texts: Do Metal Carbonyl complexes exhibit multiple back donation at the same time?

texts:
I came across a question which renewed one of my doubts that I had regarding bonding in metal Carbonyl complexes. According to me, metal should exhibit multiple back donation at the same time.
Everywhere on the web, I have only found metal carbonyl’s synergistic bonding in a single picture. But my doubt arises from the consideration from looking at the complete picture. According to me, In Metal Carbonyl complexes, the metal should exhibit multiple back donation to $\ce{ \pi^*}$ orbitals of Multiple Carbonyl Ligands according to the number of $\ce{d\pi}$ electron pairs present. I would like to explain this further through an example:
Bonding in $\ce{Cr(CO)_6}$
Now I do know that the orbitals taking part in complex bonding are a blend of d,s and p but I only know CFT but will still be explaining my doubt while keeping that in my mind.
Here the metal, Chromium has $\ce{3d\pi}$ electron pairs which according to CFT are present in $\ce{d_{xy},d_{xz},d_{yz}}$ orbitals, I don’t know how it will be according to LFT but the blended orbitals still(maybe) should be oriented in that direction and that is what I simply wish to use. Since, $\ce{Cr(CO)_6}$ is octahedral, thus the back donation for only 3 Carbonyl Ligands is possible at the same time, And this is where my question arises, that are there 3 back donations from $Cr$ at the same time or just a single back donation?
At first, I thought that I could simply confirm multiple back donation thingy by comparing bond lengths of $Cr-C$ in $\ce{Cr(CO)_6}$ and some other compound say $\ce{Cr(CO)_3(NH_3)_3}$, if I was correct the bond length of $Cr-C$ would be shorter in the latter case, BUT I didn’t find any data regarding the latter compound, I tried to search here and there but no luck but I found this post on Chemistry SE, if I assume it is right then crudely,I can say that my idea is correct about the bonding in $\ce{Cr(CO)_6}$, but I would like to have a further and deeper insight into this.
TL;DR Do Metal Carbonyl complexes exhibit multiple back donation at the same time or just a single back donation?


texts: How exactly does the oxidation of TEMPO by NaOCl/KBr work?

texts:
I would like to understand the exact process by which TEMPO is oxidized to the nitrosonium cation by NaOCl, as in the part of the mechanism shown in the diagram (1) surrounded by the red box:

The confusion for me is that TEMPO clearly needs to donate 1 electron to $\ce{OCl-}$ in order to form the neutral, nonradical nitrosonium cation, but we also get a $\ce{Cl-}$ anion, so there must also be a 2 electron process involving the $\ce{Br-}$ "co-catalyst" coming into play. How do I reconcile these 1 electron and 2 electron processes so as to draw a formally appropriate mechanism for this part of the reaction?

What exactly happens to the $\ce{OCl-}$ oxygen, and how does it happen?

(1) Org. Synth. 2005, 81, 195. DOI:10.15227/orgsyn.081.0195.


texts: Hydronium ion concentration to compare pH values

texts:
I'm having a bit of trouble with this question:

  Which has a higher $\mathrm{pH}$ value, $\pu{0.001 M}$ $\ce{HCl}$ or $\pu{0.1 M}$ $\ce{CH3COOH}$ $(K_\mathrm{a} = \pu{1.8E-5})?$

I have calculated that for the $\ce{HCl}$ solution (since it's a strong acid) the $[\ce{H3O+}] = \pu{0.001 M}.$

Then, for the $\ce{CH3COOH}$ solution I got $[\ce{H3O+}] = \pu{1.33E-3 M}$ (by solving a quadratic equation).

Since the $\ce{CH3COOH}$ has a higher concentration of hydronium ions, doesn't this mean that it will have a lower $\mathrm{pH}$ than the other solution? I'm confused because the answer says it's the other way around.


texts: In a copper wire, how many electrons does each atom give away?

texts: As an ion, copper can give off 1, 2, 3 or 4 electrons. But it has 1 s electron in the last shell and 10 d electrons. So as a metal, how many of those are delocalised and free to move around, and how many are staying with the atom?


texts: How are point group character tables typeset correctly?

texts:
I want to know how to typeset character tables of point groups correctly. Consider the following two extremes using the $C_{\text{2v}}$ (or is it $\text{C}_{\text{2v}}$?) point group as an example.

Firstly, one where all the symbols (except for the symbols denoting vertical) are cursive (your default LaTeX math mode behaviour):

Second, a table where all the symbols are in roman font.

Which is correct? Or is it a mixture?


texts:
If melting points and freezing points are the same, what state is pure equilibrium?

I understand melting points and freezing points are the same; adding or removing temperature of melting points for specific variables, like water at $\pu{0^\circ C}$ will melt or freeze them. Then, I have to ask the question, what is in between freezing and melting? What is that state? What is the behavior of the atoms if you somehow managed a perfect system where there wasn't extra heat being added nor removed and equilibrium was exact.


texts: How was the dissociation constant of water determined?

texts:
I was studying about pH and pOH of different acids and bases and I read about the dissociation constant of water ($\ce{H2O}$).

It turned out to be $1.00 \cdot 10^{-14}\ \mathrm{mol^2\cdot L^{-2}}$ at $25~\mathrm{^\circ C}$.

Could I get some insights to how was this specific value determined?


texts:
Synthesis and Chiral Resolution of C3-Symmetric Tribenzotriquinacenes, Eur. J. Org. Chem. 2016, Early View article

  DOI: 10.1002/ejoc.201600890

I came across this graphical abstract with M and P overlayed. After reading the article it became clear that M and P were being used as stereochemical descriptors, presumably of some kind of axial chirality/screw sense.

When I've previously looked, I've often seen either (+)/(-) (where + is the right-handed screw and - is the left) since this is actually describing the physical property of the molecule as measured, in the same way that (+)-proline describes the way in which the molecule interacts with plane polarised light. In many cases (R) and (S) are also used to describe axial chirality (BINAP, for example).

A quick google of the issue seems to suggest that (-) --> M and (+) --> P (cf. Wikipedia, confirmed by the IUPAC goldbook), but I was wondering if there is something more systematic going on here (i.e. a (+)-molecule doesn't always have an (R)-configuration).

In my head, the fact that there are descriptors like M and P (cf. E/Z and R/S) suggests that one should be able to look at the molecule and assign these by some kind of priority rule rather than by physical measurement (and by extension, does M/P actually predict +/- in a way that R/S doesn't).


texts: Is oxidation always thermodynamically favorable?

texts:
In biological systems, energy is often extracted from molecules with reduced carbon backbones — the oxidation of those molecules has $\Delta G < 0$ and that energy can be captured, often in the reduction of other molecules. I'm wondering if it is always the case that oxidation is thermodynamically favorable and reduction thermodynamically unfavorable.

I suppose I'm not asking if the oxidation of any molecule is favorable (I'm pretty sure that's not the case), but for redox reactions that do occur, is it ever the case the oxidation half reaction is thermodynamically unfavorable and the reduction half reaction thermodynamically favorable?


texts: How can I neutralise H2 gas without burning it?

texts:
I was thinking of maybe making it bubble into a solution containing something that would react with H2 yielding either a dissolved substance or a precipitate from the reaction.

Maybe a solution with a small amount of H2O2 in it?


texts: Is the following paragraph about steam distillation accurate?

texts:
I've been struggling with the various methods of purification of organic compounds. If a question comes up in my examination, asking me to explain steam distillation in my own words, I'd like to know if this applies and if this is accurate.

i) Steam distillation is utilized to separate volatile constituents which are immiscible with water but steam volatile.

ii) Steam from a steam generator is passed through a heated flask which contains the liquid to be distilled.

iii) The volatile component separates and thusly, one obtains a mixture of steam and the volatile organic compound.

iv) This is then condensed and separated by means of a separatory funnel.

In steam distillation, the liquid boils when the sum of vapour pressured due to organic liquid and that due to water become equal to the atmospheric pressure.
i.e Patm=Pw+Pc

Since $Pc<P$ ; liquid vaporises at temperature lower than its boiling point. That is, if water insoluble substance and water are the components, the mixture boils at a temperature close to, but below 373K.
Example: Aniline-Water

Please be highly specific. There should be no error, however minute.
Many thanks.


texts: How to estimate the concentration of OH that comes from just the autoprolysis of water in a basic solution?

texts:
In my analytical chemistry course, a question reads:

What is the pH of a 0.10 M solution of THAM?  Is it valid to neglect the autoprotolysis of water?  Justify and explain your answer by estimating the concentration of $\ce{OH-}$ that comes from just water in this solution.

I'm guessing it has something to do with ionization of water ($\mathrm{K}_\mathrm{w}=1 \times 10^{-14}$), any insight would be greatly appreciated.  The calculated pH neglecting autoprotolysis of water is 10.5.


texts: Is there any specific formula to find periodic table periods and valence electrons

texts: I am developing a program, that uses a lot of stuff related to the periodic table. As of now, I am making a part of it the determines the period and family. I know that both of those have to do with how many valence electrons each element has. So I want to know if there are formulas to find the amount of valence electrons, family, and periods?


texts: I am curious how, from the perspective of quantum chemistry, the hydrogen bond is modeled. In particular I am interested in using such a model to estimate the amount of energy released per $\ce{H2O}$ molecule, if say two of them approach each other e.g. in case of condensation. Any hint for precise literature would be great!


texts: Observations when mixing potassium Triiodide and Sodium thiosulfate

texts:
I have a reaction equation, it's all balanced but I don't understand what the physical change is. It is as follows:

$$\ce{2Na2S2O3 + KI3 \to 2Na2S4O6 + 2NaI + KI}$$

It was used to prove if $\ce{S2O3^2-}$ was in the solution or not. I'm not sure but I think it changes color to violet and back to colorless due to $\ce{I-}$ but if someone could definitively say what you are supposed to observe it would be helpful.


texts: How to compare the rate of decarboxylation?

texts:
For the following acids compare the rate of decarboxylation on heating
I $\ce{Ph-CO-CH2COOH}$
II $\ce{Ph-CO-COOH}$
III $\ce{CH3-CH2-COOH}$
IV $\ce{HOOC-CH2-COOH}$

I tried this question by forming carbanions and comparing their stability. But I am stuck at comparing I and IV.


texts: Are there any Endothermic Pyrophoric Substances?

texts: I've recently been reading about pyrophoric materials, specifically as they relate to rocketry, and this made me curious if there are any substances which are the complete opposite of pyrophoric. Essentially, are there any materials which react on contact with air (i.e. either gaseous nitrogen or oxygen), but endothermically? If so, do they react at STP, or only under special circumstances?


texts: Is real water made up of heavy water and light water?

texts:
I need to know, is real water made up of heavy water which is formed with deuterium, and light water which is water by protium?
We know that hydrogen has three major isotopes, including protium and deuterium.
We also know that water, $\ce{H2O}$, is made up by hydrogen and oxygen.
All this might mean that real water itself can naturally contain some heavy water - Deuterium oxide. Is this correct?


texts: Why would the following reaction not proceed through SN2 reaction?

texts: I made a guess that the OH- group cannot do a backside attack on the carbon because the C double bond with O and the 5 carbon ring may act as steric hindrance and prevent it from forming a bond but I'm not really sure.


texts: Reaction between Copper nitrate and ascorbic acid

texts:
I am confused on the products of reaction between copper nitrate and ascorbic acid. When I searched this online, one of the reactions I got was: $$\ce{2Cu(NO3)2 + C6H8O6 <=> 2CuO + 4H2O + CO2}$$

I am really confused as to how they determined that to be the product. My thinking was that the ascorbic acid breaks into $$\ce{HC6H7O6 <=> H+ + C6H6O6-}$$ and so the hydrogen ion, whose activity is higher than copper, replaces the copper to form nitric acid. I was thinking that this could be a double displacement reaction and so the copper ascorbate would become a precipitate. What am I thinking wrong here?


texts: Effect of protein hydrophobicity on metal interaction

texts:
I'm studying how metals and proteins interact (metal-protein complexes). I've found that almost all proteins could bind with metal at higher $\mathrm{pH}$ values, but also found some proteins showed lower intensity in metal-protein complexes.

I understand $\mathrm{pH}$ has an effect on the charge state of amino acid side chains of proteins, but I really had less information about the effect of $\mathrm{pH}$ on protein hydrophobicity, and hydrophobicity's effect on the protein's ability to bind metals.


texts: How does higher carbonyl compounds disolve in water?

texts: We know that higher the carbon, the more is hydrophobic the compound nature is, Still when we take a compound like sugar , a hand of sugar, it readily dissolves in water? can someone explain me reg this


texts: What is the difference between radii of Gyration and hydrodynamic radii of a polymer?

texts: Why do you consider that the relationship between RH and RG should depend on the quality of the solvent?


texts:
How can I make o-bromoaniline from aniline (as a major product)?

I know how to make p-bromoaniline from aniline, by acetylation followed by treatment with $\ce{Br2}$/$\ce{CH3COOH}$ and hydrolysis. But in this process the ortho isomer (if formed) will be the minor product.


texts:
Group 11 metals namely $\ce{Cu, Ag, Au}$ are known for their low reactivities. They are thus rightly called coinage metals and have been historically used to make currency owing to this very property of theirs. My question is, what is the reason behind this behaviour?

Is it because of the stability of fully filled and half filled orbitals? But then the counterexample of $\ce{Cu-Zn}$  presents itself. These are neighbours in the periodic table, and the differentiating electron in each goes completes a full or half-filled orbital, yet $\ce{Zn}$ is quite reactive.

This behaviour can be seen (sort of) between $\ce{Hg-Au}$ as well which differ in one electron and yet are completely different in terms of their properties.

EDIT: The other two questions referred to as duplicates of this one cite different properties of the elements that make them unreactive. Gold has strong $\ce{Au-Au}$ bonds (due to relativistic effects) and $\ce{Zn}$ is more reducing than copper due to factors like hydration energy and the enthalpy of atomization. But this does not answer my question because:

I was looking for the root cause of this behaviour. If gold is stabilized by relativistic effects, why don't these effects operate on other transition metals? If zinc has high hydration enthalpy, what is the reason?

Since all the coinage metals occur in a single group, I really wanted an explanation that could apply to all of them, such as a peculiarity of their electronic configuration that renders them inert to most available reagents.


texts:
Is there any mechanism available for reduction of alkyl azides to amines.
One of the reactions is conversion by $\ce{Na}$ in ethanol or by $\ce{LiAlH4}$.
But how do these proceed?
$\ce{LiAlH4}$ will produce a hydride ion which attacks where?


texts:
In my book it is given

  Reducing property increases down the group in gaseous or molten state .
  The increasing order is  Li , Na , K , Rb ,Cs

In according to me reducing property is based on ionisation property . As Cs has highest ionisation property so it can easily loose elctron (oxidation potential)

  But in aqueous solution incresing order is given as
  Na , Cs ,Rb , k ,Li

For this what could be the reason .


texts: Double bond crossed lines representation

texts:
I have been studying organic chemistry for years, and I do not remember the spotting double bond represented with crossed lines, except maybe one ore two more times in addition to the following one

which is taken from the Aescin Wikipedia graphics here.

I guess it is a drawing or rendering mistake, or a representation of unspecific E/Z configuration. If the latter is true, where can I find more info on usage of this symbol?

UPDATE:

A comment by gilleain leads to GRAPHICAL REPRESENTATION OF
STEREOCHEMICAL CONFIGURATION (IUPAC Recommendations 2006). Relevant paragraph is:

  ...
  The most common convention for depicting double bonds with unspecified configuration in molecules of all sizes uses a wavy bond.
  ...
  A crossed double bond has sometimes been used to indicate unspecified double bond configuration or a mixture of configurations. This type of bond is not considered acceptable for general use, although it may still be required by some computer software.

There's still missing piece of information about which software and by what means it "requires" this representation.


texts: Does boiling milk really make the nutrients in it less useful to the body when ingesting it?

texts:
Does “denaturing” nutrients in milk by boiling it make them less useful, or actually more useful, as they undergo “denaturation” anyway during digestion?

I've read online that boiling milk "denatures" nutrients such as protein, calcium, and others contained in milk, rendering the milk less nutritious.

I've also read that because the nutrients in milk (and other foods) undergo "denaturation" in our body during digestion anyway, boiling it will not make milk less nutritionally valuable, and will actually help the body to more readily absord the nutrients in it into the bloodstream right after ingestion.

What is the truth in this matter? Thanks for any knowledgeable answers!  I put the word "denature" in quotes because it's a technical term and I'm not really sure in which ways it can correctly be used.


texts: While I was looking at the periodic table today, I realised that there were gases that were much lighter than helium such as hydrogen. If hydrogen is lighter than helium, why do we insist on using helium in balloons?


texts: Mathematical justification for Le Chatelier's principle

texts:
At equilibrium

$$
\begin{align}
K &= \exp\left(\cfrac{TΔS^\circ - ΔH^\circ}{RT}\right)\\
⇒ \frac{\mathrm d \ln K}{\mathrm dT} &= \frac{ΔH^\circ}{RT^2}
\end{align}
$$

If enthalpy change is positive, change in $\ln K$ w.r.t. $T$ is positive. Hence, $\ln K$ and therefore $K$ increase (position of equilibrium shifts to the right) as $T$ increases. And, $\ln K$ and therefore $K$ decrease (position of equilibrium shifts to the left) as $T$ decreases.

If enthalpy change is negative, change in $\ln K$ w.r.t. $T$ is negative. Hence, $\ln K$ and therefore $K$ increase (position of equilibrium shifts to the right) as $T$ decreases. And, $\ln K$ and therefore $K$ decrease (position of equilibrium shifts to the left) as $T$ increases.

Can you give a similarly mathematical reasoning for why a reaction

$$\ce{A(g) <=> 2 B(g)}$$

has its equilibrium position shifted to the left as the pressure of the surroundings increases?


texts: Is there an upper limit on the coordination number of a coordination compound?

texts:
From the Gold Book, coordination number is:

  In an inorganic coordination entity, the number of σ-bonds between ligands and the central atom. π-bonds are not considered in determining the coordination number.

In high school, we mostly had complexes upto coordination number six (like $\ce{[FeF6]^3-}$). But I wondered if the coordination number could go even higher.

From my search, I was able to reach this research paper (J. Am. Chem. Soc., 1979, 101 (2), pp 334–340 DOI: 10.1021/ja00496a010) where they mention lanthanide complexes of coordination number uptil nine!

So, is nine the upper limit? Or can the coordination number go higher? Also, does the upper limit exist only theoretically, or has the corresponding complex been synthesized?


texts: Discrepancy observed for standard free energy change with temperature

texts:
My understanding of standard free energy is that it is only valid at the specified temperature, which is typically 25$^\circ$C. Thus, if T changes, so does $\Delta$G$^\circ$$_{rxn}$ according to this equation:

$$\Delta G^\circ_{rxn}=\Delta H^\circ_{rxn}-T\Delta S^\circ_{rxn}$$

(assuming $\Delta$H$^\circ_{rxn}$ and $\Delta$S$^\circ_{rxn}$ are constant with temperature, which is a common assumption I'm finding in texts)

For example, $\Delta$G$^\circ_{rxn}$ at 25$^\circ$C would be different than at 250$^\circ$C. My confusion is with regards to $\Delta G^\circ_{rxn}$'s relationship to chemical equilibrium (or reactions) as:

$$\Delta G^\circ_{rxn}=-RT~ln~K$$

I've seen resources on the internet treat this oppositely, which has caused me great confusion. Let's take the Haber Bosch as an example, where we want to find K at 250$^\circ$C:
$$\ce{N2 + 3H2 <=> 2NH3}$$
From standard tables, at 25$^\circ$C (all kJ, mole, and K):

$${H_2}: \Delta G^\circ=0, \Delta H^\circ=0, \Delta S^\circ=0.1306$$

$${N_2}: \Delta G^\circ=0, \Delta H^\circ=0, \Delta S^\circ=0.1915$$

$${NH_3}: \Delta G^\circ=-16.48, \Delta H^\circ=-46.1, \Delta S^\circ=0.192$$

For this reaction:

$$\Delta G^\circ_{rxn}=2(-16.48)-(0+0)= -32.96~kJ/mole$$

$$\Delta H^\circ_{rxn}=2(-46.1)-(0+0)= -92.2~kJ/mole$$

$$\Delta S^\circ_{rxn}=2(0.192)-[(0.1915)+3(0.1306)= -0.1993~kJ/mole~K$$

First approach (how I think it is):

1. Calculate $\Delta$G$^\circ$ at 250$^\circ$C:

$$\Delta G^\circ_{rxn}=\Delta H^\circ_{rxn}-T\Delta S^\circ_{rxn}=-92.2-(523.15 K)(-0.1993)=12.06~kJ/mole$$

2. Calculate K (assuming kJ, mole, and K for R and other values):

$$K=e^{-\Delta G/RT}=e^{-12.06/[(8.314E-3)(523.15 K)]}=0.062$$

Second approach (also commonly seen):

1. Calculate K using $\Delta$G$^\circ$ from tables, i.e., 25$^\circ$C, but inserting a new T:

$$K=e^{-\Delta G/RT}=e^{32.96/[(8.314E-3)(523.15)]}=1954.6$$

Edit: I want to also add that this reaction is more favorable at lower temperatures, so Approach 1 makes sense and Approach 2 does not, even though many treat problems this way. Also, I get $K=10^{5.77}$ at 25$^\circ$C, so the decreasing K matches up.

Question: Which one do you consider correct and why is there so much confusion and discrepancy in online tutorials? If this first approach is correct, is the error in the second common because of the misinterpretation of "standard"?

And I'd like to add: do the rules follow for $\Delta G_{rxn}$ and non-equilibrium as well? That is:

$$\Delta G_{rxn}=\Delta G^\circ_{rxn}+RT~ln~Q$$


texts:
I have asked this question in Beer, Wine & Spirits however I think the lack of chemists meant I received zero answers (two upvotes which was encouraging).

At the moment I and looking at ways of removing the oxygen from a small vessel (500cm3) of ambient air. My thought is that if I remove oxygen what's left behind is an inert mixture of gasses that can help to protect my wine. I have done some maths and if there is on average 20.95% oxygen in the air and 78.08% nitrogen, does this mean that if I completely remove oxygen then the percentage of nitrogen in the remaining gas mix increases to 98.7% (78.08/(100-20.95)? If not then can someone explain what I'm missing. If I can inject 98% nitrogen into my bottle of wine I'd be a happy chap.

If you need to know how I'm going to achieve this then it will be via an oxygen scavenger(s) placed within a sealed bag of ambient air.


texts: What exactly is Q in the Nerst equation for a ¨lemon battery¨ of Cu and Zn in varying concentrations of acid?

texts:
I want to vary $\ce{[H+]}$ and see its affect on the voltage produced by a Zn-Cu in acid "lemon battery".  My question is about the expression for $Q$ in the Nernst equation for this cell.  I think $Q$ will have three species but I'm unclear about their values.

$\ce{[H+]}$ in mol/L, which is easy to quantify as its my independent variable.
$\ce{[Zn2+]}$ in mol/L which would be initially $0$, making Q undefined. Is this right?
The partial pressure of $\ce{H2}$, is this right, and in what units?
Can Q have partial pressures and molarities?


texts:
How do I type a simple chemical equation in Microsoft Word? I can do subscripts, but long arrows are more difficult. I can't get them to align with the text.

Also, I can't figure out how to put a delta above the arrow for heat. I have tried the Chemistry add-on from Microsoft, but that does not seem to help with equations.


texts: Chlorobenzene will react with hydroxide to give phenol. But will the reaction on Chlorobenzene also work with methoxide, to give anisole?


texts:
Ethene and ethyne can be distinguished by employing the test
a. $\ce{Br2}$ in organic solvent
b. Baeyer's test
c. Phenyl hydrazine
d. Tollen's reagant

According to me it must be both a and b, but there's no such option.


texts: How does the ionic strength formula work? (simple version)

texts:
The ionic strength formula provides a way to estimate the Debye screening length. I’m having some trouble understanding the structure;

$$I = \begin{matrix}\frac{1}{2}\end{matrix}\sum_{{\rm i}=1}^{n} c_{\rm i}z_{\rm i}^{2}$$

It seem a bit tricky to find the derivation for this, but all I’m really looking for is an intuitive answer to a couple of questions;

Firstly; why is there a factor of a half out the front?
Secondly; why do we square the charge number of the ion?

I am a physicist, so please explain any chemistry concepts like I’m 5. Thank you for your patience.


texts: Why does lead nitrate powder on heating starts turning yellow from the top rather than from the bottom?

texts:
Today while in school, I observed the thermal decomposition of lead nitrate. The peculiar thing I noticed was that the lead nitrate powder in the test tube starts turning yellow (due to the formation of lead oxide) from the top and then towards the bottom. This indicates that the certain decomposition temperature is first reached at the top and later at the bottom.

I tried to apply a logic that as soon as some heat was provided to the bottom of the powder in the test tube, it was quicky transferred to the powder present above it and so on till the top. At this point, since the heat had nowhere to go (since air is a bad conductor is heat) it got accumulated at the top and hence it reached a higher temperature.

However I'm unsure of my logic because for the top powder to reach the specified temperature, the lower powder must first reach either the same or a higher temperature (otherwise the powder present above it would not get heated).


texts: What are the IUPAC names for singly- and doubly-protonated piperazine?

texts:
If ammonia, $\ce{NH3}$, is protonated, it becomes ammonium: $\ce{NH4+}$.

If piperidine is protonated, it becomes piperidinium:

If piperazine is protonated once, what does it become? By analogy, I would assume piperazinium:

If the resulting monocation is protonated again, what does it then become?  The best I've come up with are piperazine dication and piperazin-dium, but that latter seems really awkward:


texts: Causes for the irregular electron configuration of the lanthanides

texts:
I know what the electron configurations of the lanthanides are, but I was asking myself, why they are so irregular.

The configutation of Lanthanum is $\mathrm{5d^1\ 6s^2}$, but according to the Klechkowski rule, the $\mathrm{4f}$ orbital has a lower energy level and should be filled up before the $\mathrm{5d}$ orbital. Why isn't that happening?

The irregulatity of Gadolinium is more comprehensive. The electron pairing energy is higher than the energy difference of fitting that electron in the $\mathrm{5d}$ shell.

Then we come to Ytterbium which has every shell filled up. So why does it's most stable oxidation number is still $\mathrm{+III}$? I would understand why it can leave 2 electrons (it's outermost shell is the $\mathrm{6s}$-shell) but after that, we have to remove a single electron of the filled $\mathrm{4f}$ shell. Isn't that extremely unfavorable?

I hope that somebody can explain why all this happens, I would really appreciate it.


texts: How to separate paracetamol and caffeine?

texts:
How do you separate paracetamol and caffeine using high-school laboratory equipment?

I was thinking about using the fact that paracetamol has a lower melting point (169 °C) compared to caffeine (around 235 °C): I would heat them up till paracetamol melts while caffeine is still solid. What I can't figure out is how you filter the caffeine from the liquid paracetamol (filter paper would burn at such a high temperature).

I would like to know how you do the filtration at high temperature; or, if you have a better method, please let me know!


texts: Where can I find literature values for standard molar enthalpies of neutralization?

texts: I'm looking for enthalpy of neutralization literature values for inorganic weak acids. NIST, PubChem, etc. don't list them. Is there somewhere else I should look?


texts: R & S Stereochemistry of an unsaturated ring system

texts:
Using the R- & S- nomenclature assign a configurational symbol to decalin 4-methyl (above the plane), 4-hydroxy (below the plane), 7-isopropyl (above the plane), 1,9 diene. (Numbering the carbons in decalin ring-system: ring-junction carbons are 1 (top), 6 (bottom))

Carbon 7—holding the isopropyl group: I think this is S (isopropyl $ > \ce{C-C=C} > \ce{CH2} > \ce{CH}$).
Carbon 4—holding $\ce{CH3}$ & $\ce{OH}$: I think this is S ($\ce{OH}> \ce{CH3} > \ce{CH2=CH2}$).

Is my reasoning correct?


texts: Ratio between heat tranfer coefficient and thermal conductivity

texts:
Consider the Robin boundary condition for the diffusion/heat equation $u_t=a(t)u_{xx}+f(x,t)$:

$$-k(t)u_x(0,t)=h(t)u(0,t)$$

or

$$u_x(0,t)+\frac{h(t)}{k(t)}u(0,t)=0$$

where $k(t)$ thermal conductivity and $h(t)$ heat tranfer coefficient.

My Question: Is it possible that the ratio $h(t)/k(t)$ to be constant? Could anyone please help me? I have really no idea.


texts: Relative humidity and vapor-pressure in equilibrium

texts:
I have quite an unclear understanding of relative humidity. I am writing my understanding on the topic and please correct me wherever I'm wrong:
What I understood:
Let's say $\ce{H2O}$ has a (saturated) vapour pressure of $x~\pu{atm}$ at a certain temperature. Now, relative humidity (RH) is the ratio of the partial pressure of water vapour to the equilibrium vapour pressure of water at a given temperature.
So what this means is that if RH = 100% then the maximum amount of water vapours is present in the air. Now if RH = 50% means that the amount of water vapours present in the air is only half of the maximum possible.

So, does this mean the water has not been fully evaporated up to the
limit it can?
Does this mean that the equilibrium has not yet been established, and
the reaction tends to shift in the forward direction? If yes, then
what is stopping the reaction to move forward?
Does 100% RH mean the water and it's vapour are in equilibrium?

Can relative humidity be compared with an example of a sponge? There's a limit of the amount of water a sponge can absorb water. If it has only absorbed 50% means there is still room for more absorption until 100% capacity is reached.


texts: Aldrich says that these two names are synonyms of one another.  Does anyone know the etymology of arabinohexose used in this context?


texts: Type of reaction between (+)-bis salt of (+)-phenylsuccinic acid and HCl

texts:
Im confused about what type of reaction occurs between the (+)-bis salt of (+)-phenylsuccinic acid and HCl. Would this be considered an acid base reaction or a neautralization reaction?

MY THOUGHTS: I know that an acid-base reaction occurs between (+)-phenysuccinic acid and (-)-proline to make the (bis)+ salt, im confused at to whether such salt is an acid or a base, or neither... If its an acid and an acid, it would be a neutralization reaction mechanism. If it were a base, it would follow an acid-base reaction mechanism. Any thoughts on if either of these make sense based on such info?


texts: Finding the reduced pressure to distill a solution containing 0.4 g of naphthalene in 25 g of chloroform at 50 °C

texts:
Chloroform boils at $\pu{62 ^\circ C}$. For a solution containing $\pu{0.4 g}$ of naphthalene in $\pu{25 g}$ of chloroform, the boiling point is elevated by $\pu{0.45 K}$, to avoid any decomposition during distillation chloroform has to be distilled at $\pu{50 ^\circ C}$, what maximum pressure can be maintained in the flask?

My approach:
I found the molality of the solution to be $0.125m$, equating it with the formula $$\Delta T_\mathrm b=K_\mathrm b\cdot m$$ I found $K_\mathrm b$ to be $3.6\ \mathrm{K\ kg/mol}$, I am not able to proceed after this step, please provide an approach to solve the problem from here.
I also tried using the formula $$\Delta K_\mathrm b=\dfrac{R {T_\mathrm b}^2}{1000l_\mathrm v}$$ but finding out the latent heat of vaporisation did not prove to be of any help.


texts:
Shriver and Atkins' Inorganic Chemistry (5th edition) explains amphotericity of the oxides of the heavier elements in Groups III, IV and V by high covalent character of the bonds made by the elements.

It states: "The onset of amphoterism correlates with a significant degree of covalent character in the bonds formed by the elements, either because the metal ion is strongly polarising (as for Be) or because the metal ion is polarised by the O atom attached to it (as for Sb)."

I have heard of many explanations using the polarising power of cations but never have I heard the "reverse", which is the polarising power of anions. Polarisation of an anion by a highly-polarising cation means that the cation distorts the electron cloud of the anion strongly. How would that work for the polarisation of a cation by an anion?


texts: Could nitric and nitrous oxides react with glycerin to produce nitroglycerin? What conditions would I need in order to make that work?


texts: Canonical structures of (1E)-prop-1-en-1-yl acetate

texts:
I have to find all of the possible canonical structures of this molecule

And here's what I did

Are they correct and if yes, did I miss any possibility?


texts: Prediction of products in reaction of dicarbonyl with alpha-haloketone

texts:
Following is the question that was asked in my exam. a,b,c,d are the various options, one of which is the answer. I am familiar with the Reformatsky reaction, Aldol condensation, Knoevenagel's reaction and general base catalysed carbonyl reaction. 1 and 2 are my attempts at deriving the mechanism and hence getting at the products. But none of those succeeded to bring about the required products.

I need help in how to proceed through in this case and derive the products.


texts: Why are oxidation states such a fundamental quantity for elements?

texts:
Why is it that there are fixed oxidation states for most elements out there, with no to very rare exceptions?

I was taught that oxidation state is a totally artificial concept we have invented for book-keeping purposes. How is it that its applicable so widely? I understand the case of formal charges, because that is what keep into consideration when making bonds in the first place.

But oxidation state is somewhat arbitrary, because we don't think about electronegativity when we are making bonds. So can someone help me understand the intuitive reason behind it, its been bothering me for months now?


texts: How can I obtain the wave function of the dihydrogen system, by hand using Self Consistent Field DFT calculations?

texts:
After doing some energy calculations for the $\ce{H2}$ system in Gaussian, using ωB97X-D/STO-3G level of theory, and generating a .wfn file, I wanted to understand better how the computer does the Self Consistent Field calculations.

I understand that this file produced a molecular orbital expression based on the wave functions for each $\ce{H}$ atom.

I am new to this kind of calculations and I will appreciate the help a lot.


texts: Constraints on rate coefficients in chiral catalytic system

texts:
Consider some reversible chemical reaction in a closed system:
$$\ce{A <=> B + D} \tag{1}$$
where $\ce{A}$ is some input reagent and $\ce{B}$, $\ce{D}$ are some output reagents. Let's denote forward and backward rates as $k_f$ and $k_b$ correspondingly.

Now, consider the same reaction in the presence of some catalyst $\ce{C}$:

$$\ce{A + C <=> B + D + C} \tag{2}$$

Due thermodynamic constraints the equilibrium state cannot change, which means that forward and backward rates of catalyzed reaction ($c_f$ and $c_b$) must be equal to the rates of uncatalyzed reaction multiplied by the same multiplier, $k$:
$$
    \begin{matrix}
    c_f = k \, k_f \\
    c_b = k \, k_b \\
    \end{matrix}
 \tag{3}
$$

Now, consider the same scenario if the reagents and catalysts are chiral so that each of the reagents has an enantiomer:
$$\hat{E}(A) = a, \hat{E}(B) = b, \hat{E}(C) = c, \hat{E}(D) = d \tag{4}$$
where $\hat{E}$ denotes an enantiomer.

Then the first reaction splits into two:
$$
    \begin{matrix}
    \ce{A <=> B + D} \\
    \ce{a <=> b + d} \\
    \end{matrix}
 \tag{5}
$$
with the same forward and backward rates $k_f$ and $k_b$ and catalytic version splits into 4:

$$
    \begin{matrix}
    \ce{A + C <=> B + D + C} \\
    \ce{a + c <=> b + d + c} \\
    \end{matrix}
 \tag{6}
$$

and
$$
    \begin{matrix}
    \ce{A + c <=> B + D + c} \\
    \ce{a + C <=> b + d + C} \\
    \end{matrix}
 \tag{7}
$$

where (6) is just the same as the catalytic reaction (2) above but now expressed for both enantiomers and (7) accounts for the fact that chiral catalysts are not 100% enantioselective: if chiral reaction is catalyzed by a chiral catalyst, then it is also catalyzed by enantiomer of that catalyst (though with different rate coefficients).

To consider thermodynamic equilibrium in such a system we must also take inter-conversion of enantiomers (racemization) into account: the concentration of both enantiomers must be equal in equilibrium for each pair of enantiomers. This leads to the following constraints:
$$
    \begin{matrix}
    c_f + c^e_f = k \, k_f \\
    c_b + c^e_b = k \, k_b \\
    \end{matrix}
 \tag{8}
$$

where $c_f$, $c_b$ are forward and backward rate coefficients of reactions (6) and $c^e_f$, $c^e_b$ are forward and backward rate coefficients of reactions (7).

So, thermodynamics imposes two constraints on four parameters. If we consider many catalysts for reaction (5), then all of them will obey equation (8) with some value of $k$.

The question is: are there any other constraints, which can be imposed on coefficients of reactions (6) and (7)?


texts: How do you make photoresist/photohardening paint?

texts: I have been looking into making my own PCB's, but I noticed there is little information on making photo hardening paint. This is a critical component when etching the circuit, and I am very curious on the chemistry involved in making it. I understand there are better methods to make your own pcb, but I am curious how photoresist is made


texts: Why is cumene referred as isopropyl benzene? And not sec propyl benzene, since the carbon of that chain is the middle one?


texts: Why is NAD+ regioselectively reduced at C-4 to form NADH?

texts:
We could draw a resonance form with the pi electrons shifting, placing a positive charge on C-4, to which a $\ce{H+}$ along with 2 electrons are added. Thus we get an NADH molecule as shown in the picture.

If this is how the reaction happens, then why doesn't the hydrogen get added to C-2 (or C-6 which is equivalent)? There's also a resonance form where C-2 has a positive charge and could accept a hydride ion. Why doesn't this happen?


texts: Are all (pure) alkanes, alkenes and alkynes - tasteless, odourless and colourless?

texts:
non-pure alkanes have a taste, but

Are all pure hydrocarbons, tasteless, colourless and odorless?
Are there hydrocarbons that do have a taste, colour, odor?

If so, what makes these pure hydrocarbons different, even though they are only made of carbon and hydrogen?


texts:
For cleaning purposes I do bubble ozone trough $\ce{H2O}$.

However the ozone gas is moist then, but I need it as dry as possible.

I intended to use silica gel as drying agent.

However the orange silica gel that I usually use has an organic moisture indicator included.

I think that $\ce{SiO2}$ does not react with $\ce{O3}$ itself, but I worry that the organic moisture indicator will react with the $\ce{O3}$ and form compounds that influence the following processes.

Does anyone have experience of what drying agent to use on ozone?

Is there a reason to worry about the organic moisture indicator in the $\ce{SiO2}$?


texts: How do I derive the Nernst equation in the case in which R is absent?

texts:
Does anyone know what the intermediate calculations are to obtain equation 1.4.14? Taken from Fundamentals and Applications (Bard) page 31
To be more precise, how to obtain (1.4.14) from $\frac{nFAm_O}{nFAm_R}=\frac{i_l-i}{i}$


texts: How do you compare the strength of H bonds when it's the same atom on both sides of the H? Like $\ce{N-H\bond{...}N}$ vs $\ce{F-H\bond{...}F}$? Is one still stronger than the other, or are they both the same since in both cases the pull on both sides is equal?


texts: How to explain the periodic trends in boiling points in groups?

texts:
Observing the trend of boiling points of the compounds listed, choose the appropriate terms to fit into the blanks:
\begin{array}{lr}
\hline
\text{Compound} & \text{b.p.}/\pu{°C}\\
\hline
\ce{H2Te} & −2 \\
\ce{H2Se} & −41.5 \\
\ce{H2S} & −60.7 \\
\ce{H2O} & 100 \\
\hline
\end{array}
The ___ the compound, the stronger the ___ present between molecules. The stronger the ___, the higher the boiling point of the compound?
More polar, smaller, London dispersion forces, larger, less polar, dipole-dipole and ion-dipole forces

I noticed that the electronegativity for each compound increases from top to bottom, so does higher electronegativity implies higher boiling point?
I've also tried putting more polar the compound, the stronger the dipole-dipole and ion forces. No luck, I still got it wrong.


texts: Finding moles of different compounds using balancing

texts:
$$\ce{K2Cr2O7 + $x$\,H2SO4 + $y$\,SO2 -> Cr2(SO4)3 + K2SO4 + $z$\,H2O}$$

For $\ce{Cr}$ change in oxidation number is: $+12$ becomes $+6$

For $\ce{S}$ change in oxidation number is: $+4y$ becomes $+6$

For $\ce{H}$ change in oxidation number is: $+2$ becomes $+2z$

since $\ce{Cr}$ decreases by 6, $\ce{S}$ and $\ce{H}$ have to increase by 6, so

$$(4y+2)-(6+2z)=6$$

$$2y-z=5$$

Also using the principle of atom conservation (POAC) for $\ce{H}$ atoms from $\ce{H2SO4}$ to $\ce{H2O}$, we get:-

$$2x=2z$$

$$x=z$$

I can't find any more equations to solve this.


texts: How to identify a pseudo-first-order reaction?

texts:
We can easily identify a pseudo first-order reaction with the integrated rate equation, but what if only the reaction is given? For example, what if I were given a question like the following on the hydrolysis of acetic anhydride?

Identify the type of this reaction: $$\ce{(CH3CO)2O + H2O -> 2CH3COOH}$$

A. Pseudo-first-order reaction
B. Pseudo-second-order reaction
C. Zero-order reaction
D. Third-order reaction

I would like to know how I could identify the correct answer if such a question were asked.


texts:
My professor emphasizes the concept of the carboxylate "cage" or the idea that electrons participate in resonance within a carboxylate group such as in the benzoate anion but the electrons in the carboxylate group cannot leave this "cage" - i.e. participate in resonance with the phenyl substituent.

Is this idea valid?

I've already poked a hole into it by pointing out that electron donation to the "cage" is possible - i.e. consider carbonic acid with one hydroxyl group replaced by oxygen connected to a phenyl group. Valid resonance structures can be drawn in which electron density from the oxygen in the ester linkage participates in resonance with the electrons "in" the carboxylate group. So donation into the "cage" is possible. Now, this begs the question - is withdrawal from the cage possible as well? He insists no. Now, he might be hiding some edge cases for pedagogical purposes, but I don't care - if there is an exception - I want to know about it (because chemistry always gets interesting at the exceptions).


texts:
I've learned that HCl escapes HDPE. I looked up why and it turns out it's because of the small size of the molecule. That factor is unlikely to be affected by the concentration of HCl in water, but I was thinking: does water exert an "attractive" effect on HCl such that HCl would escape an HDPE container from a solution of 30% HCl (for example) over an order of magnitude more than from a 20% solution?
Does this phenomenon take place? What order of difference in HCl permeating an HDPE vessel could I expect between solutions of 10%, 20%, 30% concentration? (just to have a general idea of how big the phenomenon is, if at all)


texts: Looking for an old (1950s) "chemical experiments" book

texts:
Not sure if this is precisely on-topic, but I'll risk some reputation and give it a try.

I got a chemistry set as a kid in the early 1970s, and the subject really captured my interest. I grabbed every chemistry book I could find from our libraries. They ranged from college textbooks to "Chemical Magic" collections of demonstrations. These latter tended toward pyrotechnics, and were pretty appalling safety-wise.

There were several favorites, but there was one book in particular that stuck with me, found in a rural Virginia county library around 1976 or so. It featured adolescents in coats and ties (and maybe one in blouse and skirt) demonstrating experiments, but the experiments were a couple of levels beyond what I found elsewhere.

The ones I definitely remember:

Removing stains by soaking clothes in potassium permanganate solution, then removing the manganese-dioxide residual stain with sodium bisulfite
Preparing white phosphorus by heating red phosphorus in a test tube, and condensing the vapors onto a cold test tube nested inside it
Preparing lithium metal by melting a lithium salt in a crucible and electrolyzing it
Synthesizing Bakelite from phenol and formaldehyde

There were probably a dozen or so others. I think one involved generating chlorine gas from an aqueous solution in the bottom of a beaker, then dropping in pellets of calcium carbide to watch the acetylene spontaneously combust.

I've searched using Google, but can't seem to get past The Golden Book of Chemistry Experiments -- yes, that's another treasured memory from the time, but it's not the one I have in mind. (For one thing, the one I'm asking about had no color plates at all.)

Another near miss that's quite familiar to me is Leonard A. Ford's Chemical Magic (I remember the 1959 original). I don't have it in hand, but Google's preview let me read far enough to see familiar material -- including pyrotechnic mixes using potassium chlorate instead of perchlorate, which got me in no small amount of trouble some years later. The book I'm searching for was more oriented toward science, rather than showmanship.

If the book I've described sounds familiar, please post an answer with any additional information you find -- title and publisher would be great, but additional experiment descriptions would also be helpful. If you have a favorite book from that period that doesn't seem to match this description, I'd be interested in hearing about it as well.

Finally, if this is a bad question, I welcome guidance on turning it into a good one, or why it's not worth pursuing. Thanks!


texts: Rotational barrier of biphenyl in ground and excited electronic states

texts:
I'm studying how the energy of biphenyl varies with its dihedral angle. I know how to describe the dependence quantitatively, but still, I don't know how to explain why the rotational barrier of biphenyl in its excited state is distinctly higher than in its ground state. This is illustrated in the plot below, where you can see that the excited states have a much greater increase in $V(\tau)$ at $\tau = 90^\circ$.

Additionally, I've obtained the HOMO and LUMO of biphenyl at $\tau = 90^\circ$. Is it possible to explain this jump in energy using them?


texts: Which site is more favorable for EAS in O-Acetotoluidide?

texts:
Which site is more favorable for electrophilic aromatic substitution in O-Acetotoluidide?

The answer given in my textbook says the site para to acetamide group is more favorable, however I believe the site para to methyl group should be more favorable. Here are the reasons:

1) Because of sterric inhibition of resonance, acetamide group will be slightly out of plane thereby decreasing the quality of resonance.

2) Because of hyperconjugation by 3 alpha hydrogens, electron density will increase 3 times each at sites ortho and para to methyl group. This means that methyl group due to hyperconjugation will lead to nine resonance structures as opposed to just three in acetamide.

So, because of these two reasons, I think site ortho to methyl group should be more favorable(ortho will be less favorable because of sterric hindrance).

Am I missing something or the answer given in the book is wrong?


texts: Is there a way to remember polyatomic ions (i.e $\ce{PO4^{3-}}$, $\ce{SO4^{2-}}$ etc.). For example, our professor will ask on an exam what the equation for iron (III) carbonate.  Obviously the (III) means iron has a 3+ oxidation state. However, if one was not too familiar with the number of oyxgens or charges on specific polyatomic ions, how would you know the symbol for carbonate ($\ce{CO3^{2-}}$)? She gives us a periodic table but I dont think that will help if you dont have carbonate memorized?


texts: Change in surface tension of soapy water as oil is added

texts: I am wondering about how the surface tension of clean soapy water changes as oil is added to it?  Is the change gradual or is it abrupt as the amount of oil added exceeds the amount of soap available to surround the oil.  So if the surface tension of clean soapy water is 25 dynes/cm, then as I add oil, will that surface tension go up or will it stay essentially the same until the amount of oil added exceeds the amount of soap needed.  Or perhaps something else happens??


texts: 316 stainless steel and high concentration, high temperature Hydrogen Peroxide

texts:
I'm looking at doing some experiments with small scale rocketry and I need to find the right materials for this project, where I will be burning through lots of HTC (peroxide above 90% concentration). I've found this datasheet here that says grade 316 stainless steel is suitable to temperatures up to 48*C. Can anyone tell me whether its suitable for temperatures much higher than that, or at least point me in the right direction to find any research on the subject? I'm having trouble finding the data I need.

This is more for experimental purposes than any practical applications so the total mass of the materials used is a non-issue.


texts: Prove that internal energy is a state function

texts:
Why is it that heat and work are path functions but their sum i.e. internal energy is a state function? How is it even possible?
$ΔU=q+W$


texts: How to identify the number of pi electrons in a conjugated system to calculate the HOMO-LUMO gap with the particle in the box approach?

texts:
It's my understanding that for a particle in a 1-D box, the change in energy from the HOMO to LUMO can be approximated with the following equation:
$$\Delta E=\frac{h^2 ( N + 1 )}{8 m_\mathrm{e} L^2}$$
I am told that $N$ represents the number of π electrons in the molecule.

If you're studying a molecule like the one shown below and you want to predict the absorption wavelength from UVVIS, would you count all of the π electrons, or just the conjugated ones? It doesn't make much sense to me why you'd want to include the π electrons from the phenyl group next to the neutrally charged Nitrogen because it's not conjugated with the rest of the molecule to the same extent the other phenyl group is, and thus seems like it would be grossly inaccurate to assume that those π electrons contribute the same as the others.


texts: How should one check an instant-equilibration algorithm for conservation?

texts:
We have a system of equations that describes the equilibration between several phases $A, B, ...$.  If we define the total concentration $T = A + B + ...$, then $\partial_t T=0$ must hold.

We are further assuming equilibrium at all times, so we have devised an algorithm for this that transforms $A\rightarrow A'$, $B\rightarrow B'$ etc.  Finally, the total concentration must be conserved, so we must check if $T'=T$.  But should one also check if $\partial_t T'=0$, i.e. the conservation equation with the equilibrated variables?

Does it make sense to test both $T'-T=0$ and $\partial_t T'=0$?


texts: How to check if azobisisobutyronitrile (AIBN) is still active?

texts:
I will have some samples of azobisisobutyronitrile and I want to perform Barton-McCombie reaction. The problem is that the reagent is quite old and I need to know whether it has not decomposed.

Do you know any kind of test that I could perform? I was thinking if benzophenone in THF would not become blue after addition of fresh AIBN which would indicate the presence of the radicals. But I am not sure if such a test would be a good idea.


texts: Why does copper have a high enthalpy of atomisation when it has a half filled d sub shell?

texts: If I understood correct, the high energy of atomisation for d-block element comes from the ability to make many metallic bonds due to half electron filled d-orbitals, but it seems here that copper has no free d-orbitals yet has high enthalpy of atomisation? Is there a mistake in my understanding or is there a reason for this anomaly?


texts: What elements don't observe the octet rule?

texts: Apart from hydrogen which forms a duet, which element's don't observe the octet rule?


texts: Is passivation of stainless steel feasible in the field?

texts: Does anyone have input or experience on passivation of stainless steel, particularly in outdoor environments where submersion of components is not practical due to location or size? Nitric acid (and solutions with sodium dichromate) typically call for submersion for extended periods of time based on the concentration of the solution. Citric acid has been referenced as a more suitable alternative and is more environmentally friendly but the literature on non-submersion passivation techniques is limited. Any help or direction is appreciated.


texts: Relation between freezing point depression and vapor pressure

texts:
My lab manual defines the freezing point as "The temperature at which the vapor pressure of the substance in its liquid phase is equal to its vapor pressure in the solid phase." It goes on to explain why adding a non-volatile solute to a solvent, which lowers the vapor pressure compared to that of the pure liquid, lowers its freezing point.

What does the freezing point, which concerns liquid and solid phase, have to do with vapor pressure? If I do an experiment in a gas-tight syringe containing liquid and solid only, there will be no equilibrium with the vapor phase, but the freezing point will still change.


texts:
I'm having some issues with lithium getting darker in a glove box. Please see attached photos, Li gets dark overnight.

My sensors for $\ce{H2O}$ and $\ce{O2}$ are showing 0 ppm. I also checked oxygen and moisture contents using chemicals in case sensors were bad, and looks like there is no oxygen and moisture in the glove box. Just to make sure, I also replaced the nitrogen tank with argon (there are some reports in the literature saying Li reacts with nitrogen even at room temperature and gets darker in the presence of trace levels of moisture).

Does anyone had this problem before? Any recommendations would be of great help.


texts:
I've run into trouble on this question

  Predict the standard potential at 310 K for the cell constructed from the hydrogen electrode and metal-insoluble salt electrode $\ce{Ag(s)|AgCl(s)|Cl-}$. Assume $\Delta_\mathrm rS$ is independent of $T$.

I know the reaction is
$$\ce{AgCl +e- <=> Ag(s) + Cl- (aq)}$$
$$E^\circ=0.222$$

The left cell is a hydrogen electrode making the equation
$$\ce{1/2H2 + AgCl(s) -> Ag(s) + Cl- (aq) + H+(aq)}$$
forming a nernst equation of

$$E=E^\circ-\frac{RT}{vF}\ln\left(\frac{\alpha_{\ce{Ag(s)}}\ \alpha_{\ce{Cl-}}\ \alpha{\ce{H+}}}{\alpha_{\ce{AgCl(s)}}\ \alpha_{\ce{H_2}}^{1/2}}\right)$$

which reduces to
$$E=E^\circ-\frac{RT}{vF}\ln\left(\alpha_{\ce{Cl-}} \alpha_{\ce{H^{+}}}\right)$$

I know $R$, $T$, $v$ and $F$ but I don't understand where to begin to solve for $\alpha_{\ce{Cl-}} \text{and}\ \alpha_{\ce{H}}$

How would I find the activities?


texts: What is the difference between Half Equivalence point and Equivalence point?

texts:
OKay I learned in class that equivalence point is the time of neutralization, where the # of moles of acids and base present is in equivalence/same amount.

Now I was also told that Half equivalence point is when [HA] = [A$^-$] , the concentration of a weak acid = concentration of conjugate base.

Problem:
I'm getting a bit confused as to the differences. I've read around and am finding definitions that don't really shed any light on the differences between them. What is the difference between a half equivalence and an equivalence point?

Based on what i have been told, they sound the same to me.


texts: I have some aluminum alloy, possibly 6063 or 7050 (no clue really) which has corroded. The finish might be silver-anodized but I doubt it due to the high polish, could be urethane. The item is a fishing rod holder, used in a freshwater marine environment. Hardware is stainless and steel. Several screws and bolts need to be removed, and I was wondering if there was an acceptable reducing agent for the corrosion rather than busting driver bits and/or mangling threads.


texts: MO Theory: Why do hydrogen and lithium bond, but hydrogen and helium don't?

texts:
I've been cracking my head trying to make sense of Molecular Orbital Theory, but all sources I find are simplistic {If anyone has an online course or a book to recommend, I'd really appreciate}. Therefore, my questions are quite simplistic:

1 - Why should atoms in the first row {Hydrogen} interact with atoms in other rows  {Lithium, Beryllium, Boron, etc}? I mean, as a way to answer why two Hydrogen atoms form a Molecular Orbital in the first place, I have the postulate that it is due to Pauli Exclusion Principle: as the 1s Orbitals - and, by extension, its electron - overlap, a new orbital is formed to avoid* having two electrons with the same quantum numbers. But, when Lithium approaches Hydrogen, there is only a significant overlap between 1s and 2s Orbitals. In this sense, there is no threat* to Pauli's principle, given that the approaching electrons do NOT have the same quantum numbers. Which yields the question: how do Lithium and Hydrogen bond?

. * I understand that the universe doesn't care about what we, smart monkeys, think of it. It doesn't see things as "threats". Still, interpreting things this way makes everything easier.

2 - Why won't Helium bond with Hydrogen? The approach of He and H should form bonding and anti-bonding Orbitals, which will be filled with three electrons. This should place two electrons in the Sigma Bond, but only one in the Sigma* Bond. Therefore, the bond order is 0.5! So why HeH isn't observed?
Another way to phrase it: If He2+ can exist as a molecule, why can't HeH?

Thank you very much for your time.
Sorry if I messed something up.


texts: Thermodynamic stability of meta-xylene over ortho- and para-isomers

texts:
When talking about the example of the alkylation of toluene by chloromethane in the presence of $\ce{AlCl3}$, Hepworth, Waring and Waring (2002) mentioned that:

  At room temperature, a mixture of 1,2-dimethylbenzene and 1,4-dimethylbenzene results, but at 80 °C the product is mainly 1,3-dimethylbenzene. In fact, heating either of the 1,2- or 1,4-isomers in the presence of $\ce {AlCl_3}$/$\ce {HCl}$ results in rearrangement to the more stable 1,3-dimethylbenzene.

This leads me to question: Why would the 1,3-isomer be more thermodynamically stable than the 1,2- and 1,4-isomers? Clearly, there must be an activation energy barrier to overcome as heat is required for the conversion. The methyl group being an ortho/para-director would lead to the formation of 1,2- and 1,4- isomers. Thus, wouldn't these isomers also be the more thermodynamically stable isomers?

Reference

Hepworth, J. D., Waring, D. R., & Waring, M. J. (2002). Aromatic Chemistry. United Kingdom: The Royal Society of Chemistry.


texts: Does the mechanism of the Schmidt reaction involve a nitrene as an intermediate?

texts:
Per the mechanism described here the reaction does not involve nitrene as an intermediate.(EDIT-1---I initially thought the written mechanism described so, but as Zhe points out,I was wrong in my observation.)

But, can anybody shed some light on why the reaction does not involve nitrene; though it possibly can?


texts: rovibrational spectroscopy: why do intensities of rotational lines increase with J?

texts:
how and why do the intensity of rotational lines change with J value?

in the simplest terms possible please


texts: Baby bottles accidentally steamed with soft plastic teether - melted - Bottles still safe?

texts: I'm not sure who to ask so have been googling around -- My husband accidentally steamed our new teether for our infant son with the bottles. What he didn't remember/realize is that you're not supposed to (per the package notes) and found out quickly why when he opened the steamer and the plastic was molten and the gel on the bottom of our steamer. My concern is: I can wash and re-steam our bottles, nipples, bottle parts (some plastic), but should we be worried about some kind of chemical reaction that happened within the bubble of the steamer? I am not well enough versed in chemistry to know if this would be a problem. I'm just about out of bottles for the day so I'm hoping someone has the answer somewhere.


texts: How is presupposition of the order of reaction justified in Michaelis-Menten model?

texts:
from what I have understood, to derive Michaelis-Menten equation, we first suppose that

$\ce{E + S <=>[k_1][k_{-1}] ES->[k_2]E + P }$

and make the 'steady-state assumption', that $k_1[E][S]=(k_{-1}+k_2)[ES]$.

But from what I've learned, the order of reaction cannot be derived from its equation, but can only be decided by experiment. How can we 'presuppose' the order of these, especially when both $E$ and $S$ are macromolecules? The left side might as well be $k_1[E][S]^2$, for example.

What am I missing out?


texts: Excited states and electron addition/removal energies within Hartree-Fock, CI, etc

texts:
Coming from a DFT background, I'm used to the concept that the DFT eigenvalues do not correspond to excitation energies (i.e., the band gap, ionization potentials, etc.). To correct for these it's common to go to many-body approaches like the GW approximation to the self-energy, which is said to explicitly deal with quasiparticle addition/removal energies.

I'm curious how excited states are calculated within Hartree Fock or CI. Can one do a ground state calculation in HF or CI and then get excitation energies from the difference in these ground-state eigenvalues? Or is this similarly not possible and one needs to explicitly consider excited states in order to get the excitation spectrum (band gap, band eigenvalues for removal/addition of electron,etc.).


texts: So I'm new to this concept and I can't find any proper explanation to this. What does it mean for a reaction to occur in an acidic, basic, or neutral medium?


texts: How would you name this organic compound?

texts: Because there are at most seven consecutive carbon atom, and four alkyl groups attached to the chain of carbon, I would name it 2,4-tetramethyl heptane.


texts: How come I get different Gibbs free energy for the same reduced equation?

texts:
I want to calculate the Gibbs free energy of this reaction which can be:

$\ce{H2(g) + 1/2O2(g) -> H2O(g)}$

or

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

I am using the entropy values (J/molK): H2(g) - 130.684, O2(g) - 205.138, H2O(g) - 188.7

And enthalpy values (kJ/mol): H2(g) - 0, O2(g) - 0, H2O(g) - 241.8

With the equation ΔG=ΔH−TΔS and temperature 298.15K. How come I get ΔG = -457kJ/mol for the full equation and -228kJ/mol for the reduced equation, shouldn't  I get the same Gibbs free energy since they're the same reaction (except one is reduced)?

Shouldn't both be considered "correct" or is one "more correct" than the other?


texts: Lewis base strength and the hydrogen proton

texts:
My prof told me that we can compare Lewis base strength based on electron donation to the $\ce{H+}$ proton - i.e sigma bond formation with the $\ce{H+}$ proton - and proceeded to conclude that $\ce{S^{2-}}$ is a weaker Lewis base than $\ce{O^{2-}}$, since the former is a weaker base than the latter. He then proceeded to generalize that the oxide ion is always a stronger Lewis base than the sulfide ion.

Is this a valid method of comparing the strength of Lewis bases? I have two issues:

Isn't Lewis acid/base strength quantified using kinetics, not thermodynamics? Don't stronger LAs react faster, and weaker LAs react slower?
Even if this comparison were valid, would the comparison still be valid outside of water solution?

Does this mean that this question is invalid? No medium is specified.

I think he knows what he's talking about. In explaining the much greater stability of silver sulfide ($K_{\mathrm{sp}} \approx 6 \cdot 10^{-51}$) vs. $\ce{Ag2O}$ ($K_{\mathrm{sp}} = 3.5 \cdot 10^{-16}$), he notes that charge density does not explain this disparity. In fact, charge density would imply that the oxide salt should be more stable.

  For instance, although $\ce{O^2-}$ is a stronger B/L base than $\ce{S^2-}$, $\ce{S^2-}$ can be (and usually is) a stronger Lewis base than $\ce{O^2-}$ since S has a lower EN than O. Furthermore, recall that Lewis base strength depends on the Lewis acid with with the Lewis base interacts.

The text goes on to mention other factors such as having a metal cation with a surfeit of valence d electrons, and how that can populate the empty valence 3d orbitals of $\ce{S^2-}$. (S has 3d orbitals?)

This makes sense; a good nucleophile has less stabilized electrons - i.e. electrons that are further from the nucleus. It still seems that the questions posted above put B/L acidity ahead as the main deciding factor for sigma-donor strength.


texts:
Rotting fish seem to give off the same (very pungent) kind of smell, regardless of the kind (salmon, seabreen, tuna, etc).

What exactly is it that's responsible for this unique smell?

(Though I've answered my own question below, do feel free to post an answer of your own if you want.)


texts: Why does this reaction not proceed by sn1/sn2?

texts:
this is an assignment question but I'm stumped.

we have a polar protic solvent (also a weak base) interacting with the secondary carbon -- it looks like a good example of an sn1/sn2 to me. So why wouldn't the answer be "I and III"?


texts: Which analytical reagent can be used to detect Vinca alkaloids?

texts: I am commencing a project on increasing the sensitivity of screening of some bioactive compounds produced as secondary metabolites from the plants! All of its chemical struture is known which is a dimer of vindoline ring connected to a catantine ring through carbon-carbon analysis! However there are no reagents specified in any research papers which could specifically bind with this compound to help in its quantitative analysis! Do I have to predict the reagent according to its chemical structure or is there some specific analytical reagent which can provide a detectable reaction with it?


texts: One writes the electronic configuration in terms of shells, spdf subshells, orbitals, and spin of electrons. There are exceptions to principles we know. How does one confirm that the way of writing is correct? How did scientists understand the exceptions in case of nobium and platinum in electronic configuration? Is it possible to take an atom and find which shell its electrons are in? How did this spdf electronic configuration (along with exceptions) be first understood.


texts: If I dissolve 1  g of sodium bicarbonate powder ($\ce{NaHCO3}$) into 400 ml of distilled water, what will the pH of the resulting solution be?


texts: Does changing the electrolyte concentration in the electrolysis of water affect the speed that hydrogen gas is produced at the cathode?

texts:
I am currently completing a Year 12 Extended Practical Investigation. Due to the lock-down restrictions we are unable to complete our own practical experiment and have been given sample answers with made up lab conditions.
The experiment I chose was to investigate the difference of time taken to produce 25mL of H2 gas in an electrolytic cell when the concentration of the potassium hydroxide electrolyte was changed.
The lab conditions given were a pressure of 101kPa, a temperature of 26.0 celcius and in addition the current in the system was kept at a constant 0.600A throughout all trials of different concentrations.
When analysing the results there was a trend that showed the higher the concentration of the potassium hydroxide the faster the 25mL of H2 gas was produced. However, Through using the formulas Q=It, Q=n(e-)F and the electrochemical half equation for H2 production it seemed that due to the current and the amount of Hydrogen being formed both being constant the time taken to form the hydrogen should also remain constant.
I have found a write up for the exact experiment on https://www.qcaa.qld.edu.au/downloads/senior-qce/sciences/snr_chemistry_19_ia2_asr_high.pdf however when it comes to talk about the effect of increasing the KOH concentration it seems that there is no mention that the current was kept constant.
I would like to know if the trend shown should have occured and why.


texts:
I've been trying to get any chemical reaction that with the least volume of reagents (including possible water) would generate the highest amount of a safe gas (at a reasonable cost and with a fast reaction).

The final implementation would be having small, portable and stable reagents (preferably solid) that could be mixed at any moment to fill up a balloon. To be used by the general public without much reagent handling (e.g. irritants would be ok).

Currently by best guess has been citric acid with any of the 1st group (bi)carbonates, adding water before to each, and then mixing them.

Does anyone have another suitable reaction?
Any other safe acid?
Any more soluble option to reduce the water volume?


texts: Copolymer purity, what does AN / MA / MS mean?

texts:
I would like to buy some polyacrylonitrile (PAN) powder from GoodFellow and I have the choice between these two products:

AN316010, quality : Copolymer (99.5% AN / 0.5% MA)
AN316020, quality : Copolymer (93.9% AN / 5.8% MA/ 0.3 % MS)

What I do not understand is the meaning of these three acronyms. What is the abbreviation hidden behind AN, MA and MS?
This may be an obvious question but I was unable to find any answer so far. I guess this may be somewhat linked to a certain degree of purity of the product, but since polymers can also be sold with different Monomer / Polymer ratios, I wanted to be sure...

My best guess for now is that AN may be AcryloNitrile, but I have no idea as for MA and MS... MA may be Methacrylic Acid, but could also be Methylmethacrylate Acrylonitrile or Maleic Anhydride (see here). Any help to answer this question is more than welcome.
Although in this particular case I may simply contact the supplier to have my answer I also wonder:
Is there a general way to solve these chemical identification issues or is it up to each supplier to name these types of compounds as they see fit?


texts: Why does a paracetamol tablet clean an iron

texts: If you burn some clothes on an iron and some residue sticks to it, rubbing a paracetamol tablet over it (while it's hot) surprisingly removes the residue and cleans the iron. Please explain why this happens.


texts:
Suppose I have a beaker containing $\ce{CuSO4}$ solution and I dip $\ce{Cu}$ rod in it. What reactions are going to take place? Is the $\ce{Cu}$ rod going to acquire any positive charge?

I am asking this question to clear my doubt  regarding a Daniell cell as to why $\ce{Cu}$ rod used in the cell should be positively charged. I don't get it, though $\ce{Zn}$ rod dipped in $\ce{ZnSO4}$ solution acquires negative charge due to oxidation of $\ce{Zn}$ to $\ce{Zn^2+}$ is clear to me, but how can $\ce{Cu}$ rod dipped in $\ce{CuSO4}$ be positively charged. I suppose it to be neutral.

What is the answer to this conceptual question?


texts: Open Babel: conversion to SMILES. How to delete H?

texts:
OpenBabel is a convenient converter between different chemical formats.
If I convert to SMILES, however, although I checked the option "Delete hydrogens (make implicit)".
I still have H in the SMILES codes.

It's the same with the command line. It also does not remove H.

obabel.exe Molecule.log -osmi -d

I still have, e.g. ...C[CH]C... in the SMILES.
Of course, I could replace all occurrences of [CH] by C, but I'm not sure whether I would mess up the SMILES and/or the molecule.
How can I get rid of the hydrogen? Why is it actually in there? Did I miss any other options during conversion?


texts: is electrolysis of water less efficient with warm water? E.g 40, 50, 60... °C

texts:
I see there is High-temperature electrolysis which is a whole different animal than room temp electrolysis.
I want to know if electrolysis of lukewarm water will behave much differently. My guess is that the water molecules can more easily disassociate.
State-of-the-art electrolysis performs at ~75% energy efficiency. What would be the energy efficiency performed on lukewarm, or hot water?


texts: Will additional ascorbic acid preserve hemp milk for a longer duration?

texts:
Ascorbic acid is known as a natural preservative and many food manufacturers add it to their food to prolong its shelf life.

Hemp milk is a drink that is created by blending 1 part hemp seeds with 2/3 parts water at a high speed. Usually, hemp milk will stay fresh if refrigerated for about 4-5 days.

Hemp seeds naturally contain ascorbic acid. However, how much additional ascorbic acid is required to extend the shelf-life of refrigerated hemp milk by a given amount of days?

For example, to extend the shelf-life for an extra 5 days.


texts: How does LeChatelier’s principle (which makes qualitative predictions) relate to the quantitative changes observed when an equilibrium is disturbed?

texts: Le Chatelier formulated his principle in 1884; it predicts the direction in which equilibrium is re-established after it has been disturbed by an external cause. How does this qualitative principle relate to the known quantitative changes that occur when an equilibrium is disturbed by a change in temperature, concentration or pressure? Are there any limitations of Le Chatelier's principle as it is stated by modern sources?


texts: Canonical vs localized orbitals - stationary towards changes?

texts:
So regarding Koopman's theorem I found the the explanation that you should not use it to find the ionization potential of localized orbitals because, much unlike canonical orbitals they will not be stationary towards small orbital changes. So any minor perturbation will cause a big difference in energy.

Usually I would simply say that the canonical orbitals are the eigenvalues of the diagonalized fock matrix while localized orbitals are not direct solutions of the fock matrix.

But isn't localization simply another transformation of the matrix that keeps the energy but sort of contracts the density more around bonds or atoms to resemble the bonds or lone pairs we know from organic chemistry? How does this effect the way they behave towards small changes to the orbitals?


texts:
In this particular epoxidation/hydroxylation reaction, why does the epoxide only form at one of the double bonds and not both?

The compound initially reacts with the peroxyacid to form an epoxide, follow by an acid catalyzed epoxide opening resulting in syn-stereochemistry. My initial guess was that the epoxide would only form by the double bond that is not sterically hindered. I don't understand why the epoxide only forms at the double bond flanked by two methyl groups and not both.


texts: Photoelectric effect (AP Chemistry question)

texts:
Which of the following postulates regarding the photoelectric effect is considered to be INCORRECT according to the quantum mechanical model we currently understand?
(A) Increasing the intensity of light does not change the energy per photon.
(B) The energy of a photon which ejects an electron from a metal surface must be equal to the binding energy (a.k.a. work function) of the electron plus the KE of the electron.
(C) Increasing the frequency of a photon can allow that lone photon to eject multiple electrons from a metal surface.
(D) Some electrons in a metal are easier (require less energy) to eject than others.

Please see question above and the teacher also supplied us with answers, so I know that answer is C.
Now, I am trying to reason why C is an answer, and A seems to be reasonable from what I read in my book. D looks somewhat good even though books keep mum about it. But I am puzzled about answer B. I looked at every AP Chemistry source I could get, and I am not sure where I can find formula for energy of photon, which would be equal binding energy + KE of electron. I can imagine this might exist outside of AP Chemistry, but within a subject? I found the equation in Wikipedia, for example:

The energy of a photon causing the photoelectric effect is found through E = hf = KE + w, where h is Planck's constant, 6.626X10^(-34) J*s, f is the frequency of the electromagnetic wave, KE is the kinetic energy of the photoelectron and w is the work function for the metal.

Any help on this matter would be highly appreciated. Desirably, reference to AP Chem book with page number. Thank you so much in advance!


texts: Describe the function of a salt bridge, What would happen if the half-cell compartments of a galvanic cell were not connected?

texts: I know,  The primary function of a salt bridge is to complete the circuit, so that charge can flow from one half-cell to the other. The second function is to balance the mass by allowing the anions to move to the half-cell where addition cations are being produced.But I can't seem to figure out what would happen if the half-cell compartments of a galvanic cell weren't connected?


texts: What are the limitations of the Born-Lande' equation?

texts:
The Born-Lande' equation is used to theoretically calculate the lattice energy, $\Delta U$, of ionic compounds. It is often cited as such in literature,

$$\Delta U = -\frac{k_Az_1z_2Me^2}{4 \pi \epsilon_\circ r_\circ}\left(1-\frac{1}{n}  \right)$$

In which, $n$ is the Born exponent, $k_A$ is Avogradro's constant, $M$ is the Madelung constant, $e$ is the elementary charge, $\epsilon_\circ$ is the permittivity of free space, $z_1$ is the magnitude of the relative charge of the anion and $z_2$ is the magnitude of the relative charge of the cation  with $r_\circ$ being their closest distance apart.

However, the most apparent limitations of the Born-Lande' equation I'm able to think of are as follows.

The corresponding Born exponent, $n$, and Madelung constant, $M$, must be determined empirically or theoretically for each ionic compound.
The bonds between the cation and anion are assumed not to possess any covalent character. However, the difference in electronegativity between the cation and the anion results in covalent characteristics which I believe can be further explained through Fajans' rule. Moreover, I suspect it is the primary reason for the discrepancy between its calculated lattice energies and that of which are determined through the Born-Haber cycle.

Therefore, I would like to ask the following questions.

What other limitations does the Born-Lande' equation have?
Why are the lattice energies of ionic compounds determined from the Born-Haber cycle considerably higher than that predicted by the Born-Lande' equation?
How exactly is Fajans' rule related to the deviation from perfectly ionic behaviour?
Is it possible to quantify the discrepancy in the values of the lattice energies in terms of the covalent character of the ionic compound?
If electrons have particle-wave duality, how are we able to define ionic radii to determine $r_\circ$ if the location of an electron is described by its probabilistic wave-function?


texts: Adiabatic processes and the Ideal Gas Law

texts:
in my first year chemistry textbook it wrights that in adiabatic proccess when there is a system of canister filled with gas and a piston above(and wheights on it) if we let the piston move upward by removing some of the weights the temperature of the gas will decrease since the gas has made work.
i understand that in the opposite case when we compress a gas in adiabatic proccess the temperature will increase.

**my question is: isn't it contradicts the ideal gas law which says that the volume of the gas is proportional to the temperature and vice versa

PV=nRT

so when the volume of the gas is increasing, the temperature should increase.

also by intuition: if the volume is increased, there is less pressure , the molecules has now more space and theire kinnetic energy should increase and therefore also the temperature.

how can i look at this?

thanks
 **


texts: What happens to the argon in the Haber-Bosch process?

texts:
The Haber–Bosch process is used to synthesis ammonia from atmospheric nitrogen and hydrogen derived from a hydrocarbon such as methane. The process requires high temperatures and pressures and also requires repeated cycling of the gasses.
I would have thought that atmospheric argon and other noble gases would have slowly built up in the reactor. How are these inert gases removed?


texts: Confusion about definition of Bond Enthalpy

texts:
My Chemistry textbook defines bond enthalpy as "amount of energy required to break one mole of bonds of a particular type between two atoms in gaseous state".
Can someone confirm to me whether

  a particular type

is related to bond order, to the atoms involved, both, or something else?

Also, should not the bond enthalpy of all diatomic molecules be large as one mole of bonds to be broken. But this does not happens. Why?


texts: Why is fullerene 60 an insulator while graphite is a conductor?

texts: Graphite is good conductor of electricity because one carbon atom is bonded only three carbon atoms, which enables the presence of free electrons. In fullerene 60 the carbon atoms are also bonded to three atoms so why is fullerene concidered a bad conductor of electricity?


texts: What is the geometric configuration of the four fluorine atoms during the synthesis of xenon tetrafluoride?

texts:
Neil Bartlett (1932–2008) first synthesized $\ce{XeF4}$ (and $\ce{XeF6}$) in 1962.  In the synthesis, a nickel chamber is used, and heated to 400°C, causing the formation of $\ce{NiF4}$, which Wikipedia claims is not part of the reaction.

Due to the nature of the noble gas, xenon, one might imagine that the fluorines would need to  could be "forced" onto the $\ce{Xe}$ atom at the same time, otherwise with each addition, the molecule would be even less energetically likely.  I was trying to ascertain in what geometric form the four fluorine atoms would configure themselves to make this addition possible.

I had first assumed that the nickel was being used as a catalyst, and the fluorines could be plucked from its surface accordingly, but this does not jive with the description of the synthesis above.  According to the response below, one synthesis of the molecule does rely on forming fluoride radicals on a catalyst, but it's mysterious that the synthesis above does not mention this.

Assuming there is no catalyst, how are the fluorines at 400°C oriented to allow the addition of 2 molecules at presumably the same time?

F - F
.   .
.   .
F - F

(and is that even possible?)


texts:
I was doing a homework assignment and I got the question wrong because I was supposed to multiply the empirical formula of $\ce{C6H10S2O}$ by 3 to get the molecular formula.

I put $\ce{(C6H10S2O3)3}$ and the teacher said it should be $\ce{C18H30S6O3}$.

My question is: isn't what I put the same thing?


texts: Absorption of UV Light and what color would be seen?

texts: I am mathematically experimenting with different wavelengths of light that a fictional material would absorb. I thought of a material that absorbs a wavelength of $\pu{193 nm}$. This wavelength corresponds with the area of ultraviolet light. I am having trouble figuring out what this material would look like to a human eye. I understand that human eyes cannot see UV light. My question is, what color would this material appear as?


texts: How to prepare potassium cyanide from potassium ferrocyanide

texts:
How do we prepare potassium cyanide from potassium ferrocyanide?

It is something which I am curious about, but cannot find the answer. I am studying inorganic chemistry but this reaction cannot be found.


texts: What Could Formations of Linkage Isomers of [Co(NH₃)₅NO₂]²⁺ be like?

texts: I am trying to draw the structure of this complex $\ce{[Co(NH3)5NO2]^{2+}},$ however I am not sure if the linkage isomers of this complex like this:


texts: I was just reading this article about allotropes which relates allotropy with some specific elements and also this wiki article. Also some other articles some of which relate allotropy with catenation some with electronegativity and some with electronic configuration. I was understanding the relation of allotropy with all these factors but I am unable to get that how allotropy is dependent on them exactly. Can we predict the allotropy in elements (and also the extent to which they exhibit allotropy) just by concerning their chemical properties?


texts: Why is HCl used in hydrolysis of sucrose?

texts:
I am aware that $\ce{HCl}$ can be used to help speed up the hydrolysis of sucrose but I haven't really been able to find out why. I've read somewhere that the glycosidic link in sucrose is broken off and that the $\ce{H+}$ ions from the $\ce{HCl}$ is responsible for this.

I've also come across the ether link during my research and would like to know how this plays a part in the hydrolysis of sucrose and if the $\ce{HCl}$ interacts with it.


texts: What is the purpose of atomisation in atomic absorption spectroscopy?

texts:
What is the purpose of the atomisation process in atomic absorption spectroscopy?

I understand that solution is evaporated by the flame and then the molecules decompose into atoms.

But why must the molecules become individual atoms before the light is passed through them?


texts: Charge, multiplicity, level of theory and coordination coordinates of gold compleaxes

texts:
Good day,

I need to learn a trick in answering the following questions:

How to come up with cartesian coordinates of a complex say, [Au(CH2)2(S)PPh2]2, to be ran on Gaussian?
The charge and its multiplicity?

Kindly please help.


texts: How can I calculate the number of branches in an alkane isomer?

texts:
I am so confused. So my textbook says that

  2-Methylheptane has 1 branch
  2,2-Dimethylhexane has 2 branches

However, when I get to:

2,4-Dimethylpentane
2,2,3-Trimethylpentane
2,2,3,3-Tetramethylbutane

I have no clue how to count the number of branches from the structural formula. My textbook assumes you'd understand how to calculate the number of branches after looking at the example. Can someone please help me understand?


texts: How to identify which species will undergo Oxidation and which will go Reduction

texts:
I have been given $\ce{B2}$, $\ce{N2}$, $\ce{(O2)-}$  and $\ce{O2}$.

I have to short out  which will undergo oxidation, reduction or both.

How can I tell it when reactants are not given?


texts: Which has the greater N–O bond length, NO₂⁻ or NO₃⁻?

texts:
Which has the greater N–O bond length, $\ce{NO_2^{-}}$ or $\ce{NO^_3^{-}}$?

I don't understand why the N-O bonds should be of different lengths in these two molecules (don't the same bonds have the same length)? I didn't quite know how to determine this and so I've tried googling the answer, but none of the answers already provided helped clear things up for me... Why does $\ce{NO_3^{-}}$ have a greater N-O bond length?


texts:
I diluted sulfuric acid in deionized water in order to get a 10% $\ce{H2SO4}$ solution.

I was going to use this solution as a cathode of a porous sample to measure its electrical properties.

However, this solution has a quite high resistivity (~200 ohm.cm DC).

I checked several sources that tell me that I should be measuring a lower resistance.

Does anyone has an idea of what may be happening?


texts: Molar mass of a protein from osmotic pressure

texts:
The height of a column of liquid that can be supported by a given pressure is inversely proportional to its density. An aqueous solution
  of $0.010 g$ of a protein in $10 mL$ of water at $20^oC$ shows a rise of
  $5.22 cm$ in a mercury tube. Assume the density of the solution to be $0.998 g/cm^3$ and the density of the mercury to be
  $13.6 g/cm^3$. (a) What is the molar mass of the protein?

The answer key says the answer is $4.8*10^3 g/mol$, but I got $3.5*10^2 g/mol$. Below is my reasoning:

Osmotic pressure = pressure to raise mercury, so $MRT = rho * g * h$

$\frac{(0.010/M)}{(10.010/0.998/1000)} * 8.3145 * 293 * 10^3$ (pascals) = $13.6/1000*(100)^3 * 9.8 * 0.0522$ (pascals). Solving this equation for $M$ gets $3.49*10^2$, instead of 3.8*10^3.

Can someone please point out where I am wrong?

Please do not point this out as a duplicate, as I have already referenced the question here. I used their approach but still cannot get the correct answer.


texts:
I had homework with the following question, Eugenol is the active ingredient in the oil of cloves used to relieve toothache. Calculate the boiling point of a solution in which 0.17 grams of eugenol, (C10H12, O2) is dissolved in 10.0 grams of benzene. (Kb benzene= 2.53 0C/m; Tb(solvent) = 80.100C). Show your solution.
I solved it like this but it's wrong, I would like to know your thoughts.


texts: How to calculate ∆rGº from entropy and ∆fGº in different temperatures?

texts:
"The total oxidation of glucose occurs according to the following chemical equation:
C6H12O6 (s) + 6O2 (g) -> 6CO2 (g) + 6H2O (l)
The following table gives us the free energies of standard formation and the standard molar entropies of
compounds involved in the previous reaction.

Compound
∆fGº(298 K) kJ/mol
Smº (298 K) J/K/mol

C6H12O6
-917,2
212,10

O2
0
205,14

CO2
-394,36
213,14

H20
-273,13
69,91

Based on the previous data, determine the ∆rGº
for glucose oxidation at 308 K"
It's a question of a doctoral selection process and I want to figure out if it is formulated wrong or if there is a way to an answer.


texts: Acid and base separation on an anion exchange column

texts:
I'm new with this concept and so I would need some advice.

I want to separate an acid and a base in a water solution. The acid has $\mathrm{p}K_\mathrm{a}(\ce{HA}) = 5$ and the corresponding acid of the base has $\mathrm{p}K_\mathrm{a}(\ce{HB}) = 7.$ The column is positively charged. What $\mathrm{pH}$ should I use in order to retain the acid in the stationary phase and the base passing the column?

Well, I'm just thinking that I would want the acid to be negatively charged in order to bind to the stationary phase, and so I would use a $\mathrm{pH} > \mathrm{p}K_\mathrm{a}(\ce{HA})$ because then the solution will gain a proton and leave the acid negatively charged. Right?

What about the base, should it be positively charged in order to escape the stationary phase and be attracted to the polar water?


texts: When removing a reactant and equilibrium shifts left, doesn't this make an excess of the 2nd reactant, forcing equilibrium back to the right?

texts:
In the reaction:$$\ce{Ca^{2+}(aq) + ^-OOC-COO^- <=> Ca(OOC-COO)(s)}$$

If $\ce{Ca^{2+}(aq)}$ is removed, the reaction shifts to the left to produce more $\ce{Ca^{2+}(aq)}$ to compensate.

But when the reaction shifts to the left, isn't a side effect that more $\ce{^-OOC-COO^-}$ is also produced (as when $\ce{Ca(OOC-COO)(s)}$ dissociates it produces BOTH $\ce{Ca^{2+}(aq)}$ and $\ce{ ^-OOC-COO^- }$, and not $\ce{Ca^{2+}(aq)}$ by itself?

So if there is more $\ce{^-OOC-COO^-}$, won't the reaction want to shift to the right?

So wouldn't these two (i.e. wanting to shift left and shift right) counteract and the reaction not shift anywhere? I think there is something about Le Chateliers's that I have misunderstood, so please point it out if you see it.


texts: Relationship between enthalpy change and endo/exothermic reactions

texts:
Something that confused me, is there a relationship between enthalpy change and endo/exothermic? Does region "x" represent the enthalpy change?
What represents enthalpy change, kinectic energy, activation energy and potential energy on the graph below?
But why must, for an endothermic reaction, the value of activation energy be higher than the enthalpy change? Then, how about the backwards in equillibrium, if the forward reaction is exothermic, is it the same?
And why is, for an exothermic reaction, the value of the activation energy equal to the enthalpy change? Is that a must? Can the activation be energy greater than the enthalpy change?


texts: Why can't I balance this reaction algebraically?

texts:
$$\ce{aCu + bHNO3   ->  cCu(NO3)2 + dNO + eH2O}$$
  (Source)

I calculated:
\begin{align}
a &= c &(\ce{Cu})\\
b &= 2e &(\ce{H})\\
b &= 2c + d &(\ce{N})\\
3b &= 6c + d + e &(\ce{O})
\end{align}

And I tried substituting $a= 1$, but it couldn't solve the whole equation. How can I solve this algebraically?


texts: Why are enantiomeric excess % and specific rotation considered?

texts: I was wondering, when working in a lab in an area related to organic compounds, when and why would a chemist consider the enantiomeric excess % and how would a chemist used that information?? Same Thing goes with specific rotation, why, how, and when would a chemist use this? I was just curious because I saw this in my organic chemistry book and they relate the problems to lab work and I want to get a good grasp of tis context and it made me wondered.


texts: If ethyl bromide is treated with alcoholic silver nitrate, which product will be formed?

texts: Silver nitrate promotes ionisation , so the ethyl bromide should ionise, the alcoholic species should attack (by loan pair of oxygen) so finally an ether should be formed , but the answer given in my book is nitroethane and ethyl nitrite.


texts: What is an example of an endergonic reaction?

texts:
I am doing a project where I must find both an endergonic and exergonic reaction. The latter seems to be abundant, but the endergonic reactions seem to be purely biological. I have to present the reaction. The only thing I can think of that is endergonic (that isn't biological) is ice melting. Is there some kind of chemical reaction that's endergonic that anyone knows about? I have access to laboratory chemicals if I need to use them. If all else fails, I can do ice melting, but that sure will be pretty boring.

Thanks!


texts: What is the mechanism for electrospray ionization?

texts:
I've been asked to

  Descibe the ionization mechanism used in electrospray ionization

I know that this is
a desorption ionization source, which uses a high electrical field as the ionizing agent. The best I've been able to put together is that there is a generation of $\ce{[M + _zH]^2+}$ ions. Surfing the web has just led me to articles saying the mechanism is still being debated. What's the mechanism, if there is a definitive one?


texts: XSteam IF97 tables (MS Excel version) lack of inputs

texts:
I am using XSteam IF97 to evaluate steam power plant cycles.
However, I miss some important input options such as pressure as a function of entropy and temperature ("p_st()") - when I assume isobaric heat addition (neglecting pressure any pressure losses) while reheating the steam. I end up looking at i-s diagram which is highly inefficient while optimizing cycle for different inputs.
Is there any way around or any more sophisticated software (in the best scenario, available for MS Excel). Or how do you work with steam power plant cycles?
(I intend to avoid any commercial software)


texts: Visualizing rotation about a double bond

texts:
So I'm having trouble visualizing rotation about a double bond without using a model kit. The 2nd image has a red dot where I rotated it to make the molecule look exactly like the second image with my head and then my model kit. This is also consistent with my answer key that says these molecules are identical.

Now, the next two molecules:

I visualize rotating the left molecule at the red dot carbon and in my head, it matches up with the right molecule. However, when I pull out my model kit, it does not rotate like that and does not match up. This is also consistent with my answer key that says these molecules are diastereomers. So my question is, are there any rules that I could use or a way to visualize that will help me realize if a bond can be rotated to match a molecule without using a model kit.

Also, when people talk about it is not possible to rotate a double bond without breaking it, what exactly are they talking about that makes it different from this?


texts: Meaning of electrochemical vs nonelectrochemical steps

texts:
Can someone please explain to me what is meant by an electrochemical reaction step and how it differs from a nonelectrochemical reaction step in the same overall reaction in the context of electrocatalysis?

A simple example with H2 or H2O would be sufficient.


texts: There are three things in the world that smell like fish. But why?

texts:
As a philospher once said, there are three things in the world that smell like fish. One of them is fish.

What connects these three things that gives them this particular, characteristic smell? What chemical exactly do we smell?