texts: Why is reduction potential of water ( 2H₂O + 2e⁻ → H₂ + 2OH⁻ ) is -0.83 insted of 0, as in the case of (2H⁺ → H₂)?

texts:
I came across this value of reduction potential of water while solving a question. Also, I noticed that, for example

$$\ce{Ag+ → Ag}$$

has a fixed standard potential, and the same is used when we do it for a reaction like

$$\ce{AgCl → Ag + Cl-}$$

Then why here in the reduction of water the value differs from the $\ce{H+ → 1/2 H2}$ reaction?

Also, while doing electrolysis of water, which reaction actually happens at the cathode:

$$\ce{2 H2O  + 2 e- → H2 + 2 OH-}\quad\text{or}\quad\ce{2 H+ → H2}~?$$


texts:
Why is nitrous acid prepared in situ?

I am not sure about the above question. First of all, I don't exactly understand what is meant by "in situ". Secondly, how would preparing nitrous acid in situ, in the diazotisation of amines with nitrous acid, make it less toxic or unstable?


texts: Why do people add H(core)+F in Hartree-Fock?

texts:
I'm trying to implement my own HF code, and it seem usual that, after building the Fock matrix $F$, they add that to the pre-existing $H_{core}$, from the two-point interactions, when computing final energy.

As one example, https://github.com/ipudu/SCFpy/blob/master/SCFpy/scf.py . In lines 135-138, they include Hcore in F. Then in line 156, when they actually return the energy, they add Hcore[i,j]+F[i,j], apparently double-counting Hcore.

As another example, in http://sirius.chem.vt.edu/wiki/doku.php?id=crawdad:programming:project3 , when they compute the energy (see Step #9), they use $$E_{elec}^i = \sum_{\mu\nu}^{AO} D_{\mu\nu}(H^{core}_{\mu\nu} + F_{\mu\nu})$$

again apparently double-counting $H_{core}$. Why? What gives?

My best guess is that this is somehow related to the fact that these are double-filled orbitals, containing both spins. But then, shouldn't $F$ need a factor as well, for all it particles occurring twice as well?

In particular, I have an HF code that agrees with the 'crawdad' link above by copying their steps pretty much verbatim. I'm now trying to extend it into a generalized Hartree-Fock code, but I'm having difficulties, and in trying to understand the problem I became confused by this expression.


texts:
I am trying to learn how to draw and name skeletal chemical structures and would like some opinions and help if you may.

In the second (bottom) structure I can see that there are 6 carbons so hex would appear in the name of the structure somewhere, and I can also see that it is part of the methyl group but I have also seen that it looks very similar to 3-methyl-2-pentene which has thrown me a bit, could somebody walk me through this one step by step? Also this structure is a resonance structure if I am correct?

The other one (top) I am completely lost with, I know there is a carbon ring so that is 6 carbons plus the three which are stated, 9 in total would mean 'mon' would have to appear in the name and is also part of the methyl group, how would I go about naming this structure?

Much appreciated!


texts: Do entropy changes have an equivalent of bond enthalpy?

texts:
Is it possible to calculate entropy changes in a way similar to enthalpies from bond enthalpies? For example, to work out the enthalpy change of a reaction you can get the sum of all bonds in the products and minus the sum of all bonds in the reactants to get a reasonable approximation of the enthalpy change of reaction. Does such a thing exist for entropy?

Thanks!


texts: Difference between biosynthesis in organism versus lab

texts: Are there different terms for biosynthesis of a compound naturally in an organism versus the biosynthesis using chemicals in the laboratory or is it just "biosynthesis"?


texts:
In the carbon atom, there are electrons in 2s, 2Px, 2Py, and 2Pz. Out of these orbitals, only 2Px, 2Py, and 2s are hybridized. The 2Pz orbital is left. When making a bond there is a pi bond between two carbon atoms which is formed by the 2 Pz orbitals of the each carbon atom.  In $\ce{CH4}$, 2Pz orbital also hybridized.

The orbital 2Px and 2s always make sigma bonds. Each carbon atom connects with two hydrogen atoms in $\ce{C2H4}$. Therefore I like to imagine that 2py and 2pz orbitals can make sigma bonds with 2hydrogen atoms. Then only left orbitals are 2px and 2s. They can make double bonds between two carbon atoms. 2px and 2s always form as sigma bonds and then the double bond between carbon atoms, one is sigma bond and another also a sigma bond.

I know that according to the VSEPR theory there should be one sigma bond between two atoms. But atoms are hybridized for their comfortability. But according to my above imagination making 4 sigma bonds is more comfortable than making 3 sigma bonds and one pi bond for the $\ce{C2H4}$ molecule. Therefore, why is it not trying to make such a bond?


texts:
I'm partnered with a jewelry production company whose plating baths require $\ce{KOH}$. We're located in Indonesia, where import fees are absurdly high, and reliable suppliers are rare. A local shop sells $\ce{KOH}$ at \$5/kg, but whatever impurities are present in their mix cause enough problems to spoil the entire bath. (Expensive mistake when doing gold plating.) The only alternative we can find is a Merck redistributor, who sells $\ce{KOH}$ at close to \$100/kg, which is ridiculous.

Is there a relatively simple process we could learn (of the DIY variety) for removing impurities, turning non-lab-grade $\ce{KOH}$ into lab-grade $\ce{KOH}$?


texts: Reaction of phenol with concentrated sulfuric acid

texts:
What is the product when phenol reacts with conc. $\ce{H2SO4}$ in excess?

I have been told that the major product will be ortho at low temperature and para at high temperature. Why cannot it form both ortho- and para-substituted product as in the case of picric acid?


texts: Are the rules proposed by Slater for the calculation of effective Z right?

texts:
Today I studied Slater's rules for calculating the effective nuclear charge. One particular line, "The shielding power of the d and f orbital is lesser in comparison to the p and s orbitals", seems to appear in every single book and website I have studied from.
Slater's rules does not seem to take into account the orbitals for calculation of $Z_\mathrm{effective}$. Nevertheless, I don't disagree with the logic behind the statement.
Thus my question is: Do Slater's rules actually account for this logic? If they don't, is it faulty? And, how do Slater's rules account for the shielding effect of the individual orbitals?


texts: Why would there be differences in UV/Vis spectrum?

texts: $\ce{[NEt4]2[NiBr4]}$ dissolved in $\ce{MeCN}$ and $\ce{[NEt4]2[NiBr4]}$ dissolved in $\ce{H2O}$ have different UV/visible spectra in the visible region. How would they differ, for example would one of them have more peaks? Also how would the molar extinciton coefficients differ and what do these numbers tell you?


texts: How to apply the Principal of Atom Conservation (POAC)

texts:
27.6 g $\ce{K2CO3}$ was treated by a series of reagents so as to convert all of its carbon to $\ce{K2Zn3(Fe(CN)6)2}$. Calculate the weight of the product.

I am asking here is that, why we are  applying POAC only on Carbon atom not on Potassium Atom.


texts: Why does radiocarbon dating only work in nonliving creatures?

texts: I understand how carbon dating works, though I do not understand why it doesn't  happen while a creature is living. Because while we are alive we still have carbon 14 in us, so shouldn't it work?


texts: General expression for entropy and free energy

texts:
The specific heat capacity of a solid at constant pressure and low temperatures is given by $$c_p=aT+bT^3$$ with $a$ and $b$ are constants.

How can I calculate a general expression for the entropy $S(T,p)$ and Gibbs free energy $G(T,p)$ as a function of $T$, assuming that $S$ and $G$ are zero at $T = 0~\mathrm{K}$?

I started with trying to calculate entropy by
$$\mathrm{d}S = \left(\frac{\partial S}{\partial T}\right)_p \mathrm{d}T = \frac {c_p}{T} \mathrm{d}T$$
and
$$S = \int_0^T \frac{c_p}{T}\mathrm{d}T = (aT + bT^3)\ln T$$


texts:
What is the reason for why an exergonic reaction would still have some remaining reactants (or an endergonic reaction to have any products)? The explanation given on this page (see Chemical reactions and mixing) is that there is a Gibbs free energy change caused by the entropy change by mixing; therefore, it is always energetically favorable to have at least some of each.

At another page (see Dissociation of weak acids) on the site, the explanation as to why weak acids (with positive $\Delta G^{\circ}$ for reaction with water) dissociate at all seems to be that some molecules do have the energy required for the reaction, analogous to molecules overcoming activation energy in the context of kinetics.

Are these two explanations equivalent? The first one is a macroscopic view that involves entropy of the whole system; the second one involves the distribution of speeds of the molecules themselves.


texts: Safety concerns (Cyanide): Dicyandiamide + Polyamine condensation reaction

texts:
I am attempting to synthesize a poly-amine polymer by condensation between dicyandiamide (also known as cyanoguanidine and dicyandiamine) and diethyltriamine. The polymer is a kind of dye fixative agent for cellulosic fabrics.
The reaction liberates ammonia. Once no more ammonia is liberated, it can be considered complete.
My lab setup is a three neck flask with stirring and a temperature between 110-160 ºC. One neck has the thermometer, the other the stirrer, and the third a tube that goes to a flask filled with acidic water, to trap the ammonia. A bit of vapor escapes through the stirrer as the seals are not perfect. The trapping flask is also exposed.
Since the reaction involves dicyandiamide and heat, I was fearful that it could also liberate some kind of toxic cyanide-like gas. In the literature there is no mention of any kind of toxic emission, however, I take safety seriously. So I wanted to know if anyone can assure me that there are no toxic cyanide-like emissions. And if they were, any advice is appreciated.
Literature:

https://patents.google.com/patent/US5632781A/en
https://patents.google.com/patent/US4764585A/en
https://patents.google.com/patent/US2649354A/en


texts: Why is the van der Waals coefficient b equal to four times the volume of the particle?

texts:
In the van der Waals equation of state

$$\left[p + a\left(\frac{n}{V}\right)^2\right](V-nb) = nRT$$

the coefficient $b$ is supposed to represent the volume occupied by the particles. Why then is it equal to four times the volume and not simply the volume?


texts:
From my textbook:

The [alkali and] alkaline earth metals dissolve in liquid ammonia to give deep blue solutions forming ammoniated ions. $$\text{M}+(x+y)\text{NH}_3 \rightarrow [\text{M}(\text{NH}_3)_x]^{2+} + 2[e(\text{NH}_3)_y]^-$$

However, my teacher has told me beryllium and magnesium are anomalous in that they don't dissolve in ammonia solution. I couldn't find a reference for this claim in JD Lee's Concise Inorganic Chemistry, Fifth Edition.
I would like to know two things:

What determines a metal's solubility in liquid ammonia?
Why don't beryllium and magnesium dissolve in ammonia?


texts: Why do the pennies in the pre/post 1982 penny experiment sometimes dissolve completely?

texts:
USA pennies were nearly pure copper pre-1982.  Post 1982 they are copper clad zinc.  A common experiment in US high schools is to notch pennies with a file and add them to an HCl solution.  The old pennies remain untouched and the zinc of the new pennies dissolves, leaving the copper cladding.

Sometimes the copper cladding also dissolves and sometimes a considerable amount of the old penny dissolves.

Why does the copper dissolve?

I propose that the copper in the penny is reacting with atmospheric oxygen, forming copper oxide that dissolves in the acidic solution.

Another proposal is that the formation of a complex ion between copper and chloride ion drives the equilibrium, allowing the copper to react in HCl.  This is analogous to how aqua regia dissolves gold.

Another proposal is that the copper oxide layer on the penny reacts with copper metal in a comproportionation to form copper (I) ion that then reacts with oxygen to make copper (II) and dissolves?

Which is right?  Why does the copper dissolve?


texts: Is it easier to extract CO2 from seawater than from air?

texts: It takes some effort to extract $\ce{CO2}$ from air in order to produce synthetic and potentially 'green' fuel. Doesn't seawater provide this environmental $\ce{CO2}$ more easily?


texts: Is there a compound that contains water as a subcomponent?

texts: Is there a molecule that contains water chemically bonded to another molecule/element? Could someone provide an example or two?


texts: Options for long term storage of helium?

texts:
Specifically, if I wanted to purchase a large amounts of helium, what are my options for purchasing helium in a state that is suitable for long term storage?

It's my understanding that if I were to buy helium in bulk it would be shipped cold, as a liquid.  Keeping helium in liquid form for 10-20+ years would involve a lot of serious refrigeration.

Are there other reasonable options for bulk, long term storage?

This may not seem like much of a "chemistry" question but since this is used in chemical sciences, I assume this is a need that some may be aware and may have a good answer since this is an elemental material that some may use on a very common basis.


texts: Why is activation enthalpy found and not just rate of reaction?

texts: What is the benefit of finding the activation enthalpy and not the rate of reaction?


texts: How to interpret the Maxwell-Boltzmann distribution to find the activation energy?

texts:
I understand activation energy to be the relative difference in energy between that of the activated complex/transition state (at some temperature) and the average energy of the reactants like shown here:

(Source: Wikimedia, User Bkell)

If this is correct, I have questions about graph like this one:

(Source: webchem.net (not available anymore, Internet Archive), retrieved via the Internet Archive)

Is the location marked activation energy supposed to be the energy level of the transition state provided the energy axis is absolute?
Can the Maxwell-Boltzmann distribution be done for heterogeneous systems (i.e., two chemical reactants)?
Unrelated to the graph, why does negative activation energy result in a decrease in reaction rate (per Arrhenius equation)?


texts: How to find the rate of effusion given rates?

texts:
Question

At $25~^\circ\mathrm{C}$, a sample of $\ce{NH}$ effuses at the rate of $0.050$ moles per minute. Under the same conditions, what is the molar mass of a gas that effuses at approximately one half of that rate?

My steps and thoughts

I converted $25~^{\circ}\mathrm{C}$ to $298~\mathrm{K}$ and then I was thinking of using $pV=nRT$ and I got stuck.

I am thinking of using molar mass, but I don't know how to incorporate that.

Please, only give hints not the answer.


texts: Why doesn't nitric acid have a positive charge?

texts: From the diagrams I've seen $\ce{HNO3}$ has a dative covalent bond so why doesn't it have a positive charge?


texts: Ionization of hydrogens in hypophosphorous acid

texts:
Does anyone know why the hydrogen atoms bonded with phosphorus in $\ce{H3PO2}$ are not ionizable?

I tried looking in high school level books, but they only describe the process, not the real reason. I would appreciate if someone has the answer.


texts: Heats of formation of neutral molecules and homolytic vs heterolytic bond dissociation in mass spectrometry

texts:
I am currently studying the textbook Mass Spectrometry, third edition, by Jürgen H. Gross. Chapter 2.4.3 Bond Dissociation Energies and Heats of Formation says the following:

Great efforts have been made to generate accurate and reliable ion thermochemistry data. Once such data is available, it can be employed to elucidate fragmentation mechanisms and in addition, it is useful for obtaining some background on the energetic dimensions in mass spectrometry.
Heats of formation of neutral molecules, $\Delta H_{f(RH)}$, can be obtained from combustion data with high accuracy. Bond dissociation energies can either be derived for homolytic bond dissociation
$$\ce{R - H \rightarrow R^. + H^., \Delta H_{Dhom}} \tag{2.12}$$
or heterolytic bond dissociation
$$\ce{R - H \rightarrow R^+ + H^-, \Delta H_{Dhet}} \tag{2.13}$$
The homolytic bond dissociation enthalpies give the energy needed to cleave a bond of the neutral molecule which, in the gas phase is in its vibrational and electronic ground states, to obtain a pair of radicals which also are not in excited modes. Homolytic bond dissociation enthalpies are in the range of $3-5 \ eV$ (table 2.2). The heterolytic bond dissociation energies apply for the case of creating a cation and an anion in their ground states from the neutral precursor which means that these values include the amount of energy needed for charge separation; they are in the order of $10-13 \ eV$ (Table 2.3). Due to the significantly altered bonding situation, breaking of a bond is clearly less demanding in molecular ions than in neutral molecules.

I think this is good explanation. However, since this is my first exposure to these concepts, I'm interested in a higher-level explanation. Specifically,

What does "heats of formation of neutral molecules, $\Delta H_{f(RH)}$", mean in the context of mass spectrometry, and why is it relevant?

What is the relevance of homolytic vs heterolytic bond dissociation in mass spectrometry?

The Wikipedia articles for these two concepts, 1. Standard Enthalpy of Formation and 2. Bond Dissociation Energy: Homolytic Versus Heterolytic_Dissociation, offer more general explanations, but I'm interested in understanding in a general explanation in the context of mass spectrometry.
I would greatly appreciate it if some of the more knowledgeable contributors would please take the time to clarify these concepts.


texts:
Question
I am confused between the questions B. And C. The earlier is SN2 and later is E2. But what makes the difference?


texts: Which of the following procedures will allow the student to determine the rate constant, for the reaction?

texts: Is the answer A or B because C and D won't give me the rate constant?


texts: Are molecular optimizations in quantum chemistry really in vacuum?

texts:
I know that Gaussian (or other quantum chemical packages) assumes the molecule is alone in vacuum, that is, the molecule doesn't interact with anything, when optimizing the molecule.

But I've found that optimization at HF or DFT levels results are almost the same as experimental data, which were from the solid state by X-ray diffraction. Everyone knows that the solid state is quite different from the vacuum, for molecules interact with each other in the solid state.

Then why do the two generate nearly the same results? Or have I looked at so few samples that I neglect occasions when the two give quite different results?


texts:
I've given a question , 3-chloropyridine + NaNH2  gives out A . Compound A on further reaction with furan gives compound B.

What I think now , First step is simple elimination addition reaction .
So A should be 3-Aminopyridine . Next step is little bit confusing to me.
I think product B should be nucleophilic substituted at 2-position of Furan by -NH2 group of 2-amniopyridine .


texts: Is dihydrogen the only example of overlap between two s orbitals?

texts: I heard that $\ce{H2}$ is the only example of s–s orbital overlap. Can anyone give an example which contradicts this statement?


texts: What causes photovoltaic (solar) cells to degrade?

texts:
Photovoltaic panels can have 20 or 25 year underwritten warranties with a guaranteed remaining efficiency of 80 % of the new panel. That means, that photovoltaic panels seem to degrade somehow.

Why do they degrade? What exactly is reducing their efficiency?
How can this process of degrading be slowed down? E.g. if you don’t need your PV panels, is it possible to conserve them by covering them with a black, opaque coverage like tarp? If not, what else?


texts: Release of sulfur dioxide from odored fuel gases

texts:
Often, fuel gases such as butane and natural gas (methane) are mixed with some foul-smelling impurities such as thiols (mercaptans) and hydrogen sulfide. Presumably, anything containing sulfur would burn to sulfur dioxide. The odor of sulfur dioxide is not easily noticed while burning such fuels, but I presume that the large amount of fuel gases burnt in the world would cause a significant amount of $\ce{SO2}$ emissions.

Why is this not usually brought up? Are the amounts actually so small that they are completely insignificant?


texts: Treatment of ambidentate ligands in geometrical and optical isomerism

texts: Are ambidentate ligands considered different entities when they donate through different atoms? For example will a hypothetical square planar complex like [Pt(ONO)2(NO2)2] show geometrical isomerism?


texts: What's the difference between isoionic point and isoelectric point? My teacher uses them interchangeably, but Wikipedia states that isoionic point is when charges are balanced, while isoelectric point is when there is a net charge of 0. Is this not the same thing?


texts: Are metals hydrogen bond acceptors or donors?

texts:
In a carbonyl or $\ce{-OH}$ group, it's clear the oxygen acts as a hydrogen bond acceptor.

Do metals act as hydrogen bond acceptors or donors and if so, how can I tell as what it's acting?


texts: Is purple paint more susceptible to UV damage than other colors?

texts:
I was recently sorting some Mardi Gras beads. These are cheap plastic beads on strings, coated in cheap metallic paint. While sorting the beads into different colors, I noticed that the purple beads seem to have suffered more fading than the other colors. This is an effect I have noticed in the past: if the beads sit in the sun for a day or two, the colors fade rapidly. I'm guessing that the cause of that is that the UV radiation from the sun is breaking the molecules used for the pigments in the paints.

My first thought was that I had a pile of beads exposed to sunlight, and the purple beads in that pile had been at the top of the pile. But I noticed this happening in a few different piles that I had stored in different places and for different lengths of time. I have also noticed that the red beads and the purple/pink beads show some fading, though not as much as the purple beads. The yellow, silver, and green beads show almost no fading.

My current hypothesis is that the manufacturers use a pigment in the red and purple beads that is more susceptible to UV damage than the other pigments. So my question is: what is the chemical in these purple and red paints that is breaking down? (I guess there's also an implicit question here: is my thinking here chemically plausible?)


texts: How to assign overlapping multiplets in 1H NMR spectra?

texts:
In the above $\ce{^1H}$ NMR spectrum ($\pu{400 MHz}$, $\ce{CDCl3}$) the methyl, alkene, and $\ce{CCl3CH2}$ protons are fairly easy to assign however, the protons in the cyclohexene ring show overlap and complex splitting (which I assume is due to the axial and equatorial arrangements). How would one go about differentiating between and assigning the remaining protons to the overlapping signals (if possible)?
I've actually been trying to find more generalised information to help with the assignment of a different (but similar) cyclohexene compound but couldn't really find anything, so took a suitable example from a paper I found.


texts:
Why do all inter-halogen compounds contain an even number of atoms?

All halogens have one electron in their valence shell. One covalent bond is formed by 2 halogen atoms (sharing one electron each). If in the compound an odd number of atoms were involved, then an odd electron compound (unstable) would be formed. IF4 would contain 1 lone pair and 1 odd electron, hence unfavorable.

Is my answer correct? If you have any better explanation, please share it.


texts: Why can't helium nuclei (alpha particles) react with fluorine?

texts:
Alpha particles are basically just helium nuclei, so it will accept an electron pair to become stable.

Will fluorine, being highly electronegative, not just donate an electron pair but form a bond with helium?


texts: Azo coupling with arenediazonium salts - why isn't nitrogen gas lost?

texts:
Arenediazonium compounds contain a very good leaving group - nitrogen gas - and thus undergo nucleophilic substitution reactions rapidly. With water, for instance, they give phenols.

In the formation of azo dyes from arenediazonium salts, however, the arenediazonium cation acts as an electrophile to carry out a substitution reaction on activated benzene rings like those of phenols and anilines. Why doesn't displacement of $\ce{N2}$ happen here as well? Normally the carbon attached to $\ce{-N2+}$ acts as the electrophilic centre, so phenols and anilines should react at that $\ce{C}$ rather than at the $\ce{-N2+}$ group. Moreover, phenols and anilines have more nucleophilic centres at their $\ce{O}$ and $\ce{N}$ than at the carbon atoms of their benzene ring - so why aren't the final products be diphenyl ether with phenol, and N-phenylaniline with aniline?


texts:
I moved into a house that has a light fitting that has been made out of an old food 'tin' can.

The light hadn't worked since moving in. On trying to remove it the glass of the bulb pulled straight out into my hand. There is a white powder on the bulb and also the wire towards the bulb.

It also looks in a structure like mould or mildew, as the 'white' is also up the wire and on the beam that the light lead is hanging from.

What is the powder? Is it dangerous, as in corrosive to other materials as it fell onto the floor and myself? Or is it possible that it is more a mould?


texts:
epimers are the class of stereoisomers which differ along configuration at any carbon in a carbohydrate(generally),

And anomers are the kind of stereo  isomers that differ at the carbonylic carbon, which becomes achiral only after hemiacetal (hemiketal) formation

Websites on search give that Epimers are bigger group where Anomers are a part of them, but in certain books on biochemistry like that of Lippincott(d.ferrier) writers define Epimers as change in configuration at any carbon except anomeric carbon..

So are Anomers Epimers?


texts: Why does Birch reduction of naphthalene with isoamyl alcohol form tetralin instead of 1,4-dihydrodialin (as formed with C2H5OH)?

texts: I recently came across this question, which required me to know the difference between performing a Birch reduction on naphthalene using ethanol and using isopentanol. Why does using isopentanol lead to that extra hydrogenation?


texts: Why is the major product of the reaction of 1-naphtol with benzene diazonium chloride not the ortho product?

texts: If 1-napthol reacts with benzene diazonium chloride, it gives the para product with respect to the hydroxyl group. However, shouldn't the major product be the ortho one, because there will be intramolecular $\ce{H}$-bonding between the $\ce{H}$ atom and $\ce{N}$?


texts: What is the future of water treatment, and why we don't use enough purified sea and freshwater?

texts:
I understand thermal and membrane distillation are very expensive and that slowed down their usage, but now we can bring 100% clean energy to power them. Except the set-up, the price of materials and the maintenance, I understand these other costs are not that heavy compare to energy from the grid ?
Many global companies have been building global purification centers but I'm thinking if local initiatives can be cheaper and interesting even in developed countries ?


texts: Why does contact glue get stickier (to itself) as it dries?

texts:
I'm thinking of that type of glue that you apply to both sides, let dry and then press together. Like this. It seems counter intuitive.
Other glues behave in the opposite manner, and get less sticky as they dry. So does duct tape. So does jam. And actually everything else I can think of. The container recommends letting the two parts dry to touch dry. It grabs really well even if you leave it quite a bit longer.
So what goes on inside contact glue?


texts: When I was learning about salts that show exothermic dissolution, I noticed that the same salts used in Daniel Cell( due to similarity of size of anion and cation) were undergoing exothermic dissolution. Is there any relation between the similarity in size of anion/cation and the type of dissolution it undergoes?


texts: Which would be more acidic, benzene or cyclohexane?

texts: If benzene were to donate a hydrogen ion, then could the negative charge still be delocalised around the ring? Wouldn't that break aromaticity and thus destabilise the molecule?


texts: Flipping a molecule vs. mirror behind compound

texts:
Why aren't these enantiomers?

If you place a mirror behind the compound and look into the mirror, you get the second drawing.


texts: I'm doing a chemistry project on ionic compounds found on food labels, and I can't find a clear article on how calcium sulfate is made for edible foods. I know it comes from calcium sulfate dihydrate. I have found articles on how they turn that into calcium sulfate for fertilizer, concrete, drywall, and other materials, but not for food products.


texts: To what extent are the radius ratio rules valid for predicting the crystal structure of an ionic compound?

texts:
The ionic radii of $\ce{Ba^2+}$ and $\ce{O^2-}$ in barium oxide are $\pu{135pm}$ and $\pu{140pm}$, respectively. The ratio of the radius of $\ce{Ba^2+}$ to $\ce{O^2-}$ is approximately $0.964$.

According to the radius ratio rules the solid barium oxide should crystallise in a body-centered cubic type structure (like $\ce{CsCl}$).

But evidently the prototype structure is $\ce{NaCl}$ type.

What is the reason for this anomaly from general trend?

EDIT: I found that every alkaline earth metal oxides (Of the type $\ce{M_{alk.e}O}$) possesses rock salt (halite) structure but only $\ce{MgO}$ obeys the radius ratio rule (it has a radius ratio of about $0.64$ which is well between $0.414$ and $0.732$).

Certainly as we are going down the group the cationic radius is going to increase and so is the radius ratio.


texts:
To the best of my knowledge, energy equals work, $\mathrm{E = W}$; work equals force multiplied by distance, $\mathrm{W = Fm}$ ; force equals mass multiplied by acceleration,  $\mathrm{F = MA}$; and acceleration equals distance per second squared, $\mathrm{A = m \setminus s^2}$. However, when I substitute those values in for the dimensions of $ \mathrm{W}$, I can't transform the result of those substitutions into  $ \mathrm{W= \frac{1}{2}Mv^2}$. Perhaps I've done the algebra incorrectly.

Does the result of those substitutions transform into $ \mathrm{W= \frac{1}{2}Mv^2}$?

If it doesn't transform into that equation, why doesn't it do so, and why do we use an equation that isn't compatible with our other equations?


texts: Is there any molecule describable by three-level with mixed parity and transition dipole moments in different directions?

texts: I would like to know if there are molecules described by a three-level system with mixed parity and transition dipole moments in different directions. By mixed parity I mean all three transitions can be excited by electric field. In principle I don't think such a system is forbidden, but it would be perfect if there are some examples. Does anyone have an idea? Thanks!


texts: When comparing boiling points of two ionic compounds, what bonding factors should you assess?

texts:
When comparing boiling points of two ionic compounds, should you look at their electronegativity difference, lattice energy, or strength from LDF forces (or all 3 factors)?

For example, between LiCL and NaCl, which one has the higher boiling point?

If we look at EN difference and LDF forces, it would be NaCl, because the EN difference here would be $2.1$ compared to $2.0$ for LiCL; also, since Na has an extra energy level, it has a larger electron cloud and thus stronger LDF's.

However, if we look at it in term of lattice energy or Coloumb's law, LiCl has a larger boiling point because high lattice energy is a combination of large charge and small ions. Therefore, even though Li and Na have the same charge, Li has a smaller atomic radius than Na.


texts: Trend in the infrared stretching of molecular hydrogen to group 8 transitions metals?

texts:
While going through old notes, in relation to the Dewar-Chatt-Duncanson model, it states that the stretching frequency for $\ce{N2}$ to the group 8 transition metals ($\nu(\ce{NN})$) proceeds as:

\begin{array}{cc}
\hline
\text{Compound} & \nu,~\pu{cm-1} \\
\hline
\ce{[(SiP3)Fe(N2)]-}  & 1920 \\
\ce{[(SiP3)Ru(N2)]-}  & 1960 \\
\ce{[(SiP3)Os(N2)]-}  & 1931 \\
\hline
\end{array}

However, the notes fail to elaborate further.

I would have perhaps assumed that the trend was due to increasing size of the $\ce{3d -> 4d -> 5d}$ orbitals and thus increased pi-donation causing a weaker bond and thus lower frequency, however, this does not fit the trend observed. Thus leads me to my question: how does the Dewar-Chatt-Duncanson model relate to the observed trend?


texts:
In short, cyclobutane adopts a certain, non-planar, configuration in order to reduce ring strain caused by the fact that carbons are $\mathrm{sp^3}$ hybridised. That much is understandable.

In an exercise it was suggested to propose another kind of hybrisation for the carbons in order to justify a (theoretical) planar configuration. I thought that carbons could be $\mathrm{sp}$ hybridised. This way, $\mathrm{p}$ orbitals could form the $\ce{C-C}$ bonds and $\mathrm{sp}$ orbitals could form the $\ce{C-H}$ bonds.

I checked the answer and I was right. However, I couldn't think of something that could justify why this particular structure is not possible. That exactly is my question.


texts: Why can some ions have different valence?

texts: Like $\ce{Fe}$, it can be $\ce{Fe^{2+}}$ or $\ce{Fe^{3+}}$, same with $\ce{Ni}$ and $\ce{Co}$, what determines whether the ionic compound will be $\ce{Fe^{2+}}$ or $\ce{Fe^{3+}}$?


texts:
In what seemed like a good idea at the time, I used a can of compressed air to clean out my Magic Mill flour grinder.

Picture of one: http://ic.pics.livejournal.com/ccdesan/4606041/68177/68177_320.jpg

It did a great job of cleaning out all the extra flour stuck to the bottom of the top part. However, what I didn't realize at the time was it also left bitterant residue, ruining a batch of flour I just made!

The MSDS for the compressed air (Compucessory Power Duster) just lists diflouroethane, but it says right on the can it contains a bitterant!

The bitterant is likely Denatonium (http://en.wikipedia.org/wiki/Bitterant). Is there any household chemical that will dissolve it and the other common bitterants, or better yet, break them down into non-bitter compounds?


texts: What is the formula for theoretical buffer capacity for a diprotic buffer system?

texts:
According to Chembuddy, the formula for theoretical buffer capacity for a monoprotic buffer system is as follows:

  $$β = 2.303\left(\frac{K_\mathrm{w}}{[\ce{H+}]} + [\ce{H+}] + \frac{C_\mathrm{buf}K_\mathrm{a}[\ce{H+}]}{(K_\mathrm{a} + [\ce{H+}])^2}\right)$$

where $C_\mathrm{buf}$ is the total concentration of buffer and $K_\mathrm{w}$ is the water ionization constant.

However, I have conducted a lab in which I mix $\ce{C4H6O4}$ (tartaric acid; diprotic) with its double salt $\ce{NaKC4H4O4}$ to create a 1.0 M potassium sodium tartrate buffer solution where there are two simultaneous buffer systems. Also, $\mathrm{p}K_\mathrm{a1}$ and $\mathrm{p}K_\mathrm{a2}$ of tartaric acid are quite similar (around 1.6 difference), so I believe that this alternative equation that provides the theoretical buffer capacity for a system with multiple buffers:

  $$β = 2.303\left(\frac{K_\mathrm{w}}{[\ce{H+}]} + [\ce{H+}] + \sum\frac{C_\mathrm{buf}K_\mathrm{a}[\ce{H+}]}{(K_\mathrm{a} + [\ce{H+}])^2}\right)$$

will not be correct in my case.

Is this right? If so, is there a proper way to theoretically calculate the buffer capacity of the composite system?


texts: How does charge density affect the rate of a decomposition?

texts: For example, for the thermal decomposition of carbonates of group 2 metals, how does the charge density decreasing down the group affect the rate of this decomposition?


texts: Are photolysis reactions considered exothermic or endothermic?

texts:
I know that photolysis is when a chemical reaction (usually decomposition) is forced by photons. I also note that there is a general warming in the stratosphere, due to the photolysis of ozone $$\ce{O_3 + $h\nu$ -> O + O_2}$$ and the subsequent restorative mechanism $$\ce{O + O_2 + M ->O_3 + M}$$ where $\ce{M}$ is a third body used to carry off excess energy. To me, that says that the photolysis of ozone is an endothermic reaction, and the reformation of ozone is an exothermic reaction, as the free body takes away excess energy (assumably thermal energy).

Am I correct in generalizing that photolysis is generally an endothermic reaction? If so, could the enthalpy released by the second equation be quantified by the frequency of the photon?


texts: Why do SN1 and SN2 reactions not occur at sp2 centres?

texts:
I was told in my organic chemistry course that $\text{S}_\text{N}1$ and $\text{S}_\text{N}2$ reactions did not occur at $\text{sp}^2$ centres. When I asked why, I was not given a satisfactory explanation. For $\text{S}_\text{N}2$ it was suggested that the reaction could not proceed with inversion of configuration, as this would disrupt the orbital overlap causing the $\pi$ bond. I couldn't find any explanation in Clayden's Organic Chemistry (2nd ed.), or even a mention of it.

Could anyone please explain why? I have attached some curly arrow diagrams that seem reasonable enough to me, although I realise that being able to draw a reaction mechanism does not mean it is valid.


texts: I know this has been asked before, but can anyone explain me in simpler terms? Why is $\ce{CO2}$ a Lewis acid? The carbon atom doesn't have any vacant orbitals to accept a lone pair. How can it be a Lewis acid?


texts: What does it mean to "shear" an emulsion?

texts:
The following instructions are given for a preparation and I am wondering what it means to "shear an emulsion"?

The water phase components and the oil phase components are each mixed
in separate containers and filtered and the refractive index of each
is measured. The refractive index of the water phase is adjusted to
match the refractive index of the oil phase to within 0.0004 by
addition of water or propylene glycol as required. The water phase is
then slowly added to the oil phase at about 18.degree. C. with
sufficient mixing to form a clear emulsion with minimum aeration. This
emulsion is then sheared to form a clear gel with a viscosity of
about 130,000 to 160,000 cP.


texts:
According to both caffeine's PubChem page and ChemSpider page its boiling point lies at $\pu{173 °C}$ and its melting point at $\pu{\sim 235 °C}.$ How can it melt at that temperature if it already sublimated at $\pu{173 °C}?$ Or is that the temperature of the triple point? If so, how come none of those pages gives any pressure specifications for that temperature?
I heated up some anhydrous caffeine at home, and at my home atmospheric pressure it appears to melt (not sublimate) and starts creating vapors immediately after (but not before) melting. This is based just on what I can see with the naked eye.


texts:
So, they try to color naftalene, nitrobenzeen and benzene. Only one of them colors. They can say with certainty that this is nitrobenzeen. Right/wrong and why?
Sorry if my English isn't that great, not my native language!!
Thanks a lot x


texts: Deriving an expression for the constant pressure heat capacity

texts:
Given the relation $G = H − T S$, show that:
  $$\left(\frac{\partial S}{\partial T}\right)_p=\frac{C_p}T$$

Now I realise that $T\mathrm dS=\mathrm dQ$ and that would I suppose get the result. However, I have been asked to use the expression $G = H - TS$ to find the result. If I just differentiate implicitly I end up getting:

$$\left(\frac{\partial G}{\partial T}\right)_p+\left(\frac{\partial S}{\partial T}\right)_p=\frac{C_p}T$$

What am I doing wrong?


texts:
Both carbon and silicon expose a lot of metallic properties like metallic lustre, electrical and heat conductivity, etc, so often considered metalloids. The both form alloys with other metals such as iron.

On the other hand, the usual silicon carbide is not an alloy at all. It is tranparent, electrical insulator etc.

I wonder whether there is a different carbon-silicon compound that has more metallic properties?

Carbon (graphite):

Silicon:

Silicon carbide:


texts: Do alpha hydroxy ketones give iodoform test

texts:
So, we know that alpha hydroxy ketones give tollens test as the tautomerise into their enol form and the then have an equilibrium between the 2 keto forms.

So going ahead with the same logic. Do alpha hydroxy ketones which can tautomerise to give a methyl ketone group, can they give positive iodoform test?


texts: Leaving Group Tendencies in Amide Hydrolysis

texts:
When we do hydrolysis of amides in basic conditions, we come across a mechanism in which the $\ce{OH-}$ ion attacks the carbonyl forming an intermediate as given in the photo:

When the carbonyl gets formed again it ejects off $\ce{H2N-}$-that’s what my teacher says. But I have a problem that why this happens, why not the $\ce{OH-}$ group leaves off when the carbonyl gets formed again? After all, $\ce{OH-}$ is a better leaving group than $\ce{H2N-}$.


texts: Which element is being reduced in this reaction?

texts:
Which element is reduced in this reaction:
  $$\ce{2KMnO_4 +3NaSO_3 +H_2O ->2MnO_2 +3NaSO_4 +2KOH}$$

I am trying to figure out which elements lose their electrons, but how am I supposed to know when elements are neutral and when they are ionized? I have tried the following, but I don't believe it to be correct

$$\ce{2K^+Mn^+O_4^{-2} +3Na^+SO_3^{-2} +H_2O ->2Mn^{+2}O_2^{-2} +3Na^{+}SO_4{-2} +2K^+OH^-}$$

My reasoning being that:

Oxygen atoms are always doubly anionized
Sulfate and sulfite are also doubly ionized
Sodium and potassium are always singly cationized

Based on these rules I tried to make the bonds neutral, but my assumptions must be incorrect. Any help would be greatly appreciated


texts: Do different eigenstates of total angular momentum have necessarily different energies?

texts:
Let $H$ be the Hamiltonian of a specific atom and $J$ the total angular momentum. Since $H$ and $J$ commute, they have common eigenstate.
So we can label the atomic states by their energy and total angular momentum $\phi_E^J$.
My question is, suppose we have a state $\phi_E^J$ and another state $\phi_{E'}^{J'}$,  do we have necessarily that $E\neq E'$, that is, do states with different total angular momentum have necessarily different energies?


texts: How to calculate the pH of a buffer after adding HCl?

texts:
In a certain $\pu{1 L}$ buffer with $\pu{0.25 M}$ $\ce{NH3}$ and $\pu{0.4 M}$ $\ce{NH4Cl}$, $\pu{0.1 mol}$ of $\ce{HCl}$ has been added to the solution. What is the $\mathrm{pH}$?
$K_\mathrm{a}(\ce{NH4+}) = \pu{5.56e-10}$, and $K_\mathrm{b}(\ce{NH3}) = \pu{1.8e-5}$.

The answer says that at last there will be $\pu{0.5 mol}$ of $\ce{NH4+}$ formed from the equation:
$$\ce{NH3 + H+ -> NH4+}$$
So $\pu{0.1 mol}$ of additional $\ce{NH4+}$ is formed and the total amount of $\ce{NH4+}$ is $\pu{0.5 mol}$.
However, I do not agree with this statement and I believe that there is still a limited power of $\ce{NH3}$ accepting $\ce{H+}$ (from $\ce{HCl}$).
My theory is that $\ce{NH3}$ accepts $x$ amount of protons and will form $x$ amount of $\ce{NH4+}$, with the original $K_\mathrm{b}$. Meaning
$$K_\mathrm{eq} = \frac{[\ce{NH4+}]}{[\ce{NH3}][\ce{H+}]}$$
which I thought was $1/K_\mathrm{b}$. Is my theory correct?


texts: Difference between intercalated lithium and metallic lithium (Li-ion batteries)

texts:
I have a question about Li-ion batteries. I sometimes see the two terms - intercalated lithium and metallic lithium - used when talking about this type of batteries and I was wondering what is the difference between the two?

I understand that the intercalation means that the Li cations are transferred from one electrode to another and that is why it is called intercalated lithium (or am I wrong?). But what about metallic lithium? What does that mean?

I found this on Wikipedia:

  Li-ion batteries use an intercalated lithium compound as one electrode material, compared to the metallic lithium used in a non-rechargeable lithium battery

But what makes them different? In other words, what are the differences between intercalated lithium and metallic lithium? Can anyone help me to understand this?


texts: Supposed low temperature of calcium carbide synthesis

texts:
I came across an interesting reaction on allreactions.com under silicon tab:
$$\ce{SiO2 + 5 C(coke) + CaO ->[\pu{800–1000 °C}] Si + CaC2 + 3 CO}$$
Unfortunately the website doesn't provide sources and I wanted to read further about this reaction, particularly about the reaction time. If anyone here could point me to another source I'll be very grateful.


texts:
Usually Lewis bases as my textbook says:

  2.3 Ligands
  The ligands are the ions or molecules bound to the central atom/ion in the coordination entity. This is better visualized as the combination of a Lewis acid (the central atom/ion) with a number of Lewis bases (ligands). The atom of Lewis base that forms the bond to the Lewis acid (central atom/ion) is called donor atom ...

According to me its not compulsory for a ligand to be a Lewis base, as $\ce{BF3}$ is a Lewis acid and can act as a ligand by accepting electrons from a metal in vacant orbital of boron. Is it true?


texts: Dehydration: Methylcycloexanol + H2SO4 + THF

texts:
I came across this exercise:

  Why do we need THF?

  How the THF influence the mechanism?

I couldn't find any link or external explanation, if you do please share.

Thanks in advance.


texts: precipitation reaction - cellulose in schweizer reagent reacts with acid

texts:
In the regeneration of dissolved cellulose (in a cuprammonium solution) in an acid bath, say sulphuric acid, what is the chemical reaction?

There is a lot about the chemistry of the production of the copper ammonia complex but nothing about the precipitation step.

Is the precipitation possible with any acid?

Apologies about the tag - can't find any existing ones that are appropriate


texts: Is there any difference between "autoignition temperature" and "ignition temperature"?

texts: Is there any difference between the "autoignition temperature" and the "ignition temperature" of a substance?


texts: Is "ice point" the same as "freezing point"?

texts: I am using an old book and they almost use both terms interchangeably sometimes. Do they mean the same thing? Similiarly for "steam point" and "boiling point"


texts: What acid did I accidentally create, and how?

texts:
So, I wasn't trying to do a chemistry experiment this evening; it was entirely unintentional!

I was mixing up a batch of fertilizer for my plants (no nitrates involved, so I wasn't worried about potentially dangerous reactions).  The main goal was to add some sulfur (which over time lowers the pH) and potassium (in the form of potassium sulfate); to balance it out there also were lesser amounts of calcium superphosphate and magnesium sulfate, a little iron sulfate, and tiny amounts of trace elements (boric acid and some simple compounds of manganese, copper, zinc, and molybdenum)

The potassium sulfate tends to come in big chunks because it's hygroscopic, and I know that hot water helps dissolve it (and that the sulfur doesn't dissolve in water, even hot water), so I heated the mixture (in water) in the microwave, then stirred with a plastic utensil.  I noticed a surprising amount of offensive-smelling offgassing coming off of it.  So I put in my analog pH meter, and it pegged instantly, hard (its limit is 3,5, so it must have been much lower).   Even after adding some calcium oxide (which instantly fizzed and started gelling), the pH was still pegging hard.  And after 1 dilution (maybe 7:1?), it was still pegging, and only after the second dilution did it get stop pegging (but still showed strongly acidic).  There was heavy brown discoloring in the bottom of the plastic container, and it looked like the sulfur might have been reacting as well.

I assume I created sulfuric acid (and/or possibly phosphoric?) somehow, but I'm not sure what the reaction was!  I wasn't expecting this at all.  Normally in horticulture, sulfur takes ages to acidify soil, as it's decomposed by bacteria. I know that combusted sulfur yields sulfur dioxide, which - oxidized over a vanadium pentoxide (or other) catalyst - yields sulfur trioxide, and thus (with water) sulfuric acid... but that's clearly not what happened here.    Any clue what reaction we're looking at?


texts: Why do we always represent only the hydrogen evolution?

texts:
In corrosion of aluminium or magnesium for example, we have the anodic reaction which is the dissolution of the metal but for the cathodic reaction we only represent the hydrogen evolution.
How about the reduction of oxygen gas and water?
Why don't we mention these reaction and we focus only on hydrogen evolution?


texts: Why is covalent bonding stronger than electrostatic attraction?

texts:
I guess if we look at this problem from a "conjugate" perspective then the conjugate of a covalent bond is two elements with electrons lying around. On the other hand, with two electrostatically attracted things, the lack of a bond leaves two separate, charged particles.

But that still doesn't answer the question; why are electrons less stable than ions? I guess in the case of an ion though there are still electrons but also a nucleus the stabilize the electrons.


texts: Is the specific heat capacity of liquid iron constant?

texts: Does liquid iron have a constant specific heat capacity?  Everywhere I've looked (save one sourceless online reference to $c_p = 611\ \mathrm{J\ kg^{–1}\ K^{–1}}$ here), I find no value listed for liquid iron.  Is this because the heat capacity is temperature-dependent?  Or is this related to a measurement problem?  Or does an accepted constant value exist, but I'm just a poor researcher?


texts: Make Na or K using carbonate + charcoal?

texts:
In the 19th century, Na metal was isolated by heating up Na2CO3 + carbon to 1200 C and distilling and capturing the Na vapor under oil.

I tried it a few years ago with a small steel tube welded at the end as a  retort and indeed vapors appeared burning with bright yellow (or purple in the case of K2CO3) flame, but could not capture it.

Did anyone isolate these alkali metals with this method ?


texts: Explain why body-centered tetragonal is a Bravais Lattice, but based-centered tetragonal is not?

texts: Can you explain it using schematics? I think the reason is the symmetry that doesn't allowed to unique lattice points.


texts: Why is L-lysine only sold as L-lysine HCl and not as base (cf. L-arginine)?

texts: Both L-lysine and L-arginine enjoy popularity as supplements, but only the latter is sold either as HCl or as base. Given that L-arginine is even more basic than L-lysine (pH 12.5 vs 10.5), that is surprising! Is there a reason why? And could I isolate L-lysine base from L-lysine HCl with a simple reaction? I am thinking of mixing it with sodium bicarbonate, but then I have to remove the NaCl.


texts: Calculating energy change for calcium carbonate decomposition

texts:
The $\Delta H^0$ for the decomposition of $\ce{CaCO3(s)}$ is $178.3~\mathrm{kJ/mol}$ at $25~\mathrm{^\circ C}$ and $1.000~\mathrm{atm}$. What is the $\Delta E$ for the decomposition process?

$$\ce{CaCO3(s) -> CaO(s) + CO2(g)}$$

I'm really not sure how to get from $\Delta H^0$ to $\Delta E$. I'm not sure if the formula $\Delta H=\Delta E+P\Delta V$ is meant to be used. I know if pressure is constant — as it appears to be in this question — $\Delta H=q$. And I also know the equation $\Delta E=q+w$. As there is no work ($w$) being done, does that just mean $\Delta E=q=\Delta H=178.3~\mathrm{kJ}$? I may be extremely off track here, really not sure.


texts: Why is the melting point of magnesium oxide higher than aluminium oxide?

texts:
There's a graph of the melting points of period three oxides. The melting point of magnesium oxide is several hundred Kelvin higher than aluminiumoxide. I can't find any explanations for this on the Internet or in any of my A-level textbooks — perhaps this is something more advanced I haven't come across.

The reason I am questioning the value of its melting point is I'd expect aluminium oxide to be higher. Aluminium is a 3+ ion whereas magnesium is only 2+. Aluminium is also a smaller ion so the effective electrostatic attraction on the valence electrons should be greater. I'm also pretty sure aluminum oxide has greater covalent charterer than magnesium oxide. All of these would lead me to believe it has a higher melting point, so what is the explanation for it being less?


texts: What decides the order of priority of functional groups in organic compounds?

texts: Is the order of defined by IUPAC or we follow some special conventions to know the order of priority?


texts: How does activated carbon trap impurities?

texts:
I've tried and I've tried to find an answer to this all over the web, but I can't seem to find an in depth explanation.

To the best of my knowledge, activated carbon has a very microporous structure and uses a process called adsorbption to "trap" particles. This isn't very in depth though and I'd like to better understand the process of what's going from a scientific standpoint. How does the carbon/charcoal keep the adsorbed material attached or trapped within the carbon?


texts: What is the alternative to chromyl chloride test?

texts:
Chromyl chloride test is by far the best test to determine the presence of chloride ions in a salt because no analogous compounds are formed with fluorides, bromides, iodides and cyanides, so this test is therefore specific for chlorides. This test is actually considered selective for $\ce{Cl-}$.

But this test possess certain drawbacks. This test does not give positive results to covalent chloride like $\ce{HgCl2, SbCl3, SnCl2 }$ etc. owing to their slight ionisation and only  partial conversion occurs when added to chromyl chloride solution. Thus, this test is only positive to ionic chlorides. There are also other tests like conc. sulfuric acid test, $\ce{MnO2}$ test or lead acetate test which will almost determine the presence of chloride ions though it possess some drawbacks (see comment section).

For a particular cation or anion, a selective test is chosen in such a way that it will give positive result to any salt, no matter how complex it is and has the capability to differentiate from other analogous salts. So, why Chromyl chloride is still considered as the selective test for $\ce{Cl-}$ despite its drawbacks?


texts:
Consider this redox reaction:

$$\ce{3PCl3 + 2HNO3 (conc.) + 5H2O → 2NO + 3[HPO3] + 9HCl}$$

The metaphosphoric acid is taken in square brackets, because I have doubts about it. As I know, this reaction is endothermic. Is it possible the metaphosphoric acid is formed in this reaction (there is a water in left part of equation, metaphosphoric acid may react with it, but the temperature is decreasing)? Are there some real environmental condition where this reaction is possible? Or it's only the orthophosphoric acid is formed?


texts: How is Carboxymethyllysine formed from the heating of olive oil?

texts:
Olive oil has significant levels of Carboxymethyllysine.

But how does it form from the heating of olive oil, chemically speaking? Olive oil barely has any protein in it to begin with (though it still has some), so where would all the lysine come from?


texts: What is the reaction mechanism of nitrogen leaving from diazo compounds?

texts:
When a diazo compound is formed, and then a nucleophile is added to the mixture. Will nitrogen gas leave first or will the nucleophile have to "do" a substitution reaction? What I mean is will the carbocation be formed due to nitrogen leaving or will it be an SN2 reaction? Or will it depend on the carbon that the diazo group is attached to, (like primary, secondary, etc.) depending on the stability of carbocation formed? In short, I mean to ask if it's SN1 or SN2.

Is it a thumb rule that when an unstable diazo compound is formed, that the nitrogen leaves without any nucleophile intervention?


texts: What chemical substance is obtained by dissolving C60 in olive oil?

texts:
What chemical substance/component would be obtained of dissolving $\ce{C60}$ in olive oil? Would buckminsterfullerene (bucky-ball) change its spherical fullerene structure (soccer ball-like) into something else ($\ce{C60OO}$) or will it stay the same?

See:

Fullerene - Safety and toxicity at Wikipedia
Fathi Moussa's experiment study on rats in 2012 which doubled their lifespan
The color of the Carbon-60 in olive oil
Buckminsterfullerene-olive oil production process


texts: Rate of dehydration for butan-2-ol and butane-2,3-diol

texts:
A question taken from a test series (Vibrant, India):

Amongst butan-2-ol and butane-2,3-diol, which has higher rate of dehydration?

The carbocation formed in butane-2,3-diol is more stable as it will rearrange to get +M stability from alcohol group. However, the product will be aldehyde (due to tautomerism) for butane-2,3-diol and alkene for butan-2-ol.
As rate is determined by stability of carbocation, butane-2,3-diol should have faster rate. Also, the products don't give any extra hint. Right? But the answer given for higher rate is butan-2-ol. Is there any point that I have missed out?


texts: If you add an acetal to a solution containing water with a little bit of NaOH, will no reaction occur due to the stability of an acetal in the presence of a base?


texts: Why is gadolinium specifically used in MRI contrast agents?

texts:
Gadolinium(III) chelate complexes are routinely used as contrast agents in magnetic resonance imaging (MRI);1 the usual explanation is that paramagnetic species contain unpaired electrons, which cause relaxation of nearby $\ce{^1H}$ nuclei.

Why gadolinium, and not any of the other lanthanides?

In particular, $\ce{Tb^3+/Dy^3+/Ho^3+/Er^3+}$ have magnetic moments that are larger than that of $\ce{Gd^3+}$ (due to orbital angular momentum). At first glance, these should possess even higher relaxivity, since the rate of relaxation due to random fields is proportional to $\langle B_\mathrm{loc}^2 \rangle$.2

I do vaguely recall reading one sentence, about the fact that ground states that aren't S terms are not spherically symmetric, and there's some problem associated with this. But I can't find the reference anymore and I don't remember any other detail.

References

Werner, E. J.; Datta, A.; Jocher, C. J.; Raymond, K. N. High-Relaxivity MRI Contrast Agents: Where Coordination Chemistry Meets Medical Imaging. Angew. Chem. Int. Ed. 2008, 47 (45), 8568–8580. DOI: 10.1002/anie.200800212.
Hore, P. J. Nuclear Magnetic Resonance, 2nd ed.; Oxford University Press: Oxford, U.K., 2015; pp 65, 71.


texts: Why are zinc shot and mossy zinc not considered toxic but zinc granules are?

texts: In our lab we have three forms of zinc. We were initially experimenting with these three forms to optimize our application. We have "zinc shot", "mossy zinc", and "zinc granules". The granules are ~20 mesh. I am tasked with creating chemical standard operating procedures (SOPs) for all reagents that are considered "particularly hazardous". Zinc granules are considered particularly hazardous by our University and is an "acute toxin to aquatic life with lasting effects" in a recent safety data sheet (SDS) while zinc shot and mossy zinc are not considered hazardous by our University or on comparable recent SDSs. I see zinc powder is also considered toxic. To me this suggests particle size dictates toxicity, but why? I understand surface area influences the rate of reactions but if the effects are long lasting, then why are all forms of zinc not considered to be an aquatic life toxin?


texts: Why do rare earth metal oxides vary in color so much?

texts:
I only know a little about what causes different color, but I know it has to do with the electron orbitals and how they reflect or absorb/emit incoming light. The rare earth metals are in the lanthanide series so they all have an identical valence shell.

I've worked with lots of chemicals, but there's not much that is quite the same as the bright and exotic colors produced from the rare earth metal oxides. I worked with the oxides in powdered form in ceramic glazes and they each vary greatly in color, with colors including pink, light blue, black, creamy yellow, and white. (After firing, lime green and grey can also be introduced). Why do they each produce such different and vibrant visual colors?


texts: Orbital Interaction for electrophile and nucleophile

texts:
Clearly the above diagrams depict the interaction between empty orbital of electrophile with filled orbital of nucleophile. We may assume that the HOMO of  nucleophile being more electronegative will have energy less than that of less electronegative electophile as above.
As on the diagram on page 111 on Organic chemistry by Clayden, it is stated that the empty orbitals of Nu are too high in energy to interact with the electrophile. But if the HOMO energy is higher than the vacant orbital of electrophile will the reaction not be feasable?


texts: Expression for an expanded configuration interaction wave function

texts:
I am trying to write down an expanded expression for the configuration interaction wave function. We know that the wave function $\Psi$ is a linear combination (LC) of configuration state functions (CSF), each CSF is a LC of Slater determinants, each determinant is an antisymmetrized product of molecular orbitals (MO's), and each MO is a LC of basis functions (BF). Without saying anything about the antisymmetrizer operator $\mathcal{A} $, are the equations below in general correct? What would the expanded wave function $\Psi$ look like? I have trouble putting the expression for the MO's into the expression for the determinants.

\begin{align}
\Psi &= \sum\limits_{i} c_i ( \text{csf} )_i \\
\text{csf} &= \sum\limits_{j} d_j ( \text{det} )_j \\
\text{det} &= \mathcal{A} \prod\limits_k (\text{mo})_k \\
\text{mo} &= \sum\limits_{l} e_l (\text{bf})_l  \\
\end{align}


texts: Why droplets of water and ethyl alcohol solution freeze weirdly?

texts:
I'm doing a project where I freeze water drops and solutions with water and ethyl alcohol. It's a phenomena where drops create a conical shape at the end of their freezing. But with ethyl drops, with concentrations between 10% and 20%, they act weird. Most of them have a conical shape, but that shape, compared to shape of water, isn't symmetrical or they have weirdly shaped fragments on their tip. (not the usual fragments appearing after the drop freezes completely)
Any information about heat transfer of ethyl alcohol or about ethyl in general  would help. Thank you.

This is what I'm expecting it to look.

Sometimes this happens

Note: The temperature of the metal where I put my droplet on is about -40 degrees celcius. This rarely happens on -15 degrees.
The drops on the pictures are the same:
1) they contain 10 microliters
2) the temperature is -40 degrees, and it's constant
3) both of the drops have 17% of ethyl alcohol

I assume all forces that affect on the drops are the same, so there must be something in the structure of ethanol that I don't know about.


texts:
I was going through some displacement reactions when this struck me:

What is the position of the ammonium cation in the metal reactivity series?

I can find other positive ions like carbon and hydrogen in my textbook but not ammonium. I tried to look it up in google but the search results were not up to the mark.
I could get some comparison at this site. From there, it seems that ammonium will be above zinc, lead and iron.
This post also claims its position but does not refer it Do copper and ammonium hydroxide react?.
I know 'ammonium in the metal reactivity series' sounds a bit strange but what I basically want is its position among the metals and the positive ions. Can anyone here help me with this?


texts:
Not a duplicate of Hydrazine synthesis - I know what hydrazine is and am not going near it voluntarily!

Looked at this resource on the Internet which cites three major commercial-scale processes:

$\ce{H_2O_2}$ process (in use at Arkema and Mitsubishi Gas Chemical, developed by Produits Chimiques Ugine Kuhlmann and patented in 1976)
Bayer process (at the eponymous company)
Urea process

What processes do other major large-scale producers use and what are the driving forces behind adoption of a particular hydrazine synthesis? I can guess that Chinese producers may use the urea process, but I'm not sure.

Background: am a Space Exploration.SE regular and am interested in learning more about worldwide production of hypergolic propellants.


texts:
Please help me in naming a dispiro compound:

I propose bispiro[3.0.4.1]decane. Is this correct?


texts: Oxidation number of phosphorus in phosphine

texts: Electronegativity of $\ce{H}$ is greater than $\ce{P}$, but according to my book in $\ce{PH3}$, $\ce{P}$ has oxidation number of -3. How is it possible? Is any of the data wrong?


texts: Identifying a polyprotic acid using titration

texts:
I have the following question from a high school chemistry lab:

  If an unknown acid has more than one equivalence point, is there a reason to expect a specific $K_\mathrm{a}$ ($K_{\mathrm{a1}}$, $K_{\mathrm{a2}}$ or possibly $K_{\mathrm{a3}}$) to be a better value to identify the acid?

I understand that if an acid has multiple equivalence points, it must have more than one hydrogen disassociating. As we titrate with a strong base, we will get an equivalence point for each hydrogen. Similarly, we will get a $K_\mathrm{a}$ value for each hydrogen, but why would one of these values be better than another for identifying the acid? Would we expect one to be more accurately measured than the other(s)?


texts: Is peroxide bleaching ($\ce{H2O2}$) suitable for treating bast fibres? I read that to be successful, it needs to be combined with chlorine bleaching. Because of the end usage, I don't want to use this kind of bleaching.


texts:
I have read that Tollens' test is given by aldehydes. The aldehyde is oxidised to a carboxylate ion and silver is deposited.
My teacher had given me notes which pointed that salicylaldehyde does not give this test. However, I cannot find any explanation for the same. I have tried to search online and through books but I did not get anything.
I think it could be related to resonance from the −OH group as something similar is mentioned in my notes, but it is not elaborated. Can anyone please explain this?


texts: Attachment of disulfide (protected) thiolated oligonucleotide on gold surface

texts:
What will happen if I incubate a clean gold surface in un-deprotected
($\ce{oligo-C6-S-SH}$) thiolated oligonucleotide solution instead of deprotected ($\ce{oligo-C6-SH}$) solution. I have read clean gold surface can cleave disulfide bond.


texts: Its given in the book that at 12.18kelvin Kc=Kp. How is that equated from the equation Kp= Kc(RT)^∆ng. I am unable to sort it out, please guide me in to the topic....


texts: Rank the following protons in order of acidity

texts: I have an acid and base organic chem quiz tomorrow and I need help determining how acidic protons are. I understand the concept of atoms, resonance, induction, and orbital when considering the acidity of protons. However, when I'm given these molecules, it overwhelms me so I don't understand how to break them down. I believe that the first step is that I have to find the conjugate base for each one and then just compare? Below is photo of my worksheet. I have already filled in the correct answers. Thanks in advance for your help.


texts: Two salts in mutual saturation, which one will precipitate first?

texts: Let's say I have a satuated solution of two salts with a common ion e.g. KCl and KI, and they're at mutual saturation (let's say there are 75% by weight KCl/ 25% KI). If I slowly evaporate some water, which salt will precipitate first? What if there are 25% KCl instead? More generally, how to predict which salt will drop out of solution first?


texts:
I would like to start learning practical chemistry. I have not done chemistry before and am seeking help assembling a simple distillation setup.

I do not want to use the cold water tubes etc for the time being, I am trying to keep it as simple as possible.

I have a few questions which I am hoping someone can answer:

What are the plastic clips for?
How do I vacuum seal all the joints as simply as possible (preferably without using grease). Would tape work?
How do I seal the small side arms? (In the liebig condenser tube this isn't a problem because they don't lead to the inner distillation tube.)


texts:
Why is cubane called pentacyclo[$4$.$2$.$0$.$0^{2,5}$.$0^{3,8}$.$0^{4,7}$]octane?

I am especially intrigued by the pentacyclo part.


texts: How should I measure out a solution given in nanorods per ml to make a solution of a set number of mols?

texts:
I am trying to determine the number of nanorods that I would need to measure out to get a 1 mM solution.  For the gold nanorods that we ordered, it was mentioned that the single nanorods dimensions are 40 nm length by 10 nm in diameter.

The product's concentration is $6.3\times10^{11}$ nanorods per ml.

How would I measure out the solution to obtain a 1 mM gold nanorod solution?


texts: Reaction between a carbene and n-pentane

texts:
Does the following reaction occur when n-pentane reacts with methylene or does it form some other simpler products due to the reactivity of the carbene?

$\ce{CH3-(CH2)3-CH3 + :CH2-> CH3-(CH2)4-CH3}$

EDIT:

Do higher alkanes (pentane, hexane, octane....) show a similar reactivity with methylene or do the products depend upon the alkane?


texts: Which is the strongest base among the given anilines?

texts:
I am facing difficulty in the following problem.

In my view N,N-dimethylaniline 2 should be the strongest base because it has two methyl groups which increases electron density of N and hence it can donate it easily than in other cases. However I am not sure about it.


texts:
With regard to the 'Electron Spin Number', lots of websites mention that electrons don't really spin and that the electron spin number has nothing to do with any physical spinning.

However, my chemistry teacher is quite adamant about electrons spinning about their axes in clockwise and counter-clockwise directions.

So my question stands, "Do electrons really spin?"

Could someone cite a reliable source to read up on this (Apart from Wikipedia, thanks)


texts: Speed distribution of lighter vs heavier gases

texts:
I cannot understand why the range of molecular speed is not always wider for a lighter gas as compared to a heavier gas .

If the same energy is supplied to both gases then wouldn't the molecular speed of the lighter gas be more?


texts: How can I decide the most activated spot?

texts: All of those are activated. And to me, those 2 that are most far from the $\ce{NO2}$ group are the major products. But, between those 2, which one will be the major? Because both of them are more separated in the same way:


texts: How to calculate pH of a solution with two dominant equilibria?

texts:
Say you have acid X for which $K_a(X)$ = 1E-7 and acid Y for which $K_a(Y)$ = 0.8E-7. In separate solutions, it would be easy to calculate $[H^+]$ because there would be only one dominant equilibrium. But in solution together, both contribute significantly to $[H^+]$, and as a result, both equilibria must be driven to the left by Le Chatelier's Principle. How do you calculate the pH of such a solution? Since both contribute to $[H^+]$, the resulting $[H^+]$ is not additive, but rather a bit less than that because of suppression.

Assume X and Y are 0.1M and monoprotic.


texts: Is the conjugate base of pyrrole resonance stabilised?

texts: This is something I am conceptually struggling with, if I deprotonate pyrrole on the nitrogen in the ring, is it true that the conjugate base is not resonance stabilised, because the orbital is orthogonal to the ring? However, with a pKa of 23, I feel like it must have some resonance stabilisation.


texts: Why are more electronegative atoms better leaving groups?

texts:
My book says, "halide anions are electronegative and can easily stabilise
negative charge, hence are good leaving groups."
What exactly does "stabilising negative charge" mean?
I have read:  "It is crucial that the leaving group be able to stabilize the additional electron density that results from bond heterolysis"

Where heterolysis means "bond breaking in which the bonding electron pair is split unevenly between the products."
So is this stabilization referring to stabilizing the charge on the  $\ce{Cl-}$ ion in the above example? Does it just mean it is easier for something that can become stable to leave?
Does being more stable equate to being closer to neutral charge, or has it got something to do with steric hindrance ("steric hindrance occurs when the large size of groups within a molecule prevents chemical reactions that are observed") preventing reactions?
Another issue I have with this is why are more electronegative atoms better at stabilizing charge?


texts:
I had just started to read about carbohydrates when I came across D-(+)-glucose. My book says that the '+' sign refers to its optical rotation measured through the polarimeter, and that it could either be + or −, but throughout the book D-glucose is always designated with the + sign.

Is it possible for there to be D-(−)-glucose?


texts: What is the difference between the terms photochemical and photophysical properties? What are some examples from each category?


texts: Understanding molecule infrared absorption

texts:
My chemistry course requires us to know which molecules absorb infrared, and under which vibrational modes that they do. My professor provides us the following rule, which is very confusing for me and I still don't know how to start.

  Rules for IR absorption: (1) The frequency of the IR radiation
  matches the frequency of the vibrational mode. AND (2) There is a net
  change in the symmetry of electrical charges during the vibrational
  mode.

So, say we have a molecule such as CF2Cl2. This absorbs infrared under all vibrational modes: symmetric stretching, asymmetric stretching, and bending. How do you get to that answer?

Thank you very much.


texts:
During the (DFT-)computations that I have done over the last years, it happened quite often that I got negative energies for the LUMO and many times also for a bunch of virtual orbitals.

Is there a common explanation what negative energies for LUMO means?

I was told that it might have to do with the overestimation of correlation energy within DFT. But what would it mean if there is no error?


texts: Would a loaded cartridge ignite/explode when hit from the side or front by a bullet?

texts:
This question https://physics.stackexchange.com/a/193472/93888 explains what would happen after a cartridge is ignited: the bullet gets propelled by the gases in one direction and the cartridge (with the person, in the case of the question) in the opposite direction.

But would a cartridge explode/ignite if hit from the side (the rear part where the gunpowder is, not the side of the bullet) or the front by a bullet? Or is the rear the only side able to start the reaction?


texts: Would this be a reasonable mechanism for the formation of a diazomethene?

texts: I am mostly concerned about the first step. Are there any species in this mechanism that look too reactive for this mechanism to make sense? Any thoughts would be greatly appreciated.


texts: Selective alkylation of carboxylic acid versus phenol

texts:
Starting from the ketone shown, I plan to use a haloform reaction to transform the acetyl group into a carboxylic acid.

Following that, there are two alkylations to be carried out: one esterification on the carboxylic acid (using propargyl bromide) and one etherification on the alcohol (using 6-bromohexan-1-ol). In what order should these be performed?


texts: Will adding up protons and electrons (without neutrons) create a new element?

texts:
If protons have a positive charge and electrons have a negative charge,
can we add up several protons and electrons together to create a new element, without adding neutrons to hold the nuclei together?


texts: How can I interpret the colour of flames in terms of spectral series?

texts:
I saw different colors of fire burning different metals. But how does this work? The Balmer series requires electrons to drop back down to n = 2. But, not all alkali metals have empty space in their second principle energy level. Does one electron, from the second principle energy level, just jump to somewhere of energy and come back down.

My description is kinda confusing, but all I'm  saying is, where does that space in the second energy level come from?


texts: Decomposition reaction of tin(II) nitrate

texts:
What are the products formed when $\ce{Sn(NO3)2}$ is subjected to high temperatures?

I searched over the internet but I didn't get any satisfactory answer.


texts: Is it safe to treat platinum-carbon catalyst in an autoclave at 200 °C for 24 h in inert (nitrogen) atmosphere? If no, can you suggest safety measures?


texts: Does gravity affect the trajectory of gas particles?

texts: We're studying the kinetic theory of gases in school, and one of the points that was brought up was that: "Gases consist of particles in constant, random motion." How is it possible for gas particles to move in straight lines, entirely randomly? Doesn't gravity affect them, or is their mass so small that its effect on their movement is negligible?


texts: How to calculate the pH of a propanoate buffer after addition of sodium hydroxide?

texts:
I've calculated the pH of the buffer solution, as seen.
The question I'm referring to is part d), which asks: 'Calculate the pH of the solution after 0.01 mols of NaOH are added to  500$cm^3$ of the solution'.


texts: Why doesn't HCl form when you dissolve NaCl in water?

texts:
People say it dissolves, but shouldn't the acid form?

$$
\ce{NaCl + H2O ->[?] HCl + ???}
$$


texts:
I am doing a lab on carbon dioxide solubility in water and I have a non-linear trend which seems to agree with the accepted trend. I am examining the change in solubility as a function of temperature. In the experiment I titrated carbonated water with sodium hydroxide and used molar ratios to determine the carbon dioxide content. The following graph shows the accepted trend:

(Graph from: http://www.rocketscientistsjournal.com/2006/10/co2_acquittal.html)

I've been thinking but, can't seem to figure out why the trend is non-linear. Is there any intuition behind this trend?


texts: Using RDKit to count "RR, the number of rigid single or fused ring systems in the molecule"

texts:
I am a computer scientist, not a chemist, working with RDKit. I need to compute something described to me as "RR, the number of rigid single or fused ring systems in the molecule."
I know I can access the rings of a molecule with AtomRings and BondRings. However, I don't know how to select only the "rigid" ones. Perhaps all ring systems are "rigid" and the word is just there for emphasis and redundancy? If not, how can I tell?


texts: Elimination of bromide and acetate under reducing conditions

texts:
Here is the reaction that I didn't find the mechanism of:

The conditions are zinc dust, acetic acid (solvent) at $\pu{11 °C}$
for 1 h.
The reagents are sodium acetate; 2,3,4,5-tetraacetoxy-1,6-bromohexane.
The product is 3-4-diacetoxy-1,5-hexadiene.
There is also some evolution of gas (I don't know what it is,
$\ce{HBr}$ or $\ce{CO2}$).

What reaction can lead to this elimination when it seems that no proton is leaving the molecule (instead of bromide) and acetate is leaving?


texts: How do I lookup a polymer by its structure?

texts:
This is more of a meta-chemistry question, but, here goes...

Given the structure of a polymer, how can I search online for which polymer it is?

Specifically, I have an image like this:

I'd also like to know which polymer specifically this is, but also a method for figuring this out in the future by myself :)


texts: How to classify the hydride shift in the following diazacyclopenta[cd]pentalene system?

texts:
How is this hydride shift reaction type called?

I think it's not one of following types:

cycloaddition (Diels Alder)
electrocyclic ring opening
sigmatropic rearrangement
ene reaction
cheleotropic reaction

Therefore I'm thinking what else can been the name of the observed reaction.

The ring opening reaction with hydride shift has been taken from Heterocycles 2004, 64 (1), 447–461 (DOI: 10.3987/COM-04-S(P)48).


texts: In synthesizing PbS nanocrystals will there be any problems if I use lead IV acetate instead of lead II acetate?

texts: I am just about to start my senior project synthesis of PbS quantum dots and we ordered the wrong lead acetate. The method calls for lead (II) acetate and we got lead (IV) acetate. If we use the lead (IV) acetate will our synthesis be contaminated and not work or can we still use that chemical with two extra acetates attached?


texts: How do I find pH of a mixture of weak acids?

texts: Suppose that we are given two weak bases $\ce{HA_1}$ and $\ce{HA_2}$. We are also given the $K_\ce{HA_1}$ and $K_\ce{HA_2}$. How can we calculate the $\mathrm{pH}$ of the mixture?


texts: Do MO's span a bond or the whole molecule?

texts:
I'm reading Organic Chemistry by David Klein (2nd Ed), and when discussing the causes of torsional strain, he writes this

Based on recent quantum mechanical calculations, it is now believed that the staggered conformation possesses a favorable interaction between an occupied, bonding MO and an unoccupied, antibonding MO. This interaction lowers the energy of the staggered conformation.

This favorable interaction is only present in the staggered conformation. When the C—C bond is rotated (going from a staggered to an eclipsed conformation), the favorable overlap above is temporarily disrupted, causing an increase in energy.

I've searched online and most sources provide a similar explanation and diagram. My issue is mainly with the diagram: why are the MOs illustrated as though they span only the C—H bonds? I thought that MOs were supposed to span the entire molecule, rather than being localized along/parallel to the internuclear axes of two nuclei. Are these MOs correct? Do MOs cover the entire molecule or do they each exist between two bonding atoms?


texts: Acid catalyzed enolization and alpha hydrogen

texts:
In acidic catalyzed enolization of butan-2-one:

We have 2 alpha hydrogens available. From the mechanism of acid catalyzed enolization there is a certain carbocation character at the carbonyl carbon because of resonance, and thus I thought that the elimination would be an E1 styled one where the alkene formed is the more substituted one.

But if we look at from an 'acidic hydrogen' perspective the hydrogen on the least substituted end is the most acidic whose extraction will lead to a less substituted alkene in the enol form.

So which enol would be major in the enolization of butan-2-one under acidic conditions? Would the same enol be major in basic medium?


texts: Temperature changes in exo/endothermic reactions

texts:
In exothermic reactions, heat is released, whereas heat is absorbed in endothermic reactions. But exothermic reactions are often described as being associated with an increase in temperature, and the opposite is the case for endothermic reactions.
How does heat release result in a higher temperature of the system, and heat absorption result in lower temperature? Shouldn't it be the other way around?


texts: Why is activation energy drawn in a potential energy diagram in reactions?

texts:
I learned in chemistry class that activation energy is the av. KE that the colliding particles need in order to successfully react. However, they are always drawn as a "hill" in a PE diagram.
I do not understand why they are classified as PE, when they are KE.


texts: Where is the center of symmetry in the PbO crystal?

texts: I'm very confused as to where the center of symmetry is for the PbO  (litharge form). I know that it is in the P4/nmm space group, and that it's centrosymmetric, but beyond that I'm clueless. Thank you.


texts: Calculate concentrations in a system made up of molecules in order to calculate ionic strength

texts:
I understand how to calculate ionic strength where there are concentration data in molality or molarity units available and where the system is made up of only two components.  However, I have been struggling for a few days with what is probably a very simple problem: how to calculate ionic strength where there are more than two components and where the concentrations first have to be calculated because the system is made up of molecules.  I'm not a chemist, but need ionic strength for another calculation.

In one kg of water there are 55 moles (1000 g / 18 g mol-1) of water molecules.  To simplify calculations, my system has 55 water molecules. As an example, let's say it also has one Na atom, three Cl atoms, and one Ga atom.

I think that this (below) is the expression to use, where z is charge and m is the molal concentration of species i.  I want to use a molality-based expression because I want to do calculations at a range of temperatures and expect that it would not be right to use molarities, where temperature can affect volume.

$$\large I_\mathrm{m}=\frac 12 \sum_i z_i^2 m_i$$

So it looks like I only need to know the charges and m for all of my species.  But here's where I'm stuck on something simple.  How do I calculate m?  Is it true that in my system, there would be one mole of Na and Ga and 3 moles of Cl?  So m for Na (for example) would be 3 moles/1 kg water?

Another thing I'd like to check that I haven't been able to find out online is whether the "1/2" in the expression is only valid for two-component systems.  Is this expression valid for my system?  Thank you for any guidance.

Update:
I have realized that I have been confused.  I want to find out which reactions happen in my system at different temperatures.  As part of that, I want to find out the activity coefficients of the various species involved and the standard state free energies.  This requires knowing the ionic strength.

I was confused by something I read online and basically thought that my ionic strength calculation for each temperature would only involve the species participating in the reactions happening at each temperature.  But I now realize (hope) that actually, the ionic strength is the same at ALL of the temperatures I'm dealing with because calculating ionic strength means accounting for all species present in the system.

So if I'm now on the right track, my ionic strength would be 6.5 mol kg-1 based on using the equation above with concentrations of Ga, Na, and Cl of 1, 1, and 3 mol kg-1, respectively, and charges of 3, 1, and -1.


texts:
Applying a Legendre transformation on $U = q - w$ we get the familiar $G = H - TS$.
Making an innocent approximation delivers $\Delta G = \Delta H - T\,\Delta S$.

When one wants to predict the spontaneity of a chemical reaction, one gets the $\Delta H$ and the $\Delta S$ for the reaction in question from tables, and both refer to the system undergoing the transformation. Therefore we can write:

$\Delta G_\mathrm{sys} = \Delta H_\mathrm{sys} - T\,\Delta S_\mathrm{sys}$

In which:

$\Delta G$: Variation of the system's Gibbs energy

$\Delta H$: Variation of the system's enthalpy

$\Delta S$: Variation of the system's entropy

However: $\Delta S_\mathrm{sys} = \frac{q}{T}$, assuming the process is reversible (as usual).

So: $\Delta G_\mathrm{sys} = \Delta H_\mathrm{sys} - q$. If we are making predictions based on Gibbs energy, we are under constant pressure and so $\Delta H_\mathrm{sys}=q$.

Therefore: $\Delta G_\mathrm{sys} = q - q$, $\Delta G_\mathrm{sys} = 0$ and we are always on equilibria.

Where am I mistaken? I've already seen some say that some stuff refers to the surroundings, but that makes no sense to me. If both are at thermal equilibrium, $q$ is going to have the same effect on the entropy of the system and that of the surroundings, from $\Delta S = \frac{q}{T}$.

I'm a chemistry undergratuate and have seen no mention to anything related to this on common p-chem textbooks (Atkins, McQuarrie, Ball).


texts: Possible Synthesis of MVK from 2-Butanone?

texts:
My professor wanted me to set up a lab to synthesize Methyl Vinyl Ketone (AKA Butenone) from some MEK we have lying around (2-Butanone).

Now, I know there are multiple ways to do this, but the tricky part is finding out a safe way to go about this as MVK has a very low flashpoint.

I figured we could do an acid catalyzed alpha halogenation with Bromine and some Acetic Acid, and then follow up with an Elimation using a bulky base such as tert-butoxide.

The only problem is I have no idea how long, how much, or how cold/warm these materials need to be for the reaction to occur.  Ideally the entire reaction would take place in an ice water bath due to the danger, but at the same time I don't want to take five hours synthesizing one compound.

Let me know what you think, and feel free to recommend a different (but safe) route of synthesis, as our lab has plenty of chemicals to work with.  By the way, we only need to create about 10-20ml of the stuff, but more is better.


texts: Does the addition or multiplication rule have precedence deciding the significant figures in 5×5.364?

texts:
How many significant figures should be present in the answer of
  $5\times 5.364$?

Addition rule: The result cannot have more digits to the right of the decimal point than either of the original numbers.
Multiplication rule: The result must be reported with no more significant figures as there are in the measurement with the few significant figures.

Using rule 1,
$$5\times 5.364 = 5.364 + 5.364 + 5.364 + 5.364 + 5.364 = 26.82,$$
one would use 4 significant figures.

Using rule 2,
$$5 \times 5.364 = 26.82 = 30,$$
one would use 1 significant figure.

Which one is correct?


texts: How to calculate the concentration of a K₂Cr₂O₇ solution?

texts:
How many ml of acidified $\ce{K2Cr2O7}$  solution, which includes 21.6 g of dichromate ions per Litre, are required for the oxidation of 44.4 g of  $\ce{CH3CH2CH(OH)CH3}$?

Obviously 44.4 g of $\ce{CH3CH2CH(OH)CH3}$ means 0.6 moles. So from the stoichiometry of the the oxidation we find out that 0.2 moles of $\ce{K2Cr2O7}$ are needed. I have trouble finding the concentration of $\ce{K2Cr2O7}$ though and thats why I need help.


texts:
I've seen some EPR experiments where they add gelatin to water with spin-probes in it, as it "hardens" it immobilizes the spin-probes so that you can check effect of tumbling rate on the EPR. Cool
I would like to do the same with asphaltene in crude oil.... So I'm looking for a chemical that I can add to oil that will turn it into a more-or-less solid black gooey mess. It shouldn't be something too reactive though, because I don't want it to change the chemical aspects of the asphaltene (e.g. not make it self-aggregate). Just lock it in place.
Thoughts?


texts: Why does more s-character stabilise Carbanions?

texts:
Since carbanions carry a negative charge, more the distribution of electron density, more is the stability.
What does this have to do with more s character?
Does the distribution of electron density in a spherical fashion more favourable than p orbital distribution, as it is more symmetrical maybe?


texts: Solubility product when you add an acid to a solid?

texts:
I ran into some trouble when I was resolving some exercises about solubility product principle.The exercise says:

  A concentrated, strong acid is added to a solid mixture of $0.015\ \mathrm{mol}$ samples of $\ce{Fe(OH)2}$ and $\ce{Cu(OH)2}$ placed in $1.0\ \mathrm{L}$ of water. At what values of pH will the dissolution of each hydroxide be complete?

So, I don't know how start when you have an acid and an insoluble salt when using the Ksp equation.

I know I can't to do this.

$\ce{Fe(OH)2 + HCl -> FeCl2 + H2O}$

$\ce{Cu(OH)2 + HCl -> CuCl2 + H2O}$

Not even do I have a common ion in order to establish a reaction. Do you know where I should begin? I tried using $K_\mathrm{sp}$, but I already have molar solubility, is $0.015\ \mathrm{M}$ for both. I can't ignore that. I don't find useful $K_\mathrm{sp}$ in this case. I know there's something that I'm not understanding. Hope you can help me to figure it out.


texts:
I mean their pH value never change unless we dilute with water etc?

  An acid is a molecule or ion capable of donating a proton (hydrogen
  ion H+) (a Brønsted–Lowry acid), or, alternatively, capable of forming
  a covalent bond with an electron pair.

So acids stay acids forever?


texts: Birch reduction of 1,2-Cyclopentanedione and Diketones

texts:
This answer given to this problem was that only one of the double bonds is reduced into an alcohol. I
think i understand how the double bond is reduced into an alcohol. An electron is transferred to the carbonyl carbon and the double bond cleaves homolytically, forming a carbanion (stabilised by resonance ) and the oxygen with an extra electron which then will gain another electron and both get hydrogens to form the alcohol.
First of all is my method right? I don't think so as both the double bonds would have been reduced into alcohols. Also i was unable to see any sources for the birch reduction of di-ketones, I was only able to find it for unsaturated ketones.


texts:
Raoult's Law states that the partial vapor pressure of each component of an ideal mixture of liquids is equal to the vapor pressure of the pure component multiplied by its mole fraction in the mixture.

As we know that the liquid and vapour in a container are at dynamic equilibrium,

So the mole fraction which is mentioned in Raoult's Law is measured at equilibrium or initially?


texts: How to efficiently reduce of ilmenite to pure titanium?

texts:
I am looking for a process in which reduces ilmenite to pure titanium with the highest yield possible. We are to use a process of our choice or one that we have created in conjunction with FactSage to calculate the yield of titanium.

the materials we have available are:

Pure Metals

$\ce{Al, Ca, Mg, Na, Si}$

Pure Non-metals

$\ce{Ar, C, Cl2, H2, N2, O2, S }$

Molecules

$\ce{CH4, CO, CO2, HCl, H2O, H2S, NH4}$

There are a few process that come to mind such as reduction using Magnesium, $\ce{H2SO4}$, high temperature $\ce{CO2}$, but any help on which would be the most efficient combined with the highest yield would be great.


texts: Why is 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) often considered a prototypical room temperature ionic liquid?

texts:
It seems from a brief search of the literature that 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) is a prototypical room temperature ionic liquid (RTIL) that has been studied extensively.  However, numerous -- almost limitless -- combinations of cations and anions that give rise to ionic liquids are possible.  Why does it seem that the imidazolium cations are so extensively studied?  Is one possible reason the fact that $\text{EMI}^+$ is aromatic and thus affords the ionic liquid a high degree of stability?

Similarly, why does it seem that $\text{BF}_4^-$ (along with, perhaps, $\text{PF}_6^-$) is the prototypical ionic liquid anion?  I have seen studies of other anions (for example, $\text{CF}_3 \text{SO}_3^-$ and $(\text{CF}_3 \text{SO}_2)_2 \text{N}^-$), but $\text{BF}_4^-$ seems to be one of the most popular.


texts: Maximum coefficient of friction between nylon and polyethylene

texts:
For a research project I found out last minute that I need the coefficient of friction between nylon and Ultra-high-molecular-weight polyethylene. After hours of scouring google nothing useful turned up.

Since I actually need the maximum and not the precise value, I came here to ask what that could possibly be and if there is any literature on that. Basically I need to find out what the maximum friction could be, caused by a Dyneema (polyethylene) rope on a plastic nylon pulley.

I was hoping there is some sort of "rule" what the maximum coefficient of friction could be for 2 smooth plastic surfaces.


texts:
In my Physical Science class, we are learning about chemical formulas and how to balance them. I balanced this equation:

$$
\ce{Fe2O3 + Al -> Fe + Al2O3}
$$

One of the other students asked me if this chemical formula releases or absorbs heat.

Could anyone help me give a great explanation for this question?


texts: Feasibility of another product in peroxide effect mechanism of propene

texts:
In the Chain Propagation step of the reaction of propene  ($\ce{CH3CH=CH2}$) and hydrogen bromide ($\ce{HBr}$), why is $\ce{CH3-\dot{\ce C}H-CH2-Br}$ free radical formed when a more stable, resonance stabilized allyl free radical ($\ce{\dot{\ce C}H2-CH=CH2}$) is possible?

Source  : https://www.chemguide.co.uk/mechanisms/freerad/alkenehbr.html


texts: What's the difference between pharmacotherapy and chemotherapy

texts:
Is it fair to say that pharmacotherapy (the use of pharmaceuticals to treat disease) is a subset of chemotherapy (the use of chemicals to treat disease)?

If not, why? Aside from the fact the former involves a subset of available chemicals and the latter all chemicals, what is the difference between the two?


texts: In the structure of $\ce{HSO3-}$, we see that the H is bonded directly to the S, not to the O's, as would be the case in other oxyacids. Why is this the case?


texts: Difference between thermodynamic and kinetic stability

texts: What is the difference between thermodynamic and kinetic stability? I'd like a basic explanation, but not too simple. For example, methane does not burn until lit -- why?