texts: Is there a case when an atom of some element (e.g. carbon) does not have its expected number of protons (e.g. 6)?

texts:
Page 12 of the Study Guide for Campbell Biology, 11th Edition has the following question:

  A carbon atom has 6 neutrons. How many protons are present in the nucleus of a carbon atom?

  A. 12
  B. 8
  C. 6
  D. Can't tell; more information is required.

The answer given on page 431 is D. I think the answer should be C since carbon has 6 protons.

What type of additional information might be required?

I understand that elements are defined by their number of protons, but maybe there is some strange edge case like a moment during nuclear fusion? Is there a case when a carbon atom does not have 6 protons?


texts: Letting Copper sit in NaOH for 5 min (for monolayer assembly)

texts: i made a self-assembled monolayer of dodecanethiol on copper, before that i let the copper in a solution of $\ce{NaOH}$ for 5 min, and i need to know what this step is for, anyone can help me?


texts:
Is there a difference between these two molecules?

If so how does one tell? What is the correct nomenclature for cycloalkenes? I know that the double bond is assumed to be between C1 and C2 but why can't we number a cyclohexene to get 2,3? Is it because a lower sum is not preferred but simply lower individual numbers if possible?


texts: How to find the volume of the products in methane combustion?

texts:
The combustion of methane gas, $\ce{CH4}$, gives as products $\ce{CO2}$ and $\ce{H2O}$, both in the gas phase. If $1$ liter of methane is burned in the presence of $10$ liters of $\ce{O2}$. Suppose all volumes measured under the same temperature and pressure conditions and optimal behavior for all gases.
  $$\ce{CH4 (g) + 2O2 (g) -> CO2 (g) + 2H2O (g)}$$
  What is the volume of the products formed?

I know that for a gas, the volume is proportional to the amount of substance, that is, maintaining the temperature and pressure conditions, doubling the volume doubles the volume of moles.

The answer to the exercise is 3 liters.


texts: Monosodium Diphosphate (NaH3P2O7) Preparation

texts:
I looked on wikipedia for an answer but I couldn't even find a page for this salt, a subsequent google search didn't further enlighten me.
Does any one know how monosodium diphosphate can be prepared?


texts:
I take venlafaxine (Effexor) as medication, and having wrapped up 2 semesters of Organic Chemistry I thought it might be fun to design a synthesis for it. A picture of venlafaxine:

I came up with the following preparation (beginning with phenol) and was hoping someone could check it for me:

React phenol with $\ce{NaOH}$ to form phenolate, followed by methyl iodide to form methoxybenzene.
This forms a moderately activated ring with ortho/para direction.
Friedel-Crafts alkylation: allyl bromide (3-bromo-1-propene) and $\ce{AlBr3}$ adds propene to the para position.
Ozonolysis with DMS to give p-(acetaldehyde)methoxybenzene.
Reductive amination with dimethylamine and triacetoxyborohydride.
Radical bromination should be selective for the benzylic position.
Finally, Grignard reaction with cyclohexanone.


texts: Implications of orthonormal wavefunctions

texts:
For orthonormal functions $\psi$ and $\phi$, by definition;
$$\langle \psi|\phi\rangle=0$$
However, when a wavefunction, $f$, is expressed as a linear combination of these orthonormal wavefunctions:
$$f=c_1\psi+c_2\phi$$ operating on this function with an arbitrary operator, $\hat A$ results in:
$$\langle f|\hat A|f\rangle=\langle c_1\psi+c_2\phi|c_1\hat A\psi+c_2\hat A\phi\rangle=c_1^2\langle\psi|\hat A|\psi\rangle+c_1c_2\langle\psi|\hat A|\phi\rangle+c_2c_1\langle\phi|\hat A|\psi\rangle+c_2^2\langle\phi|\hat A|\phi\rangle$$

My question is, do the crossed terms equal zero? (i.e does $\langle\psi|\hat A|\phi\rangle$ and $\langle\phi|\hat A|\psi\rangle$ equal zero?)

I initially thought that, yes, they do equal zero because, suppose that $\psi$ and $\phi$ are eigenfunctions of the operator $\hat A$ then it follows that: $$\langle\phi|\hat A|\psi\rangle=\langle\phi|a|\psi\rangle=a\langle\phi|\psi\rangle=a(0)=0$$
However, in a problem sheet I have just done, the question relies on these terms not being zero. Is my logic wrong or does this only equal zero in the case where the functions are eigenfunctions of the operator?


texts: How does the bite angle of a ligand affect the efficiency of its catalyst?

texts: I know that optimising the bite angle of a diphosphine ligand to its metal increases catalytic efficiency, and for cross-coupling reactions larger bite angles are favoured, but how does this have an impact on the effectiveness of a catalyst?


texts: Is there any book or text where ionic radius of elements are given?

texts: So my research has me looking for ionic radius characterization. If anyone could post any link or give the name of any book where ionic radius of all elements are given that would be really great?


texts: Is (1R,3aR,4S,6aS)‐1,4‐dibromo‐octahydropentalene chiral or achiral?

texts:
Is this molecule on the left chiral or achiral?

I believe it is achiral because its mirror image (on the right) is essentially the same molecule. But I was told that it is chiral because it doesn't have an internal plane of symmetry. Could someone tell me which explanation is correct?


texts: Alkoxide as a leaving group in hydrolysis of ester

texts:
In the base catalysed hydrolysis the hydroxide ion adds to the ester to form a tetrahedral intermediate, after which the alkoxide ions leave and forms carboxylate ion and alcohol.
Also we find the rate of reaction to be quite high.
So my questions are:

Most importantly, alkoxide is a very strong base. So why is it acting as a leaving group here (apparently, a very good leaving group due to the high rate of reaction)?
Why is the tertrahedral intermediate not as stable as the corresponding ones of carbonyl compounds?
Why is this reaction essentially irreversible, considering the fact that alkoxide is a stronger base the hydroxide ion? (Therefore it should be able to displace the hydroxide in the hypothetical backward reaction.)


texts:
I was wondering why cannot boiling chips be reused.

As far as I know, they are microporous materials, often coated with PTFE.

They work by, I suppose, giving the heated substance a small cavity, in which a phase transition is favored.

Yet, the golden rule of boiling chips is: they cannot be reused.

I was wondering why they cannot be treated the way dessiccant materials (for instance, molecular sieves) are used, for instance by washing them after use and driying them in oven (especially when non-dangerous materials are involved).


texts:
It is well known that metals are typically, well, metallic and usually favor the most dense packing, like hcp or fcc cells. This may be easily rationalized as dense packing of metal ions in a sea of electrons, since metals typically have low electronegativity. The exceptions, however, do exist.

However, the simplest metals, where one would except the metallicity to define everything, have bcc cell, and not the densest packing. I'm speaking about alkali metals. Interestingly, alkali earths favor dense packings (hcp for Be, Mg and fcc for $\ce{Ca},\ce{Sr}$) except for $\ce{Ba}$ and $\ce{Ra}$ (again, favor bcc). So, the question is: why alkali metals have bcc cell and what guards relative stability of bcc/hcp/fcc cell stability in $\ce{Li/Ba}$ square? Bonus points for the fitting description for the p-block metals. I'm pretty sure there is no simple answer for d-block, as valent interactions involving d-electrons become the deciding factor there.


texts: Vibrational Spectrums of HI, HBr, HF, and HCl

texts:
Do you all know of any large graphs for the vibrational spectrums of HI, HBr, HF, and HCl? I need graphs that are large enough to see the spacing between the peaks in the spectra of HCl, HBr, and HI.

Alternately, if you know of any raw data sets for any of the above, that would work. Thanks in advance.


texts: Is it possible to hold and rotate molecules to relativistic speeds around axis in observable way?

texts: Also, is it possible to see frame-shortening effects on electrostatic forces/van der waals at the edges, or are molecules too weak or necessarily neutral to be manipulated this way?


texts: Melting ice with salt - how does it start?

texts: I know that salt reduces the melting point of ice. I can see how a little bit of salty water can melt ice to water which can dissolve even more salt. But how does it even start? There is ice, which is hard. There are grains of salt, which are hard. So how does the salt enter the ice, to begin with?


texts: The walls of a plastic vial with Mercury inside are darkening. What is causing this?

texts:
I have a sample of Mercury in a plastic vial,
The vial is a BD Vacutainer (genuine), made of polyethylene terephthalate. It is used for blood samples, and the one I used was new.

When the vial was new, it was almost as transparent as glass, as seen in the image:

vacutainer http://mm.claflinequip.com/catalog/product/cache/2/image/750x750/9df78eab33525d08d6e5fb8d27136e95/i/2/i20885.jpg

However, after about a month, here is what the vial looks like:

As you can see, the vial has darkened.

The vial was sealed with a small initial layer of hot glue about 1 centimeter from the top, then the last centimeter was filled to the brim with epoxy, to ensure it won't leak.

I have been handling the vial quite a lot, but it has been stored in the padded box as seen in the image.

What is causing the plastic to darken? Once again the vial is made out of polyethylene terephthalate if that could be useful.

Thanks!


texts: Why is the activation energy for 1,2-addition less than that for 1,4-addition to conjugated dienes?

texts: 1,2-addition proceeds faster than 1,4 addition making excess of 1,2-adduct at low temperatures. Also, since conversion of 1,2-adduct to 1,4-adduct is faster than the reverse, 1,4-adduct is in excess at high temperatures. Both facts account for the same thing, that activation energy for 1,2-addition less than that for 1,4-addition to conjugated dienes. But why?


texts: What type of bonding is there among d-block metals?

texts:
Metallic bond strength in $\mathrm{d}$-block elements increases up to the middle and then decreases. Why does pairing decrease the strength of metallic bond? What does pairing have to do with metallic bonding?

Some books [1, p. 1129] say there is covalent bonding, which is related to unpaired electrons, and that is why their inter-atomic interaction strength increases up to the middle:

  Hardness of these metals indicates the presence of covalent bonds. The unpaired $d$-electrons may overlap to form covalent bonds. The number of such covalent bonds would be regarded as a measure of overall bond strength and hardness of the metal. In a transition series tire number of unpaired $d$-electrons increases on moving from group IIIB $[(n-1)d^1,ns^2]$ to VIB $[(n-1)d^5,ns^1]$ after which pairing begins.
  ...
  The high melting and boiling points of transition elements show that they arc held by strong forces. This is due to the presence of (a) strong metallic bonding because of the overlapping of $(d-1)d$ orbitals, and (b) covalent bonding by the unpaired $d$-orbital electrons. As Zn, Cd and Hg are having completely filled $(d—1)d$-orbitals, their atoms arc not expected to form covalent bonding amongst themselves; hence they arc having relatively low m.p. than the other $d$-block elements.

Are unpaired electrons taking part in covalent bonding or metallic bonding? Why can't paired electrons take part in metallic bonding?

Gurdeep, R. Advanced Inorganic Chemistry, 3rd ed.; Krishna Prakashan Media, 2008; Vol. 1. ISBN 978-81-87224-03-7.


texts: Change in H+ ion concentration of water on boiling

texts:
I know that on boiling water, pH scale decreases but water remains neutral. At 100°C the pH=6.14 is neutral.  And at this temperature also, the H+ ion concentration and OH- ion concentration are equal.
My question is what happens to the  H+ ion concentration on boiling  relative to the concentration at 25°C? Does it increase or decrease or remain same?


texts:
Why is the solid product washed with ice-cold solvent during in the last stages of recrystallisation? Is this to remove soluble impurities? (for example) Well, what if the impurities were also insoluble in the cold solvent?

Recrystallisation is weird in the sense that we have to make some assumptions in order for the process to fulfill the 'ideal' purification of the solid product that we're trying to get to.

For example, we have to assume that all soluble impurities are washed off during suction filtration, and that no impurities manage to creep up within the molecules of the crystals when they form. Would I be correct in saying this?


texts: Single crystal x-ray diffraction experiment backwards: from CIF to genuine set of raw data without performing actual experiment

texts:
Single crystal x-ray diffraction stands among the most complex yet trustworthy analytical techniques when it comes to structure determination of solids. But how hard it would be to simulate(fake) the entire raw dataset, including all reflections, possible artifacts, experiment strategy etc. in order to fit a certain given structure? Is it even theoretically possible? Wouldn't it happen at some day that with all the computational power and trained neural networks XRD suddenly looses its good reputation?

Here
is a brief report from the editorial section of Acta Cryst. E which overviews fraudulent content, which is still relatively easily detectable with the help of tools like CheckCIF even without looking at raw data. But can one commit a "perfect crime" by faking raw data entirely?


texts: SN1 reactivity order for chloromethyl methyl ether and trityl chloride

texts:
Compare the reactivity order towards SN1 reaction for:

  (2-chloropropan-2-yl)cyclopropane
  $\ce{CH3OCH2Cl}$
  $\ce{Ph3CCl}$

Owing to the exceptional stability of cyclopropyl ethyl carbocation (see), obviously it should be on the top.

We did this question in class and my teacher told me that option 2 is more reactive than option 3, because the carbocation formed in the case of 2 is more stable. However, I couldn't quite understand the reason for it.

Anyway, I searched more for this and found the following table in March's 7th edition, page 425:

According to this table $\ce{Ar3CX > CH3OCH2X}$ in terms of reactivity towards SN1.

Today, I went to my teacher with this data and asked him about it. He told me that things in March can be wrong sometimes, I should rather check some other sources and prove it to him.

So I'd like to know what is the actual order, is 2 more reactive than 3, or vice-versa? (please mention your source) And why?

I have also checked Peter Skyes' and Morrison Boyd's, Clayden's book but it's not given there.

This issue has been discussed  previously on the site but no concrete conclusion has been reached.

Jan's answer suggests that $\ce{CH3OCH2Cl}$ should be more reactive than trityl chloride.


texts: Plot Binary Eutectic from Temperature of Melting and Enthalpy

texts:
I'm a little confused about plotting a binary eutectic diagram (temperature vs mole fraction), and finding the eutectic point.  I understand the eutectic point is the lowest temperature that a mixture of the two substances will melt, and that this is somehow related to minimizing the Gibbs free energy of the system. However, I can't figure out how to actually solve for the eutectic point or how to graph it based on the melting temperature and enthalpy of fusion of two compounds.

I found a formula $$\frac{X_A}{X_B} = \frac{T_B-T_0}{T_A-T_0}$$ where X is the mole fraction of each component, but I was getting unrealistic answers for certain mole fractions, e.g. for $$X_A=.9$$ I was getting a value greater than the melting point of A.  And for $$X_A=X_B$$ this equation can't be solved.  Also, this formula doesn't take into account the enthalpy of fusion, so doesn't seem to relate to the free energy.

The volume & entropy of the system is unknown, so I wasn't sure how to set up an equation to solve for the Gibbs free energy of either component, but I was thinking that if I had an equation, I would be able to  solve a system of equations for the lowest free energy and plot it (somehow?).

Can anyone explain the relationship between the making a eutectic diagram and the free energy of components in the system?

Edit: Thank you for the answer! That was really helpful conceptually in relating the free energy of a mixture to that of the pure substances, but I actually have a problem from the class that says:

  Calculate and graph the binary eutectic melting diagram for the system diopside - anorthite using the data given below, and assuming for both diopside and anorthite that the activity in the liquid is equal to the mole fraction.

  \begin{array}{lll}
\text{Diopside}\, (\ce{CaMgSi2O6}): & \Delta H_\mathrm{fusion} = \pu{20,000 cal/mol} & T_\mathrm{fusion} = \pu{1390^\circ C} \\
\text{Anorthite}\, (\ce{CaAl2Si2O6}): & \Delta H_\mathrm{fusion} = \pu{29,000 cal/mol} & T_\mathrm{fusion} = \pu{1553^\circ C}
\end{array}

So it must be possible to find based on these parameters right?  Is the fact that the activity is equal to the mole fraction make the difference in solving it?


texts:
Need some help with second part.....can't get it to be balanced and therefore  can't find the formula and name! Thanks in advance!

What is the empirical formula of each of the following compounds?

a) A liquid containing 2.0g of hydrogen, 32.1g of sulfur and 64.0g of oxygen.

•   Hydrogen = 2.0g / 1.0g = 2 / 1 = 2
•   Sulfur = 32.1g / 32.1g = 1 / 1 = 1
•   Oxygen = 64.0g / 16.0g = 4 / 1 = 4

Empirical formula of this compound is: $\ce{SH_2O_4}$ and the name of the compound is Sulfuric Acid.

b) A white solid containing 4.0g of calcium, 3.2g of oxygen and 0.2g of hydrogen.

****•   Calcium = 4.0g / 40.1g = 0.09975062344 =
•   Oxygen = 3.2g / 16g = 0.2 =
•   Hydrogen = 0.2g / 1g = 0.2 =****

Empirical formula of this compound is:

c) A white solid containing 0.243g of magnesium and 0.710g of chlorine

•   Magnesium = 0.243g / 24.3g = 0.01 / 0.01 = 1
•   Chlorine = 0.710g / 35.5g = 0.02 / 0.01 = 2

Empirical formula of this compound is: $\ce{MgCl_2}$ and the name of the compound is Magnesium Chloride.


texts: In which direction does imidazole affect the pH?

texts: I'm reading something about nickel affinity chromatography and it talks about using imidazole to affect pH. In which direction does it change the pH?


texts: Where do the lone pairs go in the "true" resonance structure?

texts:
Consider the "true" resonance structure of $\ce{CO3^2-}$:

The bottom diagram leaves out the 2 lone pairs, so 4 electrons disappeared in the bottom image as compared to the top one. Are these disappeared lone pairs partial electrons, or shared? To make the bonds in $\ce{CO3^2-}$ correct, doesn't that mean each dotted line is worth double, so each bond is $1.33$ instead of $1.66$? Why don't we draw a $1.33$ electron lone pair if that's the case?

Image source: Resonance, by  Sharon Wei (UCD) and Liza Chu (UCD), Chemistry LibreTexts.


texts: Electrolysis of PbCl2 and use of Nernst Equation

texts:
The answer is -0.09V.
And the explanation is that the concentration of  $\ce{Pb^2+}$
will decrease.

My question is how will  [$\ce{Pb^2+}$] decrease?
In my opinion, [$\ce{Pb^2+}$] should remain constant. The cell is a voltaic cell meaning that $\ce{Pb}$ should oxidize to  $\ce{Pb^2+}$ to keep the cell running (since  $\ce{\frac{Pb^2+}{Pb}}$ = -0.13V). As a result, the concentration of $\ce{Pb^2+}$ will increase. But since the solution is saturated, no more lead can dissolve keeping the value of [$\ce{Pb^2+}$] constant.
Can somebody please point out the error in my explanation?


texts: I'd like to ask whether EC of a salt solution of iodized table salt differs from that of uniodized and to what extent?


texts: Wavelength-dependence of refractive index in internal reflection spectroscopy?

texts:
In many literature sources (web example), only a single value for the refractive index is assumed for the infrared element, and another is typically assumed for the sample substance. However, should not the refractive index be wavelength-dependent? So the wavelength-dependence of the penetration depth,

\begin{equation}
d_p = \frac{\lambda}{2\pi n_1 \sqrt{\sin^2\theta - (n_2/n_1)^2}}
\end{equation}

would not only be in the numerator, but also in the denominator: $n_1 = n_1(\lambda)$ and $n_2 = n_2(\lambda)$? Here $d_p$ is the penetration depth, $\lambda$ is wavelength, $\theta$ is the incident angle, and $n_1$ and $n_2$ are the refractive indices of the infrared element and sample, respectively.


texts: Relation Between Degree of Hydration and Electropositivity

texts: Why are salts of strongly electropositive elements less heavily hydrated in aqueous solution than the those of less electropositive elements? Shouldn't it be the other way round as the salts of electropositive elements are mostly ionic and hence strongly attracted by water molecules?


texts:
I want to apply tire rubber on surfaces, for various reasons - including protection against water. I think of tire rubber, as it is so widely available - helping in reducing pollution (infinitesimally) at the same time.

I am interested in a solvent which will temporarily transform the tire rubber into a (viscous) liquid - in such way that after some time, when the solvent evaporates, the tire rubber becomes solid again.

I do not need any special properties of the new rubber, there will be nothing really safety critical. If it is similar enough to the original, it is good.

Ideally, the solvent should be easy to find and I should be able to buy it without any special permits.

Think of this:

there are some granules of salt;
I add some water - and get salty water;
after some time the water evaporates and I get 1 block of salt.

Now, the salt is actually pieces of tire rubber, and the water is... what? :)

I searched on the net, and the only solvent I recognized was acetone. Does anyone have any experience with this?


texts: Developing Computational Chemistry Software

texts:
I want to learn to develop novel methods in computational chemistry (e.g. Grimme's empirical dispersion, DFTB, new DFT functionals, etc.) What is the ideal way to learn this by oneself?

I have read books on the Hartree-Fock theory and I understand it to some degree. However, there seems to always be a large amount of details which are left unsaid and brushed under the carpet. I am looking for quite practical ressources which would teach me how to actually translate the theory into code. Is there a way to learn this other than just reading books until it sinks in?


texts: Mechanism for Synthesis of Tetranitromethane from Acetic Anhydride and Fuming Nitric Acid

texts:
In my undergraduate Mechanisms-class the formation of tetranitromethane from acetic Anhydride with fuming $\ce{HNO3}$ was listed as optional knowledge in a chapter about the reactions of enols, enamines, etc. I can't find it in my notes or in the recommended literature, neither can I find information on molbase, and the two papers I can find, the original 1910 synthesis and This, are not mentioning any reaction mechanism.

I guess it somehow decomposes at the stage when the acetic anhydride is tri-substituted on one side, and somewhere there is a trinitromethane-anion involved which forms the product with $\ce{NO2+}$?


texts: Graphite, silica and diamond are covalent compounds and still they have high melting and boiling points. Why?


texts: How can a waterproofing material be "water-based"?

texts: I've been trying to determine how a particular waterproofing material, which claims to be "water based", can still be hydrophobic. First of all, the product in question is EPRO ECOLINE-R, which also claims to be an asphalt emulsion. My first guess is that the curing process causes a change in some way to become hydrophobic once applied. But I just can't wrap my head around how a product, which is designed to resist water absorption, can also be water based? I can find no information on the exact chemical makeup, other than "petroleum hydrocarbons".


texts: How does the "kreosan" Coca-Cola rocket work?

texts:
A YouTube channel called "kreosan" (made by Russian-speaking people who I believe live in Ukraine) posted a video showing rockets made from bottles of Coca-Cola.

Here's what I've figured out from the video.

First step: pour out some Coca-Cola to make room in the bottle to add gas.
Second step: add butane (looks like a canister for refueling butane lighters)
Third step: this is unclear.  He adds a gas from a large container that appears to say "GAS-1".  The YouTube description says "Coca Cola + propane = turbo ROCKET" so I guess it's propane.

Unknown: Does the rocket require both butane and propane?  I think the second
   step was just to show that you don't get very much gas out of a
   little butane canister, and all you really need is the propane from
   the last step.

Final step: invert the bottle, and some reaction pushes Coca-Cola out the mouth of the bottle with enough force that the whole bottle flies quickly as a rocket.

What is going on here?  How does inverting the bottle trigger the reaction?  Is this like the "Mentos and Diet Coke" thing where the trick was to get the carbon dioxide dissolved in the drink to come out quickly?

My understanding is that the surface of Mentos candy provides a bunch of nucleation sites for bubbles, causing a lot of carbon dioxide to come out of solution quickly.

So, does the "kreosan" rocket fly on just carbon dioxide or is there some other reaction going on here?


texts:
Could someone, please, explain to me how the standard
Hydrogen Electrode works and how it is used to measure electrode potentials? Also, why does it have a potential value of zero?


texts: Reduction of conjugated double bond by sodium borohydride

texts:
Some of my teachers were debating about whether a double bond in conjugation with a ketone is reduced or not by $\ce{NaBH4}.$ One of my teachers presented the evidence from Clayden which had an example where a cyclic ketone was reduced alongside the conjugated double bond.

However, there was no example for a straight chain compound. Also, the book said that steric hindrance may affect the reduction process and only favour the reduction of ketone.

I want to know that is there any authentic source which has an example of reduction of a conjugated double bond and ketone via $\ce{NaBH4}.$


texts: Explain on the basis of valence bond theory that tetracyanonickelate(II) ion with square planar structure is diamagnetic

texts: Answers on the internet suggest that tetracyanonickelate ($\ce{([Ni(CN)4]^{2-}}$) with square planar structure is diamagnetic because $\ce{CN-}$ is a strong field ligand and causes pairing, but my book says that VBT does not distinguish between strong and weak field ligands. So can anyone explain the logic using VBT?


texts: Are there acid/base processes in aqueous solution that are so slow that they are kinetically controlled?

texts:
This question came up in figuring out what the fundamental differences are between redox chemistry and acid/base chemistry (if any).

In redox chemistry, strong oxidants and strong reductants can co-exist in solution because they react slowly with each other (or not at all). An example from biology is a low NADH/NAD+ ratio in the same compartment as a high NADPH/NADP+ ratio.

Are there substances that act as acid or base that are far from equilibrium in aqueous solution for a long (minute, hours) time period? Or are all acid/base reactions in aqueous solution fast and reach equilibrium within seconds?


texts:
How is the disparity between the heat of fusion and the heat of vaporization for $\ce{H2O}$ best explained?

A) It takes more hydrogen bonds for water to fuse than it does to vaporize.

B) Water molecules are moving farther apart during fusion than during vaporization.

C) Water molecules are moving closer together during fusion and farther apart during vaporization.

D) Vaporization occurs at a higher kinetic energy than fusion.

E) More hydrogen bonds are broken during vaporization.

At first, I tried this problem via Process of Elimination. I looked at (B) and immediately knew that that fact was false, because water molecules move closer together during fusion, and farther during vaporization. Next, I saw (C), and though it was true, it had no involvement with the problem. (How far the water molecules move does not have anything with the disparity between heat of fusion and heat of vaporization). Then, I saw (D), and though it was also true (vaporization occurs at a higher temperature than fusion, and kinetic energy is directly proportional to temperature), I felt that it did not relate to the problem. So I have ruled out 3 of the 5 answers by now. It was the options (A) and (E) that stumped me. I did not know the relationship between the temperature and Hydrogen bonds in water, and conducted some research on the internet.

I found a useful link http://www1.lsbu.ac.uk/water/water_hydrogen_bonding.html , and saw that answer choice (A) is in fact true, if you look at the graph towards the end of the page. It has more hydrogen bonds in the solid state than in the vapor/gas state. So, I thought the answer was (A). However, I looked in the answer key provided with this question, and the answer was (E): more hydrogen bonds are broken during vaporization. I don't really see how this is, and would like assistance and answers why. Also, I would greatly appreciate an explanation for why the number of bonds increases when temperature is low, and decreases when temperature is higher. Even an explanation on how hydrogen bond numbers (approximately) change as phase changes would be great.


texts: Greatest Energy Output Reaction to Atmosphere Air

texts:
First of all i'm no chemist, this is not homework and if you need further clarification please ask. I'll be happy to provide!

Imagine that you:

have 1 kg of any given chemical X
A car battery
A semi-controlled combustion chamber (chamber temp is initially 20ºC, pressure is 1atm, the chamber is either vacuum or filled with atmosphere "air"...)
As much atmosphere "air" as you want, initially at 20ºC...
A not so potent air-pressurizer... you might be able to get 3atm out of it...

The goal here is to get the most energy out of reaction as possible. So the question is: What chemical is X?

Further details:

X doesn't have to be consumed all at once as in a explosion reaction... Damage/Destruction is not the goal
If you can combine X with something in the air, and then use it to fuel the reaction, increasing the energy output, great!


texts: Pressure-dependence of electrolysis voltage

texts:
I'm trying to better understand electro-chemistry, so please explain why this second-kind perpetual motion device won't work. I guess it's safe to assume it won't work one way or another.

There is a cycle, which starts with low-pressure water.

The water is pressurized by a compressor. This requires work, but since water is nearly incompressible, the required work is very low: the distance over which the pressurization force is applied is almost zero.
Next, the high-pressure water is split into high-pressure hydrogen and oxygen gas. This requires a certain amount of electrical work.
Next, the high-pressure hydrogen and oxygen gas are expanded through turbines, expanding cylinders or other devices that allow the expansion to apply output work. Heat is added to keep the temperature constant during expansion, to maximize the work output. Note that, unlike the compression stage, expansion deals with gases, which are very compressible; therefore, the amount of work produced is substantial.
To close the cycle, the hydrogen and oxygen gases are recombined in a fuel cell, to end up with the same amount of water, at the same pressure as when we started the cycle. This delivers some electrical work.

Of course there are going to be energy losses; I expect the fuel cell will always yield less energy than is required in the electrolyzer. However, the difference between the compression work and the expansion work can be scaled up arbitrarily by using a higher pressure difference, so at some point this difference in work must yield more energy than is lost in the electrolysis/fuel cell combination. This energy comes from the heat flowing into the expander, but simply turning heat into excess work should not be possible.

So, what is wrong? The only way I see to prevent this to work is if the electrolyzer requires more work per reaction mass (essentially its voltage) than the fuel cell, even if they are both 100% efficient. This would imply that the reaction voltage is pressure-dependent, with a higher voltage at higher pressures. Is this the case? And is this only the case if the output material is more compressible (gas) than the input material (liquid)?

(The same should be true for evaporation/condensation enthalpies, as we could have designed a very similar cycle with evaporation/condensation instead of electrolysis/fuel cell.)


texts: Which metals hydroxides dissolve in excess NH4OH?

texts:
Some metal hydroxides like $\ce{Ag(OH)}$ and $\ce{Cu(OH)2}$ dissolve in excess $\ce{NH4OH}$ to form metal ammonia complexes.

I want to know which other common metal hydroxides dissolve in excess $\ce{NH4OH}$. Also, can it be somehow predicted ? I couldn't find much relevant information on the Internet.


texts: What are the steps to creating synthetic glucose?

texts: I need to know how to go about creating synthetic glucose with generally available materials. As I am aware of both photosynthesis and glucose in nature, I will not need lessons in how plants produce it. So, how may glucose be produced by artificial means?


texts: Solubility when multiple salts are involved

texts:
Calculate the solubility of $\ce{AgCl}$ ($K_{\mathrm{sp}} = 1.6\times10^{-10}$) in $100.0~\mathrm{mL}$ of $4.00\times10^{-3}~\mathrm{M}$ calcium chloride.

The stated answer is: $2.0\times10^{-8}~\mathrm{M}$

My way of solving was:
$$\begin{align}
\frac{1.6\times10^{-10}}{4.00\times10^{-3}} &= 4.00\times10^{-14}\\\\
\sqrt{4.00\times10^{-14}} &= 2.0\times10^{-7}
\end{align}$$

Is this correct?


texts: What are the advantages of eutectic solvents over aqueous solutions for electroplating?

texts:
I'm trying to electrically strip lead contamination from aluminum.

This answer suggests using a deep eutectic solvent (DES) as the conducting liquid for plating the lead onto a copper cathode.  But now that I'm thinking about it I can't see why.  Is a DES more conductive?  More inert with respect to (these) metals?

What advantage does a DES have over conductive aqueous solutions for electroplating?


texts: What did actually happen when Staudinger tried to synthesise diamond?

texts:
It is a famous reaction that used to be a teaching lab experiment, but is now banned in Germany, because it is too dangerous. To quote-translate quite liberally from the German www.seilnacht.com:

  In a stone quarry near Zurich, Hermann Staudinger attempted to artificially produce a diamond by reacting the potassium-sodium melt with tetrachlorocarbon in a bomb tube. The attempt failed as the mixture tore the bomb tube apart.
  In einem Steinbruch bei Zürich versuchte Hermann Staudinger einen Diamanten künstlich herzustellen, indem er die Kalium-Natrium-Schmelze mit Tetrachlorkohlenstoff in einem Bombenrohr reagieren ließ. Der Versuch misslang, da die Mischung das Bombenrohr zerfetzte.

I was probably one of the last students who were still able to see this experiment, and while considerably down scaling the actual set-up, it was still one of the most powerful explosions I ever witnessed.

To me it was actually surprising that I found pages, while researching this reaction, that asked whether $\ce{CCl4}$ can act as a solvent in the Wurtz Reaction, or that in the Wurtz reaction of carbon tetrachloride and sodium no product would be formed, because $\ce{CCl4}$ is too stable to react.

However, due to this I found the following passage in Inorganic Chemistry:

  Tetrahaloalmethanes can be reduced by strong reducing agents, such as alkali metals. For example, the reaction of carbon tetrachloride with sodium is highly exoergic:
  \begin{align}
\ce{CCl4 (l) + 4 Na (s) &-> 4 NaCl (s) + C (s)}&
\Delta_\mathrm{r}G^\circ &=\pu{-249 kJ mol^-1}
\end{align}
  This reaction can occur with explosive violence with $\ce{CCl4}$ and other polyhalocarbons, so alkali metals such as sodium should never be used to dry them.

Unfortunately I reached a dead end with finding more literature about the reaction. I am especially interested in the mechanism, and the final products. I would assume that the above equation only represents a theoretical model, and the products will likely be carbon dioxide and other combustion related products. I'd be interested to know if there are any practical and/ or theoretical studies to the kinetics and thermodynamics of the reaction.

If the source does not cover tetra-, but tri-, or bihalogenated methane, I assume it is fine, too, but it should go beyond the Wurtz reaction ($\ce{2 R-Cl + 2 Na -> R-R + 2 NaCl}$).


texts: Can an atom have more than 8 valence electrons? If not, why is 8 the limit?

texts:
According to some chemistry textbooks, the maximum number of valence electrons for an atom is 8, but the reason for this is not explained.

So, can an atom have more than 8 valence electrons?

If this is not possible, why can't an atom have more than 8 valence electrons?


texts: Glycerin yield upon saponification of beeswax

texts:
I am making a custom grease (castor oil & sodium stearate) that will be suspended in beeswax. I have found that saponifying some beeswax for use in the grease results in higher operating temperatures after the grease is melted with the wax. I cannot have any glycerin in the final product, so I do not yet know how to properly make my own soap [at home].
The first reason I cannot have any glycerin, is because this will be used as a bullet lubricant for cast lead bullet, and I am concerned that the glycerin may form acrolein in the final application. The second reason is because the hygroscopic properties of glycerin are also bad. For more information, look up Felix World Famous Lube.
As far as I can tell, there are no glycerides in beeswax but I cannot find data on this topic. If there are no glycerides in bees wax, then I do not believe it is possible to yield glycerin in the saponification process of only beeswax.
I am considering a trans-esterifcation process, just to remove any possible glycerin, but I may need butanol (due to the high saponification temperature of beeswax) which is expensive to the point that I would rather do something entirely different. I may be able to use ethanol if I slowly titrate the ethoxide into the molten beeswax. I also have many open questions here, since bees wax is more than just fatty acids.
So, does beeswax contain any glycerides?


texts: How is NaBH4 able to reduce tertiary alkyl halides to alkane but LiAlH4 create an alkene?

texts: When attacking tertiary alkyl halides, aren't both of them just supposed to follow $\mathrm{S_N2}$ and substitute the leaving group with Hydride ion? Apparently only $\ce{NaBH4}$ does it and $\ce{LiAlH4}$ causes an $\mathrm{E1}$ elimination resulting in an alkene. Why does that happen? $\ce{LiAlH4}$ does secondary and primary alkyl halides to alkanes, so why not tertiary as well?


texts: What will the results be if I electrolyzed brine with these materials?

texts:
I have tried electrolyzing saltwater (brine) with copper electrodes, but I got a rusty sludge and hydrogen being produced at the anode. I read about it and it is just dissolved copper, possibly oxidized. What will the results be, if I used the following materials?

Aluminium foil
Iron
Pencil graphite


texts: How pigments actually function as colorants?

texts: Pigments are insoluble colorants that have no affinity to the substrate. So how can they function as colorants if they "can't stick"? Are pigments always applied together with a "binder"?


texts: How to compute the residence time for given flow rate in standard cubic meters?

texts:
I'm given a flow rate of a gas mixture of $3\ \mathrm{Nm^3/h}$ in standard cubic meters through a cylinder of length $50\ \mathrm{cm}$ and cross section $70\ \mathrm{cm^2}$, can I compute how long a particle will stay inside of the cylinder (which would equal the time the particle can react inside the cylinder)?

And what if the temperature changes during the reaction?

If the flow rate would be given in volume per time, I had an idea to compute this, but the use of standard cubic meters is baffling to me.


texts: Is there a reaction between ethanol and aluminum?

texts: Is there a potential reaction that would occur between ethanol and aluminum? If so, would it potentially create anything toxic?


texts:
I have this task to do:

My solution:

Is that possible? Can you please help me with the steps 2 and 3?

This is what I did, but my teacher told me I should make the diketone (compound no. 5) from the starting compound (allyl bromide) by Grignard reaction:


texts: Do catalysts increase rate of reaction only by decreasing activation energy? Or can they affect the Arrhenius factor or reaction orders? Like if one catalyst is more effective at increasing rate of reaction than another, does it mean that it's simply decreasing the activation energy more dramatically? Or are there other mechanisms at play?


texts: How do we know orbitals of atoms and elements exist?

texts: How would we know if we have never experimentally seen them?


texts: Is matter really divided in two categories?

texts:
Page 1 of almost every Textbook start with the ordinary divison of matter in 2 categories: Substances and Mixtures.
Substances, or Pure Substances sometimes, are defined

as a form of matter that has constant chemical composition and
characteristic properties.It cannot be separated into components
by physical separation method.

This  is according to Wikipedia, at least.
Mixtures always citing wikipedia, instead are

materials made up of two or more different substances which are mixed
but are not combined chemically....
Mixtures are one product of a mechanical blending or mixing chemical
substances such as elements and compounds, without chemical bonding or
other chemical change, so that each ingredient substance retains its
own chemical properties and makeup.

Is this separation so radical?
Is there something in between? What about alloys?


texts: Why is the electronic wavefunction of helium a product of the two 1s wavefunctions when ignoring electron-electron repulsion?

texts:
This question has also been asked on physics stack exchange:
Why is the helium atom wavefunction a product of the two 1s wavefunctions?

From [1, p. 116]:

In seeking an approximation to the ground state, we might first work out the solution in the absence of the $1/r_{12}$ term. In the Schrodinger equation thus simplified, we can separate the variables $r_{1}$ and $r_{2}$ to reduce the equation to two independent hydrogen like problems. The ground state wavefunction (not normalized) for this hypothetical helium atom would be:
$$\psi(r_1, r_2) = \psi_{1s}(r_1)\psi_{1s}(r_2) = e^{−Z(r_1 + r_2)}$$

Why is it only the product and not some linear combination of the two wavefunctions? I heard somewhere that it has something to do with "tensor product". Can someone provide a detailed explanation about this?
Reference:

Blinder, S. M. Introduction to Quantum Mechanics: in Chemistry, Materials Science, and Biology; Elsevier, 2012,. ISBN 978-0-08-048928-5.


texts: Why are S-thiocarbamates less toxic than carbamates?

texts:
According to Haley and Rhodes, neostigmine bromide (alternatively known as Prostigmine) has an LD50 in mice of around 0.165 mg/kg by IV injection. Pubchem claims that this is also the LD50 for neostigmine iodide. According to Pubchem, Ro-1837, the analog of neostigmine in which the ester oxygen is replaced with sulfur, having the chemical name (3-Mercaptophenyl) trimethylammonium iodide dimethylcarbamate, has an IV LD50 of 18 mg/kg.  Also according to page 209 of the book Chemical Warfare Agents and Related Chemical Problems, other S-thiocarbamates are likewise significantly less toxic than carbamates (ie. TL-1216 (subcutaneous LD50 of 0.17 mg/kg) vs TL-1239 (Subcutaneous LD50 somewhere over 80 mg/kg) ). Why is this so?
References:

Haley, T. J., & Rhodes, B. M. (1950). A note on the acute toxicity of neostigmine methyl bromide in the rat. Journal of the American Pharmaceutical Association (Scientific Ed.), 39(12), 701. doi:10.1002/jps.3030391218

https://apps.dtic.mil/dtic/tr/fulltext/u2/234270.pdf


texts: Entropy increase of both system and surroundings

texts: In "why chemical reactions happen" the author (James Keeler) says that "a process which leads to an increase in the entropy of the system can be ... exothermic." Could someone please give me an example of a process which is exothermic and increases the entropy of the system? It seems strange to me how a system can release energy in the form of heat while also increasing its own entropy.


texts: Difference between organic and inorganic chemistry

texts:
This question may seem vague at a first glance, and even lead to the thought: "come on, just go Google it!"

But it's a real question because it does not make enough sense to me (even after Googling it, a lot).

I was just presented to the words, but not to their definition.

Like: "Hey, now we will speak about organic nomenclature".

At some point, books and videos start talking about inorganic and organic as if it was a common sense thing.

A frequent rule I found while trying to understand the difference:

Organic: has carbon
Inorganic: does not have carbon

But then, some inorganic compounds do have carbon too, and there may even be some  compounds that some call organic, and others call inorganic, like $CO_2$.

As I have felt it, in my learnings so far, it's like inorganic chemistry is the default chemistry and organic chemistry goes a step beyond.

But I don't quite grasp the difference.

What is the real semantics behind the word "organic"?

For example, we humans are made of loads of water, and that's a pretty organic thing to me. But then, water is inorganic.

Diamonds are the carbon top of the cake, and do not transmit the idea of being an "organic" thing.

Another very confusing thing are polymers, chanins of loads of carbons with other elements, in many shapes and textures. To me, a piece of "plastic" is not a very organic thing, but indeed, they are!

That brings the semantics into an even more confusing level.

And of course, there must be historical reasons for those chosen words.

Could someone please point out where this distinction comes from and why it is important?

With all my respect to science and the people who made chemistry a useful thing. This question is not about critics, it's about not knowing the facts, so of course I am the ignorant here.

Related and useful: What is the definition of organic compounds?


texts: What causes differences in limits of detection?

texts:
I'm wondering what causes the limits of detection (LOD) to vary between different compounds, when calculated from the data obtained from one sample.

I've analyzed a 0,1 µg/ml sample, containing fluorene, fluoranthene and benzo[a]pyrene in toluene, using GC-MS. I calculated the LODs to be 0,04 µg/ml, 0,02 µg/ml and 0,03 µg/ml. What could be the reason for the differences between the values?


texts:
On the surface, this looks like a silly question, but I honestly can't find an answer for it.
Here's what I've found:

The dataset was introduced in Ramakrishnan R., Dral P. et al., “Quantum chemistry structures and properties of 134 kilo molecules”. Scientific Data 1 (2014). doi: 10.1038/sdata.2014.22. This paper doesn't contain the word QM9, and the dataset isn't given a name.
The aforementioned paper gives this link to download the dataset. Again, QM9 is nowhere to be found. No other name is given.
There's a readme file in the dataset folder, copied here. The first line does say Data set dsgdb9nsd, so that's my closest lead to the dataset name.
One of the authors of the paper (Pavlo Dral) has a post regarding this dataset. He says,

The data set is also called QM13 in the “Quantum Machine” website and augments previously used and smaller QM7 and QM7b data sets.

so he seemingly let someone else name it, but even then he got the number wrong (QM13 v. QM9).
On the other hand, people other than the dataset's authors name it QM9:

The quantum-machine.org page
This paper (none of the authors participated in Ramakrishnan's paper)
This master's thesis (sec 2.3.1)
This other paper (again, authors are unrelated)

It's not that I dislike the name QM9. I just want to know if there's a "proper name" for the dataset and also who chose the name QM9.


texts: Slater determinant as an unperturbed atomic wave function

texts:
I've deduced following postulates from studying my chem books.

  1) Slater determinants are eigenfunctions of an unperturbed atomic Hamiltonian, which contains kinetic and central potential energy parts of each electrons only, since spin orbitals constituting the determinants are originated from one-electron Hamiltonian eigenfunctions.

Here, atomic Hamiltonian = (kinetic part of each electrons) + (central potentials between atomic nucleus and electrons) + (interelectronic potentials)

Spin orbit interaction and the other effects are neglected.

  2) Slater determinants or their linear combinations are eigenfunctions of total spin angular momentum and total orbital angular momentum operator($S^2$ and $L^2$) simultaneously.

In addition to them, I would refer to information from Quantum Chemistry, 6th Ed., written by I. N. Levine.

(p. 312) Since $S^2$ and $L^2$ commute with the atomic Hamiltonian and with the exchange operator, the zeroth order functions should be eigenfunctions of $S^2$ and $L^2$.
(The zeroth order functions Levine mentioned above is indicating the single or linear combinations of Slater determinants in a same configuration)

Well, I can accept the fact that the atomic Hamiltonian, $S^2$ and $L^2$ commute.

However if the single or linear combinations of Slater determinants in a same configuration are the zeroth order functions (eigenfunctions of the unperturbed atomic Hamiltonian), how the fact that $S^2$ and $L^2$ commute with the atomic Hamiltonian makes the Slater determinants be the eigenfunctions of the atomic Hamiltonian??

For example, a Slater determinant corresponding to the one of the Helium-first excited states, $|1s\alpha~2s\beta|$, is an eigenfunction of the unperturbed atomic Hamiltonian(this determinant is a zeroth order function), $S^2$ and $L^2$, but not of the atomic Hamiltonian.


texts:
Ok my understanding of the electronic structure of atoms could be wrong but this is why I don't understand:Why alkali metals are so much electropositive.

Some high school professor in chemistry would say because if they lose an electron they have an electronic configuration of noble gas etc.

If alkali metals gained 1 electron then the wavefunction of the each electron in the s orbital would shield some of the charge of the nucleus for the other electron in the s orbital->the overall net charge on each electron would be decreased but because now we have 2 electrons instead of one potential energy would be decreased.

That is clearly not the case.Why?


texts: Why does adding PBS to a lipid+propylene glycol solution cause the lipid to precipitate?

texts:
I am trying to create an aqueous phospholipid suspension using ~50 mg of 1,2-dibehenoyl-sn-glycero-3-phosphocholine (DBPC), 13 mL of propylene glycol (PG), and 72 mL of phosphate-buffered saline (PBS). I am easily able to get the DBPC to dissolve in the PG when held at 85 degrees (10 above Tm), but as soon as I add any sizable amount of PBS, my solution turns cloudy with chunks of DBPC floating around, implying that the DBPC has precipitated out and aggregated.

Why would this be? I'm basing myself off of this patent, and they do mention that trying to dissolve the lipid directly in water causes aggregation, but why would adding PBS to my already dissolved lipid do this?

Structural photos below:

DBPC:

PG:


texts: Is it important to use arrows as bonds in writing coordination compounds?

texts: Why are the coordination compounds representated by arrows? Is it necessary to write every coordination compounds with the arrow side of the bond facing the metal ion and the other part the ligand?


texts:
Which of the following reaction will have greater enthalpy and why?
$\ce{C (g) + 4 H (g) -> CH4(g)}$ (reaction enthalpy = $x\ \mathrm{kJ/mol}$)
$\ce{C (graphite) + 2H2 (g) -> CH4 (g)}$ (reaction enthalpy = $y\ \mathrm{kJ/mol}$)

I thought that since $\ce{H2}$ is in its aggregation state it would have enthalpy of $0\ \mathrm{kJ/mol}$ and hence $y\gt x$.


texts: When Iron reacts with any other species, how will we know that the reaction will be of Fe(II) or Fe(III) i.e. of ferrous or ferric?

texts:
Like when iron reacts with water there forms iron oxide and hydrogen but how'll we come to know which of three equation will be right equation for reaction?
$$\ce{Fe + H2O → FeO + H2}$$
$$\ce{2Fe + 3H2O → Fe2O3 + 3H2}$$
$$\ce{3Fe + 4H2O → Fe3O4 + 4H2}$$


texts: experimentally determine oxidation state of Iron compound

texts:
I need to make several Iron compounds but I am having a bit of trouble finding a decent way to determine the oxidation state of Iron.
I'm starting with a Iron(II) compound that I try to oxidize using several methods. I can use raman to determine the compound but that requires me to create the compound I want to make and check that spectrum against my experimental sample. This is quite a bit of work and I was hoping someone could point me towards a better solution.
I can make an EDS but since my compounds usually contain carbon or oxygen as counter ion so EDS isn't very accurate. I don't (currently) have access to an XPS and I don't have unlimited access to a mass spectrometer (I have to travel quite a bit to get to one).

Can someone help me find a better way to determine the oxidation state??


texts: Which contributes more strongly to ionic conductivity, charge or mobility?

texts: Conductivity depends on the magnitude of charge as well as mobility. Which will be the dominating factor in the case of opposite trends in these two properties?


texts: How long would it take for a tank of same-spin hydrogen atoms to become a tank of H₂?

texts:
In the question
Is there an energy cost associated with flipping the spin of an electron?, it is shown that it is very unlikely for two hydrogen atoms to bond if their electrons have the same spin. The reason is the very low rate at which such a system would be able to emit photons. This makes me think that a bottle of $\ce{H1}$ could be prepared if the spin-up hydrogen was separated from the spin-down hydrogen with an apparatus like the one used in the Stern-Gerlach experiment. Is it true that the spin transition can be ignored for "all practical purposes"  (see linked question), or can tanks of spin-aligned $\ce{H1}$ only exist for times uninterestingly short for chemical purposes?


texts: Repeating unit of poly lactic acid (PLA)

texts:
Which repeating unit for poly lactic acid (PLA) is correct, picture 1 or picture 2?

 and

I read somewhere that in polymerization, acids give $\ce{OH}$ and alcohol gives $\ce{H}$, creating water. According to this explanation, picture number 2 is correct but I have seen on websites like Wikipedia that picture 1 is correct. So, which is the correct picture and why?


texts: This is a very simple question: Why are oxidized compounds generally thought to be less toxic/polluting than reduced species? This is used in waste water treatment where oxidizing agents (such as chlorine) are added to remove organic AND inorganic pollutants.


texts: Copper Tetrafluoroborate neutralisation/precipitation to reduce landfill

texts:
I have 25L drums of Copper Tetrafluoroborate waste solution.

Can it be neutralised, precipitated in some way, to minimise the amount of waste that goes to landfill?

also, landfills prefer solid waste instead of liquid, so is there any cost effective way to reduce Copper Tetrafluoroborate to a solid?


texts: Why is the manufacture of sulfuric acid known as the contact process?

texts: I was after some detail as to why the contact process was named as such.


texts: Finding the right order of carbocation stability

texts:
I should put these carbocations in decreasing order of stability.

Structure 1 is a primary carbocation.
Structure 2 is a secondary carbocation.
Structure 3 is a tertiary carbocation.
Structure 4 (a primary carbocation) and structure 5 (a primary carbocation) are less substituted, but one could form resonance structures.
Therefore I would say 5 > 4 > 3 > 2 > 1.
But I'm not sure why 5 should be more stable than 4. In both cases the positive charge is stabilized by the + I-effect through the sigma bond of the two methyl groups and both can be stabilized through the free electron pair of the heteroatoms.


texts: Rationalising diastereoselectivity of hydroboration using stereoelectronics

texts:
Using bulky reagents such as 9-BBN, hydroboration is often highly diastereoselective, giving rise to the 1,2-anti diastereomer:

This is easily explained using a steric argument, with the major product resulting from minimisation of allylic strain in the transition state. This is essentially the Houk model, though in the context of hydroboration is often described as the reactive-conformer model.
While a steric argument works in many cases, it isn't fool-proof – increasing the size of a group does not necessarily increase the selectivity as would broadly be expected by the above model.
To rationalise this, Houk has proposed a stereoelectronic component in the transition state – this is perfectly plausible as electronics evidently contribute to the conformational preference of the molecule. What Houk does not expand on is the exact nature of the stereoelectronic effects (this is not unusual, stereoelectronics are often invoked to rationalise unexpected experimental results without justification).

What is the nature of the stereoelectronic component when determining diastereoselectivity of hydroboration and in what situations should it be invoked?


texts: Computing pH of a buffer, and concentrations

texts:
You pour $50~\mathrm{mL}$ of a $0.0200~\mathrm{M}$ $\ce{HCOOH}$-solution to $150~\mathrm{mL}$ of a $0.0500~\mathrm{M}$ $\ce{HCOONa}$-solution. The $K_\mathrm{a}$ of $\ce{HCOOH}$ is $1.8 \times 10^{-4}$ and $\mathrm{p}K_\mathrm{a}$ is $3.74$.

a) Compute the concentrations of $\ce{HCOOH}$ and its salt after dilution to this $200~\mathrm{mL}$ buffer solution.

b) Calculate the $\mathrm{pH}$ of this buffer solution with the buffer formula.

Attempt at solution: Not sure how to do part a). For part b) I used the following method. We have $50 \times 10^{-3}~\mathrm{L}  \cdot \frac{0.0200~\mathrm{mol}}{1~\mathrm{L}} = 0.001~\mathrm{mol}$ of $\ce{HCOOH}$. Doing this again for $\ce{HCOONa}$ gives $0.0075~\mathrm{mol}$. Hence: \begin{align*} \mathrm{pH} = 3.74 + \log(\frac{0.0075}{0.001}) = 4.61 \end{align*}

But how can I solve a)? I'm having trouble with writing the reaction down. I'm not sure what's happening. Which chemical is neutralizing which? And what are the ions?


texts:
I want to know if N-methyl aniline $(\ce{PhNHCH3})$ can undergo diazotisation under suitable conditions and in the presence of $\ce{NaNO2}/\ce{HCl}.$

The mechanism involves loss of two $\ce{H+}$ during the formation of the diazo compound, but if we have one $\ce{CH3}$ and one $\ce{H}$ instead of two $\ce{H}$ (as we have for aniline), will the $\ce{CH3+}$ act as a good leaving group? Is diazotisation of $\ce{PhNHCH3}$ feasible?


texts: How to select the parent chain in mechlorethamine?

texts:
Here is the structure of mechlorethamine:

Although the longest carbon chain is ethyl, why does Wikipedia name the compound as bis(2-chloroethyl)methylamine (or N,N-di(2-chloroethyl)methanamine)?

It seems that that is the preferred name, rather than 2-chloro-N-(2-chloroethyl)-N-methylethanamine which does give a result on ChemSpider.

I understand that the longest carbon chain does not necessarily yield the parent chain, as with cyclic compounds (where the chain lies within the ring) and compounds with multiple bonds (where the longest chain with multiple bonds is preferred over a longer one with no multiple bonds). I am guessing that perhaps the rule of more substituents is used to determine the parent chain here, but the name on Wikipedia seems to have two substituents compared to 2-chloro-N-(2-chloroethyl)-N-methylethanamine which has three. What is happening here?


texts:
I've been asked to draw the mechanism by which benzene with $\ce{Me}$ on position 1 and $\ce{OMe}$ on position 2 goes to benzene with $\ce{Me}$ on 1 and $\ce{OH}$ on 2 by reaction with concentrated $\ce{HBr}$.

I'm really unsure as to what is going on, I think its probably most likely that $\ce{Br}$ acts as a nucleophile and attacks the $\ce{C-O}$ $\sigma^*$ and then $\ce{OH}$ attacks the $\ce{C-Br}$ $\sigma^*$ but it doesn't seem like a likely pathway as $\ce{OMe}$ has a higher pKaH than $\ce{Br}$ and substitutions don't occur at $\mathrm{sp^2}$ centres.


texts: Reduction of Benzamide in acidic conditions?

texts: I am going through a mannich type reaction and ended up with my product show in the image. I compared my answer to the answer key but I noticed that the benzamide was reduced completely. I was wondering at what process during the reaction the benazmide was reduced.


texts: Why is ethanol, water and amonium needed for DMG to react with nickel?

texts:
I had this question on a test and I'm unsure on why ethanol is required for the reaction.
I understand that you need the ammonia and water to make oxonium ions needed for the reaction to occur.
We had a hint about the solubility of ethanol in water (very high), ammonia (high) and DMG (low)


texts: How to finish silanization process correctly?

texts:
I have some 2mm glass beads and I'm doing silanization on them. For doing that, I have a small bottle that I fill 1/3 with glass beads and then pour silan solution on them and shake well. However, after 60 min that I drain the solution from bottle and as soon as I wash the beads with water, the beads are covered with a white greasy product which is hardly removed by water and finally I wash it by acetone to become transparent again.

Is this a correct method of silanization (and washing the products) to achieve the maximum hydrophobicity effect of silan or I should revise the method?


texts: Why do higher fluorine oxyanions not exist?

texts:
I asked this question from my teacher and he said that's because fluorine has a high electronegativity and does not form dative bond with oxygen. That's why only hypofluorite $\ce{FO-}$ exists and not $\ce{FO_n-}$ ($n = 2,3,4$).

But then I was wondering why $\ce{BF4-}$ exists. And according to this Wikipedia article, fluorine does form dative bond.

so why the anions in the title do not exist?

Thanks for your help!


texts: Second order reaction with different reactants

texts:
In a laser photolysis reaction $\ce{C6H5NH2}$ $(C_0 = \pu{60 µM})$ is oxidized to its radical cation. The disappearance of the cation can follow three pathways: (1) Dimerzing of the cation, (2) Reaction between the cation of the initial substance, (3) Reaction between the cation and the solvent. Decide which pathway is most likely to occur.
$$
\begin{array}{l|cccccccc}
\hline
t/\pu{µs}~(\text{efter puls}) & 0 & 5 & 10 & 15 & 20 & 25 & 30 & 35 \\
\hline
[\text{Radikalkatjon}]/\pu{µM} & 20 & 11.12 & 6.86 & 4.47 & 3.00 & 2.06 & 1.43 & 1 \\
\hline
\end{array}
$$

I first checked for the dimerizing of the cation by assuming it to be a second order reaction with the same reactants and plotting $1/[\mathrm{cation}]$ against $t,$ which didn't give a good fit. So I wanted to plot it as a second order reaction with different reactants $(\ce{A + B -> products})$ but I don't understand how that is done.
I should plot $\displaystyle\ln\frac{a-x}{b-x}$ against $t,$ but what exactly is $(a-x)$ and $(b-x)?$
I know that I should set up a reaction like:
$$
\begin{array}{l|ccc}
\hline
& \text{A} & \text{B} & \text{product} \\
\hline
t=0 & a & b & 0 \\
t=t & a-x & b-x & x \\
\hline
\end{array}
$$
And I would assume that my $a = \pu{20 µM}$ and $b = \pu{60 µM}.$ But where do I go from there? All help is appreciated!


texts: What type of chemical reaction is it when sodium bicarbonate is added to citric acid?

texts: I can't tell what type of chemical reaction it is? Is it a combustion chemical reaction? Or Displacement or decomposition or something else?


texts:
Can we picture metallic bonding as an equilibrium between electrons and cations?

Suppose:

  $$\ce{Al^3+ + 3e- <=> Al}$$


texts: Gibbs energy: the term −TdS. Where does the reversible heat go?

texts:
When we have an exothermic reaction as well as a decrease of the entropy in the system after the reaction, why does the decrease in the entropy of the system diminishes the amount of useful work we can extract from the system?

In my opinion, if we have at the final state less accessible microstates than at the  initial state, the kinetic energy (at STP most of them as translational energy) of the system must be more concentrated and therefore have a higher capability of doing useful work. Thus, it gains reversible heat from its system, "stores" it as kinetic energy and could do work.

Where is my mistake? Could you please help me, maybe with a depiction?


texts: Structures of Thiosulfate, Dithionate & Tetrathionate Ions

texts: I am trying to find the structures of thiosulfate, Dithionate & Tetrathionate Ions but I am not getting an exact answer. Please help.


texts: Significant figures used to imply stated error?

texts:
The question reads, " express each of the following quantities using significant figures to imply the stated error".

a)$2.3 \pm 0.001$

b)$1.989 \pm 0.0003$

I think the first one is 2.300 because the zero in the thousands place implies an error of $\pm 0.001$ but how do I use sig figs to imply an error of $\pm 0.0003$?


texts:
Soapstone is a metamorphic mineral with a number of constituent compounds including principally:

silicon dioxide
magnesium oxide
iron oxide
aluminum oxide
calcium oxide
water/carbon dioxide

What would be a typical procedure to analyze a sample of soapstone and determine the proportions of its constituents?


texts: Study long term properties of two polymers

texts:
This is a material-science question, and I didn't know where else to put it.

I (and two others) are mechanical engineering students and are starting a bachelor's thesis which involves some material science. We are to study two polymers, PEEK along with an unknown elastomer.

We are doing the simulation using the software ANSYS, and there are different models of e.g. creep one can choose from, and they need some constants that describes the properties. We're about to do some tensile-tests to investigate the basic properties of these materials. However I believe we also need data about the long-term properties of these materials, which we'll have to get from previous studies. Can anyone point us in the right direction where we could find the relevant studies? We're not that familiar with searching for literature.
I'm about to dive down into textbooks about this, and if anyone has any advice that would be greatly appreciated!


texts: What is the density of nitrogen at standard conditions?

texts:
I find diverging answers to what the density of nitrogen at standard conditions is.
By standard conditions I mean T=273.15 K and P=1 atm (=1.01325 bar).
Different sources state:

Wikipedia : 1.2506 g/L
Fluidat : 1.250 g/L
NIST : 1.2504 g/L
When I use ideal gas law : 1.2498 g/L (using molar mass as 28.0134 g/mol and gas constant as 8.31446261815324*10^3 J/(K mol)

Which one is more correct and why ?


texts: $\ce{BF3}$ does back bonding with fluorine and still accepts a pair of electron and is considered lewis acid why?


texts: Is this approximate equivalence table between Pople's basis sets and Jensen's DFT attuned polarization consistent basis sets (pcseg-n) correct?

texts:
I have some calculations results I runned previously using Pople's basis sets, mostly 6-311+G(d), under Gaussian09. These days I read some texts on Frank Jensen's family of polarization consistent, segmented basis sets, optimized for DFT (pcseg-0, pcseg-1, pcseg-2, pcseg-3, pcseg-4 and the respective augmented versions). Now I'm thinking about trying to reproduce my results using Jensen's basis set family and Gamess-US.

Said that, I'm not sure about the correspondence between the two sets. I understand in Pople's basis sets, for light elements (first 3 periods of the periodic table) it's common to see people using double zeta(DZ) 3-21G for rough calculations, and either double zeta 6-31G or triple zeta(TZ) 6-311G for more precise work. Both 6-31G and 6-311G can have up to two polarization functions (or none) and up to two diffuse functions (or none) associated, resulting in 2x3x3 = 12 combinations between them (not counting heavier elements, that would require f polarization orbitals). In the table 5 of Nagy, Balazs, and Frank Jensen. “Basis Sets in Quantum Chemistry.” Reviews in Computational Chemistry (2017): 93–150. Print., they group together 3-21G and pcseg-0; 6-31G(d), cc-pVDZ and pcseg-1; and 6-311G(2df), cc-pVTZ and pcseg-2. So I assume each basis set inside these 3 groups to be equivalent (but not sure). As pcseg-2 is the only triple zeta option, despite already falling in the range of f-polarized basis, I suppose that, to map these 12 Pople's basis into the respective Jensen's basis, I need some combination between pcseg-0, pcseg-1, pcseg-2, aug-pcseg-0, aug-pcseg-1 and aug-pcseg-2 over H and heavier atoms (6x6 = 36 possibilities). For me it's not trivial to choose which of the 36 Jensen's possibilities in this range best match the 12 Pople's ones not explicitly cited on the paper. My guess at the closest mapping between the 2 sets is as follow:

Type    POPLE's         DUNNING     JENSEN'S CLOSEST
DZ      3-21G                       pcseg-0 on all atoms?
DZ      6-31G                       ?
DZP     6-31G(d)        cc-PVDZ     pcseg-0 on H, pcseg-1 on heavier?
DZP     6-31+G(d)                   pcseg-0 on H, aug-pcseg-1 on heavier?
DZP     6-31G(d,p)                  pcseg-1 on H, pcseg-1 on heavier?
DZP     6-31+G(d,p)                 pcseg-1 on H, aug-pcseg-1 on heavier?
DZP     6-31++G(d,p)                aug-pcseg-1 on H, aug-pcseg-1 on heavier?
TZ      6-311G                      ?
TZ      6-311+G                     ?
TZP     6-311+G(d)                  pcseg-0 on H, aug-pcseg-2 on heavier?
TZP     6-311G(d,p)                 pcseg-1 on H, pcseg-2 on heavier?
TZP     6-311+G(d,p)                pcseg-1 on H, aug-pcseg-2 on heavier?
TZP     6-311++G(d,p)               aug-pcseg-1 on H, aug-pcseg-2 on heavier?
TZP     6-311G(2df)     cc-PVTZ     pcseg-2 on all

Is my reasoning sound and the proposed equivalence table correct, or did I get it all wrong? If wrong, could somebody please give the correct mapping from Pople's traditional basis sets to Jensen's optimized ones?


texts: Are higher branches of mathematics used in sub-fields of chemistry?

texts:
I'm wondering is there any branches of Chemistry that make use of manifolds, Riemann geometry, tensors etc. So far I have not come across anything but hoped that the wider community would know of something?

Forgive me if this is too vague a question but I'm just looking for some topics I can research myself.


texts: What is the general phenomenon taking place here?

texts:
For many cases while calculating the activity of a particular species I find them calculating like this:
$$a=\frac{p_{Mn}}{p^{\circ}_{Mn}}$$
What I really do not understand is what is evaporating into what. A detailed explanation of the topic and quantification of the parameter as activity is most welcome.
This link very well explains how thermodynamic activities are defined. However what I really do not understand is how the "estimating activity" technique is to be applied. A detailed answer to that is most welcome.


texts: Relative acidity of aqueous LiF, SnCl2, and YCl3

texts:
Which one of the following salts make the highest and lowest pH when dissolved in water?
$$\ce{LiF, SnCl2, YCl3}$$

My approach was :
considering the corresponding aqua acids, the order of acidity should be $\ce{Li(H2O)_n+ < Sn(H2O)_n^2+ < Y(H2O)_n^3+}$ and $\ce{F-}$ is less stable than $\ce{Cl-}$. So $\ce{LiF}$ is the weakest acid and $\ce{YCl3}$ the strongest.

But considering aqua acid looks weird (do they exist?) and I cannot be sure this of solution. I don't even know the right answer. Can anyone give some help?


texts: Why diazepam absorbs quickly when taken with metoclopramide? Does it because diazepam is absorbed from intestine like acetaminophen? If it does, why presence of food increases the absorption of diazepam. Meals can slow down gastric emptying and delay diazepam reaching small intestine. So if diazepam is absorbed from intestine, presence of food tends to slow down diazepam absorption, correct?


texts: What will happen if electron as a wave undergo destructive interference while travelling in its Orbit?

texts:
Today I came across a justification of Bohr's angular momentum quantization using the De- Broglie's hypothesis.

The justification said that since the electrons are having wave nature also then while travelling in its Orbit there is starting point and ending point must concide in order to avoid destructive interference of wave.

What will happen if electron as a wave undergo destructive interference while travelling in its Orbit ?

If the electron goes under constructive interference then it's amplitude should increase each time. Is it possible ??


texts: Acidity of hydrochloric acid in acetic acid

texts:
A question asked to find the $\mathrm pK_\mathrm a$ of $\ce{HCl}$ in acetic acid. The equation of $\ce{HCl}$ disassociating in water is: $$\ce{HCl + CH3COOH \leftrightharpoons CH3COOH2+ + Cl-}$$ I predicted that the $\mathrm pK_\mathrm a$ should be higher  as acetic acid is a weaker base than water so it would be less willing to accept a proton from a $\ce{HCl}$.

However when I finally calculated the $\mathrm pK_\mathrm a$, I got 8.56. This was much higher than I expected. Also doesn't this imply that $\ce{Cl-}$ is stronger as a base than $\ce{HCl}$ is as an acid in acetic acid, which doesn't sound right.

So I am asking if this value totally wrong or is it actually quite reasonable?


texts: Adding aluminum sulfate to neutralize an aqueous solution of sodium silicate with pH of 12.6

texts:
How much aluminum sulfate do I need to add to an aqueous solution of sodium silicate to neutralize the solution (pH from 12.6 to 7)?
For a water treatment school project, we remove sodium silicate from water by adding aluminum sulfate to the mixture and filtering the precipitating products by reverse osmosis. Using the following equation along with the molar masses of both molecules:
$$\ce{3Na_2SiO_3 + Al_2(SO_4)_3 + 6H_2O = 3Na_2SO_4 + 2Al(OH)_3↓ + 3H_2SiO_3↓}$$
We calculated that it would take $\pu{51.5 g}$ of aluminum sulfate to react with $\pu{55 g}$ of sodium silcate. In theory, after filtering the precipitants, the $\mathrm{pH}$ of water SHOULD be equal to 7, since sodium sulfate is a neutral salt. However, in practice, we found that it takes a lot more than $\pu{51.5 g}$ of aluminum sulfate (specifically, $\pu{83 g}$) to bring down the $\mathrm{pH}$ of the water after filtration to 7. Chemistry isn't my strongest subject and I really have no idea why $\pu{51.5 g}$ aren't enough. Is this a reversible reaction and after the species get to a certain concentration it simply reaches equilibrium? If so then how do I find the equilibrium concentrations and the equilibrium constant etc. etc.? Otherwise why did we need to add more than $\pu{51.5 g}$ to fully neutralize the sodium silicate particles?


texts: Different reactions of clean and rusty iron nails in vinegar (acetic acid)

texts:
I have submerged a iron nail in vinegar twice recently. What is puzzling me is the different results each time. The first time I submerged it, it was covered in rust. When I put it in the solution of vinegar, I got a red precipitate dissolved in the solution that I believe was Iron(II) and Iron(III) acetate. However, when I put the newly cleaned nail in ANOTHER bath of the same concentration of vinegar, I did get some bubbles but no red precipitate that was dissolved in the solution. It's only been about 2 days, though. However, there was a black precipitate on the surface of the nail, but I do not believe it is iron acetate because of its color.

I am confused as to the results because Iron is higher than hydrogen on the activity series, so it SHOULD be reacting with the vinegar to give me that red precipitate and hydrogen gas. I added some hydrogen peroxide to the solution to oxidize the iron, and the solution is getting a reddish tint to it.

Why do you think I am not getting that reddish precipitate when I put in the cleaned iron nail in the new vinegar solution? Thank you!


texts: Assign symmetric and antisymmetric stetches in IR spectroscopy

texts:
Typically the antisymmetric stretch in IR spectroscopy is higher than the symmetric stretch for a given functional group. For example for $\ce{NO2}$ the antisymmetric stretch falls at $\sim 1530\ \mathrm{cm^{-1}}$ compared to $1350\ \mathrm{cm^{-1}}$ for the symmetric stretch. Likewise $\ce{NH2}$ has a similar pattern ($3400\ \mathrm{cm^{-1}}$ antisymmetric and $3300\ \mathrm{cm^{-1}}$ symmetric).

However, in some cases this pattern is inverted. e.g. $\ce{[HCO]+}$ has an symmetric stretch at $3896\ \mathrm{cm^{-1}}$ and an antisymmetric stretch at $2814\ \mathrm{cm^{-1}}$. How can this be explained?


texts:
Is there anyone who knows a book where I can find a detailed explanation of cell overpotential diagrams, like the ones shown here?

Thanks in advance!


texts:
I have searched and searched, oh how I have searched.

I am looking for a 3-dimensional visualization of a whole atom, one that that includes all the orbital geometry. A proper "layered" view of the orbitals.

What I am not looking for:

Individual orbital geometry.
A "picture" of an atom (i.e. what looks like television static to me).
Little spherical balls.
Dot-and-cross diagrams.

I think I understand that this cannot be expressed in just one picture alone, so I look forward to discovering software, or a collection of pictures, that could help express this. Maybe something similar to an exploded view, for atoms?

Please. The universe is weird and I want to see.


texts: Regarding the free energy requirements for reacting gases

texts:
Continued from my previous question here.

With regards to the Boltzmann factor, I am confused on what type of terms we can substitute for E. I know kinetic energy is one, free energy as well, but can we also do internal energy, enthalpy etc.?
From this link it looks like internal energy and molecular kinetic energy are related and for real gases the internal energy term contains other factors. Since U is a part of G, is it correct to say that kinetic energy in Maxwell Boltzmann Distributions make up a part of free energy?
I am still unclear as to whether I can interpret activation energy as a difference in free energy between average reactant energy and activated complex like diagram 1?
Is it correct to say that, reaction cannot occur unless the reactant have free energy above that of the activated complex, but even if this was satisfied other factors such as minimum collision kinetic energy, orientation etc. must also be met for reaction to occur?

Addendum for Q3 and Previous Post:

My confusion is with regards to the relationship between Maxwell Boltzmann Distributions like diagrams 1 and 2, if there even is one.

The M-B distribution implies to me that

activation energy $E_a$ (which I assume to be that in Arrhenius equation) is absolute given it is marked on an absolute energy scale
activation energy refers to a minimum absolute kinetic energy
activation energy is constant with temperature.

My confusion:

My impression has always been that activation energy (in the Arrhenius equation) refers to the difference in free energy between the transition state and reactant and that $E_a = \Delta G^{++}$ as noted in the latter two graphs, which appear to contradict the M-B Distribution. I'm not sure if there's a formal definition for activation energy that defines what "energy" it is.
The relationship between KE and activation energy (if any)
The effect temperature has on reactant and transition state free/kinetic energies. I believe that higher temperature lowers activation energy if it is the relative energy between the two.

Diagram 1:

Diagram 2:


texts: Why does methyl not shift in the mechanism of isoborneol to camphene?

texts: After the formation of carbocation, I was confused why would the reaction not go in favor of forming bornylene. I am still not sure why but I think that $\mathrm{sp^2}$ hybridized carbon will cause a lot of strain in the ring. Another thing confuses me, why does methyl not shift in place of the ring itself breaking? Is this anywhere similar to Bredt's rule? Please help me with these two doubts.


texts: The boiling points of Alkali metal group

texts:
As I know, the melting points of Alkali metals decrease down to the group due to decreasing of the energy of the metallic bond.

But according to my understanding, after it has become to liquid the metallic bonds are not affecting furthermore because of the lattice has destroyed, so the boiling point affects only the atomic mass. Then according to my logic the boiling points should be increase down to the group. But the above graph shows the opposite of that.

What is the wrong in my logic. Please help me.


texts: Why would 1kW power supplies fail around Nitric acid (HNO3) gas?

texts:
I experienced a situation where some electrical power supplies (rated over 1kW) were exposed to nitric acid ($\mathrm{HNO_3}$) fumes at roughly 9ppm for half a day; these power supplies intermittently failed (perhaps 2 to 3 times per hour) in the presence of the fumes.  Replacing the power supplies restored proper functionality to the equipment they were powering.

At first, I thought that perhaps there was arcing inside the power supply; however, nitric acid doesn't seem to have a flash point.  I'm trying to come up with a reasonable explanation for why these particular components would fail.  Maybe the fumes increased atmospheric conductivity, which shorted across components?

If there isn't a compelling reason from a chemistry perspective, that's also a fair response.


texts: Looking at the equation of a reaction, how do we know it is endotermic or exotermic

texts:
For example, $MnCO_3 → MnO + CO_2$ is endotermic, and occurs at 473 K

the polymerization of ethylene $H_2C=CH_2$ to $n(H_2C=CH_2)$ is exotermic

I suspect it has something to do with the standard enthalpy of formation of the different terms of the equation (right side - left side = $\Delta H$ if negative, the reaction is exotermic and releases $\Delta H$ to the environment as heat, if positive, it is endotermic and needs $\Delta H$ to happen.

Is this correct?

If not, What am I missing?


texts: Effect of doubling kinetic energy on phase transitions

texts:
The kinetic energy of the molecules in a sample of $\ce{H2O}$ in its stable
  state at $ \pu{–10 ˚C}$ and $\pu{1 atm}$ is doubled. What are the initial and final phases? [US National Chemistry Olympiad, 2010]

Answer: $\ce{solid -> gas}$

My attempt: Since water freezes at $\pu{0^\circ C}$ at $\pu{1 atm}$, then the water clearly begins in a solid state. In the solid state, most of the atoms are locked within a crystal of hydrogen bonds and therefore have extremely small kinetic energies. Thus, doubling the kinetic energy should not have any impact on the phase, since gases have significantly more kinetic energy than the solid/liquid phase.

Why does the solid have enough kinetic energy such that doubling it results in sublimation?


texts: Why is the alpha hydrogen of a acetoacetic ester less acidic than the alpha hydrogen of 1,3 diketone ? I was under the impression that acetoacetic ester has more resonance structures so it more acidic. Please explain.


texts: What is the correct Lewis structure of difluorophosphate?

texts:
I can draw two possible Lewis structures for $\ce{PO2F2-}$ anion:

What is the correct structure and why is the other one wrong?


texts:
In Price & Dwek, I find a small section discussing entropy of activation for three examples

$$
1: \ce{Ce^{4+}} + \ce{EDTA}^{4-} \rightarrow (\ce{CeEDTA})\\
2, \text{S}_N\text{1 reaction}: \ce{AB} \rightarrow [A^+...B^-]^\ddagger\\
3, \text{S}_N\text{2 reaction}: \ce{AB} + \ce{C^-} \rightarrow [\ce{C...A...B}^-]^\ddagger
$$

What are the signs of the entropy of activtion $\Delta S ^\ddagger$ in 1-3?

For 1), the argument is that the formation of the complex releases water (because the complex is neutral), and so the entropy change is positive ($S_{final} > S_{initial}$ and $\Delta S = S_{final} - S_{initial}$).

For 3) (yes 3), the argument is that two molecules combine to form one, the solvation being less strongly affected compared to 1) because the charges are lower, and so $\Delta S < 0$ (two molecules have more degrees of translational freedom than one and on combination the average volume decreases).

Now for 2), I dont get it that $\Delta S > 0$. They only say

  "Separation of ions in transition state, hence a positive $\Delta S^\ddagger$."

Can somebody explain what this means? I would have guessed that the charges in the transition state require ordering of the solvation shell around the complex and so $S_{final} < S_{initial}$.


texts:
Is catechol (o-dihydroxybenzene) more prone to auto-oxidation than p-dihydroxybenzene or m-dihydroxybenzene? If so, why?

Apparently, both dopamine and caffeic acid are prone to auto-oxidation. So I wonder if it's a property of o-dihydroxybenzenes in general.


texts: Cahn–Ingold–Prelog priority of carboxylic group versus ortho carboxylic acid

texts: Should the C=C double bond below be labelled as (E) or (Z)?


texts: How to quantify the difference between two xyz files for the same molecule?

texts:
Sometimes I encounter xyz files with slightly different coordinates, for example, before and after optimization.

What is the easiest way to compare how different are they?

In the first approximation, I would define the difference as a minimum of the sum of squares of differences between individual coordinates, where the minimum is taken over translations/rotations of one of the representations.


texts: For IUPAC nomenclature, does the number of multiple bonds take precedence over the chain length?

texts:
I've received a few mixed answers to this question. Some sources say when determining the parent chain for unsaturated hydrocarbons, the longest chain should be considered before the chain with the most multiple bonds, for example:
https://www.acdlabs.com/iupac/nomenclature/79/r79_933.htm
While others say what appears to be the opposite, such as this excerpt from Wikipedia:

The steps for naming an organic compound are:
Identification of the parent hydrocarbon chain. This chain must obey the following rules, in order of precedence:

It should have the maximum number of substituents or branches cited as prefixes.
It should have the maximum number of substituents of the suffix functional group. By suffix, it is meant that the parent functional group should have a suffix, unlike halogen substituents. If more than one functional group is present, the one with highest precedence should be used.
It should have the maximum length.
It should have the maximum number of multiple bonds.
It should have the maximum number of single bonds.

Would be great if I were to receive clarification regarding this.


texts: Difference between state of matter and phase

texts:
What is the difference between state of matter and phase?
 This site  said that:

  Phases are different from states of matter. The states of matter (e.g., liquid, solid, gas) are phases, but matter can exist in different phases yet the same state of matter.

I don't really understand this. Could anyone start from scratch and explain this? Or send me a link to go to?


texts: Unable to comprehend graph of aqueous lithium bromide vapour pressure

texts:
$\ce{LiBr}$ $Vp$ chart:

http://www.mediafire.com/view/x77zc8wj11gthsj/LiBr_Vp.jpg

or

http://www.mediafire.com/view/u4dnocvbsf3atmu/Useful_Chart_LiBr.pdf

Lecture in question (p.13)

http://www.mediafire.com/view/gly78yz339hv1x1/RAC_Lecture_15.pdf

In the lecture it says that at this temperature & at this concentration crystallisation will occur... however how can this be ascertained using the chart? I do know how to read such Duhring plots..


texts: Does 2-chloro-1,3-dinitrobenzene show resonance?

texts:
I am preparing for my exam, and then I stuck up here. The answer to this question given by my teacher was

  No, this doesn't show resonance because there are two bulky groups alongside chlorine, due to this chlorine will leave the plane and as we know resonance is a planar phenomenon, it won't show resonance

My question to you is:

Why did chlorine leave the plane on the first place? And what is the whole concept behind it? Please help me with it.

My guess to this is that since these two groups are really big and bulky, and are present near Chlorine, they take up almost all the space around which causes chlorine to leave the plane.


texts: Why is double my half-equivalence point not equal to my equivalence point?

texts: Tris pKA = 8, therefore at pH = 8, the volume is 4.5mL. However the equivalence point simply can't be at 9mL, looking at this graph. It should be between approximately 9.5 and 10.5, no?


texts: Does evaporation occur while boiling as well?

texts:
If evaporation were to occur when a liquid was being boiled, then the amount of liquid changing phase would also depend on the surface area of the liquid exposed to the atmosphere (as evaporation rate increases with surface area). However I have read that the surface area doesn't affect the amount of liquid changing phase while the liquid is boiling.

So does evaporation not occur while the liquid is boiling?


texts: How to choose a colorant for a given substrate?

texts:
I know there are volumes of International Colour Index (homepage, wiki, paper), but I can't really extract from there for example what red colorants are compatible with both silk and polyester, etc.

This paper mentions that such compatibility can be estimated using numerical methods:

  "Metropolis Monte Carlo methods have been used to determine the surface
  interaction or binding energy for dyes to cellulose." [ref]

Is there a comprehensive database for this?
Is there an analytical way to determine/predict/estimate such compatibility?


texts:
I have seen the equation $S(T_2)=S(T_1)+C_p\ln(T_2/T_1)$ where $C_p$ is the molar heat capacity at a constant pressure. I understand that this assumes that the temperature range is sufficiently small that the constant pressure heat capacity does not vary significantly over it.

My question pertains to the derivation of this expression. One of the first steps is substituting $q=C_pdT$ into $dS=\frac{q_{rev}}{T}$. I am not 100% sure as to why these enthalpies are equated. Is it because the heat exchanged by a system at a constant pressure is always reversible heat, or is this not true?

If the above were true, it would explain to me why I never see an expression involving constant volume heat capacity. If the above is not true, could someone also explain why suh a form does not exist?

Finally, is the equation $S(T_2)=S(T_1)+C_p\ln(T_2/T_1)$ only applicable where the pressures are the same at the initial and final temperatures? On the one hand, the derivation assumes a constant pressure in the infintesimal changes from the initial to final temperature (and of course uses a constant pressure heat capacity!); however on the other hand entropy is a state function. So I would think that if one could find how entropy varies wit pressure at a constant temperature, and the change from the final to the initial state involved both a temperature and pressure change, then I would think that the above expression can be used to find the change in entropy due to the temperature change only, and then the additional factor from the pressure could be used?

Thank you in advance.

EDIT: For the second part, from having a quick think about the reversible heat enxchange in and isothermal process, I think $S(T_2,p_2)=S(T_2,p_1)+R\
 \ln(p_1/p_2)$. So then one could construct a Hess-like cycle to go from one temperature and pressure/volume, to another temperature and pressure/volume. The use of the cycle and step-wise calulcation works because entropy is a state function I think?

Hopefully I answered the second part of my query (I would appreciate if someone could verify that it is correct), although I am still not sure about why the heats used are the same in the derivation, and whether the expression really does refer to the same pressure at the initial and final temperatures, even though the process in getting from these two temperatures can involve pressure changes (again, thinking about $S$ being a state function, so the process itself when changing states does not matter).


texts: Pairs of enantiomers have the same chemical and physical properties (except rotation of plane polarized light) within an achiral environment. However, I am curious about the thermodynamic properties of pairs of enantiomers: say a molecule has a certain $\Delta H_f$, $\Delta S$, and $\Delta G_f$; will its enantiomer have the same exact values?


texts: Some protocols (metabolomics) use boiling methanol for metabolites extraction and cleaning glassware. Is it safe to boil methanol in a microwave?


texts: synthesis of bicyclic diol from cyclohexanone

texts:
I am trying to come up with a synthetic route for the following reaction, my ideas below it.

I think it is a bit of a long shot making this alkene as it would probably be quite strained-any other ideas?


texts: How chemists find out the electronic properties of elements (atomic numbers)

texts:
How did chemists find how many electrons, neutrons, and protons each element had?

I mean I can understand the Mendeleev's table but without really knowing how you make one...


texts: Why nature favours lower potential energy?

texts:
It is very abstract but I was asked this question recently and unfortunately I was not able to answer it decently enough.

I've seen it coming up in various forums of physics, chemistry or biology. Most of the answers I've read give examples from everyday life or approach the matter more philosophically. I'd appreciate any clarification in this matter.


texts: How to identify the reduction in a given redox equation of iron chloride and chlorine?

texts:
The equation shows a redox reaction between iron(II) chloride and chlorine gas.
  $$\ce{2FeCl2 + Cl2 -> 2FeCl3}$$
  Which equation describes the reduction process in this reaction?
  \begin{align}
\ce{2Cl- &-> Cl2 + 2e-}\tag{A}\\
\ce{Cl2 + 2e- &-> 2Cl- }\tag{B}\\
\ce{Fe^2+ &-> Fe^3+ + e-}\tag{C}\\
\ce{Fe^3+ + e- &-> Fe^2+}\tag{D}
\end{align}

I couldn't understand why the answers are not C instead of B.

The correct answer is B. A and D cannot be the answer.


texts: Estimating Surface Reactions - Liquid, Turbulent Flow

texts:
So, I need a method of estimating the influence of a surface (rate constant would do for a start), the idea is to estimate just Reactant + Surface -> Product in a turbulent liquid flow.

Now I am aware of the book "The properties of gases and liquids" by Poling and Prausnitz which gives me two terms for estimating diffusion in a liquid, one general formula from 1975 and a formula specific to hydrocarbons (applicable in my case) from 1982, namely:

Tyn and Calus, 1975:

$$D(AB) = \frac{7.4\,10^{-4} (\phi M(B))^{1/2}T}{\eta(B) V(A)^{0.6}}$$

Hayduk and Minhas, 1982:

$$D(AB) = \frac{13.3\,10^{-8}T^{1.47} \eta(B)^{\epsilon}}{V(A)^{0.71}}$$
where $\epsilon = \frac{10.2}{V(A)}-0.791$

The other variables are

$M(B)$ = molecular weight of solvent B
$T$ = temperature
$\eta(B)$ = viscosity of solvent B
$V(A)$ = molar volume of solute A
$\phi$ = association factor of solvent B (1 if unassociated)

Given that in  my special case I am looking at a liquid in a turbulent flow, I can use the kinetic theory of gases to estimate a surface collision rate - and include surface efficiency using the work on Baldwin and Howarth from 1982.

For a cylindrical pipe with the solute tending to zero, an upper limit for my rate constant for a surface reaction would be:
$k(s) = \frac{8D}{r^2}$

Now there is one big problem with this: The diffusion estimate is not for a turbulent flow (I might be able to get get a diffusion term from Fluent to get a more accurate estimate).

Secondly, at best this would give me an upper limit.

So my question is, do you know of any better more accurate methods of estimating (at least limits) a rate constant for surface reactions? (Or at least the collision rate with the surface.)


texts: What is the difference between the roles of a surfactant and a stabilizer in the process of nanocrystal growth?

texts: The crystals that I am synthesizing use two different stabilizers CTAB and SDS, but they say one is used as a surfactant and since they are both stabilizers what is the need for both?