texts: Why is the boat form of paraldehyde not theoretically possible?

texts:
Wikipedia says the following about paraldehyde:

  Theoretically, four stereoisomeric structures are possible. The
  structures (1) and (2) are known as cis- and trans-paraldehyde. The
  structures (3) (a conformer of (2)) and (4) (a conformer of (1)) don't
  exist for steric reasons.

If this is correct, it seems that the boat conformer is not theoretically possible. I would expect the boat conformer to be possible but be much less common than the chair conformer (as is the case with glucose and cyclohexane for example), but that does not seem to be the case.

Wikipedia says that conformers 3 and 4 don't exist for steric reasons, however they are still theoretically possible. To me this sounds like the nonexixtence of boat conformation is not just because of steric reasons, but there is a more fundamental reason for that.

So, my questions are:

Is it true that the boat conformer is theoretically impossible?
If yes, why is it impossible and what makes paraldehyde different from glucose and cyclohexane in this regard?


texts: Why isn't O=N-O-O the best lewis structure for NO3-?

texts:
I'm practicing lewis structures and I'm stuck on the one for NO3 -1 (nitrate ion). I understand that N has to be the central atom because it is the least electronegative, but I'm confused why all the O have to be bonded to the N atom.

With O=N-O-O, you get 3 zero formal charges and one -1 instead of one zero, two -1 and one 1, which seems better. Also, H2O2 is a straight line instead of having the both H and and one of the O around a central O atom, so I'm confused why the nitrate ion must be the opposite.

Here is the work I did:


texts: Why does Methyl Carbocation have p orbital

texts:
For a carbocation to form, it needs to lose an electron. In the example below the leaving group is Br and the products are a methyl carbocation and a bromide ion.

What I am unsure about is why the carbocation needs an empty p orbital. For a carbon atom with 6 valence electrons, the molecular orbital diagram looks like the one below. So when an electron is lost in heterolysis the $\ce{2p}$ orbital will be empty and I assume that is why the p orbital is empty. However, why do you include the empty p orbital in the shape. Does it serve a purpose?


texts:
So I'm stuck on this question because I'm having trouble breaking it down. So I know the answer already but like most stuck students I'm not sure how to get to it.

The problem is that I am not sure how to break this question down.


texts: Can thionyl chloride convert two equivalents of carboxylic acids to acyl chlorides?

texts: Specifically, I've outlined the arrow pushing heuristic for getting from a carboxylic acid to an acyl chloride in red. Now the mechanism outlined in green is the standard route for what I'm told happens with the release of SO2 gas. However, how stable is this intermediate and is it possible that it undergoes conversion twice as I've drawn in orange?


texts: Most negative and most positive value for proton chemical shifts

texts: What are the most negative and the most positive values for proton chemical shifts recorded till present?


texts: Can there be two precipitates in a double displacement reaction?

texts:
On one of my chemistry homework's, I am doing a double displacement reaction and the question is having me predict the products and make a net ionic equation for copper(|I) sulfate and barium acetate reacting.

$$\ce{CuSO4(aq) + Ba(OH)2(aq) -> Cu(OH)2 + BaSO4}$$

I was able to predict the products of it, but when I was starting to do the net ionic equation, I came across the problem that there were no spectator ions and I am not sure if two precipitates can form out of a double displacement reaction.


texts: Can other group IV elements form graphene analogs with interesting properties?

texts: Graphene has gathered quite a bit of press due to its unique physical properties which hold enormous promise in a wide range of applications from semiconductors to high strength materials. Given that carbon is similar to other Group IV element chemically, I wonder if there are graphene analogs of other Group IV elements such as silicon, tin or lead and what fascinating properties and useful applications they may hold.


texts: Free energy and kinetic energy for reacting gases

texts:
I am confused about the energies we are talking about when speaking in regards to the Maxwell Boltzmann Distribution and activation energies.

Is there an relationship between kinetic energy and free energy for ideal gases? I am wondering if it’s possible to plot the x-axis of a Maxwell Boltzmann Distribution in terms of free energy as opposed to kinetic energy or velocity.
Is the activation energy the difference in the free energy of the activated complex and the average free energy of the gas (or any reactant)?
From the answer here, the activation energy mark on Maxwell Boltzmann Distributions like this one refers to a minimum kinetic energy level. Since the activated complex/transition state is a state, I do not understand why having a minimum kinetic energy (and right collision orientation) means reactants will reach the transition state. How come there is no free energy requirement?


texts:
There. And there. Almost a year ago, a group of scientists claimed to have reached compounds of $\ce{Na}$ and $\ce{Cl}$ with weird stochiometries ($\ce{NaCl3, Na3Cl, NaCl7, Na3Cl2}$ and $\ce{Na2Cl}$).
What one of the articles says:

These compounds are thermodynamically stable and, once made, remain indefinitely; nothing will make them fall apart.
For example, $\ce{NaCl7, NaCl3, Na3Cl2}$, and $\ce{Na2Cl}$ are metals (that explains the apparent violation of electroneutrality since charge balance rules are inapplicable to metals), and only one semiconducting phase of $\ce{NaCl3}$ is stable in the pressure range between 250 and 480 thousand atmospheres.

At first, I thought this whole thing was bogus. But then, I faced another, apparently convincing, article and even one from RSC. Then the questions popped up:

Why does this happen? (Why is such a compound more thermodynamically stable at high pressure?)
How can the bonding in these be explained?

(Source)


texts: Can alkyl fluorides be formed by the Hunsdiecker reaction?

texts:
We know that the Hunsdiecker reaction is

$$\ce{RCOOAg + X2 ->[CCl4] RX + AgX + CO2}.$$

This reaction is successful with chlorine and bromine. Also, we know that if $\ce{X}$ is iodine, we will get an ester.

Can we form alkyl fluorides using this reaction? If not, why?


texts: Calculate water hardness from grams of CaCO3

texts:
We have to figure out what the water hardness in mg/L or ppm is for a $\pu{20ml}$ solution of $\pu{0.400M}$ $\ce{CaCl2}$.

We learned that the formula for hardness is mg/L of calcium carbonate per liter. I started by calculating that there would be $\pu{0.801 g}$ of $\ce{CaCO3}$ precipitate if reacted with $\ce{Na2CO3}$.  I then converted $\pu{0.801 g}$ to mg and got $\pu{801 mg}$. I finally divides this by the original $\pu{20ml}$ or $\pu{0.02 L}$ but this gives $\pu{40050 mg/L}$ but the correct answer is $\pu{400 mg/L}$.

I feel like I might be making a mistake with units as my answer is 100 times greater than the correct answer but I don't see the problem.


texts: Is there a simple assay to determine the elemental carbon content of biochar?

texts:
A little bit of background. I make charcoal for use as biochar: putting carbon into the ground where it retains water and soluble nutrients. It also provides a good habitat for the friendly soil bacteria and fungi, along with low-tech carbon capture and storage for the masses.

I would like to know how much carbon is going back into the ground, and be able to say with confidence what difference I'm making to my carbon footprint, but the two – at least – unknown factors are the ash content of the char, and the water content from quenching and dust abatement sprays. I can say with confidence that a kilo of dry char will retain 3 kilos of water, which makes it difficult to judge by the look and feel.

I'm looking for a simple assay which will tell me with reasonable confidence how much elemental carbon a sample contains.

FWIW, my understanding of chemistry is rusty: I've got an A-level (the UK university entrance qualification from 1976) but my degree is in Physics, and my background is in engineering. Thanks for any help.


texts: Which carbon(s) in cyclohexene have the highest electron density?

texts:
I think that carbons with highest electron density will be both $\ce C1$ and $\ce C2$ because of the loosely held $\pi$-bond between them, but according to the answer given the carbons with most electron density should be both $\ce C3$ and $\ce C6$.

How is this possible?


texts:
$\ce{Cu(II)}$ and $\ce{Ag(II)}$ complexes are known to exist while $\ce{Au(II)}$ is unstable and disproportionates to $\ce{Au(I)}$ and $\ce{Au(III)}$.

My guess as to possible reasons to this effect is that $\ce{Au(II)}$ like $\ce{Cu(II)}$ and $\ce{Ag(II)}$ cannot undergo Jahn-Teller Distortion, the cause of their stability, because of the extremely diffuse nature of $\mathrm{d}$ orbitals of $\ce{Au(II)}$ owing to relativistic effects. Could this be the right reasoning?

Also, what is the cause of the stability of $\ce{Au(I)}$ and $\ce{Au(III)}$ over $\ce{Au(II)}$?


texts: Will toluene vapors damage a mirror made from PETG?

texts: I'm working on a project for work and trying to avoid using an acrylic mirror because I know that doesn't hold up well against toluene, but I'm wondering if a mirror made out of PETG would?


texts: Why are catabolic reactions exergonic and anabolic reactions endergonic?

texts:
Catabolism breaks apart large molecules and anabolism creates large molecules. Catabolism is supposed to be exergonic, while anabolism is supposed to be energonic. Id on't really understand this.

By definition a chemical bond is at an energy minimum. So if catabolism is taking apart large molecules with many bonds, which are at an energy minimum, how is this supposed to release energy (be exergonic) if the bonds are already at an energy minimum?

By contrast why is it that anabolism, which is putting creating a large molecule (which is a minimum energy state) from many atoms is enderognic and thus requires energy? I mean you're creating a minimum energy state, why would this require energy?


texts: Crossing at critical temperature of a gas

texts:
This is written in the book 'Treatise on Thermodynamics' by Max Plank-

the crossing of the critical temperature at any pressure other than the critical pressure differs in no way from the crossing of any other temperature.

But from the phase diagram of the states, it seems that if we change the temperature at a pressure greater than the critical pressure, then on crossing the critical temperature the gas will liquify where as crossing at other temperatures the gaseous state won't change.
So is the statement in the book wrong?


texts: Dependence of EMF of a cell on stoichiometry

texts:
In the reaction $\ce{Zn + 2Ag+ -> Zn^2+ + 2Ag}$ , my book says that the EMF is the difference between the standard reduction potential of $\ce{Ag}$ and $\ce{Zn}$.

Shouldn't it be the difference between twice the potential of $\ce{Ag}$ and $\ce{Zn}$ since two moles of $\ce{Ag}$ are getting reduced per mole of $\ce{Zn?}$


texts: Can protection group be used in a Wolff–Kishner reaction?

texts:
How can I modify the ozonolysis of cyclohexene such that one of the aldehyde groups of the product, adipaldehyde, is efficiently protected as a base stable protecting group? I know that attempting to monofunctionalize adipaldehyde will lead to mixtures.

My aim is to then do a Wolff–Kishner reduction on the monoprotected dialdehyde.


texts: Impregnating polyethylene with oil using pressure cooker?

texts:
I have some polyethylene spiral wrap that I'm hoping to impregnate with citrus oil as an animal deterrent.

Wikipedia says that polyethylene plastic will pass through "flavourings" fairly easily. It's melting point for the grade I have seems to be around 100C.

Do you think that placing polyethylene and citrus oil into a pressure cooker and keeping the temperature to around 90C for a few hours would infuse the polymer with enough of the flavour compounds from the oils to have any reasonable effect?

Or would it just be as effective to leave the polyethylene in an oil bath and leave it sealed at room temperature for a month or so?


texts: Naming a synthetic molecule from QM9 dataset

texts:
I was trying to write a name for a synthetic molecule in QM9 dataset. The molecule is:

is 3-aminooxolane-2-carbonitrile a correct name for this?


texts:
Alkynes are capable of undergoing carbometalation, e.g. with organocopper reagents:

Why don't the corresponding alkenes undergo analogous carbometalation reactions? Is β-elimination the issue?


texts:
List some examples of state functions. Check all that apply:

  internal energy
  work
  volume
  pressure

I know that a state function is independent of the path taken, so I think work and volume are state functions. Am I correct?


texts: Is it "common practice in Fourier transform spectroscopy to multiply the measured interferogram by an apodizing function"? If so, why?

texts:
The recent paper in Nature Independent confirmation of a methane spike on Mars and a source region east of Gale Crater is interesting and the basis is a reanalysis of 2013 data taken by a X spectrometer about the Mars Express spacecraft in orbit around Mars looking down at the Martian atmosphere.
The paper itself is paywalled but the supplemental data describes the reanalysis in great detail.

The Planetary Fourier Spectrometer [38] (PFS) on Mars Express 37 is a double-pendulum infrared Fourier spectrometer optimized for atmospheric studies. It has two distinct spectral channels operating simultaneously and covering the wavenumber range between 200–2000 cm−1 (Long Wavelength Channel, hereafter LWC) and 2000–8300 cm−1 (Short Wavelength Channel, hereafter SWC). Both channels have a sampling step of 1 cm−1 and a spectral resolution of ~1.3 cm−1, when no apodization function is applied, and ~1.8 cm−1 when a Hamming function is applied to the measured interferograms (as in the case of the present work).

Key to the process is an understanding of how the raw data is preprocessed using a Hamming apodization function before spectral fitting.

Step 1: Hamming apodization function is applied to PFS interferograms. It is common practice in Fourier transform spectroscopy to multiply the measured interferogram by an apodizing function in order to reduce the amount of ringing present in the resulting instrumental line shape [77]. This reduces the spectral resolution a bit (from 1.3 cm-1 to 1.8 cm-1 in the case of PFS [78]), but also reduces the instrumental noise and the magnitude of the side-lobes in the instrumental line shape, which are a direct result of the finite maximum optical difference in the measured interferograms [79]. The Hamming function H is defined as H(δ/L) = 0.54+0.46cos(πδ/L), where δ is the optical path difference out to a maximum value of L.

Davis, S. P., Abrams, M. C. & Brault, J. W., Fourier Transform Spectrometry, Academic Press (2001).
Giuranna, M., et al., Calibration of the Planetary Fourier Spectrometer short wavelength channel. Planet. Space Sci. 53 (10), 975–991 (2005).
Naylor, D.A. & Tahic, M. K., Apodizing functions for Fourier transform spectroscopy. J. Opt. Soc. Am. A 24, 3644–3648 (2007).

I was surprised to read that raw data is filtered before fitting to spectroscopic models in order to extract concentrations. I'm not an FTIRer, but I would have instead expected that all instrumental errors would be included in the fitted theoretical spectra generation and that the raw data would be fit in its pristine, unaltered form. After all, the only thing you really know for sure when fitting is that the data is the data, it's what you actually measured. Everything else is speculation.
QUESTION: Assuming that the block quote is right and it is indeed "common practice in Fourier transform spectroscopy to multiply the measured interferogram by an apodizing function in order to reduce the amount of ringing present in the resulting instrumental line shape" why is this considered "safe" to do? Why aren't all instrumental effects incorporated into the fitting function allowing for the raw data to be fit directly instead?

The spectra in question, from Independent confirmation of a methane spike on Mars and a source region east of Gale Crater:


texts: Will gamma radiation cause "thermal" decomposition of sodium bicarbonate?

texts:
I am conducting research for a new drug that contains powdered sodium bicarbonate, and the drug will need to be sterilized after placement into it's container/closure system. Typically, this is performed with steam, at 122.5 °C for 15 minutes, but in the case of sodium bicarbonate, this would cause decomposition:

$$\ce{2 NaHCO3 → Na2CO3 + H2O + CO2}$$

The alternative is to sterilize with ionizing (gamma) radiation. Will this also cause decomposition? Any help or referral to another authority is much appreciated.


texts: Why is change in entropy negative and change in enthalpy negative for the reaction of Magnesium and Hydrochloric acid?

texts:
So

$$\ce{Mg(s) + 2 HCl(aq) -> H2(g) + MgCl2(aq) + Heat}$$

From a conceptual standpoint, shouldn't the change in entropy be
positive for this reaction because there are more moles of gas in
the products vs the reactants? Why is this not the case? Can this
be justified through a conceptual view of the problem rather than
a pure mathematical approach(simply calculating delta s as
negative)?
From a conceptual standpoint, why is the change in entropy negative for this reaction?

Screenshot of reference data (source):


texts: What is the major hydrolysis product of 2,2,2-trifluoroethyl 2-acetamido-3-phenylprop-2-enoate?

texts:
In the below reaction we have to find the major hydrolysis product of 2,2,2-trifluoroethyl 2-acetamido-3-phenylprop-2-enoate.

My doubt is why the major hydrolysis is not when $\ce{OH-}$ at the $\ce{C}$ of $\ce{CF3}$ as it is more electropostive. However the major product is given by the following reaction, why?


texts:
I'm fairly new to chemistry, and I have a hard time understanding how chemical energy is stored in carbon (I'm aware that the question can be generalised to 'how is chemical energy stored', but I'm trying to understand it in the example of carbon). In the example in my book, carbon and oxygen react to form carbon dioxide, releasing energy in the form of warmth in the process.

My book says that the energy released in this process mainly comes from carbon, which is originally the solar energy stored by plants. I have to tried to look for explanations how that energy is stored (not how the process of photosynthesis works, but in what form or what is the meaning of the 'stored energy'), but I still can't really wrap my head around it. The best answer so far was What is the nature of chemical energy?

If I understand the answer there correctly, the bond potential energy of a carbon dioxide molecule is lower than the combined bond potential energy of a carbon atom and an oxygen molecule. Given that, there are still two things I don't understand:

Why is the bond potential energy in the carbon atom and/or oxygen molecule higher than that of a dioxide molecule? How can that explained? Is this directly related to the chemical traits of the elements carbon and oxygen and the compound carbon dioxide?
Why, or better said how is said bond potential energy converted to warmth in the process?

I'm aware that there might be concepts in physics here I don't know or understand to understand a possible answer, and I would be thankful for any pointers to what subjects I should be first reading to understand such an answer.

Edit: I would like to quote here something I came across on wikipedia. I'm not providing it as an answer nor claiming it is correct, just trying to illustrate how confusing it is to find a satisfying answer for this matter. This comes from https://en.wikipedia.org/wiki/Chemical_bond#Overview_of_main_types_of_chemical_bonds:

  In the simplest view of a covalent bond, one or more electrons (often a pair of electrons) are drawn into the space between the two atomic nuclei. Energy is released by bond formation. This is not as a reduction in potential energy (sic), because the attraction of the two electrons to the two protons is offset by the electron-electron and proton-proton repulsions. Instead, the release of energy (and hence stability of the bond) arises from the reduction in kinetic energy due to the electrons being in a more spatially distributed (i.e. longer de Broglie wavelength) orbital compared with each electron being confined closer to its respective nucleus.

Italic and bold added by me. Note that wikipedia itself has a '[clarification needed]' tagging in the middle of that text, right after 'two protons', which I removed.

So if I understand that correctly and assuming that info is correct, any formation of a covalent bond would result in energy being released. But that still doesn't explain why my book is claiming the energy is particularly stored in carbon (and not in oxygen), and why it is released as warmth. In addition, the explanation on wikipedia would contradict what I referred to earlier, namely that the energy released comes from differences in bond potential energy.


texts: How does the process of nucleation work for boiling liquids?

texts:
I have a somewhat clear picture how (on the molecular level) a gas turns into a liquids as it cools. When a gas has a certain temperature, its molecules on average have a high enough kinetic energy so that electromagnetic interactions cannot hold the molecules together and they are essentially free. When the gas cools, the kinetic energies are smaller and thus electromagnetic interactions between molecules start to pull the molecules together and the process of turning into a liquid begins. As more molecules lose kinetic energy, initially small numbers of molecules start to cluster up, forming "lumps" that continue growing as more molecules gather up into these clusters. I believe this process is called "nucleation".

I found this video that helps visualize the effect:

https://www.youtube.com/watch?v=wFT6G4CIL1o

But how does the reverse take place? Let's say I'm boiling water. I have a textbook that specifically states:

  During nucleation, small droplets of liquid form in gases or gas bubbles form in water as it starts to boil.

As I heat water, the average kinetic energies of the molecules increase. How does nucleation create bubbles in this situation? I understand that a bubble is a "pocket" of gas inside a liquid. If nucleation works the same way in the process of liquid turning into a gas as it works in a gas turning into a liquid, by analogy there should be some "lumps" of gas forming inside the liquid. But what would hold these gas "lumps" together as the molecules in the gas have a higher kinetic energy as the molecules around them (that are still part of the liquid)? And how do these molecules with higher energy "find" each other to start forming clusters/bubbles? Or do I have a completely wrong visualization as to how bubbles form?


texts: Polar group strong dipole effect molecular axis

texts:
There are some fundamental charactaristics of liquid crystal. One of them is that all liquid crystals are organic compounds and at one side of their long molecular foundation there exists a polar group such as -CN, -NO2, -NH2, -OR etc.

A strong dipole effect in molecules is created by the existance of polar group; so the molecular axies are parallel.

Actually I don't understand the characteristic perfectly because of having confusion at several terms.

My questions are :

What are the polar polar groups?
What is the strong dipole effect?
What is molecular axis?

I especially want to know  about molecular axis with an extant explanation.


texts: Removing prenylated phenolics from clothing, shoes, and upholstery

texts:
I live in Southern California and sometimes hike in areas that can be overgrown with a plant called purple poodle-dog bush. As I found out the first time I went crashing through a stand of the stuff, it's a horrific skin irritant, much worse than poison oak. It has microscopic hairs that get stuck in your skin and act like syringes. The hairs have chemicals on them that are skin irritants. Wikipedia says:

  This contact dermatitis is due to prenylated phenolics exuded by hairs (glandular trichomes) of the plant. The principal irritants are derivatives of farnesyl hydroquinone and 3-farnesyl-P-hydroxybenzoic acid.

I'm not a chemist, and all the nomenclature is Greek to me. My question is this. When I hike in an area where it will be hard to avoid the bush, I try to wear long sleeves and change my clothes immediately afterwards. Will throwing my clothes in the washing machine remove these chemicals and/or break them down into harmless ones? What if my shoes aren't machine washable? Will the chemicals break down naturally within a certain period of time? Would other methods such as exposure to sunlight help? Are these chemicals soluble in water, so that simple rinsing would help? How about making sure they aren't lurking in the upholstery of my car?


texts: What does washing and drying a solution mean?

texts:
After combining two solutions, a direction in a 1970s British chemistry book says to wash the new solution with a mixture of baking soda, table salt, and water. Then it says to dry it with anhydrous magnesium sulfate.
What does washing and drying mean? Do the chemicals get physically mixed together? Doesn't that contaminate the solution?


texts: Flame Ionization Detector versus Mass Spectrometer

texts: Why is chromatographic separation more important with a flame ionization detector than with a mass spectrometer?


texts:
I intend to make the following composition of copper plating solution:
\begin{array}{c:c}
\rm material   & \rm concentration \\\hline
\rm Copper sulfate & \pu{200 \frac{g}{L}}  \\
\rm sulfuric~acid  & \pu{100 \frac{g}{L}}  \\
\ce{Cl-}       & \pu{50 ppm}   \\
\end{array}

Do I use pure $\ce{H2SO4}$ ($95$–$98~\%$) and pure $\ce{HCl}$ ($37~\%$)?

Please check if I am correct with calculation.

first, copper sulfate: $$\pu{200 g} \times 5 = \pu{1000g}$$
then ($98~\%$) $\ce{H2SO4}$: $$\pu{100 \frac{g}{L}} \times \frac{\pu{5 L}}{\rm 1.84 g.ml^{-1}~ (\rho~of~H2SO4)} = \pu{271 \frac{ml}{L}}$$
then use ($37~\%$) $\ce{HCl}$: $$\pu{0.05 g/L} (= \pu{50ppm}) \times \pu{5L} \times \pu{1.19 g/mL}\ (\rho~ \text{of}\ \ce{HCl}) = \pu{0.21 ml/L}$$

so $$\pu{5000ml} - \pu{1000ml} - \pu{271ml} - \pu{0.21ml} = \pu{3728.79 ml}$$ — fill up this much water at final


texts: Which of the following carbanion is most stable?

texts:
The carbanion which is most stable is

The answer is 1. But why won't the answer be 2 because it shows resonance, whereas 1 only shows I effect and resonance effect is more dominant?


texts: Why do NMR coupling constants change with temperature?

texts: Why do coupling constants change with temperature in NMR?


texts: How to align povidone-iodine molecules in order to look for optical polarization

texts:
In this answer I mention how early polarizing filters (e.g. sunglasses) were made by doping a polymer with iodine atoms and then stretching the film to orient the polymer molecules.

Electrons donated by the iodine could then respond to the electric field of the incident light preferentially in the direction parallel to the molecules.

This and this answer mention that one common house-hold form of antiseptic iodine is a povidone iodine solution.

I don't have a feeling for how long those povidone chains are in over-the-copunter povidone iodine solutions are, but I would like to ask how I might try to remove the solvent, which is in this case just water, and see if I could make a film of the povidone-iodine complex, align or stretch it somehow, and see if the result has any polarizing activity.

If I tried to evaporate some, would the iodine remain attached to the povidone chains, or evaporate as well?

An alternative that would align the molecules in a solution somehow would also be interesting.

Source "Skeletal formula of povidone-iodine (PVP-I) — a widely used iodine-containing antiseptic and disinfectant."


texts: Is there a chemical or historical significance in the fact that 'ethane' is just 'methane' without the 'm'?


texts: Solvent effect on gold nanoparticle and silver nanoparticle in UV spectroscopy?

texts: Can anyone explain to me that how solvent factor affect the wavelength and intensity of gold nanoparticle and silver nanoparticle in UV spectroscopy?


texts: Why oxygen is enclosed in parenthesis in some chemical reaction?

texts:
While going through my chemistry text book I came through the following reaction.

$\ce{RCH2OH + (O) -> RCHO + H2O}$

In the above reaction why oxygen atom is enclosed in parenthesis ?


texts:
I have a question about the structure of an LiH unit cell, and while this is related to a homework problem, it isn't the problem itself, I'm just looking for conceptual understanding. I've already found that there should be 4 Li+ ions and 4 H- ions in one unit cell. However, I am struggling with how they will be arranged. Because the number of LiH molecules is 4, I am fairly certain that the structure intended for this problem is face-centered cubic lattice. This is where my conflict begins. In my class we have had the face-centered cubic unit cell described as (for one element) an atom at each corner and an atom in each side. From this arrangement we get (1/8)*8 + (1/2)*6 = 4 atoms. Now, I've seen a description online of the face-centered cubic structure for NaCl as "We can think of this as chloride ions forming an FCC cell, with sodium ions located in the octahedral holes in the middle of the cell edges and in the center of the cell. The sodium and chloride ions touch each other along the cell edges. The unit cell contains four sodium ions and four chloride ions, giving the 1:1 stoichiometry required by the formula, NaCl" (Chemistry LibreTexts). For me this makes a certain amount of sense, because this would give 4 cations when you use the same counting principle as before. However, I've seen multiple diagrams online that contradict this, such as: https://images.app.goo.gl/CGAsc4xAJM39tMgi8.
This seems to claim that the center image is the unit cell, and while it does have 4 of each ion "on" it, it does not seem to fulfill the same structure as the aforementioned unit cell suggestion. Is the problem here just that they are showing 1/8th of the full unit cell for simplicity? If not, I am even more confused.

Thank you for reading this extraordinarily long question for what could be a very simple answer! And please don't roast me too hard, I've never posted here before.


texts: Relation between enthalpy and internal energy for chemical reaction at constant volume

texts:
Question

The combustion of benzene(l) gives $\ce{CO2(g)}$ and $\ce{H2O(l)}.$ Given that the heat of combustion of benzene at constant volume is $\pu{-3263.9 kJ mol-1}$ at $\pu{25 ^\circ C}$; heat of combustion (in $\pu{kJ mol-1}$) of benzene at constant pressure will be: $(R = \pu{8.314 J K-1 mol-1})$

Answer

 $\Delta H = \pu{-3267.6 kJ}$

Explanation of Solution

 $\ce{C6H6(l) + 15/2 O2 (g) -> 6CO2(g) + 3H2O(l)}$
 $\Delta n_\mathrm g = 6- 7.5 = -1.5$
 $\Delta U$ or $\Delta E = \pu{-3263.9 kJ}$
 $\Delta H = \Delta U + \Delta n_\mathrm g RT$
 So $\Delta H = -3263.9 + (-1.5) \times 8.314 \times 10^{-3} \times 298 = \pu{-3267.6 kJ}$

My question
When a reaction occurs at constant volume they equate enthalpy with internal energy which I think is wrong because according to the equation:
$$\mathrm dH = \mathrm dU +\mathrm d(PV)$$
At constant volume:
$$\mathrm dH = \mathrm dU + V\mathrm dP$$
In the question, heat of combustion is given as $\pu{-3267.6 kJ},$ while solving for constant volume $\mathrm dU$ is given as $\pu{-3267.6 kJ}.$
Why is $\mathrm dH = \mathrm dE$ at constant volume?


texts: How to know whether s-p mixing will happen in heteronuclear molecules?

texts: How do I know whether s-p mixing would occur in some diatomic heteronuclear molecules like CN, CO, NO etc?


texts: Average or individual molar heat capacity?

texts:
In finding enthalpy change $\Delta H$ during adiabatic, reversible expansion of  mixture of two ideal gases $n_1$ mol of $\ce{A}$ ($C_{\mathrm{m},v}=\frac{3}{2}R$) and $n_2$ mol of $\ce{B}$ ($C_{\mathrm{m},v}=3R$) taken in a container and during this temperature change is $T_\mathrm{i}$ to $T_\mathrm{f}$. Then what should be the value of $\Delta H$?

It can be $$\Delta H=\left(n_1\right)\frac{5}{2}R\left(T_\mathrm{f}-T_\mathrm{i}\right)+\left(n_2\right)4R\left(T_\mathrm{f}-T_\mathrm{i}\right)$$ taking individully for each gas. Or let say average molar heat capacity of gaseous mixture at constant pressure be $C_{\mathrm{m},p,\mathrm{avg}}$ then it can be $$\Delta H=\left(n_1+n_2\right)C_{\mathrm{m},p,\mathrm{avg}}\left(T_\mathrm{f}-T_\mathrm{i}\right)$$ so please help which is correct one. As per suggestion both are same.
$$C_{\mathrm{m},p,\mathrm{avg}}=\frac{\left(n_1\right)\frac{5}{2}R+\left(n_2\right)4R}{n_1+n_2}$$


texts: Why are tertiary alkyl halides obtained in higher yield than secondary or primary during free radical halogenation of alkanes?

texts:
From my textbook:

  Halogens ($\ce{Cl_2}$ and $\ce{Br_2}$ ) react with alkanes in the presence of ultraviolet light to form haloalkanes.This reaction is free radical substitution and gives a mixture of mono, di, or polysubstituted haloalkanes which are difficult to separate into pure components. Moreover, the yield of any one compound is low because of the formation of other compounds. For example, in case of butane, a mixture of 1-chlorobutane (28%) and 2-chlorobutane (72%) is obtained, where the secondary alkyl halide is obtained as the major product rather than the primary one.
       $$\ce{CH_3CH_2CH_2CH_3->[\ce{Cl_2,~UV~light}]CH_3CH_2CH_2CH_2Cl + CH3CH_2CHClCH_3}$$
    In general, the ease of substitution of various hydrogen follows the sequence:
      $${\rm tertiary > secondary >primary}$$

After reading through all the above statements in my book, I now have the following questions:

Why are tertiary alkyl halides obtained as major products instead of secondary or primary ones? It seems that a hydrogen from a tertiary carbon can be more easily replaced by a halogen than that of a secondary or primary carbon. If it is so, why is hydrogen from a tertiary carbon more easily replaced than a hydrogen from a secondary or primary carbon?
Why are fluorine and iodine not considered in case of free radical halogenation (the first two lines of the above passage extracted from the book mentions only chlorine and bromine)?
Why is a tertiary alkyl halide not produced in the above example? Even if we think it might be produced in a lesser amount, there should have been more of it than the primary or secondary alkyl halides. It seems the reason for tertiary alkyl halide not being in the equation is because it might not have formed or it might have formed in a lesser amount than primary or secondary alkyl halides. If it is either any case, it would violate the order mentioned in the book.


texts: Accelerated stability testing for chemicals: Shelf life / Expiry Date

texts:
How does one use the results of Accelerated stability testing for chemicals to determine the typical Shelf life  and Expiry Date?

e.g. Suppose the typical storage is going to be at 25 C and the expected shelf life is 2 years (as printed on the labels or the best-before date).

Now in the interest of time suppose we test at a higher temperature how do we extrapolate those numbers to the typical shelf life at room temperature.

Any standard protocols for this? Also what's a reasonable high temperature to use for the accelerated tests. I am dealing with a fairly temperature stable & nonreactive material here. 60 C?

Stability testing seems quite common in the Pharma industry etc. so I'm sure there's norms out there.

Note that I'm not dealing with a drug / medicine / food etc. This is strictly for an intermediate which will not be consumed directly by the end user.


texts: Ways to determine the concentration of alkyl halides in organic solvents

texts: I have a volatile alkenyl bromide dissolved in hexanes. I have to use the halide in a Grignard reaction but separating it from hexanes is hard (the bromide is light sensitive and very volatile). I would like to use the solution of the halide in hexanes but I don't know how to determine its concentration. I tried taking an NMR of the solution but all the peaks interfere and I can't choose two characteristic peaks to take a ratio. Is there a titration technique or some other technique to determine its concentration?


texts: What molecule is mostly responsible for the smell of petrol/gasoline when I refill my car?

texts: Is it benzene or is there another aromatic molecule in gasoline with "heavier scents"? Does anybody know of a scientific investigation to provide evidence for an answer?


texts: How to determine oxidising and reducing agents in the reaction between ammonia and hypochlorous acid?

texts:
How do I figure out what is the oxidizing agent and the reducing agent in the following reaction:

$$\ce{\overset{-3}{N}\overset{+1}{H}_3 + \overset{+1}{H}\overset{-2}{O}\overset{+1}{Cl} <=> \overset{-1}{N}\overset{+1}{H}_2\overset{-1}{Cl} + H2O}~?$$

I assigned known oxidation numbers for the elements, but I'm not sure how to proceed with the rest.

Is $\ce{NH3}$ the reducing agent? Or nitrogen? Going from $-3$ to $-1$
and $\ce{HOCl}$ the oxidizing agent, chlorine going from $+1$ to $-1$?


texts: Are there substances people can put on themselves to prevent catching fire?

texts: This can be very useful for people who are afraid of spontaneous human combustion! But seriously, I heard there are non-harmful chemicals used in some fire extinguishers, so can they maybe be put on our skin, clothes, etc. in advance to prevent ever catching fire?


texts:
Probably we can have an aqueous solution of $\ce{SO2}$ by dissolving it in water, because we would have an equilibrium between $\ce{SO2(g)}$ and $\ce{SO2(aq)}$:

$$\ce{SO2(g) <=> SO2(aq)}$$

How can I compare pH of an aqueous solution of $\ce{SO2}$ with that of pure water qualitatively?
What happens to the pH of an aqueous solution of $\ce{SO2}$ if I aerate it by bubbling air through it?


texts: No reaction in net ionic equation for lithium nitrate and sodium chloride?

texts:
I've heard that nothing in the following net ionic equation reacts:

$$
\ce{Li+ + NO3- + Na+ + Cl- -> \text{"nothing"}}
$$

Is this true? Could someone explain why there would be no reaction?


texts: Does 1,3-dichloroallene possess a C2 symmetry axis?

texts:
Is there an $C_2$ axis of symmetry in $\ce{Cl-CH=C=CH-Cl}$?

A $C_2$ axis of symmetry means that I should be able to rotate the molecule about an axis by $180^\circ$. But I would need a composition of the following two rotations

$90^\circ$ rotation about $\ce{C=C=C}$ axis
$180^\circ$ about the perpendicular bisector of $\ce{C=C=C}$.

Would that count as a $C_2$ axis of rotation?


texts: Why is heat capacity defined as a partial derivative?

texts:
I understand that the heat capacity is the gradient of the slope of q against T, which implies that C = $\mathrm{ \frac{dq}{dT}}$, so how do we arrive at C = $\mathrm{\frac{∂q}{∂T}}$?
At constant volume, $\mathrm{C_V}$:

$$\mathrm{dU = dq + dw}$$

$\mathrm{dw = p(dV)}$, but $\mathrm{dv = 0}$, so $\mathrm{dU = dq}$

How do we make the jump to $\mathrm{C_V = \frac{∂U}{∂T}}$?

3. At constant pressure, $\mathrm{C_p}$:

$$\mathrm{H = U + pV}$$
so $$\mathrm{dH = dU + pdV = (dq + dw) - dw = dq}$$
hence $\mathrm{dH = dq}$

How do we make the jump to $\mathrm{C_p = \frac{∂H}{∂T}}$?


texts: "Hairy" corrosion on anodized alu-part in water

texts:
I got a water tank with a mechanical assembly in.

The assembly consist of parts of anodized aluminium mounted on stainless steel plates (AISI 304). This is submerged down in fresh water. The tank is open to air, and there is very little movement/current in the water.

After a few weeks there has developed some "fuzzy" dots on the surface of the anodized aluminium parts. See image.

Question is what this is?

My first thought was that this is organic material from the water that fastened easier to the rougher alu surface than the steel surface?

However, now I think it is more a chemical reaction due to galvanic currents due to material difference in aluminium and stainless steel. This should dissolve the aluminium and transfer the electrones to the stainless steel plate. But would this make it look like the fuzzy growth on the alu-part?

Or could it be something totally different I haven't though off?

One thing I wonder about in this connection is that the fuzz is not more concentrated close to where it is connected to the AISI 304 plate?

! Note: The alupart is anodized, which should make it electrical isolated on all surfaces. However, the Alu-part and the steel plate is connected with a few screws, and through this has electrical connection.

Caption: Photo of the "fuzzy" anodized alu part ("Eloksert" means anodized)


texts:
Can ion mass spectrometry differentiate between 2 distinct polymorphs? Why?
In my opinion, the spectrum would be the same as only the crystal lattice differs.


texts: What does "parallel in-register" mean for a protein structure in a fibril?

texts:
I read a paper by Ross and Poirier [1, p. S12] which has the following lines (see section Commonalities of amyloid structure) that describe the structure of protein in a fibril:

  The most extensively characterized amyloid fibril is that formed from the β-amyloid (Aβ) peptide implicated in AD. Using SOLID-STATE NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY, the in-register, parallel β-sheet organization of fibrils formed by Aβ10–35, a fragment of the full-length 42-residue Aβ peptide, was first described.

I couldn't understand what "in-register, parallel β-sheet" means.

References

Ross, C. A.; Poirier, M. A. Protein Aggregation and Neurodegenerative Disease. Nat Med 2004, 10 (7), S10–S17. https://doi.org/10/dppb95.


texts: Na2CO3 + FeBr3 + H2O: why do we get Fe(OH)3?

texts:
$$\ce{3Na2CO3 + 2FeBr3 + 3H2O -> 6NaBr + 2Fe(OH)3 + 3CO2}$$

Why $\ce{Fe(OH)3}$? Where do these $\ce{-OH}$ groups come from?

This is from a series of reactions in a Russian sample exam question.

P.S.

Following Ivan't hints, I've gone through the process of reaction, and I get some water in the right-hand side of the equation. I wonder why the answer has no water in the right-hand side.


texts: Why does a NOx container get cold when NOx is released? and What is the relationship of the vapor pressure curve with the liquid-vapor dome?

texts:
The temperature at which $\ce{NO_x}$ is in equilibrium with its liquid and vapor phase at 1 atm is about –84 °C. Does that mean $\ce{NO_x}$ exists as a liquid at that temperature? What about it's vapor phase then, because it's vapor and liquid phase should be at equilibrium, right?

Also, it's that the reason why compressed $\ce{NO_x}$ when released from its closed and pressurized container (e.g. 50 bar) at 20 °C becomes a gas while its temperature drops? Therefore, the compressed $\ce{NO_x}$ was in it's liquid state at 50 bar, right?

If that's the case, then what is the relationship between the vapor pressure curve and the liquid-vapor dome? How would you use the saturated liquid-vapor tables to predict the vapor pressure for your substance? And which specific volume would you chose to define your substance: its liquid specific volume or its vapor specific volume?


texts: Why did a former emulsion of oil and water precipitate after heating and cooling when heat made it originally?

texts:
I added 100 g coconut oil, 100 g distilled water and 500 mg lecithin to an 1800 watt blender.  The motor from the blender has has a passive heating action.  I blended it at full for four minutes.  The result seemed to be a hot, uniform substance with a thin layer of foam on top.

I poured this mix into a smaller container and placed it in the fridge.  After a while it set into a solid, uniform substance with no apparent precipitation.

I then heated the substance in the microwave  for thirty seconds.  When I removed it, the components had separated and precipitated.  Cooling it in the fridge again resulted in a delicate solid sheet at the top which broke through to liquid underneath.

Why did the mix precipitate (presumably de-emulsify) after being microwaved but not occur when blended?


texts: Why does the local density approximation (LDA) overestimate atomization energy?

texts:
I have read numerous times that the local density approximation (LDA) overestimates atomization energy. For example, here is a quote from Dr. Burke's book:

  LDA typically overbinds molecules by about $30~\mathrm{kcal\, mol^{-1}}$.

What is the cause? Is it the same problem that Hartree-Fock theory has when compared to the exact Schrödinger solution (lack of correlation between electrons)? Also, how can inclusion of gradient can help solve this problem?


texts: Melting and boiling points of benzene and fluorobenzene

texts:
This species is a derivative of benzene, with a single fluorine atom
  attached. Its melting point is -44 °C, which is lower than that of
  benzene, indicative of the remarkable effect of fluorination on the
  intermolecular interactions as seen throughout organofluorine
  chemistry. In contrast, the boiling points of PhF and benzene differ
  by only 4 °C.

Why is this true? Wikipedia doesn't elaborate on why.

From what I understand the melting point is the point at which the solid and liquid forms are in equilibrium.

Boiling point is the point at which the liquid and gas phases are in equilibrium.

I know that intermolecular forces play an integral role in melting and boiling point. However, why does it seem that the strength of the intermolecular forces in the solid phase is stronger than that in the liquid phase for fluorobenzene?


texts: Which component acts as the electrophile in the synthesis of the Sudan-1 azo dye?

texts:
In the two-pot synthesis, which acts as the nucleophile, 2-naphthol or phenyldiazonium?

Solomons et al. (2014) says that phenyldiazoium is weakly electrophilic. Yet in the questions to be answered in our laboratory manual, it asks for resonance structures on the attack of phenyldiazonium on carbon 1 and carbon 3 of beta-naphthol.

I'm confused. I can't seem to find a mechanism wherein phenyldiazonium acts as a nucleophile in the internet or in my books.


texts: How would we arrange these in the increasing order of stability?

texts:
Here we have three isomers of butene there structure of who I have attached:

cis-butene
trans-butene
iso-butene

I was able to figure out that the trans isomer would obviously be more stable than the cis one due to steric repulsions among the methyl groups in the cis isomer.  But how would we judge the isobutene? As they are isomers, the number of hyperconjugative structures ends up being the same.
I had an intuition that this might relate to intermediate stability in hyperconjugation but couldn't come to any conclusions.


texts:
In the class, I was told that $\ce{H3C^.}$ has a trigonal planar structure with the unpaired electron in $\mathrm{2p_z}$ orbital. But $\ce{H3C -}$ has a trigonal pyramidal structure.

But why does this happen?
Why does $\ce{F3C^.}$ also doesn't have a trigonal planar?

Edit : I have seen one possible answer in a different question.  But is there any answer that is explained with the help of VSEPR or MOT or VBT?


texts: What is reaction between isopropyl alcohol and acetone?

texts: What would be the probable reaction between acetone, $\ce{(CH3)2CO}$, and isopropyl alcohol, $\ce{CH3CHOHCH3}$, at room temperature without any catalyst in different concentrations?


texts: Why does electrolysis take so much time?

texts:
What makes electrolysis or electroplating take so long ? What stage takes longer when ions are attracted to electrodes or when they gain or lose electrons at electrode.
And if we are talking about an electrolyte composed of positive ions and electrons , which is faster, electrons entering the circuit at positive electrode or gaining electrons by positive ions at negative electrode?


texts:
In science we learn about single, double, and sometimes triple bonds. From a quick search I have found up to sextuple bonds.

Is there a maximum bond order? If yes/no, what causes this?


texts:
I remember seeing a periodic table that had the top-left corner of the d-block shaded and marked as "brittle". If I recall correctly, the elements were $\ce{Sc,Ti,V,Cr,Mn,Y,Zr,Nb,La}$. I think (sorry, I can't find much on it on the net).

The triangular shaded area is a clear indicator of a groupwise and period wise trend (similar to how the non-metals form a triangle due to the electron affinity/Ionization potential trends).

So, I ask, what are the trends leading to the brittleness of a metal, and, more importantly, why are these trends there (usually trends can be explained in terms of simpler things like atomic size/shielding/etc)?


texts: What exactly is the mechanism of "nascent hydrogen"?

texts:
I put the quotes because Wikipedia says it's an outdated theory.

What exactly happens when nitrobenzene is converted to aniline using $\ce{Sn/conc HCl}$?

According to a few books which haven't been updated, even $\ce{Na}$/ethanol, $\ce{Zn/dil H2SO4}$ produce this. I guess a metal may have an important role in the actual mechanism.

Is there any specific reason why  $\ce{Na}$/ethanol is used to reduce cyanides to amines, and $\ce{Sn/conc HCl}$ to reduce nitrobenzene? (and not the other way around)

Even $\ce{KMnO4}$ produces "nascent oxygen"? What exactly is going on?


texts: What should you couple with the reference material in testing galvanic corrosion?

texts: I am currently studying the effect of metal coating to steel. I want to test the galvanic current between steel and aluminum by getting the current that passes through a wire that connects them in an electrolyte solution, to know if the specific aluminum will fit as a good coating for the steel. What should I use as the couple material for the steel? Should it be the coated steel or the metal to be coated? I'm using ASTM G71 as the reference method.


texts: what is the reaction between copper and an acid

texts: what happens when copper is reacted with hydrochloric acid may be dilute or concentrated.Should it displace hydrogen?if not what will happen if yes why?i think it will not react because copper is placed below hydrogen


texts: What is the structure of diferric hexaphenolate?

texts:
I was studying about the ferric chloride identification of phenol, where one product formed is diferric hexaphenolate. But I am having trouble drawing out the structure of it. With ferric ion having a 3+ charge, it must be attached to three phenolate ions. But how can this ferric triphenolate be combined with the other Fe(III) ion and three more phenolate ions? And dative bonds from the other three phenolate ions to the ferric triphenolate doesn't seem to work.

I searched about it but I only found information about ferric triphenolate. I am now skeptical even about the existence of diferric hexaphenolate.


texts:
How would a solution made of $\pu{20 mL}$ of $\ce{NaOH}$, $\pu{10 mL}$ of $\ce{HCl}$, $\pu{10 mL}$ $\ce{NaH2PO4}$ and $\pu{5 mL}$ of $\ce{Na3PO4}$, all of them in a concentration of $\pu{10 mmol/L}$, behave? I already tried every way i can think of, but none give the solution of the $\mathrm{pH}$ of this system.

Ways I tried:

After reacting the $\ce{HCl}$ with $\ce{NaOH}$, I use the $\ce{NaOH}$ that i still got to react with $\ce{NaH2PO4}$, and to calculate the $[\ce{H+}]$ I used $[\ce{Na2HPO4}]$ + $\ce{[Na3PO4]}$, but i didnt got any answers.

I used this equation $\ce{NaH2PO4 + 2NaOH -> Na3PO4 + 2H2O}$ to find the concentration and then applied to the amphoteric equation, using $K_{a_2}$ and $K_{a_3}$.


texts: Why are higher-energy bonds preferred over lower-energy ones?

texts:
My chemistry book states that for example the bond S-O is preferred over the bond S-S because the first has a bond energy that is almost twice as the second one. Since the energy released by the formation of the bonds is equal to the energy needed to let the reaction occurr,why does stronger bond are preferred over lower ones?
I mean, if a S atom needs let's say 170 kJ/mol to start a reaction with another S, shouldn't this be more likely to happen respect to a bond S-O that needs 340 kJ/mol?


texts: How derive g and u symmetry labels for orbitals?

texts:
When asked whether a molecule has an inversion center, we "invert" the coordinates of all atoms; i.e. move each atom from its position through the center of symmetry and to a new position equidistant to the center of symmetry compared to its initial position, and see if the final configuration is indistinguishable from the initial configuration. Simple enough.

I am confused when trying to decide whether molecular orbitals have g or u symmetry. Should I move the atoms through the center of symmetry, should I move "each lobe" through the center of symmetry, or some other way? What is the most general way of describing the symmetry operation for orbitals?

In Figure 1, a bonding $\pi$ orbital is depicted. This is supposed to be antisymmetric with respect to the inversion center in the middle of the bond. It seems therefore I need to invert the lobes, somehow, or move in an "X" fashion across the bond. But this seems different than for the molecular case, where we simply invert atomic coordinates. Figure 2 should be symmetric under inversion, and inverting the lobe positions lead to this result.

And what when the two overlapping orbitals are not of the same type, e.g. a $\pi$ overlap between d and p orbitals? Will the MO ever have g symmetry?

I just fail to get the unifying link between the molecular case and the orbital case.

Edit: Something just hit me: Should I always think of it as "inverting all coordinates within the entity", regardless of whether the entity is an atom or an orbital?

Figure 1. Bonding $\pi$ orbital

Figure 2. Antibonding $\pi$ orbital


texts:
Anyone who stores rust-prone instruments knows that even in temperature-controlled air spaces rust can form on uncoated steel.  Since rust requires water, this suggests that water will condense out of air onto surfaces even above its dewpoint.

How is surface condensation of water above the dew point characterized and quantified?

Or is "condensation" not the right term for this?  There does seem to be a non-linear relationship between relative humidity and the observed effects of that airborne moisture on exposed solids.


texts: Is position of equilibrium path independent?

texts:
I know that if a reaction is at equilibrium, then  changes in condition may change the position of equilibrium and the direction is such shift can be predicted by Le Chatlier's rule. But now we're studying the Haber process and my teacher applied this rule to two reactions happening at different pressures in two different containers (initial amounts added, temp were kept constant for both) . Can Le Chatlier's be used this way? I understand the idea that increasing the pressure will lead to a relatively higher mole fractions of the products in the Haber reaction ( I got this using Kp) but don't see how this is a consequence of Le Chatlier.

So basically, will the position of equilibrium be the same if I let my system come to equilibrium at a pressure A and then increase it to B or if I directly come to B?


texts: Is there a word for a compound that has both ionic and covalent bonds?

texts: For example, calcium carbide (CaC$_2$) has covalent C‒C bonds and ionic Ca$^{2+}$‒ C$_2^{2-}$ bonds.


texts: Can someone suggest me important references for deriving EOM in MCSCF?

texts:
I am currently starting a project dealing with MCSCF method. Can someone please give me references (papers or lecture notes are preferred) which may be considered as the "corner stones" in the history of the development of this method for atoms (for molecule is fine but the for atom will be nice)? I have searched and in fact obtained some papers which look important in this subject but since MCSCF is very popular I am sure there are already loads of papers of various purposes published within the subject, making locating the most important ones difficult. I am also looking for the derivation of the equation of motion (EOM) of the orbitals and coefficients.

Currently I am reading "Computational Atomic Structure - An MCHF Approach" by C. Froesche-Fischer and "The Hartree-Fock Methods for Atoms - A Numerical Approach" also by the same author. But from the terminology the author adopts it looks like these books is not the typical literature a quantum chemistry lecturer would recommend his students to read.


texts:
Pretty simple: If you do not have access to water, what could reduce damage from getting acid on your skin?

I'm a total noob - I studied philosophy - but I know bases neutralize acids. I have a vague sort of idea coal does too? Are there other ways?


texts: Water evaporation from calorimeter giving less exothermic enthalpy value?

texts:
To find the enthalpy change of combustion for an alcohol, you use a calorimeter filled with water and heat it by burning an alcohol.

I was told that usually experimental values for the enthalpy change of combustion are less exothermic than data book values, because of many reasons (eg- heat loss, incomplete combustion etc.)
One of the reasons why the experimental value may be less exothermic is because water has evaporated from the calorimeter.

I don't understand how water evaporating from the calorimeter would make the enthalpy change less exothermic. If the water evaporates, then the mass of water left in the calorimeter is lower, so it would heat up faster, so wouldn't this give a more exothermic result?


texts: Do reactions carried out in light always follow free radical mechanisms?

texts: If light is used in a reaction, is it necessarily a free radical reaction? Or are there some other reactions as well which involve light but don't follow a free radical mechanism?


texts: How can we combine all the three gas laws into a single ideal gas equation?

texts:
In all texts that I have read, it has been stated that the combined gas law for ideal gases was derived from the individual gas laws proposed by Boyle, Charles and Avogadro.

My confusion is this is that, in each individual law, some variables of the system's state are to be kept constant. However, none of these conditions are considered in the combined gas equation. Also, how is it possible for us to suggest that for two states with variables $P$, $V$ and $T$:

$$\frac{P_1V_1}{T_1}=\frac{P_2V_2}{T_2}$$


texts:
I am conducting organic reaction in Dimethoxyethane as solvent in the presence of base (NaOH), but the NaOH is not completely soluble ( Sparingly soluble) in Dimethoxyethane even after the addition of excess of solvent. Peoples says that for a reaction, the reactants must be completely soluble in solvent.

Can someone comments about solubility of Bases during organic reaction?

I actually want conduct similar kind of reaction, the paper mentioned that NaOH and organic compound stirred vigorously until to obtained clear solution. In my case my compound is completely soluble in DME but NaOH is poorly soluble.


texts: Does ionization energy have anything to do with how reactive an element is?

texts:
According to my textbook, fluorine has a pretty high (compared to elements like sodium) first ionization energy. But why does it have such a high requirement to ionize? After all, it actively seeks out atoms to bond with, even tearing through already existing bonds in its drive to do so.

I would expect that fluorine would have a very low ionization energy, as it is soooooooo close to having a full octet (just like sodium). Yet unlike sodium, it has a higher first ionization energy. Why is that?

(My guess is that fluorine's protons' affinity for electrons is so great that it simply "overpowers" the octet rule.)

Apparently, neon can also be ionized. Doesn't that mean it can bond with cations? But it is unusually stable, so why doesn't it?

I think there is an underlying law behind this that can explain these, please help!

EDIT: Fluorine has now been explained, but why can neon be ionized? After all, if you give it a positive charge by taking away electrons, won't it be able to bond to anions? But in reality, it doesn't. What is going on?


texts: What is the difference between a ligand and a co-ligand?

texts: I've seen the word co-ligand pop up in several papers. Is there a particular difference between a co-ligand and a ligand?


texts: Electrical conductivity of organic solvents

texts:
Do organic solvents such as pure ethanol and pure methanol conduct electricity? why is this so?

I have done some research and have not been able to find anything conclusive. I would think it would not conduct because I cannot see any medium for the passage of charge.


texts: Is it possible to make synthetic oil without fossil fuel?

texts:
If human ran out of crude oil and all other fossil fuel, are we still able to create synthetic oil? I've searched online about the raw material of synthetic oil, but I'm still not sure if none of the raw materials is from crude oil.

Also is there any synthetic oil with viscosity less than 10cSt?


texts:
Products known as “descalers” are said by the manufacturers (such as this one) to use electrical impulses to transform calcium bicarbonate (which builds up in pipes and water-using appliances, causing premature failure, and also leaves calcium residue on glassware, clothes, and so on) into calcium carbonate (in a form known as aragonite), which does not adhere -- so the scale problem is solved.

Truth or snake oil?


texts: How much ionising radiation is released during an atomic blast?

texts:
I've been looking for how much ionising radiation is produced during an atomic blast (as a percentage).

I have seen a claim of 5% of the energy in an atomic blast is ionising energy (Wikipedia), but if it's so little why do we put so much emphasis on radioactivity protection when discussing a nuclear blast. It just doesn't add up to me.


texts: How can I keep milk from spoiling and/or turning yellow?

texts:
I am trying to find a way to keep milk from spoiling and/or turning yellow.

Apparently there is a process for achieving this, and I am aware that there is a lady who creates milk beads for resin jewelry and she claims that she is able to prevent the milk from spoiling/yellowing over time.

I have heard that you can add baking soda to milk to preserve it, but this lady also claims that she adds nothing to the milk and that it simply undergoes a "process".

Of course, she won't share her secrets, so my question is:

What are the different ways in which milk can be preserved while preserving the white color?


texts: What causes both components of a binary gas mix to condensate at the same time for a given composition

texts:
Okay, so recently I encountered the temperature - mole fraction diagrams for binary vapour-liquid equilibrium. For now, I only consider two-component systems where the components are very similar and form ideal mixtures, e.g. a 50:50 mix of Benzene and Toluene.

I understand it from the liquid to vapour transition side (i.e. increasing T) and can do the calculations required, but when I start with only vapour (high T) and cool the mix I am confronted by the following problem:

A vapour component can only be in equilibrium with its liquid when it's partial pressure is equal to the vapour pressure (P*) of the liquid - or in the case of mixtures its reduced vapour pressure (Raoult's law: pi = xi.P*).

What bothers me is that the partial pressure of the less volatile component at the dew point is still lower than the vapour pressure of its pure liquid and with no liquid present (yet) there can be no mixing which will lower the vapour pressure. Yet both components condense.

Possible explanations I could come up with include:
A bit of less volatile component condenses and as it has similar properties, small amounts of the other component enter solution (almost like Henry's Law for solubility of gases). This affects rates of evaporation and condensation until equilibrium is reached.

Does this make sense or is there something else happening here?


texts: Process to separate Lauric Acid from Coconut Oil

texts:
I am trying to find a (relatively) simple process to separate lauric acid from other MCTs contained within coconut oil.   I am wanting to obtain a separation of +-5% purity.

One process I am trying is heating the coconut oil until it is completely liquid (~50'C), and then slowly cooling it to ~22'C using a fridge I modified with a digital temperature controller. This process sometimes works in making "solid clouds" of lauric acid in the oil, but not sufficient to separate easily from the remainder of the oil.

Is there something I can try in order to separate lauric acid from the coconut oil, using relatively simple processes?

Any comments welcome.


texts: Is there a way to Determine if an Element can undergo Disproportionation?

texts:
Can we determine the lowest and highest possible oxidation numbers of an element?
Since if we know this, then it is easy to determine whether the element will undergo disproportionation.


texts: Mechanism of Fischer esterification: Does the carboxylic acid gives off OH- or H+?

texts:
For the reaction

$$\ce{R-OH + R'-COOH ->[H+] R-COO-R' +H2O}$$

the reaction mechanism is given here.

What seems unusual to me is that the acid appears to be donating $\ce{OH-}$ rather than $\ce{H^+}$.

Can the mechanism be written as follows instead?

$$\ce{R'-COOH <=> R'-COO^- + H^+}$$

$$\ce{HA-> H^+ + A^-}$$

The inorganic acid pushes the equilibrium for the organic acid to the left and it remains undissociated.

Then, $\ce{H^+}$ from the inorganic acid first attacks the $\ce{O}$ atom in $\ce{R-OH}$ resulting in the formation of a water molecule and a $\ce{R^+}$ ion.

Next, as the equilibrium for organic acid is pushed to the right, the bisulfate ion removes the $\ce{H^+}$ from the acid creating a carboxylate ion. This carboxylate ion then reacts with $\ce{R^+}$ ion to form the ester.

In this mechanism, the carboxylic acid donates the $\ce{H^+}$.

I know one can't prove reaction mechanisms to be correct; however, which one the mechanisms given above is more likely to occur?


texts: Why is the enthalpy of vaporization greater than the enthalpy of fusion?

texts: Why is the molar enthalpy of vaporization of a substance larger than its molar enthalpy of fusion (at constant pressure); for example, in the case of ice and water.


texts: How does light emission depend on temperature by fluorescence?

texts: I have a glass, which emits green light after charging it with sunlight. I though this is fluorescence, and only photons with shorter wave length (than the green light has) can excite the electrons of this material and can be reemitted as green light. At least I remember on something like that from my studies. Now the interesting part that when I wash it with warm water, it starts to emit light too. How do you explain that?


texts: Bases are soapy to touch because of soap formation on contact with lipids present on our skin. If this is the case then why and how is boric acid soapy to touch?


texts: Which isomers (cis or trans) are more water soluble?

texts:
As a general sense I know that cis isomers are less symmetrical and more polar in nature whereas trans isomers are less polar. Now given those information, would it be appropriate to assume that cis isomers are more water soluble owing to their polarity?

Also there was a discussion in our class where my teacher told us that between the cis and trans Butenedioic acids, the cis acid is not water soluble on account of the fact that it undergoes dehydration and the carbonyl groups are bonded by an oxygen atom in between eliminating hydrogen bonds (??).

I would like to know if there is any constant character when it comes to solubility of cis and trans isomers.


texts: Stability comparison on the basis of violation of Bredts rule between 2 bicyclo carbocations

texts:
In the following question ,

Though in part A ,
both the compounds I and II seem to be unstable because of violation of bredt's rule ; that is ; they are sp2 hybridized .

Then how to compare the stability between the two bicyclo compounds?


texts: Are pesticides used on fruit easily washed off?

texts:
I was hoping there'd be someone who studies pesticides here.

Are they water soluble?
Do they get absorbed in to the fruit?
How well would you have to wash the fruit to fully remove the residue?


texts: What is the enthalpy change of neutralisation of vinegar (diluted acetic acid) and calcium carbonate?

texts: If anyone has conducted an experiment that determined this value or knows reliable sources that show the literature/thereotical value of this enthalpy change, please share your answer. Thank you very much!


texts: Why don't we produce water from combustion?

texts:
My friend who is a biology major proposed that we can produce water by burning any hydrocarbure or wood or ... to  obtain water.

$\color{red}{f(x,y,z,\Lambda)}\ce{C}_x\ce{H}_y\Lambda_z+\color{red}{g(x,y,z,\Lambda)}\ce{O_2->}\color{red}{x}\ce{CO_2}+\color{red}{\frac{y}{2}}\ce{H_2O}+\color{red}{\text{other substances}+\text{heat}}$

I know this may be a stupid question but why isn't this method used to obtain pure water? Is it maybe because it releases a lot of heat and a lot of carbon dioxyde or is it because the fuel is more expensive than water?


texts: Disrupting the chemistry of oobleck so that it behaves like a newtonian fluid

texts:
Oobleck (a mixture of cornstarch and water) is a non-newtonian fluid, so it acts like a solid when under pressure, and like a liquid otherwise. My question is this, is there anything you could mix in with oobleck (a friend suggested vinegar, I don't know why) that would cause it to stop being non-newtonian (more specifically, to act like an ordinary liquid). The motivation for this is that I'm going to have a large amount of the stuff, and will need a practical way of disposing of it, like dumping it down a drain.

Thanks in advance for any answers!


texts:
This is the reaction that took place:

This is the information from the $\ce{^1H}$ NMR spectrum:

$$\begin{array}{|c|c|c|}
\hline
\delta \textbf{ / ppm} & \textbf{Relative intensity} & \textbf{Multiplicity} \\ \hline
1.65 & 3 & \text{d, } J = 6.2\ \mathrm{Hz} \\ \hline
1.73 & 15 & \text{s} \\ \hline
2.88 & 1 & \text{dd, } J = 11.0,1.5\ \mathrm{Hz} \\ \hline
3.28 & 1 & \text{dd, } J = 6.6,1.5\ \mathrm{Hz} \\ \hline
3.58 & 1 & \text{dq, } J = 7.0,6.2\ \mathrm{Hz} \\ \hline
3.96 & 1 & \text{ddd, } J = 11.0,7.0,6.6\ \mathrm{Hz} \\ \hline
\end{array}$$

What is the product formed?

I know the product only contains carbon, hydrogen, rhodium, and chlorine, and I think its molecular formula is $\ce{C14H21ClRh}$ (perhaps $\ce{H22}$ instead of $\ce{H21}$). My initial thought was that the diene could displace one chloride ligand to form $\ce{[RhCp^*Cl(C4H6)]}$.


texts: Why is Lanthanum a "fluoride ion sensitive electrode" and hence used for measuring "flouride concentration"?

texts:
My chemistry text book says that "Atomic Absorption Spectrometry (AAS) can be used to determine the concentration of metal ions, but other methods must be used for anions. One convenient method is to use an ion-selective electrode (ISE)." What is the reason? Why can't ASP be used for determining the concentration of anions?

The author then argues that "Lanthanum fluoride crystal doped with europium" is the element used for measuring the concentration of fluorine in water because "fluoride ions bind to the crystal". What is the reason behind choosing "Lanthanum doped with europium"?


texts: Sign of work done by gas during isothermal expansion

texts:
$\pu{10 mol}$ of an ideal gas confined to a volume of $\pu{10 L}$ is released into atmosphere at $\pu{300 K}$ where the pressure is $\pu{1 bar}.$ The work done by the gas is:

Work done can be found as
$$W = -p_\mathrm{ext}(V_\mathrm{f} - V_\mathrm{i}).\tag{1}$$
$$V_\mathrm{f} = \frac{nRT}{p} = \frac{\pu{10 mol}\times\pu{0.083 L bar K^-1 mol^-1}\times\pu{300 K}}{\pu{1 bar}} = \pu{249 L}\tag{2},$$
$$W = -\pu{1 bar}\cdot(\pu{249 L} - \pu{10 L}) = \pu{-239 bar L}\tag{3}$$
As the question is asking us to find the work done by the gas, so shouldn't it be $\pu{+239 bar L},$ as work done by the gas is negative of the word done by external pressure?
But someone told me that the work done calculated is the work done by the gas and $\pu{-239 bar L}$ should be the answer. So, what mistake am I making and how do I determine if work done by the gas (and external pressure) is positive or negative under different conditions (expansion and compression)?
P.S.$\pu{-239 bar L}$ is the answer according to the answer key.


texts: How to translate the mobile phase from thin layer chromatography to column?

texts:
I recently was told that once you find a good solvent mixture for separation on thin layer chromatography (TLC), you should only use 10% of the more polar solvent (for silica) when you run your column. I tried it and it worked great!

Since I'd never heard that before, is that a standard rule of thumb, or did I just get lucky?


texts: Effects of orbital overlap and electronegativity on polarity of binary halogen acids

texts:
I have discerned these factors affecting orbital overlap:

Symmetry
Type of orbital
Nodes along the internuclear axis
$n$ quantum number of the atomic orbitals - the number of shells of electrons
Size of the atoms
Geometry of molecule
Angle of overlap

With respect to the binary halogen acids, I still have the following questions:

I can understand how one might argue that the binary halogen acids become more polar as one goes down group 7, in that electron density isn't very well shared; overlap is poor because of the small 1s orbital of hydrogen and the increasingly larger hybridized orbitals of the halogens. But this is half of what constitutes ionic character.

I.e. what about the electron on hydrogen? As the halogens get bigger, electronegativity decreases. How can the electron from hydrogen be isolated toward the halogen as EN decreases?


texts:
Alkynes can be transformed into ketones or aldehydes, via the corresponding enol, by addition of water in the presence of $\ce{Hg^2+}$.

Similarly, one would expect alkynes to be transformed into enol ethers by using an alcohol instead of water. However I've looked through most organic chemistry textbooks, and they do not seem to make any reference to this. A search on Google also doesn't turn up much. I expected the reaction between alkynes and alcohol would be more commonly mentioned.

Is the reaction between alkyne and alcohol using $\ce{Hg^2+}$ only theoretical that doesn't actually in real life, since textbooks do not introduce this reaction?


texts: Which one is the most stable canonical structure?And why?

texts:
According to my book the answer is given that structure III is the most stable because all the atoms have complete octets.

But I think it should be II because of,

(a) Structure III has positive charge on a highly electronegative atom and

(b) In structure II, the positive charge can be stabilized by the Indicutive effect of Oxygen as well as resonance.

Can anyone provide a more convincing explanation as to why III is more stable?


texts: Water-stable organoaluminum compounds in which aluminum is part of the aromatic ring

texts:
The more common organoaluminum compounds, such as trialkylaluminum, decompose on contact with oxygen-containing molecules (water, ethanol etc). However, my guess is that organoaluminum compounds with an aluminum atom being part of the aromatic system might be more stable towards oxygen compounds, since the high affinity for oxygen of aluminum could be (at least partially) offset by the high energy barrier to destroying the aromatic ring.

My questions are- is my guess correct, and is there any specific aromatic organoaluminum compound that is not destroyed (or acts reversibly at the worst) with water, ethanol, THF (etc)?


texts: What happens to an enzyme after it breaks down a starch molecule?

texts: I am a master distiller at a distillery and I am about to make some whiskey. First adding corn, cooking it and releasing it's starches. After that, will add in some malt, packed with enzymes to break down those starch molecules into sugars. My question is, what happens to the enzyme after it breaks down the starch? can 1 enzyme breakdown multiple starch molecules?


texts: Choice of buffer pH to avoid aggregation

texts:
I want to purify IgG which has a theoretical pI of 6.4-9.0 with an anion exchange column. I also want to keep the pH of my buffers as low as possible and "outside" the range of the pI to prevent aggregation.

Still, I will need to increase the pI so that IgG will have negative net charge and bind to the column. What pH do you think I should choose in order to have the IgG binding to the column and to prevent aggregation as much as possible?

Thanks in advance!


texts: How to explain this acid-catalysed acetal rearrangement mechanistically?

texts:
I have spotted a protecting acetal group and thought this would undergo hydrolysis … My working is such:

But I cannot get to the desired isomer. Could someone please help? (Diagrams would be very much apprecited thanks!)


texts: can a vapour denser than air evaporate in a closed chamber?

texts:
Imagine a closed container filled with air.

There is some liquid substance on a bottle placed on the floor of the container.

Let's heat the liquid until it starts to evaporate. Let's say 20% of the liquid evaporates.

Disregard any effect of pressure buildup in the container which would block the evaporation.

Note: the liquid we are considering generates a vapour that is denser than air, so a "cloud" of vapour would start forming at the bottom on the container, unable to rise. (unlike water vapor for example, which would be less dense than the surrounding air and would start to rise)

If it's not clear enough, imagine what happens when solid carbon dioxide (dry ice) sublimates:

Would this patch of saturated air block the evaporation of the rest 80% of liquid?

I am thinking that the liquid would be soon in contact only with saturated air and the evaporation would stop even though there would be still plenty of unsaturated air in the upper section of the container.


texts: Jahn-Teller Metal : The new state of matter

texts:
Recently it came in the news that scientists have discovered a new state of matter called Jahn-Teller metal. I tried reading up on it but couldn't understand it clearly.

Please explain in simple terms why this is a new state of matter and/or what's so special about it.


texts: Reaction of SeCl4 with alkene and possible consecutive reaction?

texts:
There is a reaction that confused me a bit:

According to my research on $\ce{SeCl4}$, it can be used as a dichlorinating agent for alkenes. However, I am totally confused about the mechanism. I've read about several mechanisms using $\ce{PhSe-SePh}$ as a precatalyst, but in this reaction, there is no other information, apart from the reagent $\ce{SeCl4}$.
If I assume that there is a dichlorination with $\ce{SeCl4}$, I think, the syn-specific dichlorination happens on "top" as the methylene group is sterically less demanding.

Now, if this happens, could there be a subsequent $\mathrm{S_N2}$ reaction with the $\ce{OH}$-group? It could form a 5-membered cycle through a back-side attack on the carbon with the chlorine substituent.

Can you confirm or correct my thoughts about this reaction? Thank you a lot in advance!


texts: experimental evidence of charge separation in zwitterions

texts:
Zwitterions vs ampholytes

The former having charge separation, the latter not. See the abstract from J.E.A. Comer's reference here.

  In particular where he says 'Both molecules have two pKa values. In clioquinol, the base pKa is lower than the acid pKa, so at pH values between the pKa values, the molecule is neutral. However, the acid pKa for ampicillin is lower than the base pKa, and the molecule is charged across the entire pH scale.'

Now, the part that I don't get is how one decides that the 'acid' pKa is this value and the 'base' pKa is that value, and therefore that there is in fact charge separation in the molecule or not (depending on whether intramolecular deprotonation from a hypothetical non-charged species is thermodynamically favoured or not).

Please correct me if I'm wrong. If you have a real substance in front of you and you want to know the pKa's, maybe you dissolve it in water and titrate it with a strong base, starting from very acidic pH, following the pH curve vs the equivalents of base added, and you should get the classic 'jumps' at the points corresponding to the pKa values.
Suppose that in the 0-14 pH range you find 2 pKa's, let's call them pKa1 and pKa2, with pKa1 < pKa2. At that point all you know is that this molecule is initially protonated N times; at pKa1 it will be half N-protonated and half (N-1)-protonated; at pKa2 it will be half (N-1)-protonated and half (N-2)-protonated.

In what was does that tell you where protonation takes place?

In the example from the reference, ampicillin and clioquinol are mentioned.
OK, I agree that from knowledge of chemistry we can say that the pKa of phenols is about 10 and the pKa of pyridinium is about 5, so I don't expect pyridine to deprotonate phenol, or clioquinol to be zwitterionic. But in fact this is an assumption - what do I know of what happens in a molecule where both groups are present, maybe in some particular arrangement that may favour reactions that wouldn't happen intermolecularly?
And for ampicillin, OK, benzylamine is usually sufficiently basic to be protonated by an average carboxylic acid. But how do we know for sure that the ampicillin molecule exists (in solution? in the solid as well?) with a deprotonated carboxyl oxygen and a protonated amino group?

Based on what experimental evidence does one decide that a molecule is zwitterionic or ampholytic, in the sense defined in the above cited abstract?

And are there 'borderline' cases, meaning: can we find in one solution molecules (of the same substance, of course) with zero total charge, but some with charge separation and some not?


texts:
Do all saturated solutions have the same density?  Based on your data, which salt is more soluble?

  \begin{align}
&\ce{NaCl} & \pu{11.812 g/10 mL} \quad &\text{or} \quad \pu{1.181 g/mL} \\
&\ce{CaSO4} & \pu{9.783 g/10 mL} \quad &\text{or} \quad \pu{0.978 g/mL}
\end{align}

I know the first part: all saturated solutions do not have the same density. For the second part I believe that solutions with higher density will be more soluble. So in this example $\ce{NaCl}$ will be more soluble that $\ce{CaSO4}$.

Would I be correct and my answer has to be based on density?


texts: How could you dissolve a coating of CaCO3(s) from a metal plate?

texts:
A metal plate has an unwanted coating of $\ce{CaCO3(s)}$. You must find a way to clean this metal plate without causing any scratches or abrasion. How might you dissolve the coating?

I know I should find a substance that will dissolve the coating, and then soak the plate in it. How do I determine an appropriate substance?


texts: For a copper/copper sulfate half reaction, do sulfate anions move to the anode and lose electrons?

texts:
In my (high school) textbook, there's an example on finding the charge on 1 mole of electrons, which involves performing the electrolysis of an aqueous copper (II) sulfate using a copper anode and a copper cathode. I've been given to understand that in electrolysis, the negative ions move to the anode, and lose electrons to the anode.

However, in this example, the copper anode loses mass as the copper goes into solution as copper ions. What I don't understand is, since the sulfate ions in this case would go to the anode, wouldn't it combine with the copper ions to form copper sulfate? Or wouldn't it donate two electrons to the copper ion so it becomes copper metal again? Since the sulfate ion moves to the anode, shouldn't this happen?


texts: What is the IUPAC name of [Co(NH3)5H2O]Cl3?

texts:
I am not sure if it is Pentaammineaquo cobalt(III) chloride or Aquopentaammine cobalt (III) chloride.
Should the prefix be ignored while naming the ligands in alphabetical order? Besides how should the name be written with proper spacing?


texts: Why would diclofenac have a higher skin permeability when formulated as diclofenac epolamine rather than diclofenac sodium?

texts:
There is a suggestion on the literature that the formation of ion pairs creates a permeation enhancement.
Usually only non-ionised compounds penetrate the skin.
Is it possible that the conjugate species does so?
Some sources claim the epolamine salt has enhanced solubility, others say it is about the same.
Appreciate any help


texts: Why is excluded volume in van der Waals equation divided by 2?

texts:
Source: Physics Stack Exchange

The excluded volume calculated based on the diagram is 8 times the volume of a molecule. The volume is then divided by 2  to give the so-called excluded volume per molecule. Why divided by 2 only?

Obviously more than two molecules can come close together, and their assigned excluded volumes can overlap with each other, giving a smaller $b$. Is $b$ just an upper limit of excluded volume?


texts:
Hydrolysis of C$_6$H$_5$COO$^{18}$CH$_3$ with aqueous NaOH produces what final product.

(a) CH$_3$$^{18}$OH

(b) CH$_3$CO$^{18}$ONa

(c) CH$_3$C$^{18}$OONa

(d) CH$_3$$^{18}$ONa

(e) CH$_3$OH

The correct answer is (a), which is puzzling to me.  I think it should be (d), as when the radiolabeled methoxy leaving group is pushed out by the reformation of the carbonyl, it will be negatively charged.  The only cation that is floating around is Na$^+$.

Where, oh were, did this magical proton appear in basic conditions?

EDIT:  Since I think my comments will get longer I'll just post my question here.  I agree that the methoxy is in equilibrium with water:

CH$_3$O$^-$ + H$_2$O $\rightleftharpoons$ CH$_3$OH + OH$^-$

But the pK$_a$ of methanol is 15.54, and the pK$_a$ of water is 15.74.  Thus this equilibrium will favor the methoxy/water side.  Thus, the slight majority of product should be a methoxy salt.


texts: As sodium ion has a 1+ charge and it can form the ionic compound NaOH with OH1-, hence it is a lone pair accepter (is this correct?). Therefore sodium ion should be an acid?


texts: How do I interpret characters that are not 1 or -1 in a point group table?

texts:
When the character in a point group table is listed as 1 or -1, I understand how an object/orbital etc. transforms to give either itself or the negative of itself.

When the character in a point group table is 2 or -2, what does this mean in terms of transformation? To understand this would be very helpful in terms of assigning the correct irreducible representations to atomic orbitals/LGOs to then determine which pairs mix.

Similarly, I do not understand how to interpret a character of sin or cos of an angle, nor a character of 0.

I am hoping there is a conceptual/visual way of explaining this as I am not up to speed on the matrix math, and the class that this is relevant too does not include that math either.


texts: If α-glucose is less stable than β-glucose, why is glucose almost always α in its compounds?

texts: Maltose, saccharose, turanose, trehalose, trehalulose, amylopectin, amylose - they are all α. Why? Also, why is cellulose β?


texts: how are colloids and suspensions solutions?

texts:
my definition of solution is a homogenous mixture of a solute and solvent.

and in my textbook they call colloids and suspensions solutions . how is this possible if both of them are heterogenous mixtures.


texts:
The anode region is on the iron where the following reaction occurs:
$$\ce{Fe(s) -> Fe^2+(aq) + 2e-}$$

and at the cathode region, the following reaction occurs
$$\ce{O2(g) + 4H+(aq) + 4e- -> 2H2O(l)}$$

However, the textbook does not explicitly state what the cathode region is. Can someone provide an answer?


texts:
The following reaction is allowed to reach equilibrium.
  $$\text{CoBr}_2(g)\rightleftarrows\text{CO}(g)+\text{Br}_2(g)$$
  What happens to the reaction when inert argon gas, $\text{Ar}(g)$, is added?

The solution to this problem states that the addition of an inert gas would not change the concentrations of the other gases, and therefore, the reaction is still at equilibrium.

However, won't adding the argon result in an increase in the pressure of the system, and, to restore the equilibrium, the number of molecules should be reduced and the reverse reaction would be favored? Can someone please explain?


texts: Can someone clarify this rationale for using polar, protic solvents in an Sn1?

texts:
In the textbook I am reading, it states that an Sn1 mechanism prefers a (polar) protic solvent because the protic solvent helps stabilize the carbocation and solvate the kleavin group, facilitating the first step of the reaction. That part I get.

The part I don't get is the protic solvent is also preferred because it behaves as the nucleophile in a solvolysis reaction, attacking the carbocation intermediate to form a new product, such as an ether with an alcoholic solvent. Wouldn't this make a protic solvent not preferable, since you want to original nucleophile reactant to act as the nucleophile, not the solvent? For example in a tertiary carbocation, with a bromine nucleophile, in an alcohol solvent, how would the bromine nucleophile attack the carbocation, if it is being attacked by the alcohol solvent (if this reaction example doesn't really work for an Sn1 reaction, for example because a bromine might react more with the solvent or might approach the electrophile more through an Sn2 reaction, even with a tertiary carbon electrophile used, then please feel free to substitute a reaction where it would be true that the solvent and the nucleophile are different in an Sn1 reaction, where one doesn't want them to "compete" against each other).


texts: Replacement for optical calcite (Glan Thompson prism)?

texts:
I notice that Glan Thompson prisms seem to be the preferred optics for doing polarimetry and have been for at least 75 years. One instrument maker says that polaroid films can be used but they tend to degrade and warp over time.

It seems strange to me that no better substitute has been found for Glan Thompson prisms given their expense. I know at one point Polaroid was saying that Sodium Nitrate crystals (which can be grown) could potentially be used, but this effort seems to have gone nowhere.

Why has no cheaper alternative been found? Aren't there growable crystals that have the birefringence necessary?


texts:
According to quantization it's said that emitted or absorbed energy is quantized.

Then, when it's said in bohr's model an electron changes its orbit (Let's say it goes to a higher energy shell from $n=2$ to $n=3$) The energy difference between the orbits is $100~\mathrm{kJ}$.  Now, according to quantization is the $100~\mathrm{kJ}$ itself a quantum. Or the $100~\mathrm{kJ}$ will be absorbed in quantized way?


texts: "Alternative" derivation of the spin-only formula

texts:
The spin-only formula

$$\mu_\mathrm{so} = \mu_\mathrm{B} \sqrt{n(n+2)} = \mu_\mathrm{B}\cdot 2\sqrt{S(S+1)}$$

is usually a good first approximation to calculate the magnetic moment of transition metal complexes. (I am aware of its limitations.) The usual derivation of this formula involves the Zeeman splitting of the ground state into its separate $M_S$ states under the influence of a magnetic field, followed by evaluating the average magnetic moment using a Boltzmann distribution.

However, if I were to write that $\vec{\mu} = \gamma_\mathrm{e} g_\mathrm{e} \vec{S}$, then I could arrive at the simpler "derivation"

$$\begin{align}
|\vec{\mu}| &= |\gamma_\mathrm{e}|\cdot g_\mathrm{e} \cdot |\vec{S}| \\
&= \frac{e}{2m_\mathrm{e}} \cdot 2 \cdot \sqrt{S(S+1)}\hbar \\
&= \mu_\mathrm{B}\cdot 2\sqrt{S(S+1)}
\end{align}$$

Is this a coincidental result? I'm assuming there is something wrong with the second "derivation", or even worse, it is just an entirely unphysical interpretation, since I am using $S$ instead of $S_z$. What is the mistake?


texts: What is the hybridisation in HCN molecule?

texts:
According to VSEPR theory hybridisation of the central atom should be sp. However, my teacher says that there exists a near-100% s-character in the carbon orbital that bonds with hydrogen due to some other reasons. I couldn't get why that would be the case. One can think of it as the nitrogen that polarizes the carbon atom, but shouldn't it lower the s-character of the C-H bond? What am I missing?
Is it based on quantum calculations (which are beyond my scope) , as a commentator points out?


texts: How to calculate what mass of halothane is inspired in one minute given the partial pressure and temperature?

texts:
If the anesthetic mixture is inspired at the rate of $\pu{100 mL/min}$, what mass of halothane, $\ce{CHCIBrCF3}$, molecular weight $M = \pu{197.4 g/mol}$, is inspired in one minute if the partial pressure of halothane is $\pu{7.6 torr}$ and the temperature is $\pu{21 ^\circ C}$.

  $\pu{0.08g}$
  $\pu{0.80g}$
  $\pu{1.80g}$
  $\pu{3.36g}$

My working:
\begin{align}
P &= \pu{0.01 atm} &&(\pu{1 atm} = \pu{760 torr})\\
T &= \pu{294 K}    &&(273 + 21) \\
V &= \pu{1 L}      &&(\pu{1000 mL} = \pu{1 L})\\
R &= 0.08          &&(\text{L-atm})\\
\end{align}
Equation:
\begin{align}
  0.01 \times 1 &= n \times 0.08 \times 294\\
  0.01 &= n \times 23.52\\
  n &= 4.3
\end{align}

Which suggest $\pu{4.3 mol}$ of $\ce{CHCIBrCF3}$ which would give the mass $\approx\pu{849g}$.

That is way off any of the answers. Can someone see what I have done wrong?


texts: How can I get analytical form of GTO primitives for a atom?

texts:
As I know, for Hydrogen atom a $1s$ Slater Type Orbital (STO) equation is (I can get it from here):
\begin{equation}\label{STO}
    \mathrm{STO} = \sqrt{\frac{\zeta^3}{\pi}} e^{-\zeta r}.
\end{equation}
With remark from Szabo A., Ostlund N.S. Modern Quantum Chemistry: Intro to Advanced Electronic Structure Theory, Dover, 1996:

For example, the standard exponent  for the $1s$ basis function of hydrogen is , $\zeta = 1.24$. This is larger than the $\zeta = 1.00$ exponent of the hydrogen atom, since the hydrogen $1s$ orbital in average molecules is known to be "smaller" or "denser" than in the atom.

Gaussian Type Orbital (GTO) equation for $1s$-orbital (where did this coefficient $\left(\frac{2\alpha}{\pi}\right)^{3/4}$ come from?):
\begin{equation}
    \mathrm{GTO} = \left(\frac{2\alpha}{\pi}\right)^{3/4} e^{-\alpha r^2}
\end{equation}
So, I have good analitical form of Hydrogen STO and GTO, and using formula
\begin{equation}\label{}
    \sqrt{\frac{\zeta^3}{\pi}}e^{-\zeta r} \approx C_1 \left(\frac{2\alpha_1}{\pi}\right)^{3/4}e^{-\alpha_1 r^2} +  C_2 \left(\frac{2\alpha_2}{\pi}\right)^{3/4}e^{-\alpha_2 r^2} +  C_3 \left(\frac{2\alpha_3}{\pi}\right)^{3/4}e^{-\alpha_2 r^2}.
\end{equation}
and copyng $\alpha_i$'s and $C_i$ from basissetexchange.org
#-----------------------------------------------------
# Basis Set Exchange
# Version v0.8.13
# https://www.basissetexchange.org
#-----------------------------------------------------
#   Basis set: STO-3G
# Description: STO-3G Minimal Basis (3 functions/AO)
#        Role: orbital
#     Version: 1  (Data from Gaussian09)
#-----------------------------------------------------

BASIS "ao basis" PRINT
#BASIS SET: (3s) -> [1s]
H    S
      0.3425250914E+01       0.1543289673E+00
      0.6239137298E+00       0.5353281423E+00
      0.1688554040E+00       0.4446345422E+00
END

I can plot Hydrogen orbital

Now I want to do the same for a Lithium atom using data
BASIS "ao basis" PRINT
#BASIS SET: (6s,3p) -> [2s,1p]
Li    S
      0.1611957475E+02       0.1543289673E+00
      0.2936200663E+01       0.5353281423E+00
      0.7946504870E+00       0.4446345422E+00
Li    SP
      0.6362897469E+00      -0.9996722919E-01       0.1559162750E+00
      0.1478600533E+00       0.3995128261E+00       0.6076837186E+00
      0.4808867840E-01       0.7001154689E+00       0.3919573931E+00
END

But, I do not understand where I can get a analitical formula for GTO's primitives. All of references,  I saw:
\begin{equation}\label{GTO}
\mathrm{GTO}(x,y,z;\alpha,\ell_1,\ell_2,\ell_3) = N  x^{\ell_1} y^{\ell_2} z^{\ell_3} e^{-\alpha r^2}
\end{equation}
with  unknown normalizing factor $N$. Sometimes I saw for $1p$-orbital
\begin{equation}
\mathrm{GTO}(p_x) = \left(\frac{128\alpha^5}{\pi^3}\right)^{1/4} x \exp(-\alpha r^2)
\end{equation}
but I don't understand where the factor $\left(\frac{128\alpha^5}{\pi^3}\right) $ comes from.
So, my general question: where can I see the analytical view of the GTO primitive (like for STO's), and how can you find $\zeta$ for atom obital? (how to read such data?)


texts: What happens to magnesium in water with acid?

texts:
I have a pure hunk of magnesium metal submerged in water. After several hours/days, the metal becomes coated with something.

Question 1:
What is the coating?

I've been told it's magnesium oxide. This would make sense to me if it was exposed to air, but it's submerged in water. Is it still MgO? I'll assume there is enough free oxygen in the water to react slowly.

If I add an acid to the mix, the coating gradually disappears. I use some malic acid crystals. Where does the MgO go?

Question 2:
What is in the water when the coating disappears?

As the coating disappears to expose the metal, the magnesium reacts more and more vigorously offgassing hydrogen, which I understand would leave magnesium malate in the water. But what about the MgO? Does the acid react with MgO? And either way, where does it go? Is the MgO just dissolved invisibly in the water or is it reacting to form something else?


texts:
There are two containers connected to each other but separated by a cork. If container(1) has a gas $G_1$ at a volume $V_1$,  pressure $P_1$ and temperature $T_1$ and similarly in container(2) there is a gas $G_2$ at volume $V_2$, pressure $P_2$ and temperature $T_2$. If the cork between the containers is removed and the temperature changed to $T_3$ what is the pressure of the mixture inside the system of containers.

My textbook gives it as:

$\frac{P_1V_1}{T_1}+\frac{P_2V_2}{T_2}=\frac{P_3V_3}{T_3}$

where $V_3$ = $V_1$+$V_2$

$P_3=\frac{T_3}{V_3}\left(\frac{P_1V_1}{T_1}+\frac{P_2V_2}{T_2}\right)$

I don't understand how that comes out. Can we just add the constants(of combined gas law) like that?


texts: The atomic size on going from aluminum to gallium decreases because of poor shielding effect of the $(n-1)d$ electrons, but on going from copper to zinc, the size increases due to the same shielding effect. Why ?