texts: Why does dry boiling discolor steel cookware?

texts:
I have a stainless steel kettle that I let boil dry. That is, I left it on a hot coil burner with nothing in it, and noticed a few minutes later that the bottom was red hot and smoking. To make matters worse, I panicked and quenched it with cool water.

Both the inner and outer surface were left discolored with various shades of yellow and purple. This seems to be a known consequence of overheating, but I can't find an explanation of what actually happened.

I understand why heat (especially combined with quenching) would warp the metal, but why would it cause discoloration (that persists after the metal has cooled)?
After hunting around, I saw several suggestions that boiling white vinegar could remove the discoloration, and to my suprise, it worked pretty well. Why does this work?


texts:
Background: Henry's law states that:

  At a constant temperature, the amount of a given gas that dissolves in
  a given type and volume of liquid is directly proportional to the
  partial pressure of that gas in equilibrium with that liquid.

And mathematically:

$$S=k\times p_{\text{gas}}$$
where $S$ is solubility, $k$ is Henry's constant and $p$ is the partial pressure of the gas.

Question: I want to calculate the oxygen solubility down the sea. Is partial pressure the atmospheric one? If it is so, we have same solubility on all sea deepness, which is contradictory. What am I missing?

Edit

I know this law can be thought as depending on this equilibrium:

$$\ce{A {(g)} <=> A {(s)}}$$


texts: If some particles of liquid in a solution convert to vapour then why can't some liquid particles convert to solid?

texts:
I was reading about the vaporisation of liquid when I came across the following statement.

  The average energy of the particles in a liquid is governed by the
  temperature. The higher the temperature, the higher the average
  energy. But within that average, some particles have energies higher
  than the average, and others have energies lower than the average.Some
  of the more energetic particles on the surface of the liquid can be
  moving fast enough to escape from the attractive forces holding the
  liquid together. They evaporate.

Now if some particles have energies lower than the average, then why don't they convert into solids in the same way the particles with higher energies convert to gases.

If we cover a vessel filled with water with a plate, after some time, we observe droplets of water accumulated at the plate because of vaporisation of water. Why don't we observe any changes that show liquid particles converting to solid?


texts: What does electrolysis of Cu(NO3)2 produce?

texts:
I have read that $\ce{Cu}$ is deposited at the cathode when copper (II) nitrate is electrolyzed. However, when I looked at reduction potentials, the reduction of nitrate to $\ce{NO}$ and $\ce{H2O}$ $(0.96\rm~V)$ is more spontaneous than the reduction of $\ce{Cu^2+}$ to $\ce{Cu}$ $(0.34\rm~ V)$. So why is Cu formed rather than NO?

What I read doesn't mention what material the electrodes are, would it make a difference if they were inert or made of Cu? I supposed if they were made of Cu, then the Cu will be oxidized and the $\ce{NO3-}$ reduced:

$$\ce{Cu + NO3- -> Cu^2+ + NO + H2O} {\rm \qquad \qquad(unbalanced)}$$

However this has a positive voltage of $1.30$, so why would electrolysis even be necessary?

If the electrodes were inert, then there were be no Cu to oxidize, so what would happen? Would the water be oxidized? $$\ce{2H2O -> 4H+ + 4e- + O2} \\\ \rm V=-1.23$$


texts: Where can I find a cannabinoids profile of hemp strains?

texts:
For my web article, I need to find out the content of individual cannabinoids in hemp strains, specifically for Kompolti, Carmagnola and Purple Haze. I mean the content of all the components, not just THC and CBD.
Do you know of any website that provides this information?
Thank you for answer


texts: Degree of dissociation of weak electrolyte at infinite dilution

texts: Why the degree of dissociation of weak electrolyte is 1 at infinite dilution and how do we get the result? Like I know that at infinite dilution the concentration of solution is 0 but what does that have to do with degree of dissociation, secondly in oswald's law of dilution we already assume that dissociation is almost negligible so we can't obtain the result from that also


texts: Preparing a solution of hydroxylamine hydrochloride in HCl, struggling

texts:
I recently came across a paper with a methodology description i cant seem to get the grasp of.

I need to make a particular solution for Fe extraction. The protocol's description is from this paper.

  Take a 100 μL aliquot of X (a soil sample previously mixed with 0.5M HCl) and mix it with 2 mL of a solution of 0.25M hydroxylamine hydrochloride in 0.25M HCl and incubate at 60 °C.

What I don't understand is how to make the solution when the volume of the two compounds is not specified? Does it imply that the 2mL of solution is made up of equal parts (1mL) of 0.25M hydroxylamine HCl and 0.25M HCl? Any help is highly appreciated. Thanks a lot in advance!


texts:
I have to questions regarding the conformations of carbohydrates.

There are 38 different conformations for an aldohexose or ketohexose, including $\alpha$ and $\beta$ anomers, namely 2 chairs, 6 boats, 6 skew-boats, 12 half-chairs and 12 envelopes.

Each of these 38 conformations can have 729 different isomers ($5~\ce{OH}$ and $1~\ce{CH2OH}$) because of dihedral and tetrahedral angle ($3^6$ isomers, 3 (gg, gt, tg for each dihedral angle)).

For example, glucose has $2~(\alpha~\text{and}~\beta~\text{anomers}) \times 38 \times 3^6 = 55404$ conformations.

Is this calculation correct?

The nomenclature of the 38 different conformations is still not clear to me, which leads me to my second question.

For chair form, the literature uses $\ce{^4C_1}$ and so on. But I'm not sure, which 4 carbon constitutes the reference plane.

Similarly other used terms are $\ce{^{3,O}B}$ for boats, $\ce{^3S_5}$ for skew conformations.

Can anyone please explain how to interpret these symbols?


texts: Why is the boiling point of sugarcane juice lower than the boiling point of water?

texts:
As the boiling point is a colligative property, one would expect that the boiling point of sugarcane juice should be higher than pure water because Sugarcane juice contains water (75–85%), non-reducing sugars (10–21%), reducing sugars (0.3–3%), organic substances (0.5–1%), inorganic substances (0.2–0.6%) and nitrogenous substances (0.5–1%)1. However, the boiling point of sugarcane juice is only 91-95°C [2]. Are there any chemistry theories that can explain this drop in boiling point?
[3]
1 Sreedevi, P., Jayachandran, L.E. & Rao, P.S. Browning and bioactive composition of sugarcane juice (Saccharum officinarum) as affected by high hydrostatic pressure processing. Food Measure 12, 1962–1971 (2018). https://doi.org/10.1007/s11694-018-9811-7
[2] Tiwari, G. & Prakash, Om & Kumar, Subodh. (2004). Evaluation of convective heat and mass transfer for pool boiling of sugarcane juice. Energy Conversion and Management. 45. 171–179. 10.1016/S0196-8904(03)00143-2.
[3]: Canilha, Larissa & Chandel, Anuj & Milessi, Thais & Antunes, Felipe & Freitas, Wagner & Felipe, Maria & da Silva, Silvio. (2012). Bioconversion of Sugarcane Biomass into Ethanol: An Overview about Composition, Pretreatment Methods, Detoxification of Hydrolysates, Enzymatic Saccharification, and Ethanol Fermentation. Journal of biomedicine & biotechnology. 2012. 989572. 10.1155/2012/989572.


texts:
What is the Lewis structure for $\ce{MgB2}$? I just read that it is a superconducting material (up to a relatively high critical temperature, 39 K) and am wondering if this has to do with its electronic structure.

In $\ce{MgB2}$, $\ce{Mg}$ has 2 valence electrons and each $\ce{B}$ has 3 for a total of 8. I know that $\ce{B}$ is "satisfied" with 6 valence electrons, but I don't see how to get 8 around $\ce{Mg}$ with 6 on each $\ce{B}$.


texts: Pattern to determine the maximum ionic charge for transition elements?

texts:
According to my textbook, main group elements follow a simple pattern when determining their maximum ionic charge. The maximum cationic charge is always equivalent to their main group number (group number minus 10 for the groups 13 to 18 according to the new IUPAC terminology) while the maximum anionic charge is eight minus that number.

For example, the maximum charge of an aluminium cation (third main group) would be $+3$, the maximum charge of a sulfur anion (sixth main group) would be $-2$.

Some elements form multiple ions, but no charge will be larger than determined by the above method

Is there a similar method or pattern to determine maximum charges of transition metals? Why or why not?


texts: Can a more electropositive metal replaced by a less electropositive one?

texts: I read from this reference that rubidium is extracted by reduction of its chloride with calcium or sodium. How is it possible?. Their electronegativities are much higher than rubidium. I think rubidium is far more reactive than either and can not be replaced from its salt by any other metal except cesium. While I have also read that cesium itself is replaced from its chloride by magnesium refer to this. How can a less electropositive metal replace a more electropositive metal from its salt? Are there some factors besides electronegativity, reduction potential and other reaction skills?


texts: Do all sigma bonds are stronger than pi bonds?

texts: Many textbooks refer that sigma bonds are stronger than pi bonds . But each individual bond ( between different atoms) have different bond energy. So how we know for sure that every possible sigma bond is stronger than every possible pi bond ?


texts: Does scotch tape only use van der Waals forces?

texts: Does it also make use of covalent bonds to stick to surfaces?


texts: Calculating rate constant and order of a multi-step reaction

texts:
If I’m given a multi-step reaction, say:

$$\ce{2 NO + O2 -> 2 NO2} \label{rxn:R1}\tag{R1}$$

with the following mechanism:

$$
\begin{align}
\ce{NO + O2 &<=>[$K$] NO3} &\quad &\text{(fast)} \label{rxn:R1.1}\tag{R1.1}\\
\ce{NO3 + NO &->[$K_1$] NO2 + NO2} &\quad &\text{(slow)} \, , \label{rxn:R1.2}\tag{R1.2}
\end{align}
$$

then will the rate constant of the whole reaction be equal to the product of the equilibrium constant of the fast reaction and the rate constant of the slower reaction?

Because this is how they made us solve it at my institute:

$$K_\mathrm{eq} = \frac{[\ce{NO3}]}{[\ce{NO}][\ce{O2}]}$$

$$
\begin{align}
\text{Rate of slow step \eqref{rxn:R1.2}} &= K[\ce{NO3}][\ce{NO}] \\
&= KK_\mathrm{eq}[\ce{NO}][\ce{O2}][\ce{NO}] \\
\Rightarrow\text{Rate of reaction} &= K'[\ce{NO}]^2[\ce{O2}]
\end{align}
$$

where $K' = KK_\mathrm{eq}$, and the order is $2 + 1 = 3$.

So, is $K'$ the rate constant for the overall reaction? And is the reaction a 3rd order reaction?


texts:
Supermarket plastic bags are made of high density polyethylene, and I am interested in the decomposition products at high temperature: what type of compounds are released and how dangerous are they? I am interested in a situation where one has placed some kind of heated food inside one of these plastic bags.

The question is, are harmful compounds from the plastic bag passed into the food (food is hot, like baked bread) contained inside the plastic bag?


texts: Effect of substituents on aniline C-N bond length

texts:
Which compound has larger $\ce{C-N}$ bond length, 4-aminobenzaldehyde (1) or aniline (2)?

I think it's the second compound. $\ce{-CHO}$ is an electron withdrawing group. This means the electron density of the ring decreases. So the carbon attached to nitrogen becomes more electronegative. Hence its p-character decreases and the $\ce{C-N}$ bond length decreases.


texts:
I have this confusion regarding the statement of Raoult's Law. It states that

The partial pressure of each component of an ideal mixture of liquids is equal to the vapour pressure of the pure component multiplied by its mole fraction in the mixture.

Does mole fraction in the mixture mean the combined liquid-vapour mixture or only the liquid which is left after evaporation on attaining equilibrium?
I had this problem in my textbook, one mole of two volatile substances each is mixed. Pure pressures of both of them are given. Should I just use mole fraction as one-half? Aren't some of the moles gonna go into vapour phase?


texts: Removal of electrons from orbitals doubt

texts: I recently encountered a question asking whether [PtCl4]2- has square planar geometry. I know that Pt has an electronic configuration of [Xe] 5d9 6s1, in the given compound Pt2+ is there, so the E.C will be [Xe] 5d8 . But I'm confused whether Pt2+ will have four pairs of electrons or three pairs of electrons and two unpaired electrons in the 5d orbital. It seems like the latter should be true because paired electrons may be harder to take out. If that is true, is it always true as a general rule that unpaired electrons are always taken out instead of paired ones if both types are there (during the formation of the oxidised form of the element)?


texts: Which one is the best notation for sodium acetate

texts:
I have seen two different notations for sodium acetate. The first one is:

$$\text{NaCH}_3\text{COO}$$

The second one is:

$$\text{CH}_3\text{COONa}$$

Now I'm confused, which one is the best to use?


texts:
I have a 2% solution of Zinc sulfate in water (in heptahydrate form) that I want to turn into 4% solution instead of having to buy 4% solution separately.

Would heating it to 100 degrees Celsius and waiting for extra water to vaporize be the right way to do it?

Thanks.


texts: Connection between Gibbs Energy of Formation and Gibbs Energy of Mixing

texts:
Recently I found the following formula, which I cannot verify to be correct. Since I found this formula in several publications I assume that it is correct but I don't know why.

First there is the Gibbs Energy of Formation $$\Delta_fG$$ and second the Gibbs Energy of Mixing $$\Delta_mG$$
The formula I found says, that $$\Delta_mG = \frac{\Delta_fG^{\circ}}{N}$$ where N is the number of particles. I am not sure if this is really N or n (amount of substance). Have anyone seen this formula and/or can explain why it is valid/how it can be derived?

Thanks!

Edit:

Indeed, my problem is also in the frame of binary alloys. Consider the reaction $$2A + B = A_2B$$ which is performed in an electrochemical cell (emf measurement). Then $$\Delta_fG^\circ = -zFE$$ because the reactants are elements and A is the active species. So far this should be correct. In this context the formula in question reads as follows $$\Delta_mG = \frac{\Delta_fG^\circ}{3}$$

The full definition of the Gibbs Energy of Mixing is $$\Delta_mG = x_A RT\ln{a_A}+x_B RT\ln{a_B}$$

Unfortunately, I cannot give more detail, because I don't understand the formula. :)


texts: I have calculated the Rf values for 6 samples. How do I determine which is really Sriracha ?


texts: Ring chain tautomerization of hydroxyacetone

texts:
My chemistry textbook says that hydroxypropane-2-one and 1,2-epoxy-2-hydroxypropane are ring chain tautomers, but it did not mention the steps for conversion of one into the other. I tried to figure them out but got stuck.

My attempt:


texts:
Blood stain on cotton t shirt.How exactly does hemoglobin connect to the fabric? The blood stain if washed in warm water can become very long lasting,being able to remain after many washing cycles.

From chemical perspective,how does it stick to the cellulose based fabric as found in cotton t shirts?


texts: What are the intermolecular forces between polychloroethylene?

texts: Does polychloroethylene have only van der Waals/London forces between its molecules? Surely, if all the chlorine atoms are on one side, due to the fact that chlorine is more electronegative than carbon, shouldn’t it have permanent dipole-dipole forces?


texts: What general uses do beta-lactam functional groups have?

texts:
I am currently working on a mechanistic study that deals with stereoselective $\beta$-lactam formation. I am well aware that there is a class of antibiotics, that involve this particular functional group. However, the wikipedia article of this compound class does not offer very much to continue, apart from the antibiotics.

Are there any other uses of the $\beta$-lactam moiety in general, apart from drug design?

I would like to be able to view my research in a broader scope. Since my part is more focussed on the reaction mechanism of the synthesis, I have not been too much concerned about the main purpose of this particular functional group, yet. This is of course apart from the obvious drug design process. For me this is just a question of interest.

As I am resurrecting this question, I am in particular looking for some interesting publications about the above mentioned question. However, I am willing to recognise, that the most common use is in drug design. If someone from this area of expertise could provide a source as a starting point for more research in this area.


texts:
If I were to buy/build a large still, that was air tight, and could hold a vacuum, and filled the reservoir with vegetable glycerin (which has a boiling point higher than the majority or desired organic compounds) and I made the atmospheric pressure inside less than normal atmospheric pressure, could I distill chemicals out of organic matter without altering them? Such as distilling willow bark to get an aspirin containing solution, or distill mint leaves without changing the chemical composition of the medicinal compounds in the plant/organic matter?

This could be a cool project. It would enable us to explore further into natural medicine. But would this procedure work?


texts: Could you explain what is unit of  molar conductivity along with derivation


texts: Water is a polar solvent, but in the supercritical fluid state, it is much less polar, I presume because of the cleavage of hydrogen bonds. On the other hand, carbon dioxide is non-polar, but as a supercritical fluid it is more polar. Why is this so?


texts: Fractional Bond Order - How to Visualize?

texts:
Consider nitric oxide, which has a real bond order of 2.5, contrary to what this UC Davis rendering might imply:

What's the best way to visualize a molecule with a fractional bond order? What exactly is "half a bond"? The electron spends half its time participating in bonding and the other half of the time as a lone electron on nitrogen?


texts: Suggestion for a Synthesis of Paracetamol — plausible?

texts:
I have seen a number of different plausible syntheses for paracetamol but they suffer from problems such poor regioselectivity of aromatic substitution (usually when nitrating phenol getting a mixture of undesired ortho and desired para). However, is the following not a plausible synthesis?

Take aniline (I believe it's commercially available but can be synthesised from mononitration then reduction).
React with acetic anhydride to make the amide — still ortho-, para-directing and mildly activating and the directing effects are not acid sensitive as in aniline.
Do a Friedel–Crafts acylation with the an acyl chloride.
React with hydrogen peroxide and sodium hydroxide to get paracetamol via a Dakin reaction.

Of course the acylation will suffer a little with regioselectivity issues but I feel like it will suffer less as the amide group is larger than a hydroxyl so favours para on steric grounds more strongly and is thus a better solution than nitration of phenol and subsequent reduction.

Nitration of phenol then reduction and reaction with acetic anhydride is the most common hit on google so I assume it's the most common method. But what's wrong with what I have suggested?


texts: Oxidation state of the sulfur atoms in the thiosulfate Ion

texts: What are the oxidation states of the two inequivalent sulfur atoms of the $\ce{S2O3^{2-}}$ molecule? For all I know is that Lewis Structure does matter in most of the cases.


texts: Shouldn't weak acids act as strong ones in alkaline solutions?

texts:
A weak acid in water dissociates reversibly as follows:

$$\ce{XH <=> X- + H+}$$

A strong base is one which dissociates completely.

Now, let's assume we're doing acid-base titrations, adding a weak acid to a strong base, trying to arrive at the titration curve.

My question is mainly why the $\mathrm{pH}$ at the equivalence point isn't $7$. Intuitively, it makes sense, one dissociates fully while the other doesn't. But if you dig into it a bit deeper you realise that that answer is incomplete.

Bear with me. You add the weak acid to the strong base until you reach the equivalence point. The strong base dissociates completely while the acid establishes an equilibrium as described above. However, thinking about it you realise that at no point should this be possible. An $\ce{OH-}$ ion from the base quickly reacts with any H+ ions produced meaning that $[\ce{H+}]$ is always near zero, meaning that more and more of the weak acid needs to dissociate to establish equilibrium. However, the $\ce{H+}$ concentration will always be 0 as any hydrogen ions are snapped up meaning that the acid will completely dissociate before it has a chance to establish equilibrium, at which point all of the $\ce{OH-}$ ions will also have been neutralised. The $\mathrm{pH}$ of this resulting solution should in other words at that point be $7$, because the acid, even though it's weak, acts as a strong one in an alkaline environment.

This however I know isn't correct. What's the issue with my logic above?


texts: Can 2‐chloropropane and acetyl chloride give the iodoform test?

texts:
Can $\ce{CH3-CHCl-CH3}$ and $\ce{CH3COCl}$ give the iodoform test?

I thought $\ce{CH3COCl}$ having the keto-methyl group would show the iodoform test, while $\ce{CH3-CHCl-CH3}$ will not since it's not a secondary alcohol but an alkyl halide.


texts: According to the Molecular Orbital Theory, what makes a compound aromatic?

texts:
For example, benzene has 6 $\pi$ electrons. Which means the p orbitals will be occupied, and only the bonding molecular orbitals.
But 1,3-cyclopentadiene has 4 $\pi$ electrons, which means 2 of the 3 molecular bonding orbitals will be occupied. Why does this make it non-aromatic?


texts: What is meant by electrons moving to lower potential energy?

texts:
I am currently learning about chemical bonds in chemistry, and came across somebody who wrote this (source):

"Chemical bonds certainly "contain" potential energy, and the atoms want to move to a lower potential energy (become more stable).

When methane,
CH
4
, forms, the valence electrons end up in more stable (lower energy) C-H bonds.

These bonds are fairly strong, so methane is relatively inert.

However, if you add energy to the methane in the form of a flame or a spark in the presence of oxygen, some of the molecules will have enough energy to overcome an activation energy barrier.

Some of the
C-H
 bonds will break.

The electrons can then enter an even lower energy state by forming
C=O
 and
O-H
bonds rather than staying as
C-H
 and
O=O
 bonds."

What is meant by this? What does it mean when electrons enter a lower energy state, do they move to an even lower ground state?


texts: Non-existence of time operator in quantum mechanics

texts:
In quantum mechanics, there is no operator for time instead of this we  we have $\psi(t)$ which is related to $\psi(0)$.

In a book, I read that if there is an operator for time, then it will not be Hermitian".
I am not able to understand how exactly why? What is the reasoning behind this statement.


texts: Is the evaporation (liquid to gas conversion) of ethanol dependent on how full you fill it up in a sealed bottle?

texts:
It seems intuitive to think that in a bottle (which is air-tight), if you fill up ethanol (or any other volatile liquid) to very full extent, thereby leaving very little headspace, the amount of ethanol evaporated would be reduced. In contrast, if there is more headspace, then more room is allowed for ethanol vapor and hence evaporation would increase. This can also be explained in terms of the smaller increase in partial pressure of ethanol vapor per molecule evaporated with a larger headspace, thereby allowing more time before the forward (evaporation) and backward (condensation) reaction reaches equilibrium.

I would like to know if I'm on track and if not, what did I miss? I do not have the right materials to test it myself and obviously this would not be sophisticated enough to be properly studied in a scientific research (hence I cannot find a specific reference).


texts: What exactly does the term "gram atoms" mean?

texts:
The Wikipedia article on the mole states:

   The term gram-atom (abbreviated gat.) has been used for a related but distinct concept, namely a quantity of a substance that contains Avogadro's number of atoms, whether isolated or combined in molecules. Thus, for example, 1 mole of $\ce{MgB2}$ is 1 gram-molecule of $\ce{MgB2}$ but 3 gram-atoms of $\ce{MgB2}$.

Can anybody explain the difference between moles and gram atoms, and how is it that 1 mole of $\ce{MgB2}$ is 1 gram-molecule of $\ce{MgB2}$ but 3 gram-atoms of $\ce{MgB2}$?


texts:
A solution having composition $p$ (left side of graph) is cooled to just above the eutectic temperature (point $s$ is at $0.18$ $x_{\ce{Si}}$ and the corresponding tie line intersects the liquidus curve at $0.31$ $x_{\ce{Si}} $); calculate the composition of the solid that separates and that of the liquid that remains.

The liquid phase is obviously 31 % silicon and 69 % gold as given in the question. The solutions manual also gives the weight percentage of the solid phase. Using the lever rule,

$$ m_\text{solid}(0.18)=m_\text{liquid}(0.31-0.18)$$
$$ \frac{m_\text{solid}}{m_\text{liquid}}=\frac{0.13}{0.18} $$
$$ \frac{m_\text{solid}}{m_\text{solid}+m_\text{liquid}} = \frac{0.13}{0.13+0.18}=0.42$$

However, the solution manual states that the wt% of solid phase is 58 %, and that of the liquid phase is 42 %. Is the solutions manual wrong, or am I losing my mind?


texts: When 3,4-dimethyl-2,4-hexadiene reacts with HBr what is the major product?

texts:
I found out from drawing it out that there are 2 products: 4-bromo-3,4-dimethyl-2-hexene and 2-bromo-3,4-dimethyl-3-hexene. I want to know which forms most of the time.

I used the fact in allyl carbons, the double bonds will travel to the carbon-carbon single bonds to form a double bond. I also used the fact that tertiary carbocations are more stable due to sigma bonds that can participate in hyperconjugation - that is delocalization of electrons by the overlap of sigma bond orbital with an empty p-orbital on an adjacent carbon.

I would like to see some of these reactions in a lab setting, but for now I'm learning organic chemistry reactions like as if it were math.


texts: How does ammonium nitrate explode on its own?

texts:
I thought ammonium nitrate was an oxidizer that needed to be mixed with fuel to form a high explosive (e.g., ANFO). But apparently there have been accidental explosions involving just the "fertilizer". Are these explosions also detonations? What is the chemical formula for the process?
$$\ce{NH4NO3 -> ???}$$
Part of my motive for asking is the news today (Aug 4, 2020) of an explosion in Beirut. Initial reports say it was caused by "2750 tons of stored ammonium nitrate".


texts: What makes determining entropy changes theoretically so hard compared to enthalpy?

texts: It is really hard to determine the entropy change of a reaction accurately because of subtle solvent effects and a lack of standard entropies. On the other hand, enthalpy is relatively easy and through a thermodynamic cycle, it can usually be calculated. But what about our knowledge of entropy limits our ability to measure it? Without using straight empirical data, why is using force field and electronic interactions not very reliable? Many reactions face this problem, like the mixing of liquids.


texts:
What is a 'corona phase'? I have come across this term in several papers, including this one

but all I have found concerning its definition is:

  [...] synthetic heteropolymers, once constrained onto a single-walled carbon nanotube by chemical adsorption, also form a new corona phase that exhibits highly selective recognition for specific molecules...

What is the formal definition of 'corona phase'?


texts: Nomenclature of a cyclohexyl ether and locant position enumeration

texts:
As far as I know, 'ethoxy' should be given the locant '1' as it is a functional group. The compound should thus be named 1-ethoxy-2,2-dimethylcyclohexane.

However, I was told that the correct name is 2-ethoxy-1,1-dimethylcyclohexane. Can anyone please explain why this is so? My teacher explained this to me in terms of the lowest locant sum rule, which I just discovered doesn't even exist.


texts: What makes diazo compounds so unstable and explosive?

texts:
I once had an Orgo TA refer to a diazo compound as "diazo-boom-boom" (the technical term).  I have always been curious as to the reason behind the instability and reactivity.

According to Wikipedia

  Some of the most stable diazo compounds are α-diazoketones and α-diazoesters since the negative charge is delocalized into the carbonyl.  In contrast, most alkyldiazo compounds are explosive

What is it about the alkyldiazos that makes them so much more unstable?  There doesn't appear to be any bond strain or other factors.  Naively, I can say that having a resonance structure should make it marginally more stable.


texts: What causes passivity of specific metals in conc. nitric acid?

texts:
I know  that specific metals like $\ce{Pb}, \ce{Sn}$ and $\ce{Al}$ become passive in conc. nitric acid. My questions are:

Why does this happen only with conc. nitric acid, and not other conc. acids?
Why is the passivity specific to these metals? Do they have something in common or are there individual reasons?


texts:
Outline the steps involved in the following transformation: $\ce{C2H4}$ to $\ce{(COOC2H5)2}$ (diethyl oxalate).

I am familiar with the transformation of $\ce{C2H4}$ to ethyl acetate $\ce{CH3COOC2H5}$ by first converting to ethanol using water and acid, then using an oxidising agent such as $\ce{KMnO4}$ to convert ethanol to ethanoic acid and subsequently reacting ethanol and ethanoic acid together.
I'm not sure if the process needed to get to the diethyl oxalate is similar to this.


texts: How to write the rates for a bimolecular collisional dissociation?

texts:
I have questions concerning two species involved in a reaction, where one species is dissociated completely by collision with another, fairly inert species. The reaction looks like this:

NO  + N$_2$ $\xrightarrow{k_f}$ N + O + N$_2$

My understanding is that the reaction requires the N$_2$ molecule in order for the reaction to proceed. So, for the rate:

$\frac{d[NO]}{dt}$ = $-k_f [NO][N_2]$
$\frac{d[N_2]}{dt}$ = 0

Is the above expression for the rate of change for NO correct?

Second, if I want to consider there being a reverse process, what I believe I need is an equilibrium constant such that:

$K_{eq} = \frac{k_f}{k_r} = exp(-\frac{h_p-h_r}{RT}) $

Where $h$ is the enthalpy of formation, R is the universal gas constant ($8.314 [\frac{J}{molK}]$, and T is the temperature of the gas. the subscripts $p$ and $r$ refer to the products and reactants, respectively. For "naturally" occuring species, the enthalpy of formation is 0.

For this particular reaction, I looked up the enthalpy of formation for the species involved:

$h_{N_2} = 0 [\frac{J}{mol}]$
$h_N = 472.68\times 10^3 [\frac{J}{mol}]$
$h_O = 249\times 10^3 [\frac{J}{mol}]$
$h_{NO} = 90\times 10^3 [\frac{J}{mol}]$

Once the equilbrium constant has been solved for, I determined the reverse reaction rate $k_r$ by dividing my known rate $k_f$ by $K_eq$. The resulting rate then, including reverse reactions would look something like:

$\frac{d[NO]}{dt}$ = $-k_f [NO][N_2] + k_r[N][O][N_2]$
$\frac{d[N_2]}{dt}$ = 0

Is the above formulation for the reverse reaction rate, and the expression for the time rate of change of the gas correct?

Thank you


texts: Reaction rate constants for methane combustion

texts:
I can't find a rate constant or activation energy for the methane combustion reaction given by:

$$\ce{ CH4 + 2O2 -> CO2 + 2H2O}$$

Do all reactions have a rate constant? The NIST web site lists several rate constants for reactions of methane that yield other products, but none for the reaction above. Is there a known rate constant for the reaction given above?


texts: What is the difference between resonance and π conjugation

texts:
I have seen electron delocalization mentioned frequently in 2 separate contexts: resonance (ozone, carbonate / nitrate...) and π-conjugation systems (aromatic compounds).
While the 2 initially sound the same, 2 different points lead me to believe otherwise:

π conjugation requires p- orbitals to be in the same plane, whereas many compounds said to have resonance ($\ce{ClO4-}$, $\ce{SO4^{2-}}$) are not planar so resonance can't be a subset of π conjugation
All molecules with (significant) resonance have multiple equivalent stable-lewis structures (nitrate has 3, sulfate has 4...) whereas many molecules with π-conjugation do not (haxa-1,3-diene has only one "most stable" lewis structure) so π-conjugation cant be a subset of resonance

NOTE ON POINT 2: I am aware that hexa-1,3-diene has minor contributing structures, but so do all possible molecules. However, the only molecules for which resonance hybrids are used are those with multiple major contributing lewis structures.
The only intersection between the 2 concepts I find is benzene; it has 3 equivalent major contributing structures implying resonance and 6 overlapping p-orbitals lying in the same plane, implying π conjugation
I feel like I'm missing some part of the bigger picture. What's actually happening?


texts: Chemical oscillators that behave like a double pendulum

texts:
Oscillating chemical reactions such as BZ-reaction or chemical clock typically result in sequential systematic changes, most notable of which is arguably coloring. Though underlying mechanism can be extremely complicated, we always expect the same sequenced cycling set of properties. For iodine clock it's always will be

  ... dark-blue > colorless > dark-blue > colorless ...

colors that we observe. Just like ordinary pendulum. But are there oscillating chemical reactions with the non-linear outcome and "chaotic" sequences for each cycle, e.g. behaving like a double pendulum?

And if such systems do exist, can we also just use similar mathematical apparatus like a system of differential equations used for a double pendulum to describe such behavior?


texts: How do I find the oxidation number of a coordination complex

texts:
I actually know how to calculate the oxidation number for coordination complexes but some complexes like the below are giving some reistance

$\ce{[Cu(NH3)_2][Fe(H2O)_3]}$ (diamminecopper(?) triaquoferrate(?))

I just wrote this example now and don't know wether it exists or not I am rather concerned about how do I find their oxidation numbers


texts: difference between solving and dissolving something

texts:
What is the difference between the terms 'solve' and 'dissolve'? Up until now I have used the two terms interchangeably, not having any sound scientific definitions for each. I have thought them both to mean to make a solid into a solution through the addition of a solvent (not sure if only for solids into solutions; is the mixing of two fluids also dissolving/solving because $\ce{CO2 (g)}$ can dissolve into water?).

I have not been able to find any scientific definitions on the internet that differentiate the two. it would also be helpful if you could clearly define any other terms related to the mixing of substances without a chemical reaction occurring (eg. immiscible, which I understand to be the state of two FLUIDS being unable to homogeneously mix)

Also, if both substances are liquids, which one is the solvent and which one the solute?


texts: Unsaturation of hydrocarbons and derivatives

texts:
What is the definition of unsaturation?
Do we consider it via baeyers test/ bromine test or
do we need to have atleast one degree of unsaturation?
And if that is so then is benzene an unsaturated hydrocarbon?...cause in benzene it just has the degree of unsaturation. And if we go by that defination...even ketones should be unsaturated


texts:
I was taught that when adding/subtracting measurements, add the absolute uncertainties, and when multiplying/dividing measurements, add the relative uncertainties.

I have a problem in a lab where I need to find the difference between two measurements that are very close together, and are each very precise; however, when I propagate the absolute uncertainties, I get a huge relative uncertainty for the final result (upwards of 50%). Here it is:

(0.050 ± 5%) - (0.044 ± 3%) = ?
= (0.050 - 0.044) ± ((0.050 * 5/100) + (0.044 * 3/100))
= 0.006 ± 0.00382

This ± 0.00382 corresponds to 63.7% relative uncertainty; am I doing something wrong? Both of the original measurements were pretty accurate (<12% RU). In this case can I just add their relative uncertainties instead of converting to absolute, which is very large in comparison with the difference between the measurements?


texts: Why is benzyl alcohol a slightly stronger acid than cyclohexanol?

texts:
Cyclohexanol has a pKa = 16, while benzyl alcohol has a pKa = 15.4

The given explanation is that the "polarity of the benzyl group stabilizes the negative charge on oxygen".

My understanding is that when resonance is not a concern, benzyl groups are primarily electron donating by the inductive effect... which would destabilize charge on oxygen.

I know the inside of the aromatic ring is more negative, and the outside is more positive. Is it this positive charge that stabilizes the negative charge on oxygen?


texts:
The solute $\ce{AgBr}$ is least soluble in

  A $\ce{H2O}$
  B $1.0~\mathrm{M}\ \ce{FeBr3}$
  C $1.0~\mathrm{M}\ \ce{CaBr2}$
  D $1.0~\mathrm{M}\ \ce{AgNO3}$

I'm confused as to why the answer is B. Is it because $\ce{Ag}$ has low solubility with $\ce{Br}$, and the higher the concentration of $\ce{Br-}$ ions the less $\ce{Ag}$ will dissolve?


texts:
In the following unbalanced chemical equation the oxidation state of nitrogen ($+5$) is both decreased ($+5$ to $+2$) and unchanged ($+5$), so I am unable to balance it .

$$\ce{Cu + HNO3(dil) -> Cu(NO3)2 + 2NO + H2O}$$

My attempt: I tried by making equal decrease in oxidation number and increase in oxidation number but I am  not getting the given answer.


texts: Calculating [HI] given Kc, [H2], and [I2] for the reaction 2HI  H2+I2

texts:
In the reaction in equilibrium

  $$\ce{2HI <=> H2 + I2}$$

  The value $K_c$ is $0.0198$ at $\pu{721 K}$. Calculate $\ce{[HI]}$ at $\pu{721 K}$ if $\ce{[H2]} = \pu{0.0120 M}$ and $\ce{[I2]} = \pu{0.0150 M}$.

We use an ICE box. Since $K < 1$, the equilibrium is to the left. We are spending products to create reagents, so...

$$\begin{bmatrix}&\ce{[HI]} & \ce{[H2]} & \ce{[I2]}\\
\text{Initial} & 0 & 0.0120 & 0.0150\\
\text{Change} & +2x & -x & -x\\
\text{Equilibrium} & 2x & 0.0120 - x & 0.0150 - x
\end{bmatrix}$$

The equilibrium is given by

$$0.0198 = \frac{(0.0120-x)(0.0150-x)}{(2x)^2}$$

Solving yields:

$$x = 0.01907$$

Therefore

$$\ce{[HI]} = \pu{0.0381 M}$$

But the options are

  $\pu{0.00211M}$

  $\pu{0.133M}$

  $\pu{0.0334M}$

  $\pu{0.006567M}$

  $\pu{0.0953M}$

While it is pretty close to $\pu{0.0334M}$, I can't see how could I have made my calculation any more accurate (or if they were the ones who were inaccurate).

Was my procedure correct?


texts: How can I restore the surface of ABS polymer products?

texts:
Recently I asked a question about de-yellowing Lego. I have a follow-up question on this.

I try to design a setup where I can de-yellow Lego and remove/obscure any scratches from the surface of Lego items.

Matt_black mentioned it might not be possible to only fill scratches etc.
With my limited knowledge I could imagine the next options:

Dissolve ABS in a solvent, but this will be an unspecific process.
Heat treatment, but I think the items will warp due to internal stress.
Maybe the surface energy of a scratch is different and you could make a marker which only releases the polymer on the scratch region?
Coat the items in some kind of transparent resin?

My questions are:

Are any of these ideas realistically feasible?
If not, are there any other options which could work?
How would this procedure work from a chemical point of view?


texts: Why does Silver form bonds with covalent character?

texts: Compounds of silver form particularly strong bonds which is accounted for by the significant covalent character of the bonding. Furthermore, is the tendency to form covalent bonds linked to the fact that $\ce{Ag+}$ is a soft acid?


texts: hydroxide ion in water -- How does the dynamic change?

texts: It's well known that $\ce{H+}$ ions in water always form $\ce{H3O+}$ ions. Likewise, $\ce{OH-}$ should exist always as $\ce{H3O2-}$ ion. If I am correct at this point, how would the dynamics be different in these cases?


texts: Are all homogeneous mixtures just solutions?

texts: Or can there be a homogeneous mixture that is not a solution?


texts: Separation and qualitative identification of cations

texts:
A liquid problem may contain the following cations: $\ce{Pb^{2+}}$, $\ce{Cr^{3+}}$, $\ce{Fe^{2+}}$, $\ce{Ca^{2+}}$, $\ce{Fe^{3+}}$, $\ce{Ag^{+}}$, $\ce{Au^{3+}}$, $\ce{Co^{2+}}$. I need to devise a scheme to separate these cations individually.

I have managed to prepare the following scheme:

But, I don't know how to separate the following cations: $\ce{Cr^{3+}}$, $\ce{Fe^{2+}}$, $\ce{Fe^{3+}}$, $\ce{Co^{2+}}$.

I thought I could use ammonia or sodium hydroxide as a reagent. If I use this reagent, all the species would be precipitated, if I am not mistaken, and therefore I could not separate them. Perhaps they could be separated by using solvents and then using identification reactions (for example, I know that Co(II) precipitates with 1-Nitrous-2-naphthol). But, at first sight, I see it as very complex.


texts: What is the reason behind the phenomenon of Joule-Thomson effect?

texts: For an ideal gas there is no heating or cooling during an adiabatic expansion or contraction, but for real gases, an adiabatic expansion or contraction is generally accompanied by a heating or cooling effect. What is the reason behind such a phenomenon? Is it related to the property of real gases or is it something else?


texts: Why is the Si-F bond one of the strongest single covalent bonds of them all?

texts:
I honestly have no clue where to begin explaining why the Si-F bond is one of the strongest single covalent bonds of them all.

I would actually predict the bond to be relatively weak on account of the relatively large size of the Si atom leading to a relatively long bond length and hence poor orbital overlap. Indeed, Si's valence orbitals being large and diffuse further suggest to me that the overlap with F's small concentrated orbitals is poor.


texts: How can I determine/quantify the presence of boron nitride on a metal surface?

texts:
We use micron-grade hexagonal boron nitride (hBN) to coat the surface of bullets that are jacketed in gilding metal.  This coating is mechanically embedded/plated onto the surface in order to increase the lubricity of the bullets as they are propelled down the rifled bore of a gun.

We can capture fired bullets in a water tank.  There is some question as to whether any of the hBN survives the temperature, pressure, and friction involved in shooting the bullet through a firearm.

How can we determine whether the hBN coating survives the firing process?  Or better yet, can we characterize the quantity that remains on the bullet, or any part of it, after firing and recovery?

Destructive methods of analysis are fine.


texts:
Take the following simple equilibrium:
$$\ce{CH3COOH + H2O <=> H3O+ + CH3COO-}$$

Ethanoic acid will act as a typical Brønsted-Lowry acid and donate a proton to water, forming a conjugate acid-base pair. In this case, H3O+ is the conjugate acid, and CH3COO- is the conjugate base.

Logic tells us that if we have a solution of ethanoic acid and water, increasing the amount of acid will decrease the solution's pH. This makes sense, since there'd literally be a higher acid concentration.

However, the interpretation I get due to the equilibrium is the opposite. I see it as increasing the concentration of ethanoic acid will mean there's a larger concentration of conjugate base, hence the solution will become more basic.

Is this flawed logic or simply a misunderstanding of Le Chatelier's principle?


texts: Constructing potential energy surface of a periodic system, how to deal with atoms moving out of the supercell?

texts:
I'm using NVE ensemble for doing molecular dynamics (MD) simulations. The periodic system I'm working with contains $50$ atoms and the "calculator" for calculating potential energies and forces is a trained neural network. The platform I'm using for MD simulation is ase (atomic simulation environment).

After I ran the MD simulation for about $3$ps under $380$K, the atoms are moving out of the supercell. The ase module for MD simulation just faithfully updates the positions of atoms in the supercell (the supercell contains 50 atoms) based on the velocity. From its source code, it seems the module does not take periodicity of the system into account.

EDIT

@LonelyProf 's helpful comment reminds me periodic boundary conditions (PBC) should be implemented in the neural network calculator. The neural network calculator consists of two parts:

Generate Behler-Parrinello fingerprint given the Cartesian coordinates of atoms in the structure model. The fingerprint is actually a vector of symmetry functions that describes two-body and three-body interactions. Two-body symmetry functions are functions of atomic spacing, three-body symmetry functions are functions of both atomic spacing and angle.

In my original implementation (decorate the neural network potential to be a readable calculator by ase), there is not a module that adjusts the Cartesian coordinates of atoms "run wild" so as to move them back to the supercell.
Calculate the energy of a structure given its fingerprints. The calculated fingerprint of a structure in step one is treated as the neural network input to calculate the energy of the structure.

When constructing the potential energy surface of a periodic system whose structure model has a fixed supercell, should I always keep the atoms within the supercell?


texts: I had prepared two different volume of solution: $\pu{500 mL}$ and $\pu{100 mL}$ with same concentration ($1\%$), but I obtain different $\mathrm{pH}$. Will volume affect $\mathrm{pH}$?


texts: Balancing redox equations with oxygens in multiple oxidation states

texts:
How do you balance this using the ion-electron method;

$\ce{CrO5 + H2SO4 -> Cr2(SO4)3 + H2O + O2}$

The oxygen has multiple oxidation states in $\ce{CrO5}$, and none of the sites I looked this up on dealt with that.


texts: Is it possible for the forward and reverse reactions to have different reaction orders?

texts:
For example, in the case of non-dissociative adsorption, the rate of the forward process is given by

$$\frac{\mathrm{d}\theta}{\mathrm{d}t} = kCN(1−\theta)$$

where $C$ is the concentration, $N$ is the number of surface sites, and $\theta$ is the fraction of filled sites.

The reverse reaction is given by

$$\frac{\mathrm{d}\theta}{\mathrm{d}t} = −kN\theta.$$

Hence, it seems like the first reaction is second-order, while the second is first order. This seems strange to me.


texts: Colligative properties and sizes of particles

texts:
Why do colligative properties only depend on the number of particles and not the size?

*My argument being that since the root cause of these properties is the occurrence of solute particles on the surface, reducing the vapour pressure of the solvent, shouldn't bigger molecules, such as urea, give a much more appreciable deviation in properties, as compared to smaller ones like NaF?


texts: Why isn't the hydroxyl group of citric acid deprotonated while the carboxyl groups are?

texts:
My AP chemistry book "Chemistry: the Central Science 12th edition" says that one molecule of citric acid generates 3 H+(aq) ions when dissolved in water. Looking at the structural formula:

There are three carboxyl groups. However, there are four instances of an -O-H link. Why don't all of these break?
My guess is that the carboxyl groups can form resonance groups and thus obey the octet rule.


texts: The order of aromaticity of benzene, thiophene, pyrrole, furan, and pyridine

texts:
I have been taught that the order of aromaticity is: benzene > thiophene > pyrrole > furan. However, I have been unable to deduce any logical explanation for that order. Also, I wish to compare pyridine's aromaticity with these, but my professor does not know about it.

According to me, all the rings are aromatic and satisfy the Huckel's rule of aromaticity with $6\pi$ resonating electrons and a planar ring. So, that point is useless for doing any comparison of aromaticity.

But, we note that $\ce{2p\pi-2p\pi}$ overlap is most favorable in conjugated systems. Hence, thiophene should be the least aromatic (since it has a $\ce{3p\pi-2p\pi}$ overlap instead).

I agree that benzene should be the most aromatic because both its resonating structures are equivalent and have no charge separation. Using exactly the same reasons, pyridine should be the second best aromatic ring (lesser than benzene because the N atom is an electron withdrawing group and is reducing the electron density in the ring)

That said, every resonating structure (except the uncharged one) for pyrrole and furan will create a formal positive charge on the hetero-atom. Since N is less electronegative than O, it will be slightly more stable than O with that positive charge. Hence, pyrrole will be more aromatic than furan.

Therefore, according to me, the aromaticity order should be: benzene > pyridine > pyrrole > furan > thiophene.  But it is obviously wrong.

Hence, my question is: what is the order of aromaticity of benzene, thiophene, pyrrole, furan, and pyridine. And why?


texts: Can magnesium chloride absorb water and ammonia at the same time?

texts:
Anhydrous magnesium chloride will absorb ammonia to the tune of ($\ce{Mg(NH3)6Cl2}$).
Incidentally, magnesium chloride is usually a hexahydrate ($\ce{MgCl2(H2O)6}$) at STP.

My question is, could magnesium chloride be induced to absorb both ammonia and water at the same time? Since both of the absorbed molecules in question are close in shape, size, structure and since six seems to be the occupancy limit for either one (at STP), would they be able to coexsist?
For example, could I expose some magnesium chloride dihydrate to ammonia and get
($\ce{Mg(NH3)4Cl2(H2O)2}$)?


texts: Nomenclature of an organic compound with benzene and double bonds

texts:
How would the following compound be named?

Attemp of solution

I believe is 4-phenyl-1,2-pentadiene


texts: Tandem mass spectrometry: a1 and immonium ions

texts: In tandem mass spectrometry of proteins one will usually end up with a mix of $b$ and $y$ fragments but also $a$ fragments and immonium fragments. My problem is that wouldn't an $a_1$ ion be the exact same as an immonium ion of the first amino acid in the peptide?


texts: What is the significance of Law of Multiple Proportions?

texts:
I cannot understand how the Law of Multiple Proportions is significant, or how does it further improve over Law of Conservation of Mass or Law of Definite Proportions. From Wikipedia:

  If two elements form more than one compound between them, then the
  ratios of the masses of the second element which combine with a fixed
  mass of the first element will be ratios of small whole numbers.

Now I must say that I don't understand anything from the "small whole numbers" part, since it is not rigorously defined. For example, $31454315/43546546$ may be a ratio of small whole numbers for me but not for you.

Nevertheless the following is the algebraic interpretation of the law, with substituting the "ratios of small whole numbers" part with: "a real constant", since the ratios of two whole numbers is always a real constant.

Compound 1: Has $m$ mass of component $A$ and $x$ mass of component $B$.

Compound 2: Has $m$ mass of component $A$ and $y$ mass of component $B$.

By the Law of Definite Proportions, the following are correct:

$x/m = c_1$

$y/m = c_2$

where $c_1$ and $c_2$ are real constants. This is because Law of Definite Proportions states that "a chemical compound always contains exactly the same proportion of elements by mass".

Dividing $x/m$ by $y/m$ gives:

$x/y = c_1/c_2$

Since the ratio of two real constants is another real constant, we can express this as:

$x/y = c_3$

Since a real constant can always be expressed as the ratio of two whole numbers, this gave us the Law of Multiple Proportions.

As I have shown above, the Law of Multiple Proportions is a corollary of the Law of Definite Proportions.

So again: What is the significance of the Law of Multiple Proportions? Isn't it just an application of the Law of Definite Proportions? How does Law of Multiple Proportions improve over Law of Definite Proportions and Law of Conservation of Mass? How does it contribute to the first scientific atomic theory?


texts: Speculation about chlorine dioxide isomer

texts:
I know that chlorine can have a positive charge in the case of oxides. But what I am wondering is if chlorine dioxide can form a ring and if so how likely it is.

$\ce{O=Cl=O -> O- -Cl-O- -> (cyclic)O-Cl-O}$

This reaction would form a triangular ring with each oxygen being bonded to 2 atoms so the charge would once again be zero. But right in the middle of it you have an ion. It isn't chloryl or chlorite since it has a charge of 2-. This ion then bends to where the oxygens are close enough to form a peroxide bond giving you cyclic chorine dioxide.


texts: Can a battery powered by iron and air really provide a feasible power source for automobiles?

texts:
I'm referring to the Shuttle Battery recently announced (read more on it here) that suggests that:

  The energy density of the device is up to 7,700 Wh/L. It is more than 5 times
  higher than state-of-the-art (SOA) Li-ion (550Wh/L), and comparable to fossil
  fuel (10,000 Wh/L).

It goes on to say that:

  It is rechargeable because it is based on a simple reversible chemical reaction, 3Fe + 4H2O = 4H2 + Fe3O4 and 2H2 + O2 = 2H2O. The proof of concept cell demonstrated zero capacity loss after 200 cycles of discharge and charge.

Now the question is: Is this even remotely possible? Or is there a red flag here somewhere that I can't seem to pick up?


texts: Does Victor Meyer test distinguish alcohols and alkyl halides?

texts: I read from a source that alkyl halides and alcohols cannot be differentiated by the Victor Meyer test. It says that both react similarly with the reagents and form the same products. Is this correct, and if so what are the reactions for alkyl halides.


texts:
How can it be explained that in the first reaction mentioned below, a 7-membered ring dominates when the leaving group is nitrogen and an epoxide forms when the leaving group is dimethyl sulfide?
This is quoted from "The Art of Writing Reasonable Organic Reaction Mechanisms", Second Edition by Robert B. Grossman, DOI: 10.1007/b97257.

The $\ce{C}$ in diazomethane is nucleophilic. The product of attack of diazomethane on the carbonyl $\ce{C}$ has a leaving group a to the alkoxide, so either a 1,2 alkyl shift or direct nucleophilic displacement can occur. The insertion product happens to dominate with $\ce{H2\overset{-}{C}-\overset{+}{N}_2}$, but with $\ce{H2\overset{-}{C}-\overset{+}{S}Me2}$ the epoxide dominates.


texts:
I was reading about the Perseverance lander on Mars and was surprised to find that it has an oxygen manufacturing instrument on board. The oxygen is needed as a part of a binary rocket fuel to get back from Mars. It makes oxygen from carbon dioxide, a technology that would be very useful for carbon capture here on Earth. I can not find the chemistry or the technology that makes this work. Does anybody know the chemistry of this instrument?
The following is the text from nasa.gov explaining the mechanism of MOXIE:

Mars’ atmosphere is 96% carbon dioxide. MOXIE works by separating
oxygen atoms from carbon dioxide molecules, which are made up of one
carbon atom and two oxygen atoms. A waste product, carbon monoxide, is
emitted into the Martian atmosphere.


texts: Why does my synthesized 4-bromoacetanilide smell like almonds?

texts:
So, I synthesized 4-bromoacetanilide in the lab by brominating acetanilide. Acetic acid was used as a catalyst. Sodium bisulfide was used to neutralize the reaction product. Then it was washed with water and recrystallized in ethanol. After that I let it dry for a week. Then I added a little water by accident but decided to store it anyways, and a few weeks later I opened the stored product and I smelt almonds. It wasn't even a weak odour, it was much like benzaldehyde, but not that strong. How would this even be possible? I can't figure it out.

2-bromoacetanilide might have been formed. I did search a little bit, and found that the decomposition of 2-nitroacetanilide - a similar product - results in hydrogen cyanide (almonds smell; very toxic). But it cannot be that, can it? Wouldn't I be like dead by now? Sniffed it three times. Or is it not really toxic at very low concentrations, but smellable?

The smell was kindof pleasant, less aromatic-like than benzaldehyde. Not strong, but also not weak when I held it close. People say HCN smells like burned or roasted almonds, but it was more like a sweet but bitter maybe ester-like odour. Something probably most similar to marzipan.

SDS Source


texts:
I am trying to find chiral centers of molecules in QM9 dataset. Browsing their SMILES representation, I noticed SMILES yield using

datasets.get_qm9(GGNNPreprocessor(), return_smiles=True)

don't have @ or @@, but it seems that some of these molecules have alternative representations. For instance, both 'Cc1ccoc1C(C)O' and 'CC@Hc1c(C)cco1' represent the same molecule, but of course the latter one outputs the chiral center:

[(1, 'S')]

while only the former is available in the dataset. I found this at https://github.com/chemspacelab/qm9-C7O2H10. Does anyone know if this can be generalized to all the molecules in the QM9 dataset? Thanks!


texts: How should the hydrated proton be represented in chemical equations?

texts:
I learned the equation

$$\ce{H2O + H+ -> H3O+}$$

And I know $\ce{H+}$ and $\ce{H3O+}$ really mean the same thing. But I am confused as to when I should use $\ce{H+}$ and when I should use $\ce{H3O+}$? Is any one of them a more accurate representation?


texts: If I were to combine solutions of $\ce{(NH4)2CO3}$ and $\ce{HNO3}$ in water, the only ionic compounds that could form are $\ce{H2CO3}$ and $\ce{NH4NO3}$ right? But since both are soluble no precipitate would form correct? So does that mean that no reaction occurred? Does it also mean that an ion like $\ce{NO3-}$ will never react in an aqueous solution because it is always soluble in water?


texts: Does the concentration of water accounts for determining the rate of a reaction?

texts:
I found this problem in my book and I'm not sure how to assess this question.

It is as follows:

  Regarding the relationship between the rates of the chemical species
  in the following reaction. Which of the following alternatives is the
  correct one?

$\ce{2H2 + O2 -> 2 H2O}$

$\begin{array}{ll}
1.&v_{H_2}=2v_{H_{2}O}\,, v_{O_2}=2v_{H_{2}}\\
2.&v_{O_2}=2v_{H_{2}O}\,, v_{H_2}=2v_{O_{2}}\\
3.&v_{H_2}=2v_{O_{2}}\,, v_{O_2}=v_{H_{2}O}\\
4.&v_{H_2}=v_{H_{2}O}\,, v_{O_2}=\frac{1}{2}v_{H_{2}}\\
5.&v_{H_2}=v_{H_{2}O}\,, v_{O_2}=v_{H_{2}}\\
\end{array}$

In the original source (which doesn't list a specific authorship) doesn't indicate the state of matter for each species. So I'm assuming perhaps that the reagents are gases and the products is liquid?.

Anyways what I've attempted to do is to establish the rate law as follows using the law of mass action:

$\ce{2H2 + O2 -> 2 H2O}$

For Hydrogen gas:

$v_{H_{2}}=-k[H_{2}]^2[O_{2}]$

For Oxygen gas:

$v_{O_{2}}=-k[H_{2}]^2[O_{2}]$

From this it can be established that:

$v_{H_{2}}=v_{O_{2}}$

For water (since it is on the products it must be established as if it were a reagent):

$v_{H_{2}O}=k[H_{2}O]^2$

And that's where I'm stuck.

Supposedly the answer is

$v_{H_2}=2v_{O_{2}}\,, v_{O_2}=v_{H_{2}O}$

But I don't see any way of how to get there. Can somebody point me exactly what did I missed?.


texts: Who are some writers that also had careers in chemistry?

texts:
I love chemistry, but I am interested in so many other things too. I believe it's important to have a complete intellectual life, and it always makes me happy to find examples of people who took their love for science and created great art with it. Many would be surprised at how many great authors were also chemists. Here are a few of my favourites:

Isaac Asimov: Professor of biochemistry, Boston University School of Medicine
Kurt Vonnegut: biochemistry major, not a successful chemist though.
Robert M. Pirsig: biochemistry major

Can anyone help add to my list?


texts: How are the pKa's of very strong acids derived mathematically?

texts: It is often said that "for very strong acids (HCl, H2SO4, etc.), the pKa value cannot be experimentally derived from standard titration and instead needs to be theoretically computed". However, I could not find any way to compute it theoretically. More specifically - I know that the pKa is a constant multiple of the logarithm of the (magnitude of the) Gibbs energy for deprotonation, and I know that the enthalpy part of the Gibbs energy can be computed easily (just decompose both sides into its constituent elements and use Hess' law), but I can't find any mathematical way to compute the entropy part on Wikipedia.


texts: Can I use a Liebig condenser for condensing sulfuric acid?

texts: I have a Liebig condenser but I read that the air cooled condenser is preferred for high temperature boiling points. My question is whether I can still use my Liebig with minimal risk... Should I just run it without coolant or even with warm water? There shouldn't be pressure build up if I just run it dry. If I used warm water though, I still have a huge temperature differential between the jacket and sulfuric acid vapour, not so much with just running it without coolant since there will be a gradient between the air temp from inner tube to outer tube.


texts: How can two orbitals constructively and destructively interfere simultaneously?

texts:
The molecular orbital theory dictates that when two atomic orbitals form molecular orbitals, then two molecular orbitals must form (i.e number of atomic orbitals = number of molecular orbitals). For this to occur there must be bonding molecular orbitals and anti-bonding molecular orbitals. The bonding MO's are caused when the orbitals constructively interfere and the anti-bonding orbitals form as the orbitals destructively interfere. I understand the concept of interference but I do not understand how two atomic orbitals (one from each bonding atom) can simultaneously interfere constructively and destructively. Moreover, I am under the impression that the anti-bonding orbitals exist even if they're not occupied. As a result, is it correct to think that it's the orbitals themselves that are the waves, not the electrons?

In summary:

How can two orbitals interfere constructively and destructively?
Do anti-bonding orbitals exist when not occupied?
Is it the orbitals themselves that are interfering with each other like waves?


texts: Determining rate constants for parallel reactions from experimental data

texts:
I have a question regarding the rates of parallel reactions. I have gathered experimental data for the overall reaction (i.e. conversions and selectivities and specific times) but due to the two reactions running parallel to each other for this reaction means I can't use a simple integrated rate plot.

Say for

$$
\ce{A ->[$\large k_1$] B} \\
\ce{A ->[$\large k_2$] C}
$$

By substitution and integration, I have found that:

$$
[A](t) = [A](0) \mathrm{exp}(-(k_1+k_2)t)
$$

and then the following equations can be derived in terms of the products formed:

$$
\frac{d[B]}{dt} = k_1 [A](0) \mathrm{exp}(-(k_1+k_2)t)
$$

which gives

$$
[B](t) = \frac{k_1[A](0)}{k_1+k_2}(1-\mathrm{exp}(-(k_1+k_2)t)
$$

when integrated. Also,

$$
[C](t) = \frac{k_2[A](0)}{k_1+k_2}(1-\mathrm{exp}(-(k_1+k_2)t)
$$

is the equation for the other parallel reaction.

My initial thoughts were to plot the graphs (as I know the values for $[C]$, $[B]$, and $[A]$) and form some simultaneous equations, but this is an exponential plot and so i'm not sure how this would work.. or if I could even plot it, as I don't know $k_1$ and $k_2$ - that is what I need to determine.


texts: Why can't a balance that can weigh to the nearest milligram be able to weigh 23.8 milligrams of something?

texts:
I'm having trouble understanding the answer to this question:

  Most chemistry laboratories have balances that can weigh to the nearest milligram, would it be possible to weigh $5.64\times10^{18}$ molecules of octadecane, $\ce{C18H38}$, on such a balance?

I worked through the equation and my end result was $\pu{0.00238 g}$ which is equal to $\pu{2.38 mg}$ so I thought that the answer was that it could, but the book states that the answer is that it cannot. Why can't it? Am I misunderstanding how weighing to the nearest $\pu{mg}$ works?


texts:
We have been asked to do a retrosynthesis of (6S)-6-[(2S)-2-hydroxy-4-phenylbutyl]oxan-2-one J from 3-phenylpropan-1-ol K:

My first instinct would be to do a functional group interconversion of the alcohol to a ketone, to then do a Baeyer-Villiger oxidation.


texts:
In the crystal field theory (CFT), when the splitting of the d-orbital occurs, it gets divided into two parts.
The upper part with higher energy is the  $\mathrm{e_g}$ and the lower part with lower energy is called the $\mathrm{t_{2g}}$ as in:

So can anyone please explain me what is this $\mathrm{t_2}$ or the $\mathrm{e}$ or the $\mathrm{_g}$ below.


texts: What factors might affect the reaction between potassium permanganate and ethylene glycol?

texts:
Our chemistry club has, for the last few years, been showing off some reactions to prospective students. One of the most popular tricks we have is a bit of an explosive one: we mix some potassium permanganate with ethylene glycol in a small bottle. The permanganate oxidizes the glycol, and we usually end up with an intense, three foot flame that shoots out of the bottle, followed by some popping, and finally, the whole thing burning to the ground.

Usually.

Recently, we've been using the exact same mixtures with the same ratios and getting wildly differing results. This entire week, all we've gotten is the glycol bubbling a little and maybe spitting out some of the permanganate, and not much more. The ratios we use are almost the same, so I'm not sure what could be causing this.

Is this reaction sensitive to age of the reactants? Ambient temperature? Humidity? What could cause the reaction to not work normally?

P.S. In spite of the home-experiment tag, the chemicals used here are lab-grade (from Sigma-Aldrich), though I'd be interested in how the purity might affect the reaction as well.


texts:
I want to ask about nucleophilic attack by Cl in Step 2.
To me there seem 4 electrophilic sites and I marked them as (a)~(d).
mechanism I've seen in lecture only deals with site (a).

maybe (c) is less electrophilic and (d) makes this reaction go backwards, so I can get past them. but when Cl- attacks (b), it could break a bond b.w (b) and (d), resulting in completely different product, as well as a bond b.w (a) and (b).

so my question is,
is nucleophilic attack on site(b) by Cl- resulting in breaking bond b.w (b) and (d) possible? if so, to what extent? if not, why?

hope somebody teach me something!!


texts: Stability of α, β, γ allotropes at different temperatures

texts:
While reading about elements or compounds I often come across allotropes (or forms) being referred to as α, β, γ forms.
Examples:

Sulfur has two allotropes: α rhombic and β monoclinic. Out of these two α is considered more stable at ordinary temperatures.
$\ce{SO3}$ has three forms out of which again α is considered more stable.
α-Form of iron is considered the most stable at ordinary temperatures.

Based on this small data, it makes me think whether α forms are always in general the more stable ones? Is it true? How does this nomenclature signify stability at different temperatures?


texts: Is there an edible, colour-less, taste-less, odour-less, water-soluble, cheaply-producable gel, solid or other substance?

texts:
Suppose, for example, that some oatmeal is fixed in gel, or some other substance. A portion of the substance-with-oatmeal is then removed and added to cold milk or some similar dairy product, where it quickly dissolves, yielding a standard bowl of milk and oatmeal. Is there such a substance?

Ideally, the substance should be unobtrusive to the eating experience. This also means that it should not dilute the milk significantly. Otherwise, some taste, colour or odour may be permissible, provided it does not clash with the taste of the meal.

The substance should also not soak the oatmeal, which is why it may not be a liquid.


texts:
A professor of mine noted that when he was in school, microscopes weren't powerful enough to resolve certain things (I forgot what it was). But current microscopes are powerful enough.
Extrapolating from this trend, he hypothesized that by the time we were his age, we would be able to see atoms.

Wait. Seeing atoms? Do we expect to see discrete little dots for electrons (I don't think so)? What exactly can we expect to "see," if anything at all?


texts:
I find when making soap that a difficult part is removing the water.
Currently what I do is melt the soap and then put the melted soap into a vacuum chamber. This draws the water out by vacuum. You cannot boil the water out of the soap at atmospheric pressure because that would damage the soap by the high heat.
The problem with using the vacuum chamber is that as the pressure falls, the soap rises up like an angel food cake and can easily assume 7 or 8 times its original volume. This means I have to have a gigantic container for a relatively small amount of soap. Also, the soap cools as it rises, so it solidifies before all the water is removed. Then, the process has to be repeated, over and over again, removing more of the water each time.
Is there any easier method I can use to remove the water from the soap.


texts: Reduction of copper oxide by hydrogen in the lab to copper

texts: In the reduction of copper oxide by hydrogen in the lab to copper, why does hydrogen need to flow through the tube even after the reduction is completed and the burner is turned off until the tube is cool?


texts: Is there any aqueous solution (or simple method) to remove trace level of sulfur dioxide/nitrogen monoxide and nitrogen dioxide in a gas stream?

texts:
I need to generate pure gas from a gas stream which is free of $\ce{SO2}$/$\ce{NO}$/$\ce{NO2}.$ The air is already pretreated by activated carbon and purafil. However, I can't find any solution for removing trace level of this pollutants. I find that many solutions of capturing for large scale like flue gas. However, it is not suitable for trace level (1–10 ppb).

I know $\ce{O3}$ can react with $\ce{NO}$ to $\ce{NO2}$. However, as I mentioned, I need the gas stream free of $\ce{NO}$ and $\ce{NO2}$ simultaneously. So, converting $\ce{NO}$ to $\ce{NO2}$ is not the answer.


texts:
Reagents to carry out above conversion, P, Q, R respectively are:
(a) $\ce{H2C=CH-CH2-Br}$, $(\ce{HO-})$, $[\ce{HO-}, Δ]$, Wacker process.
(b) $\ce{H2C=CH-CH2-Br(HO^-)}$, Wacker process, $\ce{HO-}$, $Δ$.
(c) Wacker process, $\ce{H2C=CH-CH2-Br(HO^-)}$, $\ce{HO-} (Δ)$.
(d) Wacker process, $\ce{HO-} (Δ)$, $\ce{H2C=CH-CH2-Br(HO^-)}$.

Could someone please explain the R part of this reaction? I can't understand the five-membered cyclization step. Is it aldol condensation or there's something else?


texts:
While searching the Internet for information about the tricyclopropylmethyl carbocation, I found a site (askiitians.com) where it said that its stability was due to "dancing (superfast) resonance".

What is "dancing resonance"? How does it take place, and what are the prerequisites for it?


texts: What is the difference between a mixture and a solution?

texts: Is there an actual difference, or are they synonymous?


texts: How to calculate the temperature at which a reaction becomes spontaneous?

texts:
At $25~^\circ\mathrm{C}$, $298~\mathrm{K}$, the reduction of copper(I) oxide, $ \Delta H = 58.1~\mathrm{kJ}$, $\Delta S = 165~\mathrm{J/K}$, is nonspontaneous, $ \Delta G = 8.9~\mathrm{kJ}$.
  Calculate the temperature at which the reaction becomes spontaneous.

So for this question I'm thinking I use the equation

$$ \Delta G = \Delta H - T\Delta S$$

Then plug in the values and solve for $T$? $$8.9~\mathrm{kJ} = 58.1~\mathrm{kJ} -T(0.165~\mathrm{kJ}) $$


texts: How does one calculate the electronic difference density in practice?

texts:
I am interested in calculating electronic difference density maps. These have been described for quite a long time by Bader and others. For example, below is the fourth of a series of papers which discusses these extensively.

Cade, P. E., Bader, R. F. W., Henneker, W. H., & Keaveny, I. (1969). Molecular Charge Distributions and Chemical Binding. IV. The Second‐Row Diatomic Hydrides AH. The Journal of Chemical Physics, 50(12), 5313-5333.

The idea is fairly simple. Use some electronic structure method (or in principle experimental data) to calculate the electron density of some atom or molecule by itself (but at the appropriate geometry) and then calculate the electron density of the molecule containing the atoms for which you have reference density distributions. Sum all the reference densities and take the difference from the reference densities. You then get a map with positive and negative regions that show areas of electron enrichment and depletion which hopefully provides some physical insight.

It is simple enough to calculate electron densities with most electronic structure packages and have the program print out the density in terms of expansion coefficients for the molecular orbitals which various other programs are able to read and visualize.

Now with that information in hand, is anyone aware of software packages which can do this operation I am describing? Or am I stuck with doing something like fitting the electron densities numerically and taking the differences in that way? If so, if anyone has done this before, some input in that regard would be useful.

This seems like such a simple thing to calculate, but I've been a bit confused. I know I've seen people make spin density difference plots for open-shell and excited state systems. This is such a similar calculation that it seems like one should be able to use the same tools, but I assume the latter calculations are buried in the electronic structure package somewhere and hence not easy for the user to adapt.

Any help is greatly appreciated.


texts: a racemic mixture has 50-50% of the 2 different enantiomers. There are racemate drugs out there in the world. The misunderstanding I have is that usually 1 out of the 2 enantiomers molecules have a different reaction with the body, so if you perform racemisation to form a racemic mixture, ain’t that drug going to be still harmful in your body ? Or does FDA not accept racemic mixture where 1 of the enantiomers in it are harmful to the body? Thus they only accept racemic mixture where both enantiomers have to perform the same therapeutic effect on the body ?


texts: Probably a simple question: When you're mixing potassium hydroxide ($\ce{KOH}$) with iron nitrate ($\ce{(FeNO3)3}$) to form ferrihydrate, does the temperature have to be below $\pu{60 ^\circ C}$?


texts:
The specific rotation of optically pure adrenaline is $-53$. A mixture of (R)- and (S)-adrenaline was found to have a specific rotation of $-45$. Calculate the % ee of the mixture (enter numeric value only, without % sign, rounded to the nearest whole percent).

This should be $\%~\text{ee}= \text{specific rotation sample}/\text{specific rotation enantiomer}$

But $100\times (-53/{-45})=117.78~\%$

The fraction the other way is $84.9~\%$ but doesn't stick to the formula.


texts: Why is the minus sign (-) not allowed in reaction equations?

texts:
Recently in my chemistry class, the teacher told us that while writing "half equations" (such as a sodium atom losing one electron to form a sodium ion) we were not to use a simple minus sign. We were only allowed to use a plus sign. For example, this would not be allowed:

$$\ce{Na $-$ e- -> Na+}$$

The "correct" way of writing it would be:

$$\ce{Na -> Na+ + e-}$$

My question is: Is this conventional, or somehow only related to my school? Could any example of a chemical equation utilising the minus sign please be given for clarification?


texts: Taking a procedure for ICP and adapting it to use with AAS

texts:
I was reading a paper regarding metal detection and they gave their procedure for an acid digest of a soil sample which was then analysed by ICP-OES.
They used nitric acid, hydrogen peroxide and sulfuric acid.
I want to do a similar analysis, but I only have AAS available to use.
Can I simply dilute the acid digest in a volumetric flask and analyse with the AAS?
Or are there other steps to consider?
Are the choices of acids of concern? Can they cause interference in the flame ionisation?


texts: Order of coordinates in a wavefunction - why do they matter?

texts:
For the past few weeks, I have been studying Quantum Chemistry and lately in these lectures something has bugged me:

If I do a sum:

  $1 \times 2 \times 3 \times {...} $

This is the same as simply writing the order in reverse:

  $ {...} \times 2 \times 1 $

a bit like $ab = ba$

and for wave functions, I've seen that the order of coordinates inside a wave functions seem to imply that no two wave functions are the same:

$$\psi({r_1},{r_2}) \neq \psi({r_2},{r_1})$$

and from there on there is a discussion that there must be a change in sign and so on and so forth.

But I'm struggling to work out why if I change the order of my variables, that this makes any effect.

I'm just confused by why the order is such a fuss, if that makes sense!

Why are the two wave functions different by the order of $r_1$ and $r_2$?


texts: How to determine the product from my attempt of HOCl synthesis

texts:
This is a follow up to this question. Here is my short procedure:

start with 200mL distilled water
add 7mL of 8.25% sodium hypochlorite (.11M) to the solution. The resulting solution should be 3.7*10$^{-3}$M NaOCl
add bromocresol green indicator.
add acetic acid dropwise, titrate until the solution hits a green color (pH~5).

I think at this point, the solution should contain HOCl and a small amount of dissolved sodium acetate.
$$NaOCl + CH_3COOH \rightarrow HOCl + CH_3COONa$$
I took a pH test with litmus paper and it shows between 5-6. I took a free chlorine test to determine the concentration of HOCl, and it resulted in ~1000ppm, which was what I was aiming for. The chlorine concentration stayed comfortably within its max solubility in water. I used an NaCl meter to determine the concentration in the solution and it returned 0. However, I tested for salts with silver nitrate and it precipitated both white and dark brown/black.
White precipitate indicates presence of chlorine, and dark brown precipitate indicates presence of OH. How did I get AgOH in an acidic solution? Is it simply that the silver rips apart the HOCl to form AgCl and AgOH?
My boss is concerned that I have made dilute hydrochloric acid, not hypochlorous acid. How can I prove that the solution is one product or the other?


texts: Which chemical is responsible for making marker ink permanent?

texts: As asked in the question and also, a bonus question: which property of a chemical would make it 'permanent' in terms of markers?


texts:
What is the pH of a solution made by mixing 10.00 mL of 0.10 M acetic acid with 10.00 mL of 0.10 M KOH?
  The $K_a =1.8 × 10^{-5}$ for $\ce{CH_3CO_2H}$. Assume that the volumes of the solutions are additive.

I've done the following:
Write the chemical reaction.

$\ce{CH_3COOH + KOH <=> CH_3COOK + H_2O}$

Then I calculated the number of moles of the reactants.

$\ce n({CH_3COOH})= c \cdot V = 0.001 \text{mol}$

$\ce n({KOH})= c \cdot V = 0.001\text{mol}$

Then I assume the mistake lies here:

I thought because 1 mmol of $\ce{KOH}$ reacts with 1mmol of $\ce{CH_3COOH}$ this will form 1 mmol of $\ce{CH_3COOK}$ which leads to no formation of $\ce{OH^-ions}$. Because there is no excess. Another thing I thought is that $\ce{OH^-}= 1 \text{mmol}$. So I could calculate $\ce{pOH= 3}$ but to no avail because of the answer I later saw that is shown below.

The final outcome is $\ce{pH = 8,72}$.

A hint of where my thought process doesn't make sense would be appreciated? Thanks in advance.


texts: Is a beaker/reaction vessel like the one pictured available commercially?

texts:
We're doing photocatalysis with the catalyst fixed to a 2" Si wafer, washing an aqueous solution (methylene blue, the concentration varies but in the picture I believe it's 0.1 mMol/l) over the top in beakers that look like this

(the lid is the heatsink for the 365 nm UV LED that drives the reaction; that part is pretty much optimised).

The few we have are custom made, and we need some more.  I can't find a source of anything comparable, but I'm only a physicist who doesn't necessarily know what's available or what terms to search for.

It needs two hose barbs as near the bottom as possible, and a flat base wide enough to lift a 2" wafer out (i.e. about a 60 mm minimum internal diameter).

They're also visible in this timelapse video of the reaction.

If such a thing exists, what's it called? Or is there something we could repurpose? Both the cost and the lead time of custom glassware are a bit high.


texts: What are some materias/substances that can be applied to a ball such that the ball will stck to a wall,if thrown

texts:
I am trying to make a prototype for the "valkyrie camera" seen in the video game Rainbow 6 Siege
This is how it works
https://gfycat.com/impressivegrippingauklet
the black ball seen is the camera,as you can see the camera is thrown and it sticks to a surface.
are there any materials that are capable of such action?


texts:
I am looking into the mechanism for the Nagata Alkylation; however, I cannot find anything more specific than the mechanism listed below.

I am only refering to the formation of the first intermediate, not the cyclization of the ortho-quinone methide. I would assume that the phenylboronic acid first forms an ester with the phenol and then the lewis-basic carbonyl attacks the boron. This might then make an electrophillic carbon that can undergo an alkylation reaction. I am not very sure about this proposal of mine, and I was wanting to ask if anyone had any suggestions as to how this mechanism might be occuring.


texts: What is the lining of "Silver-lined" gloves actually made of?

texts:
I bought some rubber gloves that claim to be "Silver-lined".  I think this is supposed to make the gloves easier to put on and take off.  Is there an actual silver compound lining the gloves that makes them slippery?

For example these gloves here are only $3.30.  And the description is as follows: "Silver lining enables easy on/off glide and eliminates particle shedding from the glove.".


texts: How to balance more complex redox reactions?

texts:
I'm in an advanced level chemistry course, and so far we've been introduced to balancing redox reactions. The basic ones like
$$\ce{MnO4- + Cl- -> Mn^2+ + Cl2}\tag1$$
are pretty easy for me, but I'm having trouble with equations where it's not apparent what I exactly need to put in my half reactions. Some examples of these kind of equations are:
\begin{align}
\ce{Pb + PbO2 + SO4^2- &-> PbSO4}\tag2\\
\ce{Ag(s) + CN- (aq) + O2(g) &-> [Ag(CN)2]- (aq)}\tag3\\
\ce{Cu + HNO3(aq) &-> Cu(NO3)2(aq) + NO2(g) + H2O(l)}\tag4
\end{align}

I'm not looking for solutions to any of these problems. I'm just looking for ways to correctly construct my half reactions before balancing, adding water and hydrogen ions, and balancing the charges.
Like in the first reaction on the reactants side, the first $\ce{Pb}$ has a charge of $0$ while the next one has a charge of $+4$. The $\ce{Pb}$ on the products side however has a charge of $+2$. It seems like one is being oxidized and the other reduced. And I'm also not sure what to do with the sulfate.


texts: What's the mechanism of the reaction of (E)-methyl 3-(furan-2-yl)acrylate in acidic methanol?

texts:
In the organic chemistry textbook by Clayden et al. they mention that the reaction of (E)-methyl 3-(furan-2-yl)acrylate in acidic methanol yields dimethyl 4-oxoheptanedioate without providing the reaction mechanism and leaving it to the reader to figure it out:

I've tried for over an hour now but didn't get to this product. I assumed that since the reactant already has the right number of carbon atoms I won't have some kind of dimerization to consider, only reactions involving one molecule of (E)-methyl 3-(furan-2-yl)acrylate. I think, the first step should be a protonation at the furan 3- or 5-position with a subsequent attack of methanol on the carbonyl group that was formed followed by an acetal cleavage. The problem is that I don't know how to get the second ester group and how to get rid of all 3 $\ce{C=C}$ double bonds? Unfortunately, I don't have access to ChemDraw on this computer so I can't provide some example mechanisms I came up with.


texts: Color shifting reaction in black sealcoat

texts: When I have my driveway seal coated, it turns blue a few days after it is done and then turns back to black. I've heard it called "blue flash." What actually happens chemically to cause this?


texts: Specific latent heat of fusion of a noble gas

texts: Could someone explain to me where the additional energy goes when applied to an object in the state of melting (such as water) so that the temperature of the object does not increase, and could someone please explain to me why Helium has a specific latent heat.


texts: Is sugar a molecule or a large crystalline structure composed of many molecules? What do we mean when we say sugar?


texts: Possible methods for copper (II) reduction to copper (I)

texts:
How can I make $\ce{Cu2O}$ from copper?

I am seeing if electrolysis is a good route (in the context of kitchen style chemistry) to cuprous oxide, instead of the traditional heating copper and removing the cupric oxide, etc.

With Epsom salt electrolyte, it is very easy to make copper II hydroxide (cloudy ammonia soluble, according to the wiki). This can be heated to $\ce{CuO}$ easily enough, but I have no idea if this can be reduced.

Can $\ce{CuO}$ be reduced easily? Or is there a simple way to produce (from copper) a copper (I) salt, from which a precipitate of $\ce{Cu2O}$ may be formed? What reducing agents could be used?


texts: Is it possible to have negative corrorion rate and weight loss, meaning specimen [steel] gained weight after immersion in electroyte solution?

texts: Regarding this article, I have read that the corrosion rate and weight loss of a steel specimen after immersion in different corrosive media is negative. I'm surprised that this is really possible. Is there a chemical explanation for this?


texts:
There's been ample work and media coverage on how to make a long C-C single bond. To my knowledge, the longest stable C-C bond is currently 1.704 Å, prepared by Schreiner Nature 477, 308–311 in 2011.

All around us, there's considerable plastics, made from polymerizing alkenes like polyethylene. Typical bond lengths for alkenes are ~1.33 Å, with bond dissociation energies around 611 kJ/mol, vs ~347 kJ/mol for C-C.[ref] Clearly, longer C=C bonds could decrease the energy required to polymerize the alkane.

Using either chemical databases, like the Crystallographic Open Database, or computational methods, what's the longest C=C bond you can find?

Please include in your answer:

The molecular structure, with the C=C bond either obvious or highlighted (e.g., if it's a conjugated bond)
The method used to determine the bond length (e.g., DFT geometry optimization using program X, found in database Y, etc.)
Proof that the bond is really a double bond (e.g., clear evidence of substituents, planarity, etc.)
Any appropriate literature citations


texts: Grignard vs organolithium reagent opening cyclohexene oxide

texts: Could someone please explain the reason for the two different products formed? One with RLi and the other with RMgBr?


texts: Why would water, and not saltwater, undergo electrolysis?

texts:
I am attending a cram school and there was a question that goes:

  Electrolysis decomposes chemicals by passing an electric current through a liquid or solution containing ions. Which of the following can be decomposed by means of electrolysis?
  A. Water
  B. Cream
  C. Saltwater
  D. Carbonated drink

My answer was C since the first sentence explicitly stated that electrolysis decomposes chemicals by passing an electric current through a liquid or solution containing ions, but they said that the correct answer is A. Also, I was thinking that water in itself is not conductive and therefore will not facilitate electrolysis by itself. Is the anwer really Water? And if so, why water and not saltwater?


texts: Calculating enthalpy per gram mole of oxygen bond in haemoglobin

texts:
A solution of $\pu{5 g}$ of haemoglobin in $\pu{100 cm^3}$ of solution shows a temperature raise of $\pu{0.031 ^\circ C}$ for complete oxygenation. Each mole of haemoglobin binds $\pu{4 mol}$ of oxygen. If the heat capacity of the solution is $\pu{4.18 J K^{-1} cm^{-3}}$, calculate $\Delta H$ per g of oxygen bond.

Attempt:

for $\pu{100 cc}$, heat capacity is $\pu{418 J K^{-1}}$
for $\pu{\frac{5}{64000}mol}$ of haemoglobin, $C\Delta T=\pu{12.952 J}$ is released
hence for $\pu{1 mol}$, $\pu{165862.4 J}$ energy is released
This energy is released when four bonds are formed with oxygen. Hence for 1 bond, $\pu{41.47 kJ}$ energy is released.

The answer given in the book is $\pu{-41.47 kJ}$.


texts:
I am trying to understand SCF cycle by trying to code up solved example from Quantum Chemistry by Levine (page 443, 5th edition). The problem is shown below:

One electron integrals are straight forward and I was able to get the correct answer, however I still can get correct values for two election integral, lets say (11|11). Given below is my attempt in octave

clear all;
N=2000;
zeta1 = 1.45;
zeta2 = 2.91;

r = linspace(0.000001,10,N)';
dr = r(2)-r(1);
chi = @(zetad,x) (2*zetad.^(3/2))*exp(-zetad*x).*x;
chichi = 0;
for i =1:N
    chichi = chichi + dr*(chi(zeta1,r(i))*chi(zeta1,r(i))*chi(zeta1,r')*(chi(zeta1,r)./((r(i)-r) + 0.000001)));
end
chichi*dr

However my values are way off in this case. Can anyone please shed a light on it? Value of (11|11) = 5/8 zeta1 = 0.9062.

Two electron integrals are defined in the book as:


texts: What did Richter mean regarding an acid base reaction?

texts:
Recently I've been reviewing concepts belonging to the history of chemistry. But I came stuck at trying to understand a passage which I read from wikipedia entry (and which it seems has been mentioned in different sources). This is related with the law of reciprocal proportions.

It states as this:

  It took 615 parts by weight of magnesia ($\ce{MgO}$), for example, to
  neutralize 1000 parts by weight of sulfuric acid.

There's an existing answer which explains a similar concept (law of multiple proportions) but not specifically to Richter's.

From what I understood in the law of reciprocal proportions there is a set of three elements. Two of them react with a fixed amount of a third element. The ratio of these two elements is the same when they combine between.

For example:

When $63.5~\rm{g}$ copper combines with sulphur produces copper sulphide

$\begin{array}{lllll}
\ce{Cu}&+&\ce{S}&\rightarrow&\ce{CuS}\\
63.5~\rm{g}&&32~\rm{g}&&95.5~\rm{g}\\
\end{array}$

Conversely when those $63.5~\rm{g}$ of copper combines with oxygen produces cupric oxide.

$\begin{array}{lllll}
2\ce{Cu}&+&\ce{O_2}&\rightarrow&2\ce{CuO}\\
63.5~\rm{g}&&16~\rm{g}&&79.5~\rm{g}\\
\end{array}$

Therefore the proportion between the mass of sulphur and oxygen masses is:

$\frac{m_{\ce{S}}}{m_{\ce{O_{2}}}}=\frac{32}{16}=2$

When sulphur and oxygen combine together they make sulphur dioxide.

$\begin{array}{lllll}
\ce{S}&+&\ce{O_2}&\rightarrow&\ce{SO_{2}}\\
32~\rm{g}&&32~\rm{g}&&64~\rm{g}\\
\end{array}$

Then the proportion between these two becomes:

$\frac{m_{\ce S}}{m_{\ce{O_{2}}}}=\frac{32}{32}=1$

The latter is in proportion which is half of the first ratio. Hence follows the Richter law.

But how can I use this information to understand what it was mentioned in the paragraph from above? How is exactly related with equivalent weights?

The second part of the question arises from the fact, that would it be okay to state this?

In an hypothetical reaction between $A$, $B$ producing $C$ and $D$.

$\begin{array}{ccccccc}
aA&+&bB&\rightarrow&cC&+&dD\\
\textrm{1 eq gram of A}&&\textrm{1 eq gram of B}&&\textrm{1 eq gram of C}&&\textrm{1 eq gram of D}\\
\end{array}$

Becoming in

$\textrm{1 eq gram of A}=\textrm{1 eq gram of B}=\textrm{1 eq gram of C}=\textrm{1 eq gram of D}$

Would it be accurate to put it in that way?

or?

$\textrm{number of eq gram of A}=\textrm{number of eq gram of B}=\textrm{number of eq gram of C}=\textrm{number eq gram of D}$

where:

$\textrm{1 eq gram A} =\frac{\textrm{grams of A compound equal to  the equivalent weight of A}}{\frac{\textrm{formula weight of A}}{\textrm{number of electrons transfered}}}$

which is different when considering moles:

$\begin{array}{ccccccc}
aA&+&bB&\rightarrow&cC&+&dD\\
\textrm{a moles of A}&&\textrm{b moles of B}&&\textrm{c moles of C}&&\textrm{d moles of D}\\
\end{array}$

where:

$\textrm{a moles of A}=\textrm{b moles of B}=\textrm{c moles of C}=\textrm{d moles of D}$

So, is what I wrote correct? How can I relate Richter's law of reciprocal proportions to the equivalent weights? How is it related with the paragraph from above? Perhaps does it meant to say that there is a definite amount of reagent which can react with a certain amount of sulphuric acid? Then why isn't it related more with the concept of limiting reagent rather than the equivalent weight? Can someone guide me on that?


texts: Why benzene is more easily reduced by Birch reduction than by catalytic hydrogenation?

texts:
As far as I know, H2,Pd is a better reducing agent than Na in liquid ammonia.
However, Na in liquid ammonia can reduce benzene at low temperature conditon of about -30°C.
Moreover, it is hard for H2,Pd to reduce benzene and requires very high temperature and pressure.


texts:
If the pressure is lowered in a distillation column, then the equilibrium curve will move further away from the diagonal (bulge out more) in an equilibrium diagram. This leads to a decrease in ideal step stages required to reach the separation requirement.
My question is why does the ideal step stages decrease? Is it only because of how the stages are drawn; meaning if the equilibrium curve is more bulged less horizontal and vertical stages are required. Or has it to do with the driving force increasing as pressure is lowered?
All help is appreciated. Thank you!


texts: Why does the Wurtz reaction form such an unstable compound with torsional strain?

texts:
What would be the product formed when 1-bromo-3-chlorocyclobutane with two equivalents of metallic sodium in ether?

I know that there would be a free radical formation and then it will form a compound whose bond line structure would look like a square with a diagonal.

But why is such an unstable compound being formed as there is a lot of torsional strain?


texts: Reaction mechanism for the conversion of acyl hydrazide to acyl azide

texts: How is an an acyl hydrazide converted into an acyl azide in the presence of $\ce{HNO2}$? According to me, the $\ce{-NH2}$ group of hydrazide will get converted into $\ce{-N2+}$ through $\ce{HNO2}$. However, I am unable to proceed after that.


texts: Hydrogen electrolyzer output pressure flow

texts:
This is for pressurised hydrogen storage number crunching. I have a question about the pressure and flow at the hydrogen output of an industrial size alkaline water electrolyzer. These electrolyzers are rated as hydrogen Nm3/hr and output pressure. So lets say the electrolyzer in question is rated at 15 Nm3/hr and output of 8 atm. Meaning it creates $15~\mathrm{m^3}$ of hydrogen at 1 atm at 68 °F (20 °C) every hour and has a pressure of 8 atm at the electrolyzer hydrogen output.

Now my question is if there is a back pressure of 8 atm at the output ($\ce{8atm <=> 8atm}$) is there no flow or would there be a flow of $1.875~\mathrm{m^3}$ ($15~\mathrm{m^3}$ at 8 atm) according to the combined gas law?


texts: How does the mixing of two gases increase entropy?

texts:
I have learnt that $\mathrm{d}S = \mathrm{d}Q_\mathrm{rev}/T$, where $Q$ is the heat energy absorbed by the system. Now consider an insulated compartment with two chambers, separated by a valve. Each chamber consists of a gas at a particular temperature and volume. Now, the valve is screwed open. We know that the entropy of the isolated system will increase as the gases have more freedom.

But, starting with the assumption that the walls were insulated, where did the heat energy come from?

How did the entropy increase?


texts: What is the chemical redox equation between hydrogen peroxide and melanin?

texts: I am investigating hair bleach, and want to figure out the redox reaction between $\ce{H2O2}$ (hydrogen peroxide) and $\ce{C18H10N2O4}$ (melanin). $\ce{H2O2}$ is a strong oxidizing agent in this redox equation, but I don't know how to write that out. Someone please help?