texts:
I work in a winery and we have some problems about a new process involving phlorizin. We know that phlorizin is the major dihydrochalcone found in apples.

I have been reading that this compound is also found in a grape named Albariño, a white variety of grape. What else is known about the phlorizin content in grapes?


texts: SN2 nucleophilic attack with alpha unsaturation

texts:
The following two questions prompted me to ask this question.

  Determine the order of the following compounds according to reactivity in Williamson Ether Synthesis.
  a. $\ce{CH3CH2CH2Br}$
  b. $\ce{CH2=CHCH2Cl}$

  Which of these represent the ether($\ce{CH2=CHCH2OC3H7}$) on forming peroxide in air
  a. $\ce{CH2=CHCH2OCH(OOH)CH2CH3}$
  b. $\ce{CH2=CH-CH(OOH)OC3H7}$

In both the case, I think the question is the relative ease of nucleophilic attack on carbon with $\alpha$-unsaturation. In the former, the bromine is a better leaving group. But, the presence of $\alpha$-unsaturation in the chloro compound, changes the order to b>a. In the latter, the attack of oxygen depends on the most stable electrophilic centre.

My question:-

Is $\alpha$-unsaturation favourable for nucleophilic attack? Relevant factors would be the increased electrophilicity of the carbon attached to the $sp^2$ hybridised ethylinic carbon and the repulsion of the negative nucleophile by the pi electrons.


texts: Alcoholic KOH mechanism with alkyl halides

texts:
Does alcoholic $\ce{KOH}$ only show $E_2$ mechanism with alkyhalides?

I have studied with two organic chemistry teachers, one told me that there is always $E_2$ mechanism, except in the case of tertiary alkylhalide and the other told me it can be any depending on the substrate with $\alpha$ hydrogens more than 4 or if it has resonance it will show $E_1$.

Which one is true?


texts: Hot-side and Cold-side rechargeable chemical compound

texts:
I am wondering if such a chemical/material exists which, upon triggering, becomes cold on one side and hot on the other in which after all the chemical bonds are broken/built (however it would work), and the chemical begins to move towards thermal equilibrium, it could be 'recharged' using electricity?

What I am investigating is an effect similar to that of the 'Peltier' effect in which one side of a semi-conducting material becomes very cold and the other side very hot! These devices are horribly inefficient though.


texts: pH of bleach solution slowly decreasing?

texts: I work within a science department in a school. We are demonstrating Universal Indicator and something odd has happened. Our bleach solution (~2.5% Sodium hypochlorite) turns blue when UI is added but within about 1 min it goes green and then after 1-2 mins it goes yellow. Overnight it goes clear but when more UI is added it is yellow. Why would this happen? The bleach smells like bleach and has been used in the last week for the luminol reaction which worked.


texts: How to make sense of the crystal systems names

texts:
I cannot fix the names and structures of the seven crystal systems in my head. There's a thousand books explaining their geometry and it's totally fine and understandable, no problem. But what do the names mean, etymologically?

Cubic
Tetragonal
Orthorhombic
Monoclinic
Hexagonal
Rhombohedral or Trigonal
Triclinic

OK, cubic is simple enough, hexagonal too. I know that "-eder/-hedral" means "side" and "-gon" means "angle". Why is a system with three different edges and angles triclinic? What are the rationales behind each of the names?

A rhombus has sides of equal length. Orthorhombic has only right angles (orthogonal), but the sides a,b,c have different lenghts. So why "rhombic"?


texts: Proton NMR splitting in 2-substituted furan

texts:
I have recently run proton NMR on 1-(furan-2-yl)ethan-1-ol I synthesised in the lab.

My 400 MHz spectrum consists of the following peaks:

7.36 ppm (dd, J = 1.9, 0.9 Hz, 1H)
6.31 ppm (dd, J = 3.3, 1.9 Hz, 1H)
6.22 ppm (dt, J = 3.2, 0.9 Hz, 1H)
4.87 ppm (q, J = 6.6 Hz, 1H)
1.53 ppm (d, J = 6.6 Hz, 4H).

For the peak at 6.22 ppm, I am wondering why a doublet of triplets is observed rather than a doublet of doublets. I understand the long-range splitting that results in the dd, but am just a little surprised by the dt.
I attach a picture of the doublet of triplets.


texts: How to increase the velocity of a reaction?

texts:
I'm doing relatively simple Chemistry but I've been given a formula for the velocity of a reaction.

$$v= k \cdot c_\mathrm A^a$$

and

$$k= A \cdot \mathrm e^{E_\mathrm a/RT}$$

As a result, from that formula, surely decreasing the temperature $T$ would increase the velocity of the reaction? As that would increase the value of $k$ and therefore drive up the reaction speed? Also, same thinking, increasing the activation energy $E_\mathrm a$.

I know that's wrong, because common sense. But the formula is lying to my face.


texts: Order of filling of molecular orbitals in heteronuclear diatomic molecules such as CO

texts:
Currently studying for possibly my last Chemistry exam in my life, can't understand why physics undergrads have to learn chemistry as high level as this, but oh well.

So I'm currently dealing with Molecular Orbital theory to predict the strength of bonds between various atoms and whether the resulting molecule will be paramagnetic or diamagnetic.

Now, I have discovered that for homonuclear diatomic molecules, there are two different molecular orbital filling orders, as in, for Li$_2$ all the way to N$_2$, the two $\pi_{2p}$ orbitals are filled before the $\sigma_{2p}$ orbital is filled.

From O$_2$ onwards, the $\sigma_{2p}$ orbital is less energetic than the two $\pi_{2p}$ orbitals, and thus the $\sigma_{2p}$ orbital is filled before.

For certain heteronuclear diatomic molecules, such as CN$^-$, the order of filling is the same as in N$_2$, and in molecules like OF$^+$, it appears to be the same as in O$_2$.

However, in "mixed" molecules such as CO or CO$^+$, how does one predict the order of filling of the molecular orbitals? It appears to be $\sigma_{2p}$ first, then the two $\pi_{2p}$ orbitals, following the fashion of O$_2$.

Is there a rule of thumb on how to predict which molecular orbital will be more energetic in molecules where the two atoms follow different orbital filling orders in their corresponding diatomic molecules, or is there not?

We are only asked to be able to do this for atoms lighter that Ne, it seems, so we only care about $2p$ orbitals.


texts: Disproportionation reaction of dimeric sulphur monochloride

texts:
I read that group-16 monohalides exist in dimeric forms ex. $\ce{S2Cl2,Se2Cl2,Se2Br2}$ etc.
It also states that these dimeric halides undergo disproportionation reactions and gives an example as follows: $\ce{2Se2Cl2 -> SeCl4 + 3Se}$
Now I thought what would be the disproportion reaction if we consider the case of $\ce{S2Cl2}$ Since $\ce{S(VI)}$ is more stable than $\ce{S(IV)}$ would the disproportion reaction in case of $\ce{S2Cl2}$ yield $\ce{SCl4}$ or $\ce{SCl6}$?
EDIT:  As pointed out in the comments. $\ce{SCl6}$ doesnt exist hence the same question is now considering the case of decomposition of $\ce{S2F2}$ with the essence of question still remaining the same


texts:
Why are lithium salts heavily hydrated? I am not able to understand this because I feel salts of larger cations like Caesium should be more hydrated because of the larger size, they can able to hold more water molecules.

What is the flaw in my reasoning?


texts: Naming compound containing a ring (cycloalkane) side chain?

texts:
Why is the correct name 5-cyclopentyl-2-methylheptane rather than 2-methyl-5-cyclopentylheptane? I am using the 2nd edition Hornback Organic Chemistry textbook. I got this answer from the solutions manual.

I have searched the textbook and the internet for the explanation and am still very confused. I thought the order of the side chain in the name was alphabetical, not including the prefixes? So by this logic, "methyl" should be before "pentyl," right?


texts:
I've been having trouble with reducing COD (Chemical Oxygen Demand) below approx. 500 ppm by using Fentons Reagent.

For 100 gm of the sample (initial COD 3000 ppm) I use 5 gm of 30% $\ce{H2O2}$ & 0.1 gm of $\ce{FeSO4}$. pH is adjusted to between 3 to 5. Temp. is approx. Room Temp. & I've tried reaction times up to 6 hrs.

Do these sound reasonable choices?

Any advice?


texts: Why is 1-bromotriptycene inert to nucleophilic substitution?

texts:
According to my textbook, 1-bromotriptycene is inert to any nucleophilic substitutions.

Due to steric hinderance we can say SN2 reactions cannot occur, but I think SN1 reactions should be favoured as formed carbocation will be resonance stabilised.

Can someone explain why it doesn’t undergo SN1 reactions?


texts:
Dry water or "powdered water" is essentially a bunch of extremely small water droplets surrounded by $\ce{SiO2}$.

Some time ago, I was messing around and mixed some powdered graphite with water. (The graphite was obtained from a pencil, so it was not pure. Also I mixed the two substances with a stick, not with a high-speed blender.) When a droplet of this was splashed onto the table, it could be blown around with air and even held on the hand without breaking, until it was squished.

The important part of this is, that that droplet could be placed back into the original mixture of water and graphite powder, and it would roll around on the surface.

So does anyone know if it's possible to use powdered graphite rather than silica particles to make dry water? If is is, what properties are different from the ordinary powdered water?


texts: Acidities of amines and carboxylic acids

texts:
I have been told that the first of the two acids is the stronger acid. According to this person,deprotonation for both occur at the nitrogen.The resulting conjugate bases include,respectively a neutral amine group,and a negatively charged amine group.Because negatively charged nitrogens are highly unstable from an acid/base standpoint (consider lithium diisopropyl amide)... the first must be the stronger acid (because of its more stable conjugate base).

The problem I have with this line of reasoning is that it's based on a faulty premise - that the nitrogen is the site of deprotonation.I see a much better site of deprotonation for both - and that is the carboxylic acid site. A negative charge here will not only be resonance stabilized but also inductively stabilized by oxygen.Plus, the Ka of ammonium ion is 5.6*10^-10, while the Ka of acetic acid is 1.8*10^-5.In other words - orders of magnitude of difference. I can't see why something that is structurally analogous to ammonium ion (much less ammonia) would be deprotonated preferentially over a carboxylic acid.


texts:
I know $\mathrm{S_N2}$ is favored polar aprotic solvents, which means that they may have hydrogens on them somewhere, but they lack $\ce{O-H}$ or $\ce{N-H}$ bonds, and therefore cannot hydrogen bond with themselves.

But I found that $\mathrm{S_N2/E2}$ is favored by $\ce{OH-, RO-}$ (a strong base); if I look at $\ce{OH-}$, doesn't it contain $\ce{O-H}$ and form hydrogen bonds?

Can someone please explain what aprotic solvents then?
Are aprotic solvents a strong base?
What's the difference between  aprotic solvents and a strong base?


texts:
Why is heavy water less dielectric than normal water?
Is it because of the fact that heavy water is more denser? I think it so because the dipole moment of heavy water is greater than normal water?


texts: Expedient phosponium synthesis (for Wittig)

texts:
I have been making ethyltriphenylphosphonium bromide (somewhat of a time crunch, would have used iodoethane instead of bromoethane if we didn't have to wait for it). All the syntheses I see of Wittig salts are in aromatic solvents and they take large amounts of time for what I would have expected to be a fairly quick reaction, usually at least a day, if not several. I have come across the use of iodide salts as a catalyst, some of which I had already added because I figured it wouldn't hurt.

$$\ce{PPh3 + EtBr ->[\text{aromatic}][\text{solvent}] [EtPPh3]Br}$$

Why are these conditions standard/most effective? More specifically, why is toluene (less often xylene, probably others but those are the two I've seen) used rather than some polar aprotic solvent? Also, besides increased temperature and the use of iodide catalysts, are there any common ways to decrease reaction time?

Is it simply that toluene boils at a relatively high temperature? Maybe the SN2 reaction is fairly easy once line up, but due to the large PPh3 being a bulky nucleophile, having the two reactive sites in close proximity is relatively rare, so increasing temperature is the most effect thing since random interaction is the driving force.
I can't imagine a primary alkylbromide reacts through SN1 rather than SN2. I guess maybe the higher temperature could allow for an SN1 reaction, though? I kinda doubt it, though...
I would think, even if the above was true, using THF and going through an SN2 mechanism at a lower temperature would be simpler than refluxing in toluene, and I still kind of doubt the SN1 on a primary bromide even at the elevated temperature.
Another thought is that the phosphonium salt crashes out of toluene, and therefore this equilibrium serves as a driving force for the reaction. Technically, this doesn't speed up the reaction, but it does significantly hinder the reverse reaction, so it leads to a net decrease in reaction time (and increases yield, I guess, if the reverse reaction is significant). I wouldn't really think the halide anions would be strong enough nucleophiles to be able to kick off a phosphine, though.

$$\ce{RX + PPh3}\xrightarrow{\text{toluene}}\ce{\underset{\small{(\sim none\ in\ sol'n)}}{[RPPh3]X_{$(s)$}} v}$$
$$\text{vs.}$$
$$\ce{RX + PPh3} \stackrel{\small{\text{THF}}}{\longrightleftharpoons}
\ce{\underset{\small{(more\ than\ above)}}{[RPPh3]X_{$(org)$}}}$$

I realize THF isn't all that polar, but relative to toluene or xylene, I would really expect it to facilitate this reaction better.

P.S. This question isn't really an attempt to get help with my current situation (especially since I just finished working up my last batch, anyway) as much as it is just trying to get general information about the reaction.

I will mention for anyone who might be able to use it that I first tried to run mine in toluene at around 35 °C with catalytic KI (I've now seen LiI used instead of KI, not sure how much that matters). However, I was inspired by a literature report of a 7-day reaction at 30 °C (no iodide) to move the reaction in portions to pressure tubes and take it up to 130 °C. A paper reported 7 h (also no iodide) at this temp was effective, and I found that to be overkill. I didn't really see much difference between 2 h and 7 h (again, no iodide in their reaction, which may have caused the difference).


texts: Why is UuX used as a symbol for unnamed elements on the periodic table?

texts:
Until recently, the last few elements on the periodic table had the chemical symbols (now they have formal chemical symbols!):

Uub, Uut, Uuq, Uup, Uuh, Uus, and Uuo

Why did they have these temporary symbols? Why the letter U? Is there any reasoning behind the third letter? Why not:

Uua, Uub, Uuc, Uud, Uue, etc...

I was just wondering some of the history of nomenclature and the thought process behind this specific nomenclature.


texts: What are some good examples of rate equations for a math class?

texts:
I'm a mathematician who's currently teaching a course on differential equations.  Though I don't know much about chemistry, I like to include examples from chemistry in my course, and I prefer for the details to be accurate.  Here is a typical exam problem:

  When a container of gaseous nitrogen dioxide is heated above 150 °C, the gas begins to decompose into oxygen and nitric oxide:
  $$\ce{2NO2 -> O2 + 2NO}$$
  The rate of this reaction is determined by the equation
  $$\frac{\mathrm d\left[\ce{NO2}\right]}{\mathrm dt} = -k\left[\ce{NO}_2\right]^2$$
  where $k$ is a constant.

  (a) Find the general solution to the above equation.

  (b) A large container holds 50.0 moles of $\ce{NO2}$ at a constant temperature of 600 °C.  After one hour, only 34.3 moles remain.  How much $\ce{NO2}$ will there be after another hour?

So my questions are:

Is the science in this problem reasonably accurate?  Is there anything you would change?  (I looked up a suitable value of the rate constant $k$ to make sure that the time in part b was reasonable.)
What are some other examples of reactions that are governed by simple rate laws?  Ideally, I'd like to have several examples each of reactions governed by the equations
$$
\frac{\mathrm dy}{\mathrm dt} = -ky,\qquad \frac{\mathrm dy}{\mathrm dt}=-ky^2,\qquad\text{and}\qquad \frac{\mathrm dy}{\mathrm dt}=-ky^3.
$$
(Is $y^3$ really possible?  Are non-integer powers of $y$ possible?)


texts: What is the dissociation percentage of a polybasic organic acid at a certain pH?

texts:
For my Master's Thesis I am working with the dicarboxylic acid muconic acid $(\ce{H2MA},$ $\mathrm{p}K_\mathrm{a1} = 2.9,$ $\mathrm{p}K_\mathrm{a2} = 4.0).$ It thus dissociates into $\ce{HMA-}$ and $\ce{MA^2-},$ respectively.
I am aware of how to calculate the $\mathrm{pH}$ and the subsequent dissociation percentage when dissolving a weak acid in water. But I am wondering how you can calculate it the other way around. Say I dissolve $\pu{1 g}$ of the acid in water and adjust the $\mathrm{pH}$ to 4 with a strong acid such as $\ce{H2SO4},$ how do I know what the concentration is of each species $(\ce{H2MA},$ $\ce{HMA-}$ and $\ce{MA^2-})$ at that given $\mathrm{pH}?$
In general, how can I calculate the dissociation percentage of a weak polybasic organic acid when the pH is given?


texts: If you placed silver metal into silver nitrate, would a reaction occur?

texts: thinking about oxidation and reduction, what happens to the silver metal and the silver ions?


texts: How does oil on the surface of water prevent rust?

texts:
I distinctly remember a side-by-side comparison from a book where there are two nails submerged in water, in two beakers: one nail had a layer of oil on top of the water, and that nail didn't rust; the other did.

It seems that oiling iron/steel products is supposed to prevent them from rusting:
http://www.justanswer.com/home-improvement/0n1r2-does-olive-oil-prevent-rust.html
https://outdoors.stackexchange.com/questions/1404/can-oiling-keep-tools-from-rusting

The explanation given, I think, is that the oil somehow prevents oxygen from reacting with the metal.

Can't help but wonder why. Oxygen is a non-polar molecule, so it should actually dissolve better in oils (which are also non-polar) than in water (which is highly polar) and therefore allow more oxygen molecules to contact the iron (metal) surface in some sort of equilibrium.

Let's say that the conductivity of water and its ability to form electrochemical chains between metals is irrelevant in this thought experiment (i.e., a nail submerged in water in a glass). From what I understand, the other key item that has an effect on the formation of rust in water is that the oxygen molecules have better contact with the iron surface.

This is supported by data: the concentration of oxygen in air is far higher than that in water. We know from experience, though, that wet iron rusts way quicker than dry iron does.

If I am reading it correctly, the same data shows higher oxygen concentrations in non-polar solvents than in water.

Here is the data: http://www.nist.gov/data/PDFfiles/jpcrd219.pdf

Please correct me if I am reading it wrong.

My question is:

How does oiling prevent rust?

Edit: For the sake of clarity, let's say we use deionized water in a vacuum, drop in the nail, then put some oil (let's say it's caprylic acid) on it, and expose it to standard conditions.


texts: Using Hess's law to find molar enthalpy of formation without an initial reaction

texts:
I'm having issues relating Hess's law to this question:

  The given chemical equation represent the combustion of ammonia and the combustion of hydrogen

  $$
\begin{align}
\ce{4 NH3 + 3 O2 &->6 H2O + 2N2} &\qquad &ΔH_1 = \pu{-1516 kJ} \tag{1} \\
\ce{2 H2 + O2 &-> 2 H2O} &\qquad &ΔH_2 = \pu{-572 kJ} \tag{2} \\
\end{align}
$$

  What is the molar enthalpy of formation for ammonia?

  A. $\pu{-100 kJ}$; B. $\pu{-50 kJ}$; C. $\pu{50 kJ}$; D. $\pu{100 kJ}$.

I'm not sure how I would apply the  product–reactant equation here, or rearrange the equation to get my answer since I don't have an initial reaction to compare it to. How would I go about answering this question?


texts: Why is my rusting metal chainlink fence glowing bright orange and sparking?

texts:
This is a really practical question, but I can't find anything on Google.

My metal chainlink fence is rusting and I have noticed that where the metal from one wire makes contact with another wire there is a point of bright orange glowing which sparks if the metal is moved. It does not feel at all warm to the touch, though outside temp is hovering around 0C right now.

Back story: I noticed it tonight when I went out to toss the compost in the leaf bin, and saw a very bright orange glow. I got a light and inspected it a bit closer with my wife and she noticed a second spot on the fence. Both were at junctions in the chain, where there was significant corrosion. Those locations were both heavily corroded such that visible gouges were forming at the junction where the bright orange spot was. I gave the fence a kick and both spots threw off a good number of very bright white and orange sparks. It did this about 5 or six times then stopped, and the metal was no longer orange in those spots. It did not feel hot to the touch either, though I didn't touch it when it was orange. I'm perplexed but figured it seemed like a good questions for some chemists, as I am guessing it has something to do with the corrosion process.


texts: How do STO-based computer programs implement the STO integral formulae?

texts:
In most cases, STO integrals are evaluated assuming that the orbitals are directed towards each other, using spherical harmonics; however, in GTO-based software Cartesian GTOs are used, with the orbitals being aligned along the x, y or z axis.

Is there any way to evaluate STO integrals using Cartesian STOs, or convert between Cartesian and spherical STOs? For example, if I had a pz-type STO at (0,0,0) and another one at (1,1,1), is there any way to decompose the resultant expression in terms of spherical STO integrals?


texts: How is the temperature in which vapor pressure is equal to atmospheric pressure the boiling point of the liquid?

texts: I was just learning about vapor pressure and got very confused. Vapor pressure was defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature in a closed system, which was the pressure the vapor exerts on the closed container when it reaches the dynamic equilibrium. However, this is merely a calculation AFTER it reaches equilibrium, and I don't understand how vapor pressure can also be interpreted as the measure of the tendency of a material to change into the vapor state. Also, if it is the lack of enough vapor pressure, or "tendency of the liquid to change to vapor" compared to the atmospheric pressure that's keeping the liquid from vaporizing, how can evaporation occur with lower pressure than the atmospheric pressure(because if the vapor pressure is higher than atmospheric pressure it is already boiling), since evaporation is supposed to be the molecules on the surface of the liquid randomly gaining enough energy to overcome the atmospheric pressure, implying that it has greater pressure than the atmosphere. I feel like I am overthinking the topic, but I didn't just want to give up thinking about it, so please help if possible!


texts: Angular Momentum of an orbital and orbit

texts:
While pursuing forth in Atomic Structure, I encountered the following concepts...

According to Bohr, the angular momentum of an orbit remains quantized, i.e $\displaystyle mvr = n\hbar .$

But he wasn't able to expalin the reason that why is it so.

But later Louis de Broglie gave his hypothesis:

Every particle in the universe has dual nature, one wave nature an other particle nature.

Focusing on wave nature of particle he gave an equation, known as de Broglie equation or de Broglie wavelength as

$$\displaystyle \lambda = \frac {h}{mv}.$$

This was proved years later by Davisson and Germer's Diffraction Experiment.

Now, we can also prove the quantization of angular momentum of an orbit as:

For any orbit the number of waves produced by an electron in one complete revolution is $\displaystyle \frac {2\pi r}{\lambda}.$

Substituting the values of $r,v$ given by Bohr, then

$$\displaystyle \frac {2\pi r}{\lambda} = \frac {2\pi r \cdot mv}{h} = \frac { n^2 \hbar^2 \cdot mkZe^2}{\hbar \cdot mkZe^2 \cdot n\hbar} = n$$

As $\displaystyle r =\frac { n^2 \hbar^2 }{ mkZe^2}  $ and $\displaystyle v = \frac {kZe^2}{ n\hbar}.$

Now , as $ \displaystyle \frac {2\pi r}{\lambda}= n ,$ From this we can prove that angualr momentum of an orbit is quantized.

Now according to Quantum wave mechanical model, the angular orbital momentum of an orbital is : $ \displaystyle \sqrt {l(l+1)} \hbar .$

Now which one is actually valid, because in many of the books both of the momentums are refered only by the term angular momentum.  But both are not same.

My question might sound silly, for such topic... But I would like to know which one is to be refered when we encounter angular momentum.


texts:
In Lucas test $\ce{HCl}$  is used for acid-base reaction between $\ce{Zn(OH)Cl}$ to give $\ce{ZnCl2}$ and $\ce{H2O}$ which is kind of good because $\ce{ZnCl2}$ is formed again and used in first step quickening the reaction. But why don't Lucas test use other acids like $\ce{H2SO4}$ (and add $\ce{ZnCl2}$ in bulk) or $\ce{HClO4}$ (stronger acid than $\ce{HCl}$ may faster the reaction). But why $\ce{HCl}$?

Is it had to do with acidic strength of $\ce{ZnCl2}$ and acid (I mean if stronger acid than $\ce{ZnCl2}$ may react with alcohol)?


texts: Work done by irreversible expansion of gas against piston of fixed pressure

texts:
this has been puzzling me for a while.  An ideal gas expands against a piston with mass M and area A, so that pressure external Pex= Mg/A.  The initial internal pressure of the gas is Pino > Pex.  Because the gas is expanding irreversibly, Pin > Pex, until equilibrium is reached, where Pinf  = Pex.

The physical chemistry texts I've read, including Atkins, seem to characterize the work done by the expanding gas as Pex * change in volume.  I recognize this as the equation to calculate work for lifting an object at constant velocity over a given distance.

However, since the initial internal pressure of the gas is greater than the external pressure, there is an imbalance in forces, and the mass will accelerate upwards, causing it to acquire kinetic energy that was derived from the original energy of the gas.  A rocket is an example of gas causing a mass to accelerate upwards.

My question is why the standard formula of work done by an irreversibly expanding gas is Pex * change in volume, and doesn't include a term for the kinetic energy from acceleration.


texts: Are bridge bonds in diborane longer than the terminal H bonds?

texts:
The compound diborane on alkylation loses the terminal $\ce{H}$-bonds rather than the bridge bonds indicating that the bridge bond is stronger but on the other hand it's length is found to be longer than terminal hydrogen bonds. But usually bond length is inversely proportional to bond strength.

What is the reason for this?


texts: Why is phenol more acidic than an alcohol but less reactive as an alcohol?

texts:
I understand why phenol is more acidic than ethanol but is less reactive?
Eg: why unlike ethanol it can't react with a carboxylic acid?


texts: Is there any mathematical formula for electron affinity and ionization potential?

texts: I already know about the mathematical formula for electronegativity, but it requires the ionization potential and electron affinity. How can I can easily calculate the ionization potential and electron affinity with a mathematical formula?


texts: Determination of the iodine value of a fatty oil: Does the concentration of Na2SO3 effect the iodine value?

texts:
I want to determine the iodine value of a fatty oil. For this I dissolve $\ce{1.0 g}$ of the oil in chloroform. Iodine bromide is then added and placed in a dark room for at least $\pu{30 min}$. After this, $\ce{KI}$ is added. Then, I am going to titrate with $\pu{0.1 M}$ $\ce{Na2SO3}$. Based on the added volume, I can calculate the iodine value of the unknown fatty oil.

Now I was wondering what the effect should be using $\pu{0.02 M}$ $\ce{Na2SO3}$ instead of $\pu{0.1 M}$? And is there a reason why the solution has to stay $\pu{30 min}$ in a dark room? I think there's no difference in outcome when it will be in a dark room, for example, say $\pu{3 h}$.


texts: Which is more stable Ethyl carbocation or Neopentyl carbocation?

texts:
As per my knowledge, hyperconjugation is more dominating over inductive effect, so due to three alpha hydrogen ethyl carbocation should be more stable. In some books, while solving questions I observed that answers can match if I take neopentyl carbocation as more stable.

so which one of them is comparatively more stable?


texts:
So, my question is how would I make a bridge as seen on the following molecule (right side)?

As for the molecule on the left, I am supposed to make it using that molecule as a base. The only requirement is that every other molecule I use that uses carbon, can only have a maximum of 2 carbons.
To reiterate- I need to use the molecule in the left using any inorganic compound, and organic molecules with up to 2 carbons, and turn it into the molecule in the right.
My biggest problem here, is how to make it so that the molecule only reacts in that area. I was thinking of using a mixture of condensation and $\ce{HBr}$ in order to break the $\ce{-OH}$, and temporarily remove a hydrogen.
However, again, I don't know how to make it so it would only react in that specific area.


texts: What is the mathematical relation for the change in water density at different temperatures?

texts: I am curious to the relation of the density of water at different temperature and as to also how one would come to an equation that took the temperature of the water and would output it's density? I have graphed density vs temp from tabulated values and it seems to look logarithmic, but wanted to make sure. I am interested in this as I am currently taking analytic chemistry.


texts: How do we know which compounds have higher solubility?

texts: Is there any way we can look at the chemical formula of various compounds, do some calculations or something and figure out which compounds will have higher solubility as compared to the others.


texts: Help with determining concentration of magnesium hydroxide for a specific pH level

texts:
This seems like such an obvious and elementary-level question for someone who has taken high school chemistry, but yet I'm having a difficult time solving it. I need to find the right amount of $\ce{Mg(OH)2}$ to have a $\pu{250 mL}$ solution with a $\mathrm{pH}$ of $8$ and $9.$
I first started by trying to determine the concentration of $\ce{Mg(OH)2}$ needed to obtain a solution with a certain pH. Since $\ce{Mg(OH)2}$ is a weak base, we must use a RICE table to determine its concentration at equilibrium.
$$
\begin{array}{lcccc}
  & \ce{Mg(OH)2 &<=> & Mg^2+ &+ & 2OH-} \\
\text{I} & x & & 0 && 0 & \\
\text{C} & x & & +x && +2x \\
\text{E} & x & & x && 2x
\end{array}
$$
However, the equation involving $K_\mathrm{sp}$ only involves the $x$ values in the RICE table above, not the actual concentration. How would I calculate the $\mathrm{pH}$ level for $\ce{Mg(OH)2}$ with varying molarity? I thought it was a weak base, so I'd have to use a RICE table.


texts: What's the relationship between charge and acidity/basicity?

texts:
I understand the acidity of a substance increases with electronegativity and size (valence shell space) of an atom (periodic trend) that contains a hydrogen atom (Brønsted-Lowry). However when looking at following pairs, I am not able to determine which one is a stronger acid.

$$\ce{H3O+ ,\ H2O}$$

Further, I would want to reason, the relationship between the charge and acidity/ basicity.


texts: In electrophoresis, are positive and negative molecules obviously separated?

texts:
I have just studied electrophoresis in biochemistry. The charged particles move to the oppsite charged electrodes whose speed is depended on their particle size. If that so, are negative and positive particles obviously separated into two distinct boundaries? As if we will find only negative particles near positive electrode and only positve particles near negative electrode.
Some searching I have done:

We cannot separate any two positive and negative ions because of their huge Coulombic force.
Exerted from electric field, a charged particle will move to the electrode and carry   counterion cloud together.

If (2) is true, why doesn't counterion move to its electrode but, instead, move along with charged particle?
If (1) is true, how is it possible that charged particles move to the electrode without separating from its counterion?


texts:
I am helping clean out my lab and there is some glassware that I can't identify. Attached are the photos:

Thank you!


texts: Help with derivation on why antibonding orbitals are more antibonding

texts:
I have read How can antibonding orbitals be more antibonding than bonding orbitals are bonding?. But I am intersted in a specific derivation. During lecture my professor stated that the overlap $S_{ij}$ integral can be between -1 and 1. In other words,
$$-1<\int\psi^*_i\psi_j\,dx<1$$
He further mentioned that a negative overlap integral means that the orbitals are antibonding. He also mentioned that a positive overlap integral means that the orbitals are bonding, and that an overlap integral equal to 0 means that the orbitals are nonbonding. In other words,

$$S_{ij}<0\Rightarrow\text{antibonding}$$
$$S_{ij}>0\Rightarrow\text{bonding}$$
$$S_{ij}=0\Rightarrow\text{nonbonding}$$

We then solved the Schrodinger equation using the LCAO method. In this case, we were solving for a hydrogen molecule. We only considered the 1s orbitals of each hydrogen atom. In other words,

$$\Psi_{H_2}=c_1\psi_{1s}+c_2\psi_{1s'}$$
Here, $\psi_{1s}$ and $\psi_{1s'}$ are the atomic orbitals of each hydrogen atom.
The derivation that the professor used is similar to the one here: http://www.pci.tu-bs.de/aggericke/PC4e/Kap_II/H2-Ion.htm

In the end he got two wavefunctions with different coefficients
$$\Psi_{H_2}=\frac{1}{\sqrt{1+S_{ij}}}(\psi_{1s}+\psi_{1s'})$$
$$\Psi'_{H_2}=\frac{1}{\sqrt{1-S_{ij}}}(\psi_{1s}-\psi_{1s'})$$
He then mentioned that since $S_{ij}$ is always positive, the coefficient of $\Psi'_{H_2}$ is larger than $\Psi_{H_2}$. In other words,
$$\frac{1}{\sqrt{1-S_{ij}}}>\frac{1}{\sqrt{1+S_{ij}}}$$
And this is why antibonding orbitals are more antibonding than bonding orbitals are bonding.

But, the problem is this: if $S_{ij}$ can be negative (like he mentioned), then we have no guarantee that the coefficient for the antibonding molecular orbital will be larger than that of the bonding molecular orbital. How do we know that the $S_{ij}$ will always be positive in this case? Also, why does this statement not contradict the statement "$S_{ij}$ is negative for antibonding orbitals." What am I missing?


texts:
Why does the stability of hydrides decrease down the group in nitrogen family? Does this have to do with the fact that $\ce{NH3}$'s $\ce{N}$ is hybridised ($\ce{sp^3}$) while the rest of the group prefers unhybridised central atom for hydrogens leading to steric replusion in $\approx 90^{\circ}$ alignment of $\ce{H}$s?

Other possible explanation:

Perhaps,  the orbital overlap order is: $\ce{2sp^3-1s >  1s-3p> 1s-4p>1s-5p> 1s-6p}$ which leads to greater stability of $\ce{NH3}$ over the others.


texts: How much "cleaner" does summer fuel burn?

texts:
Well, it's that time of year again: the switchover to "summer" fuel and resulting price increases. This EPA regulation system requires gasoline producers to blend additives into the gasoline that reputedly make it burn cleaner.

What exactly does it mean "burn cleaner" and how much "cleaner" is summer fuel than regular gasoline?


texts: How high in (mmH2O) is the column of water in the tube?

texts:
A long glass tube, sealed at one end, has an inner diameter of 23.4 mm. The tube is filled with water and inverted into a pail of water. If the atmospheric pressure is 735 mmHg, how high (in mmH2O) is the column of water in the tube (d of Hg = 13.5 g/mL; d of H2O = 1.00 g/mL)?

This problem really confuses me, I know I have to use the ratio of heights of the liquid columns is inversely related to the ratio of the densities of the liquids:
hH20/hHg = dHg/dH2O. I just can't seem to put it together. I would appreciate any help on this problem.


texts: Bond length comparison between sulfur tetrafluoride and thionyl tetrafluoride

texts:
I'm comparing sulfur tetrafluoride and thionyl tetrafluoride. The lone pair has more s character compared to a double bond. Therefore, sulfur in $\ce{SF4}$ should have a greater s character compared to sulfur in $\ce{SOF4}$.
Since $\ce{SF4}$ has a greater s character it's bond length would be comparativly smaller than that of $\ce{SOF4}$.
Therefore, $\ce{X}>\ce{Y}$. But my book says otherwise.
Did I go wrong anywhere?


texts: Odorless smoke from 1812 Overture cannon fire

texts:
I went to an outdoor performance of the 1812 Overture last night. At the finale, a sequence of 'cannon fire' occurred.

In past years the smoke has had the expected sulfur odor but this year the dense cloud of white smoke that drifted over the crowd had no (to my nose) detectable odor at all. In all other ways the detonations were normal- extremely loud, jet of flame, dense white smoke. Any ideas about what explosives were used?


texts: How can I determine the structure of complexes with ethylenediamine as a ligand?

texts:
I am a bit confused about how to solve this problem.  I can interpret coordination complexes like $\ce{[CoCl6]^4-}$ but I just came across a coordination complex that I am unsure of how to solve.

It is $\ce{[Mn(en)3]^3+}$ where en stands for ethylenediamine.  The problem first asks that I draw the structure (not sure how to do this as ethylenediamine is a large molecule).  I would also like to know whether this complex would be tetrahedral, octahedral, trigonal planar, etc.  I'm just kind of confused as to how to solve this problem when its a large molecule as the ligand rather than a molecule like $\ce{Cl6}$.


texts: How is the covalency of terminal carbons of a diamond satisfied?

texts:
Are the terminal carbons of the diamond lattice remain bonded to some element like hydrogen?

Or, is it that they don't achieve octate in their outer shell?


texts: Visible Light Spectrophotometer Recommendations

texts:
I’m looking into purchasing a cheap uv-vis spectrophotometer but am not affiliated with an institution at the moment given the whole COVID 19 situation. Are there any good recommendations for cheap visible light spectrophotometers that can analyze wavelengths of light on the order of 370nm and are purchasable directly to consumer?

Edit: Budget: $500-700


texts: What is the cause of yellow discharge in beaker during the electrolysis of copper electrodes using copper sulfate electrolyte?

texts:
I have conducted an electrolysis experiment using a copper anode and cathode, and copper sulfate solution in a beaker connected to a power source using alligator clips. I varied the voltage and measured the current and noticed the theoretical mass values I calculated were consistency lower than the values I obtained.

I suspect the ammeter was not calibrated properly however am not sure what affect the oxidation of sulfate ions has on the current (yellow discharge present during electrolysis) and if that would have affected my results.


texts:
Anyone know of any examples of gas mixtures that phase separate, analogously to the way immiscible liquids do?

They would have to be extremely non-ideal. I might guess one might have to be much higher molecular weight than the other and at least one if not both would have to have significant intermolecular interactions (although of different kinds).


texts: Proton-decoupled phosphorus spectrum of a ruthenium complex

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Regarding the complex $\ce{[RuH2(CO)(PPh3)3]}$, there are three possible octahedral stereochemical configurations,
a) Draw these isomers indicating which, if any, are chiral and identify the spin systems in each case
b) Sketch the expected appearance of the $\ce{^{31}P\{^1H\}}$ ($\ce{^1H}$ decoupled) spectra
c) Sketch the expected appearance of the $\ce{^1H}$ spectra

My attempt:
I think I have completed (a) but would appreciate on any advice for (b) and (c)

For the isomer on the far left I think the decoupled phosphorus NMR would show a doublet and a triplet.

The middle one I think it might too be a doublet and a triplet.

The isomer on the right I'm leaning towards doublet of doublets but I'm unsure.


texts:
Which optical isomer of Styrene Oxide  would be produced if it is synthesized via epoxidation of the halohydrin. i.e.

Is there a way to deduce this? I assume it would depend on which isomer the halohydrin itself is since that too seems to have an assymetric Carbon atom?

Well, the halohydrin itself is produced from styrene which is optically inactive by the action of hypochlorous acid. Does this enable us to deduce theoritically the optical rotation of the final product i.e. Styrene Oxide?


texts: Can someone suggest me a list of polymers or some paper where I may find polymers that are soluble in oils like silicon oil, mustard oil, coconut oil, bean oil or petroleum ether, etc.?


texts:
I found this questions on a YouTube lesson and I'm confused with the answers they have given:

"A liquid in its equilibrium with its vapour is in a sealed container at a fixed temperature. The volume of the container in suddenly increased."

Questions:
a) What are the changes in the rate of evaporation and condenation?

b) How will the equilibrium be restored ultimately and what will be the final vapour pressure?

Answers:
a) Rate of evaporation depends on the substance and applied temperature so it will be unchanged and rate of condensation will decrease as vapour pressure is decreased. (Why? Is it true?)

b) They say that the vapour pressure will be restored and the rate of condensation and evaporation will be equal as the system reaches the equilibrium. (But they said that rate of condensation will decrease and rate of evaporation will stay the same. Then how will they be equal?)

Please clarify the whole thing.


texts: When does Alcohol act as Solvent and as a Nucleophile?

texts:
I was recently solving problems related to Alcohol.

and its solution is

My doubt is why methanol act as a nucleophile here and when does alcohol acts as a nucleophile and as a Solvent?


texts: Free-Radical chlorination: Find all unique mono-chlorinated products

texts:
I'm having trouble with this problem. I suspect that there is a typo, as the methylcyclohexene described in the wording does not match the methylcyclopentene shown in the image(someone please confirm if my suspicion is correct or if I made a mistake in interpreting nomenclature, I am very new to Organic Chemistry). If it does appear to be a typo, I would like help in solving for the methylcyclopentene(the molecule described by the image).

I'm not quite sure how to tackle this problem, as this is actually the first time I've had to mono-chlorinate something with a double bond. I'm confused about how stereochemistry factors in, since there's no symmetry in the molecule, and the double bond onto one carbon suggests a sp2 triplanar configuration where there is only one H position that a radical chlorine can take. This problem isn't like anything I've seen so far, so I would appreciate any help from some veteran organic chemists.


texts: I am not quite sure how to start on 1b.We are given 2 diagrams but I am not sure how to use the second one in the question, or if we have to. I got the point group for Cl4+ to be (D2h) however, but after that I do not know how to proceed.


texts: Why does ZnO turn yellow when it is hot?

texts: Why does ZnO's color become yellow when it is hot? I have read that it is because of physical properties, but I need a more elaborate explanation.


texts: Is elemental lead as toxic as lead compounds?

texts: On the internet, nobody mentions about lead's oxidation state when talking about lead poisoning. I assume it's Pb(II) and Pb(IV), as chelation therapy is suggested as a treatment. Also, its accumulation in bones and teeth suggest its ionic state. But what about elemental lead? How is it transformed in human body? Is it as toxic as Pb(II) and Pb(IV) compounds?


texts: What is the value of isothermal compressibility of a van der Waals gas at critical point?

texts: For a van der Waals gas, isothermal compressibility is $$\kappa=\frac{V^2(V-nb)^2}{nRTV^3-2an^2(V-nb)^2}$$ If one substitutes the values of critical temperature and volume in this formula, isothermal compressibility goes to infinity. What is the physical meaning of this? Is it right to use this equation at critical point?


texts: Are there metals that react with sulfuric acid but not hydrochloric (or vice versa)?

texts: In school practicals introducing the reactions of metals with acids, it seems to be standard (as in this one from the RSC) to use both hydrochloric and sulfuric acid, but with metals which react to both or neither (e.g. magnesium, zinc and copper). It would be nice to be able to make the point that different things react with different acids, but I'm at a loss for what might fit the bill. Is there anything?


texts:
My textbook says "Nowadays picric acid is prepared by treating phenol first with concentrated sulfuric acid which converts it to phenol-2,4-disulfuric acid and then with concentrated nitric acid to get 2,4,6-trinitrophenol"

My question: Why is this a better method than simply treating phenol with concentrated nitric acid to obtain picric acid?

What I think is that maybe because $\ce{NO2}$ is a stronger deactivating group than $\ce{SO3H}$, it is more difficult to add 3 $\ce{NO2}$ to a benzene ring directly.

But we would also have to substitute $\ce{SO3H}$ for $\ce{NO2}$. Wouldn't that be hard?


texts: What constituents in soft drinks are the cause their strong pungent smell?

texts:
Wikipedia and PubChem tells us that $\ce{CO2}$ is odorless in lower concentrations but can have a mildly pungent acidic smell at higher concentrations.

However, there is no pungent smell from chemical reactions such as the combustion of cooking gas, effervescence from carbonate upon the addition of an acid, and the sublimation of a piece of dry ice.

But many soft drinks and soda waters (including Sprite, 7 up, Pepsi, Coca-Cola, and Thums Up) emit, open opening, a strong burning smell that may cause severe irritation to eye and nose. The same burning is experienced during the burping (or belching) that comes out after consuming a glass of such drink

So, I want to know, is this due to $\ce{CO2}$? Maybe the manufacturers pump too much $\ce{CO2}$ into their drinks that it reacts in a different way than $\ce{CO2}$ from LPG-oven flames or carbonate/acid reactions? Or maybe that 'burning effect' is due to some mysterious additive?


texts: can I mix. trisodium phosphate, potassium hydroxide, and sodium hydroxide together?

texts: Can I mix trisodium phosphate (tsp), potassium hydroxide, and sodium hydroxide ( or sodium hypochlorite ) and not cause a bad reaction?  And will this make for a good degreaser and cleaning chemical for me ?  I own a pressure washing business.  I do fast food resturanta, gas stations


texts: Suppose that I have 10 kg of plastic/polymer that is non solvable in water. I then divide the plastic/polymer into two equal parts.  Let us name the parts A and B in order to identify them.  I then proceed to make beads from each part. I make $n_A$ beads of radius $r_A$ from part A. I also make $n_B$ beads of radius $r_B$ from part B. Here $r_A>r_B$ and consequently $n_B>n_A$. Suppose that I put the beads from part A into 10 liters of water and I do the same for the beads from part B.  Which one is more viscous, the "solution" from part A or from part B? Note: here $n_A,n_B$ stand for some arbitrary number.


texts: Why is concentration used as a proxy for activity instead of mole fraction?

texts:
I am trying to understand how the Gibbs energy change of a chemical reaction is computed and I do not understand why concentrations (mol/L) are used as a proxy for activity rather than mole fractions (mol/total mol).

From the Wikipedia article on the chemical potential, in an ideal solution, the chemical potential of the chemical species $i$ is expressed as

$$\mu_i \approx \mu_i^\circ + RT \ln x_i,$$

where $\mu_i^\circ$ is the chemical potential of species $i$ in standard state, $R$ is the gas constant, $T$ is the temperature and $x_i$ is the mole fraction of $i$ in the system. Because real solutions are not ideal, the activity of $i$ ($a_i = \gamma_i x_i$) is used rather than its mole fraction $x_i$ in the calculation of $\mu_i$.

When $T$ and $P$ are constant, the Gibbs energy change of a reaction is formulated as

$$\Delta_r G = \sum_i \mu_i dn_i,$$

where $dn_i$ is the change in the number of particles of $i$ caused by the reaction (its stoichiometric coefficient). Consequently;

$$\Delta_r G = \sum_i \mu_i^\circ \cdot dn_i + \sum_i dn_i \cdot RT \ln \gamma_i x_i.$$

$\sum_i \mu_i^\circ \cdot dn_i$ is equivalent to $\Delta_r G^\circ$, while $\sum_i dn_i \cdot RT \ln \gamma_i x_i$ is equivalent to $RT \ln Q$ in the more usual formulation $\Delta_r G = \Delta_rG^\circ + RT \ln Q$.

Molar concentration (mol of species per volume of solution) are often considered as a proxy for the activity of solute species, while partial pressures are used for gas species (which gives the "mass action ratio" $\Gamma$ instead of the reaction quotient $Q$). While partial pressures are a concept similar to mol fractions (they are fractions of a total), concentrations and mol fractions are not the same quantity and I do not think they scale the same way. So why are $\Delta_r G$ quantities often computed using concentrations instead of mole ratios?

EDIT: Thinking about it, I think I found a simple justification for the use of concentration as a proxy for activity.

Let's consider a fictive reaction $A \leftrightharpoons B$. The chemical potential change associated with this reaction is

$$\Delta_r \mu = \Delta \mu_B - \Delta \mu_A$$

$$\Delta_r \mu = \Delta \mu^\circ_B - \Delta \mu^\circ_A + RT \ln x_B - RT \ln x_A$$

$$\Delta_r \mu = \Delta \mu^\circ + RT \ln \frac{x_B}{x_A}$$

$$\Delta_r \mu = \Delta \mu^\circ + RT \ln Q$$

mole fractions $x_A$ and $x_B$ are respectively $\frac{n_A}{n_{total}}$ and $\frac{n_A}{n_{total}}$ with $n_{total} = n_A + n_B$, so $Q = \frac{n_B}{n_A}$ ($n_{total}$ cancels). Obviously $Q$ has the same value if concentrations ($\frac{n}{V}$) are used since the volume $V$ is the same for both species and then cancels itself. This justification is obvious for a 1:1 stoichiometry. However, with other stoichiometries, either $n_{total}$ or $V$ remains as a factor in $Q$ (to the power $\sum_i \nu_i$, where $\nu_i$ is the signed stoichiometric coefficient of species $i$). I am pretty sure that $n_{total}^{\sum_i \nu_i}$ is not always equal to $V^{\sum_i \nu_i}$; this is where the difference may happen.


texts:
In an experiment in school, we heated copper wire (Cu) and yellow sulfur powder together in a crucible. I was wondering why this reaction cannot produce Copper Sulfate. I know it produces Copper Sulfide but I want to know why don't oxygen from the air, sulfur, and copper combine to form copper sulfate.

Can anybody explain this in simple high school terminology?


texts: What are the volumetric thermal expansion coefficients for butyl acrylate and methyl methacrylate monomers?

texts:
We have some tanks of butyl acrylate and methyl methacrylate monomers, and the level indicators are giving incorrect readings.  The control systems engineer who set up that system suspects that the density values used in programming the level indicators were wrong, so I measured the density of the monomers by hand today.  However, the monomer samples I had were at around 70-72 Fahrenheit, whereas the tanks are usually closer to 52 Fahrenheit.  I'm trying to find the volumetric thermal expansion coefficients for these liquids so I can correct my measurements, but I'm unable to find them.  I've checked online and in the CRC Handbook of Chemistry and Physics (which lists coefficients for some organics, but not these).

I know that the expansion coefficients are temperature dependent, but if I can get even a single value (at, say, 20 Celsius, which seems to be a fairly standard place to measure this for organics) I should be able to get my estimate close enough to be able to judge if this is the source of error in the level indicators or not.


texts: How do daily compounds such as table salt ($\ce{NaCl}$) and sugar ($\ce{C6H12O6}$) affect adhesion or surface tension of water? Considering their polarity, I guess they both increase it.


texts: How to compare stability between 5‐methylcyclohexa‐1,3‐diene and 3‐methylenecyclohexene?

texts:
Problem

Compare stability of 1 and 2:

Answer

 1 is more stable than 2.

My approach

Both have the same number of π-bonds.
Both have one resonance structure.
Both are non-aromatic.
In 1 there are three α-hydrogens, whereas in 2 there are four α-hydrogens.

As extent of hyper-conjugation is more in 2 than in 1, making 2 more stable, which contradicts the answer.


texts:
I understand that in general, when in acidic media, the nucleophile tends to attack the more substituted side of the epoxide due to electronic reasons. And when in basic media, the nucleophile attacks the less substituted side of the epoxide due to steric reasons.

What if the hydride anion attacks an epoxide? I'd imagine the hydride anion to be quite small, and able to attack both the more substituted and less substituted sides of an asymmetric epoxide. What are the experimental results?

Also I have my doubts about hydride anion even being able to open an epoxide; I am told by Clayden that hydride anion never acts as a nucleophile because its 1s orbital is too small.


texts: Why methyl group is 2,4-directing? I am an A level student and this isn't required at this level. I am looking for a simple explanation which a high school student can understand.


texts: What is the entalphy change with respect to pressure at Isothermal Process for *Real Gases*?

texts:
How much enthalpy of argon changes when the pressure is isothermally increased by $\pu{1 atm}$? (Gas should be considered as real gas under specified conditions) ($\pu{1 mol}$ of Argon gas is available at $\pu{25 ^\circ C}$ and $\pu{11 atm}$ conditions)

-Firstly I took the total derivative of Enthalpy function of pressure and temperature:

$$dH =\left(\frac{∂H}{∂P}\right)_T \cdot dP + \left(\frac{∂H}{∂T}\right)_P \cdot dT$$

Then divided terms with $dP$ because as the question asks I need $\left(\frac{∂H}{∂P}\right)_T$. After this I get:

$$\left(\frac{∂H}{∂P}\right)_V = \left(\frac{∂H}{∂P}\right)_T + \left(\frac{∂H}{∂T}\right)_P \cdot \left(\frac{∂T}{∂P}\right)_V$$

Third term is enthalpy change with temperature at constant pressure means $C_p$, so the equation turns into:

$$\left(\frac{∂H}{∂P}\right)_V = \left(\frac{∂H}{∂P}\right)_T + C_p \left(\frac{∂T}{∂P}\right)_V$$
so I rewrite this like:
$$\left(\frac{∂H}{∂P}\right)_T =\left(\frac{∂H}{∂P}\right)_V-C_p\left(\frac{∂T}{∂P}\right)_V$$

Then I used Chain rule, which is: if $z=f(x,y)$:
$$\left(\frac{∂z}{∂y}\right)_x\left(\frac{∂y}{∂x}\right)_z\left(\frac{∂x}{∂z}\right)_y=-1$$

I used this rule for writing a derivative term, $\left(\frac{∂T}{∂P}\right)_V$, with constants, and my equation turns:

$$\left(\frac{∂H}{∂P}\right)_T = \left(\frac{∂H}{∂P}\right)_V - C_p\left(\frac{\kappa T}{\alpha}\right)$$
where $\alpha$: expansion coefficient; and $\kappa T$: isothermal compressibility coefficient (kappa t).

In this way, I came up to this point but I couldn't find the exact answer. I Lost myself in thermodynamic differentials. Can anyone explain me? Where did I mistake or is my solution method incorrect?

Edit:

$$\left(\frac{∂H}{∂P}\right)_T = V - T\left(\frac{∂V}{∂T}\right)_P$$

If i wasn't wrong rhs of the equation turns into = V - T ( ßV) which equals to partial derivative of enthalpy with respect to pressure at constant temperature. But i'm confused here. There are other terms that can be used for ßV. For example alphaV or Vkappa t. Which one should i use? What is partial derivative of volume with respect to temperature at constant pressure means? Question asked about isothermally increasing pressure so should i use isothermal compressibility coefficient or isobaric compression coefficient or thermal expansion coefficient or what? Really confused here..

$$\left(\frac{∂H}{∂P}\right)_T = V - TßV$$ this is the last point i came to


texts:
I don't have a degree in anything, but I do know basic rules of science I believe. It seems pretty intuitive that heat will always flow from something hotter into something colder in order to reach an equilibrium.

My understanding of temperature is that it is a measure of how fast something's particles are vibrating.

I've been very interested in the mechanics of salt water and ice spontaneously dropping in temperature because it seems counter intuitive and goes against everything I seem to know.

As far as I know, pure ice begins to melt at 0°C and above. If I were to place an ice cube at -2°C in oil that is -5°C, it wouldn't melt because the oil has less energy than the ice cube. If anything, energy would leave the ice cube to warm the oil and the cube of ice would get colder.

So, if I have salt water at say -2°C, and I put an ice cube in the mix that is pure ice and is 0°C, how is that colder water going to impart energy into something that's warmer (the ice cube). This seems extremely bizarre and seems to go against basic rules of thermodynamics.

I know that adding more salt would lower the melting point even further, but isn't a temperature a temperature? Does the material matter? Do two substances with the same temperature contain the same kinetic energy on the molecular level? If not, then what is temperature even a measurement of?

Thank you.


texts: Prevent crystal growth by adding a chemical to a solution?

texts: If I have a solution of dissolved $\ce{NaCl}$ or sugar (or some other ionic compound), is there a chemical I could add to it that would prevent crystal growth if I boil it down? I'm looking for it to remain as a very fine powder or to keep the crystals as small as possible.


texts: What exactly happens while washing clothes

texts:
I am reading about soaps , micelles and all that. I understand how soap behaves in water contaminated by oil. Soap helps in emulsifying the oil into water.

Let us suppose now we have dirt(i.e oil, grease etc) not alone in water but present on a some cloth. Why can't we put the cloth just in water to get it clean ? What precisely is the need for agitation in a washing machine or by any other method ?

I searched and found that agitation produces foam but according to this post foam does not alter the washing process anyhow.


texts: Does crystal field splitting energy Δ increase going down a group of transition metals if the ligands are weak field?

texts:
Going down a group, the metal orbitals are more diffuse so there is greter
overlap between the metal and the ligand orbitals.
If there are no π-interactions, i.e. with σ-donor ligands like $\ce{NH3}$, then the $\mathrm{e_g}$ MOs are split further with more metal-ligand overlap, and $\Delta_o$ increases.
If there are π-acceptor interactions, then the $\mathrm{t_{2g}}$ MOs are split further with more metal-ligand overlap, but $\Delta_o$ still increases as it is the gap between the bonding $\mathrm{t_{2g}}$ and antibonding $\mathrm{e_g^*}$.
However with π-donor ligands ($\ce{Cl-}$, $\ce{Br-}$ etc), surely more overlap would cause greater splitting of the $\mathrm{t_{2g}}$ orbitals, which would decrease $\Delta_o$, as it is the energy difference between the antibonding $\mathrm{t_{2g}^*}$ and $\mathrm{e_g^*}$.

So, does $\Delta_o$ still increase going down a group if the ligands are π-donors?


texts: Can diamond be melted in a thermite reaction?

texts:
My book says

  A thermite reaction is an exothermic reaction, it releases a large amount of heat so that temperature increases up to 3500 °C.

On the other hand, it says the melting point of diamond is 3500 °C.

So my question is whether diamond can by melted in such reaction?


texts: Would cooling of a battery using cooler affect its life time?

texts: My smartphone gets over heated where I use mobile data for long period. Last day I found a cooler of an old cpu, the thing silver in colour to absorb heat(with eventually gives out heat as it has more surface area on the other side). I used to keep my phone above it and it gets cooled. So my question is whether it will cause any problem for the battery if I tries to cool it using the same? I am asking this because there are a lot of thermodynamics involved in batteries and would it cause any problem to my battery life?


texts: Do you know how can I dissolve epinephrine in water? because it is insoluble in ordinary situation. When I decreased the pH by $\ce{HCl}$ it really worked but I need pH=7 to continue my experiment. Can I add $\ce{HCl}$ and dissolve the EPI and later using buffer to reach pH=7 and in this way the EPI wont be precipitate?


texts: How do I find miller indices for a plane whose intercepts are fractions of the lattice constant?

texts:
[I'm talking with respect to cubic lattices alone.]
For instance, if a plane has $x,y,z$ intercepts $a/2,a/2,a/2$ (where $a$ is the lattice constant) the miller index would be $[2\space2\space2]$. The book I'm referring to says that for fractional intercepts, the indices do not have to be reduced to the smallest whole numbers(hence $[2\space2\space2]$).
But, miller indices are supposed to represent a set of parallel planes and I can't think of any other plane with the index $[2\space2\space2]$
Then I saw this:

The image(3rd row, 3rd image) shows the set of $[2\space2\space2]$ planes.
I'm guessing that one of them has intercepts $a/2,a/2,a/2$. What are the intercepts of the other planes, and how are they all $[2\space2\space2]$?
Or, if my method of calculation is wrong, how else do I calculate miller indices for fractional intercepts?
PS: I've only just started to learn this concept, so it's possible that my understanding of miller indices is fundamentally flawed.


texts: Number of isomers in a 3-sugar oligosaccharide

texts:
I recently read that 12288 different oligosaccharides can be formed from the D-isomers of glucose, mannose and galactose. I wanted to try to calculate this, but I keep falling very short of this number.

Each molecule has the potential to form 6 unique bonds:

The disaccharide can form 13 unique bonds:

(Note, bonds formed by anomeric carbons shown with an arrow)

So, if a monosaccharide can form 6 different bonds, this means that:

6 possible bonds x 5 bonds on 2nd sugar x 2 anomers for seconds sugar = 60 possible disaccharides

Each of these disaccharides has 13 possible bonds it can make to a third saccharide:

13 bonds x 5 bonds of 3rd molecule x 2 anomers = 130 combinations for a single dissacharide.

130 combinations per disaccharide x 60 possible disaccharides =7800 isomers.

This is probably a counting error. But maybe I am missing a stereocenter?


texts: Reactivity of Alkanes, Alkenes, and Alkynes

texts: In my textbook, it says that alkanes are generally the least reactive of the three, alkenes are slightly more reactive, and alkynes are even more reactive. However, alkanes have single bonds, alkenes have double bonds, and alkynes have triple bonds. How can the molecule with triple bonds be the most reactive if triple bonds require the most energy to break?


texts: How are σ+ values in Hammett Plots calculated?

texts:
First of all, I know a similar question has already been asked & answered about σ values in general, however, I am not 100 % sure this answer is correct for the following situation.

So for the σ values, we know we have the following formula:

$$\log \left(\frac{K_x}{K_h} \right)=\sigma_x$$

with the equilibrium values being determined for the deprotonation of benzoic acid for different substituents. So, most logically we would find electron-withdrawing groups (EWG) having positive $\sigma_x$ values and electron-donating groups (EDG) having negative $\sigma_x$ values.

However, for the Hammett plot corrected for the stabilization of positive charge through resonance ($\sigma^+$) with the reference reaction being another reaction (see figure below), we still see the same trend for $\sigma_x$ values whereas we would expect the exact opposite.

$S_N1$ heterolysis reaction of para-substituted phenyl dimethyl chloromethane">

According to the literature, this inverse trend for EWG and EDG is being done purposely by changing the formula but I cannot find the formula. Does anyone know how this is done? Thank you in advance!


texts: Why is N₂ stable but HCN and C₂H₂ unstable?

texts:
Compounds with triple bonds generally seem to be unstable. $\ce{HCN}$ and $\ce{C2H2}$ are high-energy, relatively short-lived molecules that will readily polymerise or react with other organic molecules. My naïve mental picture is that they don't really want to have a triple bond because the geometry makes it awkward, so they'll do anything to transfer an electron somewhere else and turn it into a double or a single bond instead.

But $\ce{N2}$ seems to be an exception. By my naïve reasoning, when an $\ce{N2}$ meets an organic molecule it should be eager to shrug off its triple bond and join the party. But in fact this doesn't happen, and nitrogen fixing organisms have to do quite a bit of work to get nitrogen to participate in organic molecules.

So my question is, what is it about $\ce{N2}$ that makes its triple bond so energetically favourable while $\ce{C#C}$ and $\ce{C#N}$ bonds are so unfavourable?

Note that this question isn't about reactivity with $\ce{O2}$ but rather with organic molecules. I'm interested in why it's so difficult for $\ce{N2}$ to react with organic molecules in general, given that other molecules with triple bonds seem to react with them very easily.

(Information to guide the scope of answers: I'm coming at this from a physics background, so thermodynamic concepts can be taken as understood, but I quickly get lost when it comes to electrons and orbitals and so on, hence the rather basic question.)


texts: Does caesium or francium have a lower ionization energy?

texts: $\ce{Cs}$ and $\ce{Fr}$ are in the same group of lowest first ionization energy, but which element has the lowest ionization energy, and why?


texts: Why does the ground state of a Li atom have a total spin of S = 1/2? I get that the total z component of the spin has to be either Ms = 1/2 or Ms = -1/2 because of the Pauli exclusion principle, but that could also correspond to a total spin of S = 3/2, so why is it always S = 1/2?


texts: What is the "rate factor" or "second-step rate constant" in the reaction rate equation?

texts:
The reaction rate equation can be written as:

$$r=r_0 K \prod_n a_n$$

where the $a_n$s are the activities of each reactant in the reaction equation (in the case where we find the reaction rate from reactants to products, of course. Else the other way around). These activities are multiplied together. (This is often written as concentrations instead, I have seen, which seems to be an idealization.)

$K$ is the equillibrium constant, $K=\exp\left(\frac{-\Delta G}{RT}\right)$.

I am curious as to what exactly the $r_0$ is? In the wikipedia article it is denoted $k_2$ and called the "rate constant for the second step." The second step here refers to the intermediate step at the actived-complex.

So far so good, but what is this quantity at this intermediate step? Is it a reaction rate from the activated-complex to the final product (in that case, how can this be different from the reaction rate from the reactants to this state)?


texts: Silica turning transparent during column chromatography with chloroform

texts:
Initially, my column had been loaded with n-hexane and ethyl acetate, however I ended up having to use a more polar solvent to elute my product. It was my first time running chloroform through a column packed with silica and I noticed that as the chloroform made its way down the column, the silica turned from white to transparent.

My initial hypothesis was that chloroform and silica must have the same refractive index. I looked up the values, and found them both to be ca. 1.45 (see references), so I am inclined to believe this explanation.

However, if someone here could weigh in, and either confirm/deny this. (Or, alternatively, venture a new hypothesis).

I am guessing no chemical transformation takes place when silica looses its opalescence, because if that were the case then the whole procedure becomes completely useless. However, I could be wrong.

References:

i. http://refractiveindex.info/?shelf=main&book=SiO2&page=Malitson

ii. https://en.wikipedia.org/wiki/Chloroform_(data_page)


texts: Electrolysis of brine solution gives sodium hydroxide , chlorine and hydrogen gas but catner kellener cell it forms amalgam

texts:
Sodium hydroxide is generally prepared
commercially by the electrolysis of sodium
chloride in Castner-Kellner cell. A brine
solution is electrolyzed using a mercury
cathode and a carbon anode. Sodium metal
discharged at the cathode combines with
mercury to form sodium amalgam.
My question is, why sodium ion discharge on the cathode and why not hydrogen ion?


texts: Current and reversible heat in battery reaction

texts:
In the book Battery Technology Handbook by Kiehne [1] (Google Books) on page 21, equation (32):

The reversible heat effect per time unit can be related to current flow, because each multiple of the cell reaction requires the current amount $n\cdot F$:"
$$\frac{\mathrm dQ_\mathrm{rev}}{\mathrm dt} = \frac{Q_\mathrm{rev}}{nF}\cdot i \label{eqn:32}\tag{32}$$
with $n$: number of exchanged electrons; $F$: Faraday constant $(\pu{96485 A s/equivalent})$; $i$: current in $\pu{A}$.

Two questions:

How is the current related to $nF$? current and $nF$ have different dimensions?

How can one derive equation \eqref{eqn:32}?

References

Battery Technology Handbook, 2nd ed.; Kiehne, H. A., Ed.; Electrical engineering and electronics; Marcel Dekker: New York, 2003. ISBN 978-0-8247-4249-2.

Update in order to respond to comments
I know that $\Delta G$ is connected with a reversible process and in principle, your derivation makes sense. My problem lies in the formula:
$\Delta S = \frac{Q_{rev}}{T}$ is a basic thermodynamic relation and the Gibbs Energy is defined as $\Delta G = \Delta H - T\Delta S$. So, following your derivation $\Delta H$ would be zero. Since this problem is connected with my other question, which is linked in the comments, I would expect two different heat terms, a reversible one and a irreversible one. And from the formulas there, I expect $Q_{rev}$ to be connected only with entropy.
Therefore, $Q_{rev} = -T\frac{\text{d}G}{\text{d}T}$ rather than $Q_{rev} = -\Delta G$ as the combination of your equations (2) and (4) implies.
I is quite hard to explain my problem...
There is another way to get to the equation in question, but this seems to be too simple:
Since, $\frac{\Delta G}{nF} = \text{Voltage}$, $\frac{T\Delta S}{nF} = \text{formal Voltage}$. And $\textit{Voltage}\cdot I = P = \dot{Q} = \frac{\text{d}Q}{\text{d}t}$, equation (32) seems perfectly valid, but this is a kind of a weak derivation.


texts: How can I calculate the charge distribution of a water molecule?

texts:
I would like to obtain the 3D charge density of a water molecule for plotting purposes (i.e. not necessarily super-accurate). I know this is a tough problem, but I'd like to give it a try. Since I'm currently using python, I've identified PyQuante and PySCF, and gather that I should learn how to run density functional theory (DFT) calculations. Before I do that, I'd like to find out if there is something else out there I should use instead. Multiple suggestions are welcome.

I've installed PyQuante, which according to it's README.txt may be more accessible to understanding.

For example, the color plots in this answer give a hint of what I'm talking about, though I'll ultimately plot the field strength contours and some electric field lines.

I'd like to obtain a large table of values (or expressions/expansions?), so I can create and work with surfaces and field line plots myself.

Additionally is it possible that there exist supplementary data in published articles. Where I might find that? Although this is about existing data, I actually do plan on putting in the time to have at least a minimal understanding of the calculation itself. If DFT is it, then I will be spending time studying that.


texts: Why does ethene not disintegrate upon excitation?

texts:
The average c=c double bond has somewhere around 614 kJ/mol of energy, if we convert it to eV, then the bond strength is roughly 6.4 eV.
Additionally, Ethene absorbs light at 171 nm.
However, if we calculate the energy of 171 nm it is around 7.3 eV, hence ethene absorbs energy that is higher than its bonding energy, which should lead to a complete disintegration of the double bond. So why does it not happen?
I'm fully aware that this does not happen, otherwise most bonds would break at around 300-400nm light excitation, however, I have not seen the reason why discussed.


texts: What is the correct value of the Avogadro constant? And how was it derived?

texts:
I found different values of Avogadro constant in different places. So what is the correct value?

$\pu{6.0221367*10^{23}}$ or
$\pu{6.02214129*10^{23}}$ or
$\pu{6.0221415*10^{23}}$ or anything else?


texts: Why is Gibbs free energy different for different processes?

texts:
Under constant pressure and temperature ∆G=∆H-T∆S.
Let us take a system with initial state (1) and a final state (2).Now let us change the state of the system from 1 to 2:

Case 1) Reversibly by adding heat Qrev.So now the entropy change
∆S=Qrev/T.Also the enthalpy change ∆H=Qrev.So the Gibbs free
energy change is 0(plug in the variables).

Case 2)  Irreversibly by adding heat Qirr.But since the state change in
both the processes is same, entropy change ∆S is still Qrev/T
(Since entropy change is a state function).
Similarly, enthalpy change is also a state function so ∆H=Qrev
again so the Gibbs free energy is again 0.

.Why is this happening? I feel that the Gibbs free energy in the
second case should be Qirr-Qrev.But I am not able to get that mathematically.
Where am I wrong?


texts: Would the initial step of this mechanism be exothermic or endothermic? (Protonation)

texts:
My understanding is that since an O-H bond is being formed, the protonation step must be exothermic because energy is released upon bond formation. However, if I were to draw an energy/reaction coordinate diagram for this mechanism, the more reactive protonated alcohol would be higher up in energy than the unprotonated alcohol so I'm not sure if the initial protonation step would be exothermic or endothermic.
This problem's been plaguing me for days now.


texts: When I read my ingredients on my nail polish remover, it has water as its first ingredient.  Why does nail polish have water, yet the warnings still say its flammable?


texts: Why can't this molecule avoid being antiaromatic by becoming nonplanar?

texts:
The peripheral system is clearly antiaromatic if planar, but we know that antiaromatic compounds are more unstable than non aromatic compounds.

So, I think that the molecule will lose its planarity and become non aromatic, but this molecule is antiaromatic according to my professor.

Isn't my reasoning correct?

Also, what would be the IUPAC name of this molecule?


texts: Is there any intuitive way(without involving higher maths) to explain possible variations in seven primitive types of (unit)cells? I would like explanation in context of why end centred is possible only for orthorhombic and monoclinic but not in other unit cells.


texts: I’m quite interested in chemistry, but reading the textbooks are a bit challenging. Are there any good chemistry books for the general reader that go a bit beyond the basics?


texts: Understanding the increase in pH of a buffer solution upon incremental additions of NaOH analytically

texts:
So let's say we have $200\ \mathrm{mL}$ of $1\ \mathrm M$ $\ce{CH3COOH}$ solution. In this solution we have the equilibrium $\ce{CH3COOH <=> CH3COO- + H+}$. To that we add $100\ \mathrm{mL}$ of $1\ \mathrm M$ $\ce{NaOH}$ solution. Then after reacting we get a buffer solution where $[\ce{CH3COOH}] = [\ce{CH3COO-}] = \frac{1}{3}\ \mathrm{mol\ dm^{-3}}$. In moles, we have $0.1\ \mathrm{mol}$ of both $\ce{CH3COOH}$ and $\ce{CH3COO-}$.

Then suppose we add $x\ \mathrm{mL}$ of $0.1\ \mathrm M$ $\ce{NaOH}$. This is, in effect, reacting $0.1\ \mathrm{mol}$ of $\ce{CH3COOH}$ with $0.0001 x\ \mathrm{mol}$ of $\ce{NaOH}$, the result of which is that now $n(\ce{CH3COOH}) = (0.1 - 0.0001 x)\ \mathrm{mol}$ and $n(\ce{CH3COO-}) = (0.1 + 0.0001 x)\ \mathrm{mol}$.

Could we not then model, by the Henderson-Hasselbalch equation, $\mathrm{pH} = \mathrm pK_\mathrm a + \log\left(\dfrac{0.1 + 0.0001 x}{0.1 - 0.0001 x}\right) = 4.76 + \log\left(\dfrac{0.1 + 0.0001 x}{0.1 - 0.0001 x}\right)$?

But this would mean that for the pH of the buffer solution to rise by $1$, we would need $818.82\ \mathrm{cm^3}$ of $0.1\ \mathrm M$ $\ce{NaOH}$ solution, which sounds absurd. Moreover, for different acids, like propanoic acid and butanoic acid, the same line of logic could be used to deduce that the volume required to increase the $\mathrm{pH}$ by $1$ would be the same for all, but they have different buffering capacities. So what's wrong with the logic?


texts: Strength of Pi Donor and Acceptors as Ligands

texts:
The spectrochemical series is usually known as the "strength" of the ligands. It makes sense on a basic level as the more willing a ligand is to donating its electrons (via a $\sigma$-bond), the greater the repulsion on the metal's $d$-orbitals. However, I recently learned about $\pi$-donors and $\pi$-acceptors and how they affect a ligand's placement on the spectrochemical series.
$$\ce{CO > CN- > NO2- > NH3 > H2O > OH- > F- > SCN- > Cl- > Br- > I- }$$
So from the very basic spectrochemical series I have shown here, it is said that $\ce{OH-}$ is a weaker-field ligand than $\ce{H2O}$ because it can act as a $\pi$-donor, which lowers the CFSE of the d-orbitals as the $e_g$ orbitals are stabilised by the resulting bond. However, I fail to see how this translates to a lower affinity to complex with the metal. Shouldn't this make $\ce{OH-}$ more stable as a ligand? I know that this isn't the case (proven by the structure of the $\ce{[Cu(H2O)4(OH)2]}$ complex structure, $\ce{OH-}$ takes on the weaker axial position), but I don't know why.
I'll include the molecular orbital diagram I got from chem.libretexts, which supposedly shows how the $\pi$-bonds affect ligand strength.


texts: What are the factors controlling the fate of post-adhesed volatile molecules of the olfactory epithelium?

texts:
What happens to volatile molecules that reach the main olfactory epithelium in the nasal cavity after they bind and the neural stimulus fades?

To what extent do such factors as receptor kinetics and diffusion (or any others) direct where these molecules end up?


texts: Is the carbon atom in the carbon dioxide molecule partially positive?

texts:
I had a question about nonpolar molecules that have symmetrical dipole vectors.

Let's take $\ce{CO2}$ as an example. Each of the $\ce{C=O}$ bonds are pulling in the opposite way. My teacher says that this causes all atoms in $\ce{CO2}$ to be equally charged as there mustn't be any net 'force'.

However, I disagree. Intuitively, it seems that the oxygen atoms would pull electron density away from the central carbon atom and make the carbon atom slightly positive and the oxygen atoms slightly negative, like so:

$$\large\ce{\overset{\small\delta-}{O}=\overset{\small\delta+}{C}=\overset{\small\delta-}{O}}$$

This process should make the carbon atom slightly positive and the oxygen atoms slightly negative. However, if I was right, then why don't we say $\ce{CO2}$ has a dipole (there is a separation of charge)? Perhaps I may have the wrong definition of a dipole.


texts: Why does my voltaic pile produce a higher voltage then predicted?

texts:
In my chemistry class we are building our own voltaic cells and trying to produce as much current as possible with materials we are given using redox chemistry.

My lab partner made a battery without thinking about the actual chemistry and it produced about 1.7 V per cell and 5.5 V for 3 cells in series. We tried different voltmeters to confirm that our readings were not a hardware issue.

After consulting our textbook and our teacher we realized that the theoretical voltage produced from our battery should be .71 V per cell and about 2.1 V in series of 3 cells.

Our battery setup was as follows:

Mg(s)|Al(NO3)3(aq) || Mg(NO3)2(aq) | C(s)

with magnesium as an electrode and the strongest reducing agent and ionized aluminium as the strongest oxidizing agent with sodium nitrate in the salt bridge. I understand that the aluminium ion solution should be switched with the magnesium ion solution so that the aluminium doesn't cause the magnesium to oxidize.

My question is why and how does this battery produce such high voltage? We used distilled water to clean all of our beakers but even then I don't think a little bit of copper or other ions dissolved in our electrolyte would be enough to produce that much voltage and sustain it for the hour we spent trying to figure this out. So how did the battery produce a higher than expected voltage?

I have a diagram of what our battery looked like here https://docs.google.com/drawings/d/1u1ZjI9vHCNIeAACrRZmL3CqP_AgshX-HKg-00sS0rvc/edit?usp=sharing


texts: Ground state term symbol, why is $L = |M_L|$, if L must be a maximum?

texts:
I'm trying to understand how to predict ground state term symbol of atoms.

After finding the biggest S, why the biggest L will be $L = |M_L|$, where $M_L = \sum m_l$?
I know this rule works to predict the total L, but it doesn't make sense to me that it will give the biggest L, to me it seems like this is the minimum L.

For example, the nitrogen atom has three electrons in 2p.

Following the first rule, the spin $S$ of the ground state will be the maximum possible, which is S = 3/2.

The second rule, according to some books is to maximize $M_L$, in the case of Nitrogen, according to Pauli principle, since all the spins are up, we can only get $M_L = 0$.

Now, all material I read says that L of the ground state will be the maximum one, so L = $|M_L|$, but if we expand the Clebsch-Gordan coefficients of the three states:
$|1 \,\,\,\, 0> |1 -1> |1 \,\,\,\, 1>$ we get the possibility of L = 3,2,1 and 0, so why is L = 0 the maximum possible value?

There is an amazing answer to this here, but he doesn't explain why he cuts out the the terms with bigger L.


texts: Trend in the boiling point of the hydrogen halides

texts:
The boiling points of the hydrogen halides are as follows:

$$\begin{array}{cc}
\hline
\text{Species} & \text{Boiling point / }\mathrm{^\circ C} \\
\hline
\ce{HCl} & -85.1 \\
\ce{HBr} & -67.1 \\
\ce{HI} & -35.1 \\
\hline
\end{array}$$
(source: Greenwood & Earnshaw, Chemistry of the Elements 2nd ed., p 813)

My textbook writes that this is due to an increase in the number of electrons, which increases the van der Waals forces between molecules.

But the $\ce{HX}$ molecules are polar. Shouldn't the boiling point be determined instead by permanent dipole-dipole attractions instead? Since the dipole moment decreases going from $\ce{HCl}$ to $\ce{HI}$, the boiling points should actually decrease. Why isn't this the case?


texts: Effect of effective nuclear charge increase on the stabilization of 2s and 2p orbitals

texts:
Are 2s or 2p orbitals more stabilized when going from left to right in the period? There are good arguments for both possible answers:

1) 2p orbitals are more stabilized because they penetrate less in the space of the 1s orbital, so the increase of the effective nuclear charge affects them more. When plotting the 1st ionization energy with the increase of the atomic number, it can be seen that the ionization energy increases with the increase of the atomic number, but the slope is bigger for O-F-Ne (3.97eV) than for B-C-N (3.12eV). 3s and 3p orbitals aren't stabilized so much (because they both penetrate into the space of the inner orbitals), therefore it is much easier to get a high oxidation state of sulfur than of oxygen.

2) 2s orbitals are more stabilized because the electron spends more time closer to the nucleus, hence the orbital is more affected by the increase of the effective nuclear charge. Proof: the MO diagrams for B, C and N differ from the ones for O, F, and Ne, because s-p mixing in B, C and N happens as the 2s and 2p orbitals are similar in energy. The energy difference increases towards the right (because 2s orbital is more stabilized), so 2s and 2p can't mix efficiently in O,F and Ne. If the 2p orbital was more stabilized, then the difference between 2s and 2p would be smaller through the period.

I really need some clarification here.


texts: How does sodium borate (Borax) function to promote Fe-Fe bonding?

texts: Borax is used as "flux" during metal forging to help stick two pieces of steel together. I am curious what is happening at the atomic level. How does the addition of borax promote Fe-Fe bond formation?


texts: Assumptions to be taken when rearranging terms in first law of thermodynamics

texts:
Assuming a closed system, show how the first law of thermodynamics.
$$\mathrm dU = \mathrm dQ + \mathrm dW$$
becomes,
$$\mathrm dQ = \frac{C_V}{R}V\,\mathrm dP + \frac{C_p}{R}P\,\mathrm dV$$

I have an answer, but am hesitant to say it is a final answer or even the correct one at that.
I am concerned with the partial derivatives when rearranging this equation. How do certain parts cancel out or how does one approach the problem without them? Is it safe to assume that since you know how the state variables will act in a certain process, that you can use that knowledge to provide a better or more exact answer to the problem?
Attached you will find a picture of the problem that I have done to the best of my ability (which is limited I must say).
How do I make my assumptions?
Do I assume holding one part constant to solve the equation in one way - that is via an adiabatic process, isothermal process - do the same for another path and compare?


texts: Software for visualizing molecular force vectors

texts:
I would like to visualize molecular normal modes as vectors sitting on each atom, and not as actual vibrations. I am able to do this, in part, with Molden by copying in the vector into a file readable by Molden (extension is .geo.molden, and is generated from a Molcas calculation). The vector is represented as red lines, but they do not look very nice (see image). Also the background is black, and Molden has a limited number of ways to visualize the molecule.

Is there some other software (free) that can do this? Perhaps Avogadro, VMD, or something along these lines? Specifically I would like to be able to change to different molecular visualizations, and show the vectors as arrows with a easily distinguished color.

Figure 1. This is what Molden can do... not very pretty!

Or possibly, after changing the background color to white with GIMP:

Figure 2. Not really better, since the Hydrogen atoms are represented with white by Molden, as is the label text.


texts: Calculating Optical Absorption Spectra using Ab Initio Computations

texts:
My main question is, How does one compute the optical absorption spectra of a molecule by using say, Configuration Interaction energy and associated transition dipole moments.

I am trying to use an ab initio package, Columbus to calculate transition moments (for $\ce{H2}$ as of now), however, there is some old code, called MELD, that I am supposed to refer to, that somehow takes in 4 non-zero such moments and their energies and gives a spectrum.

The input looks like this:

Linear absorption from the 1Ag; qci
Linear absorption from the 1Ag state; qci   1
How many components of dipole, and which ones?   3
1,2,3
Total no. of Bu excited states   4
Line width, frequency range, step
0.1,0.0,15.0,0.01
Energy of the 1B1u state
-1.1724565
Energies of the Bu states
-0.677388000000000      -0.262044700000000      -0.245699100000000       -0.245699100000000
Scale the energies  SCALE
 0.036749d0
Next come the dipole moments 4
           1           1  0.000000000000000E+000  0.000000000000000E+000   -1.20320100000000
           1           2  0.000000000000000E+000  0.000000000000000E+000
  0.547801000000000
           1           3  -1.05742200000000      -0.291179000000000
  0.000000000000000E+000
           1           4 -0.291179000000000        1.05742200000000
  0.000000000000000E+000

I am not sure what exactly is happening there? A reference to such calculations would be great too.


texts: Where does the additional hydrogen in the Fischer depictions of glucopyranose come from?

texts:
My book shows this figure of Fischer formula of D-glucose:

I don't understand this figure, and I wonder why the upper carbon atoms in both the right and left formulas have 5 bonds.

And from where comes this hydrogen atom in the upper left side of the figure (attached to α-D-glucopyranose).

When turning D-glucose to Fischer formula, it seems there's an additional hydrogen atom, isn't it? Why and how does this happen?!!

Could someone explain how to get from the aldehyde form of glucose (the middle structure) to the β-D-Glucopyranose and the α-D-Glucopyranose?


texts: Why is this stereocenter by the Br an R? I thought it was S? For problem b in the following image:


texts: In most aromatic compounds (e.g. benzene), their $\pi$-bonding molecular orbitals are completely occupied and their antibonding molecular orbitals are unoccupied. I'm wondering if there are any compounds where this is the case, but where the highest energy bonding MOs are only half-filled, so they contain unpaired electrons. My best guess at a molecule with that property is 1,4-dihydro-1,4-diborinine, as it has the same geometry as benzene (I think), including the adjacent p-orbitals, but it has two fewer electrons. Does this molecule still exhibit ring currents like benzene? Does it show the same type of delocalization?


texts: Dividing different units of measurement?


texts:
What makes some atoms/compounds reactive and some noble? What is the fundamental truth behind a reaction? It seems that two species can undergo number of combination to give a compound. Say Sodium and Chlorine, it seems intutive to have number of combinations from this pair such as $\ce{Na2Cl}$, $\ce{NaCl2}$, $\ce{Na3Cl2}$, and even do not react at all. But why $\ce{NaCl}$?

I had been carrying the concept of octet rule, which I now find to be exception in some cases like $\ce{AlCl3}$. So, what determines the products of a reaction? Or is it that all possible combination are formed but only few are major products, in this case $\ce{Na2Cl}$, $\ce{NaCl2}$ etc. are formed but $\ce{NaCl}$ is major product.

I think it has to do something with energy but cannot figure out what.


texts: Synthesis of a weinreb amide from an acid

texts:
The following shows the conversion of an acid to a weinreb amide:

It was taken from the IChO 2015 preparatory problem set problem 23. In this two-step synthesis, I am slighly puzzled by the first step. The rationale behind first forming the ester is that we would like to synthesise an acid derivative which can react with the amine to form the amide since direct conversion of an acid to an amide is rather difficult. However, I wonder why is the t-butyl ester formed instead of say, a methyl ester, since the former sterically-hinders the attack of the amine in the subsequent step. In fact, conversion to an acid chloride first (e.g. using thionyl chloride), instead of an ester would seem to be more optimal than conversion to an ester first since acid chlorides would be more reactive with the amine.

In summary, I would like to know why ester formation is preferred over acid chloride formation in the first step and also why a rather bulky ester is preferred over a much less bulky one. Regarding the former, I believe it could be that the formation of $\ce {HCl}$ by-product may hinder the 2nd reaction by protonating the amines. Regarding the latter, I believe there may be some electronic factors that need to be considered?


texts: Does myristyl glucoside contain alcohol?

texts: I read that "myristyl glucoside is a product obtained by the condensation of myristyl alcohol with aglucose polymer." Does that mean that alcohol is part of the final product/myristyl glucoside itself? Or is all of the alcohol removed during the making of it?


texts: Is 1000ml of 'hot-ice' solution dangerous?

texts:
So I was trying out the sodium acetate trihydrate 'hot ice' experiment, and my 300ml test worked great. So, naturally, more is better right? (cringe)

Now I have a 1000ml in a pyrex beaker cooling down, and I am belatedly wondering if this is going to generate too much heat when I set it off. I'd imagine the beaker itself is safe, I don't imagine it would do anything to the granite countertop, but it is resting on a plastic cutting board, which could conceivably melt.

How much of this can I make before I'm doing something risky?


texts: Why does nital need alcohol when etching metals?

texts:
I was reading about HNO3 and I saw it can be mixed with alcohol to form "nital", which is useful when etching metals, especially carbon steel.
I wonder why alcohol is needed? HNO3 itself is corrosive for metals. So I did a little search and some college students claimed that alcohol is for holding back the reaction rate to get a better result, but it raised more questions for me... My thought now is alcohol is not as polar as water, so HNO3 would probably be less readily dissociated. But I can't figure out the rest.


texts:
Please consider the following graph of molar volume as a function of pressure for a fixed volume.

Can we say whether this system under thermodynamic equilibrium or not?

Update Thinking about this some more, the molar density vs pressure graph may be useful too.

Is this gas in thermodynamic equilibrium?


texts:
Is the photoelectric effect possible for semiconductors?

I imagine that this might be, if possible, a two-photon process: excitation of an electron from a filled to conductance band, and then on to ejection. Is anyone familiar with such materials, or even whether this is possible?

I can't readily think of a theoretical reason against it. Two-photon events are often less likely than one-photon, however I could imagine irradiation by a laser of bandwith covering both the band-gap wavelength and that necessary for ejection would do it.

If it does indeed happen, I'd be glad to hear a short summary of how it differs from the photoelectric effect of metals.


texts: What compound has the strongest optical rotation of polarised light?

texts:
A question recently asked here whether compounds know to be chiral can have non-measurable optical rotations: Are there chiral compounds that don't rotate plane-polarized light?.

Apparently they exist and the phenomenon is known as cryptochirality.

This prompted me to think of the opposite end of the spectrum of optical rotation. Which known compound shows the largest known optical rotation?

NB when I say "known compound" I mean something that has actually been synthesised in large enough quantities to be well characterised. So no theoretical-only compounds or esoteric systems.


texts: Why does the specific conductivity against concentration curve for NaCl curve more than KCl?

texts: I understand why KCl has a higher specific conductivity than NaCl.. but I dont understand why the curvature is more significant for NaCl (KCl is a straight line). Ive provided a picture of this here, and this is also what I get from my experiment. Does anyone mind explaining why?


texts: Naming Ionic Compounds with Transition Metals

texts:
Look at $\ce{FeO2}$.  We know that $\ce{O2}$
is $-2$ then we must have $-4$ for $\ce{Fe}$

So $\ce{Fe}$ must have $+4$ charge so then is it $\ce{Fe(IV)}$ ?


texts: What do X-ray diffraction and NMR tell about the Proteins?

texts:
I have gone through a simple idea that proteins have different conformations; it is a dynamic system. Moreover, whenever we do ensemble experiments, so we get an average picture. There are some questions-:

Q.1 Often protein structures are reported in PDB (protein data bank), so what do they signify? The most stable conformation or some averaged picture of all conformation or both?

Q.2 In the case of the NMR, proteins have the freedom to move/vibrate through space as they are in the solution phase, but in XRD, they are rigid. So what will be the difference if I get one structure from XRD and one from NMR?

Q.3  Why structure of some proteins has not been resolved yet? I get it that a large protein cannot be solved using NMR; it will be much complex. However, why we cannot use XRD?
a) Why is the crystallisation of some protein hard?
b) Will there be any other challenges even if we get the crystals of a protein?

Q.4 Investigators often use different buffers to crystalise the given protein, but how they make sure that structure that they are getting in that buffer is the "actual" structure? How they make sure that crystalisation do not affect the "actual" structure of the protein.

From "Actual" Structure, I mean the structure or set of conformations that are retained in the physiological condition (in the working conditions).


texts: Does a technical umbrella term exist that covers the different kinds of biomolecules?

texts:
I want to write a sentence along the lines of:

  There are four ____ in biochemistry: proteins, lipids, carbohydrates and nucleic acids.

Does a specific technical term exist that I can use to fill the void? Or am I relatively free in my choice?