl} & 771 \\\hline
\ce{KBr} & 670 \\\hline
\ce{CsI} & 585 \\\hline
\end{array}

Yeah$\ldots$ so judging by the usual trends $\ce{CsI}$ should have the least positive lattice enthalpy in ionic compounds derived only from monoatomic ions. But that's still some lattice enthalpy!

So, could there be negative lattice enthalpies?

Notes:
a: Note that there are two major definitions of lattice enthalpy. Here, we're using the definition relevant to $\Delta H_r$ of the following endothermic reaction: $$\ce{MX(s) → M+(g) + X^- (g)}$$
While the other definition uses the enthalpy of the reverse process as the reference, only the sign might differ. Note that I had the other defintion in my mind when posting that comment.
b: All data obtained at $298~\mathrm{K}$. source


texts:
There's wastewater flowing into the reactor at $\pu{20 ^\circ C}$ and the reactor is maintained at $\pu{36 ^\circ C}$. The effluent of the reactor flows into the stripper, which is at $\pu{65 ^\circ C}$. How can you maintain the temperature at $\pu{36 ^\circ C}$ in the left reactor with fresh wastewater flowing in at $\pu{20 ^\circ C}$ and stripped wastewater flowing in at $\pu{65 ^\circ C}$?

$$\underset{\mathrm{input}}{\pu{20 ^\circ C}}\ce{->[$Q_i$]} \underset{\mathrm{reactor}}{\pu{36^\circ C}} \ce{<=>[Q_e][Q_r]} \underset{\mathrm{stripper}}{\pu{65 ^\circ C}} \ce{->} \mathrm{output}$$
When I did the mass balance, it's $Q_i = Q_s$. I don't know how you can get the $60\%$ of energy change during inflow using the energy balance.  How do you find that $Q_r = 60\%$ of $Q_i$?


texts:
I want to add a color to vapors, like the vapor that comes out of glycerine when heated.

Is there a chemical compound I can put into glycerine that makes the vapor colorful? Or is there a chemical compound over which I can pass the vapors and they get colored?


texts:
Is it possible to crystallize vegetable glycerin?

I saw a myth about it online and was wondering if it is possible.


texts: Hydrolysis of vinyl bromide vs alkyl chloride

texts:
Which of the following compounds, 1-bromocyclopent-1-ene 1 or chlorocyclopentane 2, hydrolyses faster than the second under comparable conditions? It may be acid catalysed or base catalyzed hydrolysis but the conditions must remain the same for each pair.

In my view because of the double bond in first compound hydrolysis should be easier for second, but I am not sure about it.
See part 1 here


texts:
Synthesis of silver nanoparticles  by electrochemical Method

The silver content in these products consists of both silver ions and silver particles. Typically 90% of silver content is in the form of ionic silver and the remaining 10% of the silver content is in the form of silver particles. The silver ions are produced by electrolysis are frequently described as "dissolved silver". Because the majority of the silver in these products is dissolved silver rather than metallic silver particles, it would be more technically accurate to describe these products as silver solutions. In the present work, the electrochemical synthesis of silver nanoparticles is presented.

Tech.Journal,Vol.33,Part(B),No.7,2015

Q.1  What is the scientific meaning of the following sentence?

"The duration used for exchanging the polarity was 4 min."

Q.2 How can we exchange the D.C current polarity regularly?

Q.3 What is the suitable current and any other conditions for preparing silver nanoparticles?

Q.4 How can we extract silver nanoparticles from silver solutions?


texts: Buffer Power of the amphiprotic substance

texts:
The mass balance for a generic amphiprotic substance $[\ce{AH^-}]$ this:

$$
[\ce{HA^-}]=C \cdot \dfrac{K_{a1} [\ce{H_3O^+}]}{K_{a1}\cdot [\ce{H_3O^+}] + [\ce{H_3O^+}]^2 + K_{a1} \cdot K_{a2}} \quad Eq.1
$$

where:
 C = initial concentration of the amphitrofic substance

The Eq.1 derivative  is:

$$
\dfrac{d[\ce{HA^-}]}{d[\ce{H_3O^+}]} = -\dfrac{C \cdot [\ce{H_3O^+}] \cdot K_{a1} \cdot (2 [\ce{H_3O^+}] + K_{a1}}{(K_{a1}\cdot [\ce{H_3O^+}] + [H_3O^+]^2 + K_{a1} \cdot K_{a2})^2} + \dfrac{C \cdot \cdot K_{a1}}{K_{a1}\cdot [\ce{H_3O^+}] + [\ce{H_3O^+}]^2 + K_{a1} \cdot K_{a2}} \quad Eq.2
$$

The zero of this derivative is found at $[\ce{H_3O^+}] = \sqrt{K_{a1} \cdot K_{a2}}$, where is the maximum of $[\ce{AH^-}]$.

The buffer power (BP) can be defined $BP = \dfrac{dC_B}{dp \ce{H}} = -\dfrac{dC_A}{dp \ce{H}} = - 2.3 \cdot [\ce{H_3O^+}] \cdot \dfrac{d[\ce{HA^-}]}{d[\ce{H_3O^+}]} \quad Eq.3$

For example:

If $K_{a1} = 6.2  \times 10^{-8}$ and $K_{a2} = 4.8 \times 10^{-13}$ and C=0.1, the maximum oncentration of the specie $\ce{AH^-}$ is found at $[\ce{H_3O^+}] = \sqrt{6.2  \times 10^{-8} \cdot 4.8 \times 10^{-13}}  = 1.725 \times 10^{-10} \quad pH=9.76$

The curve that represents the buffer power, plotting the Eq.3, is:

In this way I can say that at maximum concentration of the amphiprotic substance the buffer power is zero. Is this statement true?


texts: How do you calculate a half cell potential Copper(II) and Copper Sulfate?

texts:
I have to complete an experiment for school where I have copper and zinc electrodes placed into an electrolyte of copper sulfate and I have measured the potential across it at varying temperatures. For example at $\pu{60°C}$ ($\pu{333K}$) I measured the potential to be $\pu{0.880 volts}$ and at $\pu{75°C}$ ($\pu{348K}$) I measured the potential to be $\pu{0.780 volts}$.

Is there a way I can prove this result? I tried using the Nernst Equation, but my reaction quotient is equal to 1, which disproves my finding. I found out about activity coefficients, but I do not know how to apply it or the Nernst Equation to half cell potentials.

Any advice or help is greatly appreciated!


texts: Color of potassium permanganate and potassium dichromate

texts:
In $\ce{KMnO4}$, the Oxidation state of $\ce{Mn}$ is +7, which results in an electronic configuration as $\ce{[Ar] 4s^0 3d^0}$

In $\ce{K2Cr2O7}$,the Oxidation state of $\ce{Cr}$ is +6, which results in an electronic configuration as $\ce{[Ar] 4s^0 3d^0}$

As it is clearly visible there are no $\ce{d}$ electrons in either of these compounds but still, they are coloured.

My Doubt:

If there's no $\ce{d-d}$ transition in these compounds what gives these compounds their colour?
Are there other transition element compounds whose colour is not because of $\ce{d-d}$ transition?


texts:
I realize that the octet rule is more a suggestion than a rule, and that it applies mainly to non-transition metal compounds. Still, compounds that don't have an octet, like $\ce{BH3}$, tend to dimerize or disproportionate in order to achieve an octet.

In recent SE Chem posts discussing the bonding in phosphorous pentachloride and iodine heptafluoride, hypervalent bonding was used to describe the bonding in these molecules.

If we count the electrons around phosphorous in $\ce{PCl5}$ there are 6 in the three equatorial bonds (2x3) and 4 in the hypervalent axial bonds; a total of 10. However 2 of the electrons in the hypervalent bond are in a non-bonding orbital, leaving 8 bonding electrons, an octet.

If we count the electrons around iodine in $\ce{IF7}$ there are 4 in the two axial bonds (2x2) and 10 in the hypervalent equatorial bonds; a total of 14. However, 4 electrons are in a hypervalent non-bonding orbital and 2 more electrons can be viewed as being associated with a fluoride anion, leaving 8 bonding electrons, again, an octet.

Are these compounds considered to be exceptions to the octet "rule"? Do all compounds involving hypervalent bonding violate the octet "rule"? Or do these compounds comply with the octet "rule"?


texts:
$\ce{ROH + NaBr + H2SO4 -> RBr + NaHSO4 + H2O}$

What is exactly the reaction mechanism.

Is it $\ce{NaBr + H2SO4 -> NaHSO4 + HBr}$ and then

$\ce{HBr}$ reacts with $\ce{ROH}$?

If yes the why in the reaction of $\ce{NaBr}$ and $\ce{H2SO4}$ does $\ce{H2SO4}$ oxidise $\ce{NaBr}$?


texts: What is a good (small) model system for ligand metal charge transfer practises?

texts:
I am looking for an easy to calculate model system in which I could see a ligand metal charge transfer. Basically I am looking for a model complex, that might have the metal/ligand in different oxidation states: $\ce{ M^{III}(Lig)}$ versus $\ce{M^{II}(Lig^{\bullet +})}$ or $\ce{M^{IV}(Lig^{\bullet -})}$. I am calling it a charge transfer since I am not sure how else to call it.
I am also quite aware, that the description of these systems is necessarily a multireference case, so ordinary DFT methods will fail. (At least broken symmetry is necessary.)

In principle I was thinking about an iron heme complex that might exhibit that feature.

However, I have the feeling, that this kind of system is already pretty demanding to calculate the electronic structure. Since I would like to use it as an exercise and for a tutorial achieving alternative occupations I would prefer a much simpler case. It should eventually treated with broken symmetry DFT and CAS/MR methods.

Does anyone know of such a system or would suggest one. It does not have to be a real one. Purely hypothetical is just as fine.


texts: How to reduce Al2O3 in a H2 atmosphere on industrial scale?

texts:
As known, reducing $\ce{Al2O3}$, which is the main process of the aluminium production, isn't really cheap, mainly because its energy need. Its high energy need is coming from the high binding energy between $\ce{Al}$ and $\ce{O}$.

What differs from the common $\ce{Al}$ production: the whole process has to run in $\ce{H2}$ atmosphere, where the cost of the $H_2$ gas is zero.

Thus, we need a net result of $\ce{Al2O3 + 3 H2 \rightarrow 2 Al + 3 H2O}$.

Does it make the process easier? How could it work?

Remark: actually, the goal would be to extract the $\ce{O2}$ and to produce water from it, while we have a quasi-infinite $\ce{H2}$ source. The $\ce{Al}$ production here isn't important.


texts: In E1 reactions, does carbocation stability have impact on the final product?

texts: In this question, I believe there is a mistake for iii). I think that there the tertiary carbocation would be formed (more stable), which would lead to the tetra substituted alkene (even more stable). Am I wrong?


texts:
The Wittig and Corey–Chaykovsky reaction both involve an ylid, phosphonium ylid in the former versus a sulfonium ylid in the latter, attacking a carbonyl compound.

In the Wittig reaction, a concerted [2+2] cycloaddition leads to direct formation of a four-membered ring, but this does not happen with the sulfur ylids. Instead, nucleophilic addition to the carbonyl occurs to give a betaine, which then decomposes via intramolecular nucleophilic substitution by the oxyanion. Thus, in the Corey–Chaykovsky reaction, we end up with an epoxide, while the Wittig reaction affords an alkene.

Possibly formation of the strong $\ce{P=O}$ bond is a key driving force for the wittig reaction (the P=O bond strength in $\ce{Ph3PO}$ is $\pu{529 kJ mol-1}$ vs. the $\ce{S=O}$ bond strength in $\ce{Ph2SO}$ which is $\pu{367 kJ mol-1}$).

I am looking for an answer that explains the differences between the outcomes of these two reactions, and their respective intermediates. It would be great if the answer can be supported with references, and/or calculations.


texts: Is it possible for an acid and base to react to form an even stronger base or acid?

texts:
Is there a combination of an acid and a base that when mixed results in a solution that is more basic or more acidic than the initial base or acid, respectively?

If so, do such combinations have a name?


texts: Why do s-block elements impart color to a flame?

texts:
Flame tests are a common way of identifying trace amounts of alkali metals (and to a lesser extent alkaline earth metals) in mixtures. Certain salts of $\ce{Ba, Sr}$ are also used in fireworks for their ability to impart a colour to the flame.

Although predominant among s block elements this behaviour is also seen in other elements like $\ce{Cu}$ and $\ce{Pb}$. My question is, what is so special about these elements that lends them this characteristic?


texts: Is liquid water in equilibrium with water vapor at room temperature?

texts:
This question was inspired by Why does liquid water form when we exhale on a mirror?.

This question is different from Why does water evaporate at room temperature? because it asks about whether an equilibrium is established. At room temperature under certain circumstances, water molecules leave the liquid phase and end up in the gas phase, as explained in the answers to the linked question. Whether an equilibrium is established is a related but distinct question.

Consider the reversible process of water moving from the liquid phase to the gas phase:

$$\ce{H2O(l) <=> H2O(g)}$$

At room temperature and atmospheric pressure, for which of the following scenarios does this process reach equilibrium?

A glass filled with water
A bottle of water after you poured half of the water out and recapped it.
A zip lock bag filled with water (no air).
Humid air in a zip-lock bag.

According to Wikipedia,

  [...]chemical equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the system. Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are generally not zero, but equal.

I am pretty confident in my answers for 1. and 2., but I am having trouble with 3. and 4.

Scenario 1. is an open system, and unless the air is at 100% humidity, the water will evaporate. This means the forward rate is larger than the reverse rate, and it is not at equilibrium.

Scenario 2. is a closed system, and if the temperature is constant, the water will evaporate until the air is at 100% humidity and the equilibrium is reached.

Scenarios 3. and 4 are not clear to me. Would you say these are at equilibrium because there are no changes over time? Or would you say these are not at equilibrium because either product (3.) or reactant (4.) is absent? What about if there is a tiny air bubble in scenario 3., or the bag is wet on the inside in scenario 4., would that make a difference?


texts: Which Basis Set is suitable For Mercury-complex in DFT calculations? Please provide the answers with any journal reference.


texts: ethanol/water %vol/vol and freezing temperature

texts:
Main Question: Where can I find a table (or realistic formula) for isopropanol/water %vol/vol mixes and corresponding freezing temperature with public access?
Background:
Trying to get the freezing point of my car windshield wash fluid.
What I have tried so far:
Anti-freeze is may be ethanol or isopropanol. I got tables for ethanol/water %vol/vol and temperature, but could not find them for isopropanol. I learned that for ethanol the calculated (using simple formula) freezing temperature does not match the real one if using high concentrations, so this is likely true also for isopropanol, and why I am asking for this table.
Additional bonus question: is there a (household-practical) way to determine what was filled (and possibly even mixed during garage service): ethanol/isopropanal-based anti-freeze...?
(PS: wasn't sure about which forum, chemistry, physics... - please guide me if this question belongs somewhere else)


texts: Why do Grignard reagents or Organolithium compounds not displace halides as easily as acetylide ions do?

texts:
This is a snapshot from LG Wade Organic Chemistry. I have a doubt with a particular statement in the book. It says that Grignard reagents do not displace halides as easily as acetylide ions do.

But shouldn’t it be the other way round? Acetylide ions, having an sp-hybridised carbon, are much more electronegative compared to the sp³-hybridised carbon in Grignard reagents. So acetylide ions should have less tendency to displace halide ions by attacking with their lone pair compared to the alkyl group in Grignard reagent. Shouldn’t it?

Please help me sort this out!


texts: Recrystallization and purification techniques for getting a pure sample

texts:
Could someone explain in detail as to why exactly recrystallization gives a more pure solid sample? As well as why is would be better 'technique' to allow for the crystal to form slowly?

I was thinking that it would be because being a purification technique it essentially breaks the lattice and allows the structure to reform again. As for why it needs to be done slowly, well, because rapid changes in heat would cause the structure to reform into the impure solid it was.

I'm looking for a more detailed, better expressed, answer to this.


texts: How can I solvent exchange from water to alcohol?

texts: Given an aqueous colloidal solution, is there a way to transfer the colloidal particles into an alcohol (assuming the colloidal particles are also stable in the alcohol)? I see in the literature that lyophilizing the aqueous solution and re-dispensing the colloidal particles is an option, but is there a method to perform this all in the wet phase?


texts: Estimate Partition Function from a simulation

texts:
I have a system and I've carried out a long molecular dynamics simulation over it. I would like to estimate the partition function $Z.$ Theoretically, one would compute:
$$Z=\dfrac{1}{N!h^{3N}}\int \exp \left(-\beta\frac{-p^2}{2m} \right) \exp\left(-\beta V(r) \right) \ dp \ dr, $$
but if the system I'm dealing with is, say, a protein in water or something like that, this integral is of course absolutely untractable. When thinking of how to estimate the partition function of susch a system from a molecular dynamics simulation, I guess the first thing that comes to mind is the following: Consider all the snapshots obtained during your simulation, label them with the index $j$ and call $E_j$ to the energy of each snapshot. For giant thermalized systems, I guess we can neglect the probability of a concrete configuration repeating, so I believe a nice try would be:
$$\tilde{Z}=\frac{dV_{\text{ps}}}{N!h^{3N}}\sum_{j} \exp\left( -\beta E_j \right),$$
where $dV_{\text{pc}}$ is the volume of small cube in phase space (its volume would have to be adjusted manually depending oh how many snapshots one has taken).

My question, briefly put, is, how can I estimate the error of estimating $Z$ by $\tilde{Z}$?

It seems intuitive that typically $\tilde{Z}$ should be a good aproximation to $Z,$ but one can easilly think of situations where this isn't true: Imagine that my initial configuration lies in, so as to speak, a valley in the energetic landscape, surrounded by a chain of "high mountains" (high-energy configuration) and that at the other side of these "mountains" lie low-energy configuration. It is clear that in such a case there could be a considerable error when estimating $Z$ from $\tilde{Z}.$ But since one does not know the aspect of the energetic landscape beforehand, it seems difficult to deal with this.

The question stops here, but just to provide context I'll explain briefly what I'm thinking about: I want to study a chemical reaction, and to that end I would like to know the free energy profile along a certain reaction coordinate. For that, an Umbrella Sampling technique is used: you drag the reaction coordinate along the reaction path, forcing it to be at certain positions at different steps (otherwhise, the simulation wouldn't take you over the energetic barriers in short simulation times). I am aware of several methods to compute free energies, like FEP or WHAM, which is quite sophisticated, but I was guessing that if the technique I mentioned above to estimate the partition function $Z$ was correct, then the goal of getting the free energy profile would be fairly simple: you just drag along the reaction coordinate, perform molecular dynamics simulations for different restricted values of the reaction coordinate (you force the reaction coordinate to be at a concrete position by means of a harmonic potential), and at each value of the reaction coordinate you estimate the partition function as above. That's the idea and that's why I am interested in having some idea on methods to estimate the error of approximating $Z$ by $\tilde{Z}.$

Note: this question was originally in Physics.stackexchange. It didn't receive any attention at all and I asked for it to be migrated to Chemistry.stackexchange, but the flag was ignored, so I've decided to delete my question on Physics.stacexchange and post it here


texts: Can the relationship between Gibbs (free) energy change to Equilibrium constant of a chemical reaction be derived from Maxwell-Boltzmann distribution?

texts:
Can the relation between Gibbs(free) energy change to Equilibrium constant of a chemical reaction be derived from the  Maxwell-Boltzmann distribution only ? ( Theoretically , with may be an empirical and conceptual background explanation may also be granted . )
i.e. The equation which is : ${\Delta_\text{r} G}^o=-RT\ln K_\text{eq}$


texts: Conversion of Benzene to 9-Bromo 9,10 Dihydroanthracene

texts:
I tried to proceed through following steps:
Step-1:
Step 2:
Step-3:
Step-4:
I agree with the fact that yield might not be good. But is this whole reaction possible? Am I going correct? A better method and the corrections to this method are appreciated!


texts: Where to find experimental spin-orbit coupling constants?

texts:
I am searching for experimental spin-orbit coupling constants, particularly for main group elements and Cr(0) to calculate correlation consistent Composite Approach (ccCA) energetics. This method requires the application of experimental spin-orbit coupling constants (Table 1, [1]). I have found and read several other papers that use experimental spin orbit coupling constants, but none have a corresponding reference. I have also searched other places like NIST, etc. but have not found anything. Where can I find these experimental values for spin-orbit coupling constants?

References:

Peterson, C.; Penchoff, D.; Wilson, A. Prediction of Thermochemical Properties Across the Periodic Table. Annual Reports in Computational Chemistry 2016, 3–45 DOI: 10.1016/bs.arcc.2016.04.001.


texts:
In the trans-hydroxylation of alkenes to give alcohols, there is a formation of epoxide.

Does the reaction stop here if we don't add water?

Even though if we add water, why does the product depends on which medium the reaction is carried whether acidic or basic?
My text says the ring opens differently for basic and acidic medium, but both finally gives us a trans-vicinal-diol.


texts: Why should one perform an extraction with multiple small portions of solvent as opposed to one large portion?

texts: I'm performing a liquid-liquid extraction on a 1 l water sample for GC analysis. The procedure calls for three extractions with 50 ml of dichloromethane. Would one extraction with 150 ml produce a different result?


texts: Optimized General Contractions using the EMSL Basis Set Exchange


texts: I know that equilibrium constant depends on temperature and pressure. But according to Le Chatelier's principle when we change pressure of reagents the equilibrium is the same. Why?


texts: Reactions involved in Titanium Anodisation

texts:
I am writing up a lab report investigating titanium anodisation and producing oxide layers. After some searching, all I can find is the reaction $\ce{Ti + O2 \to TiO2}$, which I am having no trouble understanding.

However, I seem to be confused/mislead by the simplicity of this. The whole unit is about electrochemistry and redox reactions but I cannot find any examples (or seem to produce any either - I have tried generalizing from the rusting of iron in water) of half reactions or anything similar.

I have come about as far as including the redox reactions for the hydrolysis of water and then jumping to the above reaction but am unsure where to go from here.


texts:
So I've been trying to follow the derivation of the Goldman-Hodgkin-Katz equation on Wikipedia (https://en.wikipedia.org/w/index.php?title=Goldman_equation ) - I can follow it through after it sets up the initial model.

However, I'm having trouble using the Einstein-Stokes relationship to derive the initial model in the first place.

There is the flux from diffusion down the chemical gradient, $-D_{A}\frac{d[A]}{dx}$. The negative sign is there because I'm imagining the ions being "lost" from the side I'm considering.

Then we have the electrical field pushing ions the other way. This won't depend upon the rate of change of concentration because the electric field is uniform and so there's effectively a constant force on each of the particles. The flow will instead depend upon the constant velocity that these particles will be pushed at. So the flow will be $[A]v_d$ - the moles per unit volume being multiplied by the speed in the direction towards the membrane will give me the number of moles per unit area passing through the membrane per second.

So all I need to do is work out $v_d$ I'm guessing. So I use the electrical mobility equation, $D_A=\frac{\mu_{q}k_BT}{q}$.

$q$ will be the charge, so $nzF$ (where $z$ is the valance, $nz$ gives the moles of electrons and multiplying by $F$ gives the charge).

$\mu_q$ will be $\frac{v_d}{E} = \frac{v_d L}{V_m}$

$k_B = \frac{R}{N_A}$ where $N_A$ is Avogadro's number.

So $D_A=v_d \frac{L}{V_m} \frac{RT}{zF} \frac{1}{N_A n}$, thus $D_A \frac{V_m}{L} \frac{zF}{RT} N_A n=v_d$

Putting this back in to get the ion flux, $D_A \frac{V_m}{L} \frac{zF}{RT} N_A n [A]$.

Adding my two fluxes together to get the total flux, I get: $j_a = -D_A(\frac{d[A]}{dx} - \frac{V_m}{L} \frac{zF}{RT} N_A n [A] )$ - this is not quite what the Wikipedia article has - a stray $n N_A$ has crept in, somehow!

Please help me by pointing out where I'm making a mistake!


texts:
How a sugar unit is defined?
I am trying to understand the structure of calicheamicins, and it is noted that They consist of an enediyne headpiece and a modified carbohydrate tail consisting of four sugar units and an unusually substituted aromatic ring. I can understand in the picture where sugar unit is referred, but I would like a general definition.
Thank you


texts: Esters of catechol - Fries rearrangement

texts:
Esters of catechol undergo the Fries rearrangement

But one product is formed more than the other.

I believe it is due to the electron withdrawing nature of the $\ce{OCOCH3}$ group which prefers the attack on meta position.I was able to write a reaction mechanism for the product which is minor in this case. But I couldn't write one for the major product. I wonder how it is formed?

Does the minor product itself rearrange to give the major product or are both of  the products formed directly in this reaction?


texts: Need to find series of equation products from given reagents

texts:
I can balance equations but only if I already know both the sides. I am trying to find the following products:

$$\begin{aligned}
\ce{Na2S2O5 + O2 ->}\ ?\\
\ce{Na2S2O5 + KNO3 ->}\ ?\\
\ce{Na2S2O5 + KNO3 + Fe2O3 ->}\ ?\\
\ce{Na2S2O5 + KNO3 + C12H22O11 ->}\ ?\\
\ce{KNO3 + C12H22O11 ->}\ ?\\
\ce{KNO3 + C12H22O11 + Fe2O3 ->}\ ?
\end{aligned}$$

I'm guessing that the sodium metabisulfate will produce sulfur dioxide and sodium oxide, but that would just be plain decomposition, so I'm not sure where the oxygen would fit. I know that $\ce{KNO3 + C12H22O11}$ produces carbon dioxide and water, but I'm not sure where the nitrogen and potassium go.

Of course once I know the products, balancing and calculating specific energy is simple, if a touch laborious.


texts: Why do asymmetric stretches occur at higher wavenumbers than symmetric stretches?

texts:
I learned that the $\ce{N-H}$ bonds in a primary amine lead to two signals the infrared spectra at $\sim \pu{3400 cm^-1}$, one for symmetrical stretching and another for asymmetrical stretching. For example, here is the IR spectrum of butylamine, taken from Pavia & Lampman's Introduction to Spectroscopy (5th ed.):

The same is seen in, for example, carbon dioxide, where the asymmetric stretch ($\Sigma_\mathrm u^+$) occurs at $\pu{2348 cm-1}$ and the symmetric stretch ($\Sigma_\mathrm g^+$) at $\pu{1373 cm-1}$ (from ChemTube 3D; the NIST Webbook gives similar values).

Why is this so?


texts: Is it possible for a group to substitute itself?

texts:
When I first learned about substitution reactions, I started wondering something that I never ended up figuring out:

Suppose you have a strong nucleophile which is also a good leaving group, such as I$^{-}$. Can such a group substitute itself using the SN1 mechanism? If so, would that mean if such a group were bonded to a chiral carbon, an enantiomerically pure solution could spontaneously racemize?


texts: Are there any common (preferably somewhat complex) organic molecules that help combat ocean pollution?

texts: I'm participating in an activity where I need to present a topic/molecule in organic chemistry, and I am pretty passionate about "reversing"/helping with cleaning the ocean. I was wondering if there are any organic molecules that help with this or with lessening the effects of pollution. If you could let me know what solutions they are used in that would be a great help also. Thank you very much.


texts: I have a rather quick question on the definition of Nucleophilicity. To get straight to the point, am I right in saying that the most appropriate definition of Nucleophilicity, regardless of whether the reaction takes place in solvent or in the gas phase, is the following; Nucleophilicity is a measure of how close in energy the HOMO of a Lewis Base is to the LUMO of a Lewis Acid?


texts: Why is CO a major species only in fuel-rich combustion?

texts:
In fuel-rich combustion, my understanding is that enough fuel reacts and consumes all of the oxygen present. The combustion products $\ce{CO2}$ and $\ce{H2O}$ undergo dissociation until equilibrium is established and one of these is $$\ce{CO2 -> CO + 1/2O2}.$$

From the graph below, the equilibrium mole fraction of combustion products are plotted vs. equivalence ratio. Why is there a sudden rise in $\ce{[CO]}$ as we move into fuel rich combustion? Is this due to the drop in $\ce{[O2]}$ such that $\ce{[CO]}$ must increase to compensate for equilibrium to be established?


texts: Why is 4-t-butyl aci-nitro cyclohexane stable whereas aci-nitro cyclohexane is not?

texts: During my PhD, about fifty years ago, I had reason to use 4-t-butyl aci-nitro cyclohexane and found it to be remarkably stable. Usually aci- nitro compounds revert to nitro compounds very quickly unless they are stabilised by conjugation. There is no conjugation in this compound and the t-butyl group only serves to keep the cyclohexane ring in the chair configuration. There is no excessive steric hindrance in the chair configuration. So what's going on? My guess is that the conversion of the aci-nitro form to the thermodynamically more stable nitro form happens by the transfer of the OH proton to the carbon via the carbanion and that carbanion can be in the boat or the chair configuration. However, only in the boat configuration does the molecular orbital come near enough to the OH proton for the transfer to occur. Is this on the right track? I am not very familiar with molecular orbital theory (it had hardly started 50 years ago) so I would appreciate some input that I might be able to understand.


texts:
Would a set of chemical data with a relative standard deviation of 0.6% or 20% be more reproducible?

My reasoning is that because it's easier to make mistakes and have a wide range of data, the 20% would be more reproducible, even though it is not accurate.

A RSD of 0.6% would be extremely precise and therefore harder to reproduce.

At least this is my thoughts.  Thank you for your help!


texts: Does a Grignard reagent react with enones to give the 1,2- or 1,4- product?

texts:
Cyclohexenone, an α,β-unsaturated ketone, is electrophilic at both the carbonyl carbon, as well as the β-carbon. So, it can either undergo 1,2-addition to give the allylic alcohol 1, or 1,4-addition to give the ketone 2.

Where does the Grignard reagent add to?


texts: How to connect proteins via disulfide bonds computationally?

texts:
I want to connect proteins together to form a dimer. As seen in the picture, the monomers come close to each other along the edge of the higher-order structure (forget about the sulfate there). How can I find out, where I need to introduce an Xaa->Cys mutation so that the most stable disulfide bond is formed between the proteins? It is easy to get a visual clue where about a mutation might be good, but is there a good computational method to calculate the energies and scan through some possibilities?

(I would also go with hydrophobic or van de Waals interactions. Basically, I just want to glue those proteins together.)


texts: Why is the heat of combustion of sulphur equal to the heat of formation of SO2 and not SO3

texts: By definition the heat of combustion for compound is equal to the energy that is released on complete oxidation of one mole that substance to its highest oxidation state. In case of sulphur, online I found that ∆H for $\ce{S8 + O2->SO2}$ is heat of combustion. Clearly + 4 is not the highest oxidation state of sulphur, then why is ∆H for $\ce{S8 + O2->SO3}$ not considered as heat of combustion


texts: Why does butanoic acid have a higher boiling point than isobutyric acid?

texts:
Why does butanoic acid have a higher boiling point then isobutyric acid, when they have similar molar mass and molecular structure?

Butanoic acid ($\ce{C4H8O2}$) has a molar mass of 88.11 g/mol, the boiling point is 163 °C, and intermolecular force of H-bond.

Isobutyric acid ($\ce{C4H8O2}$) has a molar mass of 88.11 g/mol, the boiling point is 155 °C, and intermolecular force of H-bond.


texts: Are alkenes with bulky groups attached (like the one shown in the picture) chiral or achiral?

texts:
Is the compound in the picture chiral or achiral?

I think it should be achiral for the following reasons:

There is free rotation. I know, but for every configuration produced by free rotation there is an exactly opposite configuration.
Also at certain point of time all the groups can come to the same plane.

This question is from my textbook exercise. And the answer says it is chiral. But I've no idea why. Also is it optically active or inactive?

EDIT:
@K_P gave a very useful article related to these type of compounds:


texts: Why 'Enthalpy change' (Delta H) is equal to 'Heat transfer at constant pressure' (Qp)?

texts:
Why 'Enthalpy change' (∆H) is equal to 'Heat transfer at constant pressure' (Qp)?

∆H = ∆U + ∆pV, here only expansion work done by the sustem is added. If non expansion work is done on the system then it should be,
∆H ≠ Qp.
What's wrong? Explain.


texts: Instantaneous enthalpy and entropy change of reaction as equilibrium is established

texts:
Can we calculate instantaneous difference between enthalpy and entropy of product and reactants of a reaction as the reaction proceeds towards equilibrium? Ex: $\ce{R<->P}$ reaction, at some reaction coordinate, moles of $R = 1-x , P = x$, Enthalpy difference between products and reactants? Enthalpy difference if it reached equilibrium? Values of $$\Delta G^0, \Delta H^0, \Delta S^0$$ are known. Or is it impossible and the only relationship available is $$\Delta H = T \Delta S$$ at equilibrium or are their values only temperature dependent and activity independent?

We can do this for Gibbs free energy by $$\Delta G=\Delta G^0+\mathcal RT\ln Q$$


texts: Electrolysis of water - why not pure water?

texts:
In the electrolysis of water, $\ce{H2O}$ molecules are being reduced at the cathode (forming $\ce{H2}$ and $\ce{OH-}$) and oxidized at the anode (forming $\ce{O2}$ and $\ce{H_3O+}$).

It is said that:

  The electrolysis of water usually involves dilute, or moderately concentrated, salt solutions in order to reduce the power loss driving the current through the solution, but the presence of salt is not a requirement for electrolysis.

What is the reason for "power loss"? How does the presence of foreign ions change that?

The electrolysis seems possible to happen in pure water alone (as the quote also says).


texts:
What temperature is needed for carbon monoxide to reduce iron oxide?
That is at what temperature the following reaction will take place:
Fe2O3 + CO -> Fe + CO2


texts: Do crystals have stronger intermolecular forces than amorphous solids?

texts:
Do crystals have stronger intermolecular forces than amorphous solids.

Are the properties of amorphous solids vs. crystals explained by their structures?


texts:
In J. J. Thomson's cathode ray experiment, he used a discharge tube in order to make the gas inside conduct electricity.

Why do gases under low pressure conduct electricity?


texts:
Are there any practical, sane and safe solutions that can be used for silver elctroplating/electrolysis that are purchasable?

Objective is to create silver crystals, but without having evil cyanide floating around the house... copper I can handle with copper sulphate.  Silver has me stuck...

Any ideas?


texts: Assigning the IUPAC name of this compound

texts:
Going by the rules that were given to me by my professor:

I first decide the seniormost group and its parent chain. In this case, cyclohexene carbonitrile.
Then, I decide direction to traverse the ring to assign locants by the first point of difference. Accordingly, I move towards bromine.

The final name I obtain is thus "2-bromo 3-hydroxy cyclohex-4-enecarbonitrile". The answer given in my workbook however is "6-bromo 5-hydroxy cyclohex-3-enecarbonitrile". Apparently, they decided to traverse the ring in reverse direction.

Obviously, this must be some special case. Please explain the exact rule involved here. Thanks!


texts: What easy to conduct (at home) reactions could yield solid carbon?

texts: I am trying to isolate pure carbon in its elemental form. Are there any decomposition reactions or other easy to carry out reactions to yield solid carbon? and in the case that it is isolated, does it start reacting with other elements in the air?


texts: Solubility of Beryllium Compounds in Water

texts:
Why is $\ce{BeF2}$ is highly soluble in water but $\ce{Be(OH)2}$ is insoluble?
Both release $\ce{Be^{2+}}$ ion so this means they both have high hydration enthalpies and can easily overcome their lattice enthalpy.
Then, why is $\ce{Be(OH)2}$ insoluble? A simple explanation would be appreciated.


texts: Why does the sulfone ring in tazobactam open when the lactam is hydrolyzed?

texts:
One of the drugs I work with is a beta-lactam (4-membered ring with an amide bond) fused to a sulfone ring, tazobactam.

It's relatively stable in water; the lactam is not significantly hydrolyzed without being catalyzed.  When the lactam is hydrolyzed, however, typically by an enzyme, and the lactam ring opened, the sulfone ring also opens cleaving the bond between the sulfur and bridgehead carbon.  A paper by Kuzin gives the following reaction scheme (this is part of figure 2, click for the whole thing)

and says of it (emphasis mine):

  The Ser70-bound moiety (2) is thought to be the initial intermediate [...] Ring opening after departure of the sulfinate from C5 produces a reactive imine (3) and the more inert tautomeric enamine forms (4, 5).

But why is the sulfuryl (sulfone, sulfonyl(?)...) leaving only when the lactam is opened and not spontaneously beforehand?

Other fused bicyclic beta-lactam drugs don't open the other ring, where in lieu of the sulfone there is commonly a thioether (as in penicillin).  The sulfone group seems more electron hungry, but I don't see how the broken lactam bond affects this.

I've heard some people suggest that the lone pair on the nitrogen is able to make this happen, but why doesn't it then happen in the intact drug?


texts: How to create black precipitate in clear liquid

texts:
I am not a chemistry person at all, so my apologies if my question seems dumb.

I am working on the set for a short film and in one of the scenes we would like the main actor to look at a sample of water, drop something into it and watch a black precipitate form. Clouding the water.

I have looked online to see what reaction would yield the desired result, however, my chemistry knowledge is very basic.

Could somebody here help me out and let me know what I could use? Safely.
I understand that we need to handle all chemicals with care.


texts: Clarification on Recrystallization concept

texts:
Any help you could provide me would be greatly appreciated and I thank you for reading (even if you don't comment)

I am in an organic laboratory and as a 3rd chemistry major these concepts usually are pretty basic but recrystallization is kind of leaving me scratching my head. When you dissolve your compound with a small impurity in it, dissolve it in a solvent and heat, I am just confused on this part:

What I understand is that the solubility constant changes with temperature and in the case of organic compounds, solubility almost always increases with increasing temperature. So, if the compound is put in a solvent at room temperature and is heated until it is fully dissolved (solubility constant increased) then it is cooled and the solubility constant decreases and consequently solute starts precipating (crystal formation) My only issue is what is that makes the impurity go away? Thinking through it here, I know I'm so close to the Ah-hah moment but as of right now I'm mental blocked — I suppose.


texts:
Fresh ice cubes are almost instantly sticky and easily cling on to fabric and other similarly rough surfaces.

A few minutes later, however, the effect almost completely disappears.

What is the cause of this adhesion?
Why does the effect vanish after some time?


texts:
Here are some standard electrode potentials:-

$$\ce{SO_4^{2-} + 4H^+ + 2e^- -> SO_2 + 2H_2O}\\E^o=0.17\mathrm{V}\\
\ce{NO_3^- + 4H^+ + 3e^- -> NO + 2H_2O}\\E^o=0.97\mathrm{V}\\
\ce{NO_3^- + 2H^+ + e^- -> NO_2 + H_2O}\\E^o=0.78\mathrm{V}$$
When nitric acid reacts with a metal, either $\ce{NO_2}$ or $\ce{NO}$ is formed? How do you predict which is thermodynamically favourable and which reaction will actually take place? For example, when dilute nitric acid reacts with copper, Nitric oxide is liberated and when it is concentrated, Nitrogen dioxide is evolved? As Nitric acid formation is more favourable, shouldn't it proceed in all cases as increasing the concentration will decrease/increase the potential of both the reaction simultaneousy(Nernst equation)?

In the case of sulfate ion, although the reduction of sulfate is more favourable than that of hydrogen, it is hydrogen ions which are getting reduced when a metal reacts at dilute concentrations? why is this so? Moreover, at high concentrations, once again sulfur dioxide is evolved? How can we understand such occurrences? Is overpotential involved in these observances?

In the case of permanganate ions, there are so many possible redox pathways, but a different one is preferred in a different case based on the conditions. For example, in acidic medium, permanganate is reduced to $\ce{Mn^{2+}}$ while in neutral/slightly alkaline solutions, it reduces to $\ce{MnO_2}$. Why is this so? Here are the redox potential values for permanganate conversions (latimer diagrams)

I want to know the general way to explain all these phenomena, as to what drives the reaction to give one product under certain condition and another in different conditions. Explaining any one example would be enough to set the general method which I can extrapolate to understand the remaining Examples.I am comfortable with basic electrochemical equations and those of thermodynamics.


texts: How can a substance have a higher boiling point but lower melting point than another substance?

texts:
Looking at 1,3-Butadiene and Isoprene, I'm wondering: why does Isoprene have a higher boiling point, but a lower melting point than 1,3-Butadiene?

I'm thinking this might be because the Methyl group on C(2) in Isoprene might cause it's lattice to be less tightly packed, thus requiring less energy to be split (-> lower melting point). As both substances can't form any ion-ion, nor dipole-dipole, nor hydrogen bonds, Isoprene probably has a higher boiling point than 1,3-Butadiene because it has a larger surface, enabling it to develop stronger London (VdW) forces.

Can anyone confirm/ disprove this?

Thanks a lot in advance!


texts: Does the natural abundance of radioactive elements change?

texts:
Given that the half-lives differ between isotopes of a particular radioactive element, wouldn't the natural abundance change (fairly rapidly)?

For example, if we isolated a bunch of thorium, wouldn't the relative amount of the various isotopes of thorium in the sample differ over time, with the more slowly decaying isotope eventually making up the largest proportion?


texts: Do nonmetals form ions? I am asking this because I was reading something and I came across the phrase "metal ions," which left me to wonder whether or not there are nonmetal ions as well.


texts: I thought it would be cool to electroplate the rear case of an iPhone 6 or newer since it's made out of aluminum. It's been a long time since I learned about the topic, so I looked online to research this, but hardly found anything about the topic other than some aftermarket companies that sell expensive gold electroplated iPhones. Is this a feasible DIY idea? If so, are there certain metals that would electroplate to iPhone aluminum easier than others?


texts: Deciphering stereochemical notation in electrocylization reaction

texts: I not agree with this solution, for me the red bond formed must be a dotted line in the drawing, and the hydrogen atom musn't be represent with a dot. Am I right or not?


texts: Reaction mechanism for 7-hydroxy-4-methylcoumarin synthesis with an iodine catalyst

texts: 7-Hydroxy-4-methylcoumarin can be synthesized from ethyl acetoacetate and resorcinol with iodine as a catalyst. What is the mechanism for this? From what I understand it follows the Pechmann reaction but I'm having trouble to understand how it works in this particular case.


texts: How does the energy released during a bond formation typically manifest itself on atomic level?

texts: I've been reading about how energy is released when new chemical bonds are formed but it's hard to find info on how that typically manifests itself (besides that it's via heat). I read somewhere that the valence electrons will move into lower energy orbits during a bond, but I thought that always created a photon.  How and where is the heat actually "created?". When two H atoms form H2, does the new molecule start moving faster (discounted for increased mass)? What happens if there are no surrounding molecules?


texts: What piezoelectric materials can be made at home?

texts: I would like to know a few examples of transparent materials which exhibit piezoelectricity and can be purchased online or synthesized at home with ease.


texts: Why can copper have multiple coordination numbers?

texts: Is there a way to explain why the coordination number of for example $\ce{Cu^2+}$ can be either 4 or 6?


texts:
The sodium fusion test done in the lab for the systematic identification of a given organic compound is basically fusing sodium metal in a fusion tube, and then adding the compound in a small quantity, then gently heating the compound and then after the completion of initial reaction,  strongly heating to red heat and then plunging it into water.

I found that Sodium naphthalenide can be produced by the direct reaction of sodium naphthalenide with THF as the solvent. It is used for the solubilisation of sodium metal and is used as a reagent in place of just sodium metal as it is more effective.

So, the question is whether sodium naphthalenide will form in the fusion tube? If yes, why? If no, why not?

I asked a professor who said it is very unlikely to form due to the presence of oxygen (open to the atmosphere) and without the solvent. I did not get it exactly.

If the reaction does take place, then I think naphthalenide anion will probably undergo oxidation due to the oxygen, but no evidence of oxygen is specifically found. So, the reaction probably doesn't take place. Another evidence pointing towards the "no reaction takes place" side is that the contents of the fusion tube remain colourless (except for the piece of sodium metal) till we start heating it strongly, and the excess naphthalene in the tube vaporises and catches fire, blackening the tube from the outside.

Also, if it is possible, in the comments section, or in an answer, please include the energy difference between naphthalene and naphthalenide radical anion.

So, why does the reaction not take place in the absence of solvent?


texts: Can a reference electrode be inserted into an electrochemical cell horizontally?

texts:
If I have an opening on the side of my electrochemical cell, I'm wondering if I can use this to insert a reference electrode. It is normally used to insert an L-shaped tube where you place the reference electrode, and is connected to luggin capillaries. I'm wondering if we can take out the entire connection with the capillaries and replace it with only the reference electrode (sans capillaries). This is in a 3-electrode system, so if I could insert the counter electrode in this way, that would work too. In my setup, I cannot do this with the working electrode.

From what I've read, it's good practice to not have the reference electrode vertical because of bubbles on the bottom of the frit (so most tilt it slightly), but I haven't read anything about a sideways electrode.


texts: What is the best way to go about matching proton-NMR spectra to molecules?

texts: I've attatched an example question. I have already solved this one, I'm wondering about what, in your experience, is the most time-efficient way of approaching a question like this one. I can solve these questions backwards pretty decently (ie If I know the solutions, then I can justify them in pretty decent detail) but when it comes to deciding on which spectrum is assigned to which molecule, I find that it takes me ages. Is there any 'standard approach' that I should be aware of, or is it simply a matter of practice?


texts: Why can sulfur have an expanded octet but not oxygen?

texts: In my search to understand the bonding in structures like $\ce{SF6}$ I found many sources that said it was because sulfur has d orbitals to accommodate an expanded octet, which made sense to me. But I also found sources like the paper by Reed and Weinhold (1986) that say d orbitals contribute very little to the bonding in $\ce{SF6}$. An alternative explanation is that $\ce{SF6}$ has three-center/two-electron bonds. What I don't understand is why compounds like $\ce{SF6}$, $\ce{ClF5}$, $\ce{PCl5}$ exist for third row element centers, but not $\ce{OF6}$ if it has nothing to do with d orbitals? References would be great.


texts: I am really confused between them. I know that an enantiomer is an isomer having optical activity, non super-imposability of image on original configuration, same molecular formula(Correct me if I am wrong). The thing that is causing me trouble is what diffrentiates this from diasteriomerism. It would be appreciated if you provide an example to clarify like a fischer projection


texts:
I want to know the name of this equipment with a sealed graduated tube and the purpose it's being used.

I went through all the results of Google, but I was unable to find this exact equipment. I believe someone here should know this very well.


texts: Green color substance forming during electrolysis

texts:
A green-colored substance formed during electrolysis, wherein the electrolyte was magnesium sulfate and minerals in tap water.

I did not have any leads to stick into the water, so I just put a 9 volt Duracel battery in the solution. The battery didn't leak.

White flakes formed after 1 minute before green substance at 10 minutes.
So, what is the green stuff and what are the white flakes?


texts:
I am remaking a puja clock. I am using methylene chloride to make it wind itself. As you see it needs a heater to keep it moving. I'm hoping there is a liquid chemical  I can put in a copper tube that will stay hot indefinitely so I don't have to use a  battery  to make the methylene chloride keep the clock winding. The methylene chloride is about 32 °C so the liquid in the copper tube would have to be hotter then that meaning when I touch the copper tube the copper tube would have to be hotter then 32 °C also.
I've been told if I put certain chemicals in a sealed copper tube that the tube will explode because the copper causes too much heat which I presume means the tube gets hot. It would help a lot if I could use a liquid to make the heat instead of a battery powered heater


texts: I am confused about how one can determine the stability of carbanions using pKa-values. I know that the stability of carbanions can be determined by the inductive effect, hybridization of the charged-bearing atom and resonance, but when searching about how pKa can do so I don't find anything. The lower the pKa-value, the stronger the acid and hence, the weaker the conjugate base, does this have anything to do with the stability since weak bases are unreactive and thus more stable?


texts: Effect of concentration on molar conductance

texts: It has been stated that the molar conductance($\Lambda_m$) of strong electrolytes is not affected to a greater extent on dilution and so to find the limiting value of molar concentration($\Lambda_m^0$) we can extrapolate the graph of molar conductance vs the concentration ($\sqrt c$). But as the concentration would near zero shouldn't the molar conductance decrease sharply to the range of say $10^{-8}$ which is the conductance of distilled water as the amount of solute that is the strong electrolyte would be negligible to consider?Also in this case extrapolating the graph should not be possible?


texts: Carbocation Rearrangements in SN1 reactions

texts:
Would one get 1-(1-chloroethyl)-1-methylcyclobutane?

I am not sure if the driving force identification is correct? Is my going from a 2° to a 3° carbocation correct? Does anyone have any tips for knowing when to look out for rearrangements?


texts: Can hydrides react with hydrocarbons? And why?

texts: I have read there exist so called "magic" (super strong) acids which can provide a proton to saturated hydrocarbons, producing cation and hydrogen molecule. Can hydrides act in the same manner (pick a proton to form free hydrogen molecule)? And why?


texts:
$\pu{76 g}$ of $\ce{FeSO4}$ are oxidized by $\pu{0.04 M}$ solution of $\ce{KMnO4}$ in presence of $80\%$ $\ce{H2SO4}$. What quantity of water must be added to the final solution of $\ce{Fe2(SO4)3}$ for the concentration to be $\pu{0.25 M}$?

I wrote the reaction:

$$\ce{10 FeSO4 + 8 H2SO4 + 2 KMnO4 -> 5 Fe2(SO4)3 + K2SO4 + 2 MnSO4 + 8 H2O}$$

But I have no idea how to find the amount of water. I found the quantity of $\ce{Fe2(SO4)3}$ to be $\pu{100 g}$, but I have no idea to find all the water.


texts:
If a substance has a molar heat of vaporization of $\pu{3.05\times10^4J/mol}$ and a normal boiling temperature of $\pu{80.0^\circ C}$, what is the value of its molar entropy of vaporization $\Delta S_\mathrm{vap}$ in $\pu{J K^{-1} mol^{-1}}$?

I got
$$\frac{3.5\times10^4\ \mathrm{J/mol}}{(80+273)~\mathrm K}=86.4~\mathrm{J~K^{-1}~mol^{-1}}$$
however my texbook answer key says that the answer is $380\ \mathrm{J~K^{-1}~mol^{-1}}$. What am I doing wrong?


texts:
I read in the journal of organic chemistry:

  A less striking, but nonetheless significant, attenuation of the reactivity of phenyl selenide anion can be achieved by varying the counterion and/or the relative degree of solvation of the ion pair. For example, when valerolactone (3) is allowed to reflux with sodium phenyl selenide in THF/HMPA for $3\,\mathrm{h}$, one obtains an $85\,\%$ yield of the $\unicode[Times]{x3C9}$-phenylselenenyl carboxylic acid 4.

My question is what is the meaning of the bolded expression (solvation of the ion pair) above?


texts: Why is measurement in molarity preferred over molality?

texts:
NCERT Chemistry Part 1 states that:

"The osmotic pressure method has the advantage over other methods as pressure measurement is around the room temperature and the molarity of the solution is used over molality."

I do not understand how the second statement is really an advantage. Infact, if I had to guess, I would choose molality to be the easier of the two to measure as molarity might involve change in volume upon mixing.


texts: Why does the degree of dissociation change when we dilute a weak acid even though the equilibrium constant is constant?

texts:
$K$ represents the ratio of concentrations of molecules in a solution at equilibrium, which means that $Q_\mathrm{r}$ (that ratio at any given point) looks to be identical to $K$. In other words, the molecules in that solution react accordingly so that they reach equilibrium and the ratio of their concentrations is equal to $K$.

If $K$ is large enough (bigger than $10^4$ in my curriculum), this means that the the concentration of the reactants is almost zero. In other words, the  equilibrium position of that solution looks very much like a reaction that went to completion.

The more we dilute an acidic/basic solution, the higher the degree of dissociation, even though $K$ stays the same. So, does that mean that the more we dilute a solution the harder it is for it to reach the point of equilibrium for that specific molecule/solution or what?

For instance, say you found $K$ of solution to be $10^{-5}$. This means that when the reaction happens there are lots of reactants left, and not much products produced, which means that the degree of dissociation is low. But the more we dilute a solution, the closer it gets to a "complete reaction" (if you pour a small amount of weak-acid molecules into a large tank of water, it's certain that all of the weak-acid molecules are going to react with the water, i.e. the degree of dissociation approaches $100\%$).

So, how come $K$ can be independent of the initial reactants concentrations, and tell if a reaction was complete or not, when the "completion" of a reaction (the degree of dissociation) depends on the initial concentrations of reactants?


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I am trying to form 2,2-diacetoxy acid using acetic anhydride and glyoxylic acid monohydrate (Scheme below)

I could not find a suitable synthetic protocol for this, so I just added 10 equivalents of acetic anhydride to 1 equiv. of glyoxylic acid monohydrate and refluxed the mixture at 140 °C. Now the limiting agent (glyoxylic acid monohydrate) is gone, but I am not sure with how to remove excess acetic anhydride; its boiling point is too high (139.8 °C) and the pressure of the rotovap in my lab isn't that strong (I tried removing toluene before, it only worked when I increased the water bath temperature to 70 °C).
Yes, I am aware that I can make an azetrope by adding toluene, which will have a lower boiling point, but that would still require the water bath temperature to be quite high and I'm scared that my product might be broken down or perturbed at such a high temperature. Should I add ~2 N HCl and extract my product with DCM? Any other tips or guidance? I'd appreciate any help.


texts: Dissolve/alter cellulose properties for printed circuit boards

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I'm trying to find any readily available chemical/substance (i.e. household, hardware store etc.) or combination of such that breaks down paper/cellulose.

I'm a home electronics hobbyist and am using my laser printer to print circuit board layouts.  I place the paper on the blank copper board and run it through a laminate machine (high temp & pressure) to 'melt' the laser toner to the copper.  I then soak the board and paper in water to try and slush the paper free of the toner, after which I can put the board in acid and remove the exposed copper and leave my circuit pattern.

This actually works pretty well except that releasing the paper from the toner is maybe only 95% efficient/reliable.  Sometimes the toner gets pulled off the copper and/or fibers/slag from the paper remain on the board.

From doing a little research on the internet, it would seem that dissolving/breaking down cellulose is not an easy process and is quite involved for commercial applications.  However, for my purposes I don't think I need some 'perfect' solution.  If I can just get the paper to soften, or partially break down or just change its properties a bit so that it will let go of the toner more efficiently, then that would probably be sufficient for my needs.

Any ideas?


texts: 67 failures at extracting acetaminophen from Excedrin(R)

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I have adapted the lab experiment described in this J. Chem. Ed. article for the organic chemistry lab course I teach. In the past year, the first year of implementation, I have had 67 failures (100% failure rate) on the extraction part of this experiment.

The experiment involves the isolation/separation of the active components in Excedrin(R): acetylsalicylic acid, acetaminophen, and caffeine.

The experiment is in two parts. Part 1 involves analysis by TLC and separation by column chromatography. This part works beautifully. Part 2 involves separation by successive extractions with increasingly strong bases. Acetylsalicylic acid was extracted with 10% aqueous Na2CO3. Then, acetaminophen was extracted with 3 M NaOH. Finally, caffeine was recovered by evaporation of the remaining organic layer.

In Part 2 We recovered lots of acetylsalicylic acid and caffeine, but no-one recovered any acetaminophen. Below is a list of things I tried in order to improve the results. None of them worked. I know from TLC analysis of the initial organic solution that acetaminophen was present. What happened to it?

Things I have tried:

Changing the concentration of both bases (up and down).
Using a weaker base for the first extraction (like NaHCO3 or Na3PO4).
Increasing the HCl concentration used to work up the second extraction.
No acetaminophen was extracted with the weak base, nor was any left
behind after the second extraction.

Where has my acetaminophen gone?


texts: What is the mechanism for the auto-dissociation of nitrogen tetraoxide

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How does nitrogen tetraoxide dissociate into nitrosyl ion and nitrate ion?

Is it similar to the auto-dissociation of $\ce{SO2}$ into thionyl ion and sulfite ion by acceptance and donation of oxide ion?

I couldn't find a mechanism for the auto-dissociation of nitrogen tetraoxide.


texts: Chemistry behind Gale's coffee maker in Breaking Bad

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Is there a scientific basis for the coffee making equipment which Gale Boetticher describes in Breaking Bad?

He talks about maintaining the right conditions for bringing out the coffee flavor without degrading it.