texts:
I am investigating the current output from an electrochemical cell. The electrochemical cell can be broken down into several stages, for example:

Diffusion of reactants across a capillary
Diffusion in aqueous electrolyte
Adsorption and desorption at the electrode
Current generated due to anodic and cathodic though the Butler-Volmer Equation

From the readings I have done so far, current will be generated at each of these stages due to transfer of electrons. However, most authors will introduce the concept of limiting current at the rate determining step and neglect the remainder current generated from other stages.

If so, is it possible to obtain the total current output by summing the limiting current in each individual stages of the entire chemical reaction? Or focusing on solely the limiting current of the rate determining step will give a good approximation?


texts: By what mechanism do acids deprotect primary silyl ethers?

texts:
Standard protocols report the selective deprotection of primary silyl ethers in the presence of secondary silyl ethers under acidic conditions, as exemplary shown in scheme 1, a reaction by Hartmann and Kalesse.[1]

Scheme 1: Selective deprotection of a primary silyl ether[1]

Numerous other examples can be found in the literature using numerous acidic reagents such as campher sulphonic acid,[2] para-tolylsulphonic acid[3] and even acetic acid[4] or $\ce{HCl}$.[5] Similar conditions can be used in the case of TIPS ethers.[citations needed]

I was wondering what the mechanism of this transformation looks like, and especially why it seems to be selective to primary silyl ethers. Answers that reference papers actually investigating the mechanism are preferred, but others are welcome, too.

List of abbreviations:

b.o.r.s.m: based on recovered starting material
Me: methyl
PPTS: pyridinium para-tolylsulphonate
TBS: tert-butyldimethylsilyl
TIPS: tetra-iso-propylsilyl

References:

[1] O. Hartmann, M. Kalesse, Org. Lett. 2012, 14, 3064. DOI: 10.1021/ol3011387
[2] Y. Mori, K. Yaegashi, H. Furukawa, J. Am. Chem. Soc. 1997, 119, 4557. DOI: 10.1021/ja9701523
[3] S. Kiyooka, K. A. Shahid, F. Goto, M. Okazaki, Y. Shuto, J. Org. Chem. 2003, 68, 7967. DOI: 10.1021/jo034901c
[4] B. H. Hart, S. K. Verma, H. Rapoport, J. Org. Chem. 2003, 68, 187. DOI: 10.1021/jo026499s
[5] A. B. Smith III, B. S. Freeze, I. Brouard, T. Hirose, Org. Lett. 2003, 5, 4405. DOI: 10.1021/ol035697i
[citations needed] I think, you get the picture, I’m not going to go looking for even more …


texts: Why are organolithium and organomagnesium compounds nucleophilic in nature?

texts: My textbook doesn't say anything about this but does say that on addition of organolithium compounds to carbon dioxide, they give ketones and not carboxylic acids like grignard reagents. This has been attributed to the greater nucleophilic character of Organolithium compounds compared to grignard reagents. I see that greater polarity of the C-Metal bond must relate to this according to many websites but I cannot understand why! Also, during formation of the RLi compounds using alkyl halides, what does the alkyl halide dissociate into? Please help!


texts: Purchasing chemicals online often I see "Sodium Deoxycholate, ≥97% (titration)" offers. Is there any publicly available titration protocol I can use to confirm that statement in my very basic lab which does not have HPLC?


texts:
Suppose we have 1 eq of acetic acid and we want neutralize it using sodium hydroxide. After adding 1 eq of sodium hydroxide 1 eq of sodium acetate should form and neutralization should be complete but because of hydrolysis little bit of acetic acid will form again so we would have to add more sodium hydroxide and this process would go on forever so how will neutralization ever be complete?

My guess is that after adding 1 eq of NaOH the conc. of acetic acid becomes so low that it is neglected and the neutralization is assumed to be over.


texts: How to measure chlorine content using ORP sensor?

texts:
In my project I need to measure pH, turbidity, and chlorine level of treated drinking water. I found sensors for measuring pH, turbidity, and also chlorine.
The actual problem begins is that the cost of chlorine sensor is too high, so I googled for an alternative solution, which led me to use an oxidation-reduction potential (ORP) sensor.
Can anyone tell me about the relationship between pH, chlorine, and ORP value in millivolts and how to measure chlorine content in treated water using ORP sensor?


texts: How a plane of symmetry makes compounds lose their optical activity

texts: I understand that if a compound has a plane of symmetry it loses its optical activity, it is very easy to understand this when we have four different substituents on a single carbon atom but when we have larger more complicated structures for example rings with many substituents which are themselves stereogenic how can we be so sure it wont have any enantiomers if we only find one fortunate plane which produces a perfect mirror image?


texts: Why can syn-periplanar E2 elimination happen in molecules like vinyl bromides but seemingly not in other molecules?

texts: E2 eliminations occur when the leaving group and the proton are in the anti-periplanar conformation not syn-periplanar. This is beyond a merely a preference as leads to E2 reactions being stereoselective. However, when it comes to vinyl bromides for example (involving a double bond) the reaction can occur in the Z- and E- isomers (i.e both syn-periplanar and anti-periplanar). How can this be the case?


texts: Are Na and Cl ions from NaCl in water separate charged particles?

texts:
Suppose I pour some sodium chlorine into water. So, what happens is that

$$
\ce{NaCl (s) -> Na+ (aq) + Cl- (aq)}
$$

meaning that the ionic bond between Na and Cl breaks up (correct this far?)

Now, does this mean that the water actually contains separate charged Na and Cl particles? So... since chlorine boils at −34.04 °C according to Wikipedia, why is there then no chlorine gas evaporating? Because it is chlorine ions there, not chlorine atoms?

If I feed electrons some how into the solution, will chlorine gas start forming?

Also, could I use this so that I pour NaCl into water and get Na and Cl ions, and then (since they are separate) add something more to create Na[something] or Cl[something]? Something that would not form if I just mixed NaCl + [something else]. I hope I am not completely lost here..


texts: How useful is the assumption that water doesn't auto-ionize in the following?

texts: Now in the first row of the iCe-table, $[\ce{H3O+}]$ is said to be 0. But water autoionizes to some extent, so it shouldn't really be 0. I accept that, because the pH of this solution is 2.5, the autoionization effect is negligible but are there instances where this can't be ignored (e.g. where the pH is close to 7?)? Academic, industrial (or hobby) examples would all be fine.


texts:
Does anyone have a reference for the density range of common table salt $(\ce{NaCl})?$
A pure $\ce{NaCl}$ crystal has a density of $\pu{2.16 g/cm^3}.$  However, the salt granules in table salt don't pack perfectly — there's a lot of air mixed in.
I carefully measured some Morton's iodized table salt at home $(> 99\%$ $\ce{NaCl};$ remainder is calcium silicate, dextrose, and $\ce{KI}),$ and got a density of $\pu{1.40 g/cm^3}*,$ which gives a packing fraction of $1.40/2.16 × 100\% = 64.8\%.$
Interestingly, this is (within my measurement error) essentially the same as the $64\%$ random close packing limit for monodisperse frictionless hard spheres.
But I don't know how much variation there is in the density of table salt, and have been unable to find a reference online.
*Here is how I measured the density:
I started with a metal 1 tbsp measuring spoon.  I didn't trust that its volume was actually 1 tbsp, so I filled it with water and measured the weight of the water (14.25 g) with a calibrated centigram scale, and its temperature (76 F) with a thermometer.  Since water @ 76 F has a density of $\pu{0.997189 g/cm^3}$, the volume of the measuring spoon was:
$$V_{spoon} = \frac{\pu{14.25 g}}{\pu{0.997189 g/cm^3}} = \pu{14.2902 cm^3},$$
as compared with the actual volume of a tablespoon, which is $\pu{14.7686 cm^3.}$
I then weighed a level tablespoon of salt (20.00 g) and, from this, determined that
$$\rho_{table salt} = \frac{\pu{20.00 g}}{\pu{14.2902 cm^3}}= \frac{\pu{1.40 g}}{\pu{cm^3}}$$


texts: Reaction of alkyl bromide in presence of piperidine

texts:
What are the products of this reaction? I believe there'll be E2 elimination to give the products. Not sure. Help would be greatly appreciated.

The above is the product which I thought might be possible due to E2 elimination

In case there is carbocation formation, this might be the intermediate:

Could there be nucleophilic substitution?


texts: While triiodide ion is commonly known, why is that trichloride ion (and its salts) almost unheard of? While it does exist according to literature, why is the stability of trichloride ion in aqueous environment much worse than its bromine and iodine counterparts? Aren't elements down the group bulkier and hence forming weaker covalent bonds with longer bond lengths?


texts: How is phosphate stable disobeying octet rule?

texts:
Doesn't the phosphate now have 10 electrons mutually shared between the oxygen atoms? I am unable to understand how the phosphate bond would be formed if phosphate does not obey the octet rule.

Thank you!

Reference: http://www.chemguide.co.uk/organicprops/aminoacids/makedna.gif


texts:
I am studying for a big test and I ran across something that I couldn't solve no matter how hard I tried. (reading through old tests)

Burning ethanol produces carbon dioxide ($\ce{CO2}$) and water ($\ce{H2O}$).

a) Write down a balanced chemical equation that illustrates the complete burning of ethanol.

b) What is the mass of produced carbon dioxide ($\ce{CO2}$), when completely burning 575 liters of ethanol?

NTP conditions apply. Ethanols density is 0.8 g/cm³.

MC = 12 g/mol, MH = 1 g/mol, MO = 16 g/mol

For the first part I came up with $\ce{C_2H_6O (l) + 3O2(g) --> 2CO_2 (g) + 3H2O (g)}$

Then I calculated that $M_\ce{CO_2}$ = 44 g/mol and $M_\ce{H_2O}$ = 18 g/mol

I also calculated that 575 liters of ethanol weighs 460 kg

I know that m = nM

However I am not sure what to do next.
I may also be using some weird terms here as this is my translation and I've never dealt with math/chemistry in English.


texts: Don't understand why Rutherford was shocked by results of gold foil experiment

texts:
The way Rutherford's classic gold foil experiment has been presented (including by Rutherford himself) doesn't make sense to me.

As many of you know, Rutherford famously described himself as being utterly shocked at the results brought to him by Geiger in 1909: "It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you."  [Rutherford, Ernest; Ratcliffe, John A. (1938). Forty Years of Physics. In Needham, Joseph; Pagel, Walter. Background to Modern Science. Cambridge University Press.]

It makes no sense to me that he should have been so surprised.  Rutherford wrote the following the year before, in 1908: "We can conclude with certainty from these experiments that the α particle after losing its charge is a helium atom. Other evidence indicates that the charge is twice the unit charge carried by the hydrogen atom set free in the electrolysis of water." [Ernest Rutherford & Thomas Royds, Philosophical Magazine 17, 281-286 (1909).] [Publication date was 1909, but authorship date was 1908.]

Thus, at the time of the gold-foil experiment, Rutherford believed (correctly) that his "15-inch shell[s]" (the α particles) were helium atoms that had lost negative charge. So essentially Rutherford, using particles that he knew to be highly concentrated atomic-scale matter derived from atoms (α particles), was shocked to find that atoms contained highly-concentrated atomic scale matter (?!).

I'm not saying he should have known specifically about the nuclear model of the atom prior to the experiment.  I'm saying he shouldn't have been utterly shocked to find that atoms contain something that can strongly deflect α particles, given that he knew α particles themselves were simply atoms whose negative charge had been removed. [Plus he knew he was taking particles derived from very light atoms, and shooting them at very heavy atoms.]

To use Rutherford's own metaphor, it's as if he were saying: "I went to an armory and obtained some artillery shells. I then fired these at another armory, and was shocked to find, as a result, that armories contain artillery shells."

I.e., if Rutherford already knew this about helium ions, why wouldn't he expect other atoms would also have their positive charges concentrated as well? Was his thinking that neutral atoms were accurately described by a plum pudding model, yet once you removed the electrons the positive charge would collapse into a small space? If anything, given that he didn't know about nuclear binding, it would seem he should have expected the opposite—that removing the negative charges would cause the positive charges to expand and become even more diffuse.

Can someone familiar with the history of these experiments resolve this?


texts: What is the origin of the "positive-to-negative" convention concerning dipole moments in chemistry?

texts:
I'm a physics professor who often teaches students who have taken a lot of chemistry (read:  pre-meds).  In physics, the dipole moment of a charge configuration is defined as pointing from concentrations of negative charge towards concentrations of positive charge.  This is embodied in the formula we use for the dipole moment of a charge configuration,
$$
\vec{p} = \sum_i q_i \vec{r}_i.
$$
It's not too hard to see that this yields a vector that points from negative charges to positive charges.  For example, if I have a charge of $-e$ at the origin ($\vec{r} = 0$) and a charge of $+e$ a distance $d$ away, this formula yields a vector that points from the negative charge to the positive charge, with magnitude $ed$.

However, the first time I taught this material in a class with a large number of chemistry students, they were very confused;  they had always learned that the dipole vector of a polar molecule points from positive charge towards negative charge, i.e., in the opposite direction of the convention from physics.  For example, by the physics convention, the dipole moment of the water molecule points away from the point of the "V" formed by the bonds, while under the chemistry convention, the dipole moment points in the direction of the point of the "V".

How did this convention arise?  Is there an advantage to defining the dipole vectors this way in chemistry calculations?  Or is it one of those scientific conventions that someone wrote down one point, and got ingrained in textbooks ever since?  (Is it all Benjamin Franklin's fault?)

One of the answers to this question notes the difference between the conventions, but doesn't really explain why the first chemist to write down a dipole vector wrote it down that way.  I would love to know how this convention arose historically!


texts: In this MO diagram, why are the atomic Mn $3d$ orbitals higher in energy than the Ni $3d$ orbitals?


texts: Does someone know the name of this equipment?

texts: I think it is used to measure force or something like that. I broke it and have to buy a new one.


texts: Grignard reagents react with epoxides but dissolve in THF, what happens in oxetane (four membered ether ring)?

texts: Ring strain causes the epoxides to react and THF does not react because the ring strain is not large enough. Does the four membered ring react or not? Does it favor reaction with the harder or softer nucleophile perhaps - thus only reacting with some Grignard reagents?


texts: Condensation point of molecule compounds?

texts:
Which of the following gasses will condense at the lowest pressure (Assuming temperature is held constant)?

$\ce{CBr4}$
$\ce{CH2Br2}$

I believe that compound 2 will condense at the lower pressure because it can form dipole dipole forces with other molecules. I believe that London dispersion forces are weaker than dipole dipole ones so 2 should condensed at a lower pressure.


texts: Is the cathode and anode on the cell notation of an Electrolytic cell on the same side as if how you will write it for a Galvanic cell?

texts:
I was reading an online material then I came upon a cell notation for an electrolytic cell (I determined that it was an electrolytic cell because of the absence of a salt bridge). Usually, I will proceed on reading but then I realized, since cathode and anode is switched for an electrolytic cell, which side of the cell will be the cathode and the anode?

The example given was:

  $$\ce{Ag | AgCl(s), Cl- (\pu{0.200 M}), Cd^2+ (\pu{0.00500 M}) | Cd}$$


texts: In the nitration, why fluorobenzene has less products in the ortho position than Clorobenzene?

texts: Is it because, due to the eletronegativity of Fluorine, his mesomeric effect will be less pronounced, which means the electronic density will be lower, than for the clorobenzes, in the ortho positions?


texts: Why is it so hard to turn plastics into something useful or decompose it?

texts:
Even after so many years, why haven't we yet come up with a solution to the plastic problem ?

Why are plastics so hard to decompose via chemical or physical processes into something harmless or useful ?


texts:
So, it's been a good two years since I've done chemistry and I have my first university lab in a few days and I'm sort of freaking out because I can't even remember how to do stoichiometry properly. This a question off of my pre-lab review and I'm having troubles remembering what to do. I believe this is a limiting reagent question.

In Experiment 1, you will place and AlkaSeltzer tablet in each of the dilute $\ce{HCl}$ solutions you prepared. The reaction between $\ce{HCl}$ and $\ce{NaHCO3}$ should take place quickly and release gaseous $\ce{CO2}$. You will then use the mass lost for each flask to determine the amount of $\ce{NaHCO3}$ that reacted.
A student performs this experiment and determines that $\pu{1.60 g}$ of $\ce{CO2}$ were lost. How many grams of $\ce{NaHCO3}$ would have reacted to produce this amount of $\ce{CO2}$?

Firstly, I wrote out part of the equation but I'm also beginning to think it's incorrect too:
$$\ce{NaHCO3(aq) + HCl(aq) <=> CO2(g) + NaCl + H2O(l)}$$
The initial amount for $\ce{NaHCO3}$, I know, is unknown and the final amount for $\ce{CO2}$ is $\pu{1.60 g}$. Other than that though I'm at a loss for what to do next. Please help if you can, thank you!
Edit (see answer): To calculate the amount of moles in $\ce{CO2(g)}$ I used the formula $m/M = n$, which gave me 0.36355 moles for carbon dioxide. Now I use 0.36355 moles for $\ce{NaHCO3(aq)}$ since it's a 1:1 ratio.


texts: Should I include ions from the solvent in solubility product constant calculations?

texts:
I'm trying to determine the Solubility Constant $K_\mathrm{sp}$ of $\ce{Ba(NO3)2}$ dissolved in nitric acid solution $\ce{HNO3}$ from experimental data.

$\ce{HNO3}$ will be mostly dissociated so there are many $\ce{NO3-}$ ions already in the solvent before solid $\ce{Ba(NO3)2}$ is added.

When I calculate $K_\mathrm{sp} = [\ce{Ba^2+}][\ce{NO3-}]^2$, do I include in $[\ce{NO3-}]$ the ions already present in the solution before solid $\ce{Ba(NO3)2}$ is added?

For example, say I have dissolved ${0.1 mol}$ of barium nitrate in ${1 L}$ of ${1 M}$ nitric acid solution. There are now ${0.2 mol} + {1 mol} = {1.2 mol}$ of nitrate ion in the solution. Should my $K_\mathrm{sp}$ calculation be

$$K_\mathrm{sp} = 0.1\cdot 0.2^2,$$

or

$$K_\mathrm{sp} = 0.1\cdot 1.2^2?$$

I understand that the common ion effect in this case inhibits solubility somewhat, but it I think my professor told me to include ions from $\ce{HNO3}$ in the calculation, which seems wrong.


texts: Why are carbamates capable of inhibiting acetylcholinesterase?

texts: Certain carbamate compounds, such as the insecticide carbaryl or the Edgewood carbamates such as EA-3990, can inhibit the enzyme acetylcholinesterase. Unlike organophosphorus compounds, however, they do so reversibly and are bound to the enzyme for minutes, as opposed to permanently. The carbamyl functional group differs from an acetyl group in that, instead of a methyl group being bonded to a carboxyl, a carbamate has amino group bonded to a carboxyl. Why exactly does this difference allow carbamates to inhibit AChE for minutes at a time, and why is cholinesterase that has been inhibited by a carbamate not susceptible to reactivation by oximes such as 2-PAM?


texts: I mixed Miracle Gro fertilizer and Soil Mender Liquid Fish in my hose-end sprayer to save time. The mixture became very cold. Why?

texts:
Miracle Gro = Ammonium Sulfate, Potassium Phosphate, Potassium Chloride, Urea, Urea Phosphate, Boric Acid, Copper Sulfate, Iron EDTA, Manganese EDTA, Sodium Molybdate, Zinc Sulfate.

Soil Mender Liquid Fish = hydrolyzed fish.

Why would mixing these together in the jug of my hose-end sprayer cause the mixture to become very cold? Nothing else added.


texts: Are the dsp3 hybrid orbitals degenerate?

texts:
I learned in general chemistry that hybridization of n orbitals produces n hybrid orbitals with the same energy (degenerate).

However, in Housecroft and Sharpe inorganic chemistry, I read the following:

  The mixing of $\mathrm{s}$, $\mathrm{p}_x$, $\mathrm{p}_y$, $\mathrm{p}_z$, and $\mathrm{d}_{z^2}$ atomic orbitals gives a set of five $\mathrm{sp^3d}$ hybrid orbitals, the mutual orientations of which correspond to a trigonal bipyramidal arrangement. The five $\mathrm{sp^3d}$ hybrid orbitals are not equivalent and divide into sets of two axial and three equatorial orbitals; the axial orbital lobes lie along the $z$ axis.

The above excerpt seems to imply that the 5 resulting $\mathrm{sp^3d}$ hybrid orbitals are not degenerate and have different energies. However, this is contradictory to what I learned in general chemistry. Why is this so?


texts: Is it possible to figure out how many carbon-carbon double bonds are present using just the molecular formula?

texts:
One of my test review questions reads as follows:

  "The prostaglandin precursor arachidonic acid has the molecular
  formula $\ce{C20H32O2}$. Given that arachidonic acid is an acyclic carboxylic
  acid that contains no carbon-carbon triple bonds, how many
  carbon-carbon double bonds are present?"

My original instinct was to draw out the structure, but having just the molecular formula to go off of and nothing else, it seems like it would take a ton of trial and error to figure out the correct structure. Is there a simpler way to approach a problem like this to figure out the amount of double bonds?

The only other thing that came to mind was to calculate the degree of unsaturation from the formula, which came out to 5. So, I know there can't be more than that. But that could represent both double bonds and/or rings, so. Anything I'm missing?

(The answer is 4, by the way. I just need help figuring out how the process of getting there is laid out.)

Thanks.


texts:
A galvanic cell works by having two electrochemical equilibriums which have a different potential.

If you (theoretically) had a galvanic cell with two electrodes which have almost identical potentials and are sensitive to heat (at the anode the oxidation is exothermic and at the cathode the reduction is), connected the two half cells with a diode contrary to the normal current and heated the whole thing up, shouldn't it be possible to reverse the current and recharge the cell?

Please excuse language mistakes I might have made; I am not a native English speaker and therefore don't know all technical terms in English.


texts:
Styrene Butadiene synthetic rubber is also called Buna-S. It is the abbreviation of Butadiene (Bu) Sodium (Na) Styrene (S).
Why is Sodium included?


texts:
I'm wondering about how does the litmus solution work as a pH indicator.

And another question:

When you put drops of litmus solution into an colorless acid (e.g. $\ce{HCl}$), it turns red. But then if you add colorless base (e.g. $\ce{NaOH}$) to the mixture, it turns blue. How come?

I thought that the litmus solution doesn't change color after it's changed color once already after a chemical change with an acid or a base. In this case, I thought that the mixture wouldn't turn blue after adding the $\ce{NaOH}$ into the mixture. But it seems that it still works well after used once.

How come?


texts: Do really the electrons could only orbit in specific orbits with a fixed radius?

texts:
According to Bohr's model of atom

  The electrons could only orbit the nucleus in specific orbits or shells with a fixed radius. Only shells with a radius given by the equation below would be allowed, and the electron could not exist in between these shells.
  r(n)=n2
   ⋅r(1)

But when I learnt about different orbitals inside the atom in my textbook, it was said that you cannot precisely tell the location of an electron, as you know the velocity, according to Heisenberg's uncertainty principle. Besides in a video of khanacademy.org Sal said that orbitals means that if we took a number of snapshots of atoms, we would see that the electrons are denser in those orbitals but that does not necessarily mean that we wouldn't find it outside of the orbitals. The probability of finding electrons is higher in the orbitals but not 100%. But Bohr said electrons are quantized. It must be in a fixed orbital with a fixed radius. Isn't that contradictory? Which one is true? Or what is wrong in my understanding?


texts: Different solutions in cyclic voltammetry

texts:
CV is usually used to monitor corrosion (from what I have learned) because, if it is a reversible reaction, we can see the cathodic and anodic peak in the voltammogram. I know that the scan rate influences the intensity of the current peak and I also know why that happens. However, I just can't seem to find the reason why different solutions result in different current peaks in the voltammogram. Especially if the solutions get more acidic the current peak changes.
So my question is why do the peaks in the voltammogram change when we change the solution?


texts: Quantum numbers associated with electron

texts:
I wanted to get your opinion on something. I was given the electron 5p^3 and was told to find the quantum numbers associated with it. I got:
n=5
l=1
Ml=1
Ms= +1/2
However, my teacher has told me that I am incorrect and that my magnetic quantum number (Ml) should be -1. Could anyone possibly explain why this may be the case or if my teacher is incorrect. Thank you in advance!


texts: Solubility of Aluminium Halides by Fajans rule

texts:
According to Fajan's rule polarizability of anion is directly related to the size and hence  the covalent character would be more.

Now going by this definition aluminium chloride having greater covalent character would be less soluble than aluminium fluoride, but in reality it's just the opposite. How do I account for this?


texts: Is oxytocin's mirror image still oxytocin?

texts:
If you were to take the mirror image of oxytocin, does it remain the same or does it change? Say I want a tattoo of it on the left side of my chest, going from the widest part of oxytocin to the smallest part, but it won't fit the way it is depicted below.

Would it still be correct or does something need to be changed? I can just get it on the opposite side but I'd like to know the chemistry of this.


texts: Why does dimethyl ether have a bond angle bigger than 109.5 degrees?

texts: Why does dimethyl ether have a bond angle bigger than 109.5 degrees, in contradiction with VSEPR theory?


texts:
Which state has a higher entropy — the
liquid–gas equilibrium or the gaseous state? I have learned that at equilibrium the entropy is maximised. But I also learned that the gaseous state has the highest disorder (entropy), if the latter is true then why does the equilibrium exist, why doesn’t the liquid transform into the gaseous state at equilibrium completely? What factor is responsible for this?


texts:
I am reading about A cathode ray discharge tube and I still do not fully understand why that as you keep on lowering the pressure in the chamber it creates striations, Faraday's dark space and Crooke's dark space and why it does not just stay as a constant stream of light? Also why does the gas have to be at a low pressure in the first place for the constant column of light to appear?

To verify my questions are:

Why when you lower the pressure to a certain extent you can see striations, Faraday's dark space and Crooke's dark space and why doesn't it just stay as a constant column of light?
Why does the pressure in the chamber have to be very low for you to be able to see a constant column of light?


texts: Plutonium having more oxidation states than samarium?

texts:
Why does plutonium have more oxidation states than samarium?

Electron configuration of Pu: $\ce{[Rn] 5f^6 7s^2}$

Electron configuration of Sm: $\ce{[Xe] 4f^6 6s^2}$

I thought that only the valence electrons affected the oxidation states, so why does plutonium have more oxidation states (6,5,4,3) than samarium (2,3) whilst they both have the same valence electrons (including f-orbitals): ..$\ce{f^6}$..$\ce{s^2}$ ?

Elements such as scandium (Sc),Yttrium (Y) and Lanthanum (La) all have the same valence electrons (including d-orbitals): ..$\ce{d^1}$..$\ce{s^2}$ , but these elements have the same oxidation state : 3 and that doesn't change, even when going down that group and looking at actinium.

Does this have to do with the ionization energy, or the energy level or ....?


texts: What does it mean to 'fuse' ores and why do we use alkali metals in the process?

texts:
For the extraction of chromium, fusion of chromite ore with sodium or potassium carbonate in excess of air is done. What exactly happens in this 'fusion' process?
According to my textbook (class XII chemistry, NCERT): d- and f-block element, extraction of chromite ore
According to the dictionary: To melt or fuse (ores) in order to separate the metallic constituents.
Now,  while this makes sense and is sort of (implied) by my textbook? how exactly is this process done? I want to learn the technicalities related to it! Further I've heard we use alkali metals in fusion, why do we use them ?


texts: Electron Pair Geometry in Ibuprofen (Electron Pair Geometry in Organic Compounds)

texts:
I am trying to determine the electron pair geometry (and molecular geometry) of some atoms in ibuprofen. The first one I am trying to do is the double bonded oxygen. Ibuprofen is pictured below:

I counted the number of electron domains(steric number) to be 3. I counted the double bond as one and each lone pair as one. It has two lone pairs and one double bond. So this means the electron geometry should be trigonal planar.

But I am stuck on molecular geometry. There is no molecular geometry I have found in any chart that has two lone pairs and one bond. Am I making a mistake somewhere?


texts: Why is it not dangerous to dissolve NaCl?

texts:
$$\ce{H2O~(l) + NaCl~(s) ->[\Delta] Na+~(aq) + Cl^{-}~(aq)}$$

When table salt is placed in water, it dissolves due to the polarity of water molecules. When solvation takes place, negatively polar sides of water molecules attach to $\ce{Na+}$ ions, and positively polar sides of water molecules attach to $\ce{Cl-}$ ions. The ions are then carried away by water molecules through diffusion. Since the sodium is now isolated from the chlorine, what keeps it from violently exploding with water in the following chemical reaction?

$$\ce{2Na + 2H2O -> 2 NaOH + H2}$$

Also, since chlorine is poisonous, wouldn't that make drinking salted water extremely lethal?


texts: Handling vectors for double-bond graphics

texts:
I'm working on a small molecular graphics tool for visualising ball-and-stick style molecules. I'm having trouble handling the linear algebra to position the two bonds in the double bonds. My linear algebra is, unfortunately, very weak. I can follow notation but struggle with working my own way through logical algebra.

If I'm overcomplicating this significantly then I'd appreciate some guidance on how so. Here is my working so far:

I currently have the atomic coordinates of each atom. All of the above atoms are in a plane due to the $sp^2$ nature of atom $i$, though the orientation of the plane is arbitrary.

$\textbf i$, $\textbf j$ and $\textbf k$ are atomic coordinates and $\textbf a$ and $\textbf b$ are vectors between them.

The orientation of the double bond must mean that both of the lines in the double bond are positioned in the plane, and I have quantified the plane as:

$\textbf{a} \times \textbf{b} \cdot (\textbf{r} - \textbf{r}_0) = 0$

where $\textbf r$ is any vector in the plane, and $\textbf{r}_0$ is any other point in the plane.

I can also say that the points which I am looking for on each atom make vectors with the centre of respective atoms at $90 ^\text{o}$ to $\textbf b$, and that the radius at which these points are positioned is constrained to a constant value (and therefore so is the length of said vector). If we call this vector $\textbf l$ we therefore have:

$(\textbf{a} \times \textbf{b}) \cdot (\textbf{l} - \textbf{i}) = 0$

$| \textbf{l} | = \text{const}.$

$\textbf{l} \cdot \textbf{b} = 0$

where $\textbf{a}$, $\textbf{b}$ and $\text{i}$ are all things which are numerically available to me.

I feel as though, based upon geometrical constraints, these algebraic relationships are enough to find only the 4 points which I want. But my amateur self has no idea how to do that.


texts:
We've learnt about the trans effect but I have a question regarding how this plays a role with water in the equation.

trans-effect:

$$\ce{H2O < NH3 < Cl-}$$

Based on this, given cis-$\ce{[Pt(NH3)2Cl2]}$, if you were to add water to form a dicationic complex, would a substituion reaction occur between all the substituents, and then $\ce{Cl-}$ reacts again to form the trans-complex?

Since water has a weaker trans effect than both $\ce{NH3}$ AND $\ce{Cl-}$, I can't imagine that a cis-complex would form as any cis-combination of $\ce{NH3}$ and $\ce{Cl-}$ has a stronger trans effect than any combination of $\ce{H2O / Cl- / NH3}$.

Are there any other kinetic / electronegativity factors that I am missing?


texts: VSEPR theory, chemical bond and quantum mechanics

texts:
VSEPR theory correctly predicts the shapes of many symmetry-broken molecules such as $\ce{H2O}$ and $\ce{NH3}$. Take $\ce{NH3}$ for example. In VSEPR theory, the nitrogen atom is (approximately) at the center of a tetrahedron, the three $\ce{N-H}$ bonds point to three of the four vertices of the tetrahedron, and the lone pair of nitrogen points to the $4$th vertex. But quantum mechanically speaking, the electrons should all be delocalized in the entire $\ce{NH3}$ molecule. How do I unify the two pictures to understand the concept of chemical bonds and VSEPR theory in quantum mechanics? Does VSEPR correspond to some kind of trial wave function (e.g. antisymmetrized geminal power (AGP))?

Note: when I say how to understand chemical bonds in quantum mechanics, I mean in the chemical bond description of molecules, electron pairs are localized at the bonds while quantum mechanics again says everything can be delocalized. So it's the same discussion as VSEPR v.s. QM. If there are only two atoms and one bond, the quantum mechanical meaning of the chemical bond is clear.


texts:
So I'm learning about Lewis structures for university. I was reading a book written by some teachers from my university and in one exercise they ask us to draw the Lewis structure for potassium permanganate ($KMnO4$). I attempted to do it, but when I compared my answer to that of the book I realized what I did was wrong.

This is the book's structure. However, when calculating the formal charge of the central manganese atom, I got $7-6-0 = 1$, and as far I understand, the best structure has a negative charge on one of the oxygen atoms, since they are more electronegative
So I looked up the structure online and I found that both my structure and that of the book were wrong.

This is the most common structure I found. Here, the formal charge for Mn is $7-7-0=0$, for the upper oxygen atom $6-1-6=-1$ and for the other oxygen atoms $6-2-4=0$, which makes more sense according to what I wrote before about oxygen being more electronegative than manganese.

However, I also found this another possible structure, this time on Wikipedia, where the formal charge of the central Mn atom is $7-8-0=-1$, and that of the oxygen atoms is $6-2-4=0$. So according to what I mentioned before regarding the formal charge, this structure is wrong as well.
I think the only right structure is the second one. Am I right?
Thank you in advance! :)


texts: What is the proper way to prepare a solution aiming to minimize errors?

texts:
I am a undergraduate student in chemistry, and my university is very weak in teaching solution preparation. I need to prepare a 10 mg / L methylene blue solution and now the way I do is, using an analytical balance of 5 decimal places, I tare a 50 mL beaker and simply add the 10 mg of methylene blue, trying be as accurate as possible (the amount is very small due to the large molecular weight). Afterwards, I add deionized water to a certain volume and transfer to a 1 L volumetric flask using a funnel (I wash the small beaker several times to guarantee that I transfer as much as possible of the compound) and complete with deionized water until the meniscus line. And so, I shake it many times.

Is this procedure correct? If not, how can I prepare this solution avoiding errors?


texts: Which branches of chemistry and in what order to learn (self study)?

texts:
Hi I have decided to give chemistry another shot (it didn't take so well way back in high school). My main interest is for reading up on brain chemistry and pharmacology.

I currently have a textbook on inorganic chemistry [Introduction to Organic Chemistry 3rd edition: William Brown.Thomas Poon] that I picked up and am working my way through - well I have made it through chapter 1 at least [Covalent Bonding and Shapes of Molecules]. And am also making use of The UC Davis (Organic) ChemWiki.

So after finishing the chapter today I decided to take a break and play around with an experiment I sore on youtube to make copper nanoparticles using copper sulphate and ascorbic acid. In the video he was pretty lenient with the measurements [1g sulphate, 5g ascorbic, 200ml water] and I wanted to scale the reaction up a bit so I had a go at trying to figure what the reaction was so I could get the true ratio... Obviously that duck wouldn't fly (I am only just starting on chapter 2 after all) so I just went ahead and multiplied his recipe by a factor of 5.

So where I was going with that last paragraph is that even after I finish reading the organic chem textbook I'm not seeing how that's going to help me with something like $CuSO_4.5H_2O$ since i'ts got nothing to do with carbon. Should I put the organic book to the side and start of with something like the (Inorganic) ChemWiki? Is it necessary to go through both of them or would it be enough to learn one subject and fill the gaps as there encountered [this exercise is a personal mission - I don't envision any possible future where I become a full fledged working chemist]? Better yet are there any broader texts that teaches a unified chemistry that doesn't make artificial distinctions? Or should I go ahead and invent my own syllabus?

Any short-cuts would be greatly appreciated - I basically just want to get to a point where I can read a wikipedia page on neurotransmitter X, psychoactive Y, or food ingredient Z and be able to comprehend fully what is going on.


texts: Number of lone pairs as a measure of basicity

texts:
$\underline{\text{Consider the following question:}}$

The first difference I noticed in these compounds was the large number of oxygen atoms in (IV). This definitely means that there is a larger number of lone pairs in this compound. So the obvious conclusion is that compound (IV) is the most basic or the least acidic one. However none of the options seem to have (IV) as the least acidic compound.

Where have I gone wrong?


texts:
Some time ago I implemented the restricted and unrestricted Hartree-Fock methods. I had a lot of fun and I learned a lot. It goes without saying that Szabo and Ostlund's book "Modern Quantum Chemistry" has been fundamental to achieve a working code.

I would like to repeat the experience implementing a DFT code. I would like to implement it for atoms with all-electron non-relativistic calculations (scalar relativistic calculation will maybe be an interesting extension as well as the generation of norm-conserving pseudopotentials). Unfortunately I did't came across a "DFT bible" such as Szabo and Ostlund's book.

Does anybody knows good references (at the same level of Szabo and Ostlund's for in-depth discussion of the practical implementation) for the practical implementation of DFT for atoms (radial SE, logarithmic grids, different functionals, ...)?

Note that I am not searching a general DFT introduction or an explanation of real PW+NCPP implementations.

This question is similar to this one but I don't think it is a duplicate. In the previous question I was asking about a book explaining the implementation details of DFT for periodic systems. DFT applied to periodic systems usually involves a PW basis set as well as pseudopotentials and FFTs. This corresponds to a simplified version of the PWSCF code of QuantumESPRESSO.

In this question I am asking for the references that will help me to write of an atomic code, i.e. no basis set expansion and no pseudopotentials (all-electron calculation, logarithmic grid, ...). This corresponds more and less to the atomic code of QuantumESPRESSO which is usually used to generate pseudopotentials.


texts:
According to VSEPR theory, molecules adjust their shape to minimize the effect of repulsion.

Suppose I take the structure of $\ce{ClF3}$. It has three bond pairs and two lone pairs.
So to minimize the repulsion it gets T-shape (the two lone pairs are at corners of a trigonal bipyramidal shape).

But my doubt is why do we call two lone electrons a lone pair? I mean, if we keep a lone pair at some point in a molecule, how can two lone electrons be so near? Why don't we take electrons individually but always lone pairs?


texts: Why work done Is 0 and why not a negative value?

texts: If a gas expand in vacuum, $P_{ex.} =0$. Then why is the work done 0? Since the gas is expanding, it is doing some work on the piston so the work done must have some negative value.


texts: Relationship between solubility and enthalpy of solution

texts:
I'm reading my lab manual and there is a part where it goes through Van't Hoff's isochore. That's fine but then it states

  The variation of the solubility of a substance with temperature
  may thus be given by the relation

  $$\dfrac{d \ln Sol}{dT}=\dfrac{\Delta H}{RT^2}$$

where do they derive this from. Is it from chemical potentials and mole fractions. I can't really find a good derivation and explanation online.


texts: Where to find pre-optimized files for Quantum Chemistry Softwares?

texts:
Many times Geometry optimization gets very time consuming ( even with access to super-computers ). I have seen some pre-optimized libraries for biomolecules like proteins that you can easily download machine optimized files from.

I use Avogadro,  GAMESS and McMolPlt for my quantum calculations.
I am thinking such libraries should exist for some complex chemical structures ( usable on softwares mentioned above ) but couldn't find any.

At this point I am specifically interested in " Hydroxyapatite Crystals ".
Does anyone know such resources ?


texts: Are polysaccharides generally considered to be hydrophobic and/or hydrophilic? My reasoning is that although they have polar groups/electronegative atoms, the polymeric nature of polysaccharides excludes water so I'm leaning towards them being hydrophobic.


texts: Why is Enthalpy of Compound at Some Temperature Equal to its Enthalpy of Formation at the Same Temperature?

texts: This is a question I don't understand in thermo. Enthalpy of compound would be sum of U + PV at some temperature, but since we can't calculate absolute value of H, we calculate it relatively to some reference. Enthalpy of formation is heat needed to be exchanged between system and surroundings at some pressure to keep the system at the same temperature when compound is formed from elements in the most stable state. Why are these two quantities equal?


texts: What happens when a piece of copper is placed in 1M HCl?

texts:
I know that the answer is that nothing happens, but the explanation is confusing me in some places. Firstly, we are given that:
\begin{align}
\ce{Cl2 + 2e- &-> 2Cl-} & (E &= \pu{1.36 V})\\
\ce{Cu^{2+} + 2e- &-> Cu(s)} & (E &= \pu{0.34 V})\\
\ce{2H+ + 2e- &-> H2} & (E &= \pu{0 V})
\end{align}

What's confusing me is that in the solution, we'll have $\ce{H+}$, $\ce{Cl-}$ and $\ce{Cu(s)}$, which are all products in the equations (except for $\ce{H+}$). I get that for the reverse equation (oxidation), the oxidation potential is given by the negative of the reduction potential. What I'm wondering is, if we look at copper and chlorine first, is the only option for the $\ce{Cl-}$ in solution to be oxidised (with $E = \pu{-1.36 V}$)? Also, can the copper also only be oxidised (with $E = \pu{-0.34 V}$)? And if both of these are true, then does that mean that these two can't react at all, not because of the total $E$ being negative, but because they can both only be oxidised?


texts: Reaction that will produce a silica coating (glaze)

texts:
The normal way to create a coating of pure silicon dioxide glaze is to coat the object to be glazed in a slurry of silica particles and then put it in a kiln.

However, if I have an object that is too large to fit in a kiln, then there is a problem.

I am wondering if there is a reaction of some kind that will produce a glaze of pure silica. The idea is that I could coat the object with the reactants, ignite them, and then when the reaction is over the object will be coated with fused silica. Is there any way to do this?


texts: Are there other Density Functional Theories other than Kohn Sham DFT?

texts:
For some reason I thought that the term DFT and Kohn Sham DFT were interchangeable. Kohn Sham DFT is certainly one of the most popular. But are there other types of DFT that are in use today? I have been able to find orbital free DFT is gaining momentum (http://www.sciencedirect.com/science/article/pii/S0022509607000221)
But are there more DFT types?


texts: Is it correct to use the symbols (l) and (g) in every reaction?

texts:
I know that this question might sound stupid to most of the people, but for a chemist noob like me is not very clear. So, here's the main question:

Is it appropriate to use the symbols (l) for liquids and (g) for gas in any reactions, or do the reactions have to be specific for a certain application?

The reason why I'm asking this is that in most of the cases, you don't see this notation. Also, are there other notations, for example (v) for vapor, or (s) for solid??


texts: Looking for experimental data for titration curves

texts:
I am looking for real, open source and free experimental dataset (not image, scan of table) of acid/base titration curves: pH versus titrant volume for many combination (strong/weak acid/base, polyprotic acids, etc.).

I could not find something satisfactory over the internet. Where could I find this kind of dataset?


texts: How are half lifes calculated for radioactive substances that decay over many years

texts: How are the half lives (or whole lives) calculated for slowly decaying radioactive substances such as tellurium? I must be having a fundamental misunderstanding of how we are able to predict the amount of time it will take for an isotope or radioactive material to decay fully including for ones that can remain unstable for practically eons.


texts: Why selective ring opening of the compound (attached image) by acid catalyst through results in a wide variety of branched iso-paraffins?

texts:
Basically, I want to know that why through beta scission, there is a possibility of formation of so many products, for example;
2-Ethyl-4-methylheptane;
2,4,6-Trimethylheptane;
2,2,5-Trimethylhexane;
3-Ethyl(2-methyl)hexane;
2,4-Dimethylhexane;
2,4-Dimethylpentane.


texts: Why is the melting point of hydrogen fluoride lower than that of ammonia?

texts:
The melting point of hydrogen fluoride is -83.6°C, as compared to that of ammonia, which is -77.73°C. How does this make any sense?

Both hydrogen fluoride and ammonia show hydrogen bonding, which "elevates" the boiling points of these two compounds when compared to the rest of the pnictogen and halogen hydrides. However, I was under the impression that hydrogen bonding increased in strength the more elctronegative atom the hydrogen atom is bound to, explaining why the boiling point of ammonia is significantly lesser than that of hydrogen fluoride (-33.34°C and 19.5°C respectively).

However, this makes no sense when looking at melting points of the two elements.


texts: I have been trying to compare 304 stainless steel with 7075 aluminum for some personal research. This steel alloy has a specific heat capacity of 500 J/kg-C, while for aluminum the value is 960 J/kg-C. Does this mean it is harder to heat up aluminum than steel? Then, steel has a thermal conductivity of 130 W/m-K, while for aluminum the value is 16.2 W/m-K. Does this mean that steel conducts heat away better than aluminum? Thank you.


texts: Is there a web based (or otherwise) computational chemistry tool which is able to calculate lipophilicity of a given compound?


texts:
Due to circumstance, our Data Centre build has some delays and it currently looks like we're going to have to perform a hydrostatic test of our sprinkler system with live computers in it.

As I have an education as a chemist, but haven't done any serious chemistry in >30 years I thought of using another liquid than water to charge the sprinkler pipes and am looking for the following characteristics:

Same order of magnitude of compressibility as good old H2O
Non-corrosive to materials used in a Data Centre (Metal, plastic, ...)
Non-flammable
Non-conductive to electricity
Non-HAZMAT
Cheap (No liquid gold please, or the VP is going to blow a fuse) ;-)

I tried googling a bit but could not find anything easily, so turning to the experts that deal with this on a daily basis as I've sent off the idea to the sprinkler installers already mentioning my preference for CHCl3 and C2H5OH as a joke, but if they ask me which liquid I would propose, what would be the ideal solution to the above problem?

A citation to a PubChem or similar source would be appreciated


texts: How exactly are ions in a Mass Spectrometer accelerated?

texts:
After a molecule is ionised, the ion is accelerated by an electric plate up to a certain kinetic energy by the attraction of the ion to the electric plate.
However, after the ion has passed the electric plate, won't the plate still exert an attractive force on the ion?  If so, by the attraction between the ion and the electric plate, the kinetic energy of the ion were attenuated, perhaps even to the point where there would not be a net gain in kinetic energy of the ion.


texts:
I am doing an introductory course to Crystallography and I have found in the following web page: http://pd.chem.ucl.ac.uk/pdnn/symm3/sgmonoc.htm a guide for the elaboration of the diagrams of the spatial groups.

In this tutorial, they say the following: "The symmetry operator for the c-glide plane is of the form x,T-y,1/2+z, while the symmetry operator for the two-one screw axis is of the form T′-x,1/2+y,T′′-z. It is possible to show (using matrices) that the only values for T, T′, and T′′, which permit the symmetry operators to form a closed group, are 1/2, 0, and 1/2, respectively"

They could tell me how to calculate the values of T, T' and T'' using the matrices.


texts:
I've come across a lot of instances where 'power law' description of the kinetics was mentioned, but I cannot think of any integrated rate law that follows something like:

$$A(t)=bt^n+c$$

I'm pretty sure the 'power law' refers to an integrated rate law instead of rate equations like:

$$r = k\prod_i [A_i]^i$$

So what is power law kinetics anyway? Does this 'power law' have a physical meaning or just a polynomial approximation that tells nothing about the mechanism?


texts: How do we know if a newly developed chemical compound has any taste or is tasteless?

texts:
I was reading this about polystyrene, which says: "Polystyrene is an odorless, tasteless, rigid thermoplastic", and got hung up on "tasteless".

I searched Chemistry.SE for "tasteless" and found this and this, but they don't exactly answer my question in the title, because polystyrene is not considered a poison and is not a natural compound. So for such a highly-used, man-made, industrial-scale-manufactured compound, how do we know its taste (or lack of it)? Was the data acquired in an official way, through intended testing, or only from "accidents" (which I cannot imagine, so just for the sake of argument)?


texts: Is there a pressure dependent function for freezing points of water and carbon dioxide?

texts:
I'm trying to determine whether or not certain compounds form solid ice at certain atmospheric pressures. These pressures vary significantly, from 0.001 atm to 800 atm. I understand that there is no equation relating the freezing points of all elements, but is there one or two that relate to carbon dioxide and water?

Ideally I'd like a Python function (or library) or equation where the input is atmospheric pressure or kPa.

Or, failing that, if someone could point me in the direction of a phase diagram for both compounds where I can input specific atmospheric pressure values and read a specific temperature for freezing point, that would be helpful as well.


texts: I took a look into some tetrahedrane (C4H4) analogs, platonic hydrocarbon, basically very strained tetrahedral geometry at every carbon.  I was wondering what will be the predicted delta H of formation for the tetra nitro analog tetranitrotetrahedrane?  What will be the predicted detonation velocity too?  Could there be modified analogs that are even more energetic?


texts: Grasping the concept of Electronic Spin, Effective Spin and Fictitious Spin

texts:
Trying to learn alone some aspects of quantum mechanics is, sometimes, a struggle. Reading the excellent paper by Piwowarska [1] I was hoping to, finally, understand what is the origin of the so-called “fictitious spin $1/2$” in a $\mathrm d^7$ cobalt ion.

Fig. 2 Visualization of distinction between the electronic, efective, and fctitious spins and respective spin Hamiltonians in terms of the spin levels of $\ce{Co^2+}(\mathrm{3d^7})$ ions

If my cobalt is high spin $(3/2$ is the electronic spin $S),$ then the effective spin $(\widetilde{S})$ is also $3/2,$ but where is the fictitious spin $({S}')$ $1/2$ arising from if the molecule is, in fact, high spin?
Reference

Piwowarska, D.; Gnutek, P.; Rudowicz, C. Origin of the Ground Kramers Doublets for $\ce{Co^2+}(\mathrm{3d^7})$ Ions with the Effective Spin 3/2 Versus the Fictitious ‘Spin’ ½. Appl Magn Reson 2019, 50 (6), 797–808. DOI: 10.1007/s00723-018-1080-4. (Open Access)


texts: Why is addition to acid chloride favoured over SN2 at the carbon even though it has a Beta-carbonyl?

texts: I feel that the conditions highly favour $S_\mathrm{N}2$ reaction at the aliphatic center and so the aliphatic chlorine should be replaced before the carbonyl chlorine. But the solution suggests that the nucleophilic substitution of carbonyl chlorine takes place before the aliphatic chlorine.


texts: Does anyone know or could make an educated guess as to the conductivity/resistivity of molten lithium carbonate? Ideally, around 750 degrees C.


texts: Advantages of Travelling wave IMS and Drift tube IMS

texts: I am learning Ion Mobility spectrometry. I am sorry for a very fundamental question. After reading different articles, I really did not understand what is the advantage of Travelling wave IMS over Drift tube IMS (or vice versa). Can anyone explain very fundamentally, what are the adavantages/disadvantages of TW IMS over Drift Tube IMS (and vice versa)?


texts: Partial dissolution of non-polar solutes in polar solvents

texts: I have learnt that in order for dissolution to occur, the solute-solvent intermolecular forces must be strong enough to overcome the solute-solute and solvent-solvent forces. However if this is the case, why are non-polar substances such as methane able to partially dissolve in polar solvents such as water? Aren't the dispersion forces always too weak to break the pre-existing hydrogen bonds present in water?


texts:
Suppose we have a chemical reaction where a linear chain can form (reversibly) from building blocks (e.g. atoms or molecules):

$$\ce{X_$i$ + X_$k$ <=>[$k_\mathrm{fwd}$][$k_\mathrm{rev}$] X_$i$X_$k$}$$

where $k_\mathrm{fwd}$ and $k_\mathrm{rev}$ are rate constants.

What is the distribution of polymer lengths (at equilibrium)? What are some canonical references that derive these distributions under variations of the above polymerization process (e.g. step versus chain growth)?


texts: Measuring bioanode potential against Ag/AgCl reference electrode

texts:
I'm trying to make a bioanode for use in a microbial fuel cell.  I have a piece of carbon cloth in an acetate solution with river sediment.  I'd like to know the potential of the anode, so I connected it to an Ag/AgCl reference electrode also in the sediment/acetate solution (note that ref electrode has 3M KCl, about 0.2V relative to SHE).  Between the reference electrode and anode, I have a multimeter connected with the positive going to the Ag/AgCl reference electrode and negative going to the carbon cloth anode.

The multimeter reads +0.2V.  Does this mean my anode potential is 0.4V (0.2V from multimeter reading + 0.2V for reference electrode correction)?  OR, does this mean that my anode potential is 0V (-0.2V multimeter reading + 0.2V for reference electrode correction). I'm not clear if the positive side of the multimeter and negative side are connected correctly to the electrodes.  If they are connected incorrectly, then the voltage sign should be flipped.

Thank you!


texts: Do temporary dipoles form in silicon(IV) dioxide?

texts: Textbooks only ever mention covalent bonds between silicon and oxygen atoms in silica. However, as electron movement is random, one end of a silicon atom in a given instant could be more positive than the other (setting up a temporary dipole) and this temporary dipole could induce dipoles in neighboring oxygen/silicon atoms. Could somebody confirm if this is indeed the case?


texts:
I've searched online, but have not found anyone that has experienced the same.
I have a 20 gallon plastic tub with a lid.
In it keep plastic shopping bags.
Also had a box of detergent in there.
I witnessed over time, the fumes (I am guessing) from the detergent affected the plastic bags.
The big 20 gallon bin is fine tough.
But a few of the plastic bags turned brittle to the touch and broke down into tiny bits like old dry leaves when I crumple it in my hand.
Just wondering what is happening to the plastic; chemistry wise. Has the breakdown of the plastic been accelerated by the detergent fumes?
Just found it very odd, and if the process can be used to help recycle plastic by breaking it down faster
I still have the bags on hand and can make a video as proof.


texts: How would you describe the energy of solution formation involved in the dissolution of sodium chloride in vinegar?

texts:
I have found that the lattice energy of dissolving salt in water is 779 kJ/mol. While 774 kJ/mol is its hydration energy. Subtracting the two values gives a positive number therefore dissolving table salt in water is endothermic. I know that vinegar comprises of mostly water but how do you exactly explain the energy absorbed and released in the process if acetic acid is involved? Is there any constant that you know involving the dissolution of salt in acetic acid?

Our teacher wants us to include a discussion comparing water and vinegar in dissolving salt considering the enthalpy of solution but I am not quite sure what that means. I don't know if this question is too basic but I would really appreciate if I would get some answers. Thank you T.T


texts: Reaction direction change based on phase of reactants and products

texts:
I am curious specifically how the entropy of a reaction will change if the phases of the reactants and products at different conditions change.

For instance, a reaction

$$\ce{O2(g) + C(s) -> CO2(g)}$$

has a positive entropy because there is no net change in the moles of gas in the system and the product is more complex in its degrees of freedom (secondary). If one were to change the conditions (temperature and pressure) such that oxygen is a gas but $\ce{CO2}$ is a liquid or solid, would the change in entropy for the system become negative?

$$\ce{O2(g) + C(s) -> CO2(l)}$$
Or
$$\ce{O2(g) + C(s) -> CO2(s)}$$

If the $\Delta H$ is still negative but the $\Delta S$ is now positive, isn't the Gibbs energy now able to be positive or negative, making this a valid method of manipulating the directionality of a given reaction?


texts: Is there a simple way to separate deuterium oxide from tap water?

texts: I understand that tap water contains minute amounts of deuterium oxide (heavy water). Is there a simple way to separate, concentrate the $\ce{D2O}$?


texts: I make my own sugar syrups and have been observing how heating the syrup to different degrees results in syrups of radically different consistencies, I wonder why. Heating up syrups (4:3 Sugar:Water) to greater temperatures causes the resulting syrup to be relatively viscous while low temperatures yield relatively thin syrups. I do really think that my observations are valid and thought this'd be the right place to get the answers. I want to know of the chemical and physical processes involved in solutions of sugar and why their peak temperatures affect their consistencies.


texts: What is the mathematical foundation for the probabilistic nature of chemistry?

texts:
Is this best answered through quantum theory, Boltzmann statistics, or what?

For example, in a reaction energy diagram, only some of the reactants go over to the side of the products, and then get stuck there. So the progression of the reaction can be thought of in probabilities - what are the chances that something will go to products, and what are the chances the products will revert back. So you'd use the Arrhenius equation here. Could you dig deeper and find a quantum mechanical reason for this?


texts: Relationship between inhibition constant Ki and interaction energy?

texts:
Inhibition of an enzyme $E$ by an inhibitor $I$:

$$
E + I \rightleftharpoons EI
$$

The inhibition constant $K_i$ is defined as follows:

$$
K_i = \frac{[E][I]}{EI}
$$

where $[E]$ is the enzyme concentration, $[I]$ is the inhibitor concentration, and $[EI]$ is the enzyme-inhibitor-complex concentration. Inhibition is strong when $K_i$ is low; that is, when the equilibrium above is shifted toward the product.

Can the strength of inhibition be approximated by the relative interaction energy: $E_{Interaction} = E_{EI complex} - E_{Enzyme} - E_{Inhibitor}$? This seems like a logical and valid hypothesis to me, but I cannot find any sources confirming that this is justified. If the enzyme-inhibitor complex is very stable, I would think that the equilibrium above naturally is shifted toward the product, given a relatively fast kinetics. In the case of a commercial drug inhibiting the HIV-1 protease, for example, where it is safe to assume fast kinetics, I would model the strength of inhibition as the relative interaction energy: stronger interaction $\Rightarrow$ lower $K_i$ value.

The context is a simple theoretical modelling of a protein-ligand interaction using density functional theory.


texts: Why is it possible to image LUMO if these orbitals are, by definition, unoccupied?

texts:
LUMO stands for lowest unoccupied molecular orbital. If it's unoccupied, how is it possible to image it?

See for example in this paper ("Pentacene imaged with STM and NC-AFM").


texts: How to use Clausius-Mossotti equation to determine the molecular structure of a compound?

texts:
A question in my exam came as follows:

Explain the Clausius-Mossotti equation. How is it used in establishing the molecular structure of a compound?

I have studied the Clausius-Mossotti equation and I know how to derive its expression. I know that it deals with the Dielectric Constant, Molecular weight of the given molecule, the Density of the dielectric or medium between the two parallel plates of condenser, Avogadrov Number, and Molecular polarizability of medium or dielectric. However, none of my textbooks talk about how to actually use this equation to determine the actual molecular structure of any compound that is under study. My professor has not taught this either. I was unable to find any external sources that talk about this as well.
Could someone please explain the steps on (or concept about) how to determine (or establish) the molecular structure of a compound after knowing the required values?


texts:
While studying about the entropy change of surroundings in irreversible adiabatic process, I came across a sentence.

  For infinite reservoir,  all processes are considered reversible

And suddenly it resumes with the equation:

q/T = dS (surrounding)

Can anyone explain the line and how the conclusion was drawn?


texts: Is the momentary dipole in between a cell membrane due to the van-der-Waals forces?

texts:
There are van-der-Waals forces within non-polar molecules. I read it that is mainly due to the instantaneous movements of the electron cloud's distribution. When looking at symmetrical molecules like $\ce{CH4}$, the concept isn't hard to understand. But I have a question regarding the bioelectricity and action potential of human cell membrane.

e.g. Outside the cell membrane the ion concentration is high and inside it's low, thus it creates an instantaneous dipole effect between the cell wall. Can this be due to van-der-Waals forces?


texts:
The stability of the +II oxidation state in lead has been widely attributed to the so-called “inert pair effect”: the 6s subshell is stabilized through relativistic contraction due to the near-c speed of its electrons. Now, Pekka Pyykkö states in his 1988 article (p. 585) that

  In addition to the 6s2 inert pair discussed above, analogous compounds (such as GeO and SnO) are known for rows 4 and 5. While the relativistic 5s stabilization is not entirely negligible, the 4s stabilization due to the “d-block contraction” probably overweighs relativity on row 4.

How does the d-block contraction cause a change in valency? I know that due to poor shielding by d electrons, atomic radii across the fourth period don’t increase particularly. But how is it responsible for the increasing stability of the +II oxidation state in group 14 (before getting to lead, where relativistic effects play a significant role)?

Would I be wrong if I said that the cause for the increasing stability of the s electrons in germanium and tin was the existence of a full d subshell (absent in, say, silicon), which, however slightly, shields the nuclear charge for the p electrons better than for the s electrons? Or what is it that happens, exactly?

Finally, according to the orbital potential energies listed on page 16 of Appendix B of Miessler and Tarr's Inorganic Chemistry (5th ed.), the 5s electrons of tin aren’t more stable than those of silicon – their energy (–14.56 eV) is higher than the energy of the 3s electrons in the Si atom (–14.89 eV), even if only by a small amount. Compare this to germanium and lead, whose valence s orbitals are both more stable than the silicon’s 3s (–16.05 eV and –15.12 eV, respectively). How is it, then, that tin forms divalent compounds while silicon doesn’t? Is Pyykkö correct in associating the Sn valency with 5s stabilization?


texts:
What is the best method to extract ammoniumsulfate from water?

The assignment is as follows:

  Manure is being processed and the product left is a mixture between water and ammonium sulfate, transporting the mixture costs a lot of money. So we only want the ammonium sulfate.

What is the best method to do this on a big scale? Evaporation isn't a good option since it costs too much energy to heat the big amounts of water.


texts: Why don't free radicals undergo rearrangement like carbocation/carbonium ions do?

texts: Why don't free radicals and carbanions undergo rearrangement like carbocation/carbonium ions undergo in a reaction?


texts: Where to find a list of common organic reaction rate laws?? Anybody has this?? I could not find one on internet


texts: Are there any fluids which are both viscous and volatile?

texts:
I'm looking for a viscous fluid which will evaporate (completely) rather quickly.

If propylene glycol evaporated like acetone, that would be the dream ticket, but neither the viscosity nor the volatilty need be quite that high.

Non-toxic would be a plus!


texts:
Context: a retinal molecule the isomerizes from all-trans to 13-cis form, then "reisomerizes thermally".

I tried googling it but couldn't find a simple, straightforward explanation.


texts: Finding the frequency factor when raising temperature

texts:
The question is:

  A reaction rate doubles when the temperature increases from $\pu{25^\circ C}$ to $\pu{40^\circ C}$. Calculate $E_\mathrm a$ and the frequency factor.

I found the activation energy to be $\pu{35.8 kJ}$ using the two point form of the Arrhenius equation. What I'm having trouble with is finding the frequency factor. I have two unknowns, $k$ and $A$, and to me it seems like this is impossible to solve without knowing what the rate constant $k$ is. All the examples in the book solves this problem graphically, but apparently you can solve this another way according to my teacher.

The answer given for $A$ is $1.9 \times 10^6$ but what method do you use to solve for this?


texts: Why lone pair occupies more space than bond pair?

texts:
I'm not a chemistry expert and merely a high school student. In my book there is a slight introduction to VSEPR theory and therein they mention that lone pair-lone pair repulsions are maximum, followed by lone pair-bond pair and then bond pair-bond pair repulsions.

Now the reasoning they provide to this is that as lone pairs are localized on the central atom, and each bond pair is shared, the lone pair occupies more space and hence the repulsions are greater.

Now I don't understand how localisation of lone pair leads to its large size and secondly what is meant by"size"here, because it's hard to imagine size of a lone pair for me.

It's a request not to mention about advanced theories like molecular orbital theory, because I'm not familiar with aaj that right now.

EDIT
I would say that the other is also in a way similar but I could not find an answer of my question there. That's why I posted it.

Any of your help is appreciated.

Thanks.


texts:
If so, how? It seems like excessive salinity within seawater has the same destructive effect on marine organisms just like excessive acidity. But in real terms, is there any relation between salinity and the acidity of seawater?

P.S. I don't take chemistry. This is for my biology depth study. Please try to respond in a way that is eay to understand. :)


texts: Why is it wrong to use the concept of hybridization for transition metal complexes?

texts:
I have asked a lot of questions on coordination chemistry here before and I have gone through a lot others here as well. Students, including me, attempt to answer those questions using the concept of hybridization because that's what we are taught in class and of course it's easier and more intuitive than crystal field theory/molecular orbital theory. But almost all of the times that I attempted to use the concept of hybridization to explain bonding, somebody comes up and tells that it's wrong.

How do you determine the hybridisation state of a coordinate complex?

This is a link to one such question and the first thing that the person who answered it says: "Again, I feel a bit like a broken record. You should not use hybridization to describe transition metal complexes."

I need to know:

Why is it wrong? Is it wrong because it's oversimplified?
Why does it work well while explaining bonding in other compounds?
What goes wrong in the case of transition metals?


texts: Why Isn't Huckles rule applicable to more than 3 fused rings

texts:
In the following compound (Pyrene) why isn't Huckle's (4n+2) rule applicable? I do know it is applicable to only mono-cyclic ring systems but what changes when there are more than 3 fused rings?

Edit:

A similar question has been posted previously but that doesn't mention as to why only the peripheral bonds are to be considered.


texts: Determining phase from intermolecular interactions and kinetic energy

texts: If the energy of intermolecular attractions are much less than the average kinetic energy of the molecules, what is the physical state of the substance?


texts: Voltage applied when charging a galvanic cell

texts:
A working galvanic cell is constructed using an iron electrode in an iron(II) nitrate solution and a
  silver electrode in a silver(I) nitrate solution. When the cell runs down, it can be charged up again.
  Which of the following scenarios will occur during the charging process?

  $\ce{[Eº(Ag+(aq)/Ag(s)) = +0.80 V and Eº(Fe^2+(aq)/Fe(s) = –0.41 V]}$

  A. A minimum of 1.21 volts is applied to the cell and electrons move from the silver electrode to the iron electrode.

  B. A minimum of 1.21 volts is applied to the cell and electrons move from the iron electrode to the
  silver electrode.

  C. A minimum of 0.39 volts is applied to the cell and electrons move from the silver electrode to
  the iron electrode.

  D. A minimum of 0.39 volts is applied to the cell and electrons move from the iron electrode to the
  silver electrode.

  E. A minimum of 2.01 volts is applied to the cell and electrons move from the silver electrode to
  the iron electrode.

I know reduction of silver is spontaneous and oxidation of iron is spontaneous from the values given, so reduction occurs at the silver electrode and oxidation occurs at the iron electrode, so electrons flow from iron to silver.

In the reverse reaction, electrons will now flow from silver to iron. However, I'm unsure about the stoichiometry of the electron transfer occuring during charging:

$\ce{2Ag -> 2Ag+ + 2e-       -1.60V}$

$\ce{Fe^2+ + 2e- -> Fe    -0.41V}$

I multiplied the oxidation of silver by 2, as two electrons must be supplied for iron to reduce, hence getting -2.01V, and answer E. However, the solutions state A, which suggests the oxidation of silver was no multiplied by 2. Why is this?


texts: How would you write the empirical formula of an ion?

texts: How would you write the empirical formula of e.g. X2Y42-?


texts: Is phenolphthalein used in laminar wood construction panels?

texts:
Recently someone is claiming that the laminar wood panels used for building our new primary school contains a "carcinogenic and dangerous compound", namely phenolphthalein.

I couldn't find any evidence of it being used as that on the net.
Could you confirm my findings?

Thank you


texts: Can the change in the entropy of the surroundings always be obtained by dividing heat transferred by the temperature at which the transfer occurs?

texts:
Consider $\pu{1 mol}$ of an ideal monoatomic gas going through reversible isochoric heating from $\pu{100 K}$ to $\pu{1000 K}$.
Calculate $\Delta S_\pu{sys}, \Delta S_\pu{surr}.$

$$\Delta S_\pu{sys} = nC_v \int_{\pu{100 K}}^{\pu{1000 K}} \frac{dT}{T} = \frac{3}{2}R\ln10$$
Now, as I have
$q_\pu{sys} = 1350R$.
I can put $\displaystyle \Delta S_\pu{surr} = \frac{-q_\pu{sys}}{T_\pu{surr}}$ to get
$$\Delta S_\pu{surr} = -\frac{27}{20}R$$ but in a reversible process $\Delta S_\pu{total} = 0 $ but that gives me $$\Delta S_\pu{surr} = -\frac{3}{2}R\ln10$$
Where am I wrong?

Image source: Physical Chemistry, 10th ed. by Atkins and de Paula, p. 116.
Here, $\displaystyle q_\pu{sur} =$ heat supplied to surroundings.


texts: Does tetraoxidovanadium (VO4+) ion exist?

texts:
In my book (NCERT India), it is mentioned that: (page 224)

  ...$\ce{Mn2O7}$ gives $\ce{HMnO4}$ and $\ce{CrO3}$ gives $\ce{H2CrO4}$ and $\ce{H2Cr2O7}$. $\ce{V2O5}$ is, however, amphoteric though mainly acidic and it gives $\ce{VO4^3–}$ as well as $\ce{VO2+}$ salts. In vanadium there is gradual change from the basic $\ce{V2O3}$ to less basic $\ce{V2O4}$ and to amphoteric $\ce{V2O5}$. $\ce{V2O4}$ dissolves in acids to give $\ce{VO^2+}$ salts. Similarly, $\ce{V2O5}$ reacts with alkalies as well as acids
  to give $\ce{VO4^3-}$ and $\ce{VO4+}$ respectively. The well characterised $\ce{CrO}$ is basic but $\ce{Cr2O3}$ is amphoteric.

The sentence under scrutiny has been boldened. I wonder how the $\ce{VO4+}$ ion can exist.

Going by the usual oxidation numbers, four oxide anions should contribute a total of -8 charge. To balance it, vanadium needs to be in +9 oxidation state. But, vanadium has only five valence electrons $(\ce{[Ar] 3d^3 4s^2})$, so how can it even attain the +9 oxidation state? Though, it may be possible that this ion has a different structure (possibly a peroxide linkage?) that allows it to exist with a +5 oxidation state on vanadium, but I am not sure.

I have read relevant documents on the internet, including the Wikipedia page for the vanadate ion and a Scholar search, but neither yield any relevant results. I can't search it on ChemSpider Structure Search either because I don't know its structure, and a textual search yields only unrelated partial matches.

So, is it true that the $\ce{VO4+}$ ion dost not exist, or have I missed something? Or is it that there is a misprint in the book, and they intended to write another ion in place of $\ce{VO4+}$?


texts: Are the reactions in a simple cell overall exothermic? Why?

texts:
For context, I'm in high school. I'm trying to mentally connect electrolysis with the concept of energy changes and kinda having trouble.

I understand the bottom line is that a simple cell converts chemical energy to electrical energy in a spontaneous redox reaction, and in an electrolytic cell, electrical energy is used to cause a non-spontaneous chemical reaction to occur.

I've found resources that vaguely say the overall reaction (?) in a simple cell is exothermic. I find this unclear and confusing.

If the reaction is exothermic then the products should have lower energy than the reactants. What are the products and reactants involved in the system, to derive the enthalpy change from?
Where did the energy lost go?
Don't both bond breaking (oxidation @ anode) and bond making (reduction @ anode) occur? Does the bond making somehow involve more    energy? How? (does this have something to do with the cation getting    discharged at the cathode being of a less reactive element than the cation formed at the anode? must the electrolyte have a cation that fulfils this requirement?)

For the sake of simplicity assume a simple cell setup with just electrodes, external circuit, and electrolyte. Not connected to a lightbulb or something.

Thank you


texts:
Regarding oxirane production developed by Wurtz, is there an accepted mechanism?

I carried out a research but couldn't find anything. My approach was this
Is that correct?


texts: So today I suddenly stricken with this structure and started to wonder if this polymeric structure of nitrogen is possible or not? If possible then what's its stability?


texts: I have a potential problem in that I need to reliably remove ozone from a stream of ionized gases, mostly air. The flow rate is quite low, less than 400 sccm. I was thinking of something catalytic, maybe platinum mesh? There may well be a related need to remove any $\ce{NO_x}$ created. I am open to suggestions — it's mainly a health and safety issue if it vents into the air.


texts: How can you calculate the tendency of one compound to become another?

texts:
Excuse my inexperience with chemistry here. I've been poring over papers with terms like "Standard Gibbs free energy of formation", "Hess's Law", "standard enthalpy of formation", "entropy", and several others, and I haven't been able to find an answer to one simple question:
Given I have a system with compounds A, B, and C, and there is an alternative set of compounds X, Y, and Z involving the same amounts of the same elements, how do I calculate how much the ABC system wants* to become XYZ?
As an example, if I have a system with propane and oxygen, with an excess of oxygen, this system wants to combust to become carbon dioxide and water vapor. A quick Wikipedia check reveals the balanced equation for this reaction:
$$\ce{C3H8 + 5O2 \rightleftharpoons 3CO2 + 4H2O}$$
Anyone who's played around with a camp stove knows that propane and oxygen like to burn to become carbon dioxide and water vapor, and that carbon dioxide and water vapor really don't like to "unburn" to become propane and oxygen. How would I measure this tendency for the propane-oxygen system to become the carbon-dioxide-water-vapor system? Similarly, how would I measure the distate for the carbon-dioxide-water-vapor system to become the propane-oxygen system?
If I remember correctly, the tendency of a reaction to happen and the speed of the reaction are entirely unrelated, one being a thermodynamic property and the other a kinetic property, but if you wouldn't mind throwing in just enough info about reaction rate in the above case that I can look up and learn myself on that topic as well, I'd really appreciate it.
*I'm falling victim to the oh-so-elegant abstraction of molecular anthropomorphism here. Yes, I understand that chemicals don't want anything, but given I'm looking for a unit most easily expressed as the degree of desire for chemicals A, B, and C to become X, Y, and Z, these human terms play out quite well. Please do let me know if there's better terminology I could be using


texts: I have read like ''Functional Isomers of Carboxilic Acids are Esters'', then my doubt is; What about Formic Acid?


texts: In 2-bromo cyclohexanone,why bromine prefers to occupy axial rather than equatorial position?

texts: I read that the substituents generally tend to occupy equatorial position rather than axial because diaxial interactions make the molecule unstable. But why is 2-bromocyclohexanone an exceptional case? I also read that it’s because of the dipolar interactions. What actually are these dipolar interactions and how do they stabilise 2-bromocyclohexanone with bromine being on axial position. How do they outweigh the effect of diaxial interactions.


texts: Why does π-backbonding in a metal-carbonyl complex lead to a decrease in C-O bond strength?

texts: I understand that π-backbonding in this complex involves the σ-donation of carbonyl to an empty d orbital of the metal, and the π-donation of the d electrons of the metal to the π* MO of the carbonyl. But why exactly does this lead to the weakening of the C-O bond (relative to free C-O)?


texts: Colour change on exposure to singlet oxygen?

texts:
Is there a dye that is particularly well suited to radical colour change on interaction with singlet oxygen, preferably non-toxic?

Based on this answer: https://chemistry.stackexchange.com/a/27633/41616 some compounds, such as tetraphenylcyclopentadienone, seem to lose their colour intensity, but what about changing / inducing colours completely, and what is the proper term for this process (chromism?) called?


texts: Net ionic equations for an aqueous solution

texts:
Given the reaction of $\ce{Ni^{2+}}$ with aqueous ammonia to give $\ce{Ni(OH)_2}$ Would this be the correct reaction?

$$\ce{Ni^{2+} (aq) + 2NH3 (aq) + 2H2O(l) -> Ni(OH)2 (s) + 2 NH4+ (aq)}$$


texts: Intramolecular Reaction with carbocation rearrangement

texts:
I came across a question recently which is as follows,

I came up with a mechanism but I am stuck at a step as I am unable to reason out the driving force.

Step(3) has a hydride shift and its next step involves methyl shift. I want to know the driving force for step (3) or any other approach to this problem. Do let me know if I am going wrong with my approach.


texts: What is the optimal voltage for storing a 3.7 V lithium polymer battery?

texts:
According to this website, storing a lithium polymer (LiPo) battery/cell at around 40% capacity would be more beneficial for the lifespan of the LiPo cell comparing storing the battery at 100% capacity. The author also stated that "it is best to store LiPo batteries at 3.6 V to 3.8 V. This is applicable for standard LiPo batteries that hold 4.2 V per cell when fully charged."
However, the instruction of an RC helicopter (with a LiPo battery (3.7 V (4.2 V when fully charged), 180 mAh capacity)) I bought stated that if I am not using the model, I need to make sure that its voltage is at least 3.9 V at storage.
The manufacturer, upon inquiry, told me that I should store the battery fully charged and only recharge it after the voltage drops below 3.9 V. I.e., my correspondent's answer and the instruction of the helicopter is quite different from the website mentioned before.
Who is the right one? The website or the instruction and the manufacturer, according to the working principle of LiPo battery?
Some other questions relevant for the maintenance of the battery (question added that were not asked originally):
Would the charging frequency be a determinant for battery lifespan? Usually how fast would the battery lose voltage by self-discharge (is it dependent on the voltage the battery has)? Also, when charging, does the charge in the LiPo cell build up linearly (so that I will know when is 40% charge reached)? Would it be better if I do not charge the battery fully even right before using the battery in the RC helicopter?
There is a undervoltage cut-off for my RC helicopter. What is usually the percentage of the charge at which the undervoltage cut-off is reached?
A/two question(s) out of curiosity:
Would the time needed for charging a completely new and empty cell to full for the very first time be different from the time needed for charging an already-used empty cell (maybe not completely empty, since the RC helicopter has undervoltage protection) to full? What is the difference between these two charging process?


texts: Why is cetyl alcohol bent at the 9th position?


texts: Do most methylene groups sandwiched between a carbonyl and aryl group have a chemical shift around 3.5 ppm?

texts:
For example, take methyl phenyl acetate, we can see the chemical shifts is at 7.4 ppm, singlet, 5H; 3.6 ppm, singlet, 3H and 3.5 ppm, singlet 2H. Let us say we didn't know the identity of the compound and just its molecular formular C9H10O2.

I knew that of the 3.6 ppm, singlet, 3H signal I would get CH3-O, but I had trouble thinking about the 3.5 ppm, singlet, 2H. I later found out that the methylene group -CH2 was sandwiched between the carbonyl and the benzene ring, which made me think if this was a pattern for all methylenes sandwiched between a carbonyl and a benzene ring.


texts: Calculating the pH of a sodium phosphate solution

texts:
I have the following question in a chemistry homework:

  Calculate the $\mathrm{pH}$ of a solution made by dissolving $\pu{113 g}$ of sodium phosphate in enough water to make a solution with a final volume of $\pu{475 mL}$. Find the equilibrium concentration of all species present in this solution.

It shouldn't be that hard of a problem, but my teacher really doesn't explain well at a distance (with the COVID-19 situation). I have found that it dissociates into $\ce{NaOH}$ and $\ce{H3PO4}$ when in water:
$$\ce{Na3PO4(s) + 3H2O(l) → 3NaOH(aq) + H3PO4(aq)}$$

But I don't really know what to do next...

Thanks in advance!


texts:
I wondered how small a volume a mole of material could occupy, so I started with carbon, which would need 12 grams. That's 60 carats, and there happens to be a famous 60 carat diamond.

If my density/atomic mass calculations are correct, the substances with the smallest molar volume would be nickel, carbon, beryllium, and boron, with boron being the smallest. But I had trouble finding images of large-enough beryllium or boron crystals.

Are there any compounds of sufficient density and low enough atomic mass to beat boron? Can a maximal density boron crystal be made that large?

What substance has the smallest molar volume?

EDIT -- The Noor-ul-Ain diamond is closer to being 12 grams.


texts: Bromination Pathways with alkane, alkene, and alkyne substrates

texts:
I'm confused about halogenation pathways. From what I understand, there are multiple halogenation pathways. I'll try summarizing them below; let me know if I do anything incorrectly.

Halogenation with the diatomic halogen - i.e. $\ce{Br2}$. This reaction proceeds through a halonium intermediate.
Halogenation with the diatomic halogen in the presence of light or heat. This reaction proceeds via radical intermediates. From what I understand, the light or heat cleaves the weak halogen-halogen bond and we get two radicals, which can initiate the radical reactions. Also the cool thing about this reaction is that it doesn't require an nucleophilic pi bond, so if we were starting from an alkane, we don't even need to first form an alkene or alkyne; we can free-radical halogenate that alkane and then eliminate a beta proton as to make the alkene. All the other reactions mentioned here require some sort of nucleophile to start with.
Halogenation in the presence of water - i.e. $\ce{Br2}$ with $\ce{H2O}$. Again, we go through a bromonium intermediate. The $\ce{Br-Br}$ bond is instantaneously polarized and at that point we can form the bridged halonium ion and that gives water an entrance - the ring is highly strained and has partial charges all over the place - perfect for water to do something.
Are these all the halogenation pathways I need to know for an elementary understanding of organic chemistry? Did I miss any? I think I finally clarified all of them to myself through typing up this post ...
Oops yes I missed a few. NBS for example is used for allylic (or benzylic) bromination, and this directly implies the need for a starting alkene ... so this isn't as synthetically useful as free-radical bromination in the presence of light.
Addition of $\ce{HX}$ - the pi bond acts as a simple nucleophile and attacks the proton. Then the anionic halogen adds to the resultant carbocation.
Addition of $\ce{HX}$ in the presence of peroxides - the pi bond again acts as a simple nucleophile but this reaction proceeds via a radical intermediate and as a result the reaction is overall anti-Markovnikov.


texts:
I started doing IR spectroscopy a few months ago and have run into the following problem: Here's the IR background that everyone knows and loves:

CO2 peaks in the middle, water lines on either side. I get that. But what about those lines in the CH-stretch region? They are obviously very normal for an FT-IR background- everyone sees them, they're all over the internet. But WHAT ARE THEY???? No one knows- not even the IR spectroscopy veterans I've talked to. They're some kind of hydrocarbon, I guess, and they're not a gas because they are unaffected by purging. This is a spectrometer looking at no sample, with no windows, nothing, and fwiw this is using an MCT/A detector.
I feel like I should know this, but maybe I'm not using the right resources?

Thanks for any help!


texts: How to account for the interface between two different phases in a discretized diffusion model?

texts:
I have tried to set up a model for the diffusion of a gas into a liquid. The two media are next to each other and the geometry is spherical because the system should simulate the diffusion out of a gas bubble.
I have made a diffusion model for the gas phase (the left compartment) and a corresponding diffusion model for the liquid phase (the right compartment).
The two diffusion models are as follows:
\begin{align}
  \frac{\partial c_\mathrm{left}}{\partial t}
  &= D_\mathrm{left} \cdot \frac{1}{r^2} \frac{\partial}{\partial r}
     \left(r^2 \frac{\partial c_{left}}{\partial r} \right)\\
  \frac{\partial c_\mathrm{right}}{\partial t}
  &= D_\mathrm{right} \cdot \frac{1}{r^2} \frac{\partial}{\partial r}
  \left(r^2 \frac{\partial c_{right}}{\partial r} \right)\\
\end{align}

Then I have discretized the volume. So the PDEs are turned into ODEs of the form:
\begin{align}
  \frac{\mathrm{d}c_{i,\mathrm{left}}}{\mathrm{d}t}
  &= D \left(\frac{c_{i+1,\mathrm{left}}
     - 2 \cdot c_i + c_{i-1,\mathrm{left}}}{\Delta r^2}
     + \frac{2}{r_{i,\mathrm{left}}}
     \cdot \frac{c_{i+1,\mathrm{left}}
     - c_{i-1,left}}{2 \cdot \Delta r} \right)\\
  \frac{\mathrm{d}c_{i,\mathrm{right}}}{\mathrm{d}t}
  &= D \left(\frac{c_{i+1,\mathrm{right}}
     - 2 \cdot c_i + c_{i-1,\mathrm{right}}}{\Delta r^2}
     + \frac{2}{r_{i,\mathrm{right}}}
     \cdot \frac{c_{i+1,\mathrm{right}}
     - c_{i-1,\mathrm{right}}}{2 \cdot \Delta r} \right)
\end{align}

When discretizing I got the following expressions:
\begin{align}
  \frac{\mathrm{d}^2c_i}{\mathrm{d}r^2}
  &= \frac{c_{i+1} - 2 \cdot c_i + c_{i-1}}{\Delta r^2}\\
  \frac{\mathrm{d}c_i}{\mathrm{d}r}
  &= \frac{c_{i+1} - c_{i-1}}{2 \cdot \Delta r}
\end{align}

But how does one incorporate the following two boundary conditions at the gas-liquid-interface, where $H$ is Henry's constant?
\begin{align}
  c_\mathrm{left,interface} &= H \cdot c_\mathrm{right,interface}\tag1\\
  J_\mathrm{left,interface} &= J_\mathrm{right,interface}\tag2
\end{align}

Meaning that there is equal flux across the interface between the two compartments.

The concentration in the last compartment of the gas phase (before the interface) is approximated by linear extrapolation.
This means that the concentration just before the interface is given by:
$$c_{3} = \frac{c2-c1}{r2-r1} \cdot r_3 + c_1 - r_1 \frac{c_2-c_1}{r_2 - r_1}$$

In this example it is assumed that only three compartments are present on each side of the interface.


texts: Is it possible to react chlorine with hydrogen under a UV lamp during the electrolysis of salty water?

texts:
I have set up an experiment where I am generating chlorine by electrolysing water saturated in NaCl. I know chlorine gas is actually being generated because I hang wet litmus paper in the gas which quickly bleaches. I also know hydrogen is being generated because if I hold a match to the gas it reacts with a popping sound.

If I have this set up in a closed container, how come I cannot get the hydrogen and chlorine to react under a black light? What am I missing?


texts: How to find the reaction rate in an enzyme reaction?

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First time posting questions here, so let me know if I need to edit anything.
I need to decide $dC/dt$ and $dP/dt$ when the reaction is like this, where I only know we must have 2 substrates $S$ to react with the enzyme $E$ at the same time:
$$2S + E \overset{k_a}{\longrightarrow} C \overset{k_c}{\longrightarrow} 2P + E, \quad C \overset{k_b}{\longrightarrow} 2S + E$$
Is $dC/dt = 2k_a SE - (k_b + k_c)C$? Is $dP/dt = 2k_cC$? Thanks in advance.
Edit: alright, so $dC/dt$ should be $k_a S^2 E - (k_b + k_c)C$, right? Now suppose I take $E_0 = E + C$ to be the total enzyme concentration, and transform $dC/dt$ as $$dC/dt = k_a E_0 S^2 - (k_a S^2 + k_b + k_c) C.$$ By quasi-equilibrium approximation, let $$dC/dt = 0 \Rightarrow C = (k_a E_0 S^2)/(k_a S^2 + k_b + k_c).$$ Then in this equilibrium, $$dP/dt = 2k_bC = (2k_a k_b E_0 S^2)/ (k_a S^2 + k_b + k_c).$$ So if we want to find out $V_m$ and $K_m$ s.t. $$\lim_{S \to \infty} dP/dt = V_m, \quad dP(S = K_m)/dt = V_m/2,$$ then we would need $V_m = 2 k_b E_0, K_m = \sqrt{(k_b + k_c)/(k_a)}$. Any mistakes so far?


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What is wrong in this reaction?

I cannot find anything wrong, please help. Any hints would be appreciated.


texts: Formation of green precipitation whilst adding potassium fluoride to aqueous solution of copper(II) sulfate

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Aqueous copper sulfate solution (blue) gives a green precipitation with aqueous potassium fluoride. Explain these experimental results.

I've read answers like, $\ce{H2O}$ is a weak ligand and fluorine can replace it, but isn't $\ce{H2O}$ a stronger ligand than fluorine according to the spectrochemical series?


texts: How much can the pH change through dilution?

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Consider an acidic solution with Hydrogen ion concentration, $\ce{[H+]}$ of $10^{-5}\:\mathrm{M}$. Since $\:\mathrm{pH} = -\log \ce{[H+]}$ the $\:\mathrm{pH}$ of solution is $5$. Suppose we dilute solution 10 times with water. Now, $\ce{[H+]}$ is $10^{-6}\:\mathrm{M}$ and $\:\mathrm{pH}$ is $6$. Further dilution should increase $\:\mathrm{pH}$ from $6$ to $7$ and then from $7$ to $8$ and so on. Can this go in for ever? Does this not imply that an acidic solution can be made basic/alkaline simply by adding water? But that doesn't happen? What prevents it?

Is there anyone already found answer for this problem or it is just an unsolved basic problem of chemistry?


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My textbook says:

It is appropriate to remark that the trick of rationalizing apparent violations of the octet rule by invoking the participation of d-orbitals in the bonding scheme is a matter of some controversy. Some scientists feel that the d-orbitals lie so high in energy that they should not be treated as valence orbitals, but as excited orbitals which cannot confer any appreciable stability to chemical bonds. Others feel that while d-orbitals are of high energy in free atoms, their energy decreases as other atoms approach to make bonds.
This author has not been convinced of the absolute validity of either side of this argument, and interprets the controversy merely as more evidence that the description of chemical bonds in terms of a few atomic orbitals is a highly approximate procedure. The most convincing reason for invoking d-orbitals in chemical bonding is that it is a simple idea which works, if it is used carefully and not over-interpreted.

Since this book is quite an old edition, I wanted to know whether there are any newer developments in this direction. Which of the two views is generally acceptable?