texts: Is there an error in a Wikipedia article explaining the influence of oxidation states?

texts:
Referring to the series of oxoacids of chlorine: $\ce{HClO, HClO2, HClO3},$ and $\ce{HClO4}$, tabulated in the Wikipedia article on electronegativity, the article states, in the section near the end titled "Variation of electronegativity with oxidation number":
“As the oxidation state of the central chlorine atom increases, more electron density is drawn from the oxygen atoms onto the chlorine, reducing the partial negative charge on the oxygen atoms …” and illustrates it with a table. (NB There is an ambiguity in the use of the word "reducing" which is the opposite of "oxidising", but the intended meaning in terms of increasing or decreasing electron density is clear in the Wiki statement.)
But as I understand it (and as also given by the rules for assigning oxidation numbers), insofar as oxidation state represents the number of electrons that an atom can gain, lose, or share when chemically bonding with an atom of another element, the table is correct, but shouldn’t the textual statement be the converse:
“As the oxidation state of the central chlorine atom increases, more electron density is drawn from the central chlorine atom onto the oxygen atoms, increasing the partial negative charge on the oxygen atoms ...”
I reason it thus And just to be clear, let's go back one step to start with the even simpler case of $\ce{HCl}$, where clearly the oxidation states must be ($\ce{H} = +1, \ce{Cl} = -1$, respectively; total 0):
When we move on to $\ce{HClO}$, then it becomes (+1, +1, -2 respectively) as the single oxygen with stronger electronegativity than chlorine is assigned the oxidation state -2, so that balancing the total means the electronegativity of the central chlorine must change from -1 to +1 (in agreement with the table on the Wiki page, but not with the article’s statement about the direction of change of electron density.
And as we move along the series to $\ce{HClO4}$, the central chlorine is having more and more electron density sucked off it by the four more electronegative oxygen atoms, resulting in the final oxidation states (+1, +7, -8), in agreement with the table in the above-cited Wiki article, but not with the article's textual explanation.
So I conclude that the text statement in the Wiki article is currently wrong (and if so I will amend the Wikipedia article) - or else I'm wrong, and would appreciate someone pointing out my own error…?


texts: Dispersion forces - what determines which molecule will have its electron cloud repelled?

texts:
Here is an image I found which illustrates dispersion forces:

One helium has its electron cloud repelled by the other helium's electron cloud, which exposes the nucleus and gives an induced dipole which holds the atoms together weakly. But when two helium atoms approach each other, what determines which atom will have its electron cloud repelled? I would think that both electron clouds would equally repel each other. Also I am guessing that this effect will get stronger as temperature is lowered (since helium is a liquid at very low temperatures), but I am not sure why.


texts: What is the formula of manganese oxohydroxide: MnOOH and MnO(OH)2?

texts:
I found various formulae of manganese oxohydroxide. Some site says it is $\ce{MnOOH}$, other say it is, $\ce{MnO(OH)2}$. So, which one is correct?

The mineral manganite is considered manganese oxide-hydroxide $\ce{MnOOH}$, but yahoo answer claims that it is $\ce{MnO(OH)2}$.
In Winkler titration, $\ce{MnO(OH)2}$ is formed:

$$\ce{2 MnSO4(s) + O2(aq) → 2 MnO(OH)2(s)}$$

There is some uncertainty about whether the oxidised manganese is tetravalent or trivalent. Some sources claim that $\ce{Mn(OH)3}$ is the brown precipitate, but hydrated $\ce{MnO2}$ may also give the brown colour. So, is $\ce{MnO(OH)2}$ hydrated $\ce{MnO2}$?

So which one is manganese oxohydroxide- $\ce{MnOOH}$ or $\ce{MnO(OH)2}$?


texts: Decarboxylation of THCA during CO2 Extraction of Cannabis

texts:
We have a strange problem. We are performing CO2 extraction on cannabis and we are seeing considerable decarboxylation of THCA to THC.

We have high quality temperature sensors at the heat exchangers, the extractor vessels, and the separator. We have not observed any temperature spikes that would explain it.

Various parameters have been tried, i.e.

40 - 50C (104-122F) / 115 - 280 bar (1770 - 4050 psi)

We can't find any correlation between the temperatures / pressures and the level of decarboxylation.

The system has been run for 24 hours at 120bar/50C and we are getting approximately equal amounts of THC and THCA out.

The starting materials has been tested to being only slightly decarboxylated. Disturbingly, the spent material is also being decarboxylated.

The same equipment is used to test both the starting and spent material. The results on the starting material have been verified by a 3rd party lab. It seems unlikely to be a testing problem.

We have multiple extractors and we are seeing the same behaviour so it is unlikely to be a sensor issue. The temperature controllers also have their own thermostat that agrees with the extractor sensor. The extractors are all temperature controlled and all temperatures are logged every 30 seconds.

There is a research paper by Rovetto et al. that also observes significant decarboxylation but not to the extent that we are observing it:

https://www.researchgate.net/publication/315417305_Supercritical_carbon_dioxide_extraction_of_cannabinoids_from_Cannabis_sativa_L_plant_material

Is it possible that the normal decarboxylation threshold (e.g. 115C) is lowered when at high pressure?

I understand that THC extracts far more readily than THCA, however looking at the mass balance it seems that selective extraction can not explain it.

If anyone has any insights to share, I would very much appreciate it.

Thanks


texts: Why does no Robinson Annulation occur after the Michael addition?

texts:
Under basic conditions a Michael addition reaction can be used to convert compound A into product C. Explain why no Robinson annulation cyclic product is observed?

  Compound A

  Product C

I have worked out that the other compound involved in the Michael addition reaction would be compound B (below), but I don't know why no Robinson annulation reaction could occur after the Michael addition reaction?

Compound B


texts: Which of the following releases the smallest amount of energy upon gaining an electron?

texts:
$\ce{C}$, $\ce{Rb}$, $\ce{Ga}$, $\ce{Ge}$

I am confused in the sense that I don't know what it means by "released the smallest about of energy upon gaining?" would it be $\ce{Rb}$ because the shell is so big that when it loses an electron the overall energy doesn't really matter?


texts: What is the necessary volume of concentrated HCl to prepare a solution with a pH of 1.8?

texts:
I am trying to solve the following exercise:

  What volume of a concentrated $\ce{HCl}$ solution, which is $36.0\%$ $\ce{HCl}$ by mass
  and has a density of $1.179~\mathrm{g~mL^{-1}}$, should be used to make $5.00~\mathrm{L}$ of an $\ce{HCl}$
  solution with a $\mathrm{pH}$ of $1.8$.

I found the respective volumes that $\ce{H2O}$ and $\ce{HCl}$ contributed.
I then found the molarity of the $\ce{HCl}$ aqueous solution given.
I used $10^{-\mathrm{pH}}$ to get the amount concentration of $\ce{HCl}$ needed, I then proceeded to find the amount of substance of $\ce{HCl}$ by multiplying the concentration needed by $5.00~\mathrm{L}$. I then took the amount of substance of $\ce{HCl}$ needed and multiplied by the density given to get an answer of $2.4~\mathrm{L}$.

Am I correct?


texts: Can the Smirnov-Zamkow reaction be described as a pericyclic process?

texts:
The Smirnov-Zamkow reaction involves the reaction of 2-butyne and chlorine in the presence of a Lewis acid catalyst to afford a dichlorocyclobutene:

At first glance, it appears to be an example of a thermal [2+2]-cycloaddition, which, by the Woodward Hoffman rules is forbidden.[*] This either means that (1) the reaction is stepwise, or (2) the intermediates are able to arrange themselves such that both components are not reacting suprafacially.

Very few mentions of the Smirnov-Zamkow reaction appear in the literature. The only real description is found in Fleming [1] where the reaction is proposed to involve initial formation of an allene. All other references on the internet simply link back to Fleming, with no mention made of this reaction in March, Carey, or any of the other usual suspects.

Clearly the reaction isn't synthetically that useful, and its initial reports occurred before pericyclic reactions had been widely studied/rules existed governing what was 'allowed',[**] but it is a curious example, to which I can't (yet) convince myself is an allowed pericyclic reaction on the grounds of orbitals.

  Can the Smirnov-Zamkow be satisfactorily described as a pericyclic process (i.e. can it be drawn in such a way as to obey the thermal Woodward Hoffman rules), or is it best described as a stepwise process?

References:

[*]: The reaction was so strange that allegedly R.B. Woodward was left 'open-mouthed, with nothing to say' when he first read the report of the reaction taking place, under such 'mild' conditions, if a set of second year undergraduate notes are to be believed.

[**]: The reaction is actually referenced in Conservation of Orbital Symmetry by Woodward and Hoffman, they actually give a slightly different explanation to Fleming/the lecture notes I first encountered this reaction in.

[1]: Fleming, I. Molecular Orbitals and Organic Chemical Reactions (Reference Ed.), Wiley: 2010

[2]: I. V. Smirnov-Zamkov, Doklady Akad. Nauk SSSR, 1952, 83, 869 (Chem. Abs., 1953, 47, 2711g); I. V. Smirnov-Zamkow and N. A. Kostromina, Ukrai. Khim. Zh., 1955, 21, 233 (Chem. Abs., 1956, 50, 9302e); R. Criegee and A. Moschel, Chem. Ber., 1959, 92, 2181.   (I also don't speak Russian to read some of these)


texts: Why do spectra appear continuous despite their allowed transitions being discrete?

texts:
So in my physical chemistry class we have been looking into radiation, selection rules, etc.

Taking into account the discrete levels of energy an electron can have, I cannot understand why fluorescence and absorption spectra of compounds have continuous lines instead of discrete values.

If electrons in a system can only have a select number of energies, why is it that these graphs show a continuum of absorption and emission?

I also have this problem with blackbody radiation, since it is a continuous line for any temperature.


texts: Is a galvanic cell only called that if copper and zinc are used?

texts: I know other metals can be used to get the same effect but I'm interested in the name. Is it only called a galvanic cell if copper and zinc are used? Or is the name "voltaic cell" used only when copper and zinc are used? I'm confused because I've heard them being used interchangeably.


texts: What's the name of this electrolysis device?

texts:
I've seen it in a couple of videos, it's used to electrolyze water in 2 different containers at the same time to make a comparison and thus is very handy.

What is it called (besides just a hydrolizer)?


texts: Can you undo 'blackening' from Chromium after exposure to bleach?

texts:
I accidentally used toilet cleaner (instead of bathroom cleaner) containing bleach on a Chromed tap/faucet which has resulted in an black clouding over the surface of the chrome. It doesn't seem to polish out or clean off even with metal polish.

Is there any way to reverse this process or will I have to replace or chrome plate the tap?


texts:
Many demonstrations of electrolysis show the use of baking soda and a 9 volt battery for electrolysis of water. As a science experiment, I tested different voltages by adding more batteries. In my experiment, I used distilled water. After letting the electrolysis happen for 5 minutes, the 18 volt test had yellow discoloration in the water. Because I couldn't find any places online that mention this or explain what it is, I thought to ask. Perhaps it is not a common thing?

[Edit] Answer: Most likely cause was degradation of poor electrode material with too much electricity.


texts:
I've read that phenol should be stored under inert gas and protected from light.

What reactions does phenol undergo during long-term storage in the presence of air and light?
Is it really necessary to take such precautions when storing or handling phenol?
How does the stability of solid phenol compare to that of phenol dissolved in, say, cyclohexane?


texts: Do ions in a salt bridge come from the half cells in electrochemistry?

texts:
I understand the basics of electrochemsitry and galvanic cell, where there are half cells where either an oxidation or reduction reaction occur, and electrons moving between the wires provide the current.

What confuses me is the salt bridge. In this diagram here, nitrate ions, which are from the solution of a half cell, go into the salt bridge.

However, other diagrams (and answers like those to Do the salt bridge ions have to match the ions in the half-cells solutions?) do not state that the ions have to be the same (you don't need nitrate ions in the salt bridge if you have a silver nitrate solution for example).

So do ions like nitrate from the solution in a half cell enter the salt bridge?


texts: Mixing isopropyl alcohol and propylene glycol

texts:
What would happen if I mixed isopropyl alcohol and propylene glycol? I need to winterize the water base of my basketball hoop, and already added some isopropyl alcohol, but I discovered that propylene glycol would be better.

Also, I know isopropyl alcohol is toxic to ingest, but will it contaminate my soil if I drain it?


texts: Why are there exactly 5 types of two-dimensional lattices, and what distinguishes them?

texts:
In the book Chemistry: The Central Science, they introduced the following 5 types of two-dimensional lattices:
The book said that the blue square represents the unit cell, the black dots are lattice points, and the vector a and b are lattice vectors. They don't say what the solid black lines represent. I feel as though they are redundant.
According to the illustration, hexagonal lattice is just a special case of rhombic lattice where γ = 120°. So why does a rhombic lattice have 2 types of unit cells (the blue and the green) whereas a hexagonal lattice only has 1 (and why do the solid black lines for these two lattices are different?). The same question also applies to rectangular lattice. Isn't it just a special case of oblique lattice where γ = 90°?
Why does it make sense to group lattices into 5 types, and what distinguishes them?


texts: State solid synthesis of LiMn2O4 mechanism

texts:
I have difficulties finding the mechanism of the state solid synthesis of $\ce{ LiMn2O4}$ in literacy.

Starting from lithium acetate and manganese acetate, I've found the general equation easily:

$$\ce{Li(OAc) + 2 Mn(OAc)2 + 43/4 O2 -> LiMn2O4 + 10 CO2 + 15/2 H2O}$$

What I can't find is a mechanism of this reaction. I know that $\ce{Mn}$ is oxidized and $\ce{Li}$ keeps its oxidation state. Is $\ce{Mn3O4}$ a precursor in this reaction? Is $\ce{Mn2O3}$ a by-product?


texts: How can you manage SCF convergence problems?

texts:
"Failure to locate stationary point, SCF has not coverged"

This is the most annoying message after Optimization run ( even with a good primary start geometry like UFF we ay see that) .
The only solution I know is to use the output log file for another run but it is very time consuming.
Is there any way to force GAMESS to automatically do that ?( I mean makes another automatic run on current output results ).


texts: Does isopropyl alcohol have a similar affect as dipropylene glycol regarding absorption?

texts: I am an aromatherapist and am making essential oil reed diffusers.  Do you know if isopropyl alcohol has a similar affect in absorption as dipropylene glycol?


texts: Why is law of mass action only applicable for elementary reaction?

texts: Why can't we apply law of mass action for non-elementary reaction? Why does is vary with the rate law in case of non-elementary reactions?


texts:
Aluminium is along the dark line of the Periodic Table and it is $p$-block metal.

Is it metal or a metalloid?
Why?


texts: Are 6-hydroxyhexan-2-one and hexanoic acid isomers?

texts:
Are the following two compounds isomers?
(A) $\ce{CH_{3}-CO-CH_{2}-CH_{2}-CH_{2}-CH_{2}-OH}$
(B) $\ce{CH_{3}-CH_{2}-CH_{2}-CH_{2}-CH_{2}-COOH}$

Although they have the same molecular formula ($\ce{C_{6}H_{12}O_{2}})$, I think that this two compounds are not isomers.


texts: Polymerisation of methyl methacrylate - can the C=O group get involved?

texts:
When methyl methacrylate undergoes free radical addition polymerisation, the C=C pi bond is broken during the process:

I'm wondering why the C=O pi bond doesn't get broken during the polymerisation. I suspect it may be because the C=O bond is stronger than the C=C bond, but are there any other ways to rationalise this?


texts: How dangerous is cobalt(II) chloride used in silica gel balls?

texts:
I was looking up silica gel beads on Wikipedia and noticed that some (and from experience most) are doped with a colouring agent to indicate that they have absorbed all that they can.

The Wikipedia page says that usually cobalt(II) chloride or methyl violet is used, both of which are toxic. But it mentions nothing about what quantity these become toxic? I assumed the quantity in a normal silica gel bag (that come in shoes for example) isn't enough to be harmful, otherwise why would they be using it?

Also, it mentions that

  Crystalline silica dust can cause silicosis but synthetic amorphous silica gel is indurated, and so does not cause silicosis.

Are the silica gel beads synthetic amorphous, i.e. do not cause silicosis?


texts: When measuring avidity should you use the ligand concentration or the nanoparticle concentration?

texts:
Looking at avidity between a ligand-receptor, you're looking at an enhancement of the $K_d$ compared to a lone ligand.

Is it more appropriate to compare the $K_d$ using the concentration of the "free" ligand or the concentration of the free complex?

Using the ligand is odd at the lower regimes since the ligand efficency is fairly low but using the nanoparticle changes how you have to calculate the effective concentration. I've seen papers that do both and I'm curious which is most appropriate/correct


texts: Are there some similarities between J-coupling and j,j-coupling?

texts:
I'm a bit confused having heard two different terms in different lecture parts:

J-coupling

There is the J-coupling (= indirect dipole dipole coupling = scalar coupling) which arises from a hyperfine interaction between the nuclei and the interaction. The J-coupling is a coupling between the two nuclear spins of two nuclei (e.g. a C-H bond). Because of the Pauli principle the two binding electrons are anti-parallel located so the nuclear spins $I_1$ and $I_2$ also have an anti-parallel nuclear spin.

j,j-coupling

There is as well the jj-coupling (= spin orbit coupling) which describes the coupling of the different $j_i$. This coupling scheme is valid for heavier atoms. (For leight atoms the ls-coupling is valid). In atoms with bigger nuclear charges, spin-orbit interactions are frequently as large as or larger than spin-spin interactions or orbit-orbit interactions.
$\mathbf J = \sum_i \mathbf j_i = \sum_i (\boldsymbol{\ell}_i + \mathbf{s}_i).$ Wikipedia

I don't see any commonalities. Why is the term "J-coupling" similar to the term "j,j-coupling"?


texts: Number of stereoisomers of polysubstituted cubane

texts:
The molecule given below is a substituted cubane.

a) How many stereoisomers exist for this molecule?
b) How many pairs of enantiomers are possible?

How do I calculate the number of stereoisomers? Since each carbon is linked to four different groups, can I claim that all are chiral and, therefore, $2^8$ stereoisomers are possible?
If that is true, since there is no element of symmetry, can I say that $2^4$ enantiomeric pairs exist?
Edit: Looking at the comments clears things up but brings forth another question. If, say, iodine was present at any other position that would not lead to a tetrahedron, what would happen?


texts: Is a discharged battery in a state of chemical equilibrium?

texts:
A reaction that has reached chemical equilibrium no longer shows changes in reactant and product concentrations, but forward and reverse reactions are still going on. I'm confused whether a completely discharged battery is in a state of equilibrium.

Argument that an equilibrium has been reached

If I measure the cell potential, it will be zero. That means that the Gibbs free energy of reaction is zero, which is a property of a chemical equilibrium. When I discharge a battery by shorting it, there are concentration changes in the battery that cease when the battery is discharged, which looks like a reaction going toward and then attaining equilibrium.

Argument that this is not an equilibrium state

One property of a chemical equilibrium is that it is dynamic, i.e. the forward and reverse reactions are ongoing but occur at the same rate. For the battery, the reaction does not happen unless I close the circuit by electrically connecting the electrodes (e.g. shorting the battery with a wire). Even if I connect the electrodes with a wire, no current will flow because the battery is dead. So I don't see forward and reverse reactions going on. This would be like placing two beakers with 1 M aqueous salt solutions next to each other and saying they are at equilibrium. However, if the solutions were both contacting a dialysis membrane, ions would flow in either direction (at the same rate) so it would be fair to call this a state of dynamic equilibrium.

Which argument wins?

Is the discharged battery at a state of equilibrium or not? Does it matter whether the electrodes are connected electrically to decide on the answer?  Does it make sense to discuss a state of equilibrium in the context of electrochemistry in the first place?


texts: Difference between water solubilities of phenol and cyclohexanol?

texts: The solubility of phenol is 83 g/L, while that of cyclohexanol is 36 g/L. Both of them have a hydroxy group, and can form hydrogen bonds with water. Also, the hydrophobic part of phenol, as well as cyclohexanol is almost the same. Then what is the reason for phenol's better water solubility in water compared to cyclohexanol?


texts: is this the proper identification of this cyclic molecule?

texts:
Attempt:

(1S,3S)-1,3-Dichlorocyclohexane

I'm just not sure about the nomenclature for R and S configurations (our teacher was a little unclear). I gave it my best shot after looking through some textbooks but would like just a quick confirmation or someone to tell me if it's wrong.

In addition, if I exchanged the positions of the Cl and H groups on each side with each other would I get an enantiomer? ((1R,3R)-1,3-Dichlorocyclohexane)


texts: Apparent solubility of Ag2C2O4 in a buffer solution

texts:
We take the following quantities and mix them together:

  $\pu{20 mL}$ solution of $\ce{AgNO3}$ $\pu{0.001 mol//dm3}$
  $\pu{20 mL}$ solution of $\ce{H2C2O4}$ $\pu{0.200  mol//dm3}$
  $\pu{40 mL}$ buffer solution $\mathrm{pH} = 5.00$

  What is the apparent solubility of the insoluble salt formed, knowing: $K_\mathrm{a1}=6.50\cdot 10^{-2}$, $K_\mathrm{a2}=6.10\cdot 10^{-5}$ (for $\ce{H2C2O4}$) and $K_\mathrm{s}=1.10\cdot 10^{-12}$ (for $\ce{Ag2C2O4}$)?

The initial concentrations for $\ce{Ag+}$ and $\ce{H2C2O4}$ are:
\begin{align}
[\ce{Ag+}]&=\pu{2.50E-4 mol//dm3}\\
[\ce{H2C2O4}]&=\pu{5.00E-2 $$mol//dm3}$$ \text{(excess)}
\end{align}

We're dealing with the following equilibria:
\begin{align}
\ce{Ag2C2O4 &<=> 2Ag+ + C2O4^{2-}}\\
\ce{H2C2O4 &<=> HC2O4- + H+}\\
\ce{HC2O4- &<=> C2O4^{2-} + H+}
\end{align}

The pH of the solution is above $\mathrm{p}K_\mathrm{a2}$, therefore $\ce{H2C2O4}$ is found mostly as $\ce{C2O4^{2-}}$. By using the Henderson–Hasselbalch equation, we find that $[\ce{C2O4^{2-}}]=\pu{4.30E-2 mol//dm3}$.

Since we started with an excess of acid, we can consider that the variation of concentration for that particular species (after precipitation completes) is negligible. By using $K_\mathrm{s}$, we find that:

$$2S=[\ce{Ag+}]=\pu{5.06E-6 mol//dm3}$$

Is my approach correct? I'm confused because of their approach, where they invoke the following equation:

$$S=\frac{1}{2}\ce{[Ag+]}=[\ce{H2C2O4}]+[\ce{HC2O4-}]+[\ce{C2O4^{2-}}]$$

Which doesn't really make sense since we started with an excess of $\ce{H2C2O4}$.

In my opinion, this equation would make sense if we made a solution only with the buffer and an arbitrary quantity of insoluble salt.


texts:
I just wanted to check my understanding of this. Given the reaction,

$$ (1) \; \ce{A->B} $$

the corresponding rate law is $ v=k[A] $

Also consider

$$ (2) \; \ce{A <=> B} $$

with forward rate law: $ v_1=k_1[A] $ and reverse: $ v_2=k_2[B] $. This makes the corresponding rate equation $ v=v_1-v_2=k_1[A]-k_2[B] $.

My question is in the difference between the two. I've often seen reactions expressed in both ways. In $ (1) $, is the rate law assuming the reverse reaction not to occur (or at least to be completely negligible? That's why I drew it with $ \ce{->} $ instead of $ \ce{<=>} $. Am I correct in my thinking? In actuality, is it always more correct to use the rate law of $ (2) $? The rate law for $ (1) $ could also correspond to initial reaction velocity, right? This is because there is no $ B $ present at the start of the reaction.

If this is correct, then the integrated rate equations will become substantially more complicated using rate laws of form $ (2) $. I can't use simple equations like $ [A]_t=[A]_0 e^{-kt} $, as this wouldn't take into account the reverse reaction.


texts:
I have a question where I do not understand the final step to solve...here it is:

What will be the Strontium ion concentration remaining after 30.0 mL of 0.10 M Na2SO4 solution are added to 70.0 mL of 0.20 M Sr(NO3)2 solution?

First, I wrote the equation: Sr + SO4 -> SrSo4 (I know this is excluding ions, because I am primarily focused on the stoichiometry part)

I figured moles of Na2So4 and Sr(NO3)2, which correspond to moles of strontium. These are .003 moles Na2SO4 and 0.014 moles Sr(NO3)2. This is where I got stuck, looked to my book's answer explanation, and got more confused. The book states
"0.0030 mol of sulfate ion will combine with 0.0030 mol of strontium ion, leaving 0.011 mol of strontium in a total volume of 100.0 mL."

Why is the reaction leaving 0.011 moles of strontium? What was the calculation that obtained this number?

Thank you!


texts: What are the non-aqueous solvents for sodium polyacrylate?

texts:
I am attempting to use sodium polyacrylate as a sodium transport mechanism in a sulfur-bromine cell. I can upset the sodium balance with sodium salts, but the contamination introduced by the non-metallic ion from that salt is unacceptable. Water is a solvent that can be ultimately coerced into a solution compatible with the acrylic polymer I wish to matrix the polyacrylate within.

I have tried (with no success) alcohols, acetone, and ketones. Are there non-aqueous solvents I should consider that suit my needs that I have not yet tried?


texts: What is the biggest known difference between rₑ and r₀?

texts:
What is the biggest known difference between $r_e$ and $r_0$? Where $r_0$ is the average bond length of the lowest vibrational state, and $r_e$ is the location where the potential is lowest.

For a perfect harmonic oscillator, these are the same (notice that the peak probability is exactly at the minimum of the potential):

What is the largest known difference between $r_e$ and $r_0$ in a real molecule?

This is important because the CRC Handbook on Chemistry and Physics almost always gives $r_0$ because that's what can be determined more easily from experiment, but ab initio geometry optimization almost always gives $r_e$, yet many publications do not even say which type of bond length they are reporting.


texts:
The MG811 is an electrochemical sensor that measures $\ce{CO2}$. I think is something like a redox reaction but i don't understant how it produces $\ce{e-}$ so i can read them and get the $\ce{CO2}$ concentration.

I copy you the reaction that makes the sensor measures

When the sensor exposed to $\ce{CO2}$，the following electrodes reaction occurs：

Cathodic reaction: $\ce{2Li+ + CO2 + 1/2O2 + 2e- -> Li2CO3}$

Anodic reaction：$\ce{2Na+ + 1/2O2 + 2e- -> Na2O}$

Overall chemical reaction：$\ce{Li2CO3 + 2Na+ -> Na2O + 2Li+ + CO2}$

The datasheet says that it workings adopting the electrolyte cell Principle and that it's composed by the following cells:

Air，$\ce{Au}$|NASICON|| carbonate|$\ce{Au}$, air，$\ce{CO2}$

I need you to explain me how actually the sensor is working and with which material are made the electrodes.


texts: Is there any diprotoic acid where both pka's are less than 0?

texts:
The question states it all.

I'm working out special cases for a different problem and such an acid would create another special case.

Sulfuric Acid is the strongest that I remember. pKa's −3, 1.99


texts:
I am currently collecting information for an abstract and therefore I wanted to discuss different $\ce{[BO3]^3-}$ and $\ce{[BO4]^5-}$ connectivities. I also found a book on crystallography and the following passage

(Summarized translation of the original German text in [1])

  When a finite connection of $\ce{[BO3]^3-}$ units is considered group borates form. [...] $\ce{[B2O5]^4-}$ (via vertices), $\ce{[B2O4]^2-}$ (via edges) or for example $\ce{[B4O8]^{4-}}$ (four-membered ring). [...]

It's about the last example that I cannot really find any other mention in literature. Although it looks okay if you consider vertex-connected oxoborate units forming a $\ce{[B4O8]^{4-}}$ anion, I cannot seem to find any example in literature. Even the book doesn't give any example.

I found some minerals for example $\ce{Ca2B4O8}$ but it's also described as $\ce{CaB2(OH)8}$. There are examples with $\ce{[B4O8]^{4-}}$ but they always contain additional $\ce{(OH)-}$ ligands.

The any other explanation I could think of would be $\ce{[B4O7]^{2-}}$. That would have a different structure (they also sketched their molecule anion and the got the charges correct so I don't think $\ce{[B4O8]^{4-}}$ is typing mistake). So, did anyone else find any example on a $\ce{[B4O8]^{4-}}$? I would usually check the Gmelin but due to the virus spread our library is currently closed.

[1] W. Kleber, H.-J. Bautsch, J. Bohm, Einführung in die Kristallographie, 19th edition, Oldenbourg Verlag, Munich, 2010.

Edit: I also did a quick DFT, hybrid functional B3LYP with Def2-SVP on the anion and according to my bond analysis (don't know if you can trust that for a tetra-anion here) all $\ce{B-O}$ bonds inside the ring have a bond order of 1.x while the external $\ce{B-O}$ bonds have a double bond character (I guess it's treating them as $\ce{B=O}$ rather than with charges here). But in theory that thing should be stable to me.


texts:
What factor does the symmetry of a molecule play?

For example, I know water is asymmetric so does this therefore make water polar (I know in fact that is is)? It may sound ignorant due to my lack of knowledge but considering one can draw a line through a water molecule, it appears as if if is symmetrical? Why exactly is water asymmetric and how can one tell? I have heard that it is due to its bent shape and lone pair of electrons but this is too general. Just because a shape is bent does not mean it lacks symmetry?

Finally, is there a concept to finding if a given molecule is symmetrical or asymmetrical?


texts: Step up reactions in elementary organic chemistry

texts:
What are some elementary (high school level) step up reactions? (in which the length of the carbon chain of an organic molecule is increased by one)

Background: I was looking for a way to methyl chloride to acetone (spoilers: I still haven't found one :( I could use Wurtz reaction to form ethane from methyl chloride, but I don't know of a way to add one more carbon to this alkane. I found this question, but it only focuses on the ketene reagent's action on alkanes. I suppose there might be many more such "step up" reagents and their many more compounds which can be "stepped up". Hence, my question.

PS: A term related to "Step up" is "Step down", which observed in Hunsdiecker reaction and Hoffmann Bromamide reaction.


texts: What is exposed in the surface tension of water?

texts:
(I guess) I understand the covalent bonding of water and the hydrogen bonding of water between two different molecules, but I would like to know which part is the part that that exposes itself to the air in the surface tension of water. There should be something different to the rest of the liquid, otherwise there would be no frontier, right?
Is it the electropositive part of hydrogen or is it the electronegative part of oxygen that faces the air? (or may be none of them).
Surface tension in water owes to the fact that water molecules attract one another, as each molecule forms a bond with the ones in its vicinity. At the surface, though, the outmost layer of molecules, has fewer molecules to cling to, therefore compensates by establishing stronger bonds with its neighbors, this leading to the formation of the surface tension.... more here:

https://www.usgs.gov/special-topic/water-science-school/science/surface-tension-and-water?qt-science_center_objects=0#qt-science_center_objects
Thanks to all for your help (I'm in chemistry '101' for dummies so please try to be as basic as possible.
Video: https://www.youtube.com/watch?v=moITG5Q7zzI
(Hydrogen bonds https://www.khanacademy.org/science/high-school-biology/hs-biology-foundations/hs-water-and-life/v/hydrogen-bonding-in-water)


texts: What makes banana bonds possible in diborane?

texts:
Diborane has the interesting property of having two 3-centered bonds that are each held together by only 2 electrons (see the diagram below, from Wikipedia).  These are known as "banana bonds."

I'm assuming there is some sort of bond hybridization transpiring, but the geometry doesn't seem like it is similar to anything I'm familiar with Carbon doing.  What sort of hybridization is it, and why don't we see many (any?) other molecules with this bond structure?


texts: What is the pH at both equivalence points of titration between diprotic tartaric acid and NaOH?

texts:
Here's all the info I have and my attempt in solving the question:

The chemical equation for the titration:

$$\ce{C4H4O6 + 2NaOH -> Na2C4H4O6 + 2H2O}$$

Here are the 1st and 2nd $\mathrm{Ka}$ value for tartaric acid:

$$K_\mathrm{a1} = 9.2 \times 10^{-4}, K_\mathrm{a2} = 4.3 \times 10^{-5}$$

Molarity of tartaric acid = $5 \times 10^-4$

Standard solution of $\ce{NaOH }$ was made using $\pu{0.98 g}$ of solid $\ce{NaOH}$ dissolved in $\pu{250 ml}$ of water. The molar mass of $\ce{NaOH}$ is $\pu{39.997 g/mol}$.

This is what I have done so far.

n (C4H4O6) = cv = (5 × 10-4 M) (25ml ÷ 1000L) = 0.02 mol

n (NaOH) = m ÷ M = (0.98g) ÷ (39.997 g/mol) = 0.0245 mol (4dp).

C (NaOH) = n ÷ v = (0.0245 mol) ÷ (250ml ÷ 1000L) = 0.098M

N (NaOH) at equivalence point = cv = (0.098M) (0.204L) = 0.02 mol

C4H4O6(aq)+ 2NaOH(aq) → Na2C4H4O6(aq) + 2H2O(l)

I 0.02         0.02           0            -
C - 0.02      - 0.02       + 0.02          -
E   0           0            0.02          -

C (Na2C4H4O6) = n ÷ v = 0.02 ÷ (0.025L + 0.25L) = 0.0727M (4dp)

Na2C4H4O6(aq) + H2O(l) → C4H4O4Na2^+(aq) + OH^-(aq) below is ice table, stackexchange won't allow me to seperate the values.

I  0.0727          -           0              0
C   - x            -         + x             + x
E 0.0727 – x       -          x               x

Kb = Kw ÷ Ka = (1 × 10-14) ÷ (9.2 × 10-4) = 1.087 × 10-11

Kb = [C4H4O4Na2+] [OH-] ÷ [Na2C4H4O6] 1.087 × 10-11 = x2 ÷ 0.0727 x = √ ((1.087 × 10-11) (0.0727)) x = 8.89 × 10-7

pOH = - log [OH-] = - log (8.89 × 10-7) = 1.9

pH = 14 – pOH = 14 – 1.9 = 12.1


texts: How should I name this branched alkyl substituent?

texts:
The parent chain is a decane (in black), but for the alkyl substituent (in red) I'm trying to decide between:

5-(1,2-dimethylpropyl)decane
5-(2-methylbutan-3-yl)decane
5-(3-methylbutan-2-yl)decane

Which of these is correct?


texts: Why it is only carbons that have hydrogens attached (and not just hydrogens directly attached) to the charged carbon which result in hyperconjugation?

texts:
For the following compound:

Looking at figure 2, my understanding of hyperconjugation is that carbon 2 is more electronegative than the hydrogens attached to it, and so pulls charge towards carbon 2, giving it a partial negative charge. This negative charge then stabilises the positive charge on carbon 1.

Figure 2

My book says, for the compoound $\ce{C+H2CH2CH2CH3}$ there is only one hyperconjugation centre (i.e. the $\ce{CH2}$ attached to the C+).

Why can't the hydrogens attached to the C+ act as hyperconjugation centres? E.g. won't these hydrogens be less electronegative than the C+ and so the C+ will attract the electrons closer to it , somewhat stabilising the positive charge on the cabron?


texts: Bond Angles of Hypofluorous Acid - Gas and Solid Phases

texts:
This is the gas-phase structure of hypofluorous acid:

The solid-phase structure however has a bond angle of 101 degrees. Why is there a difference in the solid and gas phase bond angles?

Is this due to packing in the solid-phase? In the solid-phase the molecules should be much closer together than in the gas-phase, so I expect more intermolecular forces and interactions. However, what exactly would be responsible for the angle expansion in the solid phase? From one book I read that bond lengths often differ among the phases.

So what exactly is behind the bond angle expansion in the solid phase?


texts: What would you recommend to isolate these compounds from cooking oil?

texts:
Recycled cooking oil, aka "gutter oil", is a major problem in countries such as China. I am doing some research to see if there's a reliable and quick way to determine if something is gutter oil.

I came across a Chinese paper that uses Solid Phase Micro Extraction with Gas Chromatography/Mass Spectroscopy. In this paper, they listed out a list of chemicals that are commonly found in their samples of gutter oil.

Originally, I was planning to use Surface Enhanced Raman Spectroscopy for detecting these chemicals inside a matrix but it seems like the fluorescence of the oil is masking the raman signals of these chemicals.

All of these chemicals are dissolved in the sample oil in trace quantities. The are (listed in order of priority):

Methyl-3-butenenitrile
Hexane
5-Cyano-1-Pentene
1- decyne
Cyclohexane
Allyl cyanide
Acetic acid
benzene
Methyl cyclopentane
3-butenyl isothiocyanate
Allyl isothiocyanate
N-heptane
Toluene
1-hexanol
Xylene
Heptanone

Are there any simple extraction/filtration techniques that could isolate some of the above for the purpose of Surface Enhanced Raman Spectroscopy? I am looking for a sample preparation method that is less involved as solid phase extraction.


texts: Does a cloudy solution indicate presence of precipitates or not?The solution isn't completely opaque neither it is completely clear.


texts: What is the word for how polyprotic an acid is?

texts:
What is the word to describe the number of acidic hydrogens an acid has? I am currently thinking something like "proticity", but I am not sure  The use case world be for a table of things like this:

Acid    | Proticity
--------------------
CH₃COOH |  1
H₂SO₄   |  2
H₃BO₃   |  3

Or in a set of statements like this:

  The volume of gas produced by reaction A was 4.6 L. The proticity of Acid B was 3. The tare mass of object C was 4.76 g. The density of substance D was 7.8 g/mL.

Is there a specific word used to refer to this quantity? What word should I use to refer to it?


texts: Why ethyl cyanide and propanol have the same boiling point?

texts:
As I understand, the intermolecular forces of ethyl cyanide are of van der Waals nature (dipole-dipole) but in the propanol molecule there are hydrogen bonds which are in principle much stronger. Why then their boiling points are equal (97 ºC)? Their molar mass is very similar too.
Obviously, the triple bond of the cyanide group must be the cause, but I do not know how it can affect the boiling point, as the C-N bond is less polar than the O-H bond.


texts: Why does slaked lime water lose alkalinity over time?

texts:
When I throw 3 handfuls of white lime $\ce{Ca(OH)_2}$ into 60 gallons of tap water, the initial pH value is 11.4, but unknowingly it changes to pH 7.

What is the chemistry behind it?

How long does it take to completely change to neutral pH at open space?

I put lime in the water to pasteurize straw for mushrooms, and I need to know how long and how to make neutral pH faster so that I can pour the neutral water in the soil, so it won't ruin the soil.


texts: Why do exothermic dissolution reactions occur?

texts: I've always been taught that an exothermic dissolution means that the forming of solute-solvent bonds releases more energy than the energy consumed to break solute-solute bonds and solvent-solvent bonds. However, if the attraction that occurs between solute and solvent particles are mainly based off of intermolecular forces, why would the energy released when it is formed manage to exceed the breaking of the comparably stronger intramolecular bonds between solute-solute particles?


texts: Enol percentage comparison between 1,3 diketones and 1,2 cyclopentadione

texts: To what extent does 1,2-cyclopentadione exist in enol form? Will it be more than for 1,3 diketones? 1,3-Diketone with active methylene groups can form hydrogen bonds with a 6-membered ring structure. 1,2-cyclopentadione could also form hydrogen bonds, but it forms only a 5-membered ring.


texts: What about Miller Indices of planes passing through origin?

texts: For Miller Indices of planes if we encounter a case where the plane passes through the origin then I have heard that the only remedy can be arrived by shifting the origin to a different point.However I do not understand whether or not I am supposed to change the index of the other planes whose origin was not passing through the previous origin.Please give me a bit of justification for the case.


texts: Crystal field theory: splitting energy and stability

texts:
In crystal field theory, we admit that in a coordination compound there are only electrostatic interactions between the d orbitals of the central metal cation and the ligands (which are considered as negative point charges).
As the ligands and the central metal are brought closer together, an electrostatic repulsion is established, which causes a scission of the d-orbitals (i.e., the energetic degeneracy of the d-orbitals is lost).
When the orbitals split, an energy difference is established between the sets of degenerate orbitals, called the scission energy.
Well, can we relate this scission energy to the stability of a complex?
For example, if we have to compare the stability of [Co(NH3)6]3+ and [Rh(NH3)6]3+, could we state that the Rh complex is more stable because its scission energy is higher?


texts: Which reaction to use for standard formation enthalpy?

texts:
What reaction illustrates $\Delta H^\circ_\mathrm f$ for $\ce{CaCO3}$?

Answer: $\ce{Ca(s) + C(s) + 3/2O2(g) -> CaCO3(s)}$.

Ok so why isn't it: $\ce{2Ca(s) + 2C(s) + 3O2(g) -> 2CaCO3}$

Or

$\ce{Ca(s) + C(s) + O3(g) -> CaCO3}$ ?

For example in another similar question:

  Choose the reaction that illustrates $\Delta H^\circ_\mathrm f$ for $\ce{Ca(NO3)2}$.

Answer: $\ce{Ca(s) + N2(g) + 3 O2(g) -> Ca(NO3)2(s)}$

Can someone confirm this assumption of mine:  it's ok to use fractions in these types of equations to blance it out as long as it's in oxygen's coefficient.

As that assumption correct?


texts: Adding a polyvinyl alcohol chain onto polyethylene

texts: For school, my teacher asked what the proper procedure/reaction would be to add a polyvinyl alcohol chain onto a polyethylene chain. Can anyone help? I'll provide additional information if needed.


texts: How to know which kind of distortion takes place due to Jahn-Teller effect

texts: I have gone through a few videos and a few articles (including Wikipedia's) about Jahn-Teller distortion effect and I'm not able to follow if there is a rule which governs which kind of distortion will take place in which compound. If I want to remember which compound has which distortion, should I remember a rule or memorise the whole list?


texts:
It was nearly a year ago when I appeared for my first interview through the KVPY (a research oriented scholarship exam) when one of the questions the panel asked me was :
What is a chemical bond?
I had always pondered about the same question for ages and I had never come up to a satisfactory answer. Every book I have read keeps on talking about ionic bonds, which aren't 'bonds' at all but rather electroststic forces of attraction, and how covalent bonds are 'sharing' of electrons between two nuclei. This gets even more confusing when some books state that the 'nature' of bonding between certain atoms is around 50% ionic and 50% covalent.
Amiss all the confusion I had convinced my self that there is truely speaking no such thing as a 'bond'. All there existed was electro static forces of attraction which were either strong or either weak. (because there are only 'three fundamental forces' that I know of. )
Electrons when they are bound to multiple atoms together (like how planets around binary stars work) seemed to explain satisfactorily to me what are bonds.
However the panelist (mind you but I have heard that these panelists are actual scientists) who asked the question was not very happy with my answer and kept on trying to force me to talk about ionic and covalent bonds, by asking me how we classify them and which is stronger.
Is my interpretation correct? Why did the panelist not like my explanation?
An answer with highschool (and slightly higher) mathematics is okay, if not an explanation would be nice, otherwise it would be perfectly fine if you could point out mistakes in my argument and tell me if I was on the right track for interpretation.

In reference to the above context, would it be possible for someone to brief over a few different approaches developed to understand chemical bonding, the forces behind them, and the pros and cons of each theory.


texts: Determining the Energy Density of a Battery given the anode and cathode

texts:
everyone, I'm using nanohub's introduction to the material science of rechargeable batteries course to do some self-studying until I can go back into the lab. On one of the practice problems, it asks to calculate the energy density of a given battery system. For the first problem, it asks this for a lithium metal anode, LiCoO2 cathode system. We are asked to assume an electrode thickness of 100 micrometers and a porosity of 35%. I assumed no porosity contributions from other components such as binders. When I calculate the value I don't get something close to the answer given in the solution which is 453.6 J/kg.

I have tried calculating this and the other problems a few different ways with different units but I am not getting the correct answer. The formula I am using is

Energy density = (potential difference between anode and cathode) * cathode charge (capacity)* electrode thickness (this was given in the PS)*(1-porosity(this was also given)) below is an image of what the given information and potential answers looks like


texts:
In my school science textbook, written more than twenty years ago, it said that pure iron does not rust. Accompanying was a photograph of an ancient iron statue situated outside, which had not rusted.

Is this correct?


texts: I came across a compound $\ce{[FeO4]^{2-}}$ but $\ce{Fe}$ has +6 charge according to my calculations. How this is possible ? Or it is possible but my periodic table is kind of non-detailed one. (On the table I got $d$-metals possible charges).


texts: Why are polysaccharides not sweet in taste?

texts:
Polysaccharides are defined as polyhydroxy aldehyde or ketone which on hydrolysis yield many units of monosaccharides.
I got one answer(to my question above) as:

  On our tongue, we have things called taste receptors. These receptors are loosely categorised into sweet, sour, bitter and salty. Our sweet-receptors bind to specific types of molecules, namely monosaccharides and disaccharides. Polysaccharides are not as sweet because they do not readily bind to the sweet-receptors on our tongue, as the other smaller molecules do!

My question is that in our body (due to the presence of water),polysaccharides and oligosaccharides are hydrolysed to simpler units of monosaccarides...

So why does the latter respond to the receptors(indicating sweetness) while the former does not(while both yield monosaccarides on hydrolysis)?


texts: How could a rechargeable battery recharge itself?

texts:
I'm an engineering student preparing for my graduation, in one step of my graduation project I used a rechargeable battery(1.2 volt), i was shocked when this battery is starting to recharge it self until it reach 1.04 volt (not fully) for many many cycles and immediately when the voltmeter reads 0 volt from it, when i asked my doctors they told me that maybe its chemical issue.

so is there any explanations please?


texts: Contradiction in variation of conductance and conductivity on dilution

texts:
I do conceptually understand that on dilution conductivity decreases and conductance increases but if we look at the formula of conductivity, a contradiction seems to arise.

$$\kappa=GG^*$$
where $\kappa$ is conductivity, $G$ is conductance and $G^*$ is cell constant.

It appears that on dilution if conductivity decreases then conductance should also decrease which is obviously wrong. Where is the problem?


texts:
Indicate the correct statements:
a. $\mathrm{d}A = -S\mathrm{d}T$ for an ideal solution undergoing an adiabatic process.
b. $\mathrm{d}G = -\mathrm{d}(TS)$ for an ideal solution undergoing an isobaric process.
c. $\mathrm{d}A = \mathrm{d}U - T\mathrm{d}S$ for an ideal solution undergoing an isothermal process.

The answer is statements (a) and (b).
How, though?
$\mathrm{d}A = \mathrm{d}U - \mathrm{d}(TS)$. Since it is adiabatic, $\mathrm{d}q = 0$, or $T\mathrm{d}S = 0$.
So $\mathrm{d}A = -P\mathrm{d}V - S\mathrm{d}T$. What happened to the $-P\mathrm{d}V$ term?
$\mathrm{d}G = \mathrm{d}H - \mathrm{d}(TS)$
$\mathrm{d}G = V\mathrm{d}P - S\mathrm{d}T$, so $\mathrm{d}G = -S\mathrm{d}T$.
Why did they add the $-T\mathrm{d}S$ term?
$A$ is the Helmholtz free energy and $G$ is the Gibbs free energy.


texts:
I have always notated doubly charged ions with a superscript $++,$ such as $\ce{He^{++}}.$  For more highly-charged ions I would denote them with the number of charges, such as $\ce{Pt^{4+}}.$

Recently I have been challenged that doubly charged ions should be similarly written as e.g. $\ce{He^{2+}}.$  My internal consideration of the matter is that the fully consistent application of such a convention would necessitate writing $\ce{He^{1+}},$ which wastes space.  I have a vague recollection from my student days of being told that we use a superscript $++$ because it is the same character count as $2+,$ while avoiding the logical conclusion that one should use superscript $1+,$ and thus the logic of the naming convention was to preclude excess typesetting.  However, my Google skills have failed to turn up documentation of such a rationale $−−$ or any rationale, for that matter!

Can anyone point me to some documentation that might describe/explain the notation convention?


texts: What is the proper description/name of this amide/ester structure?


texts: Standard reduction potential of MnO4-/MnO2 couple

texts:
This is the data given:

$$\ce{MnO4- /Mn^{2+}} = 1.5~\mathrm{V}$$

$$\ce{MnO2 /Mn^{2+}}= 1.23~\mathrm{V}$$

I know that :
$$\ce{MnO4- +5e- + 8H+ ->Mn^{2+}}$$
$$\ce{MnO2 + 4H+ +2e- -> Mn^{2+}}$$

After that here's what's done which I absolutely don't get. After using $\Delta G^\circ = -nFE^\circ$, won't we have to multiply these energy values by the coefficients of the balanced equations before we can get $E_{\mathrm{cell}}$?

In particular, shouldn't the $\Delta G^\circ$ of the first equation be multiplied by two and that of the second by three?


texts: Preparation of compounds using acetoacetic ester synthesis

texts:
I've been given the following exercise in organic chemistry, and I'm at a complete loss. The text book doesn't cover the subject at all. I have some knowledge of melonic ester synthesis. As an undergraduate student in biology, I have a really hard time grasping the concepts, so an in-depth explanation would be much appreciated.

The acetoacetic ester synthesis is closely related to the melonic ester synthesis, but involves alkylation with the anion of ethyl acetoacetate rather than diethyl malonate. Treatment of the ethyl acetoacetate anion with an alkyl halide, followed by decarboxylation, yields a ketone product:

How would you prepare the following compound using an acetoatic ester synthesis?


texts: why bimolecular elimination reactions are stereospecific?

texts: I know the mechanism of this reaction but it is stated that these are stereospecific in nature . why do we call these stereospecific explain with example.


texts:
Today, in class, I learned about the two reactions.
I know connecting bond releases energy, and breaking it requires and aborb/ consumes energy.
But on my reference table I, 2C+H2 yielding C2H2 realeasing 227.4 kJ of energy. My point is why it releases energy? Also, where the activation energy comes from?

The paradox exists in that lower energy level means more stability, but nature also likes to form bonds thus to increase stability. However,  sometimes forming bonds increases the energy level.


texts: Why does a substance with an endothermic heat of solution dissolve?

texts: How does a substance with an endothermic heat of solution dissolve?


texts: Effect of side reactions on galvanic cell using iron rod as anode and sodium chloride as salt bridge

texts:
We just made a galvanic cell on a chemistry lesson using iron, iron sulfate , copper and copper sulfate.
We used a sponge soaked in $\ce{NaCl}$ solution as the salt bridge. The issue is that we measured a voltage way below the expected value and it was dropping quite fast.
The iron sulfate solution was yellow which may have indicated that the iron ions were reacting with chloride ions.
I just can't see why this reaction would cause it to stop working from a charge perspective. What is happening here?


texts:
In the laboratory, $20.0$ milliliters of an aqueous solution of calcium hydroxide, $\ce{Ca(OH)2}$, was used in a titration. A drop of phenolphthalein was added to it to indicate the end point. The solution turned colorless after $20.0$ milliliters of a standard solution of $\pu{0.050 M}$ $\ce{HCl}$ solution was added. What was the molarity of the $\ce{Ca(OH)2}$?
  (A) $\pu{0.010 M}$
  (B) $\pu{0.025 M}$
  (C) $\pu{0.50 M}$
  (D) $\pu{0.75 M}$
  (E) $\pu{1.0 M}$

I did not know how to answer such kind of question using formulas, that is why I applied logic. At first, I wrote such a reaction:

$$\ce{\underset{\pu{20 mL}}{Ca(OH)2} + \underset{\pu{0.05 M}}{\underset{\pu{20 mL}}{HCl}} = end point}$$

Then, I understood that if the volume of both reactants is equal, the molarity of $\ce{HCl}$ must be higher than that of $\ce{Ca(OH)2}$, as $\ce{HCl}$ changes the nature of $\ce{Ca(OH)2}$.

As I knew that the molarity of $\ce{Ca(OH)2}$ is just a bit less than that of $\ce{HCl}$, I chose B, and this variant turned out to be the right one.
In the book, I have such explanation:

  In the titration, the reaction is:
  $$\ce{2HCl + Ca(OH)2 = CaCl2 + 2H2O}$$
  The acid to base ratio is $2 : 1$, or (moles acid used) = 2(moles base used), so $M_\mathrm{a}V_\mathrm{a} = 2M_\mathrm{b}V_\mathrm{b}$, where $M$ is the molarity and $V$ is the volume expressed in liters. Then
  $$M_\mathrm{b} = \frac{M_\mathrm{a}V_\mathrm{a}}{2V_\mathrm{b}}$$
  $$M_\mathrm{b} = \frac{\pu{0.05 M} \times \pu{0.02 L}}{2}$$
  $$\pu{0.02 L} = \pu{0.025 M}$$

I do not understand the explanation. Although it comes up with the same variant as I did, if I had such formula I would use it this way $2M_\mathrm{a}V_\mathrm{a} = M_\mathrm{b}V_\mathrm{b}$ as we have 2 moles of acid.

Then, the answer would be $0.1$. The same formula is used on this forum. Can you help me understand what is wrong here please?


texts:
Can the anode always be considered as having a lower standard electrode potential than the cathode?
When I was studying galvanic cells, I found that for a number of reactions, it always appeared that the anode(i.e negative potential) mostly had a lower electrode potential than the cathode. Can we say that this is always true or are there some exceptions?


texts: Why does a chiral carbon affect some hydrogen's hydrogen environment?

texts:
In the screenshot attached taken from Khan Academy's video (https://www.youtube.com/watch?v=p9B4s0N5yk8&list=PL0pJUwkI0YCZRYrgKqHXZ0XCIu11afbJ8&index=3) the thick pink dot refers to a chiral carbon atom. Why is it that the two hydrogens circled red and pink that are bonded to a carbon which is then bonded to a chiral carbon atom are in different hydrogen environments? However, the three green circled hydrogens that are bonded to a carbon which are then bonded to a chiral carbon atom are in the same hydrogen environment?

From my understanding of hydrogen environment, a hydrogen environment is characterised by the functional group(s) that is attached to that hydrogen. Therefore, I think that the two hydrogens circled red and pink are in the same hydrogen environment, just like the three green circled hydrogens are in the same chemical environment.

Therefore, my question is why does a chiral carbon atom affect the hydrogen environment of a hydrogen? And especially from Khan Academy's example, only some hydrogens are affected by the chiral carbon and some aren't affected by it. Is there some loop hole in my understanding of hydrogen environment?


texts: What can I add to a dough ( kind of pizza dough) to keep it fresh after frozen?

texts: I make some "mini pizzas" with a dough recipe i learned in Brasil, I'm interested in freezing the dough after being "half baked" meaning baked for half of the time, so I can bake again after frozen. I was wondering if there is something I can add that will make this dough taste more fresh even after frozen


texts: What happens when HCl is added to acetylene in presence of mercuric ions?

texts:
Normal addition of Hydrochloric Acid to acetylene would give me a 1,1 Dichloro product.
But I read that in presence of mercuric ions only one molecule of HCl is added to give Vinyl Chloride.
Why does this happen?


texts: How can an SN1 reaction give non-racemic products?

texts: I'm in organic 1 right now and we assume that SN1 reaction will always have racemic products for the sake of simplicity. But then our professor have a question for us that these solvolysis reactions will not end up with racemic products. Could you help me find the reason why it is not racemization?


texts: How to experimentally determine the elemental composition in fingernails?

texts:
I am doing a project in my highschool about analysing C/N and C/S ratio of finger nails of various ages and sexes.
Please suggest me a way to do this. I don't know where to start, I know the various methods of estimating the amount of N or S present theoretically. Please provide info that how should I dissolve the nails etc.

I will be doing my experiment in a nice lab which has got all necessary equipment that I might need, so please answer without considering the limitations of my lab.

I got the idea by this website: https://pubmed.ncbi.nlm.nih.gov/18424895/


texts: What is the concentration of H2 for the equation H2+I2=2HI if the equilibrium constant is 64 and the initial concentrations are both 1.9

texts:
So for this, I set up the equation =

$$64= \frac{(x)^2}{(1.9-x)^2}$$

I took the sqrt of both sides and got

$$8=\frac{x}{(1.9-x)}$$

So then I did $$8(1.9-x)=x$$

And simplified I got $$15.2=9x$$

So $$x=1.688$$

So to find concentration it’s Initial- Change

$$1.9-1.688=.212$$

But it’s telling me this answer is wrong


texts: Why does the proton NMR of ferrocenecarboxaldehyde appear to be four singlets?

texts:
One singlet stems from the aldehyde H, and another from the Cp ring with 5 hydrogens attached.

However, the ring with the aldehyde group attached has hydrogens in two chemical environments which are just three bonds apart from each other. Why do they not couple? (400 MHz, CDCl3)


texts: Gibbs free energy of formation vs. Gibbs free energy of reaction?

texts:
Consider the following reaction:

$$\ce{A(s) + B(s) <=> AB(s)}.$$

I know there might be kinetic limitations but I am only interested in thermodynamic relations.

In general, the Gibbs free energy of reaction reads:

$$\Delta G = \Delta G^⦵ + RT\ln{\prod a_i^{\nu_i}}$$

and for the given reaction:

$\Delta G = \Delta G^⦵ + RT\ln{\frac{a_\ce{AB}}{a_\ce{A}\cdot a_\ce{B}}} \label{eqn:1}\tag{1}$

Since all components are pure solid substances, all activities equal 1 and therefore, $\Delta G = \Delta G^⦵$.

If $A$ and $B$ are elements, I found the following formula:

$$\Delta G_\mathrm{f}^⦵ = N\cdot RT\ln{\left(a_\ce{A}^{x_\ce{A}}a_\ce{B}^{x_\ce{B}}\right)} \label{eqn:2}\tag{2}$$

where $N$ is the total number of atoms and $x_\ce{A}$ and $x_\ce{B}$ are the mole fractions. To me, this latter formula implies, that the activities of $\ce{A}$ and $\ce{B}$ inside the product $\ce{AB}$ are of interest.

I have two questions:

What is the origin of the second formula $\eqref{eqn:2}$? In almost every source, the first type of Gibbs energy is used and I was not able to find any derivation. Also I think in principle, equation $\eqref{eqn:1}$ and $\eqref{eqn:2}$ should produce the same, but it looks very different!?
How does it come, that in one case the activity of the whole product $\ce{AB}$ is important and in another the single activities of the components of the product?

--------------------Update--------------------

Based on comments I'll try to reformulate my problem to make it more clear.

As I have learned, there should be no difference between the reaction product AB and the mixture of A and B with the corresponding stoichiometry (1:1). Is this valid in general or just for reactions like this (cf. my water-example in the comments)?

The transformation of equation (2) (in NightWriter's answer) shows, that it is an identity of the Gibbs free energy of mixing but in terms of moles of compound AB rather than in terms of moles of mixture.

If equation (1) describes the reaction (i.e. formation) of AB and equation (2) the mixing of A and B, and there is no difference between a product of reaction and the corresponding mixture of the two components to form that product, there must be some mathematical relation between equation (1) and equation (2). Furthermore, I am not certain, whether the standard-state symbol in equation (2) is correct or not.

After I read the answer and the comments again, I concluded the following: equation (1) describes the formation of AB and equation (2) the mixture of A and B at arbitrary compositions. So, if I set $x_A = x_B =0.5$, it should be possible to replace $\Delta G^⦵$ in equation (1) by $\Delta G_f^⦵ = N\cdot RT\ln{a_A^{0.5}a_B^{0.5}}$. $N$ must be chosen properly, since the two expressions are related to different things (mixture and compound). Is this correct?


texts:
I understand this is a basic question, but I'm having such a hard time wrapping my head around it. I'm trying to avoid thinking about it as an actual "particle" but as a wave, but that confuses me too.  Wouldn't a wave be the entire area the electron travels ? Or does the associated wave represent the path and not the electron? If so, where is the electron?
Here's a picture to refer to in your explanation if it helps.


texts: I need to handle large quantities of $\ce{KOH}$; close to 1000 liters of 85 % conc $\ce{KOH}$ for about an hour. Any suggestions on how I go about doing it? Also the temperature during the process might touch 500 degrees Celsius.


texts: How is the pH scale constructed , I mean the strength of an acid is determined by its pKa value and this one can be determined in different solvents if water doesn't suits it but how do you determine the pKa value of a substance in water after you have found the value of its pKa in another solvent ? Also I don't think I quite understand why the pH interval in water is running from 0 to 14 (I know that it has to do with the leveling effect but when you take this scale for other solvents the starting value can be different from 0 , if I am not mistaken for liquid NH3 the starting value is 5 ) can someone explain to me from where does this values come from ?


texts: When there is more than one amino group in a molecule, which group is more likely to react when forming an imine?

texts: Why does the third group react in this example and not the first?


texts: How do I make 3d molecular graphics similar to those shown on Wikipedia?

texts:
I want to make 3d molecular graphics similar to those found on Wikipedia. In the page for benzene, you can see the structure looks like this:

However, if I go to the interactive image as shown in here:

I get an interactive image that looks like this:

To me, the second image doesn't look nice, and I prefer the first one. However, I cant seem to find a way to get the image of first type for any molecule after converting from SMILES. I want to draw the structure of, say for example, Bismabenzene? How do I produce a graphical image for that if it's not available on Wikipedia?


texts:
I'm from Slovakia, 16, and I'm really confused about the English simple molecule (oxides, hydroxides, salts, acids) nomenclature. I guess we do it differently. To sum it up: we have suffixes from 1-8 to communicate the oxidation number of an element in a molecule. We put those suffixes at the end of the elements stem, combine it with the word for what kind of molecule it's forming (oxide, hydroxide, ...), and then we can determine from that name and the oxidation number of the other elements (if it's an oxide then oxygen if it's a hydroxide then the hydroxide anion and so on) what it's chemical formula is. Is it done the same way in English speaking countries? Do you just have to search for the oxidation number in a periodic table? If not then how?

Thanks!

Edit: we use these suffixes for oxidation numbers:

-ný/á
-natý/á
-itý/á
-ičitý/á
-ičný/ečný/á
-ový/á
-istý/á
-íčelý/á

(ý or á is based on gender of the word...)

They all represent the positive oxidation number of a part of a simple molecule, for example, Al2O3 would be "oxid hlin-ITÝ" because aluminum is hliník in Slovak and -itý means that the oxidation number of the aluminum is +3.
How would you write down $\ce{Al2O3}$ in English? And also how do you name salts, bases, and acids?

EDIT2(for Karsten Theis)

\begin{array}{|c|c|c|}
\hline
\text{Formula} &  \text{English name} & \text{Slovak name}  &\text{Oxidation #}  \\
\hline
\ce{FeCl2 }& \text{ferrous chloride, iron(II) chloride} &  \text{chlorid želez-natý}  & +2\\
\hline
\ce{FeCl3 }& \text{ferric chloride, iron (III) chloride} & \text{chlorid želez-itý} & +3\\
\hline
\ce{FeO }& \text{iron(II) oxide} &  \text{oxid želez-natý}  & +2\\
\hline
\ce{Fe2O3 }& \text{iron (III) oxide} & \text{oxid želez-itý} & +3\\
\hline
\ce{N2O}& \text{nitrous oxide} & \text{oxid dus-ný} &+1 \\
\hline
\ce{NO}& \text{nitric oxide} & \text{oxid dus-natý} &+2\\
\hline
\ce{HNO2}& \text{nitrous acid} & \text{kyselina dus-itá} &+3\\
\hline
\ce{HNO3}& \text{nitric acid} & \text{kyselina dus-ičná} &+5\\
\hline
\ce{NO2-}& \text{nitrite} & \text{dus-ita-n} &+3\\
\hline
\ce{NO3-}& \text{nitrate} & \text{dus-ičita-n} &+5\\
\hline
\ce{N^3-}& \text{nitride} & \text{nitrid} &-3\\
\hline
\ce{CrO}& \text{chromous oxide} & \text{oxid chróm-natý} &+2\\
\hline
\ce{CrO3}& \text{chromic oxide, chromium trioxide} & \text{oxid chróm-ový} &+6\\
\hline
\ce{Cr2O3}& \text{chromium (III) oxide} & \text{oxid chróm-itý} &+3\\
\hline
\ce{H2CrO4}& \text{chromic acid} & \text{kyselina chróm-ová} &+6\\
\hline
\ce{HCl}& \text{hydrochloric acid} & \text{kyselina chlóro-vodíková *} &-1\\
\hline
\ce{HClO}& \text{hypochlorous acid} & \text{kyselina chlór-na} &+1\\
\hline
\ce{HClO2}& \text{chlorous acid} & \text{kyselina chlor-itá} &+3\\
\hline
\ce{HClO3}& \text{chloric acid} & \text{kyselina chlor-ečná} &+5\\
\hline
\ce{HClO4}& \text{perchloric acid} & \text{kyselina chlor-istá} &+7\\
\hline
\ce{Al2O3}& \text{aluminum oxide} & \text{oxid hlin-itý} &+3\\
\hline
\ce{CaO}& \text{calcium oxide} & \text{oxid vápen-natý} &+2\\
\hline
\ce{Li2O}& \text{lithium oxide} & \text{oxid lít-ný} &+1\\
\hline
\end{array}

*(vodíková means that that acid only has hydrogen and not oxygen)


texts: Determining Overall Equation and Oxidation Potential

texts:
Cell 1 is composed of a reference chloranil half-cell (standardised against SHE as $+0.680 \mathrm{V}$) connected to an $\ce{Ag/AgCl}$ half-cell containing saturated ($0.125\ \mathrm{mol\ L^{−1}}$) $\ce{NaCl}$ in glacial acetic acid.

  $\ce{Ag_{(s)}\ |\ AgCl_{(s)}\ |\ Cl^{-}_{(CH3COOH)}\ ($0.125$~M)\ ||\ H+(aq)\ ($0.5$~M),\ C6Cl4O2_{(aq)(sat)},C6Cl4(OH)2_{(aq)(sat)}|\ Pt_{(s)}}$

  Cell 2 is composed of the same reference chloranil half-cell connected to an Ag/AgCl half-cell containing $\mathrm{1.0 ~mol~ L^{-1}}$ $\ce{HCl}$ in glacial acetic acid.

  $\ce{Ag_{(s)}\ |\ AgCl_{(s)}\ |\ HCl_{(CH3COOH)}\ ($1.0$~M)\ ||\ H+(aq)\ ($0.5$~M),\ C6Cl4O2_{(aq)(sat)},C6Cl4(OH)2_{(aq)(sat)}|\ Pt_{(s)}}$

  a) Write the equation for the overall reaction occurring in both cells.

  Cell 1 is used to determine the value of $\mathrm{E^o}$ for the reduction of $\ce{AgCl_{(s)}}$ to $\ce{Ag_{(s)}}$ and $\ce{Cl^{–}}$ in glacial acetic acid –
  $\mathrm{E^\circ}\ce{(AgCl/Ag)}$. The cell potential of Cell is $0.422\ \mathrm{V}$

  b) Calculate $\mathrm{E_{OX}}$ – the reduction potential of the oxidation half-cell – of Cell 1.

My Attempt

a) Electro chemistry is not my strong point and I am not too sure on the notation for the cell. I have never seen a cell that has 3 species in the anode and in the cathode half-cell. Could someone explain to me what it means?

I am guessing the oxidation half-equation is: $$\ce{Ag_{(s)} + Cl^{-}_{(aq)} -> AgCl_{(s)} + e^{-}}$$
My overall equation is then:
$$\ce{2Ag_{(s)} + 2Cl^{-}_{(aq)} + C6Cl4O2_{(aq)} + 2H^{+} -> 2AgCl_{(s)} + C6Cl4(OH)2_{(aq)}}$$

Is this correct? Also will the overall reaction for cell 2 be the same as the overall reaction for cell 1 as the only difference is that $\ce{NaCl}$ is replaced with $\ce{HCl}$.

b) Is the question a typo and really means: "Calculate $\mathrm{E_{ red}}$ – the reduction potential of the oxidation half-cell – of Cell 1." or am I missing something?

If the question is a typo, I get that the answer is $-0.258\ \mathrm{V}$, is this correct?


texts: When we make a galvanic cell using zinc rod (in zinc sulphate solution) and copper rod (in copper sulphate solution), there is a flow of sulphate ions from the copper compartment to the zinc compartment through the salt bridge. Once the sulphate ions reach the zinc compartment, what happens to them?


texts: Difference in the change in oxidation states of transition elements and p-block elements

texts: In transition elements the oxidation states differ by one (+2 to +7 in Mn). However, in the p-block elements, the oxidation states differ by two (-1,+1,+3,+5 in the halogen group). Why is this so?


texts: Rate of reaction involving different stoichiometric coefficients

texts:
Suppose I have a reaction (Say it is the Haber process):

$$\ce{N2 + 3H2 <=> 2NH3}$$

If we have to calculate the average rate of reaction of the above we follow the reasoning the rate of consumption of $\ce{N2}$ is one- third that of $\ce{H2}$ and half that of production of $\ce{NH3}$. We go ahead and divide the change in concentration of $\ce{N2}$ or $\ce{H2}$ or $\ce{NH3}$ by their stoichiometric coefficient. My doubt is why rate of reaction is taken as the rate of consumption of $\ce{N2}$? Why can't it be the rate of production of $\ce{NH3}$? Why can't we say that the rate of reaction is the rate of production of $\ce{NH3}$ or half the rate of consumption of $\ce{N2}$ or one and half times that of rate of consumption of $\ce{H2}$?


texts: How can I search molecules by constituent atoms

texts:
Given a set of atoms, I would like to find (some / the most common) molecules that include only (some/all) atoms of the set. Is there any online search engine that can do this?

  E.g.
  Atoms={C,H}
  -->
  Molecules={CH$_4$, C$_2$H$_6$, ...}

Note:

I am looking for known molecules.
It is OK if I can only find chemical formulae, so without all possible configurations.


texts: Why is formic acid a stronger acid than acetic acid?

texts:
I am told that because the methyl group is electron donating in the conjugate base of acetic acid, this destabilizes the conjugate base by exacerbating the existing negative formal charge on the deprotonated oxygen, while in formic acid the electron donating methyl is absent in lieu of a hydrogen, which is neither withdrawing nor donating.

Is this reasoning correct, and are there any other reasons why formic acid might be stronger than acetic acid?


texts:
Why is the nickel complex exhibiting the strongest pi-bonding?

From what I understand, charge density plays a role. Also we need some empty orbitals on the metal cation, since we're looking at Lewis adducts.

Also I note that some have positive overall charges; could this play a role? Metal cation <-> NO+ repulsion? So we might want a metal anion?

Also would size play a role? Size goes hand in hand with charge density. And what about "backbonding"?


texts: Distinguishing Test for Organic Compounds

texts:
Given the following pairs of samples, how do I distinguish between them?

benzamide and ethanamide
ethanoyl chloride and ethanoic anhydride

My Approach:

We could easily convert the amides to amines by reducing them with $\ce{LiAlH4}$. Now, the question reduces to identifying the methyl group against the benzene group.

I am really lost here but my guess would be that we are looking for some characteristic reaction for anhydrides.


texts: 4 compounds in equilibrium with one another - determine their equilibrium concentrations

texts:
I know that if I have two compounds in equilibrium and I know $\mathrm{\Delta G}$, then I can use $$\mathrm{\Delta G=-RTlnK}$$
to determine the concentrations of the two components at equilibrium.  I have 4 compounds that are all in equilibrium with one another
\begin{aligned}
\mathrm{\Delta G(1,4)} ~&= ~~~3.41~ \mathrm{kcal/mol}\\
\mathrm{\Delta G(3,1)}~&=-2.21~ \mathrm{kcal/mol}\\
\mathrm{\Delta G(2,3)}~&=-0.46~ \mathrm{kcal/mol}\\
\end{aligned}

I applied the equation sequentially and found that
\begin{aligned}%
[1]~&=~0.34\%\\
[2]~&=~29.1\%\\
[3]~&=~13.5\%\\
[4]~&=~57\%\\
\end{aligned}

Are those the correct concentrations? Is there an "easy" way to do it?


texts: I need to produce paper bags. Is there any simple receipt for making paper glue so that brown (packaging) paper will stick to itself?


texts: The difference between hydroxide and oxyhydroxide

texts:
I cant discern these two terminologies. Would someone be very kind to help me on it?

I think hydroxide mean M(OH)x where M is a metal ion, while oxyhydroxide means something like MO(OH). Is that right? Oxyhydroxide equals to oxide-hydroxide.


texts: Can I react a Grignard reagent (ethylmagnesium bromide) with water and then ammonia?

texts:
I came across this question where I had to convert $\ce{CH3-CH2-Mg-Br}$ to $\ce{CH3-CH2-NH2}$.
If I need to do so can I just react the given compound with water to get ethane and then react it with $\ce{NH3}$.

If the answer is no then why can't I?
Is there any set of principles in organic chemistry which govern as to which substances can be replaced with what?
Kind of like the reactivity series of metals?
For e.g.: If I react an alkane with a halogen to get a haloalkane and then react this back with hydrogen to get the alkane then I don't think so it would be correct to do so. And I don't think that organic chemistry works that way.
But how do I understand while solving a question whether I am going in the right direction.
Please help.

NB: This is not a homework question its just a question I stumbled across while my preparation for a college entrance test. (edit the title maybe)


texts:
Which base is stronger methylamine or propylamine? I know that it depends on the strength of inductive effect of alkyl group. Am I right?
But how can I determine the difference between methyl and propyl substituent?


texts: Cause of m/z = 56 peak in 4-methyl-1-pentanol

texts:
This is the mass spectrum for 4-methylpentan-1-ol:

From its structural formula, what could be the fragmentation which results in a peak at $m/z = 56?$

I was considering a few possibilities; could it be $\ce{C3H4O+}?$


texts: Do undissolved salts in saturated solvents enter equilibrium with the dissolved salts?

texts:
For instance, if there is cup of water saturated with a salt to the point where any more added salt will just float around in the solution, are those undissolved salt molecules in equilibrium with the dissolved ones? For instance, do the undissolved ones become partially dissolved for a moment, while the dissolved ones swap places with them?

Or does this behave in such a manner that whatever salts were dissolved first to reach saturation are the ones that will stay dissolved, in spite of other added salts?


texts: NaHCO3 decomposition dynamics and extent vs Temperature

texts:
I'm wondering approximately how fast and to which extent $\ce{NaHCO3}$ will decompose (to $\ce{CO2}$ and $\ce{H2O}$) at $50$, $60$, $70$, $80$, $90$, $100$, $110$, $120$, and $\pu{130 ^\circ C}$.
It seems as if J. Environ. Sci. 2019, 78, 74–80 would answer my question but unfortunately I can't access the content.
Does anyone know ?


texts: Are all exergonic reactions spontaneous?

texts:
Exergonic reactions have a negative $\Delta G$: the system loses free energy. Spontaneous reactions are also defined in the same way, as far as I know. Does this mean the two are synonymous?
There are some questions (e.g. here) asking the same question for exothermic reactions, but not all exergonic reactions are exothermic.


texts: Determining enthalpy and internal energy of formation for potassium superoxide

texts:
Given $2.14\ \mathrm g$ of $\ce{K(s)}$, determine $\Delta H^\circ_\mathrm{f,m}$ and $\Delta U^\circ_\mathrm{f,m}$ for $\ce{K2O}$.

  We know:

  The calorimeter's constant: $1849\ \mathrm{J\cdot K^{-1}}$
  The mass of water inside it: $1450\ \mathrm g$
  The change in temperature: $2.62\ \mathrm K$
  The end product is $\ce{K2O}$

The process should be: determining mol of $\ce{K(s)}$, which is $0.054\ \mathrm{mol}$. Then we obtain the amount of energy absorbed by the calorimeter/water. Here are the issues. I don't know which one changed its temperature by $2.62\ \mathrm K$ or if the calorimeter's constant already considers the water. Either way, the amount of energy released by each mol of potassium is extravagant; according to the result it is $322\ \mathrm{kJ}$ or $96.8\ \mathrm{kJ}$.

Continuing with this reasoning, the $\Delta U^\circ_\mathrm{f,m}$ should be $755\ \mathrm{kJ}$ or $193\ \mathrm{kJ}$, right? What do we need to obtain $\Delta H^\circ_\mathrm{f,m}$?


texts: Particle in a box models for polyenes and quantum dots

texts:
I'm kind of new to physical chemistry and trying to understand how, if at all, the correspondence principle (in the limit of large quantum numbers, quantum mechanics reproduces classical behavior of a system) relates to transition energies for electronic excitement in conjugated polyenes and quantum dots.

Our experiment used UV/vis spec to measure absorption and calculated theoretical values of energy with the particle in a box/sphere models. So why does the difference between experimental and theoretical energy get larger as length gets smaller?

Someone proposed the correspondence principle here, but I don't see how that has to do with going from the ground state (HOMO or valence band) state to the first excited state (LUMO or conduction band) that we're dealing with in the experiment. What am I not understanding here? Thank you!


texts: Where to find common inorganic/organometallic molecules?

texts:
I'm working on a project to create a large open repository of quantum calculations, largely for teaching purposes.

I can get thousands of common organic compounds easily from sources like PubChem or drug databases.

I'm looking for sources for teaching or other uses with VSEPR examples or other types of inorganic and organometallic molecules. Ideally I'd want 100s or 1000s with good coverage of the periodic table.

Any ideas?

To be clear, there are lots of databases of solids. I know most of those, although feel free to suggest some for archival. I really want isolated complex ions, molecules, etc.

I don't think there are many, since I haven't turned anything up besides the Cambridge database, which is restrictive about reuse.

Thanks!


texts: What is the need for so many theories of acids and bases?

texts: What is the need for the  Brønsted-Lowry theory and the Lewis theory of acids and bases?Is there any problem with the Arrhenius theory?


texts: Are there compounds more conductive than Silver (Ag)?

texts: Silver is the most electrically conductive element on the Periodic Table. However, I am interested in knowing if there are any compounds (combinations of elements) that would be more conductive than Silver (without Superconductor cooling). The extreme electrical conductivity of specific chemicals has many real world applications, from simply calling someone miles away, to processing enormous amounts of data in servers.


texts: How is carbon-halogen bond broken during Finkelstein reaction?

texts:
Finkelstein reaction is a halogen exchange reaction between haloalkane and a salt of a different halogenide:

$$\ce{R−CH2−Cl + KI -> R−CH2−I + KCl}$$

From an answer of a previous question:

  As per Le chatelliar's principle the forward reaction is favored in
  presence of dry acetone which will dissolve $\ce{KI}$ but not
  $\ce{KCl}$ or $\ce{KBr}$. On account of insolubility of
  $\ce{KCl/KBr}$; they are not available for backward reaction[...]

This reaction proceeds with $\mathrm{S_N2}$ mechanism; i.e. it is a single step reaction. $\ce{C-Cl}$ bond breaks and $\ce{C-I}$ bond forms. Now we know that energy for bond breaking comes from bond making. However we know that
$\ce{C-I}$ bonding cannot supply enough energy to break $\ce{C-Cl}$ bond.

To put in other words: chlorine is a weaker leaving group than iodine.

From where does the energy to break $\ce{C-Cl}$ bond comes then because for $\ce{KCl}$ (precipitate) to form; in first place the $\ce{C-Cl}$ bond must break?


texts: Concentration of gas phase in Nernst equation

texts: What if one or both electrodes are in gas phase? Use PV=nRT? Also the definition of hydrogen electrode gets a little sketchy if we use PV=nRT to write it's concentration, the electrode potential doesn't come out 0 that way.


texts: Why can’t I use solubility product for normally soluble compounds?

texts:
Solubility product only applies to sparing soluble ionic compounds (chemguide)

I read this in a website. But I don’t see what this should be the case. Taking $\ce{NaCl}$ for example, there’s an equilibrium established as it dissolves. Why then does solubility product not apply to this scenario?


texts: Friedel craft alkylation halo-carbon bond cleavage

texts:
In this reaction, why is the $\ce{C-F}$ bond broken instead of the $\ce{C-Cl}$
bond, even though $\ce{C-F}$ bond is stronger than the $\ce{C-Cl}$ bond?


texts: Oxymercuration and demercuration mechanism

texts:
There are two proposed mechanisms for Oxymercuration and demercuration.

The first mechanism is concerted (i.e. single transition state connecting reactants and products) characterized by an attack of the $\pi$-bond on the $\ce{Hg(OAc)2}$.

Why does mercuric acetate act as an electrophile in the first mechanism? It is in its most common 2+ oxidation state. Does this happen because mercury has empty $6d$ orbitals.

The second mechanism is a stepwise mechanism (i.e. contains at least one intermediate species along the reaction pathway between reactants and products) that is characterized by incorporating the first ionization of $\ce{Hg(OAc)2}$ followed by an attack of the nucleophilic $\pi$-bond.

$\ce{Hg(OAc)2}$ dissociates in water as follows:
$$\ce{Hg(OAc)2 + H2O<=>Hg+OAc + OAc-}$$

Which one is the actual mechanism?


texts: Why does a real gas with attractive forces between particles experience an increase in internal energy when expanding isothermally?

texts:
I am trying to understand at the molecular level why a real gas with attractive forces between particles experiences an increase in internal energy when expanding isothermally. Here's my thinking:

For a gas, the path-independent differential form of change in internal energy is

\begin{equation}
dU = \frac{\partial U}{\partial V}{ \delta V} + \frac{\partial U}{\partial T}{ \delta T}
\end{equation}

For an isothermal expansion,
\begin{equation}
{ \delta T} = 0
\end{equation}

so \begin{equation}
dU = \frac{\partial U}{\partial V}{ \delta V}
\end{equation}

(For an ideal gas, internal energy is proportional to temperature, so an isothermal expansion doesn't change the internal energy.)

The way I'm looking at the real gas situation is that:

When the real gas expands, say by free expansion into an evacuated chamber, the Δ U = Δ P.E. + Δ K.E.
The increase in volume causes the average distance between particles to increase and therefore increases the potential energy.
The increase in potential energy comes as the expense of a decrease in kinetic energy, because Δ U= 0 = Δ P.E. + Δ K.E., in the same way that throwing a ball upwards into the air causes it to lose K.E.
However, in the case of the gas, this is a very short-lived decrease in K.E., because the decrease in K.E. of the particles lasts no longer until they reach a wall.
Because the walls of the evacuated flask are maintaining an isothermal environment, they transfer heat energy to the particles inside, either by contact conduction, or radiation, thereby restoring K.E. to initial value.
U final = final P.E. (higher than initial conditions) + initial (restored) K.E., and is therefore increased.

(In the case of a volume expansion of a real gas by doing work against a piston, I believe that there would be an even larger transient drop in K.E., immediately counteracted by the introduction of correspondingly more heat because of the isothermal constraint.  So the end-of-pathway conditions are still the same, increased P.E. and restored K.E.)

Is this reasoning correct? The version of Atkins I have asserts that for a real gas
\begin{equation}
\frac{\partial U}{\partial V} > 0
\end{equation}

but doesn't provide a molecular explanation.


texts: Do the mechanism (SN1 or SN2 ) which reaction follow depends more upon intermediate stability than on substrate and nucleophilic?

texts: For eg : would the reaction of 3-methylbut-2-en-1-ol with HBr follow SN1 mechanism due to stability of your intermediate carbocation stability  or SN2 due to the compound being primary alcohol and good nucleophilic. Also please correct me if I got something wrong.


texts: How can you deduce from the structure that probenecid is an acid and ephedrine is a base?

texts:
Probenecid contains a carboxyl group, indicating an acid. But it also contains a nitrogen atom, which indicates a base? How can I decide that it is an acid and not a base?

I have the same problem with the ephedrine structure.


texts:
In searching for chemistry kits it often leads to stuff like this:

I have seen some nicer "boxed sets" for the ~$500 range, but I don't think this is really ideal. This one looks a little nicer. I am wondering two things:

Where the best "complete" home/DIY chemistry set is that you can get online. Including the chemicals themselves, and the equipment like beakers, pipettes, etc.
Where the standard places are that smaller or bigger labs like University student or research labs get their supplies.

I feel like I read somewhere a while back that it is being outlawed because of bad behavior, but I wanted to ask to see what is possible in terms of doing chemistry experiments/analysis in a DIY/bootstrap fashion to learn about things like way in the past. I don't know much about chemistry but it would be interesting to perhaps learn how to do analysis like you might (I imagine) find in biology, geoscience, ecology, or agriculture.


texts: Which reagent can I use to remove carbon from oven?

texts:
I have a practical question: today I have to clean the oven, and it doesn't have self cleaning burn down mode, nor an official scraper I can use...

It's full of charred grease and sugar. I managed to remove 98% of the charred grease with cold grease remover. But it seems that reagent has no effect on the remaining 2%, that's black fully charred carbon or sugar. I also tried vinegar, but it doesn't have any effect on it either.

I don't want to scrape it because I fear that I would scratch the oven.

So which reagent can I use to remove those pesky carbon deposits without damaging the oven, and what will be the chemical reaction?


texts: Hazardous materials handled by amateur chemists

texts:
I'm a enthusiastic and devoted amateur chemist (in disguise, I'm actually a mathematician), but lately I've been thinking to what extend it is safe to pursue my hobby. I'm after all an amateur with just high-school lab skills and some unnecessary math to back me up. I really love chemical experiments, but I don't want to get seriously injured. The point is that same very basic materials, like sulfuric acid or cyclohexylamine, already have a 3 on the NFPA 704 scale of health hazards, quoting:

  Short exposure could cause serious temporary or moderate residual injury (e.g. chlorine)

Of course I read the MSDS of the chemicals I'm working with, wear a protective lab coat and tightly connected safety goggles, plus safety gloves, but I don't have nearly the safety equipment of a normal lab (fumehood, eye showers, sprinklers, etc.) To to concretize my question:

Speaking for all amateur chemists out there: to what extend do you as a professional chemist consider amateurs like me to be safe. Can we handle level 3 or perhaps even level 4 chemicals, or should we stick with 2 (greatly reducing our potential experimenting terrain)?
What measure can we (and should we) take to ensure our safety?

I understand that the capabilities vary greatly between people, but there was not sufficient information regarding this topic (from reputable sources) for me to be found on the internet, so I though I post it here. I don't feel like this is a primarily opinion based question, as there is at least to some degree consensus that amateurs cannot (and are not allowed to!) safely handle, say for example tabun or potassium cyanide (just a ridiculous example to illustrate my point).

I hope you can appreciate my concerns and that if this is not the right place for this type of question (I think it is, there is even a safety tag here) you cordially redirect me to an other more suited place and close this.


texts:
I was looking through chemistry textbooks to find out how to determine how much current a galvanic cell should generate and what affects that current value. However, I did not find anything: textbooks just talk about the EMF of a cell.

I wanted to know what determines how much current a cell generates. Certainly, the amount of electrons produced externally contributes to the current produced by the cell. However, what about internally? Batteries have internal resistance. Is that true of cells too (it should be because batteries are made up of many cells)? What determines amount of internal resistance: does the type of electrolyte(s) affect it. If a cell uses a weak electrolyte (like acetic or carbonic acid) will it cause more internal resistance then if something like sulfuric acid (strong electrolyte) is used?

What if a cell used weak electrolyte as the cathode electrolyte and the strong electrolyte was the anode electrolyte, will that cause more internal resistance due to there being less ions in the cathode compartment as not all of the electrolyte has been dissociated into ions (thus, the cathode cation cannot be reduced)?


texts:
$$\ce{NO3- + 3[Fe(H2O)6]^{2+} + 4H+  -> NO + 3[Fe(H2O)6]^{3+} + 2H2O}$$

$$\ce{NO + [Fe(H2O)6]^{2+} -> [Fe(NO)(H2O)5]^{2+} + H2O}$$

I read that in the brown ring complex $\ce{[Fe(NO)(H2O)5]^{2+}}$ , $\ce{NO^{-}}$ is the ligand.

What I don't understand is that :

How is $\ce{NO^{-}}$ formed? Nitrate ion got reduced to NO while $\ce{Fe^2+}$ was oxidized to $\ce{Fe^{3+}}$. The electrons that were released in the conversion of ferrous to ferric ion were used in converting nitrate ion to $\ce{NO}$. So where do these extra electrons come up that convert $\ce{NO}$ to $\ce{NO^{-}}$ ? I don't want to go into the mechanism; I just want to have an intuitive understanding of what's happening in the reaction.


texts:
Let’s suppose the following reaction:

$$\ce{ 2 H2O2 —> 2 H2O + O2}\tag{1}$$ with reaction rate $v$

Now let’s suppose the same equation with different balance:

$$\ce{ H2O2 —> H2O + 1/2O2 }\tag{2}$$

I assume that the reaction rate must be the same ($v$), right? It should not change with stoichometry.

However, depending on the balancing, I get different rates for each substance as shown in the equations below, different $k$ constant and so on.

$$\begin{align}v_1 &= -\frac12 \frac{\mathrm d [\ce{H2O2}]}{\mathrm dt} = \frac12 \frac{\mathrm d[\ce{H2O}]}{\mathrm dt} = \frac{\mathrm d[\ce{O2}]}{\mathrm dt}\\[1em]
v_2 &= \frac{\mathrm d [\ce{H2O2}]}{\mathrm dt} = \frac{\mathrm d[\ce{H2O}]}{\mathrm dt} = 2\cdot \frac{\mathrm d[\ce{O2}]}{\mathrm dt}\end{align}$$

Any help?


texts: Why is a TTT diagram called isothermal transformation diagram?

texts: Why are TTT diagrams called isothermal temperature diagram?As far as I know the temperature variation is plotted with the variation of time in a TTT diagram. Then why do we call it "isothermal".What is so constant about the temperature?


texts: When ∆Suniv = zero, does the concentration of reactant equal the concentration of product?

texts:
It is my understanding that when ∆Stot / ∆Suniv = 0 then the reaction does not occur, the position of equilibrium is not shifted in a specific direction. However, does this imply that [reactants] = [products]?

The question 1e part iii asks "What can you understand about the the equilibrium when ∆Stot = 0". The answer to the question is "Kc = 1, or reaction balanced in middle, or no tendency to go in either direction"

To me, this only makes sense if the starting concentrations of the reactants and products are the same. However, at no point is it mentioned that the starting concentrations of reactants/products are equal.


texts: What's the most effective way to reliably trigger and observe hard water scale buildup at a micro level?

texts:
We live in an area that's got some really hard water. It's so hard that it kills most of the fish we try to care for in our aquariums and shrimp?... forget it. While this is sad and challenging for aquarium lovers, this constant quest my spouse is on got one of my kids really interested the concept of "hard water." One particular point that I've been struggling with was to figure out how to "see" hard water. They asked me if we could build an apparatus that would show them the build up of the scales more quickly so they could look at it under a microscope and do various experiments.

I'd really like to encourage their curiosity and so I wanted to ask, what options exist to:

trigger buildup (some kind of a "seed" on a glass pipette or...?)
capture or isolate buildup so that it can be observed with a
microscope
what kind of microscopic resolution would / should be
used to observe this (preferably semi-realtime, perhaps via
stop-motion capture, with a photo/video attachment as it
accumulates)?


texts:
Currently, I'm trying to get into the field of quantum chemistry and was reading about minimal basis sets. As I understood this is the minimal number of orbital/spatial wavefunctions needed for a specific number of electrons.

For example, H has one electron, so a minimal basis set would be $\mathrm{1s}$ (STO, STO-nG, or something else).

Li has 3 electrons, so my guess would be that we need 1s and 2s. But in the literature, also the $\mathrm{2p_x}$, $\mathrm{2p_y}$ and $\mathrm{2p_z}$ orbitals are included in the minimal basis. Why is this the case? Together with the spin degrees of freedom, the three electrons already fit in the 1s and $\mathrm{2s}$ orbitals?


texts: How effective is a level A hazmat suit for immersion in deadly substances?

texts: I know that level A type hazmat suits can protect against minor splashes, but could somebody in one survive without harm after complete immersion for a few minutes in deadly chemicals such as sodium cyanide, high concentration (100%) hydrogen peroxide, and 80% hydrochloric/nitric acid?


texts: Why is the carbon-fluorine bond stronger than the other haloalkanes?

texts: What effect makes  C-F bond  stronger than  other halo-alkanes?


texts: proteolysis - how to determine the partial or completeness of the cleavage reaction?

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Though the question is about biomolecules, we agree the underlying functions, formation, degradation etc come down to chemistry, (then physics and maths). I am posting it here to receive an understanding from chemistry perspective. I am referring this info here to grasp the concept.

e.g. Trypsin is a protease that regulates specific hydrolysis/proteolysis by cleaving at the c terminus side of Arg and Lys.

Similarly, given two catalysts: (proteases) papain and bromelain. Both are said to regulate selective peptide cleavage reactions (specificity of proteolysis) - breaking peptide (amide) bond from C-terminal analysis (enzymatic hydrolysis). This is clear to me.

These enzymes only break c-terminus peptide bonds of specific amino acids. e.g. Papain for Arg and Leu. Bromelain for Ala, Leu, Ser, Gly, Tyr.

How to determine if papain or bromelain hydrolyse a given polypeptide chain completely or partially? And what's the resulting residue and chain? I am not expecting an one-liner, I want to understand the reaction mechanism and concept clearly for further application.

e.g. what's the resulting fragments of this after Papain act on it?

Arg-Leu-Ser-Ala-Tyr