texts: How Can I Test Something for the Presence of Iodine?

texts:
I want to test a supplement for the presence of iodine.
Iodine should turn starch blue-black. So, can I powderize the supplement tablet, add water to it, drop it on a piece of bread, and if it turns blue-black, that would be an accurate way to test?


texts: Liquid to solid crystal when exposed to air

texts:
Im working on a prototype weapon based on the needler from the Halo series. And yes while I do realize that this game series is fantasy, I still find it fun to try and recreate working versions of what is in the game.

I have a concept worked out to keep the crystalline ammunition in a liquid tank and then use compressed air to fire. The liquid will be pushed through perforated holes to for the crystal ammunition. But I don't know of any chemical or compound that turns from liquid to solid, preferably crystalline when exposed to air. If someone could help me with such a substance I would greatly appreciate it.


texts: Why would CuSO4-EDTA drops be used in Pb titrations?

texts: We use CuSO4-EDTA drops (4) when preparing our lead titration samples for final titration by EDTA.  What mechanism would there be for adding this to a titration?  What benefit does it produce on Pb titration?  We digest galena with nitric and sulfuric, clean up samples with a 5% sulfate wash, and remaining sample is washed into original beaker with 50% ammonium acetate solution (ammonium acetate/acetic acid buffer).  Samples are boiled then cooled before final steps.  The samples have ~1.5g ascorbic acid, 4 copper-EDTA drops, and 4 xylenol orange drops added to each sample prior to titration with EDTA.


texts:
It does not has a 'K' in its name. It does not have a potassium in its chemical composition.

Would be nice to know why Glutamine is Q too, some of these abbreviation seems simply random.


texts: What is the difference between BET and Langmuir model for calculating the specific surface area?

texts:
Brunauer–Emmett–Teller (BET) surface area is measured by specific surface area of the adsorbent. BET surface area is measured by using non-corrosive gases like $\ce{N2}$, $\ce{CO2}$, $\ce{Ar}$ etc. BET surface area depends on size and number of gas molecules adsorbed. Langmuir surface area depends on adsorption capacity of the adsorbent.

Why is Langmuir surface area always higher than BET surface area?


texts: What is the potential to use for non-dispersion interactions?

texts: Although liquid argon’s intermolecular potential can be described using a Lennard-Jones (LJ) potential, which takes into account dispersion forces (induced dipole-induced dipole interactions), what potential do you use when also including the effects of dipole-induced dipole and dipole-dipole interactions?


texts:
Why does $\ce{O-}$ show +I effect?
On the other hand why does $\ce{OH-}$ show -I effect?
both oxygens are electron rich and are negatively charged. my teacher says that charge on the species is a headache for the species ,so according to me both the oxygens should show +I effect, that is donating electrons tendency. Plus they have lone pairs too.
How can we extend the similar explanation for the halides? they have 3 lone pairs so they should also not take up more electrons.
If carbon is double bonded to oxygen then is there any inductive effect taking place over there?

Organic is confusing me. Help would be appreciated.


texts:
Consider some general parallel first order process, where $\ce{A -> B}$ and $\ce{A -> C}$ (rate constants $k_1$ and $k_2$ respectively)
The overall rate equation of this process is said to be $-\frac{\mathrm d[A]}{\mathrm dt} = k_1[\mathrm A] + k_2[\mathrm A]$
I get the impression that this is derived from the addition of each individual rate equation, i.e. the addition of $-\frac{\mathrm d[\mathrm A]}{\mathrm dt} = k_1[\mathrm A]$ and $-\frac{\mathrm d[\mathrm A]}{\mathrm dt} = k_2[\mathrm A]$ would result in the overall rate equation shown above.
However, if this is the case, then why isn’t the rate equation actually $-\frac{2\,\mathrm d[\mathrm A]}{\mathrm dt} = k_1[\mathrm A] + k_2[\mathrm A]$? I mean, you’re adding two $-\frac{\mathrm d[\mathrm A]}{\mathrm dt}$ terms together; and so considering basic algebra, surely this would result in $-\frac{2\,\mathrm d[\mathrm A]}{\mathrm dt}$?
Or do differentials just not work in this way, and I’m simply confusing myself?


texts: What is the $K_\mathrm{a}$ of $\ce{OH^-}$ and $K_\mathrm{b}$ of $\ce{H_3O^+}$? Have these constants been determined?


texts: what is the relationship of Salt, White Vinegar and Water to create 1 liter of Hypochlorous Acid

texts: What is the relationship of Salt, White Vinegar, and Water to create 1 liter of Hypochlorous Acid (for disinfecting and cleaning purposes), and how much time do I have to put it under a 9v battery induced electrolyzing process?


texts:
This is a question I solved in class:

  At 35 degrees, $\ce{N_2O_4}$ is 15% dissociated in a flask at a pressure of 1.2 atm. Calculate
  $K_p$  Equation:
  $$\ce{N_2O_4(g)<=>2NO_2 (g)}$$

This was how the answer went...

Partial pressure of $\ce{N_2O_4} = 0.85\times 1.2$

Partial pressure of $\ce{NO_2} = 0.1\times 1.2$

then $K_p$ was calculated using the standard formula

My question:

The part I cannot agree to with my teacher is that how is the partial pressure of $NO_2$ equal to 0.15x1.2. If I begin with 1 mole of $\ce{N_2O_4}$, if 15% dissociated at 1.2 atm, I would end up with 0.3 moles of $\ce{NO_2}$... the the partial pressure would be ${0.3\over 1.15}$x$1.2$... this does not go with the general answer stated above


texts: 'Hard' soap vs. 'Soft' soap: Why do they work this way?

texts:
In school, we did an experiment using fat and $\ce{KOH}$ to create 'soft' soap.

Afterwards, we added $\ce{NaOH}$ to change it into 'hard' soap.

I read on multiple places on the internet that the difference between using Potassium and Sodium is what determines if it becomes a 'hard' soap or 'soft' soap.

Am I correct in the notion that the $\ce{K+}$, resp. $\ce{Na+}$ ions connect to the $\ce{O-}$ ends of the Fatty Acid?

Is it possible to skip the first step and create 'hard' soap by using $\ce{NaOH}$ right away?

Why does 'Soft' soap dissolve so much easier than 'Hard' soap? Or in other words: Why is it much easier for the $\ce{K+}$ to fall off than for the $\ce{Na+}$ ?


texts: Which unit cell do we obtain if spheres are arranged in ABABAB type in 2D and then that 2D layer is arranged in AAAAAA type in 3D?

texts:
Arranging spheres ABABAB type in 2D gives us close packing. Now, this layer if arranged in ABABAB (in 3D) gives us HCP and if arranged in ABCABC (in 3D) gives us FCC.

What do we get if we arrange it in AAAAA type (in 3D)? (we are talking about one type of spheres only)


texts:
My question is related to the edge between Subatomic Physics and Chemistry, but I decided that here is the best place to discuss it.

As we all know, Theoretical Physics is a well developed field of knowledge, able to describe the very tiny forms of interactions. However, after some researches for some kind of formula to perfectly describe the interactions on the atomic level (not subatomic), more specifically, a way to calculate the strength of chemical bounds, I keep comming across frustrating highschool explanations, such as

  ionic > covalent > H-bond > dipole-dipole > van der Waals

The most precise data that I was able to find comes at page number 20 and 21 of this pdf, that apparently shows some experimental results (I'm guessing).

So here is my question: is there really a unified formula? What if I want to simulate chemical interactions (proton-by-proton, electron-by-electron) on a computer, is it that complex to do, even assuming that I want a simple simulation of about 20 atoms?

Edit: When I reffer to calculating chemical bonds strength, I also include predicting many other chemical properties, as electron affinity or reactivity of the elements, which are all related.

Note: I can accept as answer any pdf that clarifies my question, because I wasn't able to find. Maybe I'm looking it with the wrong key-words.


texts: Bond order of HCO3- as compared to (CO3)2-

texts: How can we say that the bond order of $\ce{HCO3-}$ is less than that of $\ce{CO3^2-}$? I see that the resonance in $\ce{HCO3-}$ is not as effective as in latter because in latter it is equi-energy resonating structures, and thus energy released in $\ce{HCO3-}$ would be less. But how does that relate to the bond order? The bond order of $\ce{CO3^2-}$ should be $\ce{4/3}$, but why can we say that $\ce{HCO3-}$ will be slightly less than $\ce{4/3}$?


texts: Electrostatic potential map and local ionization map

texts:
What's the difference between electrostatic potential map and local ionization map?

I think that the main difference is that the electrostatic potential map doesn't take into account resonance (delocalization), but only electronegativity, therefore nucleophilicity or electrophilicity of a species is much better estimated by using the local ionization map. Am I wrong?


texts: Number of resonating structures (hypothetical)

texts:
To my knowledge, resonance happens where more than one lewis stucture can represent the compound with no shift in sigma bonds

so, suppose in a simple conjugated system even like 1-3 pentadiene , two forms are well known, i want to know if a third form where each atom has completely filled or completely empty p orbitals should also be taken into consideration, as technically, there is nothing wrong with it, I accept that it's "contribution" will be negligible, but it should be counted in all POSSIBLE resonating structures

https://commons.wikimedia.org/wiki/File:Naphthalene_resonance_structure.svg

similar argument here, a lot more can be created if we allow charge separation of pi bond

EDIT: The question is whether there is a convention of some sort which tells us which ones to count which ones not (if we cant tell the magnitude of difference in stability of the structure)


texts:
I am not sure that this is the right place for this question, but I'll try.

I am working on a scheme that I am developing on illustrator. I have a lot of chemical structure and plus I have some vectorial pictures included.

The thing is that I would like to save/export my illustrator file in a way that I can reopen it and modify it in chemdraw. I am aware that the opposite procedure is possible.

Is there any way of doing that?


texts: Is my understanding of cyclic voltammetry correct?

texts:
So recently I've been roped into doing some CV and I'm trying to wrap my head around the fundamentals of the science behind it (and electrochemistry more generally! Bare in mind I'm very much not an electrochemist...). This is where I'm at:

We have our three electrode setup, two of which are submerged in the same electrolyte solution: working electrode (WE), reference electrode (RE - Ag/AgCl in this example - contained in its own little unit with its own electrolyte solution; the contained RE unit is however submerged in the bulk electrolyte solution along with the WE and CE) and counter electrode (CE - Pt wire in this example).
When we cycle through the voltages, we're measuring the electric potential of the working electrode relative to the reference electrode (which, handily, will always remain at 0V and thus the difference in volts between the WE and RE - the voltage - will always equal whatever the electric potential of the WE is).
In order to polarise the WE (ie, either pump electrons into it or remove electrons from it) we use an external power source. We attempt to do the same with the RE but pumping electrons into it simply results in Ag being reduced, and removing electrons from it results in Ag being oxidised, and thus no net polarisation of the RE is possible (hence the 0V).
Polarising the WE negatively (eg, -0.4V, -0.6V, etc) = pumping it full of electrons, which means those electrons are relatively high in energy and readily available to reduce anything at the WE surface.
Polarising the WE positively (eg, +0.5V, +0.8V, etc) = removing electrons from it, which means the electrons that remain are relatively low in energy and thus electrons in things at the surface of the WE are likely to 'jump' into the WE, in the process oxidising whatever it is they're jumping from.

With all that in mind, here are my questions:

When we're pumping electrons into/out from the WE, do these electrons come from/go to the Pt CE? Given Pt is very inert, this means something in the electrolyte solution must be being oxidised/reduced?
What is the electric potential of the CE throughout the process? Say we've polarised the WE to +0.6V (ie, forcibly removed electrons from it), the RE remains at 0V (as it always does) - does the CE become -0.6V? After all, the electrons being removed from the WE have to go somewhere - presumably some would go to the RE as well as the CE, so the polarisation of the latter won't be the exact inverse of the WE?
The RE is contained in its little unit with its own electrolyte solution. I've seen in diagrams that a porous frit separates the RE's electroyle solution from the bulk electrolyte solution that the WE and CE are submerged in. What can traverse this barrier? I assumed it would only be certain ions (so it would effectively act as a salt bridge as seen in normal galvanic/electrolytic cells), but the word porous implies that water as well as certain ions can pass through it?

Any and all help is appreciated! If you're not too sure on the questions I'd be very happy if you just weighed in on the CV understanding part, and if you only know one/some of the questions then that'd also be great :)


texts: Does a rotary evaporator need a draft chamber and a vacuum pump?

texts:
I am using DCM ( dichloromethane) in my research, as a solvent. At the end of the day I have to separate the salute and measure it.
Up until now, I have been using a constant temperature oven, set a about 65 degree Celsius (evaporation temp of DCM). The exhaust DCM is expelled into the atmosphere and the dried salute is then cooled down and measured.

I want to replace the oven with a rotary evaporator. However I have an argument with my advisor. He claims that I require two things:

Aspirator /vacuum pump
Draft Chamber

While I agree that a vacuum pump can be of use, I do not require my solvent to boil, therefore I do not need vacuum.

As for the draft chamber, I completely fail to see its implication.
I believe that since the rotary evaporator is a completely closed system, there is no way DCM vapor could leak, rendering the draft chamber useless.


texts:
My basic knowledge about nomenclature is: A mineral acid is called hypo when it has one less oxygen than the original one,
a pyro acid when 2 molecules of acid add up with release of $\ce{H2O}$
a meta acid when one molecule releases $\ce{H2O}$ and
a per acid when it has one extra $\ce{O}$ in the structure connected with a peroxide bond.

Question 1

I was taught in my class that this structure:

is correct because when we are drawing structures of a hypo-,per-,meta- or pyro- oxyacid, one must try to maximise the covalency. Why is that so?

Also, usually in pyro- acid we find a $\ce{M-O-M}$ bond where $\ce{M}$ is the central atom(s). Like $\ce{P-O-P}$ in pyrophosphoric acid as show below:

Then shouldn't the structure of pyrosulfurous acid be like this:

 Why is the structure not similar to pyrophosphoric acid?

Question 2

We know that in hypo-acids, there is one less $\ce{O}$ in the empirical formula of the acid i.e. Hypophosphoric acid should have one less $\ce{O}$ than in $\ce{H3PO4}$ i.e. it should be something like $\ce{(H3PO3)_$n$}$. If we put $n=2$ we have $\ce{H6P2O6}$.

But why is its formula $\ce{H4P2O6}$?

I might lack some information about it or maybe I've understood the concept wrong. Please help.


texts: Why does q/m ratio(specific charge) depend on nature of gas in anode ray experiment?

texts:
I can't understand why $q/m$ ratio changes in anode ray experiment (discharge tube experiment) (which was carried out by Goldstein) with change in nature of gas?

Since $q=1.6\times10^{-19}\ \mathrm C$ and $m=1.6726219\times10^{-27}\ \mathrm{kg}$, shouldn't the ratio be constant?


texts: What is the appropriate procedure for determining the quantum numbers of an electron?

texts:
How do I find the set of quantum numbers for a specific electron in an element? For example,

  Calculate the set of quantum numbers for the 19th electron in chromium.

The electronic configuration of the 19th electron is 1s2 2s2 2p6 3s2 3p6 4s1. From here on, how do I decide what would the principle quantum number be?


texts: What is the meaning of the term 'reserve acidity'?

texts:
In $\ce{CH3COOH/CH3COONa}$ buffer, the reserve acidity of the solution is due to the $\ce{CH3COO-}$ ions.

What is the meaning of the term of 'reserve acidity' in the above statement?


texts: Why are different colors, according to sugar concentration observed in Benedict's test?

texts:
Colors range from green yellow orange to red. How does the sugar concentration and Cu2O concentration cause this?
I know Cu2O is red. Why is there a green or yellow color instead of just red or some kind of red?


texts: Bond cleavage of 3 membered cyclic ring on heating

texts:
I was told to propose a mechanism for the following conversion:

One obvious step is the conversion of cyclic ketal to ketone because of acidic conditions. But I am unable to understand how the three membered ring opened to give an alkene? (However, I can understand  that the three membered ring is unstable)

I feel that somehow, a carbocation is being generated and E1 type elimination is taking place.

What is happening exactly? And does this type of thing take place with any three membered ring under given conditions?


texts: Space filling model for nitrogen molecule

texts:
I want to make space filling model for nitrogen molecule.

I've learned that van der Waals diameter is to be taken for atom radius.

Since van der Waals radius for nitrogen is $\pu{155 pm}$ and bond length is $\pu{110 pm}$, does this mean that nitrogen molecule space filling model is two blue spheres of diameter $\pu{155 pm}$ and center to center distance $\pu{110 pm}$?

One of the reasons for this question is that samples of space filling model for this molecule (see for example Wikipedia) do not agree with these data; there's about a 11% difference between the length/width ratio of the drawn molecule, and what it should be based on the van der Waals radius and bond length.

\begin{array}{cccccc}
  \displaystyle\frac{d}{2r}
    &\sim& \displaystyle\frac{\pu{1000 pix}-\pu{716pix}}{\pu{716 pix}}
    &\sim& 0.397\\
  \displaystyle\frac{d}{2r}
    &\sim& \displaystyle\frac{\pu{110 pm}}{2\times\pu{155 pm}}
    &\sim& 0.355
\end{array}


texts: questions about the synthesis of iodobenzene from aniline

texts:
I am conducting an experiment about synthesis of iodobenzene from aniline, referring to this site(and various sites) (http://www.prepchem.com/synthesis-of-iodobenzene/). Below is my experimental process.

Put $\pu{9.5mL}$ of conc. $\ce{HCl}$, $\pu{9.5mL}$ of distilled water, $\pu{2mL}$ ($\pu{0.0215mol}$) of aniline in a $\pu{100mL}$ round flask with ice bath, and wait until the temperature of mixture drops below $\pu{5℃}$.
Dissolve $\pu{1.56g}$ ($\pu{0.0226mol}$) of $\ce{NaNO2}$ in $\pu{50mL}$ of distilled water, and cool it with ice bath.
Once the temperature of mixture dropped below $\pu{5℃}$, put the solution of $\ce{NaNO2}$. the solution must be poured very slowly not to raise temperature above $\pu{10℃}$.
Stir the mixture for $\pu{10 min}$.
Dissolve $\pu{ 3.58g}$ ($\pu{0.0216mol}$) of $\ce{KI}$ in distilled water. I used the water in very small quantities because $\ce{KI}$ is very soluble in water.
Put solution of $\ce{KI}$ to the mixture, then color of the mixture turns to be black, and gas bubbles (may be nitrogen gas) rise from the mixture.
After $\pu{1-2 h}$, gently heat the mixture (I set the temperature about $\pu{50-70 ℃}$).
Again after $\pu{1-2 h}$, it seemed that there are no more gas bubbles, so I stopped stirring and heating.
Layer separation occurred, (I guess) because iodobenzene is insoluble in water. so I moved it to separatory funnel and took the black oily organic layer presumed to be iodobenzene.
Here is the stage I am stuck on. according to the reference site, it says "use $\ce{NaOH}$ to decolorize the iodobenzene" (iodobenzene is colorless liquid). I put $\ce{NaOH}$ and made the pH of mixture 7, but its color is still black.

Question 1. Do I have to make the mixture basic to decolorize it? (actually, I tried making it basic, but it was not decolorised. Should I wait a moment after making it basic?)

Question 2. According to the reference site, iodobenzene have to be distilled using steam-distillation, but should I distill it with steam-distillation, not just ordinary distillation?

Question 3. Are there any problems with my experimental process?


texts:
When discussing problems of keeping hydrazine from freezing on spacecraft we stumbled upon a question: can pure hydrazine separate through fraction-freezing from the stabilizing substances like UDMH? That would largely depend on what form it takes. If it crystallizes, it's a risk - it's quite unstable when pure. If it turns amorphous, embedding the stabilizer within the structure, it's moot. Publicly available resources are quite skimpy on descriptions of freezing hydrazine (or I just suck at searching). So, -

Does hydrazine crystallize when freezing? Can it trigger fraction-freezing separation if it's the first freezing substance?


texts: Are the lone pair electrons on an carbonyl oxygen in sp2 orbitals?

texts:
Carbonyl Group Double Bonds

  [...]

  One pair of the oxygen lone pairs are located in 2s while the other pair are in 2p orbital where its axis is directed perpendicular to the direction of the pi orbitals.

http://chemwiki.ucdavis.edu/?title=Organic_Chemistry/Aldehydes_and_Ketones/Properties_of_Aldehydes_%26_Ketones/The_Carbonyl_Group

How can a lone pair on the carbonyl oxygen be in a p orbital? Neither of the electrons in a carbonyl oxygen can be delocalized.

This seems to be more along the lines of what I'm thinking:


texts: Sunlight degradation of butyric and propionic acid

texts:
As I understand from Wikipedia article sweat is metabolized by skin flora primarily to butyric and propionic acid. What will sunlight do to these acids? Will my cloth smell less if dried in sunlight?
My concerns is that if drying in sun will remove odour fomr clothes as sunlight will cause degradation of odor causing chemicals(what ever they may be) and bacteria.
Sunlight should break bind in organic chemicals and make them odourless


texts: Why does the dipole moment of molecules go from positive to negative?

texts:
In physics the dipole moment is said to go from the negative to the positive pole, check for instance https://en.wikipedia.org/wiki/Electric_dipole_moment (Elementary definition).

This makes sense to me since in an electric field (which is directed from positive to negative) the dipole moment aligns with the electric field, such that in the aforementioned definition the positive pole points towards the negative pole of the electric field and vice versa.
(also see: https://physics.stackexchange.com/questions/89157/motion-of-a-dipole-in-an-electric-field)

Now, in all representations of molecular dipole moments I could find online the dipole moment is directed from the positive to the negative pole.

Check for instance: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Physical_Properties_of_Matter/Atomic_and_Molecular_Properties/Dipole_Moments

or just have a look at google images for the search term 'dipole moment molecule'.

This doesn't make any sense to me, is there any good reason for this discrepancy?


texts: Why do you need to convert copper (II) hydroxide to copper (II) oxide before converting to copper (II) sulfate?

texts: This is the protocol for a practical class I once took. The idea is that copper nitrate is converted to hydroxide, oxide, sulfate and then finally solid copper. I know that $\ce{CuO(s) + H2SO4(aq) -> CuSO4(aq) + H2O (l)}$, but can't you avoid converting the hydroxide to oxide altogether and just do $\ce{Cu(OH)2(s) + H2SO4(l) -> CuSO4(aq) + 2H2O(l)}$? Note that $\ce{NaCO3}$ is decanted and washed off before reacting copper (II) oxide with sulfuric acid, but surely you can also do the same thing with copper (II) hydroxide?


texts: Cleaning stains with hydrogen peroxide and bleach

texts: A while back, I discovered that if you have a stain on a white shirt, you can remove it by putting hydrogen peroxide on the stain, then adding some bleach to it.  I have used this for getting out wine, sweat, chocolate, etc.  The reaction produces gases and heat.  What is happening in this reaction and why does it clean stubborn stains?


texts: Product of Diels-Alder reaction + Consecutive Reaction with base and heat

texts:
there is a problem regarding a Diels-Alder reaction that I do not understand (see image).

The Diels-Alder reaction of the diene and the dienophile should lead to the product A. I hope I did it correctly, because the molecular formular shall be C9H6O2N2.

Now, the base triethylamine is added and heat is applied. Because it is a very strong base I would deprotonate the proton next to the ester-group -COOR, since it has a -M effect. I think applying heat leads to decarboxylation (B = carbon dioxide). But I don't know what the product C looks like, since there is another reaction to product D.

Can you please help me?

Thank you!


texts: What is the correct order of boiling points for group 15 hydrogen compounds?

texts:
What is the order of boiling points of the following
$\ce{NH3}$,  $\ce{PH3}$, $\ce{AsH3}$, $\ce{SbH3}$ and $\ce{BiH3}$?

What I thought was, that as $\ce{H2O}$ has a higher boiling point compared to its group members due to hydrogen bonding, so should nitrogen. And then the order would follow according to the molecular weight. When I wrote this as an answer, it was marked wrong. What is the correct ordering and what is the reason for it?


texts:
A $54.0\ \mathrm{mL}$ sample of oxygen is collected over water at $20\ \mathrm{^\circ C}$ and $770\ \mathrm{Torr}$ pressure. What is the volume of the dry gas at STP?

By using the combined gas law, I came up with the answer $\pu{51.2 mL}$.

$770 - 21.1 = 748.9\ \mathrm{Torr}$ pressure for oxygen

$21.1$ = vapor pressure of water at $23\ \mathrm{^\circ C}$

$\frac{P_1V_1}{ T_1 }= \frac{P_2V_2 }{ T_2}$

$\frac{748.9V_1}{273 }= \frac{770\times54}{296}$

$V_1 = \pu{51.2 mL}$

Is this how it's supposed to be done?


texts: Why are there only two irreducible representations in the C3 group?

texts:
There are three elements in a $C_3$ group and there are three classes in this group cause it is an Abelian group.

\begin{array}{c|ccc|cc}
\hline
C_3 & E & C_3 & C_3^2 & & \varepsilon = \exp(2\pi\mathrm{i}/3) \\ \hline
\mathrm{A} & 1 & 1 & 1 & z, R_z & x^2+y^2, z^2 \\
\mathrm{E} & \left\{ \begin{aligned}1 \\ 1\end{aligned} \right. & \begin{aligned}\varepsilon \\ \varepsilon^* \end{aligned} & \left. \begin{aligned}\varepsilon^* \\ \varepsilon \end{aligned}\right\} & (x, y), (R_x, R_y) & (x^2-y^2,xy), (xz, yz) \\ \hline
\end{array}

According to group representation theory, the number of classes of a group should be the same as the number of irreducible representations of the group, which means there should be 3 irreducible representations for $C_3$ group.

In a character table, this means there should be 3 rows.

Further more, according to $$\sum_{i}l_{j}^2= h$$
in which $l_{j}$ stands for the dimension of the $j-th$ irreducible representation, and $h$ stands for the order of the group.

All of the three irreducible representation of $C_3$ group should be of 1 dimension.

But in the link above, for $C_3$ group, there are only two irreducible representations, and one of the irreducible representation is of 2 dimension, so it seems it violates the basic results of group representation theory.

So, what I have misunderstood?


texts:
Taken these reactions:

  \begin{align}
\ce{2\overset{0}{Fe} + 3Cl2 &-> 2\overset{+3}{Fe}Cl3} \tag{1}\\
\ce{\overset{0}{Fe} + 2HCl &-> \overset{+2}{Fe}Cl2 + H2} \tag{2}
\end{align}

Why does $\ce{Fe}$ have +3 charge in the first example and +2 charge in the second?


texts: Is there a difference between hydrated oxides and hydroxides?

texts:
My guess is that they are different.

I think hydrated oxides would have a lattice with the cation and oxide anions as lattice points and molecules of water trapped in interstitial spaces, while hydroxides would have the cation and hydroxide anions as lattice points with no water molecules in interstitial spaces.


texts: How to determine pH of food in order to avoid unsuitable storage containers

texts:
In an acidic (lemon-containing) sauce I had placed a metallic spoon. A few days later it had a metallic taste.

Stainless steal might be a significant source of nickel, chromium and iron [1]. Also, using aluminum utensils and packaging when cooking or storing food can contribute to the daily aluminum intake [2].

I want to avoid storing food in metallic containers which could increase my intake of metals.

The pH of some foods can be found here, but in some cases it's not of much use (when the food is a varying mixture of ingredients).

Is there an easy way to determine the pH of food? (whether the food is colored like a tomato sauce or transparent)


texts:
What kind of storage solution is required for a glass electrode?

Is 3 M $\ce{KCl}$ sufficient for this purpose? If so, what is the approximate pH of that solution (the solution I use presently has a pH $\approx$ 5)?

Can filling solutions be used as storage solutions for glass electrodes?


texts: Simmons-Smith Cyclopropanation and Sterics

texts:
I know this is a Simmons-Smith reaction. Wikipedia tells me this:

  The Simmons–Smith reaction is generally subject to steric effects, and thus cyclopropanation usually takes place on the less hindered face.

Therefore, will the cyclopropane be added to the opposite side of the methyl group; i.e. will the cyclopropane group be drawn with dashes rather than wedges?

I understand that if the methyl group is not present then we would get equal amounts of two products, which are enantiomers (as shown by the second image)?


texts:
Since the molecule has 5 bonding pairs and zero lone pairs, the shape should be trigonal bipyramidal. But one thing i am confused about is which atom(s) will occupy the axial and the planar positions, respectively, and why?

Thanks


texts: Software platforms with integration of multi vendor mass spectrometer device data?

texts:
I know about ACD/Spectrus Processor which is a software platform to integrate analytical chemistry data from multiple mass spectrometer device vendors (e.g. Agilent Technologies, Bruker, Waters) to allow data processing. Are there comparable software platforms out there which enable the integration of MS/chromatography data of different vendors for data processing?

BTW: I know that questions of this kind usually fits better to Software Recommnedations. However cause it's specific to the chemical domain I think it's more suitable to ask here.


texts: How to simulate chemical reactions in GAMESS?

texts:
I am rather newb in GAMESS field but finally, learned to make input files for most molecular simulations and could even use TD-DFT for excited states (special thanks to Geoff Hutchison for his help).

Now I want to start simulating simple chemical reactions. I looked at the GAMESS manual and think I need to make transition states and find least energy pathways but have no idea how to make input file for that.

Can anyone give me a simple input file example for a simple reaction?


texts: How to acurately measure pH in heterogeneous solution?

texts: Following my experiment, I adjust pH of $\ce{Ca3PO4}$ from acid to base (about 11)with ammonia solution by using pH meter for precipitating $\ce{Ca3PO4}$. I waited and found pH wasn't constant. In addition, I tried to wash a pH probe and be placed in the solution again but pH was changed from last value even if I didn't add more acid or base.


texts: Does sulfur have various allotropes at room temperature?

texts:
Recently I had a question in my chemistry test that said:

  Which of the following nonmetals does not have multiple allotropes at room temperature?
  A) Oxygen
  B) Hydrogen
  C) Sulfur
  D) Phosphorus

The answer was apparently hydrogen, but can't sulfur also be a correct answer? I am judging this just because in my chemistry book it says that rhombic crystalline form exists below $\pu{96^\circ C}$. Monoclinic exists above $\pu{96^\circ C}$. Are there any allotropes of sulfur at room temperature?


texts: Is Bond Formation "Strictly" Exothermic?

texts:
Is bond formation "strictly" exothermic? The IUPAC definition of exothermic doesn't make any reference to bond formation. However, I have seen the aforementioned statement before - that bond formation is "strictly" exothermic.

I suspect that the answer is "it depends" and that "it depends" at least on how accurately bonds are characterized. For example, the first reaction below is endothermic, while the second one is exothermic:

$\ce{2NO -> ONNO}$.

$\ce{2NO_2 -> O_2NNO_2}$.

Lewis structure analysis for the first reaction at best misleads because one might suspect the nitric oxide molecule as having a bond order of 2.

However, the lone electron is actually delocalized. So the actual $\ce{N-O}$ bond order should be 2.5.

In the $\ce{ONNO}$ molecule however there is no delocalization of electrons and the bond order of the $\ce{N-O}$ bond is 2. So the $\ce{N-O}$ bond is weakened, and even the formation of the $\ce{N-N}$ bond cannot compensate for this weakening.

Also, the above example reminds me of certain unstable homonuclear species. Such as $\ce{Ne_2}$, which according to MO theory has a bond order of 0 - i.e. there is no bond. So I suppose that bond formation is not always exothermic. On the other hand, if the bond order is 0, is a bond really "formed"?


texts: Cleaning up dispersed potassium hydroxide (KOH) spill?

texts:
So I tried to replace a dead triple-A alkaline battery in a waterproof compartment; it had leaked fluid + gas which had built up a bit of pressure: When opened, the material (about a dozen tiny droplets, total volume less than a pea) spattered on my hands, clothes and desk :-[

I am assuming that it was pretty concentrated KOH given that it felt slippery / turned the skin greyish before washing it off with plenty of water (no visible chemical burn or aftereffects several days later, though).

Is it good enough to wash the contaminated clothes in a regular washing machine? I did do an additional rinse cycle afterwards.
Will any droplets that I haven't been able to find become neutralized over time, or do I have to tear my study apart and wipe/hose everything down?

Some documents state that KOH absorbs atmospheric water while others state that it reacts with atmospheric CO2 to form a stable carbonate - Surely it can't do both at the same time?

Sorry for the somewhat off-topic question, but it feels like all the MDS are quite unhelpful about how to remediate a spill beyond just 'wash skin with water, remove clothes'..


texts:
Is element 111 considered to act as an eka-aurum?
Being under the same column of group 11, which usually provides enough evidence for correlation of properties for an eka-element, would this element have the similar properties such as conductivity or inertness with gold?

With the understanding of the correlation between group 11 being minimal to me, is anyone able to predict perhaps the colour, ductility, or other physical properties of this element with reason?


texts: Reduction of nitro compound using protection group

texts: I've tried researching things like cyclisation, nitro reduction and all I've found is little to nothing. I know that for the 1st arrow I need to protect the carbonyl and the 2nd arrow is the carboxylic acid but I'm not sure how to go about with the reaction or mechanism. Can you someone guide me along please?


texts: Electronegativity trends: Is it more important to prioritize families or periods?

texts:
I know that an atom that an atom is more electronegative as it moves up a group or right on a period (in terms of the periodic table).

So if you have two atom that is diagonally across from each other, which one is more electronegative? Do you prioritize groups or periods when determining electronegativity?

For example: Which is more electronegative - Sulfur, or Bromine?

Finally, does this priority also work for first ionization and atomic radius trends. (in other words, if you prioritize groups when determining electronegativity, do you also prioritize groups when determining the other two periodic table trends?)

My guess is that they would be equal, but I may be wrong.

P.S. I would be most likely to give best answer to the person who answers all my questions as a numbered list.


texts: Question on identification of a compound

texts:
Question:

Multiple correct answers are possible

My Approach:

I just found structure Q for all options A, B, C and D for which I have uploaded the structures below with their corresponding options.

Of course, option B cannot be correct since the molecular formula of the compound Q doesn't match with the one obtained after the reductive ozonolysis.
What I know about Molisch test is it gives the violet ring when an alcoholic solution of 1-naphthol is added to the carbohydrate solution. But I don't know how to proceed after this step as I don't know how to identify which of the compounds react with Molisch reagent.


texts: Is the redox method applicable to all chemical reactions?

texts: Is it possible that some chemical reactions can't be balanced through the redox method? Because it seems to me that the elements on the reactants side have the same oxidation states with the product side.


texts: Different Equivalent Weight for the same compound

texts:
Let us say that we have the following two reactions:
$$\ce{A + O2 -> B}$$ where $\ce A \text{ and } \ce B $ are different oxides of metal $\ce M$.
Weights of $\ce A$ and $\ce B$ are $\pu{5.72 g}$ and $\pu{6.36 g}$.
$$\ce{B + H2->M + H2O}$$
The weights of $\ce B$ and $\ce M$ are $\pu{4.77 g}$ and $3.81$ g, respectively.

So I was trying to infer some information from the given data and this is what I did:

In the first reaction we can calculate the equivalent weight of $\ce A$ and $\ce B$ to be $\pu{71.5 g}$ and $\pu{79.5 g}$ respectively.
In the second reaction we can calculate the equivalent weight of $\ce B$ and $\ce M$ to be $\pu{39.75 g}$ and $\pu{31.7 g}$ respectively.

If we compare the equivalent weight of $\ce B$ in the two reactions, the equivalent weight of $\ce B$ in the first reaction is twice the equivalent weight in second reaction. What exactly does this mean?


texts: Why is it that increasing the molar mass generally increases the Entropy?

texts:
I've just found read that entropy increases through these reasons:

Changing the phase of the elements to a gas.
Increasing the molar mass of that specific element increases the entropy.

I understand the first one, but I can't grasp the second one.
Because naturally you would think that $\ce{H2}$ would have a higher entropy than $\ce{Ne}$ because one mole of it is generally lighter.

But however it is said that Ne has a higher entropy because of its lower molar mass.

Why?


texts: CaSO4 precipitate in mixture of Na2SO4 and CaCl2 solutions

texts:
I have been stuck on a chemistry problem for a long time now and if anyone here can help me I would be eternally grateful.

40. Du tillsätter $\pu{100 ml}$ $\pu{0,01 M}$ $\ce{Na2SO4}$-lösning i $\pu{100 ml}$ $\pu{0,02 M}$ $\ce{CaCl2}$-lösning. Det bildas en $\ce{CaSO4}$-fällning. Hur mycket av $\pu{0,01 M}$ $\ce{Na2SO4}$-lösning måste ännu tillsättas för att den bildade $\ce{CaSO4}$-fällningen just och just ska upplösas helt? $K_\mathrm{s}(\ce{CaSO4}) = \pu{2,5e-5 M}$. $(t = \pu{25 °C})$ (2p)
a. $\pu{0,43 l}$
b. $\pu{0,48 l}$
c. $\pu{0,53 l}$
d. $\pu{0,58 l}$

Translation: We add 100 ml of 0.01 M $\ce{Na2SO4}$-solution to 100 ml of 0.02 M $\ce{CaCl2}$-solution. A precipitate of $\ce{CaSO4}$ is formed. What is the (minimal) volume of 0.01 M $\ce{Na2SO4}$-solution that needs to be added to the mix for the $\ce{CaSO4}$ precipitate to be just dissolved completely?
The problem then lists the solubility constant, $K_\mathrm{s}$, for $\ce{CaSO4}$ as $2.5\cdot 10^{-5}$.
The only way I can think of solving this myself is by looking at the added $\ce{Na2SO4}$-solution as just water and using the $K_\mathrm{s}$ value for $\ce{CaSO4}$ to see what concentration of $\ce{CaSO4}$ is possible in just water. Then calculate the amount of moles of precipitate that was actually formed to see how much water I would need to add to the mixture:
$$K_\mathrm{s}(\ce{CaSO4}) = \pu{2.5e-5 M^2} = [\ce{Ca^2+}][\ce{SO4^2-}]$$
$$\therefore [\ce{Ca^2+}] = [\ce{SO4^2-}] = \sqrt{\pu{2.5e-5 M^2}} = \pu{5e-3 M}$$
$$C = \frac{n}{V} \to n = CV$$
Amount of precipitate formed:
$$n(\ce{CaSO4}) = \pu{0.02 M} \cdot \pu{0.1 dm^3} = \pu{0.002 mol}$$
Required total volume of water to dissolve $\pu{0.002 mol}$ of $\ce{CaSO4}$:
$$V = \frac{n}{C} = \frac{\pu{0.002 mol}}{\pu{5e-3 M}} = \pu{0.4 dm^3}$$
This is wrong, but I can't figure out the right way to go about this. The answer surely has to do with how well $\ce{CaSO4}$ is dissolved in a $\ce{Na2SO4}$-solution as opposed to just water.


texts: Vibrational state dependency of the reaction cross section

texts:
I'm reading p.1238 of Mcquarrie's Physical Chemistry: A Molecular Approach textbook.
In the last line of the page, the author explains that the value of the reaction cross section in the constant total energy depends strongly on the vibrational state of the reactant. Of course, it means that not only translational kinetic energy but also internal energy(such as vibrational state) contributes to the value of the reaction cross section values.

However, the book puts a limit on the 'constant total energy'. If both translational kinetic energy and vibrational energy contribute to the reaction cross section value, does the explanation in the book imply that vibrational energy contributes more to the reaction cross section value than translational kinetic energy?
If that's true, is there a way to explain the difference in contribution qualitatively? Or is it just a matter of quantitative differences?


texts: MNDO integrals in the global coordinate system

texts:
In MNDO and its descendants (Sewart's PMx models, Austin's AM1, MNDO/d, etc.), the nonvanishing two-center two-electron "coulomb integrals" are evaluated via a classical multipole expansion in a local coordinate system, and then transformed into global coordinates via "standard rotational transformations". How exactly are these transformations carried out?

A similar question would be the methodology behind the resonance integrals in the orthogonalised methods OMx, which are similarly evaluated in a diatomic coordinate system and then transformed to the global coordinate system.


texts:
I'm doing a chemistry lab where I'm collecting data to create a solubility curve for carbon dioxide at different temperatures. I'm using carbonated water and my concern is that, by heating or cooling the solution, will it be saturated with carbon dioxide after exposing it to the air for a small period of time? I'm guessing that this will not be the case.

I know I can add carbon dioxide to water samples by exhaling into them but, is there a way to determine that it has been saturated without using a pre-existing solubility curve?


texts: XAS spectroscopy - Differences in magnitude of 2p SOC and 3d SOC?

texts: Within L-edge x-ray absorption spectroscopy, the spin-orbit coupling within the 2p shell results in the splitting of the L edge into L3 and L2 edges.As given in the following paper http://dx.doi.org/10.1063/1.4896373, the 2p SOC is 8ev whereas the 3d SOC is 0.05eV. Could some please explain why the 3d SOC constant is much smaller than that for 2p SOC?


texts: How to calculate mass of nanomaterial grown on a substrate

texts: I'm growing graphene on copper substrates and need to know the mass. The graphene is grown via chemical vapor deposition; amounts of reactants are not completely known. The best approach I've thought of is recording the mass of the substrate before and after using an analytical balance, but with the nature of the material being nano, this method may be elusive. What other method could I use to find the mass?


texts:
I don't get the difference between the gain or loss of electrons in a reaction and changes in oxidation state. Based on my notes and some research:

Gain or loss of electrons

A substance is oxidised if it loses electrons in a reaction.
A substance is reduced if it gains electrons in a reaction.

Changes in oxidation state

A substance is oxidised if the oxidation state of the element increases.
A substance is reduced if the oxidation state of the element decreases.

Whenever I see a chemical equation, I am confused as I do not know if it is a gain or loss of electrons or changes in oxidation state. I have an assignment to do which involves redox reaction, but it is the holidays and I can't contact my teacher. Could someone explain so that I could understand? For example,

$$\ce{2 Ca (s) + O2 (g) → 2CaO (s)}$$

I thought there is a change in oxidation state as on the reactants side, the oxidation state of both $\ce{Ca}$ and $\ce{O2}$ are $0$. As for the product, the oxidation state for $\ce{Ca}$ is $+2$ and $\ce{O}$ is $-2$. Therefore, $\ce{Ca}$ is oxidised and $\ce{O2}$ is reduced.

But one of the questions on my worksheet asked about electron transfer for this chemical equation, and I do not understand why it is a electron transfer.


texts: Why do we not talk about entropy when deciding feasibility of an organic reaction?...We always seem to only be interested in stability of product and intermediate(essentially delta H)and draw their respective graphs of Delta H of the reaction showing the peak of intermediate..shouldn't we look at change in  Gibbs free energy for commenting on feasibility?


texts: The definition of n-factor, what was it when it was introduced?

texts:
I realize that n-factor is an outdated concept however I am interested in its formal definition when it was introduced.
We have many definitions now on how to calculate n-factor depending on the type of reaction and compounds involved.

For acids, n-factor is defined as the number of H+ ions replaced by 1 mole of acid in a reaction.
For bases, n-factor is defined as the number of OH– ions replaced by 1 mole of base in a reaction.
The n-factor for such salts is defined as the total moles of catioinic/anionic charge replaced in 1 mole of the salt
The n-factor of such salts is defined as the number of moles of electrons exchanged (lost or gained) by one mole of the salt.

However, none of these definitions explain what n-factor actually is. Is there a formal definition for n-factor?


texts:
What  is the hybridisation of $\ce{BrF5}$ ? I find different sources giving different answers.

When I approach this problem , I don't find any exceptional case like $\ce{SH6}$ (in which hybridisation doesn't take place.) So it follows normal rules, but I find the opposite in many different books ?

I think it square pyramidal $\ce{sp^3d}$. I also face the same problem for other compounds like $\ce{H2S}$ and $\ce{PH3}$.


texts:
In the industry , it's important to maintain the column pressure control in the distillation column .

" Pressure alterations will alter column vapour loads and temperature profiles. .
So when using Temperature control as a substitute for composition control, pressure compensation is essential to achieve a desired composition . "

"Pressure variations change relative volatiles and affect fractionation process.  "
From this , I understand that if pressure acting upwards on the vapour is lesser than the pressure acting downwards , then it will affect the fractionation process.

But I do not understand the top part -
"
" Pressure alterations will alter column vapour loads and temperature profiles. .
So when using Temperature control as a substitute for composition control, pressure compensation is essential to achieve a desired composition . "

Why does it link to temperature ? And in conclusion , I'm confused about how pressure is maintained in the distillation column and for what for .


texts:
Why can $\ce{H2S}$ be reduced by $\ce{Ag}$ when left in air:
$$\ce{2 Ag + H2S -> Ag2S + H2}$$
If silver is a noble metal that should not reduce hydrogen?


texts: How would one separate a mixture of isotopes (different nuclear spins) at temperatures near 0 Kelvin?

texts:
Suppose we have two isotopes of the same element. For example, isotope A could have a nuclear spin I = 0, isotope B could have nuclear spin I = 3/2. Let us say we have a compound where this element is participating, and in this compound we have a mixture of the two isotopes A, B. Up to this point, this is a rather universal case: with the exception of isotopically purified samples, all compounds contain mixtures of isotopes for all of their elements.
Let us now cool down a sample of our compound, below liquid He temperatures, and, for the purposes of this question, let us say we can cool it down arbitrarily low temperatures. Now the different isotopes A, B will start to behave differently, presenting different physical and chemical properties, if only because their quantum eigenstates are different, and differently populated at low temperature. This is on top of their different masses, of course.
The question is:
How could one separate this mixture of isotopes A, B, presenting different nuclear spins, at sub-Kelvin temperatures?
In particular, if more than one purification procedure is possible, can one define one such procedures which is based on the different magnetic properties of isotope A and B?


texts:
Why doesn't but-2-ene exhibit tautomerism like alkenols?
By transfer of 1 hydrogen from terminal CH₃ to the middle carbon and forming a double bond between the two?


texts:
I'm wondering if it is possible, theoretically, to create compounds which perform the opposite function of a catalyst (thus an anticatalyst). That is to say, could a compound be made which raises the activation barrier of a reaction rather than lowers it?

I know enzyme inhibitors exist, but I would argue these merely disable or slow the catalyzed reaction rather than slowing the reaction down relative to its baseline speed. (If I'm mistaken and there are enzyme inhibitors that actually lead to a slower reaction than if the enzyme weren't there at all, I would also consider that an answer).

I would think an anticatalyst could be made by having an enzyme which binds a molecule in a way that reduces the favorability of the transition state (or alternatively, stabilizes the reactants, as mentioned by Nicolau Saker Neto below). The binding to the anticatalyst enzyme would also have to be favorable enough where the reactants would not just react and ignore the slower anticatalyzed pathway (one could also assume, for the sake of argument, that enough of the anticatalyst is added where the majority of the reactant molecules are bound).


texts: Creating an efficient synthetic route to this elastomeric block copolymer

texts: This was a question my professor gave me in which I have a couple of ideas to create a synthetic route which include: Either an anionic or cationic polymerization? If so, I don't think it would be cationic because I can't seem to see if there would be some sort of initiator system and i don't think there could be carbocation formation either from the looks of it. The only feasible conclusion I have come to is that it would be an anionic polymerization where you create a living polymer and react this with a second monomer to create a block copolymer? I could maybe use an organolithium to start the initation with a polar solvent however I don't actually know which monomer to start off with nor how the reaction mechanism would work out. Can someone help me? Thank you very much!


texts: Are all exothermic reactions spontaneous?

texts:
$\ce{GaAs (s)}$ is used in solar cells deployed on satellites found in the orbit of Earth. The best way to make these materials is through a technique called "molecular beam epitaxy", in which the following spontaneous chemical reaction takes place:
$$\ce{Ga(g) + As(g) -> GaAs(s)}$$
Pick the statement which best describes this process:
(A) The process is endothermic.
(B) The process is exothermic.
(C) The process leads to a decrease in the entropy of the universe.
(D) The process leads to an increase in the entropy of the system.
(E) The process leads to a decrease in the temperature of the system.

The key says the correct answer is B. I am wondering if this is because all exothermic reactions are spontaneous?


texts: CH2 group in alkyl glucoside gives two separate HNMR signals

texts:
Zoom in:

It seems like the CH2 next to the sugar gives two different NMR signals which is very interesting. Could someone explain me why?


texts:
The most stable of:

(a) $\ce{(CH3)2C(OH)2}$

(b) $\ce{CH3 C Cl (OH)2}$

(c) $\ce{CH3CN}$

is $\ce{CH3CN}$, because the other two are geminal diols. How can we tell that geminal diols are unstable?


texts: How is silica bead bonded into polystyrene?

texts:
What kind of bonds silica bead forms with polystyrene? Silica is now as ~100 $\mu$m spherical particles in bulk polystyrene that is made by melting.

How can I bond the silica particles

more tightly
more loosely

to the polystyrene?

Can this be generalized to any nano/micro particle and plastics? I am thinking now metal oxides and other thermoplastics.


texts: Why should alkylation of enols/carbonyl compounds be done at low temperature with a strong base?

texts:
Alkylation of acetone:

This reaction is done with a strong base (LDA in this case). Is this because the protons aren't particularly acidic? Secondly it should be done at low temperatures; why is this so? -78 degrees Celsius is typical.


texts:
I cannot seem to grasp the logic behind it. We say that more entropy (or more disordered system) is favorable over less entropy. But why? Why is randomness preferred over proper arrangement of atoms/molecules? The only thing I can think of is more degrees of freedom. Molecules in a more random system would have more degrees of freedom, and would thus be favorable. But, again, why? Why would more degrees of freedom be favorable? I've already asked my teachers and looked up internet, but haven't found any satisfactory answer. Also, is there any way you could also explain diffusion by the same concept (diffusion is entropically favorable, right?)?

PS: if this question is better suited for physics stack exchange, I'd be more than happy to have it migrated.


texts:
Why is the rate of water exchange at Al(III) centres so slow ?

According to this medical book (p.5) it is $10^{5}$ times faster at Mg(II).


texts: How to assign initial and final states of iodine transitions in its spectrum?

texts:
In an experiment, I gently heated iodine crystals to create vapors and then observed it absorption spectrum with a spectrometer. The temperatures throughout were moderate (maximum $40^\circ\text{C}$). I observed a series of dark bands from red region to blue-green region with spacing between consecutive bands decreasing from red end towards to blue end.

I calculated the wavelengths corresponding to these bands beginning from the first resolvable band in the red region and ending at the $30^{th}$ reading (without missing a single dark band in between). The data is as follows:

$$\begin{array}{c|c}
 \text{Colour Region} & \lambda/\text{nm} \\ \hline
\text{Red} & 624.884 \\
& 624.884 \\
& 621.831 \\
& 617.552 \\
\text{Orange} & 612.581 \\
& 609.518 \\
& 606.070 \\
& 601.798 \\
& 597.629 \\
& 594.171 \\
& 591.095 \\
\text{Yellow} & 586.862 \\
& 584.243 \\
& 581.853 \\
& 577.225 \\
\text{Yellow-Green} & 575.218 \\
& 571.819 \\
& 567.954 \\
& 565.246 \\
\text{Green} & 562.924 \\
& 560.291 \\
& 557.579 \\
& 554.399 \\
& 551.684 \\
& 550.053 \\
& 548.422 \\
& 547.490 \\
& 544.693 \\
& 541.271 \\
& 540.027 \\
& 538.548 \\
\text{Blue-Green}
\end{array}$$

Now, in order to obtain information about the parameters like bond dissociation energy, convergence limit, etc., I need to know the quantum numbers which correspond to each observed transition wavelength which are the initial and final electronic states and the vibrational states.

Question: How to find these? I know that generally, sources characterize some
standard states, like this says that $541.2\text{ nm}$ corresponds to $v''=0\rightarrow v'=27$. But what am I supposed to do with the larger wavelengths? Cuz the sources say that Franck-Condon prohibits $v''=0$ to low $v'$ transitions. But nevertheless, I do am observing larger wavelengths. Are these from $v''>0$?
How can I even be sure that these are $X\rightarrow B$ transitions? Cuz of operating temperatures?

Please provide some proper approach!

The difficulties that I am facing in this assignment of states are also elucidated in this post of mine.


texts: Is it possible to find the volume of condensed water by temperature change without knowing the initial pressure of the flask?

texts:
I found this problem in a practice sheet. The original source doesn't indicate any authorship or whatsoever.

It states the following:

  A sealed container of $\pu{6.24 L}$ in capacity has humid air at $\pu{30 ^\circ C}$ with a $RH=90\%$. The container temperature is then lower to $\pu{27 ^\circ C}$. Find the volume of condensed water. The vapor pressure of water is $\pu{32 mmHg}$ at $\pu{30 ^\circ C}$ and $\pu{27 mmHg}$ at $\pu{27 ^\circ C}$. You can consider that the volume of condensed water is insignificant.

The problem doesn't specifically mentions any other assumptions but I'm assuming that the gas is behaving ideally and since it is referring to water. I will need the density of water, which is $\pu{1 \frac{g}{mL}}$ and the formula weight of water, which is $\pu{18 g mol-1}$.

The strategy which I thought was that the moles of air will remain the same when the vessel is cooled but the total moles will change before and after, as the moles of water initially will be different when the vessel it is cooled.

Then to find the volume what I need to find is that difference in moles and use the formula weight of water and the density to get volume.

However this is a problem because, how can I characterize the vessel if I'm not given an initial pressure?

I'm aware that:

$$RH=\frac{\textrm{partial pressure}}{\textrm{vapor pressure}}\times 100$$

Therefore I can say that the partial pressure for water is:

$$0.9\times \pu{32 mmHg} = \pu{28.8 mmHg}$$

But what I need is the total pressure in the vessel. Is it possible to find it?

If I could find the total moles, what I could do is find the moles of air by difference as follows:

$$n_{air}=n_{t}-n_{water}$$

These moles will not change.

The moles of water could be found by using the ratio of the partial pressure of water to that of the total is equal to the moles of water divided by the total moles.

$$\frac{n_{water}}{n_{total}}=\frac{p_{water}}{p_{total}}$$

But as it can be seen, I'm stuck. I did not included numerical calculations because if I were to use the equation of the ideal gas:

$$PV=nRT$$

What would I had use as the total pressure? Therefore I'm trapped. Is there any way to find what it is being asked?

Edit:

Following the indications by the answer I did the following:

The number of moles of water vapor at $\pu{30 ^\circ C}$ can be found from using the equation of ideal gas:

$\left(0.9\times 32\,mmHg\right)(6.24\,L)=n_{water}(62.4\frac{mmHg\cdot L}{mol\cdot K})(30+273)K$

$n_{water}=0.009505\,mol$

Then the number of moles of water vapor at $\pu{27 ^\circ C}$:

$\left(27\,mmHg\right)(6.24\,L)=n_{water}(62.4\frac{mmHg\cdot L}{mol\cdot K})(27+273)K$

$n_{water}=0.009\,mol$

Then:

$\Delta n_{water}=0.009505-0.009=0.000505\,mol$

From this quantity the grams of water and volume can be obtained using density of water and the formula weight.

$V=0.000505\,mol\times\frac{18\,g}{1\,mol\,\pu{H_{2}O}}\times\frac{1\,mL}{1g}=0.009090\,mL$

Which would be the volume of the condensed water. Judging from the ammount obtained it makes sense that it is a very tiny volume.


texts: How to evenly ionize in mass spectrometry

texts:
I know that in mass spectrometry they charge different molecules and then run them through a magnetic field and then see where they land.

Depending on this, they calculate their masses relative to each other. To do this however, they have to ionize the different particles evenly. If one molecule is charged +2 and the other +1, then the results would be thrown off.

How do they do they make sure that the charges of all the ions are the same?


texts: Draw the enantiomer products of the reaction between 1,3‐butadiene and (3Z)‐pent‐3‐en‐2‐one

texts: From this reactants I need to draw two products with cyclohexene rings that are enantiomers to each other with chemical formula $\ce{C9H14O}.$ And also draw the reaction mechanisms. Why does it form enantiomers? I'm not sure how I should approach this.


texts:
I recently encountered a question on a test:

  Substances whose molecules have a high degree of symmetry will have:

    A. a low specific heat
    B. a high melting point
    C. a high heat of fusion
    D. a low heat of vaporization
    E. strong Van der Waals forces

Looking through a few compounds, I found that $\ce{CO2}$ is symmetric (it's shape is a straight line), $\ce{CH4}$ is symmetric (tetrahedrons seem symmetric).
Through these examples, I was able to eliminate A, B, and C, and have a suspicious feeling about E, so I guessed D and was right.

I was wondering what exactly "high degree of symmetry" meant. Through my math courses, I knew about rotational symmetry (where if you turn any 2-D shape in a plane by n degrees, it will look identical to the shape before the rotation).
Is a high degree of symmetry when the lowest possible value of n for a compound is over some constant, lets say 90 degrees, or is it something else?


texts: Naming compounds with multiple -COX functional groups

texts:
I know that this compound is named propanoyl chloride.

However I am not sure what to do when here are multiple -COX groups and they are of the highest seniority. There are two cases, when they are the same:

And when they are not:

For the first case I think it is called propanedioyl chloride, but I do not know what to do for the second. Is one of them cited as a prefix and if so which one?


texts: How does sulfuric acid react to heating?

texts:
How would $\ce{H2SO4}$ react to heat? I assume that it would form toxic sulfur (di/tri)oxide, but I can't find any information on this.
I'm concerned about fire hazards specifically, so assume very intense heating and very low concentration.


texts: what are possible isomers of (meso-stilbenediamine)(isobutylenediamine) palladium (II)?

texts: It can form a square planar and a tetrahedral complex but within square planar or within tetrahedral can there be isomers possible?


texts: Facial selectivity of iodonium formation in an iodolactonisation

texts:
I am trying to understand the stereochemistry of iodolactonisation of this cyclohexene. I can't work out if the iodonium ion would form on top or the bottom.

There is $\ce{CH2COO-}$ and $\ce{Me}$ pointing up, and $\ce{CH2OTBS}$ and $\ce{Me}$ pointing down. My guess would be iodine attacks from the top because there is a bulky $\ce{TBS}$ group pointing down as well as a methyl, however there is a semi-big $\ce{CH2COO-}$ group pointing up right next to the double bond. Would that have more of an effect as it is nearer to the double bond?


texts: Acidity comparison of charged group 16 hydrides

texts:
March's Organic Chemistry (7th ed - page 337 under "Periodic Table Correlations" in chapter "Acids and Bases") states that:

  $\ce{H3O+ > H3S+ > H3Se+}$ is the acidity order of these charged group 16 hydrides

I am trying to make out why this is true. I have seen the related questions but they are about the neutral hydrides and not charged ones.

My working was that the order of acidity should be the reverse order of the basicity of their conjugate bases. The conjugate bases are $\ce{H2O,H2S, H2Se}$. We know that basicity decreases down the group, as the lone pair becomes more dispersed over the large surface area  (corroborated for group 15). Hence, according to me, order of basicity order is $\ce{H2O>H2S> H2Se}$. Hence, order of acidity should be $\ce{H3O+<H3S+<H3Se+}$. But, in March, the reverse order is given.

What is the reason for this order given by March? And what is wrong in my logic?


texts: What is the difference between low-density and high-density Polymethyl methacrylate (PMMA) on a molecular level?

texts: I know why Polymethyl methacrylate can be made to have a low or high density but i am unable to illustrate how they look like on the molecular scale. Can someone help me with a sketch please?


texts: What is responsible for black tarnish on silver?

texts:
Silver on being exposed to air, forms a black film. Now my question is whether the film is silver sulphide (due to reaction with hydrogen sulphide in air) or silver oxide.

Both compounds are black.

In my view it would be silver oxide because oxygen is more abundant and, intuitively, silver seems react to oxygen faster than hydrogen sulphide- oxygen is more reactive than hydrogen sulphide.

But a little google search loosely hints it is silver sulphide. Any suggestions on this too?


texts: What is the charge on $\ce{N}$ in $\ce{NCl3}$? I want to know if it is positive or negative. I feel it should be positive but I am not sure.


texts: How to round correctly when calculating the average and standard deviation?

texts:
Is my Chemistry book wrong on the significant figures in this exercise?
Why did they round to 0.16 instead of 0.1580 ?

Also why did they round down the means?


texts:
I understand what occurs on a regular Li-ion battery - the positive Lithium ion moves from one electrode to the other of the battery. But what is exactly the physical mechanism for this intercalation to occur?
Is it that the Lithium in the LiCoO2 electrode lowers the chemical potential between electrodes? I am really curious about the process - any reference would also be helpful!


texts: How to prepare KF/Al2O3 i.e. potassium fluoride on alumina (/on aluminum oxide)

texts: It's surprisingly hard to find an answer to this. One book I found referenced a method wherein one would simply mix (with a mortar I assume?) equal (another source said 40:60) portions of Al2O3 and KF and that's it.


texts: Brass Instrument: Dezincification or just scrubbed off?

texts:
I do own a brass instrument (a trombone). The lacquer is damaged.
I asked how to deal with it here.

Now I learned that the brass contains zinc, and there is a corrosion process called "dezincification". Now they told me to ask here how to identify real dezincificated parts. Here are the pictures:

Main slide handle:

Bell "middle" section:

Bell inner rim:

The issue is: On trombones (other brass instruments) red rot (dezincification) usually only appears on parts where saliva touches the instrument, i.e. in the front parts. On a trombone that would be the slide. So it is kind of unlikely but not unheard of that this might be "red rot" or dezincified.

It might also just be lacquer which went off due to improper handling (like not cleaning water spots, showering/cleaning the trombone with way too hot water, etc.).

Actual questions

How do I identify dezincifiaction correctly? Can it be seen on those pictures? (most important question)
What do you think of chemical cleaning? It sounds dangerous to me. Isn’t it going to damage the instrument?
What do you think of cleaning such an instrument soap? Is this going to damage the lacquer or material?


texts: η1 or sigma complex involving cyclopentadienyl anion

texts:
When $\ce{\eta^1-C5H5-}$ acts as a ligand, does the donor carbon become $sp^3$ hybridized, and would this be a sigma donor through sigma orbitals? Or, is it $sp^2$ where the lone pair is donated through a pi orbital, making it a sigma donor through a pi orbital?

The second option seems much more likely as the ligand changes the $\ce{C}$ attached to metal randomly with time through rearrangements.

Also, does "sigma complex" and "pi complex" only differentiate the hapticity? as $\ce{\eta^1-C5H5-}$ is a sigma complex and $\eta^3$, $\eta^5$ are pi complex.


texts: Lennard Jones liquid vapor phase transition

texts:
I am trying to generate a phase diagram of pressure versus temperature in a NPT ensemble using molecular dynamics method. I am using the Lennard Jones potential with 108 particles and Berendsen thermostat and barostat to fix the parameter.

In order to observe phase transition I plot the radial distribution function (RDF) and also density versus temperature graph for various fixed temperature. However it is hard to differentiate liquid and gaseous phase from RDF.

Another peculiar thing is that there should be a discontinuity in density as the transition temperature is reached, which I observe only for solid liquid transition but not for the liquid vapor transition. The change in density should be huge for liquid vapor transition. Any idea on what possibly goes wrong?

The parameters:

Periodic boundary
cut off radius = 2.5
Truncated and shifted Lennard Jones potential
number of particle = 108
number of steps = 2000
timestep = 0.004
Berendsen barostat of scale coeefficient of 0.1 is used to scale the size of simulation box

The density versus temperature graph for pressure of 1.0MPa:

The solid liquid transition can be seen but not the liquid vapor transition.


texts:
I was doing homework for my chemistry class, and I came across a question asking to complete and balance the following acid-equation:

$$\ce{Cu(OH)2 (s) + HClO4 (aq) -> ?}$$

At first I thought it was an acid-base reaction, but clearly $\ce{Cu(OH)2}$ is a precipitate. Thus, it could not be an acid-base reaction, and I was under the impression there was no reaction at all.

However, it turns out that the answer was to the question was (courtesy of the back of the textbook):

$$\ce{Cu(OH)2 (s) + 2 HClO4 (aq) -> Cu(ClO4)2 (aq) + 2 H2O (l)}$$

How is this possible? The answer to the question was exactly the same as an acid-base reaction, despite a precipitate instead of a base in the reactants.

Anyone know why this is the answer, or if it is even correct?


texts: Bonding and anti-bonding orbitals in the light of time-dependent Schrödinger equation?

texts:
In organic chemistry, people draw 2p orbitals like this:

and then they explain how the orbitals combine to non-bonding (π*) or bonding (π) molecular orbitals, like this:

depending on whether the orbitals overlap out-of-phase (blue + white) or in-phase (blue + blue, or white + white).

But in reality, the orbitals are time-dependent solutions of the time-dependent Schrödinger equation, so they are not really like the first image above, but more like this:

So, what does it mean, when the orbitals overlap in-phase or out-of-phase? As far as I understand, the phase difference of the orbitals of two random atoms could be anything from 0 to 2π, and the cases of perfect overlap (0 phase difference) or perfect anti-overlap (π, or half-cycle, phase difference) should be quite improbable.


texts: When in X-ray Photoelectron spectroscopy, an Si $2p$ peak is defined or a C $1s$ peak is defined at a certain binding energy, how is it done? I presume it is done from mono-crystalline Si but even in that case the Si peak might not only be experiencing chemical shifts due to the $sp^3$ hybridized bulk state, the case for a C 1s peak I guess would be more complicated due to its allotropic distribution, graphene, CNTs, Fullerenes and Diamonds would in my opinion show separate chemical shifts due to the outer hybridized orbitals being differently hybridized (oriented) and strained (in the case of CNTs, Fullerenes and Graphene since they are all $sp^2$ hybridized). The best way in my opinion to get an idea of the binding energy of the samples, would be to perform the tests in a vacuum tube under very high temperature so that all species are gasseous and are not bonded in any way. I would really like to know how these discrepancies are managed.


texts: How can you calculate ring strain in beta lactams for different penicillin drugs?

texts:
I am currently working on a lab, where I am trying to calculate whether the R group in penicillin type drugs has an affect on the ring strain of the beta lactam. I know how to find ring strain in cycloalkanes through the molar heat of combustion, however I can't find any information about the combustion of beta lactams as I'm sure it doesn't happen often, so is there another way I can calculate the ring strain of the beta lactams in different penicillin type drugs?
Thanks,


texts: Solution , Solubility and Colligative Property?

texts:
Which of the following  0.1 M aqueous solution will have the lowest freezing point ?

1) Glucose
2) Urea
3) NaCl
4) K2SO4

How to relate Molarity with freezing point ?
Should I use the relation
Kf = MR(Tf)2/1000Hv


texts: Thermoplatics into Thermosetting plastics

texts:
I must confess, I am not a chemistry student but have always been a fan of it, so I am not sure if this is a blunder.

I have often wondered if Thermoplastics can ever be converted to or made to behave like a Thermosetting plastic. In other words, can a Thermoplastics be made more heat resistant?


texts: I read from a source that aniline and water can be separated by steam distillation. But isn't this senseless as steam distillation will simply add more water and make separation more difficult?


texts: why do we see characteristic colors of alkali metals in oxidizing flame?

texts:
I am a high school student and I am a little confused in a topic, My confusion is that:
We know alkali metals and their salts imparts characteristic color in oxidizing flame, for example: Lithium gives crimson red color, sodium gives yellow , potassium gives violet and Caesium gives blue, My school textbook says that this is because the heat from the flame excites the outermost electron to a higher energy level and when it returns back it will radiate in visible range as I mentioned above, but if this is the correct reason then we know the outermost electron  of lithium is the most attracted  among all alkali metals .So, it means that it would take high energy to excite its outer electron so a short wavelength of light is needed i.e probably in violet region, so when it returns back it should emit the same wavelength. Then why do we see these weird pattern of colors? I think this is not the complete reason for why do we see those colors? please explain this in brief only so that I can easily understand.


texts:
I just want to clarify my understanding of whether metathesis can be used to form other products by combining an acid and a base (do special rules apply whether its strong/weak acid/base)?

Say I want to form some $\ce{Na2CrO4}$. There's many ways to do this but the most obvious one I can think of is:

$$\ce{2NaOH(aq) + H2CrO4(aq) ->Na2CrO4(aq) + 2H2O}$$

Can you then just filter out the $\ce{H2O}$ to get your desired product? How would you do so? I'm used to looking at these in terms of net ionic equations where two aqueous reactants for a solid precipitate but since everything here would cancel out (except water) is this even a viable possibility?


texts: When is donation into an anti-bonding MO stabilising?

texts:
This has been puzzling me for quite a while and I'm not sure if it could be a misconception on my part. When is interaction of a filled orbital with a antibonding MO stabilising and when is the interaction destabilising? I will now detail a few examples of the "stabilising interactions" and the "destabilising interactions". I will use Clayden's Organic Chemistry (2nd ed.) as my primary source of examples.

Destabilising interactions

Nucleophilic attack at the carbonyl carbon (p. 127)

Here, interaction of the nucleophile's HOMO with the $\ce {C=O \pi ^*}$ LUMO destabilises the $\pi$ bond, resulting in its cleavage. This is thus a destabilising interaction.

Nucleophilic attack in the $\ce {S_N2}$ reaction (p. 340)

Here, again we see the interaction between a filled HOMO and an empty antibonding MO ($\ce {C-X \sigma ^*}$ MO) destabilising the $\ce {C-X}$ bond.

Stabilising interactions

Stabilisation of cis configuration in esters (p. 805, explained in detail here)

Here, we see that the interaction of a filled, nonbonding MO centred on the $\ce {O}$ interacts with the $\ce {C=O \pi ^*}$ LUMO to stabilise the molecule overall.

Unreactivity of dichloromethane (p. 804, see here also)

As can be seen in diagram, interaction of nonbonding electrons centred on $\ce {Cl}$ with the $\ce {C-Cl \sigma ^*}$ stabilises the molecule, as it decreases is reactivity, by raising the level of the new resultant LUMO of the molecule.

Explaining Zaitsev's rule

This is a classic explanation for the increasing stability of alkenes as substitution increases. Interaction of $\ce {C-H \sigma}$ MO with the $\ce {C=C \pi ^*}$ MO increases the stability of the alkene.

I am sure there are likely to be more examples (e.g. various other instances of hyperconjugation) but I believe these examples are sufficient to prove my point. Is this inconsistency in the use of frontier MO theory or am I merely misinterpreting its use?

Update

After pondering over this for a while, I was thinking, perhaps we should make use of an MO diagram to more clearly describe the interaction. Below is a simple, typical diagram (from p. 111, with edits). Based on my understanding, all of the above examples I have presented can in fact be described by this straightforward MO diagram. Of course, the energy gap between the two interacting MOs may be different and thus, the strength of interaction would also differ.

Now, may I alert readers to something:

  In no way does the MO diagram indicate any sort of destabilisation of the molecule.

Such an interaction between a filled MO and an unfilled MO only produces stabilisation, as seen in the diagram. Not only is the filled orbital of a lower energy and hence less likely to interact with LUMOs of other molecules, the empty orbital's energy has also been raised, making it less energetically accessible from the point-of-view of a nucleophile. In other words, the molecule is both less reactive to an electrophile, due to a energetically-lowered filled orbital, and also less reactive towards a nucleophile, due to a energetically-raised empty orbital.

If this is the case, may I question further:

  What is the basis of destabilisation in the first 2 examples I have presented above?

Reference

Clayden, J., Greeves, N., & Warren, S. (2012). Organic Chemistry (2nd ed.). New York : Oxford University Press Inc.


texts: Why does hydrolysis of ADP to AMP yields the same amount of energy as ATP to ADP, if ADP is more stable?

texts: I learned about the resonance stability of ADP and the fact, that ATP is less stable due to intramolecular instability. I was surprised to see that the energy net of conversion of ADP to AMP is the same as ATP to ADP. Shouldn't the energy net of a reaction ADP to AMP+P be lower, because it's not so readily hydrolysed?


texts:
In Modern Quantum Chemistry by Szabo and Ostlund, they give an example of a minimal basis, full CI calculation of the dissociation of $\ce{H2}$ (on p.$241$ if you have the book). In explaining why this correctly describes the dissociation, they say:

  To see this, recall that as $\mathrm{R}\rightarrow\infty$, ... that all molecular orbital two-electron integrals tend to $\frac{1}{2}(\phi_{1}\phi_{1}|\phi_{1}\phi_{1})$, where $\phi_{1}$ is a hydrogenic orbital.

I could not find where they justified this statement. The closest I could find was in a previous section describing the dissociation using RHF (p.$166$) they state:

  [Besides $H^{\text{core}}_{11}$] All other integrals go to zero as $\mathrm{R}\rightarrow\infty$, except the one-center electron-electron repulsion integral $(\phi_{1}\phi_{1}|\phi_{1}\phi_{1})$.

What justifies this first statement? Is this unique to this case of a diatomic at infinite separation? These two comments seem to contradict rather than support each other.


texts: Does the term 'Cation' always refer to a positively charged particle?

texts:
From what I was taught in middle school, cations are those ions that move towards the cathode, likewise anions are those ions which move towards the anode.

I didn't have issues with this back then, since all we studied were electrolytic cells. But now that we've crossed over to electrochemical cells, I'm having doubts.

Every piece of chemistry literature I've come across so far, always deals with positive ions as cations and negative ions as anions; even my school textbook does it! That makes sense with respect to electrolytic cells, since the cathode's negative and anode's positive therefore positive ions would move to the cathode (hence 'cations') and negative ions would move to the anode (hence 'anions').

But in an electrochemical cell, the cathode's positive and the anode's negative. So if ions are to be classed according to the electrodes they move over to, then positive ions would be anions and negative ions would be cations, which is exactly opposite to the first case (on the basis of electrolytic cells).

This is really confusing....

So should I refer to positive and negative ions as cations and anions respectively or as anions and cations respectively? Or are both acceptable, depending on the scenario?


texts: What method did John Dalton use to measure the mass of one mole of gases, for example, chlorine and hydrogen, to get their relative masses?


texts: Can thermite be lit while mixed into butane? If not is there a flammable liquid that would work?

texts: I want to create a thermite flamethrower to melt snow since I live in New England and since I am an asthmatic I struggle to shovel and it would be cool, so do you have any idea as to what liquid thermite could be lit in.


texts:
So the question is which is the most common oxidation state of halogens and I have to justify my answer. Is my following thought correct? Do I have to add something?

The most common oxidation state of halogens is $-1$. Halogens are the most electronegative elements of the periodic table. Their outer electron configuration is $n\mathrm{s^2}n\mathrm{p^5}$. If chlorine, for example, gains one more electron, the outer p orbitals are completely filled (resulting in a full octet). Since halogens are electronegative they can easily remove an electron from the nearby atom. So then the halogen becomes isoelectronic with a noble gas and it is more stable in this state.


texts: Are carbocation intermediates in equilibrium?

texts:
So for the reaction of $\ce{H_2O}$ with an alkyl ethene, in the presence of $\ce{D^+}$ ions, forms two possible carbocations:

$\ce{ R-CHD-CH2^+}$ and $\ce{R-CH^+-CH2D}$

The major product formed is the secondary carbocation as it is stabler than the primary carbocation.

So my questions are:

Are the two carbocations in an equilibrium or are they formed in
specific, fixed quantities?
If they are in equilibrium, i.e., the primary and secondary
carbocation, why and how would the secondary carbocation revert back
to being a less stable primary carbocation?
Also, is the hydride shift that converts the primary to a secondary
carbocation the only shift that can occur; even if after the shift,
a more stable carbocation can be formed (depending on the attached
alkyl group)?


texts: Why does the cathode have to be made out Cu in a Zn-Cu voltaic cell?

texts: The classic voltaic cell has a $\ce{Zn}$ anode and $\ce{Cu}$ cathode. The reduction half reaction occurring at the cathode combines aqueous copper ions and electrons supplied by the anode to form solid $\ce{Cu}$. So what is the purpose of the $\ce{Cu}$ cathode? $\ce{Cu}$ is produced anyways from the electrons supplied by the anode. Why can't we have instead of the $\ce{Cu}$ cathode, simply the wire connecting to the anode which will supply electrons to fuel the reduction half reaction?


texts: How may copper acetate ligands be manipulated to change colors?

texts:
I have a solution of copper acetate and I would like to play around with the ligands to get different colors.

Background: The copper acetate was made through mixing vinegar (5% acetic acid), $\ce{NaCl}$, and $\ce{C}_{\textrm{(s)}}$. The deep blue-colored copper acetate spontaneously formed during a month in my dark storage room.

[edit] I neglected to mention that the experiment simultaneously produced a $\pu{0.5 inch}$ deposit of what appears to be Copper Carbonate or Verdigris on the bottom of the 1-Liter beaker. Also, I have let the copper acetate solution evaporate for several years now. The former $\pu{1L}$ is now $\pu{0.5 L}$ and has begun precipitating crystals (like the ones on the wiki page). Fun fact: During the Renaissance, glacial acetic acid was made by dry distilling metal acetates and primarily copper(II) acetate.[/edit]

Question(s):

What easily obtained household chemicals may be mixed with samples of the copper acetate to change the ligands attached to the copper and thereby alter the color?
Will heating or cooling the solution change the color and/or ligands?


texts:
I have a conceptual physical chemistry question here.

  A thermos bottle containing milk is shaken vigorously. Consider the milk as the system. Will the temperature rise as a result of the shaking?

My answer to this is yes, but I'm having trouble finding an equation that explains this result.

The best i have is the molecular kinetic energy formula that $$\mathrm{ke_{avg}= \frac{1}{2}mv^2=\frac{3}{2}kT}$$
So a change in kinetic energy is $$ \mathrm{\Delta ke = \frac{3}{2} k \Delta T}$$

Is this the right approach?


texts: I have been learning chemistry for a year or two but I still can't understand this. According to maths we should place the plus or minus sign in front of a number like -2. However, In chemistry we always put the sign behind a number when writing ions like $\ce{Ba^2+}$ ,$\ce{Cu^2+}$, $\ce{O^2-}$ etc. So, I want to know why do we write it that way?


texts: How to determine enzyme inhibitor efficacy?

texts: At what percentage reduction or increase in Km and Vmax is an enzyme inhibitor regarded as effective?- is any percentage increase or reduction regarded as being a clinically useful level of inhibition, or would it have to be over a certain limit?


texts: High concentration of ferric ion catalyst decreases rate of decomposition of hydrogen peroxide in the Fenton reaction

texts:
I did a project on the Fenton reaction and rate of decomposition of $\ce{H2O2}$. I used colorimetry to measure the rate of decolourisation of methylene blue when I mixed $\pu{5e-6 mol}$ $\ce{FeCl3}$ and $\pu{0.2 mL}$ of different concentrations of $\ce{H2O2}$ (1, 3, 5, 10, 15, and 20%).

After processing the data, I found the following graph:

I was wondering why with higher concentrations of $\ce{H2O2}$ the rate decreases. I initially wanted to analyse this according to the Michaelis-Menten model (as $\ce{Fe^3+}$ ion can be regarded as a catalyst in this reaction). However, it seems my data goes in the opposite direction as the Michaelis-Menten plot. What surprised me most that it was decreasing.

I came up with a few hypotheses for this, and searched for papers, but I could not find any with results similar to mine. My main hypothesis was that because $\ce{Fe}$ ion and $\ce{H2O2}$ form $\ce{OH.}$ radicals and $\ce{OOH.}$ radicals (as reported here and here), and these radicals are what cause the decomposition of methylene blue, I thought that maybe if there was too high a concentration of $\ce{H2O2}$, there would be too many radicals, and this would in turn terminate the free radical reactions (when 2 free radicals meet). At lower concentrations, the radicals would continue propagating, hence decolourising methylene blue faster.

Moreover, I know that this is not a problem with the colorimeter, as I could see this decolourisation outside the colorimeter too. The following is a screenshot of a video I took; each reaction in the cuvette was started at the same time, and concentrations of $\ce{H2O2}$ used in order from left to right are 1, 3, 5, 10, 15, 20%.

I was wondering if anyone knew why this happened.


texts: Special case of Cannizaro reaction of formaldehyde with 100% NaOH/KOH follows 4th order kinetics

texts:
It is given that when we use $50{-}\pu{60\%}\ \ce{KOH}$ in a Cannizaro reaction of formaldehyde, the reaction follows third order kinetics, but under special cases of Cannizaro reactions it was given than when formaldehyde reacts with $\pu{100\%}\ \ce{NaOH/KOH}$ the reaction follows fourth order kinetics.

What is the reason for this change in the order of reaction with an increase in the concentration of base?


texts:
I read that melting of gold is a physical property, but I wonder if this is true.

If we want to melt gold we will need to add heat, and once we add heat to gold to melt it, there must be a chemical change, not a physical change, right?


texts: Why do surfactants lower the surface tension

texts:
Everybody knows that detergents, or generally amphiphilic substances, lower the surface tension. Of water, usually.
I wonder if that's true for any polar solvent (most likely), i.e. will the same detergents work in, say, ethanol or liquid ammonia?
What happens in a nonpolar solvent? The detergents aggregate on the surface there too, but now with the polar end sticking out. Does the surface tension go up, or down?
And what exactly is the reason for the effect on water anyway, quantitatively? Imagine a surface of water which is covered by exactly a single layer of surfactant molecules, e.g. in a Langmuir trough. Now go to half or double that amount. Is there a discontinuity in the change of surface tension? If yes or no, why?
(sorry for the jumble of questions, I'm not quite sure from which angle to tackle this. The effects seems quite obvious, but I'm not sure it is. My real question is how to explain the effect on a molecular level.)


texts: Why do Fullerenes have even number of carbon atoms?

texts: My teacher started a chapter called "Carbon and its compounds", Which is just an intro to organic chemistry . In which she taught about fullerenes structure and examples and also told that fullerenes have even number of carbon atoms. I got curious and asked why but she didn't answer me. So I went and googled it but still did not get any answer. Is there any exception or any reason behind it?


texts: Does the positivity and negativity of terminals of a battery depend on the terminal where the electrons enter the external circuit?


texts: Can I melt Barium Titanate powder into a cylinder and preserve the high dielectric?

texts:
I would like to make various solid forms of Barium Titanate e.g. cylinders, discs.

Barium Titanate powder seems widely available and has a melting point of 1,625'C. Can I melt it in an iron forge into a mould, and will this preserve the high dielectric constant?

Is there perhaps a low temp way to do this easier e.g. a solvent or additive to achieve the same? Others have tried embedding within epoxy, but with substandard K values (max 27 instead of 7,000 as per the raw powder)


texts: Regarding the infinitesimal form of the First Law of Thermodynamics

texts:
First Law of Thermodynamics is expressed as[1]

  The internal energy of an isolated system is constant.

If $w$ denotes the work done on a system, $q$ for the energy transferred as heat to the system, and $\Delta U$ for the resulting change in internal energy, then it follows that $$\Delta U = q + w \label{1}\tag{1}$$

$$\mathrm{d}U = \mathrm{d}q + \mathrm{d}w \label{2}\tag{2}$$

What I don't understand is how does $\eqref{2}$ follow mathematically from $\eqref{1}$. Taking the limit $\Delta U \rightarrow 0$ gives the left-hand side but how does $q$ change into $\mathrm{d}q$ and $w$ into $\mathrm{d}w$? I understand the interpretation of both the equations physically. Is this related to the fact that $U$ is a state function whereas $q$ and $w$ are not?

Reference:

[1] Atkins, P.; de Paula, J. Physical Chemistry, 10th ed; Oxford UP: Oxford, U.K., 2014.


texts: Relative abundance of the isotopes of iridium

texts: There are two stable isotopes of iridium, $\ce{^191Ir}$ and $\ce{^193Ir}$. If you randomly pick an iridium atom from a large collection of iridium atoms, which isotope are you more likely to select?


texts: Some ion-selective electrodes can be expensive (starting from $500). Is there any relatively inexpensive do-it-yourself alternatives that would still give very accurate results? How does one make an ion-selective electrode?


texts: Determining the nature of common pH indicators (methyl orange) using Le Chatlier's principle

texts:
I got some good information about this topic yesterday, and I understood what I was told, but I have come up with a specific way of phrasing the problem I'm having. It is slightly different than before, and I'm looking for someone to tell me if what I'm doing makes any sense or not, rather than just rote learning facts like 'methyl orange indicator is a weak acid/base'. I want to be able to use this process for any weakly acidic/basic indicator I come across.

(Note: Methyl orange is taken to be orange when it has a moderate pH (HIn, not very acidic or basic, and red between a pH of 4.4 and 3.1 - i.e. when it is In- or In+ depending on the scenario below)

Assume methyl orange, an indicator, is a weak acid. It dissociates as follows in aqueous solution;

We know that if an acid is added to this system at equilibrium, the concentration of hydrogen ions will increase. Using Le Chatlier's principle; to oppose this stress, the reaction shifts to the right, and the colour of the initial indicator (in this case methyl orange, so orange) will dominate and become more intense.

The solution will not go red, like it would if a base was added and proton concentration was decreased, as the equilibrium would shift in the other direction.

The problem is, that if you add an acid to this system in real life, a colour change occurs at a pH of 4.4, from orange to red. This means that methyl orange indicator cannot be an acid. Right?

If you instead assume that methyl orange is a weak base, it dissociates like so in aqueous solution;

So here, if you add an acid, the concentration of hydroxide ions will decrease (due to bonding between the hydrogen ions in the acid and these hydroxide ions to form water), so the equilibrium shifts to the right, to compensate.

This means that the red colour will dominate.

This result is in line with observation, as methyl indicator will change colour from orange to red at a pH of 3.1-4.4, which is acidic.

Does my reasoning therefore demonstrate that methyl indicator must be a weak base?


texts: Most numerical prefixes are based on Greek roots, but for "nine" we use the Latin root instead which seems inconsistent.  Thus, for instance, "nonane" instead of "enneane", or in mathematics "nonagon" instead of "enneagon" (although here the Greek form seems to have more traction) .  Why?  Can we use the Greek root as an alternative?


texts:
Which is more acidic between methanal ($\ce{HCHO}$) and ethanal ($\ce{CH3CHO}$).
Please explain using General organic chemistry basic concepts.

My Effort:

I saw the stability of the conjugate base.

It would be $\ce{HCO-}$ and $\ce{CH2^{(-)}CHO}$.
Due to resonance I can say that second one is more stabilized and thus a better acid.

But answer says that methanal is more acidic than ethanal.


texts:
Using a weak acid as an example:
$$\ce{CH_3COOH <=> CH_3COO^- + H^+}$$

The position of this equilibrium shifts to the right with increasing dilution.

I have found textbooks that say this, but do not provide an explanation. Why is there increasing ionization with increasing dilution?

I was wondering if it has to do with the free energy available; since ethanoic acid is a weak acid, energy has to be provided to promote the proton to a higher free energy state (transfer from $\ce{CH_3COOH}$ to $\ce{H_2O}$), therefore, "more" free energy for promotion and less contact with other $\ce{CH_3COOH}$ molecules?


texts: Assigning labels and answering questions using given DSC graph

texts:
I'm currently working through past exam papers in preparation for my upcoming Inorganic Chemistry exam and I got to this question. We really haven't looked at DSC graphs, so I'm not completely sure how to answer this. I've shown my attempt, but am looking for someone to confirm if I'm right, if not, where I went wrong.

Question:
The DSC thermogram depicted below was run on a sample of a new compound suspected of possessing mesogenic properties. The thermogram was obtained at a scan rate of 10 °C min−1 and the solid line represents the heating scan, while the dashed line represents the cooling scan.

Interpret the DSC thermogram, naming and explaining the processes occurring at peaks (a) – (e), using the correct terminology.
Does the DSC thermogram confirm that the new compound is a mesogen? If so, what can you say about the liquid crystal phase(s), and what name is given to this class of mesogen? What word describes this particular kind of thermal behaviour?

My answer: e = Crystallization, a = melting point (crystalline -> smectic), b = transition point (smectic -> nematic), d = (re)crystallization (nematic -> crystalline), c = melting point (crystalline -> nematic). Since a nematic phase is a subset of liquid crystal (synonym for mesogens), it confirms that the new compound is a mesogen. Molecules in the nematic phase are (somewhat) orientationally ordered (in contrast to the smectic phase which is (somewhat) orientationally and positionally ordered). I don't have an answer to "What word describes this particular kind of thermal behaviour?".


texts:
In school I was taught that an atomic orbital is the 3-dimensional region in which the electron is located with a probability of 90%.

However, aren't there infinitely many regions of space in which the total probability of finding the electron is equal? And if so, wouldn't that imply that it is not possible to assign a shape to an atomic orbit as there are infinitely many shapes with equal likelihood to contain the electron?