texts: I was reviewing many electron computational methods recently and got a bit confused about relation between different approaches. In particular in what is essential elemental difference between Hartree-Fock (HF) and tight binding (TB) for example? It could be stupid question, sorry, I am not that deeply familiar with theory. And just for note I am physisist more than chemist. I know that HF is more general method not essentially relying on LCAO approximation. But say we mainly use LCAO for HF anyway in most cases. In TB the hamiltonian matrix elements $H_{ij}$ are mainly used from some tabulated values or fitting with experimental data. This is good for speedy calculations. But can we just use LCAO orbitals and calculate matrix elements analytically using general manybody hamiltonian? Will not it become HF method essentially?


texts: 2 problems with elimination-addition of halobenzene using NH2-

texts:
When converting chlorobenzene to aniline, I drew the following mechanism and the book says it is correct, but there are 2 questions that I do not understand:

In the 2nd step, I am thinking that it is a nuclophilic attack, since $\ce{NH2^-}$ is a good nucleophile. However, I do not understand what makes the $\ce{C#C}$ bond in benzyne electrophilic. Doesn't a triple bond have high electron density and render it more nucleophilic instead? How can the reaction happen?

In the 3rd step, I don't know why proton transfer happens here. Isn't forming $\ce{NH2-}$ from $\ce{NH3}$ not thermodynamically viable as $\ce{NH2-}$ is a strong base?

My thought on (2): forming $\ce{NH2-}$ ion from $\ce{NH3}$ is more stable than leaving the carbanion (the aniline with an extra electron) there, but I am not sure about whether this is a correct explanation.


texts: Can I use an acid other than sulfuric for hydrogen peroxide determination?

texts:
I would like to perform a permanganometric titration of hydrogen peroxide at home following a procedure similar to http://www.titrations.info/permanganate-titration-hydrogen-peroxide, i.e. the reaction:

2MnO4- + 5H2O2 + 6H+ → 2Mn2+ + 5O2 + 8H2O

I do not have sulfuric acid or a licence. Can I use any other acids? I think HCl would release chlorine, and other than that I only have weak household acids such as acetic, ascorbic, citric and tartaric to hand. I can probably get hold of others, but sulfuric is regulated as an explosives precursor here.


texts: Work done in reversible isothermal expansion

texts:
A cylinder fitted with a frictionless piston is filled with $10~\mathrm{mol}$ of gaseous carbon tetrachloride and immersed in a large bath of water maintained at $300~\mathrm{K}$. The volume of the gas is initially at $V_1~\mathrm{L}$, and the external pressure on the piston is slowly decreased until the volume reaches $V_2~\mathrm{L}$. Calculate the work for this process, in $\mathrm{kJ}$, assuming the gas can be treated as ideal.

I think I have the general idea of how to solve this problem but I'm not sure how to find the external pressure. So far, I'm using the equation

$$\int \mathrm{d}w = \int_{V_2}^{V_1}-p_{\mathrm{ext}}\,\mathrm{d}V$$

since it is pressure-volume work and have tried calculating $p_{\mathrm{ext}}$ using $pV=nRT$ and the final volume of the system, but this doesn't seem to give the correct answer. How does it have to be solved?


texts: I have heard that mass spectrometry is very time consuming: why is this?  What is the process involved in performing a mass spectrometry experiment?  What steps are the most time consuming?


texts: When we heat a borax crystal, why does it first expand and then contract?

texts:
In the borax bead test, we take a crystal of borax and then heat it.

  A small loop is made in the end of a platinum or nichrome wire (as used in the flame test) and heated in a Bunsen flame until red hot. It is then dipped into powdered borax, and the adhering solid is held in the hottest part of the flame where it swells up as it loses its water of crystallization and then shrinks, forming a colourless, transparent glass-like bead (a mixture of sodium metaborate and boric anhydride)

Whenever I've done the experiment, I've noticed that the process looks like this:

It heats up in a second, in this time there are no visible changes
It starts expanding/blooming. Bubbles appear, and little pseudopodia(closest work I can think of) of borax flail about. This takes approx five seconds. At the end of this, the borax looks like whipped cream that's been...well.. whipped .
The thing suddenly contracts into a tiny bead.

Now, as mentioned in the quote, basically borax loses its water of crystallization, and then decomposes into $\ce{NaBO2 +B2O3}$, the small bead.

The flailing about is probably due to steam escaping.

But, the reaction proceeds in such an interesting manner, I can't help but think that there's something else going on as well.

What are the details of the mechanism of the borax bead preparation reaction?


texts:
What is the entropy change when the temperature of 1.00 mol of ideal gas is raised reversibly from 10 °C to 50 °C at constant pressure, constant volume, and assuming the heat capacity is independent of temperature?

This is all the information given. I am assuming that the formula $\Delta S = C \ln (T_2/T_1)$ is used. However, I do not know how the heat capacities are supposed to be obtained from the given information. I do not have the enthalpy or internal energy of the process. I cannot calculate the heat capacity from pressure or volume.
Please say if my reasoning is incorrect.
(These aren’t the values of the original question but this is based on Atkins Chemical Principles 5th ed. Ch 8 # 5 and 6)


texts: Is ln(K2/K1) = (∆h°rxn/R)(1/T1 - 1/T2) even when ∆h°rxn varies strongly with temperature?

texts:
In all of my physical chemistry books I find the same expression for estimating the equilibrium constant of a reaction at a non-standard temperature. The derivation starts with $R \ln K_\text{eq} = -\Delta g^\circ/T = -(\Delta h^\circ/T - \Delta s^\circ)$. Then one takes the temperature derivative of each side assuming that $\Delta h^\circ$ and $\Delta s^\circ$ can both be considered constants, which eliminates the entropy term. The equation
$\mathrm{d}\ln K = (1/R)(\Delta h^\circ/T^2)\mathrm{d}T$ is then integrated between $T_1$ and $T_2$ to give
$\ln(K_2/K_1) = (\Delta h^\circ/R)(1/T_1 - 1/T_2)$.

Here's the question: $\Delta h_\text{r}^\circ$ is really NOT a constant, but a function of temperature. Assuming constant heat capacities, $\Delta h_\text{r}^\circ$ at $T = \Delta h_\text{r}^\circ + \Delta c_p(T - T_0)$. Likewise $\Delta s_\text{r}^\circ$ at $T = \Delta s_\text{r}^\circ + \Delta c_p \ln(T/T_0)$. Where $\Delta c_p$ is the difference in the heat capacity of the products and the reactants.

I have tried to insert these expressions into the typical derivation but am getting wonky results. Can someone help me with the derivation or point me to a source where $\ln K$ vs. $T$ is derived with temperature-sensitive reaction enthalpies and entropies.

Edit 4/19/2015: Would it be more effective to invoke $\mathrm{d}\Delta g = \Delta v\mathrm{d}P - \Delta s\mathrm{d}T$ which at constant pressure, and in the case of free energy of reaction, gives $\mathrm{d}\Delta g_\text{r}^\circ/\mathrm{d}T = \Delta s_\text{r}^\circ + \Delta c_p \ln(T/T_0)$ ?

Thanks in advance for any help.


texts: How do I work out the amount of H+ ions in a sodium hydroxide and water solution?

texts: I know the $pH$, pressure, temperature and concentration of the solution. Is there a method I can use to work out the amount of $\ce{H+}$ ions?


texts: How does the crystal know where to stop stacking the unit cells?

texts:
I tried to make different crystals in the cubic system by stacking cubes in a 3D software. However, I need to tell the software where to skip rows or stop stacking the unit cells in a specific direction else it will only make a cube.

How does this work in nature? How does the fluorite "know" where to skip rows in order to make the octahedron crystal? Does it have something to do with Bravais lattices and coordination numbers?

First I thought that the unit cell needs to look like the final shape, but I think I'm wrong there.


texts: I thought zn and cu both lose 2e- to pt but someone is telling me it's wrong]


texts: Which formula to use to find the pH of a solution?

texts:
I just had my first exam yesterday, and I'm always tripped with this question that combines neutralization with buffer solution. The task is to find the pH. I did try to understand the general concept behind it. From my understanding, if $\ce{CH3COOH}$ reacts with $\ce{NaOH}$ and the acid has a higher amount of substance ($\pu{0,005 mol}$ vs $\pu{0,004 mol}$), it means that $\pu{0,005 mol}$ of acid is used to neutralize $\pu{0,004 mol}~\ce{NaOH}$, and $\pu{0,001 mol}$ of $\ce{CH3COOH}$ will remain together with $\pu{0,004}~\ce{CH3COONA}$.

To find the pH, one has to use the Henderson-Hasselbach equation and divide the amount of substance with the volume, with $\mathrm{pH} = \mathrm{p}K_\mathrm{a} - (\log c(\ce{CH3COOH})/c(\ce{CH3COONa})$. And then if $\ce{NaOH}$ has a higher amount of substance ($\pu{0,0051 mol}$ vs $\pu{0,005 mol}$ acid), it would create $\pu{0,0001}~\ce{NaOH}$ and $\pu{0,005}~\ce{CH3COONa}$.

So to find the pH, you need to find the pOH of $\ce{NaOH}$ first. So far so good. But in the solution to the problems posted, there's suddenly an acid popping up in the solution and you have to use Henderson/Hasselbach equation. For example $\ce{NH3}$ reacts with $\ce{HCl}$ and creates $\ce{NH4Cl}$, even if you have a bigger amount of substance for $\ce{NH3}$, you still get an acid on the result... I'm so confused. And then there's an example with the coefficient ($\ce{Na2CO3 + 2HCl -> 2NaCL + H2CO3}$). If $\ce{Na2CO3}$ has a higher amount of substance (let's say $\pu{0,224 mol}$) and $\ce{HCl}$ only $\pu{0,0816 mol}$, does it mean that it would result in $0,224 \times 2 - 0,0816 \pu{mol}~\ce{NaCl}$ and $\pu{0,0816 mol}~\ce{H2CO3}$? I feel so stupid now that I can't understand this simple concept and keep making mistakes (and wasted like 8 points during the exam).


texts:
In a thesis I am reading, it is said that one of the reasons for using plane-wave basis sets for first-principles molecular dynamics (aka ab initio MD) is that the Pulay forces[1,2] that arise from an MD using atomic basis sets are computationally expensive to calculate.

While I understand that having additional terms means more code to write, i.e. they make writing the software harder to write, is it true that they are CPU-intensive to compute? The criterion I would use to quantify this subjective statement is:

  Given that you have already calculated the energy and forces at that point, you have already computed a large number of  integrals required for this task and involving basis functions: overlap integrals, terms of the form $\left\langle\phi_\alpha\left|\hat{A}\right|\phi_\beta\right\rangle$ where operator $\hat{A}$ is either the hamltonian, its gradient, or any other operator necessary for the calculation of energy or forces. Would the calculation of Pulay forces require any more integrals to be evaluated, or can it be straightforwardly computed from those previously-calculated integrals alone?

[1] P. Pulay, Molec. Phys. 19, 197 (1969)
[2] See also slide 6 of this


texts: What is the difference between a coefficient and a subscript in a chemical equation?

texts:
Observe the following parts of an electron transfer equation:

\begin{align}
\ce{2Li + S &-> Li2S}\tag{1}\\
\ce{2Al + 3Br2 &-> 2AlBr3}\tag{2}
\end{align}

The first equation says $\ce{Li}$ with a small subscript 2, however the second one says Al with a coefficient 2 instead of $\ce{Al2}$.

Can someone please explain this discrepancy and inconsistency I'm seeing? Why is lithium in the first reaction written with a small $2$, while in the second one aluminium is written with a big $2$? Why can't both of them be written in the same way? Does it matter? Is there a difference? How do I tell which one to use?


texts:
I am trying to dissolve aspartic acid into vinegar as use as a carbon source in saltwater aquariums.   It does not dissolve.

I was told to increase the pH and it will work?  What is the best way to increase pH with minimal negative effects?

Sodium carbonate seems to work at dissolving; however I may be reducing the acetic acid from 5% to something lower?  Might also be creating an acetate?  Calcium hydroxide could be a better choice for the aquarium but I can't seem to get the mixing ratio right?


texts: Chemical structure of water-soluble polysaccharide

texts:
I don't know much about analytical chemistry, but I need to determine the chemical structure of a water soluble polysaccharide which is not pure and may have D-glucose, mannose and fructose. How do I actually know its chemical structure?

It's from a plant and I know it has fructan and a random polysaccharide which consists of glucose and mannose as the main part and it also has less than 20% impurities such as ash, fat, protein or other sugars. I need to know the arrangement between monosaccharides in the random polymer and the percentage of each polysaccharide.

I have read that it's amorph and linear but I'd rather to check if it is branched. The compound can be consumed with the testing.


texts: Is the lattice point in ZnO crystal structure occupied by the molecule ZnO or the ion O^2-/Zn^2+?

texts:
I learnt that ZnO has a hexagonal crystal system. I was expecting that cations or anions would occupy the lattice points in hcp while voids would be occupied by anions or cations respectively. But while googling the ZnO structure, I found this structure below which was confusing because of my notion about lattice point occupied only by cation/anion while voids occupied by its countercharged part.

But after close inspection of this above structure, I thought maybe the lattice point is occupied by the molecule ZnO itself while voids are left unoccupied as opposed to the cation/anion occuping the lattice point and anion/cation occuping the voids. Because only then,this structure is possible. Am I right in thinking so?


texts: What exactly is the parasitic white layer that forms after iron parts are treated with ammonia?

texts:
I have little to do with chemistry and my only background is the inorganic chemistry I learned at school when I was 13-14 years old.

I need to have a basic understanding of the nitrating process (for an automation engineering application, more precisely an automated furnace used for nitrating iron or steels parts with the purpose of improving their mechanical and chemical properties).

A few things are not so clear for me:

What is the chemical formula of the iron lattice mixed with nitrogen atoms (see the picture)?
What is the unwanted white layer that I understand forms on the surface of the metal part treated with dissociated ammonia?
What is this dissociated ammonia?

Gas nitriding


texts: Why are (3-methylbut-2-en-2-yl)benzene and (3-methylbut-1-en-2-yl)benzene not stereoisomeric?

texts: My answer key says neither product exhibits stereoisomerism, but both products are substituted. Why is it that I cannot assign E/Z configuration? I thought the only time you cannot assign E/Z is when the product is either mono or unsubstituted.


texts: Nucleophiles and bases (elimination and substitution)

texts:
Is it safe to say that all elimination reactions (E1 and E2) involve bases (since in elimination reactions, a hydrogen is being removed, and thus something that accepts a $\ce{H+}$ is called a base)

Whereas, In substitution reactions, bases are not involved.

To summarise:

substitution reactions- can involve bases/nucleophiles/both
elimination reactions- must involve a base, but the base can also be a nucleophile (i.e. elimination reactions cannot occur if you only have a nucleophile)


texts: Are ortho, meta and para used in IUPAC nomenclature?

texts:
I was presented with the following question in an online test:

To avoid any confusion, here are the arranged options:

A. 2-Chlorotoluene
B. 1-Chloro-2-methylbenzene
C. B and D
D. O-Chlorotoluene
Correct answer: (C) B and D.
Explanation: Chloro is given priority so numbered as 1

My question is: Are the ortho, meta and para prefixes part of the official IUPAC nomenclature or not?
I chose B, what should be the correct answer to this question?


texts: Does imidazole and hydrochloric acid yield imidazole hydrochloride salt?

texts:
I'm asking this because I found a link for imidazole-HCl buffer: , but from what I understand, a buffer is a weak acid or base with its corresponding salt. Would imidazole-HCl buffer be a salt solution, or does it have a weak acid or base as well (if it does, what is the weak acid/base)? Also, I found two different pictures for imidazole hydrochloride:

Which one is correct? Is imidazole-HCl a salt or a buffer?


texts: What is the mechanism of the fluorescein synthesis performed by von Baeyer?


texts: What I know is, elements with octet are stable, But In BF3, Boran doesn't get octet, So, How come BF3 molecule exist? If it exists, How do we know whether it is BF3 or not? Is there any proof that shows BF3 exists?


texts: Why is it the middle ring of anthracene which reacts in a Diels–Alder?

texts:
I'm wondering why maleic anhydride adds to the middle cycle of anthracene, and not the outer two.

I would have expected that a Diels–Alder with the outer ring would be better, because I expected a naphtalene part to be lower in energy than two benzene parts (more resonance stabilisation).

I guess it has to do with reactant based arguments that the atomic coefficients for the two center carbon atoms (C-9 and C-10) are higher than from the outer cycle (C-1 and C-4). I ran a calculation using http://www.chem.ucalgary.ca/SHMO and the coefficients on C-9 and C-10 were 0.44, whereas those on C-1 and C-4 were only 0.31.


texts: If silicon dioxide tends to form a crystal lattice with four $\ce{O}$'s around a central $\ce{Si}$, why isn't the molecular formula $\ce{SiO4}$ then? I'm confused why it's unique in that its molecular formula doesn't match up with its geometry.


texts: Work done in expanding a gas reversibly and irreversibly

texts:
So, my chemistry teacher gave the class following $P_{external}$ versus $Volume$ diagrams for reversible and irreversible expansion of a gas which are as follows.

(Reversible expansion)

(Irreversible expansion)
Then he gave us following results to memorize:
$$\mid \left(W_{reversible}\right)_{expansion}\mid \gt\mid \left(W_{irreversible}\right)_{expansion}\mid$$
Where W is for work.
According to him, these results are always true.
But consider the following graph

If I'm not wrong, this can also be considered an irreversible expansion.
But as we can see clearly,
$$\mid \left(W_{reversible}\right)_{expansion}\mid \lt\mid \left(W_{irreversible}\right)_{expansion}\mid$$
This thought is really bothering me. Where did I go wrong?


texts: Is mixing silicone oil with other types of oil safe?

texts:
I'm looking to lubricate some nylon gears in a servo motor, and online sources tell me silicone lubricants are one of the best ways to go.
However, when I opened up the servo, I found that it already has lubrication in place, most probably a mineral oil-based one. It looks dry though, and I'm inclined to re-lubricate it anyway.
Would having the two types of lubricant in there be a cause for concern? Should I exert effort to clean it out first?
Conversely, would there be any issues if I apply a mineral oil-based lubricant to gears that are known to have silicone oil?


texts: Preservation and bleaching of sliced mushrooms with hydrogen peroxide

texts:
According to the article Extending the Shelf Life of Fresh Sliced Mushrooms, it states that 5% (v/v) hydrogen peroxide is an effective means for the preservation of sliced mushrooms.

In regards to the preservation:

  In the USA hydrogen peroxide
  is an approved bactericide for some dairy products and is used for disinfecting fruit
  and vegetables. Its activity is due to its oxidising effects on
  bacteria and it also bleaches mushrooms during the soaking period.

How does oxidising effects cause the bleaching, hence preservation of sliced mushrooms?


texts: Is there a difference between Ca++ and Ca(2+)?

texts:
In this EKG tutorial it says

  Depolarization conducts slowly through the AV node, since it is carried by slow moving $\ce{Ca++}$ ions...

Is there a difference between $\ce{Ca++}$ and $\ce{Ca}^{2+}$?


texts: calculate SPE using dummy/ghost atoms in NWChem

texts:
I have been making some failed attempts to calculate interaction energy of 2 monomers using a dummy/ghost atom in NWChem6.5.
The code I was using to calculate the interaction energy is:

title 'bond_energy'
start dimer
geometry units angstrom
  N 5.286 28.124 48.085
  H 5.966 28.410 48.528
  O 7.110 29.056 50.252
  C 7.758 28.682 51.230
end
basis "ao basis"
  * library 6-311+g*
  bqN library N 6-311+g*
  bqH library H 6-311+g*
  bqO library O 6-311+g*
  bqC library C 6-311+g*
end
dft
  xc m06-2x
  direct
  grid fine
  iterations 10000
end
bsse
  mon first 1 2
  mon second 3 4
end
task dft energy

However, I'm not being able to replace H atom with a dummy/ghost atom (with no charge) in the calculation.
If I use bqH 5.966 28.410 48.528 in the geometry section and calculate odft then also the calculation an error.
Any suggestions or modification needed in the code to achieve this target will be highly appreciated.
Thank you.


texts: Why is syn conformer of methyl formate more stable than trans conformer

texts: As stated, I've read this in a textbook and it seems not explainable solely based on steric clash or Coulombic interactions. I know for such a simple molecule, it can be predicted ab initio using quantum mechanical models (A paper on this), yet, I'm seeking a simple explanation for this conformer preference. Would anybody kindly explain to me the logic behind this? Thanks.


texts: Need of refining aluminium and Hoope vs Hall–Héroult processes

texts:
Recently I was taught how aluminium is commercially extracted. The ore is first concentrated by leaching either by Bayer's process for red bauxite (impurity: $\ce{Fe2O3}$) or by Serpeck's process for white bauxite (impurity: $\ce{SiO2}$).

Then alumina is reduced electrolytically via Hall–Héroult's process directly to 99% pure aluminium. But for further purification to remove remaining copper or iron impurities, Hoope's process is executed to get 99.99% pure $\ce{Al}$.

Since both processes involve electrolysis, and the materials added are similar in both (except $\ce{BaF2}$) with same graphite electrodes, shouldn't we get the same purity in both process (thus not requiring a further refinement)?

Also, the arrangement of the electrodes are exactly opposite to each other. Hoope's argues that pure aluminium is lighter and thus floats so cathode is kept at top, but why doesn't that logic work in Hall–Héroult's? The difference in purity varying by 0.99% and the electrolyte used being same.

Any insight into this matter is helpful because I haven't been able to come to a convincing conclusion.


texts: Reaction of citric acid and calcium chloride

texts:
I was planning to extract citric acid from lemon juice by reacting the lemon juice with calcium chloride hoping it would react to form calcium citrate and precipitate according to the reaction
$$\ce{2 C6H8O7(aq) + 3 CaCl2(aq) -> Ca3(C6H5O7)2(s) + 6 HCl(aq)}$$
However I was not sure that the reaction would occur.  I know that the calcium citrate should precipitate out and drive the reaction forward, however it seems that the $\ce{HCl}$ generated reaction would then react with any calcium citrate bringing back to calcium chloride and citric acid.  Which reaction would move to completion or would the two reactions reach an equilibrium.  If this will not work I plan to just use calcium hydroxide instead by reacting calcium chloride with sodium hydroxide.


texts: Is the voltmeter in a galvanic cell in parallel?

texts:
Often, a galvanic cell is illustrated as having two electrodes, two electrolytes, a salt bridge, and wires linking the electrodes to a voltmeter. However, isn’t a voltmeter connected in a circuit in parallel? This set up makes it seem as if it is being set up in series. How would it work, then?

I would much appreciate it if a circuit diagram (much like the ones you get in physics) could be included in the explanation.


texts: Does the shared electron in Covalent bonds revolve around nucleus?

texts: We know that electrons are charges that revolve around the nucleus. Then, when in covalent bonds the electron is shared; does the electron obey the rule?


texts:
In $\ce{H2C=CH-Br}$ and $\ce{H3C-CH2-Br}$, which will react faster towards a $\mathrm{S_N2}$ reaction?

According to me, as double bond exhibit −I effect, hence the 1st should do a faster reaction. Am I right, or is there any other reason?


texts: Oxidation of guanine with singlet oxygen

texts:
I'm studying the oxidation of guanine using singlet oxygen and one step of the reaction is not very clear to me.

My problem is with the first step: it is a 4+2 Diels–Alder cycloaddition, and Fukui's rules suggest that this kind of reaction doesn't happen photochemically, only thermally.

However, since the reaction is between guanine and singlet oxygen, the oxygen has been photochemically excited, and I don't think it would happen thermally with oxygen at the ground state because otherwise we would have constant oxidation.

So what exactly is happening there?


texts: Why is only bromine used in the degradation reaction?

texts:
Why specifically is bromine used in the degradation reaction (Hoffmann bromamide)? Why can't the same be performed using chlorine or iodine?

In other words, what makes bromine a more convenient reagent as compared to the other halogen gases? For instance, during halogenation of alkanes, we don't use fluorine due to the explosive nature of the reaction, and we don't use iodine because of the slow rate. Is the reason somewhat analogous to this?

I thought because of kinetic factors, maybe somewhat similar to how monochlorination and monobromination are much more easier than monoiodination and monofluorination


texts: Do the ions of the two electrolytes mix in the salt bridge of a galvanic cell?

texts: I read several times in books and on the internet that they do not, but this illustration on the Wikipedia confused me because of the zink and the sulfate ions are written above the arrow (image source):


texts:
Ok so I'm confused about the mechanism for this process:

Now the idea here is that iron first becomes oxidised to Fe(III) by placing an electron in the antibonding orbital of dioxygen. This is followed by the addition of 2 electrons from an external source. This causes the splitting of the O-O bond resulting in the formation of a hydroxide ion. In addition, iron loses another electron to oxygen forming the Iron(IV) oxide species shown.

Now what I do Not understand is the overall charges on the species at the end. I feel as if the original O-Fe(III) bond was considered purely ionic hence the lack of a formal charge on oxygen, yet at the end it seems as if the O=Fe(IV) bond is covalent, otherwise there would be a negative 2 charge on oxygen!

Is there a switch between ionic and covalent formalisms in the middle of this process?

If anyone could help explain the charges with perhaps a curly arrow mechanism to indicate the numbers of electrons on each atom then that would be most appreciated!


texts: Why does potassium permanganate turn colourless when reacted with sulfur dioxide?

texts:
I learnt at school that when sulfur dioxide gas, $\ce{SO2}$, is combined with potassium permanganate, $\ce{KMnO4}$, the purple solution will become colourless.

What happens in the solution to cause this to happen?


texts:
I am learning to determine whether a monocyclic conjugated alkene is aromatic or anti-aromatic or not.
question 1:
cyclobutadiene: according to Huckel's rule, 4 * 1 = 4, it should be antiaromatic, like what is said here. However, Wikipedia says the 2 pi bonds have a 'more double bond' character, making it a rectangular shape (electrons not delocalized). Therefore, it is more like a conjugated diene, hence non-aromatic. What is the truth?
question 2:
planar / non-planar: for [18]annulene, it is aromatic (4 * 4 + 2 = 18). From Wiki,  ''it is large enough to comfortably accommodate six hydrogen atoms in its interior, allowing it to adopt a planar shape, thus satisfying Hückel's rule.'' So in this molecule, there is an extremely small steric effect. So I am wondering, is size of the inner space also a factor in determining whether a cyclic molecule is aromatic or not? If the inner lumen of the molecule is larger, it can follow Huckel's rule? Like Cyclodecapentaene, as the 2 hydrogens cannot be in planar (not comfortably accommodate) (figure 3 in Wikipedia). It is non-aromatic rather than aromatic (do not follow Huckel's rule).
question 3:
cyclooctatetraene is non-aromatic rather than antiaromatic (4 * 2 = 8) since it avoids by changing into a 'tub' shape (avoiding being the unstable planar conformation). I am wondering if other supposedly antiaromatic molecules can change their conformation to be non-aromatic (become more stable) as cyclooctatetraene does? Are there any criteria for changing the shape, or cyclooctatetraene is the only example? If yes, why? If no, what monocyclic conjugated alkene molecule is actually antiaromatic then?
Thank you very much.


texts:
Suppose we had the following reaction:

$$\ce{Polymer ($n$~units)_{(aq)} -> Polymer($a$~units)_{(aq)} + Polymer($n-a$~ units)_{(aq)}}$$

Without knowing the specific monomer unit of the polymer, and assuming the polymer is straight chain, is there anyway to determine the ΔS of the reaction? I mean, I know we can determine the sign (which will almost certainly be positive), but is there a way to make even a rough approximation of magnitude? We can assume the conformational entropy is negligible, i.e. the polymers are fairly rigid.


texts: Why do strong acids dissociate (almost) fully on a molecular level?

texts: In the Brønsted-Lowry theory, strong acids $\ce{HA}$ dissociate using water and react into hydronium ions and the conjugate bases $\ce{A-}$. However I never understood in the strong acids case what stops the products of the reaction(ions) into reforming chemical bonds (why the reaction is one-way) and what enables them when the reagents aren't strong acids. How is this explained macrocosmically and microscopically?


texts: I was attempting a fractional distillation with 1mL water and 1mL propylene glycol, and I’ve been encountering strange behavior with the heating of the mixture. The heating curve shows strange “spikes” in temperature rather than a continuous heating curve. I have ran a standard water and ethanol distillation to check for defects in my laboratory equipment, but the curve for that looks completely normal, and it seems to me like the equipment isn’t the issue. I would love any possible help in explaining this abnormality.


texts: Is there also a leveling effect for weak acids in water?

texts:
The leveling effect says that any acid stronger than the hydronium ion ($\ce{H3O+}$) will completely dissociate in water. Hence no differentiation of acid strength is possible between eg HBr and HCl in water.

I was wondering why no one ever talks about the leveling effect for acids weaker than water. Isn't it so that these acids would not dissociate at all and hence no differentiation is possible on this side either?

Also, what is the reasoning behind the fact that acids stronger than the hydronium ion will completely dissociate in water? Why can't it be an equilibrium (say if it's only slightly stronger than hydronium)?


texts: How to systematically find the reducible representation of a molecule? (eg: XeF4)

texts:
I am attempting to use the reduction formula to find the irreducible representation of $\ce{XeF4}$ to determine its IR stretching vibrations. I know the point group of $\ce{XeF4}$ is $D_{4h}$ and have the character table but I am having a hard time understanding how to get the characters for the reducible representation. I was taught to do it by considering moved/unmoved vectors emanating from the point of the molecule giving values of 1, 0 and -1 for each vector after the symmetry operations have transformed them.
Using this method I to find 2$E_u$ irreps, but I found in a paper (http://sces.phys.utk.edu/~moreo/mm08/penchoff.pdf) that $\ce{XeF4}$ also has other irreps including an Au irrep involved in IR activity. How do I find the irreps that I missed? I noticed the paper uses different reducible representations ($\Gamma_{xyz}$, $\Gamma_{unmoved}$ and $\Gamma_{Tot}$) and I don't understand why.


texts: Elimination reaction with bad leaving groups

texts:
If a halogen is present, as in case of 2-fluorobutane, which is reacted upon by alc. KOH then, shouldn't the product be according to Zaitsev's rule.

Then, why does the removal of hydrogen takes place, does this happens in case of halogens only or in case of all the bad leaving groups?


texts: What is the hybridization of diatomic nitrogen, diatomic anything like oyxgen, bromine; hydrogen and chlorine in HCl?

texts:
I'm guessing sp hybridization for nitrogen in diatomic nitrogen based on the lone pair on nitrogen and the triple bond but there is no mixing of s and p orbitals so I want to say that there is no hybridization. Are there any chemicals without hybridization? What are some examples of chemicals without hybridization

Why are lone pairs counted in hybridization if they do not contribute to the mixing of the orbitals, a.k.a. hybridization?


texts: Electron configuration and the 2p orbital

texts:
I looked through the questions already asked about this topic and they were very specific and over my head. I'm having trouble with the basics.

When drawing orbital diagrams I know electrons are placed in the 2p boxes singly first then paired because of they have parallel rotations and the Pauli exclusion principle states that an orbital can only house 2 electrons and those electrons must be of opposite spin. My question is why do electrons behave this way in the 2p orbital but not the 1s or 2s? And why does the p subshell contain three 2p orbitals?

As far as electron configurations and orbital diagrams are concerned I've gotten to Ne and the 2p configuration confused me so I though I'd ask before moving on.


texts: How do ligands and coordination complexes work in this case with copper (II) chloride?

texts:
What happens when Ammonia  is added to an (aq) solution of copper II chloride?

$\ce{CuCl2 + NH3 ->\; ?}$

I know that ligands bond with metals to form ion but I'm not sure about how they work in a reaction.


texts: Can I use a primary amine to substitute (deprotect) a tosylate at high yields?

texts:
I am trying to use tosyl chloride to allow for a easy substitution of the primary alcohol on glucose then use a BOC-diamine to substitute the tosylate to form a primary amine with a short alkyl chain. But I am having trouble finding any methods in the literature that use primary or secondary amines as the nucleophile for the substitution reaction. Most use relatively stronger nuc like sodium azide or sodium ethoxide.

Is a primary amine not a strong enough nuc? And if so what methods/reagents should I use to obtain a relatively high yield?


texts: I was wondering whether there is any quantum mechanical  equation to describe the force on a given electron in a given orbital of an atom (lets say, for the simplest case, for hydrogen atom). Also if it exists then what is the use of effective nuclear charge?


texts: Precipitation titration with Volhard method

texts:
In the Vollhard method Chloride is precipitated from a solution using escess silver ions.
$$\ce{Ag+_{(aq)} + Cl-_{(aq)} -> AgCl_{(s)}}$$
After precipitation the solution is filtered and ammonium thiocyanate is added to the silver supernate with a small amount of ferric ammonium sulfate as an indicator where thiocyanate reacts preferentially with the silver:

$$\ce{Ag+_{(aq)} + SCN-_{(aq)} -> AgSCN_{(aq)}}$$

Once the all of the silver has reacted with thiocyanate the $\ce{Fe^3+}$ will then react to form $\ce{Fe[SCN]^2+}$ which produces a dark red color and indicates an equivalent point. and the chloride concentration is calculated by difference.

$$\ce{Fe^3+_{(aq)} + SCN-_{(aq)} -> Fe[SCN]^2+_{(aq)}}$$

Since the silver in the precipitate, why will you have to filter $\ce{AgCl}$ before you can start back titration instead of treating the solution? Would filtering also necessary for $\ce{AgBr}$ and $\ce{AgI}$?


texts: A non-life process making glucose from carbon dioxide and water using electricity or light?

texts:
update (Sept. 2018): Here is a bit of news that someone might be inclined to cite in a "No, not yet, but..." answer.

NASA has announced a CO2 conversion challenge!

Get out of your element! Convert CO2 into molecules to power bio-manufacturing in space.
Convert CO2 to Glucose:
Help us discover ways to develop novel synthesis technologies that use carbon dioxide (CO2) as the sole carbon source to generate molecules that can be used to manufacture a variety of products, including "substrates" for use in microbial bioreactors.
Because CO2 is readily abundant within the Martian atmosphere, such technologies will translate into in-situ manufacturing of products to enable humans to live and thrive on the planet, and also be implemented on Earth by using both waste and atmospheric CO2 as a resource.

It looks like this will be a multi-year project.

original question (Mar. 2017):
A large mass fraction of foodstuff a person would need on a long trip (for example, in space or otherwise not on Earth) would come from its caloric (energy) value. Scenarios have been explored for decades to use solar photovoltaic (or other electric) power to generate light to grow plants locally for food. Light provides energy for photosynthesis which combines $\ce{CO2}$ and $\ce{H2O}$ and makes glucose, (later converted to and stored as starch) which then provides caloric value to food.
$$\ce{6CO2(g) + 6H2O(l) -> C6H12O6(s) + 6O2(g)}$$
I'd like to know if a purely non-life based self-contained chemical process has been developed or is at least close to continuously converting $\ce{CO2}$ and $\ce{H2O}$ to glucose, using electricity directly, or electrically generated light.
By "non-life based" I mean it's not a bioreactor based on living cells. It could certainly use processes that are similar to those used in organisms.
The process would have to be potentially able to run stand-alone with minimum consumables, in the same sense of the term "process" as is mean for the Haber Process.
I am not asking if you think it could be done, but if there is a way that it could be done, based on well-documented research towards implementing complete Artificial Photosynthesis using light or electricity, not just a demonstration where a laboratory technician regularly adds separately prepared reagents and precursors for each step.


texts:
I want to figure out/calculate the density ($\pu{g/cm3}$) of the various isotopes, here $\ce{^109Ag}$. I know it's isotopic mass is $\approx109$ and calculated the number of particles/gram. But I couldn't find out how to get the density.

From what I could find out over some mole maps I need to multiply the molar mass with a factor to get to the density but is that even possible or am I wrong?


texts: cross exchanging the coefficients and valences of cations and anions with each other in chemical formulas

texts: Why are the coefficient and valences of iron and bromine cross exchanged with each other in the formula for ferric bromide, FeBr3?


texts: How to recover 15g gold from 50 gallons of 30% Acid?

texts:
Someone mistakenly poured a solution containing $15\mathrm{g}$ of gold into a nearly full waste drum that is around $30$% $\ce{HCl}$ with a little nitric acid in there as well.

Is there a safe way of separating the acid from the gold via distillation?


texts: Aluminium in homemade liquid castile soap?

texts: I made some liquid castile soap in a slow cooker.  There was a slight scratch in the non-stick surface of the container.  I read that potassium hydroxide when coming into contact with aluminium creates hydrogen gas and hoped my container is stainless steel.  However, the container has corroded along the scratch by about a millimetre deep and wide.   The soap is good, but I am concerned that there is a small amount of alum in the product and this can be absorbed into the body.  Is the soap safe to use?


texts: Measuring Colloidal copper PPM & how to ignore the salt PPM in soluton

texts: I made some colloidal copper with 9V battery. To make this water I had to add small amount of salt. However, the salt itself shows up in PPM count of my PPM reader. So how can I discount the salt PPM and come up with correct copper PPM in distilled water.


texts: Will group 2 chlorides dissolve in water in water or react to produce distinct products? How does this differ by the type of salt?

texts:
I thought it'd dissolve... but am i wrong? I added calcium chloride to water, and it was smoking, i was so confused. Can someone explain happened? I am doing an experiment where i dissolve salts in  water, but im very confused now.
PS - my other salts are barium chloride, strontium chloride and magnesium chloride. Are these safe to use?


texts: Does glass adsorb methanol to an exceptional extent?

texts:
Does (borosilicate) glass adsorb methanol to an exceptional extent? We are doing vapor density measurements of organic solvents using a microbalance and a sealed glass sphere. Other polar molecules such as acetone present no problems, but we are getting anomalous results for methanol for some reason.
[Alternatively, does it absorb less than other solvents?]


texts:
To start off with I want everyone to know that I'm not doing this for nay kind if drugs or anything illegal, just having some fun. So I know that lithium( Li) is the least alkaline metal in group one and that it will react with water like Na ,k, Fr, Rb and Cesium (Cs). So I decided to take apart some rechargeable D cell Li batteries to gather some lithium, the first time I tried it didn't react with the water at all. The second time I did all my work covering everything in mineral oil to make sure non if it reacted with the moister in the air ,then dried it. But when I placed that in water it still did nothing after 10 minutes. I even tried hot water but still nothing. Can someone give me an explanation if what's wrong with my lithium?
The batteries came out of a cordless drill that no longer took charge in case that has anything to do with it. Thank you ( I'm sorry for any spelling mistakes or chemical symbol errors, been quite a few years since I have been out of chemistry)


texts: Use of geometry index for the determination of coordination environment

texts:
Geometry index $\tau$ is supposed to resolve proper geometry for coordination numbers (C.N.) 4 and 5 based on its extreme values ($0$ or $1$). There is also a web app Geom which handles both cases for a structure in XYZ format.

I'd like to summarize the questionable topics regarding proper and efficient usage of this method:

Q1. I'm not sure how to address the intermediate values. Say, for $\tau_5 = 0.33$: is it a square pyramidal geometry with a character of trigonal bipyramid? Or one can just name this coordination environment square pyramid and call it a day?

Q2. Are there similar algorithms developed for the higher C.N.:

capped trigonal prism vs pentagonal bipyramid (C.N. 7);
cube vs square antiprism (C.N. 8)?


texts: Thermal stability of alkali metal hydrides and carbonates

texts:
Why is it that thermal stability of alkali metal hydrides decreases down the group, but for carbonates, it increases?

I used Fajan's rule to check for ionic character but somehow this is only applicable for carbonates.


texts: How to calculate the amount of sodium sulfate needed to lower the silver ion concentration of a saturated silver sulfate solution?

texts:
How many moles of $\ce{Na2SO4}$ we have to add into a saturated $\pu{0.5 L}$ solution of $\ce{Ag2SO4}$ so that the concentration of $\ce{Ag}$ is $\pu{4.0 \times 10^-3 M}$? ($K_\mathrm{sp} = 1.4 \times 10^{-5}$)

I found out first $\ce{[SO4^2-]}$ in a normal saturated solution:
\begin{align}
K_\mathrm{sp} &= [\ce{Ag+}]^2[\ce{SO4^2-}],\\
1.4 \times 10^{-5} &= 4s^3,\\
s &= 0.015
\end{align}
So we have $\pu{0.015 M}$ of $\ce{SO4^2-}$ in this solution.
Then, I find out $\ce{[SO4^2-]}$ needed for a saturated solution of $\ce{Ag2SO4}$ but with $[\ce{Ag}] = \pu{4.0 \times 10^-3 M}$:
\begin{align}
1.4 \times 10^{-5} &= (4.0 \times 10^{-3})^2 \times [\ce{SO4^2-}],\\
[\ce{SO4^2-}] &= 0.875
\end{align}
So we need $\pu{0.875 M}$ of $\ce{SO4^2-}$ in such saturated solution.
So the difference of $\ce{SO4^2-}$ is $\pu{0.875 M} - \pu{0.015 M} = \pu{0.86 M}$. So we need to add $\pu{0.86 M}$ of $\ce{SO4^2-}$, that is $\pu{0.43 mol}$ of $\ce{SO4^2-}$ ($\pu{0.86 M} \times \pu{0.5 L} = \pu{0.43 mol}$).
Eventually, we obtained we need to add $\pu{0.43 mol}$ of $\ce{Na2SO4}$.

The above are my calculations, can anyone tell me if my steps can be justified?


texts: How to determine whether a organic compound is diamagnetic or not?

texts:
I have faced several questions regarding the diamagnetic behaviour of certain organic compounds. I know that one has to check the electronic configuration of the atoms in the compound and see if there is an unpaired electron or not? Of all aromatic compounds (benzene, cyclopropene cation, cyclopentene anion) that I have come across one thing was common they were all diamagnetic. I have the following question in my mind

Are all aromatic compounds necessarily diamagnetic and if it is true what may be the proper reasoning for that?
Moreover, the compounds which are stabilised by resonance (hyper conjugation,+M effect) are necessarily diamagnetic. I have this doubt because by the electronic configuration tertiary butane cation should be paramagnetic ($2p^1$ configuration) but is still diamagnetic.

The above is the structure of tertiary butyl cation. It is clear that if we consider the electronic configuration of the central carbon it
 is $1s^{2}2s^{2}2p^{1}$.So it must be paramagnetic. This is where my confusion is.


texts: What is the rotational symmetry number used to calculate the rotational entropy from an ORCA frequency calculation?

texts:
The quantum chemistry software ORCA gives the following warning on frequency calculations:

CAUTION: The rotational entropy is not quite correctly treated here
         because it includes a symmetry number that is not yet correctly
         implemented in ORCA!
For a nonlinear molecule the correct rotational entropy is:
    S(rot) = R*(ln(qrot/sn)+1.5)
    R    = 8.31441 J/mol/K = 1.987191683e-3 kcal/mol/K
    qrot = 4922043.1563766
    sn is the rotational symmetry number. We have assumed 3 here
       if it is different for your molecule then you should correct
       the printed rotational entropy by manually evaluating the equation
       as given above

For convenience we print out the resulting values for sn=1 - 12:
 sn= 1  qrot/sn= 4922043.1564 T*S(rot)=    10.02 kcal/mol T*S(tot)=    34.72 kcal/mol
 sn= 2  qrot/sn= 2461021.5782 T*S(rot)=     9.61 kcal/mol T*S(tot)=    34.31 kcal/mol
 sn= 3  qrot/sn= 1640681.0521 T*S(rot)=     9.37 kcal/mol T*S(tot)=    34.07 kcal/mol
 sn= 4  qrot/sn= 1230510.7891 T*S(rot)=     9.20 kcal/mol T*S(tot)=    33.90 kcal/mol
 sn= 5  qrot/sn=  984408.6313 T*S(rot)=     9.06 kcal/mol T*S(tot)=    33.77 kcal/mol
 sn= 6  qrot/sn=  820340.5261 T*S(rot)=     8.96 kcal/mol T*S(tot)=    33.66 kcal/mol
 sn= 7  qrot/sn=  703149.0223 T*S(rot)=     8.87 kcal/mol T*S(tot)=    33.57 kcal/mol
 sn= 8  qrot/sn=  615255.3945 T*S(rot)=     8.79 kcal/mol T*S(tot)=    33.49 kcal/mol
 sn= 9  qrot/sn=  546893.6840 T*S(rot)=     8.72 kcal/mol T*S(tot)=    33.42 kcal/mol
 sn=10  qrot/sn=  492204.3156 T*S(rot)=     8.65 kcal/mol T*S(tot)=    33.36 kcal/mol
 sn=11  qrot/sn=  447458.4688 T*S(rot)=     8.60 kcal/mol T*S(tot)=    33.30 kcal/mol
 sn=12  qrot/sn=  410170.2630 T*S(rot)=     8.55 kcal/mol T*S(tot)=    33.25 kcal/mol

Now, I have got the following two questions:

What is the rotational symmetry number $s_n$, i.e. how is it defined?
What symmetry number $s_n$ would a molecule with no symmetry, i.e. $C_1$ point group have? The way I understand it, the rotational symmetry number reflects the rotational symmetry, e.g. $\ce{CHCl3}$ would have $s_n=3$ as there are three equivalent structures superimposed by the $C_3$ symmetry element. So that my guess is that $s_n = 1$ in that case. Is that correct?


texts: Is it possible to make a fuel cell that runs on triglyceride?

texts:
I apologize if this is a silly question. The reason I ask is I'm wondering if it would be possible to build a fuel cell that runs on body fat. I know ones for butane exist, could they work for this? If not, is there any good reason it isn't possible?

Basically I'm imagining some kind of flexible inductive charger in your hand, or wrist for a smart watch, and connected to a fuel cell that's connected to the circulatory system and runs off body fat.

It just seems silly to lug external batteries along on long on bike rides when the whole point of the ride is to get rid of excess chemical energy anyway.

I obviously don't have the skills to pursue this, but I just want to know if the dream is silly. :)

Thanks!


texts: Nuclear spin isomerism in molecules other than H2

texts:
I was reading my teacher's material about ortho- and para- hydrogen, and I found stated that

  "every homonuclear molecule, with nuclides with spin other than zero ($\ce{H2}$, $\ce{D2}$, $\ce{T2}$, $\ce{N2}$, $\ce{^{17}O2}$...) has nuclear spin isomers".

What is not clear to me is: are there any nuclides with spin zero? Is there, hence, any homonuclear molecule without spin isomers?


texts: Alkylation of conjugated nitriles - regioselectivity

texts: Why does the enolate of the nitrile attack the alkyl chloride from the bond shown in the picture and not from the far end pi bond?


texts:
I'm reading a paper where the author has come with these consecutive elementary reactions

Where $C_2H_{4\ ads}$ is ethylene adsorved, $C_{ads}$ is carbon adsorved and $C_{CNT}$ is carbon that became nanotubes. The process he used to grow the nanotubes was CVD.

The author has derived this following equation, in which I couldn't derive myself and still doesn't make sense to me
$$\frac{d[C_{ads}]}{dt}=2k_1^+[C_2H_{4\ ads}] - (k_2^+ + k_1^-)[C_{ads}][H_2] $$

In the text he said he used these two approximations: $\frac{d[C_2H_4]}{dt}=0$ and $\frac{d[H_2]}{dt}=0$

First: I don't know why $\frac{d[C_2H_4]}{dt}=0$ is useful, as it never appears in the equation for $C_{ads}$.

Second: Why he didn't put $C_{CNT}$ there? (and even then $k_2^+$ happens to appear in the equation)

Third: Is this correct? Can someone give me some light?


texts: As Borazole ($\ce{B3N3H6}$) is aromatic, it shows electrophilic aromatic substitution. Now, my question is when borazole undergoes electrophilic aromatic substitution reaction, on which atom does the electrophile attack? Is it boron or nitrogen? Also, how to compare it's rate with the same type of reaction when carried on benzene? Should I consider stability of Wheland intermediate formed when comparing the rates?


texts: Kinetic isotope experiment used to distinguish radical and concerted mechanisms for the Diels Alder reaction

texts:
In the Pericyclic Reactions Oxford Primer it is written that:

  the deuterium
  substitution of the hydrogen atoms in the diene and dienophile that
  participate in a possibly Diels-Alder reaction, gives rise to inverse
  secondary isotope effect (as the carbon atoms change from trigonal to
  tetrahedral geometry):

  If both bonds are forming at the same time, the isotope effect when both ends are deuterated is geometrically related to the isotope
  effect at each end.
  If the bonds are being formed one at a time, the isotope effects are arithmetically related.

I don't understand the principle behind this. Why does the isotope effect occur and how does it tell us whether the mechanism is radical or pericyclic? I need an answer much more concise than what is presented in the book.


texts: Microstates, molar mass, and degrees of freedom.

texts:
What is the relationship between the number of microstates and molar mass. The key says choices II and III are correct. If III is true, why isn't I also true? Also, if II is true, why isn't IV true as well?

I think that the greater the number of microstates, the greater the number of DoF. I figured that much out.

Why would NH3 have more degrees of freedom than NO2? Is it because NH3 has more attached atoms than NO2?

Is molar mass just a red herring in the first statement? NO2 has fewer bound atoms than NH3; it seems that the number of bound atoms affects the number of microstates more so than molar mass, because in III, where the two species are structurally identical, molar mass comes into play.

So when determining the number of microstates, is the number of attached atoms more important than molar mass?

I can't seem to find any good online resources relating molar mass with the number of microstates and degrees of freedom.


texts:
Boron has an empty $2p$ orbital.
But is it an electroplhile?
I know it is a Lewis acid.


texts: What is the difference between ΔG and ΔG "with an o on top"?

texts:
What is the difference between $\Delta G$ and $\Delta G^\circ$? I couldn't figure it out.

Ex:

$\Delta G^\circ = -RT\ln K$
$\Delta G = \Delta G^\circ + RT \ln Q$

What is the difference, is it that $\Delta G^\circ$ is the value predicted by the standard free energies and that $\Delta G$ is just the actual value?


texts:
Which type of citric acid crystalline powder do they sell in grocery stores?

Is the concentration of citric acid in the crystals 100%?Is it anhydrous or a monohydrate?


texts: What is meant by "fairly" when used as a quantifier for the solubility of a chemical?

texts:
While doing homework and I found a statement that says a chemical is fairly soluble in water, but I do not understand what this means.

However, I know that when things are soluble in water they tend to dissolve. Is it that fairly soluble in water means that a part of it dissolves, while another part doesn't dissolve?


texts: Is it possible to write a redox reaction with two oxidations and one reduction together?

texts:
Let's take the Redox reaction between ${MnO_4}^-, {C_2O_4}^{2-}$ and  ${SO_3}^{2-} $

Is it possible to write the complete reaction as below or do I need to consider the two reactions separately?

$\ce{4MnO4- + 5C2O4^{2-} + 5SO3^{2-} -> 4Mn^2+ + 10CO2 + 5SO4^{2-}}$


texts: Quantum mechanical explanation for Le Chatelier's principle?

texts: We know from basic chemistry that a reaction reaches equilibrium as described by Le Châtelier's principle. What's the quantum mechanical explanation to this principle? How a change in temperature/concentration causes an equilibrium to shift, from the point of view of wave functions?


texts:
Does a liquid having higher vapor pressure have a lower boiling point?
I think so because I read in wikipedia that, "A substance with a high vapor pressure at normal temperatures is often referred to as volatile." A volatile liquid has lower boiling point.


texts:
What is the role of red phosphorus in hvz reaction?
Initially I think that red phosphurus is nothing but a catalyst. But it is not a catalyst.


texts: Nitrogen and an unknown gas is leaked into a common vessel... The gaseous mixture contains 0.4 moles of nitrogen. Molecular mass of the other gas is?

texts:
For 10 minutes each, from two identical holes, nitrogen and an unknown gas is leaked into a common vessel of 3L capacity at 300K. The resulting pressure is 4.15 bar. If the gaseous mixture contains 0.4 moles of nitrogen, then molecular mass of the unknown gas is?

attempt: According to Graham's law of effusion, $$\frac{r_1}{r_2}=\frac{V_1}{V_2}=\sqrt{\frac{M_2}{M_1}}$$ where $V_i$ is the volume of gas effused. Let $V_1$ and $M_1$ be volume and molecular mass of nitrogen. $$V_1=22.4\times0.4=8.96;M_1=28$$
Substituting, $${V_2}=8.96\sqrt{\frac{28}{M_2}}$$
and $V_1+V_2=3$, so $$8.96(1+\sqrt{\frac{28}{M_2}})=3$$
This is not possible since $\sqrt{x}\ge0$.
What am I doing wrong?


texts: Reaction enthalpy using bond energy in resonating molecules

texts:
To find out and enthalpy of a reaction using bond energy we use the formula

$$\Delta H = \sum\Delta_\mathrm{bond}H_\mathrm{reactants} - \sum\Delta_\mathrm{bond}H_\mathrm{products}$$

since we use all the individual $\Delta H$ of the bonds to calculate the enthalpy, e.g.

$$\Delta H_\ce{C2H6} = 2\Delta_\mathrm{bond}H_\ce{C-C} + 6\Delta_\mathrm{bond}H_\ce{C-H}$$

But if a molecule is in resonance, how is the bond enthalpy taken? For example,

Is bond enthalpy the sum of the bond energies of that canonical structure which is the most stable or the average of all canonical structures or something else?


texts:
I'm quite a newbie in chemistry and I'm trying to learn how logarithmic diagrams work. I have been told that you can calculate pKa and pH graphically:

pKa, when [HA] = [A-]
pH, when [H+] = [A-]

Why does this happen?


texts:
A boron trihalide ($\ce {BX3}$) is a Lewis acid, because it can accept an electron pair, as per Gilbert N. Lewis' definition.

Now my question is-

  Arrange $\ce {BF3}$, $\ce {BCl3}$, $\ce {BBr3}$ and $\ce {BI3}$ from the weakest to the strongest acid properties.


texts: Why does hybridization produce a more stable configuration?

texts:
My text, and the other sources I've checked, include information on the effects, and kinds, of hybridized orbitals; however, they do not explain what properties of hybridized bonds conduce greater stability.

Why does hybridization produce a (lower energy) more stable configuration?


texts: The products of a chain reaction beginning with acetone and sodium amide

texts:
I encountered the following question in an exam:

  $\ce{CH3COCH3 + NaNH2}$  giving out $\ce{A}$.
  $\ce{A}$ then reacts with $\ce{C2H2}$ giving out $\ce{B}$.
  $\ce{B}$ then reacts with $\ce{H+}$ to give $\ce{C}$.
  $\ce{C}$ then reacts with 1 equivalent of $\ce{H2}$ in presence of $\ce{Pd}$ to give $\ce{D}$.
  $\ce{D}$ then is heated to $\pu{400 ^{\circ}C}$ in presence of $\ce{Al2O3}$ to give $\ce{E}$.

I reasoned it as the first reaction could be an acid-base reaction, but that didn't help much. Then I tried a nucleophilic substitution, but there aren't any good leaving groups and still we get stuck after the first step.

One of the teachers reasoned it as the first reaction being reversible and it goes back to $\ce{CH3COCH3}$ which then reacts with all other and it ends up at isoprene which is the correct answer according to the answer key, but this explanation seems very flawed to me as then what was the purpose of the first step? Can someone please check and write the steps and products in each reaction?


texts: Alcohol in the bloodstream modeled by differential equations

texts:
Does anyone know any good references which use partial differential equations to model the alcohol concentration in the bloodstream? I'm a mathematician, so I'm searching for a rigorous mathematical model.

If you have any other suggestions of models in chemistry that uses partial differential equations, feel free to post them here.


texts: Good software to perform simulations on polymer (absorption spectra)?

texts: Sorry guys,I'm totally new in this field,for personal interest I'd like to start some calculations on conducting polymers ,could someone suggest a good software to perform simulations on polymer (absorption spectra)?


texts: Is there a field of chemistry that doesn't do experiments?

texts:
In other words, a field of chemistry that is all theoretical? I have heard of theoretical chemistry, but my chemistry professor said you can't really major in theoretical chemistry. He said the closest thing is physical chemistry.

I like predicting in Chemistry, but I hate labs or experiments.


texts: Effect of coffee brew water concentration on further extraction in immersion brewing

texts:
In immersion brewing coffee is extracted with an increasingly saturated solution, as opposed to percolation brewing, where the extraction is performed with a continous supply of fresh water.
Because water can only extract a certain amount of solubles from the coffee and the fastest extracting compounds are dissolved first, I wanted to ask if the increasing concentration of fast extracting compounds (caffeine, volatile oils) hamper the ability of the remaining brew water to dissolve slower extracting components of the coffee bean (e.g organic acids).


texts: Sign of enthalpy for exothermic and endothermic reactions

texts:
In Cambridge Chemistry Coursebook [1, p. 94] it’s written that

A rise in temperature is given a positive sign. So the value of $\Delta H$ is negative for an exothermic reaction. A fall in temperature is given a negative sign. So the value of $\Delta H$ is positive for an endothermic reaction.

Why is the sign of enthalpy for exothermic reaction negative? Doesn’t exothermic reaction rise the temperature of surrounding?
Why is the sign of enthalpy for endothermic reaction positive? Doesn’t endothermic reaction take in energy and cool down the surrounding?
Reference

Ryan, L.; Norris, R. Cambridge International AS and A Level Chemistry Coursebook, 2nd ed.; Cambridge International Examinations; Cambridge University Press: Cambridge, 2014. ISBN 978-1-107-63845-7.


texts: Is concentration polarisation an observable phenomenon over time in a galvanic cell?

texts:
If polarisation means: "any mechanical side-effect by which isolating barriers develop at the interface between electrode and electrolyte."

And if concentration polarisation is "changes in the electrolyte concentration due to the passage of current through the electrode/solution interface. Here polarization is understood as the shift of the Electrochemical potential difference across the cell from its equilibrium value. The cause of the changes in concentration (emergence of concentration gradients in the solution adjacent to the electrode surface) is the difference in the rate of electrochemical reaction at the electrode and the rate of ion migration in the solution from/to the surface."

Thus, should concentration polarisation cause a decrease in the performance/efficiency of a galvanic cell over time and would this be shown with a decrease of voltage/current through the cell? Or does voltage and current remain the same throughout a galvanic cell reaction?


texts: In school they ask us to count the number of resonance structures in different organic compounds to determine it's stability. The one with more resonance structures is more stable. Is this notion correct?


texts: Battery acid solution preparation from 98% ACS Sulfuric Acid

texts: I'm trying to prepare some battery acid for activating a flooded lead acid battery I had purchased. The battery concentration should be around 36-28% sulfuric acid solution. I have decided to go with 37% acid solution.  I would like to confirm if the volume of acid to be added is correct. So, using a 98% ACS reagent sulfuric acid the volume of acid to make 100mL solution should be 37.57% right? The remaining volume is distilled/deionized water to make up for the 100mL.


texts: GCMS Peak Identification: Online or Open Source / Free Programs?

texts:
Suppose I have a GCMS peak graph for a component, what are possible options to figure out what the molecule may be?

Any tips about good software that will do this? I do know that for many compounds there is a hit in the NIST library, but how does one go about automatically checking the library?

Google came up with OpenChrom. Has anyone used this? The peak library in it is unfortunately not accessible in the free version.


texts: Boiling sodium hydroxide in stainless steel cup: Solution turning to a blue color

texts:
I boiled highly concentrated sodium hydroxide in a stainless steel cup. This created a blackish layer on the bottom of the cup and turned the colour of the sodium hydroxide solution to blueish.
Am I right to assume that there was some oxidation happening at the surface of steel? Are any oxides of metals, present in common stainless steel, known to have a blue colour when dissolved in an aqueous solution?


texts: Why is entropy not zero for an irreversible adiabatic process though q=0? Ideally entropy is a state function so entropy should be zero.


texts: Mechanism of oxidation by dichlorotriazenetrione

texts: How does dichlorotriazenetrione supply chlorine to a swimming pool and how does it oxidize organic material?


texts: For molecular orbitals, how is an energy of zero set or defined?

texts:
When labeling the energies of molecular orbitals, often some anti-bonding MOs are shown with a positive energy. For example, MolCalc has the following energies for methane (the anti-bonding MO #8 at +19.47 eV depicted on the right):

I'm trying to understand what these numbers mean. I get that electrons in MOs #2 through #5 help to keep atoms bound (having them occupied contributes to bonding), whereas electrons in MOs #6 through #9 would lead to an increase in bond lengths or the molecule falling apart. On the other hand, MO #1 does not participate in bonding, right (basically, it is the inner 1s electrons of carbon)?

So what defines the zero reference point of these orbitals? It can't be the free electron because I thought at least for the hydrogen atom, even the excited states are states where the electron is still bound (i.e. energies are negative). It can't be the gradient of increasing all bond lengths (i.e. with the extreme case being separate atoms) because MO #1 would be hardly affected by that, given that it hardly participates in bonding.

This question is not limited to one particular software or author. Here is another example (source: https://www.researchgate.net/publication/234126374_Electron_rectification_through_donor-acceptor-heterocyclics_connected_to_cumulenic_bridge_A_computational_study):

I realize that the language in this question is sloppy, reflecting my poor understanding. I encourage anyone who answers to use the correct terminology.


texts: How does a shock, such as the snap of the disk in a reusable hand warmer, trigger the re-crystalization of a supersaturated solution?

texts:
Reusable handwarmers are made of something dissolved nearly to its saturation point in hot water (Sodium Acetate in the case of HotSnapz) at a high temperature, and then cooled to a temperature at which some would normally be insoluble, but remains dissolved due to a lack of a site to grow a crystal from. When the crystal finally grows, triggered by popping a little disk, the process is exothermic and it releases heat.
What I'm wondering is: how does popping the little metal disk inside the hand warmer allow nucleation to begin?
EDIT: I got a bit more information, but nothing definitive. What I’ve heard is that the metal disk may either be initiating nucleation by releasing tiny metal particles when it snaps or by snapping quickly enough to cause cavitation. The first seems unlikely, because if bits of metal were released and functioned as nucleation sites, the warmer wouldn’t be reusable - the crystals could just reform on those metal bits. Cavitation seems more plausible, though I still don’t understand how that would allow crystallization to begin.
EDIT 2: I did some experimenting, and a whack also starts nucleation, not just the disc snapping. So, any shock can cause the sodium an acetate ions to come out of supersaturated solution. How?


texts: Can the directionality of an SN2 reaction depend on solvent polarity?

texts:
Because of the effects of solvation, halide ions have differing nucleophilicity in protic solvents vs aprotic solvents, iodide being the best nucleophile in protic solvents and fluoride being best in aprotic solvents.  For the sake of simplicity, fluoride will be ignored due to its high electronegativity and unusual reactive properties, and chloride will be used instead.

So would that mean that an alkyl chloride will react with HI in a protic solvent to form the alkyl iodide?  And the alkyl chloride will not react with HI in an aprotic solvent?  And by the same token, would an alkyl iodide react with HCl to form alkyl chloride in an aprotic solvent but not in a protic solvent?

I also realize that iodide has a much greater polarizability than chloride and that must be taken into account as well.  Iodide is more a thus a more stable anion than chloride, making iodide much better leaving group than chloride.

But which factor will have a greater overall effect?  Do aprotic/protic solvents affect the leaving group capability (ie although chloride is less polarizable and more unstable relative to iodide, after leaving in a protic solvent the H-bonding "shell" will stabilize the anion and prevent it from reacting with the alkyl iodide formed.  Conversely in aprotic solvent, the chloride ion would not be stabilized after leaving and thus could reattack the alkyl iodide to reform the alkyl chloride)?


texts: What's the biggest organic molecule that could have a smell?

texts: For a molecule to have a smell it's necessary that the molecule be volatile enough to be in the air. So I think that excludes molecules which are solid at room temperature and atmospheric pressure. Maybe the question then is equivalent to: what is the highest molecular weight organic compound which is liquid at room temperature and atmospheric pressure?


texts:
What is the mechanism of a 1,2-hydride shift? I read that there is an aromatic intermediate, in that the intermediate obeys Hückel's rule.

However, Wikipedia doesn't offer any further explanation. Can someone with more knowledge elaborate on the transition state of a 1,2-hydride shift?


texts: Obtaining values for electrical mobility from ion transport numbers in a Hittorf cell

texts:
I am following the experiments detailed in the links below in order to find the electrical mobility of a variety of ionic species:

Wikipedia article on ion transport numbers and Hittorf method
PHYWE series of publications - "Transport numbers" PDF
"Determination of Transference Number by Hittorf’s Method" - PDF

I know that the ion transport number of an ionic species is the ratio of the current carried by that particular species over the total current conducted through the Hittorf cell. The change in concentration of the electrolytes, the mass of the electrodes, the voltage and current of the cell can be used to calculate this number. But, using these results, how do I calculate the drift velocity of those ions and hence values for their electrical mobility?

I tried looking at the Einstein-Smoluchowski relation but the concepts are a bit over my head right now. Any other tips, notes and comments on this experiment would also be appreciated.


texts: Number of stereoisomers and symmetry of pentane-2,3,4-triol

texts:
The answer is apparently 4, but the solution does not make sense.

I can only identify 2 chirality centers (the central carbon cannot be a chirality center) so I thought 2^2 = 4 stereoisomer possibilities, but because of the existence of a plane of symmetry, there is a meso compound: thus there should only be 3 stereoisomers.

However, the solution claims that initially, we can deduce 3 chirality centers and claim 8 stereoisomers, then eliminate some of them through the observation of plains of symmetry (there is only one as far as I can see either way). This solution does not make sense, but when I checked by looking at all of the structures, it seemed true. Can someone help me what I am missing?


texts: Isotropic Fermi Contact Couplings vs. Dipolar Coupling Constant

texts:
I need to calculate a Dipolar Coupling Constants for some fancy triplet molecule that has been measured by EPR spectroscopy.

My "normal" output from Gaussian gives me the following:

Isotropic Fermi Contact Couplings
Spin Dipole Couplings
Anisotropic Spin Dipole Couplings in Principal Axis System

Am I right that none of these are Dipolar Coupling Constants? And If so ... how can I compute them either directly with the program or by hand through some formula?


texts: How to calculate the heat capacity of a calorimeter?

texts:
I need to find the heat lost of an unknown metal dropped into a calorimeter with $70~\mathrm{g}$ $\ce{H2O}$.
The initial temperature and final temperature of the $70~\mathrm{g}$ $\ce{H2O}$ and the calorimeter are $21~^\circ\mathrm{C}$ and $34~^\circ\mathrm{C}$. I already know that the heat gained by the water is $3807.44~\mathrm{J}$.

The metal's starting temperature and mass are $100~^\circ\mathrm{C}$ and $180.45~\mathrm{g}$, but that didn't help me much as I don't know the $C_{sp}$ of the unknown metal.

What I don't know is how to find the capacity of the calorimeter, any thoughts?

I already tried a number of solutions that didn't work:

$C_{sp} \times \ce{H2O} = q(\mathrm{calorimeter})$
$q(\ce{H2O})/m(\ce{H2O}) \times \Delta T = q(\mathrm{calorimeter})$
$q(\ce{H2O}) = q(\mathrm{calorimeter})$
I knew the unknown metal was one of three metals (lead, aluminum, copper),     so I tried finding $q(\mathrm{metal})$ using the 3 heat specific heat capacities, but it didn't work out since the data provided were only approximations.


texts: Why does hydrogen burn spontaneously in fuel cell at room temperature?

texts:
It's well known that if you mix $\ce{H2}$ and $\ce{O2}$ in ambient conditions, the $\ce{H2}$ will be stable indefinitely, and will only react with $\ce{O2}$ to form water when ignited by a flame. The reason being that for the reaction

$$\ce{2H2 + O2 -> 2H2O} \label{rxn:1}\tag{1}$$

to occur, first the bonds must be broken in $\ce{H2}$ and in $\ce{O2},$ which is an insurmountable activation energy at room temperature.

So I am confused why a hydrogen fuel cell works at room temperature without ignition, as it is powered by the same chemical reaction \eqref{rxn:1}.

In particular, why can the strong double bond in $\ce{O2}$ suddenly be broken in this context without a flame?

My best guess is that somehow the electron sea in the copper wire acts as a catalyst. If this is true, what are the details of this mechanism that allows the $\ce{O2}$ bond to break at room temperature?


texts: What is the extent of a reaction between an acid and its conjugate base?

texts:
What is the extent of say, this reaction?

$\ce{H_2CO_3 + HOCO_2^- <=> HOCO_2^- + H_2CO_3}$

K for the reaction appears to equal 1, and given the stoichiometry of the reaction, this implies that the reaction reaches an extent of 50% at equilibrium.

However, is this actually true?


texts: What kind of fire extinguisher for chemistry at home?

texts:
The are various types of fire extinguishers. They can be based on

water
foam
dry powder
carbon dioxide
wet chemicals
halon
etc.

Suppose one is learning chemistry at home. What type of fire extinguisher one should ideally get? It seems the dry powder option is the cheapest ($\approx 30€$), foam mid-priced ($\approx~60€$) and the one using carbon dioxide the most expensive ($\approx~150€$). I did not find solutions based on water/wet chemicals/halon yet, though I know such exist. If there's no differences in achieved safety, I would probably pick the dry powder one.


texts: What is the quickest way to dissolve steel?

texts:
What is the quickest way to dissolve a large chunk of steel? I mean a very quick reaction, assuming that the interaction occurs in a sealed or semi-sealed environment? Reaction times of the order of a few minutes versus tens of minutes, hours or days are the objective.

I'm curious as to how quickly acids like $\ce{HNO3}$ and $\ce{H2SO4}$ can react with steel containers.


texts: Reasons behind the different colors of a solution containing Iodine

texts:
Q) Iodine dissolves in a variety of solvents, forming solutions that are
purple, brown or any intermediate shade. This property is due to:

Hydrolysis of iodine
Formation of crystalline adducts
Charge transfer between $\ce{I-I-}$ and the solvent
Charge transfer between $\ce{I-I+}$ and the solvent

I am completely aware of which concept does option 3 and 4 allude to. I know about the formation of $\ce{I3-}$ when iodine is dissolved in solution of iodides. This fact, according to me, is what option 2 refers to.

But the answer given is 3

Can someone provide an explanation as to what concept is involved here and how can we predict the answer? I read about charge transfer complexes, but the Wikipedia page was too complicated for me to understand, and also the application of that to the question under consideration was not given.


texts: Can a spark ignite hydrogen? Also, what about the tip of a cigarette? I've heard that hydrogen is very explosive. Thanks


texts: I know that both molecular size and complexity increase overall entropy, but between the two I'm not sure which increases it more. Would 1 mole of hydrogen have the greater entropy because it is two atoms instead of one, or would 1 mole of neon have the greater entropy because it is a larger atom?


texts: Do both H (enthalpy) and ∆H, or ∆H alone have a physical significance?

texts: My chemistry teacher said that H (enthalpy) alone has no physical significance it is ∆H or change in enthalpy that has a physical significance. But my book says that both have a significance and H alone represents the total heat content of the body. Thus I am in a confusion, please help me.


texts: What causes the smell in rotten meat-grease and how can I get rid of it thoroughly?

texts:
We've just spilled the can of used meat-grease we collect so that it doesn't go down the drain and it turns out it was rotten. Now the granite counter-top and the wood-laminate floor of the kitchen smell very bad even after repeated cleaning with (1) dish-soap, (2) vinegar and (3) Murphy's Oil Soap as well as an enzymatic product called anti-icky-poo.

Extensive googling suggests that the smelly chemical is either putrescine or cadaverine. Am I right about that? How can I clean my kitchen such that it does not smell so bad?


texts: Do conjugated polymers absorb very low energy photons?

texts:
I was reading that in conjugated compounds, the extent of conjugation decides what wavelength photon it can absorb. Longer the conjugation "chain", lesser the photon energy required. So, molecules like lycopene

with 11 conjugated bonds is able to absorb in the blue range, appearing red. If this is the case, consider the polymer poly-acetylene

which has a conjugated "chain" spanning "thousands". Does this mean, this molecule would absorb infra red and lower energy light?


texts: Performing a Redox Titration on a Vitamin C Sample Solution Containing Cellulase enzymes

texts:
I was wanting to performing an Iodometric Redox Titration on a Vitamin C sample solution created from allowing diced citrus fruits to sit in a water + cellulase solution. Because vitamin c is water soluble, the water +enzyme solution should possess a fair Ascorbic acid concentration, to which I planned a redox titration for its analysis.

This method determines the vitamin C concentration in a solution by a redox titration using iodine. Vitamin C, more properly called ascorbic acid, is an essential antioxidant needed by the human body (see additional notes). As the iodine is added during the titration, the ascorbic acid is oxidised to dehydroascorbic acid, while the iodine is reduced to iodide ions.
$$\ce{ascorbic acid + I2 -> 2I− + dehydroascorbic acid}$$
Due to this reaction, the iodine formed is immediately reduced to iodide as long as there is any ascorbic acid present. Once all the ascorbic acid has been oxidised, the excess iodine is free to react with the starch indicator, forming the blue-black starch-iodine complex. This is the endpoint of the titration.

Explanation taken from https://www.canterbury.ac.nz/media/documents/science-outreach/vitaminc_iodine.pdf.
I was wondering it the water + cellulase solution I’d be titrating on was viable for this way of determining Vitamin C. Will cellulase interfere with the reaction which governs this titration?


texts: Calculate the molar fraction of a mixture component given only its pressure

texts:
You have a mixture of $\ce{He, Ne, Ar}$ gases with a total pressure of $8.40$ atmospheres. $\ce{He}$ has a pressure of $1.50$ and $\ce{Ne}$ has $2.00$. What is the molar fraction of $\ce{Ar}$?

The molar fraction is

$$\frac{\text{moles of Ar}}{\text{total moles of mixture}}$$

However, to know the number of moles of any of these components, I need to know their mass in the mixture. How can I know if all I am given is their pressures?

The answer is $0.583$ and I am not sure how was this concluded. All I can tell is that $\ce{Ar}$ has a pressure of $4.9$ atmospheres by Dalton's law but that's it. By the same law I know that all gases there have the same temperature and volume, but since I don't know either value for any of them it isn't useful at all.


texts: Detecting the concentration of chlorpromazine

texts:
Is there a way to detect the concentration of chlorpromazine in a small sample ; ex: human saliva, using electro-chemical analysis? Does the sensor necessarily have to be a bulky piece of lab equipment or are there smaller sensors available for that kind of test?
Thanks in advance!


texts: Why do compounds with similar properties have different Stitch IDs?

texts:
I'm not from the Pharmacy or Chemistry background. I have been wondering why certain drug compounds have similar properties but each of them have different Stitch IDs in PubChem?

For example:

Stitch ID 9782 Betamethasone
Stitch ID 5743 Dexamethasone


texts:
I try to estimate whether particles form pairs or not.

What I know is the difference in the potential Energy $\Delta U_\mathrm{pot}$ which occurs when both particles form a pair.

When I have a system with $N$ particles, at constant volume and constant temperature the formation of pairs, should reduce the entropy of the system. So to see whether the pair formation occurs spontatnous I want to calculate the Gibbs Free Energy.

I assume that the particles behave like an ideal gas, but each particle consists of $n$ atoms has $(6n - 6)$ degrees of freedom.

The change in the gibbs free energy from system 1 ($N$ single particles, each consists of $n$ atoms) to system 2 (particles from $0.5N$ pairs, each pair consists of $2n$ atoms) I have:

\begin{equation}
\Delta G = \Delta U + V\Delta p - T\Delta S
\end{equation}

The internal energy I can calculate from the equipartition theorem:
\begin{align}
\Delta U &= U_2 - U_1\\
 &= U_{\mathrm{kin}, 2} - U_{\mathrm{kin}, 1} + \Delta U_\mathrm{pot}\\
 &= 0.5 N \cdot (6n - 3)kT - N \cdot (3n - 3)kT + \Delta U_\mathrm{pot}\\
 &= N(3n - 1.5)kT - N(3n - 3)kT + \Delta U_\mathrm{pot}\\
 &= 1.5 N kT + \Delta U_\mathrm{pot}
\end{align}

$V\Delta p$ I get from the ideal gas law
\begin{align}
V\Delta p &= \Delta N k T\\
V\Delta p &= 0.5 N k T
\end{align}

Now my problem is $T \Delta S$. All I find is the the Sackur–Tetrode equation
\begin{equation}
\frac{S}{kN} =  \ln\left(\frac{V}{N\Lambda^3}\right)+\frac{5}{2}
\end{equation}
which describes only the change the entropy of a monatomic ideal gas ($\Lambda$ is the thermal wavelength).

How can I calculate the entropy difference for the case of multiatomic ideal gas?


texts: How do I find the final concentration after an additional dilution?

texts:
I took poor notes and didn't record what the final concentration of an amylase solution I  made last year. I recorded that I took $\rm 0.2\ g/10\ ml$ of the amylase solution, and then took $\rm 1\ ml$  of that and diluted to $35 ml$.

How would I solve for the final concentration?

Would I use :

$$c_1\ V_1 = c_2\ V_2$$

$$\rm(0.2\ g/10ml) \cdot (1\ ml) = (\mathit{c_2}) * ( \mathrm{35\ ml})$$

$$c_2\rm = \frac{0.02\ g}{35\ ml} $$

Therefore, I would take $\rm 0.02 g$ of amalyase powder and add up to $\rm 35\ ml$  with distilled $\ce{H2O}$ to achieve the final concentration that I would have previously had after dilution?


texts: What are stereospecific and stereoselective reaction?

texts: I have read the defination but couldn't grasp the concept, what is the key factor that says this is stereospecific or this is stereoselective and what are the main intuitions i can get if i am given that a reaction is stereospecific or stereoselective.


texts:
Could any ingredients from this product be psychoactive in some people, if the are sensitive to them?
https://www.lush.co.uk/products/honey-i-washed-kids

I have found the product to be relaxing as advertised, but more so that I would expect from a nice scent alone.


texts: If -OMe has a small steric size then why does it increase the acidity of 2-methoxybenzoic acid?

texts:
I've read OP Tandon's book of GOC which states:

Acidity order of the below-mentioned structures is: ortho- > meta- > benzoic > para- and the reason for the highest acidity of ortho- being the "ortho effect".

If the methoxy group does not operate in the case of steric inhibition of protonation (SIP) due to its small steric size, then why does it affect the acidity of 2-methoxybenzoic acid?
A similar post (Basicity Alteration Due To Ortho Effect In Methoxy Aniline System) talks about the ortho effect in aniline systems, but that just supports the question that if the methoxy group in the ortho position isn't 'sterically bulky' enough to operate in the ortho effect, then how is it operating here, and increasing the acidity of ortho methoxy benzoic acid?


texts: Superscript and subscript together after the same atom

texts:
In the chemical formula of some ion compounds, there is the necessity to write the charge in the superscript and the numbers of atoms in the subscript, but together at the right of the same symbol like in the PO43− ion:

Does IUPAC provide universal guidelines saying that I have to typewrite the two numbers in a stacked or staggered way?


texts:
The IUPAC name of $\ce{(CH3)3C-CH2-CHI-CH3}$ should be 4-iodo-2,2-dimethylpentane as we consider iodine as a substituent, and we should start numbering from that carbon which is closest to the carbon with maximum number of substituents.
However, PubChem and Mol-Instincts state the IUPAC name of this compound as 2-iodo-4,4-dimethylpentane.
Why not start numbering from the left as there are two methyl group as substituents on the second carbon, and then count iodo on the fourth carbon as it has only one substituent in the form of iodine?


texts: Conversion of methylcyclopentanol to cyclopentanone

texts:
How to convert methylcyclopentanol to cyclopentanone?

I tried eliminating the alcohol group as $\ce{H2O},$ but that gives Saytzeff product. If only I can get the Hofmann product (methylene cyclopentane), I would subject it to ozonolysis and get cyclopentanone.

I don't know exactly what to use as the reagent to get that Hofmann product. Could there be other methods for the conversion?


texts: Concentration of sulfur in turbid solution

texts:
I recently participated in an experiment where I need to calculated the reaction orders and the reaction constant of the reaction:
$$\ce{8 Na2S2O3(aq) + 16 HCl(aq) -> S8(s) + 8 SO2(g) + 16 NaCl(aq) + 8 H2O(l)}$$
by measuring time until the solution becomes too turbid for light to travel through the fluid. Calculating the orders of reaction was possible using proportions of the known starting concentrations and time.
In order to calculate the reaction constant, I need to know a specific change in the concentration of the sulfur (I assumed that this is the element that makes the solution turbid), but I couldn't find any information on the internet. If there is no exact answer, what would be an acceptable estimate?
My data is: measured time until turbidity as a function of changing initial thiosulfat concntration (while initial HCl con. remains constant), and data with reversed roles for HCl and thiosulfat. Need to find the constant of reaction k.


texts: Would polyamide 6 filaments be effected by an acrylic micro emulsion?

texts:
I would like to hear more about: Will an acrylic micro emulsion applied to polyamide 6 filaments (that have been coated with PTFE) weaken the filaments?
Also would polyester filaments be effected?


texts: What happens when ferric chloride is dissolved in water?

texts:
Ferric chloride can be prepared by dissolving hematite in hydrochloric acid:

$$\ce{Fe2O3 + 6HCl -> 2FeCl3 + 3H2O }\tag{1}$$

But the resulting ferric chloride will be exposed from its formation to water.

After investigating a little, I found that anhydrous ferric chloride, when dissolved in water, hydrolysed and forms ferric hydroxide:

$$\ce{FeCl3 + 3H2O -> Fe(OH)3 + 3HCl }\tag{2}$$

But isn't it supposed that, when dissolved in water, hexahydrate is formed? What really happens, hydrolyses or hydrates?


texts: Why is sand/glass polar? How does lattice structure change polarity?

texts:
The molecular geometry of sand is linear. Dipole moment is thus cancelled.

But we all know from the meniscus water makes with glass that the dipole-dipole/H-O attraction  between sand and water is stronger than the hydrogen bond between water molecule. maybe I am wrong

My guess is either that electron lone pair makes it polar or the lattice structure does.


texts:
In the above reaction, I was told that the reason organocadmium reacts only with aryl chloride segment is because it is very less reactive and reacts only with most reactive sites. This was consistent with my previous beliefs that we always react most electrophilic and most nucleophilic reagents.

In this reaction also there are two electrophilic sites and I was expecting a major product from carbonyl site but opposite was true. The explanation was given that soft nucleophile prefers soft electrophiles while hard nucleophiles prefer hard electrophiles. The explanation seemed credible to me but contradictory to previous one.
Where am I going wrong?
I don't know if I have made my doubt clear enough. I am new to the community and any suggestions on improving the questions are welcome.


texts: Why hydrogen bonding in some acids make them a stronger acid when it is present even before deprotonation?

texts:
If we take the example of salicylic acid, hydrogen bonding is present in the acid as:

Even after deprotonation, it has intramolecular hydrogen bonding as:

My doubt:
p-hydroxybenzoic acid($\mathrm pK_\mathrm a = 4.54$) is less acidic than o-hydroxybenzoic acid($\mathrm pK_\mathrm a = 2.97$), the reason being hydrogen bonding in the latter after deprotonation.
If the same reason is accounted for the acidity of Salicylic acid (o-hydroxybenzoic acid) then why is the H-bonding before the deprotonation not considered (which should decrease the acidity of the compound)?


texts: Breaking of carbon chains due to annihilation of electrons using positron beams

texts:
I and my friends were taking part in a competition(physics and chem expertise needed) and we were having a few doubts about something. I was hoping if anyone of you can help in the clarification of the doubt.
We use a positron beam(from the DESY II particle accelerator) directed towards a polymer(eg polythene), which will annihilate a few valence electrons of the atoms in the chain. We’ve not found any source to support our theory that bonds will break although they should as electrons are being annihilated which support bonding. We searched and found nothing because no one else has had a similar experiment before.
We also wanted to know if we annihilate an inner core electron then will it lead the de-excitation of the valence electrons further leading to destabilization of bonds.
We can’t confirm how the electron donors will react with carbocations/radicals formed, also since there are many possibilities and we are unable to consider all of them.
The momentum of the positrons can be set to any value between 0.5 GeV/c and 6 GeV/c.
We needed some confirmation to the feasibility of the experiment.
All we need is to break the carbon chain, any other ways to do that would be appreciated.


texts: Are there materials permeable to oxygen and carbon dioxide but not nitrogen?

texts:
Are there materials permeable to $\ce{O2}$ and $\ce{CO2}$ but not $\ce{N2}$?

Would this even be possible in theory? Can it be done at even at pressures of 300 atm?


texts: Is sugar necessary for the sweetening effect of food?

texts: A lot of food packages, nowadays, are mentioning "0 g sugar" or "sugar free". Then how do those still taste sweet?


texts: Combustion and pyrolysis of sulfides and organosulfurs

texts:
Last week there was a huge fire in french chemical factory Lubrizol, we now know the main products that burnt, to simplify the discussion I extracted a few compounds:

isobutyl and isobutene polysulfide 500 tons,
dithiophosphoric acid and corresponding zinc salt (R = isopropyl) 200 tons,
various hydrocarbons (mainly mineral oil) 2000 tons
as well as  calcium sulfonate and calcium salt of methylphenol sulfide (100 tons), amides/esters of phosphoric acid, polymers, aromatic amines & alcohols, various reaction products of $\ce{P2S5}$ with isopropanol 400 tons

  What kind of sulfur compounds should we expect to be emitted from pyrolysis and combustion of such organosulfur compounds?

Note the authorities claim the smoke analysis didn't show any $\ce{H2S}$ and that the $\ce{SO2}$ level wasn't higher than everyday measurements in cities.

There is a paper on the pyrolysis of polyethylenesulfide showing cyclization leads to a bunch of products, I wonder if it is applicable here  (also I would like to know why no $\ce{H2S}$ is formed?)


texts: Entropy change of an ideal gas undergoing adiabatic expansion into vacuum

texts:
For the adiabatic expansion of an ideal gas into an empty chamber, I am told that the entropy change of the system is not zero, and that the entropy change of the surroundings is zero.

But if the expansion is adiabatic, then it should be isentropic, so should not the entropy change of the system be zero? And how can you infer anything about the change in the surroundings?


texts: Why are lithium (Z)-enolates more stereoselective than (E)-enolates in aldol reactions?

texts:
In aldol reactions, it is apparently a general rule of thumb that (Z)-enolates give higher stereoselectivity (for the syn aldol product) than (E)-enolates do for the anti product. Quoting Carey & Sundberg, Advanced Organic Chemistry: Part B (5th ed.), p 69:

  From these and many related examples the following generalizations can be made about kinetic stereoselection in aldol additions of lithium enolates.
  [...]
  (3) Z-Enolates are more stereoselective than E-enolates.

and the example given (taken from a Clayton Heathcock paper, J. Org. Chem. 1980, 45 (6), 1066–1081) is

Evans also mentions this in his paper comparing the Cornforth vs polar Felkin–Anh models (Angew. Chem. Int. Ed. 2003, 42 (15), 1761–1765):

  While Z and E lithium enolates are also formed with good configurational purity, the characteristic decline in syn/anti selectivity is observed, particularly with the E enolate.

Why is this the case? Or, why is $\Delta \Delta G^\ddagger$ for the (Z)-enolate larger (corresponding to greater selectivity) than for the (E)-enolate? I don't see anything that stands out when looking at the six-membered Zimmerman–Traxler transition states - within this model, the difference $\Delta \Delta G^\ddagger$ for both enolate geometries is simply the cost of putting a phenyl group axial instead of equatorial.


texts: Unable to find sources for uncommon specific heat

texts:
I'm calculating the energy, temperature, and gas volume outputs of gunpowder. To solve this I need to find the specific heat of Potassium sulfate (K2SO4) and Potassium carbonate (K2CO3). If anyone can refer me to any directory that can list the values for these it would be very helpful.

Thank you for your time.


texts: Deriving fluorescence intensity equations

texts:
I've been having trouble with deriving the equations in the following problem.

  The interaction between DNA and AO to form the AO–DNA complex can be expressed by the following reaction:

  $$\ce{AO + DNA <=> AO-DNA},$$

  whose equilibrium constant is
  $$K = \frac{\ce{[AO-DNA]}}{\ce{[AO][DNA]}}  \tag{1}$$

  Consider that initially there is only AO in the measuring cell displaying an emission at $\lambda_{em} = \pu{520 nm}$, and finally at equilibrium both AO and AO–DNA complex have emission at the same wavelength.

  Additionally, the binding equilibrium constant for AO intercalation to DNA (ignore AO self-aggregation and dimerization) can be determined from the equation:

  $$\frac{C_\ce{AO}}{ΔF} = \frac{1}{Δϕ}+\frac{1}{ΔϕK}\frac{1}{\ce{[DNA]}} \tag{2}$$

  $F - ϕ_\ce{AO} \cdot C_\ce{AO} = ΔF$, $F = ϕ_i \cdot C_i$, and $ϕ_\ce{AO} - ϕ_\ce{AO-DNA} = Δϕ$ is given.

  $F$ is the overall intensity, $ϕ$ is the fluorescence constant and $i$ denotes a particular component.

  1) Show that $ΔF = [\ce{AO-DNA}]Δϕ$

  2) Derive equation (2) starting from equation (1)

In terms of the first part, I tried working out formulas for both initial and final fluorescence intensities $F$ using $F = ϕ_i \cdot C_i$ but didn't really get anywhere after that. In terms of the second part, I tried substituting $ΔF = [\ce{AO-DNA}]Δϕ$ into the equilibrium equation but didn't really get further from that either. I would really like to get some tips on where to get started.


texts:
How are the number of tetrahedral voids twice the number of octahedral voids in a CCP structure? Is there some kind of mathematical proof for it? Is there some way I can understand this intuitively?

I have been trying to think about it using this picture but I cannot seem to get anywhere.


texts: What happens when 0.02 mole NaOH is added to a buffer solution?

texts:
I am asking this question for my son.

(This question is related but we still  have our confusions.)

We have one liter buffer solution of 4.74 pH which contains 0.1 mole $\ce{CH_3COOH}$ and
0.1 mole $\ce{CH_3COONa}$.

What will be the resulting pH when 0.02 mole $\ce{NaOH}$ is added to this solution? (Given $\ce{Ka} = 1.8 \times 10^{-5}$.)

As the definition of a buffer solution [A, B] goes, pH value should not change when small quantity of acid or base is added to it.

So, one way of answering the question  will be to simply comment that since
a small quantity of base has been added, the pH value will not change.

But, we find another solution (presented and accepted in some
moderately acceptable study-sheet) in the following line.

We will have a reaction like,

$\ce{CH_3COOH} + \ce{NaOH} = \ce{CH_3COONa} + \ce{H_2O}$

So, after the reaction, we have,

$\ce{CH_3COONa}$: $(0.1 + 0.02)\ \text{mole} = 0.12\ \text{mole}$

$\ce{CH_3COOH}$: $(0.1 - 0.02)\ \text{mole} = 0.08\ \text{mole}$

Now, $pH = pKa + \log{\text{[Salt]}\over\text{[Acid]}}$

Hence,
$pH = pKa + \log{{{n_\text{Salt}}\over V}
\over
{{n_\text{Acid}}\over V}}$

Which after plugging in the values gives,
$pH = 4.92$.

We are  confused about which of the above solutions is
correct.