texts: How to separate a 5 atom thick layer of Cu from Au

texts:
I've become very curious about (electrochemical) atomic layer deposition (ALD) via surface limited redox replacement.

Since the technique allows for deposition of metals in atom thick layers it's possible to create films of nearly exact atomic thickness. However, I haven't found any reference that describes how one can remove the film from the (usually Au) substrate that it's deposited on.

Hypothetically speaking, if one used ALD to generate a film of $\ce{Cu}$ that is 5 atoms thick (arbitrary length and width), how would one go about removing the film in-tact? Is it even possible?


texts: Selectivity in Suzuki coupling of 2,4-dichloropyrimidine

texts: I've seen many papers (see e.g. Synthesis 2010, 16, 2721–2724) in which the 4-chloro group of 2,4-dichloropyrimidine is selectively reacted under Suzuki coupling conditions. Is there any way where this regioselectivity of the coupling can be predicted?


texts: Predicting the product in a series of reactions

texts:
I am stuck in finding the final product $\ce{C}$ formed in the following series of reactions:

  $$\ce{Bu-C#CH ->[NaNH2] A ->[Ph-CHO][H2O] B ->[MnO2] C}$$
  where $\ce{Bu}$ denotes the butyl substituent and $\ce{Ph}$ the phenyl substituent.

I could easily predict product $\ce{A}$ and $\ce{B}$. $\ce{A}$ is simply formed by replacement of hydrogen with sodium and $\ce{B}$ by the meta substitution in benzene ring.

However, I am having trouble predicting the final product. I know that $\ce{MnO2}$ is a mild oxidising agent.


texts: Equilibrium saturation/depostion rate calculation

texts:
I found the Knudsen/Langmuir equation for calculating the sublimation rate of a solid. If I have a closed system, once the vapor reaches the saturation pressure, the solid will continue sublimating but will deposit at the same rate in a dynamic equilibrium.

Is there a relatively simply (ie, not-statistical mechanics modeling) way to calculate the dynamic rate of sublimation/deposition?


texts:
Why is it that in titration a color change occurs initially but then the solution quickly reverts to its previous color?

Thanks so much!


texts: Why does carbon dioxide not form addition compounds?

texts:
Although $\ce{CO_2}$ has four lone pairs on the two oxygen atoms, but it still does not form addition compounds by donating lone pairs. Why?

$\ce{CO}$ on the other hand, does form addition compounds by donating the lone pair from C atom.


texts: pH-dependency of the acidic dissociation of carbonic acid

texts: I know the product of $\ce{CO2 +H2O}$ yields $\ce{H2CO3}$. This is a reversible equation so $\ce{H2CO3}$ goes back to $\ce{H2O + CO2}$. However, my question is: Is there a certain pH which will dissociate $\ce{H2CO3}$ into $\ce{H+}$ and $\ce{CO3^2-}$ ions? If so, lets say you started with $2\ \mathrm{mol}$ of $\ce{H2O}$ and $1\ \mathrm{mol}$ of $\ce{CO2}$, how many moles of $\ce{H+}$ and $\ce{CO3^2-}$ ions will form?


texts: Equilibrium rate constants forward and backwards

texts:
Correct me If I am wrong, given a reaction at equilibrium, if we say add more concentration of products to the reaction, the rate going backwards would increase to try to get back to equilibrium.

I was wondering if the rate forward stays the same or slows down?


texts: Interlayer binding energy: how to convert to meV/Å²?

texts: I've noticed that in most papers the interlayer binding energy is given in units of meV/Å². But how do I get these units? Do I divide the interlayer binding energy I get by the area of my unit cell?


texts: How can I reverse engineer a commercial cleaning solution's "other ingredients"?

texts:
I have a commercial lens cleaning solution. The manufacturer of the solution claims it is not only distilled water and that the formula is confidential. I suspected it was only or mostly distilled water after testing distilled water's cleaning abilities on different types of lenses with different coatings.

I have heard that you can ship a sample to a lab and they will conduct a quantitative analysis of the solution using a mass spectrometer, but there are so many different kinds of mass spectrometry that I am not sure what I would want to order.

What kind of mass spectrometry (or other lab analysis service) would be best suited to discover the formula for a non-volatile, non-corrosive, liquid sample of lens cleaner?

If that's not possible, I just want to know how much of the solution is essentially water, and would like to know what kind of service would be best to determine that.


texts: Why does alkyl rearrangement happen in the Hofmann rearrangement?

texts:
In the mechanism of Hofmann rearrangement, one step involves migration of an R−group from carbon to nitrogen.

This reaction proceeds even if the migratory aptitude of the R-group is poor (like in the case of ethanamide). What motivates the migration of the R-group and makes the reaction proceed?


texts: How to calculate the potential via Hess's law? Is my textbook wrong about this?

texts:
Given the two reduction half-reactions for the following fuel cell, determine the standard cell potential $E^\circ_\mathrm{cell}$,
  $$\ce{CH4 (g) + 2 O2 (g) + 2 OH- (aq) -> CO3^2- (aq) + 3 H2O}.$$
  Reduction half-reactions:
  \begin{align}
\ce{CO3^2- (aq) + 7 H2O (l) + 8 e- &-> CH4 (g) + 10 OH- (aq)}&
E^\circ &= \pu{-0.1 V}\\
\ce{O2 (g) + 2 H2O (l) + 4 e- &-> 4 OH- (aq)}&
E^\circ &= \pu{+0.55 V}
\end{align}
  Answers: (a) $\pu{+0.45 V}$ (b) $\pu{-0.45 V}$ (c) $\pu{-0.65 V}$ (d) $\pu{+0.65 V}$

It is my understanding that to apply Hess' Law to this equation the top equation sign would be reversed and the outcome would be $\pu{+0.65 V}$. Often the system produces incorrect answers. I was looking through my textbook to double check this, and there is an instance where it says
$$E_\mathrm{cell} = E_\mathrm{anode} - E_\mathrm{cathode},$$
but I believe that rule does not fit this instance. Could somebody validate that this answer provided is indeed correct or not?

I would like to clarify that my answer was (d) and the system provided that the correct answer was (a).

I sent an email to my teacher to contest the question using an example from the textbook. Given that Martin has provided me with an answer concurrent with the $\pu{+0.45 V}$, then there must be a mistake in the text or I am misinterpreting something. I would really like to understand this.

At first my teacher told me that after flipping the equation you still need to subtract the anode from the cathode. So I responded like this:

  I would like to reference the E Cell example from the text. In the text it explains that $$E_\mathrm{cell} = E_\mathrm{anode} - E_\mathrm{cathode}.$$

  The example given in the book is identical to the one provided in the exam:

  \begin{aligned}
 (1): &&\ce{3 Ag+(aq) + Fe (s)   &-> 3 Ag (s) + Fe^{3+} (aq)}\\
 (2): &&\ce{3 Ag+(aq) + 3 e-     &-> 3 Ag (s)} & E^\circ &= 0.80~\mathrm{V}\\
 (3): &&\ce{Fe^{3+} (aq) + 3 e- &-> 3 Fe (s)} & E^\circ &= -0.04~\mathrm{V}\\
\end{aligned}

  By using the same logic that I have applied to the exam question the $E_\mathrm{cell}$ was found to be $\pu{0.84 V}$. This is because the sign on the $E$ value of the $\ce{Fe}$ half reaction was reversed like I did to the top equation (which consequently is the cathode).

  As the given equations line up with the primary equation and signs are flipped whenever the equations are flipped, then it is not important to decipher which is the anode and which is the cathode. This is also in accordance with Hess' Law.

That being said, I am confused whether the textbook example was incorrect, the exam question was incorrect, or my understanding is incorrect.


texts: About the way chemicals and molecules are represented

texts: The standard way of representing molecules with letters like $\ce{C}$ for Carbon, $\ce{O}$ for Oxygen etc.; and a lot of lines and double lines like a graph from Graph theory where each letter is a 'vertex', the lines like edges. I forget what this chemical notation system is called. Yet it is 2-dimensional. The formula for '$\ce{H2O}$' ,water doesn't indicate the 'angle' of 'separation' between the two Hydrogen atoms that are bonded with the Oxygen atom. Similarly a formula for some molecule like a protein might not indicate all the 'involved angles' in 3-dimensional space that 'allow' it to be folded in a precise way. So does the 2-dimensional notation system for molecules miss details of how a molecule is twisted in 3-D space?  Also can two distinct molecules 'look' the same in 2-D notation?


texts: Can a supersaturated solution get cooler during crystallization?

texts:
Suppose we have a supersaturated solution that is isolated from the environment. Some of the solutes condense into a crystal in the solution. Is it possible for the solution to get cooler during this process?

If so, why doesn't it violate the second law?


texts: What is the approximate lifetime of an SN2 transition state complex?

texts:
Imagine some SN2 reaction involving an aliphatic sp3 carbon with a halide leaving group (e.g. iodide or bromide). Given the rise of femtosecond spectroscopy (e.g. using a mode-locked Ti:sapphire laser) and even attosecond spectroscopy, I'm curious if there are any studies that have measured the properties and approximate lifetime of the SN2 transition state complex? I guess that this is in the $\approx$ picosecond regime alongside the timescales for a bond stretching dynamics (e.g. between oxygen and hydrogen on a water molecule), however, is there a more precise value that is now known?

I am be curious about results from quantum mechanical simulations (using e.g. Jaguar from the Schrodinger computational chemistry suite) for SN2 reactions?

I'll specify that I'm referring to a "concerted" SN2 reaction, not, for example, the kind of reaction described in: [Chandrasekhar, J., Jorgensen, W. L. Energy profile for a non-concerted SN2 reaction in solution. J. Am. Chem. Soc. 107, pp. 2974 - 2975 (1985).].

Also, provided that non-concerted SN2 reactions exist (example) perhaps my question is underspecified. Perhaps, I should ask instead if there are any interesting long-lived SN2 interaction complexes, or tables for transition state lifetimes from ultrafast spectroscopy studies?


texts: Why do diplumbenes (Pb=Pb double bonded compounds) break apart in hydrocarbon solution?

texts:
In group 14, the double bond becomes increasingly weaker down the group. Our lecturer told us that many distannenes ($\ce{>Sn=Sn<}$) and almost all diplumbenes ($\ce{>Pb=Pb<}$) dissociate into stannylene ($\ce{R2Sn:}$) and plymbylenes ($\ce{R2Pb:}$) when dissolved in hydrocarbon solution.
The weak nature of $\ce{Sn=Sn}$ and $\ce{Pb=Pb}$ bond has been explained by the $\mathrm{6s-6p}$ energy gap, which makes the $\mathrm{p-p}$ pi-bond unfavourable; instead the $\ce{sp^2}$  orbitals of each plumbylene moiety overlaps with the empty p orbitals of the other. Mixing between $\sigma^*$ and $\pi$ has also been used to explain the weak double bond for distannenes and diplumbenes.
If the double bond is really weak, then why don't these compounds exist as plumbylene monomers in solid state as well? How does dissolving in hydrocarbon make the plumbylene monomer more stable than the dimer diplumbene?
Hydrocarbons can only provide weak van der Waals interactions, so how can they make a large difference to the equilibrium between dimer and monomer?


texts: How to convert SPC files to ASCII without original spectroscopy software?

texts:
IR and Raman spectroscopy are typically saved in *.SPC files (chemical/x-galactic-spc), which are binary files. Collected data is save to SPC files by default, but can be exported to txt (ASCII) files.

I now have original SPC files and the original spectroscopy software is not available. Is it possible to somehow read those files with some other (generic?) software?


texts: Why is it possible to form bromoalkanes but not iodoalkanes from free radical substitution?

texts:
For a free radical substitution (FRS) reaction between iodine $\ce{I2}$ with ethane and bromine $\ce{Br2}$ with ethane $\ce{CH3CH3}$:

$E_\mathrm d(\ce{H-I})=299\ \mathrm{kJ\ mol^{-1}}$

$E_\mathrm d(\ce{H-Br})=366\ \mathrm{kJ\ mol^{-1}}$

$E_\mathrm d(\ce{C-H})=410\ \mathrm{kJ\ mol^{-1}}$

I understand that the reaction for iodoethane to form from FRS is energetically unfavourable, since the energy released from the formation of a $\ce{H-I}$ bond (from reaction between an iodine radical and an ethane molecule) is only $299\ \mathrm{kJ\ mol^{-1}}$, which is insufficient to compensate the energy needed to break the $\ce{C-H}$ bond to even form the first ethyl radical in the first place for further propagation of the reaction.

However, it is to my knowledge that bromoethane can form from FRS, despite the formation of a $\ce{H-Br}$ bond releasing only $366\ \mathrm{kJ\ mol^{-1}}$ of energy, which is still lower than the $410\ \mathrm{kJ\ mol^{-1}}$ of energy needed to break the $\ce{C-H}$ bond. This doesn't really make sense if the justification for iodoethane is correct.

I would appreciate if anyone could explain to me the reason why bromoethane can form from FRS despite being apparently energetically unfavourable too, thanks!


texts: Is specific rotation defined for mixtures of enantiomers or meso compounds?

texts:
I recently had to do an experiment where we had to make a racemic mixture of D and L complexes and then resolve the enantiomers, and measure the optical rotation of the racemic mixture, and the individual salts. After that we had to calculate the specific rotation in case.

However, when reading about optical activity, I came across the definition:

  For an optically active substance, defined by $\ce{[α]^θ_λ = α/γl}$, where α is the angle through which plane polarized light is rotated by a solution of mass concentration γ and path length l. Here θ is the Celsius temperature and λ the wavelength of the light at which the measurement is carried out.

Source: CRC handbook of Chemistry and Physics

Also, specific rotation is treated as an intensive property of a compound (i.e. one enantiomer). Given that, does it make any sense to calculate the specific optical rotation for a mixture of enantiomers (whether racemic or not)?

And applying the same logic, can we say that specific rotation has no meaning for a meso-compound ?


texts: Carbene mesomeric structure of vinyl carbocation?

texts: Why isn't a mesomeric structure with carbon having only two single bonds and a lone pair used for depiction of vinyl carbocation?


texts: Crystal structure database search for space groups

texts:
I'm usually using databases like the Springer Materials site or the free Crystallography Open Database to get crystal structure data. But none of these offers the possibility to search for all entries with a defined space group. I recently prepared a new compound and solved and refined the crystal structure. I would like to compare it to compounds known by literature to give the structure a name. It's quite common to compare structures to already existing ones. But I can't find any website that would give me the possibility to look for all entries with the same space group without knowing the elements.

Does anyone know a search engine for this specific problem?


texts: Can I determine the rate law order from stoichiometric coefficients?

texts:
I've read in two books, and seen in three separate videos courses, that you cannot determine the rate law order from stoichiometric coefficients.

Then, I have seen homework and "practice" problems that ask you to do exactly that.

Needless to say, I am confused.

This is how I am presently making sense of the issue: Given a balanced equation, and absent any other information, you can (and must) use the stoichiometric coefficients to determine the rate law. So, for example, given the equation $2A+B \rightarrow C + 3D$, the rate law would be $rate = k[A]^2[B]$.

But, this would only hold true if this were an "elementary reaction" (i.e., no equilibrium).

So, I wonder why the books and videos emphasize that you can only determine order by experiment and not from the stoichiometric coefficients. I am guessing that they do so because, in practice, you do not know if the reaction is an elementary reaction or not and therefore experiment is the only way to make that determination. And, because you don't really know if it is an elementary reaction, you can only determine the rate law experimentally.

The bottom line:

as a practitioner, determine rate law experimentally;
as a student, given no information other than the balanced equation, determine the rate law from the stoichiometric coefficients;
as a student, given rate and concentration data, determine the order (and rate law) from the data.

That is a pragmatic, but unsatisfying, solution to the problem but I would prefer a clearer explanation of what is going on.


texts: Why do we need sulfuric acid in reducing nitric acid?

texts:
From Wikipedia:

Why do we need sulfuric acid in the left part of the formula? Wouldn't FeSO4 reduce nitric acid without the sulfuric acid taking part?

P.S.

I was answered that a milder form of the reduction would still take place:

Is that right?

So we need the acid to make the reduction more advanced, all the way to N(2+) from N(5+)? How does it work?


texts: How to quantize the shape of a molecule?

texts:
I am looking for numbers which tell you something about the 3D shape of the molecule, and is also easily calculated.

One of these is the acentricity factor. I am aware of this one. My problem is you calculate acentricit, from thermochemical data, which are usually hard to find, and can contain a great degree of experimental errors.

A more suitable quantity would be constructed from the groups of the molecule. Is there such a thing? Or what are other quantifiers of molecular shape other than acentricit, factor?


texts: Acidity of thiamine - how comes hydroxide anion with pK about 15 ionizes thiamine with pK about 18?

texts: Textbooks say removing proton from thiamine's C atom will produce a resonance stabilized carbanion which is hence bioactive. That's OK, but how comes that 1) we abstract the acidic proton with the OH base whose pK is lower that for thiamine, and 2) the remaining anion acts - in bio context - in aqua medium (?), hence will immediately deprotonate water and lose its negative charge.


texts: Anomalous Electronic Configuration of Thorium

texts:
The electronic configuration of thorium ($Z=90$) is $5\mathrm f^0 6\mathrm d^2 7\mathrm s^2$. But, according to the aufbau principle, the electrons should first enter the $\mathrm f$ subshell and not the $\mathrm d$ subshell. This is not a special case of a half-filled subshell or a fully-filled subshell like we see in the respective cases of chromium and copper. Then why do we write the electronic configuration like this, first filling the $\mathrm d$ subshell and not the $\mathrm f$ subshell?

P.s I came across the anomalous configuration of thorium here: https://en.wikipedia.org/wiki/Thorium#cite_ref-Wickleder5960_19-0

But it doesn't state the reason for the anomaly.


texts: What are the possible side reactions when preparing iron(III) naphthenate?

texts:
I am trying to prepare some iron(III) naphthenate.

And the raw materials are : ferric(III) chloride, and naphthenate acid,  NaOH, toluene, deionized water

Everything worked well in lab scale: final iron(III) naphthenate dark red in color and soluble in toluene was obtained easily;

However, I encountered problem when scaling it up: it seems there are undesired side reactions, the finish goods looked like black precipitation.

Is that because naphthenate acid was oxidised by Iron(III)? or is there any other side reaction when being scaled up?

The operation:

I first dissolve NaOH and FeCl3 into water separately;
add NaOH aqueous solution into naphthenate acid while stirring at about 60°C;
add FeCl3 aqueous solution into the soldium naphthenate solution slowly;
keep reaction temperature at about 80°C for a while and remove the water;
reflux distillation to obtain finish goods (the maximum temperature might be high)


texts: How to use molality and molarity to determine the molar mass of a compound?

texts:
An aqueous solution of a certain organic compound has a
  density of $1.063~\mathrm{g/mL}$, an osmotic pressure of $12.16~\mathrm{atm}$ at
  $25.0~\mathrm{^\circ{}C}$, and a freezing point of $-1.03~\mathrm{^\circ{}C}$. The compound is known not to dissociate in water. What is the molar mass of
  the compound?

The molarity and molality can be determined with the given information.

$$m=\dfrac{\Delta T_{f}}{k_{f}}=0.554m$$ and
$$ M=\dfrac{II}{RT}=0.497M$$

$$\text{mass of }\ce{H2O}=\dfrac{1000~\mathrm{g}~\ce{H2O}}{0.554~\mathrm{mol}~\text{of solute}}\cdot 0.497~\mathrm{mol}$$

I don't understand how the last equation is used to determine the mass of $\ce{H2O}$. How are we justified in using the molarity and molality to determine the mass of water?


texts: How to name an alkyne with cyclic substituent?

texts: My attempt: 1-(1-methylcyclopentyl)-3-methylpent-1-yne. Looks so messy though.


texts: Does copper react with hydrochloric acid?

texts:
In my chemistry lab, we had 18 different reactions involving many different substances. One of the experiments involved placing a piece of copper metal in hydrochloric acid.

While observing it for a minute, my partner and I did not notice any reaction taking place. However, a minute was all we were allowed, and we could not keep it longer to observe it.

It was the only experiment that looked like it had no reaction, so I felt a little uneasy putting it down. (I didn't do anything wrong, but I guess I was unsure with myself).

I have seen some sources say that no reaction is the current result. However, I have also seen some sources saying that it does react, via $\ce{Cu + 2HCl -> CuCl2 + H2}$, yielding cupric chloride and dihydrogen gas.

Which is the correct result? If no reaction is correct, what would be the correct chemical reaction for this case?


texts: Why are tertiary alcohols more reactive towards Lucas reagent but show low rates of esterification?

texts: Generally the order of reactivity of alcohols follows the order tertiary > secondary > primary. But why is it reverse in case of esterification.


texts: Why does C=C bond replace C-O bond when two graphite platelets are rubbed against each other edge on edge?

texts:
When two small 2D carbon platelets are pushed into proximity, why do they release the edge attached molecule (maybe O) and then bond C to C?
I think the answer I seek would address the relative difference in bond strengths, and what forces are involved to remove attached molecules, probably Oxygen.   .....
BACKGROUND:   I experiment with electrostatic properties of conductive carbon films for oscillation and physical displacement applications. I use a mechanical 'tribological' method of creating 2D Carbon sheets.  In this case the method is: smearing powered graphite onto a smooth substrate, followed by agitation and polishing to a smooth highly conductive film.  The result is assumed to be hexagonal graphene film of several layers.


texts: Calculate molarity given density and mass percentage

texts:
Problem

Calculate molarity of a solution of $\ce{H2SO4}$ with density $\pu{1.198 g/cm3}$ and containing $27~\%$ mass of $\ce{H2SO4}.$

Answer

 $\pu{3.374 M}$

My approach
I converted the density to g/l. Then i took 27% of the density and converted it into no of moles. Thus, came moles per litre, which is actually molarity. Yet, the answer key that my teacher had provided had a different answer compared to mine.
Is my method wrong or is there any calculation mistake?


texts: How (in)flammable is "isopropyl alcohol" really?

texts:
I have an electric device which frequently gets very oily (it's a vaporizer for herbs). It came with a few individually packaged small "tissues" drenched in "isopropyl alcohol". I've used up them all now to clean the insides.

After each cleaning session, I wait a few minutes before I put in new herbs and heat it up again (to 365-420 degrees F). Every time, it feels scary, because "isopropyl alcohol" is said to be "extremely" flammable. I feel like it's going to explode every time, but it luckily never does. Since they shipped those with the product, and didn't mention a word about this in the "manual", I assume it's safe.

But how can it be safe? Is it not hot enough? Does it evaporate so quickly as to never actually be left in there when I heat it up?

I also bought a separate, very expensive bottle of what I assume is "high-quality" isopropyl alcohol and poured it into a glass container with a firm plastic lid, which I keep in a wardrobe. Luckily, it doesn't seem to evaporate into nothing, like used to happen with other alcohol which I previously attempted to store in the same container. After a couple of weeks, half of it had disappeared! That doesn't happen with "isopropyl" alcohol, apparently, but why doesn't it?

As you can hear, I wonder both how (in)flammable it really is, and what makes it not evaporate inside the box, but does evaporate very quickly (apparently) when not restricted by a closed container.


texts: Can we define a new unit instead of specific heat that is constant with temperature rise?

texts:
Specific heat plays an important role in calculating energy and thus, heat, enthalpy and etc.
But as I sighted the definition for calorie, I was surprised.

  A calorie is the amount of heat needed to alter the temperature of 1 gram of 14.5 °C water to 15.5 °C water in the pressure of one atmosphere.

Though the unit was redefined later, the question remained still. Why were there those temperatures? It was just then that I realized specific heat capacity varies with temperature differences and it is due to vibration movements of matter and internal energy ....
Two questions: Can there be a unit which is constant with temperature alterations that can be used instead of S.heat capacity? If so, why isn't it replacing SHC?
The resource for the quote The resource for the reason of the increase that happens to SHC with temperature rise


texts: Why does hydrogen burn with a pale blue flame while its emission spectral lines are red in colour?

texts:
I was studying oxidising flames and realized that sodium burns with a bright yellow flame the wavelength of which is around 588 nm. Then I searched for emission spectra of sodium and found that the lines around 588 nm are the most intense ones, so it appears yellow. The same happened with potassium.
But when I arrived at hydrogen, I knew it burned with a pale blue flame, but its emission spectral lines were most intense in the red region. So why does it still gives a blue flame?

As you see, it emits blue light too, but the red one is the most intense and so electrical discharge of hydrogen emits red light. But its oxidising flame is pale blue.
Would it burn with a red flame at higher temperature or something like that or are spectral lines not related to flame colours?


texts:
In terms of producing gold nano flakes, Guo et al. [1] added aniline to the solution of chloroauric acid in ethylene glycol at 95 °C. However, I couldn't figure out the step by step chemical reaction in it. Can anyone please explain me the reaction procedure or guide me to the relevant source?

References

Guo, Z.; Zhang, Y.; DuanMu, Y.; Xu, L.; Xie, S.; Gu, N. Facile Synthesis of Micrometer-Sized Gold Nanoplates through an Aniline-Assisted Route in Ethylene Glycol Solution. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2006, 278 (1), 33–38. https://doi.org/10.1016/j.colsurfa.2005.11.075.


texts: Units of rate constant (cycles per second vs radians per second) in Eyring equation

texts:
In the Eyring equation (EE),

$$k = \frac{k_\mathrm B T}{h} \exp\left(\frac{-\Delta G_{\mathrm f}}{RT}\right),$$

the units of $k$ are $\mathrm{s^{-1}}$. However, in general rate constants are usually expressed in $\frac{\mathrm{rad}}{\mathrm{s}}$. For instance, in expressions for damped oscillations of the form $\exp[(\mathrm{i} \omega - k)t]$, where $\omega$ is by definition in $\frac{\mathrm{rad}}{\mathrm{s}}$ and $k$ has to bear units providing consistent dimensions.

By expressing in the EE the energy $k_\mathrm B T$ as $\nu h$, where frequency $\nu$ is in cycles per second $\left(\mathrm{Hz}=\frac{\mathrm{cyc}}{\mathrm{s}} = \mathrm{cps}\right)$, it appears that $k$ is also given in $\mathrm{cps}$ in this equation. The desired units of $\frac{\mathrm{rad}}{\mathrm{s}}$ would be obtained if $h$ were replaced by $\hbar$. However, I have never seen the EE formulated that way. Has anybody an idea in this matter?


texts: Apparently, water or $\ce{H2O}$ combines in some way with nitrogen (from the air or elsewhere?) to form ammonia, or  $\ce{NH3}$. Where/how in the body is this $\ce{NH3}$ (or whatever nitrate) produced before it is excreted with urine?


texts: Inductive effect comparison of benzylic and allyl group

texts: I have to compare the acidity of the above two carboxylic acids. I wish to know which one has a stronger -I effect, the benzylic group or allylic group?


texts: Discrepancy between the apparent volume of the solution and the volume of the solute arising from the definition of solubility

texts:
I have solubility $s$ given in $\pu{g/mL}.$ I understand this as mass of solute $m$ divided by volume of solvent $V.$

But how about the volume of the resulting solution? I read online I should pour the solute into a measuring cylinder/cup first, and then add solvent until the volume fits the calculated value $(V = m/s),$ but this seems to be at odds with the definition of solubility.

What is the correct way to understand solubility? I can't know the volume of a solution based on solubility.


texts: 1.0 g of AlCl3 is added to 100.0 ml of water. What would be the resulting pH?

texts:
$1.0\ \mathrm g$ of $\ce{AlCl3}$ is added to $100.0\ \mathrm{ml}$ of water. What would be the resulting pH?

I think the answer may be $4.022$ but I'm not certain.

The reaction wasn't provided but I think its this:
$$\ce{Al(H2O6)6^3+ <=> H^+ + Al(H2O)5(OH)^2+}$$
Assuming all $\ce{Al}$ dissolved in water:
Initial $[\ce{Al}]=7.49\times10^{-4}\ \mathrm M$

$$x^2/(7.49\times10^{-4}-x)=1.4\times10^{-5}$$

$$x=9.56\times10^{-5}$$

$$\mathrm{pH}=-\log(9.56\times10^{-5})=4.022$$


texts: Finding excited stage of electron from its potential energy

texts:
The potential energy of an electron in the hydrogen atom is $\pu{-6.8 eV}.$ Indicate the excited stage in which electron is present.

Total energy would be equal to $\pu{-3.4 eV}.$
I used the formula
$$-13.6\left(\frac{1}{1^2} - \frac{1}{n^2}\right) = \pu{-3.4 eV};$$
$$n^2 - 1/ n^2 = 4.$$
I got answer as $3n^2 = 4,$ which is obviously not correct. Where am I going wrong? I need help either with the formula or calculation I did wrong.


texts: How can I synthesize an (E)-configured enone using the Wittig reaction?

texts:
I have been asked to synthesize the compound (E)-5-methylhex-3-en-2-one:

How can this be achieved using the Wittig reaction?


texts: Thermal decomposition of magnesium bicarbonate

texts:
I was trying to solve a problem from a regional contest where it was a mixture of bicarbonates of $\ce{Na}$ and $\ce{Mg}$ which was put at high temperature. What are the reactions of decomposition?

I've thought that the reactions are:
$$\ce{2NaHCO3 -> Na2CO3 + H2O + CO2}$$
and $$\ce{Mg(HCO3)2 -> MgCO3 + H2O + CO2}$$

But, I found out that the second reaction is wrong. Actually, the reaction is

$$\ce{Mg(HCO3)2 -> MgO + H2O + 2CO2}$$

I searched on the web and I found the decomposition of other bicarbonates, like $\ce{Ca(HCO3)2}$ is similar to the first reaction. Is there any rule? When is carbonate and when is oxide? Or is $\ce{Mg}$ an exception?

Thanks!


texts: Zinc salt with a very high relative aqueous solubility?

texts:
Zinc bromide, iodide, and chloride are highly soluble in water, both in absolute terms, and relative to other metals. I think however that there is a zinc compound with even higher relative aqueous solubility than those, perhaps one involving $\ce{NH4+}$ and $\ce{Cl-}$.
Does anyone know which salt that is, and could provide the aqueous solubility values for that salt?


texts: May I treat units (e.g. joules, grams, etc.) in equations as variables?

texts:
Suppose I have two units, Tonks, $T$, and Borks, $B$, as well as the equation $\frac{50T}{20B}=x$. May I manipulate the equation as though $T$ and $B$ were the kinds of symbols that we learned to manipulate in math class? For example:

\begin{align}
\frac{50T}{20B}&=x\\
50T&=20Bx\\
\frac{50T}{20}&=Bx\\
\end{align}


texts: Problem interpreting CV diagram in a paper

texts:
I am an undergraduate materials science student. I am currently preparing to conduct some research over the summer on alkaline electrolyte membrane fuel cells and have been reading some papers to get background information (this is a very new area to me). The surface chemistry section of the paper involves several cyclic voltammetry plots, and I am having trouble understanding a part of one of them.
To preface the diagram, the author states:

  For the Pd-black-coated electrode, a pair of symmetrical peaks is observed
  between −1.0 and −0.82 V and is assigned to the formation/
  desorption of proton−palladium species...

I interpreted these peaks to be the ones enclosed in the black box below:
Next, the author makes the following statement:

  The [proton−palladium species] formation/desorption peaks are smaller for the
  Pd−Ni or Pd−Ni−P electrodes compared with the Pd-coated
  electrode.

To my uneducated eyes, this appears to be incorrect, as at least the Pd-Ni-P peaks appear to be larger than the Pd-blk peaks. How should I go about correctly interpreting this diagram? The paper can be found here, and the diagram and statements in question are in section 3.3: Surface Electrochemistry of Catalyst-Coated Electrodes. Any guidance is greatly appreciated, and I am sorry if my question is repetitive or the answer is obvious. If additional information is needed, please let me know.


texts: Software or library for creating images of ball and stick models?

texts:
Is there any code library (in any programming language) or software capable of producing images of ball and stick diagrams?

Example of an image of a ball-and-stick model for Ammonia:

(Image source)

Preferences:

It should be capable of producing images programmatically through a code library. Any mainstream programming language (C, Java, Python, etc.) is acceptable.
It should be able to take chemical descriptions as input to produce images of ball and stick diagrams as output.
It should be free and open source.

I know that it is possible to create these models using Mathematica's ChemicalData built-in symbol, but I am looking for something that can integrate better into my existing code base (hence the preference for free and open source libraries in mainstream programming languages).


texts: There are binary diamond type structures for example S and Zn form sphalerite. I thought the reason this formed was because of the big difference in the radii of the atoms that allows the smaller atom to fit into the tetrahedral hole that the bigger atoms form. However GaAs also forms sphalerite type structure, their radii are not that different. Why do Sphalerite type structures form?


texts:
I'm having a hard time understanding what equivalent weight means physically.  I've looked at many articles on Google but the definition always seems nebulous to me.
For example, if the equivalent of $\ce{H2SO4}$ is $\pu{49 g/mol}$, what exactly does that mean?


texts:
Is it plausible that free chlorine could be formed in concentrated hydrochloric acid.

The background to this is that I have bought some 30% HCl to remove calcium carbonate scale from a reverse osmosis water purifier. The latest batch of HCl seems to have a very slight yellowish tint which I had not noticed on previous occasions. Having used some of this acid I find that the performance of the membrane seems to have deteriorated (these membranes are notably sensitive to hypochlorite).

Could some factor (perhaps exposure to direct sunlight) be responsible?

Is there a way that I could detect the presence of dissolved chlorine?

Can anyone suggest an alternative explanation?

Thanks,
Chris.


texts: Why doesn't propynal give cannizzaro reaction?

texts: Cannizzaro reaction is a disproportionation reaction which is given by aldehydes and ketones having no α-H, forming alcohol (reduction) and carboxylic acid (oxidation) as its products. The compound, Propynal has no α-H and it should be giving Cannizzaro reaction but, my textbook says that the reaction is not given by Propynal. Can someone please explain to me why Propynal doesn't give Cannizzaro reaction?


texts: What are some Internal Standards used for Ion Chromatography?

texts:
What are some internal standards (ISTDs) used for ion chromatography (IC)?
For experienced IC users, what ISTDs have you used for your sample analysis?


texts: Synthesis of chloroquine from 4-amino-7-chloroquinoline

texts: Can we get chloroquine from 4-amino-7-chloroquinoline (7-chloroquinolin-4-amine) by adding 4-chloro-N,N-diethylpentan-1-amine $(\ce{CH3CHCl(CH2)3N(Et)2})$ ?


texts:
Do we have that $\pu{1 g/mol} = \pu{1 amu}$ ?

Because we have, for the mass of an atom of carbon 12, call it $m(\ce{^12C})$, that

$$m(\ce{^12C}) = \pu{12 amu}$$

and furthermore

$$\pu{1 mol} \cdot m(\ce{^12C}) = \pu{12 g}$$

therefore

$$m(\ce{^12C}) = \pu{12 amu} = \pu{12 g/mol}$$

So finally we get that $\pu{1 g/mol} = \pu{1 amu}$ .

However, my chemistry teacher is telling me that those are two completely different things and that I am confused between the mass per atom and the mass per $6.022\cdot10^{23}$ atoms. I can't understand how, and this is really bugging me, so help is very appreciated.

Note that this requires the mole to be a number (or a "constant"), which may be where I'm wrong.


texts: Why does having equivalent resonance structures give more stability (Related)?

texts:
This question is based on @Heisenberg's Question with the same title.
I recently offered a bounty for a more detailed answer for the same question.
These are the things I would like to be in the answer:

Can molecules with 'n' canonical structures be taken as an n-state  system with coupling(At least as an approximation) ?

Suppose if it is possible.
Consider a molecule with 2 canonical structures represented by $|A\rangle$ and $|B\rangle$
Without the coupling let the energies of the two states be $E_1$ and $E_2$ respectively.
So the Hamiltonian is represented by:
$H=\pmatrix{E_1& 0\\0&E_2}$

Now with coupling the Hamiltonian in the most general case will be:
$H=\pmatrix{H_{11}& H_{12}\\H_{12}^*&H_{22}}$
The energy eigen-value with the lower energy in this case is:
$E_1 = \frac{H_{11}+H_{12}}{2} - \frac{\sqrt{(H_{11}-H_{22})^2 + 4H_{12}H_{12}^*}}{2}$
So my doubt is if the 2 states are symmetrical then $H_{11}$ and $H_{22}$ are equal right?
Then the term inside the square-root $(H_{11}-H_{22})$ becomes zero, and it seems to me that when this term becomes zero, the energy splitting becomes the least.
And yet it is resonance with equivalent canonical structures that are more stable. Why?

Are molecules with equivalent resonance structures actually more stable? Please include references or experimental evidence if the it is true.

If molecules with equivalent resonance structures are in fact more stable than others, then does it mean that resonance in molecules cannot be approximated as a discrete n-state system even for ones with 2 canonical structures (Since there might be a contradiction with arguments in 2)) Can resonance be understood only using MOT or Huckel Theory ?

Note: Please add your answer in Heisenberg's question so that I can award you the bounty.
You might understand why I'm having these doubts and the doubts itself if you read these chapter of the Feynman lectures on Physics Chapter 8 , Chapter 9 , Chapter 10


texts:
Electrons can delocalize over multiple equally probable bonding structures. Can atoms delocalize over multiple equally probably bonding structures in certain cases?

It seems to me that any such effect would be most pronounced with very small atoms such as hydrogen.

Furthermore, I would expect such effects to be mostly to occur with hydrogen bonds and cation-pi interactions.

One possibility I am imagining sticking the ends of a bunch of linear molecules that end in OH groups or fluorine atoms together.


texts: Why does hand sanitizer turn into a liquid after coming out of the bottle?

texts:
Hand sanitizer is a gel in its bottle, but when I pour it on my palm, it turns into a free flowing liquid. Why does that happen?

It doesn't turn to a liquid when I pour it on my floor or my table. It doesn't seem to be related to heat, as I tried it also with a hot surface.


texts: Painting metal, does it matter if all rust is removed before?

texts:
In the context of automobile repair work, assume a metal surface has rust on it. Does it matter if all of the rust is removed before the metal surface is painted? If it does matter, then why?

It appears that at least some will claim you can do this, e.g. the company Krylon.

How I've tried to figure this out myself:

I'm assuming that the rust-covered surface area will affect how well the paint will stick to the surface. Maybe this alone can be a problem in terms of durability and sealing the metal from the atmosphere?

If it is governed by a more complex process, what process(es) should be read into further? However, I also assume that (as the aforementioned link suggests) that making the surface as smooth as possible with loose rust and debris removed will yield better results -- i.e. results that approximate that of having no rust at all there? Will it never be as good as simply having all rust removed? I know I'm asking in a way that is difficult to quantify, but "how good" will it get, compared to having all the rust removed?

After studying the Wikipedia article on rust I also imagine that from the dehydration equilibria we have that even a small area of rust can:
$$\ce{Fe(OH)2 <=> FeO + H2O}$$

Even assuming the rust is properly sealed from the atmosphere it appears it can create new $\ce{H2O}$ under this protective layer.

But we need oxygen for the key reaction to occur:
$$\ce{O2 + 4e^- + 2H2O -> 4OH^-}$$

From this how stuff works I have:

  As the acid is formed and the iron dissolved, some of the water will begin to break down into its component pieces -- hydrogen and oxygen.

How exactly is the water broken down into hydrogen and oxygen? From a chemistry textbook (Masterton & Hurley) I have:

  For example, water does not spontaneously decompose to the elements by the reverse of the reaction referred to above
  $$\ce{2H2O(l) -> 2H2(g) + O2(g)}$$ nonspontaneous.

But electrolysis can certainly create these elements. But can it happen in this environment? Sealed under a surface of paint? What does the chemistry look like?

From chemical formula I have that we can get hydroxide from:
$$\ce{4e^- + 2H2O(l) + O2(g) -> 4OH^-(aq)}$$

However still, from where does new oxygen get introduced into the system, assuming the atmosphere is actually completely isolated from this internal system taking place under the surface of the paint?

Should it matter, assume the environment is approximately 1-atmosphere pressure and that the temperature varies between -10 to 40 degrees Celsius.


texts: Elemental Potassium as both an oxidizer and a reducer

texts:
On this table I realized that elemental potassium could adopt oxidation states of -1, 0, and +1.

http://en.wikipedia.org/wiki/List_of_oxidation_states_of_the_elements

Does this mean that elemental potassium can function as both an oxidizer and a reducer? I understand that oxidizers are reduced (gain electrons), and that reducers are oxidized (lose electrons). How can potassium anion be formed? The potassium anion must be extremely unstable due to potassium's extremely low electronegativity, correct?

Also in what compound does potassium actually have a negative oxidation state?


texts: Relation between ΔH and ΔE for the reaction in gaseous phase at constant temperature and pressure

texts:
Which of the following statements is correct for the reaction at constant temperature and pressure:
$$\ce{CO(g) + \frac{1}{2}O_2(g) -> CO2(g)}$$

$\Delta H = \Delta E$
$\Delta H > \Delta E$
$\Delta H < \Delta E$
None of these.

Since this occurs at constant temperature, $\Delta E = 0$ and $W < 0$. So, $\Delta H$ turns out to be less than $\Delta E$, but this is not the answer. Why?


texts: Is the Self Consistent Field an actual field?

texts:
I know this is really stupid. But bear with me.

In everything I have read so far, the Self Consistent Field (SCF) is always used to describe a method or a process, namely, that of iteratively solving the Schrodinger's Equation to generate new wavefunctions, using them for a new potential, and solving until convergence.

If SCF is not an actual field, why is it named as such? And then when we describe the SCF space what are we really talking about? Does the iterative process create a series of objects that spans a field?

For SCF: https://en.wikipedia.org/wiki/Hartree%E2%80%93Fock_method or if you want a textbook for reference, there's always Szabo and Ostlund's Modern Quantum Chemistry.


texts: Are there any acid-base indicators whose protonated and deprotonated forms have the same number of resonance structures?

texts:
This question asks about the color change of 7-hydroxyphenoxazone, the active compound in litmus paper, and the relation of that color change to the conjugated system in the molecule.

In Klaus Warzecha's answer, he mentions 4-nitrophenol as another, simpler indicating system, analogous to 7-hydroxyphenoxazone.

In both of these species, as noted by Klaus, deprotonation of the hydroxyl group to an -olate moiety enables a resonance between the substituents, through the molecular cores, which is not possible in the protonated species:

I'm interested in knowing whether this property of an "opened-up resonance on deprotonation" and the concomitant influence on the excitation spectrum are necessary characteristics for indicating compounds.

So: Are there any known examples of acid-base indicators (e.g., compounds exhibiting a change in visible-spectrum absorbance upon deprotonation) where the removal of the proton does not "open up" additional resonance structures in this fashion?

Clicking through some of the links on Wikipedia's $\mathrm{pH}$ indicators page, I would guess that cresol red, bromocresol green, and bromophenol blue potentially fall into this category, but I'm not confident enough in my evaluation of resonance structures to be certain.


texts: Theoretical Calculations for Potential Generated in Salt Water Battery

texts:
I am using a $\pu{1.5 M}~\ce{KCl}$ solution as electrolyte and copper and aluminium electrodes but no salt bridge. So basically there is only one beaker with the two electrodes in it with the $\pu{1.5 M}~\ce{KCl}$  solution.
I understand that its some variation of the standard Nernst Equation but most of the literature I saw applied the equation to cells with a salt bridge.
I need help figuring out the reactions in the system and the potential generated by the cell.


texts: Acid catalysed synthesis of ethyl ethoxymethylenemalonate

texts:
One synthesis of quinolones begins with the formation of an ethyl ethoxymethylenemalonate, as seen in this Organic Syntheses paper.

I've been asked if the malonate derivative would be formed if methylmalonate was treated with trimethyl orthoformate with a catalytic amount of $\mathrm{H^+}$, without heating. The nature of the solvent isn't mentioned, but I guess the reaction is carried out in a non-aqueous medium with an ion-exchange resin, since I think trimethyl orthoformate acts as a water trap.

My hunch is that there shouldn't be a significant quantity of product formed. We're dealing with an activated methylene, why not simply use a base and then carry on with our addition? I can't imagine how, under normal circumstances, the elimination product ethyl ethoxymethylenemalonate will be formed.

How can this reaction happen in a mechanistically reasonable way?


texts:
The pseudo 1st order reaction happens when one of the reactant is in large excess and its concentration doesnt change during the reaction .

Is there any other such situation when a certain higher order reaction turns out to become a pseudo first order kinetic reaction (except the situation where an N$^{th}$ order reaction has N-1 species in large excess) ?


texts: How is the mol highway used in this problem?

texts:
How many moles of propane gas, $\ce{C3H8}$, are contained in 11 grams of the gas at standard conditions? Also, can you please explain step-by-step (and include sigfigs?)

I think I might know how to do this, but I'm not sure if this process is correct.

I found online that $\ce{C3H8}$ has a mass of 44.11 grams per mol. So do I just use a proportion to find the number of moles this 11 grams of propane has?


texts: Charge distributions in the transition state of the SN2 reaction

texts:
I understand that a similar question has been posed here. However, the scope of my question is framed differently. I will present analysis of two different sources of information and I would like to question if there is a contradiction between the two.

Perspective by Carey & Sundberg (2007)

Carey & Sundberg (2007) provides the following perspective on the effect of substituents on the rates of $\ce {S_N2}$ reactions, on p. 418-419:

  The extent of the rate enhancement of adjacent substituents is dependent on the nature of the TS. The most important factor is the nature of the $\pi$-type orbital that develops at the trigonal bipyramidal carbon in the TS. If the carbon is cationic in character, electron donation from adjacent substituents becomes stabilizing. If bond formation at the TS is advanced, resulting in charge buildup at carbon, electron withdrawal is more stabilizing.

It is accompanied by  the following diagram:

What I would like to point out is that the authors claim that it is possible for the carbon atom involved in an $\ce {S_N2}$ reaction to develop a slight positive charge when the cleavage of the $\ce {C-LG}$ bond is more advanced than the $\ce {C-Nu}$ bond. Perhaps, we can see this as more electron density is leaving the carbon atom via the transfer onto the leaving group, compared to the electron density transfer from the nucleophile onto the carbon atom.

Computational study by Pross & Shaik (1982)

Pross & Shaik (1982) seeked to dispel the commonly-held belief that:

  the extent of charge development in a transition state is dependent on the earliness or lateness of that transition state. For example, in the $\ce {S_N2}$ reaction of an anionic nucleophile with a neutral substrate, most of the negative charge would be expected to be localised on the nucleophile for an early transition state ... while for a late transition state most of the charge would be localised on the leaving group ...

They used a method they referred to as the "linear combination of valence-bond configurations". They write that the wavefunction describing the transition state will reflect the fact that both configurations shown below are of equal energy at the crossing point of the diagram (Fig. 1) below by having equal weights, where the two configurations refer to $\ce {Nu^- + R-X}$ and $\ce {Nu-R + X^-}$. This would mean that the transition state would have around $\ce {-0.5}$ of the charge localised on $\ce {Nu}$ and the other $\ce {-0.5}$ localised on $\ce {X}$. Does this suggest that the carbon atom is roughly electrically neutral?

Does research presented by Pross & Shaik (1982) contradict what is mentioned by Carey & Sundberg (2007)? And is the theory presented by the textbook in that paragraph incorrect? Personally, I have never seen such an effect described in this way in other texts on the $\ce {S_N2}$ reaction.

References

Carey, F. A.; Sundberg, R. J. Advanced Organic Chemistry Part A. Structure and Mechanisms (5th ed.). Springer, 2007.
Pross, A.; Shaik, S. S. Is Charge Development a Measure of SN2 Transition State Structure? Tetrahedron Lett. 1982, 23 (51), 5467–5470. doi:10.1016/0040-4039(82)80159-7


texts: why do electron pairs not take axial positions in the VSEPR structure of ClF3?

texts: when we make a Valence shell electron pair repulsion theory based structure for an molecule after calculating its hybridisation ; when we have to decide the positions of the ions we put them in such positions so that repulsion is minimized .It follows the basic rule of lone pair-lone pair repulsion> lone pair-bond pair repulsion >bond pair -bond pair repulsion . So when it comes to deciding the position of lone pairs of electrons in ClF3 why dont we put them on the axial positions so that they have an angle of 180 deg between them as compared to 120 deg that they currently have ?


texts:
Phenyl is a functional group with an aromatic ring bonded to another group. And, phenol is a molecule that is just a phenyl bonded to a hydroxyl group.

However, some sources consider phenol itself a functional group. Are they both functional groups, or is phenol just a molecule?


texts: Is any symmetry element conserved during a supra-antarafacial cyclo addition of two cis-butadiene units

texts:
I tried to construct a correlation diagram for the [4+4] cyclo addition of two cis-butadiene units. But I failed to construct any meaning full orbitals for the "educt" side where the two butadiene molecules still have their pi-systems intact.

I thought that a C2 rotation axis is conserved during a supra-antarafacial reaction pathway but aligning the pi system of both units leads to a conflict. The backbone of the supra-facial part cannot be combined with the antarafacial unit to sustain C2 symmetry. This would only be possible for a combination of a cis-butadiene with a trans-butadiene. But without any conserved symmetry element correlation is impossible.

So I'm wondering if the Woodward-Hoffmann rules are applicable at all in this case or if I am being too strict with symmetry. Is it legit to neglect the backbone when thinking about the symmetry?


texts: How to read these graphs and what are they called?

texts:
How does one interpret/read the following graph (found here) as well as on wikipedia or

What are these called?


texts: After polishing my $\ce{GdFe2}$ sample with silicon carbide emery paper it developed trace amount of $\ce{Gd3Fe2Fe3O12}$ on the surface. Why is it being formed, are these type of compounds called anything?


texts: Does magnesium carbonate exist? what makes magnesium bicarbonate different from calcium bicarbonate

texts:
In my book, I found the following reactions:

$\ce{Ca(HCO3)2 ->[\Delta] CaCO3 + … }$

$\ce{Mg(HCO3)2 ->[\Delta] Mg(OH)2 +...}$

What makes these two reactants different? Why is one forming hydroxide while the other carbonate?


texts: Selection of parent chain (IUPAC nomenclature)

texts:
In the given compound, there are (apparently) two possibilities of choosing the parent (main) chain for its nomenclature in accordance with IUPAC rules:

(A) being the one containing 4 carbon atoms and the triple bond in the parent chain;

(B) being the one containing 6 carbon atoms and the hydroxyl group as a substituent in the parent chain.

Which one shall I choose while naming this compound? My book claims it to be (A), but I do not understand. (B) is clearly the longer chain and contains the hydroxyl group, which has a higher priority in nomenclature as compared to the triple bond. Where am I going wrong?


texts: What chemicals are going to be used to make the smoke black or white?

texts:
For the papal election, white and black smoke will be used to signal success or failure in the voting process.

From what I understand, the ballots are burnt and chemicals are added to create the color.

But what chemicals are used to get black or white smoke?


texts: Confusion regarding specific conductivity

texts: Is there any difference between the terms specific conductivity and conductance. If yes, please explain.


texts: Is Hydrogen Bonding a Type of Dipole Dipole Interaction?

texts:
I understand that dipole dipole forces is due to the attraction of the different partials charges of atoms in different molecules due to their different electro-negativities.

For hydrogen bonding, my understanding of it is that they are just a special case of dipole dipole forces. In certain molecules in where the difference in electro-negativities between the different atoms is high enough, then even stronger dipole dipole forces will be form which are known as hydrogen bonding. For example, in $\ce{H_2O}$ where the difference in electro-negativity of H and O is 1.24, hydrogen bonding occur. This is why hydrogen bonding can only occur between hydrogen and nitrogen, fluorine or oxygen.

However, my school teacher says that hydrogen bonding in fact is not a type of dipole dipole force as she says that hydrogen bonding occurs differently to dipole dipole forces. She said that hydrogen bonding occurs to the attraction of the lone pairs in oxygen, fluorine and nitrogen atoms to atoms with a positive partial charge. Hence this is why hydrogen bonding is much stronger than conventional dipole dipole forces.

But this doesn't make sense because if hydrogen bonding is due to the attraction  of H to the lone pair of electrons, shouldn't hydrogen bonding also form between H and Cl or I or any other atom that has a lone pair and is more electronegative than H?

Edit 1

From the comments below, it appears that the actual answer is more complicated than the simple explanation of hydrogen bonding given above. After doing some research, I have became aware of the Advanced Theory of the Hydrogen Bond which states that the hydrogen bond actually contains 10% covalent nature. However none actually explain how they are formed. Could someone please explain how hydrogen bonding actually in reality form.

Edit 2

So in response to the excellent answer by jheindel, is the reason why hydrogen bonding is considered partly covalent in nature is because the let say in water, oxygen's MO partly overlaps with the MO of the hydrogen atom in the other molecule. Also this is why they are much stronger than conventional dipole dipole forces?


texts: It’s been said over and over in my biochemistry books that the cis-double bonds between the Cs in the hydrocarbon tails in triglycerides causes a kink. This kink disappears when the bond is isomerized into its trans conformation. What is it about the cis bond that causes the kink?


texts: How were weights of elements and compounds determined?

texts:
I have browsed through many questions on this site but I still don't understand this:

How chemists in the past used to determine the weight of substances (which I believe they randomly called elements or compounds) without using modern techniques?

For example ... we know the molecular formula of water is $\ce{H2O}$

But how did chemists determine the composition of water?

How did they know hydrogen and oxygen, and not some other substance, made water and how could they determine the weight according to which combined?

What was the complete procedure behind it?

EDIT: Just like I said.... That answer still doesn't show us the complete picture... Moreover, the answerer has used phrases like (I don't know) and (Maybe) many times....


texts: Why sodium sulphate has water absorbing capability?

texts: At first I thought maybe sodium sulphate in contact with water produces sulphuric acid which absorbs water but I do not think it is actually a valid reason.


texts: Is chromate a suitable indicator for the titration of Ag⁺ with Cl⁻?

texts:
To titrate $\ce{Cl-}$ with $\ce{Ag+}$ we use chromate $\ce{CrO4^2-}$ as an indicator.
The titration reaction is:

$$\ce{Ag+ + Cl- <=> AgCl}\tag{R1}$$

$$K_1 = \frac{1}{K_\mathrm{sp}(\ce{AgCl})} = \frac{1}{1.8×10^{-10}} = 5.56×10^9\tag{1}$$

The theory says that after all $\ce{Ag+}$ are reacted with $\ce{Cl-}$ the end point of titration is detected when excess $\ce{Ag+}$ reacts with the indicator chromate to form silver chromate:

$$\ce{2 Ag+ + CrO4^2- <=> Ag2CrO4}\tag{R2}$$

$$K_2 = \frac{1}{K_\mathrm{sp}(\ce{Ag2CrO4})} = \frac{1}{1.1×10^{-12}} = 9.1×10^{11}\tag{2}$$

However, as you see, $K_1 < 100K_2,$ so when both $\ce{Cl-}$ and $\ce{CrO4^2-}$ are present, $\ce{Ag+}$ will react with $\ce{CrO4^2-}$ and not with $\ce{Cl-}$.

But our teacher and everywhere on Google they say $\ce{AgCl}$ precipitates before $\ce{AgCrO4}$. And that should be true since this method of titration (Mohr's method) has been used long ago.

But, how can that be true? I don't understand why. Where have I mistaken?


texts:
I am trying to understand how the authors calculated the TRP/LNAA (mol/mol) ratios in Table 1 in this paper.

For example, when I calculate the TRP/LNAA (mol/mol) ratio for HPROT, I get 0.14 instead of 1.1. What am doing wrong?

I'm using the following values for the molecular weights (g/mol):

Isoleucine 131.2
Leucine 131.2
Phenylalanine 165.2
Tyrosine 181.2
Valine 117.1
Tryptophan 204.2

And here are the tables from the paper:

  Table 1: Composition of the standard protein (PLC), alpha-lactalbumin whey protein (ALAC), protein hydrolase (HPROT), pure tryptophan (TRP), and synthetic dipeptide (SYN) condition

  \begin{array}{llll}
\hline
\text{Source} & \text{Product}~(\mathrm{g}) & \text{TRP}~(\mathrm{g}) & \text{TRP/LNAA}~(\mathrm{mol}/\mathrm{mol}) \\
\hline
\text{PLC}   & 20~\mathrm{g}/312~\mathrm{mL}  & 0.4 & 0.04   \\
\text{ALAC}  & 15~\mathrm{g}/312~\mathrm{mL}  & 0.8 & 0.1    \\
\text{HPROT} & 312~\mathrm{mL}       & 0.8 & 1.1    \\
\text{TRP}   & 0.8~\mathrm{g}/312~\mathrm{mL} & 0.8 & \infty \\
\text{SYN}   & 1.2~\mathrm{g}/312~\mathrm{mL} & 0.8 & \infty \\
\hline
\end{array}

  Table 2: Amino acid profile

  \begin{array}{llll}
\hline
\text{Amino acid profile}~(\mathrm{g}) & \text{HPROT} & \text{PLC} & \text{ALAC} \\
\hline
\text{Isoleucine}    & 1.004 & 1.800 & 2.012 \\
\text{Leucine}       & 0.745 & 2.733 & 3.306 \\
\text{Phenylalanine} & 0.480 & 1.467 & 1.309 \\
\text{Tyrosine}      & 1.216 & 1.867 & 1.451 \\
\text{Valine}        & 0.554 & 2.133 & 1.322 \\
\text{Tryptophan}    & 0.8   & 0.4   & 0.8   \\
\hline
\text{Total}         & 3.999 & 10    & 9.4   \\
\hline
\end{array}

Acronyms:

LNAA: large neutral amino acids
HPROT: hydrolyzed protein


texts: Substances comprised of large molecules are liquids at room temperature?

texts: I am looking for compounds that are liquid at normal temperatures and are physically very large, to be used in an ellipsometer adsorption experiment. I am currently working with decane. The candidates will ideally not be toxic or radioactive (such as $\ce{UF6}$).


texts:
Draw the structure of the complex $\ce{Co(NO_3)_2*6H_2O}$ i) without and ii) with one of the nitrates being in the coordination sphere as a bidentate ligand and identify if the inversion center is present in the complexes. Inversion is a symmetry operation that translates every atom through the center to the opposite side.

The first part seemed pretty straightforward and I drew the following structure:

From the structure above, I concluded that there is indeed an inversion center at the cobalt ion.

I'm not so sure about the second structure though. Since the cobalt complex already has six ligands, how could there be a nitrate as a bidentate ligand as well?


texts: Is it possible to determine the absolute value of entropy of a system?

texts:
I came across a question (in some assignments I had received) where it was asked:

  Can the absolute value of entropy of a system can be measured?

and to my surprise, the answer said yes. Till now, I knew that entropy is a state function, just like enthalpy and internal energy, and that only change in entropy can be measured.

Am I missing something here?


texts: Boiling point comparison between cyclohexane derivatives

texts: I am trying to order these according to boiling point. I think that B is the highest because it has hydrogen bonding. I am not sure how to differentiate A and C though. They both have about the same molar mass. The only thing I can think is that C has a double bond. Does this double bond make the boiling point of C higher than A because it is stronger than a single bond? Or perhaps the double bond is shorter which decreases branching in C making the boiling point lower than A?


texts: What are the best cleaning agents for carbon residues on glassware?

texts:
Introduction

Recenly I wanted to isolate some ascorbic acid (Vitamin C or chemically - $\ce{C6H8O6}$). I've put the filtered solution (I had to filter it because of the binder) in a flask and heated it. It didn't go as planned because then I didn't know that ascorbic acid decomposes at high temperatures, but I still decided to keep the product of the reaction. I left it on a hotplate at a high temperature and it all went back to carbon because it was there for too long (It was dehydrated).

The cleaning agent that I know of - $\ce{NaOH}$

I used a saturated solution of $\ce{NaOH}$ to clean it but there were still some flakes stuck on the wall that I couldn't reach.

It worked well for me - cleaned ~90% of the residue.

The question

Are there any other cleaning agent that'll work better than aqeous Sodium Hydroxide?


texts: Why is ATP, but not ADP or AMP, a sole source of energy?

texts: Why are three phosphate groups (such as in ATP) required for release of energy, but not two (ADP) or one (AMP) phosphates? How does breaking the phosphate bond release energy?


texts: Is there a reason radioactive decay is exponential, as in after an extremely long time some of the original compound remains, or is this just an empirical model? Also, why does $\ce{^{238}U}$ have a much longer half life than $\ce{^{210}Pb}$, for example?


texts: How to avoid the appearance of extra hydrogens from lattice packing of PDB file?

texts:
I'm struggling with a pdb file of a unit cell that has a $\ce{CH3}$ which becomes a $\ce{CH6}$ when some software performs replication transformations. I've tried pack it with Avogadro and Mercury.

There is a way to avoid this by only changing something in the PDB file?


texts: Difference in a array of probability density plots for the electron in its lowest-energy states of Hydrogen atom

texts:
Dynamic Periodic Table
If you visit Dynamic Peridic Table, You will notice that for n=4 l=3,2 m=0,0, and n=2,l=1, m=0 there is a difference in  the probability density plots for electron in its stationary energy state of Hydrogen atom  and image of arrays of probability density plots attached herewith titled'Hydrogen Wave Function'.
Why do we found such discrepancies? or are these plots  same?
If any member knows the answer to this question, may reply.


texts: Esterfication of 2,2,2-triphenylethanoic acid

texts:
Explain the formation of (1,1,1-triphenylmethyl)methyl ether when a solution of 2,2,2-triphenylethanoic acid in concentrated sulfuric acid is poured in methanol.

I cannot figure out where is one carbon atom lost. Has it escaped as $\ce{CO2}$? Or is there something more strange happening.

I wouldn't call this reaction an esterification. There is no ester functional group in the final compound.

I guess there's some special role of the three phenyl groups but I'm unable to come up with any mechanism. I hope dehydration is involved as one of the reaction steps.


texts: Pressure of carbon dioxide due to two simultaneous equilibriums

texts:
$1~\mathrm{mol}$ each of barium carbonate and calcium carbonate are put in a closed vessel which is maintained at $300~\mathrm{K}$ temperature. Two equilibria are established, with the respective equilibrium constants:
  $$\begin{align}
&\ce{BaCO3(s) <=> BaO(s) +CO2} & K_p&=3\mathrm{~atm} \\
&\ce{CaCO3(s) <=> CaO(s) +CO2} & K_p&=5\mathrm{~atm}
\end{align}$$
  Find the final pressure exerted by carbon dioxide.

Let $n_1$ moles of $\ce{CO2}$ form from barium carbonate and $n_2$ moles of $\ce{CO2}$ form from calcium carbonate.

Then $$K_{p1}=(n_1+n_2)RT$$
$$K_{p_2}=(n_1+n_2)RT$$

But the above two equations are not meaningful because $K_p$ values are different. (what mistake am I making here?)

Let barium carbonate be put into the vessel first. Then there will be $5\mathrm{~atm}$ of carbon dioxide. Then If I put calcium carbonate, will it affect the equilibrium mixture? The answer he gave was $5\mathrm{~atm}$.


texts: How the attraction takes place between a hydrogen atom and the acceptor atom in a hydrogen bond

texts:
In hydrogen bonds present in water,does the hydrogen atom attracts to the lone pair of electrons present on the oxygen atom or to its partial negative charge? If former is the case are there any examples in which the acceptor atom do not have a lone pair of electrons but it attracts hydrogen because of its partial negative charge.
I got confused because I saw in YouTube video where the definition of hydrogen bond was given as: A hydrogen bond is a weak bond between a partially positive hydrogen atom and a partially negative electronegative atom


texts: Why does soapy dishwater lose soapiness over time?

texts: I wash dishes by making a concentrated solution of dishsoap (eg dawn) and water.  Sometimes I'm lazy and forget to wash the container containing the soap solution, and it sits on the counter overnight.  In the morning, the solution always loses its "soapiness" - agitation no longer induces bubbles, and there is no characteristic slippery feel to the solution.  Why?  This happens regardless of the container material - glass, plastic, ceramic, or stainless steel.  Tagging oxidation because it's the only potential cause I can think of.  If so, how though?


texts: How can the effect of a pulse sequence on a strongly coupled spin system be analysed?

texts:
In introductory NMR theory there are two models which are commonly used to analyse the effect of a pulse sequence: namely, these are the vector model and the product operator formalism.

The vector model serves as a useful pictorial representation, but is generally considered too simplistic to be used when the system contains coupled spins. Usually at this point the product operator approach is introduced, based on the Liouville–von Neumann equation

$$\frac{\mathrm d\hat{\rho}}{\mathrm dt} = -\mathrm{i}[\hat{H}, \hat{\rho}]$$

and its solution $\hat{\rho}(t) = \exp(-\mathrm{i}\hat{H}t)\hat{\rho}(0)\exp(\mathrm{i}\hat{H}t)$. Then with a knowledge of the initial density matrix $\hat{\rho}(0)$ and the relevant Hamiltonians $\hat{H}$, the density matrix after a pulse sequence $\hat{\rho}(t)$ can be calculated.

Yet, it is also stated that the product operator approach "only applies to weakly coupled spin systems" (Keeler, Understanding NMR Spectroscopy 2nd ed., section 7.1.3). "Weakly coupled", of course, means that the coupling constant $J_\mathrm{IS}$ is much smaller than the difference in resonance frequencies $|\nu_\mathrm I - \nu_\mathrm S|$. This raises two questions:

Why does the product operator formalism not work for strongly coupled systems?
How can the effect of a pulse sequence on such systems be analysed?


texts: Configuration of endocyclic double bond in Vitamin A

texts: I think the double bond inside the ring of vitamin A should have an (E) configuration. Am I wrong? I don't think I'm assigning the priority correctly.


texts: Why does the exchange interaction in Hartree-Fock theory lower the total energy?

texts:
In Hartree-Fock theory, the expectation value of the total energy can be written as

$$E = \langle\Psi| H |\Psi\rangle = \sum_{a} \langle a| h |a \rangle + \frac{1}{2}\sum_{ab} \big( [aa |bb] - [ab|ba] \big),$$

where the first summation contains the single electron kinetic energy and the interaction energy of the external field. The second summation contains a classical Coulombic term plus an exchange term. The exchange term is introduced by the antisymmetrization of the wavefunction (through a Slater determinant) and takes the form of

$$[ab|ba] = \int \mathrm { d } \mathbf { r } _ { 1 } \mathrm { d } \mathbf { r } _ { 2 } \psi _ { a } ^ { * } \left( \mathbf { r } _ { 1 } \right) \psi _ { b } \left( \mathbf { r } _ { 1 } \right) \frac { 1 } { r _ { 12 } } \psi _ { a } ^ { * } \left( \mathbf { r } _ { 2 } \right) \psi _ { b } \left( \mathbf { r } _ { 2 } \right).$$

This integral is always positive, and so the exchange contribution to the total energy is always negative. Can anyone explain why the exchange contribution to the total energy is negative? In Fermi-Dirac statistics, we can see that the effect of Pauli exclusion of indistinguishable Fermions is an effective outward pressure. Hartree-Fock theory seems to suggest that the exchange interaction lowers the energy of the system, and therefore stabilizes it. Shouldn't the effect of exchange, therefore, be an effective inward pressure?


texts: Kinetic isotope effect - why transition states taken as isoenergetic

texts:
I am working on the derivation of the equation below for the difference in activation energies for the two reactions (1) and (2).

I've done the derivation, but I am unsure on some of the approximations I have used. When considering the activation energies I have just used the zero point energy for the C-H and C-D bonds - I am not sure why I can do that, but I assume its because the rest of the zero point energies cancel out.

Secondly I am confused why I can consider the transition states as isoenergetic, as to me they look like they would different energies.

Thank you for your help.


texts: Reaction pathway - Extra molecule used in one step only?

texts:
I am currently building a reaction mechanism through Gaussian calculations. I successfully found each TS and intermediates through the different jobs (opt, freq, irc) for my 3-step mechanism from reactants to my products.
However, I was questioning myself about one step in particular which could involve one extra molecule. Here's a scheme of my system:
$$\ce{A + B -> C <=> D -> E}$$
Where A and B are in same equivalence experimentally.
All steps are characterized by stable intermediates and reasonable energy barriers confirming experimental data, except one step. The step from C to D is a simple tautomerism from enol to ketone. However, this proton exchange needs to be driven by a proton acceptor like B to have a energy barrier that is closer to the reality. Then, for my system, an extra molecule B could be implied in the mechanism only from this C to D step.
Practically, you perform optimization of your TS and complex of products and reactants involving all molecules for the reaction step. However, I was wondering if I can draw a reaction pathway from A and B to E without the extra molecule B and involving it only for the step where it is required (as a sort of catalyst). Let's make it more clear:

I take the step A and B to C as already calculated
I perform C to D with an extra molecule B acting as proton acceptor for that step
I take the step from D to E

In this way, the extra B is used only in the second step of the mechanism and I can get from there the relative energies. However, in that case, how can I draw the mechanism plot with all relative energies ? C or C + B have totally different energies. Am I forced to re optimize all my system with an extra B molecule ?


texts: Energy capture photochemistry with ionizing radiation?

texts:
Chlorophyll mediates a photochemical reaction: energy from a visible light photon is used to reduce CO2 to CHO, and the energy from that photon can later be recovered when CHO is oxidized back to CO2 in an organism.

Is there any analogous photochemical reaction where energy from shorter wavelength ionizing radiation (like Xrays or gamma rays) is captured in a molecule such that it can later be recovered chemically to do work?  I do not think any biochemistry happens along these lines but maybe synthetic corroles or porphyrins have been made that can accomplish this.


texts: Why is the overall change in entropy of Photosynthesis positive?

texts:
Net Reaction:
$$\ce{6CO2(g) +6H2O(l) -> 6O2(g) + C6H12O6(aq)}$$
The net reaction shows that 12 moles become 7 moles; 6 of gas,and 1 complex molecule.
This implies a decrease in entropy over the net reaction.
However, from reading further sources, it seems that the change in entropy is positive, but they don't justify it. Why is the overall change in entropy positive, over the series of reactions that make up this process? Could this be linked to the role of UV Light in this reaction?


texts: What is the product of magnesium reacting with carbon?

texts:
$$\ce{Mg + C -> X}$$
  $$\ce{X + H2O -> Y}$$
  Determine unknowns X and Y.

Now the problem is I think the answer should be $\ce{X=MgC2}$ and $ \ce{Y=C2H2 + Mg(OH)2}$. But the given answer was $ \ce{X}= \ce{Mg2C3}$ and $\ce{Y}=\ce{C3H4} + \ce{Mg(OH)2}$

I tried to google the answer but where some website say $\ce{C3H4}$ is correct some say $\ce{C2H2}$ is.  Funny thing is in the exam just after that one we got the same question and this time the $\ce{C2H2}$ was the answer (and I wrote $\ce{C3H4}$)


texts: How to solve the Schrödinger equation of 1D hindered rotor?

texts:
I have the following equation:

$$-\frac{{{\hbar }^{2}}}{2I{}_{r}}\frac{{{d}^{2}}\psi }{d{{\theta }^{2}}}+V\left( \theta  \right)\psi =E\psi, $$

with

$$V\left( \theta  \right)=a+\sum\limits_{n=1}^{N}{{{b}_{n}}\cos \left( n\theta  \right)}+\sum\limits_{m=1}^{M}{{{c}_{m}}\sin \left( m\theta  \right)}$$

where the notations are straightforward ($\theta \in \left[ 0,2\pi  \right)$). I would like to get $K$ eigenvalues of the spectrum. How to integrate it (with some derivations)? Is there any non-commercial program which is able to provide them? I used MSTOR by Truhlar's group, but the potential does not contain the sine-terms.


texts: What sort of molecules or polymers are used in OLED displays?

texts:
OLED displays have been emerging as competitors for LCD displays for some time and are now common in mobile phones (see comparison of a Google Nexus 1 and an iPhone here)

The displays use small molecules or polymers that emit light when a current is passed through them (like a semiconductor LED). But what is the structure of the emitters?


texts: Derivation of formula for the degree of unsaturation

texts:
Degree of Unsaturation (DU) of an organic compound tells us about the total number of $\pi$ bonds (both double bonds and triple bonds) and number of rings/cyclic chains in the compound.

Degree of unsaturation forms an integral part of the four tools used to identify the structure of an organic compound (some of the others being structure after hydration and ozonolysis (there's one more I don't remember)).

Wikipedia states the formula of degree of unsaturation as:

  $$\text{Rings + $\pi$-bonds} = C - \frac{H}2 - \frac{X}2 + \frac{N}2 + 1$$
  where $C$ = number of carbons, $H$ = number of hydrogens, $X$ = number of halogens and $N$ = number of nitrogens

A more general formula is stated as

  $$DU = 1 + \frac{1}{2}\sum{n_i(v_i - 2)}$$
  where $n_i$ is the number of atoms with valence $v_i$.

What I'm interested is the underlying concept from which this formula is derived.


texts:
So I came across a question which asked to calculate the $\mathrm{pH}$ at which an indicator of given $\mathrm{K_{a}}$ would change colour. The solution was given in the following way
Since when the color change occurs $\ce{[HIn]=[In^{-}]}$,
As $\mathrm{K_a}= \left(\frac{[\ce{H^+} ][\ce{In^-}]}{[\ce{HIn}]}\right)$,
At $\mathrm{K_a}=[\ce{H+}]$ the colour change would occur.
And consequently from the $\ce{H+}$ concentration the $\mathrm{pH}$ was calculated, the solution imposes that during the colour change the equilibrium is attained, but how can that be since to observe colour change you add an acid or base which disturbs the initial equilibrium for which the $\mathrm{K_{a}}$ was defined and hence the now won't hold true.


texts: What's the technical term for supercharging an acid with an oxidizer? And does it always work?

texts:
In a recent Mythbusters episode, where they tested some Breaking Bad chemistry assertions, they debunked the hydrofluoric acid body-dissolving myth referenced elsewhere in Chemistry.SE in the question "Is it actually possible to dispose of a body with hydrofluoric acid?".

The answer is no, not really, and for the same reasons as my answer to the linked question; fluorine's just too electronegative to let the proton go do its acid thing.

To attempt to replicate the results (in this case dissolving out the bottom of the bathtub they were using), they moved to a much stronger acid, sulfuric, and then "supercharged" it with what they simply called their "special sauce" (as they said, they're not in the business of showing people how to dispose of bodies). They gave it away in the end, however, by saying the special sauce was "basically a lot of hydrogen and oxygen", and since it wouldn't be water the obvious candidate is hydrogen peroxide, a strong oxidizer (in high concentrations at least).

This seems to be a well-known trick of household chemistry; add household peroxide to cream of tartar or lemon juice, for instance, and watch those rust stains come right out. It also seems to be the bracingly direct way to form perchlorates in the lab; add hydrogen peroxide to hydrochloric acid, and behold perchloric acid (or a fuming crater, if you weren't managing the exothermic nature of this reaction properly).

So, first question, what's the technical term for this trick? It can't just be "supercharging".

Second and related question, does it work for all acids and oxidizers, or do only certain combinations of acids and oxidizers have this effect?

Lastly, for purely academic purposes, what would the basic reaction have been between sulfuric acid, hydrogen peroxide and organic tissue ($\ce{HxCyOz}$)? The sulfate anion is pretty highly oxygenated as it is, so I'd imagine the combination, unlike with a hydrohalic acid forming an oxoacid, would cause the reaction to be less acid-base, and more rapid oxidation and "combustion" of the organic tissues, leaving behind mainly carbon in water and off-gassing a large amount of steam and sulfur dioxide.


texts: Reference request for the number of solvents around a solute

texts:
I want to know if there is a way to find number of solvent molecules that are directly embracing a solute molecule (something like a reference or table that shows waters of hydration).

Particularly I am interested in solvents such as water or ethanol, and the solutes acetone, acetaldehyde, 1-butanol, methylene blue, benzene, anthracene, and phenanthrene.


texts:
Are E1 elimination reactions possible from a trans dihalide alkane (like 1,2-dibromoethane) all the way to the alkyne (like acetylene)? Or is only E2 possible from the alkene to alkyne? What is the rate of reaction?

My thoughts are that E1 is a possible reaction to form the alkyne, with E2 taking place if there are any anti peri-planar hydrogens and a strong base. So, another question might be that which of these has the faster rate of reaction - an E1 reaction or an E2 reaction with anti periplanar hydrogens that are only available through conformational energies and torsional strain?


texts: Can Aquatabs be used to clean swimming pool water?

texts:
Can Aquatabs be used to prepare/chlorinate water for swimming?  They are used  to clean water for drinking so is it safe to assume that if used in proper quantity they can also clean water for swimming?

We are currently at a place where there is no pool and the temperatures are soaring, our 3 year old son has a small pool which we take along on picnics.  I was not able to find pool chlorine somewhere over here but we do have adequate quantity of aquatabs with us.

I tested this and the water smelled/tasted just like it does in a properly chlorinated pool but want to be sure if they are adequate.

Just in case, the label says

  Each tablet contains 500mg Sodium Dichloroisocyanurate (300mg Free available
  chlorine)

I am not really worried about maintaining a pH level over the matter of days, its more of a one time thing then we can change water.


texts: What's the limit on energy density for chemical reactions?

texts:
Considering energy-releasing devices such as bombs or batteries which operate on chemical reactions and not nuclear (i.e. strong/weak) forces, what are the upper bounds on the amount of chemical potential energy that can be contained in 1kg or 1m3 of ordinary matter at RTP?

Here I'm not asking for the energy density of known compounds, necessarily, but rather an answer of the type "no conceivable compound could exceed X J/kg because ..."

Extra kudos if you can add insight into limits on the rate of energy release and efficiency considerations.


texts: This question on NaCl crystalization actually got me wondering: are there any ionic amorphous solids? Like ionic crystals are crystalline materials of electrostatically-attracted ions, can ions form an amorphous phase? I can see no reason why not, but I cannot think of any example either…


texts:
The white phosphorus has a tetrahedral structure, like this:

 [Image source: Wikipedia]

The red phosphorus, on the other hand, has a polymeric structure:

 [Image source: google images]

Then what is the hybridisation state of P atoms in these allotropes?

For tetrahedral $\ce{P_4}$ in white phophorus, we can take $\ce{sp^3}$ hydbridisation, but some sites give information that P atom uses atomic 3p orbitals, as then the the angle strain is reduced from $\ce{109^\circ\rightarrow 60^\circ}$ to $\ce{90^\circ\rightarrow 60^\circ}$.

I can't find any website which gives information about the hybridisation state of red phosphorus. My chemistry textbook also does not give any information about this.

If you can give a reference to back up your answer, it would be useful to me.


texts: Are there any trends for electrical conductivity?

texts:
Which element has the greatest electrical conductivity?
  (A) $\ce{As}$
  (B) $\ce{Ge}$
  (C) $\ce{P}$
  (D) $\ce{Sn}$

I am unsure of how to approach this problem. Is there some sort of trend for electrical conductivity or some other method to determine which of these answers the question?

I am pretty sure it is not $\ce{Ge}$ as that is used for semi-conductors, and am pretty sure it is not $\ce{P}$ because that is a non-metal but I don't know how to narrow down between the others.


texts: Units on rate constants from transition state theory and DFT

texts:
I am using density functional theory (DFT) to compute the energy profile and, by extension, kinetic parameters for a catalytic process. I know that the rate constant from transition state theory (TST) can be found via the Eyring equation:

$$k=\frac{k_{B}T}{h} e^{-(\Delta G^\circ)^\ddagger/RT}$$
I believe that the derivation of this equation from TST implies that it strictly holds for reactions of the form $A\leftrightarrow [AB]^\ddagger\rightarrow P$. It's clear by looking at the units that other molecularities won't work with this equation directly (for example, $A \leftrightarrow A^\ddagger \rightarrow P$).

My concern arises because I am using DFT (specifically Gaussian) to compute the thermochemistry (as discussed here). I am able to generate a free energy landscape for my proposed mechanism, but I am concerned about the accuracy of using the Eyring equation for various molecularities.

It's clear to me how the units work out when looking at this from the perspective of partition functions. From TST, we can say that

$$k=\frac{k_{B}T}{h} \frac{Q^\ddagger}{\prod_{i}Q_{i}} e^{-E/RT}$$

for $i$ reactants, where $E$ is the energy computed from DFT, and

$$Q\equiv \frac{q_{t}}{V}q_{r}q_{v}q_{e}$$

such that the translational partition function is effectively written in units of inverse volume. So, changing the number of reactants $i$ thereby changes the units of $k$ appropriately.

Where is the disconnect between this expression for $k$ and the Eyring equation I originally show? Presumably I can use the above expression for $k$ since the partition functions are used by Gaussian to compute the Gibbs free energies, but it would be much easier to use the Eyring equation directly, especially if I am making a Gibbs free energy profile anyway.

I'm familiar with the related question posted on StackExchange in the past. However, it does not address how to actually approach various molecularities.


texts: Does the position of a functional group in an organic compound have any effect on the compound's heat of combustion?

texts: Is there a link between where the functional group is located in an organic compound and the compound's heat of combustion? It has been mentioned before that it is difficult to accurately get the enthalpy of a reaction experimentally; thus, enthalpies of formation are used instead when calculating it.This is why I looked up the enthalpy of formation of liquid at STP data for two compounds, 1-Heptanol and 2-Heptanol, which are $\pu{403.4 kJ mol^{-1}}$ and $\pu{416.9 kJ mol^{-1}}$ respectively.


texts: Is OH + CO → CO2 + H an elementary reaction?

texts:
Is

$$\rm OH + CO \longrightarrow CO_2 + H$$

an elementary reaction? How could I tell?

I could break the reaction into

$$\rm OH\ (+ M) \longrightarrow O + H\ (+ M)$$

$$\rm CO + O \longrightarrow CO_2$$

but I don't know if the former is witnessed.


texts: Can Ferrofluids vaporise to gaseous state and Condense back to liquid state and do it many times over?

texts: Here is the Link for Ferrofluids for basic idea. After going through this Wiki link, probably many people will come to a conclusion like when Ferrofluid boils, its carrier liquid vaporises and nano particles gets settle down. Therefore Ferrofluid looses its properties(destroyed). I come to this conclusion but not 100% sure. There may be some wild science going over because "nano" particles and its size. So I decided to ask here and get some help from some bright minds across the world.


texts:
In the expression of equilibrium constant, each concentration term is raised to the power of their stoichiometric coefficient. But this could affect the equilibrium constant.
For example, we can write the chemical equation of ammonia in these two ways
$$\ce{N_2(g) + 3H_2(g)<=>2NH_3(g)}$$
and
$$\ce{\frac{1}{2}N_2(g) + \frac{3}{2}H_2(g)<=>NH_3(g)}$$
This affects the equilibrium constant. How do I decide which chemical equation's coefficients to use?
I think maybe the stoichiometric coefficients used in the equation should be in the simplest ratio of natural numbers. Is that so?
Equilibrium constant should not depend upon stoichiometric coefficients because they just tell about how many molecules are striking each other to form a certain product. It shouldn't matter what the coefficients are because they do not give information about the actual number of moles reacting. Then why does the equilibrium constant (if it does) depend upon them?
I think if you could tell me how they ended up in the equilibrium constant expression in the first place, it would make things easier to understand.


texts: Is it possible to define the coordinates of an atom using other coordinates while optimizing in gaussian 16?

texts:
I know it is possible to fix the value of composite expressions using generalized internal coordinates (gic) in gaussian 16. But is it possible to assign that value to the coordinate of another atom.

For example if I have the following coordinate file

H x1 y1 z1
H x2 y2 z2
O x3 y3 z3

Is it possible to assign x3 = (x1 + x2)/2 . When optimizing this structure I would like that the x coordinate of oxygen always be the average of the x coordinates of the two hydrogen atoms.


texts: Why does screening effect decrease due to d-orbital?

texts:
In 13th group, atomic radius increases from boron to aluminium. From aluminium to gallium, atomic radii decreases. From gallium to indium, atomic radii increases. And from indium to thallium, atomic radii decreases.

The reason for this irregular trend given is screening effect. While explaining my teacher told that due to d-orbital screening effect decreases.

I can't get why?


texts:
I am currently in charge of purchacing fabrics from asia. My personal policy is to try and stay as enviromentally freindly as possible. Your answer to the following question would be of great help and would prevent me from buying the wrong product in massive quantities.

What is a TPE fabric and how does it compare to PVC fabrics?


texts: Latent Heat, Vapor pressure and Equilibrium

texts:
So after reading about this topic i wanted to share what i learned and i wanted you guys to tell me if what i am writting is correct:

A pressure vessel has propane inside and it is pressurized. The liquid is at atmospheric temperature meaning that it is in equilibrium with the outside temperature. The pressure inside the pressure vessel will change according with ambient temperature.

If I open the valve of the pressure vessel, the gas will come out and the pressure inside the vessel will decrease and the liquid propane inside the vessel will immediately star to boil so it can re-establish the equilibrium. When boiling the liquid goes into the gaseous state and to do this it requires energy in the form of heat (latent heat of vaporization).

Since the liquid has the same temperature that the outside it cannot take heat from the outside and it will need to take this energy from itself, decreasing the temperature of the liquid.

Now there is a ΔT between the liquid and the outside temperature, so the liquid will steal heat from the outside (sensible heat) so it can incease his temeprature in order to have enough energy to go to the gaseous state.

If the flow of gas that is coming out of the vessel is constant the pressure and the temperature of the liquid and of the gas will initially decrease a little but it will stabilize, because the heat that is being taken from the outside is enough to keep the liquid boiling without decreasing more of his temperature and pressure.

If the flow of gas that is coming out of the vessel increases the outside heat may not be enough to maintain the flow of gas required, so the temperature of the liquid will start to decrease (auto refrigeration) (heat absorbed by the liquid < heat used by liquid to go to the gaseous state due to the high gas demand)

If the temperature of the liquid keeps decreasing so will the pressure and if it decreases below the atmospheric boiling point, the liquid will stop boiling and the gas will stop to come out (negative pressure inside the pressure vessel).


texts: Find atomic number given the group and period

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I want to find the atomic number of an element in a short way, when I know the exact group and period of that element.

For instance; there is a question in our textbook to find the atomic number of the element which is placed in the 4th group and the 3rd period.


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How are alkalide molecules synthesized, for example, I have read in a paper that the reaction $$\ce{2Na -> Na+ + Na-}$$ is exothermic with a $\Delta H = \pu{-438 kJ/mol}$.

I have also read that in the presence of a certain type of crown ether, under specific conditions, $\ce{Na+}$ crystallizes at around $\pu{-20 ^\circ C}$.

Can someone walk me through the mechanism through which sodide, or any alkalide, in general, is actually synthesized?


texts: Reaction of CpFe(CO)2Cl with phenyllithium

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The reaction of $\ce{(C5H5)Fe(CO)2Cl}$ with an equimolar amount of $\ce{Li+[C6H5]-}$ gives a product. Draw its structure and apply the 18 electron rule.

In a question I was given the molecular weight and percentages of each element in the compound. I worked out that there is $\ce{1 Fe}$, $\ce{13 C}$, $\ce{10 H}$ and $\ce{2 O}$.

The product seems to be an iron atom surrounded with ligands, $\ce{2 CO}$ ligands, $\ce{1 C5H5}$ and $\ce{1 [C6H5]-}$ ion.

The 18 electron rule expands to 8 valence electrons from $\ce{Fe}$, 2 electrons from each $\ce{CO}$ ligand, 5 electrons from $\ce{C5H5}$ and 1 electron from the $\ce{[C6H5]-}$ anion: $8+4+5+1 = 18$. But what would the structure look like?  Especially how is the $\ce{[C6H5]-}$ anion connected?


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As part of the biochemical process of glycolysis, NAD+ is reduced to NADH. In other words, nicotinamide adenine dinucleotide is reduced to... nicotinamide adenine dinucleotide?

Everywhere I look tells me that NAD+ and NADH refer to the same particle with the same name, just in an oxidized or reduced form. However, NADH has one more hydrogen atom then NAD+, so shouldn't these particles have different names?


texts: Why is zinc sulfate used in daniell cell

texts: Why is zinc sulfate needed in the construction of a daniell cell.  It seems that because the zinc is getting oxidized and not reduced there is no need to have a solution of zinc sulfate as it will produced when the zinc is reduced.  The sulfate ions would simply cross the salt bridge and balance out the charges.


texts: I'm in a textile unit, where we use different chemicals. My question is what type of material should I make my tank out of to store my hydrochloric acid?


texts: Why will internal energy decrease in this reaction?

texts:
1 mol zinc reacts with 1 mol sulfuric acid in a bomb calorimeter. I know since volume is constant work done will be zero .. but why will the internal energy decrease??
I know that the reaction is not endothermic or exothermic so there is no heat change involved, and as E = w + Q, the internal energy should also have been unaffected. But in an mcq book, the answer clearly states that the internal energy is decreasing.


texts: Atomic weights of non-molecular and non-stoichiometric compounds

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Consider a composition such as $\ce{FeCo4Sb12}$.

The atomic weight for a mole of substance is usually simply calculated by looking up the atomic weights (g/mole) for each involved element and adding them together proportionally:
$$M_{\ce{FeCo4Sb12}}=1\cdot M_{\ce{Fe}}+4\cdot M_{\ce{Co}}+12\cdot M_{\ce{Sb}}$$

But this compound is not a molecule. It is a representation of the amounts: there are 12 Sb and 4 Co for every Fe atom. I could also have written it as $\ce{Fe2Co8Sb24}$.

Same compound, but the calculation will give a different $M$.

The same issue comes for non-stoichiometric compounds, such as: $\ce{FeNb_{0.88}Hf_{0.12}}$. This just says that there are 88 Nb and 12 Hf for each Fe.

How should I understand the chemical formula when calculation atomic weights of crystalline or other non-molecular compounds as well as non-stoichiometric compounds?


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Schrödinger's equation yields us the solutions of 90% probability of presence of electrons in orbitals. Hence, the electrons in theory should be able to exist elsewhere in space as well.
In that case, they could exist in another atoms' vicinity, possibly in its orbital as well. So, what would be the quantum numbers in this case? Shouldn't they be affected by possible interference, hence changin quantum properties like spin, etc.
P.S. I have very limited knowledge on quantum mechanics, so please excuse me if any statement of mine is incorrect or sounds rudimentary.