texts: Ionization energy comparison between K+ and Cl-

texts:
So I have encountered a question which looks very suspicious to me.

If you have $\ce{Cl-}$ and $\ce{K+}$, Can you say that $\ce{K+}$ has more ionization energy than $\ce{Cl-}$?

We know for a fact that when you put more electrons it makes the the pulling force of the protons a bit scattered (because of the incremental of the electrons in $\ce{Cl-}$) so the ionization energy of chlorine should go down.

The opposite happens to $\ce{K+}$ when I remove electrons the pulling force of protons is stronger (Because it pulls less electrons) than it used to be so the ionization energy goes up!

So What I am proposing here that we can't just say that $\ce{K+}$ has more ionization energy than $\ce{Cl-}$ just because that happened. $\ce{Cl}$ had a really high ionization energy compared to $\ce{K}$ and the decrement of the ionization wouldn't be that big to make it less than the ionization energy of $\ce{K+}$.

(The answer was that $\ce{K+}$ has more ionization energy than $\ce{Cl-}$ in the exam paper but I questioning that)

So if there is a chart or something for this that would be awesome. I hope I can get some help here.


texts: Find amount of acid and base required to make buffer

texts:
I am wondering if it is possible to know exact amount of acid and base that we can put in together to make a buffer.

I want to make a 0.05 M extraction buffer using disodium hydrogen phosphate (DHP) and sodium dihydrogen phosphate (SDP). I want to make 100 mL of buffer so I worked out that I would require 0.78 g SDP and 0.88 g DHP.

The issue is that it sometimes takes a lot of time by mixing one solution into the other and keep it checking with the pH meter, there has to be some mathematical way to get the exact amounts which would save time and my chemicals.


texts:
What does the K° signify in the above reaction. Is it just a typo, or is it supposed to symbolize something?
EDIT: This screenshot is from the solutions manual. In the original textbook, the author has used $K ^ 0$.


texts: Why electron configuration of tungsten doesn't obey the full & half full (stability) rule?

texts:
So I was reviewing chemistry lesson and I am curious when I saw the electron configuration in the VIB group:

For $\ce{_24Cr}$ we write the electron configuration $\ce{_18[Ar] 4s^1 5d^5}$ instead of $\ce{_18[Ar] 4s^2 5d^4}$,

For $\ce{_42Mo}$ we write $\ce{_36[Kr] 5s^1 4d^5}$ instead of $\ce{_36[Kr] 5s^2 4d^4}$,

But why for Tungsten $\ce{_74W}$ we do write $\ce{_54[Xe] 6s^2 4f^14 5d^4}$ and not $\ce{_54[Xe] 6s^1 4f^14 5d^5}$?

Is it because after the $\ce{f}$ subshell the rule is not valid anymore?


texts: How would I measure the dissolved carbon dioxide content of a liquid (water to start with)

texts: I would like to measure the dissolved carbon dioxide content of a sample of water.  I was thinking that conductivity might change with carbon dioxide level, and also pH.  I would like to have the measurement sample electronically, so current, voltage, conductivity / impedance (resistance, capacitance, inductance) would all be fine.  My chemistry goes up to A-level; I am an engineer.


texts: Factors that influence the electrical conductivity of metals

texts:
The electrical conductivity of metals is a physical property of these materials. Much of the theory used to explain the electrical conductivity of metals is also based on physics understanding. However, I would like to ask if it is possible to incorporate some chemistry, from concepts in atomic structure or chemical bonding of metals, into explaining the variation of electrical conductivity across periods and down groups.

Based on chemistry alone, we would obviously expect predicted trends to be inaccurate. The chemistry reasoning would need to be complemented by physical theories to give a complete and accurate prediction of such a property. Recently, I have seen an over-simplistic explanation based on the number of valence electrons the metal atoms possess, equating more valence electrons to higher electrical conductivity. This was used to explain the higher electrical conductivity of $\ce {Cu}$, compared to $\ce {Ca}$, and it was clearly wrongly used.

On this note, I would like to ask, what are the factors, in terms of electronic structure of metals or their chemical bonding behaviour, that influence the electrical conductivity of metals?

Mott (1936) informs that for most of the first-row transition metals, it is the $\ce {4s}$ electrons which are delocalised and thus, contribute to the conductivity. Of course, in metallic bonding of these metals, both $\ce {3d}$ and $\ce {4s}$ orbitals overlap significantly and they should both be considered but Mott says that the $\ce {3d}$ electrons move much more slowly, due to their higher effective mass, thus contributing less to conductivity.

Mott, N. F. The electrical conductivity of transition metals. Proc. Royal Soc. Lond. 1936, 153, 699-717.


texts: Different machines testing for same thing

texts:
For a chemistry report, we were given a sample of water and a variety of machines to test it with - giving their respective results about whatever aspect they were testing (eg pH, metal ion concentration etc). However the issue is that two of the machines tested for the same thing (concentration of metals in the water). What should I do in this case, now that I have 2 sets of data about the same thing? Should I discard one? Should I keep both and use it for comparison (although the results do differ somewhat between them)? I feel that doing something like averaging would be very invalid, and it has me very conflicted.

If it helps, the machines in question are AAS and ICP.


texts: Simple procedure for showing presence of milk proteins in clarified butter (ghee)

texts:
By clarifying butter, e.g. by melting butter and filtering it, we rid ourselves of most of the protein in the butter, and are left with mostly fat. However, the separation of protein and fat is not complete. Some people cannot eat milk proteins due to allergic reactions, and cannot therefore use unrefined butter in their cooking.

Is there a simple "home-kitchen" procedure to test whether the filtration sufficiently removed the milk proteins? Any proteins in the ghee can be precipitated by adding acetic acid, but this is not specific to milk proteins.

Does anyone have any ideas?


texts: What are some good research topics for a high school student?

texts: I absolutely love chemistry and I really want to take part in science fairs. I am also taking an AP chemistry class. Cleaner fuel and energy sources and air pollution (especially due to smog and vehicle exhaust) interest me. My initial idea was to make solar panels work along the lines of Chlorophyll, but that is a bit too advanced for my level. Where could I get inspiration for some science fair ideas or chemistry research topics (high school level)?


texts: Do ligands in ionisation isomerism interchange?

texts:
The text says:

  This form of isomerism arises when the counter ion in a complex
  salt is itself a potential ligand and can displace ligand which can
  then become the counter ion.

For other structural isomers that I studied in coordination compounds I simply thought that those  compounds (structural isomers) separately exist. In fact I think of structural isomers in coordination chemistry this way only that these are independently existing with different properties but same molecular formula so we study them.

But the text above is confusing it seems that they convert like resonating structures or conformation isomers.

What is true? If they do interchange then isn't this a contradiction to Werner's theory that postulates that secondary valencies are non ionisable.

note:the below problems is related to one of the comments:

    Please Consider this problem-"Give evidences that [Co(NH3)5Cl]So4 and [Co(NH3)5 So4]Cl are ionisation isomers".

  Here we test by dissloving them in water and reacting them separately
  with silver and barium ions  to test for counter ions.One gives
  AgCl and other BaSo4 as ppt. .Now if there is equlibrium like keto-
  enol tautomerism then only one of the two isomers should be stable in water
  then why such kinds of evidences are given?


texts: Why is the segment of the IR spectrum below 1500 wavenumbers called the fingerprint region?

texts:
Why is the segment of the IR spectrum below 1500 wavenumbers (cm$^{-1}$) considered as the fingerprint region? It is said that "although the entire IR spectrum can be used as a fingerprint for the purposes of comparing molecules, the 600 - 1400 wavenumber range is called the fingerprint region. This is normally a complex area showing many bands, frequently overlapping each other". However, I don't understand why the range from 600 - 1400 wavenumbers can be particularly complex and is unique to the compounds, for instance, why is the fingerprint region of propan-1-ol and propan-2-ol so different from each other given roughly the same appearance for rest of the spectrum?

Spectra taken from http://www.chemguide.co.uk/analysis/ir/fingerprint.html


texts: How do water based solutions (cream, gels) etc permeable through hydrophobic skin?

texts:
Most skin care products or the sort are oily, lipid based.
Our skin is hydrophobic. I reckon the reason is to be easily permeable through the skin.

So how do these skin care or any products which are water based said to have higher absorption and provide high nutrient uptake, replenish skin?

How I see it, that it's like a slight burst in the cell since a hypertonic solution seep into the hypotonic cell(!?). And still confused how such product could replenish skin.

I am keen on the chemistry behind this concept of how a water based skin care could actually replenish the skin. In the discussion, it is better not to include, point at any specific products you loathe or adore them.


texts: How can I separate these two alcohols from each other out of the aqueous solution?

texts:
I have the following question for homework and am stumped. I am tasked with separating 3-(2-methoxyphenoxy)propane-1,2-diol and (1R,2S)-2-(methylamino)-1-phenylpropan-1-ol. They are both solvated in water.

I was thinking to work up with acid to cleave the ethers on the left compound, but that won't do much to reduce solubility for crystallization. Esterification with a large hydrophobic carboxylic acid wouldn't do much either because both compounds have hydroxyls. Anyone have suggestions?


texts: When ice is melting, we know that the temperature stays constant at 0 ℃. If we were to place ice at 0 ℃ in a sufficient amount of water at ambient temperature, would the temperature of the water itself also stay constant during the time the ice is melting, or is it only the temperature of the ice that stays constant? Does the actual cooling of the water occur after or during phase change?


texts: Why does the Reimer-Tiemann reaction give an ortho product?

texts: On treating phenol with chloroform in the presence of sodium hydroxide, a $\ce{-CHO}$ group is introduced at the ortho position of the hydroxy group. Why is this so? Why is 4-hydroxybenzaldehyde not obtained?


texts: Particle tracking in colloids and uniformity in fractional part function

texts:
I don't know if its right place to ask this question since chemistry and programming both are involved.
I was working on particle tracking of series of pictures (.tiff) of colloids. And I was Using trackpy in python.
The code gives me the position of particle to suppixel accuracy.

There is another step involved is of checking the subpixel accuracy. In this method we check the uniformity in the decimal part of the position

a quick way to check for subpixel accuracy is to check that the decimal part of the x and/or y positions are evenly distributed. Trackpy provides a convenience plotting function for this called subpx_bias

Mask size is more or less the diameter of particle.
I am not getting how does evenly distribution of decimal part ensures that we are on the right track?
And how a dip shows that we are wrong somewhere?
You can also refer to Eric weeks website. on this website it is briefly mentioned that

One failure mode is if the length scale in feature is made too small, then all the x and y coords get 'rounded off' to the nearest pixel value. The above command plots a histogram of the fractional part of the x-coords of the image. The physically distributed positions should be random -- giving a flat histogram. If the histogram has two peaks (near 0 and 1), set the size parameter in 'feature' a little bigger, determine a new masscut, and repeat until everything is happy.


texts: How to qualitatively compare bond strength?

texts:
Without any thermodynamic data, how would one compare the bond strength of one molecule to another?

I understand a major factor is bond order: triple bond strength > double bond strength > single bond strength. But what if the molecules have the same bond order.

Also, generally a higher electronegativity difference gives a stronger bond (Chemistry LibreTexts article). But what if the difference is insignificant?

For example, in an exam, I was asked to compare $\ce{O-O}$ vs $\ce{S-S}$, and $\ce{O=O}$ vs $\ce{S=S}$ bond strengths. How would I compare them?


texts: Overlap matrix for finite sized square lattice of hydrogen atoms

texts:
So I'm trying to use the LCAO method to calculate molecular orbitals on a square lattice of hydrogen atoms. To this end, I need to compute the Hamiltonian matrix. With the nearest neighbor interaction approximation, the matrix should be pentadiagonal, analogous to the Laplacian matrix.

Now the problem is that I don't want to assume orthogonality of nearest neighbor atomic orbitals so there will be an overlap matrix. I believe it's also pentadiagonal but when I solved for molecular orbitals and their energies, the result is wrong. So I wonder if anyone has done similar things and could provide me some insight? Thank you!

If needed, I can post my Matlab codes and the computed Hamiltonian and overlap matrix here.

PS: The LCAO approach I described here can be found in Simon’s Oxford Solid State Basics textbook, Chapter 6, exercise (6.5)

PPS: I'm not constructing Bloch functions because I don't want to impose boundary periodicity constraints. I'm trying to calculate band structures of finite-sized nanoparticles but not bulk material in my project.

My code:

N = 10; %Size of the lattice is N^2
S = eye(N) + diag(zeros(N-1,1)+s12,1) + diag(zeros(N-1,1)+s12,-1); % Initialize the overlap block
Hop = 4*(eye(N)) + diag(zeros(N-1,1)+v12,1) + diag(zeros(N-1,1)+v12,-1); % Initialize the hopping block

B0 = S*e_atom + Hop;   % block matrix for interactions between same row of atoms
B1 = eye(N)*(e_atom*s12+v12);  % block matrix for interactions between adjacent row of atoms
Stmp = kron(eye(N),S)+ kron(diag(1+zeros(N-1,1),1),eye(N)*s12) + kron(diag(1+zeros(N-1,1),-1),eye(N)*s12); % Pentadiagonal Overlap matrix

H = kron(eye(N),B0) + kron(diag(1+zeros(N-1,1),1),B1) + kron(diag(1+zeros(N-1,1),-1),B1); %Hamiltonian matrix, justification see my notebook

[EVec, EVal] = eigs(H,Stmp, N^2,'sm'); %EVec contains eigenvectors, EVal contains eigenenergy on diagonal
E = real(diag(EVal));
[E, ind] = sort(E);
tmp = EVec(:,ind);
EVec = tmp;

For two adjacent hydrogen atoms, denote their $1s$ orbital by $|1\rangle$ and $|2\rangle$. $s_{12}=\langle1|2\rangle$, $v_{12}=\langle1|V_1|2\rangle$, $v_{22}=\langle2|V_1|2\rangle$ where $V_1$ is the Coulombic potential centered on the first hydrogen nuclei, $e_{atom}=-13.6eV$ is the energy of electron in an isolated $1s$ orbital.


texts:
If one wants to calculate a moderate size Alkane (with say 10-15 Carbons , assuming 100 electrons , with Restricted Hartree Fock based methods) we can simply say that electron-electron part will be $100^4 = 100$ million integrals. If we remove the non-unique ones it will become $\frac{100M}{8}= 12.5 M$ Integrals. If we do a pre-screening it may become around 6 million.  Even if we go for DFT it will be around $\frac{100^3}{8} =125,000$ .

I have calculated a small system like Methane with just 10 electrons (around 400 unique/pre-screened integrals) with an efficient C++ code  (based on Rys Integration which is among the most efficient methods) and it took around 1 hour. When 400 cycles takes 1 hour I can assume that 6 million cycles may take years! But software packages do that just in seconds!

My question is if I just want to do a simple math like 2+2 for 6 million times it takes way longer than what these packages do with such complicated integrals!!
Anyone knows what their trick is? Do they have pre-calculated database or some approximation methods?

UPDATE:
there are many good hints in this question and thanks to all for that. A combination of symmetry, finding negligible integrals and using optimized methods work fine. The only unanswered part is an algorithm for finding the symmetric situations.


texts: What does "reaction rank" in Reaxys stand for?

texts: By exporting some search results from Reaxys, I found "Reaction rank" to be one of the columns in the Excel file. In my file, values descend from 107 to 52 and skip some values in-between too. Does anyone know what reaction rank stands for here?


texts:
I'd like to formulate the synthesis reaction of this polymer:

I assume this is a normal polycondensation reaction, and the monomer would then be:

Is this correct?


texts: Are there any known chemical properties of tritium water that make it unusually different from protium water?

texts:
I suppose the first question supporting the main question is, has tritium water ever been synthesized in sufficient quantity to test chemical properties?

If so, and apart from the obvious radioactive nature of the molecule, and possibly self-heating nature, what unusual properties does tritium water have over protium water?

For example, deuterium oxide is not (easily) metabolized by living things; it cannot support life in the same manner as protium oxide. Also protium water is blue and deuterium oxide is clear. What color is tritium oxide?


texts: Potassium permanganate oxidation of sugars

texts:
I am told that all three sugars below can be oxidized to their corresponding carboxylic acids using potassium permanganate.

This strikes me as bloody wrong because only hemiacetal sugars interconvert in solution with their open chain forms, and we need that open chain form to access the aldehyde/ketone for oxidation. Potassium permanganate as far as we know creates C-O bonds while not breaking any C-C bonds ... hence ... the general rule in our class is that ketones cannot be further oxidized (further oxidation would rupture C-C bonds).


texts: Major products of the reaction of 2-bromo-2-methylpropane and propanoic acid

texts:
Here's my attempt:

the electrophile is a tertiary carbocation, so that rules out sn2. I believe the nucleophile is a rather weak base since carboxylic acids are stable. However, it is polar, plus the temperature is low. Thus it seems likely that it proceeds by SN1? So would "I" be the correct answer?


texts: Why is the ionization energy for Hydrogen non-zero?

texts:
There are no other electrons to collide, repel and kick Hydrogen's single electron to a distant nucleus. And that a single electron is tightly attracted to the nucleus by the electrostatic energy between them. So it seems to me, that Hydrogen does not require ionization energy at all.

But when I checked on the sources - the Hydrogen's ionization energy is relatively high.

Even Hydrogen makes $NaH$, which just doesn't stay for long and has extreme need for becoming $Na$ metal and Hydrogen gas.

So in this case why can't we say that Hydrogen does not require ionization energy?


texts: How to calculate molarity and the number of molecules for a mixture in a simulation box?

texts:
I want to do a simulation of a mixture which consists a total of $512$ molecules of glycine, ammonia, and water molecules mixture in a cubic box of, say, length $\pu{2.6 nm}$; $\pu{2.6 nm}^3 = \pu{17.576 nm3}$ in terms of volume.

I want [1 glycine molecule + $x$ ammonia molecules + $y$ water molecules] which together comes to a total of $512$ molecules and in a box volume of $\pu{17.576 nm3}$ and molarity should be $\pu{15 M}$.

Actually here I am fixing the glycine molecule which is only one and varying only the number of ammonia and water molecules to get different molar concentrations, say, $\pu{5 M / 10 M / 15 M}$ and $\pu{18 M}$, where the total number of molecules is constant, i.e. $512$ molecules only (see the example below). Since a maximum of $\pu{18 M}$ solution can be prepared (since ammonia solubility is $\pu{31 g}$ in $\pu{100 mL}$), so, I am trying to study with varying the $\%$ composition of ammonia and water molecules.

In this case I want to get a concentration of $\pu{15 M}$.
How to calculate the number of $x$ ammonia and $y$ water molecules that need to be taken in order to get $\pu{15 M}$, considering the conversion of number of molecules to mass, amount of substance, etc..

For example:

$1$ molecule of glycine + $52$ molecules of ammonia + $459$ molecules of water is $10 : 90$ mixture (total $512$ molecules);
$1$ molecule of glycine + $104$ molecules of ammonia + $408$ molecules of water is $20 : 80$ mixture (total $512$ molecules).

Then what would be the molarity of the above two mixtures ($1 : 90$, $20 : 80$) considering the same volume ($\pu{17.576 nm}$)?


texts: A molecule absorbs light having a specific wavelength, why doesn't it absorb shorter wavelengths?

texts:
I am currently studying computational chemistry and I am trying to understand the UV-VIS absorption of molecules. I know that UV-VIS absorption is electronic excitation and requires a specific energy.

What I don't understand is why a molecule can not absorb a shorter wavelength as it has more energy? A slightly higher energy causes vibrational excitations which is then released through vibrational relaxation (releasing heat). Isn't it the case when a very shorter wavelength is used so that the electrons in the molecule are excited from more lower MOs (lower energy) to the higher ones? Isn't it still absorption? It is supposed to be by definition?

Molecule can absorb a photon that has "red" amount of energy, it can also absorb "green" and "blue" amounts. But why can't it absorb anywhere between red and green or more basically isn't it supposed to absorb anything more than "red"? Just to be clear, by red I mean the energy difference between $n = 1$ and $n = 2$.

Also, I am already aware of the fact that, for example, any energy between $n = 2$ and $n = 3$ can not be emitted fully as some of them will be lost for rotational and vibrational transitions until the energy hits the $n = 2$ state but I am not expecting this to stop a molecule from absorbing that light.


texts: Please explain the reason why E2 mechanism occurs

texts:
I known as that when the weak bases are reacting with 2° alcohol, E1 mechanism occurs. But, in the picture, E2 mechanism is occurred. Why E2 mechanism occurred?

In step [3]
Weak base : pyridine

Did I get it wrong? It is smith organic chemistry 4e, 309 page


texts:
Which of the following will give cyclic elimination by heating?

  phenol
  propanoic acid
  trimethyl isopropyl ammonium hydroxide
  cyclohexyl propanoate

Cyclic elimination by heating is Syn Pyrolytic elimination reaction. This is given by ester, quaternary ammonium salt, and amine oxide. The reaction is according to Hoffman. This cancels out option (1) and (2).

Option (4) is ester and hence the answer to the question.

But why does the ammonium salt not give the reaction? What am I getting wrong?


texts:
I have a GC-chromatogram with 4 retention times and peak widths and a column length.

How can I calculate the column length that I need in order to get baseline separation for all components in the sample?

I know I can calculate the resolution between the peaks and that it should be equal or greater than 1.5 for baseline separation, but in what way should I use the equation of Rs in order to calculate the best column length, using all retention times for the components?

Thanks in advance!


texts: Which definition of van der Waals forces is correct?

texts: I've been told by my teacher that van der Waals forces is the formal name for intermolecular forces. But on the internet, many people are saying van der Waals forces is another name for London dispersion forces. If van der Waals forces is another name for dispersion forces, why is it named after another scientist?


texts:
The central atom has a hybridization of $\mathrm{sp^3d^3}$. Thus, its structure should be pentagonal bipyramidal.

Why is it not that but a distorted octahedron?


texts:
Following a question I have asked previously, what I intend to inquire this time is quite similar as well, except, with a polymer.

So previously I asked whether such monomer PCDO is possible to synthesize.

That originated from this similar, but different polymer poly-PCDO. It is true that I also don't think this PCDO from my previous question is poly-PCDO after monomerization (I'm still not so sure though). But the PCDO molecule pop out when I was attempting to make this original poly-PCDO a monomer.

I think the synthesis of the polymer in this structure would be easier to theorize and explain.

One can dehydrate divinyl ether with benzene (or perhaps phenol) and lithonate by condensation polymer.

$$\ce{n(C4H6O + C6H6O + HLiCO3) -> (C11H9LiO4)_{n} + nH2O + nH2}$$

Due to my limited knowledge in this area, I can only assume the phenyl group would most likely bond with lithonate being bonded to the ether already. Would someone explain to me how this will or will not work?


texts: How does strength of boric acid solution increase in presence of salicylic acid?

texts:
A while ago, I read that salicylic acid can make boric acid solution strongly acidic when it's added to it.

To my knowledge, I know that boric acid becomes a strong acid in presence of cis-diols (except ethylene glycol). I also know that it happens due to increased stability of conjugate base by chelation using polyhydroxy compounds.

But I can't really make out the case with salicylic acid. I will be really thankful if you could shed some light on this topic.


texts: How a titration curve is affected when a poorly soluble salt is formed?

texts:
Suppose that I have $\pu{100 mL}$ solution of strong acid, $\ce{HA}$, at $\pu{0.10 mol L^{-1}}$.
This solution is titrated with a strong base solution, $\ce{BOH}$, at $\pu{0.10 mol L^{-1}}$.
Suppose yet that a poorly/sparingly soluble salt, $\ce{BA}$ $(K_\ce{sp}=\pu{2.30×10^{-3}})$, is formed during titration.

The reactions involved are:

ionization of strong acid: $$\ce{HA + H2O -> H3O+ + A-}$$
dissociation of strong base: $$\ce{BOH -> B+ + OH-}$$
self-ionization of water: $$\ce{2 H2O <=> H3O+ + OH-}\qquad K_{\ce{w}}=\ce{[H3O+][OH-]}$$
Equilibrium of poorly soluble salt: $$\ce{BA <=> B+ + A-}\qquad K_{\ce{sp}}=\ce{[B+][A-]}$$

Charge balance of the solution is given by the equation: $$\ce{[H3O+] + [B+] = [OH-] + [A-]}$$

Once that $\ce{B+}$ and $\ce{A-}$ are spectator ions, are come from strong substances, and disregarding the ionic strength effect, I think that titration curve don't be affected. I'm right?

If not, how to write a mass balance expression to take account into the precipitation of $\ce{BA}$?


texts: I an getting confused between enthalpy and internal energy. My textbook says that change in enthalpy is the sum of change in internal energy and the amount of work done in expansion or compression but isn't it the same as the amount of heat lost or given. So why do we need enthalpy?


texts: In an O-H bond, will polarity increase/decrease if some of the electron density on the oxygen atom is reduced?

texts: Like when an e- withdrawing group (sp2 carbon) is attached to oxygen of the OH bond, it attracts the electrons. So will the polarity of the OH bond increase or decrease?


texts: Spin spin coupling in a proton NMR of an ester?

texts:
I am learning about proton NMR and spin-spin coupling, and am confused about whether splitting occurs over an ester bond. Specifically, in the case of ethyl methanoate, HCOOCH2CH3, if I were to number the proton environments going from left to right as 1,2 and 3, would 1 and 2 cause splitting of each other?
If they would not cause splitting, then I would expect a singlet, a quartet and a triplet respectively. If they do cause splitting, then would you get a triplet, a quartet of doublets, and a triplet for 1,2 and 3 respectively? I know that with -OH and -NH the protons do not couple (although I am not sure why), so I was wondering whether the same principle may perhaps apply here...


texts: What is the oxidation state of C in this lewis structure?

texts:
What is the oxidation state of $\ce{C}$ in this lewis structure?

I know how to find it: based on the number of electrons leaving/coming to the most/least electronegative element. But it s the $\ce{OH}$ that gets me confused...


texts: What material is synthesized in the rubber egg demo?

texts:
One of the popular do-at-home chemistry demonstrations is placing an egg in a container of vinegar for two days. After that period most if not all of the eggshell has dissolved and the outer part of the egg has congealed giving the egg a 'rubber' like appearance and feel.

So chemically the vinegar (acetic acid) reacts with the egg protein (albumen).

Chemically speaking, what is this product?


texts: It is easy to find information about heavy-hydrogen water production, but not about heavy-oxygen water. How is heavy-oxygen water commercially produced (for both heavier isotopes)?


texts: How to determine Delta H from the heat of combustion?

texts:
The heat of combustion of 2-propanol at 298.15 K, determined in a bomb calorimeter, is -33.41 kJ/g. For the combustion of one mole of 2-propanol, determine (a) $\Delta U$ and (b) $\Delta H$

So I managed to determine $\Delta U$ by first finding the amount grams in one of 2-propanol and then using that number with 33.41 kJ/g...

I'm not able to determine Delta H as I'm not sure what to do... Please help and guide me.

Thanks!


texts: Can I extract solid sugar from any fruit juice at home?

texts: The goal here is to isolate the sugar from all other compounds in the juice. In this case, I'm using apple juice and grape juice. The sugar does not need to be edible, as it is being used to make r-candy. Boiling off the water from the juice doesn't work in this particular application, since the syrup is still contaminated with other compounds. I've tried mixing juice in denatured alcohol, and I didn't see any sugar precipitate (felt like a kid staying up all night waiting for Santa to come). Do y'all have any ideas?


texts:
Considering the $K_\text{a}$ of the weak acid and the $K_\text{b}$ of the weak base that form the salt, we conclude that the solution will be acidic if $K_\text{b}$ > $K_\text{a}$ and basic if $K_\text{a}$ > $K_\text{b}$

I was wondering if anyone could clarify what the book is saying.
My question is If we mix a solution with a $K_\text{b}$ of 0.1 with a solution with a $K_\text{a}$ of 0.001 would the final solution be acidic or basic?


texts: Is paper or water the stationary phase in paper chromatography?

texts: I've been looking at about 10-ish sources, and half of them say that paper is the stationary phase, and the other half say that water is the stationary phase. I understand that water is on the paper through humidity, but is there a clear stationary phase, or is it both cellulose and water (if that's possible)? Does the stationary phase depend on the humidity of the room?


texts: What does under-stoichiometric or stoichiometric mean?

texts:
When people talk about oxides like $\ce{SiO2}$ or $\ce{Al2O3}$, they use expressions like stoichiometric or under-stoichiometric. I understand that this refers to the relative composition of materials, but I don't really know what it exactly means.

Say for $\ce{SiO2}$, does under-stoichiometric mean that it isn't exactly $\ce{SiO2}$, but more like $\ce{SiO_{1.8}}$? Does the term usually refer to the oxygen composition?


texts:
I'm currently looking at Principles of Chemistry by Atkins, and I have a few questions involving entropy. These questions probably arise from my poor understanding of reversible/irreversible processes.

Why are reversible processes called reversible? Is it necessarily true that reversible processes can be reverted spontaneously, or is this a common misconception that people have?
So my chemistry textbook gives the definition of entropy as
$$\Delta S = \frac{q_{rev}}{T}$$
where $q_{rev}$ is heat transferred reversibly. However, I get lost at how entropy could increase during a reversible process.
Why is the reversibility condition necessary for the definition of entropy?


texts: How can I save and read the CI vector during CASSCF calculations in Gaussian?

texts:
I have searched through the GAUSSIAN 16 manual and have not been able to solve these two related issues:

(1) I want to be able to save the CI vector and load it as an initial guess for a different calculation. Or at least to be able to manually set the initial CI vector.

(2) During a geometry optimization, the initial guess for the CI vector changes on each geometric iteration. This does not make much sense to me, as the final CI vector is almost always very similar to the one for the previous geometry! I have noticed that this can lead to huge orbital rotations (like starting with a CI[1] = 1 vector and swapping the HOMO for a core orbital) and then this leads to convergence issues. How do I force it to use the final CI vector from the previous iteration as the starting guess?


texts: Is there any collection of charge density maps for small molecules? Any good data at all?

texts:
Despite wide variety of existing experimental methods producing electron/charge density maps, I failed to find a good dataset of experimental data for small (1-3 atoms) molecules.

There are datasets for integral properties such as https://cccbdb.nist.gov/ . It is fairly trivial to find atomic spectra data on NIST site and with some effort it is possible to obtain electronic spectra data for some molecules (though apparently there is no good unified database).

Regrettably, I failed to find any collection of experimental charge density data for small molecules. Furthermore, on second though I cannot remember where charge density maps in QC textbooks come from. Calculated charge densities are fairly easy to obtains, but experimental charge densities are a different matter. In fact, "experimental charge density hydrogen molecule" search gave me zero relevant references.

Any suggestions?


texts:
By aerial oxidation $\ce{Cu+}$ can easily oxidise to $\ce{Cu^2+}$. Which of the following should be added to $\ce{Cu+}$ to prevent it from oxidation: $\ce{F-}$, $\ce{Mg^2+}$, $\ce{Mg}$ or $\ce{F2}$?
$$
\begin{align}
E(\ce{Cu^2+/Cu+}) &= \pu{0.15 V}\\
E(\ce{F2/F-}) &= \pu{2.87 V}\\
E(\ce{Mg^2+/Mg}) &= \pu{-2.37 V}
\end{align}
$$

Why it isn't $\ce{Mg^2+}$?


texts: Why does vibrational cooling occur much faster than sponteneous emission in the condensed phase?

texts:
Following the absorption of light by an arbitrary small molecule, the molecule is found to be excited both vibrationally and electronically. The excess vibrational energy of the molecule will usually be dissipated into the solvent in less than ~10 ps, and fluorescence emission will occur in about ~10 ns.

Since there are many transitions available to accept the excess energy form the vibrations in the surrounding solvent it makes sense that the relaxation occurs very rapidly. On the other hand, electrons can move much faster than nuclei can. What must happen for an electronically excited molecule to relax through the emission of a photon and why does it take so much longer than the vibrational relaxation?


texts:
I have learnt that the species which have vacant orbital(s) are called electrophiles. But in this case, the nitrogen has a complete octet. The positively charged nitrogen ion has a valency of 4, of which 2-2 are satisfied by each oxygen atoms.

Still, $\ce{NO2+}$ acts as a nucleophile. Why?


texts: What's a good resource/book on pH measurements?

texts:
Most resources on pH and the electrochemistry behind it that I've found are IMHO too superficial. For example, they explain that an electrode with less than 80% slope should be discarded, but not why the decrease in slope happens, or why it's a problem if you can just calibrate it. Or they explain the potential generated at the Ag/AgCl eletrode and the glass membrane potential, but not the interaction between the two - does the H+ combine with the e- from the electrode? And what happens if the current is reversed? After reading for a few days I still feel like I don't understand any of it.

So far I've read a couple PDFs on nico2000.net (the 30 page Introduction to pH measurements), the 160 page book pH Measurements by C. Westcott (1978), a few manufacturer's guides to pH measurement theory and practice (by Radiohm, Emerson, Mettler) and the relevant chapters in the Analytical Chemistry books that my library had.

All help appreciated!


texts: Can someone explain the concept of entropic traps, or provide good sources to look up? The term is not present in any chemistry books I own, and I cannot find online sources explaining it.


texts: Methylene blue used as funguscide in cichlid reproduction - concentration measurement?

texts: I have an aqueous solution of methylene blue. How do I determine the concentration of this solution, so I can duplicate it?


texts: Removing harmful gases from automobile exhaust using electrostatic precipitation

texts: If I attach an electrostatic precipitator to a car's exhaust - and also make the smoke pass through an area containing $\ce{NaOH}$ in order to absorb sulfur dioxide - does that mean that the smoke that emerges will not contain harmful gasses such as $\ce{CO2}$, $\ce{CO}$ and $\ce{SO2}$? If not, what is the reason?


texts:
Now, I am doing a science worksheet and I came across an opportunity to write either "decoxide" or "decaoxide". Since the latter sounds wrong out loud, I decided to google it before I wrote it out, just to be sure. What I got instead, once I had filtered out all of the references to phosphorus or tetraphosphorus, was a whole lot of mentions of both. Both my phone's autocorrect and my worksheet itself use "decoxide".
So, I did the obvious next thing and went to r/askscience. However, after I'd gotten no responses on there, I realized my mistake and came here.
Update: How do you write "three iodine atoms"? Is it "triiodide" (which my autocorrect says is correct, and which Wikipedia apparently uses) or is it "triodide" (which my autocorrect approves of)? Or even "tri-iodide"?
Thanks for any help you guys can provide!


texts: Are the energies of orbitals that are not filled in an atom, equal?

texts: In a hydrogen atom only 1s orbital is filled. Does this mean that the energies of all other orbitals are equal? If so,why?


texts: Balancing reactions algebraic method limitations

texts:
How do I balance this reaction using the algebraic method?

Seems that the equation can't be solved.

How do I balance such reaction and does the algebraic method has limitations and wont work for balancing some reactions?

$$\ce{XeF4 + H2O -> XeO3 + Xe + O2 + HF}$$

$$\ce{a XeF4 + b H2O -> c XeO3 + d Xe + e O2 + f HF}$$

$$4 a = f$$

$$2 b = f$$

$$a =  c +  d$$

$$ b = 3 c + 2 e $$


texts: Why doesn't EDTA complex with alkali metal ions?

texts: EDTA complexes with all the other metal ions in the periodic table except those from the group 1. Why is this so ? What is the coordination chemistry behind this ?


texts: Adjusting the ph of salicylic acid using sodium hydroxide

texts:
Question
  How many milliliters of $0.202\ \mathrm M$ NaOH should be added to $25.0\ \mathrm{mL}$ of $0.0233\ \mathrm M$ salicylic acid to adjust the $\mathrm{pH}$ to $3.50$?
  The answer from the text book is $2.2\ \mathrm{mL}$ NaOH
  My attempt
  I believe the correct equation to use for this is the Henderson–Hasselbalch equation

$$\mathrm{pH}=\mathrm pK_\mathrm a + \log\left(\frac{[\ce B]}{[\ce{BH}]}\right)$$

$\mathrm pK_\mathrm a = 2.972$

So I set it up as:

$$3.50=2.972+\log\left(\frac{x}{0.0233}\right)$$

Solving for $x$ I get $0.0785$

I don't know where to go from here
since $x$ is the concentration I figure that if I multiply by $0.025$ (the volume) and then divide by the molarity ($0.202$) I would get the answer but that's not right.


texts: what keeps an identical atoms of an element together?

texts: I have learned that the atoms of different elements are held together by covalent bonding and ionic bonding but in the case same element which force keeps the atoms together i.e in  sodium which is the force that keep sodium atoms in position?which is the force acting between the atoms of sodium?


texts: So, is baking soda actually a strong base?

texts:
Based on my recent thoughts, when baking soda ($\ce{NaHCO3}$) is dissolved in water, the following hydrolysis reaction occurs:
$$\ce{NaHCO3 + H2O <=> NaOH + H2CO3}$$
However,
$$\ce{H2CO3 -> H2O + CO2 ^}$$
so the actual one is:
$$\ce{NaHCO3 -> NaOH + CO2 ^}$$
$\ce{CO2}$ escapes, so the reaction is irreversible, all the $\ce{NaHCO3}$ is converted to $\ce{NaOH}$ and the product is a strong base.

The following reaction is possible:
$$\ce{HCO3- <=> H+ + CO3^2-}$$
but it's reversible unless it results in $\ce{H2CO3}$ formation, which is the same as the first one, so it doesn't really matter.

However, I was unable to find any evidence to that but a lot of discussions on whether $\ce{NaHCO3}$ behaves like a weak or a strong base, which put me in doubt. Am I right?


texts: Mixing hydrochloric acid and sulphuric acid, both concentrated

texts:
In the chemistry lab, I stupidly decided to mix hydrochloric acid and sulphuric acid, both concentrated, in a random ratio, which was about $\pu{50 ml}$.

When I poured them in one test tube, the result was a vigorous reaction, with the green coloured liquid mixture "jumping" in the test tube and a white gas being released.

Could someone tell me what the resultant chemicals were?


texts:
I saw rubber-like silicones. Are there types of silicone that can be used in injection molding and once the process is finished - become as rigid as, let's say PVC? At the same time they should have all(/majority) of silicone's properties (citing Wikipedia):

Low thermal conductivity
Low chemical reactivity
Low toxicity
Thermal stability (constancy of properties over a wide temperature range of −100 to 250 °C)
Does not support microbiological growth
Resistance to oxygen, ozone, and ultraviolet (UV) light
High gas permeability

If such silicones exist - what are their names/formulas?


texts: Do processes involving synthesis need heat?

texts:
I came across a textbook that stated a combination process that required heat. There was no explanation whether it was a prerequisite for a combination process to have heat or it was just an example just that it was grouped under "heat process chemical changes".

Was doing a test paper that asked about 2 differences between thermal decomposition and combination processes and one of the difference was that "combination processes do not need heat but thermal decomposition processes do".

Would like to ask which interpretation is correct. From preliminary searches on Google it seems that the consensus is that any reaction that simply involves two separate substances combining in a reaction to become a single product is considered to be a combination reaction regardless of whether there is heat involved or not.

Would like to know what is the correct interpretation.


texts: How can I tell whether or not a molecule is planar?

texts:
I am doing several questions involving judgment on the planarity of a compound.

  Which of the following is not a planar molecule?

  $\ce{H_2C=C=CH_2}$
  $\ce{H_2C=C=C=CH_2}$
  $\ce{H_2C=C=O}$
  $\ce{NC-HC=CH-CN}$

I had the idea that the compound in with central atom has $\ce{sp}$ hybridisation is planar or the compound in which all the atoms has the same hybridization. But it is not working in this case. I am aware of finding out the hybridization of a atom in a compound but I feel trapped to decide the planarity of certain compounds. The question does not address this purpose.  Anyone has any idea to solve this and many related questions?


texts: On biological detergent breaking down organic material

texts:
This is again related to the crime story I'm working on.

I would like to know how much biological detergent (in kilograms) and water (in liters) and how long it would take to dissolve $60 \,\rm{Kg}$ of organic material at $50^\circ$ Celsius with standard store-bought bio-detergent. Just an estimate of the time required.

Bonus questions:

Would it dissolve hair?
Do I need a special container as to not commit the same mistake Jesse had in Breaking Bad?


texts: Why are there only less than 120 elements out there ?

texts: Why stop at 118 , Why aren't any more stable elements possible ?


texts: Products of the reaction between cyclohexanone and N-bromosuccinimide

texts:
Problem

Treating cyclohexanone with N-bromosuccinimide in the presence of carbon tetrachloride gives A. A on treatment with aqueous KOH gives B. Deduce the structures of A and B.

Solution

 A is 2-bromocyclohexanone and B is potassium cyclopentane carboxylate.

Questions

In the first step, why did the bromine atom get attached to the second position? The carbonyl group, being electron withdrawing, should direct the incoming electrophile away from it.
In the second step, I am quite sure that the product mentioned is a result of Favorskii rearrangement. But there is also a possibility for the hydroxide ion to substitute bromine. Is this possible? If yes, why is the substituted product not a major product? If not, why?


texts: How to Experimentally Quantify the Response of a Receptor to a Ligand?

texts:
In medicinal chemistry, there are multiple reasons why one would want to experimentally determine the effect of a particular molecule on a receptor e.g. measuring how 'strongly' that molecule brings about a chemical response (an agonist) or how strongly it prevents a response (an antagonist).

If we were looking at an insulin receptor antagonist (for whatever reason), then it would be easy to quantify the strength of the antagonist by a simple blood test of the test subject (human or animal), to see how much insulin was present.

What happens when we're faced with a scenario inherently difficult to quantify? How do we measure the action of a drug then?

Say we've found a natural neurotransmitter receptor agonist and want to compare this to a synthetic drug of a similar nature. I'd struggle to see how we'd experimentally be able to analyse the amount of neurotransmitter present in the synapses in each of the cases to compare.

Do we then look at less direct, perhaps qualitative methods of analysis? Such as 'state of agitation' or 'how many times the subject's arm twitched in a minute'?


texts: What would be a safe/good surfactant for ultrasonic cleaning vinyl records + distilled water and isopropyl alcohol

texts: Title pretty much says it all besides the type of records I believe are pvc (60s - current, someone correct me if there may be other materials but I absolutely don't have any shellac records) and I plan to use around 50:1 water/ISO. I'm not sure what to use as a surfactant or if it would be of any benefit, though I assume it would. Looking for something 100% safe for records though, and I do have several chemical supply companies around. Any suggestions?


texts: Total number of stereoisomers of truxillic acid

texts:
Total number of stereoisomers of the compound will be:

This was a question asked in our mock test. I've tried by considering pseudo-chirality on the carbon atoms. But I don't know where to start.
I need help finding the different stereoisomers. It would be appreciated if you could draw the different isomers.


texts: After mixing, which species has the dominant affect on the pH of the solution that remains?

texts:
A solution is created by mixing $250\,\mathrm{mL}$ of $1\,\mathrm{M}$ $\ce{HCl}$, $250\,\mathrm{mL}$ of $1\,\mathrm{M}$ $\ce{CH3COOH}$ and $500\,\mathrm{mL}$ of $1.5\,\mathrm{M}$ $\ce{CsOH}$.

The $K_\mathrm{a}(\ce{CH3COOH}) = 1.8 \times 10^{-5}$

What is the $\mathrm{pH}$ of this solution?

I am stuck between $\ce{HCl}$ and $\ce{CsOH}$ since they are both a strong acid and base (respectively) meaning that they should both have a substantial affect on the $\mathrm{pH}$.

Also when determining what the $\mathrm{pH}$ is, which species would we use in our ICE table?


texts: Decomposition of Hydrogen Peroxide Catalysed by Potassium Iodide in Basic Solution

texts:
As part of my high school project, I had to measure the initial rate of decomposition of hydrogen peroxide catalysed by potassium iodide at different pHs. At higher pHs (alkaline conditions), I found the initial rate of reaction to be slower, and I have repeated my experiment multiple times to confirm this. Any possible explanation for these results? I seem to have some trouble finding any answers online. Would appreciate some help on this, thank you!
FYI, I measured initial rate through the volume of gas evolved. There was still gas evolved for high pH, except that the rate was slower


texts: I am having some trouble with understanding the NOE. The carbon NMR spectra can't be integrated, because the protons attached to the carbon atoms will make primary carbon atom relaxation faster than tertiary, so their peaks will have bigger intensity. With a bigger acquisition time, the peaks will be more proportional. In proton NMR, nearby protons will cause the target proton relaxation to be faster. When NOE is applied, those nearby protons will be irradiated and the target proton peak will have a slightly bigger intensity. Why will it have a bigger intensity?


texts: In Goodman and Gilman what does R,S-citalopram refer to?

texts:
In Goodman & Gilman's The Pharmacological Basis of Therapeutics, 12e R,S-citalopram is referred to. The problem is that from what I am aware of citalopram only has one stereocentre, and hence I am forced to ask were the author having a stroke when they added the comma and really meant the racemic mixture of R and S stereoisomers?

Figure 1: Screenshot of the Relevant Page in Goodman and Gilman

Figure 2: Citalopram

(The latter has the stereocentral carbon highlighted)


texts:
Should I write propanol or propan-1-ol?

Personally, I'd go for the former (it being the simpler of the two), but what's the answer according to the IUPAC system of organic nomenclature?


texts: What are the similarities / differences between the terms anode / cathode and oxidizing agent / reducing agent?

texts:
I'm kind of confused on how to distinguish the terms anode and cathode from oxidizer and reducer or oxidizing agent and reducing agent. Some references prefer to use one over the other in discussions depending on the topic. Are they suppose to mean the same thing in some cases? Like an anode has oxidation taking place so it is an oxidizing agent? The substance used in the anode can be referred to as an anode but it can also be called an oxidizing agent?
I want to be able to know this more clearly and have a distinction of when to use both if I want to use both in the same discussion so that both of them have a specific idea associated with them instead of just allowing interchange between the terms even though in a sense it is also correct.


texts: why do solids and pure liquids have no effect on yield and equilibrium?

texts:
There are three parts to my question.

Part one:

Let's assume we have a reversible reaction at equilibrium  as follows : Calcium carbonate (solid) goes into calcium oxide(solid) and carbon dioxide(gas).
Let's assume that I add more calcium carbonate i.e I add more solid.
Now I understand that there would be no shift in the position of the equilibrium since we added a solid therefore we induced a very negligible change in concentration ,  but what I am confused about is doesn't more reactant mean more product and doesn't more product symbolise a shift to the right?

Part two:

I have read that the equilibrium constant $Kc$ and $Kp$ are really just close approximations of the true thermodynamic constant which uses activities hence the activity of a solid and pure liquid is always 1 .
However upon further research I discovered that for an esterification reaction the equilibrium constant is 4
-First of all, the above reaction involves all pure liquids and hence the thermodynamic equilibrium constant would be one ,however why stick to a value of 4 why not easily say it is one since all activities are 1.

Part three:

If we do take pure liquids in the $Kc$ value how do you measure the concentration of such a species, wouldn't the value be very high.My intution tells me that pure liquids are only taken when a reaction only involves pure liquids only , but they are not taken in heterogeneous reactions or when the liquid involved acts as a solvent as well.However in a case of a heterogeneous reaction only involving solids and liquids what will your equilibrium constant look like .

Lastly I have no knowledge of thermodynamics and I am still a high school student .


texts: Why is (tri-)ammonium phosphate ((NH4)3PO4) so unstable?

texts: Why is triammonium phosphate, $\ce{(NH4)3PO4}$, so much more unstable than diammonium phosphate, $\ce{(NH4)2HPO4}$, or monoammonium phosphate, $\ce{NH4H2PO4})$?


texts: Mixing Different Solutions with Different Wavelengths to Get Different Colors?

texts:
I recently was told that the reason you can mix colors (blue and yellow make green because wavelengths 605nm + 450nm = green) was based on wavelength (which seems very obvious when you think about it but please humor me).

This is kind of cool but I don't get it - is this based on the wavelength range that's transmitted?  If  605nm + 450nm = green then how would you find that exact wavelength of green? Would it be the average of the two, or is there some constant that I am missing?


texts: Chemoselectivity in reduction of 3′-nitroacetophenone

texts:
When 3′-nitroacetophenone is treated with sodium borohydride, only the carbonyl group is reduced (top); however, when reacted with tin and hydrochloric acid only the nitro group is reduced (bottom). Why is this so?

I think that sodium borohydride is too weak a reducing agent to reduce the nitro group, but I am unsure as to whether this is correct. If Sn/HCl can reduce the nitro group then why doesn't it reduce the carbonyl too?


texts: Calculate the moles of acid and conjugate base needed

texts:
Question

  Using the following salts listed below, calculate the moles of acid and conjugate base needed to make $V = \pu{100 mL}$ of $c = \pu{0.50 M}$, $pH \in 6.5, 6.7, 6.8$ phosphate buffer solutions. ($\mathrm pK_\mathrm a(\ce{H2PO4}) = 6.64$)

  Molas masses of salts:

  $\ce{KH2PO4} = 136.09 ~\pu{g/mol}$
  $\ce{NaH2PO\cdot H2O} = \pu{137.99 g/mol}$
  $\ce{Na2HPO4 \cdot 7H2O} = \pu{268.09 g/mol}$
  $\ce{K2HPO4} = \pu{174.2 g/mol}$

I tried using the Henderson-Hasselbalch equation but I am stuck at the point where I have found the base-acid ratio and I need to find the moles of the acid and the moles of the base.

$$
\mathrm pH = \mathrm pK_\mathrm a + \log\left(\frac{[\text{Conjugate base}]}{[\text{Acid}]}\right)\\
n = \pu{100 ml} \times \pu{0.5 M} =\pu{ 0.05 mol}
$$

For pH 6.5:
$$
6.5 = 6.64 + \log\frac{[B]}{[A]}\\
\frac{[B]}{[A]} = 0.72
$$
Here I got the base-acid ratio as 0.72 but what should I do next? I tried looking up for solutions and a person suggests using $A + B = 0.05$ But how do I know what A and B are just by knowing the ratio is 0.72?


texts: How do we know whether we will get a mono substituted or tri-substituted product during electrophilic aromatic substitution?

texts: For example consider the bromination of phenol we get the tri-substituted product (even though bromine is deactivating so I suppose it should deactivate the ring with each addition) while sulphonation essentially gives the mono-substituted product (even at high temperatures).


texts: Why are nitrogenous hydrocarbons sometimes colorful?

texts: Alanin and dyes contain nitrogen, is being colorful a special feature in nitrogenous substances?


texts: Equation for reaction between chlorine fluoride and potassium bromide

texts:
The equation given in the answer key was

$$\ce{ClF + 2KBr → KCl + KF + Br2}$$

However won't the $\ce{KCl}$ also react with $\ce{ClF}$ to form $\ce{KF}$ and $\ce{Cl2}$, resulting in the net reaction being

$$\ce{2ClF + 2KBr → 2KF + Cl2 + Br2}~?$$


texts:
From doing some research on the site I have found that many people have posted about solutions of $\ce{HCl}$ where $[\ce{HCl}] = \pu{1e-8 mol dm-3}$

Here they are able to deduce

$$[\ce{H+}] = \frac{[\ce{HCl}]_0}{2} + \sqrt{\frac{[\ce{HCl}]_0^2}{4} + K_\mathrm{w}}$$

where $[\ce{HCl}]_0$ is the initial concentration of  $\ce{HCl}$ dissolved.

Can we make a generalisation of this and say if $\ce{H_xA}$ is a strong acid that will dissociate fully when dissolved in water? Then if $[\ce{H_xA}]_0 < \sqrt{K_\mathrm{w}}$ then the $\mathrm{pH}$ of solution can be expressed by

$$\mathrm{pH} = -\log_{10} \left(\frac{x[\ce{H_xA}]_0}{2} + \sqrt{\frac{(x[\ce{H_xA}]_0)^2}{4} + K_\mathrm{w}}\right)$$


texts: Systematic Approach to Finding Number of Isomers

texts:
I have this compound

I want to know how many isomers (including stereoisomers) may have this constitution. Is there a systematic approach towards solving such types of problems related to the total number of isomers?

Note: The above compound has 64 stereoisomers (from textbook).


texts: NMR: Most deshielded protons (electron withdrawal)

texts:
Of these two molecules, which one would be expected to have the most deshielded signal?

First off, I think the wording of this question is wack because neither of these molecules has only one NMR signal.

In any case it's clear that the question is asking about which molecule has the highest degree of electron withdrawal ...

I chose E, because I was looking at the benzene's signals. This one has an alkyl group, which is a slight inductive donor, thereby shielding the benzene's protons (slightly). This one also has a benzylic carbonyl group, which, according to my teacher, is only a resonance withdrawer and not in any form a resonance donator. Based on this, I chose E as the more de-shielded.

The other group similarly has a C=O resonance withdrawing group, but a resonance donating -OH group. Given that the resonance effect usually trumps the inductive effect, I said that E is still the more deshielded of the two.

I realize I might have now erred in limiting my analysis of shielding to only the hydrogens on the benzene. In E, the methyl's hydrogens are fairly well-shielded still, being connected to a carbon (albeit an sp2 hybridized carbon). On the other hand molecule F has a long linear chain; the hydrogens toward the end of that linear chain will have well-shielded signals! F's linear chain is also longer than E's linear chain ...

Frankly I think this is a horrible question but in any case the answer is apparently "F" ... do you agree?


texts: Providing more than required amount of energy to an electron in an energy level

texts:
I know that an atom has energy levels i.e the energy of each electron in the atom falls in a discrete energy level.

I am also aware that, if the exact difference of energy between two levels is provided to an electron, then it jumps to the higher energy level, and that is a lower amount of energy is provided, the electron stays where it is.

My questions are:

What happens to the energy in the second case? Does it get radiated back as heat? If not, where does that energy go?
What happens if more than the requisite amount of energy is provided? Does the electron stay where it is, or does it go to the higher energy level?


texts: Is hydrolysis of polypeptides and polysaccharides "anabolic" or "catabolic"

texts:
When a polysaccharide or polypeptide is hydrolyzed into mono-saccharides or amino acids, the building blocks can be oxidized to release energy.  The oxidation is considered to be catabolic since it reduces the building blocks to simple compounds: carbon dioxide, water, ammonia, and releases energy.

Is the process of hydrolysis that breaks up polypeptides and polysaccharides a net endothermic or exothermic process?
Do the free amino acids and monosaccharides have more or less stored energy than the polypeptide or polysaccharide that they were broken down from?
Is it proper to call the isolated process of "hydrolysis" of proteins and polysaccharides "catabolic"?
Are protein synthesis, glycogen synthesis, (and triglyceride formation), by dehydration synthesis processes that require energy or release energy.  I think that they release energy which is semantically interesting since protein and glycogen synthesis are the main examples of anabolism in the body but may actually release energy which is a key component of the definition of catabolism.  Even if the energy released from protein synthesis is not generating ATP directly, wouldn't the heat produced conserve ATP in the long run.


texts: What causes the yolk of a frozen egg to be more spreadable instead of fluid?

texts:
If you freeze an egg the yolk of it gets more spreadable instead of it was fluid before. It appears that this state of the yolk is perm. So what chemical reaction causes this?

The question is of course after the egg had been melted again.


texts: Exact meaning of constant volume heat capacity

texts:
From Wikipedia:

$$
\left(\frac{\partial U}{\partial T}\right)_V = \left(\frac{\partial Q}{\partial T}\right)_V = C_V,
$$

$C_V$ is what known to be constant volume heat capacity. I don't really get the exact meaning of 'constant volume'. Does it mean that (a) the whole process takes place under a constant volume, i.e, it can be any volume as long as the volume does not change during the process, the volume is maintained at its initial value throughout the process, or (b) the $C$ is measured under a fixed constant volume $V$?

If (a) is correct, are the rates of change of $Q$ with respect to $T$ same at, for example, $V = \pu{1 dm3}$ and $V = \pu{2 dm3}$? We are not considering only perfect gases.

If (b) is correct, what is the value of $V$ for standard $C_V$?


texts: What is the logic behind the division into groups of anions and cations in qualitative inorganic analysis?

texts:
I find it very confusing and hard to memorize.
Is there a way to deduce it, like understanding how it is derived, or is it just one of a lot of ways you can do it but is the standard one?
Do people use to test every possible reagent or combination of reagents and see if something happens or is it deducible?


texts: Standard electrode potential of copper disproportionation

texts:
I am having some difficulty with the below.
It says the standard potential for $\ce{2Cu+ (aq) -> Cu (s) + Cu^2+ (aq)}$ is $\pu{0.36 V}$.
The relevant half equations are:
$\ce{Cu+ + e- -> Cu}$ (potential $=  \pu{0.52 V}$)
and
$\ce{Cu^2+ + e- -> Cu+}$ (potential $=  \pu{0.16 V}$)
To get the overall equation, I flipped the second half equation and so reversed the sign of the potential also to get $\pu{-0.16 V}$.
The first half equation is therefore reduction and the second is oxidation.
If standard electrode potential is $\mathrm{RHS (reduction)} -\mathrm{LHS (oxidation)}$, would the answer not be $\pu{0.52 V} - (\pu{-0.16 V}) = \pu{0.68 V}$? Why is it $\pu{0.36 V}$?


texts: Correct way of drawing D-configuration with this stereochemistry?

texts:
Hello! I have completely memorized how to draw all 20 amino acids in the way seen in the picture (middle, between the "ball-and-stick" and fisher projection)

By my understanding this is in the L configuration, what is the correct way of drawing them in D- configuration? Is there a simple trick? Does anyone have an image of them all drawn in D-config in the same way?

Is it basically having the COO- and NH3+ switch places. Like here:

Thanks!


texts:
I was told in this question: https://chemistry.stackexchange.com/questions/4789/synthesizability-and-energy-minimization-of-a-structure/4791#4791 to

[Count the] "number of accessible functional groups (alkenes, amines, alcohols, esters, etc) which make it easier to prepare, 5) number of inaccessible functional groups (aromatic rings, polycyclic systems, quaternary carbons, complex or long alkyl groups),"

But when I googled accessible functional groups and inaccessible functional groups no pages had a longer list. I found a SMARTS file which lists some common functional groups. Could someone help me determine which are readily synthesizable?

Thank you


texts:
I was wondering what happens when you boil dry a solution of several salts for example a solution of KCl and NaNO3. Since the ions dissociate I was wondering if the ions would combine randomly upon being boiled out of solution making the original salts as well as KNO3 and NaCl? Does this happen? If not why?

Also in a related question when you mix two solutions to form a precipitate in a double displacement reaction will the insoluble salt always form or are there situations where an insoluble salt can form but doesn't?

Thanks in advance.


texts: When and how do mineral chelates separate in the body?

texts: If one consumes an amino acid chelate such as iron bisglycinate, it is generally absorbed intact as far as I am aware. At some point, presumably the iron could be used for say hemoglobin synthesis and the glycine for collagen synthesis. How exactly does the dissociation of this chelate occur in the body to support this?


texts:
I'm looking to plate some aluminum with silver using a basic solution.
My first attempt was to use sodium carbonate to make silver acetate. I sped up the process using hydrogen peroxide. I used the silver acetate as the ion source.
This simply did not work to plate any aluminum.
I concluded that this is because the aluminum was oxidized, preventing a plating from sticking.
I've come to the conclusion that the main problem with plating into aluminum is that it's able to rapidly form a highly resilient oxide layer.
Are there any common ways to prevent this oxide layer from forming? More to the point, are there any common methods to plate aluminum, specifically with silver?


texts: Application of LeChatelier's principle for reactions with solid products

texts:
I wanted to understand application of LeChatelier's principle for reversible reactions of type $\ce{A(g) <=> B(g) + C(s)}$. Because of increase in moles, you can say lower pressure will favor the reaction going right. But does this apply even if one of the products is solid, like in this reaction? If not, why? I need to understand this intuitively, if possible, with less math.
Another related question I have is we talk about reactions having thermodynamic limitations when considering their practical applicability. i.e say a reaction such as above might only yield 20% conversion at industrially practical conditions. But isn't this a bit misleading? As long as you find a way to remove products as soon as they formed, you can push ANY reversible reaction to the right. So for all practical purposes you can say any reversible reaction can be designed to give high conversions (80-100%) if you devise a mechanism to remove products quickly from reaction space. So the thermodynamic limitation is not  really a hard limitation at all.


texts: Why would the 2+ molecular ion of butane have a mass spectrum peak at 29?

texts:
Question 7 of Edexcel's June 2014 Unit 2 exam paper reads:

  In a mass spectrum of butane, C4H10, where would a peak be seen for
  the molecular ion if it had a charge of 2+?

The answer is 29.

My question is: why?


texts: Is there a standard scholarly reference for lattice constants of crystals of the elements?

texts:
I need to discuss the lattice constants of bulk crystals of several metal and semiconductor elements. I can find plenty of tables and numbers that are probably "close enough" but for a paper I'd like to cite a standard source.
From  https://periodictable.com/Properties/A/LatticeConstants.html I have the following numbers, but I don't want to use a "dot com" as a scholarly source, and I can not figure out how to use Wolfram Alpha (the source for this website) or understand where WA gets its numbers. They list several references here https://reference.wolfram.com/language/note/ElementDataSourceInformation.html , but it will be a challenge to track them all down one by one. I'm hoping someone will recognize one of them or simply be able to mention it.
I only need (at a minimum) three decimal places for the lattice constants in Angstroms (though four is better if they are known), but what I can't find is a citable, schollarly source that covers all of these and is likely to cover other common elemental crystals when I need them in the future.
element.   lattice constant
             (a, b and c)
              Angstroms

   Au          4.0782
   Ag          4.0853
   Pb          4.9508
   Ge          5.6575
   Si          5.4309


texts: Understanding the energy produced from oxidizing 1 kg of lithium

texts:
I am reading the following paper in preperation for a research project on the theoretical energy density of batteries: Lithium - Air Battery: Promise and Challenges and on the second page they describe the following calculation:

  The oxidation of 1 kg of lithium metal releases 11,680 Wh/kg

I was wondering specifically how this number was obtained. I think that this would be the right chemical equation to use for this type of approximation but I am not sure:

$$\ce{4Li (s) + O2 (g) -> 2Li2O}$$

I am wondering if anyone can explain to me how this number was produced.


texts: Why is molarity independent of temperature?

texts: I can't find a good answer as to why molarity is independent of the temperature. Why is the concentration (in mol/l) independent of the temperature?


texts:
I'm working on a chemistry project and that features a reaction where $\ce{Br-}$ participates in a redox reaction as a reductor. Eventually, $\ce{HBrO2}$ competes with $\ce{Br-}$ to react with the same chemical as $\ce{Br-}$ reacts with.

Is is therefore true that $\ce{HBrO2}$ is also a reductor? If yes, what is the redox potential of $\ce{HBrO2}$?


texts: In the condensation reaction of an aldehyde with a hydroxyl amine, why is an oxime formed and not an amide?

texts: Condensation reactions are those that involve removal of a water molecule. When you analyze the reaction between an aldehyde and hydroxyl amine, I don't understand why it's not possible for the acidic hydrogen of the aldehyde to be abstracted by the $\ce{OH-}$ radical of the amine, thus leaving behind an amide ($\ce{R-CO-NH2}$) rather than an oxime being formed?


texts: Is it possible to copy my chemdoodle displayed structure into mestranovea? I have tried simple dragging (mac) and all the various copy/paste options... any ideas?


texts: How to estimate reaction products of competitive binding?

texts:
I have two reactions,

$$\ce{A + C \rightleftharpoons AC}$$

$$\ce{B + C \rightleftharpoons BC}$$

I'd like to estimate the relative steady state proportions

$$\frac{[\ce{BC}]_{SS}}{[\ce{AC}]_{SS}+[\ce{BC}]_{SS}}$$

and

$$\frac{[\ce{AC}]_{SS}}{[\ce{AC}]_{SS}+[\ce{BC}]_{SS}}$$

without numerically solving any differential equations, given $[\ce{A}]_{init} = [\ce{B}]_{init}$ and thermodynamic properties: $\Delta G, \Delta H, $ and $\Delta S$.

I'm hoping that there is a way to generalize this for more than two reactions in a linear way. It is for a DNA microarray optimization problem in which computational speed is important. Any thoughts?


texts: A 1 g sample of an organic compound was burned in a combustion analyzer and yielded 1.42 g carbon dioxide and 0.872 g of water. Calculate the percent carbon and hydrogen in the sample. From the percentages, calculate the empirical formula for the compound.


texts: Determining percentage of copper in brass

texts:
Source: an IB Chemistry past paper.

I looked it up and found out that brass is an alloy of copper and zinc - however, I don't see zinc in any of the equations, and therefore any brass being separated into copper and zinc, which I had originally thought would be the method to determine the percentage of copper in brass (by looking at the coefficients of the compounds in the resulting chemical equation).

My question is how do these reactions help determine the percentage of copper in brass?


texts: why does adding a non volatile solute not decrease the boiling point?

texts: If I add a solute that decreases the bond strength of the pure solvent then wouldn't the solvent molecules evaporate more easily as it has lesser force holding it down now?But in my textbook, it's written that BP always increases when we add a non-volatile solute.


texts: Can an acid or base have a pH less than 0 or more than 14?

texts:
This question has been asked earlier, but I could not understand it.
Please, someone explain it in an easier way.


texts: Can the equilibrium constant be equal to 0?

texts:
Can $K_\mathrm{eq}$ (not $Q$) be equal to $0$?

My book says:

  $K_\mathrm{eq}$ is always positive because the concentration at equilibrium, small or large, are always positive.

But it says $Q$ can be $0$, when the concentration of the products is $0$. Why can't $K_\mathrm{eq}$ be $0$? In other words, why can't a reaction exist such that the equilibrium condition doesn't produce any products?


texts: Using thermodynamics to predict the acid-base character of fluoride ion in water

texts:
I was working through the end-of-chapter exercises of the acid-base chapter in Shriver's Inorganic Chemistry when I came across the following problem:

4.7. The effective proton affinity $\ce{A^{'}_{p}}$ of $\ce{F-}$ in water is 1150 kJ $\ce{mol^-}$. Predict whether it will behave as an acid or base in water.

I was initially stumped by this problem since the $\ce{A^{'}_{p}}$ of $\ce{F-}$ is between the $\ce{A^{'}_{p}}$ values of water and hydroxide ion (1130 kJ mol- and 1188 kJ mol-), which tempted me to say $\ce{F-}$ is amphoteric in neutral water even though I know it's basic from general chemistry.
The answer that the book's solution manual provides is the following:

The proton affinities of H2O (l) and OH-(aq) are 1130 kJ mol- and 1188 kJ mol-, respectively. Consequently, the reaction below between $\ce{H3O+}$ and $\ce{F-}$ is exothermic by -20 kJ mol- (1130 kJ mol- minus 1150 kJ mol-):
$\ce{ H3O+ (aq) + F- (aq) -> H2O (l) + HF (aq)}$
The reaction below between $\ce{H2O}$ and $\ce{F-}$ is endothermic by 38 kJ mol- (1188 kJ mol- minus 1150 kJ mol-):
$\ce{ H2O (l) + F- (aq) -> OH- (aq) + HF (aq)}$
Therefore, in neutral water, $\ce{F-}$ will behave as an base.

I understand that the first reaction has an approximate enthalpy change of -20 kJ mol- and is favored because it is the reverse reaction of the following reaction between $\ce{HF}$ and $\ce{H2O}$ and reaction between acids and $\ce{H2O}$ are favorable when the $\ce{A^{'}_{p}}$ of $\ce{H2O}$ is greater than the $\ce{A^{'}_{p}}$ of the conjugate base:

$\ce{ H2O (l) + HF (aq) -> H3O+ (aq) + F- (aq)}$

However, I have a few points I don't understand:

Why does the text consider the second reaction with $\ce{H2O}$? Doesn't $\ce{F-}$ act as a base in both reactions?
If both reactions occur and $\ce{F-}$ acts as a base, then which one is dominant?
If the first reaction is dominant, then how does it proceed given the low concentrations ($\ce{1 x 10^{-7} M}$) of $\ce{H3O+}$ in neutral water?


texts:
Is there a method in chemistry to alter the energy of atomic bonds by forcing atoms closer together in a smaller volume?
Similar to how pressure squeezes atoms closer together.


texts: Why magnesium has the lowest melting and boiling point in its group?

texts:
It is written in the third point ( shown in the picture) that presence of d orbitals results in stronger metallic bond.

1) We check the strength of metallic bonding to compare the melting and boiling point in case of metals. According to the general trend, melting and boiling point decreases down in the group( in s block) because the strength of metallic bonding decreases.

2) Presence of d orbitals decrease the size of atom thus increasing the electrostatic attraction between the delocalized electrons in the metal lattice and the cation and as a result, increasing metallic bonding. But magnesium IS IN A DIFFERENT PERIOD.

Can the ineffective shielding by d electrons be so much effective in decreasing the size of cation?

3) We didn't use any of this d orbital argument in comparing melting and boiling point of alkali metals. It decreased down the group following the expected trend.

How should  we explain this fact ?


texts: Calculating exposure time to inactivate coronavirus by UV light

texts:
Sorry for a layman question. I'm having difficulties understanding some basic math apparently.

According to a paper, for a coronavirus, the UVGI dose for 90% inactivation is 339–423 μW sec/cm2.

I have a UV lamp with the following specifications:

it's 15 watts
it takes 1h30 min to 90% inactivate coronavirus in a 20 square meters room with a 3-meter ceiling.

But that doesn't make any sense if you believe the paper's number.

This is how I calculate the necessary exposure time:

the surface of the floor, ceiling, and walls in the specified room is 94 square meters (or 940,000 square centimeters.)
15 watts is 15,000,000 microwatts
from the 339–423 μW sec/cm2 in the paper, take the highest number

So since our surface is 940,000 cm2, we multiply 423 * 940,000 and that gives us 397,620,000 μW sec/surface of the room.
Since our lamp is 15,000,000 microwatts, we divide 397 million by 15 million, and we get 26 (watts provided by our lamp) * sec/surface of the room.

So 26 seconds is the necessary time exposure, but it should be 5400 secs as specified in the manual. Is there an error somewhere?


texts:
Soap is made by a saponification reaction, where a fat reacts with hydroxide ions to form a surfactant and glycerol.

To make a solid soap $\ce{NaOH}$ is used, while $\ce{KOH}$ is used for liquid soaps.

I don't understand why the alkali metal has such a great impact on the state of matter. Usually the argumentation is based on intramolecular interactions, such as Van-der-Waals forces or hydrogen bonds, but if the same fat is used once with $\ce{NaOH}$ and once with $\ce{KOH}$ the resulting surfactants are basically the same, so the interactions shouldn't differ too much.

The only reason I could think of is the size of the alkali metal. Potassium has an atomic radius of 231 pm which is quite a bit more than the radius of sodium, being 186 pm. But why the atomic radius should have an impact on the state of matter of the soap is still unclear to me. Maybe I'm also completely wrong with this assumption.

A while ago, this question was already asked here on this forum, but I wonder if the given explanation is the only reason for the different state of matter. It's absolutely true, that the reactivity of the alkali metals increases from top to bottom, but can this solely explain the phenomenon? @rch provides the solubility of $\ce{NaOH}$ and $\ce{KOH}$ to back up his answer, but I don't think that this is sufficient. You cannot simply change the hydroxide ion by a fatty acid and assume, that there are no substantial amendments in the reaction behavior, can you?

Does anyone can explain this in more detail?


texts:
At school we do an experiment with baking soda and vinegar (in a cup) both sealed in a ziplock bag. The bag is masses on a triple beam balance (example 32.7 g). Bag is tilted to allow the vinegar and baking soda to mix.

The students note the signs of chemical reaction and mass the bag again. There is always a 0.3 g – 0.5 g loss of mass. How is this explained? Cheap ziplock bags? Is some of the mass from the endothermic reaction converted?


texts:
The title is more general than my particular question, in particular I bought a "allen key" and it broke after doing a lot of force with it trying to turn a hard screw.
In order to get a harder tool I need to know the material of this one. Tell me how to test if this allen key is chrome vanadium. If i should weight it, measure volume thus density, and this picture:

broken allen
The other broke like this, it deformed:

deformed allen key, because forcing

I want to be also a little educated on this topics: probably the tool is chrome vanadium but of low quality, or maybe it is extremely expensive or hard to test for me if the new tools I bought are of another material and if it's harder than the broken ones, the new ones are chrome vanadium and "stanley" (a corporation).


texts: How to detect if a beverage has Sucralose or aspartame?

texts:
There is a drink that claims to be sweetened with stevia, but I think I taste Sucralose in there even though it is not listed on the ingredients.

Is there any easy way I could test for the presence of Sucralose to confirm my hunch?

How about Aspartame?

By easy, I mean not needing access to something like a gas chromatograph.


texts: Why would the pH of a solution not be 7 at the equivalence point of an acid-base titration?

texts:
Is it because the new substance formed might be acidic/basic ?
The internet defines this point as when the number of moles of the acid equals the number of moles of the base. But if we have for example 1 mole of NaOH and 1 mole of H2SO4 (both in dilute solutions) mixed together, the resulting solution will still be acidic because 1 mole of H2SO4 releases 2 moles of H+ right ? So we will have an extra mole of H+ which will make the resulting mixture acidic. So is this still the equivalence point even though it isnt really equal (bcz we have 1 extra mole of H+) or is it 1 mole of NaOH + half a mole of H2SO4 ?


texts: How can I purify ethanol from formic / boric / salicylic acid?

texts:
I need some ethanol pure and strong enough for technical purposes (fuel, solvent, cleaning agent, dissolving rosin for soldering flux, etc.). Food quality is not required though, denaturated one is fine too. Distilling cheap vodka is possible, but even cheap vodka is expensive because of high tax on food ethanol; also now I don't have a distiller and want to try getting ethanol without building one. Pure denaturated ethanol is sold mostly in huge industrial bulks only. But we have extremely affordable 70% ethanol-based solutions in medicine stores - they are several-percent solutions of boric, formic and salicylic acids respectively. So, my question is: how can I turn these acids into precipitate or gas for easy removal, using not so exotic reagents and conditions?

UPD: I have realized my question may be ambiguous. Every substance I'm speaking about consists of alcohol + ONE of the three mentioned acids, not all of them together. I have a choice which acid I will be getting rid of.


texts: How to find the largest cyclic substructure with RDKit?

texts:
I have a bunch of structures and of each I would like to find the largest cyclic substructure.
I'm not a chemist, so I don't know if there is a common terminology for this. I hope, I made it clear what I'm looking for.
Example:

Each structure on the top (1,2,3) as input should return the bottom structure (4).
There is the rdkit.Chem.MCS module which will return the maximum common substructure of a set of molecules.
But that's not what I'm looking for.
Any ideas? And hints where or which module to look at...? Which term to search for?
I'm aware that there is a RDKit mailing list, however, I'm asking here first, because of the possibility to easily attach images. If nobody can help me here, I will try there. Maybe it already goes into "heavier" programming which then would be more a topic for StackOverflow.


texts: Safe endothermic reaction that gets below freezing?

texts:
I have a project/idea I am working on but I am only 14 years old and I need some help.

I'm looking for an endothermic reaction that gets below freezing, but the chemicals before the reaction and after the reaction is over are safe to touch and safe for the environment. The reaction can be harmful to plant life, but only for a short time before it decays or whatever needs to happen for it to be safe. I do not want it to have long term effects.

Additionally, two important parts are that these substances need to be easy to obtain and need to not to be a fertilizer.


texts: How does baseline correction affect the absorbance in UV-vis spectrophotometry?

texts:
I did experiments with UV-Vis spectrophotometer to obtain a set of wavelengths vs absorbance for various concentrations. I found that I missed one trial of different concentration and I needed to obtain the data for the trial I missed. I remade a baseline solution and obtain the data I want. I need to graph the data from the trial I missed with the rest of data that I obtained before. I wonder if baseline correction from the previous data has effects on my another trial that did not run at the same time. Although I use the same concentration of solution for baseline solution, it will not lead to exactly the same data with the other data I did before.

I wonder if the baseline correction affects the absorbance of my new data and can I compare the new data with the previous data that has the same concentration baseline but not run at the same time?


texts: I recently have purchased a high vacuum pump and am currently repairing it, the internals have a strong smell of oil. I was going to do an oil change anyway but should I clean all the old oil. High vacuum oil shouldn't have a smell because that would indicate out-gassing? Is that right?


texts: Nomenclature of complexes: Cyano vs Cyanido ; Chloro vs Chlorido

texts:
What is the correct nomenclature for $\ce{CN^-}$ and $\ce{Cl^-}$ ligands in coordination compounds?

Wikipedia says the coding name(?) as cyanido and chlorido while this suggests cyano and chloro.


texts:
I am being asked to compare the acidities of various compounds for an assignment, but I am confused about why butyric acid is a stronger acid than thiophenol/benzenethiol.
From what I was taught, I assumed the element effect (for elements in the same group on the periodic table) would take effect. Since sulfur is larger than oxygen and has a larger electron cloud to stabilize a negative charge, it has a more stable conjugate base and thus should be the stronger acid.
However, according to PubChem, $\mathrm{p}K_\mathrm{a} = 4.82$ for butyric acid, and $\mathrm{p}K_\mathrm{a} = 6.62$ for thiophenol.
What contributes to increased acidity of butyric acid? And why does it overrule the element effect?


texts: Equilibrium and Completeness of Reaction

texts:
In class we are currently learning about equilibrium and Le Chateliers principal. The principal makes sense but seems contrary to some other concepts. For example, using stoichiometry to calculate the mass of reactants for a certain amount of products. If we know the reaction is always going to equilibrium where the forward and reverse reactions are happening at the same rate, then how will the reaction ever be "complete" because according to the principal even if the reaction were to be complete and all the reactants were gone, the reverse reaction should be occurring. This is not the case in reactions like burning magnesium.

I'm guessing that not all reactions are reversible and that the principal is correct but in some cases it would take a long time to reach equilibrium.


texts: Gibbs free energy where T, V, and P change simultaneously

texts:
So $\Delta G = \Delta H - T\Delta S - S\Delta T$.

Is there a way to express $\Delta G$ for a process where T, V, and P change simultaneously only in terms of the initial and final T, V, P? Assume this process is for an ideal gas.

Since $G$ is a state function I can calculate it separately for an isothermal process and an isochoric process, but in that case $\Delta G$ for the isochoric process has dependence on the entropy of one of the states.


texts: Understanding reason behind existence of chemical equilibrium

texts:
Many chemistry reactions are reversible in nature.
In such reactions initially reactants react to form products but after some time products also react to give reactants back again. And an equilibrium is established where forward and backward reactions occur with equal rates.

If products are more stable, why will they react again to give reactants?


texts: I was doing an evaporation experiment and I used salt and water. I started off with 5 g of salt and after the evaporation process, I was only left with 4.3 g of salt. Why is this?


texts: What is there in an atom between the nucleus and electrons?

texts: As you can see the atom consists not only of the nucleus and electron but also of "empty space is the space empty or is their something else?


texts: In the open chain structure of glucose, one can identify 4 chiral carbon atoms but some sources consider the ring structure and then say that glucose has 5 chiral carbon atoms. If asked to state the number of chiral carbon atoms in glucose, which case should I consider?


texts: How does the presence of chlorine atoms in PVC make it flame resistant?

texts:
In a paper that I'm reading, it states that:

  The presence of chlorine atoms in polyvinyl chloride make it flame resistant

and I'm just wondering why the presence of chlorine atoms will make it flame resistant. To the best of my knowledge, burning something is just providing a material with enough activation energy such that it can react with oxygen to produce products such as carbon dioxide and water. If so why does the chlorine prevent this process in any way?


texts: In powder x rd, if the crystals are randomly oriented ,why then do we get Debye rings and not random patterns?

texts: In powder x-ray diffraction ,as I have learnt the sample is multi-crystalline.So if x-ray is diffracted through these randomly oriented crystal grains, aren't we supposed to get a random pattern?


texts: Gibbs Free Energy and Equlibrium Constant

texts:
I have some problems understanding the relationship between $\Delta$$G°$ and $K$. For example, in the reaction of $$\ce{N2 + H2 <=> 2NH3}$$ where $\Delta$$G°= - 33.5$ kJ/mol.

$\Delta$$G°=- 33.5$ kJ/mol is obtained from the $\sum G^°_{\text{f, products}} – \sum G^°_{\text{f, reactants}}$
. This means that the complete conversion of 1 molar of $N_2$ gas and 1 molar of $H_2$ gas gives 2 molars of $NH_3$ gives -33.5 kJ/mol of free energy. This is assuming that the reaction goes fully to completion, yet in reality it doesn't.

From this formula below

$\Delta{G^°} = –RT \ln K_p \tag{5-6}$

$K_p$ can be obtained as $7*   10^5$, assuming at 298K and 1 atm.  My question is, since the complete reaction corresponds to  $\Delta$$G°= - 33.5$ kJ/mol of free energy, why should there be $K$ in the first place? $- 33.5$ kJ/mol tells me this value is for the complete reaction, so why should we insert this value into the equation just to get $K$ which tells me otherwise that the reaction doesn't go to completion? It doesn't make sense to me? In fact, shouldn't have K be infinity since the value that we had inserted is one obtained for a complete reaction?

Also, from this equation $\Delta{G} = \Delta{G^°} + RT \ln Q \tag{5-5}$

does having 1 mol of $N_2$ , 1 mol of $H_2$ and 1 mols $NH_3$ of in the reaction correspond to $- 33.5$ kJ/mol, since that makes $Q = 1$? And since $Q$ slowly reaches the value of $K$,  $\Delta{G} = 0$, then  $- 33.5$ kJ of free energy must have corresponded from the initial state to the equlibrium state. Yet again to me this doesn't make sense, because my understanding is that $- 33.5$ kJ is a value obtained only for the ideal scenario that the reaction goes to completion, and not from its initial standard states to equilibrium.

How does this all work out?


texts:
The reaction of fluorine with water is very different from that of chlorine with water.
$$\ce{2F2 + 2(H2O)->O2 + 2HF}\tag1$$

$$\ce{Cl2 + H2O ->HCl + HOCl}\tag2$$

I want to understand two main things:

Why hypochlorous acid is formed in second reaction why doesn't it proceed like the first one?
Has it got to anything with reduction potentials? chlorine and oxygen are very close and is that reason?

I found  this where a related question was discussed here I expect the answer to describe what happens in reaction of any halogen with water and how does its reduction potential play a role in it also are $\ce{HOI}$ and $\ce{HOBr}$ also formed?


texts: reaction between copper metal and aqueous sodium bicarbonate

texts:
I wanted to know what reaction would occur between copper metal and sodium bicarbonate?

I believe that once in sodium bicarbonate solution, the copper metal will go into solution as copper ions and replace the sodium ions. Is this wrong?

Also, if it is indeed true, what would the reaction between copper ions and bicarbonate ions be?


texts: Pent-3-enal. In the structure of pent-3-enal, the third carbon atom has aldehyde group or double bond?  Also is the priority same for all other functional groups?


texts: How do you remove residual Lawesson's reagent after thionation?

texts: I am currently synthesizing a peptidomimetic bioisostere that replaces an oxygen with a sulfur. I use lawesson's reagent to achieve this, and althought the reaction works and despite running it through a column ( 80 mL silica, 10:1 DCM:MeOH) There is still a lot of residual lawesson's reagent left over. Does anyone have experience with this reagent and removing it? Any suggestions are appreciated


texts: Determining the rate equation from a reaction where one reactant is in excess

texts:
Lets say
rate = k[A][B]n
(A is in excess, lets say at a concentration of 50mM)

My data includes the initial concentration of B, and the initial rate of reaction at that concentration

I can rewrite the rate equation as as:
 rate = kapp[B]n

I then take the natural logarithm of this equation and plot a graph of ln(rate) against ln[B], the gradient will give me the value of n.

Am I right in thinking that the y intercept will give a value of kapp? And if it does, to determine the true rate constant do I just divide kapp by 50? If not, how do you determine the true rate constant?


texts: What kind of building materials could be synthesised from basalt?

texts:
Building tall cities is made possible by the invention of concrete with steel rebar which has much more tensile strength than any other massively available material that I am aware of. Cement (the most crucial ingredient) is made by processing limestone which is an organic rock formed from corral and skeletal remains.

Rocky "earth like" planets have no limestone (or coal or oil or any other organic material) but they do have allot of basalt. What kind of materials could you manufacture from basalt? Could you make materials that have enough tensile strength to build a city?


texts: Can salt and water be obtained from a reaction between a gas and an acid?

texts:
Is it possible to get salt and water (neutralization reaction) by reacting a gas and an acid?

I don't know if it's possible or not. I'm unable to find any examples in this regard.

Would anyone be able to provide an example in support of the question?


texts: Is there an error on Wikipedia's page on characteristic rotational temperature of HF?

texts:
I am referencing this article: https://en.wikipedia.org/wiki/Rotational_temperature
So, I see that $\theta _R = \frac{(h/2\pi)^2}{2Ik_b}$.
I took the value of $I$ from https://cccbdb.nist.gov/mieigen2x.asp.
However, when I do the calculations for $\theta _R$ by plugging in the numbers, I get
$$\theta _R = 46.8324 K$$
not $30.2K$.
Here is my Mathematica snippet

My question is, has Wikipedia gone wrong, or am I messing this up somewhere?


texts: Find number grams of the solute in a dissolution given its density and Molarity

texts:
Have a dissolution of $\ce{HNO_3}$ in water. The density is
  $1.42\ce{g/mL}$ with a concentration of $\ce{16M}$. What is the
  concentration in % mass/mass?

Alright. So the % mass/mass is expressed as

$$\frac{\text{grams of } \ce{HNO_3}}{\text{grams of the dissolution}}\cdot100$$

So I need to find the grams of $\ce{HNO_3}$ first. They tell me that the Molarity is

$$16 = \frac{\text{moles of } \ce{HNO_3}}{\text{liters of dissolution}}$$

$\ce{HNO_3}$ has a molar mass of $63$. So to find out how many moles of $\ce{HNO_3}$ are in the dissolution I need to divide the grams of $\ce{HNO_3}$ by $63$... But how am I supposed to find out the grams of $\ce{HNO_3}$?

I was told that the numerator is $63$. But... $63$ is the molar mass of $\ce{HNO_3}$, not the number of moles of $\ce{HNO_3}$ in the dissolution.

Anyway, let's suppose that it is indeed $63$. Therefore

$$16 = \frac{63}{\text{liters of dissolution}} \implies \text{liters of dissolution} = 3.9$$

So there are $3.9$ liters of dissolution? I'm not sure - I feel like I got this all wrong. How do you know there are $63$ moles of $\ce{HNO_3}$?


texts: How can I measure amount of ozone byproduct coming out of hydroxyl generator

texts:
A Hydroxyl generator releases hydroxyl radicals into the air to neutralize odors and kill mold.

Most hydroxyl generators also release some amount of ozone as a byproduct. How much ozone is released varies from one hydroxyl generator to the next.

Hydroxyl is supposed to be safe to use in occupied premises. Large amounts of ozone are not.

How can I measure the amount of ozone released by my hydroxyl generator?


texts:
I need to create a figure of a molecule in which the bonds are colored in a RGB scale according to the values read from a data file. The data file contains, for example, the increase or decrease in the bond length compared to some reference structure. In this way, the intensity in a color range red-white-blue would be given by the difference between the relaxed and unrelaxed bond lengths, similarly to the figure attached.

I have tried to make this figure using jmol, but I didn't have success so far. Could anyone suggest a program that is able to do such figure? Or could someone point out any suggestion of how to do this color maps on chemical bonds?

I will be grateful for any help you can provide.

All the best


texts: Do lithium and beryllium want to lose electrons to be like helium?

texts: I can't seem to remember. I know that they all want to fill their valence shells, but, aren't these different?


texts: I was doing a little research on the Chemistry of water, and it said that water molecules have a hydrogen bond between them. What is it, and what does it do to water?