texts: What is the convention of numbering carbon atoms in organic molecules?

texts:
I am in high school and haven't had a formal chemistry course, however I am fascinated with biology and picked up a biology book more advanced than the one the school is using to read on my own. The book is: Biology by Peter Raven (2007) ISBN: 0073227390

I am confused about something in the organic chemistry section.

I don't understand the convention that is used to number carbon atoms in for example, glucose.

In case you don't know what I'm talking about, here is an example: a structural diagram of an a-glucose molecule courtesy of Wikipedia.

The numbers next to the carbon atoms, I don't understand how they are ordered. Can someone please explain? I know this is an elementary question for most of you, but the help is appreciated.


texts: Fluorine is the most electronegative halogen and therefore, there is larger difference in electronegativity between the atoms of $\ce{HF}$ than any other hydrogen halide, which means the positive charge on hydrogen atom is the greatest in this compound and hence a comparatively small negative charge is needed to attract it. If so, why is it classified as least acidic hydrogen halide if the $\ce{H+}$ is easy to remove?


texts:
I recently read about Chaos Theory and was wondering if a chemical reaction results in or shows characteristics of chaos (I found a few examples of such reactions here)

  Chaos theory concerns deterministic systems whose behavior can in principle be predicted. Chaotic systems are predictable for a while and then 'appear' to become random.

If the reaction becomes unpredictable towards the time of attainment of equilibrium we can't possibly determine how the reaction will proceed during the time frame so will the reaction attain a state of equilibrium and will it be at the time it should've without chaos being in the picture?

If the equilibrium shifts can we quantify by how much and how much more or less time will it take to attain it in general or we need to take specific reactions and analyze them?

Also after attaining equilibrium can the system again show Chaotic behaviour and if it does what can se say about the state of equilibrium?


texts: What is the relationship between pressure and stoichiometry ratios

texts:
This is the question from the textbook.

Ozone O3 can be prepared in the laboratory by passing an electrical discharge through oxygen gas. Assume that an evacuated steel vessel  with a volume of 10L is filled with 32 ATM of O2 at 25 degrees Celsius and an electrical discharge is passed through the vessel, causing some of the oxygen to be converted into ozone. As a result, the pressure inside the vessel drops to 30.64 ATM at 25 degrees Celsius .

The solutions manual subtracts 3x from the initial pressure of O2 to determine the final pressure of O2 after the electrical discharge(32-3x=final pressure of O2). X is the amount of pressure lost (32-30.63=1.36=x). My question is, how are we justified in using the stiochiometric ratios to determine the final pressure. In other words, how is (32-3x) justified when finding the final pressure of O2.

If my question is not clear. Please let me know and I'll try my best to rephrase it.


texts:
In this previous question the mechanism for the reaction of Tollens' reagent was outlined. As I understand it the oxidising agent in Tollens' is the diamminesilver(I) complex $\ce{[Ag(NH3)2]+}$ but the mechanism only showed the silver ion.

What is the purpose of adding ammonia to the silver nitrate to form the diamminesilver(I) complex: why not just use silver nitrate? Is it purely to provide a source of hydroxide ions or is the structure of the complex ion actually important?


texts: Can isopropyl alcohol vapor damage polymers?

texts:
Since isopropyl alcohol is found in many cleaning products, can the vapor emanating from the isopropyl alcohol corrode, stiffen or react with polymers?

For example, if I use isopropyl alcohol to clean my desk, will its vapor cause any damage to the mousepad, cables and synthetic rubber?

I used 70% isopropyl alcohol to clean my mousepad before, and it ruined the surface by hardening the polymer fibers. I wonder if the vapor can cause the same thing.

Thanks


texts: Why is it a requirement that the ester should have 2 alpha hydrogens in this reaction although we actually need just one for the reaction to occur?


texts: What instrument is used to detect heavy metals?

texts: If i have blood sample, organ tissue sample or food sample, what analytic technique is used in laboratory to detect the ppm levels of heavy metals? What electronic intrument they use?


texts: Discrepancies between specific heat of vaporization of water and enthalpy of formation of water and steam

texts:
According to Wikipedia, the enthalpy of formation of water is $-285.8~\mathrm{kJ/mol}$ while the enthalpy of formation of steam is $-241.818~\mathrm{kJ/mol}$, implying the following:

$$\ce{H2O(l) -> H2O(g)}\qquad (\Delta H=44.0~\mathrm{kJ/mol)}$$

Let us derive the enthalpy of the above reaction using the specific heat capacity of water and the specific heat of vaporization of water instead.

$1~\mathrm{mol}$ of water weighs $0.018~\mathrm{kg}$.

To raise $1~\mathrm{mol}$ of water from $25~\mathrm{^\circ C}$ to its boiling temperature requires $(0.018~\mathrm{kg}) \times (4200~\mathrm{J~kg^{-1}~K^{-1}}) \times (75~^\circ\mathrm{C}) = 5.67~\mathrm{kJ}$.

To turn that amount of water to steam requires $(0.018~\mathrm{kg}) \times (2258~\mathrm{kJ~kg^{-1}}) = 40.644~\mathrm{kJ}$.

Adding these two terms give $46.314~\mathrm{kJ}$, implying the following:

$$\ce{H2O(l) -> H2O(g)}\qquad (\Delta H=46.314~\mathrm{kJ/mol)}$$

Is the discrepancies between the two thermochemical equations simply due to measurement inaccuracies?


texts: How do electron donor groups affect the polarity of an O-H bond in alcohol?

texts:
My textbook (Chapter Alcohols) , says:

  An electron releasing group ($\ce{-CH3}$, $\ce{-C2H5}$) increases the electron density on oxygen tending to decrease the polarity of $\ce{O-H}$ bond.

Now, my question is that if the electron density increases on oxygen, then shouldn't the polarity of the bond increase? Why does it decrease instead?


texts: What's the future of an organic and/or analytical chemist?

texts:
what can I do with a degree in analytical chemistry other than working in the lab?
And what is the future of being an organic chemist?
Can I be a researcher in both of them?
Or it's better to take organic chemistry if I want to be a researcher?


texts: Why do strong acids have weak conjugate bases?

texts: This question is based on the Brønsted-Lowry model. I saw many answers to similar questions online. However none of them have given a detailed answer that is based on molecular structure (the answers all told the OP to rely on a reference table for a way to identify strong and weak acids).


texts: Why is it that weak bases usually contain nitrogen?

texts:
Why do weak bases usually contain nitrogen? I know there are two electrons on top for a bond of $\ce{H}$ but why is it mostly nitrogen? I know there are other elemental bases too but why do I keep seeing $\ce{N}$'s mostly?

Is there something special about nitrogen in this respect?


texts:
I have a question on the order of the spin-orbit molecular states. I understand how to find the terms that split from a parent molecular state in a diatomic molecule. But my question is on how to find whether the multiplet states are normal (regular) or inverted. For example, if we take $^3\Pi$, this state will split into $^3\Pi_{0^+}$, $^3\Pi_{0^-}$, $^3\Pi_1$, and $^3\Pi_2$. How can we know the order of these states, that is to say normal (regular) or inverted? If they are in this order: $^3\Pi_{0^+}$, $^3\Pi_{0^-}$, $^3\Pi_1$, and $^3\Pi_2$; or in that order: $^3\Pi_2$, $^3\Pi_1$, $^3\Pi_{0^-}$, and $^3\Pi_{0^+}$.
In Spectra of Diatomic Molecules book, by Herzberg, he pointed out these terms, and gave the following equation:
$$T_e=T_0+A\Lambda\Sigma$$
where $A$ is a constant for a given multiplet term.
He also stated that if $A$ is positive, this will give rise to normal (regular) terms. However, if $A$ is negative, we get inverted terms.
So is there another way to find out other than this way? And by the way, how can we determine $A$?
Thanks a lot...


texts: Why is melting point of Vanadium higher than Iron?

texts: The iron is found to have four unpaired electrons while vanadium has 3 of them. we say the binding energy is directly proportional to number of unpaired electrons and hence number of  metallic bonds in the structure. By this logic, iron should have high melting point than vanadium but no. Iron has a m.p of 1535 degree celsius while vanadium has 1917.


texts:
We have two bottle named $\ce{H2SO4~(aq)}$ and solution of $\ce{NH3}$ but we don't know their name actually. What I have to do to detect these solution  by only using :

$\ce{CuCl2}$

or

$\ce{NaCO3_{(s)}}$


texts: How to find a full electron basis set that approximate a given ECP basis set?

texts:
In computational chemistry of transition metals, there are many popular basis sets, from pople+LANL2DZ mixed basis sets, to Ahlrich and Karlsruhe basis sets like def-SVPD, def2-TZVPPD. Often the ECP versions of these basis sets were used to minimise computational expenses. However there are molecular properties such as topology analysis and energy decomposition analysis where a full electron basis set is not only recommended but also necessary.

One of the full electron basis sets commonly used in the literature is the ANO-RCC basis set. However, such a basis set is so large that it computationally infeasible in applications like the EDA2 calculation in serial qchem (where there are no parallelisation implemented) and barely feasible in generating wfx files within hours for analysis. Thus a slightly smaller full electron basis set (if any) is needed to be selected.

Say I start with some ECP basis set X, which I can read the list of all exponents and angular momentum functions used, what is the recommended approach to upgrade it into a full electron version of it so it retains most of the properties of the original basis set while making it full electron. Do I need to perform a benchmarking again and compare single point energies at optimised geometries to be sure?


texts: How do we determine if some metal will undergo passivation under suitable environment?

texts:
The passivity of certain metal fall in order:
$\ce{Ti->Al->Cr->Be->Mo->Mg->Ni->Co->Fe->Mn->Zn->Cd->Sn->Pb->Cu}$

Can we predict the order of passivation theoretically?


texts:
Here are four observations of the reactions of four metals.

Metal F and G react slowly with water
Metal H displaces metal G from its chloride salt solution
Metal E does not react with dilute acids
Metal H does NOT displace metal F from its sulphate salt solution.

What is their order of reactivity, starting from the most reactive metal to the least reactive metal?

F>H>G>E;  H>G>F>E;  H>E>F>G;  G>H>F>E;  None of these

I'm really unsure how to order them     I would say F>H>G>E but thats half guessing.
Can someone give me a clue to arrange them right?


texts:
Is it possible to have Melting point different that Freezing point

I mean is there any element/molecule in the liquid status that freeze at point X Centigrade but when it become solid then you need a higher temperature to become liquid again like X + Y degrees in the same conditions?


texts: Why are there 3N-6 degrees of freedom in molecules?

texts:
Count the degrees of freedom using the minimum number of coordinates required to specify a position.

Let's say there are 3 atoms, 3 coordinates for center of mass, and 3 for an axis. But we need 6 coordinates to specify a line in a three dimensional space: $(x,y,z)=(x_0,y_0,z_0)+t(a,b,c)$. Which line do we choose? Even if we have a line, how do we use the remaining three coordinates to specify the atoms?


texts:
I'm starting to study thermodynamics of minerals and rocks, so sorry for the basic question. I am trying to work out some exercises of a book and I found this:

Calculate the activity of $\ce{H+}$ when the activity of $\ce{Sn^4+}$ is $10^{-10}$ for the reaction $\ce{SnO2 + 4H+ <=> Sn^4+ + 2H2O}$. Standard free energies of formations $\Delta$Fof are: SnO2 = -123.20 kcal; H2O = -56.69 kcal; Sn4+ = 0.65 kcal; H+ = 0.

I used the following equations:

$\Delta$For = ($\Sigma$$\Delta$Fof,products) - ($\Sigma$$\Delta$Fof,reactants)
$\Delta$For = -RTln(K), where R = 0.001987 Kcal/molK and T = 298.15K
K = $\frac{[Sn^{4+}]}{[H^{+}]^4}$, given that the activities of SnO2 and H2O are unit.

The result I found was $3.82 \cdot 10^{-5}$, but the book says the result is $10^{-0.40}$. I assume this is a fundamental error, but given it is also a fundamental principle I need to understand it to proceed in my study.
Thanks in advance for any help.


texts: Comparison of acidic strength between nitric acid and nitrous acid

texts:
These are the structures of nitric acid and nitrous acid respectively:

To compare acid strength, we compare the stability of the corresponding conjugate base. Here conjugate bases are nitrate and nitrite anions respectively.

Now, my point is that in $\ce {NO2-}$, the resonance effect is pronounced, but in the case of $\ce {NO3-}$, we have a case of cross resonance. Put simply, in  $\ce {NO2-}$ the negative charge de-localizes to double bonded oxygen atom. In the case of $\ce {NO3-}$, same thing happens, but we have another $\ce {O-}$ here due to which there is a cross of 2 resonance effects (If I am using the correct terminology). So, resonance effect of nitrate ion should be weaker than nitrite ion and therefore nitrite ion should be more stable.

If I am true then nitrous acid must be a stronger acid, but all my sources suggest otherwise. They insist that in $\ce {NO3-}$, the negative charge is distributed over 3 oxygen atoms, and hence its resonance is more powerful. My confusion is that there are also 2 negatives that need to be stabilized as opposed to one negative in $\ce {NO2-}$.

So what concept am I missing here?


texts: How to RAISE the melting point of water?

texts: It is common that adding common salt into water will lower its melting point. But, is there any way to RAISE the melting point of water? Does it lower the boiling point of water as well? Why?


texts: Can triethylamine/pyridine be used in the synthesis of Labetalol?

texts:
As part of my homework, I had to plan the synthesis of labetalol, a blood pressure drug, from its component parts. One of the steps involved was the following SN2 reaction:

The solutions manual just shows the two being added together, but my mind harkened back to previous reactions I had learned in which triethylamine and pyridine were used when $\ce{HCl}$ was being eliminated. Would that be a reasonable thing to do in this instance, or would these amines compete with 4-phenylbutan-2-amine?


texts: I need to report MoS2 values from Mo and Sulfur numbers

texts:
I'm having a hard time figuring out how to do this and yes, I have the molecular weights, just don't know how to calculate. Been 20 years since college.

EDIT: I'm working with Copper ores. One customer reported Mo% as 5.2, S% as 5.3. The other customer reports $\ce{MoS2}$ values (this particular one is 12.34%) I need to compare these values.

EDIT #2::  I need to report 5.2% Mo and 5.3% Sulfur as ONE value - As "MoS2" if that is possible.


texts:
Why is the first one not a pair of diastereomers while the second is?

The only reason I could think of was in the first $\ce{Me}$ is the same as $\ce{CH3}$ that is same groups even though differently oriented are considered same. While in second $\ce{COOH}$ and $\ce{OH}$ are obviously different. Is my reasoning correct? If it is could someone please state it in better words so that I understand the minute details.
Also I was able to reason this ONLY AFTER the correct answer was told. How to identify if a certain pair of compounds is a diastereomeric pair?


texts: Developing a lab to identify the concentration of casein in organic milk

texts: I am currently attempting to create a feasible lab design that will enable me to identify the concentration of casein protein in organic milk without having to use spectroscopy. Thus far I have thought of separating the casein from the milk by exploiting its pH of isoelectric point of 4.6 to form curdles and filter the curdles out using a filter. Furthermore, I would rinse and leave the curdles to dry till I am left with casein powder. Following this I would compare the weight of the casein powder to the weight of the original sample of milk I extract it from. Is this a feasible method or are the any other alternative ways also not using any major equipment?


texts: Why do we not using concentrated HCl and zinc reaction to prepare hydrogen?

texts:
First apologize for this kind silly question.One of my student ask me this question but I was unable to get a perfect answer from internet.Generally dilute HCl and impure zinc are using for hydrogen production in laboratory.My question is why  do reaction stoped after some little time reaction if we use pure zinc and concentrated HCl?
Is it for coverup zinc by zinc sulphate?
It will be thankful for any kind help.


texts: Why is the Gibbs free energy for phase changes zero at constant temperature and pressure?

texts:
I get that $\Delta G$ measures the spontaneity/capacity of a system to do non-mechanical work, and that if:

$\Delta G > 0$, the reaction is not spontaneous

$\Delta G < 0$, the reaction is spontaneous

$\Delta G = 0$, the reaction is at equilibrium

So why is Gibbs free energy zero for phase changes at constant temperature and pressure?

If it is negative or positive why we say that freezing water releases heat to the surrounding and it is equal to $\Delta H$? If at equilibrium  $\Delta H$ is used to reform liquid how we say it is released to the surrounding. I know I miss something, anyone can tell me?


texts:
I've read that you can reduce lead oxide to lead by heating it with carbon. Does this also work with lead dioxide?
I took apart an old lead-acid car battery and realised then, that there are almost equal parts of lead and lead dioxide.
Already having saved and distilled the acid, I started to think there was a lot more effort involved giving all the safety steps and time than buying the items separately.


texts: Electrophilic halogenation of 4-halo-3-(tert-butyl)phenols

texts:
Question

Correct answer
A,B,C
My thoughts
Correct answer should be A,B. The main role is of the steric hindrance between the halogen atom and the tert-butyl group. So why are we even considering the electronic effects of both the groups? They are common in all the cases.
Further, the answer should be A only as its only the halogen atom changing each time, and hence the steric hindrance due to it. Why are we even considering other factors, as they are common in all the cases?


texts: Can weathering change the composition of something so that it appears different?

texts:
There's a murder trial ongoing in Ireland at the moment and one of the pieces of evidence is a spade found at the scene along with the skeletal remains. It was contended by the prosecution that this spade was belonging to the defendant but while they were similar

  "forensic evidence found the paint splatters on the spade were not the
  same as on the [defendant's] garden fence"

My question is: can something left out in the open be changed either chemically or structurally by the environment such that it appears to be similar but not the same? If so why would this not have been called out as a caveat by the expert forensics witness?

The specifics of the chemical tests weren't gone into in the media (sample article here) so I don't know how accurate it was.


texts: What are the conditions for making amines from alkyl halides?

texts:
From what I understand, to make an amine from an alkyl halide you need to heat the alkyl halide with a mixture of ammonia and ethanol. I have two questions:

Do both ammonia and ethanol need to be concentrated? Because I think I read somewhere that you use a 'concentrated mixture of ethanol and ammonia', although I'm not sure whether the 'concentrated' part refers to the ethanol or the ammonia. I'm guessing it refers to the ammonia.
What is the role of the ethanol? Does it act a a catalyst, or just a solvent, or both?


texts: Why we use -adien- / -atrien- infixes if we need to indicate double bond positions with numbers?

texts: For exemple: instead of Buta-1,3-diene why we don't use but-1,3-ene. In my mind, there would be no confusion when using the nomenclature that way because we use one number to indicate the position of each bond. Is there any particular reason for the use of these infixes?


texts: Why does the dipole moment order of group 15 hydrides increase down the group?

texts:
The order given in my book is

  $$\ce{NH3} > \ce{SbH3} > \ce{AsH3} > \ce{PH3}$$

Phosphorous is more electronegative than arsenic and antimony. Then shouldn't the dipole moment be more in case of $\ce{PH3}?$

And why does the anomaly of $\ce{NH3}$ occur?


texts:
From what I understand about concentration cells - which I never learned about when I took general chemistry - they rely on the fact that if we have differing concentrations of some solute separated by a permeable membrane, they will try to exchange solute and/or solvent to achieve the same concentration or as close to it as possible. Correct?

Now, in a concentration cell, there is no physical exchange of ions. Instead, a salt bridge facilitates the flow of electrons, which either:

a) helps convert solids into ions

or

b) helps convert ions into solids

So in the above problem, we obviously have unequal concentrations of iron(III) ions. We can describe the problem using cell notation:

${|Fe|Fe^{3+} (4.8*10^-7 M)||Fe^3+ (1.3*10^-3 M)|Fe|}$

The flow of electrons will be from half-cell A to half-cell B. These are the reactions:

Half-cell A: $\ce{Fe -> Fe^3+ + 3e^-}$

Half-cell B: $\ce{Fe^3+ + 3e^- ->Fe}$

This increases the $\ce{Fe^3+}$ concentration in half-cell A while decreasing the  $\ce{Fe^3+}$ concentration in half-cell B. This will continue until both half-cells have the same $\ce{[Fe^3+]}$.

So, we can also describe half-cell A as the anode, because it is where oxidation occurs, and half-cell B as the cathode, as it is where reduction occurs.

So far so good?

And if we want to calculate the electrochemical potential of this particular half-cell (wired up to make a spontaneous reaction), we can apply the Nernst equation as follows:


texts: Can we prepare aryl halides by heating with halogen acids?

texts: My book says, we can't prepare aryl halides ($\ce{RX}$, where $\ce{R}$ is aryl group and $\ce{X}$ is any halogen) by treating phenol with halogen acids ($\ce{HX}$, where $\ce{X}$ is halogen). It is said to be, because of partial double bond character of carbon-oxygen bond in phenols ($\ce{C6H5OH}$), which is difficult to break (I don't know how there is partial double bond character). What I thought was, if we assume there is no partial double bond character between $\ce{C}$ and $\ce{O}$, we can heat the reactants (i.e. phenol and halogen acid), so that $\ce{OH}$ bond eliminates from the phenol (which has the least bond dissociation energy than $\ce{CH}$), and $\ce{X}$ can get dissociated from the $\ce{HX}$, then it can add up to $\ce{R}$ (aryl group) to form aryl halide. So, can we prepare aryl halides by heating with halogen acids?


texts: Do dishwashing detergent and stain remover powder/stick have the similar ability to remove collar rings?

texts:
For yellow rings on shirts caused by skin grease or sweat:

Some recommended to use an "Oxyclean" stain remover or stain remover stick
for cleaning.
Some recommended to use dishwashing detergent to brush and wash the
stains, saying "dish washing liquid is designed to remove grease, and
why buy another product (that doesn't work very well -- I've tried)
when you already have one that does?"

From a chemistry perspective, do dishwashing detergent and stain remover powder/stick have similar chemical composition and a similar ability to remove collar yellow rings?

Original dirty collar

After dishwashing detergent and laundry detergent


texts: How to explain the discrepancy between the calculated absorption wavelength within the particle in the box theory and the observed wavelength?

texts:
The experimental observed wavelength for this molecule is 425 nm.

We are supposed to estimate this wavelength theoretically using this equation (energy change in a 1D box), where $N$ is the number of pi electrons.
$$\Delta E=\frac{h^2(N+1)}{8m_\mathrm{e}L^2}$$

$L$ is given as 11.84 angstroms.

I'm getting a wavelength of 200 nm. It seems to be too far off.

Molecule:

I'm counting 22 pi electrons and using that as N

This question is different from How to identify the number of pi electrons in a conjugated system to calculate the HOMO-LUMO gap with the particle in the box approach? in that this question is specifically addressing the discrepancy between the theoretical and experimental wavelengths, whereas the previous question was specific to the number to use for $N$.

Also how does this even make sense? As conjugation increases the energy gap between HOMO and LUMO should decrease. With this relationship as $N$ increases as does the energy gap. To me it makes no sense, how can it be explained?


texts: Strain Energy in di-axial vs di-equatorial

texts: I am dealing with two conformations of cis-1,4-dimethylcyclohexane. One conformation is di-axial, and the other one is di-equatorial. Why does di-axial have higher strain energy. I would make sense if the molecule was 1,3-dimethylcyclohexane because then it would the steric hinderance that would cause higher energy. Is it similar with 1,4-.. conformation? If its not steric repulsion, what factors cause di-axial to have higher strain energy?


texts: How can we rationalise the amount of crystal water in coordination complexes?

texts:
I was wondering why specific number of water molecules are attached to salts like $\ce{CuSO4.5H2O}$? Searching gave me a satisfying picture :

I think $\ce{FeSO4.7H2O}$
 should have a similar structure with $6$ water molecules in coordination sphere. But what about $\ce{MgSO4.7H2O}$? Or $\ce{Na2CO3.10H2O}$? How do we explain that?


texts:
A few weeks ago, I was given this question to complete:

  The ground state electronic configurations of Ti is $\ce{[Ar] 4s^2 3d^2}$
   State whether it follows the Aufbau principle or not. If not, explain why and state what the configuration would be if the principle was followed.

Now, I know the Aufbau principle tells us that when filling orbitals with electrons, the lowest energy orbital is filled first.

Looking at this diagram and the periodic table, I thought the filling was right - $\ce{4s}$ is before $\ce{3d}$ so I thought it was reasonable.

However, according to the Lecturer this is apparently wrong.

He says:

  The $\ce{3d}$ level is at a lower energy than the $\ce{4s}$ and should be filled first according to the principle. It takes the above configuration to minimise the d-d interelectronic repulsion energies. The alternative configuration of [Ar]3d4 would have a higher energy.

I'm slightly confused here.

How am I wrong?


texts: Comparision of ONO Bond angle in NO2 and N2O4

texts:
How can I compare the bond angle between $\ce{O-N-O}$ atoms in $\ce{NO2}$ and $\ce{N2O4}$?

In $\ce{NO2}$ there is lone pair-bond pair repulsion, and in $\ce{N2O4}$ there is bond pair-bond pair repulsion.


texts: Boiling points of alkanes, alkynes and alkenes

texts:
I know that when comparing between these three families, alkynes have the highest MP and BP, followed by alkanes and, lastly alkenes (when comparing the same number of carbons).

I know alkynes "win" because of the triple bond (pulling the carbons tightly together, etc.  I also know the alkynes have the least number of dispersion forces.

So, how come when comparing alkanes to alkenes, the number of dispersion forces "wins out" in determining MP and BP and not the double bond (which also pulls tighter than a single C-C bond)...but with alkynes, the triple bond can "beat out" the decreased number of dispersion forces?


texts: Is it possible to extract magnesium from epsom salt?

texts: Is it possible (at home) to extract magnesium from $\ce{MgSO4·7H2O}$, also known as Epsom salt (or, alternatively, from $\ce{MgSO4}$)?


texts: To understand logic and relation of biochemical cycles

texts:
I recenty learned the Kreb cycle, in that I saw many chemical are same.

I want to know if there is logic/threrom/technique in which I can write a chemical  cycle to get a product i.e I want basic reactions and how to put it in sequence to make a cycle ?


texts: Reaction of Methyl Cyanide with nitroethane

texts:
I want to know the products of reaction of Methyl Cyanide with nitroethane in presence of (Sodium ethoxide + ethanol) and then hydrolysed in concentrated Acidic medium.
According to me ,reaction should be like shown in below picture
Can anyone confirm me if mine is correct?
If not,then please tell the correct products.Thanks!


texts: Iterative method for calculating pH of a weak acid / base

texts:
The problem asks to determine the $[\ce{H+}]$ in a $0.20~\mathrm{M}$ solution of $\ce{Na3PO4}$. The $K_\mathrm{a}$ of $\ce{HPO4-}$ was given as $4.5\times 10^{-13}$, which then allows one to calculate the corresponding $K_\mathrm{b}$ as $2.22\times10^{-2}$.

As any acid-base problem, I simply set up the expression $\frac{x^2}{0.20~\mathrm{M}}=2.22 \times 10^{-2}$ with $x$ being $[\ce{OH-}]$ and solved for $[\ce{H+}]$.

However, the solution involves an interesting iteration which I have never seen before for this type of problem:

Can anyone shed some light on this?


texts: Physical reason for why delocalisation leads to stability?

texts: Why does delocalization of electrons generally make compounds more stable (e.g. in carboxylate anions, where the lone pair on the negatively charged oxygen is delocalised into the C=O π* orbital)? Is there any proper explanation involving quantum mechanics?


texts: What are glues/adhesives for cardboard boxes/crates made of?

texts:
Open cardboard boxes/crates, often for foodstuffs, are often glued to hold their shape. What is the glue/adhesive made of?

I ask to know if it is biodegradable, such that it is suitable for composting/gardening.

My preliminary research seems to indicate polyvinyl acetate (PVA), which seems to biodegrade fast enough for my application.

See example box (from CTHOE at Wikimedia):

Sorry if this is the wrong Exchange, it seemed the most suitable for my question.


texts:
For a lab assignment, I combined $\pu{10 mL}$ of $\pu{1 M}$ sodium sulfate solution with $\pu{10 mL}$ of $\pu{1 M}$ calcium chloride solution. The ionic equation I came up with is:

$$\begin{multline}
\ce{2Na^+ (aq) + SO4^2- (aq) + Ca^2+ (aq) + 2Cl^- (aq) ->}\\
    \ce{CaSO4(s) + 2Na^+ (aq) + 2Cl^- (aq)}
\end{multline}$$

I was then asked, in a lab question, the following:

  If the reaction called for $\pu{1 M}$ chloride ion with $\pu{1 M}$ calcium ion, would you still use $\pu{10 mL}$ of each solution for a complete reaction? Explain your reasoning.

To my understanding, I initially had $\pu{2 M}$ chloride ion and $\pu{1 M}$ calcium ion. With only $\pu{1 M}$ chloride ion instead, the ionic equation would change to this, or so I'm led to believe:

$$\begin{multline}
\ce{2Na^+ (aq) + SO4^2- (aq) + Ca^2+ (aq) + Cl^- (aq) ->}\\
 \ce{CaSO4(s) + 2Na^+ (aq) + Cl^- (aq)}
\end{multline}$$

As a (balanced) molecular equation, to my understanding, this would be:

$$\begin{multline}
\ce{Na2SO4 (aq) + Ca (aq) + Cl (aq) ->}\\
\ce{CaSO4(s) + NaCl (aq) + Na (aq)}
\end{multline}$$

Is this a complete reaction? I have seen conflicting definitions of a complete reaction online:

answers.com says that a complete reaction means all of the reactants are reacted into products.
However, someone on chemicalforums.com says that a complete reaction means that all of the limiting reactant is used up. The University School of Milwaukee seems to back up what the user on chemicalforums.com said ("all of at least one of the available reactants is used up and converted into products").

My main question is thus: what is a complete reaction? No matter my final equation for this lab question, I still need to know what a complete reaction is so that I can identify them in general.

My intuition says that this is a complete reaction, since all of the calcium ions and the chloride ions are converted to products. Is this correct? The leftover sodium ion makes me suspicious, so I don't know how to answer.

I later spoke to my lab instructor and he clarified that the question is asking for me to come up with two arbitrary aqueous solutions, one which contains $\pu{1M}$ of chloride ion and another which contains $\pu{1M}$ of calcium ion, e.g. $\ce{KCl(aq)}$ and $\ce{Ca(NO3)2 (aq)}$.

So in this case, I would need twice the volume of potassium chloride to get the number of chloride ions I need to balance the equation and prevent explosions, i.e. no extra sodium ions leftover.


texts: Why is water instead of hydroxide ions used to balance oxygen atoms in redox half equations?

texts:
When balancing half equations of redox reactions, $\ce{H2O}$ is used to balance any oxygen atoms? For example, this half equation

$$\ce{NO3- → NH4+}$$

is balanced into:

$$\ce{NO3- + 8 e- + 10 H+ → NH4+ + 3 H2O}$$

Why is $\ce{OH-}$ not used instead of $\ce{H2O}$? E.g. the balanced equation becomes

$$\ce{NO3- + 8 e- + 7 H+ → NH4+ + 3 OH-}$$


texts: Problem with the solubility and Ksp of zinc hydroxide

texts:
My book gave me that solubility (g/L) is $4.2\times 10^{-4}$, so solubility (mol/L) is $4.2\times10^{-6}$. Then, using the chemical formula $\ce{Zn(OH)2}$, I know that the solubility product is $K_\mathrm{sp} = \ce{[Zn^{2+}][OH-]^2}$, so:
$$K_\mathrm{sp} = (4.2\times10^{-6})(2\times(4.2\times10^{-6}))^2 = 3.0\times10^{-16}$$

However, the book says that the $K_\mathrm{sp} = 3\times10^{-17}$. Where did I go wrong?


texts: How is the trend of acidity in the sequence: phosphinic, phosphonic, phosphoric acid explained?

texts:
How is the trend of increasing $\mathrm{p}K_\mathrm{a}(1)$ value in the sequence:
phosphinic $(1.24)$, phosphonic $(2.00)$, phosphoric acid $(2.21)$
explained (the image was taken from Housecroft Inorganic Chemistry)?


texts:
Is the following reaction a comproportionation reaction?
$\ce{NH4NO3 -> N2O + H2O}$
The wikipedia definition says:

Comproportionation or synproportionation is a chemical reaction where two reactants, each containing the same element but with a different oxidation number, form a product in which the elements involved reach the same oxidation number.

In the reaction,only one reactant is involved( the definition says two) but two elements with different oxidation number react to form element in an intermediate oxidation state, so what can we say about it?


texts: XeF4 - why are there only 2 dihedral mirror planes?

texts:
I started studying molecular symmetry and I became somehow confused about dihedral mirror planes. I found a definition, which says,  that it is a vertical mirror plane, which bisects two $C_2$ axes.

But when I look at $\ce{XeF4}$ molecule, I see, that it has 4 $C_2$ axes and 4 vertical mirror planes. All of those planes are bisecting 2 $C_2$ axes and both all of them also go through some atom.

Still, there are only 2 dihedral mirror planes $\sigma_\mathrm{d}$ and the remaining two planes are just common vertical ones $\sigma_\mathrm{v}$.

So, could you please tell me what's the real difference between vertical and dihedral mirror planes?

OK, in a link given in comments by Tyberius is said, that dihedral planes are such planes, which bisects as many bonds as possible, while "normal" vertical planes bisects as many atoms as possible. Then I don't get, why ethene (see the picture below) doesn't have one dihedral plane, as one of them clearly bisects its central bond and we can't symmetrically bisect more bonds in this molecule.

$\ce{XeF4}$

Ethene


texts:
I have two questions regarding silanization:

1) How durable is a silanized glass surface? (i.e. How long a silanized surface can be kept without any change in its wettability or contact angle?)

2) What are the optimum conditions for keeping a silanized surface while it's idle and dry? (e.g. maintenance temperature, humidity, etc. Should it be kept in a desiccator or not necessarily?)


texts: Why does denaturation of albumen protein cause pH of solution to increase?

texts:
I'm interested in the denaturation of proteins by alcohols, specifically by ethanol.
I have devised a simple experiment in which I inject solutions of ethanol (of variable concentrations) into solutions of egg albumen (containing proteins such as conalbumin). I have observed a marked pH change in solution after injection of ethanol. The rate of change of pH is in fact proportional to the concentration of ethanol injected (as expected).
However, I am having trouble explaining the theory behind why ethanol's disruption of tertiary protein structure increases pH. As I understand, ethanol disrupts proteins such as conalbumin by disrupting hydrogen bonds in the tertiary structure of the molecule.
But why does this cause the pH to increase (in effect, the concentration of H+ ions to decrease)?


texts: Naming of a Hydrocarbon with a Benzene Functional Group

texts:
What would the name of this hydrocarbon be?

I thought it might have been $\ce{3-phenyl-1-butene}$, however, after searching through a number of chemical websites, I found that 3-phenyl-1-butene isn't the correct name (the structures coming up had the benzene ring attached at the 4th carbon from the $\ce{C-C}$ double bond).


texts: How to completely remove Iron II Acetate from a steel surface through a chemical reaction?

texts:
Is there any suggestion to completely remove iron II acetate from a zinc-alloy steel surface? It can't be something abrasive, or if it is, it must be completely soluble.
Background:
My bike chain, which is made of zinc-alloy steel, got some bits of rust here and there after I cleaned it and left it wet for a while. I wax my bike chain, so the there's no protection against rust. I did some research and decided to sink it in white vinegar in order to get rid of the rust, since I figured between the plates and the pins must have got a bit rusty as well. I sank the chain in pure white vinegar for 10-15' and couldn't see any visible reaction. I guess I had to leave it there for some hours/days. I decided then to put the vinegar and the chain in an ultrasonic cleaner. After some 10-15' I checked it back. The rust was gone, but to my surprise (I'm not a chemist of course :) ), the chain turned completely black/dark brown-ish. I guess the ultrasonic cleaner catalyzed the process.
I guess the brown-ish layer is iron II acetate from what I researched. Basically, the acetic acid reacting with the steel.
My problem is, I want to get the chain completely free of the iron acetate. I was able to scrub most of it off with an iron brush, but only on the outside area. There is residue between the links and inside the pins. I already tried hot water and denatured alcohol (left the chain sank for hours), but none worked.
I wax my bike chain and I do it for a few reasons. It's environmentally friendly as no chemicals are needed to clean it, just hot water. Cleaning is fast and easy and I like to keep the drive train pristine. The issue with the iron acetate is that although the chain looks clean after each waxing. After the first run, the wax turns black-ish and the chain starts to look dirty again.
I read somewhere that NaCL would turn iron III acetate soluble. Maybe that would work for II as well? In any case, I'm not sure dumping the chain into a solution of water and table salt would solve my problem.
Any comments would be very welcome. Thank you very much.


texts: Do we lose significant figures with digital instruments?

texts:
With digital scales, we get an answer to the hundredths or thousandths place, but we do not have the ability to estimate "between the lines".  Is the real significance of a measurement different when it comes from a digital scale, or thermometer or other device than when it is read with the possibility of visual interpolation?

As an example, I might have a digital scale that gives a reading of 25.36 grams.  It could be anywhere between 25.355 and 25.365 grams.  If I read a sliding scale to 25.36 grams, the 6 is an estimate and the true value could range by a few hundredths of a gram while the digital scale at most would have a range of +/- 5 thousandths of a gram.

I realize that you won't have a sliding scale that can match a digital scale anyway, but the same could occur with digital thermometers reading to 0.1 degrees and indicating a range of true value of +/-0.05 while a reported value to the nearest 0.1 degree on a thermometer could be several tenths of a degree off.   So is there any acknowledgement that the reported values have different meanings with regard to significance?


texts: Lost track of the hydrogen in step 3 of the Krebs cycle

texts:
I'm trying to follow the Krebs cycle step by step, accounting for the number of hydrogens in
each molecule before and after reactions.
I've run into a problem starting from step 3.

Isocitrate has five hydrogens.
It undergoes oxidisation to Alpha-Ketoglutarate, with NAD+ being reduced to NADH/H+.
I would say this process entails the loss of two hydrogens from Isocitrate, and the gain of those hydrogens in NADH/H+.
What I don't understand (and this lack of understanding cascades through steps 4 and 5) is that Alpha Ketoglutarate has four hydrogens.
My arithmetic says that there should be only three.
Where does the fourth hydrogen come from?
Note:
If I start from  Step 6, my accounting method works, all the way round to Step 3.
Step 6: Succinate (four hydrogens) is oxidised to Fumarate (two hydrogens), reducing FAD to FADH2.
Step 7: Fumarate (two hydrogens) is reduced to Malate (four hydrogens), by the addition of H2O, gaining
two hydrogens.
Step 8: Malate (four hydrogens) is oxidised to Oxaloacetate (two hydrogens), reducing NAD+ to NADH/H.
Etc.
I came across a similar question at https://biology.stackexchange.com/questions/93775/what-exactly-happens-to-hydrogen-atoms-in-step-4-of-citric-acid-cycle but as this was about step 4, and for me the problem occurs one step earlier.


texts: What Does the Equilibrium Constant represent?

texts:
If the Equilibrium constant stands for the extent of reaction at equilibrium, whether more of forward or backward reaction is taking place, then why is it not affected by factors like concentration of reactants and product?

For example, if you increase concentration of reactant, equilibrium will shift to the right, which means more of forward reaction is taking place, so shouldn'tthe  equilibrium constant change?


texts:
I watched a Khan academy video on organic chemistry functional groups. It mentioned the amine and amide groups.

From what I see, an amide is an amine with a carbonyl group. However, the internet says that that assumption is wrong. I am guessing it has to do with the "R" groups on the amine functional group.

But in the video, he used an example of 2 ethyls (2 carbon chains, not sure what they are called) attached to the nitrogen, and the third R group is just a hydrogen.
So what exactly is an R group, and are all amides also amines? Thanks in advance for the help.


texts: Molecular geometry of BaH2 according to VSEPR theory

texts:
I am asked to predict the correct molecular geometry of $\ce{BaH2}$ according to VSEPR theory.
I assumed that it is linear due to barium being an alkaline earth metal and therefore not having any lone pairs when bonded to two hydrogen atoms, but apparently the bond angle between the two hydrogen atoms is about 119°.
Why is that the case and how can one explain this observation with VSEPR theory?
$\hspace{3cm}$


texts: EPDM tube resistant to ozone on the long run?

texts:
I am working with ozone produced with an ozone generator and pure oxygen.

The resulting O2 / O3 gas mixture is probably about 80-85% O2 and up to 15-20% O3.

The generator does produce about 500g of O3 per hour.

Currently I am using PTFE tubes to bring the O3 where it is needed.

However I am not happy with the mechanical properties of the PTFE tubes, as they are stiff and as a result they are uneasy to work with.

I have found now that EPDM tubes are way easier to work with, but I have doubts about their resistance to O3.

While many datasheets and Wikipedia do tell that EPDM is resistant to O3, I question if it is really resistant to extreme high concentrations of O3 on the long run.

Switching from PTFE to EPDM in the future would be a good thing as EPDM is also cheaper and easier to work with.

Does anyone here have experience with high concentrated O3 and EPDM?


texts: Hydrohalogenation vs Hydration of Alkenes

texts:
So, I am doing an investigation involving the hydration and the hydrohalogenation of ethylene. Essentially, to produce the ethylene, I heat ethanol, in the presence of concentrated sulfuric acid, to obtain ethylene gas, which I plan to bubble into a solution of hydrochloric acid at varying concentrations.

Now, when the ethylene is bubbled in, I imagine that it will react in the solution and there are two possible products it could potentially form; Ethyl Chloride (from the hydrohalogenation mechanism) and ethanol (from the hydration mechanism). The problem is that I want to make a prediction of which product would be found in greater proportion, though I'm not very sure how I might go about doing this.

I'm thinking that, because the HCl dissociates to form hydronium ions and chloride ions, there are more hydronium ions than HCl molecules and therefore, hydration is likely to take precedence.

However, I've also thought that, in both mechanisms, the first step is protonation. In that case, it would also be possible that the chloride might add to the positively charged ethyl carbocation to a greater extent than the water molecules. Again, this is because both the carbocation and the chloride are charged and attract more easily. The oxygen in water is only partially charged and therefore, does not act as a good nucleophile in this case. However, I'm not sure how valid my arguments are.

Could someone help me out with pointing out flaws in this scheme of work?


texts: Are the vibrational modes of CO2 active at room temperature?

texts:
I was doing an experiment whereby I had to measure the specific heat ratios of certain gases. Carbon dioxide came out to be around 1.3, and checking with the accepted values this is close. My question is, the only way I can justify this answer is if $\ce{CO2}$ had 7 active degrees of freedom at room temperature. This implies that the molecule is vibrating.
I am not a chemist and I thought that molecules only store energy in this degree of freedom at high temperatures.


texts: Can chemicals change crystal structure by only touching?

texts: Are there any known, or suspected compounds that take the crystal structure of what ever object they are touching, i.e. if it touches $\ce{NaCl}$ it would turn into a face centered cubic crystal structure.


texts: What are "Secondary Orbital Interactions" in Organic Chemistry?

texts:
We used these to analyze the stability of molecules in an Organic Chemistry Course.
My teacher analyses the stability of compounds on 3 levels:

Atom level by studying the hybridization of the main atom
Secondary Orbital Interactions: he first draws a good resonance structure, he identifies candidates that participate in the stabilization (Candidates are often a Pi or Sigma Bond) then
He draws the Energy Diagram of the Secondary Orbital Interaction.

But I can't see what Secondary Orbital Interactions are, and why do we draw their Energy Diagram?


texts: What is the relationship between current flow and low AC voltages within electrolyte solutions

texts: I have recently been trying to find references or textbooks which may explain the principles of electrical current conductance within an electrolyte solution when low AC voltages are induced. Does anyone have specific expertise or knowledge into this area and may be able to explain or direct me to the right resources or authors? Thanks!


texts: Confusion about hybridization terminology

texts:
I was just introduced to the concept of orbital hybridization. I believe I understand the idea behind it, but there is some accompanying terminology that prevents me from achieving a greater understanding.

In the following image:

I see that one of the electrons in the $2s$ orbital of carbon is promoted to one of the $2p$ orbitals. I start to get confused when hybridization occurs, simply because there are four $\ce{sp^3}$ hybrid orbitals, as also shown in this diagram:

I learned that the name $\ce{sp^3}$ comes from the combination of one s-orbital and three p-orbitals ($\ce{s + p + p + p}$), and this makes sense to me. What doesn't make sense is why each individual hybrid orbital is called an $\ce{sp^3}$ orbital. When the $\ce{2s}$ orbital, for example, becomes an $\ce{sp^3}$ orbital, why is it referred to by its combination with p-orbitals ($\ce{sp^3}$) when it was just an s-orbital before?

Could someone please offer a simple explanation that would help clear this up? Why is each individual hybrid orbital called an $\ce{sp^3}$ orbital? It seems like all four orbitals together should be called $\ce{sp^3}$, because they all make up the combination defined by $\ce{sp^3}$ ($\ce{s + p + p + p}$).


texts: What is the chemistry of this household cleaning recipe?

texts: What would be the product if baking soda and common salt and vinegar are added together?


texts: Application of the electronegativity effect on bond angles

texts:
There's a rule in determining molecular geometry that says that if the electronegativity of the central atom increases, the bond angle of the molecule increases.

Is this is only applicable in the cases where the molecular geometry of the said compounds are similar? For example, considering $\ce{ClF3, BF3,}$ and $\ce{ PF3}$, they're primarily differentiated on the basis of them having different geometries.


texts:
For the bond lengths (ranking  them longest to shortest) I think that it would be A>C>B

My thought is that bond-B is a double bond (so the shortest), bond-A is the longest because it is only connected to one double bond when C is connected to two double bonds.

Does that logic work out for these problem types?


texts: Why doesn't diamond conduct electricity but silicon does?

texts:
Diamond's structure is a large network covalent crystal, where there are strong covalent bonds between neighboring tetrahedral carbon atoms. The explanation I was given was:

  The electrons are held tightly in the covalent bonds of the structure, so they are unable to move around. Thus, diamond cannot conduct electricity.

Why is it then, that in silicon (also a network covalent solid), which has an identical crystal structure to diamond, is known to conduct electricity relatively well and even dubbed a semiconductor? Aren't the electrons held tightly in the covalent bonds between neighboring silicon atoms?


texts:
In crystallization, crystals are formed from liquids by cooling.

How can crystals be formed from a gas by cooling?


texts: Carbocation formation and stability from bromo compounds

texts:
When heated,the following bromo-species all form carbocations via $\sigma$ bond cleavage. For each structure draw the corresponding carbocation and briefly describe how it is stabilised.

This is my attempt at answering the question:

I would like to know whether I have drawn the correct carbocation forms of each of these bromo-compounds and if my reasoning is sound.


texts: can anyone tell me the difference between absorption spectroscopy and extinction spectroscopy in terms of experiment? and how to get extinction spectroscopy, how to get absorption spectroscopy? Thank you so much.


texts:
What is the rate determining step in the following energy profile? To clarify, the reaction is:

A -> B -> C

The energy of A is greater than B which in turn is also greater than C. The intermediate A-B is higher energy that the B-C intermediate but the energy gap between B and the intermediate B-C is greater than from A to the A-B intermediate. I hope this is clear.


texts: EDTA titrations of singly charged cations

texts: It is well known that EDTA can be used for titrations involving complexations of highly charged metal cations, with the most well known being those of the alkali earth metals and transition metals. However, would it be possible to analyze metal cations such as the alkali metals or singly charged transition metals?


texts: Bibenzimidazole nomenclature: Indicated H and locants

texts:
I am trying to understand how the locants work for the following molecule (locants added by me).

I added the locants following IUPAC Blue Book rules from 2013, P-14.4. Basically, first numbering heteroatoms in the ring, assigning the highest locant to the one with an indicated hydrogen, and then number clockwise around the ring (red locants).

I assumed the same would go for the second ring, so the name would be:

$1^1H,2^1H-1^2,2^7-\text{bibenzoimidazole}$

However, Chemdraw says the name is:

$1H,3'H-2,4'-\text{bibenzo[d]imidazole}$

I get the differences between the prime and composite locants (P-14.3.1), however it shows a numbering more like:

Is Chemdraw wrong or am I missing something here? If Chemdraw is right then I'd assume that for some reason the ring assembly has preference for a lower locant, but I can't find the rule that states this in the Blue Book.


texts: Removing trace amounts of water from agricultural grade anhydrous ammonia

texts: Agricultural grade anhydrous ammonia (liquefied gas) contains 2000 ppm $\ce{H2O}$. What would be the process to remove this water to obtain refrigeration grade (<100 ppm $\ce{H2O}$) anhydrous ammonia?


texts:
I'm working with some orchid species, and i encounter a specific issue. Some of those species deposits upon their seed coat a wax layer. This layer makes seeds behave in a very hydrophobic way. You cannot dispense them in a pour water.

That behavior has many impacts. One of the most significant is that it does not let water come in touch with the actual seed and then with embryo to make it sprout.

So i tried many ways to remove that layer but nothing actually seemed to work out.

I treated seeds with the following chemicals:

a) 1% NaOCl with some dish soap water solution for 10min. After throwing seeds into this solution you could see that they can be evenly dispensed in it and come in touch with the solution. But if you wash them up with pure water for example 3 times they are getting back their hydrophobic behavior.

b) 1% H2SO4 water solution for 10min. I thought that with this treatment waxes will be removed from the seeds but nothing like that happened. Maybe they had been better dispensed in the pure water comparing to the previous treatment but nothing significantly changed.

c) 93% ethanol solution for 1, 2, 3, ... 30min. results here were also very disappointed. While the seeds are immersed into ethanol, they were very well dispensed into the liquid without any hydrophobic behavior. After three washes with pure water, hydrophobic properties came back.

Treatment time seems not to play any significant role on the results.

My conclusion is that there is no destruction of the waxes with the above chemicals. The only thing that happened probably, is the creation of a Micelle around the seed, which make it for a while (the time that it was in the solutions with soap and ethanol) non hydrophobic.

Finally my question is, if there is any way to destruct chemically, to some grade the waxes. So even when you put the seeds in a pour water not be so much hydrophobic.

Thank you.


texts: Electolysis of H2O to produce O2(g), in a small, portable unit

texts:
Full disclosure, I'm just a high school chem student, but I've got this question and I couldn't find the answer anywhere online.
I was reading an article about some futuristic "artificial gill", which kinda sounds like BS to me, but it got me thinking about this.

http://www.smithsonianmag.com/innovation/student-claims-have-designed-working-artificial-gills-180949465/

We were just learning in class about electrochemistry, and we just did electrolysis, so I was just thinking, instead of filtering the water, what if they used electrolysis to produce O2 gas?
There would still be hurdles, like diluting the 100% O2 to about 20% gas by volume, storing the necessary electric power to drive the reaction, and making sure that the unit wouldn't blow up, but could it theoretically work if we could overcome these other issues?

Basically, could you produce enough O2 gas to survive, through the electrolysis of H2O, in a unit small enough for a man to use?


texts: Would osmosis occur between two solutions of equal moles of water but unequal moles of a nonpolar molecule?

texts:
Earlier I learned that osmosis was, like diffusion, a result of the laws of entropy, kinetic energy, and random movement. However, if you have two solutions of equal moles of water, then net movement should be zero, right?

In the case above with equal moles of water, if you now have a semi-permeable membrane (allowing only water molecules to cross) and solutes dissolved in the water (at difference concentrations), then there would still be net movement of water molecules towards the concentrated solution. There was an explanation in my AP Bio textbook that the water molecules hydrating the solutes were unable to pass through the membrane, so net movement occurs because of a difference in free water concentration.

Now I am just wondering what would occur if you had a nonpolar molecule instead of a solute. Would the arrangement simply remain at this?

I just wanted to see if I truly understood this concept.


texts: What is the order of nomenclature priority among an alkyl side group, a double bond, and a triple bond?

texts:
I saw the below structure in a video on YouTube and was confused by the fact that while they were numbering it, higher priority was assigned to the methyl than the triple bond:

According to the priority table on Master Organic Chemistry, the opposite is true, and the triple bond should have priority.

Also I saw this structure:

According to the same priority table, shouldn't a double bond have higher priority than a triple bond, and hence the numbering should start from the left?


texts: What is Inversion Temperature in terms of Joule Thomson Effect? Does Critical Temperature depend upon Inversion Temperature?

texts:
I couldn't find a clear answer in my book and on the internet.
Please help! Your quick response will be appreciated.


texts: Decrease in molar conductivity with increase in concentration

texts:
Why does molar conductivity $Λ$ for strong electrolytes decrease with increase in concentration? I mean, more concentration would mean higher number of solute particles present in the solution, and as it is a strong electrolyte all of them would  disassociate and can help in conduction of electricity, so the $Λ$ should ultimately increase, but $Λ$ is given by

$$Λ_\mathrm{m} = Λ^°_\mathrm{m} - Ac^{1/2}$$

What am I missing here?


texts: Let us say that height of HCP is h then what is the distance of tetrahedral voids

texts:
In a hexaoal cose-packedstructue et $h$ be the spacing between equivalent basal planes.  Then what are the "heights" of the tetrahedral voids lying between any two adjacent, equivalent basal planes, as distances from either plane?

The book gives the answer $h/8$ and $(7h)/8$. How is this derived?  My (the original asker's) expectation, based on how I understand the hcp structure, was that the heights would be $h/4$ and $(3h)/4$.


texts: What is dielectric constant and how does it explain the reason why water is one of the best solvents

texts: When i was reading solublity of ionic compounds,they mentioned that polar compunds are fairly soluble in polar solvents and water is better solvent due its high dielectric constant.Can anybody explain what is it and how does it affect solublity.


texts: According to MO theory, do 1s orbitals in dioxygen interfere?

texts: According to MO theory, are the 1s orbitals in $\ce{O2}$ too radially contracted to interfere with each other and thus cannot form bonding and antibonding orbitals, or do they still do that?


texts: The effect of the groups at para position on SN2 reactivity

texts:
Compare the SN2 reactivity order for:

The benzyl group stabilises the transition state of SN2 reaction using the π system of the benzene ring for conjugation with the p- orbital of the electrophilic carbon which is electron deficient. (reference: Clayden, page 341)

So in my opinion, groups increasing the electron density of the ring should make the SN2 reaction go faster as compared to groups decreasing it.

Thus the order should be $2 > 3 > 1 > 4$ but the answer given in my worksheet is the exact opposite of this. I would like to know the reason for that and the flaw in my reasoning.

This is what I found in March:

  Holtz and Stock showed that electron-withdrawing groups increase the
  rate of SN2 reactions. This can be ascribed to stabilization of the
  transition state by withdrawal of some of the electron density.

I find this contradictory to the content given in Clayden that the TS is "electron deficient". In March its also given that for alkyl groups at para position the Baker Nathan order is followed (methyl > ethyl > t-butyl). (Hyperconjugation is most in methyl so it increases electron density of the ring) (Another  apparent contradiction)

So how exactly do I determine the effect of the p-substituents in SN2.


texts: Is CH₃CH₂CH₂Cl saturated or unsaturated?

texts: I believe the molecule $\ce{CH3CH2CH2Cl}$ to be saturated, since there are only single bonds between the carbon atoms, but my workbook says it's unsaturated. Why?


texts: How do I find the hybridisation of the orbitals of carbon in a molecule?

texts:
What are hybridisation states of each carbon atom in the following compounds?

$\ce{CH2=C=O}$
$\ce{CH3CH=CH2}$
$\ce{(CH3)2CO}$
$\ce{CH2=CHCN}$
$\ce{C6H6}$

How do I find the hybridisation of the orbitals of the carbon atom in such compounds?


texts: Calculating dissociation degree from pH and Ka without given initial acid concentration

texts:
Is it possible to calculate the dissociation degree (DD) from pH and Ka without directly been given the initial acid concentration?

I found the following formula:

$$\text{DD} = \frac{K_\mathrm{a}}{10^\mathrm{-pH}}$$

Is this true?


texts: By what reaction does (–)-sparteine decompose in ambient conditions?

texts: In its pure form (–)-sparteine is an only-slightly-yellow clear, viscous liquid. Yet, after only a week of being kept in dry, normal atmosphere (in a round bottom flask covered by a septa), some of it reacts with something to form a sticky, orange-brown substance. I've had to distill the sparteine I have twice due to whatever reaction is occurring, and I would like to know exactly what the reaction is so I don't have to distill every time I need it. The literature I found mentioned that it readily absorbs carbon dioxide in a 1-1 molar ratio, and I know that tertiary amines do sometimes react with CO2, but I haven't been able to piece it together as something that could happen in ambient conditions.


texts: How could I easily quantify the amount of EGCG in a sample of green tea?

texts:
I am currently conducting an experiment to study the effects of pH on the rate of thermal decomposition of Epigallocatechin Gallate (EGCG) in green tea.

One of the key steps in my procedure is quantifying this EGCG content in the green tea. What are some of the methods which I could use to determine and quantify this EGCG content?


texts: What is the internal energy at constant pressure?

texts:
What is the internal energy when a reaction is run at constant volume and $9.19\ \mathrm{kJ}$ of heat is absorbed, when run at constant pressure $8.62\ \mathrm{kJ}$ is absorbed? (for an ideal gas)

I know that internal energy for constant volume is equal to the heat then $\Delta U=9.19\ \mathrm{kJ}$, but what is the internal energy for a reaction at constant pressure? I know that $\Delta H=\Delta U+p\Delta V$ and from this I know that $\Delta H=8.62\ \mathrm{kJ}$ but how does it relate to the internal energy?


texts:
The definition of voltage I'm familiar with is the amount of electric potential energy per unit charge at a location. My prof defined the voltage of a battery to be the amount of potential energy difference an unit charge would have at the positive terminal vs. the negative terminal.

But from what I remember from high school, the "terminals" aren't points, their rods of metal:

Since the voltage is defined at a point, not cylinders or rods what does the voltage of a battery mean? Also, how does the definition connect to the "pushing" power of a battery?

I took a look at Electrode Potential but it was a bit over my head.

I'm looking for an intuitive explanation, not one using rigorous chemistry concepts. Thanks!


texts: Oxide surfaces develop a charge in H2O. Do we have any, even vague, handle on how long does an indivdual charge last on avg. before being neutralised?

texts:
We often know, from e.g. titration experiments, what the average surface charge density of a surface is.

How do these charges vary over both time and space (i.e. dynamics)? I have been unable to find much (well, any really!) literature on this.

Example

Taking the example of oxide surfaces, you have the following processes going on:

$\ce{S-O- + H3O+<=>[\text{K1}]S-OH +H2O}$ #Protonation/Autoionisation

$\ce{S-OH + OH- <=>[\text{K2}]S-O- +H2O}$ #Deprotonation/Protonation

$\ce{S-OH + H3O+ <=>[\text{K3}]S-OH2+ +H2O}$ #Protonation/Deprotonation

If you know (from experimental/theoetrical calculation of the Equilibrium Constants K1, K2, K3), that you have 100 negative charges per micrometer squared (i.e we are at high pH). Is it a more realistic picture on a picosecond/nanosecond timescale to consider it being something like 10,000 charges per micrometer squared which are being regularly neutralised over time or simply 100 charges per micrometer which are fixed?


texts: Effect of an inert gas on steam vapor pressure at equilibrium

texts:
Suppose we have a closed container with mobile walls, so it will change its volume in order to equal the external pressure(constant) to the internal pressure.
This container has inside it a liquid phase only of component 1 and a vapor phase of 1 and the inert gas(2) that is insoluble in the liquid phase.
If the external pressure is constant how will change the vapor pressure of the component 1 changing the temperature?  (suppose we know the molar partial enthalpy of the the components in gas phase and of 1 in liquid phase at the required temperature)
$$\left( \frac{\partial P_{vap}}{\partial T} \right)$$

I have tried to find this relation by equaling the chemical potentials, and proceeding in the same manner of the demonstration of the Clausius-Clapeyron equation. However I am not sure of the result. Can anybody help me in the search of this partial derivative?


texts: Is center of symmetry only valid for symmetric substituents?

texts:
The given compound is optically active. Initially I had reasoned that the compound has center of symmetry( two xylene groups across each other). Why doesn't it have a center of symmetry?

Source: MS Chouhan, Advanced Problems In Organic Chemistry, Page 116 (Chapter Isomerism Level 2 q6a)


texts: Nodes are the points in space around a nucleus where the probability of finding an electron is zero. However, I heard that there are two kinds of nodes, radial nodes and angular nodes. What are they and what information do they provide of an atom?


texts: What trends exist in the Periodic Table?

texts:
I wish to know the trends in the periodic table and why that trend exists, for the following parameters:

Atomic size
Ionization energy
Metallic character
Positive ion size
Negative ion size
Electronegativity

My progress (if my reasoning is wrong for any of these please correct me):

Atomic size - I memorized from my class lecture that the greatest atomic size is towards the bottom-left of the periodic table. I think the reason for this is because as you go down the groups (IA, IIA, etc.) you add more electrons. Adding more electrons means the atom will logically grow bigger. I am not sure why the answer is not bottom-right, though.
Ionization energy - This is the energy required to remove an electron from an atom. If there are more electrons then the electron will be further from the nucleus and by Coulomb's law, since the distance increases, the force attraction that keeps the electron in the nucleus's orbit is weak. Thus, the ionization energy is the highest toward the top-left.
I have no clue what to think for metallic character.
Positive ion size I know the answer is that it increases towards the bottom left, but I don't know why.
Negative ion size I know the answer is that it increases towards the bottom left, but I don't know why.
Electronegativity I am pretty sure is highest at F which is 4.0 and is lowest towards the bottom left. So the trend increases towards the top-right.


texts:
The following question from my textbook assignment reads

A mixture contains $1$ mole volatile liquid $A$ ($P_\mathrm A^\circ = \pu{100 mmHg}$) and $3$ moles of volatile liquid $B$ ($P_\mathrm B^\circ = \pu{80 mmHg}$). If the solution behaves ideally, the total vapour pressure of the distillate is?

Using Raoult's Law:
\begin{align}
  P_\text{total} &= P_\mathrm A^\circ \times \chi_\mathrm A + P_\mathrm B^\circ \times \chi_\mathrm B\\
  P_\text{total} &= \pu{100 mmHg} \times 0.25 + \pu{80 mmHg} \times 0.75\\
  P_\text{total} &= \pu{85 mmHg}
\end{align}
But the answer is $\pu{85.88 mmHg}$.
I tried searching online for an explanatory solution but all of them seem to use the mole fraction of solute in vapour phase without any explanation. I figured it was due to the word distillate. Can someone explain why do we need to use mole fraction of the vapour phase and not of the solute in solution?


texts: Could someone explain to me why some alkenes containing at least one couple of different substituents at the two double-bonded C atoms (that is, some of those with at least two different substituents for both C atoms) are considered achiral? For instance, for 2-chloropropene or 1-bromo-2-chloro-2-fluoro-1-iodoethene, where (and what) in the structural formula of each of them is the plane of symmetry that makes it achiral or, in other words, what do their superposable mirror images look like? Thanks.


texts: Negative charged intermediate in acidic conditions - what's the problem?

texts:
Why positively charged intermediates are preferred over negative charged intermediates, when formed during a reaction taking place in acidic conditions?

For example:

Image source: Organic Chemistry by David R. Klein

Here, per Organic Chemistry by David R. Klein says,

  That is, the mechanism does not exhibit any negative charges, which is
  consistent with acidic conditions.

Why?


texts:
Is it possible for an element to have a calculated relative atomic mass that is higher than the relative isotopic mass of its most massive component isotope?

The equation is:

$\mathrm{Relative~Atomic~Mass}=\sum[{\mathrm{(Isotopic~Mass) \cdot (Relative~Abundance)]}} \times100\%$


texts: Does Methyl Iodide (CH3I) react with water (H2O) and if it does what would be its byproducts?

texts:
Does Methyl Iodide ($\ce{CH3I}$) react with water ($\ce{H2O}$) and if it does what would be its byproducts?

A project I am designing requires a reaction with methyl iodide and a polar compound, so I was wondering if methyl iodide reacts with water.


texts: What can I use as a sacrificial electrode to stop the oxidation of aluminium?

texts:
For a solution of chromimum phosphate when putting in to solution aluminum there is removal of the aluminum.

It is possible to prevent a galvanic cell, stop the etching of the aluminum, by putting in a sacrificial anode.

In this situation I have access to metals like tantalum, titanium, tungsten and copper.

Which one of these would stop the oxidation of the aluminum.

I have slightly familiar with electronegativity and I understand that aluminum is 1.6.  I just do not know if you want some thing with a higher or lower electronegativity.

Thanks


texts: If given a half reaction, how do you determine if an element can exist in a acidic conditions?

texts:
I was given the formulas,

$$\begin{alignat}{2}
\ce{MnO4^2- \;&<=> MnO4- + e-}\quad &&E^\circ = -0.56\ \mathrm{V}\\
\ce{MnO2 + 2H2O \;&<=> MnO4^2- + 4H+ + 2e-}\quad &&E^\circ = -2.27\ \mathrm{V}
\end{alignat}$$

I gathered you have to see if it’s non-spontaneous or spontaneous and compare it with the original reaction, but, when I asked my teacher on how to start, he said “multiply the first reaction by 2 and the second by −1.”
I understand the ×2 to balance electrons, but why do you multiple it by −1? I don’t understand this question, any help would be appreciated. Thanks.


texts: It is said that atoms cannot be created. If so, then how did atoms get created after the Big Bang?

texts: I read somewhere that atoms cannot be created. If this is true, then how did the atoms form after the Big Bang? Also, does this mean that the number of atoms in our universe has remained the same since then? Also, what happens as the universe expands? Does the atoms just scatter or are new atoms being created?


texts: Why +M effect of -NH2 is more than that of -NHR and -NR2?

texts: Why does $\ce{-NH_2}$ shows more +M effect that $\ce{-NHR}$ and $\ce{-NR_2}$? My first conclusion was totally opposite of the reality. I thought, as the alkyl groups are attached to the Nitrogen the lone lone pair on nitrogen should be easily available. But it doesn't seem to be happening. What is the actual cause?


texts:
A question from JEE-Advanced(2017) :

Bromination of both Z-but-2ene and E-but-2-ene involve syn and anti addition. So, there would be 4 products as suggested in the question. But, I don't understand the terminology of 'trans-addition', mentioned in the question.

What is actually trans addition?


texts: Is there a hierarchy to functional groups?

texts:
I think I am getting slightly confused about the names we give to functional groups. I am aware that there are different types of functional groups such as alkyl, aryl and acyl groups.

I also know that there exist functional groups such as those of esters, ketones and amides which come under the acyl group. However, thinking about this recently I also realised that there existed a carbonyl group, which is also present in a ketone?

I am also a bit confused as to whether the acyl group's general formula is RCO or RCOX where X could be a variety of groups. Also, is R a part of the functional group or is it there to show what the functional group is attached to.

Could someone please make this hierarchy of functional groups a bit clearer?


texts: Is the Beckmann Rearrangement technically an "SN2" reaction at an "sp2" center?

texts:
Below is the mechanism from this link of the Beckmann Rearrangement.

In the alkyl migration step, the alkyl group migrates simultaneously as the $\ce{H2O}$ leaving group is expelled. This seems as though it is an $\mathrm{S_N2}$ reaction at the $\mathrm{sp^2}$-hybridized nitrogen atom, but I thought that it was geometrically impossible to have an $\mathrm{S_N2}$ reaction at an $\mathrm{sp^2}$ center, per this link.

What am I missing in my reasoning?


texts: How is the electron "trapped in the crystal" in irradiated NaCl?

texts: Pennsylvania State University provides irradiated $\ce{NaCl}$ (180,000 rads of gamma radiation) to teachers for a very entertaining demonstration. The salt is orange after irradiation. When it is placed on a hot plate, you see a flash of visible light and the salt returns to it normal color. The explanation provided with the salt is that "The heat allows the electrons that were trapped in the crystal structure (when the energy was deposited) to return to their original position." This language evokes a picture of a particle electron in a crystal jail for me. The explanation goes on to say that the energy is released as a photon of visible light. (I understand this part of the explanation.) So, my question is, how are electrons trapped in a crystal structure? What keeps them in an excited state?


texts:
Are lithium bicarbonate and magnesium bicarbonate both soluble in water?

Source: JEE Mains 2017 (National Level Examination of India)

Please do cite a reputed source along with your answer. Currently I have found a line from JD Lee (Concise Inorganic Chemistry 5th ed):


texts: Ring formation via oxymercuration-demercuration

texts:
I'm solving past problems from a 2014 Organic Chemistry II course (from a publicly available Harvard summer school Canvas page), when I came across this question:

The answer (which is the reactant) looks like this:

Now I understand how the alkyne would turn into an alkene, but I don't get how a furan would form from what looks like an oxymercuration-demercuration reaction. Any help would be much apprecited.


texts: Stress-Strain Graph Under Uniaxial and Biaxial Strain

texts:
I was going through a recently published journal paper by ACS (Applied Nano Materials) about gas separation using nanoporous Graphene.
DOI No. - https://dx.doi.org/10.1021/acsanm.0c02340
Supporting Information - https://pubs.acs.org/doi/suppl/10.1021/acsanm.0c02340/suppl_file/an0c02340_si_001.pdf
I'm quoting the exact part where I'm facing some problems-

Figure 2 shows the stress-calculated strain curves of graphene under
uniaxial and biaxial strains.   Herein,
nominal strain and stress are used, which are defined as the length
change divided by the original length and the tensile force divided by
the original area of cross-section, respectively (nominal thickness of
3.4 Å is adopted).
Figure 2a shows that the mechanical responses of nanoporous graphene
stretched along the armchair direction become distinct from that along
the zigzag direction with the increasing strain, resulting from the
strain-induced symmetry breaking. The strain to failure of this
nanoporous graphene loaded along with the armchair and zigzag directions
are 11 and 17%, respectively, which defines the maximum strains that
can be applied to the structure. In addition to uniaxial strain, we
also investigate the elastic responses of biaxial strain and the
strain to failure can also exceed 10% (Figure 2b). Considering the
structural stability based on these investigations, we explore the gas
separation performance of nanoporous graphene under uniaxial and
biaxial strains below 10%.

However, I understand that this is a Stress vs Strain graph. But I have some doubts regarding this -

What they mean by uniaxial and diaxial strain
What exactly they mean by armchair direction and zigzag direction
Lastly, it'll be very helpful for me if one can explain the graph clearly (I'm getting a vague understanding about that)


texts: Why is the experimental pH of vinegar (acetic acid) so much higher than expected?

texts:
I bought some sodium hydroxide on Amazon and went about titrating solutions I make with it.

As I'm an amateur chemist at home, I have limited tools. A pad of paper, some 5% acetic acid vinegar, and some pH strips.

I assumed the pH of vinegar was 2.5 ± 0.5.

Making a solution of 4g NaOH powder in 100g of (tap) water, I expected a solution of 1 mol/L. (NaOH 40g/mol)

I went about finding the ratio of concentrations, working by factors of 10 and then refining, that pH strips would indicate around 7.

At my great surprise, this turned out to be around 0.9:1 NaOH 1M to vinegar (about 20mL:22mL – the margin of error being around a factor of 1.1)

A vinegar pH of 2.5 suggests an H+ concentration of 3.2 mM; and so that that ratio would be, $1\mathrm M/3.2 \mathrm{mM} = 312:1$.
So experimentally, $\mathrm{[OH^-]}$ is about 350 times lower than expected. I'm trying to figure out why that would be.

Am I missing something obvious here? I'm looking for a mistake but can't find one.

Here are my thoughts:

Bought NaOH might not be pure

It would take a "purity" of 0.25% to explain such a difference. Unlikely.

NaOH might not dissociate completely experimentally

NaOH is a strong base. pKb would need to be extra high to explain a factor of 350.

Calculation error

I've checked and rechecked my math, everything seems to hold up. 22mL of vinegar brings 70µmol [H+], 20 mL NaOH solution brings 50µmol [OH-].

Measurement error

I've done the experiment twice. Same kind of values. Adding 80% of vinegar volume leaves the paper unmistakably dark. Adding 120% of equilibrium volume leaves the paper yellow-ish. 90% to 110%: green-ish. To measure quantity added, I use a scale with a resolution of ±0.01g. (Measurements were taken ±0.5g)

Bad pH paper

It would take really bad paper to make a pH 9 liquid appear to be pH 7, wouldn't it? A factor of 350 is about $log_{10}(350) \approx 2.5$ off on the log scale. Unlikely. Besides, aren't the indicator substances pretty standard?

Acidic tap water

I live in a big city, I've read the water analyses. Looks like the water is around pH 6.5. I don't think at this scale it would change much.

Wrong chemistry/theoretical background

It's possible a 4% w/v solution of NaOH doesn't have a pH near 14. Or that mixing it with 1.1 parts of 5% vinegar doesn't make a pH of 7. I have not yet found the basis for that. At equal quantities [H+] and [OH-] in room temperature water, I don't see a reason for the weak acid to be a factor.

So I'm pretty much stumped. Why does my solution have a pH 11.5 instead of 14? Is there an obvious chemical concept I've missed?


texts: How to separate and analyse a sample of cations of alkaline and earth alkaline cations and ammonium?

texts:
I am teaching a section of qualitative analysis and I am trying to get a better grasp on the assignments the students are doing. These are the cations they may be presented with and must identify:

$\ce{Na+}$
$\ce{K+ }$
$\ce{NH4+}$
$\ce{Ca^2+ }$
$\ce{Al^3+ }$
$\ce{Mg^2+}$

Now, this lab hasn't changed for the last 20 years, and there is only one way the students perform the separations, which happens to be the same method found in an old lab report that is easily found with Google. The method is:

Add excess 3 M ammonia to the sample.
If a gel-like precipitate forms, then $\ce{Mg^2+ }$ and/or $\ce{Al^3+ }$ ion is present. They have been converted into their respective hydrated hydroxides. Separate the precipitate from the supernatant liquid.
Since hydrated $\ce{Mg^2+  }$ hydroxide is not readily amphoteric, while hydrated $\ce{Al^3+ }$ hydroxide is, addition of excess  $\ce{NaOH}$ should cause the an $\ce{Al^3+ }$ precipitate to dissolve. If the precipitate from the previous step does dissolve with excess $\ce{NaOH}$, then $\ce{Al^3+ }$ ion is present in the original sample. If the precipitate does not dissolve, then $\ce{Mg^2+  }$ ion is present.
Time for the supernatant analysis (if there is a supernatant). If there is no ppt, then we can immediately rule out the presence of $\ce{Mg^2+}$ and $\ce{Al^3+ }$. Either way, the solution, non-precipitate portion can only contain $\ce{Na+}$, $\ce{K+ }$, $\ce{NH4+}$, and/or $\ce{Ca^2+ }$ since none of these form insoluble hydroxides at the concentration of ammonia used. Yes, calcium hydroxide is insoluble, but it doesn't form with 3 M $\ce{H3N}$; I've done the $Q_\mathrm{sp}$ vs. $K_\mathrm{sp}$ calculation.
Add sodium carbonate to the liquid portion. If a solid forms, the solid must be calcium carbonate, and therefore $\ce{Ca^2+ }$ was present in the original sample.
If no solid forms, or even if a solid forms, separate the solid from the liquid and perform further tests on the liquid to determine the presence of $\ce{Na+}$, $\ce{K+ }$, and $\ce{H4N+}$. A yellow flame tests tells us $\ce{Na+}$ is present and $\ce{K+}$ may or may not be present. A purple flame test tells us $\ce{Na+}$ is absent.
Heat the remaining solid sample (not any precipitate, but the original sample itself) to ascertain the presence of $\ce{NH4+}$. Heating a sample that contains $\ce{NH4+}$ will result in the release of white smoke. After heating the solid sample until smoking ceases or until one is certain the sample will not start generating white smoke, perform a sodium coboltinitrite test if necessary to determine whether $\ce{K+ }$ is present.

What other valid separations are there? Is this the easiest method, or are there easier ones?

What about initially adding $\ce{NaOH}$?

Add $\ce{NaOH}$. If a white precipitate forms, the sample contains $\ce{Ca^2+}$ (the white ppt is calcium hydroxide). If a gel-like ppt forms, then the sample contains either $\ce{Al^3+}$ or $\ce{Mg^2+}$. Perform the necessary tests described above to determine the nature of the gel-like ppt.
The liquid part of the solution must now only contain $\ce{Na+ }$ or $\ce{K+ }$. Ammonium ion has been converted to ammonia thanks to the hydroxide ion. $\ce{Na+}$ or $\ce{K+ }$ can easily be tested for using a flame test. The sodium coboltinitrite test can also be employed to detect $\ce{K+ }$ if the color of $\ce{K+ }$ has been masked by the color of Na+ in the flame test.

This method seems a bit faster. But are there any pitfalls?


texts: Molpro - Connection between atomic term symbols and system symmetry

texts:
Let's say I have a carbon atom with the electron configuration $1s^22s^22p^2$. We know, that using atomic term symbols we can describe the following states:

$${}^3P_0, {}^3P_1, {}^3P_2, {}^1D_2, {}^1S_0$$

Now I'd like to compute their energies with Molpro. But how should I specify those terms using just symmetry point groups?

I saw something similar using state-averaged multi computation from several different symmetries. But, I don't know, how to derive them just from the term symbol?

My attempt

I was thinking about writing the state wavefunction as the linear combination of microstates and specifying each of then separately.

I.e. let's have the state ${}^1S_0$. According to this answer it can be described like this:

$$|L = 0, M_L = 0\rangle = \frac{1}{\sqrt 3} \left( |m_{l1}= 1, m_{l2} = -1\rangle + |m_{l1}= -1, m_{l2} = 1\rangle - |m_{l1}= 0, m_{l2} = 0\rangle \right)$$

I presume, that I can choose any of the available point groups in Molpro for 1 atom. Let's say I'll choose $D_{2h}$ point group.

Then the orbitals' symmetry can be described like this:

$1s$ ($A_g$)
$2s$ ($A_g$)
$2p_x$ ($B_{3u}$)
$2p_y$ ($B_{2u}$)
$2p_z$ ($B_{1u}$)

According to this, the symmetry of the state $\left| m_{l1} = 1, m_{l2} = -1 \right>$ should be
$$(A_g)^2 \otimes (A_g)^2 \otimes (B_{3u})^1 \otimes (B_{1u})^1 = B_{2g}$$

and the corresponding wavefunction specification in Molpro: wf,6,6,0.

The state $\left| m_{l1}=-1, m_{l2} = 1 \right>$ posses the same symmetry, i.e. $B_{2g}$ and so the Molpro wavefunction specification stays the same wf,6,6,0.

Finally, the state $\left| m_{l1} = 0, m_{l2} = 0 \right>$ has the symmetry

$$(A_g)^2 \otimes (A_g)^2 \otimes (B_{2u})^2 = A_g$$, i.e.
the wavefunction will be specified like wf,6,1,0 and multi will be called
with both of the wavefunctions together

{multi;
 occ,2,1,1,0,1,0,0,0;
 core,1,0,0,0,0,0,0,0;
 wf,6,6,0;
 wf,6,1,0;
}

Is this the correct approach?


texts:
Acids of $\ce{Mo}^\mathrm{VI}$ are more stable than those of $\ce{Cr}^\mathrm{VI}$ in terms of redox reactivity.

In p-block elements, as we go down the groups, the stability of lower oxidation state keeps on increasing. I understand how this can be explained with the inert pair effect.

On the other hand, as we go down the group from $\ce{Cr}$ to $\ce{Mo}$, why does the opposite happen and there isn't any inert pair effect? Shouldn't the lower oxidation state be more stable down the groups in d-block elements? Wouldn't there be less shielding in $\ce{Mo}$ making is less electropositive than $\ce{Cr}$?


texts: What was the misconception about the search of Philosopher's Stone and how does modern chemistry deals with this topic?

texts:
I just read about Alchemy. And it seems to me that many of their principles are closely related to chemistry.

So, here is my doubt - Why is not possible to make that alchemist stone called Philosopher's Stone? What was the misconception about the research of Philosopher's Stone and how does modern chemistry can prove, or at least consider, that actually it is a Dead-end research?

Has any modern chemist ever tried to reopen the research on this topic?


texts: Why in this problem there isn't a diastereomer with the $\ce{-CH3}$ in the back (dash) and the $\ce{-CH2CH3}$ in front (wedge)?


texts: Thyroid peroxidase - can atomic iodine serve as iodinating agent?

texts:
McMurry's Organic Chemistry (7th Ed.) states, that Tyrosine is iodinated by mechanism of electrophilic aromatic substitution and the iodinating agent is $\ce{I+}$ or $\ce{HIO}$ formed by thyroid peroxidase. The mechanism is quite clear in this case.

Wikipedia article about thyroid peroxidase states that:

  thyroid peroxidase oxidizes iodide to atomic iodine ($\ce{I}$) or iodinium ($\ce{I+}$).

From this figure from previous wikipedia article it moreover seems like $\ce{I^{0}}$ would be able to function as an iodinating agent.

I would like to ask whether atomic iodine produced by thyroid peroxidase could act as an iodinating agent by itself (if yes, by what mechanism, because I think electrophilic aromatic substitution cannot be used, morover, this reaction is supposed to happen in the colloid without any additional enzymatic support) or if I just didn't understand the article and figure correctly and additional oxidation to $\ce{I^{+}}$ is indeed needed (atomic iodine is just an irreactive intermediate).

I tried to find some references for this, but I was unable to do so.

NOTE: I originally posted this in biology.stackexchange.com but got no answers, so I thought here it might be more suitable.


texts: What is the correct definition of the Gibbs free energy of activation?

texts:
Is the following correct?

  Gibbs free energy of activation is used in energy profiles where the stabilities of the species are expressed as changes in Gibbs energy, while the activation energy Ea is used in energy profiles where the stabilities of the species are expressed as changes in enthalpies.


texts: Mechanism for reaction of ketene with water

texts:
In the Arndt-Eistert synthesis, a ketene is the intermediate. The ketene is then hydrolysed in the presence of $\ce{Ag2O}$. What is the mechanism for the hydrolysis of the ketene?

Is an oxonium ion formed or will there be nucleophilic attack of $\ce{H2O}$ on the carbonyl carbon?


texts: Why/how is blood red? (colours of hemoglobin)

texts:
Oxyhaemoglobin is red, deoxyhaemoglobin is bluish-purple, and carboxyhaemoglobin is a cherry red colour.

Evidently in the porphyrin around the iron molecule in heme there is a conjugated $\pi$-system which could account for the colour, but how exactly does this work? Also, what is the role of the metal ion (specifically $\ce{Fe}$) in the middle, its oxidation state, or the ligand, in changing/determining the colour in conjunction to that? Do the globin chains play any role in determining the colour (if so, how)?

Chlorophyll, for example, also has a porphyrin motif, but it is green due to having magnesium in the middle. Vitamin B12 is also intensely red in colour (according to Wikipedia).


texts: In aldehydes with an alkene substituent, what conditions favor Wolff–Kishner reduction over Clemmensen reduction?

texts:
This module I am answering asked me to provide a reason why Wolff–Kishner reduction is favored over Clemmensen reduction in reducing (3Z)-pent-3-enal to (2Z)-pent-2-ene but either Wolff–Kishner or Clemmensen can be used to reduce pentanal to pentene.
I am currently running with the notion that the alkene substituent double bond's reactivity is the reason behind this since acid is used in Clemmensen reduction compared to Wolff–Kishner's base, and it might interfere with this alkene substituent instead of the carbonyl group in aldehyde. Is this notion correct?


texts: How much Citric Acid to neutralise bicarbonate?

texts:
I live in an area with very hard water, where the bicarbonate in the water is 357  mg/L. I would like to add some citric to the tap water to bring it down to around 50mg/L, for the curious, this is for coffee brewing.

How much citric acid would I need to add per liter? If it would be a very tiny quantity, then it would be impossible to weigh it accurately since I have a scale that is only sensitive to ~0.1g. In this case, could I make some solution which I could say add some milileters to a liter of tap water?


texts:
I am having some trouble with understanding glide axis. The following is a question asking to reconstruct the full unit cell:

And the following is the answer to the question:

I have highlighted an element which I want to focus on. I understand the rotation of 180 degrees and translation of 1/2 of a unit cell. However, I don't understand why the element undergoes a change from 1/2 + to - . My understanding of 1/2 + is that it is located 1/2 above the left element following a glide plane (c) transformation. But I don't understand why it would be transformed into a "-" after the axis screw. I also don't understand what 1/4 near the screw axis means, I'm guessing it could be that it is an axis at c = 1/4, but the transition that the highlighted element undergoes still doesn't quite make sense if that is the case.

Please provide any guidance with this question, I've been struggling to understand what is going on for a long time.

Many thanks


texts: Semi-numeric or analytic Hessian for DFT (GAMESS)

texts:
I'm trying to understand what parameter in the $FORCE group is better to use in computing vibrational frequencies (NVIB=2) of compounds after optimization. I'm using GAMESS Aug'16 on Ubuntu 14/16.04.

Initially, three separate methods for both gas and water (PCM) are used to optimize. Later, higher levels of theory are used.

B3LYP/6-31+G*
ωB97X-D/6-31+G*
PBE0 (PBE1PBE)/6-31+G*

Of course, analytic is the default for B3LYP and PBE0, but for ωB97X-D, seminum must be used, from what I've found the hard way. Is it reasonable to use ANALYTIC for the former two and SEMINUM for the latter or should I use SEMINUM across the board to avoid misconstrued results? I'm not seeing a very large difference in only phenol but a difference is noticeable. Considering my target compounds are much larger than a single ring, they may become more noticeable.

Thank you for any input.


texts: What is the activation energy of creating molecular hydrogen from atomic hydrogen?

texts: If molecular hydrogen is dissociated, or two hydrogen atoms in space collide, how much energy (in $\pu{eV}$, or perhaps $\pu{kJ/mol}$) does it take for an $\ce{H_2}$ molecule to form?


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Is it possible to obtain pure, precipitated iron with no oxidation by some chemical process?

Alternatively is it possible to electrically purify iron using an anode and cathode?


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While most common lasers are electrically powered, there are also chemically powered lasers. These are high power systems, since for lower power systems electrically powered lasers (including optically pumped) are more practical. The chemistries I'm aware of (from wikipedia) use highly toxic fuels or have highly toxic reaction products. (Iodine based lasers that I could find use chlorine gas as an input, hydrogen fluoride lasers result in hydrogen fluoride.)

Are there any chemistries that could conceivably be used as a chemical laser that do not require handling of such dangerous compounds? (That preferably are usable at a smaller scale, although I am not aware of any reason why existing chemical lasers could not be used at small scales.)

edit: The question is just out of curiosity, for practical applications other types of lasers would be more useful.


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I'm considering the following reaction:

$\ce{ZnSO4} + 2 \ce{KCl} \ce{->} \ce{ZnCl2} + \ce{K2SO4}$

The high solubility of $\ce{ZnCl2}$ would favour the $\ce{ZnSO4}$ & $\ce{KCl}$ direction of the reaction, but I'm wondering if I could turn this around by making the reaction occur in a flow of boiling hot water.

The idea would be to subject (initially dry) $\ce{ZnSO4}$ & $\ce{KCl}$ stationary phase to a flow of water in the 80-100°C range. The comparative solubility of $\ce{ZnCl2}$ at this temperature being high, I'm wondering if it being comparatively flushed away more than the other species could help drive the reaction forwards in the opposite direction?

I wouldn't get pure $\ce{ZnCl2}$ of course but I'd be happy if I could get a 90% $\ce{ZnCl2}$ solution from dry $\ce{ZnSO4}$ & $\ce{KCl}$.


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I have a task to come up with a synthesis of the following molecule (2-azaspiro[5.5]undecan-3-one), but no starting materials have been explicitly specified:

This is my idea. I think that all the steps shown are quite reasonable.Do you have any critics/suggestion?


texts: Would a single atom of a metal bond with a plate of that metal?

texts:
A question purely for my own curiosity.

I am trying to understand what "holds the atoms in a metal bar" in shape.

A general question about metals, but let's use gold as an example.

Under suitable laboratory conditions

if we isolated a single atom of gold
and dropped that onto a plate of gold

Would the atom fuse with the plate ?

Would the valence electrons of the single free atom "attract that atom into a bond with the crystal lattice" ?

I did some searching and found this:

  Metallic bond, force that holds atoms together in a metallic
  substance. Such a solid consists of closely packed atoms. In most
  cases, the outermost electron shell of each of the metal atoms
  overlaps with a large number of neighbouring atoms. As a consequence,
  the valence electrons continually move from one atom to another and
  are not associated with any specific pair of atoms. In short, the
  valence electrons in metals, unlike those in covalently bonded
  substances, are nonlocalized, capable of wandering relatively freely
  throughout the entire crystal. The atoms that the electrons leave
  behind become positive ions, and the interaction between such ions and
  valence electrons gives rise to the cohesive or binding force that
  holds the metallic crystal together.

  https://www.britannica.com/science/metallic-bond

I can think of a reason why two gold bars wouldn't fuse together when placed together:

the irregularity of their surfaces would not permit close enough contact ...
(ignoring any surface oxidation)

But I'm curious about the case of a "single free atom".