texts: Reaction-diffusion equation using Lattice-Boltzmann method

texts:
I'm struggling to get a working LBM reaction-diffusion implementation. I have a pretty weak mathematics and physics background, and thus I'm having a hard time understanding the notations around the BGK operator. I would like to know if I understood the basics correctly.

Right now, what I'm doing is the following (v is the diffusive species I'm interested in), on a D2Q5 grid, in pseudo-code:

v[0, :] = initial_condition
t = 0
while t < t_max:
    for each node x:
        compute a pseudo (pre-collision?) dv[x]/dt using the forward Euler method
    for each node x:
        real dv[x]/dt = 1/3 * dv[x]/dt
                        + 1/6 * dv[left of x]/dt
                        + 1/6 * dv[right of x]/dt
                        + 1/6 * dv[above x]/dt
                        + 1/6 * dv[below x]/dt
        (if x is on a domain boudary, use bounce-back condition)
        v[t, x] += dv[x]/dt
    t += dt

Is this correct, theory-wise, or am I missing something?

Thanks for any help. I'm happy to share my code if anyone wants to go this far to help me. Once I'll have it working (probably in python), I will distribute it without conditions.


texts:
Why something jelly forms in the water if it is kept in in a ultrasonication bath for long periods?
 When water is exposed to ultrasonication for say a month, some jelly substances form in the ultrasonicator bath. is this something related to some bioorganism growth?


texts: Is micelle formation in a soap solution a chemical reaction?

texts: I know that soap molecules have a hydrophilic end and a hydrophobic end which attract to water and oil respectively. However, does a chemical reaction take place?


texts:
I am trying to teach myself some QM.

In Christopher J. Cramers textbook Essentials of Computational Chemistry: theory and models, in Appendix C, he goes over Spin algebra.

I am unable to calculate myself that $S^2\alpha = \frac{1}{2}\left( \frac{1}{2}+1 \right) \hbar^2 \alpha$ as well as that $S^2\beta = \frac{1}{2}\left( \frac{1}{2}+1 \right) \hbar^2 \beta$

Where $S^2$ is the spin squared operator and $S = S_x + S_y + S_z$.

This seems like it should be trivial. It certainly is to him, he says that  repeated application of the following equations lead to the above

$S_x\alpha = \frac{1}{2}\hbar\beta$

$S_x\beta= \frac{1}{2}\hbar\alpha $

$S_y\alpha = \frac{1}{2}i\hbar\beta$

$S_y\beta = -\frac{1}{2}i\hbar\alpha$

$S_z\alpha = \frac{1}{2}\hbar\alpha$

$S_z\beta = -\frac{1}{2}\hbar\beta$

my understanding is that $S^2=S_x^2 + S_y^2 + S_z^2$. However, when using this operator on $\alpha$ or $\beta$ I am not sure what the eigenvalues would be..., relatedly, I am not sure even how to operate just $S_x^2$ on $\alpha$.


texts: Is there a universal minimum energy state?

texts:
I'm imagining this: if everything was separated (even on the nuclear level) and then the parts were recombined so that they were in the lowest possible energy state, do we have any way of knowing what that might be? Particularly, would it be something simple like a helium atom or could it be something very complex and unusual? And I mean that you might grab a few parts and make a helium atom or grab a whole bunch of parts and make whatever else.

I guess one problem is we need a way of totaling how much the energy is decreasing per some amount of something else. Similar to how nuclear binding energy is often expressed on a "per nucleon" basis.

I'm interested to see what people think.


texts: What is the structure of 92 m/z fragment for aspirin

texts:
Aspirin has the following structure:

What would the fragment structure be for m/z = 92?

Even though $\ce{C6H4O}$ is a molecular structure with mass 92, I don't think this will be formed since two bonds needs to be broken. Also the 92 peak is a major peak and the probability of two bonds breaking to lead to major peak is unlikely. The mass spectrum is as follows


texts:
A $22.7 \,\mathrm{L}$ helium-filled chamber at $298\,\mathrm{K}$ has a tiny hole of area $1.63 \times 10^{-5}\,\mathrm{mm^2}$ punched in it through which is leaking helium at a rate of $2.25 \times 10^{15}$ atoms per second. How many atoms of helium are in the chamber?

I'm personally not too sure how to answer this, I'm thinking that it probably uses the root-mean-square speed or collisions with the wall equation ($Z_\mathrm w$). But I'm sort of lost when it comes to substituting the values and so on. (This is also a question on last years Gas Laws test, and I was planning on solving it for practice questions)

What I tried doing was using the Collisions with the wall equation:
https://en.wikipedia.org/wiki/Kinetic_theory#Collisions_with_container
then solved for $N$, but the answer is supposed to be $N = 9.98 \times 10^{21}$, and the closest I've gotten was getting $3.38 \times 10^{22}$, so I'm sort of stuck on the procedure of solving this question.


texts: Reagents used to prepare organic ICP standards, from scratch

texts: I am trying to figure our how I can make my own calibration standards for organic ICP analysis. I assume that I need organometallic compounds to mix with base-oil/mineral-oil to prep the standards, but I can not figure out what specific compounds are commonly used for the different metals (example: For Na, maybe Sodium isopropylcyclopentadienide?). I have looked online and through some analytical chem texts but no luck. Any source for this information would be greatly appreciated.


texts: I read that phosphate reserves will exhaust  in coming years wiki, why don't we extract it from sewage , is it really that difficult to extract phosphate ?


texts: Why does shaking a soda can and opening it make the soda jump out of the can?


texts: Recently, I read about the nomenclature of bicyclic compounds, by mentioning the number of carbons between two bridgeheads. But, then I came across the structure of a weird type of compound, whose IUPAC name is tricyclo-[2.2.1.02,6]-heptane. As the name suggests it must be a polycyclic compound, having three alicycles. 2.2.1 suggests that there are 2, 2 and 1 carbons between the bridgeheads. But what about the next part? What is the actual rule for naming tricyclo compounds?


texts: Is there a certain amount of titrant that is ideal?

texts:
For an AP chem lab dealing with determining the amount of citric acid in orange juice by titrating with NaOH, one of the discussion questions goes like this:

  Choose an amount of beverage to be titrated that will require at least 10 but less than 20 mL of titrant. Explain why this range of titrant is optimal.

This question makes no sense to me. Why would there be an "optimal range" of titrant? I would think that I should fill the buret to full capacity if enough titrant is available. Would it not be better to have excessive titrant than not enough of it?

We completed the lab, and the titration required 23.05 mL of 0.1 M NaOH solution to titrate 20.00 mL of orange juice. If we had followed the instructions, we would have added less orange juice, and used less NaOH, but what is the benefit in doing so? Budget cuts? If it was about not wasting solution, why would there be a minimal requirement of 10 mL of titrant?


texts:
Question:

Four gas balloons A, B, C, D of equal volumes containing $\ce{H2}$, $\ce{N2O}$, $\ce{CO}$, $\ce{CO2}$ respectively prickled with a needle and immsersed in a tank containing $\ce{CO2}$. Which of them will shrink after some time?
a) A
b) B
c) C
d) Both A and C

My attempt: I think that the ballons filled with the gases which will react with $\ce{CO2}$ will be the ones that will shrink. Now $\ce{H2}$ reacts with $\ce{CO2}$ to form $\ce{CH4}$, so the amount of $\ce{H2}$ will decrease and the balloon will shrink. Also I know $\ce{CO}$ cannot react with $\ce{CO2}$, so the answer has to be (a). I need hep determining the correct solution.


texts: Is it possible to make a solution of zinc oxide in a high school chemistry lab?

texts:
As part of my IB Chemistry curriculum, we are required to conduct our own experiment researching our own question. I'm in the preliminary research phase and wanted to conduct an experiment looking at the effectiveness of zinc oxide (the active ingredient in many physical sunscreens) in absorbing UV light at different pHs ranging from 4 to 7.
I've found some procedures similar to the experiment I want to conduct, but all of them seem to dissolve a commercial sunscreen in ethanol and run it through a spectrophotometer. I want to isolate the active ingredient itself, and as such, I wanted to make a solution of zinc oxide -- though the molecule is not soluble in water, might there be another way to make a solution (perhaps dissolving in 2-propanol?). Then, I would ideally change the pH of the solutions using a buffer.
Does this seem viable, or is it likely I will need to purchase a zinc oxide suspension or perhaps look at a different chemical? Thank you for your help.


texts:
The starch and iodide test is to detect amylose, a polysaccharide. We add an iodide solution to a sample and observe a color change with the starch; it turns dark blue. I am doing a bio/chem experiment on how pH changes Amylase digestion of Starch.

My recent trials have all failed, as the amylase starch solution is not showing any blue colour. Since I think its because that the amylase and starch solution is too concentrated and thats why they are digesting quickly, I am wondering, what percent should my amylase and starch solution be?


texts: What does β stand for in β-potassium zirconate?

texts:
What do the Greek letters (α, β, γ...) convey when they are prefixed to a crystalline substance?

For example: β-potassium zirconate


texts:
I am looking for any help in developing a mechanism for this transformation as well as determining the stereochemistry on the starred centers. I do not see any obvious connections. I was thinking that the second to last step would involve some sort of electrocyclic ring closure since the hydrogen atom orientation is a consideration for the product. Beyond this, I can't justify any further reactivity. There is no acid to lead to carbocation-mediated ring closure. I can't see any obvious sigmatropic rearrangements nor cycloadditions that would either directly or indirectly lead to this.
I had already taken the suggestion of rotating the single bond into consideration. Can someone please confer with me on the stereochemistry, though? Kindly see below.


texts: Diluting 4 % NaOCl to get a 1 % solution

texts:
Assuming that one has a 1 litre bottle of liquid bleach containing $4~\%$ sodium hypochlorite. If I wish to dilute it down to $1~\%$ sodium hypochlorite (to use as disinfectant), would adding 3 litres of water to it, be sufficient? This should yield 4 litres of $1~\%$ sodium hypochlorite.

And that should be same as taking $\pu{250ml}$ of the liquid bleach, and then adding $\pu{750ml}$ of water, to yield 1 litre of $1~\%$ sodium hypochlorite.

Now the liquid bleach also contains a stabiliser to reduce the rate of decomposition of $\ce{NaOCl}$. How will diluting the solution affect the action of the stabiliser?


texts: How does crystal field stabilisation energy relate to the stability of a complex?

texts: I know how the crystal field stabilization energy is calculated, but how does it reflect stability? CFSE measures the energy relative to the barycentre, not the initial energy of the $d$ orbitals. For example,a $d^5$ configuration in a weak ligand field would have zero CFSE, but that certainly does not mean that the complex is unstable.


texts: Why is some ionic substance insoluble, such as BaSO4?

texts: If Ba is less electronegative than Mg, then why is BaSO4 insoluble in water and MgSO4 is soluble? I thought the greater the EN difference the more soluble the compound is because of how unequally shared the electron is.


texts: Before the CIP system was created, how did chemists ensure that the D/L system matched the R/S assignments?

texts:
The ᴅ/ʟ system I have referred to is the one chemists used before the Cahn-Ingold-Prelog (R/S) system where they arbitrarily assigned the (+) and (-) isomers of glyceraldehyde,  'ᴅ' and 'ʟ' respectively and related other carbohydrates via reactions with retention of configuration. They were eventually found to match the (R) and (S) assignments (for the lowest asymmetric carbon in Fischer projections) of those molecules today (particularly biomolecules), and that is where my question arises.

Even though the molecules were related to glyceraldehyde through reactions that proceeded with retention of configuration, it is also known that the resulting molecules may not always retain the absolute configuration of the original molecules (which depends on priorities of the new groups). And since it was before CIP's (R) and (S) system came into place, there was no way to know if the molecules had changed absolute configuration during the reactions. So how did the chemists manage to retain the configuration of all those molecules with respect to the glyceraldehyde isomers at all?


texts:
I'm having trouble finding the ionic and half equations for the following equation:

$\ce{2Sr + O2 -> 2SrO}$

From this I would have to tell which elements are being oxidised and reduced.

This is IGCSE.


texts: Can bond rotation take place in Pinacol-Pinacolon rearrangement

texts: I was given a question of pinacol pinacolon rearrangement of butan-2,3-diol where the methyl groups were anti to the respective hydroxy groups. Can the C2-C3 bond be rotated to allow hydrogen to be anti to the leaving hydroxy group, but I have heard that mechanism of this rearrangement is concerted. Therefore I can't decide the major product.


texts: Why can hydroxide not be used to synthesise ethanol from ethyl amine?

texts:
In the following reaction we have to find A and B.

I thought that A could be $\ce{Br_2}$/$\ce{KOH}$ resulting in a Hoffmann bromide reaction.

For B, I thought I would need a base such as $\ce{KOH,NaOH}$. But the answer is $\ce{HNO2}$.
Why?


texts: Can the plane of symmetry for a compound be the plane of the paper?

texts:
1,4-Dichloro-2,5-dimethylbenzene is symmetric about the plane of paper.

I have never seen a plane of symmetry positioned like this. Would it be correct to call it a plane of symmetry?


texts: How to calculate a molar mass based on density?

texts:
I have been asked to calculate the molar mass and mole fraction of a 35 w/w% HClO4 solution with a density of 1.3g per ml.

This is the equation I used to try to solve it:

$\frac{1}{M} = \frac{0.35}{100.46} + \frac{0.65}{18.02}$

Is this correct?


texts: Can the first ionization energy for a specific element be calculated?

texts:
I'm taking a first-year Inorganic Chemistry course in college, and stumbled upon this problem:

  For $\ce{Mn}$ and $\ce{P}$, calculate the first ionization energy and explain the difference between the obtained values.

Now, my course materials (written by our professor) apparently say that the first ionization energy can be computed using this formula. I say apparently because the "course materials" are poorly written PowerPoint slides with loads of unexplained terminology and abbreviations, so I may be misunderstanding.

$$
\text{IE} = \frac{Z_\mathrm{eff}^2}{n_\mathrm{eff}^2} \cdot 13.6~\mathrm{eV}
$$

where $Z_\mathrm{eff}$ is the atomic number minus the differentiating electron's shielding constant (calculated using Slater's rules) and $n_\mathrm{eff}$ is pulled out of a table of values (see here).

Unfortunately, it only seems to produce (somewhat) numerically correct results for $\ce{H}$ and $\ce{Li}$, and stops being useful for comparing them at $Z=5$. I wrote an implementation of the algorithm in Mathematica and compared the results it produces to the first ionization energies returned by ElementData (suitably converted from molar to regular), and it's a very rough approximation.

Much too rough, in fact, to be usable for the problem above: it returns $47.38$ instead of $7.43$ for $\ce{Mn}$ and $45.71$ instead of $10.48$ for $\ce{P}$. It sorts them the wrong way around, in other words.

My question is, what am I missing? As far as I can tell from Wikipedia, there's no way to simply calculate ionization energies - they have to be measured. Is there some obvious detail I haven't spotted? Another way to interpret the problem text? Some elementary knowledge I don't have?


texts: Identification of unknowns with varying solubilities and states of matter

texts:
White solid A water insoluble cleaved hot to solid gas B and C. B is insoluble in water and in $\ce{HCl}$ but soluble to $\ce{HNO3}$ the react gives solution D and E colorless gas which becomes red on contact with air. The solution D gave white precipitate F with $\ce{HCl}$. The gas C is reacted by heating with magnesium G yielding a white solid which reacts with water yielding a white solid and the gas J characteristic suffocating odor. J is a basic , H is soluble in dilute $\ce{H2SO4}$. The gas J oxidized to C while the gas under specific conditions ($\ce{Pt}$ catalyst and $800^\circ\mathrm{C}$) is oxidized to the gas E.

My attempt:
C: $\ce{N2}$,
G: $\ce{Mg3N2}$,
H: $\ce{Mg(OH)2}$,
J: $\ce{NH3}$,
E: $\ce{NO}$
\begin{aligned}\ce{
N2 + 3Mg &-> Mg3N2\\
 Mg3N2 + 6H2O &-> 3Mg(OH)2 + 2NH3\\
 Mg(OH)2 + H2SO4 &<=> 2 H2O + MgSO4\\
 4 NH3 + 5 O2 &->[\ce{Pt~$800^\circ\mathrm{C}$}] 6 H2O + 4 NO\\
 4 NH3 + 3 O2 &-> 6 H2O + 2 N2\\
}\end{aligned}

I cannot really find anything else.


texts: What is the reaction of ammonium nitrate with hypochlorous acid

texts: What would the product of ammonium nitrate and hypochlorous acid? Would there be any reaction? Would the HOCl get broken down? Trying to determine if the free chlorine content would be diminished upon mixing in an aqueous solution.


texts: How to calculate the equilibrium constant for an esterification?

texts:
I have tried to solve it algebraically, using the data I'm provided with, but still, I'm not capable of proving that in this particular case, the equilibrium constant is independent from the volume, maybe because it isn't; however, I don't know how can I possibly know the concentration of each substance in the reaction without the volume, so as to find the equilibrium constant.

  When a flask of constant capacity holds 1.2 mole each of acetic acid and ethanol with a catalyst and the temperature is kept at 25 °C, 0.80 mole of ethylacetate is produced at equilibrium. Calculate the equilibrium constant of the following reaction:
  $$\ce{CH3COOH + C2H5OH <=> CH3COOC2H5 + H2O}$$
  (Answer option: 0.25, 0.64, 2.0, 4.0, 6.0)


texts: Integration of the first order rate equation

texts:
Given the simple first order reaction $\ce{A -> P}$ derive the integrated rate law.

$$\frac{\mathrm d[\ce{A}]}{\mathrm dt} = -k[\ce{A}]$$
Collect terms:
$$\frac{\mathrm d[\ce{A}]}{[\ce{A}]} = -k\,\mathrm dt$$

Now for the bit I need help with, the integration:
Apparently the integrated form of $\frac{\mathrm d[\ce{A}]}{[\ce{A}]}= \ln[\ce{A}]$ but I'm struggling to see exactly how.

The next step (usually omitted)I think should be to split the fraction before integration
$$\frac{\mathrm d[\ce{A}]}{1}\frac{1}{[\ce{A}]}=\mathrm d[\ce{A}]\frac{1}{[\ce{A}]}=-kt$$

$$\int{\mathrm d[\ce{A}]\frac{1}{[\ce{A}]}}=\int{-kt}$$

$$\int{\mathrm d[\ce{A}]}\int{\frac{1}{[\ce{A}]}}=\int{-kt}$$

Now, to evaluate this I use the general integration law for a constant $\int{[\ce{A}]\,\mathrm dt} = [\ce{A}]t + C$ and reciprocal  $\int{\frac{1}{[\ce{A}]}=\ln[\ce{A}]+C}$. Therefore $$\int{\mathrm d[\ce{A}]}\int{\frac{1}{[\ce{A}]}}=[\ce{A}]t + C_1+ \ln[\ce{A}]+C_2=\int{\frac{\mathrm d[\ce{A}]}{[\ce{A}]}}$$

I know this is wrong because the textbooks say something different but I don't know how to correct it. Can anyone help?


texts: Number of moles of acidified potassium dichromate required to liberate 6 moles of iodine from an aqueous solution of iodate ions

texts:
I came across this question in a recent exam I had taken:

How many moles of acidified $\ce{K2Cr2O7}$ is required to liberate 6 moles of $\ce{I2}$ from an aqueous solution of $\ce{I-}$ ?

So this is how I approached it (by writing the corresponding equations):
$$
\require{cancel}
\begin{align}
\ce{ Cr2O7^2- + 14 H+ + \cancel{6e^-} &-> 2Cr^3+ + 7H2O} \\
\ce{6 I- &-> 3I2 + \cancel{6e^-}}\\
\hline
\ce{Cr2O7^2- + 6I- + 14H+&-> 2Cr^3+ + 3 I2 + 7H2O}
\end{align}
$$
Clearly, every mole of $\ce{K2Cr2O7}$ liberates $3$ moles of $\ce{I2}$ from an aqueous solution containing $\ce{I-}$.
So, I concluded that $2$ moles of $\ce{K2Cr2O7}$ are required to liberate 6 moles of $\ce{I2}$.
But the answer key given to me says that the correct answer for this question is $1$. Am I going wrong somewhere?


texts: Is there any chemical preservative better than sodium benzoate?

texts: I'm developing a fruit juice for humans, I just want a second opinion about allowed food preservatives. Does anyone happen to know if there are any chemical preservatives that can extend the shelf life of fruit juice better than sodium benzoate?


texts: What is the geometry of an alkyl radical?

texts:
I encountered this question which asks how many possible radicals are formed when $\ce{CH3CH2C(CH3)3}$ is monosubstituted by $\ce{Br2}$. The answer given is 3 while I think it  should be 4, reasoning that there is a "chiral" carbon if the radical is formed on carbon 3. While arguing with my tutor two questions came to my mind:

What is the geometry of the $\ce{CH3\dot{\ce{C}}HC(CH3)3}$ radical?
If the radical is trigonal pyramidal, does it transition quickly between the two possible states? If so are they considered two radicals?

My findings so far:

This answer on SE hints that the exact shape depends on the substituents on the alkyl radical.

Modern Physical Organic Chemistry states that all other (non-methyl) localized radicals are not planar.

Organic Reaction Mechanisms states that the geometry of free radicals is still controversial.


texts: Do Hartree-Fock (or other model Hamiltonian) electron densities fullfill the Kato theorem?

texts:
I have done Hartree-Fock calculations on a single He atom and now I tried to check numerically if the electron density fulfills the Kato theorem. It apparently doesn't. Instead I obtain a cusp corresponding to an effective charge of about $1.76$. That looks suspiciously like an effect due to the effective shielding exerted from the second electron. The Slater rules would suggest to expect an effective shielding of $0.3$ which is not that far away.
Also by theory one would expect such an effect, as HF is a "mean-field theory" treating the electrons seeing the mean potentials from the other electrons. Possibly one could even derive the exact deviation?


texts: Increasing available area of a solid will increase effective concentration?

texts: If I say that making a solid reactant into a powder will increase the yield of the product, because it increases the available area of the solid, hence increasing its effective concentration. Is this claim valid?


texts:
I'm reviewing a homework problem where we're given a hypothetical organic semiconductor which has a fluorescence efficiency of $40$% and a phosphorescence efficiency of $60$%.
From theory, I know that, the internal quantum efficiency is given by: $$\large\eta\small_{EL}=\large\eta\small_{PL}\cdot\large r_{st}\cdot\gamma_{cap}$$
where $\large\eta\small_{PL}$ is the photoluminescence efficiency, $r_{st}$ is the fraction of singlets over the total number of excitons formed and $\gamma_{cap}$ is the exciton formation number.
We assume that that simple spin-statistics arguments are valid to calculate the fraction of singlets or triplets generated by electron-hole mutual capture, and that the hole-electron capture efficiency is one.
I need to calculate the quantum internal efficiency of this diode with the additional assumption that intersystem crossing is negligible.  I am not sure where to start.


texts: Understanding the mechanism of Blanc chloromethylation

texts:
I have seen this question: Mechanism for chloromethylation of benzene.

The answer there uses a picture from wikipedia which confuses me. It gives $$\ce{H2C=O <=>C[HCl] H2C+-OH <-> H2C=O+H}$$ and the benzene attacking the $\ce{C}$ from $\ce{H2C=O+H}$, not the $\ce{C}$ from $\ce{H2C+-OH}$ as I would have expected.

Is it only a quirk in the picture or do I have some fundamental misconceptions?


texts: Reaction of acetylene with hypochlorous acid

texts: In reaction of acetylene with hypochlorus acid chloro enol is intermediate, which further reacts with hypochlorous acid to form dichloro  ketone. My question is that why chloro enol does not tautomerise to form ketone. And if the chloro enlo further reacts to form dichloro ketone, then this must be the minor product. And mono chloro ketone should be major product . But thisdoes not happen . Why ?


texts: Determine the quantitative composition of a solid sample containing Co, Mn, Al, C, and O

texts: I have a solid sample that contains Co, Mn, Al, C, and O. The sample mass is ~200 mg. I need to determine what the composition of this sample is. I've looked at atomic adsorption spectroscopy, but that method is unable to detect C or O. I've heard mention that inductively coupled plasma mass spectrometry (ICP-MS) might work, but I am looking for additional potential solutions. I have access to a large number of instruments (university instrument sharing agreement). It is fine if the sample is destroyed as part of the analysis.


texts:
Which ingredients in my homemade deodorant recipe are causing it to froth and overflow its container? Is there something I can add to stop this reaction?

Ingredients:

Magnesium oil (made from magnesium chloride flakes and distilled water)
Baking soda
Witch hazel
Aloe Vera gel
Arrowroot powder
Essential oils (lemon, orange blend and lavender)


texts: Baeyer-Villiger Oxidation restricted to Ketones

texts: According to Wikipedia, Baeyer Villiger oxidation occurs at the electron deficient oxygen site, with elimination of the carboxylate ion, and migration of an R group. But it is restricted to ketones and lactones. Why are aldehydes not included in it? Moreover, since migratory amplitude of hydrogen is lower than alkyl or aryl, shouldn't aldehydes be more prone to participate in this reaction?


texts:
Suppose 1 mol of $\ce{KI (aq)}$ is mixed with $\pu{1 mol}$ of $\ce{I_2^*}$, where $\ce{I_2^*}$ represents a di-iodine molecule which has been radioactively labelled, and the substances are allowed to react for an infinite amount of time. Assume radioactive labeling does not affect reactivity of the atom.
i) Predict the identity of all species in the mixture after an infinite amount of time
ii) Predict the number of moles of all species in the mixture after an infinite amount of time.

For part i), my answer was that after an infinite amount of time, all radioactive tracer decays and hence $\ce{I_2^*}$ becomes $\ce{I_2}$. Then following from the triiodide equilibrium equation ($\ce{I_2 + I^- <=> I_3^-}$), we have that the final species are $\ce{K^+, I_2, I^-, I_3^-}$.
For part ii), after an infinite amount of time, equilibrium is achieved for the triiodide equation, hence the rates of the forward and backward reaction are the same.
Now at the beginning we have $\pu{1 mol}$ of $\ce{I_2}$, $\pu{1 mol}$ of $\ce{I^-}$ and $\pu{0 mol}\ \ce{I_3^-}$, and at the end we have $1-x\ \mathrm{mol}\ \ce{I_2}, 1-x\ \mathrm{mol}\ \ce{I^-}$,  and $x\ \mathrm{mol}\ \ce{I_3^-}$. The number of mols on both sides of the equation are the same (my understanding of equilibrium) and hence $(1-x) + (1-x) = x$ gives us $x = \frac23$. Hence there are $\pu{1 mol}\ \ce{K^+}, \pu{\frac13 mol}\ \ce{I_2}, \pu{\frac13 mol}\ \ce{I^-}, \pu{\frac23 mol}\ \ce{I_3^-}$.
My question is, is my reasoning for the above two questions correct? (especially the equilibrium part, I'm not too certain about that). If it is not, then could I ask what the correct way to approach the above question would be?


texts: Something I've never understood in chemistry

texts:
I've never understood how to systematically write out IUPAC names. For example, how do I write out 6-aminohexanoic acid ? I tried searching for IUPAC related terms, but I didn't get the gist of it.

Can someone explain to me please?


texts: Is the molar mass of a molecules lowered by the binding energy of the chemical bonds?

texts: When calculating the molar mass, is there any measurable difference in total mass of the molecule due to the loss of binding energy?


texts: Determining the more acidic proton in cyclopenta-1,3-diene

texts:
I am in the David Klein textbook in Chapter 3 going over rule 2 of finding the more acidic proton: if the electron pair in the conjugated base is delocalized, then the conjugate base is more stable, ergo, the proton at that location is more acidic. Here's the practice problem I am stuck on:

I generated two different conjugated bases. The book indicates the red proton is the more acidic proton. Is this the proper resonance structure for the red proton's conjugate base?

If so, then this explains why the red proton is more acidic, because it has a delocalized pair of electrons, while the blue proton does not have a delocalized pair of electrons.


texts: Is the water absorbed by sodium polyacrylate available to react?

texts: I'm curious whether the water absorbed by sodium polyacrylate would react with alkali metals, or be trapped by the sodium polyacrylate.


texts: For a benzene shown in a skeletal structure, what does a substituent to the center of the ring mean?

texts: I have seen diagrams with both the substituents attached to the benzene ring by the edges and other occasions directly to the delocalized ring. What does signify?


texts: How is the central carbon in 3‐bromopentane‐2,4‐diol chiral?

texts:
My teacher told us the middle carbon in 3‐bromopentane‐2,4‐diol is chiral:
$$\ce{CH3-CH(OH)-\overset{\star}{C}H(Br)-CH(OH)-CH3}$$
Since there are two identical groups around it, I would guess it should not be chiral.
It was a pre-recorded class and I was not able ask this question. Has my teacher made a mistake?


texts: What is the difference between cross-linked bond and secondary bond in polymers?

texts:
In solid materials, there are two kinds of bonds between polymers: primary and secondary. Primary bonds can be also called cross-linked bonds.

What is the difference between the two (strength, type, response to stress/strain, etc)?
How do they compare to bonds inside a polymer?


texts: How can electrons manage to be at the same distance from the nucleus at all positions in p, d and f orbitals?

texts: In quantum mechanics electrons are arranged in certain orbitals namely s, p, d and f orbitals.The position of the electrons are determined by 4 sets of quantum numbers n, l, m and s. Electrons can only be at a fixed distance from a nucleus which is determined by the quantum number n, but in p, d and f orbitals how  does it manage to be at a fixed distance at every point in the region of these orbitals?(here is an example of p orbital in image)


texts: Using stoichiometry to split a complex mineral

texts:
Here is the problem I am stuck with, in particular just the first part of it.

I have calculated the moles $4.492 * 10^{-3} \,\mathrm{mol}$ and I am quizzed with regards to the equation that occurs. First assumption I am making is that the gas released is carbon dioxide.

Is it possible to separate out $\ce{(Mg_{x}Cu_{1-x})2(CO3)(OH)2}$ into simply the $\ce{(Mg_{x}Cu_{1-x})(CO3)}$ part that reacts with the dilute sulfuric acid to produce the carbon dioxide, the moles of which I know?


texts: Why does physisorption (physical adsorption) increase with ease of liquefaction?

texts:
This is what my textbook says about physisorption

  The amount of gas adsorbed by a solid depends on the nature of gas. In general easily liquefiable gases (i.e. with higher critical temperature) are readily adsorbed. Thus $\pu{1g}$ of activated charcoal adsorbs more sulfur dioxide (critical temperature $\pu{630K}$) than methane (critical temperature $\pu{190K}$).

I couldn't figure out why this should be so. In fact, according to my reasoning it should be the opposite. A gas which is easily liquefiable has higher intermolecular forces (here van der Waals forces) which would bound the gas molecules together and reduce physisorption. Where is my reasoning wrong ?


texts: Nomenclature - Lanthanoids vs Lanthanides (and Actinides vs Actinoids)

texts:
Apologies if this seems like a silly question.

Rare earth elements (the 4d series) are called by the names Lanthanides or Lanthanoids interchangeably. The same applies for the 5d series, which are called Actinides or Actinoids.

Which one of these two terms is more preferred? Is there an IUPAC directive preferring one over the other in scientific documents? If one is to write a paper or book regarding these elements, which term would one use? Or can both of them be used interchangeably?


texts: What does a sigmoidal and non-sigmoidal shape of a oxygen reduction reaction (ORR) voltammogram mean?

texts:
While testing materials for their ORR performance, one can encounter linear sweep voltammograms that have a well defined diffusion plateau and a good sigmoidal shape. On the other hand, the opposite can also be encountered, a curve without a well defined sigmoidal shape or plateau.
I was wondering, what is the significance of this shape, how does that relate to the ORR electrocatalytic activity of the material ?


texts: What is happening in this video of solvated electrons donated from sodium in ammonia?

texts:
I just saw the Periodic Video Liquid Electrons - Periodic Table of Videos where sodium is added to liquid ammonia. The demonstration shows that even if electrons are solvated, if you have a high enough electron density, the substance will turn shiny and reflective and metallic. Sodium is dissolved in liquid ammonia and donates the electrons to the solution.

There are a number of things happening in the demonstration that I don't understand.

There is supposed to be a separation - once a high enough electron density is reached, the solution is supposed to separate into a high electron density and low electron density layer. Why the separation instead of a uniform concentration? And why would the high electron concentration layer float on top?

Also, at concentrations below the metallic appearance, the sodium in ammonia solution starts out very strongly blue colored. Why? What is it about adding sodium to liquid ammonia that instantly produces such a deep blue, almost black color?

It seems that the demonstration did not go quite as planned, so isopropyl alcohol was added, producing sodium isopropoxide. Why?


texts: For molecules to be enantiomers, do their bonds have to point the same way?

texts:
Enantiomers are non superimposable mirror images. What is bothering me is:
If the bonds point different ways are they still considered superimposable and hence enantiomers?

To illustrate, comparing X and XI:

If I flip XI (180 degrees around the vertical axis that runs along the $\ce{C-C}$ bond), I get Y:

Is Y considered non-superimposable on X (and hence is Y e.g. XI an enantiomer of X)?

I would say yes they are non-superimposable, as in X the horizontal groups are pointing out whereas in Y they are pointing into the page (other than this, the groups are in "matching" positions). I don't think that is "superimposable", as the groups would not overlap.


texts: How can flammable gas become non-flammable when mixed with another gas with comparable percentage?

texts:
For example, R-410a is a 50-50 mixture of R-32 and R-125. R-32 is flammable (class A2L) and R-410a is not flammable (class A1).
Flammability of refrigerant is mainly a concern when it is leaked since there is no oxidizer when it is not leaked. But when leaked, it become gas in air. In the case of R-410a, it will become gas of 50-50 R-32 and R-125, which then diffuse and  mix with air. Since air in the room is far more than the leaked R-410a, the oxygen molecules will surround (i.e. collide with at some rate) R-32 molecules just like when pure R-32 is leaked. Then how does R-125 make R-32 inflammable under the same condition?
The only way that I can imagine for this to happen is that R-125 and R-32 molecules combine to form some aggregation of a couple of molecules in air which prevent the reaction with oxygen to happen - do they? What are other ways that can make this (i.e. the title) happen.


texts:
The initial proposal by Lawrence Berkeley National Laboratory scientists for naming element 103 was "Lawrencium" with the symbol "Lw", However, while IUPAC accepted the name "Lawrencium" for the element, it changed the symbol to "Lr".

Was there a stated (or unstated) rationale for this alteration? Was it in anyway connected with the competing claims from the Joint Institute for Nuclear Research in Dubna regarding who discovered the element first?


texts: How to distinguish diastereomers of unsaturated ketones by NMR?

texts:
I am synthesising a natural product that contains an α-methylated α,β-unsaturated ketone (see image below). The natural product’s stereochemistry is an (E) configured double bond. I selected this double bond as one of the retrosynthetic cuts of the overall molecule and I want to be sure that when I synthesise it that I get the correct stereochemistry. Is there any easy way to distinguish the (E) from the (Z) isomer?

Generic structure of an (E)-α-methylenone.


texts:
Why does the size of the ring affect the basicity of amines?

What is the factor deciding the basicity in this case?

I've read about the s-character increase concept but didn't quite understand it.


texts: Is the Ocean acidification inconsistent with the Bjerrum plot?

texts:
$\ce{CO2}$ dissolves in water and goes through chemical reactions and exists at different concentrations of,

dissolved $\ce{CO2}$,
carbonic acid,
bicarbonate, and
carbonate.

The Bjerrum plot says that a high concentration of carbonate results in an increased pH (i.e., basic). But many diagrams in the Internet about ocean acidification show that as carbonate is produced, it becomes more acidic (although they also shows as carbonate is produced $\ce{H+}$ is also produced).

Source
I don't know how to reconcile this kind of figure and Bjerrum plot as I feel they are not consistent.


texts:
I have been reading about endothermic and exothermic reactions, as well as change in enthalpy.

From what I have read, an exothermic reaction is where more energy is given out as bonds are made when products form than energy taken in as the bonds of reactants are broken.

Wouldn't this mean that the products have more enthalpy? However, a diagram online shows this (https://www.bbc.com/bitesize/guides/zg84y4j/revision/2):

Why does this diagram show that more energy is taken in as the bonds of reactants are broken? Isn't it incorrect?

I am only just getting started with this topic so I'm just learning concepts. I am not yet familiar with the formulas.


texts: How does adding lemon juice to sugar make better caramel?

texts:
It's a common cooking advice: if you want a somewhat softer caramel, add some lemon juice to the sugar:

  To help prevent the caramel from crystallizing, you can add an acid to the sugar before you begin: add about half a tablespoon of lemon juice to each cup of sugar and mix it with your hands

But how does it work?


texts: Improving efficiency of absorption refrigerator (ammonia+hydrogen)

texts:
Apologies if this is not the right forum for this question, I checked the Physics side and there's no questions on this, whereas there's at least one other question here about absorption refrigeration.

I have a very standard camping fridge which runs on the absorption cycle, I'm making a leap of informed guesswork and assuming it's ammonia + hydrogen based.

I'm investigating ways the efficiency or performance of the system could be improved without major surgery but I'm neither a chemist nor physicist (nor surgeon).

Here's the system as explained by the manufacturer:

And here's the actual unit, minus some lagging round the boiler:

So you can see it's pretty basic, they haven't changed the design in decades.

My main train of thought, based on the bleeding obvious, is that either more heat could be added at the boiler end, or more cooling (basically, a fan) could be added to the condenser.

However, I don't know enough about how the coolant behaves to know if this would be of any benefit - adding heat could just ruin everything, cooling beyond a certain point may make no difference, etc. etc.

Additionally, I don't know if things could be done at other points in the cycle (cooling or heating other areas such as the absorber being the obvious easy wins) to improve matters.

I would also like to add that this is mostly driven by my curiosity for tinkering with things, I realise that the real-world answer to a better fridge is to buy a compressor type one - but they're expensive (seriously, compressor camping fridges are more than a full-size household fridge+freezer) and I won't learn anything that way ;)

EDIT: Thanks for the responses, ultimately the thing was never going to be viable running on 12v so we bought a compressor-type which is about 10x more efficient (in electricity) by comparison.


texts: Is there a rule of thumb to predict when coupled cluster might dip below the variational limit?

texts:
Coupled cluster is a non-variational method, meaning that it can give energies that are below the true FCI energy (the "variational limit" for variational methods).
Often coupled cluster still gives energies far above the true FCI energy, and sometimes it gives energies that dip below the variational limit.
Are there some guidelines on when this will happen and when we are safe to assume it will not? I'm aware that coupled cluster generally works best when there is one dominant determinant (single-reference cases), so I am asking about guidelines within the single-references case, when we might expect to get energies that violate the variational principle.


texts:
Picric acid is stored under a layer of water to prevent an explosion.

What is the right way to measure the amount of picric acid that taken out? It is wet and containing water.


texts: What is produced when citric acid (powder form) is burned, is it safe?

texts:
What is produced when citric acid (powder form) is burned?

Are the fumes harmful or safe?


texts:
I know that fractional distillation is used to separate two liquids that are miscible in one another and have close boiling points.

However, I am really confused about vacuum and steam distillation - in which cases do we use these separation techniques? Can someone please give examples.


texts: Using Roman Numerals to indicate a compound

texts:
I don't completely understand it's use. Here's an example I don't understand:

Shortly after discussing $\ce{[CuCl4]^2-}$, an exam paper asked a question about copper(II) chloride. I understand that copper(II) chloride could refer to $\ce{CuCl2}$, calling it copper(II) chloride, but couldn't it also refer to $\ce{[CuCl4]^2-}$? I would understand the question in reference to $\ce{CuCl2}$, but it got confusing when I realised it could equally be referring to $\ce{[CuCl4]^2-}$, especially after it just mentioned it.


texts: Determine which molecule has stronger intermolecular force?

texts:
SiH4 and CH4

The only intermolecular force they both have is London Dispersion forces

Strength of LDF is determined by molar mass

molar mass of SiH4 = 32.132

molar mass of CH4 = 48.42

Therefore shouldn't CH4 have a stronger LDF??

The answer says that SiH4 has a greater intermolecular force...why is that?


texts: Is *rinsing* (after washing) with cold water is as efficient as rinsing with hot water?

texts:
Let say I have, a dishwashing soap, plenty of cold water (5 °C) and only have 2 L of hot water (60 °C) to clean a t-shirt with oil stains. Should I use the 2 L to wash the t-shirt and then the cold water to rinse the shirt or should I wash the t-shirt with only 1 L of hot water and then use the second liter for a first rinse and then the cold water to finish rinsing?

If the soap has already "captured" the fat molecule (in the micelles), I shouldn't need the hot water to rinse the micelles, right?


texts:
As you may know, wettability is a characteristic of each surface which determines what the contact angle would be when a droplet is put on the surface (see here for more info). Surface roughness has a significant effect on wettability. For instance, if you increase the roughness of a polymer surface, the contact angle will be increased as well (i.e. it becomes more hydrophobic).

I need to create a surface such that I can control its wettability by an external stimulus (e.g. temperature, etc.). For instance, a polymer (or any other material) in which when I change its temperature, the surface roughness is also changed (due to change in the molecules chains shape or crystallization). I need to know which materials I can use to create this kind of surface.


texts: What's the difference between precipitate and turbidity?

texts:
In many tests for various radicals, a "<color> precipitate" or "<color> turbidity" is mentioned. For example, lead acetate with chromate ions gives a yellow precipitate, but hydrogen sulphide with potassium dichromate gives a yellow(or white) "turbidity".

In the reaction itself, the turbidity is noted as a precipitate with a down arrow, but I'm wondering if there is any difference between the two. It looks like turbidity refers to a colloid/suspension being formed, but I'm not sure.

I'd like to know:

The physical differences/distinguishing features between turbidity and precipitate, if any.
The observable differences/distinguishing features between the two, if any.


texts:
The sodium fusion extract is acidified with acetic acid and lead acetate is added to it. A black precipitate of lead sulphide indicates the presence of sulphur.

What is the need for acidification of extract before adding lead acetate? Wouldn't Lead sulfide be formed if we add directly lead acetate? Can we use any other acid and its salt of lead?


texts: Why doesn't cyclopropyl methyl carbocation stabilises itself by ring expansion?

texts:
I have been taught that ring expansion stabilises smaller cyclic compounds to a great extent. So why does cyclopropyl methyl carbocation shows such type of resonance

rather than expanding its ring

thereby decreasing it's angle strain, further it will be stabilized by hyperconjugation effect and inductive effect.


texts:
My teacher told me that Neon has a larger atomic radius than Fluorine.I am of the understanding that it is merely a consequence of the way we define the atomic radius and that we use Van der walls radius for neon which is larger that the covalent radius of fluorine.

He also said that the radius of a fluorine 1- anion is more than a neon atom by using the fact that they are iso-electronic species and that since neon has a higher nuclear charge, it will pull on the 10 electrons more than fluorine.

But what definition of atomic radius am i using for neon now? Aren't we always supposed to use the Van der walls definition for noble gases? In case we do use the Van der walls radius of the neon atom and the ionic radius of the fluorine anion, how am i supposed to compare these two and come to the conclusion that the fluorine anion is larger?


texts:
The change in enthalpy of carbon in diamond form to graphite is negative. This suggests that graphite should be more stable than diamond. Is it true?

What I thought was that graphite has van der Waals forces while diamond has covalent forces so diamond should be more stable. But the melting point of graphite is more than diamond which implies that it is thermodynamically more stable. I am thoroughly confused. So which is more stable?


texts: So I was doing analysis of Ag salts and I found Agbr is curry white partially soluble in ammonia , AgI is yellowish and insoluble . BUT silver phosphate is also yellow . So can anyone tell whether or is soluble in ammonia or not ?


texts:
I have read that quinone systems are conjucated but not anti-aromatic. I had read the related questions:

Is the aromaticity broken in some resonance structures of para-nitro-aminobenzene?
Is a quinone ring aromatic?.

In one of those answers, I read a point which said that it was non aromatic:

  [...] and you must be able to draw double bonds - internal to the ring
  - from each ring carbon atom. [...]

I don't get what this means as I had never heard of such a thing in Hückel's rule. I did read elsewhere that the system must be completely conjugated which is true in this case but due to cross conjugation the electrons are not delocalised throughout the system? I don't get why cross conjugation affects the delocalisation of the electrons this much? What is the proper explanation for this?


texts:
According to me net reaction should be at $\ce{C3}$ when Reimer-Tiemann reaction is done on indole (see image), since in the resonance structure, negative charge is on this carbon.

But, the answer given is on $\ce{C2}$, and the solution given is

  In pyrolle, the most electrophilic site is $\ce{C2}$. Think in a similar way.

But, I can't either find fallacy in my reasoning, not do I convince with the solution.

TL;DR Where will dichlorocarbene attack on indole (am not interested in ring expansion).


texts:
How many dipeptides are possible by the reaction of glycine and alanine?

Glycine has no chiral centre. Alanine has one chiral centre.
The products are alanylglycine and glycinylalanine (I not sure whether this is the correct name or not. Please excuse), and I got a total of 4 isomers for each, (using D,L notation and optical isomers) so I got a total of $4+4=8$ products.

But the answer is given as $9$.

Where is my mistake?


texts:
I've seen a few videos on cola being used to remove rust, I've tried it myself too so I know that it works.

Now the thing that's bothering me is that this apparently contradicts what I've learnt about corrosion in class. If I'm not wrong, cola contains phosphoric acid, and therefore would most probably have free H+ ions floating around in there. I've been taught that H+ promotes (catalysis) the rusting of iron.

Then how come coke removes rust instead of promoting its formation? Also, why doesn't coke form rust on iron?


texts: Historically, how was the connection between NMR peaks and hydrogen atoms made?

texts:
A large part of the basis of this question may be due to the student who didn’t pay attention in the history section of the NMR course (and not during the technical details bit either) but I find the question intriguing nonetheless.

My basic knowledge of the history of NMR spectroscopy is that in the very old, almost prehistoric days, Bloch and Purcell performed some experiments that applied radiofrequency to a sample and by chance got some radiofrequency signal returned. Then I have a big black box and arrive at modern spectrometers that tune themselves into hydrogen spectra, carbon spectra and see beautiful Fourier-transformed spectra on my PC screen (unless it’s carbon, in which case the baseline is, of course, fuzzy).

I imagine that there had to be a lot of research invested until it was realised that each signal in the Fourier-transformed spectrum corresponds to a hydrogen atom, that they are shifted around depending on how electron-rich or -poor they are, how couplings work and so on. I can imagine that most of this stemmed from trial and error: a certain combination of magnetic field and radiofrequency gives a signal, Fourier transformation seems to happen anywhere, and once you have rationalised that ‘signals’ correspond to ‘hydrogens’ in a certain type of spectrum (likely the one that gave most resonance anyway) you’re half done and the rest is a walk in the park.

But there is one step that seem very unintuitive:
Realising that ‘signals’ correspond to hydrogens.

There is another important step, namely figuring out that solutes can be analysed if hydrogen-free ($\ce{CCl4}$) or at least protium free (deuterated) solvents are used. Now either it was figured out first that hydrogen is the cause for the signals, in which case choosing the correct solvents is a non-issue, but capturing signals from the solute may be. Or it was figured out that using certain solvents gave ‘cleaner’ spectra, in which case it might also be interesting to know how the solvents were chosen.

I realise that there may be a good deal of speculation, retrofitting, inflationary use of the term serendipitously, anecdotical evidence, storytelling and bad memories involved, but is it known how the discoverers of NMR spectroscopy realised that a ‘signal’ is a hydrogen atom in the molecule observed?


texts: Why is [1.1.1]propellane considerably less reactive than either [2.2.1]propellane or [2.1.1]propellane as illustrated in the hydrogenation reactions pictured below?


texts: Relative acidity of p-chlorobenzoic acid and p-flurobenzoic acid

texts:
I want to compare the relative acidity of p-chlorobenzoic acid and p-flurobenzoic acid. Both of the facts below point to p-chlorobenzoic acid being more acidic:

The carboxylic acid group is too far away from the halogen for inductive effect to have any significance. The +M effect of fluorine is greater than chlorine (due to more effective orbital overlap). +M effect is not distance dependant and hence p-fluoroobenzoic acid  should be less acidic since the negative charge on its conjugate base is destabilized.
There is resonance of the negative charge of the carboxylate ion with the empty d-orbitals of chlorine which would stabilize it.

However, in reality, p-chlorobenzoic acid is less acidic than p-fluorobenzoic acid . Why?

$\mathrm{p}K_\mathrm{a}$ of para chlorobenzoic acid $\ce{-> 4.03}$.Source
$\mathrm{p}K_\mathrm{a}$ of para fluorobenzoic acid $\ce{-> 4.14}$.Source


texts: Identifying Nucleophiles and Electrophiles

texts: Are all polar molecules both nucleophilic and electrophilic, depending on which atom you are talking about? Take water for example. Oxygen bears the partial negative charge. Oxygen is nucleophilic. Because oxygen isolates electron density from the hydrogens, the hydrogens bear partial positive charges. So would the hydrogens be electrophilic?


texts: Reaction of Lead(II) Chloride and Ammonia

texts:
While searching how to identify cations in a solution I found that ammonia could be used to distinguish between $\ce{AgCl}$ and $\ce{PbCl2}$ precipitates after $\ce{HCl}$ had been added.

Why does the addition of ammonia cause $\ce{PbCl2}$ to dissolve while $\ce{AgCl}$ doesn't? (With chemical equations if possible.)


texts: Deduce the possible structure given spectroscopic data for the aromatic compound

texts:
For $\ce{C11H13NO}$, I have the following $\ce{^1H}$ NMR data:

shift (ppm)

3.00 (6H, s)
6.55 (1H, dd, $J=15.5, \pu{9 Hz}$)
6.70 (2H, d, $J=\pu{8Hz}$)
7.35 (1H, d, $J=\pu{15.5Hz}$)
7.45 (2H, d, $J=\pu{8Hz}$)
9.60 (1H, d, $J=\pu{9Hz}$)

I also know there are two absorptions from IR at $1600$ and $\pu{1660cm^{-1}}$.

From the IR it seems reasonable to suggest an aromatic amide ($\pu{1660cm^{-1}}$). The shift of $\pu{9.60ppm}$ is huge and I think this could really only come from a proton connected to the carbon of a carbonyl. The 6H peak could be two equivalent $\ce{CH3}$ groups, and as it is singlet, I thought they could hang off the nitrogen of the amide, then it wouldn't split. The two sets of 2H atoms I thought could be from the aromatic ring. The problem is piecing all of it together!

The closest structure I have is this:

but I know this is wrong as it lacks a $\pu{9.60ppm}$ shift. How can I arrive at the correct structure?


texts: Reaction Kinetics and Stoichiometry -- Mass conservation

texts:
This question has been bothering me for some time, and I can't seem to find a good answer online.

Say I have four chemical species $\ce{A}$, $\ce{B}$, $\ce{C}$, $\ce{D}$, and these four react in the following ways:

\begin{align}\ce{
A + A &-> B\\
A + B &-> C\\
A + C &-> D\\
A + D &-> B + C\\
}\end{align}

The kinetic reaction equations for these four species should be:
\begin{align}
\frac{\mathrm{d}[\ce{A}]}{\mathrm{d}t} &= -k_1[\ce{A}]^2-k_2[\ce{A}][\ce{B}]-k_3[\ce{A}][\ce{C}]-k_4[\ce{A}][\ce{D}]\\
\frac{\mathrm{d}[\ce{B}]}{\mathrm{d}t} &= +k_1[\ce{A}]^2  -k_2[\ce{A}][\ce{B}] +k_4[\ce{A}][\ce{D}]\\
\frac{\mathrm{d}[\ce{C}]}{\mathrm{d}t} &= +k_2[\ce{A}][\ce{B}] -k_3[\ce{A}][\ce{C}] +k_4[\ce{A}][\ce{D}]\\
\frac{\mathrm{d}[\ce{D}]}{\mathrm{d}t} &= +k_3[\ce{A}][\ce{C}] -k_4[\ce{A}][\ce{D}]\\
\end{align}

where $k_i$ is the Arrhenius coefficient for that reaction.

In my mind, the stoichiometry does not seem to add up right. It seems that when the system undergoes $\ce{A + A -> B}$, the concentration of $\ce{A}$ should decrease by twice as much as a reaction like $\ce{A + B -> C}$. Similarly, the products of $\ce{A + D}$ should be split evenly between $\ce{B}$ and $\ce{C}$.

Therefore, stoichiometrically, I want to write:
\begin{align}
\frac{\mathrm{d}[\ce{A}]}{\mathrm{d}t} &= -2k_1[\ce{A}]^2-k_2[\ce{A}][\ce{B}]-k_3[\ce{A}][\ce{C}]-k_4[\ce{A}][\ce{D}]\\
\frac{\mathrm{d}[\ce{B}]}{\mathrm{d}t} &= +k_1[\ce{A}]^2  -k_2[\ce{A}][\ce{B}] +\tfrac{1}{2}k_4[\ce{A}][\ce{D}]\\
\frac{\mathrm{d}[\ce{C}]}{\mathrm{d}t} &= +k_2[\ce{A}][\ce{B}] -k_3[\ce{A}][\ce{C}] +\tfrac{1}{2}k_4[\ce{A}][\ce{D}]\\
\frac{\mathrm{d}[\ce{D}]}{\mathrm{d}t} &= +k_3[\ce{A}][\ce{C}] -k_4[\ce{A}][\ce{D}]\\
\end{align}

Is this wrong-headed? What conceptual issue am I missing?


texts: Simulating H1 NMR spectra using chemical shift/multiplicity data?

texts:
I've encountered a number of free programs/internet plugins that can output IR spectra and the corresponding chemical shift/multiplicity data if you input a chemical structure, but are there any where you can input chemical shift/multiplicity data and get an output of at least the H1 NMR spectra?

Note: by "chemical shift/multiplicity data", I am not referring to chemical shift tensors (σ). I mean simple data like "1.92 ppm (2 H, m)".


texts: Name of toxic liquid product that can be cleared with flocking agent

texts:
I'm writing a paper rpg scenario, and even if we don't need to be 100% accurate about chemistry and physics in such games, one of my players has an advanced level in chemistry and I don't want him to cringe at the situation (and I can't ask him, obviously, or he'll be spoiled).
So, I need a river to be polluted with an invisible and odorless product, that slowly destroys the fauna. As it happens in Siberia, I thought about tritium first, but I don't think it's easy to clean. So I thought about a product that could be cleaned with a flocking agent. Problem is, when I was searching for "products reacting to flocking agent" on Google I didn't find any name of product that I could use.
So, which invisible, toxic and odorless product react to flocking agent to the point the river is cleaned in one or two months maximum (and eventually produced in the 1980's) ?
Thanks a lot, and sorry if it's not the SE to ask this question.


texts:
I am looking for a type of plastic, preferably in the form of a sheet or film, that is weatherproof, durable, flexible, and both transparent and UV-transparent. Most films I've seen so far are treated to be UV-resistant, where can I find untreated plastics for purchase?
Planning to use this plastic in order to cover a solar panel, without inhibiting energy output.


texts: Can I make my own graphene at home in my kitchen?

texts: Graphene is cool. Can I make some? What do I need? Is it at all feasible to make it in quantity?


texts: What are the chemical formulae for galvanic corrosion of iron (rusting)?

texts:
The conditions for corrosion, I am searching equations are as follows:

The other metal is copper
The temperature is $25~\mathrm{^\circ C}$
The electrolyte is $\ce{NaCl}$
pH 7
A limited amount of oxygen

Which hydroxides and oxides are formed when iron undergoes galvanic corrosion? Which ones are dominant?


texts: How can chlorine have an oxidation number of 3 in chlorite?

texts:
I am studying redox reactions right now and I'm a bit confused about something:
$\ce{ClO2^-}$ is a compound ion and in a compound ion the sum of oxidation state of participating ions has to be equal the charge on compound since $\ce{ClO2^-}$ has a whole charge of $-1$ the oxidation state sum of $\ce{Cl}$ and $\ce{O2}$ must be $-1$, right? Oxygen has an oxidation state of $-2$ so $\ce{O2}$ will have
\begin{align}
2\cdot -2 &= -4\\
-4 + x &= -1\\
x &= -1 + 4\\
x &= 3\\
\end{align}

Chlorine has to have an oxidation state of $+3$.
But if you look at the periodic table chlorine is in 7th period which means it has 7 electrons in valence so it gains one electron while reacting.
Getting oxidized by definition means losing electrons so an oxidation state of $+3$ means chlorine is losing 3 electrons. I just can't get my head around why would chlorine do that? Or am I calculating the oxidation state wrong?


texts: Experimental melting-point of Arm-and-Hammer sodium bicarbonate is remarkably high(?)

texts:
Online literature reports the melting point of $\ce{NaHCO3}$ as ~50 deg. C.

Using a standard Mel-Temp II melting-point apparatus and a standard alcohol thermometer, I didn't observe any melting of any sample lower than 150 deg. C. I don't think hydration of the salt can even explain this. Is there some other material in commercial baking soda that would alter the melting point this much?

As a raw calibration, I found that some Bayer Aspirin powder (possibly containing cellulose or other binding agent) had a melting point of 120 deg. C., a good deal below the reported ~135 deg. C.

Does anyone know what may be present in commercial Arm-and-Hammer baking soda besides sodium bicarbonate? The box reports 100% purity but I have trouble believing it now.

I've heard rumors that some baking-soda products contain aluminum and this has raised some alarm about ingestion hazards. Is this valid?


texts: Can Sodium Pyruvate decarboxylate to acetic acid + CO2 in the presence of just moisture and heat?  If so, what kind of temperature is required?


texts: Calculating change in Gibbs Free Energy for a specific type of problem

texts:
Can anyone describe what is going on here?
$$Si(liq.)=Si_{(1 weight percentFe)}$$
I have come across this statement quite a few times in Metallurgical Thermodynamics.All that they ask for is change in Gibbs free energy for the process.I am completely unable to figure why this particular model is so important for a sepecific question.It would be great if someone could interpret both the analytical and the mathematical analogy to this.


texts: The effect of reactant concentration on when equilibrium is established

texts:
Take the equation
$$\ce{A(g) <=> B(g)}$$
where the reaction is first order with respect to A. The rate law is thus
$$\frac{\mathrm d[\ce{A}]}{\mathrm dt}=-k[\ce{A}]$$
Say you run the reaction, starting with $x$ moles of A. Equilibrium is established at time $y$. If you run the reaction again, this time with $2x$ moles of A, won’t equilibrium be stablished at time $y$ as well? You double the rate of reaction, but you have twice as many molecules to react, so wouldn’t time remain the same? I’ve been told that the equilibrium effect dominates over the kinetic effect; that is, it will take a time that is greater than $y$ for the reaction to reach equilibrium. I cannot fathom the mathematical basis of such a conclusion. Can someone elucidate?


texts: Can sugars like fructose-glucose or high-fructose corn syrup that are found in many types of processed food contribute to shortening a products shelf life?  Don't bacteria love things like sugar so if a product has a lot of fructose-glucose added to it, it will need even more preservative chemicals to compensate for any increase of sugar?


texts: Which software to use to output molecular orbital diagrams?

texts:
I want to output a molecular orbital diagram. Can anyone recommend a software to do this? Also I searched for a python module, but didn't found a pure solution. Maybe I am using the wrong keywords.
I want to connect two atoms with a specific electron configuration, to see at which energy levels they have pi- and sigma-bindings.


texts:
How would you go about writing the reaction between water and chromium metal under standard acid and base conditions?

I know you would have to look at the vertical lines at pH 0 and 14 but I don’t know how you would know which species to look at and whether or not you write the reduction or oxidation of water.

Also, at pH 14 how would you calculate the ${\Delta G}$ value for the reduction between water and chromium metal?


texts: How many total absorptions would appear on proton -NMR spectrum for this molecule?

texts:
I count 7 equivalent absorptions total, but answer says 8. I don't see where this eighth absorption comes from?

Heres how I'm counting starting on right side of molecule:

1 is Carbox acid H

2 is the 1 H just left of the double bonded Oxygen

3 is the 3 H's of the methyl group next to the lone H

4 and 5 are the 2 sets of equivalent H's in the ring structure

6 is is the 2 H's to left of ring

7 is the 2 methlys on the isoproplyl (these are equivalent so same signal)

How do they get 8?


texts: Why are antiaromatic compounds unstable?

texts: Antiaromaticity is so destabilizing that it can cause compounds such as cyclobutadiene to elongate or manipulate their orbitals so that the pi system is no longer aromatic. I understand that aromatic compounds are stabilized because they have a full HOMO and that antiaromatic compounds have a half filled HOMO, which according to this question is the reason that they are unstable. I don't agree with this explanation because in other compounds, half filled orbitals cause compounds to be stabilized. For example, triplet oxygen is significantly more common than singlet oxygen in nature. Also, some transition metals will promote electrons from their S orbitals to D orbitals so that they can have these shells half filled. I know that full orbitals are more stable than half filled orbitals, but are half filled orbitals destabilizing in alkenes while they are stabilizing in oxygen and metals? If not, why are antiaromatic compounds so unstable?


texts:
Yesterday, I bought some "magic" rollerball pens (those with water-based ink), available in red, blue and black.

They look and write like a normal pen, but have an eraser at the upper end, just like a pencil. You can erase the ink with this eraser, but the real miracle is: A few seconds in the freezer at −18 °C, and the ink becomes visible again.

Some additional facts:

The eraser of the pen is translucent and feels wax-like, but is quite hard for an eraser.
It does not rub off anything, you don't get that typical crumbs.
Normal erasers do not have any effects on the ink, just as expected.
It's the perfect ink eraser: You can erase a letter and directly write a new letter on it with the same pen, like a pencil.
The process can be repeated. You can erase the ink and recover it in the freezer several times.

I know those ink erasers from school or those "magic pens" which change the color of the ink of other pens, and also know, how it works.

But this pens are new to me. Has anyone an explanation of their principle of work?


texts: Finding Hybridization of Certain Atoms in Lewis Structure

texts:
So, I'm having trouble with this problem. We're given this incomplete lewis structure and asked to find the hybridization of 3 of the atoms.

I figured that the labelled Cl would be sp3 because of it's 1 single bond and the 3 lone pairs that would be on it.
I also thought the labelled C would be sp2 because of the 2 single bonds and 1 lone pair.
Now, I was confused at to what the labelled O would be. I thought maybe it would have 3 lone pairs but that doesn't seem to be correct, since my sp3 answer was rejected.

Any insight on what I'm doing wrong here?


texts: Why is enthalpy of atomization of Mn exceptionally low?

texts: Transition elements usually have high values, especially so for greater number of unpaired electrons. Why the exception here?


texts: How are organic compounds with radioactive atoms synthesized?

texts:
We often see reactions such as these in textbooks to highlight how reaction mechanisms work:

How are the radioactive substrates required for these mechanisms synthesized in the first place? There seems to be no easy way of just 'substituting' a radioactive atom in place of a non-radioactive one (especially for Benzene-14C, it might be easier to make a radioactive sodium salt using $\ce{^{24}Na}$). Also, Once the substrate is synthesized, how is it separated and purified? I'm assuming that the physical properties of these radioactive substrates would be very similar to their non-radioactive counterparts, which would make it very difficult to do so.


texts: AAS background correction with Zeeman effect

texts:
I've found here the explanation to how Zeeman effect can be used for background correction. I understand everything up to this part:
"When light is polarized parallel to the field, both atomic and background absorption occurs, and when light is polarized perpendicular to the field, only background absorption occurs."

I understand that light can be polarized, and that we are trying to somehow exclude either atomic or background absorption from one of our measures. I don't see, however, why this would be valid. Why is the perpendicularly polarized light not experiencing also the atomic absorption?


texts:
Can we justify that "For sublimation of a solid at 1 atm  $\Delta U>0$ at low temperature and $\Delta U<0$ at high temperature?"
I read several answers and came to know that $U=f(T)$ is valid only for ideal gases at $\pu{1 atm}$ pressure where $T$ is temperature.
Internal energy is the sum of kinetic energy of molecules and chemical potential energy of molecules.
For phase transition even if the temperature remains constant, its internal energy changes.
I tried  to justify  by considering that while sublimation as solid changes to gases its degrees of freedom increases and we may say internal energy is a function of degrees of freedom so  as temperature increases so $U_2 > U_1$ so $\Delta U >0$ but this contradicts what we have to prove.
Also similarly what can  we say about internal energy for other phase transitions ?

Answer given is: ABCD
source:Physical Chemistry (Vol. II) (Class XI) Chemistry Module For JEE (Main+Advanced) Paperback – 1 January 2018
by Resonance Eduventures Limited


texts: How can a group be both a good nucleophile and a good leaving group?

texts:
I'm reading about $\:\mathrm{S_N1}$ and $\:\mathrm{S_N2}$ reaction mechanisms, and I have a few questions.

My book has a couple of tables, one lists a bunch of substances grouped as good, moderate and poor nucleophiles. Among the good are $\ce{Br-}$ and $\ce{I-}$. So a couple of halogens. I'm figuring chlorine is in that group too.

Then it has a table showing ability to function as leaving group. Iodine, bromine and chlorine anions are at the top of that list too.

My question is: How can these be quite attracted to the positive charge AND quite easy to remove at the same time?


texts: Can the following compound having a centre of symmetry be called both optically inactive and meso?

texts:
The Centre Of Symmetry (COS) has been shown by a blue dot.

My questions are:

Can this molecule be called optically inactive? I have this doubt because single bonds permit free rotation and the molecule hardly
remains in the given form for long.
Can this molecule be called a meso-compound as it optically inactive?
Slightly unrelated: I'm actually a bit confused with the definition of meso. I learnt that meso compounds must have a plane of symmetry. Am
I correct?

According to Wikipedia a meso compound or meso isomer is a non-optically active member of a set of stereoisomers, at least two of which are optically active.
Update: I realized my mistake in thought procedure after asking the question.(I fell into the "Meso Trap" :-P )
I would like to add this link as it might help future viewers.
http://www.masterorganicchemistry.com/2011/01/12/the-meso-trap/


texts: Determine the equilibrium constant for this reaction

texts:
The question is:

  Ions $\ce{B}$ and $\ce{C}$ react to form complex $\ce{BC}$. If $\pu{15.0 mL}$ of $\pu{1.00 M}$ $\ce{B}$ is combined with $\pu{15.0 mL}$ of $\pu{1.00 M}$ $\ce{C}$, and our initial concentration of BC is $0$, yet the end in equilibrium for complex $\ce{BC}$ is $\pu{0.00450 mol}$ determine the equilibrium constant for this reaction.

Firstly, I converted the total volume $\pu{15.0 mL + 15.0 mL = 30 mL}$ to L and I got $\pu{0.03L}$

Secondly, I used the given $\pu{0.00450 mol}$ and divided it by $\pu{0.03 L}$ and I got $\pu{0.15 M}$ for BC

Thirdly, I did the ICE chart

After that, I used the quadratic formula to solve for $x$ and calculate the concentration for each substance, as well as getting the $K_\mathrm{c}$ at equilibrium

I got $1.53$ for $K_\mathrm{c}$ but I am not sure if the whole process is correctly done. Please point out my mistakes


texts: ORCA: meaning of numbers in ORCA.out of MOLECULAR ORBITALS for STO-3G Lithium


texts: What is the difference between fractional freezing and fractional crystallization?

texts:
More simply put, what is the difference between freezing and precipitation when considering a mixture?

Take two scenarios:

First a mineral in water. If the temperature of this solution is lowered, the solubility of the mineral will decrease and eventually precipitate out of solution. This could be done in a cascade type setup so that each time, the solution is cooled further and the liquid phase becomes more and more concentrated in water.

Second, consider a mixture of ethanol and water. Here too, I could lower the temperature until crystals first form. They would be almost pure water, leaving behind a solution higher in concentration in alcohol. I could repeat this procedure until I reach the eutectic mixture.

In both cases, a drop in temperature is allowing a solid phase to form out of an aqueous solution, yet one is referred to as partial crystallization and the other is referred to as partial freezing. I am not sure I see the difference.


texts:
I am wondering if the Rubidium ($\ce{Rb}$) in gas form can react naturally with Sapphire crystal ($\ce{Al2O3}$)?
The temperature is $500\ \mathrm{K}$ and the pressure is around $1\ \mathrm{Pa}$ to $10\ \mathrm{Pa}$.

One of the reaction that comes into my mind is
$$\ce{4 Rb + Al2O3 -> 2 Rb2O + Al2O}$$

I was trying to calculate the Gibbs free energy of the reaction, but I could just find the Gibbs free energy for Rubidium and the Sapphire, which is $\Delta G_{\ce{Rb}}=53.1\ \mathrm{kJ/mol}$ and $\Delta G_{\ce{Al2O3}}=-1582.3\ \mathrm{kJ/mol}$. I can hardly find the Gibbs free energy for the products.

Is there any other reaction that can occur naturally?


texts: Why can't we calculate the atomic radii of noble gases?

texts: My book says that only the Van der Waal's radius of noble gases can be measured as these gases generally do not form compounds (except Xenon.) Then why can't we just calculate the atomic radii by computation, say solving the Schrödinger equation? Can't we make computer simulation models of isolated atoms of noble gases?


texts: Does the emf of an electrode potential change over time?

texts: In an electrode potential with a salt bridge and high resistant voltmeter, does the emf change over time as the reactions occur?


texts: What is the valence molecular orbital of the ions of a fluorine molecule?

texts:
I have the following assignment:

  Draw the molecular orbital diagram of $\ce{F2}$, $\ce{F2+}$ and $\ce{F2-}$.
  Calculate the bond order and say, if there is a bond, which compound has the strongest bond
  and which one has the longest one.

My attempting at answering has lead me to the following conclusions:

As my understanding goes, $\ce{F}$ has $7$ valence electrons in the $2s^2$ and $2p^5$ subshells. By combining the atomic orbitals, one will obtain:

$2$ $\sigma_{2s}$ orbitals (a bonding and an antibonding), 2 $\sigma_{2p}$ a bonding and an antibonding, and $4$ $\pi_{2p}$ (2 degenerate bonding and 2 degenerate antibonding).

By filling the MO, I obtained the following bond orders: 1 for $\ce{F2}$ and $\frac{1}{2}$ for $\ce{F2+}$ and $\ce{F2-}$.

First of all, I would say that there is definitely a bond in all the three compounds since the bond order is positive. Then I would say that $\ce{F2}$ has the strongest bond (since it has the highest bond order), then $\ce{F2+}$ and $\ce{F2-}$ have longer bonds than $\ce{F2}$ due to the lower bond order, however I do not know which one has the longest bond.

As for the question:

I never came across $\ce{F2+}$ and $\ce{F2-}$. Is my reasoning correct? Do these compounds exist? Furthermore, I draw the MO using an atom of $\ce{F}$ and an ion of $\ce{F}$ (cation and anion depending on the case). Is the procedure correct?


texts: Understanding the CIP configuration for cyclic substituents with hetero-oxygen atoms

texts:
As per CIP sequence rules, the topmost $\ce{C}$ on the left gets 1st priority. Moving on to the right side of the double bond, we have:

Top $\ce{C}$: ($\ce{C}$,$\ce{O}$,$\ce{O}$,$\ce{H}$)
Bottom $\ce{C}$: ($\ce{C}$,$\ce{O}$,$\ce{O}$,$\ce{H}$,$\ce{C}$...)

Thus bottom $\ce{C}$ gets priority one on the right side.

Now, since 1st priorities are opposite, it's an E isomer. But the solution manual states that it's a Z isomer. Why is my method incorrect?


texts:
Are large oxygen containing molecules possible? Either large rings, or chains with hydrogen atoms at the ends. Like this:

$\ce{H-O-O-O-O-O-O-O-O-O-$\cdots$-O-O-O-O-O-H}$


texts: Why lithium is least reactive in water among group one elements though it has the most negative Electrode Potential value?


texts:
Recently there has been announced a new 3d printing technology which uses UV light, from lasers or a projector, to harden slices of epoxy resin so that the printed object rises out of a pool of epoxy.

There is some information about an oxygen boundary and UV light, can someone explain the chemistry of the process?
https://www.youtube.com/watch?v=UpH1zhUQY0c


texts: Mistake in Wikipedia article on fugacity?

texts:
The Wikipedia Article on Fugacity contains statement

  The contribution of nonideality to the chemical potential of a real gas is equal to RT ln $\phi$

Here $\phi$ is fugacity coefficient.I think it is wrong it should be fugacity coefficient multiplied by partial pressure of gas divided by standard pressure.So for the example of nitrogen gas at 100 atm it's chemical potential should be μ = μ$_{id}$ + RT ln 97.03 and not μ = μ$_{id}$ + RT ln 0.9703 as given in Wikipedia Article.

I am confused, who is wrong me or wikipedia ?


texts: Why does phosphorus give a free electron in silicon doping?

texts:
Extrinsic semiconductors are created by doping an intrinsic semiconductor; typically silicon is doped with phosphorus to create free electrons or boron to create "holes".

In the case of phosphorus doping, phosphorus takes the place of a silicon atom in the silicon lattice, and its fifth electron becomes a free electron.

Here is what I am struggling to understand with my basic knowledge. Phosphorus has the configuration $\ce{[Ne] 3s^2 3p_x^1 3p_y^1 3p_z^1}$.

This page gives an description of the promotion of a 3s electron to a 3d shell, allowing five bonds to form in the case of $\ce{PCl5}$. I would assume that a similar process results in four bonds forming in the silicon lattice and leaving a free electron.

But that same page later on mentions a 2007 paper which essentially says that that model is not accurate, because such a state is less stable than other ways of modeling the bond (assuming I'm understanding correctly. The problem is described here, I have not read the actual paper.

What causes phosphorus to form four bonds with silicon and leave a free electron rather than, say, forming three bonds and leaving a silicon with an unpaired electron in the lattice, or bonding with another "free" electron? Is it promoting an electron to form the fourth bond and freeing the last?

In short: Why does phosphorus form four Si bonds and leave a free electron rather than forming three Si bonds when doping silicon?


texts: Determining mole fraction of carbon dioxide knowing Kp only

texts:
I've been assigned the following problem at school:

Given the following reaction:
$$\ce{C (s) + CO2 (g) <=> 2 CO (g)}$$
Find the mole fraction of $\ce{CO2}$ provided that, in equilibrium, $K_\mathrm{p} = 14.1$.

Our teacher's solution is $x(\ce{CO2}) = 0.324$ (mole fraction).
I suspect that the problem as is provides insufficient information to arrive at the solution above. Assuming that the total pressure of the system is $\pu{10 atm}$, the resulting mole fraction is indeed $0.324$.
Is the problem truly incomplete or can it be solved without knowing the total pressure?


texts: What possibilities are there for refining aluminium on the moon?

texts:
Engines burning aluminium and liquid oxygen have been investigated for use on the moon because there is plenty of both elements in the soil - about 13% and 40% of highland soil, respectively. Propellant thus has the potential to be sourced from the moon directly, but it isn't practical unless a refining process can be found that uses the moon's environment to extract pure aluminum efficiently using local resources. A viable way to extract the oxygen is known already, using a pyrolysis process.

Is there a way of taking advantage of the moon's environment to do this effectively? You have at your disposal:

A hard vacuum
A month-long day that is strong sunlight for two weeks then a two week night - it is estimated that a furnace using concentrated sunlight could reach 3000 K.
1/6 Earth gravity
No moisture - chemicals are reduced
Powdery soil that is loose to a depth of 10 or 15 cm
Some soil samples from Apollo 16 were a quarter alumina by weight

A source of fuel in space is a prerequisite for a larger ongoing human presence there. A rocket launched from Earth can't manage to be more than about 5% payload. Shipping fuel from Earth to any off-world base by rocket would be prohibitively expensive (even if the rocket is reusable). This is why there has been so much interest in sources of water ice in space - it can be electrolysed into liquid hydrogen and liquid oxygen, which makes excellent propellant. But you have to go to the asteroid belt to get it (there are indications there might be significant reserves in craters at the moon's poles in permanent shade, but this is inconclusive). Once there is a way to refuel in space, all sorts of things become possible that are beyond our reach right now. An option that can compete with the price of mining asteroids has business potential. All such undertakings are going to require vast initial outlays that won't pay off for a decade or more. The process being considered here only has to meet that standard.

This question is a partner to a question at SE's Space Exploration site - How feasible is it to use aluminum and liquid oxygen as future propellant sourced from the moon?. I realized it was largely a chemistry question and so decided to ask about it here. There are two references in the other question: one from Wickman Spacecraft & Propellant, and one from the Artemis Data Book. I'm afraid neither discusses the chemistry and I haven't found anything else. The AIAA has several papers on it in their catalogue.


texts: Simple way to understand why chromophores often have double bonds?

texts:
Chromophores — atoms or groups of atoms within a molecule that absorb some visible wavelengths better than others — result in compounds that have color. For example, see this answer about azo dyes, and this mention of bleaching stains by oxidation of double bonds.

Without going too deep into quantum mechanics and/or molecular orbital theory (MO), is there a way to understand in a qualitative way why chromophores are often related to the presence of double carbon or double nitrogen bonds?


texts: Details of Boltzmann distribution derivation

texts:
I have 2 questions regarding the derivation of the formula which calculates the probability of molecules having a particular amount of kinetic energy $E_x$ in a system of $N$ molecules. It states that:
$$p(E_x) = \frac{\exp(-E_x/kT)}{\sum_{i=0}^\infty \exp(-E_i/kT)}$$
This formula is initially derived from finding the maximum number of permutations $\Omega$ with $N$ molecules distributed over $n$ energy compartments within a system according to:
$$\Omega = \frac{N!}{n_1!n_2!n_3!...n_i!}$$
Question 1. It is explained that one must find the maximum number of permutations by differentiating this permutation function and solving for $0$. However, I can already see from the formula that the maximum number of permutations is achieved if the denominator is equal to 1 (it can't be less), which means that there should be 1 molecule in each energy compartment $n_i$. Why isn’t it possible to reason the maximum that way? I'm aware this would need $N$ number of energy compartments resulting in some having very improbable high energy levels, but can't the difference in energy levels between the compartments be very small?

Question 2.  Suppose the molecules only possess translational kinetic energy. I understand that translational kinetic energy is continuous: it does not have discrete energy levels like rotational or vibrational kinetic energy. Since it is continuous, there are no energy compartments with exact energy values. The number of possible energy compartments within such a system should therefore be infinite and one could only derive probability densities. How is it possible nonetheless to calculate a limited number of permutations using a limited number of energy compartments? Does each energy compartment cover a certain range of energy levels?


texts:
I'm not a chemist, and nor do I study chemistry so please try to be gentle.

Glucose has the molecular formula $\mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6$ and the empirical formula $\mathrm{C}\mathrm{H}_{2}\mathrm{O}$.

Starting from the empirical formula and working the other way, am I guaranteed that $\mathrm{C}_n\mathrm{H}_{2n}\mathrm{O}_n$, where $n$ is a positive whole number, are all going to be well-define molecular formulae?

Some examples are Formaldehyde ($n=1$), Acetic Acid ($n=2$) and Ribose ($n=5$). As a starting point, does $n=3$ and $n=4$ make sense, i.e. $\mathrm{C}_3\mathrm{H}_{6}\mathrm{O}_3$ and $\mathrm{C}_4\mathrm{H}_{8}\mathrm{O}_4$ respectively?


texts: Hydrogen Peroxide - Iron Nail Galvanic Cell?

texts:
I am planning to create a simple galvanic cell made up of common household materials.

Suppose I have hydrogen peroxide (to serve as cathode), diluted in water, in one beaker, and I have a bunch of iron nails (to serve as anode), also diluted in water, in another beaker. I put a graphite electrode (in the form of a pencil) in the $\ce{H2O2}$ solution to serve as an inert electrode. Then I'll have a U-tube containing $\ce{NaCl}$ to serve as a salt bridge between the two beakers. I will then connect the two electrodes using alligator clips into an LED. Computing from their reduction potentials, I am supposed to get $2.21~\mathrm{V}$ under standard conditions.

Will the set-up work? If so, do you think it is possible to connect many set-ups in series in order to produce $9$ Volts? I will appreciate all sorts of suggestions.


texts: Sigma and pi coordination in complexes (symmetry)

texts:
According to the Miessler Tarr and many molecular orbital diagrams for octahedral complexes on the internet will σ-donors/acceptors only influence the $e_g$-orbital, while π-donors/acceptors influence the $t_2g$-orbitals. This can also be shown using the corresponding character table, but it's been a while since I used these, so I will just believe its correct. Still, I was wondering, is there no case of it ever mixing, for example, that a π-donor/acceptor does not coordinate with both lobes but in a σ-fashion? I thought about this case, and there is also an example mentioned in the book, where they show how a σ-donor and π-acceptor-ligand (I suppose they mean one with both abilities) would look like. Here they draw the lines from the π-orbitals or rather π*-orbitals in this case to the $t_2g$-orbital and the σ-orbitals are connected to the $e_g$-orbital.

One example where I know this behavior, just vice versa would be chloride as a ligand, and I have also seen schemes, where it was drawn to coordinate in a π-fashion to the metal's d-orbitals. But in this case, you have both properties. What about a hydride for example, as pure σ-ligand? Would it only influence the $e_g$-orbital or is there a way it could also somehow weakly influence the $t_2g$-orbital?


texts:
Under what condition do the reaction proceed with sole removal of oxygen in contrast with the product also ending up with chlorine substituent?

I'm familiar with both reaction mechanism, but can't seem to figure out when will a certain pyridine end up with or without chlorine. I guess one factor would be electron richness of the ring system, chlorine being deactivating subsituent ends up only on the electron rich pyridines.


texts: H NMR of vanillin detail in Nilered video

texts:
The image below is from a Nilered video How to extract Vanillin from Vanilla Sugar, where he displays the H NMR of the final product created:

The labels A, F & E make sense to me, but I'm confused about D and C - I feel they should be swapped. To my understanding, B and D share a more similar chemical environment (though not identical), specifically they are near a C-O bond, moving their chemical shift left. Also, the NMR peaks labelled D display a doublet, suggesting it is next to a single proton. Though B, C and D are all next to a single proton, C is the odd one out.

Is this a case of me missing something, or is the picture mislabelled?


texts: Why is Kc not affected by change in pressure?

texts: Why is $K_c$ not affected by change in pressure? I know the mathematical explanation, but I don't really understand the reason when only looking at $K_c$. The explanation I know is with the reference to $K_p$, but is it possible to explain without $K_p$?


texts: Where to find information about galvanic deposition of various metals?

texts:
I am looking at the process to deposit Cu and Ag onto metallic surfaces using galvanic techniques. Unfortunately this works not as expected.

For example I use 2 rods of Cu in a bath of CuSO4 with some drops H2SO4. When applying a voltage, I get -- depending on the voltage -- either a block cover that can be wiped with a towel of a very rough Cu surface. I did not try with Ag/AgNO3 yet.

Anyway I have the problem, that I am looking for information or a form where I can post my problems and get useful tips, what I can do to enhance my baths.


texts:
Having never prepared a buffer solution before, I am hoping for a little help in understanding the process.

This method I plan to use calls for a $\pu{0.1M}$ glycine buffer at pH $10.6$. Some internet searching yielded this recipe (very bottom of the page) for making a glycine-$\ce{NaOH}$ buffer at $10.6$ pH, which I assume is what I'm looking for.

Most of it seems to make sense to me. $\pu{0.2M}$ stock solutions of both glycine and $\ce{NaOH}$ would be prepared as:

0.2M NaOH solution = 0.2 * 39.9971 = ~8g NaOH/l
0.2M glycine solution = 0.2 * 75.07 = ~15g glycine/l
(Molar mass: NaOH = 39.9971; glycine = 75.07 g/mol)

And, to yield a buffer at $10.6$ pH, mix:

25ml glycine stock + 22.75ml NaOH stock + deionized water to 100ml

Where I get lost is figuring out the molar concentration of the resulting solution, since there are two different solutes. Would it be just the total number of moles present of both, something like:

(25ml + 22.75ml) * 0.2M / 100ml = 0.0955M ?

It seems pretty close to the $\pu{0.1M}$ concentration called for, but I can't seem to find any confirmation of this.


texts: Unknown alcohol sample. Chromic acid negative but iodoform positive?

texts:
I have a unknown sample of an alcohol (ceric nitrate positive) but when I did chromic acid test it was negative since it never turned into blue/green and against all odds iodoform was positive... yellow precipitate and a lot...

I have no clues of how to make sense into this. So I did lucas test as well but noticed later that it didn't help because my sample is not very soluble in water.

Judging by the great amount of precipitate I got from the iodoform test, I'm thinking that maybe my sample is indeed a primary or secondary alcohol but it has something that won't react with the chromic acid. Are there any considerations to account for when doing this test? or some limitations?

Please help!


texts: Why does NADH have 2 peaks in its absorption spectrum but NAD+ has only one?

texts:
From what I understand, in general aromatic rings absorb UV radiation. Looking at the structures of NAD+ and NADH, I see one aromatic ring that is common in both (the lower one due to adenine), which I presume corresponds to the common large peak in the absorption spectra of both molecules.

However then I see that NAD+ has an extra aromatic ring, which NADH does not, although NADH produces another peak on the absorption!

I think I am going wrong in my understanding of what an aromatic ring is. I am assuming that a ring structure having alternating double and single bonds is necessary but not sufficient for this to be an aromatic ring, (so the extra alternating bond ring in NAD+ may or may not be aromatic and responsible for another peak, but the corresponding ring in NADH does not have alternating bonds and so is not aromatic and cannot be due to another peak.

I was also wondering whether you can have aromatic compounds which are not cyclic structures? Perhaps that could explain the aromatic-like absorption of NADH despite it not have alternating bonds in a ring?


texts: Acid-Base determination of organic compounds

texts:
I'll start this question with the problem that led me to ask this question...

USNCO 2009 Problem 8 part c:

Part c. states that all four of the compounds above are more basic than ammonia, and the solution explains that it is because the "carbon-containing groups" that are attached to the nitrogen are "better electron donors" than just hydrogen (in ammonia). This "inductive effect" causes the lone pair of the nitrogen to attract the proton ($\ce{H^+}$) better, or as the solution said, "donate the electron pair" to the proton better.

This got me thinking.

My thought process was that the polarity of the hydrocarbon group and the nitrogen overall makes the atom extremely polar towards nitrogen. What I mean here is that the nitrogen has a large negative dipole. This also, in corollary, means that nitrogen has more electrons. In turn, it would attract the proton more strongly.

However, I do not know if my thought process is correct.

This is the official ACS solution to the problem in question:

What does it mean they are "better electron donors?" What is this inductive effect? If you can provide it, are there any other rules that are important pertaining to this and is there a source where I could learn these rules?

Thank you in advance.

Note: this is NOT homework, and my thought process for part c HAS been specified.

Source: https://www.acs.org/content/dam/acsorg/education/students/highschool/olympiad/pastexams/2009-usnco-exam-part-ii.pdf


texts: Why is the H−C−H bond angle in сhloromethane larger than 109.5°?

texts:
Symmetrical tetrahedral molecules (like $\ce{CH4}$) have a bond angle of $109.5$. Those with lone pairs in place of one atom (like $\ce{NH3}$) have bond angles less than $109.5$.

The standard explanation for why is that the lone pairs are "larger" than the hydrogens, creating repulsive forces that push the hydrogens down, decreasing the bond angle.

However, this explanation fails when confronted with $\ce{CH3Cl}$. According to the above logic, the $\ce{Cl}$, which is much bigger than the hydrogens, should repel the hydrogens just like a lone pair, making the $\ce{H-C-H}$ bond angle smaller than $109.5$. However, the $\ce{H-C-H}$ bond angle is actually $110.5$ (see here, I could not find a more authoritative source).

Why is this (or is my source wrong)?


texts:
I am trying to develop a procedure to test the percent mass of lipids in (update: homogenized) milk. It doesn't need to be very accurate, just an interesting application of chemical principles. As I was looking on traditional ways this is tested, I came across the Babcock method, which involves pouring concentrated sulfuric acid into the milk, heating, and centrifuging the sample. According to Wikipedia, "key to this process is that everything in milk except the fat dissolves in sulfuric acid."

The lipids of are surrounded by what is similar to a cell membrane. The fat is an emulsion with these surfacants holding it in the water. The other components of milk are water, colloidal micelles, which hold other proteins (of no interest to me). My question is, how does sulfuric acid dissolve "everything else"? In a biological procedure I know of to break cell membranes, isopropyl alcohol is used. The cell membrane in that case is broken when the alcohol behaves as a surfactant toward individual triglycerides. However, sulfuric acid does not have a nonpolar region, so how does it work to dissolve the phospholipid membrane?

Many Internet resources on this topic are not written from a chemical perspective. In addition, they seem to confuse the lipid bundles with the other colloidal particles.

Also, why not just heat the milk strongly (such as with a Bunsen burner) to break the protein, or add electrolytes to it, as is a common way to separate colloids?


texts: What primary standard acid can be used to standardise NaOH solutions by titration?

texts:
I've done an experiment to standardise $\ce{NaOH}$ using oxalic acid.

What other primary standard acid can be used to standardise $\ce{NaOH}$?

Can $\ce{HCl, H2SO4, HNO3}$ be used?

I read up and found that:

$\ce{HCl}$ and $\ce{H2SO4}$ are easily diluted, however, the concentration of the "concentrated" solution is not accurately known.

$\ce{HNO3}$ contains a little nitrous acid, $\ce{HNO2}$, which has a destructive action on many acid-base indicators.

Therefore I only found potassium hydrogen phthalate. Is there other primary standard acid that can standardise $\ce{NaOH}$?


texts: Unit cell in a hexagonal closed pack structure

texts:
My textbook says that there are only 14 possible 3D lattices(Bravais Lattices).
One of these 14 lattices is a hexagonal lattice in which only a primitive variation is given to be possible.
But then I look at hexagonal closed packed structured lattice and I can't figure out how I could possibly make that lattice using primitive hexagonal unit cell. Am I missing something here?
Source- NCERT class 12th part 1