texts: Correlation between Coulomb's law and VSEPR theory

texts:
I've always been told in chemistry lessons that lone pairs repel more due to a greater charge density than bonding pairs. And that makes sense when steric effects are involved when bond orbitals overlap.

But this conflicts with what I have learnt in physics i.e. Coulomb's law, which states that the only thing affecting the force between two charged bodies is the magnitude of the charge and the distance between them. Therefore it seems weird to me that a lone pair should "repel" more because of greater charge density, despite having the same charge magnitude as a bonding pair.

What am I neglecting or if I'm right, does that mean for large atoms (such as iodine, where electron pairs are further apart) the lone pairs and bonding pairs repel equally as per Coulomb's law?


texts: Mechanism of the oxidation of alcohols with KMnO4

texts:
Many oxidising agents, like chromate, dichromate, iodine in $\ce{NaOH}$ etc. seem to work via ester formation and elimination. For example, chromic acid will react with the $\ce{-OH}$ of alcohol to form a chromate ester, and then this will undergo an E2-like elimination, with a proton abstracted from carbon and loss of leaving group from oxygen.

However it seems that manganate works via a different mechanism. I think this because here:
http://www.masterorganicchemistry.com/2015/05/21/demystifying-alcohol-oxidations/

It says in a footnote at the bottom:

  "..main exception you’ll encounter is $\ce{KMnO4}$, which likely proceeds through a C-H abstraction/internal return type mechanism followed by collapse of the hydrate to give the new carbonyl."

I don't quite understand this brief summary of the mechanism, could someone expand on it? I don't quite understand what "internal return type mechanism" is refering to - I kind of understand it refers to something a little like the "intimate ion pair" in the $\mathrm{S_Ni}$ mechanism, but haven't been able to find online a more expanded mechanism - many places seem to show it like the case of chromic acid above, and so I am slightly confused as to what mechanism it really follows.


texts:
I am very confused about bond energy. In my book, it says "the most stable bond is the bond with the highest bond energy". However, later on it mentions that " A system with low energy is a stable system. Thus, a bond is formed when electron energy level is the lowest".
So, does high energy means more stability or less stability?


texts: How to sketch reaction coordinate plot from mechanisms?

texts: I am interested in learning about strategies for drawing reaction coordinate plots from the reaction mechanism. The sketches I am after don't need to be highly accurate or precise, but should reflect any notable intermediate states. For example, how would I draw the reaction coordinate diagram of a nucleophilic substitution of an arene showing features like the formation of the sigma complex, and the return to aromaticity via depronation?


texts: Half equations for H2O2 for its reducing and oxidising nature in acidic and alkaline medium

texts:
Is there a complete list of all the half equations for $\ce{H2O2}$ - both oxidation and reduction, in acidic and alkaline conditions? I've looked on the internet but can't seem to find a list with all of them.

These are my first attempts:

$\ce{H2O2 + 2e^- -> 2OH^-}$ (in alkaline conditions)
$\ce{H2O2 + 2H^+ + 2e^- -> 2H2O}$ (in acidic conditions)
$\ce{H2O2 -> 2H^+ + O2 + 2e^-}$ (in acidic conditions)

Are these correct and are there any more?


texts: In the textbook of "A Guidebook to Mechanism in Organic Chemistry" by Peter Sykes, it is mentioned that peroxides are radical sources and quinones are radical absorbers or scavengers, but it had no explanation, and quick search gave results about HALS, but not about quinones. Also I understand that peroxides can act as radical sources due to homolytic cleavage and its 'O-O' bond energy being very low, around 140 kJmol^-1. But can you explain how quinones are good radical scavengers? Also its mechanism, if any, would be appreciated.


texts:
I have heard that acids taste sour because of hydrogen (I don't really know exactly).  According to the definition of acids:

  An acid (from the Latin acidus/acēre meaning sour) is a chemical substance whose aqueous solutions are characterized by a sour taste, the ability to turn blue litmus red, and the ability to react with bases and certain metals (like calcium) to form salts

Some acids may not contain hydrogen.  Would they also taste sour?


texts:
I just need an explanation of why it is a strong acid in its first ionization and a weak acid its second ionization.

It becomes $\ce{HSO_4-}$. From what I have learned about oxoacids, the bond strength determines the strength of the acid. So why does it become harder for the molecule to ionize the second time after it loses a hydrogen atom. Just can't think of how it will affect the strength of the bond connecting oxygen and hydrogen.


texts: What is the order of adding chemicals in Hummers method for graphite oxide?

texts:
I am trying to make graphene oxide but failing miserably. The XRD peak is at 24 (2θ) instead of being near 10. Raman shows correct g and d peaks but are not very sharp. The colour of the end product is not yellow but grayish.

I have followed all the steps of Tour's and Hummers's methods.

But I am confused about should I add Graphite powder/flakes to $\ce{H2SO4}$ or $\ce{H2SO4}$ to the powder. And when should I add NaNO3 and how?

What I have tried is adding the $\ce{NaNO3}$ and graphite powder and mixing them and then added this mixture to the $\ce{H2SO4}$ and followed the rest of the process. Dried it at 60°C for over two days.

Also it will be helpful to know if the stirring rpm matters.


texts: What exactly happens at the critical solution temperature of a phenol water system?

texts: What makes phenol that was turbid go clear beyond the critical solution temperature? We say beyond the critical solution temperature the constituents become soluble. What is the reaction or the exact change involved in the phenol water system (say with water in excess) beyond the critical solution temperature.


texts:
...or at least I thought so, when I saw that the ink that was on my whiteboard last night became really messed up the next day.

The image below shows my whiteboard before (on the left) and after (on the right). The time span was one night.

As you can see, the words became really squiggly, and they mostly travelled downwards.

When I woke up, a few hours before I noticed my whiteboard mess, I noticed lots of condensation water on my whiteboard due to my air-conditioner (my whiteboard is made of glass, if it matters).

My theory is that the water pushed the oil surfactant* of the marker ink mostly downwards. The oil surfactant in the ink coats the board to ensure easy erasing, so the oil should be the closest chemical to the board. Since oil and water are immiscible, the hydrophobic oil ended up being pushed away by the sliding condensed water (sliding due to gravity) and the ink travelled down.

However, my theory does not explain why the ink travelled upwards in some parts of the board. I have not shown it here due to sensitive information.

Is my theory lacking? What do you guys think about this phenomenon? And no, it wasn't a prank.
Can the ink travelling in directions other than downwards be explained?

  *Regarding ingredients, all alcohol-based dry-erase marker inks contain 4
  basic ingredients:

  Release agent- an oily (can be simply a mineral oil) surfactant or co-
  solvent which will coat the board to provide easy erase barrier (such that
  the colorant slides off of the board surface and does not penetrate or
  stain over time)


texts: What is the IUPAC name of tert-pentyl? I know that isopentyl is 2-methylpentane and neohexyl would be 2,2-methylhexane, but what about tert?


texts: Which half cell equation do you switch when calculating E° cell?

texts:
Given the following standard potentials calculate the overall $E^\circ_\mathrm{cell}$:
$$
\begin{align}
\ce{Pb(SO4)(s) + 2 e- &→ Pb(s) +SO4^2-(aq)} &\quad E^\circ &= \pu{-0.356 V} \\
\ce{Pb^2+(aq) + 2 e- &→ Pb(s)} &\quad E^\circ &= \pu{–0.125V}
\end{align}
$$

I know the answer should be $\pu{0.231 V}$. I was told that $E^\circ$ cell always has to be positive. I tried doing this:
$$E^\circ_\mathrm{cell} = E^\circ_\mathrm{cathode} - E^\circ_\mathrm{anode} = \pu{0.231 V}$$
The only way I get the correct answer is if I do not switch the negative sign of the standard reduction potential of the first equation to a positive sign. Is that correct? I thought you always had to switch signs if you reversed the equation?


texts: The dissolution of calcium carbonates in water

texts: Kindly help out. It is generally know that calcium carbonates has poor solubility in distilled water. Hence its ability to form slurry becomes difficult. Studies have shown that eggshells contain basically calcium carbonates.  I conducted an experiment in modification of eggshell powders with anionic surfactant in order to improve its solubility in water.  I carried out solubility and dissolution test on the modified eggshell powder. This was compared against the raw eggshell in order to confirm its solubility rate.  ICP was used to calculate the calcium  content in the solvent filtrate.  The reusults is showing that the calcium content in filtrate was higher than that of the modified eggshell.  Please who can assist in explaining this phenomenon. Thanks.


texts: The affect of effective nuclear charge on energy gap between subshells

texts:
A few days ago my teacher taught me about $\mathrm{d}$ orbital contraction. He said that in $\ce{SF6}$ the hybridization of sulphur is $\mathrm{sp^3d^2}$. He said that although the $\mathrm{d}$ orbital is higher in energy than $\mathrm{s}$ and $\mathrm{p}$ orbitals due to increase in positive charge on sulphur, due to high electronegativity of flourine the $\mathrm{d}$ orbitals contract more than $\mathrm{s}$ and $\mathrm{p}$ orbitals, hence the difference in energy decreases and $\mathrm{d}$ orbital can participate in hybridization.

There was no problem with the explanation as it seemed perfectly plausible. But today, while teaching MOT, he told that the gap between $\mathrm{2s}$ and $\mathrm{2p}$ orbitals increases as we move from lithium to flourine due to increase in effective nuclear charge and interelectronic repulsion, which is quite opposite to what he told some days ago.

What am I missing? Which of the following interpretation is correct? A qualitative explanation involving less of quantum mechanics is that I want and involving MOT and VBT only because I know only those theories. According to advanced theories d orbitals will not participate in bonding in SF6 but according to VBT they will. As I already mentioned that I know only VBT and MOT so I have asked the question in the context of these two theories.


texts: I have recently read one post over here in chemistry exchange about tastes of ionic salts, some described lead and beryllium ones to be sweet but toxic, some my point is there any salt that is relatively non-toxic (NaCl for example) but tastes sweet (unlike NaCl)


texts: How are odor and electronic structure related to aromaticity?

texts:
I know that cyclic planer molecules with $2n + 1$ $\pi$-electrons are aromatic. Also, the color of a compound is due to electronic transitions. But how is it related with aromaticity (smell)? Is there any such relation or is it the chemical property of any compound (matter)?

If it is chemical property of matter then what is its cause?

P.S. My question isn't about nomenclature, its about what is in benzene or any other aromatic compound that make it aromatic i.e. their smell? And what specifically is the roll of electrons in their smell?


texts: Transformation of acyl group to carboxyl group in biphenyl system with two acyl groups at para position

texts:
How do I perform this reaction?

I have prepared 4,4'-acylbiphenyl and want to make one acyl group into $\ce{-OH}$ and other into $\ce{-COOH}$ group.


texts: Verify my expected product of two acid/base reactions and does chosen solvent change reaction?

texts:
My education in chemistry goes as far as what I research on the internet. I have two different acid/base reactions for which I've tried to predict the resulting product.  Can anyone here verify if I did this right or have an alternative prediction?

Reaction 1: p-toluenesulfonic acid (anhydrous) $\ce{C7H8O3S}$ reacts with potassium hydroxide $\ce{KOH}$. From this I calculated I should expect toluene $\ce{C7H8}$, potassium sulfate $\ce{K2SO4}$ and water $\ce{H2O}$:

$$\ce{C7H8O3S + 2KOH -> C7H8 + K2SO4 + H2O}\tag{1}$$

Reaction 2: p-toluenesulfonic acid (anhydrous) $\ce{C7H8O3S}$ reacts with
sodium bicarbonate $\ce{NaHCO3}$:

$$\ce{C7H8O3S + 2NaHCO3 -> C7H8 + Na2SO4 + 2CO2 + H2O}\tag{2}$$

If correct, then both of these reactions result in toluene. Does anyone think I got it right (or wrong)?

If the p-toluenesulfonic acid is dissolved in hexane, and I wish to neutralize it, neither base is soluble in hexane. If I first dissolved the base in ethanol (anhydrous) which is miscible with hexane (if I'm using the term correctly), will it neutralize the acid in the hexane, and does the fact that hexane and ethanol are involved change the reactions above? Any prediction if the ethanol was 95% instead of anhydrous?

So separating ethanol from hexane is easy if you want to keep the hexane -- just add water and separate. But if I actually have hexane/ethanol/toluene and add water and dispose of the ethanol/water solution, I'm assuming I'm left with a hexane/toluene mix. The toluene has a much higher polarity than hexane, but much lower one than ethanol. Toluene has a boiling point higher than water, and approx. 40 degrees higher than hexane.

Under this circumstance it appears removing toluene from the hexane and solute is not realistic, and would leave me distilling the toluene from my solute at a too high a temperature for the solute ($\pu{111^\circ C}$) whereas the boiling point of hexane is more like $\pu{68^\circ C}$.

If I'm correct, is there any thoughts on how to neutralize the acid in hexane without creating toluene which is not easy to separate from the hexane or am I stuck with toluene as long as I use this particular acid?


texts: Why does the derivation Gibbs-Helmholtz equation hold when the enthalpy is temperature-dependant

texts:
The derivation shown here assumes H and U are independant of temperature, right? But what if $H(T) = H_{0}+C_V \Delta T $?

Then $dG = C_V\, dT - SdT$, right? So
$ \displaystyle \left( \frac{\partial G}{\partial T}\right)_p=C_V -S$ ?

$$\begin{align}
\left(\frac{\partial (G/T)}{\partial T}\right)_p &= \frac{T(\partial G/\partial T)_p - G(\partial T/\partial T)_p}
{T^2} \\[8pt]
&= \frac{T(C_V-S) - G(1)}{T^2} \\[8pt]
&= \frac{TC_V-TS-G}{T^2} \\[8pt]
&= -\frac{H_0}{T^2}
\end{align}$$

as desired (since $G = H_0+C_V\Delta T - TS$).

But this way we see that the H in this equation would only be containing the constant term? Of course we insert H(T) to get thee exact G, but where in my thinking process did I go wrong? How would this derivation be made correctly, assuming that H changes with Temperature?


texts: What are the effects of salt additives and impurities on the CMC?

texts:
I understand what a critical micelle concentration (CMC) is, however I do not know why or how impurities or salt additives affect it when measured in specific ways. Any help is much appreciated.

So what determines whether they are stabilizing or destabilizing? If it interacts with the head group, how does this change the CMC and why? The head group already has a counter ion present?


texts:
I was wondering if substituted pyridines can work the way pyridine does in order to oxidize alcohols to aldehydes.
Of course, I'm referring to pyridines without any functional group which can undergo oxidation reactions (eg: I was thinking methylpyridine, or trimethylpyridine, with the nitrogen untouched.)

I guess that the reactivity is the same, but is there any reference to the use of this kind of reagent?


texts: Is there a way to estimate the nutritional calorific value of a chemical

texts:
The chemical in question is L Carvone. It is an ingredient of some flavors. Tastes and smells like spearmint.

What's a good way to estimate its calorific value? If any. I cannot see it as a carb / protein / fat etc.

Does it have a calorific value at all?


texts:
How to name this cyclic compound with an O in it?

I was going to name it cyclobutane, but not all of the atoms making up the ring are carbons, one is an oxygen. So, then I decided to name it butane, but that doesn't make sense because there is a ring.


texts: Why isn't CH3OH basic if it contains OH?

texts:
I was asked to find the most basic solution from the following:

  $\ce{K2SO4}$
  $\ce{CH3OH}$
  $\ce{Na2CO3}$
  $\ce{(NH4)2CrO4}$
  $\ce{BaCl2}$

I know that I have to identify the solution that contains the conjugate base of a weak acid.

Knowing this, I immediately eliminated $\ce{BaCl2}$ ($\ce{HCl}$), $\ce{K2SO4}$ ($\ce{H2SO4}$), and $\ce{(NH4)2CrO4}$ ($\ce{H2CrO4}$ — which I've heard is a strong acid).

This left $\ce{CH3OH}$ and $\ce{Na2CO3}$.

The correct answer is $\ce{Na2CO3}$ since $\ce{CO3^{2-}}$ is the conjugate base of $\ce{H2CO3}$.

However, why can the final answer not be $\ce{CH3OH}$, especially considering that $\ce{OH}$ is basic? Also, could $\ce{OH}$ be considered the conjugate base to a weak acid?


texts: Difference between batch and column mode?

texts:
I have heard Ion-exchange chromatography can be used in batch or column mode, have you got any idea how are those modes?

I have looked descriptions all over books and web (Skoog for example, both versions of analytical chemistry) but found nothing clear.

Any help?


texts: Why does coumarin predominantly exist in keto form?

texts: By applying the logic that phenol exists in enol form rather than keto form as it attains aromatic character, why is it not the case in coumarin?


texts: Using MP-AES, can I accurately say I've found a metal concentration on one wavelength and not another?

texts:
I've been given the opportunity to use an MP-AES for metal detection. I'm testing traces of metals in plants. The plant matter is digested so I have a liquid solution, I expect there to be a lot of matrix affects within this.
I have tried to use a couple of wavelengths for each metal cadmium, arsenic and lead.

Arsenic has a lot of carry over, and may be sticking to the plasma?
I'm ignoring it for now.

What I want to understand is the different ppm readings for the wavelengths, when looking at cadmium and lead. The 'u' symbol means that the concentration is below the limit of detection, but on another wavelength there is some concentrations of metals that are detected.

Is it biased to only be using the data from the wavelengths where metal has been detected? Even then, can I say that this concentration would be the correct amount in the solution?
Should I be trialling other wavelengths?

I'm struggling with what to search for when looking into the literature for something like this.


texts:
I would like to know how and under what conditions can decarboxylation of salicylic acid (o-hydroxybenzoic acid) occur. I couldn't find any sources for it online. Here are some reasons I think it would happen:

The $\ce{COOH}$ group is out of plane of the benzene ring due to the ortho $\ce{OH}$ group, making it easier to decarboxylate.
The keto form is a beta keto-acid, which makes it easier to undergo decarboxylation.


texts:
In many of the precious metal refining videos Cody (Cody's Lab) takes the sample with the precious metal and puts Litharge into it. After heating it in the furnace, while pouring it out the molten lead comes out and Cody says that the precious metal is all inside the molten lead(Later extracting it using cupellation). How does this happen?
https://www.youtube.com/watch?v=vltBwXncjCI&t=369s
From 3:01
Edit: My doubt is specifically the processes involved during Litharge Smelting.(that result in the precious metal being alloyed with lead)Why is Cody confident that all of the silver has been alloyed with the lead? Why cant the silver form a separate mass? My speculation is that all the impurities except the precious metal melts, the litharge is reduced into lead, the molten lead being denser than other molten impurities sinks to the bottom ,the silver being the densest goes to the bottom to meet lead and they alloy. Is this possible?


texts: What Determines the Value of Symmetry Factor (Charge Transfer Coefficient) and What is its Connection With Transition State Structure/Configuration?

texts: I know that symmetry factor determines symmetry of energy barrier for reduction and oxidation. It is an fraction of electric potential energy difference of electron in electrochemical double layer which raises or lowers the activation energy for reduction. What I don't understand is what determines its value in context of physical picture of electrochemical processes in double layer. Why is its value 0,5 for some reactions and 0,4 or 0,7 for some other? In some electrochemistry textbooks its value is connected to configuration/structure of transition state although I don't understand this very well.


texts:
8 Calcitriol is a steroid hormone found in human blood.

Calcitriol shows geometrical isomerism.
Give the number of geometrical isomers of calcitriol, including calcitriol.
I’m confused I think it doesn’t have a single geometric isomer because rotation is restricted in cyclic compounds! What is the concept behind it!


texts: How can I dispose of chlorine and sodium hydroxide as table salt and water?

texts:
If I used chloralkali electrolysis of brine to produce hydrogen, and can't use the other products (or not all of them), what route(s) can I take to revert them back to brine? I figured, since I have to put in energy to take the brine apart, it should have some desire to reform.

With the $\ce{H2}$ taken away, the remaining products are:

$$\ce{2 NaOH (aq) + Cl2}$$

If I just mix them, I get sodium chlorate or hypochlorite. Can I process those further?

Both $\ce{H2O}$ and $\ce{NaCl}$ have a negative $\Delta H_\mathrm{f}^\circ$ ($\pu{-285.8 kJ/mol}$ and $\pu{-407.0 kJ/mol}$ respectively), and $\ce{Cl2}$ is already in its standard state, so we would need to overcome the $\Delta H_\mathrm{f}^\circ$ of the $\ce{NaOH}$, which is negative as well ($\pu{-470.1 kJ/mol}$). Can I use ion filters to some benefit?

Routes that allow retrieval of some of the energy spent for the electrolysis are favored (i.e. the more exothermic, the better).


texts: Is dis molecule having a plane?or inversion centre or what?and what is it's point group?


texts:
The Problem

An unusual reference gives the formula below for the heat transfer coefficient of an emulsion.
$$H = 0.0061\left(X^{0.6} + 0.038T\right)\cdot V^{0.35}$$
In the formula $T$ is the temperature in $\pu{^\circ F}$, $V$ is the flow rate of the emulsion in $\pu{\frac{ft}{min}}$, $X$ is a characteristic dimension in inches and $H$ is the heat transfer coefficient in $\pu{BTU h^-1 ft^2 ^\circ F}$.
Calculate the heat transfer coefficient in $\pu{W m-2 K-1}$ when emulsion at $\pu{30 ^\circ C}$ flows at $\pu{1.25 m s-1}$ and the characteristic dimension is $\pu{0.8 mm}$.

My Attempt

I converted the characteristic dimension ($X$) from $\pu{mm}$ to $\pu{in}$.

$$\pu{0.8 mm} ⋅ \frac{\pu{39.37 in}}{\pu{1000 mm}} = \pu{0.03 in}$$

I converted the temperature ($T$) from $\pu{^\circ C}$ to $\pu{^\circ F}$.

$$\frac{(n \ \pu{^\circ F} - 32)}{1.8} = 30 \ \pu{^\circ C} $$
$$n \ \pu{^\circ F} = \pu{86 ^\circ F}$$

I converted the flow rate of the emulsion ($V$) from $\pu{m/s}$ to $\pu{ft/min}$.

$$\frac{\pu{1.25 m}}{\pu{s}} ⋅ \frac{\pu{3.28 ft}}{\pu{m}} ⋅ \frac{\pu{60 s}}{\pu{min}} = \frac{\pu{246 ft}}{\pu{min}}$$

I plugged the values of $X$, $T$, and $V$ into the equation to solve for $H$.

$$H = 0.0061\left(0.03^{0.6}\ \mathrm{in} + 0.038(86\ \mathrm{^\circ F})\right)\left(\frac{246\ \mathrm{ft}}{\mathrm{min}}\right)^{0.35}$$
Is my work correct so far? If yes, I'm a little confused as to what I should do next. How do I simplify the units in my last step in order to then convert to a value with the desired units $\pu{W m-2 K^-1}$?


texts: Analyzing alternating metals in a polymer matrix with 1 micrometer depth and only 10% metal

texts:
This is a theoretical question that I am struggling to get started on for a seminar discussion. If you were attempting to design an instrument with all the basic components (source, analyzer, detector, sample holder) what type of each component would you use and why? The sample is alternating layers of heavy metal in a polymer matrix with 1 micrometer depth and 10% metal
My instinct is that if this is a metal we should use the photoelectric effect and potentially look at scattered electrons. If we are looking at electrons some time of photomultipler could amplify the signal but how would the different electrons from different metals be analyzed? What type of source would be most appropriate?


texts: Do all gases occupy same volume at equal temperature and pressure conditions?

texts:
Why does one mole of all gases occupy 22.4 L at standard temperature and pressure? According to my thinking, it may be due to equal diffusion of all particles when at a particular temperature and  pressure.

So going by this, one mole of all gases should occupy the same $x~\mathrm{L}$ at some other temperature-pressure conditions. Is this true?


texts:
I want to ask a question about the overlap integral.

I was studying about the MO diagram of $\ce{H_2^+}$ and we managed to derive an expression which had the following term:

$$\langle \mathrm{1s}_\ce{A}(r_\ce{A}) | \mathrm{1s}_\ce{B}(r_\ce{B}) \rangle$$

and our lecturer later explained that this is known as the overlap integral.

  The overlap integral is the magnitude to which the atoms overlap when combining AOs to produce MOs.

The trouble is, I later wanted to find a proof for this idea in order to confirm my understanding of this idea, but could not find anything that could explain this phenomenon from principle.

I did come across this question, but this only explained its main definition and not actually any derivation from basic principle.

How can the overlap integral be explained from basic principle?


texts: What do the molecular orbitals of a single water molecule look like?

texts:
Some time ago, (a few years back) I heard that the orbitals of a single water molecule were solved analytically (or was it just numerically). What do they look like?

I am interested in the shape (and equations) of those orbitals. There should be an exact solution around and that is what I am looking for (no LCAO or similar please).


texts:
With the following setup: plastic container, water (impure), pencil (anode), tin foil (aluminum, cathode) and solar panels supplying electrical charge (roughly 36v at about 400-800ma), with the intention of producing lye via electrochemistry:

1) Would it be possible to produce the right kind of lye to a level sufficient to produce handsoap with this current setup?

2) How would you test the lye quality to be sure?

If not possible to make the right quality lye, is there a way to modify the setup so it's able to produce suitable quality lye for soapmaking?


texts: Contradictions in acidity and solubility of phenol derivatives

texts:
o-Nitrophenol is less acidic in comparison to p-nitrophenol due to intramolecular hydrogen bonding. This effect also is the reason for o-nitrophenol being less soluble in water.

At the same time, hydroquinone (para) is less acidic than catechol (ortho).
Of course there is the inductive effect, but a reason mentioned quite often as well is hydrogen bonding. Isn't it contradictional that the reason given for o-nitrophenol being less acidic than p-nitrophenol is the same reason given for catechol being more acidic than hydroquinone?


texts: Painting corroded 9V battery contacts with vinegar

texts:
I have an old radio with corroded 9V battery contacts, probably from a battery that corroded though I don't know.

I wanted to clean up the contacts with 5% vinegar since that works with pennies, but this is not something I can dunk in a small container since it is attached (with a very short wire) to the radio).

So I want to thicken vinegar to a gel, and not change the pH.  I would rather do this slowly, I can leave the solution on the contact for as long as necessary.

A high school chemistry teacher suggested vaseline as a thickener.  I just wanted to get a second opinion that vaseline will not somehow cause a problem?  Glycerin was also mentioned.  Could either react in any way with the metal electrode?

If I use either, presumably the acididy will decrease by dilution with the thickener.  Is this linear, or does the thickening of the solution have any other affect on acids?  I can try treating the surface for a few hours, or a day, then how could I get it off?  My guess is a cotton swap with water and detergent to clean off the gel?

I am not 100% sure what the surface of the contact is, it could be a nickel alloy, it certainly is a formerly shiny silvery metal, now somewhat dulled with green raised bumps on it from some former chemical reaction.

If you think I should just apply vinegar, or anything else for that matter, with a cotton swab I could do that, I just want to be able to apply something and clean up the surface with a minimum of effort.


texts: How to accurately determine mass transfer using balances?

texts:
I had troubles the other day using a balance that goes to the tenth of a milligram place (i.e. .0005 vs .001 g), when trying to determine how much solid I transferred. I would take some amount of mg, record it, and then set it aside. I'd take the receiving flask, tare it, and add the solid to said flask. The # I would get would either be wildly lower or slightly lower. I am very sure I am not mispouring anything.

So I am wondering, is it possible these sensitive balances cannot handle things with larger masses, or if the receiving flask is not perfectly flat, would that mess up the mass? Similarly, would the location where I put the flask or weigh paper on the balance matter (e.g. dead center, to the left, right, etc.)? Is there another thing I could do? technically I could take the difference in weigh paper with solid vs without, but that doesn't tell me what got into the receiving flask.


texts:
I am working on energy optimization of molecular structure using DFT with Schrödinger software and I found that job is running on LAV2P basis set. I want to know what is the meaning of this basis set in particular and how it is different from other basis sets.

Also, I want to compare which basis set corresponds to this in Gaussian software.

P.S. The only info that I found on my research on the internet is the full form of LAV2P.


texts:
In this article, 148 pmol/L is said to be equivalent to 200 pg/mL.

But this unit conversion site says that 200 pg/mL are equivalent to ~734 pmol/L, and this one gives 44 pmol/L for the same value.

What am I missing here? What is the correct way to perform this conversion, and why are different sites giving back different values?


texts:
I am working with a commercial monomer (monomethacryloxypropyl terminated polydimethylsiloxane) with an inhibitor of BHT @1%.

I need to remove it for making an ATRP reaction. What is the good way to do this?


texts: Completing inorganic reactions and writing spectator ions

texts:
Complete the following reactions and write the spectators for each if any
A. cobalt(II) chloride (aq) and cesium phosphate (aq)

I am not quite sure if I have the correct answer to this equation, but I have $\ce{ CoCl2(aq) + Cs(PO4)(aq)}$ (for the equation setup) and for spectator ions $\ce{Co^2+ (aq) + 2 Cl- (aq) + Cs^+ (aq) + (PO4) (aq) -> CsCl(aq) + Co(PO4)2(s)}$ and so for the spectators I have $\ce{Cs^+(aq)\ and\ 2Cl- (aq)}$, Is this correct?

B. sodium phosphate (aq) and calcium chloride (aq)

For this equation I have $\ce{6Na^+\ and\ 6Cl-}$ as spectator ions, $\ce{Ca3(PO4)2(s)}$ (as a solid)


texts: I have a slab of aluminum and one part of the slab will be exposed to a very corrosive environment. If I put a sacrificial anode elsewhere on the slab will the section that is exposed still be protected from pit corrosion? I guess I'm unsure because the pit corrosion is a result of a localized reaction and if an anode is added will it prevent the local reaction from taking place.


texts: What makes carbon special and versatile?

texts:
My teacher told me that carbon's tetravalency and high catenation ability makes it special and is the reason why there are millions of compounds of carbon.

1) Silicon is tetravalent too but doesn't create as many compounds as carbon.Why?

2) The textbook says that no other element exhibits the property of catenation to the extent of carbon. Why is this so? Does it just happen magically?


texts: I am a math student trying to implement a simple force field in python for determining the energy of a small molecule and trying to minimize it in order to find a stable configuration. I was wondering if there is a prefered system of units to be used am currently using the SI system of units however when i calculate Van der waals energies the numbers are quite difficult to deal with . Any reference of basic force fields would be much appreciated


texts: Do the units of the law of mass actions convey any meaning?

texts:
Since the number that you end up with, when calculating the value of the law of mass action for a given reaction often also has a unit, I was wondering if there is any physical meaning to this given unit or if it is basically "useless"?

Example:

$$\ce{CH3COOH <=> CH3COO- + H+}$$

$$K_c = \frac{c(\ce{CH3COO-})\cdot c(\ce{H+})}{c(\ce{CH3COOH})}\qquad [K_c] = \pu{mol L-1}$$


texts: Maybe this is better in English.SE, but I think I'm more likely to get better responses here in the "industry" site. This post got me thinking; how do you pronounce "alkyne" (a hydrocarbon with a carbon-carbon triple bond) differently enough from "alkene" (a hydrocarbon with a carbon-carbon double bond) to differentiate the two in spoken conversation? They're obviously spelled differently and so can be separated in the literature, but I can't find a satisfactory pronunciation for either that isn't "al-keen".


texts: Creating 1L of 1000 ppb stock solution of Pb2+

texts:
I’m testing on samples that require a concentration of 1000 ppb (or 1 mg/L) of Pb 2+. My first thought was to simply dissolve 1 mg of Lead nitrate in 1 L of deionized distilled water to create 1 L of stock solution at the desired 1000 ppb (1 mg/L) concentration.

Is the process as simple as that, or is 1 mg proportionally too small a mass of solute to dissolve in 1 L of distilled water? Should I create a more concentrated stock solution and dilute it to 1000 ppb by adding requisite amounts of water? What concentration stock solution would be recommended in this case?

All the best!


texts: Why did ammonium chloride fumes turned pink in this synthesis?

texts:
I was watching the synthesis of tetrasulfur tetranitride performed by Tom on his Youtube channel, Explosion & fire. He followed the basic route: adding ammonia gas to sulfur chlorides ($\ce{SCl2}$ and $\ce{S2Cl2}$). At first, everything was going normal, purple-black precipitate on the flask with white $\ce{NH4Cl}$ fumes emitting as expected and white $\ce{HCl}$ fumes resulting from hydrolysis of sulfur chlorides. But suddenly a problem occurred. The fumes turned pink.  The following is a sequence in chronological order (snapshots from his videos; temperature of ppt. in brackets):

white $\ce{NH4Cl + HCl}$ fumes on top of precipitate ($\pu{T = 25 ^\circ C}$)

fumes turned pink ($\pu{T = 27-28 ^\circ C}$)

fumes entering the condenser from flask turning it red ($\pu{T = 35 ^\circ C}$)

fumes escaping the condenser ($\pu{T > 35 ^\circ C}$)

condenser changed, $\ce{NH4Cl}$ pellets observed above it, fuming doesn't stop ($\pu{T > 35 ^\circ C}$)

Eventually, after so much fuming and snowing, the end-product was achieved (when fumes turned golden brown, the original color of $\ce{S4N4}$). So, why did ammonium chloride fumes turned pink (when it was evolving)? Is it due to the compounds in the precipitate? If so, what species could have caused that color?
I did some research and found out that $\ce{S4N4}$ is thermochromic(changes color according to temperature). From britannica:

Tetrasulfur tetranitride forms thermochromic crystals, which are crystals that change colour with temperature. They are red at temperatures above 100 °C (210 °F), orange at 25 °C (80 °F), and colorless at −190 °C (−310 °F).

There is no mention of $\ce{S4N4}$ turning pink, so I proposed pink to be an intermediate color (orange -> pink -> red) and since it is a volatile compound, it was turning the fumes pink. But if the compound was pink, why did it later turn golden-brown, the original color of $\ce{S4N4}$? The precipitate was a purple-brown-black sludge, so it was definite not the end product. Thus my proposal contradicts.
prepchem says:

Tetrasulfur tetranitride is prepared by dissolving 1 volume of sulfur
dichloride in 8 or 10 volumes of carbon disulfide, cooling, and
passing in dry ammonia gas until the dark brown powdery
precipitate which forms at first has dissolved and an
orange-yellow solution results which contains light-colored flocks of ammonium chloride.

Here, there is no mention of pink. What species could have caused fumes to turn pink in color?
I recommend to watch the synthesis in details on his second channel, Extraction & Ire: Part 1 and Part 2


texts:
I proposed the following lewis structure for $\rm NCO^\oplus$

The problem is that this structure is linear, while my book tells that the structure is not linear. What will be correct canonical structure?

Also is it correct to call the following as resonance structures?


texts: Titration of hydrochloric acid with sodium hydroxide

texts: I have a question regarding titration of hydrochloric acid with sodium hydroxide. Assume you have a solution of NaOH with pH = 12. With this NaOH you titrate a HCl solution. Then, will the pH of the titration product, regardless of how much NaOH you add, ever reach a pH of 12?


texts: How do I open volumetric flask with with 1M HCl?

texts: I have two volumetric flasks with ground glass stopper, and I have 1M HCl inside each of them. I can't open either, stopper is "glued" to the flask somehow. Potentially by hydrochloric acid. Or maybe not (I mean maybe it's stack on its own, without participation of HCl). What is conventional way to open it? I couldn't think about anything better than to put entire flask in water, but it didn't help so far.


texts: Would the Formation of Benzaldehyde Be Possible Under Specific Conditions?

texts:
Our process:
We cure an epoxy resin using SLA. The triarylsulfonium hexafluoroantimonate salts in propylene carbonate act as the photoinitiator for the oligomeric reactions between 4,4 isopropylidenedicyclohexanol and 1 chloro 2,3 epoxypropane to crosslink the resin. We then rinse the part in propylene carbonate multiple times, rinse in water once, and finally end with time in the post-curing apparatus. We were finding that the piece was not biocompatible so we turned to further testing.

We sent a cured and cleaned sample in for 24 hour extraction at 37C and tested the extract with GCMS (results on table). The uncured resin itself was also tested and found positive for propylene carbonate and cyclopentanol.

My question is specifically about the benzaldehyde that is present. Would benzaldehyde be able to form using the listed chemicals (and exposure to UV light) or would it likely be introduced from an outside contaminant?

Thanks


texts: How does acidity affect electrode potentials?

texts:
What is the role of acidity in the decrease of formal potential of $\ce{Fe^{3+}$/$Fe^{2+}}$ in a sulfuric acid and phosphoric acid mixture?

I've observed that the formal potential of the $\ce{Fe^{3+}$/$Fe^{2+}}$ electrode in a mixture of sulfuric acid and phosphoric acid, $E_0 = \pu{+0.61V}$ is much lower than the standard electrode potential, $E_0 = \pu{+0.76V}$.

I came up with a plausible explanation that phosphoric acid would cause $\ce{Fe^{3+}}$ to get precipitated as  $\ce{FePO4}$ and the presence of excess acid will help in the formation of a complex $\ce{[FeHPO4]+}$. Am I correct in my observation? How would the situation change if the medium was basic?


texts: Does space in between have any significance in IUPAC nomenclature?

texts:
The correct IUPAC name of the following compound is:

(a) 2,4,6-trimethyl cyclohexanone
(b) 1,3,5- trimethyl benzophenone
(c) trimethylcyclobutanone
(d) 2,4,6-trimethylcyclohexanone

I was confused between option (a) and (d). I opted for option (a), but our teacher told that ans is an option (d). The only difference I see between these two options is that there is space in (a). Does space have any significance in IUPAC nomenclature?


texts: Why every atom of a radioactive element, though being indistinguishable in every aspect, doesn't decay simultaneously?

texts:
First of all, I know this (or, similar) question has been discussed previously here. But the discussion there couldn't help me completely getting rid of my confusion, hence this attempt.

In any radioactive sample of a particular element all the atoms involved in that accumulation of sample are obviously seem to be indistinguishable in every aspect. Then why all the atoms don't start decaying at the same time?

In practice we obviously know that they don't disintegrate simultaneously and hence my question arises that what is that x-factor that differentiates between the atom which decays first than the others?


texts: Electrochemistry: Does ion flow from one half-cell to another?

texts:
My textbook says one of the functions of a salt bridge is that "it completes the circuit by allowing ions to move from one half-cell to another". However, according to my understanding, only the ions in the salt bridge move into the half-cells.

Take the above chemical cell as an example, only the potassium ions and nitrate ions move into different half-cell respectively. The mobile ions in the two electrolyte do not move from one half-cell to another, right?


texts: How can potassium disappear after cooking?

texts:
I read this at this webpage: http://www.whfoods.com/genpage.php?dbid=90&tname=nutrient#impactcookingstorageprocessing

  How do cooking, storage, or processing affect potassium?

  Potassium losses from cooking of high-potassium foods can be
  significant. In the case of spinach for example, potassium levels have
  been shown to drop from 6.9 to 3.0 grams in 3 and 1/2 ounces of
  spinach after blanching for several minutes (a loss of about 56%).

I don't understand this. How can potassium disappear after cooking ?


texts: How does NaCl maintain its crystalline structure?

texts:
My understanding is that $\mathrm{NaCl}$ is an ionic compound, in which $\mathrm{Cl}$ becomes (effectively) $\mathrm{Cl^-}$ and $\mathrm{Na}$ becomes $\mathrm{Na^+}$. So I understand why I would get a "sea" of particles that would stick together.

But why does the above mean that it will have a face centered cubic structure with the ions held in place so rigidly?


texts: kinetic and thermodynamic parameters of biodiesel production from lard

texts:
I want to know if someone has experimental results and calculations of the kinetic and thermodynamic parameters of Base Catalyzed Transesterification of pig fat, if not which is the method used to calculate them?

Thanks!! :)


texts: Carbohydrates: What does "typical nature" mean here?

texts:
I am a 12th grader in India. I have understood basic theory on biomolecules. I know about carbohydates (and structures of important saccharides) and $\alpha$-amino acids, proteins, and peptides.

This is a section given in my book:

I understand what is the meaning of "D"-glucose, and also how to identify the functional group. But, notice the last column in this table. I don't understand what they mean by the "typical nature" in each case.

I searched the net but couldn't find anything. Is my book using obsolete/unknown terminology for an existing concept? What is it? Please tell. Thank you!

References: Page 1, Page 2, Page 3


texts: It is a question which I faced when I was in Senior year in high school, I used my hands to handle phenol which has turned pink due to oxidation, I washed my hands with all kind of soaps but smell in hands didn't go for 3-4 days. Why was it, did it bond to my skin? What I could have done to remove smell?


texts: Coefficients and Parameters for contracted Gaussian basis sets

texts:
I'm trying to write a program to calculate fixed-point Hartree-Fock level energies of molecules (for my amusement) and everything makes sense but this. I've been agonizing over this for almost 3 hours now. I've tried pretty much every Google search I can think of (mostly returning results that were either too vague or without enough detail) and looked in almost every book/ebook I own (pretty much always too vague). Any help whatsoever would be extremely appreciated.

As far as I understand, an STO-NG contracted Gaussian basis function has the following form:

$$\phi_{\mu}^{\textrm{CGF}}(\vec{r}) = \sum_{p}^{N_{\textrm{PGF}}} d_{p\mu} (x-X_A)^{i_{p\mu}} (y-Y_A)^{j_{p\mu}} (z-Z_A)^{k_{p\mu}} e^{-\alpha_{p\mu}|\vec{r}-\vec{R_{A}}|^{2}}$$

where the contraction coefficients, $d_{k\mu}$ and exponents, $\alpha_{k\mu}$ are chosen such that $\phi_{\mu}$ provides the 'best fit' to a Slater-type orbital having a Slater exponent $\zeta$, $\vec{R_{A}}=(X_A,Y_A,Z_A)$ is a fixed reference centre (usually a nucleus) and $l_{p\mu} = i_{p\mu} + j_{p\mu} + k_{p\mu}$ defines the angular momentum of the primitive Gaussian function:

$$\phi_{p\mu}^{\textrm{PGF}} = (x-X_A)^{i_{p\mu}} (y-Y_A)^{j_{p\mu}} (z-Z_A)^{k_{p\mu}} e^{-\alpha_{p\mu}|\vec{r}-\vec{R_{A}}|^{2}}.$$

I'm having problems interpreting data files documenting contraction coefficients and exponents for various basis sets.

For example, please consider the following snippet from the Gaussian 94 STO-3G basis set file documenting contraction parameters for Carbon:

****
C     0
S   3   1.00
     71.6168370              0.15432897
     13.0450960              0.53532814
      3.5305122              0.44463454
SP   3   1.00
      2.9412494             -0.09996723             0.15591627
      0.6834831              0.39951283             0.60768372
      0.2222899              0.70011547             0.39195739
****

I have read in various places that there are enough coefficients here to describe 5 contracted functions, but I see only enough for 3 maximum (if the exponents are the same, but the coefficients change between 2S and 2P). I'd be eternally grateful if someone could explain for me, precisely how one would determine the following information from such a basis set data file:

1) Which EXACT basis functions appear within each contracted function?

2) How many contracted Gaussian basis functions there are?

If possible, would you be able to do the same for the following snippet, again for Carbon, Gaussian 94, but this time for the more complicated 6-31++G** basis set?:

****
C     0
S   6   1.00
   3047.5249000              0.0018347
    457.3695100              0.0140373
    103.9486900              0.0688426
     29.2101550              0.2321844
      9.2866630              0.4679413
      3.1639270              0.3623120
SP   3   1.00
      7.8682724             -0.1193324              0.0689991
      1.8812885             -0.1608542              0.3164240
      0.5442493              1.1434564              0.7443083
SP   1   1.00
      0.1687144              1.0000000              1.0000000
SP   1   1.00
      0.0438000              1.0000000              1.0000000
D   1   1.00
      0.8000000              1.0000000
****


texts:
Calculate the pH of a $\pu{2M}$ $\ce{H_3PO_4}$.Calculate the equilibrium concentrations of $\ce{H_3PO_4 , H_2PO_4^{-} , HPO_4^{2-}}$.

First equation:

$\ce{H_3PO_4  <=> H^{+} + H_2PO_4^{-}}\ \ \ K_\mathrm{a1} =7.5\times 10^{-3}\\$

$\begin{array}{|c|c|c|c|} \hline
\ & [\ce{H_3PO_4}] & [\ce{H^{+}}] & [\ce{H_2PO_4^{-}}]\\ \hline
\text{I} & 2 & 0 & 0 \\
\text{C} & -x & +x & +x \\
\text{E} & 2-x & +x & x\\ \hline \end{array}\\$

$$K_\mathrm{a1}=\frac{[\ce{H_2PO_4^{-}}]*[\ce{H^{+}}]}{[\ce{H_3PO_4}]}=\frac{x^2}{2-x}=7.5\times 10^{-3}$$

Solving for $x$ we get $x=\pu{0.118M}$.

$[\ce{H_3PO_4}]=2-x=2-0.118=\pu{1.882M}$

$[\ce{H_2PO_4^{-}}]=x=\pu{0.118M}$

Second equation:

$\ce{H_2PO_4^{-}  <=> H^{+} + HPO_4^{2-}}\ \ \ K_\mathrm{a2} =6.2\times 10^{-8}\\$

The solution manual says:$$K_\mathrm{a2}=\frac{[\ce{HPO_4^{2-}}]*[\ce{H^{+}}]}{[\ce{H_2PO_4^{-}}]}=\frac{0.118\times[\ce{HPO_4^{2-}}]}{0.118}$$

$[\ce{HPO_4^{2-}}]=K_\mathrm{a2}$

However I'm not sure why didn't we use an ICE table for the second equation as follows:

$\begin{array}{|c|c|c|c|} \hline
\ & [\ce{H_2PO_4^{-}}] & [\ce{H^{+}}] & [\ce{HPO_4^{2-}}]\\ \hline
\text{I}& 0.118 & 0.118 & 0 \\
\text{C}& -x & +x & +x \\
\text{E}& 0.118-x & 0.118+x & x\\ \hline \end{array}\\$

Is it because $x$ is negligible with respect to 0.118? Or should the concentrations precalculated above be in the equilibrium row of the ICE table?


texts: My textbook states that AlCl3 is both an ionic and a covalent compound .How is it so?


texts:
Where can I find typical values of the Arrhenius activation energy for arbitrary reactions? I only want to have orders of magnitude estimates, but so far I have not been able to find any good resource that lists activation energies for different types of reactions.

There are tons of papers in which people determine precise values for very specific reactions, but I am looking for a kind of database or reference that has a large collection of values. In particular, those for biochemical reactions would be useful to have.


texts: Help with finding the right catalyst and reaction conditions for hydroamination reaction

texts:
A friend of mine, final year PhD, and I, final year Bachelor, are focusing on hydroamination reactions. In particular those with secondary amines and substituted alkenes. The reaction in particular is given by

Intermolecular hydroamination of unactivated alkenes with substituted secondary amines seems to be quite difficult. However, additions of cyclic and acyclic secondary alkyl amines to a wide range of alkenes with anti-Markovnikov regioselectivity have been reported. Some of those reactions are redox-neutral and occur readily at room temperature under visible light irradiation.
Our question is: what would be an applicable catalyst for this particular reaction (secondary amine + substituted alkene) and what reaction conditions would be necessary?
Thanks in advance!
EDIT:
The reaction may also concerns the primary amine,

However, we would like to keep the substituted alkene substrate as it is.


texts: What is the proper way to calculate experimental error in this measurement?

texts:
I am working on error analysis of some of my measurements and have stumbled upon an issue with the propagation of error. According to this reading,

  The uncertainty of the average acidity ($\Delta_\text{acid}H_\text{avg}$) was calculated as the root sum square of the random and systematic errors. For example, for the $\ce{A3CSH}$ system, the random error was treated as the averaged uncertainty of the reference acids $\pm2.2\ \mathrm{kcal/mol}$ divided by the square root of the number of the reference acids, $2.2/\sqrt6 = 0.9\ \mathrm{kcal/mol}$, and the systematic error was assigned as $\sqrt{2.2} = 1.5\ \mathrm{kcal/mol}$. The root sum square of the random and systematic errors yielded $\sqrt{0.92^2 + 1.52^2} = 1.7\ \mathrm{kcal/mol}$.

Why is $\sigma_\text{sys}=\sqrt{2.2}$ instead of $\sigma_\text{sys}=2.2$?

It was my understanding that if the reported uncertainty of the reference acids are $\pm2.2\ \mathrm{kcal/mol}$, shouldn't the root-sum-square be $\sigma_\mathrm{RSS}=\sqrt{\sigma_\text{sys}^2 + \sigma_\text{rand}^2}=\sqrt{2.2^2 + (2.2/\sqrt6)^2 }= 2.4\ \mathrm{kcal/mol}$ instead.

If my method is wrong, can I have an explanation pr directed some kind of reading explaining this concept?


texts: How to determine the strongest oxyacid of chlorine?

texts:
Which is the strongest acid here?

$\ce{HClO}$
$\ce{HClO2}$
$\ce{HClO3}$
$\ce{HClO4}$

I found this question, didn't really get the first answer, but this one in particular seemed interesting.
Apparently, you calculate a $\mathrm{p}K_\mathrm{a}$ for each substance.
According to this website.
$$\mathrm{p}K_\mathrm{a} = -\log_{10}K_\mathrm{a}$$
I need to find out $K_\mathrm{a}$ then. From what I understand $K_\mathrm{a}$ is obtained from dividing the concentrations of products by the concentrations of reagents. However, how am I supposed to do so if I am not given any equilibrium reactions?


texts: Quasi-static implies that T aprox equals Tsurr?

texts:
A few days ago I re-visited my undergraduate thermodynamics notes and (as you may have seen from the amount of questions I have been posting) I have encountered many difficulties that I overlooked at that time.
And I think most of my problems come from how unclear is the concept of quasi-static process in books.
Many textbooks define a quasi-static process as:

  A process that has its macroscopic variables well defined and in the system it is at each instant of time in a state infinitesimally close to the state of equilibrium.

The first part of that definition is logical. But the second part, related to thermodynamical equilibrium confuses me.
What is clear is that if it is stated that a certain process is quasistatic, then the pressure of the system is infinitesimally similar to the external pressure, which allows us to easily calculate the volumetric work.

My concise doubt comes from the relationship of the external temperature with the internal temperature. We know that for a system to be in true equilibrium with the outside, both pressure and temperature must be the same (without considering material equilibrium).

If this is the case, T system should be infinitesimally equal to T of the environment which would completely eliminate the generation of entropy by transfer between finite temperatures.

Now, when one studies theoretical cycles, it is generally stated that they are internally reversible ( quasi-static internally and without internal friction) but irreversible at last because the unstopabble heat transfer between finite temperatures in many steps.

I see a contradiction here:
As I understand it, many define a quasistatic process as:

"An extremely slow process where internally the P and the T are equal, homogeneous". (Completely agree)
"The system  at each instant of time in a state infinitesimally close to the state of equilibrium". Dont' get it since many problems considers Pexternal=Psystem but T System different to T surroundigs.

To me, it should be called partially quasistatic process if Tsys does not equals to Tsurroundings.

Regards.


texts: Why isn't my galvanic cell making enough voltage?

texts:
I'm in kind of a pickle here. I made a galvanic cell of Lead and aluminium for a chemistry internal assessment but unfortunately, it didn't turn out so well and neither me nor my teacher has any clue why.
The E0 value of the cell is 1.53v. I got a maximum reading of 0.29v

If you don't have time to read here is what I think the sources of error could be:
1. I used filter paper as a salt bridge and I don't think it was thick enough to allow ions to flow through it.
2. I used around a 1M concentration of KCl to dip the salt bridge in.
3. I suspect either of the metals was not correct but this seems improbable as I got a voltage just not the correct one.
4. The solutions of AlNO3 and PbNO3 were kept in round-bottomed flasks with a glass cork in them for a few days before I decided to do the experiment.
5. I got a negative reading for the voltage which was weird.
6. I got a higher voltage reading only when I touched the aluminium rod to the salt bridge in the solution

I used the following procedure:

I made 0.01M, 0.1M, 0.25M and 0.5M solutions of aluminium nitrate and a 0.1M solution of lead nitrate (both well dissolved) from lab equipment.
I poured each of them into separate 50ml beakers. I then placed an aluminium rod (that was 50% submerged) into the AlNO3 beaker and a thin piece of lead (that was well sanded before each reading) that was fully submerged in PbNO3.
I connected each of the metals to a multimeter via alligator clips
I then prepared a salt bridge using 5x25cm strips of filter paper which were dipped in a solution of KCL of about 1M concentration. The filter strips were folded and stapled.
I then placed the salt bridge in both the beakers and conducted the experiments.

I'm not in school right now and I don't have time to conduct the experiment again as the assessment is due very soon.


texts: Chemical hardener to cast breastmilk into gemstones

texts: I'm looking for a chemical hardener that I can add to breastmilk to turn it into a stone. I have seen others use one but they will not share what they are using. In their video they add about 1ml of secret solvent to 15ml of breastmilk and heat it on low heat for a couple minutes. It hardens completely within a few days. Any help would be greatly appreciated.


texts: Why does 1,3-Butadiene has different standard heat of formation value calculated from calorimeter than the one calculated from bond energies?


texts: Importance of substrate stereo chemistry in semi pinacol rearrangement

texts:
Consider the following two reactions (source):

I don't quite get why the products shown are the main ones. In reaction 3A., if you rotate the carbon facing us by 120 degrees clockwise, the anisole would be antiperiplanar with the leaving group and should migrate instead of the phenyl group. In reaction 3B., the same rotation should lead to a migration of the phenyl group instead of the anisole group.

Why does phenyl migrate in the erythro isomer and anisole migrate in the threo isomer?


texts:
I just came across this reaction

$\ce{Na2S2O3 + 2HCl -> 2NaCl + SO2 + S + H2O}$

I was wondering if it was possible to predict the products of this reaction if I didn't know it (or any inorganic reaction for that matter).

Can we use arrow-pushing (as we do in organic chemistry) to get the products of an inorganic reaction? Can we devise a mechanism to find the products? It seems unrealistic to me how anyone could learn the many reaction of inorganic chemistry.


texts: How are alkanes, alkenes, and alkynes homologous series since they have no functional group attached?

texts:
I understand that a homologous series is a group of compounds with the same functional group attached to it.

I also know of an alternate definition of it as being a series of compounds with the same general formula.

But if the first definition is to be considered then how can alkanes, alkenes or alkynes be considered homologous series since there is no functional group attached to any of these, as opposed to, e.g., the homologous series of alcohols?


texts: Restricted synthesis; formation of nucleophile and electrophile from one carbon source

texts:
I am tasked by my textbook to synthesize 2-hexyne from 1-propanol. All carbon atoms must come from the starting material, 1-propanol.

My solutions manual (an older version) does not have this additional problem, so I am forced to ask here.

I understand that in this problem there is a double in carbon count in the product, so we are expected to somehow "fuse" the carbons from the starting material. I also understand that this means making an electrophilic carbon and a nucleophilic carbon from the starting materials. The electrophilic carbons that I know about are alkyl halides, alkyl tosylates, epoxides, and acid chlorides.

I'll choose to make an alkyl halide from the starting material through reaction of the primary alcohol (1-propanol) with thionyl bromide and pyridine as a base. Now I have my electrophilic carbon.

My nucleophilic carbon will be the acetylide anion. I could use a cyanide ion but that only gives me a one carbon increase. Plus that's not an allowed carbon source. So I dehydrate my primary alcohol (is this possible?) and creates 1-propene. I can brominate this in an inert solvent (i.e. methylene chloride). From here with the vicinal dihalide I can form the alkyne and then methyl acetylide. I can then react this with the alkyl halide I made previously.

How does this look?


texts:
In my backyard I have a DIY wire trellis made in part by wrapping a steel wire around a water wellhead. I noticed out the window in the dark a tiny pinprick of orange / yellow light coming from the area, and upon closer inspection it originated from a point of contact between the trellis wire and the side of the well. The wire is 5-10 years old and rusted only around this point of contact. The glow disappeared when I disturbed the wire slightly. The outside temperature was 22°F.
Any idea what could be causing this phenomenon? I might be searching the wrong set of keywords, but I can't find anything online.
Upfront I'll say the closest I found is this question. My question could perhaps be more suitable as a comment on linked question, but

I'm new to the stackexchange and cannot write comments
I'm unsure if reviving a >5yr old question is the right thing


texts: Confused about weak/strong acids, conjugated acid-base pairs and buffers

texts:
I learned that

a) the conjugate base to a weak acid is a strong base (and vice versa).

b) a buffer consists of a weak acid (base) and its conjugate base (acid).

However, this explanation of buffers says the following:

"[...] a weak acid is one that only rarely dissociates in water [...]. Likewise, since the conjugate base is a weak base, [...]"

which seems to stand in conflict with my assumption a) above. So, what is correct?

Furthermore, if b) is correct, isn't any solution of a weak acid solution a buffer, since any weak acid in water makes an equilibrium of the form

$HA \text{ (weak acid)} \leftrightarrow H^+ + A^- \text{ (conjugate base)}$

and is thus a solution of a weak acid and its base?


texts: Does rearrangement occur in Friedel Crafts alkylation or not?

texts:
In the reaction of alkylation of aromatic systems with the help of Friedel Crafts alkylation - the reagent used is alkyl halide in presence of appropriate Lewis acid.

When is rearrangement observed?

If the alkyl halide is primary, the carbocation is usually not stable - as a result, a free carbocation shouldn't be formed and the attack should occur from the acid base complex itself (this is what my instructor said). However, in cases where the alkyl halide is tertiary, or where the carbocation is stable enough to be formed - rearrangement (if possible) is observed and the reaction proceeds through a free carbocation intermediate which acts as electrophile.

So in the former case, where a full fledged carbocation isn't formed, is rearrangement possible?

For example, is rearrangement possible in alkylation of benzene with n-propyl chloride in presence of aluminium chloride? Clearly, the primary carbocation is not stable - and may arrange to secondary carbocation (only if it is formed in first place)

So what really happens, and when in general and in particular can we expect rearrangements in Friedel Crafts alkylation? Also, when not to expect rearrangements? (Of course, when the carbocation isn't formed, but when is that?)

It'd be great if you could quote some credible sources along with your answer, if you wish to add certain specific reactions etc.

P.S.

Which Lewis acids allow for rearrangement to occur? As far as I know, only in presence of stronger Lewis acids does rearrangement occur - but how strong?
Does temperature also play a role for rearrangement to occur?


texts: Why can temperature changes have units of either degrees Celsius or kelvin?

texts: One equation to calculate a heat change is $q = c_p \cdot m \cdot\Delta T$. I know that $\Delta T$ can be in either degrees Celsius ($^\circ{}\mathrm{C}$) or kelvin ($\mathrm{K}$). However, one thing that confuses me is how the units cancel if $\Delta T$ is in degrees Celsius, since $c_p$ has units of $\mathrm{J\ g^{-1}\ K^{-1}}$. How does this work?


texts: Surprising values of intermolecular forces of ethane, oxygen and xenon

texts:
I know that gases with stronger intermolecular forces should have a larger value of the van der Waals constant $a$. So I looked up a table on van der Waals constants and tried to reason about the relative values of that constant. Though I was able to explain most of the values, there was one thing I found absurd. Here:

$$
\begin{array}{cc}
\hline
\text{Substance} & a~(\pu{atm {dm}^6 mol^{-2}}) \\
\hline
\text{Oxygen} & 1.364 \\
\text{Xenon} & 4.137 \\
\text{Ammonia} & 4.225 \\
\text{Ethane} & 5.507 \\
\hline
\end{array}
$$

My intution says that dioxygen, which has a slightly higher molar mass (32 vs. 30) than ethane, but significantly less molecular size or volume, should have a only slightly lower value of $a$ than that of ethane, but here we find a significant difference! Another example is xenon; its molar mass (131) is much larger than ethane (30), but its value of $a$ is smaller. Does it have to do with the dominance of molecular size over mass? Or atomicity or atomic dipoles? I suspect that it's probably the large and branched structure of ethane that's causing this.

Why does the molecular size/volume seem to play such a dominating role in the value of the constant $a$? I thought it was primarily influenced by molecular mass.


texts:
Is there any known substance that can decrease fertility of a male?
Less specifically what about one time chemical castrations (ignoring a perfect sterilization)?
I heard about them before once but wasn't sure really.


texts: Deciding the aromaticity of two napthalene-like rings

texts:
Why is the first compound aromatic and the second compound non-aromatic?

In the first compound, the left side of the ring is aromatic but the right side isn't.
Second compound satisfies all the conditions of aromaticity but why is it non-aromatic?


texts: NMR Prediction for compounds at variable pH values

texts:
Like the title says, I'm looking for any software package that may be able to simulate a variety of NMR at a variety of different pHs. The majority of the software programs that I've found do not have an option that also incorporates a pH specification.

Any advice is appreciated, I found a few prior threads on the topic, however they were all 2+ years old so I was curious if there were any advances.

Thanks in advance for any advice.


texts:
I was doing a multiple choice problem that asked about when the following nuclear decay sequence reaches steady state (When does the activity of $\ce{^99Mo}$ roughly equal the activity of $\ce{^{99m}Tc}$ ?)

The correct answer choice said after approximately 20 hours.

Let's denote $\ce{^99Mo}$ by $\ce{R}$ and $\ce{^{99m}Tc}$ by $\ce{I}$.

By definition, the time we're looking for is the time when $\frac{\ln 2}{65}N_R=\frac{\ln 2}{6}N_I$, which is when $\frac{N_R}{N_I}=10.83$
I don't have the formula for the exact amount of the intermediate vs. time memorized, but I don't think the problem required us to know the formula. I tried estimating the amounts of the various species present after 20 hours to see if steady state is actually reached then:

Let the initial ${N_R}=1$. I know that at $t=20$, $N_R=\frac{1}{2}^{20/65}=0.8079$. To estimate $N_I$, I did $N_I\approx(1-0.8079)*\frac{1}{2}^{20/6}=0.0191$. But using this approximation, it seems like the steady state condition is not met. Thus, I was wondering, what is a better way to estimate $N_I$ to get that the decay sequence is in steady state after 20 hours?


texts:
Suppose we bring a pan and put in it some oil and turn on the heat, before the oil could get very hot and nearly boiling, we put on the potatoes that start frying.

Someone told me that if the potatoes were put in oil before it gets really hot, then they will absorb more oil than if they were put in oil after it gets really hot.

Is this true?? If yes then WHY?

Note:(given that in both cases they stay the same period of time immersed in oil).


texts: Why does symmetry have to be maintained in molecular orbitals?

texts:
Using the example of $\ce{XeF4}$:

What is the physical explanation enforcing the symmetry of the $\ce{1b_{1g}}$ orbital on the fluorine atoms? Why isn't the symmetry of a nonbonding orbital arbitrary?  If it's going to be nonbonding anyways, why can't we, for example, have a Fluorine p-orbital arrangement facing towards Xenon with three positive p-orbitals and one negative p-orbital?

To elaborate:

If I imagine a free Xenon atom in space, and the approach of four individual fluorine atoms, I would expect the bond formation to be randomized with respect to the orientation of the fluorine p-orbitals, and therefore for some arrangements to not be perfectly symmetrical, such as 3 positive p-orbitals, 1 negative, facing inward.  I understand bonds can't be made without symmetry between the Xenon and Fluorine orbitals; that makes physical sense because we can argue it by looking at orbital overlap that dictates bonds can only occur with appropriate symmetry.  But in a nonbonding case, such as $\ce{1b_{1g}}$ above, I don't understand why symmetry is also required.

Source for pictures:

https://scilearn.sydney.edu.au/fychemistry/calculators/make_mo.shtml?type=year1&theMolecule=xef4
http://www.chem.mun.ca/homes/cmkhome/SALCS&MOs.pdf


texts: Instead of using an Ag/AgCl electrode, can I simply use another beaker and connect it to my solution via a salt bridge?

texts:
I'm trying to perform a potentiometric titration as part of my high school laboratory work, by reducing iron(III) to iron(II), and measuring the voltage change as I add cobalt(II) (to reduce it).

The methods that I have found online all point to using an $\ce{Ag/AgCl}$ or calomel reference electrode and an inert sensing electrode. When I look at the diagram, both the sensing and reference electrode are immersed in the solution of iron(III). Currently, these electrodes are too expensive and my school does not have access to it.

Can I just fill a separate beaker with $\ce{KCl}$ and put my $\ce{Ag/AgCl}$ wire into it, and connect the 2 solutions using a salt bridge? Or do I need to submerge both electrodes in the same solution?


texts: Difference between oxygens in a carboxylic acid?

texts:
I've been reading about MO theory and am wondering if the traditional model of carboxylic acids is correct. Usually, how it's presented is that the carbonyl carbon is doubly bonded to one oxygen and singly bonded to a hydroxyl group. This would mean that one oxygen is $sp^3$ hybridization and the other is $sp^2$ hybridized, and the hydrogen is attracted to both (one through a covalent bond and the other through a hydrogen bond).

My book (Ansyln and Doughtery) says that

  Hybridization isn't just limited to $sp^2$ and $sp^3$ and that bonding isn't localized between only two atoms but between the molecule as a whole. (paraphrased)

How does this affect carboxylic acids? Is there actually clearly defined '$sp^2$' and '$sp^3$' oxygens, or are they chemically equivalent? It seems like carboxylic acids react as alcohols (see: thionyl chloride). But does some sort of spontaneous symmetry breaking take place when a reactant approaches?

I can't find anything detailed/reputable about this on the internet.

The question What is the hybridization of the carbonyl oxygen in a carboxylic acid? does not address my concern.  I get what the classical hybridization of the carbonyl oxygen in a carboxylic acid is. I'm just wondering if there's a better non-classical description where the oxygen atoms are equivalent until approached by another molecule or something of the sort.


texts:
I'm asked to find the Lewis Structure  of sulfuric acid, $SO_4H^-$. After struggling for a while, I sumply looked it up.

How can this be? Sulfur has 6 electrons in its valence shell, so it should form bonds so as to collect 2 more electrons and satisfy the octet rule. So, surely it should form 2 bonds?

But it's involved in no less than six bonds here. Huh?


texts: Why is the cathode reaction required in a fuel cell?

texts:
So, at the anode of a fuel cell hydrogen is split into a positively charged proton and an electron. Then, there is the membrane which can let only protons through to the cathode, whereas electrons need to follow external circuit (effectively powering it).

Question: why do we need any other reaction on the cathode? Isn't the fact that positively charged ions travel through the membrane to the cathode enough to create the EMF?

Trying to solve it I assume that the reaction is there to actually apply some kind of force to move the ions though the membrane to the cathode, otherwise they'd just stay and reunite with electrons on the anode. What is that force and how does it work?


texts: If LPG gas burners can reach temperatures above 1700 °C, then how do HCA and PAH not develop in extreme amounts during cooking?

texts:
According to What is the temperature of heat generated from LPG gas?, the temperature of (1) LPG gas is above 1700 degree Celsius.

Many of us are familiar with pan-frying meat (steak, pan-frying the chicken breast etc).

Next, consider this: when you're (2) cooking meat at high temperatures ("above 200 °C) then it'll start forming heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs), according to healthline.com and precisionnutrition.com.

Note: The way they're formed is when fat drips onto the flame or the utensil, which is at very high temperature, and then reacts with the high heat to form HCAs and PAHs.

Lastly, there is research that (3) corelates HCAs and PAHs with causing cancer in our bodies.

Sources: They're are all mentioned in the two articles that I linked above.

Question: If you combine these 3 facts, then we must be cooking a huge amount of HCAs + PAHs. It's a wonder that we aren't dead yet! How is it that we haven't developed cancer by eating meat cooked over a pan on an LPG gas (which I believe is quite common)? Or are we all consuming HCAs / PAHs slowly over time and will develop cancer? Or are one of the 3 facts above wrong?


texts:
I have seen some phase diagrams that look like this:
https://www.learner.org/courses/chemistry/images/text_img/phase_diagram_water.jpg

And also some like this:
https://en.wikipedia.org/wiki/Phase_diagram#/media/File:Phase-diag2.svg

My confusion is related to the Critical Point. The first picture doesn't really explain where the gas/supercritical fluid boundary is, and the right angle indicating the supercritical fluid boundary at the critical point seems unusual to me. I have some general questions about behavior beyond the critical temperatures and pressures.

I think my specific question is best summarized by this picture.

More specifically, suppose you have an arbitrary compound X with a Liquid/Gas critical temperature of 320 K and critical pressure of 40 Bar which follows the general shape of the above phase diagrams. I have the following questions

1) At 330 K  and 10 bar (basically beyond the critical temperature but below the critical pressure) would X be a gas? or would it be a supercritical fluid? Would we need more information to be able to decide?

2) As a more general part of 1), is it possible that a gas exists beyond its critical temperature?

3) At pressures above its critical pressure, a liquid can still exist so long as it's temperature is lower than the critical temperature correct?


texts: Identifying the molecular structure of compound with sum formula C8H14O3 formula using NMR and IR spectrometry data

texts:
I am looking to identify the molecular structure of a compound with
the sum formula $\ce{C8H14O3}$ using the NMR and IR spectrometry data below.

I was able to figure out the molecule as

My friend asked me why I didn't consider the following molecule:

I couldn't answer that. What inferences from the IR & NMR data can I observe, to explain why the structure my friend suggested is wrong?
Source for these IR & NMR Spectra: https://www.orgchemboulder.com/Spectroscopy/Problems/7.shtml


texts: Are biological macromolecules organic or inorganic compounds?

texts: We know that organic compounds are compounds which contain carbon atoms. I want to know whether all biological macromolecules (such as proteins, lipids, carbohydrates, and nucleic acids) are organic compounds, or are only a subset of them considered organic?


texts: Is 44.5 mg/L a measurement of weight or volume?

texts:
I have a test result that I am trying to fully grasp. I need to determine how much of a contaminant I need to reach that amount in 4,800 gallons. Making the conversion to liters is no problem, nor is the math necessary to figure how much I need by weight to get this much contaminant.

The one thing I am unclear on is my assumption that $44.5~\mathrm{mg~L^{-1}}$ is by weight.
In other words, if I have a result that measures $50~\mathrm{mg~L^{-1}}$ of a metal (nickel, for instance), that means if I were to be able to extract the metal and weigh it, it would weigh $50~\mathrm{mg}$.

Any help you can offer would be greatly appreciated.


texts: If all intermolecular forces are electrostatic in nature, why don’t large non polar molecule dissolve in water?

texts: If I have a large non-polar substance A that forms strong dipole-induced dipole force (DIDF) with water, with strength comparable to that of H-bonds between water molecules, will A dissolve in water?


texts:
A gaseous mixture of $\ce{NO2}$ and $\ce{N2O4}$ is sealed in 4 identical vessels with movable pistons. When the conditions are modified as described in 1) to 4), in which condition does the molar ratio of $\ce{NO2}$ to $\ce{N2O4}$ remain unchanged after a long time enough to reach equilibrium?
  1) Total pressure is increased by moving the piston at a constant temperature.
  2) Temperature is increased while keeping the total pressure constant by moving the piston.
  3) Additional $\ce{NO2}$ is introduced from outside while keeping the total pressure constant by moving the piston at a constant temperature.
  4) Additional $\ce{N2}$ is introduced from outside while keeping the total pressure constant by moving the piston at a constant temperature.

The answer provided is (3).

My attempt: I think when we add $\ce{NO2}$, the equilibrium will shift to the right so the concentration of those two will changed. I answered (4) because $\ce{N2}$ is unreactive, making the concentration of both compounds the same. Please help why the answer 3 is correct and others are wrong.


texts: Why do molecules showing a pure rotational spectra require a permanent dipole?

texts:
I understand that pure rotational spectra only exist for molecules which have a permanent dipole moment.  The common explanation is "so that they can interact with the E-field of the incoming photons", but I don't think it is clear why photons can only interact with dipoles.
I'm also aware that the answer probably has something to do with the matrix element $\langle\psi_i|x|\psi_j\rangle$ where $\psi_i$ and $\psi_j$ are the initial and final states of the molecule, and $x$ comes from the dipole moment operator.  I'm just not sure why we need this matrix element and not something else.  And as an extension, why does Raman spectroscopy depend on the polarisability of a molecule, whose operator behaves like $x^2$?


texts: Benchtop NMR spectroscopy parameter explanation; tau and number of points

texts:
I have just carried out an exploration of the effect of different solvents and conditions on the 1H caffeine relaxation by benchtop NMR spectroscopy.
When collecting the 1D 1H NMR spectra of the caffeine in CDCl3 solution, the parameter for the number of points was set up, but when the relaxation run for T1 and T2 were done, the parameter was replaced by the value of time delay, tau.
I think I kind of get a clear view from your discussion, as the number of points is needed in determining the right peaks for 1D 1H spectra. But, as for the relaxation time, the intensities behaviour during the time delay is now being the subject of interest, hence the np parameter is neglected.
This is what I understand by far.
#updated
They are the number of points (np) and tau.
I think I kind of understand how np works;

it's the discrete points of analogue FID that are being converted to
digital points along with the FID signal envelope. Therefore it's
associated with the resolution of the spectra which the lesser np used
to define the FID, the lower the resolution.
*Let me know if I interpreted this wrongly.

This question raised when I'm analysing my data though, would really appreciate it if someone can enlighten me.


texts: Does the appearance of turbidity upon addition of water to an organic solvent mixture imply the presence of nonvolatiles?

texts: I was attempting to ascertain the suitability of GCMS to analyze a solvent mixture recovered from a solgel process. The filtered mixture contains heptane and denatured ethanol as major components and small amounts of HMDS and other impurities (various hydrocarbons in the heptane plus methanol in the ethanol). I spiked the mixture with deionized water and biphasicity ensued. The upper organic layer was clear but the lower aqueous layer was very white and turbid. Does this imply the presence of nonvolatile organics that precipitated, making the mixture unsuitable for GCMS analysis?


texts:
In Hückel theory we are only interested in π systems, where $\mathrm p_z$ orbitals overlap. One of the approximations in Hückel theory is that the overlapping $\mathrm p_z$ orbitals are orthonormal:

$$
S_{ij} =
\begin{cases}
1\quad i = j \\
0\quad i \neq j \\
\end{cases}
$$

If orbital overlap leads to bond formation, how can the overlap integrals, between $\mathrm p_z$ orbitals, be equal to 0? Maybe I am missing something obvious, but doesn't a π-bond demand non-zero overlap between p-orbitals?


texts: Cation exchange capacity via IR spectroscopy? Is it as good as barium exchange? What is the intutition on how it works?

texts:
Cation exchange capacity is often regarded as the single best summary statistic for soil fertility.  Years ago, I learned how to measure it myself, in a soil lab.  I used compulsive barium exchange, whereby I knocked off all of the cations using barium, and then I somehow (I forget) got all the barium off, before measuring how much barium is in solution.  It makes sense as a means of measuring CEC.

I'm now in a situation where I need hundreds of soil samples analyzed, primarily for CEC.  The lab with the best price does the CEC measurements by IR spectroscopy.

My question:  how can you measure the potential of a soil to exchange cations using IR spectroscopy?  It's based on correlations, right?  Under what conditions does this method break down?  I assume the prediction error is non-constant over the multivariate space comprising soil properties.  In what regions of this space should I expect greater bias and/or variance in the prediction, and what would the sign of such bias be?

Or, in simpler terms, when do compulsive barium exchange and IR spectroscopy agree and when do they disagree?


texts: How can I estimate the triple point of a substance given the densities of its liquid and solid phases and its enthalpies of fusion and vaporization?

texts:
I am trying to find the triple point of H2O given only the densities of water and ice, the enthalpy of vaporization, and the enthalpy of fusion.  I know that I should be able to use some combination of the Clapeyron and Clausius-Clapeyron equations to yield a system of two equations in two unknowns, after which I can use a computational engine to solve the system.  However, I am having trouble putting this knowledge to use.

A search on stackexchange brought me to the following question, which provides some answers, but confuses me in new ways:

Triple Point Equation

The answer given shows me that I am on the right track, but I am not sure what the lowercase p with the subscripts of sol-liq and liq-vap represents, and while the answerer points out that T1 and P1 are the triple point temperature and pressure, I am not certain of what the T with no subscript is meant to be.  My best guesses so far is that the lowercase p is vapor pressure and that the T with no subscript is the standard temperature for the given phase transition.


texts: Friedel–Crafts alkylation of benzene with tetrachloromethane

texts:
There was this question in an exam at our school which asked what the major product will be when excess of benzene is reacted with tetrachloromethane in the presence of aluminium chloride.

All of us got it wrong in the exam, but we realized that it's just Friedel–Crafts alkylation with extra steps. So later we came up with two competing answers: one group claimed it is tetraphenylmethane $(\ce{CPh4})$, while the other claimed it's triphenylchloromethane $(\ce{CClPh3})$ (aka trityl chloride).

Reason in favour of $\ce{CClPh3}$: After the formation of it, the negative inductive effect of the phenyl groups will supposedly be high enough not to allow the release of the last remaining Cl to form a carbocation. Also, there will be high steric hindrance in $\text{CPh}_4$.

Reason in favour of $\ce{CPh4}$: The phenyl groups are bonded to the central carbon through $\sigma$ bonds. So they can just rotate their planes to escape steric hindrance. Also, we do not know if the combined inductive effect of the phenyl groups is high enough not to allow the release of chloride. After all, the chlorine molecule is highly electronegative.

So, we're grappling with this problem and do not know the solution to it. Any help will be highly appreciated.


texts:
Other than determining whether reactants' concentrations can affect the rate, what purpose does it serve? Does it have any real world application in chemistry research? Also what is the point of knowing that a reaction is "second-order"?

Thanks!


texts:
Question
Can a buffer solution be obtained by mixing-
A) $\ce{NH4Cl}$ + $\ce{CH3COONa}$
B) $\ce{CH3COOH}$ + $\ce{NH4OH}$
My Thoughts
I know that a buffer solution can be obtained if we mix a acid and its salt of conjugate base or a base and its salt of conjugate acid.
But I was wondering whether a buffer solution can be prepared if we mix a weak acid and weak base or if we mix an acidic salt and basic salt?


texts: What happens to potassium iodide in the "elephant Toothpaste" reaction?

texts:
General Questions on "Elephant Toothpaste"

Equations:

1)$\ce{~2H2O2(aq)->2H2O(l) + O2(g)}$

Context:

I have a few questions on the reaction commonly referred to as "Elephant Toothpaste". You see, I am doing a basic demonstration of chemistry to little kids. I certainly don't think I am qualified to perform this, (Well, I can, but I want to know the details behind this, which is why I am asking for help.) but I have no choice. So Here we go!

Procedure:

Pour ~$\pu{50 mL}$ of hydrogen peroxide1 into graduated cylinder.
A "Squirt" (Not my wording) of Dish Soap into the graduated cylinder.
~$\pu{10 mL}$ of potassium iodide ($\ce{KI}$) Solution into Graduated Cylinder.

The result is...Foam, and lots of it.
130% concentration

So, here is my question:

What happens to the potassium iodide?


texts:
Why does acetanilide gives exclusively para isomer. I know that -I of nitrogen must decrease the yield of ortho product, but still it should be made in accountable amounts. Where am I going wrong.
I am inserting the question and solution screenshots for reference. The question is from IIT JEE 2016 exam, chemistry section of paper 1

Question

Solution


texts: Why is EDTA most soluble at a pH 8? (addition of NaOH)

texts:
Although Wikipedia says that EDTA is a very soluble salt, preparing a solution (.5M) is a pain in the neck. It takes a lot of time and still doesn't dissolve. Although addition of a few drops of NaOH makes the process a bit easier (still takes a lot of time)

Now, it did not make sense to me of why NaOH made EDTA more soluble. The salt I'm using is a disodium salt of EDTA, so wouldn't Na+ turn out to be the common ion only to decrease the solubility? Then, it might be the effect of pH(?) But, being a salt of a weak acid and a strong base, theoretically shouldn't such a salt be more soluble in lower pH? The EDTA divalent ion thus formed would be a stron conjugate base and accept H+ increasing the solubility?

I know both my assumptions are wrong since adding NaOH actually helped. What might be the actual reason which is counterbalancing the above mentioned 2 effects (are they even valid in this case?)


texts: Identifying an aerogel like material or similar alternatives

texts:
A few years ago I saw this ultralight weight hydrophobic material and I have been trying to discover it's identity. I doubt it was aerogel since it was brought in by a high school student, but I cant say for sure.

It was a transparent whitish material that was very light weight but absorbed ridiculous amounts of water, expanding as it absorbed the water. They were in small pellets, approximately 2mm or smaller randomly shaped. When water is poured on it each individual absorbed large amounts of water and expanded, and each pellet became somewhat gel like (in the sense that each individual pellet was kind of squishy). Unless obscene amounts of liquid was added all it took was a quick shake to more or less absorb every drop of water. Even when squished the material generally didn't start releasing the liquid. If you ended add enough water that the material couldn't absorb anymore, it would float on the water. If left out for a few days the water would evaporate, the material would shrink, and the dry material was somewhat squishy (less so than when wet).

If it's off topic for me to ask something like this then how could I go about identifying this with a list of physical properties.


texts: The Gibbs–Helmholtz equation was developed in the 1870's, while Nernst's heat theorem was developed in the early $20^{th}$ century (according to google/wikipedia). Nernst's heat theorem tells us that the change in entropy tends to be zero in absolute temperature. But did Nernst's heat theorem provide any new insight? Because if we put $T=0$ in the Gibbs–Helmholtz equation, then  $\Delta G=\Delta H$. Anyone could have thereby concluded that as temperature approaches 0, entropy change becomes zero already in the $19^{th}$ century. I am quite confused regarding it, those were my assumptions (probably wrong), what was new about Nernst's heat theorem ?


texts: I'm reading a paper with a reaction scheme where an enzyme binds loosely to inhibitor reversibly and then the Enzyme-Inhibitor complex undergoes another reversible conformational change to a tightly bound complex. My question is about the notation used (which I cannot type because I can't find the appropriate symbols). The second reaction uses the regular equilibria symbol which is fine - no problem. However, the first reaction uses a modified form of the equilibria symbol which is one line rather than two with 'half arrows' at either end. What does this symbol mean?


texts: Tetrahedron is minimum energy conformation for atom with 4 electron domains in VSEPR theory

texts:
Background

A student asked me to prove that the regular tetrahedron is the minimum energy geometry available to describe the locations of the electron domains in three dimensions – the prediction of valence shell electron pair repulsion (VSEPR) theory for a central atom with 4 mutually repelling electron domains. With the tetrahedron demonstrated, it could then be shown using vector multiplication that the angles between all substituent atoms is $109.5^{\circ}$.

Some ideas

I can think of a few ways to start this proof:

As mentioned above, we could define a regular tetrahedron and work backwards to see if the distance between all vertices is equal and maximized. Start with the vertices: A(0, 0, 0), B(1, 1, 0), C(1, 0, 1) and D(0, 1, 1), and a central point O($\frac{1}{2}$, $\frac{1}{2}$, $\frac{1}{2}$). With these, we can get vectors that point to each vertex. Call them $\vec{r_1}$ through $\vec{r_4}$. We remember that we can calculate the angle between any two vectors using the geometric and algebraic definitions of the dot product. I won't bore you with the details of this calculation but if anyone wishes to see it, I would be happy to share it. If you do it you will see that all the angles are equal and satisfy: $\cos^{-1}\left(-\frac{1}{3}\right) = \theta_i \approx 109.47122^{\circ}$. From here we would need to calculate the six distances bewteen the four vertices to show that the distances are all equal.
Using multivariable calculus, we could treat this as an optimization problem subject to the constraint matrix, $g$; the sum square distance function, $f$; and use the optimization formalism described by Lagrange. This results in a system of 13 unknowns – the 4 points with three coordinates each plus $\lambda$ – and 13 equations – the four constraint equations plus the nine partial derivative equations from the Lagrange method:

$$g = 1 = \left\{\begin{array}{c}g_1(x_1,y_1,z_1) = {x_1}^2 + {y_1}^2 + {z_1}^2\\
g_2(x_2,y_2,z_2) = {x_2}^2 + {y_2}^2 + {z_2}^2\\
g_3(x_3,y_3,z_3) = {x_3}^2 + {y_3}^2 + {z_3}^2\\
g_2(x_4,y_4,z_4) = {x_4}^2 + {y_4}^2 + {z_4}^2\\
\end{array}\right.$$
$$f = \mathop{\sum_{i=1}^{3}\sum_{j=1}^{3}}_{i<j}\left[\left({x_i}-{x_j}\right)^2+\left({y_i}-{y_j}\right)^2+\left({z_i}-{x_j}\right)^2\right] $$
$$\nabla f=-\lambda \nabla g$$

An approach similar to the one outlined above could be used with spherical coordinates instead. This version reduces the set of variables from 13 to 8 (the four sets of two angles for each point $\theta$'s and $\phi$'s; note the spherical radius could be set to 1 or any other bond distance, $a$, so is not a variable). These could be further reduced using symmetry arguments. For example, if we take the first vertex at the point $(0, 0, 1)$, we know based on symmetry that if we look down the z axis at the xy-plane, the angle between the three other vectors must have an angle of $120^{\circ}$ with respect to one another. Let one of the other vertices have the point $(x, 0, -\sqrt{1 - x^2})$ – satisfying the radius of 1 unit constraint we have imposed. Now based on symmetry, we know that the other two points must be $(x\cos(\frac{2\pi}{3}),x\sin(\frac{2\pi}{3}),-\sqrt{1-x^2})$ and $(x\cos(\frac{4\pi}{3}),x\sin(\frac{4\pi}{3}),-\sqrt{1-x^2})$ using spherical symmetry. From here, we can write a formula for the total sum square distance between all the points and set the derivative with respect to $x$ to zero to find the maximum sum square distance. Notice we have reduced the problem with these symmetry arguments from a multivariable calculus problem to a calculus BC problem. Alternatively, we could use some other guess and check method to solve for $x$. Note, we should find the same answer using this method as the others above (and below).


texts: Structural isomers of hexaammineiron(III) hexacyanidocobaltate(III)

texts:
Find the number of structural isomers of $\ce{[Fe(NH_3)_6][Co(CN)_6]}$

This was a question solved by my teacher as follows:

The $\ce{CN}$ will show linkage isomerism while $\ce{NH_3}$ and $\ce{CN}$ will show coordination isomerism.

We will now consider cases of coordination isomerism and then use linkage isomerism.

$\ce{[Fe(NH_3)_6][Co(CN)_6]}\rightarrow 7$ isomers(due to linkage isomerism of $\ce{CN}$)
$\ce{[Fe(NH_3)_5(CN)][Co(CN)_5(NH_3)]}\rightarrow 2\times 6=12$
$\ce{[Fe(NH_3)_4(CN)_2][Co(CN)_4(NH_3)_2]}\rightarrow 3\times 5=15$
$\ce{[Fe(NH_3)_3(CN)_3][Co(CN)_3(NH_3)_3]}\rightarrow$ not counted.

The further $3$ cases are similar to the first $3$ and will result in the same number of isomers. Hence the answer is $2\times(7+12+15)=68$.

Why is $\ce{[Fe(NH_3)_3(CN)_3][Co(CN)_3(NH_3)_3]}$ "not counted"?

I feel that isomers due to $\ce{CN}$ showing linkage isomerism are perfectly valid. Please correct me if I'm wrong and sorry if the question is too trivial.


texts: When undergoing a ring flip, why doesn't the ring go directly from the half-boat confirmation to boat confirmation?

texts:
Why does the ring go through the twist-boat conformation when transitioning from half-boat to boat conformations? In other words, what is stopping the ring from transitioning directly from the half-boat to boat (and vice versa). In fact, going from boat to half-boat has a smaller energy differential than going from twist-boat to half-boat.
My guess: Because there is a more stable intermediate available between half-boat and boat, so thermodynamically it will prefer to go to that intermediate (twist-boat) first.


texts: Effect of short lived chemicals on global warming exceeding effect of carbon dioxide

texts:
From Wikipedia:  Global Warming Potential

GWP values and lifetimes:
Nitrous oxide lasts about 121 years in the atmosphere, causes about 280 times as much warming over 20 years, but about 300 times as much over 100 years.
HFC-23 lasts about 222 years, causes about 11,400 times the warming over twenty years, but about 13,600 times over one hundred years.

Carbon dioxide is widely believed to last at least 300 years, if not longer, in the atmosphere.
How can certain short-lived chemicals cause more global warming in the long term, relative to carbon dioxide, than they do in the short term?


texts: Comparing basic strengths between pyridine and 1,2-dihydropyrazine

texts:
Compare the basic strengths of above two compounds.

In the first compound (1,2-dihydropyrazine), the lone pair of one N will participate in resonance but the lone pair of other N will not, similarly in pyridine, lone pair will not participate in resonance.
I think that since the first compound atleast has $2$ nitrogens (and only one in pyridine), it should be slightly more basic than pyridine, but I came to know that it's the other way round. So how do we compare their basic strengths and what are their $\mathrm{p}K_\mathrm{b}$ values?


texts: Whats the difference between entropy and the (dis)order of a system?

texts:
Entropy is often verbally described as the order/disorder of the thermodynamic system. However, I've been told that this description is a vague "hand-waving" attempt at describing what entropy is. For example, a messy bedroom doesn't have greater entropy than a tidy room

My question is why is this the case? Also, what would better describe entropy verbally?


texts: Why Heating of certain salts like Lead salts produce crackling sound?

texts: I recently discovered that heating of certain salts produces crackling sound and that is called Decrepitation. But I couldn’t figure out the reason why that happens moreover I couldn’t find anything satisfactory on the internet.