texts: After a unitary transformation, is Koopmans' theorem still valid?

texts:
Koopmans' theorem says that the energy of the HOMO of the Hartree-Fock orbitals is equal to the first ionization energy of whatever system is being studied. This is only approximate because it assumes no changes in the orbitals in the ionic state, no relativistic effects, and no electron correlation. Ignoring those approximations, there is another feature of this which I don't understand.

The wavefunction as determined using HF can be unitarily transformed so that the total energy and wavefunction are preserved, but the "orbitals" themselves are not. Under many of these transformations, I assume that the orbital energies change. Is this true? If it is true, I assume Koopmans' theorem is still valid, but is now more complicated so that the ionization energy is some combination of orbital energies. Can anyone expand on this and let me know if my thinking is correct?

Also, what is it that is so special about the Hartree-Fock orbitals that Koopmans' Theorem has such a simple interpretation, while, if what I say above is true, it seems to be quite convoluted for other sets of orbitals?

As a note, I asked a question which more or less contained this question, but was a bit broader. The question I'm asking right now is the question I am really more interested in having answered.

You can find that other question here: Observability of Orbitals and Orbital Energies


texts:
Top hits on google are:

This site
 Aluminum hydroxide $\ce{Al(OH)_3}$ >> $ 1.3×10^{–33}$

and

This site
 Aluminum hydroxide $\ce{Al(OH)_3}$ >> $ 3×10^{–34}$

which is one order of magnitude different.

What can be the reason for this variation? Experimental conditions?
Where can I get accurate or reliable results/data of $K_{\mathrm{sp}}$ in general?


texts: Effects of gamma irradiation on pH buffer

texts:
Does anybody know if it is possible to gamma-irradiate a bottle of pH buffer to sterilise it? Are there any known effects (short-term or long-term) of the irradition process on the pH qualities of the buffer? This would be for a pH4 and pH7 buffer.

The other option I am considering is autoclaving, but I am told this will definitely affect the pH of the buffer solution, which I don't want.


texts: Effective nuclear charge and electron repulsion

texts:
To the best of my knowledge, the effective nuclear charge $Z_\mathrm{eff}$ is usually defined such that the potential energy of an electron in an atom, $\langle V \rangle$, can be expressed as

$$\langle V \rangle =
  -Z_\mathrm{eff}\langle\psi|\frac{1}{|r - r_a|}|\psi\rangle$$

The Hartree-Fock expression for $\langle V \rangle$, meanwhile, is

$$\langle V \rangle =
  - Z\langle\psi | \frac{1}{|r - r_a|} | \psi\rangle
  + \sum_i \langle\psi |\hat{J_i} |\psi\rangle
  - \sum_{i \in \sigma} \langle\psi | \hat{K}_i | \psi\rangle$$

Is there any relation between these expressions? It was taught in college Chemistry that $Z_\mathrm{eff}$ accounts for electron shielding, which is simply electron repulsion effects. Is the effective nuclear charge just a semiempirical value fitted to approximate the total potential energy of an electron in an orbital, or is there another meaning behind the number?

Based on what I know, Clementi et al’s values for $Z_\mathrm{eff}$ are not evaluated based on this principle. Could I inquire why this is not the case?


texts: Strength of substituted Carbon Double Bonds and C-halo bonds

texts:
The question asks me to identify the compound which has a stronger double bond. I came up with two kinds of reasoning but they do not agree upon a common answer.

1: $sp^2$ carbons are more electro-negative and they would like to have electron donating groups sitting next to them. So in the compound one , the extra methyl group should increase stability and therefore, one would expect the bond strengths to increase. Thus decreasing the bond length (smaller bond length is more stronger? stronger bonds imply more stability)

2: Since the methyl group partially donates electrons to the $sp^2$ carbon, the $sp^2$ carbon's tendency of pulling the double bond electrons towards itself should decrease. Thus increasing the bond length.

So where am I going wrong?

If you have any good resource/material on strength of bonds, please let me know.

EDIT (another Q):

Which double bond has higher disassociation energy?

Substituted alkene is more stable than unsubstantiated alkene. So I is more stable which means it has higher bond disassociation energy so II must be having lesser bond disassociation energy.
Due to hyper conjugation, the bond order in compound I decreases so it must have lower bond disassociation energy.

Which one is correct among the above two reasoning?

If the electro-negativity difference between the atoms is larger, then the bond will be more ionic and hence should be stronger?


texts:
I came across a question that asked the correct structure of trichloroborazine. The two options provided were :
a) the chlorine atoms attached to the three N atoms, and
b) the chlorine atoms attached to the 3 B atoms

My idea was that, since, in borazine, the N atoms have a formal +1 charge, the Cl would more readily bond to it, making (a) the correct answer.
But, turns out, it's actually (b) that's the correct structure.
Why is it so, and what is wrong with my reasoning?
Edit: If both (and other) structures are at least theoretically possible, then which one is the most stable and/or most common one, and why so?


texts: How does the rate constant vary double by doubling the concentration of a reactant?

texts:
Rate law for the reaction, $\ce{A +2B-> C}$ is found to be, Rate $\mathrm{=k[A][B]}$
The concentration of reactant $\ce{'B'}$ is doubled, keeping the concentration of $\ce{'A'}$ constant, the value of the rate constant will be:
(A) the same  (B) doubled  (C) quadrupled  (D) halved

According to me, rate constant of a reaction depends on its temperature only and is not affected by concentration. But the correct answer to this problem is option (B) doubled and not option (A). Can someone please guide me as to why option B is the correct answer?


texts:
In chromium and copper, the are the configuration fill up like
$$\mathrm{3d^5  4s^1}$$
but not $\mathrm{4s}$ first as it has lower energy level. and why only these 2 elements.


texts: Can a drink with such composition have 0 caloric value (whether manufacturer lied)?

texts:
I bought a drink which have next statements:

  The nutritional value, g/100 ml:
      no proteins, fats, carbohydrates.
  Energy value (calorific value):
      kJ / 100 kcal to mg: absent.

Can a drink with such composition have 0 nutritional/calorific value ?

Composition:

prepared drinking water,
flavoring base "Cola"

dye: caramel,
acidity regulator: phosphoric acid,
caffeine - no more than 150 ml/g,
natural flavor enhancer,

sweetener

aspartame,
acesulfame potassium,
sodium saccharin,
sodium cyclamate,

preservative sodium benzoate.

It contains a source of phenylalanine.


texts: Hair styling gels and 'liquid gels' - effect of formulation / composition on viscosity and performance

texts:
[Disclaimer: I am aware that this is a very 'first-world problem', 'light-hearted' kind of question, given the health crisis we are still going through. Just to avoid offending anyone, here's an easy solution: no need to continue to read if you disapprove :) ]
I have 3 brands of 'liquid gel', each with rather different characteristics.
Here are their compositions:
Brand 'A': Alcohol Denat., Aqua, Octylacrylamide/Acrylates/Butylaminoethyl Methacrylate Copolymer, Panthenol, Parfum, PEG-12 Dimethicone, Isoamyl p-Methoxycinnamate, Benzoic Acid, Linalool, Aminomethyl Propanol, Citric Acid.
Brand 'B': Alcohol Denat., Aqua/Water, Acrylates/t-Butylacrylamide Copolymer, Niacinamide, Hydroxyisohexyl 3-Cyclohexene Carboxyaldehyde, PEG/PPG-4/12 Dimethicone, Aminomethyl Propanol, Limonene, Panthenol, Benzyl Salicylate, Butylphenyl Methylpropional, Hexyl Cinnamal, Parfum, Fragrance.
Brand 'C': Aqua, Alcohol Denat., VP/VA Copolymer, Polysorbate 20, PEG-12 Dimethicone, Panthenol, Parfum, Linalool, Geraniol, Hexyl Cinnamal, Citronellol, Alpha-Isomethyl Ionone, Hydrogen Peroxide, Phenoxyethanol, Ethylhexylglycerin, Piroctone Olamine, Citric Acid.
My favourite brand is 'C'.
The shops where I used to buy it are no longer stocking it, they replaced it with the same stuff (same commercial name and 'strength'), but in 'gel' form, which I really don't like.
The composition of the gel is similar to the one of the liquid gel, up to a point:
Brand 'C-gel': Aqua, Alcohol Denat., VP/VA Copolymer, PVP, Propylene Glycol, Carbomer, Polysorbate 20, (PEG-12 Dimethicone - removed), Panthenol, Parfum, Linalool, Geraniol, Hexyl Cinnamal, Citronellol, Alpha-Isomethyl Ionone, Hydrogen Peroxide, Phenoxyethanol, Ethylhexylglycerin, Piroctone Olamine, Tetrasodium Iminodisuccinate, Sodium Hydroxide, Citric Acid.
Question 1: does anybody know what specific components, if any, are responsible for 'C' being liquid and 'C-gel' being indeed a rather thick gel ?
Question 2: could one turn the gel into a liquid that can be sprayed, and if so, how ?
This is no academic question: I would actually like to do that. I tried diluting the gel with water, but those formulation chemists did a very good job: it stayed quite gel-like and viscous, until I really diluted it a lot, like 1:3 or more, and even then it was still a viscous liquid that the spray bottle could not spray well at all.
Could a change of pH perhaps loosen it ? By which I mean a small change; not planning to turn this into battery acid or lye :)
Question 3
When using the liquid gels (applied on wet hair and dried either naturally or with a hairdryer), I noticed very different performances.
'A' results in a very unpleasant, 'doll-like' feel and look, and a lot of static electricity, when you comb your hair. And it doesn't smell nice.
'B' is marginally better, it sort of works in terms of disentangling your hair, but it tends to get a bit sticky, and they put something in it that smells absolutely repulsive (at least to me). I hope it's not the 'fragrance'.
'C', as I mentioned, is my favourite (despite being the cheapest): it smells good, it makes your hair very smooth and easy to comb, it does not stick, and even when dry your hair stays soft and tidy (unlike with B and especially A).
So: can you identify any components, or any formulation features, in A, B and C, that cause the performance I am describing ?
E.g. what might be responsible for 'A' turning your hair into individual doll-like plastic-y, electrostatic strands?
Or, do you know if any of the components of 'B' has a particularly offensive smell ?
Or, is there any specific component in 'C' that 'lubricates' hair and prevents it from sticking?
Thanks!


texts: How many grams of acetic acid are present in 2.80 L of this vinegar?

texts:
A vinegar sample is found to have a density of $1.006 \mathrm{\frac{g}{mL}}$ and to contain $8.7~\%$ acetic acid by mass. How many grams of acetic acid are present in $\pu{2.80L}$ of this vinegar?

I multiplied: $$\left(\frac{1.006~\mathrm{g}}{\mathrm{ml}}\right)\cdot \left(\frac{1000~\mathrm{ml}}{1~\mathrm{L}}\right)\cdot 2.80~\mathrm{L} = 2816.8~\mathrm{g}$$

I then converted $8.7~\%$ into $0.087$ and multiplied it into $2816.8$, to get the answer $245~\mathrm{g}$.

Am I correct?


texts: How can I get self-diffusion coefficient from MSD (mean sqaure displacement)

texts:
I run some molecular dynamic simulations for polymer system (liquid), and I have data of MSD vs t(time). MSD-t relation looks linear proportional. Now, which one is the proper way to calculate the self diffusion coefficient?

1) D = MSD / 6t (for 3D system) and get the asymptotic value at large t.

2) Slope of normal plot of MSD-t

3) Slope of log-log plot of log(MSD)-log(t)

4) Slope of semi-log plot of MSD-log(t)

I searched for literature's but there are too many different methods, not sure what to choose here.


texts: Confusing stability order of free radical structures

texts:
I have a question regarding the solution that has been given.
Question:

In the given compound, what would be the order of ease with which hydrogen atom can be abstracted from carbon atoms I to VI?:

The solution that has been given is:

In the solution they've posted above, how is the 2nd structure more stable than the third structure? The third one clearly has resonance with the pi bond, while the 2nd one has no resonance with the oxygen atom (it can't "accept" oxygen's lone pair as it is not a carbocation, and oxygen does not have an empty $\mathrm{d}$ orbital either).
Please can anyone shed light on this issue. Thank you!


texts: How to find out the state symbol of a compound by looking at its chemical formula?

texts:
Like, in the equation between rubidium and water:

2Rb(s) + 2H2O(l) → 2RbOH(?) + H2(?)

How do we know what state symbol to use in 2RbOH and H2? I'd like to do this just by looking at the chemical formula, but it's OK if I have to memorize a list of stuff to be able to do this.


texts: Possible approximations in complex equilibrium

texts:
If  I have the following equilibrium:
$$\ce{Cu^2+ + 4NH3 <=> Cu(NH3)4^2+}$$
Given an initial concentration of $\ce{Cu^2+}$ ($C_\ce{Cu}$) and an initial concentration of ammonia $C_{NH_3}$, the equilibrium constant $\beta$ can be expressed:
$$\beta=\frac{x}{(C_\ce{Cu}-x)(C_{NH_3}-x)^4}$$

My question is: is there any approximation I can use in order to solve this expression to know the value of $x$? $\beta$ is known.

Thanks


texts: Is hybridization of the cyclopropyl anion sp5?

texts:
I have read some answers about the $\mathrm{sp^5}$ hybridisation of carbon atoms in the $\ce{C-C}$ bond in cyclopropane as well as the $\sigma$-bond resonance in methylcyclopropyl cation.
Overall, the answers say that the $\ce{H-C}$ bond is due to overlap of $\mathrm{sp^2}$ orbital of carbon and $\mathrm{1s}$ orbital of hydrogen, while the bent bonds of the ring are formed by overlap of $\mathrm{sp^5}$ hybrid orbitals.
But, overall true separation of orbitals in such cases is not defined i.e. we cannot say that some orbital is completely $\mathrm{sp^2}$ hybridised.
Similarly, if the loss of a proton occurs from cyclopropane then the following:

In such an ion, will the hybridization change and $\mathrm{s}$ and $\mathrm{p}$ characters of the orbitals be redistributed?
My assumptions for this are:

In the $\mathrm{sp^2}$ bond the lone pair due to loss of proton will pose increased steric hinderance as it occupies greater volume. This will cause increased repulsion and decreases stability. Moreover, shouldn't the $\mathrm{s}$-character increase to accommodate the increased negative charge?

Accordingly, wouldn't the $\mathrm{sp^5}$ bonds will now have greater $\mathrm{p}$-character to ease even greater strain produced?

Then, what will be the change in the hybridisation in the overall molecule on formation of this ion?
References:

Sp5 hybridization in cyclopropane?
Are the triply-bonded carbons in pyridyne (and benzyne) sp-hybridised?
Non-integer hybridization
https://www.ch.imperial.ac.uk/rzepa/blog/?p=14548


texts: Why does it require so much pressure to create diamonds?

texts: Why does it require so much energy/pressure to create diamonds, yet with silicon it is very easy and (I believe) naturally occurs in a "diamond" structure, i.e. where each atom is covalently bonded to four adjacent atoms? I guess it has something to do with the fact that the outer shell is further away from the nuclear, since that is the only significant difference between the two atoms, but I can't work out why that should matter here.


texts: Chemicals in a Rubber Compound - NSR 20, Accel CS, Accel DPG, Anitiox Q, Antioz PMB

texts:
I have a recipe for a rubber compound and am trying to understand some of the ingredients.

The ones I do not recognize are

Compound A

NSR 20
Accel CS
Accel DPG
Anitiox Q
Antioz PMB

Compound B

SMR 20
Accel NS
Accel DPG
PVI

Compound C

Orox HR
Orac CS
Orac TMTD

Is there a place to look these up on the web?


texts: Is the heat capacity infinite for a process at constant temperature?

texts:
The heat capacity of $\ce{H2}$ at constant $P$ and temperature is ______.

It was explained to me that the answer is infinity with the following reasoning:

  Since heat capacity = $\mathrm{d}H/\mathrm{d}T$ and $\mathrm{d}T$ is zero since constant temperature is part of the question, the answer is infinity.

My attempt: Since $\ce{H2}$ is a diatomic gas, its $C_p$ is $7R/2$ which gives $7~\mathrm{cal \cdot mol^{-1} \cdot K^{-1}}$.

Which method is correct?


texts: Why can't we use 30 mL of water and 70 mL of alcohol to make a 70% (v/v) solution of Isopropyl Alcohol?

texts:
Volume percentage (V/V): Solutions that are formulated from two liquids are often expressed as volume percent
with respect to the solute. The volume percent is the volume of a liquid in 100 mL of solution. The label on a bottle
of ordinary rubbing alcohol reads “isopropyl alcohol, 70% by volume”. Such a solution could be made by mixing
70 mL of alcohol with water to make a total volume of 100 mL, but we cannot use 30 mL of water, because the
two volumes are not necessarily additive:

What exactly does "not neccessarily additive" mean?


texts: Can tin(IV) sulfide be synthesized from tin(II) chloride via oxidation with sulfite in acidic media?

texts:
Will the following reaction occur?

$$\ce{2Na2SO3 + 6SnCl2 + 12HCl → 4NaCl + 5SnCl4 + SnS2 + 6H2O}$$

I'm going to synthesizing $\ce{SnS}$ and $\ce{SnS2}$ NP's, but our supply is runned out and deadline of assignment is coming to soon, so will this reaction  occur? If it is possible, what is are the conditions of this reaction?


texts: Orbitals SPDF. Why they named like that?

texts:
I know there are orbitals named S, P, D and F.

But why they named like that. is there any significance for the letter?
Is there any order in filling the orbitals?


texts: How to calculate the molecular weight for a volatile substance introduced into a Dumas bulb?

texts:
In a Dumas bulb a volatile substance is introduced. After a few minutes when the liquid has evaporated, the bulb is sealed. It is known that the initial weight of the bulb with air is $12.0468~\mathrm{g}$, $12.4528~\mathrm{g}$ with the volatile substance and $350.6264~\mathrm{g}$ with water. Calculate the molar mass of the substance if all these measurements were done at $25~^\circ\mathrm{C}$ and $1~\mathrm{atm}$ of pressure.

The correct answer is $29~\mathrm{g/mol}$.

What I've done is the following.

I've constructed a system of two equations to know the mass of the bulb and the volume it can contain.

$m_b+\rho_\mathrm{air}V = 12.0468~\mathrm{g}$
$m_b+\rho_\mathrm{water}V = 350.6264~\mathrm{g}$

The solutions are $m_b=11.6144~\mathrm{g}$ and $V=0.339012~\mathrm{m^3}$

With this I can find the molar mass of the volatile substance by knowing that its true mass was $m=0.8384~\mathrm{g}$ and the volume it occupied was $0.339~\mathrm{m^3}$ and using the ideal gas equation.

The ideal gas law, can be used to say

$M=\frac{m}{pV}RT=0.060~\mathrm{g/mol}$

Which is wrong. I've done all sorts of other things and can't get $29~\mathrm{g/mol}$. Maybe this is the craziest thing I've done until now.


texts:
I know that nitrogen is versatile enough that it can form branched chains if it is all single bonds.

For example:

$\ce{H2N-N(NH2)-NH2}$

Is this compound a nitrane (nitrogen alkane)?

If so how would I name this branched nitrogen compound?


texts: Using Le Chatelier's Principle to Change Mechanical Energy to Chemical Energy

texts:
I was interested in an application of Le Chatelier's principle, where an increase in pressure could result in a decrease in the moles of gas.

In particular, a situation where when the pressure increased, it drove the reaction in one direction (towards fewer moles), but when the pressure was lower, then the reaction went the other direction.

What pairs of two reactive room-temperature gases can both combine to make a third room-temperature gas where the change in chemical energy can be used to store the energy from the work done on the system by compression?

So far, I've found these possible candidates:

$$
\begin{align}
\ce{2 SO3 &<=> 2 SO2 + O2}\\
\ce{2 CO2 &<=> 2 CO + O2}\\
\ce{2 NH3 &<=> N2 + 3 H2}
\end{align}
$$

I'm imagining a situation where a mixture of gasses could be compressed to a significant fraction of its original volume without too big of an increase in temperature.

Maybe a catalyst might be critical to make the activation energy less of an issue.

I don't know if this is possible, though.

Additional

I'm teaching a module on energy conversion.

We have 5 common types of energy: mechanical, electrical, thermal, chemical and light.  And we are discussing conversions between them.

The example of changing mechanical energy to chemical energy I had been using was the compression of graphite to make diamonds. I wasn't happy with this one, though.

Then I half-remembered something from my college chemistry class where the direction of a chemical reaction could be shifted by changing the pressure or the temperature, and I wanted to investigate that idea.

That's the inspiration for this question.  If this process is useful, all the better.  If it's not, then it's a way to introduce some important concepts and something they'll see later in their college chemistry class.

Second Additional

If we have a cylinder of gas, a piston compressing that gas acts a bit like a spring.  But compressed gasses heat up and lose thermal energy to the environment.

Could a chemical system like this be interesting because the energy of compression is partially stored in the chemical bonds and not completely in the motion of the molecules, and so might not lose as much energy to the environment?


texts: What's the mechanism of water catalyzing a reaction of hydrogen sulfide gas and sulfur(IV) oxide to yield sulfur?

texts:
The reaction

$$\ce{2 H2S(g) + SO2(g) -> 2 H2O(l) + 3 S(s)}$$

goes in presence of a catalyst, usually $\ce{Al2O3}$ or $\ce{TiO2}$, but also just in presence of moist or water (YouTube video)

I don't understand the catalytic mechanism - why doesn't the reaction go without water and how exactly does presence of water help?


texts: What is the Series Limit in a Spectral line

texts:
What is exactly the series limit in a spectral line graph? Do we talk about series limits for each series (Eg: Lyman series in Hydrogen) or collectively for an atom?

Is series limit the transition having least energy or least wavelength?

So like for Lyman series, will series limit be that corresponding to $\ce{1 -> 2}$ or $\ce{1 -> Ionize}$?


texts: Which material would work best as "sacrificial material" for melting aluminum powder in a kiln?

texts:
I need to melt aluminum powder in a kiln, but before it melts it gets oxidized almost completely. My kiln is almost airtight, but it doesn't have inert gas inlet.
Which material would work best as sacrificial material, which would react with oxygen (and water vapor) before aluminum?


texts: How do "basic" amino acids (lysine, arginine) act as base under physiological conditions?

texts:
Why do we consider amino acids with high side chain pKa's basic, yet with a higher pKa, less of the amino acid will exist in basic form at equilibrium compared to acid form at physiological pH?

What will the concentration of the base be given the high pKa of these amino acid side chians. The answer is that the higher the pKa, the lower the concentration of the base, since with 1) with a higher pKa, then 2) you will have a lower Ka (pKa = - logKa) and therefore 3) a lower concentration of base, due to Ka = the conjugate base (times H3O+) / acid, then the numerator, the conjugate base will be  lowered in concentration with a lower Ka. This can also be confirmed with the Henderson-Hasselbach equation, where pH = pKa + log [A-]/[HA] and since pkA is increasing will make pKa > pH, meaning pH - pKa = a negative number = log [A-]/[HA], where [A-]/[HA] would then equal 10^negative number, meaning the concentration of the acid will be greater than the concentration of the base.

My question is, when you look at titration curves, we know that parts of an amino acid will act more as a base, than an acid, at higher pKa's. Meaning, if you have the amine group of an amino acid, with a pkA of 9-10, it doesn't want to give up it's hydrogen, until the pH is pretty high (10-12). Why are amino acids with high overall pKas considered basic, yet, when you look at a molecule's pKa at a high pKa, less of the molecule will exist as the base at equilibrium (meaning it is wrong to say that a molecule with a high pKA will exist primarily it is basic form)?


texts:
As far as chemistry goes, there are laws or observations that can be useful to determine the perfect shape and disposition of the wood in a campfire ?

For example what chemistry says about the 2 most popular "shapes"

teepee
log cabin

or even other variations such as the swedish stove ( 1 log with the top splitted in multiple segments )

The properties that I'm looking for:
 - easy to start
 - long lasting

The properties that I would like to have but I can discard:
 - significant heat generation


texts: Reaction of white phosphorus with aqueous sodium hydroxide

texts:
What are the products obtained in the reaction of white phosphorus with aqueous sodium hydroxide?

I know one will be phosphine ($\ce{PH3}$).

How can we find the oxidation state of phosphorus in the other product?

Thanks for help in advance.


texts: Is the P-Cl bond energy same in PCl5 and PCl3?

texts:
Is the $\ce{P-Cl}$ bond energy same in $\ce{PCl5}$ and $\ce{PCl3}$? Why?

According to wolfram alpha both have $\pu{326 kJ mol-1}$ energy. But my study material says that they are not same. I'm confused. Can someone clarify?


texts:
I want to purify crude alpha-amylase with column chromatography. I am using a spehadex 75, but for some reason I can't find any information on how to make the slurry.
I can quickly find a lot of information on how to pack and store a column, but what I really want to know is how much powder and buffer do I mix together?


texts: How does temperature and other factors affect sigmatropic rearrangements?

texts:
The image below shows a [3,3] sigmatropic rearrangement. My question is why does the increased temperature favour the right side? The arrangement is technically the same except for the methyl groups on different carbons.

Here is another example:


texts: What is a possible mechanism for the Beilstein test for halogens ? I can't seem to find a arrow pushing mechanism for this reaction.


texts:
A current is applied to two electrolytic cells in a series. In the first, silver is deposited; in the second, a zinc electrode is consumed. How much $\ce{Ag}$ is plated out if $\pu{7.5 g}$ of $\ce{Zn}$ dissolves?

What I ended up doing was

$$\frac{\pu{7.5 g}~\ce{Zn}}{\pu{65.382 g mol}~\ce{Zn}} \times \frac{\pu{2 mol}~\ce{Ag}}{\pu{1 mol}~\ce{Zn}} \times \pu{107 g mol-1}~\ce{Ag}$$

but I'm not even sure I'm doing this right.


texts:
Question
  How many grams $\ce{CO2}$ will result when burning $\pu{100 g}$ malonic acid?
  The formula for malonic acid is $\ce{C3H4O4}$ so 3 $\ce{CO2}$ molecules should result from oxidating one malonic acid molecule.
  $$\ce{C3H4O4 + 2O2 -> 3CO2 + 2H2O}$$

My attempt

$$44.01\cdot\frac{100}{104.0615}\cdot3 = \pu{126.88 g}$$

with $\pu{44.01 g}$ being the mass of a mol $\ce{CO2}$ and $\pu{104.0615 g}$ for a mole of malonic acid.

However, this doesn't seem to be right. Can anyone hint me for the correct solution?


texts: Should the mean energy be written in angular brackets or with an overline?

texts:
How would you write mean energy? I came up with two different ways:

$\displaystyle\langle G_{\textrm{f}}^\circ(j) \rangle$ with the MathJax code \langle G_{\textrm{f}}^\circ(j) \rangle
$\displaystyle\overline{G}_{\textrm{f}}^\circ(j)$ with the MathJax code \overline{G}_{\textrm{f}}^\circ(j)
Or maybe another way?

I am looking for the proper use of this notation in the scientific literature.


texts: Why is Aluminium Chloride a Lewis Acid if it's an ionic compound?

texts: In my textbook it says in the reaction $\ce{AlCl3 + Cl- -> AlCl4-}$, Aluminium Chloride ($\ce{AlCl3}$) has six valence electrons and accepts a lone pair from $\ce{Cl-}$, but wouldn't that mean the aluminium atom covalently bonded with the three chlorine atoms to get six electrons (which is wrong as it's ionic)?


texts: Electrolysis of copper without any copper initially in solution

texts: Let's say we have two copper electrodes as shown in the image, and there is a solution with copper nitrate. In this case, I know that copper will deposit onto the cathode and copper from the anode will be oxidized and enter solution when a voltage is applied across the two electrodes. However, what if instead of copper nitrate, there was just NaCl (or any other electrolyte that wouldn't cause any problems like precipitation) in solution instead? Would current still be able to flow, and if so, would the electrodes still lose and gain mass as they did before? I am fairly certain that current does flow, but I am not really sure if copper will still deposit onto the cathode and vice versa.


texts: Why does neighbouring group participation happen?

texts:
Can someone please explain why neighbouring group participation happens?

Does it stabilise the carbocation? If so then is NGP dominant over an intermolecular SN2 reaction (especially in aprotic medium)?


texts: Analysis of mixture by precipitation and complexometric titrations

texts:
I've performed an experiment about chloride mixtures. First using $\ce{AgNO3}$ as titrant, I've titrated the mixture to determine the amount of total chloride. Then by direct titration with $\ce{EDTA}$, I wanted to determine the amount of $\ce{Mg}$ ions.

I'm confused about the amount of total chloride ions as there are two sources of chloride ions.

I'd really appreciate if someone can help me here.

Thank you so much.


texts:
Given that both elements are in the same period, what information from the PES spectra indicates that oxygen would have a smaller atomic radius?
(A) The number of peaks
(B) The intensity of the peaks
(C) Binding energy of the peaks
(D) A and C
(E) B and C

Recently my chemistry teacher and I had a dispute over a test question, what would be the correct answer?
Personally, while I do agree with the fact that binding energy clearly answers the question, I also believe that the intensity of the peaks could also indicate that oxygen has a smaller radius than nitrogen, given that they are in the same period.
This is because intensity indicates the number of electrons, which indicates the number of protons, which indicates that oxygen would have a greater effective nuclear charge, and thus a smaller radius. As a result, my answer was both B and C, contrary to my teacher's answer of simply C.


texts: What gasses are typically produced when biomass is incinerated at high temperatures (600 C) in high oxygen environments and what is a typical composition of the ashes left behind?


texts: Equivalent of Szabo and Ostlund book for DFT

texts:
Szabo and Ostlund book Modern quantum chemistry [1] is extremely useful to understand Hartree-Fock and post-Hartree-Fock methods. Not only it explains the theory behind such methods, but it is also oriented towards a practical implementation. Following this book I was able to implement an Hartree-Fock code from scratch in order to perform Born-Oppenheimer molecular dynamics.

Since I already work with software packages based on density functional theory (Gaussian09 for calculations in vacuum and QuantumESPRESSO for solid state systems), I would like to implement a simple DFT code in order to better understand what is going on inside the "black box". However, I would like perform this task using a plane wave basis set: this is somewhat more involved than using Gaussian basis sets since it involves periodic boundary conditions and pseudopotentials. In addition, I will have to take care of fast Fourier transforms everywhere and of the approximation of the exchange-correlation functional.

Supposing that I will be happy with the local density approximation, there is a book out there similar to Szabo's book for DFT? Notice that I am not interested in the basics of DFT but I am searching for a good book explaining in details the practical implementation using PW.

Here some comments on the books I already considered:

Martins [2]: This book contains a lot of informations and is oriented to solid-state electronic structure, therefore it explains plane waves and pseudopotentials. However I think that it works well as a reference but not as first reading to understand in details the concepts.

Giustino [3]: Very nice book with the goal of teaching DFT to undergrad students. For this reason is too simplistic and does not go into technical details.

[1] A. Szabo and N. S. Ostrlund, Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory, Doever Publications, 1996.

[2] R. M. Martins, Electronic Structure: Basic theory and practical methods, Cambridge University Press, 2004.

[3] F. Giustino, Materials modelling using density functional theory, Oxford University Press, 2014.


texts:
According to Wikipedia:

  Also, since the reaction involves free radical species, a side reaction occurs to produce an alkene. This side-reaction becomes more significant when the alkyl halides are bulky at the halogen-attached carbon.

How would a radical reaction end up producing an alkene in the context of the Wurtz reaction?

What I do see happening is an E2 elimination creating an alkene.

Also, this raises another question - can't Grignards also create alkenes "by accident"?


texts:
Something that confuses me slightly is the trends in density when comparing periods 4, 5, and 6 in the d-block. Looking at periods 5 and 6, the density peaks at group 8, with ruthenium and osmium, respectively. The density slightly drops at group 9 and falls further through group 10-12 and the p-block.
But in period 4, just from assumption you would expect iron, the first group 8 member to be the densest of period 4, but it's not at all. Sure, iron is the densest yet, but the trend increases up to copper and only starts dropping at group 12 and beyond. Why is there this discrepancy?
Furthermore, why does density seem to peak at group 8 anyway? What is it about the d-shells that create this general pattern?


texts: Why is the melting point of PCl3 less than that of PCl5?

texts:
From just the IB chemistry bonding chapter information, you would normally deduce that $\ce{PCl3}$ and $\ce{PCl5}$ are both covalent molecules.

However, as $\ce{PCl3}$ has a dipole moment, it has dipole-dipole intermolecular attractions, implying that  $\ce{PCl3}$ has a higher melting point than $\ce{PCl5}$, which only has London dispersion forces.

So why is it that $\ce{PCl5}$ has a higher melting point than $\ce{PCl3}$ (I saw online that  $\ce{PCl5}$ is an ionic solid)?


texts: Conversion of a permeability value from barrer to SI unit

texts:
I have done a permeability experiment on LDPE in the presence of air. At $\pu{30^\circ C}$, the permeability was found to be 1.846 barrer.

Now I am trying to apply this permeability value to a calculation whereby I am trying to find what the change in pressure of a dunnage bag is (it is a bag that has the shape of a pillow) after 5 minutes. I have the following info:

$$
\begin{align}
\text{Volume of bag}&= \pu{0.2064 m^3}\\
\text{Approximate area} &= \pu{1.35 m^2} \text{ (this is just a quick approximation)}\\
\text{Thickness of LDPE} &=\pu{ 0.042 *10^-3 m}\\
\text{Time }&= 5 \times \pu{60s} = \pu{300s}\\
\end{align}$$

Is it correct if I convert barrer to SI units in the following manner?

$$\pu{1 barrer} = 7.5005\times10^{-18}\ \mathrm{m^2\ s^{-1}\ Pa^{-1}}$$

By using the following formula, I was hoping to calculate the change in pressure. However, my values don't make any sense at all!

$\displaystyle\text{Permeability} = \frac{\text{Volume}\times\text{thickness}}{\text{Area}\times\text{time}\times\text{Change in Pressure}}$


texts: Selecting between redox and neutralization reactions for a mixture of HCl, H2SO4 and NaOH

texts:
I know that you can have 2 acids reacting with 1 base. These 4 reactions are an example of this:

$\ce{3 HCl + H2SO4 + NaOH -> 3 H2O + SCl2 + O2 + NaCl}$

$\ce{6 HCl +  4 H2SO4 + 2 NaOH -> 8 H2O + 2 S2Cl2 + 5 O2 + 2 NaCl}$

$\ce{HCl + H2SO4 + 3 NaOH -> 3 H2O + Na2S + 2 O2 + NaCl}$

And

$\ce{HCl + H2SO4 + 3 NaOH -> 3 H2O + Na2SO4 + NaCl}$

I checked and all these equations are balanced. But will these reactions forming sulfur chlorides and ionic compounds with sodium and sulfur as well as $\ce{H2O}$ and for 3 of them, $\ce{O2}$, actually occur without any added heat or are they endothermic acid base reactions and thus require heat or will the stronger acid(in this case $\ce{HCl}$) be the one that reacts and the weaker acid (in this case $\ce{H2SO4}$) just make the pH of the solution lower?


texts: Separating plant extract from ethanol solution

texts:
I have to do an experiment which involves getting the extract of certain leaves. I had decided to macerate it in ethanol (70%) solution and then to evaporate the solvent using water bath/rotary evaporator.
Due to the pandemic, I couldn't get access to labs to conduct this experiment. Is there any other way to evaporate the solvent at home without the need for water bath/rotary evaporator?
This extract will be used for testing antibacterial effects. So, I'm kinda concerned about simply heating up the solution because it may destroy the necessary compounds. Would it work if I try to heat the solution in lower temperatures?
For what it's worth, the compounds I'm trying to extract is Quercetin and ß-sitosterol.
Thank you,


texts:
Easy question to kick off my chemexchange membership!

I'm learning chemistry in my spare time, and fittingly for a video art project I'm doing, decided to try a simple inorganic(?) procedure to make some crimson flames.

My research lead me to believe that lithium methoxide works wonders for this, especially in solution with methanol which only has a very faint blue flame on its own. I basically already know it works, based on some demonstrations seen on YouTube, but I'm unable to find much anything in literature about the lithium salt of methanol. So I'd like to verify my understanding of the equation:

To my understanding, dissolving lithium metal in methanol should yield:

$$\ce{Li + CH4O -> CH3LiO + H}$$

...Lithium methoxide in solution with methanol, assuming an excess of methanol, and some released hydrogen gas.

Am I correct? Can someone shortly explain the actual reaction that takes place?

Additionally: I think the solution should be relatively stable and easy to store and handle, like methanol, unless there's a reason to believe otherwise?
Also, if one wanted to produce dry lithium methoxide powder from this, what might be a good precipitant to crash it out of methanol?


texts: Is it possible to create an arbitrary, stable, unique chemical fingerprint?

texts:
Context: I want to be able to hash real-world objects

Is it possible to create a substance containing a combination of elements (or isotopes?) in a random and difficult to reproduce (but simple to verify) combination?

For example if the "fingerprint" was 69% X and 31% Y this information can be easily hashed but it should be very difficult to reproduce with exactly that combination. This substance would then be combined with the object in an unobtrusive way and it should be simple to verify that that object has that exact "fingerprint".

In my mind using DNA/RNA in some way seems like a good solution but I believe it's not very stable. I feel it would be useful only if it lasts at least 20-50 years or so.


texts: Why is the nitrile group not hydrolyzed as well during hydrolysis of imine in Thorpe reaction?

texts: while imine is getting hydrolysed, why does not nitrile group hydrolyse to give carboxylic acid?


texts: Can I get an accurate temperature reading from a flask with a built-in thermometer well?

texts: I recently purchased a flask with a built in thermometer well, but I have discovered that simply setting a rod thermometer in the well does not produce a very accurate reading. I was wondering if there was maybe a specific method for measuring temperature in wells that I am not aware of. Here are some pictures of the flask:


texts: Can equivalent mass be more than the molecular mass? Can it be applied to radical reactions?

texts:
Consider a reaction involving radicals:

$$\ce{CH3^. + Cl^. -> CH3Cl}$$

Is the definition of equivalent mass applicable here? If yes, how?

Are there reactions where equivalent mass of a reagent is more than its molecular mass?


texts: Why are all the orbitals that have the same principal number in Hydrogen degenerate?

texts: In hydrogen, all orbitals with the same principal quantum number 'n' (1,2,3...) are degenerate, regardless of the orbital angular momentum quantum number'l' (0,1...n-1 or s,p,d..). However, in atoms with more than one electron, orbitals with different values of l for a given value for n are not degenerate. Why is this? Surely the radial distribution functions are similar for hydrogen (in that there's still penetration of orbitals and so on). Or is it that orbitals with different values of l are degenerate for a value of n greater than would be occupied in that particular atom's ground state?


texts: How to calculate molality, molarity and mole fraction given density (g/mole)?

texts:
Calculate the molality, molarity and mole fraction of a $\ce{CuSO4}$
in a 17% m/m aqueous solution (density of the solution is 1.367 g/mole)

I did .17 * 1.367 to find grams of $\ce{CuSO4}$

and .83 * 1.367 to find grams of $\ce{H2O}$

Then used to them calculate:

molarity = 0.00146 M

molality = 1.287 m

Mole fraction = 0.023

I'm wondering if I'm doing it right?


texts: Does orientation matters to this extent in reactions?

texts:
In the above question I know that the three reactions involved are $\mathrm{S_N2}$ reactions and therefore there shall thrice inversion of the substitute.
So, I got the solution for the MCQ as:

However, the solution to the question says that the first structure is only correct and the second one is wrong.

As far I have learnt I know that the orientation of the whole compound doesn't matter because we can rotate the compound in our mind. Is this wrong?


texts: What pressure is created by the electrolysis of water?

texts:
I am interested to know what is a reasonable maximum working pressure I could expect against the evolution of oxygen and hydrogen when electrolysing a typical water electrolyte.

My aim is to make small quantities of isolated $\ce{H2}$ and $\ce{O2}$ for a hobby hydrogen torch and I am curious how tall I can make the middle branch of the Hofmann Voltameter before the back pressure stops the production of new gas.  Having a predictable gas pressure would allow me to use the collection spaces for gas storage. I do not like the idea of mixing the gases before the torch nozzle like some brave people do so plan to use two collection volumes.

What parameters would be most likely to effect this pressure, electrolyte makeup, temperature, voltage?

Bonus question, is the pressure of $\ce{H2}$ and $\ce{O2}$ expected to be the same in theory and/or practice?

EDIT:
It looks like there is a high pressure electrolysis process out there that operates at many atmospheres of pressure and has been used to pressurise the gas products.  I missed it in my first readings on Wikipedia and further research has confirmed it though information is limited, it seems to be a specialised process usually associated with proton exchange membrane systems I think but I am just hoping to use two metal electrodes.


texts: Are there known compounds of caesium with oxidation number >1?

texts: Given that the left neighbor of caesium, xenon, does have fluorides and oxides, it is not inconceivable that caesium can have oxides or fluorides with an oxidation number higher than 1. Are such compounds known and synthesized? Or, alternatively, are there computations that rule out such compounds as unstable?


texts: Finding the energy given out when 2 moles of reactants are mixed and ignited from a balanced equation

texts:
The question I am trying to answer is this:

I only know about Hess' law, bond enthalpies and enthalpies of combustion and have tried to use all concepts in order to somehow get an answer but none of them have worked. I first tried to write a balanced equation for what the reaction of 2 moles of reactants would look like but I don't believe it could be balanced. Then, I tried using bond enthalpies but I couldn't have done that either since the equation couldn't be balanced. Next, I tried using enthalpies of combustion, and the same thing happened. So, I'm wondering if there's anyway to answer this question, preferably with the concepts mentioned above.


texts: producing ozone through electrolysis of water

texts:
I would like to produce low concentrations of ozone through electrolysis of water. The standard setup to do this uses a graphite electrode and a platinum electrode in an $\ce{H2SO4}$ solution.  However, I'd like to produce the ozone using only water and preferably using inexpensive electrodes.  I don't seem to understand the exact chemistry of this, though.  I'd like to know:

If I use different electrodes, what changes?  I'm currently using zinc and graphite and, other than the fact that the zinc degrades, is there any downside to using it?

The $\ce{H2SO4}$ solution, I expect, increases the conductivity of the water, is that right?  Why is it used?  What if I don't use it?

How can I go about detecting the ozone in the water?  When I run my system I seem to smell something ozone-y, but I'd like a much less subjective method than that.


texts:
Amongst the following the most stable complex is:
A) $\ce{[Fe(H2O)6]^3+}$
B) $\ce{[Fe(NH3)6]^3+}$
C) $\ce{[Fe(C2O4)3]^3-}$
D) $\ce{[FeCl6]^3-}$

I know that the answer should be $\ce{[Fe(C2O4)3]^3-},$ but I could not find a satisfactory explanation.


texts: Reason for double acylation of ferrocene only occurring with certain reagent combinations

texts:
Can anyone explain why the acylation of ferrocene produces the following results:

Ferrocene + acetic anhydride + AlCl3 ==> mono-acylated ferrocene

but:

Ferrocene + acetyl chloride + AlCl3 ==> di-acylated ferrocene (an acyl group on each ring).

I have seen various statements confirming this, but not a single explanation for it! My current thoughts are that it must be something to do with the carboxylic acid produced from the reaction with the anhydride somehow hydrogen bonding/blocking the second site, but not really sure how it would work.

Any explanations greatly appreciated!


texts: Preventing build-up of Diethyl Ether Peroxides

texts:
I've never stored Diethyl Ether before but am thinking of producing minor amounts myself and storing said Ether inside of glass/PTFE bottles.

I am aware of possible pressure build-up due to vapors and storage temperature, but what always puts me off is the formation of explosive peroxides.

Now as the above Wikipedia article mentions:

  Diethyl ether hydroperoxide decomposes in the presence of sodium hydroxide and $\ce{Fe^2+}$ -containing salts.

This is obviously stating that I can stop the peroxide formation simply by adding in some $\ce{NaOH}$ which I have an abundance on hand.  However that above information is regarding hydroperoxides. The less nasty of the two peroxides.

Ethylidene peroxides are the explosive ones that detonates by simply touching it. This is what scares me. There's no information regarding the stopping of formation on the page, and frankly my google searches for "Safe storage of Diethyl Ether" and "Stop Diethyl Ether Peroxide formation" seem to come up with "put some iron wire in it" or Potassium Hydroxide.

So my question is: what is the most reliable, safe, and long-term solution to prevent building up of both of Diethyl Ether's peroxides, especially the Ethylidene peroxide, with the least amount of contamination possible.


texts: Skipping the defatting stage in extraction of alkaloids

texts:
I am attempting to extract certain alkaloids from green plant matter, which is very high in waxes and fats.

I understand that in this scenario it is common to first acidify and then use a non-polar solvent to de-fat the solution.

I am curious though: say I were to basicify and extract alkaloids without any de-fatting. If I were then to add HCl solution to the non-polar solvent which now contains the alkaloids, wouldn't this in theory be equivalent to the de-fatting stage? Wouldn't the alkaloids would now be in the aqueous layer, and the lipids would be stuck in the non-polar layer?

As the acid/base method is so common, I am wondering if there are any downsides to the method described above that I am unaware of. I only have enough material for one shot so I would just like to hear some input before I attempt this expedited method.

May main fear would be emulsions that wouldn't break up. Is this a valid concern that is remedied by a preliminary de-fatting stage? Are there other concerns I should be wary of?


texts: Synthetic route for the conversion of ethanol to but-1-yne

texts:
How do I convert $\ce{CH3CH2OH}$ (ethanol) to $\ce{CH3CH2C#CH}$ (but-1-yne) ?

I'm not too good with reaction mechanisms and conversions are beyond me.

My Attempt:

I've searched through a couple of textbooks and notes and I don't see any direct way to do the reaction.

I think I can use thionyl chloride to to convert from alcohol to chloroalkane:
$$\ce{CH3CH2OH + SOCl2 -> CH3CH2Cl + HCl + SO_2\uparrow}$$
The $\ce{SO2}$ escapes but I'm not sure how I can get rid of the $\ce{HCl}$.

Assuming that I do get rid of it somehow, I can take the resulting chloroalkane and add an alkynyl group to it hence forming the required higher alkane.
$$\ce{CH3CH2Cl + C2HNa + NaCl -> CH3CH2C#CH + \dots}$$

Again, the mechanism of these reactions elude me. I've only figured out the above from randomly stated properties of reagents. A detailed method of the conversion would be helpful.


texts: Recently, I saw a video about sodium hydride and it saw it was made up with $\ce{Na+}$ ions and $\ce{H-}$ ions. My  problem is: aren't all hydrogen ions positive? And in what conditions can $\ce{H-}$ occur?


texts: Is everything in organic chemistry arbitrary?

texts:
I am a student who is trying to study organic chemistry. I'm using McMurry's book for it. As a beginner in chemistry, I have a fundamental question about chemistry itself. Are most of the chemistry's reaction rules, proved in a way of experiment and probability? Especially for organic chemistry. I really can't get why the reactions occur and there seem to be too many exceptions. When I ask teachers, they say it is because they just found them by experiment. But it seems to be too much for to just say that all the knowledge is just from experiences. There must be some fundamental rules.

So my question is

How do we find organic chemistry reactions?
Where do we use the reactions that we find in books?
Are there other important rules in a molecule or the electrons that are in the molecule besides the induction and resonance effect?
Can't organic chemistry be more rigid (I can't find a good word for this)? Studying McMurry's book, the products of the reactions seems to be determined arbitrarily.


texts: Can the light reaction of photosynthesis happen spontaneous in pools of water?

texts:
I've just learnt that a part of the photosynthesis reaction is the light reaction, where sunlight is absorbed by chloroplasts, which then excites electrons to higher energy levels, allowing for water molecules to be broken down.

My question is whether this can also happen in pools of water? I mean, if all that is really needed is sunlight, then I don't see why water molecules in pools won't get excited and thus break down too.
If not, then how do chloroplasts assist in this?
And on top of that, why don't chloroplasts get damaged since this is similar to how UV rays damage our skin as it can excite electrons in cells and damage genes?


texts: Reaction between alumina and aqueous sodium hydroxide, which one's right?

texts:
My chemistry textbook has a rather annoying irregularity.

It cites two different reactions for the same set of reactants (aluminium oxide, sodium hydroxide and water) without the slightest mention of a particular temperature or concentration. Here they are:

In a chapter on the p-block elements:

  $$\ce{Al2O3 (s) + 6 NaOH (aq) + 3 H2O (l) -> 2 Na3[Al(OH)6] (aq)}$$

In a chapter on metallurgy, under the topic of 'Extraction of aluminium from bauxite':

  $$\ce{Al2O3 (s) + 2 NaOH (aq) + 3 H2O (l) -> 2 Na[Al(OH)4] (aq)}$$

Which one of these is correct? Or are they both correct, depending on the situation? If so, under what conditions are they correct?


texts: My chemistry teacher told us that acids taste sour and bases taste bitter. After reading Do acids without hydrogen taste sour? and https://en.wikipedia.org/wiki/Taste#Sourness I learned that sourness in fact is the taste of acidity. But why is it that bases generally taste bitter?


texts: Figuring out the volume of air trapped inside a bottle of water

texts:
I am doing a chemistry lab report on figuring out the volume of air trapped inside a bottle.  Here is the procedure:

Fill a larger container or tub about half full with tap water
Fill a 2 L plastic soft drink bottle with tap water.  Put the cap on loosely
Carefully turn the bottle upside down without spilling any water
Put the bottle into the large container of water so that the mouth of the bottle is underwater.  Remove the cap underwater
Feed the flexible tubing under the water so that one end goes inside the bottle
Put your straw into the other end of the tubing.  Do not share straws
When it is your turn, exhale into the straw to collect the air of one normal breath
With a marking pen, mark the volume of air on the soft drink bottle
Figure out the volume of the air trapped inside the bottle.  Record this volume

How might I do number 9? My proposed procedure is:

With a marking pen, mark the new volume of air on the soft drink
bottle
Record this volume, which will be smaller than the volume found in
step 8 as some of the water will have been displaced by the breath
Subtract the new volume of air from the old volume of air to find
the volume of the air trapped inside the bottle
Record this volume

Thanks!


texts: Corrosion of iron: no electron pushing mechanism?

texts:
Why does the oxidation-reduction reaction between iron, water, and $\ce{O2}$ gas to form rusts lack an electron pushing mechanism and a specific sequence of steps?
$$\ce{4Fe^0(s) + 3 O2(g) + 2n H2O(l) -> 2 Fe2O3·nH2O(s)}$$

I've noticed that most of the reactions described in undergraduate organic chemistry textbooks have detailed and widely accepted electron pushing mechanisms whereas most inorganic reactions (such as the corrosion of iron) lack electron pushing mechanisms. Why?

Also, which type of $\ce{O2}$ is involved in the corrosion of iron? The singlet excited state or the triplet ground state or doesn't matter?

$$
\underset{\text{triplet oxygen}~\ce{^3O2}}{
\ce{
·\overset{\Large .\!\!.}{\underset{\Large .\!\!.}{O}}-\overset{\Large .\!\!.}{\underset{\Large .\!\!.}{O}}·
}
}
\qquad
\underset{\text{singlet oxygen}~\ce{^1O2}}{
\ce{
\overset{\Large .\!\!.}{\underset{\Large .\!\!.}{O}}-\overset{\Large .\!\!.}{\underset{\Large .\!\!.}{O}}
}
}
$$


texts: Look for superabsorbent balls whose expansion is reversible

texts:
I am glad to find very cheap superabsorbent balls (see image below). However, I found their expansion is not reversible. The wiki entry 'Superabsorbent polymer' also says that the material will 'retain' extremely large amounts of a liquid relative to their own mass.

Is there any other superabsorbent material whose expansion is reversible? If yes, is it available as tiny balls?


texts: In a galvanic cell, why do electrons move through the wire from zinc to copper?

texts:
I understand that there is aqueous $\ce{Cu^2+}$ in this scenario which pulls on the electrons from the zinc causing the electrons to move through the wire, but how does the electronegativity of $\ce{Cu^2+}$ pull on the electrons from the $\ce{Zn}$ when they aren't "connected".

What I mean by that is the $\ce{Zn}$ metal and the wire are only connected to the $\ce{Cu}$ metal and not the aqueous $\ce{Cu^2+}$ solution. This would make more sense to me if the $\ce{Zn}$ metal was connected to $\ce{Cu^2+}$ solution via a wire rather than being connected to the $\ce{Cu}$ metal.


texts: What would an ecosystem based on reducing atmospheres be like?

texts:
I was wondering, what would it be like if instead of an oxidizing atmosphere like earth has, if an ecosystem had a reducing atmosphere instead? My professor told us that a system like that could be chemically/biologically possible. But didn't explain how. What would interaction between organisms and their reducing surroundings be like? How would these organisms survive?

I know that this means there would be an extreme lack of oxygen, and as far as I can tell, most everything on earth needs oxygen to survive. There are complex organic molecules that can be created in a reduced atmosphere, right? What are they?


texts: What is the difference between saturated and unsaturated fatty acids?

texts: Chemically speaking, what are the biggest differences between saturated fatty acids and unsaturated fatty acids? What are the effects of those differences on the geometry of the molecule? And what is the effect of that on our body?


texts: How to crystallize out reaction mixture from DMF?

texts:
Reaction was carried out in DMF, and TLC shows that the reaction has completed. But how to separate reaction mixture i.e. product from DMF?

Edit
Steglich Esterification was carried out and the product is soluble in DMF. –  user 24 (Jul 22 at 7:13)


texts: Abnormal ionisation energy trend: Group 13 and 14

texts:
I was going through some ionisation energy data, where I came across the following:

Ionisation energy order for Group 13 and 14:

B > Al ≈ Ga > In < Tl

C > Si > Ge > Sn < Pb

What could be the possible reason for reversal in trend after fourth period?
I'm not sure how accurately it can be attributed to screening effect.

An explanation would be great.


texts: How does toluene favor ortho/para in terms of kinetic and thermodynamic control?

texts: If nitration of toluene is carried out at a very low temperature, presumably the reaction would be carried out under kinetic control. During these conditions that favor kinetic products, is more ortho or para formed when compared to normal laboratory conditions?


texts: Why can't lone pairs remain in unhybridised orbitals?

texts:
I have seen that lone pairs are almost invariably counted for determining the hybridisation of an atom.

My question is why can't they remain in unhybridised orbitals.


texts: Why does copper precipitate out as a pink solid?

texts: When copper is precipitated out of a solution e.g from CuI, why does it appear pink instead of copper-coloured? Are there other situations where copper appears pink in solid form?


texts: Why is NH4OH used in Polarimetric analysis?

texts: Why is a sugar solution pre-treated with ammonium hydroxide before analyzing? And why is it specifically ammonium hydroxide instead of sodium hydroxide or calcium hydroxide?


texts: Activity of Polonium in half-time in Becquerels

texts:
I got an exercise but I don't know the exact answer.
In the catalog note of the reference source of Polonium-210 radiation with a half-life of 138 days, it was stated that one day the activity was $\pu{2 \times 10^6 MBq}$. Calculate activity after 558 days.
After my calculations the final answer was ${126468.14}$, but my professor has told me that my answer should be about 1,7 times higher.


texts:
I know that nitroglycerin is an incredibly powerful explosive due to its three nitro groups, but why is it so unstable?

What in its chemical structure makes it so sensitive to shock and temperature? Why is TNT, in contrast, so stable?


texts:
I had taken as a given that silver tarnish is a layer of silver sulfide on the surface of a utensil, and that cleaning it using a thiourea based agent like Tarn-X dissolves the sulfide layer.

However, while recently cleaning a variety of tarnished sterling and silver plated utensils, I noticed (1) the sulfureous odors emitted during the cleaning process varied considerably from one piece to the next; and (2) the tarnish on a few pieces could not be removed completely via the non-abrasive chemical process.

Knowing that many foods such as members if the cabbage and onion families have various sulfur compounds in them as flavor and aroma components, and that the sulfur containing amino acids cysteine and methionine are almost universally present in living organisms (including those we eat), I wondered: is silver tarnish a complex mixture of silver complexes that might reveal a history of the foods a person has eaten. Sherlock Holmes would know for sure.


texts: Is it possible to have an allotrope of carbon as a long unbranched chain of itself?

texts:
Is it possible to have an allotrope of carbon with formula $\ce{(=C=)_n}$?

Well, let's actually leave alone the separate question like from which "monomer" would one produce such a thing (can one actually consider it being a polymer? Or a covalent crystal?), because it seems like the most suitable candidate would be dicarbon.

All in all, might it be (under some conditions) energetically favorable for carbon to form a long unbranched chain of itself?


texts: Why is an alkenyl hydrogen more acidic than the alkyl analog?

texts:
For example, in ethene the sigma bonds are stronger overall than in ethane.

Ethene (pKa = 44)
C=C 108 kcal mol-1 (+18)
C-H 111 kcal mol-1 (+10)

Ethane (pKa = 50)
C-C 90 kcal mol-1
C-H 101 kcal mol-1

This is because the degree of s character is higher in the sp2 hybridized bonds, giving more compact and stronger bonds and thus reducing acidity.

This greater s character also makes the carbon more electron withdrawing, polarizing the bond and making the alkenyl hydrogen more acidic.

It seems counter intuitive that the stronger bonded ethene H is more acidic than the weaker bonded ethane H. I thought the increased bond strength would outweigh the increased bond polarity. It is like saying: "this bond is stronger, but it is also easier to break."


texts: Why does confinement of quantum dots result in discrete energy levels?

texts:
I'm doing a project with lead (II) sulfide quantum dots because they have optical transitions in the near infrared. I understand the simple "particle in a box" approach where confinement strengthens exponentially when the box shrinks.

What I don't get is how this confinement results in discrete energy levels? Can someone tell me how this shrinking of molecular size and confinement of the electron hole pair (exciton Bohr radius) results in discrete energy levels? Is it the electron shells being changed?


texts: How to determine the permissible values for which solution of the Schrödinger's wave equation exists?

texts:
My textbook( A Textbook of Physical Chemistry, Dr. O.P. Tandon ) says that  solution of the  Schrödinger's wave equation exists only for certain permissible values which are called eigen values.( physically possible ones).

How to determine the permissible solutions of the wave equation? Please explain.


texts: Mass chromatogram : Total Ion Chromatogram (TIC)

texts:
I am confused about what a Total Ion Chromatogram (TIC)  means. The definition I have says:

  The total ion current (TIC) chromatogram represents the summed
  intensity across the entire range of masses being detected at every
  point in the analysis.

Does this mean it is a (mixture) sample injected into a MS without the preceding chromatographic separation (as is typical in, say, a GC-MS or an LC-MS)?  Are there MS instruments sold today that are not GC-MS's or LC-MS's etc. (i.e. mass spec. sans the preceding seperation?

What's the point in doing this? Wouldn't the resultant spectrum be very noisy since it's essentially the sum over all components of a mixture of unknown proportions.

Is the GC eliminated for speed of analysis?


texts: Will acetone damage/attack anti UV coating on glasses?

texts:
My glasses collect a lot of grime in hard to reach spots. I want to dunk them in acetone to loosen the grime and clean them.

Does this put me at risk of losing the anti-UV coating? Sorry I was unable to find out what the coating chemical was.


texts: Kinetics of molecule reacting with another of itself

texts:
For the following reaction:

$$ \ce{O3 + O3 -> 3O2} $$

The rule (which makes sense for combination of two different moluecules) states that the rate constant R should be:

$$ R \propto \ce{[O3][O3]} = \ce{[O_3]^2} $$

But in the case of a combination of the same molecule this seems counter-intuitive. If you had double the amount of $\ce{O3}$, wouldn't the rate simply double (instead of increasing as the square)?


texts: Change in Entropy and Enthalpy found over a temperature range and asked to compute the change in Gibb's Energy

texts:
I was given the following question by my tutor:

"The variation of enthalpy ($\Delta H$) and entropy ($\Delta S$) in a reaction carried out at
constant pressure in the temperature range between 300 ºC and 350 ºC, are 1700 kcal and
15kcal/K respectively. Calculate the range of temperatures in which this reaction is
spontaneous."

But my book on thermodynamics says that the change in Gibb's energy for a process can only be calculated if we start and end at the same temperature (the temperature can vary during the process as heat is added or lost from the system to the surroundings, but the end points must have constant temperature and pressure.) In this question the changes in entropy and enthalpy are found over a range of temperatures where the final temperature is not the same as the initial temperature, but the pressure is always constant.

Is my tutor's question invalid, is my book wrong in saying that the temperature has to be the same at the initial and final values, or am I thinking about this wrong?


texts: Physical properties of geometric isomers

texts:
I've learnt that cis isomers have higher boiling point than the trans ones.
Why does not that rule apply on Fumaric and maleic acids?


texts: Why is 2-ethylpentane is not a valid IUPAC name, but 3-ethylpentane is?

texts: I'm currently writing all the names of alkanes having molecular formula $\ce{C7H16}$. I wish to ask why 2-ethylpentane is not a valid IUPAC name, but 3-ethylpentane is?


texts: Why does conductivity of electrolyte solutions peak at high concentrations?

texts:
I've recently done a lab about conductivity of brine over time (high concentration salt water). I passed current through salt water and measured the current over time.

The graphs I got showed that current through the solution rose to a peak before falling, and it looks almost like the positive x-value half of a quadratic function. I understand it falls because resistance increases with the progress of the redox reaction, but what causes the peak at the top?


texts: How many significant digits are appropriate when one or more digits are eliminated (during subtraction)?

texts:
Say, for example, $50.0-49.6=0.4$. Does this result have $1$ significant figure, or $3$ (as in the data: $50.0$ and $49.6$)?

Had it been $50.0-4.6$, it is understood that the answer is $45.4$, by the rules of significant figures. How do I apply them in the "$50.0-49.6$" case?

This question deals with $50-49.6$; so a related but not the same question.


texts:
Could anyone tell me how I would go about calculating the pH of 100.0 mL of 0.100 M $\ce{H2NNH2}$ ($K_\text{b} = 3.0 \times 10^{-6}$).

Furthermore, how would this pH change when 20.0 mL of 0.200 M $\ce{HNO3}$ is added to the solution?

I’m not looking for only an answer, but rather the general method to solve these types of problems

Just to include what I’ve tried:

I first thought that (for the initial solution) $\mathrm{pH} = 14 - \log(\sqrt{K_\text{b} [\ce{H2NNH2}]})$, but that doesn’t seem to be the case.


texts:
I was studying how chirality influences the diastereoselectivity of reactions when I saw 1,4-dihydro-1,4-epoxynaphthalene.

I determine chirality by looking for C with 4 different groups. I see 2 C that accomplish this requirement (sp3 C bond to the O) but both are in a rigid structure, so I can't tell if they're (or not) chiral at all. If they are, can I use the same rules to determine R or S?


texts: Synthesis of 2-benzylcyclohexan-1-ol from cyclohexanone

texts:
There are no conditions given and a mechanism is required.

I first thought it could be along the lines of Claisen rearrangement but that needs an aromatic ring. Since the Claisen rearrangement can't be used I considered a ($\mathrm{S_N2}$) reaction of benzyl bromide by the alpha carbon followed by reduction of the carbonyl.


texts: Reaction of alkyl halides with potassium cyanide

texts:
Its given in my book that alkyl halides react with alcoholic potassium cyanide to give alkyl cyanide through $\mathrm{S_N2}$ mechanism.

But why do we need to use alcoholic $\ce{KCN}$ (potassium cyanide dissolved in alcohol)? My understanding is that polar protic solvent favours $\mathrm{S_N1}$ over $\mathrm{S_N2}.$


texts: Shift in the position of equilibrium by a catalyst to favor the forward reaction

texts:
We were looking at the factors that affect dynamic equilibrium today. The teacher explained how catalysts only affect the rate at which dynamic equilibrium is achieved, and not its position.

My question is: will a catalyst specific to the forward reaction shift the position of equilibrium to favour the forward reaction? Or will it, still, only affect the rate?


texts: Effect of transition energy gap and frequency of microwave on appearance of CW EPR spectrum

texts:
Consider continuous-wave EPR for species with only one unpaired electron in the following argument.
The interaction energy in the presence of external magnetic field of strength B is given by
$$E = Bg\mathrm{m_s}\mu_\mathrm{B} - Bg_{\mathrm{N}}\mathrm{m_I}\mu_\mathrm{N} + a\mathrm{m_sm_I}$$
Taking the specific selection rules for EPR transition into account,
$$\Delta E = Bg\mu_\mathrm{B} + a\mathrm{m_I}$$

Just to check my understanding.

The figure below illustrates splitting of states in the presence of magnetic field, when the only unpaired electron is coupled to a spin-half nucleus$^{[1]}$ :

assuming $a$ and nuclear $g$ to be positive and isotropic.
Using the last equation above,
EPR I: $\Delta E = Bg\mu_\mathrm{B} -\frac{1}{2}a$
EPR II: $\Delta E = Bg\mu_\mathrm{B} +\frac{1}{2}a$
So EPR II transition energy gap is bigger. Then shouldn't the EPR II signal appears at lower field in the EPR spectrum? Logically, if the energy gap is already big, to make the gap coincides with the frequency of incident microwaves, the external magnetic field only need to be increased relatively little. But the opposite is shown in the EPR spectrum inserted. Did I understand the concept wrongly?

This second figure encountered in the same reference book$^{[2]}$ baffles me:

The figure shows that, when the frequency of incident microwaves is increased, the separation between two lines in a multiplet also increases. Doesn't that imply the hyperfine splitting constant will also change? But I read hyperfine interaction is field-independent.$^{[2]}$

Chechik V, Carter E, Murphy D. Electron Paramagnetic Resonance. Oxford: OUP Oxford; 2016.
1 page 12
2 page 36


texts:
In the reaction involving 0.1 g of calcium nitrate and 1.5 g of sodium phosphate, what is the number of moles of the limiting reagent?

Here is what I have so far:

Balanced equation:
$$\ce{3Ca(NO3)2 + 2Na3(PO4) -> Ca3(PO4)2 + 6NaNO3}$$

$\ce{Ca(NO3)2}$ has MW = 164, mass = 0.1 g and determined moles using n=mass/MW = 0.000609
$\ce{Na3PO4}$ has MW = 164, mass = 1.5 g and determined moles using n=mass/MW = 0.0091496

I was able to identify limiting reagent by:
g $\ce{Ca(NO3)2}$ --> n $\ce{Ca(NO3)2}$ -->n $\ce{Na3(PO4)}$--> g $\ce{Na3(PO4)}$
    0.1 g --s1-> 0.000609 --s2--> 0.000406 -s3--> 0.06658 g

S1 = n = 0.1/164 = 0.000609
S2 = want/have x $\ce{Ca(NO3)2}$ = 2/3 x 0.000609 = 0.000406
S3 = m = nxMW = 0.000406 x 164 = 0.06658g

Therefore as all $\ce{Ca(NO3)2}$ did not use all the $\ce{Na3(PO4)2}$ that means the $\ce{Ca(NO3)2}$ is the limiting reagent.

Now to answer the question. What is the number of moles of the limiting reagent. I am not sure if it is 0.000609 OR 0.001828 (which is moles multiplied by the stoichiometric coefficient, which is 3).


texts: Why does salty water make hard boiled egg shells more fragile?

texts:
Boiling eggs in salty water rather than regular water makes the salt react with egg shells making them more fragile. My guess is that it's either sodium or chloride reacting with the calcium in eggs. Can someone please explain what is going on in there, and why the reaction makes the egg shell more fragile?

Here's an example YouTube video this effect is mentioned.


texts: Non-equilibrium gas cap above saturated liquid-gas solution

texts:
If I could somehow instantaneously replace the $\ce{CO2}$ gas cap at the top of a soda bottle with a different gas, say $\ce{N2}$, would the bottle pressure increase as a result of the $\ce{CO2}$ de-gassing into the gas cap space?

I've come to this question because I am trying to design a method to measure the dissolved $\ce{CO2}$ content of a water liquid stream. The method involves exsolving the $\ce{CO2}$ into either an evacuated or $\ce{N2}$-charged vessel and measuring the pressure change to correlate dissolved $\ce{CO2}$. By Henry's Law the pressure in an $\ce{N2}$-charged vessel should increase as a result of $\ce{CO2}$ exsolving since the $\ce{CO2}$ partial pressure above the liquid is zero, should it not?

More clarification (hopefully) for those who have marked the question as unclear:
Let's say I have a closed system (soda water in a bottle as an example) with a $\ce{CO2}$ gas cap at a pressure of 10 psig. The gas cap, like in a soda bottle, is small relative to the total volume, say 5%. The liquid (water) in the bottle is fully saturated with dissolved $\ce{CO2}$. Now let's say I somehow instantaneously replace the $\ce{CO2}$ in the gas cap with another gas, say $\ce{N2}$, at the same pressure (10 psig). The system is still closed (we've magically replaced that gas). Will the bottle pressure increase as a result of the $\ce{CO2}$ in solution exsolving into the gas cap space, since the partial pressure of $\ce{CO2}$ there is zero? This of course is hypothethical, but it would have some similarity to how the dissolved gas content of liquids drawn (pumped) from deep within a well could be measured.

Thanks


texts: In Bohr's model what is angular momentum in the lowest orbital?

texts:
Angular momentum is given by: $n\frac{h}{2\pi}$ where $n=1,2,3...$

And angular momentum is also given by: $\sqrt{l(l+1)}\frac{h}{2\pi}$

By the first equation angular momentum should be $\frac{h}{2\pi}$ but by the second it should be $0$.

And if you say that in first equation $n$ is also $0$  then first radius of hydrogen should be $0\pu{A^\circ}$ instead of $0.53\pu{A^\circ}$.


texts: Mechanism of heterocyclic ring formation

texts:
I saw a question here about the mechanism for a heterocyclic ring formation: What is a reasonable mechanism for the following reaction?. I tried solving the mechanism but I am missing something. Let me explain my reasoning:

This is the reaction:

I started protonating the nitrile N, followed by the attack of the cyclic N to the terminal alkyne carbon. Then I couldn't figure out what happens next, so I assumed the triple bond attacks a proton and forms the acrylonitrile intermediate (I am 99.99% sure this is not what happens). Then the exo N attacks the nitrile carbon and form the 6-membered ring, followed by a proton exchange between the imino nitrogen and the protonated cyclic amino group (again, I feel this is ridiculously wrong). The lone pair on the cyclic amino group form the double C=N bond, however, I still end with a protonated N that is not in the product.

Can someone explain to me what I am missing?


texts: How to define axes if all rotation axes pass through the same number of atoms?

texts: I was wondering how one can define the axes for a molecule with several equal axes of rotation, all of which pass through the same atom. I know that the $z$-axis is usually defined as the principal axis, or the axis passing through the most atoms if none are equal. But in the case of, say, the $D_{2h}$ molecule below (assuming all R are the same), how do you define the axes? All 3 axes of rotation pass through only one atom, the central Cu.


texts: I've dissolved all 3 metals together in aqua regia due to them being mixed together as $\ce{Pt}$ black, $\ce{Pd}$ black and gold. I isolated the gold with no problem using sodium metabisulfate, but I am struggling to separate the $\ce{Pt}$ and $\ce{Pd}$. Any suggestions? I have tried sodium chlorate for palladium isolation and ammonium chloride for platinum isolation, none had worked for some reason. Any tips would be amazing.


texts: The Salt Effect stops working in extreme cases?

texts:
I and three friends did an experiment where we investigate the salt effect, also known as the uncommon ion effect.

The specifics are that we made a $\pu{1L}$ solution saturated with $\ce{CaCO3}$ and $\ce{NaCl}$, filtrated it, and measured the $\ce{Ca^2+}$-ion concentration and compared it with a pure solution saturated with only $\ce{CaCO3}$. The $\ce{Ca^2+}$-ion concentration was measured using AAS.

We expected the solution with the $\ce{NaCl}$ to have more $\ce{Ca^2+}$-ions than the one without, but that wasn't the case. The opposite was true. The concentration dropped by about 15% when the salt effect was supposed to occur.

Is it possible that there were so many $\ce{Na+}$ and $\ce{Cl-}$ ions that there weren't enough $\ce{H2O}$ molecules anymore to surround the $\ce{Ca^2+}$ and carbonate ion, causing their concentration to drop? Or is it far more likely that we simply made a mistake somewhere.


texts:
Can imines be catalytically hydrogenated? According to the DEA this appears to be possible. However I cannot find any other references to catalytic hydrogenation of imines anywhere else.

http://thedea.org/synthesis.html


texts: When looking at an ligand, how do I know its denticity? For instance, I know that though there are 2 lone pairs in $\ce{H2O}$, its denticity is only 1 due to geometrical reasons as the 2 of them can't be facing the metal ion at the same time. However, when I look at other ligands, especially unfamiliar ones, I cannot determine their denticity.


texts: why distillation of mercury is done at low pressure?

texts: While reading about extraction of mercury from it's cinnabar ore (HgS), it's purification required distillation due remove impurities like Au, Ag, etc. This distillation was done at low pressure. Why is it done at low pressure?


texts: Does aldol condensation give different products in different conditions?

texts:
I know the mechanism of aldol condensation and general method to determine products in crossed aldol reactions, or reactions between dissimilar molecules. But the following statement in my class notes baffles me:

  In presence of a base (alkaline medium) the $\alpha$ hydrogen of the lower aldehyde is more acidic and hence is removed in the first step, while in presence of an acid, the $\alpha$ hydrogen of the higher aldehyde is more acidic and hence migrates.

According to this, on reaction of propanal with ethanal, basic medium yields 3-hydroxy pentanal while acidic medium yields 3-hydroxy 2-methyl butanal.

Why is this statement true (if it is)? And can aldol condensation proceed in an acidic medium, since the presence of the base is necessary for the removal of the slightly acidic $\alpha$-hydrogen to start the reaction?


texts: Comparison of energy release from different types of fuels

texts:
I've recently been reading about the different amount of energy release for different types of fuels/hydrocarbons.
Anyways, I was wondering why butanol would release more energy (kj/mol) than methanol? I'm guessing the same theory applies for methane vs butane?


texts: What is the electrochemical reaction of this battery?

texts:
I've watched a YouTube video "Soda Can Battery - Power From Trash - DIY Project" by Source Port Services. I understand that the anode can be oxidised, but what is the reduction reaction at the cathode? They are using a salt water solution $\ce{Na+}$ $\ce{Cl-}$ and a copper cathode.

$$
\begin{array}{cc}
\hline
\text{Half-reaction} & E^\circ/\pu{V} \\
\hline
\ce{Cu^2+ + 2 e− <=> Cu(s)} & 0.337 \\
\ce{Na+ + e- <=> Na(s)} & -2.71 \\
\ce{Al^3+ + 3 e− <=> Al(s)} & -1.662 \\
\hline
\end{array}
$$

Thus we can see that the aluminium is oxidised, but there are no $\ce{Cu^2+}$ ions to be reduced also $\ce{Na+}$ reduction would lead to a negative $E_\mathrm{cell}$ standard and a positive Gibbs energy. Is it an air cathode where $\ce{O2}$ is being reduced?


texts: Why doesn't baking soda react with the solid form of an acid?

texts:
Baking soda (powder) will react when it comes into contact with a solution of citric acid crystals dissolved in a liquid medium such as water. But why doesn't baking soda react when mixed with a solid form of an acid (citric acid crystals)? Why is water needed for a reaction to occur?

Baking Soda (Solid) + Citric Acid Solution (Liquid) = Fizzy Reaction

Baking Soda (Solid) + Citric Acid Crystals (Solid) = No Reaction (??)


texts: How is the cavity of a cyclodextrin chiral?

texts: I am studying the host-guest chemistry of cyclodextrins with achiral aromatic molecules, and I found out that a useful way of studying them is by induced circular dichroism spectroscopy. This technique is used by taking an achiral molecule and placing it in a chiral environment to induce a CD signal. Apparently, the cavity of a cyclodextrin is chiral, but for the life of me I cannot see HOW it is chiral. I know the glucose molecules the ring is made of are D-glucose, but I still see mirror planes in the structure, and I cannot figure out how the cavity is chiral! Help??


texts: Does humidity increase oxygen levels in the air we breathe?

texts:
I'm testing a new form of meditation and it requires certain breathing exercises in order to generate a specific effect on the nervous system; I have noted significant differences in the results being generated based on the setting in which i practice the exercises... here is some data, hopefully you can help me put all of these pieces together, id like to base this off of solid data so i can present my findings for further evaluation.

QUESTIONS:Why do the effects of the technique increase in different settings?

Am I breathing in more O2 based on the environment i do the exercise?
Does high humidity increase the levels of oxygen in the air?
Or are other factors such as temperature & pressure contributing to the effects?

SETTING:
Steam Room:
- 100% humidity, temperature
- HIGH heat
- Pressurized steam room

Normal Room Temp Setting:
- "Normal" Dry Colorado Air (Assumed approx 78% nitrogen, 21%o2, 1% misc)
- Normal home setting

-the "effects" are intensified when performed in the sauna as compared to normal, dry Colorado air, i am trying to pin point why this might be.

Hopefully this is clear, thanks.


texts: Diffused Layer ion in Electrix Double Layer

texts:
When KI is added to AgNO3 soln, so AgNO3 is in excess, collidal particle is AgI:Ag+ with diffused layer of I-, Why is the diffused layer not of NO3- when the anion in excess is NO3-?
If we had KI in excess in the above scenario, we get AgI:I- with diffused layer of K+ which fits logic of the ion in more concentration having more probablity of being the diffused layer.

(preferential adsorbtion of ion common to lattice for primary layer doesn't seem to factor in diffused layer?)


texts: Determining the structure of N2O using hybridization

texts:
I have learnt how to determine the structure of molecules where only the central atom is hybridised like $\ce{ClF3}$, $\ce{C2H2}$, $\ce{PCl5}$, but in $\ce{N2O}$ it seems as though both nitrogen and oxygen have hybrid orbitals. How do I find the hybridization of oxygen and nitrogen in $\ce{N2O}$ and finally determine its structure?

Research Effort: I watched some lectures on hybridization, but all of them included cases in which only the central atom had hybrid orbitals. I also read the topic in my book but this issue wasn't addressed there too.


texts: Is there proof that the exact exchange correlation functional is an analytic function?

texts:
Mathematics show that some problems cannot be solved analytically. Could this be true for the exact exchange correlation functional?

Most textbooks state that the form of the exact exchange correlation functional is unknown. It is said to be an unknown mathematical object. Does this mean that said functional is an analytical function? And if so, what is the proof that shows that the functional is analytical?


texts: ClO2 chlorine dioxide how to know if it is still active or not ? by color ? by smell ? by reaction?

texts:
my wife have ClO2 tablet form. she dilutes it to be put inside mister. each time she make the dilution:
package instruction:
1 tablet to 1 liter water => 100ppm ClO2
*we name this 100ppm as "original soln"
she takes 100ml from the "Original soln" to make 1 liter of solution to do household cleaning.
may i know how much ppm is the final solution that she used to do cleaning ?
i think should be 10ppm solution , right ?  10% mix.
thx


texts: Comparing acidity in 3,4-dihydroxyfuran-2(5H)-one and 2,3-dihydroxycyclopent-2-en-1-one

texts:
I have two compounds with two hydrogens namely (a),(b),(c) and (d). I have to compare the acidity of the following hydrogens.

My approach:

I removed the hydrogen atoms one by one and compared the stabilities, as there are most resonating structures for (a) it will be most stable (most acidic too). Then followed by (b), (c) and (d).

But the answer is given different without any further explanation. Does anybody have the right approach to tackle these type of questions?


texts: Temperature dependence in absorption spectroscopy

texts:
What are some qualitative guidelines one should know regarding the temperature dependencies (of the gas and maybe the radiation, if that makes sense) for an absorption spectroscopy measurement?

How does, for example, a rise in temperature influence the absorption lines?


texts: Irreversible process (Isothermal and Adiabatic)

texts:
How exactly would we define an irreversible change for an isothermal process? Why can we say what the external pressure will remain constant? Please give an example.

Also, why can we not define both reversible and irreversible processes for adiabatic process simultaneously?
$$\Delta E_\mathrm{rev} = \Delta W_\mathrm{rev}$$
$$\Delta E_\mathrm{irrev} = \Delta W_\mathrm{irrev}$$
I got that if these both take me to the same point then $\Delta E$ will be same, but why must $W_\mathrm{rev}$ and $W_\mathrm{irrev}$ be different?


texts:
I am currently exploring the synthesis of xRNA, which contains benzo-expanded purine and pyrimidines. I have found this paper which deals with exactly this subject, and provides the following synthetic pathway for the xA ribonucleotide.

Unfortunately, the first 5 synthetic steps are omitted from the paper, and are likely to be found in one of the following three papers, none of which are publicly available.

1. 2. 3.

Nonetheless, I am interested in any synthetic pathway which will lead me from the first to the second molecule shown above. I understand the presented material, but as an undergraduate cell biologist, I am a little rusty on my synthetic organic chem.

EDIT: The first thing that came to mind was the condensation of a biscarbonyl electrophile and bisamine nucleophile like in pyrimidine synthesis.


texts: What is the name of cyclopropane with a double bond?

texts: I was drawing out all the isomers of $\ce{C5H8}$ and came upon two structures of cyclopropane attached with double bonds. The group is neither a methylene nor an ethyl... what is it? What are the names of these two molecules?


texts:
How do you apply Wade's rules to Zintl polyhedral cluster anions ?

For example, I believe $[\ce{Bi_3}]^{3-}$ is a triangle. My approach to justify would be:

5 electrons per each Bi atom
3 electrons for the charge
18 total electrons

$18 = 4\times3+6 \therefore$ arachno cluster: trigonal bipyramid ($n+2$ polyhedron) with two missing vertices $\therefore$ linear.

If it was a nido cluster $(4n+4\ \ce{e-})$, then it would be a tetrahedron with one missing vertex $\therefore$ a triangle. Am I mistaken about the observed geometry or is my method incorrect?


texts: Whenever I look up the Lewis structure for $\ce{NH2^-}$, it shows 8 electrons. Now I understand the octet rule, but I still don't see how an electron can just appear from nowhere. There are 5 valence electrons with Nitrogen, and 2 more, one from each hydrogen. I know that formal charge is calculated by subtracting the nonbonding electrons and number of bonds (or number of electrons in bonds divided by 2), but why is the formal charge of $\ce{NH2^-}$ "-1", and why the extra electron out of nowhere? Because 5 - 3-2 is still just 5


texts: What happens when an alkyne reacts with ammoniacal Cu2Cl2?

texts:
My text book provided me with 2 reactions concerning alkynes (Specifically Terminal Alkynes).
The first one was the dimerisation of an alkyne on passing it through ammoniacal $\ce{Cu2Cl2}$.
All was fine until I encountered the next reaction.
It was a test to distinguish between terminal alkynes and other alkene and alkynes.
It involved the fact that treating a terminal alkyne with  ammoniacal $\ce{Cu2Cl2}$ would result in the alkyne forming a red precipitate as copper replaces hydrogen of one of the terminal hydrogen.
However now I was confused. Which of these reactions actually happens? Or are there specific conditions for each of these reactions that my text missed out?
Please help me in this aspect.


texts:
What are possible products from these two anion analyses?

The nitrite test, reacting diphenylamine with a nitrite:

$$
\ce{(C6H5)2NH + NO2- -> ?}
$$

The sulphite test, reacting potassium permanganate with a sulphite:

$$
\ce{KMnO4 + SO3^{2-} -> ?}
$$


texts:
Adding an inert gas will not affect Q if that reaction is held at a constant volume. But, if the reaction is held at constant pressure, then adding inert gas will change Q bc the partial pressures of the gases will change.

I don't understand this. If the reaction is held at constant pressure, this means that you changed the volume when adding the inert gas. Wouldn't the partial pressures of all the reactants change by the same factor, so Q wouldn't change?


texts: What are the black flakes that appear in the solution?

texts: I put an iron nail into a 0.2M of Hcl solution in a conical flask, after 5 days, there are a lot of black flakes in the solution, what are the black flakes?


texts: How do I determine stereochemistry of the product

texts:
When pure (L) lactic acid is esterified by racemic-2 butanol then what is the nature of the stereoisomers so obtained i.e. whether they are diastereomers or enantiomers.

I studied the mechanism of esterification but I didn't find anything regarding the stereo isomerism that can affect the formation of the product.Any ideas.Thanks.


texts: Does a change in partial pressure for a gas-solid reaction, changes the equilibrium?

texts:
This is my reaction, $$\ce{Cd (g) + 1/2 Te2 (g) -> CdTe (s)}.$$
Considering the solid CdTe, $$K = P_{\ce{Cd}}^\mathrm{Eq}\cdot \left(P_{\ce{Te}}^\mathrm{Eq}\right)^{\frac{1}{2}}$$

I only have elementary knowledge on chemistry. I know that the equilibrium values of pressure are dependent on temperature. My question is - does increasing the partial pressure of one of the elements only changes the equilibrium pressure? If yes, for one or both?


texts: Negative ions and health: pseudo science or something more?

texts:
Over the last year or so I've heard from friends, who subscribe to holistic medicine, talk about negative ions, saying that they are good for your mental/physical health. Being the only one among them with a chemistry background, I was suspicious when i heard this. Below are examples I've seen that use negative ions in a medicinal context:

Negative Ions Purify Air

  Virtually all particles in the air have a positive charge, while negative ions have a negative charge. In which case, negative ions and particles magnetically attract to one another. When there is a high enough concentration of negative ions in the air, they will attract to floating particles in large numbers. This causes the particle to become too heavy to remain airborne. As a result, the particle will fall out of the air, and will then be collected by normal cleaning activities, such as vacuuming or dusting. - Ion-Imbalance

Negative Ions from the Beach

  You may have experienced the power of negative ions when you last set foot on the beach or walked beneath a waterfall. While part of the euphoria is simply being around these wondrous settings and away from the normal pressures of home and work, the air circulating in the mountains and the beach is said to contain tens of thousands of negative ions -- Much more than the average home or office building, which contain dozens or hundreds, and many register a flat zero. -WebMD

Apparently they Help You Breath

  People travel from all over the world to visit salt mines like the ones found in the Himalayas, Austria, and Germany. In Germany, the hot salt springs are so revered, companies often send overworked employees there to rejuvenate.
  Why are the salt mines so beneficial?
  Quite simply... the very dry, negative ion environment of a salt mine is key.
  Well... even if you're not able to travel to Asia or Europe to take advantage of salt mines, you can still take advantage of these negative ions to help improve the air you breathe. The solution involves pure Himalayan crystal salt...- Mercola

Well it's not surprising that two thirds of the above sources are trying to sell products (salt lamps, air purifiers).

Since we're dealing with ions here, I figure the chemistry world must have some sort of input. What's the chemical or biochemical support, or the evidence against, for the above claims? If there are negative ions present from waterfalls/oceans/salt rocks, what ions are we talking about?

To address @dissenter, one of these sites claims tourmaline is a source of negative  ions...


texts: What can I use to make evaporating fake snow?

texts: I want to create the effect that it's snowing in my living room. Ideally, there would be a chemical or substance that would be able to be sprayed out of a snow machine or pressurized canister etc. This substance would start off solid and would have a chemical reaction with the air that would cause it to evaporate into thin air, a là Harry Potter. Or even if the reaction took a couple hours it would be ok.


texts: Methanol-water mix freezing points - clarify contradictory online data > 60% w/w?

texts:
Extending an exploration of windshield washer-fluid choices to freezing points of methanol-water mixes, all web-sources located agreed to within a couple of degrees from 0-60% w/w, yet above this proportion (and below 100%), repeatedly came across conflicting data (which fell into three groups). (Yes, the disagreements are all outside the range of winter driving on this planet - except perhaps for around Vostok Station...)

w/w
various graphs by eye
various tables
engineering toolbox table
all˚C

60%
- 71
- 71
- 71
˚C

70%
-102
-137
- 82
˚C

80%
-116
-143
- 87
˚C

90%
-108
-146
- 90
˚C

100%
- 96
- 98
- 98
˚C

examples of sources for above data:
http://www.methanol.org/wp-content/uploads/2016/06/FreezingPointsMethanol-WaterSolutions.pdf    graph
https://patents.google.com/patent/WO2011153147A1/en table (~ 1/3 way into the document)
https://www.engineeringtoolbox.com/methanol-water-d_987.html        table
Thanks for any comment.


texts: How to calculate the energy to dissociate a bond into neutral atoms?

texts:
I am self studying chemistry through MiT ocw 5.111 . On practice exam 2 problem 2 there is a question which states the following

    element           ionization energy          electron   affinity
    Potassium(K)      418 kJ/mol                 48 kJ/mol
    Fluorine(F)       1680 kJ/mol                328 kJ/mol
    Chlorine(Cl)      1255 kJ/mol                349 kJ/mol

  (a) (12 points)   The ionic bond  length for KF is 0.217 nm. Calculate
  the energy (in units  of kJ/mol required  to  dissociate  a single
  molecule of KF into the neutral atoms K and F, using information
  provided above. For this calculation, assume that the potassium and
  fluorine ions are point   charges.

I proceeded to calculate the bond dissociation energy using the following formula $U(r)=\frac{z_1z_2e^2}{4\pi\varepsilon_0r}$  from which I obtained a dissociation energy of $-640$ kJ/mol. Then left with two ions F$^{-1}$ and K$^{+1}$.
 I went on to determine their ionization energies and electron affinities respectively.

To make F$^{-1}\to$ F + $e^{-}$ an electron must be lost thus warranting an ionization energy of $-1680$ kJ/mol and. To make K$^{+1}$+ $e^{-} \to$ K and electron must be gained thus referring to the election affinity of K of $18$ kJ/mol. When equated as (Energy Required - Energy Released) I arrive at

 (Dissociation Energy + Ionization Energy) - Electron Affinity = (-640 kJ/ mol - 1680 kJ/mol) + 48 kJ/mol = -2272 kJ/mol required

However I see in the answer key this is incorrect could someone guide me as to where I am going wrong here thank you.


texts: What is the cause for the difference in pH between NaCl and Ringer Lactate

texts:
Reading this article, I came across a passage which got me to think of this question:

"Normal saline contains approximately $\pu{154mM}$ of each $\ce{Na+}$ and $\ce{Cl-}$ with average pH of 5.0 and osmolarity of $\pu{308mOsm/L}$. LR solution has electrolytes $\pu{130mM}$ of $\ce{Na+}$, $\pu{109mM}$ of $\ce{Cl-}$, and $\pu{28mM}$ of lactate. The Average pH of LR is 6.5 and is slightly hypo-osmolar with $\pu{272mOsm/L}$. 6,7"

Regular $\ce{NaCl}$ solutions should have 7 as a pH, yet this solution is 5.
A lactate ringer which has a similar composition to regular $\ce{NaCl}$ is 6.5.

I thought that the pH of 5 doesn't have anything to do with the $\ce{NaCl}$ but with the reaction of blood $\ce{CO2}$ with the water in the $\ce{NaCl}$ solution lowering the pH, but clearly that was wrong.