texts: How to create a simple do-it-yourself procedure to measure diffusion?

texts:
While I am not asking the question here, a recent question concerning osmosis at the Bio SE caught my interest. In a nutshell that question was, given isotonic solutions of sugar inside and outside an immersed semipermeable bag, what will happen if a second solute--too big to escape through the membrane-- is added to the bag?

  The question has an SAT flavor but I think it should be possible to answer it with a fairly straightforward DIY procedure. So my question here is whether the outline I have in mind would work, or whether something better can be devised.

Procedure: Make an n-molar solution of dextrose. Make an (n+x)-molar solution of dextrose [n] and a second [x] solute S (sucrose? starch? urea?--something that will not pass through the membrane). Fill the bag with the dextrose/S solution. Immerse the bag in the dextrose solution.

Osmosis alone will draw water into the bag. The question to be answered by the procedure is whether there will also be a net diffusion of dextrose out of the bag so that the final concentration of dextrose is higher outside the bag than inside, i.e., higher than the initial n-molarity.

According to one internet source, dextrose will rotate plane-polarized light about $30^o$ clockwise. If my null hypothesis is that the n-molar solution and the post-osmosis/diffusion solution outside the bag have the same molarity (i.e., that there is no net movement of dextrose out of the bag), and if I am able to construct an apparatus to measure optical rotation consistently in my kitchen, could such an apparatus be sensitive enough to reject $H_o$ if sugar in fact diffuses out of the bag?

Can anyone suggest a good practical way to set this up? Suggestions for types of membranes, necessary polarizing/light equipment, second solute S, etc. all welcome. Also, if there is a simpler/better way of going about this that would be great.

Thanks for any advice.

Notes

Sucrose reportedly rotates light more (perhaps $40^o$) but it may be too large to pass through some commercially available membranes. Fructose only rotates light about $10^o$ so I don't think it can be used here. Could sucrose be used as second solute?

The thermodynamics tag is added since I think diffusion is properly an aspect of thermodynamics (see Fermi, Thermodynamics, ch. VII). Please feel free to edit if I am mistaken.


texts: Preventing Precipitation/Undilution: Shall I Try Another Solvent?

texts:
Thank you for your time in advance.
Our facility is about $\pu{4000 ft}$ in terms of elevation.
One of the main chemicals we manufacture is RAD140 or $\ce{C20H16ClN5O2}$.
We use DMSO ($\ce{(CH3)2SO}$), PEG400 ($\ce{(C2H4O)_nH2O}$), and Sucralose ($\ce{C12H19Cl3O8}$) in this solution. These solvents have heat applied to them where RAD140 is then added after. Over time and once the solution is cooled down, the solution then starts to change where larger particles or "clumps" start to form. What might we change here to prevent this sort of undiluted substance?


texts: Why is ortho-hydroxybenzoic acid more acidic than its para-isomer?

texts:
Why is ortho-hydroxybenzoic acid $(\mathrm{p}K_\mathrm{a} = 2.98)$ more acidic than its para-isomer $(\mathrm{p}K_\mathrm{a} = 4.58)$?

March's Advanced Organic Chemistry (7th ed) gives the reason to be intramolecular hydrogen bonding between the $\ce{OH}$ and $\ce{COO-}$ groups of the conjugate base.

However, note that intermolecular hydrogen bonding (between the $\ce{OH}$ and $\ce{COO-}$ of two different molecules) is possible in the para-isomer. Interestingly, this question also states that intermolecular hydrogen bonding is relatively stronger than intramolecular one. So, shouldn't the para-isomer be more acidic?


texts:
I'm Having a real struggle trying to understand symmetry representations matrices and character tables. Is there anyone who would be kind enough to help me out here? I understand it is probably a little broad but nevertheless, I will list some areas that if anyone could shed some light on I would be very appreciative.

1) What is an irreducible representation? My book just starts going into $2\times 2$ matrices like:
\begin{equation}
\left( \begin{array}{cc}
1 & 0\\
0& 1\end{array}
\right)
\end{equation}
Saying that we can represent the effect of symmetry operations as such! When the operation actually affects the molecule by changing an atom then the diagonal of the matrix swaps round seemingly !!

2) Leading on from the first question, what is a reducible representation? Why the distinction?

3) What is a basis? My book introduces them via vectors down each of the cartesian axes and then a "set" of them together (why) to give four basis's for a $C_2v$.

4) I can use the reduction formula to see how many irreducible representations are contained within a particular reducible representation, but what am I doing!


texts:
Which of the following carbocations is more stable?

I know two major factors in determining carbocation stability: resonance and the number of carbon atoms neighboring the positive carbon. Does the double bond in the  substituent of the first molecule participate in resonance?


texts:
I know my teacher told me that

  In adiabatic process there is no exchange for heat between system and surrounding.

Then he came to point. From first law of thermodynamics

$$∆U = q + W \tag{1}$$

Since in adiabatic process there is no heat exchange then,

$$∆U = W \tag{2}$$

And then he said as we know

$$∆U = nC_v∆T \tag{3}$$

So,

$$W = nC_v∆T \tag{4}$$

I don't get it. Above equation tells us that the work done when a system is given heat at constant volume equals to $nC_v∆T.$
But how can this be applied in adiabatic process, since there is no exchange of heat?


texts: Determining symmetry correction by looking at rotational quantum states

texts:
I'm trying to understand the relationship between symmetry correction and rotational quantum states, particularly in the case of dipoles with identical atoms.

For an angular momentum quantum number $J=1$ there are 3 quantum states according to $g(J)=2J+1$. Each quantum state determines the z-vector of the angular momentum $M$. The spacial direction of the angular momentum $M$ for each quantum state is then:

The orbital plane of a dipole is perpendicular to $M$.
I can see that I can re-orentiate scenario a) in space to make it look like scenario c).

Thus for $J=1$ there are actually 2 quantum states instead of 3.

I noticed that, at any value of $J$, this can be done for each pair of quantum states that have the same z-vector momentum $M_z$ but in opposite directions. The only quantum state at any $J$ that isn't part of a pair is when $M_z=0$

This would make me deduce that the number of quantum states for a dipole after symmetrical correction $\sigma$ is equal to $\frac{2J}{\sigma=2}+1$

However, here's a snippet of a source

Apart from this discussing the density of states, why does it show that after symmetrical correction the number of quantum states is $\frac{2J+1}{\sigma}$ instead of $\frac{2J}{\sigma}+1$?


texts: Increase in Viscocity in Gases with Temperature

texts: Why does viscocity increase with temperature in gases? When they gain kinetic energy, they should be more free right?


texts: Intramolecular VS intermolecular product of reaction between hexatriene and but-2-enedial with heat

texts:
I couldn't figure out how I would be able to tell whether the major product between hexatriene and but-2-enedial with heat would be from the intermolecular or the intramolecular reactions.
Hexatriene can react with but-2-enedial under thermal conditions in a diels alder reaction (intermolecular). However, hexatriene can also undergo cyclization under heat and become cyclohexadiene (intramolecular). Then it could undergo the diels alder reaction with but-2-enedial. This would lead to a different product.
I know that but-2-enedial is a very reactive dienophile; however, I also know that generally intramolecular reactions are faster than intermolecular reactions according to collision theory. Is it possible to deduce the major product without actual data from experimentation?
Please send help!


texts: Predicting the Product of a Substitution/Elimination Reaction

texts:
I am asked to explain why neither $\ce{E2}$ or $\ce{S_{N}}2$ products are formed when 3-chloro-2,2,4,4-tetramethylpentane is treated with NaOH.

I realize that since the reagent is a strong nucleophile & a strong base, it can only participate in either an $\ce{E2}$ reaction or in a combination of the $\ce{E2}$ and $\ce{{S_{N}}2}$ reactions, depending on the substrate. I think the substrate is secondary, so $\ce{E2}$ should predominate and $\ce{S_{N}2}$ should give a minor product.

The textbook solution says that since the substrate is tertiary, $\ce{{S_{N}}2}$ will not occur at an appreciable rate, and there are no β carbons, $\ce{E2}$ cannot occur.

My misunderstanding seems to stem from an inability to depict the molecule as is expected, so I am hoping someone can clarify whether or not my drawing and line of reasoning are correct.


texts: Permanent storage container with electrode for electroplating

texts:
I'm not a chemist at all but I am looking for a specific type of container which I'm sure must exist but I don't know it's name.

We want to store non-toxic (non-cyanide) gold solution for electroplating in a small (10-20ml) transparent container that has an inbuilt, permanent electrode for the plating process:

But I can't find anywhere to buy such a thing and I don't know if it has a specific name. The electrode would have to be made of a material which will not react with the gold solution, so as not to contaminate it.

Why do we want this specific setup? We want to gold plate fine wires which are inserted into the solution from the top of the container, these are fragile and expensive which is why I would rather avoid having a temporary electrode inserted into the solution each time. We have a small amount of gold solution at a time and it is expensive so I would rather store the solution in the plating container permanently. The container really needs to be transparent so we can see that the plating wires are in the solution.

Any help would be massively appreciated,

Thanks,

M.


texts: How to derive a state symmetry in D2h point group from its wavefunction?

texts:
Let's have an atomic carbon with the following electron configuration:

$$
1s^2 2s^2 2p^2
$$

One of it's levels is ${}^1S_0$, which is corresponding with the following state:

$$
\begin{align}
\left| S=0, M_S=0 \right> &= \frac{1}{\sqrt{2}}\Big( \alpha(1)\beta(2) - \alpha(2)\beta(1) \Big)\\
\left| L=0, M_L=0 \right> &= \frac{1}{\sqrt{3}}\Big( \left| p^+(1)p^-(2) \right> - \left| p^0(1)p^0(2) \right> + \left| p^-(1)p^+(2) \right> \Big)\\
\left| S=0, M_S=0, L=0, M_L=0 \right> &= \frac{1}{\sqrt{6}} \Big( \left| p^+(1)\alpha(1)p^-(2)\beta(2) \right>- \left| p^+(1)\beta(1)p^-(2)\alpha(2) \right> \\&- \left| p^0(1)\alpha(1)p^0(2)\beta(2) \right> + \left| p^0(1)\beta(1)p^0(2)\alpha(2) \right> \\&+ \left| p^-(1)\alpha(1)p^+(2)\beta(2) \right> - \left| p^-(1)\beta(1)p^+(2)\alpha(2) \right> \Big)
\end{align}
$$

Now I know, that ${}^1S_0$ state is supposed to be totally symmetric, i.e. $A_g$ in the $D_{2h}$ point group. But is it possible to derive it "rigorously" from the wavefunction?


texts: What is the best soft material to withstand prolonged contact with high heat metal?

texts:
I want the look of a leather belt around the outside of a metal fire pit (stainless steel). I thought that thick leather would work since it's used for forge gloves, but the prolonged exposure just charred it and it dried out and broke.
Anyone have any ideas about a material? Maybe lining the back of the leather with a particular material? What material would/could that be? Where would you get it?


texts: If I were to replace $\ce{Zn}$ with $\ce{Al}$ in  $\ce{Zn|Zn^2+ || Cu^2+|Cu}$. Would it produce the same results?


texts: How to synthesize 1,3-pentadiene from butanal?

texts:
How do you synthesize 1,3-pentadiene from butanal?

I have the (possible) last steps of bromination of 1-pentene at the allylic position and then an E1 reaction to give the final product. I don't understand how to get from butanal to 1-pentene though. Also if you know another way to do the synthesis then feel free to share.


texts: How to derive the pressure dependency for the Gibbs free energy?

texts:
$$\mathrm{d}G=\left(\frac {\partial G}{\partial p}\right)_T+\left(\frac {\partial G}{\partial T}\right)_p$$
The above is an exact differential. Firstly what does this mean physically? (I hear about the fact that a change in G is independent of the "path" but I don't understand this argument because I don't know what is meant by this path. Also how would something be dependent on the path?)

It can also be shown that $\mathrm{d}G$ can be written:
$$\mathrm{d}G=V\mathrm{d}p-S\mathrm{d}T $$

So by comparing coefficients:
$$\left(\frac {\partial G}{\partial p}\right)_T=V$$
It is useful to integrate this to see how $G$ varies with $p$:
$$\int_{p_1}^{p_2}\left(\frac {\partial G}{\partial p}\right)_T\mathrm{d}p=\int_{p_1}^{p_2}V\mathrm{d}p$$
$V$ can be expressed in terms of $p$ using the equation $V=\frac{n\mathcal{R}T}p$ Where $n\mathcal{R}T$ are constants. The above equation becomes:
$$\int_{p_1}^{p_2}\left(\frac {\partial G}{\partial p}\right)_T\mathrm{d}p=n\mathcal{R}T\int_{p_1}^{p_2}\frac{\mathrm{d}p}p$$
Integrating the LHS of the above equation is the crux of my question (I don't understand how that can be integrated). I am not sure whether the following step is correct mathematically, please explain why this is correct/incorrect. I cancel out the $\mathrm{d}p$'s on the LHS:
$$\int_{p_1}^{p_2}\mathrm{d}G=n\mathcal{R}T\int_{p_1}^{p_2}\frac{\mathrm{d}p}p$$
Then the result is:
$$G(p_2)-G(p_1)=n\mathcal{R}T\ln\left(\frac{p_2}{p_1}\right)$$
Or...
$$\Delta G=n\mathcal{R}T\ln\left(\frac{p_2}{p_1}\right)$$
This result is correct but I don't understand the left hand side. I've been told that the reason it's possible to write "$G(p_2)-G(p_1)$" or "$\Delta G$" is because $G$ is a state function/exact differential but, again, I don't understand this. If $G$ was not a state function/exact differential how would the result change?


texts:
Several people have said that the key to understanding chemistry is through memorizing the periodic table.

I want to ask if there is a simple technique to learn it, or if I just have to remember every element as it is?


texts: Why do molecules having a higher relative molecular mass have stronger inter-molecular forces?

texts:
Why do molecules like alkanes with higher relative molecular
mass ($M_\mathrm r$) have stronger intermolecular forces? For example, methane ($\ce{CH4}$) has a weaker intermolecular force than pentane ($\ce{C5H12}$). Pentane has a higher $M_\mathrm r$ than methane and therefore pentane possesses stronger intermolecular force than methane. These are members of the same family in the homologous series, known as alkanes.

My issue is why does pentane have stronger intermolecular force than methane? Why is there a relationship between relative molecular mass ($M_\mathrm r$) and inter-molecular forces. The stronger the intermolecular force the higher the boiling point and the melting point?


texts: Error hunting: Guidelines on detecting error cancellation and locating their sources as much as possible?

texts:
It is known in computational chemistry, when computing e.g. electronic ground states energy and geometric paramters (bond lengths, angles, torsions etc.) of a given molecule using an ab initio or DFT methods with some basis sets, there are situations where a certain combination of method and basis will give good agreement with the experiment due to error contributions in that method/basis combinations having opposite sign of similar magnitude and thus cancel out.
This phenomenon is common in e.g. MP2 calculations of small molecules, where the electronic energy is usually in good agreement with experiment due to favourable error cancellations
However, not all calculations can benefit from error cancellations, and the presence of them will often mean they are quite sensitive to the nature of the molecule and the method/basis used to model them, making said method have less say on its reliability on similar molecules (e.g. with one ligand being replaced or rearranged in configuration)
Therefore, I wonder whether there are general guidelines in terms of what sequence of calculations to be carried out to test whether a good result is due to favourable error cancellation, or that the method faithfully reproduce the experimental result.
In particular, ideally if the error cancellation can be traced all the way down to the details and implementation of the theoretical method and basis set, such as the error cancellation in some molecule is due to the dipole interaction of a oxygen functional group with one of the aromatics, or that e.g. a polarisation function on oxygen atoms in that particular basis set contribute a term that is of opposite sign to another term in gaussian orbitals that model the delocalisation of electrons in an aromatic system.

Any good references that explores error hunting in computational chemistry and attempt at localising their sources?
(preferably in inorganic systems)


texts: Freezing point of solution of Water, Ethanol and Sugar (aka, Limoncello)

texts:
I'm looking for a diagram of the freezing point of a water solution depending on its content in sugar and ethanol. More colloquially, I want to know how to balance alcohol and sugar so that my limoncello doesn't freeze in the freezer. I know that increasing both will eventually work, but that seems unsatisfying.
I've managed to find the appropriate diagram for solutions sugar-water and sugar-ethanol. There are some related research on emulsions, but the phase diagram there is done at fixed "high" temperature (7°C or above).
Is it possible to simply extrapolate from the data above ? Also, is there a formula for this ?


texts: Why is up spin in the px orbital and down spin in the py orbital considered an excited state?

texts: Why is this form of p orbital occupation an excited state? I understand that there should be one up spin and one down spin in one orbital box by Pauli's exclusion rule. But in the p orbitals, it doesn't matter, whether we put up spins first or down spins first according to Hund's rule. I thought unless up and down spin are in same box, they don't affect each other. But as what I thought is wrong, I would like to know the exact reason for this. Why is it considered to be an excited state?


texts: How can I preserve chlorophyll for long periods of time?

texts:
I'm currently working on a XIX century photographic process called Anthotype. It relies on organic colored substances that fade when exposed to sunlight. For the substances I've tried alcoholic Curcumin extract and Chlorophyll. The later is incredibly sensitive to light! But this is a problem, because after the print is done I've got no way to fix it. I've read that chlorophyll degrades more on acidic conditions and even if kept in the dark. I tried treating the photographas with a weak base (sodium bicarbonate) but it doesn't seem to help. Is there a way to pr*eserve it or preserve the color?

I've also read that on museums they basically make a copper chelate with chlorophyll and that seems to help. -it preserves the green color.

Now, I don't have copper sulphate at hand. I've read it's found as "root killer" on hardware stores, but the products at my local hardware store don't list the compounds on them and also there's no root killer specifically. Is there other salts that can make a chelate with chlorophyll? I've read that zinc will also work.

Also, is pheophytin (The main chemical formed when chlorophyll is degraded) more resistant than the actual chlorophyll?


texts: 1H splitting pattern of benzyl CH2 protons

texts:
During my PhD, I prepared the two compounds below (there was actually a slightly longer chain but it's not inherently relevant).

When looking at the 1H NMR spectra of these compounds, something slightly weird occurred.

In one of them, the CH2 group of the benzyl appeared as a singlet (s, 2H). In the other, the CH2 group of the benzyl was observed as a multiplet (an AB quartet like structure, to be specific).

Is there any rationale for why the two cases would be different, given the distal nature of the closest stereocentre (i.e. why are the two CH2 protons diastereotopic to begin with given how distal they are)?


texts: Why is the equilibrium constant unitless?

texts:
I read that the equilibrium constant is unitless because the molar activities of each of the species are used in the equilibrium expression, not the actual concentrations themselves. I understand that.

But it is taught that

$$K_c = \frac{k_\mathrm{fwd}}{k_\mathrm{rev}}$$

I’m having some difficulty understanding this equation. Consider the chemical equation

$$\ce{A + B <=>[$k_\mathrm{fwd}$][$k_\mathrm{rev}$] C}$$

The forward rate constant is a second order reaction and has units $\pu{M-1 s-1},$ and the reverse rate constant is a first order reaction and has units $\pu{s-1}.$ Therefore

$$\frac{k_\mathrm{fwd}}{k_\mathrm{rev}}$$

has units $\pu{M-1},$ but it’s supposed to be unitless. Where am I going wrong?


texts: In a molecular dynamics context, is the methyl rotation in propene a symmetric or asymmetric internal rotor?

texts:
In a prior question, I asked about the (a)symmetry of the potential energy surface of the methyl rotation of propene.  In that context, the kinetic energy of the nuclear motions is of course assumed to be negligible, and thus nuclear inertial effects are irrelevant.

Here, I want to ask about the (a)symmetry of this same internal rotation, but instead in the context of molecular dynamics (MD), where the Born-Oppenheimer approximation still applies but the kinetic energy of the nuclei is non-negligible compared to the variations in the potential energy over the course of the motion of the system. For the sake of argument, assume that the propene is in a sufficiently high rovibrational energy state for the methyl rotation that it behaves as a hindered internal rotor, and thus the nuclear motion is not "trapped" in one of the wells of the potential energy surface.

Depending on how one imagines the methyl rotation of propene to occur, it seems like it could behave as either a symmetric or an asymmetric internal rotor in an MD context.  If the $\ce{H2C=CH\! -}$ portion were held fixed, the rotating methyl would be inertially symmetric due to the local $\mathrm C_3$ axis:

On the other hand, if the methyl group were held fixed, the rotating $\ce{C=C}$ portion would be highly inertially asymmetric:

Obviously this rotation can't simultaneously be both inertially symmetric and inertially asymmetric. So which is it, and why?

My inclination is to assume that the internal rotor is asymmetrical, since the overall system does not have any axes of three-fold or higher symmetry. However, I don't know a good mathematical or group theoretic 'language' in which to define such internal rotor (a)symmetry, and so I'm unable to prove this to my own satisfaction.

The best qualitative argument I've thought of in favor of it being an asymmetric internal rotor is that the axis of the rotation (green bar) does not pass through the center of mass of the system (purple sphere / orange bar):

FWIW, I calculate the skew angle between the two colored bars in the above geometry to be about $18^\circ$. Anyways, as a consequence of this skewed orientiation, I think the methyl hydrogens would oscillate parallel to the axis of internal rotation while they rotate around the methyl carbon.  Simultaneously, I would expect a sort of corresponding "waggle" of the ethenyl fragment.

Thus, directly related to the "why" question above: If this qualitative argument is correct, how can I express it quantitatively?


texts: Can carbocation rearrangements have kinetic and thermodynamic products?

texts:
As the figure in this webpage says, at low temperatures, the major product of hydrohalogenation of 1,3-butadiene is the kinetic product, the 1,2-addition product. At high temperatures, the major product is the thermodynamic product, the 1,4-addition product, in which the pi electrons have transferred to the inner carbon skeleton to form a more substituted alkene product. The carbocation rearranged due to resonance.

However, as the figure below from David Klein's Organic Chemistry 2e book tells us--the major hydrohalogenation product of 3-methyl-1-butene is the rearrangement product, which is the more stable product. Here, the carbocation rearranged due to its inherent stability at highly substituted carbons. The temperature of the reaction was not specified.

My questions are:

Is it safe to assume that the hydrochlorination of 3-methyl-1-butene give a product ratio as shown in the figure at all temperatures (except at temperatures where decomposition may occur, if it can)?
Do alkene addition reactions also have thermodynamic and kinetic control, like the butadiene reaction exhibited, or is the thermo and kinetic product production only due to resonance?
Can carbocation rearrangements have kinetic and thermodynamic products, like the one for the hydrohalogenation of butadiene?


texts: How to measure concentration of arsenite and arsenate in a water sample

texts: A colleague and I are developing a transgenic bacterial strain that contains an arsenite oxidase gene. The bacteria can oxidize arsenite into arsenate autotrophically. We need a method to measure the concentration of arsenite and arsenate over time in a water sample. First we thought of using a pH meter, but we need to measure the arsenite and arsenate concentration over a 48 hour period, and we are worried that the pH meter wouldn't hold up. Could there possibly be a chemical that reacts with arsenite to change the color, and we could use a spectrophotometer or a colorimeter. If there are any ideas for measuring concentrations of arsenite (around 5 mM), please let me know.


texts: Is 1-methoxy-2-methylpropane a positional isomer of 2-methoxy-2-methylpropane?

texts:
My book doesn't classify them as positional isomers but the position of the methoxy group is different in both the molecules. So, I guess they should be positional isomers.

I understand that the two compounds are metamers. But can't a metamer be a positional isomer?


texts: How to make a CCl3F Fluorine NMR standard?

texts: I am running some fluorine NMR and would like to make a bulk solution of $\ce{CCl3F}$ in $\ce{CDCl3}$ to aid in assessing the amount of fluorinated product present by having my NMR solvent act as a reference. Can anyone suggest a good ratio of the $\ce{CCl3F}$  standard to $\ce{CDCl3}$ NMR solvent?


texts: Thermodynamically Reversible Processes: How does an infinitesimal step make a process reversible and how is maximum work derived from the process?

texts:
My book says 'Maximum work can be obtained only from thermodynamically reversible processes,' but why is it so? What is the cause?

Actually to me the definition of reversible process is confusing. It says that at each step during the process, equilibrium is maintained. But, let's say,we have to expand a gas in a cylinder headed by piston from pressure $P_i$ to $P_f$. Suppose,the process is done with innumerable infinitesimal steps. Then, say at each step, $dp$ is changed in the pressure.

Before the step, gas and the piston were exerting same pressure $P_i$ . Now, when the piston is raised, gas does expand to equalize the pressure,which is $P_i - dp$ . So, at the end of the step, the gas & the piston will exert same pressure $P_i - dp$ and hence will be in mechanical equilibrium.

During the step,the gas and the piston was not in equilibrium;it was at the end of the step  the equilibrium is achieved. So, during each step of the process the gas would be at disequilibrium . So,will it really be a reversible process? It is contradictory with the definition. But it is true that during each step, the system is at disequilibrium though infinitesimally small by $dp$ . So, why does the definition tell that at each step,there is equilibrium?

So, I have three questions:

Why is maximum work only obtained from reversible processes?
According to the definition, at each step of the reversible process,there must be equilibrium. But during each step, there is infinitesimal disequilibrium. So, why does the definition say so in-spite of the disequilibrium during each step?
How do infinitesimal steps make a process reversible? I will be very grateful if anyone answer these three questions.

Please help.


texts: What is the purpose of phase matching when drawing a MO diagram?

texts:
During the lecture, we were learning how to draw the MO diagram for $\mathrm{BF_3}$.
I understand that only orbitals with the same symmetry labels can interact and form molecular orbitals. My professor always elaborates a lot on "phase matching," and he would draw the orbitals out.

However, I do not understand how these orbital drawings are supposed to assist me when drawing the MO diagram. How would it affect my process for drawing the MO diagram?


texts:
This is a question from JEE Advanced  2019 (a highly valued engineering entrance exam in India), but the fact that we are ignoring basic rules of electrophilic substitution is disturbing. Correct me if I am wrong or missing something really important, but according to synergic electrophilic substitution, it should be an ortho attack from methoxy group as we know that an oxygen atom's conjugation would be more contributing than carbon's hyperconjugation and inductive effects combined.
Overall, attack from 2-position (to alkyl group) instead of 3, as done in the question is what I mean to say.

But I also know that it (attack of 3-position) will make the compound to have a bridgehead, will it be stable then? And for overall compound, the stability of the compound, do we have to do a meta attack even in an activated ring?


texts: Can someone please explain to me where the flaw is in my proposed synthesis mechanism?

texts:
For this I have to convert benzene into the product in the box using the reagents listed. The order of reagents that makes sense to me is IDGBEH. However, this is not the correct answer. Somewhere I am missing 2 steps to the synthesis and I am at a complete loss. I understand all of the basic and complex concepts of organic chemistry we've covered in my class thus far, so I'm confused as to how my proposed mechanism has an issue. If it's any help I know the mechanism is supposed to be 8 steps.

In my mind IDGBEH makes complete sense and should give me the product that I want, unless I am missing something or I misunderstood my professor.


texts: Why is liquid oxygen more reactive than gaseous oxygen?

texts:
Liquid oxygen is somewhat hairy to work with, as, if it comes in contact with essentially anything combustible, it has an unfortunate tendency to detonate violently if looked at sideways.

Gaseous oxygen obviously does not do this, as can be seen from the fact that combustible objects can sit indefinitely in gaseous oxygen without exploding when touched.

This seems backwards, as, at a given pressure, liquid oxygen is colder than gaseous oxygen, and materials are generally more reactive at higher temperatures - thus, intuitively, one would expect liquid oxygen to be less reactive than gaseous oxygen, not more.  Why is this not so?


texts: Acid catalyst decarboxylation of 1-carboxyl-tryptoline

texts:
One of my labs had the following reaction:

I understand the Pictet Spengler mechanism. However, I am confused about the decarboxylation. I cannot come up with a way in which this decarboxylation would be acid catalyzed. Here is what I have for the Pictet mechanism:

I have been trying to figure out the acid catalyzed decarboxylation for several days now but I cannot. This is the closest I can come up with, but I'm not sure that this is correct:

Thanks!


texts: How does the rate determining step determine the overall speed of the reaction if it is the first step in the reaction?

texts:
I can imagine it determining the rate of the whole reaction if it is the last step since that means that we will have lots of the reactants needed for the rate determining step, synthesized in earlier steps. Therefore, the rate of this step represents the rate of conversion of these reactants to our final products. But if it is in the beginning , you will have to include the speeds of the other steps in the overall rate which means the overall rate is not dependent on the rate determining step alone. So why is it called a rate determining step if it is in the beginning ?

NOTE : If it is the last step, then we only consider the speeds of the earlier steps until we have excess of the reactants which feed into the rate determining step. As for the rest of the time, we will only have a store of reactants which are waiting for the rate determining step.


texts: What is the name of this organic compound?

texts:
The organic compound in question is shown above. This is how I tried to name it:

Start from the left hanging  $\ce{H_3C}$.
$\ce{OH}$ gets the number 2 and $\ce{NH_2}$ gets 6. The lowest numbers possible for the functional groups keeping seniority/priority in mind.
There are two ethyl groups at 3 and 5.

Hence, the compound should be called 6-Amino-3,5-diethylhexan-2-ol.

I tried searching the web to confirm this, but nothing useful showed up.

Is this the correct IUPAC name of this organic compound?


texts:
I am a student of organic chemistry and I frequently watch online open course lectures by various professors around the globe. Of these, in https://www.youtube.com/watch?v=OYAMls5x4EI, at about 27:10, I had a question, as mentioned in the image below.

Mechanism

What factors determine where the palladium will attach?

My initial thoughts were to find out the electron-rich regions of the $\pi$ bond, and the palladium atom in the $\mathrm{+II}$ oxidation state will act as an electrophile. But I wasn't able to figure it out exactly.

I understand that the ratio of products shown in the figure can be controlled by using various ligands, especially based on their steric effects, in this case.


texts: Question about the composition of a 1902 non-polarisable electrode diagram by Jagadis Bose

texts:
In his work, "Response in The Living and Non-living" (1902); page 6, Jagadis Bose describes a method for detecting nerve response. He explains that he uses iso-electric contacts with no current in the galvanometer and diagrams a non-polarisable electrode. The following are his diagrams:

On Diagram C, one will note that he uses a strip of saltwater soaked cloth attaching to a node that contains, what appears to be, a Zinc Sulfate solution with a Zinc rod resting in this ZnSO4 solution.

Below the ZnSO4, there's a seemingly unspecified area that acts as an intermediary between the ZnSO4 and the "strip of cloth."  I have highlighted it in yellow in the diagram below.

Could someone please explain what this medium may be or what could be used in it's place?  It appears to be some kind of solid or interstitial porous material (or another compound that he does not mention). Or is it simply a generic attachment or some kind of neutral absorbent material (perhaps sand?) that acts as a medium between the Zinc Sulfate, the "node" and the moistened cloth?

Here is Diagram C enlarged and highlighted for viewing convenience:


texts:
I have a photosensitive resin MSDS. It lists a mixture of 1,6-Hexanediol diacrylate ($\ce{C_{12}H_{18}O_4}$) with its proper CAS number and Polyurethane acrylate together with the CAS number of "Butyl acrylate/methyl methacrylate/methacrylic acid copolymer" with the formula (or rather, formulas) of $\ce{(C7H_{12}O2.C5H8O2.C4H6O2)_x}$. There's also the Photoinitiator 1-Hydroxycyclohexyl phenyl ketone listed. The additives of color and reaction inhibitor are most likely irrelevant for the actual question, so I leave them out.
My organic chemistry is somewhat rusty, but the first part of the compound I can identify as having the setup $\ce{H2C=CH-CO-O-C6H12-O-CO-CH=CH2}$. This appears to be a quite nice molecule that reacts evenly on both sides under polymerization. This material is also listed as photosensitive, which I interpret that it sheds something from both ends to activate the ends.
The other, of course is a mixture of three monomers: Butyl acrylate ($\ce{H2C=CH-CO-O-C4H9}$), methyl methacrylate ($\ce{H2C=C(CH3)-CO-O-CH3}$) and methacrylic acid ($\ce{H2C=C(CH3)-COOH}$). The first two have ester groups in them, the last has its precursor, the $\ce{-COOH}$ group (carboxylic acid). All these only seem to have one active side to me.
Assuming the four main chemicals are mixed somewhat evenly and in even numbers and what might be an ample supply of the starter Hydroxycyclohexyl-phenyl-ketone, they surely will react and polymerize under UV light of about 400 nm (+- 5), as this is how the mixture behaves in its native application, an SLA printer.
However I have a problem with these parts:

What kind of reaction does happen between the compounds? I remember vaguely that some polymerizations create waste in the shape of water (was that condensation?), but I don't really see that happening here for most of the combinations and, as a result, I fail to see what the parts of the polymer might look like in their bonded state.
What type of bonds does the resulting polymer have? This is pretty much the direct result of failing to see the reaction between the compounds. I thought I had seen a possibility to form an ester ($\ce{R_1-CO-O-R_2}$) between the methacrylic acid and the hexanediol diacrylate, but then realized the later misses an alcohol group ($\ce{R-OH}$) to attack and create water from to form the bond. So I am pretty sure that these don't bond as esters to one another, but what is the correct name for these bonds that elude me?!
What would this polymer be classed as? I remember that some polymers are classed based on their monomers, manufacturing process, the chain length, bond type, and the macro-structure, putting each into several groups. These would allowing to estimate some vague properties about them. It's most certainly not a Homogenous one like pure PolyLacticAcid, as it is basically made up of 4 different monomers. It also should not form an elastic bond due to what I know from the MSDS and that the processed resin is a somewhat brittle product. But what groups it can be put into from the polymerization process?


texts: what would be p-v diagram for irreversible isothermal expansion

texts: We say that area under the curve gives the work done. So for an irreversible iso thermal expansion, we have work done= -P external( V final- V initial) signifying a rectangular graph. But we know it's isothermal so it would be along an isotherm? Or no. I believe if we have external pressure at the y-axis, graph would be rectangular and if we take pressure of gas at y-axis we would get a curve, same as isothermal reversible but would end at a lower volume than the former. So what do we take for the p-v diagram.


texts:
Doesn't it have only have one bonding electron?

Then how can it bond with 2 oxygens?

The Lewis structure doesn't make much sense to me.


texts: Do changing opt=modredundant to opt in Gaussian makes geometry optimization not to take into account frozen angles?

texts:
I am a newbie to Gaussian and just generated an input for the geometry optimization for some molecules with multi ring system. However, in the article that was a reference for those calculations, some of the dihedral angles were freezed, so I did the same with adding the needed dihedrals to constrain with lines D X X X X F.
However, someone superior told me that I shouldn't use the opt=modredundant, but opt instead. Does it mean that I shouldn't constrain angles then? Or should I just manually change it to opt and the program will still understand that the angles are constrained?


texts: What type of Organic Substance is used in LCD

texts:
I know that the liquid crystal displays contain some class of organic compound, which is somehow used to polarise light to make contrast variations(In calculator displays).

My Question is What type of Organic Compound is used in this case and How does it polarise light only when stimulated by external agents such as current in LCD's


texts: Why color of alkali metal peroxides, superoxides and ozonides deepens down the group?

texts:
This is basically a continuation of the question-"Why is potassium monoxide (K2O) coloured?"

I knew that color of alkali metal oxides deepens down the group:

Lithium oxide ($\ce{Li2O}$) is the lightest alkali metal oxide and a white
solid. It melts at 1570 °C.
Sodium oxide ($\ce{Na2O}$) is a white solid that melts at 1132 °C and
decomposes at 1950 °C.
Potassium oxide ($\ce{K2O}$) is a pale yellow solid that decomposes at
350°C.
Rubidium oxide ($\ce{Rb2O}$) is a yellow solid that melts at 500 °C.
Caesium oxide ($\ce{Cs2O}$) is a yellow-orange solid that melts at 490°C.

The reason is due to what @Oscar said in the answer of previous question:

  If we go further down the alkali metal oxides the band gap gets
  smaller, and more visible light with longer blue/green wavelengths may
  be absorbed. Then the color becomes stronger and more reddish.

But, it is observed that not only color of normal oxides deepens down the group but the peroxides and superoxides also follow the trend:

Lithium peroxide ($\ce{Li2O2}$) is a white solid that melts at 195 °C.
Sodium peroxide ($\ce{Na2O2}$) is a pale yellow solid that melts at 460
°Cand boils at 657 °C.
Potassium peroxide ($\ce{K2O2}$) is a yellow solid that melts at 490 °C.

Sodium superoxide ($\ce{NaO2}$) is a yellow-orange solid that melts at
551.7°C.
Potassium superoxide ($\ce{KO2}$) is a yellow solid that decomposes at
560°C.

Lithium ozonide ($\ce{LiO3}$) is a red solid which is produced from caesium
ozonide via an ion-exchange process.
Sodium ozonide ($\ce{NaO3}$) is a red solid which is produced from caesium
ozonide via an ion-exchange process.
Potassium ozonide ($\ce{KO3}$) is a dark red solid which is produced when
potassium is burned in ozone or exposed to air for years.
Rubidium ozonide ($\ce{RbO3}$) is a dark red solid which is produced when
rubidium is burned in ozone.
Caesium ozonide ($\ce{CsO3}$) is a dark red solid which is produced when
caesium is burned in ozone.

What is the reason behind the deepening of the color? Is it due to the same reason as @Oscar pointed out? Or is it any other reason? Although superoxides and ozonides are paramagnetic and are colored, the peroxides are diamagnetic but still they are colored. Why?


texts: Relationship between reaction quotient and potential energy

texts:
I am trying to calculate the Gibbs free energy in an NVT simulation. Although
$$\Delta G = -RT\ln Q,$$
in my simulation I can't calculate
$$Q = \frac{[\text{Products}]}{[\text{Reactants}]}$$
because I cant determine the concentrations of reactants and products.
Hence, I am looking for a relationship between reaction quotient $Q$ and potential energy $U$ as well as $p,$ $V,$ $T,$ i.e.
$$Q(U,p,V,T) = ?$$


texts: How to solve 1-deuterio-3-methylcyclohexene dehydrohalogenation?

texts:
Ive been struggling to solve this dehydrohalogenataion excercise.
How does the E2 mechanism work in this case and how is it affected by the stereoselectivity and antiperiplanar position? How do I get to the transition state and how does the chair conformations for the cyclohexane ring look like?


texts: Copper acetate synthesis without hydrogen peroxide

texts: Usually, when people synthesize copper acetate, they use a mixture of acetic acid and hydrogen peroxide. I assume this is because the acetic acid actually reacts with the various oxides on the copper, rather than with the copper itself. However, assuming I don't have access to hydrogen peroxide, can I do a similar thing (but slower), just by waiting until fresh copper surface is exposed and then taking it out. Then, I will heat it up (or just wait) until oxide layer forms again, and keep repeating until copper is corroded away.


texts: how many calories per unit of sweetness between table sugar and aspartame?

texts: How many calories per unit of sweetness between table sugar and aspartame?


texts: Reaction of carboxylic acids with primary amines

texts:
$$\ce{RCOOH + RNH2 -> RCONHR + H2O}$$

$\ce{R}$ stands for any alkyl group.

I have two queries regarding this reaction:

I understand that the reaction is an $\mathrm{S_N{AE}}$ (nucleophilic addition elimination type of reaction). But during the reaction $\ce{R-(CO)-N^+RH2}$ intermediate is formed. After this step the $\ce{OH^-}$ which was eliminated acts as base takes away $\ce{H^+}$ from  $\ce{R-(CO)-N^+RH2}$, converting it into $\ce{R-(CO)-NRH}$. But why did $\ce{OH^-}$ extract $\ce{H^+}$ from $\ce{R-(CO)-N^+RH2}$  and not $\ce{R^+}$ ? Isn't $\ce{R^+}$ always a more stable carbocation compared to $\ce{H^+}$ ?
Why does this reaction require a basic medium?


texts: How to derive the Henderson equation for liquid junction potentials given in Bard and Falkner?

texts:
The general equation for liquid junction potential is given by $$E = {-RT\over F}\sum_i\int_a^b{t_i\over z_i}d ln(a_i)$$
Where a and b are the two phases, $t_i$ is the transport number of the ions and $z_i$ is the charge on the ions.
When making the additional assumptions that (1) the concentrations are equivalent to the activities everywhere in the junction and that (2) the concentration of each ion follows a linear transition between the two phases, the above equation becomes the Henderson equation:$$E = {\sum_i{|Z_i| \over z_i}u_i[c_i(b)-c_i(a)]\over \sum_i|z_i|u_i[c_i(b)-c_i(a)]}{RT\over F}{ln{\sum_iz_iu_ic_i(a)\over \sum_iz_iu_ic_i(b)}}$$But when I tried to evaluate the integral by my self by substituting the equation of transfer number $t_i = {z_ic_iu_i\over \sum_iz_ic_iu_i}$ and putting $a_i = c_i$, I'm stuck with the following: $$E = {-RT\over F}\sum_i \int_a^b{{|z_i|\over zi}u_i\over \sum_i|z_i|c_iu_i}dc_i$$ The  integral is of the form $\int{1\over {ax + b}}dx$ where $a = |z_i|u_i$ and $b = \sum_{j \ne i}|z_j|c_ju_j$   $$E = {-RT\over F}\sum_i{1\over z_i}ln\left( {|z_i|u_ic_i(b)+\sum_{j \ne i}|z_j|c_ju_j\over |z_i|u_ic_i(a)+\sum_{j \ne i}|z_j|c_ju_j}\right)$$Which is clearly not the Henderson equation given in Bard and Falkner, and I couldn't figure out where to use the second assumption. Where was  I wrong and how to proceed?


texts: How many vibrations are expected for butatriene and cyclobutadiene?

texts:
I have butatriene and cyclobutadiene, the formula for finding the number of vibrations expected are

Linear: $3N-5$
Nonlinear: $3N-6$

where $N$ is the number of atoms.

Both of these molecules are $\ce{C4H4}$ so they both have 8 atoms (because I think you include the $\ce{H}$ atoms).
Butatriene is nonlinear so the vibrations expected would be
$$3N-5 = 3(8)-6 = 18,$$
and Cyclobutadiene is nonlinear so
$$3N-6 = 3(8)-6 = 18.$$

Is this correct? Or do you only count $C$ atoms when you do this calculation?
Would all nonlinear $\ce{C4H4}$ isomers have the same number of vibrations expected?


texts: Why is gold so popular in nanotechnology?

texts:
Gold is a very popular metal in nanotechnology. It is often used as a substrate in electronic applications, as a core of functionalized nanoparticles, and more.

Why is gold so attractive? Why are other metals not as popular? What makes gold the go-to material for new applications?


texts: Why does radium have a higher first ionisation energy than barium?

texts:
I'm wondering why radium appears to buck the general trend that first ionisation energies decrease as you move down a group in the periodic table: barium (the group 2 element preceding it) has a first ionisation energy of $\pu{502.9 kJ/mol}$, whereas radium has a slightly higher first I.E. of $\pu{509.3 kJ/mol}$ (from the Wikipedia, although my textbook agrees).

Is there any explanation for this at present? (I imagine that quantum mechanics may be involved in some way, but I'm not entirely sure how)

There are most likely other examples of the trend being broken, but this is the only one I've come across so far and I'm curious to know why this is the case.


texts: How does the Kucherov reaction work if the alkyne is aromatic?

texts: I know how the Kucherov reaction works for aliphatic alkynes, but what if the alkyne has a phenyl attached? How will the aromatic ring affect the reaction of alkynes with water?


texts: Sum of spins of electrons in a wavefunction

texts:
I wanted to ask a question about spin in an electron.

We were presented earlier today with the following information:

Using my synoptic knowledge, I recall that spin up $\alpha$ had a value of $+\frac{1}{2}$ and spin down $\beta$ had a value of $-\frac{1}{2}$.

Also, using the information above, $\alpha(1)\alpha(2)$ would have a total Spin quantum number $S$ of $\frac{1}{2} + \frac{1}{2} = 1$, $\beta(1)\beta(2)$ however I thought would result to being $S$ of $-\frac{1}{2} - \frac{1}{2} = -1$ and even so, one spin up and one spin down $\alpha(1)\beta(2) +  \alpha(2)\beta(1)$ would total $\frac{1}{2} - \frac{1}{2} + \frac{1}{2} - \frac{1}{2}= 0$. These calculations contradict the data given above for the triplets and singlets states.

I'm confused. How are the values of $S$ for $\beta(1)\beta(2)$ and $\alpha(1)\beta(2) +  \alpha(2)\beta(1)$ exactly derived?


texts: Calculation of proportion of zwitterion from this please.

texts:
This is the question. I tried to post it in the title section but it was rejected because it was considered lengthy. Question: Valine is one of the 20 natural amino acids and has an acid -COOH (pka1=2.6) and an amine-NH2(pka2=9.6). If we consider a valine solution with pH=10.6, what is the proportion (%) of the zwitterion form of the solution? A) 2.4 B) 3.6 C) 5.7 D) 9.1 E) 10.2.
Sorry if this might be too elementary but I don't know how to solve this question. I need help, thanks.


texts: RO- as leaving group in saponification process

texts: If RO- is a stronger base than OH- (and leaving groups are weak bases), why is RO- a leaving group here?


texts: Source for thermodynamic and/or transport properties

texts:
I'm working on some combustion problems using Cantera and I can't find references for the thermodynamic or transport properties for many of my chemical species. I'm looking for NASA-7 or NASA-9 curve-fits for the thermodynamics, although if there is another equation format that exists, I will make it work.  And I also need properties for transport that Cantera calls "well depth", "diameter", and "rotational relaxation".

Specifically I am looking for: HClO4, HCl (transport information), ClO3, ClO2 (transport information), ClO (transport information), Cl2 (transport information), Cl (transport information), and ClOH.

So I suppose the real question is where can I find thermodynamic and transport properties for gaseous species with chlorine? Finding data on hydrocarbons and air is simple, and I found data on liquid refrigerants but nothing on gaseous chlorine species.

Note: I checked NIST and JANAF and neither had the information. I can find constant values, but running a very detailed reaction mechanism with calorically perfect equation of state and power or Sutherland law transport isn't worth the computational cost.


texts: Why Mohr's salt and not FeSO4 in titration?

texts: During titration of $\ce{KMnO4}$, we use Mohr's salt instead of ferrous sulphate salt to prepare the standard salt solution. Is it done to prevent oxidation of $\ce{Fe^2+}$ to $\ce{Fe^3+}$ before the titration itself? But to prevent that sulphuric acid is used. So why we do not use ferrous sulphate salt instead?


texts: How can you inhibit crystallisation of hot superconcentrated magnesium sulphate

texts:
I’m trying to create a gel like solution of primarily magnesium sulphate heptahydrate or Epsom salt and water.  It’s simple to create a hot super concentrated solution but when it cools it’s obviously begins to crystallise. Continuous stirring as it cools and cooling quickly creates a slush of tiny granules which eventually settle to the bottom of the solution like sand in water if too thin.

How can a thick concentrated smooth liquid be created?

I’ve looked into ways of inhibiting crystal formation but no good examples.  Maybe an impurity if some kind and then possibly a thickener if the mix is still watery.


texts: In practice, how dangerous is liquid oxygen as an oxidizing agent?

texts:
The Wikipedia page on liquid oxygen tells us

  Liquid oxygen is also a very powerful oxidizing agent [...], if soaked in liquid oxygen, some materials such as coal briquettes, carbon black, etc., can detonate unpredictably from sources of ignition such as flames, sparks or impact from light blows.

I have heard similar warnings about LOX in texts about amateur and semi-professional rocketry, but I know nobody who has ever handled stuff like this.

In practice, say I spill some LOX and soak paper lying around (that maybe has been warmed by a desk lamp), will that burst into a fireball?

Maybe more to the point, how do I assess such risks short of conducting foolhardy experiments? Is there a way to estimate the maximum effect a given amount of spillage on a given material may have?


texts:
Consider a liquid of pure $\ce{A}$ covered by a composite membrane through which
  the vapor of $\ce{A}$ is diffusing. The membrane consists of two layers of thickness $l_1$ and $l_2$. The diffusion coefficient of $\ce{A}$ in the two layers are $D_{\ce{A},1}$ and $D_{\ce{A},2}$ respectively. On the lower side of the membrane, the concentration of $\ce{A}$ ($c^s_\ce{A})$ is controlled by the vapor pressure of $\ce{A}$. On the upper side the concentration of $\ce{A}$ is zero. The solubulity of $\ce{A}$ in the two membrane layers is the same.

  (a) Derive the expression for the flux $J_\ce{A}$ through the composite membrane

The flux through a membrane is given by the equation:

$$J_\ce{A} = \frac{D_{AB}}{L}\left(c^{(m)}_{\ce{A},F} - c^{(m)}_{\ce{A},P}\right)$$

where, $c^{(m)}_{\ce{A},F}$ and $c^{(m)}_{\ce{A},P}$ are the concentrations at the edges inside the membrane.

So I would assume that $c^{(m)}_{\ce{A},F}$ = $c^s_\ce{A}$ and $c^{(m)}_{\ce{A},P}$ = $c_\ce{A}$

and because there are two membranes I would have to combine the diffusion coefficients as well as the lengths, which I do by addition to get the equation:

$$J_\ce{A} = \frac{D_{\ce{A},1} +D_{\ce{A},2}}{l_1 +l_2} (c^s_\ce{A} - c_\ce{A})$$

I am unsure if this is the correct way of deriving the expression for the flux when there are two membranes. Am I thinking correct?

Edit

I named the third concentration in the membrane $c_m$. Then I made two equations for the molar flux.

$$J_\ce{A} = \frac{D_{A,1}}{l_1}(c^s_A - c_m)$$

$$J_\ce{A} = \frac{D_{A,2}}{l_2}(c_m - c_A)$$

When rearranging and solving for $J_A$, I get:

$$J_\ce{A} = \frac{(c^s_A - c_A)}{\frac{l_1}{D_{A,1}}+\frac{l_2}{D_{A,2}}}$$

But that is the same answer as I got before


texts:
The question given above appeared in the 2016 Indian National Chemistry Olympiad (INChO). What I think is that the epoxide ring is being opened by a base-catalysed mechanism ($\mathrm{S_N2}$). I proposed the following few steps for this:

The diisopropylamide ion, which is a very strong base, would not be a good leaving group. To obtain the desired products, how could the mechanism then proceed? And if not, then what would be the real mechanism? I did not find any reliable information on the Internet regarding ring opening using LDA.


texts:
I was wondering how the exchange of hydrogen by deuterium, like on arenes like benzene

could be monitored for a reaction on a scale larger than say 10 g of product.  While I know that C6D6 is commercially available, used for NMR spectroscopy, I recognize

the observable signal of the protons bound to carbon is attenuated by the advancement of the reaction, and
the very deuterium installed equally serves as lock signal for the 1H-NMR spectrometer (similar to the deuterium in CDCl3).  So there might be an experimental problem, from the spectrometer, too.

But what is a typical standard compound may serve as an added inner standard in such a reaction, provided protocols accessed so far mention extended heating / autoclave or/and presence some hydrogen gas to initiate the reaction as reaction conditions?  Do commercial suppliers carry out the exchange hydrogen by deuterium, and (perhaps by virtue of even larger batches) obtain the 99%+ isotopically enriched product by sophisticated distillation / zone melting, recycling the partially deuterated product?


texts: What is the exact reason that compounds such as carbon dioxide cannot interact with other compounds through dipole-dipole interactions?

texts: Whilst I understand that $\ce{CO2}$ has a linear structure, resulting in a vector sum of the dipoles of 0, I do not understand why the dipoles formed at the two oxygen atoms as a result of their increased electronegativity cannot interact with other molecules via dipole-dipole forces. Do the vectors equaling 0 somehow negate the present dipoles?


texts:
I'm tutoring few students for Chemistry. During the course, I many times use the phrase "Out of these possibilities this one is stable. So it is formed". I get questions like, "How do the molecules know?"

Honestly I don't know. How do the molecules know the future? How do they proceed to form "Most Stable" compound?

Cross Post: https://physics.stackexchange.com/questions/51894/how-do-the-molecules-of-reacting-compounds-proceed-to-form-most-stable-molecul


texts:
The buffer property of buffer solutions is most likely done by the weak acid's reversible dissociation. Can a weak base with reversible dissociation be used to prepare a buffer solution?if then what should be our choice and if not then please explain.
Note: if this has already been answered please give the url


texts: Do carbodiimides exhibit axial chirality or do the nitrogens invert rapidly enough, as in trisubstituted amines with different alkyl groups?


texts: I started to learn Chemistry with something like Hydrogen having 1 electron in the first shell, Oxygen having 2 electron in the first shell and 6 electron in the second shell... But I don't really understand how scientists know it? How do they know there are how many shells and how many electron per shell? Is that something visible? Or just an imagination theory or they using a method to measure?


texts: How to determine rotational states of a molecule?

texts: How can you determine the possible rotational states of a molecule? Atkins Physical Chemistry book says that for linear molecules there are two possible rotational states, but what is the general method for finding the amount of rotational states for other relatively more complex molecules, say for example $\ce{H2O}$ and $\ce{CH4}$?


texts: why there is no simple rule to predict the possible ionic charges of element in middle of periodic table

texts:
I know element in left two columns have 1+,2+... and right ones 1-,2-.

But in middle is all over the place. And with multiple charges.

What defines that if this element is gonna have this charge. All i have been told is that elements want to be close to as much possible to noble gasses because they are stable. Which doesn't explain much as to why such behavior is present. What does it mean to be stable. And why elements in middle find it stable just after 3 +/- charge even though they are far from noble gases.

Thanks, there are few questions in here but all very related i think.


texts: Shouldn't 1 mole of any ideal gas at open space occupy more than 22.4 L volume at S.T.P. due to diffusion?

texts: So if diffusion occurs,1 mole of any ideal gas should occupy a much greater volume in open space at STP.


texts: Which is more stable — a carbanion on a vinylic position or a carbanion on a benzylic position?

texts: I am getting a dilemma over this. Should the negative charge on the benzylic position participate in resonance with the benzene ring and make it more stable or is it the electronegativity of the $\ce{sp^2}$ hybridized carbon of the vinylic group that will make the carbanion more stable on it ?


texts: When roasting pyrite, the products are usually Fe$_{2}$O$_{3}$ and SO$_{2}$, but is it possible to get magnetite and SO$_{2}$ from roasting pyrite? Thanks for answers.


texts: Is it safe to look at a mercury gas discharge tube?

texts:
As part of a chemistry course, I recently observed a demonstration in which the instructor electrified a mercury gas discharge tube (the tube looked something like this image). The glow from the tube appeared to be a light blue, but when I performed an internet search afterwards, I found that mercury gas discharge tubes apparently emit ultraviolet light, which can be harmful to the eyes and body. I was standing within one foot of the discharge tube (which looked something like this while lit) for several minutes. The tube was completely clear, which I am assuming means that it did not contain a phosphor to block the UV light (please correct me if I am wrong or if I am misunderstanding something).
The same demonstration was performed with a hydrogen gas discharge tube, which also was completely clear (see above).
Since I was looking at the tubes, could the higher frequencies of electromagnetic radiation (e.g. the ultraviolet light from the mercury) have damaged my eyes, skin, etc.?
After the demonstrations, my eyes seemed irritated, but I'm not sure if this was just a result of the placebo effect.


texts: While finding out chiral centers should lone pair be considered as a group?

texts:
My book says it is a chiral center.

Should I count lone pairs as one of the groups while finding chiral center ?


texts:
Why does the URL https://www.iupac.org/cms/wp-content/uploads/2015/07/Green-Book-PDF-Version-2011.pdf (ending in 2011) contain the Green Book labelled 2007, and reprinted in 2008? Does a 2011 edition exist and they just uploaded the wrong file?

Same goes for the URL http://media.iupac.org/publications/books/gbook/IUPAC-GB3-2ndPrinting-Online-22apr2011.pdf (containing the exact same file).

And there is the version https://www.iupac.org/fileadmin/user_upload/publications/e-resources/ONLINE-IUPAC-GB3-2ndPrinting-Online-Sep2012.pdf with different water mark, one page more, and the front matter in a different order.


texts:
So I have a quick question about some concept I have watched in a video, it is illustrated as follows.

$$\ce{A + B <=> C + D}$$

So what the video is saying is that if you increase $\ce{A}$ then you get the products to increase and the $\ce{C + D}$ to increase as well.

My question is that shouldn't the products also depend on the $\ce{B}$ and not only just the $\ce{A}$. So to increase the products don't we need to increase both the reactants?

Here's the video for reference.


texts: What's the difference between PBE and B3LYP methods?

texts:
I can't find an answer to that question. I was told that in B3LYP, more variables implemented in the method are empirical, but I can't find anywhere if it's true, and I'm sure it's not the only difference.
I'm new to calculations, and it seems so hard and confusing, so please help me.


texts: Absence of anti-Stokes line in Raman spectrum

texts:
If we have a molecule 1H-25X which shows a band at $3000~\mathrm{cm}^{-1}$ in the IR spectrum and you want to record a Stokes and anti-Stokes Raman spectrum with a laser of 1000 nm, why is the anti-Stokes band not observed?

My guess is that if you would calculate the wavelength of the anti-Stokes line, then you would get 769 nm. In this region there might be fluorescence, which could interfere with the spectrum. Or am I wrong?


texts: Why does PbI₄ not composed of lead(II), iodide and triiodide?

texts: $\ce{Pb^4+}$ is reduced by $\ce{I-},$ so $\ce{PbI4}$ cannot exist with $\ce{Pb}$ in $+4$ oxidation state. But if I replace three $\ce{I-}$ with $\ce{I3-},$ then we can have $\ce{Pb^2+}$ similarly to how $\ce{TlI3}$ exists with $\ce{Tl+}.$ Why does this not happen?


texts: where can I find experimental compressibility factor values?

texts:
I am interested in experimental compressibility factors for various gases, such as methane and carbon monoxide. Not only for standard pressures and room temperature, but in a range from 1 to a few 1000 bars and various temperatures. Where can I get them? I've done a quick google search, but they seem to be well hidden.

EDIT: Perhaps a better question is where can I find second, third, fourth, fifth... virial coefficient for these 2 gases? I am interested at 2 temperatures: 200 K and 287 K. I found some so far, but not at 287 K.


texts: What is the major product formed on addition of Hydrogen Iodide to Pent-2-ene?

texts:
Orginal question:

(1) One of the carbocations formed (CC on the right) is only slightly more stable than the other (both are 2°).
(2) Iodine ion ($\ce{I-}$) is a slightly bigger ion and it faces more steric hinderance while attaching to one of the carbocation (CC on the right).
These two factors are contradictory hence how do i compare them and arrive at a major product?


texts: Molarity of a mix between solid and solution

texts:
$\pu{50 g}$ of solid $\ce{NaOH}$ is added to $\pu{1.5 L}$ of $\pu{2.4 M}$ $\ce{NaOH}.$ Water is then added to the mix until the solution reaches $\pu{5 L}.$ I need to find molarity of the final solution.
I am a bit confused because I have different answers with my friends, my approach was as follows.
The molarity $x$ when I add solid $\ce{NaOH}$ to $\pu{1.5 L}$ $\ce{NaOH}$ assuming $n_1 = n_2:$
$$x = \frac{\pu{1.5 g} \cdot \pu{2.4 M}}{\pu{1.55 g}} = \pu{2.322 M}$$
The molarity $y$ after I add more water also assuming $n_1 = n_2:$
$$y = \frac{\pu{1.55 g} \cdot \pu{2.322 M}}{5} = \pu{0.72 M}$$
What is wrong with my approach?


texts: How do I write a figure legend for a thin layer chromatography plate drawing?


texts: Why does automotive glass shatter into tiny pieces but glass used in our houses into shards?

texts:
Image Source : Bigstockphoto

Image source : pinterest

The first picture depicts the glass that is found from an accident site, while the second picture depicts the glass that we use in our home.

What is the difference between these two glasses? Why doesn't the first glass, which is used as a wind shield in vehicles, breaks like the glass that we use in our home?


texts: Why do single elements in a molecule have an oxidation state of zero?

texts:
For example, take $\ce{O2}$.

The oxidation state of oxygen is -2, yet once its in a molecule its oxidation state becomes zero?

How is this so?


texts: Why could it be assumed that the standard enthalpy change is independent of temperature down to 25 °C?

texts:
For the reversible reaction of pyruvic acid to 2,2-dihydroxypropanoic acid, we calculated enthalpy using NMR and extrapolated from area (integration) and peaks etc.

We then plotted $\ln K$ vs $1/T.$ I am confused by this questions because I thought enthalpy was temperature dependent.

I guess my question was unclear. The exact question we are asked is:

  With the assumption that the standard enthalpy change is independent of $T$ down to 25 °C, calculate an extrapolated value for $K$ (25 °C) and compare this to your experimental $K$ value determined at 25 °C. Is this a fair assumption? Why?

I do not understand if this assumption is fair and why?


texts:
My symmetry lecture notes state that there are seven high-symmetry 3D point groups, which have more than one rotation axis of order greater than 2: $T$, $T_d$, $T_h$, $O$, $O_h$, $I$, $I_h$. I sometimes see them called the “cubic point groups”.

My point is: most molecules (or molecular fragments) I have encoutered in these groups are always $T_d$ (tetrahedral) or $O_h$ (octahedral). What are examples of molecules in the other groups?


texts: Why does the OAc group leave in the first step of Oxymercuration?

texts: The above picture shows the first step of Oxymercuration. The electrons attack the Mercury atom but the OAc group leaves. Why is this? Hg is a transition metal with a number of available oxidation states, why cant it just accept the electrons? For similar reactions (like glycol cleavage using periodate or lead tetra acetate) how is it possible to tell whether a group will leave (retaining oxidation number) or the oxidation state changes?


texts:
What is the correct way to draw a carbene? On most/all material I have seen, both singlet and triplet carbenes are depicted as so:

With 2 "dots" representing the non-bonding electrons on either a singlet or a triplet carbene.

However in a class today my tutor was adamant that a singlet carbene should be drawn with a positive and a negative sign on the carbon. His argument as such was that "you have an empty and a full orbital and so the empty orbital corresponds to the positive sign, the full orbital corresponds to the negative sign".

So my question is - How is a carbene correctly drawn? As above or with a carbon bearing both a positive and a negative sign?


texts: What is the hybridization of the carbonyl oxygen in a carboxylic acid?

texts:
My professor sent out a review guide. One of the questions on this guide is

  The carboxylic acid carbonyl oxygen is:
  1. $\ce{sp^2}$
  2. $\ce{sp^3}$
  3. $\ce{H}$-bond donor
  4. rapidly equilibrating between $\ce{sp^3}$ and $\ce{sp^2}$
  5. 1 and 3
  6. 1 and 4

I chose (4) because of the resonance that can be drawn with a negative oxygen and positive carbon. However apparently the answer is (6). I don't understand how something can be equilibrating between two states and still be one of those states.

Could anyone explain?


texts: What is the amount of limiting reagent in this chemical reaction?

texts:
In the reaction involving $\pu{124 g}$ of aluminium and $\pu{601g}$ iron (III) oxide, what is the amount of substance in moles of the limiting reagent?

Here is what I have so far:

Balanced equation:
$$\ce{2Al + Fe2O3 -> Al2O3 + 2Fe}$$

$\ce{Al}$ has MW = $27$, mass = $\pu{124 g}$ and determined its amount using $n=\frac{\text{mass}}{MW} = 4.59$

$\ce{Fe2O3}$ has MW = $160$, mass = $\pu{601 g}$ and determined its amount using n=mass/MW = 3.756

I was able to identify limiting reagent by:

g $\ce{Al}$ --> n $\ce{Al}$ -->n $\ce{Fe2O3}$--> g $\ce{Fe2O3}$

$124 g --s1-> 4.59 --s2--> 2.295 -s3--> 367 g$

$S1 = n = 124/27 = 4.59$

$S2 = \frac{\text{want}}{\text{have}} \times \ce{Al} = 1/2 \times 4.59 = 2.295$

$S3 = m = n\times MW = 2.259 x 160 = 367 g$

Therefore as all $\ce{Al}$ did not use all the $\ce{Fe2O3}$ that means the $\ce{Al}$ is the limiting reagent.

The amount of substance in moles of limiting reagent $\ce{Al}$ (answer to the question) is $4.59$ OR $9.18$ (which is moles multiplied by the stoichiometric coefficient, which is $2$).


texts: Major product of the nitration of benz[cd]indol-2(1H)-one

texts:
Decide major product for given reaction of electrophilic aromatic substitution:

Is the major product a because of steric hindrance, or is it b because of hydrogen bonding?


texts:
This is a question from my text book.

Compare the stability of carbocation between $\ce{CF3^+}$ and $\ce{CD3+}$.

The answer is given $\ce{CF3+}$ due to backbonding.
But I see backbonding as a sort of resonance effect. And we know that for fluorine atom its inductive effect dominants its resonance effect, and so overall it is electron withdrawing. So, shouldn't the answer be $\ce{CF3+}$?


texts:
Why are the $d$-orbitals so named?

The naming of $p$-orbitals is fine.
I can easily name any p orbital according to the axis along which it is oriented.
But what about $d$- orbitals?
Why are there subscripts such as $x^2-y^2$ and $z^2$ ?
Are we supposed to read it like "x squared- y squared"?

Also why does the $d_{z^2}$ orbital has a ring like structure around it?

Is there any order in why the degenerate d orbitals are filled? Like for $p$-orbitals we have an order of filling: $p_x$ then  $p_y$ then  $p_z$.(Not too sure of this.My friend told me about this.)

My friend also told me that for d-orbitals, $d_z$ is conventionally taken as the principal orbital.(Again not too sure what he meant by that).

Although I wouldn't want to get into knowing about f orbitals,but information on that might help someone looking for answers on that.

I wonder why this hasn't been asked on CSE before.

NB: I have visited this link , but couldn't understand much.

Thank You.


texts: Explanation for increase in the number of oxidation states for transition elements from Sc to Mn of the 4th period

texts:
From Sc, to Mn, the number of oxidation states increases from one (Sc) to seven (Mn). The explanation for this is because the unpaired 3d electrons can be lost along with the 4s electrons during bonding.

Should this be the case? Wouldn't it be easier to lose an electron when it is paired because of interelectronic repulsion in the orbital? Could someone explain this? Thanks!


texts:
I don’t understand why the following question

The decomposition of nitrosyl bromide $(\ce{NOBr})$ proceeds by the following reaction:
$$\ce{2 NOBr(g) <=> 2 NO(g) + Br2(g)} \qquad K = 0.0142$$
Calculate the $[\ce{NOBr}],$ $[\ce{NO}],$ and $[\ce{Br2}]$ when $\pu{10.0 mol}$ of nitrosyl bromine is placed in a $\pu{5.00 L}$ closed vessel and allowed to decompose.

has the answers that it does:

$$
\begin{align}
[\ce{NOBr}] &= \pu{1.585 M} \\
[\ce{NO}] &= \pu{0.415 M} \\
[\ce{Br2}] &= \pu{0.207 M}
\end{align}
$$

From what I understand
$$K = \frac{\prod a_\mathrm{products}}{\prod a_\mathrm{reactants}},$$
where $a$ is the activity of the products/reactants. The activity of a gas is approximately equal to the partial pressure of the gas divided by a reference pressure (usually 1 atm). This yields unitless quantities with the magnitude of the partial pressures of each gas. Thus
$$K = \frac{P_\ce{Br2}\cdot P_\ce{NO}^2}{P_\ce{NOBr}^2}$$
Converting from a partial pressure to a concentration can be done using the ideal gas equation
$$\frac{P}{RT} = \frac{n}{V} = M,$$
where $M$ is concentration. Thus,
$$K = \frac{[\ce{Br2}][\ce{NO}]^2\cdot RT}{[\ce{NOBr}]^2}$$
However, plugging the concentrations given into the solution of this problem doesn’t yield the given value of $K.$
Am I wrong in the way I am approaching this problem, or is the problem itself wrong? If the equilibrium constant was denoted $K_c$ instead of $K,$ the given solution would be correct, but I don’t think it’s correct to assume that $K_c$ is the same as $K.$


texts: Rearrangement of Grignard reagent formed from exocycloproyl vinyl bromide

texts:
First, I prepared the grignard reagent then performed nucleophilic addition to the carbonyl carbon  and then did hydrolysis.

So basically in my product, $\ce{-Br}$ is replaced by $\ce{-CH2OH}$

But answer given is:

Why is my mechanism wrong?


texts: What is the difference between a free radical and a radical cation?  Are they different thing or do they mean same?


texts: Is there a mathematical generalization for the number of isomers (structural and configurational) of a given compound?

texts:
The original question was:

  How do I find the number of structural and configurational isomers of a given compound?
  is there any formula?

For a specific example, how would I find the number of structural and configurational isomers of a bromo compound $\ce{C5H9Br}$ formed by addition of $\ce{HBr}$ to 2-pentyne


texts: For the above question....i did the usual addition of HF across double bonds and  joined both of them and.i thought the answer would be option(b) but the answer is something else please help!!


texts: What will happen when a metal reacts with an acid which is neither dilute nor concentrated?

texts: We have always studied about metals reacting with dilute and concentrated acids, but I do not understand what will happen if the same metal reacts with an acid that is neither concentrated nor dilute?


texts: Why is the distance between the atoms shorter in the dicarbon anion compared to the cation?

texts: In general, the anions have bigger ionic radii than their corresponding neutral atoms, and the cations have smaller ionic radii then their corresponding neutral atoms. How come that does not apply to $\ce{C2-}$ and $\ce{C2+}$?


texts: Is there any difference between isotonic and isosmotic solution? Can we say isotonic solution do not show osmosis because they have same osmotic pressure?


texts: How do I purify the resulting compound after a nitro- to amine-group reduction?

texts:
I have an aromatic compound that I reduced with either $\ce{Fe + HCl}$ or $\ce{Sn + HCl}$.

How would you choose to go about extracting the compound?

I'm thinking to dry off all the $\ce{HCl}$, redissolve in water, and react out the iron salts to Iron Hydroxide, which can be filtered out.

Then dry out again, dissolve in something like acetone then filter out the sodium chloride?


texts: We have a home carbonator for makeing seltzer. It blows $\ce{CO2}$ under high pressure into water. Could I use it to carbonate corn oil? Is $\ce{CO2}$ soluble in a no aqueous solution?


texts: How do I write the deterministic rate equation for bimolecular reaction with similar particles?

texts:
I was wondering how to write down the deterministic rate equation for a bimolecular reaction with similar particles.

e.g.

$$
\ce{A ->[k_+] 2B}
$$

and

$$
\ce{2B ->[k_-] A}
$$

Now the rate equations for the above reactions are:

$$
\mathrm{\frac{\delta A}{\delta t}= - k_{+} A + k_{-} B^2}
$$

$$
\mathrm{\frac{\delta B}{\delta t}= 2 k_{+} A - 2 k_{-} B^2}
$$

Now I have included a factor of 2 in the second equation to conserve $\mathrm{A + \frac{B}{2}}$.

But I don't understand the reasoning for this factor of 2 in the second equation.


texts: Can the change in internal energy be nonzero if temperature is constant?

texts:
I have learnt that internal energy, $U$, is a state function and it only depends on temperature... So if $\Delta T = 0$ then $\Delta U = 0$.

However when I was studying exothermic and endothermic reactions it was written in my textbook that at a constant temperature and pressure, $\Delta U$ is negative for exothermic reactions. How is that possible? Shouldn't $\Delta U$ be zero since the temperature is constant?


texts:
Recently I heard my teacher say that when increasing the total pressure of the system, the reaction which is "more dependent on collisions" is favoured.
This seems to make sense, although I've looked at many resources online and on SE, and people have either given a mathematical explanation or simply talked about Le Chatelier's principle (increasing pressure favours reaction to produce less moles)
My question is: is it correct to say that increasing the pressure favours the reaction which involves more molecules colliding?
Take for example the forward reaction here which is favoured upon pressure increase. (4 molecules need to collide for forward and 2 molecules need to collide for reverse reaction)
$$\ce{N2(g) + 3 H2(g) <=> 2 NH3(g)}$$
I'd appreciate an intuitive explanation about collisions and interactions between molecules rather than something mathematical. Thanks in advance!


texts: Does raising the temperature of a complex ion (formed from a transition metal ion and ligand(s)) affect its color? For example, if the temperature of $\ce{[Cr(H2O)6]^3+}$ is raised, will its color change?


texts: I want to make electricity of aluminiun cans i.e. reverse the process of refinning aluminium. Any ideas?

texts: Recycling Al cans to produce electricity,i.e. to reverse the process of electrolysis and produce electricity


texts: How many carbons in this skeletal structure?

texts:
How many carbons are in this skeletal structure? I was told to draw a circle at the start of the structure and at each point the line turns off to get the total number of carbons but doing so would result in 6 carbons which I know is wrong but why is it wrong? And where on the structure are the carbons located?

Thanks for clearing this up for me!


texts: Which material are piezoelectric buzzers made of?

texts:
Which material are these buzzers made of?

Does it depend on the manufacturer or they all are made of the same material? The Wikipedia page does not say anything about the material. I found some datasheet online but it also does not reveal the material. Is there a reference where I could find more about the properties of this material?


texts: How to find relative lowering of vapour pressure from phase diagrams in terms of temperature?

texts:
Problem

Answer

   C

My question

Does a tie rule exist for solution solvent phase diagram to express relative lowering of vapour pressure in terms of temperature?

The phase diagram is the one provided as an explanation to colligative properties of binary solutions with one component non volatile.

Edit: Is there any relation between relative lowering of vapour pressure; relative elevation of boiling point and relative depression of freezing point ??

I think I found (  ∆p/p  = 1.23 ∆Tb/Tb) by differentiation of Clausis- Clayperon eqn and Troutons law; but am unsure.
If this is true? Can we approximate 1.23 as 1 ??( 1.23 was ∆Svap/R and ∆Svap  was put as 10.3)

Also does there exist a like rel for freezing point?


texts: Why is Borax used as a primary standard?

texts:
It's given in my book that borax is a useful primary standard for titrating against acids. I have heard that primary standard is a pure reagent and does not gain any weight by absorbing moisture. (Hence any error during weight measurement is prevented).

I got this from a website that came first on searching "primary standard"

  Primary standard is a reagent that is extremely pure, stable, has no waters of hydration, and has a high molecular weight .

But borax (represented as $\ce{Na2B4O7.10H2O}$) has water of hydration.


texts: Additional Questions Regarding the Auto-Ignition Temperature

texts:
I had some followup questions regarding a previous post I made here regarding the auto-ignition temperature and ASTM E659

For fuel temperature below AIT, we should still have finite reactants above activation energy, reacting, and heating the remaining mixture so additional reactants are above the activation energy. Theoretically as $t \rightarrow \infty$, could the fuel burn itself out like this, regardless of what temperature it is at (obviously the rate will be very different)? If so, is there an implicit rate requirement in defining the AIT that the above chain reaction process has to happen within a short duration?
Given that ignition is defined as when a flash and temperature rise is seen, does this mean that the actual quantity of fuel burnt is unimportant and it is assumed that a significant enough amount is used?
Is the reason for using an open flask in ASTM E659 likely just for simplicity, as opposed to a piston-cylinder arrangement that offers more control over air-fuel mixture?


texts: Why is the product of sodium and water, sodium hydroxide and not sodium oxide?

texts:
In the reaction $\ce{Na(s) + H2O}$ the products are listed as $\ce{NaOH(aq) + H2 (g)}$, but why would $\ce{Na2O}$ not be a possible product?

I searched and found that the reaction $\ce{Na2O + 2H2O -> 2NaOH}$ occurs as well. Does it have to do with the stability of oxides?


texts: What Causes there to be a Maximum Amount of Salt which can be Dissolved in Water?

texts: When you add salt to water and stir, after a while the salt will no longer dissolve. Why is this?


texts: What does (sol) in a chemical equation mean?

texts:
I'm reading Shrivers Inorganic Chemistry book and some of the equations have a (sol) state on them. I'm sure the book has already defined this but I cannot find where.
Examples:

\begin{align}
  \ce{[NH3OH]Cl (sol) + NaOBu &-> NH2OH (sol) + NaCl (s) + BuOH (l)}\\
  \ce{SbF5 (l) + HF (l) &-> H2F+ (sol) + SbF6- (sol)}
\end{align}


texts: By the Henderson–Hasselbalch equation, log (salt)/(acid) term is a ratio of the concentrations. So, how can dilution change the pH of the acid as the concentrations of both salt and acid would change with dilution and the term would remain the same?


texts: Why amino acids (Zwitterion) become either negative or positive at low and high pH solutions?

texts:
The amino acids are Zwitterions. In neutral pH, an Amino acid's amino group has a postive charge and Carboxyl group has negative charge. They cancel each others charge thanks to the $Hydrogen$ that's roaming between the two groups.

But, I am not able to understand why Amino acids have positive charges at a low pH and negative at high pH? Given amino acids are Zwitterions, how can both terminals have the same charge (either positive or negative) at low and high pH?

Can someone explain this from general chemistry and pH perspective (acid/base)?

PS: first posted in Biology site but community recommended it to be moved here.


texts: Why wouldn't you see blue or purple when you heat metal and only either red or yellow?

texts:
Question

Why wouldn't you see blue or purple when you heat metal?

Background and thought process

When metal gets heated the electrons gets excited and thus it emits the color that we see. But my question is why don't we see the other colors? If we heat metal to an extreme temperature it might turn white but not blue or purple. Why is this?


texts: How do enzymes affect a reaction's equilibrium?

texts:
I am not sure to understand something I read in a educational journal (1)
Introduction
Lets consider the following reversible enzyme-catalysed reversible reaction;
$$E + S \leftrightharpoons ES \leftrightharpoons E + P$$
with forward rate constants $k_1$ and $k_2$ and backward rate constants $k_{-1}$ and $k_{-2}$ respectively.
The equilibrium constant of this reaction can be expressed in terms of reaction quotient at equilibrium, in terms of thermodynamic potential and also in terms of rate constants;
$$K_{eq} = (\frac{[P]}{[S]})_{eq} = e^{-\frac{\Delta_r\mu^\circ}{RT}} = \frac{k_1 \cdot k_2}{k_{-1} \cdot k_{-2}}$$
It is possible to experimentally determine the Michaelis constants of this reaction for S and P by studying it in conditions where $[S]>>[P]$ and $[S]<<[P]$ respectively. The Michaelis constants are in fact only combinations of the rate constants;
$$K_M^S = \frac{k_{-1} + k_2}{k_1}$$
$$K_M^P = \frac{k_{-1} + k_2}{k_{-2}}$$
and the maximum forward and backward rate are respectively
$$v^+_{max} = [E] \cdot k_2$$
$$v^-_{max} = [E] \cdot k_{-1}$$
where $[E]$ is the total enzyme concentration (including $[ES]$). Which leads to the Haldane relationship by rewriting $\frac{k_1 \cdot k_2}{k_{-1} \cdot k_{-2}}$;
$$K_{eq} = \frac{v^+_{max} \cdot K_M^P}{v^-_{max} \cdot K_M^S}$$
Problem
I was thinking that enzymes did not affect the position of the equilibrium of a reaction; that position would always be determined by thermodynamics, and the presence of an enzyme would simply affect the speed at which that equilibrium is reached (by lowering the activation energy). However, I stumbled upon a document (1) suggesting that both forward and backward rate expressions ($v^+ = v^+_{max} \frac{[S]}{K_M^S + [S]}$ and $v^- = v^-_{max} \frac{[P]}{K_M^P + [P]}$ respectively) apply on the whole reaction advancement axis and that the point where $v^+ = v^-$ then determines the apparent equilibrium of the reaction. The point of this document was to show that different values of enzyme parameters could correspond to the same $K_{eq}$, therefore an enzyme can set the apparent equilibrium of a reaction to a value totally different from its thermodynamic equilibrium.
I find that point confusing; if the equilibrium of a reaction changes in the presence of an enzyme, to the point that two different enzymes can change the direction of a given reaction (which is also the subject of another article of the same journal (2)), then the equilibrium constant of that chemical reaction cannot be predicted from thermodynamics (ie based on the chemical potential of its reagents). Then, can it be said that an enzyme modifies the chemical potential change of a reaction?
(1) A. Mellors, "The Haldane relationship, enzymes & equilibrium", Biochemical education 1976 vol 4 no. 4
(2) M. L. Uhr, "The influence of an enzyme on the direction of a reaction", Biochemical education 1979 vol 7 no. 1


texts: Draw a diagram to show the shape of Chloromethane and explain why it has this shape.

texts: I know it has this shape, but I don't know how to explain it. Any help is appreciated, thanks.


texts: Difference between using Zinc Nitrate instead of Potassium Nitrate for Salt Bridge Solution?

texts:
I have a lab question which asks "Suppose that before you began this experiment you ran out of your salt bridge solution of Potassium Nitrate and the only substitute available was zinc nitrate, would this have an effect on the cell potentials you measured?"

Now I'm guessing the answer is yes, since Zinc will have a different reduction potential than Potassium, but I don't understand how to explain that in regards to the actual transfer of electrons and change in Voltage measurement.  Any ideas?

*Some background information, we used half cells of AgNO3, FeCl2, Zn(NO3)2, Ni(NO3)2, Cu(NO3)2, and measured the voltage of each combination of half-cells by connecting each to both positive and negative lead.

Thanks so much..


texts:
I'm a geology student completing a project on chemical staining and was after some chemistry help on some of the reactions taking place. I am using various different stains to identify carbonate and feldspar minerals.

One of the stains, in particular, is alizarin red S (1,2-dihydroxyanthraquinone) and is used to stain calcite ($\ce{CaCO3}$) red and Fe-calcite/Fe-dolomite blue. The stain powder is mixed with a weak (2%) HCl solution to react with the carbonate and produce the stain. However, I am just unsure about what reactions are taking place between the stain solution and the mineral that produce the precipitate on the surface of the grains.

I'm not finding literature on this reaction - probably because it has been mainly used by geologists without a solid chemistry background. Any help would be much appreciated.


texts: How to find the percentage contribution of a compound via gravimetric analysis?

texts:
You have a sample of silver alloy and would like to know how much silver is in it. Dissolve the silver sample in nitric acid. Filter to remove any insoluble material. Add an excess of $\ce{KCl}$ solution, which causes the formation of silver chloride precipitate. Filter, dry, and weigh the precipitate. What do you estimate the percentage of silver in the original sample is if its mass was $5.2~\mathrm{g}$, and the mass of silver chloride was $6.4~\mathrm{g}$?

The atomic mass of silver is $M(\ce{Ag})= 107.87~\mathrm{\frac{g}{mol}}$. That of chlorine is $M(\ce{Cl}) = 35.45~\mathrm{\frac{g}{mol}}$.
My answer is $81\%$, because $5.2/6.4 \cdot 100 = 81$. However, I am quite unsure.


texts:
The problem is stated as follows:
The surface of a steel gear made of 1022 steel (0.22 wt% C) is to be gas-carburized at $927$ °C. Calculate the time necessary to increase the carbon content to 0.30 wt% at 0.030 in below the surface of the gear. Assume the carbon content of the surface to be 1.20 wt% and $D_{927^{\circ}C}=1.28 \times 10^{-11}\frac{m^{2}}{s}$

The formula is $\frac{C_{s}-C_{x}}{C_{s}-C_{0}}=ERF(\frac{x}{2\sqrt{Dt}})$

The solution manual is setting $C_{x}=0.30$, but should it not be $C_{x}=0.30+0.22=0.52$, since the initial carbon content in the steel is $C_{0}=0.22$?


texts:
Is entropy change of the system for reversible process same as entropy change of the system for irreversible change? Is Q for reversible change equal to Q for irreversible change? Or the change in entropy of the surrounding is same in any case because surrounding is bigger than system, so the change in surrounding is small?
And finally, does internal energy of the system depend on entropy of the system and how?

I registered just so I could ask this question. I would be very grateful for answer.


texts: Does motor oil get more viscous when heated & what is the meaning of the SAE motor oil code?

texts:
The motor oil in my 2004 Pontiac Vibe is 5W-30.

My (incorrect) understanding of this SAE nomenclature is that 5W means "Viscosity index of 5 in the winter" (or when really cold - like $\pu{-30 ^\circ F}$) and "Viscosity index of 30 at operating temperature" (or when the car has been running for a little while).

So how is this accomplished? I usually think of something like butter or coconut oil that solidifies at a lower temperatures and becomes fluid again as heated. To my understanding oil has a higher viscosity at lower temperatures (generally speaking).

Everyone keeps talking about "additives" that help accomplish this feat in "multi-grade" oil. What are these additives? Generally, how do they work? I'm no chemist and neither are these auto mechanics, so I figured this might be the right place to ask.

Since my understanding of the SAE motor oil code is incorrect, illumination on its exact meaning would be helpful.

A full blown chem answer and an "explain it like I'm 5" would be most appreciated :) I never studied chemistry past high school, so be easy on me!


texts: HCl + NaOH: Why H prefers to move to O instead of staying with Cl?

texts: The question is - fundamentally why does H "decides" to replace Na? Why is it more preferable than staying with Cl?


texts: Formation of peracetic acid from acetic acid and hydrogen peroxide and its stability in their presence

texts:
I've been trying to find out as much as I can about peracetic acid, especially regarding its use as a sanitizer. In the Wikipedia entry it notes that

  Peracetic acid is always sold in solution as a mixture with acetic acid and hydrogen peroxide to maintain its stability.

This is definitely born out by commercial examples: Loeffler Lerasept PAA (a sanitizer I've used before) lists 31% hydrogen peroxide, 17% peracetic acid, 16% acetic acid and 1% phosphonic acid among its ingredients.

But, my understanding was that mixing acetic acid and hydrogen peroxide makes peracetic acid. From the same Wikipedia article:

  It forms upon treatment of acetic acid with hydrogen peroxide.

So my question is: what exactly keeps the excess hydrogen peroxide from reacting with the excess acetic acid to simply form more peracetic acid? Does the phosphonic acid inhibit this reaction? Is there something else not listed that does this? Or is it just some bit of chemistry I'm not aware of?


texts: $\ce{Cl-}$ is a monodentate ligand. It has four lone pairs then why it can't donate two lone pairs to central atom and act as a bidentate ligand?


texts: Suppose a heated 5.00 g sample of sodium bicarbonate lost a mass of 1.00 g, what percent of impurity is in the sample?

texts:
The 5.00 g is a mixture of sodium bicarbonate and an unknown substance, making it impure.

Balanced decomposition equation:

$$\ce{2NaHCO3(s) -> NaCO3(s) + H2O(g) + CO2(g)}$$

There are 0.06 mol of $\ce{NaHCO3}$ in a pure 5.00 g sample of sodium bicarbonate.
Theoretically, 0.0298 moles of $\ce{H2O}$ and $\ce{CO2}$ would be lost durin the decomposition of 5.00 g of sodium bicarbonate.
0.0298 mol converted to grams is:
0.536 g of $\ce{H2O}$
1.31 g of $\ce{CO2}$


texts: Do you know a simple fast front-end MD software for OS X

texts:
I need a GUI front-end simple MD software for OS X, something similar to ascalaph maybe.

What I need to do is a rigid optimization of waters around a protein. I don't have many water molecules around, so a few tips about how to not let them fly away would be nice too.


texts: Elevated boiling points in alkanes with even number of carbons

texts: Why do alkanes with even number of carbon atoms have greater boiling points than those with odd number of carbon atoms?


texts:
The hydrogen in $\ce{C4}$, $\ce{C6}$, $\ce{C10}$ and $\ce{C8}$ belong to same hydrogen environment.
The hydrogen in $\ce{C3}$, $\ce{C1}$, $\ce{C11}$ and $\ce{C13}$ belong to the another hydrogen environment.
Hydrogen in $\ce{C12}$ and $\ce{C2}$ belong to the once again, another hydrogen environment.

$\ce{C3}$, $\ce{C1}$ , $\ce{C11}$  $\ce{C13}$, $\ce{C12}$ and $\ce{C2}$ all have two hydrogen on the neighboring carbon atoms.
So my question is why aren't they classified as one hydrogen environment? Instead, why are the categorized under two different environments?


texts: Why isn't dry CaCl₂ used to dry HCl gas instead of concentrated sulfuric acid?

texts:
In our chemistry books, it is said that concentrated sulphuric acid is used to dry $\ce{HCl}$ gas.

But, concentrated sulphuric acid is a strong oxidising agent so, why isn't $\ce{HCl}$ gas oxidised to $\ce{H2O}$ and chlorine gas?

Why dry $\ce{CaCl2}$ (Calcium Chloride) isn't used as drying agent?

[Note: $\ce{CaCl2}$ have no reaction with $\ce{HCl}$ as they both have chloride ion in common]


texts: How to determine which salt will precipitate from a solution containing multiple ions?

texts:
I have a solution containing $0.2\:\mathrm{mol}$ of $\ce{Br^-}$ ions and $\ce{SO_4^2-}$ ions each.
Now if I add excess  $\ce{AgNO3}$ in this solution,
what will precipitate?
 $\ce{Ag2SO4}$ or $\ce{AgBr}$ or both?

And if I add just $0.2\:\mathrm{mol}$ of $\ce{AgNO3}$, what will precipitate?

(I don't want to calculate anything. Just wanted to know qualitatively that which compound precipitates.)


texts: Does double replacement reaction only happen to aqueous reactants?

texts:
I was taught that double displacement reactions occur when reactants are aqueous. However, I came across this reaction

$$\ce{ZnO(s) + H2S (g) -> ZnS(s) + H2O (g)}$$

This is the reaction that is used to remove hydrogen sulfide that is naturally found in methane gas. This reaction indeed looks like a double replacement reaction. However, the reactants are not aqueous.

Additionally, this reaction happens at the temperature of $\pu{700 K}$. Does that mean if enough energy is given, double replacement reactions can occur without an aqueous medium? How so?

Source 1, Source 2


texts: Cyclopropane instability to addition reactions

texts:
In a question I saw comparing the reactivity (to addition reactions) of cyclopropane, cyclobutane and cyclopentane, it was said that cyclopropane was most prone to addition reactions.

Ring strain does make it prone to reactions, but how can addition reactions make it any more stable?

In that context, how can you compare the three?


texts: Why is hot concentrated sulfuric acid preferable to cold?

texts:
Why is hot concentrated sulfuric acid sometimes used to react with metals instead of concentrated sulfuric acid which is at room temperature?

I have ascertained that concentrated sulfuric acid has quite strong oxidizing properties.  Still, some metals which are below the hydrogen in electrochemical series do not react with concentrated sulfuric acid which is kept at room temperature.  When the acid is warm/hot, the reaction takes place.

All I want to know is how does temperature affects its oxidizing properties?