texts: How do restricted open shell calculations mathematically proceed in the context of the self consistent field iterations?

texts:
I'm specifically concerned with HF theory. I understand restricted closed shell calculations use the Roothaan equations. If I understand correctly these equations assume each filled molecule orbital is doubly occupied. Each of the electrons in a pair is described with the same spatial wave function.

I also think I understand the Pople-Nesbet equations which allow the wavefunction for each electron to be described with their own spatial wavefunctions furthermore their spins are not constrained hence spin contamination can result.

I however, have not been able to figure out how restricted open shell calculations work. All I understand is that the spin is constrained. I do not understand if the wavefunctions of the paired electrons are described with the same wave function (similar to the Roothaan restricted closed shell approach) while the unpaired electrons are simply allowed to have their own spatial wave function. Coming back to the title question is there a bunch of equations with a famous person’s name (Roothaan, Pople-Nesbet) that are used to describe the scf procedure for restricted open shell calculations or does it use some combination of Roothaan and Pople-Nesbet?


texts:
The usual units are J/K, however
the only reason temperature has different units than energy is because we didn't used to know temperature was just the average kinetic energy of atoms/molecules.  Hence, using a more reasonable system, the units would be J/J which just cancel.
I get that we're stuck with having different units for temperature now, just as we're stuck with the inconvenient convention that electrons are negative and protons positive.  But since we already have a constant in the definition of entropy anyway, why haven't we defined it in a way as to convert the temperature units to energy and so make entropy dimensionless?
Or, better yet, why not, for the purposes of thermodynamics problems, just use subsume the Boltzmann constant into the units for temperature in the first place?  That would make certainly make for a less messy system of units and make the units of both temperature and entropy better match the definitions of the quantities.  I get that we can't just switch the temperature unit system for everyone, but I'm rather surprised scientists working in thermodynamics (thermodynamicists?) haven't adopted that unit convention within the field.


texts: Impact of pH? Change in Binding Affinity of protein-ligand complex based on pH and Kd?

texts:
When the $\mathrm{pH}$ was $5.0$, the temperature was $\pu{25 °C}$,the $K_\mathrm{D}$ was $\pu{5 μM}$, and [L] was equal to $K_D$, the protein(s) were half bound.

Question considers half bound condition where $[L]= _$

  If $K_\mathrm{D} = \pu{20 μM}$ and $\mathrm{pH} = 6.5$, what is the impact on binding affinity?

I understand that $K_\mathrm{D}$ is the inverse of $K_\mathrm{a}$ and that $K_\mathrm{D}$ describes the degree of dissociation at equilibrium for the reaction, thus a low $K_\mathrm{D}$ corresponds to a high binding affinity complex.

I don't understand how to account for $\mathrm{pH}$ change though.


texts: Can I reactivate a chemoluminescent reaction?

texts: I have created a firefly jar with glow sticks to sell at a school fair. The firefly jar lasts only for an hour or so. I have heard that glow sticks can be reactivated. The firefly jars contain the chemicals found in good sticks. Is there any way to make the jar glow again?


texts:
when CuSO4.5H2O is dissolved in water, what physical and chemical effects happens to its water of crystallization?
While solving a stoichiometric problem the ques was that 1litre of CuSO4.5H2O was dissolved in 1 liter water and the concentration of Cu2+ ions were asked. When calculating molarity the volume which those 5 water of crystallization were also taken along with the solvent water.
I had the doubt that if the 5H2O is attached to CuSO4.5H2O then how can we include that also while calculating volume of solvent (for denominator of molarity). Those 5 water molecules are not free, they are bonded then why do we consider it?


texts: The effects of adding neutrons to an atom

texts:
So neutrons are neutral in terms of charge, and adding neutrons to an atom affects its atomic mass. But when neutrons are added to the nucleus, the nuclear radius would be affected. Couldn't that affect how the charge of the nucleus is distributed within the nucleus?

With an atom large enough that, say, 40 neutrons could be added (and still be stable), I would imagine that the nucleus would be slightly rearranged to accommodate this (so that neutrons and protons are distributed throughout the nucleus and there isn't a shell of 40 neutrons surrounding what is the pre-existing nucleus).

I imagine that this redistribution (if it does occur) would dilute the charge coming off of the nucleus (as the protons are farther apart and the nucleus is less dense in terms of charge), which would lead the electron shells to be farther from the nucleus. This would increase atomic radius, affecting a wide-range of chemical characteristics. I could equally see an opposite effect, where the nuclear charge is strengthened (which would decrease atomic radius).

Is this an actual reaction to the adding of nuclear charges? If so, does it occur in large enough quantities to play a significant role in chemistry? Or have I just made a false assumption?


texts: Interpreting straight lines in a graph of isotherms of carbon dioxide

texts:
I am having difficulty in understanding pressure-volume graphs of $\ce{CO2}$ at different temperatures which describes liquefaction of $\ce{CO2}$.

I know that at the critical temperature of $\pu{31.1^\circ C}$ it is possible to liquefy the gas at the critical pressure of $\pu{73atm}$.

But I am having difficulty in understanding some statements about the graph.

  (i)At temperatures below $\pu{30.98^\circ C}$ the behaviour of $\ce{CO2}$ towards compression is quite different.For example at $\pu{21.5^\circ C}$,  $\ce{CO2}$ remains a gas up to point $\mathrm B$. At point $\mathrm B$ a liquid of certain volume appears.Further compression do not change pressure but volume decreases till point $\mathrm C$ is reached. In fact, the gas and liquid $\ce{CO2}$ coexist along the horizontal line BC.The decreases of volume represents condensation of more and more $\ce{CO2}$ gas till the point C is reached.

I know that if we are compressing a gas  its pressure should increase but why its pressure is constant along the line $\mathrm{BC}$?

  (ii)At point C all the gases has been condensed and further application of pressure simply compresses the liquid .The line $\mathrm{CD}$ represents the compressibility of liquid Carbon Dioxide.

I have studied in my earlier classes that liquids cannot be compressed but how can the liquid $\ce{CO2}$ has a tendency of compression here?


texts: What are the reaction products in my dishwasher from a steel colander?

texts:
In my dishwasher I noticed that a steel colander and a coffee maker (the Moka Pot) both became discolored after being in the dishwasher. The metal is clearly reacting with something. They aren't made of aluminum (I don't think) and I've never seen this reaction before when I do dishes in the sink.
To clarify: the metal on my coffee pot and the colander was relatively smooth and shiny, and then after they were in the dishwasher they became grayer, and the texture was clearly rougher. That said, i was able to remove the discoloration with a Scotch-brite plastic pot scrubber sponge or Brillo pad, with a little elbow grease.
So, the chemicals I saw on the back of my dishwashing liquid were:
NaCl, Na$_{2}$SO$_{4}$, Citric Acid, Na$_{2}$CO$_{3}$, Sodium percarbonate, sodium silicate and a couple of organics (it says enzymes, but I don't know how much of that is marketing hype). I looked up the rinse aid (it's Finish brand) and I came up with alcohol ethoxylate, sodium polycarboxylate, sodium cumene sulfonate and tetrasodium EDTA, Methylisothiazolinone and methylchloroisothiazolinone, and CI Acid Blue dye.
I do not know the xact metal composition of my colander or coffee pot, though I suspect it's is stainless steel I don't know which particular type and what the exact mix of carbon, chromium, etc. is. I can say that the colander is one that is quite old; it's age is measured in decades. The coffeepot not so much; I got that maybe a decade ago? At least that. Both are made of a gray steel that has a slight "rough" feel; it's not the super-shiny modern variety. The Colander in particular seems a type of metal I recall being quite common with cheaper kitchen stuff in the 70s and 80s.
In any case, I wanted to know what the following might be:
-- The reaction products of the dishwashing chemicals dissolved in the water; clearly there is something going on
-- If I need be concerned about toxicity, since this is something that touches food. I would assume there is less of an issue if I scrub the discoloration off. And it's not likely to be in concentrations that are harmful one-off, but why ingest weird stuff if you don't have to and all that.
Any insights are appreciated; this is something I was rather curious about (and may make a good demo for a chemistry class).
ETA: In the images you can see the darker gray on the metal -- that was the discoloration.
ETA II: apropos of blacksmith37 's comment/ answer I checked if there was any magnetism and the fridge magnet does not stick so it's either aluminum or a steel that is non-magnetic.

enter image description here


texts: According to Pubchem, the XLogP of octanol is 3 and that of water is -0.5. Why aren't they both 0 or 1 which seems to make more sense to me?


texts: Does ordered mesoporous carbon (for example, CMK-3) contain aromatic rings?

texts:
I'm studying the article Synthesis of ordered mesoporous phenanthrenequinone-carbon via π-π interaction-dependent vapor pressure for rechargeable batteries, in which authors explain some properties of the resultant composite of phenanthrenequinone (PQ) and ordered mesoporous carbon CMK-3 by the $\pi-\pi$ stacking between these moieties.

While PQ obviously contains aromatic rings, does the ordered mesoporous carbon do? As far as I know, $\pi-\pi$ stacking is possible only between aromatic compounds.

UPD1: So I did several things to elaborate on this question.

First, I tried to figure out, how ordered mesoporous carbon is produced. In this article authors report on several ways therefor; most of those include pyrolysis of hydrocarbons. Well, in my non-professional opinion, this means, that the product will contain hydrogen in some form. Thus, there will be hydrocarbons, including, probably, cyclic and aromatic (for example, pyrene is often a product of burning, as far as I know). Is this right?

Second, I tried to figure out whether it is in general necessary for $\pi$-stacking to have both compounds aromatic. This answer suggests, that not, but that p-orbitals are needed. Can anyone confirm, please? Also, in this article (still to be read) there should be some insights.

Third, I decided to check on the question what is $\pi-\pi$ stacking in general, by reviewing this article. While I'm still in process of reading it, I've already understood, that there's a lot of confusion in this field since there is a variety of this interaction types; possibilities depend strongly on the molecules themselves and their surroundings. Am I wrong?

Fourth, I tried to track back one of the statements regarding multi-walled carbon nanotubes $\pi-\pi$-interacting with PQ from this article (nanotubes just seem to me somewhat more clear than CMK-3, the chemical formula of which I even don't know). This led to surprisingly branched and sad journey to several articles aged past to '70s, not in any of which the $\pi$-stacking was ever proven, but always assumed (I have a long report for myself on this journey, here it is, however, not the correct place to post it). Anyways, it's an ongoing literature research and I decided to make a pause when the amount of articles to check reached six.


texts: E/Z configuration of the central double bond in a highly branched poly-ene

texts: What would be the configuration of the marked double bond in the attached molecule?


texts: Nucleophilic addition reaction of ketone to form alcohol - no acid treatment?

texts:
I'm preparing for a chem prac on reduction of a ketone group (in particular, the C=O in benzoin) using a nucleophilic addition reaction.

In the experimental method, all we do is react benzoin with $\ce{NaBH4}$, the nucleophile. The solvent we're using is a mix of ethanol/water. From what I've learned, the reaction forms a $\ce{C-O^-}$ alkoxide group which then needs to grab a proton from something to form the alcohol.

In the procedure, we mix ethanol/water, and that's it - no addition of dilute acid to then protonate the alkoxide. We're told to add hot water. Am I right in saying that addition of hot water provides a source of protons to protonate the alkoxide?

Thanks :)


texts: Are common rock (I.e. Rock from mountain, river, bricks, or even concrete) actually silicon oxides? Or it is just one of compositions?


texts: Why is $\ce{NaCl}$ more soluble in water than $\ce{NaOH}$? Well, this is a question from Chemical Equilibrium and the question hints for explanation in terms of Le Chatelier's principle.


texts: Why is an isothermal process not unique in nature?

texts:
To be clear, I have got two doubts,

One, about the non-uniqueness of an isothermal process &
Two, about the uniqueness of an adiabatic process.

The first doubt

The Wikipedia page of isothermal process states that:

  For an adiabatic process, in which no heat flows into or out of the gas because its container is well insulated, Q = 0. If there is also no work done, i.e. a free expansion, there is no change in internal energy. For an ideal gas, this means that the process is also isothermal.[4] Thus, specifying that a process is isothermal is not sufficient to specify a unique process.

Now I am confused about the meaning of the last line.

  Thus, specifying that a process is isothermal is not sufficient to specify a unique process.

I am not able to understand the significance of that last statement. Does it mean that any two states, say A & B, can be connected by more than one isothermal processes?

The second doubt

Similarly, I had read in my textbook that an adiabatic process is unique in nature. That is, between any two states only one adiabatic process can exist. To say the same thing in other words,
if two thermodynamic states are connected by a reversible adiabatic process, then the same two states cant be connected by an irreversible adiabatic process

Kindly help me understand these statements with the help of some PV/VT/PT diagrams.

Any help would be deeply appreciated.


texts: I found this in a second hand store, and I think it has to do with freeze drying. Is there any validity to this assumption? What is this called? Also, the little tuberculina at the bottom are stuffed with fiberglass I believe.


texts: when do we indicate the "+ or -" sign in uncertainty

texts: how can we know when to indicate "+ or -" sign in uncertainty calculations because I noticed some problems has been solved by this sign and some has not.


texts: Allotropy in Nitrogen and Bismuth of Group 15

texts:
Which elements of Group 15 of the periodic table have allotropes?

P, As and Sb have well-known allotropes:

P: White, Red and Black;
As: Yellow, Black and Gray (Grey);
Sb: White, Yellow and Black.

What about Nitrogen and Bismuth?

The same source suggests that Nitrogen has an allotrope named Dinitrogen while Bismuth has none.
Chemwiki says:

  $\ce{N2}$ does not have any allotropes.

and doesn't comment on Bismuth.
Royal Society of Chemistry says yes for Nitrogen and no for Bismuth.
Inorganic Reactions and Methods: The Formation of Bonds to N, P, As, Sb, Bi (Part 1), Volume 7 has an article which suggests that Bismuth allotrope exists.
This not so reliable source says no for Bismuth.
Wikipedia doesn't mention anything for Bismuth but for Nitrogen:

  At atmospheric pressure, molecular nitrogen condenses (liquefies) at $\pu{77 K}$ ($\pu{−195.79^\circ C}$) and freezes at $\pu{63 K}$ ($\pu{−210.01^\circ C}$) into the beta hexagonal close-packed crystal allotropic form.

  Unstable allotropes of nitrogen consisting of more than two nitrogen atoms have been produced in the laboratory, like $\ce{N3}$ and $\ce{N4}$. Other (as yet unsynthesized) allotropes include hexazine and octaazacubane.

According to me, nitrogen has allotropes and bismuth doesn't, but the above sources contradict. Any clarifications and reasons for them showing or not showing allotropy would be appreciated.


texts:
Layman here. I was looking at vitamin C serums in skincare and wanted to know more about it. It has been awhile since taking chemistry in college so my understanding is rusty.

I want to better understand this diagram (Source: U of Iowa) that talks about the different forms vitamin C:

All I remember of $\mathrm{p}K_\mathrm{a}$s was that high $\mathrm{p}K_\mathrm{a}$s means the acid is very strong and dissociates all the way while lower $\mathrm{p}K_\mathrm{a}$ means a weaker acid. So I'm a little lost on how to interpret this diagram in terms of the $\mathrm{p}K$ values, ie the $\ce{OH}$ group is deprotonated from $\ce{AsCH2}$ to $\ce{AsCH-}$ but I'm not sure how the $\mathrm{p}K$ value fits in all of this? Layman me wants to say at $\mathrm{pH}=4.1$ is when deprotonation happens, but I have a feeling that isn't right.


texts: Why does adding salt to water help distillation?

texts:
I've been looking at instructions on how to get lanolin from fleece and a lot of the instructions mention that adding salt to the water before distillation will increase the lanolin yield. Why is this?

I would think that the distillation would separate the water but not the salt leaving the lanolin contaminated with salt.


texts: Is a beta pleated parallel sheet always formed from more than one peptide?

texts:
I can conceptually grasp the beta pleated anti-parallel sheet by imagining a curved length of string i.e. one polypeptide, starting with the N- terminus on the left and ending with the C-terminus at the end of the string, opposite the N terminus.
I can't do the same for the beta pleated parallel sheet if it is only formed of one polypeptide. How could a fold in a single strand cause the N and C termini to be parallel with each other?
Or is it that parallel sheets are always composed of more than one polypeptide?

Would single chain parallel sheet look more like this:


texts: What pressure units should be used when calculating electrode potential with Nernst equation?

texts:
Example 17: Calculate the electrode potential of given electrode
  $$\ce{Pt,Cl2 (\pu{1.5 bar}) | 2 Cl- (\pu{0.01 M})}\,; \quad E^\circ_\ce{Cl2/2Cl-} = \pu{1.36 V}$$

  Solution: The reaction of electrode is
  $$\ce{\underset{\pu{1.5 bar}}{Cl2 (g)} + 2 e- -> \underset{\pu{0.01 M}}{2 Cl-}}$$
  $$E = E^\circ - \frac{0.0591}{n}\log{\frac{[\ce{Cl-}]^2}{P_\ce{Cl2}}} = 1.36 - \frac{0.0591}{2}\log{\frac{(0.01)^2}{1.5}} = \pu{1.483 V}$$

In the solution, the author has directly used the pressure (which is in bars) in the Nernst equation without first converting it to its SI units. How can this be right?


texts: Why does Helium have such a low van der Waals coefficient but not as low a Lennard Jones coefficient?

texts:
Helium has the lowest polarizability of any atom, and therefore ought to have the smallest London dispersion force. Indeed, if you look at the van der Waals constant of helium, you find that it has the lowest value of $a$ by a lot. $a$ roughly corresponds to the amount attraction between particles.

The long-distance force between neutral particles can be roughly modelled by the Lennard-Jones potential. Even though Helium should have the weakest $r^{-12}$ term of any atom, if you look up the experimental values of the Lennard Jones coefficients, you find that they're the same for Helium as they are for the rest of the Nobel gases. What gives? Why is its Lennard Jones potential roughly the same when its London dispersion force is so weak? (Perhaps my source is just wrong?)


texts: What makes some chemicals form steep density gradients in solution?

texts:
Caesium chloride and sucrose are both suitable for isopycnic centrifugation, and presumably not much else is. I'm unclear as to the mechanism by which they form useful density gradients. Wikipedia says,

  The $\ce{CsCl}$ molecules become densely packed toward the bottom, so even
  layers of different densities form.

(No doubt $\ce{CsCl}$ is molecular, despite being the chloride of a group I element, because $\ce{Cs}$ has such low electropositivity, but I digress.) But what is it about these molecules, not to mention those of sucrose, that causes their packing to be so strongly isopycnic in solution?


texts: Is trans-1,2-dimethylcyclopropane optically active or not?

texts: According to my book it is optically active, but no valid reason is given. But what I found is there exists an alternating axis of symmetry, and so my conclusion is the compound would be inactive or has a meso isomer. Am I wrong?


texts:
The Henderson-Hasselbalch equation for the $\mathrm{pH}$ of a buffer solution of the monoprotic acid $\ce{HA}$ is given by
$$\mathrm{pH}=\mathrm pK_\mathrm a+\log{\frac{[\ce{A-}]}{[\ce{HA}]}}$$
Since concentration appears in both the numerator and denominator of the fraction $\frac{[\ce{A-}]}{[\ce{HA}]}$ and $\mathrm pK_\mathrm a$ is constant (at a fixed temperature), it appears that dilution of the solution with pure $\ce{H2O}$ would not change the $\mathrm{pH}$. However, since
$$\mathrm{pH}=-\log{[\ce{H+}]}$$
 the amount of substance of $\ce{H+}$ must increase in order for $\mathrm{pH}$ to stay constant upon dilution.

Where is this additional $\ce{H+}$ coming from? I know that diluting an acid causes it to dissociate to a greater extent. But at the same time, you would be diluting its conjugate base and causing it to associate more, cancelling the dissociation of the acid.


texts: Electrocatalysis of Hydrogen Evolution Reaction with metal oxides

texts:
I'm new to the topic of electrocatalysis so I have a few questions. Also, I don't have much knowledge about thermodynamics, but I will try to ask anyway.

I'm looking for a material to catalyze the Hydrogen Evolution Reaction for $\ce{H2}$ production. So, for pure metals we have the Volcano curve:

Then, with this curve, I found in literature that we can mix metals from the different branches (positive and negative slopes) and get a new alloy with an intermediate M-H energy strength (which is desirable to improve the catalyst activity.)

But, I want to know if there exists the same curve (and the same logic) for metal oxides, because I need to predict if an alloy of rhenium oxides with copper oxides are going to be a better catalyst than only rhenium oxides.

Is there some method of theory to predict this before going to the lab and doing some experiments?


texts: NaCl water electrolysis without membrane, how measure the free chlorine concentration?

texts:
I'm trying to made electrolysis using water and NaCl. I need at the end a concentration of 2 g/l. How can I measure the free/active chlorine? Do you know a way to "measure" the chlorine during the reaction without chlorine sensor? Using for example the measure of conductivity of the water, the electrode current and voltage and the temperature or the salt remaining?

The electrolysis is 'open' without membrane, a titan electrode is directly put in the water + NaCl.


texts:
A thin film sample of polycrystalline Copper(I) Oxide (Cuprous Oxide, $\ce{Cu2O}$) on quartz looks reddish in the center but bluish/grayish at the sides where the film is thicker.

The same thin film on a Silicon Oxide wafer looks greyish, with a slight tint of blue.

XPS analysis shows that the bulk of the film contains no traces of Copper(II) that can be detected within the instrument's detection limit ($\pu{0.1-0.5 at.\%}$?).

The $\ce{Cu2O}$ film is grown by CVD using a metal-organic precursor and water.

What can be causing the gray color of the $\ce{Cu2O}$? Can it be the morphology/porousity of the $\ce{Cu2O}$? If it is trace amounts of contaminants, what are some good guesses?


texts: Isolating barium(II), copper(II) and zinc(II) from aqueous solution

texts:
Q15 Each metallic ion was separated from an aqueous solution containing $\ce{Ba^2+},$ $\ce{Cu^2+},$ and $\ce{Zn^2+}$ by the procedure shown in the following figure. From ①–⑥ in the table below choose the correct combination of ions that predominates in the precipitates a, b and the filtrate c.

For the precipitate a, I know the answer is $\ce{Ba^2+}$ ion because it has a highly negative standard reduction potential than the other ions, so it tends to displace the sulfuric acid to form insoluble barium sulfate.
But I don't know which one can displace $\ce{NaOH}.$ $\ce{Na+}$ ion reduction potential is a lot more negative than both $\ce{Cu^2+}$ and $\ce{Zn^2+}$ ions. I suspect there is something in 'added in excess' part, but I don't know how can it be any different.


texts: Is "propanol" a correct name in IUPAC nomenclature?

texts:
My teacher said that propan-1-ol can also be named propanol in the latest IUPAC recommendations. I doubt this because Wikipedia only mentions propan-1-ol as the IUPAC name (propanol being relegated to the "other names" section).

Is "propanol" an acceptable name?


texts: The interactions of the high energy gas particles

texts:
When we are talking about the idealization of the gas, why for high temperatures its particles interact less? I would say you have a bigger probability of the collisions among particles.
Quantum effects for very low temperatures or the elastic/inelastic collisions?
I am not sure and I didnt find anything satisfying on the internet.


texts: Is there a systematic approach to determing structural formula from NMR spectra?

texts:
I have not been able to find a methodologically consistent approach. If NMR spectroscopy is a rational analysis, it must not be beyond logical description in principle.

Here is what I have surmised so far:

Calculate degrees of unsaturation (I understand this)
Determine functional groups from IR spectra (I understand this)
Figure out chemical shift of each peak (I usually understand this)
Calculate integration of each peak (I usually understand this)
Determine number of neighboring protons (I usually understand this)
"Put the molecule together" (Variable results)

I "usually" understand steps 3-5, but sometimes I can't honestly figure out how many peaks I am looking at. How can I reliably tell the difference between lines within a peak due to coupling and distinct peaks when they are sometimes so close together?

Step 6 is difficult. Sometimes I can deduce an answer, and sometimes I am wondering how to tell the differences between hundreds of isomers. How can I systematically determine the right answer (or even be able to recognize IF there is single valid answer)?


texts:
In a physical chemistry course, we went to the lab and made a microstamp out of an elastomer. This stamp has gaps of 25 µm in width. When the elastomer had hardened, we placed it on a microscope slide and dropped a single drop of epoxy glue to one side of the stamp. Due to capillary forces, the glue migrated slowly to the other side of the stamp.

In my script, there is an equation to calculate the rising height of a liquid due to capillary forces. Our goal is to calculate the surface tension of the glue, knowing the migration speed, the density and the contact angle.

As our stamp is in the horizontal plane, there is no rising height, so how do I manipulate the formula to calculate the surface tension of the epoxy glue in the horizontal plane?

Here is the formula of my script:

$$
h = \frac{2 \sigma \cos \theta}{\rho g r}
$$

Where $\sigma$ is the surface tension, $\theta$ the contact angle, $\rho$ the density of the liquid, $g$ the gravitational acceleration and $r$ the radius of the gap.

And a little picture of our experiment. The glue migrates from the right to the left.


texts:
This may be a silly question but why is water wet?
All the previous questions on water do not explain the reason why is water wet. They assume that its a natural property. However we need to understand why is it wet in the first place. This could apply to other liquids such as milk, juices but the essential element is water.

Similarly another basic property which we take for granted is heat caused by fire. What causes fire to be hot as an inherent property? For the purpose of discussion consider simple fire by burning wood or paper.


texts: How can oxygen atoms suddenly appear on the product side of an equation?

texts:
The question states the following  equation:
 $$ \ce{C(s) + 2H2(g) -> CO2(g) + 2H2O}$$
 And then asks you to calculate the enthalpy change for it, given enthalpies of combustion.

The stated values are $C(s)$ -393,  $\ce{H2}(g)$ -286,  and $\ce{CH4}(g)$ -890

I'm curious as to why oxygen atoms have suddenly appeared on the products side. The only thing I have been able to think is that it refers to the enthalpy of formation of methane, and that the answer would be -393 + (2*-286) + 890. But it still doesn't make sense to me considering the equation provided. I understand the products are the products expected from combustion, but no oxygen has been added on the reactants side.


texts: What exactly is meant by 'multi-configurational' and 'multireference'?

texts:
Some topics here have touched on this before (see 1, 2, 3), but I haven't found a clear definition yet.

I would like to know what exact property of the wave function these terms refer to. It would also be helpful to have a clear definition of 'reference' and 'configuration'. I'll try to explain below where my problems are in clearly understanding/defining these terms:

Starting with Hartree-Fock, it is obvious that the wave function in HF is both single-reference and 'single-configurational': there is only one Slater determinant.

Going to configuration interaction methods, the wave function now becomes a linear combination of several Slater determinants. The additional Slater determinants are excitations of the ground state determinant: virtual orbitals from HF are taken and replace previously occupied orbitals in the determinant. However, these orbitals still have the same coefficients as in HF - only the coefficients in front of the Slater determinants are optimized for the linear combination. If I'm correct, 'configuration' here refers to one particular Slater determinant - a method is, therefore 'multi-configurational' if the wave function that is used has two or more (different) Slater determinants, correct? That also means that none of the CI methods (be it CIS, CISD,..., or Full CI) are multireference methods?

Continuing with CASSCF, this method is basically Full CI limited to the chosen active space of orbitals. It is therefore multi-configurational. At the same time, it is also often referred to as being 'multireference'. The only difference to CI, however, seems to be the optimization of the coefficients in the Slater determinants themselves, hence, this must be the defining criterion for 'multireference'? What does 'reference' here refer to?

Now there is also multireference-CI. From the above definition, I would expect this to be a form of CI where I also optimize the orbitals, but that does not seem to be the case. The Wikipedia article on MRCI starts with:

  In quantum chemistry, the multireference configuration interaction (MRCI) method consists of a configuration interaction expansion of the eigenstates of the electronic molecular Hamiltonian in a set of Slater determinants which correspond to excitations of the ground state electronic configuration but also of some excited states. The Slater determinants from which the excitations are performed are called reference determinants.

This is confusing to me: Is 'excitation of the ground state electronic configuration' vs. 'excited states' referring to the optimization of the Slater determinants themselves? Or does 'excited state' refer to configurations with different total spin? That would be a different definition of 'reference', but then CASSCF would only be a multireference method if it uses the corresponding SA-CSFs, regardless whether the Slater determinants are optimized or not?


texts:
Why is a supercritical fluid not a liquid? My book says that because in a container above the critical temperature and critical pressure, a fluid of density similar to liquid exists uniformly in the container and there is no surface or meniscus that separates the liquid from the gas. Does that mean that a liquid always has a meniscus which separates it from the liquid's vapour?

Does that mean that in free space without no gravity, a gas/vapour will try to expand and the liquid will try to contract and form spherical blobs due to surface tension? Can I draw the conclusion from this that a liquid is the phase when attractive forces are dominant and repulsive forces are dominant in gas/vapour phase?


texts: Electrochemical concentration cells -- how anion levels change

texts: It seems clear that in the anode, the anion concentration will increase as it enters from the salt bridge to balance the cations leaving from the oxidized electrode. But what is happening to the anion concentration in the cathode?  Cations are leaving the salt bridge to replace those being reduced on the electrode.  So is the anion concentration just constant?


texts: What is the relationship between the two definitions of the difference between basicity and nucleophilicity?

texts:
(Clarification: this is a question about terminology, not so much about when to use different concepts.  I think I do understand which characteristics of a species to use when trying to determine something about a reaction in some circumstances.  I just don't know what word to call it.)

When someone on the internet (here or elsewhere) is asked the difference between "basicity" and "nucleophilicity", they typically give one of the following two answers:

Basicity is about how well a species donates electrons to a proton, while nucleophilicity is about how well a species donates electrons to a more general atom or ion (especially carbon).
Basicity is about thermodynamics (i.e. equilibrium constant) while nucleophilicity is about kinetics (i.e. activation energy).

While these two answers may be related, they do not seem identical!  So I am wondering which one is actually correct, or whether there is some way that they are both correct.  In particular, I'm wondering what happens when you have a situation that puts those two descriptions at odds with each other.

We could have a reversible reaction involving carbon (though I know that's not the usual situation) that does in fact have some equilibrium.  When we're talking about that reaction's equilibrium, do we still use the word "basicity"?
In a reaction with a proton rather than a carbon, when we're talking about kinetics, do we still use the word "nucleophilicity"?

I hope I've gotten my question across OK.


texts: The irregular trend in ionization enthalpy of 3d elements

texts:
The d block elements display several exceptional behaviours, and one of them is the irregular trend in ionization enthalpy of 3d elements.

The reason given by my textbook is very confusing, which I'm unable to grasp. I would appreciate if someone explains me this statement in a simple way.

  The irregular trend in the first ionisation enthalpy of the $\ce{3d}$ metals, can be accounted for by considering that the removal of one electron alters the relative energies of $\ce{4s}$ and $\ce{3d}$ orbitals. So the unipositive ions have $\ce{d^n}$ configurations with no $\ce{4s}$ electrons. There is thus, a reorganisation energy accompanying ionisation with some gains in exchange energy as the number of electrons increases and from the transference of s electrons into d orbitals

Text source: NCERT (d & f block elements/ page 215)
Image source: Inorganic Chemistry Cengage Part-2 ( page 6.13)


texts: Sound absorption in carbon dioxide with temperature

texts: I am doing speed of sound measurements in $\ce{CO2}$ using ultrasonic pulses at 125 kHz. $\ce{CO2}$ is particularly difficult because it strongly absorbs ultrasound due to its multiple vibrational modes. The problem we have discovered is that absorption increases substantially as temperature rises. Is this expected, and if so is there a simple relationship between temperature and absorption coefficient?


texts: Why does gallium nitride allow an AESA radar to be more powerful than a radar with elements made of gallium arsenide?

texts: AESA (Actively Electronically Scanned Array) radars use thousands of individual transmit/receive elements to create a radar.  All in service AESAs use gallium arsenide as the material in the t/r elements.  It is said that gallium nitride allows a tenfold increase in the power emitted by these elements?  What allows GaN to emit so much more radio frequency energy than GaAs?


texts:
It is commonly accepted that you can hang your wet clothes outside to dry even when the winter temperature is below freezing. It is mentioned here
http://grist.org/living/ask-umbra-can-i-line-dry-my-clothes-in-the-winter-too/
that water in the clothes will freeze to ice, then sublimate into water vapor, making the clothes dry.

Question: Why does the ice in the clothing sublimate, while the ice on the roads don't sublimate? Why is there a difference between what happens to ice on the clothing versus ice on the roads?


texts: Mechanism for the addition of chlorine to benzene to form hexachlorocyclohexane

texts:
I am familiar with electrophilic substitutions of benzene, with chlorine using a halogen carrier catalyst such as $\ce{AlCl3}$, to produce chlorobenzene, and I am aware of the mechanism.
But, apparently, one can get the addition of chlorine to benzene, where the delocalised structure is disrupted and hexachlorocyclohexane is formed.

I would like to know the mechanism for this addition reaction.


texts: How do salts of a weak acid + weak base behave in solution?

texts: Say you have Ammonium Formate in solution, the salt formed by the reaction of Formic Acid and Ammonia.  Would both the Formate ion and Ammonium ion protonate and deprotonate, respectively, to form their conjugates until equilibrium is reached?  I would also assume that one of the ions would form more of their conjugate than the other depending on which ion in the pair is a stronger acid/base.  My question arose when researching the Leuckart reaction, which wikipedia states that if ammonium formate is used, it dissociates to formic acid and ammonia before participating in the reaction.  I also found it peculiar that ammonium formate is listed as soluble in diethyl ether, which typically doesnt dissolve salts.  This behavior would make more sense if ammonium formate dissociated into formic acid and ammonia.


texts: How is charge density a useful measure of polarising power and polarisability?

texts:
How do you use charge density ($Z/r$) as a measurement of polarising power and polarisability, and hence hard/soft acid character?

So far I've been looking at different polarising power and polarisability and how that affects a substance in whether it is a hard or soft acid/base, but I don't understand how charge density comes into play, and how we can use it to understand the characteristics.


texts: Decrease in Surface area leads to Increase in load capacity for mesoporous material?

texts:
So at the bottom of page 86 it says that when SBA-15 is functionalized with Glutaraldehyde it results in a substantial decrease in the surface area and pore diameter of the mesoporous material.
This paper rationalizes this by saying that the bridge chain insertion causes an increase in hydrophobicity that improves its ability in loading ibuprofen.  Can someone please why this is the case!!?? thank so much it just seems very conterintuitive.

http://ac.els-cdn.com/S0927776514001751/1-s2.0-S0927776514001751-main.pdf?_tid=cea489ec-ec87-11e6-a9e2-00000aab0f01&acdnat=1486398051_2d9403232650bb1a93cf30c41e9a1d72


texts: Which atom bears the negative charge in cyanide? I am confused by the MO diagram

texts: In heteronuclear species, whichever atomic orbital a molecular orbital is closer to in energy contributes more to that molecular orbital, right? In other words, if the orbital is occupied, more electron density is around the atom whose atomic orbital is closer in energy to the molecular orbital. This feature of MO diagrams can predict dipole behavior and which atom bears charge in ions. If this is the case, and we know that carbon bears the negative charge in cyanide (and hence is a carbon nucleophile), why does the MO diagram for cyanide appear to have the HOMO (the "attacking" orbital) concentrated on the nitrogen rather than the carbon atom? Based soley on the diagram and not the accompanying image of the HOMO, I thought, since the HOMO is closer in energy to the nitrogen 2pz atomic orbital rather than the carbon 2pz, the HOMO should have more contribution from nitrogen and the LUMO should have more contribution from the carbon.


texts:
Phys.org's How sulfur helped make Earth habitable before the rise of oxygen says

Mapping the bonds and vibrational modes of molecules containing sulfur isotopes is helping to shed light on the chemical reactions that took place in Earth's atmosphere during the Archean era, before the atmosphere became oxygenated about 2.5 billion years ago.

and

The sulfur in the Archean Earth's atmosphere was emitted by volcanic activity, and through a process called mass independent fractionation, sulfur's various isotopes... became enriched in a manner that does not correlate with their mass.

It links to Computational analysis of vibrational modes in tetra-sulfur using dimensionally reduced potential energy surface and says that this paper

...explores some of the molecular bonds of a sulfur-4 (S4) molecule, and how these bonds affect the vibrational modes of the molecule, which in turn may influence the mass independent fractionation process.

Question: If the formation of tetra-sulfur is expected to be an important aspect of atmospheric chemistry in Earth's past, why is there so little experimental information on this molecule? Is it profoundly difficult to make, or to measure? Pardon the simple language, but What is tetrasulfur like? Why is there so little experimental information about it?
Wikipedia says only:

Tetrasulfur, S4
S4 has been detected in the vapour phase, but it has not been well characterized. Diverse structures (e.g. chains, branched chains and rings) have been proposed.[citation needed] Theoretical calculations suggest that S4 adopts a cyclic structure.

Source


texts: Consider 2,3,4-pentanetriol.Is the middle carbon atom a stereocentre?I know how to count the stereoisomers, but is the middle carbon a stereocentre by definition?Let us say we have a 2R and 4S configuration.Now if we change the orientation of the OH group at the 3rd carbon, we do get a different compound,but both the compounds are optically inactive, so it doesn't seem it should be called a stereocentre.If we consider 2R,4R, or 2S,4S if we change the configuration at C3, we get the same compoound.So I feel the carbon at C3 should not be a stereocentre.But it seems that in the first case, we are changing the C3 configuration and getting a new diastereoisomer, so C3 might be a stereocentre after all.Which one is correct?If C3 is a stereocentre, what would be its R,S nomenclature?


texts: Electrolysis of water in 0.1 M hydrochloric acid

texts:
For water electrolysis in acidic media ($\ce{TiO2}$ anode and $\ce{Pt}$ cathode) the half reactions for water splitting and $\ce{O2/H2}$ evolution are as follows:

Anode: $\ce{H2O + 4 H+ -> 4 H+ + O2}~~(E = \pu{-1.23 V}\text{ vs NHE})$
Cathode: $\ce{4H+ + 4 e- -> 2 H2} \quad\quad~~(E = \pu{0.00 V}\text{ vs NHE)}$

If I use $\pu{0.1 M}$ $\ce{HCl}$ as my acidic electrolyte, what reaction will occur at the anode (the standard oxidation potential for $\ce{2Cl-}$ to $\ce{Cl2}$ is $\pu{-1.36 V}$ vs NHE). In $\pu{0.1 M}$ $\ce{HCl}$ electrolyte, there should be $\ce{H_2}$ evolution at the cathode. Will the anode maintain $\ce{O2}$ or $\ce{Cl2}$ evolution (or maybe both?)


texts: Rate law of reactions, what about the proportions?

texts:
Consider the reaction

$$\ce{A + B + C -> D + E}$$
and $\mathrm{rate} = k[\ce{A}][\ce{B}]^2.$ My book said if we double the amount of $\ce{A},$ then the reaction rate will double.

I understand this, but what about the law of definite proportion?


texts: I am confident enough about my knowledge about spiking and the process of standard addition but I came across this process which claimed to have a percent recovery of 115% and it was considered as a good recovery process. How it is considered a good recovery? Is it because you add too much of the spike and recovered most of them?


texts: Why does the Oxymercuration Demercuration mechanism lead to stereorandomization?

texts:
I'm having a doubt on the mechanism of oxymercuration Demercuration reaction.
How does the reaction, initially heading towards anti addition(after cyclic transition state formation) ,get spoiled by $\ce{NaBH4}$ and ends up being stereorandom? Can anyone point out the importance of using mercury as well? The explanation would be greatly helpful.

Thank you


texts: Why interconversion in tautomers is so rapid?

texts:
Looking at the examples in Tautomer on Wikipedia, it seems that the hydrogen needs to travel a significant distance (~20Å) for the interconversion to take place. What lets it happen so fast? Why interconversion is preferred over maintaining its position?

(source)


texts: Electronic configuration of vanadium ion in a compound with magnetic moment 1.73 bm

texts:
Vanadium has $Z = 23$ and so the electronic configuration of an isolated neutral atom in the gas phase would be $\ce{1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^3}$.

Now, magnetic moment of 1.73 means 1 unpaired electron (calculated using the formula $M^2 = n(n + 2)$). So, vanadium will have to lose 4 electrons.

I worked out the ion's electronic configuration to be $\ce{1s^2 2s^2 2p^6 3s^2 3p^6 4s^1}$. But internet and other sources say it's $\ce{1s^2 2s^2 2p^6 3s^2 3p^6 3d^1}$. Note the $\ce{3d^1}$ instead of $\ce{4s^1}$.


texts: Why does copper not react with nitrogen?

texts: Please describe why copper only reacts with oxygen and not nitrogen in the air. Isn't nitrogen a negative ion, and copper positive, so wouldn't that mean that copper and nitrogen would want to form bonds?


texts: How can meta-cresol be made, given that the hydroxyl group is ortho,para-directing?

texts:
How is it possible for m-cresol (3-methylphenol) to be synthesized?

The methylation of phenol would lead to the ortho- and para-isomers instead.


texts:
$\ce{ZrO2}$ has great properties, biocompatibility, chemical resistance, decent scratch resistance, great thermal resistance and refraction, but it could be better. It, like glass, will slowly react with $\ce{HF}$ and other fluorine substances, specifically oxidizing agents with fluorine.

Normally to make stuff resistant to fluorine the only thing to do is react it with fluorine in such a way that the reacted surface stays where it is. Steel flasks, for example, can be polished in a low oxygen environment and treated with fluorine to make the surface of the steel an iron fluoride.

Unlike iron oxides, fluorine won’t react with it because fluorine is a more effective oxidizing agent and essentially nothing else can break apart the intramolecular bonds keeping the iron fluoride together under normal conditions. It’s like, you can’t burn something twice, you can’t fluorinate something twice. That might not work with $\ce{ZrO2}$, I was going to say cause it doesn’t burn or oxidize but it’s already an oxide so that’s a bad reason.

Anyways PTFE doesn’t react with fluorine cause it’s just fluorine and carbon already.

So here’s my question: Can you do that with $\ce{ZrO2}$? Would Zirconium form a stable molecule with fluorine? If so, would it have similar properties, or at least be solid at STP? If not, is there another way of making $\ce{ZrO2}$ fluorine resistant? Or something else like $\ce{ZrO2}$ that’s more fluorine resistant?


texts: Does gas chromatography follow the "like interacts with like" rule of thumb?

texts:
The "like interacts with like" rule of thumb works well when there are polar and non-polar molecules that are mobile (liquid-liquid extraction, membrane vs cytosol, questions of solubility).

Polar molecules interact with polar molecules rather than with non-polar molecules because the interactions are stronger.
Non-polar molecules "hang out" with non-polar molecules because that
way, they don't disrupt the stronger interactions between polar
molecules.

The latter is sometimes called the hydrophobic effect when
   water is present as a solvent. Self-assembly of detergents into
   micelles, folding of proteins, formation of lipid bilayers are all
   rationalized by "like interacts with like".

In a previous post, the question was asked why polar molecules have lower retention times than non-polar molecules when running gas chromatography with a non-polar column. One of the answers invoked "like interacts with like" as rationalization.

I have two questions:

Do polar molecules have lower retention times than non-polar molecules on a non-polar GC column (to make it comparable, the molecules should have similar boiling points)?
Does the "like interacts with like" rule of thumb apply to gas chromatography, given that there are no interactions in the gas phase and there is no hydrophobic effect in the stationary phase (i.e. the non-polar stationary phase interacting with the polar analyte would not disrupt any polar-polar interactions)?

In the post I referred to, the question started with a convincing statement:

  I remembering reading that the interaction between a polar molecule and non-polar molecule is stronger than the interaction between two non-polar molecules.

This would suggest non-polar molecules have the weaker interaction and elute first, even on a non-polar column.


texts: Why does the pH of this solution rise instead of fall when exposed to the atmosphere?

texts:
I have a couple of big barrels with a $50\,\mathrm{L}$ demi-water solution of the following nutrients:

$$
\begin{array}{rl}
200~\mathrm{\mu M} & \ce{NH4NO3} & +\\
30~\mathrm{\mu M} & \ce{KCl} & +\\
10~\mathrm{\mu M} & \ce{CaCl2} & +\\
10~\mathrm{\mu M} & \ce{KH2PO4} & +\\
\\
10~\mathrm{\mu M} & \ce{Fe-EDTA} & +\\
\\
0.7~\mathrm{\mu M} & \ce{ZnSO4} & +\\
0.8~\mathrm{\mu M} & \ce{MnCl2} & +\\
0.2~\mathrm{\mu M} & \ce{CuSO4} & +\\
0.8~\mathrm{\mu M} & \ce{H3BO4} & +\\
0.008~\mathrm{\mu M} & \ce{(NH4)6Mo7O24}\\
\end{array}
$$

After mixing those nutrients, I adjust the $\mathrm{pH}$ of the barrels to $5.5$ by carefully adding $\ce{HCl}$ and continuing mixing until the $\mathrm{pH}$ stabilizes at $5.5$.

Then, when I measure the $\mathrm{pH}$in the barrels again after four days, I notice that it has risen to about $5.8$-$5.9$. This is contrary to my expectation. I'd have expected $\ce{CO2}$ from the air to be dissolved in the solution, thus lowering the $\mathrm{pH}$ rather than raising it.

Could someone explain to me what could be happening here?


texts:
Question:

  How many moles of iron will by passage of $\pu{4 A}$ of current through $\pu{1 L}$ of $\pu{0.1 M}$ $\ce{Fe^{3+}}$ solution for $1$ hour. Assume $\ce{Fe^{2+}}$ is not present in the solution initially.

Attempt:

Using Faradays' Law, we have:

$\text{mass delivered = } \mathrm {Z\times I\times t} = n\times M$  where $\mathrm Z = \dfrac{\text{Equivalent mass }}{\pu{1F}}$

Equivalent mass of Iron here would be $\dfrac{M}{3}$ where M is molar mass.

So,

$n \times M = \dfrac{M}{3}\times \dfrac{\pu{1 mol}}{\pu{96500 C}}\times \pu{4 \frac{C}{s}} \times \pu{60 \frac{s}{min}} \times \pu{60 \frac{min}{hr} \times \pu{1 hr}}$

$\implies n = 0.049$ moles.

But answer given is $\pu{0.0245 moles}$

Where have I gone wrong? I can't figure out why there's a difference of factor of 2 in the answer.


texts: Relationship of Dielectric constant with ionic bond

texts: How is dielectric constant related to formation of ionic bond?


texts: What is a good way for a laymen to purify alcohol to near 200 proof?

texts:
I'm making herbal and medicinal mushroom tinctures and extracts.  Normally I'll use everclear but it isn't cheap and 95% alcohol.  Also I don't know what that other 5% is.  Is it just water?

Is there a way I can reduce alcohol to near 100% without a still?  I've heard poring it over epsom salts through a few layers of coffee filters will remove some of the non alcohol contents.  Is this true?


texts: Adding non stoichiometric amount of NH3 to copper solution

texts:
Consider the following reaction: $$\ce{Cu(H2O)_n^2+ + 4NH3 -> Cu(NH3)4^2+}$$
The amount of ammonium hydroxide added to your penny solution was not controlled (i.e. you did not add
“stoichiometric” amounts). Discuss what would happen to its absorbance value, and explain why, if the amount
added was too low and too high. (Assume the mark on the volumetric flask was not overshot in either scenario.)

I was hoping to get a second opinion on what happens to the absorption in the case where you add too much $\ce{NH3}$ and the case where you add too little.
I think that if I had added not enough $\ce{NH3}$ that some of the copper would not turn into $\ce{Cu(NH3)4^2+}$ and thus the absorption reading would be lower.
As for adding too much... I think it would be okay to add too much. I don't think it would affect the absorption.


texts: Why 4‐methylidenespiro[2.4]heptane cannot be converted to 1‐chlorobicyclo[3.2.0]heptane?

texts:
According to the solution, the following reaction is not correct:

But why? I have tried solving in the following steps:

Forming a carbocation by breaking the double bond.
Expanding the ring.
Adding a $\ce{Cl-}$ anion.

This should thereby form the compound that is shown. But the solution is given that this reaction is not correct. Can you please explain to me why?


texts: Order of Basicity of Nitrogen Trihalides

texts:
I was asked to arrange nitrogen tri-halides in order of increasing basicity. On looking up the answer online, it turned out to be the following: $\ce{NF3}$ < $\ce{NCl3}$ < $\ce{NBr3}$ < $\ce{NI3}$
The reason given was that more electronegative halides attract negative charge & hence reduce its availability.

I thought that the order should be $\ce{NF3}$ > $\ce{NI3}$ > $\ce{NBr3}$ > $\ce{NCl3}$ because:

all the halides except fluorine have vacant d-orbitals. So, back-bonding should reduce the basicity of all but $\ce{NF3}$.

$\ce{NCl3}$ shows more effective back-bonding as compared to $\ce{NBr3}$ which shows more effective back-bonding than $\ce{NI3}$. Better the back-bonding, lesser is the availability of the lone pair on the nitrogen atom.

It seems to imply that electronegativity is a more dominant factor as compared to back-bonding. But when we compare the acidity of boron tri-halides, we consider back-bonding to be the dominant factor. Same goes for Ipso effect.
So, what is wrong with my assumptions?
PS: I got the order from Yahoo! answers(which is pretty unreliable BTW)
PSS: I often come across questions of this sort which ask me to compare acidity & basicity of two or more compounds(both organic & inorganic). I think of looking at the pKb/pKa values of the chemicals can help me to reliably get the order in some cases. But I couldn't find any source/compilation of those values. Do you know any source which lists the pKb/pKa values of chemicals? If so, please add it to your answer. It may prove to be really useful for me & other people.


texts: Calculate the degree of polymerisation. It's molecular weight and its repeat structure are given

texts: I understand how to calculate the degree of polymerisation normally, but in this question, the extra H and OH outside the bracketed monomer have thrown me off. Do I include their atomic masses in the overall Atomic mass for the degree of polymerisation or are they not part of the monomer chain and so not part of the calculation?


texts: Why does the tautomerism of purine favor 9H-purine?

texts:
I tried to explain the equilibrium by comparing the basicity of different nitrogen atoms in a purine anion, but I can’t see any obvious difference. Seems like that the 9-N will be the most basic because it can have two adjacent imine structure while keeping the structure of pyrimidine untouched. Computational results will be appreciated.

P.S. I don’t think the question is a duplicate of the “purine nitrogen basicity” one because that one compares the basicity of nitrogens in a neutral purine molecule whereas my question compares the basicity in a purine anion.


texts: What is the chemical name of this derivative of aniline?

texts:
What is the chemical name of the following compound?

$$\ce{(C6H5)-N=CH2}$$

I doubt that it might be N-phenyl methanal oxime . But  , it can't be oxime of OH ion is absent.  What would it be?


texts:
If heat $Q$ flows from the surrounding nature temperature at $T_\text{surr}$ to the system at temperature $T_\text{system}$, then $$\Delta S_\text{total}=\frac{+Q}{T_\text{system}}+\frac{-Q}{T_\text{surr}}$$

This definition is from my book in which heat is exchanged between system and surrounding. This formula for me would only be valid when both the system and the surrounding is undergoing reversible processes but nothing about it is said over here. Does this mean this formula assumes both the heat gained and heat lost are rebersible processes? Isn't entropy defined for reversible processes?


texts: Electronegativity of heavier elements of Group 15

texts:
While reading about p-block I got to know that in Group 15 elements

  electronegativity value decrease down the group but amongst the heavier elements difference is not that much pronounced.

I understood that electronegativity decrease down the group as the atomic size increase but I don't understand why in heavier elements electronegativity difference is not significant.
What is the reason for this?


texts: What will be the major enol form of methyl acetoacetate?

texts: I presume the best enol form would have a double bond between the two $\ce{C=O}$ so they're conjugated, but I'm not sure how the resonance would play out.


texts: How to divide the peaks of two anion ions using ion chromatography?

texts:
I used an ion chromatography system (Dionex IC-2000) to determine the inorganic ions and acid from the samples collected in the atmosphere.

For measuring $\ce{SO4^2-, NO3, Cl-}$, and low molecular acid together, I used a gradient elution method to divide them and quantify their amount.

However, I found that an artifactual band always overlapped with malonic acid shown like this:

This figure was captured in the situation of the single standard of malonic acid.

I want to divide the overlapped peaks efficiently, and have not found any solutions?

Any useful suggestions or tips would be highly appreciated.

My gradient dissolution method

0.000   Autozero
        Concentration =     1.50 [mM]
        Curve =     5
        Load
        Wait    CycleTimeState
        Inject
        ECD_1.AcqOn
        ECD_Total.AcqOn
        Channel_Pressure.AcqOn
        Concentration =     1.50 [mM]
        Curve =     5

7.000   Concentration =     1.50 [mM]
        Curve =     5

8.000   Concentration =     3.00 [mM]
        Curve =     5

59.000  Concentration =     3.00 [mM]
        Curve =     5

59.500  Concentration =     1.50 [mM]
        Curve =     5

60.000  ECD_1.AcqOff
        ECD_Total.AcqOff
        Channel_Pressure.AcqOff
        Concentration =     1.50 [mM]
        Curve =     5


texts:
I was consulting Wade and I came across this problem and solution:

While I agree with the solution manual, I can't help but wonder if my proposed mechanism is correct.

I had the water attack the hydrogens attached to the alkene. I knew that alkenes are slightly electron-withdrawing and this makes the hydrogens an appealing target for a base.

Once the hydrogens were cleaved, I had the remaining pair of electrons attack the carbocation. Is this a valid pathway? Valid as in plausible? Would you accept this mechanism on a test?

The main problem I see with this mechanism is that yield is exceedingly low as sp2 carbons are not especially acidic, and water is a poor base. On the other hand the original problem does specify that this product is minor. But then, it appears that I chose the more minor of two minor pathways.


texts: Finding the repeating unit of polymerisation given two constituent molecules

texts:
The compounds $\ce{H2NCH2CH2NH2}$ and $\ce{HOOCCH2COOH}$ react to form a polymer. What is the structure of the repeating unit of the polymer?
A. $\require{enclose}\ce{\enclose{horizontalstrike}{(}HNCH2CONHCH2CH2NHCO\enclose{horizontalstrike}{)}}$
B. $\ce{\enclose{horizontalstrike}{(}HNCH2CH2NHCOCH2CO\enclose{horizontalstrike}{)}}$
C. $\ce{\enclose{horizontalstrike}{(}OCCH2CONHCH2NHCO\enclose{horizontalstrike}{)}}$
D. $\ce{\enclose{horizontalstrike}{(}HNCH2CH2NHCOCH2NH\enclose{horizontalstrike}{)}}$

I came across this question which requires me to find the structure of the repeating unit of the polymer made by the reaction of two different compounds. However, I am not sure as to which repeating unit would suffice for this particular polymer.
As far as I know, there should be double bonds present at the ends of the repeating unit, so that the pi bond can break and allow the formation of additional bonds, and hence, a chain of molecules. However, using that line of thought I cannot seem to figure out the answer to the question.
I just need a direction, a hint or a clue as to how I should approach problems like such.


texts: How do I create a transparent liquid for ferrofluid display?

texts:
Hello~ I am a media art artists working in Korea.
Recently, create a kinetic artwork using ferrofluid.
I need to create an artificial pond with a diameter of 3 meters. So I need a lot of suspension liquid.

Prototyping
https://youtu.be/3o33upltO34

simulation videos
https://youtu.be/NE19B_2byGA

Unfortunately, I tried my solution failed.
- case 1: Deionized water 40% / isopropyl alcohol 40% / Propylene Glycol 20% (Stains occur on the glass )
- case 2: Deionized water 60% / Coco betaine surfactants 40% ( no stain but, This seems strange movements)
- case 3: Deionized water 35% / isopropyl alcohol 35% / Coco betaine surfactants 30% (Stains the glass )
- case 4: Deionized water 60% / LES surfactants 40% ( no stain but, This seems strange movements.)
- case 5: Deionized water 60% / APG surfactants 40% ( no stain but, Decomposed into many particles)
- case 6: Windex(Glass Cleaner) 100%  ( no stain but, Decomposed into many particles)

I used glass types
- pyrex glass (Small stains occur)
- tempered glass (Small stains occur)
- soda-lime glass (Big stains occur)

I was always cleaning solution into a container before adding the alcohol.

And most it had hardened over time, the ferrofluid.


texts: Reduction of an Allylic Enoate to afford allylic alcohol in presence of Benzyl Acetal Groups

texts:
I have a question that requires finding a reagent for the reduction of an enoate to the corresponding allylic alcohol. Preferably done in one step too with an acid workup at the end too.

What types of reducing agents would work?

Would Lithal be too strong and reduce the acetal groups or would it be okay?


texts: Ring contraction when cyclohexene oxide is treated with methyl Grignard

texts:
My book writes that:

  Recall that epoxides rearrange with Lewis acids in a pinacol-like fashion, and that Grignard reagents in THF exist in the following equilibrium:

I approached this question by reasoning that the Grignard reagent would lead to opening of the epoxide:

but the answer given in the book is instead

How is the five-membered ring formed?


texts: How can the intense color of potassium permanganate be explained with molecular orbital theory?

texts:
In the permanganate ion, manganese is in the $+7$ oxidation state, therefore it is a $\ce{d^0}$ ion. $\ce{d^0}$ and $\ce{d^1^0}$ ions don't absorb visible spectrum radiation because there are no electrons to jump to higher crystal field orbitals (or in the case of $\ce{d^{10}}$ ions, there are no free orbitals for electrons to jump to). I think that the explanation to this question has something to do with the ligand donating electrons into $\ce{Mn^{VII}}$'s empty d orbitals or molecular orbital theory or $\ce{d-d}$ transition or none of them.

Also, chromate is also colored wherein $\ce{Cr^{VI}}$ is a $\ce{d^0}$ ion, therefore its not absorbing radiation due to electrons jumping to higher orbitals in the crystal field. What is causing it to absorb visible radiation?


texts: Challenges Associated with Earth's field NMR

texts:
The ACS recently hosted a virtual conference and there was an interesting talk on NMR experiments using the Earth's magnetic field. What surprised me was the number of molecules studied with Earth's field NMR so far is around 22. Another interesting aspect was that NMR at low magnetic field strength is richer in the number of lines as compared to the extremely strong magnets used today. I think spectroscopists might be happier if they get a rich spectrum (good for finger printing).
This site has many NMR researchers, my question is why Earth's field NMR never caught up? The number of molecules studied so far is very low. Is it theoretically very challenging or the analytical sensitivity is hopelessly low?


texts: Excitation of electron in Niels Bohr's atomic model

texts:
Professor taught us that an electron gains or looses only those energies which are equal to difference in two energy levels. That is $E_1 + \Delta E = E_2$ or $E_1 + \Delta E = E_3.$
What if we give, say, $\pu{11.3 eV}$ and the remainder is $\pu{-2.2 eV},$ so the electron jumps to $n = 2$ where the energy is $\pu{-3.4 eV}$ and the remainder $\pu{-1.2 eV}$ is released?
I'm really confused with the working here.


texts: Is Bromide anion acting as a base in reaction with ethylamine and methylbromide?

texts: What is happening in Step 2 and would you please give the reaction mechanism for it as well?


texts:
Are these structures equivalent?

Image 1:

http://i.minus.com/jnojtCx6wYvqD.png

Image 2:


texts: I have just minutes ago been splashed with industrial grade methanol. It seemed like a small amount (1-3mL) on my skin. I already washed the affected area thoroughly with soap and water. Online I've reviewed SDS's for methanol and they all seem to say that immediate medical attention is needed, and that the person exposed can be asymptomatic for a while. Does a small splash like that warrant medical evaluation?


texts: How can I measure a droplets contact angle without a setup?

texts: I have to use a phone camera to replicate the Sessile drop analyzer, but there doesn't seem to be a standard to different parameters, such as how far away should my camera be from the droplet or how much liquid should I use for my droplets? Is it possible to get accurate results this way, and how should I go about it?


texts: When I was drawing the lewis structure for $\ce{H2SO4}$ I got this configuration, now I know this isn't the best configuration but I don't see whats wrong with it. The number of valence electrons is right, the free electrons are on the most electronegative element and the formal charges are all 0. I'm not sure if there's a rule I'm missing.


texts: Calculating the cell potential of a half cell from two half cell equations

texts:
I understand the premise of the question and how to solve it but I don't quite understand why I'm a factor of 2 out:

Construct a potential diagram (at $\mathrm{pH} = 0$) for the reduction of aqueous $\ce{HNO2}$ to $\ce{NO}$ and then to $\ce{N2O}$ given that $E^0$ for the $\ce{HNO2/NO}$ and $\ce{NO/N2O}$ couples are $\pu{+0.98 V}$ and $\pu{+1.59 V}$ respectively. Calculate $E^0$ for the following half-reaction:
$$\ce{2HNO2 + 4H+ +4e- <=> N2O + 3H2O}$$

So by constructing the two half-equations:
$$\ce{HNO2 + H+ +e- <=> NO + H2O~~~~~~~~~~~~(E^\circ= +0.98V)}$$
$$\ce{2NO + 2H+ +2e- <=>N2O +H2O~~~~~~~(E^\circ= +1.59V)}$$
And so by adding 2 times the first equation to the second, you obtain the desired overall equation. And so you would add the individual reduction potentials to obtain the overall potential:
$$\pu{+0.98 V + 1.59 V} = \pu{+2.57 V}$$
The answer stated however is $\pu{+1.29 V}$, ie, half of my answer.
Why do we need to divide by $2$ at the end here? The standard reduction potential doesn't depend of stoichiometry, and when doing similar questions combining two half cells into a full equation (with no electrons in the equation), simply subtraction or adding the equations is sufficient. Why the difference here?


texts: Need help to calculate results of an electrochemistry cell potential lab work

texts:
So, the lab work is this. I made an AgCl electrode of a silver wire by coating it with AgCl. This was done by electrolysis by immersing the wire in HCl and using platinum as a counter electrode and applying current to the system. After that, the AgCl electrode was immersed into HCl dilutions of different molalities and the cell potential was measured against a hydrogen gas electrode (normal hydrogen electrode NHE).
The measurements were done at temperature of 25 °C. The results of the measurements are as follows:
\begin{array}{llc} \hline
c\,(\pu{mol/kg}) &\sqrt{c}\, (\sqrt{\pu{mol/kg}}) & \mathrm{E\,(V)} \\ \hline
0.001 & 0.032 & 0.6322 \\
0.002 & 0.045 & 0.6815 \\
0.004 & 0.063 & 0.6497 \\
0.006 & 0.077 & 0.6280 \\
0.008 & 0.089 & 0.6153 \\
0.010 & 0.100 & 0.6049 \\
0.020 & 0.141 & 0.5700 \\
0.050 & 0.224 & 0.5030 \\ \hline
\end{array}
Because the cell potential can be calculated by (as the pressure gradient of the hydrogen electrode was 0):
$$ E(m)= E^0 + \frac{2ART}{F} \sqrt{\frac{m_{\text{HCl}}}{m^0}} $$
By plotting the table values we get (excluding the first data point as an outlier):

We can see from the equation that the $E^0$ would be about 0,708 V. However, literature references say the standard potential of the AgCl electrode is about 0,222 V. Any idea what I am doing wrong here?
Then I also should plot the HCl mean activity coefficient values calculated from the formula:
$$
E(m) = E^0 - \frac{2RT}{F} \ln \left[ \gamma_{\text{HCl}} \left( \frac{m_{\text{HCl}}}{1\ \text{mol/kg}} \right) \right] \\
\Leftrightarrow \ \gamma_{\text{HCl}} = e^{ \frac{(E^0-E)F}{2RT} } / \frac{m_{\text{HCl}}}{1\ \text{mol/kg}}
$$
Thus I get values:
\begin{array}{cc} \hline
m & \gamma_\ce{HCl} \\
\pu{mol/kg} \\ \hline
0.001 & 4371.98 \\
0.002 & 837.44 \\
0.004 & 777.51 \\
0.006 & 790.73 \\
0.008 & 759.33 \\
0.01 & 743.74 \\
0.02 & 733.46 \\
0.05 & 1080.77 \\ \hline
\end{array}
But literature references (CRC Handbook of Chemistry and Physics - 97th Edition, p. 5-101) gives greatly different values:
\begin{array}{cc} \hline
m & \gamma_\ce{HCl} \\
\pu{mol/kg} \\ \hline
0.001 & 0.965 \\
0.002 & 0.952 \\
0.004 & 0.929 \\
0.01 & 0.905 \\
0.02 & 0.876 \\
0.05 & 0.832 \\ \hline
\end{array}
Any help would be greatly appreciated.


texts: What volume of water will dilute an acidic solution back to neutral?

texts:
Now we are talking about simple dilution, not acid-base neutralization, so we expect asymptotic behavior that never quite gets us back to pH=7; that is, an infinite amount of water would be required. However, most pH probes read to two decimal places, so diluting to reach pH=6.995 is a sufficient end condition. So, given an initial pH of $pH_0$ and an initial solution volume $V_0$, what additional volume $V$ of pure water would be required to dilute the pH to 7.00 (6.995)?

I've wondered this for a while, and today I attempted to solve it. I may have found the solution, but I am skeptical of its implications. If I have 1 L of a solution at pH=2, my derived formula indicates it would require additional volume of about 8.6 million liters of water for the solution to read neutral. Is this reasonable?

My derived formula:

$$V=\Big(\frac{1}{1-10^{-0.005}}\Big)\Big(10^{6.995-pH_0}-1\Big)V_0 \\
\approx \Big(86.36\cdot10^{7-pH_0}-87.36\Big)V_0$$

Derivation:

Moles of $H^+$ from original soln: $n_0 = [H^+]_0V_0$

from added water: $n = [10^{-7}]V$ (via autodissociation)

Total moles: $n'=n_0+n$

Total volume: $V'=V_0+V$

New molarity after addition of $V H_2O$:

$$[H^+]'=\frac{n'}{V'}=\frac{[H^+]_0V_0+[10^{-7}]V}{V_0+V}$$

$$\Rightarrow V=\Big(\frac{[H^+]_0-[H^+]'}{[H^+]'-[10^{-7}]}\Big)V_0$$

(Note that $V \to \infty$ as $[H^+]' \to 10^{-7}M$, an infinite volume is require to exactly reach neutral pH).

Letting $[H^+]'=10^{-6.995}M$ (paragraph 1), $[H^+]_0=10^{-pH_0}$, and multiplying top and bottom by $10^{6.995}$, obtain:

$$V=\Big(\frac{10^{6.995-pH_0}-1}{1-10^{-0.005}}\Big)V_0$$

Question: Is this derivation valid? Are there assumptions I should or should not have made? Would it truly take 8.6 million times the original volume to dilute a pH=2 solution back to neutral pH=7.00?


texts: Does acetoacetic ester give haloform test?

texts:
According to my class notes, acetoacetic ester doesn't give haloform test, but I feel that it should.
I know that the methyl group on acetoacetic ester is not responsible for the haloform test. First, the active methylene group is attacked by the base and halogen ion is substituted there. After the attack of $\ce{OH-}$ on the carbonyl carbon we will also get an ethanol molecule (from the ester part), which apparently should give positive haloform test.
I am confused. Which is correct?


texts: What are the products in a reaction between a metal and an acid?

texts: When magnesium metal and hydrochloric acid react, hydrogen gas is released (and not chlorine gas). However, when metals such as copper is placed in nitric acid, NO(g) is released and not hydrogen. So, how do we know that chlorine gas is not released in the first reaction? Does this have to do with reduction potential?


texts: How can residual entropies be reconciled with the Third Law?

texts:
The third law of thermodynamics states that the absolute entropy of a pure crystalline substance is $0$ at $0\,\mathrm{K}$. In the analysis of chemical reactions this absolute scale is sued to calculate the entropy change.  However, it is also noted that some substances like $\ce{CO2}$ have residual entropy at $0\,\mathrm{K}$ because their structure is not perfectly crystalline.

Now my question is, given all of the above why is it that in thermodynamics tables such as in the book "Physical Chemistry" by Bawendi the entropy of $\ce{CO2}$ is listed as $0$ at $0\,\mathrm{K}$ when it should be some finite (albeit small) number? The same goes for other substances like $\ce{H2O}$ whose entropy is listed as $0$ at $0\,\mathrm{K}$ when it should be a finite number.

I understand that different tables use different reference scales and the entropy of $\ce{CO2}$ could be arbitrarily taken as $0$ at $0\,\mathrm{K}$. However the problem is then if the tables give the entropy of a substance relative to the entropy of the same substance at $0\,\mathrm{K}$, then the reference scale for each substance is different. This is fine but in all the example problems in the textbook mentioned above (and others) they use the entropy values listed in the table for each substance without accounting for the different reference states.

For example, if I have the reaction

$$\ce{A + B -> AB}\,,$$

the entropy change is

$$\Delta S ~=~S_{\ce{AB}} - S_{\ce{A}} - S_{\ce{B}}\,,$$where $S_{\ce{A}}$ is the entropy of $\ce{A}$ and so on.

Now in order for this to work the entropies must be taken relative to the same reference state (like when we use heat of formation to calculate enthalpies). However in the Bawendi book they use the values listed in the tables for each substance, which are again relative to the entropy at $0\,\mathrm{K}$ of that particular substance. This would all be fine if the entropy at $0\,\mathrm{K}$ was indeed $0$ for all substances but it is not. Could someone please explain why a lot of books do this? or is there something that I am missing?


texts:
My textbook says that a $\ce{C^{4+}}$ cation cannot be formed because it requires a lot of energy to remove 4 electrons. Formation of  ionic bonds involve "removing" electrons and there seems to be enough energy there. So what's different for carbon?
The textbook also mentions that a $\ce{C^{4-}}$ anion cannot be formed because 6 protons cannot hold on to 10 electrons. Elements like chlorine form ionic bonds and end up with 18 electrons and 17 protons. I know there's just one more electron. So is $\ce{NaCl}$ possible because it's not very hard to hold on to 1 extra electron? In that case at what exact point does it become hard to hold onto the extra electrons?


texts: Why doesn't a buffer solution change ph(Appreciably?)

texts:
Consider a buffer solution containing weak acid $\ce{CH3COOH}$ and its salt $\ce{CH3COONa}$:
\begin{align}
\ce{CH3COOH &<=> CH3COO- + H+} \tag{1}\\
\ce{CH3COONa &-> CH3COO- + Na+} \tag{2}
\end{align}

These two reactions take place and now we are majorly left with $\ce{H+}$, $\ce{CH3COOH}$, $\ce{CH3COO-}$, $\ce{Na+}$ in the solution. Since, $\ce{Na+}$ is a spectator ion, we can ignore it.

We know that buffers resist change in pH on adding small quantities of $\ce{H+}$ and $\ce{OH-}$. Let us add $\ce{H^+}$ to this solution.

A buffer solution must contain some things that could remove these $\ce{H+}$ ions, otherwise the pH would change. As we add $\ce{H+}$ to this buffer solution, it will react with $\ce{CH3COO-}$ to form $\ce{CH3COOH}$.

But here's the catch.

$\ce{CH3COO-}$ is getting removed and $\ce{CH3COOH}$ is getting formed. According to Le Chatelier's principle (LCP), the equilibrium should shift towards in the forward reaction (in reaction (1)). Shifting of equilibrium in the forward reaction should increase the concentration of $\ce{H+}$ and hence decrease the pH of the solution.

Now, one might say that $\ce{CH3COOH}$ is a weak acid and it would not decompose much. So, we can actually ignore the amount of $\ce{H+}$ so generated.

Let's "assume" that's true for a while and move ahead.

Let us add $\ce{OH-}$ ions to the solution.

Remember there's $\ce{H+}$, $\ce{CH3COOH}$, $\ce{CH3COO-}$, $\ce{Na+}$ present in the solution. $\ce{OH-}$ can react with either (a) $\ce{H+}$, or (b) $\mathrm{CH_3COOH}$.

Here comes the tricky part.

Let us only consider hydroxide ions reacting with $\ce{H+}$

If $\ce{OH-}$ reacts with $\ce{H+}$, water will be formed.

Here although hydroxide ions are getting removed, $\ce{H+}$ are also being removed from the solution. Now, because of the removal of $\ce{H+}$ shouldn't the solution become less acidic and the pH should increase.

Now, some might say as soon as $\ce{H+}$ is removed, the equilibrium in the first reaction shift towards the right.

But wait, didn't we just ignore that (in the case when we added $\ce{H+}$ in the solution)?

Can anyone explain why is there a contradiction?

P. S.: I have ignored the $\ce{H+}$ and $\ce{OH-}$ from water because it is irrelevant to the discussion.


texts: Would I use PBr3 or HBr in this synthesis?

texts: In the above reaction, I know that I have to use either $\ce{HBr}$ or $\ce{PBr3}$ and then $\ce{NaCN}$, DMF, $\ce{H+}$ and $\ce{H2O}$. However, I'm just confused on when to use $\ce{HBr}$ or $\ce{PBr3}$. How is the stereochemistry controlled?


texts: In the wet medium of an ocean, how does a hard shell form?

texts:
In general, if you were to try make something hard in a liquid medium (especially water) it is quite difficult to make the material solid.

Things such as mollusks though, have no problem generating hard shells in a wet medium.

What exactly are the physics behind this formation?


texts: For Fe2O3 what could an XPS peak at 711.9 eV mean

texts: For an XPS spectra of Fe2O3 film on graphite there are peaks at Fe 2p1/2 = 724.2 eV and Fe2p3/2 = 709 eV but there is another peak at 711.9 eV that I can't identify. Any ideas on what this might be would be great.


texts:
Is the distance of some $n^{th}$ shell ($n$ $\neq$ outermost shell) from the nucleus of an atom different for different elements?

If so, then how much is the difference or how could we calculate it?


texts: Flux a specific concentration of a tracer constituent of a gas

texts:
I need to flux 250 ppm of CO2 at 1000 ml/min.
I have a gas system with a tank containing CO2 (CO2 at 5000 ppmvol, Oxygen 21%vol and Nitrogen the rest), connected with a mass flow controller (MFC1, flux max at 150 ml/min) and I have a tank of dry synthetic air (O and N), connected with a second mass flow controller (MFC2) that can be fluxed at a max of 1000 ml/min. Since I don’t have the possibility to measure the ppm of the CO2 after the dilution, I need to know a right way to dilute the CO2 in my tank (that already contains a mix of CO2 and air).
I know that I can digit the values of 50 ml/min for MFC1 and 950 ml/min for MFC2, obtaining a final flux of 1000 ml/min. But, in this way, I don’t understand the final concentration of CO2.
I don’t know if applying this formula 5000ppm*(MFC1/tot flux) [that means 5000ppm*(50ml/min : 1000 ml/min)] I am double diluting my gas (because I am considering two times the air, once mixed with the CO2 tank and the other ones in the other air tank). Or, I don’t know if this formula [5000ppm*(50ml/min : 950ml/min] is the correct one, since apparently I consider air in the CO2 tank and air in the other tank.
I don’t even know if my approach to this problem is wrong and both formulas are not correct (e.g. I should consider other parameters; the carbon dioxide is a pollutant and so it follows particular rules/formula/conversion).
Thanks.


texts: Is the standard enthalpy of formation always non-positive?

texts:
If the standard enthalpy of formation is defined as

  the energy change when 1 mole of a substance is formed from its elements in their standard states

and forming chemical bonds is an exothermic process, then does this mean all standard enthalpies of formation are non-positive?

Why do some compounds such as $\ce{NO}$, $\ce{NO2}$ have positive standard enthalpies of formation? Is this because to form $\ce{NO}$, we must first break the bonds in $\ce{N2}$ and $\ce{O2}$ (endothermic) to form the bond in $\ce{NO}$ (exothermic, smaller energy produced than the energy required to break the bonds of original standard state elements)?


texts: Equilibrium Constants For Phenol Tautomers

texts:
I encountered the following equilibrium constant values for the keto-enol interconversions of phenol in Organic Chemistry (Solomons, Fryhle, Snyder, 3rd Edition):

I wonder what could explain the differences (though I'm not sure whether they're significant) between the equilibrium constants of the two keto-enol interconversions wherein in one case the double bond of carbon with the oxygen and the hydrogens are oriented in ortho position and in para position in the other.

Edit: Can this difference concern the medium the reaction is catalyzed in or directive influence of groups?
Do explanations for equilibrium constant differences exist for other tautomer interconversions or are such queries quite speculative?


texts: Predict XPS Spectrum of Organic Monolayers on a Semiconductor

texts: X-ray photoelectron spectroscopy (XPS) is a particularly useful technique for examining the surfaces of all sorts of materials. Organic monolayers are particularly difficult to characterize completely via this technique due to the fact that many carbon peaks do not differ much by chemical shift. Traditionally quantitative information is obtained via a lot of guess-work and forced peak fitting. It would be better to predict peaks shapes and peak positions beforehand to aid in the interpretation and prevent a terribly mis-guided interpretation. How well can theory help the non-specialist with this? I wouldn't have the time to develop a program to do this either. Preferably one could point me to the right direction in terms of a research paper/software.


texts: How the equation that describes evolution of alkyl nitrates has been derived?

texts: I was reading this paper, Bertman, S. B., J. M. Roberts, D. D. Parrish, M. P. Buhr, P. D. Goldan, W. C. Kuster, F. C. Fehsenfeld, S. A. Montzka, and H. Westberg (1995), Evolution of alkyl nitrates with air mass age, J. Geophys. Res., 100(D11), 22805–22813, doi:10.1029/95JD02030 (link attached), and had a hard time trying to derive equation (12) from equation (11). If anyone knows how to do that, help would be highly appreciated.


texts: can I put hand sanitiser in PVC bottles or must the bottles be PET.  With the shortage of bottles I am keen to know if a 70% ethanol or isapropyl based sanitiser will distort or soften a PVC bottle in the short term or long term?


texts: How to find probability in different basis representations?

texts:
The matrix representation of the Hamiltonian is given in the position basis: $\{|+a\rangle,|-a\rangle\}$.
$$H = \begin{pmatrix} E_{0} & E_{-A} \\ E_{-A} & E_{0} \end{pmatrix}$$

The initial state of a system is also given in terms of the position basis:

$\mid \psi \rangle  = \frac{1}{5}[3|+a\rangle + 4|-a\rangle]$.

To find the probability of the a particular energy eigenvalue, why is it incorrect to choose the coefficient of $|-a\rangle$ so that it would be $\left(\frac{4}{5}\right)^2$?

Instead, we have to transform to the Hamiltonian basis, using the eigenvectors of the Hamiltonian. Why can't we use the position basis?


texts: Why doesn't the atomic number change by two in the process of production of Americium?

texts:
Looking at the bomardment of uranium-238 this is what I see.

First, I see a uranium-238 atom with 92 protons bombarded with a neutron. The neutron then undergoes beta decay into a proton. So we then get Neptunium as the neutron decayed into a proton and hence, atomic and mass number increase by one. An electron is also released from the atom.

That makes sense.

Looking at the second equation of the bombardment of Plutonium-239.

Plutonium-239 with 94 protons gets bombardment with 2 neutrons. These neutrons undergo beta decay to produce protons. Thus, the atomic and mass number must increase by two. The mass number, indeed, does increase by two. The atomic number does not. An electron is also released? Not sure why aswell.


texts:
I am experimenting with IR video cameras. They have a broad sensitivity peak at 940 nm. There is a filter blocking 750 nm and shorter in front of the sensor.

I am looking for an IR fluorescent substance to use for markers in the scene the camera is observing. Something that can be turned on with ultraviolet illumination bursts so I can differentiate between my markers and other IR sources.

My hope is for some affordable and harmless substance. Something that could be mixed with polyester, acrylic or epoxy potting compound wold be nice.
An already solid watherproof material is even better.

My searches so far have found some IR fluorescent stains for microscopy but I am afraid they are expensive.

This might be a physics question also but I think chemists works a lot with IR absorption and IR fluorescence.


texts: How to evaluate the expectation value of the Hamiltonian for a three electron Slater determinant?

texts:
I'm having trouble with a few concepts dealing with slater determinants and many electron systems. In particular, when dealing with 3 electron systems, I know that

$$
\psi_0 = \frac{1}{\sqrt{6}} \det
\begin{bmatrix}
    1s(1)\alpha(1) & 1s(2)\alpha(2) & 1s(3)\alpha(3) \\
    1s(1)\beta(1)  & 1s(2)\beta(2)  & 1s(3)\beta(3) \\
    2s(1)\alpha(1) & 2s(2)\alpha(2) & 2s(3)\alpha(3)
\end{bmatrix},
$$

where the $1s$ and $2s$ are spatial functions and $\alpha$, $\beta$ are spin functions.

Performing the determinant expansion yields 6 terms, and it turns out that $\psi_0$ is an eigenfunction for the unperturbed Hamiltonian (in atomic units)
$$
\hat{H}_0 =
-\frac{1}{2} \nabla^{2}_{1} -\frac{3}{r_1} -\frac{1}{2}\nabla^{2}_{2}
-\frac{3}{r_2} -\frac{1}{2}\nabla^{2}_{3} -\frac{3}{r_3}
$$
 and that the resulting eigenenergy is
$$E^{0}=E_{1s}+E_{1s}+E_{2s}.$$
How does one show this?

My confusion mainly stems from the difficulty in acting the Hamiltonian on the determinant expression above. For example, how does one compute (in bra-ket notation)
$$
\frac{1}{\sqrt{6}} \hat{H}_0
| 1s(1)\alpha(1) 1s(2)\beta(2) 2s(3)\alpha(3)\rangle?
$$
This is only the first term in the expansion, and once I have some intuition on how to do this properly, then the general pattern should emerge quite clearly. Any help and guidance would be greatly appreciated!


texts: Can you make a magnetic fluid that's drinkable

texts: I need to make a ferrofluid that is drinkable so I obviously can't use the traditional method of using iron as it is harmful. Are there any chemicals that are not harmful that can take on magnetic properties or and magnetic metals that are not harmful to consume?


texts: Which is more electronegative: hydrogen or astatine?

texts:
Which is more electronegative - hydrogen or astatine? I'm a bit confused because my teacher taught me that for an atom to be electronegative it has to be on the top of the periodic table and/or on the right. But hydrogen is on the top-left and astatine is on the bottom-right of the periodic table.

How does one determine which is more electronegative?


texts: What is the true depiction of the periodic table?

texts:
Normally with the periodic table the lanthanide series is separated out because it's long and would make the table wide. I looked for an expanded version and found this:

I found it kind of strange that scandium and yttrium are above the lanthanide and actinide series on the far left.

Does it make sense for those two elements to be there? I always assumed each column had certain characteristics like same number of valence electrons, that there were certain characteristics that held true for the whole table, but in this format I don't know how to understand the patterns or why the table ends up taking this shape.


texts:
I am not sure of the explanation for the following statement:

  The reducing property of dioxides of group 16 elements decreases from $\ce{SO2}$ to $\ce{TeO2}$.

Is the statement valid? If yes, how do I explain it theoretically?
If not, what would be the actual trend in that case?


texts: Which chemical reaction to use to remove carbon/peat from sieved earth/gravel?

texts:
I produce gravel for my aquarium by sieving and rinsing earth from my garden. After boiling and disinfecting it (with a solution against parasites) the rest of the organic material are composted or become invisible duff inside the gravel during the initial cycling of the aquarium. The only thing remaining visible are peat and other carbon particles of the size of the gravel which I currently need to remove mechanically.

Is there a way to remove them /shrink or reduce them to small pieces with a (chain of) chemical reaction(s) which

can be performed with a maximum of chemicals and equipment which can be bought at a supermarket or building supplies store
doesn't harm the fish after introducing them into the aquarium some weeks after the treatment - both through toxines and an instable PH value (more than +/- 0.5)
leaves the color and the size of the gravel untouched because my motivation to use custom gravel are mostly aesthetic and reducing the size would risk to block my undergravel filter (has a filter chamber with a separator for gravel of a certain size)

I thought about:

burning the particles, but that seems wasteful in terms of energy and requires some equipment (burner, fire proof permeable net, etc.)

I'm looking for a solution for some kg of 1mm to 3mm gravel in a 100 l aquarium filled with drinking water with a PH value of 7.2 to 8.

In case it's necessary to have more exact info what the particles in the gravel consist of, I'll ask a separate question how I can figure this out.


texts: Removing wood stain from a ceramic surface

texts:
I have a bathtub that I accidentally poured wood stain into. Now the stain is all over the white ceramic surface of the tub. I tried using bleach but it didn't do anything. I'm curious if there is a chemist who would know the answer.
I used Varathane® Premium Fast Dry Interior Oil-Base Cabernet Wood Stain with the following properties (Technical Specifications — PDF):


texts: I am planning to try electroplating a steel ring with copper, than nickel, and than finally gold.  It seems to me that this would be as simple as using a bath of HCl for electrolytes and attaching the object to be plated to the cathode and the metal to be plated to the anode.  I though I would then simply run a current through the setup.  However, I have seen several "recipes" for electroplating using other electrolytes such as copper and nickel sulfate or dissolving the gold in aqua regia or cyanide before the plating.  Is this necessary, as the metal to be plated will dissolve into solution when electricity is run through the circuit anyway.  I would prefer to buy fewer chemicals if possible and reduce the complexity of the process, while obtaining the best results.


texts: Why should you round to proper significant figures after you complete a calculation rather than while doing the calculation?

texts: In class, my teacher mentioned that you should complete a calculation without considering significant figures and then at the very end, round to the proper number of significant figures. Why couldn't we just round the numbers after each step of the calculation? Is there a difference?


texts: Computational chemistry: is k a quantum number

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I am trying to use the natural band offset method to calculate band offsets of junctions. In order to do so, I need to find the core electron eigenstates. I tried using FP-LAPW software Elk. But in the output of the core electron eigenstates there is a "k" value.

The value is listed among "n" and "l", so my thought is that it may a quantum number. But I am not sure. I was able to find that it may be the "projection of the total spin I on the nuclear symmetry axis". Could someone help me identify what k means?


texts: What is the correlation between electronegativity and the sharing of electrons?

texts: For example in a C-O bond, the electronegativity difference is 1.2. does this mean that the Oxygen has 1.2 of the shared electrons and Carbon 0.8 (or some other numbers)? Is there a specific equation that can give us how the bonding electron pair is shared?


texts: How is titanium metal obtained from natural resources?

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How does titanium occur in nature?

Is it available as a native metal or only in the form of ores?

Which precesses are typically used to convert the natural resources to the solid metal?

Any hints on where to find further information are welcome. Thank you very much in advance.


texts: Sudden pressure rising in a pipe of an old plant transporting 33% ammonia solution

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We pump 33% ammonia solution along a single pipe line before we introduce it to the mix. We've had two occasions now where the ammonia pressure has rapidly risen in the pipe. It happens when the fluid is at rest, meaning all valve shut and no pumps running. The pressure just escalates. The pipe was rinsed with recycled water, but this is a weak solution of what the ammonia is mixed with anyway.

Is there any material/condition that the ammonia solution could react with to cause this sudden over pressure?

Please note:

The ammonia tanks are outside (+1–2 degrees Celsius).
The internal temperature is (+15–19 degrees Celsius).
There is no pressure release system.
The system is 8yrs old.


texts: Zinc in a single displacement reaction with hydrochloric acid

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I understand that on the metal activity series, zinc can displace hydrogen from acids, but not from cold water. But is there a structural reason for this. For example, why can zinc displace hydrogen from hydrochloric acid, but not from water?

Thanks


texts: Why does the alkaline hydrolysis of benzamide yield ammonia?

texts: Nucleophillic addition to the carbonyl group is governed by the rule that a less basic group is displaced by a more basic group since $\ce{NH2^-}$ is more basic than $\ce{OH-}$ the reaction should not proceed forward but it does why so?


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I know that Raney nickel can deprotect thioacetals. Can it deprotect acetals as well?

I found this image which shows that it deprotects and removes many protecting groups. But there was no reference to deprotection of acetals.


texts: Electroplating to create a scratch-free surface?

texts: Can electroplating improve the texture of a steel ball bearing so that it will have a smooth surface free of scratches even a few microns wide? I'm trying to find a way to remove scratches (about 10 microns wide) from carbon-steel electrodes and have recently started looking into electroplating. I have already ruled out electropolishing and using rotary/vibratory tumblers.


texts: Are Isopropyl Alcohol (2-Propanol) and 1-Propanol tautomers?

texts: They both are structural isomers, but are they tautomers too?


texts: Protein purification pressure limits confusion, about the X-MPa limit for FPLC?

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I have always been a bit confused about column pressure limits. I have to elaborate a bit on the problem to get to my question:

In protein purification we use the äkta purification machines (e.g. äkta explorer), which always come with a high pressure and low pressure alarm setting for the column in their unicorn software. The most common column is the IMAC 5-mL HisTrap column to capture proteins that contain e.g. a 6xhistidine tag. When I check the column specifications I can see that the column has a flow limit of 0.3MPa which should be rounded up to 0.5MPa for the alarm (as the flow restrictor gives an additional 0.2 MPa pressure).  The second type of column is the SEC column, one example is the analytical "superdex 200, 10/300 GL" for separation of protein between 10 and 300 kDa. The specification of this column is that the  $\Delta$p is 1.5 MPa, however, its typical that most people are sceptical to go above 0.5 MPa for any type of column.

So my questions regarding pressure are as following:

The 0,5MPa limit for a HisTrap column is what is called the $\Delta$p pressure limit?
It always the specified  $\Delta$p for each individual column that I have to care about? (not the pre or post column pressure limits)?
Can I then assume that it is always safe to run the column all the way up to the specified $\Delta$p limit to e.g. equilibrate or wash the column? So for the mentioned SEC column, I could run in at a  $\Delta$p value of 1,5MPa and assume that the column and protein are just fine?