texts: How do we know the concentration of hydroxide ions in this derivation?

texts:
In the derivation of the pH of a solution of a salt prepared from a weak acid and strong base, I used two equilibrium reactions:

  $$\ce{ CH3COOH(aq) + H2O(l) <=> H3O+(aq) + CH3COO-(aq)} \qquad k_{eq} = K_a \\
    \ce{ 2H2O(l) <=> H3O+(aq) + OH-(aq) } \qquad k_{eq} = K_w$$

Reversing the first equation and adding it to the second gave me the "hydrolysis reaction":
$$ \ce{ CH3COO-(aq) + H2O(l) <=> CH3COOH(aq) + OH-(aq)} \qquad k_{eq} = \frac{K_w}{K_a} $$
My textbook uses this third equation to derive the pH of the salt solution by asserting that the equilibrium concentrations of the reactants and products of the third reaction are:
$$ \ce{[CH3COO-(aq)]} = C-C\alpha \\
   \ce{[CH3COOH(aq)]} = C\alpha \\
   \ce{[OH-(aq)]} = C\alpha $$

What I am confused about is, why is the equilibrium concentration of hydroxide ions $C\alpha$, and is only governed by the third reaction? Why
does the second equilibrium not contribute any hydroxide ion concentration? That is to say, the derivation assumes the water equilibrium does not exist, and all the hydroxide ion concentration comes only from the third reaction.

Also, even if we suppose some $x$ concentration of hydroxide ions and use it in the 'equilibrium constant expressions' of both the second and third reactions, we have more unknowns then conditions. So that's a problem too.

All in all, I need to know that, why, inspite of hydroxide ion participating in two equilibria, is the hydroxide ion concentration decided by only one of the reactions. And even if approximation is involved, if we try to be accurate, why do we have fewer conditions than variables?

Thank you.


texts: Will Chlorodifluoromethane (R22 refrigerant) react with calcium metal?

texts:
I am attempting to recycle or find a use for chlorodifluoromethane, however I do not want to risk venting it into the atmosphere or exposing myself to hydrofluoric acid. Ideally, I would like to produce chlorine/fluorine salts for safe storage/disposal.

Edit: Upon further research, calcium fluoride appears to be a non-toxic salt of fluorine. MSDS warns that R22 will react with alkali metals as well as calcium, magnesium, etc. What conditions are required in the following reaction?

$$\ce{HCFCl2 + Ca -> CaF2 + ...}$$

Where all the fluorine is consumed by calcium. I am not concerned with other chloride salts since fluorine toxicity is my main concern.


texts: Why are water droplets shaped like that?

texts:
With nothing to do, I stared at the droplets that get condensed on the glass panel of my window.

Upon examination, these droplets appear to be in some sorta pattern. There are big droplets as well as small ones that fill the space between the big ones.

The ones in the middle, between rows of small droplets are usually big one.

All these intrigue me to think about what are that factors that contribute to this pattern.

My guess: I think vapor gets condensed on dust particles thus forms those droplets in the picture. But what accounts for the different sizes of the droplets?


texts: The rusting of steel may be promoted by brushing with HCl followed by brushing with hydrogen peroxide solution. What is the chemistry involved?

texts: A welder showed me a way of promoting rust on steel by brushing on muriatic acid and then a hydrogen peroxide / water solution. What's going on, chemically speaking?


texts: Lowercase "a" in organic chemistry nomenclature?

texts:
In the IUPAC name for geosmin has a lowercase a mixed into it:
(4S,4aS,8aR)-4,8a-dimethyloctahydronaphthalen-4a(2H)-ol.

Does anyone know what it stands for or can reference me to a source that does?


texts: I am seeing Doublet of Doublets peaks when I should see just a doublet

texts:
The following is a tutorial question I need to do:

I initially thought the answer was isobutyl formate (CAS:542-55-2) but what confuses me is the dd peak at $\pu{3.9-4.0 ppm}$. To my knowledge, isobutyl formate should give just a doublet at that region. What am I missing out?


texts: What is the reason for phase separation?

texts: I have seen phase separation as a phenomenon taking place. However I do not understand why this phenomenon occurs as a counter example to the natural laws of diffusion along the concentration gradient. During phase separation the richer side becomes richer with the atoms which it already has and becomes more and more deficient with the poorer atoms and vice-versa. Similar things will occur in the opposite case as well. How can phase separation be explained in detail, for example with factors like the chemical potential?How do you quantify whether 2 liquid interactions will be unfavorable or not?


texts: Textbook Claim: "... in all cases it is the electrostatic force acting between charged particles that is responsible for all the forms of bonding."

texts:
I am reading an introductory semiconductor physics textbook. The textbook states the following:

  Several types of atomic bonding have been identified, including ionic, covalent, van der Waals, hydrogen, and metallic. Whatever the name given to the type of bonding, in all cases it is the electrostatic force acting between charged particles that is responsible for all the forms of bonding.

My concern is with the validity of the latter sentence; that is, that all cases of bonding are electrostatic forces acting between charged particles.

Wikipedia says the following:

  A chemical bond is a lasting attraction between atoms, ions or molecules that enables the formation of chemical compounds. The bond may result from the electrostatic force of attraction between oppositely charged ions as in ionic bonds or through the sharing of electrons as in covalent bonds.

If electrostatic forces act between charged particles (ions), and atoms are, by definition, neutral particles, then, since atoms do bond, how can it make sense to say that all bonding is electrostatic forces acting between charged particles?

And my interpretation of the Wikipedia article is that the electrostatic force of attraction is responsible for bonding between oppositely charged ions, as in ionic bonding, whereas it is not responsible for bonding through the sharing of electrons, as in covalent bonding.

So is the textbook's claim that all types of bonding are electrostatic forces acting between charged particles false?

I would appreciate it if people could please take the time to clarify this.


texts:
Since latent heat is not sensible, it seems like it would be useful in creating an efficient battery. Sensible heat interferes with electron flow in standard lead-acid and other batteries. The latent heat-electron interface might occur separately from the energy storage. Has this idea been explored?

Of course, I may be incorrectly assuming that latent heat does not itself add resistance to an electric circuit...


texts: Difference between quick lime, slaked lime, lime water and soda lime

texts: The chemicals "quick lime", "slaked lime", "lime water" and "soda lime" all have "lime" in common. What is the difference between them?


texts: What is the electron count in this nickel complex?

texts:
Our class has started learning about electron counting using the ionic method. I was having a little difficulty, especially when there are two metals in one complex, so I looked at Wikipedia for help.

The Wikipedia page for organonickel complexes says:

  In $\ce{(allyl)2Ni2Br2}$ and $\ce{(allyl)Ni(C5H5)}$, nickel is
  assigned to oxidation number +2, and the electron counts are 16 and
  18, respectively.

I understand that in $\ce{(allyl)Ni(C5H5)}$, the allyl and cyclopentadienyl ligands both have a $-1$ "charge", so the nickel has a +2 "charge". Thus, the electron count is: $4 + 8 + 6 = 18$.

However, I am struggling to calculate the electron count in $\ce{(allyl)2Ni2Br2}$. Using the same logic, $\ce{Ni}$ is in the +2 oxidation state. Since the structure (see below) does not have a metal-metal bond, we do not have to add $1$ when counting electrons. So, I think the electron count should be $\frac{4*2 + 8*2 + 2*2}{2} = 14$, not $16$. How does Wikipedia get that $\ce{Ni}$ has an electron count of $16$ in $\ce{(allyl)2Ni2Br2}$?


texts: calculate the final concentration of this equation

texts:
A student mixed 260ml of 1.2 M lead(II) nitrate with 300ml of 1.90M potassium iodide. What is the final concentration of $\ce{NO3^{-}}$ ?

the answer is 1.11M , but he used the moles of lead(II) nitrate to find out the moles of $\ce{NO3^{-}}$ ,, and I think he should had used the moles of potassium iodide since it is the limiting reactant.

could anyone explain ?


texts: How to calculate the enthalpy of reaction using Gaussian 09?

texts:
I'm having a hard time trying to understand what's the correct way to calculate the enthalpy of reaction given that I've already calculated the frequencies of my compounds in Gaussian. Below I show the reaction of interest:

As you can see in the figure, experimentally, this reaction leads to the formation of ionic species. As for my calculations, I have all four species optimized (all of them separated, I'm not working with complexes) with their respective frequencies.

As for the enthalpy, I'm using the following formula:

$$
\Delta_\mathrm{R} H=
  \left[(\text{Iodide anion}) + (\text{cationic product})\right]
  - \left[(\ce{FeCpI(CO)2}) + (\text{phosphine reactant})\right]
$$

All terms are the sum of the electronic energy and the thermal enthalpy as given by Gaussian.

Am I doing it correctly? Because I'm not sure, if I have to consider both products together or separated as I'm currently doing. Can you give me some light on this?


texts: How is different flame color of alkali metals related to nuclear charge?

texts:
Why do different alkali metals produce different flame colors ?

According to my teacher,different atoms have different nuclear charge and due to difference in effective nuclear charge,the orbit to which an electron jumps differ even though energy provided from Bunsen flame is same.And on coming back it emits energy in the form of light.

This is very different from the reason I found when I googled my doubt. I wanted to know whether the explanation teacher me gave was correct.


texts: How does the cyclopropyl group influence conjugation and aromaticity?

texts:
While answering the question Why isn't cyclobutane planar?, I recollected that cyclopropane and its derivatives behave like double-bond compounds, e.g. a cyclopropyl group can potentially be conjugated with neighboring $\ce{C=C}$ bonds and affect aromaticity, like in spiro[2.4]hepta‐4,6‐diene which has pronounced aromatic character (I remember this example from an early edition of March's Organic Chemistry):

Cyclopropyl group is generally known to be a poor $\pi$-electron acceptor, but a very good $\pi$-electron donor [1]. So, I'm wondering whether the cyclopropyl conjugation in general may result in altered aromatic properties, and to what extent; also, on how Hückel's $4n + 2$ rule is applicable here.

I've picked up existing cyclopropane derivatives which I think mimic electronic configuration of well-known aromatic and non-aromatic compounds, assuming each cyclopropyl group acts as a double bond:

[3]Rotane $\ce{C9H12}$ [2] (1) vs. benzene (1a);
Dispiro(2.2.2.2)deca-4,9-diene $\ce{C10H12}$ [3] (2) vs. cyclooctatetraene (2a);
9,10-bis(Spirocyclopropyl)-9,10-dihydroanthracene $\ce{C18H16}$ [4] (3) vs. dibenzo(a,e)cyclo-octatetraene (3a).

Crystal structure of (1), obviously planar triangle (1a is planar as well):

Crystal structure of (2), planar $\ce{C6}$ ring (2a is not planar):

Crystal structure of (3), all three $\ce{C6}$ rings are planar and are within a single plane (3a is not planar):

Provided with these three examples of planar systems for illustration (you can also pick up the systems of your interest), I would like to state a couple of questions:

Is there always a conjugation between a cyclopropyl group and an adjacent double bond? In other words, do cyclopropane's "bent" bonds always have extensive $\pi$-character and can therefore act as an alkene?
1a. Are electronic structures 1 and 1a; 2 and 2a; 3 and 3a similar, and to what extent?
Can we use Hückel's $4n + 2$ and $4n$ rules for cyclopropyl-containing monocyclic rings? If not, how to estimate aromaticity/anti-aromaticity in such systems?

Bibliography

de Meijere, A. Angew. Chem. Int. Ed. Engl. 1979, 18 (11), 809–826. DOI 10.1002/anie.197908093.
Boese, R.; Miebach, T.; De Meijere, A. J. Am. Chem. Soc. 1991, 113 (5), 1743–1748. DOI 10.1021/ja00005a043.
Haumann, T.; Boese, R.; Kozhushkov, S. I.; Rauch, K.; de Meijere, A. Liebigs Ann./Recl., 1997 (10), 2047–2053. DOI 10.1002/jlac.199719971007.
Rosenfeld, S.; White Tingle, C.; Jasinski, J. P.; Whittum, J. E.; Woudenberg, R. C.; Van Epp, J. J. Am. Chem. Soc. 1994, 116 (26), 12049–12050. DOI 10.1021/ja00105a054.


texts: Which computational method/basis set should I use for small molecular ions?

texts:
I apologize for a perhaps newbie question.

I would like to compute the potential energy surface for several small molecular ions, like $\ce{H2+}$ and $\ce{H3+}$, using quantum chemistry software. What are the proper method and basis set to do that and why? I am thinking about ROHF/STO-3G or UHF.


texts: How to calculate the amount of chlorine emitted yearly by a leak in the air conditioning system?

texts:
A leak in the air conditioning system of an office building releases $12~\mathrm{kg}$ of $\ce{CHF2Cl}$ per month. If the leak continues, how many kilograms of $\ce{Cl}$ will be emitted into the atmosphere each year?

My working out is as follows:

\begin{align}
12~\mathrm{kg} &= \mathrm{CHF}_2\mathrm{Cl} \\
\text{Cl mass in compound} &= \frac{35.45}{86.448}\times100\% = 41\% \\
\end{align}

$41\%$ of $12~\mathrm{kg}$ is $4.92~\mathrm{kg}$, so I multiplied it by $12$ to get the annual result.

$$
4.92~\mathrm{kg} \times 12(\text{months}) = 59.04~\mathrm{kg\ year}^{-1}
$$

I don't have access to the answer so I'm not sure whether or not my answer is correct. Also, this process seems a little to simple to be correct. I say this because the question prior to it was very difficult. Can someone please tell me if I am right, and if I'm not, where did I go wrong?


texts: Is it more energy efficient to desalinate seawater by flash boiling or by flash freezing?

texts:
In Saudi Arabia I think there are two types of desalination using flash boiling
from electric power production and also from flash freezing using solar absorption
refrigerant freezing.  One requires fossil fuel the other solar energy.


texts: Volume increase when air is enriched with water

texts:
When air is enriched with water, how much volume increase can be expected?

I am aware that the volume increase will not be proportional (i.e. $\pu{1L}$ air + $\pu{10mL}$ gasified water will result in a volume of less than $\pu{1.01L}$).

So how big is the volume increase actually?


texts: Approximating strength and hardness of alloy

texts:
I do not have any formal education in metallurgy, but I am trying to make a game mechanic based on it.

I need to be able to alloy together different metals and alloyable materials such as carbon in different percentages, and get an approximation of the strength and hardness of the resulting alloy. If anyone has any ideas how what I would need to do to calculate such a thing I would be very appreciative.


texts: I'm shooting video of paint moving in mineral spirits.  To make for a little more action, is there a household granular/solid I could add to the mineral spirits that would gently effervesce ala alka-seltzer in water?


texts: Why would the loss of H₂ to space mean that the Earth's geochemistry would be based on acid/base reactions?

texts:
I am reading a paper[1] that contains the line:

  Most of the $\ce{H2}$ in the Earth's mantle escaped to space early in the Earth's history; consequently, the overwhelming majority of the abiotic geochemical reactions are based on acid/base chemistry, i.e., transfers of protons without electrons.

The connection between the loss of $\ce{H2}$ and acid/base chemistry is not clear to me.

Why would the loss of $\ce{H2}$ to space make acid/base chemistry the default?

Falkowski, P. G., T. Fenchel, and E. F. Delong. (2008) The microbial engines that drive Earth's biogeochemical cycles. Science 320:1034-1038.


texts: Conducting cyclic voltammetry in an air sensitive manner

texts:
Does anyone have suggestions on ways to conduct cyclic voltammetry on an air sensitive material without shipping the entire set up into a glovebox?
This is for redox active organometallic compounds.


texts: How do I find out the total no of geometrical and stereo isomers of the compound given as $\ce{C2FClBrI}$? Is there any way I can list out all the possible structures mathematically without having to think about each structure in my mind? Any suggestion how you would do it would be wonderful.


texts: Can nitrate and sulfate ions be oxidised during electrolysis of their molten compounds?

texts:
$$\begin{align}
\ce{O2 + 4H+ + 4e- \;&<=> 2H2O}\quad\quad &&E^\circ = +1.229\ \mathrm{V}\\
\ce{S2O8^2- + 2e- \;&<=> 2SO4^2-}\quad\quad &&E^\circ = +2.01\ \mathrm{V}
\end{align}$$

From the above, I know that an aqueous solution of a sulfate salt undergoing electrolysis will not oxidise to peroxydisulfate ions over water being oxidised to oxygen at the anode unless it is at extremely high concentrations.

However, what if the solution is molten? Will the product at the anode be peroxydisulfate?

Also, can nitrate ions be oxidised? Perhaps to peroxynitrate or peroxynitrite?


texts: Why is the resonance concept not required in molecular orbital theory?

texts:
In valence bond theory, resonance plays a pivoting role; why isn't such concept needed in MO theory? Why is it told that "MO theory provides a global, delocalized perspective on chemical bonding"?

(This is a follow up to What is actually the difference between valence bond theory and molecular orbital theory?)


texts: Does hydrogen peroxide - urea become more active when illuminated?

texts:
Dentists' tooth whitening systems and consumer kits use gels containing carbamide peroxide, also known as hydrogen peroxide - urea.

Dentists use a light activator: (image from Wikipedia).

Consumer kits typically include 35% carbamide peroxide gel. Some of them use an LED light too, while others don't.

Wikipedia seems to be in two minds about it, stating

  Recent research has shown that the use of a light activator does not improve bleaching, has no measurable effect and most likely to increase the temperature of the associated tissues, resulting in damage

while also talking about which light is "best":

  The ideal source of energy should be high energy to excite the peroxide molecules without overheating the pulp of the tooth

Is a light source relevant here, or is it merely a marketing gimmick?


texts: How is sulphur trioxide formed and why is it stable?

texts:
Structure of $\ce{SO3}$ (sulfur trioxide):

In the molecule, if each oxygen atom shares two electrons with sulfur atom then how does the sulfur atom remain stable? It already has 6 valence electrons and needs only 2 more to become stable but the oxygen atoms share total of 6 electrons with sulfur atom. So how is the molecule stable?


texts:
I'm working often with spectral data of various gases, and the bulk of the data analysis is assigning the peaks with maximum signal (y-axis) to frequency (x-axis). Often we have several thousand data points, and it can be quite difficult to manually find peaks. I've tried getting around this in Excel with clever IF/AND statements, but the major obstacle is signal noise: I simply cannot devise a clever Excel statement to help me pick peaks.

For example, using an =IF(AND(greater signal than adjacent points),"max","") statement gives tons of extraneous hits where the noise causes a slight fluctuation in the data. Similarly, creating a column of slopes and doing an =IF(slope goes from + to -),"max","") statement also gives bad data.

The most elegant solution I have is to pick an arbitrary value # that most of my peaks are above and use an =IF(AND(slope goes from + to -,B>#),"max","") statement. That seems to work for stronger peaks (maybe 70% of the peaks on a good day), but I still have to go in and manually look at the weaker peaks (and often when doing these spectra many energetic transitions that need labeling are statistically unlikely-->low signal). I'm wondering if anyone here has a better solution able to detect local maxima not resulting from noise with a better success rate.


texts:
Does the epoxide ring open in this case? I guessed it does, but it really doesn't. The answer given (among the four options) is another epoxide, with some sort of substitution. Could someone please explain the mechanism for this reaction?

Also, what exactly is the condition for ring opening of epoxides? Thanks for the help!


texts: Is it possible with openbabel to generate random 3D geometries (i.e. conformers) of a molecule without taking energy into account? Ideally with the property of being truly random, so that after generating conformers like this for a sufficient amount of time, a good coverage of the conformational space is obtained. Because the --conformer options of openbabel takes energy into account, but I want to input the geometries into a qc program that then calculates the energies for the conformers.


texts: Can someone tell the me the data bank which has all the STO-3G basis sets for many electron atoms?

texts:
I am trying to express the slater orbitals of Helium atom in terms of 3 gaussian functions (STO-3G basis set). Is there any data bank or reference table in which I can find the exponents and coefficients in it ?
Also in primitive cartesian gaussian , it seems like both $2s$ and $2p$ has the same functional form. For $2p$ it is $x\exp(-\alpha x^{2})$ , $y\exp(-\alpha y^{2})$ and $z\exp(-\alpha z^{2})$. What is for  $2s$ orbital in primitive gaussian function ?


texts:
In the ACKS2 polarizable force field paper, I found a thing called the atom-condensed softness matrix. In another paper, I found this expression for it:

  $$
\chi_{kl} = 2 \sum_{i}^{\text{occ MOs}} \sum_{j}^{\text{unocc MOs}} \frac{\langle\psi_{i}|g_{k}|\psi_{j}\rangle\langle\psi_{j}|g_{l}|\psi_{i}\rangle}{\epsilon_{i} - \epsilon_{j}} \delta_{\sigma_{i}\sigma_{j}},
$$
  where

  $\epsilon_{i}$: orbital energy of the $i$th KS orbital
  $\chi$: (non-interacting) response matrix
  $\psi_{i}$: spatial orbital
  $g_{i}$: potential basis function

What is the physical meaning of it, or at least what information we can get from this matrix?
If in KS-DFT we consider the system as non-interacting, why do we consider interaction between two species in this equation? (if I understand it right - between molecules $i$ and $j$)


texts: Does the third law of thermodynamics apply to all compounds and elements?

texts:
According to wikipedia, the third law of thermodynamics is "The entropy of a perfect crystal, at absolute zero (zero kelvins), is exactly equal to zero.".

Then, theoretically, could all substances, including molecular compounds, attain absolute zero? Another way of thinking of this question is whether all compounds could become perfect crystals.


texts:
Suppose we have a compound, say copper sulfate. I know that sulfate is a poly-atomic ion, having valency 2. And, in this case, copper also has valency 2. So, to fullfill their 'octet' requirements, they both react. The problem is: Suppose we take the metal zinc and bring it in contact with copper sulfate. Now, a displacement reaction occurs, in which zinc replaces copper because of its higher reactivity.

Copper sulfate is a compound that is neutral; both the cation and anion have completed their octets; why then does zinc replace copper? Or, in other words, after completing the octet, why it is necessary for sulfate to leave copper and react with zinc?


texts: Is it considered safe to sonicate with flammable solvents?

texts: I use a sonicator at work in a cleaning process. It involves sonicating acetone, NMP, and IPA. We would like to move forward with other flammables as well. We currently do the work in a hood, but no other precautions are taken. OSHA has no guidance. What is your experience with this issue?


texts:
Before a sodium atom and a chlorine atom combine together to form the ionic compound $NaCl$, they are just neutral atoms. However, when an electron is transferred from the outer energy level of the sodium atom to the chlorine atom, both of these gain a charge on them; the sodium atom or ion has a charge of $1+$ and the chlorine ion has a charge of $1-$. Both of these ions attract each other and an ionic bond is formed between them.

  But what happens when an atom of an element say $Ca$ combines with a polyatomic ion say $OH^-$. Is this calcium atom an ion, is it already a charged atom when it interacts with the hydroxide ion or does it gain the charge by any transfer of electrons to the $OH^-$ ion and becomes $Ca^{2+}$ to bond with the $OH^-$ ion?

I think the polyatomic ions say $OH^-$ is already an ion and not an uncharged compound of elements that gains charge as in the case of $NaCl$, and the bond between an ion and a polyatomic ion is due to the attractive forces between them if already they have opposite charges.


texts: Why is 295 nm a good wavelength to check absorbance when testing for aspirin?

texts:
Take aspirin (acetylsalicylic acid) and hydrolyze it with NaOH. This results in sodium acetylsalicylate and water. I think the sodium is held on with an ionic bond, so it is really salicylate dianions that are the important thing in the solution.
This is then diluted to several different concentrations. Using UV-VIS, the absorbance of these solutions are measured at 295 nm. Then a calibration line is plotted, that is, absorbance verse concentration. It will be a (pretty much) straight line according to the Beer–Lambert law. You can use this calibration line to calculate the concentration of a similar, but unknown, solution from its absorbance.
Why was 295 nm a good choice of wavelength to measure at?
The only idea I currently have is that at 295 nm there is a distinct difference between the absorbance of acetylsalicylic acid and salicylic acid. Apparently, the salicylic acid has a strong response at 295 nm, whereas the acetylsalicylic acid does not. However, I am not sure this is exactly relevant, since I'm not sure I have salicylic acid in my solution.
If I am on the right track here, then I have a follow-up question:
Apparently the lambda-max for salicylic acid is 302 nm. So, why would 295 nm be used in this experiment instead of 302 nm? Or, would anything between, say, 295 nm and 310 nm be just as good?


texts: Why are amidines more basic than amines?

texts:
Amidines can be thought of as carboxylic acid derivatives with the carbonyl oxygen replaced by a nitrogen and hydrogen atom; amidines exhibit conjugation.

Amidines are more basic (less acidic) than amines and amides by a factor of around ${10^{3}}$ and ${10^{12}}$, respectively (from pKas).

I would naturally think that conjugation would lower the energy level of MO containing the lone pair; thus, the lone pair would be more bound to the nucleus and less available to deprotonate.

This is an argument similar to explaining why pyridine is less basic than piperidine; $\ce{N}$ is $sp^{3}$ hybridized in piperidine but $sp^{2}$ hybridized in pyridine. Since $sp^{2}$ orbitals have less p character than $sp^{3}$ orbitals (2/3 vs 3/4), the lone pair on $\ce{N}$ in pyridine is at a lower energy level than the lone pair on $\ce{N}$ in piperidien, and pyridine is less basic than pyridine.

Although I realize that the positive charge on the amidine is stabilized by conjugation (as explored by a previous post comparing the basicity of amidines and amides), wouldn't my reasoning with MO theory outlined above suggest a lowering of the basicity of amidines?

References

Clayden, J., Greeves, N., Warren, S. Organic chemistry, 2nd ed.; Oxford University Press: New York, 2012.


texts: Osmotic pressure and Raoult's law co-relation?

texts:
Consider two compartments A and B joined. A contains pure water. B contains brine (dilute). Consider the Vant Hoff factor ($i$).

Obviously pressure over B is less than over A.

We also know that the excess pressure if equal to $iC{\rm R}T$ (C is concentration of brine)

Thus it follows that pressure over B is p - icrt (p is vapour pressure of compartment A, which is pure water in this case).

But from Raoult's law we also know that pressure over compartment B is PX (x is mole fraction of water in brine).

That would mean

$$p - iC{\rm R}T= px$$

Is the equality correct?


texts:
I'm designing an experiment and it involves testing various concentrations of solutions, and I will be testing 5 in total. I proposed to make up a stock solution, and distribute it evenly in 5 different beakers and add different amounts of water to each solution but my teacher doesn't like this method and says I should simply dilute down but I don't know what he means. So if I had a 1.00 mol/dm$^{-3}$ solution and wanted concentrations of 0.800, 0.600, 0.400 and 0.200  mol/dm$^{-3}$, how do I dilute it down? To be honest, the concentrations don't really matter, it's just the method of making them - would it be easier to dilute them by half each time? Each solution is going to be used up so I can't simply reuse them...

Ultimately I will need 200ml of each solution in the experiment design, and the precision of the concentrations is not very important. How can I dilute one stock solution to 4 other solutions?


texts: Temperature in the Gibbs Free Energy equation

texts:
My professor gave us 2 different ways to calculate this problem. I did it using the Clausis-Clapeyron equation.

However, I don't quite get the second method because I thought that if the change in enthalpy and entropy of formation are in standard states, the temperature (T) in the Gibbs Free Energy equation meant to be 298K? And then making the temperature in the second equation 1100K, to find the equilibrium constant?


texts: Use of the box method to determine lowest term symbol for lanthanides but not iron

texts:
I am trying to compare the predicted magnetic moment for Fe(CN)6 using the spin-only formula magnetic moment = $\sqrt{4S(S+1) + L(L+1)}$.

However, if I use the box method for Fe(CN)6 to predict the lowest term symbol of Fe3+, I get 6S. If L = 1, however, then the predicted value of the magnetic moment is similar to the experimentally derived value.

Can we not use this method because in the complex the octahedral field changes the energy levels of the d orbitals?

If this is the case, then why can we use the box formula to determine the magnetic moments of lanthanides using the formula magnetic moment = g$\sqrt{J(J+1)}$.


texts: Why is the change in entropy is different for different interpretations?

texts:
Forgive me if the title is a bit vague. Read on and I'll clarify.

So, today in class, my teacher was explaining entropy. He gave various examples explaining how the degree of randomness changes. One example in particular stuck out to me. Here it goes:

Imagine there is a container with a hypothetical boundary in the middle. Neon gas is on the left of the boundary, and Argon on the right. As long as the boundary exists, the gases can't cross it to intermix.
Now the boundary is removed, and the gases mix. This increases the randomness in the system and thus entropy increases. We get $\Delta S \gt 0$. Thus the process is spontaneous.

My Question:

How can we definitively say that entropy has increased (or that randomness has increased)?

My Reasoning:

So my teacher says that entropy increases. These following cases show that change in randomness depends on your interpretation.

Interpretation 1:

Before mixing (boundary exists):

If we take some volume of gas, say $1 \text{ cm}^3$, at a random position in the container, we might get:

Pure $\ce{Ne}$
Pure $\ce{Ar}$
A mixture of the two gases

The point is that we aren't sure what composition we get, because the distribution of gases isn't homogeneous.

After Mixing (boundary removed):

The gases diffuse and intermix to form a homogeneous mixture.

Now if we take $1 \text{ cm} ^3$ from a random position, we can be $100\%$ sure of the composition of the gases, because the mixture is homogeneous.

This means there is more uniformity now. Or, we can say that there is less randomness. This tells us that $\Delta S \lt 0$.

Interpretation 2:

Using a new approach now.

Before Mixing (boundary exists):

Take any single atom from either side of the boundary at random. My chances of correctly predicting what atom I get (either $\ce{Ne}$ or $\ce{Ar}$) are $50\%.$

After mixing (boundary removed):

I again pick any atom at random from a random point in the container. My chances of correctly predicting what atom I get is again $50\%.$

This tells us that since I still have the same chance of correctly predicting, the randomness of the system has not changed.

This gives us $\Delta S = 0$.

Same physical process, but we get 3 different values of degree of randomness ($\Delta S$) depending on our interpretation. We know that diffusion does take place, so the process is spontaneous, and hence $\Delta S \gt 0$.

My Questions:

How to accurately know whether the degree of randomness increases or not?
How is the exact value of $\Delta S$ measured in actual experiments?

Note:

Assume the gases to be ideal.
Assume the container to be sufficiently large.


texts: Finding the irreducible representation which an orbital transforms under

texts:
I have some major confusion on irreducible representations. An example of a problem I have is

  Based on the character table for the point group of each of the follwing molecules, which irreducible representation would be used to classify the Cu $\mathrm{d}_{xz}$ orbital in $\ce{[CuCl5]^3-}$?

Since this complex probably has a trigonal bipyramidal geometry, I'm starting with the $D_\mathrm{3h}$ character table:

$$\begin{array}{c|cccccc|cc} \hline
D_\mathrm{3h} & E & 2C_3 & 3C_2 & \sigma_\mathrm{h} & 2S_3 & 3\sigma_\mathrm{v} & & \\ \hline
\mathrm{A_1'} & 1 & 1 & 1 & 1 & 1 & 1 & & x^2+y^2,z^2 \\
\mathrm{A_2'} & 1 & 1 & -1 & 1 & 1 & -1 & R_z & \\
\mathrm{E'} & 2 & -1 & 0 & 2 & -1 & 0 & (x,y) & (x^2-y^2,xy) \\
\mathrm{A_1''} & 1 & 1 & 1 & -1 & -1 & -1 & & \\
\mathrm{A_2''} & 1 & 1 & -1 & -1 & -1 & 1 & z & \\
\mathrm{E''} & 2 & -1 & 0 & -2 & 1 & 0 & (R_x,R_y) & (xz,yz) \\ \hline
\end{array}$$

But i don't know what exactly I need to do.

Is the irreducible representation just the row label, i.e. the Mulliken term? Or is it one of the operations?

Looking at the column with quadratic functions, $xz$ is paired with $\mathrm{E''}$, so that's my current best guess.


texts: Can I reverse an iron redox reaction with potassium hydroxide and electricity?

texts:
For a school project, about clean energy, me and my team are trying to build an iron battery. We are using a piece of iron (anode), potassium hydroxide (electrolyte), carbon electrode (cathode) arranged as shown below:

As to generate electricity from the following chemical reactions:

$$
\begin{align}
\ce{Fe + 2 OH- &-> Fe(OH)2 + 2 e-}\tag{1}\\
\ce{3 Fe(OH)2 + 2 OH- &-> Fe3O4 + 4 H2O + 2 e-}\tag{2}\\
\end{align}
$$

Then:

\begin{align}
\ce{O2 + 2 H2O + 4 e- &-> 4 OH-}\tag{3}\\
\end{align}

And the overall reaction is:

\begin{align}
\ce{3 Fe + 2 O2 &-> Fe3O4}\tag{4}\\
\end{align}

Will this succeed in producing some electricity? And, can the redox reaction be reversed by having an external power source with sufficient voltage like a car battery, then hooking the negative terminal to the iron and the positive terminal to the carbon electrode?


texts: What makes Gorilla Glass more durable with each generation?

texts:
Gorilla Glass (GG) is one of the most recognizable brands of toughened glasses today, thanks to their marketing and widespread usage in various gadgets and automobile industry.

According to Wikipedia, it's basically an ion exchange ($\ce{Na+ <-> K+}$) within the glass (boro-/alumosilicate?) matrix which gives this material resistivity against scratches and various mechanical impacts:

(Source 1, Source 2)

Still, there is a new generation of GG released every few years, showing better properties with thinner samples, making me think it's all not just about ion exchange.

Are there other ways of "chemical strengthening" besides cationic exchange that can be utilized to strengthen the glass, keeping it flexible and less fragile at the same time?


texts:
I have a question that is bothering me since few weeks. I'm not a chemist, nor I have any experience with polymers theory, but:

Epoxy - is defined on Wikipedia as a thermoset polymer as a process of polimerization occurs that can not be reversed.

PVA - Is defined (again on Wikipedia) as a thermoplastic polymer.

So why the cured epoxy has a glass transition temperature, and therefore when heated above that temperature it softens and its shape can be modified. But when PVA glue hardens (by loss of humidity) it can not be softened by heat?


texts: At what pKa value do we consider an acid strong?

texts:
In between the traditional strong mineral acid that dissociate completely in aqueous solution, and obvious weak organic acid like acetic acid, things get murky.

For example, oxalic acid has a $\mathrm{p}K_\mathrm{a} = 1.46$ which is  about 1000 times stronger than acetic acid, but no one seems to qualify it as a "strong" acid. How about trichloroacetic acid, $\mathrm{p}K_\mathrm{a}\approx 0.5$? Well, some people start calling it "strong" acid.

So, what $\mathrm{p}K_\mathrm{a}$ value would qualify an acid as a strong acid?

I would like to know a concrete numbers, not merely “smaller $\mathrm{p}K_\mathrm{a}$ means stronger acid” as found in other questions. Just like a specific body mass of $90\ \mathrm{kg}$ would qualify a boxer to be a heavyweight boxer.


texts: How does fluorouracil inhibit thymidylate synthase?

texts:
I'm curious to know how just by adding a fluorine atom to uracil (to form 5-fluorouracil) permanently inhibits the enzyme thymidylate synthase when they bind together. This molecule is widely used as an antimetabolite in chemotherapy as it stops the synthesis of thymine.

What changes undergoes the enzyme-inhibitor compound so it is permanently bonded to the fluorouracil? Probably the chemistry is too complicated to be explained in this Q&A format, if that is the case, references like books or papers would be great.


texts: Vapour pressure and equilibrium constant

texts:
Consider a case I where I have a container halfway filled with a pure volatile solvent. Now we know that liquid molecules will start getting converted into vapour phase, and then dynamic equilibrium will be reached. The equilibrium constant here is given by $K= [P_0]$, where $P_0$ is the partial pressure of the vapours.  ($[P]$ due to pure liquids is considered as 1, so denominator is 1 and hence $K = [P_0]$).

Now we know $K$ only depends on temperature and is independent of any impurities being added, right?

Now, consider the case if I add some impurities to the pure solvent. We know there will be a lowering of vapour pressure and now if I write the equilibrium constant equation, $K = [P_1]$ , where $P_1$ denotes the new vapour pressure when impurities are present, and also $P_1 < P_0$.

So the problem is: $K$ has changed ! I mean previously $K$ was $P_0$ and now $K$ is $P_1$.

So $K$ value has changed by adding impurities. But my book says impurities has no effect on equilibrium constant. Where am I wrong?


texts:
Here's some practical application of chemistry for ya.

In short:
I have a moist, hard-to-remove carpet in a car that's hard to get dry.
I treated it with an anti fungal agent containing 1/5 hydrogen peroxide supposed to kill the mold. Measured it - it's very acidic - a condition mold will like in the near future.

How do I alkalize the carpet without creating a mess? I'd like to do this w easily obtainable everyday substances.

(Explaining "mess": E.g. pouring calcium hydroxide on it would probably be a hard-to-remove mess?)

The long story for context:
I had a leak between the interior of my car and the engine compartment let rainwater moisten the carpet.
The leak was fixed, but in the past few months had really the wrong weather for getting it dry, silica absorber packs didn't help.
So, it started to mold.

To stop it, I bought an anti-mold agent fluid. I tested its pH value and it's off the scale acidic for my litmus paper.

Mold likes acidity, hence, as soon as the mold killing by oxidation wears off, the mold will like it even more, which is why I think I need to alkalize the carpet.


texts:
My questions relates to the fundamental concept of electrochemistry, more specifically the electrode potentials.

1) First, why is there a potential difference at the interface of two phases? Considering the simplest case of a metal rod dipped in the solution of its ions, why should there be a potential difference. Out of many ways, one of the ways of understanding this provided by this site here,is in terms of equilibrium between the metal atoms and ions. But then, why is the presence of the other phase (ions for the metal piece) required to effect this equilibrium? For example, for the equilibria of ammonia and nitrogen/hydrogen, even if we take pure ammonia, the equilibrium is set up according to the surrounding conditions. Next,then can this equilibrium be described in terms of the equation $\Delta G=-RT\ln(K)$. Lastly, if this is an equilibrium, then there must also be an equilibrium between the metal and the hydrogen or the hydroxyl ions in solution as these might also take up the electrons from the metals?

2) When we measure the difference in electrode potentials of two different half cells, we are just measuring the potential difference between the two metal electrodes. How can we get an idea of the potential difference of the metal piece and its solution as the absolute value of potential of the two solutions might also differ. That is, if the two solutions are at different electrostatic potentials ( though not measurable), the potential difference between the two electrodes will not be the difference of their electrode potentials(which are the potential difference between the electrode and the electrolyte in each case). So, in order for the potential difference of the electrodes be equal to the difference in electrode potentials of the two half-cells, the solutions should be at the same potential?


texts: Adding hydrogens to multiple pdb files using Openbabel GUI software

texts:
I am  completely new to using OpenBabel software.

I have about 9000 pdb files to which, I want to add hydrogens. It will be a very hectic task to open all of them 1 by 1 and then convert each of them. Is there any way I could convert all of them simultaneously.

Also, can you please tell me how to correctly select the output file? It asks for a destination file to which, it appends/overwrites the output. Is there a way I could choose the destination where it would create another .pdb file and save the output in it? I guess I am missing something here while choosing the output file.

Thanks in advance. Also, I asked a similar question before which was closed. Considering I am new with OpenBabel, if any further information is required or if there is some issue, please tell me so that I may improve my question.


texts: Best reagent for reducing a ketone in the presence of an alkene

texts:
The following reduction is best accomplished with:

  (a) Zn/Hg, conc. HCl
  (b) N2H4, C2H5ONa
  (c) H2, Pd
  (d) All of the above

My thoughts: By looking at the question it is evident that only the C=O group should be affected. H2/Pd is used for hydrogenation which might affect the C=C double bond as well. Option (a) gives the reagents which are used for the Clemmensen reduction which is used to convert carbonyl groups to alkanes. So, I think (a) is the correct answer. Is that right?


texts:
Just wondering if anyone can tell me why bubbling nitrogen through a solution of $\ce{HCl}$/diethyl ether catalyst would remove said mix from my solution.

My current thought is that the $\ce{N2}$ will form ammonia and deprotonate the $\ce{HCl}$. But what of the Diethyl ether? I can't think of how it would be removed.

My only final explanation is that it is the $\ce{HCl}$ which is the important species to remove and the diethyl ether is just solvent ... but I would really like a second opinion!


texts: Determine if two molecule structures are the same molecule (perhaps in different conformations)?

texts:
I have two .pdb files describing two (small ligand) molecular structures. I need to determine if these two pdbs describe the same molecule, perhaps in different spatial conformations. Is there a program, or a combination of tools that will allow me to do this?

Moreover, if the two pdbs are determined to be from the same molecule, it could be that the atoms are in different orders. So I also need a way to identify the atoms in one PDB with the atoms in the other PDB.

I am dealing with thousands of pdbs, so I need an automatic way to do this comparison.


texts: Why do alcohols and ethers have approximately the same solubility in water but different boiling points?

texts:
In Morrison & Boyd, I found this question:

Butan-1-ol (b.p. $118~\mathrm{^\circ C}$) has a much higher boiling point than its isomer diethyl ether (b.p. $35~\mathrm{^\circ C}$), yet both compounds show the same solubility ($8~\mathrm{g}$ per $100~\mathrm{g}$) in water.

How do you account for these facts?

Now, as far as I know, the boiling point depends on the inter molecular forces. Since in the alcohol, there is hydrogen bonding in the O-H group, it has a higher boiling point than the ether. But in an aqueous solution, the solubility is also related to hydrogen bonding. Since there is more hydrogen bonding in the alcohol, I would expect it to have a higher solubility in water, but that is not the case. So how do we explain it? I am completely confused by this question. What is the answer?


texts: I had an argument with a friend about this question. He says it is not an acid But I think it is as it itself can increase the pH value.


texts: Why do electronegative heteroatoms increase C=O stretching frequency (bond strength)

texts:
Why does a more electronegative heteroatom (i.e. $\ce{Cl}$ or $\ce{O}$) increase the stretching frequency of a carbonyl?

I'd suspect it's that they donate their lone pairs and we end up with a negative charge on the oxygen in one of our resonance structures which makes the electrostatic attraction between the carbon and oxygen larger?


texts:
I am not chemist, however I am interested in science and know some basics.
So I have real life problem to solve and I hope there will be some people interested to help me or at least understand more how chemistry works. Anyway I would appreciate any answer.

So I have unfortunate spill of diesel addtive VIF (czech republic product). Composition is like this from the site(some translations maybe wrong):

Name - % in mixture

2-ethylhexyl nitrate - 50-100

solvent naphtha light - <5

solvent naphtha hard - <5

2,6-Di-tert-butylphenol - <5

1,2,4-Trimethylbenzene - <2.5

1,3,5-trimethylbenzen - <2.5

So I spilled this stuff in my car's trunk. Don't ask how it was, this is a fact and I cannot revert it back. It was a canister with it, so I spilled around 2 litres of it. I noticed it only after a day.

I took out the rug from the trunk and it was full of this liquid. The rug is textile. I tried to take it out with water and actually it was kind of eager to go out with water. It was lot of it, and I didn't want to do it manually. I cleaned my hands with soap and no smell was left on my hands after washing them, so I assumed I can clean the rug in the washing machine. Which was probably the worst mistake.

So instead of it being cleaned, I have

Rug that smell like the worse mechanical/technical smell in the world, however with no stains.
Washing machine which not only smells worse, but it gives this smell to anything that was washed in the machine and the smell is kind of concentrated.

So I have several questions on what can give this smell? Which component exactly? I wrote to the manufacturer with this questions, but they only told me I can try some solvent like technical petrol. But it was not an answer to the question "how to get rid of the smell"

So after reading some threads, everybody advising activated charcoal as best deodorizer.
I bought a kilo of it, and put around 200 grams to the washing machine for like 20 hours, and after that I didn't notice any change in the smell.

So the questions is: what is the formula for absorption with activated carbon? How to calculate how much of it I need to deodorize well? Will it deodorize at all? Maybe activate carbon pores are too small for the molecules or etc?


texts: Which attack occurs first: nucleophilic acyl substitution or nucleophilic substitution?

texts: If there is a compound with a site for nucleophilic acyl substitution (i.e. an ester group or the like) as well as a nucleophilic substitution (i.e. a bromine group or the like), will a nucleophile preferentially attack one of them? How do i decide which one a nucleophile would prefer attacking?


texts:
Does 2-chloro-2-methylpentane react with NaI faster in acetone or water?

I thought that since it is a tertiary halide it will proceed via SN1 reaction. So it must be faster in water as it is protic solvent.

But the answer given is Acetone. Why?


texts: Why doesn't but-2-yne show acidic character?

texts:
I found this in several sources and also found this while solving a few questions that but-2-yne does not show acidic character (or atleast not a significant  amount of acidity) compared to terminal alkynes
This could easily be attributed to the fact that but-2-yne doesnt have a hydrogen attached to a sp hybridised carbon.
However I felt that if the methyl group attached to the sp hybridised carbon was to donate a proton,  the resulting anion would be resonance stabilized,  because there has to exist a pi bond in the plane of the lone pair on the terminal carbon.
I couldn't see why this resonance shouldn't be possible,  as pi electrons are spread out over 3 atoms(though in different planes) , instead of all of them being concentrated between 2 atoms in a triple bond.
But I couldn't find an explanation anywhere for this.  Please help


texts: What methods other than linear combination of atomic orbitals does MO theory use? Which one is the most accurate and comprehensive?


texts: Do lone pairs on substituents (e.g. in aniline) count towards Hückel's rule?

texts:
Why is aniline aromatic? Doesn't it have 8 π electrons including the lone pair on nitrogen, thereby violating Hückel's rule?

The way I see it, there are 6 π electrons from the benzene ring, and an additional 2 from the $\mathrm{sp^2}$hybridized nitrogen.

I am suspecting that I am mis-applying Hückel's rule. I asked an instructor today and the only rationalization he had to offer was that "we just don't count those electrons on the nitrogen" ... which is deeply unsatisfying. He still insisted that aniline is aromatic. Can someone offer an alternate, more through explanation?


texts:
If breaking bonds is endothermic (takes energy), and work is force over a distance-
Would breaking bonds require "work"? Or do we only need heat energy? I'm trying to understand how to relate work to chemistry.


texts: Is there a relationship between Free Radicals and Beta Particles?

texts: This question is contingent on my understanding of the two terms in the title. As I was taught, a Free Radical is a reactive (high energy?) valence electron released for stability's sake because it is unpaired. I was taught that a Beta Particle is a high energy and fast moving radioactive positron or electron released to stabilize an atom. If both of these premises are true, is there a relation between the two terms, and if so, what is it?


texts: How and why are all the substituents in methyl cyclopropane eclipsed?

texts: Why does methyl cyclopropane $\ce{C3H5CH3}$ adopt an eclipsed conformation?


texts: Using electron affinity to calculate lattice energy

texts:
I am trying to calculate the lattice energy of $\ce{CaBr2}$, I am uncertain of how to incorporate the electron affinity value provided for $\ce{Br2}$ into my calculation.

Since electron affinity is the negative of the energy change that occurs when an electron is accepted by an atom in a gaseous state in the form of an ion, will I have to take the negative value of electron affinity and double it?

At this point in the Born-Haber Cycle $\ce{Br2}$ is already dissociated, and since calcium looses two electrons while forming $\ce{CaBr2}$, would it be logical for the total energy change to be a (negative) double of the electron affinity of bromine ?


texts: If magnesium reacts with oxygen to produce magnesium oxide only on the application of heat, then why isn't it categorised as an endothermic reaction?

texts: Why isn't the energy that is used to overcome the activation energy of magnesium metal atoms to react with oxygen, not taken into account?


texts: Factors affecting strengths of carboxylic acids

texts:
For carboxylic acids, I read that electron-withdrawing groups like CF3 allow the anion resulting from dissociation to be more stabilized. However if CF3 is replaced with an electron-donating group like CH3, then the stability of the anion resulting from dissociation is less stabilized. I read that the pulling of electron density away from acidic centers will increase its stability and render it more acidic. Why does withdrawing of electron density from an acidic center result in the stabilization of the anion formed from dissociation? Or is this a misconception?

Also, what determines whether a group is electron withdrawing or electron donating?


texts: Reaction of cyclohexane-1,2,4-triol with acetone

texts:
What is the product formed when cyclohexane-1,2,4-triol reacts with 1 equivalent of acetone in an acidic medium?

There are 3 possible hemiacetal products. The major one is formed via nucleophilic attack by a less hindered hydroxyl group:

There is one possible cyclic acetal formed by the two adjacent $\ce{- OH}$ groups:

But which of the two products will be formed in a larger quantity? I have heard that cyclic acetals are more stable than acyclic ones but don't know the reason (because of entropy change or something?).


texts: PIB wave functions and the effects of e- delocalization on UV absorption in conjugated systems

texts:
I'll try to keep this short and concise. What made me start thinking about this question was the material we have been covering regarding PIB wave functions in my quantum chemistry class, and material we have been covering regarding ozone absorption in my climate class. I would like to try to understand the relationship between the increased wave function domain that delocalization yields for conjugated pi electrons, and the effect that this has on the wavelengths of light that they can absorb. Like ozone, I understand that most other conjugated pi systems have strong UV absorption, so I would assume there is some correlation there.

Specifically though, I would like to know if this can be explained (at least to some extent) by a simple QM model like the 1D PIB, and if how electrons' wave functions are altered when their spacial domain is extended across the whole molecule by delocalization can explain UV absorption in conjugated pi systems.


texts: What is the name of this 3 open tube and where can I purchase one?

texts:
I would like to do some plasma activated water tests.

Does anyone know the name of this three open tube along with where I can purchase one?

The screenshot came from this video if you need a better angle to look at it.  Here's the video, the screenshot came from
YouTube


texts: Is Nuclear Spin Isomer a kind of allotrope?

texts:
In my book there's a question:

  Does $\ce{H2}$ shows allotropy ? Enlist its allotropes and their application?

I pondered  over different way Hydrogen can be arranged(I don't know but I have weak intuition that hydrogen bonding can play a role) but to no resolute

After awhile I googled to find different answers :Some are enlisting NSIs of hydrogen as allotrope

So can NSI(s) of an element can be considered allotrope ?

If yes then how Nuclear Spin Isomer  can affect their physical form/structures?

*Wikipedia also doesn't enlist any allotrope of $\ce{H2}$ as such.
https://en.wikipedia.org/wiki/Allotropy


texts: Electrophilic Aromatic Substitution: Are protonated OH-groups ortho-/para- or meta-directing?

texts:
In Electrophilic Aromatic Substitution ($\text{S}_{\text{E}}\text{Ar}$) reactions groups that can donate an electron pair into the aromatic ring, e.g. $\ce{-OH}$ or $\ce{-NH2}$, are ortho-/para-directing.

In the case of $\ce{-NH2}$-groups one has to be cautious because if the $\text{pH}$ value of the solution is too low the $\ce{-NH2}$-group will be present mostly in its protonated form, $\ce{-NH3^+}$, which lacks a free electron pair and has a meta-directing effect because of its strong $-I$ effect. This brings up the question: What is the situation like with protonated $\ce{-OH}$ groups, $\ce{-OH2^{+}}$? In contrast to $\ce{-NH3^+}$ this group still has a free electron pair which could, in principle, interact with the aromatic ring ($\Rightarrow$ ortho-/para-directing) but it should also have a very powerful $-I$ effect ($\Rightarrow$ meta-directing).

I'd say, if the electron pair can be effeciently delocalised into the aromatic ring then its ortho-/para-directing power should outweigh the meta-directing power of the inductive effect. But I wonder if there even is any appreciable degree of delocalisation present because the mesomeric structures don't look very favourable:

Thinking about it from a frontier orbital perspective I would say: The orbital of the $\ce{-OH2^{+}}$ group's free electron pair will be much lower in energy than that of the $\ce{-OH}$ group's free electron pair. Thus, the energy difference between free electron pair's orbital and the aromatic ring's $\pi$-system might be too large to facilitate a good interaction. Therefore, I'd expect a protonated $\ce{-OH}$ group to be meta-directing.

But what is the actual situation when phenols or phenol ethers undergo ($\text{S}_{\text{E}}\text{Ar}$) reactions in strongly acidic solutions? Does one get the ortho/para or the meta product?

Edit:

I looked up the $\mathrm{pK}_{\mathrm{a}}$ value for protonated phenol: It is approximately $-7$. This makes me wonder if there are any reasonable (real world) situations where the solution is acidic enough to protonate phenol (or phenol ethers) completely (even $\ce{HI}$ with its $\mathrm{pK}_{\mathrm{a}}$ of $-10$ shouldn't be enough for that, right). I'm not sure if even sulfonation or nitration reach such low $\text{pH}$ values.
But @Uncle Al's answer made me aware that I forgot about Lewis acids and I'd say that Lewis acids like $\ce{AlCl3}$ that coordinate strongly to oxygen might lead to a state that will be very similar to a $\ce{-OH2^{+}}$ group (please, correct me if I'm wrong and the coordination of Lewis acids is not strong enough to be compared to the $\ce{O-H}$-bond). If this is the case, then what about Friedel-Crafts reactions which make heavy use of Lewis acids: Would those Lewis acids interfere with the ortho-/para-directing properties of phenols? Does anyone have experience with the directional properties of a $\ce{-OH}$ group in the presence of a strong Lewis acid, maybe even in the context of Friedel-Crafts reactions?


texts:
In the reaction $\ce{C2O4^2- → CO2}$ the $n$-factor of $\ce{C2O4^2-}$ is:

So I think the answer to this question is $2$ because in $\ce{C2O4^2-}$ the oxidation number of carbon is $+3$ and in $\ce{CO2}$ the oxidation number of carbon is $+4$. Now according to the formula of calculating $n$-factor, i.e.:

$$|(\text{no. of atoms})\times(\text{change in oxidation no.}) + (\text{do the same for other atoms in the compound})|$$

So we get $n$-factor of $\ce{C2O4^2-} = |2\times(-1) + 4\times(0)| = 2$.

I guess I have used the right formula and got the right answer but still I think that my answer is wrong. Can somebody please clarify that is my answer wrong or right and if wrong why?


texts: Safety when handling cyclohexylamine in non-industrial amounts

texts:
Today I was pipetting some cyclohexylamine into smaller bottles so that I don't have to use the liter flask every time I need a little bit of catalyst or plasticizer. I pipetted several 10-20 mL portions in the open air on a regular table.

Because I lack experience I'm extra precautious with what I do. From the MSDS's of cyclohexylamine I found that 10 mL will kill an adult male, which if you look at is isn't very much, less than a swig of water.

Of course I'm wearing a lab coat, safety goggles and chemical resistant gloves, but a few things concerned me (or at least made me wonder if it was the right/safe way to handle). According to the MSDS of ScienceLab the odor threshold is 26 ppm, while according to CAMEO, the PAC-3 for cyclohexylamine is 30 ppm, which Wikipedia defines as:

  PAC-3 : Life-threatening health effects.

When I opened the bottle the amine fish odor was very strongly noticeable, I however found no irritating effect on my eyes or lungs, although according to the documents provided above I was inhaling a lethal concentration. I'm quite confused here. More easily put as a question: as long as I don't feel irritation of my lungs or eyes, am I safe? And if I do, is there enough time to clean up (i.e. the most essential things, like shutting off electricity and closing open jars of chemicals) and leave?

Finally I accidentally touched a drop of cyclohexylamine (from the pipette) when I was cleaning up, with no gloves on. Although cyclohexylamine is listed as highly corrosive, I did not feel any irritation at all. Then I rinsed my pipette 3x with distilled water and put the waste in a jerrycan, but I still haven't figured out if I can pour the diluted mixture of water and cyclohexylamine down the drain, without poisoning myself or the neighborhood. The MSDS's keep quiet about that.

Can someone clear some confusions up for me. I will be greatly appreciated!


texts: Why does small value of van der Waals gas constant "b" ensure easier liquefication?

texts:
Larger value of b signifies that the size of the molecules is larger and hence the forces acting should become larger due to increased surface area.This should ensure easier liquefication. But my book says that smaller value of b corresponds to easier liquefication. Where am going wrong?

The book says "Chlorine is more easily liquefied than Ethane because 'a' for  chlorine is greater than 'a' for ethane but 'b' for fluorine is less than 'b' for ethane. Van der Waals constant 'a' is due to force of attraction and 'b' due to finite size of molecules. Thus, greater the value of 'a' and smaller the value of b, larger the liquefaction"


texts: Food Grade Sodium hypochlorite decomposition/neutralization

texts:
I recently purchased some 55 gallon blue barrels for rainwater harvesting.  Upon closer inspection of the barrels, I noticed they previously housed food grade sodium hypochlorite which was used to wash produce.  I was searching for food grade barrels but wasn't expecting bleach.  Because I will be watering plants and fruit tress with the rainwater, I don't want the water chlorinated which would kill the bacteria I'm trying to promote in the soil.  These barrels are empty but I was advised to rinse them when I initially purchased them.

Can I assume that just rinsing with water won't completely get rid of the bleach  and that the residual bleach which may be on the walls of the barrel will not decompose or neutralize by itself?

If I were to wash the barrels with water and Hydrogen Peroxide, will this suffice to remove the chlorine?


texts: How do EM waves cause molecules to rotate, move, and cause electrons to move up energy levels?

texts: Atoms can absorb electromagnetic waves to cause electrons to jump up energy levels, when electrons go down energy levels they release a photon. But how do EM waves cause atoms to rotate, and vibrate?


texts: Buffer formation in weak acid/strong base titration?

texts: I'm a little confused about what happens when you titrate a weak acid or base. For example, let's say that you are trying to titrate a weak acid. Based on this question, it seems like the weak acid isn't initially a buffer. But, as you begin to add strong base, conjugate base is created from the reaction between the weak acid and strong base. Does this mean that a buffer is created from the titration?


texts:
I was predicting a very simple chemical equation
$$\ce{Ba + S ->}$$
And I had solved it as
$$\ce{Ba + S -> BaS}$$
The answer should make sense as barium has a charge of +2, and sulfide has a charge of −2; however, the book had said that the answer was
$$\ce{Ba + S -> Ba2S2}$$
I do indeed know how and why they got the answer, but I just want to know why my answer isn't correct, or if it is and I'm just acting silly.


texts: Why do I have to use a 1:1 ethanol:water solution to hydrolyse aspirin?

texts: I understand that water itself would not work as aspirin is not very soluble in water but Why not just use 100% ethanol?


texts: Why is the outermost part of the Bunsen burner flame not the hottest region?

texts:
Why is the blue flame the hottest on a Bunsen burner?

I thought the outermost part of the flame must be the hottest region because of complete combustion of gases taking place there. Where am I getting wrong?


texts: Can fluid catalytic cracking work on a smaller scale in a laboratory?

texts: Fluid Catalytic Cracking usually requires a very large and tall structure. Is there a way of miniaturizing the process to fit inside a chemical lab with 10 ft ceilings? Specifically: can a fluidized bed reactor operate on this scale?


texts: Hot and cold air interaction in a sealed environment

texts:
What would happen if air heated to 1200 degree's Fahrenheit in a sealed environment was injected with colder air?
No specific pressure defined yet just a general idea of potential interaction between the two.

Edit
My apologies, I meant within a sealed environment like an engine cylinder. I know that the hot air would naturally expand and push a piston but how would the injection of cold air alter this, if at all?
For example purposes we can assume the cylinder is iron while the piston is aluminum which is common design today.


texts: Is the rate determining step the step with the largest Ea?

texts:
I've seen some controversy on this question while doing a brief search. For example, this SE answer quotes Wikipedia and says that the RDS is the step with the largest $E_a$. However, this UC Davis page says that

  In the potential energy profile, the rate-determining step is the reaction step with the highest energy of transition state.

My textbooks don't explicitly mention whether the RDS is the step with the largest $E_a$ or the step with the highest energy transition state. When I was doing a past exam, one of the questions was on this topic, and the correct answer assumed that the RDS is the step with the highest energy transition state. However, I've always thought that the RDS is the slowest step, and the slowest step has the highest $E_a$. So which viewpoint is actually correct?


texts: Why is F a bad leaving group? Say in HF and HI, F is more electronegative than I, then shouldn’t HF be a better acid ?


texts: Reaction between manganese(IV) oxide and sulfuric acid

texts:
$$\ce{2MnO2 + 2H2SO4 -> 2MnSO4 + O2 ^ + 2H2O}$$

How does this reaction occur? We get the oxygen moiety of the manganese dioxide suddenly oxidized to gaseous oxygen, while the manganese gets reduced from +4 to +2.

The sulfuric acid is apparently unperturbed: its proton $\ce{H+}$ and its $\ce{SO4^{2-}}$ parts remain the same in terms of their oxidation states. What role does the sulfuric acid play here at all?


texts: Why are molecular reactions endo- or exo-thermic?

texts:
It seems strange to me that chemical reactions should be exothermic, meaning the molecules move faster after the reaction.

Normally, in physics when two moving objects collide and stick together, the resultant velocity of the combined object is less than that of the constituent objects, due to conservation of momentum.

Yet, when some molecules combine they move faster. An extreme example of this are fast reactions like explosives in which the chemicals combine and move off at high speeds, sometimes greater than the speed of sound (a "detonation").

Why would this be? Is there a theory that positively can predict this behavior? In other words, if I were to supply you the names of two chemical species of which you had no prior knowledge, could you predict ahead of time whether their reaction would be exothermic or not, and by how much? Or, can this only be determined experimentally?


texts: What is the difference between grafting and bonding in reference to polymers?

texts: I'm reading research papers and some keep mentioning grafting of polymers. Looked it up in wikipedia and it talks about adsorbing polymers, and im not sure what the difference is. Thanks for any help.


texts: Identification of salts observed in steam vaporiser

texts:
Recently I observed some precipitated salts in steam vaporizer after completion of vaporization.
I am guessing that some of the white particles may be calcium carbonate ($\ce {CaCO3}$) formed from calcium bicarbonate dissolved in water by the reaction
$$\ce {Ca(HCO3)2(aq) \rightarrow CO2(g) + H2O(l) + CaCO3(s)}$$
I am curious to know what may be the other salts and how are they formed.


texts:
Are there any easy, not enzymatic, ways to hydrolyse $\beta$-1,2 glycosidic bonds like they occur in steviosids?

I thought of something like vinegar, which is commonly used to cleave the $\alpha$-1,2 glycosidic bond of saccharose when producing inverted sugar $-$ could that also work for the $\beta$-type?

Thank you in advance.


texts: Is it wrong to allege that lemons and limes are alkaline?

texts:
Please ELI5; I've never studied chemistry. I read about  alkalinity v. basicity here and on Sciencing.com.
Lemons and limes are doubtless acidic.

Lime: The pH range of lime is 2.00 to 2.35.
Lemon: The pH range of lemon is 2.00 to 2.60. This makes lemon slightly less acidic than lime.

'The pH levels of citrus fruits can cause damage to tooth enamel. Typically, the lower the pH, the more damage is done to the teeth. Oranges have a higher pH level, at 4.35, and are less damaging to teeth than lemons at 2.75, limes at 2.88.'

So isn't it wrong for Yuri Elkaim BPHE, CK, RHN

and this unidentified author to allege lemons and limes to be alkaline?


texts: Where does the potential energy of capillary action come from?

texts: Capillary action is when water pulls itself up a paper towel, glass tube or a tree. It is going up, which results in an increase in potential energy. According to the law of conversation of energy, energy cannot be created or destroyed. Where does this potential energy of capillary action come from, or is this an exception or something? My question is different from How does water defy gravity in paper towels?, because the other question is asking why it moves up, but mine is asking where the energy comes from.


texts:
I'm writing up a practical and $\beta$-mercaptoethanol was used, with no concentration given. I've found I don't need the BME molarity since I'm giving percentage (v/v) concentration, however I'm slightly confused as to why there are different values for its concentration.

Sigma-Aldrich provide BME concentration 14.3 M (pure liquid), yet the openwetware.org protocol for SDS sample buffers gives a molarity of 14.7 M. I can't see precisely how this is derived from its density, or why there'd be different molarities floating around.

Not that it matters for my writing here, but since I don't know the molarity I'm just a bit puzzled now as to what it may have actually been, and would rather understand now than have to work it out further down the line. Any answers greatly appreciated!


texts: How to determine the volume of a substance produced when only given the equation at STP?

texts:
At standard temperature and pressure, what volume in $\pu{mL}$ of $\ce{H2O}$ is produced in the following reaction?
  $$\ce{2 KOH(l)  +  H3PO4(l)  ->  K2HPO4(l)  + 2 H2O(l)}$$

Most questions I've found have more information than this so I'm confused as to how to do this problem.

I've tried multiplying $\pu{2 mol}$ of $\ce{H2O}$ by $\pu{22.4 L}$ and then converting it to $\pu{mL}$, but I've a feeling that isn't right.


texts: Is (2R,3S)-2,3-dichloropentane optically inactive?

texts:
Two confusing thing about (2R,3S)-2,3-dichloropentane:

The 2 stereocenters have opposite absolute configuration.
But there is no plane of symmetry.

So, is (2R,3S)-2,3-dichloropentane optically inactive?

(This is actually a follow-up question of:
Monochlorination of 2-chloropentane and possible enantiomer products)


texts: How does the polarizability of an apolar compound influence properties such as its boiling temperature?

texts:
I have understood that the more polar is a compound, the higher is its boiling temperature. But I would like to know what is the justification for this answer.
I am new to chemistry so I would appreciate a simple answer.


texts: In a galvanic cell, do the ions from half cell move into the salt bridge?

texts:
I know that ions from salt bridge move into the half cell in order to maintain electrical neutrality. But in my book it's also given that ions move from half cell into the salt bridge.

For example, in a galvanic cell with $\ce{ZnSO4}$ and $\ce{CuSO4}$, zinc ions from zinc sulphate solution move into the salt bridge in one half cell and sulphate ions from $\ce{CuSO4}$ move into the salt bridge in the other half cell .


texts:
What is the base ionization reaction for LiOH? Usually, the reaction is like this: $$Base + \ce{H2O->H}[Base] + \ce{OH-} $$

But $\ce{LiOH2+}$ makes no sense. So what could the reaction be?


texts: Why do the lone pairs of electrons first occupy axial positions before occupying equatorial positions for species with octahedral geometry?

texts: Why do lone pairs not reside in equatorial positions in species with octahedral geometry?


texts: Is the Hydrogen spectrum only an emission spectrum?

texts: In a statement question it was stated that hydrogen spectrum is an emission spectrum and the scheme considered it to be ture. But my argument is that it can be both emission and abosorption spectrum. Please tell me whether I am correct.


texts: When naming an ionic compound which includes a transition metal, the oxidation state is written between parantheses, yet some metals show an exception. Which elements represent this exception, and what is the reason?


texts: Thermochemistry Problem - How did they get that volume?

texts:
The chemistry problem in my textbook is : Calculate the work one when 2.0 L of methane gas, $\ce{CH4}$ (g) undergoes combustion in excess oxygen at 0ºC and 1.00 bar. Assume the volume of water formed is negligible.

I know that we should use the work equation $\mathrm{Work=-Pressure \cdot \Delta Volume}$, and that the pressure is 1.00 bar and we must convert this into pascals. All i need is the volume and convert that to $\mathrm{m^3}$. I got the equation $\ce{CH4 + 2O2 -> CO2 + 2H2O}$, but what I don't get is that how do we find the change in volume?

The book says let $\ce{O2}$'s volume = $\mathrm{V_{initial}}$, and that the total volume of gases for initial is $\mathrm{V_{i}}$ + 2.0 L. It says the final volume is 2.0 L of $\ce{CO2}$ (which I get because it should be the same amount of liters for carbons), but then it says that the water's volume is $\mathrm{V_{i}}$ - 4.0 L of $\ce{O2}$.

Can someone please explain the water's volume? How did they get that? Why is then the total final volume $\mathrm{V_f}$= $\mathrm{V_i}$ - 2.0 L. I thought the number of moles for initial should be same as the number of moles according to Gay-Lussac's law, so then the number of volume total should be the same for both sides, but this is clearly not correct. Am I applying the Gay-Lussac's law wrong? Why is the final volume not the same as the initial volume even if the initial and final have the same amount of moles on each side?


texts:
I encountered a practice question in a textbook according to which the hyperconjugative stability of 2-butene is due to σ-π electron delocalization but somehow I believe it should be σ-π* electron delocalization instead.
I need the molecular orbital diagram (MOD) of 2-butene to figure this out but I'm not sure how to draw its MOD, because in school we've been taught how to draw MOD for homonuclear/heteronuclear diatomic molecules only.
So can someone please provide me with its molecular orbital diagram and also briefly explain how to draw MOD for such polyatomic molecules?


texts: How expensive are Hartree Fock calculations?

texts: Hartree Fock is a very simple mean field approach for finding the ground state energies of - for example - molecules. But how expensive is it from a computational view? So after calculating all one - and two-particle integrals, which is $O(n^4)$, how expensive is it to do HF then? How large molecules could one in general do with that?


texts: Understanding the solubility of Ca(HCO3)2

texts:
According to wikipedia $\ce{Ca(HCO3)2}$ has the following solubility values:

$\pu{16.1 g/100 mL} \,(\pu{0^\circ C)}$
$\pu{16.6 g/100 mL} \,(\pu{20^\circ C)}$
$\pu{18.4 g/100 mL} \,(\pu{100^\circ C)}$

So I assume $\ce{Ca(HCO3)2}$ would precipitate beyond this level. However,  the wikipedia page for calcium bicarbonate states that attempts to prepare compounds such as solid calcium bicarbonate by evaporating its solution to dryness invariably yield instead the solid $\ce{CaCO3}$:

$\ce{Ca(HCO3)2(aq) → CO2(g) + H2O(l) + CaCO3(s)}$

which leaves me wondering if, when the solution is saturated beyond ~$\pu{16-18 g/100 mL}$, a precipitate of $\ce{Ca(HCO3)2}$ will exist  in solution? or if it also dissociating beyond that point while still in solution?


texts: What do cannabinioids have in common structurally?

texts: I'm looking at the wikipedia page for cannabinioids, and trying to find structural similarities between them. For plant based ones it's hard enough, the only similarity I could find seemed to be 6 member rings and medium sized hydrocarbon chains. When you include endocannabinoids, it seems to get more complicated. What structural similarities do cannabinioids share?


texts:
If anyone could clear up some of this conceptual confusion, that would be much appreciated.

Is $\mathrm pK_\mathrm a$ an intrinsic property of a molecule? Or extrinsic? A property is extrinsic if it depends on the environment (e.g. weight), and intrinsic if it is independent of the environment (density). Source: Thoughtco: Intrinsic Property Def.
Doesn't $\mathrm pK_\mathrm a$ change according to environment/conditions the molecule is in? According to the definition, $\mathrm K_a = [\ce{H^+}][\ce{A^-}]/[\ce{HA}]$. Then, given a $\mathrm pK_\mathrm a$ table, what are all the $\mathrm pK_\mathrm a$ values calculated with reference to? What are the standard conditions in which scientists calculate their $\mathrm pK_\mathrm a$ values.
Is there a way to calculate $\mathrm pK_\mathrm a$ from known intrinsic properties of a molecule? E.g. if I give you one molecule of a compound, and only one molecule, is it possible to calculate $pK_a$ based off the intrinsic structure of that molecule, given no other information?


texts: Oxidation state of metal ion in unit cell

texts:
If a cubic unit cell for a metal nitride has nitride ions at all face and corner positions, and metal ions at all edge positions, what is the oxidation state for the metal ion in the nitride?

I think that if something is in a face position, there is half of that something present in the unit cell. So if there are nitride ions at all face positions (6) then there must be 3 total nitride ions. And at the corners, there are eighths of nitride ions. So given 8 corner positions, there must be an additional nitride ion formed by the fragments at the corners.

This gives us a total of 4 nitride ions, or a negative 12 charge that must be balanced by the metal ions at the "edge" positions. But what are edge positions? If I know what it is, then I can visualize how many metal ions there are in the unit cell.

Are the edge positions directly halfway between the corner positions and butted up against the face positions? So is there one edge position per edge of the unit cell? This gives us 12 edge positions, and each fragment is a fourth of an ion, so we have 3 metal ions total. So the oxidation state of the metal ion is +4?


texts: Thermodynamic and Transport properties input files for Chemkin

texts:
I am using Chemkin pro 2009 version. I want to model a decomposition+combustion reaction on my catalyst in a plug flow reactor.So I'll need to create my own Thermodynamic and Transport Properties file for my own material.
Can you anyone tell me what's the format for the various input files for Chemkin Pro? I have thermodynamic and some diffusion data for my system. Just need to know how to arrange that data in a text file.
Any help will be appreciated


texts: If potassium permanganate is added to a solution and it becomes brown is the substance a reducing agent?


texts: How to identify hydrogen bonds and other non-covalent interactions from structure considerations?

texts:
Chemistry is governed by a wide range of interactions, from ionic and covalent bonding, or other types of strong interactions, towards weaker types of bonding, attraction, or repulsion, that typically occur between molecules. The latter are often referred to as chemical, molecular, or non-covalent interactions. Popular examples include ion-dipole interactions, hydrogen bonds, and London dispersion forces.

These non-covalent interactions play very important roles in DNA, protein-drug interactions, catalyst-substrate interactions, self-assembly, chemical reactions, among others.

How can I identify and analyse hydrogen bonds and other non-covalent interactions, possibly from experimental and calculated structures?


texts:
At school, we are learning about semi-conductors and their applications in modern electronics. One of the features of semi-conductors is that there is a small energy gap between the valence and conduction band. My teacher explains that he bands occur because in the compound, since there are millions of atoms close together, due to the Pauli Exclusion Principle the energy levels of the atoms slightly change in value, forming band. When electrons are excite form the valence to conduction band, the substance is able to conduct an electric current.

However I fairly certain this is a superficial explanation as it doesn't really explain what the conduction and valence band is and doesn't explain why electrons in the conduction band are able to conduct electricity while electrons in the valence band can't.

After some researching on the web this is my rough understanding of semi-conductors now:

The s and p orbitals of the metals combine together to form MOs. As the AOs of millions of atoms combine together, these MOs become a continuum, forming two bands. One band is the valence band which consists of 2s sigma bonding and anti-bonding orbitals while the other band is the conduction band which consists of 2p pi bonding and anti-bonding orbitals. This explains why electrons in the conduction band are able to conduct an electric current since they are conjugated (not sure if this is the correct term) across the entire substance and hence explains why electrons in metals are described as a 'sea of de-localised electrons'.

This is just my understanding which isn't that solid. Could someone please offer a more in-depth explanation into how these bands form and correct any wrong things that I said. Also I still have some questions.

One website stated that 'it is only when these bands become filled with 2p electrons that the elements lose their metallic character'. Which I interpret as that when the conduction band is completely filled with electrons, the substance isn't able to conduct electricity any more. However why is this so? Aren't there still electrons in the pi MOs which are 'de-localised' along the substance?

Also the above explanation using MOs seems to explain why these bands form. Does this mean that the explanation that my teacher gave me about the Pauli Exclusion Principle being responsible for the formation of bands is wrong and not needed?


texts: "Nitrogen (gas) is physisorbed over iron (metal) at room temperature": Is this for real?

texts:
My copy (PDF) of Levine's Physical Chemistry (6th ed.), page 570-571, section: "Adsorption of Gases on Solids", states:

  Physical adsorption is nonspecific. For example, $\ce{N2}$ will be physically adsorbed on any solid provided the temperature is low enough.

and

  ... N2 is chemisorbed at room temperature on $\ce{Fe, W, Ca,}$ and $\ce{Ti}$ but not on $\ce{Ni, Ag, Cu,}$ or $\ce{Pb}$.

Alright, fair enough, thanks for the examples.

But

A bunch of (notoriously error-prone-citation-deficient) course books issued by my school, all unambiguously concur on the contrary:

  At $\ce{83K}$, $\ce{N2}$ is physically adsorbed over iron metal. Raising the temperature to $\ce{773K}$ then results in the nitrogen being chemisorbed over the metal as atomic nitrogen.

Which in other words is: "At room temperature, nitrogen is physically adsorbed. The nitrogen is chemisorbed after the temperature's raised to 500 degrees Celsius".

But this contradicts the information in Levine's book.

Who's right here: Levine or my book? (References are welcome) O:)

EDIT-

LinearChristmas has correctly pointed out that the temperatures at which the physical adsorption --> chemisorption transition takes place depends on pressure as well as the nature of the iron surface.

In light of this, I'll modify my question:

Q- My coursebook and Levine's lists (implicitly in Levine's case) the transition from physical adsorption --> chemisorption at different temperatures. Between the two, which one lists the more improbable temperatures?


texts: Is there any difference between getting dissolved and getting dissociated?

texts:
In the context of electrolytes only, is there any difference between electrolyte getting dissolved and electrolyte getting dissociated?

According to my professor, they are different. He says a substance may dissolve completely but it may not dissociate completely and a substance may not dissolve completely but amount that dissolves can dissociate completely and, thus, substances which dissolve (either wholly or partially), amount that gets dissolved if dissociate completely are called strong electrolytes and amount of substances which gets dissolved if dissociates sparingly are called weak electrolytes (although it may dissolve completely).

How is it possible? I mean, how can solubility be different from dissociating?

If something dissociates it means it’s dissolving and in the context of electrolytes if something dissolves in water it has to dissociate into ions and even Arrhenius’ theory of electrolytic dissociation sys that substance which are water soluble, dissociates into ions and get dispersed in water.

And if someone says they are different to them, I ask the following two questions:

If solubility and dissociation are different then what would be the criteria for getting dissolved and what will be criteria for getting dissociated (for me the criteria for getting dissolved is dissociation).
how would you arrange the following in increasing order of 1.solubility
2.dissociation

NaCl, MgCl2, FeCl2, ZnCl2


texts:
Propene in the presence of $\ce{HBr}$ and $\ce{H2O2}$ gives A.
A on reaction with $\ce{Mg}$ in dry ether gives B.
B on reaction with acetamide, $\ce{CH3C(O)NH2}$, gives C.

In the above question, I got A as 1-bromopropane and B as propylmagnesium bromide. As for C, I got
$$\ce { CH3-CH2-CH3 + CH3C(=O)NHMgBr}$$
The ratio of moles of the Grignard reagent vs. acetamide is not specified. Should I add an additional propyl Grignard and arrive at $\ce{CH3-CH2-CH3}$, $\ce{CH4}$, and $\ce{ CH3C(OH)N(MgBr)2}$ ?
I need help with figuring out the product in the reaction of B and acetamide.


texts: Why does branching decrease density and melting point?

texts:
The general explanation given is that the chains are further apart, so the intermolecular forces are less, and as they are further apart, they occupy more volume, and the density is lesser. But the length of each chain (and thus its mass) also increases, so how do we know that the density overall decreases?

As for the melting point, longer chains = more electrons = more Van Der Waals forces, so the melting point should increase.

Edit: I'm referring to branching in the context of polymerisation.


texts: Symmetry Operation on Product of Functions

texts:
In regards to direct product representations, I'm trying to find a proof for:
$R(X_iY_j)=R(X_i)R(Y_j)$
Where $R$ is a symmetry operation of a group and $X_i$ and $Y_j$ are members of different basis sets for the group. See e.g. Chemical Applications of Group Theory by F.A. Cotton, 3rd ed., p.105 or Atkins' Molecular Quantum Mechanics, 5th ed.,p.152.
A lot of books I've seen covering direct product representaions start with this equality but I haven't seen any justification for it yet.
Any help is greatly appreciated!


texts: Are there any solvents that dissolve talcum powder?

texts: I understand that talcum powder is insoluble to water, would alcohol or something be able to dissolve it?


texts: If something contains large amounts of cyclopentane and cyclohexane, what is it called? I'd like to know what is the something as well. It's a chemistry olympiad question for this year. See here, Question 3-g. Just let google translate it for you. I find some questions quite weird as well, but what can you do. Otherwise its pretty good.


texts:
I've been looking on the net for a reference which shows a phase diagram for elements at least from $\ce{H}$ up to $\ce{Ne}$. Specifically, I'm looking which of these elements can be solid or liquid in a vacuum.

I haven't really found anything, except some anecdotical comments here and there that hydrogen and helium evaporate in a vacuum at any temperature.

Any suggestions as to where these data might be published?


texts: Basic concept of the first rule of thermodynamics

texts:
There is a cylinder-piston system with some gas in it, and let's say this system is a closed system.
Say that the system is submerged in a large beaker of water whose temperature is $25\ \mathrm{^\circ C}$. A spark is used to trigger a reaction in the system, and after the reaction is completed, the temperature of the water bath increased to $28\ \mathrm{^\circ C}$, and the piston went inside the cylinder.

By instinct, I think that heat is lost by the system since the surrounding(water)'s temperature increased, and work has been done to the system. However, when I consider the thermal equilibrium, the system's temperature must be $28\ \mathrm{^\circ C}$ as well. In this case, is heat added to the system or not? Furthermore, in the equation $\Delta E = q+w$, what are the signs (plus or minus) of the three terms?


texts:
Regarding solvents, the only thing I remember from school is my teacher saying: "The same dissolves the same." regarding the polar/non-polar solvents.

From this I understand that water is polar solvent, because it has polar bonds and therefore it dissolves table salt, which also has a polar bond.

What I do not understand for example is, why does water perfectly mix with acetone? X

Another thing is, that non-polar organic solvents seem to have some very complicated rules. For example, acetone dissolves most paints and all ABS plastics. Ethanol or tetrachloroethylene do not.

Why does ethanol dissolve acetone-peroxide while acetone doesn't? X

Q: Are there some general rules to this, or is this big science that requires years of study?

X: these are just rhetoric questions. You can answer in comments but what I'm looking for are rules.


texts: Why is the 5d orbital instead of the 4f orbital filled in lanthanum?

texts:
For orbitals with the same value of $n + l$ (e.g. the $\mathrm{3d}$ and $\mathrm{4p}$ orbitals), we usually expect the orbital with the lower value of $n$ to be filled earlier. Hence, for example, the $\mathrm{3d}$ orbitals are filled before the $\mathrm{4p}$ orbitals in the transition metals.

However, the electronic configuration of lanthanum is $[\ce{Xe}](\mathrm{5d})^1(\mathrm{6s})^2$, and not $[\ce{Xe}](\mathrm{4f})^1(\mathrm{6s})^2$.

I know that the $\mathrm{5d}$ and $\mathrm{4f}$ orbitals are of similar energies, but is there any better explanation for this?


texts: Is it safe to hold silicon nitride ceramic without protection?

texts: If I have a complete silicon nitride ball bearing unit, is it safe to hold without any protection? If it cracks, or disintegrates is it also safe?


texts: What are the key chemical structures of liquid crystals used in display technology?

texts:
The majority of current flat screen TVs and computer monitors are based on Liquid Crystal displays.

Liquid crystals are compounds that orient under an applied electric field and alter the polarisation of transmitted light. This can be used to build what are effectively valves that selectively transmit light.

So what are the typical chemical structures of the chemicals that have these properties and how do the structures relates to how they work?


texts: Permanent suspension of cocoa powder into water

texts:
I have failed in permanently suspending cocoa powder into water.  I have tried heat (212'f) and pressure (40 psi) into a sugar water solution (50/50).  Also, powdered milk and evaporated milk have failed to yield a permanent suspension.  There was another method of Irish moss to coagulate the whole thing together, but that failed as well.  I need the bonding/ emulsifying agent to be edible, delicious and shelf stable.  I am a low level cook and do not have the chemistry knowledge to do this myself.
Thank you for reading.


texts: As the electronic configuration of gold is [Kr] $4d^{10} 4f^{14} 5s^2 5p^6 5d^{10} 6s^1$, the valence shell is not completely full. Why doesn't gold  corrode?


texts:
The line says

Alkaline metals and their salts impart characteristic colour to an oxidising flame. This is because the heat from the flame excites the outermost orbital electron to higher energy level. When excited electron comes back to the ground state, there is emission of radiation in the visible region of the spectrum.
Beryllium and magnesium do not impart colour to flame because electrons in beryllium and magnesium metal are too strongly bound to get excited by flame.

What if reason that Be and Mg do not impart colour to flame is not that the electrons in Be and Mg are actually bound too strongly to be excited by flame but that the radiation emitted does not fall in visible spectrum?


texts: Does a reaction have to have a rate determining step?

texts:
I am a bit confused about the concept of the rate determining step. From what I understand, a step in a reaction is the RDS if it meets the following requirements:

It is the slowest step in a reaction
It causes a bottleneck in the progress of the reaction

Therefore, if there is a catalyst, it means the slowest step in the reaction will no longer be the slowest step because the reaction can take place faster with a different mechanism involving the catalyst. Would it therefore be of any significance to say that a particular step in this reaction, say for example the step with the highest activation energy is the RDS, or is there no point in saying there is a rate determining step, ie, that it does not exist? Is it possible to say that the concept of the RDS has no significance in some reactions?


texts: What could these letters "S" in red circles mean in a biochemical diagram?

texts:
What could be the meaning of the red circles with letters S in them in the diagram below? I searched in the text but could not find.
From "Role of TREK-1 in Health and Disease, Focus on the Central Nervous System", Figure 2:


texts:
I'm struggling to understand why the following organic compound:

is named systemically as 2-ethylhexane-1,3-diol (I think its common name is etohexadiol), if the longest carbon chain in the molecule is actually 7 carbons long, as labelled here:
Wouldn't the compound have a hydroxymethyl group on the 3rd carbon and a hydroxy group on the 4th? Or do I just have some big misconception about naming alcohols (very possible).
Thanks for any help anyone can give!


texts:
My book says:
  Finkelstein reaction is particularly useful for preparing iodoalkanes. The iodoalkanes are obtained by heating chloro or bromoalkanes with a concentrated solution of sodium iodide in dry acetone.
  $$\ce{R-X + NaI ->[\ce{acetone,~reflux}] R-I + NaX}\\
(\ce{X}=\ce{Cl,Br};\ \ce{R}=\text{alkyl group})$$
    NOTE: Refluxing is a process of heating a liquid in a flask provided with a condenser. The vapours of the liquid which rise up get condensed back into the flask.
    Sodium chloride and sodium bromide being less soluble in acetone get precipitated from the solution and can be removed by filtration. This also prevents the backward reaction to occur according to Le Chatelier's principle. The reaction gives the best results with primary halides.

MY QUERY

Can we prepare alkyl chloride or alkyl bromide by Finkelstein reaction?
As we can see, first line reads that Finkelstein reaction is particularly useful for preparing iodoalkanes. The lines followed by it signify that $\ce{NaCl}$ and $\ce{NaBr}$ are less soluble in acetone. If we want to prepare alkyl chloride or alkyl bromide, we will be needed to dissolve $\ce{NaCl}$ or $\ce{NaBr}$ respectively in acetone, which is not so possible. Is it true that, we can't prepare alkyl chloride or alkyl bromide by Finkelstein reaction because of the above reasons?


texts: How are electronic configurations including hybrid orbitals notated?

texts:
I know the general scheme for notating electronic configurations is (with s and p orbitals) [noble gas core]nsel.$n$pel. etc., where $n$ is the principal quantum number and el. is the number of electrons occupying that subshell, e.g. carbon: [He]2s22p2.

Now, how do you include hybrid orbitals? The problem arises because some hybrid orbitals already have superscript numbers (sp2, sp3 …) – how do you differentiate between these superscript numbers and those denoting how many electrons fill that orbital? If I were to write out the electronic configuration for the hybridised carbon atom in $\ce{CO2}$, this would not be a problem: [He]2sp22p2, but what about the carbon atom in $\ce{CH4}$, which has sp3 orbitals? Would you write [He]2sp3, 4 or [He]2sp34 or something else?