texts: What is the purpose of tetrazole in oligonucleotide synthesis?

texts:
The ATDBio book on nucleic acids describes tetrazole as an activator required to couple nucleotides.

  The diisopropylamino group of the nucleoside phosphoramidite is protonated by the activator, and is thereby converted to a good leaving group. It is rapidly displaced by attack of the 5′-hydroxyl group of the support-bound nucleoside on its neighbouring phosphorus atom.

The first molecule in the scheme they provide is clearly already protonated; a second step in which the diisopropyl amino group is replaced by a tetrazole molecule is displayed.

What is the purpose of this step; why doesn't the support bound nucleotide attack the phosphorous, directly? Are the arguments purely kinetic (i.e. sterics and availability)?


texts: What exactly happens during dipole induction (dipole induced dipole forces)- if anyone can explain just why this happens?

texts: When a dipole is in vicinity of a polarisable molecule it induced a partial charge on the molecule by creating a dipole, is what I've been taught.I want to know whether the dipole formation of the other molecule is purely due to closeness to a dipole or there is something else too.


texts: Do you refer to a bonded atom as an "ion"?

texts: Take H2O, would you call the H a hydrogen ion? Or just a hydrogen atom?


texts: How to determine the angle between non-bonding electron pairs?

texts:
Is there a way to determine the angle between non-bonding electron pairs that aren't obvious? Take $\ce{H2S}$ for example:

The two non-bonding electron pairs would be at the yellow end of this molecule, but I am curious as to what the angle is between them? Is there even a way to tell?


texts: Can the thermodynamic predictions of redox reactions based on E and dG contradict each other?

texts:
I am referring to the following three reactions. Two of these reactions are imaginary ($\ce{M}$ and $\ce{X}$ are imaginary).

$$\begin{alignat}{3}
\ce{X- + 2e- \;&<=> X^3-} \qquad &&E^\circ_{\ce{X^3-}/\ce{X-}}=0.9\ \mathrm{V}\qquad &&&\text{(a)}\\
\ce{2H+ + MO^2+ + e- \;&<=> M^3+ + H2O} \qquad &&E^\circ_{\ce{MO^2+}/\ce{M^3+}}=0.5\ \mathrm{V} \qquad &&&\text{(b)}\\
\ce{8H+ + MnO4- + 5e- \;&<=> Mn^2+ + 4H2O} \qquad &&E^\circ_{\ce{MnO4-}/\ce{Mn^2+}}=1.5\ \mathrm{V} \qquad &&&\text{(c)}
\end{alignat}$$

Now consider the reaction between a solution having equimolar amounts of $\ce{M^3+}$ and $\ce{X^3-}$ and a $\ce{KMnO4}$ solution. (Note that all the species are in their respective standard states, so there is no need for Nernst equation.)

To find out possible reactions, following steps are taken.

Equations $\text{(a)}$ and $\text{(c)}$;

$$
\begin{align}
&{-}\text{(a)} \times 5 + \text{(c)} \times 2 : \\
\ce{&16H+ +5X^3- + 2MnO4- -> 2Mn^2+ + 5X- + 8H2O} \qquad E^\circ_1\qquad\text{(1)} \\ \\
&E^\circ_1 = 1.5\ \mathrm{V} + (-0.9\ \mathrm{V}) = 0.6\ \mathrm{V} \\
&\Delta G^\circ_1 = -nE^\circ_1F = -10 \times 0.6 \times F = -6F
\end{align}
$$

Equations $\text{(b)}$ and $\text{(c)}$;

$$
\begin{align}
&{-}\text{(b)} \times 5 + \text{(c)}: \\
\ce{&5M^3+ + H2O + MnO4- -> Mn^2+ + 5MO^2+ + 2H+} \qquad E^\circ_2 \qquad(2)\\ \\
&E^\circ_2 = 1.5\ \mathrm{V} + (-0.5\ \mathrm{V}) = 1.0\ \mathrm{V} \\
&\Delta G^\circ_2 = -nE^\circ_2F = -5 \times 1.0 \times F = -5F
\end{align}$$

My questions:

Are there any errors in above calculations? If so, please suggest corrections.
According to $E^\circ$ values, reaction $(2)$ is more feasible than reaction $(1)$. Am I correct?
According to $\Delta G^\circ$ values, reaction $(1)$ is more feasible than reaction $(2)$. Am I correct?
Is it useless to use $E$ values to predict the feasibilities of redox reactions? Should we always resort to $\Delta G$?
Is it possible for predictions based on $E$ values and $\Delta G$ values to contradict?
If not how can these results be explained?


texts: Why does delocalization (only) occur in molecules represented by resonance hybrids?

texts:
Before I start this question, I am aware tha

Electrons in all molecules are delocalized to some extent
Delocalization is a the phenomenon and resonance is an attempt to explain it.

When I asked this question from my professor, this is the explanation he gave me:

In VBT, it is difficult to approximate the molecular orbital with
localized bonding orbitals, so the electronic configuration is a
weighted average of the infinite possible electronic configurations
i.e Ψ= Aψ1 +Bψ2+Cψ3......
For most molecules, the most stable lewis structure has the majority
of the contribution and can sufficiently approximate the actual
electronic by itself. However, for some molecules, there are multiple
equally-stable lewis structures with an equal and significant
contribution and each of them has to be taken into account. For e.g,
for nitrate ion, Ψ=1/3 (ψ1 +ψ2 +ψ3)  where ψ1,2,3  represent the 3
equal lewis structures. As a result, the electrons MUST be delocalised
between the appropriate bonds

This explanation, in simple words, argues that  since the 3 lewis strucutes are identical/indistinguishable, the electron density must be equal and thus delocalised between the bonds by symmetry.
However, this doesn't really explain the physical reasoning behind delocalization. Why is (significant) delocalization more energetically stable for some molecules but not for others? And why dpes delocalization always occur in molecules with some kind of symmetry between the possible atoms for a double/triple bond?


texts: Why active mass of solids and pure liquids taken as unity

texts:
There is a similar question already asked here and answers provided say that activity of solid is taken as unity because their density dosn't changes... but I still have some doubts in it.
Suppose we have a solid for example $\ce{NH4Cl}$ which decomposes into gases $\ce{NH3}$ and $\ce{HCl}$ then $K_{\mathrm{eq}} = [\ce{NH3}][\ce{HCl}]$.
Now if we take in a container which initially has no $\ce{HCl}$ and $\ce{NH3}$ and put some amount of $\ce{NH4Cl}_\mathrm{(s)}$ in it then after some time it will achieve equilibrium. Let the amount of solid left be $x$ mol. In equilibrium the  rate of production of $\ce{NH4Cl}$ is equal to the rate of its decomposition.
Question:
Now if we add another $x$ mol of $\ce{NH4Cl}_\mathrm{(s)}$ in the container then the rate of production of $\ce{NH3}$ and $\ce{HCl}$ should be double and hence would exceed the rate of production of $\ce{NH4Cl}_\mathrm{(s)}$ which will alter the equilibrium but the equilibrium constant equation predicts this would not be the case. Where is the mistake?


texts:
I am chemical engineering and i care my nutrition and health. in my opinion, it is so important that what we drink or eat daily.
 Respectfully, I have a question about alkaline ionized water bottle, Which is sold commercially. I have some information about production of electrolyzed water technology. as i study in some articles, hard water (water with minerals such as calcium bicarbonate) electrolyzed in a electrolysis cell and Hydroxide is produced. As i knew, calcium and magnesium hydroxide are insoluble in water. But we don't see any white residue in commercial alkaline ionized water bottle. These particles (as an alkaline agents) are probably filtered, my question is " if calcium and magnesium hydroxide are filtered, why this water have pH 9 or high??"
thank you
I'd be happy and it is my pleasure if you tell me this.


texts: Volatile and non-volatile solutes in solution

texts:
What is the difference between having a volatile versus a non-volatile solute at the boiling point of the solution?
I have been getting mixed answers online concerning the differences outlined above. This is what I have gathered so far:

A non-volatile solute does not produce vapour at the boiling point of the solution.
A volatile solute does produce vapour at the boiling point of the solution.

Can someone confirm these definitions?


texts: How to calculate to actual calcium content in a pudding mix

texts: How can I determine the calcium (Ca2+ ion) content in pudding mix given the amount of milk, number of servings made with one package, the percent of recommended daily dose of calcium per serving, and the recommended daily dose of calcium?


texts: Can one figure out an optical absorption spectrum from EPR data?

texts:
I'm wondering if it's worthwhile for me as an optical spectroscopist to read up a bit on EPR. Do EPR signals reveal where, in terms of wavelength, features in the optical spectrum can be expected to appear? I know it tells me
lifetimes of states, but that's about as far as I have dug into it. I have some EPR data on a substance and I wish to figure out where to look for it's absorption with UV/Vis/NIR means.


texts: What is the difference, if there is, between this two distillation methods?

texts:
Reading about water vapor distillation, I found two differents approaches:

Direct one
Indirect one.

The first has an arrange like:

Here the chamber contains water and the plant. It is cooled and as the water vapor flows away it carries the low volatile compound vapor of the plant/vegetable. Both condense and the oils can be obtained.

The vegetal is on the same pot as water.

The second one:

Here the water vapor is generated on a first po (the blue one) and when flowing through the balloon, it carries the oil vapor. I should remark: the vegetal is on a different pot than water.

Question

Do you see any fundamental difference on the process or something related?

It might has to do with the aggregation state of the material we need to extract, but I'm not sure.


texts: Trying to understand the causes and implications of kinks in fatty acid chains

texts:
I watched this video (The Deal with Fat by SciShow):

https://www.youtube.com/watch?v=mvvx2yQRbzQ

To summarize the main points I want to discuss:

Saturated fats are chains without any double-bonds and tend to result in solid structures because they stack well.
Unsaturated fats have at least one double-bond between carbon atoms, resulting in fewer overall hydrogens. This either results in a kink (cis structure) or a straight lockout (trans) depending on whether the hydrogens around the double bond are on the same side or not.
Kinked fats are harder to stack into lattices so they tend to be liquid, so most unsaturated fats are liquid.

My questions:

I thought there were some trans fats that were healthy / naturally occurring, such as those from certain meat products. What's the difference between the healthy natural trans fats and the trans fats made from partially hydrogenated oils and such?
What exactly causes the kink? Hydrogen atoms repelling each other?
If the hydrogens are repelling each other, then how do the chains even "stack" well in the first place if they are straight? Why wouldn't they all repel each other and remain liquid?
Why do unsaturated fats, which have one double bond and tend to be kinked, straighten out and result in solids when chilled?


texts: Why is there no salt bridge for hydrogen–silver bromide cell?

texts:
What is the reason there is no salt bridge for this cell?
$$\ce{Pt(s) | H2(g) | HBr(aq) | AgBr(s) | Ag(s)}$$


texts: What is the substance turning salty water green when electrolysed?

texts:
I am a student and I take O.L. Chemistry, in my knowledge I know if I electrolysed concentrated aqueous NaCl solution I should get Hydrogen evolved at the cathode and chlorine at the anode.

I did an experiment, I add a lot of table slat to tap water to get the electrolyte ready (aq. NaCl) then I used graphite electrodes (just got it from a mechanical pencil) and passed electricity through the salty water. I used of course direct current using a 6 Volts battery I got.

Well my suggestions were half correct, Hydrogen really evolved and bubbled violently at the cathode, but at anode I didn't see any yellowish green gas indicating presence of chlorine, yet only colorless bubbles continue to evolve from the anode but was less violently than the cathode. I thought this is Oxygen evolving so I increased the concentration of solution by adding table salt but also only colorless bubbles evolves at the anode. Well I didn't really calculated how much precisely I should add salt but I added insanely a lot of table salt.

Only to discover after around 5 minutes of electrolyzing the salty water, it became darkish green in color, I didn't really knew what is this and this is my question, I used graphite electrodes so those doesn't react like if I used iron, the solution was just nice tap water and not really bad or muddy. My only suggestion is that this is actually chlorine dissolved in water ... So is this correct ?? I knew that chlorine is soulable in water but I didn't thought it will turn the whole water greenish in color....

Can anyone help me in that ? And please if you're going to answer me, answer me as if I am somebody who knows nothing in chimestry .....

Thanks in advance.


texts:
I am wondering whether Fe(II) hydrated to an octahedral complex would undergo a Jahn-Teller distortion.

As far as I am aware, this distortion comes about because of asymmetry in filling orbitals, in this case the t2g and/or eg orbitals.

I am also aware that the distortion is most obvious for asymmetry in the eg  orbitals because these interact most with the ligands.

However, I deduced the configuration t2g4, eg2 for [Fe(H2O)6]2+, which has no asymmetry in eg but does in t2g.

My question is can it distort because of this asymmetry? Would it be possible that promotion to an excited state takes place for the distortion to then be possible, with an overall stabilising effect?


texts:
NaHCO3(aq) + H3C6H5O7(aq) = H2O(l) + CO2(g) + NaC6H5O7(aq)
9 NaHCO3(aq) + 8 H3C6H5O7(aq) = 14 H2O(l) + 3 CO2(g) + 9 NaC6H5O7(aq)

List at least 2 types of reactions that the equation in question #2 can be categorized as?
If 0.950 grams of citric acid  (C6H8O7) reacts
How many moles of sodium bicarbonate will be consumed
How many moles of carbon dioxide will be generated
How many grams of carbon dioxide will be generated

One type of reaction is combustion  What would be the second?

Convert grams to moles
.950 g  citric acid x (1 mole/ 192.123 grams C6H8O7) = .005 moles of  C6H8O7

how many moles of sodium bicarbonate will be consumed
 .005 moles of  C6H8O7 x (9 moles NaHCO3/1 mole of C6H8O7) = .045 moles of NaHCO3

how many moles of carbon dioxide will be generated
 .005 moles of  C6H8O7 x (14 moles H2O/1 mole of C6H8O7) = .07 moles of H2O

how many grams of carbon dioxide will be generated
.07 moles of H2O x (18.015 grams of H2O/1mole H2O) = 1.261 grams of H2O


texts:
Pyrite ($\ce{FeS2}$) forms cubic crystals, like these ones:

I know that the crystal structure is primitive cubic, but I don’t see how cubic structure on the molecular level translates to cubic structure on much larger scales. If you are given some number of cubes, there are many different ways to assemble the cubes face to face, and only one of these ways is to create a large cube. So why is it that the pyrite in this rock forms nearly perfect cubes?


texts: Working out energies of hydrogen bonds by comparing chemical potential of vapour and condensed phase - equation derivation

texts:
I want to ask a question about working out the energy of a hydrogen bond between two water molecules, $w_{AA}$ using the chemical potentials of vapour and condensed phases.
I was reading K. Dill, Molecular Driving Forces, 2nd Ed, 2011, p. 257 which lines out the framework for the Clapeyron equation and I was confused on the following:
The book states that you can calculate $w_{AA}$ using the following formula, which is derived by calculating the chemical potentials of the vapour $\mu_v$ and $\mu_c$ respectively:
$$\mu_v = kT\ln\left(\frac{p}{p_{int}^{*}}\right) $$
where $\mu_v$ is the chemical potential of a a pure substance in the liquid phase, $p$ is the partial pressure of the vapour phase and $p_{int}^*$ is the standard vapour pressure
The chemical potential of the condensed phase, $\mu_c$ is achieved by differentiation of the Helmholtz equation, with the knowledge that the $TS$ term of $U-TS$ is set to $0$ since a pure liquid's molecules are indistinguishable upon interchange.
$$\mu_c = \left(\frac{\partial F}{\partial N}\right)_{T,V} = \frac{zw_{AA}}{2}$$
where $z$ is the number of neighbours of each molecule in the liquid phase, $w_{AA}$ is the bonding interaction between two molecules, and divided by 2 to account for any double counting.
Using $\mu_A = \mu_B$, both terms can be equated:
$$kT\ln\left(\frac{p}{p_{int}^{*}}\right) = \frac{zw_{AA}}{2}$$
and more simply written as
$$\ln\left(\frac{p}{p_{int}^{*}}\right) = \frac{zw_{AA}}{2kT}$$
and for those interested, this can be expressed as:
$$p=p_{int}^*e^{\frac{zw_{AA}}{2kT}}$$
Now, I was presented with the following question from the book:

Given that water’s vapor pressure is $1 \ atm$ at $T = 100^{\circ}$ and $0.03 \ atm$ at $T = 25^{\circ}C$, find the value of $zw_{AA}$.

This all makes sense.
However, Dill states the following

Take the logarithm of the equation to get the boiling pressure $p_1$ at temperature $T_1$
as $$\ln\left(\frac{p_1}{p_{int}^{*}}\right) = \frac{zw_{AA}}{RT_1}$$
and the boiling pressure $p_2$ at temperature $T_2$ as $$\ln\left(\frac{p_2}{p_{int}^{*}}\right) = \frac{zw_{AA}}{RT_2}$$  Subtract the second equation from the first to get $$\ln\left(\frac{p_2}{p_1}\right) = \frac{zw_{AA}}{2R}\left(\frac{1}{T_2} - \frac{1}{T_1}\right)$$ neglecting the small temperature dependence on $p_{int}^*$.

However, I'm not sure whether this derivation is correct. Below shows my working out from the second equation stated from the start of the body:
First of all, they transformed
$$\ln\left(\frac{p}{p_{int}^{*}}\right) = \frac{zw_{AA}}{2kT}$$
to
$$\ln\left(\frac{p_1}{p_{int}^{*}}\right) = \frac{zw_{AA}}{RT_1}$$
and somehow stated the relationship between the gas constant $R$ and $k$ is $R = 2k$ which doesn't make sense.
Also, the denominator term containing the $2$ disappears in both of their initial statements for $T_1$ and $T_2$ e.g. $\ln\left(\frac{p_1}{p_{int}^{*}}\right) = \frac{zw_{AA}}{RT_1}$, yet it returns in the final equation $\ln\left(\frac{p_2}{p_1}\right) = \frac{zw_{AA}}{2R}\left(\frac{1}{T_2} - \frac{1}{T_1}\right)$ and I can't see that from the following working that I did to prove this equation does not work (taking $R = 2k$ to be true):
$$\ln\left(\frac{p_1}{p_{int}^{*}}\right) = \frac{zw_{AA}}{RT_1}, \ln\left(\frac{p_2}{p_{int}^{*}}\right) = \frac{zw_{AA}}{RT_2}$$
Subtracting the second equation from the first:
$$\ln\frac{P_1}{P_2} = \frac{zw_{AA}}{RT_1} - \frac{zw_{AA}}{RT_2} = \frac{zw_{AA}}{R}\left(\frac{1}{T_1} - \frac{1}{T_2}\right)$$
which does not compare with the derived result.
My question is therefore two-fold:

How has Dill interchanged $R$ and $k$ in his solution?
Is there an error in his derivation for his final expression.

The solution (as transcribed above) is also attached as a screenshot for illustration (for illustrative purposes only):


texts: How can I find the ratio of molecular masses using the ideal gas equation?

texts:
A person evacuated a cylinder and filled in $4~\mathrm{g}$ of gas A at $25~\mathrm{^\circ C}$. Pressure was found to be $1~\mathrm{atm}$. Another person filled another $8~\mathrm{g}$ of gas B in the cylinder at the same temperature. The final pressure was found to be $1.5~\mathrm{atm}$. What is the ratio of molecular masses of A and B (assuming ideal gas behaviour)?

I tried to do it this way:

Taking the molecular mass of A as $x\ \mathrm{g}$ and that of B as $y\ \mathrm{g}$, I formed the respective ideal gas equations but the required terms ($x$ and $y$) just cancelled out.

$$N(a) = 4/x ;\quad N (b) = 8/y$$
So$$V (a) = \frac{4 \times  22.4}{x};\quad     V (b) = \frac{8 \times  22.4}{y}$$

So, ideal gas equation for A:
$$1 X \frac{4 \times 22.4}{x} = \frac {4 \times  R  \times  25} x$$
Here $x$ cancels out. Similarly $y$ cancels out in its equation.
This is the problem I am facing.

Another thing I want to know is that the total pressure (i.e $1.5~\mathrm{atm}$), will that be the sum of the individual pressures of gases A and B?


texts: Are there any reducing agents for reduction of nitrobenzene to aniline other than Sn/HCl?

texts: I was taught that Sn/HCl should be used for reduction of nitrobenzene to aniline. Can I ask if there are any alternative reducing agents (for example, LiAlH4?) to do the same task?


texts: How can change in Gibbs free energy ever be positive?

texts:
I have a question regarding this formula for Gibbs free energy of a system: $$\Delta G=\Delta H-T\,\Delta S$$
According to the second law of thermodynamics: $T\,\Delta S\ge\Delta Q$ and to my understanding, $\Delta H$ is just the same as $\Delta Q$.
Now, if $\Delta Q$ will be always smaller than (or equal to) $T\,\Delta S$ and $\Delta H=\Delta Q$, then looking at the first formula again it seems that $\Delta G$ can only be smaller than (or equal to) zero.
What am I doing wrong here?


texts: Dehydration of carboxylic acids using P2O5

texts: Why isn’t concentrated $\ce{H2SO4}$ used for the dehydration of carboxylic acids to anhydrides? What is special about $\ce{P2O5}$?


texts: Which of these reduction reagents would me most appropriate to yield this product?

texts: I am very confused, I think using reduction would be a good start, but LiAl would go straight to an OH.


texts: Molecular differences in the HB graphite hardness scale

texts: Today, I bought some graphite for my pencil. It is rated HB on the HB graphite scale, a measurement of the hardness of graphite. My question is how can there be different hardnesses of the same substance? Is there a difference between 4B graphite and 6H graphite on the molecular level? Are the different hardnesses not all arranged in the large, hexagonal carbon sheets that I had thought all graphite existed?


texts: Why doesn't phosphorus form as many oxides as nitrogen?

texts:
Nitrogen has oxides like $\ce{N2O}$, $\ce{NO}$, $\ce{NO2}$, $\ce{N2O3}$, $\ce{N2O5}$, but as far as I know, phosphorus has probably only $\ce{P2O3}$ and $\ce{P2O5}$.
Why does nitrogen have so many oxides in the first place?
Also why doesn't phosphorus have the analogous oxides?


texts: Why is phenol a solid at room temperature?

texts:
The commonly cited reason is inter-molecular hydrogen bonding. But won't the hydrogen bonding in phenol be weaker than that of most alcohols because of resonance-effect? And yet, alcohols with stronger hydrogen bonding (such as ethanol, propanol, etc.) aren't solids at room temperature.

Also, if the reason behind its state is it's molecular weight, then why is benzyl alcohol a liquid at room temperature? The hydrogen bonding in benzyl alcohol is stronger (less resonance-effect) and its molecular weight is also higher.


texts: How to make an aluminumoxide coating on an electrode?

texts:
The Questions is above.
I am not a chemist but that is what I know:

Aluminum has an Oxide Layer normally
Aluminum-Oxide Layer can be broken down with NaOH
Zink coatings are done by galvanic coating using a certain voltage

Another way to ask: Can I do this with Aluminum?


texts: Does specific heat capacity of the container have an effect on the exactitude of a calorimetre?

texts:
I'm doing a lab on what is the best material for a calorimetre. I chose glass, aluminum, styrofoam cup, paper/cardboard cup and a plastic cup. I've found that the cardboard cup was the best followed by the styrofoam cup. I thought at first it was related to the specific heat capacity of the calorimetre itself, as those values lined up with the results I got from my experiment.

However recently I've been wondering if the specific heat capacity would really have an effect on the exactitude of the results? Should I base myself more on the thermal conductivity values of the materials even though there doesn't seem to be a correlation between those values and those I got from my experiment?


texts:
The Wikipedia article on heat of combustion says:

  The calorific value [...] may be expressed with the quantities:

  energy/mole of fuel
  energy/mass of fuel
  energy/volume of the fuel

Is the energy obtained by the combustion mainly proportional to the mass of the gas, being then values in $\pu{J/mol}$ and $\pu{J/kg}$ a characteristic of the gas composition and basically independent of the pressure and temperature?

That is, for a specific gas, values in $\pu{J/mol}$ and $\pu{J/kg}$ will be mainly independent of the pressure/temperature of the gas in combustion, while value in $\pu{J/m^3}$ will be strongly dependent due to the relation between volume, pressure and mass.

In the latter case, given the heating value, $f_0$ (in $\pu{J/m^3}$) for a gas at $\pu{°C}$ and pressure $p_0 = \pu{101 kPa} = \pu{1 atm}$, we could (?) find new heating value $f$ (in $\pu{J/m^3}$) at some other temperature $t$ (in $\pu{°C}$) and pressure $p$ (in $\pu{Pa}$) applying the expression:
$$f = f' \frac{p}{p_0} \frac{273}{273+t}$$


texts:
When determining the formula of manganese (IV) oxide, since it’s made up of $\ce{Mn^4+}$ and $\ce{O^2-}$ ions, why is the formula $\ce{MnO2}$ and not $\ce{Mn2O4}$?

Any help would be greatly appreciated


texts: Why is the bond angle of N-N-N in hydrogen azide not 180 degrees?

texts:
Chen and Wang (2009) have reported an $\ce {N-N-N}$ bond angle in the hydrazoic acid molecule of $171.5$ degrees using B3LYP/6-311G** model. The wikipedia page for the molecule also reports a similar bond angle of $171$ degrees. However, this seems to go against predictions by VSEPR theory for the case of two regions of electron density (which gives a bond angle prediction of $180$ degrees). It is known that VSEPR theory is limited in its theoretical predictions. However, I would like to understand what accounts for the discrepancy in the two.

Reference

Chen, F., & Wang, F. (2009). Electronic Structure of the Azide Group in 3′-Azido-3′- deoxythymidine (AZT) Compared to Small Azide Compounds. Molecules, 14, 2656-2668. doi:10.3390/molecules14072656


texts: Why Inorganic chemistry reaction mechanisms are hard to find?

texts:
My textbook Chemistry Part 1,as in the attached photo states that[after the KClO3 reaction]
“This reaction which apparently seems to be of the tenth order is actually a second order reaction. This shows that it takes place in several steps.” If that is so, then as stated above it, all higher order inorganic chemistry reactions must have some sort of mechanism. But it is really hard to find the mechanisms(many a times one cannot find them). Why is that so??.


texts: Why do molecules have to have a change in dipole moment in order for them to be IR active?

texts:
My chemistry textbook keeps saying that in order for a molecule to be able to absorb infrared radiation, it has to have a change in dipole moment when the bond vibrates.

I don't understand why that is. Some clarification would be appreciated.


texts:
In general, I have come across a phenomenon in chemistry where solutions to certain types of problems can often seem frustrating when trying to work out by hand, as they seem to depend on each other far too much, but are actually easily representable formally using a linear relation.

In general, I have noticed that when I am trying combinations of things to see if it works that these relations appear.

For example, balancing an equation:
$$
\ce{C3H8 + O2 -> CO2 + H2O}
$$

$$
\left[
\begin{array}{c|ccc|c}
 & \ce{C3H8} & \ce{O2} & \ce{CO2} & \ce{H2O}\\
\hline
\ce{C} & 3 & 0 & -1 & 0  \\
\ce{H} & 8 & 0 &  0 & -2 \\
\ce{O} & 0 & 2 & -2 & -1 \\
\end{array}
\right]
$$

Row reducing the matrix gives a solution vector of
$$
\left[
\begin{array}{c|c}
\ce{C3H8} & -1/4\\
\ce{O2} & -5/4\\
\ce{CO2} & -3/4 \\
\end{array}
\right]
$$

$\ce{H2O}$ has an implied coefficient of $-1$, so in order to make the coefficients integers, we will multiply everything by $-4$, and get
$$
\ce{1C3H8 + 5O2 -> 3CO2 + 4H2O}
$$
which is correctly balanced. There is no guesswork in doing this.

Similarly, problems involving Hess's law can be solved using linear combinations:
$$
\begin{array}{cccc}
\ce{CH4_{(g)} + 2O2_{(g)} -> CO2_{(g)} + 2H2O_{(l)}} & {\Delta}\ce{H} = & \pu{-890 kJ mol^{-1}} & (1)\\
\ce{2CO_{(g)} + O2_{(g)} -> 2CO_{(g)}} & {\Delta}\ce{H} = & \pu{-566 kJ mol^{-1}} & (2) \\
\ce{2CH4_{(g)} + 3O2_{(g)} -> 2CO_{(g)} + 4H2O_{(l)}} & {\Delta}\ce{H} = & x\; \pu{kJ mol^{-1}} & (3)
\end{array}
$$

$$
\left[
\begin{array}{c|cc|c}
& \pu{1} & \pu{2} & \pu{3} \\
\hline
\ce{CH4_{(g)}} & -1 & 0 & -2\\
\ce{O2_{(g)}} & -2 & -1 & -3\\
\ce{CO2_{(g)}} & +1 & +2 & 0\\
\ce{H2O_{(l)}} & +2 & 0 & +4\\
\ce{CO_{(g)}} & 0 & -2 & +2
\end{array}
\right]
$$
Row reducing the matrix gives a solution vector of
$$
\left[
\begin{array}{c|c}
\pu{1} & +2\\
\pu{2} & -1\\
\end{array}
\right]
$$
The dot product with the original enthalpy vector then becomes the desired enthalpy of change, $x$:
$$
x =
\left[
\begin{array}{c}
+2 \\ -1
\end{array}
\right]
\left[
\begin{array}{cc}
-890 & -566
\end{array}
\right]
= \pu{-1214 kJ mol^{-1}}.
$$
Again, there is no guesswork. A computer could do this.

Is there a similar linear relation possible for expressing the possible number(s) of bonding electrons for each atom in a Lewis structure? (By possible number, I mean that it follows the octet rule if applicable, or in the case of hydrogen only forms a single bond.)

If so, how could it be set up?


texts: What is the specification of Martensite (displacive) transformation in ceramics comparing to the metals? I just know about Martensite transformation in metals. For example, these transformations are thermal and diffusionless. Also, the kinetic and morphology are dominant by strain energy.


texts: How do foundries prevent zinc from boiling away when alloyed with Aluminum?

texts: How do foundries prevent lower boiling point metals such as zinc from boiling away when alloyed in a furnace with higher boiling point metals such as aluminum?


texts: In which nucleophilic aromatic substitution rate is faster m-fluoronitrobenzene or p-fluoronitrobenzene?

texts: In which nucleophilic aromatic substitution rate is faster: m-fluoronitrobenzene or p-fluoronitrobenzene?


texts: In a saturated solution, why is there ongoing dissolution and crystallisation?

texts:
I was studying equilibrium, and had this question..

In a saturated solution with sugar dissolved, why is there a constant process of dissolving and crystallising? What I mean by this is, why don't the already dissolved sugar just stay that way, and the excess undissolved sugar stay that way? As I thought this would seem easier, and neater (?), wouldn't it??

Is it because the undissolved sugar is still in water, and that means it will want to dissolve, but since the solvent has reached maximum amount of solutes it has to kick some sugar out and hence there is a process of crystalisation??

I am sorry for a rather stupid question... But any explanation is much, much appreciated...


texts:
$\ce{Cl2}$ bond energy given is as 244.

1/2 $\ce{Cl2}$ will still be 244 or 244/2? My teacher said it is still 244.


texts: Emission Spectrum of Hydrogen and Helium?

texts: Why do hydrogen and helium have different emission spectra? I thought that emission spectra were the result of electrons 'jumping' from one energy level to the next - since hydrogen and helium both have electrons on n=1, l=0 and only there, why are their emission spectra different?


texts: Electrochemical manufacturing of small metal components

texts:
Metal crystals easily can be grown via electrochemical pathways. Copper is a great example of this. I recently had an idea of growing those crystals in controlled ways (i.e.: surrounding the electrode on which the crystallization occurs with a "mold" of the desired shape with holes in it) but these crystals are tending to grow towards the another electrode in the shortest way possible. Let's say that I would like to grow a copper tetrahedron on a triangular copper plate surrounded by plastic sheets which are controlling the crystal growth.

  The problems which I came across:
     1. How should I arrange my equipment to get the crystals fill the mold?
     2. Shold I worry of liquids being trapped in the crystal?


texts: Getting the pressure using the equation of states - will the answer be the same?

texts: When I get the pressure using the different equations of state (e.g. van der Waals, Redlich-Kwong, etc.), will the answer still be the same?


texts: If 2 electrons undergo destructive interference (as they show wave nature)  will they disappear or will they have no wave nature left?


texts: How can I decrease the Krafft temperature of an hexadecyl sulfate surfactant?

texts:
I need to prepare an anionic surfactant from a treatment of cetyl alcohol (hexadecanol) and $\ce{H2SO4}$, and then neutralize it using $\ce{NaOH}$ or $\ce{NH3}$; but sodium hexadecyl sulfate has a standard Krafft temperature of around 45 degrees Celsius, which is too high for our purposes.

Is it possible to reduce the Krafft temperature to room temperature by adding electrolytes, solvents or modifying counter-ions?


texts: Why does the anode solution contain Sn2+ in a Sn-Cu voltaic cell?

texts:
Suppose you have the following voltaic cell: $\ce{Sn_{(s)}|Sn^{2+}_{(aq, 1.0 M)}||Cu^{2+}_{(aq, 1.0 M)}|Cu_{(s)}}$ and the salt bridge is $\ce{KNO_3}$. What I don't understand is why you need to have $\ce{Sn^{2+}}$ ions initially in the $\ce{Sn}$ half cell. As $\ce{Sn}$ is oxidized, electrons are supposed to travel through the wire connecting the two half cells and reduce the $\ce{Cu^{2+}}$ ions in solution, but if we have $\ce{Sn^{2+}}$ ions initially in the $\ce{Sn}$ half cell, the electrons might just as well reduce the $\ce{Sn^{2+}}$ ions. Why would the electrons travel all the way through the wire when there is $\ce{Sn^{2+}}$ ions right next to them that could be reduced?

I also don't understand why the $\ce{Cu}$ cathode has to exist. All we need is $\ce{Cu^{2+}}$ ions in solution that will be reduced, so why can't we just dip the wire directly into $\ce{Cu^{2+}}$ solutions. As the reaction proceeds, a $\ce{Cu}$ cathode will be created anyways as $\ce{Cu}$ metal precipitates on the wire.

I am obviously misunderstanding something, because according to my understanding the following voltaic cell should work: In one half cell, we have a $\ce{Sn}$ anode in water connected to a wire. The wire is submersed in the other half cell which is simply $\ce{Cu^{2+}}$ solution. The $\ce{Sn}$ gets oxidized and produces $\ce{Sn^{2+}}$ ions in the water. The electrons travel through the wire and reduce the $\ce{Cu^{2+}}$ ions in the cathode solution. The anode solution will become more positive and the cathode solution will become more negative, so we still need a salt bridge.


texts: Please explain the mechanism of Cannizzaro's reaction

texts:
I did not completely understand the mechanism of Cannizzaro's reaction, especially the rate determining step i.e. the hydride transfer step, and the effect of electron withdrawing substituents on this step.
Like, I was taught that the intermediate which donates hydride, would donate hydride more readily when electron donating substituents were attached to carbon atom with the outgoing hydrogen atom, as they would increase electron density on that carbon, and therefore create a "pushing" effect on the outgoing hydride. But in all the questions I have attempted, the answer says that electron WITHDRAWING substituents facilitate hydride transfer.
Please tell how the electron withdrawing substituents affect the hydride transfer, and why. Also, please explain how to determine the products of a crossed Cannizzaro's reaction. Do we determine them using the concepts of the RDS,or otherwise?


texts: How to dissolve a spider with household chemicals?

texts:
Somehow a spider got into the little window that shows the water level on my electric kettle. The kettle doesn't come apart very easily, and it looks like I can't get this part off without breaking it.

I'd hate buying a  new kettle just because of a little spider but, I also don't want spider juices with my coffee.

Would bleach/some other household chemical dissolve the spider? Is there some other methodology you can recommend?


texts: Rhombohedral second-order Jahn–Teller effect in Au(II) complex?

texts:
I was recently listening to a talk about the following work[1] when the author mentioned that they explained the following. In this $\ce{Au(II)}$-porphyrin complex you observe two sets of $\ce{Au-N}$ bond lenghts. Meaning that there is some sort of distortion in the square plane. They explained it with a second order Jahn–Teller effect that would lead to a rhombohedral distortion.

So I started to think about that situation a bit more. Second-order JT effects are of course favored in heavy metals where the relativistic effects cause the $\mathrm{6s}$ orbital and the $\mathrm{5d}$ orbitals to come closer together in energy. But I always assumed that second order Jahn–Teller required two paired electrons. Nevermind, I'm still thinking about how this would look like. I assume, as it is a regular $\ce{d^9}$-system in a square plane geometry it will start from the tetrahedron with a strong first-order JT distortion to raise the $\mathrm{B_{1g}}$ orbital high enough that it can interact with the $\mathrm{6s}$ orbital.

But when I look for square plane distortions what comes up is a paper on rectangular and rhombohedral distortions on molecules. They say the new point group was $D_\mathrm{2h}$ but I cannnot find any $\mathrm{d}_{x^2-y^2}$ in this character table. And furthermore, at least to what I see what will happen in these non transition-metal complexes is a splitting of the two-fold degenerate low-lying orbitals.

I'm not really good with group theory or orbital interactions but would mixing the $\mathrm{d}_{x^2-y^2}$ orbital with the higher s-orbital according to second order Jahn–Teller cause a rhombohedral distortion?

Preiß, S.; Melomedov, J.; Wünsche von Leupoldt, A.; Heinze, K. Gold(III) tetraarylporphyrin amino acid derivatives: ligand or metal centred redox chemistry?. Chem. Sci. 2016, 7 (1), 596–610. DOI: 10.1039/C5SC03429A.


texts:
My book defines the basicity of the acid as the number of $\ce{H^+}$ ions furnished by one mole of the acid in solution. Well, I know that $\ce{B(OH)_3}$ is a weak Lewis acid and it accepts an $\ce{OH^-}$ to form an anion - thereby increasing the net $\ce{H^+}$ concentration in the solution.

So, what should exactly be its basicity? Should I just assume its basicity to be one as well - although it doesn't satisfy the definition?


texts: Why do Grignard reagents add to propargyl alcohols?

texts:
In Phil Baran's lectures on heterocyclic chemistry at Scripps, one of the lecture problems is concerned with this synthesis of Vioxx:

The first step supposedly involves an anti addition of the aryl Grignard reagent to the propargyl alcohol:

and this intermediate is trapped with $\ce{CO2}$ to form a lactone (a butenolide in this case), and mCPBA oxidises the sulfide to a sulfone.

Why does the aryl Grignard add to the alkyne in this case? I would expect it to deprotonate the alcohol, and it does seem to do so, but as far as I know, Grignards don't usually add to alkynes which aren't conjugated to electron-withdrawing groups. Why is this propargyl alcohol special?

On top of that, what is the rationale for the selectivity observed (both regio- and stereoselectivity)?


texts: How to calculate the pH of the neutralisation of HCN with excess of KOH?

texts:
Write the reaction between $\pu{0.05 mol}$ $\ce{HCN (aq)}$ and  $\pu{0.08 mol}$ $\ce{KOH (aq)}$ with $V = \pu{500 mL}$ and then calculate the pH.

So I wrote the reaction:
$$\ce{HCN (aq) + KOH (aq) <=> KCN (aq) + H2O}$$

Begin:
\begin{align}
  n_\mathrm{begin}(\ce{HCN}) &= \pu{0.05 mol}\\
  n_\mathrm{begin}(\ce{KOH}) &= \pu{0.08 mol}\\
  n_\mathrm{begin}(\ce{KCN}) &= -\\
  n_\mathrm{begin}(\ce{H2O}) &= -\\
\end{align}

End:
\begin{align}
  n_\mathrm{end}(\ce{HCN}) &= -\\
  n_\mathrm{end}(\ce{KOH}) &= \pu{0.08 mol} - \pu{0.05 mol} = \pu{0.03 mol}\\
  n_\mathrm{end}(\ce{KCN}) &= \pu{0.05 mol}\\
  n_\mathrm{end}(\ce{H2O}) &= \pu{0.05 mol}\\
\end{align}

The product of the reaction is a salt of a strong base ($\ce{CN-}$) completely dissociated in water:
$$\ce{KCN (aq) -> K+ (aq) + CN- (aq)}$$

And
$$\ce{CN- (aq) + H2O -> HCN (aq) + OH- (aq)}$$

Knowing this I calculated the
$$[\ce{KCN}] = \frac{\pu{0.05 mol}}{\pu{0.5 L}} = \pu{0.1 M};$$

Then I used the equation:
$$[\ce{OH-}]_1 = \sqrt{\frac{K_\mathrm{w}}{K_\mathrm{a}} \cdot [\ce{KCN}]} = \pu{1.27x10^-3 M}$$

Since I still have some $\ce{KOH}$, it dissociates completely creating $\ce{OH-}$ ions, so:
\begin{align}
  [\ce{OH-}]_2 &= [\ce{KOH}]\\
  [\ce{OH-}]_2 &= \frac{\pu{0.03 mol}}{\pu{0.5 L}} = \pu{0.06 M}
\end{align}

Finally
\begin{align}
[\ce{OH-}] &= [\ce{OH-}]_1 + [\ce{OH-}]_2 \\
&= \pu{1.27x10^-3 M} + \pu{0.06 M} = \pu{0.06127 M}\\
\ce{pOH} &= -\log[\ce{OH-}] = -\log(0.0617) = 1.213\\
\ce{pH} &= 14 - \ce{pOH} = 12.787\\
\end{align}

Is it right to calculate the $[\ce{OH-}]$ in this way?

I based my calcualtions on this equation:
Knowing that the amounts of substance in moles are defined by $Z = Z_1 + Z_2$ in $K$ liters of solution, we can consider this concentration to be
$$[X] = \frac{Z}{K} = \frac{Z_1 + Z_2}{K} = \frac{Z_1}{K} + \frac{Z_2}{K} = [X_1] + [X_2]$$


texts: Can recent developments improve the total synthesis of B-12?

texts:
The  total synthesis  of vitamin B-12 by Robert Burns Woodward and Albert Eschenmoser, is over 30 years old. At its time, it was considered a landmark in the field.

  With current developments (e.g. olefin metathesis, palladium catalysis, etc.) is it possible to optimize this synthesis?

By "optimize" I mean reduce the number of steps in the synthesis.


texts: Why does Chem3D minimize nitrogen dioxide (radical) so badly?

texts: I build from text O-N+O (the SMILES of this is O=[N+][O-]), I delete the hydrogen atom added automatically on N, then I start MM2 Minimization. Both the bond length and the angle differ from what I see in the top right image here: https://en.wikipedia.org/wiki/Nitrogen_dioxide


texts: How can I tell if a liquid is (not) emitting light?

texts:
I found an image of Nuka Cola Quantim, a soft drink from the Fallout video game series, which depicts the bottle as glowing, but it doesn't feel quite real:

Then I also saw this video of a chemiluminescent reaction of luminol:

https://youtu.be/TJj7t2mrpxc

Experienced chemists and/or photo editors might tell right away which is real and which is fake. What hints should I look for when determining if a liquid itself is glowing or is being lit by a different light source?


texts: Number of collisions of particles in a box (or a sphere)

texts:
Scenario

Imagine you randomly spread in a cubic space of volume $m^3$ (or in a sphere of volume $V_s$, as you prefer), $n_A$ particles $A$ and $n_B$ particles $B$. Particles $A$ are spheres of volume $V_A$ and are not moving. Particles $B$ have no volume (they are points) and are moving linearly (reflecting at the boundaries of the space (cube or sphere)) at a constant speed $s$.

We can assume that when a particle $B$ meet a particle $A$ (collision), we count a collision but the particle $B$ just go through the particle $A$. Whatever is the model that is easier to calculate.

Question

What function describes the probability that there is $x$ collisions in a time interval $\Delta t$. Or what is the expected the number of collisions?


texts: How to construct a QST2 input file for Gaussian16 for multiple reactants and products?

texts:
I am attempting to determine the transition state structure for the following reaction using the QST2 method on Gaussian 16:

$$\ce{CH3 + N -> HCN + H2 }$$

However, I am struggling to put together my input file. How do I format my z-matrices for multiple reactants and products? Here is what I have so far (though it is not running successfully):

%chk=sample2.chk
%mem=1500MB

#T UB3LYP/6-31G** opt=(qst2, redundant)

CH3 + N -> HCN + H2 reactants

0 3
C
X 1 1.0
H 1 r 2 90.0
H 1 r 2 90.0 3 120.0
H 1 r 2 90.0 3 -120.0

r 1.0828

CH3 + N -> HCN + H2 reactants

0 3
N

CH3 + N -> HCN + H2  products

0 1
C
X 1 1.0
H 1 rh 2 90.0
N 1 rn 2 90.0 3 180.0

rh 1.0587
rn 1.1326

0 1
H
H 1 r

r 0.741

I'm pretty new to this type of calculation on Gaussian so any help would be much appreciated!


texts: Find volume of ammonia gas required to prepare a solution of given pH

texts:
Calculate the volume of gaseous ammonia $(K_\mathrm{b} = \pu{1.8E-5})$ to dissolve (at NTP) in $\pu{100 mL}$ of water in order to obtain a solution with $\mathrm{pH} = 11.0.$ Consider volume variation negligible.

I started by evaluating molar concentration of $\ce{NH4+}$ and $\ce{OH-}$ knowing the $\mathrm{pH},$ then I used the $K_\mathrm{b}$ inverse formula to evaluate the molar concentration of ammonia. These are the results:
$$c(\ce{NH3}) = \pu{0.056 mol L-1}$$
$$c(\ce{NH4+}) = c(\ce{OH-}) = \pu{1E-3 mol L-1}$$
Then my idea was to work with water. Since $\ce{NH3}$ is a weak base it does not dissociate completely, the amount of water is
$$n(\ce{H2O}) = \frac{\pu{100 g}}{\pu{18.02 g mol-1}} = \pu{5.55 mol}$$
Then I run out of ideas. I tried to find the mamount of ammonia (but I think the result was not correct) by evaluating the degree of dissociation, but then I got lost.
The final result of the problem is $\pu{0.13 L}.$ How do I pursue the problem further?


texts: I have to find the decreasing order of dipole moment of $\ce{CHCl3}$, $\ce{CH3Cl}$, $\ce{CH2Cl2}$, and $\ce{CCl4}$. Now I know that in $\ce{CCl4}$ there will be no dipole moment. Now to compare the other three compounds I don't have logical reasoning to compare the dipole moments but I have the data to compare but in the examination we won't be having these data so I was looking for any logical reasoning to compare the dipole moments of the remaining three compounds. Thank you


texts: What is the significance of the kink in the [A] vs T graph for a 2nd order reaction?

texts:
The 2nd order graph shows a bit of a kink, whereas the 1st order graph is smooth.

What is the significance of this kink, and why does it appear in only the 2nd order graph.
What is the significance of the numerical value at this kink? The graph below show it occurs at $[A]=1.5-2$.


texts:
Define the Curtin-Hammet principle and use it to predict the expected trans/cis product ratio in the following example:

       PhCH2CH(Ph)OCOR    strong base     PhCH=CHPh
                              100C

This part-Q (12-marks) did not include any numerical data. The student is, presumably, required to derive the Curtin-Hammet equation; which, establishes the trans/cis product proportions in terms of their respective transition-state (free energies of activation) energies. But without numerical data how is the trans/cis ratio to be determined?

It may be interesting to note that stilbene, in uv light, undergoes a cis-trans isomerism-equilibrium. So, given such circumstances, the trans/cis ratio must be 50:50? Such a convenient short-cut may not have been required; nor, would it earn the 12-marks.


texts: Searching for low cost alternative for zirconia ceramic crown

texts:
I have seen one company call as you have seen below:

Call for "Development of Zircon Alternative Formulations in Ceramic Tile Glazing Industry"

So I have searched for finding the low-cost alternative for zirconia crowns by these terms:

diy ceramic crown
low-cost dental crowns

So as dental industry is more sophisticated on the ceramic and crown I searched the tooth crown and seen this result :

All-resin dental crowns are the least expensive compared to the other types of crowns listed. However, they can wear down more quickly and fracture more easily than the crowns made of porcelain and metal. For these reasons, resin crowns are rarely a long-term solution and are usually a temporary stand-in.

And found some alternative like porcelain, so I tried to find out how could create one resin crown (Do It Yourself).
So I want to find out some table or comparison, between the :

cost
strength
lifetime

Of the zirconia, porcelain and resin crown with laboratory instruments or if possible as Do It Yourself (DIY) projects.
Thanks.


texts: Reason of dissociation of water molecule in electrolysis

texts:
$\ce{H2O}$ molecule is dissociated into $\ce{OH-}$ and $\ce{H+}$ ions on reduction at the cathode in electrolysis. But what happens at the atomic level to $\ce{H2O}$ that proton and hydroxide ions get separated after gaining electrons from cathode? What really happens when water molecule gains electrons from cathode?

$$\ce{2H2O(l) + 2 e- ->  H2(g) + 2 OH-(aq)}$$


texts: How fast does the diamond lose the atoms at sunlight?

texts: recently I've read that the diamonds lose their atoms at sunlight on the surface. Would you be able to explain me how fast is the rate of this process? Does the diamond lose the atoms each time when is exposured at sunlgiht? Thank you. :)


texts: Does mercury have an NFPA 704 classification?

texts:
I've searched on a lot of websites if elemental mercury (Hg) has an NFPA classification but I can't find any.

Does mercury have an NFPA classification?


texts: Criterion for gravimetric analysis of silver

texts:
If the only criterion for gravimetric analysis of silver is solubility of  precipitate, which one of the following two compound are we supposed to choose? $K_\mathrm{s}(\ce{AgCl}) = \pu{1.78E-10}$ and $K_\mathrm{s}(\ce{Ag2CO3}) = \pu{8.13E-12}.$
a) $\ce{AgCl}$
b) $\ce{Ag2CO3}$
c) both of them are suitable
d) none of them

As I learned from textbook, one of the criteria for choosing the right one is: $K_\mathrm{s} < 10^{-7}$—thus I eliminate option d.
I also read that it is meaningless to compare the solubilities of two salts having different formulas on the basis of their $K_\mathrm{s}$ values. Therefore, I would choose option c—both have $K_\mathrm{s} < 10^{-7}.$ But from experience I found out that $\ce{AgCl}$ is used way more often—but that is probability because of other criteria—which I do not have to bear in mind in this question.
Is my reasoning correct?


texts: I have a solid mixture of trans-cinnamic acid and menthol. I’m new to this organic chemistry business and I don’t know if I can react the acid directly out of the solid mixture with a basic solution or if I need to dissolve them both into a nonpolar solvent first. Probably a dumb question but thanks anyway


texts: When there is an increase in temperature, how is the pH of the ocean affected? (Question is related to ocean acidification)

texts:
This is my current understanding:
Ocean acidification is the result of atmospheric $\ce{CO2}$  dissolving in the ocean's water. When this occurs the $\mathrm{pH}$ of the ocean decreases (from the increase in $\ce{H3O+}$ ions produced from the dissociation of $\ce{H2CO3}$).
When there is an increase in temperature, the solubility of carbon dioxide decreases which results in a lower concentration of carbonic acid (the formation of carbonic acid is from the reaction of $\ce{CO2}$ with $\ce{H2O}$ which is exothermic, so the reverse reaction is favoured).
So since the concentration of carbonic acid is lower, the concentration of $\ce{H3O+}$ ions decreases (lower concentration of acid dissociates in the water).
Therefore, the $\mathrm{pH}$ of the ocean increases as there are fewer $\ce{H3O+}$ ions present in the water.

Is my understanding correct, or have I made a mistake in my explanation?
If you can help me out I would be very grateful :)


texts:
Do conjugated double bonds take priority over a +1 formal charge?

The first one is what I solved for (ignore the hexagon that has no double bonds attached to it), and the one below it is the answer from the solutions.

Why did they move the conjugated bonds around first? This ends up causing the formal charge to move in the opposite direction than mine. Does it matter for this problem?


texts: What is the highest relative abundance for diatomic bromine?

texts:
I was introduced to this thing today, and saw a graph showing the detection of ions with different relative abundances.

Just as an example here, $\ce{Br2}$ is shown a detection chart. And at $160~\mathrm{m/z}$ the ion has the highest relative abundance, but why? Since the $\mathrm{m/z}$ ratio is just the mass, for $\mathrm{z}$ is always $+1$, the one which is supposed to have the highest peak should be at $162$?


texts: Counterintuitive Reaction of Aluminium On Steel Balls

texts:
There is a certain video which I just watched about 2 large cast iron balls. If the balls are struck together, no reaction happens, but if one is covered in aluminium foil and then struck, a large quantity of sparks are produced. This flies in the face of my metalworking experiences with these metals. When cut, steel reacts with oxygen in the atmosphere producing large quantities of sparks, but aluminium will not produce any sparks, despite being cut with an abrasive wheel or grinded with an abrasive wheel.

So why does the aluminium spark when the balls are grinded together? Could the temperature be higher forming a reaction with oxygen? Is there pure aluminium in the center of the foil which does not have the typical Alumina composition on the exterior and is being exposed to the atmosphere and is being oxidized?

Video: (CrazyRussianHacker): https://www.youtube.com/watch?v=w7yWoO7vqvI


texts: Why does sunlight cause plastics to become a faded blue color?

texts:
Due to the UV absorption, I knew that the plastics can be easily affected, especially PP. But is it normal that the change is always into faded blue from white color? and Why?

Because I made an experiments, but the results made me surprised. One sample of opaque white PP material was put on sunlight, one sample of same material having same conditions was put in lightproof black color bags. Then measurements was conducted every hour till 8 hours by using spectrophotometry which works in CIE Lab color space.

According to the results, b-value of sample exposed to sunlight had changed into the minus value, describing blue color in L a b color space, while L- and a-values are relatively stable. The b-value of another sample in lightproof bags had changed into the plus value, describing the yellow color in L a b color space, while L- and a-values are again relatively stable. So we can see that the effect of sunlight is only on b- value, which describes the values of blueness and yellowness of the sample.

My question is that what is the phenomena behind this?

What do you mean by reflected and transmitted lights? Even looked with naked eyes, easily seen that it becomes slightly faded blue color. The object is opaque white color PP material.


texts: Why is the boiling point of stibane higher than that of ammonia?

texts:
I recently came across the fact that the boiling point of $\ce{SbH3}$ (stibane) is greater than that of $\ce{NH3}$ (ammonia). I was expecting $\ce{NH3}$ to have a greater boiling point as a consequence of intermolecular hydrogen bonding. I understand that as molecular mass increases, van der Waals interactions between molecules also increase, but believing that hydrogen bonding will be a more dominant factor than van der Waals interactions, I expected $\ce{NH3}$ to have a greater boiling point.

Now, I already know that:

$\ce{NH3}$ and $\ce{SbH3}$ are gases at room temperature.
Gases including $\ce{NH3}$ do not showing hydrogen bonding in gaseous phase, which I also don't understand why.

But I want to know:

Why does $\ce{NH3}$ have a lower boiling point than $\ce{SbH3}$ even though it shows hydrogen bonding?
Why does $\ce{NH3}$ not show hydrogen bonding in gaseous phase?


texts: Same Activation Energy for Forward and Backward Reactions

texts: While reading about equilibrium, I read that the equilibrium constant, $K_\mathrm{c}$, changes with temperature due to the forward and backward reactions having different activation energies. Is it possible for a reaction to have the same activation energy for the forward and backward reactions, such that $K_\mathrm{c}$ does not change when temperature changes? If so, please provide an example.


texts: How does cotton and polyester come together during the production process to produce clothing items? Also, why is it cheaper to have cotton and polyester in a clothing item versus clothing that is made of just 100% cotton?


texts: How to balance the redox reaction between bismuth(III) sulfide and nitrate anion?

texts:
I have to solve the following redox reaction which occurs in an acidic environment, using the half-equation method.

$$\ce {Bi2S3_{(s)} + NO3-_{(aq)} -> BiO3-_{(aq)} + SO4^2-_{(aq)} + NO_{(g)}}$$

There seems to be a lot elements that change their oxidation numbers, except for oxygen:

$\ce{Bi}$ from $\ce{+III}$ to $\ce{+V}$
$\ce{S}$ from $\ce{-II}$ to $\ce{+VI}$
$\ce{N}$ from $\ce{+V}$ to $\ce{+II}$

What should I begin with? How would one go about grouping three redox pairs?


texts: Do any substances in a liquid state work as well as water to put out fires?

texts: Is there a liquid substance or compound that works as well to put out fire as water does?


texts: Why does the degree of polymerisation remain the same throughout chain-growth polymerisation?

texts:
It is known that the degree of polymerisation, which is the average number of monomer units in each polymer chain formed, increases as the reaction proceeds for step-growth polymerisation as longer and longer chains are formed throughout the reaction. However, the degree of polymerisation supposedly remains approximately the same through the reaction for chain-growth polymerisation. Why is this the case? Shouldn't the degree of polymerisation also increase throughout the reaction?

More interestingly, it is also mentioned in Introduction to Polymer Chemistry (3rd ed.) that:

  Also, unlike the stepwise process, average chain length decreases with increase in reaction temperature.

If this is the case, wouldn't the degree of polymerisation decrease as reaction proceeds?

I was thinking, could it be because in the chain-growth process, polymer chains of roughly the same length are formed as the reaction proceeds. For example, at the start, a chain is initiated and the chain propagates until the number of monomer units it contains is $\ce {100}$. Once it has reached this length, the chain terminates. As the reaction proceeds, more chains are initiated but all of which terminate when the chain length is about $\ce {100}$ monomers. Is this what actually happens?

Reference

Carraher Jr., C. E. (2003). Introduction to Polymer Chemistry (3rd ed.). CRC Press


texts: Dissolving to Create a Solution with Ethanol

texts:
If at 95% Ethanol can dissolve chemical X at 1mg/1mL then theoretically if you have 500mg of chemical X you can dissolve it in 500mL of $\ce{EtOH}$ to get 1mg/mL correct?

My question is, if you have 75.5% $\ce{EtOH}$ for example in a 750mL solution - how many mL will you need to create the 1 mg/mL concentration of quantity of 500mg chemical X?

Is it just 19.5% more of the 500mL volume or do you have to figure out the molarity of each and then go from there?


texts: Neutral anions in salts and strong acids are similar - is it a coincidence?

texts:
Recently I was studying salts and my professor provided a list of anions which are considered neutral in salts (that is, they do not change the $\mathrm{pH}$ of an aqueous solution when added as a salt): $\ce{Cl-}$, $\ce{Br-}$, $\ce{I-}$, $\ce{NO_3^-}$, $\ce{ClO_4^-}$.

Now I'm looking at this and I realized the list seems to be almost identical to a list of strong acids: $\ce{HCl}$, $\ce{HBr}$, $\ce{HI}$, $\ce{HNO_3}$, $\ce{HClO_4}$, $\ce{H_2SO_4}$.

Is this a coincidence? If it's not, what's the reason, and why is $\ce{SO_4^2-}$ not on the list of neutral ions?


texts: Comparing heat of hydrogenation per mole of butenes and 1,3-butadiene

texts:
The question asks us to select the compound with the smallest heat of hydrogenation per mole out of the following:

a) 1-butene

b) trans-2-butene

c) cis-2-butene

d) 1,3-butadiene

Since all four compounds form the same product (butane), a comparison without actual data should be possible. 1,3-butadiene is conjugated so it is the most stable compound and therefore its heat of hydrogenation should be the smallest.

But it requires 2 moles of hydrogen for complete conversion to butane. And the answer is actually trans-2-butene.

So would we consider each heat of hydrogenation "per mole of hydrogen" or "per mole of the given compound"? The question isn't clear about this and also, if we do consider it as "per mole of hydrogen" then is it correct to simply half the value heat of hydrogenation for 2 moles?


texts: Why is the Ag+ concentration in a beaker fixed in the reaction between excess AgCl (s) and KI (aq) from the start?

texts:
This arises as a sub-question for the following question: Calculate the concentration of I- in a solution obtained by mixing 0.10 M KI with an excess of AgCl(s).
I tried to look at How does addition of AgCl affect concentration of iodide in KI solution?, but it didn't answer my question which I detailed below.
My textbook says to solve it in the following way:
1) Ignore the 0.10 M KI since it doesn't matter.
2) Since you have excess AgCl(s), you can calculate the Ag+ concentration using its sp.
sp=1.77×10−10=^2
=1.3×10^−5
This is the Ag+ concentration
3) Substitute calculated Ag+ concentration into equilibrium for sp of AgI.
sp=8.51×10^−17=[Ag+][I−]
8.51×10^−17=[1.3×10^−5][I−]
[I−]=6.4×10^−12
My confusion arises due to step 3. Why can you assume that the Ag+ concentration is fixed and substitute the concentration into the sp for AgI? Why would you need not create an ice table for the sp of AgI where the first calculated Ag+ concentration is the "initial" condition? For example, this is what I mean: I inserted a picture of an ICE Table that I would think to use, but the textbook thinks otherwise. I'm confused why I'm wrong. Thank you!!


texts: What role does sulfuric acid play in the titration of oxalic acid and potassium permanganate?

texts:
The titration is between oxalic acid and potassium permanganate, with $\ce{H2SO4}$ added to oxalic acid. My question is what role other than a dehydrating agent and maybe catalysing does the $\ce{H2SO4}$ play in this titration.

The question came to me while reading a book (Advanced Chemistry by Philip Matthews - Cambridge university press), I was reading about titrations and this question came to me, but it isn't mentioned in the book.


texts:
The following reaction has been troubling me for a while now.

Since peroxides won't give the anti-Markovnikov product when used with HCl, I cannot think of any reagents that would result in the product shown in the image above. There doesn't seem to be any Wagner–Meerwein rearrangement either. This left me wondering, what reagent(s) should be used to form the product shown above.


texts: Why does oxygen form a double bond in $\ce{O2}$ but sulfur, also from group 16, forms single bonds in $\ce{S8}$?


texts:
Is there any difference between electronegativities of isotopes of the same element. For example consider the above compound. Will all the resonance structures be equivalent?

Also if I place the above compound in water (which will act as a Bronsted acid), which carbon will get the H atom?


texts: How to calculate the concentration of all relevant species in a buffer of a given pH?

texts:
You prepare $1.0~\mathrm{L}$ of a $0.25~\mathrm{M}$ acetic acid solution with a final $\ce{pH}$ of $6.0$. What are the molar concentrations of all relevant acetic acid species ($[\ce{HA}]$ and $[\ce{A-}]$) given that the $K_a$ for acetic acid is $1.74 \cdot 10^{-5}~\mathrm{M}$?

I am getting confused with this problem.

Since the $\ce{pH}$ is given, I know what the $[\ce{H^+}]$ is.
So now when I try to do the ICE table

$$
\begin{array}{l|ccc}
               & \ce{HA} &  \ce{H+}  &  \ce{A-} \\\hline
\text{Initial} & 0.25    &  0        &  0       \\
\text{Change}  &  -x     &  +x       &  +x      \\
\text{End}     & 0.25 -x &  +x       & +x       \\\hline
\end{array}$$

And from here I begin to assume $[\ce{H^+}] = [\ce{A^-}]$, which I am not sure about.
Then I set $x = 10^{-6.0} = 1\cdot 10^{-6}$ so I get $[\ce{A^-}] = 1\cdot 10^{-6}~\mathrm{M}$ and $[\ce{HA}] = 0.24999~\mathrm{M}$ which I think is incorrect, and to even further ensure my that it's incorrect, when I attempt to check the $K_a$ value with this, it does not match.

My second approach:
$[\ce{HA}] = 0.25~\mathrm{M}$

In this I determine the $\mathrm{p}K_a$ from the $K_a$ which turns out to be $4.759$, which indicates that there should be more $[\ce{A-}]$ than $[\ce{HA}]$.

I now use the Henderson–Hasselbalch equation:
\begin{align}
    6.0   &= 4.759 + \log\left(\frac{[\ce{A-}]}{[\ce{HA}]}\right)\\
   17.40  &= \frac{[\ce{A-}]}{[\ce{HA}]}\\
   17.40  &= \frac{[\ce{A^-}]}{0.25~\mathrm{M}}\\
[\ce{A-}] &= 4.35~\mathrm{M}\\
\end{align}

I feel more confident about my second answer.

Can someone please help me out with this particular problem and perhaps tell me procedure I should use as well as what the correct answer should come out to be and why?


texts: How to remove CH3 labels from a molecule's image? [OpenBabel in Python]

texts:
I would like to remove CH3 labels from svg images generated in openbabel in Python.
I am thinking I should use obConversion.SetOptions("w",openbabel.OBConversion.OUTOPTIONS) and replace "w" with another character. This does not work. Do you have any ideas? The image is below, for reference.


texts: why does phosphorus makes 5 bonds with oxygen in P4O10 whereas 3 bonds in P4O6?

texts: how phosphorus forms 2 types of bonds with oxygen i.e. 5 in $\ce{P4O10}$ and 3 in $\ce{P4O6}$ when only three are needed to complete its octet?


texts: How can I separate the vinegar from a 5% white vinegar to make a more concentrated solution.

texts:
I was under the impression that if I put a semi full bottle of vinegar in the freezer the water would freeze but the vinegar would not until a lower temp.  Therefore I could remove the bottle after the water freezes and pour off the vinegar. Apparently the water and vinegar doesn't separate nicely before freezing so this didn't work so well.

I've seen boiling suggested but I'm afraid I'll lose some of the vinegar in the process.

What is the simplest way to concentrate the vinegar at home?


texts: Mendeleev accurately predicted the properties of gallium(eka aluminium). In his justification of properties he says(according to image given) the melting point of the element would be low. What could have been his insight considering the fact that melting points of  aluminium and indium are 660.3°C and 156.6°C respectively?


texts: Solubility of Potassium Dichromate in Water

texts:
According to Wikipedia, the solubility of Potassium Dichromate increases very significantly with the temperature.

At 20°C, 13g/100ml, and at 100°C, 104g/100ml.

Therefore, it should be possible to dissolve about 520g of potassium dichromate in 500 ml of boiling water, but only about 65g in the same water, but at room temperature.

Today, I acquired about one kg of technical potassium dichromate and tried recrystallizing it, by weighing 507g of raw dichromate and dissolving it in about 500ml of water, room temperature. I expected it to no dissolve fully until the water was heated to boiling.

However, as soon as the water got slightly warm (45°C-50°C) everything dissolved. I added more raw material, and it kept dissolving until in the end everything (~970g) was added and dissolved before reaching boiling temperature.

Now, it is very slowly cooling down, and at about 35°C I seeded some small crystals and they're growing.

What went wrong in my calculations of the solubility? Anything I should've considered and missed?

Thanks.

PS.: Things I've already considered and ruled out:
Crystallization water: As far as I reseached, potassium dichromate doesn't have crystallization water, unlike, for example, copper (II) sulphate.
High humidity: My raw material was a free flowing powder, < 1mm particle size, uniformly deep orange colored. Had I high humidity, it'd clumping and not free flowing.
Contamination with potassium chromate, sodium chromate: Any of those wouldn't be soluble enough to explain what I observed.


texts: Can H+ ion exist independently since it does need to form any bonds.Why do we say that it needs to be in H30+ ion form?


texts: What are the strategies to deal with fluorescence from oil in Raman Spectroscopy?

texts:
I have a sample (for the purpose of this question let's call this Sample A) consisting of oil (edible olive oil) mixed with a contaminant (Contaminant B) from the Polycyclic Aromatic Hydrocarbons family.

I have tested pure forms of Contaminant B with gold nanoparticles and I am able to see great signals. (Surface Enhanced Raman Spectroscopy)

When I try to perform SERS on Sample A I notice that the peaks are suddenly gone. I suspect the following:

The signals from the PAH is being shadowed by the fluorescence of
the oil
The signals from the PAH is being absorbed by the oil
molecules, leaving no observable peaks
The oil molecules is
preventing the PAH molecules from being in close physical proximity
to the gold nanoparticles for SERS's enhancement

Question ONE: Which of these is true?

Question TWO: How can I solve this problem?
I can only think of:

Photobleaching (not really practical for the purpose of my paper)
Chromatography on Sample A (tried Acetone and Methanol but to no avail)
Adding an agent that could eliminate fluorescence from the oil molecules (I have no idea what could achieve this)
Adding an agent to digest or destroy the oil in Sample A leaving just the PAH in the remaining solution (again, no idea what this could be)


texts: Ratio of conjugate bases of a tricarboxylic acid

texts:
A tricarboxylic acid $\ce{H3A}$ has three different types of $\text{p}K_\text{a}$ $(\text{p}K_\text{a, 1} =2.0,$ $\text{p}K_\text{a, 2}=5.0,$ $\text{p}K_\text{a, 3}=8.0)$.

Identify the ratio of the three charged components($\ce{H2A-}$,$\ce{HA^{2-}}$ and $\ce{A^{3-}}$) in $0.2 ~\text{M}$ solution of tricarboxylic acid $\ce{H3A}$.

$\pu{0.55 M}$ of the strong base $\ce{NaOH}$ is added into a solution of $\pu{0.20 M}$ tricarboxylic acid $(\ce{H3A})$. Calculate the final pH. (Assume that the addition of $\ce{NaOH}$ will not influence the volume of the solution.)

I managed to get $\pu{0.04 M/L}$ for the $\ce{H2A-}$ species but I do not know how to find the concentration of the acids.


texts: Is there a polar liquid with a high electrolysis potential?

texts:
I'm trying to use $\ce{Na2SO4}$ for intercalation of sulfate ions in van der Waals stacked materials (as anodes). With water as the solvent, there is some indication of hydroxyl radical forming due to the applied potential being larger than the standard potential of water electrolysis (1.23 V).

I am aware that hydroxyl scavengers such as ascorbic acid can be used to, well, scavenge hydroxyls. Yet I'm wondering if there is a solvent for $\ce{Na2SO4}$ that would only decompose at a higher potential difference.


texts: Why does covalent bonding not break down if observer effect can be applied to atomic electrons?

texts:
The observer effect in quantum mechanics states that when unobserved, quantum particles such as electrons can simultaneously occupy two different states. In an atom of any element, where there are electrons around the nucleus, this effect is hinted at in some publications:

Electrons can occupy several energy levels, or orbitals, simultaneously. (Scientific American.(2012, October 9). Bringing Schrödinger's Cat to Life. Retrieved from https://www.scientificamerican.com/article/bringing-schrodingers-quantum-cat-to-life/.)

This idea is so weird. It is equivalent of saying that when unobserved, all the electrons of an atom can both be in their normal configuration and be in a totally different configuration. Only the act of observation forces the electrons into their normal configuration. Take the example of neon atom. According to the observer effect, when unobserved, its electron configuration can both be 1s4 2s3 2p3 (one of many possible alternative configurations) and 1s2 2s2 2p6. Only when observed will the electron configuration collapse into its normal version of 1s2 2s2 2p6.
I don't know if this understanding of observer effect on atomic electrons is valid. If it is, there are at least two serious problems. First, the Pauli exclusion principle will break down, because the alternative electron configuration allows more than 2 electrons in the same orbital (specified by the principal quantum number, the angular momentum quantum number, and the magnetic quantum number). Second, the foundation of covalent bonding is that when two or more atoms pool together electrons in orbitals that overlap, the total energy of the system is reduced to the minimum. If the observer effect on atomic electrons is valid, the energy required to maintain the system may get even lower than that in covalent bonding, and then covalent bonding will break down. All that's needed is for each atom to achieve an alternative electron configuration.

Thanks, everybody. I now understand this question better. Yes, the observer effect does apply to atomic electrons by allowing each of them to occupy several orbitals, subshells, or even shells at the same time. However, if we look at all the electrons and summarize their states into an electron configuration scheme, the scheme will still be the same as that obtained through the aufbau principle.


texts:
I have been reading VOGEL'S qualitative analysis and I came across the reagent Yellow ammonium sulphide. It's written here that it is used to distinguish Group 2B elements. But my question is that how will addition of H2so4 affect YAS itself?

Answer given is that it turns the cloudless solution into white /yellow but how does it exactly do this ?what is the reaction?


texts: Methodology and basis set for study in UV-Vis

texts:
I am currently working with a system of 30 atoms of a organic molecule. I need to make a study related to determine the UV-Vis graphic as precisely as possible.

I am using DFT method. However, I am having trouble to find a methodology and basis set to obtain a proper result of the experiment.

Does anybody know what methodology and basis set I should use?

P.S: I have already tried B3LYP with 6-31G(d), 6-31G(d,p) and 6-311++G(2d, 2p) in sequence but the results weren't good.


texts:
In the book "Organic Chemistry" by Morrison and Boyd,It is written that

  Sodium borohydride cannot reduce weaker electrophiles like esters though Lithium aluminum  hydride can reduce esters to alcohols due to stronger activating effect of Li+ ion than Na+

What is activating effect?

(Google search did not give appropriate results.)


texts: Software for generating a lattice from a unit cell for molecular crystals?

texts:
I am looking for a software package which can take a unit cell (and lattice parameters, etc.) and from that generate a crystal lattice. Ideally it will have functionality for orthorhombic, hexagonal, and other types of unit cells which are slightly less trivial than a cubic lattice.

Finally, it should work for molecular crystals.

I have seen the ASE lattice class (https://wiki.fysik.dtu.dk/ase/ase/lattice.html), but it isn't so clear to me how to define a lattice for a system when the unit cell is quite large.

As an example, I have a unit cell for a clathrate hydrate which contains 68 water molecules and I want to generate a lattice from this unit cell. How would one usually go about doing this?

My guess is that one way around this is to use some kind of MD package and just give the unit cell along with the lattice parameters and the type of lattice. Then, after applying periodic boundary conditions, somehow get the package to print out the coordinates of atoms beyond just the original unit cell. This feels a bit hacky to me, but if this is normal and someone knows a relatively simple way to do this, then let me know. Answers involving either open-source or purchasable software are acceptable, although open-source is always preferred :)

As an aside, it seems to me that it may not be too hard to just write code to do this for my specific cases, so if anyone has a good reference for generating the lattice given the type of unit cell, lattice parameters, and a set of Cartesian coordinates, that would also be helpful.


texts: What happens during oxidative and hydrolytic rancidity of fats?

texts: I understand that when lipid molecules - triacylglycerol - are hydrolysed, the fatty acids 'break' off from the glycerol backbone. And when fatty acids oxidise, these in turn can break into smaller end products. Does hydrolysis always happen first? I have made this image - would it be a fair representation of what happens when oils turn rancid?


texts: How to convert P2O5 concentration to H3PO4 concentration?

texts:
Why are some elements such as phosphorus reported as $\ce{P2O5}$ concentrations when the materials have no $\ce{P2O5}$ in them. I would like an explanation of how the conversion is done between real life and this idealized state.

For example. the Wikipedia page on phosphoric acid states that a $\ce{P2O5}$ concentration of 70% is equivalent to nearly 100% $\ce{H3PO4}$. Can someone explain this conversion?


texts: Calculating phase diagram of mixed component natural gases (Bubble and Dew points)

texts:
I'm developing a piece of software which calculates and plots the Phase diagram (PT) for a mixed component natural gas.

For reference I have a common used natural gas plotted using a commercial software. See image above. The Bubble curve is purple and ends at the critical point. Dew curves with different quality (liquid phases of 25%. 10%, 5%, 1%) continues after the critical point.

My results, after plotting with Excel seems to be a bit different. I have not calculated the critical point, but the Bubble and Dew curves are similar. See screenshot below.

The blue curve is the first found Bubble pressure at any temperature (within the Bubble range of course). The green curve is the second found Bubble pressure at any temperature. Likewise with the Dew, orange is the first found Dew temperature and red the second found Dew temperature.

What I can't understand is why the second roots of Dew and Bubble both cross each other, and extend inside the phase envelope.

Is it a calculation error? Or do you have to calculate both Bubble and Dew and cut off the curves where the cross each others path, or turn into the phase envelope?

PS. I use Van der Waals mixing rules to mix the gas solution. I use Peng-Robinson EOS.

Otherwise I've been following this approach

https://cheguide.com/bubble_p_flash.html

https://cheguide.com/dew_p_flash.html


texts: Protonation of a compound having alcohol and ethereal linkage

texts:
I approached the problem this way:

The ethereal oxygen gets protonated(due to greater + I , the electron density on it is higher, hence it is more likely to behave as a lewis base).

Consequently the product formed is pent-2-en-1,5-diol

Apparently that is the wrong answer, could anyone help me understand what exactly happens here and why my answer is wrong?


texts:
Synthesize the following compound using only toluene as the carbon source-

I have never done something like this before and I have no clue on how to start.
I am even more confused by the fact that the top two phenyl groups are meta substituted despite having a methyl group which is suppose to be ortho and para directing.

From an answer below it states I need to use Friedel–Crafts acylation. However I am not entirely sure how to do this. This is my guess:

Convert toluene into benzoic acid using $\ce{KMnO4}$ and then react half of it with $\ce{SOCl2}$ to form $\ce{C6H5COCl}$. Then react that with the other half of the benzoic acid followed by Wolff–Kishner reduction to form the below molecule:

After this, I am not sure how to chlorinate it so that I do another acylation.


texts:
Why is RO (alkoxide) a better leaving group than OH, despite RO being more unstable due to the electron donating effect of the alkyl group on RO?

I read that the suitability of leaving groups is dependent also on their nucleophilicity, as good nucleophiles will tend to re-attack the molecule it left from. To what extent is this true?


texts: Which mechanism is not seen during hydrolysis of esters?

texts:
Which mechanism is not seen during the hydrolysis of esters?

AAC2
BAC2
AAL2
BAL2
AAC1

I know that hydrolysis of ester is pseudo-first order reaction but I found this question where there are completely unknown reaction mechanisms.


texts: Why is energy released as electrons move?

texts: Why is it that energy is released from electrons when they move from one atom to a more electronegative one?


texts: What would be the intermolecular forces between the molecules of methanetetrol?

texts:
Methanetetrol has the following chemical formula: $\ce{CO4H4}$. It is also referred to as orthocarbonic acid.

Since the molecule has a molecular geometry of a tetrahedron, similar to that of a molecule of methane, I would assume that the dipoles at the bonds cancel each other out. Hence, making the molecule non-polar with no dipole or charge separation overall. Thereby, the intermolecular force between the molecules of methanetetrol should be London dispersion forces.

However, I've been told that the intermolecular force between the methanetetrol molecules is hydrogen bonding since the four $\ce{OH}$; hydroxyl groups in the molecule are capable of making 4 hydrogen bonds with 4 subsequent methanetetrol molecules.

Hence, my question is how can methanetetrol have hydrogen bondings as the intermolecular force between its molecules if the molecules do not have a dipole; or so I believe, i.e. what do you think is the intermolecular force between methanetetrol molecules?


texts: Difference between microcanonical and canonical ensemble

texts:
I feel a little unclarity about this. Canonical ensemble is pictured as many systems in heat reservoir of infinite capacity having $N$ (number of particles), $V$ (volume) and $T$ (temperature) constant whereas microcanonical ensemble is the analogous system having $E$ (energy) instead of $T$ fixed. From my simple viewpoint of introductory pchem, it seems obvious to me that heat capacity is constant hence how is it possible for canonical ensemble to have different energies while having same temperature. Feeling temporarily frustrated I grab McQuarrie's pchem it reads on the topic:

  "Each system has the same values of N, V, and T but is likely to be in
  a different quantum state, consistent with the values of N and V"

A light shines into my lower mood state.
So we talk about very little changes where the concept of heat capacity must be taken with reserve? That is, it is possible that system sucks heat from this infinite heat reservoir which is used to promote a particle in the system to higher rotational state for instance, which causes the system to acquire a tiny bit of energy while temperature will not change at all? Temperature is understood as describing translational motion of particles, right? Is my idea of the difference between these to ensembles correct?


texts: Regularity of electron configuration for heavier atoms

texts:
Edit: Is there structure in the nucleus that might be responsible for part of the regularity of the (ground-state) Aufbau process? The periodic addition of electrons is more than one might naively predict from Coulomb forces alone--so is this an intrinsic property of electrons or does the nucleus somehow mediate or influence the Aufbau process?

This is a very naive question.

Only after making graphs of electron counts by orbital for elements in sequence and seeing the symmetry of some of the heavier (and possibly non-realizable) elements (below is 170 or so, from the Wiki electron configuration data page) did it occur to me that the picture seems to imply a lot about the nucleus that I do not recall from general chemistry.

In particular for heavier elements, despite some irregularity along the way, it seems to imply that there are mirroring forces inside the nucleus that govern the buildup of electrons and that in some sense the nucleus is at least as complex as the rest of the atom. Not only are the electrons balanced in terms of charge numerically, but there is seemingly some structural (for lack of a better word) equivalence as well.

If someone could give a qualitative synopsis of what is known about this and/or correct any misconceptions that would be great. An introductory reference would also be of interest.


texts: What test can be used to differ amide and amine?

texts: For aliphatic amide and amine. I know we can use $\ce{NaOH}$ because amide will give off $\ce{NH3}$, but what will amine yield if we test it with $\ce{NaOH}$?


texts: Why are silver halides insoluble in nitric acid

texts:
The silver halides $\ce{AgCl},~\ce{AgBr},~\ce{AgI}$ are insoluble in $\ce{HNO3}$. This is given in J.D.Lee's inorganic chemistry text. (The strength of nitric acid is not specified though).

But won't this reaction take place?
$$\ce{X- + HNO3 -> X2}$$

This example is taken from JD Lee's book itself:
$$\ce{6Br- + 8HNO3 -> 3Br2 + 2NO + 6NO3- + 4H2O}$$

because  concentrated Nitric acid is a powerful oxidizing agent.


texts: Is there an open Chemical database that includes GHS/CLP classifications?

texts:
I'm looking for a Chemical database that

is up to date (via a firm, experts or crowdsourcing)
is open and free to use (best via an API)
contains the CLP/GHS classifications for chemicals

I have not found any database that has these three points (e.g. ChemSpider is actually not really open and does not contain CLP/GHS classifications)

I was really hoping any of you might know of one?


texts:
The compressibility factor is given by:
$$
z=\frac{P\overline{V}}{RT}
$$
The Nelson-Obert chart is:

This chart brings the following information:

At very low pressure (Pr << 1), gases behave as an ideal gas regardless of temperature.
At high temperatures (Tr > 2), ideal gas behavior can be assumed with good accuracy.
The deviation of a gas from ideal gas behavior is greatest in the area of the critical point.

Where:

$$
T_R=\frac{T}{T_{(At\ critical\ point)}}\\
P_R=\frac{P}{P_{(At\ critical\ point)}}
$$

What I don't understand is:

Does this chart describe the ideal behavior of a supercritical fluid or a superheated gas or plasma?

Having in mind any phase diagram:


texts:
One of the sections about retrosynthesis in Warren's book addresses how to access $\gamma$-hydroxy carbonyl compounds like ZM181.  This is again one of the examples to advice the reader to check the results for plausibility: while epoxides often may be a suitable building block, here, the intermediate would react further with the ester present to yield a lactone (second line) instead:

In the edition accessible to mine, Warren apparently does not detail out if an alternative approach with chloro- or bromoethanol (third line) to yield ZM181 were viable.
Question: Would be the approach of the third line, chloroethanol and ethyl acetoacetate to yield ZM181, still viable outside academia, too?
I'm aware the intramolecular transesterification to yield a five-membered cycle needs to be considered as a possible product for both approaches.  On the other hand, I think either route could be favoured by choice of the reaction conditions, i.e.

complete single deprotonation of ethyl acetylacetonate in dry THF by one equivalent $\ce{NaH}$ (not two), then followed by the addition of the expoxide may ease the formation of the lactone. The reasoning of $\ce{NaH}$ is to ensure all of the starting material is deprotonated once with the irreversible escape of $\ce{H2}$. Or,

the partial, equilibrium based deprotonation of the $\beta$-dicarbonyl compound by $\ce{K2CO3}$ in a mixture of THF/water, in presence of the bromo ethanol already present, might reduce the concentration of alcoholate and thus lower chances of the formation of the lactone.  This line of thought accounts for the different $pK_a$ of the reagents present, e.g., water could protonate free alcoholate, too.

Reference: Stuart Warren Organische Retrosynthese, Teubner, Stuttgart 1997.


texts: Combining acid dissociation constants to determine pH of diprotic acid

texts:
If I have a diprotic acid with $K_{\mathrm{a1}}$ and $K_{\mathrm{a2}}$ as the acid dissociation constants, why can't I calculate the final $\mathrm{pH}$ using $K = K_{\mathrm{a1}}\cdot K_{\mathrm{a2}}$ and the following net reaction?

$$
\ce{H2A + 2H2O ->  A^2- + 2\,H3O+} \\
K = \frac{4x^3}{I-x} \\
\mathrm{pH} = -\log_{10}[2x]$$

where $I$ is the initial concentration of $\ce{H2A}$. For instance $I$ could be $1\ \mathrm{M}$, and we could use $K_{\mathrm{a1}} = 5.9 \times 10^{-2}$ and $K_{\mathrm{a2}} = 6.4 \times 10^{-5}$ (constants for oxalic acid).

Solving it the standard way, one acid dissociation at a time, gives $\mathrm{pH} = 0.67$ whereas the combined way (above) gives $\mathrm{pH} = 3.9$. In what way is using this combined equilibrium constant neglecting the total hydronium concentration?


texts: How fast do electron's quantum spin flip?

texts: In a recent lecture it was taught that carbenes with their electrons in a triplet configuration do not undergo concerted reactions as one of the electrons must first undergo a spin flip; on what timescale does this occur?


texts: What is the difference between a radical and a neutral alone atom?

texts: I've done a bit of googling but can't find a clear answer to this question. Is there any difference to e.g. an alone neutral chlorine atom and a chlorine radical?


texts: Inorganic chemistry handbook with reaction lists

texts:
There is a handy handbook on common inorganic substances' properties called "Reactivity of Inorganic Substances" (eds. R. A. Lidin, V. A. Molochko, and L. L. Andreeva). It was originally written in Russian and then translated into English (see the review here). The entries in this handbook go like this (sorry for the Russian, couldn't find the English version):

You see that the compound's name is followed by the brief summary of its physical properties (color, solubility in water), general notes on its stability under ambient atmosphere, and then the list of the chemical reactions which were considered by the authors to be the most important or illustrative for this particular substance.

The question is - are there any reputable handbooks that are similar to this one, with not only the summary of the physical properties, but the summary of possible chemical reactions as well, or is this book one-of-a-kind?


texts:
The following reaction is at equilibrium $$\ce{4HCl(aq) + O2(g) <=>2H2O(l) + 2Cl2(g)}\quad \Delta H>0$$Which one of the following changes will result in an increase in the concentration of $\ce{Cl2(g)}$

  adding some $\ce{H2O}$
  decreasing the temperature
  adding a catalyst
  decreasing the pressure
  removing some $\ce{HCl}$

Decreasing the pressure (4) is the answer but I don't understand why. I though decreasing pressure shifts the equilibrium to the side with the larger number of moles which is the left?


texts: How can I produce hydrogen gas efficiently and cheaply?

texts:
I have been intrigued by one of the principles of chemistry lately- electrolysis. In my knowledge, electrolysis is a quite dangerous operation as the decomposition of water produces hydrogen and oxygen gas, both which are flammable. However, its potent to be volatile isn't what I am concerned with; rather, it is the production of these gases sufficiently and cheaply that I have been wondering about.

Thus, what is the cheapest way available right now to build an efficient electrolysis apparatus that could be used for a relatively long amounts of time? In addition to this, what are the side effects with electrolysis of water? In addition to this, could solar panels be used in the process of electrolysis? I want this electrolysis apparatus to be as independent from the grid as possible!


texts: What are some possible classification tests that one can use for o-nitrobenzoic acid?

texts:
I have analyzed an IR spectrum and found out that my compound (o-nitrobenzoic acid) has a nitro group, carboxylic group, and benzene ring.

I was curious to know: if regioselectivity effects the solubility of the compound? If/If not regioselectivity effects the solubility of o-nitrobenzoic acid, what would be the best solubility test to run for o-nitrobenzoic acid since it has a carboxylic acid and a nitro group in the ortho-position? And, if I wanted to test o-nitrobenzoic acid functional groups, what would be some good classification tests to run?


texts: Internal and external pressure during a gas expansion

texts: There is a solid substance in a rigid cylinder with a piston placed on top such that the distance between the piston and the bottom of the cylinder is essentially zero, and then the substance decomposes and forms gas that expands and pushes the piston up against a constant external pressure to a maximum point. It then falls slowly as heat from the reaction is lost to the surroundings. Is it true that at the maximum point, the internal pressure is equal to the external pressure?


texts: How do I calculate the viscosity of a mixture of toluene and isopropanol?

texts: I am trying to understand why my nanoparticles will only electrophoretically deposit in a non-polar solvent and a non-polar/polar solvent mix but not in the polar solvent. I am hoping to use zeta potential and Hamaker's equation to understand this


texts: Obtaining activity coefficients of conjugate acids of some common carboxylic acid molecules

texts:
Recently, I have been wondering about justifying the notion on how some common acids (e.g. carboxylic acids) are themselves weaker bases than water to the point that we don't usually consider them to act as base. To begin, we use the formula for $\mathrm{p}K_\mathrm{b}$ and consider for example acetic acid (written in organic chemistry convention, with $\ce{OAc^-}$ being the acetate group $\ce{CH_3COO^-}$ for unfamiliar readers)

$$\mathrm{p}K_\mathrm{b} = -\log \left(\frac{a_{\ce{H2OAc+}}a_{\ce{OH-}}}{a_{\ce{HOAc}}}\right)$$

where everything is measured at room temperature, 1 atm.

As usual, if the solution is dilute enough, we can approximate the activity with concentration.

However, the species $\ce{H2OAc+}$ seemed to be not very popular as NIST have few data on its thermodynamic parameters. While it is in principle possible to perform an experiment to measure $a_{\ce{H2OAc+}}$, if it is indeed very weak as a base, then the measurement result will only be reflecting the acetate ionisation equilibrium and masked any tiny result of $a_{\ce{H2OAc+}}$ if any.

  How does one obtain the necessary thermodynamic parameters for a potentially highly unstable protonated species in aqueous medium in order to work out the $\mathrm{p}K_\mathrm{b}$ of the common carboxylic acids?


texts:
I gathered that many of amorphous solids are made by quickly cooling the liquid material, thereby giving it no time to form any long-range order (crystallinity). So it makes a perfect sense that when high heat is applied to amorphous solid, it will regain its crystallinity, and will no longer be glassy.

But is this behavior non-continuous? That is, can sustained low thermal excitation give rise to the crystallinity in amorphous solids given enough time? Or is there a threshold temperature (or a level of thermal/mechanical excitation) below with no excitation can bring back the crystallinity?


texts: How can I predict whether a reaction will occur?

texts:
I'd like to know how can I predict if two substances will react. I already know that there's a reaction if one of the products is a weak electrolyte or a precipitate but that leads me to the question:

  If we have two substances such as salts and they react with one another forming two other salts, when is the reaction double replacement and when there is no reaction?

I'll try giving two examples from the problems I came across:

Which one of the following substances will react with one another in a solution –

$\ce{(NH4)2CO3, CuCl2, K2SO4, Ba(NO3)2, HCl}$
$\ce{Na2CO3, Ba(NO3)2, Na2SO4, AgNO3, CaCl2}$


texts: Why does electron configuration in the periodic table is different when you follow the aufbau principle?

texts:
. In periodic table for example Ag has an electron configuration of [Kr] 4d10,5s1 but when you do it yourself using Aufbau principle it should be [Kr] 5s2 4d9. Why is that?

When ask for Ag + valence electron configuration answers may now vary because of the existence of two electron configurations from the periodic table and using aufbau principle...


texts: Reason for isotropy in amorphous substances

texts: I'd be thankful if someone explains why amorphous substances are said to be isotropic and crystalline substances anisotropic


texts: Confusions about inductive effect and acid strength

texts:
If one of the hydrogens in the alkyl side chain of ethanoic acid is replaced with an atom of Chlorine, the acid has a larger Ka value. My book says this is since the Cl "borrows" electron density from the Carbon it is connected to. And, in this example, this carbon borrows some electron density from the Carbon in the acid group, and thus the oxygens of the acid have less charge density. The bold part is what I don't get.

The C to which this 1 chlorine is attached gets a bit electron deficient but not as much deficient as the C in the acid group (since this has two oxygen atoms attached). So how can it borrow density away from the C in the acid group? In my mind, to borrow some charge density you have to be more electronegative than what you're attached to, and the more deficient carbon should have a greater pull.

What am I missing in this?


texts:
I have been looking everywhere for hours now, and can't find anything on a simple lab reduction of an alcohol to an alkane that doesn't involve any "fancy" reagents such as tosylates, metal catalysts etc.
I would have expected that under acidic circumstances, the oxygen donates an electron to the proton from the acid, and a hydride from a general reducing agent such as LAH or NaBH4 then attaches itself to the carbon, pushing out a molecule of water, and alkane.
However, I have found no proof or mention of the existence of such a reaction. If this is is impossible, then why, and what would be the best general purpose way to reduce an OH to a H


texts: Why don't elements having the same valency as Carbon bond so readily?

texts:
I haven't been in touch with Chemistry as a subject of study for several years now. Still- if I remember correctly, Si, Ge, Sn, Pb all have same number of electrons as Carbon in their outer orbits.

So why is Carbon so ubiquitous? I believe the number of electrons an element can give or accept decides how readily it bonds with other elements. For instance, inert gases have no room for extra electrons and hence, are inert.

So why don't other elements in the column of Carbon bond as easily? In other words, why aren't we made up of Pb primarily instead of C?

I remember asking this question to my high school chemistry teacher, but as far as I can remember, he wasn't able to give a satisfactory answer. Forgive me for asking this , if this question is too naive. But I genuinely wondered a lot about it back in my school days and still don't know the answer.