texts: Why does Pb normally have an oxidation number of +2?

texts:
Why does $\ce{Pb}$ have an oxidation number of $2^{+}$ while carbon and other elements in the same group have an oxidation number of $4^{+}$?

Furthermore, why doesn't carbon also have a $2^{+}$ oxidation number, as can't it also give up its two electrons in the p-suborbital to have a full s-suborbital? Why does it prefer to gain four electrons instead to fill the p-suborbital?

Similarly, why can't $\ce{Pb}$ gain four electrons just like carbon instead of giving up two?

Finally, doesn't this mean that $\ce{Pb}$ forms ionic bonds? Why doesn't carbon do the same?


texts: Is there any book where specific heat capacities are given?

texts: I want to find the value of the specific heat capacity of aluminium nitrate nonahydrate, in order to calculate mixing effects in a chemical reaction. I am looking for a source, such as a book or link to an online PDF, which would be appreciated.


texts: Reversibility of the binding of carbon monoxide to haemoglobin

texts:
I recently learnt the basic mechanism of haemoglobin: oxygen forms coordinate bonds with the $\ce{Fe^2+}$ ion in haem groups, and this reaction is reversible to allow oxygen to be released. I also learnt that carbon monoxide does the same thing as oxygen, however, this reaction is said to be irreversible due to larger bond strengths etc. meaning that it can't be released.

What isn't clear to me is what happens to carbon monoxide if it does bind to a haem group. If the reaction is irreversible, then how is carbon monoxide removed from the body if you were to breathe it in?


texts:
Time and time again textbooks and websites state how wonderful it is that the deviations of Hydration Enthalpies from a linear relationship can be accounted for by the CFSE parameter for the particular complex.

My question is what is the mechanistic explanation in terms of water and the metal ion interacting ? Why does CFSE lead to much more negative hydration enthalpies ?

EDIT : A simplie overview of what I'm talking about : http://sst-web.tees.ac.uk/external/u0000892/Web%20thing/CoordChem/CFSE5.htm


texts: How to interpret a singlet term symbol for an s¹p¹ configuration?

texts:
I am interested in the $^1P_0$ singlet state of $\ce{Hg}$ ($\ce{5d^10 6s^1 6p^1}$).

I interpret this to be the two following electron configurations below, because for an $S = 0$ state the two electrons have to have different spins.

Are these two both a valid state? Do they both have the same energy? How would I tell if it's only one of them?


texts: Detect the presence of non stereochemically annotated atoms in mol files

texts:
I'm facing a problem now and I don't know where to start from. I'm treating databases in which there are mol-files that have stereo-chemical carbons, which, sometime, are not annotated as being R/S or Z/E in the stereochemistry column.

I would like to be capable of finding all asymmetric carbons to check if the stereochemical center is annotated or not. Does anyone knows of a software, a library or elegant piece of code to figure out this problem. I'm working with RDkit (Python) and I can access to chemaxon if needed.


texts: Mass spectrometry: systematic mathematic transformation for calibration

texts:
Given a NaI mass calibration in the m/z 300-2000 range on a QTOF instrument as shown below:

and given any uncalibrated mass spectrum that has been measured with the same instrument settings. What is a general mathematical transformation that calibrates the mass spectrum to the NaI calibration. masses of the NaI clusters are of course known, i.e.

Overall, it seems the masses always deviate by about 0.1 m/z by being always a little bit too high than the reference in this case.

My question now is, how a simple mathematical approach could look like to calibrate mass spectra using the NaI reference. The simplest approach would be to just create a peak list out of the NaI spectrum, i.e.
472.8, 622.7, 772.6, ..., 1971.7
and perform a linear fit against the calculated NaI masses, i.e.
472.7, 622.6, 772.5, ..., 1971.6.

Which looks like this:

Where the slope of the line is 1.00003175282 and the intercept is
-0.153462368663.

Because the overall mass range is high, while the variations in mass are of course small, this gives the ridiculously high $R^2$ of 0.999999999556.

Now I could just apply this linear function

f(m/z) = m/z * slope + intercept

to uncalibrated mass spectra. Is this simple approach viable? Because it does not take into account that the mass deviation might be different depending on the m/z region. From your experience, is it likely for a QTOF-instrument to show significantly different mass deviations in different mass regions? Would it be better to make a "polygonal chain" and divide the overall mass range in separate regions instead?


texts: Confusion on light absorption by electrons

texts:
Say an atom's electron can jump between energy levels n = 2 and n = 3 with x joules of energy. If a light beam of frequency f provides x+y joules (where y is a positive number), that is, more than enough to excite the electron to the next energy state but not enough to reach n = 4. The electron should accept this quantized quantity of energy and then
later emit it. On emission spectra, however, the extra "y" J of energy are not accounted for, only the minimum value x to transition between n = 2 and n = 3 (the energy difference between orbital levels). Where, then, does the extra y energy go? It cannot simply "not be absorbed" because it exists along with the rest of the energy, x, in quantized packets. If it contributes to raiseing the KE of the electron, it must at some point be emitted, but that would give way to an incorrect value on the emission spectra. What am I missing?


texts: What are the oxidation states of galium and arsenic in GaAs semiconductor?

texts: According to the book I'm referring to ("S.M. Sze Semiconductor Devices"), gallium has an oxidation state of +1 and arsenic has that of -1. This should not be possible as each of these elements forms a covalent bond with four atoms of the other element (structure of GaAs semiconductor). For that to be possible, shouldn't both of them have one electron in $\ce{3s}$ subshell and three electrons in $\ce{3p}$ subshell?


texts: What are the other end products in sulfur oxoacid formation?

texts:
I got this reaction and I can't figure out the end products
$$\ce{SO2 + S + CaO + Na2SO4 -> Na2S2O3 +  ~?}$$
I am guessing some calcium sulfur salt should form, but which one?


texts: Show that there can be 18 electrons in a "g" subshell

texts: I'm learning about quantum numbers right now, and I can't figure out how to calculate the number of electrons in each shell without memorizing it. Is there a formula to find the possible numbers of electrons in the s, p, d, f, and other (theoretical) subshells? If it helps, this problem is put under the "Quantum Numbers, Exclusion Principle" topic.


texts: Grignard alkoxide intermediate as starting material for ether or ester synthesis

texts:
I'm having a Grignard reaction between a ketone or aldehyde with RMgX in mind.
The average workup uses water to hydrolize the intermediate alkoxide. But could this intermediate be used without isolation to prepare an ether or ester? For example by simple addition of RX, tosyl chloride, acetyl chloride ...

I don't know if the compoud is reactive enough, however. But it is an alkoxide and you probably wouldn't even need additional base for e.g. HCl scavenging. Maybe someone here knows more about the reactivity or maybe there are some literature examples?


texts: While reading about hydrogen on Wikipedia, I read that hydrogen has a purple glow in its plasma state. This confused me because although hydrogen is present in its plasma state on the sun, the sun doesn't appear purple to us (rather, it is yellow-orange). Why is this the case?


texts: Dilution of whisky – the molecular perspective

texts:
Not a chemist. I'm trying to understand this abstract. In particular:

  We found that guaiacol is preferentially associated with ethanol, and, therefore, primarily found at the liquid-air interface in mixtures that contain up to 45 vol-% of ethanol.

So guaiacol is amphipathic which means that is a largish molecule in which one end is hydrophilic and the other hydrophobic (or lilophilic). At least that's my understanding from Wikipedia. So, how did they arrive at the "therefore primarily found at the liquid-air interface" part? At the surface the molecule attaches one end to the alcohol and one end to the air?

Sorry for any naive interpretation of chemistry on my part.

Edit:
Just run across this article discussing the matter.


texts: What is the keto form of a hexahydroxybenzene?

texts:
159. The keto isomer of the following compound is:

The answer has been given as (c). I cannot seem to understand why is it not possible for the keto form to only have one OH convert into keto form shown below:


texts: Materials that resist adhesion with molten glass even when hot

texts:
I'm looking for ways to manipulate molten glass with (e.g. bending a heated glass tube).

This article mentions that oxides tend to adhere, hence molten glass to heated stainless steel.

What materials could I use to manipulate hot glass? Perhaps I could coat the glass or instrument doing the manipulation with some sort of powder or liquid?

The glass is soda lime glass which has a transition temperature of 550 degrees C, so the temperature it needs to cope with will be a fair bit above that.

Thanks


texts: Why isn't the scandium(2+) cation isoelectronic with potassium?

texts: I saw that I got this question wrong on a test, and was very confused.  Why aren't they isoelectronic?  $\ce{Sc^2+}$ with atomic number 21 should have 19 electrons since 21 - 2 = 19, which is the same as the number of electrons as Potassium with 19 protons and electrons.  Does it have something to do with being in different sublevels, one being s and the other d and all?


texts: What does nutella add to the Coke+Mentos reaction?

texts:
Inspired by this question on SFF.SE.

The Diet Coke + Mentos experiment has been a popular one for a while now, and I've read a little bit about the science behind it.

I recently discovered this video, where an Italian man adds Nutella to the mix1, to his great excitement.

However, I'm not clear on why he did this; I couldn't see a significant difference in the reaction (although my view was somewhat obscured by the condom). What does the Nutella add to this reaction?

1 Do not watch this video in a public place without headphones on (or the sound turned way down); he gets very, very excited when his abomination experiment (literally) blows up in his face


texts:
What is the effect of temperature on diffusion rate of gases? Do the diffusion rates of gases decrease with an increase in temperature? Why?

I just read it somewhere that the diffusion rate of gases decreases when temperature increases. So i just wanted to know if its true.


texts: Reaction of dimethyl sulfate with Protocatechualdehyde

texts:
I know that $\ce{(CH3)2SO4}$ reacts with phenols to give methoxybenzene. But the question that came in INChO-2018 was:

  When one equivalent of $\ce{NaOH}$ and one equivalent of dimethyl sulfate reacts with Protocatechualdehyde, K is formed in 87% yield. When carried out with excess of $\ce{NaOH}$ and only one equivalent of dimethyl sulfate, M is formed in 95% yield. Identify K and M.

How would I know that ether formation take place at p- to $\ce{-CHO}$ group or at m- to it?

This is Protocatechualdehyde


texts:
If NaCl dissolves in water, it is said that it happens because the hydration energy is greater than the lattice energy. If so, the enthalpy of solution attained is about +3.88kJ/mol, implying that it is endothermic.

From what I have understood, the hydration enthalpy is exothermic and thus its effect should be noticeable. That is, when we add up the lattice and hydration, the negative sign should have come in our final answer.
Why does this not happen? Where have I gone wrong?


texts: Successive ionization energies (work functions?) for metals

texts:
Are there tables for successive ionization energies for metals (like for gases)? All I can find are work functions to remove one electron from the surface of a metal into vacuum (and to keep it there). However, I guess it gets harder to remove electrons the more electrons already have been removed, right?

Maybe there's a way to relate that energy to the average degree of ionization of the material. Is it possible at all?

Finally, is it harder to ionize a metal gas or a metal solid? Although most work functions are a little bit smaller than the (1st) ionization-energies of the same material in gaseous state but I still think ionization of solids is harder. Am I correct?


texts: I just came to know concentrated HCl forms fumes because it dissolves in water vapors present in air. But why are these fumes white, HCl solution is transparent.


texts: Why is the rate of reaction calculated as d[A]/dt?

texts:
For example, for a simple chemical reaction like

$$\ce{A -> C}$$

the rate of the reaction could be calculated as the rate of appearance of $\ce{C}$ or the disappearance of $\ce{A}$, which makes a logical sense. But if the reaction is

$$\ce{A + B -> C}$$

as I read somewhere the rate could be calculated the same way as the first case either as the disappearance of $\ce{A}$ or $\ce{B}$, or the appearance of $\ce{C}$. Is it logical to calculate the rate as the disappearance of $\ce{A}$ or $\ce{B}$ as the rate?

Think about it, isn't the appearance of $\ce{C}$, the combined effect of the disappearance of both $\ce{A}$ and $\ce{B}$, which mean if the rate of the equation can be calculated as the change in concentration of $\ce{C}$ using the product, shouldn't the rate be calculated as the change in concentration of $\ce{A}$ plus the change in concentration of $\ce{B}$ through some time change $t$?


texts:
I've just begun reading about halonium ions and I noted that only the first four halogens are acknowledged to be able to form halonium ions, but hydrogen astatide can be formed.

I can't seem to find any answers on the internet, but knowing that astatine is super reactive and radioactive, I suppose it may be due to this that forming an "Astatonium" molecule would be nearly impossible?

On the Wikipedia entry of hydrogen astatide, it states that there is an Astatonium — listed as a conjugate acid. However, a quick Google search of the term Astatonium only reveals 14 results.


texts: Synthesis of 1-methylcyclopentene from cyclopentene

texts: I have to put a methyl group on a cyclopentene. My teacher made this solution (the picture). But my first guess was just to use $\ce{CH3Cl}$ and $\ce{AlCl3}$. Why can't you do that?


texts: Which of the following para-substituted benzyl alcohols reacts fastest with HBr?

texts:
I had a question in a recent test which asked me to pick the compound that would react fastest with $\ce{HBr}$ with the options being:

p-nitrobenzyl alcohol
p-chlorobenzyl alcohol
benzyl alcohol
p-methoxybenzyl alcohol

The answer was p-methoxybenzyl alcohol.

Now what I don't understand is that $\ce{HBr}$ would produce nucleophilic $\ce{Br-}$, which would be looking to attack a region of electron deficiency. In that case option (1) p-nitrobenzyl alcohol would the right answer because the nitro group is an electron withdrawing group, thus making the ring more electron deficient.

Could someone please explain as to why this logic fails?


texts: How many natural products are there in existence?

texts:
Hi I'm doing a project on natural products and I'm wondering if somewhere there is at least an estimated number of how many exist?

If this exists somewhere can you please provide a reference.

Please and Thank you! :)


texts: Will selenium react or bond, ionic or covalent, with vanadium?

texts: I was recently asked if $\ce{Se}$ will bond with $\ce{V}$, creating a compound $\ce{SeV}$ . I am not sure if this is even possible but if so I'd like to find out.


texts:
When writing the formula for an ion, should the operator come before or after the number that indicates the ion's charge?

Here are some examples:

$\ce{SO_4^{-2}}$ or $\ce{SO_4^{2-}}$
$\ce{Fe^{+2}}$ or $\ce{Fe^{2+}}$

I'm not great at chemistry, so I'm sorry if it's a stupid question.

I just haven't been able to find many answers.


texts:
I came across this question:

I propose two things to happen:

It can undergo Aldol condensation

or

it can undergo SN by replacing $\ce{-Cl}$ with $\ce{-OH}$.

But apparently, both these mechanism give the wrong product. I’m unable to find out what is going on.


texts:
Propose a mechanism for the following transformation.

I gather that this mechanism might be similar to decarboxylation of keto acids:

However, I am unsure of how to begin.


texts: Why does copper form bubbles in vinegar in this situation?

texts:
I watched this video in which the host tries to show the principles behind the voltaic pile.

The host first immersed zinc in vinegar and bubbles are observed forming around zinc. I've learned that this is because hydrogen ions in vinegar get electrons from zinc atoms and become gaseous.

Then the host take a conductor and attach at one end the piece of zinc and at the other a piece of copper. Bubbles start to form around copper too! (fig1)

Why does this happen?
Why do some electrons travel through the conductor instead of being attracted immediately by the hydrogen ions in the vinegar?
What if the conductor instead was very long and the pieces of copper and zinc far apart? (fig2)


texts: I am wondering how does PCC actually work in not oxidizing aldehyde. Like the reaction mechanism I saw online, it seemed as if not having a acidic solvent is what made aldehyde not tranform to carboxylic acid when PCC is present. So the why can't you just use chromium containing compounds without the acidic solvent and then you will be able to isolate aldehyde.


texts: Why there is a color fading ( to colorless) when Cerium Ammonium Nitrate (CAN) is mixed with ethanol or butanol?

texts: I have mixed CAN in butanol and also ethanol (separately), the solution became dark red immediately but after a couple of minutes the color totally faded and turned into a transparent solution, I am curious to understand the reason behind it.


texts: Determining the chemical formula of a polyiodide Salt

texts:
I've got a compound with formula $\ce{N(CH3)4.I(I2)_x}$. By mass I've got $\pu{0.138 g}$ of $\ce{I2}$ present out of $\pu{0.189 g}$ of polyiodide added. How do I find $x$?

This is the exact part of the question that I got stuck. It's more of the concept that I am not getting instead an equation that I can just use.

We begin with using $\pu{0.25 g}$ of tetramethylammonium. Then used $\pu{0.825 g}$ of iodine, and finally collected $\pu{0.8 g}$ of polyiodide salt.

Then we titrated $\pu{5 mL}$ of the polyiodide solution with $\pu{0.2 M}$ thiosulphate solution. Final titre used is $\pu{5.40 mL}$.

Calculated below:

$\pu{1.09e-4 mol}$ of thiosulphate used to reach end point
$\pu{5.43e-5 mol}$ of iodine present in the $\pu{5 mL}$ polyiodide solution
$\pu{5.43e-4 mol}$ of iodine present in $\pu{50 mL}$ original sample
$\pu{0.138 g}$ of $\ce{I2}$ present in original sample
$\pu{0.189 g}$ is the full mass of original sample
Thus giving 73 percent iodine by mass

So for the final ratio i got $1:2.7$ which can be rounded to 1:3. The formula thus is $\ce{NMe4.I(I2)_x}$, where I think $x=3$.

But I can't seem to make sense of this. I mean when $\ce{I(I2)_x} = (\ce{I2$x$}+1)$ could it mean $2x+1=3$, therefore making $x=1$?


texts: Which procedure(s) will allow a student to differentiate between solid sodium sulfate and solid sodium sulfite?

texts:
I. Make solutions of each and look for a precipitate when added to 0.10 M Ba(NO3)2.
II. Add crystals of each to 0.10 M HCl and watch for bubbles.
III. Make solutions of each and test with a pH indicator.

The answer is II and III only. I understand how III works, but I don't see how sulfite and sulfate can be differentiated by adding HCl; don't both get reduced to SO2 bubbles?


texts: Maximum number of Spectral Lines "A better quantum model shows that there will be n^2 transitions"?

texts:
I was parsing the following post What is the maximum number of emission lines when the excited electron of a H atom in n = 6 drops to ground state? and came across with the reply from @porphyrin.
cite : "lease note that these answers are only true in the Bohr model, a better quantum model shows that there will be $^2$ transitions. The orbitals are now labelled with increasing orbital angular momentum, ℓ=0,1,2,3..."
Please, does someone can point me out to references or more extended explanations, from where does the $^2$ come from?
Update
The general formula for calculating number of spectral lines is (n2−n1)(n2 −n1+1)/2; which "merely" relate to triangular numbers n(n+1)/2. I wonder about $n^2$ since the sum of two consecutive triangular numbers give a square number; what does the (n-1)n/2 constituent part describe? Is this due to Pauli exclusion Principle; Bose/Einstein Vs Fermi/Dirac distribution?
Really appreciate.
PS: I don't have 50 reputation to comment directly


texts: Is neutron a compressed form of hydrogen atom?

texts:
As I know:

$E_\mathrm{p} = \pu{938.272 MeV}, \quad
    E_\mathrm{e} = \pu{0.511 MeV}, \quad
    E_\mathrm{n} = \pu{939.565 MeV}$
$E_\mathrm{n} − (E_\mathrm{p} + E_\mathrm{e}) = \pu{0.782 MeV}$
$M_\mathrm{p} = \pu{1.6727 x 10^-24 g}, \quad
    M_\mathrm{e} = \pu{9.110E-28 g}, \quad
    M_\mathrm{n} = \pu{1.6750E-24 g}$

Furthermore, following reaction also happens:

$\ce{p+ + e− -> n + ν}$

So i was wondering if this is a combination reaction at atomic scale and if the neutron is really a highly compressed form of hydrogen atom? As mass difference is negligible and higher energy of neutron can be regarded as the moving energies of electron(i.e. rotational, kinetic and others) are locked down into potential energy and charge of electron and proton neutralizing eachother?


texts: Sigma bond behaving as stronger nucleophile despite presence of pi bond?

texts:
In my book, the following reaction is given

The solution states that the sigma bond between hydrogen and carbon (3 degree) in isobutane attacks $\ce{H+}$ from $\ce{HF}$ to generate tert-butyl carbocation. This carbocation then adds on to ethene to generate another carbocation followed by some rearrengements until the given product is obtained.

My doubt is, since pi bonds are stronger nucleophiles (because of loosely held electrons) then why in this reaction the carbon-hydrogen sigma bond attacks $\ce{H+}$ instead of $\ce{HF}$  adding to the pi bond?

Source: MS Chouhan; Advanced Problems In Organic Chemistry; 11th ed; Ref. Q.26 MS Chouhan - Alkenes


texts: What is hard and soft water and how does the process of dissolution work?

texts:
This is a very basic question about solubility, especially solution of table salt in water and solution of sugar in water. I have heard about terms like hard water, soft water, filtering of water to remove impurities etc., but I don't understand these well enough. My questions are:

If table salt is dissolved in water, why do we call it a solution? Don't say that a chemical reaction has taken place and some new product say $\ce{NaH2OCl}$ etc. is formed.
By mere filtering using a cloth or a machine, how can we get rid of minute impurities, (which make water hard) which are not even visible to naked eyes?


texts: Decarboxylation under acid, water, and extreme heat

texts:
I am asked whether dimethyl malonate or methyl acetoacetate decarboxylate when hit with acid, water, and extreme temperatures.

I believe the answer is both because both are esters, and esters, upon being hit by such conditions, return to their respective carboxylic acids.

From there, both carboxylic acids can undergo decarboxylation because both resulting carboxylic acids are beta-keto acids. Technically, dimethyl malonate becomes malonic acid, which can still undergo decarboxylation (but malonic acid isn't of the beta-keto class; rather the dicarboxylic acid class).

Acid and heat treatment of methyl acetoacetate initially gives 3-oxobutanoic acid but this can decarboxylate under the heat as well.

Is my analysis correct?


texts: Among $\ce{LiF}$, $\ce{LiCl}$, $\ce{LiBr}$ and $\ce{LiI}$ is $\ce{LiI}$ the most soluble compound ? As the lattice energy depends on size and smaller the size of ions greater the lattice and as $\ce{LiI}$ has greater size therefore should it be most soluble? Since lattice energy is inversely proportional to solubility, according to me $\ce{LiI}$ is most soluble and $\ce{LiF}$ is least. Is this correct ?


texts: What are some examples of pure substances with no liquid state?

texts:
For example,

A molecular substance that decomposes before melting, and under pressure can only assume a liquid state that doesn't contain the same molecules, for example a mixture of the elements of which it's composed
A polymer that breaks down into monomers when it melts, and doesn't have a liquid state with the same polymeric bonding regardless of the pressure
An ionic solid that sublimates upon heating, and under pressure can only assume a liquid state that clearly does not exhibit ionic bonding

What are some such substances? (Non-pure substances, such as wood, are non-examples.)


texts: Is it possible to build a non-degrading battery?

texts:
I am not a chemist, nor do I know anything about chemistry. What I am interested in are batteries. I don't really care about the whole "Charge in minutes, last for days" types of batteries (the famously hyped graphene battery) But is it possible to have a battery that will never degrade and always keep its performance without upkeep/maintenance?

I just didn't know if there were some types of laws in chemistry that prevents this from happening. I would ask in electrical engineering but this sounds to me more of a chemistry question.


texts: Difference between solubility and dissolution?

texts: How is solubility different from dissolution? And how are they both different from solvation?


texts: Do bare protons exist, even transiently, in aqueous solution?

texts:
Generally $\ce{H^+}$ ions in water remain in the form of hydronium ions ($\ce{H3O+}$), and not as "free" aqueous protons, as far as I've been taught.

My question: is this always the case, even when considering dynamics at extremely short time scales? By this I am not meaning interconversion with the Zundel ($\ce{H5O2+}$) or other states. I mean to say, does bare $\ce{H+}(\mathrm{aq})$ ever exist  on, say, a femtosecond time scale?


texts: How to perform solvent extraction of a solid

texts:
Suppose I have a solid compound from which I want to extract a target chemical I know is soluble in acetone.  So I crush and mix the compound in acetone, dissolving the target and suspending the detritus.

What are methods for filtering the detritus from the solution? I have frequently seen coffee filters used for this purpose.  Are commercial coffee filters considered "lab-grade?"  Or, suppose that the target chemical has some affinity for cellulose, what alternatives exist for suspension filtration?
Now, having the target chemical in solution I assume it is easiest to extract it by evaporating the acetone.  Is there a process for this that doesn't leave any of the target stuck to the glass or whatever was containing the solution?


texts: Mechanism of sulfur trioxide reaction with water to make sulfuric acid

texts:
This question touches on whether sulfur is hypervalent (whether it expands its octet when bonding).

The first picture shows both sulfurs with an expanded octet.

The problem is that in the top half of the below picture, we are supposed to end up with sulfuric acid, but we actually end up with sulfuric acid plus two lone pairs (if I drew the mechanism correctly). Did I? (I actually separated out the top part of the picture into two parts - first, hydrogen attacking oxygen; second, oxygen attacking sulfur - so the arrow pushing wouldn't get confusing).

The second picture follows updated chemical fact. According to Wikipedia, sulfur trioxide has one double bond and two dative single bonds. Sulfuric acid is also a charge separated species with four single bonds, not two single bonds and two double bonds. I seem to end up with the proper product here without any hand-waving.


texts: X-Ray Diffraction: Phase Identification Strategy

texts:
I am having some trouble with qualitative phase identification using x-ray diffraction (XRD). Here follows some basic information about the experiment:

Instrument: PANalytical X'Pert$^3$ Powder

Software: PANalytical Highscore Plus

Database: PAN ICSD

Sample: respirable fraction aerosol samples from ferro- and silica manganese plants.

The goal: which manganese phases are present, and which dominate?

Grasping the software is not what I am concerned about. I lack an analytical strategy. I know how to determine the background, but I am not sure when the background is appropriately determined. Too high? Too low? Does this strongly affect the phase identification?

Then I do a peak search, and 50 peaks are detected. Should I focus just on the major peaks? Are the minor ones important too? When I do a search-match analysis, I get 400 suggested phases, where 20 phases share the highest score. Then another 20 phases share the highest score minus 1. I lack criteria needed to accept a phase as present, and discard other phases as not present.

I am not able to find good literature on this subject. I did find an article called "Hints on Phase Identification Using Powder X-ray Diffraction", which certainly raised a lot of potential problems and procedures, but which did not necessarily solve these problems or explain why the procedures would help. Does anyone know of any books or other literature that could help me?

My problem boils down to lack of "strategy" or "analytical procedure", and maybe someone here could offer some advice. I hope my question is "answerable", and not too broad; I know there is a "specific-and-precise-question" policy in here.


texts:
Molprobity and some other protein structure validation tools report a Cβ deviation statistic and offer plots for it (example below).  Apparently if the Cβ is greater than 0.25 Å, some attention should be given to the residue.

The statistic is given in units of angstroms, but I'm not sure what it's actually referring to.  With the Rama plot, it's the peptide dihedral angles, but what is this?  And why are the graphs 2-D despite the one dimension given?


texts: Calculating the total uncertainty of the final product

texts:
I have performed a large number of calculations in order to determine the ethanol content of wine. These included titrations using burettes, mass measurements using analytical balances, and others. I know the uncertainties of the apparatus.

I am given a task to find the ethanol content of wine (done) but also to calculate the total uncertainty by propagation of errors.
As I understand it, the total uncertainty is given by

$$\delta F=\sqrt{\left(\delta q\right)^2+\left(\delta w\right)^2+...}$$

But - does this include the standard error? That is, to calculate the total uncertainty of the final value, will I need to find the standard error for all the sets of titrations (eg - for titration 1, a set of 3 values, find the standard error taking into account all results, even non-concordant ones, and do this for titration 2), and treat those values as fractional uncertainties? Should I add this value to the fractional uncertainties of the burette measurements (ie its own measurement uncertainty, not the standard errors from the readings), and to the measurement uncertainties of the other apparatus?

Finally - does the operation which I apply to the values that the uncertainties effect change the equation for the total uncertainty? Or do I just use the same equation as above?


texts: Why aren't solid pure transition metals colourful?

texts: I understand that the compounds of transition metal are colourful because of the appropriate energy gap between different d orbitals. But why aren't they also colourful in their solid pure state? For example, why isn't Fe colourful whereas, its compounds are?


texts: Are the bonds within bismuth pentafluoride (BiF5) covalent or ionic?

texts:
When googling $\ce{BiF5}$ most results call it bismuth pentafluoride such as Wikipedia.

I was under the impression that, since it is an ionic-bonded compound, Roman numerals should be used to identify the charge of bismuth, followed by fluorine with an ide ending such as the following:

  Bismuth(V) Fluoride

So, I am wondering whether the bonds are either not ionic or that I've misidentified it?


texts: Why does reduction of naphthalene with nickel/hydrogen lead to trans-decalin?

texts: Is there any reason why $\ce{H2/Ni}$ leads to trans-decalin? I knew from high school that catalytic hydrogenations are always syn.


texts: Is chirality a property of only molecules with exactly 1 chiral centre?

texts:
I have seen chirality being defined in a number of ways in terms of a molecule not being superimposable with its mirror image.
My syllabus has a statement: "know that optical isomerism is a result of of chirality in molecules with a single chiral centre". This seems odd because surely you can have a have optical isomerism between molecules with more than 1 chiral centre so why a single.
Overall, I am asking for either a confirmation that the statement is incorrect or an explanation of where my understanding is wrong.


texts: What is the energy of the London dispersion force holding together two atoms of the same element?

texts:
I read somewhere that the energy is around $U=-\frac{3\alpha I}{4r^6}$ where $\alpha$ is the polarizability and $I$ is the ionization energy but I'm obtaining way too large energies for a lithium crystal.

The shortest distance between two lithium atoms in the crystal is $304 pm$

The first ionization energy of lithium is $520.2 kJ/mol$

I've found various polarizability constants online in papers but I can't really figure them out or the units they are using.

Also, I suspect that I want the dispersion force between $\ce{Li^+}$ ions and not neutral $\ce{Li}$ atoms.


texts: How is the thermal stability of nitric acid related to its structure?

texts:
How is the thermal stability of nitric acid related to its planar structure?

In textbooks it is written that nitric acid is unstable at room temperature and decomposes where $\ce{H2SO4}$ and $\ce{H3PO4}$ are stable and decompose at much higher temperature.$\ce{H2SO4}$ and $\ce{H3PO4}$ have tetrahedral structures.


texts: Measuring turbidity using a spectrophotometer

texts: I am conducting a lab investigating on the effect of aluminium sulfate concentration on turbidity. In my high-school, we only have a spectrophotometer. Is there a way to measure turbidity with a spectrophotometer? Do I need to dye my solution or alter it in some other way? How do I prepare my blank?


texts: Constructing a grenade (for a novel I'm writing.)

texts:
Ok, before any eyebrows get raised, this is for a novel that I'm writing and inspired by this answer from worldbuilding and this reference answer. I just want to make sure the device I'm trying to use is as close to accurate as can be.

So, in the novel, I've devised a compartmentalized glass urn. The urn contains three compartments, one will house a mixture of a finely powdered combination of charcoal, sulfur, and saltpeter. The second compartment would contain slightly acidic water and the third one would contain limestone. What I'm expecting is that when the urn is dropped, the shattering of the glass would cause the water to react with lime resulting in an exothermic reaction which would help to ignite the gunpowder mixture. Is this idea liable to work or is too quixotic and fanciful to consider ? If so, what adjustments can I make to it so that it works? Do keep in mind that the sources have to be natural as it is an apocalyptic world.

Also, can I just call it a mixture of a finely powdered combination of charcoal, sulfur, and saltpeter or does it need to be prepared in a special way or maybe there is a special term for it?

Apologies if this is not the right place to ask the question but I could not think of any other apt place.


texts: Deriving heat capacity in terms of internal energy U and natural variables S & V

texts:
My lecture notes have the following equation regarding heat capacities:

$$
C_p = C_v + T\left(\frac{\partial p}{\partial T}\right)_v\left(\frac{\partial V}{\partial T}\right)_p
$$

(just to be clear, all terms after the brackets in this question indicate a constant process of that term)

It then states that by using internal energy $U$, volume $V$ and entropy $S$, you can express heat capacity at constant pressure, $C_p$, just in terms of these 3 variables:

$$
C_p = \frac {\left(\frac{\partial U}{\partial S}\right)_v\left(\frac{\partial ^2 U}{\partial V^2}\right)_s }{\left(\frac{\partial ^2 U}{\partial V^2}\right)_s\left(\frac{\partial ^2 U}{\partial S^2}\right)_v - \left(\frac{\partial ^2 U}{\partial S \cdot\partial V}\right)^2}
$$

with no inbetween steps given.

From a previous derivation of $C_v$ I know that:

$$
C_v = \frac{\left(\frac{\partial U}{\partial S}\right)_v}{\left(\frac{\partial ^2 U}{\partial S^2}\right)_v}
$$

and I think I understand at the least how to express the $\left(\frac{\partial p}{\partial T}\right)_v$ term, because you can express $p$ and $T$ in terms of $U, S, V$ like so:

$$
\begin{align*}
-p &= \left(\frac{\partial U}{\partial V}\right)_s \\
T &= \left(\frac{\partial U}{\partial S}\right)_v
\end{align*}
$$

The real killer is the second term $\left(\frac{\partial V}{\partial T}\right)_p$, because the only thing I know I can do with this equation is use the Maxwell relation:

$$
-\left(\frac{\partial V}{\partial T}\right)_p = \left(\frac{\partial S}{\partial p}\right)_T
$$

but this still leaves a constant temperature term $T$ which is not present in the final equation. So, any help with this would be really appreciated.


texts:
The pH of lemon juice is about 2.1.  What is the citric acid concentration, [HCit], in the lemon juice?

I am given that $HCit \leftarrow \rightarrow H^+ + Cit^-$ and that $K_a = 8.4 \times 10^{-4}$.

$K_a = \frac{[H+][Cit]}{[HCit]} = 8.4 \times 10^{-4}$, and $[H+]$ is $10^{-2.1}$. However, without knowing $[Cit]$, how can I get [HCit]? Any help would really be appreciated!


texts: If the rate law order is three, does that mean that three bodies collide at some elementary step?

texts:
I am doing a chemistry review about rates, and I get asked "Which of these statements is false?"

The answer is

  In reactions that are second order in one reactant and first order in another, the slow step generally involves a three-body collision of the reactants.

I imagine it looks like

$$
rate = k[A]^2[B]^1
$$

So at the slowest elementary step there should be
$$
2A + B = something
$$

Which is a three way collision between two A molecules and a B.

What am I doing wrong?

EDIT:

Question number 2 (http://www.mesacc.edu/~paudy84101/CHM152F2005/Exam1%20Key.pdf)

This is not my review, in case you are wondering.  I just have the same question.


texts: Why do alkyl chlorides have lower boiling points than the corresponding alkyl bromides and iodides?

texts:
To my knowledge, the $\ce{C-Cl}$ bond is stronger than the $\ce{C-Br}$ and the $\ce{C-I}$ bond.

I always thought that the stronger a bond, the harder it is to break so the boiling point would be higher.

If that is the case, why does, among $\ce{RCl}$, $\ce{RBr}$ and $\ce{RI}$ (R = alkyl), $\ce{RI}$ have the lowest boiling point?


texts:
The following reaction confuses me - I don't understand how and why it happened (couldn't figure out the mechanism):

I thought this is some Wolff Kishner sort of reduction, but the reagents don't match (no alkaline medium). I am not sure how hydrazine lead to cyclisation - for starters, I guess it added to the carbonyl oxygen (aldehyde, as it is more reactive) as an ammonia derivative to form a hydrazone. What's next?


texts: What distinguishes a Lewis Complex from an Adduct or are they synonymous?

texts: I cannot think of a distinction - the terms seem to be used interchangeably when talking about products of Lewis acid-base reactions. However, I am concerned that I may have overlooked a subtlety. Please can you clarify?


texts: Why is diborane cleaved symmetrically by trimethylamine but unsymmetrically by ammonia?

texts: I know that soft bases cleave diborane symmetrically but hard ones don't. However, what makes ammonia harder than trimethylamine? And why does hardness/softness affect this?


texts: Which bond angle will be larger in a compound like CH2X2?

texts:
Just thought of a certain situation.Say for example in a compound like difluoromethane $\ce{CH2F2}$ or $\ce{CH2Cl2}$ obviously the tetrahedral structure will be distorted.

But my question is which bond angle will be larger: the angle between halogen-halogen, halogen-hydrogen or hydrogen-hydrogen? Why?


texts: Electrolysis - What is the basis for the discharge rules?

texts: At the cathode, the one that is discharged is the less reactive one (compared to hydrogen) so why at the anode is the one that’s discharged more reactive (less stable) ?


texts: Why won't removing the salt bridge cause the battery to recharge?

texts:
If I understand correctly, the salt bridge in a battery is used to move positive ions towards the side that is becoming more negative, and negative ions towards the side that's becoming positively charged, to prevent the reaction from quickly reaching equilibrium. The ions in the salt bridge never leave the salt bridge.

But if we removed the salt bridge, wouldn't the forces between the $\ce{SO_4^{2-}}$ ions or $\ce{Zn^{2+}}$ ions cause the reaction to go in reverse and cause them to reattach to the electrodes?


texts: What is the analogue of "molecule" for ionic compounds?

texts:
In a system, if we have $\pu{18 g}$ of $\ce{H2O}$ ($M_\mathrm r = 18$), we can say we have a mole of water molecules or $6 \times 10^{23}$ molecules. But in another system, if we have $\pu{342 g}$ of $\ce{Al2(SO4)3}$ ($M_\mathrm r = 342$), what is the best way to say that there is one mole of "aluminum sulfates" or $6 \times 10^{23}$ "aluminum sulfates"?

Since it is a ionic compound, we can't say molecules, but I can't find an analogous form for ionic compounds. I thought about saying "a mole of aluminum sulfate ionic aggregates", but it still doesn't too good, since I've never seen a definition of ionic aggregate as a unit of the ionic compound formula. It only tells the way the ions organize themselves: as an aggregate.

I know it is a silly question, but in terms of language and symbolism, it is important to me as a chemistry teacher.


texts: Predicting the products obtained after addition of bromine and then elimination using alcoholic KOH

texts:
If we have an alkene reacting with bromine, then I know that the the reaction happens by a cyclic intermediate. But if we add alcoholic KOH to the products formed, then what will be the major products formed?

I don't understand the meaning of trans addition in case of only one π and σ bonds where the bond formed after addition is free to rotate as it is σ bond.  If bromine adds in an anti manner, then can it not convert to the cis form?

I am not sure if using the terms like 'trans' and 'cis' in case of σ bond is correct. I am not sure whether it's a molecule of bromine or HBr will be eliminated after addition of alcoholic KOH.


texts: Friedel-Crafts Alkylation and hybridization

texts:
Why must the alkyl halide be sp3 hybridized with respect to the carbon connected to the halogen for the alkylation to occur?

Why, for example, can't we use acetylide with a bromine substituted for hydrogen on one side in conjunction with aluminum tribromide to alkylate benzene?

If anything this seems to be more favorable as an sp carbocation is likely less stable than an sp3 carbocation.


texts: What are the differences and similarities between an aliphatic and an alicyclic compound?

texts: I read that alicyclic compounds are compounds that are both aliphatic and cyclic and i know that aliphatic compounds are acyclic while alicyclic compounds are cyclic but are there any other differences and similarities between them and what is exactly an aliphatic compound?


texts: Reaction of aldoxime and a ketoxime with acetic anhydride

texts:
In mt book I saw these two reactions:

I don't know what is the mechanism for these reactions & that's why I am unable to understand how these products are formed & why they are so different. Please explain the mechanism in detail.


texts: Diffusion between phases based on chemical potential

texts: How is the concept of diagram(b) different from that of (e) and (d) from (f)?Someone told me in one of my earlier posts (Why will A atoms diffuse from β phase to α phase and B atoms from α phase to β phase?) that he is used to see graphs with two minimia but somewhere where we had two phase separately named as $G^{\alpha}$ and $G^{\beta}$ vs the composition curve he seemed something that he saw for the very first time. Please help me to differentiate the two of them and also answer the question that I have in this post.


texts: Why are many chemical relationships logarithmic?

texts:
I've noticed that in many relationships in chemistry, one variable is linearly related to the logarithm of another. Why is this the case?

For example, I carried out an experiment where the dependent variable, the amount of solute adsorbed to a surface, was almost perfectly linearly correlated (Pearson correlation coefficient = 0.93) with the pOH, which is a logarithmic quantity.

Edit: Would this perhaps be better in stats.stackexchange.com?


texts: Which orbitals of the hydrogen atom are degenerate for n=3?

texts:
Which of the following orbitals are degenerate in the hydrogen atom with $n = 3$?

  A. II and III only;
  B. I and IV only;
  C. I, II, and IV only;
  D. II, III, and IV only;
  E. all.

The answer says its E. All of them.

First of all isn't there only 1 electron in hydrogen? And how could the $\mathrm{s}$ orbital be degenerate? Doesn't degenerate mean there are multiple places pairs of orbitals can be?


texts: Technique to measure the volume of a crystal

texts: I am doing a project on crystal growth. I am making potash alum in two different conditions, one in the fridge and the other one in room temperature. I wanted to how can I measure their volume? Techniques?


texts: How are 3 center-4 electron bonds any different from 2 center-2 electron bonds?

texts:
How are the bridge bonds in $\ce{Al2Cl6}$ different from the terminal bonds?
We could have just mentioned the bridge bond formed by $\ce{Cl}$ as a coordinate bond. Why introduce this extra concept?
I can understand why 3 center-2 electron bond would have been introduced but not this one.
My guess is that during the formation of the molecule vacant orbitals take part in hybridisation which is different from usual but after formation of the bond, there is no difference.


texts: Synthesis of potassium trioxalatocobaltate(III) trihydrate

texts:
I've synthesized the compound potassium trioxalatocobaltate(III) trihydrate and for it I have two reaction equations. One of them is:

$$\ce{CoCO3 + 3K2C2O4.2H2O -> K2[Co(C2O4)3] + 2CO2}$$

and the other:

$$\ce{K2[Co(C2O4)3] + PbO2 -> K3[Co(C2O4)3].3H2O}$$

I see that the lead dioxide oxidizes $\ce{Co^2+}$ to $\ce{Co^3+}$ in the second step but I can't figure out what happens in the first. Does cobalt(II) make a ligand complex with the oxalate group?
One of the beginning steps was a also to mix oxalic acid and potassium oxalate. I assume (but I am not sure) that it was done to dissolve the potassium oxalate as other acids might have led to an unwanted reaction that would hinder the reaction following reaction with $\ce{CoCO3}$. I wanted to know that this was in fact the case.


texts:
They say that enthalpy of reaction is the heat when at constant temperature and pressure. So if enthalpy is

$$\mathrm dH = \mathrm dU + p\,\mathrm dV = T\,\mathrm dS - p\,\mathrm dV + p\,\mathrm dV + μ\,\mathrm dN = T\,\mathrm dS + μ\,\mathrm dN$$

and heat is $T\,\mathrm dS,$ then what happens to the chemical potential term if enthalpy is heat?


texts: Why a specific temperature for value of 1 calorie?

texts:
Everything in chemistry often comes with a strong reason and facts behind it, but I stuck in definition of $1$ calorie.

My reference book define one calorie as amount of heat required to raise the temperature of one gram of water from $14.5$ degrees Celsius to $15.5$ degrees Celsius.

Why $14.5$ and $15.5$, why temperature such as  $0$ to $1$ or $19$ to $20$ degree Celsius is not chosen?

Please forgive me if this question is too easy and I can't figure out the logic related to it.

I shall be glad to have your suggestions.


texts: When we say that “potassium” is reactive, are we referring to a potassium atom or bulk potassium as in the solid metal? In other words does “potassium” refer to a type of atom or an agglomeration of potassium atoms?


texts:
Why do we find big spaces in the periods of the Periodic Table between $\ce{H}$ and $\ce{He}$, $\ce{Be}$ and $\ce{B}$, and $\ce{Mg}$ and $\ce{Al}$?

What is the logic of such organization of the periods?


texts: Is it possible in very acidic solutions for the nitrogens ($\ce{N}$) to get another $\ce{H+}$, making it $\ce{R-NH2+-R}$? Since it has a free electron pair, it might be possible right? If so, at which pH?


texts: Will adding dilute potassium permanganate to impure methanol in alkaline conditions work as a good colorimetric method? I am planning to produce salicylic acid from methyl salicylate (by hydrolysing the ester and producing methanol), and was wondering how I can show that the reaction goes to completion under alkaline conditions. If not, what would be a good method to show this?


texts: Is there a way to dehydrate hydrated aluminum chloride for use as a Lewis acid?

texts:
I heard that one can use thionyl chloride to dehydrate it, but I'm not really sure if it would be available for amateur chemists since it's listed on the UN Convention for (the Elimination of) Chemical Weapons.

And no, I'm NOT thinking of getting cryolite either.


texts: Finding one of the two unknown potentials with a given voltage of a net reaction

texts:
A half-cell consisting of palladium rod dipping into a $1\ M$ $\ce{Pd(NO_3)_2}$ solution is connected with a standard hydrogen half-cell. The cell voltage is $0.99\ volt$ and the platinum electrode in the hydrogen half-cell is the anode. Determine $E^ο$ for the reaction $\ce{Pd\longrightarrow Pd^{2+} + 2e}$.

Now the question is: can I find a numerical value of the needed $E^ο$, if I can't use half-cell potential of $\ce{Pt^{2+}\!−\!Pt}$?


texts: Which of sodium or lithium will be more reactive with oxygen?

texts:
I do not understand how you can work out which element will react more readily with another element.

For example, I have lithium (Li) and sodium (Na) and I am trying to work out which element will be more reactive with oxygen. How do I manage to work that out?


texts: Would a salt bridge work through which the ions could not diffuse into the half cells?

texts: Instead of covering the ends of the salt bridge in an electrochemical cell with a membrane, one could also plug them on both sides with a conductive non-porous material, for example gold, which doesn't go into solution. Would the accumulation of the ions at the plugs and their electrostatic force field be enough to keep the cell running?


texts: Mechanism for the intra-molecular exchange of an ester and a nitrile group

texts:
When the isolated product 4 is treated with sodium ethoxide in ethanol it rearranges to 5 as shown:

My TA says that you need to start with a reverse Claisen at the ketone but I am not quite sure where to go from there. I do not know how to move the nitrile alpha to the carbonyl furthest from the methyl group.


texts: Viscosity and concentration of solutions

texts:
I will need a fluid around a specific viscosity, using a mixture of water and something like sugar.

Is there a way to calculate viscosity based on concentration?


texts:
The IUPAC name for Acetophenone is : 1-Phenylethanone.
An other name is : Methyl phenyl ketone.
My question here why there's a space in "Methyl phenyl ketone" although there's no space in "1-Phenylethanone"?


texts: Understanding the derivation of Gibbs Free Energy

texts:
In the equation: $$ΔG=ΔH−TΔS$$

I am having trouble understanding my professor's derivation of it from
$$ΔS_{\mathrm{univ}}=ΔS_{\mathrm{sys}}+ΔS_{\mathrm{surroundings}}$$

where he says $$ΔS_{\mathrm{surroundings}}= \frac{-ΔH_{\mathrm{sys}}}{T}$$
which I have learned is only true for a reversible process.
How is it possible that this heat can be reversed? And why can't we say that the change of entropy for the system is also equal to the equation. I understand that it would mean the reaction is at equilibrium, but would it not be since heat is reversible?
$$ΔS_{\mathrm{sys}}= \frac{ΔH_{\mathrm{sys}}}{T}$$


texts: Among thioester and ester which has more electrophilic carbonyl carbon?

texts:
In few reactions I’ve seen that nucleophiles preferably attack thioester’s carbonyl carbon instead of ester’s carbonyl carbon

According to me, the initiation of reaction is decided by the electrophilicity of the carbonyl compound, in esters O being more electronegative makes c=o more electrophilic, thus attack should have been at ester, but many reactions suggest that attack first occurs at thioester.

What makes thioester’s carbonyl carbon more electrophilic?


texts: Im sure there is a chemist/lab tech that knows a simple solution to my problem, as I cant seem to find a solution.  When trying to strip and re-season cast iron cookware, I occasionally have problems with rust.  I live near the ocean, so there is a lot of humidity in the air.  I strip the cast iron by putting in the oven on the self-cleaning setting for an hour.  This normally works perfectly.  However, sometimes at the end of the hour, I open the door and see the pan has developed surface rust.  Obviously, heat + iron + water = rust.  I am sure there is a way to absorb the moisture in the oven, but I cant find anything.  I looked at desiccants, but they release moisture in the oven when heated - at least the ones I saw.  Is there a desiccant that works at oven temperatures?  Or is there another solution?  Remember, food will be cooked on the cast iron, so the solution has to be food safe in the end.


texts: IUPAC nomenclature of 1,2,3,4-tetramethylcyclobutane

texts:
I'm having a hard time naming these molecule myself.

For the first molecule I start with one of the stereocenters, give priority "4" hydrogen and "3" to the attached CH3. How are the other two attached nodes given priority "1" and "2" in an anticlockwise fashion, like in the graph below?
For the second one I have the analogous problem, who is "1" and "2" in each stereocenter?


texts: How do scientists know they have discovered an element?

texts:
I have a background in math not chemistry and perhaps this question is inappropriate but I will try. I read that after pitchblende was discovered Martin Klaproth in 1879 a latter date discovered that the pitchblende contained another element which he called uranium.
How did he know the uranium was an element and not just another compound that could not be broken down further?  I read Mendeleeve published the periodic table in 1869 but how about before this date? Somehow the first few elements had to be discovered without the benefit of that publication and scientists had to know the substance discoverd and in question was not a compound but an element.


texts: Equilibrium Constant of a Salt knowing the solubility

texts:
Calculate the equilibrium constant in $\ce\\M ^ 3$ of the heterogeneous system in aqueous solution:
$\ce{CaF2 \leftrightarrows Ca^{2+} + 2F-}$
Knowing that the solubility of the salt is $15.9 \ce{mg/L}$.

They are three and gave the same result.


texts: What are the products of the hydrolysis of ICl3?

texts:
I have learnt that interhalogens on hydrolysis give a halic acid derived from the smaller atom and an oxoacid derived from the larger atom. For example hydrolysis of $\ce{BrF5}$ would give me $\ce{HF}$ and $\ce{HBrO3}$.

Similarly the hydrolysis of $\ce{ICl3}$ should give me $\ce{HCl}$ and $\ce{HIO2}$ but my textbook says that $\ce{HIO2}$ is too unstable to be isolated. What then would be the products of the reaction?


texts: When calculating a dihedral angle for a chemical bond, how is the direction defined? What are the most common convention?

texts:
I understand the geometry and calculation of a dihedral angle, discussed in this question. It is not clear how the direction is defined for a chemical bond.  On the wiki page for dihedral angles, it states that, "the dihedral angle $\phi$ is the counterclockwise angle..." between the planes $P_{123}$ and $P_{234}$ (where $P_{123}$ is defined as the plane containing atoms 1, 2, and 3 in the diagram below, and likewise for $P_{234}$).

$\hspace{45 mm}$

This counterclockwise definition means that the direction of the dihedral angle is defined using the left-hand rule about the line connecting atom 2 to atom 3.  The left-hand rule is unusual in mathematics and geometry.  Alternatively, this example may be defining the directionality of $\phi$ simply so the result is a positive angle less than $180^\circ$.

I have not been able to find any chemistry standards on this.  Is there a common convention?


texts: Hybridisation of the negatively charged carbon atom in a carbanion

texts:
Given the carbanion, $\ce{R3C-}$, the carbon is $\mathrm{sp^3}$ hybridized, unless it is participating in resonance. This is clear from its steric number.

However, I am having trouble in drawing its orbital diagram. I know that if this was a neutral carbon atom, it would look like this:

$\mathrm{3s}$: _
$\mathrm{2p}$: ↑ ↑ _
$\mathrm{2s}$: ↑↓
$\mathrm{1s}$: ↑↓

Which would hybridize to this:

$\mathrm{3s}$: _
$\mathrm{2sp^3}$: ↑ ↑ ↑ ↑
$\mathrm{1s}$: ↑↓

Now if I was to examine the carbanionic state, would I simply be adding one electron to the top most diagram, then re-hybridize that? Or would I add two electrons because the carbon is not sharing the electrons with any other atom? That's another question I have with orbital diagrams. Do we break each bond homolytically, and base our diagram off of that? This would give:

$\mathrm{3s}$: _
$\mathrm{2p}$: ↑ ↑ ↑
$\mathrm{2s}$: ↑↓
$\mathrm{1s}$: ↑↓

I am not sure how I would rehybridize that. Have I drawn the radical form?


texts: How to understand activity with different standard state

texts:
There is a description of activity in Wikipedia as below. How shall I understand it? Fox example, I have a solution with pH = 7 ({H+} = 10^-7). The molarity based activity of H+ will be a = 10^-7 (standard state is 1mol/L). However the molar fraction of H+ is 10^-7/55.5 (the 55.5 is the molar of water per liter), which is far away from 10^-7. What is the problem of my understanding? Thanks!

The activity is the same regardless of the ways to express composition and the standard state chosen so the above expressions are equal.


texts:
A paper talks about the residual stress when coating polymers.
It says that residual stress is the sum of the "heat stress" (due to the difference in thermal expansion coefficients) and the "shrinkage stress" (due to the solvent evaporation and changes in volume). It then states that heat stress usually increases with temperature while shrinkage stress decreases with temperature. Therefore the shape of the graph of residual stress vs temperature would be a parabola with the minimum changing depending on the polymer/system system.
It then goes to find the starting point of the shrinkage stress and states that it is dependant on the glass transition temperature.
From what I understand, that would happen when the glass transition temperature is between room temperature and the drying temperature.
However, if the glass transition temperature is below both room temperature and drying temperature, what would happen? How this would affect the shrinkage stress? Or did I get the whole connection between glass transition temperature and shrinkage stress wrong?
Thank you


texts: Mathematically, how does the exchange integral for a closed-shell system reduce to zero?

texts:
I am looking at the Hartree-Fock method of approximation for a closed-shell two-electron system.

I have the basis functions

$$
\chi_1(\vec{x}_1) = \psi_1(\vec{r}_1) \alpha(s_1) \\
\chi_2(\vec{x}_2) = \psi_1(\vec{r}_2) \beta(s_2)
$$

where $\vec{x}_i$ is the combined spatial and spin coordinates. The opposite spins are illustrated by the $\alpha$ and $\beta$ labels.

The above gives the total wave function to be the following Slater determinant

$$\Psi(\vec{r}_1,\vec{r}_2,s_1,s_2) =
\begin{vmatrix}
\psi_1(\vec{r}_1)\alpha(s_1) & \psi_1(\vec{r}_1)\beta(s_1) \\
\psi_1(\vec{r}_2)\alpha(s_2) & \psi_1(\vec{r}_2)\beta(s_2)
\end{vmatrix}
$$

Let's bypass a lot of math, and just look at the exchange integral, where the spin and spatial parts have been separated:

$$
\int ds_1 \alpha^*(s_1)\beta(s_1) \cdot \int ds_2 \beta^*(s_2)\alpha(s_2) \cdot \int d\vec{r}_1 \int d\vec{r}_2 \psi_1^*(\vec{r}_1) \psi_1^*(\vec{r}_2) \dfrac{1}{r_{12}} \psi_1(\vec{r}_2) \psi_1(\vec{r}_1)
$$

So the spin integrals do not survive in this case, due to the closed shells, but I am not sure if I see why. Is there some orthonormality for the spin states at play here?


texts: If graphite's just a huge polymer of benzene why isn't it an aromatic compound (polymer?)

texts: My teacher had once told me that graphite was just an insanely huge polymer of benzene (Those weren't his exact words but the gist). Today While we were studying aromaticity in organic compounds we steadily advanced from benzene to napthalene the annulenes and so on. What really stuck me was how as the number of  benzene rings increased the stuff tended towards graphite (atleast thats what the structure seemed to indicate). So the main question is why isn't graphite aromatic if its just a big collection of benzene molecules


texts: How are orbitals displayed in computational Chemistry software?

texts:
In typical software like Gaussian or GAMESS, the molecular orbitals (or even the basis functions) can be displayed as surfaces.

I understand that the surface is probably constructed from a series of points that give a fixed value when substituted into the wavefunction. However, how are these points calculated? Since typical software usually use GTOs, I’d like a formula if possible using those.

Thanks!


texts: Why can an s orbital only hold two electrons?

texts: According to Pauli’s exclusion principle, an $s$ orbital contains at most two electrons with the opposite spin (up and down). Why can't an $s$ orbital contain a third electron whose state is the linear combination of spin up and down?


texts:
Does the chlorination of 4-methylcyclopentene generate two enantiomers or two diastereomers?

I think it makes two enantiomers (or one pair of enantiomer) since the starting compound is achiral, but the answer key says it's two diastereomers.
When I tried making the products using molecular model kit, I think  I got enantiomers.


texts:
I am trying to model the interaction between an electrode and a saline solution through an RC circuit.

A reference electrode is placed in the saline solution to measure the voltage between the electrode used to inject or retrieve charges and the reference electrode.

I then perform a 3 phases cycle using current square waves.

Phase 1: Charge injection through the electrode

During this phase, $e^{-1}$ are injected in the saline solution. At $t = 0$, $C$ is not charged, thus the voltage measured between the electrode and the reference electrode is equal to the votlage drop on $R1$.
This phase uses a current $i$.

Phase 2: Wait a bit

During this phase, charges are not injected or retrieved through the electrode. Thus, $C$ is discharging its charges in $R2$.
This phase is very short, and $C$ will not be fully discharge at the end.

Phase 3: Retrieve charges through the electrode

During this phase, the current flows in the other direction: $e^{-1}$ are retrieve from the saline. At $t = 0$, since $C$ was not fully discharge, the voltage measured between the electrode and the reference electrode is equal to the votlage drop on $R1$ plus the votlage drop on $R2$.
This phase is 3 times longer than the first one and uses a current $-i/3$. Thus, the same amount of charges is injected and retrieved.

The measured voltage looks like:

The general equation for the voltage measured given by the circuit above is:

$$V_{measured} = K*e^{-\frac{t}{R2*C}} + R1*i + R2*i$$

with $i$ the current through the system.

As you can see, the time constant only depends on $C$ and $R2$, however, when fitting an exponential on the data, I get 2 completely different time-constant for the first phase ($e^{-1}$ injection phase) and the third phase ($e^{-1}$ retrieve phase). For the third phase, the time-constant is about 5 times larger...

My current guess is that either $C$, or $R2$, or both are not linear and do not behave the same way depending on the current flow direction. Especially since I think phase 3 is influenced by phase 1. What could explain this behavior? What chemicals reaction happens when a current is injected and retrieved? How could I model this phenomenon?

Thanks for the help to understand this behavior :)


texts: Which temprature is taken in Gibbs free energy equation, of the system or the surrounding?

texts: Which temprature is taken, the temprature of the system or the temprature of the surrounding? I think it should be the temprature of the surrounding. This is because if we take the temprature of the system then change in Gibbs free energy would always be zero as then, change in enthalpy of the system would always be equal to change in entropy of the system multiplied by temprature of the system.


texts: How to compare the oxidizing power of perhalate ions

texts:
In my book the oxidizing power in descending order of the following is given as: $\ce{BrO4-} > \ce{IO4-} > \ce{ClO4-}$

My doubt is regarding their order of oxidizing tendency.

I thought that chlorine has the highest electronegativity, so can help oxygen stabilize the $-1$ charge the best and be least reducing (electron donor) and most oxidizing.  Looks like that’s not the case.

Another possibility was that iodine was the largest ion there, it’s far bigger than oxygen, so maybe it produced some instability which made the negative charge unstable, or in other words it became more reducing. In that case it should be least oxidizing (which is also not the case unfortunately).

I couldn't just make out whats so special about $\ce{BrO4-}$ that makes it the most oxidizing ion

Although this question gives a bit of a good hint but doesn't answer my question completely.


texts: Can acidified or neutral KMnO4 oxidise toluene to benzoic acid?

texts: Why is alkaline $\ce{KMnO4}$ used in the oxidation of toluene to benzoic acid? Can acidified or neutral $\ce{KMnO4}$ be used in this conversion?


texts: What does the plus-minus sign with a value in parentheses mean?

texts:
I always see the plus-minus sign with a value in parentheses after a physical property is described such as melting and boiling point, like this:

$$\text{Melting point }(\pm 1~^\circ\mathrm{C})$$

What does it mean?


texts: Is the concentration of negative ions always equal to that of positive ions?

texts: Is there any way in which a solution can have more negative charge than positive charge, or vice versa? For example, in the context of acid-base chemistry, is there any scenario in which $[\ce{H+}]\ne[\ce{A-}]$? I have never heard of a solution with a non-neutral overall charge, but is it possible in some extreme scenario?


texts:
I came across a problem:

I have 2 LEDs with different emission spectra (blue and green).
I have 1 molecule with a known excitation spectrum (channelrhodopsin2 protein).
I turn on 1 LED at a time.

I want to approximately estimate the ratio of the (level of excitation generated upon green over blue emission) in the full spectrum.

I initially thought it was the dot-product between the emission and excitation functions. But my colleague told me that I have to add the lambda and he offered equation 3 from this website

:

$$J = \int_o^{\infty} F_D(\lambda)\epsilon_A(\lambda) \lambda^4 d\lambda$$

FD(λ) is the normalized emission spectrum of the donor
$\epsilon_{A}$ standards for the molar absorption coefficient of the acceptor
λ is the wavelength.

I'm not sure how this equation applies to the problem at hand, in special I don't know what should the exponent from lambda be.

I have measured the power of both LEDs, and I don't care about the real level of excitation, just the ratio between the excitation generated from the 2 LEDs.


texts: What type of interactions occur when CH4 dissolves in CCl4

texts:
When ionic compounds dissolve in polar solvents many types of factors come into play determining their solubility. Some of them may be: ion- dipole interactions, lattice energy, high dielectric constant of the solvent etc.

But I was unable to understand what kind of interactions take place between non-polar solvent and non-polar solute. I was reading about the solubility of $\ce{CH4}$ in $\ce{CCl4}$ and since they were both covalently bonded I couldn't explain the interactions. Any references would help too.

So my question is:

What type of interactions occur when $\ce{CH4}$ dissolves in $\ce{CCl4}$


texts: How does a reaction exhibit kinetics with a non-integer reaction order?

texts: What does it mean when the order of reaction isn't an integer, e.g., a reaction order of 2.43. Not with something acting as a catalyst but rather as a inhibitor. Why does the inhibitor produce an unusual reaction order? Specifically fluoride ions slowing down the reaction between calcium carbonate and acid by forming calcium fluoride.


texts: Can I use one alkaline battery to recharge another?

texts:
Unfortunately, I don't have batteries to waste to test this myself, but I am curious...

Let's say you have two identical batteries. AA Duracell.

Now let's say you run one of the batteries through an LED until the LED starts emitting at half the intensity it was emitting at when you first started (effectively draining the battery to half voltage)

Now, lets' say you touched the positive ends of both batteries for a reasonable amount of time, and then did the same for the negative ends.

Given that the used battery would have a much lower voltage, raw electrical current would travel from the unused battery into the used battery.

So this brings me to my question -- Would the batteries now effectively have the same amount of energy in them? I am not just talking voltage, but chemically too, or would the similarity in voltage on both batteries immediately disappear if either of them were used (because while, yes, either end of the battery does contain equal electrical charge to its counterpart, either end of each battery does NOT contain equal chemical potential)

To simplify this, would touching two batteries as described above effectively drain the unused one, and charge the used one?


texts: Applications of magnesium sulfate monohydrate MgSO4 · H2O

texts:
How is magnesium sulfate monohydrate $\ce{MgSO4 * H2O}$ used for in chemistry and how does it work as a valuable laboratory drying agent?

I could not find too much information in my book or the internet besides the basics (chemical formula, physical or chemical characteristics, etc.), but I did find what it can be used in. For example, fertilizer, feed additives for livestock, nutrient flavor enhancer, pharmaceuticals, leather and fur production, coloring fabrics, fermentation in beer, paper production, sewage treatment, cosmetics, but nothing about how or why chemistry labs would use it. What is its purpose?

Each time I tried to look it up other products that sounded similar but not the same appeared such as $\ce{MgSO4 * 7H2O}$ , manganese sulfate, manganous sulfate, etc.


texts: Recrystallizing Sodium Acetate from solution

texts:
I made sodium acetate using the following reaction:

$$\ce{NaHCO3 + CH3COOH ->CH3COONa + H2O + CO2}$$

The resulting solution of sodium acetate isn't pure, it has impurities. I want to crystallize the sodium acetate to extract the pure crystals. I crystallized some if it in the fridge, sodium acetate has a higher freezing point than water but I would like to know the technical side of it. Do temperature and saturation affect the crystallization and how can I crystallize sodium acetate reliably?


texts: Microwaving a glass of water, what happens?

texts:
Most of us here would already know the simplified idea behind microwaving food: Microwave radiation hits the water molecules present in food, which excites them and causes 'em to vibrate rapidly in situ resulting in the heating up of food. Very straightforward.

But what if you decide to microwave a glass of water?

I can't seem to find any reliable literature that deals with this. A lot of highly unreliable sites spout nonsense from "The water becomes poisonous" to "The water becomes radioactive", so I've immediately dismissed those. However, some sources suggest that the "water will explode".

Now I was under the impression that the water would perhaps come to a boil a bit faster than it would by simply lighting a fire underneath it.

So after reading the last few sources it wasn't really difficult to believe that an explosion might occur. At first I simply extrapolated my theory of 'rapid boiling' to the theory of 'Very rapid boiling' and was content with that. It made sense to me since I presumed that, just as in the conventional method of boiling water, bubbles of water would be formed at the bottom of the glass albeit at a much faster rate, build up, rise, thus resulting in an explosion. But after some reflection, I noticed a problem with this 'extrapolation'.

Why do the bubbles even form in the first place when you conventionally heat water? Simply lighting a fire below a beaker of water does not ensure that the entire content o the beaker is uniformly heated at the same time. Obviously the layer of water molecules in direct contact with the bottom of the beaker will get heated rather quickly. They rise up, colder water descends, etc etc, you know the deal: convection. It's the sizable temperate difference between the bottom region and the rest of the water, that enables the water at the bottom to get vaporized at some point forming bubbles while the water immediately above it is still in the liquid state.

The problem I see that prevents me from extending this theory to microwaving water is that the mode of heating is different in the case of the microwave: Radiation

Now since radiation is faster at heating a given volume than convection is; for all practical purposes, I think it'd be safe to accept that the water in the beaker will be heated uniformly (The beaker's pretty normal sized...it's dimensions aren't of an order of magnitude greater than that of the speed of light/electromagnetic radiation, so it'll be alright to take the apparatus as being 'uniformly heated'. Had to say this before someone inevitably points out in the comments that all the water being heated to constant temperatures like this at the exact same time is impossible).

So if the beaker is heated uniformly, then I see no reason for bubbles to form...in other words, I don't see an explosion coming.

So what really happens if you microwave a glass of water?

Will it quickly and steadily vaporize? Will it explode? Or does something else happen? And why does it happen?


texts:
I completely don't understand how this method works. My book says that this method works by the principle of self-absorption which occurs by the emitted radiation of hollow cathode lamp when it works on high intensity of electricity, due to which we have more atoms who lead to an extension of emission lines. This is how self-absorption occurs.  Does anyone have any proper explanation for this?

What does this self-absorption actually mean?

How does that lead to a correction?


texts:
Going through the Bohr's model and his assumptions, I came across with this formula to find the energy of the n-th level of any atom:

$$E = - \frac{Z k_e e^2}{2r_n} = -\frac{Z^2(k_e e^2)^2m_e}{2\hbar n^2} \approx \frac{-13.6Z^2}{n^2}~\pu{eV}$$

Now, let's say we take as an example the atom of hydrogen, the energy of the $n = 1$ and only level is ($\pu{-13.6 eV}$). Now, according to Wikipedia (not really a reliable source) this can be interpreted as

  An electron in the lowest energy level of hydrogen ($n = 1$) therefore has about $\pu{13.6 eV}$ less energy than a motionless electron infinitely far from the nucleus.

I don't really understand why there is a "minus" in the result. Why does it say that it has less energy than a motionless electron when he, himself, suggested that the electron's acceleration does not result in radiation and energy loss?

I also understand this formula only worked for the atom of hydrogen (that's why I took it as an example) and due to this problem and that's why the Sommerfeld model was postulated.


texts: What is Hydrogen bond Auto-correlation function

texts:
Can somebody explain the Hydrogen bond Auto-correlation function in Computational Chemistry (Molecular Dynamics and Simulations) and what does Intermittent and Continuous Hydrogen bond means?

Why the graph decays over time? and it's applications?

This is with reference to the paper: Chandra, A. Effects of Ion Atmosphere on Hydrogen-Bond Dynamics in Aqueous Electrolyte Solutions. Phys. Rev. Lett. 2000, 85 (4), 768–771. DOI: 10.1103/PhysRevLett.85.768.


texts: What is a possible conventional interpretation of Wilfred Hagen's puzzling Electron Paramagnetic Resonance spectrum?

texts:
In searching for a conventional interpretation, Wilfred Hagen of Delft Technical University is stumped by an Electron Paramagnetic Resonance spectrum (aka Electron Spin Resonance spectrum) in "Distinguishing electron paramagnetic resonance signature of molecular hydrino":

A sharp, complex, multi-line EPR spectrum is found, whose detailed
properties prove to be semi-quantitatively consistent with
predictions20 from hydrino theory with an average error less than 0.09
G (0.2%) over a 39 G span of 37 lines. We have sought but failed to
find reasonable alternative, ‘conventional’ interpretations for the
detected paramagnetism.

Figure 2. EPR of postulated molecular hydrino H2(1/4) caged in solid
Ga(O)OH polymer. Trace a: wide-scan overview spectrum showing a single
feature only close to the free electron g value. Trace b: zoom-in of
the single feature in trace a shows two main lines of equal intensity,
separated by circa 4 Gauss, and whose center is distinctly shifted
from the free electron value to g = 2.0045. Trace c: further zoom-in
on one of the lines now recorded with a very small modulation
amplitude reveals a fine structure of multiple lines with apparent
peak-to-peak derivative line width of 0.17 Gauss and separated by
circa 0.32 Gauss. Trace d: extensively averaged spectrum taken under
conditions optimized for maximal signal-to-noise ratio at the expense
of minor over-modulation and power saturation, exhibits a complex
pattern of triplet satellite lines. Data collection times for traces
a-d were 10, 16, 375, and 2400 min, respectively. All spectra were
taken at ambient temperature. Trace e is a simulation using field
positions predicted by hydrino theory. Other experimental conditions
and simulation parameters are given in the METHODS section.

He provides the most plausible conventional interpretation:

Alternative interpretation. Alternative to the hydrino analysis in Fig
2e the spectrum in Fig 2d can also be approximately reproduced under a
conventional phenomenological spin Hamiltonian assuming an unusual
combination of two isotropic radicals of unequal intensity each with a
g value of 2.0046. This model would require the two main lines to be
due to an isotropic S = 1/2 system split by an I= 1/2 nucleus with
$A_{iso}\approx$ 3.9 Gauss with additional hyperfine structure form a
combination of some 5 nuclei the majority of which has also I = 1/2. A
second S = 1/2 system should give rise to the satellite lines due to a
different combination of some 5 nuclei, one of which should have I = 1
(e.g. $^{14}N$) to account for the repeating triplet pattern (see Extended
Data Fig. 7 for a detailed analysis).

However, he rejects it:

We consider this alternative explanation of the EPR highly unlikely on
the following grounds. The reaction mixture only contains H2, O2, H2O,
and Ga. Even in the presence of trace contaminants of, e.g., C, N, we
cannot envision how the high-temperature plasma reaction conditions
and sample formation in strong aqueous base could lead to the
formation of stable radical structures of considerable complexity. The
ToF-SIMs, EDS, and XRD analyses also eliminate alternatives.
Furthermore, since the sample is a solid, for complex radicals one
would expect to see anisotropy in the spectra. In particular
absorption-shaped peaks that come with axial or rhombic symmetry of
the spin Hamiltonian are not observed.


texts:
I was doing a laboratory experiment the other day and they asked us to heat a beaker that contained camphor and to cover it with a watch glass with ice on it.

I understand the crystallization process and I also know that the melting point of camphor is 149 C, so it is never reached during the experiment, but I do not get the sublimation process. How can the vapor pressure increase until it reaches a value close enough to the atmospheric pressure to sublimate without reaching its melting point? I think I am missing out an important fact, but I don't know which.


texts: What did I do wrong with my lotion bar that it was grainy at the bottom of the mold?

texts:
I want to create a with cocoa butter bar and coconut oil, that emulsifies quickly when rubbed in your hands. I made a tiny batch with a 6:1 ratio (6 tbsp CB and 1tbsp CO) and they have held together just fine in a variety of temperatures. (The only thing I did different with these besides the smaller ratio of coconut oil is melt both oils together instead of separately).

I went ahead and made a larger batch and tried a tad bit more coconut oil 11(oz):2.5(oz) and I got bars that were totally grainy (I assume it was the coconut oil?). Interesting, the last 5 bars of the batch were fine when I popped them out of the mold. I am assuming the coconut oil is lighter and rose to the top and was poured out first, leaving very little for the last few molds. I"m having difficulty attaching a photo to this message but I can try again.

I heated separately both the cocoa butter and coconut oil in glass measuring cups and hot water on the stove. max temp 170F for 20ish minutes ( is that too hot perhaps?).

Then I mixed the two oils together and mixed them with a blender stick for 40 seconds. Scooped bubbles off that rose to the top.

As I was making sample sized bars, I poured 5/8 oz of mixture into individual silicone molds. But outside in 32F for 15-20 minutes. Then room temp 65-69F for 24 hours.

Ingredients used:
Cocoa Butter - Unrefined, Organic
Coconut Oil - Virgin, Cold pressed, Organic

Questions:
Should I use less coconut oil? I am looking for a bar that emulsifies quickly in your hand that is not too sticky.

If not coconut oil, might another natural product help soften the cocoa butter to that end?

Am I heating the oils too high or too long?

Is there a way to cure the bars successfully?Make sure there are no tiny bubbles in the mold?

Thank you so much for your time and expertise.


texts: Can someone explain why the electrical conductivity of magnesium chloride decreases with increasing concentration?

texts: I was under the impression that the electrical conductivity should increase initially, then begin to plateau, then fall past the saturation point for strong electrolytes. However, from this, I see that the conductivity of magnesium chloride does not follow this ( it is decreasing with increasing concentration) , BUT the data could be wrong though. Would someone mind explaining what I should expect when I conduct the experiment myself?


texts:
What happens when you have a solution of a salt, and then try to dissolve another salt in that solution? I know about the common ion-effect etc, but how do you solve problems like this:

How much AgCl can you solve per L in a 3.8g/L NaCl solution?


texts: In this example, why is there is a ring formation with the attack of the OH from the intermediate itself rather than a continuation of addition? I know my proposed product is wrong, however I just want an explanation as to why this occurs.


texts: Reaction of urea and thiourea with nitrous acid

texts:
I was told that urea on reaction with nitrous acid gives nitrogen gas, carbon dioxide and water. While on the other hand, thiourea on reaction with nitrous acid gives $\ce{H+}$, thiocyanate ion and water.

I tried looking for the mechanism and thought that this would be related:

I carried out the above procedure on both the nitrogens of urea and was able to obtain the products of the first reaction enlisted above. Now, my questions are:

• Isn't the nucleophilicity of the lone pairs of urea's nitrogens negligible, and any reaction should proceed via attack by oxygen's lone pairs? (I thought that this was similar to amidines and amides)

• Why are the products of the reactions with urea and thiourea different, as the carbonyl oxygen, or sulphur doesn't seem involved in the reaction according to me

• More importantly, is this even the correct mechanism?


texts: Why would Ammonium Nitrate spontaneously combust/detonate when damp?

texts:
Why would small amounts (1g or less) of Ammonium Nitrate spontaneously combust/detonate when damp? Possible temperature excursions to +70degC. Unfortunately I cannot give you the context for commercial confidentiality reasons.

I was under the impression it was very stable in small quantities.


texts: If you are given ΔH for this reaction which occurs at constant pressure, what additional information you need to determine ΔE?

texts:
Reaction: $\ce{2Al + 3Cl2 → 2AlCl3}$

Answer: We must have either temperature, or the values of P and ΔV in order to calculate ΔE from ΔΗ.

Since ΔH is given, we can use the formula ΔE=ΔH-PΔV to calculate change in internal energy, and only pressure and ΔV are required to calculate ΔΕ.
So my question is, why do we need temperature in this question?


texts: Physical reason for the ideal lattice approximation

texts: Why can we approximate a lattice as being infinite when we describe it as an ideal crystal? Is there any physical reason or is it just because the number of ions (/atoms) is so huge that we can treat an ion in the middle of the crystal as if it was surrounded by an infinite number of them, and just forget what happens on the surface?


texts: Why aren't nitriles very good electrophiles?

texts: I was wondering why nitriles do not react as electrophiles like carbonyl unless they have to, given that the C-N triple bond is still pretty polarized. The LUMO will be higher in energy than a carbonyl due to the higher electronegativity of oxygen, but I don't see why nitriles are far worse in electrophilicity.


texts: Electroplating metal inside polymer foam with acetone

texts:
In my research we have a method of making polymer open-cell foams with high tortuosity and pore sizes on the order of 50–200 nanometers. I can make thicknesses of 100 µm to 2 mm thick (and up to 5 inch diameter disk). I am looking for some cool things to do with this material, and one idea was to try to fill it with metal and then dissolve the polymer away to leave a nanoporous metal structure.

The problem is that so far I cannot get water to penetrate inside the pores, I tried up to 4 MPa pressure and it just won’t go through (small pores and hydrophobic) but acetone will get absorbed in very quickly. My question is, could there be a way to use acetone as an electrolyte and deposit metals (copper, nickel, whatever) to fill these open-cell pores?

I haven’t taken chemistry since intro chem back in undergrad so I really don’t know much of anything about electroplating, so I will be very grateful for any help on this experiment. Thank you very much, I hope I was clear in explaining what I am trying to do.


texts: Why are lead and zinc commonly found together?

texts:
Copper, silver, and gold are often found in combination. That makes sense to me, because they are members of the same chemical family. Likewise, I would expect nickel palladium, and platinum to be found together.

But lead and zinc are often found together, even though they are not of the same chemical family. At least, these metals seem to appear "jointly" more often than lead and tin, even though these are members of the same family.

Why would that be, or am I missing something?


texts: I held gallium under a heat lamp. It didn't melt. I didn't even find a thin film of liquid gallium. Can anyone explain why? Does gallium rust?


texts: When using hydrazine as a reduction agent to reduce graphene oxide, which is the product hydrazine oxidises to?


texts: Why is the gram no longer a function of the atomic mass number?

texts:
According to Wikipedia,

  ... the definition of the gram is not (as of 2011) mathematically tied to that of the atomic mass unit

Why did we change that?


texts:
I am currently working on a heterogeneous photocatalyst project.  We are having significant problems with the catalyst not staying suspended in an aqueous solution.  What can I do to prevent aggregation of an oxide catalyst.  I suspect there are lots of possible solutions.
Some extra details about my specific system:

Aqueous solvent (pH: ~7)
Nanoparticles around 100-200 nm
Isoelectric point around pH 3 - 4
Roughly 0.2 mg of catalyst / mL


texts: How to judge if a reaction is exothermic or endothermic

texts: Mix $\ce{HCl}$ and $\ce{NaOH}$ together (reactants are at the same temperature) in a calorimeter. The temperature increases, and the book says it's an exothermic reaction. I don't get it. The thermometer is in the solution which means it measures the temperature of the solution. It's the system. The temperature of the system increases, this means that heat flows in. How could this be an exothermic reaction?


texts: Are molecular properties robust towards manipulations?

texts:
Machine learning algorithms analyze molecules by looking at their molecular representations (e. g. SMILES and graph) and turning them into feature maps that help the algorithm to distinguish them. In the case of graph representations, algorithm tends to generate similar feature maps for the molecules that have similar topologies.
I was wondering if it is a correct assumption, generally speaking, that molecules with similar molecular graphs tend to have similar properties. That is, if we slightly modify one molecule, the output is expected to be close to the original molecule.

EDITS:
It seems this assumption is the base for Chemical Similarity. It goes on to say

[...] descriptive network properties and graph theory can be applied
to analyze large chemical space

At the end of the day, I think it is true that it all depends on what type of properties I'm dealing with. But my understanding is that this chemical similarity provides a base for more complex problems to build upon. For instance, if I want to modify a particular property, I would just add that into my initial analysis of the molecule.


texts: Is the number of hyperconjugation structures for a hydrocarbon with number of 'alpha' hydrogens 'a' equal to 'a' or 'a+1'?


texts:
When you mix ice cream and a soft drink (like coke,)  a reaction happens that creates a thick foam.  I am assuming the foam id composed of carbon dioxide gas and milk curd, which is produced by the milk reacting with an acid.

Is the milk curd produced by the carbonic acid or the phosphoric acid?
Is the carbon dioxide released by the added sugar, or another ingredient?
Are there other important processes going on in there?


texts: Entropy change when indistinguishable particles suddenly become distinguishable

texts:
We have that

$$
S = \frac{U}{T} + k\ln Q
$$

Using that for indistinguishable particles in the canonical ensemble

$$
\ln Q_{\mathrm{indis}} = N\ln \frac{q_{\mathrm{tr}}e}{N} + N\ln q_{\mathrm{rot}} + N\ln q_{\mathrm{vib}} + N\ln q_{\mathrm{el}}
$$

Similarly for distinguishable particles we have that

$$
\ln Q_{\mathrm{dis}} = N\ln q_{\mathrm{tr}} + N\ln q_{\mathrm{rot}} + N\ln q_{\mathrm{vib}} + N\ln q_{\mathrm{el}}
$$

Then we assume the indistinguishable particles suddenly become distinguishable. By how much does the entropy of the system change?

$$
\Delta S = S_{\mathrm{dis}} - S_{\mathrm{indis}} = k(\ln Q_\mathrm{dis} - \ln Q_\mathrm{indis}) = Nk[\ln(N)-1]
$$

In the special case that the system contains only one particle ($N=1$), the entropy changes by $-k$.

Intuitively, it does not matter whether one particle becomes distinguishable from the rest if there is only one particle; Assigning a label to just one particle does not really modify the information within the system.

So how can this be understood?


texts: If capsaicin is insoluble in water, what makes chilli water taste spicy?

texts:
I have always been told that the 'heat' from chillies came from capsaicin which is oil based. Recently I began wondering how environmentally friendly chilli based insecticide/repellent sprays could work if they are water based. A chemist friend confirmed for me that capsaicin is not soluble in water.

I minced a chilli and added this to a coffee mug of boiling water, left overnight then strained through a coffee filter. The resulting chilli water is definitely spicy, but why? What has dissolved into the water (or is the mixture some sort of emulsion of tiny oil droplets?).


texts:
The Miller-Urey experiment shows that it easy in a primordial atmosphere
similar to early earth to generate amino acids,my question: is it theoretically possible to simulate this experience on any computer ?


texts: How can different no. of unpaired electrons lead to different colours of co-ordination compounds?

texts:
To make the question clear I would like to take an example. $\ce{K_3[Fe(CN)6]}$ and $\ce{K3[FeF6]}$ shows different colors in solutions. It is given in my textbook that it is because of different number of unpaired electrons.
But, how can the no. of unpaired electrons affect the frequency of light emitted?

The colors of co-ordination compounds are due to d-d transition of electrons. $\ce{CN^-}$ is a strong field ligand while $\ce{F^-}$ is a weak field ligand. Thus, there will be difference in the crystal field splitting energy in both of the given compounds. This, results in a different energy gap between the eg and t2g energy levels in them. Thus, when electrons undergo transition different frequencies corresponding to different energy gap is emitted.

I was hoping this as the answer. But, in my textbook the reason is attributed to only the difference in no. of unpaired electrons. Why is it so?


texts: Slight variation in NMR integrals of CH protons vs. CH2 or CH3

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While acquiring some NMRs I find that there is a consistent pattern in that protons attached to sp2 carbons tend to have slightly smaller integrals than protons attached to sp3 carbons:

(peaks in aromatic region are from a para-disubstituted benzene ring; peak at 4.92 ppm is from a trisubstituted alkene; 4.50 is a NH; the remainder are aliphatic CH2's or CH3's.)

I calibrated the total sum of integrals to 21; one can see from the spectrum that the aromatic and olefinic peaks are slightly smaller than integral values, and the others are slightly larger. Obviously it doesn't hinder the analysis of the spectrum, but it was an interesting trend (the same was observed in multiple spectra).

Am I reading too much into this, or is there a reason behind it? I strongly suspect there is something - perhaps related to the marginally slower relaxation of these protons, since there are no geminal protons (only vicinal protons)?

If it is of relevance - a 60° pulse is used (pulse program zg60). The number of scans ns is 16, and the relaxation delay d1 is 1 second. I'm happy to provide any other necessary acquisition parameters, or to provide the full structure of the compound if it's necessary.

P/S I found something in Findeisen & Berger's 50 and More Essential NMR Experiments, in which they mention that the integral of an aromatic proton in strychnine is smaller than expected as it has the longest relaxation time. Even though the authors used ns = 1, too short a delay between the receiver gain adjust and the scan was used, which led to incomplete relaxation and hence a smaller integral.


texts: What makes pentane, hexane, heptane, and octane dangerous, while butane and nonane aren't?

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In particular, how do a methylene more (in the case of the pentane) and a methylene less (in the case of the octane) make the difference in harmfulness to the environment in comparison with, respectively, the butane and the nonane?

I saw that butane and nonane are not classified as dangerous, but I have just done a research and it turns out nonane is harmful to fish, just like octane, but the difference is that the nonane becomes aqueous more difficult because of its low solubility. But I read that its soluble part is still dangerous for aquatic life. Then the question is: Shouldn't it be classified as dangerous anyway?
The propane, as well, appears to be harmful to the fish, while I can find nothing but "not classified as dangerous", as for the butane. Is LDC3's answer the explanation?


texts: How to calculate the boiling point of a solid substance?

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Say that I have a solid substance; I know its density, mass, volume, melting point, specific heat, the pressure which it is under, and nothing else. (for now.)

How do I find the heat at which it boils? (So it goes solid -> liquid -> gas)