texts: Kinetic vs thermodynamic control of HBr to 1,3-Butadiene

texts:
The author claims that the transition state leading to the formation of the 1,2 product from the allylic carbocation is lower in energy since the carbon (which is attached to Br in the 1,2 product) is more electrophilic.

This makes sense to me, however, doesn't the transition state represent the energies of both, the reactants, and the products? In which case the thermodynamically favored product (1,4 product) should also have a lower energy transition state.


texts: How does water defy gravity in paper towels?

texts: How can water be absorbed into a paper towel such that it continues to be absorbed up into the material against the force of gravity? What property of paper towels/water causes this? I can understand that cohesive forces cause water molecules to follow other water molecules, but why do the molecules begin this climb in the first place?


texts: Finding the weighted parameters of the vertex adjacency matrix for a derivative of azulene

texts:
In my last question ( Numbering in a derivative of azulene ), I asked about the numbered of a molecule in order to find the Vertex Adjacency Matrix (VAM) of the same molecule. To explain my question properly, I will do my best to show my effort from A to Z as follows:
In general in order to find the VAM we use the formalism described by

To apply it onto the molecule I am studying, I first applied it to azulene and with agreement with the paper Quantum Interference, Graphs, Walks, and Polynomials the VAM represented by A is:

Now by having the correct numbering to my molecule (Numbering in a derivative of azulene), it also should be a 10 x 10 matrix. The difference is instead of hydrogen we now have Oxygen and hydrogen Sulfide involved in positions 1,5 and 2,6 as shown:

To find VAM the only way was to study the VAM of weighted Graphs as shown below:

Here are my questions:
1- Should I include  the parameter h only for the weighted carbons since the numbering of the molecule I am studying includes only carbon?
2- If 1 is no, how should I include the k parameters described before hand?
Any other suggestions to find VAM is appreciated.


texts: Why is the polarity of the B-N bonds in borazine the reason for its reduced delocalisation of π electrons?

texts: My professor mentioned that borazine is aromatic, but not as much as, say, benzene. The reason he gave for this was that the B-N bonds in borazine, being polar, inhibit resonance. He also mentioned that the same inhibition of resonance occurs in h-BN. Why is this so? What difference does bond polarity make?


texts: What does the signals in a XPS spectrum mean?

texts: I was trying to figure out the different peaks in a XPS spectrum for Molybdenum, but I could not understand them. About XPS, I know that this technique is based on the binding energy of the electrons of different elements


texts:
I'm new to SMILES strings, and have noticed that they're not standardised.
Firstly, what is the reason for different structures of SMILES strings to represent the same compound?  Why not have a standardised format?
Secondly, are there any tools to convert between different SMILES strings for a given molecule?


texts:
I'm a bit confused.
I've got this "toy" ...
with the help of this site I was abled to find out that the reaction stops with a lack of air. Link to the old question.

The battery/fuel cell or however you call it consists out of following components:

magnesium plate
isolator which consists out of something like paper, the surface feels more like cotton
the black plate is called "black cathode" in the manual, my hypothesis is that it might be rubbered graphite or a polymer, because it has a very low electrical resistance.
the electrolyte is a $\ce{NaCl}$ dispension- I think it just need to lower $\ce{H2O}$'s electrical resistance
plastic stuff is only the case of the "cell"

I did some research about this and the results are very confusing to me.

In the manual they call it a fuel cell.
My chemistry teacher says that in his hypothesis it is impossible to be a fuel cell and has to be a battery. -Because of the great answer to my last question I doubt it or at least I'm too confused to agree.

My research results:

►Battery:

news about a battery for cars
an article about the upper link and about the toy

►Fuel cell:

Wikipedia-MAFT
a kind of datasheet of a "battery" which is in development

►My hypothesis for beeing called fuel cell

→ because fuel cells require according to their definition a constant source of fuel, it might be called fuel cell because of the fact that the "thing" requires air to react.

►My hypothesis for beeing called battery

→ oxygen as fuel?- some people might see it different and call it battery because of that (then there's no constant fuel source →battery) .

►My idea about the chemical equation is:

$\ce{Mg + H2O → Mg(OH)2 + H2}$  (but I doubt it, because I can't imagine that it is responsible to sell a toy which emitts $\ce{H2}$ - or what else happens with it?-maybe the black cathode has to do something with it?)

If you've got a better idea about the chemical equation- let me know.

I would like to know if there's a mistake in my thoughts- and if it's actually a battery or a fuel cell.(the main problem).

And if you've got a better idea about the black cathode component's material- let me know please.

please don't mark it as duplicate to my older question-there's a difference because I added information about the theories and reasearched a lot about it and found the reasons/arguments I've posted here out- the last question was doing it by its components.


texts: Does #4 LDPE Plastic Bottle Leach into Water?

texts:
I understand that Water Bottles expire due only to the fact that the plastic can degrade over time and leach into the water making the water's taste not as desirable as the manufacturer might intend.
Does anyone happen to know the degradation rate/expiration for #4 LDPE? I'm using a plastic water storage vessel for long term water storage in m emergency preparedness supplies and would like to make sure the plastic doesn't leach. Please let me know! Thanks!


texts: I know that it is less than 7.0, but would be nice to know exact value of pH of natural fermented kvass (not soda-like counterfeit). Another aspect is to know if kvass is more gentle than Cola (pH=2.5) ?


texts: Work done by gas while expanding against constant external pressure?

texts:
This is the graph for the same between pressure (y) and volume (x):-

Here, why do we assume the gas pressure to be same as the external pressure everytime in during the process of expansion?


texts: Does nitrogen tetrafluoride act as an acid or a base in its reaction with water?

texts:
$\ce{NF4+}$ ion reacts with water as:

$$\ce{NF4+ + H2O -> NF3 + H2F+ + {1\over 2}O2}$$

My question is, does $\ce{NF4+}$ function as an acid or base in this reaction, and why?


texts: Half-life and shelf-life of second-order reaction

texts:
For integrated rate laws, I have attempted to find the shelf-life and half-life of second-order reaction:

However, the answers I have obtained (which are labelled with a red cross) are very different from the correct answers (bottom-right corner). I am wondering which parts were done incorrectly.


texts:
We were dealing with the Third Law of Thermodynamics in class, and my teacher mentioned  something that we found quite fascinating:

  It is physically impossible to attain a temperature of zero kelvin (absolute zero).

When we pressed him for the rationale behind that, he asked us to take a look at the graph for Charles' Law for gases:

His argument is, that when we extrapolate the graph to -273.15 degrees Celsius (i.e. zero kelvin), the volume drops down all the way to zero; and "since no piece of matter can occupy zero volume ('matter' being something that has mass and occupies space), from the graph for Charles' Law, it is very clear that it is not possible to attain the temperature of zero kelvin".

However, someone else gave me a different explanation: "To reduce the temperature of a body down to zero kelvin, would mean removing all the energy associated with the body. Now, since energy is always associated with mass, if all the energy is removed there won't be any mass left. Hence it isn't possible to attain absolute zero."

Who, if anybody, is correct?

Edit 1: A note-worthy point made by @Loong a while back:

  (From the engineer's perspective) To cool something to zero kelvin, first you'll need something that is cooler than zero kelvin.

Edit 2: I've got an issue with the 'no molecular motion' notion that I seem to find everywhere (including @Ivan's fantastic answer) but I can't seem to get cleared.

The notion:

  At absolute zero, all molecular motion stops. There's no longer any kinetic energy asscoiated with molecules/atoms.

The problem? I quote Feynman:

  As we decrease the temperature, the vibration decreases and decreases until, at absolute zero, there is a minimum amount of motion that atoms can have, but not zero.

He goes on to justify this by bringing in Heisenberg's Uncertainity Principle:

  Remember that when a crystal is cooled to absolute zero, the atoms do not stop moving, they still 'jiggle'. Why? If they stopped moving, we would know were they were and that they had they have zero motion, and that is against the Uncertainity Principle. We cannot know where they are and how fast they are moving, so they must be continually wiggling in there!

So, can anyone account for Feynman's claim as well? To the not-so-hardcore student of physics that I am (high-schooler here), his argument seems quite convincing.

So to make it clear; I'm asking for two things in this question:

1) Which argument is correct? My teacher's or the other guy's?

2) At absolute zero, do we have zero molecular motion as most sources state, or do atoms go on "wiggling" in there as Feynman claims?


texts: quantum number - question about the ms-value

texts: I've got the quantum number $\ce{(3,2,2,-1/2)}$, and the question is which electron belongs to this quantity. The answer is orbital $\ce{3d^1}$. But I don't understand why. I would have understood it, if the ms-value was $\ce{+1/2}$. But how can you have $\ce{-1/2}$?


texts: Why Frenkel defect does not impact the density of the solid?

texts:
The following text is from Chemistry Part I - Textbook for Class XII (NCERT), chapter "The Solid State", page 23, topic "1.9 Imperfections in Solids", sub topic "1.9.1 Types of Point Defects - (iii) Frenkel Defect":

This defect is shown by ionic solids. The smaller ion (usually cation) is dislocated from its normal site to an interstitial site. It creates a vacancy defect at its original site and an interstitial defect at its new location.
Frenkel defect is also called dislocation defect. It does not change the density of the solid.

(Emphasis mine)
Earlier I've learnt that a vacancy defect results in decrease in the density of the substance, and an interstitial defect increases the density of the substance. I could understand, due to the presence of vacancy or interstitial defects, the density varies locally or in other words density of the substance is not uniform throughout.
According to the quoted text, Frenkel defect creates a vacancy defect at one location and an interstitial defect at a different location (not at the same location), so I think the density will again have local variations and so the density changes. But it is given Frenkel defect doesn't alter the density. What is the reason for this fact? Why does the same logic fail here?
The Wikipedia article on "Frenkel defect" gives the following statement:

Frenkel defect does not have any impact on the density of the solid as it involves only the migration of the ions within the crystal, thus preserving both the volume as well as mass.[citation needed]
Source : Frenkel Defect - Effect on density

If density is plainly defined as the ratio of mass and volume it doesn't seem to change, but in reality I think there will be variations within the crystal having this defect. But why is this fact not specified in many sources?


texts: If a single electron fills a degenerate energy level, does it fill all degenerate orbitals at once?

texts:
For example, if a single electron fills the 2p orbitals. Since all orbitals are degenerate, there is no reason why there would be any preference for px, py, pz. Is the electron hence in a superposition of these 3 orbitals?

And what if we consider hydrogen for n=2, where 2s, 2px, 2py and 2pz are degenerate?


texts: Why do different elements form different types of carbides?

texts:
What property of the elements make them form different types of carbides like:

$\ce{Be}$ and $\ce{Al}$ - $\ce{Be2C}$ and $\ce{Al4C3}$ (Methanides) contains $\ce{C^4-}$ ion

$\ce{Na}$ and $\ce{Ca}$ - $\ce{Na2C2}$ and $\ce{CaC2}$ (acetylides) contains $\ce{C2^{2-}}$ ion

$\ce{Li}$ and $\ce{Mg}$ - $\ce{Li4C3}$ and $\ce{Mg2C3}$ (sesquicarbides) contains $\ce{C3^4-}$ ion.

Boron - $\ce{B4C}$ (covalent carbides)

Titanium and tungsten - $\ce{TiC}$ and $\ce{WC}$  (interstitial carbides)


texts: Comparing electronegativities of aluminium and gallium

texts: If I were to compare the electronegativities of Al and Ga, shouldn't I be saying that the electronegativity of elements (in general) decreases down the group, I say this by thinking of the position of fluorine amongst the halides and about the metallic character trends (which increases down the group) so Al should be more electronegative. However Wikipedia's data page says otherwise. For aluminium it's 1.61 whereas for gallium it's 1.81 (I'm using the Pauling Scale). I then calculated $Z_{eff}$ values for both of them using Slater's rule which indicated a greater effective nuclear charge for gallium, so is this due to the poor shielding by d-orbitals?


texts: Bomb calorimeter enthalpies of straight chained alcohols

texts:
Can anyone suggest a website which contains the literature values (using a bomb calorimeter) of the enthalpies of n-alcohols?

I have been trying to find it but I am unable to locate bomb calorimeter values (I do not want the bond dissociation energies.


texts: Comparing basicity using inductive effect

texts:
In the following two compounds .

1)

2)

We have to compare basicity .

According to me CH$_3$ is an electron donating compound so in second compound it will increase charge density in nitrogen so second compound should be more basic.

But in the book it is written first is more basic . How


texts: How are the Laguerre polynomials and spherical harmonics related to the electronic quantum numbers?

texts: How are the Laguerre polynomials and spherical harmonics related to the quantum numbers $n, l, m_l$ of an electron in an atom?


texts:
Amorphous solid possess short-range order but no long-range order (e.g. amorphous silica, the short-range order is originated from the tetrahedral bonding between Si and O). Is it possible to have multiple domains with different short-range orders in one amorphous solid?

If so, should we treat this solid as a single phase or multiple phases? Can we detect the existence of multiple domains?

Relative concept: polyamorphism

(It seems that polyamorphism implies that amorphous phases can be distinct from each other.)

Amorphous silica, https://en.wikipedia.org/wiki/Structure_of_liquids_and_glasses


texts: Are crystallographic omit maps only used with molecular replacement?

texts:
(This is in the context of macromolecular X-ray crystallography.)
From Lamb et al. 2015:

Model bias is the result of how maps are calculated: because the
phase estimates [of the structure factor] for the calculation come from the model, maps will
tend to show electron density for an atom in the model whether it is
truly there or not. A simple omit map is normally a difference (Fo −
Fc) map calculated after omitting specific atoms from a model, like a li-
gand or a functionally important loop.

From this the purpose of an omit map is rather clear.
But what I don't understand is when omit maps are used w.r.t. the source of the phases. From what I can tell, if the phases have been determined experimentally (e.g., using MAD), there cannot be any extraneous electron densities in the atomic structure model. This drives me to the conclusion that omit maps are used when the source of the phases is molecular replacement (I presume this is what the "model" alludes to).
Is this correct? Are omit maps only used with molecular replacement?
Edit: I am also confused with regards to how an omit map actually works. If the phases are what determine the final electron density irrespective of the amplitudes used, how does deleting a part of the atomic model, getting the phases from that and recalculating a new map (with these phases and the experimental amplitudes) actually help?
Edit 2 (from comments): I got the impression that if we don't have the phases (say for a part of a model), it just wouldn't get built even if we have the amplitudes for that part, right? Or is it that in this case (of omitting a part), there would be an electron density (because the amplitudes are still there), just that it would be featureless?!
I would be very glad to receive some clarifications and/or pointers.


texts: Neutralization reaction with insoluble salt (weak acid, strong base)?

texts:
Consider the following reaction.

$\ce{2 HF(aq) + Ca(OH)2(aq) -> CaF2(s) + 2 H2O(l)}$
The reaction produced a fairly insoluble salt.

Assume that this reaction proceeds entirely to completion as the acid and bases were initially in equimolar quantities with respect to their stoichiometry.

What is the resulting pH of the solution at equilibrium?

After the entire neutralization reaction has taken place we have the following reactions taking place in the solution.

$\ce{CaF2(s) -> Ca^2+(aq) + 2F- (aq)}$ with some $K_\mathrm{sp}$ value
and this reaction
$\ce{F- (aq) + H2O(aq) -> HF(aq) + OH- (aq)}$ with some $K_\mathrm{b}$ value

How would you go about calculating the values of $\ce{F- (aq)}$? I ask because every time some $\ce{CaF2}$ breaks off those free ions are used in the base reaction with water which according to Le Chatelier would result in more $\ce{CaF2}$ dissolving.

Does the chemically determined $K_\mathrm{sp}$ value in textbooks take into consideration the reaction of fluoride ions deprotonating water?


texts: Why constant volume combustion gives higher energy than constant pressure?

texts:
I have noticed when I have done some combustion equilibrium that enthalpy is higher when doing a constant volume combustion than pressure constant combustion.
Why is it so ? What are the reasons explaining that ?
Is it because at constant pressure combustion the variation of enthalpy is equal to heat transfert $\Delta H = Q $ whereas at constant volume combustion the variation of enthalpy is $\Delta H = Q + V\Delta p$ ?
If so that suppose that heat transfer $Q$ is the same for both constant pressure and constant volume combustions. Is that so ?
Thank you


texts: What chemical properties that allow for colour exist in the dark?

texts:
Of course if there's no light around, there's no colour that you can see. On the other hand, the wall must have some property that makes it be blue. That property is still there in the dark.
— Mike W.

Is Mike referring to the property of excited states, or the property that the states are excitable (via split d-orbitals or conjugated orbitals)?
I understand that anything that we see as coloured but not glowing is transmitting unabsorbed light — the complementary colour of the absorbed light — which is only possible when electrons jumping from ground to excited states.
What I'd like some clarity on is whether those excited electrons fall back to their ground state in the absence of light (another potential reason why colour does not exist in the absence of light). If the electrons do, then I guess the property Mike's referring to is the excitability of the electrons — which makes sense.


texts:
Consider an alcohol and an amine compound with roughly the same molar mass. If I understand correctly, the boiling point for the alcohol is greater for two reasons:

The $\ce{O-H}$ bond is more polar than $\ce{N-H}$ because oxygen is more electronegative than nitrogen.
The oxygen atom has two lone pairs of electrons to act as hydrogen acceptors, whereas the nitrogen has only one.

The question is, which one of these reasons (if they are valid) contributes more to the increase in boiling point?


texts: Is sodium aquo complex a Brönsted-Lowry acid?

texts:
I know that according to Brönsted-Lowry theory, a base is a proton acceptor while an acid is a proton donor. Also, the acid-base pair that differs by a single proton is a conjugate pair.
If this is true, then the sodium ion is a conjugate acid of sodium hydroxide. But if we look at $\ce{Na^+}$ itself, we find that it cannot donate a proton. Someone in the comments under this answer suggested that in its hydrated state, $\ce{Na^+}$ can act as a Brönsted-Lowry acid. How?


texts: Temperature dependency of enthalpy H and entropy S

texts:
In textbooks, I often read that the temperature dependency of the enthalpy of reaction $\Delta_\mathrm{r}H$ and the entropy of reaction $\Delta_\mathrm{r}S$ can be neglected (in a limited $T$-range).

But why is this valid? What is the intention behind this?


texts: Is there a chemical reaction between tungsten carbide and acrylic?

texts:
My company machines acrylic (Poly(methyl methacrylate) $\ce{(C5O2H8)_n}$), and notices that tungsten carbide tools break down quickly compared to high-speed steel, even though carbide is harder and lasts longer than steel when cutting most any other material.

Obviously, there is mechanical breakdown because of friction, but is it possible that there is also a chemical reaction between the acrylic and the carbide that is causing this faster breakdown?


texts: Final concentration of stock solution upon dilution

texts:
If we have a stock solution that is $\pu{1 mg/mL}$, and we have $\pu{0.1 mL}$ of that stock to which we add $\pu{0.9 mL}$ of water, what is the final concentration?

For this I assumed I had to use the concentration formula:

$$\mathrm{M_{1}V_{1} = M_{2}V_{2}}$$

I thought the initial concentration was $\pu{1 mg/mL}$, since that is my stock. I thought the initial volume was $\pu{0.1 mL}$, since that is what they needed from the initial stock. I assume the final volume is $\pu{1 mL}$, since that is the total volumes of the components.

$$\mathrm{(1\;mg/mL)\cdot(0.1\;mL) = (M2)\cdot(1\;mL)}$$

$$\mathrm{M_2 = \frac{0.1\;mg}{1\;mL}}$$

$$\mathrm{M_2 = 0.1\;mg/mL}$$

I feel I am right due to the units evaluating properly out, since the original concentration is giving in $\mathrm{mg/mL}$ , the final should be also in $\mathrm{mg/mL}$, right?


texts:
The $\ce{N-N}$ bond length in $\ce{N2O4}$ is $\pu{1.64 Å}$ which is much longer than in the case of Hydrazine $\ce{N2H4}$ $\pu{(1.47 Å)}$. This means that the bond is quite weak. Another unusual case I see that $\ce{N-N}$ bond length in $\ce{N2O3}$ ( the blue asymmetric form ) is $\pu{1.86 Å}$ !!
That is very weak for a Nitrogen single bond. Is there a satisfactory explanation for the same? And amazingly molecules with such long bonds tend to have a nonplanar structure due to bond rotation but $\ce{N2O4}$ is planar.
I found a similar question on N2O4 but the answer to the planarity question wasn't so satisfactory. Also, I wanted the extend upon the weak bond question.


texts:
A tablet of weight $\pu{200 mg}$
was analysed for its morphine content using a HPLC system in conjunction with a single wavelength UV detector operating at $\pu{260 nm}$.
The tablet was prepared for analysis by crushing and extraction using a solvent system similar to the HPLC mobile phase i.e. $70\%$ acetonitrile, $30\%$ water. $\pu{50 mg}$ of codeine was added as the internal standard and the mixture made up to $\pu{50 mL}$. The resulting solution was analysed by HPLC using the instrument conditions given below. A standard solution was obtained by taking $\pu{50 mg}$ of each component, dissolving in mobile phase and making up to $\pu{50 mL}$.
Using the results obtained below, calculate the morphine content of the unknown tablet (both as %w/w and mg/tablet).
Standard Solution Analysis
\begin{array}{c|cc}\hline
&\textbf{Retention Time (min)} & \textbf{Peak Area} \\ \hline
\textbf{Morphine} & 2.00 & 153000 \\
\textbf{Codeine} & 3.25 & 212000\\ \hline
\end{array}
Analysis of tablet solution
\begin{array}{c|cc}\hline
&\textbf{Retention Time (min)} & \textbf{Peak Area} \\ \hline
\textbf{Morphine} & 2.02 & 17600 \\
\textbf{Codeine} & 3.29 & 212500\\ \hline
\end{array}

I understand the use of the internal standard methodology, however I am unsure which values I should use in the equation as although I have been given the internal standard solution I also have been given the second standard solution of both codeine and morphine.
The question is asking to find the content of morphine in the sample tablet (200 mg) via the use of an internal standard solution of codeine (50 mg) which was made up to 50 mL ([codeine] = $\pu{1gL^-1}$). This was given as well as another standard solution of codeine (50 mg) and morphine (50 mg) made up to 50 mL ([codeine] = $\pu{1gL^-1}$).
The equation I have been given is
$$D_\textrm{rfx} = \frac{A_x}{ A_\textrm{is}} \times \frac{C_\textrm{is}}{ C_x}$$
where subscripts and symbols have the following meaning: $x$ = unknown, $\text{is}$ = internal standard, $A$ = peak area, $C$ = concentration.
First we need to calculate the detector response factor ($D_\text{rf}$) of the standard solution - but which standard solution?
Assuming that the standard solution conc. of both morphine and codeine are $\pu{1gL^-1}$, this gives a $D_\text{rf}$ for the standard solution of 0.722.
Using the calculated $D_\text{rf}$  value, the $D_\text{rf}$ equation can be rearranged to find the concentration of codeine in the sample tablet.
However my question is which values need to be used for the $A_x$ and $A_\textrm{is}$ - do they need to be both morphine or just the two values from the sample peak areas?


texts: Confusion between various formulas of Gibbs free energy

texts:
According to the assumptions of Constant P and T and no non mechanical work, we get
ΔG=ΔH-TΔS
But there is another form of the Gibbs free energy equation which takes Reversible process and no non mechanical work as assumption
dG=Vdp-SdT
If I Use the assumptions constant Pressure and Temperature, according to the above equation we get dG=0,which contradicts the first equation.
What is the mistake I am making? Also, when ΔGsystem=-TΔStotal


texts: Is the Hollywood portrayal of the effects of ingesting HCN correct?

texts:
In the 2012 movie Skyfall, the antagonist Raoul Silva rues that the "hydrogen cyanide" he took ("Do you know what it does to you, hydrogen cyanide?") didn't kill him, leaving him horribly disfigured instead.

Firstly; Could it have actually been HCN that he took?

From what I know about this, HCN is a gas at room temperature, and gases aren't typically the poison of choice for suicide pills. To begin with, suicide pills are preferrably kept as small as possible to make it easy to conceal. Keeping the size constraint in mind, simply filling it with HCN gas wouldn't allow the pill to store enough to (seriously) harm you, much less kill you.

From what I gather, suicide pills (WW2 era) often contain a concentrated solution of potassium cyanide, and not HCN.

Well, I'm bringing this up since this is a James Bond movie, so... what're the chances the MI6 could've compressed a significant amount of HCN in the suicide pill (possibly pressurizing it until it's a liquid), without having the easy-to-crush-between-the-teeth pill exploding on account of pressure? I'm not sure how easy it is to liquify HCN, but if it is possible to do so at room temperatures without an exorbitant amount of pressure, could that have been the 'suicide pill' he had taken?

Are there any known instances ( some half-arsed experiments and such) where a gas at room temperature was liquified and stored within such a small volume.

Secondly: Could hydrogen cyanide, or any other simple cyanide compound for that matter, cause such a disfiguration?

More than having tried to kill himself with some sort of HCN pill, I was taken aback to see what it did to Silva.

Just look at what happened to the guy:

Seriously, just look at him:

This is what I found on Wikipedia, on cyanide poisoning:

  If cyanide is inhaled it can cause a coma with seizures, apnea, and cardiac arrest, with death following in a matter of seconds. At lower doses, loss of consciousness may be preceded by general weakness, giddiness, headaches, vertigo, confusion, and perceived difficulty in breathing. At the first stages of unconsciousness, breathing is often sufficient or even rapid, although the state of the person progresses towards a deep coma, sometimes accompanied by pulmonary edema, and finally cardiac arrest. A cherry red skin color that changes to dark may be present as the result of increased venous hemoglobin oxygen saturation. Cyanide does not directly cause cyanosis. A fatal dose for humans can be as low as 1.5 mg/kg body weight.

I don't seem to find anything on 'severe-tissue-damage-and-jawbone-dissolution', so I'm still skeptical.

I mean, sure, HCN is a weak acid, but that is not what a weak acid does to you.

So did Raoul Silva bite down on a cyanide pill (of sorts...) or did he gargle a bottle of drain-cleaner and just forget about it?

Is there anything realistic about that scene, or is it just another movie gaffe?


texts: How to get the freeze point of mixed liquids?

texts: I recently bought in Italy a bottle of "Alcool puro" which is in fact 95% Alcohol and 5 % Water. So alcohol has a freezing point of -114°C and water a freezing point of 0°C. How can I calculate then the freezing point of the "Alcool puro"?


texts:
According to Wikipedia, $\ce{HeH+}$ and fluoroantimonic acid are the strongest.

According to Nature, Carborane acid is the strongest, but Wikipedia says fluoroantimonic acid is stronger.

Links:

$\ce{HeH+}$ / Wikipedia - stating HeH+ the second most acidic
$\ce{HeH+}$ / Wikipedia 2nd source - stating $\ce{HeH+}$ the most acidic (see in 'Notes' section)
Fluoroantimonic Acid / Wikipedia - stating it is the strongest acid (super_acid)
Carborane Acid / nature.com - According to Nature and even Google itself, it is the strongest acid created but according to wikipedia Flouroantimonic acid is stronger.

So, which is the strongest ?


texts:
What is the order of stability of the cycloalkyl carbocations?

I think the stability should increase as we move from cyclopropyl carbocation to cyclohexyl carbocation, since the angle strain is continuously decreasing. I understand this as, the difference between the stable 120 degree angle of a carbocation and the actual bond angle of the cycloalkyl cation is decreasing on moving from cyclopropyl to cyclohexyl carbocation.

But someone recently told me that the cyclopentyl carbocation is more stable than the cyclohexyl carbocation, citing the faster rate of SN1 reaction observed in 1-chloro-1-methylcyclopentane than in 1-chloro-1-methylcyclohexane.

So what is the actual stability order of these cations?


texts: Can we predict with any reliability whether a chemical is carcinogenic in people?

texts:
I know that some chemical compounds have been known to be carcinogenic in humans.

But can we make a reliable prediction of how likely a substance is to be carcinogenic based on the chemical and physical properties of the substance ? How good will the prediction be ?

It would be good if the following methods were compared

Computational chemistry
Crystallography
Bacteria models such as the Ames test
Animal models such as rats and mice
Chemical kinetics experiments
Predictions based on the fact that a substance is from the same class as a known carcinogen or non carcinogen


texts: Will alkoxide ion in protic medium attack on double bond or carbonyl group?

texts:
I want to know what will happen next here-
I thought that the alkoxide ion would attack the aldehyde to form a secondary alcohol, but apparently, as the two pi-bonds are in conjugation, so, the ion attacks the carbon of the C-C pi-bond. Why is this so?


texts: The C-13 chemical shift of acyl chlorides vs ketones

texts:
In lectures, we were taught that ketones and aldehydes tend to have chemical shifts of around 200ppm, while acid derivatives (carboxylic acids esters etc) tend to have values around 160-170 ppm.

The reasoning given by my supervisor was that despite acid derivatives having more electron withdrawing groups, due to conjugation, the net effect was that these additional groups donated electron density to the carbonyl carbon, hence shielding it more than the carbonyl carbons in ketones/aldehydes (i.e. the conjugative effect dominates over the inductive effect). This all makes sense for me except for acyl chlorides.

The reason why acyl chlorides are not adding up for me is that in the very next topic, we were taught that the CO double bond of an acyl chloride is stronger than that of a ketone/aldehyde! Since carbonyl bonds are strengthened by anything that withdraws electrons, I can only conclude that the Cl has a net electron withdrawing effect (i.e. its inductive effect dominates the conjugative effect).

Since the Cl group appears to actually withdraw electron density, going back to NMR, shouldn't the carbonyl carbon in acyl chlorides resonate at a higher frequency than the carbonyl carbon in a ketone/aldehyde?


texts: This is from an adapted version of Concise Inorganic Chemistry by J.D Lee.The part on primary valency is confusing me.It mentions that primary valency is the oxidation of the central metal (a number) ,on the other hand I have read that primary valencies are non directional (this description suggests primary valencies are a physical thing).In compounds like $\ce{[Co(H2O)4Cl2]Cl}$ the primary valency is 3 but 2 of the chloride are directional.Can a ligand be both primary and secondary valency simultaneously?


texts: The definition of an acid is a compound with a hydrogen cation and a non-metal anion. Water is a hydroxide bonded to a hydrogen atom. This hydroxide has a net negative charge, too, since the negative oxygen's charge is stronger than the positive hydrogen's. Water has a pH of 7, though, meaning that it's neutral. Why isn't water acidic


texts: If SOCl2 reacts with alcohols via SNi, why doesn't POCl3?

texts:
A bit of a follow-up to Why is thionyl chloride preferred for preparing alkyl chlorides from alcohols?.

The reaction with $\ce{SOCl2}$ is also used instead of $\ce{PCl3}$ and $\ce{PCl5}$ when retention of stereochemistry is required. Phosphorus trichloride and phosphorus pentachloride both lead to inversion.

The mechanism proceeds via a $\mathrm{SN_i}$ pathway, or internal nucleophilic substitution. This step has been highlighed in red; an intimate ion pair$^{[\text{see below}]}$ is given in square brackets. Adding a nucleophilic solvent such as pyridine considerably increases inversion with $\ce{SOCl2}$ via an attack at the sulfur atom. Green marks blocking of the intramolecular substitution; blue is for inversion.

As far as I know, $\ce{POCl3}$ has not been seen following an $\mathrm{SN_i}$ mechanism (even without pyridine). Why?

If possible, please provide a qualitative mechanistic reason. Something that is readily explained by waving hands. Regardless of whether such an approach is achievable, quantitative (calculational) answers are also most welcome.

References discussing intimate ion pair formation

F. A. Carey, R. J. Sundberg. $(2007)$. Advanced Organic Chemistry
Part A: Structure and Mechanisms, $4$th edition, pp 269$-$276. ISBN: 0-306-46242-7
W. A. Hughes, E. D. Cowdrey, C. K. Ingold, S. Masterman, A. D. Scott. 'The Mechanism of Elimination Reactions. Part 1. Unimolecular Olefin Formation from Alkyl Halides in Bulphur Dioxide and Formic Acid'. Journal of the Chemical Society, $(1937)$, 1271$-$1277. DOI: 10.1039/JR9370001271
E. S. Lewis, C. E. Boozer. 'The Kinetics and Stereochemistry of the Decomposition of Secondary Alkyl Chlorosulfites'. Journal of the American Chemical Society, $(1952)$, 74, 308$-$311. DOI: 10.1021/ja01122a005
D. J. Cram. 'Studies in Stereochemistry. XVI. Ionic Intermediates in the Decomposition of Certain Alkyl Chlorosulfites'. Journal of the American Chemical Society, $(1953)$, 75, 332$-$338. DOI: 10.1021/ja01098a024
C. C. Lee, A. J. Finlayson. 'Rearrangement In The Reaction Between Thionyl Chloride And $3$-Methyl-$2$-Butanol. Canadian Journal of Chemistry, $(1961)$, 39(1): 260$-$261. DOI: 10.1139/v61-030
C. C. Lee, J. W. Clayton, D. G. Lee, A. J. Finlayson. 'Rearrangement Studies With $\ce{^14C-XIII}$: The Thermal Decomposition Of $1$-$\ce{^14C}$-$2$-Butyl Chlorosulfite'. Tetrahedron, $(1962)$, 18 1395$-$1402. DOI: 10.1021/ja01098a024
H. Patin, G. Mignani, C. Mahe, J-Y. Le Marouille, A. Benoit, D. Grandjean. 'Ferrocenyltrithiocarbonates: I. Direct access from α-ferrocenylcarbinols by a $\mathrm{SN_i}$ mechanism. Absolute x-ray structure determination of (R)-ferrocenylmethylmethane S-methyl-trithiocarbonate'. Journal of Organometallic Chemistry, $(1980)$, 193, 1, 93$-$103. DOI: 10.1016/S0022-328X(00)86079-9
J. L. Kice, G. C. Hanson. 'Mechanisms of SNi reactions. Effect of aralkyl group structure on ion-pair return in the decomposition of aralkyl thiocarbonates'. Journal of the American Chemical Society, $(1973)$, 38 (7), 1410$-$1415. DOI: 10.1021/jo00947a037
M. B. Smith. $(2013)$. March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, $7$th edition, pp 311, 486$-$487, 490, 598, 1316. ISBN: 978-0-470-46259-1
 The $\mathrm{SN_i}$ (substitution nucleophilic internal) mechanism: retention of configuration. Powerpoint presentation, Università degli Studi di Napoli Federico II.
James. $\ce{SOCl2}$ and the $\mathrm{SN_i}$ Mechanism. Master Organic Chemistry, Alcohols. webpage


texts:
When I was kid and got a huge cut on my finger, I remember my grandmother putting lots of kerosene on my wound, as there was no health facility around.

I want to confirm. Do chemists agree on the antiseptic role of kerosene, or was grandma just using useless remedy?


texts: Is it possible to functionalize silica gel as Activated Carbon can be? How?

texts:
Activated carbon and Silica gel both have a high surface area.
If I understand correctly it is possible to trap stuff inside activated charcoal pores to give it specific retention properties (by exposing it to functionalizing conpounds while heated to open up the pores?).
Is it possible to likewise trap stuff in silica gel pores? What can be trapped in there and how is this done?


texts: Relationship between surface area and vapor pressure

texts:
How is vapor pressure independent of the surface area and volume of a liquid, although rate of evaporation depends on surface area?

Please someone help me I am totally confused.


texts: As mentioned in the title, why do we use the Kovat's Index in gas phase chromatography? It seems a little arbitrary to compare everything to the order that n-alkanes (such as n-pentane, n-hexane, and n-heptane) emerge from the column, and I am curious to know reasons why we use such an index.


texts:
According to Wikipedia, a vacuum airship is a hypothetical airship that is evacuated instead of using a lighter gas. Really, once I first saw this, I thought, "Why did I never think about this before?!" Indeed, whenever I pictured an evacuated container, I thought it would just sit there.  But no. Instead here on Earth, a theoretical vacuum airship could lift 1.28 grams per liter of evacuated space, a 14% boost over helium, owing to the density of air.

Of course, the air is also the destroyer of this powerful capability; it exerts 14 psi, or ~0.1 MPa!! According to Wikipedia's calculations, a hemispherical shell would have to withstand $$450,000 kg^{-1} m^5 s^{-2}$$ which is over 3 times the buckling pressure of diamond.

Give up? Not yet. There is a couple of interesting ideas I thought about:

Why hemispherical? Wouldn't other shapes do well also? For example, a sphere, or a cylinder (maybe a cylinder with radius=height). From what I know (not much..) about spherical items, I suppose it would distribute the pressure evenly. Wouldn't that mean that diamond could easily sustain 100 kPa (withstands up to 600 GPa)?
Is there no other way around this obstacle? Could we make use of any exotic forces or structural methods? (One interesting suggestion: Gradually evacuate the helium-filled airship, slowly going up, so that when we reach a total vacuum the airship is basically in space? In that case there wouldn't be any powerful pressure from air...)


texts: How long does it take to saturate H2O with O3

texts:
Let’s assume I have one liter of distilled $\ce{H2O}$ in an stainless steel container – from the bottom side of the container I do bubble ozone trough the $\ce{H2O}$.

Of cause it is not pure O3, so let’s assume that the gas consists of:

7% $\ce{O3}$

83% $\ce{ O2}$

10%. $\ce{ N2 / NO2 / NO}$

The gas flow is about 5 liters per minute and the corona discharge consumes about 500W.

How long will it approximately take, till full saturation of the
  $\ce{H2O}$   with   $\ce{O3}$  will take place?


texts: Mechanism of oxidation of phenol to quinone by chromium(VI)

texts:
In the supplementary information for Org. Lett. 2005, 7 (19), 4297–4300, the following experimental method for the synthesis of 2-bromo-6-methylcyclohexa-2,5-diene-1,4-dione is given:

  To a suspension containing 20.0 g (75.8 mmol) of 2,4-dibromo-6-methylphenol in 50 mL of 80% acetic acid in water and 25 mL of acetonitrile, was added 8.34 g of $\ce{CrO3}$ in 25 mL of water. The reaction mixture was heated to 60℃ for 1.5 h, cooled to room temperature, diluted with 400 mL of water and extracted with three 200 mL portions of chloroform.

I've summarised the reaction here:

How does this work, mechanistically? My first guess would be a nucleophilic substitution of $\ce{Br}$, followed by an oxidation by $\ce{CrO3}$; but I can't imagine there are many free hydroxide ions floating around in a solution of acetic acid.


texts: Photolysis of N-bromo compound in acidic conditions (radical cyclisation)

texts: For the proposed mechanism, I believe that the N-Br bond is firstly broken by the absorbed light hv, then the radical formed on the N will perform an intra-molecular attack on the end of the carbon chain to form a 5 membered ring. Then the sulphuric acid becomes deprotonated by the nitrogen lone pair? Just want to check whether this is correct.


texts:
I'm a freshly graduated physics and math teacher moved into a small school from the late 1920s.  The equipment here is old and confusing, at the very least.  I have found many things which I have never seen before.  I would like some help identifying what I have and what I can do with them, if anything.

(Click the images to view them at full size.)

1. A load of copper pots.  For boiling something perhaps?

2. Some sort of wash bottle?  Why is the cork on there?

3. I managed to make out "unitized wash bottle" on the back.  This serves the same function as the last one, I presume.

4. It reminds me of a graduated cylinder until the frosted top and the "arms" that poke out the sides.  What is this for?

5. This reminds me of halogen bulbs.  Again, I have no idea what this is for.

6. I've taken to calling this "trumpet" glass pipe.  What is it used for?

7. This large bulb has confused me since day one.  I feel like it needs some sort of current passed through the ends.  It reminds me of a cathode ray tube in a way.  I'm completely lost on this one.

8. Here.  Have a free safety poster!  Not as good as old Carol, though.


texts: Transformation of virial coefficients from molar volume to pressure

texts:
I have the following virial equation for a real gas:

$Z = \frac{PV_m}{RT} = 1 + \frac{B}{V_m} + \frac{C}{V_m^2}$

I would like to transform the coefficients $B$ and $C$ so the equation is expressed in terms of pressure:

$Z = \frac{PV_m}{RT} = 1 + B'P+ C'P^2$

My book says that the transformations are:

$B' = \frac{B}{RT}$ and $C' = \frac{(C-B^2)}{(RT)^2}$

How are these derived? I can get the first one by:

$Z(\frac{1}{V_m}) = Z(P)$ and only considering $B$:

$1 + \frac{B}{V_m} = 1 + B'P$,

$\frac{BP}{RT} = B'P$,

$\frac{B}{RT} = B'$.

For the second one I also consider C:

$1 + \frac{B}{V_m} + \frac{C}{V_m^2}= 1 + B'P + C'P^2$,

$\frac{BP}{RT} + \frac{CP^2}{(RT)^2}= \frac{B}{RT}P + C'P^2$,

$\frac{CP^2}{(RT)^2}= C'P^2$,

$\frac{C}{(RT)^2}= C'$.

This result (mine) differs to the one given by the book. They have an additional $-B^2$ term in the numerator. Where is that term coming from?


texts: How to solve this dimensional analysis/stoichometry problem

texts:
This problem has been giving me a headache for the last hour on my homework. Does anyone have any pointers in the right direction?

  Finally, on January 28th, 2014, in Germany, a barn containing 90 cows exploded when a stray spark caught the methane trapped in the building on fire. Assume that the 90 cows were producing 250 L of methane per day and that there was a 15 hour collection in the barn when it ignited. What mass of water was generated in the explosion?

This problem is specifically about combustion, and I'm assuming I'd have to multiply the combustion equation for methane by 90 somehow. I'm also assuming I'd have to divide 250 / 15 to get the correct liters of methane produced at this time.


texts: How to predict disproportionation products from Frost diagram?

texts:
I read that concave points in a Frost diagram disproportionate. But what are the products of the disproportionation?

For example, in the Frost diagram for manganese at pH = 0, the species $\ce{HMnO4-}$ is concave with respect to $\ce{MnO4-}$ and $\ce{H3MnO4}$. But at the same time, it is also concave with respect to $\ce{MnO4-}$ and $\ce{MnO2}$. How do I know which set of products $\ce{HMnO4-}$ disproportionates to in acidic solution at pH = 0?


texts: Does the van der Waals equation remain valid when repulsive intermolecular forces dominate?

texts:
The van der Waals equation for a real gas is:

$$RT =\left(p+\frac{a}{V_\mathrm{m}^2}\right)(V_\mathrm{m}-b)$$

We have understood this formula by saying that $a$ is the term which is for force of attraction between the gas molecules and thus the pressure of a real gas will be less than that of an ideal gas.

Therefore some factor must be added to the pressure of a real gas to make it equal to ideal gas pressure so that it can be used in $p_\mathrm{ideal}V_{\mathrm{ideal}}= nRT$.

Also, if we see the compressibility factor graph , suppose for $\ce{N2}$:

(Source: TutorVista)

If $Z < 1$, then attractive forces are dominating. We see that after a particular temperature, the value of $Z$ becomes greater than $1$, implying that the repulsion forces are dominating in $\ce{N2}$.

Now, since repulsive force dominates, the pressure of the real gas will increase and be greater than that in ideal case.

To find the $p_{\mathrm{ideal}}$ now, we will need to deduct some value from the $p$ of real gas, which means $a$ should be negative. However, this is not so as $a$ can never be negative.

No value can ever be deducted from $p$ in the van der Waals equation.

Then how does the van der Waals equation still work and give the correct data?


texts:
Why do we have glycogen in the muscles and not glucose?

I know this is in contrast to liver cells, which, on demand, readily do break down their stored glycogen into glucose and send it through the blood stream as fuel for other organs. Glycogen is also a suitable storage substance due to its insolubility in water, which means it does not affect the osmotic pressure of a cell.


texts:
Two questions:

First, how does the gate provide a positive charge by running a current through it? I really just don't see how this positive charge could be achieved, unless you had some sort of battery in the gate itself and attached a wire to donate some of the electrons flowing through to the cathode of some other battery. Is it possible to get electrons out of the gate by some other means?


texts:
I receive $120~\mathrm{mL}$ bags of medicine in sterile water. The medicine is refrigerated and then packed with a significant amount of ice packs in an insulated bag. Generally three times the volume of all the medicine. When I remove the ice packs, they are still solid two hours after being packed. So, they are very cold.

Is there enough energy to freeze the water directly in contact with the ice packs when packed and then melt immediately? The air temperature is around $21~\mathrm{^\circ C}$ at the time.


texts: Does sulfuric acid formed in a previous step dehydrate a secondary alcohol?

texts: In the following reaction won't the sulphuric acid dehydrate the secondary alcohol after it's formed?


texts:
Problem
From the theoretical tour of the Mendeleev Olympiad in Chemistry:

a) Calculate the minimal amount of sulfuric acid that should be diluted with water to yield $\pu{100 mL}$ of solution that could completely dissolve $\pu{0.4 g}$ of rust.

Answer

 a) After the dissolution of a $\pu{0.4 g}$ portion of rust, the total concentration of iron(III) in a $\pu{100 mL}$ portion of solution is $\displaystyle\frac{\pu{0.4 g}}{\pu{107 g mol-1}\times\pu{0.1 L}} = \pu{0.037 M}.$ As there are no competing reactions (sulfate ion does not form stable complexes with iron), it is easy to find the minimal solution acidity after the dissolution using the solubility product $K_\mathrm{s} = [\ce{Fe^3+}][\ce{OH-}]^3$:

 $$[\ce{H+}] = K_\mathrm{w}\left(\frac{[\ce{Fe^3+}]}{K_\mathrm{s}}\right)^{1/3}  = \pu{0.0097 M},$$

 that is $\pu{0.49 mmol}$ of sulfuric acid in a $\pu{100 mL}$ solution. In addition, $\pu{0.037 M}\times 3\times\pu{0.1 L}\times 1000/2 = \pu{5.6 mmol}$ of sulfuric acid has reacted with iron hydroxide, therefore, the total amount of sulfuric acid required for the dissolution is $\pu{6.1 mol}$ (2 points).

My thoughts
This task seemed incredibly easy, but the solution overcomplicated some aspects, from my point of view.
The concept of "rust" was simplified in this problem since it was stated from the beginning that here "rust" means, in fact, $\ce{Fe(OH)3}.$ So, I wrote the chemical equation (which, because it is a neutralization reaction, should have an astonishingly large constant and is an equilibrium practically shifted fully towards the products):
$$\ce{2 Fe(OH)3 + 3 H2SO4 -> Fe2(SO4)3 + 3 H2O}$$
$\ce{Fe(OH)3}$ has a molar mass of $\pu{106.87 g/mol}$. Finally, the amount of sulfuric acid is
$$n(\ce{H2SO4}) = \frac{\pu{0.4 g}}{\pu{106.87 g mol-1}}\times\frac{3}{2} ≈ \pu{5.61 mmol}.$$
After checking the solutions, not only I realized I were wrong (even though my final answer was part of theirs), but I also were confused by the explanations given. For some reason, the solubility product was included, even though its constant is so insignificantly small in comparison to the constant associated with the reaction I wrote above.
What I thought was happening in this system was that $\ce{H2SO4}$ would neutralize the rust and that was basically it. While I am familiar with the concept of equilibrium and I understand that $\ce{H2SO4}$ doesn't nullify the concentration of $\ce{Fe(OH)3},$ in the light of the huge constant the neutralization is expected to have, the solubility product, $K_\mathrm{sp},$ should be negligible.
However, it seems that not only it is not negligible, but it also seems to be able to influence the final result significantly. But why is that? Why do we bother calculating the additional acidity from the hydroxide ions resulted in the solubility reaction? Why can't we solve the problem stoichiometrically, the way an inorganic chemist would approach it? Please correct my reasoning wherever you consider it wrong.


texts: Why do more substituted alkenes undergo epoxidation, but the less substituted alkenes undergo hydrogenation?

texts:
We know that, in case of a choice, catalytic hydrogenation will hydrogenate the less  substituted alkene, because the less substituted alkene is less stable. But, we also know that, in case of a choice, peroxyacids perform epoxidation of the more substituted alkenes, because the latter are more electron-rich (i.e. more nucleophilic) (details)

In one case, we are favoring the stability of the pi bond. But in another case, we are prioritizing the nucleophilicity of the pi bond. Why is this so?

I believe this definitely has something to do with their respective mechanisms, which I've studied from Libretexts (hydrogenation and epoxidation). The only difference I see is that in hydrogenation, the pi bond first attaches to the catalyst surface, and then a hydrogen atom (already attached to that surface) is transferred to the pi bond. But, in epoxidation, the alkene directly attacks the electrophilic $\ce{-OH}$ group of the peroxy acid. So, this explains the need for more nucleophilicity in the latter case, but how does this explain the need for less stability in the former case? Or is this direction of reasoning entirely wrong?


texts: Which is a better oxidising agent: concentrated nitric acid or dilute nitric acid?

texts:
I was reading the Wikipedia page on nitric acid and saw the reaction of concentrated $\ce{HNO_3}$ and dilute $\ce{HNO_3}$ with $\ce{Cu}$.
It is mentioned that:

Copper reacts with dilute nitric acid at ambient temperatures with a 3:8 stoichiometry:
$$\quad\qquad\qquad\qquad\ce{3 Cu + 8 HNO_3 -> 3 Cu^{2+} + 2 NO + 4 H_2O + 6 NO_3^−}$$
With more concentrated nitric acid, nitrogen dioxide is produced directly in a reaction with 1:4 stoichiometry:
$$\ce{Cu + 4 H^+ + 2 NO_3^− -> Cu^{2+} + 2 NO_2 + 2 H_2O}$$

My question is: If concentrated nitric acid is a better oxidising agent, then why does it oxidises only 2 moles of $\ce{Cu}$ per 8 moles of nitric acid against the 3:8 ratio in dilute one. Why is there change of -1 in oxidation state of $\ce{N}$ in concentrated solution as opposed to -3 in dilute solution?
Does this indicate dilute $\ce{HNO3}$ is better oxidising agent than concentrated one?


texts: Deducing compounds from spectroscopic data for isomers of formula C4H8O

texts:
Here's the problem:

I already know the $\pu{3600 cm-1}$ line indicates the $\ce{-OH}$ group and the $\pu{1640 cm-1}$ line indicates the $\ce{C}$-double-bond-$\ce{C}$ alkene.

From the $\ce{^13C}$ NMR data: the two carbons with chemical shifts of 100+ are $\mathrm{sp^2}$ carbons and the remaining two are $\mathrm{sp^3}$ carbons.

I have tried to work out compound D, and suggest this structure:

I am stuck on figuring out compound C. I suggest the structure below, but am unsure whether if it is correct.


texts:
I'm having trouble with this question from a first year undergraduate chemistry paper. The question states

How many lines will appear in the line spectrum of the Boron atom if the valence electron in the ground state is excited to the 3p orbital?

If in another experiment, the electron of $\ce{B^4+}$ in $n=6$ is excited to $n=7$, how many lines will appear in this line spectrum?

Boron has an electron configuration of $\rm{1s^22s^22p^1}$, so this means it would have to jump from $2\rm{p}$ through $3\rm{s}$ to $3\rm{p}$. I don't understand how I would work out the number of lines that would be seen in the emission spectrum though.
Update:
The memo gives an answer of 6 possible lines - I think the reasoning behind this is that for the valence electron in the ground state (which is 2p) it could jump (depending on how much energy is given to the system) from 2p -> 3p or 2p->3s or 3s->3p but because we don't know the spin on the electron, whether positive or negative we say there are 6 possible lines (3 lines for each possible electron state). Not sure if that reasoning makes sense or not?


texts: How it is possible to make Aqua Regia in the lab?

texts: How to make "Aqua Regia" in the lab conditions? Which lab equipment must be used?


texts: Does silver oxide react with hydrogen sulfide?

texts:
Electronic connectors are often silver plated. However, silver tarnishes fairly quickly and heavily. There exists a widespread misconception that the tarnishing of silver contacts is harmless, because silver oxide has about the same conductivity as silver itself. The problem however is that silver does not oxidize under normal conditions. The tarnish on the contacts is not silver oxide, but silver sulfide that develops due to the presence of some hydrogen sulfide in the air. Unlike silver oxide, silver sulfide is not a conductor, but a semiconductor with various potential adverse effects for the connection.

I have come across a reference that suggests oxidizing silver contacts before using them in order to prevent the development of the silver sulfide layer. This implies that silver oxide does not react with hydrogen sulfide in the air under normal conditions. Is this claim correct?

EDITS

I have corrected the typo by changing "sulfur dioxide" to "hydrogen sulfide" in the title and body of the question. Thanks for pointing this out in the answer!


texts: What is pre-concentration (context: Breath analysis)?

texts:
What is the meaning of pre-concentration both in general and specific to this context of

a) "In addition to consistent sampling protocols,.. pre-concentration, and analysis of breath samples require standard methodology, calibration standards..."

b) "Offline breath analysis involves some form of pre-concentration of analytes followed by a separation step using high-resolution GC-MS based detection"


texts: Double surface in the pressure temperature concentration curve for a binary mixture

texts: In the 3 dimensional diagram given, when a constant pressure plane intersects with the double surface, it produces a looped curve without a maxima or minima. What is the double surface and how is the looped curve produced? And since the line joining $T_\ce{A}$ and $C_\ce{A}$ is the temperature-pressure curve of pure A and similarly for B, I cannot understand what the curve joining the 2 critical points (of A and B) means.


texts: Is helium-4 a liquid at zero temperature and zero pressure?

texts:
As far as I know, for all substances other than helium, if you extrapolate the solid-gas line on the phase diagram, it passes through the origin. That is, no matter how low the temperature is, you can still vaporize the substance by lowering the pressure, and no matter how low the pressure is, you can still freeze the substance by lowering the temperature.

This makes sense to me on thermodynamic grounds. If we keep lowering the pressure at a given temperature, the entropy of vaporization increases without bound (although only logarithmically) and at some point the gas phase is favoured, whereas if we keep lowering the temperature at a given pressure, then the entropy term in free energy becomes negligible and the solid phase is favoured by enthalpy.

The phase diagrams I've found online for helium-4, however, don't follow this rule. They seem to show that helium-4 is exclusively a liquid in a neighbourhood of the origin. Example here: http://ltl.tkk.fi/research/theory/helium.html

I wonder whether this is true, and if so, how it can be possible. How can it be that no matter how low the pressure is, helium-4 will not boil? I understand that superfluidity is a quantum phenomenon but I can't see how my previous reasoning could not apply.

Edit since some people think this is a duplicate: Again, my question is whether helium-4 will not boil at zero pressure, and if so, how that can be; it concerns the liquid-gas transition and not the solid-liquid one.


texts: Can Hückel's rule be applied to inorganic compounds?

texts:
Hückel's rule helps us know which molecular orbital, bonding or antibonding contains more electrons, and it is derived from the same. And on the basis of this, we can find out the stability of the compounds.

But, this rule was specifically introduced for cyclic organic compounds to know if they are aromatic or not. But again, the reasoning remains the same across all compounds, that is, if more electrons are in BMO than in ABMO – stable; otherwise not.

So, I was wondering why we couldn't use the same rule for cyclic inorganic compounds? I don't know, but I might be missing out somewhere. Any help would be appreciated.

Also: This pdf here, agrees that Hückel's rule can be applied to inorganic cyclic compounds, but with a 'maybe'.

  Whereas organic
  compounds need to be planar to be aromatic, no such limitation applies to inorganics. An inorganic compound may be expected to be aromatic if it satisfies a “counting rule”; the familiar
  Hückel rule applies to planar aromatics and the Hirsch rule works for spherical analogs.


texts:
I have to solve an exercise that I've been trying for a long time without success.

Information that I have:

  pH @ certain temperature of an aqueous dissolution of an acid
  molar concentration of the acid

Unknown:

  approximate $\mathrm{p}K_\mathrm{a}$ (is not meant to be calculated with calculator I suppose that is the reason they say "approximate")

So far I tried to express the chemical equation and its two steps to finally get $\ce{H3O+}$ and an oxid.
I've calculated backwards the Hydronium concentration $[\ce{H3O+}]$ with the $\mathrm{pH}$ formula. $$ \mathrm{pH} = -\log([\ce{H3O+}])$$.
I've written down the formula to calculate $K_\mathrm{a}$ from where I expected to be able to calculate $\mathrm{p}K_\mathrm{a}$.

I don't know how to extract now the concentrations of every component on the $K_\mathrm{a}$ formula in order to be able to calculate that. Moreover, what am I suppose to do with the temperature?

I hope you can give me guidance in the process to solve such exercises.


texts:
I m a high school chemistry learner. I have learnt that acids are substance that can liberate H+ on hydrolysis. For that they must be connected to an electronegative atom.
In carbonyl ( mainly aldehyde and ketone) the H atom is not directly attached to Oxygen. So I may not consider it as an acid.
But today while performing a chemistry practical when I added Blue litmus solution to aldehyde it turned red.
This leads me to a confusion about whether they are acidic or neutral or What can I infer from the colour change of blue litmus.


texts: What are the products for the redox reaction HCl + SnCl₂ + KMnO₄?

texts:
In the redox reaction, where $\ce{HCl}$ is the excess reactant do these reactions produce following half reactions?
\begin{aligned}
(1)&&\ce{SnCl2 &-> Sn^{4+} + 2e-}\\
(2)&&\ce{8H+ + KMnO4 + 5e- &-> Mn^{2+} + 4H2O}
\end{aligned}

Where does the $\ce{HCl}$ come into play here, or do you consider it at the end when you have a final equation?

This is a redox reaction where $\ce{KMnO4}$ was added to $\ce{HCl}$ and $\ce{SnCl2}$ (hydrochloric acid was simply used as an excess reagent)


texts: Initial guess for Unrestricted Hartree-Fock calculation

texts:
I am implementing an Unrestricted Hartree-Fock (UHF) calculation, following Ref. [1]. It works fine for a odd number of electrons ($N_\alpha\neq N_\beta$) since, despite the same initial guess for $\alpha$ and $\beta$ spins, the density matrices at the second step will be different and I get different orbital energies for different spin orbitals. The problem arises when I have an even number of electrons ($N_\alpha=N_\beta$) . Authors of Ref. [1] state that (p. 216)

  When $N_\alpha=N_\beta$, a restricted solution of Roothaan equations is a solution to the unrestricted Pople-Nesbet equations. This restricted solution always exists and necessarily results if an initial guess $P_\alpha=P_\beta$ is used. [...] In seeking this second solution [the unrestricted one], it is imperative that an initial guess $P_\alpha \neq P_\beta$ be used or the equations will necessarily yield the restricted solution.

Unfortunately there is no clue on which initial guess should be taken. In fact in this book, for the restricted case, the Fock matrix is initially approximated by the core Hamiltonian (Guess=Core in Gaussian09), which consists in taking $P_\alpha=P_\beta=0$.

Since the core Hamiltonian guess cannot be differentiated for $\alpha$ and $\beta$ spins, I implemented Huckel guess (Guess=Huckel in Gaussian09) following Ref. [2] which consists in approximating the initial Fock matrix with the following:
$$
F_{ij} = KS_{ij}\frac{H_{ii}+H_{jj}}{2}
$$
$H$ is the core Hamiltonian, $S$ is the overlap matrix and $K$ is a constant. I tried to slightly change the coefficient $K$ (the suggested value is 1.75) for different spins in order to get a different initial guess. However, the SCF procedure converges towards a value that is higher in energy than the restricted solution. This should not be the case, in particular for a dissociating $\ce{H2}$ molecule (i.e. distance $R=4.4$ Bohr).

How I can properly differentiate the initial guess for $\alpha$ and $\beta$ spins?

EDIT

The reference of Gaussian09 states the following:

  Requests that the HOMO and LUMO be mixed so as to destroy α-β and spatial symmetries. This is useful in producing UHF wavefunctions for singlet states. [...]

I belive that this is the solution to my problem, but what does actually means HOMO and LUMO be mixed in practice (i.e. before starting the calculation)?

[1] Szabo and Ostlund, Modern Quantum Chemistry, Dover, 1996.

[2] M. Lee et al., Extended Hückel and Slater’s rule initial guess for real space grid-based density functional theory, Computational and Theoretical Chemistry, 2015.


texts: Why can't alcohols turn blue litmus red?

texts: I came across the fact that alcohols cannot turn blue litmus red. The fact confuses me as they are acidic and acids do turn blue litmus solution red. What prevents alcohols from turning blue litmus solution red?


texts: Why does superglue lose strength at high temperatures?

texts: I'm not a chemist. When I superglue my fingers together, by accident, I put them under warm water to peel off the superglue. Why does superglue become less "sticky" at higher temperatures? Is it the water or the temperature?


texts: Total number of stereoisomers of cyclobutane-1,2,3,4-tetracarboxylic acid

texts:
Question

Find all stereoisomers of:

My attempt
I got four isomers, and none of them seem to be optically active as they either have a plane of symmetry or a point of symmetry:

However, my sir keeps insisting there are five isomers. Could anybody help me identify the fifth one?


texts: How to calculate galvanic cell spontaneity?

texts: I was wondering how to calculate cell spontaneity for a galvanic cell. Do you just look up the enthalpy values of electrode reactions? Does the electrolyte solution you choose have an effect on cell spontaneity?


texts:
What is the difference between Hexagonal Close Packing (HCP) structures and the hexagonal crystal Bravais lattice? I've looked up some sites but can't seem to understand them. It would help if you backed up the answer with your specific explanation of Bravais lattices and unit cells.

Edit:
I thought the difference was that the lattice consisted of many unit cells and the unit cell packing could be like hexagonal, cubic or simple. But then I looked at the stoichiometric defects which talked about molecules being in interstitial spaces. But in the unit cell, the spaces are already filled. So how is that possible.


texts:
I am doing some research on indoor environmental quality and come across a number of spikes in CO in a dwelling.

This is a dwelling in central London with no gas-fired equipment: electric cooker and heating from a centralised district heating system.

Could this be from cooking? And/or people themselves?


texts: Do Sodium Alkynides react with esters in the same way that Grignard reagents do?

texts: We know that Sodium alkynides react with aldehydes and ketones like Grignard reagents. But do they behave the same way with esters?


texts: Why does hydrogen bonding take place? Is there any kind of electron donation? Or does something like an ionic bond take place?


texts: Can ICE tables give two solutions? What does this mean physically?

texts:
The following question comes from General Chemistry: Principles and Modern Applications, 11th ed. by Pettruci.

  Exercise 15-33. A mixture consisting of 0.150 mol H2 and 0.150 mol I2 is brought to equilibrium at 445 °C, in a 3.25 L flask. What are the equilibrium amounts of H2, I2, and HI?
  $$\ce{H2(g) + I2(g) <=> 2HI(g)}\qquad K_c=50.2\text{ at }445\,\mathrm{^\circ C}$$

First, I found the concentrations of H2 and I2:
$$
\begin{aligned}
\phantom{}[\ce{H2}]=[\ce{I2}]&=\frac{0.150\text{ mol}}{3.25\text{ L}} \\
&=0.0461538\text{ M}
\end{aligned}
$$

Setting up the ICE table:

$$
\begin{array}{|l|c c c c c|}
\hline
&\ce{H2}&+&\ce{I2}&\rightleftharpoons&\ce{2HI} \\
\hline
\text{Initial}&0.0461538&&0.0461538&&0 \\
\text{Change}&-x&&-x&&+2x \\
\text{Equilibrium}&0.0461538-x&&0.0461538-x&&2x \\
\hline
\end{array}
$$
Then,
$$
K_c=50.2=\frac{(2x)^2}{(0.0461538-x)(0.0461538-x)}.
$$
Most solutions I've seen for similar problems involve taking the square root of both sides of this equation. However, they only take the principal root, effectively ignoring a second valid solution. Here, I'll do the proper solution for finding $x$:
$$
\begin{aligned}
 \\
50.2&=\left(\frac{2x}{0.0461538-x}\right)^2 \\
\sqrt{50.2}&=\pm\frac{2x}{0.0461538-x}
\end{aligned} \\
\begin{aligned}
7.0852&=\frac{2x}{0.0461538-x}&&\text{or}&7.0852&=-\frac{2x}{0.0461538-x} \\
0.327009-7.0852x&=2x&&&0.327009-7.0852x&=-2x \\
0.327009&=9.0852x&&&0.327009&=5.0852x \\
x&=0.0359936&&&x&=0.064306
\end{aligned}
$$
As you can see, there are two positive (and therefore, valid) solutions for $x$. However, only one of the solutions results in a positive $[\ce{H2}]_\mathrm{eq}$:
$$
\begin{aligned}
\phantom{}[\ce{H2}]_\mathrm{eq}=0.0461538-x
\end{aligned}
\\
\begin{aligned}
\phantom{}[\ce{H2}]_\mathrm{eq}&=0.0461538-0.0359936&&\text{or}&[\ce{H2}]_\mathrm{eq}&=0.0461538-0.064306 \\
&=0.0101602\text{ M}&&&&=-0.0181522\text{ M}
\end{aligned}
$$
And $x=0.0359936$ does indeed lead to the correct answer according to the textbook.

My question is: was it just a coincidence that I was able to eliminate one of the possible solutions for $x$? In other words, is there a scenario where I could end up with two possible $[\ce{H2}]_\mathrm{eq}$s? If not, what forbids this?

Edit: To reiterate, I am aware that one of the solutions is to be eliminated for being "non-physical". My question is whether it is possible for both solutions to be physical.


texts: Why aren't the amine groups in the nucleic acid bases protonated?

texts:
Nucleobases G, C and A carry an amine group ($\ce{-NH2}$). In amino acids, the amine groups are considered protonated at physiological pH. Why isn't it the case for the amine groups of nucleobases?

I found some references discussing the protonation of nucleobases, but I am not enough expert in either DFT (http://www.ncbi.nlm.nih.gov/pubmed/19049279) or Mass Spectrometry (http://www.ncbi.nlm.nih.gov/pubmed/17920289/) to  get a rational from this. Plus, neither they nor the references they cite and that I have briefly examined actually consider protonation of the amine groups.


texts:
I've recently moved to a old house and found some stuff in the attic, along that I found some really beautiful silverware(??) that unfortunately was VERY tarnished, one of the pieces was totally black while some had small places where I could see, in the back of one of them there's a label stating Silver 90.

I googled and found that using a solution of hot water, baking soda, salt, vinegar and strips of aluminium foil would help clean them. I submerged them and after some time I took them out and started to scrub them and the gross black stuff was going out, showing some silver and some yellowish. I them took a sponge and kind got carried away.

The pieces now all have this yellowish stains.

The one that was completely black had no silver-color in any part of it after cleaning, except the bottom, while the rest is all yellow now.

Here's one of the pieces

(the back is a white paper, white-balance is crazy with this piece)

My question is: Is this yellow stain any kind of dirt that wasn't removed in the process, or is this the underlayer of the piece(meaning that the silver is gone in those parts)? And above all, is the method used the best way to remove dirt from silver?


texts: How to rationalise the difference in the melting points of acids and alcohols with inter molecular forces?

texts:
Acids: arachidic acid, palmitic acid, lauric acid, etc.
Alcohols: butan-1-ol, pentan-1-ol, etc.

The melting points of acids with $\ce{-COOH}$ at the end compared to melting points of alcohols, $\ce{-OH}$ at the end, is higher. I need to relate this to intermolecular forces. I was going to say that because of many more electrons in the acids, there are greater London dispersion forces and also more polarity (dipole dipole forces) because of the $\ce{COOH}$ at one end. Is this correct?


texts: Understanding how to choose the right reaction for electrochemistry

texts:
I am quite new here and studying a bit of electrochemistry. In the course of my studies I encountered a problem I couldn't figure out:

  A sample of iron ore weighing $\pu{0.2792 g}$ was dissolved in an excess of a dilute acid solution. All the iron was first converted to $\ce{Fe(II)}$ ions. The solution then required $\pu{23.30 mL}$ of $\pu{0.0194 M}$ $\ce{KMnO4}$ for oxidation to $\ce{Fe(III)}$ ions. Calculate the percent by mass of iron in the ore.

Having thought about this question somewhat, it is clear that I will have to use  the redox reactions for iron of

\begin{align}
  \ce{Fe^0(s) &-> Fe^2+ + 2e-} \\
  \ce{Fe^2+ &-> Fe^3+ + e-}
\end{align}

Furthermore, seeing as the reaction is occurring in an acidic environment, I thought to make the assumption that $\ce{KMnO4}$ will dissociate into its constituent ions, leaving me with picking between either the reaction of

$$\ce{MnO4^- + 2H2O + 3e- -> MnO2 + 4OH-}$$

or

$$\ce{MnO4^- + 8H+ + 5e- -> Mn^2+ + 4H2O}$$

When it comes to the technical working of this problem I think I can sort it out, but my issue resides in finding the correct mechanism. If anyone is willing to help me out with what I am sure is a simple problem for the experienced members of this community, I would be extremely grateful.

In addition to this I was wondering if anyone could recommend a resource to learn more holistically about these sorts of reactions, as this question in my textbook is part of the challenge portion, and hence there is not as much material regarding the exact mechanisms of these processes.


texts: Is molecular weight of proteins additive?

texts:
I have an elementary question regarding calculation of molecular weight of a complex of two proteins. Essentially, I have two proteins binding as

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

I have the concentration of [A] and [B] in ng/ml, which I can convert to nM using its molecular weight (available in kDa). I have only concentration of [AB] in ng/ml, but I am not able to convert that into nM. Is the assumption that molecular weight of [AB] is equal to sum of molecular weights of [A] and [B] correct assumption?

I am not able to see the intuition behind this logic, and if someone can help me here, I would be very thankful.


texts: There is a problem that states: Find the molecular geometry of each molecule and the hybridization of each atom in the molecule. The two molecules are HNO and HCN. I found HNO to be sp3 hybridized and HCN to be sp hybridized. However, it says that only N and O are hybridized in the first. While all three are hybridized in the second. Why is hydrogen listed as sp hybridized?


texts: Spontaneous and Favoured Chemical Reactions

texts:
I have some problems in understanding what is the difference between a reaction which is spontaneous and a reaction which is termodynamically favoured. I'm looking at the equation of Gibbs Free Energy:
$$\Delta G = \Delta G^0 + RT ln \prod a_i^{\nu_i}$$
I know that a reaction is spontaneous if $\Delta G <0$ and a reaction is Termodynamically favoured at a given T, by convenction, if $\Delta G^0<0$.
So the condition of $\Delta G^0<0$ is a necessary, but not sufficient condition to be spontaneous?
Thanks a lot!!


texts: What methods could be used for determining the concentration of Zn2+ in a solution?

texts: I know that complexometric titration with EDTA is one method. What other methods could be used?


texts: What does the intramolecular aldol condensation of 6-oxoheptanal form?

texts:
I know that when 6-oxoheptanal is treated with NaOH, an intramolecular aldol condensation will take place. But will a five-membered ring or seven-membered ring be formed?

I know that the five-membered ring is more stable in comparison to the seven- membered ring, but as per the mechanism of aldol condensation the first step is removal of acidic hydrogen (which is also the slowest step i.e. the rate determining step {if I am not wrong}).

So if I remove the acidic hydrogen on C-7 (the terminal methyl group), then the (primary) carbanion formed will be more stable than if I were to deprotonate on C-5.

So I think that the major product should be the seven-membered ring.

Am I right? Or is my reasoning incorrect?


texts:
Chiral molecules are classified as dextrorotatory (+) or levorotatory (-) depending on whether they rotate plane-polarized light (ppl) to the right or left.

My question is, how is such a measurement made? What instrumentation is used and how would you determine that ppl has been rotated right or left?


texts: At what temperature will proteins and fats boil in a vacuum?

texts:
A question was asked on another stackexchange site:

  This is not nice perspective, but eventually it will happen. An astronaut falls out of spaceship because of damage caused by collision with other object, or because of suit decontamination. The fluids from the body would evaporate, and if any bacteria would survive, than only as spores. Does it mean the perfect mummification of the body? Or there will be some decay, caused by enzymes from damaged cells, for example?

Given that the water in the body will outgass taking with it much of the rest of the body, are there any cited sources that specify the pressure at which proteins, fats and bones will break down and become vapour?


texts: Why does increasing the temperature of a *solid* increase its entropy?

texts:
I understand why increasing the temperature of a fluid would increase its entropy, as the particles are free to move, and therefore an increase in kinetic energy would allow the particles to move more, thus increasing the fluid's entropy.

However, this doesn't make sense to me in the case of a solid - increasing the solid's temperature would result in an increase in K.E., but this would only result in the particles vibrating more. As entropy is defined as the 'disorderliness' of a system, and the molecules in a solid always remain in the same 'order'  regardless of temperature, how is temperature proportional to entropy in a solid?


texts: How do I find out the number of bonds an atom must link to?

texts:
I've always been told that carbon bonds with four hydrogens and that nitrogen bonds with three hydrogens, like in benzene and hexazine, respectively.

What's the name of this type of bonding and how does one come up with the number?


texts: What kind of chemical used in a chromatography run could be denoted with the letters D.H.?

texts:
A fellow translator is having trouble translating (into Russian) the mysterious D.H. abbreviation in the following passage:

  Slight variations of the ratio of the mobile phase constituents or adjustments of the mobile phase flow-rate can be made occasionally, in order to provide a suitable elution times for Methyl p-hydroxybenzoate and D.H., and to meet the requirements of the system suitability tests.

If by some chance it's a widely known compound, or at least there are several chemicals that could be abbreviated thus, I'd be grateful for answers. A crapshoot, I know, but I became curious.

It could be some rare chemical; in that case it would be futile to try figuring it out.


texts: Reading number of outer shell electrons and other properties from periodic table?

texts:
How can one read from the periodic table the number of outer shell electrons that an atom has, to predict how these atoms will make bonds with other atoms? For example to see that hydrogen ($\ce{H}$) has 1 electron free, while carbon ($\ce{C}$) has 4 and oxygen ($\ce{O}$) has 2? This allows us to infer that carbon can make four bonds with 4 different hydrogen atoms. It's not clear what in the periodic table would tell us this; it is neither in the group nor in the period of an atom, it seems.

Related to this: can someone summarize concisely all the properties (like number of free outer shell electrons) that one can read off about each element from its position in the periodic table? I was having a hard time finding a concise summary of these.


texts: I have read about inositol nicotinate which is used as a medication for deficiency in vitamin B-3. I think that if acetic acid was applied to this medication it would form pyridinium ion and acetate ion, but I don't know if the acetic acid will react with inositol in a transesterification reaction, and form nicotinic acid and ionsitol acetate, so if the latter happens how could I prevent it and push the reaction towards the first route?


texts: Carbon with two double bonds and oxygen name

texts:
I have a compound like this:

$$\ce{CH2=C=O}$$

I wonder if it is a functional group or a normal group. As a functional group I couldn't find out.
Is it a normal compound or a functional group and what is it's
IUPAC name


texts: Manuals for a Cahn TG-171 Thermogravimetric Analyzer

texts:
Recently a Cahn TG-171 Thermogravimetric Analyzer was donated to my school. We did not get a service or user's manual with it, and some of it still needs to be put back together.

I have tried to contact Thermo Fisher who bought Cahn Instruments, but they no longer support the TG-171. Any sort of information on the setup of this instrument would be appreciated.

Update:
In particular, one of the main questions I now have is "what must I do to use the balance?" Currently there are eccentric screws (as shown in the photo) preventing the balance beam from moving so it is unable to register mass change. Do I loosen both sets and use a counterweight of a calibrated mass? Is there a common procedure for setting up balances of this type?


texts: Why are atomic radii calculations all over the map?

texts:
If you look up an element on Wikipedia, it will list covalent, ionic, Van Der Waals, high-and-low -spin, and finally 'empirical atomic radius'.

Then, on the page for atomic radius, the chart of 'empirically-determined atomic radii' shows numbers that are all higher than on the individual elements' pages.

Then, farther down on the Atomic radius page, it lists 'calculated radii' which are even higher!

(Almost always, in all these cases, these numbers are supposedly referring to covalent states).

The latest measurements seem to be getting further and further away, smaller and smaller, from the calculated radii.  What gives?

The 'high-spin covalent' number refers to electron spin, not nuclear, right?  But when is a covalent bond in a high spin state?  I thought most molecules were in a singlet state?


texts: What determines the coefficients in the wavefunction of a hybrid orbital?

texts:
I was studying the hybridization of carbon atoms and I came to figure out that the $sp$ hybridization wavefunction is given as
$$|sp_{+}\rangle =\frac{1}{\sqrt{2}}\left(\psi_{2s}+\psi_{2p_x}\right)$$
$$|sp_{-}\rangle =\frac{1}{\sqrt{2}}\left(\psi_{2s}-\psi_{2p_x}\right)$$

From a simple mathematical point of view, Why don't I have states that look like the ones below?
$$\frac{1}{\sqrt{2}}\left(-\psi_{2s}+\psi_{2p_x}\right)$$
$$\frac{1}{\sqrt{2}}\left(-\psi_{2s}-\psi_{2p_x}\right)$$

Even for the $sp^2$ hybridization, the states are
$$\frac{1}{\sqrt{3}}\psi_{2s}-\sqrt{\frac{2}{3}}\psi_{2p_y}$$
$$\frac{1}{\sqrt{3}}\psi_{2s}+\sqrt{\frac{2}{3}}\left(\frac{\sqrt{3}}{2}\psi_{2p_x}+\frac{1}{2}\psi_{2p_y}\right)$$
$$-\frac{1}{\sqrt{3}}\psi_{2s}+\sqrt{\frac{2}{3}}\left(-\frac{\sqrt{3}}{2}\psi_{2p_x}+\frac{1}{2}\psi_{2p_y}\right)$$
I don't know how the construction of the hybrid orbitals are done mathematically...all that I know is that in case of the $sp^2$ hybrid orbitals, the formulation should be
$$\psi_{sp^2}=\alpha\psi_{2s}+\beta\psi_{2p_x}+\gamma\psi_{2p_y}$$
where $\alpha^2+\beta^2+\gamma^2=1$. But, mathematically there should be infinite solutions to this equation with this one constraint, where do this extremely precise values of $\alpha$, $\beta$ and $\gamma$ arise from?

P.S. :  I am not a student of chemistry, but just an engineer.


texts: Cheap spectral analysis to analyze water quality

texts:
I need some guide about spectrometers

I saw a lot of DIY spectrometers to analyze light.

Does anyone try to use those DIY spectrometers to analyze water?
 To detect heavy metals? or a chemical? or any pollutant in the water?

In theory, a spectrometer can detect chemical, biological components and a lot of other things (I have no idea about the technical part)

My question is, making this homemade spectrometer using a webcam, is enough to detect heavy metals in the water ?


texts: Which is better: Increase in collision frequency or increase collision energy

texts:
What would have a greater effect on the rate of a reaction, increasing the frequency of collisions or increasing the collision energy of the particles? (assuming that using a catalyst is not an option)

I got this from a past paper question:

Explain in terms of collision frequency and collision energy how the rate would change if the temperature was increased, and which of these causes the greater effect.

I know the first part of the question.

I assume that the collision energy is more significant, which is why we use catalysts, but not sure how.


texts: Why did the alpha-particles in Rutherford's experiment not collide with the electrons?

texts:
In Rutherford's experiment to show the existence of nucleus in an atom, the alpha-particles were exposed on the surface of certain metal i.e. gold. He observed that more than 99% of these particles were able to go straight and pass through the gold atoms. Thus he was able to conclude that atoms are mainly empty space.

But why did these particles not collide with the electrons present in the gold atoms? I think that the reason behind it is that the speed of the electrons travelling in orbits did not cause any obstacle in the travelling path of the alpha particles.


texts: Nomenclature of saturated aliphatic hetrocyclic amines with an alkyl group on the nitrogen

texts:
For example, how would I name the following amine?

Since two of the alkyl groups on nitrogen are linked to each other (in a ring), I can't figure out what they should be called, as they don't fit into the usual alkyl (methyl/ethyl/etc.) mould.


texts: Does water ionically bond to chloride ion?

texts:
This user absolutely insists that when a chloride ion is present in water (for example, when $\ce{NaCl}$ dissolves in water) that $\ce{Cl-}$ ion is ionically bound to the hydrogen atom:

https://biology.stackexchange.com/questions/34449/why-do-i-smell-chlorine-when-my-sinuses-are-clogged?noredirect=1#comment55324_34449

I then insist that this would form $\ce{H2OCl}$, but that's impossible due to the lack of valence electrons of $\ce{H}$:

https://biology.stackexchange.com/questions/34449/why-do-i-smell-chlorine-when-my-sinuses-are-clogged?noredirect=1#comment55386_34449

Who is right?


texts: Organic solvent for cleaning autosampler syringe

texts: I work in a laboratory where gas chromatography is used extensively. We handle phthalates. What are the possible wash solvent for autosampler syringe? I've been using acetone.


texts:
Does an axis of symmetry determine chiralty?

Is axis of symmetry considered a true symmetry?

From the above two links, I read that a compound having axis /alternating axis of symmetry is NOT necessarily achiral. For example, trans-1,3-dimethyl cyclopentane has an axis of symmetry but it is still chiral and hence optically active.

My doubt is, then why would we look for alternating axis of symmetry in the first place? Where/How is it useful?


texts: Why can air accommodate more water when the air has a higher temperature?

texts:
The amount of water(g) that air can accommodate depends on temperature. The absolute humidity then is defined as the percentage of water to air and decreases when the temperature decreases. The relative humidity is the ratio between the current and the maximum humidity, which increases with decreasing temperature. The temperature at which the relative humidity reaches 100% is called the dew point.

Anyway, why can air keep more water when it is warmer?


texts:
I have a question about fluorescence resonance energy transfer (FRET), and the requirements needed for this technique.

Q: Which of the following need to be met for FRET?

A) Strong overlap between the donor emission spectrum and the acceptor absorption spectrum
B) Molecules must be $<10\,\mathrm{nm}$ apart
C) Molecules must be $>10\,\mathrm{nm}$ apart
D) Low quantum yield of the donor
E) Small extinction coefficient of the acceptor

I'm aware that A and B are true, and C is not a requirement. But what about a low quantum yield of the donor or a small extinction coefficient of the acceptor? Do the size of these numbers really matter?


texts: How to find mole fraction of solvent and solute in a vapor pressure lowering problem?

texts:
At $25$ degrees celsius, the vapor pressure of pure benzene ($\ce{ C6H6}$) is $93.9$ torr. When a non-volatile solute is dissolved in benzene, the vapor pressure of benzene is lowered to $91.5$ torr. What is the concentration of the solute and the solvent, expressed in mole fraction?

Through Raoult's formula, I found that the mole fraction of the solvent, benzene, is:

$$P_{solution}=x_{\ce{C6H6}}\cdot P^{o}_{\ce{C6H6}}$$

$$91.5=x_{\ce{C6H6}}\cdot 93.9$$

$$0.974 = x_{\ce{C6H6}}$$

Now the only thing I am having trouble finding is the mole fraction of the solute:

$$x_{\ce{C6H6}}=\frac{n_{\ce{C6H6}}}{n_{\ce{C6H6}}+n_{\ce{solute}}}$$

I was wondering, is it even possible to calculate the mole fraction with just the given info? I think that it might not be possible, since I need the grams of solute dissolved or grams of solvent to do this.


texts: Synthesis of 3-Methylenecyclopentene from 1-methylCyclobutene

texts:
How do I make 3-Methylenecyclopentene

from 1-methylcyclobutene?

I thought to do ring opening reaction to add 1 carbon atoms but this won't add double bond in product. How to start please?


texts: diH2O, dH2O, and DI H2O. What do they mean?

texts:
What do $\ce{diH_2O, dH_2O}$, and $\ce{DI H_2O}$ mean?

I'm not asking for a description of deionized water and distilled water. I'm asking what the three abbreviations/formulas mean.

In other words, I'm asking someone to fill in the blanks below.

$\ce{diH_2O = \_\_\_\_\_}$
$\ce{dH_2O = \_\_\_\_\_}$
$\ce{DI H_2O = \_\_\_\_\_}$


texts: Problem regarding failure of equivalence concept

texts:
Chile salt peter, a source of $\ce{NaNO3}$ also contains $\ce{NaIO3}$. The $\ce{NaIO3}$ can be used as a source of iodine, produced in the following reactions.

  \begin{align}
\ce{IO3- + 3 HSO3- &-> I- + 3 H+ + 3 SO4^2-} \tag{i}\\
\ce{5 I- + IO3- + 6 H+ &-> 3 I2 (s) + 3 H2O} \tag{ii}
\end{align}

  One litre of chile salt peter solution containing $\pu{5.80 g}$ $\ce{NaIO3}$ is treated with stoichiometric quantity of $\ce{NaHSO3}$. Now an additional amount of same solution is added to the reaction mixture to bring about the second reaction. How many grams of $\ce{NaHSO3}$ are required in step (i) and what additional volume of chile salt peter must be added in step (ii) to bring in complete conversion of $\ce{I-}$ to $\ce{I2}$?

My working out using Mole concept:

My working out using equivalence:

Why does the equivalence concept not work?
Please tell me what is wrong and what is the correct method to use equivalence.


texts: Why do bonding and anti-bonding states split in energy (mathematically)?

texts:
I am a physicist, and when I hear about the splitting of energy levels for MO antibonding and bonding states, I have a rough intuition that tells me this is reasonable to expect, but I can't think of (nor find) a good formal explanation.

My best shot at understanding this is borrowing from Avoided Crossing and saying that if I have a 2 atom system with a total Hamiltonian $ H = H_1 + H_2 $ that is the sum of each individual atom Hamiltonians, then I can take the Eigenstates for each individual Hamiltonian as a basis.

$$\begin{align}
H_1 | \psi_1 \rangle &= E_1 | \psi_1 \rangle \\
H_2 | \psi_2 \rangle &= E_2 | \psi_2 \rangle
\end{align}$$

Then the total hamiltonian in this basis becomes,
$$\begin{align}
H &= \left(\begin{matrix}
E_1 & \langle \psi_2 | H_1 | \psi_2 \rangle \\
\langle \psi_1 | H_2 | \psi_1 \rangle & E_2
\end{matrix}\right)
\end{align}$$

In the limit of the atoms being really far apart, I would assume the off diagonal terms would vanish, and then the eigenstates are just the atomic orbitals. But if the atoms come closer together, then we get off diagonal terms which causes the splitting as described in avoided crossing.

Is this correct?


texts: How is Persian blue rock salt made and what does it contain that makes it look blue?


texts:
I was asked to find the pH of a diprotic species $\ce{BHA}$ where $B$ is the cation and $\ce{HA}$ is the anion given the first and second dissociation constant of acid $\ce{H_2A}$ and the base dissociation constant .

My book gives answer as $$\ce{[H+]}=\sqrt{K_{a_1} \left(\frac{K_w}{K_b}-K_{a_2}\right)}$$

I tried writing down the expression for the first and second dissociation constant and the base dissociation.Then I wrote mass balance as

$$\ce{[HA-]_{initial}=[HA-] + [H2A] + [A^2-]}$$

However I couldn't proceed after this. Any ideas.


texts: Potential energy surface when spin changes

texts:
I'm trying to compute potential energy surface of S4 molecule (in MOLPRO 2015) along S2-S2 bond (it has a trapezoidal shape) from equilibrium to the dissociation threshold, all the other coordinates are fixed. S4 is a singlet (0 unpaired electrons) in the ground state but a quintuplet once it's dissociated (2 independent S2 molecules in the ground state, each has 2 unpaired electrons). I tried to do CCSD(t) calculations with spin 0 and 2. With spin=0 I get the right energy at the equilibrium but too high energy at the dissociation limit and it's vice versa for spin=2. I need a single surface to solve the Schrodinger equation in so I was thinking about just taking minimum between the two surfaces but I'm not sure if it's a correct way to do it.

This problem doesn't seem to be that rare so I think there should be a well known way to tackle it. I think MRCI can use a mix of the two states, adjusting coefficients in the process to make the transition smooth, but I'm not sure how to properly do it.


texts: Does activation energy depend on steric factors?

texts:
I thought that activation energy depends on steric factors.
By Arrhenius equation it must depend on steric factors since $A$ depends on steric factors. $$k=A\cdot\mathrm e^{-\frac{E_\mathrm a}{RT}}$$ (for bimolecular reaction)

But my book says it doesn’t.

Does it depend on steric factors or not and why?


texts: Questions on nucleophilic substitution of haloalkane

texts:
In the nucleophilic substitution reaction of haloalkanes with  ammonia, instead of sharing it's lone pair with the carbocation, ammonia loses one of it's hydrogen and forms a primary amine, and the lone pair remains on the nitrogen. I can't understand why it is so. Why can't the nitrogen bond with carbon, it'll still have a fully filled octet.
I have an unrelated query too - in the formation of nitroalkane by nucleophilic substitution of haloalkane and the reagent being silver nitrite. My sources point out that the silver atom is bonded to the oxygen atom attached to nitrogen by a single bond. I know that since the bond is covalent it wouldn't readily break at first in the reaction (correct me if I'm wrong), this leads to nitrogen sharing it's lone pair. Why doesn't oxygen share its lone pair?
I think my thought process is wrong about haloalkane reactions. I believe that when the carbon halogen bond breaks carbon will only have 6 electrons in its valence shell, so there's no problem with it accepting a lone pair. But what
about groups like $\ce{OH-}$ they give one electron alone to carbon when carbon needs two. I'm so confused could somebody please explain?


texts: Stability of F- Cl- Br- I-? In aqueous state

texts:
If we talk about hydrolysis F- will be more heavily hydrolysed so it should be more stable in aqueous state.
But I know that HI is a stronger acid than HF. So the stability of conjugate acid ie I- should be more than F-. As dissociation takes place in water.


texts: Can cis and trans isomers have widely different flash points?

texts:
Sigma seems to have two products listed for sale as "Cinnamic Aldehyde". One compound clearly seems the trans isomer but the other one seems like an unspecified mixture. (They even have two different CAS nos.: 14371-10-9 vs 104-55-2 )

What surprises me is that the corresponding SDS lists the Flash Point of one as 71°C and the other as 125°C.

Is this really possible or is this just an error? The boiling points listed seem fairly close: 250°C vs 248°C.

P.S. Even if one accounts for methodological differences in Flash Point Determination e.g. closed cup vs open cup those are typically at worst 10°C apart. Here the flash points seem a good 55°C apart.

What gives?


texts:
For me it is clear how I could solved the kinetic of a parallel reaction like this

But, how can I solve if this would be the case:

Thanks in advance!


texts:
A few days ago, I was creating a solution which involved boiling water. I had two 4L beakers on identical hot plates. After around 10 minutes, the first one boiled. Waiting another 30 minutes, the second one had still not started boiling, although small bubbles had formed at the bottom. Shortly afterwards, I heard a ping and the second beaker cracked and leaked water.

Is there any possible correlation between the long boiling time and the beaker breakage? Both beakers should have been heat-safe, although they were from different brands. I'm not convinced of the cleanliness of the beakers, so if this could've been caused by a contaminant, that's a definite possibility.