texts: Antisymmetrized Product of Strongly Orthogonal Geminal (APSG) method

texts:
To get a deeper understanding of electronic structure methods, like Hartree-Fock, MP2, and Coupled Cluster method, there are many small programs (codes) available in Python, C++ or Fortran, for example, Daniel Crawford's website, Joshua website

Does any one know any implementation of a simple Antisymmetrized Product of Strongly-orthogonal Geminals (APSG) method (Geminal Model Chemistry) for, say, two geminals (LiH, or H4, etc.) in Python or another programing language?

I will be grateful if someone can share this type of code (implementation) to get a better understanding of geminal based methods.


texts:
I have searched through printed books and the Internet, but I cannot find a definitive answer on an issue that fascinates me: what forces keep the various compounds belonging to a solid solution together?

If I correctly understand, a rock is a solid solution, and I know that the atoms of a single mineral species are bound by its particular covalent and ionic bonds, but what keeps different minerals together in a rock? Do they mix by sharing "neighbouring" cations and anions? I am not sure whether intermolecular forces such as Van der Waals forces are present, but I would definitely expect stronger forces in a solid solution or between the minerals of a rock.


texts: Are there phosphorescent/fluorescent materials that absorb near infra-red waves and emit higher wavelengths?

texts: This SO discussion here lists some chemicals (and interestingly chlorophyll) that absorb visible radiation and emit infra red. I was wondering if there were chemicals that absorbed near infra-red and emitted much larger wavelengths (near microwave).


texts: What type(s) of gloves are effective against DCM and acetone?

texts: I know that standard latex and nitrile gloves don't stop common organic solvents such as DCM and acetone. However, I was reading a Reddit thread and there were comments that if you are coming into contact with solvents you are just wearing the wrong type of gloves. In a non-manufacturer specific fashion, what types of gloves will stop DCM and acetone? What will it slow down long enough for me to have a chance to finish what I'm doing and change my gloves in a safe manner? I am looking for a guide on what gloves to use. I just had DCM on my mind since nitrile doesn't slow it down, and it burns. And acetone, since it is hard to stop.


texts: Which is more activating among Phenol, Sodium Phenoxide & Anisole? Also arrange them in increasing order of their activating effect

texts:
This is in reference to Kolbe's Reaction, actually I think that Sodium Phenoxide is the most activating because, in Kolbe's Reaction we don't make react $\ce{CO2}$ directly with phenol for the electrophilic substitution(Maybe because of it's comparatively less activating effect), but we do make Sodium Phenoxide react with $\ce{CO2}$ (Maybe because of it's comparatively more activating effect) so that it will get attach to the Ortho position of Benzene Ring.
Along with this, please also tell me why in Kolbe's Reaction, the main product is Ortho directing & in most of other reactions, the main product is para directing?


texts: I've noticed that as the chain length of n-alkanes increase, their number of carbon environments tend to 5 peaks, and no more, no less. Why is this? I've looked on multiple NMR (C13 NMR, I might add) databases and they show that there are 5 carbon environments. The outer carbons are all distinct environments like you'd normally expect, but the inner part of it (e.g. the innermost carbons in tridecane, C13H28) is all one environment. I hope somebody could shed some light on it. It's stumped both me and my chemistry teachers.


texts:
Here is the structure of the Zundel cation (courtesy Wikipedia):

The outermost shell electron count is $16$.

May I have the MO diagram of this cation?

This seems very complicated so I don't know where to start.

Thanks.


texts: Can the decompistion of one carbonate inhibt the decomposition of another carbonate?

texts:
If two different carbonates of Group II, are mixed in equal amounts and then heated could one of the carbonates decomposition inhibt the other ones decomposition?

I don't understand how it would because (as far as I am aware) the reaction is not an equilibrium.

However I was told that if:

  Equal masses of barium carbonate and magnesium carbonate powders are mixed together, and then heated using a Bunsen burner flame until there is no further change.

then

  The residue left after heating reacts with aqueous hydrochloric acid to produce carbon dioxide.

This suggests that not all of the carbonate decomposes. However (from Wikepedia)

Maximum temerature of a Bunsen burner flame is 1560 degrees celcius
Thermal decompistion of barium carbonate starts at 1360 degrees celcius
Thermal decompistion of magnesium chloride starts at 350 degrees celcius and is considered complete above 900 degrees celcius

This suggests that all the carbonate decomposes, however I am skeptical of this (Wikapedia) data.

So is thermal decompistion being inhibted? Or is barium carbonate simply not undergoing full decompistion (Wikapedia data is wrong)?

I couldn't find anything about it but maybe barum carbonate, like magnesium carbonate needs a much higher temperature than stated to fully decompose?


texts:
I have a chemistry question but I'm not sure which subtopic it'd go under, so I'm asking it here. I'd really appreciate any help I can get, if you have an answer, or if you can tell me where I can find the answer. I should also mention I don't know anything about chemistry, so I'm sorry if my question sounds stupid :-)

I was wondering if it's possible for dry ice (the industrial ones or those that are sold at stores) to stay cold/frozen in a rather warm/hot room temperature for around 2-4 hours. Let's say blocks of 3x3x4 inches. I just want to know if that's feasible or not.


texts:
How can i estimate calcium EDTA in a given sample?
We tried estimation by using mercuric nitrate but in vain we cant get a sharp end point.


texts: What is the state of aggregation (gas, liquid) of oxygen in blood?

texts:
Atmospheric oxygen is in O2 and a gas. Then we inhale the air, our efficient lungs do the magic to filter out the oxygen and push them into the blood stream.

When we say hemo and globin transport the oxygen using the iron ions. In what state oxygen is transported in the blood? as a gas or a liquid or an ion? It is hard for me to conceive of the idea that oxygen would be in gaseous form in the blood. "GAS in blood?" e.g. Arterial Blood Gas Test

Also, how does the lungs convert the gas into something that is compatible to be in blood?

References:
Amount of Oxygen in the Blood


texts: Solubility in homogenous mixtures of solvents

texts:
Alcohol and water are miscible.  I am coming across some chemicals that are soluble in alcohol and insoluble in water.  If I know solubility in two solvents separately, is solubility in a mixture of the two always straightforward, or are there confounding variables?

E.g., if some chemical will dissolve to 100g/L alcohol at 25°C, then will its solubility in a 50/50 mixture by volume of water and alcohol at 25°C always be 50g/L?

Does this generalize to all miscible solvents?


texts: Why are non-spontaneous reactions driven in the presence of energy?

texts:
Here is my understanding. If you have an endergonic reaction (m) with $\Delta G_m=-m$ and you couple it to an exergonic reaction (n) with $\Delta G_n=n$, where $n>m$, then the endergonic reaction can proceed as the overall $\Delta G$ for the system is negative. I understand why having the endergonic reaction occurring is not a violation of the second law of thermodynamics and why it is made possible in that sense.

I was recently studying electrolysis and they talked about hooking up an electrochemical cell to a power supply and using electrical energy to drive a nonspontaneous redox reaction. If you include the power supply in the system, then the $\Delta G$ is negative, as the power supply gives a lot of energy.

This is my confusion: if the redox reaction is nonspontaneous (let’s call it R1), then it must be spontaneous if the opposite direction (let’s call it R2). However, in the presence of electrical energy… R1 is made spontaneous? Therefore it can occur? But what of R2? Shouldn’t that reaction be even more spontaneous, as it were? Shouldn’t the system try to minimize its energy by preferentially allowing R2 to proceed, even in the presence of an energy source? Thus, why would R1 occur? Why does shoving energy into a system cause a nonspotaneous reaction to occur when it would be more favorable to continue having it occur in the opposite direction?

I would also appreciate it if anyone could extend this to general energy coupling, say with hydrolyzing ATP and a nonspontaneous biological reaction. Why is the original spontaneous reaction not made more spontaneous?


texts: Fundamental forces behind covalent bonding

texts:
I understand that covalent bonding is an equilibrium state between attractive and repulsive forces, but which one of fundamental forces actually causes atoms to attract each other?

Also, am I right to think that "repulsion occurs when atoms are too close together" comes from electrostatic interaction?


texts: E2 step in dehydration of primary alcohol using concentrated sulfuric acid

texts:
The familiar two-step $\mathrm{E2}$ mechanism of the dehydration reaction of ethanol using concentrated sulfuric acid is given below (forgive me for not using diagrams):

$\ce{H-CH2-CH2-OH + H2SO4 -> H-CH2-CH2-OH2+ + HSO4-}$
$\ce{HSO4- + H-CH2-CH2-OH2+ -> H2SO4 + CH2=CH2 + OH2}$

I have certain doubts about the viability of the second step, as $\ce{HSO4-}$ is a weak base.

Maybe $\ce{H2O}$ is used as the base in the second reaction instead? If so, is the catalyst regenerated at all?


texts:
It is intuitive that the second ionisation will require more energy than the first. However, I'm having trouble explaining exactly why. I came across this other question on a similar topic: Why second ionisation energy greater than the first?

The answer made sense until the answer said:

  Technically, there would be an increased attractive force ($\propto kq_1q_2/r^2$) from the nucleus, because the electrons on average will now be closer to the nucleus.

Considering, say, chlorine, when a valence electron is removed, it makes sense that the electrostatic repulsion between valence electrons would decrease. However, by removing 1 electron, why does this increase the attractive force? I don't see how would increase the coulombic force between the nucleus and a valence electron, since the magnitude of both charges are constant.

If it was the radius changing, why should the electrons be closer to the nucleus just because 1 electron is removed?


texts: Electronic model with highest prediction rate

texts: Amongst many models, including the valence bond model (VB) or the molecular orbital (MO) model, which are the ones with best predictive power? (e.g. the MO is thought to predict spectroscopic properties better than the VB)


texts:
From the bonding energy of following bonds that I found in a Wikipedia article, I calculated the reaction energy that would be released when oxygen and hydrogen are reacted to produce water. The phase of each component is unknown.

$$
\begin{array}{lc}
\hline
\text{Bond} & D_0/\pu{kJ mol-1} \\
\hline
\ce{H-H} & 436 \\
\ce{O-H} & 497 \\
\ce{O=O} & 498 \\
\hline
\end{array}
$$

Therefore,

$$\ce{2 H2 + O2 -> 2 H2O} + \pu{618 kJ}$$

However, this Wikipedia article suggests that $\pu{241.8 kJ}$ of energy is released for every mole of hydrogen, which is $\pu{483.6 kJ}$ per $\pu{2 mol}$ for the context of the equation above.

Even when I consider the vaporization of water, which is $\pu{40.65 kJ mol-1}$, the total energy will amount to $\pu{536.7 kJ}$ per $\pu{2 mol}$, which is still far away from $\pu{483.6 kJ}$ per $\pu{2 mol}$ that is suggested in the Wikipedia article.

Where could this extra energy be going?


texts: Why is hexafluoridonickelate(IV) diamagnetic?

texts: As fluoride is a weak-field ligand, it should not pair up the electrons. So why is $\ce{[NiF6]^2-}$ diamagnetic?


texts: When is a reaction feasible at room temperature?

texts:
Gibbs free energy determines whether a reaction will occur spontaneously or not. Still, the activation barrier of a reaction determines if a reaction will occur at a given temperature. At any non-zero temperature every energy level will be populated somehow, but when is population high enough to say that a reaction will take place?

So when is a reaction called feasible at room temperature? A source on this with an energy range for the barrier that can be overcome at a specific temperature (kJ or kcal/mol) so that one considers the reaction actually taking place would be much appreciated.


texts: Proof of Brillouin's theorem using the diagonality of the Fock matrix

texts:
I'm working my way through Szabo and Ostlund's Modern Quantum Chemistry. I am having trouble understanding the proof and significance of Brillouin's theorem. According to the book:

  Now, by definition, solving the Hartree-Fock eigenvalue problem requires the off-diagonal elements to satisfy $\langle \chi_i|f|\chi_j\rangle = 0,  (i \neq j)$.[1]

However, isn't the Fock matrix only diagonal because we used "nice enough" spin orbitals that we constructed by unitary rotations? That is, for any other choice of spin orbitals, the Fock matrix is not diagonal but is still a perfectly valid matrix with a mostly-eigenvalue statement, right?

What am I missing here?

[1] A. Szabó, N. Ostlund, Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory, Dover Publ., 1989, p. 129.


texts: Why doesn't hydrogen displace metals from their oxides?

texts:
As I understand it, a displacement reaction is where a more reactive element kicks out a less reactive element from a compound.

For example, chlorine is more reactive than iodine, so chlorine will displace iodine from potassium iodide, yielding potassium chloride and iodine.

If magnesium reacts with water you get magnesium oxide and hydrogen. But hydrogen is generally a lot more reactive than magnesium, so isn't this backwards? The above paragraph predicts that hydrogen would displace the magnesium from magnesium oxide.

So why does it actually happen the other way round?


texts: Why is benzenediazonium fluoroborate stable at room temperature and insoluble in water?

texts:
I think that as it is diazosalt it shouldn't be stable at room temperature. But it is stable. How is that possible?
And it is ionic hence insoluble in water.
Why?


texts:
A very large swimming pool filled with water of temperature equal to $20\ \mathrm{^\circ C}$ is heated
  by a resistor with a heating power of $500\ \mathrm{W}$ for $20$ minutes. Assuming the water in the
  pool is not in any contact with anything besides the resistor:

  Is the change of entropy of the resistor positive, negative, or zero?

My Attempt

We know that entropy is given by the formula:

$$\mathrm dS = \frac{q_\text{rev}}{T}$$

My first thought was that since the resistor is giving off heat energy to the water, $q$ must be negative and therefore the entropy change must be negative. However, does the fact that there is a continuous current of electrons passing through the resistor complicate this simple calculation? I am thinking that the current of electrons increase the entropy of the resistor and offsets the decrease in entropy due to heat loss. Am I correct?

  The answer in the book is that the entropy change is $0$.


texts: Objectively, what makes the solubility of $\ce{C5H11OH}$ greater than the $\ce{C5H11Cl}$ in water?


texts: Determining change in entropy and enthalpy during mixing of gases

texts:
Question taken from KVPY 2011. Answer key is A.

Logically it makes sense that $\Delta S_{\text{system}}>0$, because the process is spontaneous and as per second law, this means $\Delta S_{\text{universe}}>0)$. System is isolated ($\Delta S_{\text{surrounding}}=0$), hence system's entropy must be increasing.

However, it is also given that $$\Delta S_{\text{system}}=\frac{\Delta q}T$$ So does this mean that heat is transferred in some way? How is that possible for an isolated system?

Also, if there is no heat transfer, we can conclude that $\Delta H = 0$. But is that true?


texts: What's the most appropriate name for this reaction?

texts:
I recently wrote a test in which I was asked:

  What is this reaction $\ce{CH3CH=CH2 ->[CO + H2O][H+]CH3-CH(COOH)-CH3}$ known as?

  Wurtz Reaction
  Koch Reaction
  Clemmensen's Reduction
  Kolbe's Reaction

My thoughts on this:

It's definitely not Wurtz Reaction, because that reaction eliminates terminal halogens and attaches together two alkyl groups. Also, that reaction needs sodium in dry ethereal medium.
It's definitely not Clemmensen's reduction, because that needs zinc amalgam and acid. (Although acid is present, the reduction won't take place without the zinc, right?).
Now, my options are Koch and Kolbe's reactions. As Koch's reaction (Gatterman-Koch Formylation) adds a carbonyl group, and not a carboxylic acid group, I decide to go with Kolbe's reaction. However, as per Wikipedia, this reaction requires carbon dioxide and sodium phenoxide. The carbon dioxide can be taken care of, by the water gas shift reaction that converts $\ce{CO + H2O->CO2 + H2}$. But now, there's no sodium phenoxide. What to do now?

Basically, my doubt is whether there's a mistake in my procedure of eliminating the options, or if there's something I'm missing out somewhere which may lead to make a different choice?


texts: Determine which orbitals will form hybrids with one another

texts: I've been teaching myself chemistry, so any help is greatly appreciated.  I've been reading an online tutorial that claims the two orbitals that merge in Aluminum trihydride are  1 orbital of 2s and 2 orbitals of 2p.  This confuses me, because I would expect the orbitals of the electron configuration would form a hybrid with one another, that is, Al electron configuration is [Ne]3s^2 3p^1.  Therefore, why do the lower orbitals form a hybrid? Also, what is the rule in general to determine which orbitals will form hybrids?


texts: What can this chemical be? (Qualitative Analysis)

texts:
I have an unknown white powder, which is an ionic solid, and I need to identify what it is by using qualitative analysis. I've run quite a few tests, but I am having a lot of trouble identifying the anion. The data I've collected is below.
General Properties:

It is a white powder, and I know that it is an ionic solid.
It's density is around $\pu{2g/mL}$ (this is not an exact number)
It appears to be a hydrate (as it loses mass when heated over a bunsen burner)
It is fairly soluble in water. It definitely isn't very insoluble, but I have to add a significant amount of water in order to get it to dissolve.
The powder has a very strong smell (although it's hard to describe).
A solution of the solid is colorless.

Cation Test

A flame test produced a deep orange / orange-red flame

Adding $\ce{Na2CO3}$ to a solution of the solid results in the formation of a white precipitate

Adding a base, such as $\ce{NaOH}$ to a solution of the solid results in the formation of a white precipitate

Based on this data, I am fairly confident that the cation is calcium, but please correct me if there are any other metals that fit the pattern described above or if additional tests are necessary.
Anion Test
This is what has really been messing with me, because I can't seem to get a conclusive test for any anion.

Adding $\ce{AgNO3}$, $\ce{BaCl2}$, or $\ce{Pb(NO3)2}$ to a solution of the solid did not result in the formation of any precipitate, regardless of how much I added.
Adding $\ce{H2SO4}$ results in the formation of a white precipitate (and no bubbles or anything). However, I'm fairly sure that this precipitate is not related to the anion, but rather producing $\ce{CaSO4}$ (from the cation).
Adding $\ce{HCl}$ or $\ce{HNO3}$ to a solution of the solid did not result in any bubbles (neither did adding $\ce{H2O}$ directly to the pure solid)
Adding Ferric Nitrate to the solution just retained the orange color of the ferric nitrate. A dark red color or precipitate was not observed.
Adding $\ce{HCl}$ did not result in the smell of vinegar.
Adding $\ce{AgNO3}$ followed immediately by $\ce{HNO3}$ also did not result in a precipitate.
Adding ammonium molybdate and nitric acid to the solution and heating it caused the solution to turn yellow, but did not yield a precipitate (even after centrifuging). This test was done twice with different ratios of ammonium molybdate to nitric acid, and the exact same result was observed both times.
The brown ring test was conducted, and came back with a negative result. It is possible that this test was done wrong, because the acidified ferrous sulphate was added drop by drop on top of the solution, rather than by rolling it down the side of the test tubes, which may have interfered with test results.

Are there any tests for ions that I have missed? I've done almost every test I know trying to identify the anion, but no dice. The results for the ammonium molybdate test are also confusing to me, because I expected either a yellow precipitate (to confirm phosphate) or no reaction, but the test seems to have gone halfway by just turning yellow. Any guidance on what I should do next would be very much appreciated.


texts: Silver nitrate mirror on 3d printed sla resin

texts:
For a project, I need to develop special array of reflectors.

Usually this is done through a process of plastic injection and vapor deposition, however the prototyping cost is very high.

Another solution I would like to explore is to 3d print the array of reflector with SLA printer like Form 3 and then deposit silver through the process of silver nitrate on solution.

However, I wonder if that could work and if the bond would be good enough, if the resin part would need prior treatment.

Another method could be by depositing a conductive layer and then do electroplating.

I'm not a chemist and don't really know where to start looking.

Thanks


texts: Are vitamins in tablet are more efficient than the vitamins in their natural source?

texts: In medical shop I have seen that there are loads of vitamins tablets available but I was wondering like does vitamins in tablet are more efficient than the vitamins which are available in their natural source like in fruits ?


texts: Mechanisms involved in iodination of salicylamide protocol

texts:
In the laboratory, I performed an eletrophilic aromatic subsitution by reacting $\ce{I+}$ with salicylamide. The mechanism for this reaction is pretty straightforward, but it's the mechanisms for the supplementary reactions used in this lab that I can't seem work out.

In order to prepare the electrophile  $\ce{I+}$, sodium iodide was reacted with sodium hypochlorite:

$$\ce{ ClO- (aq) + I- (aq) + 2H3O+(aq) -> I+ (s) + Cl- (aq) + 3H2O (l)}$$

The equation (I think) is right, but can anyone provide some mechanistic insight or literature on how the hypochlorite manages to oxidize the Iodide?

Does it first have to go into an iodine ($\ce{I2}$) form? The reason I propose this is because as the hypochlorite was added to the salicylamide/sodium iodide absolute ethanol solution, color change was observed from dark red-brown to increasingly lighter shades of yellow.

It seems a similar question was asked about a year ago, but I was hoping to take it a step further.
Once the reaction had finished, a 10% (w/v) sodium thiosulfate solution was added. I assume this was because thiosulfate is a well known bleach (hypochlorite) neutralization agent: $$\ce{HOCl + 2 S2O3^2- -> Cl- + S4O6^2- + OH-}$$

Assuming the above equation is correct, how exactly (mechanistically) does thiosulfate neutralize hypochlorite/hypochlorous acid? The $\ce{S-S}$ bond of the tetrathionate is whats tripping me up.


texts:
I read a book where it states the following:

  There are many types of flame and there are even flames which don't produce smoke.

After reading it, it just got stuck in my mind. Is there a flame which doesn't produce smoke? If so, then what is it?


texts: A 4.00 L sample of gas is cooled from 67 °C to a temperature at which its volume is 2.60 L

texts: A $4~\mathrm{L}$ sample of gas is cooled from $67~\mathrm{°C}$ to a temperature at which its volume is $2.6~\mathrm{L}$. What is this new temperature? Assume no change in pressure of the gas.


texts: Reporting reaction energies calculated using electronic energies rather than enthalpies

texts:
I understand that electronic energy includes a combination of

electron-electron repulsion energy,
nuclear-nuclear repulsion energy, and
electron-nuclear attraction energy

at 0 K, and the energies are relative to a zero with all particles infinitely far apart.

So is this when it's appropriate to use electronic energies rather than enthalpies when determining reaction energies at 0K and when particles are infinitely far apart?


texts: multi state or multistate or multi-state

texts:
I am not sure if this question belongs to English language StackExchange.

In the context of multiconfigurational methods, what is the correct way to write multi-state character:

multi-state character
multistate character
multi state character

Personally I would go with option 1.


texts: Product of treating 1,3‐dibromocyclobutane with alcoholic KOH at elevated temperatures

texts:
Passage-II

  $$
\ce{
A ->[\text{1.}~\ce{NH2-}(\pu{2 mol})][\text{2.}~\ce{CH3-I}(\pu{2 mol})]
B ->[\ce{HgSO4}, \ce{H2SO4}][\ce{H2O}]
C ->[\text{dil.}~\ce{OH-}][Δ]
D [Mixture]
}
$$

  31. "A" gives

  A) Lucas test
  B) Silver mirror test
  C) White precipitate with ammoniacal $\ce{AgNO3}$
  D) Yellow precipitate with ammoniacal cuprous chloride

  32. How many isomeric products are existed in the mixture "D"?

  A) 2
  B) 4
  C) 6
  D) 8

What would be 'A' in the reaction? Any help would be deeply appreciated.

I know that alc. KOH does elimination, but I was confused whether it would eliminate one bromine each from two rings and create a bond between both the rings or it would simply eliminate both bromines from same ring and create two conjugated double bonds (cyclobut-1,3-diene).

EDIT: There is one more possibility: both the bromines get eliminated and a diagonal bond is formed in the ring (cyclobutane with any two diagonal carbons joined).


texts: Why are Erlenmeyer flasks shaped the way they are?

texts: The title says it all. We could conceive a good number of other possibilities. Why did Erlenmeyer arrive at this design?


texts: [Co(H2O)6]3+ vs [Co(NH3)6]3+ oxidising water

texts:
Cobalt(III) complexes cannot be prepared by addition of the ligand to a solution of the metal cation because the aqua cation $\ce{[Co(H2O)6]^3+}$ has no stable existence in solution. It is strongly oxidising with an E° = +1.84 volts for $\ce{[Co(H2O)6]3+ -> e— [Co(H2O)6]^2+}$. It oxidises water according to the equation:
  $$\ce{2 [Co(H2O)6]^3+ -> H2O + 2 [Co(H2O)6]^2+ + 2H+ + 1/2O2} (2)$$

  Complex formation, however, can modify the standard electrode potentials considerably (for example, E° = +0.10
  volts for $\ce{[Co(NH3)6]^3+ -> e— [Co(NH3)6]^2+}$ and therefore, oxidation from Co(II) to Co(III) is easily
  accomplished in the presence of coordinating ligands".

Why is it that $\ce{[Co(H2O)6]^3+}$ oxidise water, but $\ce{[Co(NH3)6]^3+}$ does not? I understand how values of reduction energy potential effect the proceeding of a reaction, but what is it about $\ce{[Co(H2O)6]^3+}$ that makes it able to oxidise water more?


texts: Why is Specific heat of Ammonia higher than water?

texts:
The specific heat of water is lower than that of $\ce{NH3}$, but why?
$\ce{H2O}$ forms more hydrogen bonds if I am right, besides there's more electronegativity for Oxygen.
But still, $\ce{NH3}$ has higher Specific heat. I found this link saying $\ce{NH3}$ has lower molar mass, but its just by one gram so it shouldn't be having much effect right?


texts: Dissolving Metal Reductions of Organic Compounds

texts:
I'm having trouble understanding why dissolving metal reductions, like (for example) sodium with alkenes in liquid ammonia, sodium with aldehydes/ketones in ethanol, or the Bouveault–Blanc reduction, reduce the substrate instead of the solvent. If you put sodium in ethanol (or any protic solvent), the ethanol is reduced and hydrogen gas is released. I can't see how the presence of a ketone (for example) will create a more favorable reaction.

For once, it doesn't seem thermodynamically favorable - reduction of the ethanol will release hydrogen gas, largely increasing the entropy, while reduction of the ketone produces no gas. Even if it is thermodynamically favorable, however, reduction of the ethanol seems much more favorable kinetically, since there are much more solvent molecules than substrate molecules. What is going on here?


texts: Concentration uncertainty due to volume measurement with cylinder

texts:
(All volumes were measured using a measuring cylinder which has a $\pm\pu{0.5 cm3}$ uncertainty)

You have a $\pu{50 cm3}$ of $\pu{0.5 M}$ solution to begin with
You then make a  $\pu{0.4 M}$  solution by mixing $\text{40 cm}^3$ of the above solution with $\pu{10 cm3}$ water.

If I'm not mistaken, the uncertainty for the volume should be $\pm\pu{1.0 cm3}$ because the second solution is the result of two measurements (and also uncertainties).
My question is: what is the uncertainty for the concentration?


texts: Sign of work done by the system in first law of thermodynamics equation

texts:
In the equation, $\Delta E = q - W$, according to my book, $W$ is positive when it is done by the system and negative when it is done on the system.

But in this problem:

  $\pu{3600 kJ}$ heat is entered in a gas cylinder, calculate the value of $∆E$ if the volume is not constant and work of $\pu{-800 kJ}$ was performed by the gas.

the sign is different. How should I make the equation?


texts: Which lone pairs/bonding pairs go into which pi molecular orbitals?

texts:
I was just doing some practice midterms and I came across this question. The answers were posted, but there are no explanations for anything. I wasn't able to find anything about this online, either.

Here are pictures of the question.

Here's the first part:

Here's the second part:

Part e) is what is throwing me off. I was flitting back and forth between O and N, and O, N, and C, but in the end got it wrong. It says to base the answer off of part d), but there are two filled orbitals! How do I know which pair of electrons occupies which orbital?

Does the sp3 lone pair of the nitrogen occupy the lowest occupied MO or the highest occupied MO? Because it appears from the correct answer that it occupies the higher one - but why is that? The other delocalized pair of electrons is the pi electrons in the C=O double bond, and I get that maybe they have different energies, but I can't think of any reason one pair should occupy one particular orbital over the other.

Furthermore, according to the movement of electron pairs in the resonance structures of f) (which were all correct according to the answer key), the third structure suggests the lone N pair is shared between the carbon and the nitrogen, not the oxygen and the nitrogen. What gives?

Also, as a side question - the reason why the solvent is polar aprotic, despite having the capacity to shed a hydrogen from the carbon to form an induction-stabilized carbanion, is because protic solvents have the labile hydrogen attached exclusively to an oxygen or a nitrogen, correct?


texts: How to sequester Na+ which prohibits the formation of a micro-emulsion in solution

texts:
I am mixing alkaline solutions ($\ce{Na2CO3}$) with crude oil containing carboxylic acids to create micro-emulsions. The carboxylic acids react with the alkaline moieties to create an in-situ surfactant which creates the micro-emulsion.

Up to here everything is going well. I produced the micro-emulsion I wanted. The next step is to have these micro-emulsions taking place when there are also contaminants ($\ce{Na+}$ and $\ce{Ca^2+}$) also present in the alkaline solutions, which prevent the micro-emulsion from forming.

I added EDTA to sequester the $\ce{Ca^2+}$ and it seems to have worked. What can I do about the $\ce{Na+}$?


texts: Why was the unit micrometers spelled backwards in old research papers?

texts:
I have recently been doing a literature research project on polymers and have been reading a lot of papers from the 1950s and 1960s (mostly in American journals from American authors). I saw this intriguing text:
 "the spectra was taken using light of $\pu{300 m\mu}$ through $\pu{600 m\mu}$. I think they mean micro meters. I would write that as $\pu{\mu m}$, not $\pu{m \mu}$.

I've seen this in more than one paper, but they're all at least forty years old. Was this some standard back then? Most of them are in the same journal (Journal of Polymer Science A), maybe that has something to do with it.


texts: Computational Chemistry: calculation of sterical effects

texts:
Is there a way to calculate sterical forces between atoms/groups of atoms (preferably with free and open source tools)? I have heard that this is possible within the framework of NBO. I am using ORCA, nwchem and Gaussian09 mostly. Sterics are obviously one of the most important aspects of organic chemistry but still I could find close to no resources on the computational chemistry aspects of it. It would be nice to have a way of quantifying sterics and also visualizing it somehow.

Does anyone have some experience on that?


texts: Can it be isolated at room temperature?  Or even at any temperature?


texts: Purification/Extraction of Sodium Permanganate

texts:
I read this question and answer, and it seemed like a rather nice way to make sodium permanganate.  Using the method with sodium hydroxide, I produced a solution. Once filtered and decanted, it was dark green.

At first this seemed somewhat strange, as I would expect to see a red color for sodium permanganate. Though, after a bit of research it seems this is actually sodium manganate. The color matches, and considering it only exists in very basic conditions, and since there is a lot of sodium hydroxide in the solution, this would make sense. To test this further, I added some sodium bicarbonate to, oddly enough, act as an acid. The sample of solution quickly turned the pink color I had expected.

So, I currently have some amount of sodium manganate, sodium hypochlorite, sodium hydroxide, and sodium chloride in this solution.

At first I hoped I might be able to extract this using organic solvents, but unfortunately wikipedia claims potassium permanganate decomposes in organic solvents and alcohol. I assume the sodium permanganate or manganate would do the same.

Upon boiling down the solution I would end up with a mess of crystals of various shades of blackish and whitish.

So, my real question here is, if there is a way or ways to remove the other substances (sodium hypochlorite, sodium hydroxide, sodium chloride) and attain more or less pure sodium permanganate crystals.


texts: Abbreviations in electronic configurations

texts:
I am teaching my students how to write the electronic configuration of the elements of the periodic table.
For example, following the rules on how to fill the orbitals, the electronic configuration of iron is
$$\ce{Fe}:~\mathrm{(1s)^2(2s)^2(2p)^6(3s)^2(3p)^6(4s)^2(3d)^6}.$$
Thus, its abbreviated form is
$$\ce{Fe}:~[\ce{Ar}]~\mathrm{(4s)^2(3d)^6}.$$
However, I has not been easy to find the explanation on why in any periodic table it is written as
$$[\ce{Ar}]~\mathrm{(3d)^6(4s)^2}$$
instead of
$$[\ce{Ar}]~\mathrm{(4s)^2(3d)^6}.$$
Same case for many other elements. Why is that?


texts: Energy a system at room temperature can supply?

texts:
"This reaction requires XYZ activation energy, therefore it cannot happen at room temperature." is a sentence I find often in organic chemistry textbooks. Activation energies are steadily given in textbooks too. Even though it is a nice piece of info, which gives a feeling of how (not) sluggish a reaction can be, it would be nice to know how much energy can such a system actually supply? Like, I don't know - 30 kJ/mol or 35 kJ/mol.
How much energy do particles in a system at normal conditions (25°c, 1 atm) have? I am note sure if there even is an answer, taking into consideration Maxwell-Boltzmann distribution, and an endless array of reactions... but maybe there is?


texts: Assuming ideal gas behavior, how can I tell when the change in enthalpy is equal to the change in the inner energy?

texts:
If ideal gas behavior is assumed, for which of the following reactions does $\Delta H = \Delta U$?

\begin{align}
\tag{a} \ce{N2O4               &-> 2 NO2(g)}\\
\tag{b} \ce{CH4(g) + 2 O2(g)   &-> CO2(g) + 2 H2O (l)}\\
\tag{c} \ce{SO2(g) + 1/2 O2(g) &-> SO3(g)}\\
\tag{d} \ce{Br2(l) + 3 Cl2(g)  &-> 2 BrCl3(g)}\\
\tag{e} \ce{Cl2(g) + F2(g)     &-> 2 ClF (g)}\\
\end{align}

The correct answer is (e), and I just want to make sure I understand why.  For $\Delta U = \Delta H$, no work can be done as $\Delta U = H - W$ (where $W$ is work done by the gas).

This means that the total number of molecules can't change, otherwise a change in volume will occur, causing work to be done upon molecules or the molecules to do work.  Likewise, phase changes will also require work to be done on the molecules.  Thus, we rule out (a), (b), (c), and (d)?

I'm not sure if this is too simplistic or the correct way of thinking about this problem.


texts: Why do acids ionize in solution if they are covalently bonded?

texts:
Maybe I am wrong, but I thought acids were covalently bonded since hydrogen doesn't form ionic compounds. For example, wouldn't $\ce{HCl}$ look like:

Since the electrons are shared, why does it break into $\ce{H+}$ and $\ce{Cl-}$ in solution?


texts:
I was trying to understand stereoisomerism. I am having trouble creating a 'flow chart' of Stereoisomerism. While there are many sources available over the internet and books, I don't find a standard answer. Some sources mention conformers and geometrical(cis/trans) under diastereomers while others seperate them completely. According to definition of diastereomers available on Wikipedia,

Diastereomerism occurs when two or more stereoisomers of a compound have different configurations at one or more (but not all) of the equivalent (related) stereocenters and are not mirror images of each other.

While this definition includes geometrical isomers very well into it, not much clarity arises regarding conformers as it used the word configurations rather than conformation.

Also I was finding difficulty in placing Mesoisomers in the chart.

It would be really nice if you could draw the flow chart and post it here.

Thank you!


texts: The property F in an equation for chemical potential

texts:
While studying the lamba sensor that works on yttria-strabilised-zirconium (YSZ) I came across the following equation:

$$p_{O_2}^{gas}=p_{O_2}^{ref} \cdot \exp\left(\frac{4FV_{ref}}{RT}\right)$$

What is $F$ in this equation?

Some more info

The "wall" of the lambda sensor is as shown in the picture with the voltage $V_{ref}$ measured across:

The equation apparently is derived directly from the chemical equilibrium (chemical potentials equals to zero):

$$\mu_{O_2}+4\mu_e=2\mu_{O^{--}}$$

They come to the following where they end at the final formula:

$$V_{ref}=\frac{RT}{4F}\ln\left(\frac{p_{O_2}^{gas}}{p_{O_2}^{ref}}\right) \implies p_{O_2}^{gas}=p_{O_2}^{ref} \cdot \exp\left(\frac{4FV_{ref}}{RT}\right)$$

I understand the partial pressures. The gas constant $R$ and temperature $T$ are also clear. If I am correct, $V_{ref}$ is the voltage across the material of the sensor wall, as in the picture, so this is also clear.

The equation is the final result from which the oxygen amount in the gas can be found, since the partial pressure of the oxygen in the gas can be calculated. My question is: What is $F$ in the equation?


texts: Aqueous Chemistry: Ranking Ion Concentration

texts:
I am trying to rank the concentration of $\ce{PO4^3-}$, $\ce{NO3^-}$, and $\ce{Na+}$ that remain in a reaction. The reaction occurs when 100mL of 1.0M $\ce{Na3PO4}$ solution is mixed with 100mL of 1.0M $\ce{AgNO3}$ soln. I have written the equation as:

$\ce{Na3PO4(aq) + 3AgNO3(aq) -> 3NaNO3(aq) + Ag3PO4(s)}$

From this equation I find that there are 0.3mol of $\ce{Na+}$ by 0.1L * 1.0M * 3mol Na, and
0.1mol of $\ce{PO4^3-}$ by: 0.1L * 1.0M * 1mol $\ce{PO4^3-}$ ,
and finally 0.3mol of $\ce{NO3-}$ by 0.1L * 1.0M * 1mol $\ce{NO3-}$.

By these calculations, the concentration of the nitrate ion and sodium ion should by equal. However, the correct answer is that the most concentrated ion is sodium followed by nitrate followed by phosphate. Could someone please explain where I'm going wrong.

Thanks!


texts: Which one is the strongest base among the following compounds?

texts:
I am confused between option (2) and (4). Both lone pairs of nitrogen are localized, so next, I looked at the hybridization of $\ce{N}$ in each compound. As in (2), the $\ce{N}$ is $\mathrm{sp^2}$ hybridized and therefore is more electronegative, I assumed it would be a weaker base compared to (4).

But the answer is (2). I drew the protonated structures and found that there is resonance in the compound (2).

I was taught that electronegativity is more important in questions like this. Is this a wrong concept? Any help is appreciated!


texts: Stereo chemistry of Hoffman elimination reaction?

texts:
Does Hoffman elimination go through syn or anti elimination?

I referred Solomons and Fryhle,Paula bruice,L G Wade but none mentioned about the stereo chemistry of the reaction.

Does it vary as per the reaction conditions or is it unknown?


texts: Calculate the wavelength of the radiation released when an electron moves from n= 5 to n=2

texts:
Calculate the wavelength of the radiation released when an electron in a hydrogen atom moves from $n = 5$ to $n = 2$.

How can I find this wavelength?


texts: Can gas be made to block radiation better?

texts:
Can any gas block radiation? I ask this because I would like to know if the properties of any gas element would chemically react differently with radiation from adding an electrical current.

This picture shows an Earth magnet's field deflecting plasma naturally in a vacuum.

Does any gas extend the electromagnetic shielding properties of a magnetic field?

I am interested if the lack or composition of an atmosphere's chemical properties would inhibit or complement the deflection and absorbing of cosmic radiation when coupled with a magnetic field.

Can contained pure $\ce{O2 O1 O3}$ be cycled back with electricity to replenish $\ce{O3}$ broken down by radiation while giving the gas an electromagnetic field?


texts: Chemistry of charging an insulator material

texts:
Earlier this year, I had learnt in Physics class that rubbing two different materials against each other can charge the materials (i.e. cause each material to either be positively-charged or negatively-charged). I had learnt that the charging process is an electron transfer phenomenon. The charging of conductors by rubbing (i.e. friction) is easily understood because conductors allow charge carriers to flow through them easily. Such as in the case of metals; adding more electrons to the sea of delocalised electrons is not difficult.

However, what happens during the charging of an insulator material, such as a polymer like poly(ethene), what happens to electrons which are transferred to these materials? Do they go into particular orbitals?

One thing I am sure of is that the electrons are surely localised to the region of the insulator they are transferred to. Thus, they are definitely not free moving.


texts: What reagents change the time of a chemical clock?

texts: I am doing a research task involving an iodine chemical clock reaction. I need to figure out which reagents in the experiment are responsible for changing the time before the colour change in the clock. The current method (see image attached) shows the quantity of materials required for a ~2 minute iodine clock. For this research task, we are required to find the quantity of materials necessary for a ~10 minute iodine clock. Can you please clarify which reagents cause the increase/decrease in time of the chemical clock reaction?


texts: Does rubber use one or two sulfur atoms to crosslink?


texts:
Can non-ferrous metals/alloys (copper, brass, bronze) be tempered (made harder) by temperature control alone, like ferrous metals? I understand it's simple to anneal copper, brass, etc., just by making them hot enough.

I'm Wondering if it's possible to temper non-ferrous metals without having to either work-harden it or media-blast it (essentially work hardening).


texts: Relationship between electric dipole moment and polarization?

texts:
$$\vec{p}_\text{ind} = \alpha \vec{E}$$
The induced dipole moment is the polarizability times the electric field vector.
$$\vec{P}(\omega) \propto \chi^{(1)}(\omega) \vec{E}(\omega)$$
The polarization is proportional to the susceptibility times the electric field vector.

In spectroscopy we used the dipole approximation. Unfortunately, I often mix up the different formulas. Is there a relationship between both formulas, or do both equations tell us exactly the same thing?


texts:
Assuming this is the correct place for a post like this, I need to write a piece of code to show the oscillations in the Oregonator. I have successfully done so for the Brusselator, but have been unable to find the appropriate rate constants and starting concentrations for the Oregonator.

Any help or information on a better place to post this would be appreciated.


texts: FFC Cambridge Process and impure reactants

texts:
The FFC Cambridge process with platinium electrodes allows the reduction of almost any metal oxide to a pure metal, with an oxygen byproduct.
So far, so good.  What I'm trying to understand is how it would handle mixtures of of materials.  For example, if it was a mixture of iron oide and titanium oxide, what would it do?  Which oxide would be reduced preferentially?  (I think in reverse order of reactivity?) If it was contaminated with calcium carbonate, would the chloride ions switch places with the carbonate?
Ultimately this is a question about how electroylsis works with complex solutions - so what would it do?


texts: I have been curious about this question for a while. If you want to warm up a large amount of water, is it feasible to do this by adding a substance that has an exothermic reaction with the water? What is the relevant chemistry one has to know to work out how much the water would be heated up by?


texts: Finding equilibrium concentrations, trouble simplifying equation

texts:
For $\ce{CO (g) + H2 (g) <=> CH2O (g)}$

with Kc = 0.068 @ 273K

initial concentrations being $\ce{[CO]}$ = 1.25M, $\ce{[H2]}$ = 2.00M, $\ce{[CH2O]}$ = 1.00M

I did $\frac{1.00}{((1.25)(2.00)} = 0.4$, which is more then Kc, so it's leaning to the left, will produce more reactants, and products will lower. So the I did:

$\frac{1.00 - x}{(1.25 + x)(2.00 + x)} = 0.068$

Multiplied the bottom and got $X^2 + 3.25x + 2.5$

so

$\frac{1.00 - x}{X^2 + 3.25x + 2.5} = 0.068$

I then tried multiplying the denominator by 0.068 and rearranging to solve for $x$ from there, but that's where I got stuck. $X$ is supposed to be 0.65.


texts: I'm analyzing a dataset generated with LC-MS from cells that were fed $\ce{^13C}$-Glucose. There are 3 groups in total each with a different media conditions. My goal is to identify differences between these groups. When I look at the distribution of labeling (MDV) I don't see any difference across the different metabolites but when I look at the relative abundance I see large differences. How can I interpret this, when the labeling patterns are the same but the relative abundance is significantly different? Thanks.


texts: What is the chemistry behind the reaction of KNO₃, K₂CO₃ and Sulfur?

texts:
I'm preparing a chemistry show where I end the show with yellow powder bang.

The powder is a mixture of:

$$\ce{K2CO3 + KNO3 + S} $$
My question is, what's the reaction between these chemicals?


texts: Adding hydrogen ion concentration while calculating pH

texts: I have just started learning how to calculate pH and I have noticed that adding [$\ce{H+}$] makes a negligible difference in few cases whereas in other cases it makes a major change in the final value. Why is that?


texts: C-13 NMR: Why are sp hybridized carbon atoms less shielded than sp3 hybridized carbon atoms but more shielded than sp2 carbon atoms?

texts: For example, when you look at hex-1-en-5-yne, you'll find out that the terminal carbon with the triple bond has a reading of 69.7 ppm and the internal carbon with the triple bond has a reading of 86.1 ppm. This is significantly more downfield than the other sp3 carbons which have readings of 22.4 and 32.4 ppm, respectively. The other sp2 carbons have readings of 134.3 and 116.4 ppm, respectively. You can also see that the terminal carbons are more shielded, which makes me wonder why also they appear to be more electron rich?


texts: Why is the crystal field splitting energy larger for square planar than octahedral complexes?

texts:
I recently came across a fact that for the same combination of metal and ligand, the crystal field splitting energy for square planar complexes is larger than that of the corresponding octahedral complex.
In fact, I came to know that

  Δsp is greater than Δo by a factor of 1.3 to 1.7

Is it possible to explain why it is greater theoretically or was it just observed through experiments?
And can that factor of 1.3 to 1.7 be justified?

EDIT:

My attempt:

In Octahedral field placement of ligands,both dx2-y2 and dz2 orbitals of the metals face direct contact with the ligand (when compared to only dx2-y2 orbital in the corresponding square planar complex) and hence they must experience more repulsion.Due to this,there must be greater enhancement of the energy levels and hence the splitting energy of the octahedral complex must be higher than the corresponding square planar complex.What is wrong in my reasoning?


texts: Is electric current always necessary to make cathodic protection possible?

texts: Can a cathodic protection system still work if there is no current between the anode and cathode?


texts: Why does chlorine have a higher electron affinity than fluorine?

texts: Since fluorine has its valence electrons in the n=2 energy level, and since chlorine has its valence electrons in the n=3 energy level, one would initially expect that an electron rushing towards fluorine would release more energy, as it would land in the n=2 energy level, whereas in chlorine, the electron would land only in the n=3 energy level, and would then not release as much energy.  Thus, one would expect fluorine to have a greater electron affinity than chlorine.  However, why is it that chlorine has a higher electron affinity (349 kJ/mol)  than fluorine (328.165 kJ/mol)?


texts:
I'm solving a quantitative problem involving the process of making oleum from pyrite.

The problem specifies that, at the end of the reaction, we find sulfur which does not come from the impurities present in pyrite.

Where is that sulfur coming from? Is it from the thermal decomposition of $\ce{FeS2}$?

$$\ce{FeS2 -> Fe + 2S}$$


texts: Why does the weaker C–H bond have a higher wavenumber than the C=O bond?

texts: My understanding is that a stronger bond has a higher wavenumber in IR spectrum. But why does the C–H vibration have a higher wavenumber than the C=O vibration? The latter is a double bond, so I think it should be a stronger bond than the C–H single bond.


texts: Understanding the Jahn–Teller elongation and compression for octahedral complexes (stabilisation/destabilisation of d orbitals)

texts:
I am currently learning about Jahn–Teller effect. For elongation I wondered why the d orbitals with $z$ component are stabilised when the metal–ligand bonds are getting longer? I thought a longer bond would mean a less efficient overlap of the d orbital on the transition metal with the orbital on the ligand.
And if yes, shouldn't it be raised so the difference in energy between the d orbital and the ligand’s orbital be greater? I thought the ligands’ orbitals would be lower in energy each time.
Where am I going wrong with my thinking?


texts: Given that hydrogen atoms that are attached to a compound must be ionizable for the compound to be an acid, what prevents a hydrogen from being ionized? Is it solubility. If the bond is nonviolent, water could not dissolve the compound, and so hydrogen atoms are not ionizable. Is this correct?


texts:
Which of the following reagents will convert benzene to isopropylbenzene? Choose all that are appropriate.

I know for certain that (b) can be used, but I also think the following mechanism with (d) is also possible:

Is my line of thinking correct with this one?


texts: What is the precipitate of this reaction of magnesium?

texts:
$\ce{MgSO4}$, on reaction with $\ce{NH4OH}$ and $\ce{Na2HPO4}$, forms a white crystalline precipitate.
Identify the precipitate.

My approach: I guess the white crystalline precipitate is $\ce{Mg(OH)2}$, since it is white and insoluble in water.


texts: Small scale gas-to-liquids via Fischer–Tropsch — is it even possible?

texts:
I'm really interested in the Fischer–Tropsch gas-to-liquids (GTL) process. A lot of people are using wood or other biomass feedstock to make syngas on small scales (farms, shops, etc.).
Practically, what would be required to build a small scale GTL reactor to run a Fischer–Tropsch process on a small scale in a shop? Is that even possible to do safely?


texts: Why is trimethylsilanol a stronger acid than tert-butanol?

texts:
The Wikipedia article about trimethylsilanol says the following:

  Trimethylsilanol is a weak acid with a $\mathrm{p}K_\mathrm{a}$ value of 11. The acidity is comparable to that of orthosilicic acid, but much higher than the one of alcohols like tert-butanol ($\mathrm{p}K_\mathrm{a}$ 19).

Why is it so? A silicon atom is more electropositive than a carbon atom, therefore the conjugate base should be more destabilized by the +I effect of the $\ce{Si(CH3)3}$ group compared to the $\ce{t-Bu}$ group.


texts: What is the mechanism for the reaction of an organic hydroperoxide with sulfuric acid?

texts:
The question asked to react the organic hydroperoxide substrate, $\ce{R-OOH}$, with dilute sulfuric acid, $\ce{H2SO4}$.

In the last step, I removed a proton, making it act like a catalyst, along with the removal of $\ce{H2O2}$. But I am very unsure about its correctness.

Please confirm or correct if this is a wrong answer.


texts: Why do only some metals make protective oxide layers?

texts: Almost all Alkali metals and Alkaline Earth metals react with air to form their respective oxides, but why does only Magnesium forms a protective oxide layer? What properties of magnesium oxide allow it to form a layer?


texts: Why is honey more viscous than water? And, if we boil honey to just below its boiling point, will it become equally viscous as water at normal temperature? How does changing temperature affect viscosity?


texts: Why is the expectation value of Hermitian conjugate operators $RR^\dagger$ always real and non-negative?

texts:
I've been reading through a derivation of the wavefunctions and energy levels for the quantum harmonic oscillator. It defines

$$\hat R^\pm=\frac{1}{\sqrt{2}}[\hat p \pm \mathrm{i}\omega \hat q]$$
in mass-weighted coordinates $q=x\sqrt{\mu},$ such that $\hat p= -\mathrm{i}\hbar(\mathrm d/\mathrm dq)$ and $\hat q$ is the position operator.

It then asserts that that $\langle \psi|\hat R^+\hat R^-|\psi\rangle$ must be real and non-negative, since $\hat R^+$ and $\hat R^-$ are hermitian conjuagtes. I know that $(\hat A\hat B)^\dagger = \hat B^\dagger \hat A^\dagger$ and so $\hat R^+\hat R^-$ is a hermitian operator meaning that the bra-ket must be real, but I can't see why it should be non-negative. Could anyone shed some light on this?


texts:
I already have two questions touching on this subject and there is a third question as well.

The thing is that all the other question talk about cleaning silver with aluminum foil and carbonated water. The recipe I use though is to soak the silverware and the aluminium foil in salt water (simply mix table salt and cold water). I got the idea many years ago watching a commercial for a product called "SilverStar" or something like that on TV-Shop which was essentially a 0.5 cm thick aluminium plats which you were supposed to but in a bowl with saltwater and all your jewellery and it would magically become polished.

The explanations for the "recipes" using carbonated water are all along the lines that the acid dissolves part of the aluminum and then the aluminum ions in solution somehow react with the silveroxide.

The question then is if I only use table salt and (still) water will the chemistry be more or less the same but only much slower (relying on CO2 dissolving in the water from the air) or is there something else going on?

My understanding of what was happening with the salt water was that the salt water acted as a "wire" and the aluminium acted as the "sacrificial metal" in a Cathodic Protection. I always thought that you could essentially put the aluminium in one bowl and the silver in another and connect them with a copper wire.

So the question is twofold

What is the purpose of the table salt in my recipe?
Is there any (chemical) difference between "my" recipe with table salt and the more mainstream one with different flavours of carbonated water?


texts: Solubility of Aluminium Hydroxide in Sodium Hydroxide Solution

texts: Aluminium hydroxide is not soluble in water at all, however I was doing some reading and read that it does in fact dissolve in a solution of sodium hydroxide. This just seemed a bit strange to me, so I was wondering if anyone could explain why this is the case.


texts:
Question: which molecule out of $\ce{SO2}$ and $\ce{SO3}$ has larger $\ce{S-O}$ bond length?

Both are $sp^2$ hybridised. Since $\ce{SO3}$ has more bond pair - bond pair repulsions, shouldn't $\ce{SO3}$ have more $\ce{S - O}$ bond length so it can reduce repulsion?


texts: Making carbon powder using fireplace and weak acid

texts:
I am doing a little home experiment trying to make as pure carbon powder as I can. I plan to then used it to eat up oxygen from a container where I want to try to melt aluminum.
My process was following:

I have put some sawdust in an iron can.
I covered the opening of the can with clay, leaving only a small opening.
I put the can in a fireplace and let it heat to about $\pu{800 ^\circ C}$.
After removing, I ended up with about 1/3 volume of black powder.
I washed the powder with water and filtered the water out.
I placed the wet powder in a beaker and added more water.
I added about 12% hydrochloric acid to dissolve calcium and metal oxides and hydroxides.
The solution started bubbling slightly, so I left it for several hours with occasional mixing.
I washed the resultant powder with water twice and left it to dry.

Did I manage to purify the carbon in the powder somewhat? Did the use of acid bring any benefit?


texts:
This was a question in a chemistry exam:

  How many moles of hydrogen is required to convert 1 mole of this compound into a saturated compound?
     $\ce{CH3COCH3}$ (acetone)

Some teachers said that it's saturated so the answer is zero.
Others said that one mole is required to break the bond between $\ce{C}$ and $\ce{O}$ and convert it into an alcohol.

So which answer is correct and please mention a reference if available.


texts:
Does anyone do mass spectrometry with a magnetic sector to separate ions by mass and an array of detectors in a line to measure the ions? If not, why don't they?

Something like this this setup for measuring the spectrum of light?


texts: Extraction of glucose and fructose from golden syrup

texts:
Not so long ago, I asked how to make golden syrup.

Now I am wondering how to extract glucose and fructose from it. I would then like to separate the fructose from the glucose (while keeping both of the materials.)

When I made the syrup I used citric acid as a catalyst.

How would you start the extraction if I only need glucose and fructose (separated)? I have no idea.


texts: Can final volume differ from initial volume in a constant volume process?

texts:
A sample of 1.00 mol perfect gas molecules with $C_{p,\mathrm m} = 7R/2$ is put through the following cycle: (a) constant-volume heating to twice its initial volume, ...

(Problem 2.5, Atkins Physical Chemistry 8th ed.)

The problem says that in a constant volume process the final volume is twice the initial volume.

Is this even possible? How can volume become twice if it was constant all the time, it wouldn't have exploded to twice its size suddenly after the process ended right?


texts: Doubts Regarding Ceric Ammonium Nitrate Test for Alcohols

texts: I read about Ceric Ammonium Nitrate Test for Alcohols and a red colour is produced if the solution has an alcohol functional group however as a side note it was mentioned that this test is only useful for compounds having less than 10 Carbon atoms. Why is it so?


texts: Why is black-body radiation curve smooth without a sharp cutoff?

texts:
Planck's law is able to predict a graph that is consistent with experimental observation:

In essence, unlike Rayleigh-Jeans law that assumes equipartition theorem to hold (that each mode of motion shares equal energy at thermal equilibrium, so all modes excited at thermal equilibrium ⇒ ultraviolet catastrophe), Planck's hypothesis proposed that oscillators of frequency v will be excited only if they can acquire energy of at least hv , where h is Planck constant.1
So based on this argument, I am not sure why the shaded region of the graph will slope in a smooth manner when wavelength is being decreased. Say if you are only able to supply energy of hv, then all oscillators with frequency > v should not be excited and hence will not contribute to energy density ⇒ ρ = 0:

I expect the behaviour to be same as that in photoelectric effect: if frequency of incidence wave is below threshold frequency, you will never observe photoemission. But the actual observed graph is the first one. Where did I go wrong? I am not a physicist so a not-too-complicated explanation will be appreciated.

1 Peter Atkins, Julio de Paula. Physical Chemistry (8th Edition). OUP. 2006. Page 247.


texts:
I'm looking for polymer to fit injection molding (thermoplastic):

The final injected part (small part of volume approximately $\pu{300mm3}$) should be transparent, because a stainless steel tube will be inserted to a hole inside the part and adhesive using UV will be accomplished to attach the tube to the part.

Good mechanical properties of the polymer would be a bonus. For example, polycarbonate can be used, but I'm looking for additional material.


texts:
As stated in my textbook, the effective nuclear charge can be calculated by taking the non-valence electrons away from the atomic number, as also stated in the first calculation on Wikipedia: https://en.wikipedia.org/wiki/Effective_nuclear_charge

The textbook also states:

If we assume that the noble gas core is completely shielding, then the 10 inner electrons
of the neon core make the effective nuclear charge 10 less than the nuclear charge.

My understanding is it implies noble gases have 0 effective nuclear charge.

However, as many sources state noble gases have 8 valence electrons, shouldn't their effective charges be +8?


texts: The reaction mechanism for epoxides to react with LiAlH4

texts: Does anyone know the mechanism for the reaction of epoxides with Lithium aluminium hydride (product of course being an alcohol)


texts: Why hydrogen gas tube produce hydrogen atomic spectrum

texts:
To measure the atomic hydrogen spectrum people often uses hydrogen gas tubes as light source.
Since the gas in the tube is the molecule $H_2$ , why we obtain the spectrum of atomic hydrogen?
My guess is that because the voltage is so high, so that the molecules are totally dissociated.
If you could give me some reference I would be grateful.


texts: Comparing size of ions lithium, gallium ions

texts:
How is the size of $\ce{Li+}$ ($\pu{0.68}$) larger than $\ce{Ga^3+}$ ($0.62$)?

This is very difficult for me to understand  why they say that size of Li+ with 3 protons and just 2 electrons should be considerably more than that of $\ce{Ga^3+}$. I understand the poor shielding effect of $\ce{3d^{10}}$ electrons but it isn't obvious to me why it will make its size smaller than $\ce{Li+}$ which has just one shell with 2 electrons and more effective nuclear charge. Where is my logic wrong?


texts: How to get rid needle clogging on electrospinning of PLA/PCL/PMMA/Collagen?

texts:
For my thesis research, I dissolved PLA and PCL in chloroform: methanol (3:1), PMMA (350.000 MW, 13 wt%) in acetone, and collagen in acetate acid--and then, I mixed them together. The problem is when I tried to electrospinning with this solution, the needle clogging happened every time. It causes uncontinuous fiber synthesis. Fortunately, when I tried to observe some fibers from the solution, the result was 'no beads' appear.

I use needle 21 G with electrospinning parameters 20 kV and flow rate 2 ml/h.

Is there any suggestions for me on how to get rid needle clogging? Thank you.


texts:
Why do potassium, rubidium, cesium all have lower standard potentials than sodium?

Sodium has a higher charge density than any of them, so its enthalpy of hydration should be larger, right? The argument applies for why lithium has a more negative standard reduction potential than the other three, but why doesn't this argument apply for sodium?


texts:
I'm studying for my chemistry final and having a hard time with this question on one of the practice exams. Here's the question:

At $20$ degreees Celsius, Henry's Law constant for Ar is half of that for Kr. If a gaseous Ar/Kr mixture containing 20% molar fraction of Kr is placed over water at $20$ degrees Celcius, what is the ratio of concentrations of Ar to Kr in water?


texts: Why is volume inversely proportional to pressure?

texts:
If temprature is directly proportional to volume (Charles's law) and
temperature is directly proportional to pressure (Gay-Lussac's law), then why is pressure and volume are inversely proportional?


texts: Why do nitro groups confer explosive tendencies?

texts:
When suggesting nitration of an aromatic compound in the synthesis of some organic molecule, it was raised that this route should be avoided as to prevent things from going "ka boom."

An explanation was not forthcoming.

So, why do nitro groups tend to make organic molecules explosive? Is it because the $\ce{NO2}$ group really "wants" to be $\ce{N2}$ since a) diatomic nitrogen has a super high bond strength and b) diatomic nitrogen is a gas usually and therefore conversion to diatomic nitrogen would be entropically favorable? Is it because carbon's most oxidized state is also a gas and the $\ce{C=O}$ bond isn't a wimp either - hence the reason many organic compounds are flammable?

Also, what happens first in an explosion? Does carbon become oxidized first, which then provides the activation energy necessary to decompose the nitro group? I ask this because organic carbon compounds by themselves which are flammable - i.e. toluene - aren't considered explosive, but trinitrotoluene is an explosive.


texts: Does adding NH3 to an HCl solution facilitate the dissolution of aluminum compounds?

texts:
If we compare the two solutions hereafter, which one would better leach/dissolve aluminum metal/compounds present at/near the inner surface of the glass:
Solution A: $10\,\%\, \ce{HCl + H2O}$
Solution B: $10\,\%\,\ce{HCl + 1\% NH4OH + H2O}$
I'm asking because I'm looking for a solution to leach away aluminum (and other lesser trace metal ions) from the surface of borosilicate glass such that it won't contaminate puriss solutions in the glassware, and one suggestion was to use "salmi" (which I believe is $\ce{NH4Cl}$), so I'm now wondering if $\ce{NH3}$ in solution somehow facilitates the "grabbing" / solubility of aluminum in an $\ce{HCl}$ solution.


texts: Material that doesn't melt at 800 deg F, but can be dissolved?

texts:
I'm a sculptor and I have a chemistry/plastic question. I thought here would be a good place to ask.
I'm looking for a substance (probably a plastic) that has these characteristics:

Doesn't melt at the annealing temperature of Copper (doesn't melt at 700 degrees Fahrenheit)
Can be dissolved/made non-solid/melted by a process that will not affect copper (a specific acid?)
Is available in a wire form
Is relatively flexible

I want to wind long coils of tiny copper wire around a flexible core (the plastic I'm looking for), form that coil into complex shapes, then get rid of the core so as to be left only with the copper wire showing

I understand these requirements are perhaps impossible to meet...Just wondering if someone with good knowledge of plastics maybe has an idea.


texts: Most stable conformational isomer of 3-methoxycyclohexan-1-ol

texts:
Among the following, the most stable isomer is?

I am aware of the fact that equatorial substituents are more stable than axial substituents but couldn't proceed to apply it here. However the answer key gives the answer as d) in which both substituents are in axial position.


texts: What is the physical significance of the universal gas constant R?

texts:
While studying work done in isothermal processes I was told that the universal gas constant $R$ is the work done by the gas per mole per kelvin. I am sure I am missing something basic but I didn't find anything beyond that statement when I looked for an explanation.
This is what I found on Wikipedia:

The physical significance of $R$ is work per degree per mole.

In doing what, is 8.314 joules of work done by one mole of an ideal gas?


texts: N-hydroxysuccinimide as a good leaving group

texts:
In the synthesis of carboxylic acid derivatives (esters, amides), I often see N-hydroxysuccinimide used in conjunction with a coupling reagent (EDC, DCC). The reason given for this (from online) is that N-hydroxysuccinimide is a good leaving group.
Can anyone explain why this is so? I am unable to think of any reasons for why N-hydroxysuccinimide has a weak conjugate base compared to a general alkoxide.
Thank you.


texts:
List in order of increasing radius:

a) Rb, K, C5, Kr

For this one I got C, Kr, K, Rb

b) Ar, Cs, Si, Al

This I got: Ar, Si, Al, Cs

Does anyone know if this is correct? I don't have the solution for these in my book :S


texts:
Why are there only 7 types of unit cells and 14 types of Bravais lattices?

I was reading about solid-state chemistry for the first time and this limitation made no sense to me.

I tried to do the math and realized that there could be many more possibilities. Usually, the standard unit cell is described on the basis of whether the sides are at 90 degrees to each other and whether the sides are equal or not. However, any angle other than 90 could be chosen as the reference angle. So why 90?

Is it because only these 14 systems are found in nature and there is no need to study others?

Moreover, why are there only 4 sided shapes or hexagonal shapes?
Why not pentagonal or trigonal?

Any reference from any site or textbook would be appreciated.


texts: Mechanism - Dialkyne boron complex + Iodine?

texts:
Exam tomorrow and I was flicking through one of our handouts to find this reaction (D). I'm certain we don't need to know the mechanism but I was quite inquisitive as to how the iodination works.

The hydroboration part is fine, I just don't understand how it fuses the two alkynes.

I've tried to work it through as in the reaction above (C)


texts: A few questions about the conditions of the Diels Alder Reactions

texts:
I'm attempting to extract the diels alder reaction into a generic reaction and am trying to gain a better understanding of it.

Can a conjugated diene react with another conjugated diene via the diels alder reaction? And is the reaction limited to only dienes or can it be expanded to polyenes?

Does anyone happen to have a link as to the details on hetero diels alder reactions and the structures that can undergo such reactions and limitations on chemical species that can react via this reaction.


texts:
My daughter has a chemistry exam on Tuesday. She is doing quite well with her revision except for the following table which she is having difficulty remembering.

Does anyone know of an easy way to remember this? Or perhaps if someone could explain why these exceptions are insoluble that will help her instead?


texts: What are the partial charges in an SN2 transition state?

texts:
What are the partial charges of on the atoms in a SN2 reaction?

The nucleophile is normally negatively charged and has a lone pair of electrons. This would make you think the transition state would have a negative charge on the nucleophile. The leaving group also is taking the electrons from the molecule with it. So what is the charge separation?

Here are conflicting images.

First image

Second image


texts: Increase in Yield of products in an exothermic reaction

texts:
Given an exothermic reaction $\ce{N2 + 3H2 -> 2NH3}$ (which was initially in equilibrium). The temperature is then increasing with time. I am supposed to predict the yield of ammonia with time.

According to an exothermic reaction, the equilibrium constant K is supposed to decrease with increase in temperature. But it is found that the yield increases initially before decreasing continuously as expected. What causes the initial increase in the yield?

I suppose that the heat overcoming the activation energy could provide an explanation, but is there any other concept which is not fully reliant on the kinetics of the reaction?


texts: What is the plastic material of the CD cases?

texts: What is the material of which the transparent part of CD cases are made of? It is nicely rigid and really lightweight.


texts: Why do cyclic hydrocarbons have higher boiling points than their acyclic isomers?

texts:
As pointed out in the comments to this question, cyclic hydrocarbons have higher boiling points than their acyclic isomers. The major attractive force for hydrocarbons should be the London forces, which scale with surface area. My intuition has me thinking the cyclic molecules have less surface area, but they might enable more productive interactions over larger parts of their surface area due to their fixed conformations. I would love to see a study or some data that supports my intuition.

Boiling point data

  Three carbons

Cyclopropane - BP $=-33\ ^\circ\text{C}$
Propene - BP $=-47.6\ ^\circ\text{C}$
Propane - BP $=-42\ ^\circ\text{C}$

  Four carbons

Cyclobutane - BP $=12.5\ ^\circ\text{C}$
Methylcyclopropane - BP $=4\ ^\circ\text{C}$
1-butene - BP $=-6.7\ ^\circ\text{C}$
Butane - BP $=-1\ ^\circ\text{C}$

  Five carbons

Cyclopentane - BP $=49.2\ ^\circ\text{C}$
1-Pentene - BP $=30\ ^\circ\text{C}$
Pentane - BP $=35.9\ ^\circ\text{C}$

  Six carbons

Cyclohexane - BP $=80.7\ ^\circ\text{C}$
1-Hexene - BP $=63\ ^\circ\text{C}$
Hexane - BP $=68.5\ ^\circ\text{C}$


texts: How do noble gases bond with themselves?

texts:
Noble gases have full electron shells, which virtually blocks any other element from bonding with it. However, I've heard about cases where they bond to each other  - for example, helium can apparently form a dimer $\ce{He2}$.

How is this possible?


texts: Reaction between sulfur and sodium hydroxide

texts:
Sulfur reacts with sodium hydroxide in the following way:

$\ce{3S + 6NaOH->2Na_2S + Na_2SO_3 + 3H_2O}$

It is a disproportionation reaction: sulfur's oxidation changes from zero to -2 in sodium sulfide and from zero to +4 in sodium sulfite.

But how to remember the products of this reaction? By rote memorization?

The preparation of sodium sulfide is apparent. Is there a way to understand why sodium sulfite forms? We have the hydroxide ion, and it somehow reacts with sulfur to yield the $\ce{SO3^{2-}}$ ion - but how?


texts: Why does Pb(II) promote ligand substitution?

texts:
I have heard of an article where divalent lead $\ce{PbL2}$ ($\ce{L}$ is ligand) reacts with something (again not sure, as I dont know the article) and what it reacts with gains a ligand.

In less confusing words:

$\ce{PbL2 + MXn}$ ($\ce{X}$ is another ligand, not necessarily halogen) ==> $\ce{PbL(n-1)X + MX(n-1)L}$
Or something similar. That is what I got from hearing about the article. I was wondering if you guys can share your thoughts as to why happens?


texts: what would happen if you got a full package of wet silica gel on your hand after it tore open?

texts: I accidently opened a bag of silica gel and got it on my hand what will happen to my hand because now it kinda feels weird.


texts: Why are the halogens good disinfectants?

texts:
I've been searching around the internet for a while and I know that Chlorine, Bromine and Iodine are used as disinfectants.

My question is, what is the property of the halogens that make them suitable for killing microbes? Is it just their toxicity?


texts: Does an orbital have its own energy, separate from the electron? Can I picture them as a entity independent from the hosted particle?

texts: Does an orbital have its own energy, separate from the electron? If so, is it possible for an electron to have a different energy than the orbital it occupies?


texts:
Looking at the following reaction, I understand how the product forms, however, can somebody help me understand why two products are formed? Would the identical mechanism produce the two products?

Edit: This is how I understand the mechanism.


texts: Halogen vs H-Bond Donor/Acceptor: How do they differ?

texts:
I know that in rational design sometimes the researcher might use Cl or F instead of  a H-Bond donor/acceptor. What kind of interaction does a halogen provide compared to the H-bond donor/acceptor? When might it be better to use one compared to another for best binding affinity?
Below is a picture of a small molecule in an active site. I am considering if should use a H-bond donor or a Halogen to complement the carboxylic acid (skinny line structure with red oxygen in upper left). I want the most attraction to occur between the small molecule and the active site.


texts:
A chemist adds $\pu{0.115 g}$ of a group 2 element to water and the resulting solution is made up to $\pu{400 cm3}$ by adding distilled water. The equation for the reaction is shown below. $\ce{M}$ represents group 2 element.
$$\ce{M + 2 H2O -> M(OH)2 + H2}$$
The concentration of hydroxide ions $\ce{OH- (aq)}$ in the solution is $\pu{6.56e-3 mol dm-3}$. Determine the molar mass of $\ce{M}$ to one decimal place. Use your answer to identify $\ce{M}$.


texts: Rate law for breakdown of ozone to oxygen

texts:
For the following problem:

  Example 3: Write the rate law for $\ce{2 O3 -> 3 O2}$ given that the first step is fast and reversible, and the second step is slow.

  $$
\begin{align}
&\text{Step 1 (fast, reversible)} &\qquad \ce{O3 &<=>[$k_1$][$k_{-1}$] O2 + O} \\
&\text{Step 2 (slow)} &\qquad \ce{O + O3 &->[$k_2$] O2 + O2}
\end{align}
$$

  The rate is determined by the slowest step.

  The rate of formation of $\ce{O2}$ is equal to $2$ times the rate of the slow step $(k_2[\ce{O}][\ce{O3}]),$ since two molecules of $\ce{O2}$ are formed.

  Thus, rate of formation of $\ce{O2} = 2k_2[\ce{O}][\ce{O3}],$ but $“\ce{O}”$ is an intermediate, solve for $“\ce{O}”$ in
  terms of products and reactants and rate constants.

  Since the first step is fast and reversible and the second step is slow, the first step is in equilibrium and we can write

  $$\frac{[\ce{O2}][\ce{O}]}{[\ce{O3}]} = \frac{k_1}{k_{-1}} = K_1 \quad\text{or}\quad [\ce{O}] = \frac{k_1[\ce{O3}]}{k_{-1}[\ce{O2}]}$$

  Substituting:

  $$
\begin{align}
\text{rate} &= \frac{2k_2k_1[\ce{O3}]^2}{k_{-1}[\ce{O2}]} \\
\text{rate} &= k_\mathrm{obs}\frac{[\ce{O3}]^2}{[\ce{O2}]}
\end{align}
$$

The solution indicates that the rate of formation $\ce{O2}$ is $2k_2[\ce{O}][\ce{O3}]$. Why isn't it $2k_2[\ce{O}][\ce{O3}] + k_1[\ce{O3}]$, because the first reaction also produces $\ce{O2}$?


texts: Calculating bond length in VMD (Visual Molecular Dynamics)

texts:
Is there a way to calculate bond length in VMD (Visual Molecular Dynamics)?
I have a lot of trajectory files of water molecule, and I need to calculate the bond length of $\ce{O-H}$ bond, and find the average.

I know that there is a GUI based method to calculate bond lengths in VMD, but can I do the same using a script?


texts:
Is storing carbon dioxide in limestone a good idea? Wouldn't that lead to a reaction like

$\mathrm{C}\mathrm{O}_2 + \mathrm{H}_2\mathrm{O}\to {\mathrm{C}\mathrm{O}_3}^{-2} + 2\mathrm{H}^+$

And then the (unbalanced) reaction

$\mathrm{Ca}\mathrm{C}\mathrm{O}_3 + \mathrm{H}^+\to \mathrm{C}\mathrm{O}_2 + \mathrm{Ca}(\mathrm{O}\mathrm{H})_2$

So now the the ground turns into a water caustic water solution. Is this right?


texts: How is silver chloride more soluble in brine than water?

texts:
I heard that:

  Silver chloride is more soluble in very concentrated NaCl solution (brine) than in pure water.

Is it true? I mean won't the common ion effect operate? Or may be this is due to some kind of complex formation as NaCl solution is highly concentrated ???


texts: Single-molecule magnet with electrically-controlled permeability: How does the Titan Shield from Deus Ex work?

texts:
In a recent installment of Deus Ex game series there is an augmentation called "Titan Shield" (it has nothing to do with $\ce{Ti}$ element):

A neodymium skin underlay matrix built of nano-meshed rare earth magnets and powered with hook-ins to the Biocell electrical system, the TITAN skin augmentation can be activated at will and then dissipated instantaneously.
When activated, dimorphic magnetorheological fluid is ejected from tiny nozzles installed throughout the skin. Simultaneously, the neodymium underlay electrifies, causing the fluid to solidify and seal the user inside an iron shell, effectively protecting them from all physical damage. The shield is resistant to gunfire and all forms of conventional explosives, but is vulnerable to EMP-based weaponry.

Titan Shield in action. From the official trailer of Deus Ex: Mankind Divided.
The second part regarding dimorphic magnetorheological fluid (MRF) looks quite plausible: such smart fluids, combining micro-sized spherical iron particles with nano-sized iron wires in order to prevent sedimentation and increase its responsiveness to external magnetic field are well known and can be prepared relatively easy [1].
Also, MRFs are used in vehicle suspension systems for more a decade now and they can withstand physical impact and dampen incoming momentum [2]. Typical design suggests putting a piston rod with MRF inside a coil which is upon electrifying controls solidification [3].
But the first part regarding "nano-meshed rare earth magnets" that can be triggered via sending electrical impulses caught me off guard. I thought that as long as conventional lanthanide-based magnets are permanent and have constant permeability in absence of external magnetic field, nanoscaled/single-molecule magnets are also permanent and cannot be used to dinamically change rheological properties of magnetorheological fluid.
Are there any existing examples of single-molecule magnets with permeability that can be controlled via altering current flow just like in case of electromagnets? If not, is there an explanation why it is not possible?
And yes, I do ask for this:)
References

Ngatu, G. T.; Wereley, N. M.; Karli, J. O.; Bell, R. C. Smart Mater. Struct. 2008, 17 (4), 045022. DOI: 10.1088/0964-1726/17/4/045022.
Gołdasz, J.; Sapiński, B. Insight into Magnetorheological Shock Absorbers; Springer, 2015. DOI: 10.1007/978-3-319-13233-4.
Liu, Q.; Jing, T.; Mo, A.; Xu, X.; Zhang, W. IEEE, 2015,; pp 2495–2500. DOI: 10.1109/ROBIO.2015.7419714.


texts: Which mechanics or law is predominately seen on the nanoscale?

texts: Nanotechnology and sciences are the study or the manipulation of matter on an atomic, molecular, and supramolecular scale especially at nano meter range. We know that at macro molecular level a system can be described using Newtonian/classical mechanics (eg: $F=ma$) whereas for an electronic level quantum mechanics are used. In nanotechnology and science which mechanics is seen predominantly; is it Newtonian, quantum or both and why?


texts: Elimination of bromine with sodium iodide and electrocyclization

texts:
I've been trying to solve the following reaction scheme for a while now and I am having trouble especially with the products E and F.

For product D I got the following, but I'm unsure about compound E, which should be a reactive intermediate.

While trying to figure out the structure of compound E, I drew the following structure, but I'm not sure how the rearrangements will happen to get rid of the charges and get product E. I do expect that E won't be aromatic but that F will be.

All in all, I am wondering what products E and F will be and how to figure them out.


texts: Why can't Cu + HCl -> CuCl2 + H2 happen?

texts:
1)How can I tell if a reaction like Zn + Hcl -> ZnCl2 + H2 can happen or not?

2)How can I tell if a reaction forms a precipitate and how do I know where the arrow goes? Like 2 AgNO3 + K2CrO4 -> Ag2CrO4 (precipitate) + 2 KNO3

I might come back with some new questions, but for now, thanks.


texts: Does a positive electron affinity actually correspond to the release of energy?

texts: I read about the periodic properties — ionisation energy and electron affinity — in my book. It was quite intuitive that energy is required to remove an electron from the atom but I wonder why energy is released when an electron is added to an atom? Is it actually released or is it because of our convention that energy of electron at infinite distance from nucleus is 0, that we consider it to be released?


texts: In a half cell reaction, Is the potential halfed?

texts:
If you have an electrolyte of $\ce{Zn^2+}$ and $\ce{SO4^2-}$ (Neutral) Then you dip in it a Zinc electrode.

Zinc potential is $\pu{-0.74 V}$ (relative to SHE). So that means there is a $\pu{-0.74V}$  difference between the electrolyte and the electrode.

But When you dip in the solution the electrode makes the solution more positive and it self more negative the same amount so the overall potential of the electrode will be $\pu{-0.74 V} / 2 = \pu{-0.37 V}$, and the solution will be at $\pu{+0.37 V}$.

Is this true? (assuming the solution is not connected to any other salt bridge or porous disk)

Edit: Absolute electrode potential is really the difference between the electrolyte and the electrode potential.

And the question is just this if you have an electrode inside an electrolyte with no salt bridge will it's potential be halfed.


texts: To what degree can the Rare Earth Elements be interchanged in its workaday applications?

texts:
In their humdrum pedestrian "high-tech applications due to their unique magnetic properties", how interchangeable are the Rare-Earth Elements (REEs) if, e.g., the US lacks one of them?

RRautamaa comments on Pentagon in talks with Australia on rare earths plant.

  Rare earths are not rare, but they're chemically very similar. (This is because when you go to higher atomic numbers, they start filling the $\mathrm{f}$-shell, but the $\mathrm{f}$-shell is lower in energy than the $\mathrm{d}$-shell, so it's "hidden" by the $\mathrm{d}$-shell. The $\mathrm{d}$-shell is the valence shell and is the same in all of them, so their chemistry is almost the same.)

  Separating two chemically similar substances is expensive. Separating 15 of them is much worse. This means that the mining part is easy, but the processing plant on the site costs about $500 million. This is why rare earth mines are so few in number.

This question was spurred by the Pentagon's halt on May 22 2020 on rare earths funding program pending 'further research'. "Of course, the problem with rare earth elements has never been scarcity. They're actually pretty common. The problem is just that the cost of mining them exceeded their market value everywhere but China, so China ended up with a monopoly and the ability to drive up the price. So it's not clear that this changes much.


texts: How does a lone pair of a central atom affect the dipole moment?

texts: Dipole moment is the degree of polarity, i.e. the seperation of positive and negative charges. But I am not getting the intuition why and how lone pairs affect the polarity and dipole moment. I cannot connect the  separation of positive and negative charges  definition with lone pair.


texts: Reaction mechanism of thiol to disulfide oxidation under basic conditions?

texts:
I have been looking everywhere for an explanation to a reaction mechanism concerning the oxidation of DTT (or just thiols to disulfides in general) using oxygen as the oxidant. I'm aware that oxidizing DTT with oxygen ($\ce{O2}$) will give me the oxidized form of DTT and $\ce{H2O2}$. However, I'm running my reaction in $\ce{MeOH}$ and $10\% \; \ce{KOH}\; (w/w)$ in $\ce{H2O}$ while bubbling it through with air. So, I get that the air is providing the oxygen source, but why run it in basic conditions? Why not just in water?

Below is how I think the oxidation might look in the presence of only oxygen as if DTT was left out in the open:

I have a hard time seeing why the basic conditions are needed besides it keeping the thiols de-protonated? Is the high $\mathrm{pH}$ to prevent the formation of $\ce{H2O2}$?

Does the mechanism below make sense?

I hope all this rambling made somewhat sense and I really REALLY hope that there is someone out there who can help me because I'm stuck.


texts: I was just trying to understand the oxidation states of organic compounds. A more electronegative atom than carbon increases it's oxidation state by 1 and less electronegaitve atom decreases it's oxidation state by 1. Consider the molecule  propene $\ce{CH3-CH=CH2}$  the oxidation state of left carbon is -3, that of the middle one is -1 and that of the right one is -2? So, what is the oxidation state of carbon in   propene? Same complexity arises in 2-propyne or any such molecule.


texts: Are Group 2 metal fluoride salts less soluble in organic solvents than Group 1 fluorides?

texts: It is clear that Group 1 metal fluoride salts DO NOT readily form solutions in organic medium. The amount of solvation that can occur leading to the eventual release of a fluoride ion depends on many factors, one is the polarity of solvent (described by dielectric constant). Most examples seen in the literature seem to evolve around using $\ce{CsF}$ or $\ce{KF}$ in the vicinity of 18-crown-6 ether as common examples for the release of fluoride ions (not considering TBAF). However, I cant seem to find any description for $\ce{MgF2}$ or $\ce{CaF2}$ salts and how their solubility in organic medium affects the release of fluoride ions.


texts: Why does permanganate oxidation of 2-nitronaphthalene not form phthalic acid?

texts:
My teacher told me that among the following compounds only compound 3 will form phthalic acid when reacting with hot $\ce{KMnO4}$.

I do understand why the other compound will not form phthalic acid.


texts: What does the slope of a Levich plot represent?

texts: I know that the limiting current is proportional to the square root of the rotation speed, but what does the slope of the plot represent?


texts:
In class we did an experiment to measure chloride in different water sources, including a lake.  We used Ion-selective electrode of Ag/AgCl technique.
We did the calibration curve and all steps and measurments in different sources of water are consistent, for example drinking water was a bit below 250ppm. But when measuring lake water we get a measurment of 0, why could this be happening?
I can't find a reason


texts: How to calculate the formal charge of sulfate ion?

texts:
I found a site with this formula if you will,

  Formal Charge = [Number of valence electrons on atom] – [non-bonded electrons + number of bonds]

I don't think I am using it correctly in finding the formal charges of each atom in $\ce{SO_4^{2-}}$. $\ce{S}=2$, $\ce{O}=-1$ and the other $\ce{O}=0$ and if you add them together I don't get the overall charge of -2.
 How do you work out formal charges?


texts:
According to my books the bond order of $\ce{CO+}$ is  $3.5$. But shouldn't it be $2.5$? On googling this, I found the following answer that is on Stack Exchange but its only talks about the bond length.

I am unable to understand why it is $3.5$ as I am in class 11.


texts: What is the Gibbs free energy difference between conformational states

texts:
In statistical mechanics, for a system of $N$ particles $x_1, \ldots, x_N$ in three dimensions, the Gibbs free energy is defined in terms of the Hamiltonian $H$ as
$$ G = -k_\mathrm B T \log \int_{\mathbb{R}^{3N}} \mathrm e^{-H(x_1, \dots, x_N)}\,\mathrm dx_1 \dots \mathrm dx_N.$$
People talk about the "free energy difference between conformations". For instance, for some region $A \subset \mathbb{R}^N$, the particles could be in a certain conformation, and for some other region $B \subset \mathbb{R}^N$, the particles could be in another conformation.

Question

  In this paper, equation (3), what is the (implied) definition of $F_A$ or $F_B$ in terms of equation (2)?

Equivalent Question

  Is the free energy difference between the two conformations defined as
  $$G_B - G_A = -k_\mathrm B T\log \frac{\int_B \mathrm e^{-H(x)}\,\mathrm dx}{\int_A \mathrm e^{-H(x)}\,\mathrm dx}?$$

Auxiliary details

The above definition made sense to me, until I was told that "it does not make sense to talk about the free energy of a conformation". An alternative I see is to think of two Hamiltonians $H_A$ and $H_B$, and instead define the free energy difference as

$$G_B - G_A = -k_\mathrm B T \log \frac{\int_{\mathbb{R}^{3N}} \mathrm e^{-H_B(x)}\,\mathrm  dx}{\int_{\mathbb{R}^{3N}}\mathrm e^{-H_A(x)}\,\mathrm dx}. $$

Are either/both/neither of these definitions correct?

I apologize if the question is exceedingly obvious. I am unable to find a straightforward answer by Googling. Any references are welcome.


texts: Addition of hydrogen bromide to 1,3-butadiene: thermodynamic and kinetic control

texts:
The reaction of one equivalent of hydrogen bromide with 1,3-butadiene gives different products at under different conditions:1

The addition of hydrogen chloride also gives rise to similar products.2 I can see that the low-temperature product is formed via an electrophilic addition, with Markovnikov regioselectivity. But how is the other product formed, and why does the major product differ with temperature?

References

1 Kharasch, M. S.; Margolis, E. T.; Mayo, F. R. The peroxide effect in the addition of reagents to unsaturated compounds. XIII. The addition of hydrogen bromide to butadiene. J. Org. Chem. 1936, 01 (4), 393–404. DOI: 10.1021/jo01233a008.

2 Kharasch, M. S.; Kritchevsky, J.; Mayo, F. R. The addition of hydrogen chloride to butadiene. J. Org. Chem. 1937, 02 (5), 489–496. DOI: 10.1021/jo01228a010.


texts: The effect of nitric acid on the rate of corrosion of copper

texts:
I conducted an experiment concerning the rate of corrosion of copper when submerged in three solutions. In the first solution, 5ml concentrated nitric acid and 10 ml distilled water was added. In the second solution, 5ml concentrated nitric acid, 7.5 ml distilled water and 2.5 ml 5 molar NaCl solution was added. In the last solution, 5 ml nitric acid, 5 ml distilled water and 5 ml NaCl solution was added. I expected the rate of corrosion to be the fastest when submerged into a solution where more NaCl solution is evident, but this was not the case. My results were quite the opposite. The rate of corrosion was the fastest in the '5ml concentrated nitric acid and 10 ml distilled water' solution, which confused me. I repeated the experiment multiple times, but the results came out the same.(I used colorimetry to determine the rate of corrosion)

I proceeded to take the temperature of the three solutions and that's when I discovered that temperature played a huge role in the rate of corrosion. The solution with an addition of only distilled water had the highest initial temperature, while the solution with the addition of only the NaCl solution had the lowest initial temperature.

However, I don't quite understand why my results are the way they are. Isn't salt supposed to accelerate the rate of corrosion?

(the color of the distilled water solution after corrosion was blue, while the color of the NaCl solution was green).


texts: What reactions occur when mixing copper sulfate and sodium hydroxide?

texts:
I tried reacting copper sulfate with sodium hydroxide to get copper hydroxide, which should precipitate, according to the following equation:
$$\ce{2NaOH + CuSO4 -> Cu(OH)2(s) + Na2SO4}$$
I looked on Google Images, and the color of copper hydroxide is light-blue, but something interesting happened when I mixed these two solutions: the precipitate formed - and was originally light-blue, as expected - however, it turned into this black-green sludge within a few seconds. I'm thinking a complex ion might have formed between the $\ce{Na2SO4}$, and the $\ce{Cu(OH)2}$. I just saw a video on this, posted by NileRed, but he doesn't go into detail. Does anyone have an idea of what's going on?