texts: Sample: How to calculate mass of nanopaticles with given density and Vol %

texts:
I'm trying to calculate the wt% and the mass of the nanoparticles in a ferrofluid solution.

Attached is data from the supplier:

**EMG 605 Specifications and Physical Properties**
- Appearance:   Black-brown fluid
- Carrier Liquid:   Water
- Nominal Particle Diameter:    10 nm

- Saturation Magnetization (Ms): 220 Gauss or 22 mT (SI)
- Viscosity @27°C:  <5 cP or <5 mPa·s
- Density @25°C:    1.18 g/cc or 1.18x10^3 kg/m3 (SI)
- Initial Magnetic Susceptibility:  0.24    or 3.02 (SI)
- :Magnetic Particle Concentration  3.9 % vol.
- pH:   9-10
- Nature of Surfactant: Cationic


texts: Bond rotation energy comparison of aromatic compounds

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Which of the above compounds has a lower bond rotation energy?

Here is my progress: We basically need to find which compound has more single bond character. Now both compounds will break the double bond, and give the electron pair so as to make both cycles aromatic. But what do I do after that?


texts: Formation of methane using Kolbe's electrolysis reaction

texts:
I have read in my book that methane cannot be formed using Kolbe's reaction (mechanism — Organic Chemistry Portal). And honestly, I kinda think I get where they are coming from: that two radicals are required to get a hydrocarbon which can in the least be two methyl radicals (of course when substrate is sodium acetate) which can combine to give ethane.
Why can't we use a mixture of sodium formate and sodium acetate and expect some methane to be released? Why shouldn't it work?


texts: Why is H⁺ ion considered the source of acidity, and OH⁻ considered the source of basicity?

texts: As the title implies, what caused the association between $\ce{H+}$ and acidity, and between $\ce{OH-}$ and basicity?


texts:
I've just read this article about meta-materials with 0-refractive index, which potentially may "permit" light with super-luminous rate /under rate is meant the propagation of light's phase, which doesn't transmit information => there is no valuation of the laws of physics/.

Generally speaking, the refractive index of materials depends on the (dominant) molecular interactions within them, on their morphous structure, etc. As you know, these molecular properties govern lots of other chemical features like the viscosity, the density, to some extend the aggregate state, and so on... On this account, it should not come as a surprise that there exists a clear correlation between the refractive index and the properties, mentioned above - e.g. fluids of higher density tend to have higher refractive properties; same goes for viscosity; and so on... Based on those remarks one is able (at least) to guess how they can improve / worsen the refractive index of a given fluid - discussed for instance in this research on aerosols.

My question, though, is how does the refractive index of alloys, polymers, crystals, and solids in general relate to their other chemical properties?

Furthermore, is there a way at least to guess what materials one should potentially try to use in order to create / synthesize a meta-material, like the one from the article, that breaks the limits?


texts: Temperature measurement using thermometer

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I have two samples of water – 'A' and 'B'. My thermometer measured them to be 90 °C. They both have different volumes. So, the kinetic energy of the particles of sample A and B is same or different? Through this question, I want to ask whether temperature measurement results depend upon how many particles hit the bulb of my thermometer or it is independent of this? If it is independent of this, then how thermometer works?

Please provide me the simplest answer as I am in class 9 only.

As another example, let me consider a gas which has the density of 2 mol/22.4 L. Its temperature recorded by my thermometer is 60 °C. Then its density is reduced to about 10 atoms/22.4 litre. Now, its temperature is the same?


texts: The time scale of calculations in computational chemistry

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Is it possible to determine or get a range of the time required for a specific calculation with knowledge of the type (MM or QM), class (semi-empirical, ab initio or DFT), the degree of theory (MP, CI, etc.) and the basis set (STO-3G, 3-21G, 6-31G(d), etc.)
 used in the calculation and the computer ability (processor, RAM, etc.)?


texts:
I am getting confused about this the more problems I do on it. My understanding was that only strong acids and strong bases will react to produce water and a salt. Something like this:
Molecular Eq: $\ce{HCl(aq) + NaOH(aq) \rightarrow H2O(l) + NaCl}$
Net Ionic Eq: $\ce{H+(aq) +OH- (aq) \rightarrow H_2O(l)}$

Makes perfect sense, both the acid and base break apart and combine with each other. But then I ran across something like this:
Molecular Eq: $\ce{2 CH3CO2H (aq) + Ba(OH)2 (aq) → Ba(CH3CO2)2 (aq) + 2 H2O (l)}$
Net Ionic Eq: $\ce{2CH3CO2H (aq) + 2OH- (aq) → 2CH3CO2- (aq) + 2H2O (l)} $

The net ionic eq tells me that $\ce{CH3CO2H}$ will not break apart, but the molecular equation tells me that they will break apart and form a salt with $\ce{Ba}$.

I'm so confused by this. Why are they giving two opposing pieces of information? Am I missing something here?


texts: What will be the possible conditions to react bromo alkane with diethyl phenylmalonate?

texts:
How to react 1-bromopentane with diethyl phenylmalonate?
I used NaH (1.5eq) but the yield is less than 30%. I used KOH but yield is low. I used tBuOK and it did not work, I used K2CO3, but not working.
I tried it, K2CO3 2eq with 18-crown-6 and KI 0.1eq, in acetone but starting material is not consumed, almost only 30% has been finished after more than 72 hours and TLC shows a different spot, it does not look like desired product. Starting material is recovering when I use K2CO3, but not in case of NaH 1.5eq with DMF or THF but yield is less than 30%. Toluene with NaH under reflux condition is also behaving like K2CO3 and my next step is hydrolysis and decarboxylation.
I need guideline about what I am missing here.


texts:
When propene react with ICl , it gives an inoptically active compound ,why.

According to me there is chiral carbon so it should be optically active


texts: How can you explain the solubility of BeF2?

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I know that Be has a tendency to create bonds with an increase covalent character so I can tell that BeF2 is more covalent than let's say MgF2. So why is BeF2 soluble in water while MgF2 is barely soluble ? Shouldn't the ionic compound be more soluble ?
My guess is that the lattice enthalpy of BeF2 is not as great as the enthalpies of the other fluorides so it can be break down with much more ease and the energy gained from hydration outweighs the energy needed to separate the ions.


texts: Finding identities of diatomics from Spectroscopy and Mass Spec Data

texts:
Let's say I have a sample of 2 (assumingly different) diatomics A and B.

Through spectroscopy I found the data below:

For molecule A:
$$\begin{align}
B&\approx2.17690\ \mathrm{cm^{−1}}\\
D&\approx4.79000\times10^{-5}\ \mathrm{cm^{−1}}\\
I&=1.28590\times10^{-46}\ \mathrm{kg\ m^2}\\
\tilde ν_e&=928.15\ \mathrm{cm^{−1}}
\end{align}$$

For molecule B:

$$\begin{align}
B&\approx1.51695\ \mathrm{cm^{−1}}\\
D&\approx7.1049\times10^{-6}\ \mathrm{cm^{−1}}\\
I&=1.84533\times10^{-46}\ \mathrm{kg\ m^2}\\
\tilde ν_e&=1401.86\ \mathrm{cm^{−1}}
\end{align}$$

Through Mass Spec, I found 2 strong spectral lines at $30.0077086\ \mathrm{g\ mol^{-1}}$ and $41.9766928\ \mathrm{g\ mol^{-1}}$. How do I deduce which is which and further, how do I determine the bond length. [FYI, I'm thinking the former mass is the molecule NO and the latter NaF just by guessing]

I'm thinking that the heavier molecule will have the larger inertia value. And from the inertia equation $I=\mu R^2$ I'll derive the bond length $R$. but how do I find the $\mu$ from the actually mass of the molecule from the mass spec data?


texts:
Is there a quick way to determine if a salt (or ionic compound in general) crystal should be birefringent from its formula without having to know/look up the crystal structure?  When I'm looking for protein crystals, if I know the condition has a lot of salt in it, but it shouldn't be birefringent (e.g. NaCl), it's a hint that birefringent crystals I do see might be protein.

Is the only non-birefringent crystal type (e.g. not glasses) cubic?  Does it matter if it's primitive, face-centered, or body-centered?

Back to looking for a generalization, are most (all?) salts with polyatomic ions birefringent?    All +1/-1 (NaCl, KBr, etc...) aren't?


texts: If I prepare the silver nitrate solution or any other solution, how can I know the shelf life of this solution? I know that it depends on the stability of the substance, but maybe there is some document which give information and is interesning how realy it was found.


texts: Are the electrons also distributed for the alpha decay?

texts:
Consider this reaction of alpha decay:

$$ \ce{^{222}_{88}Ra -> ^{218}_{86}Rn + ^4_2 He} $$

My question is, whether or not the electrons also get distributed in the reaction like the nucleons?


texts: ML6 Type Coordinate Complexes - Drawing a Molecular Energy Orbital Diagram

texts: In class we recently discussed how to draw out molecular orbital energy diagrams for compounds such as NH3 (ammonia). Building upon this, we touched on how to construct a molecular energy diagram for ML6 type coordinate complexes, namely [Cr[NH3]6)3+. I am confused as to where to begin our diagram formation. All I know right now is that we consider that NH3 coordinates to Cr through it's a1 HOMO. I don't know how to proceed beyond this.


texts: Hypervalency in elements in the second period

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In my experience, most texts that address hypervalency say that it only occurs from elements in the 3rd period and onwards. This explains the occurrence of $\ce{Cl2O7}$ or chlorine heptoxide. However, some 2nd period nonmetals like $\ce{C}$ and $\ce{O}$ show hypervalency.

Examples:

$\ce{CH5}$ - This is unlikely to occur but it does sometimes happen that carbon bonds to 5 atoms instead of 4.
$\ce{H3O+}$ - Here oxygen is hypervalent.

How is it possible for carbon and oxygen to each have 9 electrons if each orbital only holds 2 electrons? Do they switch between electrons or something?


texts: clarification on background limits in electrochemistry

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I’m teaching myself electrochemistry, and this question is from the general introduction of the book I’m using. According to Bard’s Electrochemical Methods book, in a given cell, the background limits ‘are the potentials where the cathodic and anodic currents start to flow at a working electrode when it is immersed in a solution containing only an electrolyte added to decrease the solution resistance (a supporting electrolyte).’ I don’t fully understand the significance of the italicized, but my main question comes from the following figure, which shows that the onset of H+ reduction and Br- oxidation (Where the background limits are) occur at different potentials. This is counter-intuitive for me, since, according to introductory electrochemistry from gen chem courses, one half of a reaction cannot occur without the other for a given applied potential.

How can this occur?


texts:
Diisobutylaluminium hydride(DIBAL-H) reduces only carboxylic acid, ester or both?

The answer given was that it only reduces ester.

Is it correct that under any condition carboxylic acids are not reduced by DIBAL-H?


texts: Standard Reduction Potentials and Electropositivity

texts: I was looking through a table of standard reduction potentials and the trend seemed like it correlated with electropositivity. Is it reasonable to qualitatively compare two metals to see which has a higher standard reduction potential based on electropositivity? If not, why is this unreasonable?


texts:
I work with modeling a number of aqueous solutions, but mostly it boils down to single-component saline solutions. The industry standard for determining various saline solution quantities such as conductivity, activity, and density as a function of salinity and temperature is OLI.

OLI also provides capabilities that are way over the top for what I'm looking for (e.g. corrosion, scaling), and I'm wondering if an alternative exists that is less capable and hopefully less costly.

I have experience with writing and compiling software, so user-friendliness is not that important for me.


texts:
$\ce{CH3-CH(F)-CH2-CH2-CH(C2H5)-CH2-CH3}$

Will the correct IUPAC name be 3-ethyl 6-fluoro heptane or 5-ethyl 2-fluoro heptane?


texts: Why is 2-pyridone so much more acidic than a regular amide?

texts: I am comparing the structures of 2-pyridone and a regular (cyclic) amide-what is the main factor contributing to the increased acidity of 2-pyridone compared to a normal amide. For pyridone, I thought the proton was orthogonal to the pi-system, so no delocalisation of the negative charge could take place, so I am confused how it is more acidic?


texts:
I guess you are all familiar with the oxidative addition or reductive elimination reaction in organometallic chemistry. If you read further into the topic you may find different pathways like via radicals, nucleophilic substitution, ionic paths or even the famous concerted mechanism.

In general we get a σ-type donation from the, let's take dihydrogen as the approaching ligand, hydrogen's occupied bonding orbital into an empty metal-centered orbital. Some sources say it's a p-orbital but I think the energy gap would be a bit too large so the $\ce{d_{z²}}$-orbital seems a bit more likely to me. On the other hand we get a back-donation from the occupied metal d-orbitals into the σ* of the H-H molecule.

Now while this may be likely for something as symmetric as hydrogen I still have my doubts about this. Firstly the question remains for all reactions if something is really concerted or if two electrons are ever donated at once or if there is a very fast cascade of two single-electron transfers. And related to this, can this actually happen the way it is graphically shown in literature or is the orbital overlap simply too poor for a good transition? You may also ask this for the Dewar-Chatt-Duncanson model or any other insertion reaction. As the metal d-orbitals approach from an angle the overall overlap should be lower than in a head-on σ-type bond. And I think there are already papers, where for the alkene case a pre-coordination via a hydrogen is proposed:

I remember that my professor used to mention a so called 'slip-mechanism' but I cannot find anything related to that. If I remember correctly it was just about this topic. As the overlap is quite poor it seems more likely that the addition process is carried out in two fast single-electron transfer steps where you have a 'slipping' towards one side followed by a slipping towards the other side.

I tried to draw it in chemdraw. This is of course too much but it shows what I mean by 'slipping'. Imagine there is still a weak connection between the orbitals even though it slips to the other side much like in π-bonds (pink dashed lines) but at the moment where the electron is actually transfered it slightly slips and twists to increase the orbital overlap

Has anyone heared about something like that before? That the mechanism may not be a 100% concerted but actually two very fast single electron transfers?


texts: Is there any difference between medical and cleaning ozone?

texts: What are the main differences between medical ozone (auto-hemotherapy, …) and cleaning ozone (for example, the kitchen cleaning devices for vegetables and food). I noticed that they can produce a lower amount of ozone per hour while the medical ones have bigger amount of production.


texts:
Could you use the Wittig reagent to attack a metal–oxo bond and replace the oxygen with a carbene?
Specifically, is it possible for the Wittig reagent to do σ-bond metathesis with an electrophilic metal attached to an oxygen?
As I'm trying to understand the mechanism, I would really appreciate an explanation for why or why not along with the answer.


texts: Reviving a 6 Volt lead-sulfuric acid battery

texts: I have a 6 Volt sulfuric acid battery used to power a golf cart that has all the acid drained out, and the usual solution was to add more water to the battery however I am afraid that would not work this time since there is no acid left. Could I solve it by adding more acid from other batteries? or do I need to be accurate in the amount of acid added? or could I just solve it by adding water? If you could also give me an explanation as to how these batteries work and why adding water has any benefit I would appreciate it.


texts: How to dock aggregated structures comprised of "elementary" protein units like LEGO pieces?

texts:
There are proteins with intrinsic symmetries. For example:

I was wondering how to use transformations such as: rotations, translation, replications to construct possible structures using 2 types of proteins.

Assume I found a binding site of the 2 proteins using Molecular Dynamics simulators.

For example the above one and this one:

Can I use group theory way to find possible configurations of the 2 proteins?
How can I use the tensor product of the symmetry groups ($G_1 \times G_2$) to find possible structures?
What graphic/framework would you recommend do perform all the manipulations on the proteins?
Is it possible to use the transfer to create some algebraic structure that will help to construct a mechanical configurations comprised of proteins?
Is there any tool from Baker's Lab I can use for this task?
Amy recommendation for a tool I could use to replicate, rotate and shift structure would be appreciated us well.

TL;DR:

My goal is to use group theory or Monte Carlo simulation driven by group theory insight to create macro molecular structures using multiple (dozens) instances of the two proteins (the LEGO building blocks).
Any idea that relates symmetry, transformations, group theory to create structures is much welcome.

Clarification:

Given a binding point between 2 proteins, which software can I use to create the dimers into macro-structures like in LEGO namely only by replicating, translating and rotating the Lego pieces?


texts: Is bonds in CO is all 3 coordinate bonds or 2 covalent and 1 coordinate bonds?

texts: Below image is as available in India's Class 11 NCERT Chemistry book vol 1 Page 104. I am confused as it states all 3 bonds are kind of coordinate bonds. Should it not start with 2 covalent bonds and 3rd as coordinate bond from oxygen to satisfy carbon? There are several sites confirming my expectation. This book is in a place to force students to study and repeat in exams to get marks. So wondering does it get this right? or teaching wrong?


texts: Why is temperature constant when an ideal gas expands into a vacuum?

texts:
An ideal gas in a box has pressure $p$ and temperature $T$. This box is kept in a vacuum, within a large container.

When the box is punctured, what happens to the temperature of the gas as it expands to fill the entire container?

I was taught that the temperature will remain constant. How is this possible? I understand that the pressure $p$ will decrease and the volume $V$ will increase, but for the temperature $T$ to remain constant, the decrease in $p$ must exactly counterbalance the increase in $V$. Is this the case?


texts: How can I know if the reagent I have will act as a( base) and attack a H or act as a (nucleophile) and attack a C atom?...is there any rules or something?


texts: I am currently in the process of studying enzyme catalysis and am struggling to get to grips with this concept. As far as I understand, the propinquity effect allows substrates to bind with enzymes in the conformation which would facilitate the reaction, thus increasing the reaction rate. Could someone expand on the why and/or how enzymes are able to do this? What specific reactions benefit from this the most?


texts: Minimizing Gibbs Free Energy for Multiphase Equalibria

texts:
I'm a geologist and don't have a strong background in chemistry or thermodynamics.  Any help on solving this problem is much appreciated.
I'm trying to minimize Gibbs free energy to get initial estimates of Henry Coefficients ($K_i$) for a flash calculation.
Several publications presented the equation for Gibbs free energy for multiphase systems as the equation in the photo below.  My question is relatively straight forward: how do I calculate the chemical potential of each component (methane, ethane, propane, water) as a function of temperature?

Also, I have Matlab scripts to calculate fugacity. However, it calculates a fugacity for each phase (gas and liquid). I'm not sure how to calculate the reference fugacity of each component while knowing that part of each component is in two phases?

From there, I can use simulated annealing in MATLAB for cycle through potential compositions to evaluate the minimum.

$n_i$ = mols of component $i$

$\mu_{i0}$ = chemical potential of reference state

$f_{i0}$ = fugacity of the reference state

$f_{ij}$ = fugacity of component $i$ in phase $j$

$n_{ij}$ = moles of component $i$ in phase $j$


texts: How are turbostratic graphite phases formed?

texts: Turbostratic graphite is graphite in which there is quenched rotational disalignment between adjacent graphene sheets, i.e. one sheet is rotated with respect to its neighbor. I suppose this could be considered a crystallographic defect of sorts. How do these turbostratic layers form, and can they possess long range order, such as glide or helical symmetry (e.g. similar to a twisted nematic phase)?


texts: Order of positive mesomeric effect of halides

texts:
I learned that the order of $+M$ effect (mesomeric effect) for halogens is as follows: $\ce{F} > \ce{Cl} > \ce{Br} > \ce I$.

I wonder why this is so?


texts:
I have a doubt about decomposition of alkali metals.
Why does $\ce{LiNO3}$ decompose to give $\ce{Li2O}$ and $\ce{NO2}$ where as other alkali metals decompose to give corresponding nitrite and oxygen?


texts: Is there a way to turn alcohol into a solid gel?

texts:
I'm wondering if there is a way to turn alcohol or another bacteria killing substance into a solid gel form, sort of like the gel you can use to clean a keyboard.

  Source: Aliexpress.com Computer Cleaning Compound

I'm wondering if you could put either alcohol or other sanitizer into this sort of gel, without the sanitizer having a "best before" date.

I'm a complete beginner when it comes to chemistry so forgive me if there's an obvious reason why this wouldn't work. If it does work, or partially, could you give me a run down on what I would need or need to test to achieve my goal?


texts: why do I get chlorine gas production during electroetching?

texts:
I was electroetching stainless steel plates with table salt as electrolyte and the power supply was providing 5V, 6A when I placed the anode and cathode about .25 inches apart. I started smelling a swimming pool chlorine smell and when I pulled out the anode, it had a yellow film on it which smelled strongly of chlorine also, which I am guessing is some sort of chlorine precipitate. I thought that distinct smell came from chloramines though, not a chlorine gas, so I don't know exactly what compound I was smelling.

However when I returned the plates to .5 inches apart and heated the solution from about 15C to 35C, I was drawing 5V, 8A since the heat allows the reaction to happen more vigorously. However, I no longer smelled any chlorine even though there was a higher power consumption. What is going on here? Clearly the distance between the two plates affects this, but can someone give a chemical explanation as to why?


texts:
I recently purchased a used set of lens for my telescope. They came in a nice aluminum case with foam inserts, but the foam has an odor. I am currently using just the sun to try to rid the foam of the musty odor. It's slow going. I was wondering if there would be any adverse interaction if I sprayed the ester foam inserts with isopropyl alcohol? I am hesitant to spray anything on the foam for odor removal, for fear any lingering residue may harm the lenses in the long term.

The foam looks like a gray ester poly foam. Bottom is solid, top is convoluted.

Thank you.


texts:
How many geometrical isomers will exist for compound of this type which has cycloalkene having carbon atoms greater or equal to 8 in the middle of chain?

I know that due to ring in middle of chain geometrical isomerism exist and also due to cycloalkene having carbon atoms greater or equal to 8. But I am confused in a case when a  cycloalkene exist in middle of the chain. Whether we will consider geometrical isomers due to cycloalkene or due to both, i.e. the ring and also due to cycloalkene case?


texts:
As part of a simulation I am developing I have an acid in aqueous solution represented as a concentration field of mass density (units g/L) at various points in space (denoted $[S]$). I want to calculate the pH of the solution. I am attempting to use the method for weak acids outlined here, but am struggling with the dimensionality of the variables,

$$[H]^2 + K_a [H] - K_a C_a = 0.$$

Looking at the quadratic equation, and knowing that $K_a$ has no units, it implies that $[H]$ and $C_a$ are also dimensionless. Does this mean that $[H]$ is in fact the activity of the the solution, and not the $H^+$ concentration? And is the relationship between $C_a$ and $[S]$ $$C_a = \gamma \frac{[S]}{M(S)c^\ominus},$$

where $\gamma$ is the activity coefficient, $M(S)$ is the molar mass of the acid, and $c^\ominus = 1$M is the standard amount concentration?

Followup question:

The solution to the quadratic equation is

$$[H] = \frac{-K_a \pm \sqrt{K_a^2 + 4K_a C_a}}{2},$$

thus $[S] = 0 \implies [H] = \frac{-K_a \pm K_a}{2} = -K_a$ or $0$.

As $pH = -\log_{10}\left([H]\right)$ and $K_a > 0$  there is no real solution, but logic would dictate that $pH = 7$ in this case. Where am I going wrong?


texts:
In GAMESS, a calculation of optimisation gives data about partial atomic charges (like Mulliken or Lowdin charges). Can you please let me know how to calculate the other types of partial atomic charges (like Hirshfeld, Maslen or Politzer charges)?

FYI: I have used B3LYP and MP2 for optimization.


texts:
I need to know what a redox reaction is. How could a redox reaction possibly be identified? Also, I have a confusion whether,

$$\ce{H -> H+  +  e-}$$
$$\ce{e- + Cl -> Cl-}$$
$$\ce{H + Cl -> HCl}$$

is a redox reaction.
Furthermore, could anyone please tell me if ionization and reduction and gaining electron and oxidation are referring to the same phenomena?


texts: Which equilibrium constant is appropriate to use?

texts:
I have learnt that the standard free energy change is related to the equilibrium constant of a reaction by,
$$\Delta G^\circ = -RT \ln K$$

Here, does $K$ refer to $K_p$ or $K_c$?

Also, please give me the derivation of this formula.

On the net, I saw that we can use either $K_p$ or $K_c$. But doesn't that give two different free energy values?

Moreover, if the formula was derived for gaseous reactions (using $K_p$), how can we just extend this to other reactions saying that we can use $K_c$ as well?


texts: On mathematics behind molecular orbital energies

texts:
When explaining the mathematics behind calculating molecular orbital energy , namely HOMO and LUMO energies, using quantum chemistry, Chainer Chemistry documentation states that

  From mathematical viewpoint it requires a solution of an internal
  eigenvalue problem for a Hamiltonian matrix.

I have never heard of internal eigenvalue problem in mathematics. Is this a term specific to quantum chemistry and what it means?
Is the Hamiltonian matrix same as Kohn-Sham Hamiltonian?


texts: Arrange in order increasing reactivity towards nucleophilic substitution

texts:
Arrange the following compounds in order of increasing reactivity towards SN2 reaction

According to me, the order should be P>Q>S>R as more hindrance should result in lesser reactivity but answer given in the book is P>R>Q>S. Why is the reactivity of R greater than that of Q and S even though the leaving group is on a $2^\circ$ carbon.


texts:
Why do we use oxidizing and reducing flame in different analytical tests?

For example, in the charcoal block reduction test, we use reducing flame. Why? How does this affect the salt to be reduced into metal?


texts: When does a reaction equation require the reversible sign and when does it not?

texts: Sometimes my professor puts the $\to$ symbol and sometimes he uses $\leftrightharpoons$. How do I know which to use? I get that one means the reaction only heads one way while the other means that the reaction holds at an "equilibrium" where the reactants are converting into products and the products are converting into reactants. But if I'm only given a word problem that lists 2 reactants and their concentrations, how do I know which to use?


texts: Why do different substances have different boiling points?

texts:
For example, why does for example oxygen turn into gas at a much lower temperature than water?

Does it have anything to do with the molecular structure? A water molecule does have a more complex structure than oxygen, though the R-410A (a mixture of two gases commonly used in heating pumps) is much more complex than water, and it boils at -48.5 degrees Celsius.


texts: What are modern approaches to describe and/or quantify aromaticity?

texts:
I know that Schleyer described an approach for evaluating aromaticity using nucleus-independent chemical shifts (NICS, see e.g. Chem. Rev. 2005, 105 (10), 3842–3888) quite some time back. I also somehow have the feeling that there should be a more direct way to describe aromaticity than via chemical shifts.

What are modern approaches to describe/quantify aromaticity? Could anyone point out some links/references on recent developments in the field?


texts: Determine formula of hydrocarbon from combustion data

texts:
Source: Oct/Nov 2015 Paper 33 IGCSE Chemistry exam (discounted during marking)
Can someone explain how to find the answer for the last part of the question?
Note: I got the answer pentane with 5 carbon atoms. Is it the correct answer?

Hydrocarbons burn in excess oxygen to form carbon dioxide and water. $\pu{20cm^3}$ of a gaseous hydrocarbon burned in an excess of oxygen ($\pu{200cm^3}$). After cooling, the volume of the residual gas at r.t.p. was $\pu{150{cm}^3}$, $\pu{50{cm}^3}$ of which was x=oxygen.
(i) Determine the volume of the oxygen used. [1]
(ii) Determine the volume of the carbon dioxide formed. [1]
(iii) If the hydrocarbon was an alkane, deduce a formula of the hydrocarbon.


texts: Why does hydration of alkene takes place in presence of an acid such as H3PO4 or H2SO4?

texts: Why acid is used? Can’t the hydration be done without acid? If not, why?


texts: How can I calculate the amount of HF in aquoues solution of NH4F and an aquoues solution of NH4HF2?

texts:
Dissociation of $\ce{NH4F}$ and $\ce{NH4HF2}$ in water is complete, I assume:
$$\ce{NH4F -> NH4+ + F-}$$
and
$$\ce{NH4HF2 -> NH4+ + HF2-}$$

Can I calculate the amount of $\ce{HF}$ in these solutions from this equilibrium?

$$\ce{HF + F- <=> HF2-}$$

$$\mathrm{K_2}=\dfrac{\ce{[HF^{2-}]}}{\ce{[HF][F^-]}}=4,7$$

If I know the concentrations of NH4F in water and NH4HF2 in water.


texts: I have 'sodium bicarbonate' powder , which is supposed to be (NaHCO3) , is there a way for me to do a test on it at home , without some special equipment and determine whatever its 100% pure or it has some additives?


texts:
If -2 is a oxidation number and 2- is the charge, then what is - by itself, is it a oxidation number or charge? As in $\ce{Ag+}$.

Also do you see $\ce{Cu + 2Ag+ -> Cu^{2+} + 2Ag}$ as a redox reaction?

Because I don't see any increase or increase in the oxidation number of any element in this equation. All I see is charges


texts: Why does the reaction between 2‐methylbut‐3‐en‐2‐ol and hydrogen bromide show allylic shift?

texts:
In the following reaction

shouldn't the minor product be the major one as the carbocation formed before attachment of bromine is 3°? Also, can someone tell me why the product includes only nucleophilic substitution as there is no other condition mentioned to judge whether it should show elimination or substitution.

Please mention if what favours allylic shift in such type of reactions.


texts: Why is tetraamminecopper(II) a square planar and not a tetrahedral species?

texts: In $\ce{[Cu(NH3)4]^2+}$, the $\ce{Cu^2+}$ ion has 9 electrons in the $\mathrm{3d}$ orbital with only one unpaired electron. How is it a square planar geometry? Where is that unpaired electron going?


texts: How to make approximation of rotational partition function of diatomic linear molecules?

texts:
Using the rigid rotor approximation to the level energies, and such other appropriate assumptions, we can approximate rotational partition function, $Q_{\mathrm{rot}}$, of linear molecules as follows:
\begin{eqnarray}
  Q_{\mathrm{rot}} & = & \sum_{J=0}^{\infty}{(2J+1)\exp\left(-\frac{E_J}{kT}\right)}\\
  & \simeq & \sum_{J=0}^{\infty}{(2J+1)\exp\left(-\frac{hB_0J(J+1)}{kT}\right)} \\
\end{eqnarray}
In the book, Microwave Molecular Spectra (Gordy & Cook, 1984), Chapter 3, Equation 3.64, the authors made approximation as:
$$Q_{rot}\simeq\frac{kT}{hB_0}+\frac{1}{3}+\frac{1}{15}\left(\frac{hB_0}{kT}\right)+\frac{4}{315}\left(\frac{hB_0}{kT}\right)^2$$
Also, there is another approximation made by McDowell, R. S. 1988, Journal of Chemical Physics, 88, 356:
$$Q_{rot}\simeq\frac{kT}{hB_0}\exp\left(\frac{hB_0}{3kT}\right)$$

And we can see from the picture that $Q_{\mathrm{rot}}\simeq\frac{kT}{hB_0}+\frac{1}{3}$ is also a good approximation. Then I can guess how to derive McDowell's approximation, but I cannot derive Gordy & Cook's approximation.

What I have got are as follows:

Since $$n\exp(-x(n+1)n)+\int_{(n+1)n}^{(m+1)m}{\exp(-xy)}\,\mathrm dy+(m+1)\exp(-x(m+1)m) \\
\leq\sum_{J=n}^{m}{(2J+1)\exp(-x(J+1)J)} \\
\leq\sum_{i=n^2}^{m^2+2m}{\exp(-xi)}$$ hence, $$\int_{0}^{\infty}{\exp(-xy)}\,\mathrm dy=\frac{1}{x} \\
\leq\sum_{J=0}^{\infty}{(2J+1)\exp(-x(J+1)J)} \\
\leq\sum_{i=0}^{\infty}{\exp(-xi)}=\frac{1}{1-\exp(-x)}$$

i.e., $$\frac{kT}{hB_0}<Q_{\mathrm{rot}}<\frac{1}{1-\exp\left(-\frac{hB_0}{kT}\right)}$$

While the latter one approximates $\frac{1}{1-\exp\left(-\frac{hB_0}{kT}\right)}\approx \frac{kT}{hB_0}+\frac{1}{2}+\frac{1}{12}\frac{hB_0}{kT}-\frac{1}{720}\left(\frac{hB_0}{kT}\right)^3$ when $T$ is rather high.

Is there anyone knowing how to derive Gordy & Cook's approximation? Please tell me and I appreciate it very much.

Besides, another little question, are such approximations still useful as nowadays computers are greatly powerful?


texts: Why objects usually don't exibit fluorescence/phosphorescence?

texts:
We learn in school that the color we perceive is determined by the light that is reflected back at us. Not all wavelengths of light reflect back at our eyes, some wavelengths are absorbed.

I'm confused about this absorption. From my understanding, molecules can absorb light typically rotationally, vibrationally, and electronically. rotationally and vibrationally are associated with the microwave and infrared region. Electronic excitations can be in the visible, but I always had the impression that the excited electrons would collapse down to the ground state and emit light. Thus, I don't think I know any mechanism which visible light can be absorbed without emitting light, albeit, longer wavelength light typically.


texts: Experimental difficulty with the iodine clock reaction

texts: I did the iodine clock reaction using sodium metabisulfite and potassium iodate. As I understand it, increasing concentration is supposed to speed up your reaction rate. I did 10 trials. The first 5 I varied the concentration of metabisulfite and kept the iodate constant. Trials 6-10 I varied the potassium iodate and kept the meta constant. I don't understand why as I increased concentration, the reaction rate became slower? For example in trial 6 I had 2 ml of sodium metabisulfite and 4 ml of potassium iodate, that only took 7 seconds. In trial 10 I had 2 ml of meta and 10 ml of potassium iodate and that took 17 seconds? Does anyone know what I did wrong? Increasing concentrations should have increased collisions and made the rate faster, but it did the opposite! Please help me figure out why things went wrong!


texts:
Here the central chlorine atom is best described as $\ce{sp^3}$ hybridized. This makes sense; the molecule is pyramidal. Also, due to the molecule's pyramidal geometry, this rules out the possibility of effective resonance due to less overlap between the  $\ce{sp^3}$ lobes, which are angled, as opposed to the parallel pi lobes.

This explains quite well the difference in acidity between nitric acid and chloric acid; nitric acid is stronger than chloric acid. At first it seems difficult to differentiate between the acidities of both; the nitrate anion also has three peripheral oxygen atoms, which provide a similar (negative) inductive effect by delocalizing electron density.

With regard to electronegativity, the chlorate anion seems like it should be more slightly stable than the nitrate anion, implying that chloric acid is stronger than nitric acid; chlorine is more electronegative than nitrogen (if only slightly so - difference is 0.12 on the Pauling scale).

Oxidation state analysis suggests that the two should be similar in acidity; both the chlorine and the nitrogen have oxidation states of +5.

So it seems that the best rationalization of why nitric acid is stronger than chloric acid is the "better" (overlapping pi orbitals) resonance form of the nitrate anion.

With respect to the above rationalization,

1) How, exactly, do parallel pi orbitals enable "better" resonance? I get the principle of maximum overlap. If I had to guess, I would say that more overlap enables greater distribution of electrons among the relevant orbitals ... is there a more concise and scientific way of putting this? Is this even correct?

2) Are parallel pi orbitals necessary for resonance? I got the impression it is from organic class. Or are parallel pi orbitals only necessary for a special form of resonance - conjugation? Is the picture on the bottom referring to conjugation?

3) Are there any other ways to rationalize the difference in strength between these two acids?


texts: Calculate the mole fraction of component B in this solution? (partial pressures)

texts:
The vapour pressure of a pure liquid solvent A is $\pu{0.80atm}$. When a non volatile substance B is dissolved in the solvent, its vapour pressure drops to $\pu{0.60atm}$. Calculate the mole fraction of component B in this solution.

All I can think of is that $P_A=x_A * P_A^*$, which is Raoult's Law. But I don't know how to apply it.


texts:
In one of my projects (which is about alpha-voltaic cells, don't worry, I know that thorium isn't a strong alpha source, it's only for measurements) I would need to get water soluble thorium compound from a small sample of thorium dioxide  for purification with selective reactions and further measurements. Would any mineral acid work? I found some sources and publications on the internet by google searching but the biggest amount of information I could get is that

  "...Several hot acids can solve it..."

Which is not nearly as accurate as I would need it because I don't want to spend the budget of the project on expensive acids which doesn't even work instead of better equipments. (Their price is from their necessary purity)


texts: How do you make sense of acid base reactions in organic chemistry?

texts:
My question is in regards to acid base reaction that take place in larger chemical reaction in orgo. Like, I understand acid base reaction, how to qualitatively check which is stronger acid or base or where equilibrium lies, very well. But i feel that when I am trying to study the mechanism of series of other reaction like grignard mechanism, oxidation of alcohol, reaction with aldehydes etc… I see many intermediate acid base reaction in these mechanism that don’t make sense in terms of what I learned earlier when I was exclusively studying acid base reaction.

For instance, I have seen many intermediate acid base reaction in larger reaction where an oxygen atom of one molecule attack H atom attached to oxygen atom in another molecule. And then I am thinking what the point of this reaction because equilibrium is gonna be in middle and not favor products since the conjugate base create will be acid right away anyways.

Other times I have seen H20 act as an acid while molecule with sulfur atom act as a base. And again I am thinking how this is possible because isn’t sulfur a stronger acid then water. When I  asked two of my teacher about this. One of them said she actually made a mistake. But the main professor actually said that she is correct and to explain this, she said that water would even be hydronium ion here and when there is lot of water around, this water can serve as acid. However I couldn't fully understand what she meant by that? Can anyone please explain what she meant by this or how these acid base reaction possible. I have attached picture of what I am mean below to explain it my problem more clearly.


texts:
Heat liberated by a given amount of an ideal gas is $\pu{1200 cal}$ at $\pu{300K}$. What is the Gibbs free energy change for the gas in this process?

My attempt: I know that for a reversible process the net Gibbs energy change of the system + surrounding will be zero. But I have no idea how to calculate the Gibbs energy change of the system alone. The only equation I know involving Gibbs energy is $ΔG=ΔH-TΔS$, but this equation will give me the net Gibbs energy change and not the change in free energy of the system alone.


texts: How to write down the composition of eluent mixtures for TLC

texts: I obtained some Rf values via TLC by adding two or three drops methanolic triethylamine to an eluent mixture of let's say DCM/MeOH = 9:1. I couldn't find an example of how a mixture like that is written down in short in publications. I think that calculating the absolute content of dissolved ammonia wouldn't be suitable.


texts: Can ingredients in Tiger Balm cause any harmful effects on PVC figures?

texts: My roommate often uses Tiger Balm and sometimes browses through my collection of vintage Star Wars figures. Can the residue on his fingers cause harm to the PVC figures or cause the paint to crack or chip?


texts: Copper (II) chloride reduction with Hydrogen gas

texts:
I've been looking into making pure copper (I) chloride, but using ascorbic acid is relatively expensive for me. I'd also like to avoid having water in any part of the synthesis to minimize the contamination with copper (II) chloride. Therefore, I came up with the idea of doing the synthesis in ethanol and bubbling through H2 according to the reaction

$$\ce{2 CuCl2 (aq) + H2 (g) -> 2 CuCl (s) + 2 HCl (g)}$$

So my main question is: could this work?


texts: Can molecule have just h-bonds between its parts

texts:
I'm just starting to study chemistry so sorry for the probably obvious question to you, guys.
According to the definition of molecule in Wikipedia:

A molecule is an electrically neutral group of two or more atoms held
together by chemical bonds.

According to that definition, I assume that parts of the molecule could be theoretically connected just with the h-bonds. As far as I understand the example of that case is DNA two strands of which are connected by only h-bonds (though many and many ones).
According to Khan Academy:

When atoms combine by forming covalent bonds, the resulting collection of atoms is called a molecule.

And now, as a newbie, I'm a little bit confused with all of that. So, could you help me with the following questions:

Is that true that two strands of DNA do not have covalent bonds to each other and connected only with h-bonds?
If the p. 1 is true could parts of molecule be connected only by h-bonds by definition?
If the p. 3 is true then why DNA is a molecule but two water compounds (H2-O***H-O-H) are not?


texts: What is the n factor of h2o2 undergoing disproportionation reaction liberating oxygen

texts:
There is a lot of confusion about the n-factor of hydrogen peroxide in its disproportionation into water and oxygen.
$$\ce{2H2O2 ->  2H2O + O2}$$
Some sources(1,2) say n-factor of $\ce{H2O2}$ is 2
and other say n-factor of $\ce{H2O2}$ is 1 for this reaction.
Actually my main problem is "the relationship between normality and volume strength of $\ce{H2O2}$". According to my respected teacher:
$$\pu{Normality = \frac{Volume~strength}{5.6}}$$
and
$$\pu{Molarity = \frac{Volume~strength}{11.2}}$$
implying that n-factor of $\ce{H2O2}$ is 2 but I am calculating n-factor of $\ce{H2O2}$ as 1 because the definition of n-factor is "the no of electron gained  or lost per mole".
As we can see 2 electrons are participating in this reaction                            so electron exchanged per mole is 1 which is equal to n-factor. Please clarify.
Sources

https://socratic.org/questions/what-is-equivalent-weight-of-h2o2-in-decomposition-reaction#629354
https://www.meritnation.com/ask-answer/question/what-is-the-n-factor-of-h2o2-and-o2-in-the-reaction-h2o2-h2o/some-basic-concepts-of-chemistry/8526405


texts: pH of rain with and without thunderstorm

texts:
I just came to know that pH of rain water will be lesser when it is accompanied by a thunderstorm than when it is not accompanied by thunderstorm.
Why would it be so?
Will the temperature increase due to excessive friction (of air) and lighting and thus more ions of water will dissociate reducing the pH?
Or will it be because of production of acids in air during thunderstorm?
Help.


texts: Potential term in the hydrogen atom Hamiltonian

texts:
Here is how I saw the Hamiltonian being written in one Quantum Mechanics book:

$$\hat{H} = -\frac{\hbar^2}{2m_\mathrm{e}r^2} \left[\frac{\partial}{\partial r}\left(r^2\frac{\partial}{\partial r}\right) + \frac{1}{\sin \theta}\frac{\partial}{\partial\theta}\left(\sin\theta \frac{\partial}{\partial \theta}\right) + \frac{1}{\sin^2\theta}\frac{\partial^2}{\partial \phi^2} \right] - \frac{e^2}{4\pi\varepsilon_0}\frac{1}{r}$$

Well, that's all very nice and complicated, but looking at the last term, and seeing the use of $r$ in there,

$$-\frac{e^2}{4\pi\varepsilon_0}\frac{1}{r}$$

creates a small doubt in me - what is this $r$ there?

In electrostatics, this was simply the distance between the two charged particles, and that would mean that this was the distance between the proton and the electron, but isn't the position of the electron non-deterministic? Shouldn't that thing be a probability distribution of the distance instead? And why isn't it squared?


texts: Reaction of ethylene glycol with acidified potassium permangnate

texts: One would expect the reaction of ethylene glycol with acidified potassium permangnate to result in oxidation of ethylene glycol to oxalic acid. But a Q&A guide book tells me it is oxidized to formic acid. Which is wrong: the book or my reasoning?


texts: Molecule where an sp3 chalcogen is connected to an sp2 atom

texts:
I am looking for a small molecule where an $\mathrm{sp^3}$ atom from Group 16 (O, S, Se,...) is connected to an $\mathrm{sp^2}$ or resonant atom of another column?

Background: The universal force field defines the above case in its torsion
rules and I would like to find an example/application of such a structure
to understand it better.

Thanks!


texts:
My question: could it be practical, on an industrial scale, to take a mixture of alkanes (mostly ethane,  propane, and butane) convert them to their alcohol forms, send them through a 300-mile pipe, and convert them back to their source alkanes? (They would not have to be handled as a mixture—they could be separated at the source and piped separately.)

I ask this because a company is building a pipeline through my area that is intended to carry alkanes in liquid form (under 1500 psi of pressure, so that they stay liquid). These are known in the industry as “natural gas liquids”.  It looks like this could be a very dangerous pipeline. An engineer friend suggested the alcohol conversion strategy. Even if it were a lot more expensive, it would be far less dangerous and that might justify the cost. Any thoughts?


texts: Calculate Gibbs energy of dinitrogen pentoxide using its vapor pressure and sublimation

texts:
I am having trouble with the following problem:

  Dinitrogen pentoxide, $\ce{N2O5}$, is a solid with a high vapor pressure. Its vapor pressure at $\pu{7.5 °C}$ is $\pu{100 mmHg}$, and the solid sublimes at a pressure of $\pu{1.00 atm}$ at $\pu{32.4 °C}$. What is the standard Gibbs energy change for the process $\ce{N2O5(s) → N2O5(g)}$ at $\pu{25 °C}$?

Okay so my attempt is to first use the Clapeyron equation to find $\Delta H$ for usage in the reversible process entropy formula. The Clapeyron equation is $$\ln\left(\frac{P_2}{P_1}\right) = \frac{-\Delta H}{R}\left(\frac{1}{T_2} - \frac{1}{T_1}\right)$$ Plugging everything in I got $\pu{50807.79 J}$.

Next I found the change in entropy in a reversible process:

$$\Delta S = \frac{\Delta H_\mathrm{vap}}{T_\mathrm{vap}}.$$

Now here is where I have a problem. I calculated the enthalpy of vapor pressure. So I would expect to use the temperature that corresponds to the enthalpy of vaporization. Problem is, the book lists this as the wrong answer. I got within a few significant figures when I used $T_\mathrm{sublimation}$.

I calculated the final answer by using

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

The corresponding values are plugged in. I am not sure if I even solved the problem correctly, but if I am, why is that temperature used?


texts: Calculate the molarity of Na+ ions in 20 mL of a .130 M solution of Na2Cr2O7?

texts: The answer is $\pu{0.260 M}$, but I keep getting $\pu{0.0052 M}$ because I thought the right way to do it was by multiplying $\pu{0.130 M}$ by $\pu{0.02 L}$, then multiplying by $2$ moles of $\ce{Na+}$. What would be the right way?


texts: Can two precipitates form in a precipitation reaction that starts with only two compounds in water?


texts: How can Iodine bond with 5 Fluorines in Iodine Pentafluoride?

texts: According to this lewis diagram, Iodine has 12 valence electrons? How is the possible? Only thing I can think of is that I'm mistaken in counting the covalent bonds as two valence electrons each. Do they only count as one in this scenario?


texts: Isopropyl alcohol still leaves evaporation residue after distillation

texts:
I just finished distilling two liters of IPA because evaporating 5 ml on a watch glass revealed it to contain quite a bit of dissolved impurities. However, it still leaves some residue, even though I used a 200 mm vigreux column.

All glassware was thoroughly cleaned beforehand. I do not get such issues with distilled acetone, for example.

What gives?


texts: How to know whether to add latent heat when calculating final temperature?

texts:
From the examples in my textbook, it is usually very easy to see whether you need to account for the latent heat when calculating the final temperature. For example, if you add 2 x 13 gram ice blocks to a 250 ml cup of water, it is obvious that the ice will melt, and you will have to account for the latent heat of fusion for the ice.

However, what if it isn’t so obvious whether one of the substances will undergo a phase change? For example, what if we added 15 grams if ice to 20 ml of oil? If the final temperature is below 0, then we don’t need to account for the latent heat for ice, otherwise we will have to. How do we determine whether the ice will experience a phase change, and more generally, how do we determine whether one of the substance will experience a phase change?


texts: What are the constraints on the two electron integral matrix?

texts: In semi-empirical methods, the two electron integral matrix is simplified and the entries are replaced by actual values instead of integrals to evaluate. However, while doing that, the variational principle does not seem to directly hold; in other words, you can put values in the two electron integral matrix that make the energy go down infinitely. To make the variational principle hold, what are the contraints that the constants you put in the two electron integral matrix obey?


texts: Heat Capacity temperature dependence and Gibbs energy

texts:
I got this problem in school as a tool to get ready for International Chemistry Olympiad, but I have some problems with this challenge.
So, the problem is to calculate as precise as possible the Gibbs free energy for $\ce{CaCO3}$ decomposition at 1200 K.

I know that $\mathrm{d}G=\mathrm{d}H-T\cdot\mathrm{d}S$.

But $\mathrm{d}S$ and $\mathrm{d}H$ are temperature dependant, so

$$\mathrm{d}H=\mathrm{d}H_0+\int_{T_0}^TC_p\mathrm{d}T=\mathrm{d}H_0+\mathrm{d}C_p\cdot\left(T-T_0\right)$$

and

$$\mathrm{d}S=\mathrm{d}S_0+\ln\left(T/T_0\right)\cdot\mathrm{d}C_p$$

But molar heat capacity at constant pressure is also temperature dependant, and the equation is

$C_p=a+b\cdot T+c/T^2$, where a, b, c coefficients for each compound at specific phase.

But the problem is with both solids, because this equation can not be used for them, because in 1200 K they are not gases and Einstein’s Quantum Mechanics and Debye models do not work, because Einstein’s approximates are maxed at $C_p\approx3R$, which is about 24.9, but $C_p$ at 298 K, 1 atm for both solids in tables are > 24.9.

Where is the problem? I would appreciate any possible lead to mistake/ correct answer.


texts: Suitability of liquid plastic resin for plumbing application

texts:
Which synthetic resins are suitable for fabrication of plumbing components e.g pipe sections?

I'm trying to find an easy way to mold/house/encase a custom designed data logger.
The water temperature ranges between 10 to 50 degrees C.

EDIT: I'm planning this for both indoor & out door use. Under direct sunlight.


texts: Finding theoretical mechanism of sodium thiosulphate and hydrochloric acid

texts:
In class we conducted an experiment where we timed reactions between sodium thiosulphate and hydrochloric acid. We kept the concentration of the $\ce{HCl}$ constant, while changing the concentrations of sodium thiosulphate.

We then graphed this data to discover there is a linear relationship between the concentration of thiosulphate and 1/time, indicating the it is a first order reaction. This means in the rate determining step there will be one thiosulphate ion.

In the analysis question it asks you to come up with a theoretical mechanism. I'm having alot of trouble with this because the first order relationship found on the graph indicates there is 1 thiosulphate ion in the rate determining step, but the overall equation also has one thiosulphate ion.

Can anyone help me out, I have tried multiple methods but none seem to add up to the overall equation.

$$\ce{2 HCl (aq) + Na2S2O3 (aq) -> 2 NaCl (aq) + SO2 (g) + S (s) + H2O (l)}$$


texts: Why H2S2 is hydrogen disulfide and not hydrogen persulfide?

texts:
Context: I was checking this question and in the answer, the compound $\ce{FeS2}$ was named "iron disulphide" (it was previously named "iron persulfide" but later changed after responding to the comments).
The structure of "hydrogen disulfide" is quite analogous to hydrogen peroxide i.e. containing the sulfur-sulfur linkage bond ($\ce{-S-S -}$) similar to peroxide bond. The bond angles of both compounds are also similar. So, why name it "disulfide" instead of "persulfide"?
In a group, compound are named in a similar manner in order to follow a certain fashion/trend. For e.g. methane, silane, germane (group 14). So, why $\ce{H2O2}$ is hydrogen peroxide and $\ce{H2S2}$ is hydrogen disulfide? Why isn't it named hydrogen persulfide as per analogy?
Related:
Why is H2O2 named hydrogen peroxide?


texts: Which d-orbital configurations form an octahedral complex?

texts:
With reference to crystal field splitting in octahedral complexes, my textbook shows the following table of distribution of $d$-orbital electrons in octahedral complexes, based on the energy difference of $t_{2g}$ and $e_g$ orbitals:

Table

Do ALL the $d$ orbital configurations (i.e. pertaining to all examples given) form octahedral complexes? I doubt it because not all of them have two vacant $d$ orbitals, especially in the case of weak field ligands where Hund's rule is never violated.


texts: Predict the products of the following reactions with Mechanism

texts:
1

My Attempt : The correct answer is C. I tried rearranging similar to claisen rearrangement but I have no clue how to go forward. I know that option A is wrong and that the product is pretty easily predictable.
But I cannot predict either the product or the mechanism.A detailed solution for each reaction  would be very helpful.
Thank you.


texts:
After doing the Lewis structure of Bromate Ion and in order to find the molecular geometry using VESPR method, we have:

central atom: Br

Electrons of the central atom: 7

Electrons that contribute the 3 Oxygens : 3

Electrons that contribute the central atom for the π bonds: -2

Charge of ion (negative) : 1

Total electrons : 9

But if we divide 9 with 2 in order to find the σ-bonding pairs, we get 4,5. what is wrong? Because after searching the molecular geometry of BrO3- it says that it is trigonal pyramid.


texts: How to distinguish between carbon-carbon double bond lengths?

texts:
Which of the following compounds should have the longest carbon-carbon double bond?

  $\ce{CH2=C=CH2}$
  $\ce{H3C-CH=CH2}$
  $\ce{(H3C)3-C-CH=CH2}$
  $\ce{(H3C)2C=CH2}$

I know that single bond > double > triple length-wise, but how do you distinguish between double bonds?


texts: Models for diastereoselectivity in nitronate additions

texts:
In the scheme below (taken from the referenced Chem. Eur. J. paper on the synthesis of Tamiflu), there is a step in which a nitronate anion (the anion derived from 5) is added into an electrophile 6, undergoing what is essentially a Michael addition.

This Michael addition sets the nitro stereocentre, as the nitronate can evidently react from one of two faces. This isn't entirely unusual, the same thing happens with enolates during aldol reactions, and the facial selectivity is explained using various models depending on whether the reaction goes via an open or closed TS (i.e. Zimmerman Traxler vs open chain models).

Clearly the nitronate anion is able to exist in several conformations, however if one draws the Newman projection, then the conformation leading to the product is the one in which H is perpendicular to $\ce{C=N}$ as if were the large group (not the most sterically favored since the ester and the alkyl chain are clearly larger).

I'm hoping someone might know the name of a model that explains the selectivity (in the same way that a Zimmerman Traxler TS rationalises a chelated aldol and the Felkin Ahn model may be used to rationalise the stereochemistry from addition into chiral aldehydes). The closest thing I can think of is the Houk model, however, this itself doesn't give the correct product and I can find no literature from Houk's group that mentions this class of reactions.

  Ref: H. Ishikawa, T. Suzuki, H. Orita, T. Uchimaru, Y. Hayashi, Chem. Eur. J. 2010, 16, 12616. DOI: 10.1002/chem.201001108.

  High-Yielding Synthesis of the Anti-Influenza Neuraminidase Inhibitor (−)-Oseltamivir by Two “One-Pot” Sequences


texts: Identifying phycobiliprotein based on wavelength

texts: I have the absorption spectrum of a specific phycobiliprotein. Its maximum wavelength is 620.6 (nm),this is the only data I have. How can I know what type of phycobiliprotein it is?


texts: Auto ignition of tert-butyl mercaptan mixed with mineral oil

texts:
I am designing an experiment that involves immersing pieces of pipe lining in a mixture of tert-butyl mercaptan (2 %) and white mineral oil (98 %) at 230 °C (the standard temperature for the test). If I was using pure tert-butyl mercaptan I would be concerned with it exploding, due to its auto ignition temperature being 250 °C. However, if the white mineral oil contains only 2 % tert-butyl mercaptan would the risk of autoignition be present at 230 °C?

I figure Mineral oil has vapour pressure of less than 1mm Hg. Tert butyl mercaptan has vapour pressure of 303 mm Hg. For the tert butyl mercaptan (2%) in mineral oil (98%) mixture I calculated that the partial pressure for tert butyl mercaptan would be 6.06 mm Hg and for mineral it would be 0.098 mm Hg. Therefore, the composition of gas above the surface of the mixture would be tert butyl mercaptan 98% and mineral oil 2%. If this is the case then the auto ignition temperature of pure tert butyl mercaptan of 250 °C would apply to the resultant gas and it would not be safe operate at 230 °C. Is this right?


texts: What is the electron configuration for Og with a charge of 2-?

texts: I was writing a cool program that determines the electron configuration of elements for me, and I wondered what would happen if you went over 118 — the "limit" of my program.  So, what is the electron configuration after you go over 118 electrons?


texts: What is the mole fraction of dihydrogen in a mixture, given the relative rates of effusion of its components?

texts:
A mixture of $\ce{H2}$ and $\ce{He}$ at $\pu{300 K}$ effuses from a small hole in a gas chamber. What is the mole fraction of $\ce{H_2}$ in the original mixture, if $3.0$ times as many $\ce{He}$ atoms as $\ce{H2}$  molecules escape from the hole in one minute?

The answer apparently relies on the fact that $\ce{H2}$ collides with the walls $\displaystyle\frac{1}{\sqrt2}$ as often as $\ce{He}$, and we therefore need $\sqrt{2}$ as many $\ce{He}$ atoms as $\ce{H2}$  molecules to yield an equal amount of substance escaping. Considering that the ratio is in fact 3, the final answer is then that the mole fraction of $\ce{H2}$ is

$$x(\ce{H2}) = \frac{1}{3\sqrt{2} + 1}.$$

Can anybody please explain how they got the $\displaystyle\frac{1}{\sqrt2}$ part?


texts: How do we calculate a character table from its basis functions

texts:
This question is a actually a homework question, I'm given the basis functions of all the irreducible representations of $C_{2v}$ group, then I'm asked to complete the character table of $C_{2v}$ point group.

For example, for $A_{1}$ irreducible representation, I'm given the basis functions {$z$, $x^2$, $y^2$, $z^2$, $z^3$, $z(x^2-y^2)$ } which I can choose from one of them.

My questions are:

Why we need to complete the character table based on those basis functions? Simply by using the two orthogonality theorems of characters we can readily fill the character table.
How can I use the basis functions given to complete the character table? Should I represent those symmetry operations by using the basis (x, y, z), then transform the basis to those given to calculate the characters? I think it is too tedious.


texts: In the ene-yne metathesis how to know which product will form predominately, as the mechanisms to both are plausible?


texts: Is the final temperature of a solution affected by the order of mixing components?

texts:
For example, I have two beakers each containing water. One is at 90 $^{\circ}$C and one is at 10 ${^\circ}$C.

Will the final temperature of the solution I make from mixing the two components be different if I slowly poured the 90 ${^\circ}$C water into the 10 ${^\circ}$C water and vice versa?


texts:
I want to make $\ce{N2O}$ in my school chem lab.

I'm thinking of making it from $\ce{Zn_{(s)}}$ in $\ce{HNO3_{(dil)}}$ :

$$\ce{
Zn_{(s)} + HNO3_{(dil)} -> N2O + Zn(NO3)2 + H2O
}$$

I'm not able to get $\ce{Zn_{(s)}}$, so I would like to make it on my own in lab.


texts:
It's stated: when two hydrogen atoms form a covalent bond, the distance between them corresponds to the lowest energy. The letters A, B and C show the correspondence between shifts in electron density and the distance apart of the atoms

I am having a difficulty understanding why the figure looks the way it does and what is the energy plotted on the y-axis, can anyone explain?


texts: Which is more likely to form: silver chloride or silver phosphate?

texts:
If silver nitrate is added to an aqueous solution (such as tap water) that contains both chloride ions and phosphate ions, which precipitate is more likely to form: silver chloride, silver phosphate or both should form?
And how do you know?

This is NOT a homework question. I'm 32 and learning chemistry on my own as a hobby and doing experiments using a Chemistry Kit for kids.
The reason I'm asking the question is because I did the experiment on the tap water at home and I didn't get any silver phosphate precipitate, but I did get a milky white appearance which I'm assuming is silver chloride (or another halide). I'm wondering if I got no silver phosphate precipitates because all the silver ions were "used up" by the chloride ions or simply because the concentration of phosphate ions is either zero or too small.

I tried to figure out if silver chloride formation takes precedence (so to speak) over forming silver phosphates using enthalpies of formation, but I got lost with that a bit.


texts: Amine salts are soluble in water but insoluble in organic solvents like ether. Why is it so? I guess there is something related to polar nature of amine salts. But I am not sure. Can someone elaborate?


texts: Comparing the stability of geminal diols

texts:
Arrange the given gemdiols in decreasing order of their stability:

I thought that high angle strain would correspond to low stability, and therefore I compared the stability of the rings, which yields the answer as C > B > A, but, the answer given in my textbook is the opposite i.e., A > B > C.
On googling, I found out that, in this case, when the corresponding ketone hydrolyses to form the gemdiol then the one which gets greater relief of angle strain will have higher stability. But why do we have to check that? And I don't  know the reliability of the source. Moreover, what is wrong in my reasoning?


texts:
I was studying reductive behaviour of $\ce{H2S}$. So, there is one reaction in my textbook.

$$\ce{3H2S + K2Cr2O7 + 4H2SO4 -> 3S + Cr2(SO4)3 + K2SO4 + 7H2O}$$

This reaction oxidizes $\ce{S^2-}$ to $\ce{S}$. But I thought why not $\ce{SO2}$?

$$\ce{H2S + K2Cr2O7 + 4H2SO4 -> SO2 + Cr2(SO4)3 + K2SO4 + 5H2O}$$

The reaction seems stoichiometrically plausible, but this reaction must need highly concentrated oxidants. I know the 1st reaction happens at low concentration of $\ce{H2SO4}$. Maybe then using high concentrated $\ce{H2SO4}$ would do the work for 2nd one.

I am not sure, though I am confident that the 2nd reaction will happen. What do you think?


texts: Why can primary cells not be recharged effectively?

texts:
Primary cells cannot be recharged effectively because their reaction products are not in contact with the electrodes. True or false?

I got it correct just by rote-learning the theory so the answer is true. But when I tried to understand it properly I'm getting confused between a galvanic cell and a primary cell. They both work on the same principles (chemical energy is converted to electrical), but they are not the same thing? Since in galvanic cells are where there are 2 beakers with 2 electrodes, 1 in each, their products are always in contact with electrodes, opposed to primary cells where it is not modelled in the same way (i.e. just a battery where the products can move away from the electrodes)?


texts: How do I know which atoms react during hydrolysis?

texts:
In the hydrolysis of propanamide ($\ce{CH3CH2CONH2}$) how do I know which molecules react with the water?

$$
\ce{CH3CH2CONH2 + H2O -> ?}
$$

I don't know how to split the molecule. In the videos I've watched (example) it seems as they just assume you know this.


texts: Why do some materials turn black and others white after combustion?

texts:
Most solids objects turn black after they are burnt.
But some turn white.
Why is that ?


texts: Why does rice become sticky after cooking?

texts:
Rice when not wet isn't sticky at all. But when you soak it in water for some time it gets sticky.

What's the chemical change that occurs in rice that makes it sticky?


texts: Michaelis Menten derivation for 2 enzyme substrates

texts:
We know the Michaelis Menten derivation for the following reaction:

$$\ce{E + S <=> ES -> E + P}$$

However, what if the reaction took place in a different scenario whereby:

$$\ce{E + S <=> ES1 -> ES2 -> E + P}$$

What would the derived Michaelis Menten equation be now?


texts: Resolution of enantiomers? How to determine chiral compounds apart from each other?

texts: How exactly is the interaction between two chiral compounds so they can tell the difference between S or R?


texts: How many samples would be worth when following a desorption? How to relate with limit of detection?

texts:
I am following the desorption of a compound from a polymer. Let's imagine that it occurs at a certain rate and most of the compound is desorbed after 5 days (as in the figure). Then, I could use many analytical techniques to follow the compound desorption by measuring at, e.g., t = 1 day and t = 4 d. The concentration difference between these two points is large enough to be detected.

However, if I the desorption is much slower (as in the figure below) and I can only take samples for 10 days, the only way to characterise the desorption rate would be with a much more sensitive analytical technique, as I would need to detect changes from, e.g. 0.98 to 0.96

My question is, supposing that I have a good guess of the concentration differences that I will encounter, how can I choose an analytical technique beforehand based on reported limits of detection and/or quantification? How can I relate limits of quantification with the ability to differentiate a sample at 0.98 and another one at 0.96?


texts: How is a counterpoise corrected geometry optimization done?

texts:
I understand the problem of basis set superposition error (BSSE) and I know how the counterpoise correction for single point energies is calculated.

Today I found out that many software packages allow for counterpoise correction during optimization calculations, but how does this actually work, especially for methods where analyical gradients are used for optimization?

During geometry optimization we calculate the first derivative of the energy to get energy gradients which we follow down to our minima. I understand that I could use counterpoise correction if I calculate those gradients numerically, which is quite easy to understand but very expensive to do, but it seems that counterpoise can also be used in combination with analytical gradients. How is the counterpoise implemented to get counterpoise corrected gradients?


texts: Mathematical equivalence of ionic-bond resonance structures and d-orbital participation in hypervalent molecules

texts:
It is now routine in the scientific community that "main-group hypervalent molecules, under certain conditions, tend to be better represented by resonance structures involving ionic bonds, rather than the utilisation of d-orbitals". For example, PF5 is better represented by a total of 5 "[PF4]+ [F]-" resonance structures, than sp3d hybritals on the phosphorus atom.
However, after reading the Wikipedia article for  "molecular orbital"s carefully, I began to think that they are, strictly speaking, mathematically the same-

The article said that "When the energy difference between the atomic orbitals of two atoms is quite large, one atom's orbitals contribute almost entirely to the bonding orbitals, and the other atom's orbitals contribute almost entirely to the antibonding orbitals. Thus, the situation is effectively that one or more electrons have been transferred from one atom to the other. This is called an (mostly) ionic bond.": maybe the ionic nature of a molecular orbital formed by a 3d orbital of P and a 2p orbital on F can be considered a special case of this statement, as P's 3d orbitals >>>>> F's 2p orbitals in terms of energy levels.

The question is- is my guess true?


texts: Is the amount of cubic inches in a cubic foot exact up to infinite significant figures?

texts:
I know we are supposed to use SI units and I know they are defined very well.
But does that mean that Imperial units of length/volume aren't exact? Don't they  have infinite significant figures in the equations?
I couldn't find it in the SI brochure.
I'm asking because I need to convert from cubic feet to liters and trying to decide how many significant figures to use. My first thought is that the conversion factors are exact and I should use all the numbers my calculator comes up with. But the conversion factor wasn't in the back of my book so maybe cubic inches in a cubic foot aren't exact?


texts: I'm writing a research paper on psilocybin.  I need to know the correct chemical structure.  When I look online it it shows different ones.  There is one with two OH molecules attached to the phosphorous and there is one with one OH and one O- attached to the phosphorous.  There is also one that I found with a O+ attached to the phosphorous.  Are they all they same or are they interchangeable?  Are there different ones?  I can't find a clear answer.  Any help is greatly appreciated.


texts: Comparing first, second, and third ionization energies between atoms

texts:
Among the elements boron, carbon, nitrogen, and magnesium, what are the first ionization energies from least to greatest? What about the second and third ionization energies?

I understand the first ionization energy is given by the following formula: $\ce{X -> X+ + e-}$, the second ionization energy is given by: $\ce{X+ -> X^2+ + e-}$, and the third ionization energy is given by: $\ce{X^2+ -> X^3+ + e-}$.

The electron configurations of the elements listed are:

$B: 1s^2 2s^2 2p_x^1$

$C: 1s^2 2s^2 2p_x^1 2p_y^1$

$N: 1s^2 2s^2 2p_x^1 2p_y^1 2p_z^1$

$Mg: 1s^2 2s^2 2p^6 3s^2$

I know that magnesium has the lowest first ionization energy because it undergoes the most electron shielding; it is shielded from the positive nuclear charge by the ($1s^2 2s^2 2p^6$ electrons).

I can deduce that nitrogen has a higher I.E. than carbon because they are both shielded by the same electrons, the $1s^2 2s^2$ electrons, but nitrogen has a higher nuclear charge. The same reasoning can be used to conclude that carbon has a higher first ionization energy than boron.

I did the above reasoning with respect to the first ionization energies. How do I apply a similar logic with the second and third ionization energies? Do the second and third ionization energies follow periodicity with respect to periods and groups? What is that trend, if any?


texts: Does anyone know where I can find the reaction rate coefficient and design equation for the electrolysis of brine and sodium hydroxide solution?

texts:
equation 1) $\ce{2 Cl^{–} -> Cl_2 + 2e^{-}}$

equation 2) $\ce{2 H2O + 2 e^{–} -> H2 + 2OH^{–}}$

These equations are the key reactions in the chlor-alkali process. I want to model a reactor for this process based on a CSTR (continuous stirred tank reactor). However I really need reaction rate coefficients (k values) and design equations. Any help would be much appreciated!


texts: How can the density of water be maximised?

texts:
What is the maximum possible density of water at room temperature?
The density of the water in the Dead Sea at 37°C is 1.24. Would it be possible to increase the density using salts we add to our food, or possibly by using different salts than are present in the sea?


texts:
I have a research about electrospun membrane synthesis where I dissolve PLA pellets in chloroform:methanol (3:1) for 3 hours and also PCL pellets in chloroform:methanol (3:1) for 3 hours too. Another thing is I also dissolve PMMA powder in acetone for 15 minutes before the texture hardened. After that, I have to blend all of those solutions together to become homogenous solution.

The question is: Actually, I've tried to mix those 3 solutions with steps I tried to mix PLA and PCL first for 3 hours and then I mix it with PMMA for another 3 hours. I am wondering, is there any other steps to mix all of them efficiently (or with shorter time)?

If you could refer your answer with journals, I'd be glad to read it too. Thank you in any advance.


texts: Is it possible to arrest the post-actinic effects of photodegradation in ABS polymers?

texts:
Polymers like acrylonitrile butadiene styrene (ABS) are adversely effected by UV exposure, both visually (by yellowing) and with regard to other material properties [1]. What's worse is that the degradation of the material continues for a long time after the initial UV exposure (see [2] for quantitative observations of this effect in other polymers). Can these effects be stopped after the fact?

Context: The unsightly degradation of ABS is a problem for collectors of old computer hardware. "Retrobrighting" techniques [3] (using hydrogen peroxide and UV/heat) can de-yellow the old plastic very effectively (albeit with unknown side-effects on the material) but the improvement has turned out to be temporary. The re-yellowing occurs in the same pattern as the original yellowing from photodegradation and it does so even if the material is protected from further UV exposure! [4]

Discussion: There are many dubious claims about the causes of ABS yellowing and the effect of "retrobrighting". Most often the yellowing is claimed to be caused by bromine and the hydrogen peroxide is claimed to "bond with bromine free radicals and restore the color" [eg. 3, 5]. I did not find any evidence to support these claims so far.

While radicals play a role in the photodegradation, I think the yellowing could rather be due to chromophores like polyenes being built up [6]. The hydrogen peroxide might convert the carbon-carbon double bonds of the polyenes to epoxy links, thereby destroying the chromophores [7] and restoring the original color.
(Intense exposure to direct sunlight also seems to destroy the chromophores temporarily(?) [8]). The problem is that this does not remove the causes of the post-exposure yellowing and therefore over time the yellowing reoccurs [4]. (If the hydrogen peroxide would truly capture the radicals as often claimed, I'd assume that the yellowing would stop permanently.)

Question: Is there any known and practical method to arrest the degradation of polymers after UV exposure? In particular, if this continuing degradation is caused by the presence of radicals in the material, can these radicals be neutralized or removed somehow?

Update: I'm reading about hindered amine light stabilizers[9] (HALS) which are thought to scavenge the radicals involved in photodegradation. I wonder if HALS have any effect if applied to already aged and exposed plastic. Does anyone know?

References

Yousif E, Haddad R. Photodegradation and photostabilization of polymers, especially polystyrene: review. Springerplus. 2013;2:398. Published 2013 Aug 23. https://doi.org/10.1186/2193-1801-2-398
James E. Picket, Reversible post-exposure yellowing of weathered polymers, Polymer Degradation and Stability, Volume 85, Issue 1, July 2004, Pages 681-687, https://doi.org/10.1016/j.polymdegradstab.2004.03.008, PDF (linked under YouTube video [8]): https://drive.google.com/file/d/1vE41ASE14kZVGjEFz_tsiLRLK3c928Eh/view
"HOW TO CLEAN & WHITEN YELLOWED PLASTICS" http://www.retrofixes.com/2013/10/how-to-clean-whiten-yellowed-plastics.html
"Retr0Bright (or RetroBright) treated plastics re-yellowing even with minimal light exposure?" https://www.classic-computers.org.nz/blog/2013-01-15-retr0bright-only-temporary.htm
"What makes ABS plastic turn yellow?" https://chemistry.stackexchange.com/a/74620
https://www.u-helmich.de/che/Q2/farbe/02/farbigkeit-03.html
"Peroxide", https://mysite.du.edu/~jcalvert/phys/perox.htm
Perifractic's Retro Recipes, "Incredible Retrobrighting Discovery! Deyellow Plastic with just Sun?! No bleach/dismantling!", May 4, 2019, YouTube, https://youtu.be/8P1OVj0IcqY
https://en.wikipedia.org/wiki/Hindered_amine_light_stabilizers


texts: Gattermann-Koch reaction - Role of cuprous chloride

texts: I am unable to figure out what the role of $\ce{CuCl}$ in Gatterman-Koch reaction is. Does it provide $\ce{Cl-}$ ions by dissociating into $\ce{CuCl2}$ and $\ce{2Cl-}$, but that can also be achieved by using more $\ce{HCl}$? So why do we add $\ce{CuCl}$ in the reaction?


texts: What happens when a symmetry element is added or removed from a point group?

texts: What new point group is formed if symmetry element i is added to C3 point group?


texts: Why is the first ionisation energy of a sodium cation bigger than that of a neon atom?

texts:
I understand that the 1st ionization energy gets bigger for elements along a period from left to right and along a group from down to up.

But why is the 1st ionization energy of $\ce{Na+}$ bigger than $\ce{Ne}$?

I would have guessed the opposite.


texts: How to judge accuracy and precision of measurement devices?

texts:
I am unsure about the accuracy and/or precision of measuring instruments.
For example, if we have a graduated cylinder, a pipette and a beaker, how and why can we assert them that they can be used with accuracy, precision, or both?


texts: Half-equations for the combustion of sulfur dioxide

texts:
Given the following redox equation:

$$\ce{2SO2(g) + O2(g) <=> 2SO3(g)}$$

$\ce{SO2}$ is being oxidized to $\ce{SO3}$ and $\ce{O2}$ is being reduced to $\ce{SO3}$.

I figured a way to write the half equations:

Oxidation half reaction: $$\ce{SO2 + H2O -> SO3 + 2H+ + 2e-}$$

Reduction half reaction: $$\ce{O2 + 4H+ + 4e- -> 2H2O}$$

After balancing and summing, I get: $$\ce{2SO2 + 2H2O + O2 + 4H+ -> 2SO3 + 2H2O + 4H+}$$

By cancelling $\ce{H2O}$ and $\ce{H+}$ we obtain the desired redox equation.
The used half equations necessitate the presence of water and acidic medium at first, but in reality we need neither water nor an acidic medium.
Is there a better way of constructing half-equations that do not require any extra materials at the beginning? I mean the real half equations that express how combustion is made in reality. I thought that we don't need water and acid to perform it.
In the "preparation" section here they didn't mention water or acid.
In addition, I guess oxygen must have sulfur trioxide as the corresponding reduced form instead of water.
Am I mistaken?


texts: Keto-enol tautomerism in a bicyclo compound

texts:
Question

Which one is more stable- the keto or enol form. The compound given is this:

Solution

The enol form would violate Bredt's Rule and would therefore be unstable. Hence the keto form is more stable

My doubt
But I am not entirely convinced. Can't we have alpha hydrogens migrating from either of the carbon atoms I've indicated by arrows? Probably they're expecting us to assume that the alpha hydrogen would migrate from the bridge-head carbon, but I just wanted to know if there's any loophole in my concepts. Any help would be appreciated.


texts: Difficulty in cis, trans isomers in Alkene

texts:
I have a difficulty in appointing cis trans isomer to an Alkene compound .

I have looked it up and drawn out a few -

Which "point" should I look at to understand in order to allocate cis and trans ? I know it's between the first and last line . Thanks!


texts: As an atom get's bigger (on increasing atomic no.) , electrons have to move faster and faster around the nucleus, Why?

texts: Does speed even make sense at such small scales ? Heisenbergs Uncertainty principle ?


texts:
I built a galvanic cell using 0.01 M solutions of copper sulfate and zinc sulfate. I used copper and zinc electrodes and immersed them into the proper solutions (copper into copper sulfate, zinc into zinc sulfate).

I used approximately 30 mL of each solution and put them into separate beakers. I connected the solutions using a salt bridge that was filled with 0.01 M potassium nitrate solution. I used cotton to cover the ends of the salt bridge (a plastic tube).

I measured the voltage across the copper and zinc electrodes and I got around 1 V. However, there is no current being produced according to an ammeter. The galvanic cell cannot light up a small light bulb for instance.

Furthermore, I took voltage measurements over a 50 minute period and the the voltage looked relatively constant throughout the period, though very slightly lower at the end.


texts: Deriving the irreps of the d-orbitals under C3 and S6 operations in octahedral symmetry

texts:
Contextual background: I am trying to reproduce the symmetries in the graph on this page (MO diagram for $\ce{ML6}$ complex). I have reproduced the metal s and p orbital representations as well as the linear combination of representations for the $\ce{L6}$ fragment. All that remain are the metal d orbitals.

So I know the five d-orbitals collectively reduce to the $\mathrm{e_g}$ + $\mathrm{t_{2g}}$ representation. I put my five d-orbitals at the origin and went through the operations for the reducible representation. Everything else adds up, except I can't find that $-1$ in the $C_3$ and $S_6$ operations.

Character table

$$\small\begin{array}{c|cccccccccc|cc}\hline
O_\mathrm{h} & E & 8C_3 & 6C_2 & 6C_4 & \begin{aligned}3C_2 \\ \scriptsize=C_4^2\end{aligned} & i & 6S_4 & 8S_6 & 3\sigma_\mathrm{h} & 6\sigma_\mathrm{d} & & \\ \hline
\mathrm{A_{1g}} & 1  & 1  & 1  & 1  & 1  & 1  & 1  & 1  & 1  & 1  & & x^2+y^2+z^2 \\
\mathrm{A_{2g}} & 1  & 1  & -1 & -1 & 1  & 1  & -1 & 1  & 1  & -1 & & \\
\mathrm{E_g}    & 2  & -1 & 0  & 0  & 2  & 2  & 0  & -1 & 2  & 0  & & \begin{aligned}(2z^2-x^2-y^2,\\ x^2-y^2)\,\,\,\,\,\, \end{aligned} \\
\mathrm{T_{1g}} & 3  & 0  & -1 & 1  & -1 & 3  & 1  & 0  & -1 & -1 & (R_x,R_y,R_z) & \\
\mathrm{T_{2g}} & 3  & 0  & 1  & -1 & -1 & 3  & -1 & 0  & -1 & 1  & & (xy,xz,yz) \\
\mathrm{A_{1u}} & 1  & 1  & 1  & 1  & 1  & -1 & -1 & -1 & -1 & -1  & & \\
\mathrm{A_{2u}} & 1  & 1  & -1 & -1 & 1  & -1 & 1  & -1 & -1 & 1  & & \\
\mathrm{E_u}    & 2  & -1 & 0  & 0  & 2  & -2 & 0  & 1  & -2 & 0  & & \\
\mathrm{T_{1u}} & 3  & 0  & -1 & 1  & -1 & -3 & -1 & 0  & 1  & 1  & (x,y,z) & \\
\mathrm{T_{2u}} & 3  & 0  & 1  & -1 & -1 & -3 & 1  & 0  & 1  & -1 & & \\ \hline
\end{array}$$

Work

$$\begin{array}{c|cccccccccc} \hline
O_\mathrm{h} & E & 8C_3 & 6C_2 & 6C_4 & 3C_2 & i & 6S_4 & 8S_6 & 3\sigma_\mathrm{h} & 6\sigma_\mathrm{d} & & \\ \hline
\mathrm{E_g}    & 2  & -1 & 0  & 0  & 2  & 2  & 0  & -1 & 2  & 0 \\
\mathrm{T_{2g}} & 3  & 0  & 1  & -1 & -1 & 3  & -1 & 0  & -1 & 1  \\ \hline
\Gamma_{\text{d-orbitals}} & 5 & ? & 1 & -1 & 1 & 5 & -1 & ? & 1 & 1 \\ \hline
\end{array}$$

As can be seen, everything matches up but the $C_3$ and $S_6$ operations. I tried using Molecule Viewer and rotating the d-orbitals, but I still don't see the $-1$. They all look like zero to me.

I would expect the $\mathrm d_{x^2-y^2}$ orbital to correspond to $E_g$ from the character table, but I only see it rotate into a "$\mathrm d_{y^2-z^2}$" orbital, with the orbitals along the y and z axes instead of x and y axes. The $\mathrm d_{z^2}$ orbital rotates into a "$\mathrm d_{x^2}$" orbital, lying along the x axis instead of the z axis.

Anyone know which d-orbital rotates into $-1$ for a $C_3$ operation? I assume a $-1$ for $S_6$ is the same orbital, but if not then does anyone which that one is as well?

Thank you


texts: What are physical properties and chemical properties?

texts:
As the question title says, I would like to know what the physical and chemical properties are. If possible, please include examples. Since it seems to be related, I would also like to know what physical and chemical changes are. I believe that things such as crushing a can is a physical change, but I am not sure what would constitute a chemical change (perhaps doing something that rearranges the molecules?)

Edit: I originally wanted to ask if cooking an egg constitutes as a chemical or physical change, but I thought that that would be closed as too vague. If possible, please explain which one it is too. Thanks!


texts: The Principle of Internal Standardization (in the context of ion chromatography)

texts:
I am trying to grasp how internal standardization works in principle, and I am having some trouble wrapping my head around it. It is not the choosing of an IS I think about, orwhen it might benefit the analysis, but just the underlying principle.

I add a known amount of the IS to every sample: unknown samples, blank samples, calibration samples, and quality control samples. Each of these samples contain equal amounts of the internal standard (or as "equal" as our pipettes may give). Considering the calibration, when the calibration samples are analyzed, I see two peaks in the chromatogram: the analyte and the IS.

Let's say I ran calibration samples of 0, 1, 2, 5, 10, and 20 ppm, each one consiting 20 ppm internal standard. The analyte peaks will grow for each calibration sample, but the IS peaks remain more or less stationary. I construct the calibration curve by plotting the ratio of analyte peak area to IS peak area (or height), as a function of the analyte conentration in the calibration samples.

I have been told that there is a constant ratio involved, one that is used to correct analyte concentrations for loss of analyte, or varying sample introduction system. If the IS peak is lower, then the analyte concentration will be corrected upwards. This apparently is because this ratio I mentioned is constant, so when reducing the denominator, the nominator must increase. Mathematically, this is trivial; however, what is this mystical constant, and what is its value? Is that arbitrary? Can I choose this constant's value myself?

I am quite confused. Hopefully someone here can help my out!


texts: Why does Fe(CO)₄ adopt a tetrahedral, as opposed to square planar, geometry?

texts:
Why does $\ce{Fe(CO)4}$ adopt a tetrahedral, as opposed to square planar, geometry? Here's my analysis:

Factors for square planar:

coordination: 4
$\ce{Fe(0)}$: d8
$\ce{CO}$: strong field ligand (gives large d-splitting)

Factors for tetrahedral:

oxidation state: 0 (gives weak d-splitting)
$\ce{CO}$: relatively bulky (?) ligand

Other thoughts:

The general guidelines for determining whether or not a row 1 transition metal complex is square planar or tetrahedral (given it  has 4-coordination and d8 electrons), are the strength and bulkiness of the ligand. Generally, strong field ligands like $\ce{CO}$ and $\ce{CN^{-}}$ gives square planar complexes. In fact, $\ce{[Ni(CN)4]^{2-}}$ is square planar. Thus, the only way I could explain why $\ce{Fe(CO)4}$ would be tetrahedral would be because of its low oxidation state. Is this correct?


texts: Why does equilibrium constant change when the reaction is multiplied by a number and nothing in the real has been changed?

texts:
As far as I know, a large equilibrium constant shows that the a reaction like the one below  wants to complete:

$$\ce{B <=> A}$$

If A and B are gases, then K is:
$$K_1=\frac{[A]}{[B]}$$

but when I multiply the reaction by 20 , K is
 $$K_{20}=\frac{[A]^{20}}{[B]^{20}}$$ while the same number of moles of B are consumed. If $\small K_1 = 10$ then $\small K_{20} = $$10^{20}$ so the reaction must be approximately complete. Why does this happen while the reaction materials didn't change?


texts:
I was thinking about simple method to convert a cis-alkene alkene like cis-2-butene to trans-2-butene.
I came up with this method (the method can also be used to convert trans alkene to cis alkene):

First use a peracid like m-CPBA to convert the cis alkene to an epoxide:

Then I used the Wittig reagent $\ce{PPh_3}$ to get a betaine. For the $\ce{- O-}$ to be able to attack $\ce{PPh3}$, they should be on same side. So rotation about $\ce{C-C}$ bond:

Finally, the leaving of $\ce{POPh3}$:

I would like to know if my method is correct and if there are any other methods to bring about the conversion.


texts: How to light a candle with small amounts of safe to use chemicals?

texts:
Already saw some youtube video where they lit a camp fire with glycerol and potassium permanganate and tried those but the amount of the stuff you need to create enough heat is just too much.

So is there a way to light a candle with small amount of something and something, like having the candle wick dipped/powdered with something and then just letting it get into contact with something else?


texts: How nickel plated copper strip can be welded? What is the optimum thickness of nickel layer?

texts:
I have a trouble with  (resistance) spot welding of nickel plated copper strip to 18650 battery. I tried to weld 0.1mm, 0.2mm and 0.3mm copper strips with 5 micrometers and 10 micrometers nickel plate thickness. Actually i have tried all of the combinations, that is i have tried to weld 0.1mm with 5 microns to 0.3mm with 10 micrometer or 0.2mm with 10 micrometers to 0.1 with 10 micrometers… Additionally, i adjusted power of spot welding machine, i tried with full power and half of the maximum power… Unfortunately all of the trials have failed.
According to you what is the main problem in my case? What is the optimum nickel plate thickness for spot welding application and how it is determined?


texts:
Imagine that I am trying to identify the presence of ions from among the metals $\ce {Li,Na,K,Ca,Sr, Ba}$ in some solution through their emission spectrum.

By mistake the wire used to introduce samples into the flame exciting the ions is contaminated with $\ce{Al(NO3)3}$. The emission energies for Aluminum are $\pu{3.9\times 10^{-19}~J/atom, 3.58\times 10^{-19} ~J/atom, 2.97\times 10^{-19}~ J/atom}$.

How will this mess up the identification of the other ions?

Since $3.58\times 10^{-19}$ matches one of the Ca peaks and $2.97\times 10^{-19}$ matches one of the Sr peaks I imagine I could misleadingly identify these two as being present when they were not?


texts: Why does aluminum chloride have a higher lattice energy than aluminum fluoride?

texts:
From the table below (source: McMurry's Chemistry [1, p. 212]), it is evident that $\ce{AlCl_3}$ has a higher lattice energy than $\ce{AlF3},$ even though $\ce{F}$ is smaller than $\ce{Cl}$. Why is this so?

However, the melting point of $\ce{AlF3}$ $(\pu{1291 °C})$ is larger than that of $\ce{AlCl3}$ $(\pu{192.4 °C}).$ I think the huge melting point difference is because $\ce{AlCl3}$ is more covalent, while $\ce{AlF3}$ is more ionic. That being said, does lattice energy account for the covalent and ionic character of compounds?

References

McMurry, J.; Fay, R. C.; Robinson, J. K. Chemistry, 7th ed.; Pearson: Boston, 2015. ISBN 978-0-321-94317-0.


texts: Mysterious precipitate in reaction of copper sulfate and calcium hypochlorite

texts: So I can’t seem to figure this reaction out. I’m pretty new to chemistry and am still learning it in high school so please don’t think I’m stupid. I have reacted 2 solitons (copper sulfate) and ( calcium hypochloride / dry chlorine) and got a light blue  precipitate that resembles copper carbonate. This precipitate is what I cant seem to identify. I don’t think it’s copper chlorate because the precipate is too light blue. Any answers will be helpful thank you in advance.


texts: Why do α-hydroxy ketones give Tollens' test?

texts:
I know that tautomerism causes the $\alpha$-hydroxy ketones to give the all the tests of an aldehyde. But how does it exactly tautomerise and what's the intermediate?

Does benzoin gives Tollens' test? If not, why? I'm really confused with this. I read somewhere that benzoin doesn't give Tollens' test as it does not have an alpha carbon to form enediol intermediate. Please help.


texts: Why does the t-buOK abstract the following hydrogen. Doesn't it promote the Hoffman product so it should take the hydrogen from a secondary carbon instead of a tertiary one? Thank you


texts: Measuring the Kc of equilibrium between NO2 and N2O4

texts:
I'm trying to measure the $K_c$ of the equilibrium reaction

$$\ce{2 NO2 (g) <=> N2O4 (g)}$$

in different temperatures. How would I do this do this in a normal school laboratory? I was thinking of shining (laser) light through a test tube that contained $\ce{NO2 (g)}$ and looking at the intensity of light emitted. $\ce{NO2 (g)}$ is dark-reddish brown and $\ce{N2O4 (g)}$ is colorless. That means that the more to the right the equation is, the more light will be emitted.

However, I don't think this would give me accurate values for $K_c$. Are there any other methods that I could use to do this which preferably don't require advanced equipment (which I don't have)?


texts: Difference between ideal & ideal-dilute solution

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These two terms has been frequently used in Physical Chemistry by Atkins. He describes Raoult's Law using ideal solution while Henry's law using ideal-dilute solution.

I thought, at first they were same but Atkins in order to contrast the two laws presented graphs in  which one curve was for ideal solution & another was for ideal-dilute solution. Though he wrote two different sections for these solutions, I really couldn't contrast what the difference actually is between ideal solution & ideal-dilute solution. I googled it but to vain! Can anyone please help what he is trying to say by these two terms?


texts: Looking for raw interferogram data / raw FID data from FT-IR / FT-NIR / FT-NMR

texts: I'm trying to get my hands on some raw interferogram data / raw FID data from an FT-IR / FT-NIR / FT-NMR so I can run some tests using FFT with it (it needs to be real data). Here's a picture below of the data I'm looking for highlighted in yellow.  I'm looking for Alkali metals (Sodium, Potassium, but also Magnesium, Gold, Silver, Platinum and Palladium).  Any ideas where I can get these or if someone can send them to me as a text/data file?  I've searched NIST but everything is already converted


texts: Is the weakening of O-H bond due to -I effect of sugar groups?

texts: In DNA molecule after formation of phosphodiester bond with two nucleosides the O-H bond of phosphate group becomes highly weak and the H+ is lost. This makes the DNA acidic but what causes the weakening of O-H bond? Is it due to the -I effect of sugar groups?


texts: Why is the Dulong–Petit law not applicable to the elements Be, B, C, or Si?

texts:
According to the Dulong–Petit law, the molar heat capacity of a solid element is approximately $3R$ (where $R$ is the gas constant $\pu{8.314 J K-1 mol-1}$.)

This is useful for calculating the atomic mass of an element when its specific heat capacity (i.e. heat capacity per unit mass) is given.

However, the Dulong–Petit law is said to not apply to the solid elements Be, B, C, and Si. Why is this so?


texts:
In Brown, Theodore E.; LeMay, H. Eugene; Bursten, Bruce E.; Murphy, Catherine; Woodward, Patrick; Stoltzfus, Matthew E.. Chemistry: The Central Science (Page 35). Pearson Education. Kindle Edition, an assignment is:

  Make the following conversions: $\pu{2500^\circ F}$ to $\pu{K}$

The answer given is $\pu{1644 K}$ but I say it's $\pu{1600 K}$. What is the correct answer?