texts: Do Fermi resonances show in Inelastic Neutron Scattering spectra?

texts: The Raman and FTIR spectra of a urea based mixture shows a strong Fermi resonance in the N-H stretching region, which difficults its interpretation. In an inelastic neutron scattering spectra of the same mixture, would the Fermi resonance be as obvious? Or not show at all?


texts: How does Borax Solution act as a buffer?

texts: What type of buffer is it? If it's a Weak Acid-Conjugate Base type of buffer, what is the weak acid and conjugate base?


texts: What are the products of [Ti(H2O)6]Cl3 + H2SO4 + K2Cr2O7 --->

texts: I am slightly lost on how to proceed with this equation. I know potassium dichromate is a strong oxidizing agent but I am unsure of how to deal with it along with the titanium complex. I was wondering if I could get tips on how to handle these types of equations.


texts: I think (111) surface refers to a flat surface of atoms that intersect with x,y,z axis at 1.


texts:
I am not able to solve this question. Here's my working

Have I done this in the right way? Because my textbook gives answer as 4 moles


texts: Is the activation energy always inversely proportional to the reaction rate?

texts:
When I obtained the activation energy using the Arrhenius equation for a 10-minute glowstick (rapid, rigorous reaction), it was almost 4 times that of a 12-hour glowstick (slow, mild reaction).

However, I learned in chemistry that a reaction with a lower activation energy need less energy for successful collisions, therefore will have a higher reaction rate.
This clearly does not hold true in my case, since a shorter 10-minute glowstick obviously has a higher reaction rate compared to that of a 12-hour glowstick(and thats why it only glows for 10 minutes).

Can anyone provide an explanation to this?


texts: Potentiometric determination of fluoride

texts:
We did an experiment of potentiometric determination of fluoride ions. In several beakers we added several concentrations of NaF solutions and then we added water. We calculated with the electrode the potentials.

Then in different beakers we added again NaF solutions, but now we added total ionic strength adjustment buffer (TISAB). We calculated again the potentials. I see that the potential values in the beakers with TISAB are bigger than those with water. Why?

I know that TISAB works in order to adjust the total ionic strength and to work against the interfering ions, but at this point why is there a difference? Does the hydroxide ion play such a big interference role such as the ferric ions, for example?


texts: Units for dissociation constant and relationship to Gibbs Free Energy

texts:
How does one "convert" between an equilibrium constant calculated from the Gibbs free energy for a dissociation reaction and experimentally determined dissociation constants?

$$
\Delta G^\circ=-RT\log(K_{eq})
$$

I think I understand the derivation of this equation and why the equilibrium constant should be unitless if it's defined in terms of activities.
But I have a binding reaction that has an estimated free energy change of $-32~\mathrm{kcal/mol}$, which yields a dissociation constant on the order of $10^{-24}$ at $298~\mathrm{K}$.
Is it correct to just multiply the equilibrium constant by the standard concentration (1 molar) to get a more typical dissociation constant with units? A yoctomolar dissociation constant seems kind of strange to me, but I'm not sure where I've made a mistake.


texts:
I was reading about the octet rule and saw exceptions in it. Different theories I read further and one of those was Sugden's concept of singlet linkage which state that the octet rule is never violated.

My question is that why Sugden's concept is not taught us or is not as popular as covalent bond or dative bond? Is there any problem with this concept? Does it have any limitations?


texts: How to Scan Aromatic Dihedrals To Obtain Force Field Parameters

texts:
I am trying to generate new force field parameters based on quantum mechanical calculation. I used amber manual "parameter development" title for this and I calculated bond-angle-non bond parameters but I am having a hard time obtaning dihedral parameters for aromatics Let's consider about pyrazin.  These are gaff2 pyrazin parameters :

ca-ca-nb-ca   2    9.600       180.000          2.000
h4-ca-nb-ca   2    9.600       180.000          2.000
nb-ca-ca-nb   4   14.500       180.000          2.000
h4-ca-ca-nb   4   14.500       180.000          2.000
h4-ca-ca-h4   4   14.500       180.000          2.000

When I scanned "ca-ca-nb-ca" dihedral angels, I found that  dihedral bond is breaking at 100 degre and 111 kcal/mol energy. According to manual, if this is an ordinary dihedral ca-ca-nb-ca   should have been (111/2=)55,5 kcal/mol V/2 value. But in gaff2 it is just 9.60kcal/mol. There is a huge difference.  So, how to obtain such aromatic ring dihedral parameters by using QM calculation?
My advisors said: "you should use twist scan not rotational scan" but I am not sure even if "twist-scan" exists and I am not sure "rigid" scan is the true answer.
Thank you.

NOTE: Here is the picture.every step is 10 degree.


texts: Are the stereoisomers of nucleosides actually anomers?

texts:
An anomer is an epimer at an (hemi)-acetal carbon like $\ce{R2C(OR')2}$.

Why is the 1'-position of a nucleoside referred to as the anomeric center despite the lack of acetal functional groups?


texts: Electron Affinity of Lead as compared to Bismuth

texts:
For "nitrogen family" and "carbon family" the trend goes that in a period, the electron affinity in case of group 15 is less than that of group 14. This is attributed to the half-filled p-subshell which tends not to gain an electron. But this true till antimony only. Bismuth has a greater electron affinity as compared to lead.
My question is, why so? What is there that brings about this particular exception?


texts: Calculation of volume required for titration with dibasic acid

texts:
Here is a problem:

  Titrate $1 M$ sulfuric acid with $\pu{50 ml}$ of $1 M$ sodium hydroxide solution. What volume of sulfuric acid will be required for neutralization.

This is a simple problem. My reasoning is since both reactants are strong we will have $\pu{0.05 L}$ $\ce{OH-}$ ions and for neutralization we need an equal number of $\ce{H+}$ ions. Since $\ce{H2SO4}$ is a strong acid and ignoring the second dissociation which is weak, we get an equal number of $\ce{H+}$ as $\ce{H2SO4}$ ions. Since concentrations are equal, the volume is simply $\pu{50 mL}$.

Apparently this is wrong. I think the source of confusion is what is meant by "required for neutralization". If you write out the molecular equation for this reaction and do stoichiometry you get a different volume.


texts: Why does Naphthalene turn into needle-shaped crystals by sublimation?

texts: I wonder why crystals of Naphthalene are needle-shaped after sublimation. Googling the fact, I could only confirm that it is true but failed to find the reason. Could someone please shed some light as to why this happens?


texts: Substance of higher latent heat of melting than water, similar melting point

texts:
I saw ingeniously simple "cooler box" yesterday - a double-walled plastic box with some liquid between the walls. You freeze it, and it keeps temperature near the freezing point of that liquid, until the liquid melts, while you can store dry foods inside.

Now, the efficiency of such a box will depend on volume of the liquid, to a lesser degree - how far below its melting point it was frozen, and on latent heat of its melting. (and insulation of course, but that's an entirely different matter.)

While I suspect the liquid used in the box I saw was just water with a little coloring added, I wonder if I could do better than that. Is there a substance that can be reasonably obtained by a DIY tinkerer, that has a latent heat of melting significantly higher than water, and a melting point at normal pressure somewhere "within reason" - achievable by normal kitchen freezer, and not above "food inside will spoil"? (bonus points for it not being overly dangerous...) Or maybe is there some way to increase latent heat of melting water ice by adding something to it?


texts: Why does the Förster resonance energy transfer scale as 1/r⁶?

texts: The title more or less contains my question - why does the Förster resonance energy transfer (FRET) (photon?)-based energy transfer mechanism, which folks sometimes use as a spectroscopic ruler to measure the inter-particle spacing between dye pairs, exhibit $1/r^6$ scaling for energy transfer efficiency?  Since we're in 3-space when performing a FRET measurement, I could understand some $1/r^3$ contribution due to us having an expanding sphere of radius $r$, but where does the rest of the distance-dependent efficiency dropoff come from?


texts: The open circuit voltage of a battery: Does it decrease with increase in pH of electrolyte while the voltage across a load increase?

texts:
Why does the open circuit voltage of a battery decrease with increase in $\mathrm{pH}$ of electrolyte, but the voltage across a load increase?

I tested a cell which had aluminum sulfate as its anode electrolyte ($\pu{12 g}$ aluminum in $\pu{50 mL}$ water and a $\mathrm{pH}$ of 3.2), and potassium hydroxide as the cathode electrolyte ($\pu{5 g}$ of $\ce{KOH}$ in $\pu{200 g}$ of water, $\mathrm{pH}$ of 12.3). The anode electrode was aluminum foil and the cathode was platinum. The open circuit voltage (OCV) of the cell was $\pu{0.9 V}$, and when connected to a $\pu{1 k\Omega}$ resistor, the voltage was $\pu{0.324 V}$.
When I increased the concentration of $\ce{KOH}$ from $\pu{5 g}$ to $\pu{10 g}$, and all other material concentrations were kept constant, the OCV decreased from $\pu{0.9 V}$ to $\pu{0.7 V}$, but when I attached the $\pu{1 k\Omega}$ resistor, the voltage increased to $\pu{0.42V}$.
I do not understand why increasing $\mathrm{pH}$ is causing the OCV to decrease, but increase the voltage under a load to increase.
I am guessing for the voltage under the load that maybe the higher concentration of $\ce{KOH}$ leads to more ions in solution thus increasing the current flow. But if this assumption/hypothesis were true, shouldn't the OCV also increase?
Can someone please help?


texts: Is this a valid structure for the nitrate ion?

texts: Why is the below structure not considered a valid structure for the nitrate ion? Is it because adding a double bond reduces the formal charges present on the nitrogen? Does the above form exist anywhere?


texts: Standard state of a substance - definition

texts:
In chemistry, the standard state of a material (pure substance, mixture or solution) is a reference point used to calculate its properties under different conditions. IUPAC recommends using a standard pressure $p^\circ=10^5\ \mathrm{Pa}$. Strictly speaking, temperature is not part of the definition of a standard state. For example, the standard state of a gas is conventionally chosen to be unit pressure (usually in bar) ideal gas, regardless of the temperature.

Source: Wikipedia

Now, as we can see the definition for the standard state of gas is independent of its temperature as well as volume. But the properties of gas depend on those and standard state is a reference point for calculating properties. So shouldn’t the definition of standard state for an ideal gas include temperature or volume?


texts:
When HF meets glass, Hexafluorosilic acid is formed (assuming some water is present). It appears that Hexafluorosilic acid and further attack glass? How is this so, considering that all F atoms are "used up" (already bonded to Si atoms)?

http://www.cdc.gov/niosh/ipcsneng/neng1233.html


texts: Equivalent Wyckoff position in different groups

texts:
I am not a chemist, I am a physicist, so please bare with me if what I am asking is rather obvious.

If I have two symmetry groups ($P4/mmm$ and $P\!-\!1$), is there a way to find their respective Wyckoff positions for which they are equivalent? Meaning finding the Wyckoff position for each of those groups, so that those positions in specific share the same symmetries. Hopefully I made myself clear.

I really doubt it's as easy as to look at the Wyckoff groups symmetries but I don't know.


texts: Where does the energy of formation of covalent bonds come from?

texts:
Consider two $\ce{H}$ atoms. Since the proton in one attracts the electron in another, they attract each other, and form a covalent bond ($\ce{H-H}$). Bond forming requires energy (436 kJ/mol for an $\ce{H-H}$ bond) – where does that energy come from?
If I put two $\ce{H}$ atoms in a container, would they form an $\ce{H-H}$ bond by themselves, or would I need to add energy to the system in order for them to bond?


texts: How can I keep homemade laundry detergent from disassociating?

texts: We've been using this recipe to make laundry detergent. Works fine, but after a few days it disassociates into a clear bottom layer and a pink top layer. It's mildly annoying to have to re-stir it every time. Can we do something about it?


texts:
What would be the effect of putting a solution in a strong electric field? Would the reactions in the solution be affected?

I'm thinking yes – lots (if not all) – chemistry is dependent on charge (partial/real charges) and by applying an electric field, we'd be affecting the very property of the molecules/ions that drives reactions.

Has this been researched?


texts:
If carbon monoxide can exist then why can't we have silicon monoxide?
Both carbon and silicon belong to group 14 and have similar chemical properties.


texts: Do I have to consider the water in the hydrate of a salt in a mass percent calculation?

texts:
When calculating the mass percent of an element in a compound, I understand that you divide the molar mass of the element by the molar mass of a compound.

In a case such as $\ce{NH4MgPO4.6H2O}$ is the "$\ce{6H2O}$" part of the compound?
If asked to find the mass percent of Hydrogen in this, what number would you use.

As well, I don't fully understand what the $\ce{6H2O}$ in the molecular formula means? Does it just mean that it is aqueous?

Any clarification would be helpful!

As well, what would be the name of that compound? Would it just be Ammonium Magnesium Orthophosphate? Or would it be something else because of the $\ce{6H2O}$?


texts: How does impurity of distilled water vary with time in air?

texts:
If I place distilled water in a glass beaker, how long is it expected to stay distilled?
What are the causes of it's impurity through air or other sources?


texts: Can nucleophilic attack be faster than rearrangement?

texts: Let's say in a reaction, unimolecular (SN1), we have $\ce{CH3-CH(CH3)-CH2+}$ carbocation, and a nucleophile $\ce{Nu-}$. Generally the carbocation is first rearranged and then there is attack of $\ce{Nu-}$, but can't it be that a very strong nucleophile, strongly attracted towards the cation, attacks the cation befor it rearrange to give kinetically controlled product (KCP) (at least at lower temperatures) ?


texts: How can one determine the oxidation number of nitrogen in $\ce{KCN}$?


texts: Electrochemical half cell without redox couple

texts:
In a book about electrochemistry the situation of a cell is described of which one half cell has an "undefined thermodynamic potential" as no redox couple exists:

$$
Pt/Cu^{2+}\ (0.01\ M),\ Cd^{2+}\ (0.01\ M),\ H_2SO_4\ (1\ M)
$$

Estimating the potential where reduction of Cu sets in by thermodynamic data when a potential is applied,

$$
Cu^{2+} + 2e \rightleftharpoons Cu,\ +\ 0.340\ V\ vs. NHE\\
Cd^{2+} + 2e \rightleftharpoons Cu,\ -\ 0.4025\ V\ vs. NHE\\
O_{2+} + 4H^+ + 4e \rightleftharpoons H_2O,\ +\ 1.229\ V\ vs.\ NHE,
$$

they argue that there is a rest potential range $0.340\ V ... 1.229\ V\ vs. NHE$ where no current is to be expected. Beyond these values current flow is expected. I don't understand this, because I understand $0.340\ V\ vs. NHE$ to be the standard potential of copper reduction under standard conditions, but the concentration of 0.01 M is not "standard" (= 1 M), right?

On the other hand, I'm afraid I have a general lack of understanding a system where one species of a redox pair is missing, because argueing in terms of Nernst's equation for such systems always leads to infinitely large (or small) potentials. In the case of copper above Nernst is not applicable in my opinion (correct ?), but what does the general relation

$$
 \lim_{[R] \rightarrow 0} (E_0 +  \frac{RT}{nF} \ln\frac{[O]}{[R]})=\infty
$$
for the reaction $O+ne\rightleftharpoons R$ mean? And how can one figure out the rest potential range for a half cell on thermodynamic basis (neglecting kinetics)? What does the situation for copper looks like where [R] does not appear in Nernst's equation? When the solution in the book is right, why?


texts: Why does nitrogen have a maximum covalency of 4?

texts:
As nitrogen has $1$ lone pair and $3$ electrons, either it should have maximum covalency of $5$ or $3$. But why does it have a maximum  covalency of $4$ instead?
Why did it leave $1$ electron? Why did it have to break a lone pair?


texts: How can a compound having a plane of symmetry be Chiral?

texts:
The compound( Given in the image below) is treated with $\ce{excess H2 in Pt}$.
Here, (a) - The given compound. (b) - What the answer should be according to me.
(c) - What the actual answer is:

Q1 - How is the chirality center at the top right even a chiral center, as the carbon has 2 identical groups attached to it?

Q2 - How is the compound as a whole a chiral compound? As far as I'm aware, compounds having a plane of symmetry (passing through the two 'chiral' centers in this compound) are supposed to be achiral?


texts: Reaction of alkyne with sodium in ethanol

texts:
What is the product obtained on the reaction of but-2-yne with $\ce{Na}$ in ethanol?

I know that $\ce{Na}$ in liquid $\ce{NH3}$ converts an alkyne to an alkene by anti addition, and $\ce{Na}$ in ethanol is the principle reagent in Bouveault Blanc Reduction, but what about this reaction.

The answer given in my book is a trans-alkene. Is this a standard reaction? Also does it depend if it is a terminal alkyne or not? (I guess yes, because the terminal alkyne will try to deprotonate)


texts:
Why is density of water maximum at 4 degree celsius?

We were having a discussion to this question in class and I could gather the following points.

1) $H_2O$ exists in a cage like structure in ice form, due to extensive hydrogen bonding.

2) density=mass/ volume : We are not changing the mass here, therefore increase in volume will directly correspond to decrease in density and vice versa.

2) This cage like structure can trap gases and result in increase in volume. Therefore, forming of this cage like structure will result in increase in volume and breaking of this structure will result in decrease in volume.

3) At 273K , this cage like structure of ice exists as shown. On heating, we find that molecules gain kinetic energy and this cage like structure breaks. Due to this breaking, the volume decreases. At 277 K or (4 degree celsius), it so happens that the entire cage like structure is broken which results in decrease in volume resulting in maximum density.
Therefore, density of water is maximum at this temperature.

4) At this stage, the cage has been entirely broken. Now, the molecules form this cage like structure again due to which volume again starts to increase as a result of which density decreases.

Here's what I couldn't understand:

  1) I cannot understand why trapping of gases results in increase of
  volume. The gases are trapped in the free space inside the cage.
  Whether that free space is occupied by gases or whether it remains
  unoccupied shouldn't result in increase of volume. Then why it's said
  that trapping of gases inside the cage like structure formed by ice
  results in increase in volume?

  2) I am not sure I heard the 4th point right because it clearly
  doesn't make sense. If at 277K, the cage like structure broke, why it
  will reform on further heating. On heating, we are giving the
  molecules more kinetic energy.They should roam about and not get tied
  down to a cage like structure. Why that cage like structure is being
  formed again after 4 degree celsius?


texts:
EDTA (Ethylenediaminetetraacetic acid) has a structure like this

But why, as the name 'Ethylene' suggests, doesn't it should have a double bond between carbons?


texts: I'm a high school student considering the concentration of solutions, and whether the concentration is constant at the bottom or towards the surface. Even then, how would I know that the solution is consistent and not more concentrated in places compared to others? Is there any visual way or method for identifying non-consistent concentrations in solution i.e. Copper (II) sulphate, Iron (II) sulphate


texts: How can I lower the flash point of stearic acid (Palm Based Fatty Acids)

texts: I am trying to build a environmentally neutral firelighter that does not use petroleum based accelerant. I have found that the flash point is way to high to be viable in Stearic Acid (Hexadecanoic acid / Octadecanoic acid). Is it possible to have a "safe", "environmentally friendly" and biodegradable additive to lower the flash point? I am open to suggestions and alternatives. Any assistance in this is appreciated.


texts:
Which one of the following substituents at para-position is least effective in stabilizing the phenoxide ion $\ce{PhO-}$
(a)$\ce{-CH3}$
(b)$\ce{-OCH3}$
(c)$\ce{-COCH3}$
(d)$\ce{-CH2OH}$

According to me it should be $\ce{-OCH3}$ because of its mesomeric effect which will counter the mesomeric effect of $\ce{O-}$.
$\ce{-CH3}$ has a positive inductive effect but, the mesomeric effect of $\ce{-OCH3}$ should be stronger and destabilize the phenoxide ion to a greater extent


texts: Relative molecular mass of an unknown gas in a mixture

texts:
A gaseous mixture contains oxygen and another unknown gas in the molar ratio of 4:1 diffuses through a porous plug into 245 seconds, under similar conditions same volume of oxygen takes 220 seconds to diffuse. What is the molecular mass of the unknown gas?

I used the Graham's law of diffusion to find the molecular mass of mixture.
i.e.
$$\frac{r_\text{mix}}{r_{\ce{O2}}}=\frac{220}{245}=\sqrt{\frac{M_{\ce{O2}}}{M_\text{mix}}}$$
$$M_\text{mix}=39.6$$

But what's next? How do I calculate the $M_\text{gas}$?


texts: How can one explain niobium’s weird electronic configuration?

texts:
As cited in an answer to this question, the ground state electronic configuration of niobium is:

  $\ce{Nb: [Kr] 5s^1 4d^4}$

Why is that so? What factors stabilize this configuration, compared to the obvious $\ce{5s^2 4d^3}$ (Aufbau principle), or the otherwise possible $\ce{5s^0 4d^5}$ (half-filled shell)?


texts: Stability of ferrous ions and iron(II) hydroxide in acidic conditions

texts:
I was reading a chemisty textbook when I came across the following statement.

  $\ce{Fe(OH)2}$ is not stable, even more so in basic conditions. [---] $\ce{Fe^2+}$ ions are also less likely to oxidise in the low pH range.

First attempts

No explanation was given. At first, I was hoping for a simple case of Le Châtelier – Braun principle. However, the equilibrium

$$\ce{4[Fe(OH2)6]^2+ (aq) + 4H3O^+ (aq) + O2 (g) <=> 4[Fe(OH2)6]^3+ (aq) + 6H2O (l)}$$

would suggest the opposite. Next, I considered a simple approach to complex stability. As a general guideline, metals in lower oxidation states favour cationic complexes. The opposite is also true. Therefore, one might conclude then that if anionic complexes are not preferred, $\ce{Fe^2+}$ ions ought to be stable.

One example would be that the hydrolysis is more hampered in acidic media.
$$\ce{[Fe(OH2)6]^2+ (aq) + H2O (l) <=> [Fe(OH)(OH2)6]^+ (aq) + H3O^+ (aq)}$$ Furthermore, in very basic conditions the hexahydroxidoferrate(II) would form. $$\ce{[Fe(OH)2(OH2)4] (s) + 4OH^{-} (aq) <=> [Fe(OH)6]^4- (aq) + 4H2O (l)}$$

However, this rule breaks down for $\ce{[Fe(CN)6]^4-}$ which is rather stable with $K_\mathrm{instability} \approx 10^{-37}$.

Half-reactions

As you might imagine, I was trying to avoid using half-reactions and the Nerst equation. Iron chemistry is rich and there are a myriad of possibilities. Before we move forward, let us note that the corresponding ion electronic structures are
$$\ce{Fe^2+:[Ar]{3d^6}};\\
  \ce{Fe^3+:[Ar]{3d^5}}.$$
So it seems that ferric ions are indeed more stable. Yet the reduction half-reaction
$$\begin{align}
  \ce{Fe^3+ + e- &-> Fe^2+} &
  E^\circ &= +0.77~\mathrm{V}
\end{align}$$
 implies the opposite. (Is this due to solvation?)

I did find a useful Pourbaix diagram (Andel Früh: Pourbaix diagram of Iron; $c(\ce{Fe}) = 10^{-6}~\mathrm{mol/l}$, $T = 25~^\circ\mathrm{C}$; wikimedia.org):

What we can tell is that ferric ions themselves are not favoured at a higher pH. In fact, the opposite is true. It just requires a strong oxidizer. This does not mean ferrous ions are not oxidized in basic conditions, it is just that the stable species are iron(III) oxide hydrates (probably iron(III)oxidehydroxide hydrates as well).

Problem

I have not really thought about this particular issue before, so I would definitely love to hear your ideas.

Why are ferrous ions and iron(II) hydroxide more stable at lower pH?
Why is the ferrous ion generally more stable, even though the electronic structure suggests otherwise?
This Pourbaix diagram does not take into account possible complex formation. If someone could explain the issue via complexes as well, I would greatly appreciate it.


texts:
I recently learned that there is such thing as a hybridization in chemistry, but I don't really get it.

For example, in $\ce{C2H2}$ (Ethene), they say the there are 3 electrons in three ${sp^2}$ and one electron in a normal $p$ orbital. How do we decide what orbitals get hybridized and what doesn't?


texts: Any large databases of IR Spectra that you are able to download many spectra in bulk

texts: I am currently working on a machine learning project, in which I need access to many IR spectra, the more the better, in order to build a classifier that will used some unsupervised learning in order to work out the functional groups present in the IR Spectrum. The only databases I have found so far do not have such a feature. Any help would be greatly appreciated.


texts: Energy per atom in a parallel radioactivity equation

texts:
I was reading an example in my textbook and the question goes like this:

In a parallel radioactive decay, find energy liberated per atom of 'A' in MeV.

The solution is proceeded like this:
$$
 \lambda _{1}/\lambda _{2}= \frac{(T_{1/2})_2}{(T_{1/2})_1}=\frac{20}{60}=\frac{1}{3}
$$
Energy per atom of A is $$= 20\times\frac{1}{4}
+40\times\frac{3}{4}=35 MeV
$$
I have understood how we have got the first step, but I'm unable to understand the second step. Why are 1/4 and 3/4 specifically being multiplied to 20 and 40, respectively? Also, where are we using the ratio we got in the first step, in the second step? It has got me all confused. In short, how is energy per atom of A calculated?


texts: Why does DMF (dimethylformamide) have 3 peaks in its 1-H spectrum?

texts: I get that the carbons can't rotate around the nitrogen due to its partial double bond character, but how does this result in the hydrogens being in different environments? As such would this mean all non rotatable bonds would result in hydrogens all with different peaks?


texts: Why do some compounds without carbonyl group give positive 2,4-DNPH test?

texts:
I was performing some experiments in Chemistry Lab today in which I had to find the functional groups present in a compound.

It being a very basic undergraduate course introducing us to the Chemistry lab, the functional groups were quite basic, and we just worked with mono-functional group compounds, including Carboxylic Acids, Amines, Aldehydes, Ketones and Phenols.

When performing the 24DNPH test on a white powdery substance (which I think had the carboxylic acid group), I got an yellowish-orange precipitate which was further characterized when I added dil. $\ce{HCl}$ to the test tube.

However, the sample gave negative Fehling's, Tollen's and Legal's tests (Legal's test is the sodium nitroprusside test).

Later, I even performed a test on another substance which gave positive primary amine test, as it gave me a scarlet dye in an azodye coupling reaction with $\beta$-naphthol. (This has stained my hand with reddish spots :D).

Point is, even this substance gave me a yellowish precipitate on adding 24DNPH, but it wasn't the normal orange/red precipitate which we see on reacting actual carbonyl compounds with 24DNPH.

This left me wondering, what compounds are these yellow precipitates that I had got?

I'd be very happy if someone can answer this as it is really intriguing me for a long time.


texts: I would like to identify if a wine glass is made of lead crystal (a destructive method is allowed). Lead crystal is said to be eroded by dishwasher detergent. I don't have a dishwasher, what causes the stains? Could I quickly identify lead crystal by exposing it to hot caustic soda?


texts: Would boiling distilled water in a kettle full of limescale increase the hardness of the water?

texts:
If I had a kettle which had limescale on it (due to several episodes of boiling hard water), and I would use it to boil distilled water, would that mean that some of the precipate dissolve into the distilled water, making that water harder than originally? If so, by how much?

I understand CaCO3 has very low solubility in normal conditions and requires CO2 to dissolve in higher amounts, but I'm not sure about how much is "low".


texts: How do hydrogen bonds break the ionic bonds of a crystal lattice?

texts: In the case of water dissolving sodium chloride. I was under the impression that hydrogen bonds were much weaker than the ionic bonds in sodium chloride, so how do they overcome the ionic bond strength? Do the ions simply get swarmed with enough water molecules so that the combined dipole interaction forces break the ionic bond? Or is it possible that because the sodium chloride dissolution reaction is endothermic the hydrogen bonds on their own are not enough to break the ionic bonds so the reaction must draw energy from the surroundings to do so (the reaction must be entropically favorable to do so, right?)?


texts: Is there a way to extract the diamagnetic and paramagentic components from NMR output from Gaussian16?

texts:
I'd like to be able to split the NMR value in Gaussian16 into its diamagnetic and paramagnetic terms. I'm coming over from ADF, where this can be done easily. Is there a straightforward command to give Gaussian16?

Thanks!


texts: What happens to the gas inside cold drinks as the cold drink is frozen?

texts:
According to Henry's law the amount of gas dissolved is directly proportional to the pressure exerted by a gas on the surface of the liquid.

And we know if we increase the temperature, the amount of dissolved gas decreases as it is an exothermic process and due to increase in entropy of system too , and if we decrease the temperature the amount of gas dissolved increase.

So what will happen to the gas inside the bottle if we freeze the cold drink bottle

  Does all the carbon-dioxide dissolve??

Assuming the bottle doesn't burst


texts: Fundamental equation of thermodynamics for magnetocaloric materials

texts:
The fundamental equation of thermodynamics, as us chemists (and chemical engineers!) are used to seeing it, is

$$ dG = - S~dT + V~dP + \sum_{i}\mu_i~dN_i$$

This gives the Gibbs free energy as a function of temperature, pressure, and composition, assuming there are no other relevant forces other than mechanical pressure.

The other day I watched a video on the magnetocaloric effect.  Obviously, there are non-pressure magnetic forces acting in such systems.  What's the proper form of the fundamental equation for magnetocaloric materials?

Suppose that the magnetocaloric material used is chemically pure and non-reactive during the magnetization process.  Then we could get rid of the $\sum_{i}\mu_i~dN_i$ term.  I suppose its also reasonable to assume that pressure is constant during magnetization / demagnetization process, and that the volume of the material is unchanged by magnetization so probably we could dispense with the $V~dP$ term as well (is that true?).

That leaves us with $dG = -S~dT + \rm{MAGNETIC~STUFF}$.  The $\rm{MAGNETIC ~STUFF}$ term probably has a $B$ or $H$ or something like that in it to represent the imposed magnetic field, but what else goes in there?


texts: What is the precise definition of standard molar entropy?

texts:
I understand what the standard molar entropy is, and how to use it in calculations, but I'm interested in understanding exactly how it's defined and measured.

My recollection from a long time ago is that it goes roughly like this:

for each element, assume that its entropy goes to zero at 0 kelvin when it's in some standard state
then, for the compound of interest, calculate and/or measure the entropy difference between the compound and its constituent elements at 0 K.

However, I'm not even sure that's exactly correct, and there are a lot of details that need to be filled in if it is right. Most of the following issues will be covered by the exact definition, but to be more elaborate, these immediately come to my mind: what exactly is the standard state for each element? Do all elements form a perfect crystal at 0 K, and how can we prove this? Should I think of the third law (zero entropy at zero kelvin) as being a definition that sets an otherwise arbitrary baseline, or can it be proven that the quantum mechanical von Neumann entropy really is zero for pure elements at 0 K?

An internet search turned up plenty of information about the values of standard molar entropy for various compounds and how to use them, but I wasn't able to find a resource with a detailed description of its definition.

What is the precise definition (preferably with reference) of standard molar entropy?


texts: Do magnesium and tin have the same volume?

texts: Having the same atomic radii of 145 pm, should one mole of tin and one mole of magnesium take up the same volume? Since tin is much heavier, that means tin is much denser than magnesium. Is this true, or is there an error in my thought process.


texts:
Can natural gas appliances run on Hydrogen? If so, does the appliance have to be modified and how significant of a modification would it need?

Thanks


texts: Hydroboration oxidation reaction on trans,trans,trans-1,5,9-cyclododecatriene

texts:
The given solution:

Could some one please explain the mechanism of the reaction? How it proceeds and why it proceeds that particular way? Also, what is the use of $\ce{CO}$?


texts:
We accept that, via observations that an electron possesses a negative charge and a proton a positive charge, both of which attracting each another. My dilemma lies here, what is the reason for the force of attraction or repulsion? If it may be due to the desire to become more stable and is logically comprehensible via mathematics of potential energy – but why does a body seek the desire to become more stable at all in the first place?

Though this question may be silly, and some might say this goes into metaphysics, but does anyone know why, or do we assume that everything – or the universe to be more precise, acts as it is, accepting it as a fact, and construct our calculations and laws above it? Are all chemical and physical knowledge based on taking the mechanics of the universe for granted?

The question was bothering me for sometime and finally decided to ask in search of an answer.


texts: Why are Tertiary Radicals more stable than Tertiary Carbocations?

texts: I think tertiary carbocation must be more stable due to Hyperconjugation and +I effect....


texts: How do I make a simple home distillation device?

texts:
Like this:

I have two medium sized glass flasks. I understand I need a T-shaped adapter from the first flask that will connect the thermometer and the condenser. So, I also need the condenser and a L-type adapter that will connect the last flask with the condenser.

Is the condenser really necessary for a completely beginner set up?

Do I really need the adapters? I'm worried they will not fit. How high are the costs for these parts?

Thanks for any replies. I know some theoretical chemistry stuff, but with this glassware I've got no idea what I'm doing.

EDIT: Thanks guys, I accidentally found a very nice chemical equipment store and a nice lady there sold me all the parts. I only didn't get the thermometer because it was way too expensive (and I can make something similar myself). It cost 80 eur. Flask (1l), adapter, condenser, another adapter, mount for the flask and rubber pipes. The thermometer was extra 35.


texts:
Per this article, "Gelatin is a thermoreversible, cold-setting polymer." Further, Jell-O is flavored gelatin.

Is the phrase "thermoreversible, cold-setting polymer" equivalent to the term "plastic?"

Is Jell-O, therefore and despite the unappealing sound of it, flavored plastic?


texts:
I have to bottles of Lamy blue-black fountain pen ink. It turns out that some months ago the composition of the ink was changed by the manufacturer and there is no difference in the package.
Before, this ink used to contain Iron-Gall. Which makes the ink more permanent (old inks contained most of the times Iron-Gall). As Iron-Gall is an oxidizer, it has been removed from the ink because it can damage the pens if not cleaned regularly.

I don't know much about chemistry and I wonder if any of you could tell me a way to know if my ink has Iron-Gall and therefore is safe for long lifespan documents.
I was wondering if litmus paper would do the trick comparing this ink with normal black ink (which does not have Iron-Gall).


texts: Artificial foods — Could you make them? And would they compare to their "organic" counterpart?

texts:
This is partly just a hypothetical, but basically.
If you were to take all the chemicals in an apple and put them together, could you make an apple? (Probably closer to apple sauce though.)
If this is possible, How would my almost-apple paste compare to a normal apple when it comes to nutrition?
I imagine it would not be nearly as healthy as a normal apple. As from my research, supplements to a vitamin do not have the effect that the vitamin would have if consumed naturally.

I know apples contain Alpha-linolenic acid, Ferulic acid, Isoquercetin, Lutein, Neoxanthin, Niacin, Thiamine, Riboflavin, Pantothenic acid, Vitamin B6, Folate, Vitamin C, Vitamin K, Carbohydrates, Sugar, Calcium, Iron, Magnesium, Manganese, Phosphorus, Potassium, Zinc, Asparagine, D-Categin, Farnese, P-Coumaric-Acid, Avicularin, Quercitin, Rutin, Ursolic-Acid, and Protocatechuic-Acid.

This is presumably not a comprehensive list by any means. I also only really used apples as an example. If there's another food you feel would be easier to "build" then please use that.

Thank you for giving this a read! And I apologize if I posted in the wrong place, I'm new to stackexchange.


texts: Orbital mixing in square planar D4h complexes

texts: Consider a square planar $\ce{ML4}$ complex with $D_\mathrm{4h}$ symmetry. Which orbital should the $\mathrm{a_{1g}}$ SALC of the ligands mix with, $\mathrm{3d}_{z^2}$ or $\mathrm{4s}$? Both of those AOs transform as  $\mathrm{A_{1g}}$.


texts: What is a "hydrogen-like" or "hydrogenic" atom?

texts:
I'm studying some chemistry on my own in anticipation for the new school year and in my book, I came across the Rydberg equation for the first time. I worked through some examples and everything was fine until I came across this comment on the question, "Calculate the wavelength of the radiation released when an electron moves from n=5 to n=2":

  For future reference: the Rydberg formula only works for hydrogen-like
  atoms.

What is meant by "hydrogen-like"? I've heard that solving for multi-electron systems is (near) impossible, so I understand why hydrogen is used here, but I don't understand what "hydrogen-like" is.


texts: Hydrogen is flammable, and for any fire to burn it needs oxygen. Why does a compound made of hydrogen and oxygen put out fires instead of catalyzing them? I understand that hydrogen and water are chemically different compounds, but what causes water to be non-flammable?


texts: Why is the boiling point of m-dichlorobenzene less than that of p-dichlorobenzene?  Shouldn't the former have a higher boiling point because it possesses a dipole moment? I think the van der Waals forces should be equal in both cases.


texts: Solubility of Aluminium Fluoride in other other fluorine-containing solvents

texts:
I encountered a problem which required me to compare the solubility of $\ce{AlF3}$ in various solvents, namely $\ce{HF}$, $\ce{KF}$ & $\ce{KHF2}$ .
Further, this problem neither supplied, nor expected me to utilize  any solubility data. Infact, the problem only asked for the expected order, discounting any exceptional factors that may affect the actual numerical data.
My thoughts regarding this are as follows;

As $\ce{AlF3}$ is a Lewis acid, I expect it to have higher solubility in solvents which have lone pair containing donor ; possibly the fluoride ion from $\ce{KF}$ may be such a species
Further, in aqueous acidic solution, I expect a lower solubilty owing to common ion effect lowering the solubility
I am unsure and unclear regarding the action of $\ce{KHF2}$
Perceptions regarding H-bonding and complex formations also seem to apply, but I am unable to formulate these coherently

Given these points, can someone help me to organize my thoughts? I wish to know the lines along which I should guide my thoughts.


texts: 3-index integral schemes for density fitting

texts:
Density fitting allows us to approximate the 4-index 2-electron integrals using 3-index integrals:

$$(ij|kl) \approx \sum_{Q}^{N_{aux}} (ij|Q)(Q|kl)$$

My question is, what schemes are used for the evaluation of the 3-index integrals? Do we simply modify existing schemes such as Obara-Saika and McMurchie-Davidson or are completely separate schemes given for this purpose?


texts: Textbook suggests secondary alkyl halides do not undergo SN1 reaction

texts:
The 8th edition of Organic Chemistry by Paula Bruice suggests that secondary alkyl halides do not undergo SN2 reactions. However, many other sources state the opposite. So, what is the correct answer?

  Tertiary alkyl halides undergo SN1 solvolysis reactions with poor nucleophiles such as water and alcohols, but methyl halides and primary alkyl halides do not. A recent investigation of Huges and Ingold's data showed that secondary alkyl halides also do not undergo SN1 solvolysis reactions.* Thus, methyl halides, primary alkyl halides, and secondary alkyl halides undergo only SN2 reactions.

The textbook refers to Murphy, T.J. J. Chem. Ed. 2009, 86, 519-524.

I'm curious as to whether this assertion has been upheld or disproved by other members of academia.


texts: Strength of Dipoles, Covalent bonds and H-Bonds

texts:
My textbook says:

  Dipole-dipole forces are 1% as effective as covalent bonds and the strength of a hydrogen bond is generally twenty times less than that of a covalent bond.

What do these statements mean?


texts:
$\pu{105 mL}$ of $\pu{0.10 M}$ $\ce{AgNO3}$ is added to $\pu{125 mL}$ of $\pu{0.35 M}$ $\ce{K2CrO4}.$ Will a precipitate form? $(K_\mathrm{sp}$ for $\ce{Ag2CrO4}$ is $\pu{1.12E-12}.)$

Answer:

   Yes, $Q = \pu{4.0E-4}$ which is greater than $K_\mathrm{sp}.$

Can someone please help me out with this question? I know that I have to find $Q_\mathrm{sp}$ and compare this to the $K_\mathrm{sp}$ given, and if $Q_\mathrm{sp}$ is bigger, then a precipitate will form. However, I do not know how to find $Q_\mathrm{sp}$ when two substances are mixed together.


texts: I titrated orange juice with NaOH. I used no indicator, but at around the point of inflection, the juice changed colour to a more mustard-ish colour. What is the reason for this colour change?


texts: "Chemicals" released in headphone with burned cable

texts: My friend works at a headphone company at the support service and today she came across someone who claimed that he threw his broken headphone away because he had heard dangerous chemicals could be released when the cable burned through (because they would be exposed to the outside world possibly) which was according to him affirmed at a local waste disposal service. As I am unable to find any confirmation for this claim online, I decided to go ahead and post the question here. I was a bit unsure whether to post on chemistry.SE, biology.SE or engineering.SE, but went ahead with this one in the end, hope it's not off topic, but if it is then my apologies.


texts: In entropy change of surroundings, what is T?

texts:
This question is simpler than the previous one about intuition of entropy; I just need to know whether the $T$ term in $dS_{Surr} = \frac{-dH}{T}$ refers to the temperature of the surroundings or the system. I think it needs to be both, no? For example, for water to boil, the system must have $T \geq$ 100 degrees C. But can it be said that at high temperatures the decrease in entropy of the surroundings due to endothermicity of the boiling reaction is less significant than at low temperatures, as per division by T, so at high temperatures of the surroundings boiling occurs spontaneously?

It seems like both explain the phenomenon, especially since boiling occurs over time in both a sample of water at 110 degrees C in a 32 degrees C environment until it cools and boiling eventually occurs in a 110 degree C furnace if the temperature of the water starts at 32 degrees C.


texts: Molecular Orbitals. Relative phase vs Bonding Anti-Bonding

texts:
Most intro explanations of molecular orbital formation go something like this:
as two 1s orbitals of H atoms approach each other, their wave functions begin to overlap, and due to constructive and destructive interference, a bonding and an anti-bonding orbital is formed.

Since initially there can be an arbitrary difference in phase between the two 1s orbitals, does this mean that the energy of the molecular bond is a function of the phase difference and that a bonding orbital will form only for a range of phase differences ?


texts: How to write a reasonable mechanism for the reaction of alcohols to synthase ketone?

texts:
In the section of reactions of alcohols in my textbook, there are no mechanisms or explanation for this reaction:

I am interested in Jones Oxidation particularly. I researched a little bit on internet but can't find a satisfying mechanism for it. Thanks in advance!


texts: At high enough temperature, diatomic molecules in a dilute gas should dissociate. Where do their electrons go? Will they dissociate into neutral atoms or into ions? Does it depend on the substance? What for $\ce{H2}$, $\ce{O2}$, $\ce{HCl}$, $\ce{HF}$? Which quantum mechanical technique can decide the question - Hartree-Fock?


texts: Calculate optimal surroundings for given reaction mechanism to lower activation energy?

texts:
Let's take a reaction that's fairly well understood, which in this case means that the reaction mechanism is known, maybe something like this from here:

If we know the reaction mechanism, we also know or can infer with some reasonable degree of accuracy the paths of all the atoms between reaction start and finish.

Is there a way to calculate surroundings, perhaps just electron densities to begin with, in which the activation energy is minimal for this reaction? (Yes, I realize that another way to put this is "can we begin designing a catalyst for this reaction mechanism?")


texts: Does brewing tea with hard water reduce the amount of bioavailable fluorine?

texts:
I read that brewed tea contains a relatively large concentration of Fluorine.

Fluorine can have negative health effects such as Skeletal Fluorosis. EDIT: I understand some Fluorine is necessary and has benefits. This is just to inform why I have structured this hypothesis. I am interested in the chemistry not the health effects as that is a different topic.

Tap water and especially hard water contains lots of Calcium ions.

Would Calcium and Fluorine bond to form Calcium Fluoride? I'm obviously not a chemist, but I assume it would be a lower energy state than the soluble ion pair in the tea, correct? It forms Fluorapatite on tooth enamel.

This Calcium Fluoride SDS indicates that eating solid CaF2 straight won't immediately kill you, so I assume Calcium Fluoride does not decompose in HCl stomach acid, correct?

So with that logic would the following be true?

Mol bioavilable F-  =  Mol F- from brewed tea  -  2*(Mol of Ca2+ in hard water)

If that is the case, it brings up some other interesting questions, like if moderately hard municipal water actually has any Fluorine in solution or not...

EDIT: To select a best answer I need to know:

if Ca ions bond with F ions in solution to form CaF2
and to know the percent or time-rate solubility of CaF2 in stomach acid.

Thanks!


texts: Plasticisers and other impurities from polyethylene laboratory bottles?

texts:
Does polyethylene (PE), widely used for wash/squirt bottles in labs, contain soluble compounds such as plasticizers that can accumulate in organic solvents (e.g. alcohols, acetone) after prolonged storage? I noticed an odd, "plasticky" smell from old propanol/ethanol from such bottles and the bottles, once emptied, also give off a similar smell. This smell is not present in fresh, analytical grade solvents or new, unused bottles.
Can plastic bottles be a source of e.g. bisphenol A and get absorbed by the skin, when applying alcoholic hand rub from such bottles?
It has been shown that plastic labware can contaminate their content with various autofluorescing compounds.
PS.: I have the exact model, but I'm not sure if one is allowed to post links to specific products/manufacturers here...


texts: In SAXS experiment, you observe strong Bragg peaks at q values of x, y and z. What are the d-spacings of the corresponding diffracting planes?

texts:
If d=2pi/q
then would it simply be that
d=2pi/x, 2pi/y and 2pi/z?
This feels to simple and i feel like maybe some version of the 4pisin(theta)/lambda equation should be here soemwhere but I cant figure out how.


texts: Best solvent for crystallization + mass recovered from crystallization + purity of the product

texts:
I have a chemistry final tomorrow and this question on my sample exam through me for a loop. I'm not entirely confident I can work out problems B and C, but those questions rely on the answer to A.

If you could please especially explain how I'm supposed to read the solubility chart to understand which solvent is the best, that would be awesome.


texts: Ignoring spin, consider an electron in a hydrogen 2p orbital, what is its orbital magnetic moment?

texts:
I know that a magnetic dipole moment is given by $$\mu=\frac {-e}{2m}I$$ and that the z component of angular momentum is $$m_j\hbar.$$ However, I have also seen that angular momentum $I$ is given by $$I=\hbar\sqrt{l(l+1)}.$$ Is this also the component in the z direction or is it different? Are both expressions for angular momentum right? Which one do I use to answer the question?

(This question was asked in a problem sheet that I have been asked to do over the vacation. See below for context of question).


texts: Why does this reaction take place in terms of electronic structure?

texts:
I need to know, in terms of electronic charge - the electrophiles and nucleophiles involved - how the electronegativity of the potassium and hydrogen atoms alongside the hydroxide and H+ ions result in this reaction taking place. You could also think of this as asking why this reaction is exothermic from an organic chemistry perspective - why are the products more stable in terms of their electronic arrangement. It might be helpful to have the mechanism explained perhaps.

$$\ce{2K + 2H2O -> 2KOH + H2}$$

Of course, I have learnt before that potassium is higher up the reactivity series than hydrogen, but what does this mean on a deeper level - what factors mean that potassium is more reactive than hydrogen in terms of electron arrangement.


texts: Given an unbalanced chemical equation, is it possible to determine the largest possible coefficient that could be used in the balanced equation?

texts: I am writing a program to balance chemical equations, and would love to know if there is an algebraic way to determine the greatest possible coefficient that I would need to check.


texts: Why does the phosphorus trifluoride molecule have dipole moment?

texts:
My book says that from drawing the Lewis structure for the molecule below, you can conclude that it has dipole moment. Can someone please explain why?

I understand that the dipole moment expresses the polarity of the bond. And that the dipole moment of a molecule is the sum of the dipole moments for each bond in the molecule.


texts: How do I synthesize 3-hydroxydihydrofuran-2-one from formaldehyde?

texts: I want to synthesize 3-hydroxydihydrofuran-2-one from formaldehyde but I do not know of a method. I tried a Mannich reaction and lactonization after dehydration.


texts: Is the reaction between a carboxylic acid and alcohol endothermic?

texts:
I would say that it is endothermic, and then by increasing the temperature, one could get more product, disturbing the equilibrium.

Is this true, though? During an esterification, some bonds are broken, releasing energy. The opposite reaction splits the ester and adds the atoms back, which I suppose releases energy which is then bound in the bonds adding back the water molecule.


texts: Great books in Experimental Organic Chemistry?

texts: This summer I've quite a lot of free time, so I decided to study experimental Organic synthesis. I don't even have basic experimental chemistry knowledge, however my theory is pretty firm( Clayden level maybe ). What I need is good experimental organic chemistry books. Books with good illustrations will be welcome.


texts:
Ethanoic
 (acetic) acid can undergo fermentation by methanogens to create
$\ce{CH4}$ and $\ce{CO2}$. Is there any way that I could perform this
reaction without any microorganisms, specifically with the concentration
 of ethanoic acid found in vinegar, for example with UV light and such?

Also, if this is impossible, what species of bacteria is required?


texts: Do you include the "10 H2O" in the formula for borax?

texts: When you calculate the mass of borax needed to make up a standard solution, do you include $\ce{\cdot 10 H2O}$ in the formula for borax? Why or why not?


texts:
In an aldol condensation reaction, I synthesized a molecule out of two unknown reactants. These reactants I found to be 4-chlorobenzaldehyde and acetophenone which made 4-chlorochalcone. I was given an H NMR spectrum to identify and label the hydrogens for the molecule but am having trouble reading it!

There is a quintuplet with an integration of 6 but no where in the molecule am I seeing 6 hydrogens that share a chemical environment (I counted 7 environments). Is this possible or could I have come up with the wrong product structure?

Any help deciphering this would be great!


texts: Suppose a non-polar solid is dissolved in ethanol. Water is added to the solution. Will the solid separate, if it isn't soluble in water?


texts: Does exothermic solvation mean solute is more soluble at low temp?

texts:
(I'm surprised this question or a very similar one hasn't been asked, so I wouldn't be surprised if I just failed to find a question with my search that does answer this question.)

I dissolved some $\ce{K3PO4}$ in water a while back, and the solution became very hot. I commented on this to my labmate, and he said "So that means it's more soluble at low temperature, right?" I evaded response because I disagreed but didn't have a thought-out response yet.

I think he thought of the reaction as:
$$\ce{K3PO4 -> 3K^+ + PO4^{3-} + heat}$$

But I think that's missing an important step. I think it's more like this:
$$\ce{K3PO4 -> 3K^+ + PO4^{3-}}$$
$$\ce{PO4^{3-} + H2O <=> HPO4 + OH- + heat}$$

Phosphoric acid's third pKa is pretty high, so the second reaction is pretty significant. This, I would say, is why this particular reaction is so exothermic. So, in this case, I don't really think the heat plays into the solubility of potassium phosphate.

Sometimes, though, solvation comes with a positive change in temperature. For instance, the enthalpy of solvation of sodium iodide is $\mathrm{-7.53\ kJ/mol}$. Sodium iodide, though, is still more soluble at high temperatures. I could be missing something here, though.

In the cases where it is specifically the solvation reaction that causes a temperature change, is it the true that lower temperatures always increase solubility of salts with exothermic solvation reactions (and vice-versa)?

I'd say that the answer is no because the solvation should be dependent on $\Delta H - T\Delta S$ and, since the enthalpy change half of that formula is temperature independent, as $T$ goes up, solvation should be favored by any solvation that has a positive change in entropy. However, I can't really think of any solvation that has a negative change in entropy.


texts:
I am reading a book (Into That Darkness) about the Nazis, where there is the following passage:

  causing unimaginable suffering to the deportees who were either left waiting, naked and without food or water, in the open, sometimes for days, or else were crammed into railway cars the floors of which had been covered with lime and were left to suffocate on sidings

What is the meaning of “the floors of which had been covered with lime”?

Is “lime” short for something? Was the floor covered with this intentionally, or did this “lime” accumulate naturally? What would be the consequences of this to the people in the railway cars?


texts: What is the absolute configuration of carbon 4 in glucopyranose?

texts: My colleague and I have been wrestling with the assignment of chirality to the 4th carbon atom in glucopyranose. In the linear form of glucose, the 4th carbon is definitely (R); therefore it will retain that chirality as it forms the hemiacetal. However, looking at the ring, we are having a hard time figuring out why the 3rd carbon gets priority over the 5th by CIP priority rules. Both the 3rd and 5th carbons are attached to $\ce{C,H,O}$. The question is where do you go after that to assign priority?


texts: Why do we sometimes write reactants above the reaction arrow?

texts:
We write:

\[\ce{Alcohol ->[\ce{KMnO4}] Acid}\]

The alcohol forms a carboxylic acid, i.e. gains an $\ce{O}$ from $\ce{KMnO4}$. This means $\ce{KMnO4}$ is a reactant! Then why is it written above the arrow?

What else do we write above the arrow?


texts:
When we add tollens reagent (diamminesilver(I) cation, $\ce{[Ag(NH3)2]+}$) to glucose it forms a silvery mirror on the walls of the container. Since the sides are coated with actual Silver,

is there any possible reagent/method to take the silver out from the sides of the test tube.?
will it be in its pure form or will there be organic/inorganic  impurities?


texts: Safety of IPA and sodium hypochlorite mixture?

texts:
Is the mixture of 97% isopropyl alcohol and 0.5% of sodium hypochlorite safe?
Do they react together and form any compounds ?

Does this mixture present more danger to humans and animals than its ingredients separately ?


texts:
I’m a little confused on this topic. If I have a solid that I dissolve in water and that undergoes an exothermic reaction, can I assume that the specific heat $c$ of the solution instantaneously after the dissolution occurs is equal to $\pu{4.18 J g-1 °C-1}$? Does dissolving something in water change the specific heat of the solution? Or can I just say that the specific heat of the solution (solid plus water) equals the specific heat of water?

My first instinct was to think that yes, dissolving a solid in water does change the specific heat of the solution. If this is true, then I thought I might determine the overall specific heat of the solution by taking the specific heat of water and multiplying it by the percentage of the solution that is water, then adding that to the specific heat of the solid times the percent of the solution that is ions from that solid.

I’ve overthought this quite a bit, and I’ve tried to find an explanation on the internet. I’m pretty sure I’m thinking about this incorrectly, and I apologize if this is a bad question. Any clarity you could provide would be much appreciated.


texts: Amount dry acid or sodium bisulphate needed for varying hardness values

texts:
My question is regarding the use of sodium bisulphate to lower the hardness of water. I am attempting to come up with a label to let consumers know how much product (dry acid or sodium bisulphate) is needed for varying hardness values.

Using the equation $$\ce{CaCO3 + 2NaHSO4 -> Na2SO4 + CaSO4 + CO2 + H2O}$$I have found the following ratios:

$\pu{120 mg/L}$ $\ce{CaCO3}$ requires $\pu{0.288g}$ $\ce{NaHSO4}$,
$\pu{180 mg/L}$ $\ce{ CaCO3 }$ requires $\pu{0.432g}$ $\ce{NaHSO4}$,
etc.

My question: How much calcium will react with bisulfate? And how can I use this information to determine the change in hardness? Will starting pH of the water affect the calculation?


texts:
I know this may be a too generic question, but here it goes anyway.

It is already know that solid water (ice) organizes its molecules in a lattice (in a variety of 16 different crystals and one amorphous phase). See, for instance, http://en.wikipedia.org/wiki/Ice .

Now, what about liquid water? Is it the case that there are a (limited) number of local structures, like stable clusters or lattices configurations, combining and dissociating over relatively short periods of time, that dominate the liquid phase, loosely resembling the organization of a solid phase (the principal difference being that the hydrogen bonds would be weaker and would break more easily because of thermal agitation)? If so, what are those frequent structures?


texts: Can isotopes of a given element be represented by different symbols?

texts:
Can isotopes of any given element be represented using a completely different chemical symbol? What's the IUPAC's take on this?

Sure, ordinarily you would add the isotope's mass as a superscript to the element's symbol to differentiate it from other isotopes: For example, carbon-12 ($\ce{^{12}C}$) and carbon-14 ($\ce{^{14}C}$); however the base-symbol $\ce{C}$, for carbon, doesn't change.

But the isotopes of hydrogen don't seem to follow this strictly. Often, I see deuterium ($\ce{^{2}H}$) and tritium ($\ce{^{3}H}$) represented by $\ce{D}$ (I see this one in organic chem textbooks a lot) and $\ce{T}$ respectively. Does this "convention" fit in with IUPAC norms? If so, can isotopes of other elements be represented differently as well?


texts:
My book asks me to consider reacting 1-butene with NBS and light.

I know that NBS and light leads to radical formation, and this is an allylic/benzylic bromination problem.

However, my book only provides one product.

Aren't both products expected? Actually, I would expect one product in excess (the book actually listed my minor product as the sole product). There are at least two resonance contributors, and the more major one has the more substituted radical.


texts: Newman projections: how to tell which groups are bulkiest to determine what is the most stable conformation?

texts:
The scenario

Let's say we have a molecule where in the Newman projection the front carbon has a hydrogen, methyl and an ethyl, and in the back carbon there's a hydrogen, something like a S, Cl or Br (bigger than carbon but only one atom), and something like another ethyl or isopropyl:

My understanding

Methyls/ethyls/isopropyls etc. would cause more steric hindrance than something like S, Cl or Br because they consist of multiple atoms and take up more space, so in the scenario above, the front carbon's ethyl should be 180° away from the back carbon's ethyl/isopropyl, and the S/Cl/Br's position would be dependent on the ethyl from rotation. I think the following should be the most stable conformation:

My question

I've seen some similar examples where (in the same type of scenario) the S/Cl/Br was considered "bulkier" and was put 180° away from a big isopropyl, when something like an ethyl could have been there instead, but was put only 60° away from the big isopropyl (see the first illustration). I'm not sure if these examples were just wrong or if I'm completely misunderstanding how to determine what's bulkiest, so any advice on how to determine that would be super. If a table that ranks most-to-least bulkiest exists, please share.


texts: Reaction between chlorine gas and oxygen at 600 degrees Centigrade

texts: Chlorine gas will not normally react with oxygen gas directly at STP. However, would the two react at standard pressure and 600 degrees Centigrade?


texts: How do I compare the C=C bond lengths in this cumulene?

texts:
How do I arrange these chemical bonds in an increasing/decreasing order based upon their lengths?

I understand that the bond (a) will be longer than (b) because (a) is a bond between sp² hybrid and sp hybrid carbon atoms, as opposed to (b) which is a bond between two sp hybrid carbon atoms. But how do we compare bond (c)?


texts: Is there a computer program capable of showing protein conformational changes based on pH?

texts:
As it is known, changes in pH change the attractions between the groups in the side chains of the protein.
Acidification can, for example, cause protonation of the $\ce{COO-}$ end to $\ce{COOH},$ reducing interaction forces and provoking the unfold of the protein.
I would like to know if there is any software (or any resource) that, given the quaternary structure of a protein, allows you to visualize or obtain an analysis of how this structure will vary according to different pH values.


texts:
If glycerine $\ce{C3H5(OH)3}$and methyl alcohol $\ce{CH3OH}$ are sold at the same price per kilogram, which would be cheaper for producing an antifreeze solution for the radiator of an automobile radiator?

I think that more depression in freezing point will result in a better antifreeze solution. It depends on molal freezing constant. How can I predict this?


texts:
$$\ce{CH2=CH-CH=CH2 ->[\ce{H2/Pt}][\pu{1 equiv}] ?}$$

I thought $\ce{H2}$ should add to one of the π bonds and form but-1-ene. But the answer is but-2-ene.

I couldn't understand this.


texts:
Hartree-Fock method introduces electron (spin)orbitals and they are commonly used for qualitative rationalization of many molecular properties. However, MOs have meaning only if we ignore electron correlation. Post-HF non-DFT methods build correlated wave-function, but due to correlation extracting independent orbitals from them is not possible.
Electron density still is a somewhat informative concept even with no orbitals involved, but we like to talk about $\pi$-systems, sigma-bonds and the like and relate electron transitions to molecular features. So, I'm interested in existing approaches to analysis of post-HF wavefunctions (for example, obtained from Coupled Cluster method).
Are there any well-known approaches to analysis of correlated wavefunctions that do not rely on concept of orbitals that allow to relate some molecular properties to local structural features?


texts:
I was wondering if it is possible to make formaldehyde (1) from urea (2).

I noticed that they have a similar structure, but the two hydrogen atoms in formaldehyde are replaced with two amide groups in urea. Would it be possible to remove those groups and replace them with hydrogen?


texts: Is it possible to have Zero order Elementary Reaction?

texts:
I was going through a question, which got me confused. Is decomposition of NH3, an elementary reaction?

I have studied that  for elementary reactions, Order = Molecularity,
if so, then why they are different in this reaction.
If this is not an elementary reaction, Then molecularity has no significance. Each step should have its own molecularity. isn't it?
So, Is it possible to have zero order elementary reaction ?


texts:
My chemistry textbook states that $[\ce{H3O+}][\ce{OH-}] = K_w$ in all aqueous solutions, which we know of as $K_w$. However, I was wondering why this was true. The textbook states that it is true because $K_w$ is an equilibrium constant, but why are we allowed to assume that the other ions take no part in this reaction?

To clarify further, consider the following reaction
$$\ce{HCl + H2O (l) <=> H3O+ + OH- + Cl- }$$
Of course this isn't balanced, but why doesn't the hydrogen ion on the left affect the equilibrium constant?


texts: Equivalent conductivity of barium chloride at infinite dilution

texts:
Find out the equivalent conductivity of barium chloride at infinite dilution given that the ionic conductivities of $\ce{Ba^{2+}, Cl-}$ are $\pu{127 ohm^-1 cm^2 equivalent^-1}, \pu{76 ohm^-1 cm^2 equivalent^{-1}}$ respectively.

Equivalent conductivity is defined as.

  The equivalent conductance of an electrolyte is defined as the conductance of a volume of solution containing one equivalent weight of dissolved substance when placed between two parallel electrodes 1 cm apart, and large enough to contain between them all of the solution.

One gram equivalent weight would be simply half of the entire compound so
$$\text{Equivalent Conductivity} = \dfrac{1}{2} \times 127 + \dfrac{1}{2} \times 2 \times 76$$

This comes out to be 139.5 however the answer is 203.


texts: Trend of second Electron Affinity for N,O,F,P,S,Cl

texts:
I am aware of the definition of electron affinity and electron gain enthalpy (EGE). N has positive EGE1, and EA of P,S,Cl is more than N,O,F respectively. I want to arrange them in order of their EA2 in periods and groups.

My attempt : F,Cl attain noble gas and it's EA would be close to IE (ionization energy) of alkali metals, so, quite small. O and S would be halogen with quite high EA. P and N would be S and O so, somewhere in between the above two.

Hence, O>N>F and S>P>Cl.

for groups, I would still say that 3rd period would have more EA than 2nd but the only data that I have (from another chemistry.stack question) is 2nd EA of O is more than S.

Some help regarding data availability of EA2 is needed and fault in my logic.


texts: Why does magnesium bromide transfers from a carbon atom to nitrogen in piperidine?

texts:
In this reaction, why does $\ce{MgBr}$ goes to the $\ce{>NH}$ group and form a bond with nitrogen by removing $\ce{-H}$.
Also where does the negative charge go?


texts: Calculating enthalpy change and energy required to convert lead sulphide to lead

texts:
Consider the following:
  $$\begin{alignat}{2}
\ce{PbS(s) + 3/2O2(g) &-> PbO(s) + SO2(g)}\qquad&&\Delta H^\circ = -413.7~\mathrm{kJ} \\
\ce{PbO(s) + C(s) &-> Pb(s) + CO(g)}\qquad&&\Delta H^\circ = +106.8~\mathrm{kJ}
\end{alignat}$$
  a. Calculate the enthalpy of the following process:
  $$\ce{PbS(s) + 3/2O2(g) + C(s) -> Pb(s) + SO2(g) + CO(g)}$$

  b. What is the energy needed to make $454\ \mathrm g$ of $\ce{PbS}$ into $\ce{Pb}$?

My efforts:
a.

$\ce{PbS(s) + 3/2O2(g) -> PbO(s) + SO2(g)}$
$\ce{PbO(s) + C(s) -> Pb(s) + CO(g)}$
$\Delta H_\mathrm r^\circ = \Delta H_{\mathrm r(1)}^\circ + \Delta H_{\mathrm r(2)}^\circ$
$\Delta H_\mathrm r^\circ = -413.7~\mathrm{kJ~mol^{-1}} + 106.8~\mathrm{kJ~mol^{-1}} = -306.9~\mathrm{kJ~mol^{-1}}$

b. How do I find the energy needed?

Molecular mass of $\ce{PbS}$ is   $239.2650~\mathrm{g~mol^{-1}}$

so we have $\frac{454~\mathrm{g}}{239.2650~\mathrm{g~mol^{-1}}} = 1.897~\mathrm{mol}$ of $\ce{PbS}$

So energy required is $1.897~\mathrm{mol} \times 306.9~\mathrm{kJ~mol^{-1}} = 582.2~\mathrm{kJ}$


texts: Bond dissociation energy for polar molecules

texts:
This formula relates to how Pauling determined the values for electronegativity for all the elements and how delta (if big) shows that the molecule is very polar. Delta being:
$\Delta =\Delta H\left(AB\right)-\Delta \:0.5\left(\Delta \:H\left(A2\right)+\Delta \:H\left(B2\right)\right)$
$\Delta H\left(AB\right)$ is the experimental bond dissociation energy. The difference in experimental and theoretical bond dissociation energy is caused by the electronegativity of the molecule.
The more electronegative the atom the bigger the delta value. But why is that?


texts: Why was rhenium used as an igniter in flash bulbs?

texts:
It looks like it typically had a current passed though it to ignite zirconium threads.

What properties of rhenium made it the best metal to use for this?


texts: If polycarbonate plastic is a polar material with ester bond linkages which usually hydrolyze in acids, why is it resistant to both weak and strong acids (as polar substances)?


texts: Relationship between freezing point depression and hydrogen bonds

texts:
Freezing point of a solvent is decreased due to the added solute particles in it. e.g. ions. Therefore electrolytes contribute to lowering freezing point (say for physiological conditions).

If a particular solution has a non-electrolyte solute, which is held together with hydrogen bonds (forming dimers), I want to know how do H-bonds affect the freezing point?

Pure water itself forms hydrogen bonds. Yet at 0'C it freezes theoretically. How to approximate effect of the hydrogen bonds in an acidic solution to its freezing point depression theoretical value? e.g. do H-bonds in CH3COOH halve the freezing point depression value?


texts: When does Hartree-Fock fundamentally fail?

texts:
The Hartree-Fock approximation (HFA) works by assuming each electron sees the effective electric field from all the other electrons as some self-consistent field.

The HFA is known to give pretty decent results, but often gets the last quantitative bit of accuracy wrong. This last bit is attributed to mysterious many-body or "strongly-correlated" effects.

There are many examples of HFA quantitatively giving wrong answers (energies are wrong, incorrect numerical results,  etc.). But, are there general phenomena that HFA gets totally wrong? I'm thinking of something where the chemistry/physics is fundamentally different from what HFA would tell you. Said differently, when do "strong correlations" actually matter and fundamentally change things in a chemical context?

I've tried reading up on this topic in the physics literature, and it is incomprehensible despite being an ex-physicist myself. Most of the discussion is about high temperature superconductors and complicated transition metal oxides. I can't understand the basic phenomena without all the specific details.


texts: Should compounds in a generic reaction be italicised (typography)?

texts:
As of recent, I provided an answer to the question Law of mass action & collision theory. Therein I wrote a generic reaction

$$\ce{$r_1$R1 + $r_2$R2 + \ldots + $r_n$R_n <=> $p_1$P1 + $p_2$P2 + \ldots + $p_m$P_m}.\tag{1}$$

It seemed natural to write stoichiometric coefficents in Italic, and use upright Roman for the species themselves.

Italic would be in line with the fact that the coefficients are numbers, and vary with reactions (are different for different transitions).
Upright Roman is how we usually write chemical species, e.g., $\ce{NaCl}$.

Though if I were to overthink, the $\ce{R_$i$}$ would also seem to be variables as such. Since this is a generic reaction, $\ce{R_$i$} \in \{\mathrm{every\ imaginable \ chemical \ species}\}$. Using this logic, I ought to write $(1)$ instead as

$$r_1R_1 + r_2R_2 + \ldots + r_nR_n \ce{<=>} p_1P_1 + p_2P_2 + \ldots + p_mP_m.\tag{1'}$$

Is there an official example or guideline how to handle this situation?

Personally I wholeheartedly support option $(1)$ but is this what is recommended?

What about the subindices? Upright or Italic?

Note that this qualitatively differs from Proper typography of “$\ce{NO_x}$”. There the number of elements actually changes within a chemical species (marks the number of carbons in alkanes for example) whereas here it is more for labelling purposes.


texts: On seeing this graph closely I noticed the there a element with no proton. But with no proton there will be no electron too and don't think that an lone neutron would form an element. So is that given a half-life on neutron OR there exist a element (isotope) with no electron?


texts: Electrophilic nature of bromine free radical

texts:
My chemistry teacher told me that Bromine radical is a weak electrophile, and that it is more likely to join the more electron rich part of a molecule.

However I could not verify his statement from any book or Google.

Hence I am asking this question on this website: Is bromine radical electrophilic in nature or is there some other reason as to why bromine radical joins the more electron rich part of the molecule?


texts: Why density functional theory favors a uniform electron density?

texts:
Why density functional theory (DFT) favors a uniform electron density when we use it to calculate ground state electronic structure self-consistently?

For example, when we use DFT for calculating the (ground state) electron density of two $\text{H}$ atoms with a separation somewhat larger then the bond length of an $\text{H}_2$ molecule, there will still be a non-negligible electron density between the two atoms as if there is still a covalent bond. As a result, the calculated electronic ground state is essentially an excited state of the system.

I cannot remember where did I read this, and I don't understand why DFT has such a problem. I think the problem resides in the fact that we use a local exchange-correlation functional $E_{XC}$ like LDA and GGA. But I don't understand why a local $E_{XC}$ will lead to a uniform electron density.


texts: Why would red fuming nitric acid become white fuming nitric acid if left out at low temperature?

texts:
I'm reading this answer which refers to both red fuming nitric acid (RFNA) and white fuming nitric acid (WFNA).
Those two Wikipedia articles say:

Red fuming nitric acid (RFNA) is a storable oxidizer used as a rocket propellant. It consists of 84% nitric acid (HNO3), 13% dinitrogen tetroxide and 1–2% water. The color of red fuming nitric acid is due to the dinitrogen tetroxide, which breaks down partially to form nitrogen dioxide. The nitrogen dioxide dissolves until the liquid is saturated, and evaporates off into fumes with a suffocating odor. RFNA increases the flammability of combustible materials and is highly exothermic when reacting with water.
White fuming nitric acid (WFNA) is a storable liquid oxidizer used with kerosene and hydrazine rocket fuel. It consists of nearly pure nitric acid (HNO3). WFNA is commonly specified as containing no more than 2% water and less than 0.5% dissolved nitrogen dioxide or dinitrogen tetroxide.
WFNA as an oxidizer has somewhat less performance than red fuming nitric acid (RFNA) but is considerably safer (though extremely corrosive), as it has little to no dissolved nitrogen tetroxide, which is an extremely toxic and volatile chemical. If not inhibited, it will form nitrogen tetroxide on contact with most metals and some organic materials. WFNA can be converted from RFNA by simply leaving the RFNA out in low temperature for a couple of hours. (emphasis added)

I'm asking about that last sentence; why would red fuming nitric acid convert to white fuming nitric acid by leaving it out at low temperature?


texts:
I'm from Slovakia, 16 and like chemistry a lot. I want to pursue it in the future but there aren't any good universities here where you can get a Ph.D. in chemistry so I want to go abroad, preferably to America or the UK. But there's a problem: I don't even know how to name molecules in English. I want to prepare for the future so I want to learn that before I go to UNI. And there's another problem. I can't find a source that I can learn from. I just want to know the basics: oxides, salts, acids, and hydroxides. If anybody could send me a link to a site that I can learn it from I'd be very thankful.

P.S.
I don't know if it's done in English the same way, but we use oxidation numbers to get the chemical formula from the name and in reverse. That's what I want to know but in English.

EDIT: I just want to know the basics RN and I don't want to start off with organic chemistry and stuff like that. I just want to know how to take a simple molecule, for example, AlCl3 and know how to say its name. Is it aluminum (III) chloride or aluminum trichloride? Or something like SO4 and SO3. Is it sulfate and sulfane or what? I just want to know how to name molecules and write down their chemical formula.


texts: Why doesn't silica gel dissolve in ethyl acetate when something like aspirin does. Both silica gel and ethyl acetate are highly polar. I though like dissolved like.


texts: What happens to a molecule when it is unstable?

texts:
I'm just starting OChem and I see that for a SN1 reaction, the rate of the reaction changes with the number of alkyl groups attached to the carbocation that is formed. The textbook (Klein) explains that this is due to the electron-donating nature of alkyl groups which helps to stabilize the carbocation. I was wondering, why doesn't instability help to increase the rate of reaction? Wouldn't the instability of a primary carbocation give it more energy to attract a negative substituent given that it is now more positively charged than a tertiary carbocation?

Thanks,

Reference: Klein, David. Organic Chemistry as a Second Language, First Semester.


texts: Why is the attached hydrogen of 1,3-diethyl-5-(1-phenoxyethyl)benzene homotopic?

texts: The circled hydrogen is considered homotopic with reference to the hydrogen identified by the arrow. I predicted this as they are on identical substituents but am now confused because there orientations with respect to the molecule with the benzene are different. Am I misinterpreting something about the molecular structure?


texts: Relationship between the symmetry number of a molecule as used in rotational spectroscopy and point group

texts:
While doing a problem set I noticed that the symmetry number of a molecule turns out (usually) to be half the number of symmetry elements that the point group the molecule belongs to.

When I say symmetry number I refer to the symmetry number used in rotational spectroscopy — i.e. the number of indistinguishable orientations of the molecule. This accounts for suitable symmetrisation of the rotational wavefunction and the nuclear wavefunction of the molecule.

For example benzene belongs to point group $D_\mathrm{6h}$, which has 24 symmetry elements. It also has symmetry number 12, i.e. 1/2 the number of symmetry elements in it's point group.

Another few examples:

Water. Point group $C_\mathrm{2v}$, with 4 symmetry elements. Has 2 as symmetry number.
Ammonia. Point group $C_\mathrm{3v}$ with 6 symmetry elements. 3 as symmetry number.
Ethene. Point group $D_\mathrm{2h}$ with 8 symmetry elements. 4 as symmetry number.

This seems to be a general trend. It sort of makes sense intuitively that the 2 should have a relationship, but I can't formalise the reason for this.

Obviously for diatomics/linear molecules this doesn't apply. This is because rotational motion around the axis of symmetry is not physical — moment of inertia around this axis is zero, as all mass along axis. Thus there are no rotational levels associated with this axis. But ignoring diatomics/linear molecules, where we have neglected/ignored an axis of rotation, the above relationship seems to hold.

Why is this the case? I'd appreciate both a mathematical derivation and a more intuitive argument.


texts: How do I determine crystal field splitting (for example, for [Ni(CO)4])?

texts:
How to know how many electrons are there in $T_{2g}$ and $E_g$ orbitals?

I think rather than a broad answer, an example would help. So, consider the compound $\ce{Ni(CO)4}$ and how to calculate CFSE for it?


texts: Carbon-13 NMR of dimethyl 3,4,5,6-tetraphenylphthalate?

texts: I am trying to assign the peaks here to dimethylphenylphatalate but all the benzene rings are throwing me off. All I can get is that the further most signal is the carbonyl carbon (168.71) and the one prior to that (143.27) might be the ester carbon (from the methyl). Can someone help?


texts: I am having trouble understanding what KLI approximation is. Could someone explain it to me in an intuitive/simple way?


texts:
I am going through Hartree-Fock calculations in detail, but the textbooks I am referring all considered homonuclear molecules as examples. So I am trying to come up with my own the Slater determinant for Methane. Kindly let me know if my application is correct!
For Methane, we have in total 10 electrons (Carbon 6e, and four Hydrogen with 1e each). We also know that valence shell electrons of C and H engage in bonding. The $1s$ shell of Carbon does not engage in bonding. I am also going to denote $+$ for spin-up and nothing for spin-down. Please note that $1s$ for first two columns in the following matrix describes the $1s$ orbital of carbon which does not involve in bonding.
$$\begin{pmatrix}1s(1)^+ & 1s(1) & S_1(1) & S_1^+(1) & S_2^+(1) & S_2(1) & S_3^+(1) & S_3(1) & S_4(1) & S_4^+(1) &\\\ 1s(2)^+ & 1s(2) & S_1(2) & S_1^+(2) & S_2^+(2) & S_2(2) & S_3^+(2) & S_3(2) & S_4(2) & S_4^+(2) \end{pmatrix}$$
For brevity, I am not writing out the rest of the eight rows in matrix. Now  $S_n$ (spatial part of the wavefunction $S_n$), above in the matrix, is defined as the following:
$S_n=c_{n,1}1s + c_{n,2}2s + c_{n,3}2p_x + c_{n,4}2p_y + c_{n,5}2p_z$, where $n$ runs from $1$ to $5$. Why? because we know that these electrons engage in bonding, hence we have to take a superposition of orbitals (mixing). So in total we have 5 equations e.g. $S_1, S_2,...,S_5$.
Now each such superimposed MO (the $S_n$) can hold 2e each for a total of 10 electrons. Now the carbon $1s$ took away 2 electrons, so 8 electrons remained. And I have hit redundancy, because theoretically each $S_n$ can take 2e, so I have 10 electrons which can be accommodated, but I have only 8. Moreover in the Slater matrix above, I can't find a way to fit in $S_5$.
I am missing something. I would be glad if someone can throw some light on this.


texts: Why is a face-centred cubic unit cell not regarded as equivalent to a body-centred tetragonal unit cell?

texts:
When studying crystal lattices, I decided to learn which combinations of unit cells and lattice systems lead to the 14 Bravais lattices. I learnt that, for example, no centred triclinic unit cell exists.

Later while searching the Internet and Stack Exchange, I found an answer saying that an end-centred cubic cell can be transformed into a (smaller) tetragonal unit cell as shown in th picture below.

Then I thought on and realised that a face centred cubic lattice can be transformed into a (smaller) body-centred tetragonal unit cell, and into an even smaller one, too.

So, why are some centred unit cells (for hexagonal, triclinic and rhombohedral lattices) considered non-existent, while others (e.g. face-centred cubic) are considered to exist even though they, too, can be reduced?


texts: What concentration is phenolphthalein indicator ? 1% or 0.1%

texts:
I read some information about phenolphthalein indicator, some websites suggested phenolphthalein indicator of 1%, others mentioned phenolphthalein indicator of 0.1%. What is the difference of both of these concentrations when we use them in titrations?
I assume that 1-2 drops of phenolphthalein indicator of 1% can be used as an indicator but for phenolphthalein indicator of 0.1%, it needs to drop more with 4-5 drops to obtain the same effeciency.
Look forward to hear from you all


texts:
Why do only unsaturated hydrocarbons undergo addition reactions? For example, ethene or ethyne will undergo an addition reaction with chlorine, whereas ethane will not.

Furthermore, why does benzene not undergo addition reactions, even though it is not saturated?


texts: Boron nitride polymerization with silicon based molecules

texts: Since boron nitride is similar to carbon hexagonal structures and silicon is a main component of inorganic polymers. Is it possible to make it from a polymer under certain conditions, if so what catalysts are needed?


texts:
I’ve learnt that in crystallography, there are many crystallographic directions that are “equivalent.” For example, in a cubic crystal system, the [011] and [110] and [101] directions are “crystallographically equivalent.” See the image below:

I cannot begin to fathom how they are equivalent. These are vectors after all, and from what I can tell with my rudimentary knowledge of maths, these vectors are not equivalent in direction. Yet all materials science textbooks and powerpoints insist that, for cubic systems, any permutation of positive and negative indices will yield a same equivalent direction. That is, the [011], [110], and [101] vectors are… the same vector?

I share the same confusion with planes, even if they aren’t vectors. For cubic systems, just as for directions, any arrangement of positive and negative indices produces an equivalent plane. For example, (100) and (010) are the same plane, when to me they clearly look different.

So what exactly is “crystallographic equivalence”?


texts: The proper explanation for the general formula of the DU?

texts:
I found a formula for the degree of unsaturation (DU) in Clayden’s Organic Chemistry. It explains, simply, the unsaturation with the difference in H atoms. Then I stumbled upon the general formula:

$$DU=1+\frac12\sum n_i\left(v_i-2\right)$$

$n_i$ is the number of atoms with valence $v_i$.

Can someone explain from where this equation was derived? And how come the valence term was introduced?


texts: No. of photoelectrons vs frequency and intensity

texts: We know that when the intensity of incident light increases, number of photoelectrons ejected increases irrespective of the frequency (assuming it to be greater than threshold frequency. But does it depend on frequency too in some situations like in case of high frequency or something?


texts: Program to compute multipoles of water at CCSD(T)-F12 accuracy

texts:
I want to compute traceless cartesian electrostatic multipole moment tensors up to fourth order (hexadecapole), at CCSD(T)-F12 accuracy using a large basis set. I'd like to be able to choose the expansion center, and to do this for small molecules like water.

What code (program) can do this?

I know molpro can do it, but the license is quite expensive. I have access to Gaussian16 which gives the multipoles by default, but not traceless and not for this method, and i also can't figure out if there is a way to choose the expansion center coordinates.

It is not easy given a code to figure out if it has the required capabilities, and there are many codes, so some advice would very much appreciated!


texts:
I was presented with the following reaction when we were just learning about acids and bases:

$$\ce{2NaOH + H2CO3 -> H2O + Na2CO3}$$
however I had thought it might've been something like

$$\ce{NaOH + H2CO3 -> H2O + NaHCO3}$$

They both seem to fit the notion of a neutralization reaction creating a salt so how do I know that the first one is correct? The second reaction looks fine to me (is it that bicarbonate is too reactive?) and more intuitive as the carbonic acid just gives a proton away ending up as an ion to bond with $Na$, so how do I distinguish between these kind of cases?


texts: How is ammonia used in production or processing of steel?

texts:
There are some large tanks of ammonia in nearby iron works.

I wonder, what do they need it for? What is the application of ammonia in steel industry - what processes of making or processing steel require this much ammonia?


texts:
I'm wanting to do a follow up to this Q&A on the cooking stack regarding browning avocados. I specifically want to expand my experiment to include the options in Wayfaring Stranger's Answer. Unfortunately, I managed to get the wrong stuff, and shipping rules make exchanging it problematic.

I am the proud owner of $500~\mathrm{g}$ of sodium bisulfate ($\ce{NaHSO4}$), instead of sodium bisulfite ($\ce{NaHSO3}$).

Dammit Jim! I'm a cook not a chemist!

What I have learned is that that both compounds are used as food additives towards the same end, and that my stuff has a slightly higher LD50. That's it.

Can anyone advise as to substituting my compound for the other? I'm not interested in tasty guacamole at this point, I'm really only looking at browning. If I'm trying to more or less duplicate the more successful experiments of the University of Florida, should I start with the same ratios? Or more or less of the additive? I can get sodium metabisulfite (also an anti-oxidant food additive) locally, if that would be a better option.

EDIT: So far, answers have all been consistent in that I have a half-kilo of white powder that is useless to me. I will make a trip to the wine-making shop and acquire some sodium metabisulfite. That still leaves me with the question of how much? The University of Florida got the results I'd like to duplicate with $30~\mathrm{mg}$ of sodium bisulfite per $100~\mathrm{g}$ of avocado. Should I start with the same ratio of sodium metabisulfite?


texts:
I am following an article for synthesis of the nanoparticles.

There is a gold nanoparticles synthesis rout which is called UPD. In this rout, the underpotential deposition of Ag onto the surface of the Au particles is used. There are two metals (Au and Ag) in the obtained nanoparticles, but they aren't called bimetallic nanoparticles. Why is it called "gold nanoparticles synthesis" and not "gold-silver bimetallic nanoparticles synthesis"?


texts: What properties of later elements are predicted by scientists?

texts: Though scientists have predicted up to element 172 (unseptbium) what properties do they predict any elements later on the extended periodic table may have?


texts: What type of isomers are cis-but-2-ene and 2-methylpropene?

texts:
One of my homework problems is asking whether cis-but-2-ene and methylpropene are cis-trans isomers or constitutional isomers. But I'm not sure about whether cis-trans isomers include those which the two functional groups exist on the same carbon in the double bond. So does it?

I've searched on Google and looked in my textbook, but they doesn't seem to have anything.


texts:
According to Wikipedia,

  The $\ce{C60}$ molecule is extremely stable,[26] withstanding high temperatures and high pressures. The exposed surface of the structure can selectively react with other species while maintaining the spherical geometry.[27] Atoms and small molecules can be trapped within the molecule without reacting.

Smaller fullerenes than $\ce{C60}$ have been distorted so heavily they're not stable, even though $\ce{M@C28}$ is stable where $\ce{M\,=\,Ti, Zr, U}$.

Some of us have heard and learned about the "rules" of aromaticity: The molecule needs to be cyclic, conjugated, planar and obey Huckel's rule (i.e. the number of the electrons in $\pi$-system must be $4n+2$ where $n$ is an integer).

However, I'm now very skeptical to these so-called rules:

The cyclic rule is violated due to a proposed expansion of aromaticity. (See what is Y-aromaticity?)
The must-obey-Huckel rule is known to fail in polycyclic compounds. Coronenefigure 1 and pyrene figure 2 are good examples with 24 and 16 $\pi$ electrons, respectively.
Again, Huckel fails in sydnone. The rule tells you that it's aromatic, while it's not.

The planar rule is not a rule at all. We're talking about "2D" aromaticity when we're trying to figure out the $n$ in $4n+2$. The "3D" rule is as following:

  In 2011, Jordi Poater and Miquel Solà, expended the rule to determine when a fullerene species would be aromatic. They found that if there were $2n^2+2n+1$ π-electrons, then the fullerene would display aromatic properties. - Wikipedia

This would mean $\ce{C60}$ is not aromatic, since there is no integer $n$ for which $2n^2+2n+1 = 60$.

On the other hand, $\ce{C60-}$ is ($n = 5$). But then this rule strikes me as peculiar because then no neutral or evenly-charged fullerene would be aromatic. Furthermore, outside the page for the rule, Wikipedia never explicitly states that fullerene is not aromatic, just that fullerene is not superaromatic. And any info on superaromaticity is unavailable or unhelpful to me; including the Wikipedia "article" on that topic.

So, is $\ce{C60}$ aromatic? Why, or why not?


texts:
Regarding this question, how can one solve this without access to thermodynamic data?

I suppose we should keep the following information in mind:

1) Double bonds are not double the strength of single bonds. Same goes for triple bonds. Reason has to do with orbital overlap with regard to sigma and pi bonds.

2) In order of increasing stability: $\ce{O_2, O_3, O}$. We know this because diatomic oxygen is what usually exists in large quantities at ground level; ozone is a pollutant because it is quite reactive and can thus harm tissues; we don't usually hear of monoatomic oxygen.

Therefore:

a) Cannot be the answer. Going from ozone to diatomic oxygen is exothermic. At least part of this reaction is exothermic.

b) Definitely not the answer. Going from ozone to diatomic oxygen exclusively.

c) This is endothermic, but perhaps not as endothermic as creating monoatomic oxygen.

d) Looks pretty endothermic; we are splitting oxygen.

e) Definitely not the answer, this is fundamentally exothermic.

How can we definitely pick out the right answer? What reasoning would you employ?


texts: Does the pyrolysis of $\ce{CaCl2 · 2 H2O}$ give $\ce{CaCl2 + 2 H2O}$ or $\ce{Ca(OH)2 + 2 HCl}?$


texts:
I want to remove a hardened steel bolt in a block of zinc (there is a through-hole, so I have two sides to work with). I have done this previously with aluminum and steel before, using a solution of alum to loosen the steel bolt.

Will I have as smooth a time using the alum method in the present case, or will the alum react with the zinc?