texts: Spin state change during crystallisation for [NiCl2(PPh3)2]

texts:
$\ce{NiCl2(PPh3)2}$ is a complex that is borderline between tetrahedral(high spin) and square planar(no unpaired electron, high splitting parameter) because $\ce{Cl-}$ is a weak field ligand and $\ce{PPh3}$ is a strong field ligand. Apparently, the tetrahedral and square planar states of the compound are interconvertible. The tetrahedral high spin state is blue, and produced directly by reacting hydrated nickel chloride and triphenylphosphine in alcohol. But when the complex is crystallised out from a cholrinated solvent like dicholoromethane, it converts to the red square planar complex.

Is there any theoretical explanation as to

1) Why the square planar form is favoured in the crystalline state?
2) What role does the chlorinated solvent play in isomerising the complex to its sq. planar form?

And are there any other examples like this?


texts:
What is the difference between an assay and an extemporaneous preparation?

Can an extemporaneous preparation be labelled as the BP mixture?


texts: Why does Gibbs free energy correspond solely to non-expansion work?

texts:
First of all: I know this question has been asked before (Why does the Gibbs free energy only correspond to non-expansion work?), and although I understand the mathematical derivation given there, I struggle with the concept.

If both $\Delta G$ is negative and the change in enthalpy is negative (exothermic), I don't see why we cannot use that heat to do mechanical work? So how is it that it only cooresponds to non-mechanical work?


texts: If losing electrons means getting oxidized, then does it mean that ALL metals are reducing agents, since they themselves get oxidized?

texts:
I was just going through my last year's school textbooks and while I was reading this chapter on Redox, this above question crossed my mind.
Shouldn't it be true that since ALL metals lose electrons to get stable, they should also get oxidized. And since they getting oxidized themselves, they should act as reducing agents... Always?
If the answer is no, please provide an example of the exception.


texts: Chemical elements or compounds with yellowish white color

texts: Are there chemical elements or compounds that have a yellowish white (cream) color in their natural state?


texts:
What mass of precipitate forms when a solution containing 6.24 g of potassium sulfide is reacted with a solution containing 19.2 g of barium nitrate?

I have already identified the limiting reagent $\left(\text{K}_2 \text{S}\right)$ as well as the mass of the precipitate.

My question, however, is: why is the Barium Sulfide formed in the product a solid and not aqueous? I thought the problem translated into the molecular equation: $$\text{K}_2 \text{S}_{\text{(aq)}} + {\text{Ba}(\text{NO}_3)_2}_{\text{(aq)}} \ce {->} 2{\text{KNO}_3}_{\text{(aq)}} + \text{BaS}_{\text{(aq)}}$$

But according to the answer key I was given, $\text{BaS}$ is a solid precipitate, not aqueous. How can that compound be a solid if, according to solubility rules, all sulfides plus an alkali earth metal are soluble? Shouldn't it be aqueous, not solid?

Please help, thanks :)


texts: Why is the increase in covalent radius from As to Bi not as big as from N to P?

texts:
The following is the radius of Group $15$ elements:
$$\begin{array}{c|c}  \hline
 \text{Element} & \text{Covalent Radius }(\pu{pm}) \\ \hline
\ce{N} &75 \\
\ce{P} &110 \\
\ce{As} &121 \\
\ce{Sb} &140 \\
\ce{Bi} &155 \\ \hline
\end{array}$$
Source:
General Properties and Reactions. (2020, August 15). Retrieved April 6, 2021, from https://chem.libretexts.org/@go/page/31730
From the above table it is clear that the increase in radius decreases as we go down the group.

My Attempt to Reason it
The electronic configurations of $\ce{N, P}$ and $\ce{As}$ are:

$\ce{N: [He]} \ \mathrm{2s^2 2p^3}$
$\ce{P: [Ne]} \ \mathrm{3s^2 3p^3}$
$\ce{As: [Ar]} \ \mathrm{4s^2 3d^10 4p^3}$

First let us compare $\ce{N}$ and $\ce{P}$
$\ce{P}$ has $\ce{8 e-}$s and $\ce{8 p+}$s more than $\ce{N}$. The $\ce{8 p+}$s increase the nuclear charge. But, due to the addition of $\ce{e-}$s, the shielding effect also increases i.e., there is more repulsions caused by the core $\ce{e-}$s.
Out of the $\ce{8 e-}$s, $3$ goes into $\mathrm{2p}$, $2$ goes into $\mathrm{3s}$ and $3$ goes into $\mathrm{3p}$. The shielding effect due to $\mathrm{s}$ and $\mathrm{p}$ is appreciable. As a result, the effective nuclear charge is not that high. But due to the addition of extra shell i.e., $3$, the size increases by almost $\pu{35 pm}$.
Now Let us compare $\ce{P}$ and $\ce{As}$
Now in $\ce{As}$, there are $18 \ce{e-}$s and $18 \ce{p+}$s more than that in $\ce{P}$. Out of the $18 \ce{e-}$s, $3$ goes into $\mathrm{3p}$, $2$ goes into $\mathrm{4s}$, $10$ goes into $\mathrm{3d}$ and $3$ goes into $\mathrm{4p}$.
In this case, majority of the $\ce{e-}$s  are in the $\mathrm{3d}$ orbital. The shielding effect due to $\mathrm{3d}$ is not much. In fact, the order of the ability of orbitals to shield is:
$$\mathrm{s} \gt \mathrm{p} \gt \mathrm{d} \gt \mathrm{f}$$
Due to this, the effective nuclear charge is more and therefore the size doesn't increase as much as it increase on going from $\ce{N}$ to $\ce{P}$.
Is my reasoning correct? If not, what is the reason behind this?


texts: Dioxin synthesis in a rocket stove riser?

texts:
I'm building a rocket stove for cooking with a wok at the top of the riser.  At the top of the riser I'm seeing temperatures of 500-700 deg C, and I believe at the bottom it's likely under 1000 deg C ( though others with optimised builds see temperatures closer to 1100 deg C ).  The firebox is comprised of firebricks with the roof and floor lined with ceramic fiber blanket, and the manifold, and riser are all lined with ceramic fibre blanket.

I gather that in the combustion of wood ( biofuels ) you can see de novo synthesis of dioxins and furans in two temperature windows 200-400 deg C, and 600-800 deg C with the latter being much less.

One sees more efficient combustion with the introduction of heated secondary air into the riser, but at these temperatures steel spalls and dies.  Steel pipes need to be replaced every year.

I have placed a copper pipe into the combustion chamber to provide secondary air and threaded it to the riser.  It didn't melt.

So, my question is, does copper help in catalysing the formation of dioxins ( catalytic stoves increase dioxin formation ) and does it matter at temperatures at the bottom of the riser since they should be destroyed?

Edit:

  Copper (Cu) is the most potent catalyst for dioxin formation, but Iron (Fe), Zinc (Zn), Potassium (K) and Sodium (Na) have also been found in multiple studies to be correlated with increased dioxin/furan formation. Some studies have also indicated that Manganese (Mn), Magnesium (Mg) and Nickel (Ni) may also serve as catalysts for dioxin formation. Studies have conflicted on whether Aluminum (Al) encourages or inhibits dioxin formation. One study below indicated that Silicon (Si) is negatively correlated with dioxin formation.

https://www.ejnet.org/dioxin/catalysts.html


texts: Why are there no dihedral mirror planes in the D3h point group?

texts: Consider the molecule $\ce{BH3}$, which belongs to the $D_\mathrm{3h}$ point group. Why are the three mirror planes in this point group labelled as $\sigma_\mathrm v$ instead of $\sigma_\mathrm d$? Don't they bisect the angles between a pair of rotational axis $C_{2}$ axes as shown in the diagram below?


texts: What can I use instead of AOT in the following protocol?

texts:
We want to nanoencapsulate our pesticide using the following protocol; but we don’t have AOT surfactant. So, what can I use instead of AOT in the following protocol?

  Sodium alginate solution in water was emulsified into dioctyl sodium sulfo-succinate (AOT) solution in methylene chloride by sonication for 1 min over ice bath. The primary emulsion was further emulsified into 150 mL of aqueous PVA solution by sonication for 1 min over ice bath to form a secondary water-in-oil-in-water emulsion. The emulsion was stirred using a magnetic stirrer, and 50 mL of aqueous calcium chloride solution was added gradually to the above emulsion. The emulsion was stirred further at ambient conditions for 18 h and then under vacuum for 1 h to evaporate methylene chloride.


texts: Acid-Base Reaction in MacGyver Episode "Countdown"

texts:
This question is about the old MacGyver show, Season 1, Episode 14, "Countdown." Could someone please explain how/why MacGyver neutralizes the acid in the bomb? He claims it is an electrolyte switch, and proceeds to neutralize it with oven cleaner and milk before draining it out.

wouldn't the milk act as a buffer?
wouldn't the neutralized solution also contain electrolytes?

Thanks!


texts: Why does the surface of an acid appear to have a stronger "dissolving power"?

texts:
In this Periodic Videos YouTube video by Brady Haran and the University of Nottingham, we see a piece of gold being dissolved in aqua regia, while Professor Poliakoff explains why aqua regia can dissolve gold even though its constituent acids can't.

The piece of gold was placed partway into the acid. I noticed that the acid appears to attack the gold the strongest at the liquid's surface, and the gold was first "dissolved through" along a line at the surface, leaving a little plate of undissolved gold dangling in the acid by one corner. You can see this best from about 4:10 to 4:30 into the video.

I was wondering if there's some effect at the surface of the liquid that causes this.

(I apologize if this is more physics than chemistry,  and also for my Google-fu not being enough to find ready answers.)


texts: How are molecular orbitals obtained in quantum chemistry?

texts:
When trying to solve for a molecule's molecular orbitals, we start off with the total molecular hamiltonian. However, given the difficulty of solving the Schrödinger Equation for this complicated hamiltonian we can introduce the Born-Oppenheimer approximation. By assuming that the nuclei of molecules are relatively fixed, our molecular hamiltonian can be reduced to the electronic hamiltonian. Then, we can use the electronic hamiltonian and solve for the electronic wavefunctions of our molecule.

This calculation for the wavefunctions is significantly easier. What is confusing to me is what the solution to the electronic Schrödinger equation represents.

Are these solutions considered the molecular orbitals?


texts: Naming terminal monosubstituted alkenes conformations

texts:
Alkenes can be described by E/Z nomenclature and cis/trans nomenclature.

However, is there a way to name alkene conformations which are monosubstituted? For example, how could one describe the difference between the following conformations?

Any suggestions are welcome, even if they aren't IUPAC accepted -- I would just like to hear what the community thinks would be a good way to differentiate these type of structures.


texts: Why does ATP has a lower entropy than ADP

texts:
I was confused about why ATP has a lower entropy than ADP when ATP has 1 more phosphate group. According to https://chem.libretexts.org/Textbook_Maps/Biological_Chemistry/Metabolism/ATP%2F%2FADP#Why_is_ATP_hydrolysis_an_exergonic_reaction.3F It states that

  The entropy, which is the level of disorder, of ADP is greater than that of ATP.  Therefore, due to thermodynamics, the reaction spontaneously occurs because it wants to be at a higher entropy level. Also, the Gibbs' free energy of ATP is higher than that of ADP. Naturally, molecules want to be at a lower energy state, so equilibrium is shifted towards ADP.

Can someone please explain to me why does ATP has a lower entropy than ADP?


texts: Suitable reagents for nitration of thiophene

texts:
I know that for nitration of benzene we can use concentrated nitric and sulfuric acid. As furan and pyrrole are less aromatic than benzene, they can be protonated more easily and undergo polymerisation. We can use $\ce{AcONO2}$ and $\ce{AcOH}$ instead.

Give the order of aromaticity: benzene > thiophene > pyrrole > furan, I'm not sure whether thiophene is suitable for use with concentrated nitric and sulfuric acid.


texts: Does aqueous ammonium fluoride solution release hydrogen fluoride vapors?

texts:
Can $\ce{HF}$ vapors be released from $\ce{NH4F}$ solution in water $(w(\ce{NH4F}) = 40\,\%)$ at room temperature?
I assume that dissolving $\ce{NH4F}$ in water produces small amount of $\ce{HF}.$


texts: For $\ce{HCl(aq) -> H^{+}(aq) + Cl^{-}(aq)}$, if $\ce{HCl}$ has a concentration of 1 molar then $\ce{H+}$ and $\ce{Cl-}$ also have 1 molar. But for $\ce{HF(aq) <=> H^{+}(aq) + F^{-}(aq)}$, if $\ce{HF}$ has a concentration of 1.5 molar, then why doesn't $\ce{H+}$ and $\ce{F-}$ have 1.5 molar as well?


texts: Halogens and the free energy of activation in a resonant benzene system

texts:
If we look at the right-hand-side table here: http://en.wikipedia.org/wiki/Hammett_equation, we notice something particular.  It appears that the free energy of activation (for example, measured in terms of the acidicity of a carboxyl group on a benzene ring), and with respect to substituents in the para- position on the benzene ring, increases as one moves down column 17 on the periodic table.

Why is this happening?  Shouldn't we expect the opposite to be true?  Consider that, as we travel down column 17 corresponding to the halogens, electronegativity decreases and the probability of resonance contributions via pi-bonding should increase.


texts: Is there air in the volume of crystallized sodium hydroxide?

texts:
I have a container of crystallized NaOH (98%) which has a volume of 500ml. Now, as per wikipedia, Sodium Hydroxide's density is 2.13g/cm3. This should give the weight of a 500ml container of NaOH at 1065g.

However, when measured, the crystalls weighed in at around 560g (minus the weight of the container). Is it because the NaOH is not in liquid or a homogenous crystal? Is the rest of the volume around the crystals air?


texts: Does the probability of fluorescence increase when energy of incident X-rays match the electron's binding energy?

texts:
When analyzing manganese-rich samples with X-ray powder diffraction, sample fluorescence becomes a significant effect.
Is this because the incident X-rays' energy - which, if Cu K$\alpha_1$, is approximately 8.048 keV - is getting close to the K$\alpha_1$ (approximate binding energy) of the inner-most electrons of Mn (5.899 keV)?

Sample fluorescence from Fe and Co is even stronger, which fits with the trend mentioned above. So, is this indeed a trend? If not, how do I generalize the increase in probability for sample fluorescence?


texts: Effect of inductive effect on boiling point,melting point and dipole movement

texts:
In my book the following was written:-

  Inductive effect is a permanent effect operating in the ground state of the organic molecules and hence is responsible for higher melting point, boiling point and dipole movement of polar compounds.

How is inductive effect responsible for higher melting point, boiling point and dipole movement of polar compounds?

Why is inductive effect responsible for higher melting point, boiling point and dipole movement of polar compounds only?


texts: Cyanide's Lewis structure - electronegativity or octet rule?

texts:
The formula for the cyanide ion is $\ce{CN-}$. That gives us a total of ten valence electrons to work with. There are two obvious ways to build the Lewis structure.

  $\ce{:^-C#N:}$

  $\ce{:C=N^-::}$

(I hope that was clear. I'm not sure how to make ASCII Lewis structures. In that second example, the nitrogen has two lone pairs.)

In the first example, each atom has a complete octet, but the carbon has a formal charge of -1. In the second example, the carbon atom does not have a complete octet, and the nitrogen (the more electronegative atom) has a formal charge of -1.

My understanding is that when formal charge cannot be avoided, negative formal charge should reside on the most electronegative atom.

Which rule takes precedence over the other? Using cyanide as an example, should I:

Follow the octet rule and go with the first example?
Follow the electronegativity rule and go with the second example?
Treat them as resonance structures?


texts: Mechanism for formation of amide by reaction of amine with ester

texts:
This is the mechanism given in my lecture handout:

I have a problem with the third species along. Surely the negatively charged oxygen would protonate before the other oxygen would. Also, why does this reaction work at all? The amine group is more basic than the "alcohol group" that must leave to form the amide so why wouldn't that protonate first and then just leave (i.e no reaction)?


texts: Dissolving of non polar gases in water (liquid)

texts:
How does dissolving happen for non polar gases in water? Is it like being in the space between the water molecules or does there occur some kind of interaction occur between gas molecules and water molecules?

Also if the gases dissolve in water, how can their solubility be increased? I have also heard what's called Henry's law accounted for this?

Answers on molecular scale would be more appreciated.


texts: In cellulose fibres, such as cotton or hemp, I've noticed different percentages of lignin and cellulose. How does this affect their tensile strength and toughness? Are there any other important factors? Thanks!


texts:
A question asks:

  This question refers to isolated gaseous atoms. In which atom are all electrons paired? Ba, Br, S or Si?

I thought it was Ba as its electron configuration is [Xe] 6s2.

However, the answer says Si, which seems incorrect to me.

Could someone please confirm the answer for me?

Thanks


texts: Balancing the chemical equation using Oxidation Number Method

texts:
Permanganate ion reacts with bromide ion in basic medium to give manganese dioxide and bromate ion. Write the balanced ionic equation for the reaction.

Please balance the equation using the oxidation number method. The skeletal ionic equation is:

$$\ce{MnO4-(aq) + Br-(aq) -> MnO2(s) + BrO3-(aq)}$$

This question is asked in Problem 8.9, NCERT Textbook Class XI, Pg. no. 267. My answer to this question is different from the answer given in the book. I'd love to know the correct answer to this question.


texts: Absolute configuration in stereochemistry: R/S nomenclature

texts:
I have all the rules of Fischer projections figured out.

But, when the problem asks for finding the configuration of a molecule with 1 chiral carbon and in a Fischer projection form, do we need first to make the manovrations that are allowed ( like fliping 180 degrees, or changing the places of 2-2 substituents )  or do we directly find the priorities ?


texts:
Why is cyclopentadiene more reactive than 9-anthracenemethanol when acting as a diene?

Both molecules are locked in an s-cis conformation, which is favourable. I'm thinking that it's due to the extensive conjugation in 9-anthracenemethanol?


texts: Is there a relation between polarity of molecules and their electric susceptibility?

texts:
So it is written in our text that electric susceptibility ($χe$) (the response of say water molecules in the presence of an external electric field) is related to the molecular behaviour of various substances, but it doesnt explore it, and says its out of scope for me. When I tried to find the related equations, I could not find a clear answer.
To be more clear,
We know that the capacitance of a parallel plate capacitor increases when  water(k, dielectric constant = 80) is inserted as a dielectric as opposed to oil (k = 2.2), or any other non-polar substances (with small values of k). Now my question is, whether the dielectric constant (related to electric susceptibility as $k=χe + 1$) depends on the polarisation of the molecule.
Also, given $$P = χe. E$$ where P is the dipole moment per unit volume, called polarisation of the linear isotropic dielectric.
Can I tell someone that the reason Dielectric constant of water (80) is so much higher than oil (2.2) is because water is polar and oil is non polar. If so, what equation should I quote as proof to this statement?
To me it seems empirically true, but I would like to see if the theory supports the fact that polar molecules have a higher electric susceptibility as compared to non polar ones.


texts: If benzene is more stable than cyclohexane then why is the heat of hydrogenation of benzene negative, ie heat is released during the formation of cyclohexane from benzene ?


texts: Can a chemical reaction have two balanced equations?

texts:
I was recently studying Xenon compounds and read this reaction:

$$\ce{6XeF4 + 12H2O -> 4Xe + 2XeO3 +  24HF + 3O2}$$

However this reaction can also be written as the following:

$$\ce{4XeF4 + 8H2O → 2Xe + 2XeO3 +  16HF + O2}$$

Now both of these are valid but wouldn't that create problems, like in quantitative analysis or in kinetics of the reaction?


texts: GC-MS unexpected peaks during 1-octanol quantification

texts:
Note: This experiment was performed as part of a teaching lab experiment which has concluded, so I would not be able to alter any experimental conditions. I was also unable to modify any of the variables used in the GC-MS experiment itself, but I may be able to provide these upon request.

I would like help in the interpretation of this spectrum from experienced chromatographers, I expect more information to be required other than the spectra provided, but due to my inexperience I am uncertain what they might be. Please do point them out in the comments if necessary.

This is a spectrogram plot performed in Mathematica of the relevant data for octanol quantification (octanol normally elutes at approximately 5.8-5.9 minutes, and did so in the positive control samples.)

The GC-MS machine was not used by any other group during the 2 days, and the only samples run on it during the 2 days were either ddH2O (with or without octanol) or sterile filtered cultures of E. coli in M9 growth media+glucose (with or without octanol).

All images are thumbnailed, click on the link to open a full resolution image.

Representative samples taken on Wednesday, consistent high levels of tailing. All samples are in ddH2O.

ddH2O

25mg/L octanol

100mg/L octanol

Samples taken on Friday, varying amount of tailing

ddH2O

Blank growth media

100mg/L octanol in ddH2O, not tailed

50mg/L octanol spiked into growth media

100mg/L octanol in ddH2O, tailed

The noise present (at m/z 59 and 78) seemed inconsistent with the column (100% DMPS) nor any of the alternatives present on a list of possible column bleed spectra.

Octanol's solubility seems to be 2300mg/L as seen here, and I don't find it very likely that the low solubility of octanol in ddH2O resulted in the tailing.

What could have caused the noise at m/z 59 and 78, and why was the tailing so different despite near-identical experimental conditions?


texts: Amber paramfit "monomer (or ligand)" problem

texts:
I am trying to parameterize a novel molecule which has atoms not included gaff or parm force field. I finished parameterizing vdw-bond and angle force field. Also I did PES Scan for dihedrals and I wrote them in a frcmod file as truncated fourrier integral. Yes, actually most probably I will not need paramfit parameterization but I wondered and I tested paramfit.

Here is tutorial:
http://ambermd.org/tutorials/advanced/tutorial23/index.html#Introduction

I succesfully finished this tutorial and after this I tried to apply paramfit to my "monomer" and "not included any force field" molecule. But xleap gives some error message and I locked completely.
I changed gen_conformers.sh (Don't click if you don't want to download!) for my molecule and I couldn't obtain different conformations.

Then I tested where was the mistake. I created leapin file like this:

source oldff/leaprc.ff99
addAtomTypes { { "B" "B" "sp3" } }
addAtomTypes { { "O" "O" "sp3" } }
addAtomTypes { { "C" "C" "sp3" } }
a=loadmol2 bor.mol2
loadamberparams bor.dat
impose a {1 1}, { {"H1" "O2" "B3" "O4" 72.000} }
impose a {1 1}, { {"O12" "B3" "O4" "C5" 19.000} }
impose a {1 1}, { {"B3" "O4" "C5" "C6" 108.000} }
impose a {1 1}, { {"B3" "O12" "C13" "H18" 11.000} }
saveamberparm a a_1.prmtop a_1.mdcrd
check a
quit

then I run this file with this command:

xleap -f leapin

but after that leap.log file:

  Checking Unit.
Building topology.
Building atom parameters.
Building bond parameters.
Building angle parameters.
Building proper torsion parameters.
Building improper torsion parameters.
 ** Warning: No sp2 improper torsion term for  C-H-C-H
        atoms are: C2 H5 C1 H6
 ** Warning: No sp2 improper torsion term for  C-H-C-H
        atoms are: C1 H2 C2 H3
 ** Warning: No sp2 improper torsion term for  C-H-C-H
        atoms are: C1 H2 C2 H4
 ** Warning: No sp2 improper torsion term for  C-H-C-H
        atoms are: C1 H3 C2 H4
 ** Warning: No sp2 improper torsion term for  H-H-C-H
        atoms are: H2 H3 C2 H4
 ** Warning: No sp2 improper torsion term for  C-H-C-H
        atoms are: C4 H10 C3 H11
 ** Warning: No sp2 improper torsion term for  C-H-C-H
        atoms are: C3 H7 C4 H8
 ** Warning: No sp2 improper torsion term for  C-H-C-H
        atoms are: C3 H7 C4 H9
 ** Warning: No sp2 improper torsion term for  C-H-C-H
        atoms are: C3 H8 C4 H9
 ** Warning: No sp2 improper torsion term for  H-H-C-H
        atoms are: H7 H8 C4 H9
 total 7 improper torsions applied

and after that, even if I changed angles many many times in "impose" command

 impose a {1 1}, { {"B3" "O4" "C5" "C6" 108.000} }

I obtained the same *.inpcrd files and I couldn't generate different conformation gaussian job file.
So how can I apply paramfit for a ligand? (or monomer)


texts:
What will methyl (2-oxocyclohexyl)acetate produce when reacted with sodium borohydride?

I feel the answer should be 2-(2-hydroxypropyl)cyclohexan-1-one:

Because the carbonyl carbon on the aliphatic chain should be more electrophilic than the one on the ring due to the presence of two neighbouring electronegative oxygen atoms. Correct me if I am wrong but I think the reaction begins with the hydride ion which acts as a nucleophile?

On the other hand the answer given in my book is 1-(2-hydroxycyclohexyl)propan-2-one:

Can someone please help me out here?


texts: How do you calculate molar specific heat?

texts: I know how to calculate the specific heat, but not molar specific heat. What is molar specific heat and how do you calculate it?


texts:
Why do cations violate Baldwin's rules?

For example, the following acetalization mechanism is plausible even though it contains a 5-endo-trig step:

Image taken from: Clayden, J. Organic Chemistry; Oxford University Press: Oxford, 2013


texts: Calculating the entropy of vaporization at temperatures other than the normal boiling point

texts:
I would appreciate if someone could explain why this is so:
To find the entropy of transition at another temperature, we have to break the calculation down into three steps . For example, to find the entropy of vaporization of water at 25  C and 1 bar, imagine that we
1. heat the liquid to its normal boiling point, 100 C
2. allow it to vaporize,
3. then cool the vapor back to 25  C

Why do you do these three processes? I don't understand why this would give you the entropy of transition at another temperature...


texts: How do chemists verify certain phenomena like 1,2-hydride shifts, 1,2-methyl shifts and ring expansions?

texts:
I've been learning about organic chemistry independently on a ship without an instructor or university resources like a lab setting for the past year. I was wondering how do chemists verify that their mechanisms are correct?

For example, take 3-methylbutene and add the reagent HCl. From the 1,2-hydride shift we get 3-chloro-3-methylbutane. For a 1,2-methyl shift take 3,3-dimethylbutene with the same reagent HCl. We know that from the mechanism we get 2-chloro-2,3-dimethylbutane. But how do you verify that these are the major products?


texts: I need to identify the peaks in this boron mass spectrum

texts: As part of a bigger project we were given this image. Its a mass spectrum produced in an accelerator with a Boron cathode. It was implanted in diamond. I assume the first peak is just $B^-$ but I have no clue what the rest is. Any help would be appreciated


texts: Mechanism for an Étard reaction (chromium complex)

texts:
In the following reaction, a chromium complex is formed during the Étard reaction:

I have the following questions:

How is this complex formed?
How does its hydrolysis take place? (What's the mechanism?)

Wikipedia gives a different mechanism for the same reaction. I am in doubt which is correct?

@Jan is this the correct mechanism?


texts: The hydrogen ion in acidified potassium manganate (VII)

texts:
Recently, I am playing with redox reaction and I come over a compound acidified potassium manganate (VII) ($\ce{KMnO4/H^+}$). I get confused that why they put $\ce{H^+}$ beside $\ce{KMnO4}$. Doesn't the hydrogen ions flow freely in the solution or something else.

And so, when we are writing a chemical reaction with occur $\ce{KMnO4}$, we sometimes exclude the $\ce{H^+}$. Why that so?


texts: How could click reaction take place at low concentration?

texts:
I have DBCO-functionalized resin, and the DBCO group is validated with FAM-azide.

But I cannot use this resin to react with FAM-Azide-labled primer, which has very low concentration (20 μM, it is already very concentrate at DNA-scale).

I think that might be caused by concentration, because the reaction between DBCO-resin and FAM-azide is also not significant at such low concentration.

I have already tried long reaction time and higher temperature.
How could I get this work?


texts: What are these "certain chemical compounds" denser than osmium?

texts:
The Wikipedia entry for density states

  Osmium and iridium are the densest known elements at standard
  conditions for temperature and pressure but certain chemical compounds
  may be denser.

I have not been able to turn up what these chemical compounds are.  I can imagine a salt or some molecule in which dense atoms (e.g. of mercury) are packed in a conformation such that these atoms are held closer together than in the pure metal, so giving the molecule a higher density than the pure metal or of higher molecular weight metals like osmium.

I know there are elements with higher molecular weight than osmium and I have read about superdense exotic states of matter.  I am curious about this chemical (presumably comprised of atoms with lower MW that osmium) which is more dense than osmium - presumably at earthly temperatures and pressures.  Or an osmium-containing molecule more dense than metallic osmium would qualify.

If someone can answer this question he or she might also consider editing the Wikipedia article to clarify.


texts: Calculating the heat of formation of propane given its enthalpy of combustion

texts:
Given the equation $\ce{C3H8 + 5O2 -> 3CO2 + 4H2O}$ and that enthalpies of formation for $\ce{H2O (l)}$ is $\pu{-285.3 kJ/mol}$ and $\ce{CO2 (g)}$ is $\pu{-393.5 kJ/mol}$, and the enthalpy of combustion for the reaction is $\pu{-2220.1 kJ/mol}$, I need to find the heat of formation of propane.

My initial idea was to use Hess's law, and I got
$[3(-393.5) + 4(-285.3)] - [-2220.1] = \pu{-101.6 kJ}$

I then doubted myself because Hess's law gives the $\Delta H^o_\text{rxn}$ which is different from the $\Delta H^o_\mathrm{f}$ for  $\ce{C3H8}$ that we are trying to find.

So I used another approach using the individual equations for the formation of $\ce{H2O, CO2}$, and $\ce{C3H8 + 5H2O -> 3CO2 + 4H2O}$ and combining the equations to get the equation for the formation of $\ce{C3H8}$ (which is $\ce{3C + 4H2 -> C3H8}$). After manipulating the equations, I got $+2220.1 - 1141.2 - 1180.5 = \pu{-101.6 kJ}$.

I got the same answer, and I want to understand why Hess's law still works even though the equation I used in Hess's law had nothing to do with the formation of $\pu{1 mol}$ of $\ce{C3H8}$. I understand my second method, but why does the first method work?


texts: Cooling Curves differences between Solution and Pure Solvent

texts: To put it short, why is the cooling curve for a solution slanted during the phase change? The pure solvent plateaus at a fixed temperature, but for a solution, the phase change occurs over a range of temperatures. What explains this phenomenon?


texts: How to find the molar mass of an iron compound based on its mass and mole fraction in the compound?

texts:
I'm trying to solve this question:

  We have a molecule composed of $3$ iron atoms, and $4$ atoms of another element. We are given the following information: it has $\pu{2.36 g}$ of iron for $\pu{3.26 g}$ of molecule.

I want to find the molar mass of the compound, I have tried so far:
$$ m = \pu{3.26 g} = \pu{0.00326 kg}$$
Since it has $3$ atoms of $\ce{Fe}$ and $4$ atoms of an unknown substance, therefore:
$$3 + 4 = 7~\text{atoms},\\
  \pu{1 mol} = \pu{6.022* 10^23 atoms}\\
\frac{7}{\pu{6.022* 10^23}} = \pu{1.16 * 10^-23}$$

As we know: $M = m / n,$ I tried to divide $0.00326$  by $\pu{1.16 * 10^-23}$ and I obtained $\pu{2.79429 * 10^19}$, but the correct answer is $\pu{231.43 g/mol}$.

What I have done wrong?


texts: Fehling's solution turning yellow and then black?

texts:
While testing for formaldehyde (an aldehyde), I added Fehling's solution to the sample and let the test tube simmer in a water bath for some time. I returned ~15 minutes later to see a black/dark grey precipitate awaiting me, which looked very metallic (Almost like Tollen's test, but darker)

I try again and this time heat the tube for only five minutes: I obtain a buff yellow coloured precipitate which, on standing, gives me the same metallic precipitate I observed earlier.

I expected that Fehling's solution will give a red precipitate of $\ce{Cu2O}$ but it looks like the formaldehyde seems to be oxidizing it all the way down to metallic copper. Also, what is the reason for a yellow precipitate to form rather than a red one?

I could not take any pictures: We're not allowed to carry phones/cameras into the lab.


texts: What is the peak at 3200 cm⁻¹ in the IR spectrum of Benzocaine?

texts:
Benzocaine has the following IR spectrum:

and here is it's structure:

From what I understand:
The two leftmost peaks are the antisymmetrical and symmetrical stretchs of the amine group.
Just before the fingerprint region at about 1690 is the carbonyl ester peak and to the right of it (also before the fingerprint region) is the benzene C-C bonding peaks.
The messy broad peaks just before 3000 are the C-H bonds of the non aryl C.
The tiny peak at ~3040 is probably the aryl C-H bonds.

However I can't assign the peak at ~3200. It could be water of crystillisation in the sample (anywhere from 3100-3600cm^1) but surely there wouldn't be any in a proffesional sample? I also considered whether it could be due to -NH3^+ but the sample is made in a procedure that ensures the solution is alkaline before final purification...

Please could someone point me to a resource that will allow me to assign this peak or explain what it is to me?


texts: Relationship between magnitudes of forward and reverse kinetic rate constants

texts:
Consider the reversible unimolecular reaction:

$$\ce{A <=>[k_1][k_2] B}$$

We know that the forward reaction is often considerably more thermodynamically favourable than the reverse reaction, and therefore the relationship $k_1 \gg k_2$ holds between the rate constants. The rate constants are in the same units, and so it is possible to write this relationship. A similar example would be a reaction that is bimolecular on both sides, $\ce{A + B <=> C + D}$, etc.

However, consider this reversible reaction:

$$\ce{A + B <=>[k_1][k_2] C}$$

Assume the reaction proceeds at rate $k_1 [\ce{A}][\ce{B}]$ in the forward direction and $k_2 [\ce{C}]$ in reverse. If the overall reaction rate has units $M s^{-1}$, then $k_1$ necessarily has units $M^{-1} s^{-1}$ and $k_2$ has units $s^{-1}$.

My question is: For this second case, we can no longer impose that $k_1 \gg k_2$, due to difference in units, but can we say anything about their relationship? Does setting $k_1$ to some value constrain the choice of $k_2$ in any way?


texts:
My instructor pointed out that furfural undergoes haloform reaction - I don't understand how. I couldn't figure out the mechanism on my own, and couldn't find much online either. (regarding the products, or the mechanism) Could someone please help me out?

As far as I know, only methyl ketones and alcohols  oxidisable to the same undergo haloform reaction - so something unexpected must be happening here.

It'd be great if you could provide a detailed mechanism and explanation, and if possible provide sources.


texts: At what temperature does a polyester release toxic gases?

texts:
I've bought a "Shrinky Dinks" printable sheets and now I'm feeling unsure about using it since I've read that heating polyester materials may be very harmful for health, and the final purpose of this material is to melt it at about 325°F.

Searching on the web I've noticed that the information isn't that straight forward about the product even in the official website, where they do mention about having specific certifications, but I cannot understand them fully since I'm not used to all the technical language they use.

So that's the reason why my question is about the temperature I can safely heat this material at.

Thank you for reading my question.


texts: How to calculate the volume of dry hydrogen in magnesium/ HCl reaction

texts:
I am not sure if the equivalents of $\ce{H2}$ in the equation
$$\ce{Mg (s) + 2HCl (aq) -> MgCl2 (aq) + H2}$$
is that of dry or wet hydrogen.

If the $\ce{H2}$ refers to wet hydrogen in the equation, how should I find the volume of dry hydrogen given the pressure of wet and dry hydrogen and the volume of wet hydrogen?


texts: Factors affecting hardness of water - EDTA titration

texts:
I am thinking of doing a project involving EDTA complexometric titration to determine the hardness of the water. I am not sure if the pH will affect the hardness of the water. If it did, I would control it by changing the buffer solution's pH. If buffer pH does not affect the hardness of the water, are there any other factors that I could potentially explore.

Thanks


texts: Chemical that won't freeze below melting point

texts:
I have an organic chemical (can't say due to an NDA) that has a nominal melting point of 28 °C. When I raise it above this temperature, it melts, but then it will stay a liquid indefinitely at lab temperature (≈22°C), and in the fridge (4 °C) for at least a week. When put in the freezer (-20 °C), it will freeze, and then stay a solid at lab temperature indefinitely.

Is there an explanation for this phenomenon? I'm assuming this may have something to do with the kinetics of the crystallization, but I've never seen something with this level of hysteresis.


texts:
If 3 L of 1 M NaOH solution is prepared by mixing properties of stock solutions of $x$ L of 2.5 M NaOH and $y$ L of 0.4 M NaOH and no water is to be used, find $x : y$.

My attempt:

$$3 = 2.5x + 0.4y$$

Now I am stuck how to calculate $x:y$.


texts: Which is the most stable out of the following linked cyclohexadienes?

texts:
I am unable to find the answer to this question. I was guessing it should be (2) due to symmetry but my book says it is (3) without any explanation.

I know that stability is determined by how low the energy of formation is. Does this have something to do with the different sorts of dienes that are present? Like, one type of diene would have less energy than another?

If nothing else, it would be helpful if someone could indicate the names of these compounds, because I don't even have the faintest idea where to start searching for more information.


texts:
Does DIBAL-H reduce alcohol? I was reading an article by Rentsch and Kalesse [1] and I came across this reaction, but could not figure out how the final compound is formed:

Reference

Rentsch, A.; Kalesse, M. The Total Synthesis of Corallopyronin A and Myxopyronin B. Angew. Chem. Int. Ed. 2012, 51 (45), 11381–11384. DOI: 10.1002/anie.201206560.


texts: How can one optimise the formation of copper acetate?

texts:
Mixing solid copper, $5\%$ vinegar, and hydrogen peroxide ($\ce{H2O2}$) causes copper acetate to form. The process will occur very slowly without hydrogen peroxide. Adding $\ce{H2O2}$ speeds the formation of copper acetate.

How can I test the solution to see if all of the acetic acid has been converted into copper acetate?

If possible, provide answers that employ only household items or readily available devices.


texts: Is it possible to make liquid nitrogen with a bottle of CO2 gas and a freezer?

texts:
I really want to make liquid nitrogen(or oxygen) without using dry ice, a specially made freezer, or other chemicals.

I have a mixture of some sponges, rotten grass, sugar and water, which makes pressure in the bottle(produces $\ce{CO2}$). Which temperatures can I expect if I freeze it and then quickly opens the bottle after 24 hours of freezing. Is it possible to make liquid nitrogen out of it?


texts:
I wanted to know how Tollen's test is given by tartaric acid. Google searches say that it belongs to some "Hydroxyl" group. I know that it oxidises aliphatic and aromatic aldehydes along with α-hydroxy ketones and some other compounds such as alkynes and it's mechanism.
Can someone help me out in the mechanism of oxidation or provide some more detail on this reaction?


texts: How is the acetoxy group ortho/para-directing in electrophilic aromatic substitution?

texts:
Why is the $\ce{-OAc}$ group o,p-directing in electrophilic aromatic substitution?

How can I compare the activating effect of $\ce{-OAc}$ with $\ce{-OH}$ and $\ce{O-}$? Is it to do with the number of lone pairs on oxygen?


texts: Clearly the amide will be unreactive given the poor quality of the leaving group and poor electrophilcity due to delocalization. However, does it react with organolithiums for example?


texts: USNCO question - Finding pH of salt solution from pKa of its parent acid

texts:
The question from 2017 USNCO is as below:

What is the $\mathrm{pH}$ of a $\pu{0.25 M}$ solution of $\ce{NaCN}$? (The $\mathrm{p}K_\mathrm{a}$ of $\ce{HCN}$ is $9.21$.)
(A) $4.91$
(B) $8.61$
(C) $11.30$
(D) $13.40$

The answer sheet states (C).
My understandings/reasoning:

salt hydrolysis: solution of salt derived from strong base and weak acid is basic;
$\ce{NaCN}$ is derived from the base $\ce{NaOH}$ (strong) and acid $\ce{HCN}$ (weak according to given $\mathrm{p}K_\mathrm{a}$);
Solution is basic, so (A) is incorrect.

However, I am unable to proceed from here.


texts: How to conveniently separate Cd impurities from ZnO without contaminating it?

texts:
How could I separate Cd impurities from ZnO without contaminating it and without using overly expensive equipment or extremely dangerous solvents?

I don't want to contaminate it by introducing other heavy metals or being left with more than trace levels of undesired solvents.

I'd be fine losing some amount (say max 10-20%) of my ZnO in the process, if necessary.

Please ask me for any further clarity I could bring to this question.

I know nothing about this so I'd be happy with any contributions on how to easily separate any reasonable portion of $\ce{Cd}$ salts from $\ce{ZnO}$ in general (precipitating it out or solving it away from $\ce{ZnO}$ for instance). Cycling the zinc through a series of reaction and then back to ZnO would be fine also (if not leaving trace levels of anything biologically harmful).


texts: Does hydrogen really have seven isotopes?

texts: I know that there are 3 isotopes of Hydrogen. But according to this website it is showing 7 http://periodictable.com/Properties/A/KnownIsotopes.htmlWebsite


texts: I'm a 3D printing hobbyist and a few months ago I bought some Ethyl Acetate after learning online that it might have a similar effect on PLA as acetone has on ABS. From the tests I made, I was either sold a bad batch or the reaction speed is next to 0 thus making the ethyl acetate useless to smooth out PLA. I have thus placed it in a drawer to test it more at a later time. The liquid was kept inside its original plastic bottle that was then placed inside a glass jar to ensure that none of the vapors got out. Today I opened the drawer again to have a look at it and I noticed a very strong odor consistent with that of the ethyl acetate. Also the label on the plastic bottle separated as if the glue has been dissolved away. As ethyl acetate is highly inflammable I'd like to ask what would be a correct way to store it without leaking the vapors.


texts: What is the mechanism for this nucleophilic conjugate addition?

texts:
What is the mechanism for this reaction-

My working so far:

But my final product doesn't match with the one given. Where did I go wrong (if at all)? How should I have proceeded?


texts:
I am conducting a school-based research project to determine the concentration of EGCG.
One of the problems I am facing is that most of the procedures I find on the internet are of a university research lab level, which isn't feasible for me. Interestingly however, I found a suitable procedure for titration of red wine.
Is there a similar method I could use to determine the concentration of EGCG


texts: POMs catalysis of benzyl alcohol oxidation, why Ni is the best cation with POM for that catalysis?

texts:
Why is nickel the optimal cation for benzyl alcohol oxidation with POMs and hydrogen peroxide?

In this article (Chinese Journal of Chemistry, Volume 30, Issue 2, 2012), they came to a conclusion that Ni gives better conversion then the other metals (Zn, Co, Mn, Cu, Fe) when they used it with Keggin type POM $\ce{Ni3(PW12O40)2}$. See the next note about the active structure:

How would you prove that Nickel is the best?


texts: How can we get the pure mass of an unclean metal?

texts:
So I'm facing a small chemistry problem that I can't find a way to solve. I'm not looking for answers, I'm just looking for how can I approach this problem.

The problem is as follows :

  We put 5 g of non-pure zinc (with some impurities) into a 200 ml solution containing hydronium ions. At the end, we get some gases and we are left with 0.05 mol of hydronium ions in the solution.

  Find the pure mass of zinc in that non-pure 5 g of zinc.

I really don't have any idea how to approach this problem. I have written and balanced the chemical equation:

$$\ce{Zn + 2H^+ = Zn^{2+} + H2}$$

I've arrived at the above equation from redox half-reactions. From here I don't know where to go.

Generally I would use the degree of purity formula:

$$P = \frac{C\cdot M}{10\cdot d}$$

where $P$ is degree of purity, $C$ is concentration, $M$ is the molar mass, and $d$ is the density, but this one is used for gases and liquids only. Besides, we've never studied how to compute the density of a metal.


texts:
According to me , the $\ce{Cl—Se—Cl}$ bond angle should be greater than $\ce{Cl —Se—O}$
bond angle because since oxygen is more electronegative than $\ce{Cl}$ , the orbital directed towards $\ce{O}$ will have more p character hence, the bond angle should be less than $\ce{Cl—Se—Cl}$ bond angle.

But in my book its written that the $\ce{Cl—Se—O}$ bond angle is greater. Why?


texts: Epsom salts - heavy metal contamination myth?

texts:
This recipe for home-made handwash (liquid soap) consists of bar soap, water, Epsom salts, and coconut oil.

The author specifically warns against using 'artificial' Epsom salts, preferring the naturally occurring type, because the 'artificial' type is supposedly contaminated by heavy metals incl. arsenic.

  Note – Be sure to get natural salts as some are man made and a full of
  unwanted chemicals. A lot of Epsom salts are made from synthetic
  materials, they are manufactured in factories from neutralized
  Sulfuric Acid, which is very high in heavy metals and arsenic. The
  REAL Epsom salt is naturally occurring mineral deposit in spring.

According to Wikipedia, Epsom salts are made by reacting sulfuric acid with magnesium oxide or magnesium carbonate.

I find it difficult to believe that 'artificial' Epsom salts would have appreciable amounts of heavy metal contamination, as neither sulfuric acid nor magnesium oxide are known to be frequently contaminated with heavy metals. A quick search on Google Scholar gives no results on the topic of heavy metal contamination in Epsom salts.

The only way I am aware that heavy metals might enter the process is if the sulfuric acid was produced from smelter stack gases, which do have appreciable heavy metal content. This is done at Mount Isa Mines, where $\ce{SO2}$ from the copper smelter stack gas is scrubbed out to make sulfuric acid, but the entire output of this plant goes straight to fertilizer production.

Is the above claim about heavy metal contamination of Epsom salts credible, or just an urban myth?


texts: Why are Tyrosine and Tryptophan considered hydrophobic?

texts: Since Tyrosine and Tryptophan are amino acids, their polarity is determined on their side chains or R groups. If their R groups are polar, the amino acid is polar. Both Tyrosine and Tryptophan are listed as non-polar molecules. However, Tryptophan has nitrogen in its side chain and Tyrosine has oxygen, both of which have a high electronegativity compared to the carbon that makes up the bulk of both molecules, which is something commonly seen in polar amino acids like Serine, which has oxygen in its side chain. This should mean that Tyrosine and Tryptophan are polar, so why are they non-polar, even with an electronegative atom in their side chains?


texts: On the detection of molecules in electrospray ionisation (ESI)

texts: Of the ESI spectra that I have encountered, positive & negative mode, the detected species always have charge (positive or negative) corresponding to the charge mode that the machine is in. Is it therefore the case that the ESI detector can only detect charged species, or that the overwhelming majority of species are charged?


texts: Understanding Standard Hydrogen Electrode

texts:
I came across a question today.

A galvanic cell is composed of two hydrogen electrodes, one of which is a standard one. In which of the following solutions should the other electrode be immersed to get maximum e.m.f. ($K_a=10^{-5}$ for acetic acid and $k_a=10^{-3}$ for phosphoric acid)
(A) $0.1$ $M$ $\ce{HCl}$
(B) $0.1$ $M$ $\ce{CH3COOH}$
(C) $0.1$ $M$ $\ce{H3PO3}$
(D) $0.1$ $M$ $\ce{H2SO4}$

I thought "Well, seems like all I need to do is find which solution will give the most number of hydrogen ions because its hydrogen ions which will suck those electrons from the other half cell which will be the cause of current. And concentration is same for all. So there is no chance for a weak acid. So option (B) cannot be correct. All other seems like a strong acid. So it should be $\ce{H2SO4}$ as it gives $0.2$ $M$ of hydrogen ions for $0.1$ $M$."
But my thought was absolutely wrong. Why?


texts: fuel with the narrowest boiling temperature?

texts: What commercially available fuel, such as kerosene or diesel, has the least variation in different hydrocarbon chains and thus the most uniform boiling point? I ask this because I'm searching for a fuel to use in a rocket engine, but unrefined fuels such as regular petroleum, which have a lot of variation in its constituents, will start to coke the engine plumbing when exposed to high temperatures. I understand that most commercially available fuels will do this, but are there any fuels which at the very least minimize this.


texts:
Which one of the processes is NOT spontaneous?

  \begin{align}
\ce{Ni + Sn^2+ &-> Ni^2+ + Sn} \label{1} \tag{1} \\
\ce{Cu + Fe^2+ &-> Cu^2+ + Fe} \label{2} \tag{2} \\
\ce{Ni + 2Ag+ &-> Ni^2+ + 2Ag} \label{3} \tag{3}
\end{align}

I failed this class last semester so I'm redoing the tests to see if I can get this over with, however I'm confused with this question. To find out if a process is spontaneous I need to identify the oxidizing and reduction agents.

\eqref{1} $\ce{Ni}$ is the reduction agent and $\ce{Sn^2+}$ is the oxidizing agent;
 \eqref{2} $\ce{Cu}$ is the reduction agent and $\ce{Fe^2+}$ is the oxidizing agent;
 \eqref{3} $\ce{Ni}$ is the reduction agent and $\ce{Ag+}$ is the oxidizing agent.

For a redox reaction to be spontaneous the reduction potential of the oxidizing agent needs to be higher than the reduction potentials of the reduction agent, therefore \eqref{1} and \eqref{3} are not spontaneous, but only one of the reactions can be not spontaneous. Where did I go wrong?


texts:
I read a paper about enzyme-catalysed synthesis of octanamide.

What is octanamide used for?


texts: Does a change in oxidation number in a redox reaction mean that an actual electron transfer occured?

texts: Oxidation numbers are fictitious charges that pretend the entire molecule is an ion i.e. it artificially localizes electrons onto atoms within a single molecule. In a redox reaction, we find that an oxidation state of one molecule changes compared to a different molecule. Does this mean an actual electron was transferred given that oxidation numbers are fictitious? I'm trying to rationalize this, my guess is that the answer is yes because oxidation numbers are a formal way to localize electrons within a molecule, but differences in oxidation number across molecules only happen with physical electron jumps.


texts: Why do many hypervalant chemicals have non-constant bond angles?

texts:
According to the VSEPR model, when a molecule in formed in the shape of $\ce{AB_{x}}$,

like $\ce{IF7}$, $\ce{SCl6}$, and $\ce{PCl5}$,

its structure is found by reducing the repulsions between peripheral atoms. This gives rise to many shapes, most of which have constant bond angles. Examples of those with constant bond angles include

$\ce{CH4}$ with 109.5° bond angles
$\ce{CO2}$ with 180° bond angles.

My question is then, why do some have non-constant bond angles?
The following do not

$\ce{IF7}$ with 72° and 90° bond angles
$\ce{PCl5}$ with 120° and 90° bond angles.


texts:
The Avogadro project suggests that we redefine the Avogadro constant to be equal to our best known estimate, $N_\mathrm{A} = 6.02214179 \times 10^{23}$, and redefine the kilogram based on the Avogadro constant.
What happens if we define the Avogadro constant to be exactly $6 \times 10^{23}$ and reassign atomic weights correspondingly?
Would any unforeseen complications arise from here?
Example:
Under current definitions, $N_\mathrm{A}$ atoms of carbon-12 weigh 12 g. If we redefine the constant to have the value $N_\mathrm{A}^\prime = 6.0\times 10^{23}$, then $N_\mathrm{A}^\prime$ atoms of carbon-12 would weigh $\pu{11.955879 g}$, which we would have to assign as the new atomic mass of carbon-12.


texts: What is a better laboratory set up for dehydration of ethanol to form ethene?

texts:
as shown in the question, I will have to design a lab on dehydrating ethanol to form ethene. The current method I am using is by heating up ethanol and sulfuric acid with a hot plate under a water bath and collecting ethene by water displacement method. But I wonder how I can improve this method, without changing the chemicals involved.
And I also want to find out how to identify the formation of double bond to test ethene is formed. I used potassium permanganate but because the ethene is a gas, I am not sure if there are other methods of testing it without having the gas escaping.
Thank you in advance.


texts: What is the mechanism of alkane combustion?

texts:
I understand that combustion of hydrocarbons (such as alkanes) produces energy by breaking bonds:

$$\ce{C_nH_{2n} + $\frac{3n}{2}$ O2 -> nCO2 + n H2O}$$

And I can find dozens of explanations of how combustion works in an engine.

What does the chemical reaction (not equation) of hydrocarbon polymer combustion actually look like?

In other words, how is a hydrocarbon polymer actually broken down to form energy?

What process actually breaks up the polymer into its respective monomers (methane?) for combustion to take place?

Please explain. I would also love a visual (like this or this ) if someone could find one!


texts: If gases assume the volume of the container that they are in, then wouldn't a gas that isn't enclosed in a container have an infinite volume?

texts:
But if the volume was infinite for gases not enclosed in a container, then how would the ideal gas law even function?

Thanks to anyone who can point out the piece of this puzzle I am not considering!


texts: Valid resonance contributors for 2-methylthiazole

texts:
There's a problem from an old exam that I was trying to do. The original structure is given on the left and they want all the possible resonance forms that have closed-shell atoms (octet for S) and formal charges of -1, 0, or +1 on all atoms. There's then a bold note that says, "As always, you should remember that linear atoms (sp hybridization) are not expected in rings of this size." So, my professor said that the circled electron pair in red is localized to the nitrogen atom, which therefore means that the resonance contributor on the right is invalid.

So, just to double check my logic, I'm assuming that the circled pair on right is localized because by moving them as if they were a delocalized pair, it would change the hybridization of nitrogen from sp2 to sp, which would make it's electronic geometry linear. Therefore, the pair on the nitrogen is localized because of the bold note (As always, you should remember that linear atoms (sp hybridization) are not expected in rings of this size) correct?


texts: Handling and storing sodium hydroxide, hydrochloric acid, hydrogen peroxide and isopropyl alcohol

texts:
I'm an electrical engineering and I hope you can give me some advice as I'm not much into chemistry.
I'm trying to start making my PCB (Printed Circuit Board) at home but I'd like to have some advice concerning how to handle and where to store these (potentially dangerous) chemicals.

I need NaOH as a developer, hydrochloric acid + hydrogen peroxide as etchant (they should be a better alternative than Ferric Chloride) and isopropyl alcohol (to make soldering flux).

As far as I understood I need:

Glasses (to protect against vapors and splashes)
Gloves (to protect when mixing the chemicals)
Some kind of protective clothes (not sure if I need to, but obviously I'm not wearing nice clothes when doing etching)

I have a few questions though:

Do I need kind of mask / filter (to put on my nose) - are these vapors dangerous ?
I read gloves should be stored in quite cold locations and not be exposed to sunlight. Does that apply to the chemicals listed above too ? I'd like to store them outside but maybe it's not safe ...
Hydrochloric acid comes in 36% concentration but I think I'll need to dilute it to 1%-5% max. After it has been diluted it should be quite safe, isn't it ?
Is it safe to store them inside a house (as long as it's well ventilated) ?


texts: Writing equation of reaction in stoichiometry of redox titrations

texts:
While solving some questions on the stoichiometry on redox titrations, I come across this question:

  Calculate the volume of $0.05\ \mathrm{M} \ \ce{KMnO4}$ solution required to oxidize completely $2.70\ \mathrm{g}$ of oxalic acid in acidic medium.

I know how to solve this question. The only problem I am facing is that the reaction equation is not given. How do I know what the products of this reaction would be? Can someone help me in how to write the equation of the reaction by the information given in the question.


texts: In which state does the bifluoride anion exist?

texts:
Statement 1. The $\ce{HF2-}$ ions exist in solid state and also in
  liquid state but not in aqueous state.
  Statement 2. The magnitude of hydrogen bonding between $\ce{HF}$ is weaker than that between $\ce{HF}$ and $\ce{H2O}$

  Both are correct and 2 explains 1
  Both are correct but 2 does not explain 1
  1 is correct and 2 false
  2 is correct and 1 false

The answer given is 1.

I know the second statement to be true. $$\Delta H (\ce{H-F...O})=40{-}45\text{ kJ/mol},\Delta H(\ce{H-F...F})=20{-}23\text{ kJ/mol}$$

But I am completely unsure about statement 1 and the relation of the two statements. I think the existence of the afforementioned ion in aqueous solution must not be absent, as I have read somewhere that this ion acts as the conjugate base of the molecule $\ce{H2F2}$ which dissociates into hydrofluoric acid.


texts: What does it mean when something is said to "contain ions"?

texts:
(I'm looking for a very basic level explanation because my only chemistry experience is one fast-paced high school course.)

So, according to the professor of that course, ions are never found in nature as ions; everything would be neutrally charged. My question is, how can something have ions in it, without having them be neutralized? Doesn't nature want to lower potential energy, which would mean bonding the ions asap? Or am I misunderstanding things and said ions are already bonded to other ions, but they are still called ions even though the charge of the whole molecule should be neutral?


texts: Balancing complex redox reaction of gold treated with sodium cyanide

texts:
How would you balance this reaction:
$$\ce{Au(s) + NaCN(aq) + O2(g) + H2O(l)-> Na[Au(CN)2](aq) + NaOH(aq)}?$$
Here’s what I’m came up with. First we can balance any atoms besides hydrogen and oxygen in the reaction (like $\ce{Na}$ and $\ce{CN}):$
$$\ce{Au(s) + 2 NaCN(aq) + O2(g) + H2O(l) -> Na[Au(CN)2](aq) + NaOH(aq)}$$
Then we can write out the half reactions:
$$
\begin{align}
\text{Anode:} &\quad &\ce{Au(s) &-> Au+} \\
\text{Cathode:} &\quad &\ce{O2(g) &-> H2O}
\end{align}
$$
Since the oxygen is going from an oxidation state of $0$ to $-2$ in the cathode half reaction, I figured you can rewrite $\ce{OH-}$ as $\ce{H2O}$ on the right hand side of the equation.
For the half reactions, I figured we can eliminate the ions whose oxidation number don’t change but I’m not sure whether you should include $\ce{NaOH}$ in the anode or cathode half reaction.


texts: Determining actual safety from a vague material safety data sheet

texts:
My desktop computer system employs a liquid cooling loop featuring a 6-litre external reservoir and radiator combination "cooling tower" unit. It isn't a cooling tower in the strict sense as it does not achieve temperature reduction through any evaporative method - only by radiating heat through the metal structure. However, the reservoir is not sealed and I have noticed a reduction in the level of liquid over the past few months since I started using it - I must assume that I'm breathing-in this liquid in some amount.

The coolant used describes itself as:

  XSPC EC6 is a high performance, eco-friendly coolant for PC water-cooling. It’s based on a blend of refined vegetable extracts with non-toxic corrosion inhibitors and non-toxic dyes. It offers superb protection for copper, brass, steel, nickel, aluminium and has been tested with a range of acetal and acrylic plastics

Never one to trust marketing materials, I requested a material safety data sheet from the manufacturers, and details of the ingredients. I only received an MSDS back without an ingredients listing. The MSDS reports the following:

  COMPOSITION / INFORMATION ON PRODUCT COMPONENTS
  Hazardous Components for EC
  Low oral toxicity proprietary antifreeze formulation based on refined vegetable extracts and non-toxic corrosion and scale inhibitors.
  Classified as GRAS (Generally Regarded as Safe) as a food additive and not classified as harmful for handling or transport purposes.
  However we recommend good working practices are employed and personal protection gear is worn when handling any chemical.

  [...]

  EXPOSURE CONTROL/PERSONAL PROTECTION
  Respiratory Protection: Respiratory protection if there is a risk of exposure to high vapour concentrations.

  [...]

  TOXICOLOGICAL INFORMATION
  Acute Toxicity: LD 50/oral/rat: >20000 mg/kg

  [...]

  ECOLOGICAL INFORMATION
  Mobility: The product will dissolve rapidly in water.
  Ecotoxicity: The product is rated as:
  Algae EC50 (72h):>100mg/l.
  Fish : LC50 (96h):.100mg/l, Oncorhynchus mykiss
  Bacteria: >1000 mg/l Daphnids (acute) EC50 (48h):>100mg/l

My guess is that it's some glycol-based solution - I'm disappointed they don't reveal the actual ingredients.

Is this substance anything I should be concerned about? Is there any  carcinogenic potential?

Also, how can I determine the specific heat capacity of the coolant? As it is used in a reservoir system instead of an active heat-exchange system the heat-capacity is important - I would like to be able to calculate exactly what TDP (Thermal Design Power) computer components I can use and how long I can run them for at-load without fear of overloading the cooling system.


texts: What would the van der Waals parameters look like for gaseous metals?

texts:
So basically I'm trying to do some calculations on laser based machining, and it involved vaporizing a small mass from a target metal workpiece. I was assuming that a certain m mass of the metal vaporizes nearly instantaneously, and the resulting vapor expands from that initial volume.
I was using the van der Waals corrected gas equation, and wasn't sure how to quantify a and b for gaseous metals (take Al for example). I tried searching online, but couldn't find any values for gaseous metals.
Any help or resources I could refer to would be appreciated.


texts: How to explain disagreement between Le Châtelier's principle and the simplified Gibbs free energy equation?

texts:
For example, for the dissolution of a salt in water that is exothermic, heating the solution would drive the reaction towards the solid form of the salt according to Le Châtelier's principle.

However, according to the simplified Gibbs equation $(\mathrm dG = \mathrm dH - T\mathrm dS),$ the reaction would be spontaneous towards the products due to the increase in entropy and the negative enthalpy.

To me, these seem to contradict each other. How is this reconciled? Am I making a mistake somewhere?


texts: What is the mathematical meaning of the plus sign (+) in chemical reaction equations?

texts:
Reactants and products are connected with plus signs in a chemical reaction equation, e.g.
$$\ce{CH4 + 2 O2 -> CO2 + 2 H2O}.$$
Is there a strict mathematical interpretation of what looks like sums before and after the reaction arrow? If so, what do the sums represent, and what are the mathematical objects we would use for the chemical species?
Often, when we use a chemical equation to solve a problem, operations other than addition come into play. For an equilibrium constant expression, concentrations of species are multiplied, not added. In stoichiometry, the chemical equation is interpreted as ratio of changes in amounts. In kinetics, we divide by the coefficients to be able to compare rates of changes of different species (and there is an equal sign, not a plus sign between the rate expressions of the different species.
So why are there plus signs between species in a chemical equation, and what is their mathematical interpretation?


texts: What defines the specific enthalpy of atomization?

texts:
1 mol of $\ce{F2}$ is turned into $\ce{2F}$ (atoms).

Is this the specific enthalpy of atomization, or two times that?


texts: Why did life end up with the big 4 elements, and specifically nitrogen?

texts:
This question is mostly about the human body, but it's also about life in general.

It's not difficult to notice a big different between the abundance of elements on Earth & that in the body. I've been pondering why. Such a huge question, but here I choose to focus on the big 4. Below is my current understanding, please correct me if I'm wrong or add things that I miss.

An umbrella reason for why $\ce{O}$ & $\ce{H}$ are prevalent is because $\ce{H2O}$ is such a wonderful solvent. Life generally depends on reactions to function, and they happen best when immersed in a liquid. Water is good and copious, hence life use it.

Another reason for $\ce{O}$ to be the most common element in our body is that it can oxidize things, which can become handy.
For $\ce{H}$ is that it's basically a proton, thus can be a "filler" in most situations.
$\ce{C}$ is the backbone of life because it's the element with the best bond force. In other words, not a goldilock but the GOLDilock. Life loves to handle such flexible tool, thus it uses carbon.
That leaves the question for $\ce{N}$. Why do we even use nitrogen? It's not anywhere close to the top of abundance in the Earth's crust. It does not have attractive characteristics like $\ce{O, C or H}$. One may say that it's dominant in the air, but just because there's a lot of $\ce{N}$ doesn't mean we evolve to use it. We can always eat dirt to get some hypothetical elementary replacement for $\ce{N}$, for example. Besides, life began in the ocean and there's little $\ce{N}$ there. Do fish have different big 4? I haven't looked into it, but I doubt it.

Both $\ce{H2O}$ and $\ce{C}$ have something "best" in their belt. I guess $\ce{N}$ must have some stuff of highest quality, too, but I have no clue what it is. So, even though my knowledge of the other 3 elements is crude, I'm bugged by nitrogen the most.


texts: Why is benzenediazonium fluoroborate water insoluble and stable at room temperature?

texts:
Benzenediazonium fluoroborate is water insoluble and stable at room temperature.

Why is this salt, water insoluble? Also I am told that benzenediazonium salts are stable only at low temperature(<5°C) and decompose at higher temperature, so what is the reason for such exceptional stability of Benzenediazonium fluoroborate?


texts: Why does water weaken ion ion attractions?

texts:
My lecturer has told me that water, having a high dielectric value, will "shield" ions and reduce ion-ion attractions.

I really don't see why. Having water molecules surround these two ions doesn't mean that Coloumb's force doesn't exist anymore - nothing in $F=\frac{kQq}{r^2}$ has changed just because water molecules are surrounding them. I recognise that the water molecules will arrange to face the ions in a polarised way (oxygen to the $+$ ion and hydrogens to the $-$ ion). However, I don't see how having a shell of water surrounding you will reduce the attraction. I guess it would prevent them from coming closer due to the sheer physical size of the water shell, but wouldn't there still be attraction?
Can someone explain to me why the ion-ion attraction decreases when water is there?


texts: Would a quarternary ammonium electride conduct electricity?

texts:
If suppose, I crystallised a quarternary ammonium electride could this conduct electricity similar to a metallic conductor? Metals have lattice atoms as charged metal ions are a sea of electrons. This leads me to believe a quartnernary ammonium electrides are quite similar, with lattice points being quartnernary ammonium ions and a sea of electrons.

Is this true? Can I consider quarternary ammonium electrides as metallic conductors?


texts: Effect of temperature on equilibrium constant in terms of entropy change

texts:
This question was asked in the JEE examination of 2017 :

[A]  option is incorrect since the system is losing heat and hence $$ \Delta S\lt0$$
[B]   Lets assume we have an endothermic reaction  $$\ce { A <=> B - Heat} $$
Now if we increase the temperature, the reaction will shift to the product side and hence the entropy of the surroundings will decrease more as compared to the initial conditions. Therefore the Unfavourable change in entropy(decrease in entropy) should increase.
[C]  Though the reaction is endothermic, since we are supplying heat to the system, the net change in entropy of the system is positive.
[D]  Lets assume another exothermic reaction $$ \ce{A<=>B + Heat}$$.
When we increase the temperature, the reaction will shift to the left side and hence less heat will be given off to the surroundings. Therefore, favourable change in entropy(increase in entropy) decreases.
Hence, according to me, the correct answer should only be [D], but [B] option is also given correct. What is the error in my explanation?


texts:
Often (or always?) one enantiomer of a certain drug will be effective and the other ineffective or harmful. The famous example is thalidomide, where one enantiomer caused mutilation of the unborn child and the other relieved morning sickness.

Are there any other examples where the other enantiomer of a drug that is used today or in history causes some adverse side effect, but has obviously been separated from the product to leave the effective drug, in addition what is(are) that side effect(s)?

Does absolute configuration at chiral/stereogenic centres affect the effectiveness of a drug molecule or perhaps cause unwanted side effects?


texts: What are the products formed when CH3CH2OH reacts with NaH?

texts: When $\ce{CH3CH2OH}$ reacts with $\ce{NaH}$, why are the products $\ce{CH3CH2ONa + H2}$? Why not $\ce{CH3CH3 + NaOH}$? Can you please explain in detail?


texts: Which substance(s) can solve gelatin (on film stock)?

texts: I want to loosen the exposed layer on film stock which is made up of gelatin. Anything which would make gelatin dissolve that's not overly toxic? Thanks


texts: Is photosynthesis endothermic and exothermic at the same time? ... somehow?

texts: Photosynthesis is obviously an endothermic reaction, I mean, what would be the point otherwise, right? This is probably just sheer and utter stupidity on my behalf, but why does Wikipedia say the heat of formation of glucose is negative? As you can probably see I'm on a quest of understanding enthalpy as a concept and I'm still quite new, but some sort of ultranoob clarification would be very much welcome.


texts:
I'm not sure if this question is for chemistry.

I had a bottle of (cheap) wine. It had a strong taste of soot, to an extend that I suspected that in the filling process some machine oil might have gotten into it.

I discarded the bottle, but some time later, I've found the same taste, to a lesser extend, in some other wine. Now it looks like my taste buds have become more sensitive to that, as I can taste it now (depending on what, I don't know) quite frequently, mostly on a low scale.

Any idea to explain that?


texts: High errors in frontier orbital energy calculation using DFT

texts:
In a recent paper by Faber et . al., Mean Absolute Error and DFT (B3LYP) error (relative to the experiments) for 9 properties of QM9 dataset molecules has been reported.
\begin{equation}
\begin{array}{l|ccccccccc}
{} & {\mu} & {\alpha} & {\varepsilon_{\text {HOMO }}}& {\varepsilon_{\text {LUMO }}} & {\Delta \varepsilon} & {\left\langle\mathrm{R}^{2}\right\rangle} & {\text { ZPVE }} & { U_{0}} & {C_{v}} \\
 \hline & {\text { Debye }} & {\text { Bohr }^{3}} & {\text { eV }} & {\text { eV }} &{\text { eV }} & {\text { Bohr }^{2}} & {\text { eV }} & {\text { eV }} &{\text {cal/molK}}\\ \hline
 {\mathrm{MAD}} & {1.17} & {6.29}& {0.439} & {1.05} & {1.07} & {203} & {0.717} & {8.19} & {3.21} \\
 {\mathrm{DFT}} & {0.10} & {0.4}& {2.0} & {2.6} & {1.2} &{-} & {0.0097} & {0.10} & {0.34} \\ \hline\end{array}
\end{equation}

I was wondering why the DFT results for frontier orbital energies
have such high errors in comparison with atomization energy $U_0$.
For instance, the error reported for $\varepsilon_{\text {HOMO }}$
is $2.0$ while the breadth of values is $0.439$. Now compare this
with the error $0.1$ for $U_0$ with breadth of values for the
dataset reported as $8.19$, which is much more diverse.
A study on different DFT methods has been conducted by Zhang and
    Musgrave, which discusses inaccurate computation of frontier
    orbital energies. Some works have proposed the use ML methods to
    predict these values with very low errors. Since DFT is Ab initio,
    would suggesting to use ML methods even make sense?

Edits:

In the first paper (by Faber et al.) we read

  Frontier molecular orbital energies (HOMO, LUMO and HOMO-LUMO gap) can
  not be measured directly. However, for the exact (yet unknown)
  exchange-correlation potential, HOMO and LUMO eigenvalues correspond
  to the negative of the vertical ionization potential (IP) and
  electron affinity (EA), respectively.

Based on this, I was wondering if DFT is the main approach to compute frontier orbital energies or this paper is just trying to find it using DFT in order to include the errors for DFT method.


texts:
Is $\ce{LiOH}$ a weaker base than $\ce{NaOH}$?

Note: I'm not interested in "why," but rather what the "real" $\mathrm{p}K_
\mathrm{b}$ values are.

$$
\begin{array}{lcc}
\text{Data for Alkali Metal Hydroxides} \\
\hline
\text{Cation} & \mathrm{p}K_\mathrm{b} & \text{Solubility} & \text{Solubility} \\
\text{} & \text{} & \pu{g/100 ml} \text{ at } \pu{20 ^\circ C} & \pu{moles/L} \text{ at } \pu{20 ^\circ C} \\
\hline
\ce{Li} & -0.36 & 12.8 & 5.34\\
\ce{Na} & 0.2 & 111 & 27.75\\
\ce{K} & 0.5 & 112 & 20.0  \\
\ce{Rb} & ? & 180 & 17.6\\
\ce{Cs} & -1.76 & 200? & 13.3?\\
\hline
\end{array}
$$

The $\mathrm{p}K_\mathrm{b}$ data is from Wikipedia ($\ce{Li}$, $\ce{Na}$, $\ce{K}$, and $\ce{Cs}$). Wikipedia doesn't have a value for $\ce{Rb}$ and I couldn't find one.

The solubility data is from the Wikipedia Solubility Table. Wikipedia doesn't have a solubility value for $\ce{CsOH}$ at $\pu{20 ^\circ C}$  and I couldn't find one, About $\pu{200 g}$ would be a reasonable guess, which would be $\pu{13.3M}$.

One point is that the Wikipedia article for lithium hydroxide says "It ... is the weakest base among the alkali metal hydroxides."

Another point is an earlier question "Why is $\ce{LiOH}$ a weaker base than $\ce{NaOH}$". User Lighthart references a paper "Ions in water: The microscopic structure of concentrated hydroxide solutions" by Imberti et al. but the abstract at least doesn't seem to address the strength of the alkali hydroxides directly (I don't have access to the paper itself since it is behind a paywall).

Is this one of the Bertrand Chord paradox problems where it depends on how we define "stronger"?

With a $\mathrm{p}K_\mathrm{b}$ of -0.36, $\ce{LiOH}$ would seem to be a stronger base than either $\ce{NaOH}$ or $\ce{KOH}$.
Certainly more moles of $\ce{NaOH}$ dissolve in a liter of solution at $\pu{20 ^\circ C}$ than any other alkali hydroxide.

EDIT 3/22/2016 11:31 pm

Found a different table of $\mathrm{pK}_\mathrm{b}$ data for the alkali hydroxides: Source-2

EDIT 3/23/2016 12:12 am
Source-3 CRC Handbook of Chemistry and Physics, 92nd edition, "Dissociation Constants of Inorganic Acids and Bases. Only $\ce{Li}$ $(\mathrm{p}K_\mathrm{a}= 13.8)$ and $\ce{Na}$ $(\mathrm{p}K_\mathrm{a}=14.8)$ are listed as $\mathrm{p}K_\mathrm{a}$ of the cations. It is the same data as in this pdf file which is from another edition.

$$
\begin{array}{lcc}
\hline
\text{Cation} & \text{Wikipedia} & \text{Source-2} & \text{CRC}\\
\hline
\ce{Li} & -0.36 & 0.18 & 0.2 \\
\ce{Na} & 0.2 & -0.56 & -0.8 \\
\ce{K} & 0.5 & -1.1 & \\
\ce{Rb} & ? & -1.4 & \\
\ce{Cs} & -1.76 & -1.76 & \\
\hline
\end{array}
$$


texts: What is the limiting value of band gap that makes a material semiconductor?

texts: What is the limiting value of band gap (in eV) that makes a material semiconductor? Or what is the value of band gap that separates insulator and semiconductor?


texts: Hess Cycle, determining enthalpy change of formation

texts:
I am asked to find the enthalpy change of formation of the following:
$$\ce{N2 + 1/2O2 -> N2O}$$

I am given the following enthalpies of reaction:
\begin{align}
\ce{C + N2O &-> CO + N2} &\Delta H_f =-193 \tag{1} \\
\ce{C + 1/2O2 &-> CO} &\Delta H_f=-111 \tag{2}
\end{align}

How do I calculate enthalpy change of formation of the nitrous oxide?

I thought it would just be adding the two enthalpies together because I substitute the second equation into the first one, but this is wrong.


texts: Is there any way of testing antioxidant ability of different substances?

texts:
For my investigation, I am looking at the antioxidant levels of different types of tea. How could I compare the antioxidating ability of each tea?

For example, I know there is a method calling for DPPH radical and absolute ethanol, which I do not have at my disposal. Do you know any other method I could use?


texts: How to determine if a given reaction requires heating to initiate?

texts:
At room temperature, some reaction propagate merely upon intermixing the reagents (e.g. autoignition of triethylborane), while others require additional heat to initiate (e.g. crystallization of calcium chloride).

How can I determine if a given chemical reaction would require heating above room temperature to initiate? And to what temperature?


texts: What alkali and alkaline earth metal oxides will turn moist red litmus blue and finally white?

texts:
How many of the following will turn moist red litmus blue and finally white?
$\ce{Li2O}$, $\ce{KO3}$, $\ce{RbO2}$, $\ce{Cs2O2}$, $\ce{BeO}$, $\ce{MgO}$, $\ce{BaO2}$, $\ce{SrO}$.

Since bleach convert moist red litmus blue and then white, but how we can identify which compound will act as bleach ?


texts: What are some convenient examples of so-called dissolved organic matter (DOM) for lab work?

texts:
Background, I have come across a chemical reaction system, occurring in nature, that apparently involves the presence of dissolved organic matter (in a catalytic role).
My research returns, for example, the following as examples of DOM per an educational source:

Dissolved organic matter (DOM) consists of soluble organic materials derived from the partial decomposition of organic materials, including soil organic matter, plant residues, and soluble particles released by living organisms, including bacteria, algae, and plants.

So my question is basically other than grinding up a plant,  are there other examples of dissolved organic matter that I can conveniently employ?
One idea is perhaps organic tea (which is still a bit general) as a dissolved organic colored solution.
But,  possibly better (in terms of convenience and reactivity) suggestions would be appreciated.
The cited reaction, by the way, is as follows:

$\ce{ O2 + 2 .CO3- + DOM -> 2 .O2- + 2 CO2 + DOM }$

Namely, the conversion by the action of oxygen on the carbonate radical anion to the superoxide radical anion and CO2, all in the presence of DOM.


texts: Rate of SN2 reaction depending on following different conditions in case of primary halides

texts:
Most important points to remember when thinking of $\mathrm{S_N2}$ reactions are that they are nucleophilic reactions, a pentavalent transition state is formed, depends on steric hindrance, strength of the bonds, nucleophilic and substrate used i.e. what kind of leaving group is attached to it, etc. I know and understand these.

I also know that in the following conditions the rate of $\mathrm{S_N2}$ increases, but I don't seem to understand the reason behind it.

1) The presence of unsaturation on beta-$\ce{C}$ in primary halide increases $\mathrm{S_N2}$ reaction rate.

I really don't seem to understand this one, I know for the alpha $\ce{C}$ it would be difficult because the halide and the carbon will acquire partial double bond character which would make it very difficult to break.

2) The presence of carbonyl group at alpha carbon is most suitable for $\mathrm{S_N2}$ reaction.

My reason: it might be because of tautomerism, i.e., due  to its conversion to enol form it will increase the reactivity.

3) Presence of hetero $\ce{O,N,S}$ atom at alpha carbon in primary halides increase $\mathrm{S_N2}$ reaction.

This too, I fail the understand.


texts: Do chemicals undergo granular convection?

texts: Do chemicals of an average weight, such as Polyethylene Glycols, undergo granular convection (the Brazil nut effect)?


texts: Electrolytic refining of precious metals — why the anode rather than the cathode?

texts:
In electrolytic refining, metals like platinum and gold are deposited as anode mud.

Why aren't they deposited on the cathode since they have higher reduction potential?


texts: Stability comparison of 2-methylpropene and trans-but-2-ene

texts: Actually, in a book I found that  2-methylpropene is more stable than trans-but-2-ene. But, my teacher and also I am convinced that trans-but-2-ene is more stable than 2-methylpropene. My reasoning is that 2-methylpropene is less stable due to the steric repulsion of the -CH3 on one sp2 hybridised carbon. Also, 2-methylpropene is more reactive for the electrophilic addition reactions involving carbocation intermediate as a 3° carbocation will form and in case of trans-but-2-ene, a 2° carbocation is formed. Please say if I am correct and if not, please explain the correct comparative analysis.


texts: Calculating the pH of a 'buffer' solution?

texts:
Question: Determine the $\mathrm{pH}$ of the solution resulting when $\pu{100 cm^3}$ of $\pu{0.50 mol dm-3}$ $\ce{CH2ClCOOH}$ is mixed with $\pu{200 cm^3}$ of $\pu{0.10 mol dm-3}$ $\ce{NaOH}$.

The given solution:
Concentration of acid: $\frac{0.030}{0.300} = \pu{0.10 mol dm-3}$
Concentration of base/salt: $\frac{0.020}{0.300} = \pu{0.067 mol dm-3}$
$$\ce{[H+]} = \frac{K_\mathrm{a} \times \ce{[HA]}}{\ce{[A-]}} = \frac{1.3 \times 10^{-3} \times 0.10}{0.067} = \pu{1.9 \times 10^{-3} mol dm-3}$$
$$\mathrm{pH} = 2.72$$
Now, here is why I am confused: this calculation is for a buffer solution, where $\ce{HA}$ and $\ce{A-}$ are a conjugate acid/base pair. However, chloroethanoic acid and sodium hydroxide are not conjugate acid/base (are they?) - so why does this calculation work? What is the intuitive way to think about this?


texts: What is the most commonly used radius of an atom or molecule to describe the area that must touch another area of another molecule for the two to react. Is there one radius that always works or does it depend on the reaction? Of course the actual distance at which bonds can form or break varies but I was wondering if at some distance the atoms can somehow bring themselves together for bond 'swapping'


texts: Why do lattice structures form into powders?

texts:
For example, when you react magnesium with oxygen over heat, it forms a lattice of ions. Why does a strong lattice of ions like MgO turn out to be a powder, rather than a solid block?

(Sorry if the answer is obvious; I'm only just being introduced to this)


texts: Separate toluene from acetone and isopropyl alcohol

texts: I found a cellulose thinner that is made of toluene 60-80%, acetone 10-20%, and 2-propanol 5-10%. As acetone and 2-propanol are water soluble, but toluene isn't, would it be possible to just add a lot of water and then remove it, and then end up with just toluene?


texts:
I'm quite new to the field, and actually am a mathematician. I was wondering if there is a way to model (find the equation of) the reaction progress (more specifically, the activation energy functions) using some equation?

Optimally I'd like to use some graphing calculator like Desmos to write the equation and get a similar function.


texts: How to dissolve hardened aluminum silicate beads back into solution?

texts:
TLDR: We use the adsorber beads (which is essentially alumino-silicate beads) to adsorb some  stuff from our process stream. The spent beads are dissolved in NaOH and sent to our wastewater treatment facility for precipitation and separation through filter presses.
Anyway, due to unavoidable circumstances, the dissolved beads in caustic solution was held up overnight before it could be pumped to wastewater treatment. The dissolved beads solidified in the vat, and would not re-dissolve on adding excess caustic. To be clear, it does dissolve only at the top of the vat, but cannot penetrate the interiors.
Can someone explain the chemistry of what might have formed (polymerization, silica gel, etc?) and how do I go about dissolving it? Should I just blast some holes in the solid with pressurized water, and then put caustic into it for increased penetration?
Much appreciated.


texts: Can aqua regia/royal water be produced with sources of chloride and nitrate other than hydrochloric acid and nitric acid?

texts:
According to Professor Poliakov and a question on Chemistry Stackexchange here, gold dissolves in aqua regia because the nitrate ion oxidizes the gold into $\ce{Au^3+}$, and the chloride bonds to the gold to form tetrachloroaurate III ions ($\ce{AuCl4−}$). This means that the actual acidity of the compound plays no role in the actual oxidization and dissolution of gold. Therefore, if I just provide nitrate ions and chloride ions, the reaction should still proceed (ex: use $\ce{NaNO_3}$ for the source of nitrate ions and $\ce{NaCl}$ for the source of chloride ions). According to the equations given by an answer to the Stackexchange question earlier, aqua regia can react with gold in two ways: $$\ce{Au + 3HNO3 + 4HCl <=>> AuCl4- +  3NO2 + H3O+ + 2H2O}$$

$$\ce{Au + HNO3 + 4HCl <=>> AuCl4- + NO + H3O+ + H2O}$$
And so therefore, by my supposed substitute for the dangerous acids, they can react with gold with the following reactions:
$$\ce{Au + 3NaNO3 + 4NaCl +3H2O<=>> AuCl4- +  3NO2 + 6NaOH + Na+}$$

$$\ce{Au + NaNO3 + 4NaCl + 2H2O<=>> AuCl4- + NO + 4 NaOH + Na+}$$

The sodium hydroxide that is produced by the reaction could be a problem, but we can then add a weak buffer like $\ce{HCO3-}$ or $\ce{H2CO3}$ afterward to deal with it.

Am I correct, or is something else at play in this reaction?


texts: Finding the value of pressure equilibrium constant

texts:
Question:

  A rigid vessel containing only $\ce{NO2(g)}$ is heated to $\pu{337^{ \circ}C}$  and allowed to come to equilibrium according to the following reaction:
  $$\ce{2NO2 <=> 2NO + O2}$$

  The density of the resulting mixture is measured to be $\pu{0.52 g/L}$ at a total pressure of $\pu{ 0.75 atm}$. What is the value of $K_\mathrm p$?

The answer key says it should be $\pu{0.65 atm}$, but I can't get that number. I first tried to find mols using the given density and molar masses, and then finding the partial pressure of each component using the mol fractions, but it doesn't work out.


texts: How is this sugar classified as an aldose?

texts:
I have made the following image in paint, so forgive me if it isn't the most appealing sugar. I have a hard time visualizing how the following sugar is an aldose.

My speculation for the Fischer projection of the alleged carbohydrate is:

My speculation is as a result of the lack of primary alcohol at the end of traditional carbohydrates like D-glucose for example means that there is not carbon group alpha or beta to carbon 4 in the furanose ring. The fact that there is still a CHO group on Carbon 1 would make this sugar an aldose? Is this logic correct, and is that the Fischer projection for the sugar shown above in the Haworth projection?


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I know that energy is absorbed due to chromophores which enable electron transition which uses up energy. But I am a bit unsure about what happens after the absorption and where this absorbed energy went.

I am not very sure if the energy is dissipated since it would contradict with the law that energy can't be destroyed. If the energy is lost as heat, then it is a bit contradictory again according to the equation $E= hc/\lambda$.
The wavelength would be big for infra-red and thus, the energy lost must be less than the absorbed energy from UV.

So how exactly are these flavonoids shielding UV radiation? And also, if these flavonoids are in the excited state, it makes me feel that they might be quite reactive and may form free radicals.


texts: Comparison of carbocation stability in bicyclo compounds

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Question

Which is the most stable carbocation ?

Answer

 3.

My attempt
I answered as 1 as the first one had +M of -O- and hyperconjugation effect as the positive charge is at para position. Why is the answer 3? It just has +I and +H of the second chain and +M is stronger than +I


texts: Is the kinetic energy turning into activation energy when the reaction takes place?

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So I want maybe a simple question that I had on a test today. For a reaction to take place it needs a minimum energy called activation energy. At school I heard that this energy is coming from the kinetic energy of the particles that collide. When the reaction takes place, is the kinetic energy small because it turned into activation energy?
If you need any clarification just ask me and sorry for any misspell or grammar error.


texts: How to use salt spray data in real environments?

texts: I want to convert resultant hours of salt spray corrosion test to estimated values in years for real life environments such as marine. In other words, How could I predict the result of real life tests using salt spray data?


texts: I prepared some sodium aluminate by reacting a strong $NaOH$ solution with aluminium foil and filtering the result. I now have a clear solution and I'm not sure what it is. I stopped adding aluminium when the reaction rate showed down dramatically in a hot water bath. Basically what I'm asking is what are the properties of sodium aluminate since Wikipedia is severely lacking in information on sodium aluminate


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In Chemistry class yesterday, I learned that real gases with low atomic masses behave like an ideal gas at high temperatures and low pressure. Since on earth at sea level the pressure is close to $1\ \mathrm{atm}$ (which is a low pressure) and temperature is close to $288.15\ \mathrm K$ (high temperature), I can use the equation $PV=nRT$ to approximate properties of the gas. (I got these values from Wikipedia, under Standard Sea Level).

$$\left(\text{pressure}\right)\cdot \left(\text{volume}\right)=\left(\text{number of moles}\right)\left(R\right)\left(\text{temperature}\right)$$

In physics we learned that pressure is the force per unit area. On earth the atmospheric pressure is earths gravitational pull on the air. The gravitational pull of any object on earth is $G_\text{pull}=\left(\text{mass}\right)\cdot \left(9.8\ \frac{\mathrm m}{\mathrm s^2}\right)$. Because the gravitational pull is $G_\text {pull}=\left(\text{mass}\right)\left(\text{acceleration due to gravity}\right)$.

Since different planets have different masses the acceleration due to gravity on these planets are different. Below I listed the values:

$G_\text{Mercury}=3.59\:\frac{\mathrm m}{\mathrm s^2}$

$G_\text{Venus}=8.87\:\frac{\mathrm m}{\mathrm s^2}$

$G_\text{Mars}=3.37\:\frac{\mathrm m}{\mathrm s^2}$

For planets like Mercury, Venus, Mars the approximation of $PV=nRT$ still can be used since they would have even lower pressures than Earth. But what about planets like Jupiter and Neptune

$G_\text{Jupiter}=25.95\:\frac{\mathrm m}{\mathrm s^2}$

$G_\text{Neptune}=14.07\:\frac{\mathrm m}{\mathrm s^2}$

Jupiter and Neptune have more pressure at ground level than that of Earth. So can $PV=nRT$ still be used? If yes, how well? If not, is there a different formula that can be used to find the volume and number of moles on these other planets?

Any input is appreciated. I am just being curious and didn't find anything on Google.


texts: How to make p-chloroanisole from methanol and benzene?

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I am tasked to synthesise para-chloroanisole from methanol and benzene. Other reagents are permitted.

Would it be correct to have the benzene attack the methanol $\ce{H}$ and then attack the carbocation that forms with the methoxy ion? From there use $\ce{Cl2}$ and $\ce{AlCl3}$ which would install para and ortho or a combination?

Also if you write one equivalence, does that suffice to say that you are only having it attach once, so that you would only have a max of two groups at the end for each possible product e.g. addition at the 1,2 positions and 1,4 positions?


texts: Hartree-Fock orbital energies can be interpreted physically, e.g. in Koopmans theorem, while one cannot assign active MCSCF orbitals to energies in general. What about GVB, say for example GVB(PP) orbitals, does it make sense to assign energies to those?


texts: How to extract thymol from oregano leaves?

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This is my second graders in highschool project of science report.

I try to a make natural hand sanitizer using thymol from oregano leaves as  the antiseptic ingredient instead of alcohol.

I want to extract using a maceration method.

What solvent should I use?
How to separate thymol from the solvent?


texts: Organic compounds containing two hydroxy groups on one carbon (gem dihydroxy) are unstable and tend to lose water molecule. However, Boron, sulfur and phosphorus with two OH groups are stable. What is the reason?


texts: Factorizing Slater determinant into product of spin-up and spin-down slater determinant

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I am reading the book on MONTE CARLO METHODS IN AB INITIO QUANTUM CHEMISTRY by Hammond and Lester. (Chapter 5-Variational Trial Functions, Section 5.3-Hartree Fock and Beyond, Sub-Section 5.3.3 Hartree Fock and Correlation Energies)In section 5.3.3, the book says the following,

"In Monte Carlo, we may factor the determinant into electron spin components, i.e., $\psi_{D}=\psi_{\alpha}\psi_{\beta}$. This factorization is justified because all possible permutations of this term that are present in the full antisymmetric $\psi$  are operationally equivalent: each term simply corresponds to a relabeling of the electrons. Expectation values, and even local values of any observable, are unchanged."

I couldn't understand how these two are equal. Is it really possible to factorize this into two slater determinants? How does one justify that this is true?


texts: Database for experimental diatomic ionization energies

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I am looking for a database, in which the experimental ionization energies (and e.g. heat of formation) of atoms and diatomic molecules are listed as files.
If it comes with a Python package, that would even better.

I found the Pitt Quantum Repository, but there seem to be only theoretical values.


texts: Number of pi-electrons in an energy state

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I am learning quantum chemistry and I am trying to understand the statement in a .pdf I'm reading which states
"The energy transition associated with the spectral transitions observed is:
$$\Delta E = E_{LUMO} - E_{HOMO} = \frac{(N+1)h^2}{8mL^2}$$
where $L$ is the length of the "box" (it's talking about particle in a box), $m$ is the mass of the electron, and $N$ is the number of $\pi$-electrons in the system. I know due to the solution of the Schrodinger equation that $$E = \frac{n^2 h^2}{8mL}$$
So, $$\Delta E = E_{HOMO} - E_{LUMO} = E_{k+1} - E_{k} = \frac{(2k+1)h^2}{8mL^2}$$
So, I want to figure out why $2k = N$?