texts: A Book on Preparation and Reactions of organic compounds

texts:
I have to learn many methods of preparations of various hydrocarbons and their reactions. For this, I went through many articles and some books but didn't found the details of reactions anywhere (There are details for only some of these) For example, why do we chose Nickel as the catalyst other than anything else to prepare ethane by catalytic hydrogenation of ethene? And why this reaction has to take place at 300°C and not at a lower or greater temperature?

I have 'a lot of hydrocarbons and a lot of methods to prepare them and a lot of their reactions' to learn so I want a book which has been designed especially to cover this topic so it could provide the details I want. Basically my course/syllabus includes Methods of preparation and reactions of methane, ethane, ethene, ethyne, benzene + alkyl-halides, alcohols, phenols, ethers, Aldehydes, ketones, carboxylic acids and Esters.


texts: Is it possible to detect the component of an unknown substances using FTIR?

texts: Currently I'm doing research involving photo-polymer which contains unknown substances. Is it possible to detect each component of the substance by using FTIR? Will it be able to separate the photoinitator component, the monomer, and the oligomer?


texts: Difference between probability and probability density of finding a particle in space

texts:
What is the difference between probability and probability density of finding a particle in space?

I am at basics of the wave function and this thing confused me.

Probability = $[\psi(x, y,z)]^2(\mathrm{d}x,\mathrm{d}y,\mathrm{d}z)$

Probability density at point $(x,y,z)$ in space = $[\psi(x, y,z)]^2$.

The latter one is the probability of finding particle in an infinitesimally small volume element $\mathrm{d}V=\mathrm{d}x, \mathrm{d}y, \mathrm{d}z$ situated at $(x,y,z)$. Then what's the former one?


texts: Need some help proving the following statements in Thermodyamics?

texts:
So in my second year thermodynamics class we are currently talking about entropy and deriving its definition from the 1st law.

$$\mathrm{d}q_{rev} = dU - dw_{rev}$$
$$= C_{V}(T)dT + PdV$$
$$= C_{V}(T)dT + \frac{nRT}{V}dV$$

And then it just says since the mixed second partial derivatives aren't equal, i.e.

$$(\frac{\delta Cv(T)}{\delta V})_T \neq (\frac{\delta(\frac{nRT}{V})}{\delta T})_V$$ dq is not an exact differential (no proof of this is given). It then stipulates by dividing both sides of the equation by T

$$\frac{\mathrm{d}q_{rev}}{T} = \frac{C_{V}(T)}{T}dT + \frac{nR}{V}dV$$
suddenly it becomes an exact differential because

$$(\frac{\delta Cv(T)/T}{\delta V})_T = (\frac{\delta(\frac{nR}{V})}{\delta T})_V$$
Can anybody give me a proof of this with calculus because my textbook gives 0 proof whatsoever and it irks me because I want to understand the theory underlying this. Thanks!


texts: Can we use prefixes like iso, neo, etc in IUPAC nomenclature of organic compounds?

texts: Shouldn't the name of the compound in the picture be 5-(1-ethyl-2-methylpropyl) nonane instead of the given name?


texts: Why is trichloromethane more acidic than trifluoromethane?

texts:
In Concise Inorganic Chemistry by JD Lee (4th edition; adapted by Sudarshan Guha), page 78 under the topic "Back Bonding" it is given:

  $\ce{CHCl3}$ is more acidic than $\ce{CHF3}$ which is explained as follows:

  $$
\begin{align}
\ce{CHCl3 &<=> H+ + ^-CCl3}\\
\ce{CHF3 &<=> H+ + ^-CF3}
\end{align}
$$

  The lone pair on the $\ce{C}$ atom gets delocalised through 2pπ–3dπ bonding in $\ce{^-CCl3}$ which is not possible in the case of $\ce{^-CF3}.$

My doubt is, fluorine being the most electronegative element exerts a greater negative inductive effect (compared to that of chlorine) which stabilises the conjugate base formed. So I feel trifluoromethane must be more acidic than trichloromethane. But the reverse order is observed.

Please explain why is this so. Should we want to prefer the conclusion from back bonding over inductive effect?


texts: Are highly nitrated cyclopentadiene compounds possible?

texts: Has anybody synthesized di- or higher nitrated cyclopentadienes possibly with methyl or other groups in the 1 position (analogs of TNT)?


texts: Does the multiplication and division significant figures rule apply to unit conversions as well?

texts:
My chemistry teacher told our class that answers to calculations that involve multiplication and division should be given to same number of significant figures as the factor, dividend or divisor with the lowest no. of sig.figs.

For example, to calculate the no.of moles of calcium in a pure 40g sample of calcium, the dividend (the mass) has 1 sig.fig. and the divisor (the molar mass) has 3 sig.figs. Hence the no. of mole sis given to 1 sig.fig.

40/40.1 = 1 mol of Calcium

Does this same rule apply to unit conversions? For example if I wanted to convert 12.4 milligrams to grams, I would need to divide 12.4 milligrams by 1000. 12.4 has 3 sig.figs. whereas 1000 has only 1 sig.fig. Does that mean the figure in grams must be given to 1 sig.fig?


texts:
Let's take the reaction $2A + B \rightarrow C$, with the assumption that this is an elementary reaction. If I'm only given this information, how would I derive the following forward rate law from scratch?

$$
\frac{dC}{dt} = k[A]^2 [B]
$$

I tried to find an answer online but most sources jump straight to the above format for a rate law. I also understand that there are many experimental considerations which can affect what is actually observed (e.g. pseudo $0^{th}$rate law behavior) but I just want to know if there's a way to derive these rate laws given just the reaction. Thank you.


texts:
Between 3-chlorophenol and 3-fluorophenol, which one is more acidic?

In this case, I know that both F and Cl are electron-donating groups. Furthermore, I know that F is more electron-donating than Cl. But I can't figure out whether that makes 3-chlorophenol more acidic, or 3-fluorophenol.


texts: Retrosynthesis of a cyclopropane type molecule

texts:
I'm trying to work out a retrosynthesis of the following molecule:

The issue I'm having is regarding the building up of the carbon skeleton. I know I can build the cyclopropane group using a carbene (diiodomethane, zinc) on the alkene. However, the alkene is proving difficult to build, I can't see why an obvious way around building this (Witting/from the equivalent alkyne) wouldn't work here. Is there something I am missing here like a rearrangement?


texts: Would there be need for periodic DFT if we are able to get all the forcefields of all the elements in the periodic table in ReaxFF?

texts: Since ReaxFF combines the advantages of DFT and Classical MD, would there be any need for periodic DFT calculations if we can have all the forcefields of all the elements of all the possible systems?


texts: Why does the cyclization of open-chain glucose occur via the C5 hydroxyl group?

texts:
In converting glucose from its acyclic (open-chain) form to either cyclic form (alpha or beta) why is the C5 hydroxyl group used instead of the bottom-most hydroxyl group?

Also, are these structures considered isomers? All sources I've seen only say "form" or "representation."


texts: What are introductory level books on chemical engineering?

texts:
I'm currently enrolled in a chemical engineering course in my college, and in my first year, I'd like to get a nice introductory book on that field of study.
I'd prefer that the book covers several topics, but less in-depth analysis of each.

Unfortunately the big-list in the Resources for learning Chemistry post does not yet cover this topic yet. With respect to the meta discussion the answer to this question will be amended to that list (and this question can be closed as duplicate after the fact).


texts: Is there always a need for a salt bridge to let a galvanic cell work continuously?

texts:
I read in a book that "Sometimes, both the electrodes dip in the same electrolyte solution & in such cases we do not require a salt bridge".

How is this possible?


texts: solubility trends of alkaline earth metals

texts: Why is the solubility trend of group 2 oxalate compounds inconsistent with the actual order in the periodic table?


texts: Mechanism of rearrangement reaction found in synthesis of retinol

texts:
Today I was solving a problem that was about the synthesis of retinol. This is a step I didn't understand:

In the solution, it's written that the mechanism goes through this intermediate:

I have not seen anything like this yet.


texts: Can basic column liquid chromatography separate two extremely similar alkaloids?

texts:
Say a sample has two alkaloids, one with a molecular weight of 521.44 g/mol and one with a weight of 521.66 g/mol.

Would column chromatography be able to separate these two alkaloids?

Also, what if a sample has, say 15 different alkaloids. Will all of these separate in liquid column chromatography?

Thanks.


texts: I read somewhere that EXAFS (Extended X-ray absorption fine structure) gives us the distances between central atom and its neighboring atoms. Is that true? Why can't we get the distance between two atoms, which none of them are central? How is EXAFS method distinguishing between central atom and other ones? So for example for CF4, I think we get one EXAFS peak for C...F distance and not F...F distance, why?


texts:
I use methane gas for cooking and there are times in which, despite burners being clean,
the flame doesn't burn that well and/or is quite red.
I suspect that said gas actually has some air added in, either intentionally as a fraud or not,
and would like to test for its purity.
Are there any ways I'd check this?

Thank you


texts: Why is Standard heat of reaction equal to difference between standard heats of formation of products and reactants?

texts:
The knowledge of standard heat of formation of various substances can be used to calculate the heat of reactions under standard conditions. The standard heat of any reaction is equal to the difference between the standard heat of formation of the products and the reactants

Why is that so? I'd prefer physical derivation for this:
$$\Delta H^\circ = \sum\Delta H^\circ_{products} -  \sum\Delta H^\circ_{reactants}$$


texts: I would like to know what the name is for the structure drawn below. This looks like a pyramid with 4 atoms at each vertex. Does the name of the structure depend on whether the atoms are all the same or if they are a combination of different ones?


texts: Calculating Vapor Pressure from Delta G/ Kp

texts:
For the process, $\ce{CH3OH(l) -> CH3OH(g)}$
  $\Delta G^\circ = 4.30\ \mathrm{kJ/mol}$ at 25 °C. What is the vapor pressure
  of $\ce{CH3OH(l)}$ at 25 °C in mmHg?
  (A) 0.176 mmHg
  (B) 14.0 mmHg
  (C) 134 mmHg
  (D) 759 mmHg

This question is from the 2012 National Chemistry Olympiad (US).

Attempt at solution:

$\Delta G^\circ = -RT\ln K$
$4.3\times10^3\ \mathrm{J/mol}=-8.314\ \mathrm{J/(mol\cdot K)}\cdot 298\ \mathrm{K} \cdot\ln K$
thus
$0.1763\ \text{(unitless)} = K$

Now, I’m supposed to know that $K$ is in units of atm and convert to mmHg accordingly. How would it know that this unitless quantity is atm and not pascal or mmHg?


texts: Thermal stability of charged and uncharged alpha helices (the concept of alpha-helix capping)

texts:
I just learned that charged alpha helices are less thermally stable than uncharged ones. The only difference I see between them would be a larger dipole moment in the charged helix, but how would this contribute to stability?

Here a picture for clarification:


texts: Regioselectivity in Ziegler–Natta polymerisation of α-olefins

texts: Why does the Ziegler–Natta polymerization display the regioselectivity shown in the image? Internal nucleophiles (coordinated to the metal) should attack the alkene on the less substituted end, like in the Heck reaction, whereas external nucleophiles should attack the more substituted end (like in the Wacker reaction). Why is this not the case for alkene polymerisation?


texts: How are polarizabilities measured experimentally?

texts:
Most common spectroscopies that produce either a full spectrum, a tensor, or a scalar value have a specific instrument associated with them that is relatively self-contained and not custom. For example, (linear) IR spectra come from benchtop FT-IR spectrometers, NMR chemical shifts use a FT-NMR spectrometer (which is capable of many experiments), and so on. One spectroscopic property that serves as a benchmark for electronic structure theory and is important for designing optical materials is the (electric dipole) polarizability, which "is defined as the ratio of the induced dipole moment $\mathbf{p}$ of (a molecule) to the electric field $\mathbf{E}$ that produces this dipole moment":

$$
\mathbf{p} = \alpha \cdot \mathbf{E}.
$$

Physically, this corresponds to how easy it is to shift a system's charge density or electron cloud around. More explicitly, it is a symmetric rank-2 tensor:

$$
  \begin{bmatrix}
    p_{1} \\ p_{2} \\ p_{3}
  \end{bmatrix}
  =
  \begin{bmatrix}
    \alpha_{11} & \alpha_{12} & \alpha_{13} \\
    \alpha_{21} & \alpha_{22} & \alpha_{23} \\
    \alpha_{31} & \alpha_{32} & \alpha_{33}
  \end{bmatrix}
  \begin{bmatrix}
    E_{1} \\ E_{2} \\ E_{3}
  \end{bmatrix},
$$

as the applied electric field may have 3 independent Cartesian coordinates, and the system being measured may have some anisotropic response to this field. In some cases, calculating the tensor may be time-consuming, but formulation is well-understood and there are standardized methods for doing so. However, it is not obvious to me how it is measured experimentally. There is the Lorentz-Lorenz equation (rearranged),

$$
\alpha = \frac{n^2 - 1}{n^2 + 2} \frac{3}{4\pi N},
$$

which relates the refractive index $n$ of a system or medium to its polarizability. There is also the Clausius-Mossoti relation, which relates the dielectric constant $\epsilon$ to the polarizability, as the refractive index and (complex) dielectric constant are related:

$$
n \propto \sqrt{\epsilon}.
$$

This implies to me that if you can measure the refractive index with a refractometer, then that is the preferred way of measuring the polarizability.

Is the refractive index the most common method of experimentally measuring the polarizability? Can it be measured directly, or must be through a relationship such as those above?
Does this relationship hold for oriented (anisotropic) polarizabilities, or only averaged (isotropic) ones?
The refractive index and the polarizability are frequency-dependent properties. How is the static (frequency-independent) polarizability measured? Or, is it even possible without extrapolation from multiple frequency-dependent data points?


texts: How to Prepare a 80mL Carbonic Acid-Bicarbonate buffer solution of ph=7.4 in laboratory?

texts:
I have the following materials which I can use:

0.1 M sodium bicarbonate solution
Sodium Bicarbonate powder
0.1 M HCL
Distilled Water
Universal Indicator

It will be a great help if you can provide with step by step instructions on preparing this 80 ml Buffer solution at an exact ph of 7.4.

Kind Regards,


texts:
A is a non cyclic hydrocarbon chain with $\ce{C_{3x-1}H_{6x}}$ as a molecular formula which is mainly used in cars as fuel, its cracking leads to hydrocarbon (B) which belongs to the same family of hydrocarbon A, also two molecules of ethene form the second product in the above reaction.

My effort:
To determine if it is an alkane, we compare the given subscripts on $\ce{C}$ and $\ce{H}$ ($3x-1$ and $6x$, respectively) to those in the general formula for an alkane, $\ce{C_{n}H_{2n+2}}$. Let $n=3x-1$ where $n$ is the number of carbon atoms.

$$6x\buildrel{?}\over{=}2(3x-1)+2=6x$$

and therefore A is an alkane, with the molecular formula satisfying the form $\ce{C_{n}H_{2n+2}}$.


texts: Alkene Electrophilic Addition Reaction Stereoselectivity When Two New Asymmetric Centers Form

texts:
I had a question about the stereoselectivity in electrophilic addition reactions (specific to alkenes) that form additional asymmetric centers in their products. I understand that when a reactant with one preexisting asymmetric center forms a product with an additional asymmetric center, the two possible product stereoisomers are a pair of diastereomers because the configuration for the preexisting asymmetric center will stay the same while the configuration of the  newly formed asymmetric center will vary. Since diastereomers differ in stability, their transition states differ as well, therefore the product with greater stability will come from a transition state with lower energy, which will require less activation energy to form. The product stereoisomer with greater stability therefore forms faster and becomes the predominant product.

However, the textbook also says that the electrophilic addition reactions that form products with two additional asymmetric centers from a reactant without any asymmetric center form four stereoisomers of which two pairs are enantiomers with each other.

It is also mentioned that this kind of reaction is not stereoselective. I don't understand how this is the case; the members that form enantiomers with each other might be energetically identical, but the stereoisomers that are diastereomers to each other must be energetically different, thus having different stability. If the logic from the first case applies the same here, wouldn't the reactions that form two new additional asymmetric centers also be stereoselective since they form diastereomers?


texts: How does increasing temperature reduce the efficiency of solar cells?

texts:
I've seen several answers and trying to confirm.

1) Does temperature increase the ground state energy of electrons once they reach the positively doped semiconductor, thus reducing the voltage between excited electrons from negatively doped semiconductor and ground state they will reach on positive side.

-This was the most compelling and easy to understand answer for me.

-However I'm not sure if it makes sense that "ground states" would rise with increasing temp.

2) Does temperature increase vibrations in wires and semiconductors, such that excited electrons following voltage difference lose energy in collisions along their path from N-doped to P-doped?

Combination of the two? Am I way off?

I am a molecular biology student with some basics in photochemistry. Somewhat familiar with solar cells and looking to dive deeper on the subject so feel free to reference.


texts: What is electrodialysis and is electrolysis prevented or suppressed?

texts:
Recently, I was introduced to a method of desalinization called electrodialysis in which a current was applied to salt water in such a way that the positive and negative were separated and drawn through membranes, leaving less salty water in between.  how do the membranes facilitate a one-way flow of ions?

Also, this method sounds a lot like the electrolysis.  How is electrolysis prevented or suppressed?


texts: Relation between constant-pressure and constant-volume heat capacities: Cp - Cv = nR

texts:
For an ideal gas, we have

$$C_p - C_V = nR$$

where
$C_p$ is heat capacity at constant pressure,
$C_V$ is heat capacity at constant volume,
$n$ is amount of substance, and
$R=N_\mathrm A\cdot k_\mathrm B=8.314\,462\,618\,153\,24\ \mathrm{J\ mol^{-1}\ K^{-1}}$[source] is the molar gas constant.

How can I prove this?


texts: Why leveling effect is reduced when strong acid is dissolved in a weaker acid than water?

texts:
I am reading a book that basically states what is the title.

This is something I observed when I was doing ICE charts: when acid and base neutralize, we always assume complete neutralization.

Interestingly, when we put acid in water, which can also be considered a Brønsted-Lowry base, we called it ionization of acid, and thereof acid ionization constant.

Leveling effect happens when multiple strong acids dissolve completely and we don't know which is stronger.

Here is the question: does complete neutralization always take place with a base and an acid, why?


texts: Why are some chemicals packaged in incompatable containers?

texts:
I've noticed that some organic chemicals are sold in HDPE containers despite compatibility charts indicating that such containers are not appropriate acetone.

For example, this acetone listing from Walmart above uses an HDPE container, but when incompatible solvents are packaged in HDPE containers the containers can experience a relaxation in the polymer stress from blow molding causing the bottle to contract as shown below.

How can they use incompatible containers and still safely package solvent products?


texts: Kinetics of Decomposition of Hydrogen Peroxide

texts:
Consider the decomposition of Hydrogen Peroxide:
$$\ce{H2O2 -> H2O + 1/2O2}$$
The  rate law for this reaction is :
$$\text{Rate} = k[\ce{H2O2}]$$
Further
$$\text{Rate} = -\frac{\mathrm d[\ce{H2O2}]}{\mathrm dt} = \frac{\mathrm d[\ce{H2O}]}{\mathrm dt} = 2\frac{\mathrm d[\ce{O2}]}{\mathrm dt}\tag1$$

Now consider :
$$\ce{2H2O2 -> 2H2O + O2}$$
The  rate law for this reaction is :
$$\text{Rate} = k[\ce{H2O2}]$$
Further
$$\text{Rate} = -\frac {1}{2}\frac{\mathrm d[\ce{H2O2}]}{\mathrm dt} = \frac {1}{2}\frac{\mathrm d[\ce{H2O}]}{\mathrm dt} = \frac{\mathrm d[\ce{O2}]}{\mathrm dt}\tag {2}$$

My question:

Which one is correct - eq $(1)$ or eq $(2)$?

What is the general principle for deciding this?

Update:
As I have been informed through comments that both the equations are equally true, I have another doubt:
Consider half-life time of the reaction (first order kinetics):
$$t_{1/2} = \frac {\ln 2}{k}$$
As stated in the comments rate constant of both the reactions denoted by $k_1$ for $eq 1$ and $k_2$ for $eq 2$ are different. This means that the half life time of these reactions are different.
But the half-life time for first order kinetics is independent of initial concentration and no matter what equation we use , the actual reaction happening in the jar is the same. Provided this, how can there two different half-life times?


texts: Relating Gibbs Free Energy to Equilibrium Constants

texts:
I am having some trouble relating these two concepts. I know that if K=1 then delta g is zero, and that we can interpret signs and magnitudes. However, i am having trouble determining required temparature based on given aimed K, and standart Gibbs free energy of a reaction.
Here is the kind of problem that i have trouble with:


texts: Why does the solubility of haloalkanes in water decreases as the length of the carbon chain increases?

texts:
Due to the polar halogen-carbon bond in haloalkanes, they are more soluble than hydrocarbon in water. But the solubility is still very low because the overall influence of the dipole-dipole interaction is small.
Cool.
But why does the influence of the halogen decreases as the length of the carbon chain increases?
Shouldn't this be increasing the solubility of haloalkanes in water instead? As an increase of carbon in the chain translate to more electrons and more movements of electrons increase the dispersion forces. This increase in inter-molecular forces means that its closer to of the strength of hydrogen bonding in water


texts: History of octanol-water partition coefficient

texts: We are aware that one of the basic information about a material is the logP value it has. The logP is worked out from the partitioning between the octanol and the water phases. Does anyone know who was the first to introduce this octanol-water partition coefficient? I had a look through the literature but was not able to find the author of that rule.


texts:
The order of basicity of halides is $\ce{F-  >Cl- > Br- > I-}$

My teacher explained this on the basis that the smaller is the ion, the greater is the charge/size ratio, hence it more unstable and more likely to gain a proton.

However if this is the case, why is the magnitude of electron gain enthalpy in the order $\ce{Cl- > F- > Br- > I-}$ and not $\ce{F- < Cl- < Br- < I-}$ since we are calling $\ce{I-}$ the most stable and so on?

(The reaction is going on in an aqueous solution.)


texts: Are the units of mole of oxygen molecules the same with the units of mole of nitrogen molecules?

texts:
Suppose we have in a box $3 \,{\rm mol}$ $\ce{O}$ and $3 \,{\rm mol}$ $\ce{N}$. Is the addition of these two quantities meaningfull? We do it all the time when we want to find the molar fraction. I can't understand if it dimensionally correct to add these two things. If a mole is like a dozen then a mole of eggs and a mole buildings can't add up.
I think a crucial step that is omitted when we want to find the molar fraction is that we should convert these moles of arbitrary entities (eggs, buildings, molecules) to same entities. I can't find anything else to justify such a process (addition of different kind of moles). Would be the following way a proper way to find the mole fraction?
$$n_{_{T}}= \frac{\,{\rm mol} \, \text{of molecules}}{\,{\rm mol} \, \text{of O molecules}}\cdot n_{_{O}} + \frac{\,{\rm mol} \, \text{of molecules}}{\,{\rm mol} \, \text{of N molecules}}\cdot n_{_{N}} $$
So $n_{_{T}}= 6\,{\rm mol}$. What about the molar fraction of oxygen? $$\chi_{_{O}}=\frac{n_{_{O}}}{n_{_T}}= \frac{\text{3 mol of O molecules}}{\text{6 mol of  molecules}}=0.5 \text{ of what?}$$
We know the ratio must be dimensionless but why? We deviding moles of $\ce{O}$ molecules by moles of molecules. Are these units different or not?


texts: Difference between precipitation and crystallisation

texts:
What is the main difference between precipitation and crystallization.
Is precipitation a chemical change and crystallization a physical change.
How can we say that the resulting solute is precipitate or a crystal?
Is it necessary that when we want precipitates to form then its ksp should be less than its Qsp or the precipitates form even after mixing two unsaturated aqueous salt solutions?


texts: Would the detaching of dendrites from electrodes in a cell, result in the crystal dissolving back into the electrolyte?

texts:
Dendrites that form on the electrodes of cells shorten the cell's lifetime, and result in reduced capacity before the end of life.

If the dendrites could be detached from the electrode, would they then dissolve back into the electrolyte, or would they remain as solids suspended in it? How does this effect battery lifetime and capacity?


texts: Find whether a gas cools or heats up on Joule-Thomson expansion

texts:
A gas that follows $P(V - nb)= nRT$ is subjected to Joule-Thomson expansion. Tell whether it cools or heats up.

$$\mu = {\partial T \over \partial P} = {\partial P(V - nb)/nR \over \partial P} = \frac1{nR}\left(V - nb + {\partial V \over \partial P}\right) = \frac1{nR}\left(V - nb - {nRT\over P^2}\right)$$

Now how do I determine whether $\mu >0 $ or $\mu < 0$ without knowing anything  about temperature or anything else ?


texts: CN* band spectrum in spark emission spectroscopy

texts:
An arc between carbon electrodes in air has enough energy to activate the nitrogen in the air.  The nitrogen then behaves as nitrogen in the combining form and by reaction with the carbon from the electrodes, the CN bands are produced. To prevent this, special arrangements, such as using an inert gas  to remove adsorbed nitrogen from the surface of the electrodes, have to be made.

In our experiment, no particular precautions were made, and nevertheless CN bands were not found.

Why?


texts: How does Dalton's Law relate to scuba diving?

texts: My assignment is to create a report that emphasises on the important of chemistry more specifically the gas laws in scuba diving. I know that Dalton's Law is when the total pressure of a gas mixture equals the sum of the partial pressures that make up the mixture but i don't know how it relates to scuba diving. Can someone give me some hints?


texts: Can sonochemistry be used as a catalyst for basic reactions?

texts:
Recently, I have been interested in the field of sonochemistry, using ultrasonic irradiation to induce chemical changes in a system via the phenomena of acoustic cavitation.

From my rather brief research, I have come to the realization that this phenomena can be used as a catalyst for many reactions. However, I want to know if the most basic form of sonochemistry (using an ultrasonic bath) can be used to speed up very simple inorganic reactions involving dissolved common chemicals.

I am very interested in the implications of this emerging field in chemistry, but am curious as to whether I can perform a few basic experiments using common chemicals and an ultrasonic bath and compare reaction times for a high school science project.


texts: Franck-Condon factors in photoelectron spectroscopy

texts:
Franck-Condon factors have been used to predict / assign the vibrational structure of photo-electron spectra.

$FCF=|\langle\psi''_{vib}|\psi'_{vib}\rangle|^2 = |\langle\psi''_{vib,1}\psi''_{vib,2},\ldots,\psi''_{vib,n}|\psi'_{vib,1}\psi'_{vib,2},\ldots,\psi'_{vib,n-1}, \psi'_{vib, emitted}\rangle|^2=|\langle\psi''_{vib,1}|\psi'_{vib,1}\rangle|^2\ldots|\langle\psi''_{vib,n}|\psi'_{vib,emitted}\rangle|^2$,

Question: what is $\psi'_{vib,emitted}$? Is it just a free particle, with its wavefunction spanning all space, hence it doesn't have any effect on the integral?


texts: I would like to know if it would be possible to make Acetic Acid from Wood. I know that you can charcoal wood to get the gases, cool it, and get the liquid. This would yield a bunch of chemicals in a mixture. I also know that you can steam wood to get wood vinegar. Would it be possible to extract Acetic Acid from either the Pyrolysis Gas or Wood Vinegar? Or would I need a different method of extraction or just not be possible at all?


texts: I have a metal rod in my leg from previous surgery. I believe it is titanium. Would this significantly affect/be affected by an nmr machine? I noticed that a sign by it said not to bring metal objects in the room and I wanted to be sure.


texts:
When going through one of my chemistry textbooks, I saw that the electrolysis of aqueous lead nitrate led to oxygen being formed at the anode and lead being formed at the cathode.

However, in school, I was taught that only metals less reactive than hydrogen will form at the cathode.  This electrolysis contradicts what I learned, as lead is more reactive than hydrogen, and should remain as ions in solution.

Therefore, my question is: What forms at the cathode during electrolysis of aqueous lead nitrate and why?


texts: Reaction of sodium hydroxide with ethanol

texts:
I am carrying out a titration to determine the solubility of a carboxylic acid in mixtures of water and ethanol. I will be titrating a diluted (previously) saturated solution of water, ethanol and the acid against sodium hydroxide.

Can the sodium hydroxide interact with the ethanol so as to give an incorrect result?


texts: What happens when you mix milk and coke?

texts:
Add small amounts of milk to a bottle of coke, and you end up with a white-ish precipitate with a clear liquid on top. "The Internet" seems to agree that phosphoric acid in coke reacts with something in the milk (possibly proteins, it seems to me). The Telegraph even wrote that it is the "milk molecules" that react.

So what is the reaction(s) that takes place?  I can't find any proper sources that explain this in chemical terms.

Telegraph's milk-molecule analysis:
 This is what happens when you add milk to coke
or via the Internet Archive (without pictures).


texts: How uniform is the distribution of elements in the universe?

texts:
I was wondering about element distribution in the universe, specifically if any inconsistency in the relative distribution of elements would have any significant effects on the chemistry of a galaxy. How likely is it that there could be significant differences in element quantities from one galaxy to another, so that certain common, or 'important' chemical compounds or reactions might not be possible/probable.

For example could a galaxy not have the proper relative quantities of elements used in organic chemistry to allow the sort of organic chemistry we see occurring in many places in our own local space (comets and cosmic dust)?


texts: Why does DFT-D finds different optimized geometries for the same structure when using different input geometry files?

texts: When I change c lattice parameter and optimize the structure with DFT-D, every time I get a significantly different geometry with different energy? Why is this happening with DFT-D?


texts: Why the melting point increase up to arsenic and then decrease down the group 16?

texts: I am already google this but can't find the answer that staisfy me. I know down the group, mass and atomic size increase which result in increase in van-der-waal forces. But in group 16 the trend is not regular, why?


texts: What is the driving force for imine formation?

texts:
I know this that when a primary amine is reacted with a carbonyl compound, an imine is formed:

I'm wondering why the position of this equilibrium lies to the product side / right-hand side. Why is the formation of the C=N double bond favoured?


texts: Why don't we have hyperconjugation with C-C bonds?

texts: C-C bonds are weaker than C-H bonds.So why is hyperconjugation with C-C bonds not possible?


texts: Should the fact that all atoms involved having an octet, or the rule that more electronegative element should have negative charge and less electronegative element have positive charge, be given greater priority while determining the stability of resonance structures?


texts: Utility of Bent's Rule - What can Bent's rule explain that other qualitative considerations cannot?

texts:
Does Bent's rule have any utility? I got a vehement earful for "NO." Points raised by my professor:

Coulombic considerations can be used to rationalize bond angles, strengths, and lengths without the use of Bent's rule.
Orbitals are not real so why invoke orbitals when simpler Coulombic considerations are available? (Occam's razor)
The Coulombic effect is also real as opposed to orbitals.

Consider carbon tetrachloride and chloromethane.

Obviously, carbon tetrachloride has the stronger and shorter carbon-halide bond because in chloromethane, the methyl group is slightly electron donating, and this repels the terminal chlorine, which lengthens the carbon-halide bond. No application of Bent's rule is necessary.

Sure, you can justify this difference with Bent's rule; s-character is concentrated in orbitals directed toward more electropositive substituents; the carbon is more electropositive than chlorine; thus, the bond has more s-character around the chlorine and more p-character around the carbon in chloromethane. This greater p-character around the carbon in chloromethane weakens the carbon-halide bond relative to the bond in carbon tetrachloride. And greater p-character in a bond is also correlated with a compression in bond angles.

However, bond angles are also explained nicely through Coulombic effects. The C-H bonds in chloromethane are obviously shorter due to the electron-withdrawing nature of chlorine and the carbon-chlorine bond is obviously expanded due to methyl group/chlorine lone pair repulsion. This shortening of the C-H bond lengths explains the H-C-H bond angle expansion in chloromethane, and the lengthening of the C-X bond explains the X-C-H bond angle expansion.

Is there any case in which other elementary considerations (Coulombic, VSEPR, van der Waals repulsions) fall short in the realm of molecular geometry and Bent's rule can step in to pick up the slack? Anyone got some sort of vindication for Bent's rule?


texts: I would like to ask if anyone has a list or knows which covalent compounds have metals in them. For example, beryllium and aluminium are both metals but they bond covalently with chlorine to form beryllium chloride and aluminium chloride respectively. Other than these 2 compounds, I do not know any other and thus would like to ask this question.


texts:
I have the following question: Assume that you have two solutions. One of  $50\ \mathrm{cm^3}$ $\ce{HCl}$ $\mathrm{pH} = 1.3$ and one of $150\ \mathrm{cm^3}$ $\ce{Ba(OH)2}$ $\mathrm{pH} = 12.3$. If we mix these two solutions what will the $\mathrm{pH}$ of the mixture be?

I have done the following:
$\mathrm{pH} = 1.3 \Rightarrow [\ce{H+}] = 10^{-1.3} = 0.05\ldots\ \mathrm M  \Rightarrow n = 0.05\ldots \times 0.05 = 0.0025\ldots$
$\mathrm{pH} = 12.3 \Rightarrow \mathrm{pOH} = 1.7 \Rightarrow [\ce{OH-}] = 10^{-1.7} = 0.019\ldots \Rightarrow n = 0.019\ldots \times 0.15 = 0.0029\ldots$

My problem is I do not know how to proceed


texts:
Yesterday I saw a bill of some book which I bought 6 months back. Then this question struck my mind: "Why does paper turn yellow over time"?

I remember my teacher saying some organic compound was used to make paper white. And this effect is reversed over long periods of time. Can anybody explain?


texts: How many stereoisomers can exist for 4,5-bis(3-hydroxyoct-1-en-1-yl)cyclopentane-1,3-diol?

texts:
Q.10 For the given compound $\ce{X}$, the total number of optically active stereoisomers is ____.

This is from JEE Advanced 2018 second question paper.
I thought the answer to be at least 32 because of exactly 5 stereocentres present.  One of the double bond cannot show geometrical isomerism possibly.
But the answer given in the answer key is 7:

I did not find any plane of symmetry because of the different kind of double bonds.


texts: How do you list all possible reactions and intermediates of a reaction?

texts: Ins this video https://youtu.be/txk-VO1hzBY?t=2391 the speaker claims that $$\ce{H2 + O2 -> H2O}$$ involves 23 reactions and 11 species. How do you list all of that ?


texts: How many unique molecules exist? And how many exist only by synthesis?

texts:
I'm interested in

How many  unique molecules (of all types: organic and inorganic, etc), exist  in the world accessible by man (let's exclude black holes and the centers of stars etc)?
What subset of those distinct types are only in existence because of synthesis by man?

To make it simpler, ignore variants such as molecules with different atom isotopes and different bond configurations (e.g. cis, trans). E.g. standard water and "heavy water" are both $\ce{H2O}$ and count as one.

I'm looking for a theoretical estimate, so orders of magnitude only are required. I'm not looking for a count of records in some database catalogue of chemicals.

Please explain methods for determining your estimates. This isn't really helpful.


texts: How to calculate the composition of a mixture of iron oxides containing inert impurities with titration data?

texts:
An $\pu{8 g}$ sample of $\ce{Fe3O4}$ and $\ce{Fe2O3}$ containing some inert impurity was treated with excess of aqueous $\ce{KI}$ in acidic medium, which converted all iron to $\ce{Fe^2+}$. The resulting solution was then diluted to $\pu{50 mL}$.

  $\pu{10 mL}$ of it was taken and the liberated iodine required $\pu{7.2 mL}$ of $\pu{1 M}$ sodium thiosulphate to reduce all iodine.

  Another $\pu{25 mL}$ was taken and the iodine was removed. The remaining solution required  $\pu{4.2 mL}$ of $\pu{1 M}$ $\ce{KMnO4}$ to oxidize all $\ce{Fe^2+}$.

  Calculate the percentage of composition of the mixture.

The initial solution already contains $\ce{Fe^2+}$ from $\ce{FeO}$, which does not react until the second titration.

Working backwards, milliequivalents (m.eq) of $\ce{Fe^2+}$ is $5\times 4.2\times 1 = 21$ in $\pu{25 mL}$ solution. So in $\pu{50 mL}$, the amount of $\ce{Fe^2+}$ is $42$ m.eq.

Similarly, the m.eq of iodine from titration with thiosulphate is $36$.

From the first reaction (with $\ce{KI}$),
$$\text{m.eq of iodine liberated = m.eq of $\ce{Fe^2+}$ formed.}$$
The excess $\ce{Fe^2+}$ is from $\ce{FeO}$ which is present in $\ce{Fe3O4}$.

The amount of $\ce{FeO}$ is $6$ m.eq.
Hence its weight is $\frac{6}{1000}\times\frac{72}{2}=\pu{0.216 g}$ since $n$-factor is $\mathrm{2}$.

Since $\pu{1 mol}$ of $\ce{Fe3O4}$ contains $\pu{72 g}$ of $\ce{FeO}$, the mass of $\ce{Fe3O4}$ is $\pu{0.6945 g}$. But this answer is wrong. Is there anything wrong in my procedure?


texts: Why does the proton transfer from the oxygen to the nitrogen atom in imine formation not occur through an intramolecular process?

texts:
In my book Organic Chemistry by David Klein, 2nd edition, the book shows that the oxygen atom first takes a proton from an acid, then, the conjugate base of the acid takes a proton from the nitrogen atom, in the second and third steps of the mechanism shown above. However, I believe that an intramolecular reaction where the oxygen atom takes the hydrogen atom would be more kinetically favored, due to the fact that intramolecular processes are much faster than intermolecular processes.

My question is therefore: Why is the reaction pathway proceeding through the acid deprotonation/protonation more favored than the intramolecular reaction?


texts: pH and acid value relation for an organic chemical

texts:
Would there be a general relation between the pH (say, as measured by a pH strip) and the titration-measured "acid value" of a organic chemical?
The acid value is typically defined as "the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of chemical substance."
If you determine the acid value of something which technically does not have an acidic moeity e.g. (say) an oil or benzaldehyde I suppose what you are tracking is the residual acidity of some impurities?
Would pH then be a function of ill defined parameters like some ppm amount of residual water etc. (since pH would be strictly defined for an aqueous solution).
For context: The situation I have is an liquid organic chemical where the spec typically is an upper limit of the acid value. But someone started wondering whether there would be a pH strip correlation.


texts: We have a well that delivers hard water and we do not have a water softener. (There was a “green sand filter” that utilizes permanganate to oxidize other metals on the system, but it has been disconnected.) Analysis of the well water shows the presence of iron in noticeable amounts. No other metal ions were specifically identified. The system does have an ozonator to oxidize Fe(II) to Fe(III). Over the last couple of years, the porcelain toilet bowls have developed a blue ring at the air/water interface. When you scrub on the blue ring, it doesn’t feel like there is a deposit present (like normal hard water deposits). The ring is unresponsive to ammonia (household), strong acid (6 M HCl) or strong base (Drano), as well as to hydrogen peroxide (30 %).  (We haven’t tried a good reducing agent yet.) So, my question is, does anyone have an idea of what is causing the blue color? Is it possible that porcelain reacted chemically with salts, urea, uric acid, oxygen, etc?  Not an earth-shattering theoretical question, but I’m chemically curious as to what this could be if anyone has any ideas.


texts: Why mixing water with ethanol produces heat energy?

texts:
Sorry if I'm asking something stupid but I'm trying to understand where this energy gets from. As far as I could find, it is not a reaction as both chemicals left unchanged, so it might have something to do with hydrogen bonding but I can't connect these two facts together.

UPD: it is not homework question (I have a degree in a completely unrelated field) and I did try to find a reasonable explanation in search engines but with no luck. Atm my theory is that ethanol creates H-bonds with water and those bonds have less energy than the ones between H2O-H2O and the excess of the energy goes away as heat but I don't have anybody who could confirm or reject that. As for the forums - Stack Exchange branches to me is the most credible source so I went asking here first.


texts:
I'm really confused as none of the definitions of radical on the internet compare to this.

This is from my college textbook of Applied Chemistry-

  Radicals

  Every inorganic compound is made up of two electrically charged parts
  called radicals. One part has positive charge and is called basic
  radical, while the other part has negative charge and is called acid
  radical. Hence,

  An atom or a group of atoms which forms a part of an inorganic compound is called a radical.

  For example :

  Sodium Chloride is made up of two parts:

  (i) Sodium radical (Na+)  and   (ii) Chloride radical (Cl-)

  The two radicals combine to form sodium chloride molecule.

  Copper sulphate is made up of two parts:

  (i) Cupric radical (Cu2+)  and   (ii) Sulphate radical (SO42-)

  The two radicals combine to form copper sulphate molecule.

  It should be noted that a radical cannot exist independently.

This definitely doesn't mean the same as free radicals. I don't think it means "functional group" because how can sodium be a functional group?!. Functional groups are in organic chemistry, right?

Can someone explain what the term "radical" means here?


texts: Law of Definite Proportion: Do the numbers indicating moles count?

texts:
I need to find the ratio of a substance as it converts from a bicarbonate to a carbonate:
ex:

$\ce{Fe(HCO3)2 -> FeCO3 + CO2 + H2O}$
$\ce{Fe(HCO3)2} / \ce{FeCO3}$ = $3/2$ *using molar masses

But what if the substances aren't  the same number of moles?
ex:

$\ce{2Fe(HCO3)2 -> FeCO3 + CO2 + H2O}$

Would the ratio be:

$\ce{2Fe(HCO3)2 / FeCO3} = x$

or still:

$\ce{Fe(HCO3)2} / \ce{FeCO3} = 3/2$

How do moles factor into this equation and why?


texts:
A table in the book 'Chemistry NCEA Level 1' has 4 headings, the first of which is 'Volume (mL) ammonia solution provided (conc 2 g L-1)'
Could someone please provide a comprehensive explanation of what the end part in brackets means.
This is for a chemistry newbie, as you may gather from the book title.
(this isn't really homework but I couldn't find a relevant tag. It's just someone studying chemistry for fun.)


texts: Why does ligand substitution occur when OH- is a better ligand than NH3?

texts:
$$\ce{[Cr(H2O)3(OH)3](s) + 6NH3 -> [Cr(NH3)6]^3+ + 3H2O + 3OH-}$$

When excess $\ce{NH3}$ is added to triaquatrihydroxychromium(III), why does ligand substitution occur when $\ce{OH-}$ is a better ligand than $\ce{NH3}$?

Wouldn't the 3 $\ce{H2O}$ molecules be deprotonated to $\ce{OH-}$ and therefore form $\ce{[Cr(OH)6]^3-}$?

This also seems to occur when excess $\ce{NH3}$ is added to tetraaquadihydroxocobalt(II):

$$\ce{Co(H2O)4(OH)2(s) + 6NH3 -> [Co(NH3)6]^2+ + 4H2O + 2OH-}$$


texts: How does resonance fail in approximating chemical structures?

texts:
In the book "Concise Inorganic Chemistry" by Prof. JD Lee, it says here:

  These contributing structures do not actually exist. The $\ce{CO3^2-}$ does not consist of a mixture of these structures, nor is there an equilibrium between them. The true structure is somewhere in between and is called a resonance hybrid. Resonance was widely accepted in the 1950s but is now regarded at best as clumsy and inadequate, and at worst as misleading or wrong!

I want to know where exactly does resonance fail in approximating the structures?


texts: How does one calculate chemical shift in a gauge independent manner?

texts:
The literature on ab initio calculations of chemical shift in NMR experiments usually provide Lamb's and Ramsey's formulae as the solution. Yet the expressions explicitly depend on vector potential gauge choise. Some authors claim that the theory is intrinsically gauge invariant, giving no proper proof yet. Can the solution be expressed in an explicitly gauge invariant form? Some literature on this.

NOTE: I know about London orbitals theory, yet it's still not fully understood by me, how it can deliver a type of expression I want. Some suggestion on where this is clarified are very welcome.


texts: How to oxidise iron in spinach to iron(III)

texts:
I'm planning an experiment to test the iron content of spinach. I plan to ash spinach, grind it, then dilute it in a solution which would hopefully oxidise the iron ions in it to $\ce{Fe^3+}.$ This is in order to get a reaction with ammonium thiocyanate solution in the end, which will allow me to determine concentration by colorimetry.
What should I dilute my ashed spinach into to oxidise the iron in it? Preferably something safe with the thiocyanate.


texts: Does a tertiary carbocation rearrange to another tertiary carbocation?

texts:
I strongly believe that a carbocation should not rearrange to another if there are no immediate benefits(like a Greedy Algorithm).

The doubt hit me while solving this question. The answer mentioned in the book answers (b) but my answer comes out to be (a).

Here is the mechanism:


texts: Forming Basis Functions from 6-31G Basis Set for Carbon Atom

texts:
I am a computer science grad and I am working to write an electronic structure calculation program and I am stuck at forming basis functions using 6-31G Basis set for atoms having higher atomic numbers (p,d,f shells).

For example, consider a gaussian g as

g(alpha) = (2*alpha/pi)^(3/4) * exp(-alpha*r^2).

Looking at the Carbon (1s2 2s2 2p2) basis set data for 6-31G basis set

C     0
S   6   1.00
      0.3047524880D+04       0.1834737132D-02
      0.4573695180D+03       0.1403732281D-01
      0.1039486850D+03       0.6884262226D-01
      0.2921015530D+02       0.2321844432D+00
      0.9286662960D+01       0.4679413484D+00
      0.3163926960D+01       0.3623119853D+00
SP   3   1.00
      0.7868272350D+01      -0.1193324198D+00       0.6899906659D-01
      0.1881288540D+01      -0.1608541517D+00       0.3164239610D+00
      0.5442492580D+00       0.1143456438D+01       0.7443082909D+00
SP   1   1.00
      0.1687144782D+00       0.1000000000D+01       0.1000000000D+01

How many basis functions will carbon have in this case? I have been following a lecture series which does HF SCF calculation for a simple H2 molecule where each Hydrogen atom has two basis functions as per 6-31G basis set.

H     0
S   3   1.00
      0.1873113696D+02       0.3349460434D-01
      0.2825394365D+01       0.2347269535D+00
      0.6401216923D+00       0.8137573261D+00
S   1   1.00
      0.1612777588D+00       1.0000000

I can write the two basis functions in the form

b1= 0.0334*g(18.73) + 0.2347*g(2.825) + 0.8137*g(0.64);
b2= g(0.161);

In a similar manner, how would I go about writing the basis functions for Carbon atom. Any advise would be very helpful as I am stuck in this for couple of days and haven't been able to find any substantial resource for this.

I did stumble upon this previous post but having a hard time figuring out how did 9 basis functions come for Carbon.


texts: Is the concept of frontier orbital interactions chiefly a kinetic concept?

texts:
Frontier molecular orbital theory has proved to be an immensely useful concept. The concept of HOMO-LUMO interactions are frequently employed in detailing the mechanistic descriptions of reactions in organic chemistry. It seems to me that there are numerous examples of HOMO-LUMO interactions seem to be responsible for kinetic phenomena.

For example, secondary orbital interactions allow the preference for the endo product in the Diels-Alder reaction under kinetic control.

Nucleophilicity, which is often linked to the energy of the HOMO of the nucleophile, is also often regarded as a kinetic phenomenon. In fact, Lewis basicity itself may even be seen as a kinetic concept. For example, we make the assertion that phosphine is a better nucleophile (and also better Lewis base) compared to ammonia because $\ce {P}$ is less electronegative than $\ce {N}$ and thus, the HOMO of $\ce {PH3}$ is thus higher in energy, compared to that of $\ce {NH3}$.

Should we thus classify frontier orbital interactions as a kinetic concept?


texts: How do I dissolve sodium oleate in distilled water

texts: I wanted to know how to dissolve sodium oleate powder in distilled water?  Does it have to be at a certain temp?  I need a 2% solution


texts: How to test for halides without ammoniacal silver nitrate solution?

texts:
If I have an halide e.g magnesium iodide, how can I test what halide the compound contains?

I understand there is a method using silver nitrate and ammonia but what other methods are there?


texts:
$\mathrm{pH} = -\log[\ce{H+}]$ while $\mathrm{pOH} = -\log[\ce{OH-}]$

Why does $\mathrm p$ represent $-\log$ of something? Is it due to some historical reason or due to some scientific reason?


texts: Why is the photon energy of lithium flame coloring lower than that of cesium?

texts:
Why does $\ce{Li}$ give a red flame color which has lower photon energy compared to $\ce{Cs}$ which gives a violet flame color according to $E=h\nu$?

This is my attempt: Since lithium has smaller size it has a high ionization energy, thus, if an electron jumps from a higher energy level to the ground state then it releases a large amount of energy compared to cesium which has a larger size and lower ionization energy. Therefore lithium's photon energy should be higher compared to cesium. But it is not. Why?

The problem is the photon energy of flame coloration should gradually decrease down the group of alkali metals but rather it's increasing.


texts: How to calculate the concentration of a monoprotic organic acid that was extracted into an ethyl ether layer?

texts:
Compound A is a monoprotic organic acid. If $\pu{25.0 mL}$ of a $\pu{0.456 M}$ solution of A in water was extracted with $\pu{25.0 mL}$ of ethyl ether and it was determined experimentally that $\pu{5.45 mL}$ of $\pu{0.523 M}$ $\ce{NaOH}$ was required to neutralize the bottom layer from the extraction, what is the concentration of compound A in the ether layer?

My attempt:

$\pu{25.0 mL}$ of a $\pu{0.456M}$ solution of A in water

This gives the total millimoles of your unknown acid that is split between the two layers.

$\pu{5.45 mL}$ of $\pu{0.523 M}$ $\ce{NaOH}$ was required to neutralize the bottom layer

That gives the number of millimoles in the bottom layer.
So the number of millimoles in the ether layer must be the difference, and there are $\pu{25 mL}$ of ether.
I think I figured the concentration out: $0.523\times\frac{0.00545}{0.25} = \pu{0.114 M}$
Or do I need to determine the amount in the aqueous layer by subtracting this number? I.e. $0.456 - 0.114 = \pu{0.34 M}$
I am left with either the answer being $\pu{0.34 M}$ or $\pu{0.114 M}$.
I think the answer is $\pu{0.34 M}$, because the $\pu{0.114 M}$ applies to the bottom layer which is water and needs to be neutralized by the $\ce{NaOH}$ solution, therefore the top layer (ether) has the remaining $\pu{0.34 M}$ of compound A.


texts: Calculating thermodynamic quantities for hydrogenation of iron nitride

texts:
HW#6.3 If the reaction
$$\ce{Fe2N(s) + 3/2 H2(g) <=> 2 Fe(s) + NH3(g)}$$
comes to an equilibrium at a total pressure of $\pu{1 bar},$ analysis of the gas shows that at $\pu{700 K}$ and $\pu{800 K},$ $p_\ce{NH3}/p_\ce{H2}$ are $2.165$ and $1.083,$ respectively, if only $\ce{H2(g)}$ was initially in the gas phase and $\ce{Fe2N(s)}$ was in excess:
a. Calcualte $K_p$ at $\pu{700 K}$ and $\pu{800 K}.$
b. Calculate $Δ_\mathrm{r}S^\circ$ at $\pu{700 K}$ and $\pu{800 K}$ and $Δ_\mathrm{r}H^\circ$ assuming that it is independent of temperature.
c. Calculate $Δ_\mathrm{r}G^\circ$ for this reaction at $\pu{298 K}.$

At first I ignored the excess data, then I assumed that the pressure exerted by the solids is null and adding partial pressures I got an answer (sum of pressure of gases equals 1).
The problem is that part a in the book gives answer $K_p = 1.777$ at $\pu{700 K}$ which I think is wrong. Please help.


texts:
I tried a slightly different set up of a Galvanic cell by inserting the $\ce{Zn}$ electrode into the $\ce{CuSO4}$ solution and the $\ce{Cu}$ electrode into the $\ce{ZnSO4}$ solution. This gave a voltage reading of 0.85 V. I also observed that the $\ce{Zn}$ electrode was getting coated with copper as the reaction progressed.

I had two hypotheses in mind -

The reaction is limited to only one half cell: the $\ce{Zn}$ electrode is oxidised and the $\ce{Cu^2+}$ in the solution is reduced. This explains the coating on the $\ce{Zn}$ electrode, but it does not explain the voltage. Doesn't the voltage mean that there is some interaction between the two cells?
This is my main question: Is it possible that the $\ce{Cu}$ atoms on the electrode are losing electrons that then travel through the circuit and reduce the $\ce{Cu^2+}$ ions in the second half cell? A test for $\ce{Cu^2+}$ ions in the $\ce{ZnSO4}$ solution after the reaction had progressed was inconclusive.

What exactly is happening in this set up?


texts: What are protecting groups in organic chemistry?

texts:
My textbook does not give a very good explanation of what protecting groups are, how they are made, or how they function in Grignard reactions and others. It just gives a couple of examples of protecting groups and that's all.

So my questions are:

How are compounds chosen to be protecting groups? What are the criteria?
I noticed that protecting groups tends to be large molecules, is that always the case?


texts: Stability of unsaturated syn/anti 3-ladderane

texts:
In an oral exam for physical organic chemistry, one student was asked to explain the differences in the ionization potential ($IP$) of syn and anti tricyclo[$4.2.0.0^{2,5}$]octa-3,7-diene (unsaturated 3-ladderane, see Figure).

Apparently, the $IP$s were as follows:

$IP_{1,syn}=9.04$

$IP_{2,syn}=9.38$

$\Delta IP_{syn}=0.34$

and

$IP_{1,anti}=8.97$

$IP_{2,anti}=9.93$

$\Delta IP_{anti}=0.96$

Koopman's Theorem $IP=-\epsilon_{HOMO}$ might help us here. I think it leads us to an orbital diagram. How do I have to combine the $\sigma$-bonds with the $\pi$-system to be able to explain the difference in the $IP$? Maybe you know a paper for it? I checked out Joseph J. Gajewski's Hydrocarbon Thermal Isomerizations (2004), but he only discusses mechanistic features, no theoretical aspects.


texts: Why is it rational that salt-bridges (in proteins) are described as a combination of H-bond and ionic bond?

texts:
This is a fundamental question that came to me as I was trying to draw the electrostatic attraction between Aspartate (D) and lysine (K). I have always considered the charge on nitrogen, in the lysine side-chain (-NH3+), as a real charge. This is because it has always been described to me as an ionizable amino-acid, that can form salt-bridges to carboxylic anions e.g. aspartate (D) or glutamate (E).
The general definition of a salt-bridge is:  a strong electrostatic attraction, a combination of H-bond and an ionic-bond. This is simple enough to memorize and makes sense when one is studying enzyme structure. However, as I started to draw this salt-bridge attraction between lysine (K) and aspartate (D) - it started to seem counter intuitive that a salt-bridge is a type of ionic-bond, as the hydrogens on nitrogen seem to be in the way? I also started to wonder when the charge on nitrogen is real, or simply a formal charge.

Questions on the the definition of salt-bridges in proteins:

Why is a salt-bridge not just simply a hydrogen bond (i.e. not partially ionic)?
If I accept the notion that this is (partially) an ionic bond, how can I tell that there is a real charge on the nitrogen (an not just simply a formal charge)? And furthermore, why won’t the hydrogens (protons) on the ammonium group ‘disrupt’ the ionic attraction?
Is there, perhaps, a defining bond energy that would classify it as ionic (and it happens to be just within this?) otherwise we would simply call it a hydrogen bond?

I also noted that the question is very similar to this , but it does not really highlight how salt-bridges are a combination of both H-bonds and ionic-bond.


texts: How can I find the heat that will be released in kJ per gram for the reaction of Al with Fe2O3?

texts:
Find the heat that will be released in kJ per gram when aluminium ($\ce{Al}$) reacts with $\ce{Fe2O3}$ as follows:
  $$\ce{2Al(s) + Fe2O3(s) → Al2O3(s) + 2Fe(l)}$$

The information given is:

$\Delta H = 12.40 \space \rm{kJ/mol}$ (for $\ce{Fe}$)
$\Delta H = -822.2 \space \rm{kJ/mol}$ (for $\ce{Fe2O3}$)
$\Delta H = -1669.8 \space \rm{kJ/mol}$ (for $\ce{Al2O3}$)

If it asked me to find the heat released in kJ/mol that would be easy:

$$
\Delta H^\circ = \sum \nu_{i}\Delta H^\circ_f (\rm{products}) - \sum \nu_{i}\Delta H^\circ_f (\rm{reactants})
$$

I assumed that there is one mole and I found the mass in grams by multiplying the molar mass of each compound by one mole.

Then I divided the $H^\circ_f$'s by those amounts to get the new values "expressed in kJ per gram"

Then I used the previous equation and I got an answer around 10 but the correct answer is 15.24 kJ/g.

The question is: is the way I used wrong, or is there something else I didn't pay attention to?


texts: What does the prefix "dihydro" in the systematic name of luminol refer to?

texts: I'm doing a research project on the fascinating chemiluminescent molecule luminol, and figured it would be a good idea to start breaking down the systematic name of the chemical and linking the terms to the structure. The systematic name of luminol is 5-amino-2,3-dihydrophthalazine-1,4-dione, and I get it all apart from the "dihydro" - any help? Thank you very much in advance! :)


texts: Number of hydrogen bonds of organic compounds?

texts:
How to count the organic molecules ' hydrogen bonds in average?

What are the numbers of hydrogen bonds formed among alcohols ,alkanoic acids ,aldehyde , ketones , amine ,amide , and ether when they are dissolved in water?


texts: Is carbon dioxide more acidic than carbon monoxide?

texts:
Which of the given compounds is most acidic? $\ce{CO}$ or $\ce{CO2}$ ?

How do I solve this question, and how do I explain it?

I took the oxidation state of carbon in both. The oxidation state in $\ce{CO2}$ is higher, therefore it is more electronegative, so therefore $\ce{CO2}$ may be more acidic.
For $\ce{CO }$ I don't know about the charge so that I can use it to understand if it would give electron or accept electrons, so that I can apply Lewis acid/base theory.


texts:
Questions 8 and 9 refer to the analysis of a salt whose formula is $\ce{Pt(NH3)_xCl_y}$.

  $0.02$ moles [sic!] of this salt required $40.0~\mathrm{cm^3}$ of $2.0~\mathrm{mol\,l^{-1}}$ nitric acid for exact neutralisation.

  The number of moles of $\ce{NH3}$ per mole of salt is

  A 2

  B 4

  C 6

  D 8
  $0.02$ moles [sic!] of the salt were dissolved in nitric acid and excess silver(I) nitrate solution was added. The precipitate formed was filtered, washed and dried. It weighed $5.74~\mathrm{g}$.

  The number of moles of chloride per mole of the salt is

  A 1

  B 2

  C 3

  D 4

For question 8, I first found the no. of moles nitric acid to be $0.08\ \mathrm{mol}$, which is four times the number of moles of the salt. However, I just can't see how I would get $x$ from this. (The answer to this question is somehow B which makes even less sense since that's the number of moles of nitric acid for each mole of salt.)

For question 9, I tried to write a balanced equation for the formation of the precipitate but I don't think that's possible seeing that we don't know $x$ and $y$. Now, I know that the number of moles of the precipitate (silver chloride) is $0.04\ \mathrm{mol}$ which is twice than that of the salt. Yet again, I don't know how I would get $y$ from this. (The answer to this is also B, which is also the number of moles of precipitate for each mole of salt.)
 It would be appreciated if someone could explain how one can obtain the values lf $x$ and $y$ here.


texts:
Which of the following statements is true regarding an ionic bond in $\ce{FeS}$?

  Iron atoms gain electrons and sulfur atoms lose electrons.
  Iron and sulfur ions bond by electrostatic attraction.
  The ionic radius of an iron ion is equal to its atomic radius.
  Breaking an ionic bond between $\ce{Fe^{2+}}$ and $\ce{S^2-}$ releases energy.

My attempt:

I know metals lose electrons. I thought the answer was iron and sulfur ions bond by electrostatic attraction, but a classmate and I have a disagreement, so now I am not sure. I don't think the ionic radius of an iron (II) ion is equal to its atomic radius.

I think it is either 2 or 4.


texts: Reaction Mechanisms: Free Radical Halogenation

texts:
In Free Radical halogenation using chlorine and sunlight, why does the chlorine-free radical get attached to the allylic carbon?
Will it be correct to say that it follows the anti-Markovnikov rule?
But if so, there is no $\ce{H2O2}$ present...
The substrate can be considered as but-2-ene.


texts: Finite probability from discrete distribution and zero probability from continuous distribution in Maxwell-Boltzmann statistics

texts:
I have difficulty understanding a certain concept with the derivation of the Maxwell-Boltzmann distribution $f(v)$ function from Boltzmann statistics. The derivation starts with the Boltzmann statistics formula that gives the probability for an energy $E_x$:

$$p(E_x) = \frac{\exp(-E_x/kT)}{\sum_{i=0}^\infty \exp(-E_i/kT)}$$

From this formula the Maxwell-Boltzmann distribution function is derived:

$$f(v) = \left(\frac{m}{2\pi kT}\right)^{3/2} \cdot \exp\left({\frac{mv^2}{2kT}}\right)$$

I understand that this formula gives the probability density of a particle with velocity $v + \mathrm{d}v$. The reason that the formula gives the probability density for velocities between $v$ and $v + \mathrm{d}v$ is because velocity and thus energy are considered continuous, and therefore just 1 specific value of energy or velocity would have a probability of 0. Therefore, a range of speeds must be taken to give a non-zero probability.

If one specific value of energy or velocity should give a probability of 0, how come the formula for the Boltzmann statistics gives a non zero probability for a specific value of energy $E_x$?
And how can one reason a formula that considers a specific value of energy or velocity to be zero from a formula that doesn't? Is there a way to explain this?

I don't find this to be a duplicate of my other question. My other question states a misconception about translational energy being continuous in general. This question states how the derivation is done between two formulas, one considering energy to be continuous and the other doesn't.


texts: What makes Gold so different from Platinum?

texts:
Looking at Wikipedia, Gold & Platinum are in adjacent seats.

    Platinum                                Gold
[Xe] 4f14 5d9 6s1                     [Xe] 4f14 5d10 6s1
Atomic number of 78                   Atomic number of 79
Atomic pass of 195.084u               Atomic mass of 196.96657 ± 0.000004 u

How does that single electron make such a huge difference?


texts: I always thought vodka was just alcohol and water, and that the ideal vodka was one lacking all flavor components characteristic of the grain or potato mash that it was distilled from. I once saw a vodka process diagram showing multiple distillation and charcoal filtration steps--suggesting an effort to remove all flavor components. But looking at the prices being charged for high end vodkas, I am wondering what the draw is. Are there flavor components in these high end vodkas that make them that much more desirable than pure alcohol that people pay more than $50 a bottle for them?


texts: Is corovin Polypropylene or flat polyester?

texts:
I'm wanting to know what material 'corovin' is as described on some duvet covers.  Googling it, some places say it is just another name for 'Polypropylene' while other places say it is 'flat polyester' whatever that means.

Which is correct?  As far as I'm aware Polypropylene and polyester are different types of synthetic fibers.

Thanks


texts: Importance of concentration of gold in gold parting

texts:
I read following lines about gold parting:

  Gold is not attacked by $\ce{H2SO4}$ or $\ce{HNO3}$, but copper and silver dissolve in them, when concentration of gold is less than $30\%$. If however, the gold content in sample is more than $30\%$, then copper and silver are also not attacked by acid of any strength. Hence, before acid treatment, impure sample is melted to add necessary amount of silver to reduce gold content to quartation.

My question is why aren't silver and copper attacked by acids of any strength when concentration of gold exceeds $30\%$?

Also at the end it's written that:

  Gold is separated and fused with borax and nitre and $100\%$ gold is obtained.

Why do we fuse with borax and nitre $(\ce{KNO3})$ at the end? I don't see any need to do as gold won't react with either of them.


texts:
What is the resultant pressure if 0.6 mol of
ideal gas at 273 K and 1.18 atm in a closed
container of constant volume is heated to
563 K?
Answer in units of atm


texts: Why are full and half filled orbitals the most stable?

texts: Why are degenerate orbitals (restricted to a single spin) less stable when neither fully filled nor completely empty? Why, in most molecules, are half-filled and fully-filled shells more stable than partially filled shells? I understand that transition metals often promote electrons to their d orbital to make it half filled because this makes them "more stable." Why would this be the case? Relatedly, why are orbitals filled with single electrons in one spin before doubling up to form pairs and complete orbitals? Why must degenerate orbitals follow hund's rule? It seems like it would be more stable for electrons to pair up as they are added to an orbital rather than to become additional radicals in the orbital. Is hund's rule a result of maximizing stability, or is there some other principle at work?


texts: Conversion of Z-matrix to Cartesian coordinates

texts:
To begin with, I wrote a script that gets Cartesian coordinates of molecule as input in the below. These are $x,y,z$ coordinates of H2O2 molecule.

1 O          -1.7529   -0.5188    1.3324
2 O          -0.4737   -0.1091    0.7774
3 H          -2.2902    0.1678    0.8933
4 H           0.0636   -0.7957    1.2164

Then, the script constructs a Z-matrix with them, like this:

Z-mat :
O
O   1   1.45335189476
H   1   0.976176039452  2   96.5694760083
H   2   0.976131061897  1   96.5720363573   3   -179.995395182

Now I need to perform the reverse operation and use this Z-matrix as input and define $x,y,z$ coordinates for each atom. This is converting a Z-matrix to Cartesian coordinates.

My question is after setting first atom as 0,0,0

1 O          0   0   0

and the second one as 0,0,(distance from first) to put it on the z-axis

2 O          0   0   1.45335189476

How should I treat the 3rd and 4th atoms?

The 3rd atom must have coordinates that are something like this if read correctly:

3 H          0   distance*sin(angle)  z2+distance*cos(angle)

Taking z2 as the z-coordinate of atom 2. I am not sure if I should calculate this as z2 + distance.cos(angle) or z2 - distance.cos(angle) and what it depends on, if both are possible.

For the 4th atom, I use spherical coordinates

r, theta, phi = (0.976, 96.572, -179.995)

to calculate $x,y,z$ values from the formulas

x = r * sin(theta) * cos(phi)
y = r * sin(theta) * sin(phi)
z = r * cos(theta)

If there aren't any mistakes up to this point, how I will calculate Cartesian coordinates of the 4th atom using these $x,y,z$ values?

While searching I found TMPChem's work on GitHub and it does exactly what I want. However, in his work, there is a mathematical part that I don't understand:

# get local axis system from 3 coordinates
def get_local_axes(coords1, coords2, coords3):
    u21 = get_u12(coords1, coords2) #calculating vector between that points 1-2
    u23 = get_u12(coords2, coords3) #calculating vector between that points 2-3
    if (abs(get_udp(u21, u23)) >= 1.0):
        print('\nError: Co-linear atoms in an internal coordinate definition')
        sys.exit()
    u23c21 = get_ucp(u23, u21) # unit cross product
    u21c23c21 = get_ucp(u21, u23c21) # unit cross product
    z = u21
    y = u21c23c21
    x = get_ucp(y, z)
    local_axes = [x, y, z]
    return local_axes

What is "getting local axis system from 3 coordinates"?

Here is some context of how this function is used:

bond_vector = get_bond_vector(atom.rval, atom.aval, atom.tval)
disp_vector = np.array(np.dot(bond_vector, self.atoms[i].local_axes))
for p in range(3):
    atom.coords[p] = self.atoms[atom.rnum].coords[p] + disp_vector[p]

The bond vector definition is here:

def get_bond_vector(r, a, t):
    x = r * math.sin(a) * math.sin(t)
    y = r * math.sin(a) * math.cos(t)
    z = r * math.cos(a)
    bond_vector = [x, y, z]
    return bond_vector

Again, the only part I don't understand is # get local axis system from 3 coordinates. What is that function doing?


texts: Reason behind markovnikov's rule in hydration of alkenes via mercury catalysis

texts: Recently I came across an interesting reaction regarding the hydration of alkynes using mercury catalysis (HgSO4) in the presence of sulphuric acid. I've read that after the mercury complex acts like a protecting group by preventing any carbocation rearrangement, water attacks the more substituted site to open up the 3-membered ring formed as an intermediate. But this is a nucleophilic attack (SN2 type) and the more substituted site is more sterically hindered and carries less partial positive charge on it( due to influence of other groups). So why does this occur via Markovnikov's rule itself?


texts: I have a question about the mechanism of the Diels-Alder reaction. Is this a two-electron or one-electron process as described by Fig (a) or (b) respectively or does not matter? How do we know that?


texts:
Over the course of my studies, my lab coat has absorbed a non-negligible amount of different chemicals, some of them nasty organic polymers, some are more insoluble inorganic compounds like $\ce{Cr2O3}$.

Even after washing the lab coat some stains remain. Is there a way to get rid of those, or should I rather buy a new lab coat?


texts:
Why is sodium carbonate less soluble in water than sodium bicarbonate? If you think about their structures, the only thing that is different is that sodium carbonate has two sodium atoms, while sodium bicarbonate has one sodium atom and one hydrogen atom instead of the second sodium atom. Sodium and hydrogen have different electronegativity values, giving sodium bicarbonate polar character.

Does the difference in solubility have to do with the dipole moment of the molecules? If so, how can it be explained in more detail?


texts: What is the difference between galvanization and sacrificial protection?

texts: If we use zinc in both methods, then the same process occurs: zinc corrodes in preference to iron, and eventually zinc has to be replaced. So what's the difference?


texts: Is a triplet state or singlet state more stable? How can an atom have a long lifetime in a triplet state even though two electrons have the same spin?


texts: What causes energy peaks during a molecular dynamics energy minimization?

texts:
I'm minimizing the energy of a protein with NAMD using the fixedatom feature. I put my protein in a water box, and I allow all atoms other than the protein backbone to be unconstrained. After running the minimization, I used VMD's NAMD Plot for NAMD's log file and the TOTAL3 total energy option, which resulted in some energy peaks that weren't present until this step:

Are those peaks normal to have? If not, what causes them?

Here is the NAMD log file. The NAMD configuration file used for the minimization is:

#############################################################
## JOB DESCRIPTION                                         ##
#############################################################

# Minimization and Equilibration of
# Human Pi GST in a Water Box
# N, V, E simulation

#############################################################
## ADJUSTABLE PARAMETERS                                   ##
#############################################################

structure          ionized.psf
coordinates        ionized_h_free_min.pdb

set temperature    310

firsttimestep      0

# output
set output              Cry1_side_free
outputname              $output
dcdfile                 ${output}.dcd
xstFile                 ${output}.xst
dcdfreq                 50
xstFreq                 50

binaryoutput            no
binaryrestart           no
outputEnergies          100
restartfreq             1000

#############################################################
## SIMULATION PARAMETERS                                   ##
#############################################################

# Input
paraTypeCharmm      on
parameters          /usr/local/lib/vmd/plugins/noarch/tcl/readcharmmpar1.3/par_all27_prot_lipid_na.inp
temperature         $temperature

# Force-Field Parameters
exclude             scaled1-4
1-4scaling          1.0
cutoff              12.
switching           on
switchdist          10.
pairlistdist        14.0

# Integrator Parameters
timestep            1.0  ;# 2fs/step
#rigidBonds          all  ;# needed for 2fs steps
nonbondedFreq       1
fullElectFrequency  2
stepspercycle       10

# Constant Temperature Control
langevin            on    ;# do langevin dynamics
langevinDamping     5     ;# damping coefficient (gamma) of 5/ps
langevinTemp        $temperature
langevinHydrogen    off    ;# don't couple langevin bath to hydrogens

# Periodic Boundary Conditions
cellBasisVector1     -75.1629982   0.0   0.0
cellBasisVector2     0.0    -78.31999779 0.0
cellBasisVector3     0.0    0.0  -98.59599972
cellOrigin          -12.303732872009277 19.206361770629883 -36.690704345703125

wrapAll             on

# PME (for full-system periodic electrostatics)
PME                 yes
PMEGridSizeX        80
PMEGridSizeY        80
PMEGridSizeZ        100
dcdUnitCell     yes
# mobile atom selection:
# protein
fixedAtoms              on
fixedAtomsFile          fixedatoms_backbone.pdb
fixedAtomsCol           B

#############################################################
## EXECUTION SCRIPT                                        ##
#############################################################

# Minimization
minimize            10000
reinitvels          $temperature


texts: Is the S–O bond strength in sulfur trioxide or sulfite anion larger?

texts: Can you please explain the difference between the bond enthalpies in sulfurtrioxide $\ce{SO3}$ and the sulfite anion $\ce{SO3^{2-}}$?


texts: Why is equilibrium achieved at different stages of a reaction?

texts:
In other words, I want to know why some reactions attain equilibrium early in the reaction while some reactions obtain equilibrium at the end of the reaction.

Why is this the case?


texts: Can d(x²-y²) form π bonds with other p- or d-orbitals?

texts: $d_{x^2-y^2}$ doesn't change sign when transformation of $x\rightarrow-x$ or when similar transformation with $y$ is made. However no such thing occurs with any p- or d-orbital. Thus, can we say that $d_{x^2-y^2}$ don't form $π$ bonds with any p/d-orbitals?


texts:
A question in my book was as following:

  Benzine and chloroform are considered very toxic organic solvents that dissolve in each other and in a solution of benzine and chloroform there is 0.45 mol of benzine. Find the  the percent of mass( percent concentration solutions) in this solution.

In the answer, It assumed that the number of moles in the solution is 1 mole then subtracted 0.45 to get the number of moles of chloroform.

Why did he do that? Why specifically 1? It will obviously change if I assume any other number. (Unless I multiply the number of moles of benzine by that number)
Or should we just say that for every a certain amount of moles of that solution has a percentage and every other percentage is right if it follows the same instructions?


texts: I want to make NaOH from NaHCO3, what is the easiest way to do it without electrolysis?

texts:
I want to make NaOH from NaHCO3.
I can't use electrolysis as I lack the proper equipement.


texts: How to drain engine oil by understanding oil viscocity issues

texts:
I asked this on the stackexchange automotive site but didn't get much response perhaps because it entails some chemistry knowledge. I could have asked without mentioning the automotive details however I think it puts the question into context making it easier to give a good answer.

When you drain an engine of oil in some engines about 12.5% of old oil remains because it coats engine parts, sits in galleys, and some is at the bottom of the sump container(below the drain plug) and won't come out unless you tilt the car which is quite impractical.

The general approach is to remove the older oil by dilution\further oil changes. As an example if you have a 4 liter capacity and an oil change allows you to fill 3.5l new oil, this means 0.5l\12.5% of old oil remains and so a further oil change will reduce the initial 12.5% to 1.5% and a further oil change to 0.19%.

However from my understanding this won't work when you mix oils of different viscosity because oils of different viscosity do not mix when they settle at cold\low temperature(which is where it will be at point of drain). But they do mix when they are at hot\engine temperature.  Is this correct?
Do I need to be using the same viscosity oil to ensure dilution happens at point of drain e.g. 5w30 needs to be mixed with 5w30 but adding 5w40 to 5w30 won't get the dilution effect? What would happen if you added 10w40 to 5w30, would you get dilution at point of drain?

Also how do the oils settle in practice? would the thinner oil sit on top of the thicker oil?  Therefore if you are trying to dilute with a thinner oil the thicker oil may settle below the drain plug and sit below thinner oils in galleys so it may not dilute\get drained with successive oil changes?
Suppose I had a container with 0.5 liter of 5w30 and 3.5 liters of 5w40 would the latter sit below the former? What if you had 5w30 mixed with 10w40?

Also can factors besides viscosity e.g. additives in oil or any other factors affect dilution?

My issue is that I have 0.5 liters of black and thick looking oil in my engine(which I think is affecting performance) and I don't really know the viscosity of the oil they put in.  I don't want to do countless and costly oil changes trying to get it out so approaching this in an educated way may help.

Thanks.


texts: Why is the thione tautomeric form of 2-Mercaptopyridine favoured?

texts:
During some organic chemistry studies (through an old online course material) I ran into a doubt about the equilibrium in tautomeric forms of some heteroaromatics.

First, the context:

On the course webcast, it was said that on the molecule 2-pyridone we have a tautomerism equilibrium like in the image below, where the pyridone form is favored instead of the 2-hydroxipyridine form.

Pyridone Tautomerism Equilibrium

Each tautomer have 2 major contributors for resonance, listed on the image below (for the 2-hydroxipyridine and 2-pyridone respectively):

On the 2-hydroxipyridine resonance forms (left) we have on the left side of the equilibrium an aromatic uncharged molecule and on the right side an aromatic charged molecule. However the most electronegative heteroatom (oxygen) is positively charged and the nitrogen negatively charged. This makes this resonance form a weaker contributor.

On the 2-pyridone resonance forms (right) we have on the left side of the equilibrium a non aromatic (8pi $\ce{e-}$) uncharged molecule and on the right side an aromatic (6pi $\ce{e-}$) charged molecule, where the oxygen is the negatively charged heteroatom, matching the electronegativity character of each heteroatom. This favors the 2-pyridone tautomer.

Another factor mentioned was the dimerization of the molecule, which was geometrically favored in the 2-pyridone form, as seem below:

So far so good, the doubt comes when the tautomers of 2-mercaptopyridine are discussed.

Tautomers equilibrium of 2-mercaptopyridine:

It's known that the thione form (right) is favored. It's not explained as detailed as in the pyridone case why, so I decided to analyse it.

I've drawn the 2 major contributors of resonance on each tautomer. I'll show and discuss them.

First the thiol tautomer form resonance contributors:

On the left we have an uncharged aromatic (6pi $\ce{e-}$) molecule. On the right we have a charged and non aromatic (8pi $\ce{e-}$) molecule, with a positive charge on sulfur and a negative charge on nitrogen.

Now the thione tautomer form resonance contributors:

On the left we have a non aromatic (8pi $\ce{e-}$) uncharged molecule. On the right we have a charged aromatic (6pi $\ce{e-}$) molecule, with a negative charge on sulfur and a positive charge on nitrogen.

I could make the following assumptions after drawing those:

1) Considering only aromaticity, none of the tautomeric forms are favored, since both forms have one aromatic contributor and one non aromatic contributor.

2) Considering the heteroatoms electronegativity, knowing nitrogen is more electronegative than sulfur, the thiol tautomer would have the right charges on its charged resonance contributor, being more stable than the thione tautomer.

3) Considering the geometry for dimerization, the thione tautomer seems to have a better geometry for the hydrogen bonds and would be favored over the thiol tautomer.

Only assumption (3) is in favor of the thione formation, however it's the favored tautomer. Why so?

In the course webcast, the teacher makes it sound like having the negative charge on the sulfur and the positive charge on nitrogen would be the right charge distribution. Wouldn't the opposite be true considering that sulfur is less electronegative than nitrogen?

Here's a youtube link to the webcast mentioned:
Hydroxypyridine-Pyridone Tautomerism

Thank you in advance!

EDIT NOTE:

When I originally wrote the question, I made a mistake while counting the thiol tautomer pi electrons on the resonance form of the right. I originally counted 6pi $\ce{e-}$, but it actually has 8pi $\ce{e-}$ (4 from the carbon-carbon pi-bonds, 2 from the nitrogen lone pair and 1 from the sulfur-carbon double bond), which means the right resonance form isn't aromatic. Thus aromaticity doesn't favor neither of the tautomers. The question still makes sense though, so I'm fixing the mistake and keeping it.


texts:
Just wondering if I'm interpreting this correctly. So in SEM, and particularly the EDS mode, the beam irradiation refers to the beam irradiation from the thermionic emission gun. This paper measures the EDS spectra with varying degrees of irradiation in a 2D structure of BiOCl, noting that the structure of the compound changes under high beam irradiation to disintegrated domains of bismuth nanoparticles. I'm wondering is this a problem that is often encountered in EDS when trying to analyse the elemental composition of a sample in many other compounds?
Many Thanks


texts: The "rules" for LCAOs in Molecular Orbital Theory

texts:
In our course on physical chemistry, which involves MOT, we have been taught that in the LCAO approach, the wave function for a molecule … say hydrogen ion ($\ce{H2+}$), can be approximated by a linear combination of two atomic orbitals.

From what I could gather from the very little I know about variational method is that this linear combination is going to be then optimised to give the minimum energy to find the ground state of the molecule in question. Is this correct?

Also, if we are simply using the linear combination as a test/guess function for a variational method, why should we restrict ourselves to only (say $+$ and $-$) two combinations?
That is, how does the rule "Number of molecular orbitals = Number of atomic orbitals constituting them" arise?

Also, why is there the restriction in form of the rule that "Only atomic orbitals of close energies and proper symmetries combine to give MOs"?


texts: Electrolysis of copper sulphate using copper electrodes: Mass lost from anode is greater than mass deposited on cathode

texts:
In short, the aim of my experiment is to determine how the concentration of sulphuric acid in solution affects the mass liberated and deposited at copper electrodes, when copper sulphate is electrolysed.
Over all data points, what I observed is that the mass deposited at the cathode was lower than the mass liberated at the anode. Theoretically, the two should be equal, and even experimentally I expected the opposite to be true, due to oxygen production taking place at the anode which could disrupt the liberation of copper. The voltage was kept constant at 3V, so I monitored the current over the duration of the experiment. I observed that the current increased, which further suggested that more ions were released at the anode than deposited on the cathode, as  that represents an increase of positively charged particles in solution and thus an increase of current density.
Now, perhaps the liberation of oxygen facilitates the oxidation of the copper anode? Is this my misunderstanding?
Additionally, I was unable to find conditions which would stop the production of hydrogen at the cathode. The voltage required to electrolyse water is 1.23V, but if I set my voltage to that low, no plating took place either. Is hydrogen also expected to be produced alongside the plating process? Maybe, the hydrogen production was disrupting the plating? In that case, what is the explanation for why hydrogen was produced at the cathode in the first place? Since copper is lower in the reactivity series than hydrogen,  no hydrogen should be produced.
Can someone point out the flaws in my experiment or where I've misunderstood things. I don't have much experience with electrochemistry. Thank you!


texts: Question on the formula to calculate enthalpy change from calometric data

texts:
I have a sample question here.
"In an experiment, a student placed 20cm^3 of a solution containing 0.04 mol of HCl in a plastic cup and added 20cm^3 of solution containing 0.04 mol of Na2CO3. The highest temperature rise is 15K. If the heat capacity per unit volume of the final solution is 4.2JK^-1cm^-3, what is the enthalpy change of reaction?"
And what I calculated was:
Assuming that the density of the final solution is equal to the density of pure water, 1.00gcm^-1
∆H = (mass of final solution x heat capacity of final solution x maximum ∆Temperature)/ number of moles of the limiting reagent = (40 x 1 x 4.2 x 15)/ 0.04 = 63kJmol^-1
However, the correct answer was 126kJmol^-1.
Am I using the formula correctly here? Or is there something wrong in my calculations?


texts:
Can ethyl alcohol fumes be suppressed by a household air purifier/filter? In general, how are the fumes suppressed? How is it done?

Can somebody direct me to some information regarding this? I've been searching but do not have the strongest background in chemistry (I'm a mechanical engineering student). I've done some research on filtering media as well as ethyl alcohol itself.


texts: Why is the pKa (COOH) of alanine and glycine similar but the pKa (NH3) different?

texts:
Alanine is heavier with a ($\ce{-CH3}$) than glycine which has an ($\ce{-H}$). What makes them have different $\mathrm{p}K_\text{a}(\ce{-NH3+})$ $(\mathrm{p}K_\text{a}: \text{Ala}=9.69, \text{Gly}=9.60)$ but similar $\mathrm{p}K_\text{a}(\ce{-COOH})$ $(\mathrm{p}K_\text{a}=2.34)$ when the rest of the amino acid is similar? Why does changing a hydrogen for a methyl group affect the $\ce{-NH3+}$ but not the $\ce{-COOH}$?

Also there are three amino acids (glycine, leucine, aspartine) which have same $\mathrm{p}K_\text{a}(\ce{-NH3+})$ but different $\mathrm{p}K_\text{a}(\ce{-COOH})$.


texts: Chemical reaction between dichloromethane and solid carbon dioxide

texts:
I studied heat transfer liquids with low melting point (coolants), and how fast their temperature decreases when they are contacting with solid carbon dioxide. Nearly all liquids (brines, glycols etc.) that I studied have similar behavior, except dichloromethane.

When I put solid carbon dioxide grains into dichloromethane, the temperature of the liquid dropped nearly immediately! At first, the temperature was $\pu{20^\circ C}$, and after just $\pu{5 s}$ the temperature of the liquid was $\pu{-70^\circ C}$! Do you know why is it possible? When I freezed $\ce{KCl}$-brine, the temperature had been decreasing from $\pu{20^\circ C}$ to $\pu{-40^\circ C}$ for more than $\pu{5 min}$!

This property of dichloromethane may be very useful. I think it is due to its low viscosity.

Can you help me and explain this phenomenon?


texts: What elements in Tomato and Spinach make them cook quickly when cooked together?

texts: I have started experimenting on cooking these days and I have noticed that when I add spinach leaves and tomato, they cook very quickly. The spinach melts very fast and the tomato melts fast also - after adding a spoon of table salt. My question is what is the reason behind it. Is it something to do with oxidation?


texts:
It is known that the benzene dimer has two stable structures, T-shaped ($\ce{C_{2v}}$) or parallel-displaced ($\ce{C_{2h}}$) structure.

Now the question is: does the dissociation energy ($\ce{D_0}$) $$\ce{(C_6H_6)_2 -> C_6H_6 + C_6H_6}$$ depends on the structures?
Or it is independent of the structures?


texts: Why does hyperconjugation help for ring cleavage?

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The question was to rationalize it the ring cleavage happens concerted or non-concerted.

The papers "The Mechanism  of  the Thermal Decomposition  of
1-Pyrazolines and Its Relationship  to
Cyclopropane Isomerizations" (Crawford 1965/1966; Original papers: here and here) have shown the loss of $\ce{N_2}$ is supposed to be concerted.

I think the C-C/C-D(H) bonds of the central position of the ring are involved in a hyperconjugative fashion, so its hybridization does matter.  The out-of-phase linear combination of the $\sigma^\star$ orbitals looks like a p-orbital, therefore I expect a through-space interaction.

I've drawn the the out-of-phase combination as following:

Now my problem is, that I don't see why the out-of-phase combination is involved in hyperconjugation, because I think the overlap is best in the educt, less good in the transition state and has no orbital overlap to the product because the out-of-phase $p$ orbital is kind of perpendicular to the $sp$ Walsh orbitals which lies in the C-C-C plane.

How can hyperconjugation help to understand the observed kinetic isotope effect results?

Summary:

How does the FMO picture (HOMO-LUMO) with all involved bonds for hyperconjugation looks like?
Can the ratio 66%:34% be explained?
What does reactant 3 make compared to 2?
How can the ratio 1.07/1.20 be explained?

Do you have any ideas?


texts: When is the carbaldehyde suffix correct?

texts: Is benzene carbaldehyde a correct name for Benzaldehyde? I'm (always) getting confused between common and IUPAC names. If the above name is correct then is it a common one or IUPAC? And why don't we use it more often?


texts: Which is more acidic acetic acid or propanoic acid?

texts:
I got the answer from $K_a$ value that acetic acid is more acidic, but I have also read that inductive effect decreases as the length of alkyl group increases so acetic acid having a methyl group should have greater +I effect than ethyl group in propanoic acid.

And this comparitive large +I effect of methyl group in acetic acid should make it less acidic (as polarity of $\ce{O-H}$ bond decreases) than propanoic acid with ethyl group with less +I effect.


texts: Is there a difference between ‘ammonium hydroxide’ and ‘aqueous ammonia’?

texts:
Water ($\ce{H2O}$) can be added to ammonia ($\ce{NH3}$) in order to form ammonium hydroxide ($\ce{NH4OH}$):
$$\ce{NH3 + H2O -> NH4OH}$$

But we know that ammonia is gaseous at STP so writing $\ce{NH3 + H2O}$ equals writing $\ce{NH3(aq)}$ right?

If yes, then the equation will look like:
$$\ce{NH3(aq) -> NH4OH}$$

So my question is: is ammonium hydroxide $\ce{NH4OH}$ simply aqueous ammonia $\ce{NH3(aq)}$? Or am I missing something?
Can I resume the first equation like this?
$$\ce{NH3(g) + H2O(l) -> NH3(aq)}$$


texts: Hydrolysis of nitriles: Amide vs Carboxylic acid

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I was recently studying the preparation of amides,and one of the methods listed was acid hydrolysis of a nitrile. Up until now I thought acid hydrolysis of nitriles yielded carboxylic acids. How are the methods to get amides and acids different?
I can view the amide as sort of an intermediary stage while getting to the acid,but how do you stop the reaction at amide? Do you use stoichiometric quantities of the acid? This is puzzling me.


texts: What's the difference between alpha-glucose and beta-glucose?

texts: What's the difference between $\alpha$-D-glucose and $\beta$-D-glucose? Are they isomers? Or do they differ in their elemental composition?


texts: Is it relevant to pursue a master degree or a doctorate when applying to a job in the petroleum field?

texts:
I have a few more questions of this type for an interview. ( University work )
Thanks in advance.


texts: Should residual sodium be considered in measuring sodium content of sweat?

texts:
I read an article, "Fully integrated wearable sensor arrays for multiplexed in situ perspiration analysis", which describes the design of a wearable band that detects various components in sweat in order to monitor the wearer's health. One of the components detected is sodium.

My thought is that as the wearer sweats and the sweat evaporates, there will be a small amount of sodium left on the skin. When he sweats again, there should be an increase in the concentration of sodium due to the addition of more sodium from the new sweat to the residual sodium left on the skin.

I didn't see this addressed in the paper and am unsure if my thinking is correct. If I'm correct, wouldn't the sensor then need to have a component that does a calculation of how much sodium is due to the new sweat and how much is residual? Would it need to "know" how much sweat was produced to achieve this? What if the sweat under the band doesn't evaporate at the same rate as the surrounding skin due to being trapped under the band?


texts: Why do the splittings in mirrored COSY crosspeaks differ?

texts: I have a COSY spectrum of a mixture of butanal and butyl bromide and I don't understand why the cross-peaks have various/different splitting on the other sides of the diagonal. I think it may have something to do with polarisation transfer but I'm not sure.


texts: Why is viciously shaking a jar of water work in the thermodynamic sense?

texts:
According to thermodynamics, internal energy can only be increased either by doing work on the system or heating the system. Work done on the system is defined by $$W=-P_\text{external}\times\Delta V$$

So when a jar of water is viciously shaken, the temperature of the water inside is increased. How is work done correlates over here?