texts: What is the reason why protons and electrons do not collide?

texts:
can someone give me an intuitive picture of why electrons don't collide with protons?

I know that electrons move in a sort of cloud, which is our 'orbital', and that they mainly behave like electromagnetic wave because of their very tiny mass. However, how comes they don't collide with the protons? I seriously didn't find a good explanation of these neither by professors I talked to nor by books, so a thousand points from me if you are able to get me into this.

Keep in mind that I am not looking for values, equations, or quantitative explanation of this, for that I have read enough, but for a picture. Think about the subatomic particles as you see them in your mind and describe their relationship.


texts: Standard Enthalpy of Formation for Branched Alkanes

texts:
I'm looking at the heat of formation for branched and straight alkanes and I've noticed a few odd trends I'm having trouble explaining. For straight-chained alkanes, the addition of carbon atoms to the main chain seems to consistently decrease the value of $\Delta H_\mathrm f$. This seemed logical as the compounds become more stable. However, for branched alkanes, I'm having a bit of trouble explaining them. The more bent it is the more stable it seems to be, as $\Delta H_\mathrm f$ decreases. But I'm not quite sure why.

Does it have something to do with geometry? This is a bit confusing because the boiling points of branched alkanes are less than that of their straight-chained isomers, implying that they're more stable. The location of the methyl groups seems to also have a part to play as if they're in the center (most spherical shape) they'd be least stable, but still, have higher $\Delta H_\mathrm f$ than straight-chained ones.


texts: The nitrogen oxide NO exists and has an uneven number of valence electrons. This is "impossible". Why does it exist ? Why is it not dimerized ?


texts: Relationship between rate equation and equilibrium constant

texts:
I have read mannaia's answer on the question of 'rate order and confusion', as well as Nicolau Saker Neto's answer to a related question. They have both been very helpful.

As I understand, the equilibrium is actually derived from the rate constants of a reaction. At dynamic equilibrium, the rate of the forward reaction is equal to the rate of the backward reaction, hence in a hypothetical reaction

$$
\ce{pA + qB <=> rC + sD}
$$

with the rate equations $Rate_{fwd} = k_{fwd}[A]^{a}[B]^{b}$ and $Rate_{bck} = k_{bck}[C]^c[D]^d$, with $a, b, c,$ and $d$ not related to $p, q, r$ and $s$.

The equilibrium is derived as such:
\begin{align}
  R_{fwd} &= R_{bck}\\
  k_{fwd}[A]^{a}[B]^{b}&=k_{bck}[C]^c[D]^d\\
  \frac{k_{fwd}}{k_{bck}} &= \frac{[C]^c[D]^d}{[A]^a[B]^b}\\
  \therefore k&=\frac {k_{fwd}} {k_{bck}}\\
\end{align}

Based on the derivation, and the fact that the stoichiometric coefficients of the reactants in the rate-determining step (RDS) of the reaction is equal to the order of the reactants in the rate equation, is it correct to state that the reaction equations given as the equilibrium equation is actually the rate-determining step of two reactions?


texts: For gold, the word carat defines its purity whereas in diamonds it indicates its weight.  This seems inconsistent -- what does the unit 'carat' actually refer to?


texts: Grubbs, Wittig & hydroboration reactions and Woodward-Hoffmann rules

texts:
Several organic mechanisms I know involve [2+2] cycloadditions and retro-[2+2] cycloadditions, namely:

The Wittig reaction
Hydroboration of an alkene
Olefin metathesis (using Grubbs' catalyst)

How are these in accordance with the Woodward–Hoffmann rules? I think that there are two $(4q+2)_s$ components and that's not an odd number, which is the criterion for a reaction to be thermally allowed.


texts:
I'm confused by the following from this webpage:

The cathode is a metal oxide and the anode consists of porous carbon. During discharge, the ions flow from the anode to the cathode through the electrolyte and separator; charge reverses the direction and the ions flow from the cathode to the anode.
On discharge, the anode undergoes oxidation, or loss of electrons, and the cathode sees a reduction, or a gain of electrons. Charge reverses the movement.

This says that the metal oxide electrode is always the cathode and the porous carbon electrode is always the anode. As far as I know, that designation should be correct on discharge but backwards on charge. The anode is always whichever electrode is doing the oxidation, and the cathode is the electrode doing the reduction.
My naive understanding would be this:

The cathode is the electrode with the reduction half reaction. The anode is the electrode with the oxidation half reaction. This is true for both charge/discharge.
The anode is the one that produces electrons and cathode receives electrons. This is true for both charge/discharge.
When switching between charge/discharge, the redox reactions reverse, and the cathode/anode designations also switch to preserve cathode==reduction and anode==oxidation.
During discharge, the battery functions as a galvanic cell, where the redox reaction produces electric energy, electrons go down their electrical gradient from the negative electrode to the positive electrode. The anode is the negative electrode, the cathode is the positive electrode.
During charge, the battery functions as an electrolytic cell, where electric energy drives a nonspontaneous redox reaction, electrons go up their electrical gradient from the positive electrode to the negative electrode. The anode is the positive electrode, the cathode is the negative electrode.
In a lithium ion battery, the positive electrode is the metal oxide and the negative electrode is the porous carbon. The anode/cathode designations switch depending on whether the battery is charging or discharging.

Please help me understand this.


texts:
Question 28 from [1, p. 4.4]:

An ideal gas is expanded irreversibly from $\pu{5 L}$ to $\pu{10 L}$ against a constant external pressure of $\pu{1 bar}.$ The value of heat involved $(q)$ in this isenthalpic process is
(a) $0$
(b) $\pu{+500 J}$
(c) $\pu{+5 J}$
(d) $\pu{-500 J}$

It is mentioned in the problem that the process is isenthalpic, which means the change in enthalpy must be zero. So, my conclusion was there is no heat involved here. But the answer given is (b).
References

Neeraj, K. Advanced Problem in Physical Chemistry for Competitive Examinations, 2nd ed.; Pearson India Education Services Pvt. Ltd: Dehli, Chennai, 2015. ISBN 978-93-325-4373-7.


texts: In thermodynamics, whenever heat is released from the system to the surroundings, temperature of surroundings remains unchanged but entropy increases. But entropy is a function of temperature. How is it possible?


texts: Solubility increases as Temperature increases.. Ks increases with temperature meaning dissolving is endothermic... But what about NaOH?

texts:
Question: I was self-studying and came across some confusion across a question. My confusion lies in this: Solubility increases as temperature (T)  increases, Ks increases with T, meaning dissolving is endothermic. But what about $\ce{NaOH}$?
The problem I am putting forward is more to do with the equilibrium Ks, especially using the Le Châtelier's principle. We all know that the solubility of ionic substances increases as increases in temperature. That is a fact, we don't have to argue with that. We also know that dissolving $\ce{NaOH}$ is exothermic, so we don't need to discuss that. However the two statements (observations) contradict the Le Chatelier principle, because if the dissolution of $\ce{NaOH}$ is exothermic, the solubility should decreases with increase in temperature! Why doesn't it?


texts: What was wrong with Schroedinger's interpretation of the wavefunction?

texts:
I've read in a couple of different places, and was told when first learning about quantum mechanics, that Schroedinger interpreted the wavefunction as being representative of the charge distribution of the electrons in a system. This idea was later replaced by Max Born's interpretation of the wavefunction as the probability density of the electrons in a system which is the common view now.

It's quite apparent that quantum mechanics is built on this idea of probabilistic interpretations, and so without it QM would have problems. It's not obvious to me, however, how one makes the jump from interpreting the wavefunction as a charge density to a probability density. Or maybe a better question to ask is this: why did Schroedinger interpret the wavefunction as a charge density? Specifically, what physical motivation is there for this interpretation? Furthermore, in what situations does this interpretation fail? I could imagine some problems with Pauli Exclusion, but perhaps not. In that case, one would still give as an axiom that the wavefunctions of fermions are anti-symmetric upon particle exchange and then one would have that there could be no charge density in that region of space, and everything might still be fine...

So, to narrow things, in what situations does the interpretation of the wavefunction as a charge density fail?


texts: Molecular kinetic interpretation of pressure

texts: Regarding the molecular kinetic interpretation of pressure, we arrive at a point in the $F=\frac{\Delta P}{\Delta t}=\frac{2mvx}{\Delta t}$, that is to say, the force exerted in the shock on the wall is calculated by dividing the change in the amount of movement of the wall by that time, which I understand should be the time of duration of the shock, but nevertheless the time used is the time between two shocks, the time in which the molecule travels the distance of the edge of the vessel for one side and returns...this does not contradict the definition of impulse that refers to the duration of the shock??


texts:
So we tried the reaction between Titanium metal with hydrochloric acid and hydrofluoric acid at a similar concentration. While boiling temperatures and constant heat over a long period of time are required to etch $\ce{Ti}$ using $\ce{HCl}$ even cold $\ce{HF}$ is enough to immediately break the protective oxide layer and the metal vigorousely reacts in the solution afterwards.

My question is now why $\ce{HF}$ is so much better at etching and dissolving $\ce{Ti}$ compared to aqua regia or $\ce{HCl}$?

Of course there is a protective oxide layer on the metal but boiling it in $\ce{HCl}$ will also form a purple solution after a while and the color intensifies if heat is applied over a long period of time. So even after the layer is destroyed the metal itself continues to react with the $\ce{HCl}$. For $\ce{HF}$ it reacts way faster so I assume it's not an issue with the protective layer itself but rather the reaction with the pure metal.

I know for glass and $\ce{HF}$ it's a combination where $\ce{H2F+}$ reacts with $\ce{Si-OH}$ endgroups and increases the electron density on the bridging oxygen which makes them more basic and the $\ce{Si-O-Si}$ bond breaks to form $\ce{Si-OH}$ bonds. But this is all for the oxides and I assume the titanium dioxide will be dissolved in a similar manner.

For metals I couldn't find much information on the topic. I know there are some similar elements, Niobium, Silicon, etc. they all require $\ce{HF}$ to be etched or dissolved.

Maybe it's the case because a $\ce{Ti-F}$ bond, much like a $\ce{Ti-O}$ "bond" is way stronger than a $\ce{Ti-Cl}$ bond? Which would explain why $\ce{HF}$ starts the reaction faster as this unique $\ce{HF/H2F+}$ mechanism seems to work pretty well for tough oxides.

Maybe it's also just the fact that more energy is produced when a $\ce{Ti-F}$ bond forms but the fast reaction starts immediately so it shouldn't just be the heat that is produced enhancing the reaction.

The process itself is a redox-reaction but the essential part here is the $\ce{H+}$ not the counter-ion. So from a redox perspective it should be pretty much the same, unless the redox potential and the overall redox reaction is influenced by the $\ce{Ti-F}$ bond formation, like the hydration enthalphy adds to the oxidative potential of oxygen and suddenly $\ce{Cu(I)}$ turns into $\ce{Cu(II)}$ once the insoluble $\ce{CuCl}$ is added to water.

(Also I'm sorry, but I cannot create a suitable tag with my score at the moment)


texts:
Earlier today I was preparing an ester (propyl ethanoate) and I noticed that instead of putting the propanol, ethanoic acid and $\ce{H2SO4}$ in the test tube and warming it (taking time and external energy) I could instead mix sulfuric acid with the ethanoic acid, which made the test tube go very hot, and then by adding the propanol and shaking it split into two layers. On pouring this into water I ended up with an immiscible layer which appeared to be an ester (it was sweet smelling and considering the reaction it would be likely to be an ester).

I cannot think of which reaction was causing the heating up initially. The test tube was clean so the only reactants were the sulfuric acid and ethanoic acid, and it appeared that a gas was being given off (as shaking it with a rubber cap on caused it to pop out of the tube, but no effervescence could easily be seen). Can anyone help? Furthermore, would the eventual product be propyl ethanoate or something else (it was suggested that it was dehydrogenating the ethanoic acid so the actual product would be something like propyl ethenoate, but from a quick look on the internet this would seem to require an iron catalyst (or another catalyst) and a high temperature, neither of which was present)?


texts: Why doesn't 1-cyclopropylethyne give a positive reaction in the bromine-water unsaturation test?

texts:
1-cyclopropylethyne has a triple bond:

Hence it seems like it should yield a positive unsaturation test with bromine water. But, my book states that the opposite is true.

I guess this may be due to steric crowding on the C atom bearing the cyclopropyl ring, but I'm not sure.

What is the exact reason that 1-cyclopropylethyne does not yield a positive bromine water unsaturation test?


texts: How were elements and molecular formulæ determined in the old days?

texts: Before modern chemical techniques, say in the 19th century and earlier, how did (al)chemists determine whether a substance was an element or a compound? If it was a compound, how did they determine its molecular formula and structure?


texts:
What is the type of structural isomerism in which isotopes move around?

Examples

$\ce{CH2D-NH2}$ and $\ce{CH3-NHD}$
$\ce{CH2D-NH-CH3}$ and $\ce{CH3-ND-CH3}$
$\ce{CH2D-NH-CH2CH3}$ and $\ce{CH3-NH-CHD-CH3}$ and $\ce{CH3-NH-CH2-CH2D}$

here $\ce{D}$ refers to deutrium.

My progress: So I know that there are various types of isomerism, like

Tautomerism - Differ in the position of protons and electrons. Usually I see that this occurs with changes in bond orders. So I don't think it will be this.
Ring-chain isomerism - When there is a difference in the number of carbons in a ring
Functional isomerism - When the functional group changes. I don't know if $\ce{-NH2}$ is a different functional group from $\ce{-NHD}$.
Metamerism - This is when there is a change in carbon chain on both sides of a bridging group. I don't know if a change in isotopes would count as a change in carbon chain.
Chain isomerism - When the carbon skeleton changes. Here the skeleton carbon is the same.
Positional isomerism  - When a functional group attaches itself on different carbon of the same chain. Not applicable here.

This is not a homework question. This question was to fill the gap in my knowledge of isomerism with isotopes.


texts: I performed aan acid catalysed haloform reaction in acetic acid to an acid. I need to evaporate acetic acid which I used as solvent and It is around 150 ml. What are the alternatives , I have a rotavap in lab but 150ml AA is too much for a rotavap I guess.


texts: Stabilization of ipso and para position in Birch reduction by EWG of aromatic ring

texts: I'm trying to grasp the Birch reduction. In the lecture about it, it's said that the EWG group stabilizes ipso and para position through resonance. I tried to understand that by drawing resonances without success. What is wrong in it?


texts: Does alcohol hydrogen in the enol tautomer of a β-dicarbonyl have sp² character?

texts:
My reasoning for the somewhat implausible "$\mathrm{sp^2}$" character of the hydrogen between these two oxygens on the enol structure of the right comes from recognizing that if it were, then we would have 6 $\mathrm{sp^2}$ atoms with 6 π-electrons, so maybe that extra bit of instability from having a higher orbital on hydrogen could be sort of taken care of by being stable like an aromatic compound and forming a hydrogen bond.

So how could I go about figuring out if this is true, either with MO theory or something else?

(source: ucdavis.edu)


texts: Is there an electronic structure method which accounts for 3-, 4-, ..., n-electron exchange integrals?

texts:
Something I learned recently which really helped me in understanding exchange is that the case of exchanging two electrons is really a special case of enforcing symmetry (or anti-symmetry) in which the permutations of labels in cycles out to length $N$ are used. $N$ is the number of particles.

Just to write it out, the two-electron exchange integral is defined as,
$$K_{ab}=\int d\textbf{r}_1d\textbf{r}_2\psi^*_a(\textbf{r}_1)\psi_b(\textbf{r}_1)r_{12}^{-1}\psi_b^*(\textbf{r}_2)\psi_a(\textbf{r}_2)$$
where everything means what it normally means and I took this integral and notation straight out of Szabo and Ostlund.

Now, this is clearly only a permutation of two electrons, and introduces the only correlation present in Hartree-Fock by allowing for exchange of spin-paired electrons.

Shifting gears, I've been reading Quantum Mechanics and Path Integrals by Richard Feynman and Albert Hibbs. In the chapter on Statistical Mechanics, they talk about liquid helium, which has a peculiar transition around $2K$ in which the heat capacity begins to increase. Feynman was the first to explain that this is due to the exchange interaction, and at this temperature is when permutations of the atom labels larger than just one (i.e. two particle exchange) become important. The following statements from the book are relevant to electrons (as opposed to helium because $\ce{^4He}$ is a boson!).

In a different context, the calculation of partition functions, the authors state:

  If we were dealing with Fermi particles, e.g., the isotope of helium which has three nucleons, we would have to include an extra factor of $\pm1$, positive for even permutations and negative for odd permutations. There would also be some extra features which depend upon the spin of the atom in our result.

And more directly about electrons,

  Consider the behavior of electrons in a solid metal. The mass of the electron is so much smaller than that of a molecule that the critical temperature is much higher. At room temperature, electrons in a metal are described accurately only by equations which include the exchange effects of these cyclic permutations. From this point of view, room temperature is very cold for electrons.

So, hopefully we have now reached a place where it is clear why I am a bit confused. Namely, to my knowledge, we only ever consider the exchange of two electrons of the same spin in our electronic structure methods. First, is this actually true? That is, are there methods which implement (in principle) $N$-electron integrals to describe all permutations of the labels?

Second, is the comparison I am making even strictly valid? That is, in the case of a partition function, which is what Feynman is talking about, permutations of even length tend to cause the electrons to stay further away from each other. This is the behavior we are used to with exchange. In contrast, for permutations of odd numbers, the contribution to the partition function picks up a minus sign. So, the total partition function for a system of fermions is an alternating sum of positive and negative terms in the path integral formalism. Can I simply substitute partition function for wavefunction and sum for integral and find what would happen in the electronic structure case? That is, will the 3-electron exchange integral (assuming this is real and I'm not mistaken) be a negative number, so that we can picture the wavefunction relaxing a little bit from the so-called "heaps" which form due to exchange?

Finally, if I'm not just delusional about this whole thing, is there evidence that permutations beyond the two labels are important for describing any known chemical processes?

References:

[1]: Szabo, A., & Ostlund, N. S. (2012). Modern quantum chemistry: introduction to advanced electronic structure theory. Courier Corporation.

[2]: Feynman, R. P., Hibbs, A. R., & Styer, D. F. (2010). Quantum mechanics and path integrals. Courier Corporation.


texts: Bond Angles and intermolecular interactions

texts:
It's fun to consider bond angles of molecules in isolation. For example, what is the number of different bond angles exhibited by the most polar form of $\ce{SIBrClF2}$?

However, can bond angles really be considered in isolation? The method I would employ to determine the number of different bond angles only considers the molecule in isolation; I just consider van der Waals repulsions between the component atoms. Molecules generally do not exist in isolation. We can study molecules in the gas phase as to minimize intermolecular forces, but still, intermolecular forces exist, as it is hard to isolate exactly one molecule.

In the case of $\ce{SIBrClF2}$, I would expect a number of rather strong dipole-dipole interactions among the $\ce{SIBrClF2}$ molecules.

Therefore my question is: are there any cases in which considering solely intramolecular forces leads one astray when determining the bond angles of a molecule? I.e. one might look at a molecule and expect a certain bond angle to be < 180 degrees but find out the angle is in fact > 180 degrees due to intermolecular forces prying the bond angle open?


texts:
Is cyclohepta-1,3,5-triene aromatic?

I think it should not be, because even though the π-system possesses six π-electrons, the conjugation is not complete around the ring.


texts: Can someone tell me why - in experiments to observe corrosion of iron nails - we often use a preparation of agar gel (with $\ce{NaCl}$, phenolphthalein, etc.) instead of an aqueous solution?


texts:
What is the structure of $\ce{LiCl.2H2O}$?
I think when $\ce{LiCl}$ is put in aqueous medium, it will break into $\ce{Li+}$ and $\ce{Cl-}$. Then $\ce{H2O}$ will give LP to Li and hydrate it. But why 2 $\ce{H2O}$ molecules? 2 means 2 coordinate bonds? Octet is not filled? Then why does this happen?


texts:
I know that polyethylene's melting point is between 115–135 °C, however I would like to know if can it start dissolving between 50-60 °C?

In a real example, if I put warm food (straight from the oven, I think it can be max. 50-60 °C) into a re-closable polyethylene plastic bag and close it, will any chemical reaction affect the food (from the polyethylene's side)? Or is polyethylene safe at that temperature, and if the bag is warm it doesn't mean that any chemical reaction is started? I didn't experienced any alteration, but I'm not an expert and don't know much about chemistry yet, so I would appreciate some guidance.


texts: How does the presence of various NMR active nuclei in a compound affect coupling and signal multiplicity?

texts:
I am basically wondering how the presence of various NMR active nuclei present in a organic molecules affect the shift values and coupling states normally seen in a molecule lacking these nuclei.

Can NMR active metallic moieties in organometallic compounds such as magnesium 25 in a Grignard reagents couple with the spin of protons in H-NMR or carbon 13 atoms in C-NMR? Do the peaks show up in the same range and how are the shift values affected?

In a structure containing many active NMR nuclei (such as a structure containing appropriate isotopes of chlorine, phosphorus, and nitrogen) is special decoupling software or supplemental instrumentation needed to interpret these spectra or are there other techniques to readily discern structure?


texts:
What is the fundamental difference between chemical adsorption and physical adsorption.

Why do some compounds chemisorb and others physisorb?


texts: Validity of graph-based molecular representation in ML

texts:
I was reading about molecular graph based generative models, which attempt to generate new molecules by training on a subset of a molecular dataset, such as QM9. In these works, there are 2 types of constraints that define the validity of the output:

The sum of the order of the bonds that are incident to an atom may
not exceed its valency.
The output should be a single connected graph.

While we can go further and do DFT calculations to see if these are also stable structures, I was wondering if there are any other simple constraints that we can impose to check the validity of the output molecular graph, without the need for DFT-type calculations.


texts: Comparing the Hückel and extended Hückel methods

texts:
I'm very confused about the differences between these methods. From my textbook, it states that the Hückel method only takes into account the π bonding interactions, while the extended Hückel method takes into account all the valence electrons. But what exactly does this do?

To my knowledge, the s, pz, px, and py orbitals are all orthogonal to one another and wouldn't mix anyways. Are shielding effects the only thing accounted for by extended Hückel theory?


texts:
Arrange the following in decreasing order of acidity

I think it's S>P>R>Q

(Q) forms an anti aromatic conjugate base. So its the least acidic compound here.

(R) forms forms a conjugate base which is only stabilized by electron withdrawing (inductive) effect of $\ce{S}$.

(P) forms an aromatic conjugate base and (S) forms am ion stabilised by resonance (two resonance structures). But negative charge in $\ce{O}$ is more stable than negative charge on $\ce{C}$. So (S)>(P).

Is this correct?


texts:
Wikipedia has the following reaction:

  $\ce{Mg2Si + 4 HCl → 2 MgCl2 + SiH4}$

This seems to be a double displacement (metathesis) reaction, where $\ce{Si}$ has oxidation state $-4$. However, I thought that silane had silicon in the $+4$ oxidation state? For example, in this reaction:
$\ce{3 SiO2 + 6 H2 + 4 Al → 3 SiH4 + 2 Al2O3}$, silicon remains in the $+4$ oxidation state.

Why is there the discrepancy between the oxidation state of silicon in silane?


texts: Does hybridization take place in other atoms apart from central atom in a molecule?

texts: I have seen my textbooks always give formula and description of hybridization of central atom of a molecule. But I wonder will other atoms present (not Hydrogen) go in hybridization or only the central atom only uses hybrid orbital and other use pure orbital?


texts:
I am trying to find the structure of an unknown molecule. What is the splitting pattern of these sets of lines?

I think my unknown molecule is butanol and the hydrogens this splitting pattern is referring to are the middle ones, i.e. $\ce{H3C-CH2-C\color{\red}{\mathbf{H}}_2-CH2-OH}$.
They would couple with the hydrogens on the right as a triplet and the ones on the left as a triplet, but would they also maybe do a W-coupling and couple with the methyl on the left.

So what would the coupling pattern be?


texts: Is iron (III) oxide-hydroxide the same as iron (III) hydroxide?

texts:
Firstly, the Wikipedia article on iron(III) oxide-hydroxide says that $\ce{FeO(OH).H2O}$ is sometimes described as iron(III) hydroxide ($\ce{Fe(OH)3}$). If that is so, does iron(III) hydroxide not exist?

Secondly, the hydrated iron oxides section of the Wikipedia iron(III) oxide page says that on treatment of $\ce{Fe^3+}$ salts with alkali we get $\ce{Fe2O3·H2O}$ (also written as $\ce{Fe(O)OH}$) and not $\ce{Fe(OH)3}$. Is it the same as $\ce{FeO(OH).H2O}$ mentioned in the Iron(III) Oxide-Hydroxide page? If not, how are the two compounds different?

Thirdly, the iron(III) oxide-hydroxide page gives the following reaction:
$$\ce{FeCl3 + 3 NaOH → Fe(OH)3 + 3 NaCl}$$
Doesn't this directly contradict what's given in the iron(III) oxide page? And does $\ce{Fe(OH)3}$ here mean $\ce{FeO(OH).H2O}$.

Fourthly, the Wikipedia page on rust says that rust is composed of hydrated iron(III) oxides $\ce{Fe2O3·nH2O}$ and iron(III) oxide-hydroxide ($\ce{FeO(OH)}$, $\ce{Fe(OH)3}$). What are these hydrated iron oxides and how do they differ from hydrated iron(III) oxide-hydroxides $\ce{FeO(OH)·nH2O}$ described in the iron(III) oxide-hydroxide page?

Fifthly, the page on iron(III) oxide-hydroxide identifies $\ce{FeO(OH).H2O}$ as hydrated iron oxide, while the hydrated iron(III) oxide and rust page have me believing that $\ce{Fe2O3·nH2O}$ is hydrated iron(III) oxide. Are they wrong or is $\ce{FeO(OH).H2O}$ also a hydrated iron oxide?

I would also be interested in knowing the structure of these compounds, whether the water is just hydrogen bonded or if it takes part in some complex formation and where I can learn more about such unusual compounds.


texts: Coordination complex - nitrito-N & nitrito-O

texts:
I am currently learning the coordination compounds and encountered a new isomerism called linkage isomerism.
I am thinking that if I want to get some $\ce{[Co(NO2)6]^3-}$, I should have to dissolve $\ce{CoCl3}$ in water to get $\ce{[Co(H2O)6]^3+}$, then add some concentrated $\ce{HNO2}$ to displace the six water molecules away (although I don't know why $\ce{NO2-}$ is a stronger ligand than $\ce{H2O}$).
Questions:

Will I get a 50-50 mixture of nitrito-N & nitrito-O co-coordination complexes? Or will there be a chance of getting random combinations of nitrito-N & nitrito-O coordinate bonds to a $\ce{Co^3+}$ (e.g. 4 nitrito-O + 2 nitrito-N)?
If I just want to get nitrito-N complex, are there ways to prevent the formation of nitrito-O complex? Or the mixture must form and then we need to do some other reactions to get rid of nitrito-O complexes?


texts: What would happen if we had a different kind of metal in our bloodstream?

texts: It is a common fact that we have iron in our blood. But what if we had something different in its place? Like instead of iron what if it was copper, or silver, or what if we had gold in our blood stream instead? Theoretically, what would that do?


texts: Why is water transferred from a beaker of pure water to a beaker of sugar solution when placed in the a closed container?

texts: I know that there is something to do with the vapour pressure of pure water being higher than the vapour pressure of the sugar solution, but I still can’t really explain what happens on a molecular level. Could someone help?


texts: Does every solute spend at least $t_M$ in the mobile phase?

texts:
In 'Fundamentals of Analytical Chemistry' 9th edition by Skoog, West, Holler and Crouch, there is the following passage (page 865).

  The dead time (void time), $t_M$, is the time it takes for an unretained species to pass through a chromatographic column. All components spend at least this amount of time in the mobile phase.

Apologies if it seems a silly question, but how does that make sense? Wouldn't all components spend exactly that amount in the mobile phase? That is, of course, assuming a constant flow rate for the mobile phase. Is this where I have gone wrong?


texts: What gas is evolved when using vinegar, hydrogen peroxide, and salt to etch copper, and why?

texts:
The question of how vinegar + hydrogen peroxide + table salt can be used to etch copper has been asked before (Full equation when using vinegar, hydrogen peroxide, and salt to etch copper). However, the accepted answer seems to miss a key fact when observing this reaction, so I wanted to ask for clarification in the hope that someone can explain the unaddressed fact.

When the vinegar + hydrogen peroxide + table salt solution is used to etch copper, there is a gas that vigorously forms on the surface being etched. However, none of the reaction products in the accepted answer for the full equation for this reaction are volatile. So if none of the reaction products are volatile, how can a gas be released?  Clearly, there is something missing from the accepted answer. Does anyone have any ideas?


texts:
This is regarding to the newly-discovered 2-D materials that can support electron flow, such as phosphorene and transition metal dichalcogenides. How do they conduct electricity?

I also read that their electric properties change with the number of layers. For example, the band gap of black phosphorus changes from 0 - 2 eV with the number of layers. Why is this so?


texts: Can a volume of gas be measured by change in PSI?

texts:
I had a visit from an air conditioner repairman who brought with him a tank of refrigerant. He measured the system and determined that the pressure was about 20 psi too low. So he added refrigerant to the system until it was right.

When it came time to pay him, he said, "well I had to raise your system by 20 psi so it's going to be [20 x price for 1 psi]."

The price was fine, but I am still wondering: would it have taken the same amount of gas to raise my system from 0 to 20 psi as it would to go from 80 to 100, say?

Or, in other words, is it absurd to charge by pressure delta instead of some more reliable measure of what was dispensed from the tank?


texts: If Beer's Law appears to apply to a high concentration (>0.01M) of a solute, is it valid to use for concentration calculation?

texts: Internet consensus seems to define "high concentration" for Beer's Law as >0.01M. If one has a solution at higher concentrations than that, but the absorbance vs. concentration is still linear, is it valid to use Beer's Law to calculate concentration from absorbance data (assuming that the concentration is less than the highest point for which one has experimental data)?


texts: Can we prepare alkyl Fluoride by Finkelstein reaction?

texts:
My book states that:

  Finkelstein reaction is particularly useful for preparing iodoalkanes. The iodoalkanes are obtained by heating chloro or bromoalkanes with a concentrated solution of sodium iodide in dry acetone.
  $$\ce{R-X~+~NaI->[\ce{acetone,~reflux}]R-I~+NaX}$$
  $(\ce{X=Cl,~Br;~R=alkyl ~group})$
  Sodium chloride and sodium bromide being less soluble in acetone get precipitated from the solution and can be removed by filtration. This also prevents the backward reaction to occur according to Le Chartelier's principle. The reaction gives the best results with primary halides.

My question:

Can we prepare alkyl fluoride (not aryl fluoride) by Finkelstein reaction?

My book mentions about another reaction called Swarts reaction, through which alkyl fluoride is prepared. In Swarts reaction, alkyl fluorides are prepared by heating alkyl chlorides or bromides with salts such as mercurous fluoride ($\ce{Hg2F2}$), silver fluoride ($\ce{AgF}$), cobalt fluoride ($\ce{CoF3}$) or antimony trifluoride ($\ce{SbF3}$). Why can't we prepare alkyl fluoride by treating sodium fluoride with alkyl halide (Finkelstein reaction)?


texts:
There are fun and practical applications of soapy solutions for bubble making.  An example of a practical one is detection of gas leaks from fittings and unions.

Given various household products, what would have the best combination of wetting agents or surfactants for bubble creation at temperatures above 0C and up to 40C?  For example, hand soaps, dish soaps, etc. realizing that many products vary in ingredients and design intent.  For example, most laundry detergents are designed to have reduced foaming.

What common household chemicals or products will make effective soap bubble solutions?

Addendum:
1. The following article describes creating soap bubble mixtures:  https://www.scientificamerican.com/article/bring-science-home-best-bubbles/
2. It mentions the use of glycerin and/or corn-syrup as a thickening agent.  "Glycerin and corn syrup form weak bonds with the water molecules and slow down the evaporation process, thus improving the life span and durability of the bubble. Glycerin makes stronger, longer-lasting bubbles, but corn syrup is often substituted in bubble solutions because it is cheaper."  (This is consistent with comments for the question.)

A significant remaining question is what detergent product might perform better over others, or what detergent product characteristics might perform better over others.  Obviously one without anti-foaming agents.


texts: Usage of ammine vs amine in nomenclature

texts:
In the nomenclature of complex salts we use ammine for NH3 instead of amine.

I thought this was to differentiate between ammine ligand and amine in organic ligand (like en).

However, Wikipedia cites the usage has historical reasons. So why exactly do we use ammine instead of amine?


texts: Why does color of halogen deepens and the boiling point decreases down the group?

texts:
Why does the color of the halogens deepens as we go down the group? also why there is a change in physical state of halogens down the group?

\begin{array}{c|c}
\mathbf{Gas} & \mathbf{Color} \\\hline
\text{fluorine} & \text{very pale yellow (almost invisible to naked eye)}\\
\text{chlorine} & \text{yellow-green} \\
\text{bromine} & \text{red-brown}\\
\text{iodine} & \text{violet-black}\end{array}


texts: How is the Maxwell-Boltzmann curve obtained?

texts:
Is it purely qualitative and determined by experiment?

Or is there some function which defines the familiar graph?

(Image source: Wikipedia)


texts: How does a lipid such as PC, with N(CH)3+ bind to a silica gel with many OH groups?

texts: I'm trying to determine the polarity of two lipids(phosphatidylcholine (PC) and phophatidylglycerol (PG)) and my experimental results indicate that that PC is the most polar, yet when I look at their structure i see that PG contain many $\ce{OH}$ groups, making it seemingly more polar than the $\ce{N-CH3}$ groups which are found on PC. But since PC, must be the most polar I'm trying to figure out how the positive charge on the nitrogen in  $\ce{N(CH3)3}$  influence the polarity and whether it can somehow bind to the  $\ce{OH}$ on the silica gel.


texts: Reaction of ethylene glycol with PI₃ (P + I₂)

texts:
We know that $\ce{2P + 3I2 -> 2PI3}$

Ethylene glycol reacts with $\ce{PCl3}$ to give ethylene dichloride, but why does it gives ethylene when it reacts with $\ce{P + I2}$?

I don't really know why it happens so as it is quite contradictory because in case of primary alcohols, corresponding iodoalkane is formed.


texts:
An experiment was carried out involving $\alpha$-bromoheptaldehyde dimethyl acetal. The experimental details are given below.

  A solution of enol acetate  (15.6 g, 17.7 mL) in chloroform (20 mL) was cooled
  to 0°C. A solution of bromine (16 g, 5.1 mL) in chloroform (5 mL) was added
  slowly with stirring with the rate of addition being controlled to keep the
  reaction temperature below 10°C. After the completion of addition, anhydrous
  methanol (60 mL) was added to the mixture and it was stirred for 48 hours.
  The mixture was diluted with water (200 mL) and ether (50 mL). The organic
  layer was separated, washed with water (100 mL) and with 5% aqueous
  sodium carbonate (100 mL). The organic layer was dried using sodium sulfate and
  filtered. The solvents were removed by distillation under reduced pressure.
  The residual oil was distilled under reduced pressure in the presence of a
  small amount of sodium carbonate. The fraction boiling at about 118°C at 17
  mmHg was collected to give bromo acetal as a colourless oil (19.5 g).

  (a) Do you think that this reaction should be done using a drying tube, under
  nitrogen or open to the air? Explain your answer.

  (b) Without doing TLC or any other form of spectroscopy or chromatography,
  how would you be able to tell if sufficient Bromine had been added?

  (c) Will the organic layer be the upper or the lower layer? How can you
  quickly check this experimentally?

  (d) Sodium carbonate is added just before the final distillation. Why?

  (e) The procedure calls for removal of the organic solvents by “distillation
  under reduced pressure”. Which one piece of laboratory apparatus would you
  use for this?

  (f) Suggest two serious and different hazards associated with this experiment.

My attempt

(a) It can be done in drying tube, as the reactant have to be prevented from coming into contact with water vapor from the air as the water vapor could potentially react with the reactant.

(b) By observing the colour of the reactant mixture. Since bromine is brown in colour, Once sufficient bromine has been added, there will then be excess bromine if bromine was continued to be added, hence the reactant will turn brown once enough bromine is added.

(c) The organic layer will be at the bottom. Since it is know that the density of the organic layer is more that that of the ether.The density of the organic layer can be measured and compared to that of the ether.

(d) To remove any excess acid that might be present in the mixture.

(e) Rotatory evaporator

(f) Bromine is toxic if inhaled, while methanol is a carcinogen

I am unsure of my answers though. Especially part (c) as I can't decide whether the aqueous or organic layer will be at the top. Could anyone explain this.


texts: Enthalpy and Internal Energy for Isothermal Expansion

texts:
Considering a system with constant atmospheric pressure , i.e a massless piston sitting in a cylinder containing water. At constant temperature say $\rm 100\,^{\circ} C$, the water turns into vapour and pushes the piston up.
Now shouldnt the $\Delta U=0$ as $Q = -p(V_2 - V_1)$, considering the Ideal Gas Behaviour
And then as $\Delta H = \Delta U + \Delta n\cdot R\cdot T$, then shouldn't $\Delta H = \Delta n\cdot R\cdot T$?

Then according to the question in image below, why isn't $\Delta U = 0$?


texts: Predicting melting points of substances based on their molecular/atomic structure

texts:
Wouldn't it be great to be able to predict the melting point of a metal based on the atomic number and not by looking in some table for the value that was measured experimentally by someone else? Or to predict the same melting point for a simple salt like NaCl or KI by applying some formula to the atomic numbers of the 2 atoms involved?

Can you help me understand why is it so difficult to build a theoretical model for this particular physical property? Were there attempts made in the scientific world for such a model?

--EDIT--

Yes, this is part of my question:
I want to understand if there is a connection between the theoretical explanations of properties like melting point and the current theoretical model of atomic structure. Can the electronic structure of $\ce{Fe 1s^2 2s^2 2p^6 3s^2 3p^6 3d^6 4s^2}$ tell us anything about it's probable melting point without measuring that point in the first place?


texts: Electrons distribution of oxygen atoms in ozone

texts:
While dealing with the Lewis structure for ozone, most of the explanations show the electron distribution around the 3 oxygen atoms with a single and double bond.

But if you count the number of valence electrons of the middle oxygen atom, it will add to 5 valence electrons only, but the number of valence electrons of an oxygen atom is 6.

Similarly, the oxygen atom with a single bond in ozone, is being shown with 6 valence electrons plus one single bond, which accounts for 7 valence electrons, which does not tally with the expected number of 6 valence electrons.

Can someone please explain why this discrepancy has been permitted? Or what did we miss to consider?


texts: Why does this ligand form 6-coordinate complexes with Transition elements and 8-coordinate complexes with Inner transition elements?

texts:
What change takes place in the denticity of this ligand if it is an inner-transition metal ion vs a common transition metal?
Primarily, why does the ligand behaves differently with the two situations above.


texts:
Are elemental compounds composed of different isotopes polarised? I'd expect any such effect would only really be noticeable for very light elements such as hydrogen.

I'm not sure which way the charge would be distributed and whether a deuterium protium pair would be more like deuterium protide or protium deuteride.


texts: Is there any elemental molecule which does not react well with anything but oxygen?

texts:
For example, phosphor reacts with oxygen but it also easily reacts with many halogens, metals, etc.

Is there any elemental molecule that doesn't react well with almost anything but oxygen?


texts:
From what I can tell, deprotonation of the central hydrogen leads to the more thermodynamically stable product (most substituted double bond. i.e. most stabilization by hyperconjugation). Therefore, if butanone is allowed to equilibriate in the gas phase, I would expect the deprotonated form A to be present in greater amounts than B. Therefore, I would conclude that the pKa of the central hydrogen is lower than that of the terminal one, in the gas phase.

My questions:

Is this correct? (please point out any mistakes or omissions from my argument)
How does this change with solvation, and why?

EDIT: To clarify questions: Any data on the acidity of the different sites in solution is greatly appreciated. The gas-phase specification above is simply there to be able to treat the problem solely thermodynamically (I appreciate that data on gas phase equilibration of acids might be hard to come by)

I've seen many other posts about ketone deprotonation, but browsing them I have   been unable to answer my questions. Refer: "Which enolate of butanone is more stable?", "Regioselective enolate formation"


texts: Aluminium foil on windows: what is the residue, and how to remove it?

texts:
I put aluminium foil on some windows' glass pane wetted with plain tap water, as a typical trick to stop sunlight. After 5 days, I removed the foil to find some kind of whitish pattern on the glass. The pattern follows the imperfections in the aluminium foil: bubbles, wrinkles, even a very slight embossed pattern in the foil.

To remove the pattern, I tried window cleaner, rubbing alcohol, vinegar, washing soda. Nothing worked.

Finally I tried caustic soda, at a solution stronger than that recommended for drain opening, and it mostly worked; but still there are patches where you can see the pattern if light reflects in the glass in just the right angle.

My question is: what caused this pattern? And, how can I get rid of its remains?

My next ideas are to try bleach or a stronger solution of caustic soda, but I'm afraid of etching the glass - what would be the maximum concentration advisable?

Also - if aluminium foil reacted to tap water like this, what happens when wrapping food and even cooking with it?

(I asked basically this same question in the DIY SE, but it's not getting actual answers, so I am hoping to get better insights here)


texts: Length of C-H bonds in hybridized bonding orbitals

texts:
What is the effect of hybridization and double-bond formation on the rest of the atoms/molecules attached to the central atom?

For example, in a benzene molecule, the Carbon-Carbon bonds are intermediate between single and double bonds. But what is the effect of the presence of the double bonds between the carbons on the bonds between the carbon and hydrogen? Do the bond lengths decrease because of the sp2 hybridized bonding orbitals?


texts: PP05 plastic "not dishwasher safe" but does not deform? Leaching chemicals?

texts:
It's plastic shaker cups, they came with instructions saying they are not dishwasher safe but they did not deform in the dishwasher. Does this mean it's probably unsafe to clean them using the dishwasher due to stressing the plastic, unleashing chemicals?
Thinking of the study showing additives in PP5 plastic had estrogenic activity.
Sorry, probably really hard to give a straight forward answer to this question.


texts:
I wanted to know what is the coordination number of the metal atom in π-complexes like Zeise's salt, ferrocene and dibenzene chromium.

I found some data on it but its a bit contradicting. Can anyone tell me what's right exactly cause what I found on web is a bit different from what my teacher said. It would be great if someone also tells me the reason and way of finding the coordination numbers in such compounds.


texts: Can all nine essential amino acids be produced synthetically?

texts: I would like to know if all nine of the essential amino acids can be produced synthetically with high purity without amines or other impurities through microbial activity during the production process.


texts: I recently ordered a 500g sample of Ferrous Chloride powder. However the powder is in light brown color, and on dissolving it in water, it gives a similar brown hue and it is not a clear solution. From what I saw on various preparation methods on YouTube, all the solutions are green in color. Is there something wrong with my sample? Could this be due to Iron Oxide formation? Kindly help.


texts: Finding the percent void of the crystalline structure of NaCl

texts:
Find the percent of void in the crystal structure of $\ce{NaCl}$.

I am trying to calculate the percent void of the packing structure of $\ce{NaCl}$. Let's denote radius of anion as $r$, radius of cation as $R$. What I know

$$\text{side length} = 2R + 2r$$

$$R + r = \pu{2.50 Å}$$

The ratio of cation radius to the anion radius is $0.600$. The equation to find void space:

$$100 \times \frac{\text{total volume} - \text{volume of spheres}}{\text{total volume}}$$

Yes, this is a homework question, but I'm stuck and I just need some help to get started.


texts: Molality of the solution prepared from a hydrated salt

texts:
A solution is made up by dissolving $\pu{13.8 g}$ $\ce{Na2CO3 · 10 H2O}$ in $\pu{103.5 g}$ of water. What is the molality of $\ce{Na2CO3}$ in this solution?

I can't solve it. I tried converting to moles with $\pu{13.8 g mol}/\pu{286 g} = \pu{0.04825 mol}$. Then I did $\pu{0.04825 mol}/\pu{0.1035 kg} = 0.466$ but it didn't work.


texts: Is it necessary to add prefixes of halogens (more than 1) to the iupac name alphabetically?

texts:
If I draw structure of 2-bromo-4-chloropentane and
4-chloro-2-bromopentane I get same result, when I try to draw structure. So why is it necessary to name prefixes alphabetically. Can we write iupac name not alphabetically.


texts: Lanthanide bond lengths and dissociation

texts: Due to lanthanide contraction, covalent character increases and ionic character decreases in lanthanides. Since a covalent bond is weaker than an ionic bond, $\ce{Lu(OH)3}$ should dissociate more easily than $\ce{La(OH)3}$. But that is not the case. Why?


texts: What happens to gunpowder when it gets wet?

texts: What happens to the gunpowder and other explosives when they get wet? I know that they stop "working" (won't explode anymore) but for what reason? Is it anyhow similar to the fact, that wet wood is burning worse than the dry one?


texts: What are all the structural isomers of a tertiary amine with the sum formula C6H15N?

texts:
According to the solutions there exist 7 different structural isomers 'containing 3 degree amines' for the molecular formula  $\ce{C_6H_{15}N}$

I tried and made a few, here are those

I have been trying since an hour and all I made were the repetitions of these 5 only. Could anyone suggest me the remaining 2?


texts: What substances could be used to gelify 60% hydrogen peroxide? I imagine anything organic like agar would be broken down by the radicals. I tried looking up what dentists use and the only thing that came up was glycerine, which I know from experience doesn't make gels with water, so I doubt it would work with $\ce{H2O2}.$


texts:
For 1,2-cyclobutanediol, it's given in my book that it has 3 stereo isomers.
Here's the passage:

My questions:

How can it have stereo-isomers?
What will the meso compounds look like?


texts: Calculate pH of a weak acid and weak base neutralization reaction

texts:
I'm an industrial pharmacist needing some help with some chemistry basics.

I'm trying to calculate the theoretical pH of an effervescent preparation containing 2 mmol citric acid ($\ce{H3C6H5O7}$), 4 mmol sodium bicarbonate ($\ce{NaHCO3}$), and 0.4 mmol sodium carbonate ($\ce{Na2CO3}$). These powders are dissolved in 100 ml of pH 6.0 water.

Citric acid: $\mathrm{p}K_\mathrm{a1}$ = 3.13, $\mathrm{p}K_\mathrm{a2}$ = 4.76, $\mathrm{p}K_\mathrm{a3}$ = 6.39
Sodium bicarbonate: $\mathrm{p}K_\mathrm{a}$ = 10.329, 6.351 (carbonic acid)
Sodium carbonate: $\mathrm{p}K_\mathrm{b}$ = 3.67

I don't know how to calculate pH in a case like this, where both acid and base are weak and polyprotic. If someone can do an example calculation, I'd really appreciate it.


texts: What chemicals could be added to human urine to cause harmful chemicals to precipite out?

texts:
What chemicals could be added to human urine to render it drinkable with no harmful side effects?

Urine is salty and contains other dissolved solids. Thus, drinking untreated urine would result in osmotic pressure actually removing water from the body.

So, what chemicals would be needed to cause the salts and other dissolved solids to precipite out or otherwise be rendered harmless?

I am thinking about a tablet, capsule or drops that would render human urine drinkable within 5 minutes or so.


texts: Why doesn't hydroxide concentration equal concentration of carbonic acid and bicarbonate in a sodium bicarbonate solution?

texts:
To find the pOH of  solution of  $\pu{0.42 M}$ of $\ce{NaHCO3}$, given a   $\ce{Kb}$ of $\pu{2.4E-8}$, my solution manual does the following steps:

Reaction is similar to : $\ce{HCO3- + H2O <=> H2CO3 + OH-}$
$\displaystyle \ce{Kb} = \pu{2.4E-8} = \ce{\frac{[OH-][H2CO3]}{[HCO3-]}}$
$\displaystyle \ce{Kb} = \pu{2.4E-8} = \ce{\frac{[OH]^2}{[0.42]}}$ , as we have $\pu{0.42 M}$ of $\ce{NaHCO3}$ so approximately $\pu{0.42 M}$ $\ce{HCO3-}$, and $\ce{[OH-] = [H2CO3]}$
Solve equation for $\ce{[OH-]}$, giving $\ce{[OH-]} = \pu{10^{-4}}$  and hence $\ce{pOH} = 4$

What I don't understand is: Given the equation $$\ce{HCO3- + H2O <=> H2CO3 + OH-},$$ doesn't this show $\ce{HCO3} = \ce{H2O} = \ce{H2CO3} =\ce{OH-}$, as they are all in a $\mathrm{1:1:1:1}$  molar ratio in the equation.

So wouldn't $\ce{OH-}$ also just equal $\pu{0.42 M}$?


texts: Why do some gases have lower value of Z for a particular pressure?

texts:
In the above graph,the minima of the curve for methane is more than that of nitrogen. Also, for a given value of pressure, the value of $Z$ for methane is less than that of nitrogen. They seem to meet at high pressure. Why do some gases have lower value of Z?

The same thing is observed if you compare methane and carbon dioxide. But they don't seem to meet at high pressure. This is because the $Z$ for methane increases at a faster rate. Why does Z increase faster for some gases?

The real gas equation is $$\left(P+\frac{a}{V^2}\right)\left(V-b\right)=RT$$
I tried expressing $Z$ in terms of $P$ and $T$ by eliminating $V$.

$$V=\frac{ZRT}{P}$$
$$\left(P+\frac{aP^2}{Z^2R^2T^2}\right)\left(\frac{ZRT}{P}-b\right)=RT$$
$$ZRT-Pb+\frac{aP}{ZRT}-\frac{aP^2b}{Z^2R^2T^2}=RT$$
Multiplying by $Z^2$ on both sides,
$$Z^3RT-Z^2(Pb-RT)+\frac{ZaP}{RT}-\frac{aP^2b}{R^2T^2}=0$$
$$f(Z,P)=0$$
(I am assuming constant temperature)

Should I find $\frac{\partial f(Z,P)}{\partial P}$ and make it equal to zero to get information about the minima?


texts: Quick and simple explanation of molar mass, molecular mass and atomic mass

texts:
As a physics student, I hardly deal with such quantities and when I do, I blunder through.
I think it’s a good time to be given a good explanation for these since I’m in a class of Nuclear physics. I have tried googling but it seems that some sources are ‘misleading’ and most have more than 1 terminology for the same thing!
Horrifying but real.

Please tell me what is the difference between molar mass, molecular mass and atomic mass and what are their associated twin terminology.


texts: Is a negative pH value possible in room temperature...teachers don't tend to teach about the pH of acid or base solutions which are higher than 1M.


texts: Why does a Diels–Alder reaction not occur here?

texts:
I have  recently come across this organic chemistry problem.
I thought it would undergo simple Diels–Alder reaction
But it didn't turn out to be. The product to me looks like a nucleophilic attack of (I) on (II).
Can anybody say me why exactly this abnormality seen and what is the mechanism of this reaction?


texts: Why is energy released when lattice formation takes place?

texts:
Whenever an ionic bond formation takes place it does so by forming a lattice and a subsequent amount of energy is released. What are the cause of release of energy and where does this energy come from and what is its form?
I am really confused. Any help is appreciated.


texts:
Which of these solution have the lowest vapor pressure in 298 K? Please give a brief explanation.

0.01 m $\ce {CaCl2}$
0.01 m $\ce {NaCl}$
0.02 m $\ce {NaCl}$
0.015 m $\ce {CaCl2}$
0.01 m $\ce {Na2SO4}$

(This problem is taken from an Indonesian Chemistry Olympiad)


texts: Does the amine group participate in resonance in aniline?

texts: When we draw resonance structures of aniline, 8 electrons participate in resonance, making it antiaromatic. But in our school textbook, it is said to be aromatic. Does the lone pair of $\ce{NH2}$ participate or not? If it doesn't, then it would make sense.


texts: Which invariant reactions are congruent?

texts: I am studying the concept of incongruent melting and invariant reactions. I was wondering, would all the invariant reactions that I show below be incongruent? As I understand it, we can only have congruent melting when the liquid to which our solid melts to has the exact same composition, and by the definition of these invariant reactions, this seems not to be the case in any of them.


texts: Numbering in phenolphthalein versus ascorbic acid

texts:
According to Wikipedia, the recommended IUPAC name for phenolphthalein is 3,3-bis(4-hydroxyphenyl)-2-benzofuran-1(3H)-one, and for ascorbic acid is (5R)-5-[(1S)-1,2-dihydroxyethyl]-3,4-dihydroxyfuran-2(5H)-one.

Why does the numbering in phenolphthalein start from the $\ce{O}$ atom next carbon atom, while in ascorbic acid it starts on the $\ce{O}$ atom? If we want to prioritize the keto group, why doesn't the numbering start on the carbonyl carbon? And other groups attached to the furan on both molecules don't seem prioritize any of the 2 counting.


texts: Chemical breakdown of sunflower seed to determine the allergy-causing substance

texts: I have a severe anaphylactic reaction if I ingest a sunflower seed, and carry an Epi-Pen at all times. What is it in the seed kernel that could be so problematic and is it going to also be present in sunflower oil and in the sunflower organic derivatives used so much now in lotions, shampoo, and many other products today? I try to avoid any food or product that states that it contains sunflower in any form but it is becoming more difficult to avoid, especially when many crackers and such state "may contain sunflower or canola or other" oils. I even fear putting lotion on that might contain it!


texts:
I was asked to " Use VSEPR theory to predict the most stable structure for $\ce{SF3Cl}$ and justify your answer. "

I managed to interpret the structure as seesaw and with a lone pair on the equatorial position. However, I had chosen that the most stable structure was that with Chlorine on the equatorial position because I thought that the Chlorine-Sulfur bond length would be greater than that of Chlorine-Fluorine.

However, the answer key stated the Fluorine was more electronegative, and therefore would be more stable on the axial (with chlorine as equatorial).

I was wondering if the answer key was accurate and if so, how would I compare the effects of electronegativity and bond length? I had considered electronegativity but I had thought it would simply make the bond even shorter, increasing repulsion.

Thanks!


texts: Is activation energy directly related to the reaction rate? (keeping the temperature, concentration, catalyst, particle size and pressure constant)

texts:
For different chemical reactions, does the activation energy of that reaction directly relate to the reaction rate? In other words, would a reaction always be slower if it had a higher activation energy than another reaction?

Of course, one of the reactants will be kept constant and the other reactant will differ for each reaction.

If pressure, catalyst, temperature, concentration, particle size, and other factors affecting reaction rate is kept constant, would the activation energy for each reaction be inversely proportional to the reaction rate?


texts: Prove that idempotency is a necessary and sufficient condition for a densiy matrix to be N-representable

texts:
As I understand, a necessary and sufficient condition for a density matrix $P$ to be represented by a wavefunction $|\Psi\rangle$ is that it is idempotent, i.e. $P^2=P$. It is easy to see that if $P=|\Psi\rangle\langle \Psi|$ then $P$ is idempotent:
$$
P^2=|\Psi\rangle\langle \Psi|\Psi\rangle\langle \Psi|=|\Psi\rangle\langle \Psi|
$$
since by normalization $\langle \Psi|\Psi\rangle=1$. However, I have had trouble with the other direction - how can I show that if $P^2=P$ then $P=|\Psi\rangle\langle\Psi|$ for some $\Psi$?

I have been able to demonstrate that if $P^2=P$ then
$$
P=\sum_{j} |\Psi_j\rangle\langle\Psi_j|
$$
where the sum over $j$ has no more terms than the dimension of the density matrix $P$. My argument was analogous to the one found here. I suspect that I'm almost there - I think it's just a change of basis that I haven't seen yet. How can I complete this proof?


texts: Favoured position in nitration of pyrrole

texts:
I try to figure out the preferred position of nitration (determine whether compound A or B is the major product) by looking at the resonance structures of the intermediate cation.

The solution then showed that for compound A, there is no intermediate 2. I wonder why. Thanks


texts: How to derive the energy of solvation equation?

texts:
The work done as a ion is solvated is given by: $-z^2e^2/8\pi\epsilon r$ but since the top line can be written $Q^2$, for simplicity I will say the equation is $-Q^2/8\pi\epsilon r$. Is this derived from integrating potential with respect to charge $Q$?

i.e    $$w=\int_Q^0 VdQ$$ where $$V=Q/4 \pi \epsilon r$$

I believe this would give the correct units and equation but is this an acceptable derivation?

Also, as a, sort of, side question why can't I write:

$$\triangle w=\int_Q^0 VdQ$$.

I understand that work is an inexact differential but I fail to understand the argument regarding paths - surely if you change the charge of a particle from one value to another, you must be doing the same amount of work no matter how you do it. This argument must be wrong but I don't know why and why does this mean I cant write $\triangle w$? I know you can do this for things like entropy and enthalpy because they are state functions - I just don't understand the difference. Thanks.


texts: chemical reaction that causes electrolysis of salt water without adding electric current

texts: I am producing hydrogen using house hold items in a capacitor like arrangement in salt water. I assume this is chemical electrolysis. The apparatus produces gas for many weeks that burns orange. Its easily assembled from stuff you would normally find in the trash. Do I have something of interest, or is this common chemistry?


texts:
The question might seem quite easy to answer but still I am unable to find any useful information. I am aware of laporte- or symmetry-forbidden transitions and for f-f also spin-forbidden transitions in lanthanides but still I can't seem to find any good solution how they can happen.

For a d-d transition there are many exceptions depending on the arguments you come up with. From inverse symmetrical polyhedra that use ligand vibrations to become distorted to s- and p-mixing with the d-orbitals.

But f-orbitals, at least for the lanthanides, are said to not contribute to chemical bonds. Then there is often the argument about spin-orbit coupling but that would probably solve the spin-forbidden transitions. I'm not sure how it would affect the actual f-f transition being forbidden. In an old paper I also read about df- and fg-mixing. That would explain it but I am not sure if this is really the case.

So the question remains can the f-f transition in lanthanide complexes be somehow influenced to become at least a tiny bit more probable and therefore cause the transition to happen?


texts:
A friend and I are doing a project that involves the process behind manufacturing Jet A-1 and specifically the specifications highlighted in DEF 91-91. I was interested to see the information at the bottom of page 8.

Specifically:

Why are 2,6-ditertiary-butyl-phenol, 2,6 ditertiary-butyl-4-methyl-phenol and 2,4-dimethyl-6-tertiary-butyl-phenol used rather than "more common" antioxidants like ascorbic acid?
How do these antioxidants function and do they work any differently
to biochemical antioxidants?
What factors determine the effectiveness of an antioxidant?
Why are a mixture of chemicals used at different ratio's rather than just one. Do they work more/less effectively at different temperatures for example?


texts: I read that alkanes are 'colourless and odourless'. Heptane is an alkane. Why does heptane smell like heptane? Impurities?


texts:
I decided to try some cooking with sugar and put a glass bowl on the flame with half a cup of sugar in it and some water. After bubbles appeared I stirred the sugar for about a minute and then I decided to add milk, and as soon as I poured the milk, everything exploded and the glass pot shattered into little pieces rapidly.

What just happened? Why did my glass pot explode when I boiled sugar in it and added cold milk? And does this also happen with laboratory equipment?


texts: what is the physical significance of ∆H=∆U for a chemical reaction?

texts:
In case of few chemical reactions $\Delta n=0$,so according to the equation $\Delta H= \Delta U+\Delta nRT$ change in enthalpy equals change in internal energy. But what does this in essence actually mean? Like physically what does this indicate and do we get any additional information from that an equation? I got this query seeing the following equation of formation of hydrogen chloride.

$\ce{H2 +Cl2 =2HCl}$ with $\Delta n=0$.

Like can it be associated to why the reaction is zero order?


texts: Is there an algorithm that counts Joback groups in a structure?

texts:
So I was wondering, there are a lot of cheminformatics tools (eg Babel) out there, to analyze and convert representations. I also saw some codes which counts certain groups, but ignores the carbon chain, which is obviously not suited for a Joback script. My google research only turned me a "homemade" matlab code found at Reddit, but it is no way general, as the first step of it is to exclude most of the rings.

So is there any open cheminformatic tool for this problem?


texts: Is the phenyl cation or ethynylium more stable?

texts:
I recently gave an exam and I received an interesting question to which I believe the answer is wrong.

Given two compounds, a benzene molecule with carbocation at one of its constituting carbon atoms and an ethyne carbocation. Now according to me even though ethyne carbocation is pretty unstable due to the sp hybridized carbon, but if a charge is placed on a carbon in the benzene ring, too much strain is caused on the ring which destabilizes it more. I believe that the stability of the ring is a more dominating factor when carbocations are involved,  but the answer was in favour of the ethyne carbocation.

Could someone please clear this doubt if whether any other factors were taken into consideration or my basic premise is wrong?


texts: Connecting a computer to Genesys 10S Spectrophotometer

texts:
Has anybody ever connected a computer to a Thermo Scientific Genesys 10S Spectrophotometer without their (costly!) software?  I'd like to pull absorbance data off of it to perform analyses.  There are several ways I could think of to do this:

A USB flash drive could be plugged into the front of the instrument, but none of my drives are recognized by the spectrophotometer.
The PC could be connected as an external printer, but I haven't found a way to receive the data without ThermoFisher's software.
The PC could be connected as an external printer, but set the instrument to believe it is a PCL format printer.  Could the data be intercepted and converted to a usable form?

I appreciate your input.


texts: Geometrical Isomerism (Cis-Trans) in trans-2-fluoro-3-methylpent-2-ene

texts:
trans-2-fluoro-3-methylpent-2-ene this compound in also known as (Z)2-fluoro-3-methylpent-2-ene.
I have given my possible structure in the image but it is wrong, Can anyone explain this ?


texts: How to deal with solving reactions with not enough background

texts:
The book I'm studying with often confronts me with exercises that involve solving reactions such as $\ce{CA(OH)_2 + CO_2 -> ?}$.

Now, most of the time, the questions are just repetitions of material that has been taught, that reaction in particular has been shown many times in the chapter before the questions, $\ce{... -> CaCO_3 + H_2O}$, but not explained.

When I look up such reactions on the Internet to try to understand, I mostly come across people who ask others to balance the equations for them. But that is not really interesting for me, as I find balancing a trivial mathematical task.

I am, however, failing to understand why this reaction (or many other reactions) happen the way they do. My book has also mentioned that you can combine two materials, like $\ce{CO + H2}$, in different ratios, under different temperatures, pressures, and with different catalysts, to get different results (methane, methanol, and many others).

So my question is -- when asked to solve a reaction, and given only the reactants (or possibly also other factors such as mentioned above), is there a mathematical principle (for example, relying on differences in electronegativity) to solve the reaction besides being completely familiarised with molecular orbital theory and quantum mechanics? Because so far, the only alternative I can see is memorising the reactions.

I realise this question is rather broad, and possibly there is no satisfying answer to it or any answer besides to go study quantum mechanics, but to provide some context, I'm a student at high school studying chemistry not as my main subject (so on a rather elementary level), and I'm looking for a perspective how to understand the material I learn and not memorise it.


texts: Specify the formula of the product X_n Y_m

texts:
During a chemical reaction, equal moles of two diatomic molecules $\ce{X}$ and $\ce{Y}$ are allowed to react to form one gaseous compound $\ce{X_nY_m}$. After the reaction is complete, it was observed that the density of the product formed is $1.50$ greater than the density of the reactant mixture. Specify the formula of the product $\ce{X_nY_m}$.

Here is my work:

$$\ce{X_m + Y_n -> X_nY_m}$$

Density of product: $D_\mathrm{p}$ = $(m/V)_\mathrm{p}$

Density of reactant: $D_\mathrm{r}$ = $(m/V)_\mathrm{r}$

\begin{align}
D_\mathrm{p} &= 1.5 \cdot D_\mathrm{r} \\
(m/V)_\mathrm{p} &= 1.5 \cdot (m/V)_\mathrm{r} \\
m_\mathrm{p} &= 1.5 \cdot m_\mathrm{r}
\end{align}

I really dont know where to go from there. I would appreciate it if someone could give me step by step how they solved it so I could not just have the answer but also understand how they got to it.

Also, would the formula found be empirical or molecular? How do you know that it is?


texts: Neutral and positively-charged polyoxometalates - proper name for the class of compounds

texts:
Would you still call neutral and positively-charged molecular metal oxides polyoxometalates, or do you know a better/proper way to name this class of compounds (Polyoxometalloids/Polyoxometallic species/Polyoxometallides/...)?

This question occurred on the premise of an interesting paragraph in the paper (1) regarding the nomenclature of newly-synthesized polynuclear oxovanadium-lanthanide species:

  Given that polyoxovanadates are increasingly being used as diamagnetic
  ‘‘ligands’’ for lanthanide ions, the cage structure in 3 could be
  described as a tubular $\ce{[V^V12O32]^4-}$ ligand coordinating to two
  $\ce{\{Dy(OH2)4\}^3+}$ centres, with the latter plugging the ends of
  the tube and trapping the interstitial chloride. However, it is surely
  preferable in this case to consider the dysprosium units as part of
  the cage, and this to be a heteropolyoxovanadium complex. One must
  also note that, very unusually, 3 is a cationic cage system, and
  that ‘‘heteropolyoxovanadate’’, with the -ate suffix denoting a
  negative charge is here incorrect according to normal IUPAC
  nomenclature rules. On the other hand, there are examples of
  positively-charged oxygen-bridged metal cages which correspond to well
  known motifs from polyoxometalate chemistry such as the
  $\ce{\{Al^{III}13\}}$ $\varepsilon$-Keggin-ion structure
  $\ce{[AlO4Al12(OH)24(H2O)12]^7+}$.

Compound $\ce{[AlO4Al12(OH)24(H2O)12]^7+}$ (2) was investigated in 1960, though it has not been explicitly denoted as polyoxoaluminate at that time.

Here are the structures of these polynuclear complexes:

It also seems like IUPAC does not really care, always referring to polyoxometalate term. So please feel free to share your opinion!

(1) Šimuneková, M.; Prodius, D.; Mereacre, V.; Schwendt, P.; Turta, C.; Bettinelli, M.; Speghini, A.; Lan, Y.; Anson, C. E.; Powell, A. K. RSC Advances 2013, 3 (18), 6299. DOI 10.1039/c3ra40385h

(2) Johansson, G.; Gullman, L.-O.; Kjekshus, A.; Söderquist, R. Acta Chemica Scandinavica 1960, 14, 771–773. DOI 10.3891/acta.chem.scand.14-0771


texts: I have a debate with some friends who believe that saliva is just basic, but with the enzymes which make them reactive with objects in our mouth, shouldn't it be an acid in this case?


texts: Usually compounds' colours are explained by the presence of unpaired electrons which is free to excite and de-excite giving the compound a charectistic colour. NO has atleast one unpaired electron but even then it is colourless. Can anyone tell me what the reason is?


texts: What is the appropriate method to visualize electrostatic potentials?

texts:
Using a molecular viewer like PyMOL, I understand that its often incorrect to simply look at positive and negative residues and use those residues to calculate the charge density and instead, you should be using something like APBS to calculate the electrostatic potential.

What is the correct way of going about this?


texts:
In quantum chemistry, the two-electron integrals often denoted as physicist's and chemist's notations.

For spin orbital, the physicist's and chemist's notations are
$$ \langle pq | rs \rangle = \int \int p(1)^* q(2)^* \frac{1}{r_{12}}  r(1) s(2) d^4 x_1 d^4 x_2 $$

$$ [ pq | rs ] = \int \int p(1)^* q(1) \frac{1}{r_{12}}  r(2)^* s(2) d^4 x_1 d^4 x_2 $$

respectively.

For spatial orbital, I have only found the chemist notation
$$ ( pq | rs ) = \int \int p(1)^* q(1) \frac{1}{r_{12}}  r(2)^* s(2) d^3 r_1 d^3 r_2 $$

Is there any physicist's notation for spatial orbital?


texts: What is the role of NaHSO3 in syn diol formation from alkenes with OsO4?

texts: All I have found on this is that NaHSO3 reduces partially the osmate ester, so breaks off Os and leaves a syn diol. Is it possible to show this step with arrows showing the process of electron movement? I suppose this step is not the main part of the reaction, and mayn't be very important, but I would like to know if it's possible - and if it is, how it looks.


texts: Can a small amount of scandium be added to gold, platinum or palladium to create a wedding ring?

texts: The number 21 has a special meaning to us, so we would like to make wedding rings with some scandium in it (element 21). I know scandium can be alloyed with aluminium or titanium, but can it also be alloyed with say gold, platinum or palladium without detrimental effects?


texts: How to make rheoscopic fluid using glycol stearate flakes

texts:
Rheoscopic fluid can be made by adding mica powder to water. I read that mica powder can settle and condense after sitting around for a long time. So I want to use glycol stearate flakes instead.

What process is required to turn them into a rheoscopic fluid? The manufacturer states the melting point to be $\pu{135-140 °F}$. Would I simply mix them into some water and raise the temp until they melt? Should it stay in suspension after cooling?


texts: So I've got my data for some x-ray crystals of small molecules of Ag, Cu,... I was curios to know what the best way to determine what type of lattice each of these atoms may have?


texts: When 2-hydroxylpropanitrite undergoes hydrolysis by H20, it will become 2-hydroxylpropanoic acid. In the structural formula, I wrote the O-H that are connected to the carbon with double bond as OH. Is it still the same thing or it is incorrect?


texts: Radiation in space and its effects on chemical reactions?

texts:
I know that one current area of research is ways to protect astronauts from ionizing radiation when they venture out of the atmosphere of Earth, but would that same ionizing radiation be a cause of concern when performing chemical reactions in space or in the atmosphere of planets with little atmosphere?

I'm aware that radiation like ultraviolet, which is present in sunlight here on Earth, is used in organic chemistry for the homolytic fission of halides, but I'm not sure how much higher energy radiation might affect other reactions.


texts: Why is the vertical part of a titration curve longer for a strong acid by a strong base than for a weak?

texts:
As the title says, I would like to understand chemically why this occurs. My theory behind it is that in the former case both are completely dissociated, and so at the equivalence point (and approaching it), everything is controlled increasingly by the autoionization of water, whereas in weak acids there is also a much more sizable contribution of $H^+$ by the acid itself, so the change is not as drastic. If this is correct, I'd like further explanation as to why it is, since I don't quite feel comfortable enough with it intuitively.

This is not a duplicate. I am not asking why the strong acid curve is steep, but rather why the strong acid curve is steep while the weak acid one is not.!

Weak acid and strong acid titration curves with addition of a strong base


texts: Why does hydroquinone possess a non-zero dipole moment? The $\ce{OH}$ groups present at para positions on the benzene ring should cancel the effect of each other... if there is a plane change then exactly when do atoms in a molecule change planes?


texts: Why is the value of specific rotation different in different cases?

texts:
An unknown compound with a mass of $4.5~\mathrm{g}$ is dissolved in enough carbon tetrachloride to make a total volume of $250~\mathrm{cm^3}$. The observed  rotation of this solution is $+357.75^\circ$ in a $25~\mathrm{cm}$ cell using the sodium D line. But if $4.5~\mathrm{g}$ is dissolved in $125~\mathrm{cm^3}$ we observed  rotation is $+355.50^\circ$. Calculate specific rotation for this compound. (assuming length of polarimeter tube is $1~\mathrm{dm}$)

My approach is starting with the formula stated on Wikipedia.

$$\text{Specific rotation (in first case)} =
\frac{+357.75^\circ}{\left(\frac{4.5}{250}\right)(1)}=19875^\circ=75^\circ$$

$$\text{Specific rotation (in second case)} =
\frac{+355.50^\circ}{\left(\frac{4.5}{125}\right)(1)}=9875^\circ=155^\circ$$

Any idea why the two answers are different? Did I miss out something?


texts: I haven't been able to find any literature on $\ce{^{19}F}$ solid state NMR studies of $\ce{LiF}$ crystals, not even $\ce{LiF}$ powders. Is there any NMR chemists who is familiar with $\ce{LiF}?$ Any references are greatly appreciated.


texts: What is more important, to have the parent chain be the cycle or the chain that has an hydroxyl group

texts:
I know how to name alcohols, I just don't know what I should chose as the parent chain. Should I chose the cycle or the chain with the hydroxyl group. Here is an example:

My current algorithm tells me that this is 1-(propan-2-olyl)cyclohexane, because it always chooses the cycle with the most skeletal atoms for a parent chain no matter what else is present.

So my questions are:

In what situation an acyclic chain is chosen for a parent chain over a ring?
If this is one of those situations would the choice be affected if we add on hydroxyl group to both the ring and the chain?
If this is not one of those situations would the choice be affected if we increase the length of the acyclic chain and/or add more hydroxyl groups?
Something on a slightly different topic: is 1-(propan-2-olyl)cyclohexane a correct name or should it be 1-(propan-2-ol-1-yl)cyclohexane? I am not sure if the 1 is omitted or not.

P.S. Is there a place where I can find the Blue Book for free? I only have the 2004 draft and I am not sure how much of it is changed in the 2013 version?


texts: Why is perchloric acid called so? I am aware of the rules, but why is it not called hyperchloric acid? Or is it correct to also refer to perchloric acid as hyperchloric acid?


texts: Is the ethyl cation really more stable than benzylic and allylic carbocations?

texts:
Source: Concepts of Organic chemistry by O.P. Tandon, page no. 235

My book appears to state that the ethyl cation (a primary carbocation) is more stable than both allyl and benzyl carbocations.

I knew that cation stability depends on the following factors: resonance > hyperconjugation > +inductive effect.

Can someone please clarify whether the ranking shown above is true?


texts: is there a stead fast rule to predict hybridization or is it just an ad hoc concept

texts:
Before I start of this question, Ι want to make it clear that I know that hybridization, like pretty much all of chemical bonding, are just made up to qualitatively rationalize observations. I know that theres no actual orbital overlapping, resonance, excitation.... and what not, and the only real things governing "bonding" are electrodynamics and quantum mechanics
When I first came across hybridization, I learnt that it is just used to obtain the correct electron density distribution from atomic orbitals as the experimentally observe corresponding to least repulsion/energy. The go-to way to determine hybridization would then be to use VSEPR to find the most stable electron domain geometry. However, I've come across several molecules such as H2S, PH3 and Halogen molecules where there is no hybridization. How does VBT /hybridization theory rationalize this? And is there any way that I could predict it? (I obviously can't know the experimental observations for all possible molecules before hand)
Secondly, is rationalizing geometry the only reason for invoking hybridization? I have come across these 2 other reasons in several reliable textbooks:

Hybridization occurs as hybrid orbitals are able to overlap more effectively and the bond strength is proportional to the extent of overlap. While this seems somewhat logical, I can't think of a single molecule where better overlap needs to be the reason for a specific hybridization
Hybridization occurs inorder to make all orbitals degenerate before overlapping as this corresponds to the lowest energy "quantum mechanically". This one seems way too handwavy but is mentioned on wikipedia https://en.wikipedia.org/wiki/Orbital_hybridisation

Bonus question:
I have another small question that I dont want to start another thread about given the multitude of questions on hybridization already present on the site but feel free to ignore this.
Why exactly do sp,sp2 & sp3 hybrid orbitals have the same exact geometries as the ones observed in electron domains? Is it just a coincidence or are they forcefully combined in such a way to match them>


texts: How to identify the asymmetric carbon in [4-(1-bromoethylidene)cyclohexyl]acetaldehyde?

texts:
How to identify an asymmetric carbon in the molecule below? Is the carbon identified by the asterisk asymmetric or not? I would say no as it has no 4 different groups attached.

Is this correct?
I will greatly appreciate if anyone can confirm or otherwise explain why it can be asymmetric.


texts: What is a "symmetrical product" of an irreducible representation with itself?

texts:
In their classic paper outlining the Jahn–Teller theorem (Proc. R. Soc. Lond. A 1937, 161 (905), 220–235), the authors wrote "where $[\phi^2]$ denotes the representation of the symmetrical product of $\phi$ with itself". Reading this I'm thinking about a regular product of representation (scalar product with each characters).

But in the next paragraph there is this equality for the $D_\mathrm{4h}$ group:

$$[\mathrm{E_g^2}] = [\mathrm{E_u^2}] = \mathrm{A_{1g} + B_{1g} + B_{2g}}$$

Obviously something is wrong, as the direct product is a 4-dimensional representation, but the right-hand side is 3-dimensional.

I would like to add that there is a reference of Weyl 1928 unfortunately this article is in German and I cannot find anything in it.

What is the correct way to carry out this direct product?


texts: I want to combine solid elemental iodine with olive oil, to form an iodized oil - what is called an iodostearic acid or iodooctadecanoic acid,  here the double bond in the oil becomes saturated by iodine. I have not done this before and I am looking for guidance on how to do this with basic kitchen tools. Would this be as simple as adding iodine and oil in the ratio of 8 parts iodine to 10 parts oil (as the iodine number for olive oil is around 80), and then waiting several hours or days for the reaction to take place? Is heat or some catalyst needed? Please advise! Thank you.


texts:
I'm currently working on a chemistry investigation wherein I need to dilute a compound with artificial sweat. I have looked at various forums, including this, which gave answers, but is very outdated.

I have also checked on ISOs standards, but it seems that I cannot get the information I want - ISO 105-E04 - without paying a huge sum.

Do any of you know of a recipe for artificial sweat that I can easily conjure in a lab, that's also backed up by various sources?

Thanks

P.S. I cannot just use water + salt, as that would be too simple and cause too many uncertainties for my experiment.


texts: Intrinsic Reaction Coordinate calculation-- both sides of TS lead to same minimum

texts:
I am currently trying to find an addition transition state and verify it using an IRC calculation. I have found a good candidate, but the IRC calculation gives the same minimum on each side of the transition state. In my mind, this does not seem any different from a vibrational mode.

I think the TS is submerged, and I am sure this is complicating things, but it does not make sense that an IRC calculation would give the same minimum in both directions.

Any thoughts on what this signifies or how to remedy it?

Thanks


texts: Why does an ideal capacitor give rise to a rectangular cyclic voltammogram (CV)?

texts:
This question is sort of a sequel to my previous question about cyclic voltammetry (CV).  One of the responses made reference to the fact that an ideal capacitor gives rise to a rectangular cyclic voltammogram.  Can you please help me understand why this is the case?  In other words, why does an ideal capacitor reach a constant current $I$ as soon as a voltage $V$ is applied?

I indeed see nearly ideal CVs in many literature articles (CVs which are rather rectangular with rounded corners).  In other figures, though, I see relative deviation from "rectangles with rounded corners," in that I see abrupt peaks, spikes, or valleys.

For example, below I have plotted two figures from Khomenko, Electrochimica Acta 2005, 50, 2499-2506.  Just very roughly and "hand wavy," what might be the qualitative reason for the "rectangle with rounded corners" behavior of Figure 8 (left) and the "abrupt peaks" behavior of Figure 4 (right)?  Could it be that the sample in Figure 8 (left) is relatively unreactive toward apllied potential, whereas the sample in Figure 4 (right) undergoes redox (Faradaic) reactions -- indicating the presence of so-called pseudocapacitance -- when an external potential is applied?

Please know that I am not looking for an answer specific to the article to which I linked.  I am only asking this question in the context of basic, qualitative aspects of cyclic voltammetry.


texts: Tried charging a penny/dime battery. Yellow goo bubbled. What did I create?

texts:
When I was a young child, I applied 9 volts across an electric cell I made using a penny, a dime, and a salted piece of paper napkin wet with saliva.
Immediately, an unknown mustard-yellow liquid began forming and bubbling from in between them. It discolored the coins.

What reaction took place? What was the yellow stuff?


texts: Does caffeine isolated from coffee contain harmane?

texts:
I'm not sure whether the caffeine contained in otc caffeine pills is made synthetically or isolated from coffee and other plants, but if the latter is the case, is it likely that it contains the chemical harmane?

It's claimed that isolated caffeine is 99% pure and I'm wondering whether the remaining 1% is likely to contain any appreciable amount of harmane.


texts: What were the original methods for determining atomic weights?

texts:
I am reading "History of Chemistry" by William Brock and I am confused about the original methods (early 1800s) used to determine molecular weights and hence determine the correct formulae for pure substances. Now I may have the order or link between ideas wrong - which is why I am looking for clarification here. All of what I write below is "as I currently (mis-)understand".

Lavoisier is credited as introducing /emphasising the importance of accurate measurement when conducting chemical investigation.

In order to write chemical equations that capture the correct formulae of products and reactants in an irreversible reaction that runs to completion, some method of measuring the "quantities" reacting and produced is required.

By measuring masses before and after reaction in a closed system we can demonstrate conservation of mass in a chemical reaction but not much else.

The (a?) key to determining correct chemical formulae for compounds is some way of determining the "quantity" of reactants and products rather than mass. We can't use mass as the direct measure of "quantity" (was this ever tried?) because of the differing atomic/molecular weights of reactants and products (simplistically, comparing two samples of different pure materials of equal mass/weight the material comprised of "heavier atoms or molecules" will contain fewer atoms or molecule than the other (*)). The only means in the early 19th C available to determine "quantities" was gas volumes.

Now a bit of cart-before-horse here. Using modern notation and terminology

The reaction of hydrogen with chlorine

$$\ce{H2 (g) + Cl2 (g) -> 2 HCl (g)}$$

Which I can interpret by Avogadro's law: 1 volume (mole) of  hydrogen reacts (violently) with 1 volume (mole) of Chlorine to form 2 volume (mole) of hydrogen chloride gas.

Now where I have a problem (discernable to me) is this:

How do we ensure or know before we conduct the experiment that we have the correct volume (number of moles) of each gas so that there is no unreacted "reactant"?

For example mixing 4 volumes of hydrogen with 1 volume of chlorine would give

$$\ce{H2 (g) + Cl2 (g) + 3H2 (g) -> 2 HCl (g) + 3 H2 (g)}$$

4 volumes of hydrogen plus 1 volume of chlorine (5 volumes of reactant) produces 2 volumes of hydrogen chloride plus 3 volumes of hydrogen (5 volumes of "reactant"). Conclusion: hydrogen and chlorine react in the ration 4 : 1 ???

Separately, I assume the analysis and interpretation of volumes to determine the reaction is trickier for gaseous reactions that establish some kind of equilibrium such as hydrogen and nitrogen forming ammonia, the position of equilibrium (in a closed system) depending on the pressure and temperature?

Another follow up - a very basic question. Is it correct to say that once the atomic / molecular weights are established we can then work out correct empirical formulae for compounds but not molecular formulae.

(*) This idea of course depends upon the idea that different types of atoms have different "weights" but isn't that Avogadro?


texts: Is sign convention for delta H and enthapy change of a solution different?

texts:
In the Ncert Chemistry Tb, it is given that

  $\Delta H$ is negative for exothermic reactions which evolve heat during the reaction and $\Delta H$ is positive for endothermic reactions which absorb heat from the surroundings.

In enthalpy change video lesson which I got access to online, it is given that
for $\ce{NH4NO3(s) -> NH4NO3(aq)}$ since the temperature decreases during the reaction, it is positive enthalpy of solution.

How is it positive? I guess both $\Delta H$ and enthalpy change of a solution is almost change. Since the temp decreases here, it is endothermic, so it should be positive right?

Are both of the above processes different from each other and are the sign conventions vice versa for each other?


texts: Is there an example where interpreting reaction coordinate as time leads to an incorrect conclusion?

texts:
I have heard that we should not interpret the reaction coordinate in an energy diagram as time, but are there any situations in which we would arrive at an incorrect conclusion if we did so?

When I say interpreting reaction coordinate as time, I really mean as $\frac{\text{time so far}}{\text{total time for reaction}}$ (I would have written this instead of "time", but I'm not sure of a word or phrase for this).


texts: Is it correct to include the concentration of water into the concentration equilibrium constant?

texts:
For the reaction
  $$\ce{ C3Cl3N3O3 + 3 H2O -> C3H3N3O3 + 3 HClO3}$$
  write the expression for $K_\mathrm{c}$ for this equilibrium.

The mark scheme says it would be
$$K_c = \frac{[\ce{C3H3N3O3}][\ce{HClO3}]^3}{[\ce{C3Cl3N3O3}][\ce{H2O}]^3}$$

I thought $K_c$ shouldn't include water, is the mark scheme wrong? Or is this an exception that water is steam instead of liquid water?

How is one supposed to know that?

Here is another question I have just come across. (Different question, but still related.) Please take a look at the image below. Now, the mark scheme has seriously taken the concentration of $\ce{H2O}$ into account in (iii) and (iv).


texts: Is it possible to measure light absorbance for analysis of lead concentration without photospectrophotmeter

texts:
I’m designing an experiment which requires I measure final and initial lead concentrations for the determination of aqueous lead uptake by different mediums. Because lead concentrations would be measured on the ppm scale, I’d need to use a spectrophotometer to measure light absorbance by the water samplings. I could then use Beer Lambert’s Law to determine concentration.

With recent protocols surrounding COVID-19, it’s been difficult to contact an institution. I was wondering if there was any way I could measure light absorbance of my samples at home. Is there some other apparatus I could look into using (or perhaps even purchase)?

All the best!


texts:
I have a .xyz input file

8
Energy =
C     0.0354972    0.7111560   -1.7500000
C    -0.0354972   -0.7111560   -1.7500000
C     1.1823040   -1.4277968   -1.7500000
C     2.3594716   -0.7301614   -1.7500000
C     0.0354972    0.7111560    1.7500000
C    -0.0354972   -0.7111560    1.7500000
C     1.1823040   -1.4277968    1.7500000
C     2.3594716   -0.7301614    1.7500000

(this is shortened, problem stays the same) which I would like to split with obabel. However, with

obabel coord.xyz -o split.xyz --seperate -m

I only get one outputfile split1.xyz containing the whole supermolecule. This is also the case if I enlargen the z-distance between the two molecules.

Does anybody either:

Know why this doesn't work
Has a different program which I can use

I don't have the time to manually split 500 molecule files.


texts: Can Ethanol be used to carry out SN1 reaction?

texts:
My book says that the reaction of

$$\ce{Cl-CH2-O-CH2-CH3}$$ with ethanol to form
$$\ce{CH3-CH2-O-CH2-O-CH2-CH3}$$
occurs through $\mathrm{S_N1}$ mechanism, but shouldn't it actually be $\mathrm{S_N2}$?

My understanding of this statement is that the substrate is a $1^\circ$ halide and on top of that ethanol is available to us as $\ce{C2H5-O-}$, which is a considerably strong nucleophile. All possible conditions are pointing towards an $\mathrm{S_N2}$ reaction but then why does the reaction proceed through $\mathrm{S_N1}$ mechanism?


texts: How did the temperature in the solution with a lower concentration of CuCl2 increased in a faster rate?

texts:
My lab assignment is about the reaction between $\ce{CuCl2}$ and Aluminium and we tracked the temperature of the solution every 15 seconds and we needed to make our own experiment to check how different things affect the temperature of the solution every 15 seconds. So I chose the concentration of $\ce{CuCl2}$ and thus we had four cups, one with $\ce{0.1 M}$, one with $\ce{0.2 M}$, one with $\ce{0.5 M}$ and one with $\ce{0.8 M}$. Obviously the temperature in the cups with a lower concentration of $\ce{CuCl2}$ barely changed and throughout most of the experiment stayed at the exact same state.

Now, the cup with the $\ce{0.5 M}$ concentration of $\ce{CuCl2}$ changed temperature in a faster rate than the cup with the $\ce{0.8 M}$ concentration. Not only that, at the end of the experiment, the temperature in the cup with $\ce{0.8 M}$ was 28° C meanwhile the temperature of the cup with the $\ce{0.5 M}$ concentration of $\ce{CuCl2}$ was 29° C .

Can somebody explain to me how that happened?


texts: Why is an Octet Complete Cation more stable than a Resonance Stabilized Cation?

texts:
Our instructor has lately been teaching us about different types of cations namely-Classical, Non-Classical, Resonance stabilized (R.S.C) & Octet complete cation (O.C.C) & how O.C.C is more stable than a R.S.C .
One thing I did not get isn't donating lone pair like in the below given example too is resonance ,so how come these two phenomena are any different?
  (R.S.C)(O.C.C)& also, why is the latter structure more stable ?


texts: What happens to the H electron during acid reaction?

texts:
In this generic acid-base reaction:

$\ce{HX + B <=> X- + HB+}$

It's explained that the acid HX donates a proton H+ to its conjugate base HB+.  What happens to the electron that was originally in the acid's H atom?