texts: Relation between speed of sound c and compressibility

texts:
We know that
$c^2=\frac{\partial p}{\partial ρ}$

The adiabatic compressibility is defined as: $\beta_S=-\frac{1}{V}\frac{\partial V}{\partial p}$ such that the subscript "S" stands for "adiabatic"

How can I show that $c^2=\frac{1}{\rho \beta_S}$ ?

I tried replacing $V$ by $\frac{m}{\rho}$ but I get for $\beta_S=-\rho \frac{\partial \frac{1}{\rho}}{\partial p}$


texts: How can a DPPH assay to measure antioxidant activity of beta carotene be conducted?

texts:
I am currently doing some research regarding beta-carotene. With reference to other sources and their methodoloy for DPPH assay, I conducted my experiment but failed to find any significant peak in absorbance at 517nm using a UV-spectro.

My sample of DPPH is already dissolved to 0.1mM in methanol.

My methodology was mixing-
0.3cm3 DPPH
0.3cm3 beta-carotene (dissolved in propanone)
2.4cm3 methanol

I increased the dissolved betacarotene in increments of 0.3cm3 ( upto 1.5cm3) while simultaneously decreasing methanol also by 0.3cm3 (upto 1.2 cm3) for a total of 5 readings.

The mixture was shaken and left to sit (in dark conditions) for 30mins before readings were taken using UV-spectrometer. The UV-spectrometer was calibrated with DPPH.

While I achieved the expected colour change from purple to yellow, I did not get a significant absorbance at any reading at 517nm even when using pure beta carotene.

I suspect this may be due to the betacarotene being dissolved in propanone which perhaps may be the wrong solvent, or perhaps i am calibrating the UV-spectro with the wrong substance, however I would like to check if this procedure is incorrect.

Please advice accordingly. Much appreciated.


texts: Why don't the solute molecules in a volatile solvent also escape to contribute to vapor pressure?

texts:
I'm currently studying relative lowering of vapor pressure with the addition of a  solid non volatile solute.

The book explains it with the notion that some of the non volatile solute also appears at the surface between the liquid solution and the vapor. However, i don't understand why don't the molecules of the solute at the surface just escape? Obviously, a solid can't vaporize (Unless you raise the temperature, (And maybe reducing the pressure?)) however the molecules of the solute that are at the surface between the solution and the vapor and should not be held by the strong intermolecular bonds of the solid.

Hence, if i understand this correctly, they, just like the water (Or other solvent) molecules should be constantly moving around in the solution and sometimes 'bump' into other molecules to gain enough velocity to escape the solution. The few molecules that are are the surface between the solution and the air should be getting frequently hit with high energy molecules from below, which should constantly knock such molecules into the vapor. This would mean two things:

The solute also has a small partial vapor pressure
The vapor pressure should still lower, as once solute particles are knocked out into vapor, a few of the solvent particles should escape through the 'opening' before another solute can take it's place. Rinse and repeat, like a valve being opened and closed. Hence, while there would still be a lowering of vapor pressure, there shouldn't be any permanent layer being formed between the solution and the vapor.

But both of these are in contradiction to what's in the book. So where did i go wrong in my reasoning?


texts: Non-ideal velocity distribution of gases

texts:
A recent question about the velocity distribution of ideal gas molecules got me wondering. How much would the velocity distribution vary for non-ideal gases?

I was wondering about a mixture of ethane and helium. The ethane molecule would have vibrational modes that the helium atom wouldn't have. Given that the helium velocity was "ideal," how non-ideal could/would the ethane velocity be?

Some other molecule been experimentally analyzed like this? I guess that a molecule with even more atoms would have even more vibrational/rotational modes.


texts: How does propylene glycol/glycerin form formaldehyde/acetaldehyde when vaporized?

texts: So apparently, e-cigarettes produce formaldehyde/acetaldehyde because they vaporize propylene glycol/glycerin. What is the chemical reaction through which propylene glycol/glycerin forms formaldehyde/acetaldehyde? Why does propylene glycol form more carbonylated products than glycerol?


texts: Can toluene be oxidized to benzoic acid using Pyridinium Chlorochromate(PCC)?

texts:
My question stands:

Is it possible to oxidize toluene to benzoic acid using PCC?


texts:
I am doing a project in chemistry at the moment to build a rocket out of materials that can be easily bought and that react strongly to create thrust.
I was wondering if anyone knew a good chemical formula for my rocket fuel? I know lots of good fuels and reactants used in amateur rocketry however commercial fuels have been banned from the project.
Any help would be appreciated.


texts: What to do when different conditions favor different substitution and elimination reactions?

texts:
How do I know which product will occur when different conditions which favors different reactions are all together?
For example: Let's say that I have a secondary substrate (which doesn't favor anything), I use protic solvent (methanol) which favors E1 and SN1, but I use HS- as a nucleophile (should favor E2) and also heat it which also favors E2.
Second example: I have a tertiary substrate in a protic solvent which is likely to become SN1 and E1 product. But what happens if I add a strong base like OH- which favors SN2 and also heat it which favors E2?
How do I know what will be the major product?


texts: How to determine the work function and electron velocities from data on the photoelectric effect?

texts:
A metal received light with wavelength $300~\mathrm{nm}$ in experiment A and light with wavelength $500~\mathrm{nm}$ in experiment B. In one experiment the electron speed was twice the speed of that in the other experiment. Calculate the velocities and the work function ($W$) of the metal.

Because it's the same metal in both experiments we have $W_\mathrm{A} = W_\mathrm{B}$, which means that $E_\mathrm{A} - K_\mathrm{A} = E_\mathrm{B} - K_\mathrm{B}$.

We know that $E=hc/\lambda$ and $K=mv^2/2$. Because $\lambda_\mathrm{A} < \lambda_\mathrm{B}$, we have $E_\mathrm{A} > E_\mathrm{B}$ and $K_\mathrm{A} < K_\mathrm{B}$ which means $v_\mathrm{A} < v_\mathrm{B}$ and $v_\mathrm{B} = 2v_\mathrm{A}$.

Then I made the substituions in my initial equality but when I try to calculate $v_\mathrm{A}$ I obtained a negative number inside my root.


texts: Microcopy Fluorescence filter set usefulness

texts:
I have a brief doubt and maybe someone around here can give as some help. We are doing a pilot study on microplastics using a fluorescence method (red nile). The dye is solvachromic, so it's emission spectrum changes by the polarity of the media. We do have the spectra for the excitation (mostly blue light) and emission (for the solvent used).
We have an old zeiss microscope equiped with epifluorescence. The filter has emission in 460-490, FT510 and LP at 520.

My question is if the emission spectrum of red nile includes 510-520 but maxima is achievied at 560, the filter set we have will work and we will see green fluorescence?
In others types of microplastics the spectrum of emission is shifted towards the red but it includes a small extitation in green. Is this filter useful?
Hope someone can help we have applied the protocols but we doubt if there is a problem in the red nile solution or in the fluorescence filter


texts: Refractive Index (RI) variation with Temperature & disagreement between two standards

texts:
I am comparing two different international standards for the same organic compound (clear and colorless liquid) and for the refractive index one standard says

  1.531 to 1.534 (@ 20 °C)

The other one says

  1.526 to 1.527 (@ 27 °C)

Now the ranges don't even overlap.

Couple of  questions:

Would the change in testing temperature (20 °C vs 27 °C) be enough to explain this difference in standards? Would an increase in Temperature typically reduce the RI or increase it? By what percent per degree change in Temperature?
Any other testing intricacies for RI that I ought to be aware of? Is there a methodological / protocol difference that may explain this?
Is this a difference large enough to worry about? The difference in ranges is only about 0.3 %. What is the typical least count / accuracy of RI measurements in the lab?


texts: Why can entropy be measured in joules per kelvin?

texts: I'm a little confused as to what the measurement associated with entropy represents. It's obviously the joules of energy per kelvin, but how does this measure the disorder of a system?


texts: $\ce{ N2F2}$ exists in two forms cis and trans. Today my chemistry teacher tells me that among the two only cis form takes part in reactions and that it is more reactive. But I have read elsewhere that trans is less stable. As far as I understand less stable compounds are usually more reactive. So why this discrepancy?


texts: Finding OH- concentration given the H+ concentration - diverse methods

texts:
There was this exercise which asked to find the OH- concentration given the H+ concentration, i firstly calculated the pH as -log[H+], did 14-pH to find the pOH and then did 10^(-pOH) to find the concentration of OH-.

My textbook used the fact that Kw (water equilibrium constant) is essentially
Kw = [OH-] * [H+] so it did    [OH-] = Kw/[H+]

The fact is...isn't Kw temperature dependent? My textbook says that it is

25 celsius --> Kw --> 1*10^-14

whereas

60 celsius --> 9.61*10^-14

So my question is...why is my procedure temperature independent while the book one temperature dependent? My procedure would always give the same concentration of OH whereas changing the Kw the textbook would also get other ones.

Thank you.


texts: Difference between Sodium Bicarbonate and Sodium Carbonate reacting with HCl

texts:
In lab, we performed the Solvay process where we had to produce sodium carbonate as the final product. There is a certain step where we put something in the oven and after this, we expect that the product is sodium bicarbonate ($\ce{NaHCO3}$). This product does not get named in the instructions; it is simply referred to as "dry product". After this step, we were asked to add 2 drops of $\ce{HCl}$ to a small amount of the dry product in a watch glass. Finally, we should repeat the watch glass step using $\ce{NaHCO3}$ and $\ce{Na2CO3}$.

After doing these 3 experiments, I observed the same thing (bubbles). I think that the reactions were:

$$\ce{NaHCO3 + HCl -> NaCl +  CO2 + H2O}$$

and for the third one (since I added $\ce{HCl}$ drop-wise to $\ce{Na2CO3}$, $\ce{Na2CO3}$ was in excess):

$$\ce{Na2CO3 + HCl -> NaHCO3 + NaCl}$$

and then:

$$\ce{Na2CO3 + HCl -> NaCl + CO2 + H2O}$$

I believe the purpose of the 3 experiments was to identify that the dry product was $\ce{NaHCO3}$, but after adding $\ce{HCl}$, I observed exactly the same thing (bubbles) for both known reagents. So I'm confused as to what should be my answer.


texts:
Since in rusting (oxidation) of Iron, transfer of 4 electrons takes place is it possible to use this reaction under catalytic conditions to create a simple electric cell, even if it just gave a millivolt of potential.

$\ce {Fe + H2O -> FeOH3 + H2}$

Considering that we have complete control over the surroundings, like volume expansion, disposing hydrogen and other such factors.


texts: Getting 3,4-dimethylhex-3-ene from but-2-ene

texts:
How can one get 3,4-dimethylhex-3-ene from but-2-ene ?

$\hskip2in$

Using $\ce{Br_2}$ then two equivalents of $\ce{CH_3CH_2MgBr}$, I can get the corresponding alkane (3,4-dimethylhexane) but I don't see how to do it while preserving the double bond...


texts: Production of hydrogen using vinegar and metal for experiments

texts:
If
 I cannot, or do not want to use electrolysis of water to produce
hydrogen, is it a viable alternative to react vinegar (ethanoic acid)
and iron (or steel, or copper) to form iron(II) or copper acetate? (Assume steel wool or copper wires.)

If I tried to fill a balloon with the produced gas (assuming no leaks
apart from balloon), would the hydrogen leak out of the balloon faster
than it would be produced?


texts: Is it possible to burn things in a halogen atmosphere?

texts: Fires can burn in oxygen. But, can they burn in halogen atmospheres (fluorine and chlorine only)? I am wondering this because combustion reactions involve oxygen and carbon and other elements. But, can they burn in fluorine and/or chlorine? If they do, what color will the flame of paper and wood be in fluorine and chlorine atmospheres respectively?


texts: Molpro wavefunction symmetry specification

texts:
I'm beginning to use Molpro software for some computations. But I got completely confused by its description of specification of wavefunction symmetry.
It tells us, that the symmetry of wavefunction is described like
$$\text{wf},\text{nelec},\text{irrep},\text{spin},$$
where $\text{nelec}$ is the total number of electrons in the molecule, $\text{irrep}$ is the number of the irreducible representation (list of numbers in Molpro docs) and $\text{spin}$ is the total spin number.
I know, that water belongs to the $C_{2v}$ point group, and I found its character  table:

I know, that 1/-1 values correspond with variance/invariance of orbitals, i.e. $A_1$ representation corresponds to the fact, that $\ce{s}$ and $\ce{p_z}$ orbitals are
not inverted by any of the four symmetry operations.
I also know, that the electron configuration of oxygen is $\ce{1s^2 2s^2 2p^4}$ and both hydrogen atoms have $\ce{1s^1}$.
But I'm not sure how am I supposed to choose the irreducible representation of the whole molecule.
In this answer the similar problem is described and $\ce{H2O}$ molecular orbital diagram is given:

The answer tells us, that molecular irreducible representation can be obtained like this:
$$(2a_1)^2(1b_2)^2(3a_1)^2(1b_1)^2 = (A_1)^2 \otimes (B_2)^2 \otimes(A_1)^2 \otimes (B_1)^2 = A_1,$$
which is in accordance with the first example in the Molpro docs, where $\ce{H2O}$ wavefunction is specified like WF,10,1;.

Questions

So, is this the correct way to find the irreducible representation of the whole molecule? And if it is, could you, please, explain, how to get the molecular orbital representation?
How can I obtain the total spin number?


texts: Will a film of oil on water retard evaporation (of water) and prevent air and atmospheric impurities from diffusing into it?

texts:
I vaguely recall hearing that a layer of oil on water will slow down the evaporation of water, as well as serving as a barrier that would prevent (or retard) the diffusion of air and atmospheric impurities into it. How accurate is this claim?

Some Background:

I want to make zinc/air batteries. $\ce{KOH}$ is commonly used in the electrolyte, but $\ce{CO2}$ in the air can react with the $\ce{KOH}$ and form carbonates which hinders the battery's performance. It seems like oil on top will shield the electrolyte from atmospheric $\ce{CO2}$. The $\ce{H2O}$ also must be kept from evaporating, which would otherwise result in changes to  concentration. $\ce{KOH}$ is also very hygroscopic and tends to attract water from air which would also cause variations in concentration.

When the batteries get discharged, $\ce{ZnO}$ is a final product. This should almost certainly precipitate and collect on the bottom of the tank since its considered insoluble in water.

Solar panels harness a vast amount of energy from the sun during the Summer. Storing surplus enrgy for use in Winter is a daunting task. A method that's been doing rounds these days: One could collect and reduce the $\ce{ZnO}$ back to $\ce{Zn}$, deposit it on plates/electrodes, and store these plates for Winter use. The plates could be put back in the batteries and the electrolyte (a fresh solution of $\ce{KOH}$) would have to be replenished.


texts: Magnesium Bicarbonate Water Reaction With MSM - Methylsulfonylmethane

texts:
The following is a recipe for a mineral water containing magnesium and bicarbonate.

Magnesium hydroxide powder is dissolved in a plain bottle of carbonated mineral water resulting in magnesium bicarbonate. This reaction causes the $\ce{CO2}$ to be consumed and the bottle caves in on itself.

But when I added the supplement MSM (methylsulfonylmethane) and the bottle is shaken, the water inside fizzes and pressure builds up again.

So my question: what causes the bottle to re-pressurize and fizz?

And is it still safe to drink, maintaining the original minerals, magnesium bicarbonate and msm?


texts: Why are free radicals are so reactive? They can break almost any bond, including $\ce{C-H}$ bonds, which are fairly stable. Don’t they have an activation energy or something? Do they not also experience steric effects when colliding with reactants ?


texts: How would I calculate the Normality of a 0.00167 molar solution of KIO₃?

texts:
I need a 0.01 N solution of $\ce{KIO3}$ to use as a standard in a Winkler titration.  The protocol that I am using specifies that this is 0.3567 g L-1, which I have calculated to be 0.00167 M based on 214 g mol-1 for $\ce{KIO3}$.

I like to understand the calculations in the protocols that I am using, so how would I calculate that a 0.00167 M solution of $\ce{KIO3}$ is 0.01 N?

EDIT (More detail on the reactions)

The $\ce{KIO3}$ solution is added to an $\ce{NaOH} \cdot \ce{NaI}$ solution under acidic conditions for:  $\ce{IO3- + 5I- + 6H+ \rightarrow 3I2 + 3H2O}$

The $\ce{I2}$ is then titrated to standardize a thiosulfate solution.


texts: What is the origin of the bactericidal properties of silver in water?

texts:
I often hear that water gets purified by being in a silver vessel, which sounds plausible because of bactericidal feature of silver. What doesn't sound plausible, though, is the way it's explained: that silver releases ions into the water. Since silver is a noble metal, why would any "reaction" at all occur with something as neutral as water?
Is the above explanation nonsense? Does the "disinfection" of water happen only on contact with the metal?


texts: Maximum observed optical rotation through a polarimeter

texts:
Is there a maximum optical rotation of plane polarized light that can be observed using a polarimeter?

I understand that in a polarimeter, light passes through a filter that converts it into plane polarized light. This type of light only oscillates in one plane. When it is passed through an optically active solution, the plane is rotated due to interactions between the molecules. To measure this rotation, we use another a filter and try to orient it so that light passing through it appears brightest. The difference in angular orientations of the two filters is read as the observed angular rotation.

Here is an image I've taken from Solomon and Fryhle's Organic Chemistry textbook:

So is there a maximum value for this rotation? Surely after a 90 degrees rotation, the angle would be the same as another angle is we'd rotated in the opposite direction. For example, I could say that a +100 degrees rotation is the same as a -10 degrees rotation.
Could the angle be greater than 90 degrees?

The question might seem simple, but it's difficult for me to take into consideration multiple rotations of the plane polarized light before it passes through the second filter. Are the multiple rotations even possible?


texts: How to convert the factors of radiative forcing of methane compared to carbon dioxide from ratio by weight to ratio by molecule?

texts:
The intergovernmental panel on climate change's fifth assessment report (IPCC AR 5) lists the radiative forcing (RF) of methane in chapter 8 as being $28\times$ and $84\times$ as potent as $\ce{CO2}$ by weight (or tonne of methane for tonne of $\ce{CO2}$) for the global warming potential integrated over $20$ and $100$ years, $\mathrm{GWP}_{20}$ and $\mathrm{GWP}_{100}$ respectively. In order to calculate the ratios of the gases RF potential molecule for molecule in the 20 and 100 year time spans, I'd need to apply the ratio of atomic weights for these molecules. But do I need to consider the average concentration in the atmosphere of $\ce{CO2}$ when multiplying the RF ratios.

Adding to the complexity of the problem might be the fact that at various levels in the atmosphere methane may have a different lifespan, concentration and RF, i.e. in the troposphere methane has a role as a precursor to tropospheric ozone, which takes the overall RF ratio of atmospheric methane to $105\times$ $\ce{CO2}$ (Shindell et al, IPCC AR5, NASA). Or can I ignore this complexity and just derive an indicative molecule for molecule ratio of RF potency for $\ce{CH4}$ to $\ce{CO2}$ by dividing each side of the equation by the molecular weight?

My attempt at answering:

Molecular weight of methane is $\pu{16.04 g/mol}$ and $\ce{CO2}$ is $\pu{44.01 g/mol}$.
Assuming it’s safe not to consider atmospheric concentrations in this,
$\pu{1 kg}$ of of methane has $44.01/16.04 = 2.744$ fewer molecules than $\ce{1 kg}$ of $\ce{CO2}$
If methane is $105\times$ as potent as $\ce{CO2}$ by weight, it is $105 \times 2.744 = 288\times$ as potent as $\ce{CO2}$ molecule for molecule


texts: Why are Salts Removed before Ion-Exchange Chromatography?

texts: In my organic chemistry laboratory, we used centrifugation and salting out to begin the process of purification of Myoglobin from hamurger meat. After that process, we used to dialysis to remove the Ammonium Sulfate from the salting out process to begin ion-exchange chromatography. I was wondering why we had to use dialysis to remove the salts, and why the ion-exchange chromatography couldn't just occur in the presence of the salts?


texts: How did early chemists determine the major product of a solution?

texts:
For example, how did they determine using evidence that when 2-chloropropane reacted with ethoxide, a strong base, formed propene as the major product and 2-ethoxypropane as the minor product?

Could someone explain how did chemists determine the major products without NMR Spectroscopy? I have no lab experience and do not have access to them either.


texts: Lithium compounds with good solubility in organic solvents?

texts:
I want to dissolve enriched $\ce{^6Li}$ into a liquid scintillator (made almost purely of di-isopropyl-naphthalene, mixed isomers, with a tiny bit of fluors and wavelength shifters) for enhanced neutron detection and background rejection. My group's previous attempts at this have been to use Lithium-6 Chloride with surfactants, but this negatively affects the attenuation length of the scintillation light passing through the scintillator (since the droplets of the microemulsion are essentially giant scattering surfaces).

Having had some O-Chem and P-Chem as an undergrad I know some organolithium compounds are soluble in organic solvents, but those are eat the container walls nasty. I know that lithium bromide has some limited solubility in organic solvents, but I need to get to at least 0.1%, preferably 0.5% atom doping/fraction, so I need something that dissolves well. I know that lithium perchlorate is soluble in many organic solvents, but the explosive nature of the mixtures it makes with those solvents kills that idea.

This leads to my question:

Are there any lithium compounds that are not caustic, nor explosive, but are soluble in greasy organic liquids (like di-isopropyl-naphthalene)?


texts: How is solid titanium(II) oxide an electrical conductor?

texts: Most salts in the solid state are electrical insulators, since the ions are not mobile (e.g. sodium chloride). However, solid titanium(II) oxide, $\ce{TiO (s)}$, is a conductor. How is this so?


texts: Why is a head on (sigma) bond between a p-orbital and a d-orbital not possible? Is it because extent of overlap becomes too little? Can you please illustrate?


texts: Is Neutron radiation considered electromagnetic wave?

texts:
I'm confused because gamma rays are classified as an electromagnetic wave. But why is neutron radiation not considered electromagnetic wave? I know Alpha and Beta, as well as positron and proton, is not considered electromagnetic wave because it can be deflected by magnetic or electric field (because they are + or -).

But a neutron is neutral, so why is it not electromagnetic wave? Can it be deflected too by electric and magnetic field? Is that why? Or is there another reason?


texts:
Here is the excerpt of my lab manual:

"Simple distillation is more useful for purifying a liquid that contains either a non-volatile impurity or small amounts of higher or lower boiling impurities. Fractional distillation allows for several condensation-condensation cycles in a single operation. It can be used to separate liquids with comparable volatilities and to purify liquids that contain relatively large amounts of volatile impurities."

So, why does simple distillation put emphasis on small amounts and fractional distillation, on large volumes?


texts: Vapour pressure in an enclosed container with liquid at normal conditions

texts:
Can vapour pressure happen in an enclosed container with liquid at normal conditions?

I guess the answer is yes, but I don't understand why some liquid on the liquid surface may process sufficient kinetic energy to escape into gas phase.


texts: Le Chatelier's principle: what are the effects of decreasing volume?

texts:
Which of the following is increased by decreasing the volume of the
  reaction system in the following reaction: $\ce{2H_2S(g) +3O_2(g)<=>
 2SO_2(g) +2H_2O(g)} + {\text{heat}}$

  I. Rate of Reaction

  II. Equilibrium concentration of reactants

  III. Value of $\ce{K_{eq}}$

My attempt: By the gas laws, decreasing the volume of the container will increase the pressure, so equilibrium should shift to the right, as there are less gases on the right. Thus III is true. Additionally, heat is also generated by the shifting of the equilibrium, and the increased pressure on the system due to the decreasing of volume would also speed up the reaction, so I is also true. II is not true because the Equilibrium concentration of the products increases, not the reactants. So my final answer is I and III. Yet the answer key says I only. Why is that?


texts: Dipole-quadrupole polarizability term for induced dipole

texts:
For describing an induced dipole, I have usually seen the following equation,
$$
P_{i} = \alpha_{ij}E_{j} + \frac{1}{2}\beta_{ijk}E_{j}E_{k}
$$
where $P_{i}$ is the $i^{\text{th}}$ component of the induced dipole moment, $\alpha$ is the (dipole) polarizability and $\beta$ is the first (dipole) hyperpolarizability.

However, I recently read a paper with quadrupole-coupled terms coming in, like the dipole-quadrupole polarizability as shown below:
$$
P_{i} = \alpha_{ij}E_{j} + \frac{1}{3}A_{ijk} \frac{dE_{j}}{dr_{k}}+ \frac{1}{2}\beta_{ijk}E_{j}E_{k}
$$
where in the second term, $A_{ijk}$ is the dipole-quadrupole polarizability term. This equation is introduced for the case of polar molecules in the condensed phase, and in the related paper it is for water.

It appears that the contribution of dipole-quadrupole polarizability is rather small, but maybe larger than the hyperpolarizability.

Could someone explain or refer some literature so as to describe

the importance of the cross-coupled terms like the dipole-quadrupole polarizability, and
if there are some cases where the cross-coupled terms (the second term in the second equation) become negligible?

Reference: Batista, E. R.; Xantheas, S. S.; Jónsson, H. Molecular multipole moments of water molecules in ice Ih. J. Chem. Phys. 1998, 109 (11), 4546-4551. DOI: 10.1063/1.477058.


texts: Reaction involved in Combustion of Nitrocellulose-Nitroglycerine(NCNG) solid propellant?

texts: I'm working on solid propellant based microthrusters and I am using NCNG as the solid propellant. I want to know the reaction taking place and the mass fraction of the products obtained on combustion of NCNG propellant.


texts: Kinetic and thermodynamic control of sulphonation of toluene

texts:
Sulfonation of toluene with conc. $\ce{H2SO4}$ at room temperature gives ortho- and para-toluenesulphonic acid (with $95 \%$ yield), whereas sulfonation of toluene with conc. $\ce{H2SO4}$ at $\pu{150-200 °C}$ gives meta-toluenesulphonic acid (with $95 \%$ yield). Why is this so?

What I thought is that at room temperature, the reaction is kinetically controlled, and the ortho-/para- directive effects of methyl group operate leading to ortho- and para-toluenesulphonic acid.

At high temperature, the reaction would be thermodynamically controlled. So the more stable product would be formed, which happens to be meta toluene sulfonic acid. Why is this more stable?

Does it have anything to do with the equilibrium of the sulfonation reaction?

Related : Thermodynamic vs Kinetic Sulphonation of Naphthalene


texts: Quantum mechanical model of atom and the quantum numbers

texts: I studied Bohr's model of atom and then the drawbacks of it and then quantum mechanical model of atom. Now quantum model is according to uncertainty principal and dual nature of matter and it says we can not talk about fixed orbits (uncertainty principle) and can only talk of  an area of maximum probability of finding an electron known as "orbital". Now when I'm studying principal quantum number, it says it is the "shell number". So how come we are talking about fixed shells again and returning to what Bohr said?


texts:
There is a specific part of the biosynthesis of terpenes that makes me confused:

According to this mechanism, the double bond of the isopentenyl pyrophosphate attacks the primary carbocation, when it would make more sense to attack the tertiary carbocation that could be formed by resonance. Am I missing something here? Clearly, this is not a concerted process if the mechanism is displayed in this way, and an intramolecular resonance conversion would be faster than a nucleophilic attack.


texts: Different possible Lewis structures of peroxymonosulfate anion

texts:
I was trying to draw the Lewis structure of $\ce{HSO5-}$ (peroxymonosulfate), so I came up the structure on the left that satisfies the octet rule. Then, I saw that the correct structure is the one on the right. Why is the structure on the right favored over the one on the left? They both have the same formal charges. So shouldn't the one that satisfies the octet rule be favored over the one with an extended octet?

$\hspace{15 mm}$


texts: Are there more positive azeotropes than negative azeotropes?

texts:
During a lecture on Flash and Distillation, my professor (which worked as a Chemical Plant Engineer for more than thirty years, specifically on separation processes) pointed out that the most frequent type of azeotropes he encountered in his work was positive-type. At first it seemed just common practice among azeotropic distillation et similia, however page 6-180 of CRC Handbook of Chemistry and Physics says:

  Nearly 90% of the binary azeotropic data show a pressure maximum (positive).

So, I'd like to know why it's true or not that nature could be somehow biased toward a specific or more frequent type of azeotrope.


texts: Does an acetal need to have one hydrogen attached to its carbon?

texts:
I was asked to identify the functional groups in this molecule above.

So far I have found an amide ($\ce{-NHAc}$), an ether ($\ce{-OBn}$), and a conjugated diene, but I was also told that there is an acetal ($\ce{RHC(OR')2}$).

However, in the only part of the molecule where I can see a carbon atom attached to two other oxygen atoms, the carbon atom is not attached to a hydrogen atom.

Where is the acetal group in this molecule?


texts: What kind of bonds can form between benzene and transition metals in π-complexes?

texts:
I'm trying to draw the six π-orbitals (3 bonding, which are filled, and 3 anti-bonding) of a benzene ring when it complexes with metal d-orbitals and which metal orbitals have the correct symmetry ($\sigma$, π, $\delta$) to overlap with each of them. I know that metal orbitals will only form a bonding interaction with ligand orbitals if they have matching symmetry but I am not sure which ones will interact.

I think a π bond is formed between $e_{1g}$ of benzene and $d_{xy}$ and $d_{yz}$. Also a $\sigma$ bond is formed between $a_{2u}$ of the benzene and $d_{z^2}$ and $a_{2u}$. No δ bond is formed.


texts: What can be a harmless electrolytic additive for water for creating an oxy-hydrogen flame?

texts: I was thinking of preparing a tiny oxy-hydrogen flame for soldering. I am going to use 6V DC and aluminum sheet as the electrode for this. Now, I have to add some electrolyte to water, that can be a salt, base or acid. But, if I add $\ce{NaCl}$ or $\ce{HCl}$, they will produce chlorine. If I add $\ce{NaOH}$, it will eat electrodes. Adding $\ce{H2SO4}$ may produce poisonous gases like $\ce{SO2}$ and $\ce{H2S}$. So, what can be a harmless/least harmful electrolyte for such purpose? Is $\ce{Na2CO3}$ a good choice?


texts: Why more attractive metals will be oxidized? Aren't they being reduced, because they attract and receive electrons from negative polyatomic ions? So they will be anodes, where oxidization occurs. Why anodes are negative in voltaic cells and positive in electrolytic cells? Same for cathodes.


texts: Formation of Lactone from 5-amino-decanoic acid?

texts: As expressed in the title, I am trying to figure out how to form a lactone from 5-amino-decanoic acid. The thing that comes to my mind as a start is the attachment of the amino group ($\ce{NH2}$) to the carboxyl carbon and then immediately break the double bond of this carbon with oxygen … But the process gets more likely to form a lactame, where my exercise is asking a Lactone. Can anyone help?


texts: Why are correlation consistent basis sets used with DFT calculations?

texts:
Reading some papers, there is a bit of a curious observation that does not exactly make a lot of sense to me.

In Quantum Chemistry, different methods exist to carry out geometry optimisation and energy calculations. Quantum chemists can have a huge field day arguing which method and basis set to use.

A common type of calculation used for larger (though large is relative to one's computational resources) is density functional theory (DFT) - because it provides good results on a reasonable time scale.

Now here is where it gets weird:
Every method has its basis set - basis sets geared towards DFT and basis sets geared towards couple cluster methods. It is generally recommended not to use a correlation consistent (cc) basis set with a DFT method (and I guess conversely, a basis set aimed at DFT should not be used with a coupled cluster method).

Why then would people benchmark methods using seemingly inappropriate basis sets. E.g. a cc basis set with an M06 functional.

(See for example: Edward G. Hohenstein, Samuel T. Chill and C. David Sherrill; J. Chem. Theory Comput. 2008, 4 (12), 1996–2000)


texts:
I was hopping around random wikipedia articles when I came across the article for the Behemoth. In the description for the beast it says:

  His bones are as strong pieces of brass; his bones are like bars of
  iron

So it got me thinking, which of these three substances is hardest: iron, brass or bone?

(I had a quick look at the Mohs scale, which lists iron as 4, but could not find anything for brass or bone.)


texts: What is the directive influence of the tert-butyl group in electrophilic aromatic substitution?

texts:
We know that hydrocarbon side-chains on a benzene ring influence electrophilic substitutions by directing the incoming electrophile to attack at ortho and para positions. The following hyperconjugations are shown to explain directive effect of toluene:

However, the situation was different when I tried to analyse for tert-butylbenzene. Tert-butylbenzene has no $\alpha$-hydrogens so the above mechanism cannot be extended to this case. Does the following mechanism work?

Does tert-butylbenzene have any directive influence at all? If we consider only inductive effects, then the incoming electrophile may attack at the meta or para positions (ortho being crowded).


texts: Mechanism for reaction between carboxylic acid and manganese(II) oxide

texts: I am reading about redox reactions of carboxylic acids with $\ce{MnO}$ but I couldn't find any mechanism online,so can any one provide the mechanism.


texts: Why isn't sodium hydrogen phthalate used instead of KHP?

texts: Why is potassium hydrogen phthalate (KHP) ubiquitously synthesized and used as a primary standard, while sodium hydrogen phthalate isn't even available to buy?


texts:
The picture (a) is from a organic chemistry book by Clayden, Chapter 32. That means drawing (a) is right expression of the molecule.

What I wonder is that is it possible for (a) to ring-flip? If so, is (b) correct as a ring flip version of (a)? If it's not possible to ring flip, why?

Second question: Is drawing (c) also valid to draw this molecule? If it's so, is it same with (a)? or is it ring flip of (a)? If it's not, what's wrong with it?

Personally, I thought (c) was the right drawing for the molecule. Below (c), I drew the conformation of cyclohexene. The first conformation has a pseudoaxial hydrogen and the inner side of carbon faces downward. This is why I drew (c) with methyl at pseudoaxial, and inner carbon facing downward. But the book only has a drawing of (a).


texts: How do sodium-potassium pumps differentiate between sodium and potassium?

texts:
I don't know if this should be Biology, but it seems pretty Chem to me.

Does the protein of the sodium-potassium pump tell the difference between sodium and potassium cations based on size, electron affinity, mass...?


texts:
How is the following true?

$$\left ( \frac{∂S}{∂P} \right )_{T}=\frac{-C_{P}}{T}\left ( \frac{∂T}{∂P} \right )_{S}$$

I know that

$$C_{P}=T\left ( \frac{∂S}{∂T} \right )_{P}$$

which means the right-hand side of the first equation becomes

$$-\left ( \frac{∂S}{∂T} \right )_{P}\left ( \frac{∂T}{∂P} \right )_{S}$$

but how is that equal to $\left ( \frac{∂S}{∂P} \right )_{T}$ ?


texts: What indicators can be used when substituting iodine with other halogens in the Winkler method?

texts:
I'm a chemistry student who is doing an investigation with respect to the Winkler method. The Winkler method is one which is used to find the oxygen content in water. Primarily, the halide which is used is iodine. However, I want to make use of other halogens such as fluorine, chlorine and bromine, together with their respective halides. However, I am stuck on how I will actually do the titration, since the indicator used for the case of iodine is a starch indicator. I don't exactly know which indicator I should use for the other halides.

My question is this: What indicators should I use in the titrations involving the other halides?


texts: In TOF Mass Spectrometry how does the detector 'know' the difference between ions of different elements?

texts:
After the positive ions have been accelerated, I know that they travel through the drift zone at different speeds due to their masses.

But surely, a heavier ion/element that enters the drift zone first may still reach the detector before a lighter ion if that lighter ion is one of the last ions to enter the drift zone. If so, when these ions reach the detector, how does it know that the heavier ion IS heavier than the lighter ion that does not reach the detector until afterwards.

*I'm aware my question is a tad confusing, let me know if I should try and reword it!


texts: What guarantees that there is a thermodynamic equilibrium in a closed chemical reaction network independently of the mass-action kinetics?

texts: I would like to know according to which we can state that there is a unique equilibrium of a closed chemical reaction network (at constant circumstances) without supposing mass-action kinetics if time is increasing beyond all limits. Can we derive it from a non-equilibrium thermodynamic law or is it a postulate? Thank you for your answer!


texts: Half cell reactions for oxidation of water by acidified solution of potassium dichromate

texts:
From Chemguide:

I don't understand the first equation. The chromium atoms in the dichromate ion receive 6 electrons, and their oxidation state declines from 6+ to 3+. But where do the 14 hydrogen cations get their 14 electrons in order to form water with the seven oxygens?


texts: Gibbs free energy can be expressed as a function of P,T and n but are enthalpy and internal energy also (partially) functions of n?

texts:
$$G=G(P,T,n)$$
$$\mathrm dG=V\,\mathrm dP-S\,\mathrm dT+\mu\,\mathrm  dn=\left(\frac{\partial G}{\partial P}\right)_{T,n}\,\mathrm dP+\left(\frac{\partial G}{\partial T}\right)_{P,n}\,\mathrm dT+\left(\frac{\partial G}{\partial n}\right)_{T,P}\,\mathrm dn$$

This allows open systems to be considered (where $\mathrm dn$ does not equal zero). However, can enthalpy, internal energy and Helmholtz free energy also be treated in this way to allow for open systems?


texts: Mechanism of toluene oxidation with CrO3

texts:
What is the mechanism for the following oxidation of toluene with $\ce{CrO3}$ in acetic anhydride?

  Use of chromic oxide ($\ce{CrO3}$): Toluene or substituted toluene is converted to benzylidene diacetate on treating with chromic oxide in acetic anhydride. The benzylidene diacetate can be hydrloyzed to corresponding benzaldehyde with aqueuous acid.


texts: Is NaCl in water considered "solution" despite of NaCl's having some precipitation?

texts:
Is $\ce{NaCl}$ in water aqueous? For a certain amount of $\ce{NaCl}$, it can dissolve in water but if you add more $\ce{NaCl}$ it can't dissolve any more.

So, if in a certain reaction $\ce{NaCl}$ is formed with water:

$$\ce{HCl(aq) + NaOH(aq) -> H2O(l) + NaCl(aq)}$$

My question is does $\ce{NaCl}$ in the previous reaction totally dissolve in the water formed? Or in other words is this equation correct?

$$\ce{HCl(aq) + NaOH(aq) -> H2O(l) + NaCl(aq) + NaCl(s)}$$

Another question is why do we write (l) beside water rather than (aq) since it's part of the aqueous solution?


texts: What is the energy minimum of cyclopentane conformational diagram: the halfchair or envelope? How does cyclopentane flip?


texts:
Question:

Decreasing the product's concentration seemed to follow the logic of Le Chatelier's principle, so a decrease in volume will force the reaction to the left to increase the pressure (increasing the number of molecules). However, decreasing nitrogen gas concentration also has the same effect. I chose volume compression over the other because I assumed. I am probably stretching what it means by "sealed"  though. Apparently I got the question incorrect.


texts: Are there any gases that can not be turned into liquid, or liquids that can not be frozen solid?

texts: My son points out that some solids can not be melted (because they combust, for example). He wonders if there are any liquids that can not be frozen, or gases that can not be liquified.


texts: Shouldn't mineral NPK fertilizer ingredients add up to 100%?

texts:
I use a mineral based  fertilizer in powder form which - according to the label - should not contain any fiber and is fully soluble in water (I dissolved 2 times the recommended dosage and found no solids remaining in the solution):

The NPK + Mg + trace elements add up to about 60%.

What constitutes the rest?


texts:
The local hardware stores actually sell chemicals in recycled beer bottles with plastic stoppers as lids. The bottle of hydrochloric acid I bought is clearly losing gas to diffusion through the plastic, or a seal that's not tight enough--it smells bad, and the beer bottle's metallic label is slowly corroding.

How can I best seal this bottle? Some ideas are:

Try to mold a stopper from silicone. Use a (synthetic) cork, whatever's used for homebrewing. Line the stopper with a few layers of thin polyethylene or polypropylene (from consumer materials, such as air-filled plastic bags for packing).

Or could I limit the diffusion by putting a plastic bag around it? This is tough to answer experimentally (without a lab) because resisting physical degradation isn't the same as resisting diffusion.


texts: PF3 as a source of fluoride for substitution in alcohols

texts:
It is known that $\ce{PX3 (X= Cl, Br, I)}$ and $\ce{PX5 (X= Cl, Br)}$ are used to make halogen derivatives of hydrocarbons from alcohols. My question is why there's no information about using $\ce{PF3}$? At least I couldn't find any, so I assume $\ce{PF3}$ is not used for that.

A wild guess that phosphorus holds fluorine atoms tight, and no "free" fluorides are present for the last steps of the reaction to complete.


texts: How many peaks would there be in H1 NMR of ethene?

texts: Since the bonds can't rotate, would there be 2 peaks? Likewise, how many peaks would there be in trans-but-2-ene and cis-but-2-ene?


texts: Chlorofluorocarbons are heavier than atmospheric gases. Then how are chlorofluorocarbons produced at the surface able to reach the ozone with such a heavy mass ?


texts: Why can't iodide be oxidised to iodate in acidic medium?

texts:
Even if we use a strong oxidising agent like 'permanganate ion in acidic medium' it doesn't help oxidise iodide to iodate, but a relatively weaker oxidising agent 'permanganate ion in alkaline medium' helps to form iodate from iodide.
I have found one discussion similar to this but it's not convincing.
Even in alkaline medium the potential is negative although significantly lesser than in acidic medium.
Then how does the reaction even proceed in alkaline but not in acidic?


texts: Effect of pressure on the freezing temperature of water

texts:
A few lines are written in a book by B.H. Mahan regarding the change in freezing point of water on changing the pressure.

  The vapor pressure of water at triple point of water is 4.579 mm. What would happen if the external pressure applied to the system by the piston were to be increased above 4.579 mm ? First of all the va pour present would be completely converted into liquid and solid, to restore the equilibrium pressure.

I'm in total agreement of this. But the next lines appear to be odd.

  It is found experimentally that as the pressure on the system is further increased the temperature of the system must be decreased, in order for both  ice and water to remain in equilibrium.

I don't understand  the second statement. If the equilibrium is further disturbed why the system should not  behave the same as before? Why do we have to change the equilibrium constant  to restore the equilibrium?
Thanks in advance.


texts: Why does mutarotation occur only in specific media?

texts:
I was reading a book on biomolecules, and read that muta-rotation in hexoses, can happen only in media like water, which can act as an acid and as a base. Why is this so?

Essentially, it is just the formation of the open chain form, and then back to the other cyclic anomer, right? What role does the medium have in this process?


texts: Deriving the equations for two-electron integrals in Hartree-Fock theory

texts:
In Szabo and Ostlund's Modern Quantum Chemistry, the matrix elements for the hamiltonian of a two-electron system, with an operator $\hat O$, are written on pages 64-66 as

$$\langle \Psi_0 | \hat O | \Psi_0 \rangle=\int dx_1 dx_2 [2^{-\frac{1}{2}} (\chi_1(x_1)\chi_2(x_2)-\chi_2(x_1)\chi_1(x_2))]^* \cdot \hat O [2^{-\frac{1}{2}} (\chi_1(x_1)\chi_2(x_2)-\chi_2(x_1)\chi_1(x_2))]$$

for a spin orbital $\chi$ of electron x defined as the product of a spacial orbital $\psi(r)$ and spin $\alpha(\omega)$ or $\beta(\omega)$, e.g., $\chi(x)=\psi(r)\alpha(\omega)$.

This is multiplied out into

$$\langle \Psi_0 | \hat O | \Psi_0 \rangle=\frac{1}{2} \int dx_1 dx_2 \{\chi_1^*(x_1)\chi_2^*(x_2)\hat O \chi_1(x_1)\chi_2(x_2)+\chi_2^*(x_1)\chi_1^*(x_2)\hat O \chi_2(x_1)\chi_1(x_2)-\chi_1^*(x_1)\chi_2^*(x_2)\hat O \chi_1(x_1)\chi_2(x_2)-\chi_2^*(x_1)\chi_1^*(x_2)\hat O \chi_2(x_1)\chi_1(x_2)\}$$

This expanded equation is what I will base my question on.

For the core-hamiltonian (one-electron integrals),

$$\hat O=h(r_1)+h(r_2)$$

and for the electron repulsion (two-electron integrals),

$$\hat O=\frac{1}{r_{12}}$$

For the core hamiltonian, you can integrate out the electron which is not being acted upon by the operator to reduce the expanded equation to a one-electron integral.

For the electron repulsion, on page 66 the two-electron integral is simplified by stating the first two terms of the expanded equation are equal. This means:

$$\int \chi_1^*(x_1)\chi_2^*(x_2)\frac{1}{r_{12}} \chi_1(x_1)\chi_2(x_2)= \int \chi_2^*(x_1)\chi_1^*(x_2)\frac{1}{r_{12}} \chi_2(x_1)\chi_1(x_2)$$

This is what I do not follow. How is this derived? I can permute the electrons to achieve the same form, but that would introduce a negative sign.

Furthermore, for the equality to be true, does it not imply one of two scenarios: that either the spatial functions are degenerate, i.e.,

$$\chi_1^*(x_1)=\chi_2^*(x_1)$$
$$\chi_2^*(x_2)=\chi_1^*(x_2)$$
$$\chi_1(x_1)=\chi_2(x_1)$$
$$\chi_2(x_2)=\chi_1(x_2)$$

or otherwise that the electrons have the same spin and coordinate such that $x_1=x_2$

$$\chi_1^*(x_1)=\chi_1^*(x_2)$$
$$\chi_2^*(x_1)=\chi_2^*(x_2)$$
$$\chi_1(x_1)=\chi_1(x_2)$$
$$\chi_2(x_1)=\chi_2(x_2)$$

neither of which would make sense.


texts: Is it possible to compress an atom to infinite density?

texts:
I know, by nature, normally atoms are stable. But I wonder, if it is possible to compress an atom, say the Hydrogen atom, to infinite density by applying external force? After all, electrons and protons would attract each other by electrostatic forces and nuclear forces are also there at least up-to a certain distance...

Has it been done?

The reason I thought of it, was because I was trying to find the ratio of the amount vacuum to the amount of matter in the whole universe...


texts: Nature of a1g Molecular Orbital Interactions in Ferrocene

texts:
While learning about ferrocene I've come across this molecular orbital diagram.

What particularly confused me is the nature of the a'1g orbital. My professor taught that a'1g and e2g are considered HOMO bonding orbitals, but this MO diagram clearly shows the a'1g as an MO with antibonding character.
To make sure it wasn't just a bad MO diagram, I looked for other MO diagrams, but they consistently display a'1g as a higher energy orbital compared to Iron's $3dz^2$ orbital.[a][b] So, slight anti-bonding character, right?
The problem is, looking at bond-length comparison, the a'1g orbital is slightly bonding. The Fe-Cp distance for ferrocene is 1.66 Å; for ferrocenium, it's 1.68 Å.[c] Given that the removal of an electron from the HOMO a'1g orbital resulted in the lengthening of Fe-Cp distance, it should have bonding character.
So what is going on here? Why is there this discrepancy? How are these orbitals actually interacting with each other?
[a]http://alpha.chem.umb.edu/chemistry/ch612/documents/ConstructingpiMOdiagramssandwichcomplexes.pdf
[b]https://doi.org/10.1021/ja00744a011
[c]https://doi.org/10.1107/S0108270189005883


texts: Which bands are considered significant in the fingerprint region of IR spectra?

texts: I'm currently writing my characterisations for the experimental section of my dissertation and can't decide which peaks from the fingerprint region of my IR are worth reporting. Is there a threshold of %Trasmittance, anything below which is considered not to be significant? For example, I know that a strong band covers most of the y axis, a medium about a half and a weak about a third. Therefore, is it worth reporting very weak bands with only 10-15 %Transmission?


texts: How to properly dispose of sodium...or store it properly

texts:
While performing an inventory of my school's chemical storage closet today, my fellow teacher and I found some sodium tucked away in the back corner of our flammables cabinet.  One container appears to have leaked the oil the sodium was being stored in, and we aren't sure about the second container.  We don't know how long it's been there, but neither of us is going to use it, and, honestly, we don't want it.  How do we dispose of this?  Can someone with a little more chemistry know-how point me in the right direction?  Are we stuck with this?

Or...

In the event that the administration won't let us dispose of the sodium, can you tell me how to remedy the storage situation?  We don't feel that there is an adequate amount of oil in the container for proper storage of the remaining sodium, and if we have to keep it I want to make sure it is being stored correctly.


texts: I have a project to prove that the colour black absorbs more light than the colour white in a creative way. Our first idea was to time a white frying pan and black pan and see which would melt the ice cube first, but is this proving radiation? Because I looked at saw pieces of metal above where the flame would go, making me guess pans use conduction. Will a flame ever give off enough radiation to be noticeable?


texts: How can I deduce the structure of my compound from this NMR spectra?

texts:
I have no idea how to determine the substituents on the aromatic ring from this NMR spectrum. There is (or might be) a triplet on my NMR around $\pu{7.59 - 7.65 ppm}$ which has 4 hydrogens in the same environment. If so, there must be two ortho substituents on two aromatic rings but I think the 4 Hs won’t be in the same environment.
I assume the substance to be the one I added here:


texts: What would one have to do differently if they used NaMnO4 instead of KMnO4 for redox titrations?

texts:
I am doing a chemistry report related to redox titrations (using $\ce{KMnO4}$ as the titrant), and one section of the report asks me to explain what would occur if I were to use sodium permanganate ($\ce{NaMnO4}$) instead of potassium permanganate ($\ce{KMnO4}$), and more importantly, what I would have to do differently in my experiment if I were to use this new chemical.

What I know as of now.

Sodium permanganate is not widely used because it is more expensive and is much more difficult to create than potassium permanganate.
Molar mass is different when performing stoichiometric equations, which leads to different results when calculating certain values.

I looked online and found that the chemical is "hygroscopic;" however, I don't know if this changes anything in the experiment.

Is there anything else I can "change" in my experiment if I were to use $\ce{NaMnO4}$ instead of $\ce{KMnO4}$?


texts: Deliquescence/efflorescence: How can I convert between salt concentration and RH?

texts:
I am looking at two phase diagrams, one has axes of $T$ and $\%\ce{MgClO4}$ in a $\ce{H2O-MgClO4}$ mix, and the other has axes of $T$ and relative humidity. The authors of the second phase diagram say "The stability diagram is modiﬁed from [the earlier phase diagram] by converting salt concentration to relative humidity using the Pitzer model and parameters." How does changing the salt concentration affect the relative humidity, and how can I reproduce this calculation?

(I am a geologist with minimal chemistry background).

Top figure from Chevrier et al., GRL, 2009; bottom figure from Gough et al., EPSL, 2011.


texts: Bio dishwashing liquid affecting kitchen pipes?

texts:
I have a query regarding bio washing-up liquid.

We've recently experienced slow flow in our kitchen drain pipes, and the plumber whom we asked to have a look at them showed us there was some non-descriptive gunk build-up in the pipes.

We rarely cook with fat (we're vegetarians, and maybe fry a dozen times a year). Plus, we always wipe our pans, pots, and dishes with kitchen paper before doing the dishes in the sink.

We've used bio washing-up liquid for a long time now. The plumber told us that bio washing-up liquids can cause build-up problems in the pipes.

That sounded weird, so we had a quick search on Google, which revealed no information on such issues with bio washing-up liquids.

Would someone be so kind as to let us know whether this is a known issue with bio washing-up liquids?


texts: How does one understand the product of a Diels Alder reaction?

texts: am having trouble making sense of products of diels alder reaction. Like I understand the stereochemistry and everything but what I am confused about is how come textbooks don’t give a variety of products that is possible in a diels alder reaction. Like, I know that pericyclic reaction is all about the symmetry of lobes of dienphile and diene. That is exactly how the difference between antafacial and superfacial come in, in that in antarafacial since the lobes are not in symmetry, you have to twist the molecule to get symmetry. So in the same sense, I have realized that when u do diels alder reaction depending on the way you organize the lobes of the diene and dienophile you can get so many possible products. However textbooks don’t really mention this phenomenon at all. I have shown what I mean by different lobe symmetry in the picture below. Can anyone tell me what is going on or am I overthinking this or what?


texts:
If both nitric acid and nitrate ion are stabilised through resonance, what makes the nitrate ion more stable in aqueous medium?

Can the same argument be applied to nitrous acid and nitrite ion in aqueous medium?


texts: Thermodynamics: Combining the 1st and 2nd Law

texts:
I'm confused how combining the first and second laws can derive

$$dS = \left(\frac{C_p}{T}\right)dT+ \left[ \left( \frac{1}{T} \right) \left\{ \left( \frac{\partial H}{\partial P} \right)_T -V \right\} \right] dP$$

The 1st Law states $dU = dq + dw$, and the 2nd Law states $dS = \frac{dq_{rev}} {T}$

I factored out $\frac{1}{T}$ in the given equation to make

$$dS = \frac{1}{T} \left[ \left( C_p\, dT \right) + { \left( \frac{\partial H}{\partial P} \right)_TdP - V  dP } \right]$$

$C_p = \frac{dq}{dT}$

Therefore,
$$dS = \frac{1}{T} \left[  dq + { \left( \frac{\partial H}{\partial P} \right)_TdP - V  dP } \right] $$

Without analyzing $\left\{ \left( \frac{\partial H}{\partial P} \right)_T - V  dP \right\}$, I already have $dS = \frac{dq}{T}$.

Can anyone explain this for me?

Thanks,


texts: To extend the life of a cartridge razor blade, should the blade be stored in oil or alcohol?

texts:
I've read varied recommendations about extending the life of a razor blade. Some say should stick the blade in oil when not in use, others say in alcohol, others say in a bowl of rice or silica gel.

I thought this community would be able to settle this:

What is the best (scientifically proven) manner to prevent corrosion of a cartridge razor blade?

I believe my Gillette Mach3 razor blades are stainless steel.

[The reason for this question is that cartridge blades are not cheap. Some may suggest going to a DE safety razor. I have tried it. It took me 2x as long to shave, so I returned to the cartridges.]


texts: I understand the concept of incomplete combustion and that it occurs when oxygen is not a large enough supply to allow for complete combustion. My question is: how can we model combustion properly in terms of predicting the ratio of complete to incomplete combustion? Is it possible to use basic kinetic with reaction rate constants to model the rate of each reaction and then obviously model how the changing concentration from both affects each individual rate etc.


texts:
The saponification value of a fat was determined by adding $\pu{9.0 g}$ of the fat to flask containing $\pu{50.0 cm3}$ of $\pu{1.00 M}$ ethanolic potassium hydroxide. The remaining solution was titrated with $\pu{0.50 M}$ hydrochloric acid.
  Calculate the saponification value of the fat, if $\pu{15.0 cm3}$ of the $\pu{0.50 M}$ hydrochloric acid were required.

My teacher has left notes to take $\pu{15 cm3}$ of $\pu{0.5 M}$ $\ce{HCl}$ as $\pu{7.5 cm3}$ of $\pu{1 M}$ $\ce{HCl}$, which I understand. What I don't understand is why the following line is followed by $\pu{42.5 cm3}$ of $\pu{1 M}$ $\ce{HCl}$ have reacted. How do you go from $7.5$ to $42.5$?

I've calculated that the saponificaiton value is $\pu{264 mg}$ using $\pu{0.0425 mol}$.


texts: Bond length comparison in substituted phosphorus pentahalide

texts:
What would be the comparison between $\ce{P-F}$ and $\ce{P-Cl}$ bond length in  phosphorus tetrafluoride chloride $\ce{PF4Cl}$ and phosphorus trifluoride dichloride $\ce{PF3Cl2}$ in the equitorial hybrid orbital arrangements?

While determining the bond length between the two compounds I am using Bent's rule, since in the case of $\ce{PF4Cl}$ there are two $\ce{F}$ atoms in equatorial region and thus they decrease their %s character in turn resulting in a larger bond length and since there are two $\ce{F}$ atoms here the %s would be relatively less as compared to the $\ce{P-F}$ bond in $\ce{PF3Cl2}$, so this decrease in %s character in flourine atom should result in increase of %s character in $\ce{P-Cl}$ bond and reducing the bond length and $\ce{P-F}$ bond length would be greater in $\ce{PF4Cl}$.

  8. Bond lengths (pm) in substituted phosphorous pentahalides are given below:

  $$
\begin{array}{lcc}
  & \ce{PF4Cl} & \ce{PF3Cl2} \\
\ce{P-F_{eq}} & x & y \\
\ce{P-Cl_{eq}} & a & b
\end{array}
$$

  $$\text{(I)}~x > y \qquad \text{(II)}~y > x \qquad \text{(III)}~a > b \qquad \text{(IV)}~b > a$$

  Choose correct code:

  (a) Only I
  (b) II and IV
  (c) I and III
  (d) Only IV

So if I'm assuming things right  my answer about the $\ce{P-F}$ bond length is right, but here in the option for $\ce{P-Cl}$ bond length is that it's greater in $\ce{PF4Cl}$. Why? Can someone please explain?


texts: How can I interpret this solubility data?

texts:
I'm currently trying to make incense paper.  I've been instructed to mix ethanol 90% with potassium nitrate ($\ce{KNO3}$).  As ethanol 90% is hard to get where I'm located I'm currently using methylated spirits (95% alcohol) as an alternative.  The $\ce{KNO3}$ however is insoluble with the this.  If I dissolve the $\ce{KNO3}$ in water first then add to the methylated spirits the solubility improves but it is still very cloudy.
I went onto http://periodic-table-of-elements.org/SOLUBILITY to see if there were any suggestions.  The page had the below results for $\ce{KNO3}$ solubility with ethanol:

ethanol [$\ce{C2H5OH}$]: insoluble
ethanol [$\ce{C2H5OH}$] 50%: 3,7 (20°)
ethanol [$\ce{C2H5OH}$] 90%: 0,3 (20°)

I'm not sure what the 3,7 and 0,3 indicate though?  I'm not even sure what they refer to perhaps soluble parts per 1000 ?  If any one could help with what it means that would be great.  As you can guess I barely qualify as a hobbyist chemist.


texts: According to this table, more heat is released in breaking a single double bond in 1,3-butadiene than in trans-2-butene. Does this mean that the resonance of 1,3 butadiene leads to a destabilization of the compound?


texts:
I want to ask a question about polar/non-polar (a)protic solvents.

The following information was given to me in the lecture hall today regarding solvents in organic chemistry.

I recall the structure of Acetic Acid as $\ce{CH3COOH}$ but surely given the $\ce{O-H}$ dipole, wouldn't that make Acetic acid a Polar Protic solvent i.e. the $\ce{H}$ attached to the $\ce{O-H}$ can be involved in hydrogen bonding?

Am I incorrect in this instance? Shouldn't $\ce{CH3COOH}$ be classified as a polar protic solvent?


texts: jury-rigging an automotive catalytic converter for use in the Ostwald Process?

texts:
Would it be feasible to jury-rig an automotive catalytic converter for use in the Ostwald Process for the production of Nitric Acid? Given reasonable safety precautions, would it be safe enough to be practical for a home lab?

A Catalytic converter is a device used in cars to reduce Nitric oxide into nitrogen and Oxygen, as well as oxidizing Carbon monoxide and unburnt hydrocarbons into Co2 and H20.

What I'm proposing is feeding ammonia and oxygen into it at an appropriate temperature and pressure to produce the Nitric Oxide necessary to create Further oxidize into Nitrogen Dioxide, which is reacted with water to produce Nitric acid and Nitric Oxide.

4 NH3 (g) + 5 O2 (g) → 4 NO (g) + 6 H2O (g) (ΔH = −905.2 kJ)
2 NO (g) + O2 (g) → 2 NO2 (g) (ΔH = −114 kJ/mol)
3 NO2 (g) + H2O (l) → 2 HNO3 (aq) + NO (g) (ΔH = −117 kJ/mol)

So my Question is whether a Catalytic Converter salvaged from an automobile is a suitable substitute for a column packed with Platinum gauze.


texts: Why does the AraC arabinose sensing system only respond to the presence of L-arabinose?

texts:
I understand that when arabinose is present it interacts with araC and changes it shape, promoting the binding of RNA polymerase with the promoter and GFP is produced. However, I don't understand why the sensing system in E.coli only responds to L-arabinose and no other pentose sugar nor their D-isomer.

I would truly appreciate it if someone could explain why this is.


texts: Why is a triangular cavity created during wire-cutting of an organic gel?

texts: I conduct wire-cutting on a gel made with organic oil. When I use high cutting rates, the wire cuts the gel in half leaving two smooth cutting surfaces. In contrast, when I use a very low cutting rate, the oil inside the gel starts coming out and a cavity is also formed around the wire (as if, instead of cutting the fibers, the wire compresses the gel network and pushes the oil out). I'm wondering why the cavity is triangular.


texts: Why does sugar water diffuse better than water through a gummy bear?

texts:
Our science class did a lab about osmosis, where we left a gummy bear in solutions of salt and sugar, as well as tap water. When we came back, we were all surprised to see that our gummy bears in sugar water were nearly twice the size of any of the others.

This couldn’t possibly be some sort of anomaly since it happened with every group.

Our class has been searching online for reports that reproduce this result. We haven’t found one. My question is, why does this happen?


texts:
I'm not a chemist, nor an organic chemistry student, but I do a lot of research. I have a question about the end of this synthesis.

  Dissolve 5g pure phenylnitropropene in 50ml Ethanol and add to Ni solution.2 Now slowly add 3ml conc. HCl3 and 1 gram shredded aluminum w/ manual stirring. Aluminum will slowly dissolve with a more vigorous effervescence of hydrogen than the first step. Maintaining good stirring with a glass stirring rod is essential in beginning. Attempted magnetic stirring will result in frustration because nickel is ferromagnetic and will stick to stirbar preventing surface area exposure necessary for reduction. After aluminum is dissolved add three more milliliters HCl and one more gram Al. Repeat adding acid and Al until 10 grams Al and about 30ml HCl has been added. Aluminum reacts slowly. Expect addition to take about six hours, longer if temp falls below 50°C. Constant stirring towards end is not necessary, just give mix a good stir occasionally.

My understanding is that the aluminum is being added to hydrochloric acid in order to create hydrogen gas, which will adsorb to the U-Ni-A catalyst. This then allows for the hydrogenation of that double bond in P2NP, AND the reduction of the nitro group to an amine group simultaneously? Or does the aluminum serve some other purpose than to just create hydrogen gas? Or is that not what's happening at all?

If I'm completely off I'd love a step by step of what's going on here, or some key words/processes for me to look up.


texts: What would be different about a heavy-water ocean world?

texts:
The water on Earth is primarily made of $\ce{H2O}$. I'm wondering about the conditions in a hypothetical $\ce{D2O}$ ocean world.

Would it be stable over geologic timescales (~$\pu{0.1–2 Ga}$)? What would be expected to be different, if anything? Would it affect the chemistry of its atmosphere, or appreciably change the incident radiation from its host star?


texts: Is there any way that i can detect lead in gasoline, not by sending of to a lab but to be able to do this by myself?


texts: Detection of sulphide in solution also containing sulphate

texts:
Question:

The reagent(s) that can selectively precipitate $\ce{S^2-}$ from a mixture of $\ce{S^2-}$ and $\ce{SO4^2-}$ in aqueous solution is(are):

(A) $\ce{CuCl2}$
(B) $\ce{BaCl2}$
(C) $\ce{Pb(OOCCH3)2}$
(D) $\ce{Na2[Fe(CN)5NO]}$

Answer:

 (A) or (A) and (C)

Why (C) is considered as correct option even though lead sulphide forms black precipitate and lead sulphate forms white precipitate?
Question source: JEE Advance 2016


texts: In the concluding part of my previous question, wouldn't there be an explosion near the hole in the tube from where the excess hydrogen is coming out instead of a steadily burning flame?


texts: Why does a mixture of nitrous acid with concentrated nitric acid cause nitration of benzene instead of nitrosation?

texts:
A question came up in our worksheet to predict the reaction product of nitrous acid and concentrated nitric acid with benzene.

I quickly recognized it to be similar to the nitration reaction. Following this ChemGuide page, which gives the reaction of sulphonation as:

  $$\ce{HNO3 + 2H2SO4 -> NO2+ + 2HSO4- + H3O+}$$

I wrote this reaction:

$$\ce{HNO2 + 2HNO3 -> NO+ + 2NO3- + H3O+}\label{a}\tag{1}$$

and thought that this electrophilic $\ce{NO+}$ would then perform EAS on the benzene to give nitrosobenzene (aka nitrosation reaction).

However, the answer given in my worksheet is nitrobenzene instead. I am unsure if the following reaction (for the generation of the electrophile $\ce{NO2+}$):

$$\ce{HNO3 + 2HNO2 -> NO2+ + NO2- + H3O+}\label{b}\tag{2}$$

is even valid. To me, reaction $\ref{a}$ seems more favorable because it involves the formation of the more stable $\ce{NO3-}$. Then why is reaction $\ref{b}$ favored instead? Why is nitrobenzene the product of this reaction, and not nitrosobenzene?


texts: Why are triflates so widely used in coupling reactions, but not tosylates, mesylates nor nosylates?


texts: How do the pKa and pH indicate to the proper environment of protonation?

texts:
I have been reading an abstract of a paper for a couple of minutes (reference below) but I cannot understand a piece of it. The abstract:

  The ionization state and $\mathrm pK_\mathrm a$ of the inhibitor 6,8-dimethyl-N5-deazapterin bound to the recombinant human dihydrofolate reductase (rhH2folate reductase) complex with NADPH was determined by a spectrofluorimetric method. The excitation spectra for bound ligand as a function of pH from 6.1 to 9.7 indicated it was the same cationic form as for unbound ligand, which is protonated on N3. However, the lower limit for the $\mathrm pK_\mathrm a$ of the bound form was determined to be 9.1, a value about pH 2.5 higher than that for free ligand, indicating that ligand bound to the enzyme is protonated at neutral pH. The excitation spectra for bound ligand as a function of pH were generated by computer simulation by employing corrections for the pH dependence of the proportion of bound ligand (variable $K_\mathrm d$; ligand-dissociation constant) and taking account of the different $\mathrm pK_\mathrm a$ values for bound and unbound forms. A plot of $K_\mathrm d$ values against pH showed a bell-shaped curve indicating that 6,8-dimethyl-N5-deazapterin bound to rhH2folate reductase. NADPH to form a ternary complex of ionised enzyme with protonated ligand and/or protonated enzyme with unprotonated ligand; the spectrofluorimetric results are consistent with the first alternative.

I made the not-understandable part (for me) in bold. Could some one help me to understand how do the previous sentences help to indicate to this sentence? Maybe I am missing something in the previous sentences.

Jeong, S.-S.; Gready, J. E. Ionization state and pka of pterin-analogue ligands bound to dihydrofolate reductase. Eur. J. Biochem. 1994, 221 (3), 1055–1062. DOI: 10.1111/j.1432-1033.1994.tb18824.x.


texts: What software do professional chemists use?

texts:
What software is used to create skeletal formula diagrams, create 3D models and whatnot? For example, on Wikipedia pages for molecules, you see standard 3D models and skeletal models which I assume are made with certain chemistry programs rather than some widespread ones.

Also, what programs are used to write chemistry papers? I know languages like LaTeX are used for mathematics and I can see you could definitely write a chemistry paper using such a program; I am curious to what actual chemists use.


texts: Stability of carbocation directly attached to a halogen atom

texts:
I have two compounds..

How is the first one more stable?
As I have been taught that -I effect of Chlorine dominates its +R effect but to explain this case, My teacher is saying that because of the achievement of the complete octet, chlorine donates its electrons to the carbocation(showing +R effect). If that's the case then the nucleophilic addition of alkanoyl chloride should be the slowest but experimentally proven, they show the fastest nucleophilic addition reaction by increasing the electrophilicity of the carbon atom(showing -I effect). Moreover, on treatment of alkynes with HCl, we get gem dihalides(which also shows the +R effect of chlorine).

Please help me with this because I am really confused between the -I and the +R effect of halogens.


texts: Why does HF generate a carbocation with an alkene

texts:
I was reading of different ways to perform Friedel Craft alkylations.
One of the methods I came across involved an alkene in the presence of H+ or a mineral acid like $\ce{HF}$. Here $\ce{H+}$ or $\ce{HF}$ caused an electromeric shift of the pi electrons and the $\ce{H+}$ bonded there resulting in a carbocation.
However I felt like the bond strength of $\ce{HF}$ is so high that it couldn't be possible to cleave it for the donation of $\ce{H+}$ (If that's what happens. Correct me if I'm wrong).
Why does it still generate a carbocation?


texts:
The mechanism of this polymerization reaction which finds its utility in the preparation of benzene in a red hot iron tube piques my curiosity.

I've read this Wikipedia article on cyclotrimerization, but it's too high a level for a high-schooler to comprehend. Can you please explain this to me in simpler way?


texts:
The Orbital Angular momentum of an electron in an atom is given by $\hbar \sqrt{l(l+1)}$ and the Spin Angular Momentum is $\hbar \sqrt{s(s+1)}$. So what is the resultant Angular momentum of an electron in an orbit in an atom?

I came across a question which asked the value of Angular momentum of an electron in its ground state in an atom. Does this refer to resultant of both kinds of Angular momentum, or am I misinterpreting the question?

Also, what exactly does ground state refer to in an atom? Is it the 1s orbital?


texts: How can I easily explain to a layperson the difference between types of "contains"

texts:
I had a conversation with somebody who had somewhat confused ideas about food. He thought that "all food contains sugar" and when I gave a bottle of oil as the counterexample, he said the glycerol is the sugar there.

Now let's forget for a minute that glycerol is not a sugar. The point is, glycerol is indeed a "building block" of a triglyceride, and glucose is a "building block" of glucose. But still, if you are talking about a process which needs sugar, starch won't work unless you cleave it off first. Just like starch won't spontaneously conduct electricity or emit beta radiation even though it's chock full of electrons.

Given that we have somebody with a very basic level of knowledge, and who is already trying to wrap his head around several confusing concepts at once, what would be an intuitive way to get him to really grok that, just because a given atom or group is present in the structure of a molecule, it does not mean that a substance "contains" this atom or group in the same way that a wet sponge contains water? And that without going off on a long tangent of theory?


texts:
I was looking at the enthalpy of various liquids using WolframAlpha and noticed that at 30 °C, while water and ethanol have a positive enthalpy, acetone has a negative enthalpy.

If I'm understanding this correctly, this means that as acetone evaporates, the temperature of the acetone will increase (because the evaporation will release energy, thereby raising the temperature). I started searching up in temperatures to find the zero-crossing, and that appears to be around 56.074 °C.

This suggests that if a sufficient quantity of acetone is left around, it will eventually heat up to 56.074 °C (which interestingly happens to be when its vapor pressure is really close to the STP pressure).

However, if I get acetone on my hand, I get a distinctive "cool" feel — it, like other liquids, appears to be endothermic and cools down. I may be warm-blooded, but I'm not above 56 °C.

Is there something wrong with my understanding? If not, why does the theory seem to contradict my observations?


texts: Solubility of oxygen in water with temperature, why does the change in solubility decrease around 40 °C?

texts:
Better set in context using a graph:

The solubility seems to fall quite persistently from 0 °C to 30 °C, then gradually slowing down in fall, then dropping faster and faster from 80 °C. Why does that change in drop happen?


texts: Averaging of dipolar coupling in solution due to tumbling

texts:
The angular part of dipolar splitting depends on $\theta$ as:

$$3\cos^2\theta - 1$$

In the liquid state or in solution molecular tumbling occurs which causes the NMR signal to become an average of all $\theta$ which is expressed mathematically as:

$$\int_0^\pi(3\cos^2\theta-1)\sin\theta\,\mathrm{d}\theta$$

where $\sin\theta$ is described, in my the book that I'm reading, as a weighting factor to take into account the probability of finding the system with an angle $\theta$

It is this weighting factor that confuses me. Surely all angles are equally likely? It looks to me like the $\theta$ part of the triple integral one would do to integrate over a sphere using polar coordinates (notice the limits on the integral). However, even if this is correct, I am still finding it difficult to picture this volume element $\sin\theta\,\mathrm{d}\theta$.

Please help me to rationalise why the weighting factor is there and also to visualise this $\sin\theta\,\mathrm{d}\theta$ volume element.


texts: How does calcium carbide artificially ripen fruits?

texts: Lately, use of chemicals to artificially ripen fruits is in full swing. Firstly, how do they do it? Next, Are there any ways to distinguish between those that are naturally ripened and those that are artificially ripened?


texts: Are non-ionic compounds generally as dehydrating as ionic compounds in drinking water?

texts:
In order to turn sea water into drinkable water, virtually all of the salt must be removed.  By definition, salts are ionic compounds.  I am assuming that there are other non-ionic compounds devolved in the sea water, must these compounds be removes as well before water becomes safe to drink?  In general, do non-ionic compounds present the same dehydration dangers as salts when consumed in drinking water?  Why or why not?

For this question, lets not consider other toxic effects besides dehydration.


texts: How to calculate the Gibbs free energy from the equilibrium constant for the decomposition of sodium bicarbonate?

texts:
Solid $\ce{NaHCO3}$ is heated to $90~^\circ\mathrm{C}$. At equilibrium the total pressure of the gases produced is $0.545~\mathrm{atm}$. Calculate $\Delta G^\circ$ at $90~^\circ\mathrm{C}$ for the reaction.

$$\ce{2 NaHCO3(s) <=> Na2CO3(s) + H2O(g) + CO2(g)}$$

Using the $\Delta G^\circ = -\mathcal{R}T\cdot\ln(K)$ formula, I did the work below:

$$\Delta G^\circ = -(8.31)(273.15 + 90)\cdot\ln(0.545)$$

This gave me $1.83~\mathrm{kJ/mol}$ and therefore $3.66~\mathrm{kJ}$ for the entire reaction, $2~\mathrm{mol}$. Unfortunately, the answer is marked as $7.85~\mathrm{kJ}$, suggesting that $K=1$, why is this?

Shouldn't $K=(0.545)/1$ because of the gases present?


texts: How to find the molar volume of 1 gas in a 2 gas system using PV_m=ZRT?

texts: Using $PV_m=ZRT$, would I need to use the total pressure of the system or the partial pressure of the gas I am interested in to work out the molar volume?


texts: Why are thiolates more nucleophilic than alkoxides?

texts:
Why is $\ce{RS-}$ (a thiolate) more nucleophilic than $\ce{RO-}$(an alkoxide)?

According to my logic, the larger size of the sulfur atom will allow the negative charge to be dispersed more as compared to the negative charge on the oxygen atom. Thus, shouldn't $\ce{RS-}$ be less nucleophilic as compared to $\ce{RO-}$ ion?


texts: Why change on pressure affects the boiling point much more than the freezing point?

texts: I do see the mathematical solution given by the classius clapyeron equation but is there any real life and intuitive expalanation?


texts: Products of decarboxylation of sodium carboxylate

texts:
My textbook says that the decarboxylation of sodium acetate with sodalime produces methane. But if we replace sodalime with barium oxide, pure methane is produced.

What is the difference between pure methane and the methane produced in the first case?


texts: Can in any case the faster step of the reaction be rate determining?

texts:
I found a sentence in book which states the reverse step of this reaction ( I forgot what was it!)  has the faster step as rate determining .

Even Rate determining step-Wikipedia  states:

  In chemical kinetics, the rate (or velocity) of a reaction mechanism with several steps is "OFTEN"  determined by the slowest step .

which I think  'OFTEN' means not 'everytime' so,

if faster step of the reaction is rate determining. Then why it is?


texts: Solution of a first- and second-order consecutive reaction scheme

texts:
I have a compartmental model system X, a simplified version of which, looks like this:

$$
\text{System }x: \enspace \text{STO} \xrightleftharpoons[k_2]{k_1}  \text{blood} \xrightarrow[]{k_3} \text{urine}
\equiv
x_1 \xrightleftharpoons[k_2]{k_1} x_2 \xrightarrow[]{k_3} x_3
$$

The system of differential equations is then:
$$
\frac{dx_1}{dt} = -k_1 x_1 + k_2 x_2 \\
\frac{dx_2}{dt} = k_1 x_1 - k_2 x_2 - k_3 x_2\\
\frac{dx_3}{dt} = k_3 x_2 \\
$$

I can solve this system of equations using the following matrix approach.

First, I write the rate matrix [R]. From [R] one can obtain a new matrix [A] by first replacing each diagonal element of [R] by the negative of the sum of each of row elements, and then transposing it:
$$
[R] =
\begin{bmatrix}
    0            & k_2    & 0 \\
    k_1          & 0      & k_3 \\
    0            & 0      & 0
\end{bmatrix} \\
[A'] =
\begin{bmatrix}
    -k_2            & k_2    & 0 \\
    k_1          & -(k_1 + k_3)      & k_3 \\
    0            & 0      & 0
\end{bmatrix} \\
[A] =
\begin{bmatrix}
    -k_2            & k_1    & 0 \\
    k_1          & -(k_1 + k_3)      & 0 \\
    0            & k_3      & 0
\end{bmatrix} \\
$$

I can calculate the amount in each compartment by doing the following:

$$
x(t) = e^{[A]t}x(0) \enspace \text{where} \enspace x(0) = \begin{bmatrix} 0 \\ 1 \\0
 \end{bmatrix}
$$

In python:

RMatrix = model_matrix.as_matrix()
row, col = np.diag_indices_from(RMatrix)
RMatrix[row, col] = -(RMatrix.sum(axis=1)-RMatrix[row,col])
AMatrix = RMatrix.T

def content(t):
    cont = np.dot(linalg.expm(t*AMatrix), x0))

This method is working well for me.

Now, I have a little more complicated model where reactants in compartments 1 and 2 of Systems X and Y combine to get product in System Z.

$X + Y \rightarrow Z$, with a reaction constant of $k_R$.

$$
\begin{align}
&x_1 & \xrightleftharpoons[k_2]{k_1} \enspace & x_2 &\xrightarrow[]{k_3} & x_3 \\
&+  & \ &  + \\
&y_1 & \xrightleftharpoons[k_5]{k_4} \enspace & y_2 &\xrightarrow[]{k_6} & y_3 \\
&\downarrow^{k_R} & \  & \downarrow^{k_R} \\
&z_1 & \xrightleftharpoons[k_8]{k_7} \enspace  & z_2 &\xrightarrow[]{k_9} & z_3 \\
\end{align}
$$

, and the corresponding system of differential equations would be:

$$
\begin{align}
\frac{dx_1}{dt} &= -k_1 x_1 + k_2 x_2 - k_R x_1 y_1 \\
\frac{dx_2}{dt} &= k_1 x_1 - k_2 x_2 - k_3 x_2 -  k_R x_2 y_2\\
\frac{dx_3}{dt} &= k_3 x_2 \\
\frac{dy_1}{dt} &= -k_4 y_1 + k_5 y_2 - k_R x_1 y_1 \\
\vdots& \\
\frac{dz_z}{dt} &= -k_7 z_1 + k_8 z_2 + k_R x_1 y_1 \\
\end{align}
$$

I am struggling with a method to solve this system of differential equations (1st and 2nd order) to calculate the amount in each compartment at a certain time t, given the initial conditions, $k_R$, and the transfer rates $k_1$, $k_2$, $k_3$, etc...

Can I solve it using the matrix method like the one above for a system of first order differential equations? What other options in Python do I have?

Thanks in advance!


texts:
Reading this article on Wikipedia: Xenon Medical applications I see that Xenon can be used as an anesthetic, neuroprotectant and doping agent.

If it is a noble gas, and thus, chemically stable, how can it have those properties?

If Xenon does not react with any other substance, how does this happen, from a chemical point of view?


texts: How to calculate melting/boiling points at different pressures

texts:
I know water boils at below room temperature in a vacuum, and want to know if there's an equation to calculate the melting or boiling points of elements or compounds at a given pressure.

How would I go at attempting this?

The main reason I ask is because I'd like to know if Gallium, a metal which melts at $29.77^\circ C$ at atmospheric pressure would be in a liquid state at room temperature if stored under a vacuum.

Thanks!


texts: How can I control the oxygen in an erlenmeyer flask in a bioprocess?

texts:
I need to control oxygen in a erlenmeyer flask in a bioprocess.  I need to remove overall oxygen in a erlenmeyer flask, and after I need to add oxygen in controlled amounts to a culture in a shaken flask.  Someone knows how can I do it?

Thanks for advance for your ideas.


texts: Mimic a volcano eruption with household chemicals?

texts:
How can one mimic a volcano eruption using household chemicals safely?

We've tried it in a testing tube with baking soda and vinegar. This wasn't quite as impressive as expected.

On the web we've found recipes that add food coloring (red) and dish washing liquid to the mix. I guess the latter is for some bubbling effect.

What we have:

A volcano made from paper-mâché (classic volcano cone form, perhaps a bit steeper than natural)
Center hole big enough to fit a 1.5 liter water bottle

Note: this is supposed to be done with kids, so please don't propose any method that would generate poisonous fumes or similar.

Meanwhile tried a soda ($\ce{NaCO_3}$, i.e. not baking soda $\ce{NaHCO_3}$) solution poured into a dish washing solution, then adding a citric acid solution. It was pretty good, but a bit too quick. Vinegar seems to work better than citric acid, too. Also I used warm water to dissolve the reagents.


texts: Do secondary alcohols prefer to undergo SN1 or SN2 reactions when reacting with a strong acid?

texts:
For example, let us say we have 2.2-dimethycyclohexanol reacting with $\ce{HBr}$. We know that the oxygen gets protonated and then leaves as water, but the question does it leave on its own or does a backside attack happen? If its $\mathrm{S_N1}$ we have 1-bromo-1,2-dimethylcyclohexane as the major product. If its $\mathrm{S_N2}$, we have 1-bromo-2,2-dimethylcyclohexane as the major product. This is assuming we are at 0℃.

I believe that its $\mathrm{S_N1}$ because bromide is a weak base.


texts: How can the potential energy at the infinite energy level in an atom be zero?

texts:
I have recently learnt about atomic structure and the Bohr model of the atom and have observed a discrepancy between it and my previous knowledge based on physics.

For simplicity, assume the atom is of hydrogen.

Total energy of electron $$E= -13.6 \left(\frac{z^2}{n^2}\right) \pu{eV/atom}$$ where $z$ is atomic number, $n$ is energy level.

Thus, at $n=\infty$, $E=0$.

Now, by the relation Total Energy = potential energy/2 (from $TE=-KE=PE/2$),

$$PE=0/2$$ so $$PE=0$$

Now, the infinite energy level ($n=\infty$) occurs at a finite distance from nucleus (as the difference in distance between the energy levels decreases at higher energy levels).

Thus, $PE=0$ at a finite distance from the nucleus.

But, I have previously studied that $PE$ of a system of a negative charge (electron) and positive charge(nucleus) is $=0$ only at an infinite distance.

Thus, the discrepancy.

Please let me know where I have gone wrong.


texts: molar solubility of CaF2 at pH3 given molar solubility at pH7 and pKa of HF

texts:
Here was my attempt #$1$ at a solution.

$K_{sp}=[Ca^{2+}][F^-]^2$

Using the information at pH=7, I estimated that $K_{sp}\approx3.7\cdot10^{-11}$, which means that barely any HF formed.

I assumed that only $HF$ forms and not $CaOH$ because it's insoluble.

I got $\displaystyle \frac{[H^+][F^-]}{HF}=10^{-3.17}$

We have $  \displaystyle \sqrt{\frac{3.7\cdot10^{-11}}{[Ca^{2+}]}}$ fluoride ions.

We rewrite $K_a=10^{-3.17}=\displaystyle\frac{10^{-3}[F^-]}{2[Ca^{2+}]-F^-}$ and plug in the concentration of fluoride ions in terms of calcium ions.

This yields $[Ca^{2+}]=3.7*10^{-4}$, which gives a multiplier of 1.76.

The correct answer is 1.83, which I guessed based on my answer. How do I arrive at that?


texts:
In my text book, it says that strong bases are alkalis because they fully dissociate in aqueous solution. But I'm not too sure of this. Can you not have a weak alkali? And can you not have a strong base which is not an alkali?

Thank you in advance :)


texts:
I've read that lead phosphate is very slightly soluble and so any addition of protons shifts the equilibrium back to the solvated ions. What I can't understand is why the lead phosphate is more soluble in hydroxide or basic solutions also.

Source- Vogel's qualitative analysis


texts: If the ferric ion is more stable than the ferrous ion, then why is it readily reduced to the latter?

texts:
The standard reduction potential value for the ferric ion:
\begin{align}
\ce{Fe^3+ + e- &<=> Fe^2+} & E^\circ &= \pu{0.77 V}
\end{align}
The value is positive, hence it means that ferric ion is readily reduced to ferrous ion, i.e. ferrous ion must be more stable than ferric ion.
But in a book I have also seen that ferric ion is more stable than ferrous ion as it has stable $\mathrm d^5$ configuration.
I am little bit confused that if ferric is more stable, then why ferric is readily reduced to ferrous. Please explain it in detail.


texts: Preparing an inert atmosphere reaction vessel with only an input?

texts: One time, the graduate student that I work with was showing me how to prepare an inert atmosphere in a double necked round bottom flask. After drying it in the oven, she used a torch to drive out all the water vapor. Then she put septums over both openings, and inserted a needle connected to the nitrogen input through one of them, but with no outlet! I asked her to explain how any gas could escape in this set-up, and she tried but I was still very confused.


texts: How do you find the pH of lime juice through titration?

texts:
I am doing an experiment on the effect of time on the $\mathrm{pH}$ of Lime juice.
I was wondering how you would calculate the $\mathrm{pH}$ through titrations using $\pu{1 Molar}$ $\ce{NaOH}$. I have been racking my brain on this for a few hours and searching online.
Sorry if this has already been answered. Thank you for your time.


texts: Questions about Genetic algorithm paper of Gilman and Ross

texts:
I want to reproduce an (old) biochemistry paper of Gilman and Ross, i.e. " Genetic algorithm selecetion of a regulatory structure that directs flux in a simple metabolic model." ( The following link leeds to the paper: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1236362/) I know this is an old paper, but maybe someone here remembers it. I really need the answers of the following questions because the enzymatic model explained in the paper is very important for my master thesis.

First: The author defines a system of two ODEs but the initial conditions of these ODEs are not printed in the paper. The author just writes: "Initial conditions for the integration are determined by letting the network relax to steady state. " (see p. 1324 on the lower right) . But how is this meant? In this paper the author wants to optimize the mentioned ODEs , so how can I find initial conditions, when there are not all parameters of the ODEs given?

Second: On the top of page 1324 are two needstate functions defined, called $\xi_T$ and $\xi_F$. When I plot $\xi(F)$, the plot looks completely different from the one depicted in figure 3b in the paper. So the function defined in figure 3b) must be wrong. Did anyone realize that error and has a workaround for that? Of course I could define my own functions but I want to stay as close to the model in the paper as possible.

Thank you very much for your help.


texts: How does standardising a secondary standard solution make it suitable as a standard solution?

texts:
I know that a standard solution in volumetric analysis must have an accurately known solution. Primary standard solutions (e.g. anhydrous sodium carbonate) can be used straight-away as they follow the list of criteria (high level of purity, unaffected by air exposure, etc.)

I also know that secondary standard solutions (hydrochloric acid) cannot be used directly like primary standard solutions as they don't follow the criteria. But I don't understand how standardising hydrochloric acid with a primary solution (e.g. anhydrous sodium carbonate) will make it able to be used as a standard solution.


texts:
If the reaction takes place in presence of sunlight ,

CH3CH2CH3 + Cl2 gives CH3CH2CH2Cl &CH3CHClCH3

In this second compound is major product with 2° C atom attached chlorine BUT ,

In this reaction ,

CH3CH(CH3)CH3 + Cl2 gives CH3CH(CH3)CH2Cl & CH3C(CH3)(Cl)CH3

In this first compound is major product .

Why ? I cannot understand why major product changes even though reaction mechanism is same.


texts: How does a cathode half reaction work with different metal electrode and electrolyte

texts: If you had a galvanic cell with the cathode half cell using silver as its electrode and Copper Sulfate as its electrode, will the copper (s) coat the silver electrode?


texts: Why are all of the group 16 hydrides/hydrogen chalcogenides except H2O toxic?

texts: I mean ($\ce{H2O}$) is non-toxic and is needed everyday but all of the other group 16 hydrides (hydrogen sulfide ($\ce{H2S}$), hydrogen selenide ($\ce{H2Se}$), hydrogen telluride ($\ce{H2Te}$) and hydrogen polonide or polonium hydride ($\ce{H2Po}$) are toxic and flammable. We observe that water is an outlier. Why is this the case?


texts: Can atomic orbitals combine in a manner intermediate between bonding and antibonding?

texts:
When atomic orbitals combine in phase (0°) we get bonding molecular orbitals, and when they combine with opposite phases (180°) we get antibonding molecular orbitals.
Why can't atomic orbitals combine in phases between 0 and 180?


texts: Estimation of CO2 by titrimetric method using phenolphthalein indicator

texts:
We were estimating dissolved $\ce{CO2}$ in water by American Public Health Association (APHA) method. It was a titrimetric method using phenolphthalein indicator.

Titrant used was $\ce{NaOH}$ and analyte was sample water. Reactions involved:

$$\ce{CO2 (g) ⇌ CO2 (aq)}$$
$$\ce{CO2 aq + H2O ⇌ H2CO3 ⇌ H+ + HCO3^2-} \label{rxn:1}\tag{1}$$

(Only $10\%$ of dissolved $\ce{CO2}$ get converted into $\ce{H2CO3}$.)

On addition of $\ce{NaOH}$:

\begin{align}
\ce{2NaOH + CO2 &-> Na2CO3 + H2O} \label{rxn:2}\tag{2} \\
\ce{Na2CO3 + H2O + CO2 &-> 2NaHCO3} \label{rxn:3}\tag{3}\\
\ce{NaHCO3 &-> Na+ + HCO3-} \label{rxn:4}\tag{4} \\
\ce{\underset{from \eqref{rxn:1} and \eqref{rxn:4}}{HCO3-} + H2O &-> H2CO3 + OH-} \\
\ce{OH- + H+ &-> H2O} \\
\ce{HIn &⇌ H+ + In-}
\end{align}

(The equilibrium shift to the right and when $[\ce{HIn}]:[\ce{In^-}]=1:10$ pink colour appears.)

But when we calculate the concentration of $\ce{CO2}$ we consider only reaction $\eqref{rxn:2}$, which means we are calculating only a portion of the molecular $\ce{CO2}$ while the $\ce{CO2}$ that was present in the solution and reacted in step 3 and the $\ce{CO2}$ (the $10\%$) that was directly converted  into $\ce{H2CO3}$ (Rxn. $\eqref{rxn:1}$) are not taken into account.

So it means we are calculating only a part of the free $\ce{CO2}$ ($45\%$) and not all.

From this can we conclude that APHA's method is not very accurate at estimating the free $\ce{CO2}$ in water?

P. S. I read the procedure and also the calculations in a practical book.


texts: Isomerisation of alkanes under Lewis acidic conditions

texts:
My textbook says:

  n-Alkanes on heating in the presence of anhydrous aluminium chloride and hydrogen chloride gas isomerise to branched chain alkanes.

But no mechanism is given. After a little research, I found this: https://goenkanscienceblog.wordpress.com/2015/01/29/suggested-mechanism-of-isomerisation-of-alkanes/

However, it doesn't explain the role of the HCl gas. Is the mechanism correct and if so, what is the role of HCl?


texts: Why is formic acid considered an acid if it is a reducing agent?

texts:
My understanding was that since the acceptance of Lavoisier's revised Easter Memoir of 1778, all acids were understood to be oxidising agents.*

However, formic acid is often listed as a reducing agent (i.e. the opposite of an oxidising agent), despite being an acid.

Please can you reconcile this apparent contradiction for me?

* What is meant by "oxidising" or "oxidising agent" has, of course, changed since then, now referring to electron transfer rather than necessarily involving the element oxygen.


texts: Why add acid to rid of soluble carbonate or hydroxide impurities? Will it not also react with halide I'm testing for

texts: When identifying metal halides with silver ions, the positive ion $\ce{Ag+}$ will form $\ce{AgX}$ with halide in a solution. However, $\ce{H+}$ is added (typically in the form of an acid like $\ce{HNO3}$) to solution to get rid of $\ce{OH-}$ and $\ce{CO3^{2-}}$ ions first. Will the $\ce{H+}$ not also react with the halide $\ce{X-}$?


texts: In my lab manual, it is given that alcoholic KOH should be the base used in carbylamine test. However as it was not available, I used 10℅ NaOH. The test results came out positive. (Yes, it was actually a 1° amine) Is there any reason to prefer alcoholic KOH over NaOH?