texts:
Chemists have revealed that $1 \lambda^{2}, 2 \lambda^{2}$ -disilene $\left(\mathrm{Si}_{2}\right)$ is diamagnetic while disulfur $\left(\mathrm{S}_{2}\right)$ is paramagnetic $(\mathrm{S}=1)$. Draw the MO diagram (valence shell only), determine the bond order for those two molecules and conjecture which element has higher $3 \mathrm{~s}-3 \mathrm{p}$ energy gap.
(Note that $\sigma_{\mathrm{g} 3 \mathrm{pz}}$ is lower-lying than $\pi_{\mathrm{u} 3 \mathrm{p}}$ in $\mathrm{S}_{2} .$ )
It seems that the paramagnetic type is not very necessary - however, I couldn't come up with the correct MO diagram in either case.


texts:
For my school project I was going to measure the rate that salt has on the rusting of iron.

To do this I set up an experiment where I had 15 beakers containing 200 milliliters of distilled water. I poured into the beakers varying moles of salt $\ce{(NaCl)}$. I had $\pu{0mol}$, $\pu{0.25mol}$, $\pu{0.5mol}$, $\pu{0.75mol}$ and $\pu{1mol}$ of salt. So now there are three beakers for every concentration. I then put a iron nail in every beaker, put plastic wrap over them to stop some of the oxygen flow and left it be for 10 days.

What I was surprised to find was that the beakers with no salt in them had more rust than the one ones that had. It was exactly the opposite of what I expected would happen, and I can't find a website that explains how this occurs. Does anyone have an explanation?


texts: Which is more electronegative: chlorine or nitrogen?

texts:
Why nitrogen is considered to be less electronegative than chlorine. Nitrogen should be more electronegative as I was reading some content about this and I read some reasonable arguments:

$\ce{NCl3}$ in $\ce{H2O}$ gives $\ce{NH3}$ and $\ce{HOCl}$, which proves that nitrogen is negatively charged because it attracts the positively charged hydrogen in $\ce{H2O}$ to form $\ce{NH3}$ and chlorine combines with the negatively charged $\ce{HO-}$ radicals.
$\ce{HNO3}$ is stronger than $\ce{HClO3}$, though chlorine and nitrogen have the same oxidation state ($+5$): $\mathrm{p}K_\mathrm{a}(\ce{HNO3}) = -1.4, \mathrm{p}K_\mathrm{a}(\ce{HClO3}) = -1$.

But in spite of that electronegativity value for nitrogen is considered to be $3.04$ while that of chlorine is $3.16$. Why?


texts: Should temperature and pressure conditions for two reactions be same for them to combine for enthalpy calculations?

texts:
I was solving a question in which I had to calculate Enthalpy of formation of $\ce{CS_2(l)}$ using the given Enthalpy of combustion (not in standard state) of $\ce{C(s)}$, $\ce{S(s)}$ and $\ce{CS_2(l)}$.
To calculate the $\Delta H_f$ of $\ce{CS_2(l)}$, we combine the corresponding equation of combustion of these chemicals  in appropriate order to form the equation :
$$\ce{C(s) + 2S(g) -> CS_2(l) }$$
Should the temperature and pressure conditions of the combustion equations be same for me to combine them mathematically?


texts: Do light and heavy water form an azeotrope?

texts:
(Interested in the general principle too, not just for water and its variants, but with particular emphasis on it.)

When you distill a weak ethanol-in-water solution, you get a condensate that's ethanol-enriched, but that only takes you asymptotically up to 95%, because ethanol and water form an azeotrope with that composition. Is there a similar "enrichment limit" one can achieve in enriching water with deuterium, using only distillation at a fixed pressure? (I know one can "break the azeotrope, but I don't want to get into this.) Or could one, given enough stages in a cascade, approach 100% enrichment arbitrarily closely?


texts: Do any substances work like consumers of hair moisturizer believe it to work?

texts:
Yesterday, my girlfriend remarked on how pleased she was with the effects of the hair moisturizer she has been using: "I started using it just a month ago, and look, it's healed all the damage." I complimented her, then said "...but hair is dead, so it couldn't have helped heal it." She replied, "Well it fills in the cracks". I accepted her answer; lots of hard-surface sealers work that way.

However, hair moisturizer seems odd.

Unlike hair moisturizer, the effects of hard-surface sealers typically don't need dozens of reapplications to obtain.
The exceptional sealers that do need several coats, typically do not need to cure before reapplication (although I suspect that some do). However, if a person were to apply coat after coat of hair moisturizer, they'd just get greasy hair.

I suspect that the porousness of hair necessitates the use of a "wetter" solvent than the one used in most hard-surface sealers, which protracts the curing time.

I also wonder whether the porousness of hair protracts the time it takes for the moisturizer to penetrate its fractures, and thus protracts the time the user ought to wait before reapplying: assuming the presence of the solvent along the path of penetration slows the penetration of the moisturizer then, the coats applied immediately after the first coat would penetrate the hair more slowly, and so they would cure closer to its surface, and would thus produce results that differed from the ones my girlfriend was so pleased with.

Are there substances that exhibit the properties that hair moisturizer seems to exhibit. At the molecular level, what explains why these substances exhibit those properties?


texts: What do these labels for molecular electronic states mean?

texts:
What do these symbols mean in excited states?

$${}^2\!A_2,{}^2\!B_1,{}^4\!A''$$

I am confused with these representations, found in the abstract of this paper. I think it is kind of a representation of electronic excited states. The left superscript means spin multiplicity ($2S+1$). What do the other parts of these symbols mean, and how can I write these symbols with other molecules?


texts: Why is osmium the densest known element?

texts: Why is osmium so dense despite there being heavier elements after it in the periodic table?


texts: How are these two organic resonance structures different?

texts:
I've been working through some questions online (self study, not homework) predicting the various forms for molecules. One of the questions involved the following molecule (see image below). It had four structures listed in total, but the two below have me baffled. They appear to be identical if rotated by 180 degrees along the horizontal axis.

Please explain the difference between these two structures.


texts:
Why does ammonium formate has less pH than ammonium acetate . Even though both the salts have the same structure..

I thought that dissociation of acetic acid and formic acid would have a role in this phenomenon, and I thought that acetic acid forms dimer but I don't know if formic acid forms a dimer or not. Do these things have a role in their pH.?


texts: Is there such a thing as a "minimal soap" molecule?

texts:
Wikipedia's Soap gives sodium stearate as an example of soap, and apparently I've been eating it:

  Sodium stearate is the sodium salt of stearic acid. This white solid is the most common soap. It is found in many types of solid deodorants, rubbers, latex paints, and inks. It is also a component of some food additives and food flavorings.

What would be the smallest or simplest molecule that we could reasonably call a soap? Perhaps a functional definition would be that it could perform some of the functions of soap in the same way that soap does.

In Why does bleach feel slippery? and its follow-up Is it known for sure that bases feel slippery because of the production of soap/surfactant? the saponification of other existing molecules is discussed, and I'm not looking for that here.

Source


texts: How does dimethyl sulfoxide transport other molecules through skin?

texts:
Wikipedia says:

Use of DMSO in medicine dates from around 1963, when an Oregon Health & Science University Medical School team, headed by Stanley Jacob, discovered it could penetrate the skin and other membranes without damaging them and could carry other compounds into a biological system.

How does this work? Is there a term for this property? Can DMSO transport molecules through other barriers? What are the limitations on which compounds DMSO can transport? Which other compounds share this property with DMSO?


texts: Can you derive a formula for any internal energy of a gas as long as you know the degree of freedom?

texts:
I have the following formula that I derived from studying my textbook that generalizes to all ideal gases:

Monoatomic molecular gases ($\ce{He, Ne}$ etc.)

Degree of freedom: 3

$\ce \frac{3}{2}nRT = U$

Diatomic molecular gases ($\ce{O_2, N_2}$ etc.)

Degree of freedom: 5

$\ce \frac{5}{2}nRT = U$

Polyatomic molecular gases ($\ce{CH_4, H_2O}$ etc.)

Degree of freedom: 6

$\ce \frac{6}{2}nRT = U$

As you can see here, we observe that a general trend for the formula for the internal energy of a gas is:

$\frac{\text{degree of freedom}}{2}nRT$ = U

Is this correct?


texts:
This is the question i have been asking from months to my friends,teachers,and everyone but i haven't got a satisfactory answer yet(in fact i haven't got any answer).These two terms (vapour and gas) are confusing me from a long time and i can't get the difference.I shall be very thankful if someone of you give me a detailed explaination for the question.I m sorry if this question or a similar question have already been asked on the site and i shall be thankful if you provide me the link of the question so that i can get my answer there.

Finally the question is "What is the difference between vapour and gas".


texts:
I want to functionalize silver nanoparticles with thiol group.
My question is "how can I find that the thiolated compound is attached to the surface of nanoparticles or not?"


texts: The sensitivity of potassium iodide starch paper

texts:
I have some questions about the sensitivity of potassium iodide starch paper.

Patients with asthma caused by allergic airway inflammation have high levels of nitric oxide ($\ce{NO}$) in exhaled breath. This is usually measured with chemiluminescence analyzers by measuring the light generated by a chemical reaction of $\ce{NO}$ with ozone. This technique has high sensitivity, and NO can be accurately measured in the parts per billion (ppb) range.

This above method requires a complicated apparatus.

I am now considering an alternative method.

When NO is exposed to oxygen, it is converted into nitrogen dioxide:

$$
\ce{NO + O2 \rightarrow 2 NO2}
$$

When wet potassium iodide starch paper is exposed to an oxidizing gas, such as $\ce{NO2}$, its color changes to purple or blue. The intensity of the color depends on the concentration of the oxidizer.

My questions are:

If, at room temperature, 1 litre of exhaled air is enclosed in a container, inside of which a wet potassium iodide starch paper is placed, would that paper ever get a blue tint if the NO concentration in the exhaled air is only 25 ppb (parts per billion)?
How long would it take?
Would it help if the volume was bigger, for example 10 litres?
Could one improve the sensitivity in some simple way?


texts: I've heard multiple times that the Nernst Equation could be used to calculate K$_a$. How would one calculate the acidity constant, K$_a$, of a specific acid, using the Nernst Equation? The equilibrium itself is a proton transfer, not an electron one, so how would one use the equation in this case?


texts:
I would like to know how to obtain the following molecule, whose technical name should be something like N,N-dimethylindol-3-ylglyoxylamide (let's call it DMIG for short)

One of the constraints being that I'd like to limit myself to compounds that are relatively easy/cheap (and, of course, legal) to find.

I figured out that indole (A) may be a good starting point. Its very reactive spot on position 3 would make an electrophilic aromatic substitution likely to take place there.

Then, oxalyl dichloride (B) and dimethylamine (C) would be good candidates to construct the "dimethylglyoxylamide" leg.

And... my technical knowledge stops right there. Would it be possible to obtain DMIG from compounds A, B and C by "simply" putting them in solution in an adequate way?
As a layman in experimental chemistry, it seems to me that the most reactive spots in the system are the position 3 of the indole, the chlorine endings of the oxalyl dichloride and the N-H bond in the dimethylamine.
If this premise is correct (which may not be the case), then I have the intuition that not much would be required to lead to the formation of DMIG.

What process would you suggest? What other substances may be necessary? Are there other paths or more practical starting points for this synthesis?

Thanks in advance


texts: Is there a way to oxidize salicyl alcohol to salicylic acid without using chromium trioxide?

texts: I'm doing a project for school and I need to convert salicyl alcohol to salicylic acid, but I'm not allowed to use $\ce{CrO3}$ because of its toxicity. I know it is also possible to oxidize a primary alcohol to a carboxylic acid with potassium permanganate, but I read it might be a too strong oxidizer. Is there any good alternative?


texts: Counting number of acidic-H in a molecule

texts:
In a recent exam, following question was asked:

Number of acidic hydrogen present in X are:

I've found 8 of them as shown:

7 of them (marked with numerals) were correct according to solution, but 8th one (pointing with red arrow) was not. Is it because of the fact that the carbon was bridge-headed or something else?


texts: What is the need for dipole moment if electronegativity already exists?

texts:
Say we have an HCl molecule. The difference in electronegativities of the H and Cl atoms tells us how polar the HCl molecule is. The dipole moment is also a measure of the degree of polarity in molecules.

So why do we need the "dipole moment" concept if we can see how polar a molecule is by looking at the electronegativities of the atoms in the molecule? Is it because in complex molecules it is easier to measure how polar a molecule is, using the dipole moment formula?


texts: Aluminium, Carbon, Aluminium Sulphate battery. What's the reaction?

texts:
I made galvanic cells from the following items (while trying to do something else), and they give between 0.6 V and 1 V per cell.

Aluminium foil – negative terminal

Carbon (these work: charcoal sticks, graphite rods, carbon felt) – positive terminal.

Electrolyte – aluminium sulphate $\ce{Al2(SO4)3}$ in water.

With 9 cells – 3 series * 3 parallel – it lights a red LED.
Left on overnight it gets very dim, but given some recovery time, it comes back bright again.
So the current isn't high, but I wasn't expecting any.

I'm not observing any gas being evolved, or any change in the foil (yet).
The battery has been running about a week.

I know the Al sulphate reacts with water to make sulphuric acid + Al hydroxide.
Is that what's happening here?
What happens next in the reaction?
What's the final result?

Thanks for your help.
It's a long time since school chemistry lessons.


texts: Confusion about the graph plotted from the Arrhenius equation

texts:
According to Arrhenius equation $k = A\mathrm e^{(E/RT)}$, where $k$ is the rate constant, $E$ is the activation energy, $R$ is the universal gas constant and $T$ is the temperature.

Taking log both sides,
$$\log k = \log A - \frac{E}{2.303RT}$$
Why is the graph plotted between $\log k$ and $1/T$ linear? We know $E =$ threshold energy—average energy of the molecules. Now average energy is given by $\sqrt{ (8RT/\pi M)}$, it is itself a function of temperature. So the slope is variable and hence should have been some other curve.


texts: How does hybridisation affect an otherwise chiral centre?

texts:
In basic theory, a carbon atom with four nonidentical substituents attached, makes a chiral centre. Thus any molecule is chiral as long as it has a chiral centre (except meso compounds). I thought identifying a chiral centre was straight forward until I saw the following video.

Is Carbon (with the ability to bond 4 covalent bonds) the only atom qualified as a chiral centre (stereogenic centre)? Wikipedia link states, other atoms like Nitrogen or Sulfur could also be a chiral centre.

The above video shows that other atoms too can be chiral as well... However a comment in the same video, replies that a hybridised Nitrogen atom is not qualified to be a chiral centre. Original comment : That Nitrogen is sp2 hybridized, the lone pair of electron are in a unhybridized p-orbital; it would not be considered a chiral center.

With reference to this question 1-, it has number of comments, but not quite the answer I am after. On the other hand this question 2- has more emphasis on the lone pair for chirality - an atom with lone pairs can't be a chiral centre.

So given these, why can't a hybridised atom be a chiral centre?


texts: Identifying unknown solution with indicators. why is one pKa value ignored and how to treat negatives values?

texts:
Three test tubes contain an identical solution of unknown pH.

  The first one is tested with thymolphthalein and turns colourless
  The second is tested with a-naphtholphthalein and turns blue

  What colour would thmyol blue appear in the third tube?

  Note: If the ratio of one form to the other form (e.g. acid to base form or vice versa) is greater than $10:1$, the colour observed will be that of the predominant form. However, if between $10$ and $0.1$, the colour will be a mixture.

  \begin{array}{lccc}
\text{Indicator} &
\mathrm{p}K_\mathrm{a} &
\text{Colour of acid form} &
\text{Colour of base form} \\
\hline
\text{$\alpha$-naphtholphthalein} & 8   & \text{yellow}     & \text{blue}   \\
\text{thymol blue}                & 2   & \text{red}        & \text{yellow} \\
                                  & 8.8 & \text{yellow}     & \text{blue}   \\
\text{thymolphthalein}            & 10  & \text{colourless} & \text{blue}   \\
\hline
\end{array}

Steps to solve this question:

Find pH of solution via Henderson-Hasselbalch equation:
\begin{align}
  \mathrm{p}K_\mathrm{a}
  &= \ce{pH} - \log_{10} \frac{[\ce{In-}]}{[\ce{HIn}]}
\end{align}
For α-naphtholphthalein, as it appears blue, its basic form dominates and so
\begin{align}
\frac{[\ce{In-}]}{[\ce{HIn}]} &> 10:1 \\
  \mathrm{p}K_\mathrm{a}
  &= 8 =  \ce{pH} - \log_{10} (10)
   =  \ce{pH} - 1\\
\ce{pH} &= 9
\end{align}
For thymol blue
\begin{align}
  \mathrm{p}K_\mathrm{a}
  &= \ce{pH} - \log_{10} \frac{[\ce{In-}]}{[\ce{HIn}]}\\
  8.8
  &= 9 - \log_{10} \frac{[\ce{In-}]}{[\ce{HIn}]}\\
  \log_{10} \frac{[\ce{In-}]}{[\ce{HIn}]}
  &= -0.2
\end{align}

Where I get stuck:

How do I handle the negative sign in negative 0.2?
If it was positive 0.2, this would tell me that the ratio of $\log_{10} ([\ce{In-}]/[\ce{HIn}])$ is between $10$ and $0.1$, hence a mix between the acid colour and basic colour would result, giving a green solution. But I don't know how to treat the negative.
In my solution manual they ignore the $\mathrm{p}K_\mathrm{a}=2.0$ value of the thymol blue and only use the $\mathrm{p}K_\mathrm{a}=8.8$ value. Why is this the case?


texts: Crystal Field Splitting Energy and Metal Energy Level

texts:
Second and third row metals are stated to often have higher crystal field splitting energies than first row metals. The argument is usually made that the more diffuse 4d and 5d orbitals are capable of better overlap and decreased pairing energy. However, two concepts do not make sense to me:

Why do more diffuse orbitals lead to better sigma overlap? In organic chemistry it is often taught that size mismatch between orbitals contributes to poorer overlap, not better.

A 4d orbital will be higher in energy than the 3d orbital in the same group. From an MO theory perspective, I would expect this to mean that the energy difference between the ligand group orbitals and metal d orbitals increases and results in less splitting.


texts: Meaning of polarization pulse in microwave (rotational) spectroscopy

texts:
In the recent rotational spectroscopy literature, "microwave polarization pulse" is often used in conjuction with pulsed Fourier transform microwave spectroscopy (Google Scholar).

Sometimes the pulse angle is also mentioned such as $π/2$. I gather this term is similar to FT-NMR where the net magnetization vector is tipped at a certain angle. When we talk about microwave rotational spectroscopy, what is being polarized?

In other words, why do we call the microwave pulse as a polarizing pulse? I wanted to confirm that this is related to the net electric dipole moment vector of the molecules which is being oriented after excitation?


texts:
I know that relative atomic mass of $\ce{^{12}C}$ is $12~\mathrm{u}$.

Therefore mass of $1~\mathrm{mol}~\ce{C} = 12~\mathrm{g}$
\begin{align}
 \text{mass of }6.022\cdot 10^{23} \text{ C atoms} &= 12~\mathrm{g}\\
 \text{mass of }1 \text{ C atom} &= \frac{12~\mathrm{g}}{6.022\cdot10^{23}}\\
&=\boxed{1.99\cdot10^{-23}~\mathrm{g}},\\
\end{align}

but

\begin{align}
 1~\mathrm{u} &= 1.66\cdot10^{-24}~\mathrm{g}\\
\implies \text{Mass of }1~\ce{^{12}C}\text{ atom} &= 1.66\cdot 12 \cdot 10^{-24}~\mathrm{g}\\
&= 19.92\cdot 10^{-24}~\mathrm{g}\\
&= 1.992\cdot 10^{-23}~\mathrm{g}.\\
\end{align}

Which is correct?

Also what is dimension formula of relative atomic mass, molar mass?

Why is unit of molar mass $\dfrac{\text{gram}}{\text{mole}}$ and not just $\text{gram}$ Since when has this $\text{mol}$ become a unit? It's just a number.


texts: Question on symmetry-adapted, possibly antibonding combinations of core orbitals

texts:
In this question, it is said that the core electrons do mix and form delocalised, symmetry-adapted orbitals.
The boron trifluoride molecule is often said to have no anti-bonding orbitals filled, with its 24 valence electrons exactly occupying its 12 bonding/nonbonding orbitals. This is certainly true when only the valence electrons are considered. However, when one considers the 8 core electrons of BF3, at least one of the 4 symmetry-adapted combinations of the 1s electrons must be (weakly but still) antibonding. Since these 4 orbitals are fully filled, this means that BF3 does have antibonding orbital(s) filled, unless the "1s antibonding orbitals" mix with small proportions of the 2s-2p bonding orbitals (small amounts of which shall do since the 1s antibonding orbitals are much less antibonding than the 2s-2p orbitals bonding). By this logic, any molecules containing atoms other than hydrogen and helium, strictly speaking, must have some of their antibonding orbitals filled.
My question is the following- is my logic correct with there being no molecules without antibonding orbitals filled, or do there exist molecules such that the antibonding nature of such combinations of core electrons are quenched by (small amounts of) the much stronger bonding nature of bonding combinations of valence orbitals, resulting in the delocalised core orbitals being bonding in character?
P.S. All orbitals are assumed to be obtained by ab initio methods, and the bonding/nonbonding/antibonding natures are determined "even up to errors'. By "even up to errors" I mean like this: Suppose that (simply speaking) there exists a function f such that, for a given orbital A, A is mathematically known to be bonding if f(A)<=1. Suppose also that it is known that abs(f(A)-f(B)) <= abs(A-B).  (Such properties are already known for upper bounds for MSE's regarding truncated Fourier series; the basis set used for the calculation of A are of Fourier-type) If a truncated sum of the basis set used for the calculation of A (call it a) satisfies abs(A-a) <= 0.05 and abs(f(a)-0.9) <= 0.05,  then A is bonding "even up to errors".


texts:
Something I know that leads to this question:

  Water dissolved in ethanol.

It might sounds weird to say water as a solute. Textbooks always says that solvent is the one present in larger quantity. This leads to a contradiction with the saying that water is an universal solvent.

There can be water present in smaller quantity than ethanol in a water-ethanol solution. But which is the solute and which is the solvent?

How to identify the solute and the solvent in a solution besides locating the word "aqueous"?


texts:
I have difficulty understanding the first sentence of the Introduction in the paper linked below. Can someone explain to me what is spectroscopic transition frequency and thermal bath?

  The question addressed here is how the modulation of the spectroscopic transition frequency Ω(t) by fluctuations of the thermal bath is related to the observed spectral line shape.

http://pubs.acs.org/doi/abs/10.1021/jp5081059


texts: Why is ethoxyethane the preferred IUPAC name for diethyl ether rather than 1,1'-oxydiethane?

texts:
Diethyl ether has a few systematic names. Its preferred IUPAC name is generated using substitutive nomenclature: ethoxyethane. But multiplicative nomenclature could be used, in the symmetric spirit of its common name, to generate the name 1,1'-oxydiethane. The Nomenclature of Organic Chemistry 2013 (blue book) makes it clear that multiplicative nomenclature is preferred to substitutive. So why is the preferred name substitutive?

The book says these about multiplicative nomenclature:

P-51.1.5: “Multiplicative nomenclature (P-15.3, P-51.3), as a subset of substitutive nomenclature, is preferred to simple substitutive nomenclature when the criteria for its use are met…”
P-51.3: “Substitutive nomenclature is used when the conditions for constructing multiplicative names are not met.”
P-51.3.1: “Multiplicative nomenclature is preferred to substitutive nomenclature for generating preferred IUPAC names to express multiple occurrences of identical parent structures other than alkanes when
“(1) the linking bonds (single or multiple) between the central substituent group of the multiplicative group and all subsequent structural units are identical and
“(2) the multiplicative groups, other than the central multiplicative group, are symmetrically substituted; and
“(3) the locants of all substituent groups on the identical parent structures, including suffix groups, are identical.”


texts: how to display diffusion to a young audience?

texts:
I need to display some science topic pertaining to the atomic bombs, or atomic history in some way to children of approximately middle school level. So I've decided that something interesting to cover would be gas diffusion (as used to isolate U-235 for the atomic bombs). I tried to see if there were any non-toxic, easy to obtain colored gases, but I couldn't find any. So the next thing I thought of is liquids.

Now I'm wondering if I can do something similar with liquids but I'm not sure how liquids would behave. Could I set up an effusion device, fill it with water and red food dye on one side, and water with blue food dye on the other and open a hole between the two and have them slowly diffuse? Will the diffusion of these two side be related to the molar mass or concentration of the dyes? Or would it follow some other law?


texts: What substance is used for staining brass?

texts:
While working at CNC engraving, I had at my disposal a small bottle of liquid used to stain brass for creating signs etc - engrave a writing, stain the engraving, then grind/polish the flat topmost layer to remove the colored layer and leave it only in engraved depressions.

The bottle didn't reveal much about composition of the liquid, beyond some warnings about toxicity. It was a brass staining liquid, period.

The coloration it created was dark brown, that seemed black by comparison with the surrounding metal. The reaction took only a few seconds until full pitch of coloration was achieved and the liquid itself was transparent with very mild cyan-blue hue. The coloration was quite persistent; even roughly 10 years afterwards it's still good as new on the pieces I kept and required rather deep brushing to remove from the topmost surfaces.

Can you tell me what substance it was?

(below a sample with dark parts achieved through that liquid)

Edit: I found a very similar liquid on sale, but the page is equally devoid of composition details. The instructions say: [the liquid] is to be used in room temperature. It allows the finish in tones between black and light brown. The time of reaction is almost immediate. The color and speed can be controlled through dilution in water up to 50%.


texts: Why is the inversion barrier larger in PH3 than it is in NH3?

texts: The inversion barrier in $\ce{NH3}$ is approximately $5~\mathrm{kcal~mol^{-1}}$ and that of $\ce{PH3}$ is $35~\mathrm{kcal~mol^{-1}}$. This has well-known stereochemical consequences in that amines are not chiral whereas phosphines can be. How can the larger inversion barrier be explained?


texts: Magnetic properties of potassium manganate(VII)

texts:
According to me, $\ce{MnO4^2-}$ is paramagnetic and $\ce{MnO4^-}$ is diamagnetic.
On the basis of this, the corresponding potassium salts inherit these magnetic properties, i.e. $\ce{K2MnO4}$ is paramagnetic and $\ce{KMnO4}$ is diamagnetic.
However, according to my class teacher $\ce{KMnO4}$ is paramagnetic.
Is potassium manganate(VII) dia- or paramagnetic?


texts: Why is MP2 failing to calculate proper IR frequencies for [Co(CO)4]- and [Fe(CO)4]2-?

texts:
I was doing some IR calculations on different 3d transition metal carbonyl complexes during some practical courses where we were introduced to effective core potentials. While doing this we found that MP2 has some problem with the calculation of at least the asymmetrical $\nu_\text{CO}$ band (that was the only one we were interested in).

We made the calculations for $\ce{[Ti(CO)6]^2-}$, $\ce{[V(CO)6]-}$, $\ce{[Cr(CO)6]}$, $\ce{[Mn(CO)6]+}$ in octahedral symmetry and $\ce{[Fe(CO)4]^2-}$, $\ce{[Co(CO)4]-}$ and $\ce{[Ni(CO)4]}$ in tetrahedral symmetry. The method was MP2, as stated in the title, and the basis set was 6-31G(d). The program we used was Gaussian$~$09 Rev. A.02 but that was not the problem, as I did calculations with other programs with similar results. All optimized structures are considered to be true minima as there either is no imaginary frequency or it is calculated to be $\ge -50~\mathrm{cm^{-1}}$ with was stated to be a problem of the insufficient DFT grid but not further questioned.

The following graphic shows that most of the calculated values are acceptable and near their experimental values but two of them, namely $\ce{[Co(CO)4]-}$ and $\ce{[Fe(CO)4]^2-}$ differ significantly from the experimental values by nearly $300\ldots1000~\mathrm{cm^{-1}}$.

$\hskip1.4in$

After this I varied some parameters of the calculation that could influence this deviation as was:

additional diffuse functions for the better description of ions
tight optimization criteria (T) as this might reduce the imaginary frequency
no frozen core (F) just to try it
solvents: PCM(DCM), PCM(Heptane) as experimental values aren't taken in gas phase
I also optfreq'ed with B3LYP/6-31G(d)/MDF10 (B) to see if it's the method itself

The results can be seen in the following table:
$$\begin{array}{cccccccc}
\hline
\text{Basis~Set} & \mathrm{Solv.} & \mathrm{d(MC)} & \mathrm{d(CO)} & \nu_\text{CO}(calc.) & \mathrm{Int.} & \nu_\text{CO}(exp.) & \Delta\nu_\text{CO}\\
 &  & \mathrm{Ang.} & \mathrm{Ang.} & \mathrm{cm^{-1}} & \mathrm{km\, mol^{-1}} & \mathrm{cm^{-1}} & \mathrm{cm^{-1}}\\
\hline
\mathrm{E}/6{-}31\mathrm{G}^\ast & & 1.802 & 1.184 & 2830 & 2.0\cdot10^5 & 1890 & 940\\
\mathrm{EFT}/6{-}31\mathrm{+G}^\ast & & 1.799& 1.187& 2966& 2.7\cdot10^5 & 1890 & 1076\\
\mathrm{E}/6{-}31\mathrm{+G}^\ast & & 1.800 & 1.187 & 2996 & 2.9\cdot10^5 & 1890 & 1106\\
\mathrm{E}/6{-}31\mathrm{+G}^\ast & \mathrm{DCM} & 1.795 & 1.186 & 4671 & 0.0 & 1890 & 2781\\
\mathrm{E}/6{-}31\mathrm{G}^\ast & \mathrm{Hept.} & 1.799 & 1.184 & 3203 & 4.3\cdot10^5 & 1890 & 1223\\
\hline
\mathrm{BE}/6{-}31\mathrm{G}^\ast & & 1.767 & 1.169 & 1978 & 1322 & 1890 & 88\\
\hline
\end{array}$$

What can be seen:

Within MP2 there is no significant effect on $\ce{M-C}$- or $\ce{C=O}$-bond lengths.
The diffuse functions shift the frequency to higher wave numbers and
the impact of the solvent is big to huge. As without the solvents the
deviation was calculated to be somewhere around
$+1000~\mathrm{cm^{-1}}$ it is now at $+2800~\mathrm{cm^{-1}}$!
Also the intensities are horribly wrong ... they are somewhere around $2$
to $4\cdot10^5~\mathrm{km\, mol^{-1}}$ instead of somewhere around
1000 or in the special case of DCM they are completely zero.
B3LYP predicts everything within common error ranges

What are your ideas why MP2 fails with this special task?


texts: Why is density of chloroform greater than water?

texts:
Hydrocarbons (i.e., molecules containing carbon and hydrogen only) are generally less dense than water.  Yet chloroform, which is a halogenated hydrocarbon, is more dense.
Why is this?  I know water is  more dense than hydrocarbons because its polar nature would cause it to pack more tightly.  But ,why  chloroform, which is less polar than water, has a higher density than water.
It can't be molecular weight, because larger hydrocarbons like hexane and octane have a higher molecular weight than water, yet water is denser.
So is there any theory or concept which will help me find why chloroform is denser than water?


texts: How to (numerically) model a phosphoric acid titration curve

texts:
I've been learning how to simulate a 1M phosphoric acid titration curve using numerical methods in R.
So far has this has been the best curve:

Notice how it flattens out (artificially) towards the left.
I am not certain if this is a programming and / or a "chemistry" issue.

The system is defined by charge balance, mass balance, and equilibrium equations:
$$[\ce{H3A}] + [\ce{H2A-}] + [\ce{HA^{2-}}] + [\ce{A^{3-}}] = P_{CA}$$
$$[\ce{H+}] + [\ce{Na+}] = [\ce{H2A-}] + 2[\ce{HA^{2-}}] + 3[\ce{A^{3-}}] + Kw/[\ce{H+}]$$
$$K_{a, 1} = [\ce{H2A-}] [\ce{H+}] / [\ce{H3A}]$$
$$K_{a, 2} = [\ce{HA^{2-}}] [\ce{H+}] / [\ce{H2A^-}]$$
$$K_{a, 3} = [\ce{A^{3-}}] [\ce{H+}] / [\ce{HA^{2-}}]$$
I've posted a very similar question at SO and shared code for the simulation over there, using R's nleqslv::nleqslv (go have a look if you'd like to).
I thought this is also a good place for this issue. For instance, this answer (and the ones it links to) do seem to be useful, but I'm not sure how to solve that equation for $[\ce{H3O+}]$ (called $x$ over there).
I would like to know which is the best way to simulate a titration curve.
And also: are the equations I used correct? do you know what am I missing?
Thanks!


texts: Why do group 18 elements exist as gases, why are they not found in any other physical state ?


texts:
Let's say we have:

  $$
\begin{align}
\ce{A &-> B}&\quad&\text{(fast equilibrium)}\label{rxn:1}\tag{1}\\
\ce{2 B + C &-> D}&\quad&\text{(slow)}\label{rxn:2}\tag{2}\\
\ce{D + E &-> F}&\quad&\text{(fast)}\label{rxn:3}\tag{3}
\end{align}
$$

  Find the rate expression for the formation of $\ce{F}$.

Since I am writing the rate law for $\ce{F}$, should I write it as

$$\text{rate} = k_3[\ce{D}][\ce{E}]$$

because that's the reaction step that actually includes $\ce{F}$ as the product, or do I always have to write is in terms of the slow step i.e.

$$\text{rate} = k_2[\ce{B}]^2[\ce{C}]?$$

What happens with the leftover $[\ce{B}]$ and $[\ce{A}]$ in the steps \eqref{rxn:2} and \eqref{rxn:1}, respectively — do I include those concentrations as well?


texts: Nitrogen inversion barriers of trimethylamine and N,N-diisopropylmethylamine

texts:
Which would have a smaller nitrogen inversion barrier: $\ce{NMe3}$ or $\ce{N(i-Pr)2Me}?$

I think that $\ce{NMe3}$ should have a smaller inversion barrier as it is less bulky, but data shows otherwise. Are there some other effects that contribute to the inversion barrier that I might not know of?


texts: How to determine the edge length of the aluminium unit cell?

texts:
I'm having trouble understanding why I can't get the correct answer from this homework problem:

  Solid aluminum forms a face-centered cubic unit cell.  Aluminum has a density of $\pu{2.70 g/cm^3}$. Determine the edge length of the $\ce{Al(s)}$ unit cell in $\pu{cm}$.

Usually if I enter the wrong answer the it will show all the calculations to determine the correct answer. However this one does not show the calculations.

Here is the work I've done:

$\ce{Al }= \pu{26.98 g/mol}$
$\text{Mass} = \frac{26.98}{6.022\times10^{23}} = \pu{4.480E-23 g//atom}$
$\text{Mass of one atom} = \text{mass of one unit cell}$
$\text{Mass of one unit cell} = \pu{4.480E-23 g//unit cell}$
$D = \frac{M}{V}$, thus $V = \frac{M}{D}$
$V = \frac{\pu{4.480E-23}}{2.70} = \pu{1.66E-23 cm^3//unit cell}$
For a cube $V = l^3$, thus $l = V^{1/3}$
$\text{Unit cell edge length} = V^{1/3} = {\pu{1.66E-23 cm^3}}^{1/3} = \pu{1.18E-8 cm}$

The correct answer that the book gives is $\pu{4.049E-8 cm}$.

The only example I have to go off of in my book is for a simple cubic unit cell. Since $\ce{Al}$ is a face-centered cubic unit cell and has 4 particles per unit cell I tried multiplying my final answer by $4$, but that gives me $4.72$. I also tried multiplying the unit cell mass by $4$ which gave me a final answer of $1.87$. I just can't seem to get $4.049$. Any help understanding this would be greatly appreciated.


texts: Where exactly do the orbital angular momentum get their numbers e.g. +1/2

texts:
I was thinking about orbital angular momentum today and  wondering how exactly do the numbers come about that quantize them. I was doing a little research on how they come about and I  came across this image many times.
How exactly does a chemist/physicist measure this to get the +1/2,-1/2 number. Are there other values that are possible?


texts: Conditions for the reduction of carboxylic acids by LiAlH4

texts: From my textbook, the reduction of carboxylic acids by LiAlH4 "has to be in anhydrous conditions, such as dry ether, followed by aqueous acid." I read from the internet that the reduction reaction has to be in anhydrous conditions since LiAlH4 reacts violently with H2O. But why does the reduction reaction need to be 'followed by aqueous acid'? Isn't that contradictory to the fact that LiAlH4 needs to be in anhydrous conditions?


texts:
I am no chemist, nor did I pick up much understanding of chemical reactions in school. But I would like a basic understanding of how "reactive" and "potent" sulfuric acid is on rock; i.e., whether or not, and if so, how fast it would dissolve or otherwise affect the rock. Now, I know there are various types of rocks, and I'm sure this question could be too broad if not narrowed to some extent. So let me give some specifics.

My questions

Assuming a highly concentrated sulfuric acid (98%; but weaker, if perchance that would be more potent against the particular rock):

Will the sulfuric acid affect (dissolve or otherwise) it at all (and the ideal concentration to do so)?
If it affects it, then:

how fast would it dissolve/otherwise a solid piece of rock (not powder), say 1 cubic inch (though I'm looking for rate answers, so whatever the evidence gives as a rate works)?
Is rate affected by pressure (i.e., the rock "sitting" in the acid versus a pressurized spray of the acid on it)?
How much faster(?) would it dissolve it if the rock was powdered?
What are the general products/results left after the effect?

Igneous Rocks

Basalt
Gabbros, which apparently has a large amount of pyroxene and plagioclase
Granite

Sedimentary Rocks

Limestone
Dolomite

Metamorphic Rocks

(Perhaps the chemically diverse make-up of these rocks makes answering not feasible.)

Marble (perhaps reacts similar to limestone, "Geologists use the term 'marble' to refer to metamorphosed limestone"?)
Slate

While I have no problems with you giving in your answer the chemical reactions involved, I desire at least a "laymen's" summary of what occurs to each.

(Also, feel free to re-tag if there are some viable tags I was not aware of.)


texts: Explaining The Different Order of Stability for singlet and triplet carbenes

texts:
Consider the following singlet carbenes:

$\ce{CH2}$ , $\ce{CF2}$, $\ce{CCl2}$

The order of stability expected considering back bonding is;

$\ce{CH2}$ < $\ce{CCl2}$ < $\ce{CF2}$

However the correct order is:

$\ce{CCl2}$ < $\ce{CH2}$ < $\ce{CF2}$

Can someone explain why dichlorocarbene(singlet) should be less stable than $\ce{CH2}$ even when back-bonding is present in $\ce{CCl2}$ (though it may not be strong).

Also, if we consider the stability order for triplet carbenes, it turns out that the order is just reversed. I assume that back-bonding doesn't work here due to non availability of empty p orbitals. But, if this is so, then what  factor(s) determines their stability?

Edit: There seems to be a confusion with the word stability. I would rather put it as in which species is carbon's electron hunger least/most satisfied(i.e. which are least and most electrophilic)


texts: Does purified water corrode copper pipes?

texts: In other words would a reverse osmosis system corrode copper pipes due to it's purification?  Does purified water speed up copper pipe corrosion leading to pin holes, etc.?


texts: How to remember/write molecular formulas?

texts:
For example, when given the reactants and asked to write a complete formula including their products for nitrogen and oxygen...:

$\ce{N2 + O2 -> 2NO}$ (this is the correct one right)

but what naturally comes to mind is that I know what will be formed in this case as in:
$\ce{N2 + O2 -> NO}$ ( how am I suppose to know that there is 1 "O"s or that there is only  1 N!!)

Ok example two!!
The desolation of nitrogen dioxide in water(acid rain and stuff):
$\ce{NO2 + H2O -> H+ + NO3- + HNO2}$ ( correct version)

alright right here, I know that an acidic oxide + water gets you oxyacid the $\ce{HNO2}$right. But how in the world was I suppose to know $\ce{H+}$ and $\ce{NO3-}$ would be there??

So basically, is there like no way to find what the products will be without doubt with only knowing some basic rules(such as the products of an acidic oxide and water and others) or with electron configuration in example one.
Or is the only way, just to remember the whole formula.


texts: Is it possible to make micelles to pick up Microplastics from water?

texts:
I'd like to know if I could get micelles to pick up microplastics in water. I read that microplastics are sometimes charged, so can we make the lyophobic end to pick up microplastics, so that they can then be collected on the water surface and be easily disposed?
This is the idea I'm planning to pitch for a science fair, is this actually feasible?
I read that detergent micelles work well even in hard water, so can we use such detergent micelles to pick up microplastics?

Thanks!


texts: Halogenation of alcohols in the presence of ZnCl2

texts: I know that $\ce{OH-}$ is usually a bad leaving group, but why does the following reaction occur via SN1 in presence of anhydrous $\ce{ZnCl2}$?


texts:
I have a .car file that contains dimensions (periodic boundary conditions) for the unit-cell of a hexagonal crystal material I'm working with:

PBC   27.1979   27.1979   15.4999   90.0000   90.0000  120.0000 (P1)

That's the a, b, c lengths and $\alpha$, $\beta$, $\gamma$ angles.

I need to convert this information into basis vectors in cartesian space, e.g.

basis1 27.1979 ?       0.0
 basis2 0.0     27.1979 0.0
 basis3 0.0     0.0     15.4999

This may be better suited as a math question but it's computational-chemistry specific.


texts: Reaction in Zinc-Carbon-Ammonium Chloride battery

texts:
I made a dry cell battery from zinc (Zn), carbon (C) and ammonium chloride (NH4Cl) which produced a current of 0.4 amps and voltage of 1.1V. However when I could not find the redox reaction that was occurring.

What is the chemical reaction happening in the cell?


texts: When using a methane sensor a voltage is applied and much like electrolysis if the voltage is above the decomposition potential a reaction happens. Flammable gasses like methane are easily oxidized and thus produce an anodic current. But what is the cathodic current reaction in a methane sensor in air? what is being reduced?


texts: Free energy of solvation and Henry's law constant

texts:
I am trying to calculate the free energy of solvation of $\ce{CO2}$ from its Henry's law constant. As given on Wikipedia, the dimensionless Henry's law constant is $0.83$. If I try to calculate $\Delta G$ from this, I got

$$\begin{align}
\Delta G &= -RT\ln K \\
  &= -\pu{8.3145 J mol-1 K-1}\times\pu{298.15 K}\times\ln 0.83 \\
  &= \pu{0.46 kJ mol-1} \\
  &= \pu{0.11 kcal mol-1}.
\end{align}$$

However, I saw an article saying that the experimental value is $\pu{0.24 kcal mol-1}$. The article cited from the CRC Handbook of Chemistry and Physics, while Wikipedia cited from this compilation, which I think is also a reliable source.

So what did I do wrong in my calculation of $\Delta G$ from the Henry's law constant?


texts:
For many years of drinking water has been cooled in hot climates by evaporating it from the surfaces of canvas bags or porous clay pots. How many grams of water can be cooled from $\pu{35 ^\circ C}$ to $\pu{20 ^\circ C}$ by the evaporation of $\pu{60 g}$ of water?
Heat of vaporisation of water in this temperature range is $\pu{2.4 kJ g-1}$. Specific heat of water is $\pu{4.18 J g-1 K-1}$.

I'm pretty confuse by what the question is asking for. This is my attempt for the evaporation of $\pu{60 g}$ of water:
$$q = \pu{60 g} \cdot \pu{2.4 kJ g-1} = \pu{144 J}$$
I then subbed this energy unit ($\pu{144 J}$) to the heat change formula to find the mass of water. Why am I wrong?


texts: Bonding between rings and iron atom in ferrocene

texts:
How are the 10 vertical bonds in Ferrocene (sandwich structure) connected, by what type of bonds?

What is the real structure of ferrocene? Concerning the 10 vertical extra long bonds?


texts: Why do α-amino acids have a C-H bond at the α-carbon?

texts:
I've just started studying biochemistry and I read that a general $\alpha$-amino acid looks like (ignore the ionisation for now):

My question is: why isn't the general $\alpha$-amino acid formula like $\ce{CRR'NH_2COOH}$ instead of $\ce{CHRNH_2COOH}$? Coming from a physics background, the latter feels more "natural" as it is more general.
Some possible reasons I've thought of (and disqualified):

Maybe the $\ce{C-H}$ bond dissociation energy is too high: I looked at a paper [1] but the bond energies seem to be not too high (relative to say $\ce{C-C}$ bonds.
Steric factors: I don't think this applies as having a small group, like say $\ce{CH_3}$, won't create a lot more steric repulsion relative to $\ce{H}$.

If the answer is along the lines of "it is defined this way because we actually see repeating units of these structures in proteins, so we naturally define the smallest subunit accordingly", then provide chemical grounds (if possible) to justify the fact that structures like $\ce{CRR'NH_2COOH}$ are not prevalent in proteins.
[1]: Moore, B. N., & Julian, R. R. (2012). Dissociation energies of X–H bonds in amino acids. Physical Chemistry Chemical Physics, 14(9), 3148-3154.


texts: Why does the Oxidizing agent have to be higher than Reducing agent for a redox reaction to spontaneously occur?

texts: On the Standard Reduction Potentials of Half-Cells table, why does the Oxidizing agent have to be higher than Reducing agent for a redox reaction to spontaneously occur?


texts: How to measure resistance of a gel electrolyte using a multimeter

texts:
How can I measure the resistance of a gel electrolyte using a multimeter? I know the formula to measure the conductivity of a gel electrolyte is k = (1/R) * (d/a)

where k is the conductivity (S/cm), R is the resistance (of the electrolyte), d is the distance between the two electrodes, and a is the effective area of the electrodes.

I wanted to measure the conductivity of the gel electrolyte with just a multimeter. Since this is a gel electrolyte, I was thinking to substitute the thickness of the gel electrolyte as d and substitute the area of the gel electrolyte as a. (I know the area (a) has to be that of the electrodes, but I want to measure the conductivity of the gel electrolyte without the electrodes). So now all that remains is the resistance of the gel electrolyte. To do this can I just measure its resistance using a multimeter?

(I understand that you have to use two similar electrodes sandwiched between the electrolyte in order to measure the conductivity of it, but is there a way around?)

Thank you.


texts: Balancing complex haloform redox reaction

texts:
I just completed a haloform reaction experiment, using acetophenone and sodium hypochlorite to form benzoic acid and chloroform.

My lab report has a question regarding balancing the equation of the reaction.  I have been working on it for quite a while, and I can't figure out how to do it.  I've tried looking up methods but too many atoms are reliant on too many molecules!  Can someone help with this question and explain how to do it so I can really understand this process?

I need to be able to identify the limiting reactant as well, which relies on the molar ratio of the reactant to the product, so I really need to know how to do this.


texts:
I've heard of artificial coin toning, but haven't been able to find a recipe for creating a blue (or blue-ish) nickel coin.

While not a metallurgist, I work with one. She tried nitric acid, which looked more like a coating and it rinsed off -- hoping for a permanent color change.

I've read that nickel is not a reactive metal, so not sure if this is possible.


texts: What is the carbon content, by weight, of vegetable oil?

texts:
I have only a high school understanding of chemistry, so please bear with me and my ham-fisted question.  I’m trying to understand the carbon content in vegetable oil.  I get that various oils have differing densities, so the measure needs to be “by weight”.  Molecular weight doesn’t help, I need the measure in useful measures like “grams per liter” (preferred).
(Also of note, I’m not certain I got the right tags)
UPDATE: Based on feedback, I looked up oil production per hectare to determine an oil type.  It appears that the highest production per hectare (which feeds into the analysis I'm working on) for grain-based oils is rapeseed.  For tree-based fruits, it's oil palm, and then there's algae oil.
I'm trying to establish how much carbon is embodied in the oil production of one acre of crop (a bit of information that probably would have been helpful to say first).


texts:
In character tables, I know that A and B are one-dimensional irreducible representations, but what is the difference them?

And why do some character tables list them as A1/A2, B1/B2 and others have Au/Ag, Bu/Bg?


texts: Rate law of the reaction of propane with oxygen

texts:
In class, I have a demonstration where I light a bubble filled with propane. As I add oxygen, the bubbles combust faster and more quickly. I have already balanced out the chemical reaction like so:

$$\ce{C3H8 + 5 O2 → 3 CO2 + 4 H2O + heat + light}$$

I have reasoned that the reaction must go faster because the limiting reagent is oxygen, and since the air is only about 20% oxygen adding more oxygen to the bubble will speed the reaction process. I have figured out the kinetics, the oxidation, the enthalpy diagram, etc.

However, the only thing I don't know how to do in this demonstration is how to find the rate law. How would I find the rate law and equation of a combustion reaction? Wouldn't it just be second order since it's a combustion reaction? I have no idea where to even begin or why it is so.


texts:
I have an eluent from an ion-exchange column containing Cobalt (II) ions and Chloride ions. In order for the cobalt catalyst to be recycled to the main process, it must be in its acetate form.
Is there a route from cobalt chloride to acetate that is feasible at an industrial scale?

Thanks


texts: What's the reason that alkanolamines change their color at storage?

texts:
What's the reason that alkanolamines (e.g. monoethanolamine, diethanolamine, triethanolamine) of technical purity change their color (from colorless over yellowish to red-brown) at storage?
Is it because of oxidation, or UV-light?


texts: Column order, signs of MO coefficients, and density matrix construction in Hartree-Fock

texts:
I'm attempting to make a Hartree-Fock solver, using Python, following Daniel Crawford's guide.

I have been successful with the first four steps. However, I am having some trouble with this part in step 5:

$$
F^0_c C^{'}_0 = C^{'}_0 \epsilon_0
$$

I have the correct transformed Fock matrix (I can verify this as the site as step-by-step matrices that you can check against). My problem is that the MO coefficient matrix I get does not quite match the one on the site. I obtain it by multiplying the above equation by $C^{' -1}_0$ on the right:

$$
F^0_c = C^{'}_0 \epsilon_0 C^{' -1}_0
$$

Now it's in diagonalized form, which means $C^{'}_0$, the transformed MO coefficients, is the eigenvectors of $F^0_c$ and $\epsilon_0$ is a diagonal matrix of the eigenvalues. After I obtain $C^{'}_0$, I obtain the original untransformed MO coefficients $C_0$ using the next equation on the site:

$$
C_0 = S^{-1/2} C^{'}_0
$$

where $S^{-1/2}$ is the transformation matrix used to get the transformed Fock matrix from earlier. My transformation matrix, by the way, matches exactly the one on the site.

This is where my problem comes in. The $C_0$ matrix I get is this:

The one the website has as a reference is this:

If you look carefully, you will notice that mine and the reference one have the same columns; however, some are swapped around, and some have sign flips. This causes problems with the next steps, such as finding the density matrix.

I thought maybe the order should be such that $\epsilon_0$ is in order. The $\epsilon_0$ matrix I get is indeed out of order, and the same permutations and sign flips that will make it in order also makes my $C_0$ match the reference one in terms of where each column is, but NOT sign. Sadly the reference site does not have a $\epsilon_0$ matrix or $C{'}_0$ for me to compare with, only the final $C_0$, so I'm not sure if those are coming out of order also.

My first question is, will these sign flips matter? Is ordering the $C_0$ matrix in terms of getting $\epsilon_0$ the right thing to do?

I am carrying out these matrix operations with basic NumPy functions such as numpy.linalg.eig and numpy.dot. Nothing fancy there. It's worth noting that finding the transformation matrix, $S^{-1/2}$, requires diagonalizing in a similar way, but I didn't have any column switching problems there. It came out exactly as expected.

My second question relates to building the density matrix at the end of step 5. The website has this equation:

$$
D^0_{\mu\nu} = \sum_{m}^{occ} (C_0)^m_\mu (C_0)^m_\nu
$$

It says sum over the occupied MOs. The molecule being used in the example calculation is water, so two H's, and one O, so there are 10 electrons, so 5 orbitals. If I sum using the correct $C_0$ matrix I get on the reference website, from m = 1 to 5, I get the correct $D^0_{\mu\nu}$ result. However my textbook (Szabo and Ostlund, Modern Quantum Chemistry) has this equation (changing some of the notation to match):

$$
D^0_{\mu\nu} = 2 \sum_{m}^{N/2} (C_0)^m_\mu (C_0)^m_\nu
$$

Where N is the number of electrons. Well, 10/5 is 5, so I'm summing from 1 to 5 again, but now there's a 2 in front, so the sum will be doubled. Now, using the one on the website gets me the correct answer, but what could this 2 in the book mean?


texts: Diffusion experiment with dialysis membrane bag

texts:
Recently I have performed a diffusion experiment with a dialysis membrane containing methylene blue. A schematic picture of the experiment:

I want to calculate the flux (amount diffused/area*time) from the samples I have taken. However I am stuck with how to calculate the surface area of the dialysis bag so I can use Fick's law to estimate the flux. The dialysis bag is cylindrical, however when you put the 2 pins above to close it, it is not completely cylindrical anymore as you can see in the picture. Anyone that could help me out with this? If in need of membrane specifications I can post them.


texts: I'm getting tired of writing out the full formulas for hydrates, adding $\ce{.$x$\,H2O}$ to all formulas. I'm wondering if there's standard shorthand for these.


texts: Reaction of solid metals with a solution of metal ions

texts:
Explain the following experiments and their results. What is their chemical equations as well?

When immersing a Magnesium (Mg) chunk inside aqueous solution of Copper ions (Cu(II)), a red-brown sediment of Copper appears. Why?
When immersing a Silver (Ag) stripe inside aqueous solution of Calcium ions (Ca(II)), no chemical reaction takes place. Why?


texts: What is the role of a monochromator in AAS?

texts: What would happen if we didn't use a monochromator; i.e. what is its role in Atomic Absorption Spectroscopy?


texts: Why do noble metals like silver not form natural cubic crystals?

texts:
Pyrite forms cubic crystals, both in theory and in nature:

However, the noble metals, like silver, that have cubic, face-centered lattices, do not seem to form cubic crystals in nature.

One possible explanation is that silver and other noble metals are invariably contaminated by trace amounts of other elements that prevent perfect crystal formation. For example, salt (NaCl) is also cubic, and when very pure deposits of salt are found, they may have large cubic crystals, but normal salt generally does not form such crystals presumably because of contamination.

Is this the explanation why gold and silver do not form cubes when they solidify? If so, imagine we somehow obtained perfectly pure silver as a gas or liquid, would it crystallize on cooling to a cube?


texts:
Worm guts have bacteria that apparently can degrade polyethylene:

The only agents that I have heard of that can degrade a fully-saturated hydrocarbon at room temperature are fluorine (and related nasties), other halogens (with UV light), magic acid (which is extremely reactive with almost anything). None of these seem biochemically feasible.

How is the polyethylene being attacked? Are the ends of the molecules more reactive double bonds that can be be broken off one carbon at a time like beta oxidation of fats?


texts: NMR population difference from a pulse of known flip angle

texts:
I want to know how a radiofrequency pulse of known flip angle $\beta$ changes the population difference of a set of isolated spin 1/2 nuclei.

I know that the equilibrium magnetization is related to the population difference by:

  $M_0= \frac{1}{2}\gamma\hbar\Delta{n_{eq}}$

I would like to know how to calculate the x, y, z components of the magnetization after the pulse, and then calculate the population difference from these values.


texts: How to decide from the solubility product constants which hydroxide precipitates first?

texts:
Salts of $\ce{Fe^3+}$ and $\ce{Al^3+}$ are in a beaker of water. If NaOH is added slowly, what compound would precipitate first?

For me, I think it's $\ce{Fe^3+}$ because of its lower $K_\mathrm{sp}$ value when it reacts with $\ce{NaOH}$. The two equations I wrote were

$\displaystyle\ce{Fe^3+(aq) +3NaOH(aq) -> 3Na+(aq) +Fe(OH)3(s)}$
$\displaystyle\ce{Al^3+(aq) + 3NaOH(aq) -> 3Na+(aq) + Al(OH)3(s)}$

The lower the $K_\mathrm{sp}$ value, the more insoluble the substance is (the precipitate is insoluble). So, $\ce{Fe}$ would precipitate first.
Is this correct?


texts: Define, (actually define) the "stability" and "energy" of a compound

texts:
When we say a conformer or compound is of "higher energy" than another, are we quantifying energy in terms of the bond strength? Or are we going off of how much energy it takes to break the bond?  I don't think we can just assign energies to each compound... so what is this based off of?

One might answer that its based off of stability. Well, what is "Stability?" Is it how rigid/strong the bonds are? Is it how reactive the compound is?

Often times i find myself reading explanations with circular language on this topic. A higher energy conformer means lower stability or A stable compound is one that has low energy. I'm finding these definitions to be crazy ambiguous, and don't thoroughly define what these are.

If someone can clearly explain this in terms that a first year undergraduate student can understand, you have earned my gratitude.


texts: How would one construct a 3D model of a molecule based on the crystal structure of its salts?

texts: Often crystal structures found online from past published crystallography experiments are of the salt of a molecule of biologic interest, as opposed to the freebase form of the molecule itself. For example, I have a CIF file for mescaline hydrobromide (CCDC 1211316) at the moment that I would like to create a 3D model of mescaline from. Would removing the extra hydrogen atom on the amine group (i.e., changing the $\ce{NH_{3}^+}$ to $\ce{NH_2}$) and the free bromide ion suffice or will I also have to optimize the structure's geometry? If I do need to optimize it, or otherwise modify it beyond the procedure I just pointed out, please tell me how to do it with free software (Avogadro, for instance).


texts: Why must the movement of electrons through the wire be balanced by a movement of ions in the solution?

texts:
I have read through Barron's SAT chemistry prep book, in the topic of electrochemistry, the book says

  The movement of electrons through the wire must be balanced by a movement of ions in the solution.

It explains that

  Anions move toward the anode to replace the negatively charged electrons that are moving away.

Can someone help explain these two statements? I don't quite get this concept.


texts: What exactly is peptone (tryptone?) and why does it not get precipitated?

texts: According to Wikipedia Peptone (also called Tryptone) is a form of amino acid that has been treated by stomach acids. According to Google it also stays in solution when treated with acids or heat. Why is that so?


texts:
Which of the following has greater entropy?

a.  $\ce{CH3COOH~ (aq)}$

or

b.  $\ce{CH3COO^{-}~ (aq) + H+~(aq)}$

They are both in the same state, and have the same number of particles.. so how do I figure this out? My instinct says a, because the products will be more "random", but I'm not completely sure.. Any ideas?


texts: Why is the pka of the carboxylic acid part of alpha amino acids (pka around 2.3 for most amino acids) quite a bit less than the pka of a normal carboxylic acid, say acetic acid (pka =4.76)?


texts: Where does the thermal energy come from in a chemical change when two substances react with one another?

texts: We're learning about chemical reactions in class and we recently did an experiment where we combined copper and nitric acid. Both were at relatively room temperature and when they were combined the temperature rose very quickly. Isn't this contradicting the first law of thermodynamics? If the thermal energy is neither created nor destroyed but only transferred than where did all that extra thermal energy come from? please help!


texts: Possible ionization and fragmentation of chemicals

texts:
Is there any generic method where I can know/calculate/generate the possible ionization and fragmentation of a specific chemical, for example, hydrogen chloride and water?

This question is actually related to the mass spectrometer, where I am asked to identify the possible species/ions of a sample. Therefore I would like to know if there's any method to know (calculate) the outcome without memorising everything, for example the outcome of HCl.


texts: Effectiveness of esterification catalysis's [Cu, Sulphuric acid, Acid Zeolite], in Whiskey distillation

texts:
If you go on a tour of a distillery, you will normally be told at some point how the (beautifully polished) copper pot stills catalyse the esterification of ethanol and higher (fusel) alcohols, with acids from the fermentation process improves the flavor of the whiskey. (And how their still geometry creates a superior product)

Obviously the distillation process, removing water and most of the higher (fusel) alcohols contributes to this as well.

How effective is Copper in that scenario? A still would not have more than say 100 m2 of copper surface area and a batch load would be on the order of 5-50 thousand liters

How much more effective would using Sulphuric acid as a catalysis? (Obviously this would not be useful/food grade, but nice to know as a baseline)

Now (the much more interesting part)
How effective would Acid Zeolite be as a catalysis? Either as a distillation column packing medium, or adding a 'handful' to a barrel before leaving it to sit in a ware house for a couple of years/decades?


texts: Would Schweizer's reagent dissolve nitrocellulose?

texts:
Schweizer's reagent, or tetraamminediaquacopper dihydroxide, is used in the production of rayon. It does this by dissolving the cellulose which can be acidified to form strands of cellulose. I have had some success with this.

So, seeing as cellulose and nitrocellulose are rather similar, would it be able to dissolve it too? If not, why? The nitrocellulose would have to be able to survive the addition of acid, which should not be a problem since it is synthesized using sulfuric and nitric acids. So, as long as I use sulfuric acid it should work fine.

Something else that might affect it is how nitrated the cellulose is? Cellulose dinitrate and cellulose hexanitrate might act differently.

And now, assuming that it can dissolve it in some way, it could be extracted from that from celluloid plastic, like that found in ping pong (table tennis) balls?

So, by adding some ping pong ball to Schweizer's reagent, then letting it dissolve and adding it to a solution of sulfuric acid, the camphor in the celluloid would be left behind and you should end up with some sort of "nitro-rayon". This is a bit of a stretch, but to me seems feasible.

I will try this when I can, but for now I hope this is enough to prompt speculation.


texts: Using combined gas law to calculate the volume of dry hydrogen gas

texts:
Volume of wet hydrogen collected at room temperature: $\pu{40.48 mL}$, ambient pressure: $\pu{29.7 inHg}$ ($\pu{754 torr}$), ambient temperature: $\pu{295 K}$ ($\pu{22^\circ C}$), vapor pressure of water at $\pu{22^\circ C}$: $\pu{19.83 torr}$. Partial pressure of dry hydrogen: $\pu{9.87 inHg}$.
Find the volume of hydrogen under standard conditions.

The equation of combined gas law is $p_1V_1/T_1 = p_2V_2/T_2$.
Say if the volume of wet hydrogen gas is $\pu{40.48 mL}$, does this equation still work if part of that volume is water vapor? Or, in other words, does the same volume of water vapor and hydrogen gas exert the same pressure?
One of the correct way to do this problem is find the moles of dry hydrogen gas using the room temperature and volume of wet hydrogen gas, gas constant and room temp. Right here, I am kinda confused why the volume of wet hydrogen if we are trying to find the moles of dry hydrogen gas. Then rest of this solution is plugging the number of moles into the equation along with STP to find the volume of dry hydrogen gas.


texts: Can sp2 hybridised carbon show chirality?

texts:
I know that any carbon to show chirality has to be bonded to 4 different atoms (groups of atoms). So a double bond is
considered as that the carbon is achiral. I learnt from my lecturer that dissubstituted allene is an exception. If it is true that sp2 hybridised carbon cannot show chirality, are there any other exceptions?


texts: Why does bromine add to a double bond instead of a triple bond if both are present?

texts:
According to my textbook, the addition of bromine to pent-1-en-4-yne at low temperature yields 4,5-dibromopent-1-yne:

Why does bromination of the double bond occur selectively?


texts: Determine rate equations for entire kinetic scheme

texts:
I am working with the following kinetic scheme that represents pyrolysis of a biomass particle:

The paper that discusses this scheme provides the following rate constants:

K1 for the pathway of $\text{Biomass} \rightarrow (\text{Volatiles + Gases})_1$
K2 for the pathway of $\text{Biomass} \rightarrow (\text{Char})_1$
K3 for the pathway of $(\text{Volatiles + Gases})_1 \rightarrow (\text{Volatiles + Gases})_2 + (\text{Char})_2$

The rate equation provided in the paper for the conversion of biomass is
$$\frac{\mathrm d\,B}{\mathrm dt} = -(K_1 + K_2)\,B$$

The rate equation for the char 1 component is given as
$$\frac{\mathrm d\,C_1}{\mathrm dt} = K_2\,B - K_3\,C_1$$

And finally the rate equation provided for the char 2 component is
$$\frac{\mathrm d\,C_2}{\mathrm dt} = \delta\,K_3\,C_1$$

where $\delta$ is a deposition coefficient reported as 1.45 in the article. Note that all components of the system are on a mass basis such as $\mathrm{kg/m^3}$.

It is fairly straightforward to calculate the concentrations of $B$, $C_1$, and $C_2$ at each time step given an initial concentration of $B$. However, I would like to determine the concentrations of the volatiles and gases in the system too. Since it doesn't seem possible to calculate the individual volatile and gas components from the given scheme, I would like to determine the concentration of the (Volatile + Gases) group which could be labeled as G. So how would I develop the overall rate equations for B, C, and G?

$$
\frac{\mathrm d\,B}{\mathrm dt} = -(K_1 + K_2)\,B \\
\frac{\mathrm d\,C}{\mathrm dt} = K_2\,B + ? \\
\frac{\mathrm d\,G}{\mathrm dt} = K_1\,B + ?
$$


texts: Thermodynamics - Series Reaction - Estimating mols of reactants based on Free Energy of Rxn

texts:
Question

  Three reactions occur simulteneously (assume ideal) at $\pu{T = 0^\circ C}$.

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

  a) With $\Delta_r G^\circ_\text{AB} = \pu{400 J/mol}$, $\Delta_r G^\circ_\text{BC} = \pu{-100 J/mol}$, and $\Delta_r G^\circ_\text{CD} = \pu{-200 J/mol}$. If you start with 10 moles of A, calculate how many moles of B, C, and D you have when the system reaches equilibrium. Show all your work. (Hint: mass can neither be created nor destoyed)

  b) Order the equilibrium concentrations from largest to smallest. Explain how you might be able to intuitively guess this ranking.

I know that given deltaG_RxN, one can calculate Keq, and use Keq to find the moles at equilibrium of reactants and products. Since the products at the end of one reaction became the reactants of the second, I fed in the mol amount of the first equation into the second equation.

Confused because in discussion - we went over how to do part B. and I don't think my math lines up.

positive delta G_RXN = more reactants than products, and vice versa
thus in the first rxn there should be more [A] than [B] @ equilibrium

in the second rxn there should be more [C] than [B]

and the third rxn there should be more [D] than [C].

what did i do wrong math-wise?


texts: Can we oxidize aliphatic alkane to produce carboxylic acid?

texts: Toluene can be oxidized to form benzoic acid. do aliphatic alkanes give similar kind of reaction?


texts: Does 3,6-di-X-cyclohexa-1,4-diene have stereo centers?

texts:
The following question has multiple correct answers:

The book out of which the question is taken  shows that a, b and d are correct answers.

According to me c should also be correct, as it shows cis-trans isomerism, both X could go to the front (wedge bond), or one could go to the front (wedge) and one to the back (dash bond).  After all geometrical isomerism is also a sterioismersim.
I came to this conclusion considering the definition given on Wikipedia:

  A stereocenter or stereogenic center is any point in a molecule, though not necessarily an atom, bearing groups, such that an interchanging of any two groups leads to a stereoisomer.


texts:
How would I determine the systematic name of $\ce{(CH3)2CHCH2CHClCH3}$?

First of all, how do we determine which side we number the carbon atoms from? It has an alkyl group ($\ce{CH3}$) and a functional group ($\ce{Cl}$). I got lucky by going from right to left so I wrote 2-chloro-4-methylpentane but why couldn't we also label this as 4-chloro-2-methylpentane?

Do we take functional groups in preference to alkyl groups when naming them?


texts: Why aren't there iron bones and eggs in nature?

texts:
As far as I know, most of the "hard things" in living creatures composed of calcium (for example, bones plated with calcium over the keratin structure, and eggshells and seashells with $\ce{CaCO3}$). The calcium ion has an oxidation state of +2, and so does iron.

Why don't we find in nature creatures with bones of iron or eggs with iron shells, given that living creatures do use ionic iron for other purposes like in the heme group of hemoglobin?


texts: Why are pressure or volume not able to change the equilibrium constant?

texts: It is stated in my textbook that temperature is the only factor that can change the equilibrium constant. According to the Ideal Gas Law, temperature is dependent on the pressure and volume. Thus, shouldn't pressure and volume change the equilibrium constant too?


texts: Why is it possible to separate NaOH from certain compounds using acetone?

texts:
Is it due to the aldol reaction that happens? But the product of that reaction is still soluble in acetone.

Apparently if you have a solid mixture of 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone with NaOH and Na2CO3 impurites, and you dissolve them in acetone, after which you centrifuge, the solid impurites will settle out.

Why is this?


texts: Is a ring intermediate formed in hydroboration?

texts:
This was the mechanism taught to us for hydro-boration

Something really strange in that mechanism is that in step 2  hydrogen has two bonds.
Also , the  the doubly bonded $\ce{H}$ , has one bond $\ce{C-H}$ which contains no electrons

Is this mechanism plausible?

In clayden they have shown the cleavge of $\ce{H-B}$ bond  and formation of the $\ce{H-C}$ bond in the same step.
But it doesn't mention the formation of a ring anywhere.

Section 1
Let's assume that the ring does form but after cleaning the $\ce{H-B}$ the electron pair goes into the bonding orbital of H not the anti bonding molecular orbital between $\ce{C-H}$ .

Primarily my doubts  are

The bond with no electron in it (does it actually form)
The reasoning in section 1 (the previous section).


texts: Do enzyme-substrate reactions show reversibility(to a considerable amount)?

texts:
I was studying about the catalysts of enzyme-substrate reactions. My biology book says that if the density of product gets high the enzyme-substrate reactions get slower. It quite sounded like Le Chatelier's Principle. But Le Chatelier's principle only works for reactions in which backward reaction happens to a considerable amount. But I am not sure if it is the normal case for enzyme-substrate reactions.

So, Does enzyme-substrate reactions show reversibility(to a considerable amount), or my reasoning is somewhere wrong?


texts: Is there a systematic way of remembering the names and formula of Oxoacids of Phosphorus?

texts:
My question is exactly what the title says: Is there a systematic way of remembering the names and formula of Oxoacids of Phosphorus ?

I am asking this because I find it very daunting to memorize their names and chemical formula and also a significant number of questions are asked regarding them.


texts: Chemical kinetics with the reaction of tert-butyl bromide with azide ion

texts:
The reaction of tert-butyl bromide with azide ion in aqueous solution
  is proposed to proceed by the following mechanism:

  $\ce{(CH3)3CBr(aq) <=>(CH3)3C+(aq) + Br–(aq)}$

  $\ce{(CH3)3C+(aq) + N3–(aq) \to (CH3)3CN3(aq)}$

  Assuming that $\ce{(CH3)3C+ (aq)}$ achieves a steady-state concentration, but making no further assumptions about the relative magnitudes of the three rate constants,
  what is the rate law for this reaction, where $k_1$ is the forward
  reaction rate of the first equation, $k_{-1}$ is the reverse reaction
  rate of the first equation, and $k_2$ is the forward reaction rate of
  the second equation?

  (A) $\ce{k_1[(CH3)3CBr]}$

  (B) $\ce{k_2[(CH3)3CBr][N3-]}$

  (C) $\ce{\displaystyle\frac{k_1k_2[(CH3)3CBr][N3-]}{k_{-1}[Br-]}}$

  (D) $\ce{\displaystyle\frac{k_1k_2[(CH3)3CBr][N3-]}{k_{-1}[Br-] + k2[N3-]}}$

My thoughts: First of all, I read that $\ce{(CH3)3C+ (aq)}$ is a steady state concentration, which meant that $\frac{d\ce{[(CH3)3C+ (aq)}]}{dt} = 0,$ which prompted me to write out differential equations for each reactant. Thus, I got a system of differential equations:
$$\frac{d\ce{[(CH3)3CBr (aq)}]}{dt} =-\frac{k_1}{k_{-1}}\ce{[(CH3)3CBr (aq)}]$$
$$0=\frac{d\ce{[(CH3)3C+ (aq)}]}{dt} = -\frac{d\ce{[(CH3)3CBr (aq)}]}{dt} - \frac{d\ce{[(CH3)3CN3 (aq)}]}{dt} = \frac{k_1}{k_{-1}}\ce{[(CH3)3CBr (aq)}] -k_2 \frac{d\ce{[(CH3)3CN3 (aq)]}}{dt}$$
$$\frac{d\ce{[Br- (aq)}]}{dt} = -\frac{d\ce{[(CH3)3CBr (aq)}]}{dt} = \frac{k_1}{k_{-1}}\ce{[(CH3)3CBr (aq)}]$$
$$\frac{d\ce{[N3- (aq)}]}{dt} = -k_2\ce{[N3-(aq)]}$$

But I was unsure of how to use these differential equations to actually find the rate law. Could anyone provide any suggestions?


texts:
Prologue/Rant about online classes
We have been taught the electron sea model to explain metallic bonding and conduction of electricity by metals. Then out of the blue, the band theory was introduced, without even giving the definition of what a band is. So I was lost in the recorded online class with no method of asking a doubt. So in an attempt to not wait a day for asking the doubts, I took it on myself to clear my doubts. So I surfed through the web and almost reached a conclusion.. before referring to a textbook.
The actual doubt
So as far as I know, the MOs (on a large scale, like 10 raise to 23 atoms scale) having similar energies appear as bands. The outermost band of occupied MOs is called the valence band. But what I am confused about is what makes up the conduction bands. I reached a conclusion from the chemistry libre texts that conduction bands are made from the combination of the unoccupied atomic orbitals. But when I referred to my reference book, it stated that they are the anti bonding MOs of the valence band.
So what actually makes up the conduction band? Is it one of the two I mentioned above? Or is it a theoretical set of energy levels where an electron can move freely to conduct electricity?


texts: What is the entropy of mixing a gas into the whole atmosphere?

texts: Suppose I release 1 mole of pure argon into the atmosphere. What is the entropy of mixing? The equations I have found seem to only apply to the case of a fixed volume. Should I use an estimate of the volume of the whole atmosphere? Some sort of infinite approximation?


texts: Is “mass-action ratio” identical to “reaction quotient?”

texts:
Mass-action ratio
Reaction quotient

According to their definitions expressed in the above Wikipedia articles, these two concepts seem to be totally identical. Is that true? If not, what is the difference?


texts:
Why does the Grignard reagent not react as a base in case of ketones even though the α-hydrogen atom in case of ketones is acidic? Grignard reagents do react with ethyne to give hydrocarbons, so why not here?

The only thing I can put my finger on is electrophilicity of the carbon.


texts: Why don't the electrons move through the electrolyte (instead of the circuit) in a galvanic cell?

texts:
I was learning about galvanic cells and I had a problem understanding why electrons do not travel through the electrolyte solutions themselves, instead preferring to travel through metals. Can electrons travel through an electrolytic solution?

Imagine a galvanic cell, without the wiring between the two electrodes and instead we only have the salt bridge. Won't the electrons (although it is very unfavorable to happen) travel through the salt bridge and the solutions? In other terms will the transformation of the electrodes occur?


texts: Which is the most acidic hydrogen in vitamin C

texts:
I thought it would be the lower first $\ce{-OH}$ because it's close to the double bond with oxygen, so I thought there would be more electron withdrawal from the oxygen atom due to its electronegativity.But the correct answer is actually the second lower $\ce{-OH}$, which I really don't understand

My attempt to the question:


texts: What is the bond energy of Carbon-Deuterium bond?

texts: The difference in bond strength of a CH single bond and CD single bond can be explained by Kinetic Isotope Effect. I was wondering if it is possible by bond energy. I could not find the value of bond strength of CD bond. For CH bond it is 410. What is the energy for CD bond? Experimental data if available is appreciated.


texts:
In high school books, Huckel's rule is used for determining aromaticity. We were taught this example

Huckel's rule is limited to monocyclic systems. We were taught to find aromaticity by -

looking for a closed loop. The two loops that were pointed out have been drawn (in pink) in the diagram above.
Applying Huckel's rule to it i.e counting the number of $\pi$ electrons and then applying the 4n+2 formula for aromatic compounds and 4n for anti.

No explanation was provided as to  why this concept works on the grounds of 'this is out of syllabus'.

I have multiple questions regarding this 'closed loop' concept

What is it really called?
How does this loop methodology work?
What would happen if the inner loop was aromatic and outer anti aromatic?
(the example has both loops anti)


texts: Synthesis of tripeptide using Merrifield peptide synthesis procedure - Inclusion of asparagine

texts:
I am supposed to synthesize tripeptide, $\mathrm{Ala-Asn-Phe}$, using Merrifield peptide synthesis procedure. Accordingly, I have done followings:

Attached protected $\mathrm{Phe}$ as the first amino acid.
Got rid of protecting group ($\mathrm{BOC}$)
Added asparagine with 2 protecting groups - $\mathrm{BOC}$ for $\alpha$-$\ce{NH2}$ group and $\mathrm{FMOC}$ for the $\gamma$-$\ce{NH2}$ group.
Got rid of $\mathrm{BOC}$ and added $\mathrm{Ala}$ protected with $\mathrm{BOC}$.
Got rid of $\mathrm{BOC}$ and $\mathrm{FMOC}$, and used $\ce{HF}$ to release the peptide.

Is this going to work? The thing that worries me the most is the $\gamma$-amino group and using $\mathrm{FMOC}$ - is that a good idea?


texts: What is the maximum number of emission lines when the excited electron of a H atom in n = 6 drops to ground state?

texts:
When an electron in a higher energy state jumps to a lower energy state in Bohr’s model of hydrogen atom, it emits a photon which has energy equal to the difference in the energy between the final and initial energy states.
$$h\nu = E_f - E_i$$
where $\nu$ = frequency of photon emitted

Now what I know is each photon emitted corresponds to an emission line in the spectrum.

So, an electron can make the make the transition from a higher energy state to any lower energy state provided it emits a photon given by the above equation. In the question given, if an electron is in higher energy state; the maximum number of spectral lines is when the electron jumps to the next lowest energy state and so on as then photons will be emitted during each transition.

If an electron moves from $n = 6$ to $5$ we get a spectral line. Then from $n = 5$ to $4$ we get one and so on giving us a maximum of $5$ spectral lines. Now if the electron made the transition directly from $n = 6$ to $n = 4$ or any other lower energy state we would get less than $5$ spectral lines.

However, on looking up answer to the question it was given $15$. How can it produce $15$ spectral lines? When an electron from $n = 6$ jumps it has $5$ options and example it makes the jump to $n = 3$ then it has only two options $n = 2$ or $n = 1$. It can’t go back to $n = 6$ unless energy is supplied and it absorbs energy. So how can more than 5 lines be observed in the emission spectrum?

I am missing a key concept in such problems. Can someone tell me what I am missing?


texts:
Disclaimer: high school question

I was hoping to make phenol do a nucleophilic attack on $\ce{C2H5Cl}$. But then, I noted that the $\ce{O}$ atom in phenol is NOT as nucleophilic as the regular $\ce{R-OH}$ (since it delocalises with the benzene ring). So, I am afraid phenol's $\ce{O}$ atom might not be a good enough nucleophile to achieve the conversion by this method.

Is there any other method to achieve this conversion?


texts: Why are 13C CP MAS NMR signals sometimes split by N, and absent in dipolar dephasing?

texts:
A past paper question on solid state NMR I was looking at asks why, in $^{13}$C CP MAS NMR, carbons directly bonded to nitrogen are "occasionally" split, and why they're usually absent in the dipolar dephased spectra.
I assume this is probably due to quadrupolar interactions, since $^{14}$N has spin 1; the size of the quadrupolar interaction depends on the electric field gradient at the quadrupolar nucleus, and hence the symmetry of the environment, so the "occasionally" presumably occurs when the nitrogen is in a particularly asymmetric electronic environment and so has a very large quadrupolar coupling? I'm not sure why we don't see this splitting all the time.
Presumably the absence of these carbons from dipolarly dephased spectra is due to a short T$_2$ time - just like CH and CH$_2$ carbons have a short T$_2$ time due to dipolar coupling, I assume the quadrupolar interaction reduces T$_2$ time.
I'd be very grateful for help understanding this.


texts: Is it possible for Hydrogen to lose its electron?

texts: I know the basics of Chemistry and one thing I've always wondered if it is possible for Hydrogen to give up it's one electron? I know Hydrogen is eager to share its election through covalent bonds, but is there a scenario where Hydrogen will give up its only electron?


texts: What is the correct formula for diamminechloridonitrito-n-platinum(II)?

texts:
Is the correct formula for diamminechloridonitrito-n-platinum(II) $\ce{[Pt(NH3)2Cl(NO2)]}$ or $\ce{[PtCl(NH3)2(NO2)]}$?
I was taught that the sequence of symbols within the coordination entity should be written in the following order:

The symbol of the central metal atom is written first.
The ligands are written afterwards and should be mentioned in alphabetical order according to the first symbol of their formulae.
For example, for the coordination compound $\ce{[Co(H2O)2(NH3)4]Cl2}$,
$\ce{H2O}$ is cited first and then $\ce{NH3}$. (As H comes before
N)

However, it is given in my textbook that the formula for diamminechloridonitrito-n-platinum(II) is $\ce{[Pt(NH3)2Cl(NO2)]}$, where $\ce{NH3}$ is followed by $\ce{Cl}$.
I assumed that the correct formula would be $\ce{[PtCl(NH3)2(NO2)]}$ ($\ce{Cl}$ followed by $\ce{NH3}$) instead. What am I missing here?


texts:
Why does gold react with cyanide and sodium hydroxide and what is the chemical reaction's impact on gold's atomic structure and bonding?

What I think is since in the 'flotation' process, when the water, chemicals and other substances are added, gold isn't affected and neither is the pyrite, but when the cyanide and caustic acid is mixed with the slurry, it separated both substances, then the oxygen or 'air' is added into the mix, so then the gold rises to the top and frothing over the slurry. I'm not sure if i'm correct, but I don't understand how it's related to the atomic structure and bonding of gold? This process is from (Super Pit - Kalgoorlie exploration mine)

Can someone please explain how the separation of gold from the mixed compounds is related to its atomic structure and bonding? Is it to do with the 'Elution' process? Thank you in advance!


texts: Why is Iron very rare in seawater compared to many other elements?

texts:
I don't know the associated technical words to research this question.

There was high presence of Iron in the oceans in anoxic precambrian times, and today copper is 5 times more abundant in the oceans than iron.

Is the solubility of $\ce{Fe^{2+}}$ and $\ce{Fe^{3+}}$ and $\ce{Cu^{2+}}$ very different?

Why is there five times more Copper in seawater than Iron? Surface minerals have 1000 times higher PPM values for the latter? It's precipitating?

Why is there 4000 times less iron in seawater than Strontium? Surface minerals have 100 times higher PPM values for the iron?

Here are some measurements stated previously:
https://web.stanford.edu/group/Urchin/mineral.html
https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust


texts: Determination of initial excited state via luminescence

texts:
A one electron species initially in the some excited state
  ($n_i$)
  is irradiated with a light of wavelength 121 nm when
  the electron is promoted to a further higher orbit ($n_f$).
  In
  returning back to the ground state, it gives an emission
  spectrum containing 15 bright lines. Out of these 15 lines,
  9 lines were found to have wavelengths smaller than
  121 nm while 5 lines have wavelengths greater than
  121 nm.
  What is the value of $n_i$?

I got the value of $n_f$ using this:

$$\frac{(n_f-1+1)(n_f-1)}{2}=15$$
$$\therefore n_f=6$$

We do not know the atomic number($Z$), nor $E_{ground state}$, nor $n_i$. What is the approach we should use to solve this problem?


texts: Why the radius of noble gases is more than the halogens or the previous groups?

texts:
Noble gases have a larger radius than the halogens.

Sometimes it is greater than the radius of group I elements.

Why it is like that? When we talk about radius of noble gases what type of radius is referred? Is it Van der Walls or atomic?


texts: Why doesn't calcium carbonate dissolve in water even though it is an ionic compound?

texts: I studied the solubility of compounds in water. I have found that calcium carbonate doesn't dissolve in water. The teacher stated that the ionic compounds dissolve in water except some carbonates. What would be a clear elaboration of this phenomenon?


texts: Are the words "apparatus" and "equipment" synonyms?

texts: Are the terms "apparatus" and "equipment" synonyms, within a chemistry or physics laboratory? If not, what are distinguishing factors?


texts: How can the equilibrium shift, while Kc remains constant?

texts:
Consider the following reversible reaction.
$$\ce{Cr2O7^2-(aq) + H2O(l) <=> 2 CrO4^2-(aq) + 2 H+(aq)}$$
What will happen to the position of equilibrium and the value of $K_c$ when more $\ce{H+}$ ions are added at constant temperature?
$$
\begin{array}{lcc}
\hline
  & \text{Position of equilibrium} & \text{Value of}~K_c \\
\hline
\text{A.} & \text{shifts to the left} & \text{decreases} \\
\text{B.} & \text{shifts to the right} & \text{increases} \\
\text{C.} & \text{shifts to the right} & \text{does not change} \\
\text{D.} & \text{shifts to the left} & \text{does not change} \\
\hline
\end{array}
$$

The answer given is D.
I understand that when more $\ce{H+}$ ions are added, the reaction shifts in reverse. So I've understood that this is known as having the equilibrium shift to the left, toward the reactants.
What confuses me is why $K_c$ doesn't change. If the equilibrium shifts to the left, I suppose that must mean more reactants are formed in relation to the products, so $K_c$ would decrease.
But the answer key says that $K_c$ remains unchanged. This is coherent with what I've been taught, but I don't understand how the equilibrium can change yet have $K_c$ remain constant.
I'm just afraid I've got some of the theory mixed up, so I wanted to get some clarity. Could someone explain this please?


texts: Calculate the number of Carbon atoms in .0400g C7H5NO3S

texts: I understand how to get from grams to moles and from moles to molecules with Avagadro's number. That gives us 1.31x10^20 molecules of C7H5NO3S. Now we take that and multiply by 7 to get the individual Carbon atoms. This is where I get confused because my calculator says 9.17x10^20 but my book says 9.20x10^21. Please help explain!


texts: Does the acid dissociation constant fluctuate or stay constant during titration?

texts:
I'm doing titration experiment, where I record the volume of base added and the pH value, then use these two variable to make a titration graph. I'm suppose to extrapolate any data needed from the chart, and find the acid dissociation constant at 0% to equivalence point, 50% to equivalence point, and 75% to equivalence point. The ka value I determined respectively are 0.000165, 0.000457 and 0.000239. The first, and possibly the last value (by a stretch) are the only acceptable values. So my question is, does ka stay constant or can it fluctuate during titration, before settling down to the literature ka value?

I'm leaning towards it stays constant regardless and that the discrepancy is due to errors I made, but then I also think that during titration, not all of the molecules neutralizing each other are going to meet and react instantly, and that could also affect something somehow.


texts:
To simulate the action of gastric $\ce{HCl}$, we have titrated 100 ml of a meal with 0.1 N $\ce{HCl}$. To plot the data, use (R-code)

vol = read.table("http://menne-biomed.de/uni/volph.txt",sep="\t",header=TRUE)
plot(vol$vol,vol$pH,pch=16,type="l",main="Titration of 100 ml meal with 0.1 N HCl")

I am trying to determine, for example, how much 1N $\ce{HCl}$ I need to add to get a pH of 1.5; if I understand correctly, I have to fit the Hasselbalch equation.

Being a statistics guy, the numerics is no problem, I just do not understand how to get the terms in that equation together with my data.


texts: What does the pressure in the HPLC(High performance liquid chromatography) do?

texts: Well I have to do research about the HPLC. It says, that because of the pressure the stationary phase can be made out of smaller particles and the pillars can be shorter. Also the seperation of the contents is supoosed to be superior, compared to other kinds of liquid chromatographies. Can somebody explain that to me?


texts: Acidic strength comparison between sulphuric acid and nitric acid

texts:
Why is $\ce{H_2SO_4}$ more acidic than $\ce{HNO_3}$. Shouldn't it be the other way around because $\ce{N}$ is more electronegative than $\ce{S}$?

My reason: $\ce{O}$ can take electrons more easily from $\ce{S}$ than from $\ce{N}$. Hence, it will be more difficult to remove $\ce{H}$ from $\ce{H2SO4}$ than from $\ce{HNO3}$. Hence, $\ce{HNO3}$ should be more acidic.


texts: Deriving an expression from Navier-Stokes under creeping flow

texts:
So I'm trying to derive
$$\mu\nabla^2\vec{v}=\nabla P-\rho g$$
from Navier-Stokes equation
$$\begin{align}\rho \left(\frac{\partial\vec{v}}{\partial t}+\vec{v}\cdot(\nabla\vec{v})\right)&=\rho\vec{g}-\nabla P+\mu\nabla^2\vec{v}\\
\rho \left(\frac{\partial\vec{v}}{\partial t}+\vec{v}\cdot(\nabla\vec{v})\right)-\mu\nabla^2\vec{v}&=\rho\vec{g}-\nabla P
\end{align}$$
under creeping flow.
I began with looking at the left-hand side of Navier-Stokes equation, which I expanded to:
$$\rho \left(\frac{\partial\vec{v}}{\partial t}+v_x\frac{\partial\vec{v}}{\partial x}+v_y\frac{\partial\vec{v}}{\partial y}+v_z\frac{\partial\vec{v}}{\partial z}\right)-\mu\left(\frac{\partial^2\vec{v}}{\partial x^2}+\frac{\partial^2\vec{v}}{\partial y^2}+\frac{\partial^2\vec{v}}{\partial z^2} \right)$$
Because of the creeping flow I new that $v_x\approx v_y\approx v_z\approx0$. Because of this I can therefore write the left-hand side as:
$$\rho \frac{\partial\vec{v}}{\partial t}-\mu\left(\frac{\partial^2\vec{v}}{\partial x^2}+\frac{\partial^2\vec{v}}{\partial y^2}+\frac{\partial^2\vec{v}}{\partial z^2} \right)$$
But from here I am stuck. I asked a friend who said that since $v_x\approx v_y\approx v_z\approx0$ we can also remove the $\frac{\partial\vec{v}}{\partial t}$-term but I find this mathematically incorrect since the derivate of a function isn't necessarily small just because the function is small. As an example the function
$$\vec{v}(t)=((t+1000)^2-10^6)\vec{e_x}+((t+100)^3-10^6)\vec{e_y}+((t+50)^2-2500)\vec{e_z}$$ is small when $t=0$ but that isn't true for the derivate in $t=0$.
Is it something I'm missing when it comes to creeping flow? Is it that $v_x$, $v_y$ and $v_z$ are constantly small and therefore we can se them as constant functions and therefore the derivate is also neglectable?


texts:
I have a question about 1H NMR splitting of 3-methyl-1-butanol.

The spectrum looks as the following.

The assignment of the NMR spectrum is the following.

Assign.     Shift(ppm)

  A             3.673
  B             1.66
  C             1.57
  D             1.49
  E             0.922

So based on the results, A hydrogen is splitted into triplet. Is this splitted by D hydrogen? If so, why not C hydrogen on the alcohol group?

The results are retrieved from the following link: https://www.chemicalbook.com/SpectrumEN_123-51-3_1HNMR.htm


texts: About alternative magnetic effect on porcelain (for induction furnace purposes)

texts:
I am trying to use the Induction furnace mechanism (like described via this video), for heating part of the Muffle furnace, as one dental porcelain furnace prototype.
So, my plan is to put copper coil with frequency around 10 ~ 4000 HZ, and placing some iron bar inside the ceramic container (one sample shown below!):

.
I have googled the induction muffle furnace, and find only one patent by this topic (you can see below):

So, I am in doubt that some part of this project must be wrong. So, I asked here about the effect of changing the magnetic field on the characteristics of dental porcelain, if that effect were too much and create some deformation via dental porcelain coating, this prototype would not be proper for this purpose.
As I am not familiar with chemical terms and ..., If possible, suggest some proper tag to faster finding the effect of the alternative magnetic on the dental porcelain coating.
Update:
For clarifying question it must be said:

induction furnace mechanism are working fine, and for creating high
temperature the plan have had some additional metal bar to become hot
(based of induction mechanism), and create the desired heating for
melting the porcelain coating. But my question is about the effects of
alternative magnetic fields on desired characteristics of porcelain
(target).

Thanks for your consideration.


texts: As far as I have researched, fused calcium chloride is the hydrated form of calcium chloride. If that is true, then why is it called 'fused', why not simply hydrated?


texts: Why does the crystal sublime more quickly at the corners where there is a higher vapour gradient?

texts:
The crystal responds to the larger vapor gradients near the edges by
  sublimating faster there and thus rounding the crystal.

  J. Nelson, J. Atmos. Sci., 1998, 55, 910-119.

The change in shape according to the gradient makes intuitive sense to me but I can't for the life of me figure out why it does this. Maybe I'm being really foolish here, but surely a higher concentration of vapour at the corners would decrease the rate of sublimation there.