texts: How many molecules are there typically in items made of plastics?

texts:
In objects made of plastic (and other polymers), how many molecules would one generally expect to find?

Intuitively, it seems like, say, a plastic shopping bag or PET bottle couldn't be a single molecule, but on the other hand, that's one of the strengths of polymers.

So the question is, I suppose, do items made of plastic consist of a single molecule, or many molecules fused together by way of glues or mechanical action?

Edit: Following a comment, I realise that the core of my question could be clearer, so here's an alternate phrasing:

If I chose an atom in a typical plastic object and gave it a colour, and then gave every atom connected to it by way of covalent bonds the same colour by flood fill, and then chose a colourless atom in the object and repeated the process until no more colourless atoms existed in the object, how many colours would a typical plastic object have?


texts: sodium persulfate microwave heating cause crystallized particles

texts:
I use Sodium persulfate to etch a copper board to produce a PCB. I mix 1 dl sodium persulfate with 1 liter hot water. When the water get cold, I heat it up by microwave. After the microwave, I see such crystallized particles at the bottom of the jar. Please note that there were not any solid particles in the acid before the microwave. I wonder what are these particles? is it sodium persulfate? if it is so, why it is crystallized when it is heated up?
Solubility of water increases as the temperature of the water increases, right? Then why it causes solid particles in the car?

Btw, if I put these crystallized particles into the same solvent, they don't dissolve, however, if I put them into a new hot water cup, they dissolve.
If it is sodium persulfate and if they are crystallized because of the microwave, can't I reuse them again?
If it is copper particles, isn't it supposed to be in such color?


texts: Is the reaction of silver nitrate and copper endothermic or exothermic?

texts:
Is the following reaction endothermic or exothermic and why?
$$\ce{2 AgNO3(aq) + Cu(s) -> Cu(NO3)2(aq) + 2 Ag(s)}$$

I have a feeling that it is exothermic due to the fact that it is spontaneous and will end in around 30 minutes (which I am guessing is because it will run out of energy to burn) and no source of energy is there for it to gain energy from, but is this right?
I found on the internet, that I was right about the reaction being exothermic as $\Delta_rH^\circ= \pu{-147.39 kJ}$, but my real question is why? Is its spontaneity the only means of support for this answer?


texts:
What is the best alcohol for your teeth according to the pH?

Is it true that if the acidity of the drink is higher (and ph is lower) than it's worse for your teeth (enamel erosion + bacteria friendly acidic environment) than if the alcohol drink is less acidic?

Does vodka have the highest pH of all the alcohol drinks out there and therefore is the best for your teeth?


texts: What will be the possible major product(s) on heating this primary alcohol i.e. 9-fluorenylmethanol with (conc) H2SO4?

texts:
When the above compound is heated with (conc.) $\ce{H2SO4}$ the $\ce{OH}$ will probably be protonated and it will leave, producing a carbocation. After that possibly there will be a hydride shift. Now, after this step what could be the possibilities. I was thinking of ring expansion (which could potentially form phenanthrene) but again I doubt that a negative charge on a $sp^2$ carbon of the benzene ring would attack the positive charge after C-C bond cleavage. Or another possibility is formation of a double bond to form a structure like:

Which is the correct (major) product formed?


texts: Oxidizing and Reducing agent in redox reaction

texts:
In the oxidation-reduction reaction

  $\ce{Sn^{4+} + 2 Fe^{2+} -> 2 Fe^{3+} + Sn^{2+}}$

  (A) $\ce{Sn^{4+}}$ is the oxidizing agent and $\ce{Fe^{2+}}$ is the
  reducing agent.

  (B) $\ce{Sn^{4+}}$ is the reducing agent and $\ce{Fe^{2+}}$ is the
  oxidizing agent.

  (C) $\ce{Sn^{4+}}$ is the reducing agent and $\ce{Fe^{3+}}$ is the
  oxidizing agent.

  (D) $\ce{Fe^{3+}}$ is the oxidizing agent and $\ce{Sn^{2+}}$ is the
  reducing agent.

My thoughts: Because $\ce{Sn^{4+}}$ is getting reduced, and $\ce{Fe^{2+}}$ is getting oxidized, then $\ce{Sn^{4+}}$ is therefore an oxidizing agent, and $\ce{Fe^{2+}}$ is a reducing agent, which leads me to believe that A is the right answer. However, the answer key says D. I note that (D) is true for the reverse reaction, but why would A not be true then?


texts: What material most closely resembles/emulates dog's excrements?

texts:
Please get me right - this is no joke!

Our engineering team has a terrible contract - we need to find a way to get height from which some dog excrements were dropped judging by what was found on earth when it hit the ground. We need to find some invariant in excrements form, scattering of droplets/material, I don't know whatever else...

We did not start math modelling yet, because it makes no sence - we need to get somewhere physical propeties of "material", besides it is clear that the best way to start with is real-life experiments - but throwing such stuff from different heights over and over again is definitely a bad idea.

The best solution would be to find some material which is maximally close to what our target is - like ballistic gel instead of a human body.

Sorry to ask, but what material most closely resembles/emulates dog's excrements?

So far we found nothing in literature, maybe at list please a hint where to look for...

Sorry once again - this is absolutely no joke, this is for real. The height is within 70 meters limit (this is the max height), the surface is hard - it is pavement (just where people walk). Actually we need to create methodology allowing to calculate from what floor of a building it was dropped (or proove that required resolution of 2-3 meters cannot be reached) by teenage pranksters who do it regularly in different locations (they play it from their rooms and they are networked through some kind of viral social network). This is a real-life problem and we understand why it arose, but it is terrible from the technical point of view.


texts: Changes in physical properties in homologous series : Solubility

texts:
In the text that I'm reading it is stated that :

  As the molecular mass increases in any homologous series, a gradation in physical properties is seen. This is because the melting points and boiling points increase with increasing molecular mass. Other physical properties such as solubility in a particular solvent also show a similar gradation.

My question is regarding the last line; what kind of gradation in solubility is observed? Increase or decrease?


texts: Why is the yield of substitution reactions decreased at higher temperatures?

texts:
This is according to my text :

  Increasing temperature favours elimination over substitution. This is because energy of activation for elimination is higher than that of substitution since higher degree o charges in bonding is involved in elimination reaction. [sic!]

Well I understand why more elimination occurs at high temperatures (I guess this is due to $\Delta G$ being more negative due to multiple product formation as well), but why do substitution reactions have their yields decreased as temperature goes up?

This is according to the master of organic chemistry; (Even though it says that there is a relative increase, the graph shows a decrease in yield of the substituted products):

Aren't they supposed to have their output increased as well, as the activation energy barrier has already passed and rate increases with increase in temperature, or am I missing something fundamental here?


texts: Difference between isopropyl and isobutyl

texts:
Knowing the meaning of ''iso-'' prefix, i could not understand why it is used in some cases. For instance

n-propyl and isopropyl

are named according to the carbon atom which has a lack of hydrogen. The same goes for

isobutyl

where branches define the common name as well. In the end my question is: What is the logic of using iso- prefix (especially in those cases), and how can i know when to use it?

p.s- if you know the answer to my question, it is mostly appreciated to state your source of answer!


texts:
This is my synthetic pathway. For one, is it plausible? For another, is it efficient?

1) Reduction of 1-octyne with hydrogen gas and Lindlar's catalyst to 1-octene.

2) Oxymercuration to install a hydroxyl group at the most substituted carbon. This creates 2-octanol.

3) Reaction with tosyl chloride and pyridine to create a sulfonate ester - a much better leaving group than an alcohol.

4) E2 elimination with sodium hydroxide and strong heating to create the internal, Zaitsev alkene.

5) Ozonolysis to create two aldehydes.

6) Reduction of longer aldehyde with hydrogen gas over transition metal to primary alcohol.

7) Dehydration of primary alcohol to alkene using a Lewis acid (aluminium trichloride in this case).


texts:
Oxygen atom is a highly electronegative element.

Why does oxygen atom allow positive charge on its surface when its electron pair is in resonance with benzene ring?

The reason can be that its octet is complete so oxygen is not disturbed by its positive charge.


texts: What is the Chemistry behind "good" and "bad" cholesterol & their relation to Cis/Trans fatty acids?

texts:
I have searched Google for this but cannot seem to find an explanation. My question is as follows - what is the Chemistry/Biochemistry behind cis and trans fatty acids resulting in "Bad" LDL and "Good" HDL cholesterol? Is one synthesised favourably with cis/trans fatty acids as precursors?

I am under the impression that LDL results in reduced cell permeability (how?), but other than that I am struggling to find information.


texts: Hill function and stoichiometric matrix: confusion about reaction rates

texts:
When deriving the Hill function (protein $X$ and $n$ molecules of the signal $S$), my book introduces the following rates:

$$
\text{collision rate} = k_{ON} \cdot X_n \cdot S^n\\
\text{dissociation rate} = k_{OFF} \cdot [nSX],
$$

where $[nSX]$ is the complex. This translates into the following ODE:

$$
\frac{d}{dt} [nSX] = k_{ON} \cdot X_n \cdot S^n - k_{OFF} \cdot [nSX].
$$

This seems fine if I follow the $\textit{rules}$ of, for instance, this table.

On the other hand, during the class, my professor introduced the stoichiometric matrix. If we have the reaction $2A + B \leftrightarrow C$, then the corresponding system of ODEs would be:

$$
A' = -2r_1A^2B + 2r_2C\\
B' = -r_1A^2B + r_2C\\
C' = r_1A^2B - r_2C.
$$

So, my question is: why in this case we put the $2$ in front of the reaction rates while for the Hill function we do not (put the $n$ in front of it)? Is it just because the $n$ molecules of signal $S$ are not consumed nor produced?


texts:
I came across this term while searching for reference in March's Advanced Organic Chemistry.
It said:

LAH gives significant double reduction only in cinammyl systems, for example, with PhCH=CHCOOH.

This term is new for me and Google didn't have any  specific result for this.


texts: What happens to the lost mass in radioactive decay?

texts:
We were studying kinetics in class which led me to wonder what happens to the decayed matter. After all, there is a loss in mass and according to mass energy equivalence, there should be some release in energy. So I thought that heat may be released by radioactive decay, but I doubt it.
Can anyone tell me what happens to the lost mass?


texts: Vapour absorption in 'normal conditions'

texts:
When is described: "In normal conditions, viscose absorbs 11 to 14% of water vapour. In liquid water, they swell and can absorb 80 to 120% of water." (Clothing Technology)

What do they mean with 'normal conditions'? In open air?


texts: Products of the reaction between chromium(III) chloride, zinc and sulfuric acid

texts:
The aim of my experiment was to make a Cr(II) aquacomplex in situ, and for that I have the reaction:

$$\ce{CrCl3·6H2O + Zn}$$

and I add concentrated sulfuric acid to it. I know that chromium(III) reduces to chromium(II), but I'm not sure about the reaction. Would it be

$$\ce{CrCl3·6H2O + Zn -> Cr(H2O)6Cl2 + ZnCl + H2}?$$


texts: Why does a carbonyl group form instead of alkene in alcohol oxidation?

texts: I am looking over mechanism of the oxidation of alcohol by chromic acid and I am confused on why $\ce{H2O}$ abstracts hydrogen from alpha carbon and form double bond between $\ce{C}$ and $\ce{O}$ atom rather than beta hydrogen and form alkene like in usual elimination reaction we learned. Like to start from beginning i am confused why in chromate ester, which is an intermediate, entire group of $\ce{O-CrO3H}$ does not leave as learning group. Why does only $\ce{CrO3H}$ leave, leaving $\ce{O}$ atom behind which thus makes $\ce{H2O}$ abstact hydrogen from alpha carbon instead of abstracting beta hydrogen and creating alkene.


texts:
There are two possibilities:

Oxonium ion formation
Cleaving of epoxide

Firstly, I don't know if epoxide is more reactive than carbonyl group.
If epoxide reacts with the proton,

But the given answer is:

In the above mechanism, an unstable carbocation is formed because its near a carbonyl group which is electron withdrawing:


texts:
While reading a paper in a field other than chemistry, the author mentions a phenomena that he labelled "adsorption" and describes it as follows:

  ...I am told (though I do not know which liquids they are), there are
  distinct liquids such that pouring 1 litre of one into a container
  already containing 1 litre of the other does not result in there being
  2 litres of liquid in the container (adsorption).

Now, I know almost nothing about adsorption beyond what I just read on Wikipedia, but I didn't see an  example there where two liquids interacted in the way described. Instead, the examples seemed to be ones where a porous solid (e.g., activated charcoal) adsorbs some liquid.

Does this occur between two liquids? If so, what's an example and how does it work in the absence of pores?


texts: Equation for salt formation for ammonium oxalate?

texts:
I'm having trouble finding out the salt formation equation for $\ce{(NH4)2C2O4}$

I thought it was $\ce{NH3 + H2C2O4}$ but that doesn't seem to balance out.

$\ce{HC2O4-}$ seems to work, but are ions allowed in salt formation/neutralization formulas?


texts:
Normal metals like sodium or Calcium have a positive charge as $\ce{Na}^+$ or $\ce{Ca}^{2+}$.
Transition metals have a loot of variable oxidation states.

Yesterday I read about Iridium in Wikipedia and it stated that

  a +9 oxidation state has been found in $\ce{IrO_4^+}$

which is astounding for me...

So i was thinking can metals have a net negative charged ion also?

According to Google :

Since it is written that metals USUALLY have positive charges which means there may be conditions or compounds when they have negative charges too. Is it possible?

Also can Noble gasses form ions too?


texts:
I am planning an experiment on how to isolate casein and part of the process involves removing any lipids that may still be in it after filtering the precipitated casein out of the milk. I have read that one can use 95% ethanol to dissolve the lipids into it, since like-dissolves-like. This would not remove all lipids though and thus a 25 mL 1:1 solution of diethyl ether would be necessary to remove the remaining lipids for a certain amount of the collected precipitate.

What exactly occurs in the reaction when lipids are dissolved into the alcohol? What other alcohols could be used? How does one figure out how much alcohol they should use and at what concentration?

These questions may seem silly to some, yet I have conducted a considerable amount of research online trying to figure it out myself — to no avail though. I appreciate all well-intentioned answers.


texts: Why is Helmholtz free energy often defined as the useful work attainable at constant volume if constant volume implies no expansion?

texts:
From Wikipedia:
"In thermodynamic systems where the temperature and volume are held constant, the measure of useful work attainable is the Helmholtz free energy function"
https://en.wikipedia.org/wiki/Work_(thermodynamics)#Free_energy_and_exergy

By definition, constant volume means that no PV work (expansion work) is done by the system. Because of this, is it not confusing to define Helmholtz free energy as a measure of the maximum useful/non-expansion work attainable at constant volume and temperature rather than just the maximum work attainable at constant volume and temperature, since all work done at constant volume is inherently useful/non-PV work? Adding the "useful" makes it seem like the useful work is separate from work done in general for a constant volume process. Am I missing something?


texts: Melting point of aspirin, contradicting sources

texts:
Querying wolfram alpha for the melting point of aspirin (link) returns $\pu{140 °C}$. The Wikipedia page for Aspirin lists $\pu{136 °C}$ instead, citing this book.

How am I supposed to know which figure to cite? And in general, what should I do when I encounter contradicting chemical data?


texts: Why does LiAlH(O-tert-Bu)3 not reduce acyl chlorides to alcohols?

texts:
Why do $\ce{LiAlH(O-^{t}Bu)3}$ and similar bulky reducing agents not reduce acidic chlorine further?

$$\ce{CH3-COCl + LiAlH4 + H2O -> CH3-CH=O -> CH3-CH2-OH},$$
 but
$$\ce{CH3-COCl + LiAlH(O-^{t}Bu)3 + H2O -> CH3-CH=O -> no~reaction}.$$


texts: How does the derivative of concentration make sense?

texts:
First of all, I would like to make clear that I don't know very much about chemistry, and I'm not very sure this is the right place on Stack Exchange for this question, so please let me know if it needs migration.

I was reading a PDF about differential equations that mentioned equilibrium reactions and where the law of mass action was used. I looked it up on Wikipedia then looked up reaction rate because I was unfamiliar with the concept, and went to its formal definition.

How does the derivative of a concentration with respect to time even make sense? I seems to me that the concentration of a substance is  discontinuous in time and increases or decreases in steps.

Imagine a reaction

$$\ce{aA + bB <=> cC}$$

where $A,B,C$ are reactants and products and $a,b,c$ are stoichiometric coefficients. Now, we see that:

$$\ce{\frac{a}{N_A}A + \frac{b}{N_A}B <=> \frac{c}{N_A}C}$$

where $N_A$ is Avogadro's Number. These are the smallest stoichiometric coefficients for this equation. This reduced equation happens $N_A$ times in the above equation, considering it has an efficiency ($\eta$) of $100\%$. And this reduced equation takes some short time $\Delta t$. Before this reaction, the concentration of $A$ is $[A]_0 = \frac{\nu_A}{V}$ and after it, $[A]_{\Delta t} = \frac{\nu_A'}{V} = \frac{\nu_A - a/N_A}{V}$. I see no in-between that could link these two steps. How could we even define the concentration during the reaction? The only way I see it makes sense it to define the concentration on the interval $(0, \Delta t)$ as $[A]_t = [A]_0$. There is clearly a jump at $\Delta t$. And this doesn't happen only once. The graph of concentration vs time looks like a very compressed and scaled down floor function.

What am I missing?


texts:
What is the principle of the biuret test? While reading online, it is unclear to me how a bond is created between the $\ce {Cu^{2+}}$ and the proteins? What are the chemical reactions that lead to the color change?

Edit

The biuret test is a chemical test combining two products, $\ce{CuSO_{4}}$ and $\ce{OH^{-}}$ in my case. While exploring online the possible effects on protein, some sites suggest that the $\ce{OH^{-}}$ is responsible of removing on hydrogen from the amine and that is why there is a color change while other suggest that the $\ce{OH^{-}}$ would rather act as a redactor for the copper and the release of electrons from the copper would transfer the copper ion from a cupric form to cuprous one. (Copper-based assay chemistries)
I have also understood that the copper geometry is changing during the reaction, but the idea of the reduction is unclear to me.

I will ask my question again, what are the chemical reactions that lead to the color change?


texts: How to define a flame in numerical combustion?

texts:
I am running a CFD simulation (computational fluid dynamics) opposed jet case, where a stream of fresh reactants is opposed to a stream of burnt products. I am looking at the effects of stratification (different equivalent ratio on each jet) on the flammability limits of methane.

In some cases, in the reaction zone, the heat release is about $10^3$ to $10^4$ lower than compared to my reference case, which is far from the lean or rich flammability limits. Since I am sitting on or close to those limits, it is important for me to define one (or multiple) parameter for which I can say that the fuel is indeed burning.

Here is my reasoning right now, but it might be incomplete or even erroneous. To check if the fuel is indeed burning, I have been looking at the distribution of key radicals. If the mass fraction of say $\ce{H2}$, does not have peak in the reaction zone and only diffuses from one stream to another, then I can definitely say there is no flame. But a contrario, if there is a peak, can I definitely say there is a flame?

If there are some key parameters I can look at, please share. Note that since this is a numerical simulation, I virtually have access to all of the thermodynamic or chemical properties (chemical composition, reaction rates of each reaction etc...) at every point of the flow.


texts: Kolbe's electrolysis method for getting alkanes

texts: It involves the electrolysis of "Sodium and Potassium salts of Carboxylic Acids". Why only Sodium and Potassium? Will some other metal like Li, Mg, Zn etc. not work? As long as the element is a better reducing agent than Hydrogen, won't our destination be attained? What is the role of the metal here?


texts: Can gypsum form in the subsurface? If there is another source of sulfate and maybe limestone dissolution happening, if the ionic strength is high enough can gypsum crystals form in groundwater?


texts:
I was watching an online lecture on decarboxylation by soda lime and the first few examples were straight forward but after a while a felt that the questions couldn't simply have one effect and maybe other factors should also come into consideration as complexity of structures increases.

In the above reagent soda lime was added and the teacher said that cubane will be produced however though it might be straight forward based on the mechanism as a carbanion is produced in the intermediate is it correct to directly say that the mechanism should be followed as expected by one pathway without considering any other possibilities such as attempt to relieve angle strain?

Over the course of studying organic chemistry I have realized things often aren't as simple as they appear to be as many factors come into play such as ring closing or bond breaking to relive angle strain.

According to the video the product is Cubane

I know that cubane itself is kinetically stable (primarily due to lack of availability of pathways for decomposition) but the intermediate formed can it not provide any pathways for decomposition?


texts:
I have seen several band bending diagrams in journals and the web. However, I am not sure as to how they align them. Some diagram appear to align the vacuum level and some align them by Fermi Level. I have found that aligning vacuum levels is known as Anderson's Rules and is applied for semiconductor-semiconductor junctions. However, I do not know what the aligning of Fermi level is referred as. What is this convention called?

Also, what are the rules of thumb on deciding on how to align the bands?


texts: How is the bond length calculated from the total electronic energy?

texts:
In the quantum chemistry course that I currently attend, it was said several times that one of the key quantities derived from molecules by means of computation is the total electronic energy $E_\text{el}$, because from this many derived quantities can be calculated, such as bond length or $J$-coupling values for NMR experiments.

However, I've never gotten a good explanation as to how to proceed when I've calculated a value for $E_\text{el}$ and want to find out the bond lengths in the molecule in question.

What are the formulae and/or computation steps necessary for this?


texts: Effect of increasing product concentration on time of completion of reaction

texts:
This was the question asked in our chemistry exam:

In the experiment of determination of equilibrium constant of esterification of ethanol, if , instead of using
clean dry bottle, if a bottle already containing slight amounts of ethanoate and water is used to carry out the
reaction under identical (remaining) conditions, what would be the consequence?

According to our lecturer it's answer is "The reaction will take lesser time to reach equilibrium". But according to Le Chatelier's principle, increase in concentration of products shifts the reaction backwards. So it should take more time to reach equilibrium.
Please help!!


texts: Comparing explosive properties of mercury(II) cyanate and mercury(II) fulminate

texts:
I found this question online on Jiskha Homework Help:

Of the compounds mercury(II) cyanate, $\ce{Hg(OCN)2},$ and mercury(II) fulminate, $\ce{Hg(CNO)2},$ one is highly explosive, the other is not. Explain.

My teachers says that most explosives are made of nitro compounds as abnormal expansion in $\ce{N-O}$ bond has been observed in nitro compounds above a certain temperature. So, fulminate will be more explosive as it contains $\ce{N-O}$ bond.
According to Wikipedia, explosiveness of nitro and other nitrogen containing compounds (like $\ce{NI3})$ is because of possibility of forming highly inert and stable $\ce{N2}$ molecules. Thus slight amount of energy causes breaking of relatively weaker $\ce{N-O}$ bonds and highly exothermic formation of $\ce{N2}$ triple bond making it act like an explosive.
Is my teacher correct? The reasoning given on Wikipedia also points to fulminate but some other concept may be at play here. So, which is correct? Also what would be the reaction mechanism if any?


texts: Why do higher orbitals have more energy?

texts:
I have seen in textbooks and videos that an electron must absorb energy (become excited) to enter a farther-away orbital.

The amount of energy that must be gained is equal to the difference in energy between the orbitals. When the electron relaxes and returns to its ground state, it emits that energy.

However, I am not sure I understand why "higher" orbitals are of greater energy, for a couple of reasons.

When I think of the potential energy of the electron, as given by $U = \frac{kQq}{r}$, it seems that $U \propto \frac{1}{r}$, which would indicate less energy as distance increases.
I also know that the electron is attracted to the nucleus due to opposing charge. By this logic, an electron closer to the nucleus would be more stable (have a lower energy state) than an electron farther from the nucleus (which would thus have a higher energy state). This line of thinking is somewhat similar to how a ball that's still high in the air is in a higher energy state than a ball that's closer to the ground.

So #1 is inconsistent with what we are taught about electrons and orbitals, while #2 would support it.

I am attempting to clarify the misunderstanding I must have somewhere (possibly not making a proper analogy) - and better understand why higher orbitals are of greater energy.


texts: Clemmensen reduction vs. Wolff-Kishner reduction

texts:
In which cases is the Clemmensen reduction is preferred over the Wolff-Kishner reduction?

One thing is that the Clemmensen reduction is done under acidic conditions whereas the Wolff-Kishner reaction is done under basic condition, and that I think decides somewhat which to choose depending of the nature and other groups present in the reactant.

But are there any other points to keep in mind while choosing the best suitable reaction?


texts: How can I dissolve a precipitate when stuck to the side of a boiling flask

texts:
I’ve been experimenting with producing Iron Acetates and I’ve run into a snag. Here’s my process so far:

  I started by adding white vinegar and ~50% Hydrogen Peroxide to a reaction vessel with steel wool sponges and allowing it to react for a month. After that I ran the solution through a filter multiple times until it was fairly clear to remove most of the unreacted solids. After that I tested an aliquot of the fluid by placing some leather in it to see if the leather turned black. It did quite quickly. After that I placed it in a boiling flask and heated it with a flame directly (because I don’t have a big enough beaker or other apparatus to indirectly heat it) and it turned orange. I’m guessing this happened because the elevated temperature allowed it to react with atmospheric oxygen. I continued heating till the solvent was gone leaving a red-brown-black solid on the side of the boiling flask.

I want to dissolve the solid so I added ~100mL of ~50% Ethanol (Smirnoff blue label vodka) to the flask to dissolve it and left it overnight, but it’s barely dissolved at all. I thought about heating it to create pure ethanol vapor which would do the trick but I don’t have a condenser to condense the ethanol again. Is there a better way of dissolving it?


texts: Empirical Evidence and Assignment of Orbital Energies (Electron Filling)

texts:
I see a lot of questions on electron configurations from students at various levels here. Students mechanically remember how to fill orbitals and sorry to say many teachers do the same. Not a single general chemistry or even undergraduate physical chemistry book discusses the "why" part of orbital filling and what is the experimental evidence behind the electron configurations? Yes, hand-waving discussion is always present. It all comes from spectroscopy and so on.

A long time ago I asked a question here, on the physics forum and ResearchGate as how one would come up with an electron configuration from the raw spectrum of a non-hydrogen element. Experimental Assignment of Electronic Transitions in Atoms (Grotrian Diagram)  However, even trained atomic spectroscopists did not have an answer. Is it an art which has been lost and all we have now are tables?

The question is that what is the point in arguing and teaching that electronic configuration of copper is [Ar] 3d10 4s1 or [Ar] 3d9 4s2? What difference does it make in the world when the teacher and the student have no clue of experimentally verifying it except both are memorizing the rules and exceptions like a parrot? Suppose a very good undergraduate asks this question that how do we experimentally know that configuration of copper is [Ar] 3d10 4s1 or [Ar] 3d9 4s2 vice versa? Most of us may not have an answer.

I would be very happy to know a resource that talks about the experimental evidence and determination of electron configurations of heavier metals. So far my efforts have not been very fruitful.

A similar question has been asked here Evidence of orbitals but it does not fully address my old query.


texts: Is there are any universal methods or software for reaction rate modelling?

texts:
In software like DWSIM are used databanks which contains enthalpy and entropy at 298 K and more other information about chemicals. This software can create a steady-state system, where showed state of matter, temperature of reaction, etc.

But I can't find any software for calculation of reaction rate. I know, that chemical kinetics is using experimentally measured time of reaction and concentration of matter. So what should we do, if we want to know an estimated time of reaction?


texts:
I was doing a chemistry project to see if the pH of a carbonated solution effects the time taken for it to settle after being disrupted, and I am trying to map out the reaction when the components are combined.

I was able to figure out a few, but I got stuck on carbonic acid and lemon juice.  For some reason, I was getting ethane as a by product of the reaction, and I'm sure that's not right.  Could someone explain what I'm doing wrong?

the formula is $\ce{H2CO3 + C6H8O7}$


texts:
A white solid is either $\ce{Na2O}$ or $\ce{Na2O2}$. A piece of red
  litmus paper turns white when it is dipped into a freshly made aqueous
  solution of white solid.

  Identify the substance and explain with the help of balanced
  equation.
  Explain what would happen to the red litmus if the white solid
  were the other compound.

From the solution and theoretical knowledge, I know the following:

$$\begin{align}
\ce{Na2O2 + 2 H2O &-> 2NaOH + H2O2}\\
\ce{Na2O + H2O &-> 2NaOH}
\end{align}$$

The aqueous solution of $\ce{Na2O}$ will convert red litmus into blue (basic property), so, the substance is $\bf{not}$ $\ce{Na2O}$ for sure.

But, how will it be $\ce{Na2O2}$? Why does the aqueous solution of sodium peroxide turns red litmus into white?


texts: Why do chiral biological molecules only exist as one enantiomer? Does it have any advantage?

texts:
Why is it that chiral biological molecules are enantiomerically pure? The other enantiomer would have the same reactivity, and the only difference is their angle of rotation of plane polarized light. Why, then, is one enantiomer preferred over the other?

Is it that the enantiomer found in our bodies has some advantage over the other enantiomer, or is it random and luck that the structure we see naturally was chosen?

Are all the biochemicals that our body uses enantiomerically pure or are racemic mixtures too?


texts: "Cage-like" Formazine particles, how are molecules arranged?

texts:
Question: What would the  "cage-like" arrangement of Formazine molecules look like in a Formazine particle while it is still suspended in water? Would it be totally random, or have some kind of imperfect but recognizable regularity?
Formazine is used as an easily defined and prepared calibration or reference standard for turbidity measurements.

above x2: Formazine from PubChem.
From Wikipedia:

Formazine (formazin) is a heterocyclic polymer produced by reacting hexamethylenetetramine with hydrazine sulfate.
The hexamethylenetetramine tetrahedral cage-like structure, similar to adamantane, serve as molecular building block to form a tridimensional polymeric network.

From Formazine:

The readings shown by turbidimeters are not scaled in the measured light intensity, but in concentration of a reference suspension. Because the accuracy of this calibration solution determines the reliability of subsequent turbidity measurements, it is of crucial importance.
The internationally established turbidity standard for calibration is formazine. This standard can be reproduced at any time with the recipe taken from standard ISO 7027 (Water quality - Determination of turbidity).
It is extremely important to observe the prescribed preparation temperature, because it affects the particle size of the formazine particles perceptibly. The following Figure illustrates this. Errors caused by temperature variations are on the order of 1..2% per °C. Consequently, Sigrist keeps the preparation temperature constant to within ± 1°C.

above: "Particle size distributions of formazine at various preparation temperatures" from here.

above: Enlarged from TurbidityStandards.

above: Slide #10 from What is Turbidity? John Daly, ISA NorCal President, South Fork Instruments, Inc. Click for full size.


texts: Distinguishing pentanol isomers in 13C DEPT NMR spectroscopy

texts:
Pentanol has eight isomers as shown below. The circles represent carbon atoms that I think are equivalent.

Below there are eight DEPT-spectra that should represent these eight substances.

As you can see some won’t line up. What’s the problem?


texts: How do I (further) lower the pH of a pyrrolidine solution?

texts: Pyrrolidine ($2~\mathrm{mol}$) is slowly added to $164~\mathrm{ml}$ conc. $\ce{HCl}$ in $200~\mathrm{g}$ ice water to adjust the $\ce{pH}$ to $3-4$. When it is mixed, the $\ce{pH}$ is $14$, how do I lower the $\ce{pH}$ to $3-4$? I cannot add more $\ce{HCl}$ because it only calls for $164~\mathrm{ml}$.


texts: A thorough benchmark of DFT functionals without dispersion corrections

texts:
So, I'm looking for a benchmark of DFT functionals not including dispersion corrections. Something similar to Grimme's and coworkers GMTKN30 database, but for benchmark calculations done without dispersion corrections.

As in the case of GMTKN30 database, I'm interested in the same properties: general main group thermochemistry & kinetics. But

I already have calculations done many years ago without dispersion corrections since this feature simply was not implemented in most of the packages that time.
My workhorse is G3/G4 method which relies on geometry obtained without dispersion corrections anyway.
I quickly run few calculations including dispersion corrections and found no noticeable difference. Don't have time to redo all the work anyway.

I basically need to justify the choice of just a few DFT functional for my own benchmarks based on thorough literature reviews.


texts: Why don't heavy and light gases separate in the atmosphere?

texts:
Everyone must have heard that balloons are filled with helium, and the fact associated with it that helium gas is light and light gases always go upward.

There comes a question to mind: if the molar mass of $\ce{CO2}$ is greater than that of $\ce{O2}$ and $\ce{N2}$, then why doesn't $\ce{CO2}$ occupy the lower layer of the atmosphere, since it is heavier than $\ce{O2}$ and $\ce{N2}$, as in the case of balloons, where helium being light rise upwards.


texts: Why does this protein seem to have multiple chains?

texts:
I'm looking at the structure of this protein, which I beleive is supposed to be a single polypeptide chain, since on the PDB page it says:

  Unique protein chains: 1

But using the 3D viewer, there seem to be a few "loose ends" i.e. it looks like the protein is composed of multiple polypeptide chains.

This is was I see  - you can see a separate chain there at the bottom.

Where am I going wrong here?


texts:
I am currently studying about the vespr theory and I'm stuck on an ion which is dichromate (VI) ion $\ce{Cr2O7^2-}$. So this is what I am thinking about:

1) If I make the oxygen atom at the middle the centre atom, it is a bent.
2) If I make the chromium atom thecentre atom, it is a tetrahedral.

So, my problem is that whether dichromate (VI) ion bent or tetrahedral?


texts: Why does Si2H4 readily polymerize at RTP but ethene does not (requires catalyst)?

texts: In the case of both Silicon and Oxygen, the double bond is less stable than two single bonds. Consequently, surely both should polymerize, why don't they? What accounts for the difference between Carbon and Silicon in this context?


texts:
Iron(III) oxide-hydroxide, $\ce{FeO(OH)}$ has two CAS numbers, 1310-14-1 and  20344-49-4. What's the difference between them?

Why does it have two CAS numbers? As I know, the CAS number should be unique to each substance.

Wikipedia reference


texts: Cleaning with vinegar and sodium bicarbonate

texts:
Mixing sodium bicarbonate with vinegar (and sometimes adding dishwasher detergent) is quite a common tip on the internet. But I have never understood the reason.
I saw there was a question about using sodium bicarbonate and vinegar here to unclog drains, where the answer referred to the production of $\ce{CO2}$ being able to push whatever gunk blocking the drain.
However, for cleaning, the reaction is done when you use the mixture. Is there something I am missing? I am not a chemist, but my intuition is that using either bicarbonate or vinegar + dishwasher detergent alone would be more effective? Can somebody explain if the cleaning tip actually makes sense?


texts: Reaction of alkenes (localised π bond) with nitrating mixture

texts: The nitrating mixture for the nitration of benzene contains many strong electrophiles (e.g $\ce{H2SO4}$, $\ce{NO2+}$). All of these could, presumably, add across the π bond in a molecule containing a localised π bond. Do these additions occur and if so what is the major product?


texts: Gaussian calculation - PCM model for IRC compared to gas phase?

texts:
Finding a reaction pathway thanks to Gaussian calculations is tricky exercise requiring a lot of resources for each step of this time-consuming process. Thus, man needs to wonder if each calculation has to be performed or not in order to gain as much time and resource as possible.
After achieving a 3-step mechanistic path for my reaction in gas, meaning finding all optimized structures, TS, verifications by frequencies of the stationary points and IRC, I now need to use the PCM model in my calculations to provide a solvent correction to my mechanism. However, I was wondering which calculations were required for this purpose.
From the 2 options I have in front of me, which is more consistent to avoid wasting time and resources ?

Perform new optimizations for the minima and TS in my pathway using the PCM model. Then calculate frequencies to be sure of my stationary points.
Perform new optimizations of the minima and TS AND perform new IRC calculations from the fresh new TS (after solvent correction) with PCM model.

The first option means that I perform an optimization from the reverse and forward structures (already further optimized) obtained from my IRC calculation in gas.
The second option means that I calculate a new IRC to obtain new forward and reverse structures that I have to optimize again.


texts: What are the common names of this two types of plastic?

texts: I need to do some plastic molding design. I want to know the names/types of plastic which are commonly/widely used in industries (please see the pictures below).


texts: Why is cyclopentadiene more stable than its aromatic counterpart cyclopentadienyl anion?

texts:
What will be the order of stability?

The answer key says that the stability order is: cyclopentadiene > cyclopentadienyl anion > cyclopentadiene  cation

According the me it should be: cyclopentadienyl anion > cyclopentadiene > cyclopentadienyl cation
because the order of stability is aromatic > non-aromatic > anti-aromatic.


texts: Do We change sign of electrode potential when reversing an equation?

texts:
I have a cell equation as:

$$\ce{2Cr^0 + 3Cd^2+ -> 2Cr^3+ + 3Cd^0}$$

I am provided the standard reduction potentials as:

$$\begin{align}\ce{Cd^2+ + 2e- &-> Cd} &&    E= \pu{-0.4V}\\
\ce{Cr^3+ + 3e- &-> Cr} &&      E= \pu{-0.74V}\end{align}$$

Now do I use chromium’s reduction potential as $\pu{-0.74V}$ or do I flip the equation and use $\pu{+0.74V}$ (as it is getting oxidised and I have the equation for reduction)?

This is using the formula $E(\text{cell}) = E(\text{cathode}) -E(\text{anode})$, all reduction potentials.


texts: Formulae for energy of photon (E=hf and E=hv)

texts:
I have seen the energy of a photon given by the formulas:

$$E = h \cdot f \tag{1}$$
Where $E$ = energy of the photon, $h$ = Planck's constant, $f$ = frequency of radiation (Source: BBC article)

I've also seen it given as

$$E= h \cdot \nu \tag{2}$$
Where $\nu$ stands for frequency (Source: Wikipedia article)

But in this topic I've also seen

$$f=\nu/\lambda \tag{3}$$
Where $\nu$ = speed, $\lambda$ = wavelength (Source: Simple English Wikipedia article)

Is there any difference between equation 1 and equation 2? And is equation 3 unrelated?


texts: Does the reaction of 2‐hydroxy‐6‐methyl‐5‐nitrocyclohepta‐2,4,6‐trien‐1‐one with NaOH involve ring contraction?

texts:
What is the product and mechanism when 2‐hydroxy‐6‐methyl‐5‐nitrocyclohepta‐2,4,6‐trien‐1‐one is reacted with
  $\ce{NaOH}$?

The only reagent used is $\ce{NaOH}$ so I suppose it abstracts the acidic hydrogen from the $\ce{-OH}$ group. A nucleophilic attack at the carbonyl carbon is also possible, as it could form a tropylium like cation. But I am not sure as to how a ring contraction occurs. The final answer given is 3-methyl-4-nitrobenzoic acid. How does the formation of an acid group and the ring contraction take place?


texts: What "physical method" does Feynman refer to in The Feynman Lectures on Physics (Vol 1)

texts:
In the introductory chapter, Atoms in Motion, of the Feynman Lectures on Physics (Volume One), Feynman alludes to a certain "physical method", which can be used to determine the structure of α-iron (and presumably) many other complex organic compounds.
Excerpt from page 1-8 (Chapter one, page eight):

How does the chemist find what the arrangement is? He mixes bottles full of stuff together, and if it turns red, it tells him that it consists of one hydrogen and two carbons tied on here; if it turns blue, on the other hand, that is not the way it is at all.
This is one of the most fantastic pieces of detective work that has ever been done—organic chemistry.
To discover the arrangement of the atoms in these enormously complicated arrays the chemist looks at what happens when he mixes two different substances together. The physicist could never quite believe that the chemist knew what he was talking about when he described the arrangement of the atoms. For about twenty years it has been possible, in some cases, to look at such molecules (not quite as complicated as this one, but some which contain parts of it) by a physical method, and it has been possible to locate every atom, not by looking at colors, but by measuring where they are. And lo and behold!, the chemists are almost always correct.

Knowing that this lecture was originally delivered in the early 1960s, what is this "physical method" Feynman's referring to and how does it work?


texts: Why do dianions (such as malonate) bind cations more strongly than anions?

texts:
Why does a dianion (such as malonate) bind cations more strongly than its equivalent anion (acetate)?

Is it simply because of the proximal availability of another $\ce{O-}$ group that can bind to cations? Does the second $\ce{COO-}$ group on malonate distribute charge in a better way that can allow for stronger binding?


texts: Can you synthesize phenol from salicyladehyde? Well for starters I know that salicyladehyde can be obtained from phenol through Reimer–Tiemann reaction but I was wondering if the reverse was possible.


texts: Why do *tert*-butyl ethers in diluted sulfuric acid undergo elimation instead of solvolysis?

texts:
My organic textbook states the pathway for propyl tert-butyl ether in dilute sulfuric acid will follow E1 with a tertiary carbocation intermediate. It mentions that Sn1 will only occur with good nucleophiles.

It does not explain why however. Why is this any different than a tertiary haloalkane in water? I expect that the alcohol is a good leaving group, similar to water.

Vollhardt, P.; Schore, N. Molecules: Structure and Function, 7th edition; W. H. Freeman: New York, 2014, p350


texts: A monocyclic 6 carbon ring with 6 double bonds

texts: I would like to know if this molecule has ever been synthesized, if not why not, and what would its IUPAC name be?


texts: How to make silicic acid, potassium silicate or calcium silicate?

texts: I am a student of tropical agriculture. I am taking the class of agronomic chemistry and plant nutrition. I want to make use of silicate source I have at home for e.g. zeolite, wood ashes, diatomaceous earth, silica sand. I have hydroxide of calcium, potassium and sodium. Can I use any of these to make silicate for use on plant nutrition ?


texts: Does phosphoric acid remove stainless steel electropolished layer?

texts:
Electropolished stainless steel has a high corrosion resistance due to the oxide film that is created during electropolishing.  The film mainly consist of chromium(III) oxide.

Phosphoric acid is used as a rust removing agent:

$\ce{2 H3PO4 + Fe2O3 -> 2 FePO4 + 3 H2O}$

My question is: will 5% $\ce{H3PO4}$ solution remove this protective layer as well? It should, but how fast will be the protective layer removed? Does anyone have personal experience?


texts: Confusion between moles and molarity units

texts:
I am a total newbie in the field and i would like some kind of guidance.

So, I have been recently given 2 datasets with measurements regarding several phospholipid fatty acids of plasma HDL. Both datasets consist of the same classes of FAs but with different units of measurement (μΜ and mol%).

Since I have no previous experience with that kind of data, can someone give me a hint about how (and if) it is possible to convert from one unit to the other?

Thanks in advance.


texts: Finding major product when bromonium compound is acted upon by a nucleophile

texts:
The original question is:-

  The major product obtained in the following conversion is:-

(Note that Me here means methyl group)

The initial step would be the formation of a bromonium intermediate. Which would then be attacked by a nucleophile $\ce{CH_3OH}$ as it is present in excess in solvent.

What I think is, $\ce{CH_3OH}$ would attack the carbon atom close to ketone, because that’s the carbon best able to stabilize positive charge due to resonance with keto group. This is what I think will happen

But the proposed answer was

Can anyone explain me why how and why this compound is formed?


texts: How to determine methane percentage at home?

texts:
Suppose I have gas bottle and gas cooker. Suppose I have propane in my bottle and I suspect it is diluted with unknown gas.

How can I measure with simple instruments, how many propane I have (percentage)?


texts: Will dissolving pure linseed oil in ethanol decrease its drying time?

texts: I've looked at some material on the internet and it says that pure linseed oil can take months to dry completely unless a solvent is added, which decreases that time to a few days. I'm wary of industrial solvents due to their toxicity and dangerous fumes, so I was wondering if specifically pure ethanol would be a reasonable and non-toxic alternative to industrial solvents used to speed up the drying time of pure linseed oil.


texts: Strange green and gold coloured chemical

texts:
I have a reagent bottle with an unknown chemical that came with some other lab gear about 30 years ago, I stumbled on it again when clearing out some old stuff.

It is a standard brown glass Merck of about 250ml size.  It has no label and never had any indication of a label and I do not know if it is the original bottle.

The powder is a fine dark free flowing crystalline solid.  It is DARK green with a gold iridescent sheen when in bright light, something like a butterfly wing or some anti-forgery inks on banknotes.

Yet if I wet a very small portion it dissolves completely and creates a vivid dark blue solution that dries blue in a thin film.  If the crystals dry in a clump they form a smutty dark green gold pasty lump that is reminiscent of the original bulk colour.

I had to hand some potassium permanganate crystals and when I mixed a pinch of the two together and added a drop of water a gas evolved and the colour seemed to be somewhere between the permanganate and the mystery chemical blue when spread on paper.  Adding a few drops of acetic acid seemed to have no effect.

Can anyone think of an obvious candidate or some simple experiments that could be used to determine the material?


texts:
I'm working on a chemistry question where I'm supposed to use average bond energies to estimate enthalpy changes for a reaction. It gives me these bond energies to work with:

$$\begin{align}
\ce{C-H}&=&413\\
\ce{C-C}&=&348\\
\ce{C-Br}&=&276\\
\ce{H-Br}&=&366\\
\ce{CkC}&=&614\\
\end{align}$$
I know how to do the question, but I don't what $\ce{CkC}$ is. I can't find it online or in my textbook. What does the "k" mean?


texts: Why aqueous hydroxide is slippery (beyond just saponification)

texts:
A recent question mentions:

  Bases are soapy to touch because of soap formation on contact with lipids present on our skin.

This is always the reasoning I hear, as well, and searching the internet gave the same results. However, when working with nitrile gloves, glass with aqueous sodium or potassium hydroxide on the outside always feels slippery. I believe that even nitrile-on-nitrile (rubbing the fingers together) gives the same slippery feeling. This effect is even stronger for the liquid in the base bath, but I assume that's because alkoxides would be detergents similarly to soap molecules in the absence of water.

Point is, if saponification is the culprit, why does the exterior of the glove experience a similar soapy effect to that my fingers feel? Could it be negative charges on the exterior of the glass? Is it possible for hydroxide to react with nitrile gloves to cause some similar kind of electrostatic repulsion, maybe by deprotonation or nucleophilic attack of the nitrile? This seems like a reasonable idea as far as glass goes, but I don't think that reasoning crosses over to gloves. Of course, I am not sure it really happens with glove-on-glove contact. I will safely test that theory again and edit if it's incorrect.


texts: How to calculate the pressure required to converted graphite to diamond at room temperature (298 K )?

texts: I want to calculate the pressure required to convert graphite to diamond. The information that I have is the density of diamond and graphite, enthalpy change of diamond to graphite at room temperature and entropy of diamond and graphite at room temperature. Which thermodynamic relation can we use to calculate the pressure?


texts: What is the physical quantity/magnitude of pH?

texts:
I have a database to classify variables/parameters in water resources as follows:

Variable: Precipitation (P); Quantity: Length; Units of measurement: mm (millimeters).

Following the example, what would be the properly quantity of variable pH?

Variable: Potential Hydrogen (pH); Quantity: ?; Unit of measurement: pHU (pH unit, unit less, dimensionless).

Maybe concentration or activity?

[I know what pH is, It is not necessery explain, I'm looking for the most appropriate word to describe its quantity]


texts: How do I calculate the order of a reaction given slope?


texts: Does there exist a dye that will primarily bind with water in a water/oil emulsion?

texts:
I'm wondering if there exists a type of dye that will bind primarily with water when introduced to a water/oil emulsion. That way if the water is centrifuged to the bottom of the vial, it will be dyed showing better visibility for the meniscus line.

The main application of this would be for centrifugation of clear oil that has suspended water. If the oil is clear and spun out, the water may separate but seeing the distinct meniscus can be difficult. If a dye in introduced and binds to the small water content within this emulsion, once it's spun out, ideally you'd see the dyed water at the bottom. The content of water is probably 0.5 - 1.0%

I'm also somewhat aware of some water by distillation methods using dyes to detect small amounts of distilled water, but I'm unfamiliar with these and I can't find any helpful resources online about it.

I suppose it would need to be a hydrophilic dye that also resists binding to hydrocarbons?


texts:
I'm learning on my own with Chemistry The Central Science, 13th ed. book. So far it's going well.

I've come across something I don't think I understand. I've googled and "stackechanged" with no avail.

How come a combustion generates no gas products? And in what circumstances?
This is the bit of the book that left me wondering:

For a noob like me, it's counterintuitive that something "burns brilliantly in air" and only generate solid products.


texts: How to calculate the rate of consumption of aluminium with hydrochloric acid?

texts:
An experiment is done to determine the rate of the following reaction:
  $$\ce{2 Al (s) + 6 HCl (aq) -> 3 H2 (g) + 2 AlCl3 (aq)}$$

  The following data is collected:
  \begin{array}{rr}
\text{time}/\pu{s} & (\text{Mass of beaker + contents})/\pu{g}\\\hline
   0.0 & 270.230\\
  30.0 & 270.200\\
  60.0 & 270.170 \end{array}

  Calculate the rate of consumption of $\ce{Al}$ in $\pu{g/min}$.

The answer is $\pu{0.534 g/min}$, but I don't know how to get there.


texts: Non-radiative transitions or what features of rhodamine result in it being so highly fluorescent?

texts:
Rhodamine is a fluorescent dye. What features of the molecule result in it being so highly fluorescent ?

I assume the extended conjugated system with a stabilized first excited state is necessary, to absorb light in the visible region of the spectrum, and I would also think a rigid, planar structure is preferable for good Franck-Condon factors for absorption. Are there other factors involving the energy/stability of the $S_{1}$ state I should be aware of ?


texts: Can Methylene Blue Detect Spoilage in Food?

texts:
Initially, there is already a product which is a sensor based on Methylene Blue, which can detect changes in oxygen levels in a packaging. However, as our thesis project, we decided to take on this and make it more simple and replicable.

So this is our concern. We decided to try and replicate the "blue bottle experiment", which is Glucose and Sodium hydroxide mixed to form an alkaline solution and then Methylene Blue will be added. At first it will be blue, but once it settles, it will turn clear. When the solution is shaken, it will turn blue again, and then turn clear once again when settled.

In theory, if a strip of filter paper was dipped into this "blue-bottle" solution, will it turn blue once it detects high levels of oxygen? (This is provided that the filter paper will remain moist)

ps. the reason why i'm asking for professional opinions and answers is that we cannot afford to buy expensive materials if we don't know if it will work in the first place.


texts:
I have measured the pH in the water-soluble fraction of a powder. I weighed in a certain amount of powder and a certain amount of water, and extracted the water-soluble fraction. I then measured the pH in this extract.

How do I report this? The pH depends on the amount of powder and the amount of water. Should I give the weighed-in amounts along with the pH-value? Or is there a way to "normalize" the pH-values to make them comparable for all? Just giving the pH values make no sense, as no one can compare anything to them.


texts: Why is Sulfur trioxide a neutral electrophile?

texts: My chemistry book says, an electrophile is a reagent which is atrracted to electrons, therefore positive ions and reagents with incomplete octets act as electrophiles, Sulfur trioxide belongs to neither category, so how does it act as an electrophile?


texts:
Redox reaction is a type of chemical reaction, and is the result of electron transfer between chemical species. But, all chemical reactions somehow involve electron transfer!

So, are there chemical reactions without electron transfer?


texts: Reactions involving trimethylaluminium Al2Me6

texts:
I need to write balanced equations describing the following reactions:

one mole of $\ce{Al2Me6}$ with two moles of water
excess of $\ce{Al2Me6}$ with silicon dioxide
excess of $\ce{Al2Me6}$ with tin(IV) chloride

My answer so far:

a) $\ce{2H2O + Al2Me6 -> Al2Me4(H2O)2}$?
b) $\ce{SiO2 + Al2Me6 -> SiMe4 + Al2Me2O2}$?
c) $\ce{SnCl4 + Al2Me6 -> SnMe4 + Al2Me2Cl4}$?


texts: My teacher was teaching about chemical bonding and she said that pi bond needs sigma bond to exist, but she didn't know why. It is a doubt which I get in my mind, can someone explain it?


texts: Is this a valid method to find percentage of pure ethanol in an impure sample?

texts:
To generalize the problem, I will just say:

  5 gram of impure ethanol (or any other type of combustible material) is placed inside a bomb calorimeter where volume is constant. If the combustion produces a certain amount of energy, how should I find the mass in gram of pure ethanol contained in that quantity of impure ethanol?

Here is what I will do:

find the standard molar enthalpy of ethanol.
write a combustion equation.
find the energy produced in the combustion of one mole of ethanol.
then divide that amount of ethanol by the amount of energy stated in problem.

To find how many mole of pure ethanol, convert the mole into gram.

But there are two things that make me think that this way of solving the problem is not correct:

the quantity of impure ethanol is a mixture of pure ethanol and another unknown material. What if this unknown material produce part of the energy stated in the problem?
the standard molar enthalpy is measure under standard conditions (1 atm, 25 °C). However, the condition inside the bomb calorimeter is unknown.


texts:
Have the various $\ce{C-C}$ bonds in straight chain hydrocarbons, have the same dissociation energies? Or does it depend on the location of the carbon in the chain?
In other words, are the terminal bonds weaker or stronger than the internal bonds?


texts: How would a temperature profile in wall change if the rate of heat transfer increases

texts:
Given the system below, how would the temperature profile in the wall change if the heat transfer in Fluid II was very fast?

If the heat transfer in Fluid II is very fast, then the T-profile for $\ce{T_{2∞}}$ would experience less resistance and hence have a more linear slope. However, I don't understand how this would affect the T-profile inside the wall? Wouldn't Fluid II have the same temperature and interact with the interface at the same point, meaning nothing changes within the wall?


texts: Does population of vibrational states depend on population of electronic states?

texts:
We know that molecules have different energy states (vibrational, rotational, electronic). Using Boltzmann distribution we can find the popoulation of each energy state. If we have only electronic states (e.g. atoms) then we can find the population of the ground, first excited state etc. If we have a molecule (neglecting rotational levels) will the population depend on the population of the electronic state? For example in this diagram Vibrational levels distribution:

will the population ($\%$) also depend in which electronic state the distribution is evaluated?
I think that the percentages would not change. For example the ground electronic state in $υ=0$ vibrational state would have the same population with the excited electronic state in $υ=0$ vibrational state. The percentages will be the same while the number of molecules in each state will be different, e.g. in ground state with $υ=0$ we will have $100$ molecules while in the excited state with $υ=0$ we will have $30$ (numbers are just random). Otherwise it wouldn't make sense to say that at low temperatures the most populated electronic state is the ground state.


texts: Theoretical principles of molecular simulations

texts:
I am pharmacy student and would like to work in the field of drug design. We learn to work with the programs but thats not enough for me. I want to learn the theoretical principles of computational chemistry and develop software themselves, or at least parts of it.

However, I have a few questions:

Where do I start with the chemistry part?

solving the Schrödinger equation
Hartree–Fock method
Density functional theory

Which mathematical principles do I need?

Are there comprehensive literature for beginners and what would you recommend? A good book would certainly be the best start.

I need a good starting point, especially in terms of mathematics and hope you can help me.


texts: Choosing an electrolyte for a galvanic cell

texts:
I was wondering what processes are used to select an electrolyte for a galvanic cell.

I know a zinc copper battery usually has zinc and copper sulfate electrolytes. How do these electrolytes interact wishing each half cell (i.e.: how does zinc sulfate interact with water, the anion from the salt bridge and zinc itself)?


texts: Adjustment of calcium, magnesium and alkalinity in drinking water?

texts:
It's been a long time since I did any molar chemistry in school and despite doing a lot of reading on the subject this week, I am making a mess of some basic calculations. I hope that someone who understands water chemistry & molar equations a lot better than I do can point me in the right direction.

I am trying to add mineral salts to soft water to adjust the calcium, magnesium and alkalinity in a predictable manner. But I can't get past the basic equations so far.

The source water I am working with is:

12.6 mg/L Hardness as CaCO3 equivalent
11.3 mg/L Alkalinity as CaCO3 equivalent
  4.8 mg/L Calcium
  0.2 mg/L Magnesium
  1.5 mg/L Sodium

And the desired target water is:

70    mg/L Hardness as CaCO3 equivalent
40    mg/L Alkalinity as CaCO3 equivalent
20    mg/L Calcium
  4.9 mg/L Magnesium
  8   mg/L Sodium

I would prefer to have most of the hardness derive from calcium, rather than magnesium if possible. I plan to try

adding sufficient baking soda, NaHCO3 to the source water to obtain 8 mg/L sodium, then
add sufficient calcium carbonate (chalk), CaCO3 to the source water to make 50/50 GH/KH water (general hardness/carbonate hardness) i.e. 50 mg/L hardness and 50 mg/L alkalinity, both expressed as CaCO3 equivalents
add sufficient lactic acid (88%  CH3CH(OH)COOH) to neutralize some carbonate and (I hope) get to 50/40 GH/KH
add sufficient epsom salt, MgSO4*7H2O to obtain a final result of 70/40 GH/KH.
This assumes that adding lactic acid won't remove (precipitate) calcium hardness.
The solubility of calcium carbonate in water shouldn't be an issue, I can put it under pressure with carbon dioxide, C02 if necessary to dissolve it.

If the above is not feasible, then alternately

add sufficient baking soda, NaHCO3 to the source water to obtain 8 mg/L Sodium
add sufficient calcium carbonate, CaCO3 to reach the alkalinity target of 40 KH (40/40 GH/KH) i.e.. 40 mg/L hardness and 40 mg/L alkalinity, both expressed as CaCO3 equivalents
Add non-carbonate hardness by adding sufficient epsom salt, MgSO4*7H2O to obtain a final result of 70/40 GH/KH

Any help, guidance as to molar calculations and best practices in water chemistry or well honed levity welcome

Edit to add molar amounts
Source water
12.6 mg/L Hardness as CaCO3 equivalent
11.3 mg/L Alkalinity as CaCO3 equivalent
Ca 2.4 x 10-4 M
Mg 1.7 x 10-5 M
Na 1.4 x 10-4 M

Target water
70 mg/L Hardness as CaCO3 equivalent
40 mg/L Alkalinity as CaCO3 equivalent
Ca 1.0 x 10-3 M
Mg 4.1 x 10-4 M
Na 7.3 x 10-4 M


texts: Ring Strain and C=O Stretching Frequency

texts:
Why does $\ce{C=O}$ stretching frequency increase with ring strain?

Why does conjugation decrease $\ce{C=O}$ ring strain?

I am told that cyclopropanone exhibits a higher $\ce{C=O}$ stretching frequency than does cyclohexanone. I know that higher stretching frequencies are correlated with a shorter, stiffer, and stronger bond. What I can't see is why would the $\ce{C=O}$ bond have more of these characteristics in a strained ring system than in a less strained ring system.

Are there hyperconjugative effects going on?

Are there other rationalizations that we can make? I.e. would smaller $\ce{C-C-C}$ angles suggest higher $p$-character in the $\ce{C-C}$ bonds and therefore higher $s$-character in the $\ce{C=O}$ bond?


texts: Can I submerge a polyester shoe underwater to wash it, and for how long?

texts:
I'm wondering if this will damage the shoe somehow. The shoe doesn't include washing instructions. My shoe actually has four materials listed, they are:

-Polyester
-Polyuretan
-Natural rubber
-Nylon

I don't know any chemistry, I'm ignorant. I think this substances can come in many forms, so there is a lot of uncertainty. But if you answer for at least what the title asks, I'm fine, I'll make more questions for the rest of the materials.


texts: Please tell me if these are metamers ie Metamerism: In Chemistry the type of isomerism in which chemical compounds have identical proportions of the same elements and the same molecular weight, but have radicals differing in type or position, with resulting differences in chemical properties.


texts: Will 1-[2-(chloromethyl)phenyl]propan-2-one, follow a Williamson ether synthesis route or, a Diels-Alder reaction?

texts:
I was asked to find the product of potassium ethoxide reaction with 1-[2-(chloromethyl)phenyl]propan-2-one (1).

I came up with two different paths, each leading to the same product.

1-[2-(chloromethyl)phenyl]propan-2-one (1) on reaction with potassium ethoxide gives a carbanion 2.

This carbanion 2, in conjugation with $\ce{C=O}$ gives enolate 3. This enolate can follow path 1, an $\mathrm{S_N}{2}$ reaction (Williamson ether synthesis) to give 4.

The same carbanion 2 in conjugation with benzene ring gives 6 via allylic rearrangement(Path 2).6 could undergo a possible Diels-Alder reaction giving again 4.

My question is, will the reaction follow Path 1, a Williamson ether synthesis route or will it follow Path 2, a Diels-Alder reaction.


texts:
I know that Grignards react with carbon dioxide to give carboxylate anions.

But will Gilmans do the same? Will Gilmans react with carbon dioxide in a productive fashion?


texts: Intuitive Explanation for why more negative charge on ligand does not imply more splitting effect?

texts:
I have studied coordination chemistry as part of my school curriculum and we covered Crystal Field Theory as our final theory, and the book says that Ligand Field Theory and Molecular Orbital Theory are used to explain the limitations of CFT but are beyond our scope of learning.
One of the limitations of CFT according to the book is that if the ligands are point charges then it should follow that an anionic ligand should exert more splitting effect but that is not the case as we see in the spectro-chemical series.
A good example would be $\ce{S^2-}$ < $\ce{F-}$ < $\mathrm{EDTA^{4-}}$ < $\ce{CO}$
Also we can see that size is not the determining factor as then $\mathrm{EDTA^{4-}}$ wouldn't be so high as compared to $\ce{F-}$
Is there some intuitive explanation or logic for this which I can follow with my current knowledge till CFT without going too deep into MOT or LFT?


texts: One-step oxidation of hex-1-ene to hex-2-en-1-ol

texts:
Convert the following and show a Mechanism

It has to be just in a single step and on the arrow head you can't use multiple reagents altogether. Can anyone do it? I am unable to do it in a single step.

This is my attempt ..! But it is multistep, one step is required ..!


texts: Why do we say that a transition state that resembles a stable species in free energy also resembles it in structure?

texts:
My textbook states," According to the Hammond-Leffler postulate, the transition- state structure for a step that is uphill in energy should show a strong resemblance to the structure of the product of that step."
Also stating,"One way that the postulate can be stated is to say that structure of a transition state resembles the stable species that is nearest to it in free energy. For example, in a highly endergonic step the transition state lies close to the products in free energy,and we assume,therefore,that it resembles the products of that step in structure as well. "
(Source:Solomons' Organic Chemistry
Book by Craig B. Fryhle, Scott A. Snyder, and T. W. Graham Solomons)


texts: Chromium (IV) Oxide Sol Gel Process Synthesis and Properties

texts: Is it is possible to solely synthesize an CrO2 aerogel through the Sol-Gel process? All documents I find are of a mix of oxides containing CrO2 as a supporting matrix but not alone. Would the CrO2 still display ferromagnetic properties as the pure substance?


texts: How to calculate the rate constant for the reaction of mercury chloride and oxalate?

texts:
If for the reaction
$$\ce{2HgCl2 (aq) + C2O4^2- (aq) -> 2Cl^- (aq) + 2CO2 (g) + Hg2Cl2 (s)}$$
The initial concentration of $\ce{HgCl2}$ is $0.0836~\mathrm{M}$ (first order), of $\ce{C2O4^2-}$ is $0.202~\mathrm{M}$ (second order), and the initial rate of formation of $\ce{Cl-}$ is $0.52\times10^{-4}~\mathrm{M\,s^{-1}}$, then to find $k$ I would do:
$$\frac{1}{2}(0.52 \times 10^{-4}~\mathrm{M\,s^{-1}})=k(0.0836~\mathrm{M})(0.202~\mathrm{M})^2$$
And isolate for $k$. I included the one half in front of the rate of chloride ion formation because the coefficient in front of the chloride ion is 2 in the equation.

Is my method correct? The solution key states that I should set up my equation without the one half. Thus, its answer was twice as large as the one I got. If the answer key is correct, please explain why.


texts: How to calculate the pH of a buffer after HCl was added?

texts:
A buffer is made from $50~\mathrm{mL}$ of $1.0~\mathrm{M}$ benzoic acid, $K_a = 6.3\cdot10^{-5}$, and $50~\mathrm{mL}$ of $1.0~\mathrm{M}$ sodium benzoate.
a) Calculate the pH of this buffer

For this do I simply use $-\log(6.3\cdot 10^{-5})$?

b)Calculate the new pH when $0.010~\mathrm{M}$ $\ce{HCl}$ is added to $100~\mathrm{mL}$ of this buffer.

This one I do not understand.


texts: How much does the quality of glassware matter, really?

texts:
Discussing about the pros and cons of glassware from different manufacturers for chemistry experiments easily becomes a heated debate. Well, that's how it seems if you read the chemistry related blogs, discussions, questions, etc. over the internet. How much does it really matter what kind or type of glass one is using? How big the differences are across different manufacturers?

It would be nice if the answers also elaborated on the differences between laboratory and home chemistry.


texts:
I just wanted to make sure how we can know whether it is $K_c$ (equilibrium constant of concentrations) or $K_p$ (equilibrium constant of pressures) which "comes out" of the equation, $\Delta G^o= -RT \ln(K)$.

Until now, I have always taken $K_c$ when the reaction was in a solution or $K_p$ if it was a gas. But as there is a difference between their values, I'd like to know exactly which one to take.


texts: Turbidity is essentially the clarity of water. Turbidity can be measured in many ways such as a turbidimeter, secci disk or a turbidity tube (which incorporates a secci disk at the bottom). If you had a small turbid water sample - 20mL, how could you measure the turbidity without an electronic device??


texts: Why can SN2 reactions occur when the reagents are a primary substrate and a weak nucleophile/base?

texts:
The reagents are ethyl bromide and water. In this Khan Academy video at 5:20, the narrator says because ethyl bromide is a primary substrate, the reaction is neither SN1 or E1. This makes sense because SN1 and E1 favor tertiary carbocation.

But between SN2 and E2 reaction, the narrator says SN2 is more favorable. However, water is a weak nucleophile/base, while SN2 or E2 reactions require a strong nucleophile/base.

Why are SN2/E2 able to happen in this case? Is it because water can only act as a weak base but not a weak nucleophile so that SN2 is more favorable?


texts: Hydroboration, steroselectivity and anti-markovnikov product

texts:
My first question has to do with the fact that Hydroboration produces an anti-markovnikov product, why?. I don't see how that happens. A wikipedia artical says that B has a partial positive charge because it reacts slightly faster than H to form the bond but how is that possible when both H and C are more electronegative.
My second question is that why are boranes, that are highly substituted, lead to a greater yield in anti-markovnikov product?
Is it because something like 9-BBN can't be on top of a CH2 group because it's too big, and so it has to attach to the terminal C atom.


texts: What happens when C17H35COO-, a soap, reacts with an acidic solution?

texts:
My book says that-

  In acidic water, the negative fatty acid ions become fatty acids.

However, they did not include a chemical equation to demonstrate this, so I made my own:

$$\ce{C17H35COO- (aq) + HCl (aq) -> C17H35COOH (aq) + Cl- (aq)}$$

But according to this equation, the fatty acid ion is a base, since it gets a proton. So this must be wrong. Can anyone point out my mistakes (if any), and explain what happens when a negative fatty acid ion comes in contact with acidic water, and becomes a fatty acid?


texts: What kind of bonds (σ or π) are formed by px, py and pz orbitals?

texts:
Our chemistry teacher said that two  $\mathrm{p}_z$ orbital only form sigma bond whereas  two $\mathrm{p}_x$ and two $\mathrm{p}_y$ orbitals form only pi bond.

He also stated that only $\mathrm{p}_z$ orbital forms a sigma bond with the $\mathrm{s}$  orbital.

But in our book it is written that $\mathrm{p}_x$, $\mathrm{p}_y$, and $\mathrm{p}_z$ orbitals can form both sigma and pi bonds.

Please give me the correct explanation.


texts: How can I detect a specific molecule on a surface?

texts:
Based on the comments and answers, this question wasn't very clear, so I have completely overhauled this question to make it much clearer in another post:
How to create the equivalent of luminol for a compound?

Original Post/Question:

I'd like to be able to detect trace amounts of the chemical 'monomorine I' (5-methyl-3-butyloctahydroindolizine) on a surface. (It is an ant pheromone)

Is there an easy way to determine if the molecule is visible in IR or UV? (before I spend the money on this equipment)

Is there a strategy for causing a visible reaction? or even a reaction visible by IR or UV?

Advice on where to even begin would be a huge help.

(I do not have a chemistry lab with a Mass Spectrometer at my disposal)


texts: How will a NPK 15-0-15 fertilizer affect this soil?

texts:
If the soil we have has pH 7,2 and we want to add this fertilizer which has 15-0-15 (NPK). What should the fertilizer contain in order for the pH to get reduced?

I believe that $\ce{K+}$ ions should derive from $\ce{KCl}$ because it won't affect the pH.If it comes from $\ce{K2SO4}$, the soil will be more alkaline.
I'm confused about the nitrogen. Should it come from urea or NH4NO3? I believe that if the ions come from urea it will be more alkaline. Or should it come from $\ce{(NH4)2SO4}$?


texts: Kinetics Vs Thermodynamics : Apparent contradiction in the definition of Enthalpy in the two disciplines

texts:
My book gives the following curve:

It gives the following relation :$$ΔH= E_{\mathrm{activation,forward}}-E_{\mathrm{activation,backward}} \tag{1}$$
But I suspect that $ E_{\mathrm{activation,forward}}-E_{\mathrm{activation,backward}}$ corresponds to change in Internal Energy of the system ΔU.
or $$ΔU= E_{\mathrm{activation,forward}}-E_{\mathrm{activation,backward}} \tag{2}$$
However,at a constant pressure, heat of reaction or Enthalpy change $$ΔH = ΔU + PΔV \tag{3}$$
Statement (3) contradicts statements (1) and (2) or is valid only for $ΔV=0$

This source contains the same graph : https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book%3A_Introductory_Chemistry_(CK-12)/18%3A_Kinetics/18.04%3A_Potential_Energy_Diagrams

What is going on here?
In case, you feel that the graph is given only to cover a particular kind of reaction, please provide relevant comments.


texts: Which calcium salt is good enough to make calcium benzoate?

texts:
This question is inspired from the following questions:

Reaction of citric acid and calcium chloride
Precipitation of citric acid by CaCl2 and Ca(OH)2?

The answer to the 1st question says that calcium citrate is highly unlikely to form from calcium chloride and citric acid because of its inability to be present in deprotonated form and will not precipitate in acidic medium. 2nd question also addresses a similar kind of problem. But what about calcium benzoate?

Which calcium salt can succesfully precipitate calcium benzoate from benzoic acid? Would calcium hydroxide work for that? I am pretty sure calcium chloride won't work because it is a good dehydrating agent and would rip off water molecules to form something else. Calcium benzoate is also somewhat more soluble in water than calcium citrate. So, what should be the necessary measure to successfully precipitate calcium benzoate?


texts: Kinetic energy of electrons emitted in Photoelectron Spectroscopy

texts:
In multiple sources (example), I found the information that the kinetic energy $E_k$ measured using (Ultraviolet / X-ray) Photoelectron Spectroscopy is given by:

$E_k = h\nu - B.E._F - \phi_{spec}$

where $h\nu$ is the energy carried by the incident photon, $B.E._F$ the energy difference between the energy level of the electron and the Fermi energy and $\phi_{spec}$ the work function of the spectrometer.

As far as I understood the measurement process, the actually measured quantity in Photoelectron Spectroscopy is the kinetic energy $E_k$ of the electron. This energy is measured by the radius of the electron in a homogeneous electric field. Thus, the kinetic energy of the electron after the emission would $E_k = h\nu - B.E._F - \phi_{sample}$, this independent of the work function of the spectrometer. So where does this difference come from?


texts: irreversible adiabatic process against constant external pressure?

texts:
My book has these formulae for irreversible adiabatic process against a constant external pressure $p_ext$ : $$ T_f = [\frac{C_v+(p_{ext}/p_1)R}{C_v+(p_{ext}/p_2)R}]T_i$$. It is also mentioned that when external pressure = p2 $$ T_f = [\frac{C_v+(p_{ext}/p_1)R}{C_p}]T_i$$. How do I get these formulae?
I am getting confused because they are saying external pressure. In general when irreversible work don't we take into account only the external pressure and not the internal pressure? And why exactly is this so? I have assumed so far that this is because the internal pressure differs only slightly from the external pressure. Is this so? Would someone please explain this?


texts: Maximum non-PV work and reversibility at constant temperature and pressure

texts:
When we talk about systems at constant temperature and pressure, maximum amount of non-PV work can be extracted if process is carried reversibly and in that case it is equal to change in Gibbs energy of the system. When system does work, Gibbs energy of system decreases and vice versa.
When we have chemical reaction in the system (for example electrochemical process in galvanic cell) than Gibbs energy of the system changes because of that reaction.
Basically, what does it mean to carry chemical reaction reversibly or irreversibly? Does carrying reaction reversibly mean that system is at chemical equilibrium where reaction Gibbs energy equals zero?
If so, how can we extract any non-PV work (in our case non - PV work is electrical work since we are talking about galvanic cell) if system/reaction is already at equilibrium?
Electromotive force of cell is zero at equilibrium and such cell can't be used to power anything (electric motor for example).


texts: Counting basis sets in quantum chemistry

texts:
I have to use STO-nG (a "minimal basis set" - meaning that only one basis function is used for each atomic orbital in the atoms of which the molecule is made from). Let's take the example of a water molecule.

The water molecule has two H atoms and one O atom. Thus, we have a total of 7 orbitals (two 1s of H, one 1s of O, one 2s of O and three 2p of O). So when using STO-nG, would that then mean that three 1s type basis functions, one 2s type basis function, and 3 p-type basis functions are used, totalling at 7 basis functions, each being made up from a linear combination (LC) of n simple gaussians?


texts:
I refer you to this set of presentation slides. On slide 8, the author explains the preference for the staggered conformation of ethane by saying that there is a favourable hyperconjugative interaction between $\sigma^{}_{\ce{C-H}}$ of the $\ce{C-H}$ bond in one methyl group and $\sigma^{*}_{\ce{C-H}}$ of another $\ce{C-H}$ bond in the other methyl group.

However, I am puzzled by the diagram. Since both $\ce{C-H}$ bonds are similar in terms of bonding, their bonding and antibonding $\sigma$ molecular orbitals should have the same energies. Instead, the diagram shows that one of the $\sigma_{\ce{C-H}}$ bonds is lower than the other in energy. How can this be right? I have shown a screenshot of the diagram below.

Also, how can a $\sigma_{\ce{C-H}}$ donate electron density to a $\sigma^*_{\ce{C-H}}$ effectively? After all, the energy difference between them is rather significant since the orbital interaction between the atomic orbitals of $\ce{C}$ and $\ce{H}$ is large.


texts:
I have a laser cutting machine and have always read that PVC (or types of vinyl in general) are very dangerous to cut because it releases chlorine gas. Chlorine gas = toxic (plus the $\ce{HCl}$ thing), makes perfect sense. This is well-known information, and it appears all over informational sites about laser cutting materials.

But I now have someone telling me that cutting polyurethane foam is way more dangerous since it produces $\ce{HCN}$ (hydrogen cyanide). Now this information is in a few limited places and mentioned kinda as a footnote, but it is not nearly as widespread as the Chlorine gas risk that is talked about elsewhere. (I know that the chlorine gas presence during cutting of PVC effectively makes $\ce{HCl}$ gas which clearly does damage to the laser system itself which might explain the prevalence of the information about it)

I know that polyurethane is made with isocyanates, which I'm wondering if that is leading to some people seeing that word and getting confused and assuming that there is cyanide in the foam.

What is confusing about this is that polyurethane is generally considered a very "laser friendly" material to cut (stated all over the place on laser hobbyist and professional websites under acceptable materials). Producing the same gasses that were used in gas chambers seems pretty darn dangerous and like there should be red flags up everywhere.

Can anyone here speak to the chemistry of this, firstly how much if any HCN would be produced by using a 10000nm laser (meaning intense heat based, but nonflaming cutting). And if properly ventilated with an industrial air handling system designed to move the full volume of air from the cutter outside many times per minute what are the risks involved? Does HCN bond to surfaces and stick around? Or is it fully ventilated as a gas?

Clearly, I'm not a chemistry expert, so looking for someone who knows more to help me understand what is real and what is just scary sounding jargon.


texts: Free radical bromonation of 1-ethyl-4-nitrobenzene

texts: In the above reaction , I am confused between . Among them which is major product and why .


texts: Origin of the 15% difference limit between solute and solvent atom radii in the Hume-Rothery rules

texts:
According to the Hume-Rothery rules for the substitutional solid solutions the atomic sizes of the the solute and solvent must not differ by more than 15%.
Why should it be so?


texts: What is the mechanism for the conversion of thiourea to diazomethane?

texts:
I really want to know how this reaction works:
\begin{align}
\ce{SC(NH2)2 + 2 NH3 &-> CH2N2 + 2 NH4+ + S^2-}\\
(\ce{S=C(NH2)2 + 2 NH3 &-> H2C=N=N + S(NH4)2 })
\end{align}

This seems like it ought to be a pretty simple mechanism, but I don't know a lot about organosulfur chemistry and I am having difficulty explaining this reaction to myself. This reaction will also occur with thioacetamide, forming N-mathanimine ($\ce{CH3-N=CH2}$) if that helps. Also, thiourea does thione-thiol tautomerism.

MY friend and I scribbled some arrows. I don't think it's a good mechanism, but is this the general idea?

Does this make any sense?


texts: Equilibrium constant when adding more of a reactant

texts:
Suppose I have the reversible reaction:

$$\ce{A +B⇌ C} $$

The reaction is at equilibrium with equilibrium constant $K$

I am told that if I increase the concentration of $\ce{B}$, the rate for the forwards reaction will exceed the backwards one. Fair enough.

I am also told that $K$ will necessarily increase. Why though? Its true that Forward reaction > back ward reaction until we reach a new equilibrium such that more of $\ce{C}$ is produced but I don't see why this implies in any way that the final quotient $\frac{[\ce{C}]}{\ce{[A][B]}}$ will necessarily be any greater.

Certainly if we have a simple reaction:

$$\ce{A⇌ C} $$

and we add more of $\ce{A}$, then the equilibrium constant for the new final final state will remain as it was, ceteris paribus.

What am I getting wrong, because my textbook suggests that $K$ will always increase, no matter what type of reaction I am dealing with (of course, as long as all reactants are in a suspended form, e.g. dissolved or gaseous and the reaction is subject to Le Châtelier's principle).

Please, if possible, keep the answer as a level intelligible to a high-school student. I don't know much about advanced university chemistry.


texts: Why is diamond said to be transparent to X-rays? Does this statement mean that X-rays can pass through diamond? If that is the case, then how does one explain this phenomenon?


texts:
I've been reading a bit about the magnetic moment (spin-only) $\mu_{s.o}$ where they give a formula relating this to the number of unpaired electrons

$$\mu_{s.o}=\sqrt{n(n+2)}$$

where $n$ is the number of unpaired electrons.

However in our lecture today we were using the approximation $\mu_{s.o} \approx n+1$. Is this  an acceptable approximation for the magnetic moment or should I stick to using the previous one.

Obviously using $\mu_{s.o} \approx n+1 $ is easier to use for calculations but I would like someone's opinion on this.


texts:
From what I know, good inorganic chlorinating agents, $\ce{SOCl2, PCl3, PCl5}$ are able to substitute a poorer leaving group (like $\ce{OH-}$) for chlorine. For example, for substitution of the hydroxyl group to a halide to form a haloalkane, we can't just use hydrogen halides (we can if we first dehydrate it into an alkene, but that is besides the point), but instead use strong chlorinating agents like those mentioned above. I know $\ce{Cl2, HCl, ClO-, CCl4}$ etc. are also chlorinating agents, so what makes them "inferior"? Also, why are some other chlorine-containing compounds like $\ce{ClO3-, CH3COCl, C2H5Cl}$ not considered good chlorinating agents?
Is it similar to how we gauge the oxidizing strength by seeing how high the oxidation number is (the higher the oxidation state or electronegativity, the more electron-hungry it is, and the more willing it is to accept electrons)? Maybe I'm overthinking this and it's just because the bond enthalpy is lower?


texts: Why isn't viscosity considered a property of solids?

texts:
Viscosity is defined as a measure of resistance to flow which arises dues to internal friction between layers of fluid as they slip past one another while liquid flows.

Why can't we say that viscosity is a property of solids as well? Except, it would then be said that solids have infinite viscosity.


texts: Are chemical treated as ideal gases when trying to figure out heat of formation using calorimetry?

texts:
At 36:48 of this video lecture, The professor says that the reaction moving from reactants to products keeping temperature of both same and under standard condition is an isothermal constant volume process.
Some some four minutes later (41:57), he uses the sum of energy of whole cycle property and equates, the $U_{rx}$ to the other definition of other definition of heat change given by calorimeter using the law that sum of internal changes over a loop process is zero.
He gets:
$$ \Delta U_{rx} = - C_{v}^{calo} \Delta T$$
where $C_{v}^{calo}$ is energy change of calorimeter.
Now, what I find weird is that by the definition of the path-3 being isothermal, shouldn't $$ \Delta U_{rx}$$ be zero..?
My resolution for this was that maybe the gas not really ideal and that it may change energy loss by expanding but I'm not sure how I would justify this more authoritatively. So, my question is, when we talk about these chemistry reactions, do we treat gases as non-ideal?


texts: Why is it obligatory to cool down the container of a sample to measure its mass in a lab?

texts:
We were doing an experiment about hydrated crystals and more precisely how to determine $n$ in $\ce{CuSO4.nH2O}$. After we heated the crucible we were to cool it down using a Desiccator. Then this question came to my mind: Why must we cool it down? By doing researches in the Net I were only able to come up with these suggestions, but none seem very applicable for me:
Using Einstein's formula:
His famous equation:$$E = mc^2$$
This means that matter is able to be converted to energy. Thus, more energy should mean more mass because $C$ is constant. However, I argue that since $C$ is a very large number, normal and observable-in-normal-labs changes in energy aren't able to modify the net change of the mass dramatically (to a degree that the balance is able to detect)
A gut feeling, no backup research:
Anyone sane, and with regards to the value the balance has in the lab, would give slightest chances that the hot container would harm the surface of the balance and therefore, damage it. But chances are that I'm wrong too.
So, why must we cool the crucible in order to measure the mass of the sample in it using a balance?


texts:
What is the percent concentration of hydrogen peroxide which has a concentration of $500~\mu\mathrm{M}$?

Is $500~\mu\mathrm{M}$ $\ce{H2O2}$ toxic to the eyes?

A particular honey has a concentration of $\ce{H2O2}$ of $500~\mu\mathrm{M}$ after a 24-hour incubation time, after it has been diluted. I am trying to figure out what the concentration is in percent (%).

I recalculated and the result is actually $0.00153\%$ for $500~\mu\mathrm{M}$. $0.0012\%$ is the equivalent to $400~\mu\mathrm{M}$, but I need someone to confirm this. Someone on researchgate wrote that $30\%$ of $\ce{H2O2}$ is $9.8~\mathrm{M}$.


texts: Melting point of alkaline earth metal carbonates

texts:
The melting point of carbonates of group 2 elements is (From Wikipedia)

$\ce{BeCO3}$ : 54
$\ce{MgCO3}$ : 540
$\ce{CaCO3}$ : 1339
$\ce{SrCO3}$ : 1494
$\ce{BaCO3}$ : 811

A similar trend is followed by alkali metal carbonates (from Wikipedia). But in the inorganic chemistry book by Shriver and Atkins, this is given

Is there a difference between decomposition temperature and melting point? Or is the values given in the book wrong?


texts: Complete Oxidation and Redox Equations for Sacrificial Galvanic Anode

texts:
I'm trying to get a more complete picture of how the chemistry works within a typical marine setup including a sacrificial anode. The setup consists of an aluminum hull, another metal (say a stainless steel propellor) and then a zinc sacrificial anode. We can ignore the steel propellor. What are the oxidation and redox equations for the aluminum and zinc? Seems like marine blogs don't care about this level of detail and chemistry courses don't use saltwater as the solution...

I'm really curious about what is going on at the aluminum cathode. I think the oxidation equation for the zinc is something to the effect of:

$$
\ce{Zn + something -> Zn^2+ +H_2}
$$

Therefore the zinc disappears. But what happens to the aluminum? There is no aluminum in solution to precipitate so where do the electrons go?


texts:
How to determine the order of nucleophilicity for given chemical species?

Like I came across this question, to rearrange $\ce{RCOO-, OR-, OH-, H2O}$ (alkyl acetate, alkoxide, hydroxide, and water) in decreasing order of nucleophilicity and it ranked $\ce{OR-}$ first.

Shouldn't it be $\ce{OH-}$ since $\ce{OR-}$ would be more sterically crowded?


texts: Calculate the third and fourth nearest neighbours in bcc

texts:
My textbook has given data for third and fourth nearest neighbours to be 12 and 8 with distances $\sqrt{2}a$ and $\frac{\sqrt{11}a}{2}$.

I have been able to calculate for  the first and second nearest neighbour but it has become difficult to visualise for the other two to calculate. Can you help me with hints on how to proceed preferably with a diagram.


texts: difference in boiling point of 2-iodopentane and 3-iodopentane

texts: There is no difference in boiling point of 2-fluoropentance and 3-fluoropentane, so is chloro- and bromo-. But why is there a difference in the boiling point of 2-iodopentane and 3-iodopentane, up to 10 degree Celsius?


texts:
In certain applications some sorts of stainless steel (V2A, 1.4301) corrode when exposed to $\small{\ce{Cl^-}}$ in water, or at least it is strongly advised to use other steels.

The conditions that were explained to me as being especially bad were: redox potential >0, acidic environment.

Under these conditions, why do I need $\small{\ce{Cl^-}}$ to corrode steel? I would think that any electrolyte would have a bad effect.

Edit to add 26.7:
Most stainless steel contains chrome, a layer of $\ce{CrO}$ is what's protecting the steel. Most articles mention that $\ce{Cl^-}$ damages this layer. More resistant steels use $\ce{Ni}$ (and are more expensive because of that). So, to narrow down the question, how does $\ce{Cl^-}$ attack the passive layer?


texts: Calculating the amount of oxygen in a glass using candle burning time

texts:
I would like to calculate the amount of oxygen or concentration of oxygen in a glass or conical flask using candle burning time.
I am thinking of a simple way to calculate this based on the fact that the atmosphere contains $21\,\%$ oxygen. But I am not sure if this would give correct values.
Here is what I am thinking about:
I could do a candle and glass experiment and count the time for burning of candle.
First I will take a glass with atmosphere air and then keep it inverted on burning candle and count the time for burning.
Next I will take a glass with oxygen-enriched air (with unknown concentration) and then keep it inverted on burning candle and count the time for burning.
Here is a simple formula using cross multiplication, I could use
$$x = \frac{t_\mathrm{OEA}}{t_\mathrm{air}}\cdot 21\,\%,$$
where $x$ is the concentration of oxygen-enriched air, $t_\mathrm{OEA}$ is the time taken to burn in oxygen-enriched air, $t_\mathrm{air}$ is the time taken to burn in atmospheric air.
Is this possible or is there a way to do this without having to buy oxygen sensors?


texts: How to transform a tertiary alcohol to a carboxyl?

texts:
I am trying to transform a lipid with a tertiary alcohol into a carboxylic acid.

More specifically, I want to convert to diplopterol (see below) into something homologous to cholesteryl hemisuccinate (see below).

Any suggestions?

Diplopterol:

Cholesteryl hemisuccinate:


texts: Do solid insoluble ions react with soluble ions in aqueous solution?

texts: Do solid and insoluble ions (like aluminium phosphate) react with soluble ions in aqueous solution (like potassium sulfate)?  When would a solid ion react with an ion in aqueous solution in general?