texts: How much electron hybridization and bonding occurs in liquid helium?

texts:
Helium is the only element which does not freeze at atmospheric pressure, and only forms a liquid at around 4 Kelvin due to weak van der Waals forces.

I'm interested in knowing roughly how much hybridization/bonding occurs in liquid helium (e.g., energies in cm$^{-1}$ or electronvolts) at ambient pressure and cryogenic temperatures. I would guess that since the enthalpy of formation for liquid helium is about $10^{-3}$ eV per atom, the bonding energies are comparable, but I have not found any numbers on this topic in the literature.

To ask the same question without jargon: how much are the energy levels of Helium smeared when it is in the liquid phase?

For example, in solid Copper, a plot of the density of states shows that the atomic energy levels hybridize to form solid state energy bands. For the $d$-orbitals the overlaps are relatively small, giving rise to roughly 4eV wide bands. On the other hand the $s$- and $p$-orbitals have large overlaps, resulting in these atomic orbitals being broadened to be >12eV wide.


texts: Reactivity of benzyl halides towards nucleophilic substitution

texts:
I experienced some difficulty as I was doing question 22 of this quiz on nucleophilic substitution at saturated carbons:

I picked option B but the answer turned out to be C. My rationale for picking B was that I thought that IV was going to be more reactive than I because I has an additional electron-donating methyl substituent which would increase the energy of the transition state in the $S_{N}2$ pathway.

Evidently, II and III are in the 3rd and 4th places respectively because alkyl bromides are less reactive than alkyl iodides and that phenyl bromides are not as reactive towards nucleophilic substitution as the $ \pi$ electron cloud of the neighbouring benzene ring would repel the nucleophile away.

What went wrong with my thinking?


texts: Magnetic nature of tetraamminedichlorocobalt(III) chloride

texts:
I know how to predict magnetic nature when the compound contains only strong field or only weak field ligands. But in $\ce{[Co(NH3)4Cl2]Cl},$ $\ce{NH3}$ is a strong ligand whereas $\ce{Cl-}$ is a weak ligand.

So, how do we know if the ligands are causing the electrons to pair up or not? I understand VBT and CFT to predict the hybridisation and magnetic nature of compounds.


texts: What is meant by the numbers on reagents above and below arrows?

texts:
I was taught that molecules on top of arrows are reactants and below arrow are solvent.

But I've come across a series of molecules written above and below arrows with numbers and commas. Do these numbers mean that all these reagents above and below arrows are in separate containers and are added one by one?


texts: Trivial name of a compound vs its chemical formula

texts:
I had a question like below and I've had trouble with similar problems before and how to go about solving for the chemical formula.

  What is the chemical formula for lithium aluminum hydride?

The first thing that comes to mind, we have one lithium, one aluminum and one hydride. Then why is the chemical formula $\ce{LiAlH4}$? Where did the four $\ce{H}$ atoms come from? Earlier on in the course we had stuff like

  What is the chemical formula for di-arsenic trioxide?

And that one is easy, I have 2 arsenic and 3 oxygen. Given the full name I can easily deduce the formula (or the other way around). But what do you do in situations where you don't get "all the information". Do I go about thinking up how the structure works and see that it somehow logically follows that it needs to be four $\ce{H}$?

I know most basic compounds, e.g. sulphate is $\ce{SO4^2-}$, but I feel like I can't memorize some of the things. There has to be a more general way to do this. It feels like and I must have missed it. Essentially, the full systematic names are no problem, but the trivial names are giving me a rough time and I'm scared if they come up during my finals next week. Any tips regarding that?


texts: What is natural bond orbital theory used for?

texts:
My understanding is that the NBO methodology transforms the molecular orbital picture of a molecule into a collection of pairwise interactions (bond orbitals). This is obviously handy for didactic and comprehension purposes as it distils what might be a very complex and non-local MO picture into manageable lobes conforming to the introductory theories of chemical bonding (VB, orbital hybridisation) taught in high-school and early university courses.

Does natural bond orbital theory have utility outside of this role?


texts: Aren't unit cell and the relevant crystal similar?

texts:
"A crystal is formed by a large number of repetitions of basic pattern of particles in space.
The basic structural unit which when repeated in three spatial directions generates the crystal structure is called unit cell."
Problem:
Assume I take some same perfect geometrical cubes and arrange them in all three dimensional directions, a larger box similar to the smaller ones will be introduced.
From this assumption and the information above it, I deduce that a unit cell should be similar to the relevant crystal. That means, the only difference would be lying between their size.
If this is the case, why consider the geometry of unit cell and not directly the respective crystal? We know in the assumption above; the fundamental cubical boxes would be determined by same geometrical information as would the derived cubical box.
That is; if the lengths of three axes of cube are represented by letters $a,b$ and $c$ and the angles between axes are represented by Greek letters $\alpha$, $\beta$ and $\gamma$ then for a cube,
$$a=b=c$$$$\alpha=\beta=\gamma=\pi^c$$
This information is general. It is for all size of cubes. Then, why to define a unit cell and think it simpler to handle with than the crystal?


texts: Suggestions of GHS-compliant labelling software

texts:
Having amassed a rather large collection of reagents and products from previous years of chemistry experiments, I find rather annoying that their labels aren't even close to being standardized to the GHS rules.
Each supplier has its own variation, some GHS-compliant, some not, and of course for the end products of the experiments there is no standardization at all since they weren't purchased. I try to find a pre-made label for said compound on the internet, print and use it.
If there is no pre-made template for it, the next step is to find a MSDS and fill in the data in one of many online label generators. Tedious, and prone to error. And online generators come and go offline all the time meaning after some time there are several different "formats" around.
To complicate things more I do not feel comfortable at all letting some random site know that I have this or that chemical.
That said, I ask for suggestions of software for GHS-compliant label generation.

Offline only
Windows/Linux
Can use standard inkjet/thermal/dot-matrix printers (not proprietary printers)

And bonus if:

Has internal database of chemicals. If not, well, it would be a one-time effort to input the data.
Is open-source (or is cheap)


texts: What is the right quantum numbers of Copper?

texts:
Copper have $[Ar] 3d^{10} 4s^1$ electron configuration. And Zinc have $[Ar] 3d^{10} 4s^2$ electron configuration.

My question is, what is the right quantum numbers of last electron of copper? Is it $$a. n=3,l=2,m=+1,s=-1/2$$ or $$b. n=3,l=2,m=+2,s=-1/2$$

If I use A, the electron configuration of copper is $[Ar] 3d^{9} 4s^2$ and it isn't stable. But if I use B quantum numbers, it is the same with the last electron of zinc.


texts: How to achieve regioselective (base-catalyzed) enolization of a carbonyl group in a diketone?

texts:
One can convert a ketone to an enolate, either base- or acid-catalyzed.

Let's say you now have a diketone. You choose to treat this compound with base (e.g. hydroxide anion, alkoxide anion, LDA/THF, NaH).

How can one control the regioselectivity of this enolization reaction such that only one specific carbonyl group is converted to an enolate group?


texts: CuSO4.5H2O >> CuSO4 + 5H2O : chemical or physical reaction?

texts:
In a textbook it says it's a chemical reaction which involves breaking bonds.
But I don't think so since I think water molecules are just trapped in the crystal. What's the right answer and why ?


texts: Calculating heat of combustion via calorimetry

texts:
Question:

  When $\pu{60 g}$ of $\ce{C60}$ is combusted in a bomb calorimeter that has a water jacket containing $\pu{300.0 g}$ of water, the temperature of the water increases by $\pu{10 ^\circ C}$. Assuming that the specific heat of water is $\pu{4.18 J g^{-1} K^{-1}}$, estimate $\Delta E$ of combustion per mole of $\ce{C60}$.

Answer: $\pu{-150.5 kJ/mol}$

What I have tried:
$$
\begin{align}
Q &= m \times c \times \Delta T \\
Q &= 300 \times 4.18 \times 10
\end{align}$$

That's the only equation I know and it doesn't seem to work for this problem.


texts: Dissociation of water into H+ and OH-: Does the law of mass action hold at nanoscale?

texts:
Suppose water under neutral conditions is confined in a virtual spherical nanocontainer with a radius of 25 nm. To calculate the number of hydronium ions, one uses water dissociation constant which is derived from the law of mass action. In this case, considering the temperature at 25°C I come up with a number which is smaller than one.

A logical suggestion here is probability. Is there any limitation to the law of mass action, i.e. does it break down at the nanoscale level and quantum mechanics and thus probability kick in? If yes, is there any boundary to specify things with respect to the size of the system?


texts: Reaction of heated cupro-nickel in isopropanol or methanol

texts:
There are a number of youtube videos where someone heats a US quarter (which is copper sandwiched between layers of 75% copper, 25% nickel) to red heat and cooling it in methanol. This results in a coin that appears to be "copper plated". I've replicated this effect at home with rubbing alcohol and a US nickel, which is a solid piece of 75% copper, 25% nickel. The apparent copper coating is somewhat fragile, and there is a layer of black underneath.

What reaction is occurring here? Is the outer coating copper, and what could the black layer be? I've looked for an explanation online, but I've only found wildly inaccurate speculation.


texts: How to perform a relaxed scan in GAMESS?

texts:
I have the following input Gaussian input for my system. The coordinates are given in Cartesian format and it is scanning through 8 steps, with a bond distance between 1 and 5 having a difference of 0.1 Å in each step, and the bond distance between 1 and 2 is fixed.

#hf/6-31g** opt=modredundant

OPT

1 1
 O     0.086655     0.133386    -0.150088
 O    -1.636963     0.213966    -1.809353
 H    -0.149749     0.260762     0.763793
 H     0.802607    -0.484925    -0.261350
 H    -0.423645     0.140377    -0.629197
 H    -2.313930    -0.430164    -1.970372
 H    -1.720592     0.938467    -2.416119

B 1 5 S 8 0.1
1 2 F

What is the analogue of this in GAMESS?


texts: Bromination of but-3-en-1-ol in basic medium and Baldwin's rules

texts:
After formation of the bromocarbocation the alkoxide anion attacks the bromocarbocation which leads to ring formation and can proceed through two pathways

5 endo tet cyclization is disfavored but 4 exo tet cyclization is favored according to Baldwin's rules; however, the answer given in my text book is the 5 membered ring.


texts: NMR analysis regarding cis-1-isopropyl-3-phenylcyclohexane

texts:
I have come across a question in my textbook:

The textbook gives this answer:

I understand the explanation for the first compound. However, for the second structure, I am not understanding why the 2 methyl groups are diastereotopic. Is there not free rotation about the $\ce{C-C}$ bond, connecting the $\ce{CH(CH3)2}$ group to the ring such that the 2 methyl groups become equivalent? The answer key makes it seem as though there is no rotation and the methyl groups are fixed in place. I feel as if I am misunderstanding the question. Please help me clear up the confusion.


texts: Why does Cl- get eliminated from a trichloromethyl anion to give dichlorocarbene?

texts: In the formation of dichlorocarbene, sodium trochloroacetate (in tetrachloroethene) is refluxed at 130 deg C resulting in decarboxylation which forms a trichloromethyl anion. (Does this step happen because of the increase in entropy? What is the driving force for this step?) Alpha elimination of Cl- then occurs to give dichlorocarbene but as carbenes are so unstable surely this final step would be energetically unfavourable? Why does it still happen? Is it just because the reaction is being heated? Does this provide enough energy for this step to happen? Is this step in equilibrium?


texts: Why can hydrogen ions be added to balance a reaction?

texts:
This link explains the process behind balancing redox equations.

  Now you have to add things to the half-equation in order to make it
  balance completely.

  All you are allowed to add are:

  electrons
  water
  hydrogen ions (unless the reaction is being done under alkaline conditions - in which case, you can add hydroxide ions instead)

Adding electrons makes sense, because this whole process models electron transfer. Any added electrons will be accounted for elsewhere in the reaction.

Adding water makes sense as well, because it's an entire molecule -- it is essentially part of the reaction at this point.

I don't understand why $\ce{H^+}$ ions can be added simply for balancing purposes.

In the second example on the same site, the final reaction is this:

$$\ce{2MnO4- + 6H+ +5H2O2 -> 2Mn^{2+} + 8H2O + 5O2}$$

Where does the $\ce{6H^+}$ come from, in the real world? It seems like it just appears out of nowhere to make the math work out.

What is actually happening, on a physical basis, to make this type of balancing check out?


texts: Oxidation numbers of phosphorus pentachloride

texts:
I read detailed explanations of what oxidation numbers/ states represent and it boils down simply to this: If it's positive, it shows how many electrons the element lost, and in the case of a negative oxidation number, it shows how many electrons the element gained. That I understand.

What I don't get is, in Phosphorus pentachloride $\ce{PCl5}$, phosphorus forms 5 single bonds with chlorine atoms and 'gains' $5$ more electrons to accommodate a total of $10$ electrons. Shouldn't its oxidation number be $-5$ instead of $+5$?


texts: Does storing a hygroscopic reagent in a bottle makes it prone to absorb humidity from the air trapped inside?

texts:
I've got a full bottle of 99,5% acetone, which I'd really like to keep it as dry as possible, though without using molecular sieves or other dessicants.

Once I open the bottle for the first time, use part of the reagent (say 25% volume) and then close the bottle again, will the remaining 75% acetone begin to absorb water from the 25% trapped air inside the bottle?

Also, does vapor pressure plays a role on this?


texts: Evaluate mass of salt needed to add to a buffer solution knowing only pH

texts:
This is an exercise taken from an old exam, I'm struggling with the resolution.

  To a solution of a generic weak acid $\ce{HA}$ were added $\pu{2.40 g}$ of a potassium salt of the $\ce{KA}$. The solution has $\mathrm{pH} = 4.8$. Evaluate how many grams of salt are needed if we want to shift the solution to a $\mathrm{pH} = 5$.

Neither $K_\mathrm{a}$ nor $K_\mathrm{b}$ are given, nor anything. The only thing I got is just confusion.


texts: How are Grignard reagents stable in an ethereal solution?

texts:
I have heard of the leveling effect, which mentions that highly basic ions cannot exist in a solvent if it's acidity is high enough to be deprotonated by the base.
Considering that, check out the Grignard reagent. I'll use a methylgrignard for this purpose, generated in a diethylether solvent.
This Grignard reagent furnished methanide ions ($\ce{CH3-}$). This ion can abstract protons from any compound thats more acidic than methane. Diethyl ether possesses $\beta$-hydrogens that are easily abstracted due to the inductive pull of the oxygen atom:

The inductive pull may not be much, but it certainly makes it more acidic than a regular hydrocarbon hydrogen.
However we know that Grig reagents do work in ethereal solvents. How is it so?
Edit: This isn't a duplicate of the mentioned question. My question deals with acidity of $\beta$ hydrogens.


texts: Are compounds which are used to seed clouds like silver(I) iodide hygroscopic?

texts:
I have read a teensy bit of the subject matter and the explanation they provided for silver iodide's ability to being a good site for ice to form is because of its size resembling an ice nucleus.
How exactly does silver iodide adsorb water onto its surface? Is it hygroscopic?
Ice crystals growing larger due to vapour deposition or rapid freezing of supercooled water upon contact with ice makes sense. But how does silver iodide do it?
If the hygroscopic properties of silver iodide are what enables it to seed clouds, can the common salt also be used to seed clouds? I do apologize as the question wasn't aptly structured. Please do help in understanding this!
P.S. I found an article which I find is relevant to this question [1], but unfortunately, I'm not experienced enough to go about reading scientific articles.
Reference

Pena, R. G. D.; Caimi, E. A. Hygroscopicity and Chemical Composition of Silver Iodide Smoke Used in Cloud Seeding Experiments. Journal of the Atmospheric Sciences 1967, 24 (4), 383–386. DOI: 10.1175/1520-0469(1967)024<0383:HACCOS>2.0.CO;2.


texts: Solid hydrophilic transparant materials that don't dissolve in water

texts:
I am looking for hydrophilic transparant materials which are solid at room temperature and that don't dissolve in water. I need these for an experiment in which I condense droplets on a plate made out of/or coated with the material

Just thinking `chemically' I imagine that any polymer with a lot of hydroxyl groups will be hydrophilic (like Polyvinylalcohol), but PVA is water soluble. Polyethylenetereftalate (PET) is reasonable but still has a contact angle around 70 degrees (common polymer contact angles)

Does anybody know transparant materials with contact angles closer to 0 that don't dissolve in water? An additional `demand' is that the material does not break easily (like glass)


texts: Compare stability of transition metal cations in aqueous solution

texts:
I have to compare the stability of the following transition metal cations: $\ce{Co^3+, Fe^3+, Cr^3+, Sc^3+}$ in aqueous solution. (Source: Joint Entrance Exam (JEE) 2013 Mains India)

The first thing I looked at were the ions' electronic configurations:

$$
\begin{align}
\ce{Co^3+}:&\ce{[Ar] 3d^6}&\\
\ce{Fe^3+}:&\ce{[Ar] 3d^5}\\
\ce{Cr^3+}:&\ce{[Ar] 3d^3}\\
\ce{Sc^3+}:&\ce{[Ar] 3d^0}\\
\end{align}
$$

It suggests that $\ce{Fe^3+}$ should be the most stable, but the answer key given for increasing stability instead is $\ce{Co^3+ < Fe^3+ < Cr^3+ < Sc^3+}$. This seems to suggest that lower number of d-electrons leads to more stability, but I am not sure why that is true.

I also thought of the fact that more water of hydration would probably lead to higher stability, and that depends on charge/radius ratio. However, that would suggest $\ce{Sc^3+}$ to be the least stable, but that isn't the case here.

So, what factor is at play instead? And why are the stabilizing factors of half-filled d-subshell and greater water of hydration ignored?

Update: As pointed out in the comments below, to narrow down the cases, we may look at the enthalpies of formation, Gibbs free energy of formation, or the standard electrode potential - whichever one of these is the most applicable to ions in aqueous solution - to compare their relative stability.


texts: What are the products of the Grignard reaction with methyl-magnesium iodide?

texts:
I want to react my ketone with methylmagnesium iodide (the Grignard reagent). I then need to use a dilute acid solution to protonate the $\ce{MgI-O-R'}$ product to produce my alcohol: $\ce{H-O-R'}$

Now I was trying to figure out what acid to use. The first thing that came to mind was sulfuric acid. What would the products be?

In general the reaction should look like: $$\ce{R'=O + XMgI + H-A -> X-R'-OH + MgI+ + A-}$$

Now if I use sulfuric acid the conjugate base reacted with the Grignard products is something like $\ce{MgIHSO4}$. Is this correct?

This molecule doesn't look very stable so my thinking is that the $\ce{Mg}$ donates an electron to $\ce{I}$ in $\ce{MgI+}$ to form elemental iodine and $\ce{Mg^2+}$, then this reacts with $\ce{HSO4}$ to produce $\ce{Mg(HSO4)2}$ and $\ce{MgSO4}$.


texts: What is the pH of a 5M solution of hydrochloric acid?

texts:
What is the $\mathrm{pH}$ of a $\pu{5M}$ solution of hydrochloric acid?

So in order to solve this, apparently all you need to do is plug it into the equation:

$$\mathrm{pH} = -\log[\ce{H3O+}]$$

where the concentration of $\ce{H3O+}$ is $\pu{5M}$. But why can we assume this? Don’t we need to create an ice table from $\ce{HCl + H2O-> H3O+ + Cl-}$ and use the $K_\text{a}$ value of $\ce{HCl}$ to solve this?


texts: How to measure corrosion rate of an iron nail in salt water?

texts: I want to measure rate of corrosion of an iron nail. One way to calculate the corrosion rate is to use the weight loss of the iron nail. However rust does not come off easily. Do have any other ways I could measure the rate of corrosion? Can I measure the weight lost somehow?


texts: Reliance of migratory aptitude on steric hindrance and its effect on rate of reaction

texts:
I've learnt that the migratory aptitude of phenyl is greater than that for methyl, for example.
But how do I find the order of the same for any given 2 groups, like $\ce{Cl-}$ and $\ce{PhCH2CH2CH3-}$, for example?
What's the mechanism of migration in the Schmidt reaction and does its rate depend upon steric hindrance?
I have tried to come up with a few possible mechanisms for the same, but I'm not at all sure.
I was wondering about two possibilities:

If there is a carbanion formed, which is temporarily disjoint from the rest of the molecule, which then attacks at the adjacent position,

Whether the bonds make and break simultaneously, as in the case of the SN2 reaction.


texts: How to find enthalpy of solvation for gas phase cation using Hess's law?

texts:
Find enthalpy of solvation $\Delta_\mathrm{solv}H$ using Hess's law, and show the expression that allows to calculate the enthalpy of solvation.
$$\ce{Ca^2+(g) -> Ca2+(aq)}$$

I am not told which enthalpies of reaction to use. I don't need the exact value, but I do need to show the sum of each enthalpy. I managed to find the enthalpy of the following reactions:
$$
\begin{align}
\ce{Ca(g) &-> Ca+(g) + e-} &\quad \Delta H &= \pu{590 kJ mol-1} \\
\ce{Ca+(g) &-> Ca^2+(g) + e-} &\quad \Delta H &= \pu{1145 kJ mol-1} \\
\ce{Ca(s) + 2 H+(aq) &-> Ca^2+(aq) + H2(g)} &\quad \Delta H &= \pu{1925.9 kJ mol-1} \\
\ce{Ca(s) &-> Ca(g)} &\quad \Delta H &= \pu{178 kJ mol-1}
\end{align}
$$
I nearly have the reactions I need, but I am still needing
$$\ce{H2 -> 2 H+ + 2 e^-}$$
I haven't been able to find the answer.
P.S. I am aware of the enthalpy of formation of $\ce{H2}$, but don't know how/if I can use it here.


texts:
Given was the fact there are 3 isomers of pentane, two were given: pentane and 2-methyl butane. Then I was asked to draw to other one. I drew up the star like structure and checked it to be ok (coincidental I might add).

Then I drew some more and came up with amore turnstile shaped molecule.

     H
     |
   H-C-H   H   H
     |     |   |
   H-C-----C---C-H
     |     |   |
   H-C-H   H   H
     |
     H

To me this also seems like $\ce{C5H12}$ molecule and all valences seem ok. Why isn't this a valid isomer?

Edit: this is 2-methyl butane according to the book:

        H
        |
   H  H-C-H   H   H
   |    |     |   |
H--C----C-----C---C-H
   |    |     |   |
   H    H     H   H


texts: Can a boat conformer of cyclohexane be most stable?

texts:
It is well-known that the "chair" conformation of cyclohexane is the most stable of its conformers. But is there any cyclohexane derivative where other notable conformers (boat, half-chair) are the most stable?

My own intuition is that if there are 4 very bulky groups in the 1, 2, 4, 5 positions then the boat conformer would be preferred.


texts: What is reason of stability of metal (Sr and Ba) peroxides?

texts:
While studying inorganic chemistry I came across the following chemical equation.

$$\ce{M + Air\left(1/2O2 + N2\right) ->[Δ] MO ->[\text{Excess}~O2] MO2 (Stable) + M3N2}$$

$$\ce{M} = \ce{Sr, Ba}$$

My question is why peroxides are more stable than oxides here but in case of other alkali earth elements $(\ce{M} = \ce{Be, Mg, Ca})$ oxides are more stable.

These are the things that came into my mind:

The structure of $\ce{SrO2}$, $\ce{BaO2}$ are isomorphous to $\ce{CaC2}$. I don't think this is causing any extra stability.

The increased basic nature of oxides maybe de-stabilizing oxides when going down the group.

Or maybe the large size of $\ce{Sr^2+}$, $\ce{Br^2+}$ better fits with $\ce{O2^2-}$ in crystal lattice than $\ce{O^2-}$ which leads to increase in lattice energy of peroxides.

I am still a very beginner to inorganic chemistry so it should be helpful if someone explains in a bit more detail.


texts: How to detect harmful gas occurence in carboy bottle

texts:
To fill with drinkable water, I have lots of empty 19lt carboy bottles. Since they came from different people and companies, I have to check their healthiness to decide wheter they can be sterilise for reuse or not.

I need to detect if a 19lt carboy bottle was used previously for gas, lpg, diesel etc. or is there any other harmful chemical (such as urine) in it.

What could be the cheapest and trustable solution for it? Could I use gas sensors or infrared imaging or something else?

Thanks in advance.


texts: Stuck with derivation of the integrated rate equation for a pseudo first order equilibrium reaction

texts:
I was reading about the integrated rate law. However I have problems to follow the solution.
I have an equilibrium reaction:

$$\ce{A + B<=>[{k_{on}}][{k_{off}}]AB}$$

with forward and back reaction. I approximate the measurement to a pseudo first order reaction. The complex can be measured.
B can be calculated:

$$[\ce{B}]\overset{\text{def}}{=}[\ce{B_0}]-[\ce{AB}]$$

Therefore the equilibrium is

$$0 = k_\mathrm{on} \cdot [\ce{A_0}] \cdot ([\ce{B_0}]-[\ce{AB}])-k_\mathrm{off} \cdot [\ce{AB}]$$

which can be expressed also like this:

$$0 = k_\mathrm{on} \cdot \ce{[A_0]} \cdot \ce{[B_0]} - (k_\mathrm{on} \cdot A_0 - k_\mathrm{off})F$$

To solve the differential equation I simplified to this:
\begin{align}
\frac{\mathrm{d}F(t)}{\mathrm{d}t} &= c_1 - c_2 \cdot F(t)\\
c_1 &= k_\mathrm{on} \cdot A_0 \cdot B_0\\
c_2 &= k_\mathrm{on} \cdot A_0 - k_\mathrm{off}\\
\end{align}

So far the theory was easy and I am sure everything is correct, but now I am stuck. The solution of this differential equation would be straightforward:

$$F(t) = \frac{c_1}{c_2}+k\cdot \mathrm{e}^{-(c_2\cdot t)}$$

However, the solution to fit and simulate the kinetic should be (in the simplified writing). This equation is published in http://afm1.pharm.utah.edu/pnscourse/Anal_Biochem_1995.pdf.

$$F(t) = \frac{c_1\cdot (1-\mathrm{e}^{-(c_2\cdot t)})}{c_2}$$

I really would like to know, where is my mistake and how the derivations of this formula has to be.


texts: What is the correct definition of hydration enthalpy and why is it always negative?

texts:
The first definition of hydration enthalpy I found on the net is:

  The hydration enthalpy is the enthalpy change when $1$ mole of gaseous
  ions dissolve in sufficient water to give an infinitely dilute
  solution. Hydration enthalpies are always negative.

Another definition I found in a book is:

  Hydration enthalpy is the energy released when $1$ mole of a compound is
  dissolved in sufficient water to give an infinitely dilute solution.

Now I have three questions:

Which of the two definitions is the correct one? Why?
Why exactly are hydration enthalpies always negative? Suppose I have hydrated copper(II) sulphate which is mostly stable as $\ce{CuSO4.5H2O}$. I convert it to $\ce{CuSO4.6H2O}$ by adding more water forcefully. Shouldn't the hydration enthalpy be positive in this case as it will make the final product less stable than the initial one?
Which definition of hydration enthalpy applies for $\ce{CuSO4}$? I do not think $\ce{CuSO4.5H2O}$ is "infinitely" dilute by any extension of logic. Please explain this if possible.

P.S: I am a novice in thermochemistry. It would be helpful if you could keep the explanations as simple as possible.


texts:
Something I noticed whilst revising about group 15 is that the darker the allotrope of phosphorus, the more stable it is.

white/yellow – very volatile, soluble, pyrophoric
red – air stable, polymer, more stable, one cross link;
black – most stable, polymer, maximum amount of cross link.

What's the reason for this?
Or rather, why would a more stable allotrope have a darker colour?


texts: Why do green bell peppers become bitter when cooked?

texts:
Why do green bell peppers taste sweet raw, but become bitter when cooked (steamed)?
What chemical process is responsible for this? (I don't believe the temperatures are high enough for the Maillard reaction)

Please explain the downvote(s). I wondered if this might be off-topic, but since food-chemistry exists, I believe that it's not.


texts: Hydrogentaion of alkenes in absence of catalysts

texts:
I came across this question regarding hydrogenation of alkenes

Reaction A and Reaction B were carried out using the two different substrates as shown
I have depicted how i thought the reaction would occur.This gives me the correct answer for Reaction A but not for Reaction B.

Apparently instead of b,the compound c would be formed,implying simple hydrogenation of the exocyclic bonds without the formation of a transition state as in reaction a .

I cannot figure out the exact cause for this.
Does this have anything to do with the two double bonds being on the opposite sides in coumpound Y ,and therefore not being able to form the same transition state as X?

P.S: No catalysts were mentioned.Only H2(1 mole) and heat were mentioned in the original question.


texts: Where does the protons and electrons go in this redox reaction?

texts:
In the above oxidation reaction, does the 2 protons and electrons released get accepted by oxygen molecules? If not, where do they go?

Appreciate all answers :)


texts: Best way to mix essential oils with water?

texts: I am using alcohol as an emulsifier. Of course, I can use a lot of alcohol to mix the oil and water but I do not like the color and the % of alcohol in the mix. The best mix I made was 10ml water, 0.5ml (10 drops) essential oil, 5ml alcohol because the mix looks super milky and when left alone the oil does no lt deposit. I repeated this formula again but the result is different (maybe the temperature was different, or the stirring, etc). My question is: what is the best way to stir the essential oil with the alcohol? Should I heat it? Should I stir it with an instrument other than just stirring in a beaker? All emulsifying tips are welcome!


texts:
When finding ions which correspond to certain fragments on a mass spectrum; there are multiple possible ions that can correspond to the same fragment;
How should I know which one is the correct one?


texts:
Hund's rules basically state that we sould maxiumise $S$ and for a given value of $S$ maximise $L$. So let us take the case of Li. Li has 3 electrons, clearly the first 2 are in the $n=1$ state, with $S=0$ and $L=0$. For our remaining electron it must go into one of the $n=2$ states. No matter which state we put it in $S=1$, so we now use Hund's rule to maximise the value of $L$, which would indicate that we put it into the $p$ state giving $L=1$ rather then $s$ state giving $L=0$. But it does go into the $s$ state, which appears to violate Hund's rule. Why does it do this?

(p.s. my notation may be slightly out)


texts: How are these molecules chiral and achiral?

texts:
I always thought that a molecule couldn't be chiral if it had a plane of symmetry. Doesn't the chiral molecule here have symmetry diagonally across the OHs?
The achiral one doesn't look symmetrical to me, so I also don't know how it is achiral.


texts:
Creatine is a popular sports/fitness supplement, generally sold as a powder to be mixed with water (usually like 5-10g creatine per serving). However, it is not very "soluble" in water -- barely 13.3g/L at 18°C. To enhance solubility, some manufacturers sell it as a creatine-HCl formulation -- bringing it up to 88.8g/L!

This formulation, of course, is also more expensive. It makes sense why lowering the pH (making more of the creatine molecules positively charged) would make creatine more soluble, but I'm not sure if there is anything "special" about the HCl component here.

Namely, at home I have regular creatine monohydrate powder (not HCl) and a bag of anhydrous citric acid. I haven't measured the exact increase in creatine solubility after the addition of citric acid, but solubility does increase a little bit and the solution is quite sour as expected.

What I am wondering, is there anything "special" about the creatine-HCl formulation that would greatly bump up creatine solubility that could not just be done with regular creatine (non-HCl) powder and some citric acid powder to lower the pH? I know citric acid is not as "strong" an acid as HCl, but regardless whether it's HCl or citric acid that's used, the final solution pH still has to be safe for oral consumption. And adding citric acid already makes things really sour!


texts:
I was reading S.H.A.R.C. Manual (Surface Hopping in the Adiabatic
Representation Including Arbitrary Couplings) and came across the following paragraph:

  "Each state is colored, with one color as contour and another at the core of the line. The contour color represents the total spin expectation value of the state. The core color represents the oscillator strength of the state with the lowest state. See figure 7.3 for the relevant color code. Note that by definition the “oscillator strength” of the lowest state with itself is exactly zero, hence the lowest state is also light grey. This dual coloring allows for a quick recognition of different types of states in the dynamics, e.g. singlets vs. triplets or nπ ∗ vs. ππ ∗ states."

How can one recognize nπ ∗ vs. ππ ∗ from this kind of colour scheme? What does oscillator strength have to do with state character?


texts: I see that Gaussian has feature to set periodic boundary conditions specifying the parameter Tv in the input file. Does it do it via the plane wave basis set? Also, the question is whether it is efficient to use Gaussian to compute the relaxed lattice constant, band structure and DOS for solids or it is better to use programs like ABINIT.


texts: How do I prepare the following compound from diphenylmethane?

texts: I am having trouble with the preparation of this product from diphenylmethane as a starting material. One of my thoughts was to attach the butene into the structure, but I don't see how it is viable. So I would like some suggestions on how to proceed, and also with the name of the compound (butenediphenylmethane?).


texts: Enthalpy of a reaction changes with temperature, does this mean bond strengths change with temperature?

texts:
During chemical reactions, the bonds between atoms break or form to either absorb or release energy. The result is a change to the potential energy of the system. The heat absorbed or released from a system under constant pressure is known as enthalpy.

Mathematically, we can think of the enthalpy of reaction as the difference between the potential energy from the product bonds and the potential energy of the reactant bonds.

But we know that enthalpy of a reaction depends on the temperature according to Kirchoff's equations. So does this mean that bond energies also change with temperature.

Also can someone explain to me at the molecular level why does enthalpy of the reaction change with temperature?

And since the enthalpy of a reaction depend on the constant pressure at which reaction is carried out, does this mean bond strengths also depend on pressure?


texts: What does peroxide value exactly measure?

texts:
I understand that peroxide value gives a measure of the extent to which an oil has undergone oxidation, however, I looked and couldn't find any source which explains the chemistry behind PV value. More specifically, how is pv value related with oxidation?

Wikipedia states that "the peroxide value is determined by measuring the amount of iodine which is formed by the reaction of peroxides (formed in fat or oil) with iodide ion." But what is the reaction of the peroxides? And how is it related with oxidation?

Thank you


texts: Physical Chemistry: Specifically the Dissolution of Carbonates

texts:
Please note this question is different to the other that keeps being mentioned. That one is about the concentration of just  $\ce{HCO3-}$ when no $\ce {pH}$ was given.
Whereas, in this one I am trying to find the concentrations of $\ce{H+}$, $\ce{HCO3-}$, $\ce{CO3^{2-}}$, and $\ce{Ca^2+}$, with a given $\ce {pH}$.
Consider the following equations:
\begin{align}
\ce{CO2(g) + H2O(l) &<=> H2CO3(aq)} &\quad K_{\ce{CO2}} &= 10^{-1.47} \tag{1}\\
\ce{H2CO3(aq) &<=> H+(aq) + HCO3-(aq)} &\quad K_1 &= 10^{-6.35} \tag{2}\\
\ce{HCO3-(aq) &<=> H+(aq) + CO3^{2-}(aq)} &\quad K_2 &= 10^{-10.33} \tag{3}\\
\ce{CaCO3(s) &<=> Ca^{2+}(aq) + CO3^{2-}(aq)} &\quad K_{\text{cal}} &= 10^{-8.48} \tag{4}\\
\end{align}
Atmospheric $\ce{CO2}$ is at $\pu{10^{-3.5} atm}$ and the solution is pure water.
Also, in equation $(4)$ calcite crystals are added in excess ($\ce{CaCO3}$).
So far I have been able to find the equilibrium equations and have got the concentration of $\ce{H2CO3}$ to be $10^{-4.97}$ by multiplying the atmospheric $\ce{CO2}$ by the value of $K_{\ce{CO2}}$.
Having been told the $\mathrm{pH}$ of the solution is 8.26, I then calculated the concentration of $\ce{H+}$ to be $10^{-8.26}$.
Using my values of $\ce{H2CO3}$ and $\ce{H+}$ and substituting them into the equilibrium equation for (2),I have the concentration of $\ce{HCO3-}$ to be $10^{-3.06}$. Is this correct?
Continuing on with the same method I have the following concentrations for $\ce{CO3^2-}$ and $\ce{Ca^2+}$ to be $10^{-5.13}$ and $10^{-3.35}$, respectively. Am I still correct here?
Thank you in advance.


texts: Solubility of non polar substances in non polar solutions

texts:
From my understanding, the general rule for solubility is that polar molecules are soluble in polar liquids (e.g. water), and non polar substances are soluble in non polar liquids (organic solvents).

I can understand that when polar molecules are dissolved in polar liquids, the opposite dipoles are attracted to each other and hence the substance dissolves. For this reason, a polar liquid can't dissolve a non polar substance because there are no dipoles to attract, so it would just stay suspended in the liquid.

My question: if both the solute and the solvent are non polar, how does the solute dissolve without electrostatic attraction? would this not also just stay suspended in the liquid?


texts: Why is the endo product the major product in a Diels-Alder reaction?

texts:
I understand that the endo product is, at least in all cases in my textbook, the major product in a Diels-Alder reaction. However, I don't understand why this is the case.

The explanation in my textbook says that the endo product allows for more interaction between the diene and dienophile during the transition state.

I also found the following post, which suggests that secondary orbital interactions are the cause. Stereochemistry of product in Diels-Alder reaction

Then I found the following paper that indicates, at least to my understanding, that steric strain during the transition state is the main reason behind the endo rule (or at least for the example reaction in the article). https://www.ncbi.nlm.nih.gov/pubmed/24449044

So, I'm left wondering what is the reason for the endo rule?


texts: Ozone cross-section in the near-infrared

texts:
I am searching for ozone absorption cross-section in the wavelengths range 1.1 μm to 10 μm. So far I looked in the following databases:

HITRAN
Max-Planck Institute for Chemistry Mainz

and of course, googled it.
Any idea where I can find such information?


texts: Excited state intramolecular proton transfer mechanism

texts: I am trying to explain Excited state intramolecular proton transfer(ESIPT) mechanism through DFT method using Gaussian 09.Generally, in ESIPT mechanism the molecule exist in enol form in its electronic ground state. therefore the calculated energy of the ground state  enol form would be lesser than its ground state  keto tautomer.But, In my case the calculated energy of ground state keto tautomer is less than ground state enol form. moreover,the Potential Energy Surface scanning(PES)[of ground state optimized enol tautomer] was also performed with O-H bond length co-ordinate.the scanning plot has shown least energy of keto tautomer. For ESIPT,can the molecule exist in keto form in its electronic ground state?


texts:
I have no clue whatsoever about Chemistry on a academic point of view.

We wish to transport some goods.
Let's say we vacuum some of those goods, by doing like so:

We place those goods on a box, we close the box, and then we vacuum seal the box (not the goods).

Can we consider the goods to be vacuum protected?

Does that mean, that no hight heat will affect those goods?

Thank you in advance, and sorry for not using specific chemical terminology.


texts: Why is there a need to rotate the molecule in a sharpless asymmetric epoxidation?

texts:
As far as I understand sharpless epoxidation, you first need to rotate the molecule such that the vincyclic alcohol is in the upper right quadrant. Then, the epoxide forms on the top/bottom of the double bond, depending on the chirality of DET. (See image below, from masterorganicchemistry.com: Sharpless Epoxidation)

My question is that why do we need to rotate the molecule when forming the epoxide, because can't we just form the epoxide directly without rotation? And if we can't,  then we still can rotate the molecule back to its starting orientation after a epoxidation, right? Pretty confused about this.


texts: Can anomers be destinguished based on Fischer projection?

texts:
I would like to ask if it is possible to tell an anomer using Fischer projection (e.g. glucose). In high school we learned only Haworth and Tollens are hepful in this case.

However, I'm not exactly sure since normal or wedged bonds used in drawn Fischer projection should give the idea. If the double bonded oxygen is on the right that is where poloacetal hydroxyl group will be formed, should stay above the ring after cyclisation and based on normal/wedged bond connecting $\ce{-CH2OH}$ goup with the rest of the molecule one should be able to tell the anomer.

I feel like I am missing a very basic principle that causes any attempt of my logical explanation to fail.


texts: Diffusion of carbon from ferrite to cementite in the eutectoid transformation

texts:
Why does the carbon of an alloy diffuse from ferrite (0.022% C) to cementite (6.70% C) during eutectoid transformations? I know that the diffusion of a generic species (e.g. of atom A) carries A from regions where the amount of A is higher to regions where the amount of A is lower.

I found this sentence on page 337 of Callister (9th ed.).


texts: About the meaning of the names of f orbitals

texts: Our chemistry teacher encouraged us to study the history and naming of the orbitals on the web. (actually, our textbook did, but that's irrelevant to the problem) I easily could find the reason behind their naming, and what their names stood for. However, some sources stated that f as in f orbitals stands for fine, while others claimed it to be fundamental. Which of these two is correct? And why did scientists gave f orbitals that name? (as you're aware, they did it due to the f block elements' emission spectrum; my question is, what was the specification of their emission spectrum?) I'm sorry if the question looks stupid, but I can't figure it out myself.


texts: Negative retention for chloride in hydrolysate filtration

texts:
I tried to fractionate proteins as a function of their size with an ultrafiltration membrane. I observed a higher concentration of chloride in my permeate than in my feed or retentate. The proteins do not pass through the membrane and the filtration has been done at pH = 7. I asked, how is it possible to have a higher concentration in the permeate than in the feed or retentate?

I found this explanation but I'm not sure about it :

  It may be explained by the Donnan effect. Negatively charged proteins are retained in the retentate. To compensate the positive charges from the cations that are on the other side of the membrane, they attract the chloride.

Is it a possible way to explain this issue?


texts: Is the crystallization process of aqueous solutions of substances such as lithium chloride endothermic?

texts:
$\ce{LiCl}$ has an enthalpy of solution of $\pu{-37.1 kJ/mol}$, so its dissolution process is exothermic. Does this mean that it's crystallization process is exothermic? I'm asking since I've looked up "exothermic crystallization" and "the crystallization of endothermic solutions" and couldn't find anything.

So my question is: Is crystallization always an exothermic process, or is it endothermic for substances such as this whose enthalpy of solutions are negative?


texts:
From searching online I found this:

  The apparatus consists of two sets of bulbs. The first set of three bulbs is filled with solution to half of their capacity and second set of another three bulbs is filled with the pure solvent. Each set is separately weighed accurately. Both sets are connected to each other and then with the accurately weighed set of guard tubes filled with anhydrous calcium chloride or some other dehydrating agents like $\displaystyle P_2O_5$, conc. $\displaystyle H_2SO_4$ etc. The bulbs of solution and pure solvent are kept in a thermostat maintained at a constant temperature.

  A current of pure dry air is bubbled through. The air gets saturated with the vapours in each set of bulbs. The air takes up an amount of vapours proportional to the vapour pressure of the solution first and then it takes up more amount of vapours from the solvent which is proportional to the difference in the vapour pressure of the solvent and the vapour pressure of solution, i.e. $\displaystyle p_0 – p_s$. The two sets of bulbs are weighed again. The guard tubes are also weighed.

  Loss in mass in the solution bulbs $\displaystyle \propto p_s $

  Loss in mass in the solvent bulbs $\displaystyle \propto (p_0 – p_s) $

  Total loss in both sets of bulbs $\displaystyle \propto [p_s +(p_0 – p_s)] \propto p_0 $

  Total loss in mass of both sets of bulbs is equal to gain in mass of guard tubes.

  Thus, $\displaystyle \frac{p_0-p_s}{p_0} = \frac{\text{Loss in mass in solvent bulbs}}{\text{Total loss in mass in both sets of bulbs}}
= \frac{\text{Loss in mass in solvents bulbs}}{\text{Gain in mass of guard tubes}}$

  Further we know from Raoult’s law

  $\displaystyle \frac{p_0-p_s}{p_0} = \frac{\frac{w_A}{m_A}}{\frac{w_A}{m_A} + \frac{w_B}{m_B}}$

  The above relationship is used for calculation of molecular masses of non-volatile solutes.

  For very dilute solutions, the following relationship can be applied.

  $\displaystyle \frac{p_0-p_s}{p_0} = \frac{\text{Loss in mass of solvent bulbs}}{\text{Gain in mass of guard tubes}}= \frac{w_Am_B}{w_Bm_A}$

My questions:

Why "The air takes up an amount of vapours proportional to the vapour pressure of the solution first and then it takes up more amount of vapours from the solvent which is proportional to the difference in the vapour pressure of the solvent and the vapour pressure of solution"?
How can we add $\propto p_s$ and $\propto p_0-p_s$ when we don't know what the proportionality constants are or even if they are equal?
It would be better if you could explain in detail the process because I'm not getting it properly from here.For your information the text after "From Raoult's Law" and about "the setup" is purely clear to me.


texts: Causing a metal or glass marble to float in an aqueous solution

texts:
I am trying to find a way that you could cause metal (Aluminum) or glass to float in a mixture of water and some water-soluble material. I am aware that salt can be used to heighten the density of water, but I doubt it could go to that extent because both aluminum and glass are more dense than salt (possibly flawed logic, I have limited knowledge of the subject). So basically: if there is any way to cause Aluminum or glass to float in water, possibly through adding a water soluble material to the water, please let me know.

Edit: Basically what I'm doing is trying to think of creative ways to sort materials by density, for example a set of marbles. With the example of solutions with salt, you would vary the amount of salt in the mixture to alter what materials would float.


texts: How to test for and remove lead(II) sulfate from a sample of 1 M sulfuric acid?

texts:
If you had a clear, colourless sample of dilute sulfuric acid and suspected lead contamination, probably lead sulfate, how would you test for this? It's solubility is low in sulfuric acid solutions, and lower near freezing, so I thought cooling might produce a precipitate, but I'm not sure what level if any this would be able to detect. Raising the concentration by open boiling or distilling would, from what I can gather, produce a filterable precipitate, but that is not something I want to test.

Would there be any easy way to remove any detected contamination? By easy, I mainly mean not distilling or boiling and filtering conc. sulfuric. Ideally, I would be looking for a method that does not involve raising the concentration at all. Chemical conversion to something even less soluble? Electrolysis?

EDTA can be used to combat lead intoxication. Would there be a way of using it to remove lead compounds?


texts: How to change the chirality of amino acids?

texts:
Is it possible to change the chirality of the amino acids? I understand such a process is called "stereoinversion".

Take a levorotatory amino acid and turn it into it's dextrorotatory counterpart (enantiomer, optical isomer).

Anyone tried to do that? Can a high temperature change the chirality of an amino acid for example?

Racemization is good enough for me. Changing the chirality of just a small amount of the total amino acids in the sample is good enough.


texts: Recently, I learn about bonding and my teacher only focus on ionic and covelant bond, not metallic bond. So, I go on google search but I have no idea of what is it? How electrons can suddenly appear to form the bond? How can the metal highest energy level overlap if it need to obey the octet rule


texts: Predominance of III oxidation state for lanthanides

texts:
For most lanthanide metals, the stable oxidation state is III [*]. The general electronic structure is $$\ce{[Xe] 4f^{0}^{-14} 5s^2 5p^6 5d^{0}^{-1} 6s^2}\ \ [**].$$

Elements that have the d-electron are La, Ce, Gd, and Lu. Furthermore, the f-subshell is considered relatively stable in states $$f^0, f^7, \text{and} f^{14}.$$

We can conclude that La, Gd, and also Lu easily form $\ce{E^3+}$ ions. Yet, as would be predicted by this easy approach, we would also see $$\ce{Sm+, Tm+ (f^7 \ and \ f^14 ), \\ Pr^5+, Dy^5+ (f^0 \ and \ f^7)}.$$

This is definitely not the case. But the why? alludes me. According to Radiochemistry,

  The 4f binding energy is so great that the remaining 4f-electrons are regarded as "core-like". [Italic added]

Could someone explain this further? [***]

Radiochemistry then goes on to assert,

  Interelectronic repulsion in related not just to electron pairing, but also to [the] angular momentum of the electrons. [---]

  e.g., in $\ce{Pr^2+ (4f^3)->Pr^3+ (4f^2)}$ ionisation removes repulsion between [electrons] of like rotation [---]

  $\ce{Pm^2+ (4f^4)->Pm^3+ (4f^3)}$ ionisation removes repulsion between [electrons] of unlike rotation [---] [emphasis added]

What exactly is meant by "electrons of like/unlike rotation"? Plus it mentions some "quarter / three-quarter" rule which I possibly cannot rationalise for a total of 14 electrons.

Any help would be greatly appreciated.

[*] Ce, Pr, and Tb also have the oxidation state IV. Eu and Tm have the additional state II.

[**] Ordering changes with the number of electrons.

[***] I am, of course, aware that

each electron would be harder to remove as Culonic attraction increases with positive ionic charge,
lathanide contraction is a part of the explanation.

(Somewhat related: Plutonium having more oxidation states than samarium?)

EDIT

Every thanks to Brian for providing awesome title suggestions. These are the four new subquestions:

Why don't we see these lanthanide species?
Howcome orbitals become 'core-like' when electrons are removed?
What is meant by 'electrons of like/unlike rotation'?
What's up with this quarter / three-quarter rule?

Just an FYI for future chainposters, there's a sixty-second waiting period after asking two consecutive questions.


texts: Why can't small trans-cycloalkenes exist?

texts: Why when a ring has 8 carbon's and contains a double bond the trans version is very unstable to exist, for instance a molecule like cholesterol?


texts: Does imine formation occur for esters before ketones?

texts: I understand that ketones are more reactive than esters but when I take a look at the reaction on the image, it seems to me that the imine is formed on the ester before the ketone to create the heterocycle. I would appreciate it if I could get some clarification on how this reaction takes place.


texts: Calibration Ammonia Sensor and Gas Concentration

texts:
My name is Felipe and this is my first post here.
I'm working on a project to calibrate an electrochemical ammonia sensor. But I have a lot of doubts because I am a layman in chemistry. I'll list them and I'd be grateful if you could respond them.

The system I have here is basically a cylinder with ammonia gas of known concentration connected by a 0.5 lpm regulator and a tygon tube to a chamber where the sensor is.
Here are my doubts:

When I open the regulator the gas starts to flow into the chamber, the concentration of oxygen(or other gases) in the chamber can affect the concentration of ammonia gas? Or even if the gases mix, there is a fixed concentration of ammonia?
I've seen a lot of calibration videos. Why does nobody care about the tube length? I think as long as the tube length more is the waste of gas, right?
When I stop with the ammonia gas flow and disconnect the tube from the chamber. What are the precautions I should take with the contaminating ammonia in the air? Let's say I'm using a calibration gas of 50ppm


texts:
Technetium is probably the most awkward element of the periodic table for me. It seems to me that Technetium is an exception, in the sense that it doesn't have any stable isotopes, despite having a relatively low atomic number when compared to other unstable elements.

So I thought, maybe there is something special about it. Some exceptional property that causes it to be so unstable with such a low atomic number.

Please tell me. What is it that makes Technetium so unstable?


texts: Why is the trimethylammonium group a stronger electron withdrawing group than the nitro group?

texts:
I was working on a question that basically boils down to deciding whether the nitro group ($\ce{-NO2}$) or the trimethylammonium group ($\ce{-N+(CH3)3}$) on a benzene ring, is a stronger electron withdrawing group (EWG).

The solution says that the trimethylammonium group is a stronger EWG since it has an overall positive charge, while the nitro group is overall neutral.

But I am getting confused here. Why should the nitro group be neutral? The $\ce{N}$ atom has 4 bonds (a single bond to an oxygen atom, a double bond to another oxygen atom, and another bond to the carbon of the ring), so the $\ce{N}$ atom in $\ce{NO2}$ should also have a positive charge?

Further I analysed that since $\ce{O}$ is more electronegative than $\ce{N}$, it tries to shift the $\pi$ electrons of the double bond towards itself, hence increasing the electrophilicity of the nitrogen of $\ce{NO2}$, while in the trimethyl amino group, the $\ce{N}$ being the more electronegative atom gets electrons donated to it due to the +I effect of the three $\ce{CH3}$ groups, thus reducing the electrophilicity of $\ce{N}$. So $\ce{-NO2}$ should be a stronger EWG than $\ce{-N+(CH3)3}$.

Where am I going wrong?


texts: Extracting other mineral from salt in evaporated seawater

texts:
I recently stumbled upon this news:

Seawater contains 47 minerals and metals. Starting with the most abundant and proceeding to the least abundant, these are chloride, with a concentration of $\pu{18 980 ppm}$ (parts per million) in seawater, sodium ($\pu{10 561 ppm}$), magnesium ($\pu{1 272 ppm}$), sulfur $(\pu{884 ppm})$, calcium ($\pu{400 ppm}$), potassium ($\pu{380 ppm}$), bromine ($\pu{65 ppm}$), inorganic carbon ($\pu{28 ppm}$) and strontium ($\pu{13 ppm}$). Then follow boron ($\pu{4.6 ppm}$), silicon $(\pu{4 ppm})$, organic carbon ($\pu{3 ppm}$), aluminum ($\pu{1.9 ppm}$), fluorine ($\pu{1.4 ppm}$), nitrogen in the form of nitrate ($\pu{0.7 ppm}$), organic nitrogen ($\pu{0.2 ppm}$), rubidium ($\pu{0.2 ppm}$), lithium ($\pu{0.1 ppm}$), phosphorous in the form of phosphate ($\pu{0.1 ppm}$), copper $(\pu{0.09 ppm})$, barium ($\pu{0.05 ppm}$), iodine (also $\pu{0.05 ppm}$), nitrogen in the form of nitrite (also $\pu{0.05 ppm}$) and nitrogen in the form of ammonia (once more $\pu{0.05 ppm}$). Thereafter, we have arsenic ($\pu{0.024 ppm}$), iron ($\pu{0.02 ppm}$), organic phosphorous $(\pu{0.016 ppm})$, zinc $(\pu{0.014 ppm})$, manganese ($\pu{0.01 ppm}$), lead ($\pu{0.005 ppm}$), selenium ($\pu{0.004 ppm}$), tin $(\pu{0.003 ppm})$, caesium ($\pu{0.002 ppm}$), molybdenum (also $\pu{0.002 ppm}$) and uranium ($\pu{0.0016 ppm}$). Then come gallium ($\pu{0.0005 ppm}$), nickel (also $\pu{0.0005 ppm}$), thorium (also $\pu{0.0005 ppm}$), cerium ($\pu{0.0004 ppm}$), vanadium $(\pu{0.0003 ppm})$, lanthanum (also $\pu{0.0003 ppm}$), yttrium (also $\pu{0.0003 ppm}$), mercury (once more $\pu{0.0003 ppm}$), silver (also $\pu{0.0003 ppm}$), bismuth ($\pu{0.0002 ppm}$), cobalt $(\pu{0.0001 ppm})$ and,finally, gold ($\pu{0.000008 ppm}$). Altogether, there are some 50 quadrillion tons (that is, $\pu{50 000 000 000 000 000 tons}$) of minerals and metals dissolved in all the world’s seas and oceans.

Which is quite surprising for me (thought those white crystal was only $\ce{NaCl}$)
Assuming I already have TONS of general salts (mixed) from simple seawater evaporation, is there any way to separate each mineral? Let's say by pouring the salts in magnet (for material that is having magnetic properties), etc

(lithium salt pond, which seen exactly same as $\ce{NaCl}$ pond)
Apologize for shallow understanding of the topic. Any suggestion is highly appreciated since I can't find the answer elsewhere.
P.S: This question have been posted earlier in Physics


texts: How do surfactants spread in the case of multiple materials?

texts:
For example, consider a pot of water with a drop of oil floating on it, with surfactants present in the water.

Will the surfactants in the water spread evenly across all three interfaces (water/metal, water/air, and water/oil)?

Are there material-specific surfactants, such that each of the three interfaces might attract different surfactants?

If so, are there also surfactants that would tend to spread across all three interfaces evenly?


texts: I am trying to create a water drop simulation for measuring hydrophobicity of surface. I don't know how to simulate the contact angle which is related by younges equation to the surface tensions for each of the solid-liquid-gas interfaces. I have come across some models for molecular dynamics, which for chemistry novice like me (I'm a EE) are bit advanced. I am looking for simpler method in which I could simulate the interfacial tensions by some sort of derived mathematical model which would be simple enough to act as an objective function to an evolutionary optimizer.


texts: What compressible rubber like gasket material is the least permeable to CO2?

texts: I am trying to can a carbonated solution at 120 PSI.  I am trying to figure out the best material to use for the gasket on the valve cap. I am carbonating my fluid with $\ce{CO2}$ and it is loosing pressure over time due to the permeability of $\ce{CO2}$ through my gasket. I have tried about 8 materials (aluminum, copper, graphite,  buna, FMK A, Viton, ECH, PVDF) I was not able to compress the metals enough with my equipment we also dismissed a number of other materials that are known to be highly permeable to $\ce{CO2}$ or are not feasible and have not found a suitable gasket yet. I also tried using $\ce{N2O}$ as my gas but it seems to have the same permeability as $\ce{CO2}$. my gas has to be soluble in water and non toxic. I know that Viton and FMK A are the same but one supplier said theirs was more pure than anyone else.


texts: We're currently studying "the chemistry of contact lenses", which is mostly polymers and gels. I just looked at the package of two pure hydrogel lenses made out of the same monomers, but they have different water content? Why?


texts: What happens when two nitrates react with each other?

texts:
I have to determine the products of the ammonium nitrate and copper nitrate. Is the below reaction correct?

$$\ce{NH4NO3 + Cu(NO3)2 -> Cu(NH3)4(NO3)2}$$

(ammonium nitrate + copper nitrate → tetrammine copper(ii) nitrate)

Also, what would be the products of the other two reactions below:

copper nitrate + lead nitrate
lead nitrate + ammonium nitrate

Basically, what happens when you react any two nitrates?


texts: Lower an electron energy level by pressure

texts: When an atom is in extreme pressure like a little before it's Schwartzchilds radius, can the electrons in higher energy levels physically be compressed into lower energy levels?.


texts: MO Diagram "greatest stabilisation when orbitals are close in energy"

texts:
I was studying MO diagrams in Chemistry and we were given a diagram explaining this:

I understood the diagram furthest to the left describing the situation where the Electrophile (E) and Nucleophile (Nu) result in the largest energy gain when both are equal in energy.

However, the lecturer later said that when there is a large difference in energy between E and Nu (far right), the energy gain is negligible. He didn't go further to explaining why this was true.

I tried looking on the internet for an answer but was led to s-p mixing and content I am not familiar with nor find relevant to the question.

I'm confused here. What explains this phenomena? Or, is it just an effect observed without explanation - like a Postulate?


texts: How to find chemical similarity between two compounds using Tanimoto method

texts:
I came across a paper named "Chemical Similarity Searching" by Peter Willett
John M. Barnard and Geoffrey M. Downs, 1998. At one place, this paper talks of finding chemical structure similarity between two chemical compounds using Tanimoto method. Now I want to understand how it is done but could not derive anything just by reading the paper. I wanted to know if someone can explain how the distance is found taking two compounds into consideration. I wanted a step by step explanation. I have failed to derive how to find similarity from the paper. Please help.


texts: Electromagnetic energy to Chemical energy

texts: How can electromagnetic energy (photons) be efficiently converted to chemical energy? For instance, can water be efficiently split to hydrogen and oxygen using solar energy? As we are running out of non-renewable resources is there any way for us to use the solar energy so efficiently to generate power?


texts: If we put an metal electrode in water with no metal ions present potential should tend to minus infinity?

texts: If we consider an equilibrium between metal electrode and its ions in solution we know that equilibrium potential is proportional to activity of ions in solution from Nernst equation. Since this dependence is logarithmic, what we conclude is that when activity of ions tends towards zero, potential tends to minus infinity. If we do place a metal electrode in pure water, would its potential decrease continously if we disregard any kind of other processes on it like corrosion which create their own potential?


texts: Why can't chlorine atoms form hydrogen bonds?

texts:
Why can't chlorine atoms form hydrogen bonds even though they have very similar electronegativity to nitrogen, which can?

Electronegativities are as follows:

$\ce{Cl} - 3.16$

$\ce{N} - 3.04$

Is it because of the size ?


texts: Abstraction of a proton in cycloheptatriene

texts:
So, whenever there is abstraction of H+ by an acid-base reaction, I see that the proton on the sp3-hybridized carbon is taken. Why is this if you take into account that vinylic hydrogens are more acidic?

Also, on a sidenote, what is the hybridization state of a carbon in a C=C double bond where the vinylic proton was removed by a base?


texts: Dipole Moment of Normal Water vs Heavy Water

texts:
The question is in the title itself.

My guess: Higher for Normal water.

My Reasoning: Internet told me Deuterium is more electronegative than Protium. So,  there should be less difference between the electronegativity values of $\ce{D}$ and $\ce{O}$. Consequently, the dipole moment for $\ce{D2O}$ should be lower.

Is this a valid reasoning or should I take into account factors like lesser vibration amplitude of $\ce{D}$ than $\ce{H}$ that forms more stable bonds.


texts:
I have water contaminated with dissolved chlorine:

$\ce{H2O + Cl2 <=>HCl + HOCl}$

During electrolysis, this is an issue. These are my products:

$\ce{NaCl + H2O ->T[electrolysis] NaOH + Cl2 + O2 + H2 }$

However, $\ce{NaOH}$ will be neutralised by $\ce{HCl}$:

$\ce{NaOH + HCl-> NaCl + H2O}$

I guess this can be considered hydrochloric acid. I want to remove the chlorine ions from water and prevent future dissolving.

Does increasing temperature help to remove the chlorine? Does boiling make the chlorine leave the mixture?

$\ce{H2O + HCl + HOCl ->T[???] H2O + Cl2(gas)}$

PS.: I understand that there are means of separating the electrolysis columns. But this question is really about removing $\ce{Cl2}$ or $\ce{HCl}$ from aqueous solution.


texts: Experimentally proving the mechanism and rate laws of SN1 & SN2 reactions

texts:
I have been given the task of experimentally proving the rate laws and mechanisms of $\mathrm{S_N1}$ and $\mathrm{S_N2}$ reactions. Unfortunately, the only equipment I can use is limited to analytical equipment that is needed to complete A-Level and IGCSE chemistry courses. So, I cannot use NMR machines, mass spectroscopy/spectrometry, etc.

It's obviously very easy to look at a nucleophilic reaction and see how fast it goes (using $\ce{AgNO3}$), but I do not know how I would go about quantifying this, i.e. actually numerically measuring the rate so that I can use the data I collect in a rate law equation.

Furthermore, I do not know how I would definitively prove the mechanism of $\mathrm{S_N1}$ and $\mathrm{S_N2}$ reactions, through experiment. I originally, thought of measuring the rate of reactions with different primary, secondary and tertiary haloalkanes and try and use the rates I get to prove that they are undergoing $\mathrm{S_N1}$ or $\mathrm{S_N2}$, and go from there. But I don't think that would be deemed as definitive proof that what is going on is definitely, without a doubt, the exact $\mathrm{S_N1}$/$\mathrm{S_N2}$ mechanism.


texts: How does one electroplate Lithium onto a conductive metal?

texts:
In this case the anode for electroplating would be the Lithium and the cathode would be any conductive metal.

Unfortunately Lithium reacts violently with water, which is the basis of most electrolyte solutions that are used for electroplating.

So is there an anhydrous electrolyte solution or an alternative method for electroplating Lithium onto a conductive metal?


texts: Why is the effect of competitive antagonist less than the effect of non-competetive antagonists?

texts: Drugs can  be provided as a competive or non-competitive form of agonists. But the effect of non-competitive antagonists is much more than the other, so what is the cause of that? And are there some exceptions?


texts:
I'm currently working on a really simple project, an ashtray that can stop cigarette combustion.

I planned to put an aluminium block into my ashtray, with some kind of curves or holes in it, in order for the cigarette to fit in, then stop combusting by lack of $\ce{O2}$, and maybe by heat transfer, as the cigarette tip and the aluminium will be in contact.

I choose aluminium, because I've got some, because it seems quite inert to me, and because it's not too hard to work with. But I can't solve the safety estimation for this material.

Here is some information I found around :

A cigarette tip being around $\pu{900^oC}$
Aluminium point of boiling at $\pu{2519^oC}$
Aluminium toxicity seems still debated, but aluminium is more or less eatable, i.e. used as pigment in food (E173)

Of course, aluminium won't burn, but I'm afraid that heating it may produce a layer of aluminium oxide, which may scatter on the cigarette tip, or get combined with ash components.

So, how can we estimate the safety of this material under these condition?


texts: Real life chemistry :boiling carrot dices

texts:
This morning I was boiling carrot dices. And saw something quite interesting happening to the dices.

The water is not boiling. But before it boils, the dices started gathering at the center  of the pot.

Any one has any answer as to why this happened?


texts: Tips for maximizing yield, purity and crystal size during recrystallization

texts:
I have already asked a similar question on titrations before. In a few months, I have a test on chemical synthesis. It is marked on the percentage yield, purity and crystal size of the product. I do not have a lot experience in doing syntheses and I am looking for any tips that will help maximize the yield, purity and crystal size of my synthesis.
Most of the synthesis that we do, the products are obtained by recrystallization. The solid is dissolved in a solvent at a high temperature and then it is placed in a cool bath. Then the product will crystallize on the bottom of the beaker.
Reading through an analytical textbook, it states a few ways to improve yield and purity but it doesn't actually state how you would do it practically:

allow the solution cool down as slowly as possible. This will maximize crystal size.

maintain a low relative supersaturation of the solution, this will increase crystal size and improve purity

describes the process or digestion or Ostwald ripening where larger crystals grow at the expense of smaller crystals

Does anyone have any suggestions on how I would actually do these 3 above tips? Also does anyone have any other tips?


texts:
Is it possible to selectively halogenate a certain position on an alkane chain, and also get a good yield?

I understand that to form such haloalkanes, taking a different substrate other than alkane (like a substituted alkane with the substituent attached at that position) would be a good choice, but is there a favourable synthesis to convert an alkane, say, n-pentane to 3-chloropentane?

Free radical bromination works well for smaller alkanes (due to its selectivity for secondary and tertiary positions) but it would not make much good out of longer ones. One could distil out the desired product after the free radical halogenation, but that doesn't seem quite effective.

P.S. The question may sound silly but only intends to know whether such synthesis is possible or not.


texts:
For example, how does a gas stove heat a metal pot?

A combustion reaction between the gas and the air takes place, and this releases energy due to new chemical bonds being formed.

Do the atoms in the metal pot absorb these photons, which then excites the atoms' electrons and creates kinetic energy within the atoms (thus, heat)?

Or, are the atoms in the combustion reaction just moving around so fast that they're bumping into all the atoms of the metal pot, generating kinetic energy?


texts: This one has stumped me for a few days.  What is the specific name of the general chemistry principle that is responsible for the difference in melting points of pure and impure solids.  I have exhausted all other resources available and a precise principle name eludes me.


texts: Ideal gas law derivation from kinetic theory

texts:
Consider the derivation of the ideal gas law from kinetic theory presented here: http://en.wikipedia.org/wiki/Kinetic_theory

I have some questions

This derivation assumes the container is a cube, but the law holds for containers of any shape, right?
This derivation assumes each particle has the same mass, but the law holds for a mixture of gasses of different masses, like air, right?
The derivation assumes that the particle intercepts a give side with frequency $2L/v_x$. Why can we make this assumption?


texts: What's the physicochemical difference between a chromophore and a fluorophore?

texts:
Let's take Hematoxylin, which is a pH indicator and a stain for histology, and therefore a chromophore, but does not fluoresce:

Now let's take Eosin, which stains tissue pinkish, but is also fluorescent:

I would like to know which features of the molecules decide if it is a chromophore or a fluorophore. As far as I can see it (I'm a biologist with some training in organic chemistry), both have conjugated systems, although the system in Eosin spans a lot of more bonds. Is it really just the size of the conjugated system that decides this, e.g., if Hematoxylin had a larger conjugated system, would it also be fluorescent?


texts: Is my textbook using the law of partial pressures correctly?

texts:
My textbook shows that pressure fraction is equal to mole fraction because the same volume cancels:

But it violates (if I am not mistaken) the law in this example it gives:

  the main components of dry air, by volume, are N2, 78.08%, O2, 20.95%, Ar, 0.93%, and CO2, 0.04%. What is the partial pressure of each gas in a sample of air at 1atm.

The strategy it gives for solving this problem is by treating the volume percent as mole percent, and in turn as pressure percent. But obviously, each gas occupies a different volume, the law of partial pressure doesn't apply. does it?

Also, is it possible for different components of air to occupy different amounts of space in atmosphere? If atmosphere is a container, doesn't all components just occupy the same amount of space-the size of container?


texts: what's the mechanism of formation of succinimide ester?

texts:
I am forming succinimide ester:

Below is the experimental protocol I have adapted from (ACS Chem. Biol. 2012, 7(2), 316–321) pg 7 in supporting information:

Formation of Activated Ester
N-Succinimidyl Trifluoroacetate (15.0 mmol, 5 equiv) was placed in a flask. The flask was
backfilled with Nitrogen, capped with a rubber septum, and maintained under an argon atmosphere. To the flask were
added THF (15 mL, 0.2 M) and 2,2-dimethoxyacetic acid (3.00 mmol, 1 equiv). Pyridine (1.69 mL, 21.0 mmol, 7 equiv) was added by syringe dropwise (over 3
min, slightly exothermic). The mixture was stirred in the dark (3 h, producing a homogeneous solution), quenched with water (5 mL, 5 min), and diluted with DCM (45 mL) and water (50 mL). The organic phase was isolated, the aqueous phase was further extracted with a mixture of DCM and THF (3:1, 25 mL), and the combined organic phases were washed with sodium bisulfate (0.1 M aqueous, 40 mL) and dried with sodium sulfate. Volatiles were removed under reduced pressure

Could somebody provide the mechanism of this reaction? My guess is that pyridine abstracts hydrogen in the carboxylic acid, and the lone pair on oxygen attacks the carbonyl centre in N-Succinimidyl Trifluoroacetate.. Is this correct? I could not rationalise why 5 equiv. would be needed.

The reaction did not quite work out and I think it may be attributed to the fact that I did not have pure N-Succinimidyl Trifluoroacetate to begin with. When forming N-Succinimidyl Trifluoroacetate, I saw two peaks in 19F NMR at $\delta \: \pu{-72.14 ppm}$ and $\delta \: \pu{-75.62 ppm}$. I believe a peak at $\delta \: \pu{-75.62 ppm}$ was unreacted Trifluoroacetic anhydride. The 1H NMR showed that there was some unreacted N-OH succinimide. I want to figure out what kinds of side products these unreacted materials have led, but to do that, I believe I must understand the mechanism of this reaction first.

Would appreciate any help or guidance


texts: Portable library to render 2D structural formulas as vector graphics from SMILES or InChI

texts:
For a web-based project, I am looking for a piece of software to create a 2D vector graphics structural formula from a textual structure encoding scheme such as SMILES or InChI, running on the server or client, and callable via some kind of API.

I’m imagining a client- or server-side library that you could just use like this:

svg_output = lib.render_from_smiles(smiles_input);

Ideally, it would have the following properties:

Take a SMILES or InChI representation of the compound as input
Compute the structure graph and 2D positional data (positions of atoms, types of bonds, etc.)
Render the structure in some kind of vector graphics representation (SVG would be perfect, but any other open format would do)
Or, alternatively, just output the computed drawing parameters, to be passed on to a separate renderer (which would need to be written, but that is the less challenging part)
Written in a language that is easy to use and deploy in web environments (PHP, JavaScript, Python, Ruby, Go, etc.)
If a renderer is included, allow me to control the rendering style (stroke width/colours, text attributes etc.)
Open source or with license terms that are affordable to a non-profit project :)

The application just needs to render individual structures. No reaction mechanisms or anything fancy. Small organic molecules only.

I know there are various standalone software packages (ChemDraw, MarvinSketch etc.) that do this kind of thing, but I did not find anything that can be used as a library like this.

Any suggestions or ideas? Thank you!


texts:
What will be the wavelength of an X-ray, if we apply a potential difference of, say $\pu{20 kV}$ across the ends of the X-ray tube?
Alright, I started with the modified de-Broglie equation-
$$\Lambda=\frac{h}{\sqrt{meV}}$$
I pinned the values of Planck constant, electronic charge and potential difference but can't guess what would be the mass $m$ here.
The answer comes $\pu{0.62*10^-10m}$ if solved perfectly. Can anybody confirm?


texts:
If I have 2 containers, something like in the diagram. One has gas A, while other has gas B. Both containers have equal volume and at same temp. Then when I remove the corks, and let the gases flow, until when will they flow, and will I finally have a half of Gas A in one container and rest half in the other, and similarly for gas B, or will only one of them flow until total pressure in the 2 containers is same?

In other words, what is the necessary condition for flow of gas - Difference in its partial pressure, or difference in total pressure?


texts: Why can mercury oxide be decomposed into mercury and oxygen upon heating?

texts:
As I am a grade 9 student, please use simple English that does not involve many technical words in Chemistry. Thank you.

I have learnt from my teachers' handout that physical methods of separation include heating, and that a compound can only be broken down into elements by chemical methods such as electrolysis.

But why can mercury oxide (a compound) be decomposed into mercury and oxygen upon heating (physical method)?

Or is it simply because heating is a chemical method? (that my teacher probably was mistaken)


texts: Bromonium ion or Mesomeric effect ( intermediate during addition to alkenes)

texts:
It's mentioned in Peter Sykes , A Guidebook To Mechanism In Organic Chemistry , 6th edition, 13th impression by Pearson, Pg. No. 185 , that on addition of $\ce{HBr}$ to bromoethene the only product obtained is 1,1-dibromoethane. It's due to the positve mesomeric effect of bromine to stabilize the carbocation in this case, however the rate is remarkably slower as compared to addition to ethene.

1

Another reaction corresponding to addition of $\ce{Br2}$ to ethene proceeds with the formation of a bromonium ion intermediate.

2

My question is, why can't the first reaction just proceed with a bromonium ion intermediate, like (28) above can form a bromonium ion and give 1,2-dibromoethane as a product (there may be a possibility that the carbocation may be formed away from bromine to counteract the strong negative inductive effect and in that process it may interact with the lone pairs of bromine to form bromonium ion)? And if bromonium ion is unstable (that is if it can't be formed in 1st reaction) why does it form at all in reaction 2? Why can't the Bromonium ion in the 2nd reaction just undergo a 1,2- hydride shift and convert into the "more stable" ion like 29b. It should also lead to formation  of geminal dibromide .It's a circular argument.

It's clearly mentioned that bromonium ion and carbocation are canonical forms of each other , which means you expect them to convert into bromonium ion whenever there's a positively charged carbon near a bromine atom.

3

Here's a similar example of phenonium ion.

[4]: https://i.stack.imgur.com/0j5Ww.jpg .

The carbocation doesn't stay the way it is in structure 4. It rather forms 3. Notice the bond between phenyl ring and the carbon atom on the right. It's not a completely solid bond.


texts:
Why is fat nonpolar while water is polar?

In water there is the $\ce{H-O}$ bond and the $\ce{O}$ is more negative, we have
$\text{dipole = charge}* \text{distance}$

A fat molecule is like
$\ce{H-O-C-C-C-C-C-C...}$
but the carbon atoms don't matter, the polarity is still ${q*d}$, as in the water molecule, so they should have the same amount of polarity.

So why do people say fat is a nonpolar molecule?


texts: Is it stupid to put used acid into a pool after cleaning the chlorinator?

texts:
I have a salt pool, and when the chlorinator salts up with calcium, I clean it with a diluted acidic solution.

What happens to the acidic solution after the reaction happens? I.e., does the pH change?

Would it be stupid to put the used solution into the pool afterwards? Am I correct in thinking the following sentence? "We are trying to get the calcium out of the pool, but putting it back in just means the chlorinator has to get it out again." Or, it is stupid for a different reason, e.g. the acidic solution is too weak after the reaction anyway?


texts:
So I was learning about pH and pOH and it made sense. I looked at strong, weak acids & bases and learned that they dissociate completely in water. So then I moved on to water and learned about the autoionization of $\ce{H2O}$.

Here is the process:

$$\ce{H2O + H2O -> H3O+ +OH-}$$

So then I learned about the equilibrium constant and then I figured this:
$$\ce{{[H3O+][OH-]} = 1E -14}$$

  What does this mean?

So after that I was doing some basic pH and pOH calculations withe strong acids and bases.

Here is one of them:

Find the pOH of a $\ce{1E-6M} \ce{HCL}$
So here are the steps:

$$\ce{-log[1E-6M] = 6}$$
Ok so the solution had the pH of 6

At first I was like that's nice and I proceeded.

$$\ce{6+pOH=14}$$
$$\ce{pOH=8}$$

So then I was like wait a minute where did the $\ce{OH-}$ come from if it dissociates like this:

$$\ce{HCl + H2O -> H3O+ + Cl-}$$

So then I thought about it and this is what I came up with:

  Since there is some $\ce{OH-}$ then there must be some water more water that autoionized into OH and that is the only place where $\ce{OH-}$ could've come from. So that means that even though $\ce{HCl}$ completely dissociated there must be more water than $\ce{HCl}$, because referring to the original equation there is $\ce{1M}$ quantities of $\ce{H2O}$ and $\ce{HCl}$ and so in the $molarity$ of the $\ce{HCl}$ given that means there was more water and less $\ce{HCl}$ and the $\ce{OH-}$ could've only come from the autoionization of that excess water.

So that is what I thought could be the only possible explanation of the $\ce{OH-}$ in a strong acid. And that could only come from $\ce{H2O}$ .

So am I right, and If I am wrong then please tell me where the $\ce{OH-}$ came from.

  Why is the $\ce{pH}$ scale only to $14$? Because if I took a $\ce{2M}$ $\ce{HCl}$ and then I get a super acid in which the $\ce{H+}$ ions is a lot more than the $\ce{H2O}$ available to absorb them. So why is it only to $14$? Does it have to relate to the original autoionization of $\ce{H2O}$?

And If I totally grasped this wrong then can you please accurately tell me what $\ce{pH}$ & $\ce{pOH}$ and what autoionization of $\ce{H2O}$ is for a beginner and still make sense.


texts:
I am little bit confuse about relating the half life time period of a first order reaction something like

$$\ce{2A -> B + C}$$

Here the rate of reaction will be half of the rate at which $\ce{A}$ is used up.

$$\text{Rate of reaction} = k[\ce{A}]$$

$$\text{Rate of disapperance of}~\ce{A} = 2k[\ce{A}]$$

Integrating it half life will be $\displaystyle\frac{\ln 2}{2k}$.
Am I wrong somewhere?


texts: A tricky question in Eudiometry/Gas analysis

texts:
In a eudiometer $\pu{14 ml}$ of $\ce{CH4}$ and $\pu{38.5 ml}$ of $\ce{O2}$ was introduced. After explosion and cooling to initial temperature ($\pu{23°C}$) the volume of eudiometer was found to be $\pu{25 ml}$. Calculate the vapour pressure(in $\pu{mm Hg}$) of aqueous solution containing a non-volatile solute (A) at $\pu{23 °C}$. Mole fraction of (A) is $0.1$. The pressure of eudiometer is $\pu{1 atm}$ and is constant.

I wrote the balanced equation. Then applied Avogradro's law and found that the volume of gases in the eudiometer after reaction is $\pu{24.5ml}$. So the extra $\pu{0.5ml}$ must be due to some water which must have converted into gas. Using $PV=nRT$ I can calculate the no. of moles of water evaporated, but I am unable to understand the last part of the question regarding solute A. Is there some information missing in the question regarding solute A? (I assumed it as the final solution after the reaction, but still don't know how to proceed).

   Answer is 13.68.


texts: Discovery of optical activity of enantiomers - where did the idea of using polarized light came from?

texts:
According to Wikipedia, optical activity was first observed in 1811 in quartz. Louis Pasteur's contribution is also mentioned there and in other sources as a major advancement in establishing optical activity as a distinct characteristic of a compound, specifically as a differentiating factor between two enantiomers - a difference that became a standard descriptive characteristic.

My question is how did they even think of that? Why would Pasteur, Arago, Herschel, and other chemists would think of testing the effect of polarized light on chemical compounds? (vice versa actually, chemical compounds affect polarized light, but I assume they did not know that prior to that discovery...). Was it a standard lab procedure at the time?

Testing and determining physical characteristics (such as melting point, boiling point, etc.) seem reasonable and pretty straightforward, but I am wondering how did polarized light entered the chemistry lab as an identifying procedure.


texts: Molecular orbitals and "generalized" aufbau principle for heteronuclear molecular configurations

texts:
Is there any general ordering or rule for heteronuclear molecules like $\ce{AX_2}$, $\ce{AX_{n}}$, and their molecular bonding/antibonding configurations ($\sigma/\pi$ orbitals) accordingly to some order in the Molecular Orbital Theory (MOT)?

Do the molecular orbital configurations and their order depend on the scheme and the linear combination of atoms (homo and heteronuclear, di and polyatomic) or is there some "standard ordering" like the aufbau principle $\ce{1s~2s~2p~3s~3p~4s~3d~4p~5s~\dots}$ for atomic orbitals in atoms? Or are molecular configurations a totally dependent on the molecule type and geometry? That is, I want to know if there is some (general) rule for molecular orbitals (ordering and energies) just like the aufbau principle for atomic orbitals.


texts:
Which balanced equation represents a redox reaction?
  \begin{align}
&\mathrm{A.} &\ce{AgNO3 + NaCl &-> AgCl + NaNO3} \\
&\mathrm{B.} &\ce{BaCl2 + K2CO3 &-> BaCO3 + 2KCl} \\
&\mathrm{C.} &\ce{CuO + CO &-> Cu + CO2} \\
&\mathrm{D.} &\ce{HCl + KOH &-> KCl + H2O}
\end{align}

I don't understand how to identify a redox reaction. The answer key shows the correct answer as D, but I'm confused as to why.

D shows an acid-base reaction. Are all acid-base reactions redox reactions and why aren't the other answer choices correct?


texts: Can potassium nitrate and sulfuric acid be used to nitrate organics?

texts:
If we are doing a classic nitration to produce glyceryl trinitrate, one uses a mix of concentrated sulfuric and nitric acids. Additionally, one can produce concentrated nitric acid by distilling it from a mixture of potassium nitrate and sulfuric acid.
So, is it possible to do a nitration by mixing the glycerol with sulfuric acid and then adding potassium nitrate?
Disclaimer
In case anyone is wondering, I am not going to try this, and I do know how to make many better and safer explosives since I used to be a member of the alt.engr.explosives group way back.


texts:
Why crystalline solids are anisotropic whereas amorphous solids are isotropic?

Is it because in crystalline solids, X, Y and Z dimensions vary, but so does in amorphous.

Please write as simple as possible.


texts:
Cobalt (atomic number 27) has electronic configuration $[\ce{Ar}]\mathrm{(4s)^2 (3d)^7}.$

I have seen two different configurations and explanations for $\ce{Co^3+}$ from a variety of different sources:

either it loses two $\mathrm{4s}$ electrons and becomes $[\ce{Ar}]\mathrm{(3d)^6}$ in accordance with aufbau principle;
or it loses one $\mathrm{4s}$ electron and two $\mathrm{3d}$ electrons to become $[\ce{Ar}]\mathrm{4s (3d)^5}$ which is supposedly more stable due to its half filled orbitals and lack of electron pairs.

I think the one with more stability or lesser energy will be the one which is correct, but how can I find this out without experimental data? And what is the right answer?


texts: How to determine which normal mode leads to the transition state (numerically)?

texts: I would like to get the normal mode of vibration which leads to the transition state. Do you know any software for this problem? If no, could you offer an algorithm to generate it? By the way, is there any name for this vibration?


texts: Expression for fugacity coefficient derived from a pressure-explicite EOS

texts:
In the book, Thermodynamics for Process Simulation, the authors propose to derive an expression for the fugacity coefficient from a pressure-explicit equation of state, as an example among many others.

Assuming, $P = P(T, v)$ or $z =\frac{Pv}{RT} = z(T, v)$, the calculations lead to,

$$\left(\frac{\partial \ln \phi}{\partial v}\right)_T = \left(\frac{\partial z}{\partial v}\right)_T-\left(\frac{\partial \ln z}{\partial v}\right)_T + \left(\frac{1}{v}-\frac{P}{RT}\right) \tag1$$

where $\phi$ is the fugacity coefficient.

What I don't understand is, when they integrate, they get,

$$\ln \phi = z - 1 - \ln z + \frac{1}{RT}\int_{\infty}^v \left(\frac{RT}{v}-P\right)\mathrm{d}v \tag2$$

Can someone explain me how they find $z-1-\ln z$ by integrating the first two terms of $(1)$ between $\infty$ and $v$?

When integrating the first two terms, it leads to $$\left[z - \ln z \right]_{\infty}^v$$ which I understand, but then I don't get the final result.

I suppose it's linked to the values of $z$ when the volume is very large and when the volume is "$v$" but it does't make sense for me.

I would have assume to get $$\left[z - \ln z \right]_{\infty}^v = v - \ln v - \left[z(v^{\infty}) - \ln z(v^{\infty}) \right]$$ and nothing else.

But I am missing something probably obvious.

Thank you in advance for your help!


texts: Will OH- ions be reduced or H+ ions be reduced in KOH electrolyte

texts:
I was trying to see if I can make a battery that uses KOH as the cathode electrolyte with platinum as the cathode electrode, but I got confused as to what gets reduced in this solution (Aluminum sulfate is the anode electrolyte and aluminum is the anode electrode).

$\ce{K+}$ never will get reduced because that is thermodynamically unfavored, so will $\ce{OH-}$ (from the KOH ion) get reduced to $\ce{OH^2-}$? It makes more sense to me that $\ce{OH-}$ gets reduced because KOH is very basic and there will be a ton of $\ce{OH-}$ ions that can go to the electrode and accept the electron.
I just don’t know if this is favored thermodynamically or how I can calculate it.

Or will it be $\ce{H+}$ from water? Will water ionize in the first place?


texts: What are the limitations of the D, L system and the (+), (-) system for naming organic compounds

texts:
In organic chemistry, both the D, L system and the (+), (-) system are widely used, in conjunction with the modern (R, S) system.
The D, L system names an organic molecule based on the direction that its bottom -OH group points at, when the molecule is drawn with the most oxidized carbon on top in the Fischer projection. Is it true that organic molecules that cannot be drawn and analyzed in this way cannot be named according to this system? Also, is this system incapable of specifying diastereomers and epimers among stereoisomers, as it was first invented to address enantiomers?
As for the (+), (-) system, I think as long as an organic molecule does not have optical activity, it cannot be named in accordance with this system. Does this sound right?


texts: Why is pyrimidine less basic than pyridine?

texts:
From Wikipedia's article on pyrimidine:

  Because of the decreased basicity compared to pyridine, electrophilic substitution of pyrimidine is less facile.

But why is pyrimidine less basic than pyridine? Pyrimidine has two $\mathrm{sp^2}$-hybridised lone pairs available for protonation, compared with pyridine's one.


texts: Szabo/Ostlund exercise on spin orbital orthonormality

texts:
I have a question about exercise 2.1 in Szabo and Ostlund's Modern Quantum Chemistry, which concerns the inner product between different spin orbitals: $\require{begingroup}\begingroup\newcommand{\br}{\mathbf{r}}\newcommand{\bx}{\mathbf{x}}$

Exercise 2.1. Given a set of $K$ orthonormal spatial functions, $\{\psi_i^\alpha(\br)\}$, and another set of $K$ orthonormal functions, $\{\psi_j^\beta(\br)\}$, such that the first set is not orthogonal to the second set, i.e.,
$$\int d\br \, \psi_i^{\alpha*}(\br)\psi_j^\beta(\br) = S_{ij}$$
where $\mathbf{S}$ is an overlap matrix, show that the set $\{\chi_i\}$ of $2K$ spin orbitals, formed by multiplying $\psi_i^\alpha(\br)$ by the $\alpha$ spin function and $\psi_j^\beta(\br)$ by the $\beta$ spin function, i.e.,
\begin{align}
\chi_{2i-1}(\bx) &= \psi_i^\alpha(\br)\alpha(\omega) \\
\chi_{2i}(\bx) &= \psi_j^\beta(\br)\beta(\omega)
\end{align}
with $i = 1, 2, \ldots, k$ is an orthonormal set.

I feel quite confused about this question. Consider the spin-orbital integral
$$\langle \psi_i^{\alpha} \alpha (\omega) | \psi_j^{\beta } \alpha (\omega) \rangle  = \langle \psi_i^{\alpha}  |  \psi_j^{\beta } \rangle  $$
which is not necessarily orthogonal.
The result can only be orthogonal if both ket and bra vectors are in the $i$-indexed set. If so, why does the exercise mention a $j$-indexed set in the beginning?


texts: Number of unpaired electron and total spin angular moment

texts:
IIT-JEE advanced 2013 has a question:

  Give the correct order of the complex ions given below according to their spin-only magnetic moment:
  A. $\ce{[FeF6]^{3-}}$
  B. $\ce{[V(H2O)6]^{2+}}$
  C. $\ce{[Fe(H2O)6]^{2+}}$

So, my reasoning is more unpaired electron results in greater spin-only magnetic moment. So, the order should be B>A>C

But the answer is given A>C>B.

I don't know where I'm wrong.


texts: Why can't a quaternary carbon product be obtained by alkane isomerization in presence of AlCl3 and HCl?

texts: This question actually deals with the reaction in another question: Isomerisation of alkanes under Lewis acidic conditions. I have a further doubt, regarding this reaction my book says that a quaternary carbon cannot be generated. Why is this so? Also if a pure alkane is used without alkene traces will the reaction fail to take place?


texts: What reactions occur when pyridine, actic anhydride and citric acid is mixed?

texts:
The reaction of pyridine, acetic anhydride, water and citric acid is used as a colorimetric identifier of citric acid. What reactions occur and why does the color change from colorless to greenish? I have been looking everywhere for the answer and have, so far, come up with nothing.

The reaction is made from 1 ml of water containing citric acid, 1.3 ml of pyridine which is then mixed and then 5.7 ml of acetic anhydride is added. Then it is left in a water bath with a temperature of 32 degrees celsius.


texts: Does a certain "Badecker reaction" actually exist?

texts:
A book I read, mentions a certain Badecker reaction under coordination chemistry. It goes like this:

$$\ce{Na2[Fe (CN)5 NO] + Na2SO3 -> Na4[Fe (CN)5 (NOSO3)]}$$

I googled up the name, but I didn't get anything even remotely related to chemistry.

That particular book does have a pretty long history of typos and a couple of factual errors here and there (but I still use it because its got quite a few useful tips …)

So the question is; is there such a thing called the Badecker reaction (I even tried googling it up with an umlaut, Bädecker reaction, because, well … Badecker looks a little German, but then I was directed to a Wikipedia page on cadmium oxide. So what is the reaction’s name?

Also even if it doesn't go by that name, does the reaction actually even exist?