texts: Distance between two atoms that lie along a body diagonal

texts:
It is given that two atoms lie along the body diagonal of a unit cell (crystalline solid). The length of such cubic cell is $a=\mathrm{0.336\,nm}$. My book says that we should take the coordinates of the two atoms to be $(0, 0, 0)$ and $(1, 1, 1)$. By my intuition is that if we place the cube at the origin then one atom should be at $(0, 0, 0)$ but the other atom should be at $(0.336, 0.336, 0.336)$. After this we can simply find out the required distance using $$l = a[(x_2-x_1)^2 + (y_2-y_1)^2 +(z_2-z_1)^2]$$
My doubt is that what should be the second coordinate? Should it be $(0.336, 0.336, 0.336)$ or $(1, 1, 1)$? If $(1, 1, 1)$ then why?


texts: Symmetry of an in-phase and an out-of-phase wavefunction "approaching" each other in an MO

texts:
Hiho.

I have a question concerning this image (Chemistry, Catherine E. Housecroft et al., Pearson Education, 2010).

In the text, it states the following:

  "Each of the new molecular wavefunctions, $\Psi$(in-phase) and $\Psi$(out-of-phase), has an energy associated with it wich is dependent of the distance apart of the two hydrogen nuclei. As Figure 4.13 [provided image] shows, the energy of $\Psi$(in-phase) is always lower than $\Psi$(out-of-phase)."

The in-phase-function has a stabilized minimum, but the out-of-phase-function seems stable only at an infinite distance. For my intuition, the two graphs should be symmetric, since the two wavefunctions are alike and approach each other equally. Why do they behave like this?

Why are those functions not symmetric?

A following question would be, when I combine those two functions, I'll get a minimum at the x-value I marked with "minimum". Would this be the distance at which a nucleus in a stable diatomic molecule would be found like in this figure?

===

Thank you for your help and have a nice day :)


texts: Difference between Excess property and property changes of mixing

texts:
I have some confusion in my mind about the difference between an excess property and a property change of mixing. I know that the Excess property is defined as the difference between the actual value and those of an ideal mixture:
$$\ M^E(T,P,x_i)=M^{actual}-M^{id}(T,P,x_i)$$
On the other hand the property changes of a mixture is:
$$\ M^{mix}=M{actual}-\sum n_i*M_i$$
So the latter seems to me that the whole change of a mixing process is with respect to the pure, ideal gas, species.

Excess and mixing are the same for enthalpy and volume but are different for entropy and Gibbs free energy.

Now come the problem: property changes of mixing and excess properties are related each other by the residuals properties (deviations from ideal gas)?

Otherwise I do not understand why they are different.

Thanks a lot


texts: Calculation of equilibrium constant given the reaction temperature

texts:
I have only a chemical equation, like:
$$\ce{N2 + 3H2 <=> 2NH3}$$
How can I calculate the value of equilibrium constant from only this equation. Provided temperature is $\pu{298K}$. I can use other standard data. I am really stumped on this question.


texts: On another thread on this website it mentioned how it was possible to melt diamonds, but what would be the micro-level occur for that to happen. This question applies to Silicon Oxide aswell. They both have infinite structures. Which bonds would break or even weaken for them to transition states? For example, when a regular covalent solid is heated, the intermolecular forces of attraction weaken and the solid melts. How would that work for a structure like that of diamond?


texts: Shea Stearin Extraction by Dry Fractionation

texts:
I have been able fractionate palm oil and extract palm stearin using the following method:

Melt the palm oil (over 80 °C)
Keep the melted oil at 33.5 °C for 24 hours (using an immersion circulated water bath)

At this point I was able observe crystals being formed. I assume they were palm stearin crystals.

Centrifuge to separate the crystals to obtain palm stearin.

I was able fractionate almost 30 % crystals by weight.

However the same process did not really hold true while processing the shea butter to fractionate shea stearin. After Step 2, it was still in liquid form and there was no visible crystal formation. I'm further considering seeding (with crystals) or playing with the time and temperature variations.

How can I modify my approach to promote stearin crystal formation in shea butter?


texts: Are glycosides more soluble in dichloromethane than in water?

texts:
I'm designing an experiment to extract the amygdalin from apricot leaves and kernels. I want to steam the kernels and leaves, grind them, add water and then filter it using a filter paper. Then transfer the solution to a separatory funnel, add dichloromethane (DCM), shake and collect the bottom DCM layer that I'm hoping would contain the amygdalin.

This is the process I used for extracting caffeine from coffee beans and it worked because caffeine is much more soluble in DCM than in water. However, I'm not sure about the solubility of glycosides and whether this process would even work or not which is why I'm making this post.

How soluble are glycosides in DCM, is it enough to make this work? If not, what other solvents do you recommend?

Also, how can I increase the efficiency of this process in general? I've been thinking of using vacuum filtration, but I'm not sure. Tell me what you think.


texts: How to retrieve Dalton value from m/z value?

texts:
As I understand, Dalton (Da) is the standard way for representing mass unit. As for $m/z$, which is a specific notation for mass spectrometry, quoting for wikipedia:

  This notation eases data interpretation since it is numerically more related to the unified atomic mass unit

Considering this, could I say that the $m$ in $m/z$ is a $\mathrm{Da}$ unity? If so, given an $m/z$ value, can I retrieve the original mass of the atomic mass by multiplying it by the ions charge, if I have that information?

I ask this because I have a spectrum analysis file with $m/z$ in the $x$ axis and I'm asked to compare masses in $\mathrm{Da}$.


texts: Solubility curve for uranium hexafluoride (in any solvent)

texts:
I am doing a project and need a solubility curve or at least solubility data for uranium hexafluoride in any substance. It is impossible for water because $\ce{UF6}$ reacts violently with $\ce{H2O}$.

Is there any resource I could use for free to find this information?


texts: Absorption and ionization of rare earth ions

texts:
I'm studying silicate photosensitive glasses that contain $\ce{Ce}$ ions, and such glasses have an absorption band at 305 nm due to $\ce{Ce^3+}$. After that, the $\ce{Ce^3+}$ ion becomes $\ce{Ce^4+}$, which absorbs at about 270 nm.

Colleagues say that under irradiation by photons with wavelength near 305 nm, the process of photoionization take place. I find this surprising because another rare earth ion ($\ce{Nd^3+}$) doesn't ionize under excitation, but only via transfer to an excited state.

So why does the absorption of a photon by $\ce{Ce^3+}$ ions result in ionization and the appearance of a free electron, while only excitation and relaxation happens with the electrons of $\ce{Nd^3+}$ ions?


texts: Formulations for wax thermostatic element for effect in alternative temperature range

texts:
Wax thermostatic elements are used automobile cooling systems and anti-scald mixing valves to control flow rates or to adjust mixing of flow inputs. These devices operate on the principle of thermal expansion of "waxes" to convert heat energy to mechanical energy (Wikipedia article).  A review of thermostatic mixing valves for sale indicates that the common formulation for the "wax" within the element in those devices expands in the range 20 °C to 50 °C.
Is it possible to formulate a "wax" that effectively changes volume in a lower temperature range such that it could operate a mixing valve, beginning at 5 °C, for instance, or are the materials typically used in this application not effective at temperatures below 20 °C?


texts: Adding lemon to lentils changes color from black to pink, why?

texts:
I noticed that when I cook black lentils and add lemon juice to the water that's left, the water turns from black to pink!
What can be the reason for that?


texts:
There are 12 tetrahedral voids and 6 octahedral voids in hcp unit cell but I can't find any image that can show all tetrahedral voids and all octahedral voids in hcp unit cell (the common picture in Google shows 2 octahedral voids and 3 tetrahedral voids). Could someone help me to draw or find visualization image of all voids in hcp?

Thank you.


texts: Raman scattering and "electron and proton center" of molecule

texts:
I am currently studying the textbook Infrared and Raman Spectroscopy, 2nd edition, by Peter Larkin. In a section entitled The Raman Scattering Process, the author says the following:

Light scattering phenomena may be classically described in terms of EM radiation produced by oscillating dipoles induced in the molecule by the EM fields of the incident radiation. The light-scattered photons include mostly the dominant Rayleigh along with the very minor amount of Raman scattered light. The induced dipole moment occurs as a result of the molecular polarizability $\alpha$ where the polarizability is the deformability of the electron cloud about the molecule by an external electric field. Fig. 2.9 shows the response of a nonpolar diatomic placed in an oscillating electric field.

Here we represent the static electric field by the plates of a charged capacitor. The negatively charged plate attracts the nuclei, while the positively charged plate attracts the least tightly bound outer electrons resulting in an induced dipole moment. This induced dipole moment is an off-resonance interaction mediated by an oscillating electric field.

Can someone please better explain what the "electron and proton center" in figure 2.9 is supposed to be, and how it relates to Raman scattering? Is the "electron and proton center" of the diatomic molecule only at that single point that is pointed to by the arrow in figure 2.9? If so, then why? Or is each of the three points with the identical symbols an "electron and proton center"? Again, if so, then why?
I would greatly appreciate it if someone would please take the time to clarify this.
EDIT:
What does it even mean for a diatomic molecule to be "homogeneous"? I understand the concept of "homogeneous" mixtures, but not a "homogeneous" molecule.


texts: Why is copper(II) used a catalyst here instead of as an intermediate?

texts:
Photochromic glass, used for sunglasses darkens when exposed to bright light and becomes more transparent again when the light is less bright. The depth of color of the glass is related to the concentration of silver atoms.
The following reactions are involved:
reaction $1$: $\ce{Ag+ + Cl- <=> Ag + Cl}$
reaction $2$: $\ce{Cu+ + Cl → Cu^2+ + Cl-}$
reaction $3$: $\ce{Cu^2+ + Ag → Cu+ + Ag+}$
Which statement about these reactions is correct?
A) $\ce{Cu+}$ and $\ce{Cu^2+}$ ions act as catalysts.
B) $\ce{Cu+}$ ions act as an oxidising agent in reaction 2.
C) Reaction $2$ is the one in which light is absorbed.
D) $\ce{Ag+}$ ions are oxidised in reaction $1$.

I understand why B, C, D are incorrect. I also understand why $\ce{Cu+}$ is a catalyst; however, I do not understand why $\ce{Cu^2+}$ is a catalyst and not an intermediate. It appears as a product first and then as a reactant later, unlike $\ce{Cu+}$, so shouldn't it be an intermediate instead of a catalyst?
The question is question $11$ in the October November $2009$ A-level chemistry Cambridge variant $11$ paper.


texts:
I am completing a project on gallium, and I need to include its boiling point. I thought that this would be fairly simple to look up, however, it appears that different sources quote different temperatures as the boiling point, normally either ~2200 °C or ~2400 °C.

Does anyone know why two different values are presented, or which value is correct?

Below are some examples of websites quoting each figure.

2200 °C:

https://education.jlab.org/itselemental/ele031.html

http://www.rsc.org/periodic-table/element/31/gallium

https://www.livescience.com/29476-gallium.html

2400 °C:

http://www.chemistryexplained.com/elements/C-K/Gallium.html

https://www.britannica.com/science/gallium

http://www.chemicalelements.com/elements/ga.html


texts: Implicit dependence of reaction rate through reduction potential and activation energy

texts:
On one hand, the larger the reduction potential of a chemical reaction and the smaller its activation energy, the larger the reaction reaction. on the other hand the rate of a reaction depends on thermodynamic conditions, such as temperature and pressure, and the concentration of the species involved.

Now given that both the reduction potential and the activation energy of the reaction depend on thermodynamic conditions, can we deduce that the whole thermodynamic dependency of the rate of the reaction lies inside the reduction potential and the activation energy?

For the sake of clarification, that I said the larger is the reduction potential and the smaller is the activation energy the greater will be the rate of the reaction is a conclusion based on the analogy of a redox reaction and an electric circuit, the reduction potential being in place of the voltage difference, the activation energy as the energy consumer being in place of the electric resistance and the electron transferred during the reaction being in place of the electric current. It is clear that the greater the electric current, the greater the rate of reaction should be.


texts: how to identify reaction medium by looking at the equation ( for h2o2)?

texts:
$\ce{Ag2O + H2O2 -> 2Ag + H2O + O2}$
My book says the medium is alkaline as $\ce{H2O2}$ gives $\ce{O2}$ on reduction only in alkaline medium only but $\ce{O2}$ is produced in acidic medium too. Is there really a way of recognizing the medium by looking at reaction equations??


texts: Does π values vary in Hansch-Fujita equations for a given substituent?

texts:
I was reading about Hansch-Fujita equations from Hansch-Fujita paramaters and observed that the $π$ values of substituents (analogous to Hammet $σ$ values) change according to the specific environment as depicted in the following table:
I can't understand why is that the case. I mean in Hammet equations the value of $σ$ for a substituent doesn't vary when changing the environment and what varies is the $ρ$ which is a constant specific for each reaction according to Hammet Equation. That is in Hammet equation we have:
$$\log{\frac{K_i}{K}}=ρ\cdotσ$$
But Hansch-Fujita define $π$ (the analogous of $σ$) as:
$$π=\log{K_Χ}-\log{K_Η}$$
So does they have "include" the $ρ$ constant in the value of $π$?


texts:
This might be a silly question (probably is).

When a molecule absorbs it has a transition dipole moment, a measure of how strongly a certain transition will interact with light will depend on how closely a the light is to resonance with this dipole moment. The same in reverse applies for emission.

Typically in a bulk material, these dipoles are randomly spread, so luminescence is in all directions. Some molecules can be aligned, like in LCDs.

Is there a way I could align some luminescent materials such that they might emit preferentially in a certain direction? Has anyone done any work on this, what would this be called?


texts: Library / function for computation of molecular mass / molecular weight in C

texts:
We are looking for a function to be used for computing the molecular mass / molecular weight / formula weight in C, either in a library or standalone.  So far we have found the following implementations:

R language: shown here (limited implementation)
Matlab: shown here (full implementation)
Python: shown here (issue is discussed, preliminary implementation)
Perl: shown here (for protein molecular weights)

Ideally, the function would be able to handle a string input which could be either an element or compound.  In the latter case, the total number of each element forming the compound would be determined prior to atomic mass look-up.


texts: What is the standard molar weight of Carbon, and why?

texts:
The mole is defined as the amount of a chemical substance which contains as many representative particles, e.g., atoms, molecules, ions, electrons, or photons, as there are atoms in 12 grams of carbon-12 (12C), the isotope of carbon with relative atomic mass 12 (from Wikipedia).

However, when I go to websites such as http://www.webqc.org/molecular-weight-of-C.html or http://www.convertunits.com/molarmass/Carbon and I ask what is the molar weight of Carbon, I get answers such as:

  Molar mass of C is 12.01070 ± 0.00080 g/mol

When I asked on a forum why this isn't precisely 12, I was told that typically carbon is a mixture of isotopes which have relative atomic masses of 12, 13 and 14. With the ratio of each, the average value comes out to 12.0107.

But where does that number come from?  Is it by definition?  Is it by convention?  Is it a practical number?  Where do the error bars come from?  For instance, I would expect to see different isotope distributions at different geographic locations (or what about the moon, asteroids, Jupiter, etc.).   I tried googling for "standard carbon isotope ratio" but didn't find anything definitive.  Of course then I start to wonder how molar weights of other elements are defined, with varying isotopic combinations, and I have the same question.


texts:
For Plutonium 94 when I do it's element configuration I get

1s2-2s2-2p6-3s2-3p6-4s2--3d10-4p6-5s2-4d10-5p6-6s2-4f14-5d10-6p6-7s2-5f6

I found on this site that I'm correct however when I look it up on wikipedia it says

[Rn] 5f6-7s2

I know this is the short way to write it but I thought it would

[Rn] 7s2-5f6

What am I not understanding?


texts: Why aren't all bond lengths equal in cyclobutadiene?

texts: even when there is a possibility of conjugation why aren't bond lengths equal?


texts:
I was presented with the following problem in my lecture and I am confused as to what to do.

  You are required to prepare $\pu{250 cm3}$ of $\pu{0.100 mol dm-3}$ HCl by diluting $\pu{0.600 mol dm-3}$ HCl with water.

  Calculate the volume of $\pu{0.600 mol dm-3}$ HCl that must be diluted with water.

This was my attempt.

Moles of the $\pu{250 cm3}$ of $\pu{0.100 mol dm-3}$ HCl (target acid)

= $\frac{250}{1000} \times 0.100 = 0.0250$ moles.

Hence

$\frac{\pu{mol}}{\mathrm{conc}} = \mathrm{vol}_{\pu{cm3}} = \frac{0.0250}{0.600} \times 1000 = 41.66... \approx \pu{42.00 cm3}$

I'm not sure if the second step is right.

If I am right (hopefully) can someone please explain why.

Many thanks.


texts: What noble metal is most oxidation resistant?

texts:
To clarify, by noble metals in this case I mean all platinum metals + gold, no copper, silver or rhenium. These noble metals are described as having low reactivity, but which one is least reactive or most "noble" of them all?
I am chemistry noob and I have feeling this might greatly depend on what type of element/molecule is trying to react with given noble metal so to make this simple I will narrow this question down to oxidation by diatomic oxygen in air at room and elevated temperatures.
I will now writte my current knowledge and thoughts on why some noble metals might be more noble than other. Its just window into my head so you can see what I think so you are able to correct what is wrong, approve what is right and expand on what is missing.
My current understanding of what makes noble metal noble, is that its somewhere in middle of periodic table, their electron shells are half full. Elements on the left side are strongly reactive because their shells are only sparsely filled, so they give away electrons easily, they have low ionisation energy.
Elements on the right side, excluding noble gasses, are strongly reactive because they have almost full electron shell and they have tendency to tear out and "steal" electrons from less electronegative elements. That is why noble metals are in middle,they don't want to give away or get inside electrons very much.
That would be my first trait of noble metal, the more in middle it is, the more noble it is. Since periodic table is 18 numbers wide, 18 is even number so there is no integer exactly in middle, the middle is between 9 and 10.
That means elements in group 9 and 10 should be more noble than those in 8 and 11 group because they are closer to middle, so rhodium, palladium, iridium, and platinum should be more noble than gold, ruthenium, and osmium.
Another thing that I believe is that the heavier elements don't hold their electrons as strongly as lighter elements because the inner electron shells shield the valence electron shell from attractive force of nucleus. If this is true, then noble metals in period 5 should be more noble than those in period 6, that is ruthenium, rhodium, and palladium more noble than osmium, iridium, platinum, and gold.
Third factor in my opinion is first ionisation energy, the higher it is, the more it should be resistant to reacting with oxygen. From highest to lowest first ionisation energy: Gold = 9.2255 eV, iridium = 8.967 eV, platinum = 8.9587 eV, osmium = 8.4382 eV, palladium = 8.3369 eV, rhodium = 7.4589 eV, ruthenium = 7.3605 eV. If this is true, gold should be most noble, and ruthenium least noble.
I read one study about oxidation resistance at high temperatures, the study said rhodium was most resistant, even more than iridium or platinum. I also heard Platinum doesn't oxidise in air at any temperature bellow melting point, that seems contradictory to the paper I read.Furthermore, spark plugs are mode from iridium and platinum but not rhodium.
If we had all these noble metals side by side in identical shape, lets say cube with highly polished sides, and we heated them in air atmosphere to 100, 500, and 1000 degrees Celsius, which one would oxidise least?


texts:
If pH is defined as the concentration of hydrogen ions in solution, then how can a ‘neutralized’ solution (defined as having an equal amount of hydrogen and hydroxide ions) have a pH other than 7?

Wikipedia writes: “In a reaction in water, neutralization results in there being no excess of hydrogen or hydroxide ions present in solution.” In my mind, an equivalent amount of hydrogen ions and hydroxide ions means a pH of 7 (in water), but Wikipedia carries on to write: “The pH of the neutralized solution depends on the acid strength of the reactants.”

This question doesn’t seem to answer my question.


texts: Stability of Gauche and Anti form in conformational Isomerism

texts:
I came through this question: Which form is stable Gauche or Anti in F-CH2-CH2-F?
My answer: Due to lone pair repulsion Anti form should be more stable but the answer is given Gauche form. Please tell me how is gauche form more stable in this case?


texts: Ordering the lines obtained in the H line spectrum based on energy they possess

texts: I am trying to do the following question which asks me to calculate the wavelength of the green line in the visible spectrum of H. The authors claim that the green line is the second most energetic line but I believe that's a misprint because wavelength of green is second largest so energy should be second least. Am I right?


texts: Is it possible for the kinetic energy integral to be negative?

texts:
Is it possible for the kinetic-energy integral, Tij, to be negative? I was messing around with some HF code and found that the integral became negative on some off-diagonal terms. (This could also be a bug with the code.)

If the kinetic energy integral is negative, what would the physical meaning be?


texts: Find the minimum temperature at which the reaction will become spontaneous

texts:
This question came in my entrance exam and I think 273 K should be the answer because the reaction is already spontaneous. I just want to know if I've attempted it correctly.

For a certain reaction $ΔG^\circ = \pu{-45 kJ mol-1}$ and $ΔH^\circ = \pu{-90 kJ mol-1}$ at $\pu{0 °C}$. What is the minimum temperature at which the reaction will become spontaneous, assuming that $ΔH^\circ$ and $ΔS^\circ$ are independent of temperature?
(a) $\pu{273 K}$
(b) $\pu{298 K}$
(c) $\pu{546 K}$
(d) $\pu{596 K}$


texts: Does the enthalpy of formation include translational and rotational energy?

texts:
I can look up the enthalpy of formation of water vapor and get -241,826 KJ/mol. I want to use this to compute the total energy of water vapor at STP from the energies of O2 and H2 gas. What I don't know is whether I should use the electronic energies of H2 gas and O2 gas or the total energies of H2 gas and O2 gas, which include the contributions from the translational and rotational partition functions.
Basically, which of these two is the correct usage of Enthalpy of Formation?

ETotal(H2O) = Eelectronic(O2) + Eelectronic(H2) -241,826 KJ/mol + ETranslational(H2O) + ERotational(H2O)
ETotal(H2O) = ETotal(O2) + ETotal(H2) -241,826 KJ/mol


texts: Why large basis sets give better approximations to the exact solution of the Schrödinger equation?

texts:
The variational principle states that the energy of any approximate wave function will always be equal to or greater than the energy of the exact solution. Therefore the energy is minimized when performing approximations, in order to get as close as possible to the exact solution. Larger basis sets give the wave equation "more flexibility", but I am not sure I understand this fully. Here's a statistics analogy:

When performing multivariate regression analysis, we choose the regression equation of lowest order; "overfitting" the data is something to be avoided. In my head, choosing large basis sets for simple problems seems like "overfitting".

So why is it that a larger basis set leads to a better approximation? The statistics analogy may not be applicable, but it illustrates what goes on in my head.


texts: Questions about air-quality testing in high school

texts:
The Pinelands Regional High School in Ocean County New Jersey was closed for four days last week for air quality concerns after rooftop construction. Yesterday was the students‘ first day back. There have been conflicting reports of health issues, but it generally seems that the first day back is going OK.
There were two rounds of air-quality testing conducted last week. The first found unacceptable levels of multiple chemical compounds, the second, conducted two days later (after being cleaned), found no dangerous levels of any chemical.
Full results document of each test

Test 1: October 3
Test 2: October 5.

All of the unacceptable results found in round one (Indicated by red flags):
Sample: Room 164

Chemical | Actual ug/m3 | Times greater | NIOSH Res uh/m3

Ethelbenzene | 2.7 | 2.45 | 1.1
1,2,4-Trimethylbenzene | 15 | 2.05 | 7.3

Sample: Upper level - Media

Chemical | Actual ug/m3 | Times greater | NIOSH Res uh/m3

Benzene | 8.9 | 24.72 | 0.360
Ethelbenzene | 37 | 33.64 | 1.1
Xylene (p,m) | 110 | 1.1 | 100
1,2,4-Trimethylbenzene | 180 | 24.86 | 7.3
Naphthalene | 11 | 132.52 | 0.083

The clean results of round two

Chemical | Actual ug/m3 | NIOSH Res ppm

Benzene | 8.9 | 0.360
Ethelbenzene | 37 | 1.1
Xylene (p,m) | 110 | 100
1,2,4-Trimethylbenzene | 180| 7.3
Naphthalene | 11 | 0.083

This report concludes: "TTI has evaluated the results and can confirm that none of the target compounds exceeded limits for either exposure or notification at both the state and federal levels."
Confusion
There are a number of things I find confusing about this.

First, the  first round of tests analyze specific areas in the school, but the second does not identify any area.
Both rounds seem to have measured almost exactly the same levels.
The recommended NIOSH residential levels are measured in ug/m3 in round one testing, but ppm in round two. In round one, for example, the recommended maximum for benzene is 0.360, which according to this tool, translates to 0.00036 ppm. However, on the second test, has a recommended maximum of 0.1 ppm. Also, the same calculator translates benzene’s ug/m3 of 8.9 to 0.0089 ppm, but in the Test two results, it is translated to 0.0028.
Finally, parents are simply unfamiliar with these chemicals and what the levels imply, and how they affect teenagers. It is hard to fight what you can’t see or smell.

Help understanding and interpreting these results, and especially in giving parents some reassurance if it is warranted, would be appreciated. Thanks.


texts: Each electron shell can hold up to 2n² electrons. Is there a geometric reason for this?

texts: It seems such a simple formula, that each electron shell can hold in principle two times a square number. I imagine there must be a geometrical reason for this, that's to do with the way electron orbitals "fit" around the nucleus. If this is so, what is it?


texts: In the mechanism for Lucas' Test for Alcohols, I am reading two different types. One says the first step is the abstraction of a proton from HCl, but on other references, I also see that the first step is the formation of a zinc chloride complex. Anyone can clear this out for me? Thanks


texts: Is the axial position more suited for a lone pair or an electronegative element?

texts:
In one question, I found that it is given $\ce{XeF2}$ and $\ce{CO2}$ have the same shape.

$\ce{CO2}$ is linear. In $\ce{XeF2}$, if the fluorine is placed in an axial position, then only shape is linear. But in most compounds, lone pairs are placed in an axial position.

Is the lone pair or the electronegative element more appropriate for placement in an axial position?


texts: When calculating enthalpy changes of reaction using, why is only the amount of substance of one reactant used?

texts: When calculating the thermal energy released during an acid-base neutralisation using the equation $Q = mc\,\Delta T$, and then using $\Delta H = - Q/n$ to calculate the enthalpy change of neutralisation, why is the amount of substance of one reactant used ($n$ in the second equation) rather than the total amount of substance of acid and base reacting together?


texts: How do meth lab test kits detect the presence of a meth lab?

texts:
Many houses in the USA are illegally used as meth labs to produce methamphetamines, which can cause many negative health effects in their inhabitants, even after the house is sold to the next unwitting owner.

The Denver Post estimates that 7% of single family and 11% of multi-family units that are foreclosed have traces of meth residue.

With these risks, many commercial test kits for meth lab residue have appeared. However, many of them are intentionally vague about their chemical mechanisms.

What chemical mechanisms do meth lab test kits use to detect the presence of a meth lab?


texts: Determination of a chemical compound in a non-homogeneous sample

texts:
I want to know if it is possible to determine a chemical compound in a non-homogeneous sample. I am asking this because we are aiming to create a device that will detect histamine level in fish without homogenizing the samples. In all the journals we've read (which are a lot), fish samples are homogenized (blended + chemically-treated) before histamine is determined.

I am a computer engineering student with basic knowledge on biochemistry. I'm researching on this because this is our thesis topic (which our adviser has forced recommended to us).

Any help/recommendation regarding this is appreciated. Thank you!


texts:
Which one of Tropylium cation (cycloheptatrienyl carbocation) and Cyclopropylmethyl carbocation is more stable? Several references present opposing views on this topic, hence the confusion. Reasons with proper explanation will be appreciated.

Furthermore, is it possible to decide relative carbocation stability using experimental data? If yes, how?


texts:
Why are hydrogen bonds so important for life? Or more generally asked: Why is water so important for life / biological systems? Or maybe again in other words: Why does especially water provide this special property? And not a single other substitute(?) ?
I can read what the hydrogen bonds cause to happen but I would rather like to know: Why is that in detail or what makes so water so much different from any other (similar?) liquid?

I know this touches heavily biology (or also physics) but I think I will find the reason in an chemical explanation?


texts: Is the hybridization only related to atomic orbitals but not to the molecular orbitals?

texts:
What is Hybridization?

  (Spelling: Hybridisation (British English) / Hybridization (American English))
  The hybridization is a concept that describes atomic orbitals. In other words: Hybridization is an approach to model hybrid orbitals mathematically. The geometry of a molecule determines the hybridization and not vice versa.

IUPAC Gold Book's definition of hybridization:

  Linear combination of atomic orbitals on an atom. Hybrid orbitals are
  often used in organic chemistry to describe the bonding molecules
  containing tetrahedral ($sp^3$), trigonal ($sp^2$) and digonal ($sp$) atoms.

For a certain molecule structure we can allocate the atomic orbitals of one atom to hybrid orbitals which are also localized on this atom and which cannot be redistributed over the molecule to over atoms, e.g. a hydrogen can only have a s orbital but no sp hybrid orbitals because it has no p atomic orbitals.

The allocation can be done using the following relations:

$\ce{1s + 3p ->4sp^3}$
$\ce{1s + 2p + p ->3sp^2 + p}$
$\ce{1s + 1p + 2p -> 2sp + 2p}$

We say: "The atom X is best described by a $\ce{s^\text{x}p^yd^z...}$ hybridization."

Combining two orbitals / two hybrid orbitals / one hybrid orbital (e.g. $\ce{sp^2}$) with a orbital (e.g. $\ce{s}$) we obtain bonds. $\sigma$-bonds with $\ce{sp}$ orbitals (ethyne) of the atomic centers have lower energy than $\sigma$-bonds with $\ce{sp^2}$ orbitals (ethylene), lower in energy means: they are better acceptors.

What is my question now?

I'm thinking if we can also describe a bond (a molecular orbital) with a hybridization, e.g. if we can combine a $\ce{sp^2}$ hybridized carbon with a $s$ atomic orbital of hydrogen to make two $\ce{sp}$ molecular orbitals (a bonding $\sigma$ orbital with $sp$ character and an antibonding $\sigma^\star$ orbital with $\ce{sp}$ character; just be saying for a $\ce{C-H}$ bond: $\ce{s} + \ce{sp^2} = 2 \ce{sp}$, what's probably wrong).

I guess this question has to be answered with No, because we cannot say a bond has hybridization.

The question might arise why I'm thinking of the hybridization of molecular orbitals.

Over several years I've heard statements like this:
The $\ce{C#C}$ bond of ethyne ($\ce{HCCH}$) has higher s character (50%) than the $\ce{C=C}$ bond of ethylene ($\ce{H2CCH2}$) (33%) that's why ethyne has a lower $\mathrm{p}K_\mathrm{a}$ than ethylene (25 versus 44 at standard conditions in water as solvent) because a bond with higher s character can better stabilize a negative charge, because the s orbitals are penetrating deeper into the shell as the p orbitals do.

Again, I think hybridization is only a good model for atomic orbitals (=localized on atom) not for linear combinations of atomic orbitals (=bonds).

Can we really say the $\sigma$ bond in ethylene has $sp^2$ character?


texts: We know that some solutions show positive deviations and some show negative deviation from Raoult's law.The former is endothermic and the latter is exothermic. And again, the volume change show positive and negative terms.  In which case entropy change is more? And why is that?


texts: Correlation between redox pseudocapacitance, surface area, and cell potential with metal oxide electrodes

texts:
I'm having difficulty intuitively reconciling two different ideas concerning metal oxide thin films in contact with aqueous solutions:
1) that charge storage by both redox pseudocapacitance and electrical double layer formation depend on the thin film's surface area (i.e. more surface area = more active sites and interstitials = more redox reactions at surface groups & more counterion adsorption at interstitials = more adsorbed charge),
2) but that interfacial potential due to the presence of the same protons / hydroxyls / H2O does not depend on surface area (i.e. hydrolysis of H2O and adsorption of, or reaction with, H+ and OH- just changes the electrochemical potential of the surface groups, leading to an interfacial potential, measured as a cell voltage between two electrodes, that doesn't depend on surface area).
For the sake of clarity, the specific relation I'm describing in 2) is the pH-dependent voltage of certain metal oxide films. There is a lot of literature for, for example, iridium oxide showing that pH sensitivity of these electrodes is independent of surface area (from 10 square microns up to several square millimeters).
I can clearly see that, for example, the Nernst equation for electrodes at equilibrium features no term for amount of charge present; in this case, cell potential differences are altered only by the number of electrons transferred in the dominant redox couple(s) and their relative activities. This makes sense from a potential energy standpoint. However, from an electromagnetism perspective, additional point charges (assuming for a second that orbital electrons not used in bonds or that free protons can be described only as point charges) generate a linear, additive electrostatic potential; of course, solution counterions and/or free charge carrier redistribution in the metal oxide balance to negate an electric field outside of this localized area, but this doesn't change the fact that the potential energy in this regions is higher.
Of course, voltage is an integral over a path (in this case, between the ohmic contacts of a working electrode and reference electrode), and the electric field should be symmetric about the solution interface, but if all charges are balanced at equilibrium then how do we measure a cell potential at all? Is there just some scaling law at play here, where the charge magnitude inherent to each point charge multiplies, when redox reactions take place, at a faster rate than the number of point charges (active sites) per surface area?
Perhaps someone with a good intuitive understanding of cell potentials and redox potentials could shed some light on where my thinking is incorrect here.
Side note: I have viewed this, this, this, and this but they didn't have the answer I was looking for. I also thought about writing this question a little more generically than what I have here but it's long enough as it is.


texts: How is Langmuir adsorption isotherm different from Freundlich's?

texts:
I see no difference between the two. Both say that the degree of adsorption reaches a limiting value at high pressures and at very low pressures degree of adsorption is directly proportional to the pressure.
Where does the difference lie?


texts: Rate and mechanism of the reaction of Mg and HCl

texts:
In the reaction between hydrochloric acid and Magnesium the overall reaction is:

$$\ce{Mg + 2HCl -> MgCl2 + H2}$$

My proposed mechanism of reaction is that $\ce{HCl}$ dissociates in $\ce{H2O}$ like so:
$$\ce{H2O + HCl <=> H3O+ + Cl- }$$

And then the $\ce{H3O+}$ oxidises the magnesium like so:

$$\ce{2H3O+ + Mg -> Mg^{2+} + H2O + H2}$$

This, in an experiment to determine the rate of the reaction, measuring the $\ce{H2}$ produced would measure this mechanism, because it is the step in which hydrogen gas is evolved. Presumably these Magnesium ions are then in solution. I would therefore deduce that the step:
$$\ce{2H3O+ + Mg -> Mg^{2+} + H2O + H2}$$
Is the rate-determining step, because it is the step in which magnesium ions are formed and go into solution.
My rate law, deduced from these mechanisms, would look like this:

$$\ce{rate  = k * [H3O+] }$$
Because it is the concentration of the $\ce{H3O+}$ which determines the formation of the Mg ions. From there, I would assume, the $\ce{Mg^{2+}}$ and the $\ce{Cl-}$ would remain in solution, as the reaction is carried out in the acid, obviously consisting of water.

From this, can I say that the rate law for the reaction

$$\ce{Mg + 2HCl -> MgCl2 + H2}$$

is merely:
$$\ce{rate  = k * [H3O+] }$$
But $\ce{[H3O+]}$ is:
$$\ce{[H3O+] = (K*[H2O][HCl])/[Cl^{-}] }$$
Where K is the equilibrium constant of the acid equilibrium.

So can we write our rate law like:

$$\ce{rate = k*(K[H2O][HCl])/[Cl^{-}] }$$
Where K is the equilibrium constant and k is the rate constant and might look like this (following the Arrhenius equation):
$$\ce{k = A e^{-E_a/(R T)}}$$

To make our rate law like this:
$$\ce{ rate = A e^{-E_a/(R T)} *((K*[H2O][HCl])/[Cl^{-}]) }$$

My question is: Is my rate law correct for this reaction? If not, where have I gone wrong?

Additionally: This was one of our practicals. We ended up concluding that rate goes up quadratically or exponentially with concentration. This rate law would seem to indicate a linear increase, not exponential. I assume in my rate law there is no contribution from the solid Mg. Obviously in a powder, more surface area is exposed, and a high rate is experienced. Is there a way to factor this into my rate law?
Thanks for the help! :)


texts: What happens when heating water in a pressure vessel?

texts:
Suppose that I take a pressure vessel that can withstand up to 2000 PSI. Now I fill it with water (not completely, but around 90%) and start to heat it with a direct flame. What I want to know is, what will happen?

Although I don't know anything about it, here are some guesses that I think might happen:

The water will begin to convert into gas. But since the volume is limited, therefore the pressure would increase (and keep on increasing) and the vessel may burst after the internal pressure crosses 2000PSI.
The water won't convert into gas and would just take all the heat energy into itself. In other words, nothing would happen.

Those are my guesses and it would be great if you can help me out.


texts: Clarifications on the calculation of the $\Delta\mathrm{G}$ of a reaction

texts:
I'm trying to calculate the $\Delta\mathrm{G}$ of the following reaction. Are my calculations correct? I'm also a bit puzzled, 'cause this is a endoergonic reaction right? But the $\Delta\mathrm{G}$ is negative, so the reaction would be spontaneous if my calculations are correct and if the activation energy is reached right?

CH3OH + H2O --> HCOOH + 4H        Delta H = 99.49 kJ/mol

% Standard enthalpy of formation of every compound

% -238.7 kJ/mol CH3OH
% -285.830 kJ/mol H2O
% -425 kJ/mol HCOOH
%    0 kJ/mol H2
% -393.51 kJ/mol CO2

% Standard entropy of formation of every compound

% 126.8 J/mol*K CH3OH
%  69.91 J/mol*K H2O
% 129 J/mol*K HCOOH
% 130.6 J/mol*K H2
% 213.6 J/mol*K CO2

delta_H_1 = -425 - (-238.7 - 285.830);
delta_S_1 = 129 + 130.6 - (126.8 + 69.91);
T = 273.15 + 20;

delta_G_1 = delta_H_1 - T * delta_S_1;

Correct version

delta_H_1 = -425 - (-238.7 - 285.830);
delta_S_1 = 129 + 4*130.6 - (126.8 + 69.91);
T = 273.15 + 25;

delta_G_1 = delta_H_1 - T * delta_S_1;


texts: How do polymer properties change when moving from bulk to nanosized fibers?

texts: Polymer are used in many applications, but how do the properties change when they are fabricated on the nanolevel? Im especially interested in polymeric and polymer derived nanofibers, and why they excel at their respective applications. Thanks!


texts: Batch conversion of Waters mass spectrometry file formats

texts: Are there any free tools for converting raw mass-spectrometry files into open formats? In particular, is there any way to convert Water's .raw MS files into a readable format in a batch-wise fashion (talking about hundreds of mass spectra, so it needs to be at the command line ...)? After a long search, I only found MassWolf which seems very outdated and which also doesn't seem to provide any command line batch processing. Isn't there something like OpenBabel for analytical chemistry file formats?


texts:
I'm confused about $\mathrm{sp^2}$ hybridization in the formation of $\ce{NO3-}$ ion. Valence electrons of N are $\mathrm{(2s)^2}$ and $\mathrm{(2p)^3}$.

Is one of $\mathrm{2s}$ electrons kicked up to one of the $\mathrm{2p}$ orbitals, and then the remaining $\mathrm{2s}$ electron hybridized with the two remaining $\mathrm{2p}$ orbitals which have unpaired electrons? If so, that gives $\mathrm{sp^2}$ orbitals to bond with $\mathrm{p}$ orbitals of the oxygen atoms.  However, there is now that remaining unhybridized $\mathrm{p}$ orbital of nitrogen, which has 2 electrons, so how can it be involved in $\pi$ bonding?

I would appreciate someone explaining this. I'm sure I'm missing something simple, but my book doesn't have an explanation of $\mathrm{sp^2}$ hybridization for Group V elements.


texts: Why the boiling and melting points of n-alkanes are higher than those of iso- or neo-?

texts:
Starting with an example, n-butane has boiling point of $\pu{55^\circ C}$, whereas that of iso-butane is $\pu{-10.2^\circ C}$.

Why there is so much difference in the boiling points?

*EDIT : On the contrary, branched alkanes are more stable. For example, 2-methylpropane is more stable than n-butane. Why?*


texts: Can glutamic acid and arginine form H-bond at physiological pH?

texts:
I was wondering if, say, glutamic acid and arginine can form H-bonds at physiological pH?

According to the figure arginine has a $\ce{NH3+}$ group and glutamic acid a $\ce{COO-}$ group at physiological pH.
I know hydrogen bonding is possible amongst $\ce{NH2}$, $\ce{HF}$ and $\ce{OH}$. But $\ce{-NH2}$ is in the protonated form and the $\ce{-COOH}$ in the deprotonated form.

What will happen:

Will $\ce{-NH3+}$ donate its $\ce{H+}$ to $\ce{-COO^-}$ to form $\ce{-NH2}$ and $\ce{-COOH}$ and then form hydrogen bonds?
Will they attract each other because of the opposite charge, with resulting H-bonding
No H-bonding will occur.

(maybe the first and second option are combined, I didn't really know how to formulate it)

UPDATE
How is the H-bond possible in the following figure (I would think this is just an electrostatic interaction, this figure suggest it would a combination of both):

source of picture: Wikipedia


texts: Reactivity of carbonyl derivatives with a nucleophile

texts:
As observed, the reactivity of carbonyl derivatives with a nucleophile goes like:

Acid halide > acid anhydride > acid > amide > ketone > aldehyde. So is nucleophile a code word to nucleophilic substitution (nucleophilic acyl substitution in this place)?

My professor gave the explanation by saying that look out of $\delta^+$ charge on the carbonyl carbon of each compound, the one that has the most is the one which reacts most with a nucleophile.

And, if we consider that, then the order according to professor is:

Acid halide > aldehyde > ketone > acid anhydride

Is there anyway this order may be correct?

I'm a student btw, so I got no knowledge about the lab and practical stuff.


texts:
I was preparing for the Canadian Chemistry Olympiad and I ran into the following question on one of the past exams:

  If enzyme A binds to the substrate 25 times stronger than enzyme B, what is the ratio of the catalytic rate between enzyme A and enzyme B if the energy of the two transition states is identical? What is the difference in activation energy between the two reactions?

I feel as if I can make a qualitative prediction, but cannot derive a quantitative prediction. I suspect, since enzyme A bind more strongly to the substrate than enzyme B, it would have a greater activation energy, and thus result in a slower reaction.

I suspect that it is necessary to use the equation
$$ \begin{align}
k = \frac{kT}{h} e^{-\Delta G^\ddagger/RT}
\end{align} $$

But the relationship between the two activation energies does not seem simple

$$\begin{cases}
\Delta G^\ddagger_A = \Delta G_{E + S \rightarrow T} - 25\Delta G_\text{bind} \\
\Delta G^\ddagger_B = \Delta G_{E + S \rightarrow T} - \Delta G_\text{bind}
\end{cases}$$

Plugging this into the the original equation, and solving for $k_B/k_A$, I get the following:

$$ \frac{k_B}{k_A} = \frac{e^{\Delta G_\text{bind}/RT}}{e^{25\Delta G_\text{bind}/RT}} = e^{-24\Delta G_\text{bind}/RT}$$

Since $\Delta G_\text{bind} < 0$, $k_B/k_A > 1$, supporting my qualitative prediction. Yet this does not give me a useful ratio, since it is dependent on the binding energies of enzymes A and B. This makes me suspect I am missing/overlooking something, any insight would be appreciated.


texts:
Most people that have ever visited a viticulteur (winemaker) will know that it is common wisdom that vibrations are bad for the wine quality. When I was just a kid the winemaker always told me that we should be silent because the wines needed to sleep, but later a different one explained that this must have been to stop me from running around and causing vibrations.

Even scientific research (e.g. Chung et al. 2008 Journal of Food Composition and Analysis (21)8) has shown that vibrations will indeed change the wine and, among others, accelerate the aging process.

What I am wondering is why these vibrations matter? Is it a chemical effect, in which the vibrations accelerate certain chemical reactions? Or is it more physical in nature, in which the vibrations increase mixing rates and therefore somehow change the evolution of the wine?

If it helps to get your minds working: Vibrating wine in a glass


texts:
I am looking to synthesize potassium metavanadate. Possible precursors that I have are $\ce{V2O5}$ and $\ce{NH4VO3}$.

I have considered the following procedure:
Combine $\ce{V2O5}$ and $\ce{KOH}$ then adjust pH and precipitate out with $\ce{CH3OH}$. The problem is multiple species exist at various pH values, so I am looking for a method to obtain $\ce{KVO3}$. I read a while ago a source for synthesis of different alkali metal vanadates, but I cannot find it again.


texts:
What happens to the $\ce{C-H}$ bond strength in methane as the degree of halogenation is increased (e.g. from $\ce{CH4}$ to $\ce{CH3X}$ to $\ce{CH2X2}$...)

Also, what is the effect of varying the halogens from fluorine to iodine?


texts: What are the effects of radio waves on matter?

texts:
Different regions of the electromagnetic spectrum interact differently with matter:

Microwave radiation can induce molecular rotation.
Infrared radiation can induce molecular vibration.
Visible and ultraviolet light can induce electron excitation.
X-rays and gamma rays can induce ionization.

Is there any activity specific only to radio waves? I kept on thinking how radio waves are used in NMR but I don't know what to call it.


texts: My aim is to "To determine the concentration of citric acid in lemon juice using titration technique." and as following i need to standardise the NaOH in order to titrate it with validity. Is there a procedure and step to standardising NaOH. Thank you


texts: Do dark lines on porcelain dishes indicate usage of aluminium for the color?

texts:
"I heard" that gray lines forming on porcelain indicate usage of aluminium in the coating. I would primarily like to verify this information.

Bowl #1 and bowl #2 have been used both for several months and were bought in different shops. The same observation goes for other dishes. Some don't feature lines, other dishes feature those after days already. The dishes who tend to display those patterns have been bought all at the same place (a large chain of stores specializing on furniture). The lines are most likely caused by cutlery as in cups the same lines are found forming ellipses at the bottom from the stirring. Again some cups don't feature those patterns others do.

Bowl #1 with no lines despite usage for a while:

Bowl #2 with lines:

Bowl #2 with lines - picture taken HDR mode:


texts:
If a weak acid is added to a neutral solution, it creates equal amounts of  $\ce{H3O+}$ and conjugate base.

So what then what happens to the original $\ce{H3O+}$ created by the weak acid when a strong acid is added to a solution.

From what I understand, some of the newly created $\ce{H3O+}$ from the strong acid will react with the conjugate base of the weak acid, preventing the pH from getting lower. But as I stated above, what about the original $\ce{H3O+}$ from the weak acid? For every molecule of the conjugate base that reacts with a $\ce{H3O+}$ from the strong acid, there must have been a $\ce{H3O+}$ created from the weak acid. So how is pH actually prevented from being lowered?


texts: Can Hartree-Fock be considered the quantum mechanical "Monopole" term in a quantum mechanical multipole expansion?

texts: From what I understand, Hartree-Fock simplifies the exact electron-electron interaction with its two electron integrals. It reminds me of the classical energy of a charge distribution combined with the multipole expansion. Is it valid to think of it in this way?


texts: I know that flame tests can be used to distinguish between some metal ions, and that the colours come from excited electrons returning to the ground state.  My question is, why don't non-metal anions also produce colours?  Are their emission spectra in the non-visible range?  Is there a simple reason why?


texts:
I read this today in a book that $\ce{P=O}$ in $\ce{P4O10}$ consists of a coordinate bond and pπ-dπ backbonding, but why does this happen?
Can't phosphorus share its lone pair with one of the lone pairs available in oxygen to form the double bond?


texts: Possibility of removing two water molecules from glycerol

texts:
Not a chemist, but from a chemical formula perspective, how hard would it be to create acetone by acidifying glycerol?
$$\ce{C3H8O3 + 2 H+ <=> C3H6O + 2 H2O}$$
Has anyone ever heard of this being attempted? If it isn't possible, why?


texts:
I know that elements of the 3rd period and beyond can use their empty 3-d oribtals for bonding. But why is there a limit on their covalency?
eg. Al has 5 3d orbitals. And it has an empty 3p orbital. Which means that it's maximum covalency should be 9. But it is 6. Why is it so? Is it because of the small size of Al leading to increased repulsions? Also, why do the elements of the 3rd period use 3d before 4s for hypervalency? 4s has less energy so shouldn't it be used first?


texts: Difference between inorganic and organic semiconductors: electronic structure or configuration, or?

texts: Organic semiconductors differ from inorganic semiconductors. In organic semiconductors the molecules are held together by weak van der Waals interactions and in inorganic semiconductors by covalent bonds. So the bonds are different. How do you express the main difference between the twos? Is it the electronic structure or rather the electronic configuration, or something else?


texts: How to check for geometrical isomerism in cyclic compounds?

texts:
I have no problem with identifying whether a given molecule has geometrical isomerism if it's not cyclic. But cyclic compounds are confusing for me. For example, how to check whether the following molecule posses geometrical isomerism?

For a molecule to show geometrical isomerism different molecules should be attached to the double bonded carbons. So, I'm sure that geometrical isomerism (if it is present) is along the double bonded carbons. But how to check whether different groups are attached to it when the double bonded carbons are the part of a cycle?


texts: How much pressure is needed to make dry ice?

texts:
By compressing $\ce{CO2 (g)}$ the gas gains a lot of heat. When the hot compressed carbon dioxide is left to cool, it attains the temperature of the surrounding material. When it is released into the pressure outside (about 100kPa), it will get so cold (actual temperature depending on how much the carbon dioxide was compressed), that it will freeze (below 78.5 degrees celcius).

How much pressure is needed to make dry ice at 293K (20 degrees celcius)?


texts: Does the triplet sigma state of a diatomic molecule experience spin-orbit coupling?

texts:
I know that states with spin S=0 in a diatomic molecule have no spin orbit coupling, independent on the value of the projection of the total electronic angular momentum.

I expect the same is true if the absolute value of $\Lambda$ is equal to zero independent on the spin of the diatomic molecule.

Is it correct that a diatomic molecule with a $^3\Sigma$ state has no spin orbit coupling?


texts: Nucleophilicity with respect to the solvent

texts:
I am currently studying nucleophilicity of molecules and am getting a set of conflicting information, so I wanted to clarify nucleophilicity trends with respect to solvent.

Master Organic Chemistry discusses how nucleophilicity increases down the periodic table with protic solvents and decreases down the periodic table with aprotic solvents; the main argument is that a solvating shell will form with the protic solvent, making the smaller atoms less likely to form a bond. When this effect is removed, the trend is reversed.

However, during my lectures, my professor said that there is no such change in the trend: the larger atoms such as $\ce{I-}$ will always be more nucleophilic than $\ce{F-}$ due to the fact that it is more polarizable and likely to donate an electron pair. The textbook that I am using, Organic Chemistry by Wade, also does not discuss this trend reversal depending on the solvent. The only discussion talks about how $\ce{F-}$ would be a poor nucleophile as it is small and holds its electrons "tightly."

A practice problem provided during class also asked to compare the nucleophilic strength between $\ce{H2O}$ and $\ce{H2S}$ in polar aprotic solvent; similarly, the correct answer provided was that $\ce{H2S}$ would be a stronger nucleophile as it is larger and more polarizable.

I would appreciate it if someone could clarify this matter.


texts: Why does the oxidizing strength of the chlorates decrease with increasing oxidation number?

texts:
Here is a table of the standard reduction potentials of the chlorates from wikipedia:

Intuitively, one would expect that the more positive the oxidation state, the more oxidizing that compound would be. However, as we see, the standard reduction potentials become more negative as the oxidation state of the $\rm Cl$ atom becomes more positive. So, why does the oxidizing strength of the chlorates decrease with increasing oxidation number?


texts:
I am trying to compute the oscillator strength in a molecule. Therefore I've got its Energy level values plus both wave functions $\Psi_i$ and $\Psi_j$ for the transition I want to calculate the oscillator strength for.

In general, the oscillator strength of a transition from $E_i \rightarrow E_j$ is defined as

$f_{ij} =\frac{4m_e\pi\nu}{3e^2\hbar}D^2$

where D stands for the transition moment integral which shall be

$D_{ij} = \int\Psi_j\hat{\mu}\Psi_i$.

Now I am wondering how the transition dipole operator $\hat{\mu}$ is defined, since I didn't find helpful.


texts: 1 mole of substance is equal to atomic/molecular mass in grams?

texts:
I have been reading the answer of this question here- Why is weight of 1 mole of substance equal to atomic/molecular mass in grams

I feel that the answer writer was wrong to say that -"the ratio of g/mol to amu/atom is exactly one"

I  feel so because he proved that the ratio of g/mol C12 to amu/atom C12 is exactly one.He never proved that the ratio of g/mol to amu/atom is exactly one.If I am wrong then please correct me!


texts: Why does egg yolk turn white when washed with water?

texts:
I recently noticed that whenever I washed the egg yolk stuck on some utensils the water becomes milky white.
It has to be the egg yolk that turns white and give off the white color to water right?


texts: opperating a distillation column far from flooding

texts:
I know that flooding will ruin the performance of a distillation column. There are many correlations (Eckert, kister, billet, etc.) that will tell you when a column will flood based on your fluid conditions. Most design guides suggest choosing a diameter that will lead 70-80% of the flooding condition. This makes sense as the size of the column (IE, the cost) is as small as possible while still giving you a 20-30% margin of error.

However, what if due to other constraints you want the column to be large so that it is only operating at 10% of the flooding conditions (IE, a much larger diameter than normal). Would this column still operate? Is this type of operation just avoided because it is not economically practical and a smaller column would do the same thing operating closer to flooding?


texts: When did the realistic typesetting of chemical structures start?

texts:
In many old chemistry books there were limitations on how chemical structures could be represented driven, presumably, by the desire to use available typesetting methods to save costs.

For example, this is a page from a book on industrial chemicals published in the 1930s:

The distorted hexagons are 6-membered aromatic rings but are typeset from vertical and 45° lines with none of the double bonds explicitly shown.

When and how did chemical typesetting become more "realistic" with, for example, proper hexagons for aromatic rings and the correct description of double bonds where appropriate?


texts:
I want to understand the mechanism of desilylation of trimethylsilyl under fluoride conditions in methanol, because I can't find any useful info that makes me understand the mechanism that takes place.

Thank you in advance!


texts: Why do transition metals tend to form positive ions instead of negative ions?

texts: I have learnt that elements on the left-hand side of the periodic table such as sodium and magnesium prefer to lose electrons to form a cation because this requires less energy to obtain a stable octet, and vice-versa for the right-hand side of the periodic table e.g. fluorine. However, using this reasoning I am not sure why all transition metals tend to lose electrons rather than gain them.


texts:
How does trans-cyclooctene exhibit chirality if there are no stereocenters?

Related follow-on questions:

Are all higher cycloalkenes chiral?
Do more double bonds cause a bigger number of stereoisomers in cycloalkenes?


texts: Why is guanidine considered a strong base?

texts:
I've studied $\mathrm{p}K_\mathrm{a}(\ce{H2O}) = 15,$ and anything with a $\mathrm{p}K_\mathrm{a}$ lower than should be an acid. Guanidine has a $\mathrm{p}K_\mathrm{a}$ of $13.8$ and is being called by Wikipedia a strong base. Why is it so?
According to Wikipedia, ammonia is a weak base. Then why is its $\mathrm{p}K_\mathrm{a}$ much higher than the $\mathrm{p}K_\mathrm{a}$ of guanidine?


texts: Synthetic ruby - damaged by heat less than its melting point?

texts:
A bit of a jewellery question but chemistry related. I want to encase a synthetic ruby (corundum, Al2O3) in silver by melting the silver around it. Either in a furnace or by casting. The MP of silver is 960 °C.

The ruby will be facteded and polished. Now, in theory the ruby should be unharmed given that its MP is double that of the silver and is much harder. However, would there be any damage to its optical properties?


texts: What is the mechanism for the oxidation of a lactol to a lactone?

texts: Recently, I came to know that lactols can be converted to lactones but I wasn't able to find the suitable reagent and the reaction mechanism. Can someone elaborate the same?


texts: Optical activity of (1r,3R,5S)-3,5-dimethyl-4-methylidenecyclohexan-1-ol

texts: Could anyone explain why compound L is not optically active?


texts: Do Slater's rules apply to neutral lithium (at least approximately)?

texts:
For lithium, the electronic configuration is $\ce{(1s)^2(2s)^1}$. I tried to calculate $Z_{eff}$ for the $\ce{2s}$ orbital of the neutral atom as follows:

$$Z_{eff} = Z-\sigma$$
$$Z_{eff} = 3-(2\times0.3)$$
$$Z_{eff} = 2.4$$

But the Wikipedia article's table of effective nuclear charges (linked below) states that $Z_{eff}$ is 1.279 for the $\ce{2s}$ lithium orbital, which is not even close to my answer (above). So do Slater's rules not apply to lithium or I have done something wrong?

Wikipedia article: https://en.wikipedia.org/wiki/Effective_nuclear_charge


texts: How to identify the structure of an organic acid based on its reactivity, mass and NMR spectrum?

texts:
Taken from OCR A Chemistry Unified Chemistry Sample Paper.

  Information about a monobasic organic acid D is shown below.

  D reacts by both electrophilic substitution and electrophilic addition.
  The molecular formula of D is $\ce{C_xH_yO2}$.
  The mass spectrum of D has a molecular ion peak at $m/z = 148$.
  The $\ce{^13C}$ NMR spectrum of D contains seven peaks.

  Determine and draw a possible structure for D. Explain your reasoning from the evidence provided.

I understand that D must contain a benzene ring (electrophilic substitution) and a double carbon bond (electrophilic addition). However, I'm at a loss about how to deduce the molecular formula. Taking away $M_r(\ce{O2})$ from $\pu{148 g mol^-1}$, gives $M_r(\ce{C_xH_y})= \pu{116 g mol^-1}$. The mark scheme gives the molecular formula as $\ce{C9H8O2}$. I can't see how the values of $x$ and $y$ were deduced. All you know is that D contains a $\ce{C=C}$, benzene ring and most likely a $\ce{-COOH}$ group (due to monobasic nature).


texts: What determines whether a double displacement reaction will occur?

texts:
In normal displacement reactions, reactivity plays a large role and sometimes the reaction doesn't even happen. So is there anything limiting double displacement reactions? For example $\ce{2KI + Pb(NO3)2 -> 2KNO3 + PbI2}$. If reactivity plays a role in this reaction, why does it occur? Isn't the halogen ion (iodide) more reactive than $\ce{NO3-}$?

(I'm a high school chem student so this may come off as a newbie question, sorry)


texts: Is (high) pressure required to form (quartz) crystals?

texts:
I've been reading a lot of sources about the hydrothermal synthesis of quartz using autoclaves. I want to try doing this myself, but before I can I need to know the minimum pressure required.

If you need a refresher, hydrothermal synthesis uses steam as a solvent, and creates a supersaturated solution that places the quartz molecules onto a seed to grow a pure crystal.

I've gotten many different numbers in terms of how much pressure [from the steam] is required for the process, ranging from 7500 psi to 30000 psi. I want to work with as low of a pressure as possible.

So then my question is: is high pressure necessary for quartz crystal formation? My understanding is that the pressure in the case of hydrothermal synthesis is created from having large amounts of steam in order for more material to be dissolved in said steam, so the crystal will form faster. So is this the case, in which having a lower pressure will work, or is pressure required for the crystal to form properly? As in, does the pressure actually affect the crystal structure in some significant way?


texts: Does more branching lead to lower boiling point in alkanes?

texts:
List the following alkanes in order of increasing boiling point.

  A. $\ce{CH3(CH2)4CH3}$
  B. $\ce{(CH3)2CHCH(CH3)2}$
  C. $\ce{CH3CH2CH(CH3)CH2CH3}$

  Answer: $C<B<A$, low to high.

Why is it that B has not a lower boiling point than C? Is it not more branched? I believe branching decreases surface area, leading to less intermolecular interactions, and to a higher boiling point.


texts: Why does sp2 hybridization imply adjacent sp2 hybridization?

texts:
EDIT:  I misquoted my teacher; he said something more along the lines of: in conjugated systems, if an atom is $\ce{sp^2}$ hybridized, then every atom it is bound to is also $\ce{sp^2}$ hybridized. Would this be accurate?

My teacher said that if an atom is $\ce{sp^2}$ hybridized, then every atom it is bound to is also $\ce{sp^2}$ hybridized.

1) Why is this true?
2) Is this even true?

I'm guessing this has to do with physical limitations. For example, consider a carbonyl oxygen. Oxygen is $\ce{sp^2}$ hybridized. The carbon the oxygen is bound to has already "used up" two of its four bonds. The carbon can only form two more sigma bonds in addition to the one sigma bond it already has in the $\ce{C=O}$ double bond.

But what about "hypervalent" (if there are such beasts) molecules? Here we come to a self-consistency issue. My teacher still believes in hypervalent molecules - i.e. he draws sulfuric acid with six bonds.

So let's consider sulfuric acid in its hypervalent form, with two double bonded $\ce{sp^2}$ oxygens. There are a total of six bonds and four sigma bonds, implying $\ce{sp^3}$ hybridization.

So my revised set of questions is as listed:

1) Is my teacher being inconsistent with himself here?

2) Does $\ce{sp^2}$ hybridization still imply $\ce{sp^2}$ hybridization for linked atoms? Note that sulfuric acid does not disprove my teacher's statement if we take sulfuric acid to have four bonds, not six (i.e. sulfuric acid is properly represented as charge separated due to the high ionic character of its $\ce{S-O}$ bonds. If I remember correctly, on a time-average basis, 1.7 electrons are in oxygen's valence and only 0.3 electrons are in sulfur's valence per bond.


texts:
Here's what I read about which base to use in Claisen Condensation reaction (two esters or ester + carbonyl compound forming a beta keto-ester or beta-diketone):

  The base used must not interfere with the reaction by
  undergoing nucleophilic substitution or addition with a carbonyl
  carbon. For this reason, the conjugate sodium alkoxide base of the
  alcohol formed (e.g. sodium ethoxide if ethanol is formed) is often
  used, since the alkoxide is regenerated. In mixed Claisen
  condensations, a non-nucleophilic base such as lithium
  diisopropylamide, or LDA, may be used, since only one compound is
  enolizable. LDA is not commonly used in the classic Claisen
  or Dieckmann condensations due to enolization of
  the electrophilic ester.

Here's what I didn't understand, particularly -

Why is the conjugate sodium alkoxide base of alcohol generated, used? The paragraph talks about regeneration of alkoxide ion; but I didn't really understand that part. (Seems like something related to chemical equilibrium?)
They said that Lithium Diisopropylamide is NOT generally used due to enolisation of electrophilic ester. What do they mean by it? Why can't we use LDA? Which bases can we use instead?

Could someone please answer the above two questions, with proper explanation? Thanks a lot!


texts: How to save the force on a molecule in GROMACS?

texts:
I am a new student of molecular dynamics. I have started using GROMACS a month ago.

I have a small box of 8192 molecules each with 3 atoms. I froze the last molecule and ran the simulation. I even converted the .trr file from binary to .gro and checked that the last molecule indeed stayed in the same place.

However, I want the .trr file to print the force on each molecule or each atom - in the x, y, and z-direction.
I even set the nstfout in the grompp.mdp file to a reasonable non zero number - 5000.

However, the .trr file - when converted to .gro - did not show the force. Can someone tell me what I am doing wrong and how to get GROMACS to save/reveal the force in the .trr file?


texts: Substitute for alkali-iodide-azide reagent for BOD test of water samples

texts: To measure the biological oxygen demand (BOD) of water samples, I am following a procedure that uses manganese sulphate, $\ce{H2SO4}$, and titration with standard sodium thiosulfate solution. Alkali-iodide-azide reagent is an important part of the procedure, but my school lab does not have this reagent. Is there a substitute for it?


texts:
A reaction proceeds towards the direction of lesser Gibbs free energy (at constant $T$ (temperature) and $P$ (pressure)). So, we could say that Gibbs free energy at equilibrium is minimum.

On the other hand, we have $$\Delta G=\Delta G^\circ + RT\ln Q$$, where $Q$ is the reaction quotient. At equilibrium, $Q=K_\text{eq}$, and we already know that $\Delta G^\circ =-RT\ln K_\text{eq}$.

Substituting, we get $\Delta G=0$ at equilibrium. But, we know that $G$ minimized itself—thus there was a change in $G$ and $\Delta G < 0$.

What am I missing here?


texts: What home products are reactive with glass?

texts: Glass seems to be one of the most stable solid substances - which chemicals, particularly home products that react with glass?


texts: Approach to model solvent in a lattice: e.g. H2O in NaCl

texts:
If a lattice contains a solvent, lets say $\ce{NaCl}$ and water of crystallisation, what is the condition for a solvent molecule to change it's location?

From my current point of view I assume that such a water molecule is bound to a lattice ion by ion-dipole forces. It vibrates at that location until, randomly, the particle energy exceeds the binding energy. Then it goes to a new location, in the direction that minimizes Gibbs free energy.

How is the water molecule energy distributed? Currently I use Maxwell-Boltzmann distribution. However, Maxwell-Boltzmann is for non-interacting particles and therefore not quite a good fit for molecules that interact with a ion. Further, my chemistry book suggest that ion-dipole bonds have a binding energy of >$50~\mathrm{kJ~mol^{-1}}$, which will in my calculations rarely allow a jump at all.

I ask this question because I'm working on a particle-drying simulation. I intend to use a Random Walk simulation to obtain diffusion coefficients under special circumstances: e.g. if the lattice salvation behaviour is somehow weird. The model must not be physically correct in all details. Even bigger "model" error will most likely be small in the simulation results.

Note: I asked this question already here but have not received an answer. As suggested there, I open it in Chem.SE.


texts: Ca energy release when gaining an electron

texts:
Why does $\ce{Ca}$ have a negative electron affinity, i.e. energy is released when it gets an electron (ca. $\pu{-2 kJ/mol}$), when $\ce{Be}$ and $\ce{Mg}$ have positive values?

I know that the electron will be settled in the $\ce{3d}$ orbital which has a lower principal quantum number than $\ce{4s}$, but still, why would energy be released?


texts: Oxygen in water: How is it single if it's always double?

texts: This is simple question, I think. At college (I'm an Intro Chem. student), the professor explained that oxygen is always found in molecules of 2 oxygen atoms combined together - $\ce{O2}$. On the other hand, molecule of the water is $\ce{H2O}$. So I don't get, how is it that O is single in this molecule, if it's always found coupled?


texts:
$\hspace{6.4cm}$
I would like to know how to name the alkyl groups connected to the above molecule. For example, would the far left alkyl group be considered a methyl ester group? Would the alkyl group bound to the oxygen be a methylene ester group?


texts: Spectral database in the UV-Vis/NIR and IR regime

texts:
I'm searching for a bunch of spectra (some tens), preferably with intense bands in the Vis spectrum, to play around with (calculating chromaticity, etc.).
They should range from

250 nm to 2500 nm (UV-Vis/NIR)
400 cm-1 to 4000 cm-1 (IR)

and should be available as raw data like jdx format or the like.

I allready know the famous NIST and SDBS, but those have large gaps in the desired spectra, if not one completely missing.

Anybody knows databases where you can search by availability of spectral data in a specific regime?


texts:
I would like to double check the English grammar of a sentence of an elimination reaction, but I cannot find an answer.

I'd normally say "the elimination of A with X as the leaving group", where A is the initial compound.

So my question is saying "the elimination of X from A", correct? I've never been told not to, but I feel it is wrong chemically, so I would change it to "the leaving/loss of X from A", which unfortunately sounds casual.

EDIT.
So based on the answer below I was totally wrong —I am glad I asked!— and to recap with A as reactant and X as leaving group and optional parts in parenthesis:

✓ → ✗ — the elimination of A (with loss of X)
✗ — the elimination of X (from A)
✓ — the loss of X (from A)
✓ → iffy — the leaving of X (from A)
✓ → ✗  — A gets/is eliminated
✗ — X gets/is eliminated from A
✓ — A undergoes elimination (with loss of X)


texts: Why does the binding of DMSO to metal via the S atom (k-S) strengthen the S=O bond?

texts:
So, DMSO (dimethyl sulfoxide) can form metal complexes in both $\ce{\kappa-O}$ and $\ce{\kappa-S}$ mode i.e. binding with the oxygen or the sulfur respectively. The general explanation given is that softer metal ions bind to the soft centre $\ce{S}$ and hard metal ions bind to the hard centre $\ce{O}$.
From the IR data it can be inferred that the binding of DMSO to a metal ion via $\ce{O}$ causes the $\ce{S=O}$ bond stretching frequency to go down. For example the $\ce{S=O}$ stretch in free DMSO (liquid) is $\pu{1055 cm-1}$, whereas the stretch in $\ce{[Co(dmso)6]+}$ appears at $\pu{950 cm-1}$. This makes sense to me because the oxygen can only act as $\pi$ donor (apart from the usual $\sigma$ donation), and donate electrons to the metal $\mathrm{t_{2g}}$ from bonding $\pi$ orbitals, which will weaken the bond between $\ce{S}$ and $\ce{O}$.
However, when DMSO binds to a metal ion via $\ce{S}$, the $\ce{S=O}$ bond stretching frequency goes up. For example, in $\ce{PdCl2(dmso)2}$ shows the $\ce{S=O}$ stretch at $\pu{1116 cm-1}$.
But how is this possible? The sulfur is already electron deficient due to the strongly electronegative $\ce{O}$, and should be a $\pi$-acceptor, and accept electrons from metal into the $\pi^*$ orbitals. This means that the $\ce{S=O}$ bond should also be weakened in this case. But this does not happen. Why? Does it have something to do with the molecular orbitals of DMSO?
[Note: According to this post, the $\ce{O}$ is mainly $\pi$-donor and the $\ce{S}$ $\pi$-acceptor for DMSO, and I agree with the argument in that answer. But it does not say anything about the strengthening of the $\ce{S=O}$ bond in $\ce{S}$ bonded complexes.]
The pictures of HOMO and LUMO of DMSO respectively:


texts: Are these two structures of 1,3-dichlorocyclobutane enantiomers?

texts:
According to me they are not enantiomers because the mirror image can be rotated by  $180^\circ$ to get the same compound.
Giving it a little more 3-D look:

But the book says they are enantiomers. I don’t understand how?


texts:
So the two conditions for a reaction to be spontaneous are:

tendency to achieve minimum energy
tendency to achieve maximum randomness.

Both these things are contrasting and the only way I see them working are when they work independent of each other. Do these work simultaneously?

I am really having a hard time in figuring out a reaction where energy decreases and entropy increases. Can this happen?


texts:
Hydrogen is generally considered a non-metal, and a non-metal and a metal often makes a salt. However, lithium hydride seems like a special case. The wikipedia article does not clearly state if the compound is a salt or not, only describing it as "salt-like".

Structurally, it makes sense to classify it as a salt, due to the network structure, but are there any clear definition to settle where the compound belongs?


texts: Chemical reaction for the flow color change from blue to red and again to blue

texts:
I am trying to demonstrate color change in the liquid as it passes through a channel to demonstrate blood getting purified after passing through certain organs of the body.
I want the initial color of the liquid to be blue in color and as it passes and comes out of a small pipe, it should change into red color and again after going through a small pipe, I want it to change back into blue color.
In short, blue to red to blue.
I have tried to search things online and I found the following.  There is a reaction which involves sodium hydroxide and sucrose. Under stirring upon addition of $\ce{KMnO4}$ the color change happens. But I am not quite sure if I will be able to handle stirring.
So, I am looking for something simpler than that. I am really not that sure if such a reaction exists.


texts: What will happen to bottle of cola after 50 years?

texts:
I'm going to make a time capsule for 25 or 50 years, and I don't know wether it's safe to put food, e.g. bottle of cola there. Will it explode and ruin the capsule? Will it be ok to drink it, if it won't explode?
Also, what about Snickers or a hamburger in a ziploc package with air sucked out of it with vacuum cleaner?

So: will Snickers, Hamburger in a ziploc, Bottle (or can) of Cola, all not opened, go crazy in 25 years? In 50 years? If so, can they go out of their packages and ruin the contents of the time capsule? If not, will it be safe to consume one of them?


texts: Is it possible to have a negative overall activation energy for a whole reaction mechanism?

texts:
I am trying to find out correlation for ignition delay for alkane fuels. The activation energy part of the correlation gives me a negative value.
For the ignition delay formulation, is it possible to have an overall activation energy part being negative?

$$\tau = P^aT^b\phi^c\exp\left(\frac{E_\mathrm{a}}{RT}\right)$$


texts: Have Ionic Liquids been used to refine aluminum on an industrial scale?

texts: Ionic liquids have been shown capable of reducing aluminum trichloride to solid aluminum at 3kw-hrs per kg of Al(s) produced instead of the current ~15kw-hr/kg. However, this would seem to neglect the fact that bauxite is aluminum trioxide not trichloride. This is no small detail and leads me to wonder if it is an insurmountable hurdle to the widescale adoption. Has this technology been implemented (or slated for implementation) on an industrial scale? If not, what holds it back?


texts: What's the mechanism for the oxidation of primary alcohol to carboxylic acid with HNO3?

texts:
Can someone help me find the mechanism for this reaction. I've been looking for it, but I
haven't found it. Thank you.


texts: Why the magnitude of dipole moment influences on FTIR % transmittance?

texts:
In 3:50 of this video two FTIR spectras are shown. He explains that the % transmittance (double bond in his example) depends on the dipole moment, $\mu = \delta \cdot d$.

I understand that the absorbance center frequency depends on $\delta, d$, but why the percentage of transmittance depends on $\delta, d$? A private case of this would be a symmetric bond ($\delta=0$): why the transmittance is 100%?


texts: If a reaction requires a "strong" acid - what does this mean? Does it mean any acid of a specific concentration or pH? Are only certain acids classed as "strong"? I have read on Wikipedia that it needs to ionise completely in an aqueous solution - in this case, is a strong acid (for example, HCl) still classed as a strong acid if it is in a 0.00001M solution?


texts: H-N-H bond angle in ammonia boron trifluoride adduct

texts:
In the reaction:

$\ce{NH3 + BF3 -> NH3-BF3}$ does the HNH bond angle increase or decrease?

Surely, the FBF bond angle decreases because boron changes from $\ce{sp^2 -> sp^3}$. But how can we comment upon the NHN bond angle? In my first attempt, I expected it to increase because though N still remains in $\ce{sp^3}$ hybridisation  lp-bp repulsions are greater than bp-bp repulsions.

But the answer key states that the NHN bond angle will decrease. Please let me know how to determine this.

I couldn't find the bond angle data on net or in JD Lee.


texts: Do acid derivatives (anhydrides/amides/acyl halides) give positive Iodoform test?

texts: Technically, having a methyl carbonyl group should enable them to give positive Iodoform test.


texts:
I know osmium powder will produce osmium tetroxide when exposed to air,but what about solid piece of osmium,such as pellet or ring,finely polished to minimize surface area,will this produce significant tetroxide at 24 degrees celsius air?

How much tetroxide will 1 cm2 surface area of polished osmium produce in 24 hours when exposed to air at 24 celsius?


texts: What does this three-number isotope notation mean?

texts:
What does the superscript $3+$ mean?
$$_{21}^{45}\mathrm{Sc}^{3+}$$

I understand that $45$ is the atomic mass number and $21$ is the number of protons. Is the $3+$ to indicate that it is a particular isotope, or does it have some other meaning?


texts: I (might) have accidentally combined these mold-killers at home: Any adverse reactions?

texts:
A trailer is a small enclosed space. About 2 months ago we had some mold and I applied some mold killer to a few spots that I could not remediate. Below I've listed 2 products I used. (I definitely used product #1, and it's possible I applied product #2 to the same 1 x 2 foot area.)

Air testing shows the mold is gone, but there's still something in the air that one can feel isn't good to breath in. It tickles your throat, tightens up throat and sinuses, headache, and sometimes makes you cough. (Again, this isn't a medical question. I don't live in the trailer, it's sitting.) The only way to find out what that is though, is to disect what 2 products were sprayed. Would mixing these 2 products create something super nasty? (Like formaldehyde, Chlorine, Chloroform, etc., the list goes on.)

We did a Volatile Organic Compound (VOC) test a few weeks ago and it turned out to be pretty much negative. It did pick up some very low levels of toluene, hexane, ethyl benzene, and xylene, but far from anything alarming. The levels were far below the EPA's acceptable exposure levels, but the reason I mention these chemicals is in case they are valuable information and tip you off on anything.

Also, in case this is a tip for anyone; All my fabrics smell and they really make me cough (etc.). After I moved out of the trailer to remediate it, I noticed that all of my cloths, towels, bedding, etc. (i.e. all fabrics) had a weird chemical smell until they were washed. It sort of smelled like a smokey chemical smell... but not really smokey. Hard to explain. But what's really interesting is; I had a pile of clothes I'd left in a closet. The other day I put them in my car to drive to my new house, and I started coughing in the car, the headache set in again, irritated throat... all the same symptoms, only now its some kind of gassing coming off my clothes that were in the trailer. Weird! It makes me wonder if you're aware of a specific chemical that can stick to clothes like that?

I have 2 questions:

QUESTION 1: Is/was it dangerous to mix these 2 products? Did I create an even worse chemical in doing so? (I've listed their chemical composition at the bottom of this post)

QUESTION 2: Is there a chemical method to 'pull' chemicals like these out of the trailer? For example, I've heard about people putting ammonia in a bowl and leaving in their trailer to pull out formaldehyde. Not sure if that is a valid chemical method?

Product #1: Mold Armor Mold Remover & Disinfectant

Ingredients:

Ethanol is the main ingredient. These ingredients below are the small/active ingredients

Quaternary ammonium compounds, benzyl-C12-16-alkyldimethyl, chlorides (< 0.1 %)
Decanaminium, N,N-Dimethyl-N-octyl-chloride {Decyldimethyloctylammonium chloride} (< 0.1 %)
Octanaminium, N,N-Dimethyl-N-octyl-chloride (< 0.1 %)
Decanaminium, N-Decyl-N,N-dimethyl-chloride (< 0.1 %)

See product documentation (SDS), here.

Product #2: Concrobium Mold control

Ingredients:

Water is the main ingredient. These 3 ingredients below are the small/active ingredients

Trisodium phosphate
Sodium carbonate (.95%)
Sodium bicarbonate

See product documentation (SDS), here.

Edit

I reworded my question. Again, not a medical question. This is a chemistry question about mixing 2 products, and their reactions.


texts:
In which of the following reactions is the equilibrium farthest to the left?

a) $\ce{P4O10 + $x$ H2O <=> 4 H3PO4(aq)}$

b) $\ce{AlCl3 + $x$ H2O <=> [Al(H2O)6]^3+ + 3 Cl- (aq)}$

c) $\ce{Li2O + $x$ H2O <=> 2 Li+(aq) + 2 OH- (aq)}$

d) $\ce{H2S + H2O <=> H3O+ + HS- (aq)}$

e) $\ce{CaC2 + $x$ H2O <=> Ca^2+(aq) + 2 OH- (aq) + C2H2(g)}$

The correct answer is d, but I'm not sure how to compare these equilibria.  I know that the answer can't be e, since the evolution and purging of gas will drive the equilibrium forward.  Also, the dissociation of ions in water is favorable due to solvation, so that rules out c and b.

But I'm not sure how to compare the remaining two reactions.

Any help would be greatly appreciated.


texts: An automated approach to visualize several xyz structures

texts: I have several .xyz files (each composed of several molecules) and I'd like to find an automated way to visualize and save them. I'd appreciate any guidance.


texts: What is the relationship between something magnetic and unpaired electrons?

texts:
I don't get how some elements are magnetic. Can someone please explain the relationship between something magnetic and unpaired electrons?

Why is cobalt magnetic?


texts: Cooling down from −78 °C to −88 °C without cryogenics

texts: Say I have a gas cylinder with nitrous oxide and cool it down to −78 °C with dry ice. Is there an endothermic process/reaction that would extract the remaining heat from $\ce{N2O}$ and bring it down by 10 °C to its boiling point of −88 °C? I know this could be done by using cryogenics like liquid nitrogen, but I want to avoid those.


texts: Will the total equilibrium pressure increase in gas phase reaction PCl5(g) = PCl3(g) + Cl2(g) after chlorine is removed?

texts:
Will the total pressure be greater than the initial equilibrium pressure if all $\ce{Cl2}$ is removed and the following reaction is allowed to re-equilibrate?
$$\ce{PCl5(g) <=> PCl3(g) + Cl2(g)}$$
Assume constant temperature and volume.

I know that when $\ce{Cl2}$ is removed, the reaction will go forward and I also know expressions of $K_\text{p}$ and $K_\text{c}$.  I also know Le Chateliers Principle. I have thought about it for a long time but have not made any progress.


texts: Reaction of PLA plastic with methane or carbon dioxide

texts:
PLA (polylactic acid) plastic is commonly used for 3D printing, and I would like to create a 3D printed part that can be used in an experiment with methane ($\ce{CH4}$) and carbon dioxide ($\ce{CO2}$) gas sensors.  Does $\ce{CH4}$ or $\ce{CO2}$ gas react with PLA plastic?  What are the long-term effects of these gases in contact with PLA plastic?

Anaerobic biodegradation can break down PLA, producing $\ce{CH4}$ under some environmental conditions (DOI: 10.3390/ijms10093824).  But is PLA resilient to $\ce{CH4}$, or is there a chemical reaction?  I can't seem to find any reference to such an effect in the literature.

The experiment that I am conducting involves the measurement of environmental sources of $\ce{CH4}$ and $\ce{CO2}$ gas.  A hose needs to be passed into a 3D printed chamber that encapsulates the sensors.  A molecular sieve material blocks water and sources of moisture before the gas enters the chamber.  The chamber will not be heated in any fashion (room temperature or colder), and detection of the gas by the sensors is by diffusion.


texts:
Fundamentally, they're both carbohydrates, although the cellulose in wood is essentially polymerized glucose, which combined with its isomer fructose forms sucrose.

So why does wood readily burn while table sugar chars?


texts: Does the speed of an ion affect the current that can flow through a solution?

texts:
Typically, when a cathode and anode are inserted into a solution that allows current to flow, the ions are moving with a certain kinetic energy.

If the ions were to gain kinetic energy (through transfer of thermal energy for example), will more current be able to flow, and will the potential difference increase?

My assumption for this is that increased ion kinetic energy will speed up the rate of ions being attracted to each electrode, thus causing more charge to arrive in a given period of time. As $I = Q/t$ where $I$ = current, $Q$ = charge and $t$ = time, would this mean an increased current?

Edit: I've performed a basic experiment in which I got a Tupperware container, stuck in some multimeter probes, and tested the difference in potential (voltage) for $\ce{NaCl}$ (table salt) in solution when cold and hot, then for water cold and hot. I appreciate there are many issues with reliability, but the general results were:

Water cold = 0.082 V
Water hot = 0.000 V (actually went into the negative then stabilised at 0)
NaCl cold = 0.065 V
NaCl hot = 0.130 V

Now, my real experiment involved $\ce{AgNO3}$ being titrated into $\ce{KCl}$ (mixed with deionised water and a little $\ce{HNO3}$ to acidify) – assuming the temperature remained constant, what effect could increasing the ions' velocity have on conductivity, without heating it up (increasing kinetic energy) to alter viscosity?


texts: How do tie-line slopes affect raffinate/extract envelope in ternary phase diagrams?

texts:
I am struggling to understand ternary phase diagrams for reactor engineering. The course slides offer little to no help so I'm hoping to find an answer to this question

  How does the slope of the tie-lines affect on which side of the
  equilibrium line the extract/raffinate is?

From what I understand is that if the lines slope down, the extract is on the right and the raffinate is on the left. If they slope up, the sides are flipped. Is this correct?

Sidenote: does anyone know a good resource where ternary diagrams for chemical/reactor engineering are well explained?


texts: Conversion factor for conductivity of an aqueous solution

texts:
I am not 100% sure if this is the right place to ask, but please point me in the right direction if not.
I am designing a conductivity meter, and when it comes to displaying the results in mS/cm or µS/cm, I also need to convert to EC. The first place I found was THIS website which seems great as it has all the units that I can convert here and there, no problem. This site states that 1EC is equal to 1µS/cm.
I had started to do most of my calculations based on the conversions from this website. However, when getting a reference calibration liquid, I noticed it was set to 2.76EC/2.8mS, which goes against what was stated in the website. I then found THIS website which shows 1EC as equal to 1mS/cm. I have now seen another place online (closed the tab and can't find it!) that also agrees with this.
Another website I have found HERE gives a bit more information on the conversion, and states that EC is measured in deciSiemens per meter (dS/m), and 1EC = 1dS/m, which would be 1mS/cm. Then later, it has a conversion thing at the bottom which has a statement saying:

Conversions:

1 deciSiemens per meter (dS/m) = 1 mmho/cm = 1
milliSiemens per cm (mS/cm) = 1000 microSiemens per cm (uS/cm) 1
mhos/cm = 1 S/cm = 1000 mS/cm

Electrical Conductivity units (EC's) IF
measured in uS/cm: 1 EC= 1uS/cm = 0.001 dS/m = 0.001 mS/cm = 1 mS/m

(Example 1.5 dS/m = 1.5 mS/cm = 1500 uS/cm = 1500 EC)

And surely that contradicts itself where it says 1EC = 1µS/cm, then the example after says that is not the case?
I just wanted to ask and be sure on this.... When converting, is 1EC equal to 1mS/cm, or 1µS/cm?


texts: Calculate molar mass of a compound from a given molecular mass

texts:
The mass of one molecule of a compound is $2.19\times10^{-22}\ \mathrm g$. What is the molar mass of the compound?

My attempt:
Using the formula moles=mass/molar mass, I found how to calculate molar mass using the formula molar mass=moles/mass.
Therefore, I was under the impression that, surely, $6.02\times10^{23}$ divided by the mass of the compound would have resulted in the molar mass. However, the answer was wrong.


texts:
Although the phenolate ion has more resonance structures (4) compared to acetate ion (2), acetate is more stable because it has two equivalent resonance structures of same energy.

Why does having equivalent resonance structures give more stability? Shouldn't a compound with more resonance structures be more stable?


texts: How do you create primary amines from alcohols?

texts: By a primary amine I mean a compound where the hydroxyl group of the corresponding alcohol is replaced with an amine group.


texts: Relative reacting tendency of H2/Pd towards double bond and triple bond in straight carbon chain

texts:
If both double bond and triple bond is present in a straight carbon
  chain the which one (double bond or triple bond) will be reduced by
  $1$ equivalent of $\ce{H2(Pd)}$ ?

My guess is that the triple bond should react as it is more reactive but I'm not sure. Also does the answer depend on whether the double bond and triple bond are conjugated with each other or not?

Let us consider two examples (A) and (B):

(A)

(B)

Which bond will be reduced in case (A) and (B) ?