texts:
I'm a formulation chemist. My co-worker, is also a formulation scientist but has no previous formal training in chemical safety or lab chemistry settings.
I always work in the hood unless I’m just mixing fruit extracts or something non-volatile. My coworker doesn't ever work in the hood as they believe that since this goes in food it must be safe.
The lab is small and our work stations are pretty close. My coworker opens up reagent bottles and performs all other tasks on the bench top.
I don't think their reasoning is correct since in food items, the chemicals we work with are present in the ppm to ppb ranges whereas when a pure bottle of them is opened on a lab bench, they are in high concentrations. In addition we face prolonged exposure  ($8$ hr work days,$5$ days a week). The two scenarios are very different.
Also, I feel like I’ve had a sore throat ever since I’ve started working there.
I just don’t think these are prudent lab practices. Am I overreacting or does my coworker need to start working in the hood?


texts: What am I doing incorrectly with this IR/ Mass spec data?

texts:
Hello, I am trying to determine the chemical formula for the following compound.  From the IR spec, I see there is a carbonyl present.  Moving on to the mass spec, I see an M+ peak of 142, with what appears to be no Cl/Br present.

This brings me to a chemical formula of C10 H6 O (12 x 10 + 6 + 16 = 142), with a degree of unsaturation of 8, which seems off.

I feel I am doing something wrong and any help would be greatly appreciated, thank you!


texts: Why the migrator aptitude are different about different books?

texts:
In Solomons 8th

H> phenyl >3 order alkyl > 2order alkyl >1 order alkyl > methyl

In Wade 8th or Bruice 5th, they also means

H > 3 order >2 order ≈phenyl > 1 order

why the description are different about phenyl?


texts: How did J. J. Thomson prove that the cathode rays were made of negative particles and not negative rays?

texts: In Thomson's experiment, he used a discharge tube to prove that the cathode rays that emanate from the cathode were made of "a stream of negatively charged particles" because they were repelled by an applied negatively charged electrical field. Why did Thomson conclude from this experiment that the negatively-charged cathode rays were made of particles, and hence the discovery of the electron? Why did this force him to conclude that the rays were really particles? What am I missing here?


texts: Molecular explanation of the Hofmeister Series

texts: The Hofmeister Series is a useful metric in understanding how to precipate proteins. However, wikipedia and many other source indicate that the order of the series is rather empirical. I'm curious about the variety of explanations of the mechanism of the series as well as the application of the series to other non-protein macromolecules.


texts: Difference between polypeptides and polyamides

texts:
I can't seem to find a very good explanation of the difference between polypeptides and polyamides. So far, I know that polypeptides are a type of polyamides, but that is about it. My guess is that the term polyamides refers both to the polymers made from amino acids and those made from diamines and dicarboxylic acids, but polypeptides are only those made of amino acids, but this is just a guess...

Thank you in advance!


texts: Molecules having higher enthalpy of vaporization and boiling point than another but with lower entropy of vaporization?

texts:
I came across the Trouton's rule that predicts the entropy of vaporization of most molecules to be around 85~88kJ/(K mol). It is said to fail when there is hydrogen bond between molecules.

When I checked the entropy of vaporization for linear alkanes, it increases with molecular mass which looks reasonable to me because a liquid with greater volume should expand more once it transits completely into gas than those with lesser volume. Eventually, the increase does slow down as the values get close to ~90kJ/(K mol).

For linear monohydric alcohols, their entropies of vaporization were higher than that predicted by Trouton's rule which I have found to be explained by their lower entropies in liquid phase due to hydrogen bond. However, I found that the entropy of vaporization of alcohols decreases instead with molecular mass. But since the boiling point and enthalpy of vaporization both increase with molecular mass. Shouldn't their entropy of vaporization increase with stability like alkanes?

So my question is: Is there any way to explain the decreasing ratio between the enthalpy of vaporization and the boiling point with increasing molecular mass for linear monohydric alcohols?


texts: How can hypochlorous acid produce the hydroxide ion?

texts: Hypochlorous acid ($\ce{HOCl})$ is an acid so it should produce $\ce{H+}$. However in reactions with alkenes, it produces the hydroxide ion like bases do. How is this possible? What is the mechanism?


texts: Book Recommendation for Molecular Orbital Theory

texts:
I posting my question here since I have seen similar questions but I haven't found the specific answer I am searching for. I am seeking textbook recommendations on Molecular Orbital Theory with comprehensive sections and explanations on diatomic molecules. I want to learn how to construct the molecular orbital energy-level diagrams and to write the electronic configuration for diatomic molecules.
I have seen several books and papers such as Mulliken's papers, Spectra of Diatomic Molecules book by Herzberg, Molecular Quantum Mechanics by Atkins, and other modern books, etc but unfortunately, I haven't found sections that treat other than simple diatomic molecules. To be more specific, homonuclear diatomic molecules and Hydrides (i.e. LiH, BH, CH, ...) in the case of heteronuclear diatomic molecules. So I am looking for books that treat molecular orbital theory more than simple diatomic molecules (moderate and heavy heteronuclear diatomic molecules) and I haven't found any!
Any help in this regard is much appreciated.


texts: Chemical reaction and shift in magnetic susceptibility sign

texts:
I'm trying to find an easy experiment involving a chemical reaction in which two paramagnetic reactants A and B react to give a product which is diamagnetic (or the reverse). The idea is to show that A is paramagnetic, B is paramagnetic, but A+B --> C is diamagnetic.

Or, another experiment: an experiment in which a change in temperature changes paramagnetic to diamagnetic (or the reverse). I've seen such an experiment but cannot remember the details. All I can say is that there was a color change and, at the same moment, a paramagnetic/diamagnetic shift


texts: What molecules are produced in carbon arc lamp and how do they produce light?

texts:
I am curious about the chemistry of the arc lamp (an indirectly for the incandescent bulbs) thus I would like to ask the following.

It is a common understanding that the electrons pushed inside an arc lamp -- let's assume a carbon one, that is with electrodes in graphite -- will collide on the atoms of the carbon crystal and increase their kinetic energy rising those in the cathode to about 3600 degrees and those in the anode to 4200 degrees. My questions are:

Why is the cathode, where the electrons arrive first and at full energy, cooler than the anode?
What kind of molecules are produced at the electrodes? It is said that carbon evaporates at the electrodes when the current is allowed to flow between them. What is the vapour of carbon? From wikipedia, dicarbon is listed, but what would be the reaction from graphite (pure carbon) to dicarbon?
If dicarbon is produced by evaporation on the arc lamp, would that be produced also in the old incandescent lamps that used carbon filaments, such as that made by Edison?
Does dicarbon react with oxygen? Does it oxidise to carbon dioxide or monoxide?
And finally, how does dicarbon produce light? I imagine that it must be at a high energy state and photons are released with the decay of the electrons to their ground levels, is that correct? Is there some kind of quantitative measure of why arc lamps are more luminous than incandescent or halogen lamps?

Thank you


texts: Connection of term symbols with specific microstates for atomic carbon

texts:
I'm currently studying atomic term symbols. I wanted to try it on a simple atomic carbon with the electron configuration $1s^22s^22p^2$.

I know, that only open-shell electrons are involved in the term symbol classification, so that leaves us working with solely 2 electrons in $2p$ sub-shell.

First of all, we have ${6}\choose{2}$$= \frac{6!}{2!(6-2)!}=15$ possible microstates for the $1s^22s^22p^2$ configuration.

The microstates are listed in the following table:

And, if I understand it correctly, we can categorize them into several "subsets" labeled with the corresponding term symbols.

The atomic term symbol is defined as ${}^{2S+1}L_J$.

In our case, the possible values of S, L and J are following:
$$\max(M_L) = \max(L) = +2 \Rightarrow L = 0,1,2$$
$$\max(M_S) = \max(S) = +1 \Rightarrow S = 0, 1$$
$$J = L+S, L+S-1, \ldots, |L-S| = 3,2,1,0$$

Considering possible values of $S$, multiplicity can be $1$ or $3$, i.e. singlet or triplet. Values of $L$ enable symbols $S,P,D$.

So, our presumed set of states is ${}^3D, {}^1D, {}^3P, {}^1P, {}^3S, {}^1S$.

${}^3D$ "contains" $S=1$ and $L=2$. In that situation, both electrons would have to be spin-up and positioned together in the orbital with $m_l = +1$. That is impossible, as it contradicts Pauli exlusion principle. I.e. the state ${}^3D$ does not exist.

${}^1D$ is possible ($L=2,1,0, S=0$), so we can compute the number of corresponding microstates $N$  with the formula $N = (2L+1)(2S+1) = 5\cdot 1 = 5$.

Using the same formula, ${}^3P$ is going to contain 9 microstates.

With the "substraction method" described in this video, we can arrive to the conclusion, that both ${}^1P$ and ${}^3S$ won't exist.

And finally, ${}^1S$ will contain the last one state.

Question

Now I know the possible term symbols, but I'm not sure, which microstates belong to them specifically.

It's clear, that microstates 13 and 15 will belong to ${}^1D$, but how can I determine it for the other states? ${}^1D$ should contain 3 more microstates with $S=0$ and $m_L$ being equal to -1, 0 and +1, but there are multiple candidates for every configuration.

So how could I distinguish between, e.g. microstates 7 and 9 or 8, 11 and 14?

I don't understand this point, as even $J=2$ for ${}^1D$, so it can't be used to distinguish among the "similar" microstates and to assign them properly.


texts: What is the relation between the following two optical isomers?

texts: I think they should be diastereomers, but the answer to this question is enantiomers, if it is enantiomers then how?


texts: Why is use of calcium carbide as an artificial fruit ripening agent banned?

texts:
Fruits like mangoes can be ripened using agents like ethylene, acetylene or calcium carbide. Of these, the latter is dangerous and is banned in most countries. Wikipedia says it is because calcium carbide has traces of arsenic and phosphorus. Is there any other reason?

Will it still be unsafe if pure calcium carbide is used?


texts: Remove empty space from structures with R and S groups

texts:
We receive structures from a server within our company. Those structures are transferred as MOL files. Some of these structures contain R and/or S groups. Some of the creators of these structures create a really large empty space between the actual structure and the groups. We have currently ~30.000 structures in our database. Around 2.000 of these structures are flawed.

I have attached how such a structure might look at the bottom, as the image is quite large.

What I am trying to do now is to remove that empty space.

The process is currently receiving the MOL files wrapped within an XML file that does have additional information to store along with the structure. That process is written in Java. Up to now we do not have any library within the project to process and manipulate structures, as we have just parsed the MOL as String from the XML file and written it into a CLOB field in the database.

I know that libraries like the CDK exist, but right now I do not know if it can help me with that task.

I have pasted the actual mol file here.

If we open it with a viewer it looks like this:


texts:
Given
$$\ce{2 SO2(g) + O2(g) <=> 2 SO3(g)} \quad \Delta_\mathrm{r}H = \pu{-196.0 kJ mol^-1}$$
and $\Delta_\mathrm{f}H(\ce{SO2}) = \pu{-296.0 kJ mol^-1},$ find $\Delta_\mathrm{f}H(\ce{SO3}).$

I have chosen to solve this by constructing a Hess cycle and have come up with the following:

This method has lead me to the correct procedure of solving the equation: $$\Delta_\mathrm{r}H = -2\Delta_\mathrm{f}H(\ce{SO2}) + 2\Delta_\mathrm{f}H(\ce{SO3})$$
However, it is not entirely complete in my opinion and I am unsure on how to proceed in completing it, specifically on what I should place below the two arrows.
I am aware that it should be some combination of $\ce{S + O2}$ but am unaware on how exactly the coefficients would work.


texts: Proof of Concentration dependence of molar conductivity

texts: If we go by the simple electron model, Conductivity/Concentration=carrier charge*mobility and mobility is only dependent on temperature for electrons. My question is regarding strong electrolyte, I can somewhat understand the mean activity coefficient calculation using ionic strength, but still, how does the √c dependence of molar conductivity comes about in Kohlrausch Law?


texts:
What reagents are required to form 1-[1,5-dimethyl-3-phenyl-4-(propan-2-yl)-1H-pyrrol-2-yl]propan-1-ol with 1,2-dimethyl-4-phenyl-3-(propan-2-yl)-5-propyl-1H-pyrrole as starting material?

Is it possible for the starting material to react with a halogen gas e.g. bromine to form a bromine on the carbon and then react with e.g. NaOH to form the OH with Br as the leaving group?


texts: is it possible to make ethanol from ethane through a chlorination / hydrolysis two-step procedure?

texts:
$\ce{C2H6}$ is chlorinated in presence of sunlight to form $\ce{C2H5Cl}$ and $\ce{HCl}$.
$\ce{C2H5Cl}$ is then reacted with water to form $\ce{C2H5OH}$ + $\ce{HCl}$


texts: What will be the major product on chlorination of m-nitrophenol?

texts: I came across a question asking for the major product on chlorination of m-nitrophenol. In my opinion the deactivating nature of nitro group should control the regioselectivity, but I found out the answer to be 4-chloro-3-nitrophenol. But why is the activating nature of the hydroxyl group dominating over the deactivating nature of the nitro group?


texts: Peak at m/z = 39 in mass spectrum of 3-chloropropene

texts:
I've noticed that in the mass spectrum of 3-chloropropene, there is a peak at m/z = 39, which to me, indicates the formation of the C3H3 ion.

However, given that 3 bonds would have to be broken to form this ion, how can the frequency of this cleavage be explained?


texts:
My friend recently bought a ruby gem from a store and asked me how to test whether its an original one or a duplicate.

Are there any ways to test it using only domestic materials?


texts: Electrolytic conductivity vs metallic conductivity in a galvanic cell

texts:
I'm analyzing the current output of a galvanic cell with aluminum electrode in aluminum sulfate solution and platinum electrode in acetic acid solution.

What I am confused about is whether molar conductivity will account for current resistance in the cell even though the electrons are being transferred through the metallic electrodes. Or is it just the metallic conductivity that accounts for current resistance?

If molar conductivity is also one of the reasons for current resistance in the cell, how is it?


texts: Does Amoxicillin (as trihydrate) degrade in stomach acid?

texts: I crushed my antibiotics (amoxicillin + potassium Clavulanate). Does it deform in the stomach acid and therefore become useless? Or does the acid have no effect and the amoxicillin goes directly into the intestines and blood stream subsequently?


texts:
I have progressed quite enough in infrared spectroscopy, and now I'm looking at the spectrum of alkanes in detail. I found out that straight chain alkanes have this long chain band in the spectrum:

The infrared spectrum of decane. Taken from: Introduction to Spectroscopy, Pavia et. al.

On the other hand, cyclic one's don't have this band:

The infrared spectrum of cyclohexane. Taken from: Introduction to Spectroscopy, Pavia et. al.

I also found this info in my book:

  $\ce{CH2}$ - The bending (rocking) motion associated with four or more $\ce{CH2}$ groups in an open chain occurs at about $\pu{720cm^-1}$ (called a *long-chain band).

I am still perplexed. Why can't the $\ce{CH2}$ groups in the cyclic chains undergo rocking vibrations? Why is this specific to the open chained ones?


texts: Are intermolecular forces a type of chemical bond?

texts:
My chemistry teacher told me that chemical bonds are of two types: intramolecular and intermolecular. He said that intermolecular forces come under the category of intermolecular chemical bond.

I have never read such statement anywhere. Nor can I find anything on the Internet that would support this statement.

My understanding is that chemical bond is a force that holds atoms together in a chemical species. Since intermolecular forces do not hold atoms together, they should not be termed as chemical bond.

So, are intermolecular forces a type of chemical bond?


texts: Concentration of a species outside buffer region (polyprotic acid titration)

texts:
I'm wondering if you titrate a polyprotic acid, say, $\ce{H3PO4}$, with a strong base, and you successfully pass the first equivalence point and are maybe at the $\mathrm{pH}=\mathrm{pK}_{a2}$ point now, how would you find the concentration of $\ce{H3PO4}$?

Is there none left? I don't have a specific homework question, I'm just wondering.

Attempt at a solution:
I thought maybe you would find the equilibrium concentration of $\ce{H2PO4-}$, find the $\mathrm{pH}$, and use the $\mathrm{pH}$ to find $\ce{OH-}$. Then, you could write the equilibrium, $$\ce{H2PO4- + H2O <=> OH- + H3PO4},$$ and without making an ICE table, substitute your equilibrium values into the $\mathrm K_a$ expression.


texts:
One mole of Van der Waal gas is compressed from $\pu {20 dm^3}$ to $\pu{10 dm^3}$ at $\pu{300 K}$. Given $a = \pu{3.60 dm^6 mol^-2}$ and $b = \pu{0.44 dm^3 mol^-1}$. Find $\Delta H$.

$\Delta H = -\mu C_p \Delta P + C_p \Delta T$

Since for VDW gas $ \displaystyle \mu C_p = {2a\over RT}- b$.

The process took place at $\pu {300 K}$ which means $\Delta T = 0$.

$\therefore  \Delta H = -\mu C_p \Delta P + C_p \Delta T = \left(-{2a \over RT} + b\right)\Delta P = \pu{0.4399 kJ/mol}$.

But the answer is $\pu {-30.5 J/mol}$

I think my mistake is taking $\Delta T = 0 $ but if that were the case what should I take as $\Delta T$, I don't even know the process.

Is the author's answer correct ?


texts:
In the reaction mechanism of formation of Acetal from Hemiacetal, why doesn't H+ attack the Oxygen of OR Group instead of the OH?

Since O in OR group has +I effect from two alkyl groups, shouldn't it donate its lp more easily?


texts:
Looking at prop-2-yn-1-ol spectrum that was taken from:

Spectrometric identification of organic compounds. Robert M. Silverstein and G. Clayton Bassler. J. Chem. Educ., 1962, 39 (11), p 546. DOI: 10.1021/ed039p546.

Why OH peak is so sharp? And why it is located around 1 ppm? The book does not specify the solvent used.

At the same time if one takes a look at 1H NMR spectrum of the same compound taken on 90 MHz machine in CDCl3. Source: Spectral Database AIST with SDBS No. 74HSP-00-252

Why the OH peak shifted so much? But it is still as sharp as in other spectrum.  Please someone explain such pattern.


texts: Hyperconjugation in bridged carbon systems

texts:
While studying about hyperconjugation, I came across the following compound which posseses one α-hydrogen (with respect to the $\mathrm{sp^2}$ hybridised carbon atom with an empty $\mathrm{p}$-orbital), however, apparently does not show a hyperconjugation effect.

This led me to draw an ‘assumption’ that an alpha hydrogen on a bridged carbon atom may not get involved in hyperconjugation when placed next to a carbocation, alkene, free radical, or an arene. Is this true? If so, then why?


texts: How many electrons does each shell hold?

texts: why some times 2nd shell onward it can hold 8 electrons and other times it is like they can hold K2 L8 M18 N32? when do i have to use first method(K2 L8 M8 N8) and when to use second method (k2 L8 M18)? I'm really confused.


texts: Stereospecificity of the bimolecular electrophilic substitution reaction

texts:
We know that $\mathrm{S_N2}$ reactions always go with inversion at the saturated centre (they're stereospecific) and $\mathrm{E2}$ reactions are always anti (also stereospecific).

I recently observed in a paper an example of what was called an $\mathrm{S_E2}$ reaction, but can't understand how the stereochemistry could be predicted in this case? Is it also stereospecific, or is there some other factor involved?


texts: Which functional group gets reduced first?

texts:
The following is a reduction reaction. In the reduction of 2 to 3, keto group undergoes reduction by nucleophillic addition.

Ester could undergo nucleophillic acyl substitution to give an aldo group, further reduced via nucleophillic addition again.

My question is, during such reductions, is keto group reduced first or ester group gets reduced first?


texts:
I came across an interesting question with some physical chemistry students today. Based on the following steps, we're uncertain whether the statement in the title is/could be true. Assuming $dN = 0$,

Enthalpy's natural variables are Entropy and Pressure:

$$dH(S,p) = TdS + Vdp \space (1)$$

Enthalpy can be expressed as a total derivative of Temperature and Pressure:

$$ dH(T,p) = \frac{\partial H}{ \partial T}\vert_p \space dT + \frac{\partial H}{\partial p}\vert_T \space dp \space (2)$$

Total Enthalpy is $$H = U + pV = TS - pV + \sum_i \mu_i N_i + pV = TS + \sum_i \mu_i N_i \space (3)$$

Thus, taking partial derivatives in (2),
$$ dH(T,p) = SdT + 0 \space dp \space (4)$$

This means that, if $ dH(S,p) = dH(T,p)$,

$$ SdT = TdS + Vdp \space (5)$$ must be true. Can anyone see something wrong?

This seems to boil down to a math question: are two differentials of the same function (always) equal if expressed by different variables?


texts: Stereoselectivity of 1,3-dipolar cycloadditions

texts: How do the 1,3-dipolar cycloadditions follow the endo rule as in the reaction below, where the anti diastereoisomer is formed predominantly?


texts:
I would like to create tiny colored drops slowly falling down in a transparent liquid.

The diameter of the droplets must be around 2mm, and their speed must be approximately 0.5 mm / sec.

For that, I need the colored liquid to be slightly more dense than the static liquid.

The easiest setup is to drop water into oil with a syringe.

However, when I drop water from air, the oil surface tension prevents water drops to fall slowly into the oil.

And when I put the needle in the oil, the water accumulates around it and creates huge drops.

I would also like to pump back the water at the bottom to re-inject it later on; so the two liquids must be immiscible.

Is there a simple way to solve this problem?

A better setup would be to increase the oil density so that I can drop it in water (which is cheaper, so much better if I need to scale up my system). I asked another question for that purpose but I could not find any cheap heavy compound miscible with oil.


texts: How to read mutual solubility curves of salts with a common ion?

texts:
Came across a few graphs that represent the mutual solubility of two compounds in a solvent, for e.g., solubility of $\ce{KCl}$, and $\ce{NaCl}$ in $\ce{H2O}$.
On these particular graphs, I can see $x$-axis as $\pu{g}/\pu{100 mL}$ of $\ce{KCl}$, on $y$-axis as $\pu{g}/\pu{100 mL}$ of $\ce{NaCl}$. And the graph has multiple lines each representing a curve at a specific temperature.
I just wanted to understand how to read these type of graphs:

To me the graphs represent a point wise mechanism. For example, if I pick a spot on the $x$-axis, with $\pu{50 g}$ $\ce{KCl}$ at $\pu{80 ^\circ C}$, does that mean if I dissolve $\pu{50g}$ $\ce{KCl}$ at $\pu{80 ^\circ C}$,then I will not be able to dissolve $\ce{NaCl}$ in it?
Or does it mean if I have a starting condition where I have $\pu{50g}$ $\ce{KCl}$ at $\pu{80 ^\circ C}$, and I start adding $\ce{NaCl}$, then $\ce{KCl}$ will precipitate out at a slow rate till I reach point A at a very rapid rate?
The graph doesn't appear complete, or is at least missing additional info to make sense of it. I want to know what that info is.


texts:
The following is the molecule I am confused about.

Earlier in my textbook it gives an example of how to name benzenes with 2 or more hydroxyl groups:

My textbook (Nelson 12 Chemistry) is infamous for its crappiness but my school is too lazy to change it, so I've been asking a few of these questions in recent weeks.

What is the proper, IUPAC name of the first molecule depicted in this question?
Are there any other commonly accepted names for this molecule and under what convention are they named?

Personally, I would name the first molecule benzene-1,2,4-triol, but the textbook gives the name 1,2,4-trihydroxybenzene, using the hydroxyl groups as substituents.


texts: How might one determine whether Ni is more dense than Cu using only the atomic masses of Ni and Cu, and the fact that Ni has a simple cubic unit cell, and Cu has a face-centered unit cell. You are not given the radii of each element. I feel like this question cannot be answered with the given information only, considering as Ni and Cu have very close densities (0.06 g/cm^3 difference).


texts: What are pharmaceutical uses for Vanillin?

texts: What are some pharmaceutics that use vanillin? Is vanillin just an aroma and taste agent to pharmaceutics?


texts: Mismatch in the trends of atomic size and atomic radius

texts:
In the periodic table, the atomic radius decreases as we move from left to right in a period. However, the atomic volume should also decrease as a result of the decrease in atomic radius, as volume is given by $\frac43\pi r^3$. Instead, the atomic volume initially decreases upto group 14 and then increases, as is shown by the Lothar Meyer curve:

I am aware that the atomic volume is given by gram atomic mass divided by density. However, these form two contradictory theories - according to the Lothar Meyer curve, should atomic radius not follow the same behaviour? Or conversely, according to the measurement of atomic radius, should the Lothar Meyer curve and atomic volume not decrease across a period?


texts:
The rate of reaction can be measured from a concentration vs time graph of a particular reactant in a reaction.

But, if in your reaction you have different reactants of different orders surely they will each give a different concentration vs time graph and so different rate at any time t. This implies that the rate of reaction can have multiple values depending on which reactant you follow.


texts:
Van der Waals  had stated that at high pressure, pressure exerted by ideal gas on the walls of container is more than real gas.

However in this graph, one can clearly see that, the at high pressure volume of real gas tends to be more than volume of ideal gas. Hence real gas should be exerting more pressure on the walls of the container, as it occupies more volume. So why does this not hold true?


texts:
AAS (Atomic Absorption Spectroscopy) is a quantitative analytical technique used to measure very small concentrations of ions in substances. The main idea is that the sample is atomised in a flame and then light is shot through the atomised sample and the absorbance is measured.

However I don't get why they use an atomic emission lamp (a lamp made of only 1 element). What's wrong with using a normal incandescent lamp or some lamp that produces all the wavelengths at once (it would save you having to change the lamp for every test)? I've heard that multi-element lamps make the machine less sensitive due to noise but I don't understand how. If we tune the monochromator to the particular wavelength we want, it should be the same as with using an atomic emission lamp?


texts: Ways to change the spontaneity of a reaction

texts:
I can think of any other way to influence the value of $\Delta G$ than (1) change the temperature (2) providing an external source to overcome the negative cell potential

The relationship between $\Delta G$ and $E_{\mathrm{cell}}$ is $\Delta G =-nFE_{\mathrm{cell}}$

Between $\Delta H$, $\Delta S$ and $\Delta G$ is $\Delta G=\Delta H - T\Delta S$

Sometimes, temperature won't do anything to change the spontaneity. But if we change $\Delta G$ through $\Delta E_{\mathrm{cell}}$ by providing external voltage in excess of the negative voltage, and though $\Delta G$ we are also able to influence enthalpy and entropy(???).

This is the part I am not sure about. Besides the title question, a sub-question is: how in this way can we change the enthalpy and entropy?


texts: Reagent to reduce aliphatic aldehyde to alcohol while protecting double bond

texts:
I have a straight chain, aliphatic aldehyde (liquid) with a double bond in it. I want to reduce the terminal carbonyl group to an alcohol but without touching the C=C double bond. The double bond is at a beta position with respect to the end carbonyl group.
Any suggestions whether there are any reactions that may do this?
Below I am showing the configuration of the double bond relative to the end group to avoid confusion.


texts: How does Combinatorial Chemistry differ from Rational Drug Design?

texts:
I stumbled on Vertex Pharmaceuticals - Wikipedia.

It was one of the first biotech firms to use an explicit strategy of rational drug design rather than combinatorial chemistry.

Then I looked up Combinatorial Chemistry. What is Combinatorial Chemistry

     Combinatorial chemistry is a laboratory technique in which millions of molecular constructions can be synthesized and tested for biological activity.  It has generated massive numbers of targeted molecules for testing and the developing techniques of high throughput screening has automated the screening process so larger numbers of biological assays can be done.  All this together has reduced the discovery-to-market time from what used to be 10-14 years to 5-8 years.

But this doesn't explain how Combinatorial Chemistry differs from Rational Drug Design? Isn't Combinatorial Chemistry rational too? Mustn't chemists pick reactants rationally? Even if she can't predict the products, she won't picked her reactants randomly.


texts: Why is HF considered a covalently bonded compound?

texts: Why is the bond between H and F in HF considered polar covalent whereas HCl, HI, and so on are all ionic? The electronegativity difference between them suggests that it too should be ionic, yet all textbooks say that HF is covalent. Is there a good reason why?


texts: Regioselectivity of electrophilic aromatic substitution in imidazo[1,2-a]pyrazine

texts:
I am supposed to rationalise the regioselectivity of bromination of 8-chloroimidazo[1,2-a]pyrazine, as depicted in the scheme.

The left ring kind of looks like a pyridazine. If it's anything like a pyridine it'll be bad at electrophilic substitution without activation, so bromination at C–5 or C–6 is out. I guess it has to be one of the carbons in the five-membered ring. But why is it C–3 and not C–2? I am trying to draw out resonance structures and reason that way.


texts: Strongest negative inductive effect group between trimethylammonium, ammonium and dimethylsulfonium groups

texts:
Which of the following group exerts the strongest -I effect?

  $\ce{-N(CH3)3+}$
  $\ce{-NH3+}$
  $\ce{-S(CH3)2+}$
  $\ce{-F}$

My idea is that positive species exerts more -I effect than neutral species. thus, 4) is neglected. Moreover, as nitrogen and sulfur have almost the same electronegativity 3) has two methyl groups and 2) none so 2) should exert more -I effect. However, the answer key says it to 1). Why is this?


texts: Lindemann–Hinshelwood mechanism for a gas reaction

texts:
The effective rate constant for a gaseous reaction which proceeds by a Lindemann–Hinshelwood mechanism is  $\pu{1.01E-5 s^-1}$ at a concentration of $\pu{4.6E-6 M}$ and $\pu{2.21E-5 s^-1}$ at a concentration of $\pu{8.71E-5 M}.$ Calculate the rate constant for the activation step in the mechanism.

From what I've understood the equation that I should be using is:
$$ \frac{1}{k_\mathrm{eff}} = \frac{k^{'}_\mathrm{a}}{k_\mathrm{a}k_\mathrm{b}} + \frac{1}{k_\mathrm{a} [\ce{A}]}\label{eqn:1}\tag{1}$$
However I don't quite understand how this equation is derived from this:
$$\frac{\mathrm d[\ce{P}]}{\mathrm dt} = k_\mathrm{eff}[\ce{A}],\tag{2}$$
where
$$k_\mathrm{eff} = \frac{k_\mathrm{a}k_\mathrm{b}[\ce{A}]}{k_\mathrm{b} + k^{'}_\mathrm{a}[\ce{A}]}\tag{3}$$
If we assume that  $k^{'}_\mathrm{a}[\ce{A}] \gg k_\mathrm{b},$ shouldn't $\displaystyle k_\mathrm{eff} = \frac{k_\mathrm{a}k_\mathrm{b}}{k^{'}_\mathrm{a}}?$
I have only seen a similar problem using the pressure and they get a new equation from \eqref{eqn:1}, which looks like:
$$\frac{1}{k}-\frac{1}{k^{'}} = \frac{1}{k_\mathrm{a}}\left(\frac{1}{p} - \frac{1}{p^{'}}\right)\tag{4}$$
which they use to solve for $k_\mathrm{a}$ and that is the rate constant for the activation step. I don't quite understand how they get that equation either.
How is \eqref{eqn:1} derived and how can it be rewritten as the last equation to solve for $k_\mathrm{a}$?


texts: I understand that the degree of freedom is the number of ways in which a molecule can  acquire energy. I don't want you to explain the definition, but I want to see how it works. Please explain how is that a real thing, I want to see it. Try to describe the ways in which the molecule can acquire energy . I really can't see it.


texts: Removal of octadecanoic acid from paraffin wax

texts:
I have some very plain candles. I don't think they contain anything but paraffin wax and octadecanoic (stearic) acid, since they are odorless and very hard to bend, tending to crack instead (even at around 45 degrees Celsius). I want to make some moldable wax plugs for bottles without heating over about 50 degrees Celsius (it'll burn my hands, I have no other tools to use). How can I get rid of the acid? I don't particularly care if the acid is destroyed; but it would be nice if it wasn't so I could make soap or something.

Some possible ways I've thought of:

Distillation. I can't do this because it stinks and clogs up my glassware. Also, stearic acid decomposes around the same temperature as paraffin wax boils.
Dissolution of octadecanoic acid in some alcohol. Wax won't be dissolved because alcohols are polar and wax is not. However, I don't know how to actually do this as the wax may block access to most of the acid.
Neutralization of the acid using aqueous solutions of sodium hydrogen carbonate, sodium carbonate, or sodium hydroxide. This seems like the fastest way of removing acid; however the base may not come into contact with the octadecanoic acid due to separation of the layers.

What seems like the best or most effective method of removing the acid?


texts: Do the groups involved in geometrical isomerism have to be in similar planes to show geometrical isomerism?

texts:
In my textbook, under the topic "Conditions for geometrical isomerism", the following has been given:

  Groups responsible to show geometrical isomerism must be nearly in the same plane.

Is this statement really true? Because, we are well aware that disubstituted cycloalkanes which show geometrical isomerism are not planar. Eg: 1,2-Dimethylcyclopropane

Kindly explain with examples.


texts: Derivation and application of the Henderson-Hasselbalch equation

texts:
Write down an expression for the dissociation constant, $K_{\mathrm{a}}$, of a very weak monobasic acid $\ce{HA}$ in an aqueous solution in terms of the concentrations of $\ce{H+ (aq), A- (aq) and HA (aq)}$ in the solution.
  Hence, show that

  $$
\mathrm{p}K_{\mathrm{a}} = \mathrm{p}\ce{H} - \mathrm{log}_{10} \frac{[\ce{A- (aq)}]}{[\ce{HA (aq)}]} \text{ where } \mathrm{p}K_{\mathrm{a}} = - \mathrm{log}_{10} K_{\mathrm{a}}
$$

  At a particular temperature, $\pu{2.00e-3 mol}$ of the acid $\ce{HA}$ was dissolved in water and the solution diluted until the volume was $\pu{75.00 cm^3}$. When $\pu{25.00 cm^3}$ of a $\pu{0.004 mol dm^{-3}}\,\ce{NaOH}$ solution was added to that acid solution, the $\mathrm{p}\ce{H}$ of the resulting solution was found to be 6.0. Calculate the dissociation constant, $K_{\mathrm{a}}$, of the acid $\ce{HA}$ at that temperature.

Below you can see what I have tried with my current answers.

For 1, I got $$K_{\mathrm{a}} = \frac{[\ce{H+ (aq)}][\ce{A- (aq)}]}{[\ce{HA (aq)}]}.$$
For 2, I got the same answer.

But I am stuck on 3. These are the things I already know:

Moles of NaOH added: $(25/10000) * 0.004 = \pu{0.001 mol}$
Moles of acid HA present initially: $\pu{0.002 mol}$

How can I proceed further?


texts: Why is zinc oxide reduced at a temperature of 1400 degrees Celsius?

texts:
I am attaching a graph of the Ellingham diagram on which my question is based.

If we interpret the graph, $\ce{ZnO}$ is reduced by $\ce{C}$ at a temperature of $\pu{800 ^\circ C}$ to $\pu{1000 ^\circ C}$. However, the actual temperature required is about $\pu{1400 ^\circ C}$. Why is this the case?


texts: Safest way to conduct a reaction with bromine under reflux conditions

texts:
I am conducting an electrophilic aromatic bromination reaction according to literature. The substrate and intended substitution pattern do not matter, but the reported procedure requires the dropwise addition of bromine at room temperature followed by refluxing overnight. (The solvent’s boiling point is very close to bromine’s so it may be assumed that both compounds reflux.) The reaction is not conducted under inert atmosphere and as with every organic bromination I expect HBr to be a (gaseous) by-product.
Obviously, the reaction is being conducted in a fume hood whose front opening is closed as far as possible. Nonetheless, I want to limit the amount of bromine vapour that gets released into the surrounding atmosphere. I came up with the following setup:

Figure 1: A two-necked flask with a dripping funnel and reflux condenser. The glassware on top of the reflux condenser should be a drying tube (no accurate clip-art was found) containing damp $\ce{Na2S2O3}$ between cotton wool.
The dripping funnel is obviously used to add bromine dropwise to the reaction mixture and is sealed on top. The reflux condenser is open to the atmosphere through a drying tube; I filled the drying tube with sodium thiosulphate to quench any bromine vapour that makes it up there.
I did not attach the coolant flow to the reflux condenser until after the dropwise addition. This may have been a mistake, as bromine vapours had already diffused all the way up and penetrated the cotton wool and thiosulphate. It seems that these were far less effective in holding back any vapour than I had anticipated. Luckily, our coolant system is closed-circuit and the temperature adjustable. Thus, I set the cooling temperature to $\pu{0 ^\circ C}$ which seemed to reduce bromine’s vapour pressure sufficiently to clear the air in the drying tube. However, I believe there must be a better solution.
How can I run this reaction in reflux conditions while preventing bromine vapour escaping as much as possible? I had thought of sealing the entire reaction apparatus, but the reaction gives a gaseous side product (HBr) which could cause an undesired increase in pressure. I had also considered using a balloon to close off the reaction atmosphere, but I fear that both bromine and HBr will react with the rubber and destroy the balloon rapidly. What other methods exist that I may have missed?
Side note: the literature I am following was published in 1987. As expected of this era, they do not note specific precautions against bromine release.


texts:
On the following page: https://cccbdb.nist.gov/pglist.asp It appears that the point symmetry group of sulphuric acid is $C_2$. I know that $C_2$ means that there is an axis of symmetry of order 2 (180 degree rotation).
But, I am not able to visualize it in the molecule.


texts: My research is fuel cell. I need to do a open system fuel cell, but in cathode side always have gas leak. Have any one have experience to tell me, how to prevent gas leak?


texts: A liquid that forms a surface membrane that prevents evaporation but allows oxygen to pass through

texts:
I'm a biologist. I have a water solution with living cells in a tiny well (10 um). I need to keep the solution from evaporating for several days in a warm incubator. I'm looking for a liquid to place on the surface of the solution that will create a surface membrane/film that prevents or slows evaporation but continues to allow oxygen exchange. I welcome any other suggestions for achieving the same result, prevent/slow evaporation while allowing oxygen exchange.

Here are some things that we've tried and some constraints:

Increasing the humidity in the incubator is not sufficient (we've tried)
Lowering the temperature in the incubator is not an option (we want the cells to keep doing what they do)
Sealing the well is not an option (we need the solution to remain oxygenated)
What can be added to the solution is limited to substance we are sure won't react with the cells


texts: How can one distinguish an IR spectroscopy alcohol band on an organic molecule versus the alcohol bands from water in the sample?

texts:
I'm reading this IR spectra and trying to determine if the large broad band at 3388 is alcohol from an intermediate or from water in the sample. The details of the reaction, conditions, and mechanism can be found below if it's helpful.

I attempted to run a double aldol condensation of p-anisaldehyde and acetone using 2 mL of 3 M NaOH, 0.3 mL of p-anisaldehyde, and 1.6 mL of 0.625 M acetone in ethanol. I let the reaction run for 30 minutes at room temperature and recrystallized the product.

I drew all of the steps I think the reaction mechanism could have stopped that have an alcohol here:

Thanks for any advice.


texts: How does Fick's Law apply to complex diffusion and diffusion within living cells? How can Fick's Law be modified for unsteady-states?

texts:
I am trying to understand how diffusion in an unsteady system such as a living cell occurs and if Fick's law can be modified to predict the change in the concentration in the cell over time.

Fick's Law is used to determine the diffusion flux to the concentration in steady state systems and is represented by the equation

$$ J = - D \frac{\partial\varphi}{\partial x} $$

where $J$ is the diffusion flux, $D$ is the diffusion coefficient, $x$ is the position/dimension of length, and $\varphi$ is the concentration.

How can Fick's Law and Fick's second law be used to determine how the concentration of a substance within a living cell will change over time? Is this possible? Or is there another equation used in a case like this?


texts: Are all gases equal in their ability to carry with them lower volatility matter at a given temperature?

texts:
As we all know water is a great solvent in it's liquid form relative to other substances. I wonder however how it performs as a gas relative to other stuff.
Does anyone know how well steam carries compounds with it compared to other gases at the same temperature and pressure?


texts: Does increasing one of the electrolytes in a galvanic cell increase the voltage?

texts:
I would like to know how you could increase the voltage in zinc and copper galvanic cell:
$$\ce{Zn(s) + Cu^2+ → Zn^2+ + Cu(s)}$$
I know that temperature and surface area is a factor that affects the voltage, but I would like to specifically know about how concentration changes the voltage.
If I want to increase the voltage, which electrolyte do I change? The anode or cathode? And what's the reason for that?


texts: what is the difference between excitation and emission spectroscopy?

texts: I know about absorption spectroscopy but really confused between excitation and emission spectroscopy. If they are different, then how?


texts:
In refrigerator, heat energy got extracted from cold sink and dumped into hot source. This is not spontaneous so work must be done. I came across the following while reading a textbook:

  For refrigeration, if no work is done,
   ΔS= qh/Th+qc/Tc;

  -qh=qc, implying ΔS= qh/Th-qh/Tc =qh(1/Th-1/Tc)

  qh>0, 1/Th-1/Tc<0, so ΔS<0 so not spontaneous. Therefore, we need to add heat energy to the stream of heat energy flowing from the cold sink to hot source, so that the entropy increase at hot source 'covers up' the decrease in entropy at cold sink, and the total entropy increases.

It does indeed make sense if we look at the value of entropy, but how can this be feasible physically? You want to move heat energy from cold sink to hot source. In terms of molecular motions, the molecules at hot source always vibrate more vigorously and give energy to molecules at cold sink spontaneously. To achieve your purpose, you literally make the molecules at hot source vibrate faster?

If you still do not get what I am asking, imagine you have a flask of water and you want it to flow from A to B. If you punch a hole at B to remove some water at B, the water will flow to B, but adding water to B definitely will not cause more water to flow to B. Now replace water with heat energy, A with cold sink and B with hot source, I think adding heat energy to hot source should not cause cooling of cold sink.

What is my misconception here?


texts: How to interpret this formula about hydrogen bond energy

texts:
I want to evaluate some chemistry related formulas, which I don't understand.
In proteins, hydrogen bonding often occurs between the oxo group = O oxygen of one amino acid and the α-amino group (N − H) of another amino acid.
The bond energy is determined by the distance between oxygen and hydrogen and by the angle enclosed by the N-H and H-Bonds.
Let's assume the $E = (\frac{1}{d_{HO}^{10}} - \frac{1}{d_{HO}^{12}}) * cos(\alpha)$ model describes the energy of the hydrogen bond.
What is the meaning of the number 10 and 12 in the formula?

I know the angle and the distances between one O, one H and one N atom (that's all the input we got).
maybe related:
https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/hydrogen-bond


texts: Who devised the term elements? Who was the one who brought the term elements to us? Also please give a bit information on background of the man.


texts: Does simmering sparkling water change/decrease its mineral composition significantly?

texts:
I know that heating sparkling water will cause it to lose $\ce{CO2}$.

Does this have any other effects on the water that remains, such as reducing its mineral content?  I understand when non-carbonated mineral water evaporates, its minerals stay behind and create a greater mineral concentration in the water that's left. Does sparkling water behave in the same way, or do other reactions occur that cause the water to change in additional ways?


texts: Why there is no temperature scale tied to normal human body temperature?

texts:
Fahrenheit:

  The lower defining point, 0 °F, was established as the temperature of
  a solution of brine made from equal parts of ice and salt.

Celsius:

  0 °C was defined as the freezing point of water and 100 °C was
  defined as the boiling point of water

Why hasn't anyone used human body normal temperature as 0? It would be much more logical for humans to base temperature scale on our body, not something that is outside.


texts: What makes "Color-Safe Bleach" color safe?

texts:
The ability of bleach ($\ce{NaOCl}$) to change the color of garments and introduce "bleach stains" is a well-known issue. In this question:
Does bleach turn a substance white or colorless?, the accepted answer says the mechanism is breaking apart long pigment compounds.

As per Clorox's website, Clorox2 color-safe bleach uses hydrogen peroxide ($\ce{H2O2}$) and:

  "[a]t the concentration used in the laundry, hydrogen peroxide is a much less aggressive bleach than sodium hypochlorite."

I'm trying to parse this ad-copy statement into GenChem vocabulary. Is the idea that while $\ce{H2O2}$ is also a powerful oxidizing agent, it isn't strong enough to disrupt the pigment molecules in dyes (like $\ce{NaOCl}$), but still powerful enough for general cleaning / stain removal? Or is it simply a result of having a diluted product?


texts: How will the equilibrium partial pressure of carbon dioxide be affected?

texts:
\begin{equation}\ce{CaCO3(s) -> CaO(s) + CO2(g)}\quad\Delta H^\circ = +556\ \mathrm{kJ/mol} \tag{endothermic}\end{equation}

How will the equilibrium partial pressure of  $\ce{CO2}$ be affected if the volume is decreased?

So, I thought of course the moles will increase when you decrease the volume hence $pV = nRT$, thus $p = \frac{nRT}{V}$. Therefore, $p$ is inversely proportional to $V$. But, the right answer is NO CHANGE, can anyone help me to understand why?


texts:
I thought that only way a nucleus can be NMR active is when the atom has an odd mass, which means that there is an odd number of protons or neutrons and an even number of the other particle. I thought that for an atom with even mass, the number of neutrons and protons are equal, and therefore the magnetic moments would cancel.

Now I reading that if both the protons and neutrons are odd numbered (giving even total mass) the nucleus is still NMR active. What is the reason for this?


texts:
How many grams of oxygen are present at 25.0 C in a 5.00L tank of oxygen enriched air? The total pressure is 30.0 atm and the only other gas is nitrogen with a pressure of 17.0 atm.

After converting the temperature to Kalvin, I do not really know what to do.
How can I find the grams of oxygen with another molecule in the container?


texts: Should the concentrations in weight % of the components of a solution always add up to 100%?

texts:
There's a paper with this statement of a alkaline solution:

  Nanostructured CuO films were formed by immersing the cleaned tabs into a hot $(\pu{96 \pm 3 ^\circ C})$ alkaline solution composed of $\ce{NaClO2}$, $\ce{NaOH}$, $\ce{Na3PO4 * 12 H2O}$, and DI water $(\pu{3.75 : 5 : 10 : 100 wt.\%})$.

I have looked online and read that normally the wt.% should add up to 100%. However, this statement says that DI water is at 100%. Is there something I am missing?

paper in context - https://arxiv.org/pdf/1310.2975.pdf


texts: What is the electronic configuration of Cr (+1) ion

texts:
I believe it should be $\ce{d^5}$ , but i found out that it is $\ce{d^4s^1}$. Is it so?
I have not found any explanation for the following. So why the strange configuration?


texts: Boiling point of: Halogenoalkanes vs alkanes vs alcohols

texts:
We know that Boiling point (alcohol) > Boiling point (halogenoalkane) > Boiling point(alkane) with same number of $\ce C$ atoms, but is the following, good explanation of that?:

Since e.g. $\ce{CH_3CH_2-O^{\delta_1 \textbf{-}}-H^{\delta_1}+}$, similar with $\ce{ClCH2CH3}$ and with $\delta_2\textbf{-}(\text{at}\ \ce{Cl})\Longrightarrow \delta_1 \textbf{-}\stackrel{\text{bigger, electronegative}}{>}\delta_2 \textbf{-}$, thus electron pair is closer to oxygen atom, so more energy is needed to move that electron in alcohol than in halogenoalkane, so higher temperature is needed to reach boiling point.

Does this have any sence, if not then could somebody explain why does it not have sence?


texts: Determining Enthalpy Change of the Combustion of Ethanol

texts:
A worked example went something like this:

Use the following experimental data to determine the enthalpy change when 1 mole of ethanol (C2H5OH) is burnt:
Mass of water = 150.00 g
Initial temperature of water = 19.5 °C
Maximum temperature of water = 45.7 °C
Initial mass of spirit burner = 121.67 g
Final mass of spirit burner = 120.62 g

Being a worked example, I saw the worked solution and understood the process completely. What's bothering me is a fundamental flaw in the procedure that has seemed to be neglected completely.
We are relying on the idea that the combustion of ethanol will produce some energy, the amount of which can be calculated with the increase in temperature of the beaker of water on top. However, if there was no ethanol, no combustion, the flame giving rise to the combustion would still manage to heat the water up; in this sense, we do not know whether it is the flame supplying the energy to the rise in water, or the exothermic reaction that takes place with ethanol. How does the existence of such a flaw make the procedure useful to any extent? Is there anything I'm missing?


texts: How can I Solidify / cure silicon caulk used to create tubing

texts:
Curing and preventing silicon caulk from sticking to itself
Food Grade RTV Silicone Sealant Adhesive Clear 10.3oz when creating tubes.
Some videos show using hot water and some videos show using cold water and hydrogen peroxide Video link on using silicone to create tubes.  Anyone know of a more exact formula / ratios most people seem to just be guessing.
I'm not making a fuel line

I'm not making a fuel line but different size tubes which will be transporting water vapour / mist created using a ultrasonic transducer (used in pond foggers) to test with (testing a fogpoinc delivery system).
PS:  I know to use dark tubes to prevent algae growth in the tubes (this is just a delivery test setup).
I created / 3d printed different screw caps (extrusion molds) to create different size tubes to test with
See example:

Question:
Anyone know of a more exact formula / ratios curing and preventing silicon caulk from sticking to itself while creating the tubes shown in the video.  The video shows using water and hydrogen peroxide but doesn't specify the ratios to use.


texts: Why is the concentration term in van der Waals correction for ideal gas squared?

texts:
In van der Waals correction for ideal gas equation, the pressure term has a correction where concentration term is squared. I saw derivations for this and they say that the concentration is squared because the number of particles at surface and the force exerted by other particles on the particles at surface, both are dependent on the concentration. I don't get this, could someone please explain why this is so mathematically?
Edit- upon reading more, I found that van der waal gave credit to Laplace for coming up with the pressure reduction term being directly proportional to the square of the density. Could you also explain this?


texts: What is the equation that describes the variation in concentration of an inhibitor in an heterogeneous catalysis?

texts:
I find myself in quite a pinch: I have to sustain a Chemical Physics exam, and I know for a fact that the professor often asks this particular question:

  Suppose that we have both a reacting species and an inhibitor in a homogeneous solution, and we insert a solid catalyst in it. What is the equation that describes the variation of the inhibitor's concentration in this heterogeneous catalysis?

I know for a fact that four different types of flows are included (or at least the professor explained it that way): two "scalar" flows, identified by the consumption of reagent and the consumption of inhibitor, and two "vectorial" flows, identified by the creation of a gradient in concentration of the two species.

However, I can't seem to find or even build up a satisfying equation that describes it. Can someone help?


texts:
What are the irreducible representations of the C-O stretching modes in free CO, $\ce{[Fe(CO)5][Fe(CO)4]^2-}$?

I think Free CO irreducible representation is A2.

For $\ce{[Fe(CO)5]}$ irreducible representation is 2A1'+E'+A2'' but I am really not sure about $\ce{[Fe(CO)4]^2-}$.


texts:
I'm reading about water models and their dispersion coefficients, and going back to S. C. Wang's work according to the citation of an equation (Google books here)

As you can see one citation's to a biographical work, and the other to a German work.

Nowhere in the chapter I'm reading (chapter 5, ‘Resolution’, in Rowlinson’s 2002 Cohesion: A Scientific History of Intermolecular Forces) does it say what $C_6$ stands for, and it doesn't seem to be a series of $C_n$, so I'm a little confused.

There's the equation, apparently a Casimir-Polder integral

$$E_\mathrm{DS} = ‒\sum_{n=6,8,10,...} \left(\frac{C_n}{r_n}\right)$$

in something else I'm reading, but it's biochemistry and so they're skipping over actually defining these things (so I can see DFT would be density functional theory but can't actually figure out what either $E_\mathrm{DS}$ is, nor the meaning of a $C_6$ coefficient. Looking for $E_\mathrm{DS}$ is just bringing up a bunch of articles' editors in search results (Eds.).

Can anyone enlighten me as to the latter - the meaning of a $C_6$ coefficient with respect to [London] dispersion forces?

My own answer to this after more reading

  The oscillating electrons in a molecule generate not only instantaneous dipoles but also quadrupoles and higher multipoles. It is to be expected, therefore, that the London dispersion energy is only the first term in a series expansion for the attractive energy

that starts in $$u(r) = −C_6r^{−6}$$

The term comes originally from the wave equation (as Rowlinson's text does eventually describe), the number six arising from a Cartesian coordinate system for each of the two interaction partners


texts: How do CO2 Fire extinguishers procure their CO2

texts: How do CO2 Fire extinguisher manufacturers get such a large amount of Carbon Dioxide? Do they get it through a chemical reaction or burning hydrocarbons?


texts: How does the blue color of starch solution change depending on temperature and what is the cause for this?

texts:
I was doing a project for my school and im not sure the following answer is correct:
"After adding iodine liquid to starch solution the colour turns blue. By heatig the mixture loses its colour. "
I am not sure if that is fully correct, i also don't know what even is the cause for this change.
If anyone can check the answer and explain what would the cause be, i would be very grateful. Thanks!


texts: Why does one bicyclic diastereomer react faster than the other one?

texts:
I have been asked to explain the following observation:

I have a number of issues with this:

1) The fast reaction must be a syn-elimination. But how can syn E2 elimination occur? If an E2 elimination is stereospecific because it must go through an anti-periplanar transition state surely syn-peri-planar elimination cannot happen.

2) How does the slow reaction even happen? The H and the Cl are never going to be in the same plane (syn or anti).

As a side question: does the boat conformation (which the bicyclic molecule must adopt) have equatorial and axial sites like the chair conformation does?


texts: How to visualize or think about spin waves (magnons)?

texts:
According to Wikipedia: "A magnon is a quasiparticle, a collective excitation of the electrons' spin structure in a crystal lattice."

I have little pictures in my mind for other quasiparticles. For example, I can picture a phonon as (quantized) vibrations in a crystal lattice, or I can picture excitons as an electron jumping between band gaps (or HOMO-LUMO, etc.), or plasmons as quantized oscillations/sloshing of an electron gas.

I have no mental image for what a spin wave looks like. Can someone help me understand this? What would a collective spin excitation look like? Do the spins just precess faster or something of the sort? Also, how would we measure a spin excitation or spin wave?


texts: Concentration of electrolyte in rust removal

texts:
I will be attempting rust removal from a steel gas tank of about 5 liters by means of electrolysis, with steel wire acting as the anode.

For the electrolyte I've been advised to dissolve $\ce{Na2CO3}$ in water. Approximately what should the concentration be? Just looking for a ballpark estimate.


texts: Reaction energies of solids from quantum chemistry?

texts:
I was reading a paper by Catlow et al. [1], and they mentioned the dissolution of copper into copper ions, which is given by this equation:

  $$\ce{Cu2O(s) + 2 h+ <=> Cu+(aq) + 1/2 O2(g)} \tag{2.5}$$

where $\ce{h+}$  is a hole.

I am wondering whether it is possible to calculate the free energy of this reaction using quantum chemistry software? And which software will be able to perform this? I believe that this is not possible using periodic DFT due to the presence of charged ions.

References

Catlow, C. R. A.; Guo, Z. X.; Miskufova, M.; Shevlin, S. A.; Smith, A. G. H.; Sokol, A. A.; Walsh, A.; Wilson, D. J.; Woodley, S. M. Advances in Computational Studies of Energy Materials. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 2010, 368 (1923), 3379–3456. DOI: 10.1098/rsta.2010.0111.


texts: Influence of the neighbouring molecules in a crystal at the example of XeF4

texts:
For reasons of symmetry I (without deeper chemical knowledge) supposed, that $\ce{XeF4}$ has a shape like $\ce{CH4}$. But according to Wikipedia its

  crystalline structure was determined by both NMR spectroscopy and X-ray crystallography in 1963. The structure is square planar, as has been confirmed by neutron diffraction studies.

In a crystal the neighbor atoms have some influence on another and sometimes the chemical formula shows the numerical ratio between the elements but not draw the full picture of all interactions between the neighbor elements. Does the influence of the neighboring molecules in a $\ce{XeF4}$ crystal makes the square planar shap? Is it imaginable that an isolated $\ce{XeF4}$ molecule has a tetrahedral shape?

Additional question. What is the crystalline structure of $\ce{XeF4}$?


texts: How to find normal boiling temperature if vapor pressure is known in any temperature?

texts:
I can calculate the vapor pressure of the Acetone at any given temperature using the Antoine equation. Is it possible to find the normal boiling temperature of the Acetone?
(It has to be done by just using the vapor pressure at various temperatures without using any constant specific to Acetone)


texts: How to balance the reaction equation between copper (I) sulfide and nitric acid?

texts:
What is the sum of stoichiometric coefficients of redox reaction: $\ce{Cu2S + HNO3 -> S + NO2 + Cu(NO3)2 + H2O}$?

This exercise is from a multiple choice exam. I have balanced the equation:
$$\ce{1 Cu2S + 4 HNO3 -> 1 S + 2 NO2 + 1 Cu(NO3)2 + 2 H2O.}$$
Therefore I have calculated the sum of coefficients as $\sum a = 11$. This has not been offered as an answer and the correct answer is 20.


texts: Composition and pH of water produced by air conditioners

texts:
I would like to know if there are specific studies or research regarding the condensed water that is generated by air conditioners.

Many people feel that this water is acid and corrosive but could not find anything that confirms or denies this belief.

If someone could send me a link or document with a reliable scientific research would help me.


texts: Oxidation of alcohols by Ceric Ammonium Nitrate

texts:
I have realized that reaction with ceric ammonium nitrate essentially results in coordination of alcohol with $\ce{Ce(IV)}$ and my teacher referred that we should be able to proceed it to form ketone by dissociating $\ce{C-H}$ of the alcohol.I have the following doubts:
A) Precise mechanism as I am literally lost as to why the $\ce{C-H}$ being as strong bond is dissociated. what is the driving force here?
B) What is the final oxidation state of cerium as it seems that $\ce{Ce(III)}$ is produced but we initially had $\ce{Ce(IV)}$. Is there an electron transfer mechanism here?


texts: Why does the Most Stable State of an Atom Tend to be One with Full s and p Subshells?

texts:
I'm new to posting on stack exchange, although I've read a lot of it before. This question seems like it might end up being marked as a duplicate, but I've looked through a lot of the similar questions and I feel like I'm still not getting it (most answers end up just explaining that the octet rule is wrong).
I'm currently taking AP Chemistry and we've been talking about electron configuration. As I understand it, atoms generally are at a lowest energy state when they fill their outermost s and p subshells (resulting in the octet rule, as the 2 + 6 electrons in these shells add up to 8). As far as I can tell, this is mostly due to Coulomb's Law being stronger with a smaller radius and the shielding effect impacting how much protons pull on electrons. But what I don't understand, then, is why an atom would tend to gain electrons in order to fill its valence shell. Wouldn't the lowest energy state be to lose a whole shell and decrease the radius and the shielding effect? It would make the atom very positively charged, but that doesn't seem to be a problem for something like Si4+. For that matter, why have any electrons at all? Wouldn't the most stable state be for an atom to repeatedly lose electrons and just be a nucleus? Presumably this has to do with the ionization energy being too high, but why is that the case? If it's just as simple as because the electrons are attracted to the nucleus, why can any electrons be removed at all? What am I missing or where is the flaw in this reasoning?
P.S. I've found electron configuration really interesting so far, but we haven't been doing much of anything with the math that explains it. I'm taking multivariate calculus right now, and I would really like to learn about the math behind it all. Is it too early for me to start? If not, does anyone have any good introductory sources to learn about that?


texts: Why does CH2F2 have such a low melting point?

texts: The molecule is highly polar but the melting points are way lower than non polar compounds such CCl4 or other similar non polar compound. Do even dipole dipole  have an affect on boiling point or is the size of the molecule all that matters.


texts:
This is an example in my textbook that I am trying to figure out

$1/[\ce{A}] = 1/[\ce{A}]_0 + kt$

In this case:
$[\ce{A}] = 4.62\times10^{-2}\ \mathrm M$
$[\ce{A}]_0 = 0.217\ \mathrm M$
$k = 0.540\ \mathrm{M^{-1}\ s^{-1}}$

so I get this
$1/(4.62\times10^{-2}\ \mathrm M) = 1/(0.217\ \mathrm M) + (0.540\ \mathrm{M^{-1}\ s^{-1}})(t)$

the answer should be 31.5 seconds

I can’t get this answer I must be missing something
in the order that it should be.


texts:
I read that silver in the presence of hydrogen sulfide corrodes to form silver sulfide and hydrogen.
$$\ce{Ag + H2S -> AgS + H2}$$
But in the reactivity series silver is placed much below hydrogen.
So, how is this displacement reaction taking place at all?
Reference:
J. Chem. Educ. 2000, 77, 3, 328A; doi 10.1021/ed077p328A
Single Replacement Reactions. Chemistry LibreTexts.


texts: I have problem with my experiment. My experiment is acid hydrolysis of ethyl benzoate. The acid that I used is sulfuric acid. My problem is when I get the precipitate  (impure benzoic acid) I have to filter it from the solution (of course) and I need to remove the sulfuric acid from my sample or else my filter paper will not dry. But the major problem is sulfuric acid takes longer time to dry. It could takes even month. I've tried leave it for a month and it still wet. My lecturer asks me to rinse my sample + filter paper with cold water (distilled water). And when I did my sample which is the precipitate is LESS. Maybe because I used large amount of cold water. Is there are suggestions or methods to remove the sulfuric acid?


texts: Fractional distillation of crude oil and resulting fuel ratios

texts:
I understand from the diagram below that different fuels condense at different temperatures. But I don't know anything about crude oil (and very little about chemistry in general).
Could I simply refine 100% of crude oil to gasoline by heating it up to 150 °C (value taken from diagram).

Put another way, are the ratios of end products from refining crude oil fixed?


texts: In regards to the addition of hydrogen to alkynes, does the amount of moles of Hydrogen matter?

texts:
Is there any difference between having the addition of 1 mole of hydrogen to 2-pentyne with a platinum catalyst compared to the addition of 2 moles of hydrogen(H2). I was under the impression that both would result in an alkane yet I have 2 problems of that nature.
would one only result in a alkene, though I thought that only happens with the poisoned catalyst.


texts: How to convert wedge–dash structure into Fischer projection?

texts:
I am very confused when a compound with more than one chiral centre is given. How to find whether the two compounds are enantiomers or diasteromers?

Please also explain how to convert more than one chiral compound with wedge–dash structure to Fischer projection.


texts: What factors affect the chemical stability of a compound?

texts:
My question is essentially about the factors that make certain atoms in certain compounds leave the compound they are currently in in order to bond with another atom/compound.

For example, I've been taught that if you react a halo-alkane with a strong base, like KOH, a substitution occurs in which OH and the halogen change places. Why does this happen (if it does)?

Would an electronegative atom rather want to bond with another extremely electronegative atom, or one that has extremely little electronegativity? Basically, would fluorine want another fluorine, or rather something like caesium?

$$\ce{Cs + F \to CsF}$$
$$\ce{F + F \to F2}$$

My thought is that fluorine 'loves' electrons so much, and there is nothing else that loves electrons more than this guy, so this has to be the most stable compound ever that is not dissociable by any other compound/atom.


texts: What are point groups and the benefits of using them?

texts:
I have heard vague information about point groups and symmetry before but I am unsure how they actually help me predicting physical properties of molecules. How do I assign point groups and what good does it do me?

Please answer at a low level.


texts: Mechanism for the reaction between nitric acid and hydrochloric acid in aqua regia

texts:
After finding out that the following reaction takes place in aqua regia :

$\ce {HNO_3 + 3HCl -> 2H_2O + Cl_2 + NOCl}$,

I quickly got curious about what the mechanism for this interesting reaction would look like. Upon doing some thinking on  my own, I obtained the following:

$\ce {Step 1: HNO_3 + HCl -> H_2NO_3^ + Cl^-}$

$\ce {Step 2: H_2NO_3^+ -> NO_2^+ + H_2O}$

$\ce {Step 3: NO_2^+ + Cl^- -> NO_2Cl}$

$\ce {Step 4: NO_2Cl + HCl -> NOClOH^+ + Cl^-}$

$\ce {Step 5: NOClOH^+ + Cl^- -> Cl_2 + HNO_2}$

$\ce {Step 6: HNO_2 + HCl -> H_2NO_2^+ + Cl^-}$

$\ce {Step 7: H_2NO_2^+ + Cl^- -> NOCl + H_2O}$

I wasn't able to find any research papers online which published a mechanism for the reaction so I asked my friends to verify if the mechanism was plausible. They agreed that it was plausible and when asked which they thought was the rate-determining step, they replied Step 1 because nitric acid is acting as base. However, I disagree with them and would like to propose Step 5 since it is probably not easy for the chloride ion to abstract a chlorine cation from the intermediate to form dichlorine.

I would like to ask if anyone could find any steps in my mechanism which are unlikely to occur and also do state the reason for why they think so in their response. Also, do share your thoughts on what the rate-determining step would be.

Actually, I am most doubtful about Steps 1 and 2. I was wondering if the nitronium ion forms at all as they could just occur in a concerted manner.


texts: Are these chemicals suitable for disinfecting my water tank?

texts:
This is the same question that I asked before, only for another product this time. I have more detailed information about this product, including a data sheet.

There is an 8000 liter tank containing water for household use like showers and washing dishes and clothes (but not drinking or cooking). For more details, read here or here.

I need to combat harmful organisms and microorganisms in the tank, but I live in a remote rural area and can't just buy any chemicals I want. Thus, I am asking whether this product will work.

Here are the ingredients of the product:

  Water
  Sodium Hypochlorite
  Sodium Chloride
  Sodium Carbonate
  Sodium Chlorate
  Sodium Hydroxide
  Sodium Polyacrylate

Here is a full data sheet.

If this product is suitable, what is a good amount and frequency?

If this product is not suitable, which ingredient is the culprit?


texts: Distilling milligram quantities of oil like it's late 1970s

texts:
In a currently retracted* manuscript by Tomas Hudlicky [1, Retraction Watch] the following has been noted:

  Fifty years ago professors took an active part in all laboratory instructions and they taught
  advanced techniques to research undergraduates, graduate students, and even postdocs.
  During my postdoctoral stay in Geneva Professor Oppolzer personally showed me how to distill 3 mg of
  an oil after I commented that it could not be done.
  Such practices are all but absent at present.
  Students are not taught by professors, most of whom have not been at the bench for decades, but
  by more senior personnel in the research laboratory.

Does anyone know or can suggest a plausible method used by Prof. Wolfgang Oppolzer to distill milligram amounts of oil, considering this demonstration has likely took place between 1977 and 1978 (according to this CV)?

I flipped through the distillation handbook of that time [2], especially focusing on section 5.1.1 Micro- and semi-micro-distillation, and I suppose it was possible that some version of an extremely miniaturized distillation apparatus combined with a set of spinning band columns or concentric tube columns operating under reduced pressure could've been used:

  The separation of essential oils with spinning band columns at 4 to 13 torr has been reported by Spiegelberg [9].
  Examples of separations of high-molecular organic compounds with a concentric tube column are given by Jantzen and Witgert [3] and Fischer [7].

Bonus question: how relevant mastering this distillation technique would be these days?
Are there better alternatives and what are they? (Gas chromatography, I presume?)

* Thanks to M. Farooq for drawing my attention towards the article and motivating to find and actually read the original paper.

References

Hudlicky, T. “Organic Synthesis—Where Now?” Is Thirty Years Old. A Reflection on the Current State of Affairs. Angew. Chem. 2020, ange.202006717. DOI: 10.1002/ange.202006717. (Retracted 2020-06-05)
Krell, E. Handbook of Laboratory Distillation: With an Introduction into the Pilot Plant Distillation, completely rev. 2nd ed.; Techniques and instrumentation in analytical chemistry; Elsevier Scientific Pub. Co. ; Elsevier North-Holland: Amsterdam; New York, 1982. ISBN 978-0-444-99723-4.


texts: What is the effect of dilution on the degree of dissociation of a weak acid or base?

texts:
Please ponder on an equilibrium of a very weak base, say $\ce{MOH}$. This base undergoes a very low ionization, even in its pure form (pure form implies that there isn't the presence of a solvent). The concentration of  $\ce{OH-}$ ions, that our base generates, can be assumed to be $ \le 10^{-6} $. Now, let us add some water to $\ce{MOH}$ so as to dilute it. Ostwald's dilution law states that if the degree of dissociation ($ \alpha $) is very less as compared to unity, which in this case, is, it can be calculated by the equation $ \alpha = \sqrt{\frac{K_a}{C}} $. This leads to the conclusion that as I make the solution less concentrated (by dilution), $ \alpha $ increases.

But if I think of it in a different way, I get confused. For instance, please consider the simultaneous equilibria:
$$ \ce{MOH <=> M+ + OH-} \tag{1}$$
$$ \ce{H_{2}O <=> H+ + OH-} \tag{2}$$
Since the concentration of $ \ce{OH-} $ ions our base generated in its pure form was comparable to the concentration of $ \ce{OH-} $ ions generated by water, they may cause the first equilibrium to be shifted in the backward direction, thus leading to a decrease in $ \alpha $ upon dilution. Is there any point I'm missing which makes me conclude the opposite of what one concludes from Ostwald's dilution law?


texts: What component(s) of instant coffee make it deliquescent?

texts:
If I put small, separate piles of instant black coffee powder, sugar, powdered creamer, and even something very ionic like table salt out in humid air and come back in a few days, only the instant coffee will have absorbed enough water to change to a sticky tar-like blob while the other three won't change their appearance.

Is it known what substance it is in the  instant coffee powder that makes it hygroscopic and even deliquescent; giving it the ability to almost "make itself into coffee" by removing so much water from the air that it dissolves?


texts: Irreducible representations and system states connection

texts:
Let's say I have the molecule $\ce{N2+}$. Its symmetry point group is clearly $D_{\infty\mathrm h}$. But I'm confused by its irreducible representations. I know there are 8 of them, but as I understand it, they're all representations of the same group, just with different bases.

But today I found out, that they're not completely "equal", i.e. that they mark different states of the system ($\mathrm{A_g}$ is the ground state, $\mathrm{B_{1u}}$ is one of the excited states etc.).

What I'm completely missing is - how are irreducible representations linked with the system states?

Please, try some "low-level" explanation, I'm a beginner both in quantum chemistry and group theory.


texts: Why does a wooden spoon creates bubbles when put in hot oil?

texts:
This question might be a bit weird, but I just asked myself why a wooden cooking spoon creates bubbles when put in oil at about 170°C. This is a common trick to find out, if Oil has the right temperature for frying.
My idea is, that the water in the wooden spoon starts to evaporate, but why does this just start to happen when the Oil reaches approx 170°C? Why does this not happen at 100 or 120°C ?


texts: Can I normalize my data in order to compare it?

texts:
I have three chromatograms of the same eluted protein but at different concentrations, since it got diluted during purification process) and hence peak maximums at very different absorbances.

The highest is around 100 AU and lowest 20 AU.
I want to present these and look at the difference in peak shape (because I want to look at aggregation). Can I simply multiply the data that generated the peak max at 20 AU by 5? Because then it is easier to compare the shapes of the peaks when they  overlay each other.

Is this something one would do or is it totally forbidden?

Thanks in advice.


texts:
I used a detergent powder mixed with water to clean my espresso machine. Some micro particles of powder are stuck into machine's inner tank. So when I pull the hot water out of the machine's nozzle, it contains micro powders and it tastes powdery.
What solution can I use instead of water to wash out all those sticky powders?
A harmless solution to break bond between powders and solve the powder into itself.


texts: All resonance structures of the hydrogen molecule

texts:
This answer written by Jan says that "a professor of mine claimed to have drawn some 18 (or was it 80?) different resonance Lewis structures."

Please reproduce those resonance structures of the hydrogen molecule.

If nobody is able to come up with that many, the answer with the most resonance structures would be accepted.


texts: Are the following expressions for base dissociation constant equivalent?

texts:
Given a weak base such as $\ce{C2H5NH2}$, I usually see the expression for $K_\text{b}$ as

$K_\text{b} = \frac{[\ce{C2H5NH3+}][\ce{OH-}]}{[\ce{C2H5NH2}]}$.

Are the expressions

$K_\text{b} = \frac{[\ce{C2H5NH3+}]}{[\ce{C2H5NH2}][\ce{H+}]}$,
$K_\text{b} = \frac{[\ce{C2H5NH3+}][\ce{H2O}]}{[\ce{C2H5NH2}][\ce{H3O+}]}$

equivalent? Do they represent the same process (if so, why do the latter two not work with calculations?) or fundamentally different ways of dissociation? Which one represents what's happening molecularly most accurately? Given the Brønsted-Lowry definition of a base as a proton acceptor I'd think that the second one is most accurate, but I rarely see it used.


texts: Problem in defining the Inductive effect

texts:
Inductive effect is introduced in many textbooks by giving an example of an alkyl halide $R-X$.
The bond C1-X is polar due to electronegativity difference, therefore X gains partial negative charge ∆(-), and C1 gains partial positive ∆(+). Due to some deficiency of electrons in the C1 , C2-C1 bond becomes polar and above process is repeated.
So by this point of view, if we take $R-Li$, as C1-Li bond is polar, Li gains ∆(+) and C gains ∆(-) and above thinking process is repeated again.
Thus we can conclude that Carbon chain can act as both +I and -I depending upon the situation on hand.

So why do we always consider an alkyl chain to be a +I group?

Example, if on a carbon chain, there is a carbanion, we still consider alkyl group to be +I, but it should have been the opposite.


texts: Why are solids and liquids ignored in the equilibrium constant?

texts: If a reaction is taking place and is going towards equilibrium, wouldn’t the reactant be consumed to form products and vice versa? If this reactant/product is a solid or liquid, wouldn’t the number of moles when the reaction reaches equilibrium decrease/increase from its initial number of moles? Wouldn’t this change in moles from start of reaction to point of equilibrium be important to the equation, since it’s a ratio of products to reactants at equilibrium?


texts: Chiral centres with stereoisomeric substituents

texts:
The structure of one particular isomer of 4-chlorohepta-2,5-diene is shown here. I am confused about how two of the propenyl groups attached to the central carbon have the same atoms with different configurations.

More specifically:

Is the carbon shown in the image is a chiral carbon or pseudo-chiral carbon?

Will this compound show optical isomerism, i.e. does it have an enantiomer?

Are the two alkenyl groups considered to be different from each other, or the same?

If the attached side centers were chiral centers (e.g $\ce{-CHClCH3}$) with different configurations, instead of geometrical isomers, then would this compound show optical isomerism?


texts: Comparison of chemical shift of methyl group attached to alcohol and carboxylic acid

texts:
I understand that hydrogens can be deshielded by electron-withdrawing groups, and the more powerful the group, the greater the chemical shift.

However, I ran into a problem when qualitatively compare the chemical shifts of the hydrogens in the methyl group of methanol and ethanoic acid: the carboxylic acid group is stronger than the alcohol group, the oxygens of the carboxylic acid group isn't directly attached to the methyl carbon, unlike the alcohol oxygen.
How would I qualitatively compare the chemical shifts of the methyl groups of methanol and ethanoic acid?


texts:
I've read quite a few other answers on this site such as this one, but can't quite seem to understand fully yet.

Say we have a container with gases reacting such that the number of moles on both sides of the equation are not equal. If we then, for instance, reduce the volume of the container, the total pressure increases and the value of the quotient Q will also change. The net reaction then favours a particular direction so that the mole fractions change sufficiently for Q to return to the value of K, which remains constant.

This is commonly described by saying equilibrium shifts to either the left or the right. Whilst it is true that after the system has again reached equilibrium the mole fractions have changed (so in a sense, the new equilibrium has shifted to one side in terms of number of moles), the value of Q is equal to its initial value so in this sense the position of equilibrium as defined by K has not changed.

The same applies to changing the concentration of a species; the actual concentrations of every species after the system has re-equilibrated will be different, however the value of Q will have returned to its previous value.

The only situation that I can think of where the position of equilibrium actually shifts is when a change in temperature alters the value of K.

My question is, essentially, is the term 'position of equilibrium' more of a qualitative descriptor of the composition of reactants and products? I initially thought it meant the value of Q at equilibrium (or K), but evidently in gaseous reactions the equilibrium yield does change with changes in pressure though K remains constant, so such a definition would not work.

Thank you!


texts: How do you optimize an organo-metalic compound containing cerium in in Gaussian?

texts:
I am trying to perform optimisation of the molecule attached. I need to get partial charges and frequencies. The issue is that it doesn't converge with following input:

%nprocshared=8
%mem=16GB
%chk=CTB.chk
#n opt b3lyp/gen pop=(ReadRadii, savechelpg) SCF=QC
CTB
0 2
Ce -6.41954 5.21611 0.61820
...
N -4.38490 3.87720 0.35349

H -5.52145 4.13584 -2.66372
Ce 0
SDD
****
H Si C N 0
6-31G
****
Ce 2.88

As well I get error message:
Restarting incremental Fock formation.
Gradient too large for Newton-Raphson or scaled steepest descent --
use steepest descent instead.


texts: Solutions of Group 1 and Group 2 metals in Ammonia

texts:
When we add Group-1 and Group-2 metals to liquid ammonia, they dissolve to form metal cations and solvated electrons.
$$\ce{M + NH3(liq) -> M+ + e-}$$
Now, when the G-1 solutions evaporate, we get the metal back, but in the case of G-2 solutions (except Beryllium), they give a metal complex, $\ce{[M(NH3)6]}$.

"Evaporation of the ammonia from solutions of Group 1 metals yields the metal, but with Group 2 metals evaporation of ammonia gives hexammoniates $\ce{[M(NH3)6]}$ of the metals. These slowly decompose to give amides."
Page No. 335, Chapter 11-'Group 2 - the alkaline earth elements', Concise Inorganic Chemistry

and,

"The alkaline earth metals except beryllium form similar solutions [to alkali metals] readily, but upon evaporation, a solid 'ammoniate', $\ce{[M(NH3)x]}$ is formed."
Page No. 249, Chapter 9-'Chemistry in Aqueous and Nonaqueous Solvents', Inorganic Chemistry: Principles of Structure and Reactivity

What is the reason for this contrasting behaviour, and do all Group 2 metals(except beryllium) exhibit such a property?
Source:
1. Lee, J.D.; Concise Inorganic Chemistry; Wiley-Blackwell; Dec. 1998
2. Huheey, James E., Keiter, Ellen A., Keiter, Richard L.; Inorganic Chemistry: Principles of Structure and Reactivity, 4th Edition; Pearson Education Inc.; 1993


texts: Which coordination complex does not absorb visible light?

texts:
A question was asked in one competitive exam (AIPMT 2010). It said:

  Which of the following complex ions is not expected to absorb visible light?

  $\ce{[Ni(CN)4]^2-}$
  $\ce{[Cr(NH3)6]^3+}$
  $\ce{[Fe(H2O)6]^2+}$
  $\ce{[Ni(H2O)6]^2+}$

The exam is notorious for not releasing solutions of their own question papers, hence, several online sites have come up with their own versions of explanations for why the official answer is option A - $\ce{[Ni(CN)4]^2-}$, most of them copying the solution from one another!

I understand CFT and VBT (not LFT!) in terms of coordination theory. I ask this question on this community to get a definite response, as to what should be the correct answer to this question and why?


texts: Heat given off from an electrochemical cell compared to mixing reactants

texts:
My confusion regarding the difference between the heat given off in a reaction that takes place in an electrochemical cell compared to in a beaker/appropriate container when the reactants are simple mixed, arose from the following problem question:

For the reaction:

\begin{align}
\ce{HgCl2~(s) + H2~(g,1~bar) &-> 2Hg~(l) + 2H+~(aq) + 2Cl- }\\
\Delta G^\circ &=-51.64~\mathrm{kJmol^{-1}},\\
\Delta S^\circ &=-61.6~\mathrm{JK^{-1}mol^{-1}},\\
\Delta H^\circ &=-70~\mathrm{kJmol^{-1}}.\\
\end{align}

Part (a) of the question then asks: "Determine how much heat is given off at $298~\mathrm{K}$ per mole of $\ce{HgCl2}$ if the cell is operated reversibly"

The correct approach is to use $T\,\mathrm{d}S=\mathrm{d}q$ giving a value of: $18.36~\mathrm{kJmol^{-1}}$

Then part (b) asks: "Now determine the heat given off if the reaction is brought about by simply mixing the reactants"

I realised that the electrical work done in the cell would now be given off as heat so I just added the value for the Gibbs free energy to the value calculated in (a) and got: $70~\mathrm{kJmol^{-1}}$. This answer is correct but my tutor noted that this value is the value for the enthalpy change which would have been a shortcut to the answer. I didn't spot this and I don't understand why this is the case so wouldn't spot it again, should another question like this come up. Please can you clear up why this value is the enthalpy change.

I have some issues with the above working (it is all correct but I don't fully understand it).

Firstly, in part (a) I had to use the Clausius inequality (except it was an equality since the process was carried out reversibly) to find $\mathrm{d}q$. However, why must I use this equation because $\Delta H=q_p$ - the process was carried out at a constant pressure?

Secondly, if the heat given off in part (b) is $70~\mathrm{kJmol^{-1}}$ doesn't this violate the Clausius inequality? I must be wrong but it seems that this must be the case since $\mathrm{d}S \geq \frac{\mathrm{d}Q}{T}$ and using the value for the entropy change ($\Delta S^\circ=-61.6~\mathrm{JK^{-1}mol^{-1}}$) and the new calculated value for the heat given off ($70~\mathrm{kJmol^{-1}}$) then dividing this by $298~\mathrm{K}$ gives a value larger than the value for the entropy change but the Clausius inequality says that the change in entropy is greater than or equal to $\mathrm{d}q/T$. What is going on there?


texts: What is the proper laboratory technique to place a solid in a beaker that will be weighed?

texts:
I was doing a lab at school yesterday which involved transferring a precise amount of solid reagent into a beaker.

The way my professor told me to do it was to tap the reagent container so that the solid would fall out into the preweighed beaker and then weigh the beaker. However, I always thought that the correct procedure was to weigh a piece of paper, then place the solid onto the paper, reweigh the paper to obtain the correct mass reading, and then use the paper to pour the solid into the beaker.

What are the advantages of using the teacher's way over the way I proposed?


texts: Should β-mercaptoethanol and anything that touches it be handled only under fume hoods for safety aspects?

texts:
Background: I recently started in a lab that regularly uses β-mercaptoethanol (βME) for protein purification. I know that the chemical is an irritant for the lungs if inhaled (mucus membranes), damaging if in contact with eyes, toxic if in contact with skin. However, I have had projects in different labs that handle this chemical differently. Some strictly only open it in the fume-hood, have designed waste in the fume-hood for any pipette tips that touch βME and always discard any protective gloves that they used while handling this chemical directly after use – so not to spread residual βME all over the lab. This also goes for any buffers that have βME in it.
In the lab that I currently work in, they open the concentrated bottle of βME in the fume hood, but they don't care too much about discarding pipette tips in designated waste nor change gloves after use (and I know that the gloves smell like βME after opening the bottle). In addition, they do not work with lammeli buffer in the fume hood (they use 4 × lammeli for SDS-PAGE). However, from the safety manual of lammeli-buffers — which also contains βME (and you can immidiately smell that) it seems to be just as hazardous as the concentrated βME.
I don't have hypochondria when it comes to lab safety, but I would like to develop a rational understanding of how dangerous this is common chemical is. In addition I believe that the fridge which we store βME in smells quite strongly of βME. Should the bottle be stored in a secondary container (plastic bag) in addition?
Question: How do people who commonly use this chemical treat it during their everyday lab routines? How hazards is it to regularly inhale trances of βME from e.g. the fridge or when people work with lammeli buffers on the lab bench? What do people think about discarding their gloves after working with it, before they start touches other lab equipment?


texts: What are the specific disadvantages of using a bio-catalyst (called Lipolase) in the synthesis of the drug pregabalin?

texts:
I am studying the synthesis of a drug pregabalin, for which both chemical and bio-catalysts are used. Using a biocatalyst is way better than chemical route, as explained here. In fact, The invention of the bio-catalyst route got 2006 IchemE award in Green Chemistry and Engineering.

I am interested in knowing is this: are there any disadvantages of using bio-catalysis in this reaction? (Some general disadvantages can be seen here) Suppose you are in a debate and you have to favor the chemical side, what would be your arguments?


texts: Acid-catalysed isomerisation of phenyl epoxide to aldehyde

texts:
How does $\ce{H3O+}$ cause the formation of an aldehyde from the following epoxide?

I thought that the epoxide would undergo opening to form a 1,2-diol, as illustrated below. Am I wrong?


texts:
From the articles in the internet , I found that there are two reactions which are being called Lieberman nitroso test .

One is the test of 2 degree amine in which a 2 degree amine is converted to N - nitroso amine using nitrous acid  . And this product reacts with phenol to form a red solution which turn blue on addition of alkali . Confirming the presence of 2 degree amine .

And another is the direct reaction of phenol with nitrous acid to form Indo-phenol giving same characteristic red and blue colour .

I am confused and have tried to refer to a lot of sources but with no success .


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We know that in butadiene there are 4 MOs. This is the MO with one node:

My question is: Why, with one node, can't we have something like this ?


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I had used spare pieces of metal to perform electrolysis. They all had the disadvantage that they corrode when used as anode - and some of the oxides are toxic (copper, chromium).

I've found that carbon, which can be harvested from pencils and old batteries does not corrode contrary to my expectations (I'd expect it to produce $\ce{CO2}$). But soldering on carbon is completely impossible. Also, I need some bigger electrodes.

So are there any metals that do not corrode during electrolysis?

I'm using sodium carbonate as electrolyte.


texts: Why do some solutions eventually stop boiling and start "popping" as they get more concentrated?

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A very long time ago I performed an experiment in my kitchen, part of which was to remove all water from a solution. Unfortunately I don't remember what was in it, but the point is that as the solution got more concentrated, it gradually stopped boiling, and would instead remain completely still for seconds, until a huge bubble would form instantly at the bottom of the test tube, making a pop sound and shooting some of the solution out of the tube. The effect got stronger and stronger until it became too strong for me to feel safe to continue.

I was unable to get an explanation of this effect out of my school teachers at the time. What I expected was that as the solution got more concentrated, the dissolved compound would start to precipitate, until eventually no water is left. Why did the popping occur instead?


texts: Carbon atoms which carbocation and carboanion are BOTH less stable then arene/vinyl

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I'm trying to come up with a compound class in which iodine atom would be a bad leaving group both whether it leaves or takes charge with it (I know that $\ce{I^+}$ on its own would be horrible leaving group, but I'm thinking of a reaction where it oxidizes and so might leave forming a carbanion).

Aryl and vinyl carbons are both good candidates, but I'm wondering if some other compounds might work better or just as well.

So the question is about finding a compound $\ce{RR'(R'')C-I}$ such that both $\ce{RR'(R'')C^+}$ and $\ce{RR'(R'')C^-}$ are not stable. Or in other way, a compound with both $\mathrm pK_\mathrm a$ higher and $\mathrm pK_\mathrm b$ lower than that of aryl or vinyl.


texts: Nucleophilic substitution in aromatic compounds

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Predict the major product in following reaction:

In my view this reaction will proceed via benzyne intermediate and $\ce{NH2-}$ will act as a base and substitute one of the chlorine. After benzyne formation as $\ce{Cl}$ is ortho/para directing my view was that $\ce{NH2-}$ will attach to the meta position.
However, the answer key says overwise. Any ideas?


texts: Why is Finkelstein reaction not conducted using NaF?

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I was studying the Finkelstein reaction and all sources through which I have studied this reaction indicate that the reaction uses $\ce{NaI},$ where $\ce{I-}$ acts as the nucleophile which will then replace $\ce{X}$ from the alkyl halide $\ce{R-X}.$

This is an $\mathrm{S_N2}$ reaction, hence we use a polar aprotic solvent (PAS, usually acetone) as PAS stabilizes the $\ce{Na+}$ cation. We know that while using a PAS the order of nucleophilicity is

$$\ce{F-} > \ce{Cl-} > \ce{Br-} > \ce{I-}.$$

The part I am struggling with is that even though $\ce{F-}$ is a better nucleophile than $\ce{I-}$ in a PAS, why do we still use $\ce{NaF}$ rather than $\ce{NaI}?$