texts: Le Chatelier's principle: Are there any exceptions?

texts:
The way Le Chatelier's principle is presented in most introductory chemistry books (high-school) is as though it's an indisputable law of the physical world (in the sense that we're never shown an exception, not that its universality is explicitly stated).

This is supposed to differ from the more frequently encountered  half-assed  "laws" like Ohm's Law or Hooke's Law (which are really just generalizations drawn from a few, everyday cases... not real "laws" as such).

Now I'm curious. Is there really no exception to Le Chatelier's principle (for a closed, isolated system)?

Wording this differently: Is there any situation (closed, isolated system) where conditions conducive to Le Chatelier's principle are in place, yet the expected Le Chatelier's "response" (the tendency to oppose change) is not observed upon effecting the said change (in parameters such as concentration, temperature, volume, etc.)?

If there are any exceptions that one comes across in everyday life, I'd prefer to hear those (but since that's extremely unlikely, I suppose just about any exception will do).

Are there any theoretical grounds for exceptions to Le Chatelier's principle?

If Le Chatelier's principle cannot be violated, then why is it so?

What sparked this question, is the following statement from a (school-issued) book of mine:

  The dissolution of NaOH in water is exothermic. According to Le Chatelier's principle decreasing the temperature of the solution should favor solubility, however, in reality solubility of NaOH increases with temperature. This is therefore an exception.

However, if it weren't for the sharp users of Chemistry.SE I would've accepted my book's claims (since it corroborates seemingly well with common experience). O:)

I did find this article on the ACS page, but it's paywalled >_<


texts: Confusion regarding DFT basics, i.e. the connection between Hohenberg–Kohn theorems, external potentials and the Kohn-Sham method

texts:
I have a question on the basics of DFT, which bases on the Hohenberg-Kohn theorem: there exist an unique mapping between the external potential, the electronic wave function and thus also the electronic density n(r). In other words, from wikipedia, where ${\displaystyle v(\mathbf {r} )}$ is defined as an external potential,
"If two systems of electrons, one trapped in a potential ${\displaystyle v_{1}(\mathbf {r} )}$ and the other in ${\displaystyle v_{2}(\mathbf {r} )}$, have the same ground-state density ${\displaystyle n(\mathbf {r} )}$, then ${\displaystyle v_{1}(\mathbf {r} )-v_{2}(\mathbf {r} )}$ is necessarily a constant."
My confusion comes from the Kohn-Sham equations, i.e.
${\displaystyle v_{\text{eff}}(\mathbf {r} )=v_{\text{ext}}(\mathbf {r} )+e^{2}\int {\frac {\rho (\mathbf {r} ')}{|\mathbf {r} -\mathbf {r} '|}}\,d\mathbf {r} '+{\frac {\delta E_{\text{xc}}[\rho ]}{\delta \rho (\mathbf {r} )}},}$
${\displaystyle \left(-{\frac {\hbar ^{2}}{2m}}\nabla ^{2}+v_{\text{eff}}(\mathbf {r} )\right)\varphi _{i}(\mathbf {r} )=\varepsilon _{i}\varphi _{i}(\mathbf {r} ).}$
which was derived by decomposing the energy functional of the interacting-electron system into solvable energy functionals of a non-interacting electron system affected by an alternative external potential ${\displaystyle v_\mathrm{eff}(\mathbf {r} )}$, plus an exchange-correlation functional that attempts to account for the difference between the two systems. The optimal orbitals are obtained through this iterative scheme.
My question is, since the HK theorem states the unique mapping between between an external potential and the electron density / wavefunction, why would we obtain a common electronic state when ${\displaystyle v_\mathrm{eff}(\mathbf {r} )}$ - ${\displaystyle v_\mathrm{ext}(\mathbf {r} )}$ is not necessarily a constant?
${\displaystyle v_\mathrm{eff}(\mathbf {r} )}$ in this case is the external potential experienced by a single non-interacting electron defined by the first Kohn-Sham equation, while ${\displaystyle v_\mathrm{ext}(\mathbf {r} )}$ is the external potential exerted by the stationary nuclei to the electrons, in the electron-interacting picture.

I guess more specifically, I assumed that the KS method meant that we can solve a simpler system of non-interacting electrons affected by a specific ${\displaystyle v_\mathrm{eff}(\mathbf {r} )}$ that would give the same electron density of the same system but with interacting electrons.
However, the "external potential" governed by the interacting and non-interacting systems are different, so how come they will yield the same ground state, when we minimize their respective energy expressions?


texts: Can cycloalkanes undergo electrophilic addition? If so, what is their mechanism?

texts: Cycloalkanes have the same general formula as alkenes. Doesn't this mean that cycloalkanes can be saturated by turning into alkanes the same way alkenes use? If so, what is the reaction mechanism? In the reaction mechanism of the electrophilic addition of alkenes, a pair of electrons are taken from a C-C double bond and donated to one atom of the attacking binary compound. In the reaction mechanism of the electrophilic addition of cycloalkanes will one entire single bond be broken and the pair of electrons in it donated to one atom of the attacking binary compound? This way it is possible to produce an alkane from a cycloalkane undergoing electrophilic addition, but in terms of energy requirements, I find it a bit unlikely. I think it would be useful if someone could help me clarify this.


texts: Solubility and Evaporation - Would the concentration still be 1 ppm?

texts:
A certain salt has a solubility of 1 mg/1 L.
I have 1 mg of this certain salt dissolving in 1 L of water, I have a concentration of 1 ppm.

1st Question:
If the solution is left open to evaporation, 0.5 L of water (50 %) evaporated, would I still be getting concentration of 1 ppm while 0.5 mg of this salt became solid again and left at the bottom of the solution?

2nd Question: (if it's a yes to the 1st question)
If I then fill the container back to 1 L mark with water, would the concentration be 1 ppm again after the salts are completely dissolved?


texts: Are bones generally harder to corrode than human skin?

texts:
I am making a fantasy universe and really I am also curious to know if bones generally are harder to corrode than human skin in our world and at what rate?

I was thinking to compare how a skeleton would react to corrosion compared to a regular human. Maybe some chemists had any insight to this. I see many fantasy universes incorporate "acid" as an element but neglect bases and corrosions as a whole.

Bonus question, is it possible to find a list on how different metals react to strong acids and bases. I have heard of the Reactivity series, but not much beyond that, or perhaps I just don't understand how to use it.


texts: Why is oxygen absorbed in a colorless alkaline solution of pyrogallol and why does it turn dark brown?

texts:
My book says:

  Oxygen is absorbed in colorless alkaline solution of pyrogallol and turns dark brown?

I'd like to know why and how.


texts:
The problem:

  Chloroform, $\ce{CHCl3}$, is formed from methane and chlorine in the
  following reaction:

  $$\ce{CH4(g) + 3Cl2(g) ->3HCl(g) + CHCl3(g)}$$

  Calculate $\Delta rH^{\circ}$, the enthalpy of formation for this
  reaction, using the enthalpies of formation of $\ce{CO2(g)}$
  (-393.509kJ/mol-rxn), $\ce{H2O(l)}$ (-285.83kJ/mol-rxn) and
  $\ce{CHCl3(g)}$ (-103.1kJ/mol-rxn) and the enthalpy changes for the
  following reactions:

  $$\ce{(1) \ \ CH4(g) + 2O2(g) -> 2H2O(l) + CO2(g) \ \ \ \ \Delta
 rH^{\circ}=-890.4kJ/mol-rxn \\ (2) \ \ 2HCl(g) -> H2(g) + Cl2(g) \ \ \ \ \Delta
 rH^{\circ}=+184.6kJ/mol-rxn }$$

My attempt at the problem:

Given the hint in the problem statement and by looking at the two given reaction equations i assumed that i needed to create another equation. I created an equation for $\ce{CHCl3(g)}$ from $\ce{CO2(g)}$ and $\ce{H2O(l)}$ and calculated it's $\Delta rH^{\circ}$ from the enthalpies of formation as shown below (Let's call this equation 3):

$$\ce{2CO2(g) + 5H2(g) + 3Cl2(g) -> 2CHCl3(g) + 4H2O(l)}$$

$\Delta rH^{\circ} = -562.502kJ/mol$

Here's where i run into difficulties: I can see that in the 'target reaction' we have HCl on the right and CHCl3 on the right, so it stands to reason that equation 3 will stand as it is presented but equation 2 will switch direction (and the sign of the enthalpy of reaction swop too). I don't want to switch the direction of equation 1 around because it has CH4 on the left and in the target reaction CH4 is on the left. We could multiply equation 1 by 2 and equation 2 by 3 in order to have equal amounts of chlorines and Co2's so we can cancel them, however we are now left with hydrogens on the left and H2O's on the right with no way to cancel them. Hydrogen and water obviously don't appear in the target reaction so i have gone wrong somewhere along the line.

Am i missing a reaction equation? Is there something i can do to cancel the unwanted reactants in the reaction equations? Any help would be greatly appreciated.


texts: Regarding acid-base reactions, how does one know when a hydrophobic base substance is fully protonated?

texts:
When there's a weak base substance (hydrophobic powder), and it needs to be completely protonated by adding an acid (eg: HCl), how does one know when it's completely protonated? Since the powdered base substance isn't soluble until protonated, doesn't that mean that it won't be reflected when measuring the pH (via the commonly used pH test strips)?

I'm under the impression that when the base is suspended in water, as HCl is added and given time to react, the pH would float round 7 or 8. Then when it's fully protonated, the pH will start to dip below 7, which would mean there's now an excess of HCl since there's nothing for it to bind with, which would be too much.

I don't exactly have a specific substance base substance in mind. This is more a general question about acid-base reactions involving a solid base.

Thank you


texts: Why does the graph of compressibility factor(z) vs pressure increase after reaching the minimum?

texts: I understand why it decreases for most of the gases but i cannot understand why it increases after reaching a certain minimum.


texts: What is the displayed formula for methylpropene?

texts: I am currently studying organic chemistry at school and I came across a question in my textbook which asked me to find the full displayed formula of methylpropene. I knew that there would be three carbons because of the 'prop' and that there would be a one-carbon side chain on the first carbon. However, in my chemistry textbook the one-carbon side chain is on the second carbon (the middle one). I don't know whether this is correct or not. Could someone please explain to me what the correct answer is?


texts:
Three of the bond energies of $\ce{O2,\ O2^{-},\ O2^{2-},\ O2^+}$ have the values approximately $200, 490$ and $625\ \mathrm{kJ\ mol^{-1}}$. The value for one of the species is uncertain and, therefore, not given. Write the bond energies of each compound.

My Attempt

I know that higher the bond order of a compound, higher its bond energy. So the bond order of $\ce{O2,\ O2^{-},\ O2^{2-},\ O2^+}$ are $2,\ 1.5,\ 1,\ 2.5$  respectively.

However I am not sure which one's bond energy is not known. I am thinking that it might be $\ce{O2^{+}}$ since it is unstable, however it is just a total guess.

Is there some way to logically deduce which one it is, or is this one of these things that we are just suppose to know?


texts: Does Wurtz reaction follow an ionic mechanism or a free radical mechanism?

texts:
In a Wurtz reaction, is the intermediate formed a carbanion or a free radical?
And if we can assume both mechanisms to be true, how can we decide the reactivity of a tertiary halide?


texts: Why is kerosene destroying just my red LEDs?

texts:
Due to the nature of the problem, I've decided to post this on chemistry.stackexchange and not electronics.stackexchange, since I believe that the problem is chemical in nature.

Long story short - we have an electronic product that is submerged in fuels (kerosene being one of them) and uses an RGB LED (click here for datasheet). Due to a sealing problem in the enclosure, fuel has managed to get in and cover the PCBs. What's interesting is the effect that has had on the PCB. The PCBs functionality has been completely unaffected, apart from the fact that the red LED in the RGB LED module has completely stopped working. We've replicated this ourselves manually by submerging 2 new PCBs in kerosene for a day and then taking them out and powering them up and seeing that the red LED stops working entirely. The green and blue LEDs continue to work just fine.

Examination of the failed boards shows that there are no other electrical faults. It is just the red LED that completely stops illuminating.

Looking at the last page on the datasheet, the LED material is listed as AlGaInP / GaAs. Is there any obvious reaction between kerosene and these materials that would explain why just the red LED stops working?

Update After leaving the PCBs to dry, the red LED starts working again! So the problem is not permanent.


texts: How can I determine the size of tropolone molecule?

texts:
How can I determine the size of a tropolone molecule?
It's a seven-membered aromatic ring with =O on the first carbon and -OH on the second carbon.
Is there any software available?


texts: Enthalpy of dissolution of NaOH in small amount of water

texts:
is there a way to calculate enthalpy of dissolution of NaOH in small amount of water?
I know that enthalpy of dissolution of sodium hydroxide in water is –44,5 kJ/mol. However it assumes the orders of magnitude higher amount of water than NaOH. (Which is not my case.) Is there any formula which does not omit the volume of solvent? (Or a tool which can answer questions such as: "How much heat is released if you make 60% solution of 80% solution?")
Thanks for help.


texts: Body centered cubic lattice vs Primitive cubic unit cell

texts:
I was reading about Bravias lattices(cubic crystal system) when got confused about an article in my book.

Please refer to Counting body center as lattice point when basis consists of 2 atoms.

The answer there makes me think about these two cases:-

In figure 1, the crystal is produced by conbining the body centered lattice frame with a single atom motif.

In figure 2, the crystal lattice is produced by combining a primitive cubic lattice frame with a motif made of 2 atoms.

Both things lead to that same result so would we calk the final crystal formed a a body centered cubic lattice or a primitive cubic lattice?

P.S : The book I am using(a private institution book, tution book to be precise) has unclear definitions creating a lot of problem so pardon me if you had found me saying weird things.


texts:
For reaction $\ce{2A→B}$ (elementary step), according to the rate law, rate $= k [A]^2$.

In some calculations, we use $k[A]^2$ as the production rate of B. Why isn't it ${1 \over 2} k[A]^2$?

In this case, is the consumption rate of A also $k[A]^2$? If so, why are they the same when in fact two molecules of A produce one molecule of B?

I'm really confused about this part. Can anyone explain why coefficient doesn't play a role in this calculation? Thanks!


texts: Palladium hydride forming water and heat at room temperature

texts:
I just read that saturated palladium hydride, $\ce{PdH}$0.7, when exposed to oxygen will generate heat and water on it's surface, $\ce{4 H}$(Pd) $\ce{+O2}$(g) $\ce{\to 2 H2O}$(g, l).
What is going on?


texts: In chair form of cyclohexane the C-H dipole moments cancel out each other but in boat form i don't think all dipole moments will be cancelled out. Also if boat form is polar then what will we say overall about cyclohexane is it polar or nonpolar?


texts: Which organic compound's NMR and IR are these? Can't find out. (Data available: Melting Point ~ 116 °C)

texts: Which organic compound's NMR and IR are these? I have figured out that the compound is a 1,4 substituted benzene. And the substituents are probably not -COOH and -OH from the spectroscopy. Kindly help me in figuring the other groups out. (Data available: Melting Point ~ 116 °C, gives sooty flame)


texts: Acid catalysed dehydration of alcohol with a bicyclo group

texts:
Pathway 1: Rate determining step is the formation of carbocation. In this pathway, a conjugated tertiary carbocation is generated as an intermediate.

Pathway 2: One of the resonance form of intermediate carbocation proceeds to produce a more stable  product (due to benzene ring) through alkyl migration. Though, the resonating form of carbocation is conjugated secondary carbocation which is less stable than the carbocation formed through pathway 1.

My questions are:
1- Is tert-butyl (don't know the correct term) migration possible in pathway- 2?
2- What are the major and minor products? Which factor will decide the major product: stability of final compound or the most stable intermediate?


texts: What favors the active transport in a membrane?

texts:
I was reading about active transport in membranes where ATP is used. ATP "reacts" with the protein pump and converts into ADP and also make a conformational change to the pump. Now this conformational change can transport molecules from low concentrations to high concentrations areas i.e. opposite in their concentration gradient. My problem is that for this to happen we must couple the hydrolysis of ATP with the "reaction" of transport along the membrane.
But I can't find it in textbooks and also I can't imagine if such coupling makes sense. In many textbooks it is stated that the energy that released due to the hydrolysis fo ATP is used to drive the pumping. I don't know if it is possible to couple two reactions with no common intermediates. Also in the pictures that show the active transport like the one in the left side the molecules can't go through the lipids.

So the molecules just move from low to high but the moving from high to low (diffusion) is blocked because the molecules can't move through the lipids. In other words it isn't like molecules make something that it would be otherwise violated because at first the motion from one side to the other is blocked. I mean even if we have no ATP the molecules won't flow from high to low concentration. Then what is the point of "active" transport? For a moment I thought to describe the above scheme for active transport as the following reaction: $$\ce{ATP + H2O + M_{in}} \rightleftharpoons \ce{ADP + P_i + M_{out}} $$
Which can be thought as the sum of:
$$\ce{ATP + H2O } \rightleftharpoons \ce{ADP + P_i}$$
and
$$\ce{M_{in}} \rightleftharpoons \ce{M_{out}}$$
But as I stated I haven't find a coupling reaction with no common intermediates and also it doesn't make sense to write the second equilibrium as the molecules can't go through the lipids. Also from the second reaction we should expect the concentrations on both sides to be equal (because the equilibrium constant must be equal to unity) no matter the concentration of ATP.
So can the first equilibrium alone describe the "active" transport? I mean if this reaction is exergonic then indeed by varying the amount of ATP we can alter the concentration of M outside of the membrane due to the Le Chatelier principle.


texts: Understand Hexabromocyclododecane CAS numbers

texts:
Hexabromocyclododecane has 16 possible stereo-isomers. So far so good.
I found that:

134237-50-6 is the CAS of alpha-Hexabromocyclododecan

134237-51-7 is the CAS of beta-Hexabromocyclododecan

134237-52-8 is the CAS of gamma-Hexabromocyclododecan

3194-55-6 is the CAS of a mixture of different Hexabromocyclododecan

Now, I have two more CAS which are a bit opaque to me:

678970-15-5

Pubchem says it's the same as 134237-50-6
However, ChemIDplus says it's alpha-Hexabromocyclododecane, (-)-

138257-18-8

Pubchem says it's the same as 134237-51-7
However, ChemIDplus says it's beta-Hexabromocyclododecane, (-)-

Question: Describe each of the CAS different chemicals or are 678970-15-5 and 138257-18-8 just synonyms. If they are different chemicals, what does (-)- mean here?


texts: Why are Kc and Kp interchangeable in the free energy-equilibrium equation?

texts:
In this equation that relates Standard free energy and the equilibrium constant:

$\Delta Gº=-RT \ln K_{eq}$

My textbook (and my teacher) say both $K_p$ (constant related to pressure) and $K_c$ (constant related to concentration) can be used in the place of $K_{eq}$.

When using the equation that relates $K_p$ with $K_c$

$K_p=K_c(RT)^{\Delta n}$

We would get two different $\Delta Gº$ values, which shouldn't be possible.

My question is, why can we use both constants if their values are different?


texts: Why is 5,6-dimethylidenecyclohexa-1,3-diene non-aromatic?

texts:
The compound 5,6-dimethylidenecyclohexa-1,3-diene is supposedly non-aromatic:

But I have no idea why this is so. The compound is probably planar. All the atoms on the ring are $\ce{sp^2}$ hybridized. So, the p-orbitals are in conjugation. There are 4-$\ce{\pi}$ electrons, as I suppose the external pi bonds do not participate in resonance. So, it should be antiaromatic. Why is it non-aromatic?

I am a school student, so an detailed description would be helpful.


texts: Dextro or laevo-rotatory compound conversion

texts:
Will applying an external electric field to a racemic mixture will convert the optically active compound(mixture of both Dextro and laevo-rotatory) into a particular dextro or laevo-rotatory compound?
I thought that if I apply an external field, then all the chiral molecules will arrange in a particular direction i.e their spatial arrangement in the solution aligns in a specific direction, resulting in a particular dextro or laevo-rotatory compound.
Is my thinking right or I am misunderstanding the topic?


texts: What's the reason for discrepancy between DFT calculated image and NC-AFM-acquired one in this article?

texts:
Looking at the images in this article, I've noticed that the molecule electron density images showed as calculated via DFT look very symmetric, while those obtained by NC-AFM appear somewhat distorted. Namely, the ring at the left (the one with $\ce{OH}$ group) looks elongated, while the one at right is, on the contrary, compressed in horizontal direction, and the $\ce{OH}$ group seems to be tilted to the $\ce N$ atom. Also, the calculated image seems much more smeared, while the measured one gives some highly localized density "rods" for the bonds.

I've made a gif-combination of these two images so that the difference was easier to see:

Here the B is DFT-calculated version, while F is one measured by NC-AFM.

I can suppose one or several of the following might be among the reasons for this:

The substrate of $\ce{Cu(111)}$ wasn't taken into account when calculating(?), while in the measurement it appears to distort the molecule
DFT, being an approximate method, gives too simplified results
Smear vs thin rods difference might because in the DFT case the picture is of electron density while in AFM case the image shows AFM frequency shifts, which is not necessarily the same.
The probe of the microscope distorts the molecule

What are the true reasons for the differences?


texts: Calculating the potential of an electrochemical cell (Nernst equation)

texts:
This is the problem:

Calculate the ${E_\mathrm{cell}}$ (not ${E°}$) at 25°C.
I found that the reaction is $$\ce{Cu(s) + Fe^2+(aq) -> Cu^2+(aq) + Fe(s)}$$ $\ce{Cu}$ gets oxidized and $\ce{Fe^2+}$ gets reduced.
I added the ${E°_\mathrm {Cu^{2+}/Cu}}$ and ${E°_\mathrm{Fe^{2+}/Fe}}$ to get ${E°_\mathrm{cell} = -.101}$ . But I'm not even sure if I'm supposed to add them or subtract them because I've seen both done, which is really confusing me. In what situations do you add, and which situations do you subtract half reaction potential values?
I then plugged this calculated value into the Nernst equation.
I said Z = 2 and plugged in the correct constants. However, I am not sure if I calculated Q correctly. I did [anode]/[cathode], but is it supposed to be [products]/[reactants]? It is unclear to me because my instructor did the latter, but I keep seeing the former everywhere else because that is how you would calculate it in an equilibrium problem. I know it doesn't make a difference in this specific problem, but I want to know for future problems when concentration of all components are given (such as if they are all aqueous).
From these steps, I calculated that ${E_\mathrm{cell} = -.164 V}$
How to approach this question?


texts: Why is standard reduction potential an intensive property?

texts:
My book says that

  Since the number of electrons lost must equal the number gained, the half-reactions must be multiplied by integers as necessary to achieve the balanced equation. However, the value of e° is not changed when a half-reaction is multiplied by an integer. Since a standard reduction potential is an intensive property (it does not depend on how many times the reaction occurs), the potential is not multiplied by the integer required to balance the cell reaction.

However, I do not understand why the reduction potential is unaffected by the number of mols. If you have a greater number of mols of the metal, doesn't that allow for a greater potential difference?


texts: What is the effect of the temperature on the no of moles in an equilibrium system?

texts:
Here's something that makes me confuse. What will happen to the total no of moles in a system if the temp is raised. Will it increase? If so how is that possible.?
Say we have an equlibrium,
$$\ce{2P <=> Q + R}$$
The temp is $300\:\mathrm{K}$ and total no of moles is 6 moles.
If we increase the temp upto $500\:\mathrm{K}$ will the total no of moles change to 10 moles when the volume and pressure kept constant?


texts: How to assign the signals in the H-NMR of Aspirin?

texts:
I need to assign the H-NMR of aspirin, below is aspirin with the H's labelled.

The peaks I have are:

2.30ppm   (I this is a singlet and would be F)
7.07ppm   (I think this is E)
7.29ppm   (I think this is D)
7.53ppm   (I think this is C)
8.05ppm   (I think this is B)
11.44ppm (this is a singlet and would be A)

For B,C,D,E I need to say what kind of splitting pattern there would be and how many coupling constants are present and there approximate value. I think I know the assignments of them but I don't know the splitting pattern or coupling constants.

Would E and B be doublet of doublets because they couple with D and C so they would have ortho and meta coupling?

Would D and C be coupling with each other and B and E so would they be doublet of doublets of doublets, with two ortho and one meta coupling?


texts: Questions About an Appropriate Textbook on Electrochemistry for Self-Study

texts:
Apologies if this is a somewhat frequent request (I promise I did scour various sources before posting, but none quite applied to me), but I was hoping for some insight from the community regarding an electrochemistry textbook that I could self-study.
To give some background, I am an electrical engineering student with a minor in physics (and I have in the past taken courses in organic and physical chemistry, although that was some time ago so I forget much, if not all of that) who is interested in learning more about batteries. I am ultimately interested in their operation as storage for large-scale renewables, but I would love a deep understanding of the electrochemistry involved beforehand. I've never been happy with the hand-wavy explanations that I've seen in the past, so I wanted something fairly rigorous.
My thought was to read McQuarrie's Physical Chemistry: A Molecular Approach first (this would be a good accompaniment to my actual courses in quantum and statistical mechanics at any rate, presumably with more of a high-level focus on the chemistry which would be an interesting angle). If this is a bad idea, please let me know!
Where I am more lost is in the next step, in picking up a book that looks virtually only at electrochemistry. I've come across three books which are listed below, but I am not sure about which would be appropriate or if anyone has some insight as to why I should pick one over another.

Electrochemical Systems by Newman
The venerable Electrochemical Methods: Fundamentals and Applications by Bard and Faulkner (I'll probably get this at some point no matter what, but I'm interested in what would be a best touch with electrochemistry after McQuarrie).
Physical Electrochemistry: Fundamentals, Techniques, and Applications by Eliaz and Gileadi.


texts: Why does benzaldehyde undergo Cannizzaro reaction?

texts: Benzaldehyde has an aromatic ring in it which has a pi cloud of electrons surrounding it. Would they not repel the nucleophile when it attacks?


texts:
We installed 20 2" drop in anchors to anchor several signs in place near the entrance of our pool. We have to remove the signs about twice a year and after the end of the past season, I noticed there is a small amount of rust forming. I purchased the 304 because it was not going to be in direct contact with the water and because it was solid, not coated, as opposed to the 314, which was only coated. It seems as though the 304 was also just coated so it is beginning to rust. I need to provide some sort of plan as to how to remove the 304 anchors and replace with 316.

Drop in anchors are not made to come out of concrete as the driving pin expands the bottom into place. I had thought about drilling them out but I am hoping to use that as a last resort because I don't want to damage our new concrete and need to keep the holes in tact. I read that Nitric acid can dissolve stainless steel. Will this work in my situation? Or will that also damage the concrete?


texts: Does radioactivity affect chemical reactions?

texts: Do compounds of radioactive elements show a different behaviour? What happens when the radioactive part of the given compound decays? e.g. Radium chloride; what happens to it when radium decays?


texts: Could this solution be resolved by titration?

texts:
I have a mixture of $\ce{NH_4NO_3}$ and $\ce{NH_3}$ at $\ce{pH}$ of about 13.

It is possible to determine the concentration of both on them by acid-base titration?

I was told it's possible, and that you need first titrate with $\ce{HCl}$ and then with $\ce{NaOH}$.

Thanks.

Edit: In the lab were I was working, there were an auto titrator, that had a program that could tell the concentracion of $\ce{NH_4NO_3}$ and $\ce{NH_3}$ in a solution, just by titrating it and controlling the $\ce{pH}$ with a pH meter. I simply don't understand how it does it, because depending of the $\ce{pH}$, $\ce{NH_4+}$ and $\ce{NH_3}$ would be in the same form and I don't know how you could tell them apart.


texts: For Hess' law type questions, when do you take the inverse of the constant and when do you switch the sign?

texts:
For example, when you're given the enthalpy $\Delta H$ of a  reaction and you want to switch that reaction around in order to add it to something else, you switch the sign. Furthermore, when adding two reactions, you add their $\Delta H$ values.

But when you're working with equilibium problems and you have the $K$ of a reaction, if you want to switch the reaction you take the inverse of $K$ and when you add reactions you multiply $K$ values.

When working with cell potentials $E_{cell}$ of a redox reaction, you switch the sign if you switch the equation around, but when you're adding two equations you do not multiply $E_{cell}$ by whatever you multiply the coeffecients on the species by.

Are there any types of patterns other than the three I've described here? Any help is greatly appreciated.


texts: Volume additivity between solute and solvent molecules

texts:
for a given mixture of NaOH solutes in water, I understand that the volume of NaOH and water do not add up. Is this due to the ionic bonds between Na+/OH- ions and water molecules, which causes the molecules to be more packed together, resulting in a smaller solution volume?
Thank you!


texts: Cell voltage required for refining copper

texts:
If you put Zinc or Iron solids into aqueous copper (II) sulphate solutions, copper solids form spontaneously due to the fact, that Zinc/Iron oxides into ions more willingly than Copper does.

And if you put Silver bars into the same solution, hoping to get copper solids forming on them,
(yes, electroplating copper on silver)
you'd need a theoretical minimum of $\rm 0.46\,V$, as that is the difference between the standard reduction potential of $\ce{Ag}$ and $\ce{Cu}$ ions.

Our question is this.
While purifying/electrorefining copper, how much voltage is required to make it happen?
If we simply think in standard potential dimensions, we wouldn't need to do anything. And yet, common sense tells me that surely wouldn't be right.

So, how much, and why?


texts: I am looking to completely dissolve negative film strips. Acetone was my first try and did not work. If anyone knows/ or has any ideas i would be so greatful.


texts: dependence of Intensity on penetration of light

texts: I want to know about a transparent material,In which penetration of light decreases as intensity of light increases.


texts: How to prepare a water sample for photometry

texts:
The purpose of measuring N P K Ca Mg S is to determine the amount of material consumed by different types of plants in different periods.
The initial solution, which is prepared as a nutritious solution, includes highly accurate and measured doses of substances such as Potassium Nitrate, Magnesium Sulphate, Calcium Nitrate, Potassium Monophosphate, Ammonium Nitrate, and other materials that supply the micro-nutrients required by the plants.
The resulting solution is very clear and i use this solution to irrigate the plant
after 1 or 2 day i re-irrigate but it's done with deionized water
i can measure the runnoff water (drain water) of the pot for the amount of material available (such as NO3,PO4,K,Ca,Mg,SO4) with photometer because water is transparent

The problem occurs when the initial solution of humic acid and fulvic acid is added. In this case, the water released is very dark and it is not possible to use this water in photometry.
I have searched a lot, but the easiest way is to use photometer and chemical reagents to measure the concentration of the material.

my question is :
- how i can remove humic and fulvic acid from water without change in the amount of other materials or low changes (needed material is: N P K S Ca Mg)?
- or how i can measure N P K S Ca Mg in dark water with photometer?

detail:
error measuring up to 15% is acceptable


texts: Why do gases only transmit sound waves whose wavelength is long relative to the mean free path?

texts: Also, when is this fact useful in practice?


texts: Can we force reactions with positive delta G?

texts: Do these reactions always have to be paired with another energetically favorable reaction with a greater delta G magnitude, or is there a way to force reactions with a positive delta G to happen?


texts: Is Gibbs energy minimized for processes at constant temperature are pressure only?

texts:
I've had this doubt for quite a while, This link
https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Map%3A_Physical_Chemistry_for_the_Biosciences_(Chang)/04%3A_The_Second_Law_of_Thermodynamics/4.08%3A_Dependence_of_Gibbs_Energy_on_Temperature_and_Pressure

Clearly states that Gibbs energy can be used to predict the reactions that are happening at constant temperature and pressure.

Still I've faced many questions like "Effect on equilibrium on a system of ideal gases (in a closed container) upon addition of inert gas (while maintaining constant volume and temperature of the container). The answers of such questions involve the concept of equilibrium and they say - Since the partial pressures of the species involved in the reactions isn't affected (upon adding inert ideal gas) so the equilibrium is not affected. Thus the reaction doesn't move in any direction, it remains in equilibrium. (The equilibrium constant involve partial pressures of gaseous species)

But my question is why can we even use the equilibrium constant and reaction quotient to predict the direction of reaction as the total pressure of the system clearly rises. (Its not constant).

The usual expression of equilibrium constant relating activities of reactants and products is derived from taking Gibbs energy change for a reaction and then using dG = 0 at equilibrium. But the latter is only true for systems under constant pressure and temperature.

Example of the link to question -

Addition of inert gas at "constant volume"?

Please tell me where I'm wrong as I'm really confused right now!


texts: What is the correct lewis structure of SCH⁻?

texts:
I need to find the Lewis structure of the ion $\ce{SCH^-}$.

I think the Lewis structure should be:
$\ce{S=C-H}$, with one lone pair on the carbon and two lone pairs surrounding the sulfur.

Is this correct?


texts: How to calculate the specific heat of ethanol?

texts:
I am currently stuck with this question. Can somebody please help me with this?

  100 g of water was heated from $\pu{15 °C}$ to $\pu{70 °C}$ by burning $\pu{20 g}$ of ethanol. How much energy per mole does this ethanol have?

So far I have calculated that there are $\pu{0.43 mol}$ in $\pu{20 g}$ of ethanol using the formula $n = m/M$.
\begin{align}
m &= \pu{20 g}\\
M &= 12 + 3 + 12 + 2 + 16 + 1 = \pu{46 g/mol}\\
n &= 20/46 = \pu{0.43 mol}\\
\end{align}

From here, I'm not sure if I should divide the energy used to heat up the water by the amount of substance. By using the specific heat formula,

$$Q = c \cdot m \cdot \Delta{}T
= \pu{4.2 J//g \cdot K} \cdot \pu{100 g} \cdot \pu{55 K}
= \pu{23100 J}$$

$$\text{Energy per mole} = \frac{\pu{23100 J}}{\pu{0.43 mol}} = \pu{53720.93 J//mol}.$$

Is this the right answer?


texts: Are sp, sp2, and sp3 hybridisation only relevant to the carbon atom?

texts:
When we are talking about $\mathrm{sp, sp^2}$ and $\mathrm{sp^3}$ hybridisation, is it only relevant to the carbon atom only?
For the following molecules:
Acetone (propanone), acetic acid (ethanoic acid), tert-butanol (2-methyl-2-propanol), benzene, cyclohexane, 2-butyne.
Which of these contain at least one $\mathrm{sp}$ atom?
I am confused because for acetic acid and tert-butanol, the oxygen atom in the two molecules are bonded to a carbon and a hydrogen - that means 2 bonds.
Would this be and $\mathrm{sp}$ hybridisation? But doesn't $\ce{O}$ forms $\mathrm{sp^3}$ hybridisation as an alcohol function?


texts: Naming substituted branched alkanes with different projections

texts:
Hi all, I would like some help with naming these two compounds.

For compound 1, I know it is a 2-methyl-pentane, but I am unsure how to name the 3,4 $\ce{OCH3}$ compounds. I know that in the final name, it would be 2-methyl-3,4-di[$\ce{OCH3}$]-pentane (or vice verse depending on alphabetical order.).

For compound 2, I am absolutely lost and would appreciate any help. At first I though it would be a bicyclic cycloalkane, but I steered away from that idea because of the three bridgeheads. Is it possible to have three bridgeheads? I just learned this content yesterday in class and have scoured through my textbook but have seen no mention of a compound like this one. If you could at least give my a general idea of how the 3D structure looks, that may help me. Thank you!


texts: How to predict the type of intrinsic defect?

texts:
Intrinsic defects occur when a pure material crystal shows either vacancy or interstitialcy. When an ionic compound has vacancy, the imbalance in charge has to be compensated with another defect. When a vacancy is balanced with another vacancy it is called Schottky defect , when it is compensated by an interstitial defect, it is called Frenkel defect. When species are exchanged on the sites, the defect is called anti-site defect.

Knowing all of that, how do we predict the type of intrinsic defects in a given material such as $\ce{HgSe}$ or $\ce{Ba3N2}$ ?


texts: Dependence of primary alcohol oxidation on presence of water and "strong" or "weak" oxidants

texts:
It is known that the oxidation of primary alcohols can result in aldehydes or carboxylic acids. The product obtained from the reaction is described as dependent on reagents and conditions;[1]

  "Primary alcohols are oxidized to either aldehydes or carboxylic acids, depending on the reagents chosen and the conditions used."

A distinction is typically made between "weak" (eg. PCC) and "strong" (eg. chromic acid) oxidants[2], the former being capable of giving an aldehyde product while the latter carries out the oxidation to carboxylic acids. However, the accepted mechanism for the reaction shows that the oxidation always results on an aldehyde, which can then be further oxidized to a carboxylic acid through an hemiacetalic aldehyde hydrate forming in the presence of water.[1][3]

  "Most other commonly used oxidizing agents [...] oxidize primary alcohols directly to carboxylic acids. An aldehyde is involved as an intermediate in this reaction but can’t usually be isolated because it is further oxidized too rapidly."

This indicates that it is the presence of water in the reaction medium which determines the product of the oxidation. Thus, "weak" oxidants could still yield a carboxylic acid in aqueous solutions (in fact, they are always noted to be used in anhydrous conditions) and "strong" oxidants will result on an aldehyde when used with organic solvants. If so, I fail to understand the classification of "weak" and "strong".
Furthermore, some sources, like Wikipedia, seem to imply the existence of a direct oxidation from primary alcohol to carboxylic acid, but I've been unable to find such a mechanism in bibliography, always ending up with the hydrate intermediary method.
To summarize:

Is the distinction between "strong" and "weak" oxidants meaningful or does the presence of water always determine the reaction product?
Does a method for the direct oxidation of primary alcohols to carboxylic acids without an aldehyde hydrate exist?

McMurry, John. Organic Chemistry. Brooks Cole, 2011. 8th edition.
Alcohol Oxidation: “Strong” and “Weak” Oxidants
Reagent Friday: Chromic Acid, H2CrO4


texts:
As a non chemist I am most often charmed when visiting Wikipedia articles of chemical elements and see images of very pure specimens of element after element, proton by proton, and often also metal cube specimen made from smithing similar pure deposits.

The wiki article Periodic table allows me to do so easily; here are some elements I found looking almost the same and don't think I personally could distinguish between them without some instrument:

molybdenum and manganase
titanium and chromium
rutenium and cadmium
sodium and aluminium
silicone and germanium

My problem

Generally all examples are of synthetic specimens of about 99.9% purity but that me to wonder what test can a chemist make in a natural environment, say inside a natural cavemine, to determine which natural deposit contains what after the mining and positioning a seemingly multimineral natural deposit;
Of course, I understand that with natural deposits of mainly carbon or copper, or iron (water exposed and rusty) natural deposits, let alone with very pure specimens of these elements, it will be easy because of color, but I believe that generally or mostly color by itself won't be enough due to various color biases and I assume that today there are in-place very-accurate tests that can be done, especially for different parts of a multimineral deposits.

My question

How can chemists distinguish pure chemical element specimens that look almost "the same" as well as what deposit is what in a multimineral mined rock?


texts: Can a polypropylene 55 gallon drum previously filled with chemicals used in the chrome plating process (possibly Nickel Sulfate) ever really be "cleaned out" for re-use? Can polypropylene ever absorb and retain such chemicals, or are these drums practical for this use because they do not?


texts: Conservation of angular momentum in electronic transition

texts:
My book says the "angular momentum is always conserved in a transition". But if suppose we have a s electron then it's angular momentum is $\hbar\sqrt{l(l+1)}+\hbar\sqrt{s(s+1)}$ $\implies \hbar\frac{\sqrt{3}}{2}$ and suppose it transits to a p electron (which is in accordance with the selection rule as $\Delta l=1$) which has an angular momentum of           $\hbar\sqrt2 + \hbar\frac{\sqrt{3}}{2}$. As the angular momentum of a photon is $\hbar$ then it means (mathematically) that we would have to add $\sqrt2$photons to the atom but that's not possible. Then how is the angular momentum conserved??

Also I can't see why the spin angular momentum of a photon is $\hbar$ as spin angular momentum is $\hbar\sqrt{s(s+1)}$ and as $s=1$ for a photon so it should be $\hbar\sqrt2$.

P.S. the book I am using is Elements of Physical Chemistry by Peter Atkins and Julia de Paula.


texts: Variation of Arrhenius equation with concentration

texts: In the Arrhenius equation do Arrhenius constant and activation energy depend on concentration ? (Their units do)


texts: Hydrogen bonding in staggered vs eclipsed conformations

texts:
In my first semester of organic chemistry, we learned that staggered conformations have lower energy/higher stability.

However, my thought is that if you have interacting OH groups, the hydrogen bonding would make the eclipsed conformations more stable than the staggered conformation. Is this be the case? Why or why not?

For example, a small molecule containing two carbons, each with an alcohol group (or more attached).

--
Related question:
In a 1,3-diaxial interaction, would multiple OH groups (or anything that exhibits hydrogen bonding) lend to stability?


texts: Method for increasing concentration of extracts

texts:
I am using reagent grade propylene glycol (99.9% pure) and vegetable glycerin (99.7% pure) separately as solvents to extract certain active essential oils/molecules of various plant flowers.

The question is about after saturating the solvents with the essential oils. Can you further reduce the infused solvent solution volume?  I am starting with 50 fluid ounces and want to reduce the solvents to 30 fluid ounces.

The goal is to concentrate the the solvent solution and not harm the active ingredients suspended in the the two solvents.  The solvent boiling temperature is known and the essential oils/molecules are destroyed 80 degrees below the solvent's boiling points.


texts: Why the dilution of solvent doesn't affect the solid phase, in comparison to the liquid phase?

texts:
Dilution of the solvent adds new energy states to the liquid, but does
  not affect the solid phase.

The above line appeared on the following page under the section "5: Colligative properties and entropy" and the last paragraph

Actually, I can understand a little bit. According to me, while freezing the solvent freezes separately from the solute( ie If we freeze salt and water solution, the salt will be separated out from ice). Therefore, whatever the presence of the solute maybe, the solid form of solution consists of solid 'ice', which is identical in every case and hence have identical entropy.

Am I going right? Is there an alternative explanation?

I am not clear with the concepts of what actually happens when we freeze a solution. Any Links regarding it or any other related stuff will be welcomed.


texts: Let us say that we have water reacting with t-butyl chloride. When the chlorine atom departs we have a t-butyl cation which becomes an attractive substrate to the nucleophilic oxygen in water. My question is in the reaction that follows, does the hydrogen break off from water first allowing oxygen to attack the carbocation or does water immediately form a bond with the carbocation and then deprotinates the extra hydrogen?


texts: How many dichlorinated products including stereoisomers can be isolated when (S)-2-chlorobutane reacts with Cl2 /hv?

texts: This is my attempt at solving this problem. I get 6 products. However my book says the answer is 5 products.


texts: Reactions of Grignard Reagent: 1,2 vs 1,4 addition

texts:
So I was reading through Grignard reagent and I came across this answer by jerepierre, which mentions:

  In general, Grignard reagents and organolithium reagents add directly to the carbonyl carbon, while organocuprates (organocopper reagents) add to the beta-position of an unsaturated ketone.

Now, I want to know, what is the meaning of 'in general'? Can anyone please provide me some cases where the general rules are not followed.

Also, I came to know that:

give 1,4 addition with $\ce{PhMgBr}$ to give:

(that reference is difficult to provide at the moment).

Can someone please explain why this happened?


texts: I have a substance that is insoluble in water but soluble in hydrochloric. If dissolve this substance in the acid, would neutralizing the solution with sodium bicarbonate then cause the substance to separate from solution?


texts: Structure of benzene dimer in an vibrationally excited state

texts:
It is known that the benzene dimer has few stable structures, T-shaped, parallel-displaced, and sandwich structure.

Now if we excite the dimer such that it goes to a higher vibrational level (which is close to the dissociation limit but the dimer is still bound).

What happened to the structures then?
Can we still have different structures or it will be some kind of mixture?


texts: Using equilibrium constant in gibbs equation

texts:
In my chemistry textbook, it is written that :

  Gibbs energy for a reaction in which all reactants and products  are in standard state, $\Delta_\mathrm{r}G^\circ$ is related to the equilibrium constant of the reaction as follows:
  $$\Delta_\mathrm{r}G^\circ=-RT\ln K$$

A solved example was given there for the above equation.

  Calculate $\Delta_\mathrm{r}G^\circ$ for conversion of of oxygen to ozone, $$\ce{3/2O2(g)->O3(g)} $$ at $298\ \mathrm{K}$ if $K_p$ for this conversion is $2.47\times 10^{-29}$.

The answer to above problem is simple. Just substitute the values in the gibbs equation and get the value of $\Delta_\mathrm{r}G^\circ$ but the thing that I can not understand is that in the equation they substituted the value of $K_p$ directly in the equation without converting into $K_c$ for equilibrium constant.

So my question is:
 In the gibbs equation what does equilibrium constant stand for? ($K_c$ or $K_p$).


texts: Find the standard Gibbs' free energy of formation at 298.15 K for O2 gas dissolved in the saturated aqueous solution?

texts:
The solubility of $O_2(g)$ in water at $25^o \text{C}$ and $\text{1 bar}$ pressure of $O_2(g)$ above the solution is $0.00126$ $mol$ $O_2(g)/kg$ $water$.  Find $\Delta_fG_{298.15}^o(O_2(g),sln)$.

I kinda have a clue on how to solve this, but there's just one variable I'm stuck on figuring out. I'm not sure how to get the molal-scale activity coefficient for O2 gas in solution. The answer is $\Delta_fG_{298.15}^o(O_2(g),sln) = \text{16.8 kJ/mol}$... now how would I get there?

Here's a derivation I went through to show what I have tried. The chemical potential for $O_2(g)$ relative to some reference standard state is for a real solution on the molal-scale is:

$\mu_{O_2(g)} = \mu_{m,O_2(g)}^o + RTln(\gamma_{m,O_2(g)}\frac{m_{O_2(g)}}{m^o})$

By subtracting the standard molar Gibbs energy of reactants in their elemental state, $G_{elem}^o$, and knowing that the chemical potential of a pure substance is equal to the chemical potential of that substance in a saturated solution, $\mu_{O_2(g)} = \mu_{O_2(g)}^*$, and we should get:

$\mu_{O_2(g)}^* - G_{elem}^o = \mu_{m,O_2(g)}^o - G_{elem}^o + RTln(\gamma_{m,O_2(g)}\frac{m_{O_2(g)}}{m^o})$

$\Delta_fG_T^o(O_2(g)) = \Delta_fG_T^o(O_2(g),sln) + RTln(\gamma_{m,O_2(g)}\frac{m_{O_2(g)}}{m^o})$

where $\Delta_fG_{298.15}^o(O_2(g))$ is $\text{0 kJ/mol}$ since oxygen gas is in its elemental state, and $\Delta_fG_{298.15}^o(O_2(g),sln)$ is what I am supposed to solve for. So, the final equation I think I'm supposed to use is:

  $\Delta_fG_T^o(O_2(g),sln) = -RTln(\gamma_{m,O_2(g)}\frac{m_{O_2(g)}}{m^o})$

But I don't have $\gamma_{m,O_2(g)}$... so how could I do this? This is due next Tuesday, but it would be nice to have it addressed asap.


texts: How much pressure does Gallium exert when it freezes?

texts: Assuming the liquid Gallium is in a sealed container, how much pressure will it exert on its container when it freezes?


texts: Does restriction on spin in orbits exist?

texts:
For a valence electron in Antimony (Sb) with the electron configuration:

$Kr(5s)^2(4d)^{10}(5p)^3$

The 3 valence electrons have the quantum numbers $n=5,l=1,m=1$, resulting in the following possibilities for $(n,l,m_l,m_s)$:

$(5,1,−1,−\frac{1}{2});(5,1,−1,\frac{1}{2});(5,1,1,−\frac{1}{2});(5,1,1,\frac{1}{2});(5,1,0,−\frac{1}{2});(5,1,0,\frac{1}{2})(5,1,−1,−\frac{1}{2})$

$(5,0,0,−\frac{1}{2});(5,0,0,\frac{1}{2})$

Then looking at the actual quantum numbers of Sb (from a former exam) it is given as:

$(5,1,−1,-\frac{1}{2});(5,1,1,-\frac{1}{2});(5,1,0,-\frac{1}{2})$

$(5,0,0,−\frac{1}{2});(5,0,0,\frac{1}{2})$

Where did the quantum sets with $l=1$ and $m_s=−\frac{1}{2}$ go? When I look at the valence electrons in Kr the set is with $l=1$ and $m_s=−\frac{1}{2}$:

$(4,1,−1,−\frac{1}{2});(4,1,−1,\frac{1}{2});(4,1,1,−\frac{1}{2});(4,1,1,\frac{1}{2});(4,1,0,−\frac{1}{2});(4,1,0,\frac{1}{2})
(4,0,0,−\frac{1}{2});(4,0,0,\frac{1}{2})$

Summing up the question: Why can the valence electrons in Kr have $l=1$ and $m_s=−\frac{1}{2}$ and the ones in Sb not? Perhaps it is a mistake in the exam?


texts: Expanded structure formula and Lewis dot structure, whats the difference?

texts:
I am teaching my self the basics of chemistry and I have done lewis dot structure before. Right now I am going into carbon chemistry which often use structure formulas to represent compounds. There is this formula called the expanded structure, and from what I can see, the expanded formula is just the same as the Lewis except we use the lines to represent bonds etc?

So my main question is whats the difference between them and do we have to assign the formal charges in the expanded structure formula? Also, do we show the dots (valence electrons) in the expanded formula? Thank you.


texts: How can I calculate the equilibrium between several reactions?

texts:
If I mix xNaOH + yCdCl2 + zZnCl2 in an aqueous medium, how can I calculate the final equilibrium quantities of the resulting salts (which I suppose may be the following):

Q1 NaOH
Q2 CdCl2
Q3 ZnCl2
Q4 NaCl
Q5 Cd(OH)2
Q6 Zn(OH)2

Also (only if it will take more than an hour for >99.999% of the reaction to occur), how can I calculate the respective quantities of each vs time?

Suppose the reaction occurs at ~25C, unless a better prescribed temperature is suggested.


texts: What actually happens in strong acid- weak base reactions?

texts:
I'm going back through my notes from a chemistry class, which I did well in despite not having a very good conceptual understanding, in order to hopefully develop that understanding, but there's something I can't find in the book or online. Why is it that, when solving for the pH of a solution that results from the mixture of a strong acid with a weak base or a weak acid with a strong base, we can treat the acid-base reaction as going to completion before solving any resulting equilibrium problem, or completely ignoring any equilibrium in the pre-mixed solutions.

For a concrete example, when mixing 40.0 mL of 0.50 M ammonia with 25.0 mL of 0.30 M hydrochloric acid, the approach the class would have me use is to first solve the limiting reaction problem as if the reaction goes to completion. Doing so, we see that there are 0.0075 mol of chloride ions, 0.0075 mol of ammonium, and 0.013 mol of ammonia. Then, because we don't have excess hydrogen ions, nor excess hydroxide, nor only neutral ions, we solve the equilibrium problem of ammonium with ammonia.

What I don't understand is how we can ignore the fact that the ammonia solution would have already been in equilibrium when mixed with the hydrochloric acid, and as I understand it should be constantly arriving towards equilibrium as the reaction is taking place.

Alternatively, if there had been excess hydrogen ions, I was told to use the concentration of hydrogen ions from the completed reaction, but that would also be ignoring the fact that the ammonium contributes to the pH (because it again ignores it's equilibrium).


texts: How to balance this redox reaction taking place in a basic medium?

texts:
How to balance this reaction which is taking place in a basic medium?
  $$\ce{Al + MnO4- -> MnO2 + Al(OH)4-}$$

My Attempt

Reduction half reaction:

$$
\begin{align}
\ce{4 H+ + MnO4- + 3 e- &-> MnO2 + 2 H2O}\\
\ce{28 H+ + 7 MnO4- + 21 e- &-> 7 MnO2 + 14 H2O}
\end{align}
$$

Oxidation half reaction:

$$
\begin{align}
\ce{Al + 4 H2O &-> Al(OH)4- + 8 H+ +7 e-}\\
\ce{3 Al + 12 H2O &-> 3 Al(OH)4- + 24 H+ + 21 e-}
\end{align}
$$

Adding half reactions:

$$
\ce{3 Al + 7 MnO4- + 28 H+ + 12 H2O + 21 e- -> 7 MnO2 + 3 Al(OH)4- + 14 H2O + 24 H+ + 21 e-}
$$

Adding $\ce{OH-}$ and eliminating $\ce{e-}$ and formed $\ce{H2O}$.

Final equation:

$$
\ce{3 Al + 7 MnO4- + 2 H2O -> 7 MnO2 + 3 Al(OH)4- + 4(OH)-}
$$

Please tell if I am wrong.


texts: Can pure elements have different colors?

texts:
This question was inspired by this: Are there colorful metals besides gold and copper?

I was wondering how the color of a pure element could be changed. I know that it is possible for color to change when electrons to get excited, but I'm curious about how that works. Can you change the color of any element if you heat it up enough (I'm talking about the pure elements here, not compounds)? If not, then what limitations are there about changing color? And to ask something a little more specific, could the color of pure gold be changed without adding it to an alloy or compound?

Note: These questions Why does iodine have different colors in different media? What does a molecules color have to do with its bond/orbital energies?
do talk about this topic, but I felt like they didn't answer my query satisfactorily.


texts:
It takes some work to find a list of the actual pH of various foods.  (Searches are confounded by a popular "alkaline diet" theory that the pH effect on a human body of consuming various foods is not a function of the pH of the food itself.)
It appears that almost all food has pH < 7.0 (most much lower), and I can't find any with pH > 7.5.
Is there a biochemical reason that there is no significantly alkaline food?


texts: How hazardous are peroxide-able ethers if stored properly?

texts:
This question is directed towards laboratory scientists and technicians who actually deal with ethers that can develop peroxides upon concentration (e.g. diethyl ether, THF, dioxane). I am already very familiar with the literature, the normal precautions (dispose of after 1 year, test for peroxides, etc.), how to remove peroxides (shake with ferrous salt or metabisulfate).

My question is how hazardous are peroxides in reality if stored properly. If a peroxide-able ether upon concentration is stored in a cool dark cabinet, is rarely opened, has an inhibitor (BHT or ethanol), and argon is used above the headspace, it is likely that the ether can be used for longer than a year?

Again, I need the input of an actual practitioner. Simply quoting written material will not help me, as I have consulted LOTS of written material and I believe I understand the theoretical issues. I am looking for practical experience.  I have heard informally that some ethers are available in European countries as OTC solvents, and so it leads me to think that the standard warnings may be too severe. Thanks!


texts: Why do electrons follow from Zn to Cu but not Cu to Zn in the lemon battery experiment?

texts:
In the lemon battery experiment, as I understand, both $\ce{Zn}$ and $\ce{Cu}$ meet acid in the lemon, cause $\ce{Zn}$ and $\ce{Cu}$ release electrons to form $\ce{Zn^{2+}}$ and $\ce{Cu^{2+}}$.

So why do the electrons follow from $\ce{Zn}$ to $\ce{Cu}$ but not from $\ce{Cu}$ to $\ce{Zn}$?


texts: What properties of an element determines the maximum number of bonds it can make?

texts:
From my conjecture, I think it's a mix between valence electron and the principal energy state, but I'm not sure.

For example, C, N, O and F can only make a maximum of four bonds, as they can only have up to sp3 hybrid orbitals.

For Si, P, S and Cl, they can make a maximum of nine bonds, as they can have sp3d5 hybrid orbitals.

That's what I think, but I'm probably incorrect in some aspect.


texts:
Checking out the molecular structure and the melting points of various hydrocarbons I concluded:

1)branching increases the melting point of a hydrocarbon molecule

2)symmetry increases the melting point of a hydrocarbon molecule

symmetry increases it way more than branching does.

ordering in terms of melting points:

2-methyl butane < pentane < 2,2-dimethyl propane

2-methyl butane is branched but has a bad symmetry, pentane has a good symmetry although not being branched, 2,2-dimethyl propane has a good symmetry and is branched.

2-methyl pentane < 2,3 dimethyl butane < 2,2 dimethyl-butane < hexane

so 2-methyl pentane has a bad symmetry

2,3 dimethyl butane has a bad symmetry as well but more branched compared to 2-methyl pentane

2,2 dimethyl butane has a bad symmetry but it is more branched than the previous two.

Then hexane has the highest melting point. it is not branched at all and not symmetrical. so why does it have the highest melting point?

I kept the text a bit long before asking the question because I wasn't sure if I understood the concept correctly. Can you please answer my question about hexane and correct me if I have some mistake in my interpretation of the whole thing?


texts: What does "correct orientation" in a chemical reaction mean conceptually?

texts:
My chemistry teacher was talking about how there are two requirements for a reaction to occur:

The reactants must have enough energy; and
they must also have the correct orientation for a reaction to occur.

What does it mean for molecules to have the "correct orientation", perhaps using the gas-phase reaction as an example?

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


texts: Derivation of van 't Hoff equation for temperature dependence of equilibrium constant

texts:
While I was reading about the usefulness of the quantity $\Delta H$, I found that it can be used to calculate the how the equilibrium constant varies with temperature. How can this be done?

Does it agree with the predictions of Le Chatelier's principle (that for an exothermic reaction, increasing the temperature disfavours product formation, and vice versa)?


texts: Why the "Diverse Ion Effect" increases Ksp?

texts: I've read in chemwiki about the diverse ion effect. Assuming I have an aqueous solution of $\ce{NaCl}$ and an associated $K_\mathrm{sp}$. If I add $\ce{KI}$ there is an associated $K_\mathrm{sp}'$ for $\ce{NaCl}$ where $K_\mathrm{sp}' > K_\mathrm{sp}$. This actually means that I can dissolve more $\ce{NaCl}$ than I could before. Why does this happen? Shoudln't the new solution actually be closer to saturation and $K_\mathrm{sp}' < K_\mathrm{sp}$?


texts:
I learned that square brackets ex: $[\ce{H2O}]$ can be used to denote the concentration of water molecules in a fluid. The notation  used much in equilibrium problems and such.

However, sometimes I have seen curly brackets {} being used in similar scenarios, but I never really understood the difference. When are curly brackets used and what do they mean?

I found this example from an exam where the problem is to see if a solution of $\ce{Ca(OH)_2}$ in water is concentrated enough to result in precipitation.

Following is what how they solve it in the example:

Solubility constant for $\ce{Ca(OH)_2}$ is given as $K_\mathrm{s} = \{\ce{Ca^{2+}}\}\{\ce{OH^-}\}^2$ (100% saturation point I think)
$Q = \{\ce{Ca^{2+}}\}\{\ce{OH^-}\}^2 \approx [\ce{Ca^{2+}}][\ce{OH^-}]^2$ (actual saturation I think)

Where $Q$ is the actual saturation of the solution. And the answer is that no precipitation occurs since $Q < K_\mathrm{s}$ in this specific example.

So they seem to suggest that {} is something different than the concentration [] and that it can be approximated to the concentration.


texts: Is the new equilibrium total pressure of this equilibrium reaction always more than its initial total pressure?

texts: In the case of the reaction $$\ce{2NO2 <=> N2O4}$$ at equilibrium and considering Le Chatelier's principle, if we add more $\ce{NO2}$, the pressure of $\ce{NO2}$ will increase acutely and then begin to decrease until the system reaches its new equilibrium. Why is the new equilibrium have a higher pressure of $\ce{NO2}$ than the original equilibrium? How can we tell this just by looking at it? Will it always be larger?


texts: Hydrogenation stereochemistry-Pd,Pt, Ni catalysts

texts:
When my textbook talks about hydrogenation using Pt, Pd or Ni heterogeneous catalysts, it never mentions if it is anti or syn addition.
It simply jumps on to say that for alkynes, NiB2 (P-2) catalysts and Lindlar's catalysts are syn hydrogenation.
Can someone tell me if using Pt gives syn or anti for alkynes?


texts: Methods to quantify lead(II) concentration in water on the ppm/ppb level

texts:
While there are several ways to quantify metal concentrations in water, a lot of them are only specific to select metals. For example, there is the orthophenanthroline method for quantification of Fe(II) concentrations via spectroscopy. How can lead(II) concentrations be determined using a similar spectrophotometric method?

If spectroscopy isn’t the most efficient way to quantify these concentrations, is there a better way to do it?

The salt used to release $\ce{Pb^2+}$ ions into solution is $\ce{Pb(NO3)2}.$


texts: Acidity order in substituted Phenylboric acid

texts:
Here, we are asked to find the acidity order. For the first one, the answer given is ii > i > iii (c) and for the second one, it is iii > ii > i (b). Any logic that I think for one of these problems mostly fails to properly explain the other one.
Now here is the best explanation that I have got till now:
In the first problem, the substituent at ortho and para positions destabilizes the anion because of the resonance of the lone pair of oxygen. But, this effect is reduced when the group is at ortho position because of steric inhibition of resonance, and with that, the ortho group shows -I inductive effect at close proximity to the negative charge. The meta group shows only -I effect and does not destabilize anion in any way so it is the most stable.
For the second problem, NO$_2$ stabilizes by the resonance effect as well as inductive effect. But, when it is located at the ortho group, it largely loses the resonance capabilities and also destabilizes by a bigger extent by disturbing the back bonding in boron and oxygen. In the first problem, the destabilization because of reduced back bonding was lower than the destabilization by the resonance of lone pair. Thus, in the second one, the para-substituted acid is the most stable followed by the meta and then ortho.
So is this thought process correct or there is a better explanation?


texts:
In the above reaction, we use a non-polar compound (such as CCl$_4$) as a solvent. Then, why does the Br$_2$ polarise on attack by the alkene, even though a non-polar solvent does not encourage polarisation of a compound. Is the mutual polarisation enough for the reaction to occur.

Further, in different books the mechanism is either explained by the above mechanism or by the Molecular Orbital Theory (the alkene's filled $\pi$ orbital (HOMO) will interact with bromine's empty $\sigma$* to give the product).

Which one of these is the more popular and/or the officially accepted explanation.


texts: Signs of Exchange and Correlation Potentials

texts:
The exchange and correlation potentials refer to those defined in density functional theory. (See also http://en.wikipedia.org/wiki/Local-density_approximation)

Define the exchange potential as $V_{x}(n) = \partial E_x(n)/ \partial n$, when $E_x(n)$ is the exchange energy density of the whole system(not per particle). Define a similar quantity $V_c(n)$ for the correlation contribution. My question is, are the two potentials (generally) of the same sign?

Another question: It seems that the prediction of the ionization potential using the -ve energy of HOMO is not good (See the section Exchange-correlation potential on http://en.wikipedia.org/wiki/Local-density_approximation). Using a simple slater exchange potential and a reasonable correlation potential (for a uniform electron gas), the result (?; not sure about its correctness; feel free to point it out if you think it's wrong) is about 0.7*13.6 eV, which is not good. Of course one need not use DFT for hydrogen; it however serves as a test case. Is there any reason to believe the results will improve as the atomic number increases?

Thanks a lot.


texts: Heats of combustion of pentadiene isomers

texts:
This is a problem from the book Organic Chemistry by Carey and Giuliano (10th edition), the problem is:

Match the heats of combustion with the compounds:
The compounds are 1,3-pentadiene, 1,2-pentadiene and 1,4-pentadiene and the heats of combustion are given as 761.6 kJ/mol, 768.9 kJ/mol and 777.1 kJ/mol.

I know from my knowledge of organic chemistry that 1,3-pentadiene is the most stable of the three compounds (since its π bonds are in conjugation), therefore its heat of combustion corresponds to the minimum of the given heats of combustion, ie. 761.6 kJ/mol, however I am confused about how will I compare heats of combustion of 1,2-pentadiene and 1,4-pentadiene.


texts: Why do metallic bonds have delocalized electrons, whereas covalent bonds only share electrons? Does it have something to with the atomic masses of the individual non/metals or something else? I'm really interested to know.


texts: Why is NOₓ conversion low at fuel rich conditions in a three-way catalytic converter?

texts:
$$
\begin{align}
&\text{Oxidation:} &\quad \ce{2 CO + O2 &-> 2 CO2}\\
& & \ce{``HC" + O2 &-> CO2 + H2O}\\
& & & \\
&\text{Reduction:} &\quad \ce{2 CO + 2 NO &-> 2 CO2 + N2}\\
& & \ce{``HC" + NO &-> CO2 + H2O + N2}
\end{align}
$$

$\ce{NO_x}$ conversion is low at oxygen rich conditions (lean operation) because no $\ce{CO}$ or $\ce{HC}$ are available for the reduction.
But why is $\ce{NO_x}$ conversion also low at fuel rich conditions, so an optima exists? Rich conditions lead to high $\ce{CO}$ and $\ce{HC}$ emission and that should be perfect condition for $\ce{NO_x}$ reduction.


texts: Conversion of an epoxide into an alcohol

texts: I need help changing an epoxide into an alcohol, i.e. the second step in the scheme below. I found a reaction that created two hydroxyl groups but cannot find one that only produces one:


texts:
How strong is the "hydrophobic force"?

Hydrophobic interactions are weak interactions but can have greater strength than hydrogen bonds. I find the strength of the hydrogen bond in literature to be near 1 pN. Finding the strength of the "hydrophobic bond" has proven to be a bit more elusive. I would guess that there is a hydrophobic interaction strength spectrum (dipole strengths and such), but would also guess there is a fundamental order of magnitude of strength of the hydrophobic interaction.
Hydrophobic interactions result from the hydrophobic effect and manifest in measurable attractive forces. For example, the Polyhydroxyethylmethacrylate (pHEMA) backbone has dipole induced interactions, hydrophobic interactions, and hydrogen bonding; each of these interactions being identifiable in molecular position on the backbone (aliphatic regions being identified as hydrophobic sites).
To date, i have found a measurement of such resulting attractive forces in a specific interaction to be near 15 pN (oil-oil droplet AFM approach)[1]. However, I can also find literature that discusses forces in avidin-biotin  complex which are dominated by hydrophobic interactions; resulting attractive forces range from 80 to 250  pN [2].
[1] Tabor et al, 2013; DOI: 10.1021/jz402068k
[2] Moy et al, 1994; DOI: 10.1126/science.7939660


texts: How to determine whether inversion takes place?

texts:
Predict in which of the following reaction inversion of configuration takes place:

In my view, C) involves $\mathrm{S_{N} i}$ and therefore doesn't involve inversion of configuration. In D) the syn addition of $\ce{H2}$ across the double bond takes place and doesn't change the configuration. However I am not sure about A) and B).  Any ideas?


texts: What exactly does the excitation spectrum tell us about a sample in Florescence Spectroscopy, what information does it tell us? I know that we will get an output of concentration vs intensity but that's it.


texts: How to accurately calculate the electromotive force for various conditions in a salt water battery?

texts:
This question is on the same topic as this one but more complex.
So, let's consider the cell with $\ce{Zn}$ and $\ce{Cu}$ electrodes inside the $\ce{NaCl}$ solution.
On the $\ce{Zn}$ electrode we have
$$\ce{Zn + 2Cl^- -> ZnCl2  + 2e^-},$$ and on the copper one
$$\ce{H3+O + e^- -> 1/2 H2 + H2O}.$$

For both reactions we can find standard electrode potentials, but they are given for normal conditions, and $1~\mathrm{M}$ concentration of $\ce{Zn^{2+}}$ and $\ce{H3+O}$. To calculate the EMF for non-$1~\mathrm{M}$ concentration we use the Nernst equation. In this case we have something like
$$E=E_0 - \frac{\mathcal{R}T}{n\mathcal{F}}\ln{\frac{[\ce{Zn^{2+}}]}{[\ce{H3+O}]}}.$$
But really in the initial $\ce{NaCl}$ solution we do not have any $\ce{Zn}$ ions (so their concentration is very close to zero and unknown to us). Of course, in few microseconds some $\ce{Zn}$ from electrode will be dissolved creating some finite potential. But in the experiment when putting $\ce{Zn}$ electrode into the same solution we always observe the approximately same EMF value, $\approx 0.8~\mathrm{V}$. How to predict theoretically this value?

Furthermore, my question is how to calculate the EMF of such cell as precisely as possible for different experimental conditions, e.g. different temperature?

I have made an experiment showing that the EMF of a 'cell' with $\ce{Zn}$ and $\ce{Cu}$ electrodes into $\ce{NaCl}$ solution is decreasing when heating the $\ce{NaCl}$ solution.

It's strange, let me explain why. The Nernst equation tells us that EMF is increasing with $T$ when $[\ce{Zn^{2+}}]$ is less than $[\ce{H3+O}]$ (because $\log$ is negative), and otherwise EMF is decreasing with $T$ ($\log$ is positive). But in my opinion the concentration of $\ce{Zn}$ ions is always less than $[\ce{H3+O}]$ because we do not have $\ce{Zn}$ in the initial solution. So then logarithm is always negative so EMF is growing with $T$.
In this case, why do I observe the EMF decreasing for $\ce{Zn-Cu}$ pair?

And the last question. When we talk about $\ce{Zn-Cu}$ pair we assume that zinc dissolves; and the hydrogen gas is created on the copper electrode.
But why do I have the EMF when putting into a $\ce{NaCl}$ solution the $\ce{Al}$ ($\ce{Fe, Cr, etc}$) electrodes instead of $\ce{Cu}$, and remain instant the $\ce{Zn}$ electrode? I am not sure that hydrogen is created in such pairs: all these metals have a negative standard electrode potential. Measured EMFs of all these ($\ce{Zn-Al, Zn-Fe, Zn-Cr}$) pairs are significantly different, so the second metal is important in these cases. What reactions are going on in such pairs?


texts: Relationship between Energy Level and electron position

texts:
In Bohr's Model of the atom there are set energy levels that are used to show the energy of the electrons in the atom. In the quantum model there are orbitals that show a probable location of the electrons within the atom.

How does the changing energy level of an electron affect it's position in the atom? For example, Helium has two electrons that both fit in the first "s" orbital. When the Helium electrons absorb the correct quanta of energy they would jump up to the next energy level, but what happens to their position in their orbital? As I understand, they can't move to the second "s" orbital, right, so would their distance from the nucleus just become greater while remaining in the first "s" orbital, or is its change in energy level a difference in the oscillation of the electron within its orbital?


texts: How can I make a fairly saturated copper (II) sulfate solution by heating?

texts:
I have an investigation to do for my chemistry class. I'm looking at copper complexes and using ammonia to create a precipitate in the copper (II) sulfate solution, then redissolving the precipitate to complete the ligand exchange. When I tried the experiment the first time, I was unable to make a good solution. I dissolved about $3.5$ grams of $\ce{CuSO4·5H2O}$ into $200$ mL of water, and couldn't get any more to dissolve. I titrated in $1$ mL of ammonia and the solution turned cloudy (I assumed this was the precipitate). After $4$ mL I stopped, as the solution hadn't changed at all. This was all carried out at room temperature.

I know the two best ways to make a more concentrated solution are time and heat. I don't have that much time, as I'm on winter break and I'll need to complete the experiment as soon as possible when I go back next week. It would probably take a week to get the solution concentrated enough, so I've decided to use heat to help the dissolution along. After looking around the internet, I found very little that was helpful. One page outlined how to make a supersaturated solution, which was not what I wanted. It advised heating to $100^{\circ}$ Celsius, so I suspect that will be too hot for my experiment. A video done by students showed them making a solution at $50^{\circ}$ Celsius, but they used copper (II) oxide. I'm not sure if that makes the procedure significantly different.

I'm not sure what temperature is necessary for this to work. If all else fails, perhaps I'll change my topic to an investigation of the relationship between heat and solubility rates. I'll finally know how to make a saturated solution in a reasonable amount of time.

Other notes: I'll be using a hot plate (Fisher Scientific, 11-500-4H) for the heating, not a Bunsen burner. The ammonia is stock/commercial, and the concentration isn't on the label.

Thanks in advance.


texts: What is the difference between wet paint, dry paint, and in between those stages?

texts:
A day after painting a closet, I set a piece of wood on the wall of the closet that was painted a day ago as well. Within minutes, both of their layers of paint fused together (please correct me if there is a better term than 'fused').

I'm assuming that the paint approaches a state of being a solid, but the process is never stopping, (as I've heard:) similar to how concrete is much stronger thousands of years after it is made rather than a couple of years.

So I understand that it started off as a liquid with a high viscosity, and liquids with high viscosity's turn into a solid when spread thin, but why does that even happen. As well, was I right when I explained that it is constantly 'drying', explaining why it was able to fuse with the other layer of the same paint even a day later?


texts: Are there any general chemical rules for choosing initiators for a polymerization reaction?

texts:
I'm working with some very basic free-radical initiated polymerization reactions. For the most part, I just follow a recipe I'm given (by a member of my group or the broader literature), it works, and I don't worry too much about the chemistry of why it works. Clearly, that will only work for so long, and I'd like to better understand the chemistry of what I'm doing.

  So what general rules can I use to predict what kind of initiator will polymerize a given monomer?

To give a concrete example of what I mean: I know that some persulfate-based initiators will polymerize some acrylamide-based monomers. Can I generalize that to all persulfate initiators and all acrylamide monomers? What about methacrylamides? What about styrenes? Essentially, at what point have I changed the reactants so much that the chemistry doesn't work anymore?

Odian's Principles of Polymerization (4th ed) reviews some things that have been done, but doesn't discuss any general rules. Are there other good sources for this information?

EDIT: I am looking specifically for chemical reasons. Are some initiators better at reacting with some monomers? Are there any issues like side reactions I should take into account?

EDIT(2): from @Ben Norris's answer and the ensuing comments, it sounds like, as long as I can get the initiator to radicalize, and everything is soluble in the solvent, then I will be able to use any initiator with any monomer. Is that correct? I've found another textbook on this, Polymer Chemistry: An Introduction by Malcom Stevens, and that seems to support this.


texts: How can I carry out a titration to identify mercury in wastewater?

texts: First, I would like to do a some form of extraction to only get the mercury, then followed by a titration to identify the concentration or the presence of mercury.


texts: Why do boiling points of alkanes and alcohols become closer with increased chain length

texts:
I came across this graph, which clearly shows a large difference between the boiling points of alkanes and their equivalent alcohols.

However, it is clear that as chain length increases, the difference in boiling point between alkanes and alcohols decreases.

What is the main reason for this?

I have read that it is due to the dispersion forces increasing in both alcohols and alkanes, but wouldn't this not really have an effect on the hydrogen bonding of the alcohol? (meaning that boiling point should be consistently higher)


texts: When are the prefixes bis, tris etc. used in nomenclature of complexs?

texts: Are the prefixes bis-, tris- etc. used only for ligands that are bidentate in complex nomenclature?


texts: How to now if the OH group on the C5 carbon of a cyclic sugar is up or down in Fischer Projection

texts:
I know when using fischer projection I have to look if it's a D or L configuration. if it's D: up = right and down = left and if it's L: up = left and down = right. I think the concept is clear to me, however I dont't know if the OH group on the C5 carbon atom is pointing up or down. For example:

When I have to draw those cyclic molecules to fischer projection I never know if the OH group which will be shown in the fischer projection (not in the clyic structure because it's a hemi-acetal then) is pointing up or down. What is the rule for this?

I want to get this:

But I don't know how to know the side of the circled OH group


texts:
The alkyl chains of saturated fat molecules can readily rotate about their carbon-carbon single bonds, giving them flexibility and viscosity.

What is different about the carbon-carbon double bonds of unsaturated fat molecules, preventing inter-conversion of cis and trans forms?


texts: What is the difference between dissolution and absorption?

texts:
Let us first look at the definitions from Gold Book:

Absorption:

  The process of one material (absorbate) being retained by another (absorbent); this may be the physical solution of a gas, liquid, or solid in a liquid, attachment of molecules of a gas, vapour, liquid, or dissolved substance to a solid surface by physical forces, etc

Dissolution:

  The mixing of two phases with the formation of one new homogeneous phase (i.e. the solution).

I've re-read them again and again, but have been unable to come up with the terminology to exactly differentiate between the two. In fact, I've reached some interesting counter-examples.

Here's one: we always says "sugar dissolves in water" and never "sugar absorbs in water" (Ngram). But, going by the first definition which reads: "physical solution of a gas, liquid, or solid in a liquid", can't we say that the physical solution of solid sugar in liquid water is an example of absorption as well? The water is retaining sugar particles in its bulk after all, so why couldn't we call water an an absorbent and sugar an adsorbate?

Another one: we say that "cotton absorbs water" but never "cotton dissolves water" (Ngram). But, going by the second definition: "mixing of two phases with the formation of one new homogeneous phase (i.e. the solution)" can't we say that the solid cotton mixed with liquid water to form a new homogenous phase? After all, the wet cotton needs to be dried to separate the two components, so they clearly are homogenous.

Interestingly enough, the Gold Book definitions seem to have been created to deliberately introduce confusion. Notice that the definition for "absorption" mentions both the words "solution" and "dissolution". So, why did the Gold Book need to refer to dissolution to explain absorption?

Dissolution and absorption definitely are different from each other, otherwise some explicit relation should've been mentioned in the Gold Book. For example, the definition for "chirality centre" reads "A chirality centre is thus a generalized extension of the concept of the asymmetric carbon atom to central atoms of any element" clearly highlighting their relation (the former is a superset). Such isn't a case in the definitions for dissolution and absorption. So, they are different.

So, to summarize, my questions are:

What exactly is the difference between absorption and dissolution? And, as a direct consequence, given a physical process: how would I identify if it is a dissolution or absorption?
In the two examples (sugar and cotton) I highlighted, where is my reasoning wrong in applying "dissolve" in place of "absorb" and vice-versa?
Is there any subset/superset relation between absorption and dissolution? If so, how's that apparent from the Gold Book's definition?
Why did the Gold Book need to refer to dissolution to explain absorption? Couldn't it have explained them both in separate terms without creating confusion?


texts:
In my textbook “solutions” are defined as follows:

  Homogenous mixtures of two or more substances are known as solutions.

Should the two substances always be non-reacting?

The definition has no indication of this, buts it’s just something that came to my mind.
Won’t the solution still be homogeneous so shouldn’t we still call it a solution?


texts: Diastereoselectivity of the Pauson Khand Reaction

texts:
I hope someone may help me. I don‘t know how to determine the diastereoselectivity of the product of the Pauson Khand reaction in generally.
In the following I’ve got 3 practice examples,however in the third one I’ ve got no solution. I know the product and the regioselectivity.


texts: Bond strength by Similar size or Overlap?

texts:
Which of the sp³-sp³ or sp³-sp² forms a more stronger bond.. As we know that former one will make weaker bond as both are larger orbitals but in latter one.. One is bigger and other smaller.. So latter one would be a stronger bond..
But if we see by other thing tbat similar Orbitals make more effective bond.. Then sp3-sp2 should make a weaker bond.. So which of the two would actually make up for a stronger bond?


texts: Does fluoride anion ever act as a strong field ligand?

texts: In the case of $\ce{[Fe(H2O)6]^3+}$ there are $5$ unpaired electrons as water acts as a weak field ligand. But instead of fluoride acting as a weak field ligand in the $\ce{[MnF6]^4-}$ , why does it act as a strong field ligand? In what conditions does it act as a strong field ligand and a weak field ligand?


texts:
I am trying to determine the experimental pKa for two weak acids that were titrated against 0.20M NaOH.

I have read elsewhere that you can take the point where the graph becomes steep and divide the value of base added by two the corresponding pH value would then be the pKa, but how do i choose which value since it may not be obvious which point the graph becomes steep.

Below I can see that the pka for acetic acid should be close to the theoretical value calculated of 4.76 and the Tris-HCl pka should be approximately 8.3 but there must be a better way than just guessing from a graph.

My textbook doesn't explain how to experimentally find pH just that it's the point where $[A^-]/ [HA]$. I am hoping someone can give me an equation to work with or guide me in the right direction.

Thank you,


texts: Balancing reduction equations for galvanic cell

texts:
Problem: Compute the potential of the following galvanic cell: $$(\ce{Mg (s)} \mid \ce{Mg^2+ (aq)}\ (0.30\ \mathrm{M}) \mid \mid \ce{Sn(OH)4^2- (aq)}\ (0.10\ \mathrm{M}); \mathrm{pH} = 9 \mid \ce{Sn (s)})$$

Attempt at solution: I know we have to use the formula $$E_\text{cell} = E - \frac{0.0592}{n} \log Q$$ The anode is situated on the left; this means electrons are going away there. So we have for the oxidation half-reaction: $$\ce{Mg -> Mg^2+ + 2e-}$$ The potential for this is $E_1 = 2.36\ \mathrm{V}$. Then I’m not sure how to write my reduction half-reaction. I just wrote: $$\ce{Sn(OH)4^2- + 2e- -> Sn(s)}$$ and $E_2 = -0.91\ \mathrm{V}$. But this doesn’t seem correct, because if I add both reactions to get the sum, my charges aren’t balanced anymore. Also, I wonder what happens with the $\ce{(OH)4^2-}$ ? It’s not on the right side of the arrow anymore.


texts:
Recently I ran out of dish washing detergent, so I decided to pick up one of the recipes online, to make my own "ecological" dish washing detergent alternative.

The recipe was:

Mix ingredients:

400ml of water
200mg of kitchen salt
100ml of vinegar
juice squeezed from 3 lemons

boil for 10 minutes

After I stopped boiling and left the mixture to cool down, the fluid turned dark gray. Bottom of my stainless steel pot turned black. Here is a photo of it (after I did some scrubbing, but you can still see black on the side):

What happened? (What chemical reaction?) Additionally, are any of the formed substances known to be toxic?


texts: Can fluorine ever have a positive oxidation state?

texts: I know fluorine is the most electronegative element but can we humans ever synthesize fluorine in a positive oxidation state like +1?


texts:
What exactly is petuntse, the "china stone" used as one of two ingredients in porcelain along with kaolin?

The Wikipedia article (and books I have read) describe petuntse as a mineral containing feldspar. Well, fine, but there are a lot of minerals that are certainly not petuntse that contain feldspar. Feldspar is one of the most common minerals, so saying it is a material with feldspar in it, is not specific.

What is the specific composition of traditional petuntses used to make porcelain?


texts: Spraying aluminium hydroxide nanoparticles onto PLA as fire retardant?

texts: Several scientific papers study FR-PLA (fire resistant PLA) in which Aluminium Hydroxide nanoparticles are melt blended into the PLA (example source: Advances in Flame Retardant Poly(Lactic Acid). Would spraying the nanoparticles (dispersed in a liquid -source - maybe non flammable silicon oil) onto a 3D printed PLA help with fire resistance or not make a difference?


texts: How does Fermi's golden rule yield a specific rate?

texts: According to Fermi’s golden rule, the rate of an electronic transition is proportional to the magnitude squared of $\langle i|\hat{H}|f\rangle$.  Since energy is always relative to some reference point, I could add an arbitrary constant to the Hamiltonian, and it would do nothing but shift all the energy eigenvalues by that constant.  So I don’t understand how Fermi’s golden rule can yield a specific rate – changing the Hamiltonian by an arbitrary constant will (despite not changing the system) change the calculated rate.  Can anyone explain?


texts: What is the hybridization of chromium in chromate and dichromate ions?

texts: I was recently reading about the transition metals and some important compounds of them. I came across a rather interesting diagram in my book... a tetrahedral structure for the chromate ion. The only tetrahedral structure I know arises from an sp3 hybridization of the central atom, but as far as chromium is concerned, I think that a d3s would be more practical(?).. But then again, which specific orbitals of 3d would hybridize to give a tetrahedral structure?(this is beyond me, i seriously do not understand the shapes of the d orbitals)


texts:
CH3-O-CH2CH2Cl

How will this compound be named? Both, methoxy and chloro are given equal preference, since they are prefix functional groups. The answer given in the book is 2-chloro-1-methoxyethane, but why is it not 1-chloro-2-methoxyethane, as the C of chlorine comes before M in the alphabetical order?


texts: Calculating ΔH with non-integer coefficients in the balanced equation

texts:
I am working a practice problem out Ebbing's General Chemistry and for part of the problem I needed to calculate $ΔH.$ The problem considers the burning of ethane in oxygen to yield carbon dioxide and water vapor.

The coefficients used in the solution manual were 1 for ethane 7/2 for oxygen 2 for carbon dioxide and 3 for the water vapor. The coefficients I used were 2, 7, 4, and 6, respectively.

Naturally, it follows the $ΔH$ value I got is twice as large. Can anyone provide clarification here?


texts: How do nylon and polypropylene blend together in the production of a toothbrush?

texts: Why is nylon (nylon 6) and polypropylene chosen together to make a toothbrush? Specifically, how are they blended together during the production process, and what determines their price?


texts:
Brown butter is butter that has been heated until the water content has boiled off and the remaining liquid has turned brown. It is often called for in cooking and baking, for example in recipes for financiers.

Discussions of the process typically explain the brown color as browning of the milk solids in the butter due to the Maillard reaction. However, even when these milk solids are removed, as is done in most recipes by filtering or careful pouring, the brown color remains.

I believe I understand how the flavor components of the brown butter survive filtering - the volatile products of the Maillard reactions remain dissolved in the liquid fat - but is there a similar explanation for the brown color? Or is it down to the coarseness of the filters allowing small suspended particles through with the liquid?

Any details on the particular compounds responsible for the color, or the chemical processes involved in creating them, would be much appreciated.


texts: Can one describe the bonding of Na to F in terms of molecular orbital theory? What about valence bond theory?

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I would kindly appreciate an explanation in terms of the two accepted quantum mechanical theories -valence bond & molecular orbitals- for the electronic energy level structure in natrium fluoride $\ce{NaF}$.

I read here that from a non-quantum perspective the $\text{3s}$ electron of $\ce{Na}$ "jumps" to join the $7$ electrons of the $\text{2p}$ level of $\ce{F}$. This way, the $\text{Na}$ atom becomes the $\ce{Na+}$ ion, while the $\ce{F}$ atom becomes the $\ce{F-}$ ion. All nice until now but handwaving, or high-school level if you prefer.

So how is then the $\ce{Na-F}$ bond (thus the molecule) defined in terms of the electronic wavefunctions of the two original atoms?

How is this generalized to $\ce{MgF2}$ to explain a bond angle of 180 degrees (is this right?)? What about the crystal structure explained quantum mechanically?

Sorry if I ask too much in one shot.


texts: Find the displacement of mercury in a vertical tube

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So we have a 1m tube sealed at both ends. It is initially horizontally placed and the middle 0.1m contains mercury and the two ends contain air. Now the tube is turned vertical, we have to find the amount of mercury displaced.

Let the pressure in the upper end be $P_1$ and the pressure in the bottom end be $P_2$. The area of cross-section is $A$ and the lengths in the upper and bottom end are $(0.45-x)$ and $(0.45+x)$,respectively.Let $x$ be the mercury displacement.

By Boyle's Law
$$P_1V_1=P_2V_2$$
$$P_1A(0.45-x)=P_2A(0.45+x)$$
A single equation is insufficient to solve this, what should I do.


texts: Electrolysis of concentrated sodium chloride solution using A.C. power supply

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I heard that A.C current is never used for electrolysis as the polarity of the electrodes keep changing and this can result in explosive reactions. However, why can't we use this to our advantage?

When electrolysing brine, chloride ions are discharged at the anode to form chlorine gas and hydrogen ions are reduced at the cathode to form hydrogen gas. When using A.C., the polarity of each electrode would change several times every second (depending on the frequency of current), causing both hydrogen and chlorine to be produced at both electrodes. So in theory, a gas syringe could be set up at each electrode to collect the hydrogen and chlorine, which would then react to form HCl gas which can be collected.

What is wrong with this process? We are able to collect both HCl and NaOH, two very useful compounds. Why is this process not used industrially?


texts: Reduction potential for reduction of O2 to H2O2 in alkaline medium

texts: I've read that $\ce{H2O2}$ is a good reducing agent in alkaline medium and can reduce $\ce{Fe^3+}$ ions to $\ce{Fe^2+}$ in alkaline conditions. But I need to verify this using the standard reduction potential values (at 298 K) for $\ce{Fe^3+}$ to $\ce{Fe^2+}$ and $\ce{O2}$ to $\ce{H2O2}$(in basic conditions). But I haven't been able to find any reduction value for $\ce{O2}$ to $\ce{H2O2}$(in basic medium). Can someone provide me the data for this?


texts: Reaction of Metallic Tin with NH4Cl and treatment with Sulfur

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Metallic $\ce{Sn}$ is reacted with $\ce{NH_4Cl}$ and the resulting solution is treated with Sulfur.

What is the gaseous product?
What is the color of final precipitate?
The above resulting solution is added to $\ce{AuCl3}$, resulting in a purple    coloured solution. What is the composition of the solution?

I do realise the answer to (3) will be the purple of Cassius i.e colloidal gold in $\ce{Sn(OH)2}$ (as per Vogel's Qualitative Inorganic Analysis textbook fifth edition). But I can't figure out the answer to the first two questions (I tried Googling with no fruitful search).