texts:
I'm a maker and I've been interested in 3d printing for years.

I have found a technique for dissolve the PLA supports in a model printed in 3D in HIPS

I have printed the model in HIPS and the support in PLA
I have put the 3D model in a ultrasonic cleaner in the solution with water and sodium hydroxide

(1 liter H2O + 200 grams NaOH)

The PLA has dissolved after 3 hours with temperature 65° and 1 hour of ultrasonic sound.

I attach a youtube link with a similar experiment

https://www.youtube.com/watch?v=uWYn5wJ72zY

Is it possibile use another substance / solution less dangerous and less toxic?

In theory, the PLA is biodegradable. Is it correct?

Ps:
I want use this combination of materials HIPS for model and PLA for Support.

Thank you in advance for the answers.


texts: Reaction of benzene diazonium salts with different compounds

texts:
1. $ \ce{ArN2+Cl-}$ gives addition product with $\alpha,\beta$ unsaturated acids, with decarboxylation being integral part of reaction. For example,
  $$\ce{ArN2+Cl- + Ph-CH=CH-COOH -> Ph-CH=CH-Ar +CO2 + HCl}$$

  2. With $\ce{SnCl2/HCl, ArN2+Cl-}$ given phenyl hydrazine $\ce{ArNH-NH2.HCl}$

I can not find mechanism of any of these reactions, first reaction seems  similar to Meerwein reaction (without $\ce{Cu^2+}$), but certainly can't follow similar mechanism. Second reaction is completely different from either. What are the reaction mechanisms of each?


texts: How much CO₂ should one expect in an IR spectrum?

texts:
I ran an IR spectrum ($\ce{KBr}$ pellet) and found a sharp absorbance at $2360 \text{cm}^{-1}$, which was unexpected. As far as I can tell, this indicates either a nitrile or $\ce{CO2}$.

I know that there is no nitrile in my product. Would you expect atmospheric $\ce{CO2}$ to show up to a noticeable degree in a typical IR spectrum?


texts: I suspended iodine over steel nails. What are these droplets that formed?

texts:
I suspended about 15g of iodine crystals over a couple of nails to see how quickly they would begin to rust.

After a week, these droplets had formed. When prodded they broke apart like water drops.

What are these? My guess is that the iodine sublimated and then combined with water vapor.

The original question that prompted this experiment.

The setup (~one week prior)


texts: Is Iodoform test restricted for only methyl ketones?

texts: Do only methyl ketones give iodoform test? Where can a keto methyl group be present in?


texts: Lone pair electrons on secondary carbon vs primary carbon

texts: I know that a molecule is more stable when a free radical is on a secondary carbon over a primary carbon, but how about when there is a lone pair of elections that can be placed on a secondary or primary? Is there any difference in the stability of the molecule or does that only apply to free radicals?


texts:
I was trying to write a C++ code following the instruction given in this website. The problem is in the two electron integral file, only 228 entries for 7 molecular orbitals are provided. But my code says it should be 406 (please see below)

int NFI=0; //NFI=number of four electron integrals
for (int i=0; i<NAO; i++){
 for (int j=0; j<=i; j++){
  for (int k=0; k<=i; k++){
   for (int l=0; l<=k; l++){
    int ij=i*(i+1)*0.5+j;
    int kl=k*(k+1)*0.5+l;
     if (kl<=ij){NFI += 1;}
   }
  }
 }
}
printf("%d\n",NFI);

I'm using 4 criteria as can be seen in this code snippet. Can anyone explain me why the number of unique integral is 228, not 406?

As per suggestion, I compared my index with the index provided, here they are

1 1 1 1                   1     1     1     1
2 1 1 1                   2     1     1     1
2 1 2 1                   2     2     1     1
2 2 1 1                   2     1     2     1
2 2 2 1                   2     2     2     1
2 2 2 2                   2     2     2     2
3 1 1 1                   3     3     1     1
3 1 2 1                   4     4     1     1
3 1 2 2                   5     5     1     1

Left 4 numbers are generated from my code and right 4 numbers are given in the input file. (3,1,1,1) is missing in the data file provided (I checked the whole file), but it fulfills the criteria of $ij \geq kl$.


texts: Is a gas leak considered incomplete combustion?

texts:
This may be a dumb question, but if I leave the stove-top valve open (or I have a gas leak due broken tubing), would that be considered incomplete combustion?

From my knowledge, I figured a reaction is necessary for combustion to occur and that just the leaking of a gas would not qualify.


texts: Is there any porous material that can have narrow parallel and "perfectly straight" cavities/holes through it (or bored through it)?

texts:
I'm basically looking for a material that can allow photons to pass through its cavities, but only those photons that travel at an angle (almost) exactly perpendicular to the materials surface. Non-perpendicular photons should be absorbed by the material upon impact as much as possible.

I can imagine perhaps a stack of graphene sheets, or a bunch of parallel carbon nanotubes? Or maybe a high precision laser drilling through ...something else? Clearly I'm no chemist or material scientist, so I'm hoping to tap into the knowledge of this community.


texts: Physical significance of chemical potential and fugacity

texts:
I'm studying equilibria and thermodynamics and came across these two terms.
My problem is, unlike other thermodynamic properties that I can understand physically like volume, pressure, enthalpy etc. do these two quantities have physical significance or, is it just that we define fugacity (without any physical meaning) just to make sure the equation
$$\mu - \mu_0 = RT\ln\frac{p}{p_0}$$
looks the same for real gases? If yes, then what is the motivation for the name “fugacity” meaning literally “escaping tendency”?
Similarly, do we just define chemical potential randomly, since it's extremely useful in various calculations when the composition varies, or does it have some physical significance?
Also, why do we call it chemical potential?


texts: If I react selenium powder with copper chloride powder above the melting point of selenium (221 °C), will I end up with a chunk of copper selenide, with the chlorine given off as gas, or will I lose some or all of the Se as as selenium chloride gas?


texts: How does one determine the relative basicity of a nitrogen in a molecule?

texts:
I'm trying to solve this problem:

Specifically, how does one know which nitrogen is more basic? I'm assuming that for the first molecule, that it's the nitrogen without the proton, since it seems like the other nitrogen has already been protonated (and already has acted as a base.)

Is my reasoning correct? How does one solve the other molecules?


texts: Can organomercury compounds synthesize accidentally from household cleaning products?

texts:
I had broken a CFL partially on carpet last week. It was a spent bulb, and the outer glass shell broke but not the fluorescent tube - apparently the tube did have a small hole in it which found out after all my other steps when I saw it in the garbage.

When I cleaned it up first, I used a mild spray cleaner which contained methyl esters and various surfactants - I found this out now, not then, or I wouldn't hzve used it. Wiped it all up with a paper towel, then vacuumed in case I missed small pieces. I did ventilated at that point.

About two hours later, my cat made a mess on the rug. At that point, I sprayed down the carpet with resolve (which says it contains hydrogen peroxide). Wiped that all down with a towel, then revacuumed...and realized I hadn't cleaned out the dust cup. I think I then emptied that outside and cleaned out the HEPA filter.

My concern now is what I may have exposed myself to in that botched cleanup. Any ideas on what may have formed? Do I need to be concerned?


texts: finding out fractions of ions(different valencies/charges) of an element in non-stoichiometric compounds

texts:
Analysis shows that nickel oxide has the formula $Ni_{0.98}O_{1.00}$. What fractions of nickel exist as $Ni^{2+} $and $Ni^{3+}$?

What i did:

Let the number of $Ni^{2+}$ and $Ni^{3+}$ atoms be $x$ and $y$ respectively

one  atom/ion of $Ni^{2+}$ satisfies one  $O^{2-}$ atom

$2 \over 3$ atom/ion of $Ni^{3+}$ one  $O^{2-}$  atom

and then i wrote down the equations:
$x + $$3 \over 2 $$y =1$  and  $x+y=0.98$

Then i solved the equations to get the answers:

$x=0.94 $  $and$ $y=0.04$

Is what i did correct? If not then guide me how to solve the question


texts: Is CO2 produced when KHCO3 reacts with H2O?

texts: We have been doing experiments on the rate of photosynthesis to find out the importance of $\ce{CO2}$ and we used $\ce{KHCO3}$ in one beaker and found that the plant kept in that beaker produced greater amount of oxygen that those without it. Sources say that $\ce{KHCO3}$ acts as a source of $\ce{CO2}$ but I'm not sure of it. What is the reaction taking place to produce $\ce{CO2}$?


texts: Acidic nature comparison; benzoic acid and phenylacetic acid

texts:
The $\ce{pK_a}$ values of benzoic acid and phenylacetic acid are around 4.2 and 4.31 respectively.
In benzoic acid, you have the resonance being the dominating effect, destabilizing a conjugate base anion. In phenylacetic acid, resonance doesn't work anymore, and only the -I inductive effect remains, which should stabilise the anion.
Why, then, is benzoic acid the stronger acid?


texts: Is it customary to express heat loss as a negative number?

texts:
In my chemistry class, we had a problem akin to the following:

  If an object with mass bla and specific heat bla is placed into a bla g calorimeter with an initial temperature of bla and a specific heat of bla, and the temperature of the calorimeter rises to bla at the end of the experiment, how much heat was lost by the object?

I performed the calculations and got an answer of, let's say, $8 J$. When I submitted this answer, I was told that it was wrong, and the correct answer would have been $-8 J$. Wouldn't this response to the above question mean that the object gained heat?


texts: Significance of p functions in compounds of the lighter alkaline and alkaline earth metals

texts:
It is often said that lithium follows the duet rule instead of the octet rule, in the sense that there is no practical difference in, say, energies or shapes of lithium-containing compounds, whether the lithium $2 \mathrm p$ orbitals are included in the calculation or not, unlike the case of "usual" main-group elements.
My question is the following:
Does this hold for $\ce{Be, Na}$ and $\ce{Mg}$ as well, or must the $\mathrm p$ orbitals be included in calculations on compounds of (any or all of) these three elements?


texts:
Is the name of the following compound 3-(ethenyl)-5-(prop-1-enyl)-2-(prop-1-ynyl)-4-(prop-2-enyl)cyclopent-2-en-ol?

The problem I am facing is that how do I arrange 5-(prop-1-enyl), 2-(prop-1-enyl) and 4-(prop-2-enyl). In which order do I write these in the IUPAC name?


texts: Do chaotropic and kosmotropic affects occur in polar non-aqueous media?

texts: For example can I introduce salts that have a chaotropic or kosmotropic affect on ethanol? Or is this phenomenon restricted to water? If this phenomenon does occur in other polar solvents, does it follow the Hofmeister series as well? Are there any papers out there on this phenomenon in polar non-aqueous solvents?


texts: Ramachandran Plot for Phi and Psi angles of peptides

texts: Why do we consider the normal and extreme limits for Ramachandran plots to be less than the Van Der Waal distances between two atoms?


texts:
I was reading Linus Pauling's book How to Live Longer and Feel Better, and in various places in the book he discusses a correlation between increased sucrose intake and increased blood plasma cholesterol levels, as reported in a study by Milton Winitz.

Pauling writes:

  ... the metabolism of sucrose yields in it's first step equal amounts of glucose and fructose.  ... Fructose metabolism goes in part by a different route such that it produces acetate, which is a precursor of the cholesterol that we synthesize in our liver cells.

I was wondering specifically what the metabolic pathway from sucrose to cholesterol is and given say 100 grams of sucrose, how much will be turned by the body into cholesterol.


texts: What is the energy change of ethene reacting with hydrogen gas?

texts:
$\ce{CH2CH2(g) + H2(g) -> CH3CH3(g)}$

Using this table, source: http://www.kentchemistry.com/images/links/Kinetics/TB08_003.GIF

C-C enthalpy = 348 kJ/mol
C-H enthalpy = 413 kJ/mol
H-H enthalpy = 436 kJ/mol

The way I see it, H-H has to break, C-C has to break, and then two C-H bonds have to form.

(Units omitted) Therefore, should the answer be: $413 \cdot 2 - 348 - 436 = 42 \, \text{kJ/mol}$

So then it has to be an endothermic reaction.  Is this correct, or am I wrong?


texts:
I was wondering if anyone could help troubleshoot an experiment I'm working on.

I'm running an experiment to measure the microbial respiration of compost samples using a $\ce{NaOH}$ trap.  Each sample is in a jar with 20 ml of 1M $\ce{NaOH}$ and is placed in an incubator for 24 hrs.  After 24 hrs, 20ml of .5N BaCl2 and an indicator are added to the $\ce{NaOH}$ and it is then titrated with $\ce{HCl}$.  I run a few blanks each time, with an $\ce{NaOH}$ trap in a jar without a compost sample. This is repeated over 4 days In theory, I should need less $\ce{HCl}$ to neutralize the $\ce{NaOH}$ which has been sitting with the compost samples then the $\ce{NaOH}$ just by itself.  Sadly, after hours and hours of work in the lab, this has not been the case!

I have 45 different samples of different types of compost. Each time I run the test, about a third of the samples require more $\ce{HCl}$ to neutralize than the blank.

The blanks are all consistent in the amount of $\ce{HCl}$ needed, I ran three last night and one the night before.  The test also seems to be picking up samples which are respiring heavily- when there are moldy samples, they require only a small amount of $\ce{HCl}$.  I can't really decipher a trend with the ones that require more $\ce{HCl}$ to titrate than the blank other than that it's somewhat consistent. 41% of the samples which needed more $\ce{HCl}$ than the blank on day 2 also needed more on day 1, and of the day 2 "error samples", 88% were from a treatment which had an "error sample" on day 1.

I thought perhaps this had to do with ammonia volatilizing from some of the samples, but this doesn't necessarily make sense with the samples which are taking more $\ce{HCl}$ than the blank. I also noticed that on the samples which require more $\ce{HCl}$ to titrate than the blank, there seems to be more precipitate (barium carbonate?) that settles out after the titration.

Do you have any idea what could be happening or what I am doing incorrectly?  It's definitely a long process to do this measurement for 48 replicates over 4 days - I'm hoping the data isn't totally worthless.

Thanks

Edit: Pictures

On the left are samples which required less HCl to neutralize than the blank.  (I forgot to add an extra 20ml of BaCl2 to the second from left, which I had added an additional 10 ml NaOH to, so that one is an error).  In the middle is the blank and a sample which required the same amount of HCl to neutralize as the blank.  Then on the right are samples which required more HCl than the blank to neutralize.


texts: Recognising a rate-determining step in E1

texts: If there is a hydride/methyl shift possible in E1, then is the carbocation formation the rate-determining step (RDS), or the shift, or is it considered a cumulative step and happens all at once?


texts: How are reaction enthalpy and entropy affected by temperature

texts:
The equation for Gibbs Free Energy demonstrates how the standard change in Gibbs Free Energy for a reaction is affected by temperature.

$$\Delta G^\circ =   \Delta H^\circ - T\,\Delta S^\circ$$

However, to my understanding, the equation makes the inherent assumption that the standard change and enthalpy and the change in entropy for the reaction is unaffected by temperature. I have heard that this is not true and that reaction enthalpy and entropy are indeed dependent on temperature. However, I do not know how exactly temperature affects the two and why.

Would a reaction occurring at a higher temperature be more or less exothermic? Or does it perhaps depend on the reaction itself?

I know that the entropy of a substance increases at higher temperatures but I do not know how this correlates to the situation of a reaction since I'd assume that both the reactants and the products would be at a higher entropy.


texts: What is diamagnetic in diamagnetic dilution?

texts:
I'm reading a paper where the authors study a peptide solution where each peptide may have two spin labels attached to them. They put the peptides on the surface and study them using a diamond sensor.

They perform the experiment in two ways. First, they put only peptides with attached spin labels. Then, they dilute the solution with peptides that do not have spin labels, in a ratio 1:10.

They refer to this dilution as "diamagnetic dilution". I do not know why it's called diamagnetic. I've tried to look for a definition but the term only appears in highly technical papers that I can't understand very well.

Does anyone know why this is called "diamagnetic dilution"?

Ben

Edit: The article I'm referring to is this one:

https://advances.sciencemag.org/content/3/8/e1701116

But my question is general.


texts:
So the hexaaquacopper (II) ion has an octahedral structure with 6 aqua ligands datively bonded to the central Cu2+ cation:

My question is: how is this possible if the electronic configuration of the Cu2+ cation is [Ar]4s-0 3d-9. This only leaves one empty 4s orbital and 3 4p orbitals available for dative bonding which would suggest that a tetraaqua complex should form but this is not the case?


texts: Why can wood burn all the way to charcoal instead of just creating a passivating charcoal layer?

texts: I know burning to charcoal is actually incomplete combustion because charcoal can also burn. When a strike anywhere match burns, it burns all the way to charcoal but the charcoal doesn't further burn. How can all of it burn to charcoal? According to https://en.wikipedia.org/wiki/Pyrolysis, the heat causes pyrolysis which undergoes flaming combustion generating more heat. Once some charcoal has already formed, why doesn't it just passivating the wood blocking further endothermic pyrolysis. I know wood is porous but at the small scale, should't it's surface become passivated by charcoal blocking further pyrolysis? Does it occur for a similar reason that iron can continue rusting after it already formed a rust layer by producing a porous rust layer? Could nonporous single crystal cellulose also burn to charcoal? If so, can you give me a detailed mathematical description of how it would continue burning to create a thicker charcoal layer and how iron can just keep on rusting?


texts:
(Yes, I know the question sounds super-trivial... but bear with me here)

Most chocolates (especially milk-chocolate) tend to melt into this sticky (albeit delicious) mess at temperatures slightly above room temperature. Why does this happen?

From my experience (as a high-school student), most organic solids (at room temperature) tend to either sublime or decompose at moderate temperatures; by "moderate", I mean a temperature range between 25 degrees Celsius (typical room temp) and 50 degrees Celsius (a very hot day in Arizona).

Now why do I find this particular property (ease of melting) of chocolate intriguing all of a sudden? Because chocolate is an organic cocktail of all sorts of compounds such as sugars, lipids, proteins, alkaloids, blah blah blah; yet in the moderate temperature range, it doesn't sublime nor does it decompose (chill the molten chocolate, and you'll still get chocolate)... it first softens and then melts, unlike most other organic substances in that temperature range.

So, what makes chocolate so special? And why does milk chocolate (tend to) melt faster than dark chocolate (higher-cocoa content).


texts: Does 50% hydrogen peroxide dissolve gold?

texts: We have seen that the silver electrodes on a piezo element are being seemingly dissolved by exposure to our mixture of $50\,\%$ hydrogen peroxide. I was wondering if we were to switch to gold electrodes instead of silver could this mitigate the issue. I have not found much if gold is resilient to $\ce{H2O2}$ and was looking here to see if anyone has some expertise.


texts: How does alkaline hydrolysis of peptides occur?

texts:
I have been learning about zwitterions and the isoelectric point, and have been trying to apply this to hydrolysis of peptides. From the diagram in my textbook, I can see that when acid hydrolysis occurs, the amino acids formed from the hydrolysis act as bases because the pH is below their isoelectric point, so they accept the $\ce{H+}$ ions forming positively charged ions.
Now when it comes to alkaline hydrolysis, I don't understand why the peptide would not just be hydrolysed, and then act as an acid and donate the extra $\ce{H+}$ ion on its amine group to the $\ce{OH-}$ ions to form negative ions and a $\ce{H2O}$ molecule. Instead, in my text book it shows something like this:

$$\ce{-NH-CH(CH2SH)-C(=O)-NH-CH(CH3)-C(=O)- + NaOH \\-> -NH-CH(CH2SH)-C(=O)-O^{-}Na^{+} + H2N-CH(CH3)-C(=O)-}$$

I'm really sorry if this makes no sense whatsoever...


texts: Why does a 4-bonded nitrogen atom appears negatively charged after an optimization?

texts:
I have a molecule bearing a quaternary ammonium and I optimized it using M062X (also Hartree-Fock) using basis sets 6-31G(d,p) and 6-31G+(d,p) respectively. After optimization, I expect that the charge on the quaternary nitrogen would be positive. However, it's negative.

I ran the Gaussian to compute NBO charges and analysed the checkpoint files as well as log files. Nowhere could I see a positive charge on any nitrogen atom.

Why is this happening? And how can I obtain a positive charge on the quaternary nitrogen?

Many thanks in advance.


texts: Change of first order rate constant with temperature

texts:
In the decomposition of $\ce{N2O5}$, the time taken to reduce the concentration of $\ce{N2O5}$ half of the original amount is 12 min at $\pu{50^\circ C}$, while 5 h at $\pu{25^\circ C}$ and 10 days at $\pu{0^\circ C}$.

How can we understand that the given assertion is correct because the temperature is different every time?


texts: Why does bond angle decrease in the order H2O, H2S, H2Se?

texts: I know that bond angle decreases in the order $\ce{H2O}$, $\ce{H2S}$ and $\ce{H2Se}$. I wish to know the reason for this. I think this is because of the lone pair repulsion but how?


texts: Why do heavier transition metals show higher oxidation states?

texts:
In p-block elements, higher oxidation states are less stable down the group due to the inert pair effect. This is not the case for transition metals.

Why do heavier transition metals show higher oxidation states than lighter ones? Is the inert pair effect not valid for transition metals also?


texts:
Calcium oxide has a melting point of $\ce{2700^\circ C}$ and sodium chloride has a melting point of $\pu{801^\circ C}$.

If they have the same crystal structure and ions are about the same distance in each crystal, why is there such a big difference?


texts: Mechanism of enolether formation with ethyl orthoformate in estr-4-ene-3,17-dione (Djerassi's norethisterone synthesis)

texts:
The second step of Djerassi's synthesis of 19-nor-17α-ethynyltestosterone (norethindrone), involves the protection of the ketone in position 3 via enolether formation, as in the picture:

What is the mechanism of this reaction? I couldn't find it anywhere. I suppose it should be similar to an ether synthesis, but I'm not sure about the precise mechanism.
(On a side note, I assume that the other ketone in 17 remains intact because of controlled reaction conditions.)


texts:
I'm reading a standard where under the specification for a substance it says:

  Solubility in Alcohol: 1 ml in 3 ml 50% alcohol remains clear to 8
  ml.

Just wanted to confirm my interpretation: I make a 50-50 Ethanol + Water solution (w/w) and then add 1 ml of test-sample to 3 ml of this solution. This should remain clear.

Then I continue adding more of the alcohol solution till total quantity is 8 ml & throughout the mixture must stay clear?

Is this right? Any comments?

Edit:

Here is a supplier specification from Sigma Aldrich which has a variation of the same wording:


texts: Why does magnesium have an exceptionally low melting point?

texts: Why does magnesium have a lower melting point than both calcium and beryllium? It does not seem to fit into the group trend.


texts: Why does raising the surrounding pressure raise the vapor pressure of a liquid?

texts: What’s the qualitative explanation behind the fact that an isothermal increase in surrounding pressure raises the vapor pressure of a liquid? The quantitative expression relating surrounding pressure and fugacity is well-known, but I’d like a qualitative one.


texts: Is CH₃CH(CH₂CH₃)₂ the same as CH₃CH(CH₃CH₂)₂

texts:
The carbon in front of the parenthesis is bonded to 2 CH2 which then bonded to CH3, it cannot bond directly to CH3. I assume the correct way of writing the formula of this molecule will be CH₃CH(CH₂CH₃)₂.
However, the university lecturer says its ok to write CH₃CH(CH₃CH₂)₂ because it is a common knowledge that CH3 cannot bond to both CH2 and C at the same time which indicate that the carbon in front of the parenthesis is bonded to CH2.
Trying to understand the lecturer's explanation, does it mean that in a parenthesis, it doesn't matter whether one person writes the order of bonding forward or backward and it is up to the reader to figure out whether the carbon in front of the parenthesis is bonded to the first or the last carbon in the parenthesis?
I am a non-native English speaker and I hope my question is explained clearly. Tried my best to phase this. Please let me know if any part of the question does not make sense.


texts: Which is more acidic: Me3CCH2COOH or Me3SiCH2COOH?

texts:
Acidic strength of organic acid depends on two factors – inductive and resonance effect.

Now, electron donating groups have +I effect. As a result of which they increase electron density around carbon and adjacent atoms. It results in increased electron density in $\ce{C-O-H}$ bond of acid, making the release of proton difficult. So effect of electron releasing group is that it decreases the acidity of acid.

The trimethyl silicon ($\ce{Me3Si}$) is also electron releasing group but it has lesser donating tendency than trimethyl carbon, $\ce{Me3C}$. Therefore, $\ce{Me3Si}$ inductive effect is lesser than $\ce{Me3C}$ group. Consequently, $\ce{Me3SiCH2COOH}$ is more acidic than $\ce{Me3CCH2COOH}$.

Is this right? Actually, my book writes that $\ce{Me3SiCH2COOH}$ is lesser acidic than $\ce{Me3CCH2COOH}$.


texts: Is it possible to add copper nitrate solution and lead so that a single displacement reaction occurs to yield lead nitrate. I recently melted lead and added cooper nitrate to the molten lead. I then collected the copper nitrate solution I had poured and repeated the process of melting the lead and pouring the solution over it. I figured that eventually the copper will be displaced by the slightly more reactive lead. Will this method yield lead nitrate?


texts: How are t-butyl substituents named according to IUPAC nomenclature?

texts:
What is the IUPAC name of this structure?

I've actually came up with two names, the first one is "1-tert-butyl-5-heptyl-2-propylcyclononane" and the other one is "1-(1,1-dimethylethyl)-5-heptyl-2-propyl-cyclononane". I'm confused which one is right or if both are correct.


texts: Volume change inside a balloon upon decreasing the the outer pressure

texts:
A balloon is filled with hydrogen at room temperature. It will burst
  if pressure exceeds 0.2 bar. If at 1 bar pressure the gas occupies
  2.27 L volume, upto what volume can the balloon be expanded?

Now i can easily figure out that the pressure is 0.2bar at a volume of 11.35L. However, when i check the answer in my book, it says that the volume of the balloon should be less than 11.35L.

However, if you decrease the volume from 11.35L, wouldn't the pressure become greater than 0.2bar, hence bursting the balloon?


texts:
Can somebody help me in identifying the name of $\ce{SnMg2O4}$?
Other examples are $\ce{ZnAl2O4}$ (zinc aluminate), $\ce{ZnIn2S4}$ (zinc thioindate).

Please kindly provide the reference if possible.


texts: Questions on formation of cyclic ethers using Williamson Ether synthesis

texts:
question 1:

In the synthesis, both intra- and intermolecular SN2 can undergo, in which only intramolecular reaction gives the cyclic ethers. However, both reactions happen in the reaction mixture. How can I alter the reaction conditions / add other reagents such that the intramolecular reaction becomes more favorable?
One solution I found is diluting the solution since the rate of 2nd order (intermolecular) reaction drops faster than 1st order (intramolecular) reaction. However, I wonder is it practical to dilute the solution to a large extent for purity, compromising the increased reaction duration and is there any faster and simpler reactions?
question 2:
This synthesis involves SN2, so I am thinking if there is a tertiary carbon bonded to the leaving group, it is impossible to form a cyclic ether. Therefore, are there any other ways I can synthesis cyclic ethers with the starting material as monohaloalcohol?


texts:
I have been reading about resolution in mass spectrometry and there are a few things I do not understand.

The resolving power is determined by $m/(m_2-m_1)$ at full width half height of a peak. The higher the value obtained the better. This is where I struggle to form a link between the resolution of the mass spectrometer and the resolving power. In image (a) below the resolution of the mass spectrometer is 1000 and would have a very low mass resolution value, but in image (b) the resolution is 5000 and the nominal peaks masses are separated, therefore providing a high mass resolution value.

Why can a mass spectrometer with a resolution of 5000 resolve the nominal masses and the mass spectrometer with a resolution of 1000 cannot? And how does the mass resolution come into play? Also, what do the values of 1000 and 5000 mean?


texts: Why is Thorium (At. no. 90) an f-block element at all?

texts:
Being an exception of the Aufbau principle, Thorium has an electronic configuration of $\ce{[Rn]}\mathrm{7s^25f^06d^2}$ instead of the expected $\ce{[Rn]}\mathrm{7s^2 5f^2 6d^0}$.

Two other elements, Lanthanum and Actinium, also showed such an anomaly as $\mathrm{6s^2 4f^0 5d^1}$ and $\mathrm{7s^2 5f^0 6d^1}$, respectively. But we placed them both in the d-block of the periodic table.

Since, even in Thorium, the last electrons occupied d-orbitals only (disobeying Aufbau), then why is it placed in the f-block of the periodic table. I mean, it should be placed in the d-block, shouldn't it?

Edit: Note that here, I don't intend to ask or know how or why the 2 electrons disobeyed the Aufbau, and occupied the higher energy 5d instead of lower energy 4f.

Rather, I want to know only that why it is kept in the f-block when the last orbitals which the electrons occupied were of d-subshell.


texts: Why doesn't the Brady's test (2,4-DNPH) work on carboxylic acids?

texts: Why does the Brady's test, the reaction of 2,4-dinitrophenylhydrazine with aldehydes and ketones, fail with carboxylic acids?


texts: Where can I find the standard molar entropy for ammonium bicarbonate?

texts:
I'd like to know the standard molar entropy S0solid for ammonium bicarbonate to use in an example in class, to calculate ΔS0 for the reaction, NH4HCO3(s) → NH3(g) + H2O(g) + CO2(g).

Already checked: Wikipedia, NIST Chemistry WebBook, Google. I don't have access to the CRC handbook.

(Arthur and Chester Miller already found the standard enthalpy of formation for ammonium bicarbonate, in this forum, in 2016; and it's in the German Wikipedia.)


texts: Nucleophilicty order of various nucleophiles

texts:
Which one is more nucleophilic in strength $\ce{Br-}$ or $\ce{OH-}$?
I am confused since $\ce{OH-}$ is more electronegative than $\ce{Br-}$ but also a strong  base which contradicts for a better  nucleophile .


texts: Does the catalyst alter the Potential energy Surface?

texts: Catalyst provides alternative pathway to the reactants. Does it also mean that the potential energy surface is altered?


texts: Negative charges in acid-catalyzed reactions

texts: Whenever my professor draws a mechanism in an acid-catalyzed reaction, he always says you can't form negative charges. Why is that?


texts: Catalytic iodine in synthesis of phosphonium salts

texts:
From Clayden et al.

  However, iodine is expensive and a way round that problem is to use a
  catalytic amount of iodide. The next phosphonium salt is formed slowly
  from benzyl bromide but the addition of a small amount of LiI speeds
  up the reaction considerably.

  The iodide reacts as a better nucleophile than Ph3P and then as a
  better leaving group than Br–. Each iodide ion goes round and round
  many times as a nucleophilic catalyst.

In a private conversation with ron I asked him how this catalyzing effect worked, he said that question would be more suited here and I agreed with him. It seems a bit strange at first that a strong nucleophile can also be a good leaving group (he really wants that nucleus, right, why would he leave?).

This is the explanation I came up with (probably wrong, but it is always better to first think self): Iodine is a stronger nucleophile here than bromine because of its higher energy HOMO, which lies closer to the energy of the $\ce{C-X}$ $\sigma^{*}$ (here $\ce{X}$ = $\ce{Br}$) LUMO. So it will react more rapidly than bromine, resulting in an equilibrium.

Now iodine is also a good leaving group, firstly because the $\ce{C-I}$ bond is higher is energy than the $\ce{C-Br}$ bond (less stable bond). And secondly (quoting Ron from another answer. Well explained, no need to rewrite it again): the larger the atom, the more polarizable it is. The more polarizable an atom the more stable is its corresponding anion because we have our charge spread out over a larger volume which is a stabilizing feature. So $\ce{I^{-}}$ will be more stable, making it easier for iodine to leave.

My thought was that iodine can easily knock of bromide but not remain in that position for very long (therefore the equilibrium). Now, if $\ce{PPh_3}$ happens to meet the benzyl iodide it is more eager to react with it than with the benzyl bromide (lower energy $\ce{C-X}$ $\sigma^{*}$). The resulting phosphonium salt is either to stable to be attacked by iodine again or precipitates out (or both?), so that benzyl bromide continues to be transformed into benzyl iodide.

Is this correct?


texts:
How does a SHE electrode work?

Does the $H_2$ gas get absorbed on the platinum electrode? How is it reduced? How are electrons transferred from the adsorbed gas to the solution? How is $H^+$ liberated or how does the $H^+$ in the solution take electrons from the adsorbed $H_2$?

If platinum doesn't adsorb the $H_2$ gas, what is its use? How does it provide a surface for reduction/oxidation of hydrogen?

Also in a concentration cell, why is it, in evaluating Q(reaction quotient)
you take pressure of a gas numerically and put it directly as a concentration?

And in evaluating log(Q) in nernst equation, Q isn't always unitless. But inside log, you can put only a unitless number, isn't that so?

And in concentration cells, if [c1] > [c2], then c1 acts as cathode. In Gases, considering Pressure=k[C], where k is a constant fixed at a particular temperature. then in gas concentration cell opposite happens if pressure 1 > pressure 2 then pressure 1 part acts as anode.

What is P? is it pressure of the gas above the solution?

In net, how does a gas electrode work?


texts: Why should duplicates compounds be removed from compound libraries before screening/activity prediction?

texts:
This is one of the first steps to be done while analysing chemical data or applying training models to predict chemical activity. However, I am unclear as to why is this done. Doe sit have a major effect on the result if duplicates are not removed? What is the main reason why we remove duplicate compounds?
Thanks


texts: "Carbon snakes" - what physico-chemical process causes the exothermic response?

texts:
Making a "carbon snake" requires the mixing of strong sulphuric acid with sugar, as explained in this about.chemistry webpage - the reaction causes rapid dehydration of the sugar and produces steam in the process, which expands and forms the 'carbon snake', following the incomplete chemical reaction:

$\ce{C12H22O11 + H2SO4 → 12C + 11H2O}$  + mixture of excess unreacted water, sulfur dioxide and acid (and presumably a bundle of other chemicals)

My question is, what physical/chemical processes cause this rapid dehydration and exothermic reaction?


texts: How do I determine the molecular vibrations of linear molecules?

texts:
I know how to do it for just about every other point group, but the $D_{\infty \mathrm h}$ and $C_{\infty \mathrm v}$ character tables aren't as straightforward. In particular, I'm interested in the vibrational modes of carbon dioxide, $\ce{CO2}$.

$$\begin{array}{c|cccc|cc} \hline
C_{\infty\mathrm{v}}  & E & 2C_\infty^\phi & \cdots & \infty\sigma_\mathrm{v} &  & \\ \hline
\mathrm{A_1} \equiv \Sigma^+ & 1 & 1 & \cdots & 1 & z & x^2 + y^2, z^2 \\
\mathrm{A_2} \equiv \Sigma^- & 1 & 1 & \cdots & -1 & R_z & \\
\mathrm{E_1} \equiv \Pi      & 2 & 2 \cos\phi & \cdots & 0 & (x,y), (R_x,R_y) & (xz,yz) \\
\mathrm{E_2} \equiv \Delta   & 2 & 2 \cos 2\phi & \cdots & 0 & & (x^2-y^2,xy) \\
\mathrm{E_3} \equiv \Phi     & 2 & 2 \cos 3\phi & \cdots & 0 & & \\
\vdots & \vdots & \vdots & \ddots & \vdots &  & \\ \hline
\end{array}$$

$\,$

$$\small \begin{array}{c|cccccccc|cc} \hline
D_{\infty\mathrm{h}} & E & 2C_\infty^\phi & \cdots & \infty\sigma_\mathrm{v} & i & 2S_\infty^\phi & \cdots & \infty C_2 & \\ \hline
\mathrm{A_{1g}} \equiv \Sigma^+_{\mathrm{g}} & 1 & 1 & \cdots & 1 & 1 & 1 & \cdots & 1 &  & x^2 + y^2, z^2 \\
\mathrm{A_{2g}} \equiv \Sigma^-_{\mathrm{g}} & 1 & 1 & \cdots & -1 & 1 & 1 & \cdots & -1 & R_z & \\
\mathrm{E_{1g}} \equiv \Pi_{\mathrm{g}} & 2 & 2\cos\phi & \cdots & 0 & 2 & -2\cos\phi & \cdots & 0 & (R_x,R_y) & (xz,yz) \\
\mathrm{E_{2g}} \equiv \Delta_{\mathrm{g}} & 2 & 2\cos 2\phi & \cdots & 0 & 2 & 2\cos 2\phi & \cdots & 0 & & (x^2-y^2,xy) \\
\vdots & \vdots & \vdots & \ddots & \vdots & \vdots & \vdots & \ddots & \vdots & & \\
\mathrm{A_{1u}} \equiv \Sigma^+_{\mathrm{u}} & 1 & 1 & \cdots & 1 & -1 & -1 & \cdots & -1 & z & \\
\mathrm{A_{2u}} \equiv \Sigma^-_{\mathrm{u}} & 1 & 1 & \cdots & -1 & -1 & -1 & \cdots & 1 & & \\
\mathrm{E_{1u}} \equiv \Pi_{\mathrm{u}} & 2 & 2\cos\phi & \cdots & 0 & -2 & 2\cos\phi & \cdots & 0 & (x,y) & \\
\mathrm{E_{2u}} \equiv \Delta_{\mathrm{u}} & 2 & 2\cos 2\phi & \cdots & 0 & -2 & -2\cos 2\phi & \cdots & 0 & & \\
\vdots & \vdots & \vdots & \ddots & \vdots & \vdots & \vdots & \ddots & \vdots & & \\ \hline
\end{array}$$


texts: Equilibrium constants for lewis acids such as Ca2+

texts:
I need to calculate the theoretical $\mathrm{pH}$ in a $50~\mathrm{mL}$ water solution where $6.4\times10^{-4}~\mathrm{g}$ of $\ce{Ca^{2+}}$ is present. The reaction I base this on is the following

$$
\ce{Ca^{2+}_{(aq)} + 2H2O_{(l)} \rightleftarrows Ca(OH)2_{(s)} + 2H^+_{(aq)}}
$$

$$
K = \frac{[\ce{H+}]^2}{[\ce{Ca^{2+}}]} \Rightarrow [\ce{H+}] = \sqrt{K \cdot [\ce{Ca^{2+}}]}
$$

Is there a database of standard equilibrium constants for such Lewis acid reactions?

I appreciate any help!


texts:
The marking scheme says that the molecule has both alkene and ketone.
So there is carbon to carbon double bond.ok.check there is alkene.But what about ketone.Ketone has this structure:

So can we technically say that there is ketone in it?


texts: How does dimethylsulfoxide serve as a cryoprotectant?

texts: In cell culture, dimethylsulfoxide (DMSO) is added to prevent the formation of ice crystals which may lyse the cells. Exactly how does dimethylsulfoxide act as a cryoprotectant?


texts: What happens if I have an acid/base equillibrium and remove hydronium ions until there is 50/50 of acid and conjugate base?

texts: Suppose I had an acid HA, and it reaches equilibrium in water. Then I remove the hydronium ions. I don't know how I would do this, maybe adding some hydroxide ions. My question is can I do this and will I be able to eventually create a 50/50 mixture of acid and conjugate base? Is this a very good buffer?


texts:
FYI to start- I'm not a chemist by training, so assume I'm missing some basic knowledge of the field.
I've been trying to do some electrodeposition with an iridium tetrachloride-based solution, and my success at doing so is random at best. In talking to a chemist, they suggested that I buy new glassware and perform nitric acid or sulfuric acid cleaning on all of my glassware; according to them, my cleaning the glassware with regular dish soap (I've been using Dawn) has most likely coated everything in surfactants and those are releasing micelles of surfactant into all of my solutions.
I believe what this person is telling me, as I can read about surfactants forming micelles. However, in a search of both academic (e.g. Scopus) and non-academic sources (read: Google), I can't find any  detailed information on this issue, or its prevention, in lab settings; I also can't find details about how these surfactant micelles actually affect a process like electrodeposition. I seem to only be able to find random informal glassware cleaning SOPs from different labs, but no good reading on surfactant contamination in electrochemistry experiments.
Am I searching the wrong keywords? Is this too broad a question? Is this just common knowledge among chemists because of their knowledge base?
Thanks!


texts:
I want to ask a question about the shoulders of peaks when separating overlapping peaks.

I have the following spectrum circled with relevant shoulders:

I believe that the spectrum above shows an overlapping triplet and doublet, but I want to know what causes these shoulders in the NMR spectrum. I'm stuck to whether to decide there is further splitting of a small $\ce{J}$ value or to just assume it's a shoulder.

Below shows analysis of this region from Acta Pharm. 54 (2004) 163–176.

What is causing these shoulders? Are they part of the signal or just a result of poor preparation leading to artefacts?


texts: Diluting a sample of weak base before titration. What happens to equivalence point pH of diluted vs undiluted?

texts:
A student titrated a 10.00 mL of 0.20 M methylamine ($\ce{CH3NH2}$) and determined that 10.00 mL of $\ce{HCl}$ was needed to reach the equivalence point.
If you diluted your original sample of methylamine by adding 10.00 mL of water to your sample before you started adding $\ce{HCl}$, which of the following statements would be true?
a) You now only need to add 5.00 mL of $\ce{HCl}$ to reach equivalence.
b) The equivalence point pH would be the same as in the undiluted titration.
c) Both (a) and (b) are true.
d) Neither (a) nor (b) are true.

The answer is d) Neither (a) nor (b) are true.
I always thought that both the $\mathrm{p}K_\mathrm{a}$ and equivalence $\mathrm{pH}$ of an acid stay the same no matter what the concentration. Except where it is so dilute, ionization from water would have an effect. But I don't understand why or how it would change. I can't find anything in the textbook or online, can someone please explain this?


texts: Is there a difference between NaCl or table salt (processed) and salt from the Himalayas?

texts:
So, I was doing some research on bonding and electronegativity and one of the examples used was NaCl (Sodium Chloride) which is salt. We don't buy processed salt, rather we buy salt from the Himalayas.

Apparently this is better salt because it is not processed, made, etc.
But, is there a difference between NaCl and Himalayan salt in regards to their molecular structure?


texts: Mechanism of arene side chain oxidation by permanganate

texts:
When treated with hot, concentrated acidic $\ce{KMnO4}$, arenes are oxidised to the corresponding carboxylic acids. For example, toluene is oxidised to benzoic acid.

I've tried to examine how this happens, using the mechanism of oxidation of double bonds via cyclic intermediate as a reference, but I can't manage to cook up a satisfactory one.

In an older book, I have read that there is no (known) mechanism for many organic oxidation reactions. I'm inclined to think that this may have changed.

So, is there a mechanism for this? If so, what is it?

If not, what are the hurdles in finding this mechanism? For example, what problems are there with other proposed mechanisms (if they exist)?


texts: Does salt vaporise? If I boil salt-water and leave it there until half of the water vaporises, will it be twice as salty as in the beginning? Or exactly the same? Or somewhere in between?


texts: What am I doing wrong with the fuel and packing I am using for a cannon I made?

texts: Recently I have been using flash powder in a cannon that I made, for a chemistry project, however, it is not causing the rubber ball I put in it to propel out of the tube. First I put in 30g of flash powder, then pack a small wad of paper on top, and lastly insert the ball in an aluminum foil bowl. The fuse is then inserted into the bottom and lit on fire, but the only thing that has been happening is fire flaming from the end of the tube and melting parts of the rubber ball. Do you have any small suggestions, as I am running out of time to figure this out? I attached a picture of the cannon. (Also I do not have time to make black powder).


texts: Molar absorption coefficient - why are the molar absorptivities defined to be the same?

texts:
In spectroscopy, the isosbestic point is said to be where the molar absorptivities of two species is the same.

$$A= \epsilon(X+Y) \times c(X+Y) \times l$$

reduces to $$A= \epsilon_t \times c \times l$$

the absorbances and the length are the same at this point, but the concentrations are not;

why are the molar absorptivities defined to be the same?

Is c taken to be the relative contribution, rather than the exact concentration?


texts: Does the iodoform reaction form hydrogen iodide or water?

texts:
I am currently learning about the iodoform reaction, i.e. when CH3COR compounds react with iodine and sodium hydroxide to form iodoform.

My course book and Chemguide both says that the reaction is as follows:

$$ \mathrm{CH_3COR + 3I_2 +4OH^- \rightarrow  CHI_3 + RCOO^- +3I^- +3H_2O}$$

However, this picture from Wikipedia suggests that hydrogen iodide is formed instead of water:

Which one is correct?


texts: Order of citation of alkyl and halide prefixes in IUPAC names

texts:
I've been playing around with ChemDraw and found that it assigns the priorities of substituents in a way I wouldn't have expected, depending on the length of the alkyl substituent. I'm not a nomenclature buff, so I'd like to know if it's correct and if so, why.

$n = 1$: 1-ethyl-2-iodobenzene
$n = 2$: 1-iodo-2-propylbenzene
$n = 3$: 1-butyl-2-iodobenzene
$n = 4$: 1-iodo-2-pentylbenzene

What determines the priorities of the alkyl group and the iodo group?


texts: Is there any chemicals that I can add to soy bean wax

texts:
I recently decided to make homemade candles in my spare time since all 6 kids have left the house.

After much research and trial and error and reading many articles, I have found that Soy wax does not release fragrance oil well on its own, and needs an additive/chemical of some sort, but being that I am not a chemistry kinda gal, I don't want to buy certain acids or whatever and risk blowing up my kitchen, or making deadly fumes just because I am not aware of what chemicals can or can't go together.

You can add additives such as Vybar to certain waxes such as paraffin and it will help the color retention, and a few other things, but I am wanting something in the raw form that I can add to the soy wax before it solidifies so when the wick is lit, the fragrance will smell. Soy wax alone has a reputation of not releasing fragrance without using an additive/acid/compound to it. I just don't want to mix something that would be, or could be dangerous.

Any suggestions would be greatly appreciated..


texts: Am I understanding this IR spectrum correctly?

texts: Is it safe to say that this IR spectrum belongs to a carboxylic acid because of the 3100-2700 stretch indicating OH group, and the sharp peak at 1728 showing a carbonyl group?


texts: Mathematical form of four hybrid orbitals

texts:
The mathematical form of the four $\ce{sp^3}$ hybrid orbitals are given below.
  \begin{align}
\ce{
\tag{a} sp^3 &= 1/2s + 1/2p_x + 1/2p_y + 1/2p_z\\
\tag{b} sp^3 &= 1/2s + 1/2p_x - 1/2p_y - 1/2p_z\\
\tag{c} sp^3 &= 1/2s - 1/2p_x + 1/2p_y - 1/2p_z\\
\tag{d} sp^3 &= 1/2s - 1/2p_x - 1/2p_y - 1/2p_z\\
}\end{align}
  For each hybrid orbital the number in front of the $\ce{s}$ and three $\ce{p}$ functions, called a coefficient, describes the contribution and relative ratio of each canonical orbital to the hybrid wave function. Add up the coefficients and prove to that these orbitals are $\ce{s^1p^3}$.

Yes, I know that the grammar is terrible on that last sentence, that is how it is written. So, I know that for an $\ce{sp^3}$ orbital it is one part $\ce{s}$ orbital and three parts $\ce{p}$ orbital. However, I have no idea what this question wants me to do. Adding up the coefficients gives me $2$, $0$, $0$, and $-1$, but I have no idea if that is how it wants me to add it up (you could ignore the sign and get $2$ every time, and show that $1/2$ is a quarter of $2$, thus proving that each component contributes a quarter to the hybridized orbital, but this seems too simple and incorrect).


texts: Why do orthoesters react with Grignard reagents, but acetals and ketals don't?

texts:
My book mentions the synthesis of aldehydes and ketones using alkyl ortho esters. It's called Bodroux-Chichibabin aldehyde synthesis.

Now, later, the book mentions this:

R- displaces EtO-, giving an acetal or ketal, which are unreactive with Grignard reagents, so a secondary alcohol is not formed.

Why do orthoesters react with grignard reagents, but acetals and ketals don't? They have essentially the same functional groups, just two instead of three.


texts: Do superhydrophobic/hydrophobic materials generally have a lot of friction or only a little friction

texts: Also, are there any exceptions that you know of?


texts: Major product of a cyclopropanol with silver ions

texts:
I'm having trouble predicting the major product of the reaction of 1-(chloro(cyclohexyl)methyl)cyclopropan-1-ol and silver ions:

I thought that in presence of $\ce{Ag^+}$, the three-membered ring would open forming a ketone with chlorine atom in the $\alpha$-position. Then I thought that there might also be some migration of the ketonic group to the ring, but I'm not sure.


texts:
I am currently studying Ultrasonic transducers – Materials and design for sensors, actuators and medical applications by Kentaro Nakamura. In chapter 1.2.1 Ferroelectricity, the author says the following:

$\ce{BaTiO_3}$ is realised as a ceramic, originating as a mouldable paste, which is dried and sintered to form the final material. The properties of the paste result from the mixing of particles with a liquid and its basis in particles leads to a material comprising crystallites or grains tightly bound together, with properties differing between the individual grains and the collection of grains in the bulk ceramic because of the effects of the interfaces between the grains. Following the principle of minimisation of energy, and taking into account the resulting internal dynamics of the relative positions of the ions, $\ce{BaTiO_3}$ divides itself into multiple domains within each grain, each domain having a common polarisation, but with the polarisation differing in direction from that of neighbouring domains by either $90^\circ$ or $180^\circ$.

My concern is with this part:

The properties of the paste result from the mixing of particles with a liquid and its basis in particles leads to a material comprising crystallites or grains tightly bound together, with properties differing between the individual grains and the collection of grains in the bulk ceramic because of the effects of the interfaces between the grains.

What is meant by "basis" in "... its basis in particles leads to a material comprising crystallites or grains tightly bound together, ..."? I don't understand what this means. Is this possibly a typo or incorrectly used term by a non-native English speaker? If so, then does anyone know what they meant (or what it should say for this described process)?


texts: Calculating temperature change of helium due to Joule-Thomson effect

texts:
We are trying to fill a rocket helium tank that is 78 liters with helium, final pressure of $\pu{10500 psi}$. We plan to pressurize high pressure tanks to $\pu{20000 psi}$ using a compressing pump system, so that on launch day we don't have to wait for the 78 liter tank to fill slowly by the compressing system. We plan to fill the rocket tanks from the high pressure tanks in a cascade manner (the number and volume of the tanks may vary, depending on the solution of the JT equation(s).

The problem is that helium has a negative JT coefficient. It will heat up during the transfer from the high pressure tanks to the lower pressure tank if I understand it correctly.

So, the concern is how hot will it get. Will the O-rings/seals melt? I have some equations, but it seems to me there may be too many unknowns.

I've seen others make certain assumptions on this site, but its not clear to me how that works. Can anyone advise how you would proceed?


texts: Designing a theoretical synthesis of methamphetamine from phenylpropyne

texts:
I am asked to synthesize "methamphetamine." Note that there is no configuration designated for this molecule, and methamphetamine refers to a very specific configuration. In any case, here are the steps I took:

Reduction with hydrogen gas and Lindlar's catalyst. This transforms the alkyne into a cis alkene.
Epoxide formation with m-CPBA.
Ring opening with sodium methylamide. This is a base, and it should attack the less sterically hindered side of the epoxide - the side without the phenyl substituent. This opens the ring and gives me almost what I want. Now I just have to remove the hydroxyl group.
Removal of hydroxyl group: I decided to use TsCl and heat. The tosylate group should leave upon heating and a secondary benzylic carbocation that'd form. Sodium hydride was added as to add to the carbocation formed when the TsCl leaves. However, a possible issue is that the hydride anion, being a good base, would give me the elimination product as well.

Alternate pathway below


texts:
Thia is the question and my approach.

I just want to confirm if it is the correct product. I have not gone for elimination as it will give anti-aromatic product.


texts: NMR for an octahedral complexes sources of peaks

texts:
I wanted to ask a question about splitting pattern in NMR.

I was given the following information to assign to a Compound C and justify why the splitting patterns are as given:

I was confused about both the peaks.

I recall giving a previous question regarding NMR here.

Using the first bit of information

  singlet in the proton-decoupled $\ce{^{31}P}$

I can't seem to understand why, because there is no plane of symmetry going across the plane of the octahedral 4 ligands (from left to right) so they wouldn't see "the same electronic environment."

Also, regarding the $\ce{^1H}$ I tried to justify this by saying that as there were 2 different $\ce{P}$ atoms in axial but they both faced different environments, the splitting would be triplet too, with the same splitting constant, hence a triplet, but I was unsure about this.

Why is the proton-decoupled $\ce{^{31}P}$ only displaying a singlet?


texts: Irreversible chemical reaction in a battery

texts:
Inside an ideal battery, the chemical reaction is reversible (at equilibrium), thus the oxidation-reduction reaction $\ce{Zn + Cu^{2+} -> Zn^{2+} + Cu}$ is happening in both ways at the same rate right?

Now, for a real battery, there's resistivity inside it due to many factors, thus the chemical reaction is irreversible. My question is, during the irreversible reaction, is the reaction happening in both ways but at different rate due to resistivity inside the battery or it is just like the combustion reaction happening in one way?


texts: Finding rate of reaction from a concentration vs. time graph

texts:
A tangent drawn on “conc. of product vs. time” curve of a 1st order reaction makes an angle 30 degrees with the $y$-axis at 20 min. Find the rate after 20 min.

I first tried to find the equation like this:
$$k=\frac{2.303}{t}\log\frac{a}{a-x}$$
Let $\frac{k}{2.303}$ be $c$ to make calculations less messy. Here, $a$ is the initial concentration of reactant.
$$\frac{a}{a-x}=10^{ct}$$
$$x=a\left(1-10^{-ct}\right)$$
$$\frac{\mathrm dx}{\mathrm dt}=a\left(c\cdot\ln10\cdot10^{-ct}\right)=ak10^{\frac{kt}{2.303}}$$
Now, the tangent makes an angle of 30 degrees with concentration axis (or $y$-axis in this case). So the angle made with time axis (or $x$-axis) is 60 degrees. Hence $\frac{\mathrm dx}{\mathrm dt}=\tan\theta=\sqrt{3}$. But the value of initial concentration is not given for finding rate constant. Should I go for a different approach or am I making any conceptual mistake?


texts: Effect of the counterion on the colour emitted by a metalic salt

texts:
Could someone please enlighten me on what would be the theoretical effect of a counter ion on the colour of the flame emitted by a metallic salt in a flame test?
Eg. NaCl - what would be the effect of the non-metal on the general colour of the flame of the compound?

I am looking into specific groups of metallic salts based on 3 metals: Sodium, Potassium and Copper II.
I have searched throughout the literature but have not found an answer yet.


texts: As we know that the orbitals in a sub shell are degenerate, so is it necessary to fill up the electrons starting from x then to y and then z (if in p-subshell) or they can be filled like shown in the photo.


texts: Is 1,1,2,2-tetramethylcyclohexane not meso? (And visualizing cis-1,2-dimethylcyclohexane)

texts:
Considering the fact that cis-1,2-dimethylcyclohexane is not meso, does that mean that 1,1,2,2-tetramethylcyclohexane is also not meso?
I'm also having trouble understanding how the chair conformations of cis-1,2-dimethylcyclohexane are enantiomers when I draw them like this:
I can see the enantiomers when I draw them like this, though:

Thank you so much!


texts: Why don't electrons pair in [Fe(NH3)6]2+?

texts: Why doesn't electron pairing take place in $\ce{[Fe(NH3)6]^2+}$ though $\ce{NH3}$ is a strong ligand field producer?


texts: Static electricity with calcium carbonate particles

texts:
We are working with small calcium carbonate particles (microfossils) but one of the problems is they stick to the plastic or metal tools we are using, presumably due to static charge. For example, small particles on plastic tray will stick to the surface even if it is upside down.

I'm guessing the static potential is related to how much calcium carbonate wants to gain or give away electronics?
What is this called in this context?
How do I choose a material that has a low potential for static electricity (i.e. sticking) with calcium carbonate particles?


texts: How to predict if hydrogen atoms could be placed in the interstials of a lattice

texts:
Palladium hydride is an example of a hydride which contains H atoms in palladium's crystal lattice (which is fcc).

I would like to know if it's possible to predict if another hydride, $\ce{NbH_{x}}$ could exhibit the same behavior.

I know that in an ionic solid, the fraction $$\frac{r_{+}}{r_{-}}$$
Can be used to predict the geometry around a cation.
Can I use this expression for niobium hydride? In the case of niobium, the crystal structure is bcc, so it contains tetrahedral and octahedral interstial sites.


texts: treating PLA (Polylactic acid) plastic to make it biodegradable

texts:
I am using PLA for 3D printing, and I know it does not degrade well in the wild. I would like to know if there is a chemical process I could use to treat it at home.
Specifically, I am looking for a cleaner alternative than throwing my 3d printing scraps in the garbage, so I wouldn't be generating toxic components when doing this, ideally. I would like the plastic to degrade (in a few years maybe?) when I put it underground, while limiting the amount of toxic matter propagates in the soil.
I have read that hydrolyzing PLA could help achieving this.
I also found threads on disolving it How to dissolve PLA (polylactic acid)?
But as I am looking for an ecological process, I think I need to stay away from this as the fumes may be very toxic and polluting
Thank you for your help!


texts: spatial degeneracy in the states of atoms and molecules

texts: I would like to know if the exact ground state of a closed-shell atom or molecule can have a spatial degeneracy. If we ignore relativistics effects, the Hamiltonian of the system $H$ commutes with the Spin  operators $S^{2}$ and $S_{z}$, so, to each eigenstate of $H$, there are another $2S + 1$ eigenstates that have the same energy. In the case of a closed-shell system, $S = 0$ and there are no spin degeneracy. However, my doubt is about spatial degeneracy, that is, if it can exist two states $\Psi$ and $\Psi'$ with the same energy eigenvalue that have the same spin. (in this case, $H$ is the full Hamiltonian, that includes electron-electron interaction)


texts: Why can't we oxidise allylic alcohol to aldehyde using pyridinium chlorochromate?

texts: I read in my book that we cannot use pyridinium chlorochromate (PCC). Why is that?


texts:
Is there any specific reason why Iodine Flasks are used instead of Erlenmeyer Flasks when doing Iodine Determination tests?

Iodine Flasks are quite expensive when compared to Erlenmeyer Flasks.

Does the funnel-shaped top form serve a specific function?


texts: Is the vinegar and baking soda experiment safe for children?

texts: To be more specific, could the carbon dioxide fumes produced in the reaction be harmful to a small child? I don't have a strong background in chemistry, and I was prompted to ask this question when it was suggested by a friend that a mixture of 2 cups of vinegar and baking soda is commonly used to euthanize rodents. I'm aware rodents are more sensitive than humans, but I was concerned that a small child could inadvertantly breathe enough fumes to cause harm. I think it would be a great experiment to introduce children to chemistry if not unsafe. Thanks for any advice or guidance.


texts: Why is iodine the heaviest bonded element in circumstellar/interstellar space?

texts:
As I understand, the heaviest bonded element found in space to date is iodine, in the form of iodide in sodium iodide. This is the only element heavier than iron on this list, and that makes sense to me because the nuclear fusion inside stars only continues until iron. The only way that heavier elements are formed is when a star is near death and the energy is so high in the center of the star that more nuclear fusion occurs, and then the elements are flung into space.

If this is true, then wherever they found the sodium iodide should be traces of more heavier-than-iron elements. Why then hasn't an element such as, say, bromine been found? Especially when it behaves so similarly to iodine.

This had stumped me for a while and information on the topic is sparse, so I'd just like some input on if it may be a limitation on observation of space or an astrochemical scenario where somehow iodine is more likely to form bonds in space than its heavier-than-iron counterparts


texts: Why does heating glucose in the excess of HI produce n-hexane?

texts:
Alcohols react with acid halides such as $\ce{HI}$ to create alkyl halides, as such:

$$\ce{C2H5OH + HX → C2H5X}$$

However, this doesn't seem to be the case with glucose, as the entire chain is reduced to an alkane instead. Is this due to the steric hindrance factor of the large chain or perhaps the aldehydic group attached to it?

An explanation would be appreciated.


texts: Why are the t2 orbitals above the e orbitals in a tetrahedral complex using the crystal field theory?

texts: In case of octahedral coordination entity formation, the $\mathrm{e_g}$ is above in energy level diagram than the $\mathrm{t_{2g}}$ due to more electrostatic force acting when the orbitals are along the axes in case of $\mathrm d_{z^2}$ etc. But in case of tetrahedral, why is the energy diagram inverted and becomes somewhat like this? I can't think of any possible reason. Can anyone please help?


texts: What's the name of the problem of finding equilibrium concentrations?

texts:
Is there any specific name of the problem of finding equilibrium concentrations with known equilibrium constants and initial concentrations?

Would it be appropriate to call it "direct equilibrium problem", by analogy with the similar problem in chemical kinetics--finding concentrations as function of time for known rate constants--that is called "direct kinetic problem"?


texts: Whats the symmetric, anti-symmetric and non-symmetric part of the direct product of irreducible representations?

texts: I am trying to understand how to see if a vibrational mode is Jahn-Teller active or not. According to the group theoretical description of the Jahn-Teller effect one needs to check if the symmetric part of the direct product the irreducible representation (=irrep) of the electronic state with itself contains the irrep of the distortional mode in its symmetric part. And this is where I have trouble to understand. I can understand that one can decompose tensors (tensor products) into a symmetric and an anti-symmetric part, but I fail to understand how to apply that to the the direct product of two irreps, as they are in most cases one-dimensional. Can someone explain to me what exactly means "symmetric, anti-symmetric and non-symmetric part" in this context and how to see that in specific cases?


texts: Resistivity of pure water vs salt water for electrolysis

texts:
OK so I have a group project. Were "building" an ammonia plant. Part of the plan is to gather the $\ce{H2}$ we need from the splitting of pure water. We've been told $1000\ \mathrm{kg}$ of $\ce{NH3}$ must be produced an hour.
One of the problems asks for the voltage and current needed to split pure water to make enough $\ce{H2}$. I can do the half reaction, that's easy $1.22\ \mathrm V$.
But I've done this loads of times with kids and a $9\ \mathrm V$. I know that adding a little salt speeds up hydrogen gas production.
Does the $1.22\ \mathrm V$. assume that its pure water and I don't have to worry about the resistivity?


texts: What is the geometry of the intermediate during an SN2 reaction?

texts:
Suppose we have 2-bromo butane. The carbon connecting to the bromine will have the following valence electron configuration:

$$\underset{2s}{[\uparrow]}\underset{2p}{[\uparrow \vert \uparrow \vert \uparrow]} $$

This hybridizes to an sp3 configuration which yields a trigonal pyramidal configuration.

Suppose in an SN1 reaction the bromine comes off. Then the connecting carbon will have a valence electron configuration of

$$\underset{2s}{[\uparrow]}\underset{2p}{[\uparrow \vert \uparrow \vert\;]} $$

which yields an sp2 or trigonal planar configuration.

Suppose we instead have an SN2 reaction such as with NaOH. Then the intermediate would be a carbanion that has a carbon that has 5 bonds.

$$ \underset{2s}{[\uparrow ]} \underset{2p}{[\uparrow \vert \uparrow \vert \uparrow]} \underset{3s}{[\uparrow]} $$

would be the wrong configuration but I'm having trouble understanding what the right one would be.

A trigonal bipyramidal molecular geometry seems to me like it'd fit the shape of what the carbanion would be but the numbers don't seem to add up to me.

In a trigonal bipyramidal geometry there needs to be two $sp$ orbitals two point up and down.

I learned from How are the hybrid orbitals of sulfur hexafluoride shaped? that higher orbitals are usually only slightly involved so the resulting bonds would only have a small d characteristic. For example, instead of a $sp^2d$ hybrid something like a $sp^{2.75}d^{0.25}$ characteristic is more likely.

Would the rest of the bonds have something like a $sp^{2.67}d^{0.33}$ characteristic?

According to molecular orbital theory what would the shape of that carbanion be and how would the groups attached to it be arranged?


texts: Isn't the mechanism of aqueous sodium hydroxide and 1-bromobutane involves both heterolytic bond fission and attacking by a nucleophile?

texts:
What is involved in the mechanism of the reaction between aqueous sodium hydroxide and 1-bromobutane?

A. attack by a nucleophile on a carbon atom with a partial positive charge

B. heterolytic bond fission and attack by a nucleophile on a carbocation

C. homolytic bond fission and attack by an electrophile on a carbanion

D. homolytic bond fission and attack by a nucleophile on a carbocation

I think that A and B would be correct answers, but the correct answer is only A. Bromine accepts both two electrons from the carbon atom and the nucleophile attacks on that carbocation of the carbon atom. Why choice (B) is incorrect? I also searched the internet and found that this reaction is SN1, but why it occurs with the primary carbon, which is usually a reactant in SN2 reaction.


texts: I know chemistry has been around for a long time, but I was curious who the first chemist in recorded history. I am aware that Antoine Lavoisier was one of the first modern chemistry and is considered to be the "Father of Modern Chemistry", but was he is the first chemist?


texts: Clarification of Kinetic Energy during Phase Change

texts:
This website states that:

During a change of phase the temperature does not change, but the internal energy does.  The internal energy is the sum of the kinetic energy of the molecules and the chemical potential energy of the molecules.  During a change of phase, the average kinetic energy of the molecules stays the same, but the average potential energy changes.

I'm confused as the two bolded statements seem to contradict each other.

My interpretation is that during a phase change, the temperature remains equal, but the kinetic energy of its particles increase/decrease.

Could this please be clarified and confirmed?


texts:
We were taught that the kinetics of a reaction is determined by the reactions ‘rate determining step’ which is also the slowest step of the reaction. For E1 as well as E2 reactions the slowest steps are easily determined by the mechanism and I derived the rate laws for those.

In the case of E1cb reactions, which step can be taken as the slowest step?

Is it the one in which the acidic hydrogen is extracted by the base or is it the one where the elimination takes place (carbanion intermediate)?


texts: Mechanism of hydrolysis of acyl chlorides

texts:
The following mechanism for acyl chloride hydrolysis was given by my professor :

However I do not understand why in the second step, oxygen has a partially negative charge, should it not gain a positive charge as it is bonded to three atoms, furthermore shouldn't the $\text{O}-\text{H}$ bond breaking homolytically form a $\text{H}^-$ ion and not a proton?
Should the arrow be reversed in the second step?


texts: MOPAC: can we run THERMO immediately after the geometry optimzation?

texts:
With MOPAC, I am trying to set up single run with geometry optimization followed by calculation of THERMOdynamic parameters.

Is there viable way for that?


texts: Why do the 4f and 5d orbitals have similar energies?

texts: I've come to know this phenomena when learning about the exceptions to the aufbau principle. But there is no explanation of why 4f and 5d have similar energies (as I've read in some websites).


texts: Does water really have strong EM absorption at 3 kHz in solid and 2 GHz in liquid? Why the huge shift?

texts:
While writing this answer to the question Transmitter receiver coil separation for Electromagnetic Terrain Conductivity Measurement I ran across this large PDF file of a book Soil and Environmental Analysis; Physical Methods Soil and Environmental Analysis; Physical Methods, 2nd Ed. K. A. Smith and C. E. Mulllins, Eds. 2000 Dekker, New York.

Figure 5. on page 29 is shown below. It shows a plot of the real and imaginary part of the permittivity of water in solid (ice) and liquid forms.

The shapes are the roughly the same; the real part is around 80 to 90 at low frequency and drops to perhaps 2 to 1 at high frequency, with the imaginary part reaching a peak as the slope of the real part is maximum as one would expect.

The difference however is that the peak in the absorption is around 3 kHz for ice and 20 GHz for liquid!

Is the physics behind this strong absorption peak the same in both cases?
If so, what is it about the transition from solid to liquid that can move it seven orders of magnitude?


texts: Why do Grignard reagents react with epoxides but not THF?

texts: THF is used as a solvent for Grignard reagents, but epoxides react with Grignard reagents. There is only a small difference between epoxides and THF, what causes the difference in reactivity towards Grignard reagents?


texts: Relationship between Yield and Applied Potentials

texts:
This question revolves around this question from Atkins' Chemical Principles 5th ed., Chapter 13, Question 13.116:

  Consider the electroplating of a metal $+1$ cation from a solution of unknown concentration according to the half-reaction $\ce{M+ (aq) + e- -> M (s)}$, with a standard potential $E^\circ$. When the half-cell is connected to an appropriate oxidation half-cell and current is passed through it, the $\ce{M+}$ cation begins plating out at $E_1$. To what value ($E_2$) must the applied potential be adjusted, relative to $E_1$, if $\pu{99.99 \%}$ of the metal is to be removed from the solution?

How is this problem solvable? I know that at applied potential $E_1$ the cell potential is $0$ ($\Delta G = 0$), so that means at $E_2$, the equilibrium constant must demand a yield of $\pu{99.99 \%}$. However, doesn't this yield depend on what the oxidation half-cell is?

For example, the oxidation reaction could be one from cerium(III) to cerium(IV) or from chloride ions to chlorine gas, both of which have different effects on the equilibrium constant. I've gotten as far as $-nFE = RT\ln{K}$, where I do believe $E = E_2 - E_1$ and $E$ is positive to ensure negative Gibbs free energy change.

This is an even number question so there is no given answer. I would really appreciate a solution or at least explanations clearing up any misconceptions that I may have / clues to how to solve this problem. This is not a homework problem.


texts: Why don't we see these lanthanide species?

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

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

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

Why is this not the case?

$^{[1]}$ Ce, Pr, and Tb also have the oxidation state IV. Eu and Tm have the additional state II.

$^{[2]}$ Ordering (relative energy) changes with the number of electrons.

I strongly recommend having a look at these questions:

Howcome orbitals become 'core-like' when electrons are removed?
What is meant by 'electrons of like/unlike rotation'?
What's up with this quarter / three-quarter rule?

Original topic: Predominance of III oxidation state for lanthanides


texts: Energy decomposition analysis. Are there schemes that actually splits up the steric term?

texts:
In quantum chemistry, there are many types of energy decomposition analysis (EDA) which partitions the interaction energy between two or more fragments into steric, polarisation, exchange and orbital energy terms

For example, in a Morukuma type decomposition method employed by ADF, the interaction energy is partitioned into electrostatic, pauli and orbital energy, which the last term can be further decomposed by Natural Orbitals for Chemical Valence (ETS-NOCV) to show the $\sigma,\pi,\delta$ contributions

In ALMO-EDA in Qchem, the energy is instead decomposed into electrostatic, pauli, dispersion and polarisation by using fragment electrical response functions (FERF) as an ortogonalisation scheme

Both methods were generalised to be applicable to multiple fragments in some more recent parts of the literature since 2014

Despite extensive work and examples on decomposing the electronic term, be it polarisation, orbital interactions or similar, it seems there isn't an example where the steric term is decomposed into contributions for each fragment. For example, considering a trimer of molecules, all such EDA schemes always report the steric or pauli repulsion term as the sum of contribution of all fragments, thus there is no information on how much sterics each fragment contributed in the complex.

Attempt to recover individual steric contributions of each fragment using the intuition that pauli repulsion in most EDA schemes are computed based on how much molecular volume is excluded in the overlapping region of the fragments and assuming that those depletion regions are additive, found that compared to the full 3 fragment EDA, the sum of steric terms for the pairwise fragments is off from the total steric by around 100-400 kJmol-1, suggesting there are higher order interactions not accounted for such as two fragments depends on the third one at the same time.

Is there a reason why it is not meaningful to decompose the steric or pauli term into fragment contributions?


texts:
What is the colour of elemental Ag? I have doubt whether it is black or silver in colour.

In Tollens' test, we get a silvery precipitate of elemental silver - hence silver in colour.
I have read somewhere and also in the following links as a reference that it was not mere speculation

http://books.google.co.in/books?id=AFY2gKwh4AsC&pg=PA553&lpg=PA553&dq=elemental+silver+precipitate&source=bl&ots=nzfsQcBAm6&sig=jTCQk7-k0HzAByI25ESI6OSclJs&hl=en&sa=X&ei=S1d7U6aXIY-OuASHp4HIDQ&redir_esc=y#v=onepage&q=elemental%20silver%20precipitate&f=false

(towards the end)
and

http://books.google.co.in/books?id=cZL_-hyw98sC&pg=PA675&lpg=PA675&dq=elemental+silver+precipitate&source=bl&ots=DDhdhikKhU&sig=zIq-qQM7VI4i5enohZVi3oIagHw&hl=en&sa=X&ei=S1d7U6aXIY-OuASHp4HIDQ&redir_esc=y#v=onepage&q=elemental%20silver%20precipitate&f=false

Please confirm this. Thanks in advance.


texts:
I was solving some problems and I had a doubt a problem since the resulting pressure gives me a negative value. The problem was the following:

  Could $100~\mathrm{g}$ of $\ce{N2}$ in a $200~\mathrm{mL}$ container exert a pressure of $25~\mathrm{atm}$ at $28~^\circ\mathrm{C}$ if it behave like an ideal gas? If your answer is no, what pressure would exert the gas, knowing that the van der Waals constants for $\ce{N2}$ are $3.11~\mathrm{\frac{L\,atm}{mol^2}}$ and $0.076~\mathrm{\frac{L}{mol}}$.

I have converted the 100 grams of $\ce{N2}$ to moles of $\ce{N2}$, and with that I've replaced the data in the van der Waals formula, using $a = 3.11~\mathrm{\frac{L\,atm)}{mol^2}}$ and $b = 0.076~\mathrm{\frac{L}{mol}}$. The result was a negative pressure, and I am pretty sure that's impossible (or at least that's what my chemistry teacher said).

This is what I did:

$$\begin{align}
P &= \frac{nRT}{V-nb} -\frac{an^2}{V^2}\\
  &= \frac{(3.57~\mathrm{mol})(0.082\mathrm{\frac{L\,atm}{K\,mol}})
    (301.1~\mathrm{K})}{(0.2~\mathrm{L})
   -(3.57 ~\mathrm{mol})(0.076\mathrm{\frac{L}{mol}})}
   -\frac{(3.11~\mathrm{\frac{L~atm}{mol^2}})
    (3.57~\mathrm{mol})^2}{(0.2~\mathrm{L})^2}
\end{align}$$

The result was:
$-1626.19~\mathrm{atm} - 9.9075~\mathrm{atm} = -1636.0975~\mathrm{atm}$


texts: How can a bond be more stable and more polar at the same time?

texts:
When comparing the acidic strength of the halogen acids, we see that the acidic strength decreases as $\ce{HI>HBr>HCl>HF}$. It is said that the reason for this is the bond strength of $\ce{HI}$ is the least, while that of $\ce{HF}$ is the greatest. But, the polarity of the bond in $\ce{HF}$ is the greatest, how then is the strongest bond?
I understand that fluorine has smaller valence atomic orbital (2p) than, for example, iodine (5p), and so has more effective overlap with the s-orbital of hydrogen. But how do we reconcile this fact with the fact that the fluorine hydrogen bond is more polar too? The electrons remain more with fluorine in $\ce{HF}$ than with iodine in $\ce{HI}$, so intuitively it seems that the hydrogen fluorine bond may be more easily broken by a base than the hydrogen iodine bond. So what is going on?
In short, how can a bond be stable when it is highly polar?

Edit
My question is regarding bond strength, and not the acidic order. For example, in organic compounds, the leaving group ability of the halide ions decreases as$^1$:
$$\ce{I^{-}>Br^{-}>Cl^{-}>>F^-}$$
This means that the fluorine-carbon bond is the hardest to break. But fluorine has very high electronegativity, and so the bond must be highly polar. But inspite of this, fluorine has the highest bond strength!
So is this just a misconception I have? If it isn't a misconception, then why does the highly polar bond have the maximum bond strength?
Thank you!
$^1$: https://chem.ucr.edu/documents/curricularmaterials/neumantextbook/Chapter7.pdf


texts: What is the empirical formula of a compound where the mass ratio of sulphur and oxygen is 2:3?

texts:
This is how I tried to solve it:

$$\frac{2}{3} = \frac{0.67}{1}$$
$$\frac{32.06}{16} = \frac{2.00}{1}$$
$$\frac{0.66}{2.00} = \frac{0.33}{1}$$

I assumed by the result that if for every $\pu{1g}$ of $\ce{O}$ there are $\pu{0.33g}$ of $\ce{S}$ then if we have roughly $\pu{1g}$ of $\ce{S}$ there must be $\ce{3 O}$ atoms.
Is this result acceptable or do you know easier, clearer methods for this kind of example?


texts: Copper chloride color in electrolysis of salty water

texts:
I tried a simple water electrolysis experiment at home, with $\ce{NaCl}$ as electrolyte, and a $12 \,\rm{V}$ battery.

My wires were made of copper and $\ce{H2}$ bubbles were only forming at negative terminal (cathode). On the positive side (anode), nothing was happening.

After $3$-$4$ minutes, water started to change into a greenish-blue color and I realized that it must be copper reacting with chloride ions. After $15$ minutes, my solution was light blue with exceed $\ce{NaCl}$ at the bottom, after taking the wires out the solution started to turn into a yellow color in about $10$ minutes.

What was the yellow solution and why didn't cathode produce any oxygen?

I'm also worried that the yellow solution might be chlorine because I later boiled the solution.


texts: When study biology in class, I don't know how my teacher get to the topics on pH value. So, she says that pH stands for percentage hydrogen. Then, I thought there is something strange about it cause acid has a higher percentage of hydrogen then base. But why does an acid have a low pH value? Is there any mistake on the pH definition or my understanding?


texts: Ballistic behavior of molecules on potential energy surfaces

texts:
I came across the following sentence in a publication$^1$: "At this point we have to remember that the computed MEP path [sic] represents the reaction in the absence of any kinetic energy, while in reality the true reaction path, to some degree, will be ballistic." Further, they write that, "This path is accessed because after the transition state the molecule is 'ballistic'."

A minimum energy path (MEP) is calculated "step-wise", taking the previous geometry as a starting point, and the program follows the gradient. In classical terms, this might be to place a ball on a tilted plane, releasing it, and stopping it after a given distance, and repeat.

When they say that, in a real reaction, the molecules will have kinetic energy and be ballistic, I think they mean that the potential energy surface (PES) may be explored in directions slightly different than the gradient. This can be compared to releasing a ball on the top of a changing surface and allowing it to roll freely, where the ball will not follow the gradient when its velocity is high.

I cannot find a decent explanation of this anywhere, and it would be nice to get some input.

$^1$ De Vico, Liu, Krogh, and Lindh, 2007. J. Phys. Chem. A 111:8013-8019. doi:10.1021/jp074063g.  Cited passages are on p. 8016, Section 3.3.


texts:
I am trying to convert a pdb file of gold nanoparticle to the xyz file format to get the atomic coordinates. But when I try to use openbabel to do this, I get the following error.

*** Open Babel Error  in ReadMolecule
ERROR: not a valid PDB file

My command is obabel shelxpro.pdb -O shelxpro.xyz

(shelxpro.pdb is at http://www.sciencemag.org/content/318/5849/430/suppl/DC1
inside the .zip folder 1148624_data.zip)

Also when I try to visualize this structure with Jmol or VMD, I get only part of the expected structure.

Is there a way to fix either one of these issues?


texts: Symmetry and SALC: choosing coordinate basis

texts:
When we construct symmetry adapted linear combinations of orbitals (aka SOs) to build an MO diagram, we choose the z axis as the axis of highest symmetry and all other axis to make symmetry operations of a group easier to perform.

If we choose z-axis to point in some other direction, we will get a representation that is clearly not irreducible, but yet we would be unable to reduce it with the chosen basis because all orbitals mix (e.g. considering the case of 3d orbitals of a TM octahedral complex and having $d_{z^2}$ at a slant to the z-axis). I wonder if someone could explicitly explain why in this case the approach fails and highlight its limitations in general.

Thank you!


texts: Rationalizing Strength of Binary Halogen Acids with MO Theory

texts:
Help me walk through the logic here:

1) HF is a weaker acid than HCl.

2) This is as far as I can understand. How does sigma star affect the acidities of the binary halogen acids?

  If a covalent bond was formed, you would expect a decreasing acidity
  down the periodic table of the halogens, because the energy of the σ∗
  would increase forming a less attractive LUMO (lowest unoccupied
  molecular orbital), which would result in less hydrogen atoms being
  pulled of the halide (i.e. lower acidity, higher pKa).

Here are some questions about the above excerpt:

1) Covalent bond formed between what?

2) Why would the sigma star orbital be populated if the hydrogen were removed and a bond formed in place of it? Or is a bond going to be formed with the hydrogen still present?

Update:

https://usflearn.instructure.com/courses/986898/files/31117039


texts: Could observer effect cause electrons in one orbital to be found in another?

texts:
The observer effect states [1] that

when unobserved, absolutely small particles like electrons can simultaneously be in two different states at the same time.

If we look at an atom of any element, all of its electrons are subject to the observer effect. As the electrons are known for wave-particle duality, the Schrödinger equation can be solved to yield a wave function for each electron in the atom. An orbital is a probability distribution map of a wave function squared, and each orbital can accommodate up to two electrons.
For a single electron, it is not hard to imagine that the observer effect operates upon it to the extent of the probability distribution map specified by its orbital. That is, the electron can simultaneously have two positions if unobserved, and these two positions will not go beyond the space occupied by its orbital.
However, I'm wondering if an electron can have two positions when unobserved, where these positions are in different orbitals. For example, an electron falls under both the $\mathrm{2s}$ orbital and the $\mathrm{2p}_x$ orbital, if unobserved, and observation forces it to collapse into either $\mathrm{2s}$ or $\mathrm{2p}_x.$
Reference

Tro, N. J. (2015). Principles of Chemistry: A Molecular Approach, Global Edition. United Kingdom: Pearson Education Limited.


texts: What is the physics/chemistry behind gold dissolution in water/seawater?

texts:
Global ocean contains some amount of dissolved gold (around 0.05-0.005 ppb).

Is it ions of gold?
Is it just suspended atomic gold (like water vapor in gases - just suspended molecules)?
Can pure gold (in metal state) be dissolved in pure water at any rate (even it is very slow process)?
If it can be dissolved in pure water what is the physics behind? just diffusion?


texts: What household compound will neutralize naphthalene-stained washer (for clothes)?

texts:
Please help me tag this post.

Googling provided no answers except for vinegar, which did not work.

I washed this blanket for the first time that was purchased off of ebay.  There was a smell emitting from the washer as it was washing clothes.

This is no ordinary "mothball smell".  It is extremely stinky, like 30 magic markers were opened in the wash.  It's almost as if the blanket was DIPPED in naphthalene.

I tried running it empty with all the vinegar we had which was about 6-10 cups, together with powdered laundry soap, and both hot and cold wash cycles.  Will it help if I added some throw-away cloth in it to clean it out?  I even put it on a 2-hour wash.  The smell is as potent as when we started!

Will airing it out reduce the smell?  Ideally, I would like to completely remove the naphthalene, not just the smell.

Is cold better than hot water for this?  And lastly, what household compound can I buy that will neutralize the naphthalene?

Thanks.


texts: The pKa values of almost all carboxylic acids lie much above 0. But this is violated by trifluoroacetic acid(-0.25). How can this be justified?


texts: How is the ln k term in the linearised Arrhenius equation acceptable?

texts:
In my syllabus we only study about rate laws under the topic "Rates of reactions", but as I was interested in it, I started to search about that topic. And then I found the Arrhenius equation

$$\ln k = \ln A - \frac{E}{RT}.$$

But according to this equation rate constant $k$ doesn't have units because we are taking the natural logarithm of it. According to rate laws, rate constants have units and they depend on the reaction.

Are we talking about two different rate constants here? I searched this on internet and all the books I could refer but I couldn't find an answer.


texts: Order of priority in hybridization of d-orbitals

texts: During hybridization of d-orbitals why the $d_{z^2}$ and $d_{x^2-y^2}$ orbitals are used up before the $d_{xy}$, $d_{yz}$ and $d_{zx}$ ?


texts: Calculating Compressibility factor from the Van der Waals' Gas equation

texts:
So this problem has been bugging me for a long time. According to Wikipedia the compressibility factor $Z$ is defined as the ratio of the volume occupied by a real gas divided by the volume occupied by an ideal gas at the same temperature and pressure.

$$Z = \frac{V_\text{real}}{V_\text{ideal}}$$

Now the ideal gas equation is

$$P_\text{ideal} V_\text{ideal} = nRT$$

Now from here we can substitute the value of $V_\text{ideal}$ into the $Z$ expression to get $$Z = \frac{P V_\pu{m}}{RT}$$

Where $V_\pu{m}$  is the molar volume of the gas and $P$ is the value of $P_\pu{ideal}$ that was in the ideal gas equation.

OK so far so good.

Deriving the compressibility factor value from the van der Waals' gas equation:

We know for real gases the pressure exerted by them is always less than the pressure exerted by an ideal gas so we correct the pressure by the term
$an^2/V^2$

$$P_{\text{ideal}}= P_{\text{real}} + \frac{an^2}{V^2}$$

And the volume occupied by the gas molecules can be written as
$$ V_{\text{ideal}} = V_{\text{real}} - nb$$

On substituting the above values of $P_\text{ideal}$ and $V_\text{ideal}$ in the ideal gas equation, we get our van der Waals' Gas equation

$$\left(P+\frac{an^2}{V^2}\right)(V-nb) = nRT$$

Please note that in the above equation $P$ is $P_\text{real}$ and not $P_\text{ideal}$. Now I'm going a step further to calculate the value of $Z$ from this equation by shifting the terms and I got this $$Z = \frac{P V_\pu{m}}{RT} = \frac{V_\pu{m}}{V_\pu{m} - b} - \frac{a}{RTV_\pu{m}}$$

Now here's the problem that I'm facing: In the above expression the value of $P$ is not the $P_\text{ideal}$ but it is the value of $P_\pu{real}$ that we had in the van der Waals' gas equation. Doesn't that contradict the whole definition of Compressibility factor that we had learned in the first place? How this expression for $Z$ can be correct?
Thanks for reading.


texts: How to assign peaks to mannose using H-NMR and COSY?

texts: I did a H-NMR experiment with D-mannose in deuterated DMSO. I have difficulty assigning the peaks. I know doublet a is the anomeric centre C1 and that triplet f is the OH attached to C6. Doublets b,c,d and e also correspond with the OH groups. Looking at the COSY you see that a and b are next to each other which suggests that b is the OH on the anomeric carbon C1. However, COSY also shows that b and h are next to each other. How is this possible if with COSY you are only able to look 3 bonds further?


texts: What is the composition of the oil-like fluid that seeps out of dry-cells over time?

texts:
An experience a lot of us might've had; a dry cell (not completely depleted) when left in an electrical device for long periods of time, has this viscous fluid coming out that usually corrodes the terminals of the battery.

I almost always find this fluid, present as a sorta thin film over the terminals and the casing of the battery.

I'm told that the Ammonium Chloride in the cell, being slightly acidic reacts with the zinc casing of the cell, which is why dry cells don't last long (My teacher mentioned this during our Electrochem. class, he didn't mention anything about that fluid I was talking about though). Could this fluid possibly the result of that reaction? What are its chemical constituents?


texts: Does vinegar neutralize the strongly basic compounds in cement?

texts:
I have heard that washing one's hands with vinegar is effective in neutralizing the strong bases in cement and is more effective than water.

I want to know how cement burns and what bases are involved in this reaction.

I have tried googling "cement burns" and found websites explaining the importance of washing one's hands with vinegar as a preventative measure. I have tried searching PubMed but I've found mostly case reports that do not address how chemical burns actually happen.

If anyone knows of some good papers or books that cover the topic of chemical burns in greater detail than what I've found; please let me know.


texts: Why do people consider caffeine ineffective after its half-life?

texts:
Assuming you take $\pu{200mg}$ of caffeine, it's half life is roughly 6 hours. So after 6 hours there should still be $\pu{100mg}$ of caffeine in your body.

Then why is it generally said that after six hours caffeine's effect should wear off? Shouldn't it only be diminished since there is still $\pu{100mg}$ of caffeine in your body?


texts: We know from experimental data that $\ce{H-O-H}$ bond angle in water is approximately 104.5 degrees. If its two lone pairs were bonds (which is unfortunately impossible) also $\ce{O-H}$ bonds and a perfect tetrahedron resulted, then VSEPR theory would predict that the bond angle would be 109.5 degrees - this number can be easily derived using the geometry of a tetrahedron. However, how would people give estimates of the actual bonding angle of water, which is caused by a slightly greater repulsion by the lone pairs than there would be if they were bonds? What physics would be involved in the calculation? Thanks!


texts: What is the major product of the reaction of 2-ethoxypentane with hydrogen iodide?

texts:
What is the major product formed by heating 2-ethoxypentane with $\ce{HI}$?

The options are:

According to me the correct answer should be option-1 because 2-methylbutyl carbocation is more stable than ethyl carbocation as there are more +I groups attached in 2-methylbutyl carbocation.
But according to my book the second option is correct.
Is my answer correct?
If not please explain


texts: Yellowing/Browning from Mixing Ascorbic Acid with Calcium Carbonate and Glycerol

texts:
I slowly get some yellowing / browning upon mixing ascorbic acid with calcium carbonate and glycerol and letting it sit at room temperature over time.
At first I thought it was ascorbic acid oxidating but it seems to happen even when kept in a full sealed container.
It's very humid where I'm at so I expect there is water in there too and suspect it accelerates the reaction as I get small amounts of a brown liquid in there as well.
Anyone knows what I'm dealing with?