texts: Q-chem equivalent solvent settings for Gaussian NMR ab inito methods

texts:
I'm attempting to use Q-Chem 5.0 to replicate CHESHIRE-esque  http://cheshirenmr.info/ ab initio calculations of chemical shift values. Unfortunately Gaussian seems to be the predominant tool in this space, and translating from Gaussian16 to Q-Chem is quite a challenge with respect to the solvent model. Currently, just to debug, I am

Performing geometry optimization in Gaussian B3LYP/6-31+G(d,p)
(gas phase)
Using those geometries in both Gaussian mPW1PW91/6-311+G(2d,p)
(giao, scrf) and Q-Chem. For Gaussian, the solvent setting is
scrf=(solvent=chloroform,smd).

For step #2, both agree in the gas phase (to within 3 digits!) but in solvent I get very different answers (Q-Chem is off by ~3ppm in 13C vs Gaussian's 2.1ppm for my dataset.) I think this suggests that I am using the Q-Chem solvent model wrong, which is considerably more complex than what Gaussian seems to expose.

For a start, I have been using:

$rem
BASIS  6-311G**
METHOD  mPW1PW91
JOBTYPE  NMR
SOLVENT_METHOD  smd
$end

$smx
solvent  trichloromethane
$end

in my solvent settings for Q-chem, with the above results. Can anyone recommend a set of Q-chem solvent settings that might yield more accurate chemical shift values and approximate whatever Gaussian's solvent model is doing? I'm also totally open to a different set of best-practices for Q-chem.


texts:
I am working on my scholarship exam practice (around high school and first year university level). I could actually solve the problem below but my solution is pretty time consuming. It would be appreciated if I could find other aspects in solving this.

  Exactly $\pu{4.32 g}$ of oxygen gas was required to completely burn a $\pu{2.16 g}$ sample of a mixture of methanol and ethanol. How many moles of ethanol are contained in the sample? (Answer: $\pu{0.04 mol})$

What I did is setting $x$ and $y$ as the mass of methanol and ethanol, respectively. Then I formed 2 equations. First one was $(x + y = \pu{2.16 g})$ and another was the equation $(3x/64 + 3y/46 = \pu{0.135 mol})$ from the number of moles of oxygen gas, derived from two complete combustion equations. And then I solved simultaneous equations. I am wondering if this was the only way to solve this problem. If you think differently, please let me know.


texts: Potassium chlorate from potassium chloride and hydrogen peroxide

texts: Why can't you make potassium chlorate using the chloride anion from the potassium chloride and having oxygen bond with it from hydrogen peroxide?


texts: Where the equibrium will shift when we add one mole to both reactants and products in PCl5 giving PCl3 and Cl2

texts: I know that if we add 1 mole to reactant side then the reaction will shift forward and if on product side the it will shift backward according to Le Chatelier's principle.Then what will  happen if I add 1 mole on both sides?Please explain.


texts: What happens when the amount given doesn't allow for equilbrium to be achieved in a reaction?

texts:
The reaction $$\ce{A.3H2O(s) <=> A.H2O(s) + 2H2O (g)}$$ has a $K_p = \pu{400 mmHg2}$
One millimole each of $\ce{A.3H2O}$ and $\ce{A.H2O}$ are taken in a $\pu{1 liter}$ container at $\pu{300 K}$
Relative humidity is $80 \%$ and saturation water vapor pressure is $\pu{85 mm Hg}$ at $\pu{300 K}$. Find the final composition of the container

My attempt
\begin{align}
K_p &=(P_\ce{H2O})^2 = 400 \\
\therefore P_\ce{H2O} &= \pu{20 mm Hg}
\end{align}
Now,
\begin{array}{lc} \hline
\ce{&A.3H2O &<=> &A.H2O &+ &2H2O(g)} \\ \hline
i &1\times10^{-3} && 1 \times10^{-3} && \pu{68 mm Hg} \\
c &+x && -x && -P \\
e &2\times10^{-3} && 0 && \pu{30 mm Hg} \\ \hline
\end{array}
$\pu{38 mm Hg}$ drops because $\pu{2 millimoles}$ of water vapor was consumed
$$ P=\frac{1}{12}\frac{300\times 2\times 10^{-3}}{1} = \pu{38 mm Hg}$$
The answer should have been $\pu{20 mm Hg}$ pressure of water vapor but I am afraid there isn't enough reactant to make that much vapor pressure.
I asked a friend and he suggested that we can take $\pu{2 millimoles}$ each of the reactants as they are solid and don't influence the $K_p$ expressions while also not influencing the ratio of the added moles.
I do not get why this can be done but this allows for the vapor pressure at equilibrium to become $\pu{20 mm Hg}$ as required


texts: what contributes to the temperature of a vacuum

texts: what is the temperature of Vacuum since temperature of a system is related to the average of the molecular kinetic energy and there is no molecule in a vacuum? i know there could be radiations but i want to know how much the contribution is?


texts: Question about the Law of Definite Proportions

texts:
If we know that:

$1g$ of carbon + $1.33g$ of oxygen = carbon monoxide

$1g$ of carbon + $2.66g$ of oxygen = carbon dioxide

My question is: why is that in the second case where we doubled the amount of oxygen we don't get double the amount of the first case (2 times carbon monoxide)

Or why don't we get the same amount of carbon monoxide and the remaining mass of the products is simply oxygen that didn't form any bonds.

Basically, what forces the reaction to occur in a certain way just because the proportions are different but the elements are the same.


texts: How should I construct the orbitals of dilithium using only pen and paper?

texts:
For a week I have lessons about quantum chemistry and I have a trouble understanding how to arrive at the good answer for the drawing of the orbital $(\ce{III})$ for $\ce{Li2}$ (see the second picture).

In the first picture I did an example of my reasoning with a basic molecule such as $\ce{LiH}$ just to show you how I figure it must work.

And in case someone would like to mention it, yes I haven't drawn the $\mathrm{p}_x$ and $\mathrm{p}_y$ orbitals because it is not the point here.

With LiH

With $\ce{Li}_2$

The question is on this last picture, if you have trouble to read tell me.


texts:
Fedorov et al. assign the $^1$H-NMR ($\ce{CDCl3}$) chemical shifts of the $\ce{CH2}$ group in 2-(bromomethyl)phenylboronic acid

to three singlets at $4.75$, $5.09$ and $5.15~\ce{ppm}$ in a ratio of $3:3:14$.

Can someone explain their reasoning?


texts: What is the reason for colour in 2,4-Dinitrophenylhydrazine derivatives?

texts:
2,4-Dinitrophenylhydrazine is an important laboratory reagent for the detection of Carbonyl (C=O) group. It reacts with Carbonyl group by the typical Nucleophilic Addition-Elimination reaction and if positive the test results in the formation of bright yellow orange coloured derivatives.

I was reading from a source and it says the reason for showing color is -"Extended conjugation". Okay that may be the reason but what exactly happens that they look such beautiful bright yellow, orange solids ?


texts:
I know that acidity of an acid increases across a period (with electronegativity increase of the atom bonded to hydrogen) and hence $\ce{HF}$ is more acidic than $\ce{H2O}$ or $\ce{NH3}$. But the reason I learnt it is this way, is that difference in electronegativities of the atoms increases and hence bond becomes more polar and weaker (hence easier to donate a proton).

But shouldn't bond strength increase with difference in electronegativities? Also bond length of $\ce{HF}$ is shorter than that of $\ce{H2O}$ ($\pu{92 pm}$ vs $\pu{96 pm}$) and bond enthalpy of $\ce{HF}$ is $\pu{565kJ/mol}$ as opposed to $\pu{490kJ/mol}$ of water. Isn't this contradictory? Why is $\ce{HF}$ still more acidic than $\ce{H2O}$?
Is it because  the conjugate base of $\ce{HF}$ is highly solvated and more stable in an aqueous solution?  Is there not a direct correlation between ease of bond dissociation and acidity?

P.S.: I understand the acidic trend down the group (stability of conjugate base increases and since the halogen atom becomes bigger, resulting in weaker bonds).


texts: Oscillator Strength and Absorption Intensity in TDDFT

texts:
When I run a linear-response time-dependent DFT calculation in my favourite electronic structure program, for each excitation I'm given an oscillator strength, $f_i$, and transition dipole moment $$\boldsymbol{\mu}_i = \int\Psi_0\hat{\mu}\Psi_i \text{d} \bf{r}$$
What formulae relates the transition dipole moments, the oscillator strength and the observed absorption relative intensity?
And more specifically, how can I calculate the relative experimental intensity of TDDFT transitions from the oscillator strengths and transition dipole moments?


texts:
$$\log_{10}~\mathrm{pg}/\mathrm{ml}$$

I do not understand the scale.  How do I convert this to a standard concentration (without the logs)?


texts: How does hyperconjugation in alkenes affect bond lengths?

texts:
I understand how the diagram below results in hyperconjugation stabilising alkenes.

Essentially, the C-H sigma bonding orbital interacts with the pi bonding orbitals creating two molecular orbitals. It also interacts weakly with the pi* orbital which lowers the energy of psi 1 and 2 stabilising the system.

What I do not understand is the effect this has on bond lengths. We have done a computational investigation in the lab and have found that both the C-H and C-C bonds are weaker, while the C-C bond between the double bond and the alkyl substituent is stronger. I don't understand why.

I have received an explanation for this phenomenon using resonance structures, but I am really looking to understand how to reconcile these observations with the MO diagram above.


texts:
While comparing the relative stabilities of acetic acid and formic acid why don't we consider the 3 possible hyper conjugative structures which would stabilize the positive charge on carbon thus making the conjugate of acetic acid more stable.

My professor told me hyper conjugation does not operate here. But what is the reason behind this?


texts: Specific heat capacity and the periodic table

texts:
Can someone explain me how can I use the periodic table in order to find the specific heat capacities of some elements? (for example, of Aluminium )
The question I have encountered is as follows:

Given the specific heat capacities of the following liquids, use the periodic table in order to find the specific heat capacities of the metals $Al, Fe, Cu, Au $ .
$ H_2 O - 4.18 J  /g \cdot C $, $ C_2 H_5 OH - 2.46 $ , $CCl_4 - 0.861 $ , $CCl_2 F_2 - 0.598 $ .


texts: How does bismuth's lone pair affect its properties as a metal and alloy?

texts: Bismuth is really the only metal to exhibit a lone pair in its outermost shell, this means that it and its salts should be a Lewis base. As bismuth can act as a Lewis base, how does this affect its properties as a metal specifically in regards to alloying? For instance, if I have a 1:1 mole ratio of aluminum and bismuth in an alloy, will the aluminum and bismuth form dative bonds?


texts: What is the binding mode of the ligand in complexes with quadruple metal-metal bonds?

texts:
I'm wondering which atomic orbital is left in a complex with quadruple metal-metal bond to bind the steric ligand, since all d orbitals except the x2-y2 are used for the metal-metal bonds?

or is it the x2-y2 atomic orbital that forms the bonding?

and if so: what atomic orbital is used in metal-metal quintuple complexes?

Here is an example complex: https://en.wikipedia.org/wiki/Quintuple_bond


texts: Fatty Acid synthesis - enzymes that vertebrates cannot make

texts: In the fatty acid elongation and desaturation reactions, how are enzymes that insert double bonds after the 9th carbon different from those that insert  at the 9th or before? Vertebrates (at least mammals) don't have these enzymes.


texts: Any way that I can extract sugar from drinks? Without boiling the drinks

texts:
Any method? Materials, engineering, any technology.
I am a product design student, so any possible method is useful to me.
I am thinking to add this kind of technology into my concept.


texts: Why does magnesium have the lowest melting point of all earth alkalis?

texts: Why does magnesium have the lowest melting point of all earth alkali metals?


texts:
My friends and I were talking casually about electrolysis, fuel cells, and whatnots when the following question arose:

Is $\ce{H2 (g) -> 2H+ (aq) + 2e-}$ endothermic or exothermic?

I have the following questions (by the way I am a physicist):

Is the reaction sensible? (I think it probably is, but no one is sure.)
I said the reaction was endothermic, with the following reasoning. According to this table, the standard enthalpy change of formation $\Delta H_\text{f}º$ of the reactant is zero, so if $\Delta H_\text{f}º$ of the products are positive then the reaction is endothermic.

Electrons are fundamental particles so their $\Delta H_\text{f}º$ is zero. As for $\ce{H+ (aq)}$, its $\Delta H_\text{f}º$ is the atomization enthalpy of hydrogen (218 kJ/mol [ref]) + ionization enthalpy (first ionisation energy: 1312 kJ/mol [ref]) + proton hydration enthalpy (-1150 kJ/mol [ref]). Therefore,

$2 \Delta H_\text{f}º[\ce{H+ (aq)}]$ = 2 (218 + 1312 - 1150) kJ/mol = 760 kJ/mol

which is a positive number, so the reaction is indeed endothermic. Am I right?


texts:
I know that the elements H, N, F, O, I, Cl, and Br are found naturally as diatomic gases. But can any other elements be found as diatomic gases, or even solids or liquids.

Why or why not?


texts: How is chirality center defined for an atom with 5 substituents?

texts:
I understand that carbon atoms normally only have up to 4 substituents and the R and S chirality centers are defined for 4 substituents. Is there a similar convention of 'chirality' for an atom with 5 substituents?
The SMILES website (section 3.3.4 General Chiral Specification) shows that general 'chirality' for 5 and 6 substituents exists. But the text there focuses on how to convert them to SMILES strings. Is there any references about the classifications and nomenclatures?
https://www.daylight.com/dayhtml/doc/theory/theory.smiles.html
Sorry I am not a chemistry major and my nomenclature may not be correct.


texts:
Did I name the functional groups that are present in the following molecules correctly?  All I was given is the picture below. I have drawn my attempt in the picture.

Edit1: response to k--

Edit2: response to Mithoron


texts: Why does reduction always accompany oxidation and vice versa?

texts: We've all learnt that the reduction always accompanies oxidation and vice versa Why is this so? Why is it not possible that a species releases an electron and the electron just "floats around"? Is this related to the stability of a free electron?


texts: Why is potassium permanganate used to kill mollusks?

texts: I know that potassium permanganate is used as a disinfectant for bacteria. Permanganate acts as a strong oxidizing agent that can rip the electrons off of bacterial cell membranes, resulting in a disruption that can lead to death. I've also read that potassium permanganate can be used as an oxidizing agent to kill mollusks (source: http://www.chemistry.wustl.edu/~edudev/LabTutorials/Water/PublicWaterSupply/PublicWaterSupply.html). I've tried looking into it and I can't find anything helpful. Does permanganate kill mollusks in the same way? If that is the case, will the disruption of the outer cells of the mollusks really kill the whole organism? Any insights would be helpful, thanks in advance!


texts: Chiral centers in albuterol-like compounds

texts:
My question is apart from the C in the straight chain with $\ce{-OH}$ group, should $\ce{N}$ be counted as chiral center since it also has tetrahedral geometry and all different substituents?

There are more such examples.


texts: Determine compound acidity based on structure

texts:
In an exercise I have the following structures

Moclobemide:

Paracetamol:

Hexobarbital:

I know for example by heart that paracetamol is an acid. What is the best approach in determination of acidity of a compound based on it's structure?

I'd like to know for example if these compounds are:

Basic
Acidic
Amphoteric

I know for example that many metals (Zn, Pb, etc) can be amphoteric (act as $H^+$ donors or acceptors). But I don't know how to determine what a complex structure is.

Please offer a detailed explanation, with links if possible.

Best Regards,


texts: Are there any organic compounds that do NOT contain hydrogen ? And if so, what are they?

texts: Organic compounds are typically defined as compounds containing carbon and nearly all contain hydrogen as well. Which organic compounds do not contain hydrogen?


texts:
In Grossman, The Art of Writing Reasonable Organic Reaction Mechanisms, he provides the following explanation. The question asks to explain why the difference in pKa values between PhSH and EtSH is much smaller than PhOH and EtOH. In the solutions manual he writes:

Why is p orbital overlap dispositive for the strength of resonance stabilization exactly? I don't get it.
Furthermore, is this something I can simply take for granted about
the size of atoms or does this derive from a more general
principle about orbital overlap it would be useful to take forward?
In other words, its there a way I may have deduced this from
something else?
Could you show me any other and perhaps trickier examples where p orbital overlap modulates resonance structures in this way, in terms
of size or otherwise? I'm just always looking for more practice
material that's out of my wheelhouse so I can get exposure. Thanks
guys.


texts: Is silicon dioxide more acidic than the oxides of nitrogen? How to find acidic strength of compounds which don't have hydrogen atoms?


texts:
Hexamethylene triperoxide diamine, "Hex" for short, is an explosive organic compound.

I want to know the products of this reaction:

$$\ce{C_6H_{12}N_2O_6 -> ? + Energy}$$


texts: Migration of ethyl group in pinacol rearrangement

texts: For this substrate, will the methyl or ethyl group migrate preferentially? I know that the migratory aptitude of Et is greater than that of Me, but I saw a lecture where the prof said migrating Et will break the bonds and that only shifting of Me is possible. Is it right? What will be the product formed?


texts:
At what conditions does equilibrium attain in the galvanic cell. What exactly happens at the equilibrium state of a galvanic cell redox reaction.
Consider the setup Zn|Zn2+||Cu2+|Cu,
   Where

Anode: $\ce{Zn -> Zn^2+ + 2e}$
Cathode: $\ce{Cu^2+ + 2e -> Cu}$
Final reaction: $\ce{Zn + Cu^2+  -> Zn^2+ + Cu}$

Here the electrons would flow from Anode to cathode through a metallic wire which connects the two half cells.
There comes a stage where the $\ce{Zn^2+}$ ions get piled up in anode compartment and depletion of $\ce{Cu^2+}$ ions in the cathode compartment. At one stage the reaction stops which is when the cell/battery power is all utilised.
But where does the equilibrium state come from?
Will the equilibrium reaction occur when the salt bridge is connected?
The reason I stressed more on equilibrium state is because of the equilibrium constant appearing in the Nernst equation. I'm pretty much in  a confused state reagarding the concept.
Any help would be greatly appreciated.


texts:
I want to understand the basics of biochemistry, from a physicist point of view. I am looking for a textbook that discusses things like the covalent bond and the oxidation number, starting from first principles (quantum mechanics), and builds up to explain things like why ATP is an energetic currency of metabolism, the organization of glycolysis, and oxidative phosphorylation. Of course I do not expect to have detailed mathematical derivations of all of these. But I do want to end up with a firm grasp of the physical principles involved.

Maybe there is single textbook covering these areas, so I would also appreciate suggestions to build a "reading-list", which can include classic papers.

Thanks.


texts: What is the difference between TIC and TICC?

texts:
I have picked up a textbook on mass spectrometry, and I am finding it did not clearly distinguish between total ion chromatogram (TIC) and total ion current chromatogram (TICC) in the section (1.3 Ion Chromatograms) I just read. I suspect there was some sort of typo, but I don't have the experience to tell yet.

Here is an abridged excerpt from the textbook that has confused me:

  The total ion current (TIC) can either be measured by a hardware TIC
  monitor before mass analysis (nA to uA range), or its equivalent can
  be reconstructed or extracted after mass analysis. [...] Thus, the TIC
  represents a measure of the overall intensity  of ion production of
  ion production or of mass spectral output as a function of time,
  respectively. The TIC obtained by means of data reduction, [...], is
  termed total ion chromatogram (TIC). The term total ion current
  chromatogram (TICC) refers to a chromatogram obtained by plotting the
  total ion detected in each of a series of mass spectra recorded as a
  function of retention times of the chromatographically separated
  components of a mixture (which is essentially implicated by: TIC).

I would like to an explanation of the difference between total ion chromatogram (TIC), and total ion current chromatogram (TICC).


texts: Why are conductance and conductivity additive in nature?

texts:
In my book, it is written that:
$κ_{electrolytic solution} = κ_{electrolyte} + κ_{solvent}$
$G_{electrolytic solution} = G_{electrolyte} + G_{solvent}$
Where $κ$ and $ G$ are conductivity and conductance respectively. But why are conductance and conductivity additive in nature? Why is it that we can simply add conductance and conductivity? What is the proof of the above two expressions? Can someone please provide an explanation for the above? I am so confused. Please help.


texts: Mechanism: explanation of final step in synthesis of the thyroid hormones (T4, T3)

texts: In the following mechanism for the synthesis of T3 (triiodothyronine) on thyroglobulin, what are the factors causing the last step to occur? Does it have something to do with the electron density of the intermediate and/or bond strength? (NB thyroperoxidase abstracts the electrons in the first step so I don't know if it's involved much in the last step)


texts: Effect of oxidation aluminium reflectivity

texts:
Aluminium is a fairly good reflector, but oxidation will reduce it's optical reflective properties.

Aluminium is used for reflectors either being deposited on a substrate, or polished and protected by a protective layer to avoid oxidation.

How will the oxide layer of a several year exposed polished aluminium (indoor) will impact the reflectivity.

Will it be considerable or minimal ?


texts: Analysis of methylphenidate (Ritalin) HCl extended release tablets

texts: For a project I have to determine the drug concentration release profile of self-made methylphenidate HCl (MHCl) extended release tablets (hydrophilic matrix). We are thus doing a dissolution test as described conform the US/Eur. Pharmacopeia. However a problem we are facing is that we are not sure how to analyse the samples that we take from the dissolution test. This is because we are not sure what detection method to use. The problem is that we cannot directly get the right concentration for our primary detection method which is UV spectrophotometry. This is because MHCl has a very low extinction coefficient and thus a relatively higher concentration is needed to get the measurable absorption range of 0.2-0.8, but since the tablet dose is only 18 mg this is difficult to accomplish. We thought of doing two things: a solid phase extraction followed by UV or picric acid ionpairing followed by colorimetry. We asked our professor if the SPE followed by UV was possible, but he said that in this case it wasnt practical cause of the such low amount of drug in the tablets. So that leaves us with the picric acid analysis method. Problem is that we havent ever performed a colorimetric analysis before, though it looks pretty similar to spectrophotometric. From what we understand we need to measure the absorbance at a specific wavelength that the picric acid-MHCl complex is absorbing at. But how can we calculate the MHCl concentration from this? How much picric acid do we need to use to know for sure that all the MHCl has formed pairs with the picric acid? It's kind of confusing still and appreciate it if anyone could point us to some literature or give us insight on how to analyse these samples. Thanks in advance.


texts:
I would like to make colloidal silver to kill mold. I think $\pu{100ppm}$ (weight) would be nice. I read a paper on it and in it they used citric acid + distilled water as fluid, two silver plates as electrodes, $\pu{300v}$ ($\pu{50Hz}$ Ac to reduce oxide buildup on electrodes), $\ce{N2H2}$ as reducing agent and a surfactant to encapsulate the uncharged $\ce{Ag}$ particles to prevent them from clotting and building aggregates.

I would like to make something similar. So I have a couple of questions:

About the electrolysis: Is there a problem with making the distance between the electrodes larger? In the paper, there was a distance of $\pu{2cm}$ between the electrodes. I'm planing on having perhaps $\pu{20-30 cm}$. What would be the impact?

Suggestion on alternative reducing agent for $\ce{Ag+}$ ions: Preferably something that is nontoxic and does not promote mold. I have heard of tannic acid and ammonia. Could it work? In the best of world, I would like a reducing agent that evaporate from the solution. It needs to work in a electrolysis environment of $\pu{240-300V}$ AC without contaminating the electrodes. Is there a way to calculate which reducing agent would work?

Why do they use citric acid in the water if it is to allow conductivity in the beginning? Could I omit it? If all the $\ce{Ag}$ particles are reduced to be without charge then the water will not conduct? I think I need it. Correct me if I'm wrong.

About surfactants: Could I use ordinary soap? But I do not think I need it since I'm not after a specific size and I think the $\pu{100ppm}$ solution is not saturated and hence the particles do not grow that much. Is there a way of measuring the $\pu{ppm}$ of uncharged species in a non lab environment or the best way is trough weighing the plates before and after electrolysis?


texts: How deep does a counter electrode need to penetrate the solution in electrochemical experiments?

texts: I ordered platinum-wire counter electrodes that are shorter than I was expecting. How much should it be submerged in my solution (right now it is only the tip that is submerged)? My experiment is hydrogen permeation using an H-cell with counter and reference electrodes in each side and my working electrode in the middle. My solution is 1 M NaOH. Should I order longer electrodes? How do I know if it is submerged enough?


texts: Syntactic vs Semantic validity of molecular graphs

texts:
While reading this paper on molecular graph generators using deep learning algorithms, I encountered the terms syntactically and semantically valid molecular graphs:

  $\dots$ to ensure the generation of syntactically and semantically valid
  graphs.

The output molecular graph should at least satisfy the following constraints:

Valency: Number of incident edges to an atom shall not exceed the valency of the atom on that node
Connectivity: The output graph should be a single connected graph.

I was wondering what semantic and syntactic validity means in this context? Which type are each of these constraints?

Some concepts from computer science:

  Syntax is the structure or form of expressions, statements, and
  program units but Semantics is the meaning of those expressions,
  statements, and program units.

But I can't make an exact connection to molecular graph's case. Also,

  In computer science, the syntax of a computer language is the set of
  rules that defines the combinations of symbols that are considered to
  be a correctly structured document or fragment in that language

Then, valency and connectivity, unlike the linked paper in the answer below, should be syntactic constraints.


texts: Why is it possible, that an equilibrium shifts?

texts:
So in class, I've learned about Equilibrium. So it is basically when the rate of the reverse and the forward reaction are the same. So I was like that sounds pretty easy, I can understand this. And then suddenly there was a twist (there always is in class). The teacher was like: so if you increase or add a stressor, the equilibrium will shift to stop it. How can equilibrium shift, I thought it was a concept not a "thing" to move up or down. Is it because it shifts to maintain the Equilibrium Constant?

I do not understand this. If this question has already been asked then please point me to that. I have even searched online and could not find an explanation in layman's terms.


texts: Why doesn't fluorine harm the ozone layer the way chlorine and bromine do?

texts:
I don't understand the chemistry here: fluorine is a halogen too.
I read that fluorine in the atmosphere readily forms HF, which is (somewhat) stable and doesn't catalytically break down ozone.
But, shouldn't loose chlorine in the atmosphere form HCl similarly?


texts: So, we have the Freundlich's Isotherm equation as $\frac{x}{m} = kp^{\frac{1}n}$, where the LHS measures the extent of adsorption with the corresponding pressure $p$ in the RHS with the two constants, $k$ and $n > 1$. But, I got a little confused with the dimensions on both the sides. Since $\frac{x}{m}$ is dimensionless, so should be the RHS. Therefore, I reasoned that the constant $k$ having units should cancel out the units of $p^{\frac{1}n}$. But yet I'm confused, and I don't think its right. What is going on?


texts:
Firstly, note that this is not a duplicate of Acid in Imine Formation. Clayden, Warren, & Greeves (2012) states explicitly on p. 231 that imine formation requires acid catalysis, and that the reaction takes place optimally under slightly acidic conditions, close to neutrality. This makes sense as we need to form the $\ce {-OH2^+}$ allowing water to leave. However, if we look at this list of literature, we would observe that most of the imine formation reactions do not necessarily require acidic conditions and some even take place under solely basic conditions. How do we explain this?

Reference

Clayden, J., Greeves, N., & Warren, S. (2012). Organic Chemistry (2nd ed.). New York : Oxford University Press Inc.


texts: What type of FDA process does a 222nm Kr-Cl excimer UV-C light have to go through

texts: There are plenty of articles and preliminary research about this type of light being able to kill virus as effectively as 254nm UVC light, but not harmful to human skin and eye. This is wonderful news to the current mess created by COVID-19. Not sure whether there are companies already applying for FDA approval, and what kind of process does it need to go through which will basically translate to how long we have to wait to see this available?


texts:
Question: Which of the following does not form a stable hydrate?

I think they mean nucleophilic addition of water. For compound (C), on reaction with water, the product formed is

The product has lesser bond angle strain than the reactant. Hence, the compound formed is stable. This is because $\ce{sp^2}$ hybridised carbonyl carbon requires $120^{\circ}$ but only gets $60^{\circ}$ in cyclopropanone. But converting it into a diol makes the angle $109^{\circ}$ which reduces strain to a large extent. In fact, cyclobutanone is also reactive to water.

For (B) however, there is not much change in the bond angle strain. The initial angle is already close to the required angle.

What can I say about (A) and (D)?


texts: What do you call acids that can disassociate more than 1 H+? Is it like Class n acids for acids that can disassociate n H+?


texts:
How to determine the oxidation states of the metal atoms when both cation and anion are coordination complexes?

For example, how to determine the oxidation states of $\ce{Pt}$ in the following compound?:

$[\ce{Pt(NH3)4}][\ce{PtCl6}]$


texts:
I was thinking about galvanic cells the other afternoon and I was wondering the situation
if a chemical engineer designs a galvanic cell using copper and zinc as electrodes, what would the structure, function and output voltage of the cell be, and how might you possibly increase the voltage?


texts: Reaction of 2,3-dichlorobutanoate with a decarboxylating agent followed by hydrochloric acid and then aq. potassium hydroxide

texts:
Question

$$\ce{CH3-CH(Cl)-CH(Cl)-COO- ->[-CO2]A->[HCl]B->[aq KOH]C}$$ Product C is:
a) $\ce{CH3-CH2-CHO}$
b) $\ce{CH3-CH(OH)-CH2-CH2-OH}$
c) $\ce{CH3-CHO}$
d)$\ce{CH3-C(=O)-CH3}$

Answer

 The answer given is (a)

My attempt

Where did I go wrong?


texts: Why are hydrogenation reactions exothermic?

texts: I learned that all reactions that yield hydrogen are endothermic (such has reforming) and reactions that use up hydrogen are exothermic (FCC cracking, hydrogenation, etc.). But why is this so? I know what exothermicity/endothermicity means, but I haven't found a specific explanation for the correlation with hydrogen generation or consumption yet.


texts: CIF fields that are available for some atoms, but not others

texts:
I've been working on another CIF file, this time for (-)-threo-methylphenidate based on Pharma Res, 1995 (sadly the relevant crystallography data isn't supplied in the free preview at Springer). I have several questions relating to this file, the most pressing is that so far I have this loop:

loop_
_atom_site_label
_atom_site_chemical_conn_number
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
_atom_site_adp_type
_atom_site_B_iso_or_equiv
_atom_site_type_symbol
N1   1    -0.8852(9) 0.120(1)   -1.0300(8) Biso 3.1(2) N
H1a  2    -0.9650000 0.08500000 -1.0010000             H
H1b  3    -0.8800000 -0.0800000 -1.0330000             H
C2   4    -0.739(1)  0.049(2)   -0.940(1)  Biso 3.9(2) C
H2   5    -0.7460000 -0.0800000 -0.9360000             H
C3   6    -0.614(1)  0.092(1)   -0.988(1)  Biso 5.1(3) C

that is generating this error in enCIFer:

Too many or too few data values in the loop

which I'm going to take a stab in the dark and say that it's because two fields (Biso & $B_{eq}$ value) aren't supplied for each atom in this loop (namely it is missing from the hydrogen atoms). The problem is that the paper I cited didn't specify these for hydrogen atoms. Should I use separate loops for hydrogen & other atoms (i.e., one loop for hydrogens, another for the other atoms)? I ask because I fear that this might make molecular modelling software treat the hydrogens & the other atoms as being part of separate molecules.


texts: Is there a specific chemical property or concept that explains/predicts the triboelectric series?

texts: Is there a chemical property (perhaps electron affinity?) that can be used to predict where a substance would fall in a triboelectric series such as this one? Or would the cause of the charge imbalance vary on a case by case basis?


texts: Comparison between Molecular Orbital Theory and Valence Bond Theory

texts:
I have been reading about introductory Molecular Orbital Theory lately. Till now, I have used Valence Bond Theory to evaluate bonding. I have a few questions about it:-

In VBT, we used the idea that bonds form when orbitals overlap. In Oxygen molecule, two bonds forms in VBT as the other orbitals were far enough to not overlap . But in MOT we say that all the orbitals overlap to form new MOs. Aren't the two statements contradictory?

In Coordination Compounds, when we study about non-classical $\pi$-acceptor ligands,we say that Bond Order of the ligand decreases when it receives electron pair from transition metal in its Anti-Bonding orbital. However, if I try to use VBT for the same, I feel that Bond Order should increase or at least remain the same as any kind of overlapping leads to stability in VBT. Where am I wrong?

Please try to explain the matter without using complex mathematics.


texts: Can I remove flesh from seeds with hydrochloric acid?

texts: I have some crenellated seeds with which I make jewellery and I need to remove the remaining fruit flesh from them.  I have tried lots of things including ammonia, vinegar, bleach and a ultrasonic jewellery cleaning machine.  the only thing that works is a wire brush which takes forever and results in grazed fingers.  I wondered if some solution of the hydrochloric acid I use in the pool would work.  If so, what concentration should I use and how long should the seeds be immersed in it?  If not, what do you think would work?


texts: Carbon monoxide formation in broken boilers

texts: It's common knowledge, that if you're boiler is broken, it might produce carbon monoxide ($\ce{CO}$) as a byproduct, which is very toxic, even in small quantities. My question is, why do broken boilers do this?


texts: How to calculate energy gap when determining electron configuration?

texts:
The weird electron configuration of Niobium was well explained on this post:

How can one explain Niobium’s weird electronic configuration?

It was pointed out that electrons fill orbitals with higher exchange energy and lower repulsion energy, only if the sum of the positive exchange energy and negative repulsion energy overcomes the energy gap between orbitals.

The only problem is that I do not know how to quantify the energy gap.

How can I calculate the energy gap between orbitals?


texts: How does this method of calculating the water equivalent of a calorimeter work?

texts:
I am doing a AP Chemistry lab in which we determine the heat capacity of a calorimeter (a concept that seems like it should depend on a lot more than just the calorimeter.) We have to calorimeters with water of different temperatures (which is tracked the whole time) but equal mass. We then mix them. We then track temperature again. We then extrapolate to the time of mixing (with a linear regression for some reason.) We look at how much energy was lost by the hot water and gained by the cold water based on all 3 lines (each calorimeter before, and the mixed calorimeter after.) Next we take the difference of the energy gained and energy lost at a single instant divide by the temperature change of the cold calorimeter (I have no idea why the cold one) and this is the calorimeters heat capacity.

I am having trouble understanding this, since at a single instance, the energy gained by the hot water and lost by the cold should be equal, and any difference would be error. It also seems completely random to divide by the temperature of the cold water and not the hot. What is going on here?

P.S. Later in the lab, extrapolating to the time of mixing is used to find the energy change due to a reaction, which makes more sense.

P.S.S One Calorimeter was fully mixed into the other (I forget which one, but either way does not make sense, and calorimeters themselves (like the material it was made from) had negligible heat capacity.))

P.S.S.S It is the teacher's first year doing this lab I think.


texts:
Today my teacher asked an interesting question that "what is the role of salt ($NaCl$) in cooking the vegetables"? As the class was in funny mode, students gave answer like "it makes vegetables tasty" (which also seems reasonable). When I came home I realised the importance of question, so I am here.

I suppose that addition of salt is related to boiling point of water (If I'm thinking right). But still so confused that I don't know a generalised answer.

I shall be thankful if someone of you can tell me the role of salt in cooking vegetables (Please give as much as information you can).


texts: Why is lead(II) present in two groups of cation analysis?

texts: Well, I found that lead cation $\ce{Pb^2+}$ is present in both group 1 and group 2 of cation analysis. But why?


texts: which are the possible ways to detect impurity in drugs?

texts:
I want some information regarding the protocol for determining any type of impurity in pharmaceutical substances or drug product.
Which type of impurities can be identified by HPLC and MS?
what is the difference between related substances and impurity?


texts: Accounting for Vinylic Carbocation instability

texts:
I read that due to geometrical constraint, positive carbons in an aryl carbocation exhibit sp^2 hybridization instead of sp^1. The empty p-orbital is forced into a hybridized position via geometrical constraints. This then explains the instability of the carbocation as the positive carbon is attached to a significantly more electronegative carbon. Understanding that carbons with more "s-character" display more electronegative behavior, please clarify the following questions:

1) What is the hybridization of the positive carbon in a vinylic carbocation?

2) Are geometrical constraints present in vinylic carbocations?

3) What makes a vinylic carbocation unstable?

Origin: Why are vinylic and arylic carbocations highly unstable?


texts: Why is it lead(II) chromate and not lead(II) chromate(VI) tetraoxide?

texts:
I am just beginning in chemistry and learning how to name the different molecules. I have this molecule: $\ce{PbCrO4}$.

I would give it the following name: lead(II) chromate(VI) tetraoxide. Lead and chrome have both multiple oxidation states. And as you have to specify about which ion you are speaking, it seems to me this would be the most correct name.

But this is the correct name apparently: lead(II) chromate.

Could someone please explain:

why you just specify the oxidation state for the first element and not the other? As they are both metals and both have multiple oxidation states.
why you don't say tetraoxide, although there is clearly a number 4 written?


texts: Energy comparison between an atom and its ion

texts:
Is it possible to compare energy(enthalpy or similar) between an atom and its ion, possibly in the same state(gas)?

For example, $\ce{O}$ and $\ce{O^+}$(intentionally cation), $\ce{Na}$ and $\ce{Na^+}$.

At first I though of ionization energy, but its RHS(products) has electron, so I thought it can't be used to directly compare them.


texts: Why doesn't an sp3s hybridisation exist?

texts:
Trying to prove that nitrogen doesn't split its lone pair to form 5 bonds, I thought of a situation that I couldn't rule out; the paired electron being excited to the 3s orbital, so that five bonds could be formed- in an "$\ce{sp3s}$" hybridisation.
I know hybridisation is just an observation-based explanation, but I'd like to know how to rule wacky situations like this out.
Can this - and all other nonstandard hybridisations you can come up with - be ruled out by reasoning that the electron excitations involved take up too  much energy?


texts: Is there a way of finding solubility/solvent from basic information?

texts:
Let's say I have a compound and I want to find a solvent for it.
Looking on some where like Wikipedia, it is quite easy to find solubility, in various solvents for common compounds. However it can be quite lacking for less well know compounds (For example Glycin).
Although one can quite often find a list of some basic metrics (Polarizability,  log D, etc) for the compound. Say on:
Chemspider
Given those basic metrics is it possible to infer what some likely solvents would be? Or What would be the name of those techniques?
*Assuming normal temperature and pressure etc


texts:
The following question was given in FIITJEE study material:

I guess (i) step is de-esterification, which gives the compound of option (A).
In next step, I wouldn't expect it to decarboxylate, instead I guess it'll dehydrate. So, according to me, final product is:

which I can't see in the options. Then, what should be the final product?

 The correct answer given was: (C)


texts: What commonly availible salts are strong dessicants?

texts:
I'm looking into building an absorption chiller as a decidedly non-professional DIY project. For safety reasons and because temps. > 0°C are sufficient, I won't be using ammonia but some saline solution as absorber and water as cooling agent.
The obvious choice for the salt would be LiBr, as this is used in comercial installations. However, I'm not sure I can procure it (chemicals suppliers don't sell to private persons in germany) and it's not cheap (~ 30€/100g).
What other salts are strongly hydroscopic and commonly availible?
Alternativly, where can I find a concise list with the physical properties of many common (=household) salts?


texts:
Hydrogen peroxide is decomposed as follows:
$$\ce{2H2O2 -> 2H2O +O2}$$
This is a disproportionation redox reaction of $\ce{H2O2}$ involving the 2 half reactions
$$\ce{H2O2 -> O2 + 2H^+ + 2e-}$$
$$\ce{H2O2 + 2e- + 2H^+ -> 2H2O}$$
But I noticed semantically that it can also be the sum of the two following half reactions:
$$\ce{2H2O2 -> 2O2 + 4H^+ + 4e-}$$
$$\ce{O2 + 4H^+ + 4e- -> 2H2O}$$
Both reactions are feasible according to the following:

$$\begin{array}{ccc}
\text{Oxidised species} & \text{Reduced species} & E^\circ (\mathrm{V}) \\
\hline
\ce{H2O2} & \ce{H2O} & 1.763 \\
\ce{O2} & \ce{H2O} & 1.23 \\
\ce{O2} & \ce{H2O2} & 0.695 \\
\end{array}$$

Can it happen in the second way?
If yes, can you explain the mechanism in simple terms?


texts: Reaction of orthocresol with butyrolactone in presence of AlCl3 and heat

texts:
What will be the major product of the following reaction?

Please also help me with the mechanism. I'm not sure whether C- acylation or O- acylation will occur here. And if O- acylation does occur, I think the heat will cause a Fries' rearrangement. What will be the major product of this rearrangement?

Also, if simple Friedel Crafts acylation occurs, will AlCl3 affect the reaction due to formation of -O-AlCl3 (Lewis acid-base interaction), something like what happens in the case of Friedel Crafts reactions with aniline? (I know aniline cannot undergo FC reactions due to deactivating effect of -NH-AlCl3 interactions)

I'm unable to upload a pic of the question due to some technical problem, but what I mean is reaction of ortho cresol and butyrolactone in AlCl3, along with heat.


texts: Why are electrons transferred in an ionic bond?

texts: I've been taught at school that in an ionic compound like $\ce{NaCl}$, electrons are transferred from the $\ce{Na}$ to the $\ce{Cl}$ to form $\ce{Na+}$ and $\ce{Cl-}$ which both have full outer shells. But what causes these electrons to be transferred?


texts: What can cause artesian well water to smell?

texts:
Recently, our water from the artesian well started to smell (again). It only smells bad for only few seconds than the smell disappear.  We have sulfur-iron removal system, water softener, UV lamp. Only the water from the system I listed above smell, because we also have a Reverse Osmosis installed in the kitchen and the water filtered from it does NOT smell.

We did a hydrocarbon test that was negative. We also did a normal "drinkable water" analysis and it passed with nothing ususual. My question is what are the possibilities of that smell?

PS. I can confirm the smell is not sulfur (different from rotten egg)
See this post for our water results before installing the system if it may be useful


texts:
In the general equation of the compressibility factor $Z$, we define $Z$ as
$$Z=\frac{pV}{nRT}$$
Here, what is $p$? Is it $p_\text{real}$ or $p_\text{ideal}$?
Also, what is $V$? $V_\text{real}$ or $V_\text{container}$?


texts: Why are critical micelle concentrations so large?

texts:
Dissolving a non-polar molecule in water incurs a free energy cost of about $10 kJ/(mol \cdot nm^2)$ (source: http://bionumbers.hms.harvard.edu/bionumber.aspx?&id=101826)

The entropy gained from dissolving a solute is $k_B \ln(c_0/c)$ where $c$ is the number density of solutes in the water and $c_0$ is the number density of solutes when separated out from the water. Thus, I would expect the critical micelle concentration to be approximated by

$$c_{crit} \approx c_0 \exp\left(-\frac{10 kJ / (mol \cdot nm^2) SA}{k_B T}\right)$$
with $SA$ the surface area of the surfactant.

For SDS, using the information at https://en.wikipedia.org/wiki/Sodium_dodecyl_sulfate, I estimated that

$$c_0 \approx 1/(.5 nm^3)$$
$$SA \approx 4 nm^2$$
and
$$k_B T \approx \frac{1}{40} eV$$

This gives me

$$c_{crit} \approx 2*10^{-7} mol \cdot L^{-1}$$

but the measured value is nearly $10^{-2} mol \cdot L^{-1}$.

Where are the missing five orders of magnitude coming from? Are there, perhaps, additional degrees of freedom gained when SDS dissolves besides just the location of the molecule?


texts: proving an unknown organic compound using reactions

texts: I have been given three spectras (MS, IR, H NMR) to analyse, from them I have found that the compound is chlorobenzene (and I've confirmed online). The task I have gotten asks me to further justify my findings by using reactions and predicting and analysing the spectra of the products. However, I am quite unsure how I'm going to predict and analyse the spectra of the products from the reaction to prove my compound.


texts:
In two containers we have Xenon. The volume of the first container is 2780 L, temperature is 300 degree Celsius, and n = 200 mol. Volume of the second container is 4000 L, temperature is 1300 degrees Celsius and n = 100 mol. Temperature in both of the containers is constant. How much Xe do we have to transfer from one container to another so that the pressure in both containers is the same?
I have calculated pressure in container one and that is p1 = 342817.92 Pa, and in container two p2 = 326979.2275 Pa. Then I have substracted this two values which gives me 15838.6925 Pa. After that I have divided this value with two, to figure out how much do I have to decrease pressure in container 1, and that gives me 7919.34625 Pa.
After substracting this value from p1 I get the new pressure in container 1 which is 334898.5738 Pa which is the same as the pressure in container 2. From the new p1 I have calculated new n1 = 195.3798 mol, so I have to transfer 4.620 moles, or 606.593 grams to container 2.
My question is: When I take into the consideration the new n2 = 100 mol + 4.620 mol = 104.620 moles, and then I try to check if the p2 new is the same as p1 new I don'5 get the same result. p1 new = 334898.5738 Pa, and p2 new = 342086.14 Pa. Is my calculation wrong?


texts:
It is reported that iodine forms compounds like $\ce{(CH3COO)3I}$, $\ce{I(ClO4)3}$ and $\ce{IPO4}$ which contains $\ce{I+}$ and $\ce{I^3+}$ and are not bonded covalently as in interhalogen compounds.

Generally, Halogens form anions of the type $\ce{X-}$ to achieve stability by attaining noble gas configuration. However iodine loses electrons when it forms a cation and does not attain noble gas configuration. So why does iodine form cations while no other halogen does?


texts:
By reviewing a couple of articles and videos I decided to give some try to develop a PCB tinning solution at home. Based on most of the articles, the easiest way to develop this solution is by using the following chemicals:

Stannous Chloride ($\ce{SnCl2}$)
Thiourea ($\ce{CH4N2S}$)
Sulfuric Acid ($\ce{H2SO4}$)

After checking with a couple of stores, I noticed that Thiourea is not available to buy in any of the stores. Now my questions are:

What Thiourea does in this solution?
Is there any substitute available for Thiourea (for this process)?
Is it possible to prepare Thiourea from any other chemicals? (It seems using Ammonium Thiocyanate ($\ce{NH4SCN}$) can do that job, but it looks like a lengthy and complex process to do at home.)
Is there any possible way to build a tinning solution without using Thiourea?


texts: What are some general tests that would determine an unknown compound?

texts:
I know a little bit about unknown compounds but I am still new to the topic here. I know that you could use filtration, chromatography and distillation. You can also combine the unknown with others to form a compound. And you can measure properties and such and such to figure out what the compound is.

If I were to do this, what should I watch out for, and what would be the best way to proceed? I would appreciate it if you don't go "PhD" on me.

This question will be ambiguous for most people, but I am looking for a general idea and what you would normally do, instead of "what I would do in this situation".


texts: How can bromine water be used to distinguish between benzoic acid and salicylic acid?

texts: I have come to learn that bromine water can distinguish benzoic acid from salicylic acid. I know that salicylic acid on reaction with bromine water forms 2,4,6-tribromophenol. I think that benzoic acid will form m-bromobenzoic acid. So with this respect how can bromine water distinguish the two compounds?


texts: Why do most carboxylic acids have high pKa (~5) in spite of having a conjugate base ion that is stabilized by resonance?

texts:
This is from my textbook:

  Carboxylic acids owe their acidity ($\mathrm pK_\mathrm a$ of about $5$) to the resonance-stabilized carboxylate anions formed by deprotonation.

Why are they such weak acids? If the anions are resonance-stabilized, I would expect them to be much stronger acids.

Stated another way: this screenshot of the textbook page shows a representative protonation/deprotonation equilibrium for a carboxylic acid:

Why is the reaction favoured in the reverse direction if the carboxylate ion is more stable than the reactant?


texts: How does salt and water promote corrosion?

texts:
I was always wondering why iron only rusts when it gets wet. I know that for example aluminium oxidises on its own on regular basis.

I also heard many complains that salt used to remove snow from roads increases corrosion rate of car undercarriage.

Recently, I was researching how to produce iron oxide to improve rocket candy fuel - and among with oxidising substances, especially hydrogen peroxide, salt water was suggested.

What do these things have to do with aerial oxygen reacting with iron? I have also noticed that copper roofs turn green. Copper stuff kept away from rain doesn't do that so fast.


texts: Acidic tendency of copper(II) ion vs. calcium(II) ion

texts:
In my Chemistry textbook, a table is shown wherein ions originating in various salts are categorised according to their acidic or basic tendencies. Among others, $\ce{Cu^2+}$ and $\ce{Ca^2+}$ are present in the table; however, the copper ion is classified as being acidic, whilst the calcium ion is classified as being neutral.

I don't really see how they differ, apart from the amount of electrons they have in non-valence shells and the subshell that holds their valence electrons. Either way, since this is in the context of Brønsted–Lowry and not Lewis, I have no clue how the textbook got to its conclusion; does it have to do with copper parttaking in any redox reactions, or perhaps a certain stability calcium has?


texts:
I want to extract elemental silicon from pure silicon dioxide powder.

From what I've read, one way to do it is by adding carbon from graphite at very high temperatures, which is difficult.

A better way to do it is to mix with magnesium powder and heat it to about $800 ^\circ \rm C$.

Some places mention the use of a hydrogen atmosphere, is that necessary?

What is the best way to do it, the best temperature? If I use a torch, wouldn't the exhaust gases purge the oxygen and serve as an inert atmosphere?

How do I know the reaction is over?


texts: Why do alkyl substituents stabilize alkenes?

texts:
My textbook states that because $sp^2-sp^3$ bonds are stronger than $sp^3-sp^3$ bonds, alkenes are more stable than alkanes. The rule given is that bonds with more $s$ character are stronger.

However, it then states that an alkene with more alkyl substituents at the C=C double bond is stronger than an alkene with just hydrogens attached around the double bonded carbons. Carbon $sp^2-1s$ Hydrogen bond is stronger than Carbon $sp^2-sp^3$ Carbon bond. So how can my textbook use bond strength to explain why the alkyl substituted alkene is more stable than the non-substituted alkene?


texts: Can air inside a high temperature (1300C) Kiln cause an explosion?

texts:
I saw many kiln designs that lack an opening for hot\pressurized air to come out , or any pressure valve.

But when air is heated to such a high temperature (1300C) inside a closed chamber (the kiln), won't the pressure inside increase enough to explode the kiln ?
(These kilns usually operate for several hours under this high temperature)


texts:
Can I use a 1:1 mixture of isopentyl alcohol and water as mobile phase to carry out paper chromatography of a mixture of red and blue ink?

We generally use ethanol water mixture as mobile phase for separating mixture of blue and red ink using paper chromatography. Can I expect better results with isopentyl alcohol and water mixture?


texts: Can o-phenanthroline be used as a complexing agent for lead(II)?

texts:
I’ve been trying to find a method to perform a spectrophotometric analysis to determine lead concentration (on the ppm level). This would require some chelator capable of forming a coloured complex with lead in the aqueous phase.

Fe(II) ion can bind to o-phenanthroline to form an orange colour (with deeper hues based on the present concentration of iron irons).  I was wondering if lead(II) can too complex in the same way.

Note: The source of lead is $\ce{Pb(NO3)2}.$ This means some nitrate ions will be present in solution after dissociation of this chemical in water.


texts:
Today, at my chemistry class, we were learning how to convert Celsius to Kelvin with exact values. I said we add 273.15 K to given Celsius but my colleague said we add 273.16 K.

Yes, I did check on internet, we use 273.15 K for conversion, but I also found some relation with 273.16 K and I don't understand the concept of that. It's something to do with thermodynamics and triple point of water.


texts: Difference between calcination and pyrolysis

texts:
What is the difference between calcination and pyrolysis?

I understand they both involve heat treatment but each under a different type of atmosphere, which leads to some sort of reduction reaction? What are the differences in underlying mechanisms?


texts: Is circularly polarized light ever used to isolate particular chiralities?

texts: Chiral molecules tend to absorb one circular polarization of light more than the other. Is this ever used to isolate a particular enantiomer?


texts: Why does a matchstick burning in a container cause suction?

texts:
As you see in the picture, a burning match in a container causes suction and this is a traditional therapeutic method to relieve bone pain.

What is the reason? I think it should be related to gas changes ($\ce{O2}$ being used for combustion and etc.), but I am not sure about it.


texts:
I'm trying to understand why ChemReference sometimes lists the valence electrons as a number I don't expect. Take Oxygen, for instance. It should have six valence electrons, however the site lists two. Why?

I hear that, for transition metals, the d-orbitals count towards the valence. Is there another rule like that I need to know about that might explain Oxygen?


texts: Is is possible to Generate ~1ppm Copper in Solution from Elemental Copper?

texts:
I am designing a hydroponic system and need to control algae.  Copper is a known algaecide and lettuce actually needs some copper to grow well.  I had read stories about people using copper pennies in things like bird baths to reduce algae.  Pennies in the nutrient solution reservoir did not seem to affect the algae much.

I had a thought that by increasing the surface area, I might get a better result.  Fine copper wool is available for finish sanding, and I was thinking about running the nutrient solution through that to try to get some copper into solution.  The nutrient solution is ~pH 6 and 25C and has the (somewhat generic fertilizer) contents shown below at about a 1g/L (~2000uS EC) concentration.  The flow rate is ~4L/min, but only for about a 10 seconds every 300 seconds.  Another option is just to leave the copper in the water reservoir so that it is always in contact with the nutrient solution.

Is it possible to get ~1ppm of copper into solution from an elemental copper source in the nutrient solution?

It doesn't matter if it takes a week or so, as long as there is some chance of the copper going into solution.

EDIT:

I found this paper on Cu/Zn soluability vs pH.  It contains the graph below.

Is it true that assuming that Cu2+ ions have 63.546 g/mol weight, and 1ppm = 1mg/L, that 0.001g/L * 1/63.546 mol/g => 15uM solution, and thus the graph indicates that at pH 6.5 there will definitely be more than 1ppm of copper in solution at 25C?


texts: What are the product(s) of red phosphorous when burned?

texts:
A match box lighter strip typically consists of powdered glass and red phosphorous. When this part is burned, it's residue is like a sticky dust that, when applying friction, will release smoke or vapor. You can do it with you fingers and it looks really cool.

So what's the chemistry behind this?


texts:
Let a collection of molecular graphs have at most $N$ nodes, $d$ node types (atom type), and $t$ edge types (bond types). A graph from this collection is normally represented by the tuple $(F, E)$ with

\begin{equation}
\text { node-label matrix } F \in \mathbb{R}^{N \times(1+d)}\quad \text { and }\quad \text{edge-label tensor } E \in \mathbb{R}^{N \times N \times(1+t)}
\end{equation}

In a statistical model, $i$-th row in matrix $F$ represents the probability of different node types for a node $v_i$. Similarly, filament $(i,j,:)$ of tensor $E$ represents the probabilities of edge $\epsilon_{i,j}$ in the graph.

In these models, usually, probabilities of nodes and edges are assumed to be independent. This, however, is not a realistic assumption. Type of atoms and bonds are obviously not independent from each other. For a node of certain type, the incident edges collectively must have total type values not exceeding a threshold, where the “type value” is some numeric property of an edge type.

Question:

I was wondering if the type of the node is only dependent on its immediate neighboring edges (incident edges) or we can argue that it also is affected by the edges farther from the node.


texts: Which is most stable resonance structure of 4-nitrophenoxide ion?

texts: According to my coaching module the first structure is more stable. Why is this so? I feel both must be approximately equally stable since negative charge is on oxygen in both cases. Would someone please give me a hint?


texts: Why are methanol flames less visible than other flames?

texts:
The combustion of methanol tends to generate flames that are less visible than the flames generated by the combustion of other substances?

My guess is that methanol burns quickly as it has a relatively simple structure that provides some of the oxygen needed for combustion.  I am assuming that the flame comes from a mixture of fuel and air that is undergoing reaction.  If the reaction is fast enough, then there will be less flame.  However, methane and hydrogen both have visible flames, much more visible than methanol, leading me to wonder how the one oxygen in methanol makes so much of a difference.


texts: How to predict the reason for color in a transition metal complex?

texts: I know about two reasons for the color of transition metal complexes that are dd transition and charge transfer phenomenon but I am confused when a complex can show both of the above-mentioned phenomena then how to choose which can be the dominating reason for the color of the complex.


texts: (Single) Amino acid rotational degrees of freedom

texts: When defining the rotational degrees of freedom for a single molecule, should we just include the psi and phi angles (red lines in the picture) or the rotation around every single bond (yellow lines in the picture) or both?


texts:
Can anyone tell me what  the difference between these two compounds is:

N(alpha)-acetyl-ornithine

N(delta)-acetyl-ornithine

The only difference I can think of is the chiral properties of the nitrogen atom, i.e. nitrogen inversion.

If that is the case, does it make sense to differ between these to compounds, or will they be constantly interconverted?


texts: does it make any difference writing NO2 instead of O2N


texts:
A student has equal volumes of $\pu{1.0 mol dm-3}$ sodium hydroxide and ammonia solutions. Which statement about the solutions is correct?
A. Sodium hydroxide has a lower electrical conductivity than ammonia.
B. Sodium hydroxide has a higher hydrogen ion concentration than ammonia.
C. Sodium hydroxide has a higher pH than ammonia.
D. Sodium hydroxide has a higher hydroxide ion concentration than ammonia.

The answer is C, and I understand why. What I do not understand is why D isn't correct also? Could someone clarify this for me?


texts: Say dilute $\ce{HCl}$ is used to convert some alkaloid to salt form, then the alkaloid is dried with heat, would gaseous $\ce{HCl}$ be released in the process?  Is there a threshold concentration of the acid, below which,  this would be acceptable from a safety point of view?


texts:
How "strong" of a solvent is Pine Sol? Is it relatively benign like Isopropyl Alcohol, stronger like Acetone, or ridiculous like TCE?

Without a background in chemistry (mine is electrical engineering), I'm trying to get a "feel" for what materials I can use what solvents on.

For example, "strong" solvents shouldn't be used on wood, plastic, etc whereas "moderate" ones can't be used on thin/"weak" plastics but sturdier plastics are OK for short periods of time (i.e. I can use them for cleaning a plastic welding mask in the garage but shouldn't use them on the plastic LCD screen).

If I'm asking the wrong questions, please feel free to answer the question I should have been asking - but keep in mind I'm looking right now for the medium-fidelity answer, not the 100%-physically-correct-by-understanding-chemical-bonds answer.


texts: How do you name this compound using IUPAC system (including steps)?

texts:
And including stereochemistry (cis trans or R S )

I know you start numbering from the double bond because there are no functional groups like -OH, you take the longest carbon chain which is six carbons in this question, so now it should be 3-bromo-3-methyl-1-hexene. My quarrel is with the stereochemistry and how do you name the compound regarding the widge and the dash (cis and trans or R and S)

I also know CIP priorities, it's just the widge and the dash being at the middle of the compound that confuses me.

trans-2-bromo-2-vinyl-pentane ?
R-2-bromo-2-vinyl-pentane ?


texts: Gas Law - increasing temperature with constant volume held

texts:
I've set up a simple experiment to look at the ideal gas laws. My experiment is relatively simple in that I have a metal tube which is capped on one side. I am then pressurising the tube with air to 100 psi and locking it off.

My thought is that as the pressure increased, with volume held constant, the temperature of the tube should rise. However, after 30 minutes of observation, there is no rise in temperature. Am I missing something? I was expecting to see the temperature of the tube rise.

The tube is SS 316 with a ball valve capping it off at one end and using the pump to hold the pressure once it is reached.

Thank you.


texts: Why can't electrolysis utilize specific ions for reduction/oxidation

texts:
In the electrolysis of water, reduction half equation is $$\ce{2H2O + 2e- -> H2 + 2OH-}$$ with a standard $E$ value of $-0.83\ \mathrm V$.

If $\ce{H+}$ is present in water, why can $$\ce{2H+ + 2e- -> H2}$$ not occur, with potential $0\ \mathrm V$, which is more favourable?


texts: Why isoelectronic species give similar spectral lines?

texts:
In my perspective those species should give similar spectra those which have same energy of different energy levels as the transition would yeild same energy photon
But still the answer to this question is always the isoelectronic species
Not the ions of the element


texts: Does ice melt faster when submerged in water?

texts:
Suppose you have a container with a drain at the bottom full of frozen H2O which you leave a room temperature to melt. Will the ice melt faster if you drain the water as it melts?

I would expect that the water, being warmer than the ice, will speed the melting of the ice. However, I would also expect that draining the water would remove allow more air to enter the system and heat the ice faster. Which explanation is correct?

Related question: if the container is a cooler to fill with warm beverages, will the beverages cool faster in a wet or dry ice-filled cooler?


texts: How dangerous is an industrial scale styrene spill?

texts:
A few years ago a cisterna truck full of styrene crushed on the road near a small town nearby, spilling 4 tons of the chemical. It apparently has caused a small ecological catastrophe killing fish in the local river with concentrations of 3.7 ml/l in the water, and half of the population - some 2000 people were evacuated in the next 2 days, but it was not mandatory, and what seems more strange to me, I've seen all the firefighters not wearing any gas masks while pouring some white foam on the truck. Also, no one mentioned that styrene is a cancerogen.

Initially, there was no info on the chemical spilled, and I didn't know or care much then, but today I incidentally found out it was styrene, and I got curious. So, were those measures somehow inadequate, or on the contrary - far-fetched, and just how bad this is?


texts: Triphenylphosphine vs. trimethylphosphine in reduction reactions

texts:
Triphenylphosphine is used typically as a reducing agent for organic peroxides as it is a good nucleophile. So, if I wanted to computationally model a reaction like: $$\ce{PR3 + ROOH -> OPR3 + ROH}$$

Can something like a trimethylphosphine be used instead of triphenylphosphine, since it is an even better nucleophile, and the strength of the P=O is what's driving the reaction/reduction? Or am I missing some information?


texts: Overall polarity of polychlorinated benzofuran

texts:
I have been struggling over this weekend to find an answer for the overall polarity of this molecule: 2,3,7,8-tetrachlorobenzofuran

In order to find intramolecular forces, I determined the difference in electronegativity:

C-C = 0 and C-H = 0.4 --> non-polar covalent bond

C-O = 0.8 --> polar covalent bond
C-Cl = 0.6 --> polar covalent bond

As the molecular shape is not symmetrical, and there are polar bonds present (unbalanced), I thought it is a polar molecule. However, the research suggests that it is "non-polar molecule, therefore insoluble in water".

Can I ask the reason why it is considered a non-polar molecule?


texts: Can plastic leak into water from a HDPE "2" plastic container at room temperature?

texts:
Here in USA supermarkets often sell water in plastic 1 gallon jugs. These jugs seem to all be stamped with the text "HDPE" (meaning that the material is High-density polyethylene) and a resin number of "2" on the bottom.

I had one of these jugs, containing distilled water, on a counter in the kitchen, and another one in the refrigerator. For some reason the water on the counter had a light plastic taste, whilst the water in the fridge did not.

Could this taste be because of plastic leaking into the water? Or what else could cause the plastic taste?


texts: Comparing acidic strengths between benzylammonium ion and phenol

texts:
Question

Compare the acidic stengths between benzylammonium ion and phenol.

I first tried to remove the H+ ion from both of them and tried to compare the relative stabilities of resulting conjugate bases, but I am not sure, which one would be more stable.
The first one would be a neutral compound and the second one would have resonating structures on which the negative charge gets mostly delocalised to carbon.
I have seen somewhere on the internet that benzylammonium ion has a $\mathrm{pK_a}$ value of 9.33 while phenol has a $\mathrm{pK_a}$ value of 10. If this data is correct, then how do we explain the acidity order?


texts: Why is a volumetric flask shaped the way it is?

texts: A volumetric flask does not look like an Erlenmeyer flask, but has more of a pear shape. Is it just to distinguish more easily between them while they are on the shelf?


texts: How to correct the pH and composition of bottled water?

texts:
For some time I've been buying a brand 'A' of (non-sparkling) bottled water.
It wasn't easy to find one that I liked, because I make tea with it, and most other brands I tried made murky, smelly, dark tea, with a disgusting film on top, whereas this one was perfect.
Unfortunately, I just found that the supermarket doesn't stock brand 'A' anymore (I know, it's not a big problem, by any standards; just discussing a bit of science, for fun).
So I picked the closest one I could find (brand 'B'), naively thinking that the main 'factor' to look at was pH.
Brand 'A' had a pH pf 6.7; brand 'B' was 6.9. I thought: close enough.
Actually: wrong.
I made tea with brand 'B' water, and while it wasn't as horrible as with higher-pH ones I had tried before, it was nowhere as good, it made that slimy film, and smelled a bit off.
So I looked at the composition of the two brands side by side, converting the concentration from mg/L to mmol/L:
$$
\begin{array}{lcc}
\hline
\text{Component} & C_\mathrm{A}/\pu{mmol L^-1} & C_\mathrm{B}/\pu{mmol L^-1} \\
\hline
\ce{HCO3-} & 0.38 & 4.72 \\
\ce{SiO2}  & 0.32 & 0.00 \\
\ce{Na+}   & 0.13 & 0.18 \\
\ce{K+}    & 0.02 & 0.16 \\
\ce{Mg^2+} & 0.04 & 1.60 \\
\ce{Ca^2+} & 0.10 & 1.07 \\
\ce{F-}    & 0.01 & 0.00 \\
\ce{Cl-}   & 0.02 & 0.06 \\
\ce{NO3-}  & 0.03 & 0.00 \\
\hline
\end{array}
$$
Clearly there is much more 'stuff' in water 'B' than in 'A', and in fact the residue is 289 mg/L in the former, 43.6 mg/L in the latter.
One thing that caught my eye was the charge balance, which seems a bit off for 'B' (+0.91 mmol/L), whereas it's a bit closer to 0 for 'A' (-0.02 mmol/L).
But OK, my main question at this point is: can I add something to water 'B' so that it 'behaves' a bit more like 'A', for the use that I mentioned?
My hypotheses so far are that:

the pH should be lowered
$\ce{Ca^2+}$ and $\ce{Mg^2+}$ are responsible for the formation of that 'film', and I might prevent that by adding something that forms soluble coordination compounds with these ions (and more stable than the ones they form with whatever it is in tea that reacts with them)

Obviously I am not going to use stuff that is not edible, like EDTA; and for the pH correction, I'll have to rely on calculations, not going to stick a pH-meter into it.
So my best bet at the moment is: citric acid.
Though I am not sure how I should calculate the correct quantity to add to the 5 L bottle I buy (surely I can't aim to convert most $\ce{HCO3-}$ to $\ce{H2CO3}$, or the final pH would have to be too low).
What do you think?
Any ideas/comments/suggestions?


texts: What does it mean when it is said that an sp³ orbital has 25% s character?

texts:
My textbook frequently mentions:

  $\mathrm{sp^3}$ hybrid orbital has 25% $\mathrm{s}$-character and 75% $\mathrm{p}$-character.

What are these "characters"? And how do these characters influence the bond and the hybrid orbital?


texts: Is it right to say that fluorescent lamps are actually fluorescent?

texts: Fluorescence occurs rapidly ($\approx 10^{-6}$ to $10^{-9}$ s) but phosphorescence is slow, and is therefore observable ($> 10^{-4}$ s). So, is it right to say that fluorescent lamps actually fluoresce when they actually do is to phosphoresce? Or am I wrong in saying that?


texts: Acetic acid completely dissociates in liquid ammonia and I would like to know the $\mathrm{p}K_\mathrm{a}$ value for the acid in that solvent. Can anybody point me to a reference?


texts: What would follow in the series sigma, pi and delta bonds?

texts:
I realise, that this question is a stretch, but I was wondering, how would a bonding orbital be called if it was formed from two $f_{x(x^2−3y^2)}$ or $f_{y(3x^2−y^2)}$ orbitals. Have there been any suggestions on this, was it anywhere proposed or discussed? I am not arguing about the existence of such a thing, but as a thought experiment, how would it be called? Phi, $\varphi$?

I am also throwing in a reference request here, since I am interested in any literature related to the topic.

Some background:

A $\sigma$ orbital is an orbital, that has no nodal plane between the bonding partners. It is $C_\infty$ symmetric with respect to the bonding axis (in first approximation - of course $d_{xy}$ orbitals can align in a $\sigma$ fashion, too, but for the sake of the argument, let's not consider this.) The point group of this orbital can further be assumed as $D_\mathrm{\infty h}$. It shares therefore most features of an $s$ orbital, hence $s$igma, $\sigma$.
The most prominent example for this is probably the dihydrogen, $\ce{H2}$, molecule.
A $\pi$ orbital has one nodal plane and the bonding axis of the involved atoms is part of this plane. It is therefore asymmetric, $C_1$, with respect to this plane. However, it is $C_\mathrm{s}$ symmetric with respect to the plane that is perpendicular, also sharing the bonding axis. The orbital has further the point group $C_\mathrm{2v}$. It has therefore most features of a $p$ orbital, hence $p$i, $\pi$.
The most prominent examples for $\pi$ bonds are probably ethylene, $\ce{C2H4}$, and acetylene, $\ce{C2H2}$.
A $\delta$ orbital has two nodal planes between the bonding partners. These are perpendicular to each other. The bond orbital is asymmetric with respect to both of them. As a result, it is $C_\mathrm{s}$ symmetric with respect to the bisecting mirror planes. The point group of this orbital is $D_\mathrm{2h}$. Therefore it has shares features with a $d$ orbital, hence $d$elta, $\delta$.
One example is the $\ce{[Re2Cl8]^{2-}}$ ion, see Wikipedia's quadruple bond.
I imagine two $f$ orbitals aligning with the bonding axis being simultaneously a $C_3$ symmetry axis, giving it an overall $D_\mathrm{3h}$ point group. Since there is no greek letter starting with an $f$, I think the logical thing would be to choose $\phi$ as it sounds a like. (I cannot be the only one thinking that.)

The following graphic should somewhat demonstrate what I mean:

I have to admit, that I have not done much research about this. It was more like an impulsive question for me to ask.


texts: Why is bis(1,2,2,6,6-Pentamethyl-4-Piperidinyl) Sebacate used as a "bottom coat" for a superhydrophobic coating?

texts:
According to this MSDS sheet, a compound named bis(1,2,2,6,6-Pentamethyl-4-Piperidinyl) Sebacate is used in the "bottom coat" layer before a "top coat" of superhydrophobic NeverWet coating is applied.

The top coating composition can be inferred from this MSDS sheet, and is a dimethyl siloxane reaction product with silica (likely a fumed silica nanoparticle that's been reacted with dimethyl silanol).

Functionally, what bis(1,2,2,6,6-Pentamethyl-4-Piperidinyl) Sebacate must be doing is creating a reactive surface on the desired substrate for subsequent application of the siloxane nanoparticles.  It's not clear if the nanoparticles will be reacting with this bottom coat, or forming some sort of complex (and if so what the nature of this complex is).

According to Wikipedia, sebacic acid is a dicarboxylic acid with an 8 carbon linker, so my guess is that is the backbone of the base-coat molecule.  Apparently sebacic acid is a monomer widely used in the production of plastics, so there is likely a polymer or "pre-polymer" (made-up term) being deposited.

Any idea what the molecule might look like and what the mechanism and functionality might be for forming this base coat for the hydrophobic coating?

EDIT: looks like I found the molecule (CAS # 41556-26-7), and it looks like some sort of bifunctional crosslinker.  My question still stands as to how it functions and how it might be preparing a surface for addition of a superhydrophobic coating.


texts: Why do certain solutes dissolved in water release heat and other solutes absorb heat?


texts: Is it possible to observe ATP energy transport in table experiment?

texts:
Is it possible to take AMP or ADP, then phosphorylate it convert to ATP to charge with energy, then transport to other place an then observe energy freeing?

In table / home / school experiment?


texts: Finding $c$ with Dulong-Petit law on non-molecular substance

texts:
The Wikipedia article states the Dulong-Petit law as follows:

$$c=\frac{3R}M$$

$c$ is specific heat capacity $[\mathrm{\frac J{kg\; K}}]$ and $R$ the gas constant. $M$ is the molar mass in [g/mole], and "grams per mole" makes us think of a number of moles of a substance, as were it a molecular material.

In crystal structures there is no such thing as a "mole" of the substance. An example could be $\ce{CoSb3}$. $\ce{CoSb3}$ is not a molecule, but the simplest formula unit of the endlessly repeating crystal. So which $M$ to plug into the Dulong-Petit formula is not obvious here.

A researcher gave me the following version of the Dulong-Petit formula for this case (which I have used successfully):

$$c=\frac {3R}{M}n$$

The $M$ still means molar mass [g/mol], treating the formula unit as were it a molecule.
The $n$ is the number of atoms in the formula unit. So here, $n=4$. Simple.

I do not see how this version is equivalent with the former version. How does "treating the formula unit as was it a molecule" balance out with "multiplying with the number of atoms"? How is

$$\underbrace{\frac{3R}M}_{molecular}\Leftrightarrow \underbrace{\frac{3R}Mn}_{crystalline}$$

equivalent?


texts: Can someone walk me through this gas mixture question?

texts:
Argon $(\ce{Ar})$ and helium $(\ce{He})$ are initially in separate compartments of a container at $\pu{25 °C}.$ The $\ce{Ar}$ in compartment A which has a volume $V_\ce{A}$ of $\pu{9.00 L}$ and a pressure of $\pu{2.00 bar}.$ The $\ce{He}$ in compartment B of unknown volume $V_\ce{B}$ has a pressure of $\pu{6.00 bar}.$ When the two compartments are connected and the gases allowed to mix, the total pressure of gas is $\pu{3.60 bar}.$ Assume both gases behave ideally.

  $$
\begin{array}{|l|l|}
\hline
\text{Chamber A} & \text{Chamber B} \\
V_\ce{A} = \pu{9.00 L} & V_\ce{B} = \pu{??? L} \\
p_\ce{A} = \pu{2.00 bar} & p_\ce{B} = \pu{6.00 bar} \\
\hline
\end{array}
$$

  [4 marks] Determine the volume of compartment B.

I've been stuck on this problem for a while.  Could someone walk me through the beginning steps? I should be good to go with some guidance.  Would I use Boyle's law in attempt to find the final volume once the partition is removed?


texts:
Good morning,
I know that Henry's law describes the gas solubility in water with partial pressure of a specific gas.
For example the oxygen concentration in water, under atmospheric pressure, is

$\mathrm{C = P_{O_2} * k}$, where $\mathrm{P_{O_2}}$ is $\mathrm{0.21}$ bar.

But if I have a steam-water mixure, how I can calculate the solubility (for example in a deaerator)?
What data I need to calculate that solubility?
Thanks


texts:
Which between $\ce{HI}$ and $\ce{HF}$ has a greater dipolar moment?
I think it is $\ce{HI}$ because the atomic radius of $\ce{I}$ is greater.


texts:
I have about 100g of Sodium azide and would like to store it properly. Any suggestions as to where? I though of storing it in a locked vault but there are chemicals such as Arsenic sulfide, aniline, and Potassium cyanide, but the presence of metals in the cabinet makes me a bit queezy.

Many thanks in advance.


texts:
The Wikipedia definition of chemical substance states:

  A chemical substance, also known as a pure substance, is a form of matter that has constant chemical composition and characteristic properties. It cannot be separated into components by physical separation methods, i.e., without breaking chemical bonds. Chemical substances can be chemical elements, chemical compounds, ions or alloys.

A molecule made up of the same element (e.g. $\ce{H2}$) is not a compound; however, molecules aren't listed in the final sentence. Is a non-compound molecule a chemical substance?

I believe it is and here's my overall understanding of the terms in this space, and any corrections would be appreciated:


texts: Reactions of tin (IV) iodide with potassium iodide and water

texts:
In the reaction of tin (IV) iodide in acetone and water, the solution turns a urine yellow.

Is this simply due to the hydrolysis of tin (IV) iodide:

$$\ce{SnI4 + 2H2O -> SnO2 + 4HI}$$

why is the acetone needed though?

and for the reaction with $\ce{KI}$:

$$\ce{SnI4 + KI -> ?}$$
I understand it forms iodine, but what happens to $\ce{Sn}$ and $\ce{K}$ - do they react with the acetone for instance?


texts:
I've been using QuteMol for generating 3D animated molecular images and I've encountered a problem; for some reason that's a complete mystery to me when I create a pdb file for etravirine (using MarvinSketch to create a sdf file and then using OpenBabel to convert the sdf to pdb and add implicit hydrogens) and load it I found the bromine atom was all by itself with no bond connecting the two and I would like a bond in the image. Any ideas? Thanks in advance.

The following image is the result I'm getting from QuteMol.


texts:
I heard somewhere that some plastics are pretty good at resisting decently strong acids. To what degree is this true? Does latex protect against corrosives? Are plastics good at "resisting" bases or other strong solvents?

I'm not a chemist, so I apologize if my question seems dumb. I couldn't find much info on the subject of latex vs corrosives via Google.

Also, I don't plan on handling any dangerous chemicals; I'm just curious.


texts: Calculating molecular weight of an acid based on titration data

texts:
If $\pu{2.600 g}$ of a weak diprotic acid were dissolved in $\pu{100 mL}$ of distilled water and a $\pu{10 mL}$ aliquot of this solution required $\mathrm{21.60\ mL}$ of $\mathrm{0.1000\ M\ NaOH}$ to reach the first endpoint, what are the equivalent and formula weights of $\ce{H2A}$?

I assumed to do this: I calculate the grams of acid in solution which is

$$\mathrm{\frac{2.600\ g}{100\ mL} \cdot 10\ mL = 0.2600\ g}$$

After that I would calculate the moles of NaOH used

$$\mathrm{0.1000\ mol/L \cdot 21.60\ mL \cdot 1\ L/1000\ mL = 0.002160\ mol}$$

Then I use this to find the moles of acid present in solution; this is the part I am unsure about. I am assuming: because at the equivalence point half of the acid has been converted to it's conjugate base and so ($\mathrm{2\ mol\ NaOH = 1\ mol\ H_2A}$).

If this is correct then

$$\mathrm{0.002160\ mol\ NaOH \cdot 2\ mol\ H_2A/mol\ NaOH = 0.004320\ mol\ H_2A}$$

Which I then divide the g/mol

$$\mathrm{\frac{0.2600\ g}{0.00432\ mol} = 60.19\ g/mol}$$

Because the acid is diprotic the equivalence weight would be

$$\mathrm{\frac{60.19\ g/mol}{2} = 30.09\ g/mol}$$

I don't think this is the correct answer because I am trying to do this using real titration data I took in lab and the MW seems to be at $\approx 1/2$ the value it should be. If I am not supposed to double the NaOH moles, is there a reason for it?


texts: Color of complexes d-d transition or electron exchange

texts:
I always have the problem of finding whether a complex has colour due d-d transition of electrons or if it is due to electron exchange. Is there a general way to tell whether a complex has d-d transition or electron exchange?
Is it the right method to check if a metal has d electrons and if it does. Its color must come from d-d transition and if not the color must come from charge transfer?


texts: What is the Lewis structure of Ozonide ion?

texts:
What will be the Lewis structure of the ozonide ion, including formal charges?

Do all oxygen atoms have filled octate?


texts: Why is the voltage produced by a voltaic cell affected by temperature as described by the Nernst Equation?

texts:
I understand why changing the concentrations of the electrolytes in a voltaic cell affects the voltage. Given a zinc-copper cell for example, if I were to increase the concentration of the zinc sulphate electrolyte, the equilibrium between zinc ions and zinc metal would shift towards the side of the zinc metal. This would cause the reduction potential for zinc ions to increase, decreasing the overall cell potential. Please correct me if I’m wrong as this is how I understand it!

However, I don’t quite understand why temperature affects the voltage the way it does. According to the Nernst equation, if the reaction quotient is greater than one (meaning that the zinc sulphate concentration is greater than the copper sulphate concentration in this example), increasing temperature decreases voltage. Conversely, if the reaction quotient is less than one, increasing temperature increases voltage.

I am familiar with Le Chatlier's principle, but if I were to apply it to this scenario, given that the redox reaction taking place is exothermic, it would suggest that increasing temperature would always decrease the voltage produced since it would cause a shift towards the reactant side. This, of course, does not correspond with the relationship predicted by the Nernst equation.

I have looked all over the internet but I could not find any answer to this seemingly straightforward question. Any help is greatly appreciated!


texts:
Since the six strong acids dissociate completely into their ions, and the reaction goes to completion, does this mean that acids such as $\ce{HI}$ and $\ce{HCl}$ have the same acidic strength?

I know that 0.10 M $\ce{HI_{(aq)}}$ and 0.10 M $\ce{HCl_{(aq)}}$ both contain 0.10 M $\ce{H3O+_{(aq)}}$, which leads me to believe they are equally strong acids. Is this correct?


texts: Why doesn't the Pilling-Bedworth ratio of silicon cause issues in silicon technology?

texts: According to Wikipedia, silicon has a Pilling-Bedworth ratio of 2.15. In theory this should mean an SiO2 film on silicon should have a fairly large amount of compressive stress and high probability of fracturing. After all, 2.15 is even higher than the 2.14 PB ratio of iron, which flakes quite readily as rust. However in practice this is obviously not the case, and in fact the growth of oxide films on silicon is usually performed quite simply by thermal growth without any further technique. Is this simply due to the low thickness of these films or is there another reason silicon oxide behaves nicely?


texts:
Is it possible that $\ce{2 OH-}$ from water could react to form $\ce{H2O2}$?

I mean most autoionization forms $\ce{H3O+}$ and $\ce{OH-}$.

However I think it is possible that $\ce{H-}$ and $\ce{OH+}$ forms, though the amount formed of these 2 is small. This is from water acting as an acid and H+ acting as a base.


texts:
I recently learned that attempts to compare the spectra of two isomers of $\ce{C_3H_3^+}$ were frustrated by the difficulty of separating the two species.

What makes these isomers difficult to separate?


texts: What are the ozonolysis products of phenanthrene?

texts:
What is / are the product(s) of ozonolysis of phenanthrene?

I am not sure I understand how to proceed. Which of the $\ce{C=C}$ double bonds is most susceptible to this type of reaction?
I am confused given the resonance and aromatic character of the compound which doesn't make me feel comfortable doing ozonolysis the usual way.


texts: How to calculate the entropy change of benzene when it changes from vapour into liquid?

texts:
Given information:

  The boiling point of benzene at atmospheric pressure is $353~\mathrm{K}$
  the enthalpy of vaporization of benzene is $30.8~\mathrm{kJ~mol^{−1}}$ at this temperature.
  The molar heat capacities of the liquid and vapour are $136.1~\mathrm{J~K^{−1}~mol^{-1}}$ and $81.7~\mathrm{J~K^{−1}~mol^{-1}}$,
  respectively, and may be assumed temperature independent.

  Calculate the entropy change of the system, the surroundings and hence the universe when $1~\mathrm{mol}$ of benzene vapour at $343~\mathrm{K}$ and atmospheric pressure becomes liquid benzene at $343~\mathrm{K}$. Also, will this process occur spontaneously?

I know that $\mathrm{d}S = \frac{\mathrm{d}H}{T}$ therefore,
$\displaystyle\mathrm{d}S = \frac{-30.8 \times 10^3~
\mathrm{J}}{343~\mathrm{K}}=-89.8~\mathrm{J~K^{-1}}$ which is the entropy of the system.

How do I continue from there, utilising the molar heat capacities given?


texts: Why do electron donating groups stabilize free radicals? I have read this fact in various websites and it is not mentioned why. Isn't a free radical like a highly reactive individual molecule? Why does it require electrons? And won't the requirement of electrons depend on the octet of the central atom of the free radical?


texts: Comparison of chemical shifts among alkanes in NMR spectroscopy

texts: I was reading through the factors influencing chemical shifts in proton NMR. I found the order of chemical shifts in the image above. Why is this order supposed to be as it is? I thought it would be the reverse as the inductive effect is the maximum in tertiary carbon, so the hydrogen attached to that carbon is shielded the most and thus has the least chemical shift. But why isn't that true?


texts: If ozone is a gas, and gases have the highest entropy, then how does the ozone gas stay within a few layers of the atmosphere, even though they span for kilometers?


texts: Reducing the thickness of a layer of elemental sulfur

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I want to make a very thin film of elemental sulfur. While mechanical polishing can bring a film to 10 microns in thickness, but I need to bring my thickness lower (hundreds of nanometers). Although I searched, I was unsuccessful in finding any methods for chemical etching elemental sulfur.

Are there any methods for reducing the thickness of elemental sulfur below 10 microns, preferably to lengths on the order of hundreds of nanometers?


texts: Can someone explain to me charge shift bonding? I recognize that it is proposed as another domain of bonding - one different from ionic and covalent bonding. I am also told that $\ce{C-F}$ exhibits charge shift bonding. But why—and firstly, what exactly is charge shift bonding? All the literature I have consulted are at too high of a level for me, for example this 1992 article in the Journal of the American Chemical Society.


texts: Collision rates between two molecules in a liquid

texts: How would I calculate the collision rate between kaolinite and amylopectin particles in a liquid with a density of ($\pu{1.01g/m^3}$) and a viscosity of ($\pu{0.000434 Pa s}$)? I know this is related to orthokinetic flocculation, however, I do not know the exact equation. If anyone knows the equation, can you please inform me of it?


texts: Periodic boundary conditions in DFT for cylindrical system

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As I understand it, a DFT calculation uses periodic boundary conditions, whenever you want to simulate a bulk material. This is convenient because all information can then be extracted from the fundamental unit cell.

Currently I am faced with the problem of calculating the band structure of a carbon nanotube, which has a cylindrical geometry, i.e. only bulk in only one direction, say z, and circular in the x and y directions. As my unit cell I am using a ring of C-atoms surrounded by vacuum and I then employ periodic in the z-direction. Obviously, for large diameters, this approach involves a rather large unit cell, which makes the calculation slow.

My question is: Is there an alternative way to do this, which exploits the cylindrical symmetry of the system? Specifically what I have in mind is to also apply periodic boundary conditions in the other directions, but where the Schrödinger equation is expressed in cylindrical coordinates with the middle of the nanotube as the origin.

Another, less important, question is also: Do you ever NOT use periodic boundary conditions in DFT? For example, when you do a calculation for an atom, it always seems like you have to add vacuum around it, which is essentially, because you are applying pbc, and do not want it to interact with other unit cells. Is there another way to solve this problem, where you assume the density to vanish far away?


texts: Hydrogen peroxide and ThickenUp (potassium chroride)

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Retr0bright is used to whiten yellow plastic.
The original recipe contains xantham rubber that is a bit hard to find.
I'm thinking about using Nestlé ThickenUp that contains xantham rubber, but it also contains potassium chloride. I know you should be careful with mixing hydrogen peroxide with other chemicals.
Does anyone here know if mixing 12% hydrogen peroxide with ThickenUp should be avoided or is considered safe?
Content of ThickenUp is corn and potato maltodextrin, xanthan gum, potassium chloride.


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What is the product when ammonium bicarbonate reacts with hexa-2,5-dione?

I thought of formation of 2 moles of NH3, water and carbon dioxide. And then the usual addition followed by elimination to the carbonyl group. But is it the case? Or will some cyclic compound result?


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Many text books say that there is a proportionality between the peak area of the chromatogram and the concentration. However, in my opinion, there should be a proportionality between the concentration and the peak intensity, not the peak area. The peak intensity is increasing proportionally with respect to the absorbance of the substance. Hence, by using the Beer-Lamberant law, we can induce there is a proportionality between peak intenstiy and the concentration.

Is there any mathematical relation between the peak area and the concentration?

Any help will be appreciated.


texts: How could the ideal gas law be discovered from experiments on real gases?

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The gas laws, namely Boyle's Law, Charles' Law, Avogadro's Law and Gay-Lussac's Law, are all experimental laws. Combining these laws, we get the ideal gas law $pV=nRT$. Also, "real life" gases do not exactly follow this law, so there are more laws for "real life" gases: van der Waals' law, Dieterici equation, etc., which approximately describe these laws within certain boundaries of the gas parameters: pressure $p$, volume $V$ and temperature $T$.

But there seems to be an apparent logical flaw: the ideal gas law $pV=nRT$  was found by experimenting on "real life" gases, but these "real life" gases do not follow the ideal gas law. How could this be the case?