texts: Why not an Avogadro's principle for solid matter?

texts: Avogadro stated that for any ideal gas, 1 mole of particles will occupy a specific volume at a specific ratio of pressure and temperature. So why doesn't this apply to a liquid or solid?


texts: Mustard oil test for distinguishing between primary aliphatic and primary aromatic amines?

texts:
Can the mustard oil test be used for distinction between primary aliphatic and primary aromatic amines?

An alkyl isothiocyanate is formed when mustard oil is reacted with a primary aliphatic amine. But does mustard oil give a product with aromatic primary amines so as to make a considerable distinction?


texts: How to calculate the remaining mass in the mother solution after multiple extractions?

texts:
During an extraction, a solute ($\ce{S}$) will partition itself between the two solvent phases with a partition coefficient ($K$) defined as:

$$\ce{S(solvent 1) <=> S(solvent 2)}$$

$$K = \frac{[\ce{S}]_2}{[\ce{S}]_1}$$

Solute $\ce{S}$ is found to have a partition coefficient of 15 between solvent 1 and solvent 2; i.e., with 15 times as much in solvent 2. Suppose $\pu{150 mL}$ of a $\pu{0.02 M}$ solution of $\ce{S}$ in solvent 1 is extracted with \ce{\pu{50 mL}} of solvent 2. What fraction of $\ce{S}$ remains in solvent 1? If three $\pu{50 mL}$ extractions are performed, what fraction of $\ce{S}$ remains in solvent 1?


texts: Did Mendeleev predict the existence of neutrinos?

texts:
According to this Wikipedia page, Mendeleev originally believed that the inert gases belonged in Group 0 (to the left of the alkali metals). Thus, helium would be placed in the second period to the left of lithium and argon would be placed in the third period to the left of sodium. Apparently this made sense to him at the time, since atomic theory was in its infancy (and Mendeleev didn't like it) and quantum mechanics was only a twinkle in the eyes of Planck, Bohr, and others.

Based on this arrangement, there is an open spot above helium and to the left of hydrogen for an ultralight inert gas he called "proto-helium". We now know that hydrogen must be the lightest known element, meaning Mendeleev was wrong about the placement of the inert gases. However, host of the other holes in Mendeleev's table were filled with real elements having properties nearly identical to what Mendeleev predicted.

Mendeleev predicted that proto-helium would have a miniscule mass (ca. $ 5.3\times10^{-11}$ amu) and high (near relativistic) velocity. Mendeleev believed that this near massless particle would be able to permeate all matter, rarely interacting chemically. He thought that they might be responsible for radioactive decay.

A neutrino is massless (or nearly so), and travels at the speed of light (if massless) or just under (if it has mass). Otherwise, it ignores the electromagnetic force, and so has no chemical interaction. Neutrinos are often produced during radioactive decay.

The relevant references point back to Mendeleev's original writings (in Russian), which I cannot access, so I cannot verify if he made a prediction about "proto-helium". Did he predict this particle? Has anyone previously made the connection between Mendeleev's proto-helium and neutrinos?


texts:
I have some questions regarding how to read a MALDI mass spectrum in a paper. I am a biologist by training, so I would like some analytical chemists to help me out.

The researchers ran a western blot, and immunoblotted for a protein of interest. They cut out this band from the western blot, subjected the protein to trypsin digest, and used these peptide fragments for MALDI-TOF analysis. I know for a fact there will be other proteins at the same apparent molecular mass which would have also been included in the analysis, which should be taken as contaminants in the resulting spectrum.

They produced a graph with the absorbance intensity x 1,000 on the dependent axis, and mass:charge (m/z) ratio on the independent axis.

The authors point to two peaks, which they say correspond to two peptide fragments from the tryptic digest of their protein of interest. They provide the supposed peptide fragment sequences and m/z ratio data for these two peaks, and I checked to make sure they are the same as reported. The authors expect to see two peaks: protein of interest is digested to two fragments, A + B.

I have two questions:

Peak 'A' and peak 'B' are of different intensities. Peak 'A' is 20-fold greater than peak 'B'. However, the tryptic digest must yield equimolar amounts of peptide fragments A and B. Is it possible that these intensity peaks can be 20-fold different? Wouldn't the absorbance intensity correlate to total analyzed peptide mass?
Is it normal to multiple absorbance intensity by a (seemingly arbitrary) factor, in this case, 1000? Since the absorbance intensity of peak 'B' is < 0.5 (after scaling up), could this represent noise rather than signal in the analysis?


texts: Would singlet oxygen in the engine cause a more efficient combustion?

texts:
Today someone told me about a new product — a mesh that is made from 5 different metals and when oxygen passes through it, singlet oxygen appears for a short period of time.
This mesh needs to be installed in a car air filter and the "better" oxygen creates a better combustion inside the engine. This is supposed to save fuel, give the engine more power etc.

My questions are:

Is it possible or this is just more one of the advertising lies that stores are trying to sell us?
if an interaction like this is something that can be acquired, will it really cause a better combustion inside the engine?
What are the downsides of interactions like this?
Can a mesh like that be permament without the need to replace it every couple of weeks or months?


texts: Aren't isothiocyanate and thiocyanate ligands monodentate?

texts: I will keep it brief; if I generalize what an assignment is telling me, then a metal complex with 2 (iso)thiocyanate ligands would be named "bis(isothiocyanate)...metal(oxidation state) or bis(thiocyanate)...metal(oxidation state). From what I can tell (1) (2), (iso)thiocyanate ligands are exclusively monodentate... so why do they get the bis-tris-tetrakis-etc. prefix? I thought that those were reserved for polydentate ligands (3) or ligands already containing one or more di-tri-tetra-etc. prefixes. Thanks!


texts: Xylene leaves a stain after evaporating?

texts:
I'm using xylene to clean a sacrificial polymer layer off of a PMGI surface in a ventilated hood.

For some reason, when xylene dries naturally from the surface there is a liquid stain that can be seen visibly on the PMGI. The stain can be removed by spraying with more xylene and then blowing it off with N2.

This stain will happen even if I apply xylene to a clean PMGI surface that has never been coated in the sacrificial layer so it isn't just incomplete cleaning. It seems like a contaminant is coming from the xylene.

My xylene is specified to have only 5 ppm of residue after evaporation. Is this enough to leave a visible stain after a thin layer evaporates?


texts: Do all decomposition reactions involve heat?

texts: When water decomposes into Hydrogen and Oxygen as in 2H2O—-> 2H2+O2 does this involve heat? Is it always implied that heat is involved in a decomposition reaction or does this just spontaneously occur? Chemistry 1st semester so excuse the fundamental nature of the question. Thanks


texts: Why is the speed of ideal gases mass dependent while the kinetic energy is not?

texts:
The rms speed of an ideal gas is $v_{\text{rms}}$ = $\sqrt{\frac{3RT}{M} }$ and the kinetic energy is $E_\text{k} = \frac32RT$. From this, it is concluded that the speed is mass dependent, while the kinetic energy isn't.

This doesn't make sense to me. I know the speed and kinetic energy for things other than ideal gases are surely mass dependent. The heavier an object is, the slower it is and will have a bigger kinetic energy. Why isn't this true for ideal gases?


texts: Why is the active space for the dinitrogen cation defined this large in my example?

texts:
I have a Molpro script which computes $\ce{N2^+}$ potential energies.

The significant part is the input for the wave function:

 {multi;
   occ,3,2,2,0,3,2,2,0;
   closed,1,0,0,0,1,0,0,0;
   wf,13,5,1;
   state,3;
 }

Why is the active space specified by OCC flag so large? It specifies 14 molecular orbitals, which means that both nitrogen should habe 7 atomic orbitals. Which atomic orbitals are additionally included?

The ground states of $\ce{N2^+}$ molecule has this electron configuration:

Thich can be specified as occ,3,1,1,0,2,0,0,0;.

What advantage does occ,3,2,2,0,3,2,2,0; have in the script and how can I understand and visualize those additional orbitals?

Explanation of OCC card

The OCC card in Molpro specifies symmetries of the orbitals in active space. In this case, they're specified in $D_\mathrm{}$ point group, according the following table:

$$D_\mathrm{2h}\\
\begin{array}{ccc} \hline
\text{No.} & \text{Name} & \text{Function}\\
1& \mathrm{A_g}    & s  \\
2& \mathrm{B_{3u}} & x  \\
3& \mathrm{B_{2u}} & y  \\
4& \mathrm{B_{1g}} & xy \\
5& \mathrm{B_{1u}} & z \\
6& \mathrm{B_{2g}} & xz \\
7& \mathrm{B_{3g}} & yz \\
8& \mathrm{A_u}    & xyz \\
\hline
\end{array}
$$


texts:
The Re2Cl8 2- ion is composed of two square planar ReCl4 units joined by four Re- Re bonds (quadruple bonding) and has D4h symmetry.

(a) Determine the symmetries (irreducible components) of the MOs responsible for the d-d metal-metal quadruple bonding in this molecule.

This is the entire question. However, I only need help genereating the irreducible representations. There are four sets of irreps that need to be generated that are based on the dz^2 orbital, dxy orbital, dyz orbital, and dxz orbital. I have only been able to determine the irrep for the dz^2 orbital. Here is what I did:

I transformed the dz^2 orbital under every symmetry operation from the D4h point group. (E, 2C4, C2, 2C2', 2C2'', i, 2S4, sigma h, 2 sigma v, and 2 sigma d. )
I got a reducible representation of E=2, 2C4=2, C2=2, 2C2'=0, 2C2''=0, i=0, 2S4=0, sigma h=0, 2 sigma v=2, 2 sigma d=2
Lastly, I used tabular reduction to get that dz^2 = A1g +A2u

For the other three d orbitals I can not seem to get the correct irreps.


texts: Why can Na not be used for the Wurtz reaction of compounds having an acidic group like alcohol or carboxylic acid?


texts: Which diagram shows the effect of catalysis on chemical equilibrium?

texts:
My course book has the diagram in figure (1) to represent the effect of a catalyst on chemical equilibrium. I drew the second diagram in figure (2).

When reviewing the diagram in figure (1), I observe the following mistakes:

The rate of catalyzed and uncatalyzed forward reaction  at equilibrium will be the same, which seems to be wrong because the value of rate constant of catalyzed forward reaction ($k_f$ catalyzed) more than the value of rate constant of uncatalyzed forward reaction ($k_f$ uncatalyzed), so the rate of catalyzed forward reaction at equilibrium = ($k_f$ catalyzed) $[A][B] > $ ($k_f$ uncatalyzed) $[A][B]$, so  it isn't the same as the diagram.
The rate of catalyzed forward reaction before equilibrium less than the rate of uncatalyzed forward reaction before equilibrium, which seems to be wrong too.

I need feed back about the diagram or both are wrong and about my reasoning.


texts: Deviation in bond angles (from standard $109°28'$ ) in hydrides of group 15

texts:
Here are the approximate bond angles for first three members of group15.

$\ce{NH3}$: $107°$

$\ce{PH3}$: $94°$

$\ce{AsH3}$: $92°$

As we move down the group the bond angles approach towards $90°$. I don't understand why there is such a major deviation from the standard angle of $109°28'$.

In the case of $\ce{NH3}$, the deviation is justified because of the presence of lone pair(lp-bp repulsions) , but for others, this much deviation is quite unexpected.

What causes this large deviation in angle?


texts: Why is the product of the reaction between iron and steam is iron (II, III) oxide and not iron (II) oxide or iron (III) oxide?

texts:
The reaction between Iron and steam in my textbook is given as this:

$$\ce{3Fe + 4H_2O <=> Fe_3O4 + H_2} $$

My question is why these following reactions are not possible or do not happen.
$$\ce{Fe + H_2O <=> FeO + H2}$$
$$\ce{2Fe + 3H_2O <=> Fe_2O_3 + 3H2}$$

I mean, how do the atoms know to form iron (II,III) oxide instead of Iron (II) oxide or iron (III) oxide in this reaction?


texts:
Would these answers be correct?
. Of 100% of the NaCL molecules dissociated, the Van't Hoff factor i, would be equal to 2 for NaCl. We assumed it equaled two when we figured out Kb of the NaCl solution.
a. Now we want it find the percent dissociation of the NaCl molecules by finding i using the equation below (use Kb = 0.512℃/m and your calculated molarity of NaCl solution ) show all work
 i = ( ▵Tb) / Kb x m)
i experimental = 1.8 [ {1.8/2} * 100% = 90% dissociation]    i theoretical = 2 (100% dissociation)

my answer - % dissociation = (1.74/2) *100% = 86.9%

b. . Do you feel comfortable in making the assumption that the NaCl in your experiment was completely dissociated? Why or why not?
I do not feel comfortable in making the assumption that that the NaCl in my experiment was completely dissociate because it lead to a 16.6% difference in my experiment

Thank you


texts:
I did a reaction and I measured the volume of gas produced against time. I need to find the rate constant of the reaction.

I am trying to plot a graph of ln(vol of gas produced) against time so that the gradient will be equal to -k so i can calculate the rate constant k. I am using the equation ln[A]t = -kt + ln[A]o

The problem is I can't plot ln0. I timed the reaction every 5 mins and gas wasn't produced until 15mins had passed. This means that the volume of gas produced for time values 0, 5 and 10 mins is 0cm^3, but ln0 doesn't exist.

How do I use my data to create a graph to calculate the rate constant?

My results were:

Time 0___5___10___15___20___25___30___35___40___45___50___55___60 ____(in mins)

Vol _0___0___0_____5___10___18____22___28___36___44___51____60____70___(in ml produced)


texts: Does H3CO3+ ion exist and what is its structure?

texts: Why doesn't $\ce{H3CO3+}$ ion exist and why doesn't the carbonyl group in carbonic acid $(\ce{H2CO3})$ seem reactive?


texts: Does correct bond lengths and angles imply that water is in a potential minimum?

texts:
So I come from the math community (so please disregard my ignorance on the topic).
If I have a water molecule and write the potential energy surface associated with it, my understanding is that I will find that the atoms configuration minimizes the potential energy function, so it will be a critical point of the potential energy surface.
My question is: suppose I have the building blocks of water, i.e 2 hydrogens and an oxygen, if it were the case by some magic, I added energy to the system that resulted the correct bond length and angles that correspond to water. Does that mean I have the water? That is to say ,geometrically, that I have taken a trajectory from the original potential minimum of just the original building blocks to a new potential minimum by adding energy. Since this new configuration has the correct bond length and angles, and potential energy, does that mean this atom configuration must indeed be water?
Thank you.


texts: Does benzene react with steam to create an alcohol?

texts: Benzene has a molecular formula of $\ce{C6H6},$ right? Surely it has some alkene-like properties because of the double bonds, so can it undergo a hydration reaction to create alcohol?


texts:
I’m not able to get the qualitative idea of azeotropic mixture.

What does it mean in simple language?


texts: Is it because for single electron atom, energies of all the orbitals with the same n are the same (degeneracy). For example, hydrogen atom energy levels, the electrons are degenerate and also, single electron atom is independent of angular momentum described by orbital number?


texts: How is the potential energy between two atoms measured?

texts:
In class, we learned about the interatomic potential graph.

How does one actually measure the potential energy between two atoms experimentally to ensure the graph is correct? What device is used?


texts: How to find entropy of chemical network reaction?

texts:
I have the following system of reactions:
$$
\begin{aligned}
\ce{X_1 + Y_1 &<=>[$k_{21}$][$k_{12}$] X_2} \\
\ce{X_2       &<=>[$k_{32}$][$k_{23}$] X_3} \\
\ce{X_3       &<=>[$k_{13}$][$k_{31}$] X_1 + Y_2} \\
\ce{X_2 + Y_3 &<=>[$k_{42}$][$k_{24}$] X_4} \\
\ce{X_4       &<=>[$k_{34}$][$k_{43}$] X_3 + Y_4}
\end{aligned}
$$
Here $\ce{X_1},\ldots,\ce{X_4}$ represent the state of the molecule that catalyzes the reaction, and $\ce{Y_1},\dots,\ce{Y_4}$ represent a reactant or a product that is consumed or produced by the reaction.
I need to find the free energy flow $J_G$ with respect to $\ce{Y}$ and the entropy generation $R_S$ with respect to $\ce{X}.$
Could anyone recommend the approach to this problem?


texts: How can you detect iron hydroxide or iron sulfide in quarried rocks?

texts: We have a quarry that produces some gray rocks that sometimes turn green, then orange and the color bleeds, making the rocks unsuitable for our purposes. But it can take up to 6 months out in the weather to see if the gray rock will end up having this problem. It's been suggested that the compounds causing the problem in the rock are iron hydroxide and iron sulfide. Is there a way to detect these chemicals sooner, or the chemicals that precede them, so that we don't have to wait 6 months to weed out the bad rocks? Would also appreciate knowing any resources that might help figure it out.


texts: Calculating Electrode Potential for Electrolytic Cell at Non-Standard States

texts:
Recently, I came across an interesting question that left me rather baffled. I was asked to calculate the minimum voltage required for the electrolysis of 1.0 M of NaCl in neutral solution using the following equation:

$$\ce{2H2O + 2Cl- (1M) -> H2 (1 atm) + Cl2 (1 atm) + 2OH-} (\pu{1*10^{-7}~M})$$

I was left in a dilemma, if I were to use the Nernst Equation, I would get:

$$E = E_0 - \frac{RT}{nF \ln Q}$$

$$E = -1.36-(+0.83) - 0.012839\times\ln \pu{(1*10^{-7})^2}$$

$$E= \pu{-2.19 V} - (-0.4135) = \pu{-1.78 V}$$

So $+1.78$ V is needed to drive the reaction, theoretically and assuming ideal conditions.

However, I went online to search a bit, and came across a line written in Wikipedia that

  ... the standard potential of the water electrolysis cell is −1.23 V at 25 °C at pH 0 ([H+] = 1.0 M). At 25 °C with pH 7 ($\ce{[H+]} = \pu{1.0×10^−7 M}$), the potential is unchanged based on the Nernst equation.

Does that mean that regardless of the pH, electrode potential for water is still the same, or is there some rule or standard definitions that I'm missing out?

In this case, does this scenario apply only to water, what about other cases where other reagents are used at non-standard states, will my original method (using the Nernst Equation) work?


texts: Does 6-methyl-2-(methylamino)pyrimidin-4-ol show aromaticity?

texts: Does this structure show aromaticity? Or does this not work with nitrogen?


texts: Role of NaI in Formation of Silyl Enol Ethers using Chloro(trimethyl)silane

texts:
I am forming silyl enol ethers using Chloro(trimethyl)silane (TMSCl), and below is an experimental protocol I am following

  Silyl Enol Ether Synthesis

  In an oven-dried 100 mL three-necked flask, Et3N (37.2 mmol) and carbonyls (30.0 mmol) were added. The mixture was stirred and heated to 30~35 ºC, and TMSCl (37.2 mmol) was added dropwise over 15 minutes. The mixture was stirred at the same temperature for 0.5 hour.
  A solution of NaI (37.2 mmol) in acetonitrile (35 mL) was added dropwise to the mixture over 0.5 hour and stirred for 1 hour. The mixture was then heated to 40-45 ºC and stirred at this temperature for 2 hours.
  The mixture was then cooled to room temperature and 30 mL of cold pentane was added. The mixture was poured into 30 mL of ice-cold water and extracted with pentane (15 mL × 2). The combined organic phases were dried over anhydrous Na2SO4, filtered and concentrated in vacuo. After distillation under reduced pressure, the products were obtained as colorless oils and stored at 0 ºC under an atmosphere of nitrogen for use.

I don't understand the mechanistic background of Step 2. What does NaI do?

Side question: when adding TMSCl in Step 1, I saw some white fume. I am guessing TMSCl was reacting with moisture in the air but what would be the product of H2O+ TMSCl? Is it HCl and TMS-OH?


texts: Rate constants and their relationship to quantum yields

texts:
Question

  A dye molecule has a singlet excited state lifetime of $\pu{0.85 ns}.$ The
  quantum yield of triplet formation is $35~\%.$ What is the rate constant for
  intersystem crossing from the singlet to the triplet excited state?

Solution

  $$\mathrm{QY} = \tau_\mathrm{isc}/\tau_0 = 0.35 = \tau_\mathrm{isc}/0.85$$
  Therefore
  $$\tau_\mathrm{isc} = 0.35 × 0.85 × 10^{-9} = \pu{0.297E-9} = \pu{0.3E-9}$$
  But $k_\mathrm{isc} = 1/\tau_\mathrm{isc}.$
  So, $k_\mathrm{isc} = \pu{3.3E9 s-1}$

My working

$$\phi_{T} = \frac{k_\mathrm{isc}}{k_0} = \frac{\tau_0}{\tau_\mathrm{isc}}$$

and then substituting the values

$$0.35 = \frac{0.85}{\tau_\mathrm{isc}},$$

hence

$$\tau_\mathrm{isc} = \frac{0.85}{0.35} = \pu{2.43 ns},$$

so

$$k_\mathrm{isc} = \frac{1}{\tau_\mathrm{isc}} = \frac{1}{\pu{2.43E-9}} = \pu{4.11E8 s-1}.$$

But apparently in the solution the quantum yield $\displaystyle\phi_T = \frac{\tau_\mathrm{isc}}{\tau_{0}}$ and then the working follows as above to yield $k_\mathrm{isc} = \pu{3.3E9 s-1}.$

Am I mistaken or is the solution mistaken?


texts: Does dissociation require energy to occur?

texts:
I assume spontaneous separation to ions of salt solution (or acid) requires energy to occur, right?

Where does that energy come from? Is it from the heat of the solution?

Now, if someone devised a way to draw potential energy from those separated ions, could he make this process continuous (assuming solution would draw heat from its surroundings), or would it eventually stop to work?


texts:
I'm taking an undergraduate level class on computer based drug design.  The class is more for biology students than people with a strong understanding in physics and computer science.

With that said, I'm having trouble discerning the difference between what molecular docking and scoring functions are.

To me they seem like they are the same thing since they have the same goal, which is to figure out which ligands have the strongest binding affinity to a target protein. But what are the different ways each method accomplishes that and when would each method be used if (to me) each method does the same thing? Is a scoring function a way to check the validity of a docking simulation, if so how?


texts: What closure relations can we use in molecular modelling?

texts: Following my question here about the BBGKY hierarchy I was wondering does anyone have any experience in using the method outlined. In particular how would I take an equation off the page and for some reduced phase space density or distribution function and start obtaining meaningful results and simulations? I understand that it is necessary to implement closure relations along the way. If anyone has experience in doing this sort of thing, could you outline (qualitatively) what steps I need to take etc.


texts: Why do we observe signal coalescence during dynamic NMR?

texts:
At low temperature, the rotation around the N-C amide bond of dimethylformamide is slow, so the two methyl groups are in different chemical environments. The H NMR thus shows a peak for each of the methyl groups.

As the T is increased, we see that the peaks begin to coalesce, until eventually they coalesce into a single average peak. The basic explanation is that, since the methyl groups are exchanging their chemical environment at a rate faster than the NMR time scale, they are considered to be within the same average chemical environment.

I am not very comfortable with this explanation, because it could also be argued that 50% of the time the methyl will be emitting signal A, and 50% of the time it will be emitting signal B - and the FID signal should still contain two signals. Alternatively, if the rotation is continuous, then I could expect a very broad peak extending from A to B.

My guess is that there is something about the structure of the signal and the Fourrier transform that I do not understand. Could someone help me out understanding why this coalescence occurs?

Thank you!


texts: Flame test color for non-ionic compounds

texts: What color would a non-ionic compound, such as $\ce{NH4OH}$ or $\ce{HCl}$, produce in a flame test? Is no color produced, or is it different for each compound?


texts:
The heavier the atom, the more unstable it gets, right?

That is not true about Uranium and we know it.
I wondered why. A brief explanation stated that since more neutrons are there in the nucleus there is more nuclear force to 238U than 235U. Seems legitimate, but then that should have been true about the other radioactive species. Again, we know that's not true.

So, either the explanation about the Uranium exception is not totally true or the principle of the heavier-atom instability (of course, exceptions occur at elements like U) is not a principle. Or maybe there is a relation between these two (nuclear force and atomic weight) which is beyond me.

My hunch is that the latter is true; searched some sites which had an answer to the question, but no acceptable results gained.


texts: How to interpret a luminescence intensity vs wavelength graph?

texts:
Luminescence is defined as the amount of light emitted by a atom. But what confounds me of this graph is the fact that all the peaks are of the same height. In addition, there are no peaks in between two peaks.
 why are the peaks of the same height?
Andwhy are there only six peaks, if photons can be emitted having the wave length of say, 110nm?

I am sure those are ultraviolet rays.


texts: Where does Oxygen come from in KO2 reaction with CO2?

texts:
$\ce{KO2 + CO2}$ gives $\ce{K2CO3 + O2}$

I think it should be from $\ce{KO2}$ as $\ce{2KO2}$ can split to $\ce{K2O}$ and $\ce{3/2O2}$. This $\ce{K2O}$ being unstable reacts with $\ce{CO2}$ to form $\ce{K2CO3}$.

Only problem is, is the first step possible?
Is $\ce{O2}$ released from $\ce{KO2}$ or $\ce{CO2}$?


texts: Dow's Process for the manufacture of phenol

texts:
When chlorobenzene ($\ce{C6H5Cl}$) reacts with aqueous ($\ce{NaOH}$) solution it first forms sodium phenoxide ($\ce{C6H5ONa}$), and then phenol upon reacting with $\ce{H+}$.

But my question is, why can't $\ce{Na}$ directly replace $\ce{Cl}$ from chlorobenzene by breaking $\ce{Na-O}$ bond instead of breaking $\ce{O-H}$ bond?


texts: Can a reaction have carbocation resonance followed by a hydride shift?

texts:
Consider 5-methylcyclopentadiene:

If HX attacks at carbon 1, we have an option of 1,2 or 1,4 (carbocation resonance) addition. In the case of 1,4 addition, since the carbocation (secondary) will be one bond away from a tertiary carbon, will there be a hydride shift, thus yielding in 1,5 addition?

In essence, can you have both carbocation resonance and a hydride shift in one reaction? Or is it that once a carbocation is resonance stabilized, there is no need for stabilization via hydride shift?


texts: Why are electrolysis cell plates turning a brown color?

texts:
I have been experimenting with electrolysis for producing oxyhydrogen and using potassium carbonate as an electrolyte.  After several hours of electrolysis, I notice the plates began to tarnish and after 24 hours, are now dark brown.  The plates are made of 316 stainless steel and the electrolyte remains clear.

When I chose to use K2CO3; I thought that it would not decompose during electrolysis but now I suspect that it is decomposing and electroplating the stainless steel plates with carbon. If this is the case; will this have an adverse effect on the plates ability to conduct and produce oxyhydrogen? Also, is CO2 being produced?


texts: In 1 dimension, the curvature of Ψ = K.E. of wave. Is this the case for 2 dimensions and 3 dimensions also? Moreover, is curvature of Ψ = K.E. of wave = 2nd derivative of Ψ?


texts: Is the Fischer Esterification mechanism very simplified?

texts:
Example mechanism:

Is that very simplified, or is that pretty much what is very likely happening at the molecular/atomic level when you do the reaction in real life?  (Of course besides the free $\ce{H+}$, that is obviously hydronium, protonated alcohols, or the acid itself.)


texts: Is water an Arrhenius acid? We define Arrhenius acidity with respect to water, but what will water itself be? It can donate $\ce{H+}$ as well as $\ce{OH-}$.


texts:
Are the oxides of nitrogen (such as $\ce{NO}$ and $\ce{NO2}$) emitted from the exhaust of a diesel engine soluble? If so, in what solvents is it soluble?

I want to analyse the nitrogen oxides in the exhaust gas of a diesel engine. Is it possible to collect the gas by solvent extraction method?


texts: If the formula for change in enthalpy is ΔH=ΔU+pΔV, and ΔU = q - pΔV then shouldn't the formula be simplified to ΔH = q regardless of whether the volume or pressure is constant? Is this only true when pressure and volume is constant?


texts: Why is copper (II) oxide used in quantitative analysis of carbon?

texts:
What is the significance of using cupric oxide in the quantitative analysis of carbon?

As far as I can tell from my research, only $\ce{CuO}$ is used to oxidize carbon to $\ce{CO2}$. Why can't we use other oxidants like $\ce{HNO3}$ or other metal oxides such as hematite? Is the use of $\ce{CuO}$ prevalent because of low cost or does it has some other special property?


texts: How do ion–dipole bonds manage to break apart an ionic lattice?

texts: I was reading this answer and its reasoning behind the dissolution of NaCl seems to lie in entropic favorability. However, as it states, many, if not most, dissolution reactions are favored by enthalpy (i.e. exothermic). Reasoning with energy alone, without entropy, it seems that ion–dipole forces are greater than the Coulombic forces between the ions themselves. However, how can this be? Aren’t ionic bonds second only to covalent bonds? How can water molecules form ion–dipole bonds with ions that are stronger than the ionic bonds within the lattice?


texts:
At $25~\mathrm{^\circ C}$, $10.24~\mathrm{mg}$ of $\ce{Cr(OH)2}$ are dissolved in enough water to make $125~\mathrm{mL}$ of solution. When equilibrium is established, the solution has a $\mathrm{pH}$ of $8.49$. Estimate $K_\text{sp}$ for $\ce{Cr(OH)2}$ (Ans : $1.47\times 10^{-17}$)

I have calculated it but not have the same answer as this.
I tried it this way:

$\mathrm{pH}$ is $8.49$, then $\mathrm{pOH}$ is $5.51$. I use this formula: $\mathrm{pOH} = -\log[\ce{OH}]$
The $[\ce{OH}]$ is $10^{-5.51}$
Find molarity $\ce{Cr}$: $(10.24\cdot(1/1000)\cdot(1/86))/(0.125)=9.525\times 10^{-4}$
Substitute into $K_\text{sp} = [\ce{Cr}][\ce{OH}]^2$

But after I substitute value of $[\ce{Cr}] = 9.525\times 10^{-4}$ and $[\ce{OH}]$ of $(2\times 10^{-5.51})^2$, I get answer of $3.6\times 10^{-14}$.

Where have I gone wrong? Any Suggestions?


texts:
I have rarely seen any chromium $(\ce{Cr})$ square planar complexes and I have been told that $\ce{[Cr(CN)4]-}$ is tetrahedral.

So, if the statement is actually correct, are there any other known examples of square planar complexes of chromium?


texts: What is the yellow precipitate formed from reacting diamminsilver fluoride and potassium iodide?

texts:
These two compounds, silver diamine fluoride and potassium iodide (actually a solution called Lugol’s solution), are being used together in dentistry.

When combined they form a yellow precipitate. I cannot find any articles that state specifically what is formed. I would like to know what the yellow precipitate is and the steps involved in the reaction of the two chemicals. The equation is:
$$\ce{Ag(NH3)2F + ssKI -> ?}$$


texts: Mechanism of hydroboration oxidation reaction

texts:
I know that the hydroboration reaction is used to add $\ce{H2O}$ to the double bond in an anti-Markovnikov fashion.

I went to the Wikipedia page and found the following mechanism:

But I could not understand as to why the addition is syn.


texts: Why does the rate of the reaction decrease with an increase in temperature?

texts:
Why does the following reaction

$$\ce{2NO + O_2 -> 2NO_2}$$

have negative reaction coefficient, i.e., why does the rate of the reaction decrease with an increase in temperature ?

I have been taught that this is the only reaction that has this property.


texts: Can the Galvanic cell use a different ionic solution?

texts:
It makes sense that
water-soluble salt when dissolved in water, they conduct electricity. Then when using the old method of the Volta Battery(using copper and zinc) with a different water-soluble salt dissolved in water, can it make electricity too?
Plus, If I use a ammeter to check its current, then does all of the water-soluble salts do not go to zero?


texts: How do Invert Sugars deter crystallization in Sucrose solutions?

texts:
Invert Sugars, by themselves, are notorious for their reputation to crystallize fast (think honey), but their addition to solutions of Sucrose (think simple syrup) deters the crystallization process. Take Caramel, Sucrose that has already decomposed into Fructose and Glucose and subsequently into the numerous products of caramelization: It crystallizes or, at least, turns grainy without the addition of Invert Sugars or a weak acid (Citric, Tartaric) (although the crystallization process is retarded, taking days even at low temperatures). Why do Invert Sugars deter crystallization when added in small quantities in solutions such as Caramel, which, I think, do already contain Invert Sugars as they are already largely decomposed? I would like to know of how Invert Sugars physically interact with the other sugar molecules and prevent them from coming together, even though they're not really resistant to crystallization (as pointed out above).

An additional (and optional) question: Why does the rate of cooling of a sugar solution affect its crystallization? So, while a slowly cooled solution crystallizes more, a faster cooled solution is more likely to crystallize less spontaneously.


texts: How can subtilisin still function without its catalytic triad?

texts:
I read chapter 9 in the book Biochemistry (5th edition), by Berg, Tymoczko, and Stryer (provided in the NCBI site here). It describes the mechanism of action of the chymotrypsin enzyme. The catalysis is performed through the catalytic triad consisting of serine-195, histidine-57, and aspartate-102.
What intrigued me is the following section on the related enzyme subtilisin, which also has a catalytic triad but with different residue numbers:

9.1.5. The Catalytic Triad Has Been Dissected by Site-Directed Mutagenesis
[...] As expected, the conversion of active-site serine 221 into alanine dramatically reduced catalytic power. [...] The mutation of histidine 64 to alanine had very similar effects. [...]
These observations support the notion that the serine-histidine pair act together to generate a nucleophile of sufficient power to attack the carbonyl group of a peptide bond. The conversion of aspartate 32 into alanine had a smaller effect, although the value of $k_\mathrm{cat}$ still fell to less than 0.005% of its wild-type value.

My problem is in what it says next:

The simultaneously conversion of all three catalytic triad residues into alanine was no more deleterious than the conversion of serine or histidine alone. Despite the reduction in their catalytic power, the mutated enzymes still hydrolyze peptides a thousand times as rapidly as does buffer at pH 8.6.

A graph of the relative rates can be taken from this link:

My question is: how can it be that after replacing all the triad residues, the enzyme still possess such a great catalytic activity? What is the mechanism behind that phenomenon?


texts:
Does smoldering combustion only occur in an environment where oxygen levels are low? Will it always transition into flaming combustion (whenever there is ample supply of oxygen?

Or can it keep smoldering even when there is an ample supply of oxygen?

Some smoldering areas in forests continue to smolder for years where there is an ample supply of oxygen -> it's open air.


texts: Why isn't aluminium involved in biological processes?

texts: There are so many biological processes which are dependent upon ions of lighter metals (upper part of periodic table) such as $\ce{K+}$, $\ce{Na+}$, $\ce{Mg^{2+}}$ and even early transition elements ($\ce{Fe}$, $\ce{Mn}$, $\ce{Cu}$, $\ce{Ni}$), but I haven't yet come across dependence of biological phenomena on aluminium. Is this because there is less use of trivalence or is there some other reason?


texts: If I have an igneous rock shown by geologic study to be 10,000 years old, approximately what percentage of the atoms (or protons, etc) in the rock might be the same ones that were in it 10,000 years ago?  Is it reasonable to even think of a "particular", individual atom?  Is it the "formation" of particles that persists over time, or is it the actual "matter"?


texts: What are D_b and D_a in the Generalized Fugacity Coefficients table?

texts:
I've been referring the book: Chemical Process Principles: Part-II Thermodynamics. I found a table that gives me fugacity coefficients in a tabular form corresponding to various reduced pressures and reduced temperatures. This is it:

I dont know what the $D_b$ and $D_a$ in the table. In the bottom of the table, I see:

$$\left(\frac{f}{p}\right)^{'} = \left(\frac{f}{p}\right)(10^{D({z_c}-0.27)})$$

Is the $D$ in this equation related to the $D_b$ and $D_a$ in the table?


texts: Why does molecular oxygen absorb in the IR range?

texts:
I am studying spectroscopy and know that $\ce{CH4}$ and $\ce{CO2}$ are known as greenhouse gases because they are IR active. This is because they have asymmetric stretch or bend vibrational modes which result in electric field changes and involves emission or absorption of IR light.

But, $\ce{O2}$ is a symmetric molecule and should be IR inactive. I am wondering why there are still strong $\ce{O2}$ absorption bands in the IR range if it is expected to be transparent to IR light?


texts: What compound(s) contribute to bleach's smell and are they dangerous?

texts:
Just a few hours ago, I had to deal with a mold problem on some untreated wood and was told by a hardware store worker that bleach was an effective way to deal with the problem, following up with some wood filler paste. I did as I was told and left the room airing out with a window open and two fans running for multiple hours. In fact, they are still running right now; I was surprised to find that the smell of bleach was still lingering in the room. I also noticed that some bleach had gotten onto my hands and they smelled of bleach even after multiple washings with soap and water.
What chemical(s) are causing the smell to linger, in the air as well as on surfaces? Are they particularly dangerous, or just relatively mild product(s) from the degradation? Is there a way to eliminate the smell without producing harmful products?
I used a spray bottle with undiluted bleach and did not wipe anything up with damp paper towels. Even so, I assume that it isn't really too dangerous, given that it is unlikely I used more than 10 mL of the stuff, and there is no way most of that 10 mL is still aerosolized and/or inside the room. Regardless, I have looked on other questions in this StackExchange, and a lot of them talk about the breakdown of bleach, but I just want to be certain the room is safe enough to sleep in tonight. Thanks!
EDIT: After removing the cloth used to clean the wood (I don't know why I left it in there), the smell is less pungent but still noticeable. Figured this might be useful information to include.


texts: Moles of Reduction Product in the Oxidation of Aluminium by Nitric Acid

texts:
If, in 2 M $\ce{HONO2}$, 2 mols $\ce{Al (s)}$ are oxidized to $\ce{Al(OH2)6^3+ (aq)}$, mols of reduction product hydrogen is
  (a) two;
  (b) three;
  (c) four;
  (d) five;
  (e) six.

Regarding the above question, how would one solve it?

Would it be valid to simply say that I know that 6 electrons are being transferred because we have this skeleton equation (balanced for charge):

$$\ce{Al -> Al(OH2)6^3+ + 6 e-}$$

And given that 6 electrons are being transferred and that hydrogen is a reduction product, we must obtain hydrogen from some source in this system. The source would probably be hydronium ion, since hydronium ion is less stable than water. Plus abstracting protons from water to form hydrogen gas wouldn't make much sense in strongly acidic solution (we'd be forming hydroxide ions as well)! And knowing the following reaction:

$$\ce{2 H+ + 2 e- -> H2}$$

Can we just say since we know that 6 electrons are being moved, and that hydrogen gas is a product, we know that the immediately above reaction is occurring, and according to its stoichiometry, 2 moles of electrons yields 2 moles of hydrogen gas?


texts: Why are complexes of type MA3B3 not optical active?

texts:
Complexes of type $\ce{MA3B3}$ have two geometrical isomers, namely:

fac-isomer
mer-isomer

If we look closely at the mer-isomer, it has a plane of symmetry, so it is optically inactive.
But the fac-isomer has no plane of symmetry. Still, it is optically inactive, why?
Being a 12th grader, I wonder where am I wrong in my understanding of optical isomerism in coordination complexes.


texts: Can I use harvested plants to gain electric power?

texts:
I was just thinking - plants are mostly acid. Even grass is quite acid. Could you create battery cell from squashed plants (after cutting them in pieces)?

How much effective would it be? Could you compare it to solar panels? Would you need to replace electrodes often?


texts: derivation of enthalpy internal energy relationship

texts:
A question asks us to derive a relationship between the enthalpy change and the change in internal energy for a reaction.
Now, I know the relationship is:
$\Delta H = \Delta U + V \Delta p + p \Delta V$
But i thought enthalpy was conveniently defined this way ( not derived) so that enthalpy change equals heat change at constant pressure. So which


texts: If phosphorus trioxide is present in the atmosphere of Venus, could it not react with water to form (sufficient) phosphorous acid?

texts:
Sufficient phosphorous acid to be decomposed in the measured quantity of phosphine ?
From Phosphine gas in the cloud decks of Venus:

We also rule out the formation of phosphorous acid ($\ce{H3PO3}$). While phosphorous acid can disproportionate to $\ce{PH3}$ on heating, its formation under Venus temperatures and pressures would require quite unrealistic conditions, such as an atmosphere composed almost entirely of hydrogen.

But according to Vega mission results and chemical composition of Venusian clouds there is $\ce{P4O6}$ in the atmosphere which according to Wikipedia would react with water to form phosphorous acid.
However there is supplementary information in the chapter "Equilibrium thermodynamics in the atmosphere and surface" at the end of the article "Phosphine gas in the cloud decks of Venus":

As an example of our approach, we present a calculation for phosphorous acid ($\ce{H3PO3}$). This compound will spontaneously decompose on heating to form phosphoric acid  and phosphine; this is a standard laboratory method for making phosphine. Phosphorous acid is not stable in gas phase, but could in principle be formed in cloud droplets by reduction of phosphoric acid.

Edit for some additional informatiom.
Also from the supplementary information (page 13):

Reactions of $\ce{P4O6}$, $\ce{P4O10}$, $\ce{H3PO4}$ and $\ce{H3PO3}$ were considered (the last of these only in solution phase in the clouds),..

So not considered was the possible occurence of $\ce{H3PO3}$ below the clouds.
The Recent Evolution of Climate on Venus (page 23) states:

The evaporation of $\ce{H2SO4}$ occurs at about 48 km, the average cloud base.The vapor phase continues to exist down to 432 K (38 km), where it is thermally decomposed.

So below 38 km, and above 160 ⁰ C there would be water in the gas phase, free from sulfuric acid, that could react with $\ce{P4O6}$.
Could have that possibility been ruled out for some reason ?


texts: Why does dissolved oxygen concentration decrease with increasing atomic number of metals?

texts:
I am looking at how metal ions ($\ce{Fe^2+}$, $\ce{Ni^2+}$, $\ce{Cu^2+}$, $\ce{Zn^2+}$,  and $\ce{Ag+}$) affect the biochemical oxygen demand in water and used the Winkler's method to find out the oxygen concentration of each solution. I graphed this with oxygen concentration ($y$ axis) and increasing atomic number ($x$ axis) and found that the order: $\ce{Fe^2+}$, $\ce{Ni^2+}$, $\ce{Cu^2+}$, $\ce{Zn^2+}$,  and $\ce{Ag+}$ had decreasing value of oxygen concentration (almost a decreasing exponential graph like an "l" shape rather than a straight negative linear line) but I do not really know the specific chemistry behind it.
I thought with an increase in atomic number, there will be an decrease in dissolved oxygen concentration because as the atomic number increases, the proton number increases. The greater nuclear charge attracts the water molecules more and a ligand can be formed. Thus, as the atomic number increases, the metal ion will form a ligand with water molecules more easily, and the dissolved oxygen concentration will decrease as more water molecules will form ligand with the metal ion.
But I am confused because with increasing atomic number, the atomic size gets smaller and wont that make it harder to form a ligand bond with water?


texts: What happens to the colour change of an equilibrium reaction when one of the reactants begins to form a complex? (specific problem included)

texts:
I'm working on an equilibrium lab/quiz for my chemistry class and I came across this reaction:

$\ce{Fe^{+3}\ \text{(pale yellow)} + SCN- <=> FeSCN^{+2}}\ \mathrm{(red)}$

Then the lab said a stressor was added: $\ce{Na2HPO4}$ was added to the equilibrium reaction -- which formed a complex with some of the $\ce{Fe^{3+}}$ ions.

This stressor changed the solution's color from an orange to a pale-yellow as seen in the image below:

(left: before stressor ($\ce{Na2HPO4}$) was added; Right: after stressor ($\ce{Na2HPO4}$) was added)

I was asked to explain why that after $\ce{Na2HPO4}$ is added (which actively forms a complex with the iron ion ($\ce{Fe^{3+}}$)) the system/solution turns increasingly pale-yellow.

Basically I want to know what is happening chemically when $\ce{Na2HPO4}$ is added, and more specifically why their is the resultant color change from orange to pale-yellow.

My basic confusion: wouldn't the formation of a complex between $\ce{HPO4^{2-}}$ and $\ce{Na2HPO4}$ actively remove the $\ce{Fe^{3+}}$ ions responsible for the pale-yellow color of the solution? Making the solution less rather than more yellow?

Thanks!


texts: How does ring size affect SN2 reactions?

texts:
Suppose we have to compare the $\mathrm{S_N2}$ reactivity order for cyclopropyl and cyclopentyl chloride. How can we do that?

I think that cyclopentyl should be more reactive towards $\mathrm{S_N2}$ because of larger bond angle and therefore lesser steric hindrance to the atttacking nucleophile but I am not sure about this.

Also, can the trend be generalised i.e. does increasing ring size lead to faster $\mathrm{S_N2}$?


texts:
Question

Attempt
Since CN is better nucleophile than both OMe and Cl, I believe that it should replace both. But none of the options match my answer. Where am I wrong? Please help.


texts: How to compare the acidity of this multicyclic hydrocarbon to the acidity of cyclopentadiene?

texts:
This is the question:

  Which one is more acidic?

According to me, cyclopentadiene should have been the answer, as losing a proton would make it aromatic; whereas the first option doesn't need deprotonation to be aromatic, it already is. However the first option is given as the correct one.

I have come up with the following reasonings as to why the first option should be more acidic:

Deprotonation might impart aromaticity to the pentagonal rings too which would act as the driving force to lose the proton.
The negative charge on central carbon (after deprotonation) would be in conjugation with the $\pi$ electrons of the three rings which would make the entire molecule planar and hence reduce the strain on the three bonds that are directly linking the benzene rings. This could be another driving force for deprotonation.

The second reasoning seems much convincing to me but I fail to understand how can I compare that factor with the aromaticity factor involved in cyclopentadiene.


texts: Assigning the 13C NMR spectrum of bromobenzene and 4-bromobenzophenone

texts:
I've been trying to assign the peaks of 4-bromobenzophenone (I have the peaks, just need to assign them to the correct carbons), but my assignments and what it should be don't seem to agree. As part of this, I tried (and failed) to correctly assign the NMR of bromobenzene.

Bromobenzene's spectrum:
https://www.chemicalbook.com/SpectrumEN_108-86-1_13CNMR.htm

Bromobenzene, my labelling of the carbon environments: https://imgur.com/a/NiVUd

Here's what I've thought so far for bromobenzene:

The halogen atom is a deactivating substituent for the cyclic ring. The two effects of the halogen are the inductive and conjugative effect.

1) The inductive effect falls away with distance. Therefore, carbon environment 2 experiences a stronger inductive effect than carbon environment 3, and likewise for carbon environment 3 compared to 4. Therefore, due to the inductive effect only, carbon 2 has a more positive, and so higher shift than carbon 3, which has a higher one than 4 i.e. 2>3>4.

2) The conjugative effect acts mainly on carbon 2 and 4 by resonance arrows (as bromobenzene is ortho/para directing). Therefore, carbon environment 3 has a more positive environment, and therefore higher shift, than 2 and 4 i.e. 3>2=4

However, when it comes to carbon 1, it is directly attached to the bromine. The inductive effect is strongest for the carbon 1, therefore, and the conjugative effect isn't the same strength here as for carbons 2/4 and so carbon 1 should be the highest shift?

According to my rationalisations, carbon 1 should have the highest shift, followed by 2/3 (order is hard to determine) and then 4. This is not seen in the spectra.

Where am I going wrong then? I don't see how you can (qualitatively) predict that:

1) carbon environment 1 actually has the lowest shift

2) carbon environment 2 has a higher shift than carbon environment 3 i.e. the increased inductive effect outweighs the increased conjugative effect for carbon environment 2.


texts: What are the enthalpy and entropy contributions to carboxylic acids dissociating in water?

texts:
Carboxylic acids such as acetic acid do not dissociate much in the gas phase. In aqueous solution, however, they act as acids (proton donors).

$$\ce{CH3COOH(aq) <=> H+(aq) + CH3COO-(aq)}$$

Are reaction entropy and reaction enthalpy positive or negative, and what are there magnitudes?

In the gas phase, we have clear expectations:

$$\ce{CH3COOH(g) <=> H+(g) + CH3COO-(g)}$$

The reaction enthalpy will be positive (we need to break a bond) while the reaction entropy will be positive (more gas particles). As the reaction does not go forward in the gas phase, the enthalpic contribution must be of larger magnitude.

So another way of stating the question is to ask what the effect of solvation is on the enthalpy and entropy of reaction.


texts: Basic Intro to Quantum Chemistry. Two Slit Experiment and Bohr Model

texts:
We just learned about the 2 slit experiment in Quantum Chemistry today, where electrons behave as waves when nobody is looking and behave as particles when they are being observed.

So, what would happen If I were to observe an atom (such that all it's electrons now behave as particles instead of waves) for a long period of time?

I know that real atoms have wave electrons, but when you observe them, don't they "turn" into particle electrons and obey Newtonian law like the 2 slit experiment? So what keeps the electrons from falling into the nucleus when you observe them? I was considering how the earth doesn't "fall" into the sun because of a momentum perpendicular to the centripetal force, but the mass of an electron is so much smaller than the nucelus, I'm not sure it will work.

If anyone can give a simple explanation that would be great, I asked the professor and he only said the the Bohr model was inaccurate and it's difficult to observe electrons.

Thanks in advance.


texts:
I have some chemistry equipment but I am not sure what it is for; I think it may be apparatus for measuring elevated boiling points. I have included a drawing of how I think it should go together. Basically, it consists of a conical flask connected to a graduated boiling tube (D) (for volume); the conical flask has a two-holed bung: one aperture contains a delivery tube (B) connected to the boiling tube (there are small holes in the delivery tube within the boiling tube, and the other has a glass cylinder passing vertically upwards, which is angled at the bottom (A; this might be to do with maintaining atmospheric pressure?). The boiling tube has a bulb on the upper portion. The boiling tube is contained within a larger glass container (C). There is an aperture in the boiling tube opening into the larger container (E). The larger container has a spout at the bottom.

So the liquid in the conical flask is heated and passes through E and condenses in the boiling tube (D). I am not sure if the delivery part, E, has to be lower, so that as the liquid condenses the delivery tube becomes submerged in the liquid. Then I am guessing the liquid that condenses in the boiling tube will at some point be hot enough to pass from the boiling tube, through aperture E into the larger container (C). Quite what is happening, I am not sure...

If anyone has seen this equipment and knows how it works, that would be much appreciated.


texts: How does Hofmann elimination work in this reaction?

texts:
In my Chemistry class, we were given this question to solve, and I'm not sure I fully understood the solution.

I understand that since the substrate is bulky, Saytzeff elimination can't happen, so it has to be Hofmann. What I don't understand is how it happens here. Where does the base attack the substrate? Essentially, I'd like to know the mechanism of the reaction.

Also, our teacher made us write that had all three substituents on the nitrogen atom been methyls, Saytzeff elimination would have been followed as there wouldn't have been any other choice. However, even if all three substituents were methyls, wouldn't the substrate still be bulky? Why would it follow Saytzeff elimination?


texts: Cheap but efficient disinfectant / biocide for home lab

texts:
EDIT

I am forced to reword my question about a chemical mixing ratio.

I have seen in Wikipedia that peroxide ($\ce{H2O2}$) and Acetic Acid can be mixed to Peracetic acid - this is an equilibrium.

I have also seen in Wikipedia that peracetic acid mixed with acetic acid will be explosive - in other words: If I don't get the mixing ratio just right then the "peracetic acid" will actually be "peracetic acid dissolved in acetic acid". I need to avoid this situation.

I have also read in Wikipedia that "thinning" the peracetic acid will shift the equilibrium and so this might end up in an explosive solution - I need to avoid this.

I have also seen at amazon.de that peressigsäure/alkohol is widely used as a disinfectant and I suppose the ratio of ethanol should be at 69% in order to kill most any microbes.

I need to mix a weak solution of $\ce{H2O2}$ and acetic acid and 69 % ethanol so that the peracetic equilibrium is held to be non explosive. And I also need to mix a more potent solution of $\ce{H2O2}$ and acetic acid and 69 % ethanol so that again, the peracetic equilibrium will fit and not be explosive.

As far as I understood it is not done by having the potent solution in the fridge at 0 degree Celsius and on demand simply thinning the potent solution to a weaker disinfectant - the peracetic equilibrium would then shift and it might become explosive.

Sorry, I am not really fit to calculate concentrations in Vals and Mols - but I could of course deal with any complex mathematical formula (on paper or on the calculator - or I could even code a small mixing calculator in java or c#).

So I would ask you to give me the right formula for my problem:

Component A = 12 % $\ce{H2O2}$

Component B = 20 % Acetic Acid

Component C = 98 % Ethanol

Component D = $\ce{H2O}$

AND I need 1 liter of mixture so that Alcohol appears with 69 VOL % and that peracetic acid appears with $x$ % ($x$ between 2 and 10) and no acetic acid will be in the mixture aside from the equilibrium.

I could then simply vary the $x$ (the conecntraction of peracetic acid) in the formula and mix as needed.

please, show me how to calculate the concentrations.
thanks!


texts: What's a good measure of the Eigen-ness of a wavefunction?

texts:
Just wondering if someone can recommend an easy-to-compute measure for the Eigen-ness of a wave function, such as the wave functions computed using ab initio method?

For a wave function solved using a small basis set, the Eigen-ness should be smaller than that of wave function computed using larger basis set.

Naturally for arbitrary wavefunction $|\psi>$ one can compute :
$<\psi | (H/E-1)^2 | \psi>$,
where E is the expectation value, which is the dispersion of the energy. This, however, is too difficult to implement.


texts: Using a H NMR spectrum to determine the structure of a protein supplement

texts:
This question is about the H NMR spectrum of creatine.
Creatine is a supplement taken by athletes to increase body mass. Recently, supplements containing derivatives of creatine have been marketed. These are usually more lipophilic in an attempt to improve uptake.
The 1 H NMR spectrum of one of these supplements in D2O is shown, with some parts magnified:

This particular supplement exists in an ionised form at pH1 but does not exist in an ionised form at pH 12 (I am unsure about this and will come back to it in my question below!)
Using this information we are asked to suggest a structure for the supplement. I was almost right. The answer is:

The mark scheme says that three things can be extracted from the NMR spectrum and the information given:

My question(s):

I don't understand the relevance of the pH statement. How does that relate to the structure? How does that relate to the ester group? (this is mentioned in the mark scheme which is attached just above this)

How can we use the integrals to calculate that there are 10 C-H protons? I measured the heights of the traces and got, 2.7cm, 4.75cm and 6.9cm but I'm not sure how this leads to '10 C-H protons'...

Would really appreciate help on this question and a breakdown of the key points discussed. Many thanks!


texts: Significant figures in conversion factors?

texts:
Example: I have $\pu{64 cm^{3}}$ of milk. How much is that in gallons?

When I use the conversion factors $\frac{\pu{1 mL}}{\pu{1 cm^3}}$
$\frac{\pu{1L}}{\pu{1000 mL}}$ $\frac{\pu{1.0567 qt}}{\pu{1 L}}$ $\frac{\pu{1 gal}}{\pu{4 qt}}$.

I know the final answer should only have two significant figures, but how many significant figures should the intermediate conversion factors have?

I have heard that:

conversion factors should have one more sig fig than the least precise measurement. (So three in this case)
But I also heard that we shouldn't round anything until the end.
(So use all 5, and round after conversions are complete)

The reason why I got confused is because of my textbook:


texts: What exactly happened when I added KOH to hydrogen peroxide?

texts:
I recently added a potassium hydroxide, $\ce{KOH}$, pellet to a small droplet of hydrogen peroxide (30 %), $\ce{H2O2}$. You could clearly see the potassium hydroxide dissolving in the droplet when instantaneously the solutions began to fizz strongly (boil and/or release oxygen gas, I'm not sure) and release a lot of heat.

I'm not sure what happened, but I've got a few ideas of what might have happened:

There is some kind of reaction between the $\ce{KOH}$ and $\ce{H2O2}$.
The $\ce{KOH}$ released a lot of energy when dissociating into the aqueous solution and then boiled the water, maybe reaching the temperature of  150.2 °C in which it also triggered the decomposition of $\ce{H2O2}$ into water and oxygen gas.
On Wikipedia I read:

  The rate of decomposition increases with rising temperature, concentration and pH.

So when $\ce{KOH}$ is dissolved, the solution has a high pH and this might trigger the decomposition of hydrogen peroxide

I did notice after a pH test that the plastic lid on which I had condensed some of the evaporated water had a very high pH, so this would most likely contain some dissolved potassium hydroxide.

In case a reaction happened, what could that specific reaction be?


texts: Why does Devarda's alloy include copper?

texts:
Devarda's alloy is used in the detection of nitrates. However, judging by the reaction equation, only aluminium plays the role of reducer:

$$\ce{3NaNO3 + 8Al + 5NaOH + 18H2O -> 8Na[Al(OH)4] + 3NH3(g)}$$

Why does it contain copper? Is copper also capable of acting as a reducer here?

I know that zinc, the third component, is capable of that.


texts:
From the information from Google the radius of $\ce{Ca^2+}$ cation is $100 \,\pu{pm}$ and of $\ce{F-}$ anion is $132\, \pu{pm}$, so essentially $\ce{F-}$ ion should form the Bravais lattice (FCC/CCP) as it is larger in size and $\ce{Ca^2+}$ should go to the tetrahedral voids but in reality it is just opposite.

How can smaller sized calcium cation form the Bravais lattice?

(The data has been taken form first results form Google search)

Please do correct me if I am conceptually wrong somewhere.


texts:
I understand thermodynamics in a physicsy way - at the level of Callen's Thermodynamics. However, my chemical thermodynamics is quite rusty: concepts like fugacity and activity coefficients are only vaguely familiar from undergrad courses.

I'm looking for a well written, rigorous and succinct guide to advanced chemical thermodynamics - at the level where I can read papers on ENRTL equations of state, or understand Pitzer models fully. If it is geared towards chemical engineers (like myself) that would be a bonus.

Basically, I consider Callen's book a classic, and wonder if there's anything that good within chemical thermodynamics.

Does such a book exist? Thanks


texts: Is this rearrangement in carbocation possible?

texts:
Generally, in the following type of reactions, positive charge on $\alpha$-Carbon causes ring expansion, but in the following example positive charge is formed on $\beta$-Carbon and the cation is cyclo-propyl methyl.

So is the above rearrangement even practically possible?


texts: What is the correct way to calculate the rate constant for the reaction of NO and O2?

texts:
The following data are given for the reaction of $\ce{NO}$ and $\ce{O2}$:

$$
\ce{2NO + O2  ->  2NO2}
$$

The the reaction is second  order  in $\ce{[NO]}$ and first order in $\ce{[O2]}$, and the rate of disappearance of $\ce{NO}$ is $2.5 \times 10^{-5}~\mathrm{mol\over L\,s}$ at the instant when $\ce{[NO] = [O2]} = 0.01~\mathrm{mol\over L}$.

The question asks me to calculate the rate constant.

I've thought of two ways of approaching the calculation—which of these solutions is correct?

1) Take the rate of the reaction as one-half the rate of disappearance of $\ce{NO}$:

$$
\begin{align}
R &= {1\over 2} * 2.5 \times 10^{-5} = k \ce{[NO]^2[O2]}=k(0.01)^3 \\
k &= 12.5~\mathrm{L^2\over mol^2\,s}
\end{align}
$$

2) Take the rate of the reaction as equal to the rate of disappearance of $\ce{NO}$:

$$
\begin{align}
R &=  2.5 \times 10^{-5} = k \ce{[NO]^2[O2]} = k(0.01)^3 \\
k &= 25 ~\mathrm{L^2\over mol^2\,s}
\end{align}
$$


texts: Is the vapor pressure of a liquid dependent on the pressure of the atmosphere in which it is measured?

texts: The figure below shows how vapor pressure of a liquid is measured. Initially the flask is at atmospheric pressure. Then the liquid is dropped in the flask. Once equilibrium is reached, the pressure from the vapor created is recorded. My question is - if the flask were initially at a different pressure - let's say 5 atm - would the vapor pressure of the liquid be different? My thinking is that the additional pressure in the flask would keep more of the liquid molecules in liquid form.


texts: Is nitrogen with 3 different substituents and lone pair a chiral center? Does it make the whole compound chiral too?

texts:
Is nitrogen considered a chiral centre or stereocenter when it has three different substituents attached to it along with a lone pair.
By definition LG Wade says

An  asymmetric  carbon  atom  is  the  most  common  example  of  a  chiral  center  (or chirality  center),  the  IUPAC  term  for  any  atom  holding  a  set  of  ligands  in  a  spatial arrangement  that  is  not  superimposable  on  its  mirror  image.  Chiral  centers  belong  to an  even  broader  group  called  stereocenters.  A  stereocenter  (or  stereogenic  atom)  is any  atom  at  which  the  interchange  of  two  groups  gives  a  stereoisomer.*  Asymmetric carbons  and  the  double-bonded  carbon  atoms  in  cis-trans  isomers  are  the  most  common types of stereocenters.

So by the definition of chiral centre and stereo center , if here I interchange two of the substituents then I get a non super-imposable structure which is the mirror image of original compound. Sure, it can undergo inversion, but the definition only says about non super-imposability of mirror image and getting a new stereoisomer on interchanging 2 substituents.
Also if we are calling the nitrogen as chiral centre will be also called the compound to be chiral??
Here The answer says it can only be chiral if we slow down the inversion... But the definition doesn't have any condition about how fast the inversion is , it's just checking super-imposability of mirror images
Note : I'm not just asking about the compound being chiral, but the chiral center. Kind of like (R,S)-2,3 dichloro butane is not chiral molecule, but has a chiral center.
It's not a duplicate as by definition of IUPAC Chiral center is the term for any atom holding a set of ligands in a spatial arrangement that is not superimposable on its mirror image. They don't talk about how fast the inversion is at all


texts:
When performing a titration of a monoprotic acid and a monoprotic base, water can not be added to the titrant but water can be added to the analyte. To prove this statement to myself, I decided to analyze the equation for a hypothetical titration where the acid is the analyte and the base is the titrant:

[Acid] = (Volume of Base) $\cdot$ [Base] / (Volume of Acid)

So, if water is added to the base in the burette, the volume of base would increase but the molarity of the base would decrease and the effects seem to cancel out, leading to the same [Base] calculation. However, when water is added to the acid in the flask, the volume of acid increases which would lead to a decrease in the [Acid] calculation.

This contradicts the common protocol and knowledge when adding water to the burette or flask. Many answers I have seen state that the moles of acid and base stay constant if water is added to the analyte; however, wouldn't this also increase the volume of analyte and skew the calculation of [Acid]?

It would be awesome if someone could explain the effects of adding water to the burette and analyte on the equation above.


texts:
Can analytical precision be finer than a lower detection limit?
For example, if the lower detection limit of an analytical method is reported as 0.010 ppm. Is it possible to have an analytical precision of 0.001 ppm, and therefore a measurement like 0.116 ppm?
Obviously this depends significantly on the method, but in theory is this possible?


texts: Which mechanism should a reaction between the cyclopentylmethanol and the HBr should follow?

texts: I just thought that the reaction should follow $\mathrm{S_{N}2}$ mechanism this is because the alkyl halide is primary but the book says that the reaction will follow $\mathrm{S_{N}1}$ mechanism resulting in the formation of tertiary carbonation and a ring expansion product. Can anyone please explain the reason behind this ?


texts: How does mCPBA convert an amine to an N-oxide?

texts:
Is this how the mechanism works?
Since it is a very stereoselective reagent I thought maybe it proceed via one step only, but how would that then work?


texts: When using Pymol or Coot molecular visualization software to solve x-ray crystallography structures, how can I mutate a cytosine to a 5-methylcytosine?


texts: What does $\mathrm{A}_r(\mathrm{H})$ represent when calculating the average natural weight of an elemental atom?

texts:
I have a question that explains the weights and abundances of various hydrogen isotopes, and the question concludes by asking to:

  Calculate the atomic mass of hydrogen $\mathrm{A}_r(\mathrm{H})$ (with the $r$ in subscript).

The answer simply summed the mass of each isotope multiplied by its natural abundance. However, the text never mentioned the meaning of $\mathrm{A}_r(\mathrm{H})$ and I couldn't find anything online.


texts:
I was looking through the following presentation:
http://folk.uio.no/helgaker/talks/SostrupIntegrals_10.pdf

Looking at the section on 4-electron integrals, I couldn't help but notice that the slides wrote that the 4-electron terms (Kij and Jij) were Gabcd x Dcd. [see slide 25]

I realised that Dcd was referring to the dipole-moment integral. Maybe I just missed something here, but what does the dipole moment integral have got to do with the 4-electron integrals?

This is particularly confusing for me since I notice that the guide here (which uses the same notation afaik) uses Dij^2 as the auxiliary kinetic-energy integral.

https://joshuagoings.com/2017/04/28/integrals/


texts: Activity of NaCl aqueous solution at high ionic strengths: Common-ion effect

texts:
Is there any theoretical way to estimate the activity of $\ce{NaCl}$ at high ionic strengths in water and that in $\pu{7 M}$ $\ce{NaCl}$ solution? This question is based on whether  solubility of $\ce{NaCl}$ in $\pu{7 M}$ $\ce{LiCl}$ solution should decrease. Solubility of $\ce{Na+}$ in $\ce{LiCl}$ solution can be approximated to

$$
[\ce{Na+}]=\frac{(K_\mathrm{sp})_{\ce{NaCl}}}{m_{\ce{LiCl}}}
$$

We have, however, assumed that both $\ce{NaCl}$ (and $\ce{LiCl}$) are in their unit activities, which is not true. How to get conservative estimates for $a_{\ce{LiCl}}$ and $a_{\ce{NaCl}}$ at high ionic strengths, say $\pu{7 M}$?


texts: What are the reasons that make platinum a good electrocatalyst for oxygen reduction reaction?

texts:
Researchers are trying to find new electrocatalysts for energy related reactions in fuel cells in order to replace the expensive platinum-based materials.

I would like to know what are exactly the properties of platinum that make it have such a good performance (1 step reduction reaction of oxygen/4 electron process)?

Thank you in advance.


texts:
Consider a plant that uses the energy it receives from the sun to do work (to undergo photosynthesis) to produce glucose. The minimum amount of work this plant can do to produce 1 mole of glucose is equal to the change in Gibbs free energy that goes into producing one mole of glucose. I calculated the change in Gibbs free energy that goes into producing one mole of glucose to be $\Delta G =2878.94\ \mathrm{kJ}$. Therefore the plant does $2878.94\ \mathrm{kJ}$ of work. Also if we calculate the change in enthalpy for the same process we get, $\Delta H = 2803.04\ \mathrm{kJ}$. Therefore the heat from photosynthesis under these conditions is, $Q=\Delta H - \Delta W = -69.9\ \mathrm{kJ}$.

This confuses me because it implies that photosynthesis under these conditions gives off heat. How can this be?


texts: How to remove pyridine from Reaction mixture containing chiral molecule with diacetal protection group?

texts: While working with chiral molecule, we have pyridine in our reaction mixture. Molecule has four chiral centre and protection group-diacetal and acetyl groups which may break in harsh conditions. Please suggest work up methods to remove pyridine.


texts: Major product for aldol condensation between acetophenone and acetaldehyde

texts:
Crossed aldol condensation is done between acetaldehyde and acetophenone by using NaOH as the base. So, here we can get 4 possible products. But which one would be the major?

I know that acetaldehyde will act as electrophile to which addition will occur. But what will act as nucleophile to give major product: acetaldehyde or acetophenone?

I don't have any solid reasoning whether acetaldehyde enolate or acetophenone enolate will give major product with acetaldehyde.


texts: Kinetic isotope effect in nitration of benzene

texts: What is the effect of changing all the hydrogen atoms in benzene to deuterium? For example, which of the following reactions occurs at a faster rate?


texts: Coulombic energy of repulsion and exchange energy

texts:
In this Wikipedia link about the excited states of oxygen, this diagram is shown.  The left most molecular orbital diagram is the first excited state of oxygen, and the MO diagram in the middle is the second excited state of oxygen. It seems to imply that the energy of pairing is less than the exchange energy, and thus the first excited state exhibits the two electrons with opposite spins in the same MO, while the second excited state exhibits the two electrons with opposite spins in separate MOs.

However, in Miessler, Fischer & Tarr, Inorganic Chemistry, 5th Edition, this diagram is depicted, implying that the energy of pairing is greater and more unfavorable than the exchange energy.

These two diagrams seem to have different orders for the first and second excited states. Which energy energy state, having both electrons with opposite spin and in the same orbital, or having both electrons with opposite spin and in separate orbitals, has higher energy?


texts: Yield of alkyl chloride in the Hunsdiecker reaction

texts:
Apparently the yield of alkyl chlorides is low as compared to that of alkyl bromides when preparing alkyl halides using the Hunsdiecker reaction.
Why does this occur? The only factor I can see is the lower stability of the free radical of chlorine as compared to that of bromine, as the reaction proceeds by the free-radical mechanism.
Is that what causes the lower yield?


texts: Can Iron(III) oxide oxidize elemental iron in a nitrogen environment under room temperature without any catalysis?

texts:
Will there be electron transfer to allow this process to happen:
$\ce{2 Fe(III) + Fe(0) -> 3 Fe(II)}$


texts:
I noticed (lim) is sometimes added to the SN1 or SN2 notation. I suppose it means limiting, but still do not understand it completely. Can someone please explain how is SN1 and SN2 different to SN1 (lim) and SN2 (lim)?

Text from the first row:

Existence of an intermediate with a lower coordination number

No intermediate

Existence of an intermediate with a higher coordination number

Text from the first collumn:

Stoichiometric mechanism

intimate-mechanism

Ingold-Definition

Dependance of the speed on the nature of the entering group

Text from the last row:

The speed does not depend on the entering group.

The speed does depend on the entering group.


texts: Do microwaves heat polar molecules or molecules with polar bonds?

texts:
IR is only absorbed my molecules with polar bonds
regardless of the overall polarity of the molecule , what about Microwaves ?


texts:
In the image above, four variations of tartaric acid are shown:

The variant in the top left is the "basic" skeletal formula of tartaric acid.
The one on the top left is D-(-)-tartaric acid.
The one on the bottom right is L-(+)-tartaric acid.

How would you name the one on the bottom right using the dextro- and levo- method instead of the S and R method?


texts: Reaction mechanism for the synthesis of 9,10-phenanthrenequinone

texts:
In my lab course I had to synthesize 9,10-phenanthrenequinone (phenanthrene-9,10-dione) from phenanthrene and chromium(VI) oxide. The synthesis was made as explained in Organic Syntheses, Coll. Vol. 4, p.757 (1963)

The reactants are: phenanthrene (1.00 eq), chromium(VI) oxide (7.50 eq), sulfuric acid (15.0 eq), water (83.3 eq)

I now have to explain the reaction mechanism, but unfortunately I don't find it in any of my textbooks, neither on the internet.

Here is my assumption:

The chromium(VI) oxide reacts with water and forms chromic acid.
The chromic acid can oxidize an alcohol to a ketone (Jones-Oxidation)

So what misses is the alcohol. Somehow I have to get the 9,10-phenanthrenediol, which could react as alcohol in the Jones-Oxidation.

How could this possibly work. Remember, I don't have $\ce{OsO4}$, which could easily dihydroxilate an alkene.

EDIT 1: As an answer to the proposed mechanism by @Zhe:

Is this ok in your eyes?

EDIT 2: An other idea for the first step (dihydroxilation)

A person of the scientific staff of my university told me, that the $\ce{CrO3}$ should react in a very similar way as $\ce{OsO4}$ does. As I'm using 7.50 eq of chromium(VI) oxide, there is enough for the dihydroxilation and the Jones-Oxidation. He said that a radical mechanism is rather unlikely, because I'm working with water as solvent and water is an inhibitor for radical reactions. This is the mechanism I came up with, regarding these new information.

What do you think about this possibility?


texts: Selenium is a good conductor of electricity in presence of light. This phenomenon is called photoconductivity. How does this phenomenon occur? Are there any other elements or compounds in which this phenomenon is noted?


texts:
I have recently read that for an isothermal expansion ∆u =0 which implies that work done =heat released as temperature  remains constant ....but also I read that q=m×c×∆T which in this case should be zero as ∆T=0,,,then this implies work done = 0 ..but this is not true

Where am I committing mistake


texts: Why does the extent of racemisation in an SN1 reaction depend on the solvent used?

texts:
Why is it that the extent of racemisation is greater in an $S_N 1$ reaction caried out using a polar protic solvent but the racemisation is not as extensive if an aprotic solvent is used although the carbocation intermediate is common in both?
eg:- 2-Bromobutane is solvolysed with $\ce{H2O}$ and $\ce{CH3OH}$ but the racemisation is 98% in water and 73% in methanol


texts: Obtaining ammonium perchlorate via double displacement reaction

texts:
I was tasked with figuring out how to make some $\ce{NH4ClO4}$(ammonium perchlorate). I found that one way of making it was to react potassium perchlorate and ammonium chloride in a double displacement reaction. according to:

$\ce{KClO4 + NH4Cl -> NH4ClO4 + KCl}$

Then I got to work on finding ways of making the necessary reactants without having to buy them by doing additional reactions with easier to find chemicals. After some work I came up with these two reactions:

$\ce{KCl + NH4NO2 -> NH4Cl + KNO2}$ (to make the ammonium cloride)

and

$\ce{KCl + HClO4 -> KClO4 + HCl}$ (to make the potassium perchlorate)

My question is (the newbie part) how should I now go about these reactions? Should I be mixing the reactants together in an aqueous solution? In water? Should I be mixing them into an ionic solution in an electrolytic cell? Or hell do I just mix them together as a granulated form and apply a little heat? How do I get these reactions to occur?


texts: Why do we want to operate at dew point or bubble point when doing flash calculations?

texts:
I'm trying to dimension a flash drum for a separation between water and isobutane. I now the total inlet flow (F), the composition of the inlet flow ($z_1$ for isobutane and $z_2$ for water) and the total pressure (P). My supervisor told me that if my inlet flow to the flash was gas I would want my flash drum to operate at dew point temperature. And vice versa I would like my flash drum to operate at bubble point if my inlet flow was liquid. Therefore I have to do a dew or bubble point calculation for the temperature. Why is this true? According to her this is something you always want you flash drum to operate at.
If I had known the outlet molar flow of vapor (V) and liquid (L) I would have used the following iterative model:

We know F, $z_i$, P, V and L
Guess T
Calculate $P_1°$ and $P_2°$ from a model (as an example Antoines equation)
Calculate $x_i=\frac{Fz_i}{V\frac{P_i°}{P}+L}$
Check if $\sum x_i=1$. If not true redo from point 2. If true you have found the flash temperature.

However this isn't possible since I don't know the outlet flows V and L.
So to recap my question is: Why does the flash need to operate at dew or bubble point temperature? Is it because it's most cost  efficient to do so? Do I get the best separation at this temperature (and if so why)? Any other reasons why this temperature is the best to operate at?


texts: Finding stationary solutions and verifying differential equations

texts:
Consider a trimolecular system where the following chemical reactions occur:
  $$\ce{A + B ->[k_1] A + C}\tag1$$
  $$\ce{A ->[k_2] B}\tag2$$
  $$\ce{C ->[k_3] C}\tag3$$
  Write the differential equations that model the evolution of the three component molar concentrations and determine the stationary solutions (there are two). Finally, if initially $[\ce{A}]=0.75$, $[\ce{B}]=0.25$ and $[\ce{C}]=0$, calculate the time when the mole fraction of $\ce{A}$ is half of its initial value.

I think that the differential equations, following the expression for the reaction velocity, are
$$\frac{\mathrm{d}[\ce{A}]}{\mathrm{d}t}=-k_2[\ce{A}]$$
$$\frac{\mathrm{d}[\ce{B}]}{\mathrm{d}t}=-k_1[\ce{A}][\ce{B}]+k_2[\ce{A}]$$
$$\frac{\mathrm{d}[\ce{C}]}{\mathrm{d}t}=k_1[\ce{A}][\ce{B}]$$
However, I don't know how to proceed with the stationary solutions. I guess that one of them would be obtained doing:
$$-k_1[\ce{A}][\ce{B}]+k_2[\ce{A}]=0$$
but I'm not sure.

Finally, I got the relations
$$[\ce{B}]=\left(\frac{1}{4}-\frac{k_2}{k_1}\right)\exp\left(\tfrac{k_1}{k_2}(-\tfrac{3}{4}+[\ce{A}])\right)+\frac{k_2}{k_1}$$
$$[\ce{C}]=-\left(\frac{1}{4}-\frac{k_2}{k_1}\right)\exp\left(\tfrac{k_1}{k_2}(-\tfrac{3}{4}+[\ce{A}])\right)+1-\frac{k_2}{k_1}-[\ce{A}]$$
but I have no idea how to obtain the time. Any help would be appreciated.


texts: What really are the units of enthalpy change?

texts:
A reasonable definition of standard enthalpy change of formation would be:

'The enthalpy change when one mole of a compound is formed from its constituent elements under standard conditions'

Enthalpy change itself is understood as 'the exchange of energy between a chemical reaction and its surroundings at constant pressure.'

I am a little confused on what the units of enthalpy change should be. For example, for the enthalpy change of formation of water, this is shown: ΔHfo = -285.8 kJ mol-1

Now, if enthalpy change already contains 'one mole of a compound' in its definition, do we really need to include the per mole (mol-1) part in the enthalpy change? If enthalpy change is the change in just energy, how are the units kJ mol-1 and not just kJ ? I am sorry if I am overthinking here.


texts: Stability Comparison between the Tropylium and Tricyclopropylcarbinyl Carbocation

texts: Why is the Tropylium carbocation less stable than the tricyclopropylcarbinyl  carbocation?  The tricyclopropylcarbinyl carbocation undergoes a sigma-tropic rearrangement whereas tropylium is highly stable due to conjugated system, that being, it is resonance stabilized and the number of canonical forms of tropylium is more. Then, why is it less stable?


texts: Order of reactivity of substrates towards Wurtz reaction

texts:
In a book I refer, it is said that:

Both Ionic [carbanion] mechanism as well as free radical mechanism are widely accepted for Wurtz reaction.

When I read this statement, I was thinking, which of these mechanisms would be able to explain the order of reactivity of different substrates towards Wurtz reaction. My conclusion was that the rate of the reaction should follow the below mentioned order:

$1^\circ > 2^\circ > 3^\circ$ if it takes place through carbanion mechanism; and
$3^\circ > 2^\circ > 1^\circ$ if it takes place through free radical mechanism

where $1^\circ$ refers to primary alkyl halide, $2^\circ$ refers to secondary alkyl halide, and $3^\circ$ refers to tertiary alkyl halide.
So, my doubt is what is the correct consolidated order of reactivity of alkyl halides towards Wurtz reaction?
I know my question could be a possible duplicate of this.
However, I did not get a satisfactory explanation over there and hence have asked it as a new question.


texts: why doesn't alcohol react with sodium hydroxide but react with potassium hydroxide?

texts: I have read that ROH+ NaOH doesn't form alkoxide ions because water is a stronger acid than all alcohols except methanol. However while reading xanthate test I found that alcohol reacts with KOH to form alkoxide ions. Why is it so?


texts: How to predict which complex is formed and which are soluble?

texts:
How does one come to know (in this table) which metal cations form ammonia complexes and which ones form hydroxy complexes on reaction with $\ce{NH4OH}$
Reference:

J.D Lee - Concise Inorganic Chemistry by Sudarshan Guha


texts: Reason for the greater energy of the eclipsed conformer of alkanes?

texts:
My textbook states:

  In the staggered form of ethane, the electron clouds of C-H bonds are as far apart as possible, thus there are minimum repulsive forces, minimum energy and maximum stability. On the other hand, when the staggered form changes into the eclipsed form, the C-H bond clouds come closer to each other resulting in increased electron cloud repulsion. To check the increased repulsive forces, molecule will have to possess more energy. And therefore it is less stable

My question pertains to the statement in bold text. Am I correct in thinking that in the eclipsed conformer the electron clouds repel more, this repulsion would (sort of) want to break up the molecule so to fight this breaking tendency, the molecule has to possess greater energy to control these new repulsive forces?

If I am wrong, what does this statement mean?


texts: Increasing Covalent character increases Colour intensity

texts:
I observed some trends as follows:-

$\ce{PbCl2}$ white and $\ce{PbI2}$ yellow
$\ce{SnCl2}$ white, $\ce{SnCl4}$ red and $\ce{SnI4}$ black
$\ce{AgCl}$ white, $\ce{AgI}$, $\ce{AgBr}$ and $\ce{Ag2CO3}$ yellow

In all these cases as the size of anion increases ( polarisability increases)  or charge on cation increases (polarising power increases) colour exhibited becomes darker.. How does increasing covalent character affect this?  Or is there  any other reason?


texts: Are there any observable effects of casein binding to capsaicin?

texts:
I would like to complete an experiment on balancing capsaicin. Since both capsaicin and milk are bases on the pH scale, I prefer not to use the common term "neutralizing".

I will be extracting the capsaicin and I do not wish to taste-test it. Is the bound casein protein with the hydrophobic capsaicin oil visible? Will it curdle in order for me to obtain quantifiable amounts?


texts: We know different types of atoms have different spectral lines. But what exactly are the spectral lines representing? What causes white light to have a continuous spectra while other atoms show discontinuous spectral lines?


texts: I'm still learning about MO theory – and I thought that I would do some calculations with GAMESS to become more familiar with the concept. Even though I look forward to delving into the realm of quantum math in the not-so-distant future – it's very difficult to get a grip on all of the terminology. I'm using the GAMESS Avogadro extension to write some input files, but I don't know which options to use. Which options should I use if I want to study the orbitals of, say, shikimic acid? RHF, MP2, AM1 / MINI 6-31G(d)? Computer specs: 3.6GHz i5 with 16GB of RAM


texts: What is more acidic: D3O+ in D2O or H3O+ in H2O and why?

texts:
What is more acidic:

$\ce{D3O+}$ in $\ce{D2O}$

or

$\ce{H3O+}$ in $\ce{H2O}$

and why?

I think it's $\ce{D3O+}$ in $\ce{D2O}$ as I saw somewhere that this property is used in mechanistic studies (the inverse isotope effect), but I need a proper explanation.

EDIT: I found a statement about this in Clayden:  Water $\ce{H2O}$ is a better solvating agent for $\ce{H_3O^+}$ than $\ce{D2O}$ is for $\ce{D_3O^+}$ because O–H bonds are longer than O–D bonds hence $\ce{D_3O^+}$ in $\ce{D2O}$ is stronger than $\ce{H_3O^+}$ in $\ce{H2O}$. That is the origin of the inverse solvent isotope effect.

This is in contrast with all the answers given yet, so I am pretty confused.


texts: Determining Charge of Protonated Alkaloids

texts:
During the extraction of many alkaloids, you lower the pH in order to protonate the compound, making it polar and water soluble. With Mescaline, you must precipitate it as a salt.

What I don't understand, is how can you figure out the mole ratio between the Mescaline and the conjugate base of the acid (for example acetate). My understanding is you'd have to figure out the charge of the protonated mescaline. How? Thanks

Edit:

The reason is not so I can ionize all of the mescaline. I want to know this so I can calculate the molar mass of the mescaline salt. That way I can take the weight I have of product, and calculate (using the molar mass) the weight equivalence of freebase mescaline, for dosage purposes. Also, it's just interesting knowledge that I'd like to know.


texts: Does Gibbs free energy of formation always equal zero for elements in standard state?

texts: I was looking through the appendix in my chemistry textbook when I noticed that every compound that had a $\Delta H_f$ of zero also had a $\Delta G_f$ of zero. So of course the compounds that have a $\Delta H_f$ of zero are the elements in their standard states but why does that make their $\Delta G_f$ zero? Does every compound that has a $\Delta H_f$ of zero also have a $\Delta G_f$ of zero? What exactly is $\Delta G_f$?


texts:
According to my lecturer, if the geometry prevents planarization of the C-centre than an E1 is impossible. As chair and boat are the only stable conformations of a 6 membered ring of carbons, does this mean that such a ring can never undergo an E1?

Furthermore, why must the C-centre be planar for E1? I guess it allows for maximal stabilization by hyperconjugation?


texts: Full equation when using vinegar, hydrogen peroxide, and salt to etch copper

texts:
What is the full chemical equation when you use the following reactants to etch copper:

vinegar / acetic acid (5%) $\ce{CH3COOH (aq)}$
hydrogen peroxide (3%) $\ce{H2O2 (aq)}$
salt $\ce{NaCl (s)}$
copper $\ce{Cu (s)}$

Yes there are previous questions asking the same thing (one and two). However, the answers to both give only parts of the reaction, not the full equation.

Looking elsewhere on the web, I've come across this Instructables article that says copper(II) chloride $\ce{CuCl2}$ is formed when the copper ions bond with chloride ions from the salt. And therefore the solution is greenish in color instead of the blue it would be if copper(II) acetate $\ce{Cu(CH3COO)2}$ was formed as answered in question two. (When doing this at home, I also got a distinctly greenish color when salt was used, and a distinctly blue color when it was omitted).

  Table salt, or $\ce{NaCl}$, brings chloride ions $\ce{Cl-}$ to which $\ce{Cu^2+}$ ions will bond to form cupric chloride or $\ce{CuCl2}$ instead of being left in solution (those ions would endlessly come back and forth from $\ce{Cu}$ to $\ce{Cu^2+)}$. You can see this during the reaction (if you leave the reaction with no salt it will turn blue which is the color of copper(II) acetate and stop, whereas if you put salt it will turn green, the color of cupric chloride, and carry on).

Another article on the web says both copper(II) acetate and copper(II) chloride are produced, but no equation is provided:

  Equal parts vinegar and peroxide worked fine, dump in plenty of salt (to the point of having undissolved salt in the bottom of jar) since it is consumed in the reaction. You should see a vigorous fizzing at the copper surface. Add more salt as the reaction slows.

  The solution will turn green as the copper is converted to copper acetate and/or copper (II) chloride

Can someone please give the complete chemical equation of the reaction that occurs when acetic acid, hydrogen peroxide, and salt are used to etch copper? I can't seem to find it anywhere on the web.

Context:

I want to dispose the products of the etching process safely. If copper(II) acetate is the product as suggested in answer two, then following the recommended approach for disposal is safe:

  You can bypass the problem by collecting the etch solution, and submerge aluminum foil.

  $$\ce{3Cu(CH3COO)2 (aq) + 2Al (s) -> 2Al(CH3COO)3 (aq) + 3Cu (s)}$$

  React with the aluminum until the bluish color disappears, then collect the solid copper + remaining aluminum to throw in the trash. You can now flush the solution down the drain.

However, if the product is instead copper(II) chloride, the approach is not safe as the $\ce{AlCl3}$ formed is considered a hazardous waste and shouldn't be flushed down the drain.

$$\ce{2Al (s) + 3CuCl2 (aq) -> 3Cu (s) + 2AlCl3 (aq)}$$


texts: How are the atomic orbitals for multi electron atoms obtained?

texts: The problem with Schrödinger's equation is that it isn't exactly solvable for multi-electron species. In the past, atomic orbitals were used to construct a solution for molecules (LCAO). My question is, how were the multi electron atomic orbitals (the ones used for the LCAO) discovered? . Were the atomic orbitals solutions for a one electron system? In other words, were the atomic orbitals calculated the orbital for a $\ce{He+}$, $\ce{Li^2+}$, $\ce{Be^3+}$, etc? What were some approximations that are used to obtain the solution for multi-electron species?


texts: How do I find the rate constant when I only have product concentrations?

texts: I have done an experiment on the hydrolysis of aspirin, which is pseudo-first order. I need to find the rate constant, but I only have the final ($0.0278\mathrm{~M}$) and initial ($0\mathrm{~M}$) concentrations of the product (salicylic acid), the volume of the solution ($0.06\mathrm{~L}$), the change in time ($24$ hours), and the temperature ($25\mathrm{~^\circ C}$). Is there a way to find the rate constant of this reaction? My main problem is that I do not know the initial or the final reactant concentrations; I cannot simply subtract the concentration of product formed from initial reactant concentration to find the final reactant concentration, as I do not have either reactant concentration.


texts: A chemistry approach to environmentally friendly yoga mats… NBR, NR, TPE, PER

texts:
I'm currently seeking your expertise while creating a line of environmentally friendly yoga mats, and I apologize in advance if any chemistry knowledge of mine has been absent since college and I lack the technical capability of this forum. I typically have a scientific approach to problem solving, and I'm hoping I can apply the same methodology to finalizing the material composition of my product.

Instead of blindly accepting the industry suggestions of natural rubber, NBR, TPE, and PER, I wanted to start with the physical characteristics required and work backwards to determine the ideal (perhaps innovative) material that would work best. My requirements are: 1) Eco-Friendly, 2) high fidelity printing compatibility via heat transfer

1) Environmentally friendly: PVC is not an option for the reasons I'm sure you would know. One would assume natural rubber would be the obvious choice, however if it degrades and has to be replaced every 2 years or so, I'd think the long term production effects might actually be more harmful then something more sustainable. From reading an article on PER it seems like it is essentially phthalate free PVC, and although processed different to be phthalate free the vinyl chloride monomer still exists and could be viewed as toxic, although to a lesser degree then PVC. Nitrile Rubber (NBR) is another option but it sounds like although it might be more heat resistant then natural rubber, it degrades similar to natural rubber. Various types of TPEs are also an option, but I've found minimum answers towards their actual eco-friendliness.

2) Heat resistant printing - Sublimation printing has typical been used on polyester, but from what I've researched should be compatible with any polymer. Unfortunately it requires a heat transfer of about 400 deg F, which I believe would scorch/melt natural rubber.

I know its a stretch, but I would love to get your input on the above materials or any other polymer that might be an option. I don't want to blindly commit to an "eco-friendly" material without fully investigating their chemical properties.

Thank you in advance for your help, and I'm definitely open to all of your respected critiques and suggestions.
Regards,
Shane


texts: What is the minimum operating temperature of chemical hand warmers?

texts:
I have been looking at chemical hand warmers such as Hot Hands, Grabber and HotSnapZ. Unfortunately, I cannot find a minimum operating temperature for these types of devices. Logic tells us that they won't work at -273°C and will probably work at 0°C, but I'd like to have an idea of where the cutoff lies between them.

From Wikipedia here and here, it looks like they all contain some amount of saltwater. The lowest freezing temperature I can find for saltwater at saturation (26%) is -21°C. Is it reasonable to assume that a frozen hand warmer will not work? Would the other components in the hand warmer lower the freezing temperature even more?

TL;DR
What is the minimum temperature at which a chemical hand warmer can still provide heat?