texts:
Okay I know that as the temperature rises the number of particles in a given volume decreases. The molar volume likewise increases. So the number of molecules per liter would decrease as the temperature rises meaning that a 1M solution is only 1M at a specific temperature.

But why is molarity dependent on temperature? I mean sure the density does decrease as the temperature rises but still there is a small chance that the molarity will stay the same.


texts: Does Bent's Rule only apply to molecules where there is hybridisation?

texts:
I would just like to ask if the pre-requisite for using Bent's Rule is that the bonding in the molecule involves hybridised orbitals.

I was thinking of why the bond angle in hydrogen sulfide (~ 92 degrees) is larger than the expected 90 degrees. I thought that Bent's Rule would be able to offer a good explanation for this as the s orbital character concentrated towards the electropositive hydrogen atoms results in stronger bond pair-bond pair repulsion, increasing the bond angle. However, I realised that my entire argument may fall apart if Bent's Rule does not work for bonding involving unhybridised orbitals.


texts: In an octahedral complex, what happens to the electrons donated by the ligand?

texts:
I am trying to understand how complexes are coloured. After some reading, I found out this was due to the d-d splitting induced by the coordinate bonds of ligands to the central metal ion. The electrons in the d-orbitals then transition between each other, and absorb light in the process.

However, I do not understand what happens to the electrons donated by the ligand. Don't they form a sigma bond with the d-orbitals of the metal ion? In which case, wouldn't they go into the d-orbitals and 'fill it up', thus disallowing transitions?

Or is it the case that the d-orbitals of the central metal ion are not involved in the bonding at all?


texts: Colour of metal complexes with the same type and number of ligands

texts:
Crystal Field Theory says that because of d-orbital splitting caused by different ligands we have 2 different energy levels for d-orbitals.

It also says that transition metals are coloured because photons excite electrons, and when they have the crystal field splitting energy through a specific wavelength of light, the electrons to go to the higher energy d-orbital.

When electrons come back down they emit the same wavelength of light and that's the colour we see.

But then why is $\ce{[Ni(H2O)6]^2+}$ green and $\ce{[Cu(H2O)_6]^2+}
$ blue? They have the same type and number of ligands.


texts: Few basic questions about ionic bonding and batteries (lead)

texts:
I've got a few very very basic questions about ionic bonds and their role in batteries.

My assumptions (correct me if I'm wrong):

Ionic bonds occur between a metal and a non-metal (the non-metal takes
the metal's electron to fill its valence shell). Therefore the metal atoms are left with a positive charge and the non-metal a negative charge.
Because of this, the atom tries to stabilise its ionised charge and tries to bond with the oppositely charged atom.
Batteries take advantage of this chemical bonding to produce electricity.
In a lead battery there is a PbO2, the electrolyte and Pb.
The electrolyte is a non-metal and therefore it tries to fill it's valence shell with the electrons from PbO2. This creates an overall positive charge in the PbO2 and a negative charge in the solution.
For some reason this negative charge is then transferred over to the Pb which gives it an overall negative charge.
The Pb then wants to release this negative charge and pushes excess electrons which flow through a circuit to the PbO2 that is lacking electrons.

This leaves me with a few questions:

Why does the electrolyte solution choose to take electrons from PbO2 (I assume it has something to do with the O2)?

After the electrons are taken and there is a positive charge in the PbO2, and a negative charge in the solution, why don't they just bind together?

I thought ionic bonds occurred when an metal had it's electrons taken from it. How then does the Pb receive additional electrons from the non-metal solution?

If the Pb does want to receive the extra electrons, why would it instantly try to push them away through the circuit? I'd understand if the whole negatively charged atom was trying to be pulled to the positively charged PbO2 - but from what I've read it tries to push the excess electrons, not the atom - so why even receive the electron if it doesn't want it?


texts:
What would happen if I mixed a single water molecule in a beaker of hexane? Would it sink or float?

How about 2 water molecules? 3? Etc?

In other words, how many water molecules does it take to be hydrogen bonding together to become more dense than hexane?


texts: Why does changing the temperature shift the equilibrium?

texts:
I know that raising the temperature in a reversible chemical reaction causes the equilibrium to shift to the endothermic side.
I know that $\Delta G = \Delta H − T\Delta S$, but I don't know how to put them together to show why the equilibrium would shift.
To summarise, I already know what happens when, and I'm interested in why.


texts: A question about the equality of heat and changes in enthalpy

texts:
I am wondering how the heat release or absorbed by a chemical reaction can be equal to the change in enthalpy of the reaction at constant pressure if there are changes in the amounts and potentials of each chemical in the reaction mixture. To be more specific, at constant pressure,
$$\mathrm dH = T\,\mathrm dS + \sum_{i} {\mu_i\,\mathrm dN_i}$$
How can we just ignore the summation for something like a chemical reaction?


texts: Predict which hydrogen is more acidic in the following organic compounds?

texts:
Between 2-chloro-2-phenylpropionic acid and hydrogen phthalate, which is the more acidic compound?

I'd say the $\ce{H}$ on the second one is more acidic as the $\ce{-COOH}$ group is directly attached to the aromatic group. Is that correct?


texts: Why do we dip noble metals (Ir, Pd) into NaOH for an oxide coating in thermal oxidation?

texts:
I've noticed that a common technique for creating a layer of oxide onto palladium or iridium is to dip it into high concentrated NaOH prior to putting it in a furnace for ~800C.

I've been reading numerous papers and it leads me to a textbook that I can't find accessible: Kauko, Y. and Knappsberg, L. (1939) Z. Elektrochem. 45, 760

The papers that I've been reading are
W. T. Grubb and L. H. King, Analytical Chemistry 1980 52 (2), 270-273
DOI: 10.1021/ac50052a013

and

https://doi.org/10.1016/0005-2795(76)90263-4

if anyone can help me solve this problem, I would be eternally grateful!


texts: Why does hydride acidity increase across period and down group in periodic table?

texts: Why exactly does hydride acidity increase across period and down group in periodic table? What is the explanation with respect to electrons? I can't figure this out because for 1st period etc H is an anion while for the right and middle of the periodic table H is a cation in compounds formed. I feel confused. Does this have something to do with electronegativity of element that forms hydride?


texts:
This is my first time taking a $\ce{{}^{13}C-NMR}$ spectrum and while I'm aware the signal to noise ratio is much lower compared to $\ce{{}^{1}H-NMR}$, I didn't realize it was quite this bad. I took a spectrum and I only see the $\ce{CDCl3}$ triplet. What concentration range is generally appropriate given say 256 scans (10 minutes on our machines?), or is it rare to see any good results after without drastically increasing the scan time?

Spectrum for reference (taken on a 300 MHz Varian Mercury):


texts: Are there any compounds with these properties?

texts:
I'm looking for a chemical compound that satisfies the following criteria:

Solid at room temperature
Decomposes into gases, primarily oxygen when supplied with an electrical current, preferrably exothermically.
Kinetically stable

Any ideas?


texts: What makes formaldehyde 'safe' or 'dangerous'?

texts:
I know that formaldehyde naturally occurs as a metabolite and can be found in our own and other animals' bodies, plants, and unprocessed food.

But formaldehyde is also registered as a carcinogenic VOC and is considered bad when it's in plywood and cosmetics.

Is this judgement based on dosage, form (e.g. gas/liquid), or amount released?


texts: What are "O-hydrocarbons"? A pharma translator's question (Russian to English, "О-углеводороды")

texts:
A translator colleague is translating from Russian a plan for study of a number of leachable and extractable substances (pharmacology). This Russian text mentions one particular class of chemicals which theoretically could become leachables:

  "Hydrocarbons (alkanes, alkenes, alkynes, O-hydrocarbons)".

She can't understand what this could mean.

The Russian term is О-углеводороды.


texts: When I was reading Organic textbook, I saw a statement of 'F- is more stable than CH3- because the F has a greater electronegativity'. I agree with the explanation 'because of its high electronegativity, F can hold the electrons very well'. But I am just confused about: as the F has great electronegativity, it can react with other cations/electrophile very easily, making it reactive thus unstable. So I am just very confused about this contradiction.


texts: Intuitively, why is it that when the HOMO-LUMO gap is small then the bonding molecular orbital produced is of significantly lower energy?

texts:
What is an intuitive explanation for why a small HOMO-LUMO gap between the electrophilic and nucleophilic species would produce bonding molecular orbitals much lower in  energy, giving rise to greater stabilisation upon electron population. I would like an intuitive explanation, not a mathematical one (such as by the Klopman-Salem equation).

Having done some thinking on my own, my explanation is that the closer the energy levels of the HOMO and LUMO, the greater the extent of orbital overlap. Is this logical? More importantly, is it accurate?


texts: Silver identification of the group I of cations

texts:
I was wondering if this actually happens in a chemical reaction
$$\ce{AgCl_{(s)} + 2NH_4OH_{(aq)} \rightleftharpoons  Ag(NH_3)_{2(aq)}^+ + Cl^{-}_{(aq)} + 2H_2O_{(l)}}$$
My teacher wrote something like this but on Internet I saw that it yields to $\ce{Ag(NH_3)_2Cl}$ and water, so can someone explain it to me.


texts: If I mix up 46.29 grams of Potassium Nitrate powder (KNO3) in 1000mL of water and then take 1 ml of that solution and put it into 1 gallon of water what will the ppm of "K" and "NO3" be separately.  For the 1000 mL solution and the 1 gallon of water.  A calculator I was using says it should add 7.5 ppm NO3 and 4.73 ppm of K to the 1 gallon.  If you could tell me how you came up with your answer that would be great.  I can come up with the 7.5 ppm but if I use the same logic for the K it does not work so I must not be doing it correctly.  Thank you for any help!


texts: While electrolyzing concentrated aqueous sodium chloride, why is it that chlorine is discharged but not sodium?

texts:
Hydrogen and hydroxide both exceed sodium and chlorine in terms of reduction and oxidation potential respectively.
While electrolyzing a concentrated solution of aqueous NaCl, it is known that chlorine is discharged at the anode (contaminated with traces of oxygen). However, at the cathode, hydrogen is charged in place of sodium. Why is this so? I have read many explanations, but they never provide the reasoning.
I suspect these particular properties of factoring in preferential discharge:

Atomic mass (and consequently weight).
Magnitude of oxidation & reduction potentials.


texts: Rotational spectroscopy application of different equations

texts:
So we were given two problems and I don't understand why one was solved one way, and another was solved another way

Estimate the bond length of 12C16O (pure rotational spectrum) given J''=3 (15.356 cm-1) and J'=9 (38.356)

To solve we used

$12B = (38.356 - 15.365)=1.916$

to solve for B and then used to determine the bond length.

In another problem we are told that the J=3 to J=4 transition for a diatomic occurs at 0.50 cm-1. What is the J=6 to J=7 transition for this molecule assuming rigid rotor.

In this problem We used

$E(rotation) = Bh[J'(J'+1) - J''(J''+1)]$

Which when solved/rearranged becomes

$E(rotation) = 2BhJ'$

Which can be rearranged to solve for B, because we know the energy as a wavenumber. This B is then used to calculate the transition wavenumber for 6 to 7 transition.

I am lost as to why in the first one we can simply assume each transition is 2B apart and so 6 transitions would be 12B and solve whereas in the second we cannot make this assumption.


texts: What is the correct pH value of weak and strong alkalis?

texts:
In the book titled fundamental chemistry for Cambridge O level, it states at page 149,

  Ammonia solution with a pH of 11.1 is a weak alkali and that's why it shows much lower conductivity of 0.50 US/cm.

However at p. 147 it's written that

  a solution with a pH of 10 is a strong alkali.

So either the correlation of pH with conductivity is incorrect  or the statement that ammonia solution with a pH of 11.1 is a weak Alkali is wrong.   What are the pH values for a weak and strong Alkali?

Is there anything wrong with the two diametrically opposite sentences/ statements given in the book?


texts:
This may be too subjective for this forum, but I'll take my chances.

For the purposes of a "quick and dirty" illustration of London forces, I'm looking for best practices and creative ideas.  For something like dipole-diple attractions, there are some largely-agreed-upon conventions:

But for London forces, there is a shortage of good ways to illustrate them in notes or on the board.  Personally, I have used these in the past:

But there must be other, clearer, more clever means of illustrating London forces. I've searched the questions here on London forces but I don't see that this issue has been addressed.

EDIT: I'm interested in ways of showing modest organic molecules interacting via London forces.  The vast majority of illustrations found via Googling show only rather small molecules or atoms.  It seems to me that the illustration ought to convey the notion of the molecules at close range (or snuggling, as I generally tell students), since London forces are impossible otherwise.


texts: Comparing Basicity of Aniline Derivatives

texts:
Why is 4-hydroxyaniline more basic than 2-hydroxyaniline? Hydroxyl is an electron donating group, and their resonance structures suggest that they both isolate a negative formal charge on the carbon that is bonded to the amine group (which is also an electron donating group) so it would be more unstable. However, there is a clear difference in basicity between the two, the former having a pKb of approximately 8.53 while the latter has a pKb of 9.28. What accounts for this huge difference?

I also have another question. 3-hydroxyaniline avoids putting the negative formal charge on the carbon that is bonded to the amine group, and it has a pKb of 9.83. This makes sense because that means 3-hydroxyaniline is more stable in terms of resonance and thus its conjugate acid would want to liberate more protons than the other two, rendering 3-hydroxyaniline less basic than the other two. However, aniline has a pKb of 9.37, which means that it is more basic than 3-hydroxyaniline. However, hydroxyaniline has a higher electron density than aniline so shouldn't it be more basic than aniline?


texts:
I frequently need to discriminate between 304 and 316 stainless steel which cannot be done by eye.

304 SS has 18% chromium and 8% nickel

316 SS has 16% chromium, 10% nickel and 2% molybdenum

How can I do a chemical assay to discriminate between them and ideally identify their precise composition to 1% or better accuracy? I assume the basic procedure is to create a solution, then do a titration of some kind.

If the first step in your answer is... "dissolve the sample in acid," be aware that stainless steel is pretty resistant to most acids and I need a procedure that will work within 24 hours.

Also, please no answers like "use an xrf machine" or some surface detection technology. I need a chemical process that assays the whole sample, not just its surface.


texts: Why is 1-Ethyl-1-methylcyclohexane achiral?

texts:
I was wondering why the 1-Ethyl-1-methylcyclohexane molecule is achiral.
Thank you in advance.


texts: Volume of NaOH needed to precipitate copper(II) but not calcium

texts:
I have $\ce{NaOH}: C = \pu{0.1M}, V_{\ce{NaOH}}$ that I want to progressively add in a solution (in water) of:
$$\begin{align}
\ce{Cu^{2+}}&: \pu{0.01M}; & K_\mathrm{sp} &= 10^{-18.6} \\
\ce{Ca^{2+}}&: \pu{0.01M}, & K_\mathrm{sp} &= 10^{-5.26}
\end{align}$$
with initial volume: $V_\mathrm{init} = \pu{0.1L}$. I want to add $\ce{NaOH}$ as long as $\ce{Cu(OH)2}$ precipitates, without causing any precipitation of $\ce{Ca(OH)2}$.

Knowing  that the equilibrium will be displaced to the left and I will have precipitation, I have done:
$$
\begin{array}{ccc}
\ce{Cu(OH)2 &->&Cu^2+ &+ &2OH^-}\\
&&0.001&&0.1V_{\ce{NaOH}}\\
&&0.001-x&&0.1V_{\ce{NaOH}} - 2x\\
\end{array}
$$

Also, since I want to achieve $99.999\%$ precipitation of $\ce{Cu(OH2)}$ I have got: $$x = 99.999\cdot10^{-5}$$

Using all that in the expression of $K_\mathrm{sp}$ I get :
$$10^{-18.6} = \left (\frac{0.001 - 99.999 \cdot 10^{-5}}{0.1+V_{\ce{NaOH}}} \right)\cdot\left(\frac{0.1\cdot V_{\ce{NaOH}} - 2\cdot99.999\cdot10^{-5}}{0.1 + V_{\ce{NaOH}}}\right)^2$$

However for this expression I get a value of $V_{\ce{NaOH}}$ that is extremely small. Is there anything wrong with my reasoning and if yes, how can I determine the volume for which i get the precipitation I want?


texts: Why don't we explode after drinking water?

texts:
It is known that acid should be added to water and not the opposite because it results in an exothermic reaction.

Our stomach contains HCl, so why don't we explode when we drink water?


texts: How does the Mentos-Coke explosion work?

texts:
We all might have seen this in some videos or in real life. But how exactly does this work? What is the chemical reaction involved?
And why is the reaction of Mentos with Diet Coke more vigorous?

From left to right: action of five Mentos candies (per bottle) with Perrier, classic Coke, Sprite and Diet Coke
Image source


texts: Using absorbance to find amount of a substance in a sample

texts: If you use absorbance to find the amount of one substance that a sample contains, and do three determinations, should you just average the three values and use that? Or just talk about them individually?


texts: Effect of pH on volatility (odor) of organic acid

texts:
Based on two assumptions:

Ionic solutes can generally be considered nonvolatile
As the pH of a solution of organic acid is increased, an increasing percentage of it is deprotonated, or ionized (Henderson-Hasselbach eqn).

I think I should be able to decrease the volatility of an organic acid solution by increasing pH. However, in several rough experiments with acetic acid, I don't observe a very strong reduction in odor with increasing pH. Even a theoretically neutralized solution retains a significant vinegar odor.

Any ideas why this might be?


texts: What is the mechanism of APTES mono-layer formation on glass substrates?

texts:
The reagent APTES is a fairly common "ink" for microcontact printing, a technique that forms covalent bonds between the silanols found on the surface of the glass and the silane in the the APTES. It's also been demonstrated that the mono-layer then polymerizes somewhat, forming bonds between neighboring silanols.

What is the mechanism by which the printing and polymerization occur?
What is the reason for using APTES instead of a more reactive trichlorosilane?


texts: Acid-Base Titration of ammonium dihydrogenphosphate?

texts:
How can I determine the concentration of ammonium dihydrogenphosphate solution?
In this compound, the ammonium cation and the dihydrogen anion are both weak acids.
I have a weak solution of this salt, $C_A\approx 0.05\mathbf{M}$, that I need to quantitatively determine.
My first thought was acid-base titration because it's cheap and easy but the presence of two weak acids complicates things.
Would it be possible to determine the concentration of ammonium and dihydrogen in one equivalence point, as $2\times C_A$?


texts: Is the kilogram still consistent with the old definition?

texts:
My old understanding was that a gram is the amount of mass in a cubic centimeter of water.

But then I recently learned that the second was redefined to be some 9 billion cycles of a Caesium atom. Then from this the definition of a meter changed from 1 ten millionth the distance between the equator and north pole, to $1/299 792 458$ the amount of distance that light travels in a second. From this I would have assumed that now a hundredth of that meter would redefine the gram, which would then be multiplied by $1000$ to get the kilogram. But I read that instead the kilogram is some reference mass kept in a safe somewhere.

Are these definitions nevertheless consistent with each other or are we just doing away with the linkage between the centimeter and the gram via the water cube?


texts:
Imagine a bottle 85% filled with water and the rest is just air, and the cap is closed. Here are now my questions.

Since the cap is closed completely, the air bubble is formed. Is that air bubble compressed? In other words, since air has the least force of attraction between its molecules, they are more free than the molecules of water. Now since water is creating a pressure against the air bubble, does it mean that the molecules in the bubble are now closely packed than usual?

Is it possible for the air bubble, if compressed a lot, to mix with water?

If the air bubble is able to hold itself even in water, why do we say that air has lesser force of attraction that water?


texts: How does alcohol keep smell and taste flavors in wine?

texts: Nowadays alcohol free wine is also sometimes available. Now is seems that this wine has less taste and flavors in it. The cause for this is that alcohol seems to the capability to keep these flavors longer inside the wine. But how can alcohol do this?


texts: Evaluating inductive effects in cyclic compounds

texts:
I was required to find the products on heating the hydroxide of;
Now it's easy enough to find the answer; Hoffman elimination isn't going to happen from the methyl, and the n-propyl doesn't have $\beta$-hydrogens as acidic as that of the ethyl. It doesn't feel like the hydrogens in the ring are more acidic, either, so the product involves ethene. Simple enough.
But this lacks rigor. How do I actually evaluate the inductive effect on the $\beta$-carbons on the ring? If I have to compare it to some other fragment less obvious to win than ethyl, where do I start counting the carbons that inductively push electron density onto the $\beta$-carbons on the ring?


texts: How to determine which p-type GTO to choose in HF method?

texts:
I am trying to understand the working principle of basis sets in quantum chemistry. As far as I understand in the Hartree-Fock method, the basis set is used to calculate the matrix representation of Fock operator in each iteration in the SCF procedure. Usually each basis function in a chosen basis set is represented as a linear combination of several primitive Gaussian type orbital (GTO). I want to use cc-PVDZ basis for C atom which I can take from the EMSL Basis Set Exchange Library. For example in the Gaussian format:

!  cc-pVDZ  EMSL  Basis Set Exchange Library   10/19/17 2:40 AM
! Elements                             References
! --------                             ----------
! H     : T.H. Dunning, Jr. J. Chem. Phys. 90, 1007 (1989).
! He    : D.E. Woon and T.H. Dunning, Jr. J. Chem. Phys. 100, 2975 (1994).
! Li - Ne: T.H. Dunning, Jr. J. Chem. Phys. 90, 1007 (1989).
! Na - Mg: D.E. Woon and T.H. Dunning, Jr.  (to be published)
! Al - Ar: D.E. Woon and T.H. Dunning, Jr.  J. Chem. Phys. 98, 1358 (1993).
! Sc - Zn: N.B. Balabanov and K.A. Peterson, J. Chem. Phys. 123, 064107 (2005),
! N.B. Balabanov and K.A. Peterson, J. Chem. Phys. 125, 074110 (2006)
! Ca     : J. Koput and K.A. Peterson, J. Phys. Chem. A, 106, 9595 (2002).
!

****
C     0
S   8   1.00
   6665.0000000              0.0006920
   1000.0000000              0.0053290
    228.0000000              0.0270770
     64.7100000              0.1017180
     21.0600000              0.2747400
      7.4950000              0.4485640
      2.7970000              0.2850740
      0.5215000              0.0152040
S   8   1.00
   6665.0000000             -0.0001460
   1000.0000000             -0.0011540
    228.0000000             -0.0057250
     64.7100000             -0.0233120
     21.0600000             -0.0639550
      7.4950000             -0.1499810
      2.7970000             -0.1272620
      0.5215000              0.5445290
S   1   1.00
      0.1596000              1.0000000
P   3   1.00
      9.4390000              0.0381090
      2.0020000              0.2094800
      0.5456000              0.5085570
P   1   1.00
      0.1517000              1.0000000
D   1   1.00
      0.5500000              1.0000000
****

In the lines such as S   8   1.00 I know that the letter S is the orbital type, 8 is the number of GTO in this orbital's expansion, but what is 1.00 for?
The GTO for a p-type orbital has the form $x^l y^m z^n \exp(-ar^2)$ where the powers satisfy $l+m+n=1$ and thus there are three possible sets of $\{l,m,n\}$. But for instance in that link for lines with p-type orbitals, which possibilities shall I pick? The same question for d-type orbitals.


texts: Relationship between molar mass and density in solids

texts:
In ideal gases, it's pretty clear that 1 mole of gas occupies 22.4 L at STP. By knowing this, it's easy to calculate density given molar mass. However, this isn't true for solids. If I know molar mass of a solid, I cannot derive it's density.
I want to clarify whether my understanding of why we can't derive density in case of solids is correct. For solids, since each solid has its own lattice structure, knowing how the molecules are arranged is necessary, because if there is more space between molecules, it will have a lower density, which isn't really an issue in (ideal) gases where the arrangement of molecules/atoms is uniform.


texts: How to arrive at the preferred IUPAC name for 1,2-diphenylethane?

texts: I am reading a textbook that mentions the molecule 1,2-diphenylethane, $\ce{C14H14}$. A Google search leads to PubChem, where it is mentioned that the IUPAC name for the molecule is 2-phenylethylbenzene. I'm trying to understand how one names the molecule, using IUPAC nomenclature. However, I'm struggling to find any material that describes how apply IUPAC nomenclature to these "double benzene" (polycyclic aromatic hydrocarbon?) molecules. I would greatly appreciate it if someone could please redirect me to a page that describes this and describe the naming process for this particular molecule.


texts: Why is average bond enthalpy measured by homolytic fission?

texts:
Average bond enthalpy: the energy required for 1 mole of a specific gaseous bonds to undergo homolytic fission

Why specifically homolytic fission? Is it to allow comparison, but if that were the case, couldn't heterolytic also be used?


texts: Is there a way to concentrate the vitamin content of a particular food?

texts:
I'm looking for a way to extract vitamins out of common food sources of, well, vitamins.

Let's take, as an example, Vitamin A which is commonly found in carrots. A carrot (weighing around 60g) should contain around 500µg of retinoic acid (RA). RA is not soluble in water so in principle if I just dehydrate the carrot (which has around 50g of water) I would be left with around 10g of matter that still contains those 500µg of RA. I think that, with this simple procedure, I would be concentrating the amount of RA in my sample.

But maybe (surely) there are better ways to achieve this, to extract/purify a particular vitamin from food. Any ideas?

Also, some Vitamins are, instead, soluble in water, so we would need to apply another method for those.

And, finally, I would like to accomplish this using simple (household, if possible) techniques. It doesn't matter if I don't reach 100% purity, not even 1%, but if I can extract a 1g sample from my original carrot that has most of the RA still in it that would be huge.


texts: Why electronegativity instead of electropositivity

texts:
When I learnt about polarity, I always come to the term electronegativity and always use the electronegativity chart. However, when I studied further, they have the word electroposivity.

So, I've been thinking why we use electronegavity more often than electropositivity? And why we have a electronegativity chart instead of electropositivity chart?


texts: How do blue shifts in Raman spectra indicate a co-crystalline compound?

texts:
The short conference paper The Acetylene-Butane Co-Crystal: A Potentially Abundant Molecular Mineral on Titan (mentioned in EurekaAlert's 'Bathtub rings' around Titan's lakes might be made of alien crystals) says:

Experimental: Acetylene (purified to remove acetone stabilizer) and butane (99% purity) were condensed into a liquid nitrogen-cooled cryostage (Linkam Scientific Instruments Ltd.) at 90 K or 130 K. Raman spectra within the cryostage were obtained using a high-resolution confocal dispersive micro- Raman spectrometer (Horiba Jobin Yvon LabRam HR) equipped with a 50 mW Nd:YAG laser (frequency- doubled 532 nm) as the excitation source. Thermal stability studies were performed by warming in 5 or 10 K increments and obtaining Raman spectra following a 5-minute equilibration time.
Results: Blue shifts (12–29 cm-1) of the C≡C and C-H stretching modes indicate the formation of a co-crystalline compound. We observed similar shifts for co-crystals comprised of benzene and ethane (2–12 cm- 1 red shifts; Vu et al. 2014) and of acetylene and ammonia (7–16 cm-1 red shifts; 42–66 cm-1 blue shifts; Cable et al. 2018). These shifts indicate a change in the chemical environment of the molecular species, typically modification of a host crystal lattice to accommodate a guest molecule.

Question: Is it common to conclude that such blue shifts in Raman spectra "...indicate the formation of a co-crystalline compound"? There is a solid with both molecules in close contact so they interact, but how does this point specifically to there being  a o-crystalline compound?


texts: Chemical equilibrium and Le Chatelier Braun for ammonia production

texts:
In the book of Chemical, biochemical and engineering thermodynamics 4th edition from Stanley I. Sandler (Wiley, 2006), there is a problem about the ammonia producing reaction at page 770.

13.17 The simple statement of the LeChatelier-Braun principle
given in Sec. 13.1 leads one to expect that if
the concentration of a reactant were increased, the
reaction would proceed so as to consume the added
reactant. This, however, is not always true. Consider
the gas-phase reaction
Show that if the mole fraction of nitrogen is less than
0.5, the addition of a small amount of nitrogen to the
system at constant temperature and pressure results
in the reaction of nitrogen and hydrogen to form ammonia
whereas if the mole fraction of nitrogen is
greater than 0.5, the addition of a small amount of
nitrogen leads to the dissociation of some ammonia
to form more nitrogen and hydrogen. Why does this
occur?

So I approached this problem the following way:

\begin{align}
  \ce{N_2 + 3H_2<=>2NH_3}
\end{align}

The equilibrium constant:

$$K_c=\frac{[NH_3]^2}{[N_2][H_2]^3}$$

Now when we write this in terms of reactant consumption X:

$$K_c=\frac{(2x)^2}{([N_2]-x)([H_2]-3x)^3}$$

Now, when I use some values to try to prove this. I never get a negative X value, so I am not getting ammonia dissociation? Mind that I am not an expert on chemical thermodynamics and this question was also proposed to us in an industrial chemical engineering class where we discussed the Haber-Bosch process.

Can someone help me out here? Why is this not working? Or what is the right strategy to approach this problem.

Thank you in advance


texts:
I was looking up some ion channel blockers. What does (+) or (-) below mean?

(+)-Bicuculline

(-)-Bicuculline methiodide


texts: What will be the major product of of the Wurtz reaction of 3,6-dibromocyclohexa-1,4-diene?

texts: According to me, the answer should be (A) because that's a Wurtz reaction, but the answer given in the book is (B).


texts: How do I draw a curly arrow diagram for the oxidation of primary alcohol to an aldehyde and subsequently to a carboxylic acid?

texts:
I've determined the chemical equations for both the mechanisms, but I'm unable to draw curly arrow diagrams for the two reactions using potassium dichromate as the oxidising reagent. I'm not sure how to go about doing this, and I can't seem to find anything online related to do this.

From what I've studied,
oxidation of primary alcohol to aldehyde:

$$\ce{3CH3CH2OH + Cr2O7^2- + 8 H+ -> 3CH3CHO + 2 Cr^3+ + 7 H2O}$$

and, oxidation of primary alcohol to carboxylic acid:

$$\ce{3CH3CH2OH + 2Cr2O7^2- + 16 H+ -> 3CH3COOH + 4 Cr^3+ + 11 H2O}$$

I've found information pertaining to drawing curly arrow diagrams for the oxidation of secondary alcohols to ketones, but I'm unable to apply the same to my query.


texts: When to include or exclude lone pair counting electrons according to Hückel's rules?

texts:
When counting the number of pi electrons, in furan only one lone pair was included, but the other one was not.

In the cyclopentadienyl anion (2nd aromatic compound in the picture) the lone pair was counted.

When to include and exclude lone pairs in Hückel's rules?


texts: Difference between chemical energy and potential energy

texts:
I know that chemical energy is the potential energy stored in the arrangement of atoms within molecules. Forming new chemical bonds releases energy.

what does potential energy mean?
Is it the energy released when new chemical bonds are formed?
Or is it the needed energy to break the bonds of the compost?


texts: Is methoxide a better nucleophile than hydroxide?

texts:
What is more nucleophilic, $\ce{OH-}$ or $\ce{CH3O-}$?
When I look it from the viewpoint of steric hindrance, the answer seems to be $\ce{OH-}$, but when I see it from the viewpoint of extra electron density provided by hyperconjugation of $\ce{CH3}$, the answer seems to be $\ce{CH3O-}$.


texts: Since everyone knows an acid would dissociate(partially or fully) in its aqueous solution and liberate $\ce{H+}$. We also calculate the $\pu{pH}$ of the solution using $[\ce{H+}]$ and this$(\ce{H+})$ is what gives the solution acidity. Now consider we have just got a strong acid i.e pure acid without having any water in it, for example, $\ce{H2SO4}$ and no water in it, would the sulphuric acid dissociate in this case i.e without the aid of water? If it does not dissociate would this substance be acidic, since there would be no $\ce{H+}$ in that case?


texts: Predicting relative solubilites of salts without Ksp values

texts:
Is there a way of comparing which salt is more soluble without knowing their $ K_{sp}$ data or performing experiments?

For example, comparing $\ce{Hg2Cl2}$ and $\ce{Cr2(SO4)3}$.

I am not sure but can I compare lattice and hydration energy relatively or the ion size and estimate?

Experiments will give concrete results but I was wondering if there is another method just to gauge the solubility.

(The relevant chat discussion)


texts: Unknown possibly handmade glassware- description in information below

texts:
Okay, Another random item from the cupboard (unknown users or discipline of life sciences unknown) could be anything up to 40 years old....

This appears to be a 2 neck quickfit adapter (B19 and B14) leading to a long narrow tube which loops back on itself then loops again into a closed vessel. None of the other technicians can remember using this item but some of the items do look certainly altered by a glassblower if not entirely made by a glassblower. Whole item is 30cm in length...

Any thoughts on what it could be used for or what it might be?


texts: How do orbitals overlap in difluorosilane?

texts:
In $\ce{SiH2F2}$ four orbitals of silicon $(\mathrm{3s},$ $\mathrm{3p}_x,$ $\mathrm{3p}_y,$ $\mathrm{3p}_z)$ overlap with two hydrogen $(\mathrm{1s})$ and two fluorine $(\mathrm{2p}).$
I want to know how these orbitals are paired for overlapping.
Is it based on strength of overlapping?


texts: Gibbs free energy of phosphorus pentachloride decomposition reaction

texts:
The equilibrium constant at $\pu{227 °C}$ for the equation

  $$\ce{PCl5(g) <=> PCl3(g) + Cl2(g)}$$

  is $K_p = \pu{4.50E3 bar}.$ Calculate the value of $Δ_\mathrm{rxn}G^\circ$ at  $\pu{227 °C}$.

  With the temperature at $\pu{227 °C}$ and the partial pressures of the gases of  $p(\ce{PCl3}) = \pu{0.286 bar},$ $p(\ce{Cl2}) = \pu{0.713 bar},$ and $p(\ce{PCl5}) = \pu{3.06E-6 bar},$ calculate the value of $Δ_\mathrm{rxn}G.$

I calculated $Δ_\mathrm{rxn}G^\circ$ to be $\pu{-34.97 kJ mol-1}.$ Wouldn't it just be

$$Δ_\mathrm{rxn}G^\circ = -\pu{0.0083145 kJ mol-1 K-1} × \pu{500 K} × \ln(\pu{4.5E3})?$$

For the second part of the question I got $\pu{11.20 kJ mol-1},$ but apparently this is also wrong, no doubt because I got the first part wrong.

Would someone care to explain to me?


texts:
Is there any way to calculate the surface area of compounds such as 2,5-dimethylhexane or 3-methylpentane? If not, is there a database that has information on surface area of these compounds (not polar surface area). I'm doing an in-depth research between the correlation of surface area and boiling and melting point in branched chain isomers and really need to calculate the surface area of these branched chain isomers.

if it's through a program, please specify if the program is free to use


texts: Explain the 3c 2e or 3c 4e bond in these compounds

texts:
Can someone please explain how these compounds are formed/how the 3c 2e comes into existence.

Polymeric structure of BeCl2 - 3c 4e
BeH2 - 3c 2e
CH5+

Please explain in terms of the hybridization of the central atom and how the electrons are shared etc. Thanks!

My approach -

I know that in B2H6 there is a banana bond (3c 2e), but in BH3 it makes more sense - both B go into sp3 hybridization, and one hybrid orbital of each is empty where some overlapping takes place due to the H bonded with the other B, thus causing the electron pair to jump from one B to another. Thus named banana bond. With CH5 I don't understand how C is able to hybridize in a way such that it can have a banana bond. I read that it is of the form CH3 and H2 and 3c 2e bonding in between them, but I don't understand how it takes place.
For BeCl2 there are 2 Be having 2 Cls each and also coordinate bond by other 2 chlorines. Is that right?
But for BeH2, how can there be a 3c 2e bond? I mean based on the same principle, there must be a bond between Be, H that can jump to the other Be with same H, but Be doesn't have enough electrons to do this. Thus my confusion.


texts: Why is the energy of an electron always negative?

texts:
I just wrote my chemistry exam a few hours ago. However, I am still confused about the following question:

  Why is the energy of an electron in an orbital always negative?

I wrote that from the following equation

$$E_n = -R_h\left(1-\frac{1}{n^2}\right),$$

we can see that the energy will always be negative.

Is my answer correct?


texts: Percent of silver by mass in an unknown sample

texts:
Question
  If all of the silver in a $7.563~\mathrm{g}$ sample of a mineral, which was dissolved by using nitric acid, is precipitated as silver thiocyanate ($\ce{AgSCN}$) by using $82.46~\mathrm{mL}$ of a $0.2500~\mathrm{M}$ potassium thiocyanate solution, what is the percent silver (by mass) in the sample?

My Attempt
I'm pretty sure the relevant chemical equation here is $\ce{Ag^+ + SCN- -> AgSCN}$.

Molarity is mols solute over L solution, so the number of mols of $\ce{KSCN}$ used is $0.25~\mathrm{M} \times 0.08246~\mathrm{L} = 0.020615~\mathrm{mol\ KSCN}$. According to the chemical equation above, the molar ratio is 1 to 1 so there is $0.020615~\mathrm{mol\ Ag}$  involved. That accounts for all of the silver in the original mineral sample, I believe. Therefore, there are $2.22370~\mathrm{g\ Ag}$, so the percent silver by mass is $2.22370~\mathrm{g\ Ag} \div 7.563 ~\mathrm{g} = 0.294$. Put into percent, that's $29.4\%~\mathrm{Ag}$ by mass.

I'm unsure about this because  I totally ignored the nitric acid.


texts: How to calculate molar concentration from equilibrium equations with no initial concentration given

texts:
Consider the following equations:
\begin{align}
\tag{1}
  \ce{CO2 (g) + H2O (l) &<=> H2CO3 (aq)} &
  K_\ce{CO2} &= 10^{-1.47}\\
\tag{2}
  \ce{H2CO3 (aq) &<=> H+ (aq) + HCO^-_3 (aq)} &
  K_1 &= 10^{-6.35}\\
\tag{3}
  \ce{HCO^-_3 (aq) &<=> H+ (aq) + CO^-_3 (aq)} &
  K_2 &= 10^{-10.33}
\end{align}
I am also told atmospheric $\ce{CO2}$ is at $\pu{10^{-3.5} atm}$ and the solution is pure water.
So far I have been able to find the equilibrium equations and have got the concentration of $\ce{H2CO3}$ to be $\pu{10^{-4.97}}$. However, from this I do not know where to go in order to find the concentration of bicarbonate.


texts: Reasoning for baking soda treating poison ivy rashes

texts:
A quick Google search will show that baking soda (sodium bicarbonate) mixed with water in a 3 to 1 ratio will make a paste to be applied on poison ivy rashes. This is commonly advertised as a home remedy to poison ivy rashes.

Treatment for poison ivy ranges from mechanically removing the rash (scratching, which can make it worse), drawing the urushiol oil out, drying the rash, and simply waiting it out as your immune system takes care of it. Which method does this sodium bicarbonate paste use?

Basically, why should someone cover a poison ivy rash with a sodium bicarbonate paste other than it allegedly being an affective home remedy? Is there an scientific/chemical explaination as to why it might work?


texts: Reactions of diborane, silane, methane, aluminium, boron, sodium, phosphorus trichloride, white phosphorus and iron with water at RT

texts:
How many of the following will evolve $\ce{H2}$ gas when dissolved in water under room conditions?
$\ce{B2H6},$ $\ce{SiH4},$ $\ce{CH4},$ $\ce{Al},$ $\ce{B},$ $\ce{Na},$ $\ce{PCl3},$ $\ce{P(white)},$ $\ce{Fe}.$

Initially, it seemed easy to me and I got 7 (all except $\ce{PCl3},$ $\ce{CH4}).$ Correct me if I am wrong here.
However, the answer given was 3, which given were most likely $\ce{B2H6},$ $\ce{SiH4}$ and $\ce{Na}.$
What did I do wrong here? Does the temperature condition hold that much difference here? How do you predict products like these?


texts: Manufacture an artifact with compression

texts:
Room-temperature superconductivity has finally been demonstrated, as reported by Quanta (and others), with the caveat that it requires compression of the substrate at nearly 2 Mbar.  Obviously, this is an impractically high pressure, but if a different material were found that only required a much lower pressure, would it be feasible to manufacture wires under compression?  If so, what is the current state of the art?  I have not been able to find any examples of such a product.  Most apropos to chemistry, what is a practical upper-bound on tension/compression we can expect from currently known materials?
A trivial example would be to put a spring in a box, which only requires compressing the spring and sliding it into a box.  For the wire, one could perhaps imagine a strange "cylindrical press" (not sure if there is such a device) and a jacketing material with extremely high tensile strength into which the wire is thus threaded (or, more likely, the jacket is somehow rolled onto it).
A more sophisticated system would be a compressive jacket which is applied in a relaxed state, possibly at high temperature, and then cools/shrinks into a high-tension state which applies the necessary compression.


texts: Could you please explain how the bent molecular geometry of water is due to hydrogen bonding? I was under the impression that it was because of the lone pairs (VSEPR Theory).


texts:
For EDS mode of SEM, would you need to create a conductive path to ground for a BiOCl sample material. I have researched and found that gold and carbon can be used for such purposes, but I thought that BiOCl is conductive enough for grounding to occur.

The reason I'm asking this is I was reading a research article, and I came across the following EDS spectra of BiOCl:

I believe that on the left side "Cl" in purple is mislabelled, as Chlorine only has K-series emission, and the energy of such emission is greater than oxygen, so this led me to believe that the material is has to be smaller than Oxygen, and Carbon seems to be the obvious choice, but the research paper doesn't mention using anything apart BiOCl, and the mount which consists of Al and Cu.

Many Thanks


texts: Difference of reaction between NBS/CCl4 and NBS/AcOH

texts: With NBS/$\ce{CCl4}$ allylic bromination occurs. But with NBS/$\ce{AcOH}$ bromination occurs on the alkene double bond. Why does this difference occur and how? I.e what will be the mechanisms of both?


texts:
Why is ionization potential considered a periodic property???
A periodic property is a one which appears at regular property
But we see that every element has some kind of ionization potential


texts:
A friend and I recently produced some aluminum hydroxide, $\ce{Al(OH)3}$ for a project, and we wondered how it functions as an electrolyte. We know it has a low conductivity and solubility, but we wanted to know for knowledge's sake. We put some aluminum hydroxide in a bowl and used a power supply running at 31.9 volts (The resistance was high enough for the current to be immeasurable). We also used aluminum electrodes (aluminum foil).

The electrodes were bubbling and a white precipitate was forming on the top, and it seems we have less hydroxide than we started with...

So what exactly did we do?
$%edit$


texts: Increasing concentration of products in a reversible reaction

texts: My teacher says it is not possible to add more products to increase its concentration. This is because products are complex ions. Maybe I just misunderstood what she said. Can somebody verify and explain this to me?


texts: Why does the gauche conformation of ethane-1,2-diol show hydrogen bonding?

texts:
Why does the gauche conformation of ethane-1,2-diol show hydrogen bonding even though there is no 6-membered ring system? If we don't consider one of the $\ce{H}$ (which is what is usually done), then there is only a 5-membered ring formed. How then does hydrogen bonding take place?

(Also, I feel that there must be some reason apart from 6-member ring for hydrogen bonding which I'm not aware of)


texts: How to name this quintuply-bonded chromium dimer?

texts:
Depicted below is a chromium compound with a metal–metal quintuple bond. It boasts two identical bridging ligands, derivatives of 1,3-diphenylbenzene. The aim of this question is to figure out

the proper name.

Proper means without losing information. When answering, application of the 2005 Red Book and 2013 Blue Book is desired.

  Effort

  Identify central atom, derive ending: chromium
  Naming unsubstituted ligand, derive ending: 1,3-diphenylbenzene $\longrightarrow$ 1,3-(diphenyl)phenyl
  Allow for chromium's probably higher priority $\longrightarrow$ 2,6-(diphenyl)phenyl
  Add in the isopropyl groups $\longrightarrow$ 2,6-{[2,6-di(1-methylethyl)]diphenyl}phenyl
  Look for stereoisomers of ligand: probably none
  Count central atoms: two
  Identify and denote ligand connectivity to central atoms: 1κ$C^1$,2κ$C^7$
  Exploit symmetry, count ligands, prefix di already used: two $\longrightarrow$ bis
  Combine: bis(2,6-{[2,6-di(1-methylethyl)]diphenyl}phenyl-1κ$C^1$,2κ$C^7$)chromium
  Account for the bridging nature of ligands: add μ
  Notice metal–metal bonding: add $(Cr$—$Cr)$
  Probably (***) count number of bonds between metals: five $\longrightarrow$ $(5\ Cr$—$Cr)$
  Combine:

  bis(μ-2,6-{[2,6-di(1-methylethyl)]diphenyl}phenyl-1κ$C^1$,2κ$C^7$)chromium$(5\ Cr$—$Cr)$

  Change parentheses to allow for two chromium atoms: add []

Final proposed name (***):

bis[(μ-2,6-{[2,6-di(1-methylethyl)]diphenyl}phenyl-1κ$C^1$,2κ$C^7$)chromium]$(5\ Cr$—$Cr)$

Is this correct? Where have I gone wrong?

*** Point 12 conflicts with the Red Book. See IR-10.2.3.5 which says

  For the purpose of nomenclature, no distinction is made between different metal–metal
  bond orders.

This is at odds with imposed criterium of preserving information, hence was ignored. ***

Assembling the chemical formula will most likely be covered in a follow-up question.


texts: How do you recognize a carbohydrate molecule?

texts: I am studying carbohydrates in organic chemistry and I am confused a bit on what they are and how you recognize whether a molecule is a carbohydrate or not. For example, will a carbohydrate always have an $\ce{OH}$ group with either an aldehyde or a ketone group? Can it also contain other atoms like nitrogen or bromine? Can it have ether, ester?


texts: Determination of hardness of water using EDTA

texts:
Finding hardness of water by using EDTA. For determining permanent hardness we take the sample of about $\pu{50 mL}$ and then add Eriochrome Black T (EBT) indicator that results in wine red color due to calcium complex made by and also ammonia buffer. Then titrating it with ethylene diamine tetra acetic acid (EDTA) where change in color (i.e. sky blue) marks the end point of titration.

While carrying out experiment we add EBT as an indicator. Is there any criteria to add so in a fixed particular amount?


texts: If volatility depends on intermolecular forces, then why in Raoult's law, two substances have different volatility?

texts: I have a doubt, Ideal solutions are solutions where intermolecular forces between solute-solute and solvent-solvent are nearly equal to solute-solvent. Since intermolecular forces between A-A = B-B, doesn't that mean, they both have same volatility? But in Raoult's law, the graph shows that one of the vapour pressure is lower than the other resulting in two substances  having different volatility. I'm confused, where did I go wrong?


texts: Why do internal combustion engines only burn to carbon monoxide, not dioxide?

texts: Why don't diesel and regular car engines burn all the way to $\ce{CO2}$?


texts: Why are there more fluoride compounds formed with Xenon?

texts:
Based on WebElements, of the Noble Gases, $\ce{He}$ and $\ce{Ne}$ do not react with any of the halogens; however:

$\ce{HArF}$ has been detected at low temperatures (thank you to @bon and @Martin in the comments)
$\ce{KrF2}$ can be synthesised at low temperatures.
Xenon can react with fluorine to produce $\ce{XeF2}$, $\ce{XeF4}$ and $\ce{XeF6}$
Radon can react with fluorine to produce $\ce{RnF2}$

I understand that fluorine is the only halogen that seems to react with the Noble Gases (partly due to the related question Why Aren't Chlorides Of The Noble Gases As Prevalent As Their Fluorides?.  My question is

Why are there more fluoride compounds formed with Xenon compared to the other Noble Gases?


texts: Common flame-retardant plastic film materials?

texts:
More questions for my DIY hot air balloon:

What are some very common (i.e. easy to purchase) plastic film materials that have very good flame-retardant properties?

How is the "degree of flame retarding" of a plastic film material rated, so that I can compare materials by their manufacturer's rating?

Are there any common "spray on" flame retardant treatments that could work? Or is a flame retardant plastic film the only way to go to really stop it from bursting into flames?


texts: Why does tungsten(VI) oxide have higher melting point than tungsten(VI) fluoride?

texts:
I'm learning about ionic bonding and polarizability. Larger anions with higher charge should make more polarized ionic bonds. $\ce{O^2-}$ is both larger and has higher charge than $\ce{F^-}.$
So, why does $\ce{WO3}$ have a melting point of $\sim\pu{1473 °C}$ and $\ce{WF6}$ have a melting point of $\sim\pu{17 °C}?$
I should add that ionic compounds usually have higher melting point than the covalent ones, which makes it strange that $\ce{WF6}$ is the one with the lowest melting point, as I would think that to have the most ionic bond.


texts: On the angle subtended between the angular momentum vector and the applied field for a single spin

texts: According to Dr James Keeler of Cambridge University in one of his lectures at Queensland University, the angle theta can be any angle, but I struggle to see how this is true. There are only a certain number of I values that nuclei take and as illustrated in the figure above, each magnetic quantum number corresponds to a fixed theta. Is my logic flawed?


texts: Is it possible to use magnet to influence the reaction in order to favor one outcome over the other? ie addition reaction that favor the minor.


texts:
I made four different samples of poly acrylic nitrile (PAN) by going through a precipitation polymerization. The system was initiiated by the redox system $\ce{K2S2O8}$, $\ce{FeSO4}$ and $\ce{Na2S2O5}$.

The difference between the four samples was the used amount of $\ce{Na2S2O5}$. So my understanding was, that the $\ce{Na2S2O5}$ recovers the oxidized $\ce{Fe^{3+}}$ back to $\ce{Fe^{2+}}$. Therefore more initiations would take place. I noted the time each sample needed until they start to blur. To my surprise at a certain point, the more $\ce{Na2S2O5}$ was added the longer took the sample to precipitate. Now I wonder why this is the case. I'm thankful for every answer!


texts: Can I approximate the CO concentration of a combustion product, if I know the CO2 and O2 concentration?

texts:
Assume I have the product (exhaust gas) from a combusted air/petrol mix. The mixing ratio was richer than stoichiometric (i.e., air:fuel < 14.67 in this case), so there was no excess of oxygen.

I know the $\ce{CO2}$ and $\ce{O2}$ concentration of the combustion product, say 11% and 2% respectively. I also know that the combustion product only consists of $\ce{CO2}$, $\ce{H2O}$, $\ce{CO}$ and leftover $\ce{O2}$. (All fuel combusts to $\ce{H2O}$ and either $\ce{CO2}$ or $\ce{CO}$.)

Is it possible to approximate the $\ce{CO}$ concentration of the combustion product with that information?


texts:
I have a decanter which I use fairly often to pour out wines. I typically rinse it with hot water after the last wine has come out, but I cannot prevent it from forming 'residual' wine stains over time.

The last time I wanted to clean it, I looked on the internet for advice on cleaning. There are tons of it (Stained wine decanter), but I noticed that there are quite a lot of things around that don't work (or don't work well) and I figured that the question is basically plain chemistry.

Therefore, my question is, can somebody explain how I can best clean the wine stains from my decanter? Please, also explain the chemistry behind the method you propose so I know why it should work.


texts:
In a question I was solving, it was mentioned that:

  [...] closo-boranes are compounds having the general formula $\ce{B_nH_n^2-}$ [...] an example is $\ce{B6H6^2-}$.

Why do these boranes possess a (2−) charge? I am aware that in electron-deficient compounds such as these, there are different types of bonds between boron atoms (such as three-centre two-electron bonds), but I don't know why this should lead to a negative charge.


texts: What is the link between electrode surface areas and EMF?

texts:
I was wondering if someone would help me with my question.
I was completing a question which asked about the effect of increased surface area of a platinum electrode on the EMF of the overall cell.

This is the cell: Pt | H2O2(aq), O2(g) || IO (aq), I2(aq) |Pt

When I answered, I thought the EMF would increase due to the surface area of the electrode being able to now accept more electrons but I found out the answer is that the EMF is unaffected by any change in surface area, why is this?

Thanks for any help anyone can provide!


texts: Why are oxyacids strong oxidizing agents?

texts:
I saw that all the oxyacids are strong oxidizing agent.
I don't know why all the oxyacids are strong oxidizing agents?
What is the reason?


texts: What prevents self-condensation in the Perkin reaction?

texts:
An acid anhydride is condensed with an aromatic aldehyde in the Perkin reaction. The latter is non-enolisable, and thus the former forms the enolate which attacks as a nucleophile. If the attack is made at the aromatic aldehyde, an aldol-like product is formed which can be hydrolysed to the acid.

However if the acid anhydride enolate attacks another acid enolate, in a nucleophilic addition-elimination step, this results in the leaving of a carboxylate ion and the generation of an active methylene group (similar to Claisen condensation). There may be proton transfer between the two later. Surely this is more favourable than the first mechanism? Why doesn't this occur though?

Similarly, in the Stobbe condensation, instead of attack by the enolate at the ketone or aldehyde, cannot the succinic ester be attacked again?


texts: Does Cyclooctatetraene decolourise Br2 water and why?

texts:
I am thinking yes because it is not aromatic according to Huckle's rule. However, why in terms of orbitals etc?

I am a first year and so I am new to these concepts.


texts:
As the title says. I have surfed all of the net but could never find the answer to this question. Why do atoms need 8 electrons to stabilize? I mean why not 7 or 5 or 10 electrons? Why specifically 8? And what does stabilization of atoms even mean? Are the atoms going to burst without 8? Why do they need 8 electrons?

This is a question which is not often discussed in chemistry and I need an answer which really makes any sense. Not just `it is because the atoms need to fill their octet.


texts:
I'm an amateur writer and one of the topics I deal with is what happens when a slightly-mad scientist and engineer is given an opportunity to work with full-on “magic.”  So there are situations where magic is analyzed and other situations where the technology that comes from that analysis seems on par with “sufficiently advanced technology”... and there are plenty of dangerous shenanigans that result; one of which is when an experiment on regenerative healing magic is contaminated with HeLa cells, accidentally creating a magically-fueled, self-sufficient cancerous growth.

One of the solutions I was looking at was Piranha Solution, but I got to wondering if that concept could be ramped up.

Thus, I was wondering if fluoroantimonic acid and dioxygen difluoride mixture would work in a similar, if more volatile and violent, manner, or if there would be other, undesirable reactions?

If it would work, what ratio would be the most effective?


texts: Determination of molecular formula of hydrocarbons by combustion analysis

texts:
So, I've this question in my textbook:

  $\pu{20 mL}$ of unknown gaseous hydrocarbon reacts with excess oxygen gas. It decreases by $\pu{30 mL}$ upon cooling down. It decreases farther $\pu{40 mL}$ after it passes through an alkali solution. What is the formula of the hydrocarbon?

There is an answer provided, and I get the part where they calculate the "$x$" or how many carbon atoms one molecule of the hydrocarbon has. But, I cannot understand how they calculate the number of hydrogen atoms. There is a strange line,

  $$\pu{20 mL} + 20(x + y/4)~\pu{mL} - \pu{20x mL} = \pu{30mL}$$

The statement is:

  combustion of hydrocarbon and the following cooling down of the resultants mean the decreased volume of water vapor is $\pu{30 mL}$.

I do not get this line. Do they mean that the combined volumes of the reactants and the resultants are the same? That's an incorrect inference, isn't it?

P.S. Sorry for poor translation. The question is in my native language.


texts: Is every compound that has a H-bond donating group soluble in water?

texts: I am wondering if there is any general rule of thumb


texts: How does metal ions assist oxidative rancidity?

texts:
Oxidative rancidity is defined as the oxidation of unsaturated lipids and the carbon-carbon double bond with the presence of typically oxygen gas. Sometimes aldehydes and ketones are released as products.

How does the presence of metal ions catalyze this reaction? What are, if any exist, the reaction intermediates?

EDIT:

Here are some of the things I thought about:
The reason why light favors the oxidative rancidity of lipids while temperature does not, (at least not as far as I know) may be an indication that the reaction can not occur with out ionized oxygen atoms, which photolysis of oxygen may produce. This will also explain why simply increasing the temperature will not work, since increase in temperature does not lead to an increase in oxygen ions. The presence of metal ions would than be hypothesized to assist the oxidative rancidity of lipids by helping with the formation of oxygen ions. However, that calls in question whether or not should the metal be ionized to start with, because if the metal ions were cations to begin with, say it is $Na^+$ from table salt, how would that increase the concentration of oxygen ions?


texts: Why do we say there's no carbon dioxide present?

texts:
Were were estimating dissolved $\ce{CO2}$ in water by  American Public Health Association method. It was a titrimetric method using phenolphthalein indicator.

Titrant used was $\ce{NaOH}$ and analyte was sample water.

Our instructor said that on adding phenolpthalein if the water sample turns pink prior to the experiment (addition of $\ce{NaOH}$) then it can be concluded that no free $\ce{CO2}$ is present . But how's it so?


texts: Neither Raman nor IR Active vibrational modes of water

texts: How can we find vibration modes of water that are not in IR and Raman spectroscopy? I thought these modes creat when a transition happens between 2 modes i.e from mode to another mode.


texts: We know that at equilibrium Gibbs free energy is minimum. We also know that at equilibrium both forward and reverse reactions occur simultaneously, and we also know that for a reaction to be spontaneous Gibbs free energy should decrease in that direction. So if at equilibrium we have minimum Gibbs energy then both forward and backward reactions will be non spontaneous, since they are characterised by an increase in Gibbs free energy, therefore there should be no forward and backward reactions and hence, no dynamic equilibrium. Then why does a dynamic equilibrium exist?


texts: Liquifying a gas above critical temperature

texts: Is there any theoretical/hypothetical way through which a gas can be liquified above critical temperature? For example applying inifinjte amount of pressure to the system?


texts:
I'm trying to understand the gains phosphorus has from forming $\ce{P4O10}$. The molecular structure is such that every oxygen atom forms two bonds (either two with one phosphorus atom, or one with two), while every phosphorus atom forms five bonds.

I'm clear about the gains the oxygen has from this -- it fills its outer shell to the octet rule, mimicking neon effectively. But what about phosphorus? We're talking about a covalent bond, so forming five bonds would leave it with five extra electrons, which is two more than it needs to reach an optimal configuration.

I remember reading somewhere (possibly on this site) that ionic bonds can be regarded as an extreme form of covalent bonds, where the difference in electronegativity is so great, that the metal gives its extra electrons to the non-metal. Can we assume that the difference in this case is also large enough, such that phosphorus effectively 'gives' away five electrons, therefore reaching neon too? Or am I oversimplifying it?


texts: How to make this citric acid substance I made not sticky?

texts:
So I made this solid material by boiling citric acid crystals and water then letting that cool to harden.  It hardened into this solid that is really easy to mold and is transparent but it has this really annoying sticky texture that I want to get rid of.  I don't know if its the water causing this texture or not but can someone tell me how I can get rid of this and whats happening?

Thanks


texts: How to determine polarity of components in TLC

texts:
Estimate how a TLC-analysis would look like for the following reaction when you take a TLC at: a) the start of the reaction, b) after 65% conversion and c) after full conversion of A. (You may assume that A-C separate on the TLC-plate)

I am having a very difficult time understand how you can determine which compound is more polar by just looking at the structure. I don't know what to look at or what to prioritize.
When attempting to answer this question I assumed that B would be more polar (why: because it contains a nitrogen which is more electronegative than oxygen). So B should be closest to the baseline and A should be further away. What I then thought was that C should be in between A and B because the reaction reacts something polar and something less polar. This was not correct. Our professor drew the TLC-analysis like this:

And I don't really understand how I can determine that the product is more polar than both of the reactants. Is it because it contains both an oxygen and a nitrogen?
I would truly appreciate it if someone could give me some general rules or steps to follow to easily determine the polarity of different compounds.


texts: Arrange the following questions in the order of basicity? Also Tell why?

texts: The main confusion is between the compound (a) and compound (b) because in compound (c) we get aromatic ring(above) upon cleavage of double bond on N so it must be best whereas in compound (d) we get an anti aromatic ring (above ) so it must be least but what about coumpound (a) and (b).


texts: How does hyperconjugation lead to stability?

texts:
I know that hyperconjugation leads to delocalization of electrons between filled and unfilled orbitals and thus greater stability (that's what most textbooks said).

However, I think that it reduces the bond strength, because by saying that the electrons delocalized would mean that the electron density between two atoms decreases and hence the 'glue' (bond) that hold the two atoms together becomes weaker.

Any misconception here? Because my statement seems to contradict with the fact that hyperconjugation increasing stability. Why reduction in bond strength increase stability? (or does it actually decrease the bond strength?)


texts: How to find the change in internal energy (q+w) for an expanding monoatomc ideal gas?

texts:
If a monoatomic ideal gas simultaneously expands against a constant external pressure and drops in temperature, how do you find the internal energy change?
Known values are: $T_1$, $T_2$, $p_1$, $p_2$, $p_\text{external}$ and $T_\text{external}$.

Finding the work done by the expansion is easy, but I don't understand how to change in heat.
It is not a reversible process, so it can't be found from the work, and it's not isothermic, so it isn't zero. It can be found if I have the heat capacity but that is not given.
Edit:
The pressure changes from $p_1$ to $p_2 = p_\text{external}$


texts: Steric effects of a lone pair and piperidine

texts:
I know that in piperidine, the lone pair on the nitrogen can occupy either an axial or a equatorial position in the two chair forms. I also read that the axial position for the lone pair is preferred by a small margin in the gas phase (so intermolecular forces are minimized).

Now, this was presented as an argument against the idea that lone pairs are "sterically demanding" or "bulky" or repel other entities of negative charge more strongly than do bonding pairs, etc. The conclusion was that a lone pair must occupy less space than a hydrogen atom since it prefers the axial position in piperidine!

This argument seems correct at first, but could there be other factors affecting why the axial lone pair conformation might be more stable than the equatorial lone pair conformation? Also, are there any other examples in which the lone pair behaves "unexpectedly," at least with respect to elementary theory?

ETA: On the other hand one could make the argument that this isn't a apples to apples comparison; we are comparing a lone pair of electrons with a bonding pair of electrons plus a hydrogen atom. So it may be that this is a steric rather than an electronic (i.e. repulsive) effect.

Or could there be some sort of hyperconjugative effect going on? Carbon withdraws electron density from hydrogen; hydrogen becomes slightly partially positive, is attracted to lone pair?


texts: Is there such a thing as a list of "standard" odors?  In everyday context, there are various descriptions to odors such as "fruity" and "plastic-like".  But are there more accurate and normalized names of odors?


texts: In one task/example there is gas phase reaction and it is said that reaction takes place at pressure of 1 bar and standard Gibbs energy of reaction is needed to be calculated. In this task 1 bar is meant to be equilibrium pressure of a mixture. Problem I have is that total pressure initially is less than 1 bar since number of moles is increasing in reaction, but if so why do we calculate standard reaction Gibbs energy since such quantity is applicable for predicting equilibrium conditions at constant pressure? How can standard reaction Gibbs energy predict equilibrium state if pressure during reaction is changed?


texts: In this reaction after the attack of lone pairs on $\ce{H+}$ ions, a stable $3^{°}$ carbocation is formed. But seeing the six membered ring and the double bonds already present, I can't help but think that there's some way of obtaining a benzene ring through rearrangements. Can someone suggest a mechanism for this?


texts: Which one out of a keto group or a hydroxyl group would get protonated first if both are present in a compound (attachment)

texts: In the solution provided by my teacher he protonated the ketone, moved the +ve above by resonance did methyl shift and then did dehydration to form a benzene type system. Is this only because for this particular care aromaticity was being obtained or is the keto group always first protonated


texts:
From Wade's "Organic Chemistry" [1, p. 1003-1004]:

  MECHANISM 21-7 Conversion of an Ester to an Amide (Ammonolysis of an Ester)

Step 2, loss of a poor leaving group is justified by claiming the step is exothermic, hence the TS energy isn't very high (as would be the case w/ $\mathrm{S_N2}$ since it's neither exo or endo)

Why is this step exothermic though? No neutralization of charge and no net additional bonds were formed (1 pi bond formed, 1 sigma bond broken)

Reference

Wade, L. G. Organic Chemistry; Pearson Education, 2012,. ISBN 978-0-321-81139-4.


texts: What value should I use for P in the ideal gas equation for an unknown molar quantity?

texts: I did a chemistry lab, in which baking soda and vinegar were reacted in a ziplock bag, and I was to calculate the proper quantity of reactants to fill the bag with CO2. The molar quantity of gas was found using the ideal gas law, where volume, temperature, and pressure were all known. Pressure, however, was set to the rooms air pressure, and I was wondering why that would be the case. Wouldn't a plastic bag full of gas have a fairly high pressure? If its pressure were in equilibrium with the air, wouldn't none of the gas flow out when the bag is opened?


texts: Why is there a greater degree of separation in a dipole-dipole interaction?

texts:
My textbook says this:

  Electrostatic forces between two ions decrease by the factor $\frac{1}{d^2}$ as their separation distance, $d$, increases. Dipole–dipole forces, however, vary as  $\frac{1}{d^4}$. Because of the higher power of $d$ in the denominator, the attractive forces diminish with increasing $d$ much more rapidly than does  $\frac{1}{d^2}$. As a result, dipole forces are effective only over very short distances.

Now mathematically I understand why this is true, but I don't understand why this is the case in reality. Can someone shed some light on this?


texts: How to produce hot water-soluble soap balls? What is their chemical background? What about medical capsules?

texts: There are water-soluble balls for soap baths. Then there are medical capsules that disappear in mouth. Is it possible do this kind of capsules and water-soluble containers at home? If not, what do I need to do them? What is the chemistry behind them?


texts: What is the best way to illustrate the recovery of an extraction method?

texts:
I'm currently working on PFAS (perfluoroalkyl compounds) extraction from soils and their analysis by HPLC-MS/MS.

I wonder what kind of graph can be the best to illustrate the recovery of the method. I have tried with a boxplot on R and I think it's interesting because it shows the variability between all the soils that I used for the validation. The problem is that if their is different recovery between this matrixes (depending on the physico-parameter of the soils) we can't see it neither identify it.

What do you think about it?  According to you, what is the best way to illustrate recovery and how can I do it on R?

Thank you for your answers!


texts:
I have been trying to model various species decomposition/combustion in Chemkin Pro.
Chemkin only lets you to allow to input gas phase and surface site solid species in your input files, but I have various fuels/propellants in liquid state whose decomposition/combustion I need to model.
Is there any way to input liquid species reaction mechanism's in Chemkin by inputting them as gas species but somehow manipulating the Arrhenius coefficients, so that the software will ultimately model the liquid species in question?
Also if there's some other way to accomplish this instead of manipulating Arrhenius coefficients, I would be grateful for the input


texts: Why does CaCO3 react with HCl, but not with H2SO4?

texts: I have a wonderful reaction of marble chips, $\ce{CaCO3}$, with hydrochloric acid, $\ce{HCl}$, and carbon dioxide was released beautifully (fast, large volume, easy to measure and makes good visual effect too). But there is no reaction between $\ce{CaCO3}$ and $\ce{H2SO4}$. Why not?


texts: What is the materials science behind thermal diffusion in multispectral camouflage?

texts:
I've been interested in infrared and near-infrared camouflage (called multispectral camouflage) for a couple of days now, and I've found a video or two of certain companies that have created fabrics that both reject outside thermal and near-infrared radiation, and allow for scattering of infrared and near-infrared radiation originating from the body as body heat.

It's been three days and I've been searching for the materials science behind the camouflages, but I can't find anything relevant.

So, what materials/substances do you think they are using for this type of camouflage and why?


texts:
Although I am okay with rationalising bridging halides and $\mu$-2 CO I can't seem to figure out others, including $\mu$-2 hydride, CN- and NO.

When considering the electron count of bridging ligands, this is my rationale so far:

-Neutral bridging ligands contribute to the overall complex the number of electrons they would have when terminally bonded. These electrons are given in any proportion. This means that $\mu$-2 bridging CO gives 1 electron to a metal centre, for example.

-Ionic counting gives even numbers of electrons for ligands; I am unsure if this is still the case for bridging ligands - I suspect not?

Considering NO, I would therefore believe it to be a 2 electron donor to one metal and a 1 electron donor to the second metal.

Considering hydride, more specifically the dimer form of titanocene, I have been taught that each Ti centre is 16 electrons. I have been told, separately, that each hydride contributes half an electron in neutral counting, and 1 electron in ionic. This would lead to a 16 electron complex for "Titanocene" if there is a Ti-Ti bond, however this source: https://link.springer.com/content/pdf/10.1007%2Fs40828-015-0010-4.pdf seems to imply that it is in fact an 18 electron complex, with each individual hydride contributing more than its total electron count? Is this source correct (and my lecturer wrong) in how you would count this complex?

Considering CN-, this is similar to hydride I believe, and should be treated in the same way - is this correct?


texts:
When I have a solution of $\ce{Na2SO4}$, the sodium sulfate should ionize:
$$\ce{Na2SO4(aq) -> 2Na+(aq) + SO4^{2-}(aq)}$$

In my mind, the sodium ions should just float around, but because $\ce{HSO4-}$ is a weak acid:

$$\ce{HSO4- (aq) + H2O <-> H3O+ (aq) + SO4^2- (aq)}$$

The sulfate ion should be a weak conjugate base, and hence the sodium sulfate salt should be a weak base. This was my line of reasoning, until today my friends told me it is actually a neutral salt, which was confirmed by searching online. So why is it a neutral salt? (i.e. what's wrong with my reasoning?)


texts: For what reasons, is isopropyl alcohol widely used as a cleaning solvent?

texts:
I have worked in electronics and aeronautics industry 30 years ago, and I have always wondered, what were the specific properties of isopropyl alcohol, which make it used instead of other alcohols like common methyl or ethyl alcohol ?

Edit:

I know that it's less toxic than other solvent and that it is easier to separate from water (by adding salt) than other alcohols (reduce producing costs ?), but some reasons might be less pertinent than others.


texts: How does the stereochemistry of the enolate affect the stereochemistry of the aldol product?

texts: Cis enolates usually produce syn aldols and trans enolates produce anti aldols. How do exemptions from this "rule" arise?


texts: Calculating concentration of an ionic compound

texts: $n$ liters of $k$ M $\ce{NaCl}$ are poured into $m$ liters of $l$ M $\ce{NaCl}$. Determine $\ce{[NaCl]}$, $\ce{[Na^+]}$, and $\ce{[Cl^{-}]}$.


texts: Why doesn't this β-hydroxycarboxylic acid undergo dehydration upon heating?

texts:
This is a β-hydroxyacid, but why doesn't it get dehydrated to give an α,β-unsaturated acid on heating?

The mechanism which I think should occur is:


texts: Are all reactions with ΔG < 0 spontaneous?

texts: Given the formula $\Delta G = \Delta H - T\Delta S$. It is commonly written that all spontaneous reactions necessarily have $\Delta G < 0$. I was curious if the converse is true: Are all reactions with $\Delta G < 0$ spontaneous. If not, why?


texts: What determines the strength of reducing and oxidizing agents?

texts:
The best reducing agents are located at the bottom left of the periodic table (low electronegativity) and the best oxidizing agents are located at the top right of the periodic table (high electronegativity), excluding noble gases.

Is electronegativity the factor that determines the strength of reducing agents and oxidizing agents?


texts: Relating Thermodynamic & Transport Properties to Electrochemical discharge curve

texts:
What are the fundamental thermodynamic & transport properties that the discharge cycle of a rechargeable battery with an intercalating cathode (like Li-ion) should depend upon? The few that I could think of are

transport properties of the ion through electrolye & cathode material.
stress/strain properties of the cathode material due to intercalation.
chemical interaction of the solvent & ions with the cathode material.
electrochemical potential difference between anode & cathode.

My question is what formalism relates all these properties systematically to the experimentally observed discharge curve such as voltage as a function of capacity, repeatability of discharge curves etc.


texts: Buffer made of salts of polyprotic acid: reactions

texts:
I was trying to make a buffer with $\ce{K2HPO4}$ to use it in a bacterial culture.
If I use $\ce{K2HPO4}$ I think I have to add $\ce{KH2PO4}$. I am trying to think it writing the equations of the process but I have troubles.
I think the buffer's reactions will be:

Salt dissociation in water:
$$\ce{KH2PO4_{(aq)} <=> K+_{(aq)} + {H_2PO4^-}_{(aq)}} $$
$$\ce{K2HPO4_{(aq)} <=> 2K+_{(aq)} + {HPO4^{-2}}_{(aq)}}$$

Anion hydrolysis:
$$\ce{HPO4^2-_{(aq)} + H2O_{(l)} <=> H2PO4^-_{(aq)} + OH-_{(aq)}}$$

$$ \ce{H2PO4-_{(aq)} + H2O_{(l)} <=> HPO4^2-_{(aq)} + H3O+_{(aq)}}$$

If I add acid:
$$\ce{K2HPO4_{(aq)} + H3O+_{(aq)} <=> H2O_{(l)} + H2PO4-_{(aq)}} $$

If I add base:
$$\ce{H2PO4-_{(aq)} + OH-_{(aq)} <=> H2O_{(l)} + HPO4^2-_{(aq)}}$$

Is it correct? And if so, is it possible to add only $\ce{K2HPO4}$ and water to make the buffer?


texts: What is the correct structure of sodium thiosulfate?

texts:
Which structure of sodium thiosulfate is correct? One book says the second one (the one with co-ordinate bonds) and the other one says the first one?

According to me the structure 2 is correct as in that structure the octet of the middle S atom is complete whereas in the first one there's an excess.


texts: Liquid which neither dissolves in water nor oil

texts:
I am looking for a liquid which is not miscible (or very close) with water or vegetable oil.  Ideally, I want to have a container which shows three layers (the three liquids) with clear boundary layers.

I was thinking that I should find a non-polar compound of very high molecular weight - such that difference in the density of that compound and oil is enough to draw it down out of the oil.  However, I haven't found it yet.

I would prefer a compound which is non-toxic and non-flammable if possible.

It feels like such a simple question, I must be missing something.


texts: Energy required for obtaining required mass of aluminium from alumina via electrolysis

texts:
How do I know how much energy I need to obtain 20 g alumunium from alumina with 5 V?

I calculated the quantity of electricity is 2.22 F.

Any help appreciated!


texts: Are there examples of crystals with random but static mixtures of two unit cell configurations?

texts:
The image in this question turned out to probably be wrong, but it still makes me wonder. Are there examples of crystals where the atoms within a unit cell can have two (or more) different configurations or orientations who's energies are so close that a sample crystal at room temperature could have a random but static mixture of the two?

With sufficiently large organic molecules (e.g. proteins) this could be true and possibly even common, but I'd like to know about a simple example with a small number of atoms in the unit cell. It might be produced by rapid cooling or crystallization from solution in unusual conditions, and it might be detectable (at least in some cases) by a slight broadening in high resolution X-ray diffraction peaks. (sort of a solid-state version of Raleigh scattering perhaps?)


texts: Why is this PH3 considered to be an unhybridized molecule?

texts:
Also, don't hybrid orbitals appear in all molecules?

The answer by "ron" says "the molecule can be viewed as being unhybridized":
How does lone pair of a central atom affect the dipole moment?


texts: Preparation of alcohols from Monosubstituted cyclic ethers

texts: Can methyl oxirane(epoxide) (a mono substituted 3 membered cyclic ether) form alcohols by reacting it with Grignard reagent? If yes, can you please explain the reaction with mechanism? If no, why?


texts:
I want to ask that cross cannizzarro could be possible between any aldehyde + ketone mixture(without alpha H) and we get products as aldehyde get oxidised and ketone get reduced(along with self oxidations and reduction products of aldehyde)? Is it correct?

I think it is possible after going through the mechanism but searched in different books and doesn't get anything about it...


texts: How is more than one pinacolone is possible?

texts:
This question came in one of my school tests. They had given us an unsymmetrical pinacol i.e 1,1-diphenyl-2-methylpropane-1,2-diol and asked us whether it will give only one pinacolone or not.

According to me, I had assumed that carbocation will be formed on the diphenyl-substituted carbon due to which a methyl shift will occur and we will get only one product. But my teacher marked it wrong and said that more than one pinacolone is possible here.

How is it possible?


texts: To what microscopic quantity does Gibbs energy correspond to?

texts:
Is the Gibbs energy of a system equal to the potential energy of a system? The answers to this and this questions seem contradictory. Also, this does not seem to tell that Gibbs energy is equal to the potential energy. By potential energy, I mean the Electric potential energy between the atoms, electrons and nuclei.(I'm not considering other potentials due to nuclear forces or gravitational forces.)

If Gibbs energy is not potential energy, then what is the physical significance or physical interpretation of Gibbs energy at the molecular level? I know that Gibbs energy is equal to the maximum non-expansion work that can be extracted. I just want to know what does that mean at the molecular level.


texts: I think the bridge head nitrogens won't react.The answer is B C A. Can someone help me, please


texts: Is it possible to displace cerium from cerium sulphate using aluminium to get pure cerium metal?

texts: I'm unable to find cerium any reactivity series, hence the question..


texts: Hemoglobin equilibrium - effect of increased carbon dioxide and lactic acid

texts:
The binding of oxygen by haemoglobin giving oxy-haemoglobin is partially regulated by the concentration of $\ce{H3O+}$ and dissolved in $\ce{CO2}$ in blood
$$\ce{HbO2 + H3O+ +CO2<=>H+.Hb.CO2 + O2 + H2O}$$
If there is production of lactic acid and $\ce{CO2}$ in a muscle during excretion then is more oxygen released or is more $\ce{HbO2}$ formed?


texts:
The question "Why does a hard-boiled egg have more entropy than a normal egg?" was recently asked on one of my tests.

I said that entropy will decrease as a hard boiled egg has molecules in a more organised way than an raw egg, but I was marked wrong with a remark that entropy will increase because the proteins and other molecules are decomposed into simpler substances due to heat.

I did ask why I was not correct but what I got was the same explanation along with the decomposition reactions.

I don't feel this explanation is satisfying.

For example, do not 10 objects on a table organised properly have more entropy than 5 objects thrown anywhere on the table?

The definition of entropy is the measure of disorder in the system. So clearly in my above example the 10 objects are more organised and thus less disordered than the 5 objects in the second case and same can be said for the main question.

Can somebody please explain to me why a hard-boiled egg has more entropy than an un-boiled egg (I like if the explanation has some math)?


texts: Dissolvant for the black spots around the rear mirror of the front window of my car

texts:
I make pictures for Mapillary.
I would like to place my dashcam as high as possible, but those black spots get in the way.  Scraping them off does not work.
But I can feel their relief.
If no one has a better idea I will begin the trials with a sticker remover.

I do not find the exact word for those spots any more.


texts:
This is apparently a true statement:

"In a hydrogen atom, the 2s and 2p subshells have the same energy."

Why is this the case? Why would they be of the same energy? Wouldn't the 2p be slightly higher in energy than the 2s?


texts: Reaction rate in terms of temperature change

texts:
For exothermic reaction where concentration changed in hard to measure, can I interpret the rate of reaction in terms of temperature change?
For example, if the experiment is iron rusting reaction with salt as a catalyst in water and I measure the temperature change and plot a graph of temperature vs time, can I say that the steeper trendline has a faster reaction rate?


texts: What is the behavior of a Zwitterion during ion exchange chromatography?

texts: We're interested in purifying a protein that has an azide moiety using ion exchange chromatography. Due to its unique structure, the moiety is a Zwitterion with a novel chemical behavior. My question is how will the molecule behave when I run it through an ion exchange column? Will it be considered positively charged, negatively charged, or neutral or is it much more complicated?


texts: How does the addition of acetone cause a shift from hexaaquacobalt(II) to tetrachloridocobaltate(II)?

texts:
For this reaction, at equilibrium,

$\ce{[Co(H_2O)_6]^2+ + 4Cl^- <=> [CoCl_4]^2- + 6H_2O}$

$\ce{[Co(H_2O)_6]^2+}$ and $\ce{[CoCl_4]^2-}$ are red and blue in aqueous solution, respectively.

When acetone is then added, the solution changes from red to blue. What causes this?


texts: Ground state electron configuration of chromium

texts:
What is the ground state electron configuration of chromium?

Is it $\ce{[Ar]}4s^23d^4$ or

Is it $\ce{[Ar]}4s^13d^5$


texts: Why does phosphine have a dipole moment and a higher boiling point than carbon tetrafluoride?

texts:
Phosphine, PH3, and carbon tetrafluoride, CF4, are small molecules of a similar size and the same mass of 88 au. CF4 has a dipole moment of 0, which is unsurprising given its tetrahedral shape. However, I would expect P-H bonds to be non-polar (P and H have electronegativities of 2.19 and 2.2) and therefore the molecule to also have a dipole moment of about 0, despite being trigonal pyramidal and therefore asymmetrical. So I would expect it to exhibit similar intermolecular forces and a similar boiling point to CF4. Yet PH3's dipole moment is quoted as 0.58 D. And PH3 has a boiling point of -88 °C and CF4's is -128 °C.

Why does phosphine have such a higher dipole moment and boiling point than CF4 despite it having non-polar bonds?


texts:
Recently I did a reaction in the lab (the reaction itself is not important) whose product was colloidal sulfur. As I watched the sulfur particles form I noticed something strange: At first the sulfur particles appeared white, but after a while the solution turned yellowish (probably when the size of the sulfur particles grew a little). I know that sulfur's colour is yellow by nature, because of its absortion soectrum, and I understand that the white colour is probably due to Mie scattering of light by the colloidal particles.

My question is: Why aren't the particles yellow? if the absortion spectrum has as a consequence a yellow colour I would expect that spectrum to remain valid at all dimensions of the particle, the particle can't just randomly decide to stop absorbing light of some wavelenght when it reaches a threshold size... can it?

I know that Mie scattering predicts that a particle will scatter all wavelenghts equally if its size is comparable or bigger than the wavelenght of light, but I would have thought that if the particle absorbed a specific wavelenght that wouldn't change with size.


texts: Lemon juice, the ultimate anti-foaming agent?

texts:
As an amateur soda maker, I have noticed an odd phenomenon: lemon juice sodas do not foam. Virtually every juice I have tried foams to some degree when mixed with carbonated water. Lemon juice does not. I have read "folk" explanations for this as being due to the "acidity" of the lemon juice, but this is not correct because other acidic juices like lime and orange juice foam. Why is it that lemon juice has an anti-foaming action?

Further information: it should be noted that "pasteurized" (ie, boiled) lemon juice does foam. Only fresh-squozen lemon juice is anti-foaming. Therefore, what is doing the anti-foaming may likely be some volatile compound.

My understanding of anti-foaming is that it is caused primarily by localized depression of surface tension, and that liquids having heterogeneous species promote anti-foaming because of the surface tension differential between those species at the surface. Therefore, one possible theory is that the lemon juice has some volatile oil which populates the surface of the water only in spots and is causing the surface tension breakage. Even if this theory is correct, it remains to determine what this mysterious volatile oil is that is the cause.


texts: What might be the reason for the longer stem found in some separation funnels?

texts:
Most separation funnels have a stem around 50 to 70 mm long (often less if fitted with a ground taper joint) that is used to direct the output into a receiving flask.

While the stop-cock has a small bore matching the small end of the funnel to reduce dead volume the stem tube is generally short and has an internal diameter around 6 to 10 mm to prevent a valuable liquid column being retained in the stem.

Having received a separation funnel c.1970 with a stem of around 200 mm (below the stop cock) I was curious what benefits it could offer over the disadvantages of more difficult clearing of the liquid column in the stem and possible much more likely mechanical mishaps when waving the thing around.  I went looking and found that long stem variants are available from numerous vendors but without any explanation of what their purpose might be.  I have not seen any demonstrations or descriptions that use or call for a long stem separation funnel so I am curious how they are used.

Could the long stem relate to the occasional presence of long stems in regular 60 degree filter funnels and thistle funnels. Could it have some application for faster draining with the addition of the weight of the liquid column?

P.S. The funnel in question is not the Gilson type with an intermediate diameter cylindrical section between the bulb and stopcock. The stem has a larger bore than the stopcock so not a capillary.  It has a typical ground glass stopper.


texts:
Which of the following undergoes disproportionation with $\ce{NaOH}$?

  $\ce{SiO2}$ (silicon dioxide)
  $\ce{CO2}$ (carbon dioxide)
  $\ce{SO2}$ (sulfur dioxide)
  $\ce{SO3}$ (sulfur trioxide)
  $\ce{NO2}$ (nitrogen dioxide)

From the above we can conclude that $\ce{SiO2}$, $\ce{CO2}$ and $\ce{SO3}$ do not undergo disproportionation as they are all in the maximum oxidation states. $\ce{NO2}$ is in the +4 oxidation states so it disproportionates in to +3 and +5 upon addition of aqueous $\ce{NaOH}$. But what about $\ce{SO2}$? It can also disproportionates because it is in +4 oxidation no. But the answer states only $\ce{NO2}$. Can anyone please explain the reason?


texts: What do '(6S)' and '5' mean in (6S)-5-formyltetrahydrofolate?

texts:
Tetrahydrofolate:

I guess (6S) means some sixth S-center and 5 some other kind of numbering.


texts: Why does energy need to be "compensated" in order for solvation to occur?

texts:
I am currently learning about the physical properties of alcohols.

I understand that the main intermolecular forces between alcohols and water are hydrogen bonds. When these two are mixed, the intermolecular hydrogen bonds between alcohol and water are broken and hydrogen bonds between alcohol and water molecules are formed. I also read that as an alcohol's hydrocarbon chain gets longer, it is less soluble, as the hydrocarbon part is hydrophobic and that is becoming more significant (while the OH becomes less significant).

There's one part I'm confused about. I read a website which stated that:

  The energy released when these new hydrogen bonds are made more or less compensates for that needed to break the original ones.

I understand what the author is trying to say here, but I'm confused about why this needs to happen? Why does the energy need to be "more or less compensated"? Why can't long alcohols just break their hydrogen bonds and form weaker van der Waals forces with the water (the hydrocarbon part cannot form hydrogen bonds).


texts: Can I make a buffer with a weak acid without adding it's conjugated base, when the desired pH of the solution is exactly the pKa of the weak acid?

texts:
An acid will be 50% dissociated when the solution it's in have a pH equal to the acid pKa ('afirmation 1', for later reference).

We also know that a good buffer solution have equal concentrations of an acid and it's conjugated base.

That's why to make a good buffer we look for an acid that have a pKa close to the pH we want to maintain.

So, suppose I have a solution with a pH 6.2, and I want to add a buffer to maintain this pH at 6.2.

Suppose also, that I have a ideal weak acid for this situation: with a pKa of exactly 6.2.

Using the Henderson–Hasselbalch equation, we know that we need to have the same concentration of the acid and it's conjugated base in the buffer. To add the conjugated base, we use a salt of the refereed acid.

So my question is: If we just throw the acid at the solution without the salt, since the solution pH is exactly the pKa of the acid, the acid will dissociate 50% (afirmation 1), and we will end up with what we wanted: The same concentration of the weak acid and it's conjugated base.

So, in principle, it's possible to make a buffer without adding the salt?

Is this logic correct? If not, what error I'm making?

Thanks


texts: Why can alkali metal hydrides usually not act as nucleophiles towards carbonyl groups?

texts: Think for example of $\ce{KH}$ or $\ce{NaH}$ in enolization reactions. This remark was made in one of my textbook, but I could not remember why this was actually the case. Why can't $\ce{NaH}$ or $\ce{KH}$, being hard nucleophiles, add to carbonyl groups?


texts: Why does the liquid in an Oralmedic stick flow uphill after I turn it upside-down?

texts:
I was experimenting with an Oralmedic stick, which is basically a cotton swab with a hollow stick that has liquid medicine inside, and observed something very unexpected.  I followed the usage instructions, which say to snap the cotton bud at one end. As expected, the liquid inside the stick began flowing down into the cotton bud at the other end.

Out of curiosity, I turned the stick upside-down, to see what would happen. I was really surprised to see that the liquid still kept flowing in the same direction, which was then uphill after I inverted the stick!

How is this possible?


texts: Does the subscript $\ce{X}_{cc}$ mean concentrated? I have never seen this notation. How often is it used and what are the general guidelines to denoting concentrated reagents?


texts: Why are amines more soluble than ethers in water?

texts: For example, diethyl ether ($\ce{C2H5OC2H5}$) has a limited solubility of $6.05\rm~\frac{g}{100~mL}$ water at $25\rm~^\circ C$. However, diethylamine ($\ce{(C2H5)2NH}$) is a lot more soluble in water. Why are ethers less soluble than amines? Both can form 2 hydrogen bonds with water (ethers accept two H-bonds, and amines donate an H-bond and accept an H-bond). Oxygen is more electronegative than nitrogen, so shouldn't ethers be more soluble?