texts: Do the spins of outer orbitals block measurement of spin of inner orbitals?

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Do the outermost s1 and s2 electrons block an outside observer from measuring the larger inner group orbitals for elements heavier than Nitrogen (for instance, would Chromium's 4s1 electron or Manganese's 4s2 electrons prevent you from detecting the spin of the 3d5 electrons in either case?)

I edited this into an individual question from the original list of them per moderator instruction.


texts: What is inhibiting polystyrene's ability to dissolve in traditional solvents like ethanol or acetone?

texts:
My friend and I have been struggling with this problem for a couple days. Because polystyrene has a similar structure to many plastics, we assumed that it would dissolve in acetone. However, after running several tests, we found that polystyrene would not dissolve in a measurable quantity even if we let it sit in acetone for a significant amount of time.

Here is the plastic we are attempting to dissolve:

https://imgur.com/rdawCIP

And here is a plastic more easily dissolved:

https://imgur.com/hAVMUsM

We understand that most molecular-bonded plastics dissolve via van der Waals dispersion forces, so why isn't polystyrene dissolving? My theory is that the benzene ring is interfering with the dissolving process -- that only half the compound of polystyrene is interacting with the acetone and thus it does not dissolve like a polyethylene (which obviously has twice as much surface area to dissolve).


texts: Strongest chloride complex as predicted by HSAB theory

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Why won't $\ce{Ni^2+}$ form a complex with $\ce{Cl-}$, while the ions $\ce{Cu^2+}$ and   $\ce{Co^2+}$ form the complexes $\ce{[CuCl4]^2-}$ and $\ce{[CoCl4]^2-}$?

According to the HSAB theory, $\ce{Cl-}$ is considered a hard/borderline base. So I figured the strongest complex would be the one in which the center ion is the hardest acid. The $\ce{Co^2+}$ ion is the largest and the least electronegative. So it should be the softest acid (although they are all considered borderline). It forms a complex with $\ce{Cl-}$. $\ce{Ni^2+}$ should be the hardest acid, and yet it does not form a complex with $\ce{Cl-}$ at all. Why is that?

References:

http://www2.chemistry.msu.edu/courses/CEM812/HSAB_Theory.pdf
R. Pearson, Chemical hardness and density functional theory, J. Chem. Sci., Vol. 117, No. 5, September 2005, pp. 369–377


texts: Keto Enol Equilibrium for Claisen Condensation Products

texts: Do Claisen Condensation products prefer the di-keto form, or a keto/enol form due to increased conjugation and hydrogen bonding?


texts: In the Lewis structure for barium fluoride, why does barium lose its valence electrons?

texts:
I searched for $\ce{BaF2}$ Lewis structure, and found out that the Barium atom loses its 2 valence electrons to form $\ce{F- Ba^2+F-}$.
Before seeing it I thought each of $\ce{Ba}$'s valence electrons form a single bond with each of the fluoride atoms $\ce{F-B-F}$ which also completes the octet for F atoms,  and the formal charge in this case will be $7-6-\frac{1}{2}(2) =0$ for F atoms and $2-0-\frac{1}{2}[2\cdot 2] = 0$ for Ba, which works out.
I'm looking for an explanation on why Ba loses its electrons to form $\ce{F- Ba^2+F-}$ instead of $\ce{F-Ba-F}$.


texts: Why are some ions mutagenic and others are not?

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It is my understanding that when ionic species (such as $\ce{He^2+}$, or alpha particles) enter the human body, they tend to react with biomolecules, causing damage by (for example) mutating DNA.

If such ions can cause severe damage to the human body, why are other ions like $\ce{Na+}$ or $\ce{Cl-}$ safe to consume and not prone to causing similar mutagenic effects?


texts: Is it valid to calculate concentrations given equilibrium constant and initial concentration?

texts:
Suppose we have the following reaction:
$$\ce{2A <=> B + C}\tag{1}$$
which can be thought the sum of the following reactions:
$$\ce{A <=> B}\tag{2}$$
$$\ce{A <=> C}\tag{3}$$
with equilibrium constants $K_1$ and $K_2$ respectively. The $K$ for the first reaction will be the product of $K_1$ and $K_2$ i.e. $K=K_1K_2 $. Now if we are given that initial we have $x$ mol of $\ce{A}$ and no amount of $\ce{B}$ and $\ce{C}$, one can calculate the amount of B and C present at equilibrium using the equilibrium constant $K$:
$$K=\frac{y\cdot y}{(x-2y)^2}\tag{4}$$
If we solve (4) for a given $x$ (initial amount) then concentrations of $\ce{B}$ and $\ce{C}$ must be equal. But how can this be possible if $K_1$ and $K_2$ have different values? I mean the following equality must holds:
$$[\ce{C}]= [\ce{B}] \Longleftrightarrow K_1{[\ce{A}]} = K_2\ce[{A}] \tag{5}$$
Edit I am asking if it is valid to use the equilibrium constant $K$ to find the concentrations of $\ce{B}$ and $\ce{C}$ because every reaction can be thought of as sum of other reactions. It is a common exercise in many general Chemistry textbooks where you are given a reaction with an equilibrium constant and you must find the concentrations at equilibrium. Well the substitutions into equilibrium constant that they make is the one that I have also did (assuming 0 initial concentration for both $\ce{B}$ and $\ce{C}$. So what is going wrong?


texts: How are unstable transition states determined?

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The Wikipedia article about the Grignard Reaction says that

  The addition of the Grignard reagent to the carbonyl typically proceeds through a six-membered ring transition state.

This got me thinking: How was it determined that the Grignard reaction has the ring as a transition state? In fact, how are unstable transition states in general determined?


texts: Do the compounds NaₓIrO₂ and NaOsO₂ exist?

texts:
Based on some physics background, I want to know whether have scientists synthesized these two materials: $\ce{Na_{$x$}IrO2}$ and $\ce{NaOsO2}$ in the lab, if so, what properties do they have?

I will be very appreciative if someone could recommend me some relevant articles.

  Would you be willing to share your interest in these two materials? For example, is there a specific application in mind? If so, we might be able to suggest alternate materials should these two not exist.

I want to seek a material that has triangular lattice structure, strong spin-orbital coupling (e.g. 5d element) and large (or moderate) coulomb interaction between electrons. For example, $\ce{ABO2}$ type, $\ce{NaOsO2}$ compounds, where $\ce{A}$ and $\ce{B}$ are alkali and transition-metal ions, respectively. So far, I know $\ce{IrTe2}$ may be a one.
Do you mean that both $\ce{NaxIrO2}$ and $\ce{NaOsO2}$ do not exist?

  Is there any information on iridium and osmium oxides in these low oxidation states?

For example, $\ce{Na2IrO3}$ and $\ce{Li2IrO3}$. But these two belong to the honeycomb lattice structure, and what about the triangular lattice structure?


texts: Regioselectivity of bromination of alkenes

texts:
Recently, in my chemistry lesson, we were discussing the mechanism of the bromination of alkenes. The teacher brought up the involvement of the cyclic bromonium intermediate. She also mentioned that the nucleophile attacks the more substituted carbon atom in the bromonium ion. However, this raised many questions among my classmates. Firstly, based on steric reasons, the nucleophile is more likely to attack the less-substituted carbon since there is less hindrance. Hearing this, the teacher then said that the reason for the preference is based on electronic factors. However, this makes little sense as well, considering that the presence of more alkyl groups will decrease the partial positive charge on the more substituted carbon, making it less attractive to the nucleophile (be it $\ce {Br^-}$ or $\ce {H2O}$).

I went to seek clarification by looking at more authoritative texts, such as Advanced Organic Chemistry: Part A: Structure and Mechanisms by Carey and Sundberg, as well as Guidebook to Mechanism in Organic Chemistry by Peter Sykes. However, they were citing very weird reasons that were not very intuitive. Here are some extracts from relevant chapters of the two texts:

From the former,

  Unsymmetrical alkenes nevertheless follow the Markovnikov rule because the partial positive charge that develops is located predominantly at the carbon that is better able to accommodate an electron deficiency...

From the latter,

  With an unsymmetrical alkene, e.g. 2-methylpropene (32), the more heavily alkyl-substituted carbon will therefore be preferentially attacked by the residual nucleophile, $\ce {Cl^-}$.

Why do the alkyl groups result in greater cationic character when they are in fact, electron releasing?


texts: Having trouble understanding activity series of metals & electronegativity

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I want to know how do metals replace hydrogen in a substance such as water. Isn't water happy with its configuration? It has shared enough electrons so that both hydrogen and oxygen complete their orbitals.

I know that alkali metals are very active and they have very low electronegativity. And elements such as gold have much higher electronegativity while being considered very inactive. Maybe I have a wrong understanding of what electronegativity is but isn't the element with higher electronegativity supposed to be more active and be able to replace those with lower ones?


texts: A question about potential difference across a membrane

texts: Membrane potential of living cells arising from the difference of concentration of ions on both sides of the membrane, but why didn't someone use selective polymers as AEM (Anion Exchange Membrane) and apply pressure to cause accumulation of anions on one side of the membrane forming a potential difference?


texts: Predicting bonds from properties of compounds

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You are given compounds $x, y$ and $z$. $x$ conducts electricity in aqueous solution as well as in molten state. $y$ conducts electricity in aqueous form only. $z$ conducts electricity in neither the aqueous nor the molten state. Predict the intramolecular bonds in each compound.

Compound $x$ is clearly ionic. In water, the ions disassociate and form free charges for flow of electricity. In the molten state, the ionic bonds break, and again free charges can flow.

I'm not sure about the other two compounds.


texts:
I came across this wonderful compound, triptycene.

Why is triptycene an aromatic compound, even though it is non-planar? I thought planarity was a requirement for aromaticity.


texts: How long does a wine sauce need to simmer for to reduce the alcohol to less than one percent

texts:
Perhaps you can shed some light on this topic for me.  I've recently researched the topic of boiling off alcohol while cooking--specifically how long one needs to simmer alcohol to boil it off.

I'd come across a couple of sites which showed tables of simmering times and percentage of alcohol remaining.  Since I am a math-head, I noticed that something didn't quite jive in the tables I was viewing.

I thought to ask a chemistry expert to see if there is something unusual going on chemically to explain these inconsistent values in the tables.

I don't want to make this a novel, so I will use only a few entries in the tables to illustrate my point.

Simmering time                    Alcohol remaining

15 minutes                                  40%

30 minutes                                  35%

2 hours                                     10%

So what the table suggests is that if you simmer a solution containing alcohol, after the first 15 minutes, you will have 40% of the original amount of alcohol in the solution.  If you simmer for an additional 15 minutes (total of 30 minutes) you will have 35% of the original amount of alcohol left in the solution.

So, (according to the table) if I have a solution which originally contains 100 ml of alcohol in the solution, and I simmer it for 15 minutes, I will have 40 ml of alcohol left in the solution.  Then if I simmer it another 15 minutes (30 minutes total), I will have 35 ml of alcohol remaining in the solution.

However, If I start with a solution containing 40 ml of alcohol in the solution (let's say it's the solution from above after the first 15 minutes), and I simmer it for 15 minutes, I will be left with 16 ml of alcohol in the solution (again, according to the table).  You can see my dilemma; 16 ml does NOT equal 35 ml.  The math doesn't work.

I am wondering about the nature in which they'd come up with these values or the methodology they used in their experiments.

Can you help me to understand what is going on here?


texts: Why aren't these two resonance structure same?

texts:
Draw the resonance structures of Fluorobenzene.

In the solutions the structures below were given, I wonder why these structures are not just same. Both of these structures have a negative formal charge on the ortho position.

Are the above structure of Fluorobenzene same ?


texts: Why is the fragrant molecule linalool volatile when it has hydorgen bonding?

texts: I've done a bit of research on volatile molecules and from what I've read, highly volatile molecules should have weak intermolecular forces (easy to go from liquid to gaseous state)....however it seems like the molecule linalool is an exception to this....I'm wondering if anyone can reconcile this contradiction (?) for me?


texts:
Why do we encounter only Tosyl groups and not anything at the end of the benzene group (ie not to replace the SO2Cl part..rather the Me part at the other end)
I mean something like a CF3 or NO2 would help make it a better leaving group right?


texts: how to speed up Ferric Chloride and copper reaction

texts:
im doing pcb etching process (for those who don't know pcb is that thing with electronics on it lmao) using Ferric Chloride and it's taking forever

is there any chemicals i can find that will speed up this process (could it also be found at home, salt or acid for instance)

thanks in advance


texts: Maximum distance for intramolecular proton transfer

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In this reaction (formation of ester from ketone / aldehyde), intramolecular proton transfer happens, since it can stabilize the formal positive charge by resonance after that. This transfer happens across 3 atoms. ($\ce{O-O-C}$)

However, in this step (formation of acetal from $\ce{C=O}$) using alcohol, the book says it does not occur, since the $\ce{O}$ and $\ce{H}$ are 'too far' apart. This 'transfer' happens only across 2 atoms ($\ce{C-O}$). Which is less than the above reaction ($\ce{O-O-C}$). If that can occur, why can't the proton transfer here not occur?
What is the real factor that determines whether an intramolecular proton transfer can happen?


texts: Axial or planar chirality in spiro[3.3]hepta-1,5-diene

texts:
The two spirocyclic compounds drawn below are enantiomers. My question is, do they exhibit axial or planar chirality?

3D representations:


texts: Bond Lengths in FCC, BCC and HCP Structures

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I was wondering what the crystal structures of FCC, BCC and HCP actually look like, and where atoms are placed in their configuration?

Specifically I'm looking at elemental nickel, iron and cobalt in their lowest temperature lattice type. (Below their curie temperature to be exact.)


texts: Why is ionisation energy defined for gaseous species?

texts:
Most high school and college textbooks usually define the first ionisation energy as such:

  The first ionisation energy is the energy required to remove 1 mole of electrons from one mole of gaseous atoms in the ground state to form 1 mole of gaseous singly-charged cations.

I've not been able to receive a satisfactory answer from my teachers, as they either admit they do not know, or treat it as a convention.

Is there a rationale for this definition? Thank you :)


texts: What pulls the electrons from iron in rust formation?

texts:
In the first step of formation of rust in iron, there is something that pulls electrons from the iron lattice, resulting in the formation of $\ce{Fe^{2+}}$. The reaction is:

$\ce{Fe  -> Fe^{2+} + 2e-}$

After that positive iron is repelled from the lattice, it is dissolved into water and a lot of reactions take place.

What is the thing that pulls the electrons from iron? (I guess it must be something positive, right?)


texts: Does the hybridization of sp3d2 type exist?

texts:
Is the hybridization of $\ce{XeOF4}$ $\mathrm{sp^2}$ rather than $\mathrm{sp^3d^2}$, because the latter type of hybridization does not exist?
Every answer in the Quora thread "How can we find the hybridization of $\ce{XeOF4}$?" concluded that the hybridization of $\ce{XeOF4}$ is $\mathrm{sp^3d^2}$. However, the very last answer posted by Steven Fawl, Professor of Chemistry at Napa Valley College (1985-present) reads: "Where to begin? Let me start here - every answer thus far is wrong! This molecule is not $\mathrm{sp^3d^2}$ hybridized. It is actually $\mathrm{sp^2}$ hybridized and I am going to prove it." The issue that I have with his post is that it only cites a couple of Wikipedia articles as his sources, and it contradicts every chemistry book that I have read by claiming that $\mathrm{sp^3d}$ and $\mathrm{sp^3d^2}$ hybridizations do not exist. The justification he gives for the latter is the following quote from this Wikipedia article:

In 1990, Magnusson published a seminal work definitively excluding the role of $\mathrm{d}$-orbital hybridization in bonding in hypervalent compounds of second-row (period 3) elements, ending a point of contention and confusion. Part of the confusion originates from the fact that $\mathrm{d}$-functions are essential in the basis sets used to describe these compounds (or else unreasonably high energies and distorted geometries result). Also, the contribution of the $\mathrm{d}$-function to the molecular wavefunction is large. These facts were incorrectly interpreted to mean that $\mathrm{d}$-orbitals must be involved in bonding (Ref.1 and Ref.2).
For transition metal centers, the $\mathrm{d}$ and $\mathrm{p}$ orbitals are the primary valence orbitals, which are only weakly supplemented by the $\mathrm{p}$ orbitals (Ref.3). The question of whether the $\mathrm{p}$ orbitals actually participate in bonding has not been definitively resolved, but all studies indicate they play a minor role.

Indeed, the abstract of Ref.2 states that:

No evidence is found to support the traditional notions of $\mathrm{sp^md^n}$ hybridization.

But this article is not publicly available and it may not reflect the current scientific consensus. Making a long story short: Are the authors of Ref.2 and Steven Fawl correct? If so, is the bonding of every hypervalent molecule analogous to $\ce{XeOF4}$ (removing 1, 2 or 3 electrons from the valence shell of the central atom and $\mathrm{sp^n}$ hybridize it)?

References:

Eric Magnusson, "Hypercoordinate molecules of second-row elements: $\mathrm{d}$ functions or $\mathrm{d}$ orbitals?," J. Am. Chem. Soc. 1990, 112(22), 7940–7951 (https://doi.org/10.1021/ja00178a014).
David L. Cooper, Terry P. Cunningham, Joseph Gerratt, Peter B. Karadakov, Mario Raimondi, "Chemical Bonding to Hypercoordinate Second-Row Atoms: $\mathrm{d}$ Orbital Participation versus Democracy," J. Am. Chem. Soc. 1994, 116(10), 4414–4426 (https://doi.org/10.1021/ja00089a033).
Gernot Frenking, Sason Shaik (Eds), eds. "Chapter 7: Chemical bonding in Transition Metal Compounds," In The Chemical Bond: Chemical Bonding Across the Periodic Table; Wiley-VCH: Weinheim, Germany, 2014, pp. 175-218 (ISBN 978-3-527-33315-8).


texts: How does expansion of electron shells work?

texts:
How does it work? I've read that its about the similarity of the energy levels of $3d$ and $3p$, but shouldn't the electron shell $4s$ be filled before $3d$ if filled? So what is done with the $3d$?
I'd also like to know in what cases will atoms of elements expand their valence electrons? Which blocks or groups or periods do this?


texts: What does the phrase "reducing atmosphere" mean in quantitative terms?

texts:
There is a debate about "how reducing" the atmosphere of the early Earth was, and this question is my attempt to grasp toward an understanding of what that that phrase really means.  As a bit of context, the Miller–Urey experiment produces a wide variety of complex organic molecules, but people say it requires a very reducing atmosphere to work, and it's disputed whether the early Earth's atmosphere was reducing enough for analogous processes to occur. Ultimately I would like to understand what it is about reducing atmospheres that allows complex organic molecules to be created so easily, but the first step is to understand what it really means to say one mixture of gases is "more reducing" than another.

If anything can be more reducing than something else, it seems like $\ce{CH4}$ gas should be more reducing than $\ce{O2}$, so I'm trying to understand the extent to which this can be quantified. However, I'm currently self-learning chemistry, and I'm having difficulty seeing connections between some of the concepts. (So apologies in advance for the rambling nature of this question.)

It seemed like one place to start might be to draw the net reaction of methane oxidation:

Obviously, if you add up the total oxidation state of every atom, you get zero - the carbon gets oxidised, the oxygen gets reduced, and the hydrogen stays the same. This must always be the case for any reaction (right?) since electrons are conserved. At first this made me think that maybe you can't really say that one thing is objectively "more reducing" than another. Though of course you can still talk about its tendency to oxidise or reduce carbon, and maybe that's what people are talking about when they say an atmosphere is "reducing" or "oxidising".

But then I came across the concept of redox potential, which does seem to be about things being objectively more reducing or oxidising than others. The problem is, the discussions of the concept that I can find online seem to be in terms of electrons "being transferred" from one molecule to another. But in the reaction above, as far as I can see, electrons aren't being transferred from the $\ce{O2}$ to the $\ce{CH4}$ but instead both molecules are being destroyed and replaced with completely different ones. So I'm having trouble seeing whether, or how, the concept of redox potential can be applied in this case.

Given this confusion, I guess my specific questions are:

When people talk about an atmosphere being "more reducing" than another, are they referring to redox potential or something else, such as the degree to which the atmosphere reduces or oxidises carbon? If it's the latter, is it something that can be quantified, or is it more of a subjective judgement?; and
What is the relationship between the concepts of the redox potential of a substance on the one hand, and the oxidation states of atoms on the other? Can the concept of redox potential be applied to gases like $\ce{CH4}$ and $\ce{O2}$?


texts: Deriving an expression for dU as a function of V and T

texts:
I'm currently preparing for a physical chemistry exam tomorrow, and was given the following question for practice:

  Derive an expression for $\mathrm{d}U$ as a function of $\mathrm{d}V$ and $\mathrm{d}T$.

I'm confused as to whether they want me to derive the equation below:

$$ \mathrm{d}U=\left(\dfrac{\partial U}{\partial V}\right)_T \mathrm{d}V + \left(\dfrac{\partial U}{\partial T}\right)_V \mathrm{d}T $$

or this

$$ U = q + w $$

given an infinitesimal change

$$ \mathrm{d}U = \mathrm{d}q + \mathrm{d}w $$

where

$$ \mathrm{d}q = C\mathrm{d}T $$

and

$$ \mathrm{d}w = -p\mathrm{d}V $$

hence

$$ \mathrm{d}U = C\mathrm{d}T + -p\mathrm{d}V $$

Essentially, I need help interpreting the direction I should proceed, and advice regarding the correctness of my methods.


texts: Dynamic equilibrium - effect of adding inert gas

texts:
Well consider the reaction $A + B ⇌ C$
Adding inert gas to a container where this reaction is taking place will increase the pressure of the system. In accordance with Le Chatelier's Principle, the equilibrium should shift in the direction which opposes this change in pressure, i.e. in the direction where fewer number of molecules are created. In this specific reaction, it happens to be in the forward reaction. However, I have been taught that adding an inert gas at constant volume has no effect on the equilibrium. Why is this?


texts: Varying potential diffrence between two graphite strips in NaCl solution

texts:
I have two identical graphite strips of dimensions 3.5 cm by 1 cm. Both are 3/4 submerged in aqueous $\ce{NaCl}$ solution (0.34 mol/dm$^3$, 2% wt) separated by a distance of 7 cm. I have attached crocodile clips to each strip and a voltmeter is used to record the potential difference between the two graphite strips.

I have found that:

A. There is a potential difference that ranges between 1 mV and 100 mV; and

B. This potential difference can change quite dramatically within that range over time periods of an hour.

Does anyone know of any chemical or physical reason for these potential differences?


texts: Calculating self-diffusion coefficient from MSD programmatically

texts:
According to the Einstein relationship, the diffusion coefficient $D$ is
$$\lim _{t\rightarrow \infty} \frac{\langle \left(\mathbf{r}(t)-\mathbf{r}(0) \right) ^2\rangle}{6t} = D$$
I have run a MD simulation with $N$ particles, and I have a file which has the location of each particle at every time step.
If I want to calculate $D$, I would have to do the following:
$$\langle (\mathbf{r}(t)-\mathbf{r}(0))^2\rangle = \frac{1}{N} \sum _{i=1}^N (\mathbf{r}_i(t)-\mathbf{r}_i(0))^2$$
Divide the above by $6t$, then take the limit as $t$ goes to infinity - which in my case is the final time step of my simulation.
My questions:

Is this the right way of calculating MSD?
If it is the right way of doing this, and my system reaches equilibrium and doesn't diverge, as $t\rightarrow \infty$, shouldn't my diffusion coefficient always be $0$, because of that infinity in the denominator?


texts: Why are silicon analogs of alkenes or alkynes so difficult to make?

texts: We know that there are silicon analogs of alkanes, but according to Wikipedia, silicon analogs of alkenes or alkynes are virtually unknown. How come?


texts: Why is water's IR spectra indistinguishable from the IR spectra of a solution of glucose in water?

texts: Anhydrous glucose has an absorption spectra (glucose IR spectra) that is quite different from the spectra of water (Liq. water absorption spectra). However, when a solution of glucose is prepared in water, the absorption spectra is almost indistinguishable from the absorption spectra of water alone. Is this because glucose forms additional bonds when in water? Pointers to links that explain this in detail is also appreciated. Most links I searched on Google just stated this as an observation without explaining the underlying reason.


texts: Biphenyl has 12 π-electrons and according to Hückel’s rule, it should not be aromatic because $12 \neq 4n+2$, but it nevertheless is aromatic. Why is that so?


texts: Removing or hiding (white) magnesium carbonate residues on natural rock surfaces

texts:
As noted in this question, magnesium carbonate is often used by rock climbers to help mitigate the effect of sweating whilst climbing. While this is not a major issue on artificial walls, the residue left by climbers on natural rock is unsightly and has lead to climbing bans or adverse public perceptions.

The above picture shows a hand hold used by climbers (ca. 20cm wide) that is covered in a white residue from climbers chalk. Other likely components of this residue include salts from sweat, oils/lipids from the climbers skin, and skin particles. The rock feature is protected from the weather by the overhang above which has allowed the residue to build up over many years. Conscientious climbers attempt to brush off as much residue as possible (typically using a soft bristle brush to minimise damage to the rock substrate). Adding water to these residues makes them invisible but they reappear upon drying.

Can anyone suggest method(s) for effectively removing MgCO_3 residues from natural rock surfaces without significantly affecting the underlying rock substrate (typically, oxidised quartzite, granite, sandstone, or limestone)?

Alternatively, can anyone suggest a way to conceal with 'whiteness' of the residue (e.g via some staining process or a specific reaction) to reduce the visual impact?

Any method needs to be effectively non-toxic to prevent significant adverse impacts on the surrounding ecosystems.


texts:
According to the history section in Ethylene, it is written that:

the name ethylene was used in this sense as early as 1852

However, the earliest mention of it I could find was in 1859 (Wurtz, "Sur l'oxyde d'ethylene"; Comptus Rendus 48, p.101). I also found mentions of "ethylene" in 1862 (Wurtz, "[...]On oxide of ethylene, considered as a link between organic and mineral chemistry[...]"), and in 1878 (Frankland and Thorne, "[...]On the Luminosity of Benzol when burnt with non-luminous Combustible Gases[...]"). Can anyone find any earlier publications that mention "ethylene"?


texts: Which has higher priority according to Cahn-Ingold-Prelog priority rules, vinyl or secondary butyl?

texts:
According to my textbook, vinyl has higher priority than isopropyl, because an atom which is connected by a double bond can be treated as two identical atoms (one of them is just an imaginary atom).

How about vinyl and secondary butyl? Should the imaginary atom be treated as that nothing else is connected to it? Does secondary butyl have higher priority?


texts: The effect of NaCl on the ability of an acid to protonate benzoate

texts:
I've been doing several experiments using soda to quantify the amounts of caffeine and benzoate. Because of our methods of analysis, we had to decarbonate our soda. The experiment offered two ways for decarbonating the soda: shaking it or heating it. Then, to make sure all the benzoate in the soda is converted to benzoic acid, we add a small amount of $\ce{HCl}$ (to protonate it.)

Several years ago, I did a similar experiment to quantify the amount of caffeine. To decarbonate the soda, I added salt ($\ce{NaCl}$.)

I'm wondering if adding salt would be inappropriate in the more recent experiment. None of the lab procedures mention adding salt and, to me, this is the easiest way to decarbonate soda. Therefore, I'm thinking there may be a specific reason the salt method was left out of the procedure.

My thought is there could be some interaction between $\ce{Na+}$ and $\ce{Cl-}$ that could "neutralize" the $\ce{HCl}$ so to speak, making the protonation of benzoate less effective.

Perhaps it would make sodium benzoate instead of benzoic acid? Perhaps they just didn't think to add salt. Any thoughts on this?


texts:
Tin (II) chloride is white while tin(II) iodide is red. Why?

The answer given in my book says:

Bigger anion has higher polarizability; more polarization greater is the intensity of colour(valence shell electrons are loosely bound to the nucleus).

This answer doesn't seem to be very explanatory. Even google doesn't offer anything. It would be great if someone could explain it in a better way, focussing on the following two points:
Firstly, how does more polarization lead to greater intensity of colour?
Secondly, how is intensity anyways related to frequency of radiation?


texts: Determination of the integrated rate equation for a reaction

texts:
We were given this equation to determine its integrated rate equation:

$$\ce {A + B <=>[$k_1$][$k_2$] C +D ->[$k_3$] E + F}$$

We were given these assumptions to simplify the derivation:

$\displaystyle \frac{\mathrm d[\ce{A}]}{\mathrm dt} = \frac{\mathrm d[\ce{B}]}{\mathrm dt}$, and $\displaystyle \frac{\mathrm d[\ce{C}]}{\mathrm dt} = \frac{\mathrm d[\ce{D}]}{\mathrm dt}$
At any time, $[\ce{A}]=[\ce{B}]$, and $[\ce{C}]=[\ce{D}]$, and $[\ce{E}] = [\ce{A}]+[\ce{B}]$
$\ce{F}$ is continuously removed from the system such that $[\ce{F}] = 0$ at any given time

The answer given to us was:

$$\ln[\ce{A}] = \frac{1}{2} \ln \left( \frac{k_2+k_3}{k_1}\right) + \ln\left(\frac{[\ce{A}]_0}{2} + \frac{[\ce{B}]_0}{2} - 2 [\ce{A}]\right)$$

However, I refuse to believe that an integrated rate equation can be without the time variable. Our teacher argued that the time variable was removed by using steady state approximation, and that $\frac{\mathrm d[\ce{C}]}{\mathrm dt} =0$. However, I think there is something wrong with using the rate of formation of an intermediate in deriving the integrated rate equation for a certain reaction. Can anyone please help me?

Edit: Here is how our professor got the answer:

$$\begin{align}
\frac{\mathrm d[\ce{C}]}{\mathrm dt}=\frac{\mathrm d[\ce{D}]}{\mathrm dt} &= k_1[\ce{A}][\ce{B}] - k_2[\ce{C}][\ce{D}] - k_3[\ce{C}][\ce{D}] \\
\frac{\mathrm d[\ce{C}]}{dt} &= k_1[\ce{A}][\ce{B}] - (k_2 +k_3 )[\ce{C}][\ce{D}]
\end{align}$$

$\ce{A}$ and $\ce{B}$ are the only species initially present such that:

$$[\ce{A}]_0 + [\ce{B}]_0 = [\ce{A}] + [\ce{B}] + [\ce{C}] + [\ce{D}] + [\ce{E}] + [\ce{F}] $$

Since $[\ce{C}] = [\ce{D}]$ and $[\ce{A}] = [\ce{B}]$ and $[\ce{F}] = 0$ and $[\ce{E}] = [\ce{A}] + [\ce{B}]$,

$$\begin{align}
[\ce{A}]_0 + [\ce{B}]_0 &= 4[\ce{A}] + 2[\ce{C}] \\
[\ce{A}]_0 + [\ce{B}]_0 - 4[\ce{A}] &= 2[\ce{C}] \\
\frac{[\ce{A}]_0 + [\ce{B}]_0 - 4[\ce{A}]}{2} &= [\ce{C}]
\end{align}$$

$$\begin{align}
\frac{\mathrm d[\ce{C}]}{\mathrm dt} &= k_1[\ce{A}]^2 - (k_2 +k_3 )[\ce{C}]^2 \\
\frac{\mathrm d[\ce{C}]}{\mathrm dt} &= k_1[\ce{A}]^2 - (k_2 +k_3 )\left(\frac{[\ce{A}]_o}{2} + \frac{[\ce{B}]_0}{2} - 2[\ce{A}]\right)^2
\end{align}$$

By steady state approximation (SSA), $\frac{\mathrm d[\ce{C}]}{\mathrm dt} = 0$

$$\begin{align}
\frac{\mathrm d[\ce{C}]}{\mathrm dt} &= k_1[\ce{A}]^2 - (k_2 +k_3 )\left(\frac{[\ce{A}]_0}{2} + \frac{[\ce{B}]_0}{2} - 2[\ce{A}]\right)^2 = 0 \\
k_1[\ce{A}]^2 &= (k_2 +k_3)\left(\frac{[\ce{A}]_0}{2} + \frac{[\ce{B}]_0}{2} - 2[\ce{A}]\right)^2
\end{align}$$

Applying natural logarithms to both sides,

$$\begin{align}
2 \ln(k_1) + 2 \ln[\ce{A}] &= \ln(k_2 +k_3)+ 2\ln\left(\frac{[\ce{A}]_0}{2} + \frac{[\ce{B}]_0}{2} - 2[\ce{A}]\right) \\
2 \ln[\ce{A}] &= \ln(k_2 +k_3 ) - \ln(k_1)+ 2\ln\left(\frac{[\ce{A}]_0}{2} + \frac{[\ce{B}]_0}{2} - 2[\ce{A}]\right) \\
\ln[\ce{A}] &= \frac{1}{2}\ln\left(\frac{k_2 +k_3}{k_1}\right) + \ln\left(\frac{[\ce{A}]_0}{2} + \frac{[\ce{B}]_0}{2} - 2[\ce{A}]\right)
\end{align}$$

As you can see from the solution, he was able to eliminate time from the final equation by using the steady state approximation. Is this a valid move to get the integrated rate equation? Please help.


texts: Does 1-phenyl-1-keto-but-2-ene show positive iodoform test?

texts:
It is told often that only compounds having a methyl ketone and corresponding alcohols show positive iodoform test.

I tried to sketch a mechanism to show that 1-phenyl-1-keto-but-2-ene also gives iodoform test. However I haven't found any source that confirms that 1-phenyl-1-keto-but-2-ene shows iodoform test.
Please check if there is any mistake in the mechanism:

This mechanism is very similar to the classical iodoform reaction mechanism.


texts:
There is a rule stating that we shall add a strong acid to water, and not the other way because of safety; if we would add water to the acid, the reaction could be dangerous (boil).

What about adding strong bases and water? Which is the safer order to mix them?

I would like to know the safer addition orders, and the justification, for water+acid or water+base(?)/base+water(?). Thank you!


texts: Stereochemistry & mechanism of β-cyano enone methylation

texts:
I am helping a friend with some upper-level mechanism problems. We came across this one. This is my proposal. Do you agree/disagree? Thank you for any input.

Source question:


texts:
Not in an atomic aspect, I learned that fluorescence is the emission of light from substances until the source of light disappears (there is no emission in the dark), on the other hand, phosphorescence, due to a blocking of electrons on their way back to normal state, is the emission of light from substances even without any source (emission in the dark).

If it is so, then why do we call glowing objects in the dark as fluorescent?


texts:
Why does thionyl chloride $\ce{(SOCl2)}$ when it reacts with liquid ammonia form a trace of $\ce{S4N4}$. What is the mechanism of the reaction forming $\ce{S4N4}$.

See discussion of sulfur chemistry for details.


texts:
Why is propenoic acid more acidic than p-methoxybenzoic acid?

I looked online for their $\mathrm{p}K_\mathrm{a}$ values and found them to be $4.37$ and $4.25,$ respectively. The $\mathrm{p}K_\mathrm{a}$ of benzoic acid is $4.20.$ Why does the $\ce{-OMe}$ group make such a big effect on $\mathrm{p}K_\mathrm{a}?$


texts: In a galvanic cell why does using a more reactive metal increase the voltage?

texts:
As the title says, why does using magnesium produce a higher voltage compared to using zinc when reacting with iron? Im having trouble figuring out why the voltage changes.

magnesium+copper > zinc+copper in terms of voltage, why?

Any help is appreciated.


texts: Comparison between solubility of amines and alcohol

texts:
Why are alcohols more water soluble than amines for similar molecular weight.
I know this is a duplicate question . The reason i posted it again was that on the original question i posted my answer and requested others to correct me if i am wrong so that i could deeply understand the concept. So I am posting my answer here again please comment on it.


texts:
I understand that to create an enol, you simply eliminate a proton alpha to the relevant $\ce{C=O}$ and then tack the proton onto the $\ce{O}$ and there you have it — an alkene and an alcohol — or enol.

Given this, between pyruvate and lactate, which is more enolizable?

I'm thinking that pyruvate doesn't even have an enol tautomer … there are no protons alpha to a carbonyl group. Sure, there is the carboxylate group … but that doesn't have anything to do with keto-enol tautomerism (does it?)


texts: Explain why these ions are more strongly hydrated in an aqueous solution?

texts:
I've already answered this question. All I want to know is if my reasoning is correct.
Case 1:

$\ce{Rb+}$
$\ce{Na+} \leftarrow$ This ion is more strongly favored

Case 2:

$\ce{Mg^{2+}} \leftarrow$ This ion is more strongly favored
$\ce{Na+}$

Reasoning:
For the first case, my guess would have to be because the electrons are much closer to the center of the nucleus (the atomic radius of the atom is very small) and makes it much easier to interact the positive dipole end of the water molecule (the hydrogen molecules).
For the second case, the reason why the magnesium ion is more favored is because even though both ions have roughly the same molar mass, one is more positively charged than the other and thus is more likely to attract the negative dipole end of the water molecule (the oxygen molecule).
Is my reasoning justified or is there something in particular that I'm not paying attention to?


texts: How to find concentration of three species from given molar absorptivities

texts: If I am given the molar absorptivities of three species at a given wavelength, and I only have the concentration of one of those species, how can I determine the concentrations of each of the remaining two species? The distance light travels, the molar absorptivities and the amount of light absorbed are given.


texts: Does using same calibration curve for chemical analysis introduce correlation in sample error/uncertainty values?

texts:
I am using a hypothetical case to explain my question
Let us consider a chemical analysis method A (using a certain instrument), which is used to quantify the value of a particular species b. According the instrument manufacturer's notes, the instrument used needs to be calibrated once a month. I am analyzing several samples of b in the duration of a month, and using the same calibration curve to obtain the quantity of b along with the uncertainty bound for the value.
I want to understand the following,

If number of samples (over the period of a month) of b are using the same calibration curve to quantify it value, are their errors/uncertainties correlated (by any means, the calibration curve introduces it, however small it may be) ?
Additionally, method A has the ability to quantify several species (b, c, d,$\dots $), does errors/uncertainty of species from the same sample (containing different species like b, c,$\dots$) correlated in any way?
If there exists even a very small correlation, does it make sense to consider it for any further analysis?

I am new to the realm of chemistry (analytical chemistry to be precise), I request your help.
Thank you.
PS: Apologies if the tags are inaccurate


texts: Nature of the bonding in hexaaquaaluminium complex

texts:
$\ce {[Al(H2O)6]^3+}$ is a well-known complex ion formed by the $\ce {Al^3+}$. I have always had the understanding that only the aqua complexes of transition metal ions, such as $\ce {[Fe(H2O)6]^3+}$, would legitimately possess dative covalent bonding between the water ligands and the central metal ion. I had always thought that the primary reason for this is that ions such as $\ce {Mg^2+}$ and $\ce {Al^3+}$ lack vacant low-lying orbitals for them to be able to accept electrons donated from the ligands.

However, after further thinking on the issue, it seems quite ridiculous to say that there are no low-lying vacant orbitals on $\ce {Al^3+}$. For example, $\ce {AlCl3}$ is a fairly good Lewis acid and is able to accept dative covalent bonds from various Lewis bases. If the $\ce {3p}$ orbital in the $\ce {Al}$ atom in $\ce {AlCl3}$ is of sufficiently low energy to accept electron donation, then clearly, the $\ce {3p}$ orbital in $\ce {Al^3+}$ would certainly be energetically accessible as well since the large magnitude of positive charge on the ion would lower the oribtal energies greatly.

The answer in this post posits that the interaction between $\ce {Na+}$ and water ligands is mostly of the electrostatic nature while there is much more covalent involvement in the complexes of the transition metal ions. However, no reasons were given as to why this was so. Perhaps, someone with expert knowledge in this area of chemical bonding would like to enlighten me on this issue.

I have also read up some literature on the aqua complexes of alkali metal ions, which have been studied in great detail due to their biochemical significance. Talekar (1975) informs that the bonding between alkali metal ions and water ligands is approximately $\ce {20}$% covalent and $\ce {80}$% ionic and he further adds that the covalent component is due to donation of electrons into vacant orbitals on the alkali metal ions. However, the computational methods used at the time to compute these data may have been quite limited and thus, it may be unreliable.

Reference

Talekar, S. V. The nature of metal-ligand bonding in the primary hydration shell and in ionophores with alkali metal ions. Biochimi. Biophys. Acta 1975, 375, 157-164.


texts: If you put a paper inside an oven vacuum packed and go beyond $250~\mathrm{^\circ C}$, will it burn? There's no oxidizer. If not, what will happen?


texts: Do polyfluorosulfuric acids like H2SO2F4 exist?

texts:
I was thinking about a compound resembling $\ce{H2SO4}$ but more acidic. I thought to replace the 2 oxygens with 4 fluorine atoms getting $\ce{H2SO2F4}$, which might be more acidic. Does such a compound even exist?

I also tried searching another compound i.e. $\ce{HOSF5}$ thinking of it to be more acidic than the previous but no results.


texts: Is it true that allylic free radical is more stable than allylic carbocation?

texts: I have been studying reaction mechanisms involving allyl groups and it seems that the chances of forming of an allylic free radical are higher than forming a carbocation, I know that these things might be specific to reaction occurring, so I just wanted to find if there is any such relation between stabilities of radicals and cations.


texts: How to figure out which substance has the highest osmotic pressure?

texts:
In preparing for an exam and I'm trying to solve the following question. I'm clueless. What should I do?

  Which of the following water solutions has the highest osmotic pressure?

  \begin{align}
\tag1 \pu{0.1 mol/kg} &~ \ce{NaCl}\\
\tag2 \pu{0.1 mol/kg} &~ \ce{KF}\\
\tag3 \pu{0.1 mol/kg} &~ \text{sucrose}\\
\tag4 \pu{0.1 mol/kg} &~ \ce{MgCl2}
\end{align}


texts:
Why is this reaction successful:

Why doesn't metal-halide exchange occur easily to get Ar-MgCl and R-Br?


texts: Visualizing PDB file in VMD, how to upload molecules?

texts:
Problem: When I load PDB-file of my protein of interest in VMD, nothing happens. The molecules is uploaded, but when I push "D" the screens with with big "VMD" letter freezes instead of presenting the structure of the protein in the PDB file. This is what is looks like:

Any Ideas what causes this? Should the PDB file be in a specific folder? I am a complete novice at this, so I wont understand very complicated answers.

I have downloaded the mac version of VMD version 1.9.2, I have Mac OS X version 10.11.2.  Here is the PDB file that I want to open.


texts: Does the explosion of TNT include oxidation?

texts:
This comment below the question Rocket explosion compared to kT of TNT; has one ever knocked something over at a distance? suggests that

  ...TNT includes it's own oxidizer...

Explosion isn't the same as combustion and you don't need to add a separate oxidizer to an explosive for it to do its thing.

But technically speaking does the explosion of TNT include any steps that could be considered as oxidative? Can some intermediate products be considered to be acting as oxidizers?


texts:
Amongst all hydroxybenzoic acids the ortho isomer is most acidic and the major reason is intramolecular H-bonding in the anion.

My question is that isn't the loss of proton destabilising the molecule more than stabilising it as earlier two H-bonds were possible but after deprotonation only one bond remains??


texts: Is the 9H-fluoren-9-ylium cation aromatic?

texts: In this cation, there are two individual benzene rings which are aromatic. But in the entire π system, there are 12 π-electrons which should make it antiromatic. Which is correct?


texts: UV-Vis absorbtion spectra of a radical cation/anion. Is it different compared to its even counterpart?

texts: I am studying gas-phase Uv-Vis spectra of radical molecules. If one electron is removed/captured from the neutral even electron molecule, what can I expect from the absorption spectra? Will new peaks appear? Will they be blue/red-shifted?


texts: What are the meanings of dotted and wavy lines in structural formulas?

texts:
So I came across this diagram,the other day:

As  a chemistry student, I am well-versed with the dashed and wedged lines, but I was wondering what the wavy and the dotted line represent?


texts:
I can't make heads or tails of the information on the net — although there seems to be plenty of it, it seems contradictory.

Supposedly, calcium carbonate is used in antacids—yet there are warnings about ingestion and contact with skin.

I need to handle it in pure powder form. I'm mainly concerned about skin contact, should it be avoided? (Am I getting confused between two or more forms of calcium carbonate?


texts: How do I chill water without a refrigerator?

texts:
How can we chill water in a plastic bottle without a freezer or refrigerator?

Scenario:

I'm in the office and I have two plastic bottles of water (brought from home). I'm in the office for 3 to 4 hours and this means the bottles I brought from home will get hot (and won't be drinkable in a hot season). Now I want to make it cool so that I can drink chilled water, without access to ice with salt or a refrigerator.

Is it possible?


texts:
For context, I am a potter and am interested in collecting and processing all materials that I use by myself. One of the processes which I use is calcination of certain minerals like feldspar, so that I can turn them into fine powder.
For reference, most feldspars are mixtures of the three chemicals: $\ce{KAlSi3O8,\ NaAlSi3O8,}$ and $\ce{CaAl2Si2O8}$. I usually collect pieces of granite which have a high feldspar content. I then put the granite into my electric (oxidation) kiln and fire it above $\pu{1000 ^\circ C}$. After it has been calcined, the granite falls apart very easily, with the exception of the pieces of quartz which remain quite hard. I am then able to crush the feldspar up into a fine powder.
I gather that the heat does something to the feldspar which makes it crumble easily but chemically speaking I don't know what this involves. Does the chemical formula of the feldspar change? Does it just break down in some way?


texts: Why does a spur of ice sometimes appear when freezing water in my freezer

texts:
From time to time, a long spur of ice grows on one “cube” of my ice cube tray.
It’s quite slender, about 3mm or 1/8 inch at the base tapering to about 1mm at the tip, but it’s about 30mm or over 1 inch long!

The angle of the spur seems to always be the same - about 45 degrees.
What going on here? It seems to defy gravity!
Probably relevant: I seems to happen when the ice tray is placed near the chilled air outlet of the freezer.
Plain tap water.


texts:
I'm curious how to test purity of isopropyl alcohol? I simply got very curious today. I bought rubbing alcohol and it doesn't say what's the purity anywhere. It could be 70%, but it could also be 90%, or 99% or even 99.9%. I'm a curious man so I started googling but couldn't find anything.

If I were a chemist, how would I test the purity?


texts: Deciding more electrophilic centre between ester and thioester for SN type reaction

texts:
My question: (though it won't alter the product)

  Which carbon is attacked first, the one adjacent to sulphur or the one adjacent to oxygen?

The solution says that the carbon adjacent to sulphur is attacked first. I don't understand why.

According to me, sulphur is less electron withdrawing than oxygen (electronegativity decreases down the group), so the carbon adjacent to oxygen must be more electrophilic.

Could someone please explain as to why attack should first occur at the carbon adjacent to the sulphur atom? (or is the solution incorrect?)

P.S. Here, due to syn stereochemistry (NGP is not favourable) choice of electrophilic centre undergoing attack first doesn't influence the product at all. However, in the case where the sulphur and oxygen atoms are anti with respect to the ring, and NGP is a possibility, and then the products would greatly differ (depending on whether attack first happens on carbon adjacent to oxygen or sulphur)

Source: MS Chouhan; Advanced Problems In Organic Chemistry; 11th ed; Q35 in Chapter Alcohols, Ether, and Epoxides


texts: Rocket propellants: accuracy of vapor pressure estimation techniques

texts:
I would like to determine the vapore pressures of a couple of substances (rocket propellants) over a significant temperature
range within a ~10% error margin.

For a first test, I tried to approximate the vapor pressure curve of Dinitrogen Tetroxide (N2O4) via the Clausius-Clapeyron (CC) relation, the Lee-Kesler (LK) method and the Ambrose-Walton (AW) method and compare the results to each other and to literature values that are available for N2O4.
Unfortunately my results deviate alot (up to 60%) from the published values.

Attached you find a plot of my attempts and a small table that compares the different methods and their deviation from the literature values.
Don't let the first picture mislead you! As the table and the detailview show, even at low pressures/temperatures the deviation is quite significant!

Is this large error margin really within usual boundaries? What are your experiences with vapor pressure approximation? Could you provide some tips on how to improve my results?

Some Details on my approach

Clausius-Clapeyron:

I chose the boiling temperature at atmospheric pressure as input, but I have no idea which value to
choose for the enthalpy of vaporisation. Many source state the assumption of a constant enthalpy,
but that puzzles me, since for N2O4 it varies by some 16kJ/mol over the temperature range I'm interested in.

Which value is usually taken - the enthalpy corresponding to the values provided as input or the one for the target temperature?

Lee-Kesler / Ambrose-Walton:

As expected both methods produce very similar results and are convenient to use, since they only
rely on the critical pressure, critical temperature and the acentric factor. But MY results are really
disappointing, especially since Wikipedia promises a maximal deviation of 10%.

As a side note:

For different reasons, I don't want to use interpolation of substance specific vapor pressure tables,
but instead I would like to use one of the many vapor pressure equations. It is important that the
approximation results in a closed representation of the vapor pressure curve , therefore I would like
to avoid methods that have points of discontinuity (e.g. Antoine equation?). Since I don't have access
to public databases that cover the substances I'm interested in, approximations that rely on "exotic"
empirical parameters (Wagner, DIPPR, etc.) are also out of the question.


texts: Trouble understanding equation from density functional theory

texts:
In the review by Oliviera et. al., I do not understand how the authors get equation 14:
\begin{equation}
E[\rho]=\sum_i^Mn_i\langle\Psi_i|-\frac{1}{2}\nabla^2+v_{ext}(\vec{r})+\frac{1}{2}\int\frac{\rho(\vec{r'})}{|\vec{r}-\vec{r'}|}|\Psi_i\rangle+E_{xc}+\frac{1}{2}\sum_\beta^N\sum_{\beta\neq\alpha}^N\frac{Z_\alpha Z_\beta}{|\vec{R_\alpha}-\vec{R_\beta}|}\tag{14.}
\end{equation}
 To me the energy should be in this form:

$$E = \langle\psi|T + V_\mathrm{ext} + V_\mathrm{ee}|\psi\rangle$$

How did they manage to put some of term out of the bracket? I also have trouble retrieving (16) as they cite, are they using a Taylor expansion?

References:

Oliveira, A. F.; Seifert, G.; Heine, T.; Duarte, H. A. Density-functional based tight-binding: an approximate DFT method. J. Braz. Chem. Soc. 2009, 20 (7), 1193–1205. DOI: 10.1590/S0103-50532009000700002.


texts: How to determine concentration limits of a buffer that's limited by solubility?

texts:
I need to maintain a certain range of % of ionisation from a buffer.

For e.g. Histidine buffer. When making high concentration of this buffer at (say) pH 7.2, 25'C, [concentration] is limited to 75mM solution (250mL), due to the solubility. Adding HCl increases solubility just as much, but it also decreases pH of the solution.

I want to know if there's a calculation or a formula to figure out the concentration limits (at least the highest concentration) of a particular buffer one can plan to make instead of trial and error in the lab?


texts: How do derive the equation for relative velocity of gas molecules

texts:
The relative velocity is $$v_{rel}=\sqrt2v_{mean}$$ where $v_{mean}=(\frac{8KT}{\pi m})^{\frac12}$$$v_{rel}=(\frac{16KT}{\pi \frac m2})^{\frac12}$$ because the reduced mass of two of the same particles is half the mass of one. In general: $$v_{rel}=(\frac{8KT}{\pi \mu})^{\frac12}$$

However, my question is: what is the need for reduced mass? If $v_{rel}=\sqrt2v_{mean}$ where $v_{mean}=(\frac{8KT}{\pi m})^{\frac12}$. Wouldn't that just leave you with: $v_{mean}=(\frac{16KT}{\pi m})^{\frac12}$ Where does reduced mass come into it?


texts: Electroplating an alloy from separate metal solutions

texts:
Similarly to a question asked here, would mixing two solutions containing metallic ions in different proportions allow to electroplate something with the alloy of the metals? For example if I take a $\ce{CuSO4}$ solution and mix it with a $\ce{ZnSO4}$ solution, will I be able to electroplate brass? If I want to make 70/30 brass, would mixing a 0.7 mol/L and 0.3 mol/L solution work?

I know a "brass" solution can be made by reverse electroplating (is that the term?) a brass anode in an acid solution so mixing two solutions should have the same result, copper and zinc ions in a solution.


texts: Product of reaction between aluminium chloride and trimethylamine

texts: Can anyone tell the product of the reaction between $\ce{AlCl3}$ (aluminium chloride) and $\ce{N(CH3)3}$ (trimethylamine)?


texts: Why is Red Phosphorous used in the Nagai Method?

texts:
The most common method of producing Dextromethamphetamine (Crystal Meth) is supposedly the Nagai Method, where Pseudoephedrine, Hydriodic acid and Red Phosphorous are refluxed overnight, producing a mixture of Dextromethamphetamine, water and Red Phosphorous which may be reused.

The thing is, I don't quite understand how the Red Phosphorous ends up in the mixture as though it were acting as a catalyst.

The best mechanism I could think up was the following:

Pseudoephedrine + Hydriodic acid --> Iodoephedrine + Water
Iodoephedrine + Hydriodic acid --> Methamphetamine + Iodine

Using no Red Phosphorous at all.

The only use of Red Phosphorous I can see here would be to convert the Iodine back to Hydriodic acid, which would give Phosphoric acid as a byproduct, not Red Phosphorous.

What exactly is the Red Phosphorous supposed to be doing here?

EDIT: I notice that this question is very similar to mine, however whilst the answer to that question does address the use of the Red Phosphorous (Phosphoric acid is produced as I had assumed), it unfortunately doesn't explain how it ends up back as Red Phosphorous in the end.

Disclaimer: I am merely interested from a theoretical standpoint and have no intention of making Dextromethamphetamine. Just saying.


texts: In which country is it allowed to practice non-clandestine amateur chemistry?

texts:
I travel a bit so am flexible where I live, and have taken a recent interest in chemistry to try to gain an understanding of physical reality. I find learning from textbooks to be good, but want to have the comfort of applying a lot of this knowledge in my own lab. To see and feel how it works first hand. From my understanding, the west has a huge paranoia with clandestine chemistry, which is of no interest to me. However, it seems a vast quantity of common reagents and catalysts in organic chemistry books are banned in western countries due to this.

Would someone know how it's possible to practice amateur chemistry from home, without fear of accidentally breaking the law by using some reagent I'm not supposed to? And if not, what would be the best way to gain hands-on experience like this, where I can have complete freedom to experiment with what I want to do? I find at university I'm limited to lab sessions, and if one day I gain employment with a lab I'd no doubt not be free to conduct my own experiments. I wish to emphasize, I'm financially independent from my chemical studies, so purchasing the equipment isn't the issue. It's the legality I'm concerned about.

Is there an option to do this, to pursue amateur knowledge in chemistry, or is it illegal? Is there a country in which it isn't illegal?


texts: How to separate HCl and NaOH from an aqueous solution of NaCl?

texts:
At home I make experiments on salt (as it is easily available at home).
One day I came to know that on mixing salt and water I will get Hydrochloric Acid and Sodium Hydroxide. So I became really excited, but my excitement broke into small pieces because I don't know how to separate $\ce{HCl}$ and $\ce{NaOH}$ from the solution of $\ce{NaCl}$ and water.


texts: Why are the melting points of Sb and Bi lower than that of As?

texts: My book says it has something to do with the inert pair effect. And unlike As, Sb and Bi tend to form 3 covalent bonds rather than 5. I don't understand what's really going on here.


texts: Is the neutral di-µ-oxo-bridged manganese dimer with eight ammonia ligands a reasonable structure?

texts:
In its guide to model antiferromagnetic couplig, Gaussian uses $\ce{Mn2O2(NH3)8}$ as a model compound.[1] It argues that manganese is in II oxidation high spin state; in other words, in both manganese are all d orbitals are singly occupied. Furthermore it creates a structure, where the metal centres are octahedral coordinated. The level of theory used is U-B3LYP/3-21G, which is in my opinion not enough to discuss these complexes in the first case.

I could not find any evidence of a structure proposed by Gaussian, the closest I have gotten is given as a cation $\ce{[Mn2O2(NH3)8]^z+}, (z\in2,3,4)$.[2]

I have reason to doubt the structure given in the tutorial,[3] as in the $\frac{5}{2}$ high spin case there are only four orbitals in manganese left which could accept bonding partners. Given that two of them are used by the bridging oxo ligands, only two ammonia should bond to the manganese centres. This would lead to the formula $\ce{Mn2O2(NH3)4}$. The situation changes once you start removing electrons or pair them up. Then the question changes to whether ammonia is a strong enough ligand to induce lower spin states.

Summarising: Is $\ce{Mn2O2(NH3)8}$ a reasonable structure?

For convenience, here is the structure as proposed by Gaussian (they do create a different one within the tutorial though):

References & Notes:

Gaussian Website: http://gaussian.com/afc/
Mcgrady, J. E.; Stranger, R. Redox-Induced Changes in the Geometry and Electronic Structure of Di-μ-oxo-Bridged Manganese Dimers. J. Am. Chem. Soc. 1997, 119 (36), 8512–8522 DOI: 10.1021/ja964360r.
In my optimisations on a different level of theory I was unable to reproduce the structure.


texts: Where does computational chemistry overlap with organic chemistry?

texts:
I was wondering what research exists that combines computational chemistry and organic chemistry.

For the past three years, I've been using Amber and Gaussian (in hopes) to identify and understand trends in intramolecular interactions. This really just serves as an example of my past research which incorporated both physical chemistry and computational chemistry.

I would like to know what kind of research could be done that combines both organic chemistry with computational chemistry.

I've Googled computational research in organic chemistry, but haven't found much information. What are some examples of projects that have been done in organic chemistry that rely heavily on the computational side of things?


texts: What are the compounds in oxygen and carbon dioxide indicator solutions that gives their color?

texts:
My brother had some leftover oxygen and carbon dioxide indicator solution for one of his take-home experiments from school, so he let me have them. I want to use them for an experiment and write out some reactions, but I don't know what compound is in the indicators that gives them their color.
The oxygen indicator is green and comes with a color chart which says the following in regards to concentration of oxygen: 2ppm is red, 4ppm is purple, 6ppm is yellow, 8ppm is light green, 10ppm is dark green/teal, and 12ppm is either very dark green/blue or black.
The carbon dioxide indicator is orange and comes with a color chart saying low CO2 concentration gives a red color, medium is orange, and high is yellow.
A few websites said that you could make a bicarbonate indicator with thymol blue and cresol red, but I don't know how that makes sense if the color chart only ranges from red to yellow. As for the oxygen indicator, I have no idea what the compound(s) can be.
Thanks in advance!


texts:
Can two atoms with the same amount of electrons but differing electronic configurations be considered isoelectronic?

For example, would we consider yttrium(I) $(\ce{Y+})$ with configuration: $\ce{[Kr] 5s^1 4d^1}$ and strontium $(\ce{Sr^0})$ with the configuration $\ce{[Kr] 5s^2}$ to be isoelectronic?


texts: What makes wrinkle-free cotton, wrinkle-free?

texts:
Disclaimer:

No, I don't own any "wrinkle-free" articles of clothing. So I haven't been able to observe first-hand if "wrinkle-free" clothing is totally "wrinkle- free" (if it isn't, then perhaps "wrinkle-resistant" might be an appropriate term?).

Back to question:

At the molecular level, what is it that makes cotton "wrinkle-free"? What chemo-physical process(es) is cotton subjected to, here?

I ran a cursory Google-search, and this was the best article that I could find, albeit, it's sorely lacking in information on the actual processes involved in the production of "wrinkle-free" cotton.


texts: E2 Elimination; Anti-periplanar beta hydrogen

texts:
I'm confused by this picture I found on masterorganicchemistry.com—a very popular organic chemistry website:

I agree that the product is a product.

However, can't there be another product? Specifically, can't the methyl group by the bromine have an anti and beta hydrogen relative to the bromine?

So shouldn't there be two products?

Specifically, this one?


texts:
The recent Chemical & Engineering News article Photocatalyst shreds drinking water contaminant PFOA report the following:

Cates and his colleagues made an accidental breakthrough while testing the photocatalyst bismuth phosphate. After finding that it could break down PFOA as effectively as a previously reported photocatalyst, gallium oxide, they tried to improve its performance by varying the pH of the reaction used to make the catalyst particles. The researchers had hoped this would change the particles’ size and shape, but the process inadvertently produced bismuth oxyhydroxyphosphate (BOHP). This new catalyst has the highest photocatalytic activity for PFOA degradation ever reported.
In lab tests under UV light, BOHP degraded all the PFOA in a 130 μM solution in about an hour, roughly 15 times faster than did bismuth phosphate or gallium oxide. BOHP performed almost as well over five repetitions of the experiment, suggesting it can be reused. To simulate PFOA-contaminated groundwater, the researchers then tested a more dilute solution of 1.2 μM PFOA accompanied by 500 μg dissolved organic carbon/L. In this case, the photocatalyst also degraded all the PFOA, though it took two hours. Strathmann calls it a “promising development” that advances the application of photocatalytic treatment of PFOA.

It also includes this SEM image of microcrystals of the "inadvertently produced bismuth oxyhydroxyphosphate (BOHP)."

The accidentally synthesized BOHP (shown) can break down the toxic industrial contaminant PFOA faster than any other photocatalyst. Credit: Environ. Sci. Technol. Lett.

A quick check with google doesn't send me to the materials Wikipedia page, and I'm wondering if that is because this is an unusual substance or the crystal structure hasn't been solved yet.
Question: What is the crystal structure of bismuth oxyhydroxyphosphate (BOHP)?


texts: Why did the red colour in a flame test for strontium disappear and appear again on longer heating?

texts:
We did a basic flame test, and I understand that different salts produce different spectra because of atoms present in the salts.

When I was doing the test, I noticed that when I dipped the nichrome wire into the solution of $\ce{SrCl2}$ and placed it on the tip of the flame, I got the expected red color. However, what would happen is I would get the red color, and then it would disappear, going back to the typical bluish flame, the nichrome would glow orange hot, and the red colored flame would return.

Essentially, the red color appears, disappears, and then reappears. I thought that it might be "wicking" the strontium chloride from another part of the dipstick, but I was careful to only submerge a small part in the solution.

What's happening here?


texts:
My textbook as well as Wikipedia both state the formula $\mu_A = \mu_A^0 + RT\ln\{A\}$ which gives the chemical potential $\mu_A$ of a chemical species $A$ as function of the standard chemical potential $\mu_A^0$ and the activity (relative to standard conditions) $\{A\}$.

This formula can also be used to derive the Gibbs free energy formula as $\Delta_rG_{T, p} = \Delta_rG_{T, p}^0 + RT \ln Q_r$ where $Q_r$ is the reaction coefficient.

Both formulas appear to be widely used in chemistry, but I have not found a decent explanation for why they are correct. The texts I have seen did not provide sources for the claim and omitted explanation.

Is this an empirical formula, or is it a consequence of statistical mechanics? I would like to find a source with a clear proof or explanation for the origin of this equation. I know that some will define the activity precisely using this equation, but then the question becomes why the activity so-defined corresponds to concentration for ideal solutions. That is, why in an ideal solution, we have $\mu_A = \mu_A^0 + RT\ln c_A$ where $c_A$ is concentration of $A$ relative to standard concentration.


texts: Hybridization of orbitals and forming of bonds in the nitrogen dioxide molecule

texts:
I considered the nitrogen atom hybridizing its orbitals and then ending up having 3 $\mathrm{sp^2}$ orbitals and the oxygen with 2 $\mathrm{sp}$ orbitals. The thing which bothers me is when people draw a radical (single electron) over the Nitrogen atom after there is the bond formation between nitrogen and 2 oxygen atoms.
Let us consider the Nitrogen, it has one full $\mathrm{p}$ orbital (AKA lone pair) and 3 single electrons in 3 $\mathrm{sp^2}$ orbitals, so that means that it can form 3 bonds – first it bonds with one oxygen forming a σ bond, leaving the nitrogen with 2 electrons, now the nitrogen forms one π bond with the same oxygen and the remaining single electron forms another σ bond with another oxygen atom.
Where is the single radical on the nitrogen after all the bonding has taken place?

Moreover, as in the above picture, people draw the other oxygen (the one that did not form a π bond with nitrogen) as having 3 lone pairs, whereas, after the hybridization of the oxygen atom, I can only see it having 2 lone pairs in 2 $\mathrm{p}$ orbitals.
What is actually correct? Am I going wrong somewhere?


texts:
From Klein's Organic chemistry [1, p. 780]:

The 1,2-adduct is believed to form more rapidly as a result of a proximity effect. Specifically, the carbocation and the bromide ion are initially very close to each other immediately after their formation in the first step of the mechanism. The bromide ion is simply closer in proximity to C2 than C4, so attack at C2 occurs more rapidly.

Similarly, from Vollhardt's Organic Chemistry: Structure and Function [2, pp. 345–346]:

Ring size controls the speed of cyclic ether formation
A comparison of the relative rates of cyclic ether formation reveals a surprising fact: Three-membered rings form quickly, about as fast as five-membered rings. Six-membered ring systems, four-membered rings, and the larger oxacycloalkanes are generated more slowly.
Relative Rates of Cyclic Ether Formation
$$k_3 ≥ k_5 > k_6 > k_4 ≥ k_7 > k_8$$
$k_n =$ reaction rate, $n =$ ring size
[…]
A second enthalpic phenomenon, which has been called the proximity effect, operates, especially in 2-haloalkoxides.

The proximity effect was used to explain these two reactions. Is it applicable to every reaction?
What is the proximity effect?
References

Klein, D. R. Organic Chemistry, 1st ed.; John Wiley: Hoboken, NJ, 2012. ISBN 978-0-471-75614-9.
Vollhardt, K. P. C.; Schore, N. E. Organic Chemistry: Structure and Function, 7th ed.; W. H. Freeman: New York, 2014. ISBN 978-1-4641-2027-5.


texts: What is the percent of potassium as K₂O in the fertilizer sample?

texts:
The solubility of sodium tetraphenylborate in water is $\pu{470 g/L}$ while the solubility of potassium tetraphenylborate in water is $\pu{1.8e–4 g/L}$.  Due to the orders of magnitude difference in aqueous solubility, $\ce{NaB(C6H5)4}$ is used to gravimetrically analyze the potassium content of fertilizer:
$$\ce{K+(aq) + NaB(C6H5)4(aq) -> KB(C6H5)4(s) + Na+(aq)}$$
The water soluble components of a $\pu{10.7875 g}$ sample of 15-25-15 fertilizer were separated from the water insoluble components using vacuum filtration.  The filtrate was treated with an excess of $\ce{NaB(C6H5)4}$ and the resulting solid was isolated, dried, and the mass of the solid was determined.  Potassium tetraphenylborate $(\pu{12.4393 g})$ was recovered from the gravimetric analysis of $\pu{10.7875 g}$ fertilizer.
What is the percent of potassium as $\ce{K2O}$ in the fertilizer sample?

I know how to get to the answer; I am just unsure how to use the solubility that was given to get there. I also am not sure why the resulting dried mass is higher than the initial mass of fertilizer:
$$\ce{K+(aq) + \underset{\pu{10.7875 g}}{NaB(C6H5)4(aq)} -> \underset{\pu{12.4393 g}}{KB(C6H5)4(s)} + Na+(aq)}$$
$$M(\ce{NaB(C6H5)4}) = \pu{342.22 g mol-1}$$
$$M(\ce{KB(C6H5)4}) = \pu{358.35 g mol-1}$$
$$\pu{12.4393 g~\ce{KB(C6H5)4}}\cdot\frac{\pu{1 mol}}{\pu{342.22 g}}\cdot\frac{\pu{1 mol}~\ce{K}}{\pu{1 mol}~\ce{KB(C6H5)4}}\cdot\frac{\pu{1 mol}~\ce{K2O}}{\pu{2 mol}~\ce{K}}\cdot\frac{\pu{94.2 g}~\ce{K2O}}{\pu{1 mol}~\ce{K2O}} = \pu{1.712 g}~\ce{K2O}$$
$$1~\text{mass} = \frac{\pu{1.71 g}~\ce{K2O}}{\pu{10.7875 g}}\cdot 100\% = 15.9\%$$


texts: Is there a particular definition for the partial derivative of internal energy with respect to volume at constant temperature?

texts:
If we have specific internal energy $u=u(T,v)$ then the total differential of $u$ is given by
$$du(T,v)=\left ( \frac{\partial u}{\partial T} \right )_vdT+\left ( \frac{\partial u}{\partial v} \right )_{T}dv$$
where
$$c_v\equiv \left (\frac{\partial u}{\partial T}  \right )_v$$
Is there any particular usage of $\left ( \frac{\partial u}{\partial v} \right )_{T}$? I know it can be expressed in the following form:
$$\left ( \frac{\partial u}{\partial v} \right )_T=T\left ( \frac{\partial p}{\partial T} \right )_v-p$$
I understand what it "means", but I don't know if it has a particular meaning that is significant.


texts: Will ice be cold or not when formed using pressure?

texts:
We know that ice can be formed either by lowering the temperature of water or by applying more pressure. If we lower the temperature of water the ice so formed will be cool which is obvious.

If ice is created by applying pressure, will it be cold as well?


texts: Is it possible, chemically, to change a dextrorotatory compound to its levorotatory counterpart? E.g., is it possible to change dextrodopa to levodopa?


texts: What does the eta notation mean in the naming of a transition metal complex?

texts:
I am reading a paper (Gutel et al., J. Mater. Chem. 2007, 17, 3290-3292) and I have come across the following reaction:

  In organic solvents, the decomposition under mild conditions of
  ($\eta^4$-1,5-cyclooctadiene)($\eta^6$-1,3,5-cyclooctatriene)ruthenium(0),
  Ru(COD)(COT), under a dihydrogen atmosphere gives ruthenium
  nanoparticles (RuNPs), by releasing cyclooctane (COA).

  $$\text{Ru(COD)(COT)} + \text{H}_2 \rightarrow \text{RuNPs} + \text{COA}$$

What do the $\eta^4$ and $\eta^6$ notations represent?  Do they somehow specify the coordination "connectivity" of the Ru(0) and the COD and COT coordinating ligands?

Below, I have drawn the (two-dimensional) structures of COD and COT.  How would I draw the connectivity of Ru(COD)(COT), or is it not specified in the given name?


texts: Syntax and Typography of Atomic Orbitals

texts:
For mhchem (i.e. the \ce command you use here), I want to improve the support for atomic orbitals. (Reason: I see it quite often used here.) But only a few things about orbitals are mentioned in IUPAC documents. Many more seem to be "unwritten law".
As I am not a chemist I need your help.

1

The Green Book p. 32 defines the letters s, p, d, f, g, h, i, k ... (omitting j). They have to be typeset upright.

Question a: How far does this "alphabet" reasonably go? (Wikipedia goes up to i).

2

On the same Greek Book page, electron configurations are explained, e.g. $\mathrm{(1s)^2 (2s)^2 (2p)^1}$.

Many other sources write it without parenthesis: $\mathrm{[Kr]\mskip2mu4d^{10}\mskip2mu5s^1\mskip2mu5p^3\mskip2mu5d^4}$

Question a: What values can the left-side number take? (At Wikipedia, I see 1 to 7.) Can it be 2-digit?

Question b: What values can the right-side exponent take? (At Wikipedia, I see 1 to 10.)

3

I think I did not come across the configuration with one-electron orbitals (in Greek). $\mathrm{(1\sigma)^2 (2\sigma)^2 (3\sigma)^2 (1\pi)^1}$. (The Greek letters should be upright, but that's a drawback of MathJax.)

Would this be useful? Or not needed?

4

The examples introduce another notation, "electronic states"  $\mathrm{\cdot\cdot\cdot (2a_1)^2 (1b_2)^2 (3a_1)^2}$

a: What values could the letter take? b: The left-side number? c: The subscripts? d: The right-side exponent?

5

From Wikipedia, I learned that there are notations IUPAC does not mention: $\mathrm{p_x}$, $\mathrm{p_y}$ and $\mathrm{p_z}$. (All subscripts should be upright, because they are labels, no variables.)

But it does not end there. Here and here I saw:
$\mathrm{d_{xy}, d_{xz}, d_{yx}, d_{x^2{-}y^2}, d_{z^2}}$
This was confirmed by this book.

There are alternative styles
here ($\mathrm{{p_x}^1}$).
and
here ($\mathrm{p_{x1}}$).

a: I guess the $\mathrm{d_{z^2}}$ notation (with index z-square) is correct?

Oh, I just found this book that also includes $\mathrm{4f_{x(x^2{-}3y^2)}}$ and $\mathrm{4f_{y(3x^2{-}y^2)}}$.

b: Are there other indexes possible than x, y, z?

c: Can it be just squares? Or are other index-superscripts possible?

d: What about the 3 in the last examples? Could this also be any other numer?

(You see, I just look at the typography of things and don't know their meaning.)

e: Could there be any other forms of indexes?

f: Typographically, what does this dash stand for? Is it a hyphen or a "transition between a higher energy state and a lower energy state"?

6

Finally, there is orbital hybridization, which will lead to notations like $\mathrm{sp, 2sp, sp^2, 2sp^3, s^{0.5}p^3, s{-}s, sp^3{-}sp^3}$.

a: Can the superscript be any other value than 2 and 3? Can the "base" be any other thing than s, p and sp?

b: Is $\mathrm{2sp^3}$, is it $\mathrm{2s}$ and $\mathrm{p^3}$ or is sp one ... thing with a 2 before and a 3 in superscript.

c: Is it a hyphen or a "transition between a higher energy state and a lower energy state"?


texts: What is the maximum number of water molecules that has been recorded till date to present as water of crystallization in a compound?

texts:
Context: I was casually looking through some old questions when I found this question. The OP wanted a compound that has all the hydrates ranging from monohydrate to decahydrate. I found chromium(III) sulfate [$\ce{Cr2(SO4)3.$x$(H2O)}$ where $x=0,\ldots,18$] to be suitable. But, the actual formula of the compound is $\ce{[Cr(H2O)6]2(SO4)3·6H2O}$, so 6 of the 18 molecules are present as water of crystallization. So, I wondered, what is the maximum number of water molecules that can present in a compound as water of crystallization?
I can agree to what @BuckThorn said in his answer. It might be protein crystals. Wikipedia also supports the fact:

Compared to inorganic salts, proteins crystallize with large amounts
of water in the crystal lattice. A water content of 50% is not
uncommon for proteins.

Now, the question is what protein has the maximum number of water molecules as water of crystallization?

I did some cursory searches and looked for inorganic hydrates (see edit history: 36-hydrate is maximum I could find). I am also looking for such compounds which is in inorganic domain.


texts:
Why does neopentane have a higher melting point than n-pentane?

I know that we can say that, due to stacking, it has a higher melting point as it freezes easily. But then, why doesn't this happen in the case of n-hexane too?

n-Hexane has a melting point of −95 °C whereas 2,2-dimethylbutane has a melting point of −98 °C. Instead, if we go by stacking, 2,2-dimethylbutane should have a higher melting point.

image source


texts:
If $\pu{200 mL}$ of $\ce{N2}$ at $\ce{25 ^\circ C}$ and a pressure of $\pu{250 torr}$ are mixed with $\pu{350 mL}$ of $\ce{O2}$ at $\pu{25 ^\circ C}$ and a pressure of $\pu{300 torr}$, so that the resulting volume is $\pu{300 mL}$, what would be the final pressure in $\pu{torr}$ of the mixture at $\pu{25 ^\circ C}$?

I understand that to find final pressure, I need to add the partial pressure of $\ce{N2}$ and $\ce{O2}$. I'm not sure how to find the partial pressure using Dalton's law. To find partial pressure of $\ce{N2}$ first:

$$p(\ce{N2}) = X(\ce{N2}) \cdot \pu{0.3289 atm}$$

where $X$ is the mole fraction. How do I find it?


texts: Examples from everyday life for diastereoisomers ?

texts: Like the amino-acids and sugars that are enantiomers, can you give any examples of diastereoisomers ? where can we find them in everyday life ?


texts: Calculation of the pH of a mixture of a strong acid and weak acid

texts:
The question is to find out the $\mathrm{pH}$ of a mixture of weak acid and strong acid. My book just states the formula as $$\mathrm{pH}=-\log
\frac{C_2+\sqrt{C_2^2+4K_\mathrm{a}C_1}}{2}$$

where $C_1$ is the concentration (in mole/litre) of the weak acid (ionisation constant $K_\mathrm{a}$), and $C_2$ is that of the strong acid.

I understand that the strong acid will dissociate completely and the weak acid will dissociate with an ionisation constant. So the $\ce{H+}$ ion concentration from strong acid will be simply $C_2$ and that from weak acid will be $\sqrt{K_\mathrm{a}C_1}$. But I could not derive the above formula for the $\mathrm{pH}$ using these facts. I need help here.


texts: Preparation of oxalic acid from acetylene

texts:
I would like to, theoretically, prepare oxalic acid from acetylene.

I think that using ozonolysis would be a good idea to do so. Upon ozonolysis of acetylene, we would get:

$$\ce{O=CH_2-H_2C=O}$$

On oxidizing this using hydrogen peroxide, would I obtain the desired product?


texts: Why does Red Phosphorus react so violently with an oxidizer like Potassium Chlorate?

texts: In Armstrong's Mixture, mixing those two chemicals results in a friction sensitive explosive which produces a loud bang. According to wikipedia, it is made by adding a strong oxidizer to red phosphorus, but what is the explanation as to why it reacts so strongly? Thank you


texts: How do I decide whether ring will expand in this reaction or not?

texts:
Attempt:

After forming the carbocation adjacent to the cyclopropyl ring I had two options,

$\ce{Cl-}$ then and there without any changes
Expand ring, form a new carbocation and add $\ce{Cl-}$ there.

I chose the first option because of exceptional stability of cyclopropyl methyl carbocation. However, answer given is option C which follows mechanism  (2).

Can someone explain how to judge and decide how to proceed after the carbocation formation?


texts: Why does Ethylene Glycol have higher boiling point than Propylene Glycol?

texts:
Looking at the two alcohols, both have hydrogen bonding and are singly bonded throughout the molecule. However, propylene glycol has a larger electron cloud which to my knowledge would increase its London dispersion forces and thus its boiling point. I already know both molecules exhibit hydrogen bonding since they're both alcohols.
However, it seems that ethylene glycol has a higher boiling point despite propylene glycol seemingly having stronger IMFs. I believe this has something to do with molecular shape but I can't seem to find the definitive answer explaining why ethylene glycol has a higher boiling point.
I've used https://pubchem.ncbi.nlm.nih.gov/compound/Propylene-glycol#section=RTECS-Number and https://pubchem.ncbi.nlm.nih.gov/compound/1_2-Ethanediol#section=Odor for comparison of the two alcohols.


texts: What is the usage of orbitals more complex than f orbitals?

texts:
Every high school learner, in each corner of the world, faces the lesson History of Atom during his courses, just as I did. We learned about s, p, d and f orbitals, though there were no signs of orbitals in molecules.

Then I wondered, are there any other orbitals, simpler or more complex, than the four mentioned? Surprisingly, I learned that there are also usages for orbitals g, h, i and even k and l.

Yes, I use the word "usages". Because I believe, unless something is useful, it will never enter the domain of science. Anyway, I read in Wikipedia (though not much of it I did understand) that these orbitals are used when describing and doing the measurements of molecular orbitals.

Since no element in the periodic table has enough electrons to fill even orbital g (in its base state), in cases of molecular orbitals that have a g defined in themselves, atoms must have been excited. Excitation needs energy, doesn't it? Where does this energy come from? Isn't the formation of new bonds usually exothermic?


texts: Is there any process to determine what elements a physical sample is made from?

texts:
I'm wondering if anyone knows of laboratory services that can analyze a sediment sample to tell what it's made of.

Background: our drinking water has small black flakes appearing, and our city water department cannot tell us what they are, and they say they have no equipment to test it. Their guess is either manganese, or sediment.

I'm not sure if there's a way to test an arbitrary sample to determine what it is. I've tried a few labs but none of them have the ability to do something like that.


texts: error in making a series of standards out of a stock solution

texts:
I want to make a series of standards to make a calibration curve. The analyte is a volatile substance so I'll have to use some glass "containers" with a membrane lit so I don't lose too much of the analyte. The glass container has a certain volume so when making my stock solution the amount of solvent I will use is fixed.

So if I use a big amount of analyt to make my stock solution I will have to use a small amount of stock solution to make the desired concentrations of standards

And if I want to use a big amount of analyte to make my standards I will have to make a low concentration stock solution. Which means a low amount of analyte, because the amount of solvent I can use is fixed by having to use the container with the membrane lit.

When I make stock solution:  If I add a greater amount of analyte the error on the concentration I want to make will become smaller

When I make a standard from this stock solution it's the same thing: If I add a bigger amount of analyte, the error on the concentration I want to make will become smaller.

My question:
Which of the two will have a bigger effect? Or, in other words, is it more important that the error on making my stock solution is smaller or is it more important that the error on making my standard is smaller? I ask this because I will have to choose.

Thanks a lot in advance


texts:
While going through the quantum mechanical model of atom section in my chemistry textbook, the text states:

  The existence of quantized electronic energy levels is a direct result of the wave-like properties of electrons and {the energy levels} are allowed solutions of the Schrodinger wave equation.

What does 'direct result of wave-like properties of electrons' mean?


texts: Which temperature is meant in the Gibbs free energy equation?

texts:
In the equation for Gibbs free energy change, $\Delta G = \Delta H - T\Delta S$, does $T$ refer to the temperature of the system or the surroundings?

I know we have to calculate Gibbs free energy of the system but the criterion for spontaneity says $\Delta S_\mathrm{total}$ should be greater than zero. When we relate it to Gibbs free energy to show that Gibbs free energy change should be always negative, we keep both system and surrounding temperature same with pressure also constant. Then how can the process occur? Wikipedia says that it is chemical potential that undergoes changes there but what about Gibbs free energy change?

From Wikipedia:

  Thus, Gibbs free energy is most useful for thermochemical processes at constant temperature and pressure: both isothermal and isobaric. Such processes don't move on a P—V diagram, such as phase change of a pure substance, which takes place at the saturation pressure and temperature. Chemical reactions, however, do undergo changes in chemical potential, which is a state function. Thus, thermodynamic processes are not confined to the two dimensional P—V diagram. There is a third dimension for n, the quantity of gas


texts: How to calculate the equilibrium composition after a change in partial pressure of one component?

texts:
Question
  Ammonium carbamate dissociates as shown below.
  $$\ce{NH2COONH4 (s) -> 2NH3 (g) + CO2 (g)}$$
  In a closed vessel containing ammonium carbamate in equilibrium with ammonia and carbon dioxide, ammonia is added such that partial pressure of $\ce{NH3}$ now equals to the original total pressure. What is the ratio of the new total pressure to the original pressure?

I tried solving the problem and I know I am quite close to the answer which is $\frac{31}{27}$.
Firstly I took out $K_p$ for equilibrium assuming total pressure to be $p$.
So,

$K_\mathrm{p} = \left(\frac{2p}{3}\right)^2 \times \frac{p}{3} = \frac{4p^3}{27}$

After this the par pressure of ammonia becomes $p$ so let's say that of $\ce{CO2}$ is $\frac{p}{3} + x$.

Now since $K_\mathrm{p}$ doesn't change so:

$\frac{p}{3} + x = \frac{4p^2}{27}$ (cancelling one of the $p$)

But solving further and finding new pressure and dividing by the old one doesn't give the answer


texts: can sodium persulfate etch or damage a titanium heater?

texts:
I use Sodium Persulfate to etch copper on a PCB process. I have been using glass heater on the etching tank but the glass is too fragile; it breaks too easily.

I read that titanium heater is used commercially (in aquariums as well). I don't know much about chemistry, could anyone tell me if it is okay to use titanium with Sodium Persulfate?

Sodium Persulfate to water ratio is 1:10 and the maximum temperature is about 50 C.


texts: Why is t-BuOK necessary for this synthesis?

texts:
1-chloro-2-methylpropane --> 2-chloro-2-methylpropane.

My understanding is that an E2 reaction produces two types of alkenes, the major product for non-sterically hindered bases is the more substituted product (Zaitsev) while the major product for sterically hindered bases is the least substituted product (Hofmann). In this instance, there is only one beta carbon and thus, one product. Wouldn't sodium ethoxide be a better choice as a reagent then tert-butoxide as tert-butoxide will run into steric hindrance from the orbitals of the surrounding methyl groups?

Reading from Klein, Organic Chemistry as a Second Language, First Semester Topics, 4e, p.242, 11.80


texts: How does copper reduce dilute nitric acid to nitric oxide and concentrated nitric acid to nitrogen dioxide?

texts:
Here are the 2 equations:

\begin{align}
\ce{3Cu + 2NO3- + 8H+ &<=> 3Cu^2+ + 2NO + 4H2O} & E &= 0.62~\mathrm{V}\\
\ce{Cu + 2NO3- + 4H+ &<=> Cu^2+ + 2NO2 + 2H2O}& E &= 0.45~\mathrm{V}\\
\end{align}

The Nernst equation tells us that as we increase the concentration of nitric acid the first equation becomes less spontaneous.

My question is: how? What is the mechanism of the two reactions that decides between the first and second reactions depending upon how much nitric acid is available?

Also, any qualitative explanation for what the Nernst equation shows would be appreciated. Why does having more protons available end up in fewer protons being consumed by the reaction?

It was pointed out that the second equation above is improperly balanced.  Here's the correct equation:

$$\ce{Cu + 4H+ + 2NO3- <=> Cu^2+ + 2NO2 + 2H2O}$$

So, as pointed out in the comment by Neto, the more concentrated acid does consume more protons per reaction.

Does anyone have any insight on the mechanism of the reaction and how it changes with nitric acid concentration?


texts: Where do the bubbles in a glass of water come from?

texts:
This weekend I accidentally left a glass of water on my kitchen table for a few days while I was out of town. Unsurprisingly, bubbles formed on the walls.

As I understand from the last time I attended a chemistry class quite a while ago, this happens due to water self-ionizing (at about a ratio of $10^{-14}$ if I recall correctly).

$$\ce{H2O + H2O \rightleftharpoons H3O+ + OH-}$$

However, for some reason, the bubbles only formed up to a certain depth:

What is the reason for this? Does self-ionization happen uniformly in the glass? Do bubbles start forming from the top down and would they have reached the bottom if left untouched for longer?


texts: fluorinated ethylene propylene (FEP) is close relative of poly(tetra-fluoroethylene) (PTFE), both only contain fluorine and carbon atoms,both have very similiar properties yet FEP is relatively transparent while PTFE is opaque, why?


texts: How to determine the number of π-electrons in a conjugated system from UV-Vis data?

texts: Is there a way to determine the number of π-electrons in a conjugated system from UV-Vis data? I am modelling the electrons as particles in an infinite box of length $L$ equal to the length of the conjugated system. I am unsure how to interpret the spectra to obtain the number of π-electrons, including the systems with more than one peak.


texts: is it possible for covalent compounds to produce colour during flame test?

texts: I have heard it is the metal ions that are the reason for flame colour during a flame test. so in covalent bond, there are no metal ions does that mean covalent compounds don't produce flame colour. if not what is the reason, if yes why doesn't glucose produce colour. Also is it possible to identify whether a substance is ionic, or covalent with just the flame test. I have searched the web but there are no clear explanations.


texts: What type of analytical chemistry (such as spectroscopy) is suitable for high resolution air analysis

texts: I want to find some type of analytical chemistry method, such as spectroscopy, that is capable of analysis the chemical composition of air. If it can be used for high resolution analysis would be preferable.


texts: Where can I find a collection of density functional parameterizations?

texts: I want to implement a solution to the electronic Schroedinger equation using DFT. I know there are many, many functionals to choose from but don't know where to start. I'd like to start with a couple LDA and GGA functionals, is there a good place where I can look up some parameterization, or even the tabulated data itself to form my own parameterization?


texts: Discrepancy in current inside an electrolytic cell

texts: Suppose A(+)B(-) type fused salt is present in an electrolytic cell (not electrochemical cell). Let n electrons be entering the cell per second. Since each A(+) requires one electron to discharge, so n electrons will discharge n A(+) per second. Similarly, n B(-) are also discharged per second because the number of electrons entering and leaving the cell must be same. Now, each A(+) has unit positive charge and hence n A(+) means ne(+) charge flowing towards cathode. Also, n B(-) means ne(-) charge flowing towards anode or we can say ne(+) charge towards cathode. Does that mean total 2ne(+) charge is flowing towards cathode per second ? However, from above only ne(+) charge is entering the cell.


texts: Generalizations regarding functional groups on benzene ring

texts:
While studying several organic mechanisms (high school level), I came to an interesting generalization.

I claim that negative charge on phenoxide ion first ALWAYS delocalises onto the ring and then attacks through carbon atom (like in Reimer Tienman reaction - Wikipedia). This happens because negatively charged carbon atom is less electronegative and hence a better nucleophile than a negatively charged oxygen atom.

But a normal lone pair like that on aniline or phenol attacks by itself without delocalisation (as in Schotten Bauman reaction - Wikipedia). This is because delocalised resonance structures have a formal positive charge on the more electronegative oxygen/nitrogen and are thus less stable.

My questions are:

Does this generalization always work with regards to phenols and anilines?
Is my reasoning correct for claiming these generalizations?
Can this logic be extended to other functional groups on a benzene ring?

PS: Please also justify your answer with explanation. Even a simple counterexample will help.


texts: Enthalpy of mixing in a regular solution

texts:
In a mixture of $A$ and $B$ where $A$ and $B$ are randomly mixed and the average coordination number is $z$. If there are $n_B$ molecules of $B$ in the mixture these will be in contact with a total of $zn_B$ molecules, of which $x_Azn_B$ contacts are with molecules of A. This is the total number of BA contacts. Before mixing, these contacts would have been BB contacts in pure B and so the change in energy on mixing is, for the B molecules:
$$x_Azn_B(H_{AB}-H_{BB})$$
Similarly for A:
$$x_Bzn_A(H_{AB}-H_{AA})$$
This is the point where I get confused. Upon adding together the following expression is somehow achieved:
$$\Delta H_m=\frac{zn_An_B}{2(n_A+n_B)}(2H_{AB}-H_{AA}-H_{BB})$$
Its really just the fraction at the start of that expression I am confused by. However, now the bit I really do not understand. Differentiating with respect to $n_i$ gives $\mu_i$? And apparently this gives $\beta x_j^2$. I have absolutely no idea how. Please can someone explain what's going on here?


texts: Good choice for heat-conductive coil submerged in sea water

texts:
I know only as much about chemistry as I can remember from a year in college.  So, please speak slowly and use short words.

I'm trying to decide on an appropriate material for a heat-transfer coil that is meant to remain submerged for extended periods in salt water, within a few feet of other metal parts.

I'm designing a solar still that will use a cooling/condensing coil to take advantage of the heat differential between the solar-heated evaporation chamber and nearby (cooler) water temperature.  It will be mounted on a sailboat.  The coiling coil will probably be about 12-18 inches long and 2-3 inches diameter.

Impulse was to use copper, but I'm not sure how this will react in a salt-water environment over time.  I know that sea life will stay off of it, since copper is the active element in many bottom paints designed to minimize subsurface growth.

Any help is appreciated.  Maybe the answer is to use a sacrificial anode on the coil?  Or, maybe some other material would be more suitable for long-term use?


texts: Formation of Bonding and Anti-bonding Molecular Orbitals

texts: If two orbitals combine in-phase, a bonding molecular orbital is formed. When they combine out-of-phase, an anti-bonding molecular orbital is formed. For a single molecule, how are both orbitals present at the same time? They are formed differently.


texts: There are various compounds which have common names that end in "ylene", like acetylene and ethylene. However, how come acetylene is an alkyne whereas ethylene is an alkene. Both of these have the same "ylene" ending though. What is the cause for this discrepancy?


texts: Would it be somehow possible to conduct asymmetric synthesis if all chiral molecules would exist only as racemates in nature?