text:
Why do most sulphate salts have water of crystallization in them?
I mean looking at most of the sulphate salts (there are so many but just to name some Epsom salt, blue vitirol, gypsum...) they have some amount of water crystallized within them (Epsom salt is MgSO4.7H2O, CuSO4.5H2O is blue vitirol and so on) so why is it like that? Is there any reason why water is crystallized in almost all metal sulphates
It isn't (maybe) related to hydration energy... nor (maybe) related to the size of the sulphate ion.

can anyone suggest me a better tag for this question please I am very confused

It is not fully clear what you are asking. Can you elaborate?

@Poutnik oh I meant looking at most of sulphate salts (there are so many but just to name some epsom salt, blue vitirol, gypsum etc..) they have some amount of water crystallized within them (epsom salt is MgSO4.7H2O , CuSO4.5H2O is blue vitirol and so on) so why is that? like is there any reason why water is crystallized in almost all such sulphates ? That is what I wanted to ask. Yes definitely looking at the length of my post surely told me it wasn't enough to justify

Add it rather to the question and you may ask for the question reopening via the respectively named link. Also, you may want to think longer over written text before posting it.

@Poutnik uh okay i mean this question is still dumb and maybe i shouldnt have asked it here
but yea i am editing it thanks

Now that you've changed the meaning of the question entirely, let's look into it. BaSO4 seems to crystallize without water; so does K2SO4. Still sure about "most"? Well, maybe the majority of all salts, not just sulphates, crystallize with water in them.

@IvanNeretin oh okay but I still think (not believe) that sulphates are the most to somehow grab water in them.....you would be right though and it just may not be sulphates (like the next best bet would be chlorides)........and yea i amn't sure so waiting for more responses :)

@IvanNeretin basically I am finding for some chemical bonding-ish solution if it even exists :')

related https://chemistry.stackexchange.com/questions/110728/hydrate-decomposition-equation-steps

Anion barely does anything, it's the cation that can coordinate many water molecules.

Water of crystallization is stabilized by electrostatic attractions, consequently hydrates are common for salts that contain +2 and +3 cations as well as −2 anions. Sulfate ion has -2 charge, so it is more prone to form hydrates.

@Mithoron yes that is true....

@Nilay oh is there any reason behind for which +2 and +3 attract more?

Sulfates commonly do have water of hydration, but so do many other salts such as chlorides. For instance, iron chlorides used in laboratory experiments at my job are commonly bought as $\ce{FeCl2•4H2O}$ and $\ce{FeCl3•6H2O}$.
One difference between sulfates and some other salts is the oxygen in the sulfate ion can form relatively strong hydrogen bonds with the protic hydrogen in water, enabling incorporation of additional water molecules into the crystal that aren't coordinated with the metal ion. Thus for instance magnesium ion commonly coordinates with six water molecules, but the sulfate salt commonly incorporates a seventh water molecules in its formula unit (Epsom salt) and can even have eleven at lower temperature.

"2-" is also important. After all, that's a great deal greater than 1-.

@IvanNeretin Curiosity strikes and turns out even our old NaCl also form hydrates: From cold (sub-freezing) solutions, salt crystallizes with water of hydration as hydrohalite (the dihydrate NaCl·2H2O NaCl·2H2O). In 2023, it was discovered that under pressure, sodium chloride can form the hydrates NaCl·8.5H2O and NaCl·13H2O.

@IvanNeretin yes true

@NilayGhosh oh thats cool

hey just a quick question don't you think flourides and nitrates would also have this phenomenon?

In the case of fluorides noncoordinated water of hydration is known in some double salts; see https://pubs.rsc.org/en/Content/ArticleLanding/1977/DT/DT9770002212.

@OscarLanzi ohkk thanks!


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What is the SMARTS string for a benzene ring (any substitution pattern)
I would like to use RDKit to highlight all benzene rings (regardless of substitution pattern - e.g. phenol, chlorobenene, benzoic acid type should all be highlighted) in any given molecule. I cannot come up with a general SMARTS pattern that simply matches 'benzene ring'. This seems like it should be a lot simpler than I found it to be :<

just "[c]1:[c]:[c]:[c]:[c]:[c]1" should do the job. lowercase c means aromatic carbon, i also include aromatic bonds ":" explicitly though even without it should work quite well for your purpose.
demonstration:
from rdkit import Chem
patt=Chem.MolFromSmarts("[c]1:[c]:[c]:[c]:[c]:[c]1")
chlorobenzene=Chem.MolFromSmiles("c1ccccc1Cl")
phenol=Chem.MolFromSmiles("c1ccccc1O")
benzoicacid=Chem.MolFromSmiles("c1ccccc1C(=O)O")
for m in [chlorobenzene,phenol,benzoicacid]:
    print(m.HasSubstructMatch(patt))

spits out True three times

Thanks so much wikke!

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


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HOMO and LUMO energy levels diagrams
Good time of day. I want to draw the same beautiful pictures in my work as I will attach below taking from some articles. Are there any programms or scripts which can do this? I would be glad if someone shared their scripts.

Thank you for your time!

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


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Radioactivity of Promethium
In school I was taught while looking at the difference between lanthanides and actinides that all of the actinides were radioactive, while only promethium among the lanthanides was radioactive. The question that struck my mind was 'why only promethium'?
On further research I also found out that technetium has a similar behaviour, being located in the midst of stable elements. Why does this happen?


text:
Effect of Steric Hindrance in Pinacol-Pinacolone Rearrangement
In the acid catalysed rearrangement of vicinal diols to carbonyl compounds which is pinacol-pinacole rearrangement,
The migratory order of the groups is H>Aryl>Alkyl
My question is that how aryl groups take precedence over alkyl groups when the aryl groups cause steric hindrance.

For an aryl group, what if the ipso-carbon is bound to both carbons in question at same time in the transition state for rearrangement? What becomes of the positive charge?


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When forming an epoxide with m-CPBA, what happens when we wash our mixture with Na2S2O4?
The m-CPBA is reduced by the $\ce{S2O4^{2-}}$, but why does it leave the mixture then?
Why does the reduced m-CPBA leave with the oxidised  $\ce{S2O4^{2-}}$?

The pKa of MCPBA is~7.6, the pKa of 3-Cl-benzoic acid is ~3.8 so is much easier to remove by an aq. base wash


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When C2 axis of symmetry is present then is the compound meso?
If suppose a compound has C2 axis of symmetry then is it confirmed that the compound will be meso or it can have an enantiomeric pair? And which of following conditions are sufficient enough to declare a compound meso:- Plane of symmetry, Centre of symmetry, axis of symmetry and alternate axis of symmetry?


text:
What is the product: Ethyne + (conc)KMnO4?
In cold and alkaline medium it gives ethane-1,2-dial. But what happens in conc KMnO4? Does it give CO2? Also, what will happen to other triple bond containing hydrocarbons?

Further oxidation of oxalic acid will give 2 x CO2. Other hydrocarbon alkynes will give the pair of carboxylic acids corresponding to cleavage across the triple bond


text:
Energy Decomposition Analysis for SN2 involving ambident nucleophiles and an alkali metal counterion
I am wanting to perform an EDA on transition state structure of the nucleophilic attack of an ambident nucleophile (2 atoms that could be used in nucleophilic attack on the same molecule) on a benzyl halide. I currently have access to Gaussian16 and ORCA, as well as any other open source software that is available. I am trying to understand what factors should be of greatest importance to these transition states, but I am unsure of what EDA to use to probe this question.
I am aware of SAPT, EDA-NOCV, and ALMO-COVP for energy decomposition analyses, but was hoping to hear of any more methods I could incorporate (that I can get access to) and/or thoughts on what dominating factors in this process (i.e., which EDA method is more applicable). I'd also like to fill any gaps in knowledge, if anyone has the time to lend me a hand.
Thanks, and all the best.


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What's the mechanism in the formation of this quinone?
I need to solve this problem for homework. In an article, I saw a quinone formation, but I don't understand the mechanism. In these reactions, the authors used KI (potassium iodide) and AcOH (acetic acid) to generate an alcohol, but I do not understand why an alcohol is generated. Also, they used toluene and p-TsOH·H2O for the opening of the epoxide ring and the formation of a double bond, but I am not sure about this. Here I leave the name of the article (Maruo et al., 2013, "Biomimetic Synthesis of Zeylanone and Zeylanone Epoxide by Dimerization of 2‑Methyl-1,4-naphthoquinone"). I appreciate your help.

Although I'm not 100% positive, I assume the first step is for both conversion of the epoxide and removal of the MOM protecting groups. Acidic conditions are generally sufficient for removing MOM protecting groups, so I would expect the acidic conditions in the first step to remove the MOM groups; however, the iodide also plays a critical role  in converting the epoxide to the alkene.
In this case, conversion of an epoxide to an alkene is a net reduction. Therefore, iodide will act as a reducing agent. I assume the first step (A) to be nucleophilic attack by the iodine on the electrophilic epoxide, facilitated by the acidic conditions. We can then perform a net protodehalogentation by attacking the iodo subsitutent with another nucleophilic iodide (B). This is the key redox step. Iodide is oxidized to iodine and the substrate is reduced. Here, the only step left is to eliminate a molecule of water (C) to produce the alkene product. I assume this is the purpose of the second step of reflux in toluene with TsOH. Elimination of water generally goes better in nonpolar solvents like toluene as it can be removed directly with something like a Dean-Stark trap, shifting equilibrium towards the alkene.


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Which is more stable, a secondary allylic carbanion or a primary allylic carbanion?
I came across this picture in a polymer chemistry course, specifically on anionic polymerization of conjugated dienes (butadiene).

I dont understand why the secondary carbanion is more stable. Based on what I know, inductive effects should destabilize the secondary carbanion, so the primary carbanion will be preferred. Moreover, the hybridization and pi orbital orientation of the two ions seems to be the same.
For extra context, the carbanion could exist as an ion pair with Li+ as the counterion, although it should exist as a free ion in the most part since the solvent is polar. However, this also doesnt explain why the second structure is more stable.


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Copper Blackening Biproducts
Apologies in advance for what is likely an incredibly basic question.
I am trying to form CuO from a Cu thin film using a bath of 1l DI water, 50g NaOH, 50g NaClO2.  I am wondering what the biproducts will be?
The reaction is described in this paper.  https://pubs.aip.org/aip/rsi/article/87/5/053119/982365/In-vacuum-scattered-light-reduction-with-black


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How to integrade a group of disconnected smiles descriptors from molecular into a single smiles descriptor?
I am new to cheminfo so this question may sound stupid.
I am trying to calculate the RDF(radial distribution function) of these two compounds below:
https://pubchem.ncbi.nlm.nih.gov/compound/155293646
https://pubchem.ncbi.nlm.nih.gov/compound/15182658
and I'm using http://www.scbdd.com/chemdes/start/ where it takes SMILES of the compound as an input.
However, I notice that RDF, due to its internal algorithm, can only calculate the descriptor for one single molecule per run, but since mine have several disconnected structures for each molecule, it seems impossible to run.
I wonder if there is some package/website/software for me to preprocess disconnected molecule like those so that I can get a single and continuous SMILES descriptor from it.

Look into "desalting" modules in rdkit.


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How does X! Tandem calculate mass from an MS2 spectrum?
I am very new to proteomics, and am using the X! Tandem tool to match MS2 spectra to a list of protein sequences. I understand that X! Tandem (and other similar tools) works by narrowing down the list of proteins using the mass of the precursor ion. I understand how the mass of the precursor can be calculated using isotopes in an MS1 spectrum, but Tandem only takes MS2 spectra as input. How are they calculating precursor mass?
Thanks in advance!


text:
Why isn't the unit of rate constant for any reaction always per second?
It is formally agreed upon that $K_{eq}=\prod_{j}a_j^{\nu_j}$ where $\nu_j$ is stoichiometric coefficient of species $j$ (negative for reactants and positive for products). This equation results in equilibrium constant not having any units. Experimentally, of course $K_c$ and $K_p$ are measured (and are of practical application). But everyone agrees that equilibrium constant has no units.
Similarly, why do we not formally define rate constant as
$$
\frac{d}{dt}a_P=k\ \prod_{j}a_j^{\alpha_j}
$$
where $\alpha_j$ is order of reaction relative to species $j$ and $a_P$ is the activity of the product.
This would mean that $k$ always had the unit $\textrm{s}^{-1}$ and, depending on the approximations used, the "unit" of rate constant may depend (analogous to $K_c$ and $K_p$). Why do chemists differentiate between the constants when it comes to units?
Another thing to remember would be that $K_{eq}=k_1/k_{-1}$, so it definitely makes sense that rate constants have same units so as to treat $K_{eq}$ as a ratio.

Rate equation hardly has to be in such simple form.

You ask a lot at once, and seem to confuse some things and the reader along the way. Units and dimensions are not the same thing. And one can, and might be particularly inclined and justified to, write a rate equation like you suggest, using activities instead of concentrations (or pressures). How "formal" this is I can't say.


text:
Looking for a practical book on IR spectroscopy techniques (LIF, TLDAS, FTIR, etc)
I am looking for a book that would ideally delve into the more practical and applied side of the IR spectroscopic techniques. Anyone can recommend me a a good book about this topic?
I have somewhat of a background in quantum mechanics and optics side of things, I am more interested in the actual implementation of these techniques.
As for the abbreviations used above:

LIF: Laser-induced fluorescence
TLDAS: Tunable diode laser absorption spectroscopy
FT-IR: Fourier-transform infrared spectroscopy

Though it isn't a substitute for a literature search/visit of a research library, the entries in Wikipedia added to translate the acronyms can be one entry.  Well, perhaps with the exception of FT (hard to find a modern IR spectrometer which doesn't use it, even old editions of the Silverstein book (resources) cover it).


text:
How to separate rhodium sulfate from zirconium sulfate?
I dissolved a zirconia ceramic containing rhodium with sulfuric acid, i tought this process will dissolve only zirconia ZrO2 at 100 °C and lower but it turned out that rhodium in form of powder can dissolve also.
I Proceeded in 3 way's the last one turned brown (no water were added) compared to the first and second one's  (red; note here i diluted with water from the begining).

Are you sure rhodium is not present as a fine suspension in the solution ? Have you tried to filtrate it? After Greenwood and Earnshaw, Chemistry of the Elements,p. 1292, Rhodium is not soluble in aqua regia. The only way of dissolving it is to fuse it with $\ce{NaHSO4}$. The behavior of rhodium in presence of acids is qualified as "extreme inertness".

@Maurice https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/ejic.201601247

@DavePhD But there's 400 °C not 100.

@Mithoron this https://pubs.acs.org/doi/10.1021/ja01624a009 (cited in the above article) says 0 °C and dilute sulfuric acid to form a yellow sulfate from the trihydroxide and heating that to 100 °C yields a red sulfate.

@DavePhD But from hydroxide, not metal.

@Tintin. The video shows that rhodium is attacked by concentrated sulfuric acid if the reaction is maintained $80$ hours (more than $3$ days) at $435$°C. This is more or less equivalent to dissolve it in fused $\ce{NaHSO4}$, as I stated it $20$ hours ago. .

@ªTintin. According to the reference, rhodium is dissolved in sulfuric acid at 435°C in a sealed ampule. The inside pressure is not given. If sulfuric acid gets decomposed à 320°C at atmospheric pressure, its decomposition is probably prevented at higher pressure.Now metallic rhodium may be separated by filtration.

Please explain how you have obtained the seven figures. Fig. 1 looks an emulsion of a black stuff. How was it obtained ? Fig.2 is a colorless solution with a "mirror" on the bottom of the flask. Fig. 3 is an orange-brown solution. How was it obtained ? Fig .4 shows two plastic bottles with colorless but poorly defined content. Fig. 5 is a colorless precipitate in a colorless solution. How was it obtained ? Fig. 6  is a dark precipitate. Fig. 7 is a colorless precipitate in a pale yellow solution. How were all these solutions and precipitates obtained? Explain !

@Tintin. You aren't clear. You state that Fig. $1$ is "where you did not dilute" the acid. What is this "where" ? Is it the result of the action of sulfuric acid on zirconia ? It should be mentioned. You state that Fig. 7 is the remain slurry of it". So the remain slurry is white !! How come if the liquid is black ? You state that Fig.2 is the same solution. Well. Which same solution ? Is it the black liquid from Fig.1 ? What is this mirror ? All the other figures are equally unclear. I will not describe my trouble for all. It would take too much time.


text:
Standard formation enthalpy or entropy. What is temperature is standard conditions?
I am reading Atkins's Physical Chemistry.
In section Thermochemistry, in subsection 2.7 Standard enthalpy changes
It states that

As implied by the examples, standard enthalpies may be reported for any temperature.
However, the conventional temperature for reporting thermodynamic data is
298.15 K (corresponding to 25.00°C). Unless otherwise mentioned, all thermodynamic
data in this text will refer to this conventional temperature.

I found many examples in the book that give data at 298 K. It is omitting the decimals or is it a different criterion?
If you check wikipedia page of Standard enthalpy of formation, both numbers are used? Are there many criteria?


text:
Chlorine monoxide formation
In World War 1, the chlorine gas was handled by some soldiers by damping their hankerchiefs into sodium carbonate solution. The article chlorine monoxide suggests that the reaction release chlorine monoxide at 20-30 degree Celcius. I wonder how is the gas released at this temperature since the concentration of sodium carbonate was not given.
From this paper, it says:

Under the optimal conditions of reaction, sodium carbonate, containing approximately 10% of water, is allowed to fall slowly down a reaction tower and contacted with an upward flow of chlorine diluted to about 25% in a gas such as air, nitrogen, or carbon dioxide. The humidity in the reaction zone must be maintained at around 10%, either by saturating the incoming gas with water or by injecting steam into the reactor at regular intervals. The temperature of the reaction zone is preferably maintained at about room temperature (20-30 ᵒC), but may be raised to as high as 200 ᵒC.

So, I figure that under small amount of water, chlorine gas could form HClO via
Cl2 + H2O -> HCl + HClO
My question is:

What is the mechanism of Cl2O formation?
How does the concentration of sodium carbonate and temperature would affect the formation of Cl2O compound?

$\ce{Cl2O}$ is simply formed by dehydration of $\ce{HClO}$ according to : $$\ce{2 HClO -> Cl2O + H2O}$$ $\ce{Cl2O}$ can be considered as an anhydride of the acid $\ce{HClO}$.
$\ce{Na2CO3}$ is used to push the reaction of chlorine on water to the right-hand-side, as $\ce{Na2CO3}$ destroys $\ce{HCl}$ as soon as produced, which prevents back-reaction to occur. The equations are : $$\ce{Cl2 + H2O <=> HCl + HClO}$$
$$\ce{Na2CO3 + 2 HCl -> 2 NaCl + H2O + CO2}$$

A simple and good answer. But, assuming the excess of carbonate, I would rather write $\ce{Na2CO3 + HCl ->  NaHCO3 + NaCl}$.

@Poutnik.OK. Thank you. I know and I have hesitated to show "your" reaction, with the formation of $\ce{NaHCO3}$

Hehe, I have hesitated to edit your answer, I let it often on the question author if he/wants to use it.

So, regardless of the concentration of Na2CO3, chlorine monoxide would always be produced, wouldn't it?

@Seiji. I am not a specialist of this chemistry. Apparently the concentration of $\ce{Na2CO3}$ is not crucial. Its total amount is more important. It must be sufficient to destroy all $\ce{HCl}$ produced. But for example, I do not know if and how $\ce{Cl2O}$ reacts with $\ce{Na2CO3}$. Sorry !

@Seiji: Perhaps the gist is that (effectively) the salt NaClO stays in solution (or is bound to the hygroscopic Na2CO3)?


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Copper reaction with nitric acid
According to this paper, the green colour from the reaction of copper and nitric acid could be explained:

The color is greenish, probably as a result of a combination of the
pale-blue color of the traces of dissolved salt and the pale yellow
color of the acid. Another reason for the color difference might the
absence of water in the system; hence, no aqua complexes are
formed.

The deep green colour arises when copper contact with nitric acid solution, I think the colour might be due to copper complexes. After consulting my teacher, he said that when nitric acid solution is concentrated, the main component would be [Cu(H2O)4(NO3)2] which is responsible for the colour. I wonder if this is true?

The shift from blue to green could be also caused by dissolved NO2.

My friend once conducted electrolysis of CuSO4 experiment. The cathode turned green also. The device was new and CuSO4 solution was prepared from CuSO4.5H2O. Couldn't explain it

@Shira your green cathode is probably not the same as the copper nitrate in nitric acid. Copper plating at the cathode could be accompanied by reduction of water to hydroxide ion thus precipitating copper hydroxide. Industrial copper platers add acid when plating from a sulfate bath.

Well but copper hydroxide is not green, isn't it? Might have been some faults while experimenting

Blue to green from what I read.


text:
1,3-butadiene conformation difference
I am aware that there are 2 well-known conformations of 1,3-butadiene which is s-cis and s-trans conformation.

The s-trans conformation is clearly more stable than the s-cis conformation whose interaction of two hydrogens destabilizes. Based on the picture in Shira's question, the energy difference of the HOMO and LUMO in s-cis is lower than s-trans (calculated via wavelength). Why is that so? Could it be the contribution of the mentioned hydrogen interaction?

https://chemistry.stackexchange.com/questions/44053/relative-rates-of-two-acyclic-dienes-in-the-diels-alder-reaction

Much thanks for your suggestion, but I don't think think that I have the answer for the question


text:
synthesis of lead hydroxide
what is the best and cheapest way to do it? I tried solving lead in HCl but only a little of lead reacts with HCl so I used electrolysis to speed up the reaction but still a little lead reacted. is it because of soloubility of PbCl2? if I use nitric acid will it work better( soloubility of lead nitrate is more than others)?

Yes, poor solubility of PbCl2 is quite probably the issue.

The insoluble salt increases the oxidation potential but can cause mechanical problems if the salt is adherent; the reaction takes longer. For a small amount electrolysis in HCl and patience should work, otherwise nitric acid. Just curious why make lead hydroxide?

can I directly make Pb(OH)2 by electrolysing water? for example use CuSO4 as electrolit?

by adding H2O2 to Pb(OH)2, red lead is made. I want for making red lead.


text:
Who codified/how was it codified that oxidation is electron loss and reduction is electron gain (OILRIG)?
As far as I can tell from some reading on the subject, the terms oxidation and reduction were first used by Antoine Lavoisier and contemporaries to discuss combustion in the late 1700s. The term electron wasn't coined for another 100 years, so I'm wondering who came up with/proved the above concept, commonly codified as "OILRIG".

https://www.britannica.com/science/oxidation-reduction-reaction/Historical-origins-of-the-redox-concept will be of interest

As you state, in early chemistry, oxidation meant combining with oxygen, e.g., burning, and reduction meant removing oxygen from an ore, e.g., reducing iron oxides to metal.

Oxidation/reduction may be the lose/gain of electrons, but need not to. More general is increase/decrease of the oxidation state/number, what is the formal charge after heterolytic bond breaking according electronegativities of atoms. //  Note that electrolysis as the link between charge and oxidation/reduction is known about 100 years longer than an electron too. // The question is more suited for History of Science and Mathematics SE. I have never heard about "OILRIG", even if it is clear what it means.

i agree its more complicated than this rule of thumb poutnik. i found the mnemonic here though it is well known https://en.wikipedia.org/wiki/Redox#/media/File:Redox_example.svg


text:
Stereochemistry in bicyclo compound
In the below bicyclo compound , there are two chiral carbon atoms. So, total combinations of configurations are four : RR, RS, SR, SS. However according to answer key , only two isomers of this compound exist. I am confused that how that can be ? Are some of the above configurations give identical compounds ? I cannot figure any simple symmetry which makes so.
Thanks very much.

The two chiral centres are not independent. The stereochemistry of one affects the other.

@An_Elephant Can you show how does it affects ?

It is trivial. You must be able to see it.

@An_Elephant It is not clear to me. Can you please write a detailed explanation ?

@DoraCake One approach: 1) assign configuration of the stereogenic centers in the structure shown. 2) imagine how the four substitutents around each of them should be attached to interconvert a centre presently (R) would be (S), and vice versa a centre (S) as one  (R).  How would this look like joining the pieces together?  Best thing for many is to build a model (no affiliation, but as an example this one).

@DoraCake, to see that chiral centers in this compound are not independent try to draw a molecule with just one chiral carbon with opposite configuration. This way you will see that orientation of bond closing one of the rings from bicyclic system would be such that it will be impossible to connect it with the other atom that it is supposed to be connected with.

I think you could use a better textbook. What kind of lame question was that? There's certainly no stereoisomers at all, except on paper, but you could have some trouble even with drawing any.

This site is instructive.


text:
Reaction between lead acetate and carbon dioxide
As we know, $\ce{CO2}$ will not react with $\ce{Pb(CH3COO)2}$ but if I start electrolyzing lead acetate solution and during the process add $\ce{CO2}$ to the solution will $\ce{CO3^2-}$ reacts with $\ce{Pb^2+}$? Can it be a method to synthesise of lead carbonate?

Why would it? Electrolysis adds nothing to the picture.

Why do you want to make two different operations simultaneously, namely electrolysis AND adding CO2 ? Why ?

by using electrolysis I want to replace Pb2+ ions that react with (CO3)2- sth like a circulated situation because I don't want to use lead acetate more and more. is it possible?


text:
Why are there 2 spots in my TLC of furan?
I'm working on a monoalkylation of furan, and I'm trying to separate my product from byproducts. When comparing the TLC (10% EtOAc in hexane) of my mixture with that of furan (starting material), I observe 2 spots, one at the bottom line and one around rf~0.8.
Any clue of what this can be?
Thanks!

Try to test each of these two spots with appropriate reagents. Are they alcohols, ketones, aldehydes, etc, ?

Does the lower spot move off the baseline if you increase the polarity of the eluent?

I suspect your product is the high running spot. What you may have is a small amount of polyfuran that has a very strong UV chromophore and is sitting on the baseline

When comparing the TLC of your mixture with that of furan as you say – where is the sport of furan?


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Name of cyclic tetraatomic carbon molecule
I came across this article on stack exchange which mentioned a cyclic compound of four carbon atoms each connected with a double bond to the two adjacent carbon atoms. However, this made me think what would be the name given to such a compound. Also, could this similar compound exist? If so, what would be its name?

This abomination ist called C4, and it is very unstable. Joking aside though, his is just one possible structure of $\ce{C4}$, and they all are unstable. The image given here likely is not a good approximation to what a "quadratic" arrangement of 4 carbons would be like.

One could call such structure cyclobutadiyne. Except it's organic nomenclature name.

https://chemistry.stackexchange.com/questions/19475/hydrocarbons-with-only-4-carbon-atoms


text:
The formula of ammonium phosphomolybdate
It is written in my qualitative chemistry textbook that phosphate could be tested by introducing phosphate, nitric acid and ammonium molybdate which gives (NH4)3H4[P(Mo2O7)6].
I found out in the qualitative chemistry book of professor Nordman Joseph that the yellow precipitate would be widely accepted as (NH4)3[P(Mo3O10)4].
*Question:

Is there any strong evidence for the existence of the precipitate whose formula is given in my textbook?

The yellow precipitate could be further reduced to blue complex when added reducing agent like SnCl2 or FeCl2. I cannot seem to find any chemical equation which could depict this statement.

Review also search results for site:stackexchange.com OR site:libretexts.org OR site:wikipedia.org phosphomolybdate formula

BTW, the structure shown at https://www.chemicalbook.com/ChemicalProductProperty_EN_CB6162083.htm is pretty fancy for an inorganic compound!

The simplest way of writing the formula of ammonia phosphomolybdate is the Brutto formula, $\ce{(NH4)3[PMo12O40]}$. The phosphomolybdate ion is a polyoxometalate but we tend to stick with $\ce{[PMo12O40]^3-}$ for simplicity. Sometimes hydrate/water of crystallization is appended to the formula or the individual components are written separately like below:

$\ce{(NH4)3PO4.12MoO3.6H2O}$
$\ce{(NH4)3[PO4(MoO3)12]}$

Older versions had wackier formula probably because they didn't realize the "complex" factor:

$\ce{12MoO3.(NH4)3PO4.2NHO3 +H2O}$
$\ce{(NH4)3PO4.10MoO3.3/2H2O}$
$\ce{(OH)2PO-O-[MoO2-O]11-MoO2(OH)}$

Regarding the reduction of ammonia phosphomolybdate with tin(II) chloride, unfortunately I couldn't find any single step reaction, possible because the product molybdenum blue is very loosely defined and thus there is no concrete formula. It can be presented with a formula $\ce{[(MoO3)154(H2O)70]^{y-3}}$.
References

Pharmaceutical Chemical Analysis: Methods for Identification and Limit by
Ole Pedersen, CRC Press, 2006
Ionic Equilibria in Analytical Chemistry by Jean-Louis Burgot
Springer Science & Business Media, 2012
A Dictionary of Chemical Solubilities: Inorganic by Arthur Messinger Comey, Macmillan and Company, 1896
Analytical Chemistry by Nikolaĭ Menshutkin, Macmillan and Company, 1895


text:
Why does the 2p orbital of chlorine form a sigma bond with Be in BeCl2 and not 3p?
So I was reading my textbook when I came across, "Each of the sp hybridized orbitals overlap with the 2p orbitals of chlorine axially and form 2 Be-Cl sigma bonds."
Now this confused me because the electronic configuration of Chlorine is [Ne]3s23p5.
So, technically, shouldn't the 3p orbital of both chlorines attach to the sp orbital of beryllium? Why does the 2p orbital overlap? Also, how does it achieve this? The 2p orbitals of chlorine are all full (i.e. they all have 2 electrons). Does one 2pz electron get excited into the 3pz orbital?
I am very confused here and have tried reading online but haven't found any satisfactory answer. Any insight would be appreciated. Thanks.

Smells like a typo.

I thought so too at first, but in the very next section it says, "The three hybrid orbitals formed are oriented in a trigonal planar arrangement and overlap with 2p orbitals of chlorine to form three B-Cl bonds." This is about sp2 hybridized BCl3. A typo could've occurred once, but twice?

Would the downvoter care to explain?

Generally if you quote a textbook, it's good to provide the title, author, publisher, etc.


text:
Reaction of Mg/Hg amalgam with acetophenone

Will Mg perform here as Grignard or will something else happen?

Note the presence of the Hg, this will not be a simple Grignard. There is a clue here http://www.orgsyn.org/demo.aspx?prep=CV1P0459

@Poutnik new to this sir. I have edited, is this fine

@DUDE_WITH_J   have a read of this   https://en.wikipedia.org/wiki/Pinacol_rearrangement

@Waylander sure sir , will read it thanks for your effort !

It helps to write in full clear sentences. I reopened but please note it is expected that you show what it is makes the solution unclear.

...and the pinacol coupling reaction and migratory aptitude.

@BuckThorn ok sirr I will remember it and Can I ask theory related Q

If it's a very closely related question it might be better to continue in chat. If your questions are repeatedly poorly received the system robot might impose a temporary ban on your ability to start more posts.


text:
Aqueous solutions of salts pH question
I was reading up on this "Aqueous Solutions of Salts" article on chemlibre and was doing problem 2 at the bottom:
Question: Find the pH of a solution of $\pu{0.200 M}$ $\ce{NH4NO3}$ where ($\mathrm{K_a} = \pu{1.8E-5}$).
This is the given solution:
$$\ce{NH4+ _{(aq)} + H2O_{(l)} <=> NH3 _{(aq)} + H3O+ _{(aq)}}$$
$$\frac{x^2}{0.2-x}=\frac{\pu{1E-14}}{\pu{1.8E-5}}$$
$$x=\pu{1.05E-5 M}=[\ce{H3O+}]$$
$$\mathrm{pH}=4.98$$
Why does this solution set $\frac{x^2}{0.2-x} = \mathrm{K_b}$ instead of the $
\mathrm{K_a}$? If I understand correctly, the equation in their solution is for the dissociation of an acid?
This is my work and where I got stuck:

I'm sure I'm just missing something here but any help would be appreciated!

1) We use the relation $\mathrm{K_aK_b=K_w}$, 2) obtain $\mathrm{K_b}$, and 3) use the equilibrium condition to find hydronium ion concentration. This is the method followed by the problem...

I understand the Ka and Kb relationship through Kw but am still confused as to why we use the Kb instead of the Ka in this problem, I thought since this is an acid dissociation we would use Ka.

is there a mistake in the question? $\mathrm{K_b}$ was supposed to be given, if you ask me...

Yes, there is a mistake, or a typo. The value 1.8e-5 belongs to Kb of NH3, not to Ka of NH4+. Therefore, the used Kw/Kb value correctly provides Ka of NH4+, that is needed for the approximation Ka =  [H+]^2/(c - [H+]).

Note that using photos/screenshots of text instead of typing text itself is highly discouraged.  The image text content cannot be indexed nor searched for, nor can be reused in answers.  Specifically handwritten scripts can be difficult to decipher.  Consider  copy/pasting or rewriting of essential parts.
// You may find useful formatting guides for texts and formulas/equations/expressions.

@Poutnik talking about canned notices it would be highly helpful if you could give the texts in Meta so that junior users like me can help the newbies out there.

@HarikrishnanM It would make them too official. Different users prefer different wording or put stress on different things. I keep mine handy on notes system at keep.google.com. and modify them often. Also having many variants, sometime combining or alternating them, some becoming obsolete, so they are dynamic. // If mods want them, I will provide them.


text:
Absolute entropy of a compound at a given temperature is S0→T=∫Cp(T)Tdt + ΔH(trans)/T(trans).Is there an assumption of constant pressure here?
Change in entropy of system is given by dQrev/T, Qrev=nCpdT for ideal gas only at constant pressure,so when we find absolute entropy of a gas by integrating nCpdT from 0K, is constnat pressure maintained? It doesn't seem practical that a solid at 0K and when you take it to a gas, that gas and that solid have the same pressure which is needed to apply the mentioned formula.

Yes, it's possible for p to be constant. You can change T to go from condensed to gas phase.

Note also your equations contain errors. Should be $dq_{rev}=nC_p dT$, for instance.


text:
4 nitro groups on benzene
I was just wondering if there exists a phenol having 4 nitro groups. I tried searching the internet but couldn't find anything. If it exists what all features should it possess, and will it be more acidic than a trinitrophenol?

Even 5 is possible.

PubChem's records about tetranitrophenol, and the one about pentanitrophenol.

@Buttonwood Thank you sir.Got a great web to check all compounds which come to mind but I don't come across in my book

I would not like to try to isolate it

They "exist" but not much more then that. And are weaker acids, because of SIR.

You might find Derek Lowe's article, Can't Stop the Nitro Groups, https://www.science.org/content/blog-post/can-t-stop-nitro-groups, enlightening (and entertaining) -- you might get a real bang out of it.


text:
Why atomic isotopes cause a different melting/boiling point?
Different experiments show that replacing atoms with isotopes can change intermolecular forces. For example, heavy water has a higher melting point than normal water, and D2 has a higher boiling point than H2. But the trend is not always "the heavier the higher", as C13-methanol and ethanol, have a "lower" boiling point than C12 ones.
I've already read this topic, in which it is mentioned that vibrational energy is the cause of it. heavier atoms vibrate slower, so they have a higher melting point. (which again, the methanol case can't be explained by it).
My argument is that the "temperature" is defined as the average kinetic energy due to vibrations. So when D2O and H2O reach 0. they both have the same average vibrational energy, regardless of how much energy they hold. But with the same kinetic energy, intermolecular bonds in H2O are broken, and in D2O are not. Can someone explain why it happens? or persuade me that D2O and H20 can have the same temperature with different vibrations?

Why should they cause the same melting/boiling points?

You change something, so it has to be different. It should rather be "how" than "why".

The different masses directly indicate that the vibrations will be different (consider the classic mass on a spring from freshman physics). In any event, by changing how the different parts move relative to each other you make the interactions slightly different, meaning they respond to adding energy differently.

The argument about temperature and vibrations ignores big quantization steps for bond vibration energies, that spoil the simple proportionality rule of classical thermodynamics.

@Mithoron I have read this post. My question is, how the vibration is different at the same temperature? temperature is basically an average of vibrations.

@Poutnik can you explain more? also, here we are talking about intermolecular forces, not intramolecular bonds.

Vibrations are not limited to intramolecular forces. If they were, there would be no liquids nor solids - only gases.(excluding giant molecules like diamond structure or some polymers).

Quick search C-13 methanol has slightly higher BP slightly lower MP. Different sources? Temperature is not vibrations it is relative molecular velocities resulting in average KE. Vibrational states in molecules are populated by temperature. Kinetic isotope effects result from changing of vibrational states in the transition state making zeropoint energy difference between the isotopes important.  The effect on total energy affecting MP and BP is much more subtle. The differences are profound for H2, D2, H2O, D2O, He[3] and He[4], less so, but real, for others needing careful analysis.

You’re confusing ‘vibrations’ with ‘translations’. Temperature is more related to the movement of molecules in space (translation), as opposed to the movement of atoms within a molecule (vibration).


text:
Deviations in trend for boiling points of straight chain alkanols
I was given a set of data about the boiling points of straight chain alkanols from methanol to dodecan-1-ol and noticed that the trend line seemed to be in the shape of a polynomial 4. I have also noticed a similar pattern in a data set for boiling points of alkanoic acids ranging from methanoic acid to decanoic acid. Can anyone explain why this oscillation occurs?

https://chemistry.stackexchange.com/questions/160008/continuous-variable-for-graph-of-boiling-point-of-different-chain-lengths

https://chemistry.stackexchange.com/questions/50047/elevated-boiling-points-in-alkanes-with-even-number-of-carbons


text:
Cellulose acid hydrolysis
Recently i tried to hydrolyse some 10g of cellulose with 50ml of 75% H2SO4. Right after adding the acid, the entire solution turned blue black. With no heat applied.


text:
What is the major product of reaction of phenol with HNO3 in the presence of H2SO4?
In many articles I have seen they say the reaction proceeds to picric acid but the amount produced is very small. But the major product is formed by ring cleavage (oxidatively). Can anyone mention the major product and if possible provide the mechanism?

Without initial sulfonation step, phenol oxidation has many steps and branches..

Why do you guys keep asking about it? There's no specific product or mechanism. You just get some gunk. Still, it's unlikely to be "ring cleavage" - it's rather oxidative coupling.

If you use dilute nitric acid, you will get mononitrophenol in various proportions depending on phenol/HNO3 molar ratio. Please find yield here: https://www.researchgate.net/figure/Composition-of-the-products-of-phenol-nitration-with-nitric-acid-in-aqueous-dioxane-in_tbl1_294735990
If you use concentrated nitric acid, the reaction proceeds towards picric acid. See previous discussions:

Does nitration of phenol with nitric acid yields 2,6-dinitrophenol?
Preparation of picric acid


text:
Help with ppm calculation
Recently, me and my class had a lab about spectrophotometry, where we try to determine the concentration in ppm of an unknown sample contaminated with manganese.
In the process of calculating this concentration, we have to make a linear regression using the absorbance data from known concentrations in ppm. Me, my classmates and the teacher have conflicting answers about how to calculate the ppm concentration and I wish to confirm if my method is right or wrong. It goes as follows:
Vial 1 has 2 mL of a 0,0008 mol/L solution of manganese, diluted to 100 mL with water. Since 1 ppm = 1 mg/L, the calculation goes as follows:
There are 0,0008 x 0,002 = 0,0000016 moles of manganese in Vial 1, which by the molar mass of manganese (54,938 g/mol) is 0,0000879 grams, which is equivalent to 0,0879008 mg. Since 100 mL = 0,1 L, the ppm concentration is then 0,0879008 mg/0,1 L = 0,879008 ppm. Is this correct?
My teacher and classmates used 1 L instead of 0,1 L in the calculation for reasons I do not know, which makes it 0,0879008 ppm instead.

Be aware that using of ppm relative unit is strongly discouraged by IUPAC. as it often brings confusion.  Saying 1 ppm means 1 mg/L makes 2 implicit assumptions. 1/ It is implying 1 ppm is related to parts per million in units of mass (can be volume or amount)  2/ It is implying the density of the fluid is 1 kg/L. // The recommended way is, instead of 1 ppm,  explicitly writing 1 mg/L, if it is the case.

See CH SE META post about policy for "Am I right?" questions


text:
BS Chemistry Thesis Topic Suggestions in the Areas of Natural Products, Synthetic Inorganic and Organometallic Chemistry, Physical Chemistry
I am a 3rd year Chemistry student. In partial fulfillment of the requirements for the degree Bachelor of Science in Chemistry, we are to present an undergraduate thesis. We were highly encouraged to choose a topic that interests us, however, I find it difficult to find a topic because my interests are too broad. I also want my undergraduate thesis to be publishable internationally but I don’t know what topics would top that. I’ve had a difficult time finding topics that are relevant, unique, cost-effective, and feasible for an undergraduate that interests me. Can you suggest thesis topics in the areas of natural products, synthetic inorganic and organometallic synthesis, or physical chemistry? We are given 10 months to propose, experiment, and defend our thesis. Thank you.

Huh, while you may be encouraged to do that, I don't see how it's a good idea. Try finding a good supervisor and talk what the topic could be. More importantly you question isn't suitable for the site, as it's got no specific answer.

Here is one problem that could be studied in an undergraduate thesis : the kinetics of copper dissolution. I explain. If you put always the same copper cylinder in always the same volume of different concentrations of sulfuric acid, and if you introduce a rubber tubing producing constant bubbling of air into this solution, you will observe that the solution gets slowly more blue. You could measure the concentration of copper by a colorimeter. The strange thing is that there is no corrosion of copper in highly diluted solutions, and in high concentrations of sulfuric acid. Why ? I don't know. The corrosion is maximum for a given intermediate concentration. Which one ? I don't know, You may study many different solutions simultaneously by using as many beakers and as many pumps as needed. Another strange phenomena : when the solution gets saturated in copper sulfate, the corrosion does not stop. It continues, and well crystallized copper sulfate is slowly developing on the copper cylinder. You may weigh this amount of cristal versus time. Try ! It is easy. In my opinion, it has not been studied so far. I may be wrong,

Maybe you want to post this as a question instead?

Why do people decide to disqualify the strange facts I am mentioning ? I will not  post this strange behavior as a question now, as suggested by Buck Thorn. I have not enough measurements. It would be better to repeat this experiment, with a lot to different concentrations. I have done it with only four solutions.  It should be repeated and the kinetics seriously determined. It could be a nice subject fo an undergraduate thesis.

As you are probably aware by now, questions such as in this post tend to be considered off-topic as "opinion-based" (well, here is was voted "unfocused"), and answers are sometimes discouraged with downvotes.


text:
Why do we assume the total number of valence electron in a compound are the sum of its atoms' electrons in ground state?
Take for example H2O, when drawing the lewis structure for this, we will assume, by adding up the valence electrons of 2H and O in their ground states, the final compound has a total of 2+6=8 valence electrons. We also do a similar practice of assuming charge is preserved in writing balanced chemical reactions. But why do we assume so? Is there any law saying that the charge of a compound's reactants is preserved as they form the compound itself?
Edit - I am not questioning the balance of electrons, I am questioning that why a molecule of H2O has to be composed of its ground state electrons, why can it not be split up into a oxygen ion and 2 hydrogen atoms. I have no reason to believe that the charge of the oxygen, has anything to do with H2O, which is a new entity, in which all I know is it is composed of one 2 hydrogens and 1 oxygen.

There is a very basic, fundamental law of nature, which says that if you've put 10$$$ in your pocket, you'll get 10$$$ out of your pocket. Same thing with electrons.

Charge is preserved, it has been never observed the opposite. But charge can be interchanged between several molecular entities.

"are the sum of it's atom's electrons in ground state?" I think you mean "are the sum of its atom's valence electrons in ground state?"

It's unclear what electrons you are talking about, for instance when you state "why can it not be split up into a oxygen ion and 2 hydrogen atoms". An oxygen ion would be missing or have gained electrons, which, given the principle of conservation of charge implies the H together must have gained or lost the same number of electrons. Maybe it would help to include an image.

@BuckThorn I am talking specifically about the valence electrons. I am confused why in a chemical reaction, the charge has to be the same on both sides. One way to think justify it could be that we start out and end up with the same total number of protons and electrons, so a deficiency (or excess) of electrons will cause the them resultant molecule to be charged aswell. But I feel this is oversimplistic, it would not be too far fetched to assume bonds could alter the charge

Are you aware that electrons have a charge of -1 and protons +1? I assume as much. Chemical reactions don't destroy or create electrons or protons, therefore the total charge (sum of protons minus electrons) has to be constant. Where electrons end up is another question. That can get awfully complicated and is one of the essential question chemistry asks ("what is a bond?")

I think your question might become clearer with a schematic illustrating an example of what you mean. How would a bond alter the charge? You write: "the charge has to be the same on both sides." Yes. Chemical equations are balanced. No fundamental particles (protons, electrons) are created or destroyed. However one thing that can happen is for atoms to gain or lose charge, but because protons and electrons are the charge carriers, the total charge has to be constant.

@BuckThorn Thanks for following up. I realised my question is more about net charge itself than the conservation of it. In polar molecules like HF there is no net charge, yet they can attract electrons - they behave similarly to ions. So I guess my question is what does a net charge (excess or deficiency of electrons) mean physically. It seems like chemical objects do not need to have a non-neutral net charge in order to attract other charged particles. For another example, take halogens, despite being electrically neutral they attract electrons.

I created a seperate post for my follow up question, I figured it was too physics related - https://physics.stackexchange.com/questions/808415/do-neutral-atoms-have-a-electric-field

@KrypticCoconut Ok, I understand, I had a suspicion that that was your question. The internal distribution of charge is essentially a quantum mechanical phenomenon. That is a hand-wavy way of saying that it is weird. Electrons are particles and yet they can "spread" themselves about a molecule. You can still try to edit your question to fit this site.

Your opening question at physics, "If a atom is neutral, does it mean it does not have an net electric field?", is easy: the total field about a neutral particle (atom or molecules) is zero. There are field lines emanating and ending at the particle, but the number emanating and ending is the same.

@BuckThorn Thanks for sticking out with my question. I'm confused by what you mean the total field is zero in a neutral atom. There will still exist points of negative electric field that repulse electrons outside the neutral atom right?

The number of electric field lines emanating from positive and negative charges is the same, just in opposite directions. If you have an electron and a proton enclosed in a volume and sum the lines crossing the surface they add to zero (where you add lines heading out, subtract those heading in). This is Gauss's law. Yes, there will be lines no matter how far you go, whether neutral or not. But the lines from plus and minus charges cancel so the net field will become weaker faster as you move away from a neutral molecule.


text:
Is there intramolecular H-bonding in 2-hydroxybenzonitrile?
Is there an intramolecular hydrogen bonding in 2-hydroxybenzonitrile? If so, then the $\mathrm pK_\mathrm a$ order should be meta > ortho > para but the actual order is meta > para > ortho.
I think since the $\ce{-CN}$ group is linear in shape hence the distance between $\ce{-OH}$ group and $\ce{-CN}$ is large so there should not be any hydrogen bonding between them.

You think right.


text:
Separation of dried blood using solvent
What is the best solvent to separate the metabolites from dried blood?

Review the guide How to ask and Asking FAQs to prevent clarification requests, objections,  downvoting or closure.

What metabolites? Short of knowing that, your question sounds a bit vague.

Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.

According to the procedure that follows from Ref. [1] a mixture of water and methanol is an appropriate solvent:

Metabolites from DBS samples (3.2 mm diameter punch) were extracted onto 96-well plates in 100 µL 80% methanol. The supernatants (75 µL) were transferred onto new plates, dried under nitrogen, reconstituted in 75 µL 2.5% methanol, and transferred (65 µL) onto the final plates before injection.

Blood metabolites, unless associated with a carrier such as liposomes or BSA, are significantly water-soluble (salts or polar compounds). Methanol is thoroughly miscible with water but lowers the polarity of the mixture helping solubilize less polar compounds such as lipids, and methanol is also easily removed by evaporation.
Reference

Olarini, A.; Ernst, M.; Gürdeniz, G.; Kim, M.; Brustad, N.; Bønnelykke, K.; Cohen, A.; Hougaard, D.; Lasky-Su, J.; Bisgaard, H.; et al. Vertical Transfer of Metabolites Detectable from Newborn’s Dried Blood Spot Samples Using UPLC-MS: A Chemometric Study. Metabolites 2022, 12, 94. https://doi.org/10.3390/metabo12020094


text:
How to design a lab experiment showing differences between reversible and irreversible work?
Some of my students keep asking for more information about reversible and irreversible work. I've been trying to think of a demonstration/experiment that might highlight the broad concepts but haven't gotten far. Does anyone know of or have any experience on such demonstrations or experiments?

As inspiration, see this simulated experiment LearnChemE.com - simulations - thermodynamics - reversible-irreversible-expansion-compression-work

Make a list of processes that involve reversible work and a second list of processes that involve irreversible work.

Pull a weight on a rubber band, and let it snap back. Pull a weight on a rubber band until the band breaks. Where did that work go?

In a rapid irreversible compression, do you think that the gas satisfies the ideal gas law?

It probably does All the processes are the result of random molecular motion.

Each of them is a living example of a series of almost equilibrium reactions that extract work from a process. Compare eating a cookie, digesting it, getting energy to move etc., compared to just putting the cookie in a fire. The end products are the same: CO2 + H2O + energy. Processes are irreversible because they have the combination of negative deltaH and positive deltaS and cannot reach equilibrium. The trick is to control the entropy change.

@jimchmst
Thanks for your reviewing my post. Perhaps I wasn't clear in my original post, but by reversible and irreversible work I'm referring to expansion work (there's more on this in Atkin's Physical Chemistry). So, in essence I'd like a somewhat intuitive experiment or demonstration to show how the maximum expansion work for instance is the maximum work possible ...


text:
How dangerous is CO gas poisoning?
I have learned that there are carbon monoxide canisters, and I can't help but feel discomfort at the thought of how morbidly dangerous those will be in a hobbyist home setting. Now let's imagine that someone would mistake it for nitrous oxide or helium and inhale it out of the canister. I imagine that this will be a death sentence, and there is nothing short of a massive blood transfusion that can be done to save that person's life. Is this accurate?
P.S. Please note that I am not planing a murder or a suicide. I just find some of those morbid topics interesting, from time to time, and I think that it is good for us as people, to give some thought, from time to time, to things that can go horribly wrong

Why would hobbyist need carbon monoxide ? Are you sure it is not carbon dioxide?

I red that there have been instances of planned group suicides where people intentionally produce CO gas. So I thought - wait a minute, there is probably a more sinister way  of going about that. So after finding out that it is a useful reagent, I thought - nooo, there might be fatalities related to poor practices. And what is more dangerous then an improper home setting

I am fascinated at what biests chemical engineers contain behind pressure valves

How dangerous is it? Either you die or you fully recover, afaik. How would you make a transfusion in a time one needs to suffocate? (rhetoric question)

@Mithoron strictly speaking CO does not suffocate. It damages the blood's ability to transport oxygen and is far slower than suffocation, but more insidious as smaller amounts do the job well. and it isn't always something from which a full recovery is possible.


text:
Can triethylamine be substituted for pyridine as a base catalyst in acryloylation reaction?
I work in a polymer research lab and I'm writing a procedure to synthesize glycerol 1,3 diacrylate but in almost all the reactions I've been reading, the synthesis occurs at hot temperatures(60 C) and using pyridine.
We already synthesize poly(glycerol-co-sebacate) acrylate and in that procedure, we found that it works best using triethylamine and acryloyl chloride at cold temperatures(0 C) due to higher reactivity, so I'm wondering if pyridine can be substituted with triethylamine at colder temperatures for the glycerol 1,3 diacrylate synthesis.
In my head, I think that it should work since the role for both in their respective reactions is as a base catalyst with the main difference being that triethylamine is much more reactive than pyridine but if anyone else can give their two-sense on the matter that would be very much appreciated.
Thank you!!

Without additional info nobody here can say for sure. The proper way to go is to perform both experiments and compare yield, reaction time and product purity. In general one can say, that pyridine is less nucleophilic and less volatile. The first property is often desired, the second not such much. On the other hand, pyridine can also be used as a polar solvent or as a catalyst for acylation reactions. What this means for your system has be evaluated by yours on the basis of multiple experiments and evaluation of the same.


text:
what's the meaning of the "strikethrough" bond in the skeletal formula of this aromatic compound?

That's taken from https://doi.org/10.1039/A901537J , which is about direct amination of the depicted nitrobenzene; I'm puzzled about the meaning of that --NHR moiety, specifically why it doesn't connect with a carbon atom, but instead the other end of the "bond" ends inside the benzene ring.
Any hints about what's meant with this notation?


text:
When to use Heat of Products - Heat of reactants and Heat of reactants - Heat of products when calculating enthalpy change
In my schoolbook there are multiple questions where I have to calculate the enthalpy of formation, heat of reaction, enthalpy of reaction, etc etc. But sometimes the formula to be used is Hp - Hr, and sometimes it is Hr-Hp. So, when do I use what?
(Hr = Heat of reactants
Hp = Heat of products)

Review the guide How to ask and Asking FAQs to prevent clarification requests, objections,  downvoting or closure.

Welcome to ChemSE! Please find guidance for MathJaX / $\LaTeX$ as follows and reformat your post - Basics // MathJaX and mhchem formatting for equations and chemical formulae // Guidelines on which should be upright / italics

Also you can refer this guide on how to use MathJaX.

It's not clear without some examples.


text:
Determining the reduction potentials of elements?
How can we predict the order of reduction potentials for given elements? Consider the reactivity of metals, there is a standard explanation to determine reactivity. Eg. Sodium is more reactive than lithium due its larger ionic radius. Hence we have intuition for the order of reactivity. However, for reduction potentials, I can't seem to find an explanation. Unintuitively, the reduction potential of sodium is actually lower than that of lithium, meaning that reduction potential cannot be determined by reactivity, so there must be something else going on.
The best explanation so far, states that reduction potential is determined by ionisation energy and hydration energy, a mixture of the two? Could this be correct?
Comprehensive explanation of how we can build intuition for reduction potential would be great. Could you provide links or materials to learn about this?
Edit: Answers always explain that the reduction potential is measured relative to the hydrogen potential which makes sense. However, what are the underlying principles? Eg. For reactivity with metals, we could obviously just react them together and determine a reactivity series. However, we have an explanation for this reactivity series, which is what I want for reduction potential. Could reduction potential be determined by ionisation energy and hydration energy?

Do thorough searching, similar questions were asked multiple times on this site. Be aware of kinetic reactivity and thermodynamic reactivity are 2 different things. In Li and Na case, their order is mutually switched. Na reacts faster, but Li releases more energy per molar amount (free molar enthalpy).

"Sodium is more reactive than lithium due its larger ionic radius." That sounds like a proximate rather than ultimate explanation. What definition do you use for reactivity? Oxidation potential is a factor in the definition provided at the Wikipedia: "lose electrons (oxidize) more readily to form positive ions;"

related: https://chemistry.stackexchange.com/questions/87514/why-are-not-all-metals-included-in-the-reactivity-series/87529#87529

I think you are asking about the measurement of Standard Reduction potential. It is done by building a electrochemical cell, where the element under observation is taken as an electrode and the other half cell is the SHE (Standard Hydrogen Electrode). SHE acts as a reference point(its reduction potential is assigned as 0 V) and based on the unknown electrode it will get oxidised or reduced. In this manner we can find Std Reduction potential values.


text:
Analysis of substances
The crystalline substance X completely decomposed without the formation of a dry
residue when heated. As a result of adding a solution of calcium hydroxide to the
solution of substance X, a precipitate insoluble in water fell out. Substance X is: A

ammonium carbonate, B - sodium sulfite, B - ammonium chloride, G - sodium
hydrogen carbonate.
Explain your answer.


text:
What is the energy of sum of ionic equations?
Say energy depends on the relative number of ions in the mixture, and factors P, and T.
$$
u = u (P,T,x_1,x_2,...,x_{n-1})
$$
Mixing two solutions at the same temperature, may change the temperature if there is some interaction between the two ionic solutions. Otherwise,
$$
u_1+u_2 = u (P,T,x_{11},...,x_{2m-1})
$$
A change in temperature is a result of some interaction between ions:
$$
\Delta u = \Delta U (k_{x_{1n}x_{2m}})
$$
We know that change in energy is zero, otherwise we can ignore the change in temperature over long periods:
$$
\Delta u = 0
$$
For two ionizations:
$$
u_{I_1} + u_{I_2} = u(P,T,x_{11})
$$
for $I_1 = I_2$:
$$
2u_I = u_I
$$
since our energy $u$ is an intensive property. This also means that while the total energy is not changing, energy per unit volume may change:
$$
\Delta u_V \neq 0
$$
This simply means volumes of ionic solution matters, for one, it matters in size.
$$
U = U (P,T,V,x_1,x_2,...,x_{n-1})
$$
Is there such a function for $U_1+U_2$?

Hi. It was hard for me to follow, because some symbols seem strange to me. Nevertheless, are you interested in a general function $U$ which describes the internal energy when two ionic liquid solutions are mixed? Is that the last result?

@MetalStorm yeah, figuring out the required variables, I think I overcounted.

I know that it is not of much help, but there does not exist a universal function for the internal energy, because it will depend ultimately on a model. It is possible to arrive at a general differential relation, I can guarantee that. But, some model for the excess Gibbs energy $G^\mathrm{E}$ or other thermodynamic function will be needed.


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Why is de Broglie applied in case of photons
Q: Consider a helium (He) atom that absorbs a photon of wavelength 330 nm. The change in the velocity (in cm s¯¹) of He atom after the photon absorption is (Assume: Momentum is conserved when photon is absorbed)
Use: Planck constant = 6.6 * 10 ^ - 34 , Avogadro number = 6x1023 mol-1, Molar mass of He = 4 g mol¯¹)
My approach:
Calculate Energy of the photon by
 E = hc/wavelength
And then equating it with the change in kinetic energy, however the difference is answer is by a factor of 2^1/2
In the solution, they have done it simply by substituting in de Broglie equation. I mean how can we just substitute the mass of helium and the wavelength of photon in the same eqn? And how is my approach wrong?

Focus on momentum, not energy. For m>0 and v << c, p =m.v. For m=0, p=E/c = hc/(wavelength . c) = h/wavelength

I understand, but why is the energy approach wrong? Am I missing something about energy conservation, is energy also converted into some other form?

Why do you think the whole photon energy is transformed to the atom kinetic energy?

I mean if not K.E. then it will be transformed into which form?

It could be an electron excitation.

You might also be interested to look up  details of the Mossbauer Effect.

Einstein's special theory of relativity is the basis of the expression of de Broglie.
the actual expression was
$ E^2=(pc)^2 + (mc^2)^2 $
In case of photons the rest mass was zero. however this is not the case with helium atom. So, you cannot equate change in kinetic energy of a non zero rest mass object with the energy expression of photon mentioned above.

I don't understand how special relativity is the basis of de Broglie's expression. I think de Broglie was inspired by the photoelectric effect, so he extended the expression $h\nu$ which Einstein applied only to photons to all bodies composed of matter. Am I incorrect?

yes. He argued nature is symmetric and matter also shows wave nature.


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Does this synthesis of dimethylmercury require anything else?
I've seen that dimethylmercury can be made using sodium amalgam and methyl iodide. Are those the only chemicals needed or does the reaction require a solvent or application of heat or anything else like that? Or will the reaction take place just by mixing the two? Not trying to make it but concerned about possible accidental contamination.

I don't think we're gonna give you preparative receipt for a serious poison. BTW you cannot mix  sodium amalgam and methyl iodide - reaction takes place on the interface between them. Contact between them is enough for reaction to take place, as mentioned in earlier post.

The link you provided seems to answer my question. I was hoping there was more to it but thanks for the reply.

If you don't want to make it, this should be enough. What temperature, solvent etc. to use for actual synthesis of pure compound with good yield aren't really relevant otherwise.

Why do people keep being worried about such unlikely reaction, seems to be beyond me...


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Why does water sometimes split into H+ OH- (H3O* OH-)?
I am aware that this isnt the water splitting into H+ and OH-, and that is is just a transfer of Hydrogen via autoionisation ...
(found this on here: Why does water split into ions? //
"Water does not really split into ions. It transfers protons, reversibly, from one molecule to another:
2H2O = H3O+ + OH−
The ions represent, of course, a less stable state than molecular water, at least under ordinary conditions, so the equilibrium constant is low. Yet this reaction strongly affects the chemical prpoeryies and even some physical properties of aqueous solutions." )
...but I want to know why it is that this happens, as Kw is very small 10^-14, this doesnt happen much, but I wish to find an explaination for why this actually happens, what causes the hydrogen to be transfered to another water molecule?
Thank you to anyone who gets back to me!

This should be covered in physical chemistry under statistical thermodynamics. Have you learnt those?

I'm not sure what explanation would you what. Water is both slightly acidic and basic, and that's the result.

You mere ask why acids sometimes provide a proton and why bases sometimes accept a proton.


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In Isobaric process, is external pressure equal to gas pressure?
In which processes are external pressure and gas pressure the same or constant?

Note that questions looking like homework/test/exam/lab tasks, posted without significant attempts to understand/resolve them, are explicitly off-topic on this site and will be closed.
// Review the guide How to ask and Asking FAQs to prevent clarification requests, objections,  downvoting or closure.

What exactly do you mean by the external pressure?


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determine activation energy using the time for maximum temperature to be reached for catalytic decomposition of hydrogen peroxide
when determining the activation energy for the catalytic decomposition of hydrogen peroxide using manganese dioxide,
a common way is timing the collection of a given volume of gas or pressure when carried out at different temperatures.
Is it possible to instead use data measuring the time to reach the maximum temperature for a reaction instead.

Where have you found that the activation energy can be obtained by timing the collection of a given volume of gas at different temperatures ?


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Enamine Stability determiners
been wondering what are the factors that determine the stability of the enamine structure, like steric hindrance, resonance effects, and stuff like that. Like if I have four compounds, how do I check which one's gonna form a more stable enamine


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What type of sugar is produced A. Tutton's Paper on the Synthesis of Glucose?
https://www.nature.com/articles/037007b0
At the end of all the chemical reactions, a sugary substance is identified by what sugar it is is not specified so I would like to know what it may be. (On a side note, if there is a other method of artificial synthesizing glucose please mention it)


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The preparation of ethene from ethanol
Draw an energy profile diagram for the dehydration of ethanol to produce ethene, labeling your reactants, products as well as intermediates.
import matplotlib.pyplot as plt
Define energy levels
reactants_energy = 0
transition_state_energy = 100  # Example value
intermediate_energy = 50  # Example value
products_energy = 20  # Example value
Define labels
labels = ['Reactants', 'Transition State', 'Intermediate', 'Products']
Define energies list
energies = [reactants_energy, transition_state_energy, intermediate_energy, products_energy]
Create energy profile diagram
plt.figure(figsize=(8, 6))
plt.plot(labels, energies, marker='o')
plt.xlabel('Reaction Progress')
plt.ylabel('Energy (kJ/mol)')
plt.title('Energy Profile Diagram for Dehydration of Ethanol to Ethene')
plt.grid(True)
plt.ylim(0, max(energies) + 20)  # Adjust ylim for better visualization
plt.annotate('Activation Energy', xy=(1, transition_state_energy), xytext=(1.2, transition_state_energy + 10),
arrowprops=dict(facecolor='black', arrowstyle='->'))
for i in range(len(labels)):
plt.text(labels[i], energies[i] + 5, f'{energies[i]} kJ/mol', ha='center', va='bottom')
plt.show()


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Definition of adsorption
Wikepdia defines adsorption

Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface

Does this make, a cation getting reduced and attaching to the surface of an electrode during electrolysis, an example of adsorption? It seems to satsify the above definiton. However, no matter what I search, I never see this as an example of adsorption.

There must be countless articles on reduction of adsorbed species on electrodes. Adsorption "typically" means that there is NO chemical reaction. Since you also want to adsorb and then do an electrochemical reduction, these are two distinct steps. Any definition of any term cannot encompass all examples in the world. Definitions are limited and man-made.

Yup, that would be adsorption. If it's forming a specific bond to the surface, that would be chemisorption; if it relies on intermolecular forces (e.g., ion-ion, London dispersion forces, etc.) it would be physisorption. Found some papers for reference. > https://doi.org/10.1039/D1SE01760H > https://doi.org/10.1002/elsa.202100183 > https://doi.org/10.1021/jp500425g

Yes, adsorption is one step on the electrode, the next step will be electroreduction. Adsorption's definition does not include electrochemical reduction as the OP is thinking.


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Different method of solving a question giving different answer

Calculate the concentration of nitric acid in moles per litre in a sample which has a density, $\pu{1.41 gmL^–1}$ and the mass per cent of nitric acid in it being $69 %$.

I attempted to consider a 1L solution, and since $\pu{Density= \frac{Mass}{Volume}}$, obtained the mass of $\pu{1L}$ of the solution as $\pu{1410g}$.
I then attempted to acquire the mass of $\ce{HNO3}$, which I got as $\pu{972.9g}$ Then the number of moles of $\ce{HNO3}$ is $15.44$ moles. This makes the molarity of the solution $15.44$. Of course, this is far from correct, but I am unable to trace any mistake in my methods.
Any hints and answers are extremely appreciated.

What other methods and what other results?

Wikipedia: The concentrated nitric acid of commerce consists of the maximum boiling azeotrope of nitric acid and water. Technical grades are normally 68% HNO3, (approx 15 molar), while reagent grades are specified at 70% HNO3. The density of concentrated nitric acid is 1.42 g/mL

There is nothing wrong with your calculation (except maybe sig figs).

Dear OP, you are supposed to show your working so that the community can better gauge how it can help you. They are asking molarity from given mass %.

Your answer is correct, although a more direct calculation would be:
$C_i=y_iC=\frac{x_i\require{cancel} \cancel{M}}{M_i}\frac{\rho}{\cancel{M}}=\frac{\left(0.69\right)\left(\pu{1410g/L}\right)}{\pu{63g/mol}}=\pu{15.44mol/L}$
Where:
$\,x_i$ is the mass fraction of $\ce{HNO3}$
$\,y_i$ is the mole fraction of $\ce{HNO3}$


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Why does a nucleophile have to be replaced by a nucleophile?
I'm a highschool student for context and I was thinking why does a nucleophile need to be replaced by a nucleophile in a nucleophilic substitution reaction -  why doesn't it just replace one of the $\ce{C-H}$ bonds instead. Asked my teacher and she said, "stability". I have no clue what that means and I would like to understand what exactly this term means.

o.O Nucleophile replaces a leaving group, which has to good enough to be substituted. You thought what would leave in your scenario?

@Mithoron I thought the carbon-hydrogen bond would break and the hydrogen would leave.

Hydrogen anion would leave - it's one of worst leaving groups. No way it would happen, unless something would accept it at the same time.

BTW why didn't you consider that C-C bond could be broken? It's actually more likely scenario, but still a rare thing.

"Stability" in this context refers to a bond's resistance to breaking. A C-H bond is way more stable than a C-X bond, and therefore way more resistant to breaking. In other words, C-X bonds are easier to break because they are more unstable.

How can a nucleophile be replaced by another nucleophile? Something's highly inaccurate here with your terminology. Is it by any chance that you missed out on the term electrophile / electrophilic nature?

It is an ionic reaction. The Original compound has a polar bond with a negative leaving group and a partial positive charge on the carbon. The nucleophile approaches the carbon forming a bond while the bond to the original nucleophile breaks. [SN2 mechanism]. C-H and C-C bonds are usually nonpolar so they do not participate directly in ionic reactions. The actual reaction depends on the bond strengths, concentrations and reaction conditions.

@jimchmst Ty that makes perfect sense.


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What are a some of the best crosslinkers for uv curing of benzyl methacrylate?
I'm hoping someone can suggest some crosslinkers for uv curing benzyl methacrylate that are low in viscosity, relatively high in refractive index and most importantly that will impart hardness and rigidity to the produced homopolymer.

Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.

I'm hoping someone can suggest crosslinkers for uv curing benzyl methacrylate that are low in viscosity, relatively high in refractive index and that will impart hardness and rigidity to the produced homopolymer.

Can you please edit your question and include this description? This is lot clearer than the actual text of the question.

Just looking for some free consulting work. For requests such as this a chemist, consultant should be hired given the details and PAID for their work.


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Labelling cathode and anode for electrolysis
Determining which electrode is the cathode and the other the anode is providing to be quite confusing.
We are given the polarity of the dc supply, a cell, and then we should be able to determine the cathode and anode.

As shown by the diagram above the positively charge anode is on the same side as the positive terminal of the voltage source and vice versa. My problem with this, is that the reality is the current flows from negative to positive, and does not obey the conventional current, hence the anode and cathode should be switched.
However, every diagram I have seen has done the same thing as above. I understand that this this convention, but here we shouldn't be able to do this, if we were to observe this process, there would be a build up on the wrong electrode if we followed this convention.
How do we label it?

https://chemistry.stackexchange.com/questions/68533/which-is-anode-and-which-is-cathode

Anode is always the electrode where oxidation happens, whatever the cell. It is valid both in electrolysis and in a galvanic cell.

Pay attention to the flow of the electrons (or that the spoon is being silver-plated), not the plus and minus signs. Reduction happens at the cathode ("red cat"), oxidation happens at the anode ("an ox").


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Why are there no two steps involved in this following reaction?
I was studying the chemical properties of alkynes in which I found the following reaction with alcohols

Ethyne gas reacts with methanol to form methyl vinyl ether.
$$\ce{H-C≡C-H + CH3OH -> CH2=CH-OCH3}$$

Now I was quite surprised at seeing this reaction as in most of the other reactions(such as addition of acetic acid to ethyne). The electrophilic addition process was taking place twice. What I think is that $\ce{OCH3}$ must be a +M group (because of lone pairs on Oxygen atom, I suppose) and as a result the pi bond between the carbon atoms in methyl vinyl ether should break in the following way:

and then undergo another electrophilic addition reaction to form 1,1-dimethoxyethane (IUPAC nomenclature). Where am I wrong?

Under what conditions is this reaction reported to take place?

I checked my notes and I found out that I havent written the condition for this reaction to proceed... neither did our teacher tell us the conditions under which this reaction has to be perfomed-as far as I can remember

According to the literature this is done at high temperature and pressure in the presence of a basic metal catalyst and may be a radical process. It is certainly a high energy surface process and those are difficult to be precise about the mechanism.  see https://pubs.rsc.org/en/content/articlelanding/2016/ra/c5ra25100a


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Existence of (anti)perovskite (Cs+)3(Pt2-)(Au-) and (Cs+)(Ba 2+)(Au-)3
I know that there are oxide-aurides of cesium and rubidium from wikipedia and https://www.researchgate.net/publication/243821351_Cs3AuO_the_First_Ternary_Oxide_with_Anionic_Gold and that the component compounds cesium/barium auride/platinide exist. Would a double salt be able to exist with these components?
(may have to get Au- and Pt2- radii from lattice parameters)
(CsAu a = 4.24 angstrom)(Crystal data of Cs2Pt: hexagonal, spacegroup P63/mmc (No. 194), a=567.6(1), c=947.1(3) pm, V=264.3(1)×106 pm3, ρcalcd=5.783 g cm−3, Z=2, μMoKα=39.86 mm−1, F(000)=376, λ=71.073 pm,)

There are certain areas of chemistry where we may say with a good deal of confidence that such-and-such compound exist, even though it has never been obtained. This is not such area.

I'd bet we find caesium(>I) first.

alkaline metal anions do exist, but the cation must be protected by ligands like EDTA


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Preference in choosing SODIUM or POTASSIum hydroxide in nucleophilic substitution of haloalkanes
When you substitute a halogenated alkane to form alcohol, why is it with reagents like NaOH or KOH? I understand the need for the OH hydroxide bit, but I am not sure why you need the Na cation or K cation. Can't you use some other cation? It seems to me that use of these cations will react with the halogen atom to produce a soluble ionic product. Is this a desirable outcome? And why?

What other source of OH- would you propose using? If you want OH- acting as nucleophile you need a cation

$\ce{OH-}$ ions do not exist alone. They must be accompanied by a cation, like $\ce{Na+}$ or $\ce{K+}$. But of course, another cation can be used, like $\ce{Ba^{2+}}$ or $\ce{Ca^{2+}}$, provided its hydroxide is sufficiently soluble in water.

Perhaps the question should be rephrased Does Na+ or K+ make a difference as the title suggests.  Yes the cation can make a profound difference depending on the reaction.

OH- doesn't exist on its own. I like to think of the Na+ and K+ as “carriers.” But like @jimchmst said, the way a reaction proceeds can depend on the action.

Any reason for writing element names in all capitals?


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Properties of Gibbs free energy
I have been asked to find the correct statement/(s) from the below:
$1.$ In any closed system with P, V work only, $G$ is always minimized at equilibrium.
$2.\ ΔG$ is always zero for a reversible process in a closed system.
$3. \ ΔG°$ for an ideal gas is a function of pressure.
$4.$ For an irreversible, isothermal expansion process in a closed system with PV-work only, $ΔG$ must be negative.
The answer: only statment $4$ is correct.
I tried to use Gibbs-Helmholtz equation for $3.$
$$H = -T^2 \left( \frac{\partial (G/T)}{\partial T} \right)$$
and that for a process at equilibrium
$$ΔG° = -RT\ln(K_{\text{eq}})$$
I am still unable to conclude. How to comment about all the statements?

If this is the only question you get wrong on a test you are fine. I don't know what an isothermal expansion doing P-V work irreversibly is. G is a state function most useful for reactions that reach equilibrium and therefore are reversible. The Second Law removes the deficiency in the First Law that reactions do not go to completion but to equilibrium, the free energy functions.

The standard change is for a pressure of 1 bar.

For 1/ and 2/, consider when the Helmholtz energy is used instead of Gibbs energy. For 3/ Consider equation for dependence of Delta G on pressure. What is the constant term at the given temperature?


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Catalytic hydrogenation of Benzene
Why is Benzene not hydrogenated when a side group is catalytically hydrogenated? Some books say that the Benzene ring is also hydrogenated, others say the opposite.

It depends on the conditions - catalyst used, hydrogen pressure etc. The aromatic system makes the double bonds particularly resistant to reduction, but it can be done with the correct choice of conditions  see https://www.chemengonline.com/cyclohexane-production-benzene-hydrogen/


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Acidity of Benzoic acid
Please help me understand the electronic effects used to explain the acidity of benzoic acid. I was taught that there are two major effects namely: a) -I (negative inductive effect) b) +M (positive mesomeric effect). So my doubt is:

COOH shows -I AND -M effect so, here are we talking with respect to -COOH or the phenyl group. Please explain why and also how to identify with respect to which group i'm supposed to look for other molecules as well.

-I is shown by both COOH and Phenyl group. Now,for the above question if the -I effect (as my instructed by my teacher) shown by the molecule is w.r.t phenyl then how can we explain it w.r.t the inductive effect order i.e. -I shown by COOH is greater than that shown by phenyl so then the inductive effect of -COOH group should dominate and it will be like the phenyl group is donating or showing +I effect.

This should help: https://chemistry.stackexchange.com/questions/9334/understanding-mesomeric-effect/9342#9342

Maybe you can choose a more descriptive title? Acidity of benzoic acid is only an indirect consequence of what you discuss in the question.

Thank you!Will try!

You'll find a table here: https://en.wikipedia.org/wiki/Electrophilic_aromatic_directing_groups

There will be a mutual effect but here you are interested in the effect that the substituent on the aromatic ring has on substitution reactions (or other reactions) on the ring, so it is the M,I effect of the substituent on the ring that is of interest. Of course the substituent can be another ring.


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Different definitions for work in physics and thermodynamics
In physics, work is defined as the force applied on an object multiplied by the distance traveled by that object. However, in thermodynamics, work is defined as a function of the opposing force. For example, if a gas expands inside a cylinder with a piston, work is defined as the opposing force (exerted as atmospheric pressure for example) times the displacement of the piston. Why is it not defined as a function of the pressure exerted by the gas? The gas exerts pressure on the piston and the piston moves. As defined in physics, the work would be defined as a function of the gas pressure. Is this some kind of misconception?

Is the force exerted by the gas on the piston equal in magnitude to the force exerted by the piston on the gas?

Note thermodynamics is also a sub-discipline of physics, so physics is internally inconsistent according to this question.


text:
Make the plastic cat flap clear again?
I used something on the clear plastic cat flap to clean something sticky and lasting off and the clear plastic is now cloudy.  Is there anything I can use on the clear plastic to restore it?

Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.


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Variable in Thermodynamics
While studying Physical Chemistry, I came up with this question.
As I derive equation C_p-C_v, I found the equation (dQ/dT)p = T(dS/dT)p (d-> round)
As I know, dQ=TdS so dQ/dT=(Tds/dT). and I'm still curious that why (Tds/dT)= dS+T(dS/dT).
Can we consider T as a constant value although the differentiating variable is T?
Thank you!

Welcome to ChemSE! Please find guidance for MathJaX / $\LaTeX$ as follows and reformat your post - Basics // MathJaX and mhchem formatting for equations and chemical formulae // Guidelines on which should be upright / italics

Also you can refer How to use MathJaX.


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Behavior of polyanionic silicate chains in silico
I am trying to understand the stability of charged linear molecules, more specifically these, which contain periodically repeated high electron affinity parts, such as single-bonded oxygen (radicals). The example given in the title is chosen because it is clearly very common in solid state (natural minerals) and hopefully well studied by chemists.
As pointed out in the comments, long chain anions almost never form in vacuum, far away from cations. To be clear, the theoretical situation is similar to a silicate chain in the beginning of the simulation of the process of decaying/discharging/changing shape of the molecule.
What happens to a silicate chain without cations, in vacuum?
I guess, first it repels some of its extra electrons, but I can't imagine the changes in its shape nor the quantity of remaining charge per unit length.
Is it correct that atoms stay in the chain so that it is still $\ce{SiO3}$ (stoichiometrically)?

Separated from cations in vacuum? What makes you think anything like that happens... looks like another XY problem.

Why do you think anionic species would float in vacuum?

@Mithoron The tag "theoretical-chemistry" tells us, anything like that is actually too improbable to ever happen, that's why I can't just do the experiment and find my answer. However, it is still physically plausible: say, a long sequence of lucky collisions with high energy particles. That is not chemistry, but the resulting ion's stability and structure certainly is.

@NilayGhosh To help avoid interactions with irrelevant species. I am talking about theoretical situation.


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Is ammonium a coordination compound?
According to IUPAC Gold Book, the definition of "complex" is preferably called "coordination entity" which is stated that:

An assembly consisting of a central atom (usually metallic) to which is attached a surrounding array of other groups of atoms (ligands).

So, it is not forbidden for a non-metal to be called "coordination entity" which in fact, lots of them exhibit this term like [PCl6]-, [SiF6]2-,... The problem that I have is that of ammonium cation, it is an adduct.
So, is ammonium a coordination compound?

Nobody calls it as such - that's the important thing.

You mean nobody calls ammonium a coordination compound?

There is a key point to coordination compound. Here the metal atom accepts electrons from ligands (neutral species like H2O, NH3), forming coordination bond, hence the name. The whole species can be charged and that can be considered a complex ion, for e.g. $\ce{[Co(NH3)6]^3+}$. Ammonium ion on the other hand is two atoms covalently bonded and the species is charged, hence it is a polyatomic ion.

I want to be a little specific:
a) There is a coordination bond in NH4+ which is H3N-->H. Is it compulsory for a coordination compound to be fully coordination bond and no covalent bond involved?
b) According to coordination complex of wikipedia: https://en.wikipedia.org/wiki/Coordination_complex. I could say [PCl6]- a coordination compound. Is it wrong?

There's no "coordination bond", it's dative, or coordinate, bond. This is an arbitrary distinction, as all bonds in ammonium are exactly the same and dative bonds are no different from "non-dative" ones.


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Lone pairs are more spread out, but how does this increase repulsion?
Both lone pairs and bonding pairs consist of 2 electrons.
From my understanding, bonding pairs are localised between two atoms and thus lie further from the nucleus, and have a longer sausage shape. Lone pairs are attracted to a single nucleus, and thus can spread out more, creating a rounder shape.
Now repulsion, is really determined by couloumbs law. Both lone pairs and bonding pairs have the same charge, so it must come down to distance. Does being more spread out mean, that at a particular instance, the distance is less, thus the repulsion larger? After all the shapes of bond, only create a probablistic area where electrons may be found at an instance.
My question then comes down to, how can we use the fact that the electrons are more spread out and closer to the nucleus in a bonding pair to explain why the repulsion is greater? Just because the former is true, I struggle to immediately conclude that the repulsion is larger. So can we use the former and coloumbs law to clarify this. Repulsion must be determined by coloumbs law right?

You struggle right and it isn't easy. It is a postrationalisation of vsepr shoehorned into valence bond theory. There are attempts to use the Pauli Principle for this, but that is really hard to explain. And I'm not sure it is the truth either.

https://chemistry.stackexchange.com/questions/32211/why-are-lp-lp-repulsions-greater-than-bp-lp-and-bp-bp https://chemistry.stackexchange.com/questions/157867/quantifying-location-and-volume-of-lone-pairs-for-vsepr

"Repulsion must be determined by coloumbs law right?" Not really, it's more likely related to Pauli exclusion, mentioned earlier.

Bonds are of Lower energy that implies that the electrons are Closer to the 2 nuclei than the nonbonded electrons were to their individual nuclei. Take your thoughts one at a time and think them thru. There is so much volume about an atom or in a molecule if the bonds take up less space the nonbonded are free to take up more space and of course the inner electrons are repelling everyone. Things happen the charge explains it but use some common sense. The diffuse unshared pair pushes the bonds or the more compact bonds make space for the unshared pairs or both acting in concert.

I don't believe it is clear what repulsion you're talking about. The two electrons repelling each other? The net repulsion?

You make contradictory statements: "how can we use the fact that the electrons are more spread out and closer to the nucleus in a bonding pair to explain why the repulsion is greater?" and "bonding pairs are localised between two atoms and thus lie further from the nucleus, and have a longer sausage shape"

"Does being more spread out mean, that at a particular instance, the distance is less, thus the repulsion larger" This is very confusing. Less spread out would bring the electrons more close together and thus they would repel more.

Please check your statements, as it stands this risks being closed as unclear.


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Hyperconjugation in o-Cresolate and p-Cresolate anions
I have read that hyperconjugation as an effect works only with an empty orbital available to share sigma-electrons with. Based on that, the 'destabilizing' effect of hyperconjugation on alkoxides is not taken into account when judging their relative basic strengths.
$\ce{MeO- > EtO- > iPrO- > tBuO-}$
based on only inductive effects.
In judging the stability of cresolates, the 'destabilizing' effect of hyperconjugation is taken into account for the ortho and para positions.
My question is why is hyperconjugation being taken into account even when there is no vacant orbital to overlap the electrons with in the first place?


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Does $\ce{O-CH_}3$ substituted on the meta position relative to a group on the benzene ring have a donating or withdrawing effect?
I have been confused about the behaviour of the group $\ce{O-CH_3}$ in the following two conditions:

The acidic strengths of methoxy substituted phenols: Here, according the order of acidic strengths

$$(meta>ortho>no\ substitution>para)$$
We are able to explain the highest acidic strength of meta with the fact that at meta position, the methoxy group acts as a $-I$ group.

This question in a reputable exam:

The answer given is
Here, the ethoxy group act as a donating group, activating the ring, and due to this the carbocation formed is a benzylic one, leading to the substitution of Bromine atom at the benzylic position.
I assumed that methoxy and ethoxy have almost the same behaviour.
Would this be any different if the substituent was methoxy and not ethoxy?
If not, then how can we differentiate the times when methoxy group at meta acts as donating and when it acts as withdrawing?

I assume that I have made some kind of mistake and so the downvote. Can you please clarify what way I have expressed the question incorrectly?


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Why SO2 doesn't have dative bonds?
Why doesn't the SO2 Lewis structure have, instead of two double bonds, one double bond and one dative bond? This way, the octet rule is also satisfied for sulfur.

See https://en.wikipedia.org/wiki/Sulfur_dioxide#Structure_and_bonding

It does$ $.


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Carbonyl and thiocarbonyl 13C NMR
According to this paper, the deshielding effect of C=S group is specifically due to the delta(11), which is the least shielded component. However, the conclusion tells me that this component is governed by two transitions: σ → π(antibonding) and π → σ(antibonding) transition.
The thing confuses me is that, as the excited energy magnitude is smaller, the paramagnetic shielding should be more negative, also means the nucleus is more deshielded. When it comes to normal thought of C=O and C=S transtion, the n → π(antibonding) is lower in energy than σ → π(antibonding) and π → σ(antibonding). So why carbon on C=S has greater chemical shift than that of C=O?