texts: How will liquid nitrogen affect a steel instrument's ability to function?

texts:
I want to retrieve cryotubes from the bottom of a liquid nitrogen freezer without taking all the freezer racks out and draining the liquid nitrogen. I think I can accomplish this using a tool like this but I am not sure how well the tool will function at temperatures as low as -160 Celsius. Also, this particular tool is probably only about half as long as it needs to be.

Assuming I can find a longer version of such a tool, how can I determine whether or not I need to be concerned about using to retrieve cryotubes from a liquid nitrogen freezer? My main worry is that parts of the tool may become brittle and break or that the claw's ability grab may somehow become compromised. I am not concerned about the metal becoming excessively cold because I will be wearing gloves intended for such work.

Is there a chart or other resource that I can use to get a sense of metal's shear strength at cold temperatures?


texts: Soxhlet extraction condenser - addition of compound to refluxing setup

texts:
I've never used Soxhlet apparatus before and I have troubles understanding how to properly perform the following step from my protocol:

  To a gently refluxing suspension of 1 g Lithium aluminium hydride in 100 mL of diethyl ether, there was added 1.2 g of compound as a saturated diethyl ether solution with use of a Soxhlet extraction condenser which is modified allowing the continuous return of condensed solvent (through the thimble). After the addition was complete, the refluxing conditions were maintained."

Soo... How do I do it? I run RBF with condenser on top until reflux stabilizes and then I open it, add Soxhlet with compound and continue refluxing or I set up everything cold (RBF with ether + Soxlet with compound in ether + condenser) and then start refluxing?

Also - I'm not quite sure if I understand the thimble modification - can anyone shed some light on it for me?


texts:
Shouldn't iron oxide be able to form without water? It is just iron and oxygen. I don't really understand what the dot followed by the $\ce{H2O}$ means either. I was reading on wikipedia, but I have a rather terrible understanding of chemistry.
What purpose does water serve in rust formation, and what does it mean for a molecule to be hydrated-how is that different then just being surrounded by water molecules?


texts: Is it possible for vegetable oil to occur naturally, without being extracted? Along the same lines, it it possible for Hexane to occur naturally?


texts: Degenerate orbitals in the Hydrogen atom

texts:
I came across the following link:
Which orbitals of the hydrogen atom are degenerate for $n=3$

And all the answers said that for the hydrogen atom, the energy of an orbital depends only on n. Is this really true? And also, isn't it true that for other atoms (at least according to those who answered the other question) the energy depends upon both $l$ and $n$?


texts: Why is sulfur hexafluoride more stable than selenium or tellurium hexafluoride?

texts:
I was just reading about p Block elements from two different books. Both books say that $\ce{SF6}$ is extremely stable in 16th group due to steric reasons but my question is why is it more stable than $\ce{SeF6}$ and $\ce{TeF6}$ when $\ce{S}$ is more electronegative and smaller than $\ce{Te}$ and $\ce{Se}$ and so it would bring the electrons in bonding with fluorine closer to the central atom i.e $\ce{S}$ and thus it would bring the electrons closer and there would be more repulsion between the electron pairs.

Maybe this can be explained by Fajans rules that due to such conditions $\ce{SF6}$ has more covalent character than others and thus is more stable. But if this is the reason, where does "steric" come in here?


texts: Thin Layer Chromatography & Stationary Phase

texts:
There are two types of stationary phases used in thin layer chromatography. One stationary phase is made of aluminium oxide. Which of the following molecules would be expected to have the smallest $R_f$ using aluminium oxide as the stationary phase on the glass slide?
(a) $\ce{CH3CH2CH2CH2CH2COOH}$
(b) $\ce{CH3CH2CH2CH2CH2OH}$
(c) $\ce{CH3CH2CH2CH2NH2}$
(d) $\ce{CH3CH2CH2CH2CH3}$

$\ce{AL2O3}$ is a non-polar stationary phase, therefore if the molecule is also non-polar it would display high adsorption  to the stationary phase, and therefore a smaller $R_f$ value.
The answer is (a).
Isn't (a) polar?
Wouldn't this increase the $R_f$ value, because it doesn't adsorb to the non-polar stationary phase? Can someone please explain, correct me?


texts: What is the hybridization of terminal fluorine atoms in molecules like boron trifluoride?

texts:
What is the hybridisation of $\ce{F}$ in $\ce{BF3}$ or $\ce{CH3F}$ or $\ce{PF5}$ or $\ce{SF6}$? My book states that the p orbitals of fluorine overlaps, but I feel that sp3 hybridisation occurs in $\ce{F}$, so its sp3 hybrid orbital overlaps with the empty p orbital of boron.

According to Ron's answer,  all atoms with p or d orbitals can hybridise.


texts:
How exactly is the bonding described in complexes involving alkali metals? In particular, how much of a covalent component is there?
Take three examples:

$\ce{[Na(H2O)6]+}$: This previous answer by @tschoppi suggests that the bonding in this complex is purely electrostatic in nature due to the lack of available d-orbitals for covalent bonding. This seems like it might be true because it would explain why the water complexes are not strongly bound.

$\ce{Na2(edta)}$: This previous question suggests that the sodium here is not complexed with the EDTA but rather that it again forms an essentially ionic (i.e electrostatic) bond with little covalent character.

$\mathrm{[Na(\text{15-crown-5})]^+}$: This is very stable, suggesting a strong bond of some sort, probably with some covalent character. However, it doesn't seem to be radically different from the previous ligands, particularly EDTA, which has similar oxygens available for bonding.


texts: Nucleation and Phase Equilibrium at the Melting Temperature

texts:
I used to think that at the melting point, the solid and liquid phases are in equilibrium. That’s because the Gibbs free energy change for the transformation is 0, as is characteristic of equilibria.

However, I recently learnt about nucleation in phase transformations, and I’m very confused. My textbook tells me that below the melting temperature the Gibbs free energy change is not 0 and this energy can go into increasing nuclei surfaces and surmounting the nucleation activation energy barrier. It goes on to say that at the melting temperature, no such energy is liberated (since ∆G = 0) and the nucleation activation energy barrier cannot be achieved. Thus, no nucleation occurs at the melting temperature.

If no nucleation occurs, then how can the solid and liquid phases be in equilibrium? I know about supercooling and that the principle behind it is that it takes time for such an equilibrium to be achieved. However, if nucleation simply doesn’t occur at the melting temperature, then equilibrium will never be achieved...


texts: How to define the initial guess for the electron density?

texts:
This is a technical question. If I have  a one-dimensional box of length L, and an electron density existing in the box and integrating to N electrons. And if I want to determine the electron density that minimizes the energy of the system, assuming the following:

electron density is zero at the boundary
a fixed external potential of any kind and form
the Thomas-Fermi kinetic energy functional is used. $v_{TF}(x)=C^{TF}*\rho^{2/3}(x)$
absence of electron-electron interaction, $v_{HXC}(x)=0$

the question is related to the initial guess for the electron density. I've been trying the following definition for the initial $\rho(x)$

$g = \frac{l}{(gp-1.0)}$

$\rho(x)= \frac{N}{(l-g)}$

where

$g$ is the grid gap,

$gp$ is the number of grid points,

$l$ the length of the box, and

$N$ the number of electrons.

with this density, the minimized density does not preserved the number of electrons. Do you guys have any suggestion to define a suitable initial guess?

Also I am including a figure where the density at each grid point is plotted. I assumed two electrons and 200 grid points.

Thank you


texts: Equation or formula for calculating molecular orbital energies

texts:
Is there an equation, similar to the Rydberg formula, for calculating the energies of molecular orbitals?

For example, with the Rydberg formula, I can work out that the energy of a $1s$ orbital in hydrogen is $-13.6\ \mathrm{eV}$. Is there any way that I can calculate (or approximate) the energies of the bonding and anti-bonding orbitals in $\ce{H2}$?


texts: Is it a good idea to build a small scale ozone AOP reactor in my garage?

texts:
I have some interesting findings from my work (no conflict of interest), and I have been thinking to build an ozone lab in my garage to verify my ideas. What safety issues should I be aware of?

The purpose of the lab is to study some water/wastewater treatment process with ozone injection and advanced oxidation process. No pure oxygen or hydrogen, the power supply will be 110v, and I don't think there will be any explosive chemicals.

In term of safety, I think I need at least a fire extinguisher, basic safety wears, and an air vent to outside. Anything else?


texts: Difference between H-NMR with C$^{13}$ and C$^{13}$- NMR

texts:
I don't know if I am overcomplicating things but I am having trouble understanding the difference between H-NMR with  C$^{13}$ sample  and  C$^{13}$-NMR.

For example, if I have the molecule below and I am asked to sketch the H-NMR spectrum knowing that the carbons are C$^{13}$ and a C$^{13}$-NMR spectrum, what is the difference? For the C$^{13}$-spectrum I know that I should look at the neighbouring carbons and apply the $n+1$ rule and then look at the neighbouring hydrogens of the carbon of interest. For example, the C$^α$ has two neighbouring carbons so is split into a triplet and it also has one neighbouring hydrogen so those triplets are split into doublets making the C$^α$ show up as a multiplet of six.

However, if it is a H-spectrum with C$^{13}$ what do I look at? The correct spectrum is added below and the chemical shifts are:

So for H$^α$ I should get $2 *5 $ peaks. Which I get from H$^α$ having one carbon neighbour (spliting it into a doublet) and then having four neighbouring hydrogens (spliting each doublet into a multiplet of five). Is that the correct way of doing it? It works for H$^β$ as well but then for the H$^N$ am I only looking at the hydrogens again (so $n+1=1+1=2$ a doublet)?


texts: How to calculate molar mass of (6)UO2+2D and (6)UO2OH+D?

texts:
For a hydrogeochemistry project, I want to calculate the molar masses of some compounds. I came across a problem when encountering species like (6)UO2+2D (aq) and (6)UO2OH+D(aq). I don't know what the (6) and the +2D mean.

I started off with IPC-MS results for several trace elements and fed them to VMinteq for the speciation modelling. I tried to google the species, but that query produced no useful results. I am no chemist and I don't know "how" or "where" to search efficiently for an answer.

EDIT: another (6) appeared in FA1-UO2(6)(aq)


texts: Is there always a limiting reagent in every equation? For instance, is there a limiting reagent in $\ce{CaCl2 + Na2CO3 -> 2NaCl  + CaCO3}$ where the same number of moles are reacting with each other?


texts:
What is the difference between an ionic compound and a salt? They both have a cation and an anion bonded.

On one of my homework sheets, it says that $\ce{NaCl}$ is an ionic compound (which it obviously is). How would i determine here if $\ce{NaCl}$ is an ionic compound or a salt?


texts: Calculation of Degree of Dissociation from Ostwald's Dilution Law

texts:
A "weak" electrolyte, $\ce{A+B-}$, ionizes in solution as:

$$\ce{AB <=> A+ + B-}\tag{1}$$

$$  K_d =\dfrac{\ce{[A+][B-]}}{\ce{[AB]}}=\dfrac{(\alpha c_{0})(\alpha c_{0})}{(1-\alpha )c_{0}}=\dfrac{\alpha ^{2}}{1-\alpha }\cdot c_{0}\tag{2}$$

For a weak electrolyte the Degree of Dissociation, $\alpha$, is less than 1 and can be calculated using two different equations.

Equation (2) can be rearranged to a quadratic equation which could be solved exactly with the standard quadratic formula.

$$ c_0 \cdot \alpha^2  + K_d\cdot \alpha -K_d = 0\tag{3}$$

$$\alpha = \dfrac{-K_d + \sqrt{K_d^2 - 4\cdot c_0 \cdot (-K_d) }}{2\cdot c_0} = \dfrac{-K_d + \sqrt{K_d^2 + 4\cdot c_0 \cdot K_d }}{2\cdot c_0}\tag{4}$$

If we assume that there is little dissociation and that $\ce{[AB] \approx c_0}$ then $1- \alpha \approx 1$ and we obtain an approximate answer that is easier to calcualte:

$$  \alpha' \approx \sqrt{\dfrac{K_d}{c_{0}}}\tag{5}$$

If equation (5) does not give the true value of the Degree of Dissociation. How do you know when it is good enough?

To make it clearer, say the approximate value from formula (5) is 0.15. That is not the true value of the degree of dissociation, but would the approximate solution be good enough?


texts:
Pauli exclusion principle states that 'No two electron can exist in same state' or 'No two electron can have same set of quantum numbers'.

But in reality there is no state of electron. The state is of whole system which is composed of many electrons. It is our approximation that each electron is described by a single wave-function which we called spinorbital. So what does that statement even mean in reality?

Quantum numbers is only exact for hydrogen atom. What does quantum number even mean for a electron in a many electron system.


texts:
I understand that the hybridization in the phosphate ion is $\mathrm{sp^3}$ since phosphorous forms $4$ sigma bonds with $4$ of the oxygens and there are no lone pairs on the phosphorous atom.

The outer electronic configuration of phosphorous is $\mathrm{3s^2 3p^3}$. In the case of $\mathrm{sp^3}$ hybridisation, the $\mathrm{3s}$ and the all of the $\mathrm{3p}$ orbitals are involved. Hence, among the $4$ equivalent orbitals now obtained, $1$ of them contains a pair of electrons, while the other $3$ are singly occupied. So shouldn't phosphorous be able to form sigma bonds with only $3$ of the oxygen atoms since it has only $3$ unpaired electrons?

I am trying to compare this case with that of carbon tetrachloride. There, by $\mathrm{sp^3}$ hybridization, we were able to get $4$ equivalent orbitals each with an unpaired electron, and therefore explain its tetravalent nature. In the case of phosphate ion, one of the $4$ orbitals obtained already has a pair of electrons. So, could anyone please tell me where my understanding is flawed?


texts: Which is the best kind of filter papers to use to extract silicon nanoparticles after acid wash, hydeophobic or hydrophilic?

texts:
I'm looking for filter papers to extract silicon nanoparticles after acid etching. I found that much of my material is get wasted with my Whatman Grade 4 filter paper. I am thinking to use membrane filter papers to get the maximum amount of nanoparticles.  However, there are hydrophobic and hydrophilic varieties in the market. I'm confused. Also, is it possible to peel off the nanoparticle layer from the membrane surface?

Thank you


texts: Is there a difference between anti-anxiety and anti-depression drugs?

texts:
[PREFACE- I've already asked this on Health.SE, but I've drawn a blank there. The place is practically deserted. Also, this is NOT a personal medical question; I'm simply trying to understand the difference between the two classes of drugs.]

I've recently come across two terms "Anxiolytic drugs" and "Anti-depressant drugs". I wanted to know how they differ from each other; if they do.

I mean, sure, "anxiety" isn't the same as "depression" but do the effects of these drugs differ widely?

For example [And this is just an example];

Chlorodiazepoxide is classified as an anxiolytic drug, while Phenelzine is classified as an anti-depressant. Say I had a patient A who's been prescribed Chlorodiazepoxide; patient B has been prescribed Phenelzine by a different physician. Barring possible allergic reactions, or some kind of known sensitivity to either drug, could they possibly take each other's medication and hope for more or less, the same effect? As in; A takes Phenelzine, but B takes Chlorodiazepoxide. [I just cooked up that example, only to see the difference between the two classes of drugs]

To make myself clear, I reiterate:

I would like to know if the two classes of drugs (anti-anxiety and anti-depression) are the same or not. If not, mentioning how the chemistry behind the action of each of the two types of drugs differ would be appreciated.


texts: Creating a Battery using azobenzene in High School

texts: I’m doing a project on isomerization in high school and have stumbled across the studies involving azobenzene in energy storage using its photoisomeric properties and sunlight . Do you think that this is something I could show in a high school lab, if not I can create a design, but it would be cool to show this phenomenon to classmates/teachers as my project. What do you experienced chemists think about this, as I am not sure if it is feasible.


texts: Thermodynamics: Is Isolated system possible?

texts:
I have just started learning thermodynamics. I have learned that The system which is not able to exchange energy and matter on its own with surrounding is called isolated system.

I wanted to know that practically is it possible to make 100% isolated system?


texts: Does calcium hydroxide react with citric acid in orange juice?

texts:
I noticed that calcium-fortified orange juice on the shelf at my local grocery store contains calcium in the form of calcium hydroxide.

And I also noticed a couple other ingredients that ordinary orange juice doesn't list explicitly:  citric acid and malic acid.  Are these meant to neutralize the calcium hydroxide to form calcium citrate (commonly listed on calcium supplement pill bottles)?

I'm just curious. I want to know what final chemical(s) will end up in my stomach if I swallow this concoction.


texts: Electrolysis of salt water into sodium hydroxide with YSP

texts:
I want to electrolize salt ($\ce{NaCl}$) water into a solution of sodium hydroxide for soap making. The salt I have has yellow prussiate of soda (sodium ferrocyanide) added as the anticaking agent. What will happen to the ferrocyanide ($\ce{Fe(CN)_6}$) molecules during the electrolysis process?

I will be using an old battery charger to perform the electrolysis, $20\, \mathrm{V}$, $0.9\, \mathrm{A}$ or $1.8\, \mathrm{A}$ settings.


texts: Iodometric Titration: Would iodine react with sucrose as well?

texts: I'm currently planning to do a lab experiment about the effect of sugar addition (sucrose) to orange juice on Vitamin C (ascorbic acid), also finding the degradation rate and activation energy required. To measure ascorbic acid concentration, I am going to use iodometric titration but I am wondering if the addition of sucrose would affect the results as I am not sure if iodine could also react with sucrose, not just ascorbic acid, so that the results do not show the correct concentration of ascorbic acid in the juice. If that is the case, is there any better method to measure just the ascorbic acid content? I am currently a high school student and may not be familiar with some hard concepts, so please be mindful.


texts: Do filter-specific dyes exist? Equivalently, do dye-specific filters exist?

texts:
Apologies if this isn't chemistry enough for chemistry.se. I'm happy to go elsewhere if there are suggestions.

Blue + Red = Purple is arbitrary here. If any different colors might make this more feasible, please say so (preferably with some explanation as to why).

I'm interested in having a jug of purple liquid.

When I turn it upside-down, it will empty through two bottlenecks into two smaller jugs. I would like for one of the smaller jugs to now contain red liquid, and the other to contain blue. Eg, I would like for one bottlenecks to actively filter out the red/blue portions of the original purple liquid.

This process has to be repeatable.

That is, I should be able to turn this contraption back over on itself and the blue/red will recombine to be purple, and then for the separation of colors to happen again when it's flipped a third time. It's not very suitable for me if this system only works a few times before losing its punch, but it may be acceptable if I had to replace or clean filters once every 50 or 100 filtrations.

Looking forward to some affirmative answers, or even some suggestions on how to better search for this.


texts: Increase in Potential Energy When Bonds Are Broken

texts: Why is it that the potential energy of a system increases when the bonds present in it are broken? (i.e., when a solid turns into a liquid.) I thought the potential energy of the system was mostly contained in these bonds? If these bonds are broken, then why does the system’s potential energy increase?


texts: While washing my hands with soap I added some hand sanitizer just because it was right there on the counter and couldn't resist mixing them... Ha!  However, when I added the hand sanitizer it heated up for a moment and then cooled back down.  Why does this happen?


texts:
In NMR a spectrum consists of noise and peaks. While steps, such as repeated scans or smoothing of the spectra can reduce noise some still remains. As such one step usually taken is to bin the data so that only peaks are chosen, usually with a threshold and finding maxima/minima.
This raises the question however, which is how do you define a peak. If you use a threshold a poor baseline can result in this failing, for instance if the baseline is above the threshold set.

Is there a widely used method/rule of thumb which is used to decide if a region contains a peak, or is just noise?


texts: Show that this mechanism is consistent with the rate law - how to?

texts:
The problem is from Principles of general chemistry, 2nd edition by Silverberg, chapter 16 problem no.81:

  "Even when a mechanism is consistent with the rate law, later work may show it to be incorrect. For example, the reaction between hydrogen and iodine has this rate law: $rate = k\ce{[H2][I2]}$. The long accepted mechanism had a single bimolecular step; that is, the overall reaction was thought to be elementary:

  $$\ce{H2_{(g)} + I2_{(g)} -> 2HI_{(g)}}$$

  In the 1960s, however, spectroscopic evidence showed the presence of free I atoms during the reaction. Kineticists have since proposed a three-step mechanism:

  $$\quad \ce{ I2_{(g)} <=> 2I_{(g)} \quad\quad[fast]}\tag {i }$$
  $$\ce{H2_{(g)} + I_{(g)} <=> H2I_{(g)} [fast]\tag{ii}}$$
  $$\ce{ H2I_{(g)} + I_{(g)} -> 2HI_{(g)} [slow]}\tag{iii}$$

  Show that this mechanism is consistent with the rate law."

I cannot understand what the problem asks. I think, this reaction is consistent with the rate law by the third reaction, $\ce{H2I + I->2HI}$, which is the rate-determining step. Is my guess correct?


texts: Does a “T” in a formula subscript indicate all possible numbers of atoms? $\ce{FeO_T}$ is the specific one I came across (in the "bulk chemistry" table here: https://sciences.ucf.edu/class/simulant_lunarmare), it seems to make sense in context but I've not done chemistry since school (tried googling already) so thought I'd better check.


texts: How to avoid explosion when there is a leakage of LPG gas and coal gas/town gas? What are the conditions of that happening? The related underlying chemical reactions are hydrogen and butane combustion in oxygen, right? What is the reaction mechanism? We should avoid using any electrical appliances, electric light, electric door bells and smartphone , just anything that could produce sparks and turn off any flames, right? So I should turn off the electrical appliances immediately after noticing a leakage or should I just keep them on?


texts: What does the subscript of atomic orbital mean?

texts:
As everyone knows, the atomic orbital can be classified as $s, p_z, p_x, p_y, d_{z^2},d_{xz},d_{yz},d_{xy},d_{x^2-y^2}$ and so on. I want to know the meaning of $z^2,x^2-y^2$ and so on. Maybe this is a fundamental question, but I'm not familiar with chemistry.

I have some ideas about this:

For example, we consider the $p$ orbital: $p_z$ is symmetric about $z$ axis; $p_x$ is symmetric about $x$ axis; $p_y$ is symmetric about $y$ axis. But what's the meaning of $z^2$ or $x^2 -y^2$?
We consider the symmetry of atomic orbital with group theory. The change of orbital under the symmetry operation is the same as the orbital subscript.


texts: How to choose proper active space in method such as CASPT2 and CASSCF?

texts: I am confused about other research paper which use CASPT2 method. I am not clear about how to choose active space. What can I refer to? (tutorial reviews, papers, or any other things)


texts: Multiple solutions in the balancing of redox reactions

texts:
While looking at the reaction between potassium permanganate and hydrogen peroxide in the presence of sulfuric acid a friend and I were attempting to find a general equation to yield the coefficients of the balanced reaction depending on varying levels of acidity. I solved using half reactions and came up with equations for each coefficient in terms of the mole amounts for the manganese(II) ions and manganese(IV) oxide produced. My friend however, went about the problem by setting up a system of equations from the initial skeleton equation and yielded answers which depended on 3 variables.

From this, his method gave the answer

$$\ce{H2O2 + 4MnO4- + 6H+ -> 4O2 + Mn^2+ + 3MnO2 + 4H2O}$$

as a possibility, while my method yielded

$$\ce{7H2O2 + 4MnO4- + 6H+ -> 7O2 + Mn^2+ + 3MnO2 + 10H2O}$$

from the same ratio of manganese(IV) oxide to manganese(II). His reaction appears to balance correctly. Is there something he is missing that prevents that reaction from occurring with his coefficients, or does the half reaction method hide some possible answers?


texts: Why is the variable on the y-axis of Maxwell's Speed Distribution Curve 'fraction of molecules'?

texts:
I came across the following graph in my textbook showing the kinetic energy distribution of the gas molecules in a gas sample. Now, the thing is the textbook is telling that the area under the curve gives us the fraction of molecules with energy E. Suppose $dN_{E}$ represents the number of molecules with energy E, $N_{T}$ represents the total number of molecules and $E$ represents the kinetic energy of the molecules. Then, the fraction of molecules with energy $E$ is given by $\frac{dN_{E}}{N_{T}}$, right? So this actually represents the variable in the $y$-axis. Now, let us take the area of a small strip under the curve. It is given by $\frac{dN_{E}}{N_{T}} × dE$ which is clearly not equal to the fraction of molecules with energy $E$. Then why is the book telling that the area under the curve gives us the fraction of molecules with energy $E$? It clearly does not. I just proved it. If the area under the curve really has to represent the fraction of molecules with energy $E$ then instead of fraction of molecules i.e. $\frac{dN_{E}}{N_{T}}$ on the $y$-axis, the variable in the $y$-axis should actually be $\frac{1}{dE}\frac{dN_{E}}{N_{T}}$. Now if we calculate the area of a small strip under the curve :
$\frac{1}{dE}\frac{dN_{E}}{N_{T}} × dE = \frac{dN_{E}}{N_{T}}$
The quantity $\frac{dN_{E}}{N_{T}}$ actually gives the fraction of molecules with energy $E$. Thus, my book is wrong, isn't it? Please can someone clarify if what I have done is correct or not. Can someone explain?


texts: What is the mechanism for thermal decarboxylation of a generic carboxylic acid (not special cases like beta-ketocarboxylic acid or malonic acids)?

texts: I am looking for the mechanism for thermal decarboxylation for any RCOOH, and I am guessing that its possible for the thermal energy to cleave the R-C bond homolytically leaving a R• and •COOH. Then I would guess the R• would add its electron to the H and the O-H bond would undergo homolysis as well leaving the single electrons on the C and now O to form a bond leaving RH and CO2. However I have no idea if this is what actually occurs. Thanks


texts: Does an airborne chemical stimulant exist?

texts:
I recently read the creepypasta entitled "The Russian Sleep Experiment". In this story they lock five test subjects in a room with the intention of keeping them awake for 30 days by releasing a gaseous stimulant into the room constantly. I'll let you read the rest, it's an incredible horror story, but not very credible. Anyways I wanted to know if in real life such a gaseous stimulant exists.

During the Moscow theater hostage crisis Russian forces "pumped an aerosol anaesthetic, later stated by Russian Health Minister Yuri Shevchenko to be based on fentanyl". So it's possible for an opiate-based depressant can be made gaseous (technically aerosol).

So is there an airborne stimulant that actually exists?


texts: What is the different in stereochemistry between the product of cis alkene with mCPBA and trans alkene with mCPBA, I drew the products, they do look different but the configurations are the exact same, does that mean that they give the same products?


texts:
I am a bit confused on how to account for the stoichiometry of a reaction as follows:

$$\ce{A}(s) + \delta \ce{B}(g) \ce{->} \ce{C}(s) + \delta \ce{D}(g)$$

The solid $\ce{A}$ is stationary in the reactor, and gas $\ce{B}$ flows through it with known inlet molar flow rate. Since 1 mol of $\ce{A}$ produces $\delta$ mol of $\ce{D}$, but the solids are static, how can I determine the amount of $\ce{D}$ formed (molar flow rate)? The other known piece of information is the normalized extent of reaction, $\alpha$, which can be defined as the amount of $\ce{D}$ formed at time $t$ divided by its total amount.

Please let me know if it's not clear enough. It's been difficult for me to find clear explanations about the modeling of such type of reaction in the papers and theses I've read. The closest I've found to a definition of $\alpha$ is as follows:

$$\alpha = \int \frac{\ce{D}(t)}{\ce{D}_\text{total}} \mathrm{d}t$$

(yes, written exactly like that)

My Approach So Far

I believe I have to somehow consider both the flow rate of $\ce{B}$ and the amount of $\ce{A}$ in the reactor. If the molar flow rate of $\ce{B}$ is "too large", then the stoichiometric coefficient $\delta$ will limit the flow rate of $\ce{D}$. I've thought of doing something like this:

$$\dot{n}_{\ce{D}} = \min\{\dot{n}_{\ce{B}},\delta n_{\ce{A}}\}$$

where $\dot{n}_i$ is the molar flow rate of species $i$ and $n_\ce{A}$ is the number of moles of solid $\ce{A}$, but as you can see one of the arguments of the $\min$ operator is a molar flow rate and the other is just moles, which is problematic. Any suggestions?

Edit

Clearly, I have to use $\alpha$ somewhere. But I'm still unsure what to do here. Generically, I'd write something like,

$$\dot{n}_i = \dot{n}_{i,0} + \dot{n}_0 \nu_i \alpha$$

but I'm not sure if this is correct in this case (again, how do I use the amount of solid in the reactor?).


texts: Is there anything like "Saturated Fullerene"?

texts:
This question arose from my previous question: Can benzyne be trapped inside a polycyclic hydrocarbon?. While dodecahedrane was too small to fit an anthranilate ion or even a benzyne ion, there are lots of other cage molecules, notably fullerenes. Unfortunately fullerenes themselves have partial double bond characters in them, making them liable to undergo a Diels-Alder reaction with benzyne.

However, if it were possible to "saturate" the fullerene, it could serve as a molecular container to hold the benzyne molecule.

Is it possible to saturated fullerenes? After being saturated,  can we use it as a molecular container?


texts: What happens when I divide two molar flow rates in a chemical equation?

texts:
I don't quite know how summarize my question in the title. I have a combustion process given by this equation:
$$\ce{C10H22 + 15.5 O2 + 58.25 N2 -> 11 H2O + 10 CO2 + 58.25 N2}$$

This process occurs inside of a cylindrical combustion chamber of area A, but I think this is irrelevant for the purposes of my question. The combustion process is stationary, and the gas mixtures are ideal.

I wanted to know if, in general, this is true:
$$\frac{\text{molar flow rate of }\ce{N2}}{\text{molar flow rate of }\ce{C10H22}} = \frac{\text{amount of substance of }\ce{N2}}{\text{amount of substance of }\ce{C10H22}}=\frac{58.25}{1}=58.25$$

With molar flow rate I want to mean the amount of substance that leave/enter the combustion chamber in 1 second.

I'm a beginner in chemistry, but I'm not sure if I can convert a ratio between molar flows like I did, using directly the stoichiometric coefficients in the balanced equation.

The idea behind my reasoning is that:
$$\text{molar flow rate of }\ce{N2} = \frac{n_{\ce{N2}}(t+\Delta t) - n_{\ce{N2}}(t)}{\Delta t}$$
and:
$$\text{molar flow rate of }\ce{C10H22} = \frac{n_{\ce{C10H22}}(t+\Delta t)-n_{\ce{C10H22}}(t)}{\Delta t}$$

Therefore,
$$\frac{\text{molar flow rate of }\ce{N2}}{\text{molar flow rate of }\ce{C10H22}} = \frac{n_{\ce{N2}}(t+\Delta t) - n_{\ce{N2}}(t)}{n_{\ce{C10H22}}(t+\Delta t) -
 n_{\ce{C10H22}}(t)}$$

And, intuitively, this last equality should be proportional to $n_{\ce{N2}}/n_{\ce{C10H22}}=58.25/1=58.25$.


texts: Can someone help me finish this reaction?

texts:
This question revolves around sodium percarbonate (https://en.m.wikipedia.org/wiki/Sodium_percarbonate) and its reaction with sulfuric acid.

I didn't find anything, so I tried assembling it myself.

Wikipedia says that $$\ce{2Na2CO3·3H2O2 -> 2Na2CO3 + 3H2O2}$$ in water.

Now I'm not sure if the $\ce{Na2CO3}$ does this: $$\ce{Na2CO3 + H2SO4 -> Na2SO4 + H2O +CO2}$$ or this: $$\ce{Na2CO3 + 2H2SO4 -> 2NaHSO4 + H2O + CO2}$$

Last, the $\ce{H2O2}$ reacts with $\ce{H2SO4}$ to peroxymonosulfuric acid (https://en.m.wikipedia.org/wiki/Peroxymonosulfuric_acid) $$\ce{H2SO4 + H2O2 <=> H2SO5 + H2O}$$ in high concentrations / to a small extend.

So, my final equation could be: $$\ce{2Na2CO3·3H2O2 + 2H2SO4 -> 2Na2SO4 + 2H2O + 2CO2 + 3H2O2}$$ or $$\ce{2Na2CO3·3H2O2 + 4H2SO4 -> 4NaHSO4 + 2H2O + 2CO2 + 3H2O2}$$ or $$\ce{2Na2CO3·3H2O2 + 5H2SO4 -> 2Na2SO4 + 5H2O + 2CO2 + 3H2SO5}$$ or $$\ce{2Na2CO3·3H2O2 + 7H2SO4 -> 4NaHSO4 + 5H2O + 2CO2 + 3H2SO5}$$

Which is correct or the most correct? Any help appreciated. Thanks!


texts: Confusion on enantiomers and meso compounds

texts:
Question: Are these compounds enantiomers?

Attempt: The compounds given are mirror images. But if I rotated the three bonds in the third carbon (configuration will not change), I will get a meso compound (plane of symmetry) :

So are these compounds enantiomers or meso compounds?


texts: What single, pure compound would best replace petrol?

texts:
Petrol for use as automotive fuel is produced by blending of different product streams of oil refining. It consists of hundreds of different compounds, and the exact composition can vary widely. Certainly, not all components are absolutely necessary. Is there a single pure compound that could be used instead and that is similar or even superior to typical petrol?

In order to limit the scope of this question, I only consider pure hydrocarbons ($\ce{C_xH_y}$), i.e. no alcohols, ethers, amines, nitro compounds, or other compounds containing hetero atoms. I am only asking about fuel for spark ignition (Otto) engines, i.e. not about diesel fuel.

The relevant criteria for the comparison shall be only the knock resistance and the energy content of the compounds. Other properties may be ignored.

For similar compounds, there may be a tendency for fuel with a higher knock resistance to have a lower energy content. The challenge is to find a single pure compound with a suitable balance of knock resistance and energy content, with better values than found for typical petrol.

The knock resistance shall be expressed as research octane number (RON). Currently, the most important petrol blends in most countries have an RON of 95. However, blends with an RON of up to 102 are widely available. Therefore, the candidate compound should have at least an RON of 102.

The energy content shall be expressed as specific enthalpy of combustion $\Delta_\mathrm ch^\circ$ at a temperature of $T=25\ \mathrm{^\circ C}$. If necessary, this value can be directly calculated from the molar enthalpy of formation $\Delta_\mathrm fH_\mathrm m^\circ$ or the molar enthalpy of combustion $\Delta_\mathrm cH_\mathrm m^\circ$. For this purpose, the generated water shall be assumed to be in liquid form (although this assumption is not representative for vehicle engines and may favour small saturated compounds). The energy content of petrol can vary. For example, typical average values for $\Delta_\mathrm ch$ given by Aral in Germany are

Regular (RON = 91): $-44.2\ \mathrm{MJ/kg}$
Super (RON = 95): $-43.5\ \mathrm{MJ/kg}$
Super Plus (RON = 98): $-42.7\ \mathrm{MJ/kg}$

Therefore, the candidate compound should have at least an energy content corresponding to about $\Delta_\mathrm ch^\circ=-44\ \mathrm{MJ/kg}$.

In order to limit the choice, the candidate compound shall be a liquid at room temperature. The boiling point should be below $210\ \mathrm{^\circ C}$, preferably between $70\ \mathrm{^\circ C}$ and $150\ \mathrm{^\circ C}$. The melting point should be well below $0\ \mathrm{^\circ C}$.

By way of comparison, the following table shows the relevant parameter values for the reference compounds that are used for the octane number (heptane and 2,2,4-trimethylpentane) as well as for one candidate compound (2,2,3-trimethylbutane) that I have already found.

$$
\small\begin{array}{llllllll}
\hline
\text{Compound}&\text{Formula}&\Delta_\mathrm fH_\mathrm m^\circ&\Delta_\mathrm cH_\mathrm m^\circ&\Delta_\mathrm ch^\circ&\mathrm{RON}&T_\mathrm{mp}&T_\mathrm{bp} \\
&&\text{in}\ \mathrm{kJ/mol}&\text{in}\ \mathrm{kJ/mol}&\text{in}\ \mathrm{MJ/kg}&&\text{in}\ \mathrm{^\circ C}&\text{in}\ \mathrm{^\circ C} \\
\hline
\text{Heptane}&\ce{C7H16}&-224.2&-4817&-48.1&\hphantom{00}0&\hphantom{1}{-90.55}&98.4
 \\
\text{2,2,4-Trimethylpentane}&\ce{C8H18}&-259.2&-5461&-47.8&100&-107.3&99.22\\
\text{2,2,3-Trimethylbutane}&\ce{C7H16}&-236.5&-4805&-48.0&112&\hphantom{1}{-24.6}&80.86 \\
\hline
\end{array}$$

I would be interested in answers that search through literature data and find better candidate compounds as well as in answers that use a theoretical approach to estimate where to find the best compounds.


texts: Why does chlorination of toluene stop at two chlorine atoms?

texts:
My instructor mentioned a reaction for preparation of benzaldehyde by chlorination of toluene in presence of sunlight to form benzal dichloride, which on hydrolysis gives benzaldehyde.

However, I'm not sure why the chlorination of side chain should stop after two chlorine atoms are added? At what step does the side chain chlorination of toluene stop?


texts: I read today that water is a base because it can receive a proton when mixed with some acids. That got me thinking: is every single molecule capable of either donating or receiving a proton -- when mixed with just the right complementary molecule? Thus, is every molecule either a base or an acid to some degree?


texts: What is an "attack" in Organic Reactions?

texts: I began to study organic reactions and found the term "attack" everywhere, what this "attack" precisely mean?


texts: What are the alternatives we have to the VEDA 4 vibrational energy distribution analysis software?

texts:
Said software is very useful when you need to assign the peaks in vibrational spectra to different vibrational modes found in a hessian calculation for a given molecule, as described in Jamróz, Michał H. “Vibrational Energy Distribution Analysis (VEDA): Scopes and Limitations”. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, vol. 114, outubro de 2013, p. 220–30. ScienceDirect, doi:10.1016/j.saa.2013.05.096. It's becoming popular, the paper has nearly 450 citations as of april 2020, but it has some downsides for me:

Despite being a freeware that can be downloaded from their site by anyone, it's not free software, or at least open source, and it's windows-only;
Doesn't support people using free tools like Gamess-US or Psi4, only accepting Gaussian output files as its input, a paid and very expensive quantum chemistry software;

So I did some research for alternatives that could avoid these downsides. Among the citations to the VEDA paper, I've found what seems to be a alternative approach to solve the same problem, as described in Teixeira, Filipe, e M. Natália D. S. Cordeiro. “Improving Vibrational Mode Interpretation Using Bayesian Regression”. Journal of Chemical Theory and Computation, vol. 15, no 1, janeiro de 2019, p. 456–70. ACS Publications, doi:10.1021/acs.jctc.8b00439. Their software, called vibAnalysis, is open source, and available from a GitHub repository. It doesn't support Gamess-US or Psi4, but at least supports ORCA, which is free for academics, besides Gaussian.

I wonder if there are other alternatives I have missed in my research, specially if they run on linux and work with Gamess-US or Psi4. If somebody here could provide some guidance, I'd be grateful.


texts: What's the difference between FFKM and PTFE?

texts:
These two fluorocarbon polymers seem to me very similar, the only difference I see is that FFKM is elastomer while PTFE aka Teflon is more of hard type of plastic.

Isn't FFKM just PTFE with lower average molecular weight, that is the average molecule is shorter chain so its softer? Is the production of these two polymers vastly different or is the process mostly same?


texts:
As I’m reading about water cations and anions, I read that the benefits we gain from water are of course lots, but the most important of them is the neutralisation of acids ($\ce{H+}$) from the anions present in water such as:  $\ce{HCO3-}$ , $\ce{CO3^2-}$ and $\ce{OH-}$.

Does this mean that the higher the concentration of bicarbonates, the better the quality for drinking?

Should we choose the bottle of water with the highest concentration of these anions?

And also, when boiling the water we loose bicarbonates, so is boiled water unhealthier?


texts: Typesetting of the retardation factor (Rf)

texts:
What should be the typesetting for the symbol of the retardation factor as used in thin-layer chromatography?

These are the possibilities:

Rf - only f in italics
Rf - both R and f in italics
Rf - only R in italics

On Wikipedia, they have used all sorts of typesetting. There is also RF with a capital F.


texts: Why doesn't Oxygen form coordinate covalent bonds?

texts: We know that an Oxygen atom has two lone pairs. Why doesn't oxygen then form coordinate covalent bonds using those since it has nothing to lose?


texts: When to use -ate and -ite for naming oxyanions?

texts:
I'm now learning about nomenclature. In particular, oxyanions.

Basically, when you have an anion that is a combination of a non-metal with oxygen.

According to my book:

  It ends with -ate for the most common oxyanions of the element. It
  ends with -ite for the oxyanions that have the same charge but with
  one less atom of oxygen.

  Example:

  $\ce{NO_3^- \implies}$ Nitrate

  $\ce{NO_2^- \implies}$ Nitrite

Ok, if you give me an oxyanion that ends with -ate, I know that I can simply remove one oxygen atom and I will get the -ite.

But, what I don't understand is how does the book know that $\ce{NO_3^-}$ is Nitrate: how does the book know that $\ce{NO_3^-}$ is "the most common oxyanion for the element". How does it know that a charge of $-1$ and $3$ oxygen atoms create "the most common" Nitrogen oxyanion?

In other words, what does it even mean by "most common"?


texts: Voltage sensitive compounds that undergo a conformational change?

texts:
In nature, the Ca/Na/K channels which consist of groups protein are often voltage sensitive and undergo conformational changes in response to voltages on the order of mV.

Are there any known classes of other simpler organic or inorganic compounds which also undergo rapid conformational changes in response to applied voltages?


texts: Independant variable for Asprin pill titration with NaOH solution

texts:
I am assigned to do an independently designed chemistry experiment for school. I want to do titration of Aspirin pills with NaOH solution using Phenolphthalein as indicator. I am struggling to find and independent variable for the experiment. I thought about doing heat, but is unsure about the mechanisms of that. If anyone could help me or guide me in a direction I would greatly appreciate it!

Thank You!


texts: MOF derived supercapacitor electrode material

texts: I am working on ZIF-67 of the family MOF as a supercapacitor electrode material and got a morphology of hollow spheres. Is there any way to build this morphology over a substrate (current collector) like Nickel foams or Carbon clothes without using additional binders?


texts: What metal is under the stainless layer when it wears of?

texts:
I have this belt for several years now and the belt buckle is naturally subject to wear and tear.

On the most exposed spots the outer layer is now completely worn of and I wonder

Is this an example of passivation of the inner material?
What is the outer layer made of? Stainless steel?
What is the metal under the outer layer? It looks (and smells) like copper but why would they make it out of copper? Copper is – as far as I know – more expensive (by volume comparison, because the belt buckle can't be made smaller) than stainless steel?
Wouldn't it be cheaper to make it only from stainless steel (assuming the outer layer is from stainless steel)? It would also be better from health perspective because I suspect the inner layer causes skin irritation.

I intentionally scrubbed the bottom edge of the buckle before taking the photo to reveal the real color of the metal, on the top edge it is presumably covered by its natural oxide layer (copper has it green, right? But it's just a thin layer so it can look different I suppose).

I am kind of ashamed answers to these questions aren't already known to me because this effect happens on a lot of daily used metal objects...


texts: Why can't some salts be used in the salt bridge of specific voltaic cells?

texts:
I had an exam question in reference to a galvanic cell with $\ce{Pb{(s)}}$ as the anode in $\ce{Pb^2+}$ solution and platinum cathode in a solution of  $\ce{Fe^2+}$ and  $\ce{Fe^3+}$:

  Identify an appropriate electrolyte to use in the salt bridge.

I gave $\ce{KNO3}$ which was correct. However, the marking criteria specified that sulphate and chloride salts were not usable.

Why are these salts not usable? Is there any way to tell which salts would be usable for other galvanic cells?


texts: Why isn't it commercially suitable to dissolve sulfur trioxide in water to produce sulfuric acid?

texts:
Choose the two correct options from A-F, why isn't it commercially suitable to dissolve $\ce{SO3}$ directly in water to give concentrated sulfuric acid instead of using the contact process? The major reaction of the contact process are

  $$\ce{S + O2 -> SO2}$$
  $$\ce{2 SO2 + O2 <=>2 SO3}$$
  $$\ce{SO3 + H2SO4 -> H2S2O7}$$
  $$\ce{H2S2O7 + H2O -> 2H2SO4}$$

  A. To reduce the hazards of spillage
  B. Because the density of the product is too high
  C. To minimise transport costs of large volumes
  D. Because the last step is too expensive.
  E. Because the last step of the process is too exothermic.
  F. An aerosol of the sulfuric acid rapidly fills the container.

The solution is C and F, but I think it should be A and D. Is it because to make gas react with $\ce{H2O}$, too much pressure is needed and it will be expensive? Can someone explain why each choice is false and true?


texts: What is the structural difference between ketogenic amino acids and glucogenic amino acids?

texts: We know some amino acids could go in ketogenosis path way ,some in glucogenic and some in both. I 'm wondering to know what the differences are between the amino acids that make this situation.


texts:
i made a synthesis of this material in the lab and now i got the H-NMR specta , and by litreture i know that i got the right product.
im having trouble to match the hydrogens to the peaks,i tried to look at the molecule in it chair form, i know that the 2 hydrogens(A) attached to the cl cl group are in the highest ppm than the other 4 (B), but on the last 4 i got 2 different multiplets, which is a match to which hydrogens? i added the  spectrum


texts:
I understand that adding borane to an alkene will produce a hydroborane. Addition of -OOH will form an alcohol.

My lecture notes state that addition of borane to:

A carboxylic acid will form an alcohol
An amide will form an amine
An aldehyde/ketone will form an alcohol
A nitrile will form an amine
An epoxide will form an alcohol
An alkene will form an alkane
An alkyne will form an alkene

I can't find the mechanisms for these anywhere. I'd appreciate seeing a few of them, namely carboxylic acid to alcohol, amide to amine, epoxide to alcohol and alkene to alkane. I should then be able to have a good crack at working out the rest.


texts: Dish soap reaction on braided stainless steel hose

texts:
Just wondering if leaking dish soap can have a reaction on a braided stainless steel hose used for hot water intake of dishwasher over time (several months)? The hose which was new at the time perforated without explanation and caused a flood.
Thanks.


texts: Vacuum filtration: will Polymer elements interfere with the vacuum?

texts:
I am doing an experiment with vacuum filtration, where a Nylon filter is used to create a membrane (marked in pink in the picture attached). When I use the membrane, it frequently breaks in the process of transferring the membrane (on the Nylon filter) to another location. So I thought to put the Nylon filter onto a rigid ring, so that I can move the entire ring (with Nylon filter and my own membrane on top) without introducing cracks into my membrane. I wanted to 3D print this disk using a polymer resin, but was unsure, whether the polymer would interfere with the vacuum filtration process in some ways, or whether it would be good to use. I marked up on the picture, where the polymer ring would go (between the glass beakers).

Here is the image I mentioned to show my setup


texts:
A compound having formula $\ce{C9H7O2Cl}$   (O = oxygen) exists predominantly in enol form (A) and also in keto form (B). On oxidation with $\ce{KMnO4}$ it gives m-chlorobenzoic acid as one of the products. Identify (A) and (B).
(subjective question; no options were given)

I tried it and found the double bond equivalent as 6, 4 of which were utilized in benzene ring. Also, the benzylic carbon must have at least one hydrogen. Therefore I determined the following structure as (A):

But my book suggests (A) should be:

Please explain whether both are correct or only one product will exist.
Source: Joint Entrance Exam (JEE) 2003 India


texts: Synthesis using Cationic Hetero-Cope Rearrangement

texts: By searching for the reference of the synthesis below I arrived at an example of Cationic Hetero-Cope Rearrangement, but I can't access the paper. How does it work here, and what happens in the first step of the synthesis (the addition of iBuOH and TsOH at 80 degrees)?


texts: Electron Configuration of an element with no. of electrons > 18

texts:
Let's say that we have an element, say $\ce{Ca}$.
According to law, the last shell should contain only upto 8 e-.
Hence, electronic configuration of $\ce{Ca}$ would be 2,8,8,2.

But, according to the 2n2 rule, the M-shell can hold upto 18 e-.
So, doesn't this mean that the e- configuration of $\ce{Ca}$ can also be written as 2,8,9,1 or say, 2,8,7,3 or something?

But it's not so... Why?


texts: Stability of diboron(B2) and dilithium(Li2)

texts:
Why is $\ce{B2}$ more stable than $\ce{Li2}$?

Both $\ce{B2}$ and $\ce{Li2}$ have bond order equal to 1. Moreover, $\ce{Li2}$ has only 2 electrons in the antibonding molecular orbital while $\ce{B2}$ has 4 electrons in the antibonding molecular orbital. Thus, $\ce{Li2}$ should have been more stable than $\ce{B2}$ if we consider the number of electrons in the antibonding molecular orbital as the parameter of stability. Does the fact that $\ce{B2}$ is smaller than $\ce{Li2}$ makes it more stable?


texts: How do I synthesize $\ce{IrO2}$ from $\ce{IrCl3}$ ? Please suggest a least expensive method.


texts: Calculate the number of moles of phosphorus in 15.95g of tetraphosphorus decaoxide

texts:
I've got this question and I cannot figure out how to get the correct answer.

  Calculate the number of moles of Phosphorus in $15.95\:\mathrm{g}$ of tetraphosphorus decaoxide. ($\ce{P4O10}$)

I tried doing it like this:

Molar Mass of (element) = Number of atoms * Relative Atomic Mass = ### grams/mole

Mass of Compound in Grams = $15.95\:\mathrm{g}$

$M(\ce{P4}) = 4(30.97376) = 123.89504 \:\mathrm{g/mol}$
$M(\ce{O10}) = 10(15.9994) = 159.994 \:\mathrm{g/mol}$

$M(\ce{P4O10}) = 123.89504\:\mathrm{g/mol} + 159.994\:\mathrm{g/mol} = 283.88904 \:\mathrm{g/mol}$

$\ce{P}: (123.89504 \:\mathrm{g/mol})/(283.88904 \:\mathrm{g/mol}) = 0.4364207 \cdot (100\% = 43.64\% \ce{P})$

$15.95\:\mathrm{g} \cdot 0.4364207 = 6.9565\:\mathrm{g} \ce{P}$

$\ce{P} = 6.9565\:\mathrm{g}/ (123.89504\:\mathrm{g/mol}) = 0.056148 \:\mathrm{mol}$

But the answer in the back of the book is $0.2247 \:\mathrm{mol}$


texts: Relation between number of equivalents of reactants

texts:
Consider the reaction $\ce{Sb2S3 + F2 -> SbF5 + SF6}$. If the milliequivalents of antimony, sulfur and fluorine are x, y and z respectively, then prove that $x+y=z$.

This is what I know: Number of equivalents of each reactant in the reaction is equal, and that number of equivalents is (mass of species) /(equivalent weight). The problem I'm facing is that $\ce{Sb}$ and $\ce{S}$ are in the same compound, so I think $x$ should be equal to $y$ (this is clearly incorrect). Also, the mass of reactants used is not mentioned, so I don't know how to proceed with the question.


texts: The meaning of different parts in the naming of glucose

texts:
There are two main types of glucose, $\alpha$-D-(+)-glucose and $\beta$-D-(+)-glucose.
Can anyone please explain what is $\alpha$,D or (+)?

So (maybe by permutation and combination), how many types of glucose are there?


texts: What is the color and structure of CrO3?

texts:
What is the structure and color of $\ce{CrO3}$?

Also, is it possible to produce $\ce{CrO3}$ when dichromate is heated with sulphuric acid?


texts: Why does the Michaelis-Menten constant remain constant in the event of non-competitive enzyme inhibition?

texts:
A while back, I "answered" the question: Why does the Michaelis-Menten constant decrease in the presence of non-competitive inhibitor?

At the time of posting my answer, both the OP and I were under the impression that non-competitive inhibition reduces the Michaelis-Menten constant ($K_\mathrm{M}$).

However, the Wikipedia article on "Enzyme inhibitors" states that $K_\mathrm{M}$ remains constant in the event of non-competitive inhibition. (second emphasis mine)

  In non-competitive inhibition, the binding of the inhibitor to the enzyme reduces its activity but does not affect the binding of substrate. As a result, the extent of inhibition depends only on the concentration of the inhibitor. $V_{max}$ will decrease due to the inability for the reaction to proceed as efficiently, but $K_m$ will remain the same as the actual binding of the substrate, by definition, will still function properly.

But this goes against what I thought earlier (see my answer to the linked question). Wikipedia defines $K_\mathrm{M}$ as:

  The Michaelis constant $K_\mathrm{M}$ is the substrate concentration at which the reaction rate is half of $V_\mathrm{max}$. Here, $V_\mathrm{max}$ represents the maximum rate achieved by the system, at saturating substrate concentration.

Wikipedia attributes the invariance of $K_\mathrm{M}$ in non-competitive inhibition to the fact that the actual binding of substrate to an active site is unaffected. Now I agree that the actual binding of the substrate is unaffected here, but how does that have any effect on $K_\mathrm{M}$?

When $V_\mathrm{max}$ decreases during non-competitive inhibition (the only point I and Wikipedia concur on), shouldn't the $K_\mathrm{M}$ decrease correspondingly (based on the definition of $K_\mathrm{M}$)? Is the Wikipedia article incorrect in this regard?


texts: Surprisingly, there are very few resources online (outside of obscure lab pages) that explain exactly what standardization is (not even Wikipedia!). The context is the phrase standardize the titrant for a titration. Does this mean you titrate it with a known solution?


texts: Why are condensation reactions endergonic?

texts:
My lecture notes state that

  Condensation reactions, like all biosynthetic reactions, are endergonic.

I am unsure as to why this would be the case. I thought bond formation was an exothermic reaction, so you would get a negative enthalpy change from the bond being formed. I appreciate that you wold have a decrease in entropy when going from two small molecules to one larger molecule, but would this really counter-balance the negative enthalpy change every time? Perhaps the small molecule produced in the biosynthetic reaction, e.g. $\ce{H2O}$ for condensation reactions, is important here?

In a nutshell, I am just confused as to what ensures that all biosynthetic reactions (and condensation reactions) are always endergonic?


texts:
Background:
Well, it's summer here in Brazil, and a great way to keep cool is drinking a so called Tereré, and, of course, we do need cold water for that.

Problem: I was looking for endothermic spontaneous reactions so I can cool the water in a bottle using an inner aluminum bottle in which the endothermic reaction occurs. I already knew that Urea's dissolution is endothermic and spontaneous, but I couldn't find how much endothermic it is, i.e., how many Joules it absorbs per Mol of urea dissolved. Another problem related with urea is that it's dissolution is a slow process (I think, not sure), additionally, the urea I can find is the one use as fertilizer, and this one has lots of impurities that I'll need to take into account when calculating how much I'll need to react.

What I know is that the urea dissolves in the same amount of water in weight, that the reaction time increases as the concentration increases, but have no idea how much energy it absorbs neither the how much time it takes to react, of course it depends on the concentration, granularity, etc.

Question: Considering all of that, are there any other reagent(s) I can buy or synthesize without being a licensed chemist that can be used to cool the water? Or, do you have the information that is missing about urea's dissolution (Joules/Mol absorbed in dissolution, approximated reaction time) so I can figure out if I can use it for this purpose?


texts:
Two rigid tanks are connected by a valve. Tank A contains $0.2\ \mathrm{m^3}$ of water at $400\ \mathrm{kPa}$ and $80\ \%$ quality. Tank B contains $0.5\ \mathrm{m^3}$ of water at $200\ \mathrm{kPa}$ and $250\ \mathrm{^\circ C}$. The valve is now opened, and the two tanks eventually come to the same state. Determine the pressure and the amount of heat transfer when the system reaches thermal equilibrium with surroundings at $25\ \mathrm{^\circ C}$.
Assumptions 1: Tanks are stationary and thus the KE and PE changes are zero and there are no work interactions so $W = 0$.

To start this question I know we have to find the specific internal energy for Tank A and Tank B then use this to eventually find the total heat transfer so, I began by finding the properties of water in Tank A at $p = 400\ \mathrm{kPa}$, which are taken from Tables A-5 in Thermodynamics an Engineering Approach
At $400\ \mathrm{kPa}$ the specific internal energies are retrieved to be $$u_\mathrm f = 604.22\ \mathrm{kJ/kg}$$ and then $$u_\mathrm{fg} = 1948.9\ \mathrm{kJ/kg}$$
My question is why are we using the $u_\mathrm{fg}$ or the specific internal energy of evaporation for this question and not the specific internal energy of saturated vapour, $u_\mathrm g$?
Please ask me any further questions you need to help me!


texts: Determine reaction concentration at chemical equilibrium with multiple reactions

texts:
I have a problem understanding how to calculate the change/dependence of the concentrations at the chemical equilibrium using multiple reactions.
The concentration of my reactants and products at chemical equilibrium are given.

E.g.: For a simple reaction like $\ce{C + O <=> CO}$ at chemical equilibrium with concentrations $\ce{10C}$, $\ce{5O}$ and $\ce{2CO}$, I calculate the equilibrium constant $K_{eq} = 2/(5*10) = 0.04$. Then I can use the ICE table and calculate $x$ to derive the concentration of $\ce{CO}$ at chemical equilibrium at various input concentrations for the reactants:
e.g., for an input concentration of $\ce{22C}$ and $\ce{7O}$ (and $\ce{0CO}$) I get a concentration of about $\ce{3CO}$.

BUT how do I calculate the change of my products, if I have to consider multiple reactions with the same reactants involved?
E.g., $\ce{C + O <=> CO}$ and $\ce{C + N <=> CN}$ again with given concentrations at chemical equilibrium of $\ce{10C}$, $\ce{5O}$, $\ce{30N}$, $\ce{2CO}$, and $\ce{8CN}$.

These two reactions are obviously coupled, so solving them independently is not possible (without proper decoupling). I'm also not sure if the equilibrium constant for the reactions can be determined. If I just 'ignore' one of the reactions at a time and calculate the equilibrium constant using the remaining concentrations, I would neglect the coupling which can have a strong effect, e.g., an increase in the input concentration of $\ce{C}$ may influence one reaction by ~90% and have almost no influence at the other (depending on a saturation effect).

I'm also not sure if it is NOT allowed to throw all products and reactants together and just consider them as a single reaction like $\ce{10C + 5O + 30N <=> 2CO + 8CN}$, calculate the equilibrium constant and apply my variation of input concentration like in the example above. How would I account for the case N=0 and CO != 0?!

I think that the only reliable approach would be an iterative calculation of the concentration until convergence is achieved. But I don't have a clue how to do this.

EDIT: I have found part of the solution myself. As I mentioned above, I have to use a system of coupled equation and solve it. So here are my thoughts about it. There has to be conservation of mass (or elements), so the following equations have to hold:

$\ce{C + CN + CO -} nC = 0$

$\ce{N + CN -} nN = 0$

$\ce{O + CO -} nO = 0$

where $nX$ represents the concentration of a certain species. Second, the equilibrium constants also need to be specified like the following:

$\ce{CO - K_1*C*O = 0}$

$\ce{CN - K_2*C*N = 0}$

Solving these coupled equations numerically is no problem. I did some testing and can confirm that at least the uncoupled case ($nN = 0$) leads to exact the same results as the method above. Extending this case to include multiple and more complicated reactions should not be a problem. The only remaining question is how to determine the equilibrium constants for these coupled equations?!

EDIT: I used the same approach to solve the following system of equations for the equilibrium constants:

$\ce{K_2*K_1 - \frac{CN}{(C*N)}*\frac{CO}{(C*O)} = 0}$

$\ce{K_2/K_1 - \frac{CN}{CO}*\frac{O}{C}} = 0$

I used the solution for these equilibrium constants, plugged them into the equations above and calculated the concentrations at equilibrium. The solutions are consistent. (Note: Got myself confused and interchanged $K_1$ with $K_2$ within my computations.)

Conclusion To calculate variations of the input concentrations at chemical equilibrium 2 major steps are needed.

1) Calculate the equilibrium constants $K_x$ for every reaction $x$ at given concentrations. Solve that system of $x$ equations (details in 2nd edit) with a numerical solver of your choice.

2) Adjust/variate the input abundance and use another system of $z$ equations (conversation of mass/element and reaction equations - details in 1st edit) to calculate the new concentrations at equilibrium.

Note: Make sure to always have $n$ equations for $n$ variables.


texts: A hydrogen anion has a bigger radius than neutral H . Why is this happening ? I mean both electrons exist at the same shell so this is not it. Both H- and H have 1 proton so this is not it as well . Both electrons of the hydrogen ion have the same energy level and they don't shield the charge of the core from one another. What is it then? Pauli repulsion?


texts: Atomic mass ratios - Is the problem providing enough info?

texts:
One gram of Hydrogen reacts with exactly (almost) 8 grams of oxygen to produce $\ce{H2O}$. Another single gram of Hydrogen reacts with 16 grams of Oxygen to produce $\ce{H2O2}$.

Can the ratio $\frac{m_O}{m_H}$ be determined from this information? If not, what else do chemists need to know to find this ratio?


texts: Understanding effect of ph on solubility of salt

texts:
In the following picture why Ksp is not simply S2- ? Why is f included with one species only? Please explain the last part.

What does f represent and why it is used in molar solubility?


texts: Reduction of (4-methylcyclohex-3-en-1-yl)methoxymethylbenzene to 4-methylcyclohex-3-en-1-ol

texts:
Find the suitable reagent to carry out the following transformation:

The answer provided says that $\ce{H2/Pd-C}$ can be used to bring about the given transformation, but I am failing to understand why would the double bond remain unaffected. Moreover, the answer does not specify the number of equivalents of $\ce{H2}$ used.


texts: Comparing rate of reaction of acetic acid and sodium bicarbonate at different temperatures

texts:
Given the reaction between $\ce{CH_{3}COOH {(l)}}$ and $\ce{NaHCO_3 {(s)}}$, which happens at the same pressure but at different temperatures, is there any way to mathematically compare the rate of reactions?

I thought using the rate equations of order 2, but I use the same concentration of materials. Suppose I could have found the connection between temperature of he material and its concentration, I would be able to find my required rate-indicators.

How to find the connection between temperature and concentration, or how to describe the rate of the reaction more exactly?


texts: Why are teflon coated dishes black or dark grey in colour when teflon as such is white (and the underlying aluminum is not black either)?


texts: How solubility in alcohol imply covalent nature

texts:
lithium chloride is considered to be an ionic compound,but it is soluble in alcohol,which suggests that it also posses a small amount of covalent character.

This is an extract from my book ,when I looked it up it said ionic bonds are polar so they are soluble in alcohol.
So how does lithium chloride's solubility in alcohol prove it has small ammount of covalent character?Is my book wrong ?


texts: Why do the first and second ionizations of a diprotic acid produce the same hydronium ion concentrations in solution?

texts:
I was going through Oxtoby Chemistry when I got confused by the following passage in the textbook. It said that "two simultaneous equilibria are involved in the ionization of a diprotic acid such as carbonic acid":

I understand the chemical species for both the first and second ionizations barely dissociate, which means the hydronium ion production is very little.

However, what makes hydronium ion production identical (i.e. important point #1)? Shouldn't the second ionization occur to a lesser extent than the first ionization? Thanks.


texts: What products will the following reactions yield?

texts:
Assume these 2 reactions. I must write the Lewis structures of the products.

$$\ce{C6H5COOH + CH3CH2OH ->[\ce{H+}] ?}$$
(comment: A benzene ring + $\ce{CO_2H}$ on one end, I don't know its name)
$$\ce{CH3CH2OH + (CH3CO)2O ->[\ce{H+}]?}$$ (comment: acetic anhydride)

My approach:

For the first reaction I will get acetic anhydride (source)

For the second reaction I will get aspirin and acetic acid.

Questions:

Is the above correct?
Is there a connection between the two reactions? Is it an intermediate step of some sort? What is the importance between the two reactions?
Why is $\ce{H+}$ added?
What is the benzene ring and the $\ce{CO2H}$ called?


texts: what is the cross aldol product of ethanal and acetone(major product)?

texts: my teacher told that major product would be when acetone will form nucleophile because it will attack more positive carbon of ethanal(less +i than acetone) however i read in my book that since formation of carbanion is rds ethanal should be nucleophile (more stable due to less +i)


texts:
I am studying introductory organic chemistry, suddenly this one started looking odd,

The carbocation stability for three compounds as given by my book is shown below,

Let me call those as compounds A>B>C as given in image. It is very well known that 'N' and 'O' are electron withdrawing group(shows -I effect) and they can also show +M effect( some texts call it as Resonance effect ) by delocalising their lone pair over the vacant p-orbital of the carbocation.

Now all i want to know is, How to decide whether +M effect or -I effect will operate in this case? If I consider only inductive effects, the order would be C>A>B   which is wrong in this case.

One part of my text book says that +M effect > -I effect (in more than 99% of cases). But then too the next question arises, why +M effect of 'N' is more than that of 'O'?

I got stuck in this one and i am now asking whether such questions are feasible without conducting experiments.

Explanation with the principles which are familiar to my level would be nice.


texts: I'm looking to set up a small chemistry lab in my garage for doing demos. I think it would be good for a freshman student I'm mentoring and also as a hobby. Does anyone know where I can buy apparatus (like flasks, pipettes, heaters) and chemicals?


texts: Computing the commutator of the Fock and density matrices in AO basis (Hartree-Fock theory)

texts:
I am making a simple restricted HF code using the Python interface of Psi4. I am now evaluating convergence by tracking the change in the sum of orbital energies, but I want to do this in a better way. It is common to use the fact that at self-consistency, the Fock and density matrices commute

$$
[\mathbf{F}, \mathbf{D}] = \mathbf{FD} - \mathbf{DF} = \mathbf{0}
$$

However, the above expression is only valid in MO basis, while F and D in my code are computed in AO basis. So I need to derive an equivalent expression in AO basis. I am quite sure the correct expression is

$$
[\mathbf{F}, \mathbf{D}]^{\text{AO}} = \mathbf{FDS} - \mathbf{SDF}
$$

as this is equal to zero to within $1\times10^{-14}$. But how to derive this?

Derivation

An arbitrary molecular orbital $\phi_i$ is expanded in atomic orbital basis functions

$$
\phi_i = \sum_\alpha C_{\alpha i} \chi _{\alpha}
$$

Acting the commutator on $\phi_i$ and expanding it to AO basis yields

$$
[\mathbf{F}, \mathbf{D}] = \mathbf{FD} \sum_\alpha C_{\alpha i} \chi_{\alpha}  - \mathbf{DF} \sum_\alpha C_{\alpha i} \chi_{\alpha}
$$

Since we know the solution contains the overlap matrix $\mathbf{S}$, lets look at the definition

$$
\mathbf{S}_{ij} = \langle \chi_i(\mathbf{r}) \vert \chi_j(\mathbf{r}) \rangle = \int d\mathbf{r} \chi^*(\mathbf{r})\chi(\mathbf{r})
$$

Since this must be part of our expression, it seems to me a good approach is to multiply from the left by $\sum_\beta C_{\beta i}^* \chi_\beta^*$ (dropping the $\mathbf{r}$ dependence from now on) and integrating over $\mathbf{r}$

$$
[\mathbf{F}, \mathbf{D}] = \int \sum_\beta C_{\beta i}^* \chi_\beta^* \mathbf{FD} \sum_\alpha C_{\alpha i} \chi_{\alpha}  - \int \sum_\beta C_{\beta i}^* \chi_\beta^* \mathbf{DF} \sum_\alpha C_{\alpha i} \chi_{\alpha}
$$

from in braket notation becomes

$$
[\mathbf{F}, \mathbf{D}] = \langle \sum_\beta C_{\beta i} \chi_\beta \vert \mathbf{FD} \vert \sum_\alpha C_{\alpha i} \chi_{\alpha} \rangle  - \langle \sum_\beta C_{\beta i} \chi_\beta \vert \mathbf{DF} \vert \sum_\alpha C_{\alpha i} \chi_{\alpha} \rangle
$$

At this point I am not sure what to do - or if am I even on the right track. I can see that we have the "pieces" that make up the overlap matrix, but I don't know how to put them together. Further, due to the orthonormality of the MOs, then I can imagine that the summation terms only survive when $\alpha = \beta$. But I'm not sure how to derive this properly.


texts: How many signals would be seen in total in the 13C NMR spectrum

texts:
This is NanoBalletDancer.
How many different carbon environments are there in NanoBalletDancer – i.e. how
many signals would be seen in total in the 13C NMR spectrum?

I counted 8 signals from benzene ring carbons
4 from methyl group carbons
4 from triple bond carbons

What is the total amount of signals? Which did I miss?


texts:
I wanted to ask a question about notations on MO diagrams.

Our first lesson about MO diagrams was today and I was taken through an example with $\ce{F2}$ as shown below:

but one thing that the lecturer did not explain, and I couldn't find over the internet with explanation, was the notation $\ce{3\sigma _g}$, $\ce{1\pi _u}$, $\ce{1\pi _{g}^{*}}$ and $\ce{3\sigma _{u}^{*}}$.

Is this notation relevant to the symmetry of the orbitals, or is there something else?

I haven't found any information that can explain this thus far.


texts: When a molecule loses hydrogen atoms, does it become oxidised?

texts:
I had the following question on a bio test covering cell respiration and glycolysis, but I'm not sure if I agree with the answer.

  When a molecule loses hydrogen atoms (as opposed to hydrogen ions), it becomes
  B) oxidised

According to my textbook (Principles of Life, 2nd Edition), oxidation is defined as

  Relative loss of electrons in a chemical reaction; either outright removal to form an ion, or the sharing of electrons with substances having a greater affinity for them, such as oxygen. Most oxidations, including biologial ones, are associated with the liberation of energy.

Hydrogen atoms have one proton and one electron in their typical state. If a molecule is losing hydrogen atoms, then its net charge wouldn't change. For example, if a (hypothetical) molecule had 7 protons and 6 electrons, it would have a charge of $+1$. If it then lost a hydrogen atom, it would now have 6 protons and 5 electrons, which still yields a net charge of $+1$. Am I missing some critical piece of information, or is this still considered oxidation?


texts: How to name this compound (Carboxylic acid+amide)?

texts: It's the first one, I know that this solution is a mistake, but what is the true one? can we just use 5-amido?


texts: Elimination in α,β-dibromohydrocinnamic acid

texts: The above is a picture of α,β-dibromohydrocinnamic acid (2,3-dibromo-3-phenylpropanoic acid). In the lab today I carried out an elimination reaction on this molecule using potassium carbonate giving the carbonate anion as a base. I thought about the mechanism and I initially thought that the base would attack the hydrogen on the leftmost carbon atom (out of the two with the bromine atom on it) as I thought that this would be the most acidic proton of those two carbon atoms because of resonance available with the aromatic ring. However, the proton on the carboxylate group is surely the most acidic. How does this effect things in terms of the mechanism and the product?


texts: Why are the reactants in the solubility product constant multiplied by their coefficients and raised to the power of their coefficients?

texts:
It is probably easiest for me to explain the question in an example. Consider the following chemical reaction:

$\ce{MgF2(s) -> Mg^{2+} (aq) + 2F- (aq)}$

Plugging this into the formula for the solubility product constant, $K_{sp}=[M^{y+}]^{x}[A^{x-}]^{y}$, we get:

$K_{sp}=[\ce{Mg^{2+}}][\ce{F-}]^{2}$.

The solubility product constant for magnesium fluoride is $5.16\times10^{-11}$. To determine molar solubility, the equation to solve for magnesium and fluoride is $5.16\times10^{-11}=X\times (2X)^{2}$.

$X$ is magnesium and $(2X)^{2}$ is fluoride. This is because there are two moles of fluoride for every one mole of $\ce{MgFl_{2}}$, and one mole of magnesium for every one mole of $\ce{MgFl_{2}}$. (Please correct me if I'm wrong anywhere.)

But here's whats confusing to me. Why is fluoride denoted as $(2X)^{2}$? I know that there are two moles of fluoride per one mole of magnesium fluoride, but why does it need to be denoted by being both multiplied to its coefficient and raised to the power of that coefficient?

Sources: Magnesium Fluoride Solubility product constant


texts: Is there a compound where one element has a CCP structure with all voids occupied by others?

texts: My Google-fu hasn't got me anywhere. All results have been quite fuzzy about it, nothing explicit.


texts: General Question about transferring Solution from containers (Workplace Related)

texts:
At my workplace we will soon begin diluting a solution to specific concentrations, this is done within a specific container.
The solution to be diluted is provided by a manufacturer in the following type of bottle :

The contents inside this bottle can only be retrieved with a syringe. However, we need to transfer volumes in the ranges of $ 0.015 \,mL - 0.06 \,mL $  ,with syringes we cannot be confident (because we have to eyeball it real hard).
So we think of course to transfer from the bottle to a beaker and then using a micropipette to transfer to the desired container and dilute. The problem is that the solution to be diluted is extremely expensive , and every unnecessary transfer to a beaker will cause some of our solution to be lost , beakers need to be also washed THOROUGHLY if they are to be reused.
Question : Are there any viable instruments that have a needle to enter the bottle and enough accuracy to transfer $ 0.015 \,mL - 0.06 \,mL $ ? Can you think of any way we can get around our problem?. We hope we can do just 1 transfer from Manufacturer bottle to our desired container to be diluted. Upon researching online we have not had much luck.

Opening , and replacing the cap of Manufacturer bottle gives problems with sterile properties of solution , as well of greatly reduces the expiry date.

Transfering from manufacturer bottle to beaker and then micropipetted to desired container to be diluted , gives rise to problems of sterile , as well as time consuming due to having to thoroughly clean the beaker, causes loss of solution.

I know this question may not be appropriate for this site , but I do thank you for your help and time.


texts:
I'm trying to understand organometallic raegents but am stuck at halogen-metal exchanges.

For example if you have $\ce{PhBr + BuLi}$ you get $\ce{PhLi + BuBr}$, I don't understand why $\ce{PhBu + BrLi}$ wouldn't form.


texts:
My teacher told me that in the Nernst equation, N was the number of electrons transferred. For example, $n = 2$ in $\ce{Ni^{2+} + Zn -> Zn^{2+} + Ni}$.

However, say all of the coefficients were doubled: $\ce{2Ni^{2+} + 2Zn -> 2Zn^{2+} + 2Ni}$. Would $n = 2$ or $n = 4$ in that case?


texts: Why are alkyl halides immiscible with water?

texts:
Why are alkyl halides, though polar, immiscible with water?

I have tried to solve this question by myself and I believe that it's due to the large energy is needed to break the hydrogen bonds, which is insufficient to overcome the forces present in water. But I'm not sure if I'm right. Can anyone help me out?


texts: How do point defects in a crystal relate to Entropy?

texts:
I am interested in Non-Stoichiometry and how it relates to crystal structures; In particular I wish to learn about surfaces of metal oxides. I am aware that point defects in such crystals are a result of an entropy driven reactions. So my question is this:

Are there any good introductory resources on this subject? I have basic undergrad chemistry and physics background.


texts: Determining the formula of zirconium oxide

texts:
I am doing the following question (from the 1988 HSC Chemistry paper):

  In the 19th Century the atomic weight of zirconium (Zr) was known but there was considerable doubt about the formula of zirconium oxide. Experiments determined the relative weight of the volatile chloride to be about 233.

  Assuming that zirconium in the oxide has the same valency, this evidence suggests that the formula for the oxide is:

  (a) $\ce{ZrO}$

  (b) $\ce{Zr2O3}$

  (c) $\ce{ZrO2}$

  (d) $\ce{ZrO4}$

I am not sure what is meant by the sentence 'Experiments determined the relative weight of the volatile chloride to be about 233'. By 'volatile chloride', are they referring to zirconium oxide or something else? It seems that they are referring to something else since a chloride is a compound of chlorine with another element or group.

Also, by the statement 'assuming that zirconium in the oxide has the same valency' are they saying that zirconium has the same valency as chlorine (i.e. -1)?

Any insights are appreciated.


texts: Methylnitrobenzene ring formation Synthetic Route

texts: I know the malonic ester is probably used to make propanoic acid or some carboxylic acid, and then joined to the methylnitrobenzene. But I just can't figure out what glues to the methyl. I know the nitro can be reduced to amine and bonded to a carboxylic acid, but then what about the ends?


texts: Why are the terminal Hydrogen bonds in diborane lost during alkylation?

texts:
Considering the fact that the bridge h bonds in diborane are weaker according to the answer  to the following question..>>.Why are bridge bonds in diborane longer than the terminal H bonds?
Why is then the terminal H bonds instead of the bridge H bond
lost during alkylation of diborane?
Is it energetically more favourable? If yes,Is there any reason why it is so?


texts:
I searched a lot to find the products of the haloform reaction of acetylacetone (pentane-2,4-dione),  but I didn't find any results.

What are the products of the haloform reaction of acetylacetone?


texts: If you dissolve two different ionic compounds (that don't make a precipitate) in water and then boil the solution so all the water evaporates, the salts will re-crystallize. Is it possible that you will get two compounds that are different from the ones you orignially dissolved? Is there any way to predict whether you will get the original compounds or new ones?


texts: Can lattice enthalpy only be determined by the Born-Haber cycle?

texts: Since we are able to determine the enthapy of formation experimentally, why it is impossible to determine the lattice enthalpy directly by experiment?


texts:
Today in chemistry class we were discussing Organic Chemistry. We discussed what organic compounds basically are and then I asked the teacher whether $\ce{CO_2}$ is organic or not. She told that it is as it contains carbon and oxygen with a covalent bond. I told her it can't be as it is not found in animals (naturally). I am very confused about it.

I need some good reasons to agree with either explanation. (I have searched the internet already but found no great insights as of now).


texts: When do I use the hydronium ion in an acid-base equation?

texts:
I have a question about when to use H3O+ and when to use the actual compound. I'm not really sure how to word this question so I'll show you an example of what I mean.

Example of using H3O:

"A titration for a sample of 25mL of 0.1 M NH3 by 0.1M HCl is conducted. Calculate the pH after the addition of 12 mL of 0.1M HCl"

$\ce{NH3 + H3O -> NH3 + H2O} $
(etc)

Example using the compound:

"Calculate the pH of 75 mL of 0.1M HC2H3O2 and .2M of NaC2H3O2 to which 9.5mL of 0.1M HCL is added"

$\ce{C2H3O2- + HCl -> HC2H3O2 + Cl-}$
(etc)

My question is, when are we supposed to use HCl in the equation and when are we supposed to use H3O+? Is it only when you are using a buffer that you are to use HCl? If so, why is this?


texts: Why lanthanides and actinides are shown separate from standard Periodic Table layout?

texts:
In the standard Periodic Table layout , all the elements up to 56 are in order i.e are in the same layout table. However, lanthanides and actinides are always shown separately from the layout like in this layout:

What is the reason behind this structure?

Is this standard layout or can I represent it like this too?


texts: Reaction between chlorobenzene and methyl chloride

texts:
What will be the product of the reaction between chlorobenzene and methyl chloride in the presence of anhydrous $\ce{AlCl3}$?

I think we should get 1-chloro-4-methylbenzene as the major product, as we'll have Friedel–Crafts alkylation. Is this correct? Or will we get toluene?


texts: How much energy is required to liquify oxygen?

texts:
Does anyone know where I can find some documentation of a real-world liquification process, and the energy costs?
I can calculate the heat that must be removed from O2 gas to get to liquid, but how would this translate to an electricity cost for cooling equipment?


texts: Does the hydronium ion donate a proton to water? If the collision of 2 molecules of water can cause a proton to be transferred, does hydronium 'pass' a proton to water?


texts:
On the left, there is a region for $\ce{MgO(ss)}$.

I've been told such regions exist because stuff are not miscible. However, does that mean the composition axis on the bottom is a lie? Namely, because it says ≠100% $\ce{MgO}$ and the region signals pure $\ce{MgO}$.


texts: Imposing particle number subspace on second quantized Hamiltonians

texts:
Here is my question:
Second-quantized Hamiltonians act on any state, regardless of how many electrons the state has. They are also block diagonal on different particle-number subspaces, as they commute with the electron number operator.

Now, suppose that one writes down a molecular Hamiltonian in the second-quantized formalism. In order to get the ground state energy, does one need to project the Hamiltonian on the correct electron subspace and diagonalize?

Or is the bare diagonalization of the Hamiltonian (without projecting) sufficient to pick the subspace with the right number of electrons?


texts: What do 'sigma' and 'pi' in front of ligands in the formula of a coordination compound mean?

texts:
The following coordination compound was given in the book Concise Inorganic Chemistry by J.D. Lee (Adapted by Sudarsan Guha) under the topic 'Effective Atomic Number (EAN)':

$\ce{[Ti(\sigma -C5H5)2 (\pi  -C5H5)2]^0}$

What is meant by the quantifiers $\sigma$ and $\pi$ in front of the ligand?  I have not seen this format with other ligands? If this is to signify $\sigma$ and $\pi$ bonds, why is it not used in the formulas of metal carbonyls which have synergic bonds (a combination of both $\sigma$ and $\pi$ bonds)?

In all the 67 occurrences of 'cyclopentadienyl' in the IUPAC Red Book, I was unable to see $\ce{C5H5-}$ having a $\sigma$ or $\pi$ in front of it. Instead I only saw $\eta$ being used in the name. I came to know that it is meant to denote 'hapticity'. Is this related to the presence of $\sigma$, $\pi$?


texts: How to calculate pH of a solution when H3PO4, NaH2PO4, Na2HPO4 and Na3PO4 are mixed together in certain amounts to form a solution?

texts:
How to calculate pH of a solution when $\ce{H3PO4}$, $\ce{NaH2PO4}$, $\ce{Na2HPO4}$ and $\ce{Na3PO4}$ are mixed together in certain amounts to form a solution?

I know how to calculate pH when they are present individually but not when all of them together. I searched the net also but couldn't find any such example.


texts: Heating organic compound in a stream of nitrogen gas

texts:
This is related to estimation of percentage of oxygen in an organic compound and my textbook states:

  A definite mass of an organic compound is decomposed by heating in a stream of nitrogen gas.

I would like to ask will all oxygen present in the compound evolve as molecular oxygen? Isn't there any possibility that carbon and oxygen of organic compound combine and form CO2 thereby producing error in measurement?


texts: Why is the common magnesium ion Mg(II) and not Mg(I) when the second ionization energy is higher than the first ionization energy?

texts:
The first ionization energy for magnesium is given as $\pu{737.7 kJ/mol}$, and the second ionization energy is $\pu{1450.7 kJ/mol}$.

Given this information, doesn't it take $\pu{737.7 kJ/mol}$ to form $\ce{Mg^1+}$, while $\pu{737.7kJ/mol} + \pu{1450.7kJ/mol} = \pu{2188.4 kJ/mol}$ is required to form $\ce{Mg^2+}$?

Why is it then, that the $\ce{Mg^2+}$ ion is more common than the $\ce{Mg^1+}$ ion, while more energy is required to form the $\ce{Mg^2+}$ ion?


texts:
Suppose I am reacting HCl with CuCO3.
Experiment 1: I use 2g powdered CuCO3
Experiment 2: I use 4g powdered CuCO3
All other variables are kept constant.
Will this have any affect on rate of reaction? Will the 4g react faster because of more particles available for collision?


texts: Why do we use pV term independent of U in the equation H = U + pV?

texts:
I have read the following definition of enthalpy in my textbook:

A substance has to occupy some space in its surroundings depending upon its volume ($V$). It  does against the compressing influence of the atmospheric pressure ($p$). Due to this,the substance possesses an additional energy called $pV$ energy which is given by the product of pressure ($p$) and volume ($V$) of the system.
The sum of internal energy and $pV$ energy of any system, under given set of conditions, is called enthalpy. It is denoted by $H$ and is also called heat content of the system. Mathematically, it may be put as $$H = U + pV$$

Let's suppose we have some water in a test tube at room temperature open to atmosphere. It will have internal energy which consist of kinetic energy of  molecules, chemical energy, rotational energy and some other forms of energy. In order to occupy some space in its surroundings, the molecules of the water should vibrate in such a way that they cancel out the compressing influence of the air molecules present in the atmosphere.
So if we try to measure the internal energy of the system, isn't the energy required to make space for the surroundings already included in the internal energy of the system. Why do we add an extra term $pV$ along with internal energy $U$ to measure the heat content of the system?


texts:
I encountered this equation when studying the Electrolyte solutions chapter in my analytical Chemistry textbook, Actually the terms in summation are giving a physical clue of what $I$ is, But what's the point of that $\frac{1}{2}$ ?
I've searched the Internet and a molecular Thermodynamics book that I have but I found nothing but the equation itself.

$I=\dfrac{1}{2}\sum_{i}m_{i}z_{i}^{2}$


texts: How do you figure out the dissociation energy for ions?

texts:
Specifically $\ce{KF}$ into the $\ce{K+}$ and $\ce{F-}$ ions. I can find tables on the DE into atoms, but where would I go to find the DE between ions?

I am also given that the bond length is 2.17e-10m. Can I use that at all?


texts: How to interpret Gaussian output for excited states?

texts:
I have calculated the excited energies for benzene in Gaussian. The output therefore was:

 Excited states from <AA,BB:AA,BB> singles matrix:
 Excited State   1:      Singlet-A      5.5804 eV  222.18 nm  f=0.0000  S**2=0.000
 20 -> 22         0.41871
 20 -> 23         0.27308
 21 -> 22         0.27309
 21 -> 23        -0.41870
 Excited State   2:      Singlet-A      6.4315 eV  192.78 nm  f=0.0000  S**2=0.000
 20 -> 22        -0.27213
 20 -> 23         0.41722
 21 -> 22         0.41725
 21 -> 23         0.27213
 Excited State   3:      Singlet-A      7.9411 eV  156.13 nm  f=0.0000  S**2=0.000
 18 -> 23         0.49564
 19 -> 22         0.49673

Now I am wondering from where to where are these transitions. I know that the first one is from HOMO to LUMO. Thinking of QM I'd assume that the second transition is from HOMO-2 to HOMO+1 and the third one would be from HOMO-1 to HOMO+2. AM I thinking correct?


texts: When are we justified in making assumptions in questions

texts:
The density at $20^\circ\mathrm{C}$ of a $\pu{0.500 M}$ solution of acetic acid in water is $\pu{1.0042 g/mL}$. What is the molality of the solution? The molar mass of acetic acid is $M(\ce{CH3CO2H})=\pu{60.05 g/mol}$.
  The density at $20^\circ\mathrm{C}$ of a $\pu{0.258 M}$ solution of glucose in water is
  $\pu{1.0173 g/mL}$, and the molar mass of glucose is $M(\ce{Glc}) = \pu{180.2 g/mol}$. What is the molarity of the solution?

In question one we can assume a 1 liter solution and in question two we can assume a 100 gram sample. I understand these assumptions are needed to find other information, but when are we justified in making these assumptions?


texts: Is there open source software for SEM EDX data analysis?

texts:
This can't be unique to me and would apply to anybody who has to use equipment in other departments has had departments move etc.

What open source packages exist to read and potentially manipulate SEM EDX (electron dispersive x-ray elemental analysis) data after the data has been collected?

(In my case I have data from an Oxford Instruments EDX but there are many more manufacturers.)


texts: Wattage to produce 6L of air from Water in less than a second?

texts:
So I understand the question is probably vague to a scientist, but this is all the specifics I could mustard up with my non-scientific background.

So I understand the basics of the process and have used it occationally in a garage environment to fiddle around, but never really thought about the applications until a particular Indiegogo campaign claimed to have created artificial gills small enough to hold in your mouth and generating 45 minutes of breathable air.
The campaign have gotten a wide spread of media attention and it got me thinking, how much wattage would be required to produce 6L of air over the course of a second which happens to be a rough average of a adults lung capacity.

I understand that submarines use this process to create breathable air, but as someone mentioned they have a nuclear reactor onboard and "it would not be wise to attach that to your face".

Would shortening a Lithium Ion/Polymer battery be sufficient to create such a quick reaction? Or are we talking megawatts in order to produce such a volume of air in that time span?

Update to the numbers used:

Pointed out by @DavePhD, you don't use 6L per breath, rather 6L on average per minute.
Taking into account that this would be a physical exercise under water, you'd normally use anything between 14-17L per minute, on average 16L.

Also noted is that I should have used P instead of the term wattage, thanks @Loong


texts: Distinguishing between a nucleophilic substitution and an electrophilic substitution

texts:
Why don't we consider all nucleophilic substitution reactions as electrophilic reactions and vice versa?

For example, look at this reaction I found in my textbook. (See picture)

This is an electrophilic substitution if we consider the H+ to be replaced by NO2+.

But if we look at it as the OH- ion being replaced by a CCl3- ion, then it can also be a nucleophilic substitution reaction! I'm so confused!

Any help on this would be greatly appreciated.


texts:
High-schooler here reading up on electrochemistry.....

I came across this equation (and its derivation) in the book Physical Chemistry, by Wallwork and Grant:

Now the thing is, the equation is valid for 'uni-univalent' electrolytes (like KCl). But I want a more....'versatile' formula.

So I attempted to modify that equation to suit electrolytes of the type AB (i.e- magnitude of charge on a formula unit cation is equal to that of the charge on a formula unit anion).

I wrote down the whole thing (my formatting skills are terrible, so to type it out would be a HUGE pain in the neck), pardon the handwriting, I hope it's legible enough....

As for that last question.....I was wondering if the equation could be made even more 'versatile' 3:)

( @getafix don't think of me as clingy but...I'm counting on you for this one too! )


texts: Fock operator invariance under unitary transformation

texts:
I know how to show that the Coulomb operator of the Fock operator is invariant under a unitary transformation of the orbitals, as on page 121 of Szabo and Ostlund, but the indices in my proof for the exchange operator are just not working.  What might I be missing?
I have

\begin{align}
\sum_i\hat{K}_i'(1) &=\sum_i\int dr_2\chi_i'^*(2)\chi_j'(2)/r_{12} \\
 &=\sum_i\int dr_2\sum_kU_{ki}^*\chi_k^*(2)\sum_lU_{lj}\chi_l(2)/r_{12}\\
 &=\sum_{ikl}\int dr_2U_{ki}^*U_{lj}\chi_k^*(2)\chi_l(2)/r_{12}\\
 &=\sum_{i}\int dr_2\chi_i^*(2)\chi_i(2)/r_{12}\\
 &\neq\sum_{i}\int dr_2\chi_i^*(2)\chi_j(2)/r_{12}.
\end{align}


texts: Can we use HPLC to purify an organic reaction product?

texts: I know HPLC is a form of column chromatography that uses high pressure to pump a sample mixture/eluent through a column. However, I'm not sure if this technique is being used to purify and isolate organic products? After doing some research, I found that automated flash chromatography systems use LPLC technique rather than HPLC. I can't understand why high pressure can't be used in these automated systems?


texts: How to calculate the composition of a borate buffer with a defined pH using the Henderson-Hasselbalch equation?

texts:
I am struggling with what appears to be an extremely easy pH problem that uses the Henderson-Hasselbalch equation. The problem and answer provided by the book is given below. I understand where the book is getting the answer but it appears that they are overlooking something.

From what I understand, the Henderson-Hasselbalch equation allows you to calculate the pH of a solution based on the concentrations of acid and conjugate base at equilibrium. In the problem, you start off with a solution of just the conjugate base. Then you add pure acid to the solution to get a desired pH. However, the book seems to assume that the acid you add completely contributes to the concentration of undissociated acid at equilibrium [HA]. How can this be the case? Some of the acid you add will surely dissociate. Anyways, here's what the book did...