texts:
One of the first things learnt in organic chemistry is that wedged bonds can be thought of as bonds coming out of the plane of the paper towards you, and hashed bonds can be thought of as bonds going behind the plane of the paper away from you.

What is rarely discussed, is the difference between actual 'wedged' bonds, and the 'block' variety. The diagram below from Organic Chemistry Strategy and Control by Stuart Warren goes some way to explaining that in theory at least, the two sets of bonds exist to allow us to describe absolute or relative stereochemistry.

(In practice, this is rarely followed, and individual groups/labs tend to, rightly or wrongly, favour one type over another for stylistic reasons).

What has always baffled me, however, is the direction in which the wedged bonds originate/point towards.

In most modern usage, the small end of the wedge/hash is at the chiral centre, and gets larger towards the substituent, however some (mainly older chemists, whom I'm going to give the benefit of the doubt and assume aren't just bad at using ChemDraw) chemists have the hashes differently to the wedges, as per the molecule below.

Is this something that is advisable (presumably it's meant to show some kind of 3D perspective)/are there any actual IUPAC rules/guidelines on this other than following what looks good/is conventional?


texts:
If the forward reaction causes an increase in entropy then the backwards reaction causes a decrease in entropy, so the backwards reaction is non-spontaneous. If so, then why does the backwards reaction begin to happen spontaneously and an equilibrium position is reached? I get that when you have mixing you also have a higher entropy because there are more microstates available in the given energy configuration, but why is an equilibrium position reached if the backwards reaction is supposed to be non-spontaneous? And why not just get a 50:50 mixture of that's what will increase entropy.

P.S.
1) I do A2 chemistry.
2) Graphs are more than welcome.
3) Arguments in terms of disorder are not preffered, but please use microstates and 'ways to arrange energy'.


texts: Is there a reason for the mathematical form of the equilibrium constant?

texts: Why are the two molarities multiplied and not added, and why is each raised to the power of the coefficient rather than multiplied by it? What is the reasoning behind this form? Was it simply determined that the probability of reaction was proportionate to both and thus they are multiplied together? I'd like to know whether its form is purely empirical or has a theoretical backing.


texts: Reduction of carbonyl compound by LAH (in anhydrous ether) followed by reaction by acidic water

texts:
What will be the final product upon reaction of $\ce{CH2=CH-CH2-C6H4-CH=CH-CHO}$ with $\ce{LiAlH4}$ (in dry ether) followed by acidic water?

LAH will reduce the carbonyl group to alcoholic group and the alkene group which is directly attached to carbonyl and aryl group to saturated bond. But it will not reduce the isolated alkene group.

Hence, the final product must be $\ce{CH2=CH-CH2-C6H4-CH2-CH2-CH2-OH}$


texts: According this scheme the bromine act as a nucleophile and attacks pyrimidinium generating Br+ species? I always thought that Br2 acts solely as electrophile with Br- as by product.


texts: Is considering HVO3 + n ROH = HVO3(ROH)n as an endothermic reaction logical?

texts: Here is an article on vanadium solvent extraction with 2-ethyl-1-hexanol: Separation and Purification Technology 2017, 188, 358-366 The suggested extraction reaction is HVO3 + n ROH = HVO3(ROH)n, which shows a solvation mechanism. The extraction process turned out to be endothermic based on experimental results. However, the beforementioned reaction does not suggest any solute-solute and solvent-solvent interaction breaking to the best of my knowledge. As I understand, it only indicates solute-solvent stabilization, which is logically exothermic. Then, is it acceptable to write such a reaction for an endothermic process?


texts: Second order reaction with two reactants

texts:
I'm interested in the second order reaction $\ce{A + B -> P}$. Mass action kinetics is assumed.

Let $[A]_0 = a$ and $[B]_0 = b$, then $[A] = a - x$ and $[B] = b - x$. The rate law becomes
$$-\frac{\mathrm dx}{\mathrm dt} = -k([A]_0 - x)([B]_0 - x)$$

Why is the right-hand side of the differential equation negative? Shouldn't it just be the left side when we look at the decrease of the reactant $\ce{A}$? Or is it because $x$ is equal to the concentration of $\ce{P}$?


texts: Reaction of 1,1-diphenylethanol on Montmorillonite K10 under microwave radiation

texts:
What is the product of 1,1-diphenylethanol + Montmorillonite K10 Clay undergoing microwave radiation? What is the mechanism for it?

My effort:

1,1-diphenylethanol + Montmorillonite K10 Clay catalyst used in a microwave-assisted synthesis of pyrazoles from enaminones.

Used for:

Support for catalysts
Preparation of clay nanopaper composites of nacre-like structure

Catalyst for:

Conversion of triose sugars with alcohols to alkyl lactates
Deprotection of ketone dimethylhydrazones

Is my answer correct?


texts: The energy gap between a pi-conjugated system with (2 bonding and 1 anti-bonding orbital) and (1 bonding and 2 anti-bonding) orbitals

texts:
I asked a question previously about "why" it is the case the expanding the size of pi-conjugated systems decreases the required energy to excite an electron from a HOMO to a LUMO band: Why does the energy gap for π - π* transitions shrink with the size of the pi-conjugated system?.  The user "Philipp" (and others) very patiently and kindly explained the reason for this by pointing out the expansion in the number of possible bonding and anti-bonding configurations for a polymethine-like pi-conjugated system.

However, there's something I'm missing that has to do with what is probably my lack of knowledge about chemistry.  If we look at this image: http://i.stack.imgur.com/Ti3cx.png (provided by "Philipp") why is that that we have an energy gap between $\Psi_2$ and $\Psi_3$ smaller than the energy gap for a simpler, smaller pi-conjugated system where the HOMO corresponds to a single pair of p-orbitals in a bonding conformation and the LUMO corresponds to the same single pair of p-orbitals in an anti-bonding conformation (i.e. this system: http://i.stack.imgur.com/9cscv.png)?

My guess that this would be because the bonding interactions that exist in the larger pi-conjugated system mitigate the penalty for having the one anti-bonding interaction?

Update --- Could we justify the above guess using something like an overlap integral (if we know the shape of the two bonded p-orbitals forming a pi-bond)?  If so, this would be quite intuitive.


texts: In the mass spectrum of niacin (3-pyridine-carboxylic acid), what ion corresponds to the peak at m/z = 105?

texts:
The mass spectrum can be found here.

I am interested to know what ion this is and why the peak at $m/z = 105$ is higher than the peak at $m/z = 106$ (which I believe corresponds to $\ce{C5H4NCO+}$).


texts: Dissociation constant of molecular dinitrogen as a function of temperature?

texts:
I'm looking for the dissociation constant of molecular dinitrogen ($\ce{N2}$) as a function of temperature,

$$\ce{N2 <=>[$K$] 2N} \quad K=\frac{[\ce{N}]^2}{[\ce{N2}]}$$

Casas & Bermelo (1978) reported three data points for nitrogen (I couldn't access their references):

$$K_{298}=2\cdot 10^{-160},\ K_{2000}=10^{-3},\ K_{20000}=1.29\cdot 10^5$$

Are these the accepted values today? Is there a more complete database online?
Would it be correct to fit an exponential function using these data points to extract $K$ for other temperatures?


texts: We have now 10% ethanol mixed petrol. Seller says that if this petrol comes in contact even 10 ml of water, all ethanol which is mixed in the petrol will be extracted by water, is it true?


texts: Is there an example of a bond with negative bond enthalpy?

texts:
My textbook says bond breakage is "generally endothermic." This implies there are some bonds out there that release energy when broken.
Is there a classic example? Perhaps diatomic Helium?


texts: Why does this region fit NMR spectroscopy technique?

texts:
I was reading a paper and came across a sentence (highlighted one) about NMR spectroscopy.

  Several Leishmania Rabs, like Rab1, Rab5a, Rab5b, and Rab7, have been functionally characterized. LdRab5a is a GTPase that has been shown to
  bind to GTP and hydrolyze it to GDP. It specifically regulates
  fluid-phase endocytosis. Although the G1–G5 loop sequences
  are well conserved in LdRab5, it has unique
  interswitch region with substitutions and a 20-residue insertion
  with respect to the human Rab5. The unique insertion
  feature of LdRab5a prompted us to choose NMR spectroscopy as the most suitable technique for determining
  its structure.

  It is pertinent to mention that NMR solution
  structure has not been determined for any Rab protein
  from any organism. This would also provide the opportunity
  for exploring the residue-specific dynamics for LdRab5a in
  particular and reveal the general implications for the Rab
  family of proteins. Hence, we have undertaken the determination
  of solution structure and characterization of backbone
  relaxation dynamics for LdRab5a by using NMR
  spectroscopy.
  However, stabilization of LdRab5a through systematic
  and specific mutations and deletions was necessary to arrive
  at a construct that was stable enough for recording long
  multidimensional NMR experiments.

Why do we need to have a unique interswitch region so as to use the NMR spectroscopy technique?


texts: acyclically stereocontrolled reaction: organolithium and 2-chiral compound

texts:
Aoyagi et al. (J. Am. Chem. Soc., Vol. 115, No. 24, p 11393) reported that the addition of 2-lithio-1,3-dithiane to the alpha-chiral (S)-2-Acetylpiperidine gives the (2 S,3 S)-configured product. It is stated that the diastereoselectivity of this 1,2-addition (dr = 6.2) is predicted by Cram's model involving complexation of the Li-ion by the piperidine-N. I tried to reproduce the diastereoselectivity in the following scheme:

As you can see I come up with the wrong product by applying Cram's rule with a O,N-complexed Li-ion (right side of the scheme). By applying the non-chelate Cram rule (left side; biggest substituent oriented anti to the carbonyl, attack via smallest group) I get the correctly configured (2 S,3 S)-product.

Where is the mistake?


texts:
My teacher stated:

  At standard conditions, 1 liter of air at 21% oxygen possesses $\pu{0.21 L}$ of oxygen. Since at STP, 1 mole of gas occupies $\pu{22.4 L}$, simply divide $0.21/22.4$, to arrive at 0.0094 moles of oxygen.

I have a question regarding this. What if I trap $\pu{100 ml}$ of air in a vessel and maintain $\pu{273 K}$ and pressure $\pu{1 atm}$? So, in that case, what does it mean that oxygen has volume of $\pu{21 ml}$? Won’t the volume of oxygen and nitrogen be same inside vessel? Or am I wrong somehow?


texts:
These are the two resonating strctures of NO given in my textbook. In the first resonating structure, oxygen is shown to have 9 electrons. How can that be possible since oxygen does not have the third shell so it has no orbital available to accommodate any more electron?

Also, why don't elements donate only one electron in such cases. I know unpaired electrons cause repulsions but in cases like NO where its not possible to avoid an unpaired electron, cannot oxygen donate only one electron to nitrogen. If it does that, we could have this structure. Is this structure possible?

Also, just out of curiosity, between oxygen and nitrogen, on whom will be one electron pair more stable? I am not able to decide this on the basis of electronegativity.


texts: Is pigment grade titanium dioxide likely to contain any impurities that are toxic?

texts:
I have a bag of titanium dioxide of pigment quality, unknown source. I am curious to know if the manufacturing process of titanium dioxide makes it likely that it contains any toxic by products / impurities.

Would it for example be safe to use pigment grade titanium dioxide to manufacture sunblock?


texts:
Assume that we have a space with just two $\ce{H}$ atoms and their distance to each other is $d$. Let's say they don't have initial velocity. What is the force with which they will act on each other?

This question might have some mistakes in itself, but the main thing I'm trying to learn is how an atom of element $X$ interact with an atom of element $Y$.


texts: Charge separation and stability in resonating structures

texts:
I know that when there are like charges on a resonating structure, the farther apart they are, more stable is the structure due to reduction in repulsive forces.Is the same true for opposite charges? which structure is more stable -
1)with positive charge on one C and negative on adjacent C
2)with positive charge on one C and negative charge on C separated by 4 carbons between them?


texts: Who came up with the box and arrow diagrams for electron configurations?

texts: In general chemistry texts, the electron configurations are sometimes shown in boxes with up and down arrows to show the concept of paired spins. My impression for years was that Hund used such diagrams. However, flipping through his book Linienspektren und Periodisches System der Elemente which used the s,p, d, f notation in a modern way, there is no such use of box diagrams with up and down arrows. Does anyone know who introduced this so-called box notation? Thanks.


texts: Hybridisation of cobalt in tris(oxalato)cobaltate(III)

texts:
Will the hybridisation of of $\ce{Co}$ in $\ce{[Co(ox)3]^3-}$ be $\mathrm{sp^3d^2}$ or $\mathrm{d^2sp^3}$? The question in which I found it has mentioned the answer to be $\mathrm{d^2sp^3}$ while I was thinking of the other one.
According to me, oxalate is a weak field ligand and it should not cause the pairing of electrons in the half-filled $\mathrm d$ orbitals.


texts:
Everyone knows the simplified photosynthesis-equation from school:

$\ce{6CO2 + 6H2O -> C6H12O6 + 6O2}$

Most people assume that the carbondioxide is being split into carbon and oxygen during photosynthesis, and the equation seems to confirm this. But we know that is not true, and that the oxygen derived from photosynthesis actually comes from the watermolecule being split into hydrogen and oxygen (see e.g. this course note and wikipedia).

Clearly there is much more going on as the formula most of us learned in school suggests, so my question is: what is the correct and complete equation for photosynthesis?


texts: What is the difference between a dπ-dπ and delta bond

texts: I have always been wondering the difference between a dπ-dπ bond and a delta bond. What are the situations that either bond is formed in overlap of two d orbitals.


texts: How do octahedral seed crystals yield polyhedral Cu₂O crystals?

texts:
In an article I am trying to understand, the following occurs: (summarized below)

  Synthesis of octahedral $\ce{Cu_2O}$ seeds:In a typical synthesis, 2.9946 g of $\ce{Cu(CH_3COO)_2}$ was dissolved in deionized water (20 mL) using a beaker under a constant stirring at 70°C for 2 min. A dark precipitate was produced when a sodium hydroxide solution (9 M, 10 mL) was added dropwise to the above solution. After being stirred for 5 min, D-(+)-glucose powder (0.3 g) was added into the dark precursor with a constant stirring for another 60 min at 70°C,and then was allowed to cool to room temperature naturally. Afterward, the obtained products were centrifuged at 5000 rpm for 1min (XIANYI TG16-WS centrifuge). The precipitates were centrifuged twice more in deionized water and anhydrous ethanol, respectively. And finally were dried at 70°C for 12 hours in a vacuum oven.

My understanding of this paragraph is that copper acetate reacted with sodium hydroxide to form copper hydroxide and sodium acetate. A reducing sugar reduces the copper hydroxide to $\ce{Cu_2O}$. The ethanol dissolves the sodium acetate to leave only $\ce{Cu_2O}$ (octahedral) crystals.

The next morphology of $\ce{Cu_2O}$ crystals, "polyhedral M-pyramid $\ce{Cu_2O}$ architecture," was grown through essentially the same process, except using seed crystals from the first batch of octahedral crystals.

How do octahedral seed crystals give rise polyhedral ones?


texts: What are the factors that affect the redox reactions?

texts:
In my work, I used $\ce{Co(OH)2}$ and $\ce{Ni(OH)2}$ as an active materials to fabricate as symmetric supercapacitors in which I used 1-butyl-1-methylpyrrolidinium dicyanamide as an electrolyte.

From my CVs curve, I found that $\ce{Co(OH)2}$ have a high redox peaks while for $\ce{Ni(OH)2}$, it shows no redox reaction peaks. What might be the factor that affects this? As I've known both active materials have similar layered liked-structure. Is it the electronegativity differences between an electrolyte and the materials?

What could possibly affect the redox reactions and how could I study more on the reaction mechanism?


texts: Thickening and/or slowing evaporation of IPA-based ink

texts:
The conundrum

I have a security printing ink that I make by adding an IR-absorbing dye to a 50/50 mix of Isopropyl Alcohol and distilled water. The ink solution is pale green but dries virtually invisible to the human eye.

The problem is that when the ink is applied to the stamp the ink evaporates within seconds but I need it to remain viable for ~10 minutes. Even if I shortcut the 10 minutes to just a few seconds, the ink evaporates enough to cause an uneven distribution (i.e., it is faded in some areas.)

Requirements

Provides an even distribution of ink (to me, this means viscous)
As little bleeding as possible (to me, thin coat on stamp, also viscous)
Stays viable on a stamp for ~10 minutes
Allows the final inked product to be virtually invisible after ~24 hours

A solution that works (almost)

I have solved this problem before with a different ink. It was a UV-reactive ink which uses an identical IPA/water solvent. I was able to meet all of my requirements by adding 14% Glycerin to the solution. The increased viscosity really helped with consistent and clean (no bleed) marks. The slower evaporation gave me plenty of time to stamp. There was much rejoicing.

However, the Glycerin has an unwanted side effect with the IR ink in that it remains visible on the substrate. I'm guessing this is because the Glycerin prevents the ink from fully drying. I tried heating final product to see if that dried out the Glycerin but it didn't help.

You may ask why the UV ink ended up being invisible (requirement #4). Simple - that ink is clear to begin with.

My questions

I think what I need is a viscous fluid (maybe not as viscous as Glycerin) that evaporates slowly but fully in ~24 hours. Does such a wonder exist?
Glycerine solves all of my problems and creates one (visible marks.) Is there a way to use Glycerin, while still getting an invisible mark? (I've tried varying the amount of glycerin, but it's a trade-off of usability and visibility.)
Is there another chemical (hopefully easily obtainable by an individual) that could work as well as Glycerine while also allowing invisible marks?
I would love to understand this problem better so I can troubleshoot it myself (I'm a software engineer, not a chemist.) Any random insights would be welcome.
It seems to me that viscosity is inversely proportional to evaporation rate. Is that true?

Background info

I am trying to apply this ink to long thin strips (~7mm each) of a porous paper substrate (wrapped around plastic.) This needs to be done hundreds of times. To simplify the alignment process, I have a large rubber stamp with a series of ~100 duplicate strips embossed into it. This stamp is placed face up into a rig with alignment grooves on either side. From here, I apply the ink to the stamp and then slide each strip, one by one, into a pair of adjacent grooves and press down to stamp. This is much faster than re-inking a single thin stamp for every strip. This process takes about 10-15 minutes.


texts: Is a meta-sodium sulfonate group on a benzene ring electron withdrawing or donating?

texts: I am wondering if a sodium sulfinate group would decrease or increase the electron density of the aromatic ring


texts: In the lattice model, what's a nearest neighbor?

texts:
I was reviewing my grad Thermodynamics textbook to go over a concept that I never learned well: the Lattice model.  One set of equations1 has:
\begin{align}
zN_1 &= 2N_{11} + N_{12}\\
zN_2 &= 2N_{22} + N_{12}\\
\end{align}
where $z$ is the coordination number, or the number of nearest neighbors (defined twice).

My trouble is a simple thought experiment:

pure solution of $1$
$z = 10$
$N = 100$

So then the first equation becomes $10{\times}100=2{\times}N_{11}+0$, so $N_{11}=500$. Five-hundred nearest pairs, right?  But if I actually had a solution of 100 species 1 each with 10 neighbors, then I'd expect (ignoring boundaries) to have about $100{\times}10=1000$ pairs of $1-1$.

I can't seem to figure out what is meant by $N_{11}$.  Could someone explain it?

1 J. Prausnitz, R. Lichtenthaler, and E. Gomes de Azevdeo. Molecular Thermodynamics of Fluid-Phase Equilibria, 3rd Edition, p.331, Eq.7-68.


texts: Is there such a thing as a temperature-controlled reflux column?

texts:
You know the deal - you're doing a distillation in the lab, but want a fraction that comes over at a very specific temperature. I find it very hard to control the temperature in my air-cooled reflux column. For anyone that's ever had to wrap their reflux column in aluminum foil, you know what I'm talking about.
Is there a piece of laboratory equipment that controls the temperature of the reflux column within a degree or so of an arbitrary setpoint? I'm thinking something like a condenser column (Liebig, Graham, etc) where the water (or other working fluid) that circulates through the jacket also passes through some sort of temperature controller so that the water/fluid keeps the walls of the condenser at a tightly controlled temperature. Any tips on where to find this kind of device?
I know of vacuum-jacketed reflux columns, but I'd prefer something where I didn't need to use a very long tube in order to separate close fractions.


texts:
I want to know why concentration of solids and liquids are taken unity in expression of equilibrium constant( heterogenous equilibrium). It is usually mentioned that the density of solids and liquids( ideally) does not change and hence concentration does not change and so rate does not depend on solids and liquids. I accept that it is true. But will not it change the actual value of $ K_c$? We use $K_c$ everywhere like calculating extent of reaction, in thermodynamics- calculation of standard gibbs free energy and so on...

How the assumption of unit concentration in expression  is justified?

I want to give you an example:
 Suppose in expression of $K_c$ the concentration of water(liquid) is involved  then the concentration wil be $(1000 g/L)/(18g/mol)$ ( density/ gram molar mass) Now if we take the concentration of water(liquid) unity then definitely value of $K_c$  will change and this change will be reflected. for example: when we want to predict extent of reaction $OR$ put value of $K_c$ in different equations relating it like $G^○=-RTlnK_c$


texts: What utility does the Tau bond model of orbital overlap have?

texts:
In his book on molecular orbital theory, Molecular Orbitals and Organic Chemical Reactions, Ian Fleming notes that Pauling formulated an early alternative model to Huckel theory for explaining the bonding of simple conjugated polyenes. Evidently, this came to be called $\tau$-bonding. Fleming describes it as a modification to, or offshoot from, the hybridization model, in which orbitals similar to sp3 hybridized orbitals are combined. Fleming says that the $\tau$-bond model makes the extent of the conjugation less obvious, but that the model

  [...] might have some virtues, not present in the Huckel model, especially in trying to explain some aspects of stereochemistry.

I don't have access to the relevant primary literature, and the treatment of the subject in Fleming's book amounts to one paragraph with an accompanying diagram. A search online was relatively fruitless.

My questions are:

Is $\tau$-bonding just the historical precursor to the bent/banana-bond model, or does it have some unique independent significance that makes it directly relevant to modern chemists?
What are the specific "virtues" that Fleming might have been referring to, and what, if any, advantages does the $\tau$-bond model have over Huckel theory and/or other approaches grounded in MO theory?


texts: I can detect a distinct smell when I am near water going over a weir. I could tell that I was near "white water" if I was blindfold. Can anyone tell me what causes this odour?


texts: What compounds are produced when you heat CuO and sugar?

texts: I'm wondering on what compounds are produced when you heat CuO and sugar?


texts: What is the difference between these two formulas for pH of weak acids?

texts:
In the German Wikipedia article on $\mathrm{pH}$, I found the following formula for calculating the $\mathrm{pH}$ of weak acids (which are there defined of having $4.5 < \mathrm{p}K_\mathrm{a} < 9.5:$
$$c(\ce{H3O+}) = c^\circ\cdot\sqrt{K_\mathrm{a}\cdot c_0/c^\circ}\label{eqn:1}\tag{1}$$
I am a bit confused about this as in school, I learned that the $\mathrm{pH}$ (or more precisely, the concentration of $\ce{H3O+};$ one would have to take $-\log c(\ce{H3O+})$ to get $\mathrm{pH})$ for weak acids is
$$c(\ce{H3O+}) = \sqrt{K_\mathrm{a}\cdot c_0}\label{eqn:2}\tag{2}$$
I see that these formula are somewhat similar, but they aren't identical. The Wikipedia formula \eqref{eqn:1} includes $c^\circ,$ of which I could not find out what it is (it also appears in the equations for strong and very weak acids).
So I have two questions:

What is $c^\circ$?
Are these formulae different and if yes, how?


texts: How do atomic orbitals interfere both constructively AND destructively to give two molecular orbitals?

texts: I am an organic chemistry student learning how atomic orbitals interfere to give rise to molecular obitals. The image below suggests that each of the hydrogens' atomic orbitals interfere both constructively AND destructively. How is this possible? More fundamentally, how does the 1s atomic orbital of a hydrogen atom have both positive and negative phase in the first place? I realize that there is a similar question on this topic but I wasn't able to understand the answer to that post due to my limited background in quantum mechanics and was hence was looking for someone who could explain in simple terms.


texts: Reaction rate unit conversion: how to convert from molarity to ppm

texts:
How can I convert a reaction rate $k$ with units of $\mathrm{1\over M~~s}$ to $\mathrm{1\over ppm~~s}$?

For context: I want to make a numerical simulation of a system of reactions that happens in air (and in water droplets suspended in the air), I have already built a part of the model for which I used $\mathrm{ppm}$ for my concentrations and thus, e.g., $\mathrm{1\over ppm~~s}$ as the units for the $k$ values of second-order reactions in the system. (Reactions of different orders have different units, obviously, but those details are irrelevant to the question.) The article I have on hand lists a $k$ value for the reaction I need in $\mathrm{1\over M~~s}$ and the reaction takes place in the liquid phase.I assume that the PPM is weight-based although the article in question does not actually specify this.

I am asking the above question because I am not sure if this conversion is necessarily as straightforward as a simple factor of $10^{-6}$.


texts: Predict the species formed by the reaction of mercury(II) chloride and iodine

texts:
$\ce{HgCl2}$ and $\ce{I2}$ both when dissolved in water containing $\ce{I-}$ ions the pair of species formed is

A. $\ce{HgI2, I3-}$
B. $\ce{HgI2, I-}$
C. $\ce{HgI4^2-, I3-}$
D. $\ce{Hg2I2, I-}$

Answer: option (c)
In this question, I was able to predict the formation of $\ce{I3-}$. So, I could eliminate option (b) and (d).  But, between option (a) and (d), I could not distinguish. Is there any specific way to guess answers for these type of questions in exam?


texts:
I need to make a saturated solution of $\ce{Na2CO3}$ and according to the available data I should add $22\ \text{g}$ in $100\ \text{ml}$ of water at $25\ ^\circ\text{C}$.

I wanted to make $300\ \text{ml}$ solution, which would require $66\ \text{g}$. But, even after adding $110\ \text{g}$ of the salt, no turbidity appears which might indicate saturation. So I believe that the solution is still not saturated.

However, when I kept the flask overnight, almost the entire salt precipitated out in large crystalline chunks. I am a bit confused as to what the problem might be. Has anyone faced this kind of trouble?


texts: Cation-anion radius ratio of manganese difluoride

texts:
How to determine the cation-anion radius ratio for $\ce{MnF2}?$

I tried to calculate the $r_\mathrm{c}/r_\mathrm{a}$ ratio using the relationships:
$$2r_\mathrm{c} = c$$

and

$$(2r_\mathrm{c} + 4r_\mathrm{a})^2 = 2a^2,$$

but that gives $r_\mathrm{c}/r_\mathrm{a} > 1$ with the given $a$ and $c$ parameters, which is impossible. $\ce{MnF2}$ has a rutile structure, so the predicted ratio should be between $0.414$ and $0.732.$


texts: Why don't alloys self-galvanically corrode?

texts:
Total chemistry newbie here (so this may be a fairly obvious question). With that said, I've had a niggling question that I can't quite resolve myself;

Given that galvanic corrosion is driven by the different electronegativities of different elements, why don't alloys made of significantly different elements self-galvanically corrode very quickly?

Essentially, if I were to place two electrically connected lumps in a conducting bath, one of copper and one of tin (with an anodic difference of 0.3V), I would expect them to corrode relatively quickly. Yet if I make these lumps small enough (i.e. make an alloy of them) the resulting bronze mass is fairly resilient. At what size do the individual lumps of copper and tin change from being rapidly corroding to something stable?


texts: How do chemists decide on which detergent to use?

texts:
I found betaine in my face wash. I think it is there because it has a hydrophobic (non-polar) end that can pick up grease, and a hydrophilic (polar) end that means it is attracted to polar solvents, such as water.

My question is why are betaines used over other detergents? What are the factors that contribute to the which detergents are used in face wash (or indeed shampoo/shower gels)?


texts: Do endothermic reaction have higher energy products than reactants?

texts: If a reaction absorbs energy does  that mean it has a net gain of energy?


texts:
In the title I am refering to silver spoons, which, when used to consume milk products (like yogurt), get a weird taste. It could be described as umami/meaty, a little bit like onions. I came to the conclusion that it must be the silver, because this taste is never observed when using steel spoons.

My guess was: the silver (or maybe its oxide?) reacts with an ingredient of the milk product.

My question is: Is this documented/known process/reaction or is this some kind of misperception on my part? If the former is true, what exactly is happening? (By)-products?


texts: How to give an evidence in support of the arenium ion mechanism?

texts:
Outline the mechanistic steps involved in the arenium ion mechanism for
  aromatic electrophilic substitution. Draw the energy profile diagram for the proposed mechanism. Give one evidence in support of the proposed mechanism.

I can solve the first two questions but I got confused about what the last question exactly asking for. Any help will be appreciated.


texts: Y-axis of the reaction co-ordinate graph

texts: In the graph of the reaction co-ordinate, is the $y$-axis that is used  $∆H,$ $∆U$ or $∆G$?


texts:
I'd expect an extended enolate to be more stable than a normal enolate, when both can form, but my textbook suggests otherwise.

What is the stability of an extended enolate compared with a normal enolate? For example, following an enolate alkylation of the molecule depicted below, which product ($\alpha$- or $\gamma$-alkylated) will form?


texts:
I use Gaussian 09 to obtain the Hamiltonian and overlap matrices, $H_0$ and $S_0,$ where the B3LYP functional and the 6-31G basis set are adopted. Then how to
transform the system to an orthogonal basis using Löwdin transformation?

$$
\begin{align}
H_1 &= S_0^{-\frac{1}{2}}H_0S_0^{-\frac{1}{2}} \\
H &= U^\dagger H_1U
\end{align}
$$


texts: Electrospray Ionization Mass Spectrometry(ESI-MS) is a technique in mass spectrometry to get an idea about molecular ion peak. In the ESI-MS spectra of an amide compound, I observed that the molecular ion peak is much less abundant as compared to two other peaks, which correspond to the carbonyl and amine fragments between which the coupling reaction was carried out. But, TLC confirmed that there was no amine or acid remaining in the mixture after the reaction(EDC coupling).Hence my question is, although amide is a very stable bond, can it fragment in ESI-MS?


texts: Why would breathing pure oxygen be a bad idea?

texts:
My textbook mentions that SCUBA tanks often contain a mixture of oxygen and nitrogen along with a little helium which serves as a diluent.

Now as I remember it, divers take care not to surface too quickly because it results in 'the Bends', which involves the formation of nitrogen bubbles in the blood and is potentially fatal.

If that's the case, why not use pure oxygen gas in SCUBA tanks? It seems like a good idea since it would

a) Enable divers to stay underwater for longer periods of time (I keep hearing that ordinary SCUBA tanks only give divers a pathetic hour or so of time underwater.
b) Possibly eliminate the chances of developing 'the Bends' upon surfacing. Well, it seems plausible, that is if the diver were to take a 10 minute deep-breathing session with pure oxygen to flush out whatever nitrogen's there in his lungs before hooking up a cylinder of pure oxygen and going for a dive. So if there's no gaseous nitrogen in his lungs and blood, then he wouldn't have to worry about nitrogen bubbles developing in his system.

Now those two possible advantages aren't hard to overlook, but since no one fills SCUBA tanks with pure oxygen, there must be some reason that I've overlooked, that discourages divers from filling the tanks with pure oxygen. So what is it?

Also, I hear that the oxygen cylinders used in hospitals have very high concentrations of oxygen; heck, there's one method of treatment called the Hyperbaric Oxygen Therapy (HBOT) where they give patients 100% pure oxygen at elevated pressures.

Hence I doubt whether the increase in pressure associated with diving is the problem here. So I reiterate:

Why is it a bad idea for divers to breathe pure oxygen underwater?

I guess most of the recent answers have kinda missed a main point, so I'll rephrase the question:

Why is it a bad idea for divers to breathe pure oxygen underwater? If it is indeed due to pressure considerations as most sources claim, then why doesn't it seem to be a problem when patients are given 100% pure oxygen in cases like the HBOT (which is performed at elevated pressures) ?


texts: Titrating and the addition of acidic distilled water

texts:
I have read numerous online questions similar to the one I am about to ask. But for most of them the answer has been that the reason one can add water to the unknown concentration solution during a titration is because:

Water has a pH of 7
This is a volumetric analysis, so as long as one record the volume of the titrant and analyte used then there is no problem.

My questions are these:

Due to the effect of $\ce{CO2}$ in the atmosphere mixing with the distilled water, it is obvious that the pH of distilled water is on the acidic side (which we confirmed using a pH sensor). Therefore, why does the addition of distilled water not affect the pH? If it is acidic that should mean there are $\ce{H3O+}$ molecules in the distilled water when we add it into the analyte.

How do we take into account the imbalance of the moles of $\ce{H3O+}$ molecules versus $\ce{OH-}$ in each drop of the acidic distilled water (ex. pH of 5.6)

The only solution I have in mind right now is that all of these are acceptable uncertainties (such as the effect of the addition of an indicator), and that significant figures will wipe out these small errors.


texts:
In my experiment, I used an atomizer to generate $\ce{KCl}$ aerosols. I saw that the nozzle that was dipped into the 10% wt $\ce{KCl}$ solution got partially clogged after an hour. I then had to disassemble the nozzle in order to clean it, which I did by rinsing it with water and drying it with a stream of air.
 Is there any way to avoid the clogging?


texts: How to do RPA (Random Phase Approximation) in VASP?

texts:
I'm new to VASP and as such don't know much of its intricacies yet. I want to find out the interlayer binding energy of a given molecule and to do that I already opted for the use of different functionals (DFT-D3, SCAN, etc.) to find the total energy of my system in case of the bulk material and in case of the isolated layer. From these two I calculated the interlayer binding energy but am still about an order of magnitude of.

Now, I thought of using RPA in VASP to maybe get closer results.
My question(s): How do I implement RPA into VASP? I've read the wiki entry on it but am still not sure how to modify the other INCAR tags. Do I add RPA while also utilizing some functional (i.e. one of those I already used) or is RPA sufficient on its own?
And are there other methods with which I could get better values?


texts: What happens if don't use MgCl₂ in buffer solution in Ca²⁺/Mg²⁺ titration?

texts: What happens to a complexometric titration of calcium carbonate (analyte) with $\ce{EDTA}$ (titrant) when no magnesium(II) chloride crystals are added to the buffer ($\ce{NH3/NH4^+ + EDTA}$) solution? In a water analysis (where water sample is the analyte and $\ce{EDTA}$ is the titrant)?


texts: reaction between semicarbazide and a mixture of cyclohexanone and benzaldehyde

texts: Why is cyclohexane-semicarbazide precipitated, but after a while the precipitate is benzaldehyde-semicarbazide?


texts: Are there biodegradable pigments that are soluble in oil, but not in water?

texts: I'm hoping to find a purple pigment that preferably, but not necessarily, can be used at room temperature. The goal is a pigment that will break down in septic systems.


texts:
I know crown ethers can be used to complex metal ions.
Question: What important properties do 18-crown-6 change during the benzannulation from 18-crown-6 to DB18C6 (dibenzo-18-crown-6)? How do these change?
(Disclaimer: I know that DB18C6 does not necessary to be synthesised from 18C6)
Motivation: I saw that some complexations of metal ions use 18C6, but some of the other use DB18C6.
Thoughts and Research: As crown ethers are used to make size-specific ions complexes, the sizes of the hole in the ethers are important. But the benzannulation does not change the size, so I suggest that the process changes the equilibrium constant of $\ce{M(ether)X_n}$ or the rate of complexation. Investigated by this article, the distribution constant between polar phase and non-polar phase increases significantly and the equilibrium constant in non-polar phase increases. I understand the former because of the property of benzene ring. But how can the latter one happen? Are there another reasons why DB18C6 is chosen?


texts: Is rotation of a mirror image allowed in order to determine chirality? Doesn't rotation alter the mirror image of the molecule?

texts:
So, chiral molecules are those which have non-superposable mirror images.

trans-1,2-Dimethylcyclopentane is chiral; 2-butanol is chiral; both don't superpose on their mirror image.

Then my book cited 2-propanol as achiral. How?

The mirror image doesn't seem to superpose with the molecule. How can it be achiral then?

Then the book provided a pic where the author showed how 2-propanol is achiral; he rotated the mirror image & then superposed! Done! 2-propanol is achiral!

But really how can rotation be allowed? After all the mirror image is a stereo-isomer; if it is rotated, wouldn't it be changed?

I'm not getting, why rotation is allowed before superposition. Not every-time, the mirror image is rotated before superposition.

Can anyone please explain how rotation is allowed before superposition?


texts: Electronic configuration of excited states of iron

texts: The electron configuration of the ground state of $\ce{Fe}$ is $\mathrm{1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^6}$. What are the configurations of its first and third excited states? The first excited states seems to be $\mathrm{[Ar]4s^1 3d^7}$, but isn't the angular momentum not conserved because $l=0$ for $\mathrm{s}$ and $l=2$ for $\mathrm{d}$?


texts:
First off, huge fan of chemistry, not a chemist – do be nice :D

Would an image like this make sense as an infographic for the molecular composition of the air? I especially wonder if the different sizes of the molecules (or do they all have the same size?) and the constellation make sense in theory.

Many thanks


texts: Addition of 1 equivalent bromine to 1,3 pentadiene at temperature below 0 degree Celsius gives which compound?

texts: As far as I know reactivity of alkenes towards addition with halogens is directly proportional to their nucleophilicity, so bromine in this particular case should attack the double bond at Carbon-3 but in my textbook answer Bromine has been made to react with double bond at carbon-1


texts: Why is pyridinium chlorochromate selective compared to chromate, dichromate etc.?

texts:
One can use PCC (pyridinium chlorochromate) to oxidise an alcohol selectively up one level - to an aldehyde/ketone, without further oxidation to a carboxylic acid.
Why is pyridinium important to this selectivity?

I understand that usually PCC is dissolved in dichloromethane and not in anything like THF, and this prevents the formation of a hydrate, which can then act "like" an alcohol in it's oxidation to a carboxylic acid, but I can't figure out why it's important that pyridinium is used.


texts:
Using Diffuse Reflectance Spectroscopy, I have obtained the band gap for $\small\ce{SiO2}$ (purchased from a chemical retailer) in the range of 3.25 to 4.75 eV.

I would like to know if the values are in the right ballpark and, if not, would like to review the DRS procedure that I carried out.  I would also like to know if the band gap determined through DRS would have such a wide range.


texts:
Why are heavy metal ions such as those of Hg and Cd toxic to animals?
While studying green chemistry I came to know about the Minamata disease caused by Hg and other disorders due to the accumulation of Hg and Cd so why at all are heavy metals toxic is the reason chemical or biological?


texts: Why is the equilibrium constant being calculated differently here?

texts: In my NMR textbook, it says the equilibrium constant for a dynamic process (e.g., A in equilibrium with B) is calculated by the concentration of A divided by the concentration of B.  Is this a typo?  I thought the equilibrium constant was products over reactants.


texts: How to predict (know) the products of the reaction SnO+NaOH?

texts:
I would like to know how to complete the reaction $\ce{SnO}+\ce{NaOH ->}$, how can I form a salt and water from this?

I've seen that the complete reaction is:

$$
\ce{SnO + 2NaOH ->Na2SnO2 + H2O}
$$

How to know what will be formed?


texts: Does the benzene ring in styrene show a negative inductive effect on the ethenyl group?

texts: I know that a group exerts an inductive effect on another one if there is a difference in electronegativity. In the case of styrene (1) all the atoms are sp2-hybridized. So, how could the phenyl ring show a negative inductive effect on the ethenyl group?


texts: Difference between single point energy and dimerization energy

texts:
I am investigating potential energy surface characteristics of some electrostatic monomeric interactions e.g. $\ce{F-H}$...$\ce{F-H}$.

I'm using DFT and SCS-MP2 to perform the necessary calculations for single point energies. Is it possible to compare single point energy with the electrostatic dimerization energy of the monomers?

Concepts or references will be highly appreciated.


texts: Can a stable vinylic carbocation be formed?

texts: Is it possible to prepare/form a vinylic primary carbocation? Will it be stable (low energy) or not?


texts: What defines a proton as "labile" in NMR?

texts:
What makes some protons labile and others not? For example the OH and NH2 protons get exchanged but CH ones don't.
When we use the D2O test, we say the labile protons get exchanged for D so their peaks disappear. But can't the H be re-exchanged? And why doesn't the H now in the solvent give its own peak?


texts: Is calculus and differential equations really that useful in physical chemistry? How does knowing that helps me in physical chemistry? And how much of calculus must I know in order to do physical chemistry topics such as thermodynamics? Because I am currently a chem major and am wondering what maths courses would be relevant. I currently completed single variable calculus and intend to go on to multivariate calculus as well as differential equations. I wonder how useful that'd be.


texts:
The thermal decomposition of siderite equation: $\ce{FeCO3 -> FeO + CO2}$ looks correctly balanced to me, you can notice $\ce{1 Fe , 1 C , 3 O}$ on the Left side and the same number of molecules on the other side.

However my text book writes it as $\ce{2FeCO3 -> 2FeO + 2CO2}$
and I wanted to know why mine is not correct.


texts: Green kerosene in copper container goes colorless

texts:
I recently got hold of an old blowlamp that had not been touched for more than 30 years.
The fuel tank of the blowlamp is made of brass.
I poured the old kerosene from the blowlamp into a clean polyethene flask, the kerosene was clear and quite green in color. The flask got about half full.

The next day the kerosene had turned colorless and there was a brown  precipitate. The flask was not shaken or subjected to strong light.

What happened here? Something that had been stable for years suddenly reacting. If it is a reaction with oxygen, does oxygen diffuse that easily through kerosene?

Was the green substance an inorganic copper salt dissolved in the kerosene or was it some kind of organic "copper kerosenate"?


texts: Comparing bond lengths in metal carbonyls

texts:
Question:

It's solution is given as:

Now I don't understand which d$\pi$ electrons have been considered here. For example, in $\ce{Fe(CO)_5}$, according to this, number of d$\pi$ electrons would be 4. I cannot see how it is 4. Secondly, is it the right method to compare the bond lengths?
I thought of this in terms of electron density, more is the electron density in the complex, stronger would be the metal ligand bond, hence weaker the carbon-oxygen bond, hence more the C-O bond length. But, since the atoms are different, I don't know if this idea would work in this case.


texts: Porous materials: Is the expression of a mean free path $\overline{\ell}$ of the gas molecule valid for a binary mixtures?

texts:
Suppose that I have a binary gas mixture at low pressure. Can I calculate the mean free path $\overline{\ell}$ of the gas molecule in a pores of solid material by substituting a molecular weight of a single component by Molecular weight of the binary mixture $M_{m,\rm mix}$ as well as the specific gas constant of this mixture $R_{\rm mix}$, such that I get:
\begin{equation}
\overline{\ell} \:=\: \dfrac{3.2\cdot \mu_g}{p}\cdot \left(\dfrac{R_{\rm mix}\cdot T_{\rm abs}}{2\pi\cdot M_{m,\rm mix}}\right)\:\:\:\rm\left[m\right]
\end{equation}
I am calculating $\overline{\ell}$ in order to determine the main diffusion mechanism in the pores (Bulk diffusion (Fick), Knudsen or its combination).


texts: Create a buffer using CH3COOH and NaCH3COO that has a pH of exactly 3.75.?

texts:
a 50 mL sample of your buffered solution will have to be able to withstand the addition of 25.0 mL of 0.100 M NaOH solution.

the buffered solution will break after the addition of no more than 35.0 mL of the 0.10 M NaOH.

Can someone give me an overview of how to approach this? Thanks


texts: Should I include solvation in quantum chemical calculations of a simplified protein-ligand interactions?

texts:
I am running a B3LYP-D3/6-31+G geometry optimization of a protein-ligand interaction. Well, not quite, I have simplified the protein to four amino acids surrounding the active site, but I keep the entire ligand (170 atoms total).

I am wondering if I should optmize the geometry in solution, i.e. will including solvation effects make my results (energies) be more realistic? My mind is split.

On the one hand, I am modelling a biological system which usually takes place in aqueous solution. On the other hand, my system is so simplified, that it no longer has much root in reality. By "placing my molecules in water", the water molecules will interact with parts of my system that otherwise would not interact as strongly (there would be much less water inside the protein than outside it, I mean). So, I feel there is no guarantee that my results will improve, and I am not able to find any data indicating one or the other. If I included the entire protein, then the case would be different, perhaps, since at least then that protein would be "solvated correctly".

So, given the simplified system, will solvation improve the resulting geometry, and thus the interaction energy between the protein residues and the ligand, or not?


texts: Reforging tungsten/tungsten carbide temperatures

texts:
I was wondering about the reforging of tungsten and the temperature needed.

As I understand it, tungsten melts at $\pu{3442 ^\circ C}$ and tungsten carbide at $\pu{2870 ^\circ C}$. However, once a jeweler makes the rings they will never take them back to alter them.

Does the temperature needed to melt a pure tungsten ring change after the initial forging (with all heat treating and cooling included) or is there no change?

If there is a change:

What temperature is needed for tungsten?
What temperature is needed for tungsten carbide?
What atomic/chemical changes took place?


texts: A possible reaction of heating Terephthalic acid

texts: There is no reaction of terephthalic acid heating effect on internet (atleast Wikipedia). I have written the most probable reaction possible as per my knowledge. Please tell if it is spontaneous and possible or not. Also give real conditions of doing the reaction if possible.


texts: What is the mechanism for the hydrolysis of the boron-alkoxide complex in NaBH4 reduction?

texts:
According to this question, the stoichiometry of the reduction of a ketone is such that sodium borohydride can reduce up to 4 ketones by forming a boron-alkoxide complex.

The next step would involve the hydrolysis of the complex, and I've been searching through textbooks to no avail. What would the mechanism for this hydrolysis look like?


texts:
Disclaimer: Potentially more of a physics question, but this area is muddy.

I'm trying to find 720 nm LEDs but they're proving to be very uncommon. In fact, there seems to be a gap between 660 nm up to ~730 nm. I've only been able to find one supplier of 720 nm LEDs (data sheet here). These LEDs also tend to be very low powered compared to their counterparts in the nearby range. For example, a typical 690 nm LED outputs 690 mW, whereas the 720 nm LED only ouputs 170 mW, and that's the strongest one I could find (which is no longer carried).

My gut feeling says this has to do with the material being used in the LED (in this case GaAlAs). Perhaps it's very difficult to dope the material in such a way that it emits 720 nm light? I've already noticed that these LEDs are prone to burning out. Is the material just not very good for this purpose? Hopefully someone with more insight into this topic could shed some light (heh) on the situation.


texts: I have heard that benzene is a dangerous chemical for humans; it causes cancer and so it's use is restricted/regulated. But many organic compounds that we use contain benzene in some form such as oils, foods, even medicines (paracetomol). So is benzene really harmful to people's health?


texts: Planar transition-state of proline racemization facilitated by proline racemase

texts:
The racemization of proline can be facilitated by the enzyme proline racemase.

Since the active sites of enzymes complement the conformation of the transition-states of the molecules they act upon, the most effective enzyme-inhibitors often resemble these transition states.

This enzyme can be inhibited by the transition-state (TS) analog pyrrole 2-carboxylic acid.

The strength of the bond between the TS-analog and the enzyme, is approximately 160 times stronger than the proline-enzyme bond.

When I was first reading about this, I did not believe it because of the negative charge on the alpha-carbon. I decided to draw the resonance structure of the transition state, to find a double bond between the alpha and carboxyl carbons.

My guess is that this resonance structure would make the transition state relatively planar (as is pyrrole 2-carboxylic acid).

But my question is, how "planar" is the transition state, and how might one determine the exact bond angles at the alpha-carbon?

TLDR: How "planar" is the transition state of proline isomerization, and how might one determine the exact bond angles at the alpha-carbon?

(P.S. Sorry for the bad scaling of my ChemDraw pictures, I don't know how to fix it.)


texts:
I noticed when brushing my teeth that toothpaste causes water to spread away from it. If you put a bit of toothpaste water mixture on your finger and touch it to a wet sink you will see the water on the sink travel away from your finger.

My question is what chemical in toothpaste is causing this to happen and in particular what property of the chemical is causing it.


texts: Mechanism of thyroid hormone synthesis: iodation and free radical formation

texts:
In the synthesis of thyroid hormone, what part of the thyroid peroxidase hormone is specifically responsible for abstracting the free radicals from the aromatic side chains in the iodated tyrosine residues on thyroglobulin?

Also, why are some of the tyrosines converted to monoiodotyrosine, and others diiodotyrosine? Does this have to do with steric hindrance, or the ring de/activating properties of the thyroglobulin backbone, or something else?


texts:
In the example calculation from the conformer search package fafoom is a mysterious pattern that I'd like to understand.

The SMILES code of the given example structure is:

CC(=O)N[C@H](C(=O)NC)C

There is a first not so hard pattern for the smart_cistrans pattern identifier

C~[$(C=O)]-[$(NC)]~[C]

which tells the program that peptide bonds behave like cis-trans isomers. That is relatively easy to see but I don't really understand it to adapt it on further problems.

But there is another identifier for torsion angles that for me is even harder to understand:

[*]~[!$(*#*)&!D1]-&!@[!$(*#*)&!D1]~[*]

The [*]'s at the beginning and at the end look like defining any atom ... but the cursing signs in the middle don't tell me anything.

Dear reader, if you understand how those patterns are generated, I would ask you break them down piece for piece that I can use them afterwards on my own.


texts: Mathematical relation between bond angle and fraction of s or p character

texts:
In Concise Inorganic Chemistry by J.D.Lee (Adapted by Sudarsan Guha, Fourth Edition), on page 75, under the topic "Effect of Electronegativity - When the surrounding atom is same with different central atom having lone pair" it is given:

The effect of electronegativity as postulated in VSEPR theory explains the order of the angle for the above molecules (Hydrides of groups 15 and 16) but cannot rationalize very small angles (~$90^\circ$) in $\ce{PH3,AsH3,SbH3}$ and $\ce{H2S,H2Se,H2Te}$ with respect to $\ce{NH3}$ and $\ce{H2O}$ respectively.
To explain this, Drago suggested an empirical rule$^{[1]}$ which is compatible with the energitics of the hybridisation. It states that if the central atom is in the third row or below in the periodic table, the lone pair will occupy a stereochemically inactive s orbital$^{[2]}$, and the bonding will be through p orbitals, and bond angles will be nearly $90^\circ$ if the electronegativity of the surrounding atom is less than or equal to $2.5$.
The above rule is based upon the relation between hybridisation and bond angle for two or more equivalent s-p hybrid orbitals, where the fraction of s character (S) or fraction of p character (P) is given by the relationship:
$$\cos \theta = \frac{S}{S-1}=\frac{P-1}{P}$$
for $\theta \in (90^\circ,180^\circ)$
The following are links to previous questions asked on Chemistry Stack Exchange regarding concepts in this quoted text.
[1] : Drago's Rule : What is Drago's rule? Does it really exist?
[2] : Stereochemically (in)active s orbital : What is a stereochemically active or inactive s orbital?

This formula,
$$\cos \theta = \frac{S}{S-1}=\frac{P-1}{P}$$
relates the bond angle $\theta$ and the fraction of s/p characters. I tried to plug in some standard values.
For example, On substituting the expression with S=0.25 or P=0.75, I get $\frac{S}{S-1}=-0.33...$ and $\frac{P-1}{P}=-0.33...$. I know they both give the same as in sp$^n$ hybridisation where only s and p orbitals are involved, the sum of fractions of the s character and p character i.e., S+P=1, and I was able to interconvert the expressions $\frac{S}{S-1}$ and $\frac{P-1}{P}$ with simple substitution - S=1-P or P=1-S.
On finding the cosine inverse of -0.33...,
$\cos ^{-1} (-0.33...)=109.471^{\circ}$
which is exactly equal to the tetrahedral angle ($109.471^{\circ}$). From this, we can obtain the bond angle in sp3 hybridisation. And similarly, we can do it for sp, and sp2 hybridisation which I've skipped here.
It is also possible to the reverse with this formula, i.e., given the bond angle we can compute the fraction of s or p character. For example, for $\ce{AsH3}$, the H-As-H angle is $91.8 ^{\circ}$, and from the calculation, it can be shown that each As-H bond consists of almost 97% p character and 3% s character.
My doubt is how did they arrive at the given formula? Is there any derivation* for this or is that simply an experimental result? Will this work for all values of S and P (under the constraint S+P=1)? What is the logic behind this formula?
I am unable to find any useful information about this on the internet.

*Simple or easy to understand derivation which can be understood by a high school student.


texts: How can methane absorb infrared light within wide range of frequency but CO2 can't?

texts: Methane is one of the most potent greenhouse gases in Earth's atmosphere.I saw a lot of answers related to it but lacks de facto exegesis to it.


texts: I have three different HDPE polymers with different melting index but they don't have any elasticity. Physical form of polymers is granules. Can I change glass transition temperature (Tg) and impact resistance with additives?


texts: Does sodium produce water when it reacts with water?

texts:
My 10th grade chemistry book states that:

  "Metals react with water and produce a metal oxide and hydrogen gas. Metal oxides that are soluble in water dissolve in it to further form metal hydroxide. Metals like potassium and sodium react violently with cold water. In case of sodium and potassium, the reaction is so violent and exothermic, that evolved hydrogen immediately catches fire."

So $\ce{Na}$ should react like this:

(i) $\ce{2Na + H2O -> Na2O + H2}$

(ii) $\ce{Na2O + H2O -> 2NaOH}$

When hydrogen catches fire -- that is, when hydrogen reacts with $\ce{O2}$, right? -- does it form $\ce{H2O}$?
If water is not formed, then does the water level decrease?
Is (ii) an exothermic reaction?


texts: How to determine the order of a reaction with not a commensurate rate equation

texts:
As an example of such reactions let's take decomposition of $\ce{N2O}$ which I got the equation from a textbook :

$\ce{N2O = N2 + 1/2 O2}$

with the rate equation of $$-r_{\ce{N2O}}=\frac{k_1[\ce{N2O}]^2}{1+k_2[\ce{N2O}]}$$

So how do we determine the overall order of reaction or order of reaction with respect to a reactant/product ?


texts: What would be the effect of adding liquid beyond the calibration mark on a volumetric flask?

texts: If this happens in the course of preparing a volumetric solution, what should be done?


texts: Determination of solubility equilibrium using galvanic cell reactions

texts:
This is the problem:

We can determine the solubility equilibrium for silver bromide using cell:

Ag (s) | AgNO3 (aq) || KBr (aq) | AgBr (s) | Ag (s)

We know that:

$\text{AgBr} + \text{e}^- \rightarrow \text{Ag} + \text{Br}^- \ \ \ \text{E}^0=0.095 \text{V}$

$\text{Ag}^+ + \text{e}^- \rightarrow \text{Ag}\ \ \ \text{E}^0=0.799 \text{V}$

First of all isn't that cell diagram incorrect? As far as I understand it is the silver reducing from silver nitrate to metallic silver thus being cathode. And vice versa for the silver bromide that is being produced more as silver is oxidating. Shouldn't the cell diagram be like this instead:

KBr (aq) | AgBr (s) | Ag (s) || Ag (s) | AgNO3 (aq)

Anyways, if we consider the Nernst equation:

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

and assume that the galvanic cell is in equilibrium when there is no voltage (i.e. $E=0$). We can then write:

$$\ln{k}=\frac{E^0nF}{RT} \\ \leftrightarrow k=e^{\frac{E^0nF}{RT}}$$

Then plug in the numbers:

$$\ln{k}=\frac{(-0.095+0.799)\ \text{V}\cdot 1 \ \text{mol}\cdot 96485.31 \ \frac{\text{C}}{\text{mol}}}{8.31451\ \frac{\text{J}}{\text{mol}\cdot \text{K}}\cdot 293.15 \ \text{K}} \\ \leftrightarrow
k= 1.26754\cdot 10^{12}$$

But the right answer is:

$$1.26 \cdot 10^{-12}\ \text{mol}^2/\text{dm}^6$$

Any ideas what am I doing wrong?


texts: Which hydrogen halides react with group 14 oxides?

texts:
$$\ce{6HF +SiO2->H2SiF6 +2H2O}$$

$\ce{HF}$ reacts with $\ce{SiO2}$ to form $\ce{H2SiF6}$.

  Do other hydrogen halides like $\ce{HCl}$ and $\ce{HBr}$ react with group 14 oxides in the same way?


texts: Why does acetonitrile have a larger dipole moment and boiling point than acetaldehyde?

texts:
Experimentally, acetonitrile has a larger dipole moment than acetaldehyde, but I've never understood why.

I always thought that the charge separation between carbon/oxygen is larger than that of carbon/nitrogen, and since the $\ce{C=O}$ bond should be longer than the $\ce{C#N}$ bond, the dipole moment $\mu = \delta d$ would be larger with both larger charge separation and larger distance.

I assume geometry might have something to do with it but I can't really explain such a large boiling point difference.

Data: Dipole moment values:

acetonitrile: $\approx \pu{3.4D}-\pu{3.5D}$ (source)
acetaldehyde: $\approx \pu{2.7D}$ (sources: 1, 2)


texts: Source of the no. of isomers in alkanes, and other organic molecules

texts: I would like to ask if there is a source where I can find all the isomers for the alkanes, or other organic molecules. With other words, a list where each molecule of that group is stated in ascending order, and beside there is a value for the no. of isomers it can form.


texts: Why does bromine increase the viscosity of olive oil?

texts:
Does bromine bond to the carbon in unsaturated fatty acids and break the double bonds between oxygen and carbon? Does this increase the viscosity of olive oil?
Could someone give an elaborated explanation?

This question arose from a lab experiment. Viscosity goes up because less double bondings makes the fatty acids more “packable”. But why would bromine want to break the bonds?


texts: Does the term “substance” refer to any sample of matter that is tangible? In other words is “substance” a macroscopic concept or can we also refer to individual particles such as atoms, molecules, etc. as substances?


texts: Reduction of triphenylmethane dyes in ink

texts:
Right now I'm trying to explain why the ink from an ink pen turns colourless in water.

I know that the pH is responsible as it breaks apart the conjugated system of double bonds. I'm just not sure on which part, to $\ce{OH-}$ comes into play (example: Water blue).

My suggestion would be that $\ce{OH-}$ can be reversible added to double bond in the center forming two phenyl rings and one ring with 2 double bonds (which will rearrange into a phenyl ring with the double bond from the following amide-group) with a $\ce{C-OH}$ in between.

Under acetic conditions, the $\ce{OH-}$ is eliminated.

Is that correct and does anyone know a mechanism, explanation etc. for that reaction somewhere on the Internet?


texts: Why would the first Tg be higher than a rescan Tg of an epoxy by DSC?

texts:
I have some small cured epoxy shafts I am cutting segments out of for checking Tg by DSC. First scan gave a Tg of 118 °C, follow on was 109 °C. Scans were repeated on a new sample of the shaft with similar results.

250 °F curing dicy based epoxy system. Neat resin before cure has exotherm onset at 127 °C and the curve's peak is 142 °C by DSC.

Any idea why the first scan would be higher than the rescan?


texts:
If I wanted to perform a Virtual Screening for one molecule and several ligands, take for example, the docking between TDO protein and several antidepressant drugs:
How would I be able to correlate the docking affinity with a physiological effect?
Is it necessary to perform clinical studies also?
I think this question could be extrapolated to many cases of MD, but let's take the molecules discussed as an example. TDO catalyzes the oxidation of L-tryptophan (L-Trp) to N-formyl-L-kynurenine, as the first and rate-limiting step of the kynurenine pathway. It is an enzyme, and as such a molecule with a high docking affinity would probably inhibit it´s action.
But what if the molecule was a membrane transporter? How could we determine if the binding to a ligand prevents the binding of the receptor, or on the contrary favors it?
PS: Not sure if this question belongs to this forum, if it´s more suitable in bioinformatics or another let me know.


texts: Volume in decimetres cubed dimensional analysis

texts:
In chemistry class, we were learning about concentration, which is the number of moles of a substance per decimeter cubed of water, expressed as $\mathrm{mol} \cdot \mathrm{dm}^{-3}$.

However, I was confused when my teacher wrote decimeters cubed as $\mathrm{dm}^{-3}$ instead of what I presumed would be $\mathrm{dm}^3$. I asked why and he didn't know. Why do chemists write it like this?


texts: how to increase Keq(equilibrium) with temperatrue

texts:
$$\ce{C_{(s)} + H_2O_{(g)} <=> CO_{(g)} + H_{2(g)}}$$

$$\Delta H = +131\ \mathrm{kJ}$$

If the reaction is in a state of equilibrium under standard conditions, what can be done to increase the value of $K_\text{eq}$?

My question is would you have to increase or decrease the temperature to increase $K_\text{eq}$?

I know the basic principle that you have to decrease the temperature to increase $K_\text{eq}$, but in my notes that was for $\ce{A +B<=>C}$ and the reaction above is not in that form, Instead it has two products. Would this still apply?


texts: Entropy change when liquids at two different temperatures are mixed

texts:
Two quantities of water ($M_\mathrm{r}=18$) each of mass $216\ \mathrm{g}$ are mixed together in a
  vessel. The temperatures of the two quantities before mixing are $303\ \mathrm{K}$ and $333\ \mathrm{K}$. The entire system is perfectly insulated and the vessel has a negligible heat capacity. Calculate the change in entropy after equilibrium has been established, and comment on your result in the light of the Second Law of Thermodynamics.
  Note that $C_{\mathrm{m},p} = 75.5\ \mathrm{J\ K^{−1}\ mol^{−1}}$ for liquid water in this temperature range.

Is it correct to assume that the temperature of the water at equilibrium will be half way between the two values (i.e. $318\ \mathrm{K}$)? If so, I think the rest of the problem can be solved by using $\Delta S=\frac{C_V}T\Delta T$. Is this correct or is it more complicated?


texts:
I am given the reduction potential of $\ce{Fe^{3+}}$ to $\ce{Fe^{2+}}$ as well as the dissociation constants $\ce{K_D}$ for a $\ce{Fe^{3+}}$ complex and a $\ce{Fe^{2+}}$ complex (effectively, the ratio of concentrations of the $\ce{Fe^{3+}}$ complex and $\ce{Fe^{2+}}$ complex, if I divide one constant by the other).
I need to find the reduction potential of the $\ce{Fe^{3+}}$ complex.
How would I go about this?
Is it possible that I could use the reduction potential of $\ce{Fe^{3+}}$ to $\ce{Fe^{2+}}$ as an estimate for that of the $\ce{Fe^{3+}}$ complex, and then use the
Nernst equation to plug in the concentrations of the two complexes?  Or is there no guarantee that these two potentials would be close?

Specifically, these are iron-siderophore complexes.


texts: Are there any polyprotic acids where Ka2 is greater than Ka1?

texts: My chemistry textbook says that in the ionisation of a polyprotic acid with Ka1, Ka2 and so on, 'the first Ka is usually the largest.' I took the word 'usually' to mean that there are exceptions to the rule, but I haven't been able to find any cases where Ka2 is greater than Ka1.


texts:
Problem

When the number of electrons in bonding molecular orbitals is equal to number of electrons in anti-bonding molecular orbitals bond cannot be formed between two atoms because
A) Bonding effect by the electrons in bonding M.O.s is cancelled by the antibonding effect of electrons in antibonding M.O.s
B) Antibonding effect by the electrons in antibonding orbitals is more than the bonding effect by the electrons in bonding M.O.s
C) Average energy of bonding and anti-bonding M.O.s is more than the average energy of atomic orbitals from which they are formed
D) Average energy of bonding and antibonding M.O.s is equal to the average energy of atomic orbitals from which they are formed

Answer

 B and C

My thoughts
I get the reason for option B as anti-bonding orbitals have higher energy comparing to the bonding orbitals, so naturally their destabilizing effect must be greater than the stabilizing effect offered by the bonding orbitals.
But I really can't understand the average energy concept of orbitals as expressed in the option C . could you help clarify what exactly is the energy concept regarding the molecular orbital and atomic orbital ? and how they can be compared?
Correct me wherever I'm wrong.


texts:
I'm looking for a recipe including concentrations and amounts to prepare the iodine clock reaction.
I only have Hydrogen Peroxide, KI, Starch powder and Sodium Thiosulphate.
Firstly, do I need anything else or can the reaction be done with these ingredients alone ?
If these are sufficient then can someone please include the recipe.
I have found numerous recipes online but most contain other ingredients or don't go into concentrations or masses/volumes.


texts: How is taste of chemical compounds determined?

texts: How do we know the taste of compounds, and their smell too, when some of them are poisonous. My textbook had that Lead is sweet in taste, but it's poisonous. So, how exactly do we determine their taste and odour of such compunds?


texts: Why are there so many reactions for the discharge of LiCoO2?

texts:
I've just managed to understand a bit the meaning of having the notation of 0.5 in a molecular formula, when I found a set of multiple notations for the same discharge process that started to confuse me.
One can find this set of notation for the discharge reaction of a LiCoO$_2$ cathode:

$CoO_2 + Li^{+} + e^{-} \rightarrow LiCoO_2$ (see here)
$LiCoO_2 - Li^{+} - e^{-} \rightarrow Li_{0.5}CoO_2$ (see here)
$Li_{1-x}CoO_2 + xLi^+ + xe^- → LiCoO_2$ (see here)
$2Li_{0.5}CoO_2+Li^{+}+e^-\rightarrow 2LiCoO_2$ (see here)
$Li_{0.5}+0.5Li^+ + 0.5e^-\rightarrow LiCoO_2$ (see  here)

and the list can continue...
Why are there so many notations for the same thing? It's so confusing for someone who is trying to understand this. Aren't they representing the same discharge process? What changes? And why do we have to have so many notations?
Sorry if this is too puerile, but notations were always a source of confusion for people trying to learn something from different sources.


texts: How do I analyse this data? (optimization experiment)

texts:
I conducted an experiment to find the optimal concentration for sugar in yeast respiration, and this is the data I found:

What do I do from here? Do I just fit a linear model on the increasing portion, another one on the decreasing portion, and see where they meet and say that's the optimal value? If not, do I try to fit another type of model? How do I justify that model?


texts: Will t-butoxide still form less substituted alkene when there is a possiblity for more stabilisation?

texts:
Consider this reaction:

Will a usual Hoffman elimination take place or will a carbocation form by leaving of $\ce{Br}$ and rearrange to give a conjugated alkene like this one:

I have heard that reactions with t-Butoxide are E2 and hence carbocation are not formed. So wouldnt the major product still be the least substituted alkene?


texts: How are clathrate hydrates formed in the lab?

texts: How do chemists create clathrate hydrates in the lab (for example, those of $\ce{CO2}$, $\ce{O2}$, $\ce{H2}$ or $\ce{CH4}$)? I'm assuming that they just place a pressurized container of water and the gas in question into a freezer (or liquid nitrogen). However, I'm probably somewhat incorrect and don't have the resources currently to perform such an experiment.


texts: Can a saturated hydrocarbon have side chains?

texts:
Saturated hydrocarbons: Each carbon atom is bonded to as many hydrogen atoms as possible. In other words, the carbon atoms are saturated with hydrogen (Source).

or

  Saturated means that the hydrocarbon has only single bonds and that the hydrocarbon contains the maximum number of hydrogen atoms for each carbon atom Latech.edu.

But if a carbon chain has side chains, the carbon from the side chain takes the place of a hydrogen. So it doesn't have as many hydrogens as it could have right?

But then I guess I could say that anything except methane has less than the max (4) number of hydrogens.

So what exactly is meant by maximum number of hydrogens?


texts: Visualizing s and p orbitals from contracted basis set

texts:
I was thinking about basis sets used in Quantum Chemistry programs and thought of why not try to visualize them.
I started with GTO from EMSL website for $\ce{H2}$, specifically cc-pVDZ basis
which is the following,
! s functions
H    5    3
     13.0100000            0.0196850              0.0000000              0.0000000
      1.9620000            0.1379770              0.0000000              0.0000000
      0.4446000            0.4781480              0.0000000              0.0000000
      0.1220000            0.0000000              1.0000000              0.0000000
      0.0297400            0.0000000              0.0000000              1.0000000
! p functions
H    2    2
      0.7270000           1.0000000              0.0000000
      0.1410000           0.0000000              1.0000000

I framed the basis functions for $s-$orbital as following,
$$0.019685\times exp(-13.01  r^2) + 0.137977\times exp(-1.962  r^2) + 0.4446\times exp(-0.478148  r^2)$$
$$1\times exp(-0.12200 r^2)$$
$$1\times exp(-0.02974  r^2) $$
This is only the radial part (the associated spherical harmonic is not here), but still I can plot the above against $r$.

The above plot is for the $s-$functions.

I am able to do the same thing for $p-$functions, and I get similar Gaussians (not shown here) with different widths, and centered at zero.
Shouldn't the lobe of $p-$ be centered larger than zero (which implies that the functional form I am using is not correct/incomplete for $p-$function). Or the lack of explicit spherical harmonic functions does not allow the $p-$functions to be similarly visualized. Could someone clarify.


texts:
My textbook said $\ce{NO2+}$ and $\ce{NO2-}$ both have resonance structures, now I am a little bit confused since I cannot figure out the resonance structure for $\ce{NO2+}$.

What is it?


texts: Number of stable molecules of artificial molecule XY4

texts:
Suppose element X has $5$ stable isotopes, and element Y has $6$ stable isotopes. Find the number of natural molecules, knowing that an X has a charge of $+4$ and Y has a charge of $-1$.

What I tried was this: for element X we have $5$ options, and for each element Y we have $6$ options. Therefore the total number of options would be $5 × 6 × 6 × 6 × 6$.

But this answer is clearly wrong, as it counts the same type of molecule, multiple items. (AAAB) and (AAABA) count twice which we don't want to happen. (A is an isotope of Y and B is some other isotope of B)

What can I do?


texts: What is the difference between hexaaqua(metal) ions $$\ce{Fe^{3+},Al^{3+}, Cr^{3+}}$$ and a hydrate? Since both of these absorb water into it own molecular structure. Would it be that hydrates have neutral charges where as these have positive charges? Why did we name Hexaaquairon ion it's name rather than Iron(3) Hexahydrate.


texts: Why is potassium monoxide (K2O) coloured?

texts: Potassium monoxide is rarely formed and is a pale yellow solid. I don't understand how is this compound coloured because in oxide anion electron cannot excite in the next orbital due to huge energy difference. Also there are no empty molecular orbitals like there are in peroxide and superoxide anion. The colour cannot come from $\ce{K+}$ cation because electron cannot be excited. So how is this compound coloured?


texts: Is there an inexpensive solvent I can use to dissolve thermal paste without scrubbing?

texts:
I'm removing large voltage regulators from circuit boards which are often coated with a generous amount of thermal grease. I've found that 70% isopropyl alcohol works great for softening this and removing it with some light scrubbing.

The problem I have is that, without a lot of additional effort and scrubbing, the surfaces will often retain a film from the grease. There are also areas which I may have missed or were unable to reach when scrubbing.

This type of grease is often electrically conductive and can cause a short circuit if accidentally brushed over the pins of a chip. It's also just plain annoying when it gets on your hands.

Is there an inexpensive solvent that I can use to dissolve the thermal paste without having to scrub the components? I felt that it would be more appropriate to ask this here on the chemistry stack exchange as I'm also interested in understanding how other solvents would work better for this.

I tried leaving the components in a bag of 70% isopropyl alcohol but this confirms that it only softens it. The thermal paste don't actually free itself from the surface without some mechanical force.

See here for a photo where the surface looks clean but you can see where I scraped my finger across it through the bag and it removed more of the grease.

The color of the component becomes a dull grey due to the grease becoming embedded in the pores of the plastic which is what it's supposed to do. I would like to know if there is a way to simply drop these into a chemical and have the grease dissolve away on its own without damaging the package.


texts: Do atoms react to fill outer shell or 8 valence electrons?

texts:
I recall in middleshool chemistry we simply said electron shell configurations were 2,8,8,many which I would have no problems with.

But now I'm learning that shells contain $2n^2$ electrons where n is the shell number.

Then why is "full outer shell" and "8 valence electrons" still used interchangeably when describing stability? i.e we are taught that atoms react in ways that achieve an outer shell of 8 valence electrons. But at the same time, they react to form full outer shells.


texts: How effectively bound Na2CO3 and BaCL2 water

texts: How fast does $\ce{BaCl2}$ bind water from its surroundings, becoming a hydrate, compared with same process with $\ce{Na2CO3}$?


texts: I’m confused, because it seems like Hückel’s rule is satisfied (two electrons from the nitrogen lone pair and four from the double bonds) and that the molecule should be aromatic. Where am I going wrong here?


texts:
I know that Gibbs free energy change represents the amount of the non-expansionary work that a reaction is capable of doing but what happens to this energy at equilibrium? Why is the system unable to do work? Why is the Gibbs free energy change equal to zero at equilibrium?

Edit: Please don't simply write the derivation that we use to conclude that ∆$G$ must be zero at equilibrium. Please try to explain the physical significance behind this fact.

Please also note that I have already searched this website for an answer to my question, found only the following question but the answers only explained the Math:

Gibbs free energy-zero or minimum

Thanks ever so much in advance :) Regards.


texts: The difference between the different types of rhodamine

texts:
What is the difference between different type of rhodamine, for example rhodamine red and rhodamine green?
are these two type of rhodamine (red & green) have a good Raman signal?
We would like examples of Raman signals of these two types of rhodamine.


texts: How is hyperconjugation into antibonding orbitals stabilizing?

texts: So I learned that hyperconjugation is electron delocalization from a $\ce{C-H}$ $\unicode[Times]{x3C3}$ bond into an empty p orbital (on a carbocation for example) or an antibonding orbital. I get how it's stabilizing in the case of an empty p orbital, but how is it stabilizing in terms of delocalization into an antibonding orbital, since by definition electron density in antibonding orbitals is destabilizing?


texts:
I performed the iodine spectrum experiment to observe vibronic transitions. I heated the iodine crystals to produce vapors (at a little above room temperature) and observed absorption spectrum with a diffraction grating and a spectrometer. But I am getting some quirky results as indicated following.

In Ref 1 and Ref 2, it is stated that near room temperatures, $I_2$
is in the ground electronic state and in the lowest vibrational state too ($X,
v''=0$ state), so transitions are observed only from thsat state.
Ref 2, Ref 3, Ref 4 and Ref 5 state that from $X, v''=0$ state, Franck-Condon principle tells that transitions can be observed only to $B, v'$  states with $v'$ ranging around $20-50$, and they also cite the standard values of energies corresponding to particular $v'$ values so as to numerate the observed bands accordingly.

Now, at near room temperatures, I after numerating my bands, observed that I was seeing dark bands for $v'=0$ onwards! (I after assigning the standard band, numerated the lower energy bands backwards.) So, one of the above points have to be false!

Questions: Please tell what can possibly go wrong? If I'm getting some contributions from $X, v''>0$ states, how to identify them (since Ref 4 clearly states that the bands with transitions from $x, v''>0$ states "should not be included in this numeration" in for calculating the parameters from Birge-Sponer plot)?


texts: Overview of material characterization methods

texts:
I have been searching for quite some time now, but I feel like it is impossible to find some sort of chart where I can determine which characterization method (microscopy, spectroscopy, electrochemical, DMA etc.) is the best in which situation. There are so many methods and an overview would really help me to understand them better.
Does anyone know if a book or a site provides such an overview? I am pretty desperate, that's why I'm asking it here.


texts: Adding apple cider vinegar to a solid DIY deodorant

texts: If I wanted to add a bit of apple cider vinegar to my oil based deodorant, to increase antimicrobial properties, would this cause me to need a preservative? My deodorant is not water based, so I don't need a preservative in my formulation currently. I also already use lemon in my recipe.


texts: Identification of aqueous solutions of sodium hydroxide, sodium acetate and potassium thiocyanate using nickel(II)

texts:
I'm very new to chem — taking an intro to chemistry course where we are currently focused on substance identification. I have two substances, both aqueous solutions of either $\ce{NaOH},$ $\ce{KSCN},$ or $\ce{NaCH3COO}.$ Both substances are colorless with a pH higher than 7.
When mixed with $\ce{NiCl2},$ substance A forms a precipitate, and substance B does not. I know that you would expect a precipitate to form when $\ce{Ni^2+}$ ions are exposed to $\ce{OH-}$ ions, and I know that you would not expect a precipitate to form when $\ce{Ni^2+}$ ions are exposed to $\ce{CH3COO-}$ ions, so if $\ce{KSCN}$ was not a potential substance, I would know that substance A was $\ce{NaOH}$ and substance B was $\ce{NaCH3COO}.$
However, I am confused as to how $\ce{KSCN}$ fits into this. It's my understanding that since $\ce{SCN-}$ is the anion of thiocyanic acid, which is a weak acid, alkali metal compounds with $\ce{SCN-}$ anions are weak bases.
I have done some research and concluded that $\ce{NiCl2 + KSCN}$ will not form a precipitate. Is substance A $\ce{KSCN}$ or $\ce{NaOH}?$ Is there even a way to distinguish the two with this data?


texts: Which Chemical Database Software Are Available?

texts:
By chemical database software I mean software with similar functionalities to Instant JChem in that they have a large database of different compounds and have the basic capabilities you, or at least I expect from a chemistry software. Namely:

Can approximate the chemical and physical characteristics of the compounds in question.
Can approximate products of reactants and their corresponding proportions.
Can show the 2d and 3d structure of compounds in the database.
Can connect to online chemical databases like PubChem, ChemSpider, NCBI, etc.
Has a molecule editor.

I would also prefer it if it is free of charge.


texts: Why was the prefix 'bi' used in compounds, such as for bicarb of soda?

texts:
According to the Wikipedia article IUPAC nomenclature of inorganic chemistry,

  he prefix bi- is a deprecated way of indicating the presence of a single hydrogen ion

A very common example is the commonplace 'bicarb of soda', or sodium bicarbonate (or using its correct chemical name sodium hydrogen carbonate). On the Wikipedia page for sodium bicarbonate there is a note that states that:

  The prefix "bi" in "bicarbonate" comes from an outdated naming system and is based on the observation that there is two times as much carbonate ($\ce{CO3}$) in sodium bicarbonate ($\ce{NaHCO3}$) and other bicarbonates as in sodium carbonate ($\ce{Na2CO3}$) and other carbonates.

However, the statement above is not particularly clear, especially as carbonates are not the only compounds that used the 'bi' prefix, such as:

Bisulphite $\ce{HSO3-}$

Bisulphate $\ce{HSO4-}$

Why was the prefix 'bi' used to indicate the presence of a single hydrogen ion in compounds?


texts:
I have to draw the 4 four isomers for the molecule  $\ce {C2H2Cl2}$  when $\ce {Br2}$ is added to it. At last the four isomers for  $\ce {C2H2Cl2Br2}$.
I have found three of them:

I can't find the last one.


texts: What would an ammonium sulfide fire look like?

texts:
I am writing a novel and the climax involves killing my protagonist in an explosion. My science knowledge is poor but I believe my scenario is entirely plausible except possibly a couple of details.

My character is in a small, poorly ventilated room. It has an equipment or instrumentation cart with some 1970s era machinery. Within it is a jar of ammonium sulfide from which the gas is pumped via leaky tubes. The leak has gotten worse and the room is very smelly. He bends over to unplug the equipment, which is not grounded. The smell is worse near the floor. Pulling the plug out of the outlet causes a spark and the gas ignites.

I hope this is perfectly logical so far. Now here are a couple specific questions.

What would that fire look like? I currently have a line of fire in the air back to the source by the jar. It then explodes. I then have gases like hydrogen sulfide produced and there is a larger, secondary explosion which kills the injured character.

Would it be better to say that all of the gas burns in a flash. Not much damage is actually done, but the jar of ammonium sulfide is heated, begins to produce hydrogen sulfide and other pyrophoric gases and then there is a spectacular secondary explosion?

I am not necessarily going to explain the science to the reader, which gives me some wiggle room. But I do want these events to be plausible.


texts: What does the Sm5Ge4 orthorhombic structure look like?

texts: I see tons of papers referencing this structure but none show what it looks like.


texts:
I want to make a diamond at home using chemical vapor deposition (CVD).

If I use a metal chamber filled with methane and hydrogen gas and heated with a microwave oven oscillator element, will the gas explode?
What is the ratio of methane and hydrogen for the diamond to be able grow?


texts: Theoretical plates in Plate theory of chromatography

texts:
In "Chromatography theory" by Scott and Cazes,
The plate volume is given as ($v_m+Kv_s$) where $v_m$ and $v_s$ are the volume of stationary and mobile phase in the column and $K$ is the distribution coefficient (basically the equilibrium constant of the solute concentration in stationary and mobile phase).
They give the definition of plate volume as

The plate volume is defined as that volume of mobile phase that can contain all the solute in the plate at the equilibrium concentration of the solute in the mobile phase.

The plate concept is introduced to explain the equilibrium attained by the solute in distributing between stationary and mobile phase. We can't assume this equilibrium in the whole column as mobile phase continuously flows during the process and disturbs the equilibrium, so column is considered to be made of number of theoretical plates in which equilibrium is attained for some finite time.
Basically, I am not able to understand the definition of plate volume. Because as the name suggests one can interpret as the column to be made of number of plates which is made of the volume of mobile phase and stationary phase in which the solute is distributed between the two phases. So, I initially misinterpreted the formula of plate volume as $v_m+v_s$.
Please explain the definition of the plate volume. It seems somewhat confusing.


texts:
Given an alcohol-water solution (Liquor products) that may have additives and/or may have been aged in wood, I'd like to boil off the alcohol and the water to leave behind the various additives in a highly repeatable fashion.
I.e. a pan on the stove works OK, but I'd potentially like to throw together something a bit more precise.
Two lines of thinking so far.   Starting with the same amount of solution in both cases:

Use test tubes and a heater block.   Hold the temp at ~180ºF to evaporate the alcohol.  ~212ºF to evaporate the water.   That should concentrate the additives in the bottom of the tube.

Place a some sort of sample paper (?) that exactly covers the bottom of a container.  That should concentrate everything into the paper.

I'm really looking for:

Keywords to search for.   Been a long long long time since I spent time in a science lab of any sort and I don't know what I'm looking for or what is available.    I don't want to throw tons of money at this-- it is just a bit of a personal exploration thing-- but I don't mind spending some $$$ to create a repeatable, quantifiable, process for doing this sort of thing.

Any suggestions on process.  I could be entirely missing the obvious easy solution here because I don't know what I'm doing. :)

A process that potentially creates samples that can be sealed in something -- ziplock bags, perhaps? -- for later reference.   The sample paper process seems to be a better fit for this.


texts: Why is phosphorus pentachloride not used in the synthesis of chlorophenols?

texts: The best method (as I have read) for preparation of chlorobenzene is by reacting it with $\ce{Cl2}$/$\ce{FeCl3}$. Why its not the best practice to react phenol with $\ce{PCl5}$ ?


texts: I am a novice in chemistry and i have a question: I know that water is not a good conductive material (since there is a perfect bond in water I think) but I am thinking that if we add chlorine which has 7 valence electrons this means that there is a hole and this increases conductivity... am I right?


texts: How do I name this alkane with a branch that has bromine?

texts:
I identified the orange portion as the longest carbon chain which is the first step.

Next, I can't call it 3-ethylhexane as the bromine is a branch from a methyl branch.

This is the problem I am facing. Since the methyl branch is on the 3rd carbon, and bromine branch is in the "branched" 2nd.

So, is it called as 3-(2-bromomethylhexane)? Or have I got it wrong?


texts: Why is the oxime tautomer more stable than its corresponding nitroso isomer?

texts:
We know, generally, that the keto tautomer is more stable than the corresponding enol tautomer. I would appreciate an explanation that goes beyond the thermodynamic reasoning, too.

In the nitroso-oxime tautomerism, the nitroso form is analogous to keto isomer and the oxime is analogous to the enol form.
Then why is the oxime more stable than the nitroso isomer?


texts: Preference of grignard between aldehyde and double bond?

texts:
Quick question, in this reaction:

2-Butenal + CH3MgBr  -->  ??

Will the grignard attack the double-bond or the aldehyde carbon?
Please explain this preference, thanks!


texts: Approximating the concentration of ions when a salt dissociates

texts:
In my textbook written that:

  Given that $K_\mathrm{sp}(\ce{Ag2CrO4})=9.0\times 10^{-12}$, consider the solubility of $\ce{Ag2CrO4}$ in a $0.100\:\mathrm{M}$ solution of $\ce{AgNO3}$.

  Initial concentrations (before any $\ce{Ag2CrO4}$ dissolves) are,
  $[\ce{Ag+}]_0=0.100\:\mathrm{M}$ (from $\ce{AgNO3})$ and $[\ce{CrO4^{2-}}]_0=0\:\mathrm{M}$

  The system comes to equilibrium as $\ce{Ag2CrO4}$ dissolves according to the reaction:
  $$\ce{Ag2CrO4(s)\rightleftharpoons 2Ag+(aq) + CrO4^{2-}(aq)}$$
  $$K_\mathrm{sp}=[\ce{Ag+}]^{2}[\ce{CrO4^{2-}}]=9.0\times 10^{-12}$$

  We assume that $x\:\mathrm{M}$ of $\ce{Ag2CrO4}$ dissolves to reach equilibrium, which means that:
  $$x\:\mathrm{M\:\ce{Ag2CrO4}(s)}\rightarrow 2x\:\mathrm{M\:\ce{Ag+}(aq)}+x\:\mathrm{M\:\ce{CrO4^{2-}}\:(aq)}$$

  Now we can specify the equilibrium concentrations in terms of $x$:
  $$[\ce{Ag+}]=[\ce{Ag+}]_{0}+\Delta[\ce{Ag+}]=(0.100+2x)\:\mathrm{M}$$
  $$[\ce{CrO4^2-}]=[\ce{CrO4^2-}]_{0}+\Delta[\ce{CrO4^2-}]=(0+x)\:\mathrm{M}$$

  Giving:
  $$9.0\times 10^{-12}=[0.100+2x]^{2} \cdot [x]$$

Also, here is line I want to discuss (again, taken from the textbook):

  Since the $K_{\mathrm{sp}}$ value for $\ce{Ag2CrO4}$ is small (the position of the equilibrium lies far to the left), $x$ is expected to be small compared with $0.100\:\mathrm{M}$. Therefore:
  $${9.0\times 10^{-12}=[0.100+2x]^{2}[x] \approx [0.100}]^{2}[x]$$

When can this approximation be made and when can it not be made?


texts:
Is DI water (also without $\ce{O2}$ gas dissolved in it after degasification) a sufficiently strong oxidizer to oxidize $\ce{Cu(I)}$ in $\ce{Cu2O}$ to $\ce{Cu(II)}$ forming $\ce{CuO}$?

Will this change at elevated temperatures (e.g., 200 °C)?


texts:
What is the structure of carbon fiber? Wikipedia doesn't give much insight.

  The atomic structure of carbon fiber is similar to that of graphite, consisting of sheets of carbon atoms (graphene sheets) arranged in a regular hexagonal pattern, the difference being in the way these sheets interlock. Graphite is a crystalline material in which the sheets are stacked parallel to one another in regular fashion. The intermolecular forces between the sheets are relatively weak Van der Waals forces, giving graphite its soft and brittle characteristics.

The Wikipedia description begs the question of how exactly are the sheets of graphene interlocked. Are there pi-stacking interactions?


texts: Why is the ionization enthalpy of francium greater than that of cesium?

texts: Why is the ionization enthalpy of francium greater than that of cesium, even though it has a larger size? I found no Google result regarding this.


texts:
I am recently taking courses in environmental chemistry and I was introduced to Pourbaix diagram. I was taught that the lines in the Pourbaix diagrams are equilibrium lines. Lets take as an example the Pourbaix diagram of the water (diagram is taken from Ibanez):

Lets look at the equilibrium line between $\ce{H2O}$ and $\ce{H2}$. The reaction describing this equilibrium line is (with equilibrium constant $K$):
$$\ce{2H+_{(aq)} + 2e- <=> H2_{(g)}}$$
Now at equilibrium taking the $\log K$ and equilibrium constant we obtaing:
$$\log K = \log p_{_{\ce{H2}}} -2 \, \mathrm{pH} -2 \log {[\ce{e-}]} $$
and by defining $\log {[\ce{e-}]} = \text{p}E$ we can obtain (assuming $p_{_{\ce{H2}}} = 1 \, \text{atm}$):
$$\text{p}E=-\text{pH}$$
So we can plot how $\text{p}E$ varies with $\text{pH}$ at equilibrium conditions. What I can't understand is why if we leave that line and move below it in a point which doesn't satisfy the equation we will have only $\ce{H2}$. How is it possible to change $\text{p}E$ without changing $\text{pH}$ if they are both related through equilibrium constant? Why all the water turns into hydrogen?


texts: Difference between Epimers and Diastereomers

texts:
My lecture notes describe epimers as compounds which differ by
configuration at only one carbon and gives the example of D-erythrose and D-threose as being epimers.

However isn't that the same thing as diastereomers? My understanding is that epimers are supposed to be some kind of subset of diastereomers, however I am not sure how or why. I tried searching the web but I got more confused with one site saying that carbohydrates in open form can have two different chirality centres and still be epimers.