texts: When is rotation around double bonds to form cis-trans isomers allowed?

texts:
Textbook Question:

The rhodopsin molecules in the retina contain a derivative of vitamin A called cis-retinal (Figure 6). On exposure to light, cis-retinal becomes an isomer called trans-retinal.

This process helps cause an electrical impulse to be transferred to the brain. Around which numbered bonds does the isomerism rotation occur?

The answer is bond 11 (shown in red).
What I don't understand is: I thought rotation is not allowed around double bonds.
So when light hits the structure in Figure $6$, how does it cause rotation around bond $11$ to form the structure in Figure $7$?


texts: Why does the viscosity of honey decrease when mixed with other viscous fluids?

texts: In order to make honey mustard, I mix honey and mustard.  But the resulting mixture is less viscous then both honey and mustard.  How does mixing two viscous substances give a less viscous one?


texts:
A $20\ \mathrm l$ steel cylinder containing $\ce{N2(g)}$ at $20\ \mathrm{atm}$ and $300\ \mathrm K$ is kept in a big jar containing air at $1\ \mathrm{atm}$ and $300\ \mathrm K$ and sealed. $\ce{N2(g)}$ starts leaking into the jar but reversibly and isothermally. When both
  mechanical and thermal equilibria are stabilized, pressure in the jar was $1.19\ \mathrm{atm}$. Determine work
  done by $\ce{N2(g)}$.

Since there is mechanical equilibrium, the pressures should be equal to $1.19\ \mathrm{atm}$ inside and outside the cylinder with nitrogen. And since temperatures are equal too, should I use this formula for work?
$$W=-nRT\ln\frac{V_{2}}{V_{1}}$$


texts: Why Does A Brønsted–Lowry Acid Accept Proton from Stronger Acid?

texts: This is mechanism of Nitration of Benzene. In the first step, Nitric Acid (pKa = -1.4) accepts a proton from sulfuric acid which is stronger acid (pKa = -9). According to Brønsted-Lowry theory we consider acids dissociate increasing proton concentration and bases dissociate increasing hydroxy concentration. On the other hand bases also accept proton from acids. Therefore should we accept nitric acid as a base in this case ? If not, why does an acid accept a proton from another "stronger" acid ?


texts: How do we obtain the π molecular orbitals for allene via Hückel theory?

texts:
For a conjugated system, for instance 1,3-butadiene, we can try to obtain the π molecular orbital energies and wavefunctions via Hückel theory. In our given molecule, there are 4 interacting Pz orbitals. By creating a 4x4 Hückel matrix and solving for the energy eigenvalues, we can arrive at 4 possible linear combinations (of p-orbitals) to get 4 molecular orbitals.

However, how can we use Hückel theory to deal with a molecule like 1,2-propadiene (allene)?

My attempt: I thought that since this molecule has essentially 2 separate π-systems:

we may be able to apply Hückel theory to each one individually. Then, we can take all the possible combinations of the individual energies to arrive at the possible total energies. But I am not sure if this is correct. What would be the correct way of approaching this problem?


texts: are the exact and kohn-sham electron densities totally symmetric?

texts:
For any molecule with open or closed shells considering the electronic state to be the ground state:

Is the exact electron density totally symmetric?
is the Kohn-Sham electron density totally symmetric?

(spatially upon symmetry operations of the molecular point group).
I refer to "exact" as the density built using the wave function of the molecular Hamiltonian in the Born-Oppenheimer approximation. And I refer as the KS electron density as the one built by a single Slater determinant solution of the KS equations with the exact exchange-correlation functional or approximations. In principle due to the Hogenberg-Kohn theorems these two electron densities should be the same, nevertheless it seems that they cannot be in certain cases. This is why I distinguish the two densities.


texts: Does the distance increase as the polarity increases?

texts: According to the dipole moment's definition, as polarity increases the distance between the centres of positive charge & negative charge increases.In the ionic bond ,as the polarity is maximum, distance between the two charged centres is maximum.Is this concept correct? If not what is the relationship between distance and polarity. I m not getting any intuition.


texts: How can I change the synthetic conditions for powder product into single crystal growth?

texts: I am working on growing metal-organic frameworks crystals based on hexatopic linker for different metals. Upon using some synthetic conditions it gave fast precipitation into powder material after heating for half hour. My question is how to modulate the synthesis to grow single crystals for Zr, Fe, Al in my case? I used metal salt:linker as 10:1 using modulator 100 equivalent to metal salt.


texts: How does dissolving a hydrate affect concentration?

texts:
Say I have 0.72 grams of calcium chloride dihydrate. If I dissolve it in water, the 2 water molecules attached onto it dissociates just like the $\ce{Ca^{2+}}$ and $\ce{Cl-}$, right?

And if so, wouldn't it lower the concentration of the calcium chloride, as compared to making an anhydrous calcium chloride solution?


texts: Why do stable enols give positive ferric chloride test?

texts: It is known that phenol and all its derivatives give violet colour with neutral alkaline ferric chloride solution. However I also found out that stable enols, like 2,4 di-oxo pentane, also give this test. The reason eludes me.


texts: Why apart from when building atoms in the first place, the 3d is the lower energy orbital?

texts:
From chemguide.co.uk:

  If the phosphorus is going to form $\ce{PCl5}$ it has first to generate 5 unpaired electrons. It does this by promoting one of the electrons in the $\mathrm{3s}$ orbital to the next available higher energy orbital. Which higher energy orbital? It uses one of the $\mathrm{3d}$ orbitals. You might have expected it to use the $\mathrm{4s}$ orbital because this is the orbital that fills before the $\mathrm{3s}$ when atoms are being built from scratch. Not so! Apart from when you are building the atoms in the first place, the $\mathrm{3s}$ always counts as the lower energy orbital."

Could you please explain why this is so?


texts: I have always thought that fuel such as petrol, diesel, etc.. are getting burnt to move the pistons in the car (I am not bringing physics). Why not hydrogen be used as a fuel but I know the incident about the Hindenburg disaster but the same thing could happen if the Hindenburg was filled with petrol. So both are combustible and that's what we want. Petrol and hydrogen do the same job what does he want?. When hydrogen is burnt there won't be any smoke so it saves the environment. PS: This is just to make this question a bit understandable I have mentioned the word "Alone" in the question.


texts: How can I relate the reactivity series to electronegativity and ionization energy?

texts:
I am trying to figure out how the reactivity series comes about. My understanding is that elements with a higher electronegativity will be more reactive than elements with a lower electronegativity, and that elements with a low ionization energy will be more reactive than elements with a high ionization energy.

Here is a chart of electronegativity (from Wikipedia):

This shows electronegativity decreasing (as reactivity increases) down Group 1 and it also decreasing (as reactivity decreases) down Group 7.

Here is a chart of ionization energy:

This shows ionization energy decreasing (as reactivity increases) down Group 1 and it also decreasing (as reactivity decreases) down Group 7.

Neither electronegativity nor ionization energy can predict both reactivity trends, so what is going on?


texts: Why don't effervescent vitamin C tablets react with the vitamin C?

texts:
I have a packet of effervescent Vitamin C tablets. When placed in a glass of water, a tablet will fizz and dissolve. They have the following ingredients (all included for completeness):

citric acid
ascorbic acid
sodium hydrogen carbonate
sorbitol
sodium carbonate
inulin
potato starch
zinc citrate
tricalcium phosphate
maltodextrin
riboflavin phosphate sodium
sweetener & flavours
tocopherol

I'm guessing that the citric acid is intended to react with the sodium hydrogen carbonate to effervesce.

Given that vitamin C (ascorbic acid) is also an acid, surely it could also react with the sodium hydrogen carbonate, removing the vitamin C from the finished drink?

Does this happen to any extent? If so, in what proportions? If not, why not?

The ingredients state how much vitamin C is present in the tablet, not in the finished product. This is also specified as a proportion of government recommended recommended daily amounts, which suggests that one would receive that amount if one took a dose as directed. If the vitamin C does react, does this mean that the label doesn't indicate how much vitamin C is available?

(I last studied chemistry at GCSE level in [high] school, so please excuse the lay question. A simple answer would be most useful!)


texts:
E2 mechanisms are known to be irreversible in general, because the forward step takes 2 species and produces three species, and a trimolecular reverse step is unlikely, purely on entropic grounds. (As mentioned in this post.)
Now does that mean that any reaction that is reversible cannot have an E2 step, on the grounds of microscopic reversibility?
Particularly, I want to ask about this hypothetical mechanism, of an isomerisation:

I am not sure how to draw its mechanism. Clearly, some elimination reaction is taking place: it can be E1, E2 or E1cB. Because this is an alkene compound, E1 seems unlikely, only E2 and E1cB are possible. $\ce{MeS-}$ seems like a bad base for both E1cB and E2, so I can't say which one is better. Can I remove E2 from the options purely because the reaction is reversible?
[Note: This is an exercise question which asks me to draw the best possible mechanism if the intermediate detected was the one in the picture. It does not matter if the actual reaction happens in that way or not, the question is hypothetical]


texts: First order, parallel reaction integration

texts:
I have parallel equations:
\begin{align}\ce{A &->[k_b] B},&\ce{A &->[k_c] C}.\end{align}
I understand how to determine formation of $\ce{A}$ (with the integration) but I really keep going in circles with integrating $\ce{B}$. If I can have some assistance in how to integrate $\ce{B}$, then I will be fine for integrating $\ce{C}$.

This is what I have:
\begin{align}
\frac{\mathrm{d}[\ce{B}]}{\mathrm{d}t}
&= k_b[\ce{A_0}] \cdot \mathrm{e}^{(-k_b+k_c)t}\\
\int_{[\ce{A_0}]}^{[\ce{A}]}\frac{\mathrm{d}[B]}{\mathrm{d}t}
&= \int k_b\cdot[A] \mathrm{d}t\\
\ln\frac{[\ce{B}]}{[\ce{A_0}]}
&= \int k_b\cdot[\ce{A_0}] \cdot \mathrm{e}^{-(k_b+k_c)\cdot t}\mathrm{d}t\\
\end{align}

To save the embarrassment, once I raise to the "$\mathrm{e}$" of both sides, I get
\begin{align}
\frac{[\ce{B}]}{[\ce{A_0}]}
&= \mathrm{e}^{\frac{k_b\cdot[\ce{A_0}]}{(k_b+k_c)}t} \cdot \mathrm{e}^{\mathrm{e}^ {-(k_b+k_c)t}}\\
[\ce{B}] &=[\ce{A_0}] \mathrm{e}^{\frac{k_b\cdot[\ce{A_0}]}{k_b+k_c}t} \cdot \mathrm{e}^{\mathrm{e}^{-(k_b+k_c)t}}\\
\end{align}

Can someone show me the steps of integrating the $\int k_b\cdot[\ce{A}] \mathrm{d}t$?
Very basic steps are available in solutions, but it still does not fully show the integration/algebra and I am just very lost.


texts: Differences between Liquid and Solid Infrared Spectrometry

texts: In general, when should I use liquid or solid IR spectrometry to analyse my compound? What should I expect to see? Would I see higher or lower frequency, broader or narrower transitions? My specific case is a tricobalt cluster, Co3(CBr)(CO)9. But I'm also curious for all compounds in general.


texts: Do the concepts of Newtonian and non-Newtonian fluids still hold at a nanoscopic level?

texts:
Recently I've spent a great deal of time thinking about enzyme diffusion in cytoplasm. One thing that keeps me awake at night is the constant referral to cytoplasm as a non-Newtonian fluid (which it surely is when looking at it as a whole), and the implications this has for the diffusive properties of singular enzymes.

If I think about a single enzyme in the cytoplasm with its immediate surroundings, I would expect to find the protein with its solvation shells, and only a few non-water components. In this context I'm unable to understand how this single enzyme could be thought to be in a non-Newtonian medium.

Furthermore, when thinking about the diffusion of the enzyme, quite a few authors refer to the Scallop theorem, and define it in the context of non-Newtonian fluids. If the enzyme is mostly surrounded by water molecules, and only occasionally runs in to other proteins or peptides, shouldn't the protein be considered to reside in a Newtonian medium?

Shortly put: How far down can you go until the classification between Newtonian and non-Newtonian fluids starts to break down?


texts:
How many alkanes of molecular weight $M$ are chiral?

As a particular case let us consider M=100.The general formula for such a alkane is $C_nH_{2n+2}$ where $n$ is the number of carbon atoms.

Putting in values of molecular weight we get $12n+2n+2=100$ which gives $n=7$. So there are 7 carbon atoms. So far I could think of the following two structures.

Since their enantiomers are also chiral giving us a total of 4 chiral alkanes. However I am interested in the general case when the molecular weight is given M. Is there some generalised result to the situation?


texts: How does pyrosulfate compare to pyrophosphate?

texts: That is, in terms of stability in aqueous solution and the energy released by the hydrolysis of the S-O-S bond compared with pyrophosphate hydrolysis. More specifically, could sulfates substitute phosphates in some kind of hypothetical biochemistry? AFAIK sulfates are generally not found in terrestrial biochemistry.


texts: How to get (2R,3R)-2,3-dibromobutane from but-2-yne?

texts:
What I had in mind was to form but-2-ene with $\ce{H2}$ and Lindlar's catalyst and then simply add bromine ($\ce{Br2}$). But this addition, if I'm not mistaken, is a trans-addition. So I would end up with (2R,3S)-2,3-dibromobutane instead of (2R,3R).

Note that this is (2R,3S)-2,3-dibromobutane:

Have I made a mistake, or is there something wrong in my way of thinking? If my solution is wrong, how could I get (2R,3R)?


texts: Why does ψ^2 ( square of orbital wave function ψ) give the probability of an electron in a given region?

texts:
Today I was introduced to the Orbital Wave Function for electrons.
$\Psi$ is a mathematical function for coordinate of electrons and has no physical meaning.
But $\Psi^2$ gives probability of an electron.
How does a function for coordinate give probability distribution when squared ? How is the $\Psi$ working ?

Please explain me in easier to understand terms with out monster equations.


texts: The chemical shift of a proton is an indication of the amount of shielding it receives from the electron density on it or other magnetic anisotropy effects present in the molecule. For the protons of the carboxylic acid functionality, the chemical shift typically exceeds $\pu{10 ppm}$. Baseline estimates given for $\ce {CH, CH2, CH3}$ protons are $ 1.7, 1.3$ and $\pu{0.9 ppm}$ respectively. However, we are often able to observe the chemical shifts of alcohol protons in the range of $\pu{1-2 ppm}$. This is rather counterintuitive since the electronegativity of oxygen is markedly higher than that of carbon and hence we would observe a mucher greater deshielding of the $\ce{OH}$ proton. For alcoholic protons, there is likely to be the presence of hydrogen bonding effects. Is the presence of these $\ce {H}$ bonding effects responsible for the less than expected deshielding?


texts:
My teacher gave us a formula for determining if a M-O-H like compound will act like a base or not.without explaining much.
Base if:$$|\chi_o-\chi_M|\gt|\chi_o-\chi_H|$$
Flipped inequality if acid.
I am not unable to understand why the formula works.I think its because if the diffrence in electronegativity between Oxygen and element m is high.
It is  more likely for M-O-H to break into M and O-H
.Not certain about that either.


texts: I speak Russian and the term used for gasoline is "бензин", pronounced like benzene. I've also noticed that in Italian, it can be called "benzina". What's the significance behind this, if any? I think gasoline contains benzene, but that seems like a very minor part of the overall composition.


texts: Is there a material that reduces copper melting point and completely dissolves?

texts:
Is there any material that you mix/alloy with copper that

will result in something that behaves similar to plastic (that is at room temperature it is solid, at maybe 500K or similar it can be easily formed/3D printed)
When heated even more (700K?) it will make the the included copper melt, and dissolves itself, leaving only solid copper.

Is this even theoretically possible? The main goal is to significantly reduce the temperatures involved, 700K is a ballpark number here. Also it doesn't need to be very thick if this makes things easier.


texts: Determining if reaction is endothermic or exothermic using equilbrium constant

texts:
For the following reaction
$$\ce{W(s) + 4 Br(g) <=> WBr4(g)}$$
at $\pu{900 K},$ $K_p = 100$ and at $\pu{2800 K}$, $K_\mathrm{p} = 5.$
Determine if the reaction is endothermic or exothermic.

At higher temperatures, the equilibrium has shifted towards the reactants since $K_p$ is significantly smaller. However, how do we determine if a reaction is endothermic or exothermic from this information?
If the reaction was endothermic, an increase in temperature would push the equilibrium to products to counteract the increase in heat. However, the equilibrium has been pushed to the reactants thus signifying the reaction is exothermic. But this assertion is on the assumption that the forward reaction is exothermic.


texts:
Given a flat and thin object laying on a table, such as a small piece of silver paper or a small piece of cardboard, I want to find a way to detect which face of it is facing up. The solution should be able to detect the faces even when the object is placed underneath other object (so that camera/vision based approaches are not feasible).

What I am thinking is to find a radiating chemical using which we can paint on one side of the object and paint the other side of the paper piece with a chemical or substance that blocks the radiation, we should be able to tell if the object is up or down.

My question is: Is there such substance/chemical and associated detector on the market that we can purchase and use?


texts: Converting SMILES string into valid sub-strings

texts:
I have a SMILES string as follows.
smi= 'CCOC(=O)C1=C(COCCN)NC(C)=C(C(=O)OC)C1c1ccccc1Cl'

Is there anyway that I convert this SMILES string into valid sub-strings which can be later processed in RDKIT.
For instance
smi_sub1= 'C1c1ccccc1Cl'
smi_sub2= 'CCOC(=O)C1=C(COCCN)NC(C)=C(C(=O)OC)'
smi_sub3= 'C1=C(COCCN)NC(C)=C(C(=O)OC)'

These sub-strings should be subset of the main SMILES string and should also be valid from the SMILES syntax point of view.
So that when I use the function MolFromSmiles, It get processed without any error or none in return?
Mol_sub1 = Chem.MolFromSmiles(smi_sub1)
Mol_sub2 = Chem.MolFromSmiles(smi_sub2)
Mol_sub3 = Chem.MolFromSmiles(smi_sub3)


texts: Why does Cu(OH)2, which is generally insoluble due to low Ksp become soluble in excess of a base, such as NaOH?

texts:
Where does the "excess" criteria come into the picture? Also, can the equilibrium
$$\ce{Cu^2+ + 6 H2O <=> [Cu(H2O)6]^2+}$$

participate in the solubility process in any case? So there are 2 questions: one regarding the solubility of $\ce{Cu(OH)2}$ and other regarding the equilibrium mentioned above?


texts: Why does hybridization significantly matter for organic chemistry?

texts:
I just recalled, and still see that almost every organic chemistry book starts with bonds, empahsizing hybridization. One thing is straight forward but the rest doesn't seem to connect well.

The thing that's clear is, energy level wise $\mathrm{sp < sp^2 < sp^3}$. When $\mathrm{p}$ character is higher, the energy is larger, the electrophilicity is higher and its affinity for reaction is high up as well. This is the opposite of what electrons constantly thriving to achieve : the lower energy state and be stable. However, hybridization allows molecules to have a shape minimizing the energy though. Through this bonding it also releases the energy (dissociation) by stabilizing itself - so bond formation is the tendency. Hybrids ($\mathrm{sp, sp^2, sp^3}$) form $\sigma$ bonds while pure-breeds (100% $\mathrm{s}$, 100% $\mathrm{p}$) form $\pi$ bond.

I had the impression hybridization regulates a standard bond among same species of atoms, e.g $\ce{C-H}$ bond in all alkanes are the same. But that's not the case when I read brief comments indicating that the $\ce{C-H}$ bond in $\ce{CH4}$ differ from $\ce{CH3-CH3}$.

What I am unable to reason is, why hybridization is so important for organic chemistry than to any other (general, inorganic..., physical)? Is it about bond strength (how fast one can bond and break) or is it about acidity or basity? Why should we (learners) or organic chemists care?

Please provide some application example. It's also great if one could point out how each $\ce{C-H}$ bond differ from alkane to alkane or any other functional group.


texts:
What is the equivalent mass of double salt like dolomite? And what if the double salt is hydrated?

Is a double salt taken as a single unit while equating the gram equivalent in any reaction?
For example, in reaction

$$\ce{CaCO3.MgCO3 + 4 HCl -> CaCl2 + MgCl2 + 2 CO2}$$

is

$$\frac{\text{wt of dolomite}}{\text{eq wt of dolomite}} = \frac{\text{wt of}~\ce{CO2}}{\text{eq wt of}~\ce{CO2}}?$$


texts: I would like to dissolve or equally blend sodium bicarbonate in liquid coconut oil. Is there a way this can safely be done at home?


texts: What are the reactions occurring during the titration of a carbon dioxide contaminated water sample with diluted sodium hydroxide solution?

texts:
During estimation of dissolved $\ce{CO2}$ in water, we took a water sample, added few drops of phenolphthalein and titrated it against dil $\ce{NaOH}$.

Questions

What are the reactions that happen:

initially  in the water sample?
after addition of phenolphthalein (if any)?
after addition of NaOH?

My speculations

Inside the sample water

I think dissolved $\ce{CO2}$ reacts with $\ce{H2O}$ to form $\ce{H2CO3}$. But then does all $\ce{CO2}$ get converted into $\ce{H2CO3}$?
After addition of phenolphthalein

In an acidic medium the equilibrium shifts to the left and the weak acid phenolphthalein ($\ce{HIn}$) mostly remains undissociated and hence colourless.

$$\ce{HIn <- H+ (excess) + In-}$$

After addition of $\ce{NaOH}$

According to my book after $\ce{NaOH}$ is added to the sample the following occurs:
\begin{align}
\ce{2NaOH + CO2 &= Na2CO3 + H2O}\\
\ce{Na2CO3 + H2O + CO2 &= 2NaHCO3}\\
\end{align}
From my understanding
\begin{align}
\ce{NaHCO3 &= Na+ + HCO3-}\\
\ce{HCO3- + H2O &= H2CO3 + OH-}\\
\ce{OH- + H+ + In- &= H2O + In-}\\
\end{align}
As the $\ce{H+}$ concentration decreases equilibrium shifts to the right
$$\ce{HIn -> H+ + In-}$$

This $\ce{In-}$ ion imparts the pink colour which at pH 8.3 becomes susceptible to our eyes.

At the beginning some of the dissolved $\ce{CO2}$ got converted into $\ce{H2CO3}$. They remain beyond the scope of estimation, isn't it?

Are my speculations correct?


texts:
Can anyone please help me come up for a curved arrow mechanism for the reaction pictured? I'm familiar with the mechanism for the general acid catalyzed dehydration of butanol, where the arrow comes off a hydrogen bonded O on the sulfuric acid to the hydrogen on butanol to the oxygen and the following steps for that reaction are pretty simple too but I can't for the life of me come up with a curved arrow mechanism for this side reaction.
Currently, I think the butanol takes a hydrogen from the sulfuric acid (arrow from butanol O to Sulfuric acid H to O), followed by the removal of the hydronium atom from the butanol chain (arrow from sulfuric acid O to carbon on butanol chain to the O on butanol chain), followed by maybe a combination of butanol and the synthesized butanol sulfate???? I'm really not sure any help would be greatly appreciated.
SOS
Edit:
This is the final mechanism I came up with. Is this right?


texts:
I'm trying to solve this problem.

  How many grams of a solution at $25\%$ do you have to add to $100\ \mathrm{g}$ of a solution at $40\%$ to obtain a solution at $30\%$.

My Attempt

It's a bit more than a simple diluition. So far I've calculated the mass of the solute in $100\ \mathrm{g}$ at $40\%$: $(40\times 100\ \mathrm{g})/100 = 40\ \mathrm{g}$

Then the mass of the solution at $30\%$ so: $(40\ \mathrm{g}/30)\times 100 = 133\ \mathrm{g}$

$133\ \mathrm{g} - 100\ \mathrm{g} = 33\ \mathrm{g}$ (of solvent you need to add)

Now, how does that $25\%$ fit in all this? Can anybody point me to a useful formula or an example? Thanks!


texts: What are the differences between the Hilbert space and real space representations in chemistry?

texts:
I would like to understand the difference between Hilbert space and real space in a molecular code.

My understanding is that the Hilbert space of a system (such as a molecule) can be represented by a set of atomic orbitals (AOs) while the real space represents a system through a grid of points in the specific space of a system. Is this true?

For a more concrete example, consider electronic excitations. Using the entire (orbital) space of a reference system, one can project out (excite) an electron to the virtual space of a reference ground state. However, I'm not sure how this is handled in a "real space" program, or what that even means.


texts: Uv vis and fluorescence spectroscopy: sensitivity

texts: Is there any reason why fluorescence spectroscopy is said to be more sensitive than Uv-Vis?


texts: (At what temperature) can salt evaporate?

texts: Related to my previous question, can sodium chloride evaporate, and if so, at what temperature? Since salt is a solid, and apparently all substances can at various temperatures exist as liquids and vapors as well as solids, salt should also have a melting and a vaporization points. At what temperatures are these points if they occur, and if they don't occur, why? (This is assuming the pressure is 1000 mb)


texts: How does one determine whether a chemical requires hazardous waste disposal?

texts:
It is pretty easy to find information about the actual hazards of a chemical in the SDS, but I have been struggling to sort out which classifications require that the compound be handled differently, especially when it comes to disposing of waste. I'd like to be able to determine what the restrictions on a chemical are by reading the SDS. For reference, I am in the USA. I know it varies state-by-state, but I am just looking for the "average" protocol, or else just the federal requirements.

For example, I calibrate/check water quality sensors. Some sensors are calibrated with NaCl, which obviously I can pour down the drain. For others I use less common/experimental stuff like p-Toluenesulfonic acid monohydrate as a stable substitute for quinine sulfate. In this case, the SDS clearly says not to pour it down the drain. What I am wondering about is how to interpret the myriad of different hazard classifications shown below, and which of them sets the legal requirement that it not be poured down the drain.

Chemical waste is not common where I work, which is why I need to be able to determine before I buy something whether I'll need to find a disposal service to handle it.


texts: I was wondering whether allenes can form rings; geometrically speaking, this seems like it would be energetically unfavorable due to their 180 degree linear geometry.


texts:
One thing which has bothered me for a while about the idea of quantized energy levels is that it's clear just how quantized they are.

Let me give an example. If I was looking the energy some electromagnetic wave would need to an $\ce{O-H}$ in water from the 0th vibrational energy level to the 1st vibrational energy level, it would be around $\mathrm{3750~cm^{-1}}$. Now, for some electromagnetic wave to cruise by and give enough energy to make that transition, how exact must the energy of that wave be?

Meaning, does it need to have exactly $\mathrm{3750~cm^{-1}}$ of energy? Well, what if the transition was actually $\mathrm{3750.3~cm^{-1}}$. Then that wave doesn't have enough energy anymore, and the likelihood of some wave having exactly $\mathrm{3750.3~cm^{-1}}$ seems a lot less likely than just being very close to that value.

So what happens in actual transitions that the molecule only takes the exact amount of energy it needs? And what happens to whatever leftover energy there might be from a wave that had enough energy to excite this water to it's first vibrational energy level? Is there ever leftover energy like I just mentioned? Also, do two waves of say $\mathrm{1875~cm^{-1}}$ each ever meet up and excite this same transition? This to me also seems so unlikely because that would involve constructive interference exactly of the two waves.


texts: I know that $\ce{He2}$ (homonuclear diatomic helium) does not exist because its bond order is zero. Since the bond order of $\ce{He2+} = 1/2$, that means that the positive $\ce{He2+}$ ion exists, but how does the positive ion exist if the neutral molecule doesn't?


texts: Why do lower oxygen concentrations lead to an increase the rate of corrosion?

texts:
Is this only the case in pitting corrosion?

Is it because metal which has access to the oxygen becomes cathodic leading to the inaccessible parts of the metal becoming anodic?


texts: Given the mass of precipitate, how can I calculate the relative amount of the original dissolved compounds?

texts:
A simple mixture of $\ce{NaCl}$ and $\ce{NaBr}$ weighing $0.180~ \mathrm{g}$ is treated with $\ce{AgNO3}$ solution to give $0.3715~ \mathrm{g}$ of precipitate. Calculate the content of $\ce{NaCl}$ and $\ce{NaBr}$ in the mixture.

The answer given in book are $\ce{NaCl}$ = $0.0682~ \mathrm{g}$ and $\ce{NaBr}$ = $0.1118~ \mathrm{g}$.

The answers I got are $0.1519~ \mathrm{g}$ $\ce{NaCl}$ and $0.0281~ \mathrm{g}$ $\ce{NaBr}$. Please tell me where I made mistake.

Working:

$$\ce{NaCl + AgNO3 -> NaNO3 + AgCl}$$
$58.5~ \mathrm{g}$ $\ce{NaCl}$ give $143.5~ \mathrm{g}$ $\ce{AgCl}$

$0.3715~ \mathrm{g}$ $\ce{AgCl}$ give $58.5/143.5 \cdot 0.3715~ \mathrm{g}$ $\ce{NaCl}$ = $0.1519~ \mathrm{g}$ $\ce{NaCl}$

$\ce{NaBr}$ = $0.180 ~ \mathrm{g}$ - $0.1519~ \mathrm{g}$ = $0.0281~ \mathrm{g}$ $\ce{NaBr}$


texts: how to remove products from reaction space?(to apply LeChatelier's principle)

texts: I thought this question merited  a discussion of its own. In industrial applications, we talk of shifting equilibrium of reaction to the right(or desired products) by removing products quickly from reaction space? I want to know what this means? If you consider a simple fixed-bed/packed-bed reactor with gaseous reactant and product (say A-->B), does it mean I need to remove B quickly from the packed-bed reactor volume to push equilibrium to the right? My point is, isn't that already happening? By virtue of flow through the reactor isn't B already constantly being "removed" from the reactor(along with unreacted A), while the reactor keeps getting hit with fresh A? so what more effort is needed to push equilibrium to the right? are there any timescales involved? or does B have to be removed quicker than A? if so, how quicker? I need to understand this better,please help. This question can apply to other types of reactors as well like fluidized-bed or moving-bed and so on..


texts: Why do shape and size have the greatest effect on the optical properties of nanoparticles?

texts: The LSPR properties of nanoparticles depend on a number of factors, including shape, size, material, crystal structure, dielectric environment, etc. However, it has been consistently shown that shape and size have the greatest effect on the optical properties of nanoparticles. Exactly WHY, however, is this true? Does anyone have an explanation at the molecular level?


texts:
What amount of oxidization is required to refer to some coal as oxidized coal, and how long does it take for coal to become oxidized in temperatures of roughly 25-40°C?

I have found a research paper from 1940 that I don't have access to here. But other than that, I have had no luck. Does anyone have any ideas or references I can refer to.


texts: What is the rationale of the IUPAC name for DDT?

texts:
The structure of DDT is

One of the benzene molecules should be the parent chain as it has a greater number of carbon atoms than the straight chain (which has just two carbon atoms). Taking benzene as the parent chain, I think that the name of the compound should be 1-Chloro-4-((1'-(4"-chlorophenyl))-2',2',2'-tricholoroethyl) benzene.

But the Wikipedia article states that the IUPAC name of the compound is
1,1,1-Trichloro-2,2-bis(4-chlorophenyl)ethane.

Why is the ethyl chain taken as the parent chain when it has lesser number of carbon atoms than the benzene ring?


texts: Reduction of acetaldehyde from rectus and sinister faces

texts:
I am asked to consider the reduction of acetaldehyde from the re and si faces. I am also asked whether the added hydrogen (labeled H* in my picture) is pro-R or pro-S in both cases. In my attached picture I replaced the added hydrogen (H*) with D to determine the absolute configuration.

If I did this correctly, addition of hydrogen from the si face results in a pro-S product with respect to the added hydrogen (H*). And addition of hydrogen from the re face results in a pro-R product with respect to the added hydrogen. Am I correct?


texts: Difference between baking soda and baking powder

texts:
I learnt that the chemical symbol for baking soda and baking powder is NaHCO3. However, when I do a simple experiment which is put vinegar into both substances. I can get different observations.

When I put vinegar into baking soda, I get a fast and fuzzy reaction. But when I put vinegar into baking powder, instead of a fast and fuzzy reaction, I get a slow and bubbly reaction.

So, my question is what properties do each of the both substances have to make different reactions with vinegar although their chemical symbols are the same?


texts: How does the relative amount of oxidation of different alcohols affect the amount of energy released?

texts:
I am investigating the enthalpy of combustion of different primary alcohols and a website I found briefly mentioned how the relative amount of oxidation of different alcohols affects the amount of energy released. I was wondering if anyone could possibly elaborate on this.

I also found a trend where carbon chain length 1 --> carbon chain length 2 has a great increase in experimental heat of combustion but then there is a smaller increases between carbon chain length 2 and 3. Would there be an explanation for this (I have a feeling it relates to incomplete combustion)?

Thanks!


texts:
Does hyperconjugation in toluene influence the attack of an electrophile in any way?

If not, where would the electrophile prefer to attack on toluene?

Looking at related answers, it seems like hyperconjugation leads to delocalisation of electrons over the ring, like in resonance. But hyperconjugation is the interaction between $\sigma$ and $π$ orbitals, how does it lead to delocalisation over the ring? I cannot understand it in terms of the molecular orbital theory.

Lastly, would the electrophile prefer to attack at Ortho position due to greater $+I$ effect and (if possible) hyperconjugation effect? Please correct me if I'm missing something.


texts: Time required for a thin layer of ethanol to evaporate?

texts:
If someone were to pour about 5 ml of 94% pure ethanol on a flat surface and at room temperature, approximately how much time would it take for it to evaporate?

EDIT: In others words, it is to know approximately how much time it would take for a small amount (about 5 ml) of pure alcohol to evaporate if poured over a surface such as a table. Would it take about 15 seconds/30 seconds/2 minutes?


texts: Monochlorination of 2-chloropentane and possible enantiomer products

texts:
I found a question to determine the number of possible chiral products of monochlorination of 2-chloropentane.So, first the products are (with possible number of enantiomers in the parentheses:

2,2-dichloropentane(no chiral product),

1,2-dichloropentane(4 or 2, I am not sure is there a plane of symmetry here)

2,3-dichloropentane(2 or 4)

2,4-dichloropentane(obviously none for a plane of symmetry)

2,5-dichloropentane(2,4?)

But my surprisingly the answer says it's only 5. That's even lower than my lower estimate. I am not sure how there are 5 enantiomers.


texts: How to derive Arrhenius equation from hard-sphere collision theory

texts:
Reading the description of the Arrhenius equation from Wikipedia:

  ...One example comes from the collision theory of chemical reactions, developed by Max Trautz and William Lewis in the years 1916-18. In this theory, molecules are supposed to react if they collide with a relative kinetic energy along their lines-of-center that exceeds Ea. This leads to an expression very similar to the Arrhenius equation.

I was wondering how to derive the Arrhenius equation from the mentioned hard-sphere collision theory. I tried to do so but got a totally different expression from the Arrhenius equation. The original derivation here written by Max Trautz seems to be in German, but I cannot read German. Does anyone know how to do the derivation?


texts: How to calculate Absolute error under square root sign?

texts: I was calculating standard deviation of a data set. Could someone help me find the square root of 15.13 with an absolute error of 0.005? Is there a rule for calculating absolute errors under square root sign?


texts: Can you calculate the oxidation potential of an ion?

texts: Is there any way to calculate the oxidation potential of [Fe(OH)(H2O)5]+? I am unsure if it can be done since I have only seen oxidation potentials provided for specific reactions of single elements, but I want to compare the tendency of two ions to be oxidized and I don't know how to go about it.


texts: How does an electrolyte react to voltages below its electrolysis potential?

texts: An electrolyte can be electrolysed by a voltage higher than the reverse reaction’s cell potential, while conducting a current in the process. But what happens at the electrodes when the applied voltage is below this cell potential, such as below 1.23 V for water or 4.07 V for NaCl? Does the reverse reaction occur simultaneously, or is the electrolyte unable to conduct a current with such a low voltage at all?


texts:
If we have a solution, of conductivity k1, and another solution of same volume having conductivity k2, then what will be the conductivity if I mix the 2?
I think that net conductance should be the sum of individual conductance of the 2 solutions in the final beaker (where volume is doubled). But then won't the individual conductance of the 2 solutions in double the volume be different from that in the initial volume?

Also, can we say that conductivity is the conductance of unit volume of solution?


texts: What elastic polymeric material look like at molecular level?

texts:
I think there are few crosslinks in elastic material. So probably, the material would look like not so dense, maybe even transparent.

I received this question from my collegue and have difficulty in answering it.
I think this question is about know how the structure of an elastic polymer looks on the molecular level.

What does the elastic polymeric material look like at molecular level?


texts:
My book states that if we add powdered $\ce{Pb}$ (lead) and $\ce{Fe}$ (iron) to a solution containing $1\ \mathrm{M}$ each of $\ce{Pb^2+}$ and $\ce{Fe^2+}$ it would result in formation of more $\ce{Pb}$ and  $\ce{Fe^2+}$
What I think:

1) Since both $\ce{Pb}$ and $\ce{Fe}$ have negitive standard electrode poential both will have tendency to form $\ce{Pb^2+}$ and $\ce{Fe^2+}$, then as a result $\ce{Pb^2+}$ and $\ce{Fe^2+}$  will increase in solution which is against the result given by book.

2) Another thing which comes to my mind is that since $\ce{Pb}$ has greater standard reduction potential than $\ce{Fe}$ so only  added Fe will convert into $\ce{Fe^2+}$ And the electrons released by it will reduce pre-existing  $\ce{Pb^2+}$  to $\ce{Pb}$ and hence the result as given by book

So my question is what exactly will happen if we conduct the following experiment.


texts: Correlation between resonance and coordinate covalent bond

texts:
So I was listening to an online chemistry lecture the other day, and the theme was "bond".

In the 'coordinate covalent bond' part, the teacher said "Examples of the coordinate covalent bond can be $\ce{SO_2}$, $\ce{HNO_3}$, etc." and I could figure out that both molecules have resonance structures: between $\ce{N}$ and $\ce{O}$ atoms in $\ce{HNO_3}$, between $\ce{O}$ and $\ce{S}$ atoms in $\ce{SO_2}$. Also I am aware of the resonance structures in the $\ce{C_6H_6}$(benzene) molecule, so I looked up the Wikipedia page and could find this sentence:

"..., while the VB description involves a superposition of resonance structures."

So I became curious about this: Is there any close correlation between resonance and coordinate covalent bond? In other words, is it safe to view a molecule as having coordinate covalent bond when it has resonance structure in it?


texts: Why rotate orbitals in a CASSCF calculation?

texts:
I'm trying to get the rate constant for the reaction of propene to give propenyl (radical) and H.

Using Molpro, I calculated the energy for the optimized geometry of the reactant using CASSCF.

It is required at one point to rotate two orbitals (the one with energy just below the HOMO and one in the valence shell).

I don't understand the point in doing this; what's the purpose?


texts: Why does O2NCl only have two resonance structures?

texts: Why is it that $\ce{O2NCl}$ has only two resonance structures? More specifically, why is the Lewis drawing where $\ce{N}$ is double bonded to $\ce{Cl}$ not considered a resonance structure along with the other two where $\ce{N}$ is double bonded to an oxygen?


texts: What is the most stable structure amongst the keto-enol tautomers of pentane-2,4-dione?

texts:
I was assigned the following question and I cannot decide which is the correct answer.

  Which is the most stable structure?
  (a) pentane-2,4-dione
  (b) 4-hydroxypent-4-en-2-one
  (c) (Z)-4-hydroxypent-3-en-2-one
  (d) (Z)-penta-1,3-diene-2,4-diol

I am confused between options (c) and (d).
Both seem to be stable due to resonance, but I think (d) should have more resonance as the oxygen's lone pair in the $\ce{-OH}$ bond will also participate in resonance making it more stable.

But the answer is given as (c).

Could you please explain why (c) is more stable than (d).


texts: All good recipes for hollandaise sauce consist of beating egg yolks vigorously and slowly add melted butter over moderately low heat.  Care must be taken to not overheat the sauce or the eggs will scramble and it won't emulsify.  Likewise, the melted butter must not be added too quickly or it will not emulsify. When done properly like a good chef, what is happening here?  Why does the sauce thicken?  What is an egg emulsion and why must the butter be added so slowly rather than faster?


texts:
I had a question in my textbook:-
Na -> Na$^+$ + e$^-$
Cl + e$^-$ -> Cl$^-$
But Na$^+$ and Cl$^-$ have a stable electronic configuration. So, why do they react to form NaCl?
So, this is my question. Is Na$^+$ really more stable than Na?
Na$^+$ doesn't react with atoms, only with ions, like Cl$^-$. Moreover, Na$^+$ has a noble gas electronic configuration, and Na is highly reactive BECAUSE of the extra electron in its valence shell. So, in this respect, Na$^+$ should be more stable, right?
Edit: I looked this up on StackExchange, and got varying answers. That's why I'm confused.


texts: A misunderstanding about the energy profile of reactions with a catalyst involved

texts:
All of us are aware of the importance of the catalysts in bio-chemistry. For a high school learner like me, catalysts ,and therefore, enzymes play a bridge-like role that connect high school bio to high school chemistry.

Yet, I got baffled about the two common energy profiles drawn for an anonymous reaction with a presence of a catalyst. The question may seem rudimentary, I agree, but the possible answers to my question were too technical for me to understand.
One of the energy profiles had several curves in the pathway for $E$, and the other one has only one curve in the pathway where the catalyst should have affected.

My guess is that the first energy profile is about a net change in $E_\mathrm{a}$ but the second one demonstrates the reality when an exothermic reaction occurs.
 Now, here are the questions:

Why are the two energy profiles different? Please be as if you're teaching thermo-chemistry to a little kid!
Why do those curves occur in the latter energy profile and is there a way to know how many of those curves will occur in the presence of a catalyst?

Image credits: chemwiki.ucdavis.edu (page here) and wiki (page here).


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

texts: It has been defined as the energy available for work other than expansion work. Why can't it be used for expansion work


texts:
I have recently read that the number of sterioisomers in a compound having n chiral centres is 2^n. (That is, if no meso form is present)

The below question asks for the number of sterioisomers in the product obtained. And the product obtained has 3chiral centres, so it should be 2^3=8, but the answer given is two.
There is no plane of symmetry.

Do I not consider the carbon attached to the benzene ring when looking for chirality?

Could someone help me out?
Question attached.
!


texts: In electrolysis, does it make any difference if the electrolyte is an molten, aqueous or dilute aqueous solution?

texts:
I'm an IGCSE Chemistry-extended student, and my question is: in electrolysis, does it make any difference if the electrolyte is in a molten, aqueous or dilute aqueous solution form?
An example mentioned in my book:

Explain  the difference in the electrolysis products of
a) molten sodium chloride;
b) dilute aqueous solution of sodium chloride.


texts:
In my textbook (Chemistry Part - I for Class XI published by NCERT), there is an equation for the energy of an electron in an energy state: $$E_n = -R_\mathrm H\left(\frac{1}{n^2}\right)$$ and there is a paragraph below it with the following text:

  where $R_\mathrm H$ is called Rydberg constant and its value is $2.18\times10^{-18}\ \text{J}$.

There is another section with the expression for the wavenumber ($\overline{\nu}$):
$$\overline{\nu}=109\,677 \left(\frac{1}{n_1^2} - \frac{1}{n_2^2}\right)\ \text{cm}^{-1}$$
with a paragraph with the following text:

  The value $109\,677 \space\text{cm}^{-1}$ is called the Rydberg constant for hydrogen.

I checked online and found that in most (all) websites (incl. Wikipedia), the value of Rydberg constant is $109\,677 \space\text{cm}^{-1}$. But when I searched for its value in joules, I found this website with the value of Rydberg constant $= 2.18\times10^{-18}\ \text{J}$.

How can Rydberg constant be written in joules?


texts:
Terpin (4-(2-hydroxypropan-2-yl)-1-methylcyclohexan-1-ol) has two $\mathrm{sp^3}$ carbons with different substituents on a cycloalkane, so it has two cis-/trans-isomers, and from what I was taught, is a stereoisomer.

The way I was taught to find stereoisomers was to count the number of double bonds that can be E/Z and the stereocentres, and do $2^n.$ There are no stereocentres, and no double bonds, so the number of stereoisomers would only be 1 (only one molecule). This disagrees with the cis-/trans-isomers number which would be 2.

I can't find anything online about these kinds of cases. Is this general rule of counting stereocentres and double bonds with E/Z not apply in every case? And is this a case that happens a lot that when I'm solving problems, I should always keep this in mind?


texts: Why is it not practical for insoluble salts to be prepared from other insoluble salts?

texts:
My textbook says that it is not practically feasible to make insoluble salts (say PbSO4) from other insoluble salts (say PbO), without explicitly mentioning the reason for the same.

My guess is: if the product is also an insoluble salt, it may deposit on the insoluble reactant, and stop further reaction. However, isn't this problem solved by simply stirring? (Is the constant stirring required the reason why such a method would not be "practically feasible"? But isn't stirring rather common for chemical reactions?)

So, what is the actual reason?


texts: Is the boundary of an atom well defined?

texts:
That question might seem weird, but that's what I have been imagining lately; going through Bohr's theory on the hydrogen atom. He clearly defines the radius of an orbit with an exact mathematical expression. But what do they mean when they say any atom (say $\ce{Na}$) has a radius $r$. Are we to consider atoms as solid, rigid spheres? If that's the case, what about water?

If all the atoms are defined as solid, rigid, spherical balls, how come an aggregation of so many solid objects be a liquid? How can it flow? So, in a nutshell what is the boundary of an atom made up of, or even this: does it have a defined boundary?

This troubles me a lot. I think maybe the modern atomic model has dealt with this problem. I haven't read it in detail, and I would be highly thankful to any references.


texts: The anti-bonding molecular orbitals are higher in energy than the constituent atoms in a diatomic molecule. That means it is less stable. Why does it form? Why can't all the molecular orbitals be bonding molecular orbitals?


texts: Chemical properties of dicopper (I) tetraiodomercurate (II)

texts:
This is a continuation from my  previous post.
Where can I find information on the chemical properties of $\ce{Cu2[HgI4]}$? I found a mention that in reaction with $\ce{Na2S2O3}$ in presence of acid it gives $\ce{HgS}$.


texts: Why do Ca-Ca distances get shorter in ionic structures, as compared to the metal?

texts:
I saw in the book Chemistry of the Elements by Greenwood & Earnshaw, 2nd ed., p 66, that the distance between calcium atoms decrease when it's forming an ionic structure.

  The closest $\ce{M-M}$ approach in these compounds [metal hydrides] is often less than for the metal itself: this should offer no surprise since this is a common feature of many compounds in which there is substantial separation of charge. For example, the shortest $\ce{Ca-Ca}$ interatomic distance is $\pu{393 pm}$ in calcium metal, $\pu{360 pm}$ in $\ce{CaH2}$, $\pu{380 pm}$ in $\ce{CaF2}$, and only $\pu{340 pm}$ in $\ce{CaO}$ (why?). [sic]

Why does this happen?


texts: Why does chlorine replace a hydrogen in propene instead of adding to the double bond?

texts:
I read about the following reaction in my book:

$$\ce{CH3-CH=CH2->[Cl2][\pu{773 K}] (Cl)CH2-CH=CH2}$$

It surprises me that the $\ce{Cl}$ doesn't attack the $\pi$ bond, rather it attacks the $\sigma$ bond.

It seems to me that the reaction follows free radical mechanism, for the high temperature of the reaction system. That's why, the $\ce{Cl}$ attacks the $\sigma$ bond.

But, I am not sure, why won't free radical $\ce{Cl}$ attack the $\pi$ bond.


texts: Why does diazo coupling preferentially occur at the para position?

texts:
When the diazonium ion couples with dimethylaniline, why is the para position favored?

Is this only due to steric factors or do electronic factors (such as ortho-para directivity) play a role here too? In particular, I suspect ortho-para electronic factors might be significant because some of the resonance structures have a cation directly next to the electron-donating group.


texts: Does unsubstituted benzoic acid not show resonance due to steric effects?

texts:
My book says that benzoic acid does not show resonance as the carboxylate anion and the benzene ring are not in the same plane due to steric effects.

But there aren't any large groups in the ortho positions to cause steric inhibition of resonance. Then, is the info given in the book wrong? If not, where does the steric effect come from?


texts:
I would just like to clarify the guidelines of drawing MOs formed from interactions between AOs. Strangely, this topic is rarely touched on in most books on molecular orbital theory. The following are some examples of what I consider to be guidelines:

When there is an in phase combination of atomic orbitals, i.e. the lobes in contact are of the same phase, the two lobes would merge into one bigger lobe.
When there is an anti phase  combination of atomic orbitals, i.e. lobes of different phase, the two lobes would seem to be "pushed away" from each other. The electron density seems to shift away from the internuclear region. For example, in the case of a p orbital, the lobe involved in the anti phase combination would shrink in size while the other lobe would increase in size.
For bonding MOs, the lobes closer to the more electronegative atom must be necessarily larger. For antibonding MOs, the lobes closer to the less electronegative atom must necessarily be larger.

Is there a well-established set of such guidelines which beginners in MO theory can follow when drawing resultant MOs?


texts: Reduction of amino acids to corresponding amino alcohols

texts:
I've stumbled upon an interesting article about reduction of amino acids and from there to reduction of L-valine to L-valinol using $\ce{LiAlH4}$ in THF.

Article says that because of the cost of $\ce{LiAlH4}$, better method using $\ce{NaBH4}$ with $\ce{I2}$ in THF has been developed.

But I haven't found anything about $\ce{HI}$. Is it possible to reduce amino acids all the way down to their corresponding amines with concentrated $\ce{HI}$ solution?


texts: Do electrons go to even lower ground states after exothermic reactions?

texts:
I am a bit confused about what happens to the energy levels during an exothermic reaction.

I understand that during an exothermic reaction, the energy of the electrons decreases.

Is the potential energy of electrons related to the energy level diagram, shown below?

So if the potential energy decreases, does that mean the ground state for the new molecules formed will be different from the old molecules?


texts: Decrease of Bicarbonate to compensate Respiratory alkalosis

texts:
I am studying this claim

  Compensatory mechanism in respiratory alkalosis is decrease of SB i.e. bicarbonate ions ($\ce{HCO3^-}$).

There are reactions

$\ce{HCO3- \rightarrow H+ + CO3^{2-}}$ (conjugate base)

and

$\ce{HCO3- + H+ \rightarrow H2CO3}$ (conjugate acid)

but since the $pK_a$ for the second reaction is greater

decrease in $\ce{HCO3-}$ yields more acids

so alleviates respiratory alkalosis.

To claim such a thing, I think you must know that the $pK_a$ for the reaction is greater, so change in bicarbonate ions' content results in bigger change in the second reaction.

How does the decrease of bicarbonate ions lead to decreased respiratory alkalosis?


texts: Find the concentration of the HCl solution when mixed with 1.265g of ACES-K+

texts:
$\pu{1.265 g}$ of N-(2-acetamido)-2-aminoethanesulfonic acid potassium salt ($\ce{ACES^-K+}$, $M=\pu{220.29 g/mol}$) is dissolved in $\pu{88.42 mL}$ of water. $\pu{27.59 mL}$ of $\ce{HCl}$ is added to the solution, resulting in $\mathrm{pH}$ of $6.54$. Calculate the concentration of the $\ce{HCl}$ solution. The $\mathrm pK_\mathrm a$ of $\ce{ACES}$ is $6.85$.

I tried setting up the equation as follows:
$$\ce{ACES + H3O+ <=> HACES +H2O}$$

The moles of ACES initial is $\pu{0.0057 mol}$ $(1.265/22.290)$ and we are trying to find $x$ the amount of moles of $\ce{HCl}$ $\ce{(H3O+)}$ we have. Therefore, using an ice table $\ce{ACES}=0.00574-x~\pu{mol}$ and $\ce{HCl}= x~\pu{mol}$.
When you plus into the equation
$$\mathrm{pH}=\mathrm pK_\mathrm a+\log(\text{base}/\text{acid})$$ I did $6.54=6.85+\log(0.00574-x/x)$ and got $\pu{0.0038 mol}$ of acid divided by total volume = $0.03321\ \pu M$. Is that correct?


texts: Finding the mM concentration of capric acid (decanoic acid) in coconut oil

texts:
Im trying to figure out the mM concentration of capric acid in coconut oil. I know that There is 8% capric acid in coconut oil, but I would like to know how much capric acid is in coconut oil in a mM ammount, not a percent. I know the molecular weight of capric acid (decanoic acid) is 172.26

The reason being: I read a study that capric acid solutions are effective against microbes and fungus at a mM concentration of 20 mM. Im wondering if coconut oil's 8% of capric acid converts to roughly around a 20mM concentration of capric acid within the oil.

Thanks very much for your answers!


texts:
Which of the following will react with dilute sulfuric acid? : copper, copper (II) oxide, copper (II) hydroxide, copper (II) carbonate.
My answer:
Metals react with acids to give salt and hydrogen. So, copper will react with dilute sulfuric acid.
Metal oxides act as base. So, they neutralise acid to give salt and water. So, copper oxide will react with sulfuric acid.
Metal hydroxides are bases. So, they will neutralise acids. So, copper hydroxide will react with dilute sulfuric acid.
Carbonates react with acids to give salt, carbon dioxide and water. So, copper carbonate will react with dilute sulfuric acid.
So, my answer is all the given options will react with dilute sulfuric acid. Is this correct? The answers are not given in the book.
I am afraid what if there are exceptions to the general reactions that I have written above and I am not aware of that.


texts: Why are paramagnetic materials attracted to ferrimagnetic materials(such as iron, nickel, and cobalt)?

texts:
Diamagnetism exists in every molecule or ionic compound. It is the ability to be repelled by a magnetic field.

So you might think from this, that liquid oxygen would either be repelled by the magnet or not affected at all, yet it is attracted to it.

$\ce{O2}$ is paramagnetic, but how can a paramagnetic material like oxygen be attracted to a ferrimagnetic material like Iron other than the fact, that neutral attracts both positive and negative charges and $\ce{O2}$ is neutral.

Is it just this, or is there another part to it, like charged iron atoms inducing a dipole in $\ce{O2}$ or something?


texts: Do electrons only fill 'spin up' first? Or could it start filling 'down spins' first?

texts: Due to Hund's rule, electrons start filling up the orbitals without pairing up. When this is happening, do the electrons all fill up the 'up' spin? Could they fill in the 'down' spin? Why do they prioritize the 'up' spin if they do?


texts: Which enolate of butanone is more stable?

texts:
Consider butanone (A) and its two possible enolates B & C.

Which of the two enolates will be more stable? B because of the more stable primary carbanion, or C because of more stable enolate (better hyperconjugation)?


texts: Pressure/ vacuum on preciptation of a borax saturated solution

texts:
Trying to go back to my collage chem/physics.  We put a supersaturated solution of borax on the stove. (heated  water, added borax till it would not take more borax).  Placed them under vacuum 15 inhg, normal pressure, 20 psi.  Initial hypothesis was crystals would grow better vacuum. They do this in space vacuum and low gravity. But we can't  get rid of gravity.

Results by weight of new jars with crystallization using the same size pipe cleaner for nucleation:

pressure: 467.4g
reg: 454.5g
vacuum:   326.3g

Definitely more crystal deposition in higher pressure, less uniform
reg  pressure most uniform deposition on pipe, less deposition
vacuum, least deposition

Did the air pressure cause the solubility to drop, resulting in more crystals?
And the vacuum less crystals because of more solubility?

I initially thought it would be the opposite.

What's the explanation?
Don't know if you would observe differences under a microscope for quality of crystals.


texts: Whether amino acids exist as zwitterions in the liquid and gaseous phases

texts: I am aware that in the solid state pure amino acids are crystalline structures composed of zwitterions, however I cannot find any information about whether somehow this changes as they move into liquid and gaseous forms- are they zwitterions in these sates and if not, why not?


texts: Does hyperconjugation stabilize a carbocation more than a free radical?

texts:
Which of the following statements is correct about methyl group?

  It stabilizes both carbocation and free radical equally.
  It stabilizes a free radical more than a carbocation.
  It stabilizes a carbocation more than a free radical.
  None of these.

I thought the answer would be (1). Keeping in mind these structures: The methyl group can stabilize the carbocation and the free radical group attached to it equally through hyperconjugation. However, the answer given is (3). How is this possible? Why is the carbocation more stable than the free radical? Are the structures I drew wrong?


texts: Why do collisions in elementary reactions of higher-orders appear to be more likely?

texts: So we are told that a unimolecular elementary reaction has a rate law of $k[\text{A}]$ where a termolecular reaction with three unique reagents, $A$, $B$ and $C$ has a rate law of $k[\text{A}][\text{B}][\text{C}]$. Now, other things being equal, and assuming for the sake of argument that the initial concentrations are all greater than 1M, this means that the termolecular elementary reaction is more likely at the outset. But that doesn't make much sense. There may be some statistical mechanics principle that's lost on me but it seems more likely that A bumps into A than, A, B and C come together all at once. So I don't quite follow this reasoning. Is it the case that $k$ is generally quite smaller in these termolecular elementary reactions?


texts: How does the electron configuration of platinum relate to its stability?

texts:
Does platinum's electron configuration, [Xe] 4f14 5d9 6s1, influence its reactivity and stability? Is the electron configuration the primary contributing factor to platinum's relative inertness?

This seems odd to me that platinum is very inert. It seems like pulling off that 6s1 electron should not be difficult as compared to other metals.


texts: Meaning of "MS1 and MS2 resolution" and "MS1 and MS2: Unit" in a tandem mass-spectrometry parameter list

texts:
I'm translating a Certificate of Suitability that very briefly describes procedures used to measure several impurities in a drug substance. There is a short description of the parameters of a Gas Chromatography-MS/MS procedure to detect an impurity called NDBA.
I don't understand the final line here:

What is the meaning of Resolution and especially of Unit? I can get by with "resolution" by simply translating it into Russian without knowing what it means, but there is no suitable Russian word to translate "Unit" - I must use either the Russian words for "Unit operation" or for "Equipment unit" or for "Measurement unit", and I have no idea what this Unit means in the original text.
I tried reading up on MS/MS but I haven't understood it well enough to guess the meaning of this line.


texts: Do Bases and Acids actually react with each other?

texts:
Let's say we have $5$ $\ce{HCl}$ molecules and we dump them into a container full of water. It's a strong acid so all $5$ $\ce{H+}$ ions would react with water and create $\ce{H3O+}$. It reacts with the water, right?

Now, we add $5$ $\ce{NaOH}$ molecules down there. They all react with some water molecules of their own as well and create $5$ $\ce{OH-}$. So now we have $5$ $\ce{H3O+}$ and $5$ $\ce{OH-}$. Those two don't react with each other, correct? They just react with the water molecules and balance each other out, giving us a neutral solution.

I am unsure of this. Is this true? Thanks in advance.


texts: Stereochemistry: synthesis of an epoxide

texts:
This is a procedure to synthesize a propylene oxide.

I wonder if the inversion occurs or not after the reaction. That is, I want to know which product is correct in the diagram above.

I thought that this reaction is an SN2 reaction, so inversion occurs. However, I'm a little confused because the whole reaction is intramolecular.
Is it correct that this reaction is SN2, and the inversion occurs?


texts: Why is solid sodium hydride a base and not an acid when reacted with water?

texts:
When solid $\ce{NaH}$ is mixed with water, the products are not $\ce{Na-}$ and $\ce{H3O+}$. The reaction yields $\ce{NaOH}$ and $\ce{H2}$ gas.

Why does solid $\ce{NaH}$ not act as a Brønsted acid in this case?


texts: Could sodium in ethanol reduce amides to amines?

texts: Strong reducing agents like $\ce{LiAlH4}$ can reduce amides to amines. Sodium in ethanol (as a source of protons) is also a very strong reducing agent. Could it be therefore used to, for example, turn formamide into methylamine?


texts: Calculating the density of a saturated salt solution

texts:
Is there a way to calculate the density of a saturated salt solution from the solubility limits or does it have to be experimentally determined?

First instinct, is to add the mass of the salt to mass of the water e.g. a solubility of $\pu{80 g}$ of salt in $\pu{100 mL}$ would have a solution density of $\pu{180 g/100 mL = 1.8 g/mL}$. However, it seems the salt should affect the volume of the solution. What additional information is needed or does this quantity just have to be empirically determined?


texts: Adjusting PBS with HCl: pH drift after dilution of phosphate buffer

texts:
It is some kind of everyday lab science and with a feel of shame I cannot answer this observation.

I noticed a pH drift (~0.5 units) of my 10X phosphate buffer (PBS), when I adjust the pH with $\ce{HCl}$ and dilute the 10X buffer afterwards.
When I prepare another buffer by mixing $\ce{Na2HPO4}$ and $\ce{NaH2PO4}$ to achieve the desired pH value, there is virtually no drift after dilution.
If using carbonate buffer, $\ce{CO2}$ is created if I set the pH with $\ce{HCl}$, but none with the also acidic $\ce{NaH2CO3}$ is used.

I just want to know how the phosphate buffer system is working and why there is a pH drift after dilution if I use $\ce{HCl}$ to set the pH. This might answer the general question, why adjusting the pH with $\ce{HCl}$ in PBS is not suggested.

I feel there could be something wrong with the counter ion maybe?!


texts: Solve this chemical or biological mystery

texts:
I hope this is the best place to pose this unique question.  Please forgive me if it's not.

I went into a closet to get a prescription medication that was filled about a year ago.

The label on the pill bottle has visible signs of something.   Identifying that something is the purpose of this question.

The "something" can be described as light brownish orange circles of discoloration.  They look a lot like mold, but I'm hoping that's not the case.  I tried to photograph them, but they don't show up well.

I took a look at a few other prescription bottles from that time period, and the labels on them also have this appearance.  Labels on newer bottles from the same pharmacy do not have this appearance.

On one bottle, there are also discolorations that are yellow, similar to what a yellow highlighter would produce (but not quite).

My concern is mold, but I'm hoping it's not.  I don't see other signs of visible mold in the area.

The closet is not near a bathroom.  The room is air conditioned and heated (depending on the season) and is kept at approximately 76 degrees Fahrenheit, and never outside the range of 61-89 degrees.  There is a MERV 16 filter on the HVAC system.

The pharmacy is very clean and is fairly new (probably less than 10 years old).  The entire pharmacy chain is probably less than 15-20 years old.  They compound medications within the confines of a special compounding enclosure; none of my medications were compounded.

I don't want to bias the answers, but I am hoping that the brownish orange circles can be explained by a chemical reaction.  I'm thinking that perhaps pharmacist hands are so covered with different chemicals that it could cause a reaction on the label over time.  I don't think the labels had the discolorations when I picked up the medications.

The areas on the labels that show the light brownish orange circles could possibly be areas where the pharmacist pushed down the label.  Areas in which people make contact with items have increased probability of growing mold; but given that a pharmacist was the one who touched these labels, there is also the increased possibility that their fingers were coating with small amounts of medications.

Given the above facts and descriptions, are there any likely chemical reactions that would cause the observed phenomena?

Please note that I'm not a chemist, so please write answers accordingly!  :-)


texts: the molecular formula of an unknown hydrocarbon

texts: A student analysed a hydrocarbon X and found it to be containing 43g carbon and 7.2g hydrogen.The relative molecular mass of X was found to be 42.What is the molecular formula of X?


texts: Why do ionic compounds have such high melting points and boiling points? Do they have IMAFs?

texts:
Molecules have IMAFs that determine the melting and boiling points. What about with ionic substances? What keeps the different compounds together? Do they experience IMAFs? I've heard that it's the ionic bond itself, but doesn't the bond remain after melting, and even if it doesn't then how come covalent bonds don't cause the boiling and melting points in molecules?
Sorry for all the questions, main ones are in the title.


texts:
Are the mechanism and the product for this given reaction right or is there anything wrong with it?
1,2 - Epoxybutane has originally the 2R configuration and the product got an R configuration as well.
I was not sure about, where the nucleophile attacks. Under acidic conditions steric hindrance will be ignored, right? In this case the hydrogen atom will be added to the less substituted carbon atom and the ring will be opened.


texts: I have some white garden pebbles which  are now  yellow with trace of rust. I have tried to soak them in bleach diluted with water without success.  Could I receive suggestions of an appropriate material to remove the rust?


texts: pH(H3O+ ion concentration) of a mixture of 2 weak acids

texts:
I need to find out the $\ce{H3O+}$ ion concentration in a mixture of 2 weak acids $\ce{HA1}$ and $\ce{HA2}$.

They will be ionised as
$$\ce{HA1 + H2O <=> A1- + H3O+}$$
And
$$\ce{HA2 + H2O <=> A2- + H3O+}$$

Then, if $c_1$ and $c_2$ are the concentration of the acids and their dissociation constants are $K_{1}$ and $K_{2}$,then how much will be the value of $[\ce{H3O+}]$ ?

The textbook states without proof  that it is approximately equal to $\sqrt{(K_{1}c_{1} +K_{2}c_{2})}$.

Any help on how to approach the result is appreciated.


texts: How to use gas laws to calculate the partial pressure of a gas that has partly condensed from a mixture?

texts:
A mixture of three gases N2, CO2 and O2 has a total pressure of 106000 Pa. The mixture is cooled to -100°C and the resulting pressure is found to have decreased to 82500 Pa. What gas is condensed and what is its partial pressure?
  (BP N2 = -196°C, BP O2 = -183°C and BP CO2 = -78°C)

I've had a look at all the formulas and laws that have been covered in my Chemistry textbook like Dalton's law of partial pressure and the combined gas equation but it appears that there is not enough information to solve it. I mean, if it asked to find the initial temperature, I could do it, but I'm not sure how to find the partial pressure of the gas(es) from the information provided.


texts:
The acid-base indicator methyl red has a $K_\mathrm{a}$ = $1 \times 10^{-5}$. Its acidic form is red while its alkaline form is yellow. If methyl red is added in a colorless solution with a $\mathrm{pH} = 7$, the color will be :
a) Pink
b) Red
c) Orange
d) Yellow

Seeing the $K_\mathrm{a}$ = $1 \times 10^{-5}$, I concluded that it is a weak acid. Thus I think that when it is added to a neutral solution ($\mathrm{pH}=7$), the resultant solution must be weakly acidic and thus its color must be red.
However, contrary to my logic, the answer given in my book is option

d) Yellow

Is there a flaw in my argument?


texts:
I would like to calculate $\mathrm{p}K_\mathrm{a}$ of lipid molecules using some software tools. I have tried ChemAxon and compared with ChemDraw professional 16.0 version they are mostly similar. I think both are in gaseous phase.

Do I have any chance to calculate the $\mathrm{p}K_\mathrm{a}$'s in aqueous phase using solvent parameters? Any software tool suggestion are highly appreciated.


texts: Does anyone know how to remove the odour remaining from a decomposed corpse which has fallen onto a wooden floor? Aparently the two main chemicals are putrescine (tetramethylenediamine) and cadaverine (pentamethylenediamine).


texts: Which electron is knocked off a Helium atom?

texts: When a He atom is ionized, which electron is removed first, the one with the spin up or down? or is it just random?


texts: can i use an isobutane stove (like jetboil) or butane blowtorch with borosilicate glass?

texts: I don't have a bunsen burner, but have a camping stove (similar to https://www.amazon.com/Stansport-183-B-Isobutane-Backpack-Stove/dp/B004EPWM5S) and a blow torch.  I'd like to do some distillation with things like salt water and juice, and am looking at a distillation set (https://www.amazon.com/Distillation-Apparatus-Equipment-Chemistry-Glassware/dp/B07R8JFK97/). Is it safe to use this with a blowtorch or camping stove?


texts: What is the density of carbohydrates/protein/fat?

texts:
As in weight per volume? I mean.. you always see them specified by weight but they have to have a volume, right?

I suppose different fat(for example) molecules would have different densities but then how do they universally have the same energy density? Are they converted to like a standardized type of fat? Thats the fat I'm interested in.


texts: Research-backed articles on cast iron seasoning

texts:
I've always seasoned my cast iron pans with vegetable oil because that was what I was taught. I'd done some research before, and even came across this StackExchange post on asking the best oil for the job.
To my dismay however, when I tried doing some research myself, all sources pointed to blog posts, particularly the Sheryl Canter one. There is not a single source on her post and she doesn't seem to be very near a materials scientist. The closest paper I could find to the topic was this one. Other than that, it was all anecdotal evidence, many people claiming many different things.
It felt almost absurd that I couldn't find a paper on something that seemed relatively common to me. This will bug me till the end of time unless I figure it out, so I need to know - does anybody have any real sources on cast iron seasoning or what factors play a part in the polymerization of different oils? Thanks in advance.


texts:
We know that for homogeneous mixtures the equilibrium constant is determined using both concentration of reactants and of products. For heterogeneous equilibrium involving a gas and a liquid or a solid, we only use the concentration of the gas because the concentration of liquids and gases are constants, and can thus be omitted from the equation. But what of the heterogeneous equilibrium between a solid and a liquid? Both are incompressible, so what do you do?

Thanks!


texts: Calculate the amount of energy released when 500 cm³ of methane gas at STP reacts with excess air according to the equation:

texts:
$$\ce{CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l)} \qquad \Delta H = -890\ \mathrm{kJ\ mol^{−1}}$$

I am not totally sure how to work this out.

What I did, though, was:
$\ce{CH4}$ $M = 16\ \mathrm{g/mol}$
So, $500\ \mathrm{cm^3} = 31.25\ \mathrm{mol}$
$\ce{CH4}$ $H_\mathrm f = -890\ \mathrm{kJ/mol}$
-> For $31.25\ \mathrm{mol}$ we have $27\,812.5\ \mathrm{kJ}$

If I am wrong, can someone explain me why?


texts: Why is the bottom white in a lucas test?

texts:
Consider this positive result from the Lucas test (adding $\ce{ZnCl2/HCl}$ to a tertiary alcohol):

My question is quite straightforward but I can't find the answer. What is in the top layer (thin and clear) and what is in the bottom milky layer? Also, what is making it milky?


texts: Nickel(II) + borohydride debenzylation reaction mechanism

texts:
I've been looking at this reaction for cleavage of benzyl esters. I've also looked at the original paper and some others, but haven't been able to find any mechanism on how this reagent does hydrogenation.

It also works with Cbz-protected amines/amides/alcohols. With palladium/platinum, the transition metal does oxidative insertions into the X-Bn bond, but I'm not sure nickel could do this insertion. If it could, I would expect this reagent to debenzylate amines, amides and ethers in addition to esters, carbamates and carbonates.

I was wondering if it is known how this reagent debenzylates esters or if anyone has any insight into the mechanism.


texts: Can hexavalent chromium be created by exposure of chromium alloys to air at room temperature?

texts:
I believe that Cr on its own (as in chrome coating) oxidizes as Cr(III) when exposed to air, and similarly I think that it is the same for Cr as a component of stainless steel.

Is it always the case that an alloy containing chromium will oxidize as Cr(III) when exposed to air at room temperature, or are there alloys which might form Cr(VI) instead?

The situation which brings this question to mind is the case of a computer hard disk platter. In the case of a "head crash" of the hard disk, layers of the platter are ground to dust. The layers as I understand are composed of various things: Some kind of carbon polymer as an outer covering, magnetic layers of things like Co-Pt-Cr or Co-Ni-Cr (I found a source which suggests "traces of boron or tantalum" are also added to this layer), and also layers composed of things like Cr-Ti or Cr-Ni. I'm wondering whether any of these layers would cause hexavalent chromium to form.


texts:
I was working on a problem regarding the relative acidity of oxoacids in the form $\ce{HYO3}$ where $\ce{Y}$ represents a group 17 element.
The question (which is from a worksheet created by a chemistry instructor at my institution) is as follows:

  Which of the following is the most acidic: $\ce{HBrO3}$, $\ce{HFO3}$, $\ce{HIO3}$, and $\ce{HClO3}$?

The given answer is $\ce{HIO3}$. However, in my understanding, the acidity of oxoacids is driven by bond polarity, which is affected by the electronegativity of atom $\ce{Y}$, as this question suggests. For oxoacids of the same structure, only differing in the atom $\ce{Y}$, I believed that the acid strength increases as atom $\ce{Y}$ increases in electronegativity. Thus I believed that $\ce{HFO3}$ would have the greatest relative acid strength. As a matter of fact, I believed that $\ce{HIO3}$ would have the lowest relative acid strength as $\ce{I}$ is the least electronegative of the four $\ce{Y}$ atoms on this list. I would appreciate it if you could help me understand why this anomaly, that $\ce{HIO3}$ is stronger in acidity than $\ce{HFO3}$ contrary to the general trend regarding the electronegativity of $\ce{Y}$, applies in this case.


texts: What effect does the concentration of a metal ion have on a flame test and why should small samples of the metal ion be used?

texts:
When we conduct a flame test, say we have a solution of $\ce{NaCl}$ mixed with methanol in a ceramic bowl and we light it with a match.

What effect will [Na+] have on the colour we see? If we're assuming that the drop in energy of each Sodium atom (once the solution is atomised) once it gets excited is the same so the wavelength of emission is the same and we see the same yellow colour, if we have a greater concentration of Na+ do we just see more yellow and our eyes would perceive that as being brighter (while the colour itself is the same, we just see more of it)?

Also, I read this on wikipedia:

  "Bulk sample emits light too, but its light is not good for analysis. Bulk sample emits light primarily due to motion of the atoms, therefore its spectrum is broad, consisting of a broad range of colors."

I get the idea that if the spectrum of emission is broad, then the colour is not really specific to the ion being tested for, but what I don't get is the explanation for this. What does "emits light primarily due to motion of atoms" mean and why does this phenomena not occur in a smaller sample say a spray of the solution or the sample on the tip of a nichrome wire? Why is it that using a larger sample, which is what I assume bulk sample means like having say 20mL of $\ce{NaCl}$ in a ceramic bowl as opposed to a 1mL spray bottle change with regards to the colour of the flame that we see?

Thanks in advance!


texts:
In general chemistry, it is common to teach students to determine a molecular dipole by having them first determine "bond dipoles" which are just based on electronegativity. Then, by adding up these vectors, one determines the direction of the overall dipole.

In quantum mechanics, however, the molecular dipole is found by calculating the expectaion value $\langle\psi|\hat{\mu}|\psi\rangle$. This can be decomposed into $x$, $y$, and $z$ components if one so desires. Regardless, the actually quite useful idea of a bond dipole is nowhere to be found.

I assume that there is not a rigorous way of defining a bond dipole so that a sum of these bond dipoles equals the expectation value above. This is because there is not a well-defined way to partition electron density which is exact. I suppose one could do this using the theory of atoms in molecules.

Nonetheless, other ideas like local mode vibrations are approximate in the sense that a local mode is not an eigenfunction of the polyatomic vibrational Hamiltonian, yet local modes are still very useful and even more accurate in some contexts.

The same is sort of true of bond dipoles in that if one imagines a very long molecule which is polar at one end, a nearby molecule which moves along this large molecule will experience a changing electric field because the dipole of the molecule is only a true point-dipole when the molecule is very far away. So, the field experienced by nearby molecules is more akin to the sum of bond dipoles in the region nearby.

So, is there a rigorous way to determine bond dipoles from first principles? Is it as simple as projecting the total dipole onto a bond axis? What is the form of this projector? Also, in cases where the partitioning of atoms is well-defined, such as the theory of atoms in molecules, are bond dipoles well-defined and do they relate to the total dipole as we expect?

Answers to any of these questions would be welcome.

To be more clear, I am talking about the bond dipoles described on this wikipedia page. They do not provide any formal way of actually calculating the bond dipoles. They mention one can get these dipoles after calculating the total dipole, but I am not sure of the uniqueness of this under unitary transformations.


texts:
Why crystalline solids have sharp melting points but melting point of amorphous solids vary within a range?

Is it because the interaction energy is equal between atoms of crystalline solids so they require equal energy to break the bond or is it because the atoms of crystalline solid are similar and are equally distant so energy gets transferred to every molecule equally so all the bonds break simultaneously.


texts: Is it possible to protect molten magnesium with Butane

texts:
I am currently experimenting with simple methods of metal casting at home. It is conventional wisdom that magnesium is better left to the professionals due to the unfortunate arrangement of its combustion and melting temperatures. I dont have access to any inert gasses or vacuum furnaces; but like a challenge.

The first thing that occurred to me was to use CO2 cylinders you can buy at the supermarket to protect my casting area. Luckily I didnt try that experimentally, since it is a known bad idea. Same applies to water vapor. Molten magnesium will happily steal the oxygen from either, leaving carbon resp. hydrogen gas behind. And a lot of heat of course.

Which brought me to the following counter-intuitive idea: if magnesium cares so little for carbon or hydrogen, could you protect your magnesium from burning with hydrocarbon gas? If I douse my casting mould in butane, then pour my molten magnesium in, I am likely to set the butane ablaze, sure. But I can deal with that; as long as my magnesium stays put.

Is this the dumbest idea ever? Or might it actually work?

To make my question more concrete: what is the known chemistry of magnesium at 700c and pure hydrocarbons? Note that there will also be a lot of silicon dioxide present, which can form a thermite with magnesium, but normally shouldn't under these circumstances. But perhaps the hydrocarbons could catalyze that reaction?


texts: Can any compound be a Lewis acid but not be a Brønsted acid?

texts: Is it possible for a compound to act as a Lewis acid but NOT act as a Brønsted acid? When would this happen? Could you please give a few examples where/why this happens ?


texts: I am interested in sealing some air-sensitive samples inside of xrd-amorphous material to allow for XRD and hopefully XRD-texturing analysis. Of course, Kapton is the common material used for this purpose, but I am unaware of a good way to seal two pieces of kapton together. Impulse sealers (ie here) are commonly used for creating plastic seals in food processing. However, they don't reach a high enough temperature to melt Kapton. I also tried to just heat the kapton with a soddering iron, to no avail. Are there other materials that maybe suitable for sample storage during xrd ?


texts: Computation of pH when an acid and base are mixed in solution

texts:
I'm doing a basic chemistry course, and we are currently learning how to compute $\text{pH}$ from the acid dissociation constant (using $\left[\text{H}^{+}_{(\text{aq})}\right]=\sqrt{K_{a}\left[\text{HA}_{(\text{aq})}\right]}$) along with computing the $\text{pH}$ of strong bases by assuming full dissociation into $\text{OH}^{-}$ ions, and then using the ionic product of water to calculate the concentration  of protons.

The question I have been given is:

  Calculate the pH of the solution obtained when $14.9\text{ cm}^{3}$ of $0.100\text{ mol dm}^{-3}$ sodium hydroxide solution has been added to $25.0\text{ cm}^{3}$ solution of methanoic acid of concentration $0.100\text{ mol dm}^{-1}$; $K_{a}=1.60\times 10^{-4}\text{ mol dm}^{-3}$

I'm not sure how I should go about solving this problem, I can calculate concentrations of hydrogen and hydroxide ions for each of the solutions but I'm unsure how to combine them (as presumably some of the $\text{OH}^{-}$ ions will react with the $\text{H}^{+}$ ions to form $\text{H}_{2}\text{O}$?)


texts: Understanding observations of dissolving surfactants in methanol, water and hexane combinations

texts:
I added various solvents to a shower gel product to see what would happen. The main surfactant ingredients in it are Methyl Gluceth 20,  Sodium Laureth Sulfate, and Lauryl Glucoside.

First I diluted the sample in water, and added it to a separating funnel along with hexane. After shaking and leaving overnight, the lower water layer was clear and hexane layer was a viscous cloudy white. I extracted the water layer (which was a bit soapy but clear), leaving the hexane layer in the funnel.

I then added methanol to the separating funnel. Adding methanol immediately caused the white soap to clump together at the interface, and the hexane layer now appeared clear. (I don't think I shook the separating funnel in this step)

I then added fresh water to the separating funnel again. This caused the white to diffuse into the lower methanol/water layer so that it could be extracted. The hexane layer was now clear.

I am trying to understand why these things happened. Here is what I think:

The surfactant molecules (e.g. SLS) have long hydrophobic tails, and hydrophobic heads. In water they will arrange themselves into micelles etc with the tails pointing in so they aren't exposed to the water. In hexane they will arrange tails pointing out so the heads aren't exposed. The majority of the molecule being hydrophobic, it will be more favourable to arrange tails-out in the hexane, so this is why the hexane layer went cloudy and water was clear (but still soapy).
When methanol was added, the surfactants clumped together at the interface, and this might be the surfactants arranging with their heads pointing to the hydrophilic methanol and the tails pointing to the hexane at the interface. But why didn't they do this with the water/hexane layers? Water is more polar than methanol (polarity index 9 vs 5.1) so maybe water is too polar even for the heads to be pointing to in that way. It probably isn't because of density because the density of SLS and others is a bit over 1 g/ml.
Adding water to the methanol layer maybe adjusted the polarity just right so that surfactant could dissolve in it, but I'm not sure how that works. Maybe since methanol has a slightly non polar region, that would help solvate the tails while the water solvates the heads?

Let me know if my thoughts sound correct or if there's something I haven't considered.


texts: I noticed sometime ago that bubbles formed in puddles/streets whenever it rained. I am wondering if someone could tell me what could cause such bubbles. I examined the bubbles again today more closely and they didn't look "soapy". I know that is not a really valid answer to rule out that leftover detergent/soap could be the cause of such bubble formation. However, the bubbles are short-lived. Furthermore, there aren't "frothy". In other words, there are no clumps of small bubbles.


texts:
First question, and this is one I've searched for in vain.

In the context of setting up cooling baths, I've come across the term "lagged" bath.  I cannot extract what this means from any available context.  I assume it has something to do with time passing (i.e. a lag), but I'm not certain.  If I had to guess, I'd assume it means allowing the cooling agent to come to equilibrium temperature, but again, not certain.

Any direct technical experience that can explain this term would be greatly appreciated.


texts: Find moment of inertia around two axes of sulphur dioxide

texts:
Problem:

  Find the moment of inertia for 2 axes of $\ce{SO2}$. The rotational constants are  given in $\pu{MHz}$. The answer is required to be $10^{-46}\rm~ kg\cdot m^2$, 7 digit accuracy.

I used $$I = \frac{h}{8\times\pi^2\times B}$$ but the answer is marked wrong. I do not understand what I am doing incorrectly. I thought maybe that $\ce{SO2}$ is asymmetric so that formula will not work.

This is an online course that has  minimal discussion assistance. I have scrounged on Google & physical chemistry textbook to see what the alternative could be. Did not see another formula. Where did I go wrong?


texts: How to decide which among these has the greatest bond rotation possible? 1 has the greatest and 2 the least, according to me, I think it is due to the presence of bulky groups. What more factors can effect bond rotation?


texts:
I've recently begun studying about waterproofing paper. Through what I learned is that the reason why paper absorbs water so easily is mainly because of it's material composition. Paper is generally made from plant fibers and these fibers in turn are made of Cellulose. These Cellulose molecules make it possible for water to be absorbed by the paper easily due to adhesion.

Basically, the network of fibers in the paper are filled with empty spaces and when the paper comes in direct exposure to water, the water molecules eventually fill up those empty holes, attract themselves through the Cellulose molecules and penetrates through the whole material. Which soaks up the paper and degrades it.

One way to solve the problem of soaked paper is through waterproofing the paper. Coating it with wax or plastic and forming a thin layer of plastic or wax which prevents water molecules in penetrating the material when the paper is exposed to water.

This water proofing concept makes it look easy to water proof paper, but the problem comes in recycling or when the paper is disposed off. When recycling paper, every bit of its fibers is disassembled but if for an instance the coating of a water proofed paper is too tight, the paper then becomes unrecyclable and become of waste. Since disassembling tightly glued on fibers could eventually destroy the material.

One evident problem here is that the coating hinders the recyclability of the paper because of its reaction with it. In conclusion, the points to be made aware off is that in order to make an effective waterproof paper but at the same time recyclable as well. Is to coat a paper with a specific type of resin/coating that has an effect of tightly bonding the fibers but at the same time easy to disassemble.

Through this understanding, I've been researching on other coating materials that could eventually be effective in water proofing. I've been trying to research on organic resins such as from trees if they would be effective. Are there any effective chemicals or resins out there that would generally be good?


texts: An alternative to dimethylsulfoxide (DMSO) for cryoprotection?

texts:
Is there an appropriate alternative to DMSO? I mean for embryo or oocyte freezing?

I am a PhD student at present. I am going to study this substance and I'm very interested in this field.


texts: Confusion in the order of precedence: alkyl side-chain vs. dimethyl at different positions

texts:
I've read that prefixes like 'tert-butyl, 'sec-butyl' and have been discarded while 'iso-propyl' is still retained by IUPAC. So I wrote another name according to the general rules. Is it correct? If not please correct me.

(The structure in question is framed)

EDIT: When I typed the name here it gave a slightly different structure so I tried putting 5-(1-methylpropyl) first, as in 5-(1-methylpropyl)-2,7-dimethylnonane, which gave the correct structure.

So, my question now is, since both substituents have same alphabetical order, why do we write 5-(1-methylpropyl) first?


texts: How do popular reducing agents react on compounds that have ester, carbonyl, and unsaturated functionalities?

texts:
Suppose we have a chemical compound like ethyl 4-oxo-2-cyclopentene-1-carboxylate

It is $\ce{-COOC2H5}$ bonded to a five-membered carbon ring with one double bond and the ring has another carbonyl group.
Suppose this compound is made to react with these reducing agents:

$\ce{NaBH4}$
$\ce{LiAlH4}$ and $\ce{H+}$
$\ce{BH3}$, $\ce{THF}$, and $\ce{H+}$
$\ce{H2/Pt}$
$\ce{H2/Pd-C}$

Then what will be the product in each cases?
I know some of the reducing agents and I want to know their reactions with a compound which is unsaturated and has an ester functionality $\ce{-COOR}$ and a carbonyl group $\ce{R2C=O}$ bonded to it.
I cannot try to understand it due to my limited knowledge in chemical mechanisms.


texts: Identifying an unknown white oxidizing powder

texts:
I am working with a unknown white oxidizing powder that melts at around 500 degrees Fahrenheit. It turns my finger green when it comes into contact with my finger for a short while. It leaves a very soft almost slimy feeling even after washing it off with normal hand soap.

When melted it becomes a dark purple color And will turn into a solid very quickly when in contact with something cool. It has on the box it came in a diamond shaped yellow sign with the word OXIDIZER then the number 5.1 which means it is strongly corrosive.

It also seems to corrode rubies and sapphires when in this liquid/powder for about 40-45 minutes in 500 degrees Fahrenheit. So I would like to know if anybody has any idea what I am dealing with? Because the company that send this powder to my employer this powder doesn't seem so happy about giving up their secret and says it comes from the dead sea.


texts: How long does it take to run an MS/MS experiment

texts:
I am not planning to do these types of experiments but I would like to know the order of magnitude of the time it takes to run an LC-MS/MS experiment. Let's assume that I have the sample prep (protein) finished and I just need to load the sample into the LC. How long would I need to wait before I would get MS/MS data?
I know that for a typical HPLC experiment, the sample takes around 20 minutes to go through the column.


texts: Is it possible to chemically bond 8 hydrogen atoms together to form an allotrope like $\ce{H8}$?


texts: The lattice energy of a solid ionic compound is the energy released when one mole of the solid compound is formed from its constituent gaseous ions at $\ce {298 K}$ and $\ce {1 bar}$. However, gaseous ions (e.g. $\ce {K^+ (g), Cl^- (g)}$) do not exist at such temperatures. Thus, how is it possible that the lattice energy of an ionic compound can be measured? A more reasonable definition would be to define the state of the compound formed as the standard state, rather than defining the state of the ions as the standard state. Wouldn't that make much more sense?


texts:
I know of this ring expansion reaction that can fuse a benzene ring with another benzene ring:

Performing this reaction twice gives us phenanthrene

How would one go about synthesizing pyrene from phenanthrene or benzene? I couldn't find any literature online, as most pyrene is obtained via fractionating and cracking petroleum. Synthesizing it from phenanthrene also turns up a dead end, as the 9 and 10 positions on it are most reactive, and I would not obtain pyrene in that way. Diels-alder reaction of phenanthrene is also not possible, as highlighted in this answer.