texts: How to remove stain from pavement after having dropped sulfuric acid on it?

texts:
I had this car battery that flipped in my car trunk.
When I got it out of there it spilled some acid on the pavement. It's a sulfuric acid battery. I added some baking soda on it and poured some more water+baking soda to make sure the acid was neutralized.

However there is still a brown-rusty stain on the pavement. I tried water and a big broom brush but it still there.

Any idea what I can use to clean up the pavement to its original color?


texts: Combining two high-VP chemicals to get a low-VP mixture

texts:
I'd like to do a class experiment as a metaphor for human relationships.  Two people each have a different chemical which evaporates quickly (at STP).  There is one glass between them.  If only one person pours his/her chemical into the glass, it quickly evaporates.  However, if both pour equal portions of their respective chemicals into the glass, it is a stable mixture which can fill the glass and not evaporate.

Are there two such chemicals that will do this?


texts: If ideal gas equation is formulated using ideal gas concept then why is the same equation used for real gases os they are not the ideal gases


texts: What is the product of the reaction of 2-bromo-1-fluoro-4-nitrobenzene with sodium methanethiolate?

texts: In the reaction depicted below shouldn't $\ce{Br}$ be replaced by $\ce{SCH3-}$ ion as $\ce{Br-}$ is a good leaving group and the $\ce{C-F}$ bond is quite strong due to back bonding of 2pπ-2pπ orbitals?


texts: Production of acetone from egg shells and vinegar

texts: I learned from these wiki pages that acetone can be produced from calcium acetate, which can be produced by the reaction of eggshells and vinegar. However, I couldn't find the required temperature. Would it be possible to produce acetone vapours by simply heating calcium acetate over a natural gas flame (~1500 degrees C)?


texts: Composition of a typical printed circuit board (PCB)?

texts:
For the purposes of x-ray absorption, I'm trying to discover the average chemical composition of a typical PCB.

My research so far has indicated that the most common type of PCB is designated FR-4.  It is composed of fiberglass and epoxy resin.  The resin often contain Bromine to add fire resistance.  Let's ignore any printed copper for the mean time.  So we are looking at H, C, O, Si, Br, and probably some other bits and pieces.  But what are the percentage of these elements?


texts: I need to write reference on 6-311++g(d,p) basis set in my work where I used it on atoms of I-II periods. Does anyone know where it was first published?


texts: Is there an experiment that visibly shows the effects of metastability?

texts:
I am attempting to create an experiment to show the effects of metastability to a public audience and get people excited about science. More specifically, I am wondering if there is any sort of liquid that can mimic the effects that water had in the book Cat's Cradle.

In the book, the idea was that a shard of a more stable polymorphic crystal of ice with a high melting point could "infect" water. This crystal would quickly spread, solidifying oceans and destroying most life on earth.

The basic question I'm asking is as follows. Is there any public display I could make to show a liquid quickly solidifying from a seed crystal? It is preferable (but not necessary) for the materials to be reasonably inexpensive and require no special equipment, so as to allow for the experiment to be done on a grander scale. Additionally, the experiment should have a low failure rate (unlike using supercooled water, which is difficult to control in large amounts).


texts: What is it about the relationship between the Fe²⁺ and Fe³⁺ in magnetite that makes it diamagnetic?

texts:
Hematite is composed of $\ce{Fe2O3}$, and is paramagnetic, whereas magnetite is $\ce{Fe3O4}$ and is diamagnetic.  Magnetite's nature is due to the presence of both $\ce{Fe^{2+}}$ and $\ce{Fe^{3+}}$ (Wikipedia even goes so far as to call it $\ce{FeO}\cdot \ce{Fe2O3}$, but explains that this is not a "solid solution").

I can surmise that in the crystalline solid, there are divalent and trivalent cations dispersed within.  I can also assume that there might be some sharing of electrons between the oxygens and each of these cations.  One would assume this also happens within the hematite crystal, so what is it about "tossing" the divalent cation into the mix of the crystalline structure that makes the magnetite diamagnetic?

Does the charge differential between the two cations cause a permanent dipole, if so, why don't all of the small dipoles simply cancel each other out?


texts: Reaction of silver nitrate and hydrochloric acid

texts:
Consider the reaction of $\ce{AgNO3}$ and $\ce{HCl}$. I read that silver chloride would be formed. But $\ce{H} > \ce{Ag}$ in reactivity, then how could $\ce{Ag}$ displace $\ce{H}$ from $\ce{HCl}$ ?

If there was a reaction, $\ce{AgCl}$ and $\ce{HNO3}$ were to form. But then these would react again to give us the original compounds back. The actual question was to write down the reaction between $\ce{AgNO3}$ and $\ce{HCl}$. I (wrongly) realized that the compounds wouldn't react because of the reasons stated.


texts: Removing PTFE marks on glass bottles after using magnetic stir bars

texts:
I am using magnetic stir bars to agitate solutions for 4 weeks at a time.  I have noticed at the bottom of the glass bottles that white marks have accumulated where the stir bar spins.  Even with soaking, thorough washing and scrubbing, acid washing, and sonicating, the marks remain.  I suspect these marks are white PTFE that has eroded from the stir bars then stuck to the glass.

I have 2 questions:

Are the marks removable?  I know PTFE is very resistant to most solvents, which makes removal seem difficult.
Is it necessary to remove these marks?  Perhaps because PTFE is so resistant to solvents, it will not affect my analysis.

I am extracting ammonium from soil extracts.  The soil extract is an acidified water solution, which I immediately add MgO to, in order to increase the pH to above 9.  This pushes the NH4+ into the headspace of the bottle.  Floating on the solution is a glass filter in a sealed Teflon packet.  The ammonium ions diffuse through the Teflon, and react with citric acid on the filter to make an NH4Cl salt.  This is then analyzed on an EA-MS for d15N.


texts: What's a non-toxic flavorless water-soluable chemical I could use for freezing point depression when making ice cream?

texts: I'd like to make a savory version of ice cream. So I can't use sugar or any artificial sweeteners for the freezing point depression needed to control ice crystal sizes. What can I use?


texts: Why is Diels–Alder adduct exo when we leave it for a while?

texts: Recently we did an experiment of Diels–Alder reaction and we left the adduct overnight. I've read a paper of Woodward that says the adduct of Diels–Alder thought to be endo, whereas in our experiment it turned out to be exo.


texts: Calculating Delta H for Non Ideal Gasses

texts:
We have to calculate delta H for a gas that follows the Van der Waals equation of state:

$$\left(p + \frac{a}{V_\mathrm m^2}\right)\left(V_\mathrm m-b\right)=RT$$

I know that $H = U + pV$ but I don't know how to approach this question.

Since I also know that $\Delta H = \Delta U + \Delta (pV)$, does that mean that I can calculate this simply by calculating $\Delta U$ (which I know how to do) and then $\Delta (pV) = p_2V_2 - p_1V_1$? Is that an appropriate method?

Because previously in other questions I have also seen it done as
$\mathrm{d}H = \mathrm{d}U + V\mathrm{d}p + p\mathrm{d}V + \mathrm{d}V\mathrm{d}p$ so I am wondering when is which equation applicable?


texts:
One day, my mom decides to light the house on fire, and after we put the fire out, all of the cobwebs in the house are black. Obviously, this is because of the smoke. Later, some renovations guy tells her something about how the cobwebs aren't really cobwebs and when a house fills with smoke, there is some weird chemical formation that makes a black cobweb-like-substance that just happens to show up right where cobwebs would be. Basically, the guy told my mom that those black cobwebs were chemical formations from smoke instead of cobwebs that became black after being in smoke. My mom will not believe me when I say that the renovations guy is wrong and they were obviously cobwebs. I ask her "What happened to the cobwebs we already had?" and "Why would a renovations guy know that it is a smoke formation if there are cobwebs in every house?"

I can't prove to my mom that she's wrong, so I'm asking a bunch of chemistry people to confirm that smoke doesn't stick to walls and form cobwebs.


texts: When we perform a organic reaction without any addtional catalyst except that the reaction is carried out under microwave condition we can accelerate this reaction in comparison with one under heating only. So, microwaves can be considered a form of catalysis according to the concept of reaction kinetics?


texts:
In 2016 synthesis and structure of tetranitratoethane $\ce{C2H2N4O12}$ were reported [1]. Currently (as of 2017-Q4) this is the only dinitrato-carbon compound with the well-established crystal structure and composition:

This article also mentions dinitratomethane (reference number updated from 6 to 2):

While nitrate esters such as nitroglycerin (NG) and pentaerythritoltetranitrate (PETN) (Figure 2A and B) are well known,  only very few examples of germinal C-nitrato compounds are known. The simplest one, dinitratomethane (Figure 2C) is a liquid which is obtained from nitration of 1,3,5-trioxane in a $\ce{HNO3/H2SO4}$ mixture [2].

Figure 2. Structural formula of nitroglycerin (A), PETN (B), and dinitratomethane (C).

However, I wasn't able neither to get the full-text of original paper from 1938, nor any more recent proofs of existence for dinitratomethane. Google Scholar returns only a couple of entries one of which is [1], and another one is a PhD thesis. There are also zero Ngrams for "dinitratomethane", which is unusual. ChemSpider also lists this compound as nitrooxymethyl nitrate (CAS 38483-28-2).
Can anyone approve or disapprove the existence of dinitratomethane $\ce{CH2N2O6}$ (feel free to utilize computational chemistry too)?
References

Fischer, D.; Klapötke, T. M.; Stierstorfer, J. Chem. Comm. 2016, 52 (5), 916–918. DOI: 10.1039/C5CC09010E.
G. Travagli, Gazz. Chim. Ital., 1938, 68, 718.


texts:
Need clarification on Q31a) in the image.
Possibly a dumb question but the book's answer might be wrong. The book says lithium ions will be reduced instead of potassium ions. How is this true when K+ ions are stronger oxidants?

Their answer for part d even reiterates that's Li+ will react in preference to K+ so I think I may be wrong...not sure how though

Thanks


texts: Calculating the pH of a saturated calcium fluoride solution

texts:
How can I calculate the pH of a saturated solution of calcium fluoride ($\ce{CaF2}$)? I am given the following values:

$$\begin{align}
K_\mathrm{sp}(\ce{CaF2}) &= 3.9 \cdot 10^{-11} \\
K_\mathrm{a}(\ce{HF}) &= 6.8 \cdot 10^{-4} \\
K_\mathrm{w} &= 10^{-14}
\end{align}$$

(The $K_\mathrm{sp}$ and $K_\mathrm a$ values are taken from the appendices of Skoog et al. Fundamentals of Analytical Chemistry, 9th edition.)


texts:
Is there a way to remove salt from water, even just partially, using chemical or filtration methods prior to a reverse osmosis?

The problems is that salt is very hard on a reverse osmosis membrane which is expensive. Is there some way to attract some of the salt out of the water before using the membrane?

One possibility I have heard of is decanoic acid which can be used to sequester salt.


texts: Heisenberg uncertainty principle and lifetime of the excited state

texts:
A key relation in optical spectroscopy also used to derive natural bandwidth is:

$\Delta E \Delta t=ℏ$

$\Delta E$ is the energy uncertainty of a state, $\Delta t$ should be the uncertainty of the lifetime $τ_b$ of the state. I don't understand why $\Delta t$ can be confounded with the lifetime itself, $τ_b$, and the relation written as

$\Delta E τ_b=ℏ$


texts: Neutralize the smell of alcohol in liquid chalk

texts:
i'm trying to mix my own liquid chalk, which is a simple mixture of chalk and a high percentage alcohol in a ~2 part chalk 1 part alcohol relation.
Unfortunately the smell is rather intensive and I would like to find a way to neutralize or cover it up.
Any suggestions?

I do not have a chemical backround.


texts: How to find the temperature relationship between the isotherms in a compressibility factor (Z) vs pressure graph?

texts:
The following graph denotes the variation of the compressibility factor (Z) with pressure at different temperatures for a real gas. Simply each of the curves represents an isotherm.

Now, suppose we are not given the temperatures and we are asked to find the temperature relationship between the isotherms, how to prove the topmost curve corresponds to the higher temperature and the lowermost curve corresponds to the lowest temperature? Is there any mathematical proof for this or is this just an experimental result?


texts: Are there reactions operated at high temperature at industrial level?

texts:
Temperature is an important parameter when you deal with a chemical reaction, first of all $\Delta G$ and $\Delta G^\circ$ depend on temperature, and as a consequence the spontaneity of a reaction depends on temperature. Second, also the equilibrium constant $K$ depends on temperature so, it is possible to modify the reaction yield by varying it.

Finally, the kinetic constant $K_{V}$, and so the reaction speed, are related to temperature. Said that, I was wondering if at industrial level, there are some important reactions which are operated at high temperature (I mean at least more than $\pu{40 °C})$ in order to obtain at least one, or more of the effects I've written (or some other that I don't know). Of course, I also include reactions such as electrolysis and electrochemistry reactions.


texts: Chlorinating specifically one carbon on a symmetrical alcohol

texts:
The final target molecule is 1-chloro-2-amino propane.

The amination step would be simple via reductive amination of 1-chloro-iso-propanone.

Obtaining 1-chloro-iso-propanone would be from nucleophillic addition-elimination of 1-chloro-iso-propanol by H2O under acidic conditions (or oxidation using potassium permanganate but no need for such a reagent when a simpler route available).

However, assuming you started with only iso-propanol and you wanted to chlorinate only one of the two terminal carbons, how would you do this? I understand $\ce{SOCl2}$ would of course be the chlorinating reagent, but with no blocking group it would simply attack both carbons. Attempting to add a blocking group would block both carbons also as they are symmetrical and identical.


texts: Limitations of extremes for the exchange-correlation functional - DFT

texts:
In DFT the exchange-correlation function is critical for the correct description of the system. I have a question about the applications and shortcoming of some functionals.
LDA delocalizes electrons so are good for conductors. And pure HF localizes electrons so it's good for molecules/atoms.

So, is it safe to say that if one doesn't include correlation and only uses HF exchange energy that crystals, or any material with long range ordering, couldn't be properly described?

And the same around, if one only uses correlation, conducting crystals are properly described but no molecules/atoms could be studied correctly?

I want to understand the applications and limitations of both extremes and I am having a hard time finding that kind of analysis online.

Thanks!


texts: Can an SN1 reaction occur in compounds with the leaving group attached to a primary carbon, which can later rearrange?

texts:
Can SN1 reactions occur in compounds where the carbocation, even though is is initially $1^\circ$, can rearrange to form a more stable carbocation?

Examples cases:


texts: Why should fire extinguishers containing carbon dioxide not be used on magnesium fires?

texts:
As the title states, why should $\ce{CO2}$ fire extinguishers containing carbon dioxide not be used on fires with magnesium metal?

I understand that $\ce{CO2}$ extinguishers work by displacing oxygen, a crucial component of a fire. Does this somehow not work when magnesium is involved, or is there another reason?


texts: dissociation of aluminum sulfate in water

texts:
I had a question as to what happens when aluminum sulfate is placed into water. After conducting research online, I got varied answers: some say that it dissociates into Al$^{3+}$ and SO$_4$$^{2-}$ ions, while others claim that aluminum sulfate will react with water to form aluminum hydroxide and sulfuric acid.

I even conducted a mini-lab by placing aluminum sulfate in water and sometimes there was precipitate (assumed to be aluminum hydroxide) and sometimes there was none.

What is really happening?


texts: Carbocation Stability: Tertiary versus Secondary Benzyl for Hydrobromic Acid Addition

texts:
I haven't been able to find anything concrete or consistent on this topic.
For the following reactions, which product would be favored, assuming that they both have to go through a carbocation intermediate?

What I've gathered so far:
The electron withdrawing group (-NO2) would destabilize the benzylic carbocation (through loss of electron density for stabilization), and would at least help push the reaction in the direction of the tertiary carbocation.

Thanks for any and all help.


texts: IUPAC nomenclature for an interesting looking organic compound

texts: How can I name this organic compound while adhering to the IUPAC standards?


texts: Entropy and enthalpy change on mixing liquids

texts:
Question:

  A concentrated solution of copper sulphate, which is dark blue in colour, is mixed at room temperature with a dilute solution of copper sulphate, which is light blue. For this process:

  Entropy change is positive, but enthalpy change is negative.
  Entropy change and enthalpy changes are both positive.
  Entropy change is positive and enthalpy does not change.
  Entropy change is negative and enthalpy change is positive.

The final conc. of the mixture would be less than the initial concentration of the concentration $\ce{CuSO4}$ given.
Therefore  I think the entropy change is positive. But, what about enthalpy?  What factors should I look into to find answer to these types of questions?


texts: Polymers that aren't brittle at the cryogenic temperatures found on Titan?

texts:
For entertainment purposes, I'm imagining a colony on a non-terraformed Titan, and wondering what is achievable. Hydrocarbons are incredibly plentiful there, while metals and even silicon would be extremely rare and precious, which makes me think that polymers would be used to an even greater extent than on Earth in nearly every form of engineering.
On Titan, the pressure is around $\pu{1.5 atmospheres}$ and the surface temperature is cryogenic at $\pu{76 K}$ on average. This makes me imagine that they would want to use a lot of polymers with extremely low glass transition temperatures (below and around $\pu{76 K}$ at $\pu{1.5 atmospheres}$), so as to have rubbery and non-brittle materials that work outdoors.
Do we know of such materials, and if not, are they physically plausible? I didn't see any examples in tables of glass transition temperatures that I found on the internet, but then again, such polymers would have a lot less application on Earth, if they even exist as solids here.
Of course, these cryogenic temperatures only apply to things that go outside, like suits, vehicles, extraction and construction equipment, buildings, and the necessary pumps and other equipment needed for life support.


texts: How are the chemical reactions of the table of standard reduction potentials experimentally determined?

texts:
My background: I've read several books and articles on electrochemistry and even do photoelectrochemical research in a lab, so I'm somewhat familiar with the concepts and techniques.

In texts on electrochemistry, the standard reduction potential and its meaning is usually axiomatically presented early on and everything follows from there. What I would like to see in a treatment of the subject is an explanation of how the chemical equations of the reduction half reactions are actually determined. For example, let's take the equation $\ce{Cu^{2+} + 2e- <-> Cu}$. How did they figure out that it is in fact two electrons reducing the $\ce{Cu^{2+}}$ ion?

One could do open circuit potential measurements to determine the standard reduction potential, but it would seem to me that you would have to know the ionic state of the element a priori to use this technique. One could also apply a voltage until the reaction "turns on" then approximate that onset voltage as the standard reduction potential, but this wouldn't be strictly true as it would be a non-equilibrium measurement and would also be subject to the kinetics of the surface. Does anyone know of a book or other treatment showing how the chemical equations are determined or better yet has experience doing this?


texts: What is a non-empirical explantation of why 1-3 methyl shifts do not occur?

texts: How could you explain why we never see 1-3 methyl shifts? Most sources just say it is really rare, but I was wondering if you could perhaps apply orbital selection rules or a frontier orbital argument.


texts: Working with stainless steel in 3 M HCl solution

texts: We are trying to mix a material using 316 stainless steel blades in a $3~\mathrm{M}\ \ce{HCl}$ solution for 4 hours in a PE container? Will the blades stand for 4 hours or do they start to corrode in 4 hours?


texts: Reaction between hydrogen peroxide and ozone

texts:
What is the reaction mechanism of the reaction:

$$\ce{H2O2 + O3 -> H2O + 2O2}$$

I have tried searching this on Google but am not getting good answers.


texts: What Methods Would I Use To Powder Cotton?

texts: I’m needing a method to turn cotton into a fine powder for use as a source of cellulose. What suggestions would you give to accomplish this with materials/tools that could be obtained at local stores?


texts: Confused about identifying delocalized electron pairs in Isoniazid

texts:
I have to identify delocalized electron pairs in Isoniazid (pairs not shown in the image below):

I know the nitrogen in the ring has a localized electron pair, since it already forms a pi bond. I'm confused about the other two nitrogen atoms. When we draw one of the resonance structures, we can see the amide nitrogen has a delocalized electron pair:

And if we push the lone pair from the amine nitrogen, we get another resonance structure (even if it is insignificant, due to all of the formal charges, it still seems to be a valid resonance structure):

Because these two lone pairs engage in resonance, I thought that they were both delocalized. But my textbook (Klein's Organic Chemistry, section 2.12, 2nd Ed.) says only one pair is delocalized:

Therefore, if the electron pairs on both the amine and amide nitrogens in Isoniazid seem to engage in resonance, why is only one pair delocalized?


texts: When two negatively charged molecules are hydrogen bonding with each other, why do the charges increase?

texts:
Context

[EDIT: As some commentators have suggested, I  should conclude that the energy minimize feature is not intended for the purpose of Hydrogen-bonding, and primarily for refining the modelling of molecules.]

Using the Chem3D automatic Huckel charge calculator, I was able to calculate the charges of the atoms in the citrate and borate ion.

Individually, the borate ion's oxygen atoms have a small negative charge, i.e. -0.07. Individually, the citrate ion's oxygen atoms have a large negative charge, i.e. -0.56.

I use the energy minimize function to make the two hydrogen bond. I then do the charge calculation, and I found that some of the citrate's oxygens' charges increased to ~-0.67, while some of them decreased, and the borate ion's increased to ~-0.5. The hydrogen atoms do increase positive charge.

I actually noticed another particular feature, the oxygen atom of the hydroxyl involved in both hbond donating and accepting has a positive charge now. The other charges remain as I've explained above. The highlighted yellow atom was just an oxygen atom that I clicked.

Question

For my own explanation, I would suggest that the hydrogen bonding is the cause of the charges being induced and increased. Yet, due to the size of the molecules, only two or four atoms seem to be involved in the hydrogen bonding. Then, why should the OTHER atoms still increase their charge? The atoms not involved in hydrogen bonding between the two molecules?

Would it be a feature of the calculator, or would this be the scenario in real life?

I am interested in how different ions are compatible with borate in terms of hydrogen bonding and screening, based on their charges. This will aid my experiments.


texts: What does it mean if a catalyst has multiple "/" symbols, such as $\ce{Mn/Fe/Al2O3}$? Does it mean either $\ce{Mn}$ or $\ce{Fe}$, or does it mean both are supported on $\ce{Al2O3}$?


texts: Why are overcoats used on aluminum if aluminum oxide forms on surface anyway?

texts: If a thin layer of aluminum oxide is formed on the surface of aluminum to prevent further oxidization, why are optical components using extra "overcoat" materials to prevent dulling of the metal over time?


texts: What molecular features create the sensation of sweetness?

texts:
There are many compounds that taste sweet. Many of the artificial ones taste much sweeter than natural sugars (which is why they contribute little to energy intake when use as sweeteners).

A range of sweeteners is shown in the figure below:

Structurally there are common features for some. We can see why sucralose (a non-metabolisable sweetener based on sucrose) might taste sweet. Rebaudioside a (a major ingredient of the sugar substitute Steria) shares some of those features. But the very sweet artificial sweeteners seem to have less in common.

Do we know what makes molecules generate the sensation of sweetness? Which features matter and why are some sweeter than others?


texts: Neutralization between Ca(OH)2 + H2SO4 in a 30% hydrogen peroxide solution

texts:
I have performed an experiment where I added an excess of $\ce{Ca(OH)2}$ base to a solution consisting of 5 mL of 30 % hydrogen peroxide (buffered at pH 5) and a very small amount of sulfuric acid (such that the pH of the original solution of 30 % $\ce{H2O2}$ and acid was 1.7).

I am having trouble understanding what reactions maybe occurring between these three substances to give a final pH of 10.5.

I know that $\ce{Ca(OH)2}$ and $\ce{H2O2}$ form $\ce{CaO2}$ when reacted, but shouldn't the final pH be equal to that of $\ce{Ca(OH)2}$ considering it is in excess? What reactions could be occurring here and why are they not allowing the pH to reach that of $\ce{Ca(OH)2}$?

Any help at all would be very much appreciated. Thank you in advance.


texts: Hydroboration oxidation reaction on trans,trans,trans-1,5,9-cyclododecatriene with carbon monoxide

texts:
The given solution:

I got this question in an entrance exam coaching test paper in India. Product P is easily covered by the mechanism of simple hydroboration-oxidation reaction, and I've understood it well. However, product Q is what intrigues me.

Looking at the product and the reactants, I can guess that the carbon in $\ce{CO}$ functions as the source for the bridging carbon in the product Q. However, I could not figure out the mechanism for the same. It is not given in my textbook, and wasn't found via Google searches either.

I'v well understood how the intermediate product (bridged by boron) had formed. However, how is the carbon monoxide supposed to displace boron from there? I can guess that once a carbonyl group bridge is formed in the middle, the alkaline hydrogen peroxide will reduce the ketone to an alcohol (to get product Q), but I am not too sure.


texts: Galvanic reaction between aluminum and carbon fiber composite

texts:
I understand that there is a galvanic reaction between aluminum and carbon fiber composite. Structural aluminum parts in contact with carbon fiber composites should be insulated by something like fiberglass.

But what exactly is it that happens, chemically? I know that aluminum has a tendency to be oxidized; aluminum oxidizes readily by itself in air. I also know that carbon fiber itself is a conductor due to delocalized electrons.

So assuming that aluminum is oxidized then the carbon fiber composite must be reduced.

What exactly is reduced? The carbon fiber, or the epoxy? What is the role of the epoxy in all of this? Wouldn't the epoxy be electrically insulating? How exactly does this redox reaction take place across the epoxy?


texts: What is the known cheapest chemical solution to extract CO2 from air on industrial scale?

texts:
As far as I know, the cheapest non-chemical solution is: grow grass, and burn it. The resulting $\ce{CO2}$ is from the air. But I am interested on chemical industrial solutions now.

As far as I know, the main difficulty of the process is that the ratio of the $\ce{CO2}$ in the air is very low. Thus, extracting it means a large entropy difference.

My layman's intuition is that maybe some substance exists - probably an organic compound - which binds especially strongly to $\ce{CO2}$ and it is easily regenerated. One would pump air through it, and then regenerate it to get the $\ce{CO2}$ back. If such a compound exists, what is it?

The process should be powered by electrical energy only. Thus, solutions such as "buy gas, burn it, and you get much cheaper $\ce{CO2}$" are not acceptable.

On "cheapest" I understand, what is cheapest in industrial size, not in a laboratory? (for example, in a large chemical factory)


texts:
When electrons gain energy they become more excited and move to a higher energy level, which increases the tendency of an atom to form a bond with another atom. Thus, surely bond making requires the absorbance of energy?

Equally when electrons lose energy they drop to a lower energy level, which would break a bond. Therefore, why isn't bond breaking exothermic?

Could someone point out the flaw in my reasoning, because I don't get why bond-breaking is possibly endothermic?


texts:
A is more acidic than B. Does that mean -I effect of phenyl is greater than its +R?

Update
This is the statement from my NCERT textbook.


texts: Is there a single MO that represents the π system of a Möbius aromatic system? If so, what does it look like?

texts:
I recently answered the question of whether twisted polyene chains were known by pointing towards Möbius aromatic system. While in conventional Hückel aromatic systems the lowest-lying π-orbital obviously has a nodal plane containing all the nuclei, this is not possible in a Möbius aromat since topologically these only have one side.

A number of Möbius aromatic systems have been both synthesised[1] and calculated;[2] for an X-ray determined structure of one, see the second structure in the figure below.[3]

One can easily see that the π chain would have green and white or plus phase and minus phase overlapping. This got me thinking and wondering: what would this system’s molecular orbitals look like? Specifically: is there a set of MOs that would correspond approximately to the π system of such a Möbius aromat? If not, how are the π bonds seen in an MO analysis? The only calculations I could find searching the literature were both very old and without nice pictures.

References:

[1]: M. Stępień, N. Sprutta, L. Latos-Grażyński, Angew. Chem. Int. Ed. 2011, 50, 4288–4340. DOI: 10.1002/anie.201003353.

[2]: H. S. Rzepa, Chem. Rev. 2005, 105, 3697−3715. DOI: 10.1021/cr030092l.

[3]: Y. Tanaka, S. Saito, S. Mori, N. Aratani, H. Shinokubo, N. Shibata, Y. Higuchi, Z. S. Yoon, K. S. Kim, S. B. Noh, J. K. Park, D. Kim, A. Osuka, Angew. Chem. Int. Ed. 2008, 47, 681–684. DOI: 10.1002/anie.200704407.


texts: How does DMSO act as a carrier for transdermal transport of large molecules?

texts:
DMSO.org claims the following:

  "[DMSO] is more successful ferrying some drugs, such as morphine
  sulfate, penicillin, steroids, and cortisone, than others, such as
  insulin."

All of these drugs that it is said to carry are much larger than a single DMSO molecule.

So what is the general mechanism by which DMSO can bring these relatively high-molecular weight compounds into your body transdermally, where they would not do so otherwise?  Does it simply “wrap them up” in a large complex, or does it possibly just complex the portions of the other compound that prevent it from crossing transdermally?  What is it about insulin for example that prevents it from being carried through the skin?

A quick internet search will give pages of documents basically saying “this is what it does”  but I’ve never found a remotely technical explanation of how this works, particularly for large molecules.  That’s what I’m asking here.

NOTE 1: I have never used DMSO medicinally and currently have no intentions of doing so.
NOTE 2: I hope this is not considered a duplicate of this question as the answer is specific to the transport of small molecules.


texts: 5-methylhexa-1,3-diene reaction with HBr

texts:
What will be the major product of the reaction?
I guess that rearrangement will take place and give 5-bromo-5-methylhex-2-ene as a product, but I'm completely not sure


texts: Why does s-p orbital separation increase with increasing atomic number?

texts:
More specifically, why does s-p energy separation increase:

Across the period
Down a group

I do know that penetration of electrons increase with lower angular momentum and lower principal quantum number. An increase in penetration means that it has a higher shielding ability.

If we have two elements in period 2 and period 3 respectively, than the $\ce{3s}$ orbital would be less effective at shielding than the $\ce{2s}$ orbital, and thus the $\ce{3p}$ orbital would be higher in energy than the $\ce{2p }$ orbital would be relative to their s-orbitals? Is this the right justification?


texts: What is the criteria for determining structure of a molecule?

texts:
Does the shape of the molecule depends on symmetry?

Why is the shape of dinitrogen trioxide ($\ce{N2O3}$):

(oxidation number of nitrogen atoms: +4, +2)

Instead of my proposal, which is much more symmetrical in terms of shape and oxidation number (of nitrogen atoms: +3, +3)

As seen from the case of $\ce{N2O3}$, which is unsymmetrical, then molecule of pyrophosphorus acid $\ce{(H4P2O5)}$ should be unsymmetrical too.

But the actual structure is symmetrical:

Instead of my second proposal

Another interesting thing is: the central atom of the two previously mentioned molecules has the tendency to have have highest oxidation state. That is: +5 in case of phosphorus atom of pyrophosphorus acid and +4 in case of nitrogen atom of dinitrogen trioxide.

Is my above mentioned conjecture is valid?


texts: What's that tangy smell on cheap plastic?

texts:
Most cheap items (from China mostly) have a strong tangy odor to the plastics (or some resin, but I can mostly smell it on plastics). The smell is always consistent over a broad range or products and I get it for at least a decade. So I do not believe this is a one-off thing and I bet most people have experienced it. The only variation is intensity.

On some really bad products that smell impregnates other things and I failed to remove it with soap, baking soda, acid, scrubbing...

I'm curious to know what exactly is that smell.

Apparently it got some attention already, but there's no consensus, and a lot of crywolf(?) e.g. Campaign to Halt the Import of
Chemical-Emitting
Smelly Plastic from China.


texts: Which rate, the forward or reverse rate of acid dissociation, is more strongly affected when diluting acetic acid in aqueous solution?

texts:
Acetic acid is a weak acid. It is in equilibrium with acetate and hydronium ions in aqueous solution:

$$\ce{CH3COOH(aq) + H2O(l) <=> CH3COO-(aq) + H3O+(aq)}$$

Ostwald's law states that the degree of ionisation of a weak acid increases upon dilution (in quantitative terms: as the square root of the volume).

Consider two scenarios:

We start out with 1.001 moles of water and 1.000 moles of acetic acid (so water is the solvent and acetic acid is the solute), and dilute it with water to twice the volume.
We start out with 100 mM acetic acid, and dilute it with water to
twice the volume.

How do the rates of the forward and reverse reaction change in these two scenarios, and how do these changes help to explain Ostwald's dilution law? (I know that once equilibrium has been reached after dilution, the forward and reverse rates will be equal again, so I am asking about the rates after dilution, but before changes to concentrations by the reaction going towards equilibrium. If mixing is slower than the acid-base reactions and you can't do the actual experiment, treat it as a thought experiment.)

This question was inspired by Why degree of dissociation/ionisation affected by dilution? . I am specifically interested in addressing the following ideas from the OP of that question:

  as there are more water molecules so the chances that say a CH3COO- ion attracting an H+ from it's surrounding water should increase

$\vphantom{bejsjs}$

  since we are adding more water to it and since water has high dielectric constant so it'll ionise CH3COOH more

$\vphantom{bejsjs}$

  since water is more so it'll hydrate the broken ion and surround it,make it harder for them to recombine

$\vphantom{bejsjs}$

  What motivates or pushes [the acid] to dissociate more?

If it helps, it would be fine to discuss what happens with a single acetic acid molecule and a single acetate anion upon dilution.


texts: Can we manipulate the rate of water's autoionization?

texts: I just got introduced to this concept and these thoughts came into my mind. Is there a way to increase the equilibrium constant of the autoionization of water?


texts:
Is the hexagonal unit cell (resulting from hexagonal closed packing) same as the unit cell of hexagonal crystal system?

The unit cell of hexagonal crystal system is described by the following sides and angles: $a=b\neq c$, $\alpha=\beta=90^\circ$, $\gamma=120^\circ$,
where $a,b,c$ are the sides of unit cell and $\alpha,\beta,\gamma$ are the angles.

This is the unit cell of hcp

In the unit cell of hcp there are 17 atoms whereas in unit cell of hexagonal crystal system there are 8. Is this true?


texts:
How can glycine act as a buffer at pH 6.00 and why? Please use
chemical equations to show how it can act as a buffer at this pH
specifically?

My work:
At pH 6.00 glycine acts as a buffer, because at pH 6.00 the condition is acidic and glycine is an amino acid, so its zwitterion forms an equilibrium, which means there is a positive charge on the N of the amino group and a negative charge on the carboxylate. So there are no sudden pH changes and we know buffer solutions resist sudden pH changes, so at pH 6.00 glycine acts as a buffer solution.
Equation:

What I need explained:
HOW does glycine act as a buffer at pH 6.00 with chemical equations, meaning to show an example of how it specifically buffers another species at pH 6.00 with the proper chemical equations.


texts:
I did a lab where I tested the solubility of carbon dioxide in water at different temperatures. I took 50 mL of carbonated water at different temperatures and then I titrated that with sodium hydroxide solution. The indicator I used was phenolphthalein with an endpoint of 8.3 pH. I'm unsure how to calculate the amount of carbon dioxide that was dissolved. I'm stuck about deciding which equation to use.

This equation would mean that there is a 1:1 ratio.
$$\ce{CO2(aq) + NaOH(aq) → NaHCO3(aq)}$$
And this equation would mean that there is a 1:2 ratio.

$$\ce{CO2(aq) + H2O(l)->H2CO3(aq)}$$
$$\ce{H2CO3(aq) + 2NaOH(aq)->2H2O(l) + Na2CO3(aq)}$$

Which one would be the correct equation to use?

Also, there are literature values for the solubility of carbon dioxide in water at different temperatures. Do those solubility values apply to my lab? I ask this because I measured the amount of carbon dioxide present in a given amount of carbonated water, I didn't add carbon dioxide to pure water to measure how much can actually dissolve.


texts: Infrared spectroscopy of substances on a OHP film

texts:
How can we record a IR spectrum of a substance coated on a Over Head Projector (OHP) sheet?
instrument has both transmission and ATR modes. IR spectrum is to be recorded for both the OHP sheet as well as the material that is coated on it


texts: The dissolution of ammonium chloride is used to cool a container of water placed in the solution. It's an endothermic process. What absorbs the heat and what loses it?


texts:
Does [Pt(CH3-CH(NH2)(COO-))2] show geometrical and optical isomerism?

According to me Pt should be dsp2 hybridised giving a square planar geometry. So it is of the form M(aa)2 type. The ligand itself has a chiral carbon. Hence it can show optical isomerism. But can it show geometrical isomerism?


texts: How can a β,γ-unsaturated ketone be converted to 1-pyrroline?

texts:
I am working towards a natural product. Presented are three intermediate compounds. After oxidation of the hydroxyl to a carbonyl, I want to introduce an imino-nitrogen atom into the structure. This way, an imino bond creates a five-membered ring, and the double bond disappears.

What reagent(s) should I choose for this type of reaction, and what does the reaction mechanism look like?


texts:
My textbook, Organic Chemistry (6th edition) by Brown, Foote, Iverson, and Anslyn, states:

  Alkynes in which the triple bond is between carbons 1 and 2 are commonly referred to as terminal alkynes.

Is not this definition incomplete? I can imagine scenarios where we have a terminal triple bond that does not reside between carbons 1 and 2 according to IUPAC rules. E.g., $\ce{CH2=CH-C#CH}$. Here, the terminal triple bond is between carbons 3 and 4 (according to IUPAC rules, doubles bonds take priority when numbering).


texts: Does CN4 with the following structure exist?

texts:
I am a mathematician, not a chemist, so my questions are rather combinatorial. I am intrigued by the possibility of the following binary compound:
$$\ce{\overset{-}{N}=\overset{+}{N}=C=\overset{+}{N}=\overset{-}{N}}$$
which ought to be isoelectronic with carbon suboxide, and thus possibly stable. Does this compound exist, even in interstellar space?


texts: Is presence of air necessary for silica gel to absorb moisture?

texts:
I am a biologist currently doing field work where I need to quickly dry leaf samples using silica gel crystals. I use the orange indicating kind that are 2-4mm in size. The setup is like this. I stuff 1-2 leaves in a manila paper envelop which I drop in a ziplock bag containing ~1/8th cup of silica gel. Then I squeeze out most of the air before sealing the ziplock. The end goal here is to extract DNA from dried leaves when I am back in the lab.

I have had varied results in terms of drying and looking to achieve the maximum efficiency. Recently it occurred to me whether squeezing air out is actually counterproductive to fast drying.

So my question is, whether presence of sufficient air necessary for silica gel to absorb moisture from leaves? Essentially I am creating partial vacuum inside the ziplock. Is that keeping silica from doing its job?


texts: Why are a calico strainer and chloroform used in a British Pharmacopoeia assay of milk of magnesia?

texts:
The following is an assay for milk of magnesia in the British Pharmacopoeia (emphasis added):

  Dissolve the sodium hydroxide in $\pu{150 cm^3}$ of purified water, add the light magnesium oxide, mix to form a smooth cream and then add sufficient purified water to produce $\pu{2500 cm^3}$. Pour this suspension in a thin stream into a solution of the magnesium sulfate in $\pu{2500 cm^3}$ of purified water, stirring continuously during the mixing. Allow the precipitate to subside, remove the clear liquid, transfer the residue to a calico strainer, allow to drain and wash the precipitate with purified water until the washings give only a slight reaction for sulfate. Mix the washed precipitate with purified water, dissolve the chloroform in the mixture.

What is a calico strainer, and why is it used here? Is it better than using, say, Büchner filtration?

As well, why is chloroform used (see emphasized text, above)?


texts: Identifying the oxygen atoms that undergo reduction

texts:
Identify the oxygen atoms that undergo reduction in the reaction below:
$$\ce{O2 + Cr^3+ -> H2O2 + Cr2O7^2-}$$

I know that the oxygen atoms in $\ce{O2}$ have an oxidation state of $0$.
In the product $\ce{H2O2}$, the oxygen atoms have an oxidation state of $-1$; and in $\ce{Cr2O7^2-}$, oxygen atoms have an oxidation state of $-2$.
Based on how the problem was solved on the answer key it was assumed that all the oxygen atoms from $\ce{O2}$ are reduced to peroxide atoms.
How do we know that there are no oxygen atoms that are oxidized to become chromate oxygens with a $-2$ oxidation state?
I understand that there are other $\ce{H2O}$ oxygen atoms available to provide the chromate oxygens that would change the oxidation state.


texts: Is the shorthand electron configuration of Br- just [Kr]?

texts:
Is the shorthand electron configuration of $\ce{Br-}$ just $\ce{[Kr]}$?

Also what about $\ce{Ca^2+}$—is it just $\ce{[Ar]}$? And, is $\ce{Na+}$ just $\ce{[Ne]}$?


texts:
I've heard and read (multiple times) two theories have have been around for a while, both of them obvious nonsense.

One states that pressure and friction make the ice melt (turn to water) where the skater's blade comes in contact with it. This is patent nonsense since a puck that weighs very little, or a pencil that weighs next to nothing, slip along the ice as well as any skater. I also find it hard to believe that the temperature of the ice (several degrees below freezing) would suddenly jump several degrees in the split second that it takes for the skate to come in and out of contact with it.

The other theory is that the ice surface itself has the same qualities as water due to some hydrogen molecules still in search of home. This is also nonsense: pour water over a concrete floor and try to skate on it; see how far you'll get.

So my question is: why is ice slippery?


texts: Will borosilicate glass absorb 808nm laser light? If it instead refracts, then what is the refractive index? Also, will borosilicate reflect lower frequencies of light like those used in non contact temp. measurements?


texts:
The linked answers do attempt to clarify on 'stability' but I wanted an answer with specific connection to resonance.

For example, the ethanoate ion can exist in many forms but, as we know from data, it exists in a form that is a hybrid of all the possible forms. Why is this?
I have heard teachers say that this is since that form has 'less energy' or is 'more stable.' I understand - from the linked answer- that these terms are open to interpretation. The criteria my teacher used was that in each of the contributing mesomers, the electrons are localised. But in the hybrid, they are delocalised. Now I understand this results in more 'stability' in some sense of the word.

But is that only criteria ? Should we not also consider the electronegativities of the atoms involved, for example? Basically, why is the hybrid form the form in which the structure exists?


texts: Laboratory setup for the distillation of sulfuric acid

texts:
Purification of Laboratory Chemicals, 5th Edition, by Armarego, reads (p. 53):

Reagents such as water, ammonia, hydrochloric acid, nitric acid, perchloric acid, and sulfuric acid can be purified via distillation (preferably under reduced pressure and particularly with perchloric acid) using an all-glass still.

as well as (p. 479):

Sulfuric acid, and also 30% fuming $\ce{H2SO4}$, can be distilled in an all-Pyrex system, optionally from potassium persulfate. Also purified by fractional crystn of the monohydrate from the liquid. Dehydrates and attacks skin—wash immediately with $\ce{H2O}$.

I've never seen sulfuric acid fume (only spread with steam when heated), and Wikipedia states a boiling point of $\pu{337 ^\circ C}$, along the fact that it slowly decomposes to $\ce{SO3 + H2O}$ above $\pu{330 ^\circ C}$, so I'm wondering, mostly from a theoretical standpoint:

How far lower can the boiling temperature effectively get under reasonably strong vacuum?

Does the vacuum not also bring down the temperature level at which sulfuric acid degrades?

What would be an ideal laboratory (not industrial!) setup and process for the safe distillation of sulfuric acid in fair enough amounts for laboratory use (say producing in a batch the equivalent of $\pu{5L}$ at 30% concentration)?

Nota Bene: I know it's a better idea to buy sulfuric acid at the desired level of purity, but that is not the question.


texts:
Question

Attempt

On seeing the question it seems like simple esterification reaction and the answer seems A. But the answer in book says C. How is it so

I also tried to develop a mechanism as follows


texts:
Does anyone know a bit about how costly and accurate are the current THC measurement techniques?

Please speculate what drives cost chemicals, consumables or instrument time.


texts: Why does the carbocation in this scheme react under elimination conditions rather than being attacked by water?

texts: In the final step of the mechanism, elimination occurs over substitution, why is this?


texts:
As I was reading Clayden: Organic Chemistry 2nd Edition, I came across an image of naphthalene showing its varying $\ce{C-C}$ bond lengths, however, I was unable to rationalize the bond lengths by drawing naphthalene's resonance forms. I have searched for a good explanation for the bond lengths shown but I have not found anything remotely convincing.

The 3 resonance forms of naphthalene are shown below however, these resonance forms are inconsistent with the bond lengths displayed by Clayden. From looking at these resonance forms I would not expect the $\ce{C-C}$ bond fusing the benzene rings to be the shortest since it has less double bond character compared to some of the other $\ce{C-C}$ bonds in the molecule.


texts: Efficiency of various Ewald-type schemes for the summation of electrostatic interactions

texts:
I am looking into implementation of Ewald summation techniques for a number of point charges in periodic 3D space (i.e. a molecular simulation box with periodic boundary conditions). The “mainstream” Ewald-type techniques I know are:

original Ewald scheme
particle-mesh Ewald (PME)
smooth particle-mesh Ewald (SPME)

However, while I can find papers describing each of those, I have not been able to find a comprehensive article/white paper/technique note comparing their implementations and their CPU timings on a typical dense system (liquid, protein in solvent, whatever…). What resources do you know of on this topic?


texts: Why was a Plimsoll symbol chosen to indicate standard state?

texts:
Historically, the Plimsoll symbol (aka Plimsoll line) was created as hull mark that would serve as a ready indicator of whether a ship was overloaded and thus running too low in the water.  It was later adopted by chemists to indicate standard state (currently defined by IUPAC as 1 bar).

Why was the Plimsoll symbol chosen for this purpose?  According to Wikipedia,

  The plimsoll symbol (⦵ or o) ... is used as a superscript in the notation of thermodynamics to indicate an arbitrarily chosen non-zero reference point ("standard state").

The language used by Wikipedia suggests it was chosen because it looks like a zero with a line through it, thus communicating "not zero".  Applying this to enthalpy or free energy seems redundant and unnecessary, though, since by definition there is no true zero reference point for either (among state functions, this exists only for entropy).  It's like having a special symbol attached to $ΔU$ to indicate that $U$ is conserved, when, of course, $U$ is always conserved.

Indeed, the problem with attaching a symbol to $U$ saying it's conserved is that it suggests that sometimes $U$ is not conserved (otherwise why would you need the symbol?).  Likewise, attaching a symbol to $U$, $H$, or $G$ saying that the reference state is non-zero suggests sometimes it could be zero.  I.e., I understand they needed a symbol for reference state.  But I'm puzzled why they chose one that communicated "non-zero" instead of just choosing something that meant "reference", period.

Nevertheless, I'm sure these people knew what they were doing, and had good reasons for what they did.  I just don't understand what that those reasons would be.  I'd thus be interested to hear from anyone out there with knowledge of the history of this.

Perhaps the answer (here I speculate) is that they wanted to communicate the obvious (that thermodynamic reference states can never be true zero reference states) — and that the reason they wanted to do this was because they anticipated tables of thermodynamic values would be used by a broad audience, some of whom might not understand the underlying thermodynamic theory.


texts:
Evaporating cold aqueous chromium(III) chloride produces violet crystals. However when hot aqueous chromium(III) chloride crystallizes, green crystals result.

Could someone please explain the chemistry behind this... I mean both the crystals contain $Cr^{3+}$, so the difference in colour cannot be due to two different oxidation states. Also, they contain the same ligand $Cl^-$. Can someone please tell me where I am going wrong?


texts: Why do some element symbols contain a single letter while others contain two letters?

texts: As the title says, why do some element symbols contain a single letter while others contain two letters?


texts: What could be the reason for clockwise numbering in c ring of cholesterol?


texts: Would the density and radius of your metal appear to be higher or lower if you forgot to tap the flask to release air bubbles?

texts:
For this lab we had to measure out copper in flasks, but tap them out before so no air bubbles would affect the weight. We have this question at the end of the lab and so I wasn't sure if the density/radius would be higher or lower if I didn't tap them out and why.

We were trying to figure out the size on an atom of copper. To find the density of the sample, we had to add about 1/3 of copper to an empty flask and weigh it with the metal. Then after we had to add enough water to just cover the metal, then gently tap and rotate the volumetric flask to remove any air bubbles. Then fill to the calibration mark with water and reweigh the volumetric flask containing the water solid mixture.


texts: Synthesis of oxalyl chloride that doesn't involve phosphorus

texts:
I have been synthesizing TCPO (bis(2,4,6-trichlorophenyl) oxalate) for chemiluminescent reactions, using 2,4,6-trichlorophenol and oxalyl chloride.

Since I am tired of paying for oxalyl chloride (and hazard class 3 shipping), I wish to find a synthetic route to produce my own stock.

The most common synthesis of oxalyl chloride uses oxalic acid and phosphorus pentachloride. This would reduce the cost, but is also problematic because phosphorus chlorides are considered to be drug precursor (21 CFR 1310.02), still too expensive, and hazardous to ship.

Can anyone recommend a synthetic route to oxalyl chloride that does not use phosphorus? Or an alternate (safer / easier / less expensive) route to TCPO?


texts: Why is a C–D bond stronger than a C–H bond?

texts: I have heard that the carbon–deuterium bond is stronger than the carbon–hydrogen bond. What are the possible reasons for it? Is this also the reason that C–H bonds participate more in hyperconjugation than C–D bonds? Please explain.


texts: Resolving ambiguity around Lattice Enthalpy in Born-Haber Cycle

texts:
According to my textbook,

Lattice enthalpy is the enthalpy change that occurs when one mole of a solid ionic compound is separated into gaseous ions under standard conditions.$^1$

According to the same textbook, this is an endothermic process, which makes sense as a lattice is generally held together by strong ionic bonds and thus would require energy to separate the atoms. The following diagram is given for the born-haber cycle in the textbook:

The diagram supports the definition as the enthalpy of the individual gaseous atoms is greater than that of the lattice, i.e. the arrow moves up. However, as I was working through past papers by the International Baccalaureate, a question asked to draw the born-haber cycle for LiF.$^2$ This was the answer:

In this case, the arrow is pointing down for the lattice enthalpy. To me, this does not suite the definition of lattice enthalpy as separating a lattice into its ions would require energy and not release energy. Hence, should the arrow not be pointing upwards for $\ce{LiF_{(s)}}$ to $\ce{Li^+_{(g)} + Cl^-_{(g)}}$? Am I making a fundamental error, is the case for NaCl different to LiF or is the answer wrong?
Works Cited:

Pearson Baccalaureate: Higher Level Chemistry 2nd Edition. By Catrin Brown and Mike Ford
International Baccalaureate


texts:
Today, I came across a question which asked name three  reagents can be used for identification of phenol. The answer given was:

  Neutral $\ce{FeCl3}$
  $\ce{ NaNO2 +HCl}$
  $\ce {(NH4)2[Ce(NO3)6]}$.

I understand (1) and (2), but I am doubtful about CAN test (3). As far as I have studied in various books, it is used for testing presence of alcohol, and phenol is not alcohol.

Can phenol be detected with a ceric ammonium nitrate test?


texts: Why is lead sulfide found in nature, whereas lead oxide is less common?

texts:
This question probably applies to other heavier metals as well.  The only rationalization I can figure out is that lead in the +2 oxidation state (which is most common) is a borderline soft acid and prefers to take electrons from a soft sulfur instead of trying to react with a hard oxygen.
Is this the right direction?  Thank you in advance.


texts: Why is the methyl radical planar? The VSEPR theory would predict an angle between 120° and 109.5°, while it is actually 120°.


texts: Why isn't mercury electrode used to produce commercial element sodium?

texts:
I know that while electrolysing a solution of brine, if we use mercury cathode, we get sodium amalgam instead of having hydrogen gas liberated. Even the Castner-Kellner process uses this to produce sodium hydroxide.

However, wouldn't the mercury electrodes be used to produce commercial elemental sodium? I feel it's much easier to electrolyse aqueous NaCl than to melt NaCl. Then why don't they use aqueous NaCl decomposition with mercury cathode to get Na metal?

Edit: Its seems even more topsy-turvy now. Regular electrolysis of Brine itself produces NaOH, then why bother with the mercury?


texts: How to write an entire trajectory into a single PDB file?

texts:
I have a trajectory (few frames) that I want to stack together and build a single PDB. I thought either to use VMD or MDAnalysis library.

With VMD if I do atomselect it takes a frame identifier as an argument. With MDAnalysis I saw this:

with MDAnalysis.Writer("all.pdb", multiframe=True) as pdb:
    for ts in u.trajectory:
        pdb.write(u)

However, I am not sure how to use it in a complete script.


texts:
There is another closely related post here , and I've also read the referenced wiki article including applications of chelation, but I still don't see what's so special about chelation. I understand the structure of the bond - the 'capturing' of a metal cation by an organic agent, but I still fail to see why this chemical reaction might be so special relative to other possible organic chemical reactions with a metal cation.

Why is chelation so special?


texts: Why do atomic orbitals have their unique shapes?

texts: Is there a scientific explanation to why p orbitals are shaped like two balloons, etc. I think it has got to do with electron repulsions. Wikipedia says they are 'characterised by unique values of quantum numbers', of which I don't understand.


texts: Why is caustic soda (NaOH) used to clean beer bottles?

texts: I see in many blogs in the internet that cleaning bottles with $\ce{NaOH}$ is very effective. I also realize that industries use caustic soda to clean bottles. Why is caustic soda very effective at cleaning bottles? What makes it so special from other solvents which made it preferable for cleaning?


texts: Is it feasible to measure the pH of solution consisting of hydrofluoric acid, methanol and water using redox potential method?

texts:
Is it feasible to measure the pH of $\ce{HF}:\ce{H3COH}:\ce{H2O}$ solution using redox potential method?

Can I use this method to calculate the $\ce{H+}$ ions in this solution and specifically, can I measure the changes in pH simultaneously as auto ionization is taking place?


texts: Why does buffering capacity increase with the pKₐ of the acid component?

texts:
For example, the $\mathrm{p}K_\mathrm{a}$ values of ethanoic, propanoic, and butanoic acid are related in the following way:
$$\text{ethanoic} < \text{butanoic} < \text{propanoic}$$

And their buffering capacities are related in exactly the same way. What causes this?


texts: When will the Lassaigne's method for detection of nitrogen and Kjeldahl's method for quantitative estimation of nitrogen fail?

texts:
Lassaigne's method:

The organic compound is fused with dry $Na$ in a fusion tube. The fused mass after extraction with water is boiled and filtered. This filtrate is called sodium extract (S.E.), which is used to detect elements other than $\ce{C}$ and $\ce{H}$ in organic compound.

If the organic compound contains nitrogen then the S.E. will form $\ce{NaCN}$. Further reactions with $\ce{FeSO4 + NaOH}$ and $\ce{FeCl3 + HCl}$ gives blue or green colour, confirming the presence of nitrogen.

This test fails in case of diazo compounds because sodium metal can not extract nitrogen from them. What about the compounds containing nitrogen in the ring or having nitro groups?

Kjeldahl's method:

Nitrogen containing organic compound is heated with conc. $\ce{H2SO4}$. $\ce{N}$ in the compound converted to $\ce{(NH4)2SO4}$. The mixture is then heated with excess of $\ce{NaOH}$. The liberated $\ce{NH3}$ gas is absorbed in excess of standard solution of $\ce{H2SO4}$. From the amount of acid reacted with $\ce{NH3}$, % of $\ce{N}$ can be calculated.

This method is not applicable to diazo, nitro and compounds having nitrogen in the ring. This is because nitrogen of these compounds does not change to ammonium sulphate upon reacting with conc. sulphuric acid.


texts: Why is fluorine more reactive than chlorine?

texts: Why is fluorine more reactive than chlorine despite chlorine having a higher electron affinity?


texts:
I was wondering if it would be possible to use $\ce{HCl}$ acid to dissolve $\ce{PbS}$.

I know that I can dissolve it in $\ce{HNO_3}$ since, the nitric acid oxidises the sulphide ion to elemental sulphur, and some sulphides like $\ce{ZnS}$ do dissolve in $\ce{HCl}$. But what about $\ce{PbS}$?

What is the extent of $\ce{pH}$ sensitivity of lead sulphide precipitate.


texts:
Recently I have been reading about the history of the Baker Nathan reaction.

  In addition to the large
  rate increase for Me vs H, all the other alkyl groups
  showed decreases with respect to Me in a regular manner
  as would be predicted by reduced hyperconjugative
  ability.

By drawing resonance structures, it is easy to see the $\mathrm{Me < Et < {}^iPr <} {}^t\mathrm{Bu}$ predicted by the inductive effect:

Therefore the more electron donating (i.e. the stronger the I+ effect) the para group is , the more stabilized the transition structure is (black $\delta^+$ on the left diagram become smaller hence less electrostatic repulsion in the $\pi$ system, hence blue $\delta^+$ and the $\delta^-$ can be larger thus facilitating the reaction). Hence $\mathrm{Me < Et <} {}^i\mathrm{Pr <} {}^t\mathrm{Bu}$.

However, for hyperconjugation, the $\sigma$ bonds overlap with the $\pi$ system resulting in electrons to become more delocalised at the C-C bond between the alkyl group and the $\pi$ system. Therefore the more hyperconjugations present, once again the more stablised the transition structure hence a faster reaction.

Since both $\sigma_\mathrm{CC}$ and $\sigma_\mathrm{CH}$ bonds adjacent to the para carbon can potentially engage in hyperconjugation (and naively the $\sigma_\mathrm{CC}$, being larger in lobe size, should expect to overlap better with the $\pi$ system), does that mean the experimentally observed trend that $$\mathrm{Me > Et > {}^iPr >} {}^t\mathrm{Bu}$$

suggest hypderconjugation of $\sigma_\mathrm{CC}$ is much weaker than that of $\sigma_\mathrm{CH}$ hence justifying the quoted message?

  If hyperconjugation of $\sigma_\mathrm{CC} < \sigma_\mathrm{CH}$ what is the underlying molecular orbital explanation?


texts: Where does the energy come from to lower the temperature of a brine solution?

texts:
Suppose I have a densely packed bucket of ice chips / cubes made from pure $\ce{H2O}$. It has been at room temperature for days, so the interior temp of the ice is likely close to 0 °C / 32 °F. (I have a working model of this in a clear ice - ice maker in a kitchen that does not have refrigeration; the ice is kept cold solely by the continuous addition of more ice.)

To a measured quantity of that ice (think about an ice bucket to cool wine) if I add:

23% of the weight of the ice in $\ce{NaCl}$ (table salt);
Some water to make a brine solution;
Stir.

The temperature of the resulting solution declines to roughly -22 °C / -8 °F.

I know that the $\ce{NaCl}$ depressed the freezing point of the water and that is why it can be liquid at this temperature. I suspect that $\ce{NaCl}$ is forming ions in the solution.

My question is: Where does the thermodynamic energy come from to lower a mass of ice and water to a significantly lower temperature?


texts: phase differences between conical intersections and light-induced conical intersections?

texts: I've read recently about light-induced conical intersections, a phenomenon  where conical intersections can be artificially introduced to molecules, and that this can be observed even in diatomic molecules (see for example here and here ). I understand that there are similarities in the way you sketch the crossing of the curves, but I dont understand where and how does the wavefunction changes sign near the light-induced conical intersection version?


texts: Stereoelectronic effects in torquoselectivity of 4π electrocyclic opening

texts:
Thermal 4π electrocyclic ring openings of cyclobutenes to form butadienes are known to proceed in a conrotatory manner, consistent with the Woodward–Hoffmann rules. However, there are two different conrotatory modes which can lead to isomeric products if the cyclobutene is suitably unsymmetrically substituted. Torquoselectivity refers to selectivity arising due to the preference of one conrotatory mode over the other.

The Houk group has reported some examples of counterintuitive 4π ring openings1,2 (simply considering steric interactions, the larger group generally wants to move outwards). In both cases only one isomer of the product is formed.

Why is this selectivity seen?

References

1. Houk, K. N.; Spellmeyer, D. C.; Jefford, C. W.; Rimbault, C. G.; Wang, Y.; Miller, R. D. Electronic control of the stereoselectivities of electrocyclic reactions of cyclobutenes against incredible steric odds. J. Org. Chem. 1988, 53 (9), 2125–2127. DOI: 10.1021/jo00244a058.

2. Rudolf, K.; Spellmeyer, D. C.; Houk, K. N. Prediction and experimental verification of the stereoselective electrocyclization of 3-formylcyclobutene. J. Org. Chem. 1987, 52 (16), 3708–3710. DOI: 10.1021/jo00392a047.


texts: Is the speed of sound the fastest rate that a chemical reaction can progress through a substance?

texts: I read that a martensitic transformation can travel at the speed of sound in that material. Is that confirmed as being the fastest speed of a chemical reaction (transformation)?


texts: What do the half-reactions need to be for balancing a redox reaction in an acidic medium?

texts:
Balance the following reaction:
  $$\ce{CuS + SO4^{2-} -> CuO + SO2}$$

Below, the number mentioned in the parenthesis is the oxidation number of sulfur.
I have found out that the oxidation half-reactions and reduction half-reactions are as follows:

\begin{align}
\ce{CuS^{(-2)}     &-> ^{(4)}SO2}&& \text{Oxidation half reaction}\\
\ce{^{(6)}SO4^{2-} &-> ^{(4)}SO2}&& \text{Reduction half reaction}
\end{align}

Problem:

In this, what about $\ce{CuO}$ in the product side? I have also learned that we need to balance the spectator ions before charges if the spectator ion is other than oxygen and hydrogen.

Here, there is no $\ce{Cu}$ in reduction half reaction. So, I think there is something is wrong in my reduction half-reaction.


texts: How to determine what organic molecule has the highest boiling point?

texts:
Compare and answer which one has the highest boiling point:

$\ce{CH3CH2CH2CH3}$ (butane) ... [$\pu{−1}$ to $\pu{1^\circ C};\ 30$ to $\pu{34^\circ F};\ 272$ to $274\ \pu K$]
$\ce{CH3NH2}$ (methylamine) ... [$−6.6$ to $−6.0\ ^\circ\pu C;\ 20.0$ to $21.1\ ^\circ\pu F;\ 266.5$ to $267.1\ \pu K$]
$\ce{CH3OH}$ (methanol) ... [$64.7\ ^\circ\pu C\ (148.5\ ^\circ\pu F;\ 337.8 \pu K)$]
$\ce{CH2F2}$ (difluoromethane) ... [$−52\ ^\circ\pu C\ (−62\ ^\circ\pu F;\ 221\ \pu K)$]

My effort:
At first, without referring to factual data (but the factual data has been provided in parenthesis, see above-options, Source: wikipedia.org), I reached the following conclusion:

Butane appears to have the lowest boiling point because there is only Van-der-Waals forces, which are weaker than dipole-dipole interactions, present in the rest of molecules.

Next I would compare between methylamine and methanol because they both have dipole-dipole interactions and most importantly that these molecules associate themselves with hydrogen bonds, but as oxygen is more electronegative than nitrogen, hydrogen bonds formed within methanol molecules would be stronger than those formed between methylamine molecules. So methylamine takes the 3rd position.

Lastly, it becomes easy for me to differentiate between methanol and difluoromethane, because according to my knowledge the latter has got fluorine which is more electronegative than oxygen, present in former. Moreover difluoromethane has got 2 fluorine, which add weight to my above argument in the way that there will be even more extensive hydrogen bonding within the molecules.

Inferences and comparison with the source's answer
Answer: Methanol
I am full of doubts as to why difluoromethane is not the answer. Revisiting my arguments again and again, I always ended up with the same conclusion i.e., mine answer would always contrast with the source's answer.
Afterthoughts & Deductive Conclusions
A few days after extensive thinking and arguing myself, I ended with the following reason, which seemed plausible to my brain. It may be possible that the because of: the presence of two fluorine atoms, small and compact nature of carbon-fluorine bond (according to bond length - bond strength - bond dissociation enthalpy relation/ theory), and the overall small and virtually spherically shape (But, in fact, it is tetrahedral geometry) of difluoromethane; the two fluorine atoms might be finding themselves in a position, in which they cannot simultaneously form hydrogen bonds with the hydrogens of other molecule. My above explanation can also imply that they might be hindering into each other's hydrogen bonds (reason can be same as mentioned in list in the previous sentence).
This reasons and explanation thus explain why the boiling point of difluoromethane falls below that of methanol. Remember that in methanol, there is less compact nature of carbon-oxygen (similar size of orbitals of carbon and oxygen as well as bigger size of oxygen atom as compared to that of fluorine), a single carbon-oxygen bond is weaker than a single carbon-fluorine bond (based on electronegativity difference and concept of dipole-development & interactions), and the last that is a molecule of methanol is less symmetrical (3-H and 1-O) as compared to difluoromethane, which is more symmetrical (2-H and 2-F).
Final conclusion and additional Info.

Solution1: $\ce{C4H10 < CH3NH2 < CH3OH < CH2F2}$ (in increasing order from left to right)
Solution2: $\ce{C4H10 < CH3NH2 < CH2F2 < CH3OH}$ (in increasing order from left to right)
Solution3: None (it's should be totally based on your own conclusions and knowledge, backed up with info. from  appreciable sources)


texts:
I had the following question at an exam:

What is the fastest reacting compound towards nucleophilic addition with Grignard reagent?
(a) Acyl chloride
(b) Aldehyde
(c) Ester

It is obvious that ester would be the slowest, but among acyl chloride and aldehyde, acyl chloride would have a highly electrophilic, but a bit sterically hindered carbon atom and the resonance will also decrease the electrophilicity, whereas the aldehyde will have a less sterically hindered and moderately electrophilic carbon atom.
Which one will prevail and how to judge?
What would happen if instead acyl chloride there were acyl bromide?


texts: Why is tetracyanonickelate square planar?

texts:
Why is tetracyanonickelate, $\ce{[Ni(CN)4]^{2-}}$ square planar?

$\ce{CN}$, for being a strong field, would not follow Hund's rule.
the central atom $\ce{Ni}$ would have a +2 charge so its configuration would change from $\ce{3d^8 4s^2}$ to $\ce{3d^8 4s^0}$
Using the statements above and using crystal field theory I get its hybridization as $\ce{dsp^3}$, which suggests that its shape must be trigonal bipyramidal while it is not.


texts: Why is the water column empty in ICE table

texts: In the ICE table pure solids and liquids have a value of one in the equilibrium expression but when we create an ICE table, why is the $\ce{H_{2}O}$ column empty? Should it not have a value of one?


texts:
Recently, I came across a book in which I was solving the exercises and found out that the solution to a question says that the fluoride ion, $\ce{F^-}$, is smaller in size than the hydride ion, $\ce{H-}$.

As far I know, the hydrogen has only one shell in contrast to fluorine. Addition of a electron to hydrogen adds a electron to the 1s orbital and thus to the first shell. Similarly in fluorine, the electron is added to the 2p orbital and therefore to the same shell.

Anions are a bit bigger than their parent atom, and there is some serious electron repulsion, but how can such a repulsion make the hydride ion bigger than the fluoride ion, given that the fluoride ion also faces some repulsion within itself. Are there some other factors - or is the fact which I reported is very wrong?


texts: What is the LUMO of a molecule with an alkene and a carbonyl?

texts:
In a molecule that has both an alkene (C=C) and carbonyl (C=O) that are NOT conjugated, such as pent-4-en-2-one, how do you determine which π* anti-bonding orbital is the LUMO?
Essentially, I'm trying to reconcile two statements that I thought were true but apparently contradict here:

Increased electronegativity of an atom lowers the energy of its molecular orbitals. This lead me to think that π* C=O is the LUMO because the higher electronegativity of oxygen would lower the energy of the anti-bonding orbital (as well as the bonding orbital).
The lower the energy of the bonding MO, the higher the energy its anti-bonding MO is. This leads me to think that π* C=C would be the LUMO because π C=C is the highest energy bonding orbital, so π* C=C would be the lowest energy anti-bonding orbital.

Any help you could provide would be GREATLY appreciated!!


texts: How to find the molar mass of an unknown metal carbonate through a gas evolution reaction?

texts:
As part of a pre-lab exercise in Chemistry, we went through the necessary calculations to identify an unknown metal in a metal carbonate. The method was gas evolution by means of hydrochloric acid (see equation below).

$$\ce{HCl + M2CO3 -> MCl + CO2 + H2O}$$

The unknown metal was Alkali, and we had three possibilities: Lithium, Sodium and Potassium as $\ce{M}$.

Using data given to us, we first converted grams of released $\ce{CO2}$ to moles. Then here was the part I was confused on-

To find the molar mass of the metal carbonate, we took the mass of the sample used (the metal carbonate) and divided it by moles of $\ce{CO2}$ released, which was just calculated. The rest here on out was a little algebra. What is the reasoning behind dividing the mass of the sample by released $\ce{CO2}$? What makes it "legal"? Yes, in the balanced equation, the ratio of $\ce{M2CO3}$ to $\ce{CO2}$ was $1:1$.


texts:
The enol and keto forms are said to be tautomers of each other, and the interconversion of the two forms involves the movement of an alpha hydrogen and the shifting of bonding electrons.

At what temperature does tautomerization stop? (E.g I can obtain both the enol and keto form without them interconverting)

To make this simple, let's just assume the molecule of choice is: acetaldehyde

In addition there is no tunneling of the two tautomers. Lastly it is known the the two tautomers of acetaldehyde are stable and do not convert at 11 K with argon matrix trapping. What's the highest temperature that do not interconvert?


texts: How do I scale up to semi-prep from an analytical HPLC

texts: I am looking for an equation that would allow me to change the variables injection volume, column size, and flow rate scaling up from an analytical HPLC to a semi prep instrument.


texts: Intensive and extensive properties of gases

texts:
Every chemistry textbook I have ever seen defines intensive and extensive properties the same way: Intensive properties are those which do not depend on how much matter is present, while extensive properties do. I came across a question while looking through sample FE exam questions for which my understanding of these properties by this definition failed. The gist of my question really just revolves around pressure and volume in largely compressible substances (i.e., gases).

It seems that, when considering a gaseous substance, these definitions are not robust enough:

Volume can be shown to be independent of the amount of material present by simply compressing the gas.
Density can be shown to be dependent on the amount of material present by keeping a fixed volume and simply adding more gas molecules.

While I have heard the convincing argument that we should simply consider smaller subsets of the original to determine intensiveness and extensiveness (for instance, if I consider half of the container instead, the volume halves from $V_0$ to $\frac{1}{2}V_0$ and the density remains constant at $\rho$), this doesn't help me to identify why the conventional definition remains in use with what seems like flawed implications. Can anyone help to clarify this?


texts: The geometry of aluminium carbide is attached. Why isn't it completely linear (in accordance to VSEPR), but bent on the Al atoms?


texts: Nomenclature Precedence Order for Unsaturation and Hydrocarbon Chain

texts: When naming branched alkenes/alkynes, the numbers of the carbons where the branches and multiple bonds are located are supposed to be the lowest possible.  Do the branches take precedence over the multiple bonds, as for example, 2-methyl-3-pentyne?  If the counting of the carbons for this molecule is flipped so that the triple bond is lower in number, it would be 3-methyl-2-pentyne.  Is the first way correct?


texts: How does mass spectroscopy of nicotine work?

texts:
Take this nicotine molecule:

And this mass spectrum:

I'm not sure how to explain all the peaks.

This might explain the peak at 42:

But can this peek als be explained by something else in the molecule?

Like the decomposition of the ring with the double bonds:

This might explain the peak at 84:

And I'm clueless on the peak at 133


texts: Which oxygen is favored for protonation when hydrolysis of an acetal occurs?

texts:
My question is about which oxygen is favored for protonation in acidic conditions. So, R1 and R2 are different in the following diagram (for example, one is propyl but the other is ethyl). I looked up my organic chemistry materials, but only symmetric cases (R1 = R2) were suggested.

I believe that there will be a competition between two pathways, and it is related to the stability of intermediate in the reaction mechanism. But how can I estimate which pathway is favored or the stability of the intermediates?


texts: Chemical change - decomposing single element?

texts: If I had a molecule of a single element such as atmospheric oxygen O2, and I added energy to decompose it into two separate oxygen atoms (i.e. O2 + ENERGY –– 2 O ) is this a chemical or physical change?


texts: Is there a method for finding the net-ionic equation?

texts:
I truly don't understand the method for finding the net-ionic equation for a reaction. It is not clear to me how you should decide what the products are, especially when there are multiple possibilities.

Example:

  Excess potassium cyanide solution is added to aluminum bromide solution.

The first thing that came to mind for the molecular equation is:

$\ce{3KCN\+AlBr3 \to 3KBr\+Al(CN)3}$

But apparently the correct molecular equation is:

$\ce{6KCN\+AlBr3 \to 3KBr\+Al(CN)6}$

I see no good reason why the one I thought of is incorrect. And to get the net ionic equation, the spectator ions are $\ce{K+}$ and $\ce{Br-}$. But why should I assume the solution is aqueous?

Another example:

  Chlorine gas is bubbled through dilute sodium hydroxide.

Well its easy enough to get the reactants:

$\ce{Cl2\+NaOH \to ?}$

What first comes to mind is $\ce{Cl2\+2NaOH \to 2NaCl\+Cl2O\+H2}$

But the correct molecular equation is $\ce{Cl2\+2NaOH \to 2NaOCl\+NaCl\+H2O}$

What should be the thought process for arriving at the correct answer here. I am truly lost.

Another example:

  Lithium oxide reacts with sulfur dioxide.

I recognize this as a synthesis reaction. However how can I predict if the product is lithium sulfite or lithium sulfate?


texts:
I would like to ask how I could derive the entropy change $dS$ for a van der Waals' gas.
I think I would need to use the total differential of entropy and then use the Maxwell relation shown below.
Firstly, I would write down the total differential for $S$.
$$dS = \left(\dfrac{\partial S}{\partial V}\right)_T dV + \left(\dfrac{\partial S}{\partial T}\right)_V dT$$
Then I would substitute $\left(\dfrac{\partial S}{\partial V}\right)_T$ by $\left(\dfrac{\partial P}{\partial T}\right)_V$ and $\left(\dfrac{\partial S}{\partial T}\right)_V$ by $\left(\dfrac{C_V\ \partial T}{T\ \partial T}\right)$.
But then I am stuck. May anyone gives me some hints on how to derive $dS$ for a van der Waals' gas?


texts: How to rationalise the drop in pH when excess aluminium nitrate is added into an aqueous ammonium solution?

texts:
Consider the flowing reaction
  $$\ce{NH3 + H2O <=> NH4+ + OH-}$$
  Explain “when excess powdered aluminium nitrate is added to the reaction mixture and the $\mathrm{pH}$ value of the solution is lowered.”

There are 3 questions that confuse me:

When $\ce{OH-}$ is removed by aluminium(III) ions, $\ce{NH4+}$ is produced, which is acidic. In that case, is the decrease in $\mathrm{pH}$ due to the formation of $\ce{NH4+}$ ions or because of the removal of $\ce{OH-}$ ions?
When $\ce{OH-}$ is removed, according to $K_\mathrm{c} = [\ce{H+}][\ce{OH-}]$, the $\ce{H+}$ ions will increase since $K_\mathrm{c}$ is a constant value. Hence, the pH decreases. Is is a correct explanation to the drop in $\mathrm{pH}$ when $\ce{OH-}$ ions are removed?
Does addition of excess aluminium nitrate mean that the equilibrium reaction will go to complete and there is no any ammonia at the end?


texts: Is there any relationship between ultrasonication and temperature

texts: In chemistry we use ultrasonication for cleaning vessels ,synthesis of chemical compounds (sonochemistry) etc.I know that during ultrasonication high temperature and pressure is formed "locally".But I want to know whether there is any equations which relates between ultrasonication and temperature .


texts: I read a news article recently about a cloud of ruthenium-106 being released over Europe. The article mentioned one of the uses for this specific isotope is in fuel cells for satellites. I tried to do some research but i couldn't find information on a fuel cell that used this specific isotope. What kinds of fuel cell or power generator use ruthenium-106?


texts: Will this SN1 reaction result in an equilibrium situation?

texts:
I'm trying to prove the rate law of an $S_N1$ reaction by measuring the rate of it, when I vary the concentrations of my reagents. However, I believe the reaction of the experiment I have designed will result in an equilibrium. The reaction is as follows:

$$\ce{t-BuOH + HCl -> t-BuCl + H2O}$$

I chose this reaction based on the theory outlined in this website, http://www.masterorganicchemistry.com/2015/02/27/making-alkyl-halides-from-alcohols/

Pretty simple. However, will the $S_N1$ solvolysis reaction, in the opposite direction occur and thus hinder my attempt to measure the rate of the reaction?


texts: Is it possible to build or embed the SMILES representation of compounds in 3D?

texts:
I would like to know if there is a proper way to get the 3D information from the SMILES string of a molecule.

Is there a standard way to embed a SMILES string in 3D space?
Are there other representations of compounds which include their spatial information too?


texts: Why can Wurtz reaction be not used for preparation of alkanes with odd number of carbon atoms?

texts: My book says that Wurtz reaction can not be used for preparation of alkanes with odd number of carbon atoms. Why is it so?


texts: What happens to dissolved ions when an aqueous solution evaporates?

texts: I'm working on a chemical design project where zeolite crystals containing $\ce{Na+}$ cations is ion-exchanged via an aqueous solution of $\ce{AgNO3}$, $\ce{Cu(NO3)2}$, and $\ce{Zn(NO3)2}$, also containing $\ce{HNO3}$. The solid product now containing $\ce{Ag+}$, $\ce{Cu^2+}$, and $\ce{Zn^2+}$ cations is removed from the solution and dried. I expect the remaining $\ce{Ag+}$, $\ce{Cu^2+}$, $\ce{Zn^2+}$, and $\ce{Na+}$ will precipitate with available $\ce{NO^-3}$ as the water evaporates, but what will happen with any remaining $\ce{NO^-3}$ anions? Can they react with water or air to form any solid/gaseous products?


texts: Are Daniell cells rechargeable (reversible)?

texts:
I know that the Daniell cell is a primary cell and the reaction occurs as:

$$\ce{Zn -> Zn^{2+} + 2e^-}$$
$$\ce{Cu^{2+} + 2e^- -> Cu}$$

However, I do not know if we can reverse the reaction by applying a potential greater than $1.1~\mathrm{V}$. Also, please give the reason if it is not

P.S.: Please do not confuse this question: Why can't a primary cell be recharged?

I asked it as neither the above link nor the internet could give me satisfactory answer.


texts: Explanation of certain chemical bond diagrams

texts:
Here's a "simple" bond diagram of 1,1,1,2-Tetrafluoroethane which I believe is a Lewis structure:

OK, that's easy enough - four bonds from each carbon atom, and each fluorine atom having one bond.

Here are some more "complicated" bonds which I have yet to do in my high school chemistry class, so I don't understand how to interpret them.

Here's caffeine:

And chloroform:

How would I go on interpreting these diagrams? Or is there missing information?

Image sources: Wikimedia


texts: What is the symmetry of the cuboctahedron (FCC metal)?

texts:
The background to this is that I've recently given a tutorial wherein we had to go through the determination of point groups for atoms in various lattices (BCC, FCC/CCP and HCP). BCC and HCP, I have no problem with. However, I've now acquired a copy of the lecturer's "official" solutions and there's a bit of discrepancy with the FCC, that I can't fathom: I get an $O_\mathrm{h}$ point group, while he gives a $D_\mathrm{3d}$ point group.
Here goes:
The coordination geometry of an atom in the FCC structure (assuming one atom/lattice point and only one species of atom, as in an FCC metal) is a cuboctahedron:
,
By my reckoning we have $3$ $C_4$ axes, one through each pair of square faces, and a $C_3$ through each pair of triangular faces.
Following the classic flowchart:

The number of high-symmetry rotational axes is surely enough to exclude $D_\mathrm{3d}$ already?
The only thing that makes me think that the lecturer hasn't just made an error is this line from the Wikipedia page for the cuboctahedron:

With $O\mathrm{h}$ symmetry, order $48$, it is a rectified cube or rectified octahedron (Norman Johnson).
With $T_\mathrm{d}$ symmetry, order $24$, it is a cantellated tetrahedron or rhombitetratetrahedron.
With $D_\mathrm{3d}$ symmetry, order $12$, it is a triangular gyrobicupola.

This is no doubt due to deficiencies in my understanding of group theory, but I don't understand how the same shape can simultaneously have multiple point groups, nor how you would select which one is relevant to a particular analysis.


texts: Why is kerosene preferred over other non-polar solvents to store sodium in?

texts:
I think we all heard this again and again in our early schooling days:

  Sodium is always stored under kerosene so that it doesn't react with air, and corrode itself.

But lately I've been wondering, why kerosene? Why not benzene? Why not cyclohexane? Why not $\ce{CS2}$? What is that makes kerosene preferred?

Is kerosene the cheapest non-polar liquid available? Or is there any particular reason that I'm not aware of?


texts: How to prove that entropy is a state function?

texts:
Consider the following steps:
\begin{align}
\mathrm{d}U &= \mathrm{d}q - p\,\mathrm{d}V\\
\mathrm{d}U &= C_V\,\mathrm{d}T\tag1\\
\end{align}
Side question: Is equation $(1)$ only true for a perfect gas or all substances?
\begin{align}
C_V\mathrm{d}T &= \mathrm{d}q - p\,\mathrm{d}V\\
\mathrm{d}q &= C_V\,\mathrm{d}T + p\,\mathrm{d}V\\
\end{align}
Divide by T:
$$\mathrm{d}S = \frac{C_V}{T}\,\mathrm{d}T + \frac pT\,\mathrm{d}V$$

The proof requires a substitution of $\frac pT=\frac{nR}V$ because when it is then differentiated with respect to $T$ it equates to zero and so does $\frac{C_V}{T}$ when it is differentiated with respect to $V$ which shows it is an exact differential. However, if you do not make the substitution you do not get zero so the two differentials do not equal each other. This would suggest that entropy is not a state function. Am I going wrong somewhere?


texts: formation of a compound due to photo-isomerisation

texts:
I was reading through a topic called photoisomerism, where I read that when a molecule is hit by a photon it changes its structure to a more stable one. Is this a one-way reaction, or is it reversible (as in is it an equilibrium)? If it was an equilibrium, what was stopping it from forming before the photon hit it?
update
since the question was a bit ambiguous, my question was after the light that was shone was removed, if the equilibrium still exists, then what was the hindrance that did not allow such equilibrium to exist before the light was shone. (i am not sure if such a reaction exists, my question is more of a hypothetical question, asking if such a reaction exists then what was hindrance from reaching equilibrium (that was achieved after the shone light was removed)  before the light was shone)(if no such reaction can exist please also explain why so)


texts: Why is so different the temperatures of a compressed gas compared to a liquid/gas mixture of the same fluid and they are both at the same pressure?

texts:
Why does $\ce{C3H6}$ gas when compressed (in a centrifugal compressor) comes out with a pressure of $\pu{16 bar}$ and $\pu{90 °C},$ and when it is a mixture of $\ce{C3H6}$ liquid/gas stored inside of a vessel reaches also the $\pu{16 bar},$ but at a lower temperature of around $\pu{38 °C}?$

I know that when it is a vessel with stored $\ce{C3H6}$ liquid, some part of the liquid will vaporize until it reaches the equilibrium with the ambient temperature (vapor pressure). I know that if the vessel is exposed to a ambient temperature of $\pu{38 °C}$ and if has enough $\ce{C3H6}$ liquid to vaporize the equilibrium will be reach at a pressure of $\pu{16 bar}.$

But what I cannot understand is why if it is only gas and if I compress the gas to $\pu{16 bar},$ why does it come out with a temperature of $\pu{90 °C}?$ Shouldn't it come out with the same temperature of $\pu{38 °C},$ like the vessel?

If anyone at least could give me the subject/effect/topic so I can study just to get an answer to this question, I would be very grateful.

Note: This isn't a homework question. I work on a LPG storage facility and the other day I started thinking about this, but I cannot understand why this happens.


texts: Are difluorine and hydrogen chloride considered isoelectronic?

texts:
Why are $\ce{F2}$ and $\ce{HCl}$ not considered isoelectronic? Both have 18 electrons.

$\begin{align}
\ce {H}\!:&\  \ce{1 e-}\\
\ce{Cl}\!:&\  \ce{17 e-}\\
\ce{F}\!:&\  \ce{9 e-}\\
\end{align}$

$\ce{F2} \implies 2 \times \ce{9 e- = 18\ e-}$

$\ce{HCl \implies 1 e- + 17 e- = 18 e-}$


texts:
I was really surpised to see that strontium is apparently more common than sulfur in the earth's crust, since it occurs in what I thought were pretty rare minerals.

Sulfur which seems to be everywhere such as in volcanoes, in the atmosphere as sulfur dioxide, in coal deposits, and is even found elementally in large lenses.

Sulfur seems to be ubiquitous. For example, fool's gold, iron pyrite is iron sulfide and it can be found in practically any stream bed. I would be hard pressed to find strontium in my local stream beds. And, of course, this sulfide is only one of many commonly sulfides.

Is strontium really more common than sulfur? It seems implausible. What is the basis for this claim?


texts: What structural property creates stickiness?

texts:
Recently, me and my mom parked her car in a spot reserved for customers of a super expensive shoe store while going to get some also fairly expensive drinks at Starbucks. When we came back, an employee at the shoe store put a sticker on my mom's window warning us he could have us towed and ticketed. Clearly they're bitter about having no customers. This sticker left a whole bunch of sticky residue on the window.

I knew from experience that water wouldn't get the job done, so I put some canola oil on a paper towel and sure enough the sticky residue dissolved into the oil and I could see it dissolved in the liquid on the paper towel.

This got me thinking. Is it generally true that a sticky substance will be nonpolar? Furthermore, is there a generalization which can be made about structures which are sticky on a macroscopic level?

My only guess is that sticky substances are usually viscous too which leads me to believe that there must be a lot of VDW/dispersion interactions involved in those materials because I understand that high viscosity is related to strong intermolecular attractions. Although, the viscosity argument doesn't work for sticky solids (unless you say that a sticky solid is actually just an extremely extremely viscous liquid).


texts: I underestimated this question and just compared the carbocation stability of all the compounds (after removal of chloride via $S_N1$) and got the order D>C>B>A... but my answer is incorrect, what am I missing out?


texts: Displacement by more electropositive metal in non aqueous environment

texts:
The more electropositive element should displace metal from it's salts' solution. This can be seen in reaction of copper salts with iron. But, if you try using for example potassium metal as the more electropositive metal in a displacement reaction you don't get a result since potassium will react with water before it has a chance to displace much of the other metal.

What makes dissolution in water favour displacement by the more electropositive metal, even if calculated gibbs free energy for the reaction would be positive? Is it the higher strength of hydrogen bonding of the more electropositive metal, or is it the lack of lattice energy of the salt that otherwise needs to be overcome?
This will depend on the answer to the first question, but is it possible to actually displace, say, Calcium with Potassium metal from any of it's salts provided that this salt is soluble and the solvent is inert towards Calcium and Potassium metal? If you had to do this in reality, what would you use, perhaps a phase transfer catalyst?

I imagine that if it's mainly the lattice energy making the difference one should be able to just use a different solvent, as it would be only important to dissociate the salt


texts: Why is the radial distribution at the nucleus 0 but not the radial wave function?

texts:
The modulus squared of the radial wave function gives the probability of finding an electron in an infinitesimal volume dv. On the other hand, the radial distribution gives the probability of finding an electron in a shell of radius r and thickness dr, or in other words, the probability of finding an electron at a radius r.
I know how the radial distribution is derived and it being 0 at the nucleus makes sense mathematically but not physically. The radial distribution being 0 at the nucleus means that an electron cannot be found in a shell of r=0 & thickness dr ( a sphere of radius dr), but we already know from the radial wave function that there is a non-zero probability of finding an electron in an infinitesimal volume at the nucleus. These results appear to contradict each other.
Is there something wrong in my physical interpretation of the 2 functions?


texts: Oxidation of formate ion by peroxydisulfate in water solution: Why are there "strange" kinetics?

texts:
As you can see, the first step is the slowest, but by using the rate-determining step approximation you wouldn't arrive at the correct rate law which is:
$r=k\ce{[HCOO^{−}]}^{1/2} \ce{[S2O8^{2−}]}$.
The first reaction is very slow, so most of the peroxydisulfate is consumed in the third reaction. The correct rate law can be obtained by applying the steady-state approximation to the two radical species.

WHAT does this mean?
So, why is the rate constant NOT according to the slowest step?

Why it is not just $k\ce{[S2O8^{2-}]}$?


texts: How do you determine a chemical formula given the molecule's crystal structure?

texts: How do you determine the chemical formula of a compound given its crystal structure?