texts: I was wondering if it would be possible to make this chemical?


texts:
How many mutually immiscible liquids can be stored in a glass bottle at S.T.P.?

According to

  PATTLE, R. E. (1950). Systems of Mutually Immiscible Liquid Layers. Nature, 165(4188), 203–204.

a system of 6 immiscible phases can be formed (including mercury), but the ammonia layer disappears after a month. They suggest gallium could add another layer, giving:

ammonia solution
isobutyl alcohol
liquid paraffin
potassium carbonate solution
methylene iodide
gallium
mercury

Could silicone oil and fluorocarbons create additional stable layers, and have there been any other systems suggested since 1950? I saw a 2006 reference with allegedly 8 phases.


texts: I’d read that it takes energy to place electrons in pairs, just less than it would take to place two electrons in different subshells. I get that. What I don’t get is, then, why would electrons want to fill their orbitals with electron pairs at all? Wouldn’t it better to just fill them up with single electrons, as per Hund’s rule, and then leave them like that? Would that not be more energetically favorable? Why do atoms insist of having full valence shells, then?


texts: How can I find whether there is oxygen present inside a well of diameter 1 m at 50 m's deep?

texts:
How can one find whether or not there is enough oxygen for breathing present inside a (dry) well of diameter 1 m at a depth of 50 m?

Many people in Nepal are killed while cleaning wells because of a lack of oxygen.


texts: Can ZnO act as a reducing agent for noble metals like Pd?

texts:
Palladium ions (e.g., $\ce{Pd^2+}$) can be reduced to $\ce{Pd}$ by more reactive metals such as zinc. Metal oxides such as $\ce{ZnO}$ are very stable but can its atoms in the oxide structure still be displaced by Pd?
I know the answer is probably "No" but in one of my samples $\ce{ZnO}$ nanoparticles were removed from the solution after I added $\ce{Pd^2+}$ solution to the system and $\ce{Pd}$ nanoparticles were formed. The solvent was methanol. After washing the solution and drying I did XPS and no trace of zinc was observed but saw $\ce{Pd}$ peaks.


texts: Why isn't the side chain of arginine totally protonated at low pH?

texts:
I was wondering why arginine cannot be protonated at $\mathrm{pH\ 0}$ on all the $\ce{N}$ atoms in the side chain, as they all have a free electron pair. As this image shows, it can only be protonated once.

Why don't the other two nitrogen atoms in the side chain get protonated? Does it have something to do with resonance with the $\ce{C=N}$ double bond?


texts: Which intermolecular interaction is dependent on the inverse cube of distance?

texts:
The intermolecular interaction that is dependent on the inverse cube of distance between molecules is:

  hydrogen bond
  ion-ion interaction
  ion-dipole interaction
  London force

Inverse cube of distance I think means an ion-dipole interaction, since we know force due to a dipole on a charge is inversely proportional to the cube of distance. But I don't understand why the answer given is hydrogen bond. What is the distance dependence of the hydrogen bond? Shouldn't the answer be (3)?


texts:
I've spent a few days googling functional groups and reading my text assigned on organic functional groups. I'm understanding very little and I just need a little clarification. I understand that at the top right and bottom left, the hexagon structure signifies an aromatic, right?

Top Left: My first guess was carboxylic acid, but with further googling, I now think it's an amide, because it contains nitrogen and oxygen?

Top Right: Since the hexagon is aromatic, I know it can only be the last three choices, but I'm going with C because the $\ce{-NH2}$ is not connected to an oxygen.

Bottom Left: Because of the $\ce{Br}$, I know it's a bromide and, assuming that my thinking is correct with aromatic, the answer should be B.

But the bottom right, I am not sure what exactly to look at here to even guess, besides that it is not an aromatic ring.

To show that I've tried the last one, all I can find is that an alkane is $\ce{CH4}$, alkene is $\ce{H2C=CH2}$, and an alkyne is $\ce{HC#CH}$ and, the aromatic being the hexagon structure, I'm unable to grasp/understand which one the last group would fall into.


texts: How would you know if the light emitted is of one wavelength or if it is a mixture of two or more wavelengths?

texts:
I am just learning some chemistry after a long time without studying it and I have thought about something.
Some copper compounds emit green light when heated to flame. So, I would like to know if it is known if an emitted light is of one wavelength or if it is a mixture of two or more wavelengths.
Thanks in advance


texts: I know that the exact (OK most of the times not the exact) energy of an electron can be calculated by solving Schrodinger's differential equation, but can we explain an electron's energy of a specific orbital using the Penetration and Shielding effect?


texts: Is it possible to create a solution with superoxide?

texts:
I am not a chemist, and somehow I cannot find any material on this topic, so I decided to ask here.

I am looking to create a solution with a specified amount/concentration of superoxide ($\ce{O2^.-}$). Can you suggest some compounds that will enable me to "isolate" superoxide in a solution?


texts: How to make 1,1-diphenyl-1-butene from benzophenone and 1-bromopropane?

texts:
I would like to know the method of syntheses of making
1,1-diphenyl-1-butene $(\ce{C16H16})$ from benzophenone $(\ce{(C6H5)2CO},$ generally abbreviated $\ce{Ph2CO})$ and 1-bromopropane $(\ce{CH3CH2CH2Br}).$

I think that the carbonyl group which is a functional group composed of a carbon atom double-bonded to an oxygen atom $(\ce{C=O})$ of benzophenone will react to the alkyl halide.

Because oxygen is more electronegative than carbon, carbonyl compounds often have resonance structures which affect their reactivity.  This relative electronegativity draws electron density away from carbon, increasing the bond's polarity, therefore making carbon an electrophile (i.e. slightly positive).

But I have no idea how it reacts and proceeds to work. Can anyone help me understand the detail mechanisms and  reaction procedures to make 1,1-diphenyl-1-butene from benzophenone and 1-bromopropane?


texts: Product of the reaction of ethyl acetoacetate with alkaline benzoyl chloride followed by addition of ammonium chloride

texts:
What does this β-keto ester give when reacted with $\ce{PhCOCl/NaOH}$ followed by $\ce{NH4Cl(aq)}?$

According to me, the $\ce{PhCOCl}$ should react with $\ce{NaOH}$ forming benzoic acid which should attack the ester on the right, forming an anhydride and a ketone.
Also, whats the function of $\ce{NH4Cl(aq)}$? Is it a proton donor?


texts: How many carbons does an alkane need to have an enantiomer?

texts: How many carbon atoms does an alkane need before it is capable of existing in enantiomeric forms?


texts: Where does this equation for the activity in the gas phase equilibrium between N₂, H₂ and NH₃ come from?

texts:
I have a question with Equilibrium Constant.

I understand that for a reaction in equilibrium $aA +bB \rightleftharpoons cC +dD$
$$K_c= \frac{[C]^c[D]^d}{[A]^a[B]^b}$$
and $K_p$ is just using the partial pressures.

I'm looking through my PChem1 tutorials and I saw that they wrote for

$$\ce{1/2 N2 + 3/2 H2 <=> NH_3}$$
$$K=\frac{a(NH_3)}{a(N_2)^\frac12a(H_2)^\frac32}$$

I believe that a represents activity. However what i don't get is what follows:
$$K=\frac{a(NH_3)}{a(N_2)^\frac12a(H_2)^\frac32}=\frac{\left(\frac{n(NH_3)RT}{p_oV}\right)}{\left(\frac{n(N_2)RT}{p_0V}\right)^\frac12\left(\frac{n(H_2)RT}{p_oV}\right)^\frac32}=\frac{n(NH_3)}{n(N_2)^\frac12n(H_2)^\frac32}\left(\frac{p_oV}{RT}\right)$$

I cant' figure out how $a(NH_3)=\frac{n(NH_3)RT}{p_oV}$

It obviously has something to do with the ideal gas equation $pV=nRT$ but I don't get how.

additional context:
The question asks for the equilibrium composition starting with 1 mol each of $\ce{N_2}$, $\ce{H_2}$ and $\ce{NH_3}$ in a 1L reaction vessel at 298K

P.s. I get that I am to use extent of reaction to solve this.


texts: Why do iron(II) ions and chromium have different electronic configurations?

texts:
What I know:

Empty 3d orbitals are higher in energy than empty 4s orbitals
Aufbau Principle (electrons always go into an empty orbital with the lowest energy)
Partially/half/fully filled 3d orbital are lower in energy than 4s orbitals
$\ce{Cr}$ is an exception: $\ce{[Ar] 3d^5 4s^1}$. It breaks the "rule" because the extra stability from half-filled 3d orbitals is favoured.
From (1) and (2) => After the $\ce{[Ar]}$ core, electrons will fill 4s before occupying 3d
When forming ions, electrons of the highest energy are removed first.
Iron(II) ions exist as $\ce{[Ar] 3d^6}$ in reality.

What I understand:

I understand why Fe is $\ce{[Ar] 3d^6 4s^2}$. [from (5)]
I understand why Cr is $\ce{[Ar] 3d^5 4s^1}$.

From (4), (5) and (3), I believe for $\ce{Cr}$ the 4s is filled before 3d too, i.e. it is $\ce{[Ar] 3d^3 4s^2}$ before the last electron is added. After the last electron is added to form $\ce{[Ar] 3d^4 4s^2}$, a 4s electron immediately moves to the 3d orbital which is of lower energy.

From (6) and (3), for transition metals, 4s electrons are removed first. i.e., I understand why iron(II) ions may be $\ce{[Ar] 3d^6}$

What I don't understand:

I know $\ce{[Ar] 3d^6}$ is correct for iron(II), but I don't understand why?

Why doesn't iron ions adjust itself as Cr does to achieve the extra stability? Is it because, in this case, it needs to excite an electron to an orbital of higher energy, whereas in Cr, the 4s electron just moves down to an orbital of lower energy?

P.S.

I've read What is the electronic configuration of Fe(II) ion? and I am not satisfied with the answers in that thread.
I've read Do ions also form special electron configurations? (just as Copper and Chromium do), and it only tells me "it is possible for ions to have special electronic configurations too!"


texts:
I have figured out that 4 one will have the highest enol content of all, and the 1 structure would come after 4 in enol content, i.e 4 > 1. Then I got confused between the 2nd and the 3rd structures.

Please give a brief explanation for the answer as well.


texts: How can there be decimal subscripts in a molecular formula?

texts:
While learning about how batteries work I have encountered the following notation for a Li-ion cathode: $\ce{Li_{0.5}FePO4}$.[1]
According to Wikipedia, the subscript number in a reaction equation represents the number of atoms in a molecule. But what does the $0.5$ represent? Is it a fraction of atoms in a molecule?

Also, $\ce{LiFePO4}$ is a cathode. I would expect that for a fully charged battery, the anode is populated with all the $\ce{Li}$, therefore the cathode should be $\ce{FePO4}$, right? I can also understand that some $\ce{Li}$ gets stuck in the cathode, but then I read somewhere that a fully charged battery, the cathode is $\ce{Li_{0.5}FePO4}$.

I have added an exaggerated sketch for what I imagine the system would be.

I know that the structure of $\ce{Li_{0.5}FePO4}$ is more complex than this, but this is only a hypothetical sketch. Also, please note that I don't have a background in chemistry, so any additional material that can help me understand the concept better is greatly appreciated.

References:

Tan, H.; Fultz, B. Rapid Electron Dynamics at Fe Atoms in Nanocrystalline Li0.5FePO4 Studied by Mössbauer Spectrometry. J. Phys. Chem. C 2011, 115 (15), 7787–7792 DOI: 10.1021/jp200127b.


texts:
An $\mathrm{E2}$ (or $\mathrm{E1cb}$) mechanism requires antiperiplanar configuration. In case of restricted rotations, like in cycles, where rotation is not possible to achieve the antiperiplanar configuration, elimination occurs to favour the Hofmann product instead of the Zaitsev, if antiperiplanar configuration is possible at the less substituted β C.

In menthyl chloride, antiperiplanar configuration is only seen with the red $\ce{H}$, so 2 menthene is the only product, although it is not the most substituted.

In the molecule above, due to restricted rotation, the leaving group $\ce{Cl}$ and the base attacking the $\ce{H}$ will be on the same side. So will elimination be possible in this case?


texts:
Yesterday, I performed the synthesis of anthranilic acid (also known as, 2-aminobenzoic acid. I was instructed to use the common route that is also featured on the Wikipedia page for this compound. That is, using the phthalimide I first synthesised, I dissolved in excess aqueous $\ce {5M}$ $\ce {NaOH}$ and then added an equimolar amount of sodium hypochlorite with heating. To obtain the anthanilic acid, we were asked to add into the large volume of the aqueous solution, glacial acetic acid dropwise with stirring, after adjusting the solution's pH to neutral using conc. $\ce {HCl}$. This was unsuccessful for me and many of my peers. That is to say, anthranilic acid did not precipitate out of solution even when we used a lot of the glacial acetic acid.

My friend and I suspected that the problem could be that there was just too large a volume of solution, such that the concentration of anthranilic acid is just too low. Hence, we decided to boil off some water to obtain a more concentrated solution. He used a hotplate to do so while being more impatient, I used a heating mantle, which was able to reach much higher temperatures much more quickly. Very interestingly, after vigorous boiling and giving off much acetic acid fumes, a white solid was formed as a deposit at the bottom of the flask. I then quickly filtered this greyish solid and performed a recrystallisation using water as a solvent on it. I obtained a white seemingly pure solid as the end product.

Not many of us obtained products yesterday for the practical. Even among the three of us who obtained products, the colour of our products varied with the other two getting products which looked slightly greyish and brown. Likely due to the presence of some impurities as the Wikipedia page does say that the pure anthranilic acid product should be a pure white colour.

The above image shows what I believe to be the most pure product on the right and the purity decreases from right to left.

I would like to ask some questions regarding this procedure I have conducted. Firstly, I believe I saw some benzoic acid crystals in one of my reaction flask, just a small amount at the bottom of the flask after I transferred the contents into a beaker. This was after the hypochlorite addition step. Could it have been one of the possible side products?

Also, how likely is my product actually anthranilic acid? It seems strange that the product crashed out of solution during the violent heating process. Although anthranilic acid is less soluble  in water than benzoic acid, this is still rather unexpected.


texts: What does Molecular Orbital Theory get wrong?

texts:
I am learning about MO theory in my advanced inorganic chemistry course and am starting to realize that it is truly the most accurate representation of how molecular orbitals look like, where they are located in the molecule, and their relative energies to each other and the original atomic orbitals from which they are composed of. We are using Symmetry Adapted Linear Combinations as the approximation method and so far this method has successfully explained all chemical/magnetic/electronic properties for any molecule investigated thus far.

My question is: Is MO theory perfect? Or does it have a flaw somewhere like every other bonding theory (Lewis, VB, hybridization) I have learned about so far in my chemistry career?


texts:
I did an undergraduate experiment and could use some help in interpreting the $\ce{^1H}$ NMR spectra.

This was the task:
About $\pu{5-10mg}$ (1-2 drops) distilled amine is weighed in a NMR tube. Put the top on the tube immediately to prevent reaction between the amine and $\ce{CO2}$  from the air. Weigh exactly 1.1 equivalent of (S)-alpha-acetoxyphenylacetic acid. Dissolve the acid in about $\pu{0.4 ml }\ce{CDCl3}$ and transfer the solution to the NMR tube.

This here is the $\ce{^1H}$ NMR:

Could I get affirmation of the choices drawn in red and what does the shift at $\pu{4.2ppm}$ correspond to? Could it be because $\ce{CO2}$ reacted with the amine?

(ChemdDraw was used to get the molecular figure and chemical shifts on the figure.)


texts: Why can enolizable aldehydes undergo Cannizzaro reactions?

texts: Why does 2-methylpropanal undergo a Cannizzaro reaction even though it has an $\alpha$-hydrogen?


texts: What does "the magnesium salt of EDTA" mean?

texts:
I am attempting to prepare an ammonium chloride/ammonium hydroxide buffer solution ($\ce{pH}=10 \pm 0.1$) for titrating water hardness with calgamite and EDTA.

In the 17th Edition of the Standard Methods for the Examination of Water and Wastewater, the reagent preparation section for titrating water hardness (Section 2340 C.) states:

Mix the $\ce{NH4Cl+NH4OH}$

  Add $\pu{1.25 g}$ magnesium salt of EDTA (commercially available).

Dilute with distilled water.

  After researching, I have assumed it to mean Magnesium Disodium EDTA (hydrate), CAS# 14402-88-1.

In reading the source material and searching online for synonyms of "magnesium salt of EDTA," I can't seem to find an exact hit on the term. Searches included PubChem, ChemSpider, Sigma-Aldrich, and Cole-Parmer, among others. Each seemed to point me toward "Magnesium Disodium EDTA Hydrate." I was hoping that with the amount of knowledge on this site, someone might recognize the term "salt of" and be able to help me out and clarify the term, or confirm that I am using the correct EDTA salt.


texts: Final amount of Hg present after $\beta$ decay

texts:
I have been trying to solve an exercise on nuclear chemistry, but I was not sure whether I should ask this on physics or chemistry but I think that if chemistry had an exercise based on this then chemistry experts might be having the way to overcome this problem. So here is what my nuclear chemistry question says:

  One gram atom of $ _{79}^{198}\mathrm {Au} $ (having a half life of 65
  hours) decays by $\beta$-emission to produce stable nuclide of Hg.
  How much Hg will be present after 260 hours?

The thing which is making me confused is $\beta$ decay. I think I have a formula for this question but that $\beta$ thing is creating a problem. I would like to make that equation public. Here it is:

$$N_t=N_0\cdot\exp(-\lambda\cdot t)$$

where,

$\lambda$ is the radioactive decay constant
$N_0$ is initial number of nuclides present
$N_t$ is the co. of parent nuclides present at time $t$


texts: Why is barium used instead of bismuth as a contrast in gastrointestinal xrays?

texts: Why is barium used instead of bismuth as a contrast in gastrointestinal x-rays? Bismuth is a heavy metal that has a relatively low toxicity in comparison to barium. Is there a particular property of barium that makes it a better contrast? Is it less expensive?


texts:
How would I synthesise LY-293,284?

Figure 1: LY-293,284

I have satisfied the conditions at the page Should we allow Synthesis questions subject to the six constraints listed below? so please don't just write off this question and close it. The constraints are satisfied as followed:

Starter material(s): 5-acetylindole.

Figure 2: 5-acetylindole

I have completed a Google search to check for LY-293,284 synthesis pathways by typing "LY-293,284 synthesis" and there were no applicable results.
I would imagine the synthesis would occur via the following pathways:

Phenylation of the 5-acetylindole to phenyl-5-acetylindole.
Oxidation of the resulting phenyl-5-acetylindole with oxidising agents such as potassium nitrate?
Di-n-propylamination of the resulting 5-acetylindolylphenol with di-n-propylamine to LY-293,284.

The synthesis I'm hoping is simple.
LY-293,284 is a 5-HT1A receptor full agonist.


texts: At what temperature CO2 becomes solid at normal pressure?

texts:
I have met contradicting evidence. The phase diagrams show that $\ce{CO2}$ solidifies at $-78.5\ ^{\circ} \mathrm{C}$:

Wikipedia confirms this

  At 1 atmosphere (near mean sea level pressure), the gas deposits directly to a solid at temperatures below $−78.5\ \mathrm{^\circ C}$ ($−109.3\ \mathrm{^\circ F}; 194.7 ~\mathrm{K}$) and the solid sublimes directly to a gas above $−78.5\ \mathrm{^\circ C}$.

Yet this article claims it happens at $133\ \mathrm{K}$ (otherwise $\ce{CO2}$ would showfall at Earth's poles).

Which claim is correct?


texts: Why is $\ce{B2}$ paramagnetic? It's just 2 borons with a triple bond between them. Aren't all the electrons paired?


texts: what kind of suspension liquid should be used with ferrofluid (so it does not stain the glass)

texts:
Please take a look at the following video:

I am working on a new project, and I need to find whats the best liquid to hold ferrofluid inside the glass (or maybe even plastic) container, so that ferrofluid (that easily stains everything) does not stain or stick to glass?

Also, is there any special preparation for the glass needed?


texts: Why does a sealed plastic bag of dish soap, water and air expand when shaken?

texts:
I've noticed that when I put dish soap, water and a little air into a sealed plastic bag, and then shake the mixture, it forms soap suds and the bag expands significantly in volume. Why does it expand?
Update:
After being prompted by the comments, I tried to re-create and measure this phenomenon under more controlled conditions, but the bag does not expand.
The less-controlled conditions, where the bag expanded in the past, were:

A plastic bag, slightly dirty from crumbs of cooked ground corn, and canola oil (the bag held arepas)
A little squirt of Ultra Ajax Triple Action Orange dish soap (not automatic dishwasher soap). The ingredients (and purpose) are:
Water (Consistency)
Ammonium C12-15 Pareth Sulfate (Cleaning and Foaming Agent)
Lauramidopropylamine Oxide (Cleaning and Foaming Agent)
SD Alcohol 3-A (Controls Thickness and Clarity)
Sodium Chloride (Controls Thickness)
Poloxamer 124 (Controls Thickness)
Fragrance (Pleasant Scent)
Methylisothiazolinone Benziosothiazolinone (Preservation)
Pentasodium Pentetate (Maintains Product Stability)
Sodium Bisulfite (Maintains Product Stability)
Dyes (Color)
Chlorinated tap water
A little air
Everything at around 30 C (a little warmer than room temperature)
Seal the bag and shake. Bag volume increased approximately 2x, with no noticeable change in temperature.

I could observe a similar phenomenon in the past by sealing my palm over the open end of a dirty drinking glass containing dish soap water and air, shaking it, and feeling outward pressure on my palm. I don't recall what the glass was dirty from.
Today, under more controlled conditions, I used a clean bag, and a clean drinking glass, and I could not create any expansion. So I think either the "dirt" in the vessel contributed to the phenomenon, or the tap water was more chlorinated on the days where I observed the phenomenon, and that somehow contributed to expansion. In today's experiments, the water doesn't smell chlorinated.
If I can re-create the expansion later, I will note the conditions as well as I can.
Update 2:
At the request of a commenter, "under more controlled conditions" as described above (and notably where the water does not smell chlorinated), I added table salt, and it did not cause expansion. When the local water authority chlorinates the water again, I will retry the experiments.
Update 3
A similar question has been posted at https://physics.stackexchange.com/questions/617113/why-does-pressure-in-a-thermos-increase-after-shaking-up-hot-water-and-soap


texts: We say that when an atom loses an electron it becomes positively charged ion, and similarly when an atom gains electrons it becomes a negatively charged ion. My question is that are 'positive' and 'negative' just labels indicating more protons than electrons or vice versa, or do the ions actually display an increased interaction towards other charged particles?


texts: Meaning of Flammability Limits and reaction in Air of Ammonia

texts:
I have read on Wikipedia that the flammable limits of gaseous ammonia are between 15–25% and I have also read that the autoignition temperature is $651\rm~^\circ C$.  And that the combustion of ammonia in air is $$\ce{4NH3 + 3O2 -> 2N2 + 6H2O}$$  My understanding of this is that with a 20% air to $\ce{NH3}$ that I could hold a flame.  Outside of that range, I cannot hold a flame.

My question is if I am at 30% air and above $651\rm~^\circ C$ will Ammonia still combust/react with Air or will it stay $\ce{NH3}$?

My follow up question would be that when if I sprayed ammonia into a heated chamber (above $650\rm~^\circ C$) would flames/the exothermic reaction only happen when the ammonia vapor and the air reach that 15–25% range as the vapor propagates into the air and not react outside that range?


texts: Why do BH3 and NaBH4 have different selectivities?

texts:
I've always known borane ($\ce{BH3}$), as a reagent for alkene hydroboration. Recently in class we talked about its use in the reduction of carboxylic acids to alcohols as well.

Now obviously $\ce{BH3}$ is an electrophile and I don't think it reacts by donating hydrides like sodium borohydride ($\ce{NaBH4}$) does - in any case it's not charged like $\ce{BH4-}$. Also $\ce{BH3}$ should be a pretty weak hydride donor, considering the covalent nature of the bonds and lack of any charge. It can reduce carboxylic acids, however, which $\ce{NaBH4}$ can't do! Where's the difference and what's the reason for this contradiction?

And what prevents borane from reducing acid chlorides (my instructor told me this)? This is something $\ce{NaBH4}$ is successful at.


texts: Why is absorption spectrum of beta-carotene different from Zeaxanthin?

texts:
Here are the molecular structures of beta-carotene and zeaxanthin

These molecules only differ in the OH groups and the conjugated backbone length is exactly the same. I read that the absorption spectrum of a molecule is decided by the conjugation length. How is it then, that the absorption spectrum of the two molecules are different as shown below:


texts: Why does higher temperature affect the rate of electrolysis?

texts: I understand that more heat energy= higher rate of electrolysis, but can someone explain using higher-level terms why this occurs and if there are any theories or rules that explain this?


texts: Is scopolamine same as scopolamine hydrobromide?

texts:
Is scopolamine extracted with methanol or acetone from Datura or Brugmansia scopolamine free base or scopolamine hydrobromide?

If you take a look at the Wikipedia page for hyoscine, the Synonyms part lists scopolamine hydrobromide as a synonym for hyoscine even though neither molecular structure nor chemical formula contains bromine.


texts:
May I use water as a condensing medium while distilling out oxalyl chloride?

As oxalyl chloride reacts with water and the products are $\ce{HCl},$ $\ce{CO}$ and $\ce{CO2},$ when there is a leak or breakage of condenser shell/tube separating water and oxalyl chloride, there may be liberation of toxic gases causing the situation more unsafe.


texts:
The reduction potential for $\ce{Au^3+ + 3e- -> Au}$ is $1.503 \text{ V}$. The reduction potential of $\ce{Cl2 + 2e- -> 2Cl-}$ is $1.36 \text{ V}$. So, the $E^o$ for $\ce{2Au^3+ + 6Cl- -> 2Au + 3Cl2}$ is $0.143 \text{ V}$.

If the reaction $\ce{2Au^3+ + 6Cl- -> 2Au + 3Cl2}$ has a positive E standard ($E^o$ = $0.143 \text{ V}$), then how is it possible for $\ce{AuCl3}$ to exist in aqueous solution without $\ce{Au^3+}$ oxidizing $\ce{Cl-}$ to $\ce{Cl2}$?


texts: How to isolate and determine an unknown molecule in a known heterogeneous mixture using HNMR

texts:
I am currently working on an assignment as part of my second year lab course. Essentially I have to determine the unknown molecule which is present at 5-15 wt% in 1 gram of Aspartame.

I am planning to do the HNMR of a pure aspartame sample then the HNMR of the heterogenous mixture. Hopefully there will be some distinctive peaks but most likely there will be many overlapping peaks between the Aspartame and the unknown.

My question: Is there any way I can subtract the HNMR of the pure sample from the heterogenous mixture. Therefore I could be left with the HNMR of just the unknown compound.


texts:
Are there any reactions with no activation energies? Our professor just told us there are no chemical cliffs. Is this true?

I read something about nuclear decay as being a reaction with no activation energies. Why is this so, and how does this work?


texts:
We have a pilot atomization setup where we atomize molten tin to produce tin powder. Unfortunately a lot of tin is wasted and oxidized.

I have found this video on which looks promising. Is this the best way of reducing tin oxide? Or do you know of anything better / effective?

Thanks!


texts: Cobalt electroplating over nickel-plated steel

texts:
From my research, I understand that cobalt can be used on top of a nickel layer to improve durability of the nickel plating on a steel object.
I am using a nickel anode and nickel acetate as electrolyte.

Would I be able to use a cobalt anode and cobalt acetate as electrolyte?
If I buy $\ce{CoSO4 * 7H2O}$ but don't have a cobalt anode, can I use a stainless steel or titanium anode?


texts: Weak acids compared to strong ones in pH > 7 solution

texts:
In the book of Molecular Cell Biology (Big Alberts) by Alberts, at page 46, it is stated that

Acids—especially weak acids—will give up their protons more readily if the concentration of > H3O+ in solution is low and will tend to receive them back if the concentration in solution is high.

Does this mean that, in a solution with high pH, the weaker acids will behave like a strong acids in water, in the sense that they will be more inclided to give up their protons compared to strong acids?


texts: Constraints on the polar angle (θ) in the particle in a sphere problem

texts: For constraint in $\phi$,  $\psi(\phi+2\pi$)= $\psi(\phi$) seems logical as after 2$\pi$ rotation we go back to the same point, therefore functions should be same. But how does it hold for $\theta$ as rotation of $\pi$ gives diametrically opposite point on the sphere, why should then   $\psi(\theta+\pi$) be equal to $\psi(\theta$)?


texts: Why six C atoms are usually seen in cyclic compounds?

texts:
When it gets to Carbon-based molecules, one very possible structure when there are more than six C atoms is the hexagon; though not mostly perfect, it emphasizes that six Carbon atoms tend to bond with each other.* Why?
I assume this is because of the "stability" that is attributed to the hexagon. Explainers have discussed mainly about this issue.
Neither me nor my teacher were convinced by the description; (Actually, all of this is because of my teacher!) since he asked that for example, why not octagon? No response.

I wondered that if I asked this in here what ideas I am going to face.... Sorry, but I'm accustomed to doing lots of "whys".
*For example; look at the pic below:

In the image above, the number of hexagonal rings is twice the number of pentagonal rings and eight times more than octagonal rings. This macro-molecule is the micro of what's happening in the nature. I don't have citations; but it takes a minute or two to see how much the number of hexagonal rings is surpassing the number of other rings. Perhaps it was so obvious, nobody mentioned it.
Update: According to @ron, and with a little payment of thought, I reached the fact that these rings aren't necessarily geometric; the important thing is that six C atoms, instead of five or eight or whatever else number of C atoms are the majority.
Image credit: Pseudopotential model for Dirac electrons in Graphene...


texts: Does changing the volume of a reactant affect the rate of reaction? Does changing the volume of HCl affect the rate of a Mg & HCl reaction?

texts:
I'm doing a experiment in which I'm testing the affect of the concentration of a reactant on the rate of reaction.

The reaction is between Magnesium and Hydrochloric Acid and so I'm changing the concentration of $\ce{HCl}$ ($\ce{0.5~M}$, $\ce{1~M}$ etc.)

In my lab report, I'm writing a list of controlled variables. So far I've mentioned the surface area and temperature of reactants. I would like to know more controlled variables.

I want to know whether the volume of Hydrochloric Acid affects the rate of reaction when added to the same amount of Magnesium metal?

According to some it doesn't and some say it does; I'm confused.

Also, please tell me why or why not the $\ce{HCl}$ volume affects the rate of reaction.

If the concentration of $\ce{HCl}$ changes between trials and the volume changes between the trial as well, then is the rate of reaction affected?

Does volume affect concentration in this case?


texts: Metal coordination in enzymes: What type and number of bonds form between amino acid residues and Fe(II)?

texts:
My understanding: Transition (d-block) metals, as found in intracellular proteins, are limited to about 10 elements including amongst others Fe, Ni, and Cu. Due to the reductive environments inside cells, they are usually/expected to be found with an oxidation state of +2 (?). However, the number of bonds that coordinate the metal, assuming that you know that the oxidation state is +2, is not completely certain (?).
Confusion about bond and coordination: As the d-orbital of e.g. Fe(II) is not completely filled it can be considered somewhat reactive/unpredictable, and we cannot for sure say what coordination it will have in an enzyme (?). Or, is there some sort of general assumption we can make about its coordination based on its oxidation number (i.e. +2)? As I was looking for literature on the matter I stumbled on the chemistry stack exchange answers regarding ‘bonds in coordination complexes’ which used Fe(II) as an example of how Pauling’s Principle could be applied to simplify how metals are coordinated.
A brief summary of this answers would include that coordinating residues can be thought to contribute ½ electron to the coordination of Fe(II); and thus, Fe(II) would typically have four coordinating interactions while Fe(III) would have six coordinating interactions, in order to cancel the charge.
Summary of question(s): If my statements above are correct, then it could be generally assumed that all +2 metals in enzymes, such as Fe(II) , are coordinated by four groups? Furthermore, the coordinating bonds are considered dative (i.e. not entirely ionic)?  Very speculatively, could it also be assumed that Fe(II) would typically be in a tetrahedral complex (why/why not)?
*update based on comments: Octahedral coordination of Fe(II) was mentioned as classical example in heme enzymes, while it is also known that non-heme enzymes can e.g. coordinate Fe(II) with three residues and a water molecules in a tetrahedral conformation. It could therefore be reasoned that coordination of the metal (e.g. tetrahedra vs octahedral) is related to enzyme function and evolution over time, and not so much the oxidation state of the metal?


texts: What is the origin of the huge difference in the autoprotolysis constant of heavy water versus regular water?

texts:
Basically, the gist of this question is, why is the autoprotolysis constant of heavy water different from that of ordinary water?

The autoprotolysis constant of heavy water at $\pu{25 °C}$ is $\pu{1.35 * 10^{-15}}$, while at $\pu{30 °C}$ it is about $\pu{1.47 * 10^{-14}}$. From this, I calculated that the enthalpy change for the autoprotolysis of heavy water is about $\pu{360 kJ/mol}$, which is already a huge difference from regular water's autoprotolysis enthalpy of approximately $\pu{+56 kJ/mol}$. The difference in entropy is also huge as well: by using the formula $-RT \ln(K) = \Delta G$ and $\Delta G = \Delta H - T \Delta S$ I calculated that the autoprotolysis of heavy water has an entropy change of about $\pu{+920 J K-1 mol-1}$, which is a world of difference versus water's approximately $\pu{-81 J K-1 mol-1}$. Can someone tell me why this huge difference in values is occurring?

Also could someone point me to a database that would contain this kind of thermodynamic data / equilibrium data because my textbooks aren't going to cut some of the questions I have in terms of raw data crunching.


texts: Most acidic compound amongs the following unsaturated ketones?

texts:
In the given picture, I know that the most acidic will be (a), because of potential of ring expansion. I tried a few times but wasn't able to get a satisfactory six membered ring. I think (a) is the most acidic compound among the 4 due to ring expansion only. Or if I am wrong, please correct me with a detailed solution.

The answer given is (a) but explanation is needed


texts: Why is the 2-position of pyridine electron richer than the 4 position

texts:
I am wondering about the electronic structure of pyridine.

If we look at nucleophilic substitution, which favored on electron poor centers, for 2-chloro and 4-chloro pyridine we see that the substitution in 4 position is about 5 times faster (Ethanol, 20°C, taken from The Chemistry of Heterocycles, page 277

This SE question and answer explain why this might be the case and the explanation there is that the lone pair of the nitrogen is repelling the nucleophile. This might be the case to certain extend, but from geometry of the attack I doubt that it has much of an effect. In addition if we look at the electron distribution in the pi system we get this picture (also taken from The Chemistry of Heterocycles, page 271)

So the 4 position seems to be electron poorer than the 2 position. Usually we explain electron poor and rich centers in heterocycles by using mesomeric forms:

And the usual comment is that the 2 position is closer to the nitrogen so the electron withdrawing effect is stronger than in 4 position and it should be electron poorer, which isn't the case.

I also did some DFT calculations using 2- and 4-pyridyl substituents and 4-pyridyl is more electron withdrawing than 2-pyridyl in that case.

Is there an understandable explanation why the 4-position is electron poorer despite beeing furtehr away from the nitrogen?


texts: Mass of strontium iodide contained in a 350 mL solution

texts:
What mass (in mg) of strontium iodide is contained in $350\ \mathrm{mL}$ of a strontium iodide solution that has a concentration of $1.93\ \mathrm{µM}$?

What I have done:

$0.350\ \mathrm{L}\ \ce{SrI_2}\cdot \frac{1.93\cdot 10^{-6}}{1\ \mathrm{L\ Solution}}\cdot \frac{341.42\ \mathrm{g}\ \ce{SrI2}}{1\ \mathrm{mol}\ \ce{SrI2}}=2.31\cdot 10^{-4}~\mathrm{g}~\ce{SrI2}=0.231~\mathrm{mg}~\ce{SrI2}$

What is not correct here?


texts: Calculating electric reduction(or oxidation) potential for complex ion formation equation?

texts:
I would like to calculate the standard electric potential($E°$) for the following equation.
$$\ce{Pt^{2+}(aq) + 4Cl-(aq) → [PtCl4]^{2-}(aq)}$$
$K_f = \pu{1.0 * 10^16}, T =\pu{ 298K}$
I figured out
$ΔG° = -nFE° = -RT\ln K$.
So, $E° = (\frac{RT}{nF})\ln K = (\frac{0.06}{n})\ln K (\text{approximated }\frac{RT}{F} = 0.06)$.
However, I'm having trouble finding $n$, or the number of moles of electrons transferred.
I'm not sure whether electrons are transferred in an complex ion formation equation.
Could you please help me with this confusion?


texts: Disregarding negative externalities and other barriers, what are some fuels that have a higher power density than gasoline?

texts:
Gasoline’s power throughput per kg is $12\,200\:\mathrm{Wh/kg}$ (Wikipedia.org). Are there any other fuels that have a higher power output that are not considered viable solutions as they are difficult to handle or have negative externalities?

Also what characteristics of their molecular structure give them the high energy throughput?


texts: Enzyme Kinetics two enzymes in complex with one substrate

texts: Given an enzyme reaction where two enzymes are required to form the complex, for example $\ce{2E +S-> E3S->2E +P}$, how would I calculate complex concentration assuming steady state approximation ($\frac{d\ce{E2S}}{dot}=0$). Does the 2 in front of $\ce{E}$ multiply the rate or is it the exponent when looking at the rates going into the complex?


texts: Fluorine Preparation:How can this be explained on basis of Lewis Acid-Base Reaction?

texts:
How can this be explained on basis of Lewis Acid-Base Reaction ?

$\ce{2 K2MnF6 + 4 SbF5 → 4 KSbF6 + 2 MnF3 + F2↑}$

References:

https://en.wikipedia.org/wiki/Fluorine#Industrial

Google Books reference (click me)


texts: Method of allylic and benzylic oxidation

texts: I am told that $\ce{MnO_2}$ oxidizes allylic and benzylic alcohols. However, what is the mechanism of this oxidation? All the professor had to offer me was that the metal ion, manganese 2+, chelates the substrate; there is some sort of interaction between a pi bond, the metal ion, and the electrophilic carbon atom bearing the hydroxyl group. No further explanation was given, and a Google search hasn't unearthed anything of use. What, therefore, is the mechanism of this oxidation? I would like to know more about the mechanism to better understand why $\ce{MnO_2}$ only touches allylic and benzylic alcohols rather than any vanilla alcohol.


texts: Chemistry of Stripper Poles: How much weight can different materials support?

texts:
I'm looking to create a light up dancing pole. This requires a translucent material that is strong enough to support the weight and force of a human being, even when it's hollowed out to so LEDs can go inside.  The material must also be reasonably affordable, so something like diamond is out of the question.

I've discovered a couple materials during my research (please recommend any I'm leaving out):

acrylic (I know there are acrylic poles out there, but I'm not sure
if they're able to support a human when hollowed out)
polycarbonate

To take the example of polycarbonate, how much weight can it support as a function of its thickness/diameter?

[Also, if the editors feel like this is an inappropriate question I'd just like to point out that the weight that different materials can support is a very appropriate question here.  My intent is not to scandalize, only to build a dance pole and learn some Chemistry in the process.  Thank you]


texts: Why is the formation of a peptide bond not spontaneous?

texts:
Why is the formation of a peptide bond from a carboxylic acid and amine not spontaneous?
I'm not looking for the free energy calculation; I have it from several sources.  I'm just asking for an intuitive explanation.  Is it because the peptide bond is planar so there's a loss of free rotation and the delta S is unfavorable?  Is the resonance stabilization in the peptide bond less desirable because the other atom (N) is less electronegative?  Do two equally sized molecules somehow have more entropy than a big molecule and a small one (water)?


texts: How do we compute the mole fraction of an ideal gas in a stream blended by mass flow controllers? For a non-ideal gas?

texts:
Consider a gas blending system consisting of two mass flow controllers, A and B, set to control flow to $f_\mathrm{A}$ and $f_\mathrm{B}$, respectively.  Consider that flow controller A is metering the pure gas of interest, which has an actual mole fraction of $x_\mathrm{A}$.  Flow controller B is metering a make-up gas which coincidently may contain trace amounts of gas A at a mole fraction of $x_\mathrm{B}$.

The mass flow controllers provide continuous estimates of $f_\mathrm{A}$ and $f_\mathrm{B}$; these are measured quantities.  Suppose also that we did some experiments and found the values of $x_\mathrm{A}$ (very close to unity or $\pu{1E6 ppm}$) and $x_\mathrm{B}$ (approaching zero, likely ones to tens of ppm).

To first order, the following equations provide reasonable estimates of the concentration of gas A in the blended stream at near atmospheric pressure, room temperature.  Experiments were carried out with $\ce{CO2}$ (gas A) in $\ce{N2}$ (gas B).  A $\ce{CO2}$ gas analyzer was used to estimate the mole fraction of gas A in the blend, $x_\mathrm{T}$.  We can compute the mass flow ratio of gas A by

$r = \dfrac{f_\mathrm{A}}{(f_\mathrm{A} + f_\mathrm{B})}$

or

$r = \dfrac{f_\mathrm{A}}{f_\mathrm{T}}$

where $f_\mathrm{T} = f_\mathrm{A} + f_\mathrm{B}$.  Further, we compute the mole fraction of gas A in the blend as

$x_\mathrm{T} = r \cdot \left(x_\mathrm{A} - x_\mathrm{B} \right) + x_\mathrm{B}$

My question again is: How do we compute the mole fraction of an ideal gas in a stream blended by mass flow controllers?

I'd like to do this in a rigorous manner, or correctly, possibly accounting for any non-ideal behavior of $\ce{CO2}$ in a $\ce{N2}$ make-up gas.

I came across this reference and believe the key to my problem is addressed therein.  The solution may involve the empirical rule of Lewis & Randall whereby the mole fraction of a component is equated to a ratio of fugacities of the component in a mixture to the pure component.  Certainly being able to compute the virial coefficients for the components may prove useful.  A key may also be converting a flow into a volume with an assumed time step.

Should I attempt to apply the some of the equations presented in the reference noted above?


texts: How can a thermometer ever show the actual temperature of an object if the object loses heat to the thermometer?

texts:
We know that when two objects are placed in contact with each other, after a period of time, the two objects will have the same temperature. Thus, if a hot body comes into contact with a relatively cold body, it will lose its heat and its temperature will reduce, while the temperature of the 'cold' body will increase.
If I put a thermometer in an object to measure its temperature, the body will lose its heat (or gain the heat, if the thermometer is hotter) until it reaches the same temperature as the thermometer. Doesn't this mean the thermometer is not giving us the EXACT temperature of the object, i.e the temperature before the measurement was taken, and is in fact, showing us a lower/higher temperature?


texts: Phenolphthalein indicator spill onto skin

texts: I was using a phenolphthalein indicator to test the acidity of some 0.1 M HCl. I was using the pipette to draw the phenolphthalein indicator out of the tiny jar but it wasn't working, so I thought that it might not have much left in it, so I tilted it at an angle to try and get the remaining indicator. However it turns out the pipette wasn't working and it was full and a couple of millilitres spilt out, some spilt onto my right index finger, but most of it spilt onto the bench. I immediately rinsed my finger under running water for about 7-10 seconds. Just wondering if it'll have any negative effects. I'm pretty sure it was 99.9% methanol and 0.08% phenolphthalein measured in weight.


texts: What is the molecular mechanism behind oncotic pressure?

texts:
I can't wrap my head around the idea of oncotic pressure and osmolarity, logically.

I imagine a blood vessel. It is filled with proteins, like a ton of proteins and solutes. So this means, according to oncotic pressure and osmolarity, that water will diffuse into this blood vessel.

I can't understand that. If I have a glass full of water, and I drop a bunch of rocks into the water (my proteins) the water will flow out of the glass. It will exert a force, a very basic force of buoyancy, that will lead water out of the glass.

How exactly is oncotic pressure generated?


texts: Michaelis-Menten rate law for enzyme which catalyzes two reactions: steady state?

texts:
Suppose an enzyme $\ce{E}$ can catalyze two reactions:

\begin{align}
\ce{S1 + E &<=> S1E ->  P1 + E} \tag{R1} \\
\ce{S2 + E &<=> S2E ->  P2 + E} \tag{R2}
\end{align}

I want to derive a rate law. Can I assume that

\begin{align}
\frac{d[\ce{S1E}]}{dt} &= 0 \tag{1}\\
\frac{d[\ce{S2E}]}{dt} &= 0 \tag{2}
\end{align}

like in the derivation of the Michaelis-Menten rate law?


texts: effect of different groups on Amine inversion

texts: I know different groups attached to the nitrogen atom affect the amine inversion barrier, but is it due to steric factors or orbital interaction factors, eg. $\ce{(i-Pr)2NMe}$ vs $\ce{NCl3}$.


texts: How big is the gauche interaction of methyl with phenyl in a disubstituted cyclohexane?

texts:
I'd like to compare the equatorial 1-methyl-2-phenylcyclohexane conformation of with axial conformation of 1-chloro-3-methylcyclohexane conformation. In which molecule there is less steric repulsion?

In other words: Do you know a guess of energy in kcal/mol for a gauche Ph//Me interaction and for an axial Ph//Cl interaction in this cyclohexane ring?

I would prefer to have a comprehensive two-dimensional table for allylic A(1,2) strain, but I didn't find any.
It might sound crazy or even unbelievable: A gauche Ph//Me interaction in 1-phenylpropane is only about 0.07 kcal/mol higher in energy than its antiperiplanar conformation (according to: http://www.sciencedirect.com/science/article/pii/S0040402001915509) compared to 0.9 kcal/mol for a gauche Me//Me.

However a diaxial Me//H only weights about 0.9 kcal/mol compaired to 2.7 kcal/mol for a diaxial Ph//H interaction; underlining that phenyl is very often more sterically hindered than a methyl, if the phenyl group can't rotate away.

You might be interested why I'm so concernced with my question:
I read the paper http://pubs.acs.org/doi/pdf/10.1021/ja035001g and I was curious why in Scheme 5 (with 5a) the phenyl group is placed axial for R1=Me, R2=H.
(In other words I would rather take into account the allylic A13 Ph//H plus gauche Me//Ph than the diaxial Ph//Cl interaction) It's because the the isomerization of the trans hydrazone costs too much energy!


texts: In the acid catalysed hydration of allene, acetone is obtained as the major product. This is because of electrophilic addition of $\ce{H+}$ across a double bond to give a vinyl carbocation, and subsequent addition of water and then tautomerism to yield the ketone. What I'm confused about is that why does not an allyl carbocation form, which would be resonance stabilised?(leading to  allyl alcohol?)


texts: I'm confused if ethyl and methyl can get any of the number 4 and 5 then what will be the order?


texts: Need something that is dishwasher safe that breaks down paraffin

texts: I work for a company that has a lab where there work leaves a lot of dishes coated in paraffin. Today I learned that they wash these in a non commercial dishwasher to remove the stuff.... one issue they paraffin solidifies and gunks up the washer. They have been replacing these every few months or so. After talking with the lab staff, they expressed concern and are open to using an extra step to remove the paraffin before washing. What most of the internet has to say is obviously do not wash paraffin in a dishwasher. Feeling a little s.o.l here, does anyone know anything that could potentially help, so we can end the vicious cycle of dishwasher destruction.


texts:
I'm curious about what the minimal conditions for some collection of water molecules to be liquid water are. What is the minimum number? What sort of bonds must hold? What other sorts of things I don't know to ask about need to be true?

In my peeking around a subject I have little familiarity with, I've seen mention of a tetrahedron, suggesting a lower bound of 4 molecules for water to be a liquid. But then I also stumbled across the following (from p. 23, here):

  Whatever the model concerned, the presence of a fifth
  water molecule is necessary to be considered in explaining
  the molecular mechanism of  defect formation and Hbond
  network rearrangement.

So it seems that although only four molecules are in this bond network undergoing constant change, there must actually be a fifth "neighbor" molecule for the bonds to function appropriately. Is this fifth molecule part of the liquid, or merely a helpful neighbor who makes the four molecules' liquification possible?

In short, what makes water a liquid (when it is)?


texts: Why does glycogen phosphorylase only act on the non-reducing end of the glycogen chain?

texts:
I read that glycogen phosphorylase only acts on the non-reducing end of the glycogen chain. This enzyme requires an inorganic phosphate molecule and PLP as a cofactor. The mechanism of the enzyme is as follows:

I attempted to workout the mechanism for the reducing end of the molecule and concluded that perhaps it results in a ring opening reaction.

Is this correct? If not what is the reason?


texts: Can there be gaps in autoignition temperatures?

texts:
I recently saw a request for solids that auto-ignite between 80C and 160C.  I can't find any, and none have yet been suggested.

Which leads me to the theoretical question: Is it possible for there to be gaps in auto-ignition temperature ranges that cannot be filled by any chemical?

More specifically: Supposed we're interested in auto-ignition of a chemical in a standard atmosphere (where the temperature is varied between storage and ignition).

First question: Is it true that any chemical that can auto-ignite in a given atmosphere at some temperature will not be shelf-stable when stored in that atmosphere at any temperature?  Or are there self-sustaining exothermic reactions that will not occur at all below a threshold (auto-ignition) temperature, and therefore would be indefinitely "shelf-stable"?

Second question: If shelf-stable auto-ignition is possible (or even typical), then are there any theoretical assertions that can be made about the possibility of auto-ignition temperature gaps?  E.g., if I know there is a chemical that auto-ignites at 20C, should it theoretically be possible to chemically dampen the reaction so as to raise the auto-ignition temperature arbitrarily?  Or is this just a "that's the way it is" property?  I.e., chemicals have the reactivity they have, and there's no reason to believe that you could pick an arbitrary temperature and find a compound that auto-ignites at that temperature?


texts: How do they ensure there is one electron on an oil drop in Millikan's oil drop experiment?

texts:
Since air is ionized using X-rays, in the 'observation chamber', there must be several electrons in the chamber, so the oil drops are exposed to several electrons so it seems intuitive that a single oil drop should catch more than one electron.

Then why is it that there's just one electron on a droplet or do they selectively choose those droplets which have a single electron residing on them?


texts: Graphene in Lithium-ions batteries: why?

texts:
I have recently been reading about the amazing discovery of a super-material: Graphene. This one carbon-layer chemical is not only one of the most resistant materials ever known, but also one of the best heat and electric conductors.
At some point, the article mentioned that the implementation of graphene in batteries - such as the lithium ion battery - would revolutionize the industry. I then found in a closet the dusty chemistry book we used in school, and I took a look at the electrochemistry section (I still remember I had enjoyed it back then).
Now that I understand - or rather believe to understand - again how a Lithium-ion battery works, I can't figure out how graphene should contribute to its improvement. Apparently, both electrodes are made of materials that can incorporate lithium ions into their crystal structure and release them easily. One would, therefore, typically employ a lithium metal oxide such as $\text{LiCoO}_2$ as cathode and graphite as anode. (By the way, what could you use as electrolyte?)
Anyhow, as I read in this paper, graphene is usually somehow incorporated to the cathode... Notwithstanding, I don't understand how this should improve the conventional lithum batteries. What are its key properties in this process?
Please consider that I am by no means a professional chemist, but rather chemistry enthusiast who has the knowledge of high-school. Thanks in advance.


texts: Discrepancies in calculating free energy values listed in Stumm and Morgan

texts:
I am hoping someone can help me with a clarifying a calculation on a fundamental thermodynamic understanding of reactions. Below is Table 2.5 from Stumm and Morgan's Aquatic Chemistry.

  Table 2.5. Influence of Pressure and Temperature on the Energies of Water Ionization a
  $$
\begin{array}{rrr}
\hline
p (\pu{bars}) &\log K_\mathrm{w} &\Delta G_\mathrm{w}^\circ (\pu{kJ mol-1})\\
\hline
    &T = \pu{298.17 K} &\\
1 &-14.00 & 79.94\\
200 & -13.92 & 79.48\\
400 & -13.84 & 79.02\\
600 & -13.77 & 78.63\\
800 & -13.70 & 78.22\\
1000 & -13.63 & 77.83\\
\hline
T (\pu{^\circ C}) &\log K_\mathrm{w} &\Delta G_\mathrm{w}^\circ (\pu{kJ mol-1})\\
\hline
&p = \pu{1 bar} &\\
0 & -14.93 & 85.25\\
10 & -14.53 & 82.97\\
20 & -14.17 & 80.91\\
30 & -13.83 & 78.97\\
50 & -13.26 & 75.71\\
\hline
\end{array}
$$
  aData from Harned and Owen (1958).

I'd like to focus on the second portion of the table, where temperature is varied. $K_\mathrm{w}$ and $\Delta G_\mathrm{w}^\circ$ values are listed, but using the given $K_\mathrm{w}$ values, I calculate different $\Delta G_\mathrm{w}^\circ$ values than what the table offers. Here is a sample calculation for $\pu{50^\circ C}$:

$$K_\mathrm{w} = 10^{-13.26} = 5.49\cdot10^{-14}$$
$$\Delta G_\mathrm{w}^\circ = -RT\ln K$$
$$\Delta G_\mathrm{w}^\circ = -\pu{8.314e-3 kJ mol-1 K-1} \cdot \pu{323.15 K} \ln (\pu{5.49e-14}) = \pu{82.03 kJ mol-1}$$

The table lists $\Delta G_\mathrm{w}^\circ = \pu{75.71 kJ mol-1}$

Not only is this answer substantially different, but the value is heading in the opposite direction of where my calculations would head (more positive vs more negative). Unfortunately, I don't have access to the original source (Harned and Owen).

Can someone please help me to understand my error?


texts: Know if a molecule is viable with Python

texts:
I'm working with python and I'd like to know if someone knows a python module which is able to check if a molecule is chemically viable (valence, connectivity constraints ...), or not. I know there is a lot of chemistry packages out there, but I didn't find any which does that.

Thanks,


texts:
What is the physical significance of molecular partition function?

I reason, that the molecular partition function

\begin{align}
q &= \sum_i \exp(-\beta\varepsilon_i),&
\beta &= \frac{1}{k_\mathrm{B}T}
\end{align}

is found in the expression for the populations of each configuration, derived from the Boltzmann distribution:

$$p_i = \frac{\exp(-\beta\varepsilon_i)}{\sum_i \exp(-\beta\varepsilon_i)}$$


texts:
something strange.
i made an electrochemistry experiment in which i have measured the potential of cell:
Ag, AgCl | (1M)KCl ║ [Fe(CN)6] 3-, [Fe(CN)6] 4-  | Pt

with different concentrations of Fe+2/Fe+3 .
from the results i have found the faraday constant:
96181 Coulon /mol
very close to the published value (99.7% accuracy).

the intercept of the graph of E (v) against ln(Fe+2/Fe+3)   is:

intercept:    0.198985714  V

(the intercept is also the standard potential for the cell)

yet, when i tried to find the standard potential of

Fe3+ +e- -> Fe2+

i got the result of +0.423 V which is almost half of the published value (+0.77 V)

E_cathode =E^° + E_anode

E_cathode=0.198985+0.224= +0.423 V

how can it be that the faraday constant is almost accurate and in the same time the result of the standard potential is far from the real one.? i'm sure i don't have any calculation mistakes, if it's necessary i can describe the method of work here.

thanks!


texts: Whose solubility increases with increase in temperature?

texts:
Solubility of which among the following substances in water increases slightly with rise in temperature?
(a)$\ce{KBr}$
(b)$\ce{KCl}$
(c)$\ce{KNO3}$
(d)$\ce{NaNO3}$

Answer is (b).
I don't know why.
According to me if temperature is increased then Bonds between any of these four must be broken due to supplied energy & solubility must decrease. And what about the other three. Do they too also show the same trend.


texts:
How many d-electrons are in the outer shell of the metals in following compounds:

ZnS

Do I just use Zn^2+ and as I know that in Ions the s orbitals are removed first I count 10 d electrons?

However ZnS makes a metal lattice. Can I use Zn^2+ then?

Help would be really appreciated


texts: Why aren't lasers used as light sources for atomic absorption spectroscopy?

texts:
Atomic absorption spectroscopy yields extremely narrow signals. It is difficult to separate white light with sufficient precision using monochromators, and hollow cathode lamps are often used as light sources instead. Disadvantage: a different lamp is needed for each element we wish to measure.

Why aren't lasers used as light sources? Lasers are perfectly monochromatic, and tunable lasers could be set to match absorption bands of many elements.


texts: Why and how carboxylate ion has greater stability than carboxylic acid?

texts:
I found it written in my textbook. I think it's a misprint, I can't think of any logic behind this statement.

I've only learned that ion is less stable specie so carboxylate ion cannot be more stable than carboxylic acid.


texts: Predicting major product of a reaction with nitrous acid

texts:
$\hspace{4.5cm}$

For the above reaction I am asked to predict $\ce{X}$, the major product.

Of the options given, I thought product (1) would be correct, seeing as how it has the most stable intermediate cation (tertiary) and a highly substituted double bond.

$\hspace{3.9cm}$

The answer however states that product (2) is the major product.

I can't understand why the second product would be favored over the first. There's no obvious stabilizing factor here in product (2).


texts:
What are the possible isomeric structures of chlorobutene $(\ce{C4H7Cl})?$

I've come up with seven:

cis-1-chlorobut-1-ene
trans-1-chlorobut-1-ene
2-chlorobut-1-ene
3-chlorobut-1-ene
1-chlorobut-2-ene
cis-2-chlorobut-2-ene
trans-2-chlorobut-2-ene


texts:
Find product A.
I tried solving but why isn't the answer this
The answer is given this


texts: Enthalpy change vs. change in internal energy in a system

texts:
I've been trying to get my head around the differences between enthalpy change and internal energy change for a system. Here's my understanding of it so far. I'd appreciate any feedback on my understanding so far on the concepts - especially if there are misconceptions (and there probably are)

Internal energy is the 'intrinsic' energy of some system, can be measured with reference to something within the system, e.g. chemical bonds, vibrational energy states, etc.
Enthalpy change is the heat (i.e. energy transferred due to temperature difference) change at constant pressure due to some chemical process.

$\Delta H = \Delta U + P \Delta V$

$\Delta H$ is characteristic of a given chemical process - i.e. this value is the same regardless of what conditions it is run under (e.g. varying pressures, volumes, starting temperatures). As long as it's the same reaction, $\Delta H$ will be the same. It's the overall energy input required to make a process work, and is split between influencing $U$ and performing $PV$ work.

$\Delta U$ is a function of the specific conditions (i.e. volume, pressure) in which a specific instance of a chemical process is run.

So it's theoretically possible to set up a chemical process (say vaporisation) to run in such a way so that $\Delta U$ is zero, and all the enthalpy change is accounted for in the $P\Delta V$ term?

And what about cases where P is not constant? What happens then? Can we calculate the value of $\Delta H$? And does $\Delta H$ even have a meaning in this case?


texts: Nucleophilic attack on cyclic intermediates in dibromination and oxymercuration reactions of alkenes

texts: Why does the nucleophile attack the most substituted carbon after the formation of a cyclic intermediate (three membered ring) in the cases of halogenation and oxymercuration of alkenes, as if there were a real positive charge. Shouldn't the most electrophilic carbon be attacked by the nucleophile?


texts: Intensive and Extensive Properties--Resistance

texts:
Is resistance an intensive quantity or an extensive one? And why?
Let me present 2 scenarios.

Resistance of a wire:
The resistance of a wire depends on area and length. This implies it depends on the "quantity" of the wire taken. Does this mean it is extensive?
Resistance of a cell:
As we know,
resistance of a cell is $R = \dot G/\sigma$, where $\dot G$ is the cell constant and the property of the cell, and $\sigma$ is the conductivity. Now, this won't depend on the amount of electrolyte taken in the cell. Does this imply resistance is an intensive quantity?

So, my final question is, whether the resistance is an intensive or an extensive quantity and why?


texts: Is Hexafluorocyclohexane the "Most Polar" Small Molecule?

texts:
Earlier this year, there was a lot of attention when all-cis 1,2,3,4,5,6-hexafluorocyclohexane was synthesized*:

Notably, C&E News quoted the lead author:

  This compound is remarkable for being the most polar nonionic compound now known to exist

Now, the original paper reports a molecular dipole moment of $\pu{6.2 D}$, which is extremely high for an alkane. It also claims the:

  unusual property of a facially polarized ring in organic chemistry

Certainly having one side of the cyclohexane ring completely substituted with fluorines is unusual, so I agree with the facial-polarity property being interesting.

But there are many small molecules (e.g., under 20-30 atoms) with large dipole moments, e.g., p-nitroaniline:

A quick PM7 calculation gives the predicted dipole moment of $\pu{7.93\pm1 D}$. So I dispute the claim from C&E News - nitroaniline is clearly more polar and non-ionic.

So my question is this: What's the largest dipole moment for a known non-ionic organic molecule under 30 atoms?

*: O'Hagan, et. al, "All-cis 1,2,3,4,5,6-hexafluorocyclohexane is a facially polarized cyclohexane" Nature Chemistry 7, 483–488 (2015)


texts: What happens to the amino acid when it is in a solution with the pH of its isoelectric point? (zwitterions)

texts:
I am learning about zwitterions and am confused about the following:

From what I understand, when amino acids are in their solid form, they exist as zwitterions which is why they have such a high melting point and are so soluble in polar solvents.
Then when placed in a solution with pH lower than their isoelectric point, they act as a base and form positive ions, and when placed in a solution with pH above their isoelectric point, they act as acids and form a negatively charged ion and a water molecule.
If the above is correct, what I am confused about is what happens at the isoelectric point. In my textbook it says that the isoelectric point is 'the pH value at which the amino acid exists as a zwitterion', however I thought it also exists as a zwitterion when not in solution. Are they refering just to the case of the amino acid being in solution and ignoring the solid state?
If this is so, I still do not understand how it remains as a zwitterion at the isoelectric point. Why does it not act as both a base and an acid and accept a H+ ion onto the O- atom in the carbonyl group and donate the extra H+ ion from its amine group? Does this have something to do with the fact that then it would no longer have any charges on it so it would not be soluble in the polar solvent?


texts: Identifying which lone pair is more basic?

texts:
In the the compound RCONH2 which lone pair is more basic? Is it the lone pairs on Oxygen atom or the lone pair on Nitrogen atom.
I believe that as O is more electronegative than N, the lone pair on O is of lower energy. Hence, the O's lone pairs are less basic. (But if one draws the resonance structure for the compound, a formal negative charge is found on the oxygen atom and the Nitrogen lone pairs are engaged in making bond)
So which atom should react first with an neutral electrophile?


texts: Why is the water reduction of oxygen favored in acidic conditions?

texts:
The standard reduction potential of diatomic oxygen in acidic conditions is +1.23 volts. However, the standard reduction potential of diatomic oxygen in basic conditions is only +0.40 volts.

Why is the reduction of diatomic oxygen by acidic media more favored than the reduction of oxygen by water that is basic?

I can think of a few reasons:

1) We are likely going to be forming negative two oxidation state oxygen anions when we oxidize diatomic oxygen. Oxygen adopts an oxidation state of negative two except in peroxides, which aren't very stable, and I don't think the oxygen radical will be very stable in solution.

Can someone provide a less fluffy reason that we're going to be forming negative two oxidation state oxygen atoms? I'd imagine that the electronegativity and electron affinity of oxygen are two reasons it might favor the negative two oxidation state over the negative one oxidation state in solution. I.e. why doesn't this occur to a significant extent?

$\ce{O2 + 2e^- -> 2O^-}$

Or this?

$\ce{O2 + 2e^- -> HOOH}$

2) From the above we can deduce that water is the product; water is pretty stable in either acidic or basic medium - i.e. it won't react to a large extent with either hydronium or hydroxide ion. Plus the oxygen in water has a -2 oxidation state. So if we look at our skeleton half reaction:

$\ce{O2 + 4e^- -> 2H2O}$

We realize that we need a source of protons. And the proton source in acidic medium is likely hydronium ion.

However, in basic medium, the proton source is water. I'd imagine that water is a poorer proton source than hydronium ion.

So would this account for the difference in standard reduction potential of oxygen in media that vary in pH?

I understand that voltage is an extension of K through the Nernst equation; is what I'm seeing here basically that the protonation of a base ($\ce{O^2-}$) is more favored in acidic rather than basic media? Could there also be kinetic factors? In other words, why is this statement true?

Also:

1) What's the mechanism for the reduction of diatomic oxygen?

2) Why is the reduction of protons at high pH less favored than the reduction of protons at low pH? My first guess: you don't find as many protons in basic solutions. But then, protons don't exist by themselves anyway. So what can the proton source be? I'm guessing that in basic pH, there doesn't exist much hydronium ion. So the only two sources of protons are water and hydroxide anion. Heterolytically cleaving the hydroxide anion to form the highly basic oxide anion doesn't seem thermodynamically favorable. Cleaving water to form hydroxide anions ... are we running into a Le Chatlier's Principle effect?

ETA: Or should I be considering proton activities? Is the activity of the proton less in basic solution than in acidic solution?


texts:
Consider the following unbalanced redox equation:

$\ce{NO_2^- +e^- -> NO3^-}$

This occurs in acidic media.

My professor would note that an negative two oxidation state oxygen "disappears" from left to right.

Oxide anions are strong bases, and since this process occurs in acidic media, and since an oxide anion has "disappeared," it must have been consumed by the strongest acid present - hydronium ion. Specifically, two equivalents of hydronium ion. These two equivalents of hydronium ion react with oxide anion to produce three waters.

Thus we balance the equation as such.

$\ce{NO_2^- +2e^- +2H_3O^+ -> NO3^- + 3H_2O}$

Now, what is the validity of this method, given that redox reactions likely don't involve an oxide anion intermediate? I can find no mention of any $\ce{O^2-}$ intermediates in redox literature.

If that is the case, how can this method still yield a redox equation that is valid in terms of mass and charge? Is there some likely intermediate that is close enough in character to the oxide anion?


texts: Which amino acids can be totally synthesized?

texts: I can't find information regarding which amino acids (say the proteinogenic ones or in general) can be totally synthesized. Is there a reference?


texts: Identifying the number of bonding and lone pairs without a dot and cross diagram

texts:
I've just learned how to predict the shapes of molecules in class today using VSEPR theory.
I would like to ask is there anyway to find the number of bond pairs and lone pairs without drawing a dot-and-cross diagram?


texts: Trying to understand why Sn2 is not possible in this reaction

texts:
I am trying to understand why the red Br doesn't react? Is it because there can't be a flip of groups? Or steric hindrance?

Thank you!


texts: How are solvents chosen in organic reactions?

texts:
Just reading through organic chemistry book (Modern Projects in Organic Chemistry by Mohrig, et al.), and it seems like the choice of solvent is usually arbitrary.

One of the experiments designed uses hypochlorite ion as the oxidizer and acetone as a solvent to oxidize 4-tert-butylcyclohexanol, but it isn't clear why this solvent is chosen.

I'm curious if there is a list that gives the suggested solvents for different kinds of reactions, as well as some insight for this particular experiment.


texts: Ordering the reduction potentials for Cr3+, Mn3+ and Fe3+?

texts:
I have been asked to order, with explanation, the standard reduction potentials for the following:

$\ce{Cr^3+ + e- -> Cr^2+}$
$\ce{Mn^3+ + e- -> Mn^2+}$
$\ce{Fe^3+ + e- -> Fe^2+}$

(all ions in aqueous conditions)

I am really uncertain what factors to consider; I am even struggling to make this a general born-haber process. I know that $\mathrm{3^{rd}}$ ionization enthalpies will come into play, and that $\ce{Fe}$ will be expected to have the highest one. Will hydration enthalpies also be relevant? Will there be a ligand exchange component (with the solvent, water) that I have to consider also?


texts: Do you get a new chemical compound if you mix sodium hydroxide and water?

texts:
Me and dad started fighting over this a couple of days ago and wagered on this.

He said mixing these two gives a chemical compound, I said that it doesn't.


texts: Carius method for quantitative analysis of halogens

texts:
Carius method: A known mass of an organic compound is heated with fuming nitric acid in the presence of silver nitrate contained in a hard glass tube known as Carius tube, (Fig.12.17) in a furnace

I want to know :

What is the significance of using $\ce{HNO3}$ ? Can we carry out oxidation with other acids like $\ce{H2SO4}$?
Why $\ce{AgNO3}$ is added to $\ce{HNO3}$ and not to the organic compound? Will it be wrong if I add $\ce{AgNO3}$ directly to the organic compound after it is subjected to fuming nitric acid?
Wouldn't precipitation of compounds other than that of halogens occur since we are carrying the reaction in a closed furnace?

Any help is greatly appreciated.


texts: How to explain Gibbs free energy is a pressure-dependent state function?

texts:
I'm aware that through deriving Gibbs free energy to infinitesimal changes, we could get the formula: $\mathrm dG = V\,\mathrm dp - S\,\mathrm dT$, giving that Gibbs free energy is pressure-dependent.

However, while dealing with the definition of Gibbs free energy: $ΔG = ΔH - TΔS$ (and $ΔH$ must be held at constant temperature, am I wrong?) most textbooks stated that it is held under constant pressure.

I still couldn't understand the relationship between Gibbs free energy and pressure and why: $\mathrm dG = V\,\mathrm dp$.


texts: IUPAC nomenclature for tricarboxylic acids

texts:
What is the rule for naming compounds with three carboxyl groups?

I have the two following coumpunds

4-(Carboxymethyl)heptanedioic acid
Pentane-1,3,5-tricarboxylic acid

They both have 7 carbon atoms in their parent chain, yet the second coumpunds is called a pentane. Also both have three carboxyl groups yet the first is a dioc acid. Also in the second one, its name is written as tricarboxylic acid. Why not trioic acid.

All these anomalies are confusing me. Can anybody explain why both are named so?


texts: What is the difference between pH and pKa?

texts: Is there any difference between the two, when talking of an acid? I am a bit confused. Please help me out.


texts: Find the increasing order of formation of ortho product

texts:
Find the increasing order of ortho product formation when Y is (i) F, (ii) Cl, (iii) Br, (iv) I.

We know that halides are ortho, para directing for EAS reactions and we consider the electronic stabilization effect as the reason for it. According to me, the order should be 1 > 2 > 3 > 4 because fluorine will give better electronic stabilization due to P(pi) – P(pi) bonding, and steric effect of iodine will reduce the amount of ortho product
But the answer given is 4 > 3 > 2 > 1.


texts: Why is no MS-gas phase NMR coupling possible?

texts:
With ever stronger magnets coming out every year, LC-NMR coupling becomes more attractive and is now used frequently in the pharmaceutical industry as well. Considering the rapid progress that is made in that direction I wondered why no MS-NMR coupling has been reported yet, especially as gas phase NMR is possible already. So I wondered:
When will it be possible to do MS-NMR coupling? What are the biggest obstacles for achieving MS-NMR coupling?


texts: Percentage ionic character when electronegativity is given

texts:
What is the ionic character of a bond, $\ce{A-B}$, in terms of the electronegativities of $\ce{A}$ and $\ce{B}$ ($\chi_\ce{A}$ and $\chi_\ce{B}$)?

I have been taught that the percentage ionic character is:

$$ \frac{\text{observed value of ionic character}}{\text{calculated value of character}} $$

but I can't understand how electronegativity is used here. I couldn't find anything on the internet either.


texts: Amount of benzoic acid required to alter pH of a NaOH-solution

texts:
I am trying to do a practice problem but I can't figure it out:

How many grams of benzoic acid needs to be added to 0.10 l of a NaOH-solution with a concentration of 1.0 mM to reduce the pH of said solution to 4.00? Assume that the added mass of acid does not alter the total volume of solution. $K_a = 6.5 \cdot 10^{-5}$

My attempt:

Benzoic acid is a monoprotic acid with a molecular weight of 122.1 $\,$ g mol$^{-1}$ and I will assume that NaOH has a 100% dissociation.

I choose to divide the problem into two parts; calculating the substance amout of acid needed to neutralize the OH$^-$ ions separate from the substance amount needed to lower the pH to 4.

Substance amount needed to neutralize OH$^-$, $n_n$:

$\ce{HA_{eq} + H_2O <=> A^- + H^+ + OH^-}$

$K_a = \frac{[H^+][A^-]}{[HA]_{eq}}$

$[HA]_{eq} = [HA] - [H^+]$

$[HA] = \frac{n_n}{V}$

Deriving an expression for $n_n$:

$n_n = \biggl(\frac{[H^+][A^-]}{K_a} + [H^+]\biggr) \cdot V$

$K_a$ is listed as $6.5 \cdot 10^{-5}$, the volume, $V$, is $0.10$ l and $[H^+] = [A^-] = [OH^-] = 1.0$ mM as listed.

Result: Plugging in these values yields the following substance amount: $n_n =1.6 \cdot 10^{-3}$ mol.

Substance amount needed to lower the pH to 4, $n_s$:

Deriving expression for $n_s$ using same method as above:

$n_s = \biggl(\frac{[H^+][A^-]}{K_a} + [H^+]\biggr) \cdot V$

In this case $[H^+] = [A^-] = 1.00 \cdot 10^{-4}$ based on pH = 4.00. ($V$ and $K_a$ same as above)

Result: Plugging in these values yields: $n_s = 2.5 \cdot 10^{-5}$ mol.

The mass of benzoic acid needed can now be calculated using the substance amount $n = n_n + n_s$:

$m = nM$

Final result: Plugging in the values for $n$ and $M = 122.1 $ g mol$^{-1}$ yields $m = 0.20$ g.

This answer is not right and I know I am doing something wrong. Teach me the ways.


texts: Why is the Chlorine missing an electron in Chlorine Monoxide?

texts:
I was asked to draw the lewis-dot structure for ClO and I drew this:

   ..  ..
  :Cl-  O.
   ..  ..

The correct answer is apparently this:

   .   ..
  :Cl-  O:
   ..  ..

How would I know that? In the first example, all the formal charges are zero, but in the second, Oxygen has -1 and Chlorine has +1.


texts: How does molecular orbital or valence bond theory explain the delocalised structure of benzene? I.e. when the carbon forms 3 bonds with other carbons/hydrogen, what happens to the remaining hybridised orbital?


texts: What's the relationship between dew point and temperature?

texts:
From a Ph.D dissertation, the writer change the land surface from nature earth to urbn and built up to compare the difference involving with this land use change.

Due to the urban heat land effect, the temperature of lower atmosphere above the surface increase, and the dew point decrease.

Dew point is a parameter represent the absolute moisture. When the temperature increase, how to analysis the dew point increase?


texts: Why Acetone does not behave like its computational values?

texts:
I am trying to simulate the excitation state of acetone. I ran TDDFT for it both in gas phase and solvated state in water (both implicit and explicit water).

The experimental data say that acetone undergoes n->π* transition, which means it has a higher wavelength in gas phase ($\mathrm{\lambda_{max}}=$~$276~\mathrm{nm}$) and a shorter wavelength in the solvated state ($\mathrm{\lambda_{max}}=265~\mathrm{nm}$).  I started with gas phase and expected something a wavelength of about $276~\mathrm{nm}$ ($4.49~\mathrm{eV}$ ), but surprisingly I got $\mathrm{\lambda_{max}}=136.172~\mathrm{nm}$ ($9.326~\mathrm{eV}$)! I really cannot understand why there is such a big discrepancy!

Here is my GAMESS input file. What is wrong with this molecule ?

!   File created by the GAMESS Input Deck Generator Plugin for Avogadro
 $BASIS GBASIS=N311 NGAUSS=6 $END
 $CONTRL SCFTYP=RHF RUNTYP=ENERGY TDDFT=EXCITE  DFTTYP=B3LYP $END
 $CONTRL ICHARG=0 MULT=1 $END
 $TDDFT NSTATE=9 $END
 $STATPT OPTTOL=0.0005 NSTEP=99 METHOD=RFO UPHESS=MSP HSSEND=.T. $END
 $SYSTEM MWORDS=1000 PARALL=.TRUE. $END
 $SCF DIRSCF=.T. DIIS=.T. DAMP=.T. $END

 $DATA
Title
C1
O     8.0     0.00000    -1.27900     0.00300
C     6.0    -0.00000    -0.05800     0.00100
C     6.0     1.29700     0.69100    -0.00000
C     6.0    -1.29800     0.69000    -0.00000
H     1.0     1.35900     1.32900    -0.90600
H     1.0     1.35900     1.33200     0.90300
H     1.0     2.15700    -0.01300     0.00100
H     1.0    -2.15700    -0.01400     0.00100
H     1.0    -1.35900     1.32900    -0.90600
H     1.0    -1.35900     1.33200     0.90300

 $END


texts: Oxidation number of Oxygen in peroxides: -2 or -1?

texts:
My textbook says that the oxidation number of Oxygen in peroxides is -2, but when I searched up the internet, I found it to be -1. It could probably be a misprint in my book, but I am still not sure. Not only that, the oxidation number of Hydrogen in hydrides is said to be +1 in my book, when it's supposed to be, I believe, -1? Please help me out on this.

My book says:
" The oxidation number of oxygen in most of its compounds (except peroxides, superoxides and suboxides) is -2. In peroxides (e.g., H2O2, BaO2, etc.), the oxidation number of oxygen is -2.

The oxidation number of oxygen in superoxides (e.g., KO2) and suboxides (e.g., C3O2 ) depends upon the nature of the compound. Exceptions also occur when oxygen is attatched to a more electronegative atom. For example, in the compounds like OF2 and O2F2, the oxidation numbers of oxygen are +2 and +1 respectively."


texts: Are there any guidelines for what constitutes an “organic acid” regarding storage requirements?

texts: I am moving a large amount of chemicals to a new lab and I’m curious about any guidelines for chemical separation. I’ve seen suggestions that organic acids and non-organic acid be stored separate from one another, and away from general chemicals. However, where would a long chain fatty acid lie, general chemical, or organic acid? When they get long enough, they become a solid at room temperature. Does storage requirements change for organic acids which are solid?


texts: How to find out unpaired electron in S2 molecule?

texts:
Theoretically electronic configuration and number of unpaired electron can be found out by using molecular orbital theory. But, practically I have seen only up to 20. For example, for Ne2

But for S2 (32 electrons) how to find out the electronic configuration and number of unpaired electrons.


texts: How do I figure out the hybridization of a particular atom in a molecule?

texts:
I'm learning how to apply the VSEPR theory to Lewis structures and in my homework, I'm being asked to provide the hybridization of the central atom in each Lewis structure I've drawn.
I've drawn out the Lewis structure for all the required compounds and figured out the arrangements of the electron regions, and figured out the shape of each molecule. I'm being asked to figure out the hybridization of the central atom of various molecules.
I found a sample question with all the answers filled out:
$\ce{NH3}$
It is $\mathrm{sp^3}$ hybridized.
Where does this come from? I understand how to figure out the standard orbitals for an atom, but I'm lost with hybridization.
My textbook uses $\ce{CH4}$ as an example.
Carbon has $\mathrm{2s^2 \,2p^2}$, but in this molecule, it has four $\mathrm{sp^3}$. I understand the purpose of four (there are four hydrogens), but where did the "3" in $\mathrm{sp^3}$ come from?
How would I figure out something more complicated like $\ce{H2CO}$?


texts: What exactly does the "per mole" unit of heat of atomization mean?

texts:
I am facing a confusion in the definition of the standard enthalpy of atomization. The confusion arises because of the "per mole" in its units ($\pu{kJ mol^-1}$).

My question: When I say "per mole", do I mean "per mole" of the product or per mole of the reactant?

When I mean "per mole" of the product, my representative reaction for $\Delta H_\mathrm{a}^\circ$ is:

$$\ce{1/4 P4(s) -> P (g)}$$

And when I mean "per mole" of the reactant, my representative reaction for $\Delta H_\mathrm{a}^\circ$ is:

$$\ce{P4 (s) -> 4P (g)}$$

Using either of them leads to different calculations involving Hess's law or other chemical reactions, hence I feel there is a need to resolve this confusion.

To add to this confusion, NCERT Chemistry (Part 1 page 171) writes:

  It is the enthalpy change on breaking one mole of bonds completely to obtain atoms in the gas phase.

but then gives a representative reaction as:

$$\ce{CH4 -> C(g) + 4H(g)}$$

which involves breaking 4 moles of bonds instead.

If someone could write the correct definition of the standard enthalpy of atomization, with more than one reputed reference to back their claim, it'd definitely resolve this confusion.


texts:
If an f orbital has 6 unpaired electrons then how many electrons can be exchanged.
According to me if 2 electrons are added then a half filled f orbital would be formed which is stable (not as much as a completely filled orbital but still quite stable) however, the answer is supposedly 15.

If one knows the reason please do tell.


texts: Litmus papers are used to test acidity and alkalinity of a fluid. Are there other paper-based tools to test for other stuff like dissolved oxygen, presence of toxicity, electric potential etc?


texts: What is the true meaning of Gibbs energy and chemical potential?

texts:
After doing some research and reading I found some problems which I will try to state as clearly as possible.

The definition of Gibbs Free Energy says "the greatest amount of mechanical work which can be obtained from a given quantity of a certain substance in a given initial state, without increasing its total volume or allowing heat to pass to or from external bodies, except such as at the close of the processes are left in their initial condition. (I have taken the definition from the wikipedia). The equation of the Gibbs energy $$ G= H -TS$$ is also clear.
But the way I understand it is this: the maximum non-expansion work , like transporting an electron, breaking a chemical bond, moving real life things etc.  which can be obtained from a system . These things made sense during the study of Second Law of thermodynamics but as I moved to Chemical Equilibrium these concepts began to tremble (for me).
In elementary classes it is said that Equilibrium is a state where the composition of reactants and products do not change over time, but in higher chemistry classes it is said that equilibrium is a condition corresponds to $$ \Delta G = 0$$ So, my first question is how do these two concepts mean same thing?  The next thing which causes problem is chemical potentials. If we adhere to the formal meaning of potential i.e. something which is stored and can be used when proper conditions are met, so chemcial potential would mean the potential of substance to react and again this is related to Gibbs energy whose definition I gave above. So, how do chemical potential and Gibbs energy can have any relation?
A question which is off topic over here but I want to mention it, why do we bother so much about standard  things like $$ \mu_\mathrm A = \mu_\mathrm A^\circ + RT \ln(p_\mathrm A)$$ why we wanted to express it in that standard (that little circle) form ?
I want to make myself clear that the conception of Gibbs energy was quite clear to me in the context of thermodynamics, we simply meant it to be the work which can be extracted from a substance, but it all-pervading use has made me to doubt myself, just like in mathematics the number $\mathrm e$ appears in odd places. Even if Gibbs energy (according to the understanding that gave above in bold) is appearing mathematically then also it would be having some  physical meaning because Thermodynamics and Equilibrium are natural sciences and not the mathematics.

Thank you, any help will be much appreciated.


texts:
When speaking in thermodynamic terms, when is a reaction reversible?

My attempt: A reaction is reversible when $\Delta\text{S} < 0$, because according to the second law of thermodynamics, "in every natural thermodynamic process the sum of the entropies of all participating bodies is increased" (Wikipedia.org), therefore if a reaction is caused and has negative change in entropy, a reversed reaction should be natural.

However, this is not the answer that is absolutely correct, nor a rigid solution or a rule. Can anyone help me out? (I have searched on the internet, and although thermodynamic reasons are preferred, I do not mind answers to be molar or solution chemistry, as long as a thermodynamic approach is included as well or a statement that there is no apparent thermodynamic rule that can be applied to this question.)


texts: DNA dye: Are there any natural dye for DNA (instead of artificial ones)?

texts:
In order to make easy and low-cost experiments, we are searching for natural dyes (or easy to make) that can color DNA, instead of for instance Ethidium Bromide that is hard to find and is expensive.

We are new to this field, but we learned that DNA dyes need to intercalate in between DNA bases. To do so, the molecule must be preferably poly-cyclic, aromatic and planar.

So the question is, is there any chemical that can be readily used for this purpose or if not, any lead about a molecule that can be easy to find by anyone.


texts: What are the products of alkene oxymercuration with diols?

texts:
I was wondering what would be the product of the reaction of alkene with a diol (such as glycol) in alkoxymerucuration/demercuration, i.e. $\ce{(CF3CO2)2Hg/NaBH4}$?
I tried to look online but I couldn't land on a paper or website that goes through such reaction. I also tried Scifinder, I marked both compounds as reactants, but zero results stemmed from the reactants!
Any input?

I'm thinking if these possibilities (I have more possibilities in my mind, but for example I selected three) are structurally accurate and energetically stable to be produced in such reaction and which is favored?

To classify them more ... to single and di addition, here is what I'm thinking:


texts: Does it sometimes take energy to create a chemical bond?

texts:
Wikipedia says so:

  Bonds can also be broken apart. Since most bonds require energy to form, they also give off energy when they are broken. But before most bonds break, the molecule has to be heated. Then the atoms start to move, and when they move too much, the bond breaks. Molecules that require less energy to break than they give off when broken are called fuels. For example, a candle will just sit there and nothing happens. But when you use a match to light it, it will burn for a long time. The match brings the energy to break the first bonds, which release enough energy to break the bonds below them, until the candle has burned down.
  But what I have learned is bonds release energy when formed.


texts: Will bases typically precipitate silver atoms from silver ions?

texts:
In class I learnt that one can dissolve many substances using acid and that this can be predicted using standard electrode potentials. For example,

$$\begin{align}
 \ce{Zn &-> Zn^{2+} + 2e^-}      &  E_0 &=  0.76~\mathrm{V} \\
 \ce{2H^+ + 2e^- &-> H2}         &+ E_0 &=  0~\mathrm{V}    \\\hline
 \ce{Zn + 2H^+ &-> H2 + Zn^{2+}} &  E_0 &=  0.76~\mathrm{V}
\end{align} $$

And so Zinc will dissolve in acidic solutions.

I wondered what bases do and so added up the standard electrode potentials of bases and silver.

$$\begin{align}
 \ce{Ag^+ + e^- &-> Ag}                 &  E_0 &=  0.80~\mathrm{V} \\
 \ce{4OH^- &-> O2 + 2H2O + 4e^-}        &+ E_0 &= -0.40~\mathrm{V} \\\hline
 \ce{4Ag^+ + 4OH^- &-> 4Ag + O2 + 2H2O} &  E_0 &=  0.40~\mathrm{V}
\end{align} $$

This suggests to me that basic solutions will typically precipitate a silver solid from silver ions and produce oxygen gas.

Does this make sense?


texts: Is the para-position of anisoles more reactive than ortho in electrophilic substitutions?

texts:
In my group’s seminar last Friday, we discussed the total synthesis of 6-demethyl-6-deoxytetracycline 1 by Woodward et al.[1] One intermediate of their synthesis is meta-substituted anisole 2 that they subsequently wish to cyclise to create the first two rings of 1 by a Friedel-Crafts acylation. Since the Friedel-Crafts acylation can proceed on both the ortho and para carbons (when viewed from anisole’s oxygen substituent), they protected the para-position using a chlorine atom (3) — introduced by electrophilic aromatic substitution of 2 with chlorine gas. They reported $97\:\%$ yield.

This confused me. I remember listening to a Concepts in Organic Chemistry lecture given at my university where the electrophilic addition to an electron-rich aryl was discussed. Our professor gave us numbers that approximately equalled a $2\::\:1$ ratio of ortho versus para substitution. The reasoning was, that the HOMO has almost equal contributions on both ortho carbons and the para carbon (while having close to no meta contributions), meaning that none of the three be favoured. This is approximately supported by the molecular orbitals of a calculated benzyl anion that the professor has uploaded to his site. (The benzyl anion was used as a model system because it gladly delocates its anionic electron pair into the ring much like oxygens would their unbonded electron pair.)

I do see that 2 has a further substituent in meta position. This substituent (alkyl) displays a weak $+\:\mathrm{I}$ effect meaning that it enhances substitution on the same atoms as the oxygen would. One of these is now ortho to two substituents (position 2) and likely reacts less — I understand that. But I would still have expected a $1\::\:1$ ratio of ortho-oxygen and para-oxygen substituted products rather than $97\:\%$ yield of the para.

How can we rationalise Woodward’s $97\:\%$? Is it wrong to say that the contributions of ortho and para carbons are approximately equal, and if so, why is the para contribution so much stronger that it is almost solely chlorinated?

[1]: J. J. Korst, J. D. Johnston, K. Butler, E. J. Bianco, L. H. Conover, R. B. Woodward, J. Am. Chem. Soc. 1968, 90, 439.


texts: Is there an 'easy' way to determine if a ligand is a pi acceptor, donor or neutral?

texts:
First of all I am confused how something can be pi neutral? something either does or doesn't have filled p orbitals for example.
given something I have never seen acting as a ligand before like trimethylphosphate how can I work out whether this is pi accepting, donating or neutral? I am thinking the donor atom would be the oxygen bonded to the Me group and P but do I only consider the orbital of the donor atom?
For a tetragonal Cu(II) complex how can a ligand even act as pi donating if since the t2g orbitals on the metal are filled?
Sorry about this messy question, I am very confused about this in general, I would be so grateful if someone could help me understand this


texts: Why can radioactive contamination be spread by people?

texts:
So I am reading a book called "Voices from Chernobyl" where witnesses, nuclear plant workers, firefighters and other persons involved in the 1986 accident give testimony of their experiences.
The very first chapter goes along the lines of the wife of a firefighter that was dispatched for duty on the very day of the incident. He suffered acute radiation and was hospitalized. His wife remain with him throughout the last days before he died. One thing it was mentioned in the book very clearly is how nurses constantly tried to warn his wife not to touch him, hug him or even share objects with him.
In this article, it is mentioned that a person who was exposed to radiation should not be a danger for others once his clothes have been disposed.
So, my question is, I am getting confused between the two readings. Is a person who has been exposed to a big dose of radiation a danger for other people? Why?


texts: Is there a heatformed vinyl-like plastic that is hard as shellac when cold?

texts:
I recently started collecting shellac records, and got the idea of releasing my own music on 78rpm shellacs.

But the exact formulas and techniques for making shellac records seems pretty much lost to history, and it seems it was a very hard material to use anyway. You can use vinyl, but then it would not be playable on the old hand-cranked acoustic type 78rpm record players, as those needles have too high pressure and would destroy the softer vinyl.

So this is probably only doable if there is a plastic that is soft and possible to press to a record shape when heated, like vinyl, but that becomes a lot harder than vinyl, like shellac, when cold, and also doesn't distort when cooling. Anyone knows of something like that?


texts:
A gas expands and does 82.7 J of work on the surroundings. At the same time, the gas loses 103 J of energy to the surroundings as heat. What is the change in the internal energy of the gas?
would this be ΔE = q + w  (-103) + (82.7) = -20.3.   I get confused with the positive and negative charges.