texts: What is the result when the polarity of the solvent is increased in nucleophilic substitution?

texts:
I read in the Guidebook to Mechanism in Organic Chemistry that increasing the polarity of the solvent slightly reduces the rate of an $S_N2$ reaction. Why does this happen?

Another question:
We know that in $S_N2$, using a polar protic solvent would reduce the rate as the nucleophile gets solvated by hydrogen bonding, but I found in Solomon's Organic Chemistry that the $S_N1$ reaction rate increases in a polar protic solvent. Why does this occur? The nucleophile still gets solvated right?


texts:
I'm writing a report on the spectrophotometric determination of iron. In my introduction I want to briefly explain the importance of iron in the human body.

Wikipedia states that "Iron is essential to life due to its unusual flexibility to serve as both an electron donor and acceptor"

1.) So is iron the only element that can do that? If not, what is it about iron that makes it the only element found in hemoglobin?

2.) What is it about being able to gain and lose electrons make it essential to life? I think it has something to do with oxygen being able to bind with iron. But there are so many elements that can bind with iron! What is special about iron?


texts: How to calculate the equilibrium constant of acetic acid-hydroxide ion equilibrium?

texts:
I am trying to calculate the equilibrium constant of the following equilibrium:

$$\ce{CH3COOH (aq) + OH- (aq) <=> CH3COO- (aq) + H2O (l)}$$

I am aware that this reaction essentially goes to completion (the position of the equilibrium lies far to the right). However, I still would like to calculate the equilibrium constant.

I know that $K_\text{eq} = K_\mathrm{a}(\ce{CH3COOH}) \times K_\mathrm{b}(\ce{OH-)} / K_\mathrm{w}$ (I have derived this from the definitions $K_\mathrm{a}$ and $K_\mathrm{b}$). I know that $K_\mathrm{a}(\ce{CH3COOH}) = 1.8\times10^{-5}$ and that $K_\mathrm{w} = 10^{-14}$. However, I am struggling to determine what $K_\mathrm{b}(\ce{OH-})$ is.

I learnt that $K_\mathrm{b}$ is called the "base ionization constant." However, $\ce{OH-}$ is a base, but it is already an ion! So, how can something that is already an ion, ionize? According to this webpage, $\ce{OH-}$ has a $K_\mathrm{b}$ of 1.0. However, what is the equilibrium that led to this number? Is it $\ce{OH- + H2O <=> H2O + OH-}$?

Moreover, if the $K_\mathrm{b}$ of $\ce{OH-}$ is 1.0, is $\ce{OH-}$ considered to be a weak base? Generally, strong bases have a $K_\mathrm{b}$ that is much greater than 1.0. On the other hand, if bases that contain hydroxide ions, such as sodium hydroxide and potassium hydroxide, are strong bases, shouldn't the hydroxide ion itself also be a strong base?


texts: why colour of CuSO4 and CuCl3 is different?

texts: These two are simple ionic compounds , not complexes [if I do not consider water of hydration] then how can I rationalise the difference in colour?


texts: Can I break starch down into glucose units?

texts:
I was wondering if starch can be broken up into individual glucose units. Because on a site I saw, it said that through acid hydrolysis starch can be broken up into amylose and amylopectin. However, as I researched amylopectin I found out it is branched and had a different bond than amylose so just to simplify everything:

Can starch be broken up into individual glucose units and through what processes?


texts:
They are now assisted by chemists who are able to fix dates through the analysis of pollen, radioactive carbon, and fluorine found in connection with fossils..

Here the text is talking about basic paleontology.

Could anyone teach me in a simple way how fluorine is connected with fossils findings?

(This is originally about English test (TOEFL), but the subject in question does not in my opinion belong to ELL)


texts: Why is there no effective alternative to metal salts in antiperspirants?

texts:
Metal salts, especially aluminum compounds are used in antiperspirants to prevent sweating. I found out aluminum chloride hexahydrate, which is found in most antiperspirants, undergoes an acid-base reaction with water which causes the proteins to denaturate, thus these proteins are precipitated out as a gel blocking the sweat glands. Additionally, aluminum is able to bind water molecules.

However, I would like to understand the biological and chemical processes in more detail as I am not quite sure why there is no effective alternative to metal salts to prevent sweating. There are many compounds that could undergo an acid-base reaction with water. There are also different metal salts which are able to bind several layers of water.

My specific questions are:

Which biological and chemical processes underlie the effect of antiperspirants that make metal salts so effective?
Why are aluminum salts used most commonly?


texts: Measuring change in concentration of hydrogen peroxide

texts:
I am conducting an experiment to find the rate constant of the decomposition of hydrogen peroxide, $\ce{H2O2}.$ For this, I was planning on using the integrated rate law:

$$\ln(\text{final concentration}) = -kt + \ln(\text{initial concentration})$$

However, I am not sure how I can measure the change in the concentration of $\ce{H2O2}.$ I would appreciate it if someone can propose a method.


texts: Difference in the functioning of alkaline and acidified KMnO4

texts:
What is the difference in the functioning of alkaline and acidified $\ce{KMnO4}$ as a reagent in organic chemistry?

E.g., in the oxidation of a primary alcohol to carboxylic acid, we use acidified $\ce{KMnO4}$ and not alkaline $\ce{KMnO4}$. Why?


texts: What does spontaneous mean in term of forward and reverse reactions?

texts: I just learnt about Gibb's Free Energy and was thinking about an exothermic reaction with a negative change in entropy. This means that the reaction would occur at low temperatures. But that means that if the system the reaction is taking place in has heat removed from it the reaction would occur. I am not sure if this next assumption is true or not, but if the reaction is not happening that means the rate of reaction is negative (rate being defined as Δ[Product]/Δtime). Since the rate is also defined as R = k[reactants], and concentration cannot be negative, this means that k must be negative, and also that k increases when temperature decreases. However this violates the Arrhenius equation, where an increase in temperature results in an increase in the rate constant. The only solution I see to this conundrum is my assumption was wrong and maybe spontaneous just means the rate of reverse reaction>rate of forward reaction, so they both have positive values for k. I wanted clarification if this was correct or not, or if I completely messed up the definition of Gibb's Free Energy in the first place.


texts: Same set of carboxylate reagents yielding two different products with an alkylide

texts:
I recently came across two contrasting products for the same set of reagents - carboxylic acid and alkyllithium, and wish to understand why exactly any difference exists between the two.

Reaction 1

Reaction 2

I understand that in steps A, B, and E, the alkylide (hydride in E) is acting as a base and abstracting the acidic proton. I'm fine with that.

However, compare step C and F. Both involve the same reagents (carboxylate and an alkylide). In step C, nucleophilic addition of the ethylide has taken place on the carbonyl group, which is a reasonable step according to me. However, in step F, an ester has been formed instead. I am unable to grasp how an ester can even form in this condition (considering both ethylide and carboxylate are negatively charged), and even if it can form, why wasn't it formed in C as well?

Source: MS Chouhan; Advanced Problems In Organic Chemistry; 11th ed; Q64 and 27 in Alcohol, Ethers and Epoxides


texts: Solution of the Roothaan Equations of H2 by Symmetry Arguments

texts:
FWIW my background is in physics and maths, but I am just starting a chemistry PhD (the last time I took a chemistry class was high school). I have only some background in representation theory, and only an abstract taste, as it was in a maths class (bonus: suggest a reasonable representation/group theory reference with applications to chemistry, preferably a concise treatment).
In Szabo and Ostlund's Modern Quantum Chemistry, section 3.5.2 they solve the ${\rm H}_2$ molecule (in Hartree-Fock theory) using a minimal STO-3G basis, $\phi_1$ and $\phi_2$ (centred on each proton). I believe I understand how to set up the Roothaan equations, guessing the density matrix, and solving self-consistently. However, they go on to say "The canonical molecular orbitals will form a representation of the point group of the molecule." Um, okay. Why? And what is meant by canonical here? They go on to say they can be labelled by their symmetry $\sigma_u, \sigma_g, \pi_u, \pi_g$, etc. (I know these terms from wikipedia, and it is discussed briefly in another chapter) I don't fully understand why they (can) do this.
Now, I understand we have two molecular orbitals so it makes sense that they choose only the 2 lowest energies. However, from the set of options above, they state without proof that the $\sigma_g$ is the lowest energy, followed by $\sigma_u$ (I also don't really understand where the wave function comes from). How do we conclude this? Is it because the hydrogen atoms are 1.4 Bohr radii away, hence close and hence we expect bonding (not antibonding?), which I understand to be represented by $\sigma_g$? If this is correct, then it's still not rigorous so I would appreciate any more explanation.


texts: Would cerium(III) in solution be oxidized to cerium(IV) in ESI mass spectroscopy?

texts:
During ESI (assuming positive ion mode for now), we apply a strong voltage ($1.0{-}\pu{5.0 kV}$) to induce ionization.

Therefore, it is common to see oxidation of metal ions (e.g. $\ce{Cu^{+I} -> Cu^{+II}}$).

I wonder if a $\ce{Ce^{+III}}$ solution would be observed as $\ce{Ce^{+III}}$ or as $\ce{Ce^{+IV}}$ due to in-source oxidation.

I feel like there should be a systematic study on this kind of effect but could not find any references for it. Any hints would be appreciated.


texts: A question about nicotinamide adenine dinucleotide

texts: In the structure of NAD+, why does the nitrogen of pyridine bind covalently to the the first carbon of glucose while the anion stabilizing the nicotine amide ion is the phosphate group? In other words, why didn't NAD+ exist as an ionic salt between nicotine amide ion and phosphate ion in the  nucleotide?


texts: The wiki tells me that if you heat carbon at atmospheric pressure it eventually turns directly into a gas without being liquid first.  At what pressure can you make liquid carbon?  Has anyone actually ever studied liquid carbon?  Surprisingly a web search did not answer these questions.


texts: Reversible equation in Chemical Kinetics — Should I use definite integral when solving the differential equation?

texts:
I found this problem:
We have the following reversible reaction: $A \ce{<=>[\ce{k_1}][\ce{k_2}]} B $, described by the kinetics equation:
$$\frac{d[X]}{dt} = k_1([A]_0-[X])-k_2([B]_0+[X])$$
Where
$[X]$ is the increase of molar concentration;
$[A]_0$ and $[B]_0$ are the initial concentrations of $A$ and $B$.
Find $[X]$ as a time dependent funcion.

What I've tried:
The differential equation above is the same as:
$$\frac{d[X]}{k_1[A]_0-k_2[B]_0 - (k_1+k_2)[X]} = dt$$
Now, we should integrate both parts.

My questions are:

Should I use the definite integral? Why? Am I right when I state that the equation becomes this?
$$\int_{[X]_0}^{[X]} \frac{d[X]}{k_1[A]_0-k_2[B]_0 - (k_1+k_2)[X]} = \int_{t_0}^{t} dt$$

If $[X]$ is the "increase" of molar concentration, then is $[X]_0 = 0$?

Is $t_0 = 0$?

Thank you!
If I am wrong, please tell me the corect way of solving this. Thank you so much!


texts: Is heat an extensive or intensive property?

texts:
Is heat extensive or intensive property?

I surfed the Internet for the same and found quite different answers. Like, heat is not a property, so it is neither. One said that since heat depends on the amount of substance, it is extensive. I thought about the latter one as well.

So, my question could be primarily divided into:

1. Is heat a property of matter?

2.1. If yes, is it extensive or intensive? Why?

2.2. If no, why?


texts:
The ligands $\ce{PPh3}$ and dppe (dppe = 1,2-Bis(diphenylphosphino)ethane) are both strong field ligands, but is one obviously a stronger field ligand than the other or are they roughly equal?

The reason why I ask this question as I am researching into $\ce{[NiCl2(PPh3)2]}$ and $\ce{[NiCl2(dppe)]}$ and I trying to find another other reasons for the geometry difference other than sterics.

My guess would be that dppe is a strong field ligand, but that is more of a guess than any real logic application.


texts: Can formaldehyde be stored at a higher temperature than room temperature?

texts:
I have studied that formaldehyde stored at temperature lower than room temperature convert into 1,3,5-oxane. So, it's not stored at colder temperatures.

But my question is - Can a similar degrading reaction happen if methanal is stored at temperature higher than room temperature?


texts:
I have trouble understanding as to what the last part of the increase in liquid level means. I believe this is the foam formed after the fermentation? I am calculating for the pressure but I have trouble as to what volume should I use to find the moles since I don't understand the last part. It would greatly help me to understand this process first.
I've been extensively searching how the fermentation process actually occurs cause I don't understand a thing about it. To find the pressure from what I know, I converted the volume of glucose to $\ce{CO2}$ to find the moles and plugged the value in the ideal gas equation $p=nRT/v$ with the volume being $\pu{0.07L}$ from $(\pu{125mL} - \pu{55mL})$, because it says the $\ce{CO2}$ in solution is negligible.
I don't know where the changes in densities come in and I don't know how to incorporate the pressure brought about by the liquid solution. I think my thought process is wrong really cause I don't understand fermentation.
https://www.homebrewtalk.com/threads/calculating-total-gas-produced-in-fermentation.165020/ This site proposed a $p_1v_1=p_2v_2$ method where $p_1$ is at STP, but I don't think this is needed in the problem.


texts: Cannizzaro reaction versus Nitroaldol reaction

texts:
In Clayden et al. on p. 696 the following nitroaldol reaction is listed:

Later in the same chapter they explain the Cannizzaro reaction. Why is the yield of this nitroaldol reaction particularly good, while a Cannizzaro reaction is also competing for the benzaldehyde? Is the nitroaldol reaction that much faster?

I looked in some literature and they mostly seem to use nitrogen bases (cyclohexylamine, $\ce{Et3N}$, $\ce{n-BuNH2}$, methylamine, etc.) for these kind of reactions (nitroaldol reaction with aromatic electrophile). The reported yields are also typically lower. See for example the "Literature method" section of the synthesis of 1-phenyl-2-nitropropene on Erowid (which seems to be some kind of precursor to amphetamines, so there is plentiful information about it in comparison to the 1-phenyl-2-nitroethene synthesis listed in Clayden. Can the yields be so different due to the steric hindrance of the additional methyl group?). What is the benefit of these nitrogen bases over $\ce{NaOH}$? Clayden et al. only mentions them with the comment that $\ce{NaOH}$ is not really necessary since nitrogen bases are sufficiently strong for nitroaldol reaction, because the typical pKa value of short chain nitro alkyl compounds is ~10.


texts: At what temperature can molecules no longer form?

texts:
// hyper simplistic terminology in use for the question - apologies.

Molecules are formed by atoms bonding together, and those bonds have an equivalent energy.

At what temperature does the thermal energy of an atom exceed the bond energy, preventing it from forming any molecule?

I think an equivalent question is "what is the temperature needed to spontaneously dissociate any molecule into its component atoms?"


texts: Cauchy-Schwarz integral screening different inequalites

texts:
Eq. (9.12.23) in [1] states that:

$$\sum_{abcd}c_{ab}c_{cd}g_{abcd}>0\tag{MEST 9.12.23}\label{91223}$$

with $c_{ab}=c_ac_b$ for $c_a$ being some distribution coefficients and $g_{abcd}$ being the two-electron integrals in AO basis. Now for $c=a$ and $d=b$ giving:

$$c_{ab}c_{ab}>0$$

Which seem obvious as long as $c$ are real numbers.
It can thus be seen that to fulfill Eq. (\ref{91223}) that:

$$g_{abab}>0 \tag{MEST 9.12.24}$$

Which fulfill the requirements for the Cauchy-Schwarz inequality, thus giving:

$$\left| g_{abcd} \right| \leq \sqrt{g_{abab}}\sqrt{g_{cdcd}}\tag{MEST 9.12.25}$$

Now since $c_{ab}=c_{a}c_{b}$ this implies that:

$$c_{aa}c_{bb}>0\tag{1}$$

which in turns further implies that:

$$g_{aabb}>0\tag{2}$$
Which surely also fulfill the requirements for the Cauchy-Schwarz inequality, giving:

$$\left| g_{abcd} \right| \leq \sqrt{g_{aabb}}\sqrt{g_{ccdd}}\tag{3}$$

Now further doing some index juggleling will lead to the following six different inequilities:

$$\left| g_{abcd} \right| \leq \sqrt{g_{abab}}\sqrt{g_{cdcd}}\tag{Ineq. 1}\label{ineq1}$$

$$\left| g_{abcd} \right| \leq \sqrt{g_{acac}}\sqrt{g_{bdbd}}\tag{Ineq. 2}$$

$$\left| g_{abcd} \right| \leq \sqrt{g_{adad}}\sqrt{g_{cbcb}}\tag{Ineq. 3}$$

$$\left| g_{abcd} \right| \leq \sqrt{g_{aabb}}\sqrt{g_{ccdd}}\tag{Ineq. 4}$$

$$\left| g_{abcd} \right| \leq \sqrt{g_{aacc}}\sqrt{g_{bbdd}}\tag{Ineq. 5}$$

$$\left| g_{abcd} \right| \leq \sqrt{g_{aadd}}\sqrt{g_{ccbb}}\tag{Ineq. 6}$$

I think I have ever only seen Eq. (\ref{ineq1}) described before, surely this could be because the rest are obvious extensions, that I just haven't thought of as being obvious before.
Or that I have made some flaws in my reasoning.
In practise are all of the inequilites used?
If not anyone got clues about why not?
Especially Ineq. 4-6 is somewhat different from Ineq. 1-3.

[1] : Molecular Electronic-Structure Theory, Trygve Helgaker, Poul and Jørgensen Jeppe Olsen


texts: Can hot food ever emit x-rays or gamma rays?

texts:
I was just wondering, if heating food up is the result of increasing the energy of bends and stretches in the bonds of the molecules, is it ever possible for tiny amounts of x-rays and gamma rays be emitted?

When we give a molecule enough energy, its electrons can jump to higher orbitals and then return to ground state, releasing EMR with a frequency proportional to the energy gap. So if we heat food, is there a chance that some electron received enough energy to jump up to a really high energy level?


texts: Why do pyrrole and furan have dipoles oriented in different directions?


texts: Relative Humidity, vapor pressure, partial pressure

texts:
The partial pressure of water in the mixture is the equilibrium vapour pressure of water at the temperature specified.

Relative humidity (RH) is the ratio of the partial pressure of water vapor to the equilibrium vapor pressure of water at a given temperature.

So at all temperatures Relative Humidity is 1 .
But this isn't so.
Where am I wrong?


texts: Explaining stereochemistry in a sigmatropic 1,3-alkyl migration

texts:
I have quite a bit of difficulty in explaining sigmatropic rearrangement reactions. Consider the following reaction:

How do I explain the formation of the shown product? When simply moving the electron pair in my head, I come to the other enantiomer, where the $\ce{-CH3}$ group shows in our direction.

I've repeated all my notes on sigmatropic rearrangements but unfortunately, I don't get it. I suppose that I should treat this like an alkyl migration. The latter should happen over a suprafacial intermediate state as we have an uneven number of electron pairs (1) and we have thermal conditions. This results in a suprafacial reaction. Knowing this, I went on and added the HOMO and LUMO orbitals and postulated intermediate steps. Note: Yes, I am aware, that pericyclic reactions happen in a concerted fashion, but somehow I need to see, why the groups on the bridging carbon have this conformation.

So, let's go on to my question...

  Is my proposed explanation okay? If not, please provide some information. I really have trouble with this kind of reactions.


texts: Can a charge smaller than that of an electron exist? If so how?

texts:
In school I've always been taught that the smallest charge possible is that of an electron( or proton) however I recently solved a question regarding a dipole and the charge came smaller than that of a proton, after  the solution given in the book however, there was a little statement written saying this can also exist in real life as well which seems off to me.. like how can you get less charge then the smallest unit of charge? If the answer is quarks well don't they exist in a combined state and wouldnt they combine to form protons and stuff (don't know too much about this topic tho.. I know a little thru YouTube videos but that's it) and hence change the charge to a multiple of that of a proton? Any insight is welcome
*Please note that this is not a homework question, it's just out of my curiosity.. thx for understanding!
Also not rly sure if I should ask this on chem stack exchange or phy..


texts: What is the process for chemical engineering?

texts:
I will be upfront -- I am not a Chemist, nor do I have much experience beyond high school Chemistry.

I have always had a vested interest in chemistry, but my engineers brain has always left me wondering -- Where do I start if I want to design a new chemical with certain properties? I have attempted to research via Google, but to no avail.

Like I mentioned above, I am very mechanically minded, and to design say a transmission is simple enough - just select what type of gear(s) (..or design your own) put them all together, and BAM! You've got a transmission! Chemicals...could possibly kill you if you screw up...

I have a strong feeling that this question is a field of study in and of itself, so I do appreciate any answers.

Thank you!


texts: Why is a trialkylamine a better leaving group, in nucleophilic reactions, than a Cl group?

texts:
Why is a trialkylamine a better leaving group, in nucleophilic reactions, than a $\ce{Cl}$ group? In the same vein, isn't a trialkylammonium a much weaker acid than $\ce{HCl}$?

$\ce{R-NR3+ -> Nuc-R + NR3}$ (Stronger leaving group)

$\ce{R-Cl  -> Nuc-R + Cl-}$    (Weaker Leaving group)

Compared to:

$\ce{H-NR3+ -> Nuc-H + NR3}$    (Weaker acid, NR3 thus weaker leaving group)

$\ce{H-Cl -> Nuc-H  + Cl-}$     (Stronger acid, Cl- thus stronger leaving group)


texts: Effect of periodic acid on cyclohexane derivatives

texts:
Periodic acid (per-iodic acid, $\ce{HIO4}$ ) cleaves vicinal diols(to carbonyls) via a cyclic intermediate.

Due to the cyclic intermediate, it needs a syn configuration for the $\ce{-OH}$ groups for the reaction.

Exactly which configurations are allowed on cyclohexane derivatives?

Let's take 1,2-dihydroxycyclohexane(boat conformer). If the two hydroxy groups are both on the axial positions (trans- ), then obviously the reaction will not take place.

What about when the two are cis- (one axial, one equatorial), and when they are both equatorial (trans- )?

(My original question had to do with diastereomers of cyclic glucose--aldohexoses--but I realised that the extra hydroxy groups make the reaction more complicated)


texts:
I just went camping and someone brought a game from Australia. There was a wooden box with the top made of a thin, soft sheet of lead with a hole in it. The participants then throw coins at the box, and getting the coin inside gives some points, while landing a coin on top gives a little less. I've been looking online, and I think the game is called "Toad in the hole".

I know that lead is toxic, but I don't know in what way. Is it toxic to touch this lead sheet? And to eat afterwards without washing hands?

Maybe lead is only toxic in some form?


texts: Finding Equivalent representation of a molecule/crystal

texts: Is there a website or online calculator to determine the reducible representation of a crystal/molecule using wyckoff positions without having to analyse the number of unmoved atoms/bonds for complicated structures?


texts: What is the general mechanism for a lactam ring reacting with water and an acid?

texts:
For example, let us say we have 2-Pyrrolidone and react it with water and $\ce{HCl}$. I do know that the product is a salt, $\ce{HO(C=O)CH2CH2CH2NH3Cl}$.

I've tried coming up with a mechanism but fell short. I do know that at the first step we must have protonation of the carbonyl-oxygen which gives us a resonance stabilized carbocation intermediate. Nitrogen can better handle a positive charge.

For the second step, we use the addition of water to the carbonyl-carbon followed by a proton transfer from the oxygen to the nitrogen. But when we do this we get $\ce{NH2-}$ which is not favorable. This is the step that I'm stuck on. After this step it would be easy to see the collapse of the tertiary carbocation intermediate.


texts: What does 0.12 N mean on a bottle of sulfuric acid?

texts:
I just bought a bottle of sulfuric acid in order to simulate acid rain for an experiment. I was wondering what $0.12\:\mathrm{N}$ on the bottle means. I need a simplified version of the explanation as I'm currently a freshman in high school taking biology, I have never taken a chemistry course before. I've read that the $\mathrm{N}$ means normal, but the explanation included a ton of jargon that I couldn't understand.

The time in question: does the $0.12\:\mathrm{N}$ mean concentration, as in $12\%$ concentration?

How would you guys suggest making simulated acid rain with this? My guess is that I would keep titrating the sulfuric acid into the water until the $\mathrm{pH}$ gets to my preferred $\mathrm{pH}$.


texts: Why is an ionic bond a chemical and not a physical bond?

texts:
Ionic bonds seem to be intermolecular but are classified as chemical bonds.

"Ionic bonding is a type of chemical bond that involves the electrostatic attraction between oppositely charged ions." -  Wikipedia, definition of an ionic bond
"The physical force of attraction which holds atoms and molecules in a matter is called a physical bond. van der Waals' forces and coulombic forces are physical forces." - Chemistry Stack Exchange, definition of an intermolecular force
"A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electrostatic force of attraction between opposite charges, either between electrons and nuclei or as the result of a dipole attraction." - Wikipedia, definition of a chemical bond

Before an ionic bond is formed, oxidation and reduction must occur. For example, let's use sodium chloride. A chlorine atom will steal the outer electron from a sodium atom. The chlorine is gaining an electron, i.e. being reduced. The sodium is losing an electron, i.e. being oxidized. I agree that this is a purely chemical process.
Now that the atoms are oppositely-charged ions, they can attract and form an ionic bond:
$$\ce{Na+ + Cl- -> NaCl}$$
My question is this: How is this bond defined as a chemical bond?
Let's take water; $\ce{H2O}$. The oxygen forms two polar-covalent bonds with two hydrogen atoms. Each hydrogen shares two electrons with the oxygen. The electrons are being shared, so this bond an intermolecular force. The atoms stay together because they both depend on the electrons they share.
Now let's take more than one water molecule. These molecules will form hydrogen bonds. The hydrogens on the water molecules do not often have an electron around them because the oxygen has a greater attraction with them. This leaves the lonely proton of the hydrogen to make that end of the water positive while the oxygen is negative with its electrons. The negative end of the water (oxygen) will become attracted to the positive end of another water molecule (hydrogen), forming our anticipated intermolecular force. Does this sound familiar?
I hope it does. According to my knowledge, an ionic bond is that, but instead of a dipole-dipole interaction, it's a monopole-monopole interaction. If you look at the bond itself and not the reaction forming it, it acts just like an intermolecular force.


texts: Will sulphuric acid react with water produced in an esterification process?

texts:
Sulphuric acid acts as a catalyst to catalyze the reactions of alcohol and carboxylic acid to form ester. Alcohol reacts with carboxylic acid to produce ester and water.

However, as sulphuric acid have strong afinity towards water, will sulphuric acid react with the water produced in an esterification process?

If so, will it mean that the equilibrium is shifted to the right as water is reacted with sulphuric acid? And will this mean that there would be less sulphuric acid present as a catalyst to catalyse the reaction?


texts:
I was washing my cup with hot water (without soap) and upon it nearing my nose, there was some sort of 'smell' (I lack a better word)-

However the 'smell' was different compared to when I was drinking just plain cold water.

So my question is, does water have a smell?


texts:
Addition polymerisation is defined in my textbook as the process in which a molecule or compound is formed by combination of small molecules (monomers) implicitly having greater molecular mass than either of the monomers.

"A molecule is the smallest part of a substance which can exist independtly."

By this definition, one should find THAT part (Smallest freely existing part) of any polymer and then extract a molecular formula for the polymer. But it does not happen in actual. For example, polythene is assigned a molecular formula $(C_2H_4)_n$.

I just want to know what kind of molecule is determined by this kind of molecular formula as far as the definition of molecule is concerned?

And by what means I can find out its (polythene's) molecular mass?


texts:
I am a total noob in chemistry, so sorry in advance if this is a very stupid question... I am trying to solve this redox reaction:

$$\ce{KClO3 + FeSO4 + H2SO4 -> Fe2(SO4)3 + KCl}$$
$$\ce{K^{+1}Cl^{+5}O^{-6}3 + Fe^{+2}S^{+6}O^{-8}_4 + H^{+2}2S^{+6}O^{-8}4 -> Fe^{+6}2(S^{+6}O^{-8}4)3 + K^{+1}Cl^{-1}}$$

When I analyze this I can see the following things:

Fe lost some electrons, it went from +2 to +6
Cl went from +1 to -1: a gain of elecetrons

But
I see something happened to the SO ions as well: on the left side you have two times $S^{+6}O^{-8}_4$ and on the right three times so something changed here as well. What happened? Do I have to take this into consideration as well for the calculation? And on top of that $O_3$ on the left side disappeared.

My current guess is that you never have to look at the change in oxidation state of oxygen atoms. Is that correct?


texts: Which gas is easier to compress, the ideal gas or a real gas?

texts:
Since the pressure of a real gas is less than that of the ideal gas  and its volume is more than that of ideal gas, I am assuming that the real gas is difficult to compress in comparison to an ideal gas.

Is my logic right? Also I'm looking for a clearer explanation!


texts: What is the difference between a time of flight mass spectrometer and a spectrometer that uses a magnetic field?

texts: Traditional mass spectrometers used electromagnets to deflect isotopes of different masses which allowed only a certain isotope to reach the detector. But how is the TOF MS different besides the fact that it doesn't use magnets? Does it have a different method of accelerating the ions which leads to them moving with a different velocity? If the methods of acceleration are same wouldn't there initially be no need for magnets to deflect the ions? Or is it the detector that works differently?


texts: Monoepoxidation of 1,2-dimethylcyclohexa-1,4-diene using m-CPBA

texts:
What is the product formed when 1,2-dimethylcyclohexa-1,4-diene undergoes epoxidation with one equivalent of m-CPBA (meta-chloroperbenzoic acid)?

In the epoxidation mechanism, the π-electrons of the double bond attack m-CPBA:

So, methyl groups attached to the double bond should increase its nucleophilicity. On the other hand, since it is a nucleophilic attack, the methyl groups should also cause considerable steric hindrance. So what should the answer be?


texts:
I am interested in making a Schlieren texture of liquid crystals to show kids at an outreach event (see image below). I have the polarizers and camera for the imaging part, but I don't know of a place to find liquid crystals.

I would prefer something cheap and chemically inert because I don't want to bring anything sensitive or hazardous. I would imagine that it should be really easy to get solutions or powders of liquid crystal materials, but I am having a hard time finding a source.

Any suggestions? I don't have access to a proper chemistry lab, but I can mix basic things in my kitchen.


texts: What type of intermolecular forces will dominate Diethyl ether?

texts: Is Diethyl ether (also known as ethyl ether) a polar molecule? What type of intermolecular forces dominate it? Dipole-Dipole Interactions, London Dispersion Forces or Hydrogen Bonding? Please Explain.


texts: Solubility of dimethyl ether in aliphatic hydrocarbons

texts:
I'm having trouble finding information on the solubility of dimethyl ether in a hydrocarbon like butane, propane, or isobutane.

I've read that its soluble in methanol, ethanol, isoproanol, chlorinated hydrocarbons, and toluene but cant find much else.

Assuming 1 atmosphere of pressure and both chemicals are at a temperature of -11°F, would the then liquid isobutane be misicible with liquid Dimethyl ether?


texts: Chemical water treatment: Acid Base reaction

texts:
I was thinking of a hypothetical waste system that uses nanotechnology to its advantage.

At the individual level, waste just passes through into pipes when flushed like it normally does.

But once it reaches the water treatment plant there is an initial filter to catch solid waste(in other words poop) and divert it to a different part of the system where it gets dried and eventually ground into a biosolid that can be used as fertilizer.

Meanwhile all the urine, vomitus, blood, and any diarrhea that didn't get caught by the initial filter is passed through a series of filters to catch smaller and smaller waste products from cells all the way to molecules like urea being blocked with a nanofilter. Only a few compounds besides water are left. Yes there are still small ions like potassium and this might actually pose a problem.

But the real threat is that $\ce{HCl}$ is still in the water. Pepsin and other enzymes have been blocked by the nanofilters but $\ce{HCl}$ is still small enough to pass through all of the filters. A nanofilter that can block $\ce{HCl}$ is so impractical that it would most likely block the water itself until either the water treatment system or the microfilters and nanofilters burst from pressure and you end up with a critical failure either way.

So there has to be a chemical reaction that either deactivates the $\ce{HCl}$ and thus renders it harmless or a reaction that leaves no trace of $\ce{HCl}$.

I was thinking that to render the water safe, $\ce{NaOH}$ should be added to increase the amount of saltwater and totally get rid of the $\ce{HCl}$. But then I realized that with potassium and other ions besides sodium and chloride still in the water this could make the water toxic due to toxic salts forming.

Potassium chloride is the least harmful of all the salts that could form besides sodium chloride. Other than the bitter taste, there is basically nothing wrong with using potassium chloride. Similar for calcium chloride. Magnesium chloride though could cause diarrhea due to the magnesium(I know at least part of that diarrhea is from magnesium because the magnesium supplement I take helps to prevent constipation). I am not as worried about hydroxides because those would react with hydrogen ions to produce water.

But those salts are not the only problem. The other problem is how much $\ce{NaOH}$ to add.

I mean to get $\ce{HCl}$ down to 0 every time, there would have to be sensors to not only know the volume of water but also the concentration of $\ce{HCl}$ and a relatively complicated math problem like this:

$$[\ce{HCl}] * x = a mol \ce{HCl} = a mol \ce{NaOH} = [\ce{NaOH}] * y$$

What is complicated about it? Well for one how would you sense the exact concentration of a strong acid or base without damaging the sensory equipment? And unless you regularly go to the water treatment plant with this nanotechnology, you won't know what the concentration of $\ce{NaOH}$ is. And the concentration of $\ce{HCl}$ will most likely vary day to day depending on factors such as these:

How often any given person vomits
Hydration level before vomiting
Amount of bile in the vomit
Dilution of stomach acid
Amount of blood in the vomit if any
Prevalence of vomiting from any cause
Total Volume of vomit

So basically my question is how can I have the part of the system after the filters be constantly sensing the exact concentration of $\ce{HCl}$, doing the math, and adding the amount of $\ce{NaOH}$ that will get the concentration of $\ce{HCl}$ down to exactly 0?


texts: Is there a difference between imidazolidinone and imidazolidone?

texts:
I've had my nose in the early literature on GFP (Green Fluorescent Protein), which contains a 4-(p-hydroxybenzylidene)imidazolidin-5-one fluorophore, and in one paper the author refers to the "imidazolidone ring".

I assumed that this change of spelling was equivalent, but I can't find anything that looks reliable on Google (there are also pages referring to imidazolinone, which looks like it refers to an aromatic ring with Nitrogens at positions 2 and 4...)

I don't think I'd know quite where to look on the IUPAC website for the info so trying here...

Can anyone help me understand the variations?


texts: How to transform an aliphatic primary amine to the corresponding nitro compound?

texts:
Could you suggest a reagent or procedure to transform an aliphatic primary amine to the corresponding nitro compound.

I know this is a bit backwards of a request because the usual procedure is the reduction of nitro groups to their corresponding amine, but there is a need of its electron-withdrawing properties for a subsequent condensation to form the intended intermediate. If this approach could be solidified, then it would make things a lot easier for this recent graduate, as the starting material is a lot less expensive.

I have found references to ozonolysis, but am unsure of it, as I have no previous experience with these sorts of reactions. I have also seen in abstracts where it is discussed formation of the diazonium compound, which was the used to form the nitro compound. There are a couple of others I have come across, but I am not sure of their efficacy or plausibility.


texts: Finding required drug concentration given Kdiss

texts:
The enzyme HIV-1 reverse transcriptae (HIV-RT) plays a significant role for the HIV virus and is an important drug target. Assume a concentration [E] of 2.00 µM (i.e. 2.00 x 10-6 mol/l) for HIV-RT. Two potential drug molecules, D1 and D2, were identified, which form stable complexes with the HIV-RT.
The dissociation constant of the complex ED1 formed by HIV-RT and the drug D1 is 1.00 nM (i.e. 1.00 x 10-9 mol/l). The dissociation constant of the complex ED2 formed by HIV-RT and the drug D2 is 100 nM (i.e. 1.00 x 10-7 mol/l).
Compute the total concentration of [D1]tot that is needed to bind 90% of the HIV-RT at the given concentration [E]tot. You do NOT have to consider competition betwwen the drugs D1 and D2! They are administered separately.

I understand how to calculate the concentration when [E]eq = [ED]eq when 50% of [D]eq is bound to HIV-RT because Kdiss = [D]eq and it makes for a simple calculation because [E]eq and [ED]eq cancel out when calculating Kdiss, but what changes mathematically need to be made to account for the change in ratio (90% rather than 50%)? Any help would be appreciated.


texts:
How does WD-40 displace water? Or does it even displace water? WD40.com explains what WD-40 stands for:

  WD-40® literally stands for Water Displacement, 40th formula. That's the name straight out of the lab book used by the chemist who developed the product back in 1953. The chemist, Norm Larsen, was attempting to concoct a formula to prevent corrosion—a task which is done by displacing water. Norm's persistence paid off when he perfected the formula on his 40th try.

If it displaces water then I always thought that that meant it was denser or heavier. I just tested to see: I sprayed a couple teaspoons into an empty glass then poured that into another glass half filled with water. The WD-40 floats! So what does it mean to say that it "displaces water"? Surely it doesn't mean that it's hydrophobic, all lubricants are hydrophobic.


texts: Why does potassium have the electronic configuration of 2.8.8.1?

texts: We all know that potassium, the 19th element on the periodic table has the electronic configuration of 2.8.8.1.  However, why not 2.8.9?  In the element scandium, it has the electronic configuration of 2.8.9.2.  I would like to know why potassium is not 2.8.9.


texts: Do self-growing hydrogels grow and strengthen infinitely?

texts:
Recently, there was a publication [1] (/., YouTube) on self-growing materials using mechanoradically-generated double-network (DN) hydrogels, closely resembling self-strengthening of muscles.

  We used a series of DN gels consisting of poly(2-acrylamido-2-methylpropanesulfonic acid) sodium salt (PNaAMPS) as the brittle network
  and poly(acrylamide) (PAAm) as the stretchable network. Each network is covalently cross-linked.

  Fig. 1. Conceptual scheme of the self-growth of materials induced by mechanical training. (A) A skeletal muscle becomes bigger and stronger
  under the application of repetitive mechanical stress and a continuous nutrient supply through metabolic cycles. (B) As a result, such a tissue is
  initially weakened (purple arrows) but then recovers or even shows enhanced performance (red arrows) due to mechanical stimuli. The green outline indicates one mechanochemical cycle. (C) Our strategy to develop self-growing materials based on mechanical training of DN gels. Mechanical stress leads to breakage of the brittle network (blue), whereas the highly stretchable
  network (pink) maintains the integrity of the gel. The mechanoradicals generated at the broken ends of the brittle network strands trigger polymerization of monomers supplied from the external environment to form a new network
  (orange). The chemistry of the newly formed network can be the same or differ from that of the original brittle network, as required.

The process is reported to be repeatable and reproducible:

  With proper conditions, our DN gel exhibits persistent growth in strength and size under repetitive mechanical training. Two requirements must be satisfied: Enough monomers should be continuously externally supplied, and the newly formed
  network should serve the role of a brittle network that then breaks during the next deformation to trigger subsequent network formation.

However, with muscle growth there are limiting factors such as hormones and bones structure, and even supplying enough protein one cannot grow the mass infinitely*. Considering constant feeding with monomer, is there a theoretical/practical limit for strength and growth for these DN-hydrogels?

*not even Tetsuo Shima — sorry, couldn't resist considering the origin of this work and the anime.

References

Matsuda, T.; Kawakami, R.; Namba, R.; Nakajima, T.; Gong, J. P. Mechanoresponsive Self-Growing Hydrogels Inspired by Muscle Training. Science 2019, 363 (6426), 504–508. https://doi.org/10.1126/science.aau9533.


texts: Why are 3 equivalents of organolithium needed in synthesis of ketone from carboxylic acid?

texts:
For the reaction of a carboxylic acid and organolithium reagents to synthesise a ketone, Clayden's, on p 219, mentions:

  Notice that three equivalents of organolithium are needed in this reaction: one to deprotonate the acid, one to deprotonate the hydroxyl group, and one to react with the lithium carboxylate.

It seems to me that "the acid" and "the hydroxyl group" refer to the same thing. A carboxylic acid molecule only has one acidic proton and it belongs to a hydroxyl group. Thus, shouldn't these two terms refer to the same thing and only two equivalences of the organolithium reagent be necessary?

Reference

Clayden, J., Greeves, N., & Warren, S. (2012). Organic Chemistry (2nd ed.). New York : Oxford University Press Inc.


texts: Which of the following groups show +M and -I effect?

texts:
Which of the following group show +M and -I effect?
(A) $\ce{-\underset{\underset{\huge O}{||}}{C}-F}$
(B) $\ce{-\underset{\underset{\huge O}{||}}{C}-OR}$
(C) $\ce{-O^-}$
(D) $\ce{-OH}$

Answer is option D. D is obviously correct, but why not option C? $\ce{-O^-}$ has electrons to donate and is electronegative.


texts: Does Nucleophilic substitution require water to happen?

texts:
I am under the impression that in a mixture of hydroxide ions, haloalkanes, water, and ethanol, under low temperatures, nucleophilic substitution will occur predominantly, with small amounts of elimination.

When no water is present and the solution is heated, elimination will occur to a greater degree. Is it possible for nucleophilic substitution to occur when no water is present as all?

Thanks a lot.


texts: How is this mystery chemical reducing carbon emissions?

texts:
My chemistry is not good enough to solve this problem, and it's driving me crazy.

At my job, a sales agent approached me to be their representative in my area for their product.  It's a product that when mixed with diesel or gasoline, it reduces carbon emissions in the vehicle to almost 0.

Now this seems impossible to me.  The burning of hydrocarbons necessarily creates $\ce{CO}$ or $\ce{CO2}$, and the $\ce{CO}$ can be converted to $\ce{CO2}$ in the catalytic converter by oxidizing it.

In the test results, $\ce{CO}$ dropped to almost 0, and $\ce{CO2}$ stayed the same or went down (also my own calculations show the change in $\ce{CO2}$ was not statistically significant with the small sample size - 3 before and 3 after tests on 3 cars).

I've seen the test results (yes, they could have been faked, but they filmed the testing process).  My buddy also personally tested it on his car and got the same results.

Anecdotal evidence shows that the car's mileage is the same.

Can anyone point me to somewhere to try and figure out what is going on here? It sounds too good to be true, and as such, there is no way I'm going to recommend my company represent this product until I know what's going on.

Here are the mean test results (ppm).  Some of them have high variance.  The only statistically significant changes are $\ce{CO}$ reduction in all cars, and all changes in the first car.  The $\ce{NOx}$, $\ce{CO2}$, and $\ce{CxHy}$ changes in car2 and car3 are not significant.

        Before                          After
        CO    CO2    CxHy    NOx        CO    CO2    CxHy    NOx
Car1    3491  9.4    0.39    46.7       33.3  7.8    0.07    9.7
Car2    164   11.5   0.13    2.7        12.9  11.4   0.37    0.7
Car3    2868  11.1   0.18    14         123   10.9   0.06    39.3

I'm suspicious this may just be ethanol, but the manufacturer swears it isn't.

The advertised ratio is 1 oz to 12.5 gallons of fuel which is less than 0.1% (I believe they used double that in the tests).  Too low to be ethanol anyway, right?

Follow-up:

I have confirmed that I was originally mistaken in that all measurements are ppm.  I received a new copy of the original results, and $\ce{CxHy}$ and $\ce{CO2}$ are indeed measured in percent, rather than ppm.  It was incorrectly rewritten in the report.  The numbers are the same, though.


texts: What word, or phrase, do chemists use to describe the color saturation of a solution?

texts:
Outside of chemistry, I've used the word saturation to talk about how blue (or how green, red, etc.) something is. In the lab that I'm writing, I have three undesirable options:

use saturation and risk ambiguity with the other sense of the word (I could include a footnote that specifies the intended sense of the word; however, my experience has taught me that TA's rarely read footnotes.),
use an awkward construction (e.g. the degree/amount of blue exhibited by the solution), or
use an unusual term or a neologism (i.e. blueness).

None of those options are especially appealing.

Is there a word that chemists use to talk about how blue (or how green, etc.) a solution is?


texts: "Nivea Sun protect & refresh" melted my tub

texts:
I stupidly applied spray sunscreen on my children inside our white, acrylic bathtub and the floor ended up with a white, very sticky residue that rubs off on things, but will not wash away with detergent. The sunscreen turns out to be based on denatured alcohol and contains Benzyl Alcohol, so I suspect it melted the top layer of the tub.
Is there anything to do to re solidify the surface or remove the sticky layer? I've seen refinishing kits at the hardware store, but I assume this requires a clean surface beforehand.
Other ingredients:
Denatured Alcohol,
C12-15 Alkyl Benzoate,
Homosalate,
Octocrylene,
Cyclomethicone,
Glycerin,
Butyl Methoxydibenzoylmethane,
Ethylhexyl Salicylate,
Acrylates/Octylacrylamide Copolymer
Butylphenyl Methylpropional,
Benzyl Alcohol
Product and ingredient list:
https://www.nivea-me.com/en-me/products/protect-and-refresh-invisible-cooling-sun-spray-spf30-40058082837740214.html


texts:
I am interested in nitrating an aromatic ester in a solution of dichloromethane. I found the following paper that describes creating a nitric acid solution in dichloromethane using KNO3 and sulfuric acid:

Strazzolini P, et al. "Nitric Acid in Dichloromethane Solution. Facile Preparation from Potassium Nitrate and Sulfuric Acid." Tetrahedron Letters 42 (2001) 1387 - 1389.

This paper describes both the nitration of Benzyl Methyl Ester and the nitrolysis of Benzyl Tertbutyl Ester and Phenyl Tertbutyl Ester using their nitric acid in dichloromethane method.
But I am having trouble understanding how they controlled the reactions to get nitration of one ester and nitrolysis of another ester. The reaction conditions seem similar, but the concentration of nitric acid in the nitrolysis reactions is about twice as high as in the nitration reaction. Could the difference be in the tertbutyl group vs the methyl group on the ester?


texts: What happens when pyridine N-oxide reacts with dichlorocarbene?

texts:
It seems that the combination of sodium methoxide (a base) and chloroform will generate dichlorocarbene, $\ce{CCl2}$, by α-elimination.

What happens after that, though? It is an ortho formylation like in the Reimer–Tiemann reaction? Or does the nucleophilic oxygen simply attack the carbene?


texts: what is the name of the molecule that has the greatest number of different atoms?

texts:
What is the name of the molecule that has the greatest number of different kinds of atoms?

For example, H2O is water has 2 different kinds of atoms which are H and O.

For example, C6H12O6 is fructose and has 3 different kinds of atoms which are C, H and O.

After warned to be a too broad question. I will rephrase it. The molecule must be stable and can be find in nature.

what is the name of the molecule has the record?


texts: If when water and carbon dioxide react they form carbonic acid, carbonate, and bicarbonate, how does seawater still have a pH of around 8? Doesn't a compound need an hydroxide ion to be a base?


texts:
Are haloalkanes considered a homologous series? For example, when assigning chloromethane to a homologous series, do we say that it belongs to the alkanes or haloalkanes?

Edit: I think that it would be a haloalkane. However, I'm unsure if haloalkanes are considered a homologous series.


texts:
I had thought that this question would be easy to answer but my searching has been unsuccessful in finding a clear answer.

For the metals, I expect that they all form oxides.  Some very readily, e.g. sodium and magnesium, and some reluctantly, e.g. gold and platinum, but I cannot find a metal which does not form an oxide.

The metalloids also all appear to form oxides.

The noble gases are obvious candidates for exceptions but xenon has a known oxide.  I think that it is expected for radon but I don't know whether that is confirmed.  A fluoride is known for krypton but no oxide yet.  No oxide is known or expected (?) for any of the lighter noble gases.

This leaves the other non-metal elements which are sufficiently few to check easily.  I find no exception except for the possible pedantic case of fluorine.  It forms a binary compound with oxygen but since it is more electronegative the compound is called oxygen fluoride rather than fluorine oxide.

Some elements are too radioactive to study e.g. francium and astatine but I expect that both would form oxides if we could manage to study them.

Edit: a good point that came up in the comments is oxygen itself.  A pedantic exception together with fluorine.

Is that correct?


texts:
Which of the following statements is true if HI is formed in the following reaction?

  $$\ce{H2(g) + I2(g) -> 2HI(g)}$$

  a. There are no collisions between the reactants in the reaction.

  b. All of the collisions between reactants have enough energy to overcome the activation energy.

  c. Some of the collisions between reactants have enough energy to overcome the reaction mechanism.

  d. Some of the collisions of the reactants have enough energy to overcome the activation energy.

I think it is d because I think it has enough energy to overcome the AE due to the equation, but I am not sure.


texts: 3 component (ternary) system in equilibrium

texts:
If the components of a system were Cl2, Br2, and I2, how could I describe this system under equilibrium conditions when the number of phases is at a maximum?

If there are 3 components, using the formula, F=M+2-P and solving for P under equilibrium conditions there would be a total of 5 phases.

Since these above components are all gases, and we know there are 5 phases, can I assume that 3 of the 5 phases will be Cl2 (gas), Br2 (gas), and I2 (gas).

For the other two phases, can I assume they consist of liquid iodine as it's commonly in the liquid phase, and cl2 (solid) as it's commonly in the liquid phase.

I'm not sure if this is correct.


texts: Why is DBU the most popular base with an amidino group? Does the basic strength have something to do with the ring size being 7 for one of the rings?

texts:
Structure of DBU

DBU is used as a very strong base(which is due to resonance stabilization of amidinium cation) with steric bulk. Is any other compound used instead? If not, why not?


texts:
In the complex ion $\ce{[Na(H2O)6]+}$, the sodium cation forms 6 coordinate bonds with water ligands. Typically this octahedral form is associated with $\mathrm{sp^3d^2}$ hybridization as far as I know, but in the case of sodium the $d$ orbitals aren't readily available, so how can this be described as $\mathrm{sp^3d^2}$ hybridization?

I would guess that its hybridization is $\mathrm{s^2p^4}$?

On further thought I think the d orbitals probably are accessible and that it is indeed $\mathrm{sp^3d^2}$ but this has a high hybridisation energy and so we dont see $\ce{[Na(H2O)6]+}$ in large amounts instead we see the ion solvated by partial charges and electrostatic rather than dative covalent interactions


texts: Why are the "extents of reaction" the same for all reactants and products?

texts:
Consider the follwoing reaction:
$$\ce{a A + b B -> c C + d D}\tag{1}$$
where $\ce A$ and $\ce B$ are the reactants, $\ce C$ and $\ce D$ are the products, and $a (<0)$, $b(<0)$, $c(>0)$, and $d(>0)$ their respective stoichiometric coefficients. The extents of reaction are respectively defined for these reactants and products as:
$$\begin{align}
\xi_A(t) &= \frac{n_A(t) - n_A(0)}{a}\tag{2.1}\\
\xi_B(t) &= \frac{n_B(t) - n_B(0)}{b}\tag{2.2}\\
\xi_C(t) &= \frac{n_C(t) - n_C(0)}{c}\tag{2.3}\\
\xi_D(t) &= \frac{n_D(t) - n_C(0)}{d}\tag{2.4}
\end{align}$$
However, I have found in many references (e.g. source) the extent of reaction defined for the whole reaction as:
$$\xi(t) = \frac{n_A(t) - n_A(0)}{a}
         = \frac{n_B(t) - n_B(0)}{b}
         = \frac{n_C(t) - n_C(0)}{c}
         = \frac{n_D(t) - n_D(0)}{d}\tag{3}$$
I do not understand how you can justify that the extent of reaction of the different reactants and products are equal.


texts:
Is there a heat capacity of an object when it is melting?

I’m questioning it since the temperature doesn’t change during phase transitions and the unit of heat capacity is joule per kelvin.


texts: How do I balance the combustion reaction of butene?

texts:
I have butene being burned in a fuel rich engine and I can't seem to balance this reaction:

$$\ce{C4H8 + $a$(O2 + 3.76 N2)
-> $b$ CO2 + $c$ H2O + $d$ C4H8 + $e$ (3.76 N2)}$$

When I try write equations for the elements, I get 5 equations and 4 unknowns which can't be solved. Here are my equations:

\begin{align}
\text{Carbon}   &:& 4     &= b  + 4d  \\
\text{Oxygen}   &:& 2a    &= 2b + c   \\
\text{Nitrogen} &:& 3.76a &= 3.76e    &  a &= e \\
\text{Hydrogen} &:& 2a    &= 2c + 8d  \\
\end{align}

I'm not sure if this makes a different but it says that water in the combustion products is removed before the dry analysis of the exhaust. The dry analysis has a composition of $14.95\% \ce{CO2}$, $0.75\% \ce{C4H8}$, $0\% \ce{CO}$, $0\% \ce{H2}$, $0\% \ce{O2}$, and balance $\ce{N2}$ (I don't know what that means).


texts: Would the lone pair be in the equatorial plane or the axial plane for bromine pentafluoride?

texts:
I've been learning chemical bonding and I'm confused about the structure of $\ce{BrF5}$.
It has a square bipyramidal geometry but a square pyramidal shape - I got that.
I don't  get why the lone pair gets placed at the top perpendicular to the equatorial plane instead of the equatorial plane, where it's more stable.

And why does the angle change a lot from 90 degrees to 84 degrees? Similarly for $\ce{ICl4-}$- why do the lone pairs go to the axial plane?


texts: Why doesn't the oxidation of cellulose oxidise all the alcohol groups, and how does it cause discolouration?

texts:
In cellulose, there are several alcohol groups - the two on the ring being secondary alcohols, and the one on the branch being a primary alcohol. I would expect all of these to be oxidised in the presence of any oxidising agent, such as heating under reflux with acidified potassium dichromate - this would give an aldehyde, and then a carboxyl group on the branch, whilst the two on the ring would be oxidised to ketones. However, as you can see in the diagram below (ignoring the sulfonation step which is irrelevant to the question), this is not the case with cellulose.

Why is the branched alcohol not also oxidised? Is it to do with it being a primary alcohol?

Further to this, the oxidation of these groups in paper causes discolouration. Is this because the double bonded oxygen atom then joins the delocalised system, increasing the size of the chromophore and hence bringing the frequency at which the material absorbs into the visible region? Or is there a different reason?


texts: How to Calculate Lennard-Jones Parameters from TDDFT?

texts:
I am trying to develop parameters for AMBER force fields and to calculate Lennard-Jones parameters for the $\ce{Fe^3+}$ ion. I did a deep search and found that the best way to do this with a high accuracy is to use TDDFT. I found many articles about this, for example (I can put more if there is need):

Marques, M. A. L.; Castro, A.; Malloci, G.; Mulas, G.; Botti, S. Efficient calculation of van der Waals dispersion coefficients with time-dependent density functional theory in real time: Application to polycyclic aromatic hydrocarbons. The Journal of Chemical Physics 2007, 127 (1), 014107 DOI: 10.1063/1.2746031.
Banerjee, A.; Autschbach, J.; Chakrabarti, A. Time-dependent density-functional-theory calculation of the van der Waals coefficient $C_6$ of alkali-metal atoms Li, Na, K; alkali-metal dimers $\ce{Li2}$, $\ce{Na2}$, $\ce{K2}$; sodium clusters $\ce{Na_n}$; and fullerene $\ce{C60}$. Phys. Rev. A 2008, 78 (3) DOI: 10.1103/PhysRevA.78.032704.

But, I couldn't understand the articles, because in some there are so many mathematical formulas, in others the method is not clear. So, to get some things clear before starting, I need to answer these questions (let's say I did my TDDFT calculation):

After performing TDDFT calculations, are there software or tutorials that I can use to calculate van der Waals parameters?
If there is no software or tutorial to calculate this, where can I start?


texts: What is a good source for large tables on the properties of water?

texts:
I'm currently doing an investigation for school on finding the Clausius-Clapeyron relation/gradient for  boiling water and comparing it to the gradients along my line of best fit. It is given by the equation,
$$
\frac{\text{d}P}{\text{d}T} = \frac{L}{T\Delta v}.
$$
I'm having trouble finding the specific volume of both water and steam (I found this for water but I'm not sure of the credibility) for $\Delta v$. I was hoping someone could reference me to a large data table for finding the specific volume, or a calculator. Thank you.


texts: What radius best represents reaction distance?

texts: Molecules must be within a certain distance for a reaction to begin as well as satisfying a myriad of other factors. Whilst the exact distance varies from reaction to reaction, is their any distance/molecular radius which provides a fairly good picture in terms of how close the centre of the molecules have to be to begin the interaction given they are in the correct orientation with enough energy etc.?


texts: How to without calculations understand the liquid-liquid extraction efficiency?

texts:
I'm asking myself this question for a very long time and I haven't found a simple an good explanation yet for the fact that it's better (if you want to clean them) to wash your hands two times with one millilitre of soap rather than one time with two millilitres.

If you are an organic chemist you will probably more ask yourself,

  Why is it better to extract a solute in a solvent $\ce{S1}$
  (non-miscible with a solvent $\ce{S2}$) doing two extractions using
  $\ce{10 mL}$ of $\ce{S2}$ rather than one extraction using $\ce{20 mL}$
  of $\ce{S2}$?

This is what I learnt at school and what I always used in organic chemistry lab sessions.

As mention above I am looking for a simple and good explanation, that is, without using any calculation. I am looking for a reasoning a bit like Feynman. I tried to resonate using dots but every time I fail and it leads me to the same result, that is, there is no better way to extract a solute...

EDIT : I put the below parts in very small because I think some people misunderstood my question. The question is just above, even though there is not interogation point.

For those who wonder if that is true or not, and as I wasn't convinced at all, I made some calculations before to be "sure" about this fact.

So let's start and imagine you want to extract iodine from water using benzene. In the following, the subscripts $aq$ will stand for the aqueous phase and $org$ will stand for the organic phase. $C_T$ will refer to the total concentration. $A$ will refer to the molecule we want to extract.

Let's call $D$ the partition coefficient between the organic and the aqueous phase, $$D = \frac{C_{T, org}(A)}{C_{T, aq}(A)}  = \frac{C_{T, org}}{C_{T, aq}}\tag 1$$

The quantity $Q$ of the solute $A$ in both phases, is determined by, $$\begin{cases} Q_{T, org} = C_{T, org} \times V_{org} \\ Q_{T, aq} = C_{T, aq} \times V_{aq} \end{cases} \tag 2$$

At the equilibrum, for the first extraction, a mass balance gives, $$C_0 \times V_{aq} = C_{1, aq} \times V_{aq} + C_{1, org} \times V_{org} \tag3$$

leading to, $$C_{1, aq} = C_{0, aq} \times \frac{1}{1+Du} \tag 4$$ where $u = V_{org}/V_{aq}$.

Then after $n$ extractions, $$C_{n, aq} = C_{0, aq} \times \left( \frac{1}{1+Du}\right)^n \tag 5$$

For the case of the extraction of $\ce{I2}$ from water to benzene, I used the solubility values found on the French Wikipedia page to calculate the partition coefficient (I am not taking in consideration the activity coefficients as I don't know them). It leads to $D = 373$ (assuming my calculations are correct)

The values I used are, $C_0 = 1.300 \times 10^{-3} \text{ mol/L}$, two extractions with $u = 0.2$ compared to one with $u = 0.4$.

For the two extractions, $C_{2, aq} = 2.27 \times 10^{-7} \text{ mol/L}$

For one extraction, $C_{1, aq} = 8.66 \times 10^{-6} \text{ mol/L}$

We clearly see the difference which is huge, even though these calculations are approximative.


texts: How to quickly diffuse a dye through still water

texts:
I'm doing an engineering experiment soon and would like to be able to quickly dye water. The water is still (i.e. not moving) and I would prefer not to physically disturb the water as best I can.

What techniques could I employ to quickly diffuse a dye through water? I was thinking that electrophoresis could be a possibility. If so, what dyes (or what could I add to a dye) to help speed up the process.

Thanks in advance.


texts: Where are the tetrahedral voids and octahedral voids located in an FCC?

texts:
A crystal is made up of atoms X, Y, and Z. Atoms X are in FCC packing, Y occupy all octahedral voids and Z occupies all the tetrahedral voids. If all the atoms along two body diagonal are removed, find formula of crystal.

Since there are 4 atoms in FCC, number of X=4. Tetrahedral voids occupy twice the number of atoms and octahedral voids occupy half of tetrahedral, so Y=4, and Z=8.
Now how I do proceed from here? I do not know where these voids are located.


texts: Finding mass of MnF3 is produced in a reaction

texts:
The question is as follows:

  If $\pu{1.23 g}$ of $\ce{MnI2}$ reacts with $\pu{25.0 g}$ of $\ce{F2}$, what mass of $\ce{MnF3}$ is produced?

$$\ce{2 MnI2 + 13 F2 -> 2 MnF3 + 4 IF5}$$

I think this is a limiting reactant problem but I'm having difficulties with starting the question off. Do I find the mass of both $\ce{MnI2}$ $\pu{(308.74 g/mol)}$ and $\ce{F2}$ $\pu{(38g/mol)}$ and divide them both by their given masses $\pu{1.23 g}$ and $\pu{25.0 g}$ respectively?

Once I do that, do I find the limiting and excess reactant, take the limiting reactant and do stoichiometry to find the mass of $\ce{MnF3}$ ?


texts: What would make guanidinium ions and urea more effective denaturants of proteins in some cases, but not in others?

texts: Some proteins do not unfold, or only partially unfold due to chaotropic agents such as guanidinium ions and urea. What are some reasons for this?


texts: Why does zinc react while its outermost suborbital is full?

texts:
Why does zinc lose electrons while its outermost configuration is 4$\rm{s}^2$ 3$\rm{d}^{10}$ both outermost suborbital are full.

Why does it react or lose electrons?


texts: Why can't Astatine form a diatomic homonuclear molecule like the rest of the halogens?

texts:
My understanding of chemistry is very elementary. I was reading about diatomic molecules and found the following image showing which elements can exist as diatomic (2 atoms) homonuclear (same element) molecules.

It seems that the most of the halogens can form such a molecule but Astatine can't? Why is that?


texts: Whether dissolving acids and salts is exothermic or endothermic, depends on the lattice and solvation energy. Breaking bonds in the lattice requires energy and is endothermic - that is clear. However, I do not see how solvation would release energy. I do understand that solvation is a type of creating new bonds (and creation of bonds generally releases energy), but how is it that the, eg., Al(H2O)6 3+ is at a lower energy level than Al 3+?


texts: What is the order of crystal field stabilisation energy for tris(ethylenediamine)chromium(III) chloride and hexaaquachromium(III) chloride?

texts:
In my book it is given that the crystal field stabilisation energy for $\ce{[Cr(en)3]Cl3}$ is more than that of the complex $\ce{[Cr(H2O)6]Cl3}.$ By what I have studied, the crystal field stabilisation energy depends on the number of electrons in $\mathrm{t_{2g}}$ and $\mathrm{e_g}$ orbitals and the pairing energy.

The number of electrons in both the compounds is the same and both undergo octahedral splitting, so that term is same for both.

Now coming to pairing energy is the energy of $\ce{en}$ more than $\ce{H2O}$ since it is a chelating group? Or it depends upon the position of the ligands in the spectrochemical series?


texts: Which double bond will react with m-CPBA to form an epoxide?

texts:
The solution to this reaction sequence given was,

What I don't understand is the last step. How do we know which double bond will react to form an epoxide?
My guess was that the double bond adjacent to the methyl group should react as it has a more double bond character than the other one which is in resonance with the lone pair of oxygen.

Any help would be appreciated.


texts:
At $t = 0$ we have 10 moles of $\ce{NO2}$ and 10 moles of $\ce{N2O4}$ satisfying this reaction in a 0.75 liter tank (the barrier is closed at this time):

$$\ce{N2O4 <=> 2NO2}$$

The system is in thermal contact with the environment.

At time t=t0 the barrier is released and the gases are free to expend to the other tank ($V_2=1$ liter)

The question is what will be the concentration of $\ce{NO2}$ when they reach equilibrium.

What I tried is calculating the chemical equilibrium before based on the concentration quotient $\text{K}_c$ (13.33) and then to use it as reference after the system reaches equilibrium. I got a weird result (negative number) Where have I gone wrong?


texts: What is this SMILES notation: C[Si](C)C |^1:1|

texts:
When converting InCHI to canonical SMILES using Indigo, I will occasionally get an output SMILES string like this:

C[Si](C)C |^1:1|

What does the "|^1:1|" part mean? I can't find this explained anywhere in either SMILES grammar documentation, nor Indigo documentation, although other chemical software seem to accept it as a valid SMILES string. Any ideas on the meaning of this annotation?


texts: After completing an experiment, a student finds that the percentage yield exceeded 100%. What could have occurred to the sample to lead to this?

texts: I am looking for a general answer; nothing too detailed. And no. This is not a homework question. It happened to me in lab and I am wondering what error I could have committed.


texts: If we have a long carbon chain like octane for example, do we determine if a carbon is unique by just looking at the immediate surrounding atoms of each  carbon (in this case 3 unique carbons), or do we need to take into account the symmetry of the whole molecule (many more unique carbons)? Edit: This is for NMR purposes


texts:
So, I am a first year chemistry student and I saw this chemistry reaction on a previous year's test. I attempted to figure out the mechanism, but I'm rather confused as to how the cyclopentane somehow donates a carbon to the cyclobutane? Why would such a rearrangement occur?

That is how far I get to before I am lost. Is methanol even a strong enough reagent for such a reaction?


texts: Any example of colloidal solution where liquid Helium is solvent?

texts:
I would like to see any information, if it exists, about colloidal solutions where Helium is "solvent".

Background of that question is, I'm wondering giving surface energy effects, how potentially small can be water ice particles at low temperatures.


texts: Why does silver sulfate not precipitate in this double displacement reaction?

texts:
Aqueous silver nitrate is mixed with aqueous sodium sulfate.  We were asked to perform this reaction in lab in my chemistry class, and we did not observe a precipitant being formed. However, the equation indicates otherwise:

$$\ce{2AgNO3 (aq) + Na2SO4 (aq) -> Ag2SO4 (s) + 2NaNO3 (aq)}$$

This shows the formation of $\ce{Ag2SO4}$, silver sulfate. I found in the Wikipedia article for silver sulfate a reference to "ruby red illumination" and thus am led to believe that, like some silver-based substances used in photographic film, the precipitant might have been immediately been affected by light in the room and thus decomposed into something soluble in water. I have not, however, been able to find references to this anywhere else; I have found here a reference to it being classified as "sparingly soluble," but I haven't the slightest idea what this means.


texts: How to reduce the surface tension of molten metals?

texts: I'd like to reduce the surface tension of molten metals to reduce air bubbles by casting them like in this video with plaster. Actually the goal is to be able to cast gold without bubbles, but I guess it will be a long journey and better to start with cheaper metals. With a quick search I found only that higher temperatures and different material for the mold can reduce the surface tension, but not much, maybe by 10%. Looks like they wanted to achieve the opposite (make sure that the surface tension is high enough and there is no wetting and chemical reactions on the surface), because they are using reusable molds, while I'll try this method with non-reusable plaster mold. Is there a way to significantly reduce the surface tension, I mean by a magnitude?


texts: Is the product of Lindlar hydrogenation of (2Z,4S)-4-methylhept-2-en-5-yne optically active?

texts:
According to me the poisoned catalyst will only reduce the triple bond so the compound produced must be optically active.. But the answer given is that the final product is optically inactive.. is it correct and if so how?

this is the final product I made:

The triple bond gets reduced to double bond as Lindlar's catalyst has been used so the reduction stops at this stage.. is this correct?


texts: Why does the rate of reaction increase less than proportionally to the increase in mass of catalyst?

texts:
I conducted an experiment where I wanted to speed up the decomposition of hydrogen peroxide with the use of a catalyst (potassium iodide).

I used 5 different test tubes with 5ml of hydrogen peroxide in each, then added different amounts of the potassium iodide: 0.2g, 0.4g, 0.6g, 0.8g, 1.0g. Then I measured the time it took for the reaction to reach a temperature of 30°C. The results I got was that the more of the catalyst I added, the faster the rate of the reaction became. However, the increase in the reaction rate decreased when more of the catalyst I added, and I don't understand why.

I would think that since temperature and amount of hydrogen peroxide are constant variables and the only variable affecting the rate is the amount of potassium iodide, if I doubled the amount the speed would also be doubled. But why is that not the case? Or does it have something to do with errors in the method?


texts: Where can I find the standard enthalpy of formation for Sodium Cyanamide (Na2NCN)?

texts: I am trying to find the standard enthalpy of formation for sodium cyanamide. Ive looked on various databases that list data about specific compounds but I can't find anything on this particular one. Where should I be looking?


texts:
I am a confused (and somewhat anal retentive) non-chemist who is trying to understand what pH is.  I have come to understand it is a measure of acidity, but I have not yet figured out what that means to a precision that I find satisfying.

Please excuse me if these are dumb questions, but they will help me understand the definition:

  Does everything have a pH?  What is the scale that pH works upon?  Does a proton have a pH?  A quark?  Does the sun have a pH?  Does the Universe?


texts: I'd like to model some compounds with DFTB, but some elements don't have parameter files in the official site. Is there a workaround?

texts:
I was reading a bit about this technique, Density Functional based Tight binding (DFTB). It's claimed it can provide a speed improvement of several fold when compared to plain DFT, still giving acceptable results. I downloaded one of its free implementations, the DFTB+ package, and started to work on their tutorial. The problem is, like a semiempirical method, this technique demands parameters. In DFTB the parameters are downloaded separately, as a series of files for each bonded element pair. The problem is, in the page linked as the repository for such parameter files, the options listed don't cover every possible element pair in the periodic table. I my case, I'm interested in heavier members of the alkaline earth group, Sr and Ba. But the only elements in this group with parameter files available are Mg and Ca.

So, I wonder if there is a workaround, short of doing the parametrization on my own, what I imagine would probably be a whole research project on itself, and far beyond my league. Perhaps that repository page just doesn't list every Slater-Koster file in existence, ond others may be found somewhere.


texts: Why are not all metals included in the reactivity series

texts: Why aren't all metals included in the activity series ? For example why isn't molybdenum included ? Now we know that hydrogen displaces those metals from their oxides that are less reactive than iron. But how do I know whether Hydrogen would also displace Mo if its not there in the reactivity series ?


texts:
My textbook reads as follows:

  When a gas is adsorbed, the freedom of movement of its molecules become restricted. This amounts to decrease in the entropy of the gas after adsorption, i.e. Entropy change is negative.

But now, I am unable to understand why it isn't a violation of the second law of thermodynamics, which states that the entropy change of a system can never be negative. Please guide.


texts:
Recently I stumbled across a book that describes enthalpy change with temperature, specifically for a product of combustion process (e.g. CO as a result of solid carbon combustion). The book says that enthalpy of formation at $298$ K is $-110.5~\rm\frac{kJ}{mol}$, meaning that this is the amount of energy that gets released during combustion.
But in a very next paragraph there are two opposite calculation for enthalpy at 2000K: one says it is $-53~\rm\frac{kJ}{mol}$ (less energy get released during combustion), and the other it is $+167~\rm\frac{kJ}{mol}$ (the energy must be brought into system)?

Can you please clarify which number is correct and does energy goes out or into the system?


texts: A function for getting the nuclide's nuclear binding energy?

texts: Is there a function $f(A)$ or $f(Z, A)$ that gets the energy of nuclear binding of one nuclide in atom? Or other way to get it? My chemistry book says only to get it from the chart which is very impractical.


texts: Can fumes from using bleach seep through plastic packaging and glass jars

texts:
A bulging can leaked inside our kitchen cabinet. I googled how to handle it. I followed the instructions I found online. I mixed 1/4 bleach and 2 cups water. Applied it on all surfaces. Then applied dish soap diluted with water.

Does this produce toxic fumes? And can the toxic fumes seep through food even if they are covered and placed about 3 meters away? The cabinet still smells like bleach. What should I do about it?


texts: How are catalysts discovered for a particular reaction?

texts:
I want to understand how are catalysts discovered for a particular chemical reactions say for example $\ce{Fe,~Mo}$ for Haber's Process reaction of $\ce{N2}$ & $\ce{H2}$.

Reactions as examples with some background (story of discovery,discoverer or method) would better serve the purpose.

For this question keep it limited to Catalysts involved in Haber's Process.


texts: What do GGN, AAP, TCN, CAP, CCN, TGQ, etc. mean in DNA analysis?

texts:
What do the letters Y, Q, P and N mean in three-letter combinations involving DNA and/or RNA?

I know, of course, about the bases A, C, G, T and U but.....

Especially in articles (and forensic tv shows) I see, connected to three-letter amino acid codes, letter combos like GTN, GGN, etc.....


texts: How to explain the increase in current with the increase in the concentration of responsible ions?

texts: I have conducted an experiment wherein I have used different concentrations of $\ce{H2SO4}$, $\ce{HNO3}$ and $\ce{H3PO4}$ as the electrolytes. I filled the acid in glass tube and used a 9V battery, wires and two graphite electrodes to complete the circuit. I also attached an ammeter to check the current variation during a time period of 1 minute. I observed that the current was higher with more concentrated solutions, although my query is that when I add more of these acids, the concentration of the $\ce{OH-}$ ions reduces; it is the $\ce{OH-}$ ions and the $\ce{H+}$ ions that dissociate. How exactly do I explain the increase in current due to increase in concentration?


texts: How many electrons can have the quantum number set n=5, l=3, ml=-1?

texts:
How many electrons can have the quantum number set $n=6,\ l=3,\ m_l=-1$?

Also, please explain why. I know that n describes the number of shells in an atom but what do n, l, and ml have to do with electrons?


texts: Given that a metal's low ionisation energy is often used to explain the metallic bond (as are other factors such as temperature and pressure and possibly a number of other factors), is there any known mathematical and/or empirically proven theory that predicts that under the given set of conditions, a transition will occur from covalent to metallic or vice versa? A metal's proximity to a stable electron shell structure (be it noble gas or complete/semi-complete d- or f- shell structure) is a generic explanation, but (without going into high level mathematical explanations) is there a firmer basis that can make the prediction of that transition, given a set of conditions? If not, is there any research into this issue?


texts: If an action increases the reaction rate in a particular equilibrium mixture, does it mean that both forward and backward rates are increased?

texts: Say for example we increase the temperature in a closed system containing gaseous reactants. The forward reaction is exothermic so the yield of the product will decrease as we increase the temperature. But increasing the temperature increases the reaction rate so does it mean that the forward and backward rates are both increased ?


texts: Difference in calculated pH and the real pH of a phosphate buffer?

texts:
I'm from Colombia and I joined this site to ask a question that I could not solve yet. I am calculating the amounts to prepare a phosphate buffer with two salts. I want to prepare a buffer system with pH = 7.0 and a total concentration of Ct = 0.1 M. All my calculations are in the image attached. When I mix the calculated amounts, the obtained pH = 6.5 in the lab. I thought it was my mistake in calculations or an error when I weighed the amounts, but I repeated everything several times and still not get the pH = 7, and the value always was 6.4 or 6.5.

I don't know the reason but I would like to know this. Please help me. I think that If the concentration of the monobasic salt is greather than the dibasic, the pH tends to decrease, but in the calculations the relation [dibasic]/[monobasic] is always less than 1 and this again causes that [monobasic] > [dibasic]. Thanks, I really need a help.


texts: How do I calculate the full configuration interaction Hamiltonian of H2

texts:
I have been trying to follow the paper titled "Towards Quantum Chemistry on a Quantum Computer" (https://arxiv.org/pdf/0905.0887.pdf) by simulating their results on a quantum computer simulator. Unfortunately, I have been having trouble classically calculating the full configuration interaction Hamiltonian for H2 using the STO-3G basis set. In the paper they use Pyquante, but I haven't been able to find good documentation on how to use it. I would be grateful if someone could show me how to calculate this using Pyquante, point me towards better documentation for Pyquante (I've only been able to find the rather poor documentation found here: http://pyquante.sourceforge.net/), or suggest a different/free quantum chemistry program that is easier to use.

For reference, I have been using Szabo and Ostlund's "Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory" to try to get a handle on this calculation. They come up with two single-electron molecular wavefunctions,

and

where  and  are the 1S orbitals about each of the atoms.

This gives 4 molecular spin orbitals and thus 6 different Slater determinant basis states. These are the basis states for which I would like to calculate the Hamiltonian.


texts: Oxidation number for nitrogen in ammonium sulfate

texts:
I'm trying to find the oxidation number of $ \ce N$ in $ \ce{(NH4)2SO4}$.

The answer is supposed to be $-3$ but I can't figure out the logic behind this.


texts: Why is UV-Vis Spectroscopy not like IR Spectroscopy

texts:
UV/Vis Spectroscopy is where electromagnetic radiation in the UV to Visible range is shone at a sample to be analysed. The absorbance of each wavelength is recorded and then plotted (very similar to Infrared spectroscopy). That's why it surprised me so much.

This graph is so smooth and with only 1 peak. This is completely different to the IR graph (below):

Why is it that UV-Vis spectroscopy only produces 1 peak? Is it something to do with orbitals overlapping and hence only producing one major peak?


texts: Effect of nitrobenzene on solution UV/Vis spectra

texts:
I am wondering if there is a difference in the maximum absorbed wavelength of light if nitrobenzene is added to an acidic or basic solution.

I've figured that resonance plays a part in some structures like phenol, where the electron density in the benzene ring increases when in basic solution and therefore the energy required to go from a $\pi$ to $\pi^*$ orbital decreases and thus $\lambda_{\text{max}}$ increases. But could resonance play a role in nitrobenzene too? And if it does, how?


texts: DFT Exchange-Correlation Two Electron Integrals

texts:
Are there any electronic structure programs that print the exchange-correlation (XC) integrals for a given DFT functional? These integrals are of the form $$\langle pq|w|rs\rangle$$
where $w$ is an XC kernel specific to a given functional and $pqrs$ label arbitrary MOs.

I'm trying to make a Python code that can do TDHF/KS, with the prior SCF done using an existing electronic structure package. I have it working fine for TDHF, but TDKS requires these XC integrals and I can't find any program that prints them (or the atomic orbital basis equivalent). Ideally, if this option exists in Gaussian or Psi4, that would be most helpful to me, but I would be interested to see if any program will print these.


texts: Who coined the term "gas evolution reaction"?

texts:
I found a paper from 1812 which specifically mentions the evolution of a gas [1].
There is a similar reference from 1808, except it uses the term evolution to speak of green light emitted when a material touches a green wire [2].
Is there anyone who knows for sure when the first time “gas evolution reaction” and the “gas evolved” and other such uses for the term “evolved” appeared in chemistry?
References

Henry, W. LX. Additional Experiments on the Muriatic and Oxymuriatic Acids. The Philosophical Magazine 1812, 40 (175), 337–343. DOI: 10.1080/14786441208638245.
Scholes, J. XI. On the Union of Gases. The Philosophical Magazine 1808, 31 (121), 68–70. DOI: 10.1080/14786440808563850.


texts: Will the following complex show optical isomerism

texts:
So there is this question which asks whether the following complex

  $\ce{[Co(NH3)4Br2]+}$

will show optical  isomerism or not.

According to my knowledge it will show optical isomerism in cis form only and not in trans form so overall the compound shouldn’t be optically active.

This what I hav been taught. And moreover shouldn’t it be optically active in every scenario to be called so?

But the ans says that it shows optical isomerism.
I don’t understand why.. is my understanding wrong?


texts: Why is the ester carbonyl peak in benzocaine IR spectrum so low?

texts: Having looked at multiple IR spectra for benzocaine, I am struggling to understand why the carbonyl C=O peak is so low in the spectra compared to where an ester carbonyl group usually is on other IR spectra


texts: How does water flows through pipes in cold countries?

texts: This question occurred to me when I looked into the fridge, where the water had frozen due to very low temperatures. If the water freezes due to low temperatures (0 degrees Celsius), then how can it flow through pipes in the cold countries (especially near the north pole) where the temperature is almost always below 0 degrees Celsius, especially in the cold months?


texts: Are there any strategies to determine bond order and hybridization rankings without drawing the Lewis Structure?

texts:
I'm not Chemist. I'm taking a chemistry class in college, and the test review contains many questions where I'm asked to rank from least to greatest based on bond order, polarity, and bond angles. I feel like I can rate on electronegativity.

The problem is that I don't know a way to rationalize this in my mind without drawing the Lewis Structures. Many times each possible choice has like 5 or so, so it takes a lot of time. We are only given 50 minutes for the test and there are many more problems that require large amounts of time.

My question is... As a chemist or someone who is more knowledgable in this field than I, are there any techniques that would help you now or when you were first learning?

Thanks.


texts: How do we know the size of atoms in body centered cubic system?

texts:
I'm told that in the normal cubic system there are $\frac18$ of an atom at each corner and these atoms' radius are such that $a = 2r$ ($a$ is the lattice constant, $r$ radius of an atom).

In bbc (body centered cubic system) they say the atoms in the diagonals are touching, and as a consequence the atoms at each corner are not big enough to satisfy the above relation $a = 2r$

Why is this? Couldn't it be like the normal cubic system but stick an atom in the center to fill up the remaining space? How do we know that they touch along the cube's diagonal and not along the edges?


texts: Why does chemisorption decrease with increasing temperatures?

texts:
Why is it that chemisorption decreases with higher temperatures?
The explanations I found online were quite vague and one of them cited Le Chatelier's principle, but I thought chemisorption is an irreversible process (because covalent bonds are formed between the adsorbate and adsorbent) so there is no reversible equilibrium.
Explanations I found online:

"Further increase will increase the energy of the molecules adsorbed and will also increase the rate of desorption. Therefore, the extent of adsorption decreases." - why does the rate of desoprtion increase?

"The initial increase is due to the fact that heat supplied acts as activation energy. The decrease afterward is due to the exothermic nature of adsorption equilibrium."


texts: Compressibility factor of hydrogen at low pressure and constant temperature

texts:
As we all know, the compressibility factor $Z$ of hydrogen and helium is always greater than $1$ at a constant moderate temperature. But, if we look at the virial equation of compressibility factor

$$Z = 1 + \frac{1}{V_\mathrm{m}}\left(a - \frac{b}{RT}\right) + \frac{b^2}{V_\mathrm{m}^2} + \cdots$$

At extremely low pressure $V_\mathrm{m}$ would be extremely large. So, the equation simplifies to

$$Z = 1 + \frac{1}{V_\mathrm{m}}\left(a - \frac{b}{RT}\right)$$

Now, the values of $a$ for hydrogen and helium are extremely small. So, we can take them as zero. The equation further simplifies to

$$Z = 1 - \frac{1}{V_\mathrm{m}}\left(\frac{b}{RT}\right)$$

Now, the value of $b$, $R$, $T$ and $V_\mathrm{m}$ are all positive. Though the value of $b$ for hydrogen is extremely small, still it is positive. So, shouldn't the value of $Z$ at some small pressure be less than $1$?

Any help would be appreciated.


texts:
How to define "soluble" in chemistry?

For example, in 1:1 v/v, benzene does not mix with water, i.e. insoluble. Common sense.

However, in an analytical procedure, it called for making a "saturated" aqueous solution of benzene, which is about 1.5 g/L. So, benzene actually  has some solubility in water.

So, my question is, is there an official definition of "soluble"?


texts: The structure of exploding buckminsterfullerene-nitrous oxide compounds

texts:
Recently, looking into structures of buckminsterfullerenes, I have found several articles claiming that attaching 12, or “several” nitrous oxide molecules to the buckminsterfullerene will cause it to degrade exothermically, heating the surroundings to several thousand degrees in “picoseconds”. The degradation would produce more nitrous oxide, further carrying on the reaction.

As I remember, they didn’t have any cited sources, or give any creditable evidence, or give the structure of the nitrous oxide-buckminsterfullerene compound. So I’m wondering, where are the NOs attached on the C60?, and what is the structure of this compound?(preferably a diagram?)

I searched it on many places, but to no avail.

Thanks,
Max0815


texts: Can there be active THC be trapped in the evaporator?

texts:
In relation to the vaporization of THC, when smoked, is it possible that there is any active THC residue that becomes trapped inside the evaporator after the flame goes out?

Wouldn't some of the vapor get stuck inside because the instrument is not a hollow tube?


texts: Why does bromide not react with water when methyl ammonium bromide is dissolved in water?

texts:
In the following reaction, the salt $\ce{CH3NH3Br}$ is formed:

$$\ce{CH3NH2 + HBr -> CH3NH3Br} $$

In water this dissociates completely into $\ce{CH3NH3+}$ and $\ce{Br-}$

In my chemistry book, it says that the $\ce{CH3NH3+}$ dissociates further in water into $\ce{CH3NH2}$ and $\ce{H3O+}$ (meaning that $\ce{CH3NH3Br}$ an acidic salt) according to the following:

$$\ce{CH3NH3+ + H2O <=> CH3NH2 + H3O+}$$

Fair enough, but why does the $\ce{Br-}$ not do the same and dissociate in water?

$$\ce{Br- + H2O <=> HBr + OH-}$$

In this way, the dissociation of the $\ce{CH3NH3Br}$ salt would not have so much of an effect on the pH, because the quantity $\ce{OH-}$ ions has also increased?


texts:
I've seen this phenomenon a couple of times--I actually saw it happen this night.
When a carbonated beverage is poured into a cup or glass, many tiny bubbles of carbon dioxide form on the bottom of the glass, then shoot up to the surface and pop when they get too big.
Today, as I was looking at a wine glass filled with a carbonated beverage, I noticed that there was something different--the carbon dioxide bubbles were rising up in a straight column from the very center of the cup; in other words, all the CO2 bubbles were coming from the point where the cup joined the stem.
Can someone explain how this phenomenon happens?


texts: What is the convention on color of molecular orbitals in publication figures?

texts:
I'm new to MO-visualization and I'm using the program Orca to generate visualizations of molecular orbitals of a system of interest. I've been able to produce some nice images in VMD but I'm not sure what they actually mean:

I've seen pictures like this before with blue/red blobs to represent molecular orbitals, but I don't know what (specifically) they are representing. My suspicion is blue=HOMO and red=LUMO, or blue = negative wavefunction and red = positive wavefunction, but I'd like to know if there is a universal standard.

For reference, this is the "Graphical Representations" panel in VMD for this system:


texts: What is the topology of a phase diagram?

texts:
This question is cross-posted from phys

Looking at various two-variable phase diagrams I was struck by that on every one I have seen so far all the phases formed simple connected regions; see, for example the phase diagrams of $\ce{H2O}$ or of $\ce{Fe-Fe_3C}$ in 1. Every phase is a connected region, no two disjoint pieces correspond to the same phase. Is this really true in general and if so why?

Going further, let us consider a three-variable phase diagram, say $p, T, y$, where $y$ maybe electric or magnetic field intensity, or some other controllable extensive/intensive variable. Is it possible that now a 3d region occupied by some phase is a kind of tube that makes a half turn so that if we fix, say, $y$ then the resulting 2d section would have two disjoint $p,T$ regions of the same phase? Can such phase "tube" exist or by some thermodynamic-geometric rule is it excluded?

A possibly more difficult question if a phase can form an annular  region, ie., homeomorphic to an annulus while surrounding another phase homeomorphic to a disk?

In short, what is the topology of the phase diagram and its sections?


texts: Migratory aptitude in pinacol-pinacolone rearrangement

texts: I am confused about the migratory aptitude of various groups, as there are many different orders for the same given in different places, especially about -Ph and -H. I would like to know if someone could reliably tell the order.


texts: How much Carbon Dioxide would be required to displace enough oxygen to prevent ignition?

texts:
In air, how much $\ce{CO2}$ would be required to prevent a match to light or a butane lighter to work?

I have a basement office that is unusable because of an apparent lack of oxygen, currently it is my guess that the oxygen is being displaced by $\ce{CO2}$.

A bit research suggests that it would take a reduction to around 14% for a safety match to fizzle out without any flame. But my naive estimate suggests 7% $\ce{CO2}$, and at that level isn't $\ce{CO2}$ deadly?
And this isn't even accounting for the displacement of nitrogen, surely that would mean the levels of $\ce{CO2}$ would be even higher.

Would a 6% increase in $\ce{CO2}$ displace oxygen by only small percentage say 2% as it's only a smaller ratio of the atmosphere? Or would the presence of $\ce{CO2}$ contribute to the lack of ignition compounding the lack of oxygen?

See my related question on the DIY stack exchange

UPDATE

An insepector from the local council has installed a data-logger, whilst he was in the basement he took a reading that I've attached below. When this reading was taken the air felt poor, but by no means the worst it's been, a candle wouldn't stay alight. An breathing during conversation seemed laboured. It looks like the assumption of displacement doesn't look correct, there's more to it.
Here's the readings:

Gas - Reading (Normal)

$\ce{CO2}$ 3.3% (0.04%)
$\ce{O2}$ 17.5% (20.8%)
Other 79.2% (unchanged?)