texts: Why is absorbance spectrum continuous and not quantized?

texts:
1) In text books, the absorption event is usually described by a figure shown below1: light excites electrons to higher states in atom or molecule. The difference between the ground state and the excited one matches the energy of the absorbed light. But electron states in atoms and molecules should be quantized, so why do we observe absorbance spectra that are smooth and continuous but not spiked and quantized?

2) Where does the energy go when the excited electron returns to its normal state? In fluorescence, the electrons return to lower states and excite light at higher wavelength than the absorbed one. But if I had a molecule that did not exhibit fluorescence, just plain absorption, does the molecule emit light at the same wavelength it absorbed or does the energy turn to heat? I mean, the electron cannot be excited forever.

3) What is the physical phenomenon behind absorption coefficient? I have been thinking that it has something to do with the lifetime of the excited state – shorter lifetimes increase the probability of a photon to be absorbed, resulting in larger coefficients. Am I completely wrong?

1Image taken from http://www.photobiology.info/Visser-Rolinski.html


texts: I know it has something to do with carbon dioxide, but what exactly happens and causes the characteristic sound we hear (especially after we shake the bottle)? How do we manage to dissolve a non-polar substance ($\ce{CO2}$) in a polar solvent ($\ce{H2O}$)?


texts: Are all amphoteric substances weak acids and weak bases?

texts:
I saw as an example that water is amphoteric (to be more precise amphiprotic), and I came up with the following questions:
Is there any substance that acts as a weak acid and a strong bases at the same time, or vice versa?
If so, or if not so, please give some explanations on the possible reasoning using their structures.
Also I have another question which is quite related but too short to be posted as an independent question, so I will ask here. The necessary condition for a substance to be amphoteric, as I heard, is that for it should have a hydrogen atom in it, and also the molecule should either have a lone pair of electron or be negatively charged. I understand the conditions about hydrogen atom and an electron pair, but why can the negatively charged property possibly be a necessary condition for a molecule to be amphoteric?
Thanks in advance.


texts: Calculating Triplet-Triplet Spin-Orbit Coupling

texts:
According to the Q-Chem manual [1], the singlet-triplet spin-orbit couplings between a singlet excited state $I$ and a triplet excited state state $J$ is:
$$\langle\Phi_\text{singlet}^I|\hat{\mathrm H}_{SO}|\Phi_\text{triplet}^J\rangle = \sqrt{\sum_{m_s=0,\pm1}|\langle\Phi_\text{singlet}^I|\hat{\mathrm H}_{SO}|\Phi_\text{triplet}^{J,m_s}\rangle|^2}~.$$

The further elaborate on the triplet-triplet spin-orbit coupling to be:
$$\langle\Phi_\text{triplet}^I|\hat{\mathrm H}_{SO}|\Phi_\text{triplet}^J\rangle = \sqrt{\sum_{m_s=0,\pm1}|\langle\Phi_\text{triplet}^{I,m_s}|\hat{\mathrm H}_{SO}|\Phi_\text{triplet}^{J,m_s}\rangle|^2}~.$$

But shouldn't the latter actually be a double sum like:
$$\langle\Phi_\text{triplet}^I|\hat{\mathrm H}_{SO}|\Phi_\text{triplet}^J\rangle = \sqrt{\sum_{m_{s,i}=0,\pm1}\sum_{m_{s,j}=0,\pm1}|\langle\Phi_\text{triplet}^{I,m_{s,i}}|\hat{\mathrm H}_{SO}|\Phi_\text{triplet}^{J,m_{s,j}}\rangle|^2}~?$$

As of porphyrin's comment, I'd like to add, why I think so.

The triplet-triplet SOC matrix looks like the following:
\begin{array}{c|ccc}
\hline m_{s,i}\text{\\} m_{s,j} & 0 & -1 & 1 \\\hline
  0 & 0 & a & a \\
  -1 & a & b & 0\\
  1 & a & 0 & b\\
  \hline
\end{array}

If the rules from the "single sum" would apply, only $b$ would count into the sum and $a$ would be neglected, because the summation only accounts for the diagonal elements.

[1] http://www.q-chem.com/qchem-website/manual/qchem50_manual/sect-tddft.html


texts: An equilibrium reaction in the presence of other fast reactions -- is it necessary also to consider the individual rate constants?

texts:
When mathematically describing an equilibrium reaction, we generally treat it as though it is enough just to specify the equilibrium constant, as it relates the concentrations of products and reactants.

If this equilibrium reaction is occurring in a highly reactive environment, however, where the reactants and the products are constantly changing due to other reactions, it seems to me that the equilibrium reaction can no longer be described by equilibrium constant only. Instead, the forward and/or reverse reaction coefficients are needed (in addition to the equilibrium constant) to describe the relationship between the reactants and the products. Is this  correct? If not, why not?


texts: How come when it rusts iron can undergo oxidation without the prescence of a another metal to undergo reduction?

texts: It seems to me rusting is an electrochemical process where oxygen, which has particularly high electronegativity, fills the role of cathode or is that an incorrect way to put it?


texts: How to calculate the enthalpy change for the formation of ethylene epoxide from ethylene?

texts:
I get everything up until the very end. We need to identify the bond enthalpies first:
\begin{align}
\ce{C=C} &= 612\\
\ce{O=O} &= 248\\
\text{SUM of these}&= 860\\
\end{align}

\begin{align}
\ce{C-C} &= 348\\
2\cdot(\ce{C-O}) &= 720\\
\text{SUM of these} &= 1068\\
\end{align}
We know that enthalpy change is = products - reactants, which is $1068 - 860 = 208$, but the problem comes here: I know a minus sign is supposed to go there, but
how do we know that? Exothermic reaction? Is it because of the oxygen, suggesting it's a combustion reaction or not?


texts: What neutralizes the active ingredients (napthalene and/or paradichlorobenzene) in moth balls?

texts:
Question: What is effective in removing residual moth ball smell from inside a car?

Issue: We used moth balls in our car to rid it of mice. (Never do this; it does not work.) We removed the moth balls after about a month. The car, free of moth balls for three months, still reeks of the moth ball smell. After driving in the car for 10-15 minutes, our clothes also smell like moth balls and require washing to rid them of the smell. Would airing the car out be effective or do I need to be more drastic?


texts: How to determine the products of a redox reaction

texts:
I'm doing a paper on water treatment methods, and in one section, I'm describing how a nearby water treatment plant is removing Trichloroethylene ($\ce{C2HCl3}$) from water by oxidizing it using Ozone ($\ce{O3}$).

However, I can't find any documents confirming the products of this reaction, so I'm going to need to determine them on my own, but I'm not sure how. I'm fairly certain the equation would be formatted as

$$\ce{C2HCl3(aq) + O3(g) -> H2O(l) + }$$

but I'm not sure of anything past that.


texts:
While working with some rust converter (MSDS, ~20% phosphoric acid by weight), a sequence of events that would make Rube Goldberg proud led to me spilling about 500mL of it all over the place. Yes I was wearing gloves and an acid gas respirator.
I'm not really well versed in chemical cleanup procedures and I needed to act fast so I kind of winged it by:

Wiping the majority with a bath towel.
There happened to be a box of baking soda right there so I dumped a bunch of it on the remaining spill.
It fizzed for a bit then I wiped that up.
I shop-vac'd the rest of the baking soda.

My question is just: Did I handle that OK? And, if not, how should I be prepared if that happens again? (I've been working with the chemical a lot lately.)
The reason I ask is, when I took off my respirator, it still smells like rust converter.
Also, it just happened so I won't be able to see any effects for a few hours but I'm hoping I don't start seeing rust spots on the metals it contacted, or dried crystals, or tear up any of the finish on the wood it contacted. But I'm hoping I got it.
Also, there are cats here and I don't really want residue to be left laying around.
So I'm wondering if that was a decent reaction, or if it was dangerous (I dunno what phosphoric acid + baking soda produces, although the space was well ventilated); and if it was effective, or if there is a better way.
Context is home shop, primarily woodworking; not a lab. So I don't have those nice metal lab tables or anything; lots of cracks, crevices, porous surfaces (concrete and wood), and stuff. And while I normally work with this stuff on a tray for small splash containment, this was a rather... violent spill (heh).


texts: Why does table salt (NaCl) dissolve branded food?

texts:
To dissolve branded food from e. g. a baking tray, there is the advice to pour table salt on it and heat it up in a baking oven or on a hotplate until the salt turns brown. From practice I confirm that it works.
But I'd like to know why it works. Can somebody please explain it in layman's terms (my chemistry knowledge is at a-grade)? What reaction(s) happen(s) here?


texts:
For the acid catalyzed opening of epoxides, the epoxide is first protonated to form the oxonium ion. I read in some textbooks that the $\ce{H2O}$ molecule, which acts as a nucleophile attacks in a $\mathrm{S_N2}$ concerted mechanism. Given that $\ce{H2O}$ is a weak nucleophile, how can a $\mathrm{S_N2}$ concerted mechanism be possible,  8 instead of $\mathrm{S_N1}$ which is expected of $\ce{H2O}$?

Also, for an unsymmetrical epoxide, why will the nucleophile attack at the more substituted $\ce{C}$?


texts: Is the recipe for my shaving cream complete nonsense?

texts:
Preamble
I have only basic education in Chemistry (excelled at Organic chemistry nomenclature, but then subsequently quit when I could not grok the simplest replacement reactions). Also I will note I could not find a tag for retail product labelling.

I bought a lot of shaving cream product that I really like. I have been reading the ingredients and I don't understand why it contains so many acids and bases. Perhaps this is an oversimplification, but I was under the impression any acid and base that were mixed would in time, resolve themselves to a salt and an extra water molecule. Let me share with you the ingredients list verbatum so you can see too:

Aqua (water)
Stearic Acid
Myristic Acid
Potassium Hydroxide
Coconut Acid
Glycerin
Triethanolamine
Theobroma Cacao (Cocoa) Seed Butter
Parfum (Fragrance)
Sodium Hydroxide
Melaleuca Alternifolia (Tea Tree) Leaf Oil
Limonene
Linalool

So it seems to me the major ingredients are acids, bases, water and fats blended together with an emulsifier (Glycerin?).

Question
Wouldn't the acids and bases react with each other shortly after mixing, leaving my product with a different mixture of compounds than in the ingredients list?

Speculation
Here is my attempt at answering, so you can an idea that I did put minimum thought into this.

Are some of these things with "acid" in the name, not really acids as I learned them (pH under 7, with a donor H+ ready to go)? And therefore they do not react?
Considering the vendor spells out cocoa butter with a long latin name, maybe they have arranged the ingredients list to impress the customer? For instance writing out Stearic Acid and KOH instead of, say, "lard" or "wax" or whatever unimpressive name is actually the product of the acid-base reaction?
Perhaps the vendor is legally required to print the reagents rather then the product(s), in some circumstances?
Perhaps there is some process in the mixing of the ingredients, or some catalyst that inhibits the reaction? And to what end? For the reaction to happen on my face when water is mixed into the product?


texts: Why are excess nuclei required to produce an NMR signal?

texts: In NMR, an excess population of nuclei is required to produce a signal. If saturation is achieved (same number of nuclei in the α and β states) no net signal can be produced. A signal is produced when a radio frequency causes one state (could be either α or β) to invert. During the process of inverting, the net oscillating electric field of the nuclei is tipped to the xy plane until they undergo relaxation back to the inverted state. Even if a particular set of nuclei are saturated, they will still undergo resonance, thus producing an oscillating electric field in the xy plane. This should be detectable; however, it is not. I am guessing that this is because the oscillating electric fields cancel each other out (since they are occurring for both the α and β states). This would result in canceling out the net electric field; however, I am not sure of my guess.


texts:
Are there general rules for Base + Metal Compound reactions like there are for Acids?

For example, acids have some general rules.

**

Acid + Metal => Salt + Hydrogen Gas

Acid + Metal Carbonate => Salt + Water + Carbon Dioxide

Acid + Metal Oxide => Salt + Water

Acid + Metal Hydroxide => Salt + Water

**

Are there equivalent rules for bases?

Base + Metal => ?


texts: What is non PV work? How is it related to Gibbs energy?

texts:
Recently, I was trying to understand more about Gibbs free energy and got stuck at this point. Some books write that if $\Delta G=0$, then the reaction is reversible while some other sources say that a reaction is reversible when  $\Delta G$ = Non-$PV$ work.
I am not able clarify things here and am unable to understand the core concept of non $PV$ work.


texts: Physical interpreation of coulomb and exchange integral

texts:
When trying to solve the Schrodinger equation for the electronic hamiltonian:
$$H_{el} = \sum_{i=1}^{N} \bigg( - \frac{1}{2}\nabla_i^2 - \sum_A \frac{Z}{r_{i_A}} \bigg) + \sum_{i>j=1}^{N}\frac{1}{r_{ij}}$$
we note that two prominent integrals arise:
These are the exchange  integral:
$$  K_b(1)\chi_a(1) = \bigg[ \int d\tau_2 \chi_b(2)^* \frac{1}{r_{12}} \chi_a(2) \bigg]\chi_b(1)$$
and the coulomb integral:
$$ J_b(1)\chi_a(1) = \bigg[ \int d\tau_2 \chi_b(2)^* \frac{1}{r_{12}} \chi_b(2) \bigg]\chi_a(1)$$
$r_{12}$ is the distance between electrons 1 and 2 and the integrals are done over all space. $\chi_b$ is an orbital labelled b.
I was wondering whether someone could give me a brief physical interpretation of these two integrals.


texts:
Using Born-Oppenheimer approximation, we separate the nuclear and electronic parts of the wavefunction, and treat them separately. We include the terms that have direct dependence on the electronic positions in the electronic Hamiltonian,

$$\hat{H}_{e} = \hat{T}_e + \hat{V}_{eN} + \hat{V}_{ee}$$

Thus, the total Hamiltonian is given by:

$$ \hat{H} = \hat{H}_{e} + \hat{V}_{NN} $$

So, what is the definition of electronic energy? According to the source mentioned below, electronic energy does not include $\hat{V}_{NN}$, which makes sense. But, all the electronic structure packages quote the Total energy as the electronic energy. The following is quoted from Gaussian website:

Zero-point correction=                  .023261 (Hartree/Particle)
Thermal correction to Energy=           .026094
Thermal correction to Enthalpy=         .027038
Thermal correction to Gibbs Free Energy= .052698
Sum of electronic and zero-point Energies=-527.492585
Sum of electronic and thermal Energies= -527.489751
Sum of electronic and thermal Enthalpies=-527.488807
Sum of electronic and thermal Free Energies=-527.463147

Why is this discrepancy? What is the actual definition of electronic energy?

Source for my argument: http://vergil.chemistry.gatech.edu/notes/quantrev/node31.html


texts: Wavelength and Colour in Coordination complexes

texts: My textbook said that coordination complexes with weak field ligands require a larger wavelength for obtaining enough energy for electron transfer(and hence, the manifestation of a colour), but if E = hv(E is the energy, h is Planck's Constant and v is the frequency), then shouldn't the wave of higher frequency be needed?


texts: Chain transfer agents and rate of free radical polymerization

texts:
In free radical addition polymerizations sometimes chain transfer agents are added. From what I understand chain transfer agents (e.g. XR' below) reduce the average molecular weight by transferring the free radical  from the growing polymer chain (P•) to another molecule (R'•).

P• + XR' → PX + R'•

My question is what effect would this have on the overall "rate" of polymerization itself, i.e say the consumption of monomer.

In other words the R'• species is then free to combine with more Monomer, right? And being a smaller molecule (in general) would it be expected to have a higher rate constant for the reaction:

R'• + M--> P•


texts:
When I measure optical density in a microplate reader the absorbance is proportional to the concentration and the height of the liquid. Is Beer-Lambert law also valid for fluorescence and luminescence?

Let's say I prepare a fluorescent solution and measure e.g. the signal of 100 μL and of 50 μL. Do I get the half signal for 50 μL?


texts: How much water would one loose if one burns hydrogen and oxygen?

texts:
By using electrolysis one can separate hydrogen and oxygen, but when burning hydrogen and oxygen together steam is released, therefore creating water. My question is:

  how much of the original quantity of water would be lost after this
  process?


texts: How to predict a COSY NMR spectra for an AMX spin system?

texts: Does anyone know how to draw (predict) a hypothetical COSY NMR spectra for AMX spin system (the spin of A M X nuclei is 1/2)?


texts: Finding is the concentration of H⁺ in a benzoate buffer solution after adding HCl

texts:
Q: A buffer with a $\mathrm{pH}$ of 4.44 contains $\pu{0.21 M}$ of sodium benzoate and $\pu{0.12 M}$ of benzoic acid. What is the concentration of $\ce{[H+]}$ in the solution after the addition of $\pu{0.050 mol}$ of $\ce{HCl}$ to a final volume of $\pu{1.3 L}$?

A: So these are the steps that I have taken for this:
The reaction is:
$$\ce{C6H5COOH +H2O -> C6H5COO- + H+}$$
The $K_ \mathrm{a}$ of benzoic acid is $6.3 × 10^{-5}$
But, $K_\mathrm{a}=\ce{\frac{[C6H5COO-][H+]}{[C6H5COOH]}}$
We don't know the concentrations of $\ce{[H+]}$ so we solve for that. We then assume at equilibrium $\ce{[C6H5COO-]}$ is equal to it.
Then: $6.3×10^{-5}=\ce{\frac{[C6H5COO- ][H+]}{[C6H5COOH]}}$ and
$\ce{[H+]}=0.00272$
But this is wrong. I think I'm doing something wrong in my problem, but really can't figure out what.


texts: I'm just wondering if anybody here knows of a Consumer-Report-like publication for lab equipment. Something that would give the specifics, as, for example, the flow rate of a distilling condenser, etc.


texts: Are forming coins starting with sodium chloride possible without the clay melting from the molten metal?

texts:
Is forming metal coins (specifically ones with copper, nickel, and zinc) possible with these steps:

Carve a sheet of sodium chloride so that it is big but not too big and so that the design sticks out of the sheet of sodium chloride.
Cut the sodium chloride so that you have 1 big circle with the design
Form a mold out of clay from the sodium chloride design
Scale it down without losing detail using a carving machine(instead of hand carving like with the sodium chloride) that carves the design on each side on a separate piece of clay(which is much easier to carve than sodium chloride).
Once the clay is in the leather hard stage(usually takes about a day) put a piece of clay of uniform thickness and hardness around each side of the coin so that you can hand carve the rim(make sure the rim is not too wide) This will make there be space for the metal
Once the rim is in the leather hard stage attach the 2 sides to a base, again made out of clay
Fire the clay
Smelt the metal
pour the metal into the clay mold
get the metal coin out of the clay mold
Heat the metal again but don't melt it
Cool the hot metal
Wash and dry the metal
reuse the clay mold so that you don't have to start all over again from hand carving sodium chloride but rather only from step 8 which is smelting the metal

One of my big concerns of this process is that a copper, nickel, zinc mixture might melt the clay as soon as the metal is poured in but at the same time I don't want to use a metal that you can bend with the pressure from your hand like you can with aluminum.


texts: Why is carbonic acid a weaker acid than acetic acid?

texts:
Is it because the $\ce{OH}$ group next to $\ce{COOH}$ in carbonic acid donates electron density to the $\ce{COO-}$ by resonance, making it a stronger base, compared to a weaker electron donating inductive effect of $\ce{CH3}$ and thus its conjugate acid is weaker?

What does the resonance contribution look like in this case?

What makes resonance a stronger factor than induction?


texts: Why is the bond dissociation energy of C-H bond higher than that of a N-H bond?

texts:
Looking at a chart of BDEs (bond dissociation energies) regarding elements bonded with hydrogen, the general trend seems to be that the BDE increases as we go to the top and to the right. This can be explained by the fact that the elements to the right have stronger attraction for the covalent bonds, making homolytic cleavage harder. Likewise, those elements near the top have shorter radii, which means that their attraction is larger too.

However, there is a single anomaly in the $\ce{N-H}$ and $\ce{C-H}$ bonds, where the BDE of $\ce{C-H}$ is higher than $\ce{N-H}$. Why is this?


texts: Compare the work done during dissolution of carbides

texts:
1 mole of each $\ce{CaC2}$, $\ce{Mg2C3}$, $\ce{Al4C3}$ react with excess water in separate open flask. Work done during dissolution shows the order

$\ce{CaC2}=\ce{Mg2C3}<\ce{Al4C3}$
$\ce{CaC2}=\ce{Mg2C3}=\ce{Al4C3}$
$\ce{Mg2C3}<\ce{CaC2}<\ce{Al4C3}$
$\ce{Mg2C3}<\ce{Al4C3}<\ce{CaC2}$

Calcium carbide gives ethyne on reaction with water. One mole of calcium carbide reacts with $2$ moles of water.
Magnesium carbide gives prop-1-yne on reaction with water. One mole of magnesium carbide reacts with $4$ moles of water.
Aluminum carbide gives methane on reaction with water and one mole of aluminium carbide reacts with $12$ moles of water.
Work done $=P\Delta V$. But since the amount of water is large compared to the amount of carbide, will the work done differ?
(Answer given is $1$)


texts: Do we consider the spatial orientation of a molecular orbital while assigning plane of symmetry?

texts:
I am following the video lectures by Neeraj Saini sir and in this video$^{\dagger}$ he said that $\ce{CO2}$ has infinite planes of symmetry.
But I think that if we take into account the orientation of $π$ bonds (which I don't know if we have to or not) then $\ce {CO2}$ molecule must  have $2$ planes of symmetry, as per the following argument:
A $\ce {CO2}$ molecule has similar $\pi$ bond orientation as that of an allene.
Now if we consider the orientation of pi bonds then $\ce {CO2}$ must have only 2 planes of symmetry.
So, to check whether infinite planes of symmetry statement is correct or not, I have the following question:

Do we consider the spatial orientation of molecular orbitals while assigning plane of symmetry? And if not then why not?

$\dagger$ Note that he uses Hindi language for the purpose of conversation.


texts: What Type of Gas Would Vinegar and Epsom Salt Create Under Electrolysis?

texts:
I'm restoring a motorcycle and have a small homemade DIY zinc plating operation which consists of vinegar, epsom salt, a piece of zinc and a power supply.

When I plate a steel piece such as a bolt or small hardware piece, the piece in the solution starts forming small bubbles and it appears to be "gassing off" something. I was wondering what type of gas this may be and if it's harmful to breathe.


texts: Trouble understanding 5 orientations of d orbitals

texts:
I understand $d_{xy}$ and $d_{yz}$ and those orientations but ones like $d_{z^2}$ are very strange to me.

Can someone please explain that to me?


texts: Why can Cu have an oxidation number of +2?

texts:
The electronic configuration for $\ce{Cu}$, adjusted for Hund's rule, is:

$[\ce{Ar}] 3d^{10} 4s^1$

So, shouldn't $\ce{Cu}$ have an oxidation number of $+1$? whereby it gives off its outermost 4s electron? Why can it also have a $+2$ charge?


texts: ApexTrack: peak tail looks like a shoulder

texts:
I'm trying to implement ApexTrack algorithm in my software by following the description written by Waters. But many chromatograms that I see have noticeable tailing of peaks: .

No matter what Touchdown% threshold I set (even 0) - it won't be able to go past the bump in the tail because the slope becomes positive for a bit.

Are there modifications to ApexTrack that could join such tail to the peak? And at the same time keep recognizing true shoulders (which you see to the left of the largest peak).


texts: Calculating the Gibbs Free Energy of Mixing

texts:
This is a Physical Chemistry Question and comes from the Atkins Physical Chemistry book.

  Suppose that $2.0~\mathrm{mol}$ $\ce{H2}$ at $2.0~\mathrm{atm}$ and $25~^\circ\mathrm{C}$ and $4.0~\mathrm{mol}$ $\ce{N2}$ at $3.0~\mathrm{atm}$ and $25~^\circ\mathrm{C}$ are mixed at constant volume. Calculate $\Delta_\text{mix}G$. What would be the value of $\Delta_\text{mix}G$ had the pressures been identical initially?

The answers are given but I don't understand how to get to $-9.7~\mathrm{kJ}$ for the first part of the question (when initial pressures are different. The gases are initially at different pressures but does that make a difference. Can I still use Raoult's Law?


texts: Why aryl halides are very less reactive towards nucleophilic substitution reactions?

texts: I've often herd that aryl halides are very less reactive towards nucleophilic substitution reactions. One of the reasons for this I found was that there is resonance effect in the compound, but how is  that responsible for it to less reactive towards S.N. reactions and in addition to resonance effect are there other factors also responsible ?


texts:
Nomenclature problem, when would ring be parent?

[(but-3-yn-2-yl)oxy]cyclopentane or 3-cyclopentoxylbutyne
I used chemsketch and it generated the former one.

The chain has a alkyne group. I thought that would make it has a seniority over the ring.
Also, the another rule said we should choose the one with more carbon as the parent chain so I am confused.

IUPAC bluebook,
P-44.1.2.2 Systems composed of rings and chains (exclusive of linear phanes)
Two methods are recognized to name systems composed of rings and chains (exclusive of linear phanes).
(1) Within the same class, a ring or ring system has seniority over a chain. When a ring and a chain contain the same senior element, the ring is chosen as parent. Rings and chains are chosen regardless of their degree of hydrogenation. As a consequence, this approach prefers the choice of a ring over a chain in systems composed of cyclic and acyclic hydrocarbons.
(2) The context may favor the ring or the chain, so that, for example, substituents may be treated alike or an unsaturated acyclic structure may be recognized, or the one chosen has the greater number of skeletal atoms in the ring or in the principal chain of the acyclic structure.
P-52.2.8 Selection between a ring and a chain as parent hydride
Within the same heteroatom class and for the same number of characteristic groups cited as the principal characteristic group, a ring is always selected as the parent hydride to construct a preferred IUPAC name. In general nomenclature, a ring or a chain can be the parent hydride (see P-44.1.2.2).


texts: Is hydrogen bonding separate from permanent dipole interactions? What I mean here is that a molecule such as ethanol has hydrogen bonding, but does it also have permanent dipoles other than the ones on the oxygen and hydrogen atoms that cause permanent dipole attraction?


texts: Why is bromobenzene more stable than benzene?

texts: Benzene is 45 kJ/mol more energetic than bromobenzene. I understand that due to resonance in bromine to benzene in bromobenzene increase the stability but such an enormous amount of energy can't only be dealt by resonance. There must be another reason. What is it?


texts: Finding the nearest neighbour, from an atom within a crystal

texts: Is there any software can give me the information of nearest neighbour, nest nearest neighbour,....(and their distance) from an atom within a crystal (described by a .cif file)? Perhaps some visualization software like VESTA?


texts: How to find the molar mass of a compound given mass, vol, temp, and pressure?

texts:
A $2.1\ \mathrm g$ sample of a liquid vaporizes and exerts $120\ \mathrm{mmHg}$ pressure at $1.5\ \mathrm L$ volume and $80\ \mathrm{^\circ C}$ temperature. Find the molar mass of the gas.

I first get the equation $PV=nRT$ and replace $n$ with $m/M$ since $M=m/n$
Then the equation becomes this $$PV=\frac{mRT}{M} \Rightarrow M=\frac{mRT}{PV}$$

$$\begin{align}
M&=\frac{mRT}{PV}\\[6pt]
\Rightarrow M&=\frac{(2.1\ \mathrm g)\times(62.364\ \mathrm{L\ mmHg/(mol\ K}))\times(80+273.13)\ \mathrm K}{(120\ \mathrm{mmHg})(1.5\ \mathrm L)}\\[6pt]
\Rightarrow M&=257\ \mathrm{g/mol}
\end{align}$$

But the answer key says $150\ \mathrm{g/mol}$. What am I doing wrong?


texts: I would like to know the differences between Fe3+ and Fe2+ ions. I'm guessing they must differ in reactivity but I'm not sure how. Also, is there a way that we can observed the differences


texts: Why are dendrites formed during dilute CuSO4 electrolysis black?

texts:
During the weekend, I wanted to conduct a kid's experiment - the copper dendrite formation. I was (partially) successful and now I would like to know what went wrong.

The procedure was taken from the weird science page (unfortunately in polish only).

The procedure was straight forward: Two, thin copper conductors on a microscope slide, connected to DC supply (voltage "over a dozen volts") and few drops of dilute $\ce{CuSO4}$ (according to the procedure, the solution should be transparent or maximum pale blue). It seemed pretty easy and the circuit was built in a few minutes. According to the description (and included pictures), I should see beautiful copper dendrites on the cathode, where $\ce{Cu^2+}$ reduces to $\ce{Cu}$, thanks to electric current (the reaction $\ce{Cu^2+ + 2e- -> Cu}$)…

In fact, the reality was slightly different (see attached figure). Below is my interpretation, but I am aware that it could be wrong:

At the beginning, bubbles on the cathode started to show. I assume it was hydrogen – high voltage (approx. $\pu{12 V}$) caused water electrolysis and $\ce{H2}$ evolution. No gas was evolving on the anode – I presume that the only reaction was oxidation of the copper wire $\ce{Cu-> Cu^2+ + 2e-}$.
A while later green flocs showed on the cathode, progressively moving towards the anode – I presume that $\ce{Cu(OH)2}$ was precipitated, due to increased $\ce{OH-}$ concentration near the cathode, caused by $\ce{H+}$ consumption.
Finally, the dendrites started to show on the cathode – but to my surprise, these were black, not orange like copper.

Why the dendrites are black? It does not look like copper but rather like $\ce{CuO}$. I’ve found the reference stating that $\ce{Cu(OH)2}$ transforms into $\ce{CuO}$ in basic solutions at room temperature, which could be an explanation (Cudennec and Lecerf, The Transformation of $\ce{Cu(OH)2}$ into $\ce{CuO}$, Revisited.). But why are these growing on the cathode instead of pure $\ce{Cu}$? And is it $\ce{CuO}$ or am I wrong?


texts:
I am building a set-up to produce a controlled flow of dry hydrogen. I'm aiming for around 99.5 percent purity.

Am I right in thinking a PEM cell and Deterite drying tube should be fine for this? Or will I need a condenser of some kind?

Any tips?


texts: Do we have some "rule of thumb" to estimate the miscibility of metals?

texts:
For example, for ordinary fluids, we have polar and apolar ones. The "rule of thumb" is that polar fluids mix with each other, and also apolar fluids mix with each other, but polar fluids don't mix with apolars.
Of course, it is not a very exact rule. For example, bensene mixes in water - but it does it badly. While the also polar ethanol mixes water very well.
What is the case with liquid metals? Does some analogous - possibly more complex - category structure exist?


texts: Electron Transfer in Organic Reactions: Why Does Brown Iron Oxide Improve Burn Rate of Rocket Candy?

texts:
On wikipedia, this statement exists about rocket propellant aditives:

  Metal oxides have been found to increase the burn rate of sugar propellants. [...] Most often used are iron oxides. Red iron oxide is used most often as it is somewhat easier to obtain than the yellow, brown, or black versions. Brown iron oxide exhibits unusual burn rate acceleration properties under pressure.

I have no idea how would already oxidized compound increase burn rate. I have failed to research which compound is brown iron oxide. All I could find was red iron oxide, iron monoxide and magnetite.

So how do oxides help combustion generally? And what makes brown iron oxide so excellent for that purpose?

I would appreciate help with adding proper tags to this question. Couldn't think of any.


texts: How to choose the level of theory for modelling reactions of polymers?

texts:
My Main purpose is using quantum chemistry for simulation of some reactions. Actually we are working on making some new polymers and I need to simulate some molecular properties of these polymers after adding some molecules to them. These include bond breaking and bond making as well as evaluation of optical properties.
That's why I started studying quantum chemistry models. I started with the Schödinger Mechanical Model and then Hartree Fock Theory, but as everyone knows these models are not that efficient for molecules larger than lithium. Then I started learning DFT and got interested in semi-empirical models, but could not learn them yet. Finally I am absolutely confused about which method should I select.
This is my question: As I have not enough time to learn all those quantum chemistry models/techniques, which method is currently best option if I just want to learn ONE method. (I have access to some super-computers in our university.)


texts: Dissolving sand (or something similar) in a bottle of water?

texts:
I would like to create an illustration to demonstrate something during a talk. The idea goes that there is sediment in a bottle of water that sits at the bottom until shaken up then adding another substance to the water makes the sediment dissolve or appear to vanish.

My question is; What would make this possible? What materials or chemicals would work?


texts: The role of PIDA in C-H activation reactions

texts: PIDA ((Diacetoxyiodo)benzene) is a hypervalent iodine(III) compound that acts an attractive oxidizing agent in most of the transition metal catalyzed reactions. Can someone explain me the mechanism of PIDA in the hydroxilation of C-H bonds?


texts:
In need of $\ce{K2SiO3}$ for my cucumber plants, I purchased a bag of potassium silicate. The molecular formula is $\ce{K2O-nSiO2-xH2O}$. Normally, my bags of fertilizer are easy to figure out. For example, $\ce{Ca(NO3)2}$, or calcium nitrate, has a molecular weight of 164.0878 g/mol. The purity is also 95%. Knowing the purity and the molecular weight, I normally can find out how many ppm of Ca or N I want to use in my hydroponic nutrient tank. With $\ce{K2O-nSiO2-xH2O}$, I don't understand $n$ and $x$. I've googled this only to be stumped. I just don't get it.

The bag of fertilizer ($\ce{K2O-nSiO2-xH2O}$) has the following information listed on it:

Wt% $\ce{K2O}$ 26.5~29.5,
Wt% $\ce{SiO2}$ 55~60,
Weight ratio ($\ce{SiO2/K2O}$) 2.0~2.2,
Mole ratio ($\ce{SiO2/K2O}$) 3.2~3.4,
Bulk Density g/L 400~600,
solid % 82~89,
particle size 270+/-50 and
purity 77%

I need to know the molecular weight, so I can figure out how many ppm of $\ce{Si}$ and $\ce{K}$ to add to the solution.


texts: Bubble formation when aluminium reacts with copper(II) sulfate solution

texts:
I recently did an experiment putting pieces of $\ce{Al}$ and $\ce{Fe}$ into copper(II) sulfate solution and I noticed when the piece of aluminium was reacting, tiny bubbles were coming out whereas with the piece of iron this didn't happen.

I think it was part of the bare aluminium that was reacting with water producing hydrogen gas but I'm not sure. Can anyone please explain this to me?


texts: Perturbation theory in Quantum/Computational Chemistry

texts:
As we know, the common methods for computation molecular properties in modern Quantum/Computational Chemistry is the Hartree–Fock method and Density Functional Theory.
But from university course of Quantum Mechanic we know also, the perturbation theory method. Why is this method not common in quantum chemistry?


texts: Differences between formulae for dipole–dipole interaction energy

texts:
I came across two formulae for dipole-dipole interaction energies on Chemistry LibreTexts — Dipole-Dipole Interactions:

$$V=-\frac{2\mu_1 \mu_2}{4\pi\epsilon_0r^3}\tag{3}$$

and

$$V=-\frac{2\mu^2_\ce{A}\mu^2_\ce{B}}{3{(4\pi\epsilon_0)}^2r^6}\frac{1}{k_\mathrm{B}T}\tag{7}$$

Which of the above two is the formula for the interaction energy of dipole-dipole interactions? Also, what is the difference between the two formulae?


texts:
We have had an ongoing debate in our lab and several bad pH electrodes. I would like to ask the following question

Do paraformaldehyde soloutions (2-4% w/v) damage pH meter electrodes?

If so, why?


texts:
From: http://bubbleblowers.com/homemade.html

  Exploratorium Bubble Formula
  from the Exploratorium web site
  2/3 cup Joy dishwashing soap
  1 gallon water
  2 to 3 tablespoons of glycerin (available in pharmacies or chemical supply houses)

  Cyndi's Bubble Recipes from the Nathan's Wish web site 1/2 cup of
  dishwashing liquid (Dawn or Joy) 2 cups of water 2 teaspoons of sugar

What role does glycerin or sugar play in bubble formula?  Are sugar or glycerin better than each other in some way w.r.t this formula?


texts: The coldest (the most endothermic) reaction

texts: What chemicals can you mix that causes the coldest (the most endothermic) reaction on a $\pu{kJ /kg}$ basis?


texts:
My lecturer has defined ionization energy or ionization potential of a species A as the molar internal energy change, ΔU, for the reaction: $\ce{A (g) -> A+ (g) + e-}$ at $\pu{0 K}$, with reactants and products being in their standard states.

How can reactants and products be in their standard states when they must be gaseous?!

He then goes on to say that we often assume  $\Delta U (\pu{0 K})\approx \Delta H (\pu{298 K})$. I presume he means that the molar internal energy change of the above process at $\pu{0 K}$ is approximately equal to the enthalpy change of the above process at $\pu{298 K}$? Why is this approximation valid?


texts:
How is the naming of formyl chloride $\ce{CHOCl}$ justified? What is the functional group in it?

Why can't I name it as methanoyl chloride as acid halide is given more preference than aldehyde?


texts: Why is chlorpromazine not characterized as tricyclic?

texts:
Chlorpromazine is an old ("typical") anti-psychotic medication with a chemical structure which I as a non chemist find almost identical to that of all "ine" tricyclic anti depressants such as imipramine, amitryptiline, nortryptiline, maprottyline, and alike.
If I understood correctly, imipramine itself and later its counterparts were all originally synthesized from chlorpromazine. That said, in any occasion I've read about chlorpromazine, never have I found it being described as a "tricyclic", but rather just as "antipsychotic" (instead "tricyclic antipsychotic" compared with "tricyclic antidepressant" as with its counterparts), so I ask: Why does chlorpromazine not characterized as tricyclic?
By the way, both chlorpromazine and tricyclic antidepressants tend to cause weight gain if it matters to the reader.


texts:
No, it's not epoxy for reinforcing steel. It's "steel reinforced epoxy."

http://www.jbweld.com/products/j-b-weld-twin-tube

How in the world does steel reinforce epoxy?

I can understand how carbon nanotubes dispersed in epoxy can help strength it, quote from paper below:

  The mechanical behavior of multiwalled carbon nanotube/epoxy
  composites was studied in both tension and compression. It was found
  that the compression modulus is higher than the tensile modulus,
  indicating that load transfer to the nanotubes in the composite is
  much higher in compression. In addition, it was found that the Raman
  peak position, indicating the strain in the carbon bonds under
  loading, shifts significantly under compression but not in tension. It
  is proposed that during load transfer to multiwalled nanotubes, only
  the outer layers are stressed in tension whereas all the layers
  respond in compression.

But back to steel - as far as I know, steel is a crystalline material and it doesn't possess any property akin to CNTs. Can someone explain how this particular epoxy works?


texts: Way to confirm dichromate ion presence where other ions are messing with the color

texts:
I'm currently working on an electrolytic setting where a stainless steel (430 series, mainly made of iron and chromium, but no nickel) anode is dissolved in acidic environment (sulfuric and phosphoric acids at moderate concentrations).

My concern is the hypothetical creation of dichromate ions, since they are carcinogenic. But I can't confirm only color-wise because of the presence of other ions that mixes all the colors.

The experiment runs for long (3 hours). At first an orange color appears, which suggests dichromate ions (but could be Fe III). But after only a little while, the solution turns to a very dark and deep green, almost blue depending on the light. This suggests chromium III ions.

Several things could be happening, such as reduction of Cr VI to Cr III at the cathode, or just creation at the anode of Cr III whose color overwhelms that of Cr VI, or even Fe II or Fe III messing with the color.

Does anyone have an idea about a means to confirm or infirm the presence of dichromate ions despite not being able to judge by the color ? And if so, how could I determine the concentration of it ?

Thanks a lot in advance.


texts: How to differentiate Zn 2+ and Al 3+ on the result of blue lake test

texts:
While performing test for basic radical in analyzing a salt qualitatively. I found out that the salt gave the blue lake test and since we were taught that only Al 3+ gives blue lake test, I thought it was Aluminium ion and wrote it the same. Later, my teacher told me I was wrong and it was Zinc ion. But then how did it give the blue lake test. How do I tell if the ion is Zinc or Aluminium?

If I could check the ion by any other reagent?


texts: Is it possible to calculated the concentration of hydroxide ions from the known concentration of hydronium ions?

texts:
I came across the following question in Chapter 15 (Acids and Bases) of Holt High School Chemistry:

  Neutralizing $\pu{5.00 L}$ of an acid rain sample required $\pu{11.3 mL}$ of $\pu{0.0102 M}\ \ce{KOH}$. Calculate the hydronium ion $[\ce{H3O+}]$ concentration in the rain sample.

This is a reasonably straightforward question requiring substitution into the equation
$$c_1V_1 = c_2V_2,$$
which lets us derive the concentration of $\ce{H3O+}$.

I initially mis-read the question (which does not mention $\ce{H3O+}$) to read it as wanting the concentration of $\ce{OH-}$. However, had I not mis-read the question, would it be a valid question?

For example, can we (after getting the concentration of $\ce{H3O+}$) via the equation above, use the equation with the ionization constant of water
$$K_\mathrm{w} = [\ce{H3O+}][\ce{OH-}]$$
to also get the $\ce{OH-}$ concentration?


texts:
I understand that sugars are named α/β according to the arrangement of the OH on the anomeric C with respect to the hydroxymethylene group (Ex. glucose), but I'm a little confused how you determine α/β when you don't have that group (Ex. ribopyranose, below).

α-D-ribopyranose

 β-D-ribopyranose

Thanks!


texts:
The bond angle in a molecule is inversely proportional to the electronegativity of the surrounding atom if the central atom is same. This also happens with $\ce{NH3}$ and $\ce{NF3}$, as bond angle in $\ce{NH3 > NF3}$.

Why then is the bond angle in $\ce{NCl3 > NH3}$?


texts: Why does the ortho effect not work here?

texts: The basicity order of aniline and 2,6-tertiary butyl aniline is the latter greater than the former. Why does the ortho effect not make it the other way around? Or am I missing something?


texts: I had conducted a Salt spray corrosion test on Zinc coated bolts. The test result showed white deposits over the bolts. I want to confirm whether its zinc hydroxide or simply the sodium chloride salt that got deposited. So any  test to differentiate between NaCl and zinc hydroxide?


texts: What is the mechanism by which reactants in endothermic reactions absorb energy from their environments?

texts:
My understanding of exothermic reactions is that, in the aggregate, the sum of the bond energies of the products is lower than that of the reactants, and definitely lower than that of the sum of any excited state intermediates, and that the resulting difference in energy is accounted for by a decrease in potential energy for the bonding electrons involved, resulting in a release of photons of equivalent energy.

Seeing as how exothermic reactions generally raise the temperature of the environment they are in, it seems logical to me that those photons are rapidly absorbed (inelastically) by atoms/molecules immediately neighboring the reaction products and thus their kinetic energies are raised, although I honestly don't truly understand the mechanism for that, either.

Similarly, for reactions that are isothermal but which are chemiluminescent, photons of a wavelength not easily absorbed by neighboring atoms/molecules simply leave the environment.

However, does that mean that the inverse is true? Is IR radiation from the environment the direct mediator of energy transfer that raises bonding electrons in reactants to anti-bonding MOs so that new MOs can form among different configurations of the original reactant atoms, thus allowing electrons to occupy the bonding MOs of the products?

I ask because the basic collision theory proposed by Trautz and Lewis doesn't seem to account for quantum mechanical models of energy, but I admit my own understanding of the topic is about as limited as my question would demonstrate.


texts: How does the degree of saturation influence the colour of the flame?

texts: If the colour of flame produced by the atom of an element is the property of that element then why do unsaturated and saturated carbon compounds give different colours of flame even though both contain the element carbon and hydrogen?


texts: Does the prefix Ortho have some significance?

texts: Are orthoboric acid and boric acid one and the same thing or we can not write H3BO3 as B(OH)3?


texts: In the picture, graphs show the constructive interference of two 1s atomic orbitals. My question is, what does the horizontal axis in wavefunction graph represent, does It represent the distance from the nucleus? We see the pick point of wavefunction on H atom, does It mean that highest probability of electron density is on the nucleus, which is impossible.  I am quite confused about the meaning of a wavefunction, can anyone help me?


texts: Best way to dissolve/emulsify beeswax and carnauba wax in water-based solution

texts:
What I can use to dissolve beeswax and carnauba wax and keep it in an aqueous solution? I do not want to use ethanol or acetone as they are too harsh.

I am adding about $\pu{5\%}$ wax to a $\pu{16oz}$ aqueous solution that also has some oil in it. I need to stop it from coagulating and be fine enough or in solution to pass through the nozzle of a spray bottle without clogging it ?


texts: Qualitative tests for sodium peroxoborate

texts:
Recently in a chemistry lab I preformed two qualitative tests on sodium peroxoborate.

The procedure for the qualitative tests involved taking a small amount(about 0.2g) dry dry $\ce{Na2[B2(O2)2(OH)4].6H2O}$ and dissolving it in water making up the solution to $10\ \mathrm{mL}$. I then divided it into to small beakers.

To one beaker I added 5 drops of 1M sulfuric acid and then add 0.02M $\ce{KMnO4}$ solution dropwise.
To the other beaker I added 5 drops of 1M sulfuric acid and then add 10% of potassium iodide solution dropwise.

What are the the balanced equations for these reactions?


texts: What does "stoichiometric amounts" mean?

texts:
Can anyone inform me what the term stoichiometric amounts means? I know what stoichiometry means. It is the:

  The relationship between the relative quantities of substance taking part in a reaction or forming a compound.

But what is "stoichiometric amount" supposed to be?


texts: Why is the side chain of lysine more basic?

texts:
According to the images below, the NH3+ on the side chain of lysine is less acidic than the NH3+ closer to the COO-. Why is this? Wouldn't the NH3+ have an intramolecular H-bond with a negatively charged oxygen on the carboxylic acid group, stabilizing it?
One possible explanation I thought of is the carbons on the side chain donating electron density through hyperconjugation, but this seems unlikely because both amines are primary.
My instructor said that the inductive effect of the carboxylic acid makes the NH3+ close to the oxygens unstable, but in solution it would be a negatively charged carboxyl group, making induction also seem unlikely.
Any help would be appreciated.


texts: How can I reduce Crystallization temperature of seed oil to be used in winter as biodiesel?

texts:
How can I reduce Crystallisation temperature of seed oil to be used in winter as biodiesel?
The glycerol has been removed from the oil, and white spirit is used to reduce its viscosity.


texts: Reason for endothermic nature of NaHCO3 + C2H4O2 reaction

texts:
Why is the classic baking soda and vinegar reaction endothermic? Here are some possible answers I've come up with:

The dissolution of the sodium acetate absorbs energy,
The release of the carbon dioxide from solution absorbs energy, or
Some combination of the above.


texts: How is the charge of covalently bonded atoms determined?

texts:
My question is about what it is - at the subatomic level - that determines the charge on atoms which participate in covalent bonding in reality. I understand that formal charge is just that - it's a formality, which gives human beings a very useful tool for modelling reality and making predictions. I, though, would like to know what is responsible for the charge we find in covalently bonded molecules.

Let me explain. If we picture an ionic bond as a highly polar covalent bond, we can see that in an atom like NaCl we have the state of affairs where the highly electronegative chlorine atom has "pulled away" an electron from the sodium atom.

(Orbitals omitted for ease of drawing)

Ultimately this means that Na, with its 11 protons has just 10 electrons, which gives it a positive charge, while Cl, with its 17 protons, now has 18 electrons, giving it a negative charge. Electrostatic forces between the two nuclei result in the bond.

Of course, it might be more accurate to say that the Na nucleus simply ceases to be significantly affected by its former 3s1 electron. As a result the 11 protons in the Na nucleus, which result in a +11 charge, are countered by only 10 electrons, giving a +1 charge overall. Meanwhile, the 17 protons of the Cl nucleus (+17 charge) experience the negative charge of 18 electrons (-18) giving a -1 charge overall.

Let's compare this with the situation we find in the carbonate ion. (Link) For the purposes of my question I won't worry too much about resonance, I don't mind too much whether we have the accurate -2/3 charge, but let's keep it simple and just look at one of the contributing structures.

(Orbitals again omitted for ease of drawing. Orange indicates an additional electron from some other source. Oxygen has only eight electrons ordinarily, but one will be gained when forming this ion)

In this case we have covalent bonding. In the case of the singly bonded oxygens, we have 8 protons and 10 electrons. This is two more negatively charged electrons than positively charged protons. This, though, is not ionic bonding, it is covalent bonding and the polarisation is not such that the electron contributed by carbon dissociates completely from the Carbon. Instead it is "shared" between the two. Nevertheless, the "sharing" is not equal and oxygen attracts the electrons more strongly than the carbon, so we have a -1 charge.

My question, though, is - why is it that the charge works out like this? Why is it that when you have oxygen (8 protons) (charge of +8) and a filled outer shell (8 electrons plus buried inner core gives -10 (charge of -1 on each electron)) you have a charge of -1 not -2, is it simply the covalent bond, is it simply the fact that the two electrons in the sigma bond are sufficiently far enough away in reality?

But then why should it be that the doubly bonded oxygen, which also has ten electrons surrounding it, has no charge at all? Meanwhile, the carbon atom in the  middle is surrounded by 10 electrons also, whereas it has only 6 protons and yet carries no charge at all.

Naively the answer seems obvious. The bonds are covalent and the electrons are "shared." So, in the double bond (which, of course, has a different nature to the single bond) one must assume that the electrons are positioned in such away that they are balanced by the protons of the oxygen nuclei. There is therefore no charge on this atom.

In the case of the Carbon atom we surely again understand that the right balance of charges and distance from the nucleus is arrived at.

Overall we have 32 electrons and 30 protons so the overall -2 charge on the whole atom makes sense.

The ultimate question I've been trying to lead up to is what is it that dictates the distribution of charge. What is the difference - at the subatomic level - between two ionically bonded atoms, a covalently bonded molecule like the CO32- ion which carries a charge, and a covalently bonded molecule like H2O - which is also polar (hence we can have hydrogen bonding) but isn't usually assigned a charge. On what basis do we assign charge?


texts: PAW vs USPP: Pseudopotentials in commercial DFT codes

texts: What is the difference between USPP (ultra-soft pseudopotential) and PAW (projector augmented wave) in commercial DFT codes?


texts: What are the molecular requirements for condensation polymerization?

texts:
I know that in order to have addition polymerization, the monomers must have a C=C double bond. However, I don't know the molecular requirements for condensation polymerization. Must the monomers contain a functional group at each and?

Any help is appreciated. Thanks.


texts:
In solid, energy bands means the 1s orbital with spin up and down become 3 states when there are 3 atoms.
But then. If you look at hydrogen atoms, the allowed bound states have energies equal to En=Ry/(n2) and n is the main quantum number ranging from 1 to infinity. In other words, there is an infinite number of available electronic states in a single hydrogen atom.
When we talk about energy bands. Which of the above is usually referred to? The few states orbitals or the almost infinite allowed bound states?
For the latter, how do you characterize the energy bands in liquid like
water? What kind of bands are formed in such cases?


texts: How to use Google’s Alpha-fold to predict the structure of a two-protein complex?

texts:
Alpha-fold won the CASP13 and CASP14 competitions last year and this year. It used deep learning to predict the secondary structure of a protein given the primary amino acid sequence.
Google has released its code a few weeks ago, and I was wondering how to use Alpha-fold to predict the complex of two proteins.
Naively, I'd concatenate the amino acid sequences of both proteins as if they were a single protein. Then I’d input the neural network with the concatenated primary sequence.
The network will predict the lowest energy conformation  of the concatenated proteins. I am afraid that the artificial backbone connection between the two proteins might lead to a completely wrong complex.
I could do some docking of the two individual proteins, but I want to find the denovo prediction of the two-protein complex.
Edit: here is an Pytroch implementation of Alpha-fold2 on github.


texts: Why does mercury in mercuric acetate have a lone pair?

texts: The configuration of mercury ends with $6s^{2}$. In mercuric acetate, mercury is in the +2 oxidation state, so does it still have a lone pair?


texts: The similarities and differences between electron transfer and charge transfer

texts:
Please explain the similarities and differences among electron transfer,electron transport, charge transfer, and charge transport from the molecular, atomic and electronic levels.

Is electron transfer different from electron transport?

Is charge transfer different from charge transport?


texts: What is a "tube lens" in a mass-spectrometer ion source and what does it do?

texts:
I came across the Russian phrase "Transporting capillary voltage: 85 V" in a text I was translating. The paragraph was describing the operating parameters of an electrospray ionization-based ion source in an MS system.

The author told me that the proper English translation is "Tube lens voltage: 85 V". I googled for electrospray "tube lens" and found this picture:

I haven't found a down-to-earth explanation of what it is yet. Maybe someone here knows and can explain this in simple words.

Why is it a "lens"? It looks like a simple channel throught which the liquid flows to the needle.


texts: What algorithm is GaussView using for the clean function?

texts:
A colleague showed me GAUSSIAN 09 which comes with GaussView 5
for drawing structures. What impressed me was the snappiness of the
Clean function.

What algorithm is used for the Clean function?

The GaussView 5 Reference can be downloaded from the publisher’s
web site. It doesn’t seem to contain the information that I’m looking
for.

Background: As part of a project called
 SAN – Self Aware Network, I have a similar problem, though with
 additional constraints. To find the distribution of points in space,
 I implemented a genetic algorithm. Unfortunately, with large
 structures, this algorithm tends to get stuck in local minima. I
 documented the algorithm in the report SAN: Location Optimizer.
 A mathematician friend implemented a
 solution using gradient descend. Yesterday, he showed me some
 nice results, but it’s nowhere as snappy as GaussView.

Update

I also contacted Gaussian technical support. Their response:
“Unfortunately, no. We do not have additional documentation about this
function, other than what is already present in the GV5 manual. This
function just uses a very simple MM expression with crude parameters
just to provide a simple way to "clean" a structure drawn "by hand" in
GaussView. It is certainly not intended to give accurate geometries
(it is expected that one is going to use some other model in Gaussian
to run a geometry optimization and get a good geometry). The purpose
is simply as another aid as part of building a structure in GaussView,
so one may "clean" a structure faster (not always) than otherwise
using "modify bond", "modify angle", "modify dihedral" tools.”


texts: What is the correct nomenclature for diphenyl methane?

texts:
Can $\ce{Ph-CH2-Ph}$ be also be named as  as (phenyl methyl) benzene instead of diphenyl methane?

I came to this thinking that $\ce{CH2-Ph}$ can be considered as side chain at side chain.


texts:
The electrophilic addition of $\ce{HBr}$ across an unsymmetrical alkene follows Markovnikov's addition, but sometimes if the addition occurs via rearrangement then should we call it a Markovnikov addition?

Earlier, in an entrance exam, a similar question was asked and they have given the correct answer which states Markovnikov's addition for a reaction that occurs without a rearrangement.

In my opinion, if addition occurs without rearrangement then it should be Markovnikov's addition.


texts: Approximate magnetic susceptibility of these liquid propellants?

texts:
This question asks if the comparatively large paramagnetic susceptibility of liquid oxygen (LOX) is considered when designing rocket tank and engine systems. This comment suggests fuels such as RP-1 (kerosene-like) and liquid hydrogen (often used in liquid-propellant rockets) do not have a susceptibility as large.

I'd like to find either the approximate or even ballpark values for the magnetic susceptibility of the following four materials, or at least a source where they might be found:

liquid oxygen (LOX)
liquid hydrogen (LH2)
RP-1 (rocket fuel), and
liquid methane (LNG)

I have tried google searches of various permutations of terms, but so far no luck beyond the one value I was able to cite in that question (LOX susceptibility here).

I'm fairly sure that the susceptibility of the other three are much smaller (100× or more) than that of LOX. For example here is what I can do now:

LOX: use the value reported in the link above; 3.5E-03
LH2: This question links to this table which lists the susceptibility of liquid hydrogen -5.44E-06 cm³/mol. If I use a density of 0.07 g/cm³ and molar mass of 2.0 g/mol (both from here) I get approximately -1.9E-07.
RP-1: decide that for paramagnetic and diamagnetic susceptibility, kerosene and crude oil are very roughly equivalent and use -1E-08 m³/kg from section I of this along with a density of order of magnitude 1000 kg/m³ to get a susceptibility of roughly -1E-05
LNG: - same argument as RP-1, roughly -1E-05


texts: Is osmosis really a special case of diffusion across a semipermeable membrane?

texts:
A general idea we have about osmosis is that it is the movement of solvent particles through a semi permeable membrane from a region of high concentration to a region of low concentration. This seems correct in case of a gas. Gaseous particles spread through any container in which they are kept, which makes it seem to us as if they moved from high concentration to lower concentration. But in the case of a liquid how is this true? For example consider a bottle half filled with water, water  never moves from high concentration to lower concentration inside the bottle.

So is it wrong to explain osmosis as a special case of diffusion?

What actually makes solvent particles move from regions of higher concentration to regions of lower concentration? Is it solute attraction? Or a difference in pressure in pure solvent phase and solution phase?


texts: Conversion of potassium dichromate solution to a less toxic solution

texts:
I have a solution of potassium dichromate ($\ce{K2Cr2O7}$) and I want to convert it to a less toxic solution. What would be the best way to do this?

I was thinking of using the dissolved potassium dichromate as an oxidizer in the oxidation of alcohols to organic acids, to eventually produce the chromium(+III) ion (what is less toxic)

Or are there any other, easier methods?


texts: Deriving kinetic equations for a complex reaction system

texts:
I have a system of protein reactions that I've derived differential equations for the kinetics of. I'm using them to run simulations to fit the rate parameters, but the simulations at present are working badly. I'd like to start by checking the system of differential equations. I realise they may be to complex for anyone to write them out here, but you know of software that could be used to check my work, please post it here. (A lot of people face similar problems)

The three monomers are $L$, $A_1$, $A_2$; the chemical equations for the monomers forming dimers are:
$L + A_1 \rightleftarrows^{k_{a1}}_{k_{d1}} LA_1$,
$\qquad$
$L + A_2 \rightleftarrows^{k_{a2}}_{k_{d2}} LA_2$,

and the dimers forming trimers are:

$LA_1 + L\rightleftarrows^{k_{a1}}_{k_{d1}} LA_1L$,
$\qquad$
$LA_1 + A_2\rightleftarrows^{k_{a2}}_{k_{d2}} A_1LA_2$,

$LA_2 + L\rightleftarrows^{k_{a2}}_{k_{d2}} LA_2L$,
$\qquad$
$LA_2 + A_1\rightleftarrows^{k_{a1}}_{k_{d1}} A_1LA_2$,

trimers forming tetramers:

$LA_1L+A_2\rightleftarrows^{k_{a2}}_{k_{d2}} LA_1LA_2$,
$\qquad$
$LA_2L+A_1\rightleftarrows^{k_{a1}}_{k_{d1}} LA_2LA_1$,

$A_1LA_2 + L\rightleftarrows^{k_{a1}}_{k_{d1}} LA_1LA_2$,
$\qquad$
$A_1LA_2 + L\rightleftarrows^{k_{a2}}_{k_{d2}} LA_2LA_1$,

dimers forming tetramers

$LA_1+LA_2\rightleftarrows^{k_{a1}}_{k_{d1}} LA_1LA_2$,
$\qquad$
$LA_1+LA_2\rightleftarrows^{k_{a2}}_{k_{d2}} LA_2LA_1$,

tetramer molecules changing their configuration

$LA_1LA_2 \rightleftarrows^{k_{a4}}_{k_{d4}} B$,
$\qquad$
$LA_1LA_2 \rightleftarrows^{k_{a3}}_{k_{d3}} B$.

Could anyone either point me in the direction of software to derive the system of differential equations, or do the derivation?


texts: What do different dissociation constants mean?

texts: What does first, second, third etc. Acid dissociation constants mean? They are written as $pK_{a_{1}}, pK_{a_2}$ etc. If any one would explain it that would be good.


texts: In the conversion of propene to 1-propanol, can we just use water in presence of peroxide instead of first converting it into 1-bromopropane and then reacting with $\ce{NaOH}$?


texts: How to quench unreacted sodium azide from reaction mixture?

texts: The reaction involved synthesis of azide formation from alkyl bromide in DMF using sodium azide. After the reaction has taken place, how do I quench the unreacted sodium azide from the reaction mixture?


texts: Comparing acidic strength in oxan-2-one and oxan-4-one

texts:
I need to compare the acidic strength in these molecules:

My Approach:

In compound I: Removing a proton would lead to conjugation between -ve charge, pi bond and lone pair of O. Moreover the inductive effect due to 'O' will stabilize the charge.

In compound II: Removing a proton(from the carbon adjacent to the pi bond) would lead to conjugation, but relatively less than one. Moreover 'O' is far away, so inductive effect does not play a role here.

From this I concluded that compound 'I' must be more acidic.
But the answer says that the second compound is more acidic.

Where am I going wrong?


texts:
MY ATTEMPT

We already know that $\Delta U=nC_V\,\Delta T$
which is for constant volume

Now we know that $\Delta H = \Delta U + p\,\Delta V$

so $\Delta H = nC_V\,\Delta T + 0$ (as at constant volume $\Delta V = 0$)

$$\Delta H=nC_V\,\Delta T$$

But I have never such an equation anywhere.

Please verify.


texts: Does magnesium sulfate in aqueous solution form magnesium (hydrogen-)carbonate when hydrogen carbonat is present?

texts:
I'm using an additive of magnesium sulfate to complement my fertilizer. The additive lists the following ingredients:

I know that it does NOT contain magnesium oxide, because due to historical / commercial reasons ingredients of phosphorus, potassium or magnesium are indicated as mass percentages of the oxides with the element in question. Also the merchant confirmed that the source of magnesium is magnesium sulfate.
I noticed the precipitation of a white powder at the bottom of my reservoir. I suspect it to be magnesium carbonate. The  mains water contains the following chemicals. The dose of magnesium sulfate is within the range recommended. The precipitation occurs even if I do NOT use any fertilizer, so I think It is a reaction with chemicals in mains water supply.

Is the precipitate magnesium carbonate?
How can I prevent this precipitation? What are factors influencing it besides the availability of hydrogen carbonate?
EDIT:
User AJKOER suggested that the precipitate is calcium sulfate. I don't think that is the case because:

The solubility of calcium sulfate is given at 2.1g / liter @ 20° C  (https://en.wikipedia.org/wiki/Calcium_sulfate). This equates to about 2.1 * 0.71 ~ 1.48g sulfates per liter. (mass of SO4 /  mass of CaSO4 = 0.71)
I'm adding only about 92.1 mg / liter sulfates from magnesium sulfates
The mains water contains only 13.3mg / liter sulfates
92.1 mg / liter + 13.3mg / liter <<<< 1480 mg / liter


texts: how can carbon dating even work? Its at atomic level!

texts:
I am a homeschooling parent, so pardon me asking stupid questions.
Everywhere I read, it is said carbon based lifeforms eat carbon and after their death that atom starts a decay.

But what I cannot understand, we dont eat or work with food at atomic levels. Yes, life forms breaks down molecules from food and use them as they wish. But that chemical process does not effect the atom structure. I dont think any life form has capacity or energy to break down atoms.

So if one atom of C14 was having a decay already before we ate it, it keeps having it while it gets digested and goes on in the same way if life is alive or dead. If another C14 was not having a decay, then it starting a decay has nothing to with the life form is alive or dead.

As Dr. Manhattan(Watchmen 2009) said atoms dont care if you are alive or dead. They stayed there at the same place before and after.

So how can a lifeform have any effect in the C14 decay at all?

Got some good answers, so I clarifying my questions:

How can we be sure that we have eaten only fresh out of factory C14? It may be already decayed by hundred or thousand of years  when we eat it. It applies to all living beings. If there is fresh C14 in the air, there is also decaying levels of C14 as old as 50K years. So when you check my c14 count, you would have a wrong answer of when I died cause origin of C14 was even before I was my great grandfather was.


texts: Explaining temperature change in an exothermic system.

texts: In a neutralization reaction, is heat given out to the system, thereby raising its temperature? Suppose we put a thermometer in the acid-base mixture and there is an increase in the thermometer reading. Is this increase simply because part of the reaction's heat given out is supplied to this thermometer, or because the water solvent is actually warmer? In other words, if we measure the temperature of the system before and after the reaction, will there have been an overall decrease in the temperature, or increase (and please explain why)?


texts: Was Wöhler’s urea synthesis carried out with or without oxygen?

texts:
I learnt and was very impressed by the urea synthesis by Wöhler in 1828. The reaction was the heating of ammonium cyanate. One of my textbooks in the library said that ammonium cyanate was heated ‘in the absence of oxygen’.

But when I tried reading other organic chemistry textbooks, they also did mention the synthesis but never talk about whether it was anaerobic. Could anyone suggest a reliable source which clearly state about this matter?


texts: Advice on forming a 10% solution of Maltol

texts:
I’m having great trouble forming a 10% solution of Maltol. Specifically, I’m trying to dissolve 3 grams of Maltol in 27 grams of solvent.

I’ve tried everything from Propylene Glycol, to Deionized Water, to Ethanol, including some mixtures of these few solvents, but none of them can work to fully dissolve all the Maltol.

The best one so far appears to be hot Deionized Water, which appears to dissolve the most Maltol. Adding a small amount of Ethanol helps dissolve the Maltol further, but not completely.

Here I’ve attached a photo of the result. The entire mixture was immersed in a hot water bath. As you can see, the Maltol appears to form fluffy clumps that float to the surface, and are really stubborn to dissolve.

If anyone could advise me on how to achieve a complete dissolution of the Maltol, that would be very much appreciated!

Thank you!


texts: What is the difference between the equilibrium position and the equilibrium constant?

texts: I used to think that the equilibrium constant was a quantitative measure of the equilibrium. However, changing concentration and pressure in a system at equilibrium that shifts the equilibrium doesn't affect the equilibrium constant, which is solely temperature dependent. This means that my definition was wrong. What is the real relationship between the two, or what do they actually mean? (I haven't been able to find any suitable definition for "equilibrium position," and the only definition I know how "equilibrium constant" is the value of the reaction quotient when a system has reached equilibrium).


texts: Weight of sodium acetate required to get to certain pH

texts:
How many grams of $\ce{CH3COONa}$ we need to dissolve in $\pu{2.50 L}$ of water to get a solution with $\mathrm{pH} = 9.00$? Given $K_\mathrm{a}(\ce{CH3COOH}) = 1.75\cdot 10^{-5}$

Like solving a puzzle, I found from the asked $\mathrm{pH}$ the concentration of hydrogen cation and hydroxide anion, and wrote to myself that I need to find the final concentration of $\ce{CH3COONa}$ to seek from it the amount and then the weight.

But my problem was in all the middle steps. I understand the the concentration of hydroxide anions that I found is after the equilibrium, but I miss the point of how to use them to find the concentration on the acetic acid by given the $K_\mathrm{a}$. I'm guessing that I need to get the $K_\mathrm{b}$ from the $K_\mathrm{a}K_\mathrm{b}=K_\mathrm{w}$ equation. But why exactly and how then, I need to find the concentration of $\ce{CH3COONa}$?

Maybe I lack the knowledge and thus the imagination for it.

Support highly appreciated!


texts: How common are automated pipetting systems

texts: It's clear that automated pipetting is faster than doing it manually, but how common is it for a lab to have an automated pipetting system, and what usually are the circumstances that a lab have before they purchase such a system?


texts: Can a Hydrogen Radical form in a chemical reaction?

texts:
Original question: During kolbe electrolysis of Formic acid, H2 is released at which electrode?

What I thought: H2 will form at cathode due to reduction of water. But will the Formic acid decompose to give H2 and CO2 by radical mechanism?

My doubt: Does H radical form in chemical reactions?


texts:
Carbon and iodine have similar electronegativities. The reason quoted for the C-I bond having polarity is that iodine is more polarisable.

But what does this actually mean? Carbon distorts the electron cloud around ioidine, but how exactly does it distort the electron cloud? And how does this affect the polarity of C-I bond?

Does it, perhaps, distort the electron cloud of ioidine away. But why would it distort the electron cloud away and not towards the C-I bond where the electrons have the opportunity to experience the attraction of two nuclei as opposed to just one?

Edit: here is a quote from a textbook  (Organic chemistry, Fourth Edition by Paula Yurkanis Bruice):

  "Carbon and iodine, however, have the same
  electronegativity. Why, then, does an alkyl halide undergo a
  substitution reaction? We know that larger atoms are more polarizable than smaller
  atoms. (Recall from that polarizability is a measure of how easily an
  atom’s electron cloud can be distorted.) The high polarizability of the large iodine
  atom causes it to react as if it were polar even though, on the basis of the electronegativity of the atoms, the bond is nonpolar."


texts: Determining the charge on an ion through mole calculation in electrolyis

texts:
During electrolysis $\pu{0.02 mol}$ of metal $\ce{X}$ is deposited on cathode when $\pu{0.12 mol}$ of electrons are passed through molten chloride of $\ce{X}.$ What is the formula of the chloride?

I have tried solving it and my answer is $\ce{XCl6}$ which is incorrect. The correct answer given is $\ce{XCl3}.$

In the explanation the book says that $\pu{0.06 mol}$ of electrons have flown to cathode and goes on to divide the amount of electrons at cathode by the amount of metal $\ce{X}$ $(0.06/0.02),$ so it's $3$ which means $1$ atom of $\ce{X}$ gains $3$ electrons, giving it $+3$ charge.

What I do not get is what about the other $\pu{0.06 mol}$ of electrons. Isn't metal $\ce{X}$ supposed to gain all of the $\pu{0.12 mole}$ of electrons? Shouldn't cathode have the total $\pu{0.12 mol}$ of electrons?


texts:
I am a student in my last year of high school and currently making a research on how to find sulfites in dried fruits. I've collected data and different methods online and combined few of them into one.
In my method I use hydrogen peroxide and barium chloride to create a white precipitate (result should be barium sulfite).

But the problem is that I never get any precipitate.
During my research it mentioned that I was to leave the dried fruit in distilled water over night (I used dried apricots).
I had 26g, 30g, 40g of dried apricot in 100mL of distilled water.
Once done, I filter out all of the liquids into a different beaker. Then filter it using filter paper. Once done I separate them into different beakers to test. And this is where I find the problem, I've done 6 trials so far, and all 6 have failed. Because I don't know what amount of H2O2 or what amount of the concentration I need to put into the apricot liquid for it to properly react, or for how long I should leave it in for it to react (I've waited 3 and 5 minutes). I'm then supposed to drop a single drop of barium chloride into the solution to produce the white precipitate. But so far I haven't gotten any sign of any precipitate. I've tried different amounts of H2O2 (1mL, 5mL, 10mL, 15mL, 20mL & 25mL with a 35% concentration in the first trials but rest of the trials were with a 3% concentration). Each with a drop of barium chloride.
Seeing that they did not react to a drop, I tried to use 5 drops each on the first few trials. Yet I still got no reaction.

Could I get some help or advice please?

Thank you


texts: How do scientists figure out the chemical structure of a given compound?

texts:
Please bear with me a bit while trying to explain my question as best as I can. I am a 4th year medical student so my command on chemistry is not too good, but I find it fascinating and intriguing, it is like magic.

My question is as follows:
How do scientists actually know the exact composition of a compound e.g. Caffeine ($\ce{C8H10N4O2}$), how do they exactly know that it has this exact amount of hydrogen or nitrogen atoms in a single molecule?
After knowing that, how do they know the precise geometry of the molecule (here I mean the hexagons and pentagons and how they connect).

And one last thing, how do they know the exact geometry and sequence of atoms in an enzyme?


texts: Reaction between lead dioxide and nitric acid

texts:
A wikipedia article suggests that lead dioxide is produced by this reaction:
$$\ce{Pb3O4 + 4 HNO3 → PbO2 + 2 Pb(NO3)2 + 2 H2O}$$

The same article also suggests that lead dioxide reacts with nitric acid in the following way:
$$\ce{2 PbO2 + 4 HNO3 → 2 Pb(NO3)2 + 2 H2O + O2}$$

I am unable to understand why then, in the first reaction, $\ce{PbO2}$ doesn't further react with the residual nitric acid. Is it because the quantity of the acid is regulated? Or is there some error in the reactions?


texts: Computing the concentration of a reactant given formation of products

texts:
At high temperatures nitrogen dioxide decomposes into nitrogen oxide and oxygen gas according to $$\ce{2 NO_2 -> 2 NO + O_2}$$

I have a question now. Let's say at a certain temperature I'm given data for the formation of $\ce{O_2}$. For example:
At $t = 0$ we have $[\ce{O_2}] = 0$ mol/L, at $t = 50$, $[\ce{O_2}] = 7.10 \cdot 10^{-4}$ mol/L, at $t = 100, [\ce{O_2}] = 1.205 \cdot 10^{-3}$ and so on until a certain time.

If I'm given that the initial concentration of $\ce{NO_2}$ is $0.006M$, how can I know what the concentration of $\ce{NO_2}$ is at certain times? I'm asked to determine the order of the reaction on the basis of the given data, and also to present graphically the rate constant.

To do that I need to know if $\ln([\ce{NO_2}])$ versus time $t$ is a straight line. But how to find $[\ce{NO_2}]$ in the first place?


texts: Why are drugs mixed with their sodium salts?

texts:
I have come across quite a few drugs that are of the form $\ce{HA + NaA}$, where $\ce{A}$ is your target organic compound. A few examples of this are:

Carmicide which is a mixture of Sodium Citrate and Citric Acid
Fucidin which is a mixture of Sodium Fusidate and Fusidic Acid

What advantages are there in conjugating a drug with its sodium salt?
A similar question says that this increases solubility and also makes the drug easier to crystallize and purify. I'm assuming that the same reasoning does not work for organic acids, considering they will dissolve/ionize quite easily. Please clarify and provide further insight into this topic.


texts: Product operator analysis for CHn groups in HSQC and HMQC

texts:
I'm taking and advanced NMR course this semester and we are learning about product operator formalism. I have a homework where I'm supposed to apply this formalism to an HSQC and HMQC experiment. The problem I have is that I should use a 3 and 4 spin systems $(\ce{CH2})$ and $(\ce{CH3})$ groups instead of just simply $(\ce{CH})$ and we only did two spin systems in class. I understand how to use the formalism and how to apply it to the experiment, but I need let's say a concept clarification. We use basic pulse sequences for HSQC and HMQC.

In the exercise, we assume that the hydrogens do not couple to each other, only to the carbon. I did the example a found out that the result (in the product operator formalism it was the same observable term which with I was left at the end) was the same for $\ce{CH3}$ group as for $\ce{CH}$ after optimization of delay time. After I thought about it, I feel it makes sense. Since the three hydrogens will do the same as one hydrogen, only I will have a different intensity afterward in the spectrum and of course different shifts. I even calculated that the optimal tau delay is the same for both $\ce{CH}$ and $\ce{CH3}$ groups.

And since HMQC basically gives the same info, I assume it will work the same, and results for $\ce{CH}$ and $\ce{CH2}$ group will also give me the same.

Is this correct? Is there any other difference in what happens during the experiment to the $\ce{CH}$ and $\ce{CH3}$ group (or $\ce{CH2})?$

Just to clarify, it is not a multiplicity editing experiment, just a simple HSQC/HMQC applied to $\ce{AX2}$ and $\ce{AX3}$ spin systems.


texts: If Oxygen has a lower electron affinity than Sulfur, then why doesn't sulfur has a lower electron affinity than selenium?

texts:
I've read that oxygen has a lower electron affinity (as shown the picture below), because it has a smaller atomic radius than sulfur and thus the electrons experience significant electron-electron repulsion.
However, I was wondering... Why is this not the case for sulfur and selenium or chlorine and bromine? Because of sulfur's and chlorine's smaller atomic radius compared to selenium and bromine, the incoming electron should also experience a slight electron-electron repulsion (just like it does with oxygen), so $\ce{Se}$ and $\ce{Br}$ should have a higher electron affinity.


texts: What is the role of various additives in a titration of vitamin C with N-bromosuccinimide

texts:
In a titration to determine the amount of vitamin C in an orange juice sample, the following were mixed with water:

oxalic acid
potassium iodide
starch
acetic acid

Then, the mixture was titrated with a solution of N-bromosuccinimide until the solution turned dark as the starch/iodine/iodide inclusion complex formed.

$$\ce{2I- + NBSucc + H+ -> I2 + Succ + Br-}$$

where NBSucc is N-bromosuccinimide and Succ is succinimide.

Source: https://media.cheggcdn.com/media%2Fd2a%2Fd2a428e0-d1b7-4cf1-bcf9-fb81813660b4%2Fphply3xn7.png

What is the role of the two different acids (acetic acid and oxalic acid) in the titration? How does the outcome of the titration depend on the concentration of potassium iodide?


texts: The wikipedia page states clearly that the coloured form of phenolphthalein is the one with two protons removed. What is the evidence that phenolphthalein loses both protons in basic solution? And does the only once deprotonated form ever appear?


texts: Calculating approximate pH of polyprotic acids

texts:
When I took up ionic equilibria and titrations after a long break, I found it hard to solve the questions regarding pH calculations of polyprotic acds. Consider these two questions as examples:-

  Find the approximate pH of a solution with $0.4M\text{ }\ce{HCO3-}$ and $0.2M\text{ }\ce{CO3^2-}$$K_{a1}=4\times 10^{-7}$,
  $K_{a2}=4\times 10^{-11}$
  Find the approximate pH of the resulting solution formed after mixing $20ml$ of $0.1M\text{ }\ce{H3PO4}$ and $20ml$ of $0.1M\text{ }\ce{Na3PO4}$. Express in terms of $pK_{a1},pK_{a2},pK_{a3}$.

I have mentioned 2 questions here because I want to know the method to solve such type of questions and not these two questions here in particular. The problem arises when there is a polyprotic acid with hydrolysable salts. For the second case, the ongoing equilibria are the dissociation of the three acids and the hydrolysis of their respective salts. For the first one, there are just two dissociation equilibria(and the dissociation of water). Even by writing down the equilibrium expressions of these reactions, I am unable to reach the final expression with pH or pOH. And, all the solutions have to be approximate (using approximations like the negligible contribution of hydrogen from the dissociation of water, low value of the successive ionization constants) and not at all accurate.

I would appreciate if someone explained how to do such numericals, taking one of the above as an example (I already have the answers for the aforementioned questions. I just want to use them to illustrate the general principle behind these questions).

Let me know if my question looks too homework-like and off-topic.


texts:
I'm given a problem where an ideal gas is expanded isothermally. I'm given the molar volumes from the start and the end and basically asked to find the change in Gibbs Energy.

I started with the equation

$$G=H -TS$$

We can write the general form $dG$

$$\begin{align}
dG & = dH -SdT - TdS \\
    & = (dE + PdV + VdP)- SdT -TdS \\
    & = (TdS - PdV) + PdV + VdP - SdT - TdS \\
    & = VdP -SdT
\end{align}$$

It's an isothermal process $\to$ (const.) $T$. Hence $SdT \to0$

Now we are left with $dG=VdP$. We need the Gibb's energy in terms of moles and molar volumes. Hence entropy (which is zero anyway) and volume need to change to molar volume. Our new equation is in terms of moles

$$dG_m=V_mdP$$

if we assume $V_m$ to be constant which it isn't but for argument sake we can get the following relation

$$\Delta G_m = V_m\Delta P=RT \ln\Big{(}\dfrac{P_f}{P_i}\Big{)}$$

since $V_m = \frac{V}{n}=\frac{RT}{P}$ for an ideal gas.

My problem is - I would like to know if I can assume the pressure to be constant and have

$$\Delta G_m = RT \ln \Big{(}\dfrac{V_f}{V_i}\Big{)} $$

Is this equation valid for finding the molar Gibbs energy, knowing the molar volumes (initial and final) and at constant temperature.

I think it's wrong because $dG_m = V_mdP$ is valid for constant $T$ but the pressure cannot be constant. I've just been struggling with trying to find a relationship with gibbs energy and molar volume and not knowing pressures.


texts: Why do bicarbonates tend to be more soluble in water than carbonates, for Group 1 and Group 2 elements?

texts:
In Group 1 and Group 2, it is usually found that bicarbonates tend to be more soluble in water than carbonates. For example: $\ce{NaHCO3}$ has higher solubility than $\ce{Na2CO3}$

As most of the trends in s block elements are explained by lattice enthalpies, I think it has something to do with lattice enthalpy, but I’m not sure how we can say lattice enthalpy of $\ce{Na2CO3}$ is higher than $\ce{NaHCO3}$.


texts: Whether for all zero order reactions rate is independent of concentration of reactants

texts:
For example,for the reaction $\ce{A + B \longrightarrow C}$,If rate law expression is:
$$\mathrm{Rate=k \times [A]^{(0.5)}\times [B]^{(-0.5)}}$$
It is a zero order reaction but whether it is independent of concentrations of reactants?


texts:
Someone painted an original graffiti:

source

I wonder what kind of reaction was depicted; what's that product substance?

The graffiti reads:
$\ce{C2H2 + C2H5OH -> C_2H_5-O-CH=CH_2}$

Does it have any more or less common uses?


texts: What decides whether a reaction releases light or heat

texts:
I understand the reason that a chemical reaction would create photons (physics is more my strong point), but why would it create heat instead? My only guess is that the light released somehow causes the molecules around it to gain kinetic energy through some process and thus create heat, but I don't know how this would occur. What decides whether a given reaction produces photons or heat?
I'm a chemistry noob so try to explain using noob-friendly terms. Also, I don't know what tags suit so please put appropriate tags if my tags aren't.


texts: If bonds are not physical things, what is meant by bond rotation?

texts: I’m not sure if this is a stupid question or not, but since bonds are not physically there as such, what does it mean when it can rotate? And how do pi bonds prevent rotation if they are not physical?


texts:
A container of volume $\pu{4.0 L}$ contains nitrogen at $\pu{25 °C}$ and $\pu{803 kPa}.$ This container is connected by a valve to another container of volume $\pu{10.0 L}$ that contains argon at $\pu{25 °C}$ and $\pu{47.2 kPa}.$ We now open the valve so that the two gases are mixing.
Calculate the partial pressure of each gas after the mixing and the total pressure of the mixture.

Using the Dalton's law of partial pressures, isn't the partial pressure of each gas exactly $\pu{803 kPa}$ and $\pu{47.2 kPa}$ and the total pressure $\pu{803 kPa} + \pu{47.2 kPa}?$
What am I missing here?


texts: Synthesis of phosphonate salt not working

texts:
I have tried four times in the past few weeks to synthesise 2-ethoxyvinyl phosphonyl dichloride by reacting ethyl vinyl ether with phosphorus pentachloride in toluene.

I have been following the literature procedure (see below) successfully up to the point where it says that I need to bubble sulfur dioxide through the reaction mixture - at which point it will turn clear. The reaction turns a pale yellow color; the next step is where I'm at my wit's end - the literature says to obtain the 2-ethoxyvinyl phosphonyl dichloride by direct distillation and every time I've tried this, it's resulted in a black, opaque solution. The literature does not say what color the final product is although my supervisor has said that it should be a yellow oil. I'm thinking that it could have decomposed upon heating, although the boiling point according to the literature is 142 °C and the bp of toluene is 110. Previously I tried the same reaction in $\ce{CCl4}$, which distilled off at 76 °C and also turned black.

I would really appreciate help on this, since it's part of my final year project and I only have a handful of lab sessions left to finish this. Thank you in advance! (Also, I've attached an image of the literature procedure below if it might be helpful).

$%edit$


texts: How can I measure carcinogenic risks of an M-ENDO-Agar LES substrate after heat destruction?

texts:
I'm about to conduct a study of possible toxic traces from the substance M-ENDO-Agar LES in substrate after destruction with heat (I think it is 160℃) for 180 minutes. The substance is carcinogenic.

I want to find a way to measure if the substrate is still toxic in any way after the heat treatment. How could I conduct such a study?


texts: Why the pH of xanthan gum in aqueous solution is 7 (neutral) when it has glucuronic and pyruvic acids in its chemical structure?

texts: Since xanthan gum has both glucuronic and pyruvic acids in its chemical structure, it should release $\ce{H+}$ ions upon solvation in an aqueous solution and make it acidic. However, the meausured $\ce{pH}$ is $7$.


texts: Why does the photoelectric effect depend on the frequency of the light?

texts:
In experiments to detect the photoelectric effect, a clean metal was irradiated by monochromatic light and electrons were emitted.

Why was monochromatic light used in the experiment, and why does the frequency of the light have to be above a threshold frequency?


texts: Why doesn't chemical equilibrium lead to uncertainties?

texts:
Let's consider a reaction

$$\ce{a A + b B <=> c C + d D}$$

We will also assume that the concentrations are low and the activity coefficient is one. Now let's say initially one has $p_0$, $q_0$, $r_0$, $s_0$ as the concentrations of $\ce{A}$, $\ce{B}$, $\ce{C}$, $\ce{D}$, respectively. Let the equilibrium constant be $K$. Let's investigate about the equilibrium composition.

If $x$ equivalents of reactants reacted, then the equation for $x$ would be:

$$K = \frac{(r_0 + cx)(s_0 + dx)}{(p_0 - ax)(q_0 - bx)}.$$

Now, my question is how do we know all the time such equations have proper roots for $x$? I mean all the conditions $x$ needs to satisfy, like $ax < p_0$ and first of all, how do we know the equation has roots in first place? It's a quadratic and it need not have real roots necessarily. This is just a simple case of 2 reactants and 2 products.

I would like to see some rigorous proof that such equations always contain proper (roots which satisfy) all the conditions or a counter example of such a chemical equation. If such counter examples exist, how does the chemical reaction proceed?


texts: How would 2-(chloromethyl)-1-methylpyrrolidine recyclize into 3-chloro-1-methylpiperidine with only water?

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My Attempt

I always get thrown off by mechanisms with just water as a solvent. I've attached my work as far as I could get but I'm not sure where to go from there. Thank you!


texts: Why can't this mixture be used as a buffer solution?

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Explain, using a chemical equation to aid your answer, why a mixture of $50~\mathrm{cm^3}$ of $0.10~\mathrm{mol\:dm^{-3}}$ ammonia solution and $50~\mathrm{cm^3}$ of $0.10~\mathrm{mol\:dm^{-3}}$ hydrochloric acid cannot be used as a buffer solution.

So writing the equation down: $$\ce{NH4OH + HCl -> NH4Cl + H2O}$$

there are $0.005~\mathrm{mol}$ of each reactant. From my notes, I think there has to be double the amount of the weak base, but I don't really understand why. Even after googling explanations, I can't find one that answers my question. Why do you need double the amount (if this is correct) of the weak base? An answer to the question above would also be appreciated.


texts: Meaning of electrochemical cell notation without a salt bridge

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An electrochemical cell is shown here.

$$\ce{Ag(s)~|~AgCl(s)~|~KCl(1M)~|~Hg2Cl2(s)~|~Hg(l)~|~Pt}$$

I am used to seeing cell representations with a $||$ for a salt bridge between the two electrode solutions (generally with the anodic solution written first followed by the cathodic solution).

I am seeing the above type of representation for the first time. Can someone tell me what it means? (including which are the anodic and cathodic solutions). Also, how do we write the reactions at anode and cathode for the above cell?


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I'm looking for a surfactant that I can add to water to decrease the surface tension by 20 to 40%.  I'm working on a new kind of mixing device that is so designed such that it mixes relatively large volumes of two liquids and cannot be made small enough for laboratory scale.  So flow on the order of 1.5 to 2.5 liters/min.  I would like to be able to run my experiments for a number of minutes, so the estimate is 10 gallons for each hypothetical liquid (total amount would be 20 gallons for an experiment that would give me about 20 minutes to adjust parameters, take photographs, etc.).  Adding something like isopropyl alcohol can get expensive very fast (10% by weight in water lowers the surface tension to about 41 where pure water is 72).
Very important:  The surfactant needs to be non-foaming as release of gas will be problematic for these tests.
Thanks for any thoughts.


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The answer i know is delocalized electrons. But how?this site tells me that:

My textbook  tells me that one carbon atom is bonded to three others and two of these bonds are single while the third is a double bond.So all the electrons are bonded and there are no free moving electrons right? Where do these delocalized elctrons come from?


texts: Does the carbocation rearrangement in a SN1 reaction specify a change in degree?

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I am asked to determine whether the following process is likely to involve a carbocation rearrangement or not:

I think it is possible through the rearrangement given above (though the rearrangement cannot become a secondary or primary carbocation). Can someone please clarify if the carbocation rearrangement specifies a change in degree?


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This question came up when I was reading about substances with negative thermal expansion. The article by Takenaka [1] gives a good list of materials displaying negative thermal expansion. I noticed that almost all the substances mentioned are alloys or crystals, with not a single pure metal included.

This raised the question: Do all metals expand on heating? If so, why? If not, give an example of a metal that contracts on heating.

References

Takenaka, K. Negative Thermal Expansion Materials: Technological Key for Control of Thermal Expansion. Sci. Technol. Adv. Mater. 2012, 13 (1), 013001. DOI: 10.1088/1468-6996/13/1/013001.


texts: What does "Anal. Calcd." stand for written out?

texts: I'm wondering what the abbreviation "Anal. Calcd. stands for exactly. It is put in front of calculated (expected) values for elemental analyses. "Analytically calculated" makes no sense for me, but maybe it's more of a language problem for me in this particular case. According to a quick Google research, some are listing it in their lists of abbreviations as "Analytical Calculated". Using the adjective instead of an adverb doesn't make it any more correct to me.


texts: What is the largest system (organic molecule) which total energy was calculated by full configuration interaction? Lets say with DZV or similar basis set. How far can we get with CI in larger basis sets?


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I've researching electrolysis recently, and all of the examples I've seen use two different metals as the cathode and anode.
In my attempts to make a hydrogen producing cell (table salt used as the electrolyte in water) I've used two steel nails as both my cathode and anode. When I power it up, one side bubbles and the other stays normal. The side where the bubbling occurred, corrodes and makes the water murky with what I presume to be rust. The other side does nothing, not even get electroplated with the other side's metal.
My question is this: Does electrolysis work the same way when the cathode and anode are made of the same metal? It might be a stupid question, but I can't find anything that answers this question specifically.